The serine proteinase hepsin is an activator of pro-matrix metalloproteinases: molecular mechanisms and implications for extracellular matrix turnover

Type II Transmembrane Serine Proteases as Modulators in Adipose Tissue Phenotype and Function

Adipose tissue is a crucial organ in energy metabolism and thermoregulation. Adipose tissue phenotype is controlled by various signaling mechanisms under pathophysiological conditions. Type II transmembrane serine proteases (TTSPs) are a group of trypsin-like enzymes anchoring on the cell surface. These proteases act in diverse tissues to regulate physiological processes, such as food digestion, salt-water balance, iron metabolism, epithelial integrity, and auditory nerve development. More recently, several members of the TTSP family, namely, hepsin, matriptase-2, and corin, have been shown to play a role in regulating lipid metabolism, adipose tissue phenotype, and thermogenesis, via direct growth factor activation or indirect hormonal mechanisms. In mice, hepsin deficiency increases adipose browning and protects from high-fat diet-induced hyperglycemia, hyperlipidemia, and obesity. Similarly, matriptase-2 deficiency increases fat lipolysis and reduces obesity and hepatic steatosis in high-fat diet-fed mice. In contrast, corin deficiency increases white adipose weights and cell sizes, suppresses adipocyte browning and thermogenic responses, and causes cold intolerance in mice. These findings highlight an important role of TTSPs in modifying cellular phenotype and function in adipose tissue. In this review, we provide a brief description about TTSPs and discuss recent findings regarding the role of hepsin, matriptase-2, and corin in regulating adipose tissue phenotype, energy metabolism, and thermogenic responses.

Venetoclax is a potent hepsin inhibitor that reduces the metastatic and prothrombotic phenotypes of hepsin-expressing colorectal cancer cells

Introduction: Hepsin is a type II transmembrane serine protease and its expression has been linked to greater tumorigenicity and worse prognosis in different tumors. Recently, our group demonstrated that high hepsin levels from primary tumor were associated with a higher risk of metastasis and thrombosis in localized colorectal cancer patients. This study aims to explore the molecular role of hepsin in colorectal cancer. Methods: Hepsin levels in plasma from resected and metastatic colorectal cancer patients were analyzed by ELISA. The effect of hepsin levels on cell migration, invasion, and proliferation, as well as on the activation of crucial cancer signaling pathways, was performed in vitro using colorectal cancer cells. A thrombin generation assay determined the procoagulant function of hepsin from these cells. A virtual screening of a database containing more than 2000 FDA-approved compounds was performed to screen hepsin inhibitors, and selected compounds were tested in vitro for their ability to suppress hepsin effects in colorectal cancer cells. Xenotransplantation assays were done in zebrafish larvae to study the impact of venetoclax on invasion promoted by hepsin. Results: Our results showed higher plasma hepsin levels in metastatic patients, among which, hepsin was higher in those suffering thrombosis. Hepsin overexpression increased colorectal cancer cell invasion, Erk1/2 and STAT3 phosphorylation, and thrombin generation in plasma. In addition, we identified venetoclax as a potent hepsin inhibitor that reduced the metastatic and prothrombotic phenotypes of hepsin-expressing colorectal cancer cells. Interestingly, pretreatment with Venetoclax of cells overexpressing hepsin reduced their invasiveness in vivo. Discussion: Our results demonstrate that hepsin overexpression correlates with a more aggressive and prothrombotic tumor phenotype. Likewise, they demonstrate the antitumor role of venetoclax as a hepsin inhibitor, laying the groundwork for molecular-targeted therapy for colorectal cancer.

Bone morphogenetic protein 2- and estradiol-17β-induced changes in ovarian transcriptome during primordial follicle formation†

Estradiol-17β has been shown to promote primordial follicle formation and to involve bone morphogenetic protein 2 (BMP2) as a downstream effector to promote primordial follicle in hamsters. However, the molecular mechanism whereby these factors regulate ovarian somatic cells to pre-granulosa cells transition leading to primordial follicle formation remains unclear. The objective of this study was to determine whether BMP2 and/or estradiol-17β would regulate the expression of specific ovarian transcriptome during pre-granulosa cells transition and primordial follicle formation in the mouse ovary. BMP2 mRNA level increased during the period of primordial follicle formation with the concurrent presence of BMP2 protein in ovarian somatic cells. Estradiol-17β but not BMP2 exposure led to increased expression of ovarian BMP2 messenger RNA (mRNA), and the effect of estradiol-17β could not be suppressed by 4-[6-[4-(1-Piperazinyl)phenyl]pyrazolo[1,5-a]pyrimidin-3-yl]quinoline dihydrochloride (LDN) 193189. BMP2 or estradiol-17β stimulated primordial follicle formation without inducing apoptosis. Ribonucleic acid-sequence analysis (RNA-seq) of ovaries exposed to exogenous BMP2 or estradiol-17β revealed differential expression of several thousand genes. Most of the differentially expressed genes, which were common between BMP2 or estradiol-17β treatment demonstrated concordant changes, suggesting that estradiol-17β and BMP2 affected the same set of genes during primordial follicle formation. Further, we have identified that estradiol-17β, in cooperation with BMP2, could affect the expression of three major transcription factors, GATA binding protein 2, GATA binding protein 4 and Early growth response 2, and one serine protease, hepsin, in pre-granulosa cells during primordial follicle formation. Taken together, results of this study suggest that estradiol-17β and BMP2 may regulate ovarian gene expression that promote somatic cells to pre-granulosa cells transition and primordial follicle formation in the mouse ovary.

Implication of Hepsin from Primary Tumor in the Prognosis of Colorectal Cancer Patients

Hepsin is a type II transmembrane serine protease whose deregulation promotes tumor invasion by proteolysis of the pericellular components. In colorectal cancer, the implication of hepsin is unknown. Consequently, we aimed to study the correlations between hepsin expression and different clinical-histopathological variables in 169 patients with localized colorectal cancer and 118 with metastases. Tissue microarrays were produced from samples at diagnosis of primary tumors and stained with an anti-hepsin antibody. Hepsin expression was correlated with clinical-histopathological variables by using the chi-square and Kruskal−Wallis tests, Kaplan−Meier and Aalen−Johansen estimators, and Cox and Fine and Gray multivariate models. In localized cancer patients, high-intensity hepsin staining was associated with reduced 5-year disease-free survival (p-value = 0.16). Medium and high intensity of hepsin expression versus low expression was associated with an increased risk of metastatic relapse (hazard ratio 2.83, p-value = 0.035 and hazard ratio 3.30, p-value = 0.012, respectively), being a better prognostic factor than classic histological variables. Additionally, in patients with localized tumor, 5-year thrombosis cumulative incidence increased with the increment of hepsin expression (p-value = 0.038). Medium and high intensities of hepsin with respect to low intensity were associated with an increase in thrombotic risk (hazard ratio 7.71, p-value = 0.043 and hazard ratio 9.02, p-value = 0.028, respectively). This relationship was independent of previous tumor relapse (p-value = 0.036). Among metastatic patients, low hepsin expression was associated with a low degree of tumor differentiation (p-value < 0.001) and with major metastatic dissemination (p-value = 0.023). Hepsin is a potential thrombotic and metastatic biomarker in patients with localized colorectal cancer. In metastatic patients, hepsin behaves in a paradoxical way with respect to differentiation and invasion processes.

Elevation of α-1,3 fucosylation promotes the binding ability of TNFR1 to TNF-α and contributes to osteoarthritic cartilage destruction and apoptosis

Background

Osteoarthritis (OA) is the most common form of arthritis and is characterized by the degradation of articular cartilage and inflammation of the synovial membrane. Fucosylation is an important feature of protein N/O-glycosylation and is involved in a variety of pathological processes, including inflammation and cancer. However, whether fucosylation impacts the OA pathological process is unknown.

Methods

Total proteins were extracted from cartilage samples obtained from patients with OA (n = 11) and OA rabbit models at different time points (n = 12). OA-associated abnormal glycopatterns were evaluated by lectin microarrays and lectin blots. The expression of fucosyltransferases involved in the synthesis of α-1,3 fucosylation was assessed by semi-qPCR. The synthesis of α-1,3 fucosylation mediated by FUT10 was interrupted by the transfection of siRNA, and the effect of α-1,3 fucosylation on OA-associated events was assessed. Then, immunoprecipitation and lectin blotting were used to investigate the relationship between the α-1,3 fucosylation level of tumor necrosis factor receptor superfamily member 1A (TNFR1) and OA. Finally, a TNFR1 antibody microarray was fabricated to evaluate the effect of α-1,3 fucosylation on the ability of TNFR1 to bind to tumor necrosis factor-α (TNF-α).

Results

Elevated α-1,3 fucosylation was observed in cartilage from OA patients, rabbit models, and chondrocytes induced by TNF-α (fold change> 2, p< 0.01). Our results and the GEO database indicated that the overexpression of FUT10 contributed to this alteration. Silencing the expression of FUT10 impaired the ability of TNFR1 to bind to TNF-α, impeded activation of the NF-κB and P38/JNK-MAPK pathways, and eventually retarded extracellular matrix (ECM) degradation, senescence, and apoptosis in chondrocytes exposed to TNF-α.

Conclusion

The elevation of α-1,3 fucosylation is not only a characteristic of OA but also impacts the OA pathological process. Our work provides a new positive feedback loop of “inflammation conditions/TNF-α/FUT10/α-1,3 fucosylation of TNFR1/NF-κB and P38/JNK-MAPK pathways/proinflammatory processes” that contributes to ECM degradation and chondrocyte apoptosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02776-z.

Clinical Significance of Hepsin and Underlying Signaling Pathways in Prostate Cancer

The hepsin gene encodes a type II transmembrane serine protease. Previous studies have shown the overexpression of hepsin in prostate cancer, and the dysregulation of hepsin promotes cancer cell proliferation, migration, and metastasis in vitro and in vivo. The review incorporated with our work showed that hepsin expression levels were specifically increased in prostate cancer, and higher expression in metastatic tumors than in primary tumors was also observed. Moreover, increased expression was associated with poor outcomes for patients with prostate cancer. Using in silico protein–protein interaction prediction, mechanistic analysis showed that hepsin interacted with eight other oncogenic proteins, whose expression was significantly correlated with hepsin expression in prostate cancer. The oncogenic functions of hepsin are mainly linked to proteolytic activities that disrupt epithelial integrity and regulatorily interact with other genes to influence cell-proliferation, EMT/metastasis, inflammatory, and tyrosine-kinase-signaling pathways. Moreover, genomic amplifications of hepsin, not deletions or other alterations, were significantly associated with prostate cancer metastasis. Targeting hepsin using a specific inhibitor or antibodies significantly attenuates its oncogenic behaviors. Therefore, hepsin could be a novel biomarker and therapeutic target for prostate cancer.

Dihydroartemisinin-Transferrin Adducts Enhance TRAIL-Induced Apoptosis in Triple-Negative Breast Cancer in a P53-Independent and ROS-Dependent Manner

Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer subtype independent of estrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2. It has a poor prognosis and high recurrence. Due to its limited treatment options in the clinic, novel therapies are urgently needed. Single treatment with the death receptor ligand TRAIL was shown to be poorly effective. Recently, we have shown that artemisinin derivatives enhance TRAIL-induced apoptosis in colon cancer cells. Here, we utilized transferrin (TF) to enhance the effectiveness of dihydroartemisinin (DHA) in inducing cell death in TNBC cell lines (MDA-MB-231, MDA-MB-436, MDA-MB-468 and BT549). We found that the combination of DHA-TF and the death receptor 5-specific TRAIL variant DHER leads to an increase in DR5 expression in all four TNBC cell lines, while higher cytotoxicity was observed in MDA-MB-231, and MDA-MB-436. All the data point to the finding that DHA-TF stimulates cell death in TNBC cells, while the combination of DHA-TF with TRAIL variants will trigger more cell death in TRAIL-sensitive cells. Overall, DHA-TF in combination with TRAIL variants represents a potential novel combination therapy for triple-negative breast cancer.

Matrix metalloproteinase-13 is fully activated by neutrophil elastase and inactivates its serpin inhibitor, alpha-1 antitrypsin: Implications for osteoarthritis

Matrix metalloproteinase-13 (MMP-13) is a uniquely important collagenase that promotes the irreversible destruction of cartilage collagen in osteoarthritis (OA). Collagenase activation is a key control point for cartilage breakdown to occur, yet our understanding of the proteinases involved in this process is limited. Neutrophil elastase (NE) is a well-described proteoglycan-degrading enzyme which is historically associated with inflammatory arthritis, but more recent evidence suggests a potential role in OA. In this study, we investigated the effect of neutrophil elastase on OA cartilage collagen destruction and collagenase activation. Neutrophil elastase induced significant collagen destruction from human OA cartilage ex vivo, in an MMP-dependent manner. In vitro, neutrophil elastase directly and robustly activated pro-MMP-13, and N-terminal sequencing identified cleavage close to the cysteine switch at 72 MKKPR, ultimately resulting in the fully active form with the neo-N terminus of 85 YNVFP. Mole-per-mole, activation was more potent than by MMP-3, a classical collagenase activator. Elastase was detectable in human OA synovial fluid and OA synovia which displayed histologically graded evidence of synovitis. Bioinformatic analyses demonstrated that, compared with other tissues, control cartilage exhibited remarkably high transcript levels of the major elastase inhibitor, (AAT) alpha-1 antitrypsin (gene name SERPINA1), but these were reduced in OA. AAT was located predominantly in superficial cartilage zones, and staining enhanced in regions of cartilage damage. Finally, active MMP-13 specifically inactivated AAT by removal of the serine proteinase cleavage/inhibition site. Taken together, this study identifies elastase as a novel activator of pro-MMP-13 that has relevance for cartilage collagen destruction in OA patients with synovitis.

Hepsin regulates TGFβ signaling via fibronectin proteolysis

Transforming growth factor‐beta (TGFβ) is a multifunctional cytokine with a well‐established role in mammary gland development and both oncogenic and tumor‐suppressive functions. The extracellular matrix (ECM) indirectly regulates TGFβ activity by acting as a storage compartment of latent‐TGFβ, but how TGFβ is released from the ECM via proteolytic mechanisms remains largely unknown. In this study, we demonstrate that hepsin, a type II transmembrane protease overexpressed in 70% of breast tumors, promotes canonical TGFβ signaling through the release of latent‐TGFβ from the ECM storage compartment. Mammary glands in hepsin CRISPR knockout mice showed reduced TGFβ signaling and increased epithelial branching, accompanied by increased levels of fibronectin and latent‐TGFβ1, while overexpression of hepsin in mammary tumors increased TGFβ signaling. Cell‐free and cell‐based experiments showed that hepsin is capable of direct proteolytic cleavage of fibronectin but not latent‐TGFβ and, importantly, that the ability of hepsin to activate TGFβ signaling is dependent on fibronectin. Altogether, this study demonstrates a role for hepsin as a regulator of the TGFβ pathway in the mammary gland via a novel mechanism involving proteolytic downmodulation of fibronectin.

