Focal cerebral ischemia in rats alters APP processing and expression of Abeta peptide degrading enzymes in the thalamus

Associations between amyloid-β load and cognition in cerebrovascular disease beyond cerebral amyloid angiopathy: a systematic review and meta-analysis of positron emission tomography studies

BACKGROUND

There is growing interest in the comorbidity of vascular and neurodegenerative pathologies in patients with cerebrovascular disease (CVD) beyond cerebral amyloid angiopathy (CAA). However, the relationship between amyloid-β and vascular cognitive impairment (VCI) remains debated.

OBJECTIVE

To investigate the association between VCI and amyloid-β deposition in non-CAA CVD patients.

METHODS

PubMed, Embase, Web of Science, PsycINFO and CENTRAL databases were systematically searched. Observational studies, including case-control and cohort studies, associating cognitive scores with amyloid load measured by positron emission tomography were selected. Meta-analyses were performed to assess the strength of amyloid-cognition associations across CVD subtypes and cognitive domains. A random-effects model using the inverse variance method was used, with heterogeneity evaluated by Q-statistics and I2 statistics. Meta-regression analyses were conducted to examine the influence of moderators, and publication bias was assessed using funnel plots and Egger's test. All statistical analyses were performed using StataMP 18.

RESULTS

Twenty-seven eligible studies encompassing 2894 participants were included. Among non-CAA CVD patients, global cognitive performance was significantly lower in those with higher amyloid-β deposition (standardized mean difference = -0.43, P < 0.001). The correlation strength varied across cognitive domains (executive function: r = -0.41; language: r = -0.36; memory: r = -0.29; all P < 0.001). The correlation was significant in patients with subcortical vascular disease (r = -0.43, P < 0.001) but not post-stroke patients (r = -0.19, P > 0.05).

CONCLUSIONS

Amyloid-β load is associated with cognitive decline in non-CAA CVD patients. This is more pronounced in patients with subcortical vascular disease than in post-stroke patients. Executive function is the most susceptible domain in VCI when the level of amyloid-β increases.

Rodent Models of Post-Stroke Dementia

Post-stroke cognitive impairment is one of the most common complications in stroke survivors. Concomitant vascular risk factors, including aging, diabetes mellitus, hypertension, dyslipidemia, or underlying pathologic conditions, such as chronic cerebral hypoperfusion, white matter hyperintensities, or Alzheimer’s disease pathology, can predispose patients to develop post-stroke dementia (PSD). Given the various clinical conditions associated with PSD, a single animal model for PSD is not possible. Animal models of PSD that consider these diverse clinical situations have not been well-studied. In this literature review, diverse rodent models that simulate the various clinical conditions of PSD have been evaluated. Heterogeneous rodent models of PSD are classified into the following categories: surgical technique, special structure, and comorbid condition. The characteristics of individual models and their clinical significance are discussed in detail. Diverse rodent models mimicking the specific pathomechanisms of PSD could provide effective animal platforms for future studies investigating the characteristics and pathophysiology of PSD.

A Study on the Pathogenesis of Vascular Cognitive Impairment and Dementia: The Chronic Cerebral Hypoperfusion Hypothesis

The pathogenic mechanisms underlying vascular cognitive impairment and dementia (VCID) remain controversial due to the heterogeneity of vascular causes and complexity of disease neuropathology. However, one common feature shared among all these vascular causes is cerebral blood flow (CBF) dysregulation, and chronic cerebral hypoperfusion (CCH) is the universal consequence of CBF dysregulation, which subsequently results in an insufficient blood supply to the brain, ultimately contributing to VCID. The purpose of this comprehensive review is to emphasize the important contributions of CCH to VCID and illustrate the current findings about the mechanisms involved in CCH-induced VCID pathological changes. Specifically, evidence is mainly provided to support the molecular mechanisms, including Aβ accumulation, inflammation, oxidative stress, blood-brain barrier (BBB) disruption, trophic uncoupling and white matter lesions (WMLs). Notably, there are close interactions among these multiple mechanisms, and further research is necessary to elucidate the hitherto unsolved questions regarding these interactions. An enhanced understanding of the pathological features in preclinical models could provide a theoretical basis, ultimately achieving the shift from treatment to prevention.

Neuroinflammation as a Key Driver of Secondary Neurodegeneration Following Stroke?

Ischaemic stroke involves the rapid onset of focal neurological dysfunction, most commonly due to an arterial blockage in a specific region of the brain. Stroke is a leading cause of death and common cause of disability, with over 17 million people worldwide suffering from a stroke each year. It is now well-documented that neuroinflammation and immune mediators play a key role in acute and long-term neuronal tissue damage and healing, not only in the infarct core but also in distal regions. Importantly, in these distal regions, termed sites of secondary neurodegeneration (SND), spikes in neuroinflammation may be seen sometime after the initial stroke onset, but prior to the presence of the neuronal tissue damage within these regions. However, it is key to acknowledge that, despite the mounting information describing neuroinflammation following ischaemic stroke, the exact mechanisms whereby inflammatory cells and their mediators drive stroke-induced neuroinflammation are still not fully understood. As a result, current anti-inflammatory treatments have failed to show efficacy in clinical trials. In this review we discuss the complexities of post-stroke neuroinflammation, specifically how it affects neuronal tissue and post-stroke outcome acutely, chronically, and in sites of SND. We then discuss current and previously assessed anti-inflammatory therapies, with a particular focus on how failed anti-inflammatories may be repurposed to target SND-associated neuroinflammation.

Effect of Global Brain Ischemia on Amyloid Precursor Protein Metabolism and Expression of Amyloid-Degrading Enzymes in Rat Cortex: Role in Pathogenesis of Alzheimer's Disease

The incidence of Alzheimer's disease (AD) increases significantly following chronic stress and brain ischemia which, over the years, cause accumulation of toxic amyloid species and brain damage. The effects of global 15-min ischemia and 120-min reperfusion on the levels of expression of the amyloid precursor protein (APP) and its processing were investigated in the brain cortex (Cx) of male Wistar rats. Additionally, the levels of expression of the amyloid-degrading enzymes neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), and insulin-degrading enzyme (IDE), as well as of some markers of oxidative damage were assessed. It was shown that the APP mRNA and protein levels in the rat Cx were significantly increased after the ischemic insult. Protein levels of the soluble APP fragments, especially of sAPPβ produced by β-secretase, (BACE-1) and the levels of BACE-1 mRNA and protein expression itself were also increased after ischemia. The protein levels of APP and BACE-1 in the Cx returned to the control values after 120-min reperfusion. The levels of NEP and ECE-1 mRNA also decreased after ischemia, which correlated with the decreased protein levels of these enzymes. However, we have not observed any changes in the protein levels of insulin-degrading enzyme. Contents of the markers of oxidative damage (di-tyrosine and lysine conjugates with lipid peroxidation products) were also increased after ischemia. The obtained data suggest that ischemia shifts APP processing towards the amyloidogenic β-secretase pathway and accumulation of the neurotoxic Aβ peptide as well as triggers oxidative stress in the cells. These results are discussed in the context of the role of stress and ischemia in initiation and progression of AD.

Is Cerebral Amyloid-β Deposition Related to Post-stroke Cognitive Impairment?

