Circulating tPA contributes to neurovascular coupling by a mechanism involving the endothelial NMDA receptors

The increase of cerebral blood flow evoked by neuronal activity is essential to ensure enough energy supply to the brain. In the neurovascular unit, endothelial cells are ideally placed to regulate key neurovascular functions of the brain. Nevertheless, some outstanding questions remain about their exact role neurovascular coupling (NVC). Here, we postulated that the tissue-type plasminogen activator (tPA) present in the circulation might contribute to NVC by a mechanism dependent of its interaction with endothelial N-Methyl-D-Aspartate Receptor (NMDAR). To address this question, we used pharmacological and genetic approaches to interfere with vascular tPA-dependent NMDAR signaling, combined with laser speckle flowmetry, intravital microscopy and ultrafast functional ultrasound in vivo imaging. We found that the tPA present in the blood circulation is capable of potentiating the cerebral blood flow increase induced by the activation of the mouse somatosensorial cortex, and that this effect is mediated by a tPA-dependent activation of NMDAR expressed at the luminal part of endothelial cells of arteries. Although blood molecules, such as acetylcholine, bradykinin or ATP are known to regulate vascular tone and induce vessel dilation, our present data provide the first evidence that circulating tPA is capable of influencing neurovascular coupling (NVC).

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Telmisartan prevents high-fat diet-induced neurovascular impairments and reduces anxiety-like behavior

Journal of Cerebral Blood Flow & Metabolism ◽

10.1177/0271678x211003497 ◽

2021 ◽

pp. 0271678X2110034

Author(s):

Gianna Huber ◽

Mikolaj Ogrodnik ◽

Jan Wenzel ◽

Ines Stölting ◽

Lukas Huber ◽

...

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

High Fat Diet ◽

Neurovascular Unit ◽

Laser Speckle ◽

Angiotensin Ii Receptor ◽

High Fat ◽

Diet Induced Obesity ◽

Whisker Pad ◽

Receptor Blockers

Angiotensin II receptor blockers (telmisartan) prevent rodents from diet-induced obesity and improve their metabolic status. Hyperglycemia and obesity are associated with reduced cerebral blood flow and neurovascular uncoupling which may lead to behavioral deficits. We wanted to know whether a treatment with telmisartan prevents these changes in obesity. We put young mice on high-fat diet and simultaneously treated them with telmisartan. At the end of treatment, we performed laser speckle imaging and magnetic resonance imaging to assess the effect on neurovascular coupling and cerebral blood flow. Different behavioral tests were used to investigate cognitive function. Mice developed diet-induced obesity and after 16, not 8 weeks of high-fat diet, however, the response to whisker pad stimulation was about 30% lower in obese compared to lean mice. Simultaneous telmisartan treatment increased the response again by 10% compared to obese mice. Moreover, telmisartan treatment normalized high-fat diet-induced reduction of cerebral blood flow and prevented a diet-induced anxiety-like behavior. In addition to that, telmisartan affects cellular senescence and string vessel formation in obesity. We conclude, that telmisartan protects against neurovascular unit impairments in a diet-induced obesity setting and may play a role in preventing obesity related cognitive deficits in Alzheimer’s disease.

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Electro-Metabolic Sensing Through Capillary ATP-Sensitive K+ Channels and Adenosine to Control Cerebral Blood Flow

10.1101/2021.03.12.435152 ◽

2021 ◽

Author(s):

Maria Sancho ◽

Nicholas R. Klug ◽

Amreen Mughal ◽

Thomas J. Heppner ◽

David Hill-Eubanks ◽

...

Keyword(s):

Endothelial Cells ◽

Blood Flow ◽

Cerebral Blood Flow ◽

Vascular Function ◽

Brain Activity ◽

List Type ◽

Capillary Endothelial Cells ◽

Metabolic Sensing ◽

Cellular Components

SUMMARYThe dense network of capillaries composed of capillary endothelial cells (cECs) and pericytes lies in close proximity to all neurons, ideally positioning it to sense neuro/glial-derived compounds that regulate regional and global cerebral perfusion. The membrane potential (VM) of vascular cells serves as the essential output in this scenario, linking brain activity to vascular function. The ATP-sensitive K+ channel (KATP) is a key regulator of vascular VM in other beds, but whether brain capillaries possess functional KATP channels remains unknown. Here, we demonstrate that brain capillary ECs and pericytes express KATP channels that robustly control VM. We further show that the endogenous mediator adenosine acts through A2A receptors and the Gs/cAMP/PKA pathway to activate capillary KATP channels. Moreover, KATP channel stimulation in vivo causes vasodilation and increases cerebral blood flow (CBF). These findings establish the presence of KATP channels in cECs and pericytes and suggest their significant influence on CBF.HIGHLIGHTSCapillary network cellular components—endothelial cells and pericytes—possess functional KATP channels.Activation of KATP channels causes profound hyperpolarization of capillary cell membranes.Capillary KATP channels are activated by exogenous adenosine via A2A receptors and cAMP-dependent protein kinase.KATP channel activation by adenosine or synthetic openers increases cerebral blood flow.

