TGFB1 and renal fibrosis: In our study, the changes of morphological structure, renal fibrosis, ultrastructure and renal function, the expressions of extracellular matrix (ECM), matrix metalloproteinases (MMPs) and its tissue inhibitors of metalloproteinases (TIMPs), the expressions of tumor growth factor β1 (TGF-β1)/Smad signaling and oxidative stress parameters as well as nuclear factor erythroid 2-related factor 2-antioxidant response element (Nrf2-ARE) signaling were tested in kidney of aged male Wistar rats after subcutaneous testosterone propionate (TP, 2 mg/kg/d, 84-day) injection.