THBS1 and systemic sclerosis: Therefore, we wanted to further clarify whether the overexpression of TSP1 in SSc fibroblasts is impacted by blocking endogenous TGFβ and PDGF signalling, SSc lesional fibroblasts were treated overnight with SB431542 (ALK5 inhibitor), U0126 (MEK inhibitor) or IFNβ.