Gq-coupled Receptors Research Articles

Genetic inhibition of KV7/M-channels increases the excitability of bronchopulmonary vagal nociceptive nerves

The KV7/M-channel, encoded by Kcnq2-5 genes, generates a “braking” potassium current (IM) and contributes to the regulation of neuronal excitability. We have previously reported that the vagal sensory nerves terminated in the mouse lungs expressed mainly Kcnq3 and Kcnq2, as well as the functional M-channels. Opening the M-channel with retigabine almost abolished the agonist-evoked action potential (AP) discharges in bronchopulmonary nociceptive C-fibers, and suppressed the irritant gases-induced, C-fiber-mediated coughing in awake freely moving mice. Inhibition of IM using XE991 slightly but consistently depolarized the nodose neurons. The use of XE991 to evaluate whether IM plays a role in regulating the activation of bronchopulmonary vagal sensory nerves was, however, limited due to its off-target effects on the fast Na+ current in these neurons. This study aimed to address this key issue using the genetic approach. We generated the sensory neuron-specific Kcnq2 and Kcnq3 double-KO mice (Kcnq2/3-KO) by crossing the Kcnq2/3fl/fl mice with the Pirt-driven Cre (Pirt-Cre) mice. Single-neuron RT-PCR assay showed that none of the 60 tested Kcnq2/3-KO nodose neurons (30 Trpv1-positive and 30 Trpv1-negative) expressed Kcnq2 or Kcnq3. Eliminating Kcnq2 and Kcnq3 did not increase Kcnq4 or Kcnq5 expression. IM, defined as the retigabine-enhanced and XE991-inhibited tail currents (elicited by repolarizing steps from -30 to -60 mV), was recorded in all 22 control neurons using perforated patch clamp technique, but only in 2 out of 14 Kcnq2/3-KO nodose neurons (probably due to Kcnq5) with a much lower IM density (0.4 and 2.1 pA/pF vs. 8.5±2.9 pA/pF in controls). These results confirmed an effective elimination of the dominant KV7 genes in the nodose neurons of our Kcnq2/3-KO mice. Genetic inhibition of Kcnq2/3 did not significantly alter the resting potential (-68.0±1.9, n=12 vs. -69.1±1.4 mV, n=13; p=0.644) or the minimal amount of currents to evoke a single AP (rheobase: 41.2±6.1 pA, n=12 vs. 48.1±6.2 pA, n=13; p=0.442) in capsaicin-sensitive nodose neurons. However, the nociceptive nodose neurons isolated from Kcnq2/3-KO mice fired more APs and at a higher frequency in response to a series of either step (50-500 pA, 600 ms) or ramp (50-800 pA, 1 second) depolarization compared to their littermate controls (P<0.001, two-way ANOVA). Extracellular recordings in ex-vivo vagally innervated trachea-lungs preparations also revealed that Kcnq2/3 deficiency led to enhanced AP discharges at the nerve endings of the bronchopulmonary C-fibers in response to the agonist of Gq-coupled protease-activated receptor 1 (3, 10 and 30 μM) applied to the mouse lungs via trachea (number of AP: 393±45, n=8 vs. 183±43, n=9; p=0.001 by two-way ANOVA). These results indicate that the M-channel may serve as an intrinsic inhibitory mechanism in the bronchopulmonary vagal nociceptive neurons by limiting the excessive repetitive AP firings. Johns Hopkins Blaustein Pain Research Funds Grant 80048814, and NIH R01 HL137807/R35 HL155671 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Regulation of the two-pore domain potassium channel, THIK-1 and THIK-2, by G protein coupled receptors.

A member of THIK (two pore domain halothane-inhibited K+) channels, THIK-1, was reported as a target of Gi/o-coupled receptors (Gi/o-Rs) in neurons and microglia. We confirmed that in HEK293T cells the THIK-1 channel is activated by Gi/o-Rs and found that Gq-coupled receptors (Gq-Rs) also activates the channel. The effects of Gi/o-Rs and Gq-Rs were inhibited by the Gi/o inhibitor pertussis toxin and phospholipase C (PLC) inhibitor, respectively. The effects of Gi/o-Rs were attenuated when consensus Gβγ binding motif at the C-tail of the THIK-1 channel was mutated, suggesting that Gβγ serves as a THIK-1 channel activator upon the stimulation of Gi/o-Rs. As to the effects of Gq-Rs on the THIK-1 channel, a protein kinase C inhibitor and calcium chelators failed to inhibit the effect of a Gq coupled muscarinic M1R. Neither the hydrolysis of phosphatidyl inositol bisphosphate induced by voltage sensitive phosphatase nor the application of a diacylglycerol analogue, OAG, increased the channel current. The mediator of Gq-dependent activation of the THIK-1 channel remained unsolved. The effects of Gi/o- and Gq-Rs on the THIK-2 channel were also investigated, by using a THIK-2 mutant channel whose N-terminal domain is deleted to improve the surface membrane expression. We observed that Gi/o- and Gq-Rs activate the mutated THIK-2 channel, similarly to the THIK-1 channel. Interestingly, heterodimeric channels of THIK-1 and THIK-2 responded to Gi/o-R and Gq-R stimulation. Taken together, Gi/o- or Gq-Rs activates the THIK-1 and THIK-2 channels in a Gβγ or PLC dependent manner, respectively.

