Emmanuel Somm
Mahdi Rahman
Ildiko Szanto
Karim Gariani1,2†- 1Service of Endocrinology, Diabetes and Metabolism, Department of Medicine, Geneva University Hospitals/University of Geneva, Geneva, Switzerland
- 2Diabetes Center, Faculty of Medicine, University of Geneva, Geneva, Switzerland
- 3Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
Signal transducer and activator of transcription (STAT) proteins are a family of seven transcription factors mediating various biological processes. STAT6 is classically known to regulate immune cell biology by transmitting signals from interleukin (IL)-4 and IL-13 into transcriptional activation of genes driving type 2 immunity. In orchestrating T helper lymphocytes and macrophages polarization, STAT6 plays a central role in the regulation of both cellular and humoral immunities. Several pathologies, including inflammatory disorders, autoimmune/allergic diseases, metabolic syndrome as well as cancer, are associated with a dysregulation of type 2 immunity related to inadequate expression and/or activity of STAT6. In the present review, following a brief introduction of STAT6 biology, we summarize the immunologic and physiological roles of STAT6 in the context of liver integrity as well as the potential roles of STAT6-mediated pathways in both hepatoprotection and liver pathophysiological mechanisms.
1 Introduction
Signal transducer and activator of transcription (STAT) proteins are a family of seven transcription factors (STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B and STAT6) involved in pleiotropic biological processes such as cell proliferation, apoptosis, differentiation and immunity (Darnell et al., 1994). STAT proteins are activated through phosphorylation in the cytoplasm by Janus Kinases (JAKs), a group of tyrosine kinases associated with receptors of different ligand classes, mainly cytokines or growth factors (Schindler and Darnell, 1995; Wang and Levy, 2012). One of the main functions of STAT proteins is the modulation of immune system reactions by transmitting signals from cytokine receptors and inducing transcriptional activation of genes involved in humoral and cellular immunity (Goenka and Kaplan, 2011; Hou et al., 1994). Depending on the pathogens and cytokine environment produced by other immune cells, the naïve T helper (Th) lymphocytes (Th0) cells undergo differentiation towards a Th1 or Th2 phenotype (Butcher and Zhu, 2021). Th1 lineage cells will produce pro-inflammatory cytokines such as Tumor Necrosis Factor alpha (TNF-α), interleukin (IL)-1 and interferon (IFN)-γ (Zhu and Paul, 2008). These pro-inflammatory cytokines activate cellular immunity by stimulating macrophages, natural killer cells and CD8+ cytotoxic T cells (Zhu and Paul, 2008). In contrast, Th2 differentiation is triggered by eosinophils, basophils and mast cells initially producing IL-4, resulting in the secretion of anti-inflammatory cytokines such as IL-4, IL-5, and IL-13 (Tolomeo and Cascio, 2024). These interleukins also induce the synthesis of antigen-specific antibodies in B cells (humoral response) (Takeda et al., 1997). STAT6 is activated by the binding of IL-4 and IL-13 to their cognate receptors and thus induces Th2 immune response (Hou et al., 1994). Adequate balance between Th1 and Th2 lymphocytes and cytokines is primordial for both the efficiency and harmlessness of the immune system. Several pathologies, including inflammatory or autoimmune disorders, allergic diseases, as well as cancer, are associated with dysregulated Th1/Th2 equilibrium and related to inadequate expression/activity of STAT6 (Tolomeo and Cascio, 2024). In consequence, STAT6 represents a main driver of the adaptive immune system.
The STAT6 gene consists of 23 exons located on chromosome 12q13.3-q14.1 in humans (Figure 1A) encoding a 94 kDa protein composed of 847 amino acids (Figure 1B). Of note, the homolog STAT6b presents an NH2-terminal truncation while the homolog STAT6c presents a SH2 domain deletion (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006). STAT6 and STAT6b are phosphorylated on tyrosine residue in response to IL-4/IL-4 receptor interaction while STAT6c is not and thus lacks the capacity to induce cell proliferation (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006). A shorter isoform of STAT6 is also specifically present in mast cells (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006). As the other members of the STAT family, STAT6 contains six domains: (1) a helical N-terminal domain (ND) responsible for interactions between STAT dimers and DNA, (2) a coiled-coil (CC) domain binding regulatory factors, (3) a DNA-binding domain (DBD) binding enhancers of the GAS family, (4) a helical linker (LK) domain involved in nuclear translocation and DNA binding, (5) a Src homology 2 (SH2) domain binding cytokine receptor following tyrosine phosphorylation and (6) a C-terminal transactivation domain (TAD) triggering transcription of targeted genes (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006) (Figure 1B).
Figure 1. (A) Chromosomal location of STAT6 gene on chromosome 12q13.3-q14.1 in humans (Source: https://www.genecards.org). (B) Structure of STAT6 protein. Location of somatic mutations identified in humans are indicated by red arrows. Numbers refer to amino acids. (C) Representation of STAT6 signaling pathway. Illustrations have been created manually using PowerPoint (Microsoft) and images originating from Servier Medical Art (https://smart.servier.com/), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). (D) Phosphorylated STAT6 promotes type 2 immunity including type 2 T helper and M2 macrophage polarization.
Mechanistically, IL-4 binds first to the IL-4 receptor α-chain (IL4Rα) which then recruits either the IL-2Rγc or the IL-13Rα1 (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006; Murata et al., 1999; Junttila, 2018) (Figure 1C). Binding of the IL-4/IL-4Rα complex to IL-2Rγc or IL-13Rα1 is required for the constitution of a functional heterodimer receptor complex, inducing a conformational change in the intracellular receptor domains that lead to the phosphorylation of the Jak kinases associated with IL-4Rα (Jak1), γc (Jak3), or IL-13Rα1 (Jak2 also named Tyk2) (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006; Murata et al., 1999; Junttila, 2018) (Figure 1C). IL-2Rγc is generally expressed in lymphocytes while IL-13Rα1 is mostly expressed in non-hematopoietic cells (Tolomeo and Cascio, 2024). The tyrosine residues in the intracellular domains of IL-4Rα act as docking sites for the SH2 domain of STAT6, resulting in homodimerization and nuclear translocation of STAT6 thereafter binding specific DNA motives in diverse transcription regulatory regions of target genes (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006; Murata et al., 1999; Junttila, 2018) (Figure 1C). Similarly, IL-13 binds IL-13Rα1 and the complex recruits IL-4Rα leading to analog activation of STAT6 (Tolomeo and Cascio, 2024; Hebenstreit et al., 2006; Murata et al., 1999; Junttila, 2018) (Figure 1C). STAT6 mainly acts as an activator of transcription but it could also acts as a repressor of transcription (Elo et al., 2010) or through other mechanisms including binding of transcriptional cofactors or epigenetic modification (Ohmori and Hamilton, 2000). In addition, STAT6 also presents post-translational modifications, such as phosphorylation, ubiquitination, adenosine diphosphate (ADP)-ribosylation and acetylation that can be targeted to develop therapeutic strategies (Huang et al., 2020).
Signaling mediated by STAT6 is required for the Th2 immune response at different levels. Firstly, STAT6 is involved in Th2 cell differentiation through a feed-forward mechanism implicating the Th2 master switch GATA-binding protein 3 (GATA3) (Scheinman and Avni, 2009). Consequently, STAT6 deficiency decreases the number of cells harboring the Th2 phenotype (Shimoda et al., 1996; Takeda et al., 1996). Secondly, STAT6 increases the pool of Th2 cells by increasing their proliferation while preventing their apoptosis through the independent growth factor-1 (Gfi-1) (Kaplan et al., 1998). STAT6 also impacts B cells in switching their immunoglobulin class (Shimoda et al., 1996). Accordingly, STAT6-deficient mice have impaired circulating immunoglobulin (Ig)E and IgG1 in response to conventional T-dependent antigens (Linehan et al., 1998) while in human, IL-4 induces B lymphocytes switch from the expression of IgM to the expression of IgG1, IgG4 and IgE (Tolomeo et al., 2022; Stavnezer, 1996). STAT6 also increases B cells’ expression of cell surface molecules including MHC class II molecules, IL-4Rα, CD80, CD86, and CD23 (Bruns et al., 2003). In addition, STAT6 inhibits B cells apoptosis by increasing the expression of Bcl-xL, which suppresses the mitochondrial apoptotic pathway (Wurster et al., 2002).
STAT6 is also a key player in macrophage activation. In fact, macrophages can oscillate between two states of polarization: the classical M1 activated state, featured by the production of pro-inflammatory cytokines, and the M2 alternatively activated state characterized by the production of anti-inflammatory cytokines. M1 activation is classically triggered by IFN-γ and toll-like receptor ligands while M2 activation is induced by IL-4 and IL-13 that activate STAT6 signaling (Sica and Mantovani, 2012). In macrophages, IL-4/STAT6 signaling also increases the activity of peroxisome proliferator-activated receptor γ (PPARγ), a transcription factor regulating both lipid metabolism and macrophage activity (Szanto et al., 2010). In addition, IL-4/STAT6 signaling also induces PPARγ-coactivator-1β (PGC-1β), that drives oxidative metabolism, and which could act as a co-activator of STAT6 in polarization of M2 macrophages (Vats et al., 2006).
