Effects on the brain microvasculature of age and circadian rhythm as risk factors for Alzheimer's disease

衰老和昼夜节律对能量产生有独立的影响（OXPHOS vs.糖酵解）

Aging and circadian/diurnal rhythm have independent effects on energy production (OXPHOS vs. glycolysis) and mitochondrial fuel choice (glucose/fatty acids), but interactions and underlying mechanisms have not been examined in the cerebral microcirculation. Studies on energy production of the cerebral vasculature have been performed during the working day for the convenience of laboratory workers, which is, contrariwise, the inactive, fasting time for rodents when glucose levels and levels of alternative fuels for mitochondria fluctuate widely. Recent papers have highlighted the importance of diurnal rhythm on disease occurrence such as strokes and for the selection of optimal timing of chemotherapy. We will improve the understanding of this important area using innovative methods and approaches developed by our laboratory, supported by exciting, novel findings, to ascertain for the first time mitochondrial and glycolytic dynamics of large (arteries) and microvessels (MVs, end arterioles, capillaries, venules) during aging in mice. Importantly, we made the unexpected finding that fibrinogen levels in brain MVs increase during aging, probably transported by circulating exosomes, and that fibrinogen induces oxidative stress and further disruption of tight junctions in brain endothelial cells. We postulate that mitochondrial dysfunction induced fibrinogen accumulation and ROS production in brain MVs leads to activation of microglia and accumulation of beta amyloid. Relevance to PAR-19-070: The brain microcirculation, including the blood-brain barrier (BBB), faces constant metabolic challenges while responding to physiological and nutritional status, which are exacerbated by diurnal rhythm and aging. A focus on cerebral MVs is warranted because adverse changes in energy production in the microcirculation promote cognitive impairment, strokes, vascular dementia, and Alzheimer’s disease (AD), and because fibrinogen accumulation causes beta amyloid accumulation and microglia activation—hallmarks of AD. Our studies are conceptually innovative based on our novel discoveries in and technically innovative due to application of new technologies. Our hypothesis is that age- or time- related mitochondrial dysfunction is a critical target for potential therapies to protect the MVs and brain against neurological damage and cognitive impairment. We have 2 aims. Aim 1: Elucidate mechanisms of mitochondrial, glycolytic, and cellular changes in brain MVs during aging. We will: a) determine mitochondrial and vascular characteristics of MVs and BBB status using in vivo multiphoton imaging in mice at 4–6 (young), 12–14 (middle age) and 18‒24 (old) months of age; b) determine the effects of aging on glycolysis and OXPHOS, mitochondrial fuel choice, and mitoROS in MVs and arteries; c) investigate the role of fibrinogen in promoting mitochondrial changes of MVs and arteries during aging; and d) explore treatment modalities for protecting mitochondria and the brain circulation against aging. Aim 2: Determine mechanisms of mitochondrial, glycolytic, and cellular changes in brain MVs during the diurnal cycle during aging. We will: a) determine mitochondrial and microvascular characteristics and BBB status in mice during the daily cycle; b) determine effects on glycolysis and OXPHOS, mitochondrial fuel choice, and mitoROS in arteries and MVs; c) elucidate mechanisms involved in mitochondrial changes in MV, arteries, and microvascular; and d) explore therapeutic approaches to improve mitochondrial dynamics in MVs and arteries, maintain microvascular function, and retain BBB status.