RESUMEN
Bcl2l2 encodes BCL-W, an antiapoptotic member of the BCL-2 family of proteins. Intercross of Bcl2l2 +/- mice on a mixed C57BL/6J, 129S5 background produces Bcl2l2 -/- animals with the expected frequency. In contrast, intercross of Bcl2l2 +/- mice on a congenic C57BL/6J background produces relatively few live-born Bcl2l2 -/- animals. Genetic modifiers alter the effect of a mutation. C57BL/6J mice (Mus musculus) have a mutant allele of nicotinamide nucleotide transhydrogenase (Nnt) that can act as a modifier. Loss of NNT decreases the concentration of reduced nicotinamide adenine dinucleotide phosphate within the mitochondrial matrix. Nicotinamide adenine dinucleotide phosphate is a cofactor for glutathione reductase, which regenerates reduced glutathione, an important antioxidant. Thus, loss of NNT activity is associated with increased mitochondrial oxidative damage and cellular stress. To determine whether loss of Bcl2l2 -/- mice on the C57BL/6J background was mediated by the Nnt mutation, we outcrossed Bcl2l2 congenic C57BL/6J (Nnt -/-) mice with the closely related C57BL/6JEiJ (Nnt +/+) strain to produce Bcl2l2 +/- ; Nnt +/+ and Bcl2l2 +/- ; Nnt -/- animals. Intercross of Bcl2l2 +/- ; Nnt +/+ mice produced Bcl2l2 -/- with the expected frequency, whereas intercross of Bcl2l2 +/- ; Nnt -/- animals did not. This finding indicates the C57BL/6J strain background, and possibly the Nnt mutation, modifies the Bcl2l2 mutant phenotype. This and previous reports highlight the importance of knowing the genetic composition of mouse strains used in research studies as well as the accurate reporting of mouse strains in the scientific literature.
RESUMEN
The C57BL/6J (B6/J) male mouse represents a standard for diet-induced obesity (DIO) and is unique in expressing a loss-of-function nicotinamide nucleotide transhydrogenase (Nnt) gene. This mutation was associated with a marked reduction in glucose-stimulated insulin secretion from B6/J islets in vitro and moderately impaired glucose clearance in vivo. To assess the contribution of this Nnt mutation, we compared DIO responsiveness of Nnt-mutant B6/J males to Nnt wild-type C57BL/6NJ (B6/NJ) males over a 14-week period of feeding a high-fat (60% of calories) diet. Initial mean body weights at 6 weeks did not distinguish the substrains and both substrains were DIO-sensitive. However, B6/J males outgained the B6/NJ males, with a significant 3 g higher mean body weight at 20 weeks accompanied by significant increases in both lean and fat mass. Mean nonfasting serum glucose over time was also significantly higher in B6/J males, as was impairment of glucose tolerance assessed at 8 and 20 weeks of age. Serum leptin, but not insulin, was significantly higher in B6/J males over time. Potential contributions of the wild-type Nnt gene were demonstrable on a lower fat diet (10% of calories) where a significantly greater weight gain over time by B6/NJ males was correlated with a significantly higher serum insulin. In conclusion, DIO developed in response to 60% fat feeding regardless of Nnt allele status. Contribution of the B6/J-unique Nnt mutation was most evident in response to 10% fat feeding that resulted in reduced serum insulin and weight gain compared to B6/NJ males.