Chronic cerebral hypoperfusion accelerates amyloid beta deposition in APPSwInd transgenic mice

Altered expression of neurofilament 200 and amyloid-β peptide (1-40) in a rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH) is damaging to white matter in the brain. So far few studies have investigated long-term axonal damage following CCH. The aim of this study was to investigate the involvement of neurofilament 200 (NF200) and amyloid-β (1-40) [Aβ (1-40)] in the pathological mechanism for neuronal damage, and to quantify changes in their expression over time in a rat model of CCH. A rat model of CCH was established using partial bilateral ligation of the common carotid arteries. The extent of stenosis was verified by measuring the changes in cerebral blood flow after surgery. Histology was used to assess hippocampal neuronal pathology, and immunohistochemistry was used to quantify the expression of NF200 and Aβ (1-40) at 2, 4, and 12 weeks after surgery. The cerebral blood flow reduced to 33.89 ± 5.48 % at 2 weeks, 36.83 ± 4.63 % at 4 weeks and 51.44 ± 4.90 % at 12 weeks. Immunofluorescence staining of neuronal perikarya sections revealed a marked decrease in the population of surviving pyramidal cells in the hippocampal CA1 region, a significant up-regulation in the expression of Aβ (1-40), and a significant reduction in the expression of NF200 following CCH surgery. Moreover, this trend was increasingly obvious over time. Our data demonstrate that CCH leads to axonal damage over time. We also confirmed that the expression of Aβ (1-40) and NF200 may be useful biomarkers of axonal damage following CCH.

Remote ischemic postconditioning: harnessing endogenous protection in a murine model of vascular cognitive impairment

We previously reported that remote limb ischemic conditioning (RLIC; PERconditioning) during acute stroke confers neuroprotection, possibly due to increased cerebral blood flow (CBF). Vascular cognitive impairment (VCI) is a growing threat to public health without any known treatment. The bilateral common carotid artery stenosis (BCAS) mouse model is regarded as the most valid model for VCI. We hypothesized that RLIC (postconditioning; RIPostC) will augment CBF during chronic cerebral hypoperfusion (CCH) and prevent cognitive impairment in the BCAS model. BCAS using customized microcoil was performed in C57/B6 male mice to establish CCH. A week after the BCAS surgery, mice were treated with RIPostC-therapy once daily for 2 weeks. CBF was measured with laser speckle contrast imager at different time points. Cognitive testing was performed at 4-week post-BCAS, and brain tissue was harvested for biochemistry. BCAS led to chronic hypoperfusion resulting into impaired cognitive function as tested by novel object recognition (NOR). Histological examinations revealed that BCAS triggered inflammatory responses and caused frequent vacuolization and cell death. BCAS also increased the generation and accumulation of amyloid beta protein (Aβ), resulting into the loss of white matter (WM) and myelin basic protein (MBP). RIPostC-therapy showed both acute increase as well as sustained improvement in CBF even after the cessation of therapy for a week. RIPostC improved cognitive function, inhibited inflammatory responses, prevented the cell death, reduced the generation and accumulation of Aβ, and protected WM integrity. RIPostC is effective in the BCAS model and could be an attractive low-cost conventional therapy for aged individuals with VCI. The mechanisms by which RIPostC improves CBF and attenuates tissue damage need to be investigated in the future.

From chronic cerebral hypoperfusion to Alzheimer-like brain pathology and neurodegeneration

Chronic cerebral hypoperfusion (CCH) is a common consequence of various cerebral vascular disorders and hemodynamic and blood changes. Recent studies have revealed an important role of CCH in neurodegeneration and dementia, including vascular dementia and Alzheimer's disease (AD). This article reviews the recent advances in understanding CCH-induced neurodegeneration and AD-related brain pathology and cognitive impairment. We discuss the causes and assessment of CCH, the possible mechanisms by which CCH promotes Alzheimer-like pathology and neurodegeneration, and animal models of CCH. It appears that CCH promotes neurodegeneration and AD through multiple mechanisms, including induction of oxidative stress, Aβ accumulation and aggravation, tau hyperphosphorylation, synaptic dysfunction, neuronal loss, white matter lesion, and neuroinflammation. Better understanding of the mechanisms of CCH will help develop therapeutic strategies for preventing and treating neurodegeneration, including sporadic AD and vascular dementia, caused by CCH.

