Elevated metabolic rate and skeletal muscle oxidative metabolism contribute to the reduced susceptibility of NF-B p50 null mice to obesity

Mice with a deletion of the p50 subunit of the proinflammatory nuclear factor kappa B pathway (NF-B p50) have reduced weight compared to wild-type control mice. However, the physiological underpinning of this phenotype remains unknown. This study addressed this issue. Compared to littermate controls, lean male p50 null mice (p50(-/-)) had an increased metabolic rate (similar to 20%) that was associated with increased skeletal muscle (SkM, similar to 35%), but not liver, oxidative metabolism. These metabolic alterations were accompanied by decreases in adiposity, and tissue and plasma triglyceride levels (all similar to 30%). Notably, there was a marked decrease in skeletal muscle, but not liver, DGAT2 gene expression (similar to 70%), but a surprising reduction in muscle PPAR and CPT1 (both similar to 20%) gene expression. Exposure to a high-fat diet accentuated the diminished adiposity of p50(-/-) mice despite elevated caloric intake, whereas plasma triglycerides and free fatty acids (both similar to 30%), and liver (similar to 40%) and SkM (similar to 50%) triglyceride accumulation were again reduced compared to WT. Although SkM cytokine expression (IL-6 and TNF, each similar to 100%) were increased in p50(-/-) mice, neither cytokine acutely increased SkM oxidative metabolism. We conclude that the reduced susceptibility to diet-induced obesity and dyslipidemia in p50(-/-) mice results from an increase in metabolic rate, which is associated with elevated skeletal muscle oxidative metabolism and decreased DGAT2 expression.