Abstract 12302: A Novel Role of Autophagy in the Regulation of Endothelial to Mesenchymal Transition
Introduction: Endothelial to mesenchymal transition (EndMT) plays a critical role in the pathogenesis of cardiac fibrosis and end-stage organ failure.
Hypothesis: We hypothesized that loss of autophagy is an essential mechanism that promotes aberrant EndMT.
Methods & Results: We silenced ATG7, an essential autophagy gene, in human umbilical vein endothelial cells (HUVECs) and evaluated autophagy and markers of EndMT. Silencing of ATG7 resulted in a reduction in the ratio of LC3-II/LC3-I, with a marked increase in p62 expression providing evidence that autophagic flux was inhibited via this approach. Strikingly, electron microscopic evaluation revealed marked morphological and ultra-structural changes in ATG7-silenced endothelial cells, with a complete loss of the conventional cobblestone appearance and an increase in spindle-shaped morphology, with marked cytoskeletal rearrangement. Whereas control HUVECs showed weak and diffused α-actinin expression, ATG7-silenced HUVECs exhibited a robust longitudinally organized α-actinin cytoskeleton typically observed in mesenchymal cells. Expressions of the endothelial cell markers, CD31, Tie-2 and VE-cadherin, were significantly low in ATG7-silenced vs. control HUVECs; coincidently, ATG7 silencing was associated with significant increase in expression of the mesenchymal markers α-smooth muscle actin, N-cadherin and FSP-1. This phenotype was confirmed in human pulmonary artery endothelial cells as well. Mechanistically, loss of ATG7 was accompanied by increased expression of TGF-β1 and its receptors as well as significant changes in the levels of several key members of the TGF-β superfamily.
Conclusions: We report a completely novel and unexpected role of the essential autophagy gene ATG7 as a guardian against aberrant EndMT. Pharmacological and genetic strategies aimed at augmenting the autophagic flux may serve to limit cardiac fibrosis, and translational in vivo studies examining this paradigm are suggested.
Author Disclosures: K.K. Singh: None. F. Lovren: None. A. Quan: None. Y. Pan: None. H. Teoh: None. M. Al-Omran: None. S. Verma: None.
- © 2014 by American Heart Association, Inc.