Acute phosphatidylinositol 4,5 bisphosphate depletion destabilizes sarcolemmal expression of cardiac L-type Ca2+ channel CaV1.2

CaV1.2 channels are critical players in cardiac excitation-contraction coupling, yet we do not understand how they are affected by an important therapeutic target of heart failure drugs and regulator of blood pressure, angiotensin II. Signaling through Gq-coupled AT1 receptors, angiotensin II triggers a decrease in PIP2, a phosphoinositide component of the plasma membrane (PM) and known regulator of many ion channels. PIP2 depletion suppresses CaV1.2 currents in heterologous expression systems but the mechanism of this regulation and whether a similar phenomenon occurs in cardiomyocytes is unknown. Previous studies have shown that CaV1.2 currents are also suppressed by angiotensin II. We hypothesized that these two observations are linked and that PIP2 stabilizes CaV1.2 expression at the PM and angiotensin II depresses cardiac excitability by stimulating PIP2 depletion and destabilization of CaV1.2 expression. We tested this hypothesis and report that CaV1.2 channels in tsA201 cells are destabilized after AT1 receptor-triggered PIP2 depletion, leading to their dynamin-dependent endocytosis. Likewise, in cardiomyocytes, angiotensin II decreased t-tubular CaV1.2 expression and cluster size by inducing their dynamic removal from the sarcolemma. These effects were abrogated by PIP2 supplementation. Functional data revealed acute angiotensin II reduced CaV1.2 currents and Ca2+ transient amplitudes thus diminishing excitation-contraction coupling. Finally, mass spectrometry results indicated whole-heart levels of PIP2 are decreased by acute angiotensin II treatment. Based on these observations, we propose a model wherein PIP2 stabilizes CaV1.2 membrane lifetimes, and angiotensin II-induced PIP2 depletion destabilizes sarcolemmal CaV1.2, triggering their removal, and the acute reduction of CaV1.2 currents and contractility.

Disrupting cortical astrocyte Ca2+ signaling in developing brain induces social deficits and depressive-like behaviors.

Astrocytes are present throughout the central nervous system and display complex intracellular Ca2+ signals. However, it is largely unknown regarding how astrocytic Ca2+ signals regulate neural microcircuits in developing brain and mammalian behavior in vivo. In this study, we specifically overexpressed the plasma membrane calcium-transporting ATPase2 (PMCA2) of cortical astrocytes and used immunohistochemistry, Ca2+ imaging, electrophysiology, and behavioral tests to investigate the effects of genetically reducing cortical astrocyte Ca2+ signaling during a critical developmental period in vivo. We found that reducing cortical astrocyte Ca2+ signaling during development led to social interaction deficits, depressive-like behaviors, and abnormal synaptic structure and transmission. In addition, restoring cortical astrocyte Ca2+ signaling using chemogenetic activation of Gq-coupled designer receptors exclusively activated by designer drugs rescued these synaptic and behavioral deficits. Together, our data demonstrate that the integrity of cortical astrocyte Ca2+ signaling in developing mice is critical for neural circuit development and may be involved in the pathogenesis of developmental neuropsychiatric diseases, such as autism spectrum disorders and depression.

Chronic angiotensin II signaling drives sustained PIP2 deficits and altered sarcolemmal Cav1.2 expression and function in cardiomyocytes.

Contractile dysfunction, hypertrophy, and cell death during heart failure are linked to altered Ca2+ handling and elevated levels of angiotensin II (AngII). This hormone signals through Gq-coupled AT1 receptors, initiating hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2). Previous work revealed acute AngII signaling and PIP2 depletion destabilizes CaV1.2 clusters in cardiomyocytes, triggering their internalization, and subsequent reduction of whole-cell Ca2+ current (ICa) and contractility. However, the effects of chronically elevated AngII on the phospholipid landscape and associated effects on ICa remain unknown. We subjected mice to sustained delivery of AngII to test the impact on phosphoinositides, ICa, and excitation-contraction coupling. We hypothesized that chronic AngII signaling leads to sustained PIP2 and CaV1.2 deficits, contributing to the diminished functional output associated with disease development. Phospholipid mass spectrometry revealed extensive alteration of phosphoinositide species, including a ∼44% reduction in PIP2 and ∼37% reduction in cardioprotective PIP3 in AngII-infused hearts compared to controls. To study the effects of this phospholipid imbalance on CaV1.2, we examined ICa, finding similar current density in both groups. However, super-resolution imaging revealed a ∼54% reduction in t-tubular CaV1.2 expression and a ∼23% reduction in cluster area. Conserved ICa density despite reduced t-tubular CaV1.2 suggests that either the channels have relocated to the sarcolemmal crest, or their Po has increased. We examined crest CaV1.2 and observed no change with AngII, thus the Po of the remaining channels must increase to maintain ICa. Western blots revealed enhanced phosphorylation of CaV1.2, phosphorylation of RyR2, and an increased expression of the catalytic subunit of PKA, suggesting a compensatory sympathetic activation underlying conserved ICa. These findings support a model wherein chronic elevation of AngII disrupts phosphoinositide and CaV1.2 levels, elucidating the role of chronic AngII in disease progression.

