No abstract

No abstract

Background: Osteoarthritis (OA) is the most common form of arthritis and characterized by degeneration of the articular cartilage. Mitogen-inducible gene 6 (Mig-6) has been identified as a negative regulator of the epidermal growth factor receptor (EGFR). Cartilage-specific Mig-6 knockout (KO) mice display increased EGFR signaling, an anabolic buildup of the articular cartilage, and formation of chondro-osseous nodules. Since our understanding of the EGFR/Mig-6 network in the cartilage remains incomplete, we characterized mice with cartilage-specific overexpression of Mig-6 in this study. Methods: Utilizing knee joints from cartilage-specific Mig-6-overexpressing (Mig-6 over/over) mice (at multiple time points), we evaluated the articular cartilage using histology, immunohistochemical staining, and semi-quantitative histopathological scoring (OARSI) at multiple ages. MicroCT analysis was employed to examine skeletal morphometry, body composition, and bone mineral density. Results: Our data show that cartilage-specific Mig-6 overexpression did not cause any major developmental abnormalities in the articular cartilage, although Mig-6 over/over mice have slightly shorter long bones compared to the control group. Moreover, there was no significant difference in bone mineral density and body composition in any of the groups. However, our results indicate that Mig-6 over/over male mice show accelerated cartilage degeneration at 12 and 18 months of age. Immunohistochemistry for SOX9 demonstrated that the number of positively stained cells in Mig-6 over/over mice was decreased relative to controls. Immunostaining for MMP13 appeared increased in areas of cartilage degeneration in Mig-6 over/over mice. Moreover, staining for phospho-EGFR (Tyr-1173) and lubricin (PRG4) was decreased in the articular cartilage of Mig-6 over/over mice. Conclusion: Overexpression of Mig-6 in the articular cartilage causes no major developmental phenotype; however, these mice develop earlier OA during aging. These data demonstrate that Mig-6/EGFR pathways are critical for joint homeostasis and might present a promising therapeutic target for OA.

BackgroundOsteoarthritis (OA) is a degenerative joint disease with poorly understood etiology and pathobiology. Mitogen activated protein kinases (MAPKs) including ERK and p38 play important roles in the mediation of downstream pathways involved in cartilage degenerative processes. Dual specificity phosphatase 1 (DUSP1) dephosphorylates the threonine/serine and tyrosine sites on ERK and p38, causing deactivation of downstream signalling. In this study we examined the role of DUSP1 in spontaneous OA development at 21 months of age using a genetically modified mouse model deficient in Dusp1 (DUSP1 knockout mouse).ResultsUtilizing histochemical stains of paraffin embedded knee joint sections in DUSP1 knockout and wild type female and male mice, we showed similar structural progression of cartilage degeneration associated with OA at 21 months of age. A semi-quantitative cartilage degeneration scoring system also demonstrated similar scores in the various aspects of the knee joint articular cartilage in DUSP1 knockout and control mice. Examination of overall articular cartilage thickness in the knee joint demonstrated similar results between DUSP1 knockout and wild type mice. Immunostaining for cartilage neoepitopes DIPEN, TEGE and C1,2C was similar in the cartilage lesion sites and chondrocyte pericellular matrix of both experimental groups. Likewise, immunostaining for phosphoERK and MMP13 showed similar intensity and localization between groups. SOX9 immunostaining demonstrated a decreased number of positive cells in DUSP1 knockout mice, with correspondingly decreased staining intensity. Analysis of animal walking patterns (gait) did not show a discernable difference between groups.ConclusionLoss of DUSP1 does not cause changes in cartilage degeneration and gait in a mouse model of spontaneous OA at 21 months of age. Altered staining was observed in SOX9 immunostaining which may prove promising for future studies examining the role of DUSPs in cartilage and OA, as well as models of post-traumatic OA.

33 34 Background: Osteoarthritis (OA) is the most common form of arthritis and characterized by 35 degeneration of articular cartilage. Mitogen-inducible gene 6 (Mig-6) has been identified as a 36 negative regulator of the Epidermal Growth Factor Receptor (EGFR). Cartilage-specific Mig-6 37 knockout (KO) mice display increased EGFR signaling, an anabolic buildup of articular cartilage 38 and formation of chondro-osseous nodules. Since our understanding of the EGFR/Mig-6 network 39 in cartilage remains incomplete, we characterized mice with cartilage-specific overexpression of 40 Mig-6 in this study. 41 Methods: Utilizing knee joints from cartilage-specific Mig-6 overexpressing (Mig-6over/over ) mice 42 (at multiple time points), we evaluated the articular cartilage using histology, 43 immunohistochemical staining and semi-quantitative OARSI scoring at multiple ages. MicroCT 44 analysis was employed to examine skeletal morphometry, body composition, and bone mineral 45 density. 46 Results: Our data show that cartilage-specific Mig-6 overexpression did not cause any major 47 developmental abnormalities in articular cartilage, although Mig-6 over/over mice have slightly 48 shorter long bones compared to the control group. Moreover, there was no significant difference 49 in bone mineral density and body composition in any of the groups. However, our results indicate 50 that Mig-6 over/over male mice show accelerated cartilage degeneration at 12 and 18 months of age. 51 Immunohistochemistry for SOX9 demonstrated that the number of positively stained cells in Mig-52 6 over/over mice decreased relative to controls. Immunostaining for MMP13 staining is increased in 53 areas of cartilage degeneration in Mig-6 over/over mice. Moreover, staining for phospho-EGFR (Tyr-54 1173) and lubricin (PRG4) was decreased in the articular cartilage of Mig-6 over/over mice. 55 Conclusion: Overexpression of Mig-6 in articular cartilage causes no major developmental 56 phenotype; however these mice develop earlier OA during aging. These data demonstrate that 57