REVIEW article

Front. Physiol., 02 September 2022

Sec. Skeletal Physiology

Volume 13 - 2022 | https://doi.org/10.3389/fphys.2022.954454

The Wnt signaling cascade in the pathogenesis of osteoarthritis and related promising treatment strategies

  • 1. Department of Orthopaedics, Xuancheng Central Hospital, Xuancheng, China

  • 2. Department of Orthopaedics, Xiangya Hospital, Central South University, Changsha, China

Abstract

Osteoarthritis (OA) is the most prevalent joint disease, characterized by the degradation of articular cartilage, synovial inflammation, and changes in periarticular and subchondral bone. Recent studies have reported that Wnt signaling cascades play an important role in the development, growth, and homeostasis of joints. The Wnt signaling cascade should be tightly regulated to maintain the homeostasis of cartilage in either the over-activation or the suppression of Wnt/β-catenin, as this could lead to OA. This review summarizes the role and mechanism of canonical Wnt cascade and noncanonical Wnt cascade experiments in vivo and in vitro. The Wnt cascade is controlled by several agonists and antagonists in the extracellular medium and the cytoplasm. These antagonists and agonists serve as key molecules in drug intervention into the Wnt pathway and may provide potential approaches for the treatment of OA. However, the complexity of the Wnt signaling cascade and the pharmaceutical effects on its mechanism are still not fully understood, which forces us to conduct further research and develop efficient therapeutic approaches to treat OA.

Introduction

Osteoarthritis (OA) is the most prevalent joint disease, characterized by breakdown of the articular cartilage, abnormal bone remodeling, and osteophytosis that lead to chronic pain and functional restrictions of the affected joints. Radiographic evidence of OA is found in the majority of people by 65 years old, and approximately 80% of people aged over 75 years old are affected (). A large number of studies have reported the incidence of OA, but its pathogenesis has not been fully elucidated.

Articular cartilage degeneration is a major cause of pathological changes in OA. Cartilage is an avascular, neural, lymphatic, and viscoelastic connective tissue, and its main function is to bear loads, promoting the frictionless movement of the joints (Kuettner et al., 1991). Chondrocytes, the only cell population in adult articular cartilage, are capable of responding to structural changes, including the synthesis of collagen and the degeneration of the extracellular matrix (ECM), although the capacity of adult articular chondrocytes to regenerate normal cartilage matrix architecture is limited and declines with age (Loeser, 2009; Tian et al., 2015). Collagens, mainly type II collagen and aggrecan, are the main components of articular cartilage (Roughley, 2001; Lambert et al., 2019). The degeneration of articular cartilage is thought to be due to a disturbance of the balance between the synthesis and metabolism activity, including decreasing the synthesis of type II collagen and proteoglycan and increasing the synthesis of matrix metalloproteinases (MMPs), thrombospondin motifs, and inflammatory factor (van der Kraan and van den Berg, 2000; ; van der Kraan and van den Berg, 2012; Wiegertjes et al., 2019).

Structure and function of Wnt protein

Wnt signaling cascades are among the most critical biological pathways and are involved in several processes, including joint formation during embryonic skeleton genesis and joint homeostasis and disease in postnatal life (Ladher et al., 2000; Hartmann, 2007; ). Wnts are proteins that have a molecular weight of 36–49 kDa, and their N-terminal peptide contains 350–400 amino acids (Sassi et al., 2014a). At present, Wnt family consists of at least 19 known members in mammals that bind to different intracellular receptors and activate several downstream pathways (Lories et al., 2013; Sassi et al., 2014a). Among the Wnt proteins, the function of Wnt3a was the first to be defined (Willert et al., 2003).

The activation of a Wnt pathway requires the interaction of Wnt proteins with two receptors, one from the Fzl family and the other from the lipoprotein receptor-related protein (LRP) family. The Fzl receptors are generally grouped into seven types belonging to the G-protein–receptor family, and the N-termini of Fzls are extracellular and rich in cysteine, which can interact directly with Wnt protein (; Yang-Snyder et al., 1996; Foord et al., 2005). LRP is a transmembrane protein and is considered a coreceptor protein of the Wnt pathway that can transduce canonical Wnt signals via interactions with axin (Mao et al., 2001; ).

Several proteins are involved in the Wnt cascade in the cytoplasm. Axin interacts with the C-terminal region of the coreceptor LRP and it antagonizes the intracellular level of Wnt signaling (Zeng et al., 1997; Staal and Clevers, 2000). Adenomatous polyposis coli (APC) is another protein in the cytoplasm, which is combined with axin, disheveled (Dvl), and casein kinase I (CK-I) to form a degeneration complex. It plays an important role in maintaining the balance of β-catenin by degrading excess β-catenin (Munemitsu et al., 1995; ; Staal and Clevers, 2000). β-Catenin is a key mediator for the Wnt canonical cascade and plays a critical role in cell adhesion and interactions among cells (Lories et al., 2013).

The canonical cascade and noncanonical cascades

The canonical cascade is dependent on the activation of β-catenin. The Wnt proteins, the Fzl receptor family, and LRP form a complex that activates the downstream canonical β-catenin pathway. Moreover, Wnt-receptor complexes are mediated and controlled by downstream degradation complexes composed of APC, axin, and glycogen synthase kinase-3 β (GSK-3β) (; Staal and Clevers, 2000; Li et al., 2012). Once a Wnt protein binds to the Fzl receptor and the LRP protein, the degeneration complex is inhibited in the cytoplasm, while the complex formed by Wnt and its receptors binds to β-catenin, allowing β-catenin to accumulate in the cytoplasm and translocate to the nucleus (Rao and Kuhl, 2010; van den Bosch et al., 2016; ). After translocation, β-catenin interacts with transcription factors from the LEF/TCF family, which is composed of TCF-1, LEF-1, TCF-3, and TCF-4 (; Yu and Virshup, 2014; ). Then, β-catenin in the nucleus blocks transcription of the target genes. If the Wnt protein does not bind to the Fzl receptor or the LRP protein, the excess β-catenin proteins are degraded by the destruction complex in the cytoplasm (Figure 1) (Johnson and Kamel, 2007).

