The function of the inter-alpha-trypsin inhibitors in the development of disease

Through the formation of covalent connections with hyaluronic acid (HA), the inter-α-trypsin inhibitor (IαI) family collaborates to preserve the stability of the extracellular matrix (ECM). The five distinct homologous heavy chains (ITIH) and one type of light chain make up the IαI family. ITIH alone or in combination with bikunin (BK) has been proven to have important impacts in a number of earlier investigations. This implies that BK and ITIH might be crucial to both physiological and pathological processes. The functions of BK and ITIH in various pathophysiological processes are discussed independently in this paper. In the meanwhile, this study offers suggestions for further research on the roles of BK and ITIH in the course of disease and summarizes the plausible mechanisms of the previous studies.


Introduction
Members of the ancient and distinctive inter-α-trypsin inhibitor (IαI) family have developed throughout hundreds of millions of years of vertebrate history (1).Hepatocytes are the primary source of the 225 kDa IαI family protein complexes, which are found in the blood at high concentrations of 0.15 to 0.5 mg/mL (2).Human IαI family consists of three different polypeptide chains, namely bikunin (BK), heavy chain 1 and heavy chain 2 (3).IαI family, which makes up the majority of family members in human serum, is thought to be dormant until it enters the target tissue, where it is cleaved by TNF-stimulated gene 6 protein (TSG-6).After that, heavy chains (HCs) are transferred to hyaluronic acid (HA), a significant part of the extracellular matrix (ECM), through the formation of temporary covalent bonds with TSG-6 (4).TSG-6 is essential for the interaction with HA because it facilitates two following ester exchange reactions: it binds HC1 or HC2 of IαI family covalently and then moves them to the HA fraction in this complex, where the heavy chain conjugates and releases free TSG-6 (5,6).HCs have been found to function as structural proteins that can directly cross-link HA that is secreted (7).IαI HC forms a strong bond with HA produced by fibroblasts in culture (7).In addition, the physiological correlation of HA with members of the IαI HC family has been linked to various cell types that show HA-containing outer membranes.For example, the maturation process of oocytes and experiments in vitro culture of mesothial cells (8).In summary, the IαI family of proteins interacts with HA to maintain the stability of the ECM, which is a critical function in numerous illnesses.This work aims to provide an overview of the mechanisms underlying the occurrence and development of IαI family proteins that have been linked to current disorders.Additionally, it offers suggestions for future research on IαI family proteins.2 The structure and function of inter-α-trypsin inhibitor family members 2.1 Bikunin Bikunin (BK), the light chain, and five homologous heavy chains come together to form the IαI family (9) (Figure 1).There are various homologous heavy chains (ITIH), and the one that has been discovered to date has five members (ITIH1, ITIH2, ITIH3, ITIH4, and ITIH5), despite the fact that there is only one type of light chain.The α-1-microglobulin/BK precursor (AMBP) encodes the light chain and α-1 microglobulin, a member of the lipid transport protein superfamily independent of the ITI family either physically or functionally (10).The ITI light chain is referred to as "BK" because it has two tandem repeats of a Kunitz-type structural domain (11).Serum proteoglycans generated from liver are known as BK isoforms.They contain chondroitin sulfate (CS) chains, which are mainly esterified by one or two glycoproteins referred to as "heavy chains" (HC).There are three primary serum isoforms that have been extensively documented: pro-alpha-proteinase inhibitor and interalpha-trypsin inhibitor, which carry one and two HC, respectively, and urotrypsin inhibitor, which corresponds to BK and is connected to the CS chain (10).These complexes create the characteristic ITI proteinglycosaminoglycan-protein structure (12).

