Accessory proteins for heterotrimeric G-protein: Implication in the cardiovascular system

Activation of the urotensin-II receptor by remdesivir induces cardiomyocyte dysfunction

Remdesivir is an antiviral drug used for COVID-19 treatment worldwide. Cardiovascular side effects have been associated with remdesivir; however, the underlying molecular mechanism remains unknown. Here, we performed a large-scale G-protein-coupled receptor screening in combination with structural modeling and found that remdesivir is a selective, partial agonist for urotensin-II receptor (UTS2R) through the Gα_i/o-dependent AKT/ERK axis. Functionally, remdesivir treatment induced prolonged field potential and APD₉₀ in human induced pluripotent stem cell (iPS)-derived cardiomyocytes and impaired contractility in both neonatal and adult cardiomyocytes, all of which mirror the clinical pathology. Importantly, remdesivir-mediated cardiac malfunctions were effectively attenuated by antagonizing UTS2R signaling. Finally, we characterized the effect of 110 single-nucleotide variants in UTS2R gene reported in genome database and found four missense variants that show gain-of-function effects in the receptor sensitivity to remdesivir. Collectively, our study illuminates a previously unknown mechanism underlying remdesivir-related cardiovascular events and that genetic variations of UTS2R gene can be a potential risk factor for cardiovascular events during remdesivir treatment, which collectively paves the way for a therapeutic opportunity to prevent such events in the future.

Network construction of aberrantly expressed miRNAs and their target mRNAs in ventricular myocardium with ischemia-reperfusion arrhythmias

Background

Hypothermic ischemia-reperfusion arrhythmia remains the main factor affecting cardiac resuscitation under cardiopulmonary bypass. Existing research shows that certain miRNAs exhibit significantly different expressions and effects in arrhythmias, however, the effect of miRNAs on the progression of hypothermic ischemic–reperfusion arrhythmias (RA) and its potential mechanism remain to be further explored.

Methods

Sprague-Dawley (SD) rats were randomly divided into two groups (n = 8): a normal control group (Group C) and a hypothermic ischemia-reperfusion group (Group IR), which were used to establish a Langendorff isolated cardiac perfusion model. According to the arrhythmia scoring system, rats in group IR were divided into a high-risk group (IR-H) and a low-risk group (IR-L). miRNAs expression profiles of ventricular myocardium with global hypothermic ischemia–reperfusion and those of ventricular myocardium with hypothermic ischemia–RA were established through high-throughput sequencing. Furthermore, the aberrantly expressed miRNAs in myocardium with and without hypothermic ischemia–RA were screened and verified. The target genes of these aberrantly expressed miRNAs were predicted using RNAhybrid and MiRanda software. Based on Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, we determined the mRNA targets associated with these miRNAs and studied the miRNA–mRNA interaction during the cardiovascular disease progression. The aberrantly expressed miRNAs related to hypothermic ischemia–RA were validated by Real-time Quantitative polymerase chain reaction (RT-qPCR).

Results

Eight significantly aberrantly expressed miRNAs (rno-miR-122-5p, rno-miR-429, novel_miR-1, novel_miR-16, novel_miR-17, novel_miR-19, novel_miR-30, and novel_miR-43) were identified, among which six were up-regulated and two were down-regulated. Moreover, target genes and signaling pathways associated with these aberrantly expressed miRNAs were predicted and analyzed. The miRNA–mRNA interaction network graph showed that GJA1 gene was considered as the target of novel_miR-17.

Conclusions

Aberrantly expressed miRNAs were possibly associated with the formation mechanism of hypothermic ischemia–RA. Specific miRNAs, such as novel_miR-17 and rno-miR-429 are probably new potential targets for further functional studies of hypothermic ischemia–RA.

