Structural Analysis of Alcohol-dependent Activation of GIRKs

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Summary With approximately ninety thousand alcohol-related deaths per year, alcohol is the third leading preventable cause of death in the United States. Alcohol (ethanol) is addictive and produces complex effects on the body, primarily through its interactions within the central nervous system. The structural, cellular and circuit mechanisms by which ethanol imparts its effects on the brain and leads to alcohol use disorders (AUDs) are poorly understood. A large number of studies have demonstrated that ethanol directly alters the function of ion channels, such as the G protein-gated inwardly rectifying potassium (GIRK) channel. Studies of GIRK channel knockout mice and human GWAS also implicate GIRK channels in mediating some of the effects of ethanol in the brain. However, current pharmacological tools for selectively modulating GIRK channels are limited. The overall objectives of this grant are to elucidate how ethanol alters brain function and identify new ligands for treating AUD. Previously, we identified and characterized a GIRK activator, called GiGA1, which selectively activates GIRK1/GIRK2 channels, does not require G proteins, reduces the excitability of neurons via activation of endogenously expressed GIRK channels, and exhibits anti-convulsant properties. GiGA1 has not been thoroughly tested in the context of AUD, however. Here, we hypothesize that GiGA1 activation of GIRK1/2 channels will mitigate some of the deleterious effects of alcohol on brain reward circuits. Specifically, we will evaluate the effects of GiGA1 on alcohol-regulated behaviors (conditioned place preference, binge drinking, and ethanol intake escalation induced by chronic intermittent ethanol vapor inhalation), determine actions of GiGA1 on alcohol-regulated circuits in the NAc using in vivo fiber photometry to measure activity and release of neurotransmitters, and develop GIRK2-selective small molecule modulators. Currently, there is a limited number of FDA approved drugs for treating alcoholism and an urgent need for new approaches for treating AUD. Defining the physical pocket for ethanol has been critical for understanding how the binding of ethanol to a channel can lead to changes in channel activity and affect brain function. Now, bridging earlier studies on how ethanol activates GIRK channels via the alcohol pocket and extending to an innovative approach of using structural biology to guide screening and selection of novel therapeutics, we are advancing compounds that directly activate subtypes of GIRK channels and probing their efficacy in mouse models of AUDs.