Elsevier

Life Sciences

Volume 88, Issues 11–12, 14 March 2011, Pages 512-520
Life Sciences

Prevention of diabetic nephropathy in rats through enhanced renal antioxidative capacity by inhibition of the proteasome

https://doi.org/10.1016/j.lfs.2010.12.023Get rights and content

Abstract

Aims

Oxidative stress may play an important role in the pathogenesis of diabetic nephropathy (DN). Recent studies have shown that the ubiquitin–proteasome pathway (UPP) and oxidative stress have interaction. We aimed to investigate whether inhibiting the proteasome has a preventive effect on DN through suppression of renal oxidative stress.

Main methods

Male Sprague–Dawley rats were randomly divided into three groups: a normal control (NC) group, a streptozotocin-induced DN model group, and a DN plus MG132 (10 μg/kg) treatment group.

Key findings

Increased 24-h urinary protein excretion rate (UPER) and renal pathological changes were all improved after MG132 administration. Furthermore, enhanced renal 26S proteasome activity and concentration in DN rats were effectively reduced after MG132 administration. Increased p47phox and nitrotyrosine (NT) expressions in kidneys of DN rats were decreased after MG132 treatment. Renal mRNA and protein expressions of NF-E2 related factor 2 (Nrf2) were up-regulated by MG132 in comparison to DN alone. Decreased renal mRNA expression of superoxide dismutase 1 (SOD1), catalase (CAT) and glutathione peroxidase (GPx) in DN rats was heightened after MG132 intervention. Depressed activities of renal SOD, CAT and GPx in DN rats were also improved by MG132 treatment. Increased renal nuclear factor κB (NF-κB) activity was inhibited after MG132 administration in DN rats at the end of 12 weeks.

Significance

Our present data suggest that inhibition of the proteasome by low-dose MG132 has a preventive effect on DN development and progression in rats through the up-regulation of antioxidant genes.

Introduction

Diabetic nephropathy (DN) is one of the major complications of diabetes mellitus and is the leading cause of end-stage renal disease, resulting in a high percentage of morbidity and mortality and involving substantial economic burden (Stafylas et al. 2007). However, to date, the pathogenesis of DN remains unclear. Oxidative stress has been suggested to be involved in the development and progression of DN. As the central cause of oxidative stress, overproduction of reactive oxygen species (ROS) can cause cellular abnormalities, reacting directly with nitric oxide to produce cytotoxic peroxynitrite and thus increasing reactivity to vasoconstrictors and modifying extracellular matrix proteins (Li and Shah, 2003, Lee et al., 2005b). ROS also damage cells indirectly by stimulating expression of transcriptional factors involved in inflammatory pathways, such as NF-κB (Kanwar et al. 2008). NADPH oxidase is a major source of ROS production and may be a key player in the regulation of cellular redox (Tomohiro et al., 2007, Thallas-Bonke et al., 2008).

An imbalance between ROS generation and antioxidant capacity favoring the former leads to oxidative stress and oxidative damage (Lim and Vaziri 2004). Oxidative damage in various tissues may be controlled or prevented by enzymic and nonenzymic antioxidant defense systems, which include reduced glutathione (GSH), SOD, CAT, GPx (Aksoy et al. 2003), and heme oxygenase 1(HO-1) (Farhangkhoee et al. 2003).

Recent reports suggest that inhibition of the proteasome with non-toxic concentrations of proteasome inhibitors up-regulates antioxidant systems to protect against oxidative stress-induced endothelial dysfunction (Lorenz et al. 2009). As the major non-lysosomal intracellular proteolytic system, the ubiquitin–proteasome system (UPS) is responsible for degrading approximately thousands of proteins, especially those of a short-lived and regulatory nature (Stangl and Stangl 2010). In addition to its role in degrading disused proteins, the UPS is involved in many cellular regulatory pathways, including transcriptional regulations (Skaug et al. 2009). Previous work has demonstrated that impaired renal function in hypercholesterolemic pigs is improved by treatment with a proteasome inhibitor (Chade et al. 2005).

The aims of our current study were to investigate whether proteasome inhibition provides renoprotection in an experimental model of DN and to study the underlying molecular mechanism involving the antioxidant effects of proteasome inhibition.

Section snippets

Animals

All animal experimental protocols were approved by the Animal Experiments Ethics Committee of the Third Military Medical University. Studies were performed in male Sprague–Dawley rats (Experimental Animal Center, Daping Hospital, Third Military Medical University, Chongqing, China), 40–50 days old, weighing 200–220 g. After a week of adaptive feeding, rats were randomly divided into a normal control group (NC, n = 24) and diabetic nephropathy group (DN, n = 48). NC rats were fed standard laboratory

Effect of MG132 on physical and biochemical parameters

As shown in Table 1, BG, KI, UPER, SCr and BUN of DN rats were significantly higher than in NC rats (all P < 0.05); BG, UPER, SCr and BUN were markedly decreased after MG132 administration for the indicated times (all P < 0.05); at the end of 4 and 8 weeks, MG132 significantly reduced KI (all P < 0.05).

Effect of MG132 on renal morphology of DN rats

At 4 weeks, glomerular and tubular lesions were not obvious; at 8 weeks, glomerular basement membrane thickening, focal mesangial cell proliferation, increased mesangial matrix, and mesangial broadening

Discussion

The results of the present study show that the induction of renal oxidative stress and inflammation in rats with STZ-induced DN was effectively suppressed after MG132 administration (10 μg/kg/day). Furthermore, we demonstrated that MG132 treatment significantly reduced kidney hypertrophy and glomerular mesangial cell proliferation, alleviated mesangial matrix accumulation, and decreased serum indices, UPER levels and KI. This is the first time for these data to provide the evidence that MG132

Conclusions

In the present study, we identified low-dose MG132 as a new intervention that effectively inhibits oxidative stress and the related inflammatory response of the kidneys and provides renoprotection via chronic, nontoxic proteasome inhibition in DN rats. Although the precise details should be explored in future studies, these studies provide a theoretical basis for further study of the clinical prevention and treatment of DN via proteasome inhibition.

Conflict of interest

There is no conflict of interest.

Acknowledgments

This work was supported by two grants from the National Nature Science Foundation of China: no. 30570763 to Dr. Bing Feng and no. 30900690 to Dr. Jiao Mu. We thank professors Zhou Shuwen, Guang Lixia and Xu Yin for technical and experimental support.

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    These two authors contributed equally to this work.

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