FIGURE 1

The noncanonical signaling pathways do not depend on the activation of β-catenin. Although the noncanonical Wnt signaling pathway plays an important role in the regulation of cell shape, adhesion, transfer, differentiation, and communication, little research has been reported on these pathways (Sugimura and Li, 2010; Wallingford and Mitchell, 2011; ). Under some conditions, it may even lead to the suppression of β-catenin (Ishitani et al., 2003). The noncanonical cascade is largely regulated by several extracellular and intracellular signaling molecules, including G-protein-coupled receptors, c-Jun N-terminal kinase (JNK), p38, and triphosphate (IP3)-intercellular calcium (Sugimura and Li, 2010). The receptors involved in the noncanonical cascade mainly include Frizzled, receptor tyrosine kinase (Ryk), and tyrosine-protein kinase transmembrane receptor (Ror2) (Usami et al., 2016).

The noncanonical cascade includes two types of signaling pathways, grouped according to the molecules regulated in the pathways. One cascade is WNT/PCP through Rho and JNK (c-jun N-terminal kinase), leading to the activation of downstream kinases, such as mitogen-activated kinases, including c-Jun, N-terminal kinase (JNK), and protein kinase, which play an important role in cell migration; the other cascade is WNT/Ca2+, through protein kinase C (PKC) and calcium/calmodulin-dependent kinase II (CaMK II), resulting in intracellular calcium release (Figure 2) (Liu et al., 2008; Sugimura and Li, 2010; Teo and Kahn, 2010; van Amerongen, 2012).

FIGURE 2

Role of Wnts in OA

A large number of studies have studied the role of Wnt in OA; even so, the mechanisms of Wnt protein have not been fully understood. The function of Wnts in OA is reflected in its ability to affect bone formation, endochondral ossification, bone growth and repair, and joint development (Lories et al., 2013). Bone growth requires chondrocytes to go through a complex process, including proliferation, migration, condensation, and adherence. During this process, chondrogenic differentiation passes through different stages in which the skeleton “model” is laid down, and the cells proliferate and become further differentiated via hypertrophy (Lefebvre and Bhattaram, 2010; Lories et al., 2013). Wnt3a can promote chondrocyte hypertrophy and differentiation through the canonical Wnt cascade, and suppression of the expression of Wnt3a could inhibit chondrogenic hypertrophy and EXT1 gene expression; furthermore, the Wnt/β-catenin pathway can regulate the expression of the EXT1 gene (Wang et al., 2019). Studies have indicated that Wnt5a and Wnt5b can induce chondrogenesis to affect chondrocyte proliferation and differentiation through the expression of the cytokines cyclinD1 and p130 (Ladher et al., 2000; Yang et al., 2003; Ge et al., 2017). ) found that Wnt5a and Wnt5b promote early chondrogenesis through the activation of the Wnt noncanonical signaling pathway. Huang et al. (Shi et al., 2016; Huang et al., 2017) found that Wnt5a could activate the Wnt/β-catenin pathway, which leads to increased release of inflammatory mediators, aggravated cartilage damage and inflammatory responses, and accelerated OA process. The Wnt/β-catenin pathway also affects the activities of osteoblasts and osteoclasts, which play an important role in bone growth and remodeling. The osteocytes can produce Wnt protein and stimulate osteocyte maturation; however, they also produce sclerostin, which competitively antagonizes Wnt protein and binds to the LRP receptor (Li et al., 2005; Robling et al., 2008). Wnt proteins such as Wnt7b, Wnt-receptor LRP, and Wnt antagonist make significant contributions to activating the Wnt pathways and regulating osteocyte maturation and bone growth (Li et al., 2005; Robling et al., 2008).

A previous study also found that Wnt7b is closely related to inflammation in articular cartilage, bone, and synovial tissues derived from OA and RA patients (Nakamura et al., 2005). Wnt7a also plays an important role in the pathological process of OA; it could inhibit IL-1β-induced catabolic gene expression and prevent articular cartilage damage in experimental osteoarthritis. Meanwhile, Wnt7a decreased during human chondrocyte dedifferentiation with both no treatment and IL-1 treatment in vitro, while Wnt5a presented the opposite result against Wnt7a in vitro (Sassi et al., 2014b; Gibson et al., 2017).

Although a series of studies reported that most Wnts could activate the Wnt cascade and noncascade pathway, resulting in cartilage degeneration, Wnt16 could activate Wnt signaling and prevent the exacerbation of cartilage breakdown through exaggerated Wnt activation (Nalesso et al., 2017; Kovacs et al., 2019). Tong et al. (Nalesso et al., 2017; Tong et al., 2019) found that Wnt16 overexpression in chondrocytes in mice significantly inhibits chondrocyte hypertrophy in skeletal development and that Wnt16 activates the PCP/JNK pathway to inhibit chondrocyte hypertrophy. Hua et al. (2022) showed that Wnt16 is a weak activator of β-catenin and that upregulating Wnt16 levels could reduce disease progression through the Wnt/β-catenin pathway in temporomandibular OA.

Due to the large number of studies devoted to investigating the role of Wnt molecules and their influence in OA, our understanding of Wnt biology has rapidly increased, as summarized in Table 1. Although several studies have emphasized the important role of Wnt signaling in bone and joint development, numerous studies have also suggested that the inhibition of Wnts and the Wnt-related pathway is beneficial for OA. Due to the complexity and diversity of Wnt signaling in different cells in joints, abnormally high Wnt activity or low expression of the Wnt signaling pathway in OA may lead to cartilage damage and ultimately accelerate OA (Figure 3). It is necessary and important to maintain balanced biological activity of the Wnt-related pathway due to the complexity of these communication systems in OA.

