L-carnitine alleviates cardiac microvascular dysfunction in diabetic cardiomyopathy by enhancing PINK1-Parkin-dependent mitophagy through the CPT1a-PHB2-PARL pathways

Abstract

Aim: To explore the beneficial effects of L-carnitine on cardiac microvascular dysfunction in diabetic cardiomyopathy from the perspectives of mitophagy and mitochondrial integrity. Methods: Male db/db and db/m mice were randomly assigned to groups and were treated with L-carnitine or a solvent for 24 weeks. Endothelium-specific PARL overexpression was attained via adeno-associated virus serotype 9 (AAV9) transfection. Adenovirus (ADV) vectors overexpressing wild-type CPT1a, mutant CPT1a, or PARL were transfected into endothelial cells exposed to high glucose and free fatty acid (HG/FFA) injury. Cardiac microvascular function, mitophagy, and mitochondrial function were analyzed by immunofluorescence and transmission electron microscopy. Protein expression and interactions were assessed by western blotting and immunoprecipitation. Results: L-carnitine treatment enhanced microvascular perfusion, reinforced endothelial barrier function, repressed the endothelial inflammatory response, and maintained the microvascular structure in db/db mice. Further results demonstrated that PINK1-Parkin-dependent mitophagy was suppressed in endothelial cells suffering from diabetic injury, and these effects were largely alleviated by L-carnitine through the inhibition of PARL detachment from PHB2. Moreover, CPT1a modulated the PHB2-PARL interaction by directly binding to PHB2. The increase in CPT1a activity induced by L-carnitine or amino acid mutation (M593S) enhanced the PHB2-PARL interaction, thereby improving mitophagy and mitochondrial function. In contrast, PARL overexpression inhibited mitophagy and abolished all the beneficial effects of L-carnitine on mitochondrial integrity and cardiac microvascular function. Conclusion: L-carnitine treatment enhanced PINK1-Parkin-dependent mitophagy by maintaining the PHB2-PARL interaction via CPT1a, thereby reversing mitochondrial dysfunction and cardiac microvascular injury in diabetic cardiomyopathy.