G-protein-, beta-arrestin- and ERK-signaling in alcohol use- and anxiety-disorders

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Project summary/Abstract G-protein coupled receptors (GPCRs) have long been a favorite target of pharmaceutical companies for treatment of myriad diseases as they are easily accessible and ubiquitously expressed. The predominant signal transduction routes for GPCRs are through the namesake G-protein pathway and by interaction with β-arrestin-linked scaffolds. Several research groups, including my own, have identified that G- proteins and β-arrestins can each uniquely modulate types of behavior. The discovery that drugs acting at GPCRs can exhibit so-called functional selectivity [i.e. activate only one pathway and not the other] has provided new opportunities for development of signaling biased drugs with fewer adverse effects. While G-proteins and β-arrestins mostly provide a divergence of signaling cascades, a small set of enzymes ambiguously play roles in both pathways. Of particular interest is the mitogen activated protein kinase `ERK' (extracellular signal-regulated kinase). ERK function and dysfunction has been linked to many diseases and disorders such as cancer, depression and drug addiction. Numerous studies have been conducted investigating how G-proteins and β-arrestins regulate ERK activity in simple cellular models. However, due to a lack of specific tools it has been much harder to establish how G-protein- mediated and β-arrestin-mediated ERK activation individually contribute to the modulation of behavior. Particularly it is of interest whether the total amount of ERK activation is the driving force behind the physiological effect, or whether the mechanism of activation (G-protein versus β-arrestin) is important. Recent pharmacological advances are now allowing us to propose experiments that will enable the dissection of G-protein and β-arrestin ERK activation in behavioral assays. For this proposal we will use G-protein and β-arrestin-biased drugs acting on delta opioid receptors as well as utilize innovative chemogenetic approaches to address our research questions. Our prior studies investigating delta opioid receptors have revealed that G-protein-biased drugs at this receptor can reduce alcohol use, whereas those delta opioids that activate ERK reduce anxiety. Upon completion of this study we will be able to address fundamental questions regarding signaling biased ERK activation related to alcohol use and anxiety-like behavior. More importantly, we will be able to describe `how biased' a delta opioid receptor drug must be and how /how much ERK it should be able to activate in order to efficaciously reduce alcohol use and anxiety, simultaneously. Such a drug would be very valuable given that alcohol use disorders are highly co-morbid with general anxiety disorders and post-traumatic stress disorders. Additionally, alcohol withdrawal induced anxiety is a major contributor to relapse and thus a bi-functional delta opioid drug would be a significantly better therapeutic option for patients suffering from alcohol use disorders than the currently available treatment options.