Profiling the Serotonin2 Receptor System Functional Capacity: Towards Identification of a Cocaine Use Disorder Biosignature
Vulnerability to developing a cocaine use disorder (CUD) starts with a background of genetics and environment and results in changes in neuroplasticity that leads to a greater drive to take cocaine. The intricate interplay between these variables differs for each individual, presenting a barrier to understanding the origin of the disorder as well as the development of treatments. Characterization of a CUD biosignature through the use of defining biological markers will greatly improve our ability to predict patient response, disease risk, accurate CUD diagnosis and potentially even identify novel targets for medications development, all the while moving CUD treatment towards an age of precision medicine. The cycling progressive nature of CUD stymies efforts to stay abstinent with vulnerability to abuse and relapse during abstinence often precipitated by impulsive behavior. The loss of impulse control has been particularly noted in cocaine-dependent subjects who also express high reactivity to cocaine-associated cues (“cue reactivity”) suggesting that impulsivity and cue reactivity are interlocked contributors to relapse, a cardinal facet of addiction. Serotonin (5-HT) neurotransmission through the 5-HT2C receptor (5-HT2CR) and 5-HT2A receptor (5-HT2AR) within the central nervous system is a critical driver of the cognitive and/or behavioral dimensions underlying impulsivity and cue reactivity. Characterization of how these receptors are regulated or altered by genetic and epigenetic means will lead to the identification of a 5-HT2R-mediate biosignature for CUD. To bridge this gap in knowledge, we first investigated the functional effects of a single nucleotide polymorphism (SNP) of the 5-HT2CR that converts a cysteine (Cys) to a serine (Ser) at amino acid codon 23 in the N-terminal extracellular domain (Cys23Ser; rs6318). We established that the Cys23Ser SNP dramatically reduces efficacy of 5-HT at the 5-HT2CR with a decrease in potency as a result of reduced plasma membrane expression from altered localization through the secretory and recycling pathway. We also demonstrate in vivo, that overexpressing the human Ser23 5-HT2CR in the medial prefrontal cortex, a key region implicated in relapse-like behaviors, of rodents exhibit dampened cocaine-seeking behavior accompanied by greater plasma membrane expression of the 5-HT2CR versus rodents expressing the Cys23 5-HT2CR. Finally, we characterized methylation patterns of the HTR2A, 5-HT2AR human gene, promoter that correlated with relapse-related behavior in cocaine-dependent participants. Taken together, we have identified genetic and epigenetic makers of the 5-HT2R system with great potential to define a high-risk relapse biosignature of CUD.
Biology, Neuroscience, Biology, Molecular, Biology, Genetics
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The University of Texas Medical Branch at Galveston