SMAD3 and necrotizing enterocolitis: In IEC6 cells, the expressions of TGF-β1, Smad3, and ZO-1 were downsized when SIRT1 expression was curbed, while other studies have found that TGF-β1 and ZO-1 can protect intestinal epithelial cells and intestinal mucosal barrier function during NEC (19, 20).