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

Abstract

AbstractAimTo explore the beneficial effects of L‐carnitine on cardiac microvascular dysfunction in diabetic cardiomyopathy from the perspectives of mitophagy and mitochondrial integrity.MethodsMale 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.ResultsL‐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.ConclusionL‐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.