Interaction between non-enzymatic glycation and the polyol pathway on mesangial cell gene expression in an aldose reductase transgenic mouse model

Abstract

BACKGROUND AND AIMS: Diabetic nephropathy is a leading cause of end-stage renal disease. The aldose reductase (AR) gene, which codes for the first and rate-limiting enzyme in the polyol pathway, has been implicated in the etiology of diabetic nephropathy, based on genetic association studies and findings from animals treated with AR inhibitors. However, the exact role of AR in the development of diabetic nephropathy and its interaction with other pathogenetic pathways, such as non-enzymatic glycation, remain controversial. In this study, we investigated the effects of increased AR gene expression on pathogenetic changes that could lead to diabetic nephropathy, in a transgenic murine model. MATERIALS AND METHODS: Transgenic mouse lines expressing the human AR (hAR) gene in kidney mesangial cells were established, using a construct that contained the type A scavenger receptor promoter. The interaction between AR and advanced glycation end-products (AGEs) was examined in primary cultures of mesangial cells derived from hAR transgenic and wild type mice, with regard to changes in AR activity, transforming growth factor-β1 (TGF-β1) and type IV collagen gene expression, in response to incubation with AGE modified BSA (AGEBSA). RESULTS: hAR mRNA expression could be detected by Northern blot analysis in the kidney glomeruli of transgenic mice. hAR mRNA and protein expression were also found in primary cultures of transgenic mesangial cells, as assessed by RT-PCR and Western blot analyses. Enhanced AR activity was seen in both transgenic and wild type mesangial cells when treated with AGE-BSA. This increase was significantly higher (p<0.05) in the transgenic mesangial cells. The rise in AR activity in the presence of AGE-BSA was accompanied by increases in TGF-β1 and type IV collagen transcripts in mesangial cells, which reached statistical significance only in transgenic mesangial cells (p<0.01) and was abolished by the addition of an AR inhibitor zopolrestat (p<0.05). CONCLUSION: These results suggested that the AR gene was involved in the increased expression of TGF-β1 and type IV collagen observed in the transgenic mesangial cells in vitro. Increased AR gene expression might contribute to the mesangial cell proliferation and matrix protein production in diabetic nephropathy, in part through an interaction with AGEs. Supported by a grant from the Hong Kong Research Grant Council (HKU7270/98M).