Diagnostic value of serum COMP and ADAMTS7 for intervertebral disc degeneration.

OBJECTIVE: Intervertebral disc degeneration (IVDD) is a major cause of morbidity and disability. Our study aimed to investigate the potential of cartilage oligomeric matrix protein (COMP) and ADAMTS7 (A disintegrin and metalloproteinases with thrombospondin motifs 7) as biomarkers for IVDD together with their functional relationship. METHODS: IVD tissues and peripheral blood samples were collected from IVDD rabbit models over 1-4 weeks. Tissues and blood samples were also collected from clinical patients those were stratified into four equal groups according to Pfirrmann IVDD grading (I-V) with baseline data collected for each participant. COMP and ADAMTS7 expression were analyzed and biomarker characteristics were assessed using linear regression and receiver operating curve (ROC) analyses. RESULTS: COMP and ADAMTS7 expression increased in tissues and serum during IVDD progression. Serum COMP (sCOMP) and serum ADAMTS7 (sADAMTS7) levels increased in a time-dependent manner following IVD damage in the rabbit model while significant positive correlations were detected between sCOMP and sADAMTS7 and Pfirrmann grade in human subjects. ROC analysis showed that combining sCOMP and sADAMTS7 assay results produced an improved diagnostic measure for IVDD compared to individual sCOMP or sADAMTS7 tests. In vitro assays conducted on human cell isolates revealed that COMP prevented extracellular matrix degradation and antagonized ADAMTS7 expression although this protective role was uncoupled under microenvironmental conditions mimicking IVDD. CONCLUSIONS: Increases in circulating COMP and ADAMTS7 correlate with IVDD progression and may play regulatory roles. Assays for sCOMP and/or sADAMTS7 levels can discriminate between healthy subjects and IVDD patients, warranting further clinical assessment.

COMP promotes pancreatic fibrosis by activating pancreatic stellate cells through CD36-ERK/AKT signaling pathways.

BACKGROUND: Pancreatic fibrosis is one of the most important pathological features of chronic pancreatitis (CP) and pancreatic stellate cells (PSCs) are the key cells of fibrosis. As an extracellular matrix (ECM) glycoprotein, cartilage oligomeric matrix protein (COMP) is critical for collagen assembly and ECM stability and recent studies showed that COMP exert promoting fibrosis effect in the skin, lungs and liver. However, the role of COMP in activation of PSCs and pancreatic fibrosis remain unclear. We aimed to investigate the role and specific mechanisms of COMP in regulating the profibrotic phenotype of PSCs and pancreatic fibrosis. METHODS: ELISA method was used to determine serum COMP in patients with CP. Mice model of CP was established by repeated intraperitoneal injection of cerulein and pancreatic fibrosis was evaluated by Hematoxylin-Eosin staining (H&E) and Sirius red staining. Immunohistochemical staining was used to detect the expression changes of COMP and fibrosis marker such as α-SMA and Fibronectin in pancreatic tissue of mice. Cell Counting Kit-8, Wound Healing and Transwell assessed the proliferation and migration of human pancreatic stellate cells (HPSCs). Western blotting, qRT-PCR and immunofluorescence staining were performed to detect the expression of fibrosis marker, AKT and MAPK family proteins in HPSCs. RNA-seq omics analysis as well as small interfering RNA of COMP, recombinant human COMP (rCOMP), MEK inhibitors and PI3K inhibitors were used to study the effect and mechanism of COMP on activation of HPSCs. RESULTS: ELISA showed that the expression of COMP significantly increased in the serum of CP patients. H&E and Sirius red staining analysis showed that there was a large amount of collagen deposition in the mice in the CP model group and high expression of COMP, α-SMA, Fibronectin and Vimentin were observed in fibrotic tissues. TGF-ß1 stimulates the activation of HPSCs and increases the expression of COMP. Knockdown of COMP inhibited proliferation and migration of HPSCs. Further, RNA-seq omics analysis and validation experiments in vitro showed that rCOMP could significantly promote the proliferation and activation of HPSCs, which may be due to promoting the phosphorylation of ERK and AKT through membrane protein receptor CD36. rCOMP simultaneously increased the expression of α-SMA, Fibronectin and Collagen I in HPSCs. CONCLUSION: In conclusion, this study showed that COMP was up-regulated in CP fibrotic tissues and COMP induced the activation, proliferation and migration of PSCs through the CD36-ERK/AKT signaling pathway. COMP may be a potential therapeutic candidate for the treatment of CP. Interfering with the expression of COMP or the communication between COMP and CD36 on PSCs may be the next direction for therapeutic research.