New therapeutic approaches for Alzheimer's disease and cerebral amyloid angiopathy

Accumulating evidence has shown a strong relationship between Alzheimer’s disease (AD), cerebral amyloid angiopathy (CAA), and cerebrovascular disease. Cognitive impairment in AD patients can result from cortical microinfarcts associated with CAA, as well as the synaptic and neuronal disturbances caused by cerebral accumulations of β-amyloid (Aβ) and tau proteins. The pathophysiology of AD may lead to a toxic chain of events consisting of Aβ overproduction, impaired Aβ clearance, and brain ischemia. Insufficient removal of Aβ leads to development of CAA and plays a crucial role in sporadic AD cases, implicating promotion of Aβ clearance as an important therapeutic strategy. Aβ is mainly eliminated by three mechanisms: (1) enzymatic/glial degradation, (2) transcytotic delivery, and (3) perivascular drainage (3-“d” mechanisms). Enzymatic degradation may be facilitated by activation of Aβ-degrading enzymes such as neprilysin, angiotensin-converting enzyme, and insulin-degrading enzyme. Transcytotic delivery can be promoted by inhibition of the receptor for advanced glycation end products (RAGE), which mediates transcytotic influx of circulating Aβ into brain. Successful use of the RAGE inhibitor TTP488 in Phase II testing has led to a Phase III clinical trial for AD patients. The perivascular drainage system seems to be driven by motive force generated by cerebral arterial pulsations, suggesting that vasoactive drugs can facilitate Aβ clearance. One of the drugs promoting this system is cilostazol, a selective inhibitor of type 3 phosphodiesterase. The clearance of fluorescent soluble Aβ tracers was significantly enhanced in cilostazol-treated CAA model mice. Given that the balance between Aβ synthesis and clearance determines brain Aβ accumulation, and that Aβ is cleared by several pathways stated above, multi-drugs combination therapy could provide a mainstream cure for sporadic AD.

Cholesterol in brain disease: sometimes determinant and frequently implicated

Cholesterol is essential for neuronal physiology, both during development and in the adult life: as a major component of cell membranes and precursor of steroid hormones, it contributes to the regulation of ion permeability, cell shape, cell-cell interaction, and transmembrane signaling. Consistently, hereditary diseases with mutations in cholesterol-related genes result in impaired brain function during early life. In addition, defects in brain cholesterol metabolism may contribute to neurological syndromes, such as Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD), and even to the cognitive deficits typical of the old age. In these cases, brain cholesterol defects may be secondary to disease-causing elements and contribute to the functional deficits by altering synaptic functions. In the first part of this review, we will describe hereditary and non-hereditary causes of cholesterol dyshomeostasis and the relationship to brain diseases. In the second part, we will focus on the mechanisms by which perturbation of cholesterol metabolism can affect synaptic function.

RAGE inhibition in microglia prevents ischemia-dependent synaptic dysfunction in an amyloid-enriched environment

Ischemia is known to increase the deleterious effect of β-amyloid (Aβ), contributing to early cognitive impairment in Alzheimer's disease. Here, we investigated whether transient ischemia may function as a trigger for Aβ-dependent synaptic impairment in the entorhinal cortex (EC), acting through specific cellular signaling. We found that synaptic depression induced by oxygen glucose deprivation (OGD) was enhanced in EC slices either in presence of synthetic oligomeric Aβ or in slices from mutant human amyloid precursor protein transgenic mice (mhAPP J20). OGD-induced synaptic depression was ameliorated by functional suppression of RAGE. In particular, overexpression of the dominant-negative form of RAGE targeted to microglia (DNMSR) protects against OGD-induced synaptic impairment in an amyloid-enriched environment, reducing the activation of stress-related kinases (p38MAPK and JNK) and the release of IL-1β. Our results demonstrate a prominent role for the RAGE-dependent neuroinflammatory pathway in the synaptic failure induced by Aβ and triggered by transient ischemia.

Animal models of vascular dementia: translational potential at the present time and in 2050

ABSTRACT: Vascular dementia is a heterogeneous syndrome, and includes subcortical ischemic vascular dementia. For translational research, subcortical ischemic vascular dementia is an appropriate target since this is the most prevalent subtype and exhibits relatively uniform clinical and neuropathological changes. These changes consist of hypertensive arteriolar changes, lacunar infarctions, hypertensive hemorrhage and white matter lesions. Among various species, rodents are most frequently used, but their small volume of white matter may impede analysis of white matter lesions. Primate models have a larger volume, but the degree of white matter lesions is inconsistent. Animal models should accommodate the effect of aging and comorbidities, and in the case of primate models, low accessibility should be overcome by repeated and quantitative examinations using modern neuroimaging techniques and functional measures, especially for memory and motor function. There is no model that replicates all features of subcortical ischemic vascular dementia and, therefore, rodent and primate models should be selected appropriately for translational research.

