Protective Effects of Vitamin D on Proteoglycans of Human Articular Chondrocytes through TGF-β1 Signaling

The extracellular matrix of cartilage primarily constitutes of collagen and aggrecan. Cartilage degradation starts with aggrecan loss in osteoarthritis (OA). Vitamin D (VD) plays an essential role in several inflammation-related diseases and can protect the collagen in cartilage during OA. The present study focused on the role of VD in aggrecan turnover of human articular chondrocytes treated with tumor necrosis factor alpha (TNF-alpha) and the possible mechanism. Treatment with different doses of VD and different periods of intervention with TNF-alpha and TGF-beta 1 receptor (TGF beta R1) inhibitor SB525334 were investigated. The viability of human chondrocytes and extracellular secretion of TGF-beta 1 were measured. The expression of intracellular TGF beta R1 and VD receptor was examined. Transcriptional and translational levels of aggrecan and the related metabolic factors were analyzed. The results showed that TNF-alpha markedly reduced the viability, TGF beta R1 expressions and aggrecan levels of human chondrocytes, and increased disintegrin and metalloproteinase with thrombospondin motifs. The alterations were partially inhibited by VD treatment. Furthermore, the effects of VD were blocked by the TGF beta R1 inhibitor SB525334 in TNF-alpha-treated cells. VD may prevent proteoglycan loss due to TNF-alpha via TGF-beta 1 signaling in human chondrocytes.