Quantification of platelet-derived growth factor A, factor B and receptor β in human renal biopsy tissue using competitive reverse transcriptase polymecase chain reaction:: comparison between immunoglobulin A nephropathy and thin membrane nephropathy

Platelet-derived growth factor (PDGF) is a pleiotropic cytokine synthesized by various resident renal cells and infiltrating cells. Its best-studied role in the kidney is in the mediation of glomerular mesangial cell proliferation. The relationship between expression of PDGFA, PDGFB and the receptor beta (PDGFR beta) in human renal biopsies of immunoglobulin A nephropathy (IgAN), a disease characterized by mesangial cell proliferation, and thin membrane nephropathy (TMN), a non-proliferative glomerulopathy, was studied. Using competitive reverse transcriptase-polymerase chain reaction (RT-PCR), the quantity of mRNA molecules of each growth factor and the receptor was determined in renal biopsies from 20 patients with IgAN and 16 with TMN. In addition, eight nephrectomy samples with paired cortical and medullary samples were studied. There was no significant difference between the disease groups for PDGFA (TMN, 1409 +/- 475 copy number/microgram RNA; IgAN, 691 +/- 133, P = 0.35), PDGFB (TMN, 2280 +/- 467; IgAN, 1465 +/- 197, P = 0.10) or PDGFR beta (TMN, 1387 +/- 273; IgAN, 1402 +/- 344, P = 0.68). Analysis of nephrectomy samples showed higher constitutive expression of PDGFA and PDFGB in the medulla as compared with the cortex. However, further analysis of cortical samples in the IgAN group again failed to show a significant difference compared with TMN. We conclude that whole tissue analysis may have masked upregulation at glomerular level although it should reflect mRNA expression in the tubulointerstitial compartment.