TABLE 1

ProteinReferencesRole of joints
Wnt3aWang X et al. (2019)Promoting the chondrocyte hypertrophy and differentiation
Wnt4Fan Liying et al. (2018)Up-regulated in the progress of differentiation in ATDC5 via Wnt-4/β-catenin signaling
Nan Yao et al. (2021)Downregulating mRNA and protein expression of Wnt-4/β-catenin reduced pathological damage and matrix degradation of articular cartilage in KOA rats
Wnt5aXianpeng Ge et al. (2017)Activating Wnt5a facilitated chondrocyte proliferation, hypertrophy, and migration
Huang G et al. (2107)Upregulated in OA and inducing catabolic signaling and MMP production in human articular chondrocytes
Wnt5bYingzi Yang et al. (2003)Promoting the chondrocyte hypertrophy, proliferation, and differentiation
Wnt6Arjen B Blom et al. (2009)Upregulated in the synovium during the early phase of mouse collagenase-induced OA.
Wnt7aGibson Averi L et al. (2017)Wnt7a protected the cartilage damaged through promoting joint cartilage integrity, inhibiting inflammatory stimuli-induced catabolic gene expression and the activities of MMP activity in joints
Sassi N et al. (2014)Down-regulated in chondrocytes during the progress of human chondrocyte de-differentiation
Wnt7bXiaofeng Li et al. (2005)Regulating the osteocyte maturation and bone growth
Ma B et al. (2012)Overexpression induced by IL-1 and accompanied with the expression of MMP-1, MMP-3, and MMP-13 via canonical Wnt-7b/β-catenin in human chondrocytes
Wnt8aCarmen García-Ibarbia et al. (2013)Downregulated of Wnt8a activity is related with hip fractures in patients compared to those with osteoarthritis
Wnt8bFlorian Witte et al. (2009)Unknown
Wnt9aXuan Fengjun et al. (2019)Wnt9a was highly expressed in superficial zone cells of articular cartilage and regulated the expression of Prg4 via Wnt/β-catenin signaling pathway
Wnt10aHuang Junjie et al. (2020)Wnt10a increased the expression of inflammatory cytokines in OA patient SMSCs, whereas Wnt10a had a mild protective effect on cartilage integrity in a rat model
Wnt10bKazushi Imai et al. (2006)Wnt10b was detected in RA and OA synovium. The expression was parallel with the degree of inflammatory cell infiltration and tissue fibrosis
Wnt11Michael S Friedman et al. (2009)Wnt11 promotes osteoblast maturation and mineralization by activating Rspo2 expression through Wnt/β-catenin signaling pathway
Wnt16Tong W et al. (2019)Wnt16 overexpression in chondrocytes of mice significantly inhibited chondrocyte hypertrophy during skeletal development through the activation of non-canonical signaling pathways
Francesco Dell’accio et al. (2008)Wnt-16 and β-catenin were dramatically upregulated in areas of the same joint with moderate to severe OA damage

Role of Wnt in OA.

FIGURE 3

The role of exosomes in Wnt signaling in OA

In recent years, exosomes are increasingly reported as part of a therapeutic strategy in OA and as having a role in regulating the renewal and regenerative capabilities of chondrocytes. Exosomes are derived from a variety of cell types with 30–100 nm cup-shaped vesicles in diameter (Wu et al., 2020). Exosomes are released from protocells by fusion with the plasma membrane, and they are mainly composed of coding and noncoding RNAs, proteins, antigen-presenting molecules, and DNA (Zhou et al., 2020; Moghiman et al., 2021). Because of their size and composition, exosomes are important therapeutic agents for many diseases and are useful materials for tissue engineering. At present, exosomes are thought to be among the most important factors regulating inflammatory activities in many diseases, such as OA.

OA is influenced by multiple cell types, including chondrocytes and synovial fibroblasts, and both of these cells are regulated by the Wnt signaling pathways and have the ability to secrete exosomes and regulate cartilage metabolism (Kato et al., 2014; ). Several researchers have found that exosomes derived from a variety of cells could influence the progression of OA through the Wnt signaling pathway (Table 2). A recent study found that exosomes derived from platelet-rich plasma could promote chondrocyte proliferation and migration and decrease OA chondrocyte apoptosis by inhibiting the expression of Wnt5a/β-catenin in IL-1β-treated chondrocytes (Liu et al., 2019). Zhao et al. (2020) also indicated the role of exosomes in suppressing inflammation by decreasing the proinflammatory markers IL-6, NF-κB, and tumor necrosis factor alpha (TNF-α) and by upregulating the anti-inflammatory cytokine IL-10 level by activating β-catenin. Moreover, animal experiments indicated that exosomes could inhibit the progression of early OA and prevent severe damage to articular cartilage by targeting the Wnt5a gene and promoting chondrocyte proliferation and migration in vitro (Mao et al., 2018). However, other scholars found that exosomes extracted from synovial mesenchymal stem cells go beyond contributing to the proliferation and migration of chondrocytes by causing the side effect of degrading the cartilage matrix. The Wnt molecules Wnt5a and Wnt5b target the downstream protein of YAP/TAZ and are responsible for this process through noncanonical Wnt cascades (Tao et al., 2017). These studies indicate that the Wnt signaling pathway is an important regulatory mechanism for exosomes in decreasing inflammatory activity and chondrocyte apoptosis, as well as promoting cell proliferation and alleviating articular cartilage damage in OA.

TABLE 2

AuthorSubjectsSource of exosomesPath involvedMain results
Liu Xuchang et al. (2019)New Zealand rabbits OA model and chondrocytesPlatelet-rich plasmaWnt5a/β-cateninPromoting the chondrocyte proliferation, migration, and decreasing OA chondrocytes apoptosis through inhibiting the expression of β-catenin, Wnt5a in IL-1β-treated chondrocytes
Dong Jisheng et al. (2021)Chondrocytes of Sprague–Dawley ratsBM-MSCsβ-CateninExosomes derived from BM-MSCs restricted the IL-1β-induced chondrocytes damage through inhibit the activation of Wnt/β-catenin pathway
Chen Zhao et al. (2020)Patient-derived chondrocytesAdipose-derived stem cellsβ-CateninExosomes downregulated the expression of pro-inflammatory markers IL-6 and TNF-α, upregulated the anti-inflammatory cytokine IL-10 expression, and protected articular chondrocytes from apoptosis via activating the β-catenin
Tao Shi-Cong et al. (2017)Patient-derived chondrocytesSynovial mesenchymal stem cellsWnt5a/5b-YAP/TAZExosomes promote the proliferation and migration of chondrocytes with the side effect of decreasing ECM secretion through via the Wnt signaling pathway induced by Wnt5a and Wnt5b
Mao Guping et al. (2018)Patient-derived chondrocytes and C57B/L10 mice with a collagenase-induced OA modelHuman mesenchymal stemWnt5aExosomes promote the chondrocyte proliferation, migration, and reduced cartilage matrix synthesis by enhancing the expression of Wnt5a. Animal experiment also indicated exosomes inhibited the progression of early OA and prevented the severe damage to articular cartilage
Zhu Chunhui et al. (2021)OA patient cartilage and CHON-001 cellsCHON-001 cellsWnt5bExosome-mediated transfer of circ_0001846 modulated IL-1β-induced chondrocytes damage by targeting the expression of Wnt5b

| Role of the exosome and Wnt in OA.

