The OPRM1 A118G single nucleotide polymorphism (SNP rs1799971) gene variant encoding the N40D µ-opioid receptor (MOR) has been associated with dependence on opiates and other drugs of abuse but its mechanism is unknown. The frequency of G-allele carriers is ~40% in Asians, ~16% in Europeans, and ~3% in African-Americans. With opioid abuse-related deaths rising at unprecedented rates, understanding these mechanisms may provide a path to therapy. Here we generated homozygous N40D subject-specific induced inhibitory neuronal cells (iNs) from seven human-induced pluripotent stem (iPS) cell lines from subjects of European descent (both male and female) and probed the impact of N40D MOR regulation on synaptic transmission. We found that D40 iNs exhibit consistently stronger suppression (versus N40) of spontaneous inhibitory postsynaptic currents (sIPSCs) across multiple subjects. To mitigate the confounding effects of background genetic variation on neuronal function, the regulatory effects of MORs on synaptic transmission were recapitulated in two sets of independently engineered isogenic N40D iNs. In addition, we employed biochemical analysis and observed differential N-linked glycosylation of human MOR N40D. This study identifies neurophysiological and molecular differences between human MOR variants that may predict altered opioid responsivity and/or dependence in this subset of individuals.
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We thank RUCDR Infinite Biologics for generating the iPS cells from human subjects and assisting with CRISPR/Cas9 gene targeting on 03SF iPS cell line. We also want to thank Dr. Davide Comoletti for the help of biochemical analysis. Research is supported by grants from NIH-NIAAA R01 AA023797 as well as Collaborative Studies on the Genetics of Alcoholism/COGA 5U10AA008401-26. AH is supported by NIH-NIAAA NRSA F31AA024033. MSS is supported by NIH-NIAAA T32 AA028254. We are grateful to the members of the Collaborative Genetic Study of Nicotine Dependence (COGEND) for the selection of human subjects, and we are grateful to the deidentified individuals who contributed tissue to the study. Pang laboratory at CHINJ is partly supported by a grant from the RWJ Foundation.
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Halikere, A., Popova, D., Scarnati, M.S. et al. Addiction associated N40D mu-opioid receptor variant modulates synaptic function in human neurons. Mol Psychiatry 25, 1406–1419 (2020). https://doi.org/10.1038/s41380-019-0507-0
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