Differential expression of nephrin in acquired human proteinuric diseases.

Background: The slit-diaphragm protein nephrin is an essential component of the glomerular filtration barrier. It is not clear whether renal injury in patients with acquired proteinuric diseases is associated with altered regulation of the nephrin gene or protein.

Methods: We examined expression patterns of nephrin protein and messenger RNA (mRNA) in renal biopsy specimens from patients with minimal lesion (n = 7), focal segmental glomerulosclerosis (FSGS; n = 14), or membranous nephropathy (MN; n = 7) and controls (n = 8) by immunohistochemistry, immunoelectron microscopy, in situ hybridization, and polymerase chain reaction (PCR) amplification of nephrin complementary DNA.

Results: In normal kidney, nephrin staining showed a diffuse interrupted linear pattern along the glomerular basement membrane (GBM). Nephrin staining in minimal lesion specimens showed a finely granular pattern along the GBM and was positive in cell bodies of visceral glomerular epithelial cells. Nephrin staining was most disrupted in FSGS specimens. Immunoelectron microscopy showed that nephrin-specific gold particles were almost absent in effaced foot processes in proteinuric patients. An in situ hybridization study showed significantly decreased nephrin mRNA-expressing cells in cases of FSGS and MN compared with controls. Reverse-transcription PCR showed significantly lower levels of nephrin mRNA in cases of FSGS and MN than controls, but no significant difference between minimal lesion cases and controls. Relative levels of glomerular nephrin mRNA correlated inversely with percentage of glomeruli with sclerosis in proteinuric diseases.

Conclusion: These results suggest that nephrin-expression patterns in proteinuric diseases are different according to the specific glomerular disease or severity of glomerular damage.