Astrocytes drive cortical vasodilatory signaling by activating endothelial NMDA receptors

Abstract

Astrocytes express neurotransmitter receptors that serve as sensors of synaptic activity and initiate signals leading to activity-dependent local vasodilation and increases in blood flow. We previously showed that arteriolar vasodilation produced by activation of cortical astrocytes is dependent on endothelial nitric oxide synthase (eNOS) and endogenous agonists of N-methyl-D-aspartate (NMDA) receptors. Here, we tested the hypothesis that these effects are mediated by NMDA receptors expressed by brain endothelial cells. Primary endothelial cultures expressed NMDA receptor subunits and produced nitric oxide in response to co-agonists, glutamate and D-serine. In cerebral cortex in situ, immunoelectron microscopy revealed that endothelial cells express the GluN1 NMDA receptor subunit at basolateral membrane surfaces in an orientation suitable for receiving intercellular messengers from brain cells. In cortical slices, activation of astrocytes by two-photon flash photolysis of a caged Ca compound or application of a metabotropic glutamate receptor agonist caused endothelial NO generation and local vasodilation. These effects were mitigated by NMDA receptor antagonists and conditional gene silencing of endothelial GluN1, indicating at least partial dependence on endothelial NMDA receptors. Our observations identify a novel astrocyte-endothelial vasodilatory signaling axis that could contribute to endothelium-dependent vasodilation in brain functional hyperemia.

The Role of Endothelial Ca2+ Signaling in Neurovascular Coupling: A View from the Lumen

“…Endothelial TRPV4 has a potentially relevant role in NVC as it can be activated by AA and its cytochrome P450 epoxygenases-metabolites, i.e., epoxyeicosatrienoic acids (EETs), which evoke vasodilation in intraparenchymal arterioles [ 9 , 125 ]. Finally, human [ 126 ], mouse [ 55 , 56 , 127 ] and rat [ 128 ] brain endothelial cells express functional NMDARs ( Figure 3 ) [ 55 ], which may mediate glutamate-induced extracellular Ca 2+ entry. Likewise, P2X7 receptors were recently found in both hCMEC/D3 cells ( Figure 3 ) [ 129 ], an immortalized human brain endothelial cell line, and in rat brain endothelial cells in situ [ 130 ].…”

“…However, in non-neuronal cells, GluN1 subunits assemble with GluN2C and GluN2D, which confer a lower sensitivity to Mg 2+ , while incorporation of GluN3 further decreases the inhibitory effect of extracellular Mg 2+ and limits Ca 2+ permeability [ 144 , 145 ]. NMDAR subunits (i.e., GluN1 and GluN2A-D) have been detected in brain endothelial cells in vitro [ 126 , 127 , 128 , 143 , 147 , 148 ] and in cerebral cortex in situ [ 127 ] ( Figure 3 ). Intriguingly, NMDARs are more abundant on the basolateral endothelial membrane, which place them in the most suitable position to mediate direct neuronal-to-vascular communication [ 127 ].…”

VEGFD Protects Retinal Ganglion Cells and, consequently, Capillaries against Excitotoxic Injury

“…the neurovascular unit, despite the fact that ECs and astrocytes carry functional NMDARs. 32,40,65,73 Excitotoxicity in the retina alters the subcellular distribution, and thus activity, of the epigenetic regulators histone deacetylases (HDACs) in RGCs. 26 The activity of one particular HDAC, namely HDAC4, regulates the expression of VEGFD.…”

On the Role of Store-Operated Calcium Entry in Acute and Chronic Neurodegenerative Diseases

“…These findings indicate that the local O 2 level is a key determinant of astrocyte Ca 2+ signaling, likely modulating their Ca 2+ -dependent functions. Playing a pivotal role in neurovascular signaling in the brain (Haydon and Carmignoto, 2006 ; Viscomi et al, 2008 ; Mishra et al, 2016 ; Lu et al, 2017 ; Lind et al, 2018 ), astrocytes have also been implicated in the pathogenesis of hypertension in stroke-prone spontaneously hypertensive rat (SHRSP) via a sympatho-excitation mechanism (Allen et al, 2006 ; Isegawa et al, 2014 ). In particular, the reduction of glial STIM1 in SHRSP has been identified as a candidate pathogenic mechanism responsible for this exaggerated sympathetic response leading to stroke.…”