Losartan improves cerebrovascular function in a mouse model of Alzheimer's disease with combined overproduction of amyloid-β and transforming growth factor-β1

Interactions between nanoparticles and pathological changes of vascular in Alzheimer's disease

Emerging evidence suggests that vascular pathological changes play a pivotal role in the pathogenesis of Alzheimer's disease (AD). The dysfunction of the cerebral vasculature occurs in the early course of AD, characterized by alterations in vascular morphology, diminished cerebral blood flow (CBF), impairment of the neurovascular unit (NVU), vasculature inflammation, and cerebral amyloid angiopathy. Vascular dysfunction not only facilitates the influx of neurotoxic substances into the brain, triggering inflammation and immune responses but also hampers the efflux of toxic proteins such as Aβ from the brain, thereby contributing to neurodegenerative changes in AD. Furthermore, these vascular changes significantly impact drug delivery and distribution within the brain. Therefore, developing targeted delivery systems or therapeutic strategies based on vascular alterations may potentially represent a novel breakthrough in AD treatment. This review comprehensively examines various aspects of vascular alterations in AD and outlines the current interactions between nanoparticles and pathological changes of vascular.

Therapeutic Implications of Renin-Angiotensin System Modulators in Alzheimer's Dementia

The Renin-Angiotensin System (RAS) has attracted considerable interest beyond its traditional cardiovascular role due to emerging data indicating its potential involvement in neurodegenerative diseases, including Alzheimer's dementia (AD). This review investigates the therapeutic implications of RAS modulators, specifically focusing on angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), and renin inhibitors in AD. ACEIs, commonly used for hypertension, show promise in AD by reducing angiotensin (Ang) II levels. This reduction is significant as Ang II contributes to neuroinflammation, oxidative stress, and β-amyloid (Aβ) accumulation, all implicated in AD pathogenesis. ARBs, known for vasodilation, exhibit neuroprotection by blocking Ang II receptors, improving cerebral blood flow and cognitive decline in AD models. Renin inhibitors offer a novel approach by targeting the initial RAS step, displaying anti-inflammatory and antioxidant effects that mitigate AD degeneration. Preclinical studies demonstrate RAS regulation's favorable impact on neuroinflammation, neuronal damage, cognitive function, and Aβ metabolism. Clinical trials on RAS modulators in AD are limited, but with promising results, ARBs being more effective that ACEIs in reducing cognitive decline. The varied roles of ACEIs, ARBs, and renin inhibitors in RAS modulation present a promising avenue for AD therapeutic intervention, requiring further research to potentially transform AD treatment strategies.

Deciphering mechanisms of action of ACE inhibitors in neurodegeneration using Drosophila models of Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder for which there is no cure. Recently, several studies have reported a significant reduction in the incidence and progression of dementia among some patients receiving antihypertensive medications such as angiotensin-converting enzyme inhibitors (ACE-Is) and angiotensin receptor blockers (ARBs). Why these drugs are beneficial in some AD patients and not others is unclear although it has been shown to be independent of their role in regulating blood pressure. Given the enormous and immediate potential of ACE-Is and ARBs for AD therapeutics it is imperative that we understand how they function. Recently, studies have shown that ACE-Is and ARBs, which target the renin angiotensin system in mammals, are also effective in suppressing neuronal cell death and memory defects in Drosophila models of AD despite the fact that this pathway is not conserved in flies. This suggests that the beneficial effects of these drugs may be mediated by distinct and as yet, identified mechanisms. Here, we discuss how the short lifespan and ease of genetic manipulations available in Drosophila provide us with a unique and unparalleled opportunity to rapidly identify the targets of ACE-Is and ARBs and evaluate their therapeutic effectiveness in robust models of AD.

The effect of curcumin on blood pressure and cognitive impairment in spontaneously hypertensive rats

BACKGROUND/OBJECTIVES

It is known that the renin-angiotensin system (RAS) in the brain could regulate cognitive functions as well as blood pressure. Inhibition of RAS for the improvement of cognitive function may be a new strategy, but studies so far have mostly reported on the effects of RAS inhibition by drugs, and there is no research on cognitive improvement through RAS inhibition of food ingredients. Therefore, this study investigated the effect of curcumin on blood pressure and cognitive function and its related mechanism in spontaneously hypertensive rat/Izm (SHR/Izm).

MATERIALS/METHODS

Six-week-old SHR/Izm rats were divided into 5 groups: control group (CON), scopolamine group (SCO, drug for inducing cognitive deficits), positive control (SCO and tacrine [TAC]), curcumin 100 group (CUR100, SCO + Cur 100 mg/kg), and curcumin 200 group (CUR200, SCO + Cur 200 mg/kg). Changes in blood pressure, RAS, cholinergic system, and cognitive function were compared before and after cognitive impairment.

RESULTS

The SCO group showed increased blood pressure and significantly reduced cognitive function based on the y-maze and passive avoidance test. Curcumin treatments significantly improved blood pressure and cognitive function compared with the SCO group. In both the CUR100 and CUR200 groups, the mRNA expressions of angiotensin-converting enzyme (ACE) and angiotensin II receptor type1 (AT1), as well as the concentrations of angiotensin II (Ang II) in brain tissue were significantly decreased. The mRNA expression of the muscarinic acetylcholine receptors (mAChRs) and acetylcholine (ACh) content was significantly increased, compared with the SCO group.

CONCLUSIONS

The administration of curcumin improved blood pressure and cognitive function in SCO-induced hypertensive mice, indicating that the cholinergic system was improved by suppressing RAS and AT1 receptor expression and increasing the mAChR expression.

The COVID-19 pandemic and Alzheimer’s disease: mutual risks and mechanisms

Coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a life-threatening disease, especially in elderly individuals and those with comorbidities. The predominant clinical manifestation of COVID-19 is respiratory dysfunction, while neurological presentations are increasingly being recognized. SARS-CoV-2 invades host cells primarily via attachment of the spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor expressed on cell membranes. Patients with Alzheimer’s disease (AD) are more susceptible to SARS-CoV-2 infection and prone to severe clinical outcomes. Recent studies have revealed some common risk factors for AD and COVID-19. An understanding of the association between COVID-19 and AD and the potential related mechanisms may lead to the development of novel approaches to treating both diseases. In the present review, we first summarize the mechanisms by which SARS-CoV-2 invades the central nervous system (CNS) and then discuss the associations and potential shared key factors between COVID-19 and AD, with a focus on the ACE2 receptor, apolipoprotein E (APOE) genotype, age, and neuroinflammation.

Recent Advances in the Endogenous Brain Renin-Angiotensin System and Drugs Acting on It

The RAS (renin-angiotensin system) is the part of the endocrine system that plays a prime role in the control of essential hypertension. Since the discovery of brain RAS in the seventies, continuous efforts have been put by the scientific committee to explore it more. The brain has shown the presence of various components of brain RAS such as angiotensinogen (AGT), converting enzymes, angiotensin (Ang), and specific receptors (ATR). AGT acts as the precursor molecule for Ang peptides—I, II, III, and IV—while the enzymes such as prorenin, ACE, and aminopeptidases A and N synthesize it. AT1, AT2, AT4, and mitochondrial assembly receptor (MasR) are found to be plentiful in the brain. The brain RAS system exhibits pleiotropic properties such as neuroprotection and cognition along with regulation of blood pressure, CVS homeostasis, thirst and salt appetite, stress, depression, alcohol addiction, and pain modulation. The molecules acting through RAS predominantly ARBs and ACEI are found to be effective in various ongoing and completed clinical trials related to cognition, memory, Alzheimer's disease (AD), and pain. The review summarizes the recent advances in the brain RAS system highlighting its significance in pathophysiology and treatment of the central nervous system-related disorders.

Differential pial and penetrating arterial responses examined by optogenetic activation of astrocytes and neurons

A variety of brain cells participates in neurovascular coupling by transmitting and modulating vasoactive signals. The present study aimed to probe cell type-dependent cerebrovascular (i.e., pial and penetrating arterial) responses with optogenetics in the cortex of anesthetized mice. Two lines of the transgenic mice expressing a step function type of light-gated cation channel (channelrhodopsine-2; ChR2) in either cortical neurons (muscarinic acetylcholine receptors) or astrocytes (Mlc1-positive) were used in the experiments. Photo-activation of ChR2-expressing astrocytes resulted in a widespread increase in cerebral blood flow (CBF), extending to the nonstimulated periphery. In contrast, photo-activation of ChR2-expressing neurons led to a relatively localized increase in CBF. The differences in the spatial extent of the CBF responses are potentially explained by differences in the involvement of the vascular compartments. In vivo imaging of the cerebrovascular responses revealed that ChR2-expressing astrocyte activation led to the dilation of both pial and penetrating arteries, whereas ChR2-expressing neuron activation predominantly caused dilation of the penetrating arterioles. Pharmacological studies showed that cell type-specific signaling mechanisms participate in the optogenetically induced cerebrovascular responses. In conclusion, pial and penetrating arterial vasodilation were differentially evoked by ChR2-expressing astrocytes and neurons.

