Swimming exercise protects against diabetic cardiomyopathy through suppression of FABP4-associated CTRP3 degradation

BACKGROUND Diabetic cardiomyopathy (DCM) is a major cardiovascular complication of type 2 diabetes mellitus (T2D) characterized by metabolic dysregulation, oxidative stress, chronic inflammation, and progressive cardiac dysfunction. Although swimming exercise has been recognized as an effective non-pharmacological intervention for DCM, the molecular mechanisms underlying its cardioprotective effects remain poorly understood. This study aimed to identify the key exercise-responsive molecular targets involved in DCM and elucidate the mechanisms by which swimming exercise attenuates diabetic cardiac injury. METHODS Bioinformatic analyses were performed using public transcriptomic datasets to identify hub genes associated with swimming exercise-mediated protection against DCM. A streptozotocin/high-fat diet-induced T2D mouse model was established and subjected to low- or high-intensity swimming exercise interventions. Cardiac function, histopathology, metabolic parameters, oxidative stress markers, and inflammatory cytokines were evaluated. Gain-of-function experiments using AAV9-mediated cardiac fatty acid-binding protein 4 (FABP4) overexpression and C1q/TNF-related protein 3 (CTRP3) mutant constructs were conducted in vivo and in vitro. Protein-protein interactions were investigated using co-immunoprecipitation, molecular docking, thermal shift assays, and ubiquitination analyses. RESULTS Bioinformatic screening identified FABP4 as the top-ranked exercise-responsive hub gene associated with metabolic pathways in DCM. Swimming exercise dose-dependently improved glucose homeostasis, insulin sensitivity, oxidative balance, systemic inflammation, and anxiety-like behaviors in diabetic mice. Concurrently, swimming exercise markedly alleviated myocardial fibrosis, cardiac dysfunction, and myocardial injury while suppressing cardiac FABP4 expression. FABP4 overexpression markedly attenuated the favorable cardiac and metabolic phenotypes observed in swimming-trained diabetic mice, resulting in impaired mitochondrial respiration and glycolysis, enhanced oxidative stress, exaggerated inflammatory responses, and aggravated cardiac remodeling. In vitro, FABP4 interacted with CTRP3 and promoted CTRP3 ubiquitination-associated proteasomal degradation. AICAR treatment weakened the FABP4-CTRP3 interaction and preserved CTRP3 protein stability in vitro. Furthermore, N63 of CTRP3 was identified as an important residue contributing to FABP4 interaction and CTRP3 protein stability. The N63A mutation reduced CTRP3 stability and attenuated AICAR-associated metabolic, antioxidative, and anti-inflammatory protection in vitro, while in vivo expression of CTRP3-N63A was associated with impaired cardiac protection during swimming intervention. CONCLUSIONS These findings identify FABP4 as an exercise-responsive regulator associated with diabetic cardiac injury and reveal a potential FABP4-CTRP3 protein-stability mechanism supported by cellular experiments and CTRP3 functional manipulation. Swimming exercise attenuates the development of diabetes-associated cardiac dysfunction and remodeling by suppressing FABP4, whereas the cellular mechanistic findings suggest that regulation of the FABP4-CTRP3 protein-stability axis may contribute to these cardioprotective effects. However, whether swimming exercise directly regulates endogenous myocardial CTRP3 stability in vivo remains to be established.