Endothelial Piezo1 channel mediates mechano-feedback control of brain blood flow

Pericytes in the Optic Nerve Head

Pericytes are a unique population of contractile mural cells and an essential part of the microvasculature. In the retina and brain, pericytes play crucial roles in regulating blood flow, maintaining the blood-brain barrier, signaling with neighboring cells, and depositing extracellular matrix. Pericyte dysfunction is an early process in a variety of neurodegenerative conditions. However, remarkably little is known about pericytes at an early site of neurodegeneration in glaucoma, the optic nerve head (ONH). This work summarizes the current understanding of pericyte contributions to ONH physiology, identifies potential roles in glaucomatous pathophysiology, and uncovers open questions at the intersection of these areas. We surveyed the literature to identify the roles of ONH pericytes in the context of health and glaucoma. Additionally, we probed for the presence of pericytes along microvasculature in mouse, nonhuman primate, and human donor ONH tissues. We identified an association between factors influencing ONH dysfunction in glaucoma and factors influencing pericyte dysfunction in other neurodegenerative conditions. Pericytes exist in the mouse, nonhuman primate, and human ONH, implicating their capacity for local function. ONH pericytes represent a promising but underexplored target for treating microvascular impairment in glaucoma. Investigating the contribution of pericytes in both healthy and disease states can help inform mechanisms of dysfunction in glaucomatous pathology, paving the way for the development of novel therapeutic strategies.

Non-invasive therapeutics for neurotrauma: a mechanistic overview

Traumatic brain injury is a leading cause of death and a major risk factor for the development of both memory and motor disorders. To date, there are no proven interventions to improve patient outcome after neurotrauma. A promising avenue of treatment has emerged in the use of non-invasive therapies for recovery after brain injury. A number of non-invasive brain stimulation techniques have been developed, such as transcranial direct current stimulation, transcranial magnetic stimulation and vagus nerve stimulation, as well as low intensity ultrasound stimulation and photobiomodulation therapy. However, standardized treatment regimens have not been developed. There is a clear need to better understand the underlying mechanisms of non-invasive therapeutics on brain injury pathology so as to more effectively guide treatment strategy. Here we review the current literature of non-invasive therapies in preclinical neurotrauma and offer insight into the potential mechanism of action and novel targets for the treatment of traumatic brain injury.

Endothelial Piezo1 stimulates angiogenesis to offer protection against intestinal ischemia-reperfusion injury in mice

BACKGROUND

Intestinal ischemia-reperfusion (I/R) injury, which occurs in the ileum and not only leads to intestinal tissue damage, but also may trigger systemic inflammatory responses, is a prevalent pathological condition that is typically associated with acute intestinal ischemia, surgical procedures, or trauma. However, the precise underlying pathogenic mechanisms have not yet been fully uncovered. In this study, we explored the specific roles and underlying mechanisms by which endothelial Piezo1 is involved in intestinal I/R injury.

METHODS

We evaluated the roles of Piezo1 using both in vivo mouse intestinal ischemia-reperfusion (I/R) injury and in vitro hypoxia-reoxygenation (H/R) models. The expression of Piezo1 was assessed using immunofluorescence and RT-qPCR. In vivo and in vitro experiments involving endothelial knockout and activation of Piezo1 with the specific agonist Yoda1 were conducted to observe the effects on angiogenesis and injury.

RESULTS

We found that in post-intestinal I/R mice, Piezo1 expression was markedly increased and was mainly abundant in ileum endothelial cells. Specific knockout of endothelial Piezo1 exhibited a more severe phenotype characterized by accelerating damage to the ileum structure, increasing inflammatory response, and inhibiting angiogenesis. Yoda1-mediated activation of Piezo1 significantly ameliorated intestinal I/R injury. Activation of Piezo1 induced by Yoda1 or H/R promoted angiogenesis in Human Umbilical Vein Endothelial Cells (HUVECs), which was inhibited by GsMTx4. Piezo1 mediated endothelial angiogenesis was linked to an increase of extracellular Ca2+ influx, which in turn enhanced hypoxia-inducible factor 1 alpha (HIF-1α) signaling pathway.

CONCLUSIONS

Our findings indicate that Piezo1 plays a crucial role in protecting against intestinal I/R injury by promoting angiogenesis in endothelial cells, possibly through the activation of the Ca2+/HIF-1α/VEGF signaling pathway. This suggests that targeting endothelial Piezo1 channels could be a therapeutic strategy for ileum I/R injury.

