Synovial fluid of patients with rheumatoid arthritis induces alpha-smooth muscle actin in human adipose tissue-derived mesenchymal stem cells through a TGF-beta1-dependent mechanism

Rheumatoid arthritis (RA) is a chronic, inflammatory autoimmune disorder that causes the immune system to attack the joints. Transforming growth factor-beta1 (TGF-beta1) is a secreted protein that promotes differentiation of synovial fibroblasts to alpha-smooth muscle actin (alpha-SMA)-positive myofibroblasts to repair the damaged joints. Synovial fluid from patients with RA (RA-SF) induced expression of alpha-SMA in human adipose tissue-derived mesenchymal stem cells (hASCs). RA-SF-induced alpha-SMA expression was abrogated by immunodepletion of TGF-beta1 from RA-SF with anti-TGF-beta1 antibody. Furthermore, pretreatment of hASCs with the TGF-beta type I receptor inhibitor SB431542 or lentiviral small hairpin RNA-mediated silencing of TGF-beta type I receptor expression in hASCs blocked RA-SF-induced alpha-SMA expression. Small interfering RNA-mediated silencing of Smad2 or adenoviral overexpression of Smad7 (an inhibitory Smad isoform) completely inhibited RA-SF-stimulated alpha-SMA expression. These results suggest that TGF-beta1 plays a pivotal role in RA-SF-induced differentiation of hASCs to alpha-SMA-positive cells.

Thromboxane A2 modulates migration, proliferation, and differentiation of adipose tissue-derived mesenchymal stem cells

Prostanoid metabolites are key mediators in inflammatory responses, and accumulating evidence suggests that mesenchymal stem cells (MSCs) can be recruited to injured or inflamed tissues. In the present study, we investigated whether prostanoid metabolites can regulate migration, proliferation, and differentiation potentials of MSCs. We demonstrated herein that the stable thromboxane A2 (TxA2) mimetic U46619 strongly stimulated migration and proliferation of human adipose tissue-derived MSCs (hADSCs). Furthermore, U46619 treatment increased expression of alpha-smooth muscle actin (alpha-SMA), a smooth muscle marker, in hADSCs, suggesting differentiation of hADSCs into smooth muscle-like cells. U46619 activated ERK and p38 MAPK, and pretreatment of the cells with the MEK inhibitor U0126 or the p38 MAPK inhibitor SB202190 abrogated the U46619-induced migration, proliferation, and alpha-SMA expression. These results suggest that TxA2 plays a key role in the migration, proliferation, and differentiation of hADSCs into smooth muscle-like cells through signaling mechanisms involving ERK and p38 MAPK.