Beyond its nuclear function, STAT6 is also associated with mitochondria in human hepatocytes, as well as endothelial and vascular smooth muscle cells (Khan et al., 2013). STAT6 possesses mitochondrial-targeting sequences and transmembrane segments anchored to the outer membrane of mitochondria (Kim et al., 2022). In this context, STAT6 interacts with mitofusin 2, inhibiting mitochondrial fusion. Mitochondrial STAT6-mitofusin two interaction can be induced by hypoxia, resulting in mitochondrial fragmentation, cytochrome c release and apoptosis (Kim et al., 2022). Moreover, IL-13/STAT6 signaling can increase mitochondrial reactive oxygen species production and decrease the mitochondrial membrane potential and ATP levels, leading to mitochondrial dysfunction and cellular senescence (Zhu et al., 2022).
Compared to wild-type (WT) mice, STAT6-deficient mice are resistant to allergic airway inflammation (Akimoto et al., 1998). On the other hand, genetically engineered mouse models with increased STAT6 activity present an exacerbated allergic inflammation (Bruns et al., 2003; Daniel et al., 2000). While human STAT6 deficiency has not yet been identified, as it may not be viable, human STAT6 single nucleotide polymorphisms are associated with multiple allergic and non-allergic diseases (Sharma et al., 2023), including atopic dermatitis, multiple food allergies, anaphylaxis, asthma, allergic rhinitis, eosinophilic gastrointestinal diseases, lymphoproliferation, osteoporosis, cerebral aneurysms, renal fibrosis, short stature, and hypotrichosis (for review see (Tolomeo and Cascio, 2024; Sturvey and Consortium, 2024)).
Pleiotropic immune and cellular process driven by STAT6 are summarized in Figure 2.
Figure 2. Stat6 signaling mediates pleiotropic immune and cellular process. STAT6 is implicated in Th2 immune response through the transcription factors GATA3 and Gfi-1. STAT6 also promote M2 (alternative) macrophage polarization through metabolic regulators PPARγ and PGC-1β. STAT6 acts on B cells, switching their immunoglobulin class, increasing the expression of various cell surface markers and inhibiting their apoptosis. STAT6 can also be anchored in mitochondrial membrane to interact with mitofusin 2, inhibiting mitochondrial fusion and triggering apoptosis and cellular senescence. Illustrations have been created manually using PowerPoint (Microsoft) and images originating from Servier Medical Art (https://smart.servier.com/), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).
In the present review, we summarize and briefly discuss the immunologic and physiological roles of STAT6 in the context of liver integrity and the potential role of this signaling pathway in both hepatoprotection and liver pathophysiological mechanisms.
2 Role of STAT6 in acute liver injury context
2.1 Ischemia/reperfusion (I/R)
Ischemia/reperfusion (I/R) injury represents an important physiological challenge, notably in the clinical context of organ transplantation. One of the components linked to hepatic I/R damage are activated CD4+ cells. A first study reported that following I/R, STAT6-deficient mice present identical hepatocellular damage and neutrophil accumulation compared to WT mice, in contrast to STAT4 deficient mice and nu/nu mice harboring a T cell deficiency that display reduced liver injury (Shen et al., 2003). Another publication has shown that contrary to WT mice, STAT6-deficient mice treated with recombinant adenovirus encoding IL-13 failed to improve hepatic function/histology during I/R injury, suggesting a mitigating effect for STAT6 in the inflammatory I/R response (Ke et al., 2004). In line with these data, administration of IL-13 reduced the production of pro-inflammatory proteins, suppressed liver neutrophil recruitment, hepatocellular injury and liver edema independently of NF-κB activation but greatly increased the activation of STAT6 (Yoshidome et al., 1999). In addition, IL-4 treatment protected liver grafts from transplantation-related I/R damage by polarizing Kupffer cells towards the anti-inflammatory M2 phenotype via the STAT6-JMJD3 pathway (Deng et al., 2020).
In the post-ischemic state, the acidic microenvironment resulting from increased anaerobic glycolysis promoted M1 but inhibited M2 polarization of macrophages and PPAR-γ signaling (Ding et al., 2021). Accordingly, the PPAR-γ agonist GW1929 inhibited M1 polarization and reduced I/R under acidic environment, representing an interesting therapeutic option in this context (Ding et al., 2021). Similarly, injection of mesenchymal stem cells prior to hepatic warm I/R restrained M1 but boosted M2 polarization of Kupffer cells via enhanced STAT6 phosphorylation, contributing to liver regeneration in fulminant hepatic failure in mice (Shang et al., 2023). Interestingly, deletion of the cell division cycle 42 (Cdc42) protein in myeloid cells alleviated hepatic necrosis and inflammation in I/R by favoring M2 polarization of hepatic myeloid macrophages via STAT6 activation (He et al., 2024). In line with these findings, the Cdc42 inhibitor ML141 protected mice from hepatic I/R injury (He et al., 2024).
2.2 Acute liver failure (ALF)
ALF is an inflammatory liver condition with high mortality. M2 macrophages, infiltrating the liver, play an important role in the prevention of ALF-related hepatocyte injury. In this context, it has been shown that mesenchymal stem cells alleviate ALF through STAT6-mediated M2 macrophage polarization (Li et al., 2021). The therapeutic potential of mesenchymal stem cells on ALF seems also to be dependent on the secretion of prostaglandin E2 (PGE2). In fact, mesenchymal stem cells-derived PGE2 inhibited NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome activity and its subsequent production of inflammatory cytokines, leading to M2 macrophage differentiation (Wang J. et al., 2021). In addition, mesenchymal stem cells treatment improved liver function by directly promoting M2 macrophage polarization via the JAK1/STAT6 signaling pathway in mouse models of ALF (Li Z. H. et al., 2023). Analogously, chemical compounds, such as the active halophenol derivative 2,4′,5′-Trihydroxyl-5,2′-dibromo diphenylmethanone (LM49), also attenuated ALF via the activation of the JAK1/STAT6 signaling pathway (Yang et al., 2021).
Taken together, the previously mentioned works suggest a protection mediated by STAT6 and its primordial role in macrophage polarization in the specific contexts of I/R and ALF. In contrast, in other biological contexts, and particularly in case of chronic hepatic damage, several other works highlight deleterious roles for STAT6-mediated immunity.
2.3 Concanavalin A (ConA)-induced liver injury
Con A is a plant lectin extracted from jack beans that binds to the mannose residues of several glycoproteins. As a translational model, ConA activates lymphocytes and when administered to mice, induces liver injury triggered by macrophage-mediated activation of T lymphocytes (Tiegs et al., 1992). In this context, STAT6 is rapidly activated under ConA administration (Jaruga et al., 2003). Accordingly, STAT6-deficient mice present abolished ConA-mediated liver injury with no change in IFN-γ/STAT1, IL-6/STAT3 or TNF-α/NF-κB signaling or natural killer T (NKT) cells activation (Jaruga et al., 2003). Mechanistically, infiltration of neutrophils and eosinophils in ConA-induced hepatitis is inhibited in STAT6-deficient mice compared to WT mice (Jaruga et al., 2003), suggesting that STAT6 plays a critical role in ConA-induced hepatitis. ConA interferes with Protein kinase C (PKC) localization and activity (Costa-Casnellie et al., 1985), (Matsumoto et al., 1993). Thus, PKC-zeta deficient mice display mitigated ConA-induced inflammation and reduced hepatocellular damage in parallel with the ablation of STAT6 tyrosine phosphorylation (Duran et al., 2004). In agreement with this deleterious action of STAT6 in hepatocyte survival, activation of Jak1/STAT6 signaling induces eotaxin in hepatocytes and triggers IL-5 production in NKT cells, both pathways promoting liver eosinophil recruitment and damage (Moscat et al., 2006). Moreover, IL-4 induces apoptosis of human hepatocytes through STAT6 activation in association with a decrease in mitochondrial membrane potential and an increase in caspase activation, independently of the Fas pathway (Aoudjehane et al., 2007). Of note, on the opposite to ConA, various phytochemicals (Chinese herbs, herb formulas) favorably regulate the STAT6 signaling pathway (Chen et al., 2022).
2.4 Parasitism
Schistosoma is a trematode that invades through the skin, affecting over 200 million people worldwide. Resistance to schistosoma infection is associated with a strong Th2 immune response in humans, which could lead to liver damage if not controlled. Interestingly, polymorphism (rs324013) in the STAT6 gene acts synergistically with IL-13 polymorphism (rs1800925) in human susceptibility to schistosomiasis (Isnard and Chevillard, 2008). Moreover, in C57BL/6 mice infected with Schistosoma japonicum, liver fibrosis is associated with enhanced phosphorylation of STAT6, in accordance with the hepatic upregulation of IL-4 and IL-13 receptors (Duan et al., 2019). Of note, egg-derived extracellular vesicles from Schistosoma japonicum contain Sja-miR-71a microRNA (miR) that inhibits both IL-13/STAT6 and Transforming growth factor (TGF)-β1/SMAD pathways via direct targeting of semaphorin 4D, leading to suppression of liver fibrosis by regulating the Th1/Th2/Th17/Treg balance (Wang et al., 2020).
