ULTRASTRUCTURAL AND FUNCTIONAL ANALYSES OF NEPHROPATHY IN CALMODULIN-INDUCED DIABETIC TRANSGENIC MICE

Background: Previous animal models of diabetic nephropathy have used d iabetic animals for which the underlying defect was either uncertain o r the diabetes was induced by potentially specific toxins. In this rep ort, we describe the renal abnormalities in a transgenic mouse model t hat develops early-onset diabetes due to overexpression of calmodulin in pancreatic beta cells. Methods: Renal tissues were collected from n ormal and transgenic mice at 112, 182, and 300 days. These were prepar ed for light microscopic observation, stained with polyethylenimine (f or anionic sites), or rendered acellular by detergent extraction prior to observation by transmission and scanning electron microscopy. Morp hometric analysis of glomerular basement membrane thickness was carrie d out by the ''orthogonal intercept'' method. Twelve-hour urine sample s of fed and fasting mice were collected for urine volume and glucose and protein analyses. Blood glucose, blood urea nitrogen, serum insuli n, and creatinine were determined in 60-90-day-old and 255-day-old mic e by established methods. Results: Morphometric analyses revealed age- related and transgene-related increases in glomerular basement membran e thickness. A 22% increase in transgenic diabetics over controls was seen at 112 days of age that developed to increases of 43% and 37% at 182 and 300 days of age, respectively. Mesangial matrix area was also increased markedly in transgenic mice. Surprisingly, even in the oldes t diabetic mice, there was no reduction in anionic sites. Moreover, de spite an eightfold increase in urine volume, these mice did not become significantly proteinuric. Conclusions: These results indicate that p roteinuria of diabetes may be delayed or prevented by maintenance of a normal complement of glomerular basement membrane anionic sites. They also demonstrate that transgenic mice can provide a valuble model for discriminating between different aspects of diabetic nephropathy. (C) 1997 Wiley-Liss, Inc.