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Functionally linked potassium channel activity in cerebral endothelial and smooth muscle cells is compromised in Alzheimer's disease.

ABSTRACT: The brain microcirculation is increasingly viewed as a potential target for disease-modifying drugs in the treatment of Alzheimer's disease patients, reflecting a growing appreciation of evidence that cerebral blood flow is compromised in such patients. However, the pathogenic mechanisms in brain resistance arteries underlying blood flow defects have not yet been elucidated. Here we probed the roles of principal vasodilatory pathways in cerebral arteries using the APP23 mouse model of Alzheimer's disease, in which amyloid precursor protein is increased approximately sevenfold, leading to neuritic plaques and cerebrovascular accumulation of amyloid-β similar to those in patients with Alzheimer's disease. Pial arteries from APP23 mice (18 mo old) exhibited enhanced pressure-induced (myogenic) constriction because of a profound reduction in ryanodine receptor-mediated, local calcium-release events ("Ca²⁺ sparks") in arterial smooth muscle cells and a consequent decrease in the activity of large-conductance Ca²⁺-activated K⁺ (BK) channels. The ability of the endothelial cell inward rectifier K⁺ (Kir2.1) channel to cause dilation was also compromised. Acute application of amyloid-β 1-40 peptide to cerebral arteries from wild-type mice partially recapitulated the BK dysfunction seen in APP23 mice but had no effect on Kir2.1 function. If mirrored in human Alzheimer's disease, these tandem defects in K⁺ channel-mediated vasodilation could account for the clinical cerebrovascular presentation seen in patients: reduced blood flow and crippled functional hyperemia. These data direct future research toward approaches that reverse this dual vascular channel dysfunction, with the ultimate aim of restoring healthy cerebral blood flow and improving clinical outcomes.

SUBMITTER: Taylor JL

PROVIDER: S-EPMC9245656 | biostudies-literature | 2022 Jun

REPOSITORIES: biostudies-literature

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Functionally linked potassium channel activity in cerebral endothelial and smooth muscle cells is compromised in Alzheimer's disease.

Taylor Jade L JL Pritchard Harry A T HAT Walsh Katy R KR Strangward Patrick P White Claire C Hill-Eubanks David D Alakrawi Mariam M Hennig Grant W GW Allan Stuart M SM Nelson Mark T MT Greenstein Adam S AS

Proceedings of the National Academy of Sciences of the United States of America 20220621 26

The brain microcirculation is increasingly viewed as a potential target for disease-modifying drugs in the treatment of Alzheimer's disease patients, reflecting a growing appreciation of evidence that cerebral blood flow is compromised in such patients. However, the pathogenic mechanisms in brain resistance arteries underlying blood flow defects have not yet been elucidated. Here we probed the roles of principal vasodilatory pathways in cerebral arteries using the APP23 mouse model of Alzheimer' ...[more]

PMID: 35727988

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Project description:Large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channels hyperpolarize coronary artery smooth muscle cells, causing vasorelaxation. Dopamine activates BK(Ca) channels by stimulating D(1)-like receptor-mediated increases in cAMP in porcine coronary artery myocytes. There are two D(1)-like receptors (R), D(1)R and D(5)R. We hypothesize that the specific D(1)-like receptor involved in BK(Ca) channel activation in human coronary artery smooth muscle cells (HCASMCs) is the D(5)R and that activation occurs via cAMP cross-activation of cGMP-dependent protein kinase (PKG), rather than cAMP-dependent protein kinase (PKA). The effects of D(1)-like receptor agonists and antagonists on BK(Ca) channel opening in HCASMCs were examined in the presence and absence of PKG/PKA inhibition by cell-attached patch clamp. In the absence of commercially available ligands specific for D(1)R or D(5)R, D(1)R or D(5)R protein was down-regulated by transfecting HCASMCs with human D(1)R or D(5)R antisense oligonucleotides, respectively: cells transfected with scrambled oligonucleotides and nontransfected HCASMCs served as controls. The predominant ion channel conducting outward currents in nontransfected HCASMCs was identified as the large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channel, which was activated by D(1)-like receptor agonists despite PKA inhibition with (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid (KT 5720) (300 nM), but was abolished by inhibiting PKG with 9-methoxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b-11a-triazadibenzo(a,g) cycloocta(cde)-trinden-1-one (KT 5823) (300 nM). D(1)-like receptor agonists activated BK(Ca) channels in all transfected cells except those transfected with D(5)R antisense oligonucleotides. Thus, the dopamine (D(1)-like) receptor mediates activation of BK(Ca) channels in HCASMCs by D(5)R, not D(1)R, and via PKG, not PKA. This is the first report of differential D(1)-like receptor regulation of vascular smooth muscle function in human cells.