Role of miRNAs in the Wnt signaling pathway in OA

MicroRNAs (miRNAs) are small noncoding RNAs with the capability of modulating essential biological processes in animals and plants. Since they were first discovered in Caenorhabditis elegans in 1993, miRNAs have been found to participate in regulating posttranscriptional gene expression, either by inhibiting messenger RNA (mRNA) translation or by promoting mRNA degradation (Saliminejad et al., 2019). More importantly, the abnormal expression of miRNAs could affect the pathological process of various diseases, such as OA, due to their role in regulating and modulating gene expression, which is related to the various physiological and pathological mechanisms in chondrocytes.

In recent decades, miRNA levels, which are posttranscriptionally related, have been extensively studied in OA, and the results show that miRNAs have both protective and destructive effects on articular cartilage in OA. MicroRNAs influence multiple intracellular signaling pathways to alter chondrocyte status, and the Wnt pathway is one of the most important signaling pathways that are targeted by miRNAs in OA. In general, miRNAs can activate or suppress the Wnt signaling pathway by targeting its components, while Wnt signaling also negatively influences the expression of miRNAs. For these reasons, miRNAs and Wnt signaling pathways are especially important for maintaining cartilage metabolism, joint inflammation, chondrocyte proliferation, differentiation, and apoptosis in OA, as presented in Table 3.

TABLE 3

NameReferencesTargetMain results
miR-1Yang Yang et al. (2021)FZD7Decrease the expression of catabolic genes
miR-127-3pDong Jisheng et al. (2021)β-CateninDecrease the expression of MMP-13, ADAMTS-5, TNF-α, and IL-6
miR-195-5pYang Shu et al. (2019)β-CateninIncrease the expression of TNF-α, IL-6, and IL-1β in chondrocytes and induce the chondrocytes apoptosis
miR-27a/bSara Cheleschi et al. (2017)β-CateninDownregulate the expression of MMP-13, ADAMTS-5, and HDAC-4
miR-140Sara Cheleschi et al. (2017)β-CateninDownregulate the expression of MMP-13, ADAMTS-5, and HDAC-4
miR-146aSara Cheleschi et al. (2017)β-CateninDownregulate the expression of MMP-13, ADAMTS-5, and HDAC-4
miR-138Xu Weiling et al. (2019)β-CateninAlleviate OA cartilage severity through increasing the level of Col2a1 and aggrecan and reducing the level of MMP-13
miR-155-5pAlessandra Colombini, et al. (2021)β-CateninProtect the chondrocytes through reducing the level of MMP-1 and MMP-3 via inhibiting the Wnt signaling pathway
miR-34aSara Cheleschi, et al. (2020)β-CateninModulate the inflammation through regulating the expression of MMP-13 and ADAMTS-5
miR-10aLi J. et al. (2015)β-CateninInhibited osteogenic differentiation and decreased mouse umbilical vein endothelial cell proliferation and migration
miR-410Zhang Yanjie et al. (2017)Wnt3aIncrease chondrogenic markers of Col2a1, Sox9, ACAN, and Has2, and alleviate OA cartilage severity
miR-497-5pHou Liying et al. (2019)Wnt3aIncrease the expression of Col2a1 and aggrecan, and reduce the expression of MMP-13 and ADAMTS-4
miR-92a-3pMao Guping et al. (2018)Wnt5aRegulate cartilage development and homeostasis
miR-374a-3pShi Feng-Lei et al. (2020)Wnt5bAlleviate LPS-induced damage in CHON-001 cells and inhibit cartilage injury
miR-1246Peng Sisi et al. (2021)GSK3β and Axin2Promote inflammation via increasing the level of IL-6, IL-8, MMP-3, and MMP-13
miR-140-3pE. Ntoumou et al. (2017)Wnt5aDownregulate in the serum of OA patients and modulate the metabolic processes of OA pathology
miR-671-3pE. Ntoumou et al. (2017)Wnt5aDownregulate in the serum of OA patients and modulate the metabolic processes of OA pathology
miR-33b-3pE. Ntoumou et al. (2017)Wnt5aDownregulate in the serum of OA patients and modulate the metabolic processes of OA pathology
miR-520bAlessandra Colombini et al. (2021)DKKModulate inflammatory functions and activate the Wnt signaling pathway
miR-302d-3pAlessandra Colombini et al. (2021)DKKModulate inflammatory functions and activate the Wnt signaling pathway
miR-520c-3pAlessandra Colombini et al. (2021)DKK-1Modulate inflammatory functions and activate the Wnt signaling pathway
miR-154-5pLi Jianwei et al. (2015)Wnt11Inhibit osteogenic differentiation via decreasing the activity of the non-canonical Wnt/PCP (RhoA-ROCK) pathway
miR-26bSun Jilin et al. (2015)WntInhibit the TNF-α, IL-1β, and IL-6 levels and reduce the proliferation of rheumatoid arthritis synovial fibroblasts
miR-335-5pZhang Jin et al. (2011)DKK1Inhibit the osteoblasts and hypertrophic chondrocytes of mouse embryos to promote osteogenic differentiation

miRNAs targeting the Wnt signaling pathway in the pathogenesis of OA.

