Figure 7 - uploaded by Kentaro Mizuta
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Schematic drawings of GABA B receptor (GABA B R)–mediated synthesis of IP 3 and intracellular Ca 2 1 signaling under ( A ) basal or ( B )
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γ-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system, and exerts its actions via both ionotropic (GABA(A)) and metabotropic (GABA(B)) receptors. Although the functional expression of GABA(B) receptors coupled to the G(i) protein was reported for airway smooth muscle, the role of GABA(B) recepto...
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... and Madison also showed that adenosine A 1 receptors induce the release of [Ca 21 ] i from the sarcoplasmic reticulum through the activation of PLC in human bronchial smooth muscle cells (6). Taken together, our findings suggest that baclofen stimulated the responses of [Ca 21 ] i via GABA B receptors, and dissociated G bg subunits from GABA B receptors activated PLC-b, which hydro- lyzes PIP 2 into DAG and IP 3 , followed by the mobilization of calcium from the sarcoplasmic reticulum ( Figure 7A). ...
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... the adenosine A 1 receptor and a 2c -adrenoceptors provide G bg subunits directly to G q -coupled bradykinin B 2 or P2Y nucleotide receptors, resulting in an enhanced binding of GTP to G q and enhanced signaling (33). These findings suggest that G bg subunits dissociated from G i -cou- pled receptors could enhance the synthesis of inositol phosphate and [Ca 21 ] i signaling by accelerating G-protein reassociation and by facilitating activation of the G q signaling pathway ( Figure 7B). ...
Citations
... We further explored the involvement of Gi upon metamorphosis as the upstream factor of the Gq-Gs pathways. Gi is known to activate PLCβ through the Gβγi complex 64,65 . Released βγ is inactivated by overexpressing normal (usually GDP-bound) Gα subunits because GDP-Gα quenches the βγ complex 66 . ...
Larvae of the ascidian Ciona initiate metamorphosis tens of minutes after adhesion to a substratum via its adhesive organ. The gap between adhesion and metamorphosis initiation is suggested to ensure the rigidity of adhesion, allowing Ciona to maintain settlement after losing locomotive activity through metamorphosis. The mechanism producing the gap is unknown. Here, by combining gene functional analyses, pharmacological analyses, and live imaging, we propose that the gap represents the time required for sufficient cAMP accumulation to trigger metamorphosis. Not only the Gs pathway but also the Gi and Gq pathways are involved in the initiation of metamorphosis in the downstream signaling cascade of the neurotransmitter GABA, the known initiator of Ciona metamorphosis. The mutual crosstalk of stimulatory and inhibitory G-proteins functions as the accelerator and brake for cAMP production, ensuring the faithful initiation of metamorphosis at an appropriate time and in the right situation.
... For normal function of GABA B receptors both subunits should be assembled together (14,15). GABA B receptors provide slow inhibitory signals through G proteins and second messengers such as cyclic adenosine monophosphate (cAMP), inositol trisphosphate (IP 3 ) or diacylglycerol (DAG) (15,16). Interestingly, in human islets and human peripheral blood mononuclear cells (PBMCs) only GABA B1 mRNA transcript was detected in contrast to murine islet and immune cells where both subunits GABA B1 and GABA B2 were found (7,17). ...
The pancreatic islets are essential microorgans controlling the glucose level in the blood. The islets consist of different cell types which communicate with each other by means of auto- and paracrine interactions. One of the communication molecules produced by and released within the islets is γ-aminobutyric acid (GABA), a well-known inhibitor of neuronal excitability in the mammalian nervous system. Interestingly, GABA is also present in the blood in the nanomolar concentration range. Thus, GABA can affect not only islet function per se (e.g. hormone secretion) but also interactions between immune cells and the pancreatic islet cells in physiological conditions and in pathological states (particularly in type 1 diabetes). In the last decade the interest in GABA signalling in islets has increased. The broad research scope ranges from fundamental physiological studies at the molecular and cellular level to pathological implications and clinical trials. The aim of this mini-review is to outline the current status of the islet GABA field mostly in relation to human islets, to identify the gaps in the current knowledge and what clinical implications GABA signalling may have in islets.