Central role for BRAF in cardiac hypertrophy: rethinking the pathological-physiological divide.

The RAF/MEK/ERK1/2 signaling cascade has been implicated in pathological cardiac hypertrophy downstream of some Gq-coupled receptors. The RAF family of kinases consists of three isoforms (ARAF, BRAF, and CRAF) and until recently most studies on this signaling pathway in the heart have focused on RAF1 (CRAF). In a recent issue of Clinical Science, Alharbi et al. utilized an inducible cardiac myocyte targeted knockout mouse model to define the role of BRAF in pathological versus physiological hypertrophy using angiotensin II and phenylephrine (PE) infusion, respectively. They reported that loss of BRAF attenuated both pathological cardiac hypertrophy and interstitial fibrosis. BRAF knockout decreased cardiac function with PE in male mice and enhanced both interstitial and perivascular cardiac fibrosis but had no effect on hypertrophy. In contrast, loss of BRAF attenuated physiological hypertrophy in female mice but had no effect on fibrosis or contractility. These observations extend those previously made by this group assessing the consequences of expressing an inducible activating mutant of BRAF in the heart and the benefit of enhancing RAF/MEK/ERK1/2 signaling by exploiting the 'RAF paradox'. Additional studies are needed to better define the role of BRAF under conditions reflective of chronic stress on the heart due to the biomechanical stimulation exerted by hypertension. In addition, the role of BRAF and its activation in overt heart failure remains to be established. Nevertheless, the new findings highlight the potential importance of additional signaling events, perhaps related to RAF1 or ERK1/2 activation, in shaping BRAF signaling in a sex- and context-dependent manner.

A Par3/LIM Kinase/Cofilin Pathway Mediates Human Airway Smooth Muscle Relaxation by TAS2R14.

TAS2Rs (bitter taste receptors) are GPCRs (G protein-coupled receptors) expressed on human airway smooth muscle (HASM) cells; when activated by receptor agonists they evoke marked airway relaxation. In both taste and HASM cells, TAS2Rs activate a canonical Gβγ-mediated stimulation of Ca2+ release from intracellular stores by activation of PLCβ (phospholipase Cβ). Alone, this [Ca2+]i signaling does not readily account for relaxation, particularly since bronchoconstrictive agonists acting at Gq-coupled receptors also increase [Ca2+]i. We established that TAS2R14 activation in HASM promotes relaxation through F-actin (filamentous actin) severing. This destabilization of actin was from agonist-promoted activation (dephosphorylation) of cofilin, which was pertussis toxin sensitive. Cofilin dephosphorylation was due to TAS2R-mediated deactivation of LIM domain kinase. The link between early receptor action and the distal cofilin dephosphorylation was found to be the polarity protein partitioning defective 3 (Par3), a known binding partner with PLCβ that inhibits LIM kinase. The physiologic relevance of this pathway was assessed using knock-downs of cofilin and Par3 in HASM cells and in human precision-cut lung slices. Relaxation by TAS2R14 agonists was ablated with knock-down of either protein as assessed by magnetic twisting cytometry in isolated cells or intact airways in the slices. Blocking [Ca2+]i release by TAS2R14 inhibited agonist-promoted cofilin dephosphorylation, confirming a role for [Ca2+]i in actin-modifying pathways. These results further elucidate the mechanistic basis of TAS2R-mediated HASM relaxation and point toward nodal points that may act as asthma or chronic obstructive pulmonary disease response modifiers or additional targets for novel bronchodilators.

