KSR2 is an essential regulator of AMP kinase, energy expenditure, and insulin sensitivity.

Kinase suppressors of Ras 1 and 2 (KSR1 and KSR2) function as molecular scaffolds to potently regulate the MAP kinases ERK1/2 and affect multiple cell fates. Here we show that KSR2 interacts with and modulates the activity of AMPK. KSR2 regulates AMPK-dependent glucose uptake and fatty acid oxidation in mouse embryonic fibroblasts and glycolysis in a neuronal cell line. Disruption of KSR2 in vivo impairs AMPK-regulated processes affecting fatty acid oxidation and thermogenesis to cause obesity. Despite their increased adiposity, ksr2(-/-) mice are hypophagic and hyperactive but expend less energy than wild-type mice. In addition, hyperinsulinemic-euglycemic clamp studies reveal that ksr2(-/-) mice are profoundly insulin resistant. The expression of genes mediating oxidative phosphorylation is also downregulated in the adipose tissue of ksr2(-/-) mice. These data demonstrate that ksr2(-/-) mice are highly efficient in conserving energy, revealing a novel role for KSR2 in AMPK-mediated regulation of energy metabolism.

Simultaneous deletion of ghrelin and its receptor increases motor activity and energy expenditure.

Administration of chemically synthesized ghrelin (Ghr) peptide has been shown to increase food intake and body adiposity in most species. However, the biological role of endogenous Ghr in the molecular control of energy metabolism is far less understood. Mice deficient for either Ghr or its receptor (the growth hormone secretagogue receptor, GHS-R1a) seem to exhibit enhanced protection against high-fat diet-induced obesity but do not show a substantial metabolic phenotype on a standard diet. Here we present the first mouse mutant lacking both Ghr and the Ghr receptor. We demonstrate that simultaneous genetic disruption of both genes of the Ghr system leads to an enhanced energy metabolism phenotype. Ghr/Ghr receptor double knockout (dKO) mice exhibit decreased body weight, increased energy expenditure, and increased motor activity on a standard diet without exposure to a high caloric environment. Mice on the same genetic background lacking either the Ghr or the Ghr receptor gene did not exhibit such a phenotype on standard chow, thereby confirming earlier reports. No differences in food intake, meal pattern, or lean mass were observed between dKO, Ghr-deficient, Ghr receptor-deficient, and wild-type (WT) control mice. Only dKO showed a slight decrease in body length. In summary, simultaneous deletion of Ghr and its receptor enhances the metabolic phenotype of single gene-deficient mice compared with WT mice, possibly suggesting the existence of additional, as of yet unknown, molecular components of the endogenous Ghr system.