Cerebral arterial pulsation drives paravascular CSF-interstitial fluid exchange in the murine brain

CSF from the subarachnoid space moves rapidly into the brain along paravascular routes surrounding penetrating cerebral arteries, exchanging with brain interstitial fluid (ISF) and facilitating the clearance of interstitial solutes, such as amyloid β, in a pathway that we have termed the "glymphatic" system. Prior reports have suggested that paravascular bulk flow of CSF or ISF may be driven by arterial pulsation. However, cerebral arterial pulsation could not be directly assessed. In the present study, we use in vivo two-photon microscopy in mice to visualize vascular wall pulsatility in penetrating intracortical arteries. We observed that unilateral ligation of the internal carotid artery significantly reduced arterial pulsatility by ~50%, while systemic administration of the adrenergic agonist dobutamine increased pulsatility of penetrating arteries by ~60%. When paravascular CSF-ISF exchange was evaluated in real time using in vivo two-photon and ex vivo fluorescence imaging, we observed that internal carotid artery ligation slowed the rate of paravascular CSF-ISF exchange, while dobutamine increased the rate of paravascular CSF-ISF exchange. These findings demonstrate that cerebral arterial pulsatility is a key driver of paravascular CSF influx into and through the brain parenchyma, and suggest that changes in arterial pulsatility may contribute to accumulation and deposition of toxic solutes, including amyloid β, in the aging brain.

The pathobiology of vascular dementia

Vascular cognitive impairment defines alterations in cognition, ranging from subtle deficits to full-blown dementia, attributable to cerebrovascular causes. Often coexisting with Alzheimer's disease, mixed vascular and neurodegenerative dementia has emerged as the leading cause of age-related cognitive impairment. Central to the disease mechanism is the crucial role that cerebral blood vessels play in brain health, not only for the delivery of oxygen and nutrients, but also for the trophic signaling that inextricably links the well-being of neurons and glia to that of cerebrovascular cells. This review will examine how vascular damage disrupts these vital homeostatic interactions, focusing on the hemispheric white matter, a region at heightened risk for vascular damage, and on the interplay between vascular factors and Alzheimer's disease. Finally, preventative and therapeutic prospects will be examined, highlighting the importance of midlife vascular risk factor control in the prevention of late-life dementia.

Mouse models to study the effect of cardiovascular risk factors on brain structure and cognition

Recent clinical data indicates that hemodynamic changes caused by cardiovascular diseases such as atherosclerosis, heart failure, and hypertension affect cognition. Yet, the underlying mechanisms of the resulting vascular cognitive impairment (VCI) are poorly understood. One reason for the lack of mechanistic insights in VCI is that research in dementia primarily focused on Alzheimer's disease models. To fill in this gap, we critically reviewed the published data and various models of VCI. Typical findings in VCI include reduced cerebral perfusion, blood-brain barrier alterations, white matter lesions, and cognitive deficits, which have also been reported in different cardiovascular mouse models. However, the tests performed are incomplete and differ between models, hampering a direct comparison between models and studies. Nevertheless, from the currently available data we conclude that a few existing surgical animal models show the key features of vascular cognitive decline, with the bilateral common carotid artery stenosis hypoperfusion mouse model as the most promising model. The transverse aortic constriction and myocardial infarction models may be good alternatives, but these models are as yet less characterized regarding the possible cerebral changes. Mixed models could be used to study the combined effects of different cardiovascular diseases on the deterioration of cognition during aging.

Assessment of radioligands for PET imaging of cyclooxygenase-2 in an ischemic neuronal injury model

Cyclooxygenase-2 (COX-2) plays crucial roles in progressive neuronal death in ischemic brain injury. In the present study, we evaluated two radiolabeled COX-2 selective inhibitors, [11C]celecoxib and [11C]rofecoxib, as positron emission tomography (PET) tracers for COX-2 imaging in normal and ischemic mouse brains. We also took advantage of our newly-generated antibody highly selective for mouse COX-2 to prove accumulation of the radioligands in regions enriched with COX-2. In vitro autoradiography demonstrated specific binding of high-concentration [11C]rofecoxib but not [11C]celecoxib to the cerebellum and brain stem of normal brains wherein COX-2 immunoreactivity in neurons was most abundantly observed. Meanwhile, both of these radioligands failed to detect COX-2 expression in PET assays despite their excellent brain permeability. Hypoperfusion-induced ischemia caused marked necrotic neuron death accompanied by gliosis and enhancement of neuronal COX-2 immunoreactivity in the hippocampus. Correspondingly, in vitro autoradiographic binding of [11C]rofecoxib was increased in the injured hippocampus compared to the uninjured contralateral region, but failed in living brains of ischemia model likewise. Our work provides the rationale for monitoring COX-2 as a biomarker reflecting ischemic brain injuries and demonstrates that [11C]rofecoxib, not [11C]celecoxib, is useful for in vitro assays of COX-2, but its affinity would be insufficient for in vivo PET visualization.

