Thioredoxin-Interacting Protein Deficiency Protects against Diabetic Nephropathy

Abstract

Expression of thioredoxin-interacting protein (TxNIP), an endogenous inhibitor of the thiol oxidoreductase thioredoxin, is augmented by high glucose (HG) and promotes oxidative stress. We previously reported that TxNIP-deficient mesangial cells showed protection from HG-induced reactive oxygen species, mitogenactivated protein kinase phosphorylation, and collagen expression. Here, we investigated the potential role of TxNIP in the pathogenesis of diabetic nephropathy (DN) in vivo. Wild-type (WT) control, TxNIP 2/2 , and TxNIP +/2 mice were rendered equally diabetic with low-dose streptozotocin. In contrast to effects in WT mice, diabetes did not increase albuminuria, proteinuria, serum cystatin C, or serum creatinine levels in TxNIP 2/2 mice. Whereas morphometric studies of kidneys revealed a thickened glomerular basement membrane and effaced podocytes in the diabetic WT mice, these changes were absent in the diabetic TxNIP 2/2 mice. Immunohistochemical analysis revealed significant increases in the levels of glomerular TGF-b1, collagen IV, and fibrosis only in WT diabetic mice. Additionally, only WT diabetic mice showed significant increases in oxidative stress (nitrotyrosine, urinary 8-hydroxy-2-deoxy-guanosine) and inflammation (IL-1b mRNA, F4/80 immunohistochemistry). Expression levels of Nox4-encoded mRNA and protein increased only in the diabetic WT animals. A significant loss of podocytes, assessed by Wilms' tumor 1 and nephrin staining and urinary nephrin concentration, was found in diabetic WT but not TxNIP 2/2 mice. Furthermore, in cultured human podocytes exposed to HG, TxNIP knockdown with siRNA abolished the increased mitochondrial O 2 2 generation and apoptosis. These data indicate that TxNIP has a critical role in the progression of DN and may be a promising therapeutic target.

Epigenomic profiling reveals an association between persistence of DNA methylation and metabolic memory in the DCCT/EDIC type 1 diabetes cohort

“…Importantly, our experiments with THP1 cells cultured under various HG/NG conditions revealed an association between persistent DNA-me triggered by prior history of HG exposure and enhanced TXNIP expression in response to HG in vitro. We, thus, speculate that transient hyperglycemic episodes during the EDIC Study would induce more TXNIP overexpression and cellular dysfunction in cases vs. controls because of TXNIP hypo-me, which is in line with the reported adverse cellular roles of TXNIP (43)(44)(45)48). This type of cellular response to episodic HG provides mechanistic information toward understanding the connections between persistent DNA hypo-me at TXNIP and its gene expression and hence, metabolic memory of diabetic complications.…”

“…Persistence of DNA hypo-me in TXNIP at two time periods was particularly interesting, because TXNIP is a reported sensor of glucose stress, a prooxidant, and a proapoptotic protein, with gene expression that is highly associated with hyperglycemia and diabetic complications, including retinopathy and nephropathy (43)(44)(45), both of which were prevalent in our case group. TXNIP expression is highly induced by HG in various cell types (46)(47)(48), which by inhibiting thioredoxin, subsequently causes oxidative stress and apoptosis.…”

Sustained kidney biochemical derangement in treated experimental diabetes: a clue to metabolic memory

“…Here we did not perform immunostaining for pAMPK localization in the rat kidney. Other researchers have demonstrated, by immunohistochemistry, increased TGF-β expression in both tubular and glomerular compartments in rodent models after 8, 12 and 24 weeks of diabetes555657. Since TGF-β is downstream to the other components of the fibrogenic pathway we studied, it is likely that the changes we observed are also present in glomerular and tubular compartments.…”

The Histone Methyltransferase Enzyme Enhancer of Zeste Homolog 2 Protects against Podocyte Oxidative Stress and Renal Injury in Diabetes

“…Although both molecular 28 and topological 5 observations indicate that the role of TxnIP in promoting oxidative injury extends beyond its negative regulation of Trx, augmented expression of the protein has been repeatedly associated with the development of diabetes complications. 5,[29][30][31][32] In this study, we found that depletion of EZH2, with either DZNep or shRNA, rendered cultured podocytes vulnerable to the deleterious effects of high-glucose concentrations, leading to an increase in ROS levels and cell death. The augmentation of high glucose-induced oxidative damage in podocytes was, at least in part, mediated by derepression of TxnIP shown by (1) increased podocyte TxnIP mRNA and protein abundance when EZH2-depleted cells were exposed to high-glucose concentrations and (2) abrogation of ROS accumulation by either TxnIP knockdown or Trx overexpression.…”