Atherosclerotic burden and cerebral small vessel disease: exploring the link through microvascular aging and cerebral microhemorrhages.

Cerebral microhemorrhages (CMHs, also known as cerebral microbleeds) are a critical but frequently underestimated aspect of cerebral small vessel disease (CSVD), bearing substantial clinical consequences. Detectable through sensitive neuroimaging techniques, CMHs reveal an extensive pathological landscape. They are prevalent in the aging population, with multiple CMHs often being observed in a given individual. CMHs are closely associated with accelerated cognitive decline and are increasingly recognized as key contributors to the pathogenesis of vascular cognitive impairment and dementia (VCID) and Alzheimer's disease (AD). This review paper delves into the hypothesis that atherosclerosis, a prevalent age-related large vessel disease, extends its pathological influence into the cerebral microcirculation, thereby contributing to the development and progression of CSVD, with a specific focus on CMHs. We explore the concept of vascular aging as a continuum, bridging macrovascular pathologies like atherosclerosis with microvascular abnormalities characteristic of CSVD. We posit that the same risk factors precipitating accelerated aging in large vessels (i.e., atherogenesis), primarily through oxidative stress and inflammatory pathways, similarly instigate accelerated microvascular aging. Accelerated microvascular aging leads to increased microvascular fragility, which in turn predisposes to the formation of CMHs. The presence of hypertension and amyloid pathology further intensifies this process. We comprehensively overview the current body of evidence supporting this interconnected vascular hypothesis. Our review includes an examination of epidemiological data, which provides insights into the prevalence and impact of CMHs in the context of atherosclerosis and CSVD. Furthermore, we explore the shared mechanisms between large vessel aging, atherogenesis, microvascular aging, and CSVD, particularly focusing on how these intertwined processes contribute to the genesis of CMHs. By highlighting the role of vascular aging in the pathophysiology of CMHs, this review seeks to enhance the understanding of CSVD and its links to systemic vascular disorders. Our aim is to provide insights that could inform future therapeutic approaches and research directions in the realm of neurovascular health.

Prognostic significance of a signature based on senescence-related genes in colorectal cancer.

Colorectal cancer, recognized as a quintessential age-related disease, underscores the intricate interplay between aging mechanisms and disease pathogenesis. Cellular senescence, a DNA damage-induced cellular stress response, is characterized by cell cycle arrest, the expression of an inflammatory senescence-associated secretory phenotype, and alterations in extracellular matrix metabolism. It is widely recognized as a fundamental and evolutionarily conserved mechanism of aging. Guided by geroscience principles, which assert that the pathogenesis of age-related diseases involves cellular mechanisms of aging, this study delves into the role of senescence-related genes in colon cancer progression. Leveraging a gene set reflective of senescence-associated pathways, we employed uni- and multivariate Cox proportional hazards survival analysis combined with the determination of the false discovery rate to analyze correlations between gene expression and survival. The integrated database of 1130 colon cancer specimens with available relapse-free survival time and relapse event data from ten independent cohorts provided a robust platform for survival analyses. We identified senescence-related genes associated with differential expression levels linked to shorter survival. Our findings unveil a prognostic signature utilizing cellular senescence-related genes (hazard ratio: 2.73, 95% CI 2.12-3.52, p = 6.4E - 16), offering valuable insights into survival prediction in colon cancer. Multivariate analysis underscored the independence of the senescence-related signature from available epidemiological and pathological variables. This study highlights the potential of senescence-related genes as prognostic biomarkers. Overall, our results underscore the pivotal role of cellular senescence, a fundamental mechanism of aging, in colon cancer progression.

Irradiation-induced hair graying in mice: an experimental model to evaluate the effectiveness of interventions targeting oxidative stress, DNA damage prevention, and cellular senescence.