Flow-sensitive ion channels in vascular endothelial cells: Mechanisms of activation and roles in mechanotransduction

The purpose of this review is to evaluate the current knowledge about the mechanisms by which mechanosensitive ion channels are activated by fluid shear stress in endothelial cells. We focus on three classes of endothelial ion channels that are most well studied for their sensitivity to flow and roles in mechanotransduction: inwardly rectifying K+ channels, Piezo channels, and TRPV channels. We also discuss the mechanisms by which these channels initiate and contribute to mechanosensitive signaling pathways. Three types of mechanisms have been described for flow-induced activation of ion channels: 1) through interaction with apical membrane flow sensors, such as glycocalyx, which is likely to be deformed by flow, 2) directly by sensing membrane stretch that is induced by shear stress, or 3) via flow-sensitive channel-channel or lipid channel interactions. We also demonstrate the physiological role of these channels and how they are related to cardiovascular and neurological diseases. Further studies are needed to determine how these channels function cooperatively to mediate the endothelial response to flow.

Endothelial TRPV4-Cx43 signalling complex regulates vasomotor tone in resistance arteries

S-nitrosylation of Cx43 gap junction channels critically regulates communication between smooth muscle cells and endothelial cells. This post-translational modification also induces the opening of undocked Cx43 hemichannels. However, its specific impact on vasomotor regulation remains unclear. Considering the role of endothelial TRPV4 channel activation in promoting vasodilatation through nitric oxide (NO) production, we investigated the direct modulation of endothelial Cx43 hemichannels by TRPV4 channel activation. Using the proximity ligation assay, we identified that Cx43 and TRPV4 are found in close proximity in the endothelium of resistance arteries. In primary endothelial cell (EC) cultures from resistance arteries, GSK 1016790A-induced TRPV4 activation enhances eNOS activity, increases NO production, and opens Cx43 hemichannels via direct S-nitrosylation. Notably, the elevated intracellular Ca2+ levels caused by TRPV4 activation were reduced by blocking Cx43 hemichannels. In ex vivo mesenteric arteries, inhibiting Cx43 hemichannels reduced endothelial hyperpolarization without affecting NO production in ECs, underscoring a critical role of TRPV4-Cx43 signalling in endothelial electrical behaviour. We perturbed the proximity of Cx43/TRPV4 by disrupting lipid rafts in ECs using β-cyclodextrin. Under these conditions, hemichannel activity, Ca2+ influx and endothelial hyperpolarization were blunted upon GSK stimulation. Intravital microscopy of mesenteric arterioles in vivo further demonstrated that inhibiting Cx43 hemichannel activity, NO production and disrupting endothelial integrity reduce TRPV4-induced relaxation. These findings underscore a new pivotal role of the Cx43 hemichannel associated with the TRPV4 signalling pathway in modulating endothelial electrical behaviour and vasomotor tone regulation. KEY POINTS: TRPV4-Cx43 interaction in endothelial cells: the study reveals a close proximity between Cx43 proteins and TRPV4 channels in endothelial cells of resistance arteries, establishing a functional interaction that is critical for vascular regulation. S-nitrosylation of Cx43 hemichannels: TRPV4 activation via GSK treatment induces S-nitrosylation of Cx43, facilitating the opening of Cx43 hemichannels. TRPV4-mediated calcium signalling: activation of TRPV4 leads to increased intracellular Ca2+ levels in endothelial cells, an effect that is mitigated by the inhibition of Cx43 hemichannels, indicating a regulatory feedback mechanism between these two channels. Endothelial hyperpolarization and vasomotor regulation: Blocking Cx43 hemichannels impairs endothelial hyperpolarization in mesenteric arteries, without affecting NO production, suggesting a role for Cx43 in modulating endothelial electrical behaviour and contributing to vasodilatation. In vivo role of Cx43 hemichannels in vasodilatation: intravital microscopy of mouse mesenteric arterioles demonstrated that inhibiting Cx43 hemichannel activity and disrupting endothelial integrity significantly impair TRPV4-induced vasodilatation, highlighting the crucial role of Cx43 in regulating endothelial function and vascular relaxation.

