Renal fibrosis increases in aged rats, which is characterized by thickening of the glomerular basement membrane and Bowman's basement membrane, increased ECM, decreased MMP-2 and MMP-9 expression, increased TIMP-1 and TIMP-2 expression, increased TGF-β1/Smad signalling, and decreased Nrf2-ARE signalling in renal tissue compared to those in younger rats. Here, TGFB1 is linked to renal fibrosis.