Presynaptic Gq-coupled receptors drive biphasic dopamine transporter trafficking that modulates dopamine clearance and motor function

Extracellular dopamine (DA) levels are constrained by the presynaptic DA transporter (DAT), a major psychostimulant target. Despite its necessity for DA neurotransmission, DAT regulation in situ is poorly understood, and it is unknown whether regulated DAT trafficking impacts dopaminergic signaling and/or behaviors. Leveraging chemogenetics and conditional gene silencing, we found that activating presynaptic Gq-coupled receptors, either hM3Dq or mGlu5, drove rapid biphasic DAT membrane trafficking in ex vivo striatal slices, with region-specific differences between ventral and dorsal striata. DAT insertion required DRD2 autoreceptors and intact retromer, whereas DAT retrieval required PKC activation and Rit2. Ex vivo voltammetric studies revealed that DAT trafficking impacts DA clearance. Further, dopaminergic mGlu5 silencing elevated DAT surface expression and abolished motor learning, which was rescued by inhibiting DAT with a subthreshold CE-158 dose. We discovered that presynaptic DAT trafficking is complex, multimodal, and region-specific, and for the first time identified cell autonomous mechanisms that govern presynaptic DAT tone. Importantly, the findings are consistent with a role for regulated DAT trafficking in DA clearance and motor function.

Loss of INPP5K attenuates IP3-induced Ca2+ responses in the glioblastoma cell line U-251 MG cells

INPP5K (inositol polyphosphate 5-phosphatase K) is an endoplasmic reticulum (ER)-resident enzyme that acts as a phosphoinositide (PI) 5-phosphatase, capable of dephosphorylating various PIs including PI 4,5-bisphosphate (PI(4,5)P2), a key phosphoinositide found in the plasma membrane. Given its ER localization and substrate specificity, INPP5K may play a role in ER-plasma membrane contact sites. Furthermore, PI(4,5)P2 serves as a substrate for phospholipase C, an enzyme activated downstream of extracellular agonists acting on Gq-coupled receptors or tyrosine-kinase receptors, leading to IP3 production and subsequent release of Ca2+ from the ER, the primary intracellular Ca2+ storage organelle. In this study, we investigated the impact of INPP5K on ER Ca2+ dynamics using a previously established INPP5K-knockdown U-251 MG glioblastoma cell model. We here describe that loss of INPP5K impairs agonist-induced, IP3 receptor (IP3R)-mediated Ca2+ mobilization in intact cells, while the ER Ca2+ content and store-operated Ca2+ influx remain unaffected. To further elucidate the underlying mechanisms, we examined Ca2+ release in permeabilized cells stimulated with exogenous IP3. Interestingly, the absence of INPP5K also disrupted IP3-induced Ca2+ release events. These results suggest that INPP5K may directly influence IP3R activity through mechanisms yet to be resolved. The findings from this study point towards role of INPP5K in modulating ER calcium dynamics, particularly in relation to IP3-mediated signaling pathways. However, further work is needed to establish the general nature of our findings and to unravel the exact molecular mechanisms underlying the interplay between INNP5K function and Ca2+ signaling.

RF33 | PSAT79 Chronic Activation of Gq-Signaling in the Mouse Adrenal Cortex Disrupts Zonation and Causes Aldosterone Production in the Zona Fasciculata

Abstract Background The mammalian adrenal cortex is composed of the zona glomerulosa (ZG), zona fasciculata (ZF), and in some species the zona reticularis (ZR). Each layer is characterized by a specific steroidogenic enzyme expression pattern that leads to selective production of mineralocorticoids, glucocorticoids or adrenal androgens. ZG-specific expression of cytochrome P450 aldosterone synthase (Cyp11b2) and aldosterone biosynthesis are renin-angiotensin-dependent processes in which the Gq-signaling pathway is activated by angiotensin II (AngII). Gq-signaling can be exogenously activated using Gq-coupled designer receptors exclusively activated by designer drug (GqDREADD) technology. Using transgenic mice with targeted expression of GqDREADD to the adrenal cortex, we previously demonstrated that short-term receptor activation increased adrenal Cyp11b2 and aldosterone production. Herein, we hypothesized that prolonged activation of mouse adrenal cortex Gq-signaling would exacerbate the aldosterone levels and promote the transdifferentiation of ZF cells to ZG cells. Methods Transgenic AS+/Cre hM3Dq (GqDREADD) female mice were engineered through crossing GqDREADD mice with Cyp11b2-regulated Cre recombinase mice. Mice were placed on a high sodium diet (to suppress physiologic renin) and orally provided the GqDREADD ligand, clozapine N-oxide (CNO; n=10) or control (n=8) for 6 weeks followed by collection of blood and adrenals. Mineralocorticoid levels were quantified using LC-MS/MS. Adrenal RNA was isolated and assessed by RNAseq for transcriptomic changes, and RT-qPCR analysis for ZG- and ZF-specific transcript markers, Cyp11b2 and Cyp11b1 (marker of ZF), respectively. Transcripts for β-catenin (Ctnnb1) and axin-2 (Axin2) (markers of the WNT signaling pathway) were also analyzed. Immunofluorescence (IF) studies examined adrenal expression of Cyp11b1 and Cyp11b2 in mice treated for 1 month. Results CNO treatment caused plasma aldosterone to increase 613-fold from 7.9 ±2.5 pg/mL to 4810.7 ±1110.7 pg/mL (p<0.01). Levels of 18-hydroxycorticosterone increased 70-fold from 144.9 ±22.0 to 10143.2 ±1479.6 pg/mL (p<0.0001). Corticosterone levels were unaffected. RT-qPCR analysis showed adrenal Cyp11b2 transcripts to be 224-fold higher (p<0.0001) in the CNO-treated group while a 30% decrease in Cyp11b1 levels was observed (p<0.01) compared to the controls. IF demonstrated hybrid ZF cells aberrantly expressing both Cyp11b2 and Cyp11b1. Within the normal mouse adrenal, the outer ZG exhibits high WNT/β-catenin (Ctnnb1) activation. To determine if chronic CNO treatment impacted overall adrenal WNT signaling, Ctnnb1 and Axin2 (a downstream β-catenin gene target) were examined. Analysis revealed no statistical difference in Ctnnb1 and Axin2 transcript levels in treated mice. RNAseq revealed that 242 transcripts were increased in adrenals from treated mice, while 109 decreased (>3-fold change; p<0.01). Induced transcripts include Cyp11b2 and its transcriptional regulators, Nr4a1 and Nr4a2. Conclusion Overall, these findings demonstrate that chronic Gq-signaling is sufficient to cause ZF cells to produce aldosterone and express Cyp11b2. The findings also suggest that the adrenocortical WNT signaling pathway is not increased by the activation of Gq-signaling. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Monday, June 13, 2022 12:36 p.m. - 12:41 p.m.