Figure 3 illustrates the experimental situations of acute hepatic disorders in which STAT6 has been implicated and Table 1 described experimental details of studies investigating the role of STAT6 in this context.
Figure 3. STAT6 is mechanistically involved in various models of acute hepatic disorders. Illustrations have been created manually using PowerPoint (Microsoft) and images originating from Servier Medical Art (https://smart.servier.com/), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).
Table 1. Detailed descriptions of the experimental studies (including design, duration, and treatment details) investigating the role of STAT6 in acute liver injury context.
3 Role of STAT6 in chronic liver injury context
3.1 MASLD/MASH and lipid metabolism
Metabolic dysfunction-associated steatotic liver disease/steatohepatitis (MASLD/MASH) is currently the most common hepatic disorder in industrialized countries, mainly due to the obesity and type 2 diabetes pandemic (Younossi, 2019). MASLD can evolve towards a state of hepatic inflammation (steatohepatitis/MASH) (Younossi, 2019). Lifestyle changes could have beneficial effects on hepatic steatosis, but efficient drugs to limit progression of MASLD/MASH are still lacking (Younossi, 2019).
The first study investigating the implication of STAT6 signaling on liver homeostasis during MASLD/MASH analyzed the hepatic proteome of STAT6-deficient mice on chow and high-fat diet (HFD) using liquid chromatography–mass spectrometry (LC-MS) (Iff et al., 2009). In this study, changes in protein content indicated a disturbed lipid homeostasis and a state of hepatocellular stress in STAT6-deficient mice (Iff et al., 2009). Notably, hepatic fatty acid binding protein 1 (FABP1) was increased concomitantly to increased steatosis in STAT6 deficiency (Iff et al., 2009). Accordingly, another study demonstrated that exogenous IL-25 administration protects against hepatic steatosis through IL-13-induced activation of STAT6 (Wang et al., 2015). IL-25 promotes hepatic macrophage differentiation towards the M2a phenotype, both in vivo and in vitro, via the IL-13/STAT6 pathway, alleviating HFD-induced hepatic steatosis (Zheng et al., 2019).
Mechanistically, several works have highlighted the role of the IL-4/STAT6 immune axis on peripheral nutrient metabolism, notably through interactions between STAT6 and the nuclear receptor family of PPARs.
In specific, STAT6 interacts with PPAR-γ to elicit macrophage polarization towards an anti-inflammatory/insulin-sensitizing phenotype (Szanto et al., 2010). Moreover, liver proteome analysis of WT and STAT6-deficient mice treated with the PPAR-γ agonist rosiglitazone has shown that STAT6 modulate the expression of pyruvate kinase M2 (PKM2), an enzyme involved in the control of glycolysis and cell proliferation (Sajic et al., 2013). Interestingly, rosiglitazone induced PKM2 in liver but repressed its expression in adipose tissue. In addition, rosiglitazone limited liver steatosis while enhancing adipose fat accumulation and insulin sensitivity in STAT6-deficient mice (Sajic et al., 2013), suggesting a complex interaction between STAT6 and PPAR-γ in the regulation of whole-body fat distribution.
STAT6 also inhibits cholesterol synthesis through the miR-197–forkhead box protein J2 (FOXJ2) axis (Dubey and Saini, 2015). In addition, activation of STAT6 by IL-4 enhances insulin action by inhibiting the PPAR-α driven nutrient catabolism and adipose tissue inflammation (Ricardo-Gonzalez et al., 2010), illustrating molecular crosstalk between the immune system and macronutrient metabolism. Interestingly, the isoflavone formononetin ameliorated hepatocyte apoptosis, inflammatory response, and liver dysfunction through upregulation of STAT6 phosphorylation and downregulation of Protein Tyrosine Phosphatase 1B (PTP1B). PTP1B diminishes STAT6 signaling by dephosphorylating its S325 residue in its DNA binding domain and also acts as a negative regulator of the insulin signaling pathway by dephosphorylating the Tyr 1162 and 1163 residues of the insulin receptor (Wang et al., 2024).
STAT6-mediated processes are involved in the modulation of diverse other aspects of macrophage differentiation. For example, deletion of Inositol requiring enzyme 1α (IRE1α) (a marker of endoplasmic reticulum stress) could activate STAT6 and shift macrophages polarization towards the M2/anti-inflammatory state (Yang et al., 2018). In addition, mice with myeloid cell-specific deficiency for the transcription factor FoxO1 are protected against diet-induced MASH, revealing that FoxO1 counteracts STAT6 resulting in an increased number of macrophages differentiating towards the M1 state (Lee et al., 2022). STAT6 also interacts with PPAR-α-mediated effects. Indeed, data obtained from the Gene Expression Omnibus (GEO) and the BXD mouse reference population demonstrated that the Th2 cytokines IL-4 and IL-13 increase the secretion of the hepato-protector fibroblast growth factor 21 (FGF21) in the liver in a STAT6-dependent manner through PPAR-α inhibition (Kang et al., 2021).
STAT6 has also been involved in bile homeostasis. In fact, STAT6 phosphorylation by IL-4 or IL-13 increases the expression of Anoctamin-1 (TMEM16A), the Ca2+-activated Cl− channel in cholangiocytes, which contributes to ductular bile formation (Dutta et al., 2020). This function of STAT6 in bile formation/secretion makes STAT6 a potential target in cholestatic liver disorders. In accordance, dilauroylphosphatidylcholine activates liver receptor homolog-1 (LRH-1) which in turn induces phosphorylation and transcriptional activity of STAT6, and thus, promoting M2 macrophage polarization. This signaling cascade prevents liver injury and cholestasis (Ghos et al., 2024). In addition, the JAK1/2 inhibitor ruxolitinib reduces portal inflammation and bile duct damage in humans (Shao et al., 2022), inhibits the signaling of IFN-γ and the secretion of pro-inflammatory cytokines (IL-6, TNF-α and MCP-1) and promotes a STAT6-dependent macrophage polarization in the context of autoimmune cholangitis. Moreover, in murine liver, natural type 2 innate lymphoid cells (ILC2s) undergo expansion and increase amphiregulin production to drive STAT6-dependent epithelial proliferation (Russi et al., 2023). In line with these data, ILC2 transcripts are positively associated with cholangiocyte abundance in patients suffering from biliary atresia (Russi et al., 2023).
3.2 Fibrosis
While liver fat storage and inflammation are quite correctable, fibrosis resulting from these insults is often considered as a much less reversible step in the progression of liver disease. It has been shown that the IL-4/STAT6 and IL-13/STAT6 signaling pathways exacerbate the progression of metabolically induced liver fibrosis in mice on HFD (Hart et al., 2017). Accordingly, IL-13 serum levels as well as the IL-13 hepatic transcript content are elevated in patients with MASH compared to controls (Shimamura et al., 2008; Weng et al., 2009). Several lines of evidence suggest that STAT6 is involved in homeostasis and functioning of cell types implicated in extracellular matrix remodeling and collagen production. In fact, in culture of human liver myofibroblasts, STAT6 was activated by IL-4 and increased production of collagens I, III and IV (Aoudjehane et al., 2008). IL-4 and IL-13 induce miR-142-5p in macrophages sustaining their profibrogenic action (Su et al., 2015). Accordingly, in vitro, miR-142-5p mimics prolonged STAT6 phosphorylation by targeting its negative regulator SOCS1 (Su et al., 2015).
Hepatic stellate cells (HSCs) represent the main source of hepatic collagen production during MASLD/MASH. In the HSC cell line LI90, that expresses IL-4 and IL-13 receptors, as well as phosphorylated STAT6, in vitro administration of IL-4 or IL-13 increased the production of collagen while suppressing cell proliferation (Sugimoto et al., 2005). In human activated HSCs obtained from MASH biopsies, gene expression of IL-13Rα2 is upregulated (Shimamura et al., 2008) and STAT6-mediated HSC activation is triggered by IL-13 secreted by ILC2 cells (McHedlidze et al., 2013). However, IL-13 can also induce the profibrogenic connective tissue growth factor (CTGF) production by HSCs in damaged liver independently of STAT6 phosphorylation (Liu et al., 2011). In addition to its transactivating activity, STAT6 seems to directly interact with several proteins to trigger fibrosis. Accordingly, a protein-protein complex consisting of TGF-β1 receptor, Glutamyl-prolyl-tRNA synthetase (EPRS), Janus kinases, and STAT6 mediates prolyl-transfer RNA synthetase (PRS)-driven fibrosis (Song et al., 2019). Accordingly, the selective prolyl-tRNA synthetase (PRS) inhibitor (DWN12088) inhibits pro-fibrotic gene expression by suppressing TGFβR1/glutamyl-prolyl-tRNA synthetase (EPRS)/STAT6 axis signaling in the context of diet-induced MASH/fibrosis (Lee et al., 2024).