Targeting Dysregulation of Metalloproteinase Activity in Osteoarthritis

Metalloproteinases were first identified as collagen cleaving enzymes and are now appreciated to play important roles in a wide variety of biological processes. The aberrant activity and dysregulation of the metalloproteinase family are linked to numerous diseases including cardiovascular and pulmonary diseases, chronic wounds, cancer, fibrosis and arthritis. Osteoarthritis (OA) is the most prevalent age-related joint disorder that causes pain and disability, but there are no disease-modifying drugs available. The hallmark of OA is loss of articular cartilage and elevated activities of matrix-degrading metalloproteinases are responsible. These enzymes do not exist in isolation and their activity is tightly regulated by a number of processes, such as transcription, proteolytic activation, interaction with their inhibitors, cell surface and extracellular matrix molecules, and endocytic clearance from the extracellular milieu. Here, we describe the functions and roles of metalloproteinase family in OA pathogenesis. We highlight recent studies that have illustrated novel mechanisms regulating their extracellular activity and impairment of such regulations that lead to the development of OA. We also discuss how to stop or slow down the degenerative processes by targeting aberrant metalloproteinase activity, which may in future become therapeutic interventions for the disease.

Serpins in cartilage and osteoarthritis: what do we know?

Serpins (serine proteinase inhibitors) are an ancient superfamily of structurally similar proteins, the majority of which use an elegant suicide inhibition mechanism to target serine proteinases. Despite likely evolving from a single common ancestor, the 36 human serpins have established roles regulating diverse biological processes, such as blood coagulation, embryonic development and extracellular matrix (ECM) turnover. Genetic mutations in serpin genes underpin a host of monogenic disorders — collectively termed the ‘serpinopathies’ — but serpin dysregulation has also been shown to drive pathological mechanisms in many common diseases. Osteoarthritis is a degenerative joint disorder, characterised by the progressive destruction of articular cartilage. This breakdown of the cartilage is driven by the metalloproteinases, and it has long been established that an imbalance of metalloproteinases to their inhibitors is of critical importance. More recently, a role for serine proteinases in cartilage destruction is emerging; including the activation of latent matrix metalloproteinases and cell-surface receptors, or direct proteolysis of the ECM. Serpins likely regulate these processes, as well as having roles beyond serine proteinase inhibition. Indeed, serpins are routinely observed to be highly modulated in osteoarthritic tissues and fluids by ‘omic analysis, but despite this, they are largely ignored. Confusing nomenclature and an underappreciation for the role of serine proteinases in osteoarthritis (OA) being the likely causes. In this narrative review, serpin structure, biochemistry and nomenclature are introduced, and for the first time, their putative importance in maintaining joint tissues — as well as their dysregulation in OA — are explored.

Oncogenic Ras Disrupts Epithelial Integrity by Activating the Transmembrane Serine Protease Hepsin

Ras proteins play a causal role in human cancer by activating multiple pathways that promote cancer growth and invasion. However, little is known about how Ras induces the first diagnostic features of invasion in solid tumors, including loss of epithelial integrity and breaching of the basement membrane (BM). In this study, we found that oncogenic Ras strongly promotes the activation of hepsin, a member of the hepsin/TMPRSS type II transmembrane serine protease family. Mechanistically, the Ras-dependent hepsin activation was mediated via Raf-MEK-ERK signaling, which controlled hepsin protein stability through the heat shock transcription factor-1 stress pathway. In Ras-transformed three-dimensional mammary epithelial culture, ablation of hepsin restored desmosomal cell-cell junctions, hemidesmosomes, and BM integrity and epithelial cohesion. In tumor xenografts harboring mutant KRas, silencing of hepsin increased local invasion concomitantly with accumulation of collagen IV. These findings suggest that hepsin is a critical protease for Ras-dependent tumorigenesis, executing cell-cell and cell-matrix pathologies important for early tumor dissemination. SIGNIFICANCE: These findings identify the cell-surface serine protease hepsin as a potential therapeutic target for its role in oncogenic Ras-mediated deregulation of epithelial cell-cell and cell-matrix interactions and cohesion of epithelial structure.