Blood pressure and cognition among older adults: a meta-analysis

Hypertension has adverse effects on cognition, can alter cerebral vasculature integrity, and is associated with the pathogenesis of dementia. Using meta-analysis, we correlated blood pressure to multiple cognitive domains among older adults free of clinical stroke and dementia. We identified 230 studies indexed in PubMed and PsycINFO relating blood pressure and cognition. After applying exclusion criteria, we selected n = 12 articles with n = 4,076 participants (age range 43-91 years). Meta-analysis yielded an association between blood pressure and episodic memory (r = -.18, p < .001) and between blood pressure and global cognition (r = -.07, p < .001). When limiting analyses to studies adjusting for vascular covariates (n = 8, n = 2,141), blood pressure was modestly related to global cognition (r = -.11, p < .001), attention (r = .14, p = .002), and episodic memory (r = -.20, p < .001) with a trend for language (r = -.22, p = .07). Findings underscore the need to manage blood pressure as a key prevention method in minimizing abnormal cognitive aging prior to the onset of clinical dementia.

MicroRNA-195 protects against dementia induced by chronic brain hypoperfusion via its anti-amyloidogenic effect in rats

Previous studies have demonstrated that chronic brain hypoperfusion (CBH) causes Aβ aggregation by upregulating expression of amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE1) protein, which is accompanied by cognitive impairment, but the mechanisms are not fully understood. In this study, we evaluated the effect of microRNA on memory impairment in rats induced by CBH. We show here that CBH generated by bilateral common carotid artery occlusion (2VO) significantly decreased the learning and memory ability in rats, as assessed by Morris water maze, and upregulated expression of APP and BACE1 proteins in the hippocampus and cortex of rats, as evaluated by Western blot and immunofluorescence. In reciprocal, qRT-PCR analysis showed that microRNA-195 (miR-195) was downregulated in both the hippocampus and cortex of rats following CBH, and in the plasma of dementia patients. APP and BACE1 proteins were downregulated by miR-195 overexpression, upregulated by miR-195 inhibition, and unchanged by binding-site mutation or miR-masks, indicating that APP and BACE1 are two potential targets for miR-195. Knockdown of endogenous miR-195 by lentiviral vector-mediated overexpression of its antisense molecule (lenti-pre-AMO-miR-195) elicited dementia in rats, whereas overexpression of miR-195 using lenti-pre-miR-195 reduced dementia vulnerability triggered by 2VO. Additionally, chromatin immunoprecipitation analysis showed that NFκB was bound to the promoter region of miR-195 and inhibited its expression. We conclude that miR-195 may play a key role in determining dementia susceptibility in 2VO rats by regulating APP and BACE1 expression at the post-transcriptional level, and exogenous complement of miR-195 may be a potentially valuable anti-dementia approach.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Cerebrovascular protection of β-asarone in Alzheimer's disease rats: a behavioral, cerebral blood flow, biochemical and genic study

AIM OF THE STUDY

Recent studies have suggested that β-asarone have neuroprotective and cardiovascular protective effects in animal model. However, the influence of β-asarone on cerebrovascular system has not been explored so far. Therefore, present study was designed to determine whether repeated exposures to β-asarone resulted in positive effects on cerebrovascular function in AD rats.

MATERIALS AND METHODS

Alzheimer's disease induced rats was established by injecting both D-galactose (D-gal) and aluminum chloride (AlCl(3)) into abdominal cavity for 42 days. After injection of AlCl(3) and D-gal or saline for 28 days, the rats were treated with volume-matched vehicle or β-asarone (25mg/kg, 50mg/kg or 100mg/kg, i.h.) or Nimodipine (40mg/kg, i.g) once daily for consecutive 14 days, respectively. Behavioral responses of animals were assessed in a Morris water maze. CBF was measured by laser Doppler flowmetry. At the end of this period all rats were sacrificed, lactic acid, pyruvic acid content, Na+K+ATPase activity were determined in brain tissue homogenate to estimate the brain biochemical changes and mRNA expression of ET-1, eNOS and APP was measured with real-time RT-PCR method.

