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BackgroundIn osteoarthritis (OA), the imbalance of chondrocytes’ anabolic and catabolic factors can induce cartilage destruction. Interleukin-1 beta (IL-1β) is a potent pro-inflammatory cytokine that is capable of inducing chondrocytes and synovial cells to synthesize MMPs. The hypoxia-inducible factor-2alpha (HIF-2alpha, encoded by Epas1) is the catabolic transcription factor in the osteoarthritic process. The purpose of this study is to validate the effects of ecdysteroids (Ecd) on IL-1β- induced cartilage catabolism and the possible role of Ecd in treatment or prevention of early OA.MethodsChondrocytes and articular cartilage was harvested from newborn ICR mice. Ecd effect on chondrocytes viability was tested and the optimal concentration was determined by MTT assay. The effect of HIF-2α (EPAS1) in cartilage catabolism simulated by IL-1β (5 ng/ml) was evaluated by articular cartilage explants culture. The effects of Ecd on IL-1β-induced inflammatory conditions and their related catabolic genes expression were analyzed.ResultsInterleukin-1β (IL-1β) treatment on primary mouse articular cartilage explants enhanced their Epas1, matrix metalloproteinases (MMP-3, MMP-13) and ADAMTS-5 genes expression and down-regulated collagen type II (Col2a1) gene expression. With the pre-treatment of 10−8M Ecd, the catabolic effects of IL-1β on articular cartilage were scavenged.ConclusionIn conclusions, Ecd can reduce the IL-1β-induced inflammatory effect of the cartilage. Ecd may suppress IL-1β- induced cartilage catabolism via HIF-2α pathway.

Increases in muscle energy needs activate AMPK and induce sarcolemmal recruitment of the fatty acid (FA) translocase CD36. The resulting rises in FA uptake and FA oxidation are tightly correlated, suggesting coordinated regulation. We explored the possibility that membrane CD36 signaling might influence AMPK activation. We show, using several cell types, including myocytes, that CD36 expression suppresses AMPK, keeping it quiescent, while it mediates AMPK activation by FA. These dual effects reflect the presence of CD36 in a protein complex with the AMPK kinase LKB1 (liver kinase B1) and the src kinase Fyn. This complex promotes Fyn phosphorylation of LKB1 and its nuclear sequestration, hindering LKB1 activation of AMPK. FA interaction with CD36 dissociates Fyn from the protein complex, allowing LKB1 to remain cytosolic and activate AMPK. Consistent with this, CD36−/− mice have constitutively active muscle and heart AMPK and enhanced FA oxidation of endogenous triglyceride stores. The molecular mechanism described, whereby CD36 suppresses AMPK, with FA binding to CD36 releasing this suppression, couples AMPK activation to FA availability and would be important for the maintenance of cellular FA homeostasis. Its dysfunction might contribute to the reported association of CD36 variants with metabolic complications of obesity in humans.