Proteome analysis of laser microdissected glomeruli from formalin-fixed paraffin-embedded kidneys of autopsies of diabetic patients: nephronectin is associated with the development of diabetic glomerulosclerosis.

To date, little proteomic information has been available from the glomeruli of diabetic patients, possibly due to the clinical limitations of renal biopsy in diabetic patients and insufficient quantities of such specimens for proteome analysis. The purpose of the present study was to identify altered protein expression profiles in diabetic glomeruli using formalin-fixed paraffin-embedded (FFPE) kidney tissues from diabetic patients. Glomeruli were laser microdissected from FFPE autopsy kidney tissues from 10 patients with diabetic nephropathy and 10 non-diabetic control patients and underwent proteome analysis using QSTAR Elite liquid chromatography with tandem mass spectrometry and iTRAQ technology. Immunohistochemical analysis was performed on 93 autopsy samples from diabetic patients with and without nephropathy (n = 45 and n = 48, respectively). Thirty-one renal and urological disease-related proteins displayed a differential abundance in glomerular samples from patients with diabetic nephropathy compared with non-diabetic control patients. Among them, we found that nephronectin, which functions in the assembly of extracellular matrix, showed clearly positive immunoreactivity in diabetic glomeruli. The numerical fraction of nephronectin-positive glomerular cross sections was increased significantly in diabetic patients with nephropathy compared to those without nephropathy (32.1 ± 31.5 versus 4.14 ± 5.65%, P < 0.0001). Furthermore, there was a significant positive correlation between this numerical fraction of nephronectin-positive glomerular cross sections and the glomerular sclerosis index (ρ = 0.881, P < 0.0001, n = 93). The present study demonstrated, for the first time, that nephronectin may be associated with the development of diabetic glomerulosclerosis and that proteome analysis with FFPE kidney tissues from diabetic patients with nephropathy is useful in understanding diabetic nephropathy.