Strontium Promotes Transforming Growth Factors β1 and β2 Expression in Rat Chondrocytes Cultured In Vitro

The transforming growth factors β1 (TGF-β1) and TGF-β2, as two distinct homodimers of TGF-β superfamily, involve in chondrocyte growth and differentiation. Emerging evidence has implied that strontium (Sr) plays an important role in the bone formation and resorption, and has strong effects on stimulating human cartilage matrix formation in vitro. However, the direct effects of Sr on TGF-β1 and TGF-β2 expressions in chondrocytes are not entirely clear. The purpose of this study was to evaluate the influence of different Sr concentrations on the expression of TGF-β1 and TGF-β2 in rat chondrocytes in vitro. Chondrocytes were isolated from Wistar rat articular by enzymatic digestion. Strontium chloride hexahydrate (SrCl₂·6H₂O) was used as a Sr source in this study. Sr was added to the culture solution at final concentrations of 0, 0.5, 1.0, 2.0, 5.0, 20.0, and 100 μg/mL. After 72 h of continuous culture, TGF-β1 and TGF-β2 mRNA abundance and protein expression levels in the chondrocytes were determined by real-time polymerase chain reaction (real-time PCR) and Western blot, respectively. The results showed that TGF-β1 and TGF-β2 expressions in chondrocytes increased dose-dependently with Sr concentration. The mRNA abundance of TGF-β1 and TGF-β2 were markedly higher than those observed for control (P < 0.01) when the Sr-treated concentration exceeded 1.0 and 5.0 μg/mL, respectively. The TGF-β1 and TGF-β2 protein expression levels were extremely significantly higher than those in the control group (P < 0.01) at above 5.0 μg/mL Sr-treatment. These results indicated that Sr could involve in the chondrocytes metabolism via regulating TGF-β1 and TGF-β2 signalling.