Approximately two-thirds of ischemic stroke patients suffer from different levels of post-stroke cognitive impairment (PSCI), but the underlying mechanisms of PSCI remain unclear. Cerebral amyloid-β (Aβ) deposition, a pathological hallmark of Alzheimer's disease, has been discovered in the brains of stroke patients in some autopsy studies. However, less is known about the role of Aβ pathology in the development of PSCI. It is hypothesized that cerebral ischemic injury may lead to neurotoxic Aβ accumulation in the brain, which further induces secondary neurodegeneration and progressive cognitive decline after stroke onset. In this review, we summarized available evidence from pre-clinical and clinical studies relevant to the aforementioned hypothesis. We found inconsistency in the results obtained from studies in rodents, nonhuman primates, and stroke patients. Moreover, the causal relationship between post-stroke cerebral Aβ deposition and PSCI has been uncertain and controversial. Taken together, evidence supporting the hypothesis that brain ischemia induces cerebral Aβ deposition has been insufficient so far. And, there is still no consensus regarding the contribution of cerebral amyloid pathology to PSCI. Other non-amyloid neurodegenerative mechanisms might be involved and remain to be fully elucidated.

SSAO/VAP-1 in Cerebrovascular Disorders: A Potential Therapeutic Target for Stroke and Alzheimer's Disease

The semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1) or primary amine oxidase (PrAO), is a deaminating enzyme highly expressed in vessels that generates harmful products as a result of its enzymatic activity. As a multifunctional enzyme, it is also involved in inflammation through its ability to bind and promote the transmigration of circulating leukocytes into inflamed tissues. Inflammation is present in different systemic and cerebral diseases, including stroke and Alzheimer’s disease (AD). These pathologies show important affectations on cerebral vessels, together with increased SSAO levels. This review summarizes the main roles of SSAO/VAP-1 in human physiology and pathophysiology and discusses the mechanisms by which it can affect the onset and progression of both stroke and AD. As there is an evident interrelationship between stroke and AD, basically through the vascular system dysfunction, the possibility that SSAO/VAP-1 could be involved in the transition between these two pathologies is suggested. Hence, its inhibition is proposed to be an interesting therapeutical approach to the brain damage induced in these both cerebral pathologies.

Inflammatory Responses in the Secondary Thalamic Injury After Cortical Ischemic Stroke

Stroke is one of the major causes of chronic disability worldwide and increasing efforts have focused on studying brain repair and recovery after stroke. Following stroke, the primary injury site can disrupt functional connections in nearby and remotely connected brain regions, resulting in the development of secondary injuries that may impede long-term functional recovery. In particular, secondary degenerative injury occurs in the connected ipsilesional thalamus following a cortical stroke. Although secondary thalamic injury was first described decades ago, the underlying mechanisms still remain unclear. We performed a systematic literature review using the NCBI PubMed database for studies that focused on the secondary thalamic degeneration after cortical ischemic stroke. In this review, we discussed emerging studies that characterized the pathological changes in the secondary degenerative thalamus after stroke; these included excitotoxicity, apoptosis, amyloid beta protein accumulation, blood-brain-barrier breakdown, and inflammatory responses. In particular, we highlighted key findings of the dynamic inflammatory responses in the secondary thalamic injury and discussed the involvement of several cell types in this process. We also discussed studies that investigated the effects of blocking secondary thalamic injury on inflammatory responses and stroke outcome. Targeting secondary injuries after stroke may alleviate network-wide deficits, and ultimately promote stroke recovery.

δ-Opioid receptor as a potential therapeutic target for ischemic stroke

Ischemic stroke is a global epidemic condition due to an inadequate supply of blood and oxygen to a specific area of brain either by arterial blockage or by narrowing of blood vessels. Despite having advancement in the use of thrombolytic and clot removal medicine, significant numbers of stroke patients are still left out without option for treatment. In this review, we summarize recent research work on the activation of δ-opioid receptor as a strategy for treating ischemic stroke-caused neuronal injury. Moreover, as activation of δ-opioid receptor by a non-peptidic δ-opioid receptor agonist also modulates the expression, maturation and processing of amyloid precursor protein and β-secretase activity, the potential role of these effects on ischemic stroke caused dementia or Alzheimer's disease are also discussed.

Interactions of Aromatase and Seladin-1: A Neurosteroidogenic and Gender Perspective

Aromatase and seladin-1 are enzymes that have major roles in estrogen synthesis and are important in both brain physiology and pathology. Aromatase is the key enzyme that catalyzes estrogen biosynthesis from androgen precursors and regulates the brain’s neurosteroidogenic activity. Seladin-1 is the enzyme that catalyzes the last step in the biosynthesis of cholesterol, the precursor of all hormones, from desmosterol. Studies indicated that seladin-1 is a downstream mediator of the neuroprotective activity of estrogen. Recently, we also showed that there is an interaction between aromatase and seladin-1 in the brain. Therefore, the expression of local brain aromatase and seladin-1 is important, as they produce neuroactive steroids in the brain for the protection of neuronal damage. Increasing steroid biosynthesis specifically in the central nervous system (CNS) without affecting peripheral hormone levels may be possible by manipulating brain-specific promoters of steroidogenic enzymes. This review emphasizes that local estrogen, rather than plasma estrogen, may be responsible for estrogens’ protective effects in the brain. Therefore, the roles of aromatase and seladin-1 and their interactions in neurodegenerative events such as Alzheimer’s disease (AD), ischemia/reperfusion injury (stroke), and epilepsy are also discussed in this review.

Attenuation of Ischemic Stroke-Caused Brain Injury by a Monoamine Oxidase Inhibitor Involves Improved Proteostasis and Reduced Neuroinflammation

Mitochondrial dysfunction and oxidative stress play a key role in ischemia/reperfusion (I/R) induced brain injury. We previously showed that ubiquilin-1 (Ubqln1), a ubiquitin-like protein, improves proteostasis and protects brains against oxidative stress and I/R induced brain injury. We demonstrate here that nialamide (NM), a non-selective monoamine oxidase (MAO) inhibitor, upregulated Ublqn1 and protected neurons from oxygen-glucose deprivation- and I/R-caused cell death in in vitro and in vivo, respectively. Post-ischemic administration of the NM in a stroke mouse model even at 3 h following I/R still reduced neuronal injury and improved functional recovery and survival. Treating stroke animals with NM also increased the association of Ubqln1 with mitochondria and decreased the total oxidized and polyubiquitinated protein levels. Intriguingly, NM-enhanced proteostasis was also associated with reduced I/R-caused neuroinflammation, as reflected by attenuated activation of microglia and astrocytes as well as reduced TNF-α level. Thus, our results suggest that MAO inhibition-induced neuroprotection following I/R involves improved proteostasis and reduced neuroinflammation.

EphrinB2 activation enhances angiogenesis, reduces amyloid-β deposits and secondary damage in thalamus at the early stage after cortical infarction in hypertensive rats

Cerebral infarction causes secondary neurodegeneration and angiogenesis in thalamus, which impacts functional recovery after stroke. Here, we hypothesize that activation of ephrinB2 could stimulate angiogenesis and restore the secondary neurodegeneration in thalamus after cerebral infarction. Focal cerebral infarction was induced by middle cerebral artery occlusion (MCAO). Secondary damage, angiogenesis, amyloid-β (Aβ) deposits, levels of ephrinB2 and receptor for advanced glycation end product (RAGE) in the ipsilateral thalamus were determined by immunofluorescence and immunoblot. The contribution of ephrinB2 to angiogenesis was determined by siRNA-mediated knockdown of ephrinB2 and pharmacological activation of ephrinB2. The results showed that formation of new vessels and ephrinB2 expression was markedly increased in the ipsilateral thalamus at seven days after MCAO. EphrinB2 knockdown markedly suppressed angiogenesis coinciding with increased Aβ accumulation, neuronal loss and gliosis in the ipsilateral thalamus. In contrast, clustered EphB2-Fc significantly enhanced angiogenesis, alleviated Aβ accumulation and the secondary thalamic damage, which was accompanied by accelerated function recovery. Additionally, activation of ephrinB2 significantly reduced RAGE levels in the ipsilateral thalamus. Our findings suggest that activation of ephrinB2 promotes angiogenesis, ameliorates Aβ accumulation and the secondary thalamic damage after cerebral infarction. Additionally, RAGE might be involved in Aβ clearance by activating ephrinB2 in the thalamus.