STAT6 has also been implicated in the fibrotic process occurring in response to carbon tetrachloride (CCl4) exposure. Of note, pro-fibrotic genes expressions are positively correlated with STAT6 activation in the liver of mice treated with CCl4 (Song et al., 2019). Interestingly, nutritional interventions modulating STAT6 signaling present anti-fibrotic properties. Oral administration of a bioactive chitooligosaccharide limits liver fibrosis in CCl4-exposed mice through mechanisms implicating the JAK1/STAT6 pathway in M2 macrophages/Kupffer cells (Liu et al., 2022). In addition, the traditional Chinese medicine Qijia Rougan Formula mitigated extracellular matrix deposition and fibrosis in the liver of CCl4-exposed rats by inhibiting macrophage M2 polarization (Zheng et al., 2023). Similarly, the monoterpenoid glycoside Paeoniflorin inhibits hepatic stellate cell activation and alleviate CCl4-induced extracellular matrix deposition via JAK2/STAT6 inhibition (Ma et al., 2020).
4 Role of STAT6 in liver cancer
STAT proteins not only orchestrate immune cell pools and activity but can also impact tumor cells. In fact, STAT proteins shape distinct metabolic/energetic processes that regulate tumor progression and even therapy resistance by transducing signals from metabolites, cytokines and growth factors (Li Y. J. et al., 2023).
Solitary fibrous tumor are rare fibroblastic mesenchymal tumors that can occur at virtually any site within the body (Thway et al., 2016). Despite the benign character of the tumor, 15%–20% of patients progress with either local recurrence or distant metastases (Tariq et al., 2021; Davanzo et al., 2018). One of the proteins that is linked to this tumor development is the NGFI-A Binding 11 Protein 2 (NAB2). NAB2 typically acts as a repressor of early growth response zinc finger DNA transcription factors. Patients suffering from solitary fibrous tumor and hemangiopericytomas present an intrachromosomal fusion between STAT6 and NAB2 genes, leading to the constitutive activation of NAB2 (Singh et al., 2021; Robinson et al., 2013; Chmielecki et al., 2013).
Beyond this case study, several evidence involve STAT6-driven type 2 polarization of immunity in cancer. In tumor micro-environment, different infiltrated cells can promote tumor growth and invasiveness, including M2 tumor-associated macrophages (TAMs). In fact, M2 macrophage polarization is involved in the inflammatory processes of breast (Rahal et al., 2018), colorectal (Chen et al., 2016), and lung (Fu et al., 2019) malignancies. In line with these studies, STAT6 pharmacologic inhibitors reduced tumor growth and metastatic process in both breast and gastric cancer through modulation of macrophage M2 polarization (Binnemars-Postma et al., 2018; Lu et al., 2018).
Analogously, several works have delineated a role for STAT6 in the development and metastasis of hepatocellular carcinoma (HCC), the most common type of primary liver cancer.
First, in vitro works have confirmed the role of STAT6 in cell cycle maintenance. STAT6 silencing significantly inhibited HepG2 and Hep3B hepatoma cells survival and proliferation (Qing et al., 2017). In agreement, nuclear expression of the metalloreductase STEAP3 significantly stimulated HCC cells proliferation by promoting cell cycle progression via a STAT6/Rac Family Small GTPase 1 (RAC1)/JNK signaling axis (Wang L. L. et al., 2021). Exposure of HuH7 and Hep3B hepatoma cells to IFN-α or IFN-β led to the formation of STAT2/STAT6 complexes, triggering the secretion of the anti-inflammatory interleukin-1 receptor antagonist (IL-1Ra) (Wan et al., 2008). Similarly, the administration of STAT6 inhibitor AS1517499 significantly attenuated tumor growth and early liver metastasis in an orthotopic 4T1 mammary carcinoma mouse model (Binnemars-Postma et al., 2018). STAT6 inhibitor treatment suppressed the M2 polarization and exerted an anti-HCC effect (Kong and Guo, 2023).
In addition, STAT6 induces the expression of the pyruvate kinase M2 (PKM2), an enzyme regulating both glycolysis and proliferation (Sajic et al., 2013). In this way, a STAT6 inhibition that dampens the expression of PKM2 could suppress the growth of tumor cells that are highly dependent of glycolysis. In fact, PKM2 activation promotes metastasis of HCC and inhibition of tumor cell autophagy (Yu et al., 2021; Park et al., 2016).
Another factor influencing the oncogenic role of STAT6 involves various long non-coding RNAs. Different long non-coding RNAs (lncRNAs) regulate STAT6 signaling with potential implication in liver oncogenesis. In the macrophage THP-1 cell line co-cultured with the liver cancer cell line H22, lncRNA-Colorectal Neoplasia Differentially Expressed (CRNDE) overexpression leads to STAT6 upregulation (Han et al., 2021). In vivo, downregulation of CRNDE mitigated tumor volume, diminished the expression of key angiogenesis-related proteins and simultaneously suppressed the expression of STAT6 and its phosphorylation. CRNDE could indirectly regulate tumor angiogenesis by promoting M2 polarization of macrophages, which is also one of the mechanisms of microenvironmental immune regulation in liver cancer (Han et al., 2021). Human and mouse Kupffer cells from metabolically induced HCC displayed increased lncRNA SNHG20 expression compared with MASLD Kupffer cells (Wang B. et al., 2019). In addition, lncRNA SNHG20 overexpression induced M2 polarization through STAT6 activation, while SNHG20 silencing concomitantly delayed STAT6-dependent M2 polarization and the progression of MASLD to HCC in mice (Wang B. et al., 2019).
After removal of the primary tumor, STAT6-deficient mice rejected liver metastasis and lived longer than WT mice in the same conditions (Ostrand-Rosenberg et al., 2002). STAT6 deficiency also corrected liver injury and inflammation induced by alpha-galactosylceramide, a specific agonist for invariant natural killer T (iNKT) cells evaluated in the context of treatment for liver cancer (Wang et al., 2013). Of note, STAT6 deficiency in Scurfy (sf) mice lacking Treg cells shortened their lifespan and increased their hepatic inflammation, suggesting a protective role of STAT6 in case of Treg cell depletion (Suscovich et al., 2012).
Anti-tumoral actions of different molecules/treatments have been associated with modulation of STAT6 signaling. For example, betulinic acid inhibits STAT6 phosphorylation and decreases M2 polarization in the microenvironment of liver cancer, resulting in antitumoral effect (Guo et al., 2023). Like the STAT6 inhibitor, the multi tyrosine kinase receptor inhibitor sunitinib suppressed M2 polarization of RAW264.7 murine macrophages and diminished JAK1-STAT6 signaling both in vitro and in vivo in mice, leading to dampening of the malignant behaviors of HCC cells (Kong and Guo, 2023). This anti-HCC action of sunitinib is related to its suppressive effect on the expression of Ki67 (Kong and Guo, 2023). More surprisingly, low-inorganic phosphate stress irreversibly repolarized tumor-associated macrophages towards the M1 phenotype by silencing STAT6 and activating the p65 subunit of NFκB (Lv et al., 2023). The major vault protein significantly increased infiltration of M2-type tumor-associated macrophages in tumor tissues of HCC patients, promoting HCC proliferation, metastasis, and invasion through enhanced STAT6 activity (Yu et al., 2023). In addition, in myofibroblasts the myeloid differentiation primary response protein 88 (MyD88) can promote MASLD-induced hepatocarcinogenesis by enhancing macrophage M2 polarization through a mechanism involving the C-C chemokine receptor type 1 (CCR1) receptor and the STAT6/PPAR-β pathway (Liu et al., 2024).
Clinically, analysis of a cohort containing hepatitis B virus-infected HCC patients (GSE14520) and data from The Cancer Genome Atlas showed that elevated STAT6 expression is a prognostic biomarker for HCC (Wang X. et al., 2019). Accordingly, bioinformatic analyses confirmed enrichment of STAT6 in pathways involved in cell cycle, cell division and lipid metabolism (Wang X. et al., 2019). Of note, STAT6 has been shown to be differentially expressed in tumor and non-tumor tissues (Wang X. et al., 2019). Moreover, STAT6 predicts a worse prognosis in HCC patients (Qing et al., 2017) and the overexpression of STAT6 was markedly correlated with more advanced clinical stages and pathological grades in HCC (Qi et al., 2020). Interestingly, STAT6 might be related to the gender prevalence of HCC. In fact, estrogen suppressed tumor growth functions by inhibiting the JAK1/STAT6 signaling pathway that drives macrophage M2 activation (Yan et al., 2012), potentially explaining predominance of HCC in men compared to women. In tumor-associated macrophages originating from HCC patients, membrane transport proteins responsible for the absorption of zinc (Zip9) promoted STAT6 phosphorylation and M2 macrophage polarization and concomitant inhibition of M1 macrophage polarization (Gou et al., 2022).
Figure 4 illustrates the pathophysiological steps leading to MASLD/MASH and HCC progression that are associated to STAT6 activity or that can be targeted by STAT6 modulators and Table 2 described experimental details of studies investigating the role of STAT6 in this context.
Figure 4. STAT6-related effects in MASLD/MASH/HCC progression. Illustrations have been created manually using PowerPoint (Microsoft) and images originating from Biorender (https://www.biorender.com/).
Table 2. Detailed descriptions of experimental studies (including design, duration, and treatment details) investigating the role of STAT6 in chronic liver injury context.