... On the other hand, DAPA promoted GABA A receptor cell surface expression mediated by enhancing BDNF secretion through activating GABA B -related PLC/DAG/PKC signaling [75]. The coupling of GABA B receptor with PLC is witnessed peripherally [76] and centrally [75]. Herein, the increased amygdaloid expression and phosphorylation of GABA B R2 subunit afforded by DAPA is accompanied with increased expression of GABA A . ...
Anxiety is a neuropsychiatric disturbance that is commonly manifested in various dementia forms involving Alzheimer's disease (AD). The mechanisms underlying AD-associated anxiety haven't clearly recognized the role of energy metabolism in anxiety represented by the amygdala's autophagic sensors; liver kinase B1 (LKB1)/adenosine monophosphate kinase (AMPK). Dapagliflozin (DAPA), a SGLT2 inhibitor, acts as an autophagic activator through LKB1 activation in several diseases including AD. Herein, the propitious yet undetected anxiolytic potential of DAPA as an autophagic enhancer was investigated in AD animal model with emphasis on amygdala's GABAergic neurotransmission and brain-derived neurotrophic factor (BDNF). Alzheimer's disease was induced by ovariectomy (OVX) along with seventy-days-D-galactose (D-Gal) administration (150 mg/kg/day, i.p). On the 43rd day of D-Gal injection, OVX/D-Gal-subjected rats received DAPA (1 mg/kg/day, p.o) alone or with dorsomorphin the AMPK inhibitor (DORSO, 25 μg/rat, i.v.). In the amygdala, LKB1/AMPK were activated by DAPA inducing GABAB2 receptor stimulation; an effect that was abrogated by DORSO. Dapagliflozin also replenished the amygdala GABA, NE, and 5-HT levels along with glutamate suppression. Moreover, DAPA triggered BDNF production with consequent activation of its receptor, TrkB through activating GABAB2-related downstream phospholipase C/diacylglycerol/protein kinase C (PLC/DAG/PKC) signaling. This may promote GABAA expression, verifying the crosstalk between GABAA and GABAB2. The DAPA's anxiolytic effect was visualized by improved behavioral traits in elevated plus maze together with amendment of amygdala’ histopathological abnormalities. Thus, the present study highlighted DAPA's anxiolytic effect which was attributed to GABAB2 activation and its function to induce BDNF/TrkB and GABAA expression through PLC/DAG/PKC pathway in AMPK-dependent manner.
... Gammaaminobutyric acid receptors are located mainly in the central nervous system (CNS) and retina. Additionally, GABA receptors have also been detected in peripheral tissues and are shown to modulate intracellular calcium concentration (9,10). These receptors can inhibit the release of many neurotransmitters, such as dopamine, serotonin, and acetylcholine, via Gprotein-dependent inhibition of neuronal voltage-gated Ca 2+ channels. ...
Purpose: Angiogenesis post-ischemia plays an essential role in preventing ischemic damage to tissue by improving the blood recovery. Determining the regulatory mechanism of ischemic angiogenesis, therefore, could provide effective therapeutics for ischemic injury.
Materials and Methods: The RNA sequencing (RNA-seq) database was used to predict the association of gamma-aminobutyric acid type B receptor subunit 2 (GABBR2) with endothelial-specific expression. The role of GABBR2 in angiogenesis was verified in vitro by downregulating GABBR2 in human umbilical vein endothelial cells (HUVECs) with lentiviral vectors. Besides, the in vivo effect of GABBR2 on the blood recovery of an ischemic hindlimb was demonstrated by establishing a hindlimb ischemia model in normal and GABBR2 adenoviral vector-infected mice. Then, the mobilization of endothelial progenitor cells (EPCs) in peripheral blood post-ischemia was determined by flow cytometry. Finally, the XF analyzer and Western blot were used to determine the effect of GABBR2 on endothelial metabolism.