Neuronal loss without amyloid-β deposits in the thalamus and hippocampus in the late period after middle cerebral artery occlusion in cynomolgus monkeys

Conflicting evidence exists regarding whether focal cerebral infarction contributes to cerebral amyloid-β (Aβ) deposition, as observed in Alzheimer's disease. In this study, we aimed to evaluate the presence of Aβ deposits in the ipsilateral thalamus and hippocampus 12 months post-stroke in non-human primates, whose brains are structurally and functionally similar to that of humans. Four young male cynomolgus monkeys were subjected to unilateral permanent middle cerebral artery occlusion (MCAO), and another four sham-operated monkeys served as controls. All monkeys underwent magnetic resonance imaging examination on post-operative day 7 to assess the location and size of the infarction. The numbers of neurons, astrocytes, microglia and the Aβ load in the non-affected thalamus and hippocampus ipsilaterally remote from infarct foci were examined immunohistochemically at sacrifice 12 months after operation. Thioflavin S and Congo Red stainings were used to identify amyloid deposits. Multiple Aβ antibodies recognizing both the N-terminal and C-terminal epitopes of Aβ peptides were used to avoid antibody cross-reactivity. Aβ levels in cerebrospinal fluid (CSF) and plasma were examined using enzyme-linked immunosorbent assay. The initial infarct was restricted to the left temporal, parietal, insular cortex and the subcortical white matter, while the thalamus and hippocampus remained intact. Of note, there were fewer neurons and more glia in the ipsilateral thalamus and hippocampus in the MCAO group at 12 months post-stroke compared to the control group (all P < 0.05). However, there was no sign of extracellular Aβ plaques in the thalamus or hippocampus. No statistically significant difference was found in CSF or plasma levels of Aβ₄₀ , Aβ₄₂ or the Aβ₄₀ /Aβ₄₂ ratio between the two groups (P > 0.05). These results suggest that significant secondary neuronal loss and reactive gliosis occur in the non-affected thalamus and hippocampus without Aβ deposits in the late period after MCAO in non-human primates.

The Effect of Chronic Cerebral Hypoperfusion on Amyloid-β Metabolism in a Transgenic Mouse Model of Alzheimer's Disease (PS1V97L)

Alzheimer's disease (AD) and cerebrovascular disease often coexist. However, it is difficult to determine how chronic cerebral hypoperfusion affects the metabolism of amyloid-β peptides (Aβ) in a living patient with AD. Thus, we developed an animal model of this condition, using transgenic mice (PS1V97L) and right common carotid artery ligation to create chronic cerebral hypoperfusion. The metabolic processes associated with amyloid-β peptide (Aβ) were observed and evaluated in this PS1V97L plus hypoperfusion model. Compared with control mice, the model revealed significantly upregulated expression of Aβ (including Aβ oligomers), with decreased α-secretase activity and expression and increased β-secretase activity and expression. Furthermore, the model revealed increased mRNA and protein expression of the receptor for advanced glycation end products (RAGE) and decreased mRNA and protein expression of low-density lipoprotein receptor-related protein 1 (LRP-1); both these are Aβ transporters. Moreover, the model revealed decreased activity and expression of neprilysin, which is a peripheral Aβ degrading enzyme. These findings suggest that hypoperfusion may magnify the effect of AD on Aβ metabolism by aggravating its abnormal production, transport, and clearance.

Modelling Sporadic Alzheimer's Disease Using Induced Pluripotent Stem Cells

Developing cellular models of sporadic Alzheimer's disease (sAD) is challenging due to the unknown initiator of disease onset and the slow disease progression that takes many years to develop in vivo. The use of human induced pluripotent stem cells (iPSCs) has revolutionised the opportunities to model AD pathology, investigate disease mechanisms and screen potential drugs. The majority of this work has, however, used cells derived from patients with familial AD (fAD) where specific genetic mutations drive disease onset. While these provide excellent models to investigate the downstream pathways involved in neuronal toxicity and ultimately neuronal death that leads to AD, they provide little insight into the causes and mechanisms driving the development of sAD. In this review we compare the data obtained from fAD and sAD iPSC-derived cell lines, identify the inconsistencies that exist in sAD models and highlight the potential role of Aβ clearance mechanisms, a relatively under-investigated area in iPSC-derived models, in the study of AD. We discuss the development of more physiologically relevant models using co-culture and three-dimensional culture of iPSC-derived neurons with glial cells. Finally, we evaluate whether we can develop better, more consistent models for sAD research using genetic stratification of iPSCs and identification of genetic and environmental risk factors that could be used to initiate disease onset for modelling sAD. These considerations provide exciting opportunities to develop more relevant iPSC models of sAD which can help drive our understanding of disease mechanisms and identify new therapeutic targets.

Alterations in the spinal cord and ventral root after cerebral infarction in non-human primates

BACKGROUNDS

Cerebral infarction does not only cause focal injury in the ischemic site, but also secondary non-ischemic damage at the remote areas of nervous system associated with the primary focus.

OBJECTIVE

This study investigated the changes in the spinal cord and ventral root after middle cerebral artery occlusion (MCAO) in cynomolgus monkeys (Macaca fascicularis).

METHODS

Adult male cynonolgus monkeys (4-5 years, 5.5-7.5 kg) were subjected to MCAO (n = 6) or sham surgery (n = 4). After 12 weeks, spinal cords and the ventral roots were harvested. Morphometric alterations in the spinal cord were detected at C5 and L5 levels via immunofluorescence. The profiles of C5 and L5 ventral roots were displayed by toluidine blue staining and transmission electron microscopic examination.

RESULTS

Significant axonal loss in the contralateral corticospinal tract and abnormally enlarged axons in the ipsilateral were observed in monkeys with MCAO. The number of neurons in the contralateral ventral horn got declined while that in the ipsilateral was almost unaffected after MCAO compared with sham controls. Glial activation post-MCAO was observed in the bilateral corticospinal tract and the ventral horn. Aberrant nerve fibers appeared frequently in the contralateral ventral roots of MCAO monkey but rarely in the ipsilateral.

CONCLUSIONS

These results indicate that focal cerebral infarction leads to pathological alterations in the spinal cord and ventral roots in non-human primates.

