Impairment of the collagenase-3 endocytotic receptor system in cells from patients with osteoarthritis

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.

Targeting Cartilage Degradation in Osteoarthritis

Osteoarthritis is a common, degenerative joint disease with significant socio-economic impact worldwide. There are currently no disease-modifying drugs available to treat the disease, making this an important area of pharmaceutical research. In this review, we assessed approaches being explored to directly inhibit metalloproteinase-mediated cartilage degradation and to counteract cartilage damage by promoting growth factor-driven repair. Metalloproteinase-blocking antibodies are discussed, along with recent clinical trials on FGF18 and Wnt pathway inhibitors. We also considered dendrimer-based approaches being developed to deliver and retain such therapeutics in the joint environment. These may reduce systemic side effects while improving local half-life and concentration. Development of such targeted anabolic therapies would be of great benefit in the osteoarthritis field.

Genome-wide DNA methylation profiling of articular cartilage reveals significant epigenetic alterations in Kashin-Beck disease and osteoarthritis

OBJECTIVE

To determine genome-wide DNA methylation profiles of knee cartilage from patients with Kashin-Beck disease (KBD) and osteoarthritis (OA).

METHOD

Knee cartilage was collected from 14 grade III KBD patients, 5 primary OA patients and 13 healthy subjects. The genome-wide methylation profiles of 5 KBD cartilage, 5 OA cartilage and 5 normal cartilage were determined by Illumina HumanMethylation450 array. Illumina Methylation Analyzer package was employed for identifying differentially methylated CpG sites. Functional annotation and enrichment analysis of differentially methylated genes (DMG) were conducted using GeneRIF database, Ingenuity Pathway Analysis (IPA) and The Database for Annotation, Visualization and Integrated Discovery (DAVID). Mass spectrometry (MS) and immunohistochemistry (IHC) were conducted to validate the functional relevance of identified KBD associated gene.

RESULTS

We identified a total of 1212 differentially methylated CpG sites in KBD vs Normal, annotated to 264 hypermethylated and 368 hypomethylated genes. Comparing the DNA methylation profiles of KBD vs Normal and OA vs Normal detected overlap of 367 differentially methylated CpG sites (annotated to 182 genes) as well as 845 KBD-specific differentially methylated CpG sites (annotated to 471 unique genes). MS and IHC confirmed the hypermethylation status and decreased protein expression of HAPLN1 gene in KBD cartilage.

CONCLUSION

Our data implicate epigenetic dysregulation of a host of genes in KBD and OA. Furthermore, we observed common causal epigenetic changes shared by KBD and OA.

Matrix metalloproteinase collagenolysis in health and disease

The proteolytic processing of collagen (collagenolysis) is critical in development and homeostasis, but also contributes to numerous pathologies. Mammalian interstitial collagenolytic enzymes include members of the matrix metalloproteinase (MMP) family and cathepsin K. While MMPs have long been recognized for their ability to catalyze the hydrolysis of collagen, the roles of individual MMPs in physiological and pathological collagenolysis are less defined. The use of knockout and mutant animal models, which reflect human diseases, has revealed distinct collagenolytic roles for MT1-MMP and MMP-13. A better understanding of temporal and spatial collagen processing, along with the knowledge of the specific MMP involved, will ultimately lead to more effective treatments for cancer, arthritis, cardiovascular conditions, and infectious diseases. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.

Low-Density Lipoprotein Receptor-Related Proteins in Skeletal Development and Disease

The identification of the low-density lipoprotein receptor (LDLR) provided a foundation for subsequent studies in lipoprotein metabolism, receptor-mediated endocytosis, and many other fundamental biological functions. The importance of the LDLR led to numerous studies that identified homologous molecules and ultimately resulted in the description of the LDL-receptor superfamily, a group of proteins that contain domains also found in the LDLR. Subsequent studies have revealed that members of the LDLR-related protein family play roles in regulating many aspects of signal transduction. This review is focused on the roles of selected members of this protein family in skeletal development and disease. We present background on the identification of this subgroup of receptors, discuss the phenotypes associated with alterations in their function in human patients and mouse models, and describe the current efforts to therapeutically target these proteins to treat human skeletal disease.

