β-catenin and its alteration in an experimental model of diabetic nephropathy.

Abstract

INTRODUCTION: The aim of our study was to determine whether beta-catenin, a

subunit of the cadherin protein complex in the podocyte cytoskeleton, would be

altered by hyperglycemia and advanced glycation endproducts (AGE) in glomerular

epithelial cells and podocytes in vitro. MATERIALS AND METHODS: Rat glomerular

epithelial cells and mouse podocytes on bovine serum albumin-coated or AGE-coated

plates with normal (5 mM) and high (30 mM) glucose doses were cultured and

examined for the distribution of bet;-catenin using confocal microscopy and

changes in beta-catenin production by western blotting and reverse

transcription-polymerase chain reaction, at 48 hours, 4 weeks, and 10 weeks.

RESULTS: Immunofluorescent staining revealed that beta-catenin and alpha-actinin

were colocalized around the cell membrane, and that beta-catenin staining was

most intense along the capillary loops, but moved internally toward the inner

actin filaments in the presence of AGE and hyperglycemia. In western blot

analysis, AGE and hyperglycemia significantly decreased the amount of

beta-catenin proteins by 31.5% at 48 hours, compared with normal control

conditions (P = .01). The expression for beta-catenin mRNA in AGE and

hyperglycemia was also decreased by 59.6% at 24 hours, compared with that of

normal glucose conditions (P = .01). No significant changes were seen in the

osmotic controls. CONCLUSIONS: Our results suggest that AGE and hyperglycemia may

induce the cytoplasmic redistribution of beta-catenin and inhibit the production

of beta-catenin at the transcriptional and posttranslational levels, which may

result in the development of kidney dysfunction in diabetic conditions.