5 Conclusion
Several pathophysiological conditions are associated with an imbalance in immune cells polarization linked to inadequate STAT6 signaling. In consequence, STAT6 could represent an interesting therapeutic target, notably in the field of liver disorders. STAT6 appears to have dual roles. In fact, STAT6 presents a protective role in limiting inflammatory I/R response and acute liver failure. An activation of STAT6 could present a valuable interest in these pathophysiological contexts. In contrast, STAT6 activation appears detrimental in cases of fibrosis and liver tumors. Accordingly, pharmacological inhibitors or specific antisense oligonucleotides inhibiting STAT6 have shown interesting properties in vitro as well as in animal models to limit liver fibrosis or HCC occurrence/progression. Other related drugs also interfering with STAT6 signaling, such as the selective inhibitor of EGFR tyrosine kinase domain Gefitinib, also inhibiting IL-13/STAT6, could present important benefits, notably to enhance immunosurveillance in an oncologic field.
Author contributions
ES: Conceptualization, Project administration, Software, Validation, Writing – original draft, Writing – review and editing. MR: Writing – original draft, Writing – review and editing. IS: Writing – original draft, Writing – review and editing. KG: Writing – original draft, Writing – review and editing. FJ: Writing – original draft, Writing – review and editing.
Funding
The authors declare that financial support was received for the research and/or publication of this article. This work was funded by the SNSF grant 215330 (F.R.J), the Foundation of the Swiss Diabetes Association, the Swisslife Foundation, the Vontobel stiftung, and the Novartis stiftung. We thank Prof. Jacques Philippe for his kind support.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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References
Akimoto, T., Numata, F., Tamura, M., Takata, Y., Higashida, N., Takashi, T., et al. (1998). Abrogation of bronchial eosinophilic inflammation and airway hyperreactivity in signal transducers and activators of transcription (STAT)6-Deficient mice. J. Exp. Med. 187, 1537–1542. doi:10.1084/jem.187.9.1537
Aoudjehane, L., Podevin, P., Scatton, O., Jaffray, P., Dusanter-Fourt, I., Feldmann, G., et al. (2007). Interleukin-4 induces human hepatocyte apoptosis through a Fas-independent pathway. FASEB J. 21, 1433–1444. doi:10.1096/fj.06-6319com
Aoudjehane, L., Pissaia, A., Scatton, O., Podevin, P., Massault, P. P., Chouzenoux, S., et al. (2008). Interleukin-4 induces the activation and collagen production of cultured human intrahepatic fibroblasts via the STAT-6 pathway. Lab. Invest 88, 973–985. doi:10.1038/labinvest.2008.61
Binnemars-Postma, K., Bansal, R., Storm, G., and Prakash, J. (2018). Targeting the Stat6 pathway in tumor-associated macrophages reduces tumor growth and metastatic niche formation in breast cancer. FASEB J. 32, 969–978. doi:10.1096/fj.201700629R
Bruns, H. A., Schindler, U., and Kaplan, M. H. (2003). Expression of a constitutively active Stat6 in vivo alters lymphocyte homeostasis with distinct effects in T and B cells. J. Immunol. 170, 3478–3487. doi:10.4049/jimmunol.170.7.3478
Butcher, M. J., and Zhu, J. (2021). Recent advances in understanding the Th1/Th2 effector choice. Fac. Rev. 10, 30. doi:10.12703/r/10-30
Chen, W., Xu, Y., Zhong, J., Wang, H., Weng, M., Cheng, Q., et al. (2016). MFHAS1 promotes colorectal cancer progress by regulating polarization of tumor-associated macrophages via STAT6 signaling pathway. Oncotarget 7, 78726–78735. doi:10.18632/oncotarget.12807
Chen, J. Y., Xiao-Yun, T., Wei, S. S., Yang, Y. J., Deng, S., Jiao, C. J., et al. (2022). Perspectives of herbs and their natural compounds, and herb formulas on treating diverse diseases through regulating complicated JAK/STAT signaling. Front. Pharmacol. 13, 993862. doi:10.3389/fphar.2022.993862
Chmielecki, J., Crago, A. M., Rosenberg, M., O'Connor, R., Walker, S. R., Ambrogio, L., et al. (2013). Whole-exome sequencing identifies a recurrent NAB2-STAT6 fusion in solitary fibrous tumors. Nat. Genet. 45, 131–132. doi:10.1038/ng.2522
Costa-Casnellie, M. R., Segel, G. B., and Lichtman, M. A. (1985). Concanavalin A and phorbol ester cause opposite subcellular redistribution of protein kinase C. Biochem. Biophys. Res. Commun. 133, 1139–1144. doi:10.1016/0006-291x(85)91255-0
Daniel, C., Salvekar, A., and Schindler, U. (2000). A gain-of-function mutation in STAT6. J. Biol. Chem. 275, 14255–14259. doi:10.1074/jbc.c000129200
Darnell, J. E., Kerr, I. M., and Stark, G. R. (1994). Jak-STAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins. Science 264, 1415–1421. doi:10.1126/science.8197455
Davanzo, B., Emerson, R. E., Lisy, M., Koniaris, L. G., and Kays, J. K. (2018). Solitary fibrous tumor. Transl. Gastroenterol. Hepatol. 3, 94. doi:10.21037/tgh.2018.11.02
Deng, M., Wang, J., Wu, H., Wang, M., Cao, D., Li, J., et al. (2020). IL-4 alleviates ischaemia-reperfusion injury by inducing kupffer cells M2 polarization via STAT6-JMJD3 pathway after rat liver transplantation. Biomed. Res. Int. 2020, 2953068. doi:10.1155/2020/2953068
Ding, W., Duan, Y., Qu, Z., Feng, J., Zhang, R., Li, X., et al. (2021). Acidic microenvironment aggravates the severity of hepatic ischemia/reperfusion Injury by modulating M1-Polarization through regulating PPAR-gamma signal. Front. Immunol. 12, 697362. doi:10.3389/fimmu.2021.697362
Duan, M., Yang, Y., Peng, S., Liu, X., Zhong, J., Guo, Y., et al. (2019). C/EBP homologous protein (CHOP) activates macrophages and promotes liver fibrosis in schistosoma japonicum-Infected mice. J. Immunol. Res. 2019, 5148575. doi:10.1155/2019/5148575
Dubey, R., and Saini, N. (2015). STAT6 silencing up-regulates cholesterol synthesis via miR-197/FOXJ2 axis and induces ER stress-mediated apoptosis in lung cancer cells. Biochim. Biophys. Acta 1849, 32–43. doi:10.1016/j.bbagrm.2014.10.002
Duran, A., Rodriguez, A., Martin, P., Serrano, M., Flores, J. M., Leitges, M., et al. (2004). Crosstalk between PKCzeta and the IL4/Stat6 pathway during T-cell-mediated hepatitis. EMBO J. 23, 4595–4605. doi:10.1038/sj.emboj.7600468
Dutta, A. K., Boggs, K., Khimji, A. K., Getachew, Y., Wang, Y., Kresge, C., et al. (2020). Signaling through the interleukin-4 and interleukin-13 receptor complexes regulates cholangiocyte TMEM16A expression and biliary secretion. Am. J. Physiol. Gastrointest. Liver Physiol. 318, G771–G771. doi:10.1152/ajpgi.00219.2019
Elo, L. L., Jarvenpaa, H., Tuomela, S., Raghav, S., Ahlfors, H., Laurila, K., et al. (2010). Genome-wide profiling of interleukin-4 and STAT6 transcription factor regulation of human Th2 cell programming. Immunity 32, 852–862. doi:10.1016/j.immuni.2010.06.011
Fu, C., Jiang, L., Hao, S., Liu, Z., Ding, S., Zhang, W., et al. (2019). Activation of the IL-4/STAT6 signaling pathway promotes lung cancer progression by increasing M2 myeloid cells. Front. Immunol. 10, 2638. doi:10.3389/fimmu.2019.02638
Ghosh, S., Devereaux, M. W., Liu, C., and Sokol, R. J. (2024). LRH-1 agonist DLPC through STAT6 promotes macrophage polarization and prevents parenteral nutrition-associated cholestasis in mice. Hepatology 79, 986–1004. doi:10.1097/HEP.0000000000000690
Goenka, S., and Kaplan, M. H. (2011). Transcriptional regulation by STAT6. Immunol. Res. 50, 87–96. doi:10.1007/s12026-011-8205-2