Brain Renin-Angiotensin System as Novel and Potential Therapeutic Target for Alzheimer's Disease

The activation of the brain renin-angiotensin system (RAS) plays a pivotal role in the pathophysiology of cognition. While the brain RAS has been studied before in the context of hypertension, little is known about its role and regulation in relation to neuronal function and its modulation. Adequate blood flow to the brain as well as proper clearing of metabolic byproducts become crucial in the presence of neurodegenerative disorders such as Alzheimer's disease (AD). RAS inhibition (RASi) drugs that can cross into the central nervous system have yielded unclear results in improving cognition in AD patients. Consequently, only one RASi therapy is under consideration in clinical trials to modify AD. Moreover, the role of non-genetic factors such as hypercholesterolemia in the pathophysiology of AD remains largely uncharacterized, even when evidence exists that it can lead to alteration of the RAS and cognition in animal models. Here we revise the evidence for the function of the brain RAS in cognition and AD pathogenesis and summarize the evidence that links it to hypercholesterolemia and other risk factors. We review existent medications for RASi therapy and show research on novel drugs, including small molecules and nanodelivery strategies that can target the brain RAS with potential high specificity. We hope that further research into the brain RAS function and modulation will lead to innovative therapies that can finally improve AD neurodegeneration.

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

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

Activation of the Central Renin-Angiotensin System Causes Local Cerebrovascular Dysfunction

[Figure: see text].

Repurposing Antihypertensive Drugs for the Management of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder that has affected millions of people worldwide. However, currently, there is no treatment to cure the disease. The AD drugs available in the market only manage the disease symptomatically and the effects are usually short-term. Thus, there is a need to look at alternatives AD therapies. This literature review aims to shed some light on the potential of repurposing antihypertensives to treat AD. Mid-life hypertension has not only been recognised as a risk factor for AD, but its relation with AD has also been well established. Hence, antihypertensives were postulated to be beneficial in managing AD. Four classes of antihypertensives, as well as their potential limitations and prospects in being utilised as AD therapeutics, were discussed in this review.

Losartan improved hippocampal long-term potentiation impairment induced by repeated LPS injection in rats

Cognitive impairment has been known as a common consequence of brain inflammation. Long-term potentiation (LTP), the generally accepted cellular mechanism for memory formation in the mammalian brain, has been shown to be suppressed by inflammation. Studies have shown that angiotensin II (Ang II) through the Ang II type 1 receptor (AT1R) has a role in brain and peripheral immune system communication and brain inflammation. Here, the effect of AT1R blockade on hippocampal LTP in rats undergoing repeated lipopolysaccharide (LPS) injection was investigated. Rats received intraperitoneal (ip) injections of LPS (250 μg kg-1  day-1 ) for seven days. Treatment with losartan (ip; 3 mg kg-1  day-1 ) was started 3 days before LPS injection and continued during the LPS injections. Rats were anesthetized, and field excitatory postsynaptic potential (fEPSP) was recorded from the stratum radiatum of the CA1 area of the hippocampus in response to stimulation of the Schaffer collateral pathway. Results showed that LTP was suppressed in the LPS-injected rats as no significant differences were found in the fEPSP slope and amplitude before and after the LTP induction. AT1R blockade by losartan restored fEPSP to the control levels. These findings indicate that Ang II, through AT1R, has a role in LTP suppression induced by systemic inflammation.

Demonstration of age-related blood-brain barrier disruption and cerebromicrovascular rarefaction in mice by longitudinal intravital two-photon microscopy and optical coherence tomography

Age-related blood-brain barrier (BBB) disruption and cerebromicrovascular rarefaction contribute importantly to the pathogenesis of both vascular cognitive impairment and dementia (VCID) and Alzheimer's disease (AD). Recent advances in geroscience research enable development of novel interventions to reverse age-related alterations of the cerebral microcirculation for prevention of VCID and AD. To facilitate this research, there is an urgent need for sensitive and easy-to-adapt imaging methods that enable longitudinal assessment of changes in BBB permeability and brain capillarization in aged mice and that could be used in vivo to evaluate treatment efficiency. To enable longitudinal assessment of changes in BBB permeability in aged mice equipped with a chronic cranial window, we adapted and optimized two different intravital two-photon imaging approaches. By assessing relative fluorescence changes over the baseline within a volume of brain tissue, after qualitative image subtraction of the brain microvasculature, we confirmed that, in 24-mo-old C57BL/6J mice, cumulative permeability of the microvessels to fluorescent tracers of different molecular masses (0.3 to 40 kDa) is significantly increased compared with that of 5-mo-old mice. Real-time recording of vessel cross-sections showed that apparent solute permeability of single microvessels is significantly increased in aged mice vs. young mice. Cortical capillary density, assessed both by intravital two-photon microscopy and optical coherence tomography was also decreased in aged mice vs. young mice. The presented methods have been optimized for longitudinal (over the period of 36 wk) in vivo assessment of cerebromicrovascular health in preclinical geroscience research.NEW & NOTEWORTHY Methods are presented for longitudinal detection of age-related increase in blood-brain barrier permeability and microvascular rarefaction in the mouse cerebral cortex by intravital two-photon microscopy and optical coherence tomography.

Renin-Angiotensin System and Alzheimer's Disease Pathophysiology: From the Potential Interactions to Therapeutic Perspectives

New roles of the Renin-Angiotensin System (RAS), apart from fluid homeostasis and Blood Pressure (BP) regulation, are being progressively unveiled, since the discoveries of RAS alternative axes and local RAS in different tissues, including the brain. Brain RAS is reported to interact with pathophysiological mechanisms of many neurological and psychiatric diseases, including Alzheimer's Disease (AD). Even though AD is the most common cause of dementia worldwide, its pathophysiology is far from elucidated. Currently, no treatment can halt the disease course. Successive failures of amyloid-targeting drugs have challenged the amyloid hypothesis and increased the interest in the inflammatory and vascular aspects of AD. RAS compounds, both centrally and peripherally, potentially interact with neuroinflammation and cerebrovascular regulation. This narrative review discusses the AD pathophysiology and its possible interaction with RAS, looking forward to potential therapeutic approaches. RAS molecules affect BP, cerebral blood flow, neuroinflammation, and oxidative stress. Angiotensin (Ang) II, via angiotensin type 1 receptors may promote brain tissue damage, while Ang-(1-7) seems to elicit neuroprotection. Several studies dosed RAS molecules in AD patients' biological material, with heterogeneous results. The link between AD and clinical conditions related to classical RAS axis overactivation (hypertension, heart failure, and chronic kidney disease) supports the hypothesized role of this system in AD. Additionally, RAStargeting drugs as Angiotensin Converting Enzyme inhibitors (ACEis) and Angiotensin Receptor Blockers (ARBs) seem to exert beneficial effects on AD. Results of randomized controlled trials testing ACEi or ARBs in AD are awaited to elucidate whether AD-RAS interaction has implications on AD therapeutics.

Drug repositioning and repurposing for Alzheimer disease

Drug repositioning and repurposing can enhance traditional drug development efforts and could accelerate the identification of new treatments for individuals with Alzheimer disease (AD) dementia and mild cognitive impairment. Transcriptional profiling offers a new and highly efficient approach to the identification of novel candidates for repositioning and repurposing. In the future, novel AD transcriptional signatures from cells isolated at early stages of disease, or from human neurons or microglia that carry mutations that increase the risk of AD, might be used as probes to identify additional candidate drugs. Phase II trials assessing repurposed agents must consider the best target population for a specific candidate therapy as well as the mechanism of action of the treatment. In this Review, we highlight promising compounds to prioritize for clinical trials in individuals with AD, and discuss the value of Delphi consensus methodology and evidence-based reviews to inform this prioritization process. We also describe emerging work, focusing on the potential value of transcript signatures as a cost-effective approach to the identification of novel candidates for repositioning.

Paroxysmal slow cortical activity in Alzheimer's disease and epilepsy is associated with blood-brain barrier dysfunction

A growing body of evidence shows that epileptic activity is frequent but often undiagnosed in patients with Alzheimer's disease (AD) and has major therapeutic implications. Here, we analyzed electroencephalogram (EEG) data from patients with AD and found an EEG signature of transient slowing of the cortical network that we termed paroxysmal slow wave events (PSWEs). The occurrence per minute of the PSWEs was correlated with level of cognitive impairment. Interictal (between seizures) PSWEs were also found in patients with epilepsy, localized to cortical regions displaying blood-brain barrier (BBB) dysfunction, and in three rodent models with BBB pathology: aged mice, young 5x familial AD model, and status epilepticus-induced epilepsy in young rats. To investigate the potential causative role of BBB dysfunction in network modifications underlying PSWEs, we infused the serum protein albumin directly into the cerebral ventricles of naïve young rats. Infusion of albumin, but not artificial cerebrospinal fluid control, resulted in high incidence of PSWEs. Our results identify PSWEs as an EEG manifestation of nonconvulsive seizures in patients with AD and suggest BBB pathology as an underlying mechanism and as a promising therapeutic target.

Analysis of gene expression profiling of amyloidogenic immunoglobulin light-chains on cultured rat cardiomyocytes

The present study aimed to investigate the toxic effects of different amyloidogenic light-chains (LCs) on cardiomyocytes, and demonstrate the differentially expressed genes (DEGs) and signaling pathways that participate in this process. Cultured cardiomyocytes were treated with recombinant κ LC peptide (AL-09) or with serum from a patient diagnosed with multiple myeloma (λ LC) with cardiac involvement. The 6xHis peptide or serum from healthy patients was used as peptide control or serum control, respectively. Cell viability was determined using CCK-8 assay and apoptosis was analyzed by flow cytometry. The DEGs were detected by RNA sequencing (RNA-Seq), followed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Changes in gene expression levels were confirmed by reverse transcription-quantitative PCR. The cell viability in the AL-09 peptide-treated (0.2 mg/ml) and patient serum-treated (1:10 dilution) cardiomyocytes decreased to 42 and -72% of the corresponding control groups. The extent of cell apoptosis increased in AL-09-treated cardiomyocytes compared with the control group. RNA-Seq showed 256 DEGs co-existed in the two paired groups, including 127 upregulated and 88 downregulated genes. The KEGG pathways for upregulated expressed genes included the ‘TGF-β signaling pathway’, the ‘Hedgehog signaling pathway’, the ‘ErbB signaling pathway’ and ‘lysine degradation’. The higher mRNA expression of bone morphogenetic protein (Bmp) 4, Bmp6, prostaglandin G/H synthase (Ptgs)1, Ptgs2, epiregulin, Tgfa and procollagen-lysine,2-oxoglutarate 5-dioxygenase 2 were confirmed. The KEGG pathways of downregulated expressed genes included genes involved with the ‘p53 signaling pathway’ and the ‘cell cycle’. The mRNA expression levels of E3 ubiquitin-protein ligase CCNB1IP1 showed significant downregulation in the AL-09 peptide group compared with those in the 6xHis peptide group. In conclusion, cardiomyocytes treated with amyloidogenic λ and κ LCs presented with decreased cell viability compared with controls. Cell apoptosis increased in κ LC-treated cells compared with controls. The gene expression profiles associated with transforming growth factor-β-bone morphogenetic protein, the receptor tyrosine-protein kinase erbB-2 signaling pathways, prostaglandins, collagen production, the p53 signaling pathway and the cell cycle were altered in light-chain-treated cardiomyocytes.

Identification and molecular docking study of fish roe-derived peptides as potent BACE 1, AChE, and BChE inhibitors

Acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and beta-secretase 1 (BACE 1) play vital roles in the development and progression of Alzheimer's disease (AD).

TGFB1-Mediated Gliosis in Multiple Sclerosis Spinal Cords Is Favored by the Regionalized Expression of HOXA5 and the Age-Dependent Decline in Androgen Receptor Ligands

In multiple sclerosis (MS) patients with a progressive form of the disease, spinal cord (SC) functions slowly deteriorate beyond age 40. We previously showed that in the SC of these patients, large areas of incomplete demyelination extend distance away from plaque borders and are characterized by a unique progliotic TGFB1 (Transforming Growth Factor Beta 1) genomic signature. Here, we attempted to determine whether region- and age-specific physiological parameters could promote the progression of SC periplaques in MS patients beyond age 40. An analysis of transcriptomics databases showed that, under physiological conditions, a set of 10 homeobox (HOX) genes are highly significantly overexpressed in the human SC as compared to distinct brain regions. Among these HOX genes, a survey of the human proteome showed that only HOXA5 encodes a protein which interacts with a member of the TGF-beta signaling pathway, namely SMAD1 (SMAD family member 1). Moreover, HOXA5 was previously found to promote the TGF-beta pathway. Interestingly, SMAD1 is also a protein partner of the androgen receptor (AR) and an unsupervised analysis of gene ontology terms indicates that the AR pathway antagonizes the TGF-beta/SMAD pathway. Retrieval of promoter analysis data further confirmed that AR negatively regulates the transcription of several members of the TGF-beta/SMAD pathway. On this basis, we propose that in progressive MS patients, the physiological SC overexpression of HOXA5 combined with the age-dependent decline in AR ligands may favor the slow progression of TGFB1-mediated gliosis. Potential therapeutic implications are discussed.