Hair graying, also known as canities or achromotrichia, is a natural phenomenon associated with aging and is influenced by external factors such as stress, environmental toxicants, and radiation exposure. Understanding the mechanisms underlying hair graying is an ideal approach for developing interventions to prevent or reverse age-related changes in regenerative tissues. Hair graying induced by ionizing radiation (γ-rays or X-rays) has emerged as a valuable experimental model to investigate the molecular pathways involved in this process. In this review, we examine the existing evidence on radiation-induced hair graying, with a particular focus on the potential role of radiation-induced cellular senescence. We explore the current understanding of hair graying in aging, delve into the underlying mechanisms, and highlight the unique advantages of using ionizing-irradiation-induced hair graying as a research model. By elucidating the molecular pathways involved, we aim to deepen our understanding of hair graying and potentially identify novel therapeutic targets to address this age-related phenotypic change.

Whole brain irradiation-induced endothelial dysfunction in the mouse brain.

Whole brain irradiation (WBI), also known as whole brain radiation therapy (WBRT), is a well-established treatment for multiple brain metastases and as a preventive measure to reduce the risk of recurrence after surgical removal of a cerebral metastasis. However, WBI has been found to lead to a gradual decline in neurocognitive function in approximately 50% of patients who survive the treatment, significantly impacting their overall quality of life. Recent preclinical investigations have shed light on the underlying mechanisms of this adverse effect, revealing a complex cerebrovascular injury that involves the induction of cellular senescence in various components of the neurovascular unit, including endothelial cells. The emergence of cellular senescence following WBI has been implicated in the disruption of the blood-brain barrier and impairment of neurovascular coupling responses following irradiation. Building upon these findings, the present study aims to test the hypothesis that WBI-induced endothelial injury promotes endothelial dysfunction, which mimics the aging phenotype. To investigate this hypothesis, we employed a clinically relevant fractionated WBI protocol (5 Gy twice weekly for 4 weeks) on young mice. Both the WBI-treated and control mice were fitted with a cranial window, enabling the assessment of microvascular endothelial function. In order to evaluate the endothelium-dependent, NO-mediated cerebral blood flow (CBF) responses, we topically administered acetylcholine and ATP, and measured the resulting changes using laser Doppler flowmetry. We found that the increases in regional CBF induced by acetylcholine and ATP were significantly diminished in mice subjected to WBI. These findings provide additional preclinical evidence supporting the notion that WBI induces dysfunction in cerebrovascular endothelial cells, which in turn likely contributes to the detrimental long-term effects of the treatment. This endothelial dysfunction resembles an accelerated aging phenotype in the cerebrovascular system and is likely causally linked to the development of cognitive impairment. By integrating these findings with our previous results, we have deepened our understanding of the lasting consequences of WBI. Moreover, our study underscores the critical role of cerebromicrovascular health in safeguarding cognitive function over the long term. This enhanced understanding highlights the importance of prioritizing cerebromicrovascular health in the context of preserving cognitive abilities.

The Role of Methionine-Rich Diet in Unhealthy Cerebrovascular and Brain Aging: Mechanisms and Implications for Cognitive Impairment.

As aging societies in the western world face a growing prevalence of vascular cognitive impairment and Alzheimer's disease (AD), understanding their underlying causes and associated risk factors becomes increasingly critical. A salient concern in the western dietary context is the high consumption of methionine-rich foods such as red meat. The present review delves into the impact of this methionine-heavy diet and the resultant hyperhomocysteinemia on accelerated cerebrovascular and brain aging, emphasizing their potential roles in cognitive impairment. Through a comprehensive exploration of existing evidence, a link between high methionine intake and hyperhomocysteinemia and oxidative stress, mitochondrial dysfunction, inflammation, and accelerated epigenetic aging is drawn. Moreover, the microvascular determinants of cognitive deterioration, including endothelial dysfunction, reduced cerebral blood flow, microvascular rarefaction, impaired neurovascular coupling, and blood-brain barrier (BBB) disruption, are explored. The mechanisms by which excessive methionine consumption and hyperhomocysteinemia might drive cerebromicrovascular and brain aging processes are elucidated. By presenting an intricate understanding of the relationships among methionine-rich diets, hyperhomocysteinemia, cerebrovascular and brain aging, and cognitive impairment, avenues for future research and potential therapeutic interventions are suggested.

Exposome and unhealthy aging: environmental drivers from air pollution to occupational exposures.

