Skeletal muscle-specific deletion of lipoprotein lipase enhances insulin signaling in skeletal muscle but causes insulin resistance in liver and other tissues

OBJECTIVE—Skeletal muscle–specific LPL knockout mouse (SMLPL^−/−) were created to study the systemic impact of reduced lipoprotein lipid delivery in skeletal muscle on insulin sensitivity, body weight, and composition.RESEARCH DESIGN AND METHODS—Tissue-specific insulin sensitivity was assessed using a hyperinsulinemic-euglycemic clamp and 2-deoxyglucose uptake. Gene expression and insulin-signaling molecules were compared in skeletal muscle and liver of SMLPL^−/− and control mice.RESULTS—Nine-week-old SMLPL^−/− mice showed no differences in body weight, fat mass, or whole-body insulin sensitivity, but older SMLPL^−/− mice had greater weight gain and whole-body insulin resistance. High-fat diet feeding accelerated the development of obesity. In young SMLPL^−/− mice, insulin-stimulated glucose uptake was increased 58% in the skeletal muscle, but was reduced in white adipose tissue (WAT) and heart. Insulin action was also diminished in liver: 40% suppression of hepatic glucose production in SMLPL^−/− vs. 90% in control mice. Skeletal muscle triglyceride was 38% lower, and insulin-stimulated phosphorylated Akt (Ser473) was twofold greater in SMLPL^−/− mice without changes in IRS-1 tyrosine phosphorylation and phosphatidylinositol 3-kinase activity. Hepatic triglyceride and liver X receptor, carbohydrate response element–binding protein, and PEPCK mRNAs were unaffected in SMLPL^−/− mice, but peroxisome proliferator–activated receptor (PPAR)-γ coactivator-1α and interleukin-1β mRNAs were higher, and stearoyl–coenzyme A desaturase-1 and PPARγ mRNAs were reduced.CONCLUSIONS—LPL deletion in skeletal muscle reduces lipid storage and increases insulin signaling in skeletal muscle without changes in body composition. Moreover, lack of LPL in skeletal muscle results in insulin resistance in other key metabolic tissues and ultimately leads to obesity and systemic insulin resistance.Lipoprotein lipase (LPL) (European Commission no. 3.1.1.34) is a key enzyme in lipid metabolism and is described as a “gatekeeper” for its role in partitioning lipoprotein-derived free fatty acids (FFAs) between tissues. Once hydrolyzed, the lipoprotein-derived FFAs are available for uptake and use by extrahepatic tissues for either storage or oxidation. LPL is most abundant in heart, adipose tissue, and skeletal muscle (1,2). The importance of LPL in fuel partitioning and utilization is underscored by observations that tissue-specific perturbations in LPL activity result in dramatic shifts in body composition and lipid and glucose metabolism (3), particularly in heart and skeletal muscle.We and others previously showed that mice with muscle-specific lipoprotein lipase overexpression are insulin resistant (4,5). Insulin resistance developed selectively in muscle, while insulin sensitivity in the liver was not affected. Overexpression of LPL in the skeletal muscle also led to excessive intramyocellular lipid deposition, suggestive of the relationship between lipid storage and insulin sensitivity.To further investigate the systemic impact of skeletal muscle LPL (SMLPL) on lipoprotein-derived fatty acid partitioning between tissues and insulin sensitivity, we generated skeletal muscle–specific LPL knockout mice, denoted SMLPL^−/−. We hypothesized that SMLPL is an important interface through which lipid-derived signals are integrated to regulate insulin signaling and that SMLPL deletion would perturb the balance of fuel utilization not only in skeletal muscle but also in other insulin-sensitive tissues.