As a key component of the Wnt signaling pathway, the activation of β-catenin depends on its transport and accumulation in the nucleus. Once it is in the nucleus, it can bind to TCF/LEF transcription factors to initiate gene transduction. Therefore, many scholars have studied the effect of miRNAs on β-catenin. ) found that miR-127-3p can protect chondrocytes from IL-1-induced damage by decreasing the expression of MMP-13, ADAMTS-5, TNF-α, and IL-6 by suppressing the activation of β-catenin. miR-138 has also been proven to have the same effect, alleviating OA cartilage severity by increasing the levels of Col2a1 and aggrecan and reducing MMP-13 levels by targeting the β-catenin gene (Xu et al., 2019). ) investigated the effects of miRNAs in both normal and OA human chondrocytes in regulating the levels of MMP-13 and ADAMTS-4. The results showed that several miRNAs, such as miR-27a/b, miR-140, and miR-146a/b, are responsible for modulating the β-catenin level and the aforementioned changes in chondrocytes. Researchers found that miR-10a reduced β-catenin at both the protein and transcriptional levels and inhibited osteogenic differentiation to reduce cartilage damage in OA (Li et al., 2015), and other researchers found that the upregulation of β-catenin induced by miR-195-5p could promote the inflammatory activity and apoptosis rate of chondrocytes (Shu et al., 2019).

Wnt and its receptors can be targeted and modulated by miRNAs. MiR-410 expression is upregulated during the process of chondrogenic differentiation in MSCs and can increase the levels of Col2a1, Sox9, and ACAN by regulating the target gene Wnt3a (Zhang et al., 2017). Wnt3a is also a target gene for miR-497-5p, which regulates the activity of the Wnt signaling pathway in OA (Hou Liying et al., 2019). Indeed, elevated levels of miR-497-5p prominently increased Col2a1 and aggrecan expression and decreased the expression of the catabolic proteinases MMP-13 and ADAMTS-4, while Wnt3a overexpression reversed these effects (Hou Liying et al., 2019). Similarly, miR-92a-3p could reduce cartilage matrix synthesis by targeting Wnt5a and enhancing its expression (Mao et al., 2018). Ntoumou et al. (2017) investigated serum samples collected from healthy people and OA patients and found that miR-140-3p, miR-33b-3p, and miR-671-3p were downregulated in the serum of OA patients and modulated the metabolic processes of OA pathology by regulating the expression of the Wnt5a gene.

Many studies have reported that miRNAs could participate in the regulation of biological processes by regulating the expression level of antagonists of the Wnt signaling pathway. DKK-1 has been extensively studied, and it has been reported that miR-335-5p can downregulate DKK-1 and activate Wnt signaling to promote osteogenic differentiation in mice (Zhang et al., 2011). ) studied the miRNA cargo embedded in extracellular vesicles (EVs) released from adipose-derived mesenchymal stromal cells. Intriguingly, they found that miR-520c-3p was upregulated, but miR-302d-3p was silenced, and both targeted DKK to activate Wnt signaling to modulate inflammatory functions.

Wnt signaling in OA experimental animal models

Some studies have investigated the role of the Wnt signaling pathway in the articular pathologies of OA. Ryu and Chun (2006) studied the effect of IL-1 on cultured rabbit chondrocytes in vitro. They found that IL-1 could increase the expression of Wnt5a, which is strongly related to cartilage destruction, by inhibiting collagen-II in OA. ) studied the expression of the Wnt and Fzl genes in experimental OA and human OA. They found that Wnt and Wnt-related genes are highly expressed in the articular cartilage and synovium in experimental OA and human OA. Among these genes, the Wisp1 gene, which induces Wnt gene expression, is significantly highly expressed in chondrocytes. Secreted frizzled-related proteins (sFRPs) are antagonists of the Wnt pathway and play an important role in the Wnt pathway; sFRP (−/−) mice are more liable to develop OA because of the increased activity of MMPs (Lories et al., 2007; Thysen et al., 2015). These findings indicate revealed the effect of the Wnt/β-catenin signaling pathway in OA. Chen et al. (; Zhu et al., 2008; Zhu et al., 2009) confirmed that an increased β-catenin protein level in the nucleus is accompanied by a reduction in β-catenin degradation in chondrocytes. These changes could result in an OA-like phenotype, including chondrocyte differentiation, increased MMP and Col10a expression, loss of articular cartilage, and osteophyte formation.

The ADAMTS family of proteases and matrix metalloproteinase (MMPs) are strongly involved in the cartilage degradation of OA (Glasson et al., 2005; Roach et al., 2005; Majumdar et al., 2007). The deletion of ADAMTS-5 or MMP-13 or double KO of both ADAMTS-4 and ADAMTS-5 prevented cartilage degradation in a surgically induced knee OA mouse model, while the expression of ADAMTS-4 and ADAMTS-5 was increased in β-catenin-overexpressing mice (Majumdar et al., 2007; Wang et al., 2013; Yang et al., 2015).

Several studies have found that the levels of MMP-3, MMP-9, MMP-13, and ADAMTS-5 were closely related to those of Wnt/β-catenin, and inhibiting the expression of β-catenin could reduce the expression of MMPs and ADAMTS-5 and reduce the damage to articular cartilage in an animal OA model (; Li et al., 2019; Xie et al., 2019). These findings revealed that MMPs and ADAMTS4/5 affect cartilage destruction and the progression of OA through the Wnt/β-catenin pathway, and targeting this pathway can be a strategy for treating or preventing OA.

Interventions in the Wnt cascade

The complexity of the Wnt signaling pathway means that regulating it is a complex and challenging process. Pharmaceutical interventions on the Wnt cascade have hitherto mainly focused on secreted Wnt antagonists. Because the mechanism of the Wnt signaling pathway requires a combination of Lrp, Fzl, and Wnt to initiate the downstream β-catenin molecule, their inhibitory actions on Wnt are different. They can be divided into endogenous Wnt pathway inhibitors and pharmaceutical inhibitors according to the mechanism of their action on the signaling pathway.

Endogenous inhibitors of the Wnt signaling pathway

The Wnt pathway is controlled by several endogenous antagonists, and the decreased expression levels of certain antagonists may alleviate the progression of OA. Our current understanding of certain endogenous antagonists of the Wnt signaling pathway in OA, as discussed in the following sections, is summarized in Table 4.

