SMAD4 and diabetic kidney disease: Strikingly, the protein levels of TGF-β1, phosphor-Smad2, Smad4, and Smad7 were reversed after 8-weeks treatment with ergosterol (Figure 6), indicating that ergosterol can inhibit the renal TGF-β1/Smad2 signaling pathway in STZ-induced diabetic nephropathy mice.