Nox2-Derived Reactive Oxygen Species Mediate Neurovascular Dysregulation in the Aging Mouse Brain

Abstract

Aging is associated with cerebrovascular dysregulation, which may underlie the increased susceptibility to ischemic stroke and vascular cognitive impairment occurring in the elder individuals. Although it has long been known that oxidative stress is responsible for the cerebrovascular dysfunction, the enzymatic system(s) generating the reactive oxygen species (ROS) have not been identified. In this study, we investigated whether the superoxide-producing enzyme NADPH oxidase is involved in alterations of neurovascular regulation induced by aging. Cerebral blood flow (CBF) was recorded by laser-Doppler flowmetry in anesthetized C57BL/6 mice equipped with a cranial window (age = 3, 12, and 24 months). In 12-month-old mice, the CBF increases evoked by whisker stimulation or by the endothelium-dependent vasodilators acetylcholine and bradykinin were attenuated by 42, 36, and 53%, respectively (P < 0.05). In contrast, responses to the nitric oxide donor S-nitroso-D-penicillamine or adenosine were not attenuated (P > 0.05). These cerebrovascular effects were associated with increased production of ROS in neurons and cerebral blood vessels, assessed by hydroethidine microfluorography. The cerebrovascular impairment present in 12-month-old mice was reversed by the ROS scavenger Mn (III) tetrakis (4-benzoic acid) porphyrin chloride or by the NADPH oxidase peptide inhibitor gp91ds-tat, and was not observed in mice lacking the Nox2 subunit of NADPH oxidase. These findings establish Nox2 as a critical source of the neurovascular oxidative stress mediating the deleterious cerebrovascular effects associated with increasing age.

IGF‐1 deficiency impairs neurovascular coupling in mice: implications for cerebromicrovascular aging

“…2). It is significant that impaired endothelial NO production was shown to contribute to age‐related neurovascular uncoupling in mice (Park et al ., 2007; Toth et al ., 2014a). The findings that in IGF‐1‐deficient mice (Fig.…”

“…The findings that in IGF‐1‐deficient mice (Fig. 2), the L‐NAME‐sensitive, NO‐mediated portion of the neurovascular coupling response was decreased suggest that cerebromicrovascular endothelial dysfunction also contributes to neurovascular uncoupling in IGF‐1 deficiency (Park et al ., 2007), mimicking the aging phenotype (Park et al ., 2007; Toth et al ., 2014a). The mechanisms by which IGF‐1 deficiency impairs cerebromicrovascular endothelial function likely involve an increased breakdown of NO by elevated levels of ROS.…”

“…Several lines of evidence support this concept. First, IGF‐1‐deficient mice, similar to aged mice (Park et al ., 2007; Toth et al ., 2014a), exhibit increased production of ROS (Csiszar et al ., 2008). Second, the treatment of primary endothelial cells with IGF‐1 significantly attenuates cellular ROS generation (Csiszar et al ., 2008).…”

“…2), a biomarker of increased ONOO − formation, indicating that increased scavenging of vasodilator NO contributes to impaired endothelial mediation of cerebromicrovascular dilation in IGF‐1 deficiency. Previous studies suggest that increased activity/expression of NADPH oxidases and increased ROS production by mitochondrial sources contribute significantly to aging‐induced microvascular oxidative stress (Park et al ., 2007; Ungvari & Csiszar, 2012; Toth et al ., 2014a). Accordingly, the findings that treatment with a pharmacological inhibitor of cellular ROS production is able to improve functional hyperemia provide direct evidence for the role of increased oxidative stress in neurovascular uncoupling both in IGF‐1‐deficient mice and in aged mice (Toth et al ., 2014a).…”

“…The resulting functional hyperemia is responsible for maintenance of an optimal local microenvironment in the cerebral tissue by increasing delivery of oxygen and glucose and removal of potentially deleterious by‐products of cerebral metabolism. Aging is associated with significant impairment of functional hyperemia (termed ‘neurovascular uncoupling’), and the ensuing disruption of the cerebral microenvironment likely contributes to impairment of higher cerebral function in elderly patients and aged laboratory animals (Zaletel et al ., 2005; Park et al ., 2007; Topcuoglu et al ., 2009; Fabiani et al ., 2013; Sorond et al ., 2013; Stefanova et al ., 2013; Toth et al ., 2014a). Yet, the specific age‐related mechanisms responsible for neurovascular uncoupling are not yet understood.…”