Roles for histone monoaminylation in cocaine-induced transcriptional and behavioral plasticity

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Project Summary: Maze, IS, Ph.D. Persistent changes in neuronal gene expression promote physiological alterations implicated in a wide variety of human neurodevelopmental and adult psychiatric disorders. More recently, cell-type and brain region specific `epigenetic' mechanisms have been demonstrated to regulate transcriptional programs contributing to addiction-like behaviors; however, our understanding of how these mechanisms mediate life-long addiction remains limited. Monoaminergic neurotransmission in the central nervous system plays a critical role in psychostimulant-induced neural plasticity, with alterations in monoamine production/function being implicated in both the development and treatment of substance abuse disorders. Although packaging of monoamines by the vesicular monoamine transporter is essential for numerous aspects of reward, recent data have demonstrated the additional presence of `reserve' pools of extravesicular monoamines in the nucleus of monoamine producing neurons. Dopamine, as well as other monoamines, has previously been shown to form covalent bonds with certain cytoplasmic proteins catalyzed by the tissue Transglutaminase 2 enzyme. We recently identified histone proteins – histones are highly abundant, post-translationally modified proteins, which constitute the building blocks of eukaryotic chromatin and form the fundamental repeating units of transcription in mammalian cells – as robust substrates for monoaminylation in brain. Our data indicate that histone H3 dopaminylation likely acts to potentiate binding of adjacent histone posttranslational modification (PTM) interacting proteins (`readers') and may play a direct and critical role in dopaminergic neuronal transcription. Furthermore, our data demonstrate that chronic withdrawal from volitional administration of extended access to cocaine in rodents results in high levels of dopamine accumulation in the nucleus of dopamine producing neurons in the ventral tegmental area (an important structure within the mesolimbic reward circuitry), as well as increased cytoplasmic to nuclear shuttling of TGM2, the H3 dopaminylase. Take together, these data suggest that persistent states of addiction may result from increased genomic enrichment of H3 dopaminylation, potentiation of aberrant transcriptional plasticity and increased drug seeking behaviors. Using a unique combination of chromatin biochemistry, chemical biology, genome-wide and functional neurobiological approaches, we plan to fully characterize the functions of histone dopaminylation, both in the context of normal neuronal function and in ethologically valid rodent models of drug abuse; understanding these highly novel molecular phenomena promises to provide new insights into the underlying mechanisms of drug addiction, and aims to identify novel targets for the development of more effective therapeutics. Lastly, given the fundamental role other monoaminergic systems (e.g., serotonin, norepinephrine) in addiction, we believe that this `paradigm shifting' work will serve as a launching pad for countless future investigations aimed at fully delineating the `epigenetic' mechanisms at play in the development of substance abuse disorders.