Abstract 15196: Autophagy Regulates Vascular Smooth Muscle Cell Phenotypic Switching: Translational Implications for Aneurysm Formation
Background: In response to diverse inflammatory and hemodynamic stressors, vascular smooth muscle cells (SMCs) undergo a phenotypic switch from a quiescent/contractile state to a proliferative/synthetic phenotype leading to production of matrix metalloproteinases, with resultant apoptosis and programmed cell necrosis. Aberrant vascular SMC phenotypic switching is a central mechanism of aortic aneurysm formation and rupture. We hypothesized that an intact autophagy machinery serves to limit vascular SMC phenotypic switching. Cellular autophagy is regulated by a number of autophagy related genes (ATG), of which ATG7 is an essential regulator of autophagy since it is required for fusion of peroxisomal and vacuolar membranes leading to autophagasome production.
Methods: We performed loss of function in vitro studies in human aortic SMCs using ATG7 siRNA, and evaluated the effects on aortic SMC autophagic flux, proliferation, migration and phenotypic modulation in the presence and absence of angiotensin II (AngII).
Results: AngII (10-6 M) stimulated ATG7 expression in cultured human aortic SMCs (p<0.01), and increased autophagic flux as assessed by the ratio of LC3-II/LC3-1 and p62 protein levels (p<0.01). Silencing of ATG7 caused a marked increase in basal and AngII-induced aortic SMCs proliferation as assessed by BrdU incorporation into newly synthesized cellular DNA (p<0.01), caused an increase in aortic SMC migration as assessed in a Boyden chamber assay and promoted cellular apoptosis. Loss of ATG7 was further associated with an increase in phenotypic switching of aortic SMCs. Specifically, the markers of the vascular SMC synthetic phenotype calponin and SM22α were ~3-fold higher in siRNA treated aortic SMCs (p<0.01).
Conclusions: The essential autophagy gene ATG7 is a previously unrecognized target to limit aberrant SMCs phenotypic modulation. Since vascular SMC phenotypic switching has been causally linked to the development and rupture of aortic aneurysms, further translational studies using autophagy stimulators should be conducted in experimental aneurysm models.
- © 2013 by American Heart Association, Inc.