NPAS2 attenuates diabetic cardiomyopathy by preserving pyruvate dehydrogenase activity and mitochondrial metabolic homeostasis

Background Diabetic cardiomyopathy (DCM) is a serious cardiac complication of diabetes, characterized by myocardial metabolic dysregulation, mitochondrial dysfunction, and structural remodeling. Disruption of circadian clock genes has been implicated in metabolic diseases, yet the role of neuronal PAS domain protein 2 (NPAS2), a core circadian regulator, in DCM remains poorly understood. Methods NPAS2 expression and circadian rhythmicity were assessed in the myocardium of T2DM and db/db mice. Cardiac-specific Npas2 knockout ( Npas2 cko ) mice were subjected to high-fat diet combined with streptozotocin (HFD + STZ) to model DCM and evaluate cardiac function, remodeling, and metabolic profiles. H9c2 cardiomyocytes were used for loss-of-function and gain-of-function experiments under high glucose/high fat (HGHF) conditions, and rescue experiments targeting pyruvate dehydrogenase (PDH) were performed to establish downstream mechanisms. Finally, adeno-associated virus serotype 9 (AAV9) mediated NPAS2 overexpression was delivered in vivo to evaluate its therapeutic potential. Results Myocardial NPAS2 expression was significantly reduced and its circadian oscillations were disrupted in diabetic mice. Cardiomyocyte-specific Npas2 deletion exacerbated HFD + STZ-induced cardiac dysfunction, hypertrophy, fibrosis, and lipid accumulation. In H9c2 cells, NPAS2 knockdown impaired mitochondrial respiration, increased apoptosis, elevated triglyceride and free fatty acid contents, and reduced PDH activity. Conversely, NPAS2 overexpression reversed these detrimental effects under HGHF conditions. Rescue experiments demonstrated that PDH overexpression mitigated the damage caused by NPAS2 knockdown, whereas PDH silencing abolished the protective effects of NPAS2 overexpression. In vivo , AAV9-mediated NPAS2 overexpression significantly improved cardiac function, attenuated hypertrophy and fibrosis, and restored lipid and glucose homeostasis in diabetic WT and Npas2 cko mice. Conclusion NPAS2 protects the heart against diabetic cardiomyopathy by maintaining PDH-dependent mitochondrial oxidative metabolism and metabolic homeostasis, representing a promising therapeutic target for DCM.