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Cannabinoid Tolerance in S426A/S430A x β-Arrestin 2 Knockout Double-Mutant Mice
Mary K Piscura1, Diana E Sepulveda1, Malabika Maulik1
1Department of Biomedical Sciences, Marshall University, Huntington, West Virginia (M.K.P., M.M., A.N.H.-R., D.J.M.); Department of Pharmacology (D.E.S.) and Graduate Program in Anatomy (M.K.P.), Penn State University College of Medicine, Hershey, Pennsylvania; and Department of Pharmacology and Neuroscience (J.G.) and Center of Excellence for Translational Neuroscience and Therapeutics (J.G.), Texas Tech University Health Sciences Center, Lubbock, Texas.
Tolerance to cannabinoid drugs involves G protein-coupled receptor (GPCR) desensitization. This study shows that specific phosphorylation sites (S426 and S430) on the cannabinoid type-1 receptor (CB1R) are key to beta-arrestin2-mediated desensitization and tolerance.
Area of Science:
- Pharmacology
- