Alzheimer's Aβ assembly binds sodium pump and blocks endothelial NOS activity via ROS-PKC pathway in brain vascular endothelial cells

SIK1 Downregulates Synaptic AMPA Receptors and Contributes to Cognitive Defects in Alzheimer's Disease

A reduction in AMPA receptor (AMPAR) expression and weakened synaptic activity is early cellular phenotypes in Alzheimer's disease (AD). However, the molecular processes leading to AMPAR downregulation are complex and remain less clear. Here, we report that the salt inducible kinase SIK1 interacts with AMPARs, leading to a reduced accumulation of AMPARs at synapses. SIK1 protein level is sensitive to amyloid beta (Aβ) and shows a marked increase in the presence of Aβ and in AD brains. In neurons, Aβ incubation causes redistribution of SIK1 to synaptic sites and enhances SIK1-GluA1 association. SIK1 function is required for Aβ-induced AMPAR reduction. Importantly, in 3xTG AD mice, knockdown of SIK1 in the brain leads to restoration of AMPAR expression and a rescue of the cognitive deficits. These findings indicate an important role for SIK1 in meditating the cellular and functional pathology in AD.

Mitochondrial Ca2+-coupled generation of reactive oxygen species, peroxynitrite formation, and endothelial dysfunction in Cantú syndrome

Cantú syndrome is a multisystem disorder caused by gain-of-function (GOF) mutations in KCNJ8 and ABCC9, the genes encoding the pore-forming inward rectifier Kir6.1 and regulatory sulfonylurea receptor SUR2B subunits, respectively, of vascular ATP-sensitive K+ (KATP) channels. In this study, we investigated changes in the vascular endothelium in mice in which Cantú syndrome-associated Kcnj8 or Abcc9 mutations were knocked in to the endogenous loci. We found that endothelium-dependent dilation was impaired in small mesenteric arteries from Cantú mice. Loss of endothelium-dependent vasodilation led to increased vasoconstriction in response to intraluminal pressure or treatment with the adrenergic receptor agonist phenylephrine. We also found that either KATP GOF or acute activation of KATP channels with pinacidil increased the amplitude and frequency of wave-like Ca2+ events generated in the endothelium in response to the vasodilator agonist carbachol. Increased cytosolic Ca2+ signaling activity in arterial endothelial cells from Cantú mice was associated with elevated mitochondrial [Ca2+] and enhanced reactive oxygen species (ROS) and peroxynitrite levels. Scavenging intracellular or mitochondrial ROS restored endothelium-dependent vasodilation in the arteries of mice with KATP GOF mutations. We conclude that mitochondrial Ca2+ overload and ROS generation, which subsequently leads to nitric oxide consumption and peroxynitrite formation, cause endothelial dysfunction in mice with Cantú syndrome.

Dysregulation of Ion Channels and Transporters and Blood-Brain Barrier Dysfunction in Alzheimer's Disease and Vascular Dementia

The blood-brain barrier (BBB) plays a critical role in maintaining ion and fluid homeostasis, essential for brain metabolism and neuronal function. Regulation of nutrient, water, and ion transport across the BBB is tightly controlled by specialized ion transporters and channels located within its unique cellular components. These dynamic transport processes not only influence the BBB's structure but also impact vital signaling mechanisms, essential for its optimal function. Disruption in ion, pH, and fluid balance at the BBB is associated with brain pathology and has been implicated in various neurological conditions, including stroke, epilepsy, trauma, and neurodegenerative diseases such as Alzheimer's disease (AD). However, knowledge gaps exist regarding the impact of ion transport dysregulation on BBB function in neurodegenerative dementias. Several factors contribute to this gap: the complex nature of these conditions, historical research focus on neuronal mechanisms and technical challenges in studying the ion transport mechanisms in in vivo models and the lack of efficient in vitro BBB dementia models. This review provides an overview of current research on the roles of ion transporters and channels at the BBB and poses specific research questions: 1) How are the expression and activity of key ion transporters altered in AD and vascular dementia (VaD); 2) Do these changes contribute to BBB dysfunction and disease progression; and 3) Can restoring ion transport function mitigate BBB dysfunction and improve clinical outcomes. Addressing these gaps will provide a greater insight into the vascular pathology of neurodegenerative disorders.

