Blocking chondrocyte hypertrophy in conditional Evc knockout mice does not modify cartilage damage in osteoarthritis.

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 (EvccKO ) model of OA. For this purpose, OA was induced by surgical knee destabilization in wild-type (WT) and EvccKO 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-1 beta as an inflammatory insult. Our results showed that tamoxifen induced inactivation of Evc inhibited Hh overexpression and partially prevented chondrocyte hypertrophy during OA, although it did not ameliorate cartilage damage in DMM-EvccKO mice. Hh pathway inhibition did not modify the expression of proinflammatory mediators induced by IL-1 beta in human OA chondrocytes in culture. We found that hypertrophic-IHH-and inflammatory-COX-2-markers co-localized in OA cartilage samples. We concluded that tamoxifen induced inactivation of Evc partially prevented chondrocyte hypertrophy in DMM-EvccKO mice, but it did not ameliorate cartilage damage. Overall, our results suggest that chondrocyte hypertrophy per se is not a pathogenic event in the progression of OA.

Disorganization of chondrocyte columns in the growth plate does not aggravate experimental osteoarthritis in mice.

Osteoarthritis (OA) is a multifactorial joint disease mainly affecting articular cartilage (AC) with a relevant biomechanical component. During endochondral ossification growth plate (GP) chondrocytes arrange in columns. GPs do not ossify in skeletally mature rodents. In neonatal mice, an altered joint loading induces GP chondrocyte disorganization. We aimed to study whether experimental OA involves GP disorganization in adult mice and to assess if it may have additional detrimental effects on AC damage. Knee OA was induced by destabilization of the medial meniscus (DMM) in wild-type (WT) adult mice, and in Tamoxifen-inducible Ellis-van-Creveld syndrome protein (Evc) knockouts (EvccKO), used as a model of GP disorganization due to Hedgehog signalling disruption. Chondrocyte column arrangement was assessed in the tibial GP and expressed as Column Index (CI). Both DMM-operated WT mice and non-operated-EvccKO showed a decreased CI, indicating GP chondrocyte column disarrangement, although in the latter, it was not associated to AC damage. The most severe GP chondrocyte disorganization occurred in DMM-EvccKO mice, in comparison to the other groups. However, this altered GP structure in DMM-EvccKO mice did not exacerbate AC damage. Further studies are needed to confirm the lack of interference of GP alterations on the analysis of AC employing OA mice.