Habitual Physical Activity Preserves the Circulating Milieu to Mitigate Age-Related Aortic Stiffening: the Potential Role of Extracellular Vesicles

Aortic stiffening is a major independent risk factor for cardiovascular disease (CVD) with aging and is mediated in part by excessive production of reactive oxygen species (ROS). Habitual physical activity generally alleviates these effects. However, the mechanisms by which this occurs is not fully understood. With aging the circulating milieu (serum) is altered towards a pro-oxidative state, which is attenuated with habitual physical activity. However, it is unclear whether the circulating milieu contributes to the disparate effects on aortic stiffening with aging and habitual physical activity. Further, the identity of the bioactive factors involved and their link to ROS are unknown. An emerging candidate is extracellular vesicles (EVs) - bioactive nanoparticles released by cells into the circulation that can affect ROS to modulate physiological function. Hypothesis: The circulating milieu will contribute to the contrasting effects of aging and habitual physical activity in aortic stiffening and possible modulation of arterial ROS bioactivity. EVs will play a role in transducing these effects. Methods: Human serum was collected from healthy young (18-29 yr) and ML/O (50+ yr) men and women. Activity status was determined by leisure-time physical activity (Active = >60 MET h/wk). EVs were isolated (via ExoQuick™) from human serum in a subset of participants. Aortic rings (~1 mm) were obtained from young adult (3-4 mo), intervention naïve male and female C57BL/6N mice to assess aortic stiffness and ROS. Aortic rings were exposed ex vivo for 48 hours to either 5% sex-matched intact human serum or 5% EVs from one of the following groups: young sedentary ( Intact Serum : N=9, 4F; EVs : N=4, 2F), ML/O sedentary ( Intact Serum : N=14, 7F; EVs : N=6, 4F) or ML/O active ( Intact Serum : N=8, 4F; EVs : N=4, 2F) adults. Aortic stiffness was assessed by elastic modulus, a measure of intrinsic mechanical wall stiffness. ROS bioactivity was quantified in ML/O groups using the CMH spin probe via electron paramagnetic resonance spectroscopy. Values were normalized to young or ML/O sedentary groups. Differences were determined via one-way ANOVA or unpaired t-test. Results: Aortic Stiffness. Intact Serum : Elastic modulus was higher in aortic rings incubated with intact serum from ML/O sedentary adults (1.63 ± 0.19-fold higher) compared with intact serum from young sedentary adults (1.00 ± 0.17; p=0.020). Compared with intact serum from ML/O sedentary adults, aortic rings incubated with intact serum from ML/O active adults had lower elastic modulus (0.74 ± 0.14, p=0.002) which was not different to aortic rings incubated with intact serum from young sedentary adults (p=0.369). EVs : Elastic modulus was higher in aortic rings incubated with EVs from ML/O sedentary adults (1.31 ± 0.05) compared with EVs from young sedentary adults (1.00 ± 0.08; p=0.01). Compared with EVs from ML/O sedentary adults, aortic rings incubated with EVs from ML/O active adults had lower elastic modulus (0.96 ± 0.06, p=0.006) which was not different from aortic rings incubated with EVs from young sedentary adults (p=0.94). Oxidative Stress. Intact Serum: ROS bioactivity tended to be lower in aortic rings incubated with intact serum from ML/O active adults (0.54 ± 0.10) compared with intact serum from ML/O sedentary adults (1.00 ± 0.17; p=0.06; N=4/group). EVs : ROS bioactivity tended to be lower in aortic rings incubated with EVs from ML/O active adults (0.64 ± 0.09) compared with EVs from ML/O sedentary adults (1.00 ± 0.17; p=0.10; N=4/group). Conclusion: These findings suggest that the circulating milieu contributes to the disparate effects of aging and habitual physical activity in aortic stiffness and that EVs may play a role in mediating these effects. F32 HL167552 (KOM), F31 HL165885 (SAM), 23CDA 1056582 (MJR), R21 AG078408 (DRS), K99 HL159241 (ZSC), K99/R00 HL151818 (ZSC). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.