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Ex Vivo MuEtinuciear NMR Spectroscopy of Perfused, Respiring Rat Brain Slices: Model Studies of Hypoxia, Ischemia, and Excitotoxscit

Biological NMR Spectroscopy ◽

10.1093/oso/9780195094688.003.0031 ◽

1997 ◽

Author(s):

L. Litt ◽

M.T. Espanol

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Nmr Spectroscopy ◽

Clinical Care ◽

Brain Slices ◽

In Vivo Nmr ◽

In Vivo Nmr Spectroscopy ◽

Permanent Brain Damage ◽

The Brain

We believe there are important roles for in vivo NMR spectroscopy techniques in studies of protection and treatment in stroke. Perhaps the primary utility of in vivo NMR spectroscopy is to establish the relevance of metabolic integrity, intracellular pH, and intracellular energy stores to concurrent changes occurring both at gross physiological levels (e.g., changes in cerebral blood flow, or blood oxygenation), and at microscopic or cellular levels. It has long been known that the brain is exquisitely sensitive to deprivations of oxygen, glucose, and cerebral blood flow. Routine human surgery on a limb takes place every day with tourniquets stopping all blood flow for up to two hours. In contrast, the deprivation of all blood flow to the brain (global ischemia) for approximately 5 minutes can result in severe, permanent brain damage. Research has gone on for more than 30 years to understand why the brain’s revival time is so much shorter, and to discover brain biochemical interventions that might dramatically extend the brain’s intolerance beyond 5 minutes, and therefore be relevant to protection and treatment of stroke. (Kogure and Hossmann, 1985; 1993) Stroke, defined as a permanent neurologic deficit arising from the death of brain cells, kills ∼ 150,000 people in the U.S.A. each year, and is the third leading cause of death (Feinleib et al., 1993). It is the next malady to escape, once one has dodged death from cardiovascular disease and cancer. Many, if not most, U.S.A. stroke victims will receive neurological clinical care not substantially different from what was provided 30 years ago. Most stroke patients will be put in intensive care units where blood pressure will be regulated and kept in a “safe” range, with the body given supportive care and the brain given an opportunity to heal itself. The problem of stroke is actually quite complex because there are several different kinds of stroke (ischemic, hemorrhagic, etc.), and because numerous systemic physiological factors are of relevance. Nevertheless, exciting advances in brain biochemistry suggest that stroke therapy and prophylaxis axe likely to improve dramatically in the near future (Zivin and Choi, 1991).

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Ion channel networks in the control of cerebral blood flow

Journal of Cerebral Blood Flow & Metabolism ◽

10.1177/0271678x15616138 ◽

2015 ◽

Vol 36 (3) ◽

pp. 492-512 ◽

Cited By ~ 56

Author(s):

Thomas A Longden ◽

David C Hill-Eubanks ◽

Mark T Nelson

Keyword(s):

Endothelial Cells ◽

Blood Flow ◽

Smooth Muscle ◽

Cerebral Blood Flow ◽

Ion Channels ◽

Ion Channel ◽

Vascular Endothelial Cells ◽

Neurovascular Unit ◽

Muscle Membrane ◽

Neuronal Stimulation

One hundred and twenty five years ago, Roy and Sherrington made the seminal observation that neuronal stimulation evokes an increase in cerebral blood flow.1 Since this discovery, researchers have attempted to uncover how the cells of the neurovascular unit—neurons, astrocytes, vascular smooth muscle cells, vascular endothelial cells and pericytes—coordinate their activity to control this phenomenon. Recent work has revealed that ionic fluxes through a diverse array of ion channel species allow the cells of the neurovascular unit to engage in multicellular signaling processes that dictate local hemodynamics. In this review we center our discussion on two major themes: (1) the roles of ion channels in the dynamic modulation of parenchymal arteriole smooth muscle membrane potential, which is central to the control of arteriolar diameter and therefore must be harnessed to permit changes in downstream cerebral blood flow, and (2) the striking similarities in the ion channel complements employed in astrocytic endfeet and endothelial cells, enabling dual control of smooth muscle from either side of the blood–brain barrier. We conclude with a discussion of the emerging roles of pericyte and capillary endothelial cell ion channels in neurovascular coupling, which will provide fertile ground for future breakthroughs in the field.