Coincident Regulation of PLCβ Signaling by Gq-Coupled and μ-Opioid Receptors Opposes Opioid-Mediated Antinociception.

Pain management is an important problem worldwide. The current frontline approach for pain management is the use of opioid analgesics. The primary analgesic target of opioids is the μ-opioid receptor (MOR). Deletion of phospholipase Cβ3 (PLCβ3) or selective inhibition of Gβγ regulation of PLCβ3 enhances the potency of the antinociceptive effects of morphine suggesting a novel strategy for achieving opioid-sparing effects. Here we investigated a potential mechanism for regulation of PLC signaling downstream of MOR in human embryonic kidney 293 cells and found that MOR alone could not stimulate PLC but rather required a coincident signal from a Gq-coupled receptor. Knockout of PLCβ3 or pharmacological inhibition of its upstream regulators, Gβγ or Gq, ex vivo in periaqueductal gray slices increased the potency of the selective MOR agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin acetate salt in inhibiting presynaptic GABA release. Finally, inhibition of Gq- G protein-coupled receptor coupling in mice enhanced the antinociceptive effects of morphine. These data support a model where Gq and Gβγ-dependent signaling cooperatively regulate PLC activation to decrease MOR-dependent antinociceptive potency. Ultimately, this could lead to identification of new non-MOR targets that would allow for lower-dose utilization of opioid analgesics. SIGNIFICANCE STATEMENT: Previous work demonstrated that deletion of phospholipase Cβ3 (PLCβ3) in mice potentiates μ-opioid receptor (MOR)-dependent antinociception. How PLCβ3 is regulated downstream of MOR had not been clearly defined. We show that PLC-dependent diacylglycerol generation is cooperatively regulated by MOR-Gβγ and Gq-coupled receptor signaling through PLCβ3 and that blockade of either Gq-signaling or Gβγ signaling enhances the potency of opioids in ex vivo brain slices and in vivo. These results reveal potential novel strategies for improving opioid analgesic potency and safety.

Targeting 5-HT2A receptors and Kv7 channels in PFC to attenuate chronic neuropathic pain in rats using a spared nerve injury model

Chronic pain remains a disabling disease with limited therapeutic options. Pyramidal neurons in the prefrontal cortex (PFC) express excitatory Gq-coupled 5-HT2A receptors (5-HT2AR) and their effector system, the inhibitory Kv7 ion channel. While recent publications show these cells innervate brainstem regions important for regulating pain, the cellular mechanisms underlying the transition to chronic pain are not well understood. The present study examined whether local blockade of 5-HT2AR or enhanced Kv7 ion channel activity in the PFC would attenuate mechanical allodynia associated with spared nerve injury (SNI) in rats. Following SNI, we show that inhibition of PFC 5-HT2ARs with M100907 or opening of PFC Kv7 channels with retigabine reduced mechanical allodynia. Parallel proteomic and RNAScope experiments evaluated 5-HT2AR/Kv7 channel protein and mRNA. Our results support the role of 5-HT2ARs and Kv7 channels in the PFC in the maintenance of chronic pain.

The complicated lives of GPCRs in cardiac fibroblasts.

