Thioredoxin-interacting Protein Mediates High Glucose-induced Reactive Oxygen Species Generation by Mitochondria and the NADPH Oxidase, Nox4, in Mesangial Cells

Anu Shah,Ling Xia,Howard Goldberg,Ken W Lee,Susan E Quaggin,I George Fantus

doi:10.1074/jbc.m112.419101

Abstract

Thioredoxin-interacting protein (TxNIP) is up-regulated by high glucose and is associated with oxidative stress. It has been implicated in hyperglycemia-induced β-cell dysfunction and apoptosis. As high glucose and oxidative stress mediate diabetic nephropathy (DN), the contribution of TxNIP was investigated in renal mesangial cell reactive oxygen species (ROS) generation and collagen synthesis. To determine the role of TxNIP, mouse mesangial cells (MC) cultured from wild-type C3H and TxNIP-deficient Hcb-19 mice were incubated in HG. Confocal microscopy was used to measure total and mitochondrial ROS production (DCF and MitoSOX) and collagen IV. Trx and NADPH oxidase activities were assayed and NADPH oxidase isoforms, Nox2 and Nox4, and antioxidant enzymes were determined by immunoblotting. C3H MC exposed to HG elicited a significant increase in cellular and mitochondrial ROS as well as Nox4 protein expression and NADPH oxidase activation, whereas Hcb-19 MC showed no response. Trx activity was attenuated by HG only in C3H MC. These defects in Hcb-19 MC were not due to increased antioxidant enzymes or scavenging of ROS, but associated with decreased ROS generation. Adenovirus-mediated overexpression of TxNIP in Hcb-19 MC and TxNIP knockdown with siRNA in C3H confirmed the specific role of TxNIP. Collagen IV accumulation in HG was markedly reduced in Hcb-19 cells. TxNIP is a critical component of the HG-ROS signaling pathway, required for the induction of mitochondrial and total cell ROS and the NADPH oxidase isoform, Nox4. TxNIP is a potential target to prevent DN.

Highlights

Thioredoxin-interacting protein (TxNIP) is up-regulated by high glucose (HG), inhibits the antioxidant, thioredoxin, and thereby is implicated in oxidative stress
Treatment with high glucose resulted in a time-dependent increase in TxNIP, which was significantly increased in wild-type C3H mesangial cells (MC) by 1 h of HG treatment, rising to ϳ15-fold by 24 h (Fig. 1A)
Collagen ␣(IV), an extracellular matrix (ECM) protein known to be associated with glomerulosclerosis was increased 1.7 Ϯ 0.43-fold after a 24-h HG treatment of C3H MC, but no change was observed in Hcb-19 MC (Fig. 1B)

Summary

Introduction

Thioredoxin-interacting protein (TxNIP) is up-regulated by high glucose (HG), inhibits the antioxidant, thioredoxin, and thereby is implicated in oxidative stress. Results: TxNIP deficiency protects mesangial cells from HG-induced oxidative stress and increased collagen by blocking mitochondrial glucose metabolism, NADPH oxidase, and Nox. Thioredoxin-interacting protein (TxNIP) is up-regulated by high glucose and is associated with oxidative stress. It has been implicated in hyperglycemia-induced ␤-cell dysfunction and apoptosis. As high glucose and oxidative stress mediate diabetic nephropathy (DN), the contribution of TxNIP was investigated in renal mesangial cell reactive oxygen species (ROS) generation and collagen synthesis. C3H MC exposed to HG elicited a significant increase in cellular and mitochondrial ROS as well as Nox protein expression and NADPH oxidase activation, whereas Hcb-19 MC showed no response.

Methods

Results

Conclusion