Static exercise improves skeletal muscle insulin resistance and is associated with Piezo1-CTTN remodeling in T2DM mice

Type 2 diabetes mellitus (T2DM) is characterized by skeletal muscle insulin resistance and impaired postprandial glucose disposal. Static exercise (SE), an isometric loading paradigm that generates sustained mechanical tension with minimal joint displacement, may engage mechanotransductive pathways in skeletal muscle. Using an integrative framework combining systemic phenotyping, histological and transcriptomic profiling, and targeted molecular validation, this study investigated whether SE improves insulin resistance in high-fat diet/streptozotocin-induced T2DM mice and whether these effects are associated with Piezo1-cortactin (CTTN)-related mechanotransduction, IRS-1/AKT signaling, and GLUT4 sarcolemmal localization. Male C57BL/6J mice were assigned to control, diabetic model, metformin, aerobic exercise, or static exercise groups for an 8-week intervention. Systemic metabolic phenotyping, skeletal muscle histology and ultrastructure, exploratory RNA-seq, immunofluorescence/immunohistochemistry, RT-qPCR, and Western blotting were performed. SE reduced fasting and random blood glucose, improved glucose tolerance and insulin sensitivity, and decreased fasting insulin and homeostatic model assessment of insulin resistance (HOMA-IR) compared with diabetic model mice. These metabolic benefits were accompanied by improved serum lipid profiles, increased myofiber cross-sectional area, reduced collagen deposition, preserved glycogen storage, and alleviated mitochondrial ultrastructural damage. Exploratory RNA-sequencing and pathway-level bioinformatic analysis (Gene Ontology [GO], Kyoto Encyclopedia of Genes and Genomes [KEGG], and Reactome enrichment analyses) suggested partial reversal of diabetes-associated transcriptomic alterations after SE, highlighting candidate mechanosensitive and metabolic pathways for downstream validation. Immunofluorescence showed enhanced sarcolemmal Piezo1 and CTTN signals and increased Piezo1/CTTN/WGA co-localization. RT-qPCR and western blot analyses showed restoration of Irs1 , Akt2 , Cttn , and Slc2a4 expression, increased IRS-1 and Akt phosphorylation, and elevated CTTN and total GLUT4 protein levels. In the additional validation set, SE restored Piezo1 protein abundance and increased GLUT4 abundance in the membrane-enriched fraction relative to untreated diabetic muscle. Immunohistochemistry showed stronger peri-membrane GLUT4 staining after SE than in untreated diabetic mice. SE improved systemic metabolism, skeletal muscle structural remodeling, and insulin signaling and was associated with increased GLUT4 membrane enrichment together with peri-membrane staining consistent with enhanced sarcolemmal localization in T2DM mice. These changes were accompanied by Piezo1- and CTTN-associated mechanotransductive remodeling. The findings support SE as a low-impact exercise paradigm while identifying a candidate mechanistic framework that requires direct causal validation.