Understanding the biological mechanisms that link HIV infection, methamphetamine dependence and consequent changes in the serotonin system that correlate to depression, stress and disruption of the hypothalamic-pituitary-adrenal axis is critical to designing new preventative and therapeutic strategies for both HIV infection and methamphetamine addiction, which have a high co-morbidity. While polymorphic variations in genes that encode the key modulators of the serotonin system, including the serotonin transporter (5-HTT), monoamine oxidase A (MAOA) and tryptophan hydroxylase 2 (TPH2) have been well-documented, epigenetic regulation of these genes is poorly understood. Epigenetics, which is defined as changes in gene expression that take place without a change in DNA sequence, is known to contribute to tissue-type and developmental stage specific gene expression, via an array of molecular modifications to both DNA and chromatin and non- coding RNAs. Borne out of a line of evidence generated in our lab, this grant explores the hypothesis that epigenetic regulation of TPH2, which codes for the rate limiting enzyme in brain serotonin synthesis, may in particular be an underlying mechanism by which HIV infection and METH dependence can cause changes in the serotonin system that lead to altered HPA axis function, neural-immune dysregulation, depression, complications for clinical treatment and ultimately, higher incidence of HIV infection, addiction and mortality. We have recently demonstrated that TPH2 5'-UTR harbors an antisense promoter, which transcribes a non- coding RNA in vitro (Chen and Miller, 2009).
In Specific Aim 1, we will validate the existence of this transcript and assess its involvement in the regulation of TPH2 gene expression. We will also assess the involvement of DNA methylation and CCCTC-binding factor (CTCF) in the regulation of TPH2 gene expression. Epigenetic mechanisms are involved in spatiotemporal expression of numerous genes, as well as in environmental regulation of gene expression. Accordingly, Specific Aim 2 will investigate the role of epigenetic modification in the tissue-specific and developmental stage expression of the serotonergic genes, TPH2, 5-HTT and MAOA, as well as in the potential epigenetic regulation of those genes by specific cytokines and methamphetamine.
In Specific Aim 3, we will assess the effect of SIV infection and methamphetamine on the epigenetic modification of the serotonergic genes, by comparing DNA methylation of serotonergic genes in postmortem tissues of SIV+ and SIV- rhesus monkeys. We will also perform a pilot study to explore whether methamphetamine exposure in SIV-infected rhesus monkeys exacerbates epigenetic modification of serotonergic genes. We anticipate that findings of this project will help us to better understand underlying biological mechanisms, develop new strategies to manipulate serotonin neurotransmission so as to treat HIV- and methamphetamine- associated neuropsychiatric disturbances better, reduce the spread of HIV and mortality among HIV+ patients, and enhance treatment strategies for methamphetamine addiction and HIV co-morbidity.
Project Narrative Understanding the link between HIV, methamphetamine abuse and changes in the serotonin system is critical to designing new preventative and therapeutic strategies for both AIDS and methamphetamine addiction, which have high co-morbidity. This project will investigate the epigenetic regulation of serotonin neurotransmission and its relevance to HIV and methamphetamine abuse. We anticipate that the research findings generated from this project will provide new insights into the regulation of the serotonin system and will lead to new strategies to treat HIV-infection and methamphetamine addiction and their co-morbidity.
