COL1A1 and pulmonary arterial hypertension: Exposure of HPASMCs to SSc-PAH sera also resulted in progressive time-related increase of the COL1A1 promoter activity (Figure 1D) with values at 8 hours (steady state) significantly higher in cells exposed to PAH [2.375 (1.597)] compared to no-PAH [1.825 (0.612); p = 0.028] and HD [1.844 (0.265); p = 0.007] sera (Figure 1E).