Hepsin: a multifunctional transmembrane serine protease in pathobiology

Cell membrane-bound serine proteases are important in the maintenance of physiological homeostasis. Hepsin is a type II transmembrane serine protease highly expressed in the liver. Recent studies indicate that hepsin activates prohepatocyte growth factor in the liver to enhance Met signaling, thereby regulating glucose, lipid, and protein metabolism. In addition, hepsin functions in nonhepatic tissues, including the adipose tissue, kidney, and inner ear, to regulate adipocyte differentiation, urinary protein processing, and auditory function, respectively. In mouse models, hepsin deficiency lowers blood glucose, lipid, and protein levels, impairs uromodulin assembly in renal epithelial cells, and causes hearing loss. Elevated hepsin expression has also been found in many cancers. As a type II transmembrane protease, cell surface expression and zymogen activation are essential for hepsin activity. In this review, we discuss the current knowledge regarding hepsin biosynthesis, activation, and functions in pathobiology.

Priming of SARS-CoV-2 S protein by several membrane-bound serine proteinases could explain enhanced viral infectivity and systemic COVID-19 infection

The ongoing COVID-19 pandemic has already caused over a million deaths worldwide, and this death toll will be much higher before effective treatments and vaccines are available. The causative agent of the disease, the coronavirus SARS-CoV-2, shows important similarities with the previously emerged SARS-CoV-1, but also striking differences. First, SARS-CoV-2 possesses a significantly higher transmission rate and infectivity than SARS-CoV-1 and has infected in a few months over 60 million people. Moreover, COVID-19 has a systemic character, as in addition to the lungs, it also affects the heart, liver, and kidneys among other organs of the patients and causes frequent thrombotic and neurological complications. In fact, the term "viral sepsis" has been recently coined to describe the clinical observations. Here I review current structure-function information on the viral spike proteins and the membrane fusion process to provide plausible explanations for these observations. I hypothesize that several membrane-associated serine proteinases (MASPs), in synergy with or in place of TMPRSS2, contribute to activate the SARS-CoV-2 spike protein. Relative concentrations of the attachment receptor, ACE2, MASPs, their endogenous inhibitors (the Kunitz-type transmembrane inhibitors, HAI-1/SPINT1 and HAI-2/SPINT2, as well as major circulating serpins) would determine the infection rate of host cells. The exclusive or predominant expression of major MASPs in specific human organs suggests a direct role of these proteinases in e.g., heart infection and myocardial injury, liver dysfunction, kidney damage, as well as neurological complications. Thorough consideration of these factors could have a positive impact on the control of the current COVID-19 pandemic.

Inhibitors of type II transmembrane serine proteases in the treatment of diseases of the respiratory tract - A review of patent literature

INTRODUCTION

Type II transmembrane serine proteases (TTSPs) of the human respiratory tract generate high interest owing to their ability, among other roles, to cleave surface proteins of respiratory viruses. This step is critical in the viral invasion of coronaviruses, including SARS-CoV-2 responsible for COVID-19, but also influenza viruses and reoviruses. Accordingly, these cell surface enzymes constitute appealing therapeutic targets to develop host-based therapeutics against respiratory viral diseases. Additionally, their deregulated levels or activity has been described in non-viral diseases such as fibrosis, cancer, and osteoarthritis, making them potential targets in these indications.

AREAS COVERED

Areas covered: This review includes WIPO-listed patents reporting small molecules and peptide-based inhibitors of type II transmembrane serine proteases of the respiratory tract.

EXPERT OPINION

Expert opinion: Several TTSPs of the respiratory tract represent attractive pharmacological targets in the treatment of respiratory infectious diseases (notably COVID-19 and influenza), but also against idiopathic pulmonary fibrosis and lung cancer. The current emphasis is primarily on TMPRSS2, matriptase, and hepsin, yet other TTSPs await validation. Compounds listed herein are predominantly peptidomimetic inhibitors, some with covalent reversible mechanisms of action and high potencies. Their selectivity profile, however, are often only partially characterized. Preclinical data are promising and warrant further advancement in the above diseases.

