Cartilage Oligomeric Matrix Protein Induced Arthritis-A New Model for Rheumatoid Arthritis in the C57BL/6 Mouse.

The most commonly used strains in experimental research, including genetically modified strains, are C57BL/6 mice. However, so far, no reliable model for rheumatoid arthritis is available, mainly due to the restriction by the MHC class II haplotype H-2b. Collagen-induced arthritis (CIA) is the most widely used animal model of rheumatoid arthritis, but C57BL/6 strain is resistant to CIA because there is no collagen II peptide associated with H-2b. To establish a rheumatoid arthritis model in C57BL/6 mice, we immunized C57BL/6NJ (B6N) mice with human cartilage oligomeric matrix protein (COMP), which induced severe arthritis with high incidence, accompanied by a strong auto-antibody response. Native COMP was required, as denatured COMP lost its ability to induce arthritis in B6N mice. An immunodominant COMP peptide was identified as the key T cell epitope, with a perfect fit into the Ab class II peptide binding pocket. A critical amino acid in this peptide was found to be phenylalanine at position 95. Recombinant COMP mutated at position 95 (COMP_F95S) lost its ability to induce arthritis or a strong immune response in the B6N mice. In conclusion, A new model for RA has been established using C57BL/6 mice through immunization with COMP, which is dependent on a COMP specific peptide binding Ab, thus in similarity with CIA in Aq expressing strains.

COMP-Ang-1 Improves Glucose Uptake in db/db Mice with Type 2 Diabetes.

Cartilage oligomeric matrix protein (COMP)-Angiopoietin-1 is a potent angiopoietin-1 (Ang-1) variant that possesses therapeutic potential in angiogenesis and vascular endothelial dysfunction. Noteworthy, we have shown that COMP-Ang-1 improves hyperglycemia and neuroregeneration in ob/ob mice. However, the mechanism of the antidiabetic effect of COMP-Ang-1 is completely unknown. Therefore, we elucidated the diabetes protective molecular mechanisms of COMP-Ang-1 in diabetic db/db mouse model. COMP-Ang-1 (0.5 ng/g body weight) or aqueous NaCl solution was injected intraperitoneally per day in 21 consecutive days into 3-month old, male db/db mice (n=10 per group). Blood glucose and HbA1c levels were determined at baseline and 21 days after COMP-Ang-1 or NaCl treatment. The effect of COMP-Ang-1 on glucose uptake was investigated by euglycemic-hyperinsulinemic clamp studies and key genes of glucose metabolism were studied by Western blot analysis. Our findings indicate that COMP-Ang-1 improves glucose metabolism in a tissue specific manner by regulating HIF-1α transcriptional genes of GLUT-1 expression.

Intravitreal AAV2.COMP-Ang1 Attenuates Deep Capillary Plexus Expansion in the Aged Diabetic Mouse Retina.

Purpose: We determine whether intravitreal angiopoietin-1 combined with the short coiled-coil domain of cartilage oligomeric matrix protein by adeno-associated viral serotype 2 (AAV2.COMP-Ang1) delivery following the onset of vascular damage could rescue or repair damaged vascular beds and attenuate neuronal atrophy and dysfunction in the retinas of aged diabetic mice. Methods: AAV2.COMP-Ang1 was bilaterally injected into the vitreous of 6-month-old male Ins2Akita mice. Age-matched controls consisted of uninjected C57BL/6J and Ins2Akita males, and of Ins2Akita males injected with PBS or AAV2.REPORTER (AcGFP or LacZ). Retinal thickness and visual acuity were measured in vivo at baseline and at the 10.5-month endpoint. Ex vivo vascular parameters were measured from retinal flat mounts, and Western blot was used to detect protein expression. Results: All three Ins2Akita control groups showed significantly increased deep vascular density at 10.5 months compared to uninjected C57BL/6J retinas (as measured by vessel area, length, lacunarity, and number of junctions). In contrast, deep microvascular density of Ins2Akita retinas treated with AAV2.COMP-Ang1 was more similar to uninjected C57BL/6J retinas for all parameters. However, no significant improvement in retinal thinning or diabetic retinopathy-associated visual loss was found in treated diabetic retinas. Conclusions: Deep retinal microvasculature of diabetic Ins2Akita eyes shows late stage changes consistent with disorganized vascular proliferation. We show that intravitreally injected AAV2.COMP-Ang1 blocks this increase in deep microvascularity, even when administered subsequent to development of the first detectable vascular defects. However, improving vascular normalization did not attenuate neuroretinal degeneration or loss of visual acuity. Therefore, additional interventions are required to address neurodegenerative changes that are already underway.

Binding to COMP Reduces the BMP2 Dose for Spinal Fusion in a Rat Model.

STUDY DESIGN: The aim of this study is to test the effect of cartilage oligomeric matrix protein (COMP) on enhancing rhBMP-2 induced spinal fusion in a prospective 8-week interventional trial of spinal fusion in rats. OBJECTIVE: To determine whether the amount of bone morphogenetic protein-2 (BMP-2) required to achieve spinal fusion in a pre-clinical model can be reduced by the addition of COMP. SUMMARY OF BACKGROUND DATA: BMPs are applied clinically at supraphysiological doses to promote spinal fusion by inducing osseous growth, but dose-related limitations include ectopic bone formation and local inflammatory reactions. COMP is a matricellular BMP-binding protein expressed during endochondral ossification and fracture healing. In vitro studies demonstrate enhanced activity of BMP bound to COMP. We hypothesized that BMP bound to COMP could achieve equivalent spinal fusion rates at lower doses and with fewer complications. METHODS: Posterolateral intertransverse process spinal fusion at L4 to L5 was performed in 36 Lewis rats. COMP (10 µg) was tested with or without "low-dose" rhBMP-2 (2 µg), and the results were compared with the "low-dose" (2 µg rhBMP-2) and "high-dose" (10 µg rhBMP-2) groups. All groups utilized insoluble collagen bone matrix carrier (ICBM). Fusion was evaluated by radiology, histology, and manual palpation. BMP release kinetics were evaluated in vitro. RESULTS: Fusion grading of microCT images demonstrated that the fusion rate with the COMP+LoBMP was statistically equivalent to HiBMP, and significantly better than LoBMP without COMP. These results were confirmed with radiographs and manual palpation. BMP release kinetics suggest that COMP increased local concentrations of BMP due to decreased growth factor retention on the scaffold. CONCLUSION: COMP enhances BMP-induced bone formation, enabling lower doses of BMP to achieve the same level of spinal fusion. COMP may function by affecting the availability and biological presentation of BMP-2. A decrease of BMP-2 required for fusion may reduce dose-related adverse effects, surgical costs, and improve clinical outcomes. LEVEL OF EVIDENCE: N/A.

Local delivery of COMP-angiopoietin 1 accelerates new bone formation in rat calvarial defects.

Recombinant COMP-Ang1, a chimera of angiopoietin-1 (Ang1) and a short coiled-coil domain of cartilage oligomeric matrix protein (COMP), is under consideration as a therapeutic agent in bone reconstruction. However, the potential of COMP-Ang1 to regenerate impaired bone and induce new bone formation has not been completely explored. In this study, male Sprague-Dawley rats underwent calvarial defect surgery and divided into two groups: scaffold treatment alone (control group) and COMP-Ang1-impregnated scaffold (COMP-Ang1 group). According to live micro-CT and histological analyses, the COMP-Ang1 group showed greater new bone formation and maturation than did the control both four and eight weeks after surgery. The values of bone volume, bone mineral density, and bone surface were also higher in the COMP-Ang1 group than in the control at the same weeks after surgery. In addition, the delivery of COMP-Ang1 facilitated significantly the expression of osteoblast-specific markers such as runt-related transcription factor 2 (p < 0.001), osterix (p < 0.001), bone morphogenetic protein-2 (p < 0.001), alkaline phosphatase (p < 0.01), osteocalcin (p < 0.001), and type I collagen (p < 0.05) in newly formed bone, compared with the control. Immunohistochemistric assay supported the COMP-Ang1-facilitated induction of bone-specific markers. Furthermore, COMP-Ang1 augmented the mRNA expression of angiogenic factors, especially of platelet endothelial cell adhesion molecule 1, stromal cell-derived factor 1, and Tie-2 in the defect site. Our current findings demonstrate for the first time that a local delivery of recombinant COMP-Ang1 promotes bone formation in calvarial defects, which is coupled with enhanced angiogenesis and chemoattraction.

Tricomponent complex loaded with a mosquito-stage antigen of the malaria parasite induces potent transmission-blocking immunity.

The development of malaria vaccines is challenging, partly because the immunogenicity of recombinant malaria parasite antigens is low. We previously demonstrated that parasite antigens integrated into a tricomponent immunopotentiating complex increase antiparasitic immunity. In this study, the B domains of a group G Streptococcus (SpG) strain and Peptostreptococcus magnus (PpL) were used to evaluate whether vaccine efficacy is influenced by the type of immunoglobulin-binding domain (IBD) in the tricomponent complex. IBDs were fused to a pentameric cartilage oligomeric matrix protein (COMP) to increase the binding avidity of the complexes for their targets. The COMP-IBD fusion proteins generated (COMP-SpG and COMP-PpL and the previously constructed COMP-Z) bound a large fraction of splenic B lymphocytes but not T lymphocytes. These carrier molecules were then loaded with an ookinete surface protein of Plasmodium vivax, Pvs25, by chemical conjugation. The administration of the tricomponent complexes to mice induced more Pvs25-specific serum IgG than did the unloaded antigen. The PpL complex, which exhibited a broad Ig-binding spectrum, conferred higher vaccine efficacy than did the Z or SpG complexes when evaluated with a membrane feed assay. This study demonstrates that this tricomponent immunopotentiating system, incorporating IBDs as the B-lymphocyte-targeting ligands, is a promising technology for the delivery of malaria vaccines, particularly when combined with an aluminum salt adjuvant.