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Brain Endothelial Cell TRPA1 Channels Initiate Neurovascular Coupling

10.1101/2020.09.14.295600 ◽

2020 ◽

Author(s):

Pratish Thakore ◽

Michael G. Alvarado ◽

Sher Ali ◽

Amreen Mughal ◽

Paulo W. Pires ◽

...

Keyword(s):

Endothelial Cells ◽

Neuronal Activity ◽

Transient Receptor Potential ◽

Neurovascular Coupling ◽

Laser Scanning Microscopy ◽

K Channel ◽

Transitional Region ◽

Capillary Endothelial Cells ◽

The Brain

Blood flow regulation in the brain is dynamically regulated to meet the metabolic demands of active neuronal populations. Recent evidence has demonstrated that capillary endothelial cells are essential mediators of neurovascular coupling that sense neuronal activity and generate a retrograde, propagating, hyperpolarizing signal that dilates upstream arterioles. Here, we tested the hypothesis that transient receptor potential ankyrin 1 (TRPA1) channels in capillary endothelial cells are significant contributors to functional hyperemic responses that underlie neurovascular coupling in the brain. Using an integrative ex vivo and in vivo approach, we demonstrate the functional presence of TRPA1 channels in brain capillary endothelial cells, and show that activation of these channels within the capillary bed, including the post-arteriole transitional region covered by ensheathing mural cells, initiates a retrograde signal that dilates upstream parenchymal arterioles. Notably, this signaling exhibits a unique biphasic mode of propagation that begins within the capillary network as a short-range, Ca2+ signal dependent on endothelial pannexin-1 channel/purinergic P2X receptor communication pathway and then is converted to a rapid, inward-rectifying K+ channel-mediated electrical signal in the post-arteriole transitional region that propagates upstream to parenchymal arterioles. Two-photon laser-scanning microscopy further demonstrated that conductive vasodilation occurs in vivo, and that TRPA1 is necessary for functional hyperemia within the somatosensory cortex of mice. Together, these data establish a role for endothelial TRPA1 channels as sensors of neuronal activity and show that they respond accordingly by initiating a vasodilatory response that redirects blood to regions of metabolic demand.

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Blood-brain barrier permeability of 11C-labeled alcohols and 15O-labeled water

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1976.230.2.543 ◽

1976 ◽

Vol 230 (2) ◽

pp. 543-552 ◽

Cited By ~ 217

Author(s):

ME Raichle ◽

JO Eichling ◽

MG Straatmann ◽

MJ Welch ◽

KB Larson ◽

...

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Time Course ◽

Brain Capillary ◽

Permeability Characteristics ◽

Permeability Surface ◽

Brain Barrier Permeability ◽

The Individual ◽

The Brain

The extraction of 11C-labeled methanol, ethanol, and isopropanol, as well as 15O-labeled water by the brain during a single capillary transit, was studied in vivo in six adult rhesus monkeys by external detection of the time course of these tracers subsequent to their internal carotid artery injection. The data demonstrate the feasibility of accurately measuring brain permeability of highly diffusible substances by this technique and show that neither water nor the alcohols studied freely equilibrate with brain when the cerebral blood flow exceeds 30 ml/100 g min-1. At a cerebral blood flow of 50 ml/100 g min-1 only about 93% of an injected bolus of labeled water freely exchanges with brain, compared with methanol (93%), ethanol (97%), and isopropanol (99%). The brain capillary permeability-surface area (PS) products computed from these data were 0.023 cm3/s g-1 (water), 0.024 cm3/s g-1 (methanol), 0.030 cm3/s g-1 (ethanol), and 0.062 cm3/s g-1 (isopropanol). This sequence of PS products is consistent with the individual lipid solubilities of the alcohols studied and underscores the unique brain permeability characteristics of lipid-insoluble water.

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An Ultrasonic Doppler Venous Outflow Method for the Continuous Measurement of Cerebral Blood Flow in Conscious Sheep

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.1994.85 ◽

1994 ◽

Vol 14 (4) ◽

pp. 680-688 ◽

Cited By ~ 42

Author(s):

Richard Upton ◽

Cliff Grant ◽

Guy Ludbrook

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Continuous Measurement ◽

Venous Outflow ◽

Sagittal Sinus ◽

Global Cerebral Blood Flow ◽

Conscious Sheep ◽

End Tidal ◽

The Brain

A pulsed ultrasonic Doppler venous outflow method was developed for the continuous measurement of global cerebral blood flow (CBF) in conscious sheep. The sheep were prepared under anesthesia with a “suture down”-style ultrasonic flow probe on the dorsal sagittal sinus placed via a trephine hole. Angiographic and dye studies showed that the dorsal sagittal sinus at the point of placement of the probe collected the majority of the blood from the cerebral hemispheres. Studies of the blood velocity profile across the sinus showed that the dimensions of the dorsal sagittal sinus changed minimally with changes in CBF in vivo. The velocity measurements were calibrated under anesthesia against an in vivo direct venous outflow method. Control CBF values for six sheep ranged from 31 to 53 ml/min for the area of brain described above; for two sheep in which the weight of the brain was determined, this gave total CBF values of approximately 34 and 30 ml min−1 100 g−1. The CBF measured varied in the expected manner with changes in the end-tidal CO2 concentration in expired breath and showed transient reductions with the barbiturate thiopentone and transient increases with the opiate alfentanil. It is concluded that the method is simple and accurate.