Peptidomic Analysis of Urine from Youths with Early Type 1 Diabetes Reveals Novel Bioactivity of Uromodulin Peptides In Vitro

Chronic hyperglycemia is known to disrupt the proteolytic milieu, initiating compensatory and maladaptive pathways in the diabetic kidney. Such changes in intrarenal proteolysis are captured by the urinary peptidome. To elucidate the early kidney response to chronic hyperglycemia, we conducted a peptidomic investigation into urines from otherwise healthy youths with type 1 diabetes and their non-diabetic peers using unbiased and targeted mass spectrometry-based techniques. This cross-sectional study included two separate cohorts for the discovery (n = 30) and internal validation (n = 30) of differential peptide excretion. Peptide bioactivity was predicted using PeptideRanker and subsequently verified in vitro Proteasix and the Nephroseq database were used to identify putative proteases responsible for peptide generation and examine their expression in diabetic nephropathy. A total of 6550 urinary peptides were identified in the discovery analysis. We further examined the subset of 162 peptides, which were quantified across all thirty samples. Of the 15 differentially excreted peptides (p < 0.05), seven derived from a C-terminal region (589SGSVIDQSRVLNLGPITRK607) of uromodulin, a kidney-specific protein. Increased excretion of five uromodulin peptides was replicated in the validation cohort using parallel reaction monitoring (p < 0.05). One of the validated peptides (SGSVIDQSRVLNLGPI) activated NFκB and AP-1 signaling, stimulated cytokine release, and enhanced neutrophil migration in vitro. In silico analyses highlighted several potential proteases such as hepsin, meprin A, and cathepsin B to be responsible for generating these peptides. In summary, we identified a urinary signature of uromodulin peptides associated with early type 1 diabetes before clinical manifestations of kidney disease and discovered novel bioactivity of uromodulin peptides in vitro Our present findings lay the groundwork for future studies to validate peptide excretion in larger and broader populations, to investigate the role of bioactive uromodulin peptides in high glucose conditions, and to examine proteases that cleave uromodulin.

β1,4-galactosyltransferase-I protects chondrocytes against TNF-induced apoptosis by blocking the TLR4 signaling pathway

Osteoarthritis (OA) is the most common degenerative disease of the cartilage and is characterized by inflammation of the synovial membrane and subchondral osteosclerosis. β1,4-galactosyltransferase-I (β1,4-GalT-I) is a crucial regulator of inflammation based on its role in the stimulation and sustenance of inflammation in OA. In the present study, we aimed at elucidating the expression pattern and potential biological activity of β1,4-GalT-I in chondrocytes isolated from OA patients. Chondrocytes were isolated from the cartilage and cultured. Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) were used to analyze β1,4-GalT-I expression. Isolated chondrocytes were stimulated with tumor necrosis factor (TNF). Our results indicate significantly enhanced expression of β1,4-GalT-I in cultivated chondrocytes upon stimulation with TNF. β1,4-GalT-I inhibited the inflammation and cell death triggered by TNF. In addition, β1,4-GalT-Iinhibited the expression of Toll-like receptor 4 (TLR4) and phosphorylation of p65 and IKK. In conclusion, our findings suggest the protective effect of β1,4-GalT-I in chondrocytes against OA induced by TNF based on its ability to block the TLR4 signaling pathway. Our results also indicate significant contribution of β1,4-GalT-I towards the anti-inflammation in the cartilage of patients suffering from OA.