Project description:ATP-sensitive potassium channels (KATP channels) are hetero-octameric nucleotide-gated ion channels that couple cellular metabolism to excitability in various tissues. In the heart, KATP channels are activated during ischaemia and potentially during adrenergic stimulation. In the vasculature, they are normally active at a low level, reducing vascular tone, but the ubiquitous nature of these channels leads to complex and poorly understood channelopathies as a result of gain- or loss-of-function mutations. Zebrafish (ZF) models of these channelopathies may provide insights to the link between molecular dysfunction and complex pathophysiology, but this requires understanding the tissue dependence of channel activity and subunit specificity. Thus far, direct analysis of ZF KATP expression and functional properties has only been performed in pancreatic β-cells. Using a comprehensive combination of genetically modified fish, electrophysiology and gene expression analysis, we demonstrate that ZF cardiac myocytes (CM) and vascular smooth muscle (VSM) express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. However, in contrast to mammalian cardiovascular KATP channels, ZF channels are insensitive to potassium channel opener drugs (pinacidil, minoxidil) in both chambers of the heart and in VSM. The results provide a first characterization of the molecular properties of fish KATP channels and validate the use of such genetically modified fish as models of human Cantú syndrome and ABCC9-related Intellectual Disability and Myopathy syndrome. KEY POINTS: Zebrafish cardiac myocytes (CM) and vascular smooth muscle (VSM) express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. In contrast to mammalian cardiovascular KATP channels, zebrafish channels are insensitive to potassium channel opener drugs (pinacidil, minoxidil) in both chambers of the heart and in VSM. We provide a first characterization of the molecular properties of fish KATP channels and validate the use of such genetically modified fish as models of human Cantú syndrome and ABCC9-related Intellectual Disability and Myopathy syndrome.

Project description:BackgroundAlzheimer's disease (AD) is a complex neurodegenerative disease marked by increased amyloid-β (Aβ) deposition, tau hyperphosphorylation, impaired energy metabolism, and chronic ischemia-type injury. Cerebral microvascular dysfunction likely contributes to AD pathology, but its precise pathogenic role has been poorly defined.ObjectiveTo examine microvascular reactivity to endothelium-dependent vasodilators and small conductance calcium-activated potassium (SK) channel activity in an intracerebral streptozotocin (STZ)-induced AD mouse model.MethodsControl and STZ-AD mice underwent Morris Water Maze and Barnes testing, after which cerebral microvascular and brain microvascular endothelial cells (MBMECs) were dissected to assess microvascular reactivity, responses to SK channel activator NS309, and ion-channel current recordings using whole-cell patch clamp methodology. Control mouse cerebral microvascular and human brain microvascular endothelial cells (HBMECs) were treated with soluble Aβ1-42 peptide to characterize microvascular reactivity and endothelial potassium currents.ResultsSTZ-AD mice exhibited impaired performance vs control mice in behavioral testing. STZ-AD mice also exhibited diminished cerebral microvascular responsiveness and MBMECs potassium current augmentation in response to NS309 compared with control mice. Incubation of control mouse cerebral micro-vessels and HBMECs with soluble Aβ (1 µM) for 2 h attenuated relaxation responses to NS309 and diminished NS309-sensitive endothelial potassium currents.ConclusionsSTZ-AD mice exhibited impaired microvascular relaxation responses to endothelium-dependent vasodilators; SK/IK channel dysfunction may be involved in the mechanism of this impairment. Acute treatment with Aβ produced dysregulated cerebrovascular endothelial SK/IK channels. Further elucidation of the role of microvascular dysfunction in AD is needed to prevent the chronic ischemia-type injury that contributes to cognitive decline.

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Functionally linked potassium channel activity in cerebral endothelial and smooth muscle cells is compromised in Alzheimer's disease.

Publications

Functionally linked potassium channel activity in cerebral endothelial and smooth muscle cells is compromised in Alzheimer's disease.

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