Thrombospondin-2 Couples Pressure-Promoted Chondrogenesis through NF-κB Signaling

Our previous studies found that the mechanical stimulation promote chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), along with up-regulation of thrombospondin-2 (TSP-2). The aim of this study was to explore the effect of thrombospondin-2 (TSP-2) on the mechanical pressure-stimulated chondrogenic differentiation of BMSCs and the possible role of NF-κB signaling in the mechano-chemical coupling regulation toward chondrogenesis.

Rat BMSCs were isolated, cultured and identified. The time-dependent expressions of TSP-2 and Sox9 in BMSCs under a dynamic mechanical pressure of 0-120 kPa at 0.1 Hz for 1 h were tested by qPCR and Western blotting. The role of TSP-2 in chondrogenic differentiation of BMSCs under mechanical pressure was validated by using small interfering RNA. The impact of TSP-2 and mechanical pressure on chondrogenesis were detected and the downstream signaling molecules were explored using Western blotting.

Mechanical pressure stimulation of 0-120 kPa for 1 h significantly upregulated the expression of TSP-2 in BMSCs. The expression of the chondrogenesis markers Sox9, Aggrecan, and Col-II were all upregulated under dynamic mechanical pressure or TSP-2 stimulation. Additional exogenous TSP-2 may potentiate the chondrogenic effect of mechanical stimulation. After knock down TSP-2, the upregulation of Sox9, Aggrecan and Col-II under mechanical pressure was inhibited. The NF-κB signaling pathway responded to both dynamic pressure and TSP-2 stimulation, and the cartilage-promoting effect was blocked by an NF-κB signaling inhibitor.

TSP-2 plays an essential role in the chondrogenic differentiation of BMSCs under mechanical pressure. NF-κB signaling is involved in the mechano-chemical coupling of TSP-2 and mechanical pressure for the chondrogenic differentiation of BMSCs.