Alzheimer's associated amyloid and tau deposition co-localizes with a homeostatic myelin repair pathway in two mouse models of post-stroke mixed dementia

The goal of this study was to determine the chronic impact of stroke on the manifestation of Alzheimer’s disease (AD) related pathology and behavioral impairments in mice. To accomplish this goal, we used two distinct models. First, we experimentally induced ischemic stroke in aged wildtype (wt) C57BL/6 mice to determine if stroke leads to the manifestation of AD-associated pathological β-amyloid (Aβ) and tau in aged versus young adult wt mice. Second, we utilized a transgenic (Tg) mouse model of AD (hAPP-SL) to determine if stroke leads to the worsening of pre-existing AD pathology, as well as the development of pathology in brain regions not typically expressed in AD Tg mice. In the wt mice, there was delayed motor recovery and an accelerated development of cognitive deficits in aged mice compared to young adult mice following stroke. This corresponded with increased brain atrophy, increased cholinergic degeneration, and a focal increase of Aβ in areas of axonal degeneration in the ipsilateral hemisphere of the aged animals. By contrast, in the hAPP-SL mice, we found that ischemia induced aggravated behavioral deficits in conjunction with a global increase in Aβ_, tau, and cholinergic pathology compared to hAPP-SL mice that underwent a sham stroke procedure. With regard to a potential mechanism, in both models, we found that the stroke-induced Aβ and tau deposits co-localized with increased levels of β-secretase 1 (BACE1), along with its substrate, neuregulin 1 (NGR1) type III, both of which are proteins integral for myelin repair. Based on these findings, we propose that the chronic sequelae of stroke may be ratcheting-up a myelin repair pathway, and that the consequent increase in BACE1 could be causing an inadvertent cleavage of its alternative substrate, AβPP, resulting in greater Aβ seeding and pathogenesis.

The non-peptidic δ-opioid receptor agonist Tan-67 mediates neuroprotection post-ischemically and is associated with altered amyloid precursor protein expression, maturation and processing in mice

Tan-67 is a selective non-peptidic δ-opioid receptor (DOR) agonist that confers neuroprotection against cerebral ischemia/reperfusion (I/R)-caused neuronal injury in pre-treated animals. In this study, we examined whether post-ischemic administration of Tan-67 in stroke mice is also neuroprotective and whether the treatment affects expression, maturation and processing of the amyloid precursor protein (APP). A focal cerebral I/R model in mice was induced by middle cerebral artery occlusion for 1 h and Tan-67 (1.5, 3 or 4.5 mg/kg) was administered via the tail vein at 1 h after reperfusion. Alternatively, naltrindole, a selective DOR antagonist (5 mg/kg), was administered 1 h before Tan-67 treatment. Our results showed that post-ischemic administration of Tan-67 (3 mg/kg or 4.5 mg/kg) was neuroprotective as shown by decreased infarct volume and neuronal loss following I/R. Importantly, Tan-67 improved animal survival and neurobehavioral outcomes. Conversely, naltrindole abolished Tan-67 neuroprotection in infarct volume. Tan-67 treatment also increased APP expression, maturation and processing in the ipsilateral penumbral area at 6 h but decreased APP expression and maturation in the same brain area at 24 h after I/R. Tan-67-induced increase in APP expression was also seen in the ischemic cortex at 24 h following I/R. Moreover, Tan-67 attenuated BACE-1 expression, β-secretase activity and the BACE cleavage of APP in the ischemic cortex at 24 h after I/R, which was abolished by naltrindole. Our data suggest that Tan-67 is a promising DOR-dependent therapeutic agent for treating I/R-caused disorder and that Tan-67-mediated neuroprotection may be mediated via modulating APP expression, maturation and processing, despite an uncertain causative relationship between the altered APP and the outcomes observed.

Chronic cerebral hypoperfusion induces post-stroke dementia following acute ischemic stroke in rats

BACKGROUND

Post-stroke dementia (PSD) is one of the major consequences after stroke. Chronic cerebral hypoperfusion (CCH) can induce vascular cognitive impairment and potentiate amyloid pathology. We investigated how CCH contributes to the development of PSD after stroke in the context of neuroinflammation and amyloid pathology.

METHODS

We designed a unique animal model for PSD. We performed middle cerebral artery occlusion (MCAO) surgery in rats mimicking acute territorial infarct, which was followed by bilateral common carotid artery occlusion (BCCAo) surgery mimicking CCH. We performed behavioral tests including neurologic function test and water maze task and histological investigations including neuroinflammation, neuronal cell death, amyloid pathology, and aquaporin 4 (AQP4) distribution.

RESULTS

Spatial memory was synergistically impaired when BCCAo was superimposed on MCAO. Neuroinflammation with astroglial or microglial activation and amyloid pathology were enhanced in the ipsilateral cortex, thalamus, and hippocampus when BCCAo was superimposed on MCAO. Glymphatic pathway-related AQP4 distribution changed from perivascular to parenchymal pattern.

CONCLUSIONS

Our experimental results suggest that CCH may contribute to the development of PSD by interfering with amyloid clearance through the glymphatic pathway and concomitant neuroinflammation. Therapeutic strategy to clear brain metabolic waste through the glymphatic pathway may be a promising approach to prevent PSD after stroke.

Physiologic Reelin does not play a strong role in protection against acute stroke

Stroke and Alzheimer's disease, two diseases that disproportionately affect the aging population, share a subset of pathological findings and risk factors. The primary genetic risk factor after age for late-onset Alzheimer's disease, ApoE4, has also been shown to increase stroke risk and the incidence of post-stroke dementia. One mechanism by which ApoE4 contributes to disease is by inducing in neurons a resistance to Reelin, a neuromodulator that enhances synaptic function. Previous studies in Reelin knockout mice suggest a role for Reelin in protection against stroke; however, these studies were limited by the developmental requirement for Reelin in neuronal migration. To address the question of the effect of Reelin loss on stroke susceptibility in an architecturally normal brain, we utilized a novel mouse with induced genetic reduction of Reelin. We found that after transient middle cerebral artery occlusion, mice with complete adult loss of Reelin exhibited a similar level of functional deficit and extent of infarct as control mice. Together, these results suggest that physiological Reelin does not play a strong role in protection against stroke pathology.

Expression of amyloid-β protein and amyloid-β precursor protein after primary brain-stem injury in rats

Amyloid-β (Aβ) protein and its precursor, amyloid-β precursor protein (β-APP), have traditionally been used in the diagnosis of Alzheimer disease. Their use in diagnosis of traumatic brain injury by forensic analysis is becoming more widespread. However, to date, no reliable small animal model exists to evaluate these brain injury indicators. To address this, we have studied primary brain-stem injury in rats to assess the appearance of diffuse axonal injury in brain sections and correlate these findings with appearance of Aβ and relative β-APP mRNA levels. Using an EnVision 2-step immunohistochemical staining method to measure axon diameter, we found that there was significant difference in axon diameters within the medulla oblongata and several time points after brain injury, ranging from 3 to 24 hours. In addition, mRNA expression levels of β-APP increased following brain injury, peaking 3 hours following injury and decreasing back to baseline levels by 24 hours after injury. These results suggest that using immunohistochemistry and reverse transcription-polymerase chain reaction to detect changes in Aβ-associated axonal changes and β-APP mRNA levels, respectively, can be useful for the diagnosis of diffuse axonal injury during autopsy at early time points following fatal brain injury.

Unexpected complication in a rat stroke model: exacerbation of secondary pathology in the thalamus by subacute intraarterial administration of human bone marrow-derived mesenchymal stem cells

This study examined whether human bone marrow mesenchymal stromal/stem cells (BMMSCs) could alleviate the secondary pathology in the thalamus after middle cerebral artery occlusion (MCAO) in rats. Atypical accumulation of both amyloid-β (Aβ) and calcium in the thalamus was significantly higher in rats receiving the BMMSCs infusion 48 hours after MCAO as compared with the vehicle MCAO group. The elevated Aβ/calcium accumulation correlated with the level of impaired sensorimotor function. Although secondary pathology in the thalamus seems to be rodent specific, it needs to be taken into account because it may impair long-term behavioral recovery and negate therapeutic treatment effects.

