Muscle Lipid Localization Relates to Insulin Sensitivity: Responses to Exercise and Weight Loss Interventions

Subcellular lipid localization in skeletal muscle associates with insulin sensitivity in humans, yet these lipid distributions do not substantially revert after 12 weeks of insulin-sensitizing lifestyle interventions. This suggests interventions may need to occur earlier, before prediabetes or type 2 diabetes develops, or that lipid localization responds rapidly to acute changes in energy balance and physical activity that may not be captured following typical weight loss or exercise training interventions. To address this gap, we assessed the effect of acute and chronic insulin-sensitizing interventions across a spectrum of metabolic health in three separate studies. Individuals with obesity and normal glucose tolerance (NGT, n= 35, 39.4±1.0 yrs, BMI 35.7±0.7) or prediabetes/type 2 diabetes (pre/T2D, n=34, 43.8±1.3 yrs, BMI 35.3±0.7) completed 12-week interventions (combined weight loss plus exercise, weight loss alone, exercise alone, or delayed control). Endurance-trained athletes (n=20, 27.3±1.2 yrs, BMI 22.1±0.4) performed 1.5 hours of acute exercise at 50% or 70% VO2max under fed and/or fasted conditions. Muscle biopsies obtained pre/post intervention or acute exercise were fractionated into sarcolemmal, mitochondrial/ER, cytosolic, and nuclear compartments and analyzed by targeted lipidomics. Triacylglycerols were inversely associated with insulin sensitivity across all compartments. Ceramides showed inverse associations in sarcolemmal, mitochondrial/ER, and nuclear fractions, but a positive association in the cytosol. In contrast, 1,2-DAGs were positively associated with insulin sensitivity in mitochondrial/ER, cytosolic, and nuclear compartments. Neither lifestyle interventions nor acute exercise substantially altered subcellular lipid distribution. Overall, subcellular lipid localization was strongly associated with insulin sensitivity yet changed inconsistently following acute and chronic interventions, regardless of metabolic status. These data suggest that more dramatic changes in weight and fitness, and/or interventions longer than 12 weeks may be required to modify muscle subcellular lipids linked to insulin resistance.