Mitochondrial quality control and age-associated arterial stiffening

Abstract

Stiffening of large elastic arteries with age increases the risk of cardiovascular diseases (CVD), but the underlying mechanisms are incompletely understood. We investigated the role of mitochondrial quality control (QC, i.e., mitophagy and biogenesis) in arterial stiffening with aging. In C57BL6 mice, aging was associated with impaired aortic expression of mitochondrial QC mediators, greater activation of the mitochondrial redox/stress sensor p66shc, elevated superoxide production and increased arterial stiffness-as indicated by ~25% higher aortic pulse wave velocity (aPWV). In old mice, supplementation with trehalose, a nutraceutical reported to enhance mitophagy, normalized mitochondrial QC markers, p66shc activation and superoxide production, and reduced aPWV and aortic collagen I (a structural protein that confers stiffness). In vitro experiments suggested that mitochondrial QC processes were enhanced in the aortas from old trehalose-treated mice, and in aortic rings studied ex vivo, both aging and treatment with the mitochondrial stressor rotenone were associated with increases in p66shc activation and intrinsic mechanical stiffness, whereas co-incubation with trehalose prevented these effects. Taken together, these findings suggest that mitochondrial stress/dysfunction as a result of impaired mitochondrial QC contributes to large elastic artery stiffening with age. Enhancing mitochondrial QC with agents such as trehalose may be a novel strategy for reducing age-associated arterial stiffness and CVD.

Keywords: Collagen; Mitochondrial biogenesis; Mitophagy.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Figure 1. Impaired expression of mitochondrial QC proteins, increased p66shc activation and elevated superoxide production in aorta of old mice; reversal by trehalose

(A) Protein expression of the mitophagy mediators Parkin and BNIP3 in aorta of young and old control (YC and OC) and young and old trehalose treated (YTre and OTre) mice. (B) The mitochondrial biogenesis/maintenance proteins SIRT3 and PGC-1α. (C) Activation (phosphorylation at Ser36) of the mitochondrial stress/dysfunction sensor p66shc. (D) Mean EPR signal in aortic rings. Representative Western blot images below. Protein expression presented relative to GAPDH, and all data normalized to YC mean value. Means ± SEM (n = 6–8 per group). *P < 0.05 vs. YC. **P < 0.05 vs. OC.

Figure 2. Increased aortic stiffness and altered structural protein expression in old mice; reversal by trehalose

(A) Aortic pulse wave velocity (aPWV) in young and old control (YC and OC) and young and old trehalose treated (YTre and OTre) mice. Representative Doppler flows at right. (B) Collagen I and elastin protein expression. Representative Western blot images below. Protein expression data presented relative to GAPDH and normalized to YC mean value. Means ± SEM (n = 6–8 per group). *P < 0.05 vs. YC. **P < 0.05 vs. OC

Figure 3. Enhanced mitochondrial QC in old trehalose-treated mice, simulation of age-related aortic stiffness by mitochondrial stress and prevention by trehalose

(A) Protein expression of the mitochondrial marker VDAC in aortas from old control (OC) and old trehalose-treated mice (OTre) incubated in complete medium (DMEM) or starvation medium (HBSS) with/without the mitophagy inhibitor chloroquine (CQ, 100 µM). (B) p66shc activation (phosphorylation) and elastic modulus (intrinsic stiffness) in aortic rings from young mice incubated for 48 h with rotenone (0.5 µM) and/or trehalose (100 mM). (C) p66shc activation and elastic modulus in aortic rings from old mice incubated with rotenone and/or trehalose. Representative Western blot images below. Protein expression data presented relative to GAPDH and normalized to control/baseline condition. Means ± SEM (n = 5–6 per group/condition). *P < 0.05 vs. control; **P < 0.05 vs. rotenone condition.