A generally conserved response to hypoxia in iPSC-derived cardiomyocytes from humans and chimpanzees

Despite anatomical similarities, there are differences in susceptibility to cardiovascular disease (CVD) between primates; humans are prone to myocardial ischemia, while chimpanzees are prone to myocardial fibrosis. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) allow for direct inter-species comparisons of the gene regulatory response to CVD-relevant perturbations such as oxygen deprivation, a consequence of ischemia. To gain insight into the evolution of disease susceptibility, we characterized gene expression levels in iPSC-CMs in humans and chimpanzees, before and after hypoxia and re-oxygenation. The transcriptional response to hypoxia is generally conserved across species, yet we were able to identify hundreds of species-specific regulatory responses including in genes previously associated with CVD. The 1,920 genes that respond to hypoxia in both species are enriched for loss-of-function intolerant genes; but are depleted for expression quantitative trait loci and cardiovascular-related genes. Our results indicate that response to hypoxic stress is highly conserved in humans and chimpanzees.

Dynorphin-Dependent Reduction of Excitability and Attenuation of Inhibitory Afferents of NPS Neurons in the Pericoerulear Region of Mice

The Neuropeptide S system, consisting of the 20-amino acid peptide neuropeptide S (NPS) and its G-protein coupled receptor (NPSR), modulates arousal, wakefulness, anxiety, and fear-extinction in mice. In addition, recent evidence indicates that the NPS system attenuates stress-dependent impairment of fear extinction, and that NPS-expressing neurons in close proximity to the locus coeruleus region (LC; pericoerulear, periLC) are activated by stress. Furthermore, periLC NPS neurons receive afferents from neurons of the centrolateral nucleus of the amygdala (CeL), of which a substantial population expresses the kappa opioid receptor (KOR) ligand precursor prodynorphin. This study aims to identify the effect of the dynorphinergic system on NPS neurons in the periLC via pre- and postsynaptic mechanisms. Using electrophysiological recordings in mouse brain slices, we provide evidence that NPS neurons in the periLC region are directly inhibited by dynorphin A (DynA) via activation of κ-opioid receptor 1 (KOR1) and a subsequent increase of potassium conductances. Thus, the dynorphinergic system is suited to inactivate NPS neurons in the periLC. In addition to this direct, somatic effect, DynA reduces the efficacy of GABAergic synapses on NPS neurons via KOR1 and KOR2. In conclusion, the present study provides evidence for the interaction of the NPS and the kappa opioid system in the periLC. Therefore, the endogenous opioid dynorphin is suited to inhibit NPS neurons with a subsequent decrease in NPS release in putative target regions leading to a variety of physiological consequences such as increased anxiety or vulnerability to stress exposure.

Regulation of G protein signaling by the 70kDa heat shock protein

G protein-coupled receptors (GPCRs) transduce extracellular signals to the interior of the cell by activating membrane-bound guanine nucleotide-binding regulatory proteins (G proteins). An increasing number of proteins have been reported to bind to and regulate GPCRs. We report a novel regulation of the alpha(2A) adrenergic receptor (α(2A)-R) by the ubiquitous stress-inducible 70kDa heat shock protein, hsp70. Hsp70, but not hsp90, attenuated G protein-dependent high affinity agonist binding to the α(2A)-R in Sf9 membranes. Antagonist binding was unchanged, suggesting that hsp70 uncouples G proteins from the receptor. As hsp70 did not bind G proteins but complexed with the α(2A)-R in intact cells, a direct interaction with the receptor seems likely. In the presence of hsp70, α(2A)-R-catalyzed [(35)S]GTPγS binding was reduced by approximately 70%. In contrast, approximately 50-fold higher concentrations of hsp70 were required to reduce agonist binding to the stress-inducible 5-hydroxytryptamine(1A) receptor (5-HT(1A)-R). In heat-stressed CHO cells, the α(2A)-R was significantly uncoupled from G proteins, coincident with an increased localization of hsp70 at the membrane. The contrasting effect of hsp70 on the α(2A)-R compared to the 5-HT(1A)-R suggests that during stress, upregulation of hsp70 may attenuate signaling from specific GPCRs as part of the stress response to foster survival.