ITIH
Apart from BK, the ITI heavy chain also serves biological purposes (13).Numerous diseases, including inflammatory reactions in local tissues, acute inflammation, tumor growth, and problems connected to psychiatry, have been linked to ITIHs, according to studies (13,14).Subsequent investigations have also revealed that ITIHs, a main constituent of ITI, plays an important role, either by itself or in conjunction with BK (13).The von Willebrand A-type structural domains and the vault are two of the modules that make up the H chain, which can communicate with the ECM.The carboxyl group of the matching H-chain's C-terminal aspartic acid residue and the C-6 hydroxyl group of the internal N-acetylamino galactose residue of Bk's chondroitin sulfate component are what link the H-chain to the protein.ITIHs can undergo an ester exchange reaction to covalently conjugate to locally generated HA.Serum-derived hyaluronan-associated protein is made up of D-glucuronic acid and N-acyl-D-glucosamine, which together make up the desialylated polymer known as HA (2).ITIHs bind covalently to HA to stabilize the ECM (15).Many extracellular proteins released by cells make up the ECM, which controls intercellular communication as well as biological activities (16).Many interacting proteins and proteoglycans that control cellular activity have an impact on the stiffness or rigidity of HA (17,18).One important element of the ECM is HA (19).Together, these molecules of the ECM-HA, proliferating cells, migration, and tumor metastasis-maintain the stability of the ECM by forming a reticular structure (20, 21).A common ECM component, HA is a high molecular weight polymer that does not need to be modified further (21).Numerous biological processes, including wound healing, differentiation, and cell motility, are facilitated by HA-binding proteins, especially membrane-bound receptors like CD44 and RHAMM (22, 23).For instance, during the healing of skin injury, synthesis is elevated.The covalent transfer of heavy chains from IαI to HA is catalyzed by TsG-6, and the resulting HC-HA complex is engaged in remodeling and inflammatory processes in both healthy and pathological contexts (24).Furthermore, HA participates in angiogenic processes.The size of HA affects its angiogenic potential: short segments of HA produced in inflammation and tissue damage are strongly angiogenic (25), while high molecular weight HA possesses vasopressor qualities (26).After degradation, HA becomes a pro-angiogenic ligand (15).For instance, it has been discovered in earlier research that HA stimulates angiogenesis in lung damage and is even linked to abnormal angiogenesis (17).Increased ITIHs protein may prevent the HA-CD44 and ECM pathways from degrading, which would have anti-angiogenic effects.This could be one of the key ways that the protein ITIHs functions as a putative oncogene.