Swimming motions evoke Ca2+ events in vascular endothelial cells of larval zebrafish via mechanical activation of Piezo1

Calcium signaling in blood vessels regulates their growth1,2, immune response3, and vascular tone4. Vascular endothelial cells are known to be mechanosensitive5-7, and it has been assumed that this mechanosensation mediates calcium responses to pulsatile blood flow8-10. Here we show that in larval zebrafish, the dominant trigger for vascular endothelial Ca2+ events comes from body motion, not heartbeat-driven blood flow. Through a series of pharmacological and mechanical perturbations, we showed that body motion is necessary and sufficient to induce endothelial Ca2+ events, while neither neural activity nor blood circulation is either necessary or sufficient. Knockout and temporally restricted knockdown of piezo1 eliminated the motion-induced Ca2+ events. Our results demonstrate that swimming-induced tissue motion is an important driver of endothelial Ca2+ dynamics in larval zebrafish.

The pathobiology of neurovascular aging

As global life expectancy increases, age-related brain diseases such as stroke and dementia have become leading causes of death and disability. The aging of the neurovasculature is a critical determinant of brain aging and disease risk. Neurovascular cells are particularly vulnerable to aging, which induces significant structural and functional changes in arterial, venous, and lymphatic vessels. Consequently, neurovascular aging impairs oxygen and glucose delivery to active brain regions, disrupts endothelial transport mechanisms essential for blood-brain exchange, compromises proteostasis by reducing the clearance of potentially toxic proteins, weakens immune surveillance and privilege, and deprives the brain of key growth factors required for repair and renewal. In this review, we examine the effects of neurovascular aging on brain function and its role in stroke, vascular cognitive impairment, and Alzheimer's disease. Finally, we discuss key unanswered questions that must be addressed to develop neurovascular strategies aimed at promoting healthy brain aging.

Amyloid beta Aβ1-40 activates Piezo1 channels in brain capillary endothelial cells

Amyloid beta (Aβ) peptide accumulation on blood vessels in the brain is a hallmark of neurodegeneration. While Aβ peptides constrict cerebral arteries and arterioles, their impact on capillaries is less understood. Aβ was recently shown to constrict brain capillaries through pericyte contraction, but whether-and if so how-Aβ affects endothelial cells (ECs) remains unknown. ECs represent the predominant vascular cell type in the cerebral circulation, and we recently showed that the mechanosensitive ion channel Piezo1 is functionally expressed in the plasma membrane of ECs. Since Aβ disrupts membrane structures, we hypothesized that Aβ1-40, the predominantly deposited isoform in the cerebral circulation, alters endothelial Piezo1 function. Using patch-clamp electrophysiology and freshly isolated capillary ECs, we assessed the impact of the Aβ1-40 peptide on single-channel Piezo1 activity. We show that Aβ1-40 increased Piezo1 open probability and channel open time. Aβ1-40 effects were absent when Piezo1 was genetically deleted or when a superoxide dismutase/catalase mimetic was used. Further, Aβ1-40 enhanced Piezo1 mechanosensitivity and lowered the pressure of half-maximal Piezo1 activation. Our data collectively suggest that Aβ1-40 facilitates higher Piezo1-mediated cation influx in brain ECs. These novel findings have the potential to unravel the possible involvement of Piezo1 modulation in the pathophysiology of neurodegenerative diseases characterized by Aβ accumulation.

Cognitive Impairment and Synaptic Dysfunction in Cardiovascular Disorders: The New Frontiers of the Heart-Brain Axis

Within the central nervous system, synaptic plasticity, fundamental to processes like learning and memory, is largely driven by activity-dependent changes in synaptic strength. This plasticity often manifests as long-term potentiation (LTP) and long-term depression (LTD), which are bidirectional modulations of synaptic efficacy. Strong epidemiological and experimental evidence show that the heart-brain axis could be severely compromised by both neurological and cardiovascular disorders. Particularly, cardiovascular disorders, such as heart failure, hypertension, obesity, diabetes and insulin resistance, and arrhythmias, may lead to cognitive impairment, a condition known as cardiogenic dementia. Herein, we review the available knowledge on the synaptic and molecular mechanisms by which cardiogenic dementia may arise and describe how LTP and/or LTD induction and maintenance may be compromised in the CA1 region of the hippocampus by heart failure, metabolic syndrome, and arrhythmias. We also discuss the emerging evidence that endothelial dysfunction may contribute to directly altering hippocampal LTP by impairing the synaptically induced activation of the endothelial nitric oxide synthase. A better understanding of how CV disorders impact on the proper function of central synapses will shed novel light on the molecular underpinnings of cardiogenic dementia, thereby providing a new perspective for more specific pharmacological treatments.