Thioredoxin interacting protein (TXNIP) regulates tubular autophagy and mitophagy in diabetic nephropathy through the mTOR signaling pathway.

Chunling Huang,Carol A Pollock,Jin-Sung Park,Xin-Ming Chen,Delfine Cheng,Christina Y R Tan,Darren J Kelly,Anthony Gill,Yuan Zhang,Filip Braet,Carolyn M Sue

doi:10.1038/srep29196

Abstract

Hyperglycemia upregulates thioredoxin interacting protein (TXNIP) expression, which in turn induces ROS production, inflammatory and fibrotic responses in the diabetic kidney. Dysregulation of autophagy contributes to the development of diabetic nephropathy. However, the interaction of TXNIP with autophagy/mitophagy in diabetic nephropathy is unknown. In this study, streptozotocin-induced diabetic rats were given TXNIP DNAzyme or scrambled DNAzyme for 12 weeks respectively. Fibrotic markers, mitochondrial function and mitochondrial reactive oxygen species (mtROS) were assessed in kidneys. Tubular autophagy and mitophagy were determined in kidneys from both human and rats with diabetic nephropathy. TXNIP and autophagic signaling molecules were examined. TXNIP DNAzyme dramatically attenuated extracellular matrix deposition in the diabetic kidneys compared to the control DNAzyme. Accumulation of autophagosomes and reduced autophagic clearance were shown in tubular cells of human diabetic compared to non-diabetic kidneys, which was reversed by TXNIP DNAzyme. High glucose induced mitochondrial dysfunction and mtROS production, and inhibited mitophagy in proximal tubular cells, which was reversed by TXNIP siRNA. TXNIP inhibition suppressed diabetes-induced BNIP3 expression and activation of the mTOR signaling pathway. Collectively, hyperglycemia-induced TXNIP contributes to the dysregulation of tubular autophagy and mitophagy in diabetic nephropathy through activation of the mTOR signaling pathway.

Highlights

Hyperglycemia activates various pathways to induce oxidative stress, pro-fibrotic factors, advanced glycation end-products and activation of the renin-angiotensin-aldosterone system, leading collectively to renal injury, excessive extracellular matrix production and albuminuria[1]
In this study we show that increased expression of thioredoxin interacting protein (TXNIP) in the diabetic kidney and proximal tubular cells exposed to high glucose contributes to dysfunctional autophagy and mitophagy through activation of the mTOR signaling pathway, while inhibition of TXNIP functionally improves autophagy and mitophagy in diabetic nephropathy
To determine whether TXNIP is involved in the pathophysiology of diabetes nephropathy, we examined the effect of modifying TXNIP expression on the development of interstitial fibrosis by measuring interstitial collagen fibril deposition using picrosirius red staining

Summary

Introduction

Hyperglycemia activates various pathways to induce oxidative stress, pro-fibrotic factors, advanced glycation end-products and activation of the renin-angiotensin-aldosterone system, leading collectively to renal injury, excessive extracellular matrix production and albuminuria[1]. Thioredoxin-interacting protein (TXNIP) as a natural inhibitor of thioredoxin is an early-response gene which is markedly induced by hyperglycemia It evokes a program of cellular defense/survival mechanisms that lead to oxidative stress, endoplasmic reticulum stress/inflammation, autophagy, and apoptosis[3,4]. We have previously shown that inhibition of TXNIP using DNAzyme technology attenuated oxidative stress, inflammasome signaling, tubulo-interstitial fibrosis and collagen deposition in the tubulo-interstitium of diabetic rats[10], and hyperglycemia led to dysfunctional autophagy in renal tubular cells with decreased autophagic clearance[11]. In this study we show that increased expression of TXNIP in the diabetic kidney and proximal tubular cells exposed to high glucose contributes to dysfunctional autophagy and mitophagy through activation of the mTOR signaling pathway, while inhibition of TXNIP functionally improves autophagy and mitophagy in diabetic nephropathy

Methods

Results

Conclusion