Guan, Yingjie

Abstract Mixed lineage leukemia 1 (MLL1), a histone H3 lysine 4 (H3K4) methyltransferase, exerts its enzymatic activity by interacting with menin and other proteins. It is unclear whether inhibition of the MLL1‐menin interaction influences epithelial‐mesenchymal transition (EMT), renal fibroblast activation, and renal fibrosis. In this study, we investigated the effect of disrupting MLL1‐menin interaction on those events and mechanisms involved in a murine model of renal fibrosis induced by unilateral ureteral obstruction (UUO), in cultured mouse proximal tubular cells and renal interstitial fibroblasts. Injury to the kidney increased the expression of MLL1 and menin and H3K4 monomethylation (H3K4me1); MLL1 and menin were expressed in renal epithelial cells and renal interstitial fibroblasts. Inhibition of the MLL1‐menin interaction by MI‐503 administration or siRNA‐mediated silencing of MLL1 attenuated UUO‐induced renal fibrosis, and reduced expression of α‐smooth muscle actin (α‐SMA) and fibronectin. These treatments also inhibited UUO‐induced expression of transcription factors Snail and Twist and transforming growth factor β1 (TGF‐β1) while expression of E‐cadherin was preserved. Moreover, treatment with MI‐503 and transfection with either MLL siRNA or menin siRNA inhibited TGF‐β1‐induced upregulation of α‐SMA, fibronectin and Snail, phosphorylation of Smad3 and AKT, and downregulation of E‐cadherin in cultured renal epithelial cells. Finally, MI‐503 was effective in abrogating serum or TGFβ1‐induced transformation of renal interstitial fibroblasts to myofibroblasts in vitro. Taken together, these results suggest that targeting disruption of the MLL1‐menin interaction attenuates renal fibrosis through inhibition of partial EMT and renal fibroblast activation.

Abstract SET and MYND domain protein 2 (SMYD2) is a lysine methyltransferase that mediates histone H3 lysine 36 trimethylation (H3K36me3) and acts as a regulator of tumorgenesis and cystic growth. However, its role in renal fibrosis remains unknown. In this study, we found that SMYD2 was highly expressed in the murine kidney of renal fibrosis induced by unilateral ureteral obstruction, and primarily located in interstitial fibroblasts and renal tubular epithelial cells. Pharmacological inhibition of SMYD2 with AZ505, a highly selective inhibitor of SMYD2, protected against renal fibrosis and inhibited activation/proliferation of renal interstitial fibroblasts and conversion of epithelial cells to a profibrotic phenotype in this model. In cultured renal interstitial fibroblasts, treatment with AZ505 or silencing of SMYD2 by specific siRNA also inhibited serum‐ or TGF‐β1‐induced activation and proliferation of renal interstitial fibroblasts. Mechanistic studies showed that SMYD2 inhibition reduced phosphorylation of several profibrotic signaling molecules, including Smad3, extracellular signal‐regulated kinase 1/2, AKT, signal transducer and activator of transcription‐3 and nuclear factor‐κB in both injured kidney and cultured renal fibroblasts. AZ505 was also effective in suppressing renal expression of Snail and Twist, two transcriptional factors that mediate renal partial epithelial‐mesenchymal transition and fibrosis. Conversely, AZ505 treatment prevented downregulation of Smad7, a renoprotective factor in vivo and in vitro. These results indicate that SMYD2 plays a critical role in mediating conversion of epithelial cells to a profibrotic phenotype, renal fibroblast activation and renal fibrogenesis, and suggest that SMYD2 may be a potential target for the treatment of chronic fibrosis in kidney disease.