Fish oil supplementation associated with decreased cellular degeneration and increased cellular proliferation 6 weeks after middle cerebral artery occlusion in the rat

Anti-inflammatory long-chain omega-3 polyunsaturated fatty acids (n-3-LC-PUFAs) are both neuroprotective and have antidepressive effects. However the influence of dietary supplemented n-3-LC-PUFAs on inflammation-related cell death and proliferation after middle cerebral artery occlusion (MCAo)-induced stroke is unknown. We have previously demonstrated that anxiety-like and hyperactive locomotor behaviors are reduced in n-3-LC-PUFA-fed MCAo animals. Thus in the present study, male hooded Wistar rats were exposed to MCAo or sham surgeries and examined behaviorally 6 weeks later, prior to euthanasia and examination of lesion size, cell death and proliferation in the dentate gyrus, cornu ammonis region of the hippocampus of the ipsilesional hemispheres, and the thalamus of the ipsilesional and contralesional hemispheres. Markers of cell genesis and cell degeneration in the hippocampus or thalamus of the ipsilesional hemisphere did not differ between surgery and diet groups 6 weeks post MCAo. Dietary supplementation with n-3-LC-PUFA decreased cell degeneration and increased cell proliferation in the thalamic region of the contralesional hemisphere. MCAo-associated cell degeneration in the hippocampus and thalamus positively correlated with anxiety-like and hyperactive locomotor behaviors previously reported in these animals. These results suggest that anti-inflammatory n-3-LC-PUFA supplementation appears to have cellular protective effects after MCAo in the rat, which may affect behavioral outcomes.

Amyloid-clearing proteins and their epigenetic regulation as a therapeutic target in Alzheimer's disease

Abnormal elevation of amyloid β-peptide (Aβ) levels in the brain is the primary trigger for neuronal cell death specific to Alzheimer’s disease (AD). It is now evident that Aβ levels in the brain are manipulable due to a dynamic equilibrium between its production from the amyloid precursor protein (APP) and removal by amyloid clearance proteins. Clearance can be either enzymic or non-enzymic (binding/transport proteins). Intriguingly several of the main amyloid-degrading enzymes (ADEs) are members of the M13 peptidase family (neprilysin (NEP), NEP2 and the endothelin converting enzymes (ECE-1 and -2)). A distinct metallopeptidase, insulin-degrading enzyme (IDE), also contributes to Aβ degradation in the brain. The ADE family currently embraces more than 20 members, both membrane-bound and soluble, and of differing cellular locations. NEP plays an important role in brain function terminating neuropeptide signals. Its decrease in specific brain areas with age or after hypoxia, ischaemia or stroke contribute significantly to the development of AD pathology. The recently discovered mechanism of epigenetic regulation of NEP (and other genes) by the APP intracellular domain (AICD) and its dependence on the cell type and APP isoform expression suggest possibilities for selective manipulation of NEP gene expression in neuronal cells. We have also observed that another amyloid-clearing protein, namely transthyretin (TTR), is also regulated in the neuronal cell by a mechanism similar to NEP. Dependence of amyloid clearance proteins on histone deacetylases and the ability of HDAC inhibitors to up-regulate their expression in the brain opens new avenues for developing preventive strategies in AD.

Hemodynamic effects of combined focal cerebral ischemia and amyloid protein toxicity in a rat model: a functional CT study

Background/Objective

Clinical evidence indicates that cerebral ischemia (CI) and a pathological factor of Alzheimer's disease, the β-amyloid (Aβ) protein, can increase the rate of cognitive impairment in the ageing population. Using the CT Perfusion (CTP) functional imaging, we sought to investigate the interaction between CI and the Aβ protein on cerebral hemodynamics.

Methods

A previously established rat model of CI and Aβ was used for the CTP study. Iodinated contrast was given intravenously, while serial CT images of sixteen axial slices were acquired. Cerebral blood flow (CBF) and blood volume (CBV) parametric maps were co-registered to a rat brain atlas and regions of interest were drawn on the maps. Microvascular alteration was investigated with histopathology.

Results

CTP results revealed that ipsilateral striatum of Aβ+CI and CI groups showed significantly lower CBF and CBV than control at the acute phase. Striatal CBF and CBV increased significantly at week 1 in the CI and Aβ+CI groups, but not in the Aβ alone or control group. Histopathology showed that average density of dilated microvessels in the ipsilateral striatum in CI and Aβ+CI groups was significantly higher than control at week 1, indicating this could be associated with hyperperfusion and hypervolemia observed from CTP results.

Conclusion

These results demonstrate that CTP can quantitatively measure the hemodynamic disturbance on CBF and CBV functional maps in a rat model of CI interacting with Aβ.

A new role for downstream Toll-like receptor signaling in mediating immediate early gene expression during focal cerebral ischemia

To better understand the role of downstream Toll-like receptor (TLR) signaling during acute cerebral ischemia, we performed cDNA microarrays, on brain RNA, and cytokine arrays, on serum, from wild type (WT), MyD88-/- and TRIF-mutant mice, at baseline and following permanent middle cerebral artery occlusion (pMCAO). The acute stress response pathway was among the top pathways identified by Ingenuity Pathway Analysis of microarray data. We used real-time polymerase chain reaction to confirm the expression of four immediate early genes; EGR1, EGR2, ARC, Nurr77, in this pathway, and insulin degrading enzyme (IDE). Compared to WT, baseline immediate early gene expression was increased up to10-fold in MyD88-/- and TRIF-mutant mice. However, following pMCAO, immediate early gene expression remained unchanged, from this elevated baseline in these mice, but increased up to 12-fold in WT. Furthermore, expression of IDE, which also degrades β-amyloid, decreased significantly only in TRIF-mutant mice. Finally, sE-Selectin, sICAM, sVCAM-1, and MMP-9 levels were significantly decreased only in MyD88-/- compared with WT mice. We thus report a new role for downstream TLR signaling in immediate early gene expression during acute cerebral ischemia. We also show that the TRIF pathway regulates IDE expression; a major enzyme that clears β-amyloid from the brain.

The potential role of kynurenines in Alzheimer's disease: pathomechanism and therapeutic possibilities by influencing the glutamate receptors

The pathomechanism of neurodegenerative disorders still poses a challenge to neuroscientists, and continuous research is under way with the aim of attaining an understanding of the exact background of these devastating diseases. The pathomechanism of Alzheimer's disease (AD) is associated with characteristic neuropathological features such as extracellular amyloid-β and intracellular tau deposition. Glutamate excitotoxicity and neuroinflammation are also factors that are known to contribute to the neurodegenerative process, but a cerebrovascular dysfunction has recently also been implicated in AD. Current therapeutic tools offer moderate symptomatic treatment, but fail to reduce disease progression. The kynurenine pathway (KP) has been implicated in the development of neurodegenerative processes, and alterations in the KP have been demonstrated in both acute and chronic neurological disorders. Kynurenines have been suggested to be involved in the regulation of neurotransmission and in immunological processes. Targeting the KP, therefore, offers a valuable strategic option for the attenuation of glutamatergic excitotoxicity, and for neuroprotection.

