Alcohol addiction is characterized by a loss of control over drinking, leading to the development of tolerance and physical dependence. Genetic and environmental factors have both been shown to play important roles in the development of alcohol addiction;however, the molecular mechanisms underlying excessive alcohol drinking are not yet fully understood. Alcohol appears to exert its effects through several signal transduction systems in the brain. Recently, the endocannabinoid (eCB) system has stood out among these systems in regards to its functional significance in alcohol addiction. It is well established that CB1 receptor stimulation increases alcohol consumption in rodents, while blockade of CB1 receptor function decreases this behavior. Several studies indicate that deletion of the neuropeptide Y (NPY) and NPY-Y1 receptor genes and lower NPY expression in the central nucleus of amygdala (CeA) promotes alcohol drinking behavior. The gene transcription factor cAMP responsive element-binding (CREB) protein is a common denominator for CB1 and NPY signaling and also plays a critical role in alcohol drinking behavior. Deletion of the CREB gene and a deficiency in CREB function in the shell of the nucleus accumbens (NAc Shell) and CeA have been associated with increased alcohol drinking behavior, while infusion of NPY into the CeA has been shown to increase CREB phosphorylation and decrease alcohol intake. The epigenetic mechanisms, due to histone modifications such as acetylation, appear to also be important in the regulation of gene expression, and may play critical roles in the mechanisms of alcohol and drug addiction. CREB activation recruits CREB binding protein (CBP) to transcriptional machinary, which catalyzes acetylation of histone H3 and histone H4 through its intrinsic histone acetyltransferase (HAT) activity thereby regulating gene expression. It is unknown if CB1 receptors and NPY systems interact with each other via CBP- mediated histone modifications in specific neurocircuitries that regulate alcohol drinking behavior. We hypothesize that CB1 receptor signaling interacts with the NPY system through CREB-CBP-mediated chromatin remodeling in the NAc and amygdala leading to the modulation of alcohol drinking behavior. The following Specific Aims will test this hypothesis: 1. To examine a) if decreased alcohol intake due to genetic deletion of the CB1 receptor is related to compensatory increases in the expression of CREB, pCREB, CBP, and also increases in histone (H3 and H4) acetylation and expression of NPY and the NPY-Y1 receptor and;b) if knock-down of CBP expression by siRNA infusion into the NAc shell and CeA attenuates HAT-induced histone acetylation (H3-K9 and H4- K8), and NPY and NPY-Y1 expression in CB1 -/- mice, thereby increasing alcohol drinking behavior. 2. To examine a) if decreased alcohol intake due to pharmacological blockade of CB1 receptors is related to increases in the expression of CREB, pCREB and CBP, and increases in acetylation of histones (H3 and H4) and expression of NPY and NPY-Y1 receptors and;b) if knock-down of CBP expression by siRNA infusion into the NAc shell or CeA attenuates HAT-induced histone acetylation (H3-K9 and H4-K8) and NPY, and NPY-Y1 receptor expression in wild-type mice treated with CB1 receptor antagonists, thereby resulting in increased alcohol drinking behavior.
This aim will also test if pharmacological activation of the CB1 receptor decreases the expression of the proposed target molecules and increases alcohol consumption. The findings of the proposed studies might lead to the development of effective pharmacotherapies for alcoholism by targeting two important neuromediators (CB1 and NPY) implicated in alcohol drinking behavior.
The interaction of genes with environmental factors may be involved in the development of alcoholism. The proposed research will take an innovative multidirectional approach in examining the relationship between alcohol drinking behaviors and dysregulation of the CB1 receptor-mediated intracellular signaling pathway leading to epigenetic modifications and will identify novel cellular targets that can be used to develop future therapeutic agents in treating alcoholism.