Most progressive glomerular diseases leading to endstage renal disease have increased extracellular matrix (ECM) within mesangial areas. Elucidation of the nature and the rate of ECM accumulation in normal and diseased states are prerequisites for understanding, and possibly interfering with, progressive glomerulosclerosis. This was the rationale to undertake detailed studies addressing these issues in normal subjects and patients with progressive glomerular diseases. Glomeruli represent a small fraction of the renal cortex and we have found that changes in their size and matrix synthesis are regulated independently of other cortical elements. Therefore, changes in whole kidney preparations do not accurately reflect those in glomeruli. For these reasons we developed a technique consisting of microdissection of glomeruli, in situ RT of mRNA, and PCR. To quantitate changes in type IV collagen mRNA expression, we developed a competitive PCR assay. The method has a level of sensitivity (0.01 to 0.1 attomole) sufficient to allow quantitation of the alpha-2IV collagen cDNA expressed in a fraction of a mouse glomerulus. This allowed us to begin studies of human glomerular diseases. We first examined nephrectomies performed for renal carcinoma, since nearly 50% of these patients have glomerulosclerosis. We found that alpha-2IV collagen cDNA was significantly elevated in patients with glomerulosclerosis. There was not a parallel increase in cell number, suggesting that the increment was due to upregulation of alpha-2IV collagen mRNA, rather than cellular proliferation. As we found in mice, glomerular alpha-2IV collagen cDNA level remained high, independently of the degree of sclerosis, even in patients who had extensive glomerular scarring. Satisfied that we had the appropriate tools to examine the pathogenesis of renal disease in humans, we started a multi-center collaboration to develop markers of progression. During this first phase we obtained either cDNA or isolated microdissected glomeruli from renal biopsies done for diagnostic purposes. The initial focus is on diabetes mellitus and IgA nephropathy. Our preliminary results indicate that the alpha-2/alpha-3 type IV collagen ration is equal to 1 in normal kidneys.