Cerebrolysin reduces amyloid-β deposits, apoptosis and autophagy in the thalamus and improves functional recovery after cortical infarction

Focal cerebral infarction causes amyloid-β (Aβ) deposits and secondary thalamic neuronal degeneration. The present study aimed to determine the protective effects of Cerebrolysin on Aβ deposits and secondary neuronal damage in thalamus after cerebral infarction. At 24h after distal middle cerebral artery occlusion (MCAO), Cerebrolysin (5 ml/kg) or saline as control was once daily administered for consecutive 13 days by intraperitoneal injection. Sensory function and secondary thalamic damage were assessed with adhesive-removal test, Nissl staining and immunofluorescence at 14 days after MCAO. Aβ deposits, activity of β-site amyloid precursor protein-cleaving enzyme 1 (BACE1), apoptosis and autophagy were determined by TUNEL staining, immunofluorescence and immunoblot. The results showed that Cerebrolysin significantly improved sensory deficit compared to controls (p<0.05). Aβ deposits and BACE1 were obviously reduced by Cerebrolysin, which was accompanied by decreases in neuronal loss and astroglial activation compared to controls (all p < 0.05). Coincidently, Cerebrolysin markedly inhibited cleaved caspase-3, conversion of LC3-II, downregulation of Bcl-2 and upregulation of Bax in the ipsilateral thalamus compared to controls (all p<0.05). These findings suggest that Cerebrolysin reduces Aβ deposits, apoptosis and autophagy in the ipsilateral thalamus, which may be associated with amelioration of secondary thalamic damage and functional recovery after cerebral infarction.

Functional up-regulation of endopeptidase neurolysin during post-acute and early recovery phases of experimental stroke in mouse brain

In this study, we provide evidence for the first time that membrane-bound endopeptidase neurolysin is up-regulated in different parts of mouse brain affected by focal ischemia-reperfusion in a middle cerebral artery occlusion model of stroke. Radioligand binding, enzymatic and immunoblotting experiments in membrane preparations of frontoparietal cortex, striatum, and hippocampus isolated from the ischemic hemisphere of mouse brain 24 h after reperfusion revealed statistically significant increase (≥ twofold) in quantity and activity of neurolysin compared with sham-operated controls. Cerebellar membranes isolated from the ischemic hemisphere served as negative control supporting the observations that up-regulation of neurolysin occurs in post-ischemic brain regions. This study also documents sustained functional up-regulation of neurolysin in frontoparietal cortical membranes for at least 7 days after stroke, which appears not to be transcriptionally or translationally regulated, but rather depends on translocation of cytosolic neurolysin to the membranes and mitochondria. Considering diversity of endogenous neurolysin substrates (neurotensin, bradykinin, angiotensins I/II, substance P, hemopressin, dynorphin A(1-8), metorphamide, somatostatin) and the well-documented role of these peptidergic systems in pathogenesis of stroke, resistance to ischemic injury and/or post-stroke brain recovery, our findings suggest that neurolysin may play a role in processes modulating the brain's response to stroke and its recovery after stroke.

Effects of cerebrovascular disease and amyloid beta burden on cognition in subjects with subcortical vascular cognitive impairment

Cerebrovascular disease (CVD) and amyloid burden are the most frequent pathologies in subjects with cognitive impairment. However, the relationship between CVD, amyloid burden, and cognition are largely unknown. We aimed to evaluate whether CVD (lacunes, white matter hyperintensities, and microbleeds) and amyloid burden (Pittsburgh compound B [PiB] retention ratio) contribute to cognitive impairment independently or interactively. We recruited 136 patients with subcortical vascular cognitive impairment who underwent magnetic resonance imaging, PiB-positron emission tomography, and neuropsychological testing. The number of lacunes was associated with memory, frontal dysfunctions, and disease severity. The volume of white matter hyperintensities and the PiB retention ratio were associated only with memory dysfunction. There was no direct correlation between CVD markers and PiB retention ratio except that the number of lacunes was negatively correlated with the PiB retention ratio. In addition, there were no interactive effects of CVD and PiB retention ratio on cognition. Our findings suggest that CVD and amyloid burden contribute independently and not interactively to specific patterns of cognitive dysfunction in patients with subcortical vascular cognitive impairment.

Lack of secondary pathology in the thalamus after focal cerebral ischemia in nonhuman primates

Remote regions such as the thalamus undergo secondary degeneration after cerebral ischemia. In rodents, the pathology in the thalamus is characterized by a robust inflammatory reaction, β-amyloid (Aβ) accumulation and calcification. Here we studied whether nonhuman primates subjected to middle cerebral artery occlusion (MCAO) display a similar pathology. Common marmosets (n=4) were subjected to transient MCAO for 3 h. Two sham-operated animals served as controls. All animals underwent MRI examination (T2) on postoperative day 7 to assess the location of the infarct. After a 45-day follow-up period, the animals were perfused for histology to evaluate β-amyloid and calcium load in the peri-infarct regions and the thalamus. There was no Aβ or calcium staining in the sham-operated marmosets. The contralateral hemisphere was devoid of Aβ and calcium staining in MCAO animals, except calcium staining in one animal. In the ipsilateral cortex, patchy groups of Aβ-positive cells were observed. Occasional calcium staining was observed in the peri-infarct regions, lesion core, and remote regions such as the substantia nigra. The most important, the thalamus was devoid of any sign of Aβ and calcium aggregation in MCAO animals. Staining for glial fibrillary acidic protein (GFAP) showed marked astrogliosis in the ipsilateral cortex and thalamus. In conclusion, our preliminary study in marmosets did not identify Aβ and calcium pathology in the thalamus following cerebral ischemia as shown in rodents.

Non-selective calcium channel blocker bepridil decreases secondary pathology in mice after photothrombotic cortical lesion

Experimental studies have identified a complex link between neurodegeneration, β-amyloid (Aβ) and calcium homeostasis. Here we asked whether early phase β-amyloid pathology in transgenic hAPP_SL mice exaggerates the ischemic lesion and remote secondary pathology in the thalamus, and whether a non-selective calcium channel blocker reduces these pathologies. Transgenic hAPP_SL (n = 33) and non-transgenic (n = 30) male mice (4–5 months) were subjected to unilateral cortical photothrombosis and treated with the non-selective calcium channel blocker bepridil (50 mg/kg, p.o., once a day) or vehicle for 28 days, starting administration 2 days after the operation. Animals were then perfused for histological analysis of infarct size, Aβ and calcium accumulation in the thalamus. Cortical photothrombosis resulted in a small infarct, which was associated with atypical Aβ and calcium accumulation in the ipsilateral thalamus. Transgenic mice had significantly smaller infarct volumes than non-transgenic littermates (P<0.05) and ischemia-induced rodent Aβ accumulation in the thalamus was lower in transgenic mice compared to non-transgenic mice (P<0.01). Bepridil decreased calcium load in the thalamus (P<0.01). The present data suggest less pronounced primary and secondary pathology in hAPP_SL transgenic mice after ischemic cortical injury. Bepridil particularly decreased calcium pathology in the thalamus following ischemia.

Pathogenesis of cerebral microbleeds: In vivo imaging of amyloid and subcortical ischemic small vessel disease in 226 individuals with cognitive impairment

OBJECTIVE

Cerebral microbleeds (CMBs) are a neuroimaging marker of small vessel disease (SVD) with relevance for understanding disease mechanisms in cerebrovascular disease, cognitive impairment, and normal aging. It is hypothesized that lobar CMBs are due to cerebral amyloid angiopathy (CAA) and deep CMBs are due to subcortical ischemic SVD. We tested this hypothesis using structural magnetic resonance imaging (MRI) markers of subcortical SVD and in vivo imaging of amyloid in patients with cognitive impairment.

METHODS

We included 226 patients: 89 with Alzheimer disease-related cognitive impairment (ADCI) and 137 with subcortical vascular cognitive impairment (SVCI). All subjects underwent amyloid imaging with [(11) C] Pittsburgh compound B (PiB) positron emission tomography, and MRI to detect CMBs and markers of subcortical SVD, including the volume of white matter hyperintensities (WMH) and the number of lacunes.

