Proteinuria and the expression of the podocyte slit diaphragm protein, nephrin, in diabetic nephropathy: effects of angiotensin converting enzyme inhibition
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Aims/hypothesis. Proteinuria, reflecting increased glomerular permeability to macromolecules is a characteristic feature of diabetic nephropathy. Nephrin, a 1241-residue transmembrane protein is a key component of the podocyte slit pore membrane and a major contributor of the glomerular filtration barrier. We investigated the expression of nephrin in human kidney tissue from patients with diabetic nephropathy to elucidate its relationship with proteinuria and the effects of anti-proteinuric therapy with angiotensin converting enzyme inhibition.
Methods. Renal biopsies were examined from 14 patients with Type II (non-insulin-dependent) diabetes mellitus and proteinuria who had been randomised to receive treatment with the ACE inhibitor, perindopril (4 mg/day) or placebo for the preceding 2 years. These specimens were compared with control human tissue sections, obtained from areas of normal renal cortex following nephrectomy for malignancy. Proteinuria was measured, specimens were examined histologically for injury and the expression of nephrin messenger RNA was assessed by quantitative in situ hybridisation.
Results. Glomeruli from placebo-treated patients with diabetic nephropathy, showed a 62% reduction in nephrin expression compared with control subjects (p=0.0003). In contrast, nephrin RNA in glomeruli from perindopril treated patients was similar to that in the non-diabetic control group. In both placebo and perindopril treated patients, a close inverse correlation was noted between the magnitude of nephrin gene expression and the degree of proteinuria (placebo: r=0.86, p=0.013, perindopril: r=0.91, p=0.004).
Conclusion/interpretation. Modulation in nephrin expression is related to the extent of proteinuria in diabetic nephropathy. These changes define, at a molecular level alterations in the glomerulus that occur in relation to proteinuria in diabetes and the effects of anti-proteinuric treatment with ACE inhibition.