Results: The RNA-seq results indicated a strong association between GABBR2 and endothelial revascularization, and the upregulation of GABBR2 was detected in both hypoxia-treated HUVECs and ischemic mouse hindlimb. Hypoxia treatment for 6 h increased the proliferation, migration, and tube formation of HUVECs, which were inhibited by GABBR2 knockdown. Additionally, GABBR2 downregulation significantly decreased the blood flow recovery of mouse ischemic hindlimb. The expressions of the EPC markers CD34 ⁺ and CD133 ⁺ significantly decreased in the peripheral blood in hindlimb post-ischemia. Mechanically, glycolysis-dominated metabolism of HUVECs was compromised by GABBR2 knockdown. Evidences of the decreased expressions of HKII, PFKFB3, and PKM1 also supported the compromised glycolysis induced by GABBR2 downregulation.
Conclusion: Our study demonstrated that GABBR2 regulated angiogenesis post-ischemia by inhibiting the glycolysis pathway.
... Finally, to investigate whether xenopsin is capable of coupling to Gaq, we tested its ability to modulate cytoplasmic Ca 2+ release, in comparison to melanopsin, with or without pertussis toxin pretreatment. Although cytoplasmic Ca 2+ release is a classic response to Gaq activation, it is known that Gai activation can also trigger Ca 2+ release (Mizuta et al., 2011). In cells transfected with melanopsin, light induced a > 1000 fold increase in cytoplasmic Ca 2+ , which was not affected by pertussis toxin. ...
Animals detect light using opsin photopigments. Xenopsin, a recently classified subtype of opsin, challenges our views on opsin and photoreceptor evolution. Originally thought to belong to the Gαi-coupled ciliary opsins, xenopsins are now understood to have diverged from ciliary opsins in pre-bilaterian times, but little is known about the cells that deploy these proteins, or if they form a photopigment and drive phototransduction. We characterized xenopsin in a flatworm, Maritigrella crozieri, and found it expressed in ciliary cells of eyes in the larva, and in extraocular cells around the brain in the adult. These extraocular cells house hundreds of cilia in an intra-cellular vacuole (phaosome). Functional assays in human cells show Maritigrella xenopsin drives phototransduction primarily by coupling to Gαi. These findings highlight similarities between xenopsin and c-opsin and reveal a novel type of opsin-expressing cell that, like jawed vertebrate rods, encloses the ciliary membrane within their own plasma membrane.
... PLC is classically activated by the G q␣ -and G q␥ -proteins dissociated from G q -coupled receptors. However, PLC was also shown to be activated by G i␥ -proteins released from G i -proteins (Tomura et al., 1997;Mizuta et al., 2011). Thus, we investigated whether PLC was the downstream mechanism activated by the G i␥ subunit and involved in the interplay between HCAR1 and other G i -coupled receptors. ...
