TGFB1 and renal fibrosis: To investigate the effect of hypoxia-preconditioned rat MSCs on renal fibrosis, we first examined the expression of α-SMA and TGF-β1 in the IRI model that had been injected with PBS, 5 × 105 rat MSCs cultured under normoxic conditions (21%O2 rMSCs), or under 1% O2 conditions (1%O2 rMSCs) at 21 days post-IRI.