Cartilage oligomeric matrix protein overexpression is an independent poor prognostic indicator in patients with intrahepatic cholangiocarcinoma.

Cartilage oligomeric matrix protein (COMP) interacts with various extracellular matrix proteins in tissues. Elevated COMP levels recently linked to worse overall survival in multiple cancer types. COMP's significance in intrahepatic cholangiocarcinoma (iCCA) remains uncertain. Here we report a retrospective study to explore COMP's impact on iCCA outcomes. We collected 182 patients' iCCA tumor tissues. COMP overexpression was associated with adverse factors like R1 resection (p = 0.008), advanced T stage (p < 0.001), large duct type (p = 0.004), and poorly differentiated histology (p = 0.002). COMP overexpression correlates with poorer DFS (HR, 3.651; p = 0.001), OS (HR, 1.827; p = 0.023), LRFS (HR, 4.077; p < 0.001), and MFS (HR, 3.718; p < 0.001). High COMP expression ties to worse overall survival (p = 0.0001), DSS (p < 0.0001), LRFS (p < 0.0001), and MFS (p < 0.0001). In conclusion, COMP overexpression links to poor prognosis and pathological features in iCCA, indicating its potential as a biomarker.

A preliminary study on the effect of loaded and unloaded exercise on N-propeptide of type II collagen and serum cartilage oligomeric matrix protein activity of articular cartilage in healthy young adults.

The serum concentration of cartilage oligomeric matrix protein (sCOMP) is considered a mechanosensitive biomarker of articular cartilage turnover, and N-propeptide of type II collagen (PIIANP), a proposed biomarker of type II collagen synthesis. Few studies have investigated the anabolic and turnover response of articular cartilage in response to acute changes in body mass during exercise. Using a repeated measure cross-over design, 15 healthy adults (age 18-30 years) performed three 30 min bouts of treadmill walking exercise under three loading conditions: (1) control (no alteration to body mass); (2) loaded (12% increase in body mass using a weighted vest); and (3) unloaded (12% decrease in body mass using lower body positive pressure). Venous blood was collected before, immediately after, and 15 and 30 min after exercise to investigate cartilage turnover (sCOMP) and anabolism (PIIANP). A main time effect (p ≤ 0.05) revealed that sCOMP levels were significantly greater post-exercise (for all three body loading conditions) as compared to before exercise, 15 and 30 min post-exercise. There was a significant condition × time interaction (p ≤ 0.05) for PIIANP, indicating that in the loaded condition, PIIANP concentrations at 15 min post-exercise were 13.8% greater than immediately following exercise, and 12.9% greater than before exercise. In summary, sCOMP concentration was acutely increased with all three loading conditions. However, PIIANP increased only after exercise in the loaded condition, suggesting an acute anabolic effect on articular cartilage. NCT05925244.

Functional characterization of a rare pathogenic variant c.875G > A, p.(Cys292Tyr) in COMP.

BACKGROUND: The protein encoded by the cartilage oligomeric matrix protein (COMP) gene is a noncollagenous extracellular matrix (ECM) protein that is important for chondrocyte formation and growth. Variations in the COMP gene cause pseudoachondroplasia (PSACH), which is mainly characterized by short-limbed dwarfing in the clinic. AIMS: To characterize the function of a rare pathogenic variant in the COMP gene (c.875G > A, p.Cys292Tyr). MATERIALS & METHODS: We performed 3D structural analysis, in vitro expression analysis, and immunofluorescence to characterize the effects of the variant on protein structure, expression, and cellular localization respectively. RESULTS: Variation modeling showed that the interactions between amino acids were changed after the variation, and there were 31 changes in the secondary structure of mutant COMP (MT-COMP). Western blot showed that the intracellular quantity of MT-COMP was higher than the wild-type COMP (WT-COMP). Cellular immunofluorescence results showed that WT-COMP was less abundant and homogenously distributed in cells, while the MT-COMP accumulated in the cytoplasm. DISCUSSION: Herein, we report a variant of COMP in a Chinese family with PSACH. We have shown that the rare missense variant, COMP c.875G > A, previously reported in ClinVar and identified in our patient, results in excessive accumulation of mutant protein in the cytoplasm, and is therefore pathogenic. CONCLUSION: Through in silico and experimental analyses, we provide evidence that COMP c.875G > A is the likely cause of PSACH in a Chinese family.

Expression of Cartilage Oligomeric Matrix Protein in colorectal cancer is an adverse prognostic factor and correlates negatively with infiltrating immune cells and PD-L1 expression.

Introduction: Cartilage Oligomeric Matrix Protein (COMP) is an oncogenic protein that has been associated with a decrease in infiltrating T-cells in periampullary adenocarcinoma. This study aimed to investigate whether this is also the case for colorectal cancer (CRC) and to evaluate the relationship between COMP expression and clinopathological features. Methods: Immunohistochemistry was used to determine the expression levels of COMP in tumor cells and stroma in primary tumors from a cohort of 537 CRC patients. The expression of immune cell markers, including CD3+, CD8+, FoxP3+, CD68+, CD56+, CD163+, and PD-L1, was evaluated previously. Tumor fibrosis was assessed by Sirius Red staining and evaluation of collagen fiber organization. Results: COMP expression correlated positively with TNM-stage and grade of differentiation. Patients with CRC expressing high levels of COMP had significantly shorter OS than those with low COMP expression (p<0.0001), and fewer infiltrating T-cells were detected in tumors with high COMP expression. Additionally, a negative correlation was identified between the expression of COMP and PD-L1 on both tumor cells and immune cells. Cox regression analysis showed that tumors expressing high levels of COMP had significantly shorter OS, independent of all evaluated immune cell markers. Tumor fibrosis was correlated with high expression of COMP in the stroma (p<0.0001), and tumors with high levels of COMP expression and denser fibrosis displayed more sparse immune cell infiltration. Discussion: The results suggest that COMP expression in CRC may exert an immune regulatory effect by increasing dense fibrosis and decreasing immune cell infiltration. These findings support the notion that COMP is an important factor in the development and progression of CRC.

Health consequences of mutant cartilage oligomeric matrix protein and its relationship to abnormal growth and joint degeneration.

Cartilage oligomeric matrix protein (COMP), an extracellular matrix protein, has been shown to enhance proliferation and mechanical integrity in the matrix, supporting functions of the growth plate and articular cartilage. Mutations in COMP cause pseudoachondroplasia (PSACH), a severe dwarfing condition associated with premature joint degeneration and significant lifelong joint pain. The MT (mutant)-COMP mouse mimics PSACH with decreased limb growth, early joint degeneration and pain. Ablation of endoplasmic reticulum stress CHOP signaling eliminated pain and prevented joint degeneration. The health effects of mutant COMP are discussed in relation to cellular/chondrocyte stress in the growth plate, articular cartilage and nearby tissues, and the implications for therapeutic approaches. There are many similarities between osteoarthritis and mutant-COMP protein-induced joint degeneration, suggesting that the relevance of findings in the joints may extend beyond PSACH to idiopathic primary OA.

CurQ+, a Next-Generation Formulation of Curcumin, Ameliorates Growth Plate Chondrocyte Stress and Increases Limb Growth in a Mouse Model of Pseudoachondroplasia.

Mutations in cartilage oligomeric matrix protein (COMP) causes protein misfolding and accumulation in chondrocytes that compromises skeletal growth and joint health in pseudoachondroplasia (PSACH), a severe dwarfing condition. Using the MT-COMP mice, a murine model of PSACH, we showed that pathological autophagy blockage was key to the intracellular accumulation of mutant-COMP. Autophagy is blocked by elevated mTORC1 signaling, preventing ER clearance and ensuring chondrocyte death. We demonstrated that resveratrol reduces the growth plate pathology by relieving the autophagy blockage allowing the ER clearance of mutant-COMP, which partially rescues limb length. To expand potential PSACH treatment options, CurQ+, a uniquely absorbable formulation of curcumin, was tested in MT-COMP mice at doses of 82.3 (1X) and 164.6 mg/kg (2X). CurQ+ treatment of MT-COMP mice from 1 to 4 weeks postnatally decreased mutant COMP intracellular retention, inflammation, restoring both autophagy and chondrocyte proliferation. CurQ+ reduction of cellular stress in growth plate chondrocytes dramatically reduced chondrocyte death, normalized femur length at 2X 164.6 mg/kg and recovered 60% of lost limb growth at 1X 82.3 mg/kg. These results indicate that CurQ+ is a potential therapy for COMPopathy-associated lost limb growth, joint degeneration, and other conditions involving persistent inflammation, oxidative stress, and a block of autophagy.

Plasma proteomics identifies CRTAC1 as a biomarker for osteoarthritis severity and progression.

OBJECTIVES: The aim of this study was to identify biomarkers for radiographic OA severity and progression acting within the inflammation and metabolic pathways. METHODS: For 3517 Rotterdam Study participants, 184 plasma protein levels were measured using Olink inflammation and cardiometabolic panels. We studied associations with severity and progression of knee, hip and hand OA and a composite overall OA burden score by multivariable regression models, adjusting for age, sex, cell counts and BMI. RESULTS: We found 18 significantly associated proteins for overall OA burden, of which 5 stayed significant after multiple testing correction: circulating cartilage acidic protein 1 (CRTAC1), cartilage oligomeric matrix protein (COMP), thrombospondin 4, IL-18 receptor 1 (IL-18R1) and TNF ligand superfamily member 14. These proteins were also associated with progression of knee OA, with the exception of IL-18R1. The strongest association was found for the level of CRTAC1, with 1 s.d. increase in protein level resulting in an increase of 0.09 (95% CI 0.06, 0.12) in the overall OA Kellgren-Lawrence sum score (P = 2.9 × 10-8) in the model adjusted for age, sex, BMI and cell counts. This association was also present with the severity of OA in all three joints and progression of knee OA and was independent of BMI. We observed a stronger association for CRTAC1 with OA than for the well-known OA biomarker COMP. CONCLUSION: We identified several compelling biomarkers reflecting the overall OA burden and the increased risk for OA progression. CRTAC1 was the most compelling and robust biomarker for OA severity and progression. Such a biomarker may be used for disease monitoring.

Physiological stretching induces a differential extracellular matrix gene expression response in acetabular labrum cells.

The acetabular labrum is a fibrocartilaginous ring surrounding the acetabulum and is important for hip stability and contact pressure dissipation through a sealing function. Injury of the labrum may contribute to hip-joint degeneration and development of secondary osteoarthritis. Understanding how extracellular matrix (ECM) production and remodelling is regulated is of key importance for successful tissue restoration. The present study hypothesised that physiological stretching enhanced the metabolic activity and altered the ECM gene expression in labrum cells. Primary bovine labrum cells were physiologically stretched for up to 5 d. 24 h after the last stretch cycle, changes in metabolic activity were measured using the PrestoBlue™ HS Cell Viability Reagent and ECM gene expression was examined using the quantitative polymerase chain reaction method. Targets of interest were further investigated using immunofluorescence and enzyme-linked immunosorbent assay. Metabolic activity was not affected by the stretching (0.9746 ± 0.0614, p > 0.05). Physiological stretching upregulated decorin (DCN) (1.8548 ± 0.4883, p = 0.002) as well as proteoglycan 4 (PRG4) (1.7714 ± 0.6600, p = 0.029) and downregulated biglycan (BGN) (0.7018 + 0.1567, p = 0.008), cartilage oligomeric matrix protein (COMP) (0.5747 ± 0.2650, p = 0.029), fibronectin (FN1) (0.5832 ± 0.0996, p < 0.001) and spondin 1 (SPON1) (0.6282 ± 0.3624, p = 0.044) gene expression. No difference in PRG4 and DCN abundance or release could be measured. The here identified mechanosensitive targets are known to play relevant roles in tissue organisation. Therefore, physiological stretching might play a role in labrum tissue homeostasis and regeneration.

Effects of Modified Duhuo Jisheng Decoction Combined with Arthroscopic Surgery on Bone Metabolism, Oxidative Stress, and Serum TLR4 and TGF-ß1 in Patients with Knee Osteoarthritis.

Objective: To analyze the effects of modified Duhuo Jisheng Decoction combined with arthroscopic surgery on bone metabolism, oxidative stress, and serum TLR4 and TGF-ß1 in patients with knee osteoarthritis (KOA). Methods: Prospectively select 82 patients with KOA from January 2020 to January 2022 in our hospital and divide them into the control group and observation group according to the random number table method, with 41 patients in each group. The control group was treated with arthroscopic surgery alone and routine anti-infection after operation. The observation group was treated with Duhuo Jisheng Decoction on the basis of the treatment of the control group. The patients in the two groups were treated continuously for 4 weeks. The improvement of patients' symptoms was evaluated by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Before treatment and 4 weeks after treatment, the scores of traditional Chinese medicine (TCM) symptoms, bone metabolism indicators (cartilage oligomeric matrix protein (COMP), collagen type II carboxy terminal peptide (ctx-II), and matrix metalloproteinase-3 (MMP-3)), oxidative stress indicators (superoxide dismutase (SOD), glutathione peroxidase (GSHPx), malondialdehyde (MDA), nitric oxide (NO)), serum Toll-like receptor 4 (TLR4), and transforming growth factor ß (TGF-ß) level were compared between the two groups. Results: After treatment, the WOMAC score of the two groups decreased (42.45 ± 10.83) in the observation group and (67.81 ± 14.63) in the control group. The WOMAC score of the observation group was lower than that of the control group (P < 0.05). After treatment, the levels of COMP, CTX-II, and MMP-3 in the two groups decreased, and the levels of COMP, CTX-II, and MMP-3 in the observation group were lower than those in the control group (P < 0.05). After treatment, the levels of SOD and GSHPx increased, while the levels of MDA and NO decreased in the two groups. The levels of SOD and GSHPx in the observation group were higher than those in the control group, while the levels of MDA and NO were lower than those in the control group (P < 0.05). After treatment, the TLR4 level in the observation group was lower than that of the control group, and the level of TGF-ß in the observation group was higher than that of the control group (P < 0.05). Conclusion: Compared with arthroscopic surgery alone, combined with modified Duhuo Jisheng Decoction can better alleviate the clinical symptoms of patients with KOA, improve their bone metabolism, oxidative stress indicators, and serum TLR4 and TGF-ß 1 level, and reduce the inflammatory injury of knee joint.

Cartilage Oligomeric Matrix Protein, Diseases, and Therapeutic Opportunities.

Cartilage oligomeric matrix protein (COMP) is an extracellular matrix (ECM) glycoprotein that is critical for collagen assembly and ECM stability. Mutations of COMP cause endoplasmic reticulum stress and chondrocyte apoptosis, resulting in rare skeleton diseases. The bouquet-like structure of COMP allows it to act as a bridging molecule that regulates cellular phenotype and function. COMP is able to interact with many other ECM components and binds directly to a variety of cellular receptors and growth factors. The roles of COMP in other skeleton diseases, such as osteoarthritis, have been implied. As a well-established biochemical marker, COMP indicates cartilage turnover associated with destruction. Recent exciting achievements indicate its involvement in other diseases, such as malignancy, cardiovascular diseases, and tissue fibrosis. Here, we review the basic concepts of COMP and summarize its novel functions in the regulation of signaling events. These findings renew our understanding that COMP has a notable function in cell behavior and disease progression as a signaling regulator. Interestingly, COMP shows distinct functions in different diseases. Targeting COMP in malignancy may withdraw its beneficial effects on the vascular system and induce or aggravate cardiovascular diseases. COMP supplementation is a promising treatment for OA and aortic aneurysms while it may induce tissue fibrosis or cancer metastasis.

[Correlation between osteopontin and cartilage oligomeric matrix protein levels in joint synovial fluid of patients with knee osteoarthritis and disease severity].

OBJECTIVE: To investigate the correlation between osteopontin(OPN) and cartilage oligomeric matrix protein (COMP) levels in synovial fluid of patients with knee osteoarthritis(KOA) and the severity of the disease. METHODS: A total of 59 patients with KOA admitted to our hospital from February 2018 to May 2020 were selected as the KOA group, including 25 males and 34 females, age ranged 60 to 75 years old with an average of(65.57±1.56) years old, the body mass index(BMI) ranged 21.4 to 30.7(26.12±1.54) kg/m2. After admission, X-ray examination was performed, and Kellgren-Lawrence(K-L) grading system was used to evaluate the X-ray examination results. There were 14 cases in gradeⅡ(K-L2 group), 27 cases in grade Ⅲ(K-L3 group), and 18 cases in grade Ⅳ(K-L4 group). Eighteen patients who underwent arthroscopy for ligament or meniscus disease without cartilage damage were selected as control group, including 7 males and 11 females, age ranged 61 to 78 years old with an average of (64.88±1.60) years old, BMI ranged 22.8 to 29.9(25.89±1.49) kg/m2. Before treatment, synovial fluid samples of subjects were collected, and the OPN and COMP levels of synovial fluid were detected by Elisa. The OPN and COMP levels of synovial fluid in KOA group and control group were compared. The clinical data of KOA patients with different K-L grades were collected, including gender, age and BMI. The biochemical indices of interleukin-1 ß(IL-1ß), OPN, COMP and matrix metalloproteinase 3(MMP-3) in synovitic fluid were detected by enzyme-linked immunoassay, and the clinical data and biochemical indices of KOA patients with different K-L grades were compared. Logistic regression was used to analyze the factors affecting the K-L classification of KOA patients, and the area under the ROC curve(AUC) was used to predict the severity of KOA. RESULTS: All the 59 patients were followed up for 8 to 27(15.75±3.27) months. The levels of OPN and COMP in synovial fluid in KOA group were significantly higher than those in control group (t=16.991, 17.387, P<0.001). The levels of IL-1ß, OPN, COMP and MMP-3 in synovitic fluid were significantly different among those in different K-L grade KOA patients(P<0.001). Compared with the K-L2 group, the levels of IL-1ß, OPN, COMP, and MMP-3 in the synovial fluid of K-L3 and K-L4 were increased (P<0.05). Compared with the K-L3 group, the levels of IL-1ß, OPN, COMP, and MMP-3 in the K-L4 joint were increased (P<0.05). Multivariate Logistic regression analysis showed that the levels of OPN, COMP and MMP-3 were independent risk factors for K-L grading of KOA patients(OR=6.653, 4.229, 1.579, P<0.001). AUC of OPN in synovial fluid predicting K-L4 KOA was 0.720[95%CI(0.588-0.851)], and the sensitivity was 94.4%. the specificity was 65.9%. The AUC of COMP in synoviac fluid predicting K-L4 KOA was 0.731[95%CI(0.592-0.870)], the sensitivity was 88.9%, the specificity was 63.4%. The AUC of OPN combined with COMP in synoviac fluid predicting K-L4 KOA was 0.839 [95%CI(0.724-0.953)], the sensitivity was 94.4%, and the specificity was 51.2%. The AUC of OPN combined with COMP in synoviac fluid predicting K-L4 grade KOA was greater than that of OPN and COMP alone(Z=4.037, 3.540, P<0.05). CONCLUSION: The levels of OPN and COMP in synovial fluid increase in patients with KOA, and they increase with the increase of K-L grade. Synovitic fluid OPN and COMP are independent risk factors affecting K-L grade of KOA patients, and they have high AUC, sensitivity and specificity in predicting of K-L4 KOA, and can be used to evaluate the progression of KOA disease.

Expression of cartilage oligomeric matrix protein (COMP) associates with capsular invasion in salivary gland pleomorphic adenoma.

BACKGROUND: Accumulating evidence shows that pleomorphic adenoma (PA) exhibits a unique capsular invasion and with a crucial role in recurrence. This study was designed to explore RNA expression profiles in salivary gland PA in an attempt to further analyse genes associate with capsule invasion. METHODS: We evaluated the expression profiles of 4 salivary gland PA patients by RNA-sequencing. The principal functions of the differentially expressed mRNAs (DEGs) were explored using GO and KEGG analysis. Then, RT-qPCR and correlation analyses were performed to verify the candidate DEGs in 59 PA patients, and immunohistochemical examinations were conducted to validate candidate DEGs. Finally, the COMP-related genes were screened using correlation and biological pathway enrichment analysis, and further validated by RT-qPCR. RESULTS: A total of 974 DEGs were significantly upregulated, and 1464 were downregulated (fold change ≥2.0; p < 0.05). Based on GO and KEGG analyses, extracellular matrix organization and the PI3K-Akt signalling pathway might play pivotal roles in the tumorigenesis of PA. 40 DEGs were screened and validated by RT-qPCR, 11 upregulated and 5 downregulated DEGs were consistent with the sequencing results. Cartilage oligomeric matrix protein (COMP) was identified to have a significant correlation with the capsular invasion of PA and expression of COMP in patients with invasive capsular PA was significantly stronger than PA. Finally, further results could reveal that 5 highest scoring genes were screened as hub genes for COMP. CONCLUSIONS: These findings suggested that COMP may be a prognostic target for PA and might contribute to its capsular invasion.

Antibodies to Cartilage Oligomeric Matrix Protein Are Pathogenic in Mice and May Be Clinically Relevant in Rheumatoid Arthritis.

OBJECTIVE: Cartilage oligomeric matrix protein (COMP) is an autoantigen in rheumatoid arthritis (RA) and experimental models of arthritis. This study was undertaken to investigate the structure, function, and relevance of anti-COMP antibodies. METHODS: We investigated the pathogenicity of monoclonal anti-COMP antibodies in mice using passive transfer experiments, and we explored the interaction of anti-COMP antibodies with cartilage using immunohistochemical staining. The interaction of the monoclonal antibody 15A11 in complex with its specific COMP epitope P6 was determined by x-ray crystallography. An enzyme-linked immunosorbent assay and a surface plasma resonance technique were used to study the modulation of calcium ion binding to 15A11. The clinical relevance and value of serum IgG specific to the COMP P6 epitope and its citrullinated variants were evaluated in a large Swedish cohort of RA patients. RESULTS: The murine monoclonal anti-COMP antibody 15A11 induced arthritis in naive mice. The crystal structure of the 15A11-P6 complex explained how the antibody could bind to COMP, which can be modulated by calcium ions. Moreover, serum IgG specific to the COMP P6 peptide and its citrullinated variants was detectable at significantly higher levels in RA patients compared to healthy controls and correlated with a higher disease activity score. CONCLUSION: Our findings provide the structural basis for binding a pathogenic anti-COMP antibody to cartilage. The recognized epitope can be citrullinated, and levels of antibodies to this epitope are elevated in RA patients and correlate with higher disease activity, implicating a pathogenic role of anti-COMP antibodies in a subset of RA patients.

COMP (Cartilage Oligomeric Matrix Protein), a Novel PIEZO1 Regulator That Controls Blood Pressure.

BACKGROUND: Vascular endothelial cells are critical for maintaining blood pressure (BP) by releasing biologically active molecules, such as nitric oxide. A non-endothelial cell resident matricellular protein, COMP (cartilage oligomeric matrix protein), plays a pivotal role in maintaining cardiovascular homeostasis, but little is known about its regulatory effect on BP. METHODS: Mice were infused with AngII (angiotensin II; 450 ng/kg per minute) for 3 days via an osmotic minipump, and BP was monitored by a tail-cuff system. Second-order mesenteric arteries were isolated from mice for microvascular tension measurement. Nitric oxide was detected by an electron paramagnetic resonance technique. Small-interfering RNA transfection, co-immunoprecipitation, bioluminescence resonance energy transfer assays, and patch-clamp electrophysiology experiments were used for further detailed mechanism investigation. RESULTS: COMP-/- mice displayed elevated BP and impaired acetylcholine-induced endothelium-dependent relaxation compared with wild-type mice with or without AngII. Inhibition of eNOS (endothelial nitric oxide synthase) abolished the difference in endothelium-dependent relaxation between wild-type and COMP-/- mice. Furthermore, COMP directly interacted with the C-terminus of Piezo1 via its C-terminus and activated the endogenous Piezo1 currents, which induced intracellular Ca2+ influx, Ca2+/calmodulin-dependent protein kinase type II and eNOS activation, and nitric oxide production. The Piezo1 activator, Yoda1, reduced the difference in endothelium-dependent relaxation and BP in wild-type and COMP-/- mice. Moreover, COMP overexpression increased eNOS activation and improved endothelium-dependent relaxation and BP. CONCLUSIONS: Our study demonstrated that COMP is a novel Piezo1 regulator that plays a protective role in BP regulation by increasing cellular Ca2+ influx, eNOS activity, and nitric oxide production.

Cartilage oligomeric matrix protein responses to a mechanical stimulus associate with ambulatory loading in individuals with anterior cruciate ligament reconstruction.

Mechanical factors have been implicated in the development of osteoarthritis after anterior cruciate ligament (ACL) reconstruction. This study tested for associations between ambulatory joint loading (total joint moment [TJM] and vertical ground reaction force [vGRF]) and changes in serum levels of cartilage oligomeric matrix protein (COMP) in response to a mechanical stimulus (30-min walk) in individuals with ACL reconstruction. Twenty-five subjects (mean age: 34.5 ± 9.8 years; 2.2 ± 0.2 years post-surgery) with primary unilateral ACL reconstruction underwent gait analysis for assessment of peak vGRF and TJM first (TJM1) and second (TJM2) peaks. Serum COMP concentrations were measured by enzyme-linked immunosorbent assay immediately before, 3.5 h, and 5.5 h after a 30-min walk. Pearson correlation coefficients and backward stepwise multiple linear regression analysis, with adjustments for age, sex, body mass index, and between-limb speed difference, assessed associations between changes in COMP and between-limb differences in joint loading parameters. Greater TJM1 (R = 0.542, p = 0.005), TJM2 (R = 0.460, p = 0.021), and vGRF (R = 0.577, p = 0.003) in the ACL-reconstructed limb as compared to the contralateral limb were associated with higher COMP values 3.5 h following the 30-min walk. Change in COMP at 5.5 h became a significant predictor of the between-limb difference in TJM1 and vGRF in multivariate analyses after accounting for the between-limb speed difference. These results demonstrate that higher TJM and vGRF in the ACLR limb as compared to the contralateral limb are associated with higher relative COMP levels 3.5 and 5.5 h after a 30-min walk. Future work should investigate the effect of therapies to alter joint loading on the biological response in individuals after ACL reconstruction.

Proteomic analysis of peritoneal fluid identified COMP and TGFBI as new candidate biomarkers for endometriosis.

Endometriosis is a common non-malignant gynecological disease that significantly compromises fertility and quality of life of the majority of patients. The gold standard for diagnosis is visual inspection of the pelvic organs by surgical laparoscopy and there are no biomarkers that would allow non-invasive diagnosis. The pathogenesis of endometriosis is not completely understood, thus analysis of peritoneal fluid might contribute in this respect. Our prospective case-control study included 58 patients undergoing laparoscopy due to infertility, 32 patients with peritoneal endometriosis (cases) and 26 patients with unexplained primary infertility (controls). Discovery proteomics using antibody microarrays that covered 1360 proteins identified 16 proteins with different levels in cases versus the control patients. The validation using an ELISA approach confirmed significant differences in the levels of cartilage oligomeric matrix protein (COMP) and transforming growth factor-ß-induced protein ig-h3 (TGFBI) and nonsignificant differences in angiotensinogen (AGT). A classification model based on a linear support vector machine revealed AUC of > 0.83, sensitivity of 0.81 and specificity of 1.00. Differentially expressed proteins represent candidates for diagnostic and prognostic biomarkers or drug targets. Our findings have brought new knowledge that will be helpful in the understanding of the pathophysiology of endometriosis and warrant further studies in blood samples.

Anisotropic Chitosan Scaffolds Generated by Electrostatic Flocking Combined with Alginate Hydrogel Support Chondrogenic Differentiation.

The replacement of damaged or degenerated articular cartilage tissue remains a challenge, as this non-vascularized tissue has a very limited self-healing capacity. Therefore, tissue engineering (TE) of cartilage is a promising treatment option. Although significant progress has been made in recent years, there is still a lack of scaffolds that ensure the formation of functional cartilage tissue while meeting the mechanical requirements for chondrogenic TE. In this article, we report the application of flock technology, a common process in the modern textile industry, to produce flock scaffolds made of chitosan (a biodegradable and biocompatible biopolymer) for chondrogenic TE. By combining an alginate hydrogel with a chitosan flock scaffold (CFS+ALG), a fiber-reinforced hydrogel with anisotropic properties was developed to support chondrogenic differentiation of embedded human chondrocytes. Pure alginate hydrogels (ALG) and pure chitosan flock scaffolds (CFS) were studied as controls. Morphology of primary human chondrocytes analyzed by cLSM and SEM showed a round, chondrogenic phenotype in CFS+ALG and ALG after 21 days of differentiation, whereas chondrocytes on CFS formed spheroids. The compressive strength of CFS+ALG was higher than the compressive strength of ALG and CFS alone. Chondrocytes embedded in CFS+ALG showed gene expression of chondrogenic markers (COL II, COMP, ACAN), the highest collagen II/I ratio, and production of the typical extracellular matrix such as sGAG and collagen II. The combination of alginate hydrogel with chitosan flock scaffolds resulted in a scaffold with anisotropic structure, good mechanical properties, elasticity, and porosity that supported chondrogenic differentiation of inserted human chondrocytes and expression of chondrogenic markers and typical extracellular matrix.

Expression and Localization of Thrombospondins, Plastin 3, and STIM1 in Different Cartilage Compartments of the Osteoarthritic Varus Knee.

Osteoarthritis (OA) is a multifactorial disease which is characterized by a change in the homeostasis of the extracellular matrix (ECM). The ECM is essential for the function of the articular cartilage and plays an important role in cartilage mechanotransduction. To provide a better understanding of the interaction between the ECM and the actin cytoskeleton, we investigated the localization and expression of the Ca2+-dependent proteins cartilage oligomeric matrix protein (COMP), thrombospondin-1 (TSP-1), plastin 3 (PLS3) and stromal interaction molecule 1 (STIM1). We investigated 16 patients who suffered from varus knee OA and performed a topographical analysis of the cartilage from the medial and lateral compartment of the proximal tibial plateau. In a varus knee, OA is more pronounced in the medial compared to the lateral compartment as a result of an overloading due to the malalignment. We detected a location-dependent staining of PLS3 and STIM1 in the articular cartilage tissue. The staining intensity for both proteins correlated with the degree of cartilage degeneration. The staining intensity of TSP-1 was clearly reduced in the cartilage of the more affected medial compartment, an observation that was confirmed in cartilage extracts by immunoblotting. The total amount of COMP was unchanged; however, slight changes were detected in the localization of the protein. Our results provide novel information on alterations in OA cartilage suggesting that Ca2+-dependent mechanotransduction between the ECM and the actin cytoskeleton might play an essential role in the pathomechanism of OA.