TABLE 4

AuthorSubjectsInhibitorPath involvedResults
Wafa Bouaziz et al. (2015)Murine chondrocytes and mice with a DMM modelSclerostinWnt3a/β-cateninSclerostin inhibited expression of ADAMTSs, MMPs, and Col10a by suppressing the canonical Wnt pathway and sclerostin through Wnt3a/β-catenin pathway
Hwanhee Oh et al. (2012)C57BL/6 mice with a DMM model and articular chondrocytesDkk-1DKK-1Overexpression of Dkk1 by intraarticular injection of AdDkk-1 inhibited DMM-induced experimental OA, DKK-1 inhibited Wnt-3a-catenin-mediated upregulation of MMP-13 and ADAMTS-4
Diederik P C de Rooy et al. (2013)Serum levels of RA patientsDKK-1DKK-1RA patients with risk alleles of genetic variants in Dkk-1 are inclined to joint destruction over time
S J B Snelling et al. (2016)Human OA cartilage and synovial tissues, human chondrocytesDKK-3DKK-3Dkk-3 is upregulated in OA and may have a protective effect on cartilage integrity by preventing proteoglycan loss
Nicole C Walsh et al. (2009)C57BL/6 J miceDKK-1, SFR1DKK-1, SFR1The Wnt signaling antagonists DKK1 and sFRP1 are expressed in inflamed synovial, suggesting that the inhibition of Wnt signaling contributes to impaired osteoblast function within arthritic bone tissues in RA
Shu-Guang Gao et al. (2016)Human OA cartilage and subchondral bone from tibial plateauWIF-1WIF-1Patients with disease had significantly decreased WIF-1 levels. Thus, WIF-1 levels are negatively correlated with the severity of the disease
Jean Cassuto et al. (2018)Plasma derived from twenty-four osteoarthritis patientsDkk-1, sFRP-1Dkk-1, sFRP1Dkk-1 and sFRP1 suppress osteogenic activation of MSCs and they are required for full osteoblastic differentiation

Endogenous inhibitors of the Wnt/β-catenin signaling pathway.

Sclerostin is an antagonist of the Wnt pathway and can antagonize the combination of Wnt with LRP and FZL. Sclerostin inhibits the expression levels of the downstream catabolic effector genes Runx-2, MMP-13, ADAMTS-4, and ADAMTS-5 by decreasing the mRNA expression levels of β-catenin in healthy chondrocytes, while sclerostin knockout mice exhibit increased expression of aggrecanases and Col10a (Lewiecki, 2014; ; Wu et al., 2017). Dkk-1 is another Wnt antagonist, and its overexpression can reduce the degeneration of cartilage and OA in animal models induced by destabilization of the medial meniscus (DMM). Dkk-1 can inhibit Wnt-mediated expression of catabolic genes, including MMPs, Runx-2, and ADAMTS-4/5 (Oh et al., 2012; ; Funck-Brentano et al., 2014). Dkk-3 is another member of the Dkk family of Wnt antagonists, and it inhibits the loss of proteoglycan and collagen from cartilage in a model of OA (Snelling et al., 2016). A previous study indicated that the expression of Dkk-1 is related to inflammation and is consistent with the process of OA, while Dkk-2 and Dkk-3 expression is associated with late stages of the disease (Walsh et al., 2009). WNT-inhibitory factor 1 (WIF-1) is an extracellular Wnt antagonist that has been investigated in several studies. ) found that WIF-1 could reduce the expression of β-catenin in the chondrocytes of OA, while other researchers found a similar tendency and confirmed that the WIF-1 level was negatively correlated with the severity of the disease in OA (Gao et al., 2016; ). The sFRP family, which has five members (SFRP1–5), was originally identified as an extracellular ligand-binding inhibitor of the Wnt signaling pathway (Thysen et al., 2015). More recent data indicate that SFRPs have a variety of physiological functions, including regulating cell metabolism and intracellular signaling by regulating or inhibiting the activity of the Wnt signaling pathway. The sFRP1 level strongly influences the synthesis of the cartilage matrix, and animal experiments showed that sFRP1(−/−) mice had greater subchondral bone plate thicknesses in a DMM model of OA (Thysen et al., 2015). sFRP3 also negatively regulated the key gene β-catenin in the Wnt signaling pathway in RA and decreased the expression of MMP-3 ().

Pharmaceutical inhibitors of the Wnt signaling pathway

Recently, a number of new and classic drugs were investigated in terms of their inhibitory effect on the Wnt pathway in OA. Most of them influence the pathological process of OA by modulating Wnt pathway activity, as summarized in Table 5. Zhong et al. (2018) found that artemisinin (ART) could inhibit the expression of proinflammatory chemokines and cytokines, including IL-1β, IL-6, TNF-α, and MMP-13, suppressing the degeneration of the articular cartilage. These results indicate that ART alleviates the IL-1β-mediated inflammatory response and OA progression by regulating the Wnt5a/β-catenin signaling pathway. Mianserin suppresses Rspo2-induced accumulation of β-catenin and phosphorylation of LRP6, which play an important role in preventing OA progression in a rat model of OA (Okura et al., 2019). Growth differentiation factor-5 (GDF-5) is strongly related to ECM homeostasis. It could inhibit the expression of MMP-13 and ADAMTS-4 and stimulate the expression of the cartilage anabolic genes Acan and Sox9 in human chondrocytes through intervention in the Wnt canonical signaling pathway by the overexpression of Dkk-1 and FRZB (). Ma et al. (2019) demonstrated that a systemic injection of rapamycin could reduce the degeneration of cartilage by inhibiting β-catenin in an animal model of OA. The mechanism by which rapamycin attenuates OA mainly relies on a reduction of apoptosis and activation of autophagy in chondrocytes. Icariin exerts a chondroprotective effect by inhibiting the expression of β-catenin in vivo and in vitro, and it may have therapeutic potential for the treatment of OA (Zeng et al., 2014). Several researchers have found that the expression of some large molecules, such as FYN and high-molecular-weight fibroblast growth factor-2 (FGF-2), is elevated and correlated with the expression of Wnt/β-catenin in human OA cartilage and mouse models. Inhibiting these molecules can reduce the levels of the extracellular matrix catabolic enzymes and delay articular cartilage degeneration by blocking the β-catenin pathway (Zhao et al., 2015; Li et al., 2018; Meo Burt et al., 2018).

