SMAD3 and chronic kidney disease: We showed that vitamin D repletion exerts its antifibrotic effects on skeletal muscle by inhibiting the expression of pro-fibrotic genes (TGFβ1, Agt, PAI-1 and Smad3) while stimulating the expression of anti-fibrotic genes (BMP7 and IL13Rα2) in CKD mice (Table 3).