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Mitochondrial fragmentation plays an important role in the progression of diabetic cardiomyopathy. Metformin has protective in diabetes-related cardiovascular endpoints when compared with conventional therapies. Mitophagy mediates the selective recognition and targeting of damaged mitochondria by autophagosomes. However, the involvement of mitophagy in metformin-elicited cardioprotection remains unknown.
In the present study, H9C2 cardiomyocytes subjected to high glucose was treatment with metformin. Mitophagy marker FUNDC1 was examined using western blot and confocal fluorescence microscopy. JC-1 and DCFH-DA fluorescence staining were used to detect mitochondrial membrane potential and reactive oxygen species (ROS).
We found that high glucose treated cells exhibited reduced levels of FUNDC1, accompanied with decreased autophagy flux (reduced LC3-II/LC3-I and increased p62). Conversely, metformin increased FUNDC1 enhanced autophagy proteins. Confocal imaging of lysotracker red-labeled lysosome and mitotracker green-labeled mitochondria further confirmed metformin increased the mitophagy which was reversed by FUNDC1 siRNA and AMPK siRNA, suggesting metformin could induce FUNDC1 meditated mitophagy by activating AMPK. Furthermore, FUNDC1 siRNA attenuated the protective effects of metformin manifesting as aggravated mitochondrial morphology disruption, ATP and membrane potential depletion, increased ROS overproduction, and apoptosis.
Taken together, metformin promoted expression of FUNDC1 to stimulate cytoprotective mitophagy via AMPK pathway, which may provide beneficial targets in the preservation of cardiac homeostasis against high glucose injury.