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Fusogenic Liposomes Deliver Resveratrol to Brain Microcirculation and Improve Neurovascular Coupling in Aged Mice

Innovation in Aging ◽

10.1093/geroni/igaa057.394 ◽

2020 ◽

Vol 4 (Supplement_1) ◽

pp. 120-120

Author(s):

Adam Nyul Toth ◽

Tabea Wiedenhoeft ◽

Stefano Tarantini ◽

Tamas Csipo ◽

Priya Balasubramanian ◽

...

Keyword(s):

Oxidative Stress ◽

Neurovascular Unit ◽

Neurovascular Coupling ◽

Laser Speckle ◽

Protective Effects ◽

Contrast Imaging ◽

Aged Mice ◽

Cranial Window ◽

Age Related

Abstract Adjustment of cerebral blood flow (CBF) to the increased oxygen and nutrient demands of active brain regions via neurovascular coupling (NVC) has an essential role in maintenance of healthy cognitive function. In advanced age, cerebromicrovascular oxidative stress and endothelial dysfunction impair neurovascular coupling, contributing to age-related cognitive decline. Recently we developed a resveratrol (3,4′,5- trihydroxystilbene)-containing fusogenic liposome (FL-RSV)-based molecular delivery system that can effectively target cultured cerebromicrovascular endothelial cells, attenuating age-related oxidative stress. To assess the cerebromicrovascular protective effects of FL-RSV in vivo, aged (24-monthold) C57BL/6 mice were treated with FL-RSV for four days. To demonstrate effective cellular uptake of FL-RSV, accumulation of the lipophilic tracer dyes in cells of the neurovascular unit was confirmed using two-photon imaging (through a chronic cranial window). NVC was assessed by measuring CBF responses (laser speckle contrast imaging) evoked by contralateral whisker stimulation. We found that NVC responses were significantly impaired in aged mice. Treatment with FL-RSV significantly improved NVC responses by increasing NO-mediated vasodilation. These findings are paralleled by the protective effects of FL-RSV on endothelium-dependent relaxation in the aorta. Thus, treatment with FL-RSV rescues endothelial function and NVC responses in aged mice. We propose that resveratrol containing fusogenic liposomes could also be used for combined delivery of various anti-geronic factors, including proteins, small molecules, DNA vectors and mRNAs targeting key pathways involved in microvascular aging and neurovascular dysfunction for the prevention/treatment of age-related cerebromicrovascular pathologies and development of vascular cognitive impairment (VCI) in aging.

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Microglia control cerebral blood flow and neurovascular coupling via P2Y12R-mediated actions

10.1101/2021.02.04.429741 ◽

2021 ◽

Author(s):

Eszter Császár ◽

Nikolett Lénárt ◽

Csaba Cserép ◽

Zsuzsanna Környei ◽

Rebeka Fekete ◽

...

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Barrel Cortex ◽

Neurological Diseases ◽

Neurovascular Unit ◽

Neurovascular Coupling ◽

Artery Occlusion ◽

Carotid Artery Occlusion ◽

Brain Ph ◽

Common Carotid Artery Occlusion

AbstractMicroglia, the main immunocompetent cells of the brain regulate neuronal function in health and disease, but their contribution to cerebral blood flow (CBF) remained elusive. Here we identify microglia as important modulators of CBF both under physiological conditions and during hypoperfusion. We show that microglia establish direct purinergic contacts with cells in the neurovascular unit that shape cerebral perfusion in both mice and humans. Surprisingly, the absence of microglia or blockade of microglial P2Y12 receptor (P2Y12R) substantially impairs neurovascular coupling in the barrel cortex after whisker stimulation. We also reveal that hypercapnia, which is associated with acidification, induces microglial adenosine production, while depletion of microglia reduces brain pH and impairs hypercapnia-induced vasodilation. Furthermore, the absence or dysfunction of microglia markedly impairs adaptation to hypoperfusion via P2Y12R after transient unilateral common carotid artery occlusion, which is also influenced by CX3CR1-mediated actions. Thus, our data reveal a previously unrecognized role for microglia in CBF regulation with broad implications for common neurological diseases.

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