The role of different G protein-coupled receptors (GPCRs) in the cardiovascular system is well understood in cardiomyocytes and vascular smooth muscle cells (VSMCs). In the former, stimulation of Gs-coupled receptors leads to increases in contractility, whereas stimulation of Gq-coupled receptors modulates cellular survival and hypertrophic responses. In VSMCs, stimulation of GPCRs also modulates contractile and cell growth phenotypes. Here, we will focus on the relatively less well-studied effects of GPCRs in cardiac fibroblasts, focusing on key signaling events involved in the activation and differentiation of these cells. We also review the hierarchy of signaling events driving the fibrotic response and the communications between fibroblasts and other cells in the heart. We discuss how such events may be distinct depending on where the GPCRs and their associated signaling machinery are localized in these cells with an emphasis on nuclear membrane-localized receptors. Finally, we explore what such connections between the cell surface and nuclear GPCR signaling might mean for cardiac fibrosis.

Histamine/H1 receptor signaling in the parafacial region increases activity of chemosensitive neurons and respiratory activity in rats.

Histaminergic neurons of the tuberomammillary nucleus (TMN) are pH sensitive and contribute to CO2/H+-dependent behaviors including arousal and respiratory activity. TMN neurons project to several respiratory centers including the ventral parafacial region (pF), where the chemosensitive retrotrapezoid (RTN) neurons are located, and since RTN neurons are an important source of CO2/H+-dependent respiratory drive, we wondered whether histamine contributes to RTN chemoreception. To test this, we characterized effects of histamine on mean arterial pressure (MAP) and diaphragm muscle activity (DIAEMG) in urethane-anesthetized, vagotomized, and artificially ventilated male Wistar rats. Unilateral injection of histamine in the pF (25 mM) increased DIAEMG amplitude without changing DIAEMG frequency and MAP. Bilateral injections of the H1 receptor antagonist diphenhydramine hydrochloride (DPH; 0.5 mM) into the pF decreased baseline DIAEMG amplitude and frequency and MAP. Despite the strong inhibitory effect of DPH on baseline breathing, the hypercapnic ventilatory response was preserved under these experimental conditions. At the cellular level, chemosensitive RTN neurons showed a dose-dependent excitatory response to histamine that was blunted by DPH and mimicked by H1 receptor agonist 2-pyridylethylamine dihydrochloride (2PYEA) both under control conditions and when fast neurotransmitter receptors were blocked. We also tested effects of 2PYEA in the presence of serotonin, another wake-on neurotransmitter that activates RTN chemoreceptors partly by activation of Gq-coupled receptors. We found that the response to 2PYEA was diminished in serotonin, suggesting that RTN neurons have a limited capacity to respond to multiple Gq-coupled modulators. These results suggest that histamine can modulate breathing at the pF level by a mechanism involving H1 receptors.NEW & NOTEWORTHY Histamine/H1 receptor signaling activates retrotrapezoid (RTN) neurons under control conditions and to a lesser extent in the presence of serotonin. These results suggest that RTN neurons have a limited capacity to respond to simultaneous activation of multiple Gq-coupled receptors.

Chemogenetic Activation of Astrocytes in the Basolateral Amygdala Contributes to Fear Memory Formation by Modulating the Amygdala-Prefrontal Cortex Communication.

The basolateral amygdala (BLA) is one of the key brain areas involved in aversive learning, especially fear memory formation. Studies of aversive learning in the BLA have largely focused on neuronal function, while the role of BLA astrocytes in aversive learning remains largely unknown. In this study, we manipulated the BLA astrocytes by expressing the Gq-coupled receptor hM3q and discovered that astrocytic Gq modulation during fear conditioning promoted auditorily cued fear memory but did not affect less stressful memory tasks or induce anxiety-like behavior. Moreover, chemogenetic activation of BLA astrocytes during memory retrieval had no effect on fear memory expression. In addition, astrocytic Gq activation increased c-Fos expression in the BLA and the medial prefrontal cortex (mPFC) during fear conditioning, but not in the home cage. Combining these results with retrograde virus tracing, we found that the activity of mPFC-projecting BLA neurons showed significant enhancement after astrocytic Gq activation during fear conditioning. Electrophysiology recordings showed that activating astrocytic Gq in the BLA promoted spike-field coherence and phase locking percentage, not only within the BLA but also between the BLA and the mPFC. Finally, direct chemogenetic activation of mPFC-projecting BLA neurons during fear conditioning enhanced cued fear memory. Taken together, our data suggest that astrocytes in the BLA may contribute to aversive learning by modulating amygdala–mPFC communication.

A neuropsin-based optogenetic tool for precise control of Gq signaling.

