Comparing the independent effects of weight loss or exercise training on skeletal muscle lipid localization and insulin sensitivity in humans

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Localized subcellular muscle lipid accumulation associates with insulin resistance, but independent effects of weight loss or exercise training are unknown. Forty-six men and women with obesity completed 12-week weight loss only, endurance exercise training only without weight loss, or delayed control interventions. Following weight loss, body weight decreased 10% along with a 42% increase in insulin sensitivity. After exercise training, VO₂peak increased 9% along with a 23% increase in insulin sensitivity. Whole muscle triacylglycerols (TAGs) increased in the control group, while mitochondrial/ER TAG decreased after weight loss and cytosolic TAGs increased after exercise training. Exercise training increased whole muscle total and 1,2-diacylglycerols (1,2-DAGs) through enhanced cytosolic storage. Total mitochondrial DAGs decreased after weight loss yet increased following exercise training and control. Exercise training increased cytosolic storage of most sphingolipids. Differential gene expression analysis revealed exercise increased mitochondrial function, whereas weight loss reduced inflammation and immune signaling. Only exercise training prevented the inhibition of mitochondrial respiration following exogenous administration of ceramides and di-C18:0-DAG. These data reveal weight loss and exercise training increase cytosolic storage of sphingolipids, weight loss decreases mitochondrial/ER TAG accumulation, and exercise training increases mitochondrial/ER and cytosolic DAGs, suggesting changes in specific subcellular lipid localization may impact muscle insulin sensitization.

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