RESULTS

The spatial navigation task latencies, the times through platform zone and the time for the first through platform zone in the target quadrant in probe task, rCBF of right parietal lobe, the contents of lactic acid, pyruvic acid, and the activity of Na-K-ATP of cortex, and ET-1 and eNOS mRNA expression in hippocampus of AG rats were different from those of BG, P<0.05; The level of APP mRNA expression in model control group rats was higher than that in BG, though there was not a statistically significant difference, P>0.05; Compared with AG, HG rats spatial navigation task latencies were shorter, in probe task the times through platform zone in the target quadrant were bigger, rCBF and blood cell concentration of right parietal lobe were higher, the contents of pyruvic acid was lower, the activity of Na-K-ATP was higher, and ET-1 mRNA expression in hippocampus was lower, P<0.05; The level of eNOS and APP mRNA expression in HG rats was lower than that in AG, though there was not a statistically significant difference, P>0.05;

CONCLUSION

The present results suggested that β-asarone may be useful in memory impairment due to its cerebrovascular protection in AD rats and may develop as a therapeutic drug for treatment of AD patients.

Cerebro-afferent vessel and pupillary basal diameter variation induced by stomatognathic trigeminal proprioception: a case report

INTRODUCTION

A patient affected by asymmetric hemodynamics of cerebro-afferent vessels underwent duplex color scanner investigations in occlusal proprioceptive un- and rebalance conditions. Pupillometric video-oculographic examinations were performed in order to spot connected trigeminal proprioceptive motor patterns able to interfere on sympathetic autonomic activity. The aim of this case report is to verify if involuntary jaw closing during swallowing, executed in unbalance and rebalance myoelectric activity, would be able to modify cerebral hemodynamics.

CASE PRESENTATION

A 56-year-old Caucasian Italian woman affected by asymmetric blood flow of cerebro-afferent vessels underwent an electromyographic investigation of her occlusal muscles in order to assess their occlusal functional balance. The extreme asymmetry of myoelectric activity in dental occlusion evidenced by electromyographic values suggested the rebalancing of the functions of occlusal muscles through concurrent transcutaneous stimulation of the trigeminal nerve supra- and submandibular motor branches. The above-mentioned method allowed the detection of a symmetric craniomandibular muscular relation that can be kept constant through the use of a cusp bite modeled on the inferior dental arch: called orthotic-syntropic bite for its peculiar use of electrostimulation. A few days later, the patient underwent a duplex color scanner investigation and pupillometric video-oculographic examinations in occlusal unbalance and rebalance conditions.

CONCLUSIONS

A comparative data analysis showed that an unbalanced dental occlusal function may represent an interferential pattern on cerebral hemodynamics velocity and pupillometric evaluations have proved useful both in the analysis of locus coeruleus functional modalities and as a diagnostic tool in the assessment of pathologies involving locus coeruleus and autonomic systems. The inclusion of myoelectric masseter examinations can be useful in patients with asymmetric hemodynamics of cerebro-afferent vessels and dental occlusal proprioceptive rebalance can integrate the complex therapy of patients with increased chronic sympathetic activity.

Exercise is more effective than diet control in preventing high fat diet-induced β-amyloid deposition and memory deficit in amyloid precursor protein transgenic mice

Accumulating evidence suggests that some dietary patterns, specifically high fat diet (HFD), increase the risk of developing sporadic Alzheimer disease (AD). Thus, interventions targeting HFD-induced metabolic dysfunctions may be effective in preventing the development of AD. We previously demonstrated that amyloid precursor protein (APP)-overexpressing transgenic mice fed HFD showed worsening of cognitive function when compared with control APP mice on normal diet. Moreover, we reported that voluntary exercise ameliorates HFD-induced memory impairment and β-amyloid (Aβ) deposition. In the present study, we conducted diet control to ameliorate the metabolic abnormality caused by HFD on APP transgenic mice and compared the effect of diet control on cognitive function with that of voluntary exercise as well as that of combined (diet control plus exercise) treatment. Surprisingly, we found that exercise was more effective than diet control, although both exercise and diet control ameliorated HFD-induced memory deficit and Aβ deposition. The production of Aβ was not different between the exercise- and the diet control-treated mice. On the other hand, exercise specifically strengthened the activity of neprilysin, the Aβ-degrading enzyme, the level of which was significantly correlated with that of deposited Aβ in our mice. Notably, the effect of the combination treatment (exercise and diet control) on memory and amyloid pathology was not significantly different from that of exercise alone. These studies provide solid evidence that exercise is a useful intervention to rescue HFD-induced aggravation of cognitive decline in transgenic model mice of AD.