MMP-13 is one of the critical mediators of the effect of HDAC4 deletion on the skeleton

Histone deacetylase 4 (Hdac4) regulates chondrocyte hypertrophy. Hdac4(-/-) mice are runted in size and do not survive to weaning. This phenotype is primarily due to the acceleration of onset of chondrocyte hypertrophy and, as a consequence, inappropriate endochondral mineralization. Previously, we reported that Hdac4 is a repressor of matrix metalloproteinase-13 (Mmp13) transcription, and the absence of Hdac4 leads to increased expression of MMP-13 both in vitro (osteoblastic cells) and in vivo (hypertrophic chondrocytes and trabecular osteoblasts). MMP-13 is thought to be involved in endochondral ossification and bone remodeling. To identify whether the phenotype of Hdac4(-/-) mice is due to up-regulation of MMP-13, we generated Hdac4/Mmp13 double knockout mice and determined the ability of deletion of MMP-13 to rescue the Hdac4(-/-) mouse phenotype. Mmp13(-/-) mice have normal body size. Hdac4(-/-)/Mmp13(-/-) double knockout mice are significantly heavier and larger than Hdac4(-/-) mice, they survive longer, and they recover the thickness of their growth plate zones. In Hdac4(-/-)/Mmp13(-/-) double knockout mice, alkaline phosphatase (ALP) expression and TRAP-positive osteoclasts were restored (together with an increase in Mmp9 expression) but osteocalcin (OCN) was not. Micro-CT analysis of the tibiae revealed that Hdac4(-/-) mice have significantly decreased cortical bone area compared with the wild type mice. In addition, the bone architectural parameter, bone porosity, was significantly decreased in Hdac4(-/-) mice. Hdac4(-/-)/Mmp13(-/-) double knockout mice recover these cortical parameters. Likewise, Hdac4(-/-) mice exhibit significantly increased Tb.Th and bone mineral density (BMD) while the Hdac4(-/-)/Mmp13(-/-) mice significantly recovered these parameters toward normal for this age. Taken together, our findings indicate that the phenotype seen in the Hdac4(-/-) mice is partially derived from elevation in MMP-13 and may be due to a bone remodeling disorder caused by overexpression of this enzyme.

MMP-13 is constitutively produced in human chondrocytes and co-endocytosed with ADAMTS-5 and TIMP-3 by the endocytic receptor LRP1

Matrix metalloproteinase 13 (MMP-13) degrades collagenous extracellular matrix and its aberrant activity associates with diseases such as arthritis, cancer, atherosclerosis and fibrosis. The wide range of MMP-13 proteolytic capacity suggests that it is a powerful, potentially destructive proteinase and thus it has been believed that MMP-13 is not produced in most adult human tissues in the steady state. Present study has revealed that human chondrocytes isolated from healthy adults constitutively express and secrete MMP-13, but that it is rapidly endocytosed and degraded by chondrocytes. Both pro- and activated MMP-13 bind to clusters II and III of low-density lipoprotein (LDL) receptor-related protein 1 (LRP1). Domain deletion studies indicated that the hemopexin domain is responsible for this interaction. Binding competition between MMP-13 and ADAMTS-4, -5 or TIMP-3, which also bind to cluster II, further shown that the MMP-13 binding site within cluster II is different from those of ADAMTS-4, -5 or TIMP-3. MMP-13 is therefore co-endocytosed with ADAMTS-5 and TIMP-3 by human chondrocytes. These findings indicate that MMP-13 may play a role on physiological turnover of cartilage extracellular matrix and that LRP1 is a key modulator of extracellular levels of MMP-13 and its internalization is independent of the levels of ADAMTS-4, -5 and TIMP-3.

•

ProMMP-13 is constitutively produced and endocytosed by chondrocytes.

•

LRP1 is a key modulator of extracellular levels of proMMP-13 and MMP-13.

•

ProMMP-13 and MMP-13 directly bind to LRP1 via the hemopexin domain.

•

Unique sites on LRP1 for MMP-13 binding have been mapped.

•

Co-endocytosis of proMMP-13 with ADAMTS-4, -5 and TIMP-3.

