Proteomic Analysis of Whole Glomeruli in Patients with IgA Nephropathy Using Microsieving

Abstract

Background: To promote understanding of immunoglobulin A nephropathy (IgAN) pathophysiology, we tried to elucidate glomerular protein profiles in IgAN, using microsieving that we established recently to isolate glomeruli from renal biopsy samples and proteomic approaches. Methods: Glomeruli were isolated from renal biopsy samples of patients with IgAN (n = 5) and with minimal change nephrotic syndrome (MCNS; n = 5) using microsieving. Proteins extracted from the isolated glomeruli were separated by 2-dimensional differential gel electrophoresis (2D-DIGE). Proteins with different amounts between the two groups were identified by mass spectrometry. One of the identified proteins, α-actinin-4 (ACTN4), was further analyzed by Western blotting, RT-polymerase chain reaction (PCR), and immunohistochemistry. Results: By 2D-DIGE, 72 out of the detected 1,170 protein spots showed significantly different intensity between the two groups (p < 0.05). Thirty-four out of the 72 protein spots showed more than 1.5-fold or less than 1/1.5-fold intensity, out of which 16 protein spots were successfully identified. No microbial protein was identified. ACTN4 molecules with a low molecular weight of approximately 77 kDa were found to increase in the IgAN group. Lack of an N-terminal part of ACTN4 was demonstrated by Western blotting. No defect of mRNA for ACTN4 was evidenced by RT-PCR. Predominant existence of ACTN4 in capillary walls of glomeruli of IgAN patients was demonstrated by immunohistochemistry in glomerular sections of patients with IgAN. Conclusion: Use of microsieving enabled us to biochemically analyze glomerular proteins in renal biopsy samples from patients with glomerular diseases. With this method, we demonstrated skewed glomerular protein profiles in IgAN.