The Role Of Autophagy On Macrophage Apoptosis,Vulnerable Plaque Progression And The Underlying Mechanisms

Atherosclerotic vascular disease which is a complex and chronic inflammatory disease of vascular wall involving multiple cardiovascular metabolic risk factors,is the leading cause of mortality worldwide.Rupture of vulnerable plaques is responsible for acute coronary syndrome and ischemic strokes,which are acute fatal cardiovascular events.Autophagy,an evolutionarily conserved intracellular degradation process,has been considered as a potential therapeutic target in cardiovascular system;however,whether macrophage autophagy could stabilize the vulnerable plaques,and the cellular and molecular mechanisms involved in have not been fully understood.Here,we developed the mouse model of vulnerable carotid plaque which was induced by endogenous renovascular hypertension combined with low shear stress in Apo E^-/-mice.Then,we tested the effects of inhibitors of phosphatidylinositol 3-kinase（PI3K）,3-methyladenine（3-MA）and mammalian target of rapamycin（m TOR）,rapamycin,as autophagy inhibitor and activator in Apo E^-/-mice,respectively.Application of rapamycin dramatically inhibited the progression of vulnerable plaques,with lower incidence of intraplaque hemorrhage and of spontaneous plaque rupture.Magnetic resonance imaging（MRI）further demonstrated rapamycin stabilized unstable plaques by decreasing the plaque area and increasing the residual luminal area.Further studies indicated that rapamycin inhibited necrotic core formation in vulnerable plaques by decreasing macrophage apoptosis.However,3-MA promoted plaque vulnerability though deteriorating these indexes.To further explore the mechanism of autophagy on macrophage apoptosis,we used macrophage apoptosis model in vitro.We found that7-ketocholesterol（7-KC,one of the primary oxysterols in ox LDL）impaired mitochondrial dysfunction,characterized by the impairment of mitochondrial ultrastructure,cytochrome c release,mitochondrial potential dissipation,mitochondrial fragmentation,excessive ROS generation,and both caspase-9 and-3 activation.Meanwhile,7-KC treatment damaged autophagy flux,assessed by increases in SQSTM1/p62,microtubule-associated protein 2 light chain 3（LC3-II）/LC3-I ratio.Interestingly,such mitochondrial apoptotic responses were ameliorated by autophagy activator,but exacerbated by autophagy inhibitor.Thus,vitro study suggested that meliorating autophagy flux inhibited macrophage apoptosis through regulating mitochondrial dysfunction.Finally,we detected that MAPK-NF-κB signaling pathway was involved in autophagy modulation of 7-KC-induced macrophage apoptosis.So,we provide strong evidence for the potential therapeutic benefit of macrophage autophagy in regulating mitochondria-mediated apoptosis and inhibiting necrotic core formation in vulnerable plaques.