Advances in the study of BK and disease
In both physiological and pathological processes, BK has pleiotropic functions.BK appears to be involved in numerous activities, according on genetic studies of mice deficient the protein.Genes related to stress, apoptosis, proteases, aging, cytokines, HA metabolism, and female ovulation processes are dysregulated when BK is absent (27, 28).Subsequent research revealed that female mice deficient the BK gene exhibit considerably lower fertility (28).This results from a malfunction in the lateral protein precursors' ability to form compounds with hyaluronic acid in the ovarian mound before ovulation.Therefore, hyaluronan, which is necessary for mammalian ovulation and fertilization, requires the delivery of serum-derived hyaluronan-related proteins by the chondroitin sulfate part of BK (29).Concurrently, research has produced intriguing findings on the Composition of inter-a-trypsin inhibitors and serum-derived hyaluronan-associated proteins.The IαI family is assembled from light chain-bikunin and five homologous heavy chains.potential of the medication BK to lower the risk of preterm labor and enhance neonatal outcomes (30).Furthermore, in pancreatitis, septic shock, and rheumatoid arthritis, it has been demonstrated that the BK core protein inhibits inflammation-associated proteases such trypsin, elastase, and fibrinolytic enzymes (31,32).As an anti-inflammatory, BK prevents the production of cytokines that are triggered by lipopolysaccharide (LPS).Through extracellular signal-regulated kinase signaling (ERK), calcium endocytosis, and endotoxin receptors, BK suppresses the generation of cytokines.Endotoxin stimulates calcium inward flow, generates phosphorylated ERK, and activates multiple transcription factors, including nuclear factor kappa B and early growth response-1, through endotoxin receptor signaling, all of which support the development of cytokines (33).It was discovered to prevent the generation of pro-inflammatory cytokines in a number of cell types in cellular tests (3,34).Mice injected BK showed a decrease in multiple inflammatory markers in animal models of inflammatory disorders (35).Furthermore, BK knockout mice, Bik (−/−), were used for in vitro cytokine experiments and in vivo animal models.It was discovered that Bik (−/−) mice induced higher levels of endotoxininduced death when compared to wild-type (Wt) mice; that application of BK significantly reduced LPS-induced lethality; and that endotoxin significantly increased endotoxin-induced lethality when compared to Wt mice.BK combined with application of BK inhibited the levels of these cytokines; additionally, BK inhibited endotoxininduced up-regulation of cytokine expression by suppressing macrophage phosphorylation of ERK1/2, JNK, and p38; this implies that BK has a major anti-inflammatory function (36).In different acute and chronic inflammatory reactions, BK is a non-invasive circulating or urine biomarker (37).
BK has been found in cancer studies to inhibit tumor cell invasion through direct inhibition of fibrinolytic activity associated with tumor cells as well as urokinase-type fibrinogen activator (UPA) expression at the gene and protein levels, potentially through inhibition of MAP kinase signaling cascades and/or CD44 dimer.By interacting with different cell types' cartilage junction proteins and BK receptors, BK can be suppressed in order to prevent cell invasion (38).Furthermore, ovarian cancer cells' gene expression patterns are changed by BK, which prevents tumor cell invasion (39).In animal investigations, it was discovered that the exogenous injection of BK inhibited the growth of intraperitoneal ovarian tumors as well as peritoneal disseminated metastases (40).Treatment with BK in the adjuvant setting and/or in conjunction with cytotoxic medicines to enhance therapeutic efficacy may be helpful in postponing the beginning of metastases in patients with advanced ovarian cancer (41).Patients with ovarian cancer who had preoperative BK concentrations higher than 11.5 μg/mL were shown to have a significantly better prognosis than those with lower amounts.Patients with pretreatment values of 11.5 μg/mL had 2.2-fold higher Hazard Ratios (risk of mortality) than those with concentrations of more than 11.5 μg/mL of BK.Patients in both groups had a median survival of 26 months and more than 60 months, respectively (42).This implies that BK has a critical function and importance in determining the prognosis of ovarian cancer patients.Remarkably, there has been no report of BK overexpression being linked to human pathology (1).
The above cellular and animal experiments suggest that BK has potential medical value.It also plays a significant role in mammalian ovulation and even directly affects fertility in knockout mice.Additionally, BK has important roles and functions as an antiinflammatory protein and an anti-tumor invasive protein.These findings may lead to new ideas for diagnostic and therapeutic approaches in the future gene therapy of ovarian cancer, inflammation, and infertility.It might offer suggestions for later gene therapy treatments for ovarian cancer, inflammation, and infertility.Figure 2 presents a summary of the physiological and pathological processes that are mediated by BK.
4 Developments in the understanding of ITIH proteins and illnesses ITIH has lately been found and thoroughly explained to be involved in several pathophysiological processes, such as inflammation and carcinogenesis (9,43).Depending on the circumstances, these proteins may be positively or negatively regulated; nonetheless, there is compelling evidence that every member of the ITIH family is crucial to the development of tumors and cellular malignant processes (9,44).ITIH proteins function as both pre-and anti-inflammatory acute phase proteins during inflammation, which leads to contradictory functions in the process.While the H3 chain is up-regulated and the related molecules behave as positive acute phase proteins, the H2 and BK chains are downregulated and the associated molecules behave as negative acute phase proteins in acute inflammation, Inflammatory situations do not seem to have an impact on H1 chain (45).Strong evidence suggests that genes in the ITIH family may be tumor suppressors because these genes are highly down-regulated in a range of human solid tumors, including lung cancer, breast cancer and colon cancer (9).ITIH proteins stabilize the ECM in a way that inhibits tumor growth, which plays a significant role in carcinogenesis (46).ITIH's covalent binding to HA and its capacity to maintain the ECM are two potential pathways.ITIH2 expression and estrogen receptor expression are substantially associated (p = 0.001) in breast cancer, according to a number of prior research.Cancer invasion and motility have been shown to be inhibited by estrogen (47).Because ITIH2 has an estrogen-binding structural domain that profoundly affects ECM integrity and may therefore be crucial for tumor growth and metastasis, there used to be a high correlation between ITIH2 expression levels and estrogen levels (48).ITIH2 is expressed in low-grade CNS cancers and normal brain tissues; however, it is not expressed in glioblastomas, especially glioblastoma multiforme, which is a highly invasive CNS tumor.This suggests that ITIH2 may have an anti-invasive function (49).The ITIH family gene has been linked in certain studies to shared genetic risk factors for schizophrenia and depression, in addition to its significant function in inflammation and malignancies.These findings imply that the ITIH family may potentially be implicated in the pathophysiology of psychiatric disorders (50).Furthermore, aberrant expression of ITIH family proteins has been found in neurodegenerative diseases (51, 52).The following table provides a summary of the roles and possible mechanisms of action of heavy chain participation (see Tables 1-5).
The ITIH family has five homologous variants that are encoded by various genes.Through an overview of current research pertaining to the ITIH family, we discovered that ITIH plays a role in numerous pathophysiological mechanisms.These comprise immunological responses, tumor growth, psychological issues, and Stress, apoptosis, proteases, aging, signaling molecules, cytokines, HA metabolism, and female ovulation processes are all impacted by bakunin.Its responsibilities and functions as an anti-inflammatory and anti-tumor invasion protein are also significant.

Summary
To jointly preserve the stability of the ECM, members of the IαI family bind covalently to HA. Hence the characteristics play a role in several physiological and pathological processes.The IαI family contains the protein BK, which is important for mammalian ovulation and human cancer.It is also an anti-invasive protein.The ITIH family is important for inflammation, immunity, psychiatric disorders, tumorigenesis, and development.Although BK has been extensively researched, its exact mechanism of action in the pathophysiological processes involving the ITIH family is still unclear.In order to examine the possible mechanisms and offer a theoretical foundation for targeted therapy of the associated disorders, a significant amount of research is required going forward.In addition, existing studies have shown that BK and ITIH family have been found to play a role in both inflammation and tumors, but whether there is an interaction between the two remains unclear.

TABLE 1
Functions and potential mechanisms of ITIH1.
stratificationWhen paired with additional proteins, ITIH1 exhibits a Lasso-logistic score that is highly effective in categorization (cross-validated area under the curve = 0.74) (61) FIGURE 2

TABLE 2
Functions and potential mechanisms of ITIH2.

TABLE 4
Functions and potential mechanisms of ITIH4.