Extracellular regulation of metalloproteinases

Matrix metalloproteinases (MMPs) and adamalysin-like metalloproteinase with thrombospondin motifs (ADAMTSs) belong to the metzincin superfamily of metalloproteinases and they play key roles in extracellular matrix catabolism, activation and inactivation of cytokines, chemokines, growth factors, and other proteinases at the cell surface and within the extracellular matrix. Their activities are tightly regulated in a number of ways, such as transcriptional regulation, proteolytic activation and interaction with tissue inhibitors of metalloproteinases (TIMPs). Here, we highlight recent studies that have illustrated novel mechanisms regulating the extracellular activity of these enzymes. These include allosteric activation of metalloproteinases by molecules that bind outside the active site, modulation of location and activity by interaction with cell surface and extracellular matrix molecules, and endocytic clearance from the extracellular milieu by low-density lipoprotein receptor-related protein 1 (LRP1).

Osteoarthritis pathogenesis: a review of molecular mechanisms

Osteoarthritis (OA), the most prevalent chronic joint disease, increases in prevalence with age, and affects majority of individuals over the age of 65 and is a leading musculoskeletal cause of impaired mobility in the elderly. Because the precise molecular mechanisms which are involved in the degradation of cartilage matrix and development of OA are poorly understood and there are currently no effective interventions to decelerate the progression of OA or retard the irreversible degradation of cartilage except for total joint replacement surgery. In this paper, the important molecular mechanisms related to OA pathogenesis will be summarized and new insights into potential molecular targets for the prevention and treatment of OA will be provided.

Low density lipoprotein receptor-related protein 1 (LRP1)-mediated endocytic clearance of a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4): functional differences of non-catalytic domains of ADAMTS-4 and ADAMTS-5 in LRP1 binding

Degradation of the cartilage proteoglycan aggrecan is an early event in the development of osteoarthritis, and a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) and ADAMTS-5 are considered to be the major aggrecan-degrading enzymes. We have recently found that ADAMTS-5 is rapidly endocytosed via low density lipoprotein receptor-related protein 1 (LRP1) and degraded by chondrocytes. Here we report that this regulatory mechanism also applies to ADAMTS-4, although its rate of endocytosis is slower than that of ADAMTS-5. Domain deletion mutagenesis of ADAMTS-4 identified that the cysteine-rich and spacer domains are responsible for binding to LRP1, whereas the thrombospondin 1 and spacer domains are responsible in ADAMTS-5. The estimated t½ value of ADAMTS-4 endocytosis was about 220 min, whereas that of ADAMTS-5 was 100 min. The difference in half-lives between the two enzymes is explained by the 13-fold lower affinity of ADAMTS-4 for LRP1 compared with that of ADAMTS-5. Studies using soluble ligand binding clusters of LRP1 showed that ADAMTS-4 binds to clusters II and IV with similar KD,app values of 98 and 73 nm, respectively, whereas ADAMTS-5 binds to cluster II, III, and IV with KD,app values of 3.5, 41, and 9 nm, respectively. Thus, ADAMTS-5 competitively inhibits ADAMTS-4 endocytosis but not vice versa. This study highlights that the affinity between a ligand and LRP1 dictates the rate of internalization and suggests that LRP1 is a major traffic controller of the two aggrecanases, especially under inflammatory conditions, where the protein levels of ADAMTS-4 increase, but those of ADAMTS-5 do not.

LRP-1-mediated endocytosis regulates extracellular activity of ADAMTS-5 in articular cartilage

Aggrecan is a major matrix component of articular cartilage, and its degradation is a crucial event in the development of osteoarthritis (OA). Adamalysin-like metalloproteinase with thrombospondin motifs 5 (ADAMTS-5) is a major aggrecan-degrading enzyme in cartilage, but there is no clear correlation between ADAMTS-5 mRNA levels and OA progression. Here, we report that post-translational endocytosis of ADAMTS-5 by chondrocytes regulates its extracellular activity. We found 2- to 3-fold reduced aggrecanase activity when ADAMTS-5 was incubated with live porcine cartilage, resulting from its rapid endocytic clearance. Studies using receptor-associated protein (RAP), a ligand-binding antagonist for the low-density lipoprotein receptor-related proteins (LRPs), and siRNA-mediated gene silencing revealed that the receptor responsible for ADAMTS-5 clearance is LRP-1. Domain-deletion mutagenesis of ADAMTS-5 identified that the noncatalytic first thrombospondin and spacer domains mediate its endocytosis. The addition of RAP to porcine cartilage explants in culture increased the basal level of aggrecan degradation, as well as ADAMTS-5-induced aggrecan degradation. Notably, LRP-1-mediated endocytosis of ADAMTS-5 is impaired in chondrocytes of OA cartilage, with ∼90% reduction in protein levels of LRP-1 without changes in its mRNA levels. Thus, LRP-1 dictates physiological and pathological catabolism of aggrecan in cartilage as a key modulator of the extracellular activity of ADAMTS-5.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Biomarkers predict radiographic progression in early rheumatoid arthritis and perform well compared with traditional markers

OBJECTIVE

To evaluate the performance of biochemical and traditional markers in predicting radiographic progression in rheumatoid arthritis (RA).

