A sensitized screen of N-ethyl-N-nitrosourea-mutagenized mice identifies dominant mutants predisposed to diabetic nephropathy

Diabetic nephropathy (DN) is a late diabetic complication that comprises progressively increasing albuminuria, declining GFR, and increased cardiovascular risk. Only a minority of patients with diabetes (25 to 40%) develop nephropathy, and there is evidence that heritable genetic factors predispose these "at-risk" individuals to DN. Comparing variability among inbred mouse strains with respect to a specific phenotype can model interhuman variability, and each strain represents a genetically homogeneous system with a defined risk for nephropathy. C57BL/6 mice, which are relatively resistant to DN, were mutagenized using N-ethyl-N-nitrosourea and screened for mutants that developed excess albuminuria on a sensitizing type 1 diabetic background contributed by the dominant Akita mutation in insulin-2 gene (Ins2^Akita). Two of 375 diabetic G1 founders were found to exhibit albumin excretion rates persistently 10-fold greater than albumin excretion rates in non-mutagenized Ins2^Akita controls. This aibuminuria trait was heritable and transmitted to approximately 50% of Ins2^Akita G2 and G3 progeny, consistent with a simple, dominantly inherited trait, but was never observed in nondiabetic offspring. During the course of 1 yr, albuminurie Ins2^Akita G2 and G3 progeny developed reduced inulin clearance with elevated blood urea nitrogen and plasma creatinine. Glomerular histology revealed mesangial expansion, and glomerate basement membrane thickening as determined by electron microscopy was enhanced in diabetic mutant kidneys. Hereditary albuminurie N-ethyl-N-nitrosourea-induced mutants were redesignated as Nphrp1 (nephropathyl) and Nphrp2 (nephropathy2) mice for two generated lines. These novel mutants provide new, robust mouse models of DN and should help to elucidate the underlying genetic basis of predisposition to DN.