TABLE 5

AuthorSubjectsInhibitorPath involvedResults
Zhong Gang et al. (2018)Human OA chondrocytes and rats OA modelArtemisininWnt5a/β-cateninART inhibits OA progression and cartilage degradation by exhibiting potent anti-inflammatory effects via the Wnt/β-catenin signaling pathway
L Enochson et al. (2014)Human OA chondrocytesGrowth differentiation factor 5 (GDF5)Wnt/β-cateninGDF5 inhibits expression of MMP-13 and ADAMTS-4 and stimulates the expression of cartilage anabolic genes ACAN and SOX9 via the DKK1-mediated Wnt signaling pathway
Long Ma et al. (2019)C57BL/6 miceRapamycinWnt/β-cateninRapamycin injection could activate chondrocyte autophagy, increase the expression of LC3 and ATG-5, reduce OARSI scores, expression of β-catenin, MMP-13, and chondrocyte apoptosis
Li Zeng et al. (2014)Human SW 1353 cells and rats OA modelIcariinWnt/β-cateninIcariin could decrease the MMP-13 expression and reduce the number of cartilage lesions via the Wnt/catenin pathway
Yun-Peng Zhao et al. (2014)C57/BL6 mice and chondrocytesProgranulinWnt/β-cateninProgranulin suppresses inflammatory action of TNF-α and inhibits the activation of β-catenin signaling in chondrocytes, protects cartilage degradation in spontaneous and surgically induced OA models
Caressa Lietman et al. (2018)Human chondrocytes and C57BL/6 J mice with DMM method of OA modelXAV939XAV939XAV-939 ameliorates OA severity associated with reduced cartilage degeneration and synovitis
Jingyuan Li et al. (2019)Sprague–Dawley rats and ATDC5 cellsXanthan gumWnt3a/β-cateninXanthan Gum reduces the OARSI score and the concentration of inflammatory cytokines in OA. Xanthan Gum acted on Wnt3a/β-catenin in ATDC5 cells to decrease the expression of MMP-13 and ADAMTS-5
Yuzhe He et al. (2019)Rat chondrocytes and an OA rat modelCostunolideWnt/β-cateninCostunolide decreases IL-1β-induced upregulation of MMPs, INOS, COX-2 and IL-6, increases the expression of Clo2a1 and Sox9 through inhibiting Wnt/β-catenin signaling pathway
Fuen Liu et al. (2020)C57BL/6 mice and human chondrocytes derived from patientsScutellarinWnt3a/β-catenin and MAPK signaling pathwayScutellarin downregulates the mRNA and protein expression of MMP-1, MMP-13, and ADAMTS-5 and promotes the expression of Col2a1 and aggrecan. Moreover, scutellarin inhibits the migration of β-catenin and phosphorylation of p38 into the nucleus
J.-B. Gao et al. (2020)Human chondrocytes and human knee OA cartilage tissueFibulin-5Wnt/β-cateninFibulin-5 increases the expressions of Col2a1 and aggrecan and reduces IL-1β-induced inflammation of chondrocytes, as well as expressions of IL-6, IL-8, and TNF-αvia reducing the activity of Wnt/β-catenin signaling pathway
Qian-Hai Ding et al. (2018)Rat articular cartilage and chondrocytesEmodinNF-κB and Wnt/β-catenin signalingEmodin dose-dependently down-regulates the expression of MMP-3, MMP-13, ADAMTS-4 and ADAMTS-5 at both the mRNA and protein level in IL-1β-stimulated rat chondrocytes. In addition, the IL-1β-induces activation of NF-κB and Wnt signals was attenuated by emodin
Shan Cong et al. (2021)Sprague–Dawley (SD) ratsIguratimodβ-CateninIguratimod improves the degeneration of articular cartilage and decreases the levels of MMP-13, TNF-α, and IL-6 in serum. Iguratimod downregulates the mRNA and protein expression of β-catenin in vivo
Xindie Zhou et al. (2016)New Zealand rabbits and chondrocytesPalmatineWnt/β-catenin and Hedgehog signaling pathwaysPalmatine decreases the expression of the MMPs and increases the synthesis of TIMP-1, whereas collagenase II and aggrecan are inhibited by IL-1β. Palmatine protects the cartilage degradation via suppressing the Wnt and hedgehog signaling pathways
Yang Xi et al. (2020)Sprague–Dawley rats and chondrocytesErdosteineMAPK, NF-κB, and Wnt/β-catenin signaling pathwaysErdosteine suppresses the expressions of IL-1β-induced production of inflammatory factors COX-2 and iNOS and attenuates the degradation of ECM by repressing the expression of MMP-1, MMP-3, and MMP-13. Moreover, erdosteine could inhibit the activation of IL-1β-induced MAPK and Wnt/β-catenin
Yi-Yue Chen et al. (2019)Human OA, normal articular cartilage samples, and chondrocytesCyclin D1Wnt3/β-cateninCyclin D1 inhibits cell apoptosis and cell cycle promotes the proliferation OA chondrocytes through activating the Wnt/β-catenin signaling pathway
Tangbo Yuan et al. (2022)107 OA patientsCurcuminWnt/β-cateninCurcumin can effectively decrease the pathological results of OA, with a remarkable safety profile; its mechanism may be the activation of the Wnt/β-catenin signaling pathway to inhibit the inflammatory reaction and apoptosis in chondrocytes
Long Ma et al. (2021)Female C57BL/6 J OA model mice with ACLT + DHA methodDihydroartemisininWnt/β-cateninDihydroartemisinin decreases MMP-13 and VEGF expression in the articular cartilage, and finally results in decreasing OARSI scores and reducing articular cartilage degeneration. In addition, dihydroartemisinin reduces abnormal subchondral bone remodeling via the Wnt/catenin
Xindie Zhou et al. (2013)New Zealand rabbits and chondrocytesTetrandrineWnt/β-cateninTetrandrine decreases the expression of MMP-1, MMP-3, MMP-13, TIMP-1, and β-catenin in rabbit chondrocytes and cartilage
De-Heng Chen et al. (2021)Human chondrocyte and C57BL/6 J OA modelOroxylin ANF-κB and Wnt/β-catenin signalingOroxylin A could rescue IL-1β-mediated hypertrophic alterations of chondrocytes and inhibit the ECM hemostasis in human chondrocytes. Oroxylin A attenuates the IL-1β-induced hypertrophic changes in chondrocytes by inhibiting the Wnt/β-catenin signaling pathway
Nan Yao et al. (2021)Sprague–Dawley ratsBushen Qiangjin capsuleWnt/β-cateninBushen Qiangjin capsule obviously reduces pathological damage and matrix degradation of articular cartilage in KOA rats and downregulates mRNA and protein expression of Wnt-4, β-catenin, Frizzled-2, and caspase-3
Wei-Ping Chen et al. (2017)Rat chondrocytesLicochalcone ANF-κB and Wnt/β-catenin signaling pathwaysLicochalcone A inhibits ADAMTS-5, ADAMTS-4, MMP-13, and MMP-1 expression via inhibiting the NF-κB and Wnt/β-catenin signaling pathways in rat chondrocytes
Tao Yang et al. (2020)Rat chondrocytesVitamin D3Wnt3a/β-cateninVitamin D3 and PNU-74654 could attenuate the effects induced by TNF-α and increase the level of col2a1 and aggrecan and decrease the expression of MMP-3 and MMP-13, ADAMTS-4, ADAMTS-5, Wnt-3a, and nuclear β-catenin
V Deshmukh et al. (2018)SW480 cells and Sprague–Dawley ratsSM04690Wnt/β-cateninSM04690 induces hMSC differentiation into chondrocytes, decreases cartilage catabolic marker levels, promotes cartilage growth, and improves joint health in a rat model of knee OA
Hanting Xia et al. (2020)MIA-induced OA rat models and chondrocytesJiawei Yanghe decoction (JWYHD)Wnt/β-cateninJWYHD increases the chondrocyte viability against IL-1β-induced chondrocyte apoptosis and preserves glycosaminoglycans in the extracellular matrix. JWYHD promotes chondrocyte viability against apoptosis and decreases MMP-3, MMP-13, caspase-3, and caspase-9 via the Wnt/β-catenin signaling pathway