Cerebral hypoperfusion accelerates cerebral amyloid angiopathy and promotes cortical microinfarcts

Cortical microinfarcts (CMIs) observed in brains of patients with Alzheimer’s disease tend to be located close to vessels afflicted with cerebral amyloid angiopathy (CAA). CMIs in Alzheimer’s disease are preferentially distributed in the arterial borderzone, an area most vulnerable to hypoperfusion. However, the causal association between CAA and CMIs remains to be elucidated. This study consists of two parts: (1) an observational study using postmortem human brains (n = 31) to determine the association between CAA and CMIs, and (2) an experimental study to determine whether hypoperfusion worsens CAA and induces CMIs in a CAA mouse model. In postmortem human brains, the density of CMIs was 0.113/cm² in mild, 0.584/cm² in moderate, and 4.370/cm² in severe CAA groups with a positive linear correlation (r = 0.6736, p < 0.0001). Multivariate analysis revealed that, among seven variables (age, disease, senile plaques, neurofibrillary tangles, CAA, atherosclerosis and white matter damage), only the severity of CAA was a significant multivariate predictor of CMIs (p = 0.0022). Consistent with the data from human brains, CAA model mice following chronic cerebral hypoperfusion due to bilateral common carotid artery stenosis induced with 0.18-mm diameter microcoils showed accelerated deposition of leptomeningeal amyloid β (Aβ) with a subset of them developing microinfarcts. In contrast, the CAA mice without hypoperfusion exhibited very few leptomeningeal Aβ depositions and no microinfarcts by 32 weeks of age. Following 12 weeks of hypoperfusion, cerebral blood flow decreased by 26% in CAA mice and by 15% in wild-type mice, suggesting impaired microvascular function due to perivascular Aβ accumulation after hypoperfusion. Our results suggest that cerebral hypoperfusion accelerates CAA, and thus promotes CMIs.

Direct stimulation of angiotensin II type 2 receptor enhances spatial memory

We examined the possibility that direct stimulation of the angiotensin II type 2 (AT(2)) receptor by a newly generated direct AT(2) receptor agonist, Compound 21 (C21), enhances cognitive function. Treatment with C21 intraperitoneal injection for 2 weeks significantly enhanced cognitive function evaluated by the Morris water maze test in C57BL6 mice, but this effect was not observed in AT(2) receptor-deficient mice. However, C21-induced cognitive enhancement in C57BL6 mice was attenuated by coadministration of icatibant, a bradykinin B(2) receptor antagonist. Administration of C21 dose dependently increased cerebral blood flow assessed by laser speckle flowmetry and hippocampal field-excitatory postsynaptic potential (f-EPSP) determined by electrophysiological techniques in C57BL6 mice. Furthermore, activation of the AT(2) receptor by C21 promoted neurite outgrowth of cultured hippocampal neurons prepared from fetal transgenic mice expressing green fluorescent protein. Finally, we investigated the pathologic relevance of C21 for spatial learning using an Alzheimer's disease mouse model with intracerebroventricular injection of amyloid-β (1 to 40). We observed that treatment with C21 prevented cognitive decline in this model. These results suggest that a direct AT(2) receptor agonist, C21, enhances cognitive function at least owing to an increase in CBF, enhancement of f-EPSP, and neurite outgrowth in hippocampal neurons.

Environmental enrichment ameliorated high-fat diet-induced Aβ deposition and memory deficit in APP transgenic mice

The pathogenesis of Alzheimer's disease (AD) is tightly associated with metabolic dysfunctions. In particular, a potential link between type 2 diabetes (T2DM) and AD has been suggested epidemiologically, clinically, and experimentally, and some studies have suggested that exercise or dietary intervention reduces risk of cognitive decline. However, there is little solid molecular evidence for the effective intervention of metabolic dysfunctions for prevention of AD. In the present study, we established the AD model mice with diabetic conditions through high-fat diet (HFD) to examine the effect of environmental enrichment (EE) on HFD-induced AD pathophysiology. Here, we demonstrated that HFD markedly deteriorated memory impairment and increased β-amyloid (Aβ) oligomers as well as Aβ deposition in amyloid precursor protein (APP) transgenic mice, which was reversed by exposure to an enriched environment for 10 weeks, despite the continuation of HFD. These studies provide solid evidence that EE is a useful intervention to ameliorate behavioral changes and AD pathology in HFD-induced aggravation of AD symptoms in APP transgenic mice.

