SU115 - GENETIC EFFECTS ON MU-OPIOID RECEPTOR LIGAND BIASED SIGNALING

Abstract

Background The mu-opioid receptor, a G Protein-Coupled Receptor (GPCR), has been shown to be associated with alcohol and substance use disorders. Specific genetic mutations have been shown, in our studies and those of others, to affect propensity towards addiction and pharmaceutical response; however, the mechanism responsible remains largely unknown. A better understanding could assist the development of personalized therapeutics. Recently, the role of ligand-biased downstream cellular signaling in mu receptors has become an active area of interest, but the role of genetic variation in this context has not been considered. In this study, we explore whether ligand-induced downstream signaling pathways are biased across mu-opioid receptor polymorphisms. Methods We are testing two Single Nucleotide Polymorphisms (SNPs) that change protein sequence, C17T and A118G, which exist on the N-terminal domain of the mu receptor and are common in human populations. Additionally, we are testing a rhesus macaque SNP, C77G, which appears to be functionally and behaviorally parallel. Here, we first transduce transcriptional response element inducible luciferase reporters from four pathways (NFkB, cAMP, MAPK/ERK, and MAPK/JNK) into multiple cell lines (SK-N-MC, CHO and HEK 293). We then transfect in a plasmid containing the specific variation of the mu opioid receptor and generate a concentration response curve with DAMGO, beta-endorphin, or morphine. Results Our previous work has demonstrated the effects of both human and rhesus polymorphisms on cAMP signaling pathways for morphine, DAMGO and beta-endorphin. For the NFkB signaling pathway, in both humans and rhesus macaques, significant differences in potency of morphine, beta-endorphin have been observed, but not DAMGO. Both human C17:G118 and T17:A118 have higher potencies for these ligands. A similar pattern is seen in the derived G77 allele in rhesus macaques. Discussion Preliminary data suggests that a mechanism by which polymorphisms in the mu opioid receptor exert their effects is through differential downstream signaling in addition to differential potencies. This has implications not only for understandings of the means by which the mu opioid receptor affects behaviors, but also for how genetic differences are likely to affect novel biased ligands.