Proceedings of The Physiological Society
Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB321
Early-life stress in male mice induces increased vascular oxidative stress in adulthood
J. Pollock1, D. Ho2
1. Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States. 2. Clinical Investigation, Tripler Army Medical Center, Honolulu, Hawaii, United States.
Epidemiological studies indicate that early-life stress (ELS) is an independent risk for cardiovascular disease (CVD). Endothelial dysfunction and oxidative stress are mediators of CVD. We hypothesized that ELS induces oxidative stress in adulthood using a mouse model of maternal separation and early weaning (MSEW). We first assessed vascular reactivity and superoxide generation of aortic rings in the presence and absence of superoxide scavengers from control and MSEW male mice. Mice were anesthetized with methohexital sodium (Brevital; 50 mg/kg IP), and aortae and plasma collected. Compared to control mice, aortic rings from MSEW mice displayed endothelial dysfunction that was reversed by superoxide scavenger, polyethylene glycol-superoxide dismutase (p<0.05, n=5-7). Superoxide production, assessed with dihydroethidium (DHE) HPLC assay, in aortae from MSEW mice was significantly greater than observed in control aortae (p<0.05, n=4), although unaffected by NO synthase inhibition. Increased expression of the NADPH oxidase subunits, NOX2 and NOX4, was evident in the aortae of MSEW mice (p<0.05, n=5). Moreover, NADPH oxidase inhibitor, apocynin, prevented vascular endothelial dysfunction (p<0.05, n=5-7), and reversed increased aortic superoxide generation (p=0.05, n=4) in MSEW mice, indicating that MSEW induces superoxide production and endothelial dysfunction, at least in part, via increased NADPH oxidase expression and activity. In a second series of studies, we assessed whether circulating factors induce endothelial oxidative stress. Mouse aortic endothelial cells (MAECs) were incubated with plasma from control mice or MSEW mice assessing superoxide production. Plasma from MSEW mice showed a significant increase in superoxide compared to control (p<0.05, n=10). Plasma free heme levels were significantly increased in MSEW mice (p<0.05, n-11), thus we assessed superoxide production in the presence or absence of hemopexin, a heme scavenger. Hemopexin reduced superoxide in MAECs treated with MSEW plasma (p<0.05, n=10), whereas no difference was found with control plasma (n=10). We further hypothesized that the heme-induced superoxide production in MAECs is through a toll-like receptor 4 (TLR4)-mediated pathway. Treatment with TAK-242, TLR4 antagonist, significantly reduced superoxide production in MAECs treated with MSEW plasma (p<0.05, n=10), whereas no effect was found with control plasma (n=10). Furthermore, aortic tissue from MSEW mice displayed significantly greater expression of TLR4 compared to control mice (p<0.05, n=8). These observations suggest that MSEW induces TLR4-dependent aortic oxidative stress and endothelial dysfunction. In conclusion, ELS may lead to increased risk for cardiovascular disease through increased heme, oxidative stress, and TLR4 activation.
Where applicable, experiments conform with Society ethical requirements