Lessons from a mouse model characterizing features of vascular cognitive impairment with white matter changes

With the demographic shift in age in advanced countries inexorably set to progress in the 21st century, dementia will become one of the most important health problems worldwide. Vascular cognitive impairment is the second most common type of dementia after Alzheimer's disease and is frequently responsible for the cognitive decline of the elderly. It is characterized by cerebrovascular white matter changes; thus, in order to investigate the underlying mechanisms involved in white matter changes, a mouse model of chronic cerebral hypoperfusion has been developed, which involves the narrowing of the bilateral common carotid arteries with newly designed microcoils. The purpose of this paper is to provide a comprehensive summary of the achievements made with the model that shows good reproducibility of the white matter changes characterized by blood-brain barrier disruption, glial activation, oxidative stress, and oligodendrocyte loss following chronic cerebral hypoperfusion. Detailed characterization of this model may help to decipher the substrates associated with impaired memory and move toward a more integrated therapy of vascular cognitive impairment.

Axon-glial disruption: the link between vascular disease and Alzheimer's disease?

Vascular risk factors play a critical role in the development of cognitive decline and AD (Alzheimer's disease), during aging, and often result in chronic cerebral hypoperfusion. The neurobiological link between hypoperfusion and cognitive decline is not yet defined, but is proposed to involve damage to the brain's white matter. In a newly developed mouse model, hypoperfusion, in isolation, produces a slowly developing and diffuse damage to myelinated axons, which is widespread in the brain, and is associated with a selective impairment in working memory. Cerebral hypoperfusion, an early event in AD, has also been shown to be associated with white matter damage and notably an accumulation of amyloid. The present review highlights some of the published data linking white matter disruption to aging and AD as a result of vascular dysfunction. A model is proposed by which chronic cerebral hypoperfusion, as a result of vascular factors, results in both the generation and accumulation of amyloid and injury to white matter integrity, resulting in cognitive impairment. The generation of amyloid and accumulation in the vasculature may act to perpetuate further vascular dysfunction and accelerate white matter pathology, and as a consequence grey matter pathology and cognitive decline.

The Fox and the Rabbits-Environmental Variables and Population Genetics (1) Replication Problems in Association Studies and the Untapped Power of GWAS (2) Vitamin A Deficiency, Herpes Simplex Reactivation and Other Causes of Alzheimer's Disease

Classical population genetics shows that varying permutations of genes and risk factors permit or disallow the effects of causative agents, depending on circumstance. For example, genes and environment determine whether a fox kills black or white rabbits on snow or black ash covered islands. Risk promoting effects are different on each island, but obscured by meta-analysis or GWAS data from both islands, unless partitioned by different contributory factors. In Alzheimer's disease, the foxes appear to be herpes, borrelia or chlamydial infection, hypercholesterolemia, hyperhomocysteinaemia, diabetes, cerebral hypoperfusion, oestrogen depletion, or vitamin A deficiency, all of which promote beta-amyloid deposition in animal models—without the aid of gene variants. All relate to risk factors and subsets of susceptibility genes, which condition their effects. All are less prevalent in convents, where nuns appear less susceptible to the ravages of ageing. Antagonism of the antimicrobial properties of beta-amyloid by Abeta autoantibodies in the ageing population, likely generated by antibodies raised to beta-amyloid/pathogen protein homologues, may play a role in this scenario. These agents are treatable by diet and drugs, vitamin supplementation, pathogen detection and elimination, and autoantibody removal, although again, the beneficial effects of individual treatments may be tempered by genes and environment.

Synergistic memory impairment through the interaction of chronic cerebral hypoperfusion and amlyloid toxicity in a rat model

BACKGROUND AND PURPOSE

Vascular pathology and Alzheimer disease (AD) pathology have been shown to coexist in the brains of dementia patients. We investigated how cognitive impairment could be exacerbated in a rat model of combined injury through the interaction of chronic cerebral hypoperfusion and amyloid beta (Aβ) toxicity.

METHODS

In Wistar rats, chronic cerebral hypoperfusion was modeled by permanent occlusion of bilateral common carotid arteries (BCCAo). Further, AD pathology was modeled by bilateral intracerebroventricular Aβ (Aβ toxicity) using a nonphysiological Aβ peptide (Aβ 25 to 35). The experimental animals were divided into 4 groups, including sham, single injury (Aβ toxicity or BCCAo), and combined injury (BCCAo-Aβ toxicity) groups (n=7 per group) . Cerebral blood flow and metabolism were measured using small animal positron emission tomography. A Morris water maze task, novel object location and recognition tests, and histological investigation, including neuronal cell death, apoptosis, neuroinflammation, and AD-related pathology, were performed.

RESULTS

Spatial memory impairment was synergistically exacerbated in the BCCAo-Aβ toxicity group as compared to the BCCAo or Aβ toxicity groups (P<0.05). Compared to the sham group, neuroinflammation with microglial or astroglial activation was increased both in multiple white matter lesions and the hippocampus in other experimental groups. AD-related pathology was enhanced in the BCCAo-Aβ toxicity group compared to the Aβ toxicity group.