RESULTS

Parietal and occipital lobar CMBs counts were higher in PiB(+) ADCI with moderate WMH than PiB(+) ADCI with minimal WMH, whereas PiB(-) patients with SVCI (ie, "pure" SVCI) showed both lobar and deep CMBs. In multivariate analyses of the whole cohort, WMH volume and lacuna counts were positively associated with both lobar and deep CMBs, whereas amyloid burden (PiB) was only associated with lobar CMBs. There was an interaction between lacuna burden and PiB retention on lobar (but not deep) CMBs (p<0.001).

INTERPRETATION

Our findings suggest that although deep CMBs are mainly linked to subcortical SVD, both subcortical SVD and amyloid-related pathologies (eg, CAA) contribute to the pathogenesis of lobar CMBs, at least in subjects with mixed lobar and deep CMBs. Furthermore, subcortical SVD and amyloid-related pathologies interact to increase the risk of lobar CMBs.

Exploring the contribution of estrogen to amyloid-Beta regulation: a novel multifactorial computational modeling approach

According to the amyloid hypothesis, Alzheimer Disease results from the accumulation beyond normative levels of the peptide amyloid-β (Aβ). Perhaps because of its pathological potential, Aβ and the enzymes that produce it are heavily regulated by the molecular interactions occurring within cells, including neurons. This regulation involves a highly complex system of intertwined normative and pathological processes, and the sex hormone estrogen contributes to it by influencing the Aβ-regulation system at many different points. Owing to its high complexity, Aβ regulation and the contribution of estrogen are very difficult to reason about. This report describes a computational model of the contribution of estrogen to Aβ regulation that provides new insights and generates experimentally testable and therapeutically relevant predictions. The computational model is written in the declarative programming language known as Maude, which allows not only simulation but also analysis of the system using temporal-logic. The model illustrates how the various effects of estrogen could work together to reduce Aβ levels, or prevent them from rising, in the presence of pathological triggers. The model predicts that estrogen itself should be more effective in reducing Aβ than agonists of estrogen receptor α (ERα), and that agonists of ERβ should be ineffective. The model shows how estrogen itself could dramatically reduce Aβ, and predicts that non-steroidal anti-inflammatory drugs should provide a small additional benefit. It also predicts that certain compounds, but not others, could augment the reduction in Aβ due to estrogen. The model is intended as a starting point for a computational/experimental interaction in which model predictions are tested experimentally, the results are used to confirm, correct, and expand the model, new predictions are generated, and the process continues, producing a model of ever increasing explanatory power and predictive value.

Bepridil decreases Aβ and calcium levels in the thalamus after middle cerebral artery occlusion in rats

Alzheimer's disease (AD) and cerebral ischaemia share similar features in terms of altered amyloid precursor protein (APP) processing and β-amyloid (Aβ) accumulation. We have previously shown that Aβ and calcium deposition, and β-secretase activity, are robustly increased in the ipsilateral thalamus after transient middle cerebral artery occlusion (MCAO) in rats. Here, we investigated whether the non-selective calcium channel blocker bepridil, which also inhibits β-secretase cleavage of APP, affects thalamic accumulation of Aβ and calcium and in turn influences functional recovery in rats subjected to MCAO. A 27-day bepridil treatment (50 mg/kg, p.o.) initiated 2 days after MCAO significantly decreased the levels of soluble Aβ40, Aβ42 and calcium in the ipsilateral thalamus, as compared with vehicle-treated MCAO rats. Expression of seladin-1/DHCR24 protein, which is a potential protective factor against neuronal damage, was decreased at both mRNA and protein levels in the ipsilateral thalamus of MCAO rats. Conversely, bepridil treatment restored seladin-1/DHCR24 expression in the ipsilateral thalamus. Bepridil treatment did not significantly affect heme oxygenase-1- or NAD(P)H quinone oxidoreductase-1-mediated oxidative stress or inflammatory responses in the ipsilateral thalamus of MCAO rats. Finally, bepridil treatment mitigated MCAO-induced alterations in APP processing in the ipsilateral thalamus and improved contralateral forelimb use in MCAO rats. These findings suggest that bepridil is a plausible therapeutic candidate in AD or stroke owing to its multifunctional role in key cellular events that are relevant for the pathogenesis of these diseases.

Characterization of insulin degrading enzyme and other amyloid-β degrading proteases in human serum: a role in Alzheimer's disease?

Sporadic Alzheimer's disease (AD) patients have low amyloid-β peptide (Aβ) clearance in the central nervous system. The peripheral Aβ clearance may also be important but its role in AD remains unclear. We aimed to study the Aβ degrading proteases including insulin degrading enzyme (IDE), angiotensin converting enzyme (ACE) and others in blood. Using the fluorogenic substrate V (a substrate of IDE and other metalloproteases), we showed that human serum degraded the substrate V, and the activity was inhibited by adding increasing dose of Aβ. The existence of IDE activity was demonstrated by the inhibition of insulin, amylin, or EDTA, and further confirmed by immunocapture of IDE using monoclonal antibodies. The involvement of ACE was indicated by the ability of the ACE inhibitor, lisinopril, to inhibit the substrate V degradation. To test the variations of substrate V degradation in humans, we used serum samples from a homebound elderly population with cognitive diagnoses. Compared with the elderly who had normal cognition, those with probable AD and amnestic mild cognitive impairment (amnestic MCI) had lower peptidase activities. Probable AD or amnestic MCI as an outcome remained negatively associated with serum substrate V degradation activity after adjusting for the confounders. The elderly with probable AD had lower serum substrate V degradation activity compared with those who had vascular dementia. The blood proteases mediating Aβ degradation may be important for the AD pathogenesis. More studies are needed to specify each Aβ degrading protease in blood as a useful biomarker and a possible treatment target for AD.

Paeonol Protects Memory after Ischemic Stroke via Inhibiting β-Secretase and Apoptosis

Poststroke dementia commonly occurs following stroke, with its pathogenesis related to β-amyloid production and apoptosis. The present study evaluate the effects of paeonol, one of the phenolic phytochemicals isolated from the Chinese herb Paeonia suffruticosa Andrews (MC), on protection from memory loss after ischemic stroke in the subacute stage. Rats were subjected to transient middle cerebral artery occlusion (tMCAo) with 10 min of ischemia. The data revealed that paeonol recovered the step-through latency in the retrieval test seven days after tMCAo, but did not improve the neurological deficit induced by tMCAo. Levels of Amyloid precursor protein (APP)- and beta-site APP cleaving enzyme (BACE; β-secretase)-immunoreactive cells, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL)-positive cells decreased in the paeonol-administered group. Western blotting revealed decreased levels of Bax protein in mitochondria and apoptosis-inducing factor (AIF) in cytosol following paeonol treatment. In conclusion, we speculate that paeonol protected memory after ischemic stroke via reducing APP, BACE, and apoptosis. Supression the level of Bax and blocking the release of AIF into cytosol might participate in the anti-apoptosis provided by paeonol.