Pharmacological inhibitors of the Wnt/β-catenin signaling pathway.

Conclusion

In recent years, there has been growing interest in trying to identify the mechanisms underlying pathological changes in OA for the purpose of developing a targeted treatment strategy for OA. Extensive studies of the Wnt signaling pathway have revealed multiple functions of the Wnt signaling cascade in the maintenance of joint homeostasis, particularly in cartilage. The Wnt cascade should be tightly regulated because either overexpression of Wnt signaling or blockade of its activation may result in cartilage damage and bone erosion. The Wnt signaling pathway involves several levels, including the extracellular, intracytoplasmic, and nuclear levels, so regulation should exist in multiple aspects. New strategies to target and control these different levels of regulatory mechanisms may lead to the preservation of cartilage or the healing of diseased joints. It is absolutely necessary to investigate the Wnt signaling pathway in greater detail, not only to develop specific therapeutic interventions that target this pathway but also to discover and utilize new biomarkers for personalizing medical approaches in the future.

Statements

Author contributions

All the authors researched the data for the study, provided substantial contributions to discussions of its content, wrote the manuscript, and reviewed and/or edited the manuscript before submission.

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.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Glossary

  • Acan

    Aggrecan

  • ADAMTS

    a disintegrin and metalloproteinase with thrombospondin motifs

  • ACLT

    anterior cruciate ligament transection

  • ART

    artemisinin

  • APC

    adenomatous polyposis coli

  • CaMKII

    calcium/calmodulin-dependent kinase II, calcium/calmodulin-dependent protein kinase type II

  • CK-I

    casein kinase I

  • Col2a1

    type II collagen alpha 1 chain

  • Dkk

    dickkopf

  • Dvl

    disheveled

  • DMM

    destabilization of the medial meniscus

  • ECM

    extracellular matrix

  • EVs

    extracellular vesicles

  • FGF-2

    fibroblast growth factor-2

  • GSK-3β

    glycogen synthase kinase-3 β

  • IL

    interleukin

  • JNK

    c-Jun N-terminal kinase

  • LRP

    lipoprotein receptor-related protein

  • mRNA

    messenger RNA

  • miRNA

    microRNA

  • MMP-13

    matrix metalloproteinase 13

  • MMx

    medial meniscus resection

  • OA

    osteoarthritis

  • PKC

    protein kinase C

  • PLC

    phospholipase C

  • Runx-2

    Runt-related transcription factor-2

  • Ryk

    receptor tyrosin kinase

  • sFRPs

    secreted frizzled-related proteins

  • Sox9

    SRY-box transcription factor 9

  • TNF-α

    tumor necrosis factor alpha

  • Wnt

    Wingless/integrated

  • WIF-1

    WNT-inhibitory factor-1

References

Summary

Keywords

chondrocyte, wnt signaling, osteoarthritis, β-catenin, therapy

Citation

Cheng J, Li M and Bai R (2022) The Wnt signaling cascade in the pathogenesis of osteoarthritis and related promising treatment strategies . Front. Physiol. 13:954454. doi: 10.3389/fphys.2022.954454

Received

31 May 2022

Accepted

08 July 2022

Published

02 September 2022

Volume

13 - 2022

Edited by

Anjali P. Kusumbe, University of Oxford, United Kingdom

Reviewed by

Saeed Khalili, Shahid Rajaee Teacher Training University, Iran

Wenhui Hu, Third Military Medical University (Army Medical University), China

Updates

Copyright

© 2022 Cheng, Li and Bai.

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: Ruijun Bai,

This article was submitted to Skeletal Physiology, a section of the journal Frontiers in Physiology

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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