PIP2 depletion promotes TRPV4 channel activity in mouse brain capillary endothelial cells

Abstract

We recently reported that the inward-rectifier Kir2.1 channel in brain capillary endothelial cells (cECs) plays a major role in neurovascular coupling (NVC) by mediating a neuronal activity-dependent, propagating vasodilatory (hyperpolarizing) signal. We further demonstrated that Kir2.1 activity is suppressed by depletion of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2). Whether cECs express depolarizing channels that intersect with Kir2.1-mediated signaling remains unknown. Here, we report that Ca2+/Na+-permeable TRPV4 (transient receptor potential vanilloid 4) channels are expressed in cECs and are tonically inhibited by PIP2. We further demonstrate that depletion of PIP2 by agonists, including putative NVC mediators, that promote PIP2 hydrolysis by signaling through Gq-protein-coupled receptors (GqPCRs) caused simultaneous disinhibition of TRPV4 channels and suppression of Kir2.1 channels. These findings collectively support the concept that GqPCR activation functions as a molecular switch to favor capillary TRPV4 activity over Kir2.1 signaling, an observation with potentially profound significance for the control of cerebral blood flow.

Endothelial TRPV4 channels modulate vascular tone by Ca2+‐induced Ca2+ release at inositol 1,4,5‐trisphosphate receptors

“…Interestingly, blocking of PLC by U73122 also reduced the slow global Ca 2+ response (i.e., TRPV4‐mediated Ca 2+ influx). Previous work has shown that TRPV4 channels are inhibited by the phospholipid, phosphatidylinositol 4,5‐bisphosphate (PIP 2 ; Harraz, Longden, Hill‐Eubanks, & Nelson, ). PLC‐mediated depletion of PIP 2 results in disinhibition of TRPV4 channels and increased Ca 2+ influx (Harraz et al, ).…”

“…Previous work has shown that TRPV4 channels are inhibited by the phospholipid, phosphatidylinositol 4,5‐bisphosphate (PIP 2 ; Harraz, Longden, Hill‐Eubanks, & Nelson, ). PLC‐mediated depletion of PIP 2 results in disinhibition of TRPV4 channels and increased Ca 2+ influx (Harraz et al, ). Thus, blocking of PLC by U73122 might be expected to decrease TRPV4 channel activity.…”

Augmented astrocyte microdomain Ca2+ dynamics and parenchymal arteriole tone in angiotensin II‐infused hypertensive mice

“…Channel inhibition is released following G q ‐protein‐coupled receptors (G q PCR) activation and downstream PIP 2 depletion. Importantly, PIP 2 was also shown to regulate inwardly rectifying potassium (Kir) channels (Harraz, Longden, Dabertrand, Hill‐Eubanks, & Nelson, ; Harraz, Longden, Hill‐Eubanks, & Nelson, ). Together, these studies support the notion that aberrant TRPV4‐mediated signaling may result in both astrocyte and vascular dysfunction.…”

“…While not specifically addressed in this study, elevated basal astrocyte Ca 2+ in hypertensive mice may interfere with the molecular mechanism that drives the NVC response and/or are involved in the clearance of metabolic by‐products (e.g., glymphatics; Iliff et al, ; Iliff et al, ). The recent evidence in capillary endothelial cells demonstrating a dynamic interaction between TRPV4 and Kir2.1 channels, whereby GqPCR activation induces PIP 2 depletion, a master regulator of both channels (Harraz, Longden, Dabertrand, et al, ; Harraz, Longden, Hill‐Eubanks, & Nelson, ; Longden et al, ) raises an important question. Could augment Ang II‐mediated signaling impair TRPV4‐Kir2.1 interactions?…”

“…Could augment Ang II‐mediated signaling impair TRPV4‐Kir2.1 interactions? For example, increased TRPV4 channel activity (Harraz, Longden, Dabertrand, et al, ; Harraz, Longden, Hill‐Eubanks, & Nelson, ) and reduced Kir2.1‐mediated hyperpolarizations (Filosa et al, ; Harraz, Longden, Dabertrand, et al, ; Longden et al, ) could drive the membrane potential of vascular cells towards more depolarized states, favoring constrictions and consequently, impairing perfusion to the brain. In addition, hypertension‐induced changes in PA tone may impair dynamic pulsatile mechanisms involved in waste clearance or glymphatics.…”