This project employs morphometric methods to evaluate kidney biopsy samples obtained under Project # Z01 DK 69062. One hundred twenty diabetic Pima Indians who participated in a randomized double-blinded, placebo-controlled clinical trial to test the renoprotective efficacy of the angiotensin receptor blocker losartan underwent percutaneous kidney biopsy. Tissue specimens from these biopsies are processed in the lab of Dr. Michael Mauer at the University of Minnesota. Digitized images of individual glomeruli are compiled to create photomontages of individual glomeruli and the montage is calibrated to give precise measurements of glomerular structure. The cell nuclei identified in the montage are numbered and labeled according to their cell type (endothelial, mesangial or podocyte) and measurements are performed to determine the average number of podocytes per glomerulus, using the method of Weibel. The volume fraction of podocytes within the glomerulus is determined by multiplying the average glomerular volume by the numerical volume density of the podocytes. Total filtration surface area is computed by estimating the total number of functioning glomeruli and multiplying it by the average filtration surface for each glomerulus measured. Hydraulic permeability of the glomerular capillary is calculated from measurements of filtration slit frequency and basement membrane thickness using the ultrastructural model of Drumond and Dean, and the single nephron ultrafiltration coefficient is computed. Previous work by our group suggests that podocyte loss is the principal structural change responsible for functional progression, characterized by increasing albuminuria and declining glomerular filtration rate. In the past year, we completed morphometric measurements from 10 normal control subjects and continued measurements on 34 additional subjects, bringing the total to 96 subjects completed to date. We also completed a manuscript describing structural and functional correlations in the first 40 sugjects. We found that increasing podocyte detachment correlates with increasing albuminuria and decreasing endothelial fenestration correlates with decreasing glomerular filtration rate. We presented this work at the American Society of Nephroloty meeting in 2010. In the coming year, we will continue making morphometric measurements on additional specimens as they become available. Finally, our morphometric data will also be combined with data generated from gene expression studies performed on the same tissue specimens to better understand how cellular processes lead to structural and functional changes. The combination of structural, functional, and genetic studies may yield new insights into how diabetic nephropathy progresses, demonstrate how angiotensin blockers slow progression, and suggest novel therapies for diabetic kidney disease.
