TGFB1 and cystic fibrosis: Stimulation with TGF-β showed a clear trend of COL1A1 upregulation, while cyclic stretch in the presence of TGF-β significantly reduced the expression of COL1A1. Immunofluorescence and western blot showed that stretch reduced collagen 1 protein expression in iPSC-CF, both in the presence and absence of TGF-β (Fig. 2b, c, Fig. S3).