Unfolded Protein Response PERK Research Articles

Abstract 436: Mfn2 is a Nodal Point Regulatory Step That Coordinates Angiogenic Phenotype in the Vascular Endothelium

Recent published data suggests that endothelial metabolism regulates angiogenesis. The key regulators of mitochondrial dynamics, mitofusins (Mfn1 and Mfn2) have been linked to cellular metabolic profile in tissues with high energetic requirements but their role in endothelial cells, were mitochondria function as signaling organelles is unknown. Here, we found that Mfn2 modulates postnatal neovascularization. Endothelial deletion of Mfn2 (Mfn2 ecko ) impaired, whereas, endothelial Mfn1 deletion (Mfn1 ecko ) did not affect clinical recovery, limb blood flow reperfusion, and capillary density compared with wild-type mice. These effects were associated with reduced eNOS activation in the ischemic leg of Mfn2 ecko mice compared with wild-type mice. Transplantation of bone marrow cells from WT to Mfn2ecko mice did not significantly improve blood perfusion in the ischemic limb of Mfn2 ecko mice. In agreement with these results, salient features of angiogenesis such as eNOS phosphorylation, cell migration, proliferation and capillary sprout formation were significantly inhibited in Mfn2 null primary mouse lung endothelial cells (Mfn2 -/- MLECs), whereas ablation of Mfn1 did not affect angiogenic signaling following VEGF stimulation. Because Mfn2 modulates the unfolded protein response (UPR) and the UPR machinery has been shown to generate angiomodulatory signals, we ascertained the effects of Mfn2 loss on UPR-mediated VEGF angiogenic signal transduction as potential mechanism. Mfn2 ablation sensitized Mfn2 -/- MLECs to proapototic UPR activation following VEGF treatment according to CHOP levels. Augmented CHOP levels corresponded with reduced eNOS phosphorylation. Inhibition of the UPR PERK signaling axis with PERK siRNA or reconstitution of Mfn2 (AdMfn2) reduced CHOP levels and significantly improved eNOS activation, EC proliferation and migration in Mfn2 -/- MLECs. Moreover, PERK siRNA or reconstitution of Mfn2 rescued the defect in capillary sprout formation in Mfn2 ecko mice. These data suggest that Mfn2 regulate angiogenic signaling in a UPR PERK axis-dependent manner and extend the role of Mfn2 beyond mitochondrial dynamics, metabolism and ER stress to angiogenesis and reparative vascular remodeling.