Restriction of spontaneous and prednisolone-induced leptin production to dedifferentiated state in human hip OA chondrocytes: role of Smad1 and b-catenin activation

Objective: The aetiology of OA is not fully understood although several adipokines such as leptin are
known mediators of disease progression. Since leptin levels were increased in synovial fluid compared to
serum in OA patients, it was suggested that joint cells themselves could produce leptin. However, exact
mechanisms underlying leptin production by chondrocytes are poorly understood. Nevertheless, prednisolone,
although displaying powerful anti-inflammatory properties has been recently reported to be
potent stimulator of leptin and its receptor in OA synovial fibroblasts. Therefore, we investigated, in vitro,
spontaneous and prednisolone-induced leptin production in OA chondrocytes, focusing on transforming
growth factor-b (TGFb) and Wnt/b-catenin pathways.
Design: We used an in vitro dedifferentiation model, comparing human freshly isolated hip OA chondrocytes
cultivated in monolayer during 1 day (type II, COL2A1 þ; type X, COL10A1 þ and type I collagen,
COL1A1 ") or 14 days (COL2A1 "; COL10A1 " and COL1A1þ).
Results: Leptin expression was not detected in day1 OA chondrocytes whereas day14 OA chondrocytes
produced leptin, significantly increased with prednisolone. Activin receptor-like kinase 1 (ALK1)/ALK5
ratio was shifted during dedifferentiation, from high ALK5 and phospho (p)-Smad2 expression at day1 to
high ALK1, endoglin and p-Smad1/5 expression at day14. Moreover, inactive glycogen synthase kinase 3
(GSK3) and active b-catenin were only found in dedifferentiated OA chondrocytes. Smad1 and b-catenin
but not endoglin stable lentiviral silencing led to a significant decrease in leptin production by dedifferentiated
OA chondrocytes.
Conclusions: Only dedifferentiated OA chondrocytes produced leptin. Prednisolone markedly enhanced
leptin production, which involved Smad1 and b-catenin activation