Gq-coupled receptors regulate numerous physiological processes by activating enzymes and inducing intracellular Ca2+ signals. There is a strong need for an optogenetic tool that enables powerful experimental control over Gq signaling. Here, we present chicken opsin 5 (cOpn5) as the long sought-after, single-component optogenetic tool that mediates ultra-sensitive optical control of intracellular Gq signaling with high temporal and spatial resolution. Expressing cOpn5 in HEK 293T cells and primary mouse astrocytes enables blue light-triggered, Gq-dependent Ca2+ release from intracellular stores and protein kinase C activation. Strong Ca2+ transients were evoked by brief light pulses of merely 10 ms duration and at 3 orders lower light intensity of that for common optogenetic tools. Photostimulation of cOpn5-expressing cells at the subcellular and single-cell levels generated fast intracellular Ca2+ transition, thus demonstrating the high spatial precision of cOpn5 optogenetics. The cOpn5-mediated optogenetics could also be applied to activate neurons and control animal behavior in a circuit-dependent manner. cOpn5 optogenetics may find broad applications in studying the mechanisms and functional relevance of Gq signaling in both non-excitable cells and excitable cells in all major organ systems.

Dynamic Desensitization of Gaq Signaling and Gaq‐dependent GPCR Crosstalk by GRKs

G protein‐coupled receptor (GPCR) signaling is subject to many regulatory mechanisms that occur over a range of time scales. Compared to analysis of slow, trafficking‐based mechanisms relatively little attention has been paid to rapid mechanisms that take place on the seconds time scale. In our study, we utilized live cell calcium imaging to investigate the acute effects of a subfamily of GRKs, GRK2 and 3 on both Gq signaling and Gi/s‐Gq crosstalk. We first focused on group 1 metabotropic glutamate receptors (mGluRs) and found that overexpression of GRK2 and 3 drives an acute desensitization of Gq‐dependent signaling. This desensitization effect occurs on the seconds time scale, is rapidly reversible, and depends on direct interaction between GRK and Gq but is independent of its kinase activity. We find that this mode of rapid desensitization is generalizable across Gq‐coupled GPCRs and is insensitive to the widely used GRK2/3 kinase inhibitor CMPD101. Finally, we studied whether the extent and timing of crosstalk between Gi and Gs‐coupled receptors with Gq‐coupled receptors is also regulated by GRK2. We find that GRK2 dramatically reduces the level of functional crosstalk and accelerated the timing of desensitization of calcium responses to Gi or Gs‐coupled receptor activation. This regulatory effect of GRK on crosstalk is dependent on its interaction with both Gq and G beta gamma, but is independent of its kinase activity as well. Together this work reveals potent forms of GPCR signaling regulation with major implications across physiological contexts.

MP49-02 MODULATION OF SENSORY GLIA GQ-GPCR SIGNALING IN VIVO AFFECTS SPONTANEOUS VOIDING AND BLADDER FUNCTION IN AN ANIMAL MODEL OF CHRONIC PELVIC PAIN

You have accessJournal of UrologyCME1 May 2022MP49-02 MODULATION OF SENSORY GLIA GQ-GPCR SIGNALING IN VIVO AFFECTS SPONTANEOUS VOIDING AND BLADDER FUNCTION IN AN ANIMAL MODEL OF CHRONIC PELVIC PAIN Alison Xiaoqiao Xie, Randall Meacham, and Anna Malykhina Alison Xiaoqiao XieAlison Xiaoqiao Xie More articles by this author , Randall MeachamRandall Meacham More articles by this author , and Anna MalykhinaAnna Malykhina More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002624.02AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Chronic pelvic pain (CPP) is a bothersome and highly prevalent symptom present in many chronic disorders of the pelvis. Afferent hypersensitivity plays an important role in the generation and maintenance of CPP symptoms including visceral pain, urgency and urinary frequency. We previously showed that activation of Gq-G protein coupled receptors (Gq-GPCR) in satellite glial cells (SGCs) decreases lumbosacral nociceptive responses and alleviates visceral hypersensitivity in a mouse model of CPP. The objective of this study was to further investigate the modulatory capacity of satellite glial activation in regulation of spontaneous voiding and bladder function. METHODS: Intravesical instillation of vascular endothelial growth factor (VEGFA) induces sensory nerve remodeling in the urinary bladder, and increases nociceptive responses in the lumbosacral sensory ganglia associated with visceral hypersensitivity. Adult C57BL/6 mice were subjected to three intravesical instillations of VEGFA within a 2-week period. Selective activation of lumbosacral sensory glia was achieved by expressing Gq-coupled Designer Receptors Exclusively Activated by Designer Drugs (Gq-DREADD) in glial acidic fibrillary protein (GFAP+) expressing glia by using Gfap-Gq-DREADD transgenic mice or targeted adeno-associated viral vector (AAV) delivery. Gq-DREADD agonist, clozapine N-oxide (CNO), was used to selectively activate Gq-GPCR signaling in GFAP+ glia in vivo. Micturition patterns were recorded by performing a voiding spot assay (spontaneous voiding) and cystometry in unanesthetized animals (bladder function). RESULTS: Activation of lumbosacral SGCs significantly altered spontaneous voiding patterns and bladder function in vivo in VEGFA-treated mice. Higher urinary output, shorter intermicturition intervals, and fewer non-voiding contractions were observed in VEGFA-treated animals following activation of Gq-GPCR signaling. The observed glia-mediated neuromodulatory effects were long-lasting and dose-dependent. CONCLUSIONS: Our data demonstrated that activation of sensory glia in the peripheral nervous system significantly regulate bladder functions. Targeting neuron-glia interactions in the sensory ganglia can be used to effectively alleviate visceral pain and regulate voiding function in vivo. Further studies are warranted to test a therapeutic potential of targeting glial cell signaling in treating hypersensitivity-related symptoms in CPP disorders. Source of Funding: Colorado Pilot Program Mentored Award, CCTSI. "Beyond the neurons: the role of peripheral glia in neurogenic bladder dysfunction". 2019-2021R01 DK129260-01. "Activating Peripheral Glia to Relieve Visceral Pain in Animal Models of Urological Chronic Pelvic Pain Syndrome (UCPPS)". 2021-2026 © 2022 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 207Issue Supplement 5May 2022Page: e853 Advertisement Copyright & Permissions© 2022 by American Urological Association Education and Research, Inc.MetricsAuthor Information Alison Xiaoqiao Xie More articles by this author Randall Meacham More articles by this author Anna Malykhina More articles by this author Expand All Advertisement PDF DownloadLoading ...

