Vascular pathology is a major feature of Alzheimer's disease (AD) and other dementias. We recently showed that chronic administration of the target-of-rapamycin (TOR) inhibitor rapamycin, which extends lifespan and delays aging, halts the progression of AD-like disease in transgenic human (h)APP mice modeling AD when administered before disease onset. Here we demonstrate that chronic reduction of TOR activity by rapamycin treatment started after disease onset restored cerebral blood flow (CBF) and brain vascular density, reduced cerebral amyloid angiopathy and microhemorrhages, decreased amyloid burden, and improved cognitive function in symptomatic hAPP (AD) mice. Like acetylcholine (ACh), a potent vasodilator, acute rapamycin treatment induced the phosphorylation of endothelial nitric oxide (NO) synthase (eNOS) and NO release in brain endothelium. Administration of the NOS inhibitor L-NG-Nitroarginine methyl ester reversed vasodilation as well as the protective effects of rapamycin on CBF and vasculature integrity, indicating that rapamycin preserves vascular density and CBF in AD mouse brains through NOS activation. Taken together, our data suggest that chronic reduction of TOR activity by rapamycin blocked the progression of AD-like cognitive and histopathological deficits by preserving brain vascular integrity and function. Drugs that inhibit the TOR pathway may have promise as a therapy for AD and possibly for vascular dementias.

The purpose of this study was to investigate activation-induced hypermetabolism and hyperemia by using a multifrequency (4, 8, and 16 Hz) reversing-checkerboard visual stimulation paradigm. Specifically, we sought to (i) quantify the relative contributions of the oxidative and nonoxidative metabolic pathways in meeting the increased energy demands [i.e., ATP production (J ATP )] of task-induced neuronal activation and (ii) determine whether task-induced cerebral blood flow (CBF) augmentation was driven by oxidative or nonoxidative metabolic pathways. Focal increases in CBF, cerebral metabolic rate of oxygen (CMRO 2 ; i.e., index of aerobic metabolism), and lactate production (J Lac ; i.e., index of anaerobic metabolism) were measured by using physiologically quantitative MRI and spectroscopy methods. Task-induced increases in J ATP were small (12.2-16.7%) at all stimulation frequencies and were generated by aerobic metabolism (approximately 98%), with %ΔJ ATP being linearly correlated with the percentage change in CMRO 2 (r = 1.00, P < 0.001). In contrast, taskinduced increases in CBF were large (51.7-65.1%) and negatively correlated with the percentage change in CMRO 2 (r = −0.64, P = 0.024), but positively correlated with %ΔJ Lac (r = 0.91, P < 0.001). These results indicate that (i) the energy demand of task-induced brain activation is small (approximately 15%) relative to the hyperemic response (approximately 60%), (ii) this energy demand is met through oxidative metabolism, and (iii) the CBF response is mediated by factors other than oxygen demand.cerebral metabolic rate of oxygen | lactate production T he physiological mechanisms underlying task-induced, focal increases in brain blood flow have been a matter of speculation, experimentation, and debate for more than a century. Roy and Sherrington opened the dialogue with the observation that "the brain possesses an intrinsic mechanism by which its vascular supply can be varied locally in correspondence with local variations of functional activity" (1) and attributed these to vasodilatory properties of "the chemical products of cerebral metabolism" (1), with the presumption that metabolism was focally increased by neuronal activity. The Roy-Sherrington principle has been interpreted to mean that blood flow changes must be a function of a tight coupling between cellular energy requirements and the supplies of glucose and oxygen. Studies using preimaging radiotracer techniques demonstrated that brain blood flow can be markedly elevated by increased partial pressure of CO 2 and by decreased partial pressure of O 2 , a form of cerebrovascular autoregulation (2). These observations provided strong support for the Roy-Sherrington principle, as CO 2 is the primary "chemical product" of glucose oxidation, and extended the hypothesis to include substrate ([O 2 ]) availability as a potent vascular regulator.The first imaging-based measurements of cerebral metabolic rate of O 2 (CMRO 2 ) during task performance were reported in the early 1980s, using 15 O positron emis...