Effects of angiotensin-II on brain endothelial cell permeability via PPARalpha regulation of para- and trans-cellular pathways

Angiotensin-II (Ang-II) is a key factor in hypertension, diabetes and aging, which are all primary risk factors for CNS disease. Furthermore, Ang-II may play under-appreciated roles in neurogenesis, angiogenesis and CNS remodeling. Therefore, any contemplated attempts for neurorestorative therapies in the CNS should consider the context of Ang-II signaling. Here, we investigate how Ang-II may regulate cerebral endothelial permeability, a key functional feature of the neurovascular unit. Exposure of human brain endothelial cell cultures to Ang-II increased its permeability to BSA-Alexa488 tracer. Immunocytochemistry and pulse-chase experiments suggested that both para-cellular as well as trans-cellular pathways were involved. Candesartan but not PD123319 blocked Ang-II permeability effects, suggesting that Ang-II effects may be mediated via type 1 receptor. Immunocytochemistry and western blots showed that Ang-II disrupted the membrane distributions of ZO-1 and VE-Cad, decreased total levels of JAM-A and Mfsd2a, and increased Cav1. These effects of Ang-II were accompanied by dephosphorylation of PPARalpha. Finally, Ang-II-induced increases in endothelial permeability were ameliorated by PPARalpha agonists. Taken together, these studies suggest that Ang-II may disrupt both para- and trans-cellular permeability in cerebral endothelium, and PPARalpha-related pathways may offer potential therapeutic targets for ameliorating these effects in cell-based regenerative medicine.

Assessment of age-related decline of neurovascular coupling responses by functional near-infrared spectroscopy (fNIRS) in humans

Preclinical studies provide strong evidence that age-related impairment of neurovascular coupling (NVC) plays a causal role in the pathogenesis of vascular cognitive impairment (VCI). NVC is a critical homeostatic mechanism in the brain, responsible for adjustment of local cerebral blood flow to the energetic needs of the active neuronal tissue. Recent progress in geroscience has led to the identification of critical cellular and molecular mechanisms involved in neurovascular aging, identifying these pathways as targets for intervention. In order to translate the preclinical findings to humans, there is a need to assess NVC in geriatric patients as an endpoint in clinical studies. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that enables the investigation of local changes in cerebral blood flow, quantifying task-related changes in oxygenated and deoxygenated hemoglobin concentrations. In the present overview, the basic principles of fNIRS are introduced and the application of this technique to assess NVC in older adults with implications for the design of studies on the mechanistic underpinnings of VCI is discussed.

Alzheimer's dementia: pathogenesis and impact of cardiovascular risk factors on cognitive decline

Alzheimer's disease (AD) is the most common form of dementia manifesting as alterations in cognitive abilities, behavior, and deterioration in memory which is progressive, leading to gradual worsening of symptoms. Major pathological features of AD are accumulations of neuronal amyloid plaques and neurofibrillary tangles, with early lesions appearing primarily in the hippocampus, the area of the brain involved in memory and learning. Cardiovascular-related risk factors are believed to play a crucial role in disease development and the acceleration of cognitive deterioration by worsening cerebral perfusion, promoting disturbances in amyloid clearance. Current evidence supports hypertension, hypotension, heart failure, stroke and coronary artery diseases as potential factors playing a role in cognitive decline in patients with Alzheimer's dementia. Although dementia due to cardiovascular deficits is more strongly linked to the development of vascular dementia, a stepwise decline in cognition, recent researches have also discovered its deleterious influence on AD development.

Smooth Muscle Cell-Specific Disruption of the BBSome Causes Vascular Dysfunction

The BBSome-a complex consisting of 8 Bardet-Biedl syndrome proteins-is involved in the regulation of various cellular processes. Recently, the BBSome complex has emerged as an important regulator of cardiovascular function with implications for disease. In this study, we examined the role of the BBSome in vascular smooth muscle and its effects on the regulation of cardiovascular function. Smooth muscle-specific disruption of the BBSome through tamoxifen-inducible deletion of Bbs1 gene-a critical component of the BBSome complex-reduces relaxation and enhances contractility of vascular rings and increases aortic stiffness independent of changes in arterial blood pressure. Mechanistically, we demonstrate that smooth muscle Bbs1 gene deletion increases vascular angiotensinogen gene expression implicating the renin-angiotensin system in these altered cardiovascular responses. Additionally, we report that smooth muscle-specific Bbs1 knockout mice demonstrate enhanced ET-1 (endothelin-1)-induced contractility of mesenteric arteries-an effect reversed by blockade of the AT1 (angiotensin type 1 receptor) with losartan. These findings highlight the importance of the smooth muscle BBSome in the control of vascular function and arterial stiffness through modulation of renin-angiotensin system signaling.

