PPIF and renal fibrosis: Furthermore, PPIF-deficient mice showed protection from renal fibrosis in the UUO model due to reduction in tubular epithelial cell apoptosis (58), and TGF-β1–induced collagen type I expression in fibroblasts isolated from these mice was comparable with that observed in WT fibroblasts, suggesting that PPIF does not play a direct role in fibrogenic responses.