Gou, Y., Yang, D., Tian, T., Zhu, X., Zhang, R., Ren, J., et al. (2022). The transcription of ZIP9 is associated with the macrophage polarization and the pathogenesis of hepatocellular carcinoma. Front. Immunol. 13, 725595. doi:10.3389/fimmu.2022.725595
Guo, L., Pei, H., Yang, Y., and Kong, Y. (2023). Betulinic acid regulates tumor-associated macrophage M2 polarization and plays a role in inhibiting the liver cancer progression. Int. Immunopharmacol. 122, 110614. doi:10.1016/j.intimp.2023.110614
Han, C., Yang, Y., Sheng, Y., Wang, J., Li, W., Zhou, X., et al. (2021). The mechanism of lncRNA-CRNDE in regulating tumour-associated macrophage M2 polarization and promoting tumour angiogenesis. J. Cell Mol. Med. 25, 4235–4247. doi:10.1111/jcmm.16477
Hart, K. M., Fabre, T., Sciurba, J. C., Gieseck, R. L., Borthwick, L. A., Vannella, K. M., et al. (2017). Type 2 immunity is protective in metabolic disease but exacerbates NAFLD collaboratively with TGF-Beta. Sci. Transl. Med. 9. doi:10.1126/scitranslmed.aal3694
He, J., Tang, M. Y., Liu, L. X., Kong, C. X., Chen, W., Wang, L., et al. (2024). Myeloid deletion of Cdc42 protects liver from hepatic ischemia-reperfusion injury via inhibiting macrophage-mediated inflammation in mice. Cell Mol. Gastroenterol. Hepatol. 17, 965–981. doi:10.1016/j.jcmgh.2024.01.023
Hebenstreit, D., Wirnsberger, G., Horejs-Hoeck, J., and Duschl, A. (2006). Signaling mechanisms, interaction partners, and target genes of STAT6. Cytokine Growth Factor Rev. 17, 173–188. doi:10.1016/j.cytogfr.2006.01.004
Hou, J., Schindler, U., Henzel, W. J., Ho, T. C., Brasseur, M., and McKnight, S. L. (1994). An interleukin-4-induced transcription factor: IL-4 stat. Science 265, 1701–1706. doi:10.1126/science.8085155
Huang, H., Zheng, Y., Li, L., Shi, W., Zhang, R., Liu, H., et al. (2020). The roles of post-translational modifications and coactivators of STAT6 signaling in tumor growth and progression. Future Med. Chem. 12, 1945–1960. doi:10.4155/fmc-2020-0224
Iff, J., Wang, W., Sajic, T., Oudry, N., Gueneau, E., Hopfgartner, G., et al. (2009). Differential proteomic analysis of STAT6 knockout mice reveals new regulatory function in liver lipid homeostasis. J. Proteome Res. 8, 4511–4524. doi:10.1021/pr9003272
Isnard, A., and Chevillard, C. (2008). Recent advances in the characterization of genetic factors involved in human susceptibility to infection by schistosomiasis. Curr. Genomics 9, 290–300. doi:10.2174/138920208785133262
Jaruga, B., Hong, F., Sun, R., Radaeva, S., and Gao, B. (2003). Crucial role of IL-4/STAT6 in T cell-mediated hepatitis: up-regulating eotaxins and IL-5 and recruiting leukocytes. J. Immunol. 171, 3233–3244. doi:10.4049/jimmunol.171.6.3233
Junttila, I. S. (2018). Tuning the cytokine responses: an update on interleukin (IL)-4 and IL-13 receptor complexes. Front. Immunol. 9, 888. doi:10.3389/fimmu.2018.00888
Kang, S. G., Lee, S. E., Choi, M. J., Chang, J. Y., Kim, J. T., Zhang, B. Y., et al. (2021). Th2 cytokines increase the expression of fibroblast growth factor 21 in the liver. Cells 10, 1298. doi:10.3390/cells10061298
Kaplan, M. H., Daniel, C., Schindler, U., and Grusby, M. J. (1998). Stat proteins control lymphocyte proliferation by regulating p27Kip1 expression. Mol. Cell Biol. 18, 1996–2003. doi:10.1128/mcb.18.4.1996
Ke, B., Shen, X. D., Gao, F., Busuttil, R. W., and Kupiec-Weglinski, J. W. (2004). Interleukin 13 gene transfer in liver ischemia and reperfusion injury: role of Stat6 and TLR4 pathways in cytoprotection. Hum. Gene Ther. 15, 691–698. doi:10.1089/1043034041361244
Khan, R., Lee, J. E., Yang, Y. M., Liang, F. X., and Sehgal, P. B. (2013). Live-cell imaging of the association of STAT6-GFP with mitochondria. PLoS One 8, e55426. doi:10.1371/journal.pone.0055426
Kim, H., Park, S. J., and Jou, I. (2022). STAT6 in mitochondrial outer membrane impairs mitochondrial fusion by inhibiting MFN2 dimerization. iScience 25, 104923. doi:10.1016/j.isci.2022.104923
Kong, Y., and Guo, L. (2023). Sunitinib suppresses M2 polarization of macrophages in tumor microenvironment to regulate hepatocellular carcinoma progression. J. Biochem. Mol. Toxicol. 37, e23333. doi:10.1002/jbt.23333
Lee, S., Usman, T. O., Yamauchi, J., Chhetri, G., Wang, X., Coudriet, G. M., et al. (2022). Myeloid FoxO1 depletion attenuates hepatic inflammation and prevents nonalcoholic steatohepatitis. J. Clin. Invest 132, e154333. doi:10.1172/JCI154333
Lee, D. K., Jo, S. H., Lee, E. S., Ha, K. B., Park, N. W., Kong, D. H., et al. (2024). DWN12088, A Prolyl-tRNA synthetase inhibitor, alleviates hepatic injury in nonalcoholic steatohepatitis. Diabetes Metab. J. 48, 97–111. doi:10.4093/dmj.2022.0367
Li, Y., Sheng, Q., Zhang, C., Han, C., Bai, H., Lai, P., et al. (2021). STAT6 up-regulation amplifies M2 macrophage anti-inflammatory capacity through mesenchymal stem cells. Int. Immunopharmacol. 91, 107266. doi:10.1016/j.intimp.2020.107266
Li, Z. H., Chen, J. F., Zhang, J., Lei, Z. Y., Wu, L. L., Meng, S. B., et al. (2023a). Mesenchymal stem cells promote polarization of M2 macrophages in mice with acute-on-chronic liver failure via Mertk/JAK1/STAT6 signaling. Stem Cells 41, 1171–1184. doi:10.1093/stmcls/sxad069
Li, Y. J., Zhang, C., Martincuks, A., Herrmann, A., and Yu, H. (2023b). STAT proteins in cancer: orchestration of metabolism. Nat. Rev. Cancer 23, 115–134. doi:10.1038/s41568-022-00537-3
Linehan, L. A., Warren, W. D., Thompson, P. A., Grusby, M. J., and Berton, M. T. (1998). STAT6 is required for IL-4-induced germline Ig gene transcription and switch recombination. J. Immunol. 161, 302–310. doi:10.4049/jimmunol.161.1.302
Liu, Y., Meyer, C., Muller, A., Herweck, F., Li, Q., Mullenbach, R., et al. (2011). IL-13 induces connective tissue growth factor in rat hepatic stellate cells via TGF-beta-independent smad signaling. J. Immunol. 187, 2814–2823. doi:10.4049/jimmunol.1003260
Liu, P., Li, H., Gong, J., Geng, Y., Jiang, M., Xu, H., et al. (2022). Chitooligosaccharides alleviate hepatic fibrosis by regulating the polarization of M1 and M2 macrophages. Food Funct. 13, 753–768. doi:10.1039/d1fo03768d
Liu, Y., Chen, H., Yan, X., Zhang, J., Deng, Z., Huang, M., et al. (2024). MyD88 in myofibroblasts enhances nonalcoholic fatty liver disease-related hepatocarcinogenesis via promoting macrophage M2 polarization. Cell Commun. Signal 22, 86. doi:10.1186/s12964-024-01489-x
Lu, G., Shi, W., and Zheng, H. (2018). Inhibition of STAT6/Anoctamin-1 activation suppresses proliferation and invasion of gastric cancer cells. Cancer Biother Radiopharm. 33, 3–7. doi:10.1089/cbr.2017.2287
Lv, Y. F., Liao, Z. Q., Bi, Q. C., Xie, C. S., Wei, X. Y., Yun, Y., et al. (2023). Irreversible repolarization of tumour-associated macrophages by low-Pi stress inhibits the progression of hepatocellular carcinoma. J. Cell Mol. Med. 27, 2906–2921. doi:10.1111/jcmm.17861
Ma, X., Zhang, W., Jiang, Y., Wen, J., Wei, S., and Zhao, Y. (2020). Paeoniflorin, a natural product with multiple targets in liver Diseases-A mini review. Front. Pharmacol. 11, 531. doi:10.3389/fphar.2020.00531
Matsumoto, N., Toyoshima, S., and Osawa, T. (1993). Characterization of the 50 kDa protein phosphorylated in concanavalin A-stimulated mouse T cells. J. Biochem. 113, 630–636. doi:10.1093/oxfordjournals.jbchem.a124094
McHedlidze, T., Waldner, M., Zopf, S., Walker, J., Rankin, A. L., Schuchmann, M., et al. (2013). Interleukin-33-dependent innate lymphoid cells mediate hepatic fibrosis. Immunity 39, 357–371. doi:10.1016/j.immuni.2013.07.018
