Targeting Mitochondrial Complex I Protects Against Palmitic Acid-Induced Endothelial Dysfunction.

BACKGROUND: Endothelial dysfunction induced by elevated free fatty acids is a critical initiating event in diabetic macrovascular complications. While mitochondrial reactive oxygen species (mtROS) are key mediators of this lipotoxic injury, the specific contribution of mitochondrial Complex I dynamics and its associated redox regulation remains to be fully elucidated. METHODS: We investigated the therapeutic potential of targeting mitochondrial Complex I in lipotoxicity-induced endothelial injury. Using rotenone (a Complex I inhibitor) and NDUFS4 [NADH Dehydrogenase (Ubiquinone) Fe-S Protein 4]-targeting siRNA, we performed in vitro interventions in palmitic acid-treated human aortic endothelial cells and in vivo studies in high-fat diet (HFD)-fed mice. RESULTS: Palmitic acid triggered endothelial dysfunction accompanied by pronounced mitochondrial oxidative stress. Mechanistically, palmitic acid lowered the oxidised/reduced nicotinamide adenine dinucleotide (NAD+/NADH) ratio and increased NADH-linked Complex I activity, a redox state consistent with enhanced Complex I-linked ROS generation. Pharmacological (rotenone) or genetic (NDUFS4 knockdown) modulation of Complex I activity suppressed mtROS overproduction, improved NAD+/NADH balance, alleviated oxidative stress and improved endothelial function. In vivo, rotenone attenuated HFD-induced systemic metabolic disturbances and vascular oxidative stress while improving endothelial barrier integrity and angiogenic responses. CONCLUSIONS: Our study suggests that dysregulated mitochondrial Complex I activity may serve as an important contributor to lipotoxic endothelial injury. These findings support Complex I modulation as a potential strategy to mitigate free fatty acid-induced endothelial dysfunction in obesity- and diabetes-related vascular complications.