The discovery of a G-protein-coupled receptor for lactate named hydroxycarboxylic acid receptor 1 (HCAR1) in neurons has pointed to additional nonmetabolic effects of lactate for regulating neuronal network activity. In this study, we characterized the intracellular pathways engaged by HCAR1 activation, using mouse primary cortical neurons from wild-type (WT) and HCAR1 knock-out (KO) mice from both sexes. Using whole-cell patch clamp, we found that the activation of HCAR1 with 3-chloro-5-hydroxybenzoic acid (3Cl-HBA) decreased miniature EPSC frequency, increased paired-pulse ratio, decreased firing frequency, and modulated membrane intrinsic properties. Using fast calcium imaging, we show that HCAR1 agonists 3,5-dihydroxybenzoic acid, 3Cl-HBA, and lactate decreased by 40% spontaneous calcium spiking activity of primary cortical neurons from WT but not from HCAR1 KO mice. Notably, in neurons lacking HCAR1, the basal activity was increased compared with WT. HCAR1 mediates its effect in neurons through a Giα-protein. We observed that the adenylyl cyclase-cAMP-protein kinase A axis is involved in HCAR1 downmodulation of neuronal activity. We found that HCAR1 interacts with adenosine A1, GABAB, and α2A-adrenergic receptors, through a mechanism involving both its Giα and Giβγ subunits, resulting in a complex modulation of neuronal network activity. We conclude that HCAR1 activation in neurons causes a downmodulation of neuronal activity through presynaptic mechanisms and by reducing neuronal excitability. HCAR1 activation engages both Giα and Giβγ intracellular pathways to functionally interact with other Gi-coupled receptors for the fine tuning of neuronal activity.SIGNIFICANCE STATEMENT Expression of the lactate receptor hydroxycarboxylic acid receptor 1 (HCAR1) was recently described in neurons. Here, we describe the physiological role of this G-protein-coupled receptor (GPCR) and its activation in neurons, providing information on its expression and mechanism of action. We dissected out the intracellular pathway through which HCAR1 activation tunes down neuronal network activity. For the first time, we provide evidence for the functional cross talk of HCAR1 with other GPCRs, such as GABAB, adenosine A1- and α2A-adrenergic receptors. These results set HCAR1 as a new player for the regulation of neuronal network activity acting in concert with other established receptors. Thus, HCAR1 represents a novel therapeutic target for pathologies characterized by network hyperexcitability dysfunction, such as epilepsy.
... Finally, to investigate whether xenopsin is capable of coupling to Gaq, we tested its ability to modulate cytoplasmic Ca 2+ release, in comparison to melanopsin, with or without pertussis toxin pretreatment. Although cytoplasmic Ca 2+ release is a classic response to Gaq activation, it is known that Gai activation can also trigger Ca 2+ release (Mizuta et al., 2011). In cells transfected with melanopsin, light induced a > 1000 fold increase in cytoplasmic Ca 2+ , which was not affected by pertussis toxin. ...
Animals detect light using opsin photopigments. One recently classified opsin clade, the xenopsins, found in lophotrochozoans, challenges our views on opsin and photoreceptor evolution. Originally thought to belong to the Gαi-coupled ciliary opsins, xenopsins are now understood to have diverged from ciliary opsins in pre-bilaterian times, but little is known about the cells that deploy these proteins, or if they form a photopigment and drive phototransduction. We characterized xenopsin in a flatworm, Maritigrella crozieri, and found that it is expressed in a larval eyespot, and in an abundant extraocular cell type around the adult brain. These distinct cells house hundreds of cilia in an intra-cellular vacuole (a phaosome). Cellular assays show Mc xenopsin forms a photopigment and couples to Gαi/o in response to light. These findings reveal a novel photoreceptor cell type and opsin/G-protein couple, and highlight the convergent enclosure of photosensitive cilia in flatworm phaosomes and jawed vertebrate rods.
... Gq and Gs signaling tends to regulate specific cellular functions in those cells differently. For example, in smooth muscle, Gq [and for certain select GPCRs, Gi (15,37)], signaling promotes contraction and growth, whereas Gs signaling antagonizes both functions (28,31,38). Consistent with this regulatory paradigm and the differential capacity of certain benzodiazepines to bias OGR1 signaling in ASM (Figs. 4 and 5), we found the Gs-biased agent sulazepam promoted ASM relaxation, whereas the relatively balanced lorazepam did not (Fig. 11). ...
