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The dopamine D2 receptor (D2R), like many G-protein-coupled receptors, signals through G-protein- and β-arrestin-dependent pathways. Preferential activation of one of these pathways is termed functional selectivity or biased signaling and is a promising therapeutic strategy. Though biased signaling through D2Rs has been demonstrated, acquiring the mechanistic details of biased D2R/G-protein and D2R/β-arrestin signaling in vivo has been challenging because of the lack of techniques that specifically target these interactions in discrete cell populations. To address this question, we employed a cell type-specific viral expression approach to restore D2R variants that preferentially engage either G-protein or β-arrestin signaling in 'indirect pathway' medium spiny neurons (iMSNs), because of their central role in dopamine circuitry. We found that the effect of haloperidol antagonism on D2R metabolic signaling events is largely mediated by acute blockade of D2R/G-protein signaling. We show that a D2R-driven behavior, nestlet shredding, is similarly driven by D2R/G-protein signaling. On the other hand, D2R-driven locomotion and rearing require coordinated D2R/G-protein and D2R/β-arrestin signaling. The acute locomotor response to amphetamine and cocaine similarly depend on both G-protein and β-arrestin D2R signaling. Surprisingly, another psychotropic drug, phencyclidine, displayed a selective D2R/β-arrestin potentiation of locomotion. These findings highlight how D2R mostly relies upon balanced G-protein and β-arrestin signaling in iMSNs. However, the response to haloperidol and phencyclidine indicates that normal D2R signaling homeostasis can be dramatically altered, indicating that targeting a specific D2R signal transduction pathway could allow for more precise modulation of dopamine circuit function.

The current dopamine (DA) hypothesis of schizophrenia postulates striatal hyperdopaminergia and cortical hypodopaminergia. Although partial agonists at DA D2 receptors (D2Rs), like aripiprazole, were developed to simultaneously target both phenomena, they do not effectively improve cortical dysfunction. In this study, we investigate the potential for newly developed β-arrestin2 (βarr2)-biased D2R partial agonists to simultaneously target hyper- and hypodopaminergia. Using neuron-specific βarr2-KO mice, we show that the antipsychotic-like effects of a βarr2-biased D2R ligand are driven through both striatal antagonism and cortical agonism of D2R-βarr2 signaling. Furthermore, βarr2-biased D2R agonism enhances firing of cortical fast-spiking interneurons. This enhanced cortical agonism of the biased ligand can be attributed to a lack of G-protein signaling and elevated expression of βarr2 and G protein-coupled receptor (GPCR) kinase 2 in the cortex versus the striatum. Therefore, we propose that βarr2-biased D2R ligands that exert region-selective actions could provide a path to develop more effective antipsychotic therapies.

G protein–coupled receptors (GPCRs) are the largest family of cell surface receptors and signal through the proximal effectors, G proteins and β-arrestins, to influence nearly every biological process. The G protein and β-arrestin signaling pathways have largely been considered separable; however, direct interactions between Gα proteins and β-arrestins have been described that appear to be part of a distinct GPCR signaling pathway. Within these complexes, Gαi/o, but not other Gα protein subtypes, directly interacts with β-arrestin, regardless of the canonical Gα protein that is coupled to the GPCR. Here, we report that the endogenous biased chemokine agonists of CXCR3 (CXCL9, CXCL10, and CXCL11), together with two small-molecule biased agonists, differentially formed Gαi:β-arrestin complexes. Formation of the Gαi:β-arrestin complexes did not correlate well with either G protein activation or β-arrestin recruitment. β-arrestin biosensors demonstrated that ligands that promoted Gαi:β-arrestin complex formation generated similar β-arrestin conformations. We also found that Gαi:β-arrestin complexes did not couple to the mitogen-activated protein kinase ERK, as is observed with other receptors such as the V2 vasopressin receptor, but did couple with the clathrin adaptor protein AP-2, which suggests context-dependent signaling by these complexes. These findings reinforce the notion that Gαi:β-arrestin complex formation is a distinct GPCR signaling pathway and enhance our understanding of the spectrum of biased agonism. A complex to complicate chemokine signaling: G protein–coupled receptors (GPCRs) represent about 30% of the targets of FDA-approved drugs. GPCRs signal through two pathways that are considered separable: one dependent on direct activation of heterotrimeric G proteins and the other on the recruitment of β-arrestin proteins. Building on their previous work, Zheng et al. showed that some, but not all, of the endogenous agonists of the chemokine receptor CXCR3 induced the formation of a Gαi:β-arrestin complex, which was independent of the relative extent of activation of either G protein or β-arrestin signaling pathways. Signaling downstream of the Gαi:β-arrestin complex was different from that stimulated by β-arrestin alone. Together, these data add to the evidence of crosstalk between G proteins and β-arrestins and may have implications for the development of GPCR-targeting drugs. [ABSTRACT FROM AUTHOR]

