- ABSTRACT The mechanisms underlying diabetes remain unresolved. The Cohen diabetic rat represents a model of diet-induced diabetes, in which the disease is induced after exposure to a diabetogenic diet (DD) in the diabetes-sensitive (CDs/y) but not in the -resistant (CDr/y) strain. Diet imposes a metabolic strain that leads to diabetes in the appropriate genetic background. We previously identified, through whole-genome linkage analysis, a diabetes-related quantitative trait locus on rat chromosome 4 (RNO4), which incorporates NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 ( Ndufa4 ), a nuclear gene that affects mitochondrial function. Here, we sequenced the gene and found a major deletion in CDs/y that leads to lack of expression of the NDUFA4 protein that has been reported to be involved in the activities of mitochondrial complexes I and IV. In the absence of NDUFA4 in the diabetic CDs/y on DD, complex I activity is reduced in comparison to that in nondiabetic CDs/y on regular diet and CDr/y on either diet; complex IV activity is reduced in both strains provided DD, and thus as a result of diet and unrelated to the gene mutation. ATP fails to increase in diabetic CDs/y in response to DD, in comparison to nondiabetic CDr/y on DD. Plasma malondialdehyde levels are elevated in CDs/y on DD, whereas SOD1 and SOD2 levels fail to increase, indicating increased oxidative stress and inability of the pancreas to generate an appropriate antioxidative stress response. These findings suggest that the Ndufa4 mutation in CDs/y on DD is directly associated with mitochondrial dysfunction, which we attribute to the lack of expression of NDUFA4 and to diet, and which prevents the anticipated increase in ATP production. The resulting enhanced oxidative stress impairs the ability of the pancreas to secrete insulin, leading to the development of diabetes. This is the first demonstration of an inherited mutation in a nuclear gene that adversely affects mitochondrial function and promotes diet-induced diabetes.