Most progressive glomerular diseases leading to ESRD have increased extracellular matrix within mesangial areas. Elucidation of the nature and the rate of ECM accumulation in normal and diseased states are prerequisites for the understanding and possibly interfering with progressive glomerulosclerosis. This was the rationale to undertake detailed studies addressing these issues in normal subjects and patients. Since glomeruli represent a small fraction of the renal cortex and since changes in their size and matrix synthesis are regulated independently of other cortical elements, changes in whole kidney preparations do not accurately reflect those in glomeruli. We developed a technique consisting of microdissection of glomeruli, in situ RT of mRNA into cDNA, and PCR. To quantitate small changes in collagen type IV mRNA expression, we developed a competitive PCR assay, which has a level of sensitivity (0.01 to 0.1 attomole) allowing quantitation of the alpha2IV collagen cDNA expressed in a fraction of a glomerulus. To see if this method applied to human diseases, we examined nephrectomies performed for renal carcinoma since a large proportion of these patients have glomerulosclerosis. We found that alpha2IV collagen cDNA was significantly elevated (3.8x) in 5 patients with glomerulosclerosis compared to 5 patients with normal glomeruli. The cDNA increase was not paralleled by cell number in the sclerotic glomeruli. We have started a collaboration with a multi-center group in order to examine either cDNA or isolated microdissected glomeruli obtained from biopsies done for diagnostic purposes in order to develop markers of progression in human diseases with a focus on diabetes.