GPCRs have diverse signaling capabilities, based on their ability to assume various conformations. Moreover, it is now appreciated that certain ligands can promote distinct receptor conformations and thereby bias signaling toward a specific pathway to differentially affect cell function. The recently deorphanized G protein-coupled receptor OGR1 [ovarian cancer G protein-coupled receptor 1 (GPR68)] exhibits diverse signaling events when stimulated by reductions in extracellular pH. We recently demonstrated airway smooth muscle cells transduce multiple signaling events, reflecting a diverse capacity to couple to multiple G proteins. Moreover, we recently discovered that the benzodiazepine lorazepam, more commonly recognized as an agonist of the γ-aminobutyric acid A (GABAA) receptor, can function as an allosteric modulator of OGR1 and, similarly, can promote multiple signaling events. In this study, we demonstrated that different benzodiazepines exhibit a range of biases for OGR1, with sulazepam selectively activating the canonical Gs of the G-protein signaling pathway, in heterologous expression systems, as well as in several primary cell types. These findings highlight the potential power of biased ligand pharmacology for manipulating receptor signaling qualitatively, to preferentially activate pathways that are therapeutically beneficial.-Pera, T., Deshpande, D. A., Ippolito, M., Wang, B., Gavrila, A., Michael, J. V., Nayak, A. P., Tompkins, E., Farrell, E., Kroeze, W. K., Roth, B. L., Panettieri, R. A. Jr., Benovic, J. L., An, S. S., Dulin, N. O., Penn, R. B. Biased signaling of the proton-sensing receptor OGR1 by benzodiazepines.
... The baseline Ca 2+ fluorescence intensity (F 0 : average intensity before muscimol administration) and measured fluorescence intensity (F) were acquired, and ∆F was calculated as F − F 0 . A neuron was considered depolarized when the ∆F/F 0 ratio remained greater than 0.3 for more than 30 s after the administration of muscimol (the definition was modified from [16]). To determine whether the Ca 2+ response was mediated by the GABA A receptor, bicuculline (10 µM, Tocris) was administered 2 min before muscimol administration. ...
The excitatory-to-inhibitory functional switch of γ-aminobutyric acid (GABA; GABA switch), which normally occurs in the first to the second postnatal week in the hippocampus, is necessary for the development of appropriate central nervous system function. A deficit in GABAergic inhibitory function could cause excitatory/inhibitory (E/I) neuron imbalance that is found in many neurodegenerative disorders. In the present study, we examined whether neonatal stress can affect the timing of the GABA functional switch and cause disorders during adolescence. Neonatal stress was induced in C57BL/6J male mouse pups by maternal separation (MS) on postnatal days (PND) 1-21. Histological quantification of K(+)-Cl(-) co-transporter (KCC2) and Ca(2+) imaging were performed to examine the timing of the GABA switch during the MS period. To evaluate the influence of neonatal MS on adolescent hippocampal function, we quantified KCC2 expression and evaluated hippocampal-related behavioral tasks at PND35-38. We showed that MS delayed the timing of the GABA switch in the hippocampus and inhibited the increase in membrane KCC2 expression, with KCC2 expression inhibition persisting until adolescence. Behavioral tests showed impaired cognition, declined attention, hyperlocomotion, and aggressive character in maternally separated mice. Taken together, our results show that neonatal stress delayed the timing of the GABA switch, which could change the E/I balance and cause neurodegenerative disorders in later life.
... Functional GABA B receptors in ASM (166,167,388) and epithelium (364) have been shown. Although acting through G i , baclofen and GABA increase IP 3 and [Ca 2ϩ ] i in the airway (363), an effect involving a G␥mediated direct effect on PLC, and potentiation of G q -mediated signaling. Conversely, GABA A receptors on ASM appear to be potent bronchodilators (122, 164,165,167,168,365,581,584). ...
Airway structure and function are key aspects of normal lung development, growth and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, COPD and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and finally, interactions with other airway cell types such as epithelium, fibroblasts and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This perspective emphasizes established and recent discoveries that underline the central role of ASM, and sets the stage for future research towards understanding how ASM plays a central role by being both upstream and downstream in the many, interactive processes that determine airway structure and function in health and disease.