Interference With Endothelial PPAR (Peroxisome Proliferator-Activated Receptor)-γ Causes Accelerated Cerebral Vascular Dysfunction in Response to Endogenous Renin-Angiotensin System Activation

Low-salt diet is beneficial in salt-sensitive hypertension but may provoke cardiovascular risk in patients with heart failure, diabetes mellitus, or other cardiovascular abnormalities because of endogenous renin-angiotensin system activation. PPAR (peroxisome proliferator-activated receptor)-γ is a transcription factor which promotes an antioxidant pathway in the endothelium. We studied transgenic mice expressing a dominant-negative mutation in PPAR-γ selectively in the endothelium (E-V290M) to test the hypothesis that endothelial PPAR-γ plays a protective role in response to low salt-mediated renin-angiotensin system activation. Plasma renin and Ang II (angiotensin II) were significantly and equally increased in all mice fed low salt for 6 weeks. Vasorelaxation to acetylcholine was not affected in basilar artery from E-V290M at baseline but was significantly and selectively impaired in E-V290M after low salt. Unlike basilar artery, low salt was not sufficient to induce vascular dysfunction in carotid artery or aorta. Endothelial dysfunction in the basilar artery from E-V290M mice fed low salt was attenuated by scavengers of superoxide, inhibitors of NADPH oxidase, or blockade of the Ang II AT1 (angiotensin type-1) receptor. Simultaneous AT1 and AT2 receptor blockade revealed that the restoration of endothelial function after AT1 receptor blockade was not a consequence of AT2 receptor activation. We conclude that interference with PPAR-γ in the endothelium produces endothelial dysfunction in the cerebral circulation in response to low salt-mediated activation of the endogenous renin-angiotensin system, mediated at least in part, through AT1 receptor activation and perturbed redox homeostasis. Moreover, our data suggest that the cerebral circulation may be particularly sensitive to inhibition of PPAR-γ activity and renin-angiotensin system activation.

Insights into the Potential Role of Mercury in Alzheimer's Disease

Mercury (Hg), which is a non-essential element, is considered a highly toxic pollutant for biological systems even when present at trace levels. Elevated Hg exposure with the growing release of atmospheric pollutant Hg and rising accumulations of mono-methylmercury (highly neurotoxic) in seafood products have increased its toxic potential for humans. This review aims to highlight the potential relationship between Hg exposure and Alzheimer's disease (AD), based on the existing literature in the field. Recent reports have hypothesized that Hg exposure could increase the potential risk of developing AD. Also, AD is known as a complex neurological disorder with increased amounts of both extracellular neuritic plaques and intracellular neurofibrillary tangles, which may also be related to lifestyle and genetic variables. Research reports on AD and relationships between Hg and AD indicate that neurotransmitters such as serotonin, acetylcholine, dopamine, norepinephrine, and glutamate are dysregulated in patients with AD. Many researchers have suggested that AD patients should be evaluated for Hg exposure and toxicity. Some authors suggest further exploration of the Hg concentrations in AD patients. Dysfunctional signaling pathways in AD and Hg exposure appear to be interlinked with some driving factors such as arachidonic acid, homocysteine, dehydroepiandrosterone (DHEA) sulfate, hydrogen peroxide, glucosamine glycans, glutathione, acetyl-L carnitine, melatonin, and HDL. This evidence suggests the need for a better understanding of the relationship between AD and Hg exposure, and potential mechanisms underlying the effects of Hg exposure on regional brain functions. Also, further studies evaluating brain functions are needed to explore the long-term effects of subclinical and untreated Hg toxicity on the brain function of AD patients.

TGF-β1 Restores Hippocampal Synaptic Plasticity and Memory in Alzheimer Model via the PI3K/Akt/Wnt/β-Catenin Signaling Pathway

Alzheimer's disease (AD) is the most common neurodegenerative disturbances. Dysfunction of synaptic plasticity and decline in cognitive functions are the most prominent features of AD, but the mechanisms of pathogenesis have not been well elucidated. In this paper, transforming growth factor-β1 (TGF-β1) was found to be reduced in the hippocampus of AD mouse which was accompanied by impaired pine density, synaptic plasticity, and memory function. Hippocampal injection of TGF-β1 rescued the AD-induced memory function impairment. In addition, TGF-β1 ameliorated synaptic plasticity and increased synaptic plasticity-associated protein expression including Arc, NR2B, and PSD-95 in mouse model of AD. Furthermore, we demonstrated that Akt/Wnt/β-catenin pathway protein expression in the hippocampus was suppressed in a mouse model of AD and TGF-β1 significantly enhanced the phosphorylation Akt, GSK3β, and increased the nuclear β-catenin. These results indicate that TGF-β1activates PI3K/Akt/Wnt/β-catenin signaling in mouse model of AD, which is important for promoting synaptic plasticity related to memory function. More importantly, suppression of PI3K/Akt/Wnt/β-catenin pathway compromised the beneficial effects of TGFβ1 in Alzheimer's model. Hence, TGF-β1 shows protective effect on neurons, which might be through the PI3K/Akt/Wnt/β-catenin signaling pathway, serving as a potential target in AD pathology.

