Loss of NF-E2 expression contributes to the induction of profibrotic signaling in diabetic kidneys

Aims: This study aimed to examine the anti-fibrotic role of Nuclear Factor-Erythroid derived 2 (NF-E2) in human renal tubule (HK-11) cells and in type 1 and type 2 diabetic (T1D, T2D) mouse kidneys. Main methods: Anti-fibrotic effects of NF-E2 were examined in transforming growth factor-beta (TGF-beta) treated HK-11 cells by over-expressing/silencing NF-E2 expression and determining its effects on profibrotic signaling. NF-E2 proteasomal degradation was confirmed by proteasome inhibition in HK-11 cells and diabetic mice. Clinical relevance of changes in NF-E2 expression to fibrotic changes in the kidney were assessed in T1D and T2D mouse kidneys. Key findings: NF-E2 expression was significantly decreased in TGF-beta treated HK-11 cells and in kidneys of diabetic mice with concurrent increase in expression of fibrotic proteins. TGF-beta treatment of HK-11 cells did not inhibit NF-E2 mRNA expression, suggesting that the post-translational changes may contribute to NF-E2 protein degradation. The down-regulation of NF-E2 expression was attributed to its proteasomal degradation, as TGF-beta- and diabetes-induced NF-E2 down regulation was prevented by proteasome inhibitor treatment. In HK-11 cells TGF-beta treatment decreased E-cadherin expression and induced pSer(82)Hsp27/NF-E2 association, likely to promote NF-E2 degradation, as Hsp27 can target proteins to the proteasome. A critical role for NF-E2 in regulation of renal fibrosis was demonstrated as over-expression of NF-E2 or silencing NF-E2 expression, decreased or increased profibrotic proteins in TGF-beta-treated HK-11 cells, respectively. Significance: NF-E2, a novel anti-fibrotic protein, is down-regulated in diabetic kidneys. Preserving/inducing NF-E2 expression in diabetic kidneys may provide a therapeutic potential to combat DN.