Mu opioid receptors play a fundamental role in mediating the actions of morphine and most clinical analgesics, as well as drugs of abuse, such as heroin. The single-copy mu opioid receptor gene (OPRM1) creates an array of splicing variants by undergoing extensive alternative pre-mRNA splicing (AS), that is conserved from rodents to humans. These splice variants are categorized into three types based on receptor structure: 1) Full- length carboxyl (C-) terminal variants with 7-transmembrane (TM) domains; 2) Truncated variants containing 6- TM domains; and 3) Truncated variants containing single TM. Increasing evidence suggests that the OPRM1 AS variants are pharmacologically important. Several C-terminal variants display marked differences in region- specific expression, mu agonist-induced G protein coupling, phosphorylation, internalization and post- endocytic sorting. MOR-1D is responsible for morphine-induced itch. Dysregulation of several variant mRNA expressions has been observed in a number of cell and animal models, as well as human diseases. Evidence from our three knockout mouse models suggest that individual C-terminal sequences generated through alternative 3' splicing play distinct roles in various morphine actions, including tolerance, physical dependence and reward. Additionally, intracerebroventricular (i.c.v.) administration of an antisense vivo-morpholino antisense oligo, which blocks 3' splicing from exon 3 to exon 7, significantly attenuates morphine tolerance in mice. Together, these studies not only strongly support our hypothesis that OPRM1 alternative splicing contributes to the regulation of complex opioid actions in animals and humans, but also provide a compelling rationale and scientific premise for further study of the molecular mechanisms controlling OPRM1 alternative splicing and assessing the impact of modulating OPRM1 alternative splicing using antisense vivo-morpholino oligos on morphine actions, as proposed in this application. The primary goal of this application is to further investigate mechanisms and functions of OPRM1 gene alternative splicing by using a variety of in vitro and in vivo approaches.
The specific aims i nclude: 1) Decoding molecular mechanisms underlying OPRM1 3' splicing by identifying cis-acting elements and trans-acting factors that regulate the 3' splicing; 2) Investigating the role of the OPRM1 3' splicing in mu opioid actions in both Be(2)C cells and mice using an antisense vivo- morpholino oligo approach. The proposed studies promise to generate significant insights into the mechanism and function of OPRM1 3' splicing, and may have the potential for developing new therapeutics for controlling pain and alleviating the detrimental side-effects of mu opioids.

Public Health Relevance

Mu opioids, such as morphine and heroin, act through the mu opioid receptor. The single-copy mu opioid receptor gene (OPRM1) undergoes extensive alternative pre-mRNA splicing, creating an array of splice variants or isoforms that play important roles in complex actions of mu opioid in animals and humans. The proposed studies aim to investigate mechanism and functions of OPRM1 alternative splicing, and provide potential targets for developing novel therapeutics for the treatment of pain and drug abuse.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA042888-03
Application #
9695967
Study Section
Molecular Neurogenetics Study Section (MNG)
Program Officer
Lossie, Amy C
Project Start
2017-09-01
Project End
2022-05-31
Budget Start
2019-06-01
Budget End
2020-05-31
Support Year
3
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Sloan-Kettering Institute for Cancer Research
Department
Type
DUNS #
064931884
City
New York
State
NY
Country
United States
Zip Code
10065
Lu, Zhigang; Xu, Jin; Xu, Mingming et al. (2018) Truncated ?-Opioid Receptors With 6 Transmembrane Domains Are Essential for Opioid Analgesia. Anesth Analg 126:1050-1057
Huang, Xi-Ping; Che, Tao; Mangano, Thomas J et al. (2017) Fentanyl-related designer drugs W-18 and W-15 lack appreciable opioid activity in vitro and in vivo. JCI Insight 2: