Blocking chondrocyte hypertrophy in conditional Evc knockout mice does not modify osteoarthritis progression

Background Chondrocytes in osteoarthritic (OA) cartilage acquire a hypertrophic-like phenotype, where Hedgehog (Hh) signaling is pivotal. Hh overexpression causes OA-like cartilage lesions, whereas its downregulation prevents articular destruction in mouse models. Mutations in EVC and EVC2 genes disrupt Hh signaling, and are responsible for the Ellis-van Creveld syndrome skeletal dysplasia. Since Ellis-van Creveld syndrome protein (Evc) deletion is expected to hamper Hh target gene expression we hypothesized that it would also prevent OA progression avoiding chondrocyte hypertrophy. Our aim was to study Evc as a new therapeutic target in OA, and whether Evc deletion restrains chondrocyte hypertrophy and prevents joint damage in an Evc tamoxifen induced knockout ( Evc cKO ) model of OA. Methods OA was induced by surgical knee destabilization in wild-type (WT) and Evc cKO adult mice, and healthy WT mice were used as controls (n=10 knees/group). Hypertrophic markers and Hh genes were measured by qRT-PCR, and metalloproteinases (MMP) levels assessed by western blot. Human OA chondrocytes and cartilage samples were obtained from patients undergoing knee joint replacement surgery. Cyclopamine (CPA) was used for Hh pharmacological inhibition and IL-1β as an inflammatory insult. Results Tamoxifen induced inactivation of Evc inhibited Hh overexpression and partially prevented chondrocyte hypertrophy during OA, although it did not ameliorate cartilage damage in DMM- Evc cKO mice. Hh pathway inhibition did not modify the expression of proinflammatory mediators induced by IL-1 beta in human OA chondrocytes in culture. Hypertrophic – IHH – and inflammatory – COX-2 – markers co-localized in OA cartilage samples. Conclusions Tamoxifen induced inactivation of Evc partially prevented chondrocyte hypertrophy in DMM- Evc cKO mice, but it did not ameliorate cartilage damage. Our results suggest that chondrocyte hypertrophy per se is not a pathogenic event in the progression of OA.