Cerebrovascular Endothelial Dysfunction: Role of BACE1

Dysfunctional endothelium is increasingly recognized as a mechanistic link between cardiovascular risk factors and dementia, including Alzheimer disease. BACE1 (β-site amyloid-β precursor protein-cleaving enzyme 1) is responsible for β-processing of APP (amyloid-β precursor protein), the first step in the production of Aβ (amyloid-β) peptides, major culprits in the pathogenesis of Alzheimer disease. Under pathological conditions, excessive activation of BACE1 exerts detrimental effects on endothelial function by Aβ-dependent and Aβ-independent mechanisms. High local concentration of Aβ in the brain blood vessels is responsible for the loss of key vascular protective functions of endothelial cells. More recent studies recognized significant contribution of Aβ-independent proteolytic activity of endothelial BACE1 to the pathogenesis of endothelial dysfunction. This review critically evaluates existing evidence supporting the concept that excessive activation of BACE1 expressed in the cerebrovascular endothelium impairs key homeostatic functions of the brain blood vessels. This concept has important therapeutic implications. Indeed, improved understanding of the mechanisms of endothelial dysfunction may help in efforts to develop new approaches to the protection and preservation of healthy cerebrovascular function.

Cooperation between neurovascular dysfunction and Aβ in Alzheimer's disease

The amyloid-β (Aβ) hypothesis was once believed to represent the pathogenic process of Alzheimer's disease (AD). However, with the failure of clinical drug development and the increasing understanding of the disease, the Aβ hypothesis has been challenged. Numerous recent investigations have demonstrated that the vascular system plays a significant role in the course of AD, with vascular damage occurring prior to the deposition of Aβ and neurofibrillary tangles (NFTs). The question of how Aβ relates to neurovascular function and which is the trigger for AD has recently come into sharp focus. In this review, we outline the various vascular dysfunctions associated with AD, including changes in vascular hemodynamics, vascular cell function, vascular coverage, and blood-brain barrier (BBB) permeability. We reviewed the most recent findings about the complicated Aβ-neurovascular unit (NVU) interaction and highlighted its vital importance to understanding disease pathophysiology. Vascular defects may lead to Aβ deposition, neurotoxicity, glial cell activation, and metabolic dysfunction; In contrast, Aβ and oxidative stress can aggravate vascular damage, forming a vicious cycle loop.

PKCε inhibition prevents ischemia‑induced dendritic spine impairment in cultured primary neurons

Brain ischemia is an independent risk factor for Alzheimer's disease (AD); however, the mechanisms underlining ischemic stroke and AD remain unclear. The present study aimed to investigate the function of the ε isoform of protein kinase C (PKCε) in brain ischemia-induced dendritic spine dysfunction to elucidate how brain ischemia causes AD. In the present study, primary hippocampus and cortical neurons were cultured while an oxygen-glucose deprivation (OGD) model was used to simulate brain ischemia. In the OGD cell model, in vitro kinase activity assay was performed to investigate whether the PKCε kinase activity changed after OGD treatment. Confocal microscopy was performed to investigate whether inhibiting PKCε kinase activity protects dendritic spine morphology and function. G-LISA was used to investigate whether small GTPases worked downstream of PKCε. The results showed that PKCε kinase activity was significantly increased following OGD treatment in primary neurons, leading to dendritic spine dysfunction. Pre-treatment with PKCε-inhibiting peptide, which blocks PKCε activity, significantly rescued dendritic spine function following OGD treatment. Furthermore, PKCε could activate Ras homolog gene family member A (RhoA) as a downstream molecule, which mediated OGD-induced dendritic spine morphology changes and caused dendritic spine dysfunction. In conclusion, the present study demonstrated that the PKCε/RhoA signalling pathway is a novel mechanism mediating brain ischemia-induced dendritic spine dysfunction. Developing therapeutic targets for this pathway may protect against and prevent brain ischemia-induced cognitive impairment and AD.

Therapeutic potential of natural molecules against Alzheimer's disease via SIRT1 modulation

Alzheimer's disease (AD) is a neurodegenerative disease mainly characterized by progressive cognitive dysfunction and memory impairment. Recent studies have shown that regulating silent information regulator 1 (SIRT1) expression has a significant neuroprotective effect, and SIRT1 may become a new therapeutic target for AD. Natural molecules are an important source of drug development for use in AD therapy and may regulate a wide range of biological events by regulating SIRT1 as well as other SIRT1-mediated signaling pathways. This review aims to summarize the correlation between SIRT1 and AD and to identify in vivo and in vitro studies investigating the anti-AD properties of natural molecules as modulators of SIRT1 and SIRT1-mediated signaling pathways. A literature search was conducted for studies published between January 2000 and October 2022 using various literature databases, including Web of Science, PubMed, Google Scholar, Science Direct, and EMBASE. Natural molecules, such as resveratrol, quercetin, icariin, bisdemethoxycurcumin, dihydromyricetin, salidroside, patchouli, sesamin, rhein, ligustilide, tetramethoxyflavanone, 1-theanine, schisandrin, curcumin, betaine, pterostilbene, ampelopsin, schisanhenol, and eriodictyol, have the potential to modulate SIRT1 and SIRT1 signaling pathways, thereby combating AD. The natural molecules modulating SIRT1 discussed in this review provide a potentially novel multi-mechanistic therapeutic strategy for AD. However, future clinical trials need to be conducted to further investigate their beneficial properties and to determine the safety and efficacy of SIRT1 natural activators against AD.