Collagenolytic matrix metalloproteinases antagonize proteinase-activated receptor-2 activation, providing insights into extracellular matrix turnover

The collagenase subfamily of matrix metalloproteinases (MMPs) have important roles in the remodeling of collagenous matrices. The proteinase-activated receptor (PAR) family has a unique mechanism of activation requiring proteolysis of an extracellular domain forming a neo-N terminus that acts as a tethered ligand, a process that has been associated with the development of arthritis. Canonical PAR2 activation typically occurs via a serine proteinase at Arg36-Ser37, but other proteinases can cleave PARs downstream of the tethered ligand and "disarm" the receptor. To identify additional cleavage sites within PAR2, we synthesized a 42-amino-acid peptide corresponding to the extracellular region. We observed that all three soluble MMP collagenases, MMP-1, MMP-8, and MMP-13, cleave PAR2 and discovered a novel cleavage site (Ser37-Leu38). Metalloproteinases from resorbing bovine nasal cartilage and recombinant human collagenases could cleave a quenched fluorescent peptide mimicking the canonical PAR2 activation region, and kinetic constants were determined. In PAR2-overexpressing SW1353 chondrocytes, we demonstrated that the activator peptide SLIGKV-NH2 induces rapid calcium flux, inflammatory gene expression (including MMP1 and MMP13), and the phosphorylation of extracellular signal-regulated kinase (ERK) and p38 kinase. The corresponding MMP cleavage-derived peptide (LIGKVD-NH2) exhibited no canonical activation; however, we observed phosphorylation of ERK, providing evidence of biased agonism. Importantly, we demonstrated that preincubation with active MMP-1 reduced downstream PAR2 activation by a canonical activator, matriptase, but not SLIGKV-NH2 These results support a role for collagenases as proteinases capable of disarming PAR2, revealing a mechanism that suppresses PAR2-mediated inflammatory responses.

Recent advances in understanding the regulation of metalloproteinases

Metalloproteinases remain important players in arthritic disease, in part because members of this large enzymatic family, namely matrix metalloproteinase-1 (MMP-1) and MMP-13, are responsible for the irreversible degradation of articular cartilage collagen. Although direct inhibition of MMPs fell out of vogue with the initial clinical disappointment of the first generation of compounds, interest in other mechanisms that control these important enzymes has always been maintained. Since these enzymes are critically important for tissue homeostasis, their expression and activity are tightly regulated at many levels, not just by direct inhibition by their endogenous inhibitors the tissue inhibitors of metalloproteinases (TIMPs). Focussing on MMP-13, we discuss recent work that highlights new discoveries in the transcriptional regulation of this enzyme, from defined promoter functional analysis to how more global technologies can provide insight into the enzyme’s regulation, especially by epigenetic mechanisms, including non-coding RNAs. In terms of protein regulation, we highlight recent findings into enzymatic cascades involved in MMP-13 regulation and activation. Importantly, we highlight a series of recent studies that describe how MMP-13 activity, and in fact that of other metalloproteinases, is in part controlled by receptor-mediated endocytosis. Together, these new discoveries provide a plethora of novel regulatory mechanisms, besides direct inhibition, which with renewed vigour could provide further therapeutic opportunities for regulating the activity of this class of important enzymes.

Serine proteinases in the turnover of the cartilage extracellular matrix in the joint: implications for therapeutics

Cartilage destruction is a key characteristic of arthritic disease, a process now widely established to be mediated by metzincins such as MMPs. Despite showing promise in preclinical trials during the 1990s, MMP inhibitors for the blockade of extracellular matrix turnover in the treatment of cancer and arthritis failed clinically, primarily due to poor selectivity for target MMPs. In recent years, roles for serine proteinases in the proteolytic cascades leading to cartilage destruction have become increasingly apparent, renewing interest in the potential for new therapeutic strategies that utilize pharmacological inhibitors against this class of proteinases. Herein, we describe key serine proteinases with likely importance in arthritic disease and highlight recent advances in this field. LINKED ARTICLES: This article is part of a themed section on Translating the Matrix. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.1/issuetoc.