The aging population worldwide is facing a significant increase in age-related non-communicable diseases, including cardiovascular and brain pathologies. This comprehensive review paper delves into the impact of the exposome, which encompasses the totality of environmental exposures, on unhealthy aging. It explores how environmental factors contribute to the acceleration of aging processes, increase biological age, and facilitate the development and progression of a wide range of age-associated diseases. The impact of environmental factors on cognitive health and the development of chronic age-related diseases affecting the cardiovascular system and central nervous system is discussed, with a specific focus on Alzheimer's disease, Parkinson's disease, stroke, small vessel disease, and vascular cognitive impairment (VCI). Aging is a major risk factor for these diseases. Their pathogenesis involves cellular and molecular mechanisms of aging such as increased oxidative stress, impaired mitochondrial function, DNA damage, and inflammation and is influenced by environmental factors. Environmental toxicants, including ambient particulate matter, pesticides, heavy metals, and organic solvents, have been identified as significant contributors to cardiovascular and brain aging disorders. These toxicants can inflict both macro- and microvascular damage and many of them can also cross the blood-brain barrier, inducing neurotoxic effects, neuroinflammation, and neuronal dysfunction. In conclusion, environmental factors play a critical role in modulating cardiovascular and brain aging. A deeper understanding of how environmental toxicants exacerbate aging processes and contribute to the pathogenesis of neurodegenerative diseases, VCI, and dementia is crucial for the development of preventive strategies and interventions to promote cardiovascular, cerebrovascular, and brain health. By mitigating exposure to harmful environmental factors and promoting healthy aging, we can strive to reduce the burden of age-related cardiovascular and brain pathologies in the aging population.

Accelerated cerebromicrovascular senescence contributes to cognitive decline in a mouse model of paclitaxel (Taxol)-induced chemobrain.

Chemotherapy-induced cognitive impairment ("chemobrain") is a frequent side-effect in cancer survivors treated with paclitaxel (PTX). The mechanisms responsible for PTX-induced cognitive impairment remain obscure, and there are no effective treatments or prevention strategies. Here, we test the hypothesis that PTX induces endothelial senescence, which impairs microvascular function and contributes to the genesis of cognitive decline. We treated transgenic p16-3MR mice, which allows the detection and selective elimination of senescent cells, with PTX (5 mg/kg/day, 2 cycles; 5 days/cycle). PTX-treated and control mice were tested for spatial memory performance, neurovascular coupling (NVC) responses (whisker-stimulation-induced increases in cerebral blood flow), microvascular density, blood-brain barrier (BBB) permeability and the presence of senescent endothelial cells (by flow cytometry and single-cell transcriptomics) at 6 months post-treatment. PTX induced senescence in endothelial cells, which associated with microvascular rarefaction, NVC dysfunction, BBB disruption, neuroinflammation, and impaired performance on cognitive tasks. To establish a causal relationship between PTX-induced senescence and impaired microvascular functions, senescent cells were depleted from PTX-treated animals (at 3 months post-treatment) by genetic (ganciclovir) or pharmacological (treatment with the senolytic drug ABT263/Navitoclax) means. In PTX treated mice, both treatments effectively eliminated senescent endothelial cells, rescued endothelium-mediated NVC responses and BBB integrity, increased capillarization and improved cognitive performance. Our findings suggest that senolytic treatments can be a promising strategy for preventing chemotherapy-induced cognitive impairment.

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis.

Age-related cerebrovascular pathologies, ranging from cerebromicrovascular functional and structural alterations to large vessel atherosclerosis, promote the genesis of vascular cognitive impairment and dementia (VCID) and exacerbate Alzheimer's disease. Recent advances in geroscience, including results from studies on heterochronic parabiosis models, reinforce the hypothesis that cell non-autonomous mechanisms play a key role in regulating cerebrovascular aging processes. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) exert multifaceted vasoprotective effects and production of both hormones is significantly reduced in aging. This brief overview focuses on the role of age-related GH/IGF-1 deficiency in the development of cerebrovascular pathologies and VCID. It explores the mechanistic links among alterations in the somatotropic axis, specific macrovascular and microvascular pathologies (including capillary rarefaction, microhemorrhages, impaired endothelial regulation of cerebral blood flow, disruption of the blood brain barrier, decreased neurovascular coupling, and atherogenesis) and cognitive impairment. Improved understanding of cell non-autonomous mechanisms of vascular aging is crucial to identify targets for intervention to promote cerebrovascular and brain health in older adults.

