Abstract 79: Differential Impact of Mitofusins on Endothelial Phenotype

Abstract

Rationale: Endothelial mitochondria are important for endothelial cell function and the development of vascular diseases. Recent published observations have shown that endothelial mitochondria display altered morphology under stress, suggesting perturbation in mitochondrial dynamics. Mitochondrial dynamics involves mitochondria fusion (regulated by mitofusins 1 (Mfn-1) and 2 (Mfn-2) and optic atrophy protein 1). The role of mitochondrial dynamics in endothelial dysfunction in vivo has never been explored. Method and Results: To understand the role of mitofusins in endothelial phenotype in vivo, we ablated mitofusins in Tie2-Cre-expressing cells. In vivo, Tie2-Mfn2 mice (ECKO Mfn2 ) had impaired recovery from hindlimb ischemia and diminished capillary density using CD31 immunofluorescence despite no difference in Tie2-Mfn-1 mice (ECKO Mfn1 ) compared to wild-type mice. We also observed exacerbated muscle atrophy in of ECKO Mfn2 but not ECKO Mfn1 mice compared to wild-type mice 28 days post HLI. Because vascular endothelial growth factor receptor 2 (Vegfr2) and endothelial nitric oxide synthase (eNOS) are involved in endothelial angiogenic response, we probed the effects of mitofusins on Vegfr2 and eNOS. There was less phosphorylated Vegfr2 and phosphorylated eNOS in ischemic limbs of ECKO Mfn2 mice, despite no difference in ECKO Mfn1 mice compared to wild-type mice at post operative day 14 according to western blotting indicating impaired angiogenic signaling in vivo. In cultured mouse lung endothelial cells (MLEC) deficient in Mfn-2, we observed significant reduction in Vegf −stimulated phosphorylation of Vegfr2 and eNOS compared to control cells. This blunted angiogenic signaling inhibited cell proliferation and migration in Mfn-2 but not Mfn-1 null endothelial cells. Conclusion: These data highlight a previously unrecognized role for Mfn-2 in angiogenesis and show that Mfn-2 not Mfn-1 is essential for mediating endothelial function.