Pharmacologically induced impairment of neurovascular coupling responses alters gait coordination in mice

There is correlative evidence that impaired cerebral blood flow (CBF) regulation, in addition to promoting cognitive impairment, is also associated with alterations in gait and development of falls in elderly people. CBF is adjusted to neuronal activity via neurovascular coupling (NVC) and this mechanism becomes progressively impaired with age. To establish a direct cause-and-effect relationship between impaired NVC and gait abnormalities, we induced neurovascular uncoupling pharmacologically in young C57BL/6 mice by inhibiting the synthesis of vasodilator mediators involved in NVC. Treatment of mice with the epoxygenase inhibitor MSPPOH, the NO synthase inhibitor L-NAME, and the COX inhibitor indomethacin significantly decreased NVC mimicking the aging phenotype. Pharmacologically induced neurovascular uncoupling significantly decreased the dynamic gait parameter duty cycle, altered footfall patterns, and significantly increased phase dispersion, indicating impaired interlimb coordination. Impaired NVC also tended to increase gait variability. Thus, selective experimental disruption of NVC causes subclinical gait abnormalities, supporting the importance of CBF in both cognitive function and gait regulation.

Hypertension impairs neurovascular coupling and promotes microvascular injury: role in exacerbation of Alzheimer's disease

Hypertension in the elderly substantially increases both the risk of vascular cognitive impairment (VCI) and Alzheimer's disease (AD); however, the underlying mechanisms are not completely understood. This review discusses the effects of hypertension on structural and functional integrity of cerebral microcirculation, including hypertension-induced alterations in neurovascular coupling responses, cellular and molecular mechanisms involved in microvascular damage (capillary rarefaction, blood-brain barrier disruption), and the genesis of cerebral microhemorrhages and their potential role in exacerbation of cognitive decline associated with AD. Understanding and targeting the hypertension-induced cerebromicrovascular alterations that are involved in the onset and progression of AD and contribute to cognitive impairment are expected to have a major role in preserving brain health in high-risk older individuals.

Demonstration of impaired neurovascular coupling responses in TG2576 mouse model of Alzheimer's disease using functional laser speckle contrast imaging

Increasing evidence from epidemiological, clinical, and experimental studies indicates that cerebromicrovascular dysfunction and microcirculatory damage play critical roles in the pathogenesis of many types of dementia in the elderly, including both vascular cognitive impairment (VCI) and Alzheimer's disease. Vascular contributions to cognitive impairment and dementia (VCID) include impairment of neurovascular coupling responses/functional hyperemia ("neurovascular uncoupling"). Due to the growing interest in understanding and pharmacologically targeting pathophysiological mechanisms of VCID, there is an increasing need for sensitive, easy-to-establish methods to assess neurovascular coupling responses. Laser speckle contrast imaging (LSCI) is a technique that allows rapid and minimally invasive visualization of changes in regional cerebromicrovascular blood perfusion. This type of imaging technique combines high resolution and speed to provide great spatiotemporal accuracy to measure moment-to-moment changes in cerebral blood flow induced by neuronal activation. Here, we provide detailed protocols for the successful measurement in neurovascular coupling responses in anesthetized mice equipped with a thinned-skull cranial window using LSCI. This method can be used to evaluate the effects of anti-aging or anti-AD treatments on cerebromicrovascular health.

Angiotensin II Type 1 Receptor Blockers Inhibit KAT II Activity in the Brain-Its Possible Clinical Applications

Angiotensin II receptor blockers (ARBs) are one of the most frequently recommended antihypertensive drugs. Apart from their activity towards the circulatory system, ARBs also penetrate the blood-brain barrier and display neuroprotective effects. Kynurenic acid (KYNA) is an endogenous metabolite of tryptophan produced by kynurenine aminotransferase II (KAT II) in the brain. Antagonism towards all ionotropic glutamate (GLU) receptors is the main mechanism of KYNA action. An elevated brain level of KYNA is linked with memory impairment and psychotic symptoms. The aim of this study was to examine the influence of three ARBs: irbesartan, losartan, and telmisartan on KYNA production and KAT II activity in rat brain. The effect of ARBs on KYNA production was analyzed in rat brain cortical slices and on isolated KAT II enzyme. Irbesartan, losartan, and telmisartan decreased KYNA production and KAT II activity in a dose-dependent manner in rat brain cortex in vitro. Molecular docking suggested that the examined ARBs could bind to an active site of KAT II. In conclusion, ARBs decrease KYNA production in rat brain by direct inhibition of KAT II enzymatic activity. This novel mechanism of ARBs action may be advantageous in the treatment of cognitive impairment or the management of schizophrenia.