Identification of transcription factor E3 (TFE3) as a receptor-independent activator of Gα16: gene regulation by nuclear Gα subunit and its activator

Receptor-independent G-protein regulators provide diverse mechanisms for signal input to G-protein-based signaling systems, revealing unexpected functional roles for G-proteins. As part of a broader effort to identify disease-specific regulators for heterotrimeric G-proteins, we screened for such proteins in cardiac hypertrophy using a yeast-based functional screen of mammalian cDNAs as a discovery platform. We report the identification of three transcription factors belonging to the same family, transcription factor E3 (TFE3), microphthalmia-associated transcription factor, and transcription factor EB, as novel receptor-independent activators of G-protein signaling selective for Gα(16). TFE3 and Gα(16) were both up-regulated in cardiac hypertrophy initiated by transverse aortic constriction. In protein interaction studies in vitro, TFE3 formed a complex with Gα(16) but not with Gα(i3) or Gα(s). Although increased expression of TFE3 in heterologous systems had no influence on receptor-mediated Gα(16) signaling at the plasma membrane, TFE3 actually translocated Gα(16) to the nucleus, leading to the induction of claudin 14 expression, a key component of membrane structure in cardiomyocytes. The induction of claudin 14 was dependent on both the accumulation and activation of Gα(16) by TFE3 in the nucleus. These findings indicate that TFE3 and Gα(16) are up-regulated under pathologic conditions and are involved in a novel mechanism of transcriptional regulation via the relocalization and activation of Gα(16).

Loss of activator of G-protein signaling 3 impairs renal tubular regeneration following acute kidney injury in rodents

The intracellular mechanisms underlying renal tubular epithelial cell proliferation and tubular repair following ischemia-reperfusion injury (IRI) remain poorly understood. In this report, we demonstrate that activator of G-protein signaling 3 (AGS3), an unconventional receptor-independent regulator of heterotrimeric G-protein function, influences renal tubular regeneration following IRI. In rat kidneys exposed to IRI, there was a temporal induction in renal AGS3 protein expression that peaked 72 h after reperfusion and corresponded to the repair and recovery phase following ischemic injury. Renal AGS3 expression was localized predominantly to the recovering outer medullary proximal tubular cells and was highly coexpressed with Ki-67, a marker of cell proliferation. Kidneys from mice deficient in the expression of AGS3 exhibited impaired renal tubular recovery 7 d following IRI compared to wild-type AGS3-expressing mice. Mechanistically, genetic knockdown of endogenous AGS3 mRNA and protein in renal tubular epithelial cells reduced cell proliferation in vitro. Similar reductions in renal tubular epithelial cell proliferation were observed following incubation with gallein, a selective inhibitor of Gβγ subunit activity, and lentiviral overexpression of the carboxyl-terminus of G-protein-coupled receptor kinase 2 (GRK2ct), a scavenger of Gβγ subunits. In summary, these data suggest that AGS3 acts through a novel receptor-independent mechanism to facilitate renal tubular epithelial cell proliferation and renal tubular regeneration.

Activity Modes in Thalamocortical Relay Neurons are Modulated by G(q)/G(11) Family G-proteins - Serotonergic and Glutamatergic Signaling

In thalamocortical relay (TC) neurons, G-protein-coupled receptors play an important part in the control of activity modes. A conditional Gα(q) knockout on the background of a constitutive Gα(11) knockout (Gα(q)/Gα(11) (-/-)) was used to determine the contribution of Gq/G11 family G-proteins to metabotropic serotonin (5-HT) and glutamate (Glu) function in the dorsal part of the lateral geniculate nucleus (dLGN). In control mice, current clamp recordings showed that α-m-5-HT induced a depolarization of V(rest) which was sufficient to suppress burst firing. This depolarization was concentration-dependent (100 μM: +6 ± 1 mV, n = 10; 200 μM: +10 ± 1 mV, n = 7) and had a conditioning effect on the activation of other Gα(q)-mediated pathways. The depolarization was significantly reduced in Gα(q)/Gα(11) (-/-) (100 μM: 3 ± 1 mV, n = 11; 200 μM: 5 ± 1 mV, n = 6) and was apparently insufficient to suppress burst firing. Activating Gα(q)-coupled muscarinic receptors affected the magnitude of α-m-5-HT-induced effects in a reciprocal manner. Furthermore, the depolarizing effect of mGluR1 agonists was significantly reduced in Gα(q)/Gα(11) (-/-) mice. Immunohistochemical stainings revealed binding of 5-HT(2C)R- and mGluR1α-, but not of 5-HT(2A)R-specific antibodies in the dLGN of Gα(q)/Gα(11) (-/-) mice. In conclusion, these findings demonstrate that transmitters of ascending brainstem fibers and corticofugal fibers both signal via a central element in the form of Gq/G11-mediated pathways to control activity modes in the TC system.