METHODS

One hundred thirty-two patients with early RA were treated with nonbiologic therapies for 2 years and studied longitudinally. Genomic DNA was analyzed for presence of the shared epitope. Levels of matrix metalloproteinases (matrix metalloproteinase 1 [MMP-1], MMP-13, and MMP-3), tissue inhibitor of metalloproteinases 1 (TIMP-1), and cartilage oligomeric matrix protein (COMP) were assessed in serially obtained serum samples. The presence of pyridinoline (Pyr), deoxypyridinoline, glycosylated Pyr (Glc-Gal-Pyr), and C-telopeptide of type II collagen (CTX-II) was assessed in urine samples. Radiographs obtained at entry and at 2 years were evaluated using the modified Larsen score.

RESULTS

Baseline and 2-year radiographs were available from 118 patients. Larsen scores worsened during the 2 years in 50 patients, while 68 patients had no radiographic progression. Levels of a variety of biochemical markers, i.e., MMP-3, CTX-II, COMP, TIMP-1, Pyr, and Glc-Gal-Pyr, correlated significantly with radiographic progression at entry and longitudinally as assessed by area under the curve (AUC). By multivariate analysis, a model including MMP-3 and CTX-II was identified as providing the best prediction of radiographic progression at entry (predictive accuracy by receiver operating characteristic [ROC] AUC = 0.76 [95% confidence interval 0.66-0.85]), while a combination of MMP-3, CTX-II, and swollen joint count formed the best longitudinal AUC model (predictive accuracy by ROC AUC = 0.81 [95% confidence interval 0.73-0.89]). Patient-reported measures (Health Assessment Questionnaire, pain scores) were of limited use. In a subset of 50 patients who were treated with methotrexate (MTX) during the followup period, median serum MMP-3 levels decreased after the initiation of MTX therapy (P = 0.0003).

CONCLUSION

These results indicate that biochemical markers are useful predictors of radiographic progression in RA and that serum MMP-3 levels decrease significantly with MTX therapy. Multivariate models that include MMP-3 and CTX-II perform better than existing traditional markers in predicting radiographic outcome in RA.

Matrix metalloproteinase-13 influences ERK signalling in articular rabbit chondrocytes

OBJECTIVE

Matrix metalloproteinase-13 (MMP-13) is an extracellular MMP that cleaves type II collagen, the major protein component of cartilage, with high specificity and has been implicated in the pathology of osteoarthritis. The present study aimed to characterize the binding and internalization kinetics of MMP-13 in normal rabbit chondrocytes and whether MMP-13 affected cell signalling.

METHODS

Rabbit chondrocytes were used in [125I]-MMP-13 binding assays to investigate the MMP-13 binding kinetics and Western analysis allowed for the assessment of intracellular signalling cascades.

RESULTS

Rabbit chondrocytes were found to express the cartilage-specific genes aggrecan and type II collagen throughout their in vitro culture period. Appreciable specific cell-association of [125I]-MMP-13 was detected after 10 min of exposure to the ligand and equilibrium was obtained after 2 h. Binding of [125I]-MMP-13 to chondrocytes was specific and approached saturation at 75 nM. Internalization of MMP-13 was evident after 20 min, reached a maximum at 30 min and had returned to baseline by 90 min. Addition of receptor-associated protein (RAP) inhibited the internalization of MMP-13 indicating a likely role for low-density lipoprotein receptor-related protein-1 (LRP1) in this process. Interestingly the presence of MMP-13 induced phosphorylation of the extracellular signal-regulated kinase 1/2 (ERK1/2) protein showing that there is initiation of a signalling process in response to MMP-13 being bound and internalized by rabbit chondrocytes. However, this activation does not involve the MMP-13 internalization receptor LRP1.

CONCLUSION

These studies demonstrate and characterize the MMP-13 binding and internalization system in rabbit chondrocytes and indicate that MMP-13 may regulate the phenotype of the chondrocytes through this receptor system.