Abstract 4: Macrophage p62/SQSTM1 Ameliorates Atherosclerosis by Sequestering Inclusion Bodies and Mediating Mitophagy
Protein and organelle turnover is critical for cellular homeostasis and is prominently mediated by autophagy. Disruptions in autophagy lead to accumulation of protein aggregates and dysfunctional organelles such as mitochondria. Recent evidence suggests that the chaperone protein p62 is a critical link for targeting polyubiquitinated protein aggregates/damaged mitochondria to autophagosomes for degradation. Herein we describe a p62-centric mechanism of handling protein aggregates and dysfunctional mitochondria in atherosclerosis. Macrophages deficient in autophagy (ATG5-/-) or rendered deficient by incubation with atherogenic lipids have significantly increased levels of p62. This coincides with 1) the accumulation of polyubiquitinated proteins co-localizing with p62 and present as cytoplasmic inclusion bodies, and 2) p62 co-localization with mitochondrial markers. Aortas from atherosclerotic (ApoE-/-) mice also have progressive and marked elevations in p62, polyubiquitinated proteins, and mitochondrial reactive oxygen species that predominantly co-localize with plaque macrophages, a process further exacerbated in the autophagy-deficient setting. The formation of cytoplasmic inclusions and maintenance of adequate mitochondrial function appears to be dependent on p62. Lipid-loaded p62-null macrophages show polyubiquitinated protein accumulation present in a diffuse/disrupted cytoplasmic pattern. These macrophages also develop larger dysmorphic mitochondria with increased polarization and decreased oxidative phosphorylation capacity. As a result, p62-null macrophages display apoptotic susceptibility to atherogenic lipids and increased IL-1β secretion likely through mitochondrial-dependent inflammasome activation. Consistent with our in vitro observations, mice with either whole-body p62-deficiency or transplanted with p62-deficient bone marrow show significantly increased atherosclerotic plaque burden and lesion complexity with increased apoptosis and necrotic cores. Taken together, these data demonstrate a previously unrecognized atheroprotective role for macrophage p62 by facilitating the formation of inclusion bodies and maintaining healthy mitochondria.
Author Disclosures: I. Sergin: None. S. Bhattacharya: None. C.J. Stokes: None. J.A. Curci: None. B. Razani: None.
- © 2015 by American Heart Association, Inc.