The systematic annotation of the three main GPCR families in Reactome

Reactome is an open-source, freely available database of human biological pathways and processes. A major goal of our work is to provide an integrated view of cellular signalling processes that spans from ligand–receptor interactions to molecular readouts at the level of metabolic and transcriptional events. To this end, we have built the first catalogue of all human G protein-coupled receptors (GPCRs) known to bind endogenous or natural ligands. The UniProt database has records for 797 proteins classified as GPCRs and sorted into families A/1, B/2 and C/3 on the basis of amino accid sequence. To these records we have added details from the IUPHAR database and our own manual curation of relevant literature to create reactions in which 563 GPCRs bind ligands and also interact with specific G-proteins to initiate signalling cascades. We believe the remaining 234 GPCRs are true orphans. The Reactome GPCR pathway can be viewed as a detailed interactive diagram and can be exported in many forms. It provides a template for the orthology-based inference of GPCR reactions for diverse model organism species, and can be overlaid with protein–protein interaction and gene expression datasets to facilitate overrepresentation studies and other forms of pathway analysis.

Database URL:http://www.reactome.org

Heterotrimeric G protein signaling outside the realm of seven transmembrane domain receptors

Heterotrimeric G proteins, consisting of the guanine nucleotide-binding Galpha subunits with GTPase activity and the closely associated Gbeta and Ggamma subunits, are important signaling components for receptors with seven transmembrane domains (7TMRs). These receptors, also termed G protein-coupled receptors (GPCRs), act as guanine nucleotide exchange factors upon agonist stimulation. There is now accumulating evidence for noncanonical functions of heterotrimeric G proteins independent of 7TMR coupling. Galpha proteins belonging to all 4 subfamilies, including G(s), G(i), G(q), and G(12) are found to play important roles in receptor tyrosine kinase signaling, regulation of oxidant production, development, and cell migration, through physical and functional interaction with proteins other than 7TMRs. Association of Galpha with non-7TMR proteins also facilitates presentation of these G proteins to specific cellular microdomains. This Minireview aims to summarize our current understanding of the noncanonical roles of Galpha proteins in cell signaling and to discuss unresolved issues including regulation of Galpha activation by proteins other than the 7TMRs.

Activator of G protein signaling 8 (AGS8) is required for hypoxia-induced apoptosis of cardiomyocytes: role of G betagamma and connexin 43 (CX43)

Ischemic injury of the heart is associated with activation of multiple signal transduction systems including the heterotrimeric G-protein system. Here, we report a role of the ischemia-inducible regulator of G betagamma subunit, AGS8, in survival of cardiomyocytes under hypoxia. Cultured rat neonatal cardiomyocytes (NCM) were exposed to hypoxia or hypoxia/reoxygenation following transfection of AGS8siRNA or pcDNA::AGS8. Hypoxia-induced apoptosis of NCM was completely blocked by AGS8siRNA, whereas overexpression of AGS8 increased apoptosis. AGS8 formed complexes with G-proteins and channel protein connexin 43 (CX43), which regulates the permeability of small molecules under hypoxic stress. AGS8 initiated CX43 phosphorylation in a G betagamma-dependent manner by providing a scaffold composed of G betagamma and CX43. AGS8siRNA blocked internalization of CX43 following exposure of NCM to repetitive hypoxia; however it did not influence epidermal growth factor-mediated internalization of CX43. The decreased dye flux through CX43 that occurred with hypoxic stress was also prevented by AGS8siRNA. Interestingly, the G betagamma inhibitor Gallein mimicked the effect of AGS8 knockdown on both the CX43 internalization and the changes in cell permeability elicited by hypoxic stress. These data indicate that AGS8 is required for hypoxia-induced apoptosis of NCM, and that AGS8-G betagamma signal input increased the sensitivity of cells to hypoxic stress by influencing CX43 regulation and associated cell permeability. Under hypoxic stress, this unrecognized response program plays a critical role in the fate of NCM.