Mitochondria-targeted antioxidant therapy with MitoQ ameliorates aortic stiffening in old mice

Abstract

Aortic stiffening is a major independent risk factor for cardiovascular diseases, cognitive dysfunction, and other chronic disorders of aging. Mitochondria-derived reactive oxygen species are a key source of arterial oxidative stress, which may contribute to arterial stiffening by promoting adverse structural changes-including collagen overabundance and elastin degradation-and enhancing inflammation, but the potential for mitochondria-targeted therapeutic strategies to ameliorate aortic stiffening with primary aging is unknown. We assessed aortic stiffness [pulse-wave velocity (aPWV)], ex vivo aortic intrinsic mechanical properties [elastic modulus (EM) of collagen and elastin regions], and aortic protein expression in young (~6 mo) and old (~27 mo) male C57BL/6 mice consuming normal drinking water (YC and OC) or water containing mitochondria-targeted antioxidant MitoQ (250 µM; YMQ and OMQ) for 4 wk. Both baseline and postintervention aPWV values were higher in OC vs. YC (post: 482 ± 21 vs. 420 ± 5 cm/s, P < 0.05). MitoQ had no effect in young mice but decreased aPWV in old mice (OMQ, 426 ± 20, P < 0.05 vs. OC). MitoQ did not affect age-associated increases in aortic collagen-region EM, collagen expression, or proinflammatory cytokine expression, but partially attenuated age-associated decreases in elastin region EM and elastin expression. Our results demonstrate that MitoQ reverses in vivo aortic stiffness in old mice and suggest that mitochondria-targeted antioxidants may represent a novel, promising therapeutic strategy for decreasing aortic stiffness with primary aging and, possibly, age-related clinical disorders in humans. The destiffening effects of MitoQ treatment may be at least partially mediated by attenuation/reversal of age-related aortic elastin degradation. NEW & NOTEWORTHY We show that 4 wk of treatment with the mitochondria-specific antioxidant MitoQ in mice completely reverses the age-associated elevation in aortic stiffness, assessed as aortic pulse-wave velocity. The destiffening effects of MitoQ treatment may be at least partially mediated by attenuation of age-related aortic elastin degradation. Our results suggest that mitochondria-targeted therapeutic strategies may hold promise for decreasing arterial stiffening with aging in humans, possibly decreasing the risk of many chronic age-related clinical disorders.

Keywords: aging; artery; mitochondrial antioxidant.

Figures

Fig. 1.

MitoQ treatment reverses age-related aortic stiffness in mice. Aortic pulse-wave velocity (aPWV) was assessed in young and old mice before (baseline) and after (post) consumption of normal drinking water (YC and OC) or MitoQ treatment (YMQ and OMQ) for 4 wk. n = 8–11/group; error bars represent means ± SE *P < 0.05 vs. YC and YMQ; **P < 0.05 vs. OC and OMQ baseline.

Fig. 2.

Representative stress-strain curve for determination of ex vivo intrinsic mechanical stiffness of aortic rings. Aortic rings were incrementally stretched until tissue failure, as described in materials and methods, and the tension (stress, kPa) corresponding to each stretch was plotted against strain (change in length relative to resting length) to generate a stress-strain curve. The elastic modulus of the region of the curve corresponding to collagen fiber stretching was determined as the slope of the line fit to the final four points on the curve before tissue failure (collagen region elastic modulus). The region of the curve corresponding to elastin fiber stretching was considered to lie between the very low-force region and the onset of collagen fiber engagement, which were identified as the first and second roots, respectively, of a seventh-order polynomial fit to the stress-strain curve (25). The elastic modulus of the elastin region of the curve was determined as the slope of the line fit between these boundaries (elastin region elastic modulus).

Fig. 3.

MitoQ treatment attenuates the age-related decline in elastin-mediated intrinsic mechanical properties but has no effect on collagen-mediated intrinsic mechanical stiffness. A: collagen region elastic modulus of aortic segments from young and old control (YC and OC) and young and old MitoQ-treated (YMQ and OMQ) mice. B: elastin region elastic modulus of aortic segments from YC, OC, YMQ, and OMQ mice. n = 8–11/group; error bars represent means ± SE. *P < 0.05 vs. YC and YMQ. #P < 0.05 vs. OC and YMQ.

Fig. 4.

MitoQ treatment attenuates the age-related reduction in aortic elastin expression but has no effect on aortic collagen expression. A: aortic collagen-I expression assessed by Western blot analysis in aortic homogenates from young and old control (YC and OC) and young and old MitoQ-treated (YMQ and OMQ) mice. Expression levels are presented normalized to GAPDH expression and relative to the mean of the YC group (error bars represent means ± SE). Representative images, comprising four continuous lanes, are presented below mean data. The collagen-I and GAPDH images represent the same segment of the same blot. Any adjustments to the images were limited to changes in brightness and contrast made using ImageJ to optimize visualization, performed uniformly on the entire image. n = 6/group. *P < 0.05 vs. YC. B: aortic collagen-I expression assessed by immunohistochemistry in whole aortic sections from YC, OC, YMQ, and OMQ mice. Expression levels are presented relative to the mean of the YC group (error bars represent means ± SE). Representative images (whole sections and enlargements of the same sections) are presented to the right of the mean data. n = 7–11/group. *P < 0.05 vs. YC. C: aortic elastin expression assessed by Western blot analysis in aortic homogenates from young and old control (YC and OC) and young and old MitoQ-treated (YMQ and OMQ) mice. Expression levels are presented normalized to GAPDH expression and relative to the mean of the YC group (error bars represent means ± SE). Representative images, comprising four continuous lanes, are presented below mean data. The elastin and GAPDH images represent the same segment of the same blot. Any adjustments to the images were limited to changes in brightness and contrast made using ImageJ to optimize visualization, performed uniformly on the entire image. n = 6/group. ^P < 0.074 vs. YC. D: aortic elastin expression assessed by immunohistochemistry in the medial layer of aortic sections from YC, OC, YMQ, and OMQ mice. Expression levels are presented relative to the mean of the YC group (error bars represent means ± SE). Representative images (whole sections and enlargements of the same sections) are presented to the right of the mean data. n = 8–11/group. ^P = 0.086 vs. YC; ^^P = 0.075 vs. OC.

Fig. 5.

MitoQ treatment does not affect the age-related increase in aortic inflammatory cytokines. Expression of inflammatory cytokines IL-6 (n = 7–10/group) (A), IL-10 (n = 7–9/group) (B), IFN-γ (n = 7–10/group) (C), and IL-1β (n = 4–10/group) (D) in aortic homogenates from young and old control (YC and OC) and young and old MitoQ-treated (YMQ and OMQ) mice. Sample sizes reflect all aortic homogenates for which cytokine levels were detectable; samples were excluded when cytokine levels were undetectable/below the limit of quantification of the assay. Error bars represent means ± SE. *P < 0.05 vs. YC. ^0.10 > P > 0.05 vs. YC (P = 0.08, OC vs. YC; P = 0.06, OMQ vs. YC).