Moscat, J., Rennert, P., and Diaz-Meco, M. T. (2006). PKCzeta at the crossroad of NF-kappaB and Jak1/Stat6 signaling pathways. Cell Death Differ. 13, 702–711. doi:10.1038/sj.cdd.4401823
Murata, T., Taguchi, J., Puri, R. K., and Mohri, H. (1999). Sharing of receptor subunits and signal transduction pathway between the IL-4 and IL-13 receptor system. Int. J. Hematol. 69, 13–20. Available online at: https://pubmed.ncbi.nlm.nih.gov/10641437/
Ohmori, Y., and Hamilton, T. A. (2000). Interleukin-4/STAT6 represses STAT1 and NF-kappa B-dependent transcription through distinct mechanisms. J. Biol. Chem. 275, 38095–38103. doi:10.1074/jbc.M006227200
Ostrand-Rosenberg, S., Clements, V. K., Terabe, M., Park, J. M., Berzofsky, J. A., and Dissanayake, S. K. (2002). Resistance to metastatic disease in STAT6-deficient mice requires hemopoietic and nonhemopoietic cells and is IFN-gamma dependent. J. Immunol. 169, 5796–5804. doi:10.4049/jimmunol.169.10.5796
Park, Y. S., Kim, D. J., Koo, H., Jang, S. H., You, Y. M., Cho, J. H., et al. (2016). AKT-induced PKM2 phosphorylation signals for IGF-1-stimulated cancer cell growth. Oncotarget 7, 48155–48167. doi:10.18632/oncotarget.10179
Qi, Z., Yan, F., Chen, D., Xing, W., Li, Q., Zeng, W., et al. (2020). Identification of prognostic biomarkers and correlations with immune infiltrates among cGAS-STING in hepatocellular carcinoma. Biosci. Rep. 40. doi:10.1042/BSR20202603
Qing, T., Yamin, Z., Guijie, W., Yan, J., and Zhongyang, S. (2017). STAT6 silencing induces hepatocellular carcinoma-derived cell apoptosis and growth inhibition by decreasing the RANKL expression. Biomed. Pharmacother. 92, 1–6. doi:10.1016/j.biopha.2017.05.029
Rahal, O. M., Wolfe, A. R., Mandal, P. K., Larson, R., Tin, S., Jimenez, C., et al. (2018). Blocking interleukin (IL)4- and IL13-Mediated phosphorylation of STAT6 (Tyr641) decreases M2 polarization of macrophages and protects against macrophage-mediated radioresistance of inflammatory breast cancer. Int. J. Radiat. Oncol. Biol. Phys. 100, 1034–1043. doi:10.1016/j.ijrobp.2017.11.043
Ricardo-Gonzalez, R. R., Red Eagle, A., Odegaard, J. I., Jouihan, H., Morel, C. R., Heredia, J. E., et al. (2010). IL-4/STAT6 immune axis regulates peripheral nutrient metabolism and insulin sensitivity. Proc. Natl. Acad. Sci. U. S. A. 107, 22617–22622. doi:10.1073/pnas.1009152108
Robinson, D. R., Wu, Y. M., Kalyana-Sundaram, S., Cao, X., Lonigro, R. J., Sung, Y. S., et al. (2013). Identification of recurrent NAB2-STAT6 gene fusions in solitary fibrous tumor by integrative sequencing. Nat. Genet. 45, 180–185. doi:10.1038/ng.2509
Russi, A. E., Shivakumar, P., Luo, Z., and Bezerra, J. A. (2023). Plasticity between type 2 innate lymphoid cell subsets and amphiregulin expression regulates epithelial repair in biliary atresia. Hepatology 78, 1035–1049. doi:10.1097/HEP.0000000000000418
Sajic, T., Hainard, A., Scherl, A., Wohlwend, A., Negro, F., Sanchez, J. C., et al. (2013). STAT6 promotes bi-directional modulation of PKM2 in liver and adipose inflammatory cells in rosiglitazone-treated mice. Sci. Rep. 3, 2350. doi:10.1038/srep02350
Scheinman, E. J., and Avni, O. (2009). Transcriptional regulation of GATA3 in T helper cells by the integrated activities of transcription factors downstream of the interleukin-4 receptor and T cell receptor. J. Biol. Chem. 284, 3037–3048. doi:10.1074/jbc.M807302200
Schindler, C., and Darnell, J. E. (1995). Transcriptional responses to polypeptide ligands: the JAK-STAT pathway. Annu. Rev. Biochem. 64, 621–651. doi:10.1146/annurev.bi.64.070195.003201
Shang, L. C., Wang, M., Liu, Y., Zhu, X., and Wang, S. (2023). MSCs ameliorate hepatic IR injury by modulating phenotypic transformation of kupffer cells through Drp-1 dependent mitochondrial dynamics. Stem Cell Rev. Rep. 19, 1965–1980. doi:10.1007/s12015-023-10566-6
Shao, T., Leung, P. S. C., Zhang, W., Tsuneyama, K., Ridgway, W. M., Young, H. A., et al. (2022). Treatment with a JAK1/2 inhibitor ameliorates murine autoimmune cholangitis induced by IFN overexpression. Cell Mol. Immunol. 19, 1130–1140. doi:10.1038/s41423-022-00904-y
Sharma, M., Leung, D., Momenilandi, M., Jones, L. C. W., Pacillo, L., James, A. E., et al. (2023). Human germline heterozygous gain-of-function STAT6 variants cause severe allergic disease. J. Exp. Med. 220, e20221755. doi:10.1084/jem.20221755
Shen, X. D., Ke, B., Zhai, Y., Gao, F., Anselmo, D., Lassman, C. R., et al. (2003). Stat4 and Stat6 signaling in hepatic ischemia/reperfusion injury in mice: HO-1 dependence of Stat4 disruption-mediated cytoprotection. Hepatology 37, 296–303. doi:10.1053/jhep.2003.50066
Shimamura, T., Fujisawa, T., Husain, S. R., Kioi, M., Nakajima, A., and Puri, R. K. (2008). Novel role of IL-13 in fibrosis induced by nonalcoholic steatohepatitis and its amelioration by IL-13R-directed cytotoxin in a rat model. J. Immunol. 181, 4656–4665. doi:10.4049/jimmunol.181.7.4656
Shimoda, K., van Deursen, J., Sangster, M. Y., Sarawar, S. R., Carson, R. T., Tripp, R. A., et al. (1996). Lack of IL-4-induced Th2 response and IgE class switching in mice with disrupted Stat6 gene. Nature 380, 630–633. doi:10.1038/380630a0
Sica, A., and Mantovani, A. (2012). Macrophage plasticity and polarization: in vivo veritas. J. Clin. Invest 122, 787–795. doi:10.1172/JCI59643
Singh, N., Collingwood, R., Eich, M. L., Robinson, A., Varambally, S., Al Diffalha, S., et al. (2021). NAB2-STAT6 gene fusions to evaluate Primary/Metastasis of Hemangiopericytoma/Solitary fibrous tumors. Am. J. Clin. Pathol. 156, 906–912. doi:10.1093/ajcp/aqab045
Song, D. G., Kim, D., Jung, J. W., Nam, S. H., Kim, J. E., Kim, H. J., et al. (2019). Glutamyl-prolyl-tRNA synthetase induces fibrotic extracellular matrix via both transcriptional and translational mechanisms. FASEB J. 33, 4341–4354. doi:10.1096/fj.201801344RR
Stavnezer, J. (1996). Antibody class switching. Adv. Immunol. 61, 79–146. doi:10.1016/s0065-2776(08)60866-4
Sturvey, ca, and Consortium, S. G. I. (2024). Human germline gain-of-function in STAT6: from severe allergic disease to lymphoma and beyond. Trends Immunol. 45, 138–153. doi:10.1016/j.it.2023.12.003
Su, S., Zhao, Q., He, C., Huang, D., Liu, J., Chen, F., et al. (2015). miR-142-5p and miR-130a-3p are regulated by IL-4 and IL-13 and control profibrogenic macrophage program. Nat. Commun. 6, 8523. doi:10.1038/ncomms9523
Sugimoto, R., Enjoji, M., Nakamuta, M., Ohta, S., Kohjima, M., Fukushima, M., et al. (2005). Effect of IL-4 and IL-13 on collagen production in cultured LI90 human hepatic stellate cells. Liver Int. 25, 420–428. doi:10.1111/j.1478-3231.2005.01087.x
Suscovich, T. J., Perdue, N. R., and Campbell, D. J. (2012). Type-1 immunity drives early lethality in scurfy mice. Eur. J. Immunol. 42, 2305–2310. doi:10.1002/eji.201242391
Szanto, A., Balint, B. L., Nagy, Z. S., Barta, E., Dezso, B., Pap, A., et al. (2010). STAT6 transcription factor is a facilitator of the nuclear receptor PPARγ-regulated gene expression in macrophages and dendritic cells. Immunity 33, 699–712. doi:10.1016/j.immuni.2010.11.009
Takeda, K., Tanaka, T., Shi, W., Matsumoto, M., Minami, M., Kashiwamura, S., et al. (1996). Essential role of Stat6 in IL-4 signalling. Nature 380, 627–630. doi:10.1038/380627a0
Takeda, K., Kishimoto, T., and Akira, S. (1997). STAT6: its role in interleukin 4-mediated biological functions. J. Mol. Med. Berl. 75, 317–326. doi:10.1007/s001090050117
Tariq, M. U., Din, N. U., Abdul-Ghafar, J., and Park, Y. K. (2021). The many faces of solitary fibrous tumor; diversity of histological features, differential diagnosis and role of molecular studies and surrogate markers in avoiding misdiagnosis and predicting the behavior. Diagn Pathol. 16, 32. doi:10.1186/s13000-021-01095-2