Old blood from heterochronic parabionts accelerates vascular aging in young mice: transcriptomic signature of pathologic smooth muscle remodeling.

Vascular aging has a central role in the pathogenesis of cardiovascular diseases contributing to increased mortality of older adults. There is increasing evidence that, in addition to the documented role of cell-autonomous mechanisms of aging, cell-nonautonomous mechanisms also play a critical role in the regulation of vascular aging processes. Our recent transcriptomic studies (Kiss T. et al. Geroscience. 2020;42(2):727-748) demonstrated that circulating anti-geronic factors from young blood promote vascular rejuvenation in aged mice. The present study was designed to expand upon the results of this study by testing the hypothesis that circulating pro-geronic factors also contribute to the genesis of vascular aging phenotypes. To test this hypothesis, through heterochronic parabiosis, we determined the extent to which shifts in the vascular transcriptome (RNA-seq) are modulated by the old systemic environment. We reanalyzed existing RNA-seq data, comparing the transcriptome in the aorta arch samples isolated from isochronic parabiont aged (20-month-old) C57BL/6 mice [A-(A); parabiosis for 8 weeks] and young isochronic parabiont (6-month-old) mice [Y-(Y)] and also assessing transcriptomic changes in the aortic arch in young (6-month-old) parabiont mice [Y-(A); heterochronic parabiosis for 8 weeks] induced by the presence of old blood derived from aged (20-month-old) parabionts. We identified 528 concordant genes whose expression levels differed in the aged phenotype and were shifted towards the aged phenotype by the presence of old blood in young Y-(A) animals. Among them, the expression of 221 concordant genes was unaffected by the presence of young blood in A-(Y) mice. GO enrichment analysis suggests that old blood-regulated genes may contribute to pathologic vascular remodeling. IPA Upstream Regulator analysis (performed to identify upstream transcriptional regulators that may contribute to the observed transcriptomic changes) suggests that the mechanism of action of pro-geronic factors present in old blood may include inhibition of pathways mediated by SRF (serum response factor), insulin-like growth factor-1 (IGF-1) and VEGF-A. In conclusion, relatively short-term exposure to old blood can accelerate vascular aging processes. Our findings provide additional evidence supporting the significant plasticity of vascular aging and the existence of circulating pro-geronic factors mediating pathological remodeling of the vascular smooth muscle cells and the extracellular matrix.

Spatial transcriptomic analysis reveals inflammatory foci defined by senescent cells in the white matter, hippocampi and cortical grey matter in the aged mouse brain.

There is strong evidence that aging is associated with an increased presence of senescent cells in the brain. The finding that treatment with senolytic drugs improves cognitive performance of aged laboratory mice suggests that increased cellular senescence is causally linked to age-related cognitive decline. The relationship between senescent cells and their relative locations within the brain is critical to understanding the pathology of age-related cognitive decline and dementia. To assess spatial distribution of cellular senescence in the aged mouse brain, spatially resolved whole transcriptome mRNA expression was analyzed in sections of brains derived from young (3 months old) and aged (28 months old) C57BL/6 mice while capturing histological information in the same tissue section. Using this spatial transcriptomics (ST)-based method, microdomains containing senescent cells were identified on the basis of their senescence-related gene expression profiles (i.e., expression of the senescence marker cyclin-dependent kinase inhibitor p16INK4A encoded by the Cdkn2a gene) and were mapped to different anatomical brain regions. We confirmed that brain aging is associated with increased cellular senescence in the white matter, the hippocampi and the cortical grey matter. Transcriptional analysis of the senescent cell-containing ST spots shows that presence of senescent cells is associated with a gene expression signature suggestive of neuroinflammation. GO enrichment analysis of differentially expressed genes in the outer region of senescent cell-containing ST spots ("neighboring ST spots") also identified functions related to microglia activation and neuroinflammation. In conclusion, senescent cells accumulate with age in the white matter, the hippocampi and cortical grey matter and likely contribute to the genesis of inflammatory foci in a paracrine manner.

Cerebral venous congestion exacerbates cerebral microhemorrhages in mice.

