SMAD3 and chronic kidney disease: In animal experiments, Wang et al. showed that exposure to a high dose of vitamin D3 decreased the levels of serum creatine, urea nitrogen, and urine protein and restored the homeostasis of calcium and parathormone, and vitamin D3 acts as a potential antifibrotic drug in chronic kidney disease via the vitamin D receptor and inhibits the TGF-β1/Smad3 signaling pathway (41).