Neurovascular integrity, including cerebral blood flow (CBF) and blood-brain barrier (BBB) function, plays a major role in determining cognitive capability. Recent studies suggest that neurovascular integrity could be regulated by the gut microbiome. The purpose of the study was to identify if ketogenic diet (KD) intervention would alter gut microbiome and enhance neurovascular functions, and thus reduce risk for neurodegeneration in young healthy mice (12–14 weeks old). Here we show that with 16 weeks of KD, mice had significant increases in CBF and P-glycoprotein transports on BBB to facilitate clearance of amyloid-beta, a hallmark of Alzheimer’s disease (AD). These neurovascular enhancements were associated with reduced mechanistic target of rapamycin (mTOR) and increased endothelial nitric oxide synthase (eNOS) protein expressions. KD also increased the relative abundance of putatively beneficial gut microbiota (Akkermansia muciniphila and Lactobacillus), and reduced that of putatively pro-inflammatory taxa (Desulfovibrio and Turicibacter). We also observed that KD reduced blood glucose levels and body weight, and increased blood ketone levels, which might be associated with gut microbiome alteration. Our findings suggest that KD intervention started in the early stage may enhance brain vascular function, increase beneficial gut microbiota, improve metabolic profile, and reduce risk for AD.

The aim of this study was to investigate the various MRI biophysical models in the measurements of local cerebral metabolic rate of oxygen (CMRO 2 ) and the corresponding relationship with cerebral blood flow (CBF) during brain activation. This aim was addressed by simultaneously measuring the relative changes in CBF, cerebral blood volume (CBV), and blood oxygen level dependent (BOLD) MRI signals in the human visual cortex during visual stimulation. A radial checkerboard delivered flash stimulation at five different frequencies. Two MRI models, the single-compartment model (SCM) and the multicompartment model (MCM), were used to determine the relative changes in CMRO 2 using three methods: The relationship between increases in the local cerebral metabolic rate of oxygen (CMRO 2 ) and increases in cerebral blood flow (CBF), which occur in response to focal neuronal activation has been a topic of long-standing interest. Techniques for measuring the percent changes (␦) in CMRO 2 and CBF using positron emission tomography (PET) and functional MRI (fMRI) of the human brain have been developed to understand hemodynamic and metabolic processes of neuronal activity. Comparison studies have shown that fMRI and PET are comparable and equivalent in the measurements of ␦CBF (1,2). However, it has been noted that a significant discrepancy exists between PET and fMRI measurements of ␦CMRO 2 . PET and fMRI also differ in their measurement of the relationship between the ␦CMRO 2 and ␦CBF observed during brain activation. Specifically, the ␦CMRO 2 values measured by fMRI are consistently larger than those measured using PET. More problematic, the flow-metabolic relationships determined by PET and fMRI appeared to be different in previous studies. For example, using a visual stimulation paradigm, a nonlinear flow and metabolic relationship was repeatedly observed with PET (3,4) while a linear correlation between ␦CMRO 2 and ␦CBF was found with an fMRI study (5). To our knowledge, this discrepancy has not been fully addressed by neuroimaging community.PET measurements of hemodynamics and metabolism are based on autoradiographic principles and can provide full quantification in physiological units. The original PET observations of ␦CBF:␦CMRO 2 uncoupling (3,6) were made using a comprehensive tracer kinetic model which requires explicit measurements of CBF, cerebral blood volume (CBV), and oxygen extraction fraction (OEF). With a visual stimulation paradigm at 10 Hz, CMRO 2 increased slightly by 5.0 Ϯ 0.2% while CBF increased dramatically by 50.0 Ϯ 6.9% were measured by PET (3). Using a simplified PET model for quantification of CMRO 2 , Vafaee and Gjedde (4) found that the ␦CBF:␦CMRO 2 coupling ratio changes nonlinearly with the visual stimulation rate. At rates below 4 Hz, CBF and CMRO 2 both rose, with a coupling ratio of ϳ2:1. As the rate was increased to more than 4 Hz, CMRO 2 fell while CBF continued to rise, resulting in a highly nonlinear relationship. As expected, the results from PET methods (3,4,7) at rates above 4 Hz we...

Apolipoprotein E ɛ4 allele is a common susceptibility gene for late-onset Alzheimer's disease. Brain vascular and metabolic deficits can occur in cognitively normal apolipoprotein E ɛ4 carriers decades before the onset of Alzheimer's disease. The goal of this study was to determine whether early intervention using rapamycin could restore neurovascular and neurometabolic functions, and thus impede pathological progression of Alzheimer's disease-like symptoms in pre-symptomatic Apolipoprotein E ɛ4 transgenic mice. Using in vivo, multimodal neuroimaging, we found that apolipoprotein E ɛ4 mice treated with rapamycin had restored cerebral blood flow, blood–brain barrier integrity and glucose metabolism, compared to age- and gender-matched wild-type controls. The preserved vasculature and metabolism were associated with amelioration of incipient learning deficits. We also found that rapamycin restored the levels of the proinflammatory cyclophilin A in vasculature, which may contribute to the preservation of cerebrovascular function in the apolipoprotein E ɛ4 transgenics. Our results show that rapamycin improves functional outcomes in this mouse model and may have potential as an effective intervention to block progression of vascular, metabolic and early cognitive deficits in human Apolipoprotein E ɛ4 carriers. As rapamycin is FDA-approved and neuroimaging is readily used in humans, the results of the present study may provide the basis for future Alzheimer's disease intervention studies in human subjects.