Palmitoylation Targets the Calcineurin Phosphatase to the Phosphatidylinositol 4‐kinase Complex at the Plasma Membrane

Calcineurin (CN), the serine/threonine protein phosphatase and the target of immunosuppressants, is a critical regulator of Ca2+ signaling. To discover novel CN‐regulated processes, we examined an understudied isoform, CNAb1, that is highly conserved across vertebrates and expressed in every human tissue. CN is a heterodimer of regulatory and catalytic subunits whose functions and regulation by Ca2+ and calmodulin are well understood for canonical CN isozymes. The few studies of CNAb1, demonstrate its unique physiological and biochemical properties, however, mechanisms that confer these properties and CNAb1‐ specific substrates remain unknown. Here, we show that the non‐canonical C‐terminus of CNAb1, generated by alternative 3’ pre‐mRNA processing, confers unique intracellular localization, enzymatic regulation and substrate specificity for this isoform. In vitro, CNAb1 displays distinct enzymatic properties, where instead of the auto‐inhibitory domain that blocks the active site of canonical CN isoforms under non‐signaling conditions, CNAβ1 is autoinhibited by a sequence motif at its C tail that blocks substrate binding. In cells, unlike canonical cytosolic CN, CNAb1 localizes to the plasma membrane and Golgi due to palmitoylation of its divergent C‐terminal tail. This palmitoylation, which is dynamically regulated by the ABHD17A depalmitoylase, targets CNAb1 to distinct set of membrane‐associated interactors including the phosphatidylinositol 4‐kinase (PI4KA) complex containing EFR3B, PI4KA, TTC7B and FAM126A. This complex recruits the cytosolic PI4KIIIA to the PM where it synthesizes phosphatidylinositol‐4‐phosphate (PI4P), a precursor of the critical signaling phospholipid, PI(4,5)P2, required for sustained Ca2+signaling through GPCRs. Using hydrogen‐deuterium exchange, we reveal multiple CN‐PI4KA complex contacts, including a calcineurin‐binding peptide motif in the disordered tail of FAM126A which we further establish as a novel calcineurin substrate. Using BRET‐based detection of phosphoinositides in live cells, we show that CN inhibitors decrease PM PI4P production during Gq‐coupled muscarinic receptor signaling, suggesting that CN dephosphorylates and promotes PI4KA complex activity. Together, this work not only discovers dynamic palmitoylation as a novel mechanism that confers unique localization, substrate specificity and regulation to CNAb1 but also uncovers a novel Ca2+/CN‐mediated, feedback loop, that promotes PI4P replenishment at the PM during GPCR signaling.

Population Imaging of Central Sensitization

Capsaicin applied locally to the skin causes central sensitization that results in allodynia, a state in which pain is elicited by innocuous stimuli. Here, we used two-photon calcium imaging of neurons in the dorsal spinal cord to visualize central sensitization across excitatory interneurons and spinal projection neurons. To distinguish among excitatory neuron subtypes, we developed CICADA, a cell profiling approach that leverages the expression of distinct Gq-coupled receptors. We then identified capsaicin-responsive and capsaicin-sensitized neuronal populations. Capsaicin-sensitized neurons showed emergent responses to low threshold input and increased receptive field sizes consistent with the psychophysical phenomenon that allodynia is observed across an extended secondary zone. Finally, we identified spinal projection neurons that showed a shift in tuning toward low threshold input. These experiments provide a population-level view of central sensitization and a framework with which to model somatosensory integration in the dorsal horn. Grant support from NINDS.