Recent Advances in the Study of Na+/K+-ATPase in Neurodegenerative Diseases

Na⁺/K⁺-ATPase (NKA), a large transmembrane protein, is expressed in the plasma membrane of most eukaryotic cells. It maintains resting membrane potential, cell volume and secondary transcellular transport of other ions and neurotransmitters. NKA consumes about half of the ATP molecules in the brain, which makes NKA highly sensitive to energy deficiency. Neurodegenerative diseases (NDDs) are a group of diseases characterized by chronic, progressive and irreversible neuronal loss in specific brain areas. The pathogenesis of NDDs is sophisticated, involving protein misfolding and aggregation, mitochondrial dysfunction and oxidative stress. The protective effect of NKA against NDDs has been emerging gradually in the past few decades. Hence, understanding the role of NKA in NDDs is critical for elucidating the underlying pathophysiology of NDDs and identifying new therapeutic targets. The present review focuses on the recent progress involving different aspects of NKA in cellular homeostasis to present in-depth understanding of this unique protein. Moreover, the essential roles of NKA in NDDs are discussed to provide a platform and bright future for the improvement of clinical research in NDDs.

Endothelial BACE1 Impairs Cerebral Small Vessels via Tight Junctions and eNOS

BACKGROUND

Cerebral small vessel injury, including loss of endothelial tight junctions, endothelial dysfunction, and blood-brain barrier breakdown, is an early and typical pathology for Alzheimer disease, cerebral amyloid angiopathy, and hypertension-related cerebral small vessel disease. Whether there is a common mechanism contributing to these cerebrovascular alterations remains unclear. Studies have shown an elevation of BACE1 (β-site amyloid precursor protein cleaving enzyme 1) in cerebral vessels from cerebral amyloid angiopathy or Alzheimer disease patients, suggesting that vascular BACE1 may involve in cerebral small vessel injury.

METHODS

To understand the contribution of vascular BACE1 to cerebrovascular impairments, we combined cellular and molecular techniques, mass spectrometry, immunostaining approaches, and functional testing to elucidate the potential pathological mechanisms.

RESULTS

We observe a 3.71-fold increase in BACE1 expression in the cerebral microvessels from patients with hypertension. Importantly, we discover that an endothelial tight junction protein, occludin, is a completely new substrate for endothelial BACE1. BACE1 cleaves occludin with full-length occludin reductions and occludin fragment productions. An excessive cleavage by elevated BACE1 induces membranal accumulation of caveolin-1 and subsequent caveolin-1-mediated endocytosis, resulting in lysosomal degradation of other tight junction proteins. Meanwhile, membranal caveolin-1 increases the binding to eNOS (endothelial nitric oxide synthase), together with raised circulating Aβ (β-amyloid peptides) produced by elevated BACE1, leading to an attenuation of eNOS activity and resultant endothelial dysfunction. Furthermore, the initial endothelial damage provokes chronic reduction of cerebral blood flow, blood-brain barrier leakage, microbleeds, tau hyperphosphorylation, synaptic loss, and cognitive impairment in endothelial-specific BACE1 transgenic mice. Conversely, inhibition of aberrant BACE1 activity ameliorates tight junction loss, endothelial dysfunction, and memory deficits.

CONCLUSIONS

Our findings establish a novel and direct relationship between endothelial BACE1 and cerebral small vessel damage, indicating that abnormal elevation of endothelial BACE1 is a new mechanism for cerebral small vessel disease pathogenesis.

High-throughput screening for agonists of ROS production in live human vascular endothelial cells

Reactive oxygen species (ROS) are important physiological molecules, and identifying agonists for ROS production can yield useful tools for future research. Here we present an optimized protocol for high-throughput screening for agonists that induce ROS production. We describe the use of a fluorescent probe in human vascular endothelial cells, which can establish whether ROS production occurs in mitochondria or in the plasma membrane of live cells.

For complete details on the use and execution of this profile, please refer to Sasahara et al. (2021).

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This is a high-throughput screening protocol for agonists that induce ROS production

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ROS production in human endothelial cells is identified by fluorescence imaging

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This reveals whether ROS production occurs in mitochondria or plasma membrane