Thway, K., Ng, W., Noujaim, J., Jones, R. L., and Fisher, C. (2016). The Current status of solitary fibrous tumor: diagnostic features, variants, and genetics. Int. J. Surg. Pathol. 24, 281–292. doi:10.1177/1066896915627485
Tiegs, G., Hentschel, J., and Wendel, A. (1992). A T cell-dependent experimental liver injury in mice inducible by concanavalin A. J. Clin. Invest 90, 196–203. doi:10.1172/JCI115836
Tolomeo, M., and Cascio, A. (2024). STAT4 and STAT6, their role in cellular and humoral immunity and in diverse human diseases. Int. Rev. Immunol. 43, 394–418. doi:10.1080/08830185.2024.2395274
Tolomeo, M., Cavalli, A., and Cascio, A. (2022). STAT1 and its crucial role in the control of viral infections. Int. J. Mol. Sci. 23, 4095. doi:10.3390/ijms23084095
Vats, D., Mukundan, L., Odegaard, J. I., Zhang, L., Smith, K. L., Morel, C. R., et al. (2006). Oxidative metabolism and PGC-1beta attenuate macrophage-mediated inflammation. Cell Metab. 4, 13–24. doi:10.1016/j.cmet.2006.05.011
Wan, L., Lin, C. W., Lin, Y. J., Sheu, J. J., Chen, B. H., Liao, C. C., et al. (2008). Type I IFN induced IL1-Ra expression in hepatocytes is mediated by activating STAT6 through the formation of STAT2: STAT6 heterodimer. J. Cell Mol. Med. 12, 876–888. doi:10.1111/j.1582-4934.2008.00143.x
Wang, Y., and Levy, D. E. (2012). Comparative evolutionary genomics of the STAT family of transcription factors. JAKSTAT 1, 23–33. doi:10.4161/jkst.19418
Wang, H., Feng, D., Park, O., Yin, S., and Gao, B. (2013). Invariant NKT cell activation induces neutrophil accumulation and hepatitis: opposite regulation by IL-4 and IFN-γ. Hepatology 58, 1474–1485. doi:10.1002/hep.26471
Wang, A. J., Yang, Z., Grinchuk, V., Smith, A., Qin, B., Lu, N., et al. (2015). IL-25 or IL-17E protects against high-fat diet-induced hepatic steatosis in mice dependent upon IL-13 activation of STAT6. J. Immunol. 195, 4771–4780. doi:10.4049/jimmunol.1500337
Wang, B., Li, X., Hu, W., Zhou, Y., and Din, Y. (2019a). Silencing of lncRNA SNHG20 delays the progression of nonalcoholic fatty liver disease to hepatocellular carcinoma via regulating liver Kupffer cells polarization. IUBMB Life 71, 1952–1961. doi:10.1002/iub.2137
Wang, X., Liao, X., Yu, T., Gong, Y., Zhang, L., Huang, J., et al. (2019b). Analysis of clinical significance and prospective molecular mechanism of main elements of the JAK/STAT pathway in hepatocellular carcinoma. Int. J. Oncol. 55, 805–822. doi:10.3892/ijo.2019.4862
Wang, L., Liao, Y., Yang, R., Yu, Z., Zhang, L., Zhu, Z., et al. (2020). Sja-miR-71a in Schistosome egg-derived extracellular vesicles suppresses liver fibrosis caused by schistosomiasis via targeting semaphorin 4D. J. Extracell. Vesicles 9, 1785738. doi:10.1080/20013078.2020.1785738
Wang, J., Liu, Y., Ding, H., Shi, X., and Ren, H. (2021a). Mesenchymal stem cell-secreted prostaglandin E(2) ameliorates acute liver failure via attenuation of cell death and regulation of macrophage polarization. Stem Cell Res. Ther. 12, 15. doi:10.1186/s13287-020-02070-2
Wang, L. L., Luo, J., He, Z. H., Liu, Y. Q., Li, H. G., Xie, D., et al. (2021b). STEAP3 promotes cancer cell proliferation by facilitating nuclear trafficking of EGFR to enhance RAC1-ERK-STAT3 signaling in hepatocellular carcinoma. Cell Death Dis. 12, 1052. doi:10.1038/s41419-021-04329-9
Wang, J., Wang, L., Han, L., Han, Y., Gu, J., and Chen, Z. (2024). Formononetin attenuates hepatic injury in diabetic mice by regulating macrophage polarization through the PTP1B/STAT6 axis. Int. Immunopharmacol. 140, 112802. doi:10.1016/j.intimp.2024.112802
Weng, H. L., Liu, Y., Chen, J. L., Huang, T., Xu, L. J., Godoy, P., et al. (2009). The etiology of liver damage imparts cytokines transforming growth factor beta1 or interleukin-13 as driving forces in fibrogenesis. Hepatology 50, 230–243. doi:10.1002/hep.22934
Wurster, A. L., Rodgers, V. L., White, M. F., Rothstein, T. L., and Grusby, M. J. (2002). Interleukin-4-mediated protection of primary B cells from apoptosis through Stat6-dependent up-regulation of Bcl-xL. J. Biol. Chem. 277, 27169–27175. doi:10.1074/jbc.M201207200
Yang, W., Lu, Y., Xu, Y., Xu, L., Zheng, W., Wu, Y., et al. (2012). Estrogen represses hepatocellular carcinoma (HCC) growth via inhibiting alternative activation of tumor-associated macrophages (TAMs). J. Biol. Chem. 287, 40140–40149. doi:10.1074/jbc.M112.348763
Yang, F., Wang, S., Liu, Y., Zhou, Y., Shang, L., Feng, M., et al. (2018). IRE1α aggravates ischemia reperfusion injury of fatty liver by regulating phenotypic transformation of kupffer cells. Free Radic. Biol. Med. 124, 395–407. doi:10.1016/j.freeradbiomed.2018.06.043
Yang, F., Cai, H., Zhang, X., Sun, J., Feng, X., Yuan, H., et al. (2021). An active marine halophenol derivative attenuates lipopolysaccharide-induced acute liver injury in mice by improving M2 macrophage-mediated therapy. Int. Immunopharmacol. 96, 107676. doi:10.1016/j.intimp.2021.107676
Yoshidome, H., Kato, A., Miyazaki, M., Edwards, M. J., and Lentsch, A. B. (1999). IL-13 activates STAT6 and inhibits liver injury induced by ischemia/reperfusion. Am. J. Pathol. 155, 1059–1064. doi:10.1016/S0002-9440(10)65208-X
Younossi, Z. M. (2019). Non-alcoholic fatty liver disease - a global public health perspective. J. Hepatol. 70, 531–544. doi:10.1016/j.jhep.2018.10.033
Yu, Z., Wang, D., and Tang, Y. (2021). PKM2 promotes cell metastasis and inhibits autophagy via the JAK/STAT3 pathway in hepatocellular carcinoma. Mol. Cell Biochem. 476, 2001–2010. doi:10.1007/s11010-020-04041-w
Yu, C., Zhu, Q., Ma, C., Luo, C., Nie, L., Cai, H., et al. (2023). Major vault protein regulates tumor-associated macrophage polarization through interaction with signal transducer and activator of transcription 6. Front. Immunol. 14, 1289795. doi:10.3389/fimmu.2023.1289795
Zheng, X. L., Wu, J. P., Gong, Y., Hong, J. B., Xiao, H. Y., Zhong, J. W., et al. (2019). IL-25 protects against high-fat diet-induced hepatic steatosis in mice by inducing IL-25 and M2a macrophage production. Immunol. Cell Biol. 97, 165–177. doi:10.1111/imcb.12207
Zheng, Y., Ji, S., Li, X., and Wen, L. (2023). Qijia rougan formula ameliorates ECM deposition in hepatic fibrosis by regulating the JAK1/STAT6-microRNA-23a feedback loop in macrophage M2 polarization. Biomed. Pharmacother. 168, 115794. doi:10.1016/j.biopha.2023.115794
Zhu, J., and Paul, W. E. (2008). CD4 T cells: fates, functions, and faults. Blood 112, 1557–1569. doi:10.1182/blood-2008-05-078154
Keywords: STAT6, Ischemia-reperfusion, acute liver damage, MASLD, MASH, fibrosis, HCC, immune polarization
Citation: Somm E, Rahman M, Szanto I, Gariani K and Jornayvaz FR (2025) Modulation of STAT6 signaling for hepatoprotection . Front. Pharmacol. 16:1659227. doi: 10.3389/fphar.2025.1659227
Received: 03 July 2025; Accepted: 31 October 2025;
Published: 02 December 2025.
Edited by:
Ramin Massoumi, Lund University, SwedenReviewed by:
Hanan Salah El-Abhar, Cairo University, EgyptAnkit P. Laddha, University of Connecticut, United States
Copyright © 2025 Somm, Rahman, Szanto, Gariani and Jornayvaz. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Emmanuel Somm, ZW1tYW51ZWwuc29tbUB1bmlnZS5jaA==
†ORCID: Karim Gariani, orcid.org/0000-0001-8089-4785; François R. Jornayvaz, orcid.org/0000-0001-9425-3137Emmanuel Somm, orcid.org/0000-0002-0649-3542; Ildiko Szanto, orcid.org/0000-0003-3566-7991