Long-Term Endurance Exercise Confers Cardioprotection against Metabolic Distress in Obese Type 2 Diabetic Female Mice without Bodyweight Loss

Introduction: Endurance exercise (EXE) has been recognized as a cardioprotective strategy against metabolic diseases, including obesity and type 2 diabetes. However, the precise molecular mechanisms remain incompletely understood, especially in female populations. This study investigates the molecular metabolic signaling nexus in a female mouse model of obese type 2 diabetes (OT2D) induced by a high-fat diet (HFD) and a single dose of streptozotocin (STZ). Methods: Female mice (n=31) were assigned into three groups: a normal diet control (CON, n=11), HFD+STZ (n=11), and HFD+STZ + a 15-week treadmill exercise (HFD+STZ+EXE, n=11). Left ventricles were collected 90 minutes after the last EXE session for analyzing key molecular signaling pathways, mitochondrial function, autophagy/mitophagy, and apoptosis. Results: EXE significantly reduced hyperglycemia and cell death, independent of body weight changes and enhanced cardiac insulin signaling (IR β , PI3K, and AKT) and restored GLUT4 levels. Also, EXE increased protein expression of lipolysis-related proteins (p-PKA, ATGL, and ABHD5) and beta-oxidation-related proteins (ACADVL and HADHSC). Intriguingly, this coincided with a remarkable increase in intramyocardial lipid content (myocardial steatosis) concomitant with de novo lipogenesis (ACSS2, reduced p-ACC via PP2A activation, DGAT upregulation). Despite myocardial steatosis, EXE restored OT2D-induced mitochondrial respiratory dysfunction by downregulating uncoupling protein 3 (UCP3). Moreover, EXE-induced cardioprotection was associated with improved autophagy/mitophagy; The mitophagy was linked to the restoration of the mitochondrial fission protein DRP1. Conclusions: These findings demonstrate that weight loss is not a prerequisite for EXE-induced cardioprotection in OT2D females. The benefits arise from a multifaceted adaptive network involving improved metabolic signaling, mitochondrial function, and cellular quality control.