Thioredoxin-interacting protein mediates dysfunction of tubular autophagy in diabetic kidneys through inhibiting autophagic flux

Abstract

Thioredoxin-interacting protein (TXNIP) expression is ubiquitous and is induced by a variety of cellular stresses, including high intracellular glucose. TXNIP is associated with activation of oxidative stress and tubulointerstitial fibrosis in diabetic nephropathy. Autophagy is a major pathway that delivers damaged proteins and organelles to lysosomes to maintain cellular homeostasis. This study aimed to investigate the dysregulation of autophagy and the regulation of TXNIP on autophagy in renal proximal tubular cells (PTCs) under diabetic conditions. The formation of autophagosomes was measured using transmission electron microscopy, and LC3-II, and the effectiveness of autophagic clearance was determined by p62 expression in diabetic kidney and in human PTCs exposed to high glucose (HG). The results collectively demonstrated increased expression of TXNIP, LC3/LC3-II and p62 in renal tubular cells of mice with diabetic nephropathy and in cultured human PTCs exposed to HG (30 mM/l) for 48 h compared with control. The formation of autophagic vacuoles was increased in HG-induced cells. Furthermore, silencing of TXNIP by siRNA transfection reduced autophagic vacuoles and the expression of LC3-II and p62 in human PTCs exposed to HG compared with control and partially reversed the accumulation of LC3-II and p62 induced by bafilomycin A 1 (50 nM/l), a pharmacological inhibitor of autophagy which blocks the fusion of autophagosomes with lysosomes and impairs the degradation of LC3-II and p62. Collectively, these results suggest that hyperglycemia leads to dysfunction of autophagy in renal tubular cells and decreases autophagic clearance. HG-induced overexpression of TXNIP may contribute to the dysfunction of tubular autophagy in diabetes.

Thioredoxin-Interacting Protein Deficiency Protects against Diabetic Nephropathy

“…Because these mouse models lack TxNIP in all cells and tissues, it is not possible to completely exclude a contribution of systemic effects (e.g., decreased inflammation) to protection from DN. However, our data in podocytes and in mesangial cells, 15 as well as in cardiomyocytes, 38,46 b cells, 13,17 and, recently, renal proximal tubular cells, 47 indicate major cell autonomous protective effects of TxNIP deficiency. The precise contribution and role of TxNIP in various cell types in the kidney to DN (i.e., endothelial, mesangial, epithelial [podocytes] and tubular cells) remain to be documented, along with tissue-specific KO mouse models.…”

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.…”

Melatonin suppresses autophagy in type 2 diabetic osteoporosis

“…High glucose levels have already been shown to inhibit autophagic turnover in several cell types, such as renal proximal tubular cells and pancreatic cells [44, 45]. However, other studies have indicated that high glucose levels can activate autophagy in cranial neural crest cells and endothelial cells [46, 47].…”