Combined Weight Loss and Exercise Training Alters Skeletal Muscle Subcellular Lipid Localization and Intermuscular Adipose Tissue Cellular Composition

Subcellular lipid accumulation and intermuscular adipose tissue (IMAT) accumulation are associated with insulin resistance, but the impact of combined weight loss and exercise training on localization of lipids and IMAT cellular composition is not known. Twenty-one adults with obesity (18 female and 3 male; 46 ± 2 years; 35.0 ± 0.9 kg/m2) completed a 3-month supervised weight loss and exercise training intervention. Insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp, and basal and insulin-stimulated vastus lateralis biopsies were collected pre- and postintervention. After the intervention, body weight and body fat decreased (11 ± 1% and 9 ± 1%, respectively), while VO2 peak and insulin sensitivity increased (14 ± 3% and 68 ± 14%, respectively). Lipidomics revealed reduced sarcolemmal and nuclear triglycerides, with unchanged whole-muscle triglycerides. Whole-muscle diacylglycerols increased because of increased nuclear 1,2-diacylglycerols without PKCε, PKCθ, or PKCδ activation. Whole-muscle sphingolipid levels increased because of cytosolic accumulation. Single-nuclei RNA sequencing showed altered IMAT cellular composition, including increased fibro-adipogenic progenitors, vascular cells, and macrophages, and decreased preadipocytes. Bulk muscle RNA sequencing indicated upregulation of genes related to muscle remodeling and cellular respiration, and there were changes in the relationship between nuclear diacylglycerols and gene expression postintervention. These findings dissociate improvements in insulin sensitivity from total muscle diacylglycerol and sphingolipid levels and highlight roles for subcellular lipid redistribution and IMAT remodeling in insulin sensitization. Article Highlights Evaluation of subcellular fractionated muscle revealed decreases in sarcolemmal and nuclear triglycerides and increases in nuclear diacylglycerols and cytosolic sphingolipids postintervention. Weight loss revealed alteration in the cellular composition of intermuscular adipose tissue and upregulation of genes related to muscle remodeling and cellular respiration. These findings dissociate improvements in insulin sensitivity from total muscle 1,2-diacylglycerol and sphingolipid levels and highlight roles of intermuscular adipose tissue remodeling for enhanced insulin sensitivity.