Summary Mutations in SURF1 cytochrome c oxidase (COX) assembly protein are associated with Leigh’s syndrome, a human mitochondrial disorder that manifests as severe mitochondrial phenotypes and early lethality. In contrast, mice lacking the Surf1 protein (Surf1−/−) are viable and were previously shown to have enhanced longevity and a greater than 50% reduction in COX activity. We measured mitochondrial function in heart and skeletal muscle, and despite the significant reduction in COX activity, we found little or no difference in reactive oxygen species (ROS) generation, membrane potential, ATP production or respiration in isolated mitochondria from Surf1−/− mice compared to wild-type. However, blood lactate levels are elevated and Surf1−/− mice have reduced running endurance, suggesting compromised mitochondrial energy metabolism in vivo. Decreased COX activity in Surf1−/− mice is associated with increased markers of mitochondrial biogenesis (PGC-1α and VDAC) in both heart and skeletal muscle. While mitochondrial biogenesis is a common response in the two tissues, skeletal muscle have an up-regulation of the mitochondrial unfolded protein response (UPRMT) and heart exhibits induction of the Nrf2 antioxidant response pathway. These data are the first to report induction of the UPRMT in a mammalian model of diminished COX activity. In addition our results suggest that impaired mitochondrial function can lead to induction of mitochondrial stress pathways to confer protective effects on cellular homeostasis. Loss of complex IV assembly factor Surf1 in mice results in compensatory responses including mitochondrial biogenesis, the nrf2 pathway and the mitochondrial unfolded protein response. This compensatory response may contribute to the lack of deleterious phenotypes under basal conditions.

Risk factors and cognitive sequelae of brain arteriolosclerosis pathology are not fully understood. To address this, we used multimodal data from the National Alzheimer's Coordinating Center and Alzheimer's Disease Neuroimaging Initiative data sets. Previous studies showed evidence of distinct neurodegenerative disease outcomes and clinicalpathological correlations in the ''oldest-old'' compared to younger cohorts. Therefore, using the National Alzheimer's Coordinating Center data set, we analyzed clinical and neuropathological data from two groups according to ages at death: < 80 years (n ¼ 1008) and !80 years (n ¼ 1382). In both age groups, severe brain arteriolosclerosis was associated with worse performances on global cognition tests. Hypertension (but not diabetes) was a brain arteriolosclerosis risk factor in the younger group. In the ! 80 years age at death group, an ABCC9 gene variant (rs704180), previously associated with aging-related hippocampal sclerosis, was also associated with brain arteriolosclerosis. A post-hoc arterial spin labeling neuroimaging experiment indicated that ABCC9 genotype is associated with cerebral blood flow impairment; in a convenience sample from Alzheimer's Disease Neuroimaging Initiative (n ¼ 15, homozygous individuals), non-risk genotype carriers showed higher global cerebral blood flow compared to risk genotype carriers. We conclude that brain arteriolosclerosis is associated with altered cognitive status and a novel vascular genetic risk factor.

By restoring mitochondrial function, methylene blue (MB) is an effective neuroprotectant in many neurological disorders (e.g., Parkinson’s and Alzheimer’s diseases). MB has also been proposed as a brain metabolic enhancer because of its action on mitochondrial cytochrome c oxidase. We used in vitro and in vivo approaches to determine how MB affects brain metabolism and hemodynamics. For in vitro, we evaluated the effect of MB on brain mitochondrial function, oxygen consumption, and glucose uptake. For in vivo, we applied neuroimaging and intravenous measurements to determine MB’s effect on glucose uptake, cerebral blood flow (CBF), and cerebral metabolic rate of oxygen (CMRO2) under normoxic and hypoxic conditions in rats. MB significantly increases mitochondrial complex I–III activity in isolated mitochondria and enhances oxygen consumption and glucose uptake in HT-22 cells. Using positron emission tomography and magnetic resonance imaging (MRI), we observed significant increases in brain glucose uptake, CBF, and CMRO2 under both normoxic and hypoxic conditions. Further, MRI revealed that MB dramatically increased CBF in the hippocampus and in the cingulate, motor, and frontoparietal cortices, areas of the brain affected by Alzheimer’s and Parkinson’s diseases. Our results suggest that MB can enhance brain metabolism and hemodynamics, and multimetric neuroimaging systems offer a noninvasive, nondestructive way to evaluate treatment efficacy.