Cerebrovascular lesions induce transient β-amyloid deposition

Previous clinical studies have documented a close relationship between cerebrovascular disease and risk of Alzheimer's disease. We examined possible mechanistic interactions through use of experimental stroke models in a transgenic mouse model of β-amyloid deposition (APPswe/PS1dE9). Following middle cerebral artery occlusion, we observed a rapid increase in amyloid plaque burden in the region surrounding the infarction. In human tissue samples, however, we were unable to detect a localized increase in amyloid burden adjacent to cerebral infarcts. To resolve this discrepancy, we generated cerebral microstrokes in amyloid precursor protein mouse models with the photosensitive dye Rose bengal, and monitored plaque formation in real time using multiphoton microscopy. We observed a striking increase in the number of new plaques and amyloid angiopathy in the area immediately surrounding the infarcted area; however, the effect was transient, potentially resolving the discord between mouse and human tissue. We did not detect changes in candidate proteins related to β-amyloid generation or degradation such as β-amyloid-converting enzyme, amyloid precursor protein, presenilin 1, neprylisin or insulin-degrading enzyme. Together, these results demonstrate that strokes can trigger accelerated amyloid deposition, most likely through interference with amyloid clearance pathways. Additionally, this study indicates that focal ischaemia provides an experimental paradigm in which to study the mechanisms of plaque seeding and growth.

Autophagosomes accumulation is associated with β-amyloid deposits and secondary damage in the thalamus after focal cortical infarction in hypertensive rats

Focal cerebral cortical infarction after distal middle cerebral artery occlusion causes β-amyloid deposition and secondary neuronal degeneration in the ipsilateral ventroposterior nucleus of the thalamus. Several studies suggest that autophagy is an active pathway for β-amyloid peptide generation. This study aimed to investigate the role of autophagy in thalamic β-amyloid deposition and neuronal degeneration after cerebral cortical infarction in hypertensive rats. At 7 and 14days after middle cerebral artery occlusion, neuronal death and β-amyloid deposits were evident in the ipsilateral ventroposterior nucleus, and the activity of β-site amyloid precursor protein (APP)-cleaving enzyme 1, required for β-amyloid peptide generation, was elevated in the thalamus. In correlation, both the number of cells showing punctate microtubule-associated protein 1A light chain 3 fluorescence and levels of light chain 3-II protein, an autophagosome marker, were markedly increased. Notably, most of the cells that over-expressed β-site APP-cleaving enzyme 1 displayed punctate light chain 3 staining. Furthermore, the inhibition of autophagy with 3-methyladenine significantly reduced the thalamic neuronal damage, β-amyloid deposits, and β-site APP-cleaving enzyme 1 activity. These results suggest that autophagosomes accumulate within thalamic cells after cerebral cortical infarction, which is associated with thalamic β-amyloid deposition and secondary neuronal degeneration via elevation of β-site APP-cleaving enzyme 1 level.

Chronic ibuprofen treatment does not affect the secondary pathology in the thalamus or improve behavioral outcome in middle cerebral artery occlusion rats

Anti-inflammatory drug ibuprofen decreases the β-amyloid (Aβ) deposition and associated inflammation in transgenic Alzheimer disease mice. Based on this, we studied whether ibuprofen could modulate the secondary pathology described in the thalamus of middle cerebral artery occlusion (MCAO) rats. Our hypothesis was that ibuprofen could decrease inflammatory reaction and Aβ load in the thalamus of MCAO rats, which in turn is reflected in improved behavioral outcome. Forty male Wistar rats (250-340 g) were subjected to sham-operation or transient occlusion of the right middle cerebral artery (120 min). Ibuprofen (4 0mg/kg/day, per os) was administrated for 27 days beginning the treatment on post-operative day 2. MCAO controls were given vehicle. Sensorimotor impairment was assessed using the limb-placing, tapered ledged beam-walking and cylinder tests during the follow-up. The rats were perfused for histology on postoperative day 29. Histological data showed that ibuprofen did not affect Aβ or calcium load in the thalamus of MCAO rats. In addition, behavioral tests did not show significant difference between vehicle- and ibuprofen-treated MCAO rats. The present data do not support the idea that ibuprofen reduces the secondary Aβ/calcium pathology in the thalamus or associated sensorimotor impairment following cerebral ischemia.

Chronic hyperperfusion and angiogenesis follow subacute hypoperfusion in the thalamus of rats with focal cerebral ischemia

Cerebral blood flow (CBF) is disrupted after focal ischemia in rats. We examined long-term hemodynamic and cerebrovascular changes in the rat thalamus after focal cerebral ischemia. Cerebral blood flow quantified by arterial spin labeling magnetic resonance imaging was decreased in the ipsilateral and contralateral thalamus 2 days after cerebral ischemia. Partial thalamic CBF recovery occurred by day 7, then the ipsilateral thalamus was chronically hyperperfused at 30 days and 3 months compared with its contralateral side. This contrasted with permanent hypoperfusion in the ipsilateral cortex. Angiogenesis was indicated by endothelial cell (RECA-1) immunohistochemistry that showed increased blood vessel branching in the ipsilateral thalamus at the end of the 3-month follow-up. Only transient thalamic IgG extravasation was observed, indicating that the blood-brain barrier was intact after day 2. Angiogenesis was preceded by transiently altered expression levels of cadherin family adhesion molecules, cadherin-7, protocadherin-1, and protocadherin-17. In conclusion, thalamic pathology after focal cerebral ischemia involved long-term hemodynamic changes and angiogenesis preceded by altered expression of vascular adhesion factors. Postischemic angiogenesis in the thalamus represents a novel type of remote plasticity, which may support removal of necrotic brain tissue and aid functional recovery.

Long term changes in phospho-APP and tau aggregation in the 3xTg-AD mice following cerebral ischemia

The risk of Alzheimer's disease increases following cerebral hypoperfusion. We studied the long-term interaction between low blood flow to the brain and Alzheimer's disease by inducing a transient global ischemic insult in aged 3xTg-AD mice and determining the effects on AD pathology 3-months post injury. We found that global ischemia does not increase the levels of amyloid-β in these mice. However, the injury did lead to enhanced phosphorylation of the amyloid precursor protein (APP) at the Thr668 site in both the 3xTg-AD mice and wild-type controls. Furthermore, we found an increase in insoluble total tau 3-months post-injury. Together these findings further elucidate the long-term impact of cerebral hypoperfusion on Alzheimer's disease.

Reduction of β-amyloid deposits by γ-secretase inhibitor is associated with the attenuation of secondary damage in the ipsilateral thalamus and sensory functional improvement after focal cortical infarction in hypertensive rats

Abnormal β-amyloid (Aβ) deposits in the thalamus have been reported after cerebral cortical infarction. In this study, we investigated the association of Aβ deposits, with the secondary thalamic damage after focal cortical infarction in rats. Thirty-six stroke-prone renovascular hypertensive rats were subjected to distal middle cerebral artery occlusion (MCAO) and then randomly divided into MCAO, vehicle, and N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) groups and 12 sham-operated rats as control. The DAPT was administered orally at 72 hours after MCAO. Seven days after MCAO, sensory function, neuron loss, and glial activation and proliferation were evaluated using adhesive removal test, Nissl staining, and immunostaining, respectively. Thalamic Aβ accumulation was evaluated using immunostaining and enzyme-linked immunosorbent assay (ELISA). Compared with vehicle group, the ipsilateral thalamic Aβ, neuronal loss, glial activation and proliferation, and the mean time to remove the stimulus from right forepaw significantly decreased in DAPT group. The mean time to remove the stimulus from the right forepaw and thalamic Aβ burden were both negatively correlated with the number of thalamic neurons. These findings suggest that Aβ deposits are associated with the secondary thalamic damage. Reduction of thalamic Aβ by γ-secretase inhibitor may attenuate the secondary damage and improve sensory function after cerebral cortical infarction.