Introduction: The COVID-19 pandemic has created a high demand on personal protective equipment, including disposable N95 masks. Given the need for mask reuse, we tested the feasibility of vaporized hydrogen peroxide (VHP), ultraviolet light (UV), and ethanol decontamination strategies on N95 mask integrity and the ability to remove the infectious potential of SARS-CoV-2. Methods: Disposable N95 masks, including medical grade (1860, 1870+) and industrial grade (8511) masks, were treated by VHP, UV, and ethanol decontamination. Mask degradation was tested using a quantitative respirator fit testing. Pooled clinical samples of SARS-CoV-2 were applied to mask samples, treated, and then either sent immediately for real-time reverse transcriptase–polymerase chain reaction (RT-PCR) or incubated with Vero E6 cells to assess for virucidal effect. Results: Both ethanol and UV decontamination showed functional degradation to different degrees while VHP treatment showed no significant change after two treatments. We also report a single SARS-CoV-2 virucidal experiment using Vero E6 cell infection in which only ethanol treatment eliminated detectable SARS-CoV-2 RNA. Conclusions: We hope our data will guide further research for evidenced-based decisions for disposable N95 mask reuse and help protect caregivers from SARS-CoV-2 and other pathogens. [ABSTRACT FROM AUTHOR]

The 'brain-gut' peptide ghrelin, which mediates food-seeking behaviors, is recognized as a very strong endogenous modulator of dopamine (DA) signaling. Ghrelin binds the G protein-coupled receptor GHSR1a, and administration of ghrelin increases the rewarding properties of psychostimulants while ghrelin receptor antagonists decrease them. In addition, the GHSR1a signals through βarrestin-2 to regulate actin/stress fiber rearrangement, suggesting βarrestin-2 participation in the regulation of actin-mediated synaptic plasticity for addictive substances like cocaine. The effects of ghrelin receptor ligands on reward strongly suggest that modulation of ghrelin signaling could provide an effective strategy to ameliorate undesirable behaviors arising from addiction. To investigate this possibility, we tested the effects of ghrelin receptor antagonism in a cocaine behavioral sensitization paradigm using DA neuron-specific βarrestin-2 KO mice. Our results show that these mice sensitize to cocaine as well as wild-type littermates. The βarrestin-2 KO mice, however, no longer respond to the locomotor attenuating effects of the GHSR1a antagonist YIL781. The data presented here suggest that the separate stages of addictive behavior differ in their requirements for βarrestin-2 and show that pharmacological inhibition of βarrestin-2 function through GHSR1a antagonism is not equivalent to the loss of βarrestin-2 function achieved by genetic ablation. These data support targeting GHSR1a signaling in addiction therapy but indicate that using signaling biased compounds that modulate βarrestin-2 activity differentially from G protein activity may be required. [ABSTRACT FROM AUTHOR]

The article presents the discussion on G protein–coupled receptors (GPCRs), a superfamily of seven transmembrane-spanning receptors. Topics include canonical signaling mechanisms of GPCRs involve coupling to specific G protein subtypes as well as b-arrestin adaptor proteins; promoting the own intracellular signaling events such as extracellular signal–regulated kinase (ERK) activity; and improving the desired pharmacological properties of drugs.