CONCLUSIONS

Our experimental results support a clinical hypothesis of the deleterious interaction between chronic cerebral hypoperfusion and Aβ toxicity. Chronic cerebral hypoperfusion-induced perturbation in the equilibrium of AD-related pathology may exacerbate cognitive impairment in a rat model of combined injury.

The influence of chronic cerebral hypoperfusion on cognitive function and amyloid β metabolism in APP overexpressing mice

Background and Purpose

Cognitive impairment resulting from cerebrovascular insufficiency has been termed vascular cognitive impairment, and is generally accepted to be distinct from Alzheimer's disease resulting from a neurodegenerative process. However, it is clear that this simple dichotomy may need revision in light of the apparent occurrence of several shared features between Alzheimer's disease and vascular cognitive impairment. Nevertheless, it still remains largely unknown whether the burden of vascular- and Alzheimer-type neuropathology are independent or interdependent. Therefore, we investigated whether chronic cerebral hypoperfusion influences cognitive ability or amyloid β deposition in amyloid precursor protein (APP) overexpressing transgenic mice.

Methods

Two months old mice overexpressing a mutant form of the human APP bearing both the Swedish and Indiana mutations (APP_Sw/Ind-Tg mice), or their wild-type littermates, were subjected to chronic cerebral hypoperfusion with bilateral common carotid artery stenosis (BCAS) using microcoils or sham operation. Barnes maze test performance and histopathological findings were analyzed at eight months old by 2×2 factorial experimental designs with four groups.

Results

BCAS-operated APP_Sw/Ind-Tg mice showed significantly impaired learning ability compared to the other three groups of mice. Two-way repeated measures analysis of variance showed a synergistic interaction between the APP genotype and BCAS operation in inducing learning impairment. The cognitive performances were significantly correlated with the neuronal densities. BCAS significantly reduced the density of Nissl-stained neurons and silver-stained cored plaques in the hippocampus of APP_Sw/Ind-Tg mice but increased the amount of filter-trap amyloid β in the extracellular-enriched soluble brain fraction, compared to those from sham operated mice.

Conclusions

The results suggest interaction between chronic cerebral hypoperfusion and APP_Sw/Ind overexpression in cognitive decline in mice through enhanced neuronal loss and altered amyloid β metabolism.

[Diagnosis and treatment of subcortical vascular dementia]

Subcortical vascular dementia (SVD) exhibits relatively uniform clinical and pathological features among various subtypes of vascular dementia, and constitutes approximately half of vascular dementia in Japan. This subtype is further classified into Binswanger's type infarction and multiple lacunar infarctions. The former is characterized by diffuse white matter lesions, and the latter by lacunar infarctions. However, the both have common pathologic mechanism related to hypertensive small vessel changes. This paper overview the notion, clinical features, pathogenesis and treatment for SVD, and also refer to the recent topics related to Alzheimer's disease.

A mouse model characterizing features of vascular dementia with hippocampal atrophy

BACKGROUND AND PURPOSE

We have previously described effects of chronic cerebral hypoperfusion in mice with bilateral common carotid artery stenosis (BCAS) using microcoils for 30 days. These mice specifically exhibit working memory deficits attributable to frontal-subcortical circuit damage without apparent gray matter changes, indicating similarities with subcortical ischemic vascular dementia. However, as subcortical ischemic vascular dementia progresses over time, the longer-term effects that characterize the mouse model are not known.

METHODS

Comprehensive behavioral test batteries and histological examinations were performed in mice subjected to BCAS for up to 8 months. Laser speckle flowmetry and (18)F-fluorodeoxyglucose positron emission tomography were performed to assess cerebral blood flow and metabolism at several time points.

RESULTS

At 2 hours after BCAS, cerebral blood flow in the cerebral cortex temporarily decreased to as much as 60% to 70% of the control value but gradually recovered to >80% at 1 to 3 months. At 5 to 6 months after BCAS, reference and working memory were impaired as demonstrated by the Barnes and radial arm maze tests, respectively. Furthermore, (18)F-fluorodeoxyglucose positron emission tomography demonstrated that hippocampal glucose utilization was impaired at 6 months after BCAS. Consistent with these behavioral and metabolic abnormalities, histological analyses demonstrated hippocampal atrophy with pyknotic and apoptotic cells at 8 months after BCAS.

CONCLUSIONS

These results suggest that the longer-term BCAS model replicates advanced stages of subcortical ischemic vascular dementia when hippocampal neuronal loss becomes significant.