Disturbed flow induces autophagy, but impairs autophagic flux to perturb mitochondrial homeostasis

R Li, N Jen, L Wu, J Lee, K Fang, K Quigley… - Antioxidants & redox …, 2015 - liebertpub.com
R Li, N Jen, L Wu, J Lee, K Fang, K Quigley, K Lee, S Wang, B Zhou, L Vergnes, YR Chen…
Antioxidants & redox signaling, 2015liebertpub.com
Aim: Temporal and spatial variations in shear stress are intimately linked with vascular
metabolic effects. Autophagy is tightly regulated in intracellular bulk degradation/recycling
system for maintaining cellular homeostasis. We postulated that disturbed flow modulates
autophagy with an implication in mitochondrial superoxide (mtO2•−) production. Results: In
the disturbed flow or oscillatory shear stress (OSS)-exposed aortic arch, we observed
prominent staining of p62, a reverse marker of autophagic flux, whereas in the pulsatile …
Abstract
Aim: Temporal and spatial variations in shear stress are intimately linked with vascular metabolic effects. Autophagy is tightly regulated in intracellular bulk degradation/recycling system for maintaining cellular homeostasis. We postulated that disturbed flow modulates autophagy with an implication in mitochondrial superoxide (mtO2•−) production. Results: In the disturbed flow or oscillatory shear stress (OSS)-exposed aortic arch, we observed prominent staining of p62, a reverse marker of autophagic flux, whereas in the pulsatile shear stress (PSS)-exposed descending aorta, p62 was attenuated. OSS significantly increased (i) microtubule-associated protein light chain 3 (LC3) II to I ratios in human aortic endothelial cells, (ii) autophagosome formation as quantified by green fluorescent protein (GFP)-LC3 dots per cell, and (iii) p62 protein levels, whereas manganese superoxide dismutase (MnSOD) overexpression by recombinant adenovirus, N-acetyl cysteine treatment, or c-Jun N-terminal kinase (JNK) inhibition reduced OSS-mediated LC3-II/LC3-I ratios and mitochondrial DNA damage. Introducing bafilomycin to Earle's balanced salt solution or to OSS condition incrementally increased both LC3-II/LC3-I ratios and p62 levels, implicating impaired autophagic flux. In the OSS-exposed aortic arch, both anti-phospho-JNK and anti-8-hydroxy-2′-deoxyguanosine (8-OHdG) staining for DNA damage were prominent, whereas in the PSS-exposed descending aorta, the staining was nearly absent. Knockdown of ATG5 with siRNA increased OSS-mediated mtO2•−, whereas starvation or rapamycin-induced autophagy reduced OSS-mediated mtO2•−, mitochondrial respiration, and complex II activity. Innovation: Disturbed flow-mediated oxidative stress and JNK activation induce autophagy. Conclusion: OSS impairs autophagic flux to interfere with mitochondrial homeostasis. Antioxid. Redox Signal. 23, 1207–1219.
Mary Ann Liebert