Cerebral microhemorrhages (CMHs; microbleeds), which are small focal intracerebral hemorrhages, importantly contribute to the pathogenesis of cognitive decline and dementia in older adults. Although recently it has been increasingly recognized that the venous side of the cerebral circulation likely plays a fundamental role in the pathogenesis of a wide spectrum of cerebrovascular and brain disorders, its role in the pathogenesis of CMHs has never been studied. The present study was designed to experimentally test the hypothesis that venous congestion can exacerbate the genesis of CMHs. Increased cerebral venous pressure was induced by internal and external jugular vein ligation (JVL) in C57BL/6 mice in which systemic hypertension was induced by treatment with angiotensin II plus L-NAME. Histological analysis (diaminobenzidine staining) showed that mice with JVL developed multiple CMHs. CMHs in mice with JVL were often localized adjacent to veins and venules and their morphology was consistent with venous origin of the bleeds. In brains of mice with JVL, a higher total count of CMHs was observed compared to control mice. CMHs were distributed widely in the brain of mice with JVL, including the cortical gray matter, brain stem, the basal ganglia, subcortical white matter, cerebellum, and the hippocampi. In mice with JVL, there were more CMHs predominantly in cerebral cortex, brain stem, and cerebellum than in control mice. CMH burden, defined as total CMH volume, also significantly increased in mice with JVL. Thus, cerebral venous congestion can exacerbate CMHs. These observations have relevance to the pathogenesis of cognitive impairment associated with right heart failure as well as elevated cerebral venous pressure due to jugular venous reflux in older adults.

Treatment with the BCL-2/BCL-xL inhibitor senolytic drug ABT263/Navitoclax improves functional hyperemia in aged mice.

Moment-to-moment adjustment of regional cerebral blood flow to neuronal activity via neurovascular coupling (NVC or "functional hyperemia") has a critical role in maintenance of healthy cognitive function. Aging-induced impairment of NVC responses importantly contributes to age-related cognitive decline. Advanced aging is associated with increased prevalence of senescent cells in the cerebral microcirculation, but their role in impaired NVC responses remains unexplored. The present study was designed to test the hypothesis that a validated senolytic treatment can improve NVC responses and cognitive performance in aged mice. To achieve this goal, aged (24-month-old) C57BL/6 mice were treated with ABT263/Navitoclax, a potent senolytic agent known to eliminate senescent cells in the aged mouse brain. Mice were behaviorally evaluated (radial arms water maze) and NVC was assessed by measuring CBF responses (laser speckle contrast imaging) in the somatosensory whisker barrel cortex evoked by contralateral whisker stimulation. We found that NVC responses were significantly impaired in aged mice. ABT263/Navitoclax treatment improved NVC response, which was associated with significantly improved hippocampal-encoded functions of learning and memory. ABT263/Navitoclax treatment did not significantly affect endothelium-dependent acetylcholine-induced relaxation of aorta rings. Thus, increased presence of senescent cells in the aged brain likely contributes to age-related neurovascular uncoupling, exacerbating cognitive decline. The neurovascular protective effects of ABT263/Navitoclax treatment highlight the preventive and therapeutic potential of senolytic treatments (as monotherapy or as part of combination treatment regimens) as effective interventions in patients at risk for vascular cognitive impairment (VCI).

Endothelial deficiency of insulin-like growth factor-1 receptor (IGF1R) impairs neurovascular coupling responses in mice, mimicking aspects of the brain aging phenotype.

Age-related impairment of neurovascular coupling (NVC; or "functional hyperemia") compromises moment-to-moment adjustment of regional cerebral blood flow to increased neuronal activity and thereby contributes to the pathogenesis of vascular cognitive impairment (VCI). Previous studies established a causal link among age-related decline in circulating levels of insulin-like growth factor-1 (IGF-1), neurovascular dysfunction and cognitive impairment. Endothelium-mediated microvascular dilation plays a central role in NVC responses. To determine the functional consequences of impaired IGF-1 input to cerebromicrovascular endothelial cells, endothelium-mediated NVC responses were studied in a novel mouse model of accelerated neurovascular aging: mice with endothelium-specific knockout of IGF1R (VE-Cadherin-CreERT2/Igf1rf/f). Increases in cerebral blood flow in the somatosensory whisker barrel cortex (assessed using laser speckle contrast imaging through a cranial window) in response to contralateral whisker stimulation were significantly attenuated in VE-Cadherin-CreERT2/Igf1rf/f mice as compared to control mice. In VE-Cadherin-CreERT2/Igf1rf/f mice, the effects of the NO synthase inhibitor L-NAME were significantly decreased, suggesting that endothelium-specific disruption of IGF1R signaling impairs the endothelial NO-dependent component of NVC responses. Collectively, these findings provide additional evidence that IGF-1 is critical for cerebromicrovascular endothelial health and maintenance of normal NVC responses.

Early manifestation of gait alterations in the Tg2576 mouse model of Alzheimer's disease.

There is strong clinical evidence that multifaceted gait abnormalities may be manifested at early stages of Alzheimer's disease (AD), are related to cognitive decline, and can be used as an early biomarker to identify patients at risk of progressing to full-blown dementia. Despite their importance, gait abnormalities have not been investigated in mouse models of AD, which replicate important aspects of the human disease. The Tg2576 is frequently used in AD research to test therapeutic interventions targeting cellular mechanisms contributing to the genesis of AD. This transgenic mouse strain overexpresses a mutant form of the 695 amino acid isoform of human amyloid precursor protein with K670N and M671L mutations (APPK670/671L) linked to early-onset familial AD. Tg2576 mice exhibit impaired cognitive functions and increased cortical and hippocampal soluble ß-amyloid levels starting from 5 months of age and increased insoluble ß-amyloid levels and amyloid plaques that resemble senile plaques associated with human AD by 13 months of age. To demonstrate early manifestations of gait dysfunction in this relevant preclinical model, we characterized gait and motor performance in 10-month-old Tg2576 mice and age-matched littermate controls using the semi-automated, highly sensitive, Catwalk XT system. We found that Tg2576 mice at the pre-plaque stage exhibited significantly altered duty cycle and step patterns and decreased stride length and stride time. Base-of-support, stride time variability, stride length variability, cadence, phase dispersions and gait symmetry indices were unaltered. The presence of measurable early gait abnormalities during the pre-plaque stages of AD in this relevant preclinical mouse model has direct translational relevance and supports the view that longitudinal monitoring of gait performance could be used in addition to behavioral testing to evaluate progression of the disease and to assess treatment efficacy.

IGF1R signaling regulates astrocyte-mediated neurovascular coupling in mice: implications for brain aging.

Aging is associated with a significant deficiency in circulating insulin-like growth factor-1 (IGF-1), which has an important role in the pathogenesis of age-related vascular cognitive impairment (VCI). Impairment of moment-to-moment adjustment of regional cerebral blood flow via neurovascular coupling (NVC) importantly contributes to VCI. Previous studies established a causal link between circulating IGF-1 deficiency and neurovascular dysfunction. Release of vasodilator mediators from activated astrocytes plays a key role in NVC. To determine the impact of impaired IGF-1 signaling on astrocytic function, astrocyte-mediated NVC responses were studied in a novel mouse model of astrocyte-specific knockout of IGF1R (GFAP-CreERT2/Igf1rf/f) and accelerated neurovascular aging. We found that mice with disrupted astrocytic IGF1R signaling exhibit impaired NVC responses, decreased stimulated release of the vasodilator gliotransmitter epoxy-eicosatrienoic acids (EETs), and upregulation of soluble epoxy hydrolase (sEH), which metabolizes and inactivates EETs. Collectively, our findings provide additional evidence that IGF-1 promotes astrocyte health and maintains normal NVC, protecting cognitive health.

Time-restricted feeding (TRF) for prevention of age-related vascular cognitive impairment and dementia.

Aging is the most significant risk factor for vascular cognitive impairment (VCI), and the number of individuals affected by VCI is expected to exponentially increase in the upcoming decades. Yet, there are no current preventative or therapeutic treatments available against the development and progression of VCI. Therefore, there is a pressing need to better understand the pathophysiology underlying these conditions, for the development of novel tools and interventions to improve cerebrovascular health and delay the onset of VCI. There is strong epidemiological and experimental evidence that lifestyle factors, including nutrition and dietary habits, significantly affect cerebrovascular health and thereby influence the pathogenesis of VCI. Here, recent evidence is presented discussing the effects of lifestyle interventions against age-related diseases which in turn, inspired novel research aimed at investigating the possible beneficial effects of dietary interventions for the prevention of cognitive decline in older adults.

Treatment with the poly(ADP-ribose) polymerase inhibitor PJ-34 improves cerebromicrovascular endothelial function, neurovascular coupling responses and cognitive performance in aged mice, supporting the NAD+ depletion hypothesis of neurovascular aging.

Adjustment of cerebral blood flow (CBF) to neuronal activity via neurovascular coupling (NVC) plays an important role in the maintenance of healthy cognitive function. Strong evidence demonstrates that age-related cerebromicrovascular endothelial dysfunction and consequential impairment of NVC responses contribute importantly to cognitive decline. Recent studies demonstrate that NAD+ availability decreases with age in the vasculature and that supplemental NAD+ precursors can ameliorate cerebrovascular dysfunction, rescuing NVC responses and improving cognitive performance in aged mice. The mechanisms underlying the age-related decline in [NAD+] in cells of the neurovascular unit are likely multifaceted and may include increased utilization of NAD+ by activated poly (ADP-ribose) polymerase (PARP-1). The present study was designed to test the hypothesis that inhibition of PARP-1 activity may confer protective effects on neurovascular function in aging, similar to the recently demonstrated protective effects of treatment with the NAD+ precursor nicotinamide mononucleotide (NMN). To test this hypothesis, 24-month-old C57BL/6 mice were treated with PJ-34, a potent PARP inhibitor, for 2 weeks. NVC was assessed by measuring CBF responses (laser speckle contrast imaging) in the somatosensory whisker barrel cortex evoked by contralateral whisker stimulation. We found that NVC responses were significantly impaired in aged mice. Treatment with PJ-34 improved NVC responses by increasing endothelial NO-mediated vasodilation, which was associated with significantly improved spatial working memory. PJ-34 treatment also improved endothelium-dependent acetylcholine-induced relaxation of aorta rings. Thus, PARP-1 activation, likely by decreasing NAD+ availability, contributes to age-related endothelial dysfunction and neurovascular uncoupling, exacerbating cognitive decline. The cerebromicrovascular protective effects of pharmacological inhibition of PARP-1 highlight the preventive and therapeutic potential of treatments that restore NAD+ homeostasis as effective interventions in patients at risk for vascular cognitive impairment (VCI).

Overexpression of catalase targeted to mitochondria improves neurovascular coupling responses in aged mice.

Moment-to-moment adjustment of cerebral blood flow (CBF) to neuronal activity via the homeostatic mechanism known as neurovascular coupling (NVC) has an essential role in maintenance of normal brain function. In advanced age cerebromicrovascular endothelial dysfunction impairs NVC responses, which contribute to age-related cognitive decline. Recently, we have shown that pharmacological treatments that attenuate mitochondrial production of reactive oxygen species (ROS) provide significant neurovascular protection, improving NVC responses in aged mice. Transgenic mice that overexpress human catalase localized to the mitochondria (mCAT) are protected from age-related mitochondrial oxidative stress and exhibit a longevity phenotype associated with resistance to several age-related pathologies. The present study was designed to test the hypothesis that mitochondria-targeted overexpression of catalase also confers protection against age-related impairment of NVC responses. To achieve this goal, NVC responses were assessed in aged (24 months old) mCAT mice and compared with those in age-matched wild-type mice and young control mice by measuring CBF responses (laser speckle contrast imaging) evoked by contralateral whisker stimulation. We found that mitochondrial overexpression of catalase resulted in improved NVC in aged mice due to preserved NO-mediated (L-NAME inhibitable) component of the response. Thus, our present and previous findings demonstrate that interventions that boost mitochondrial antioxidative defenses confer significant cerebromicrovascular protective effects, which preserve NVC responses in aged mice. Our findings provide additional proof-of-concept for the potential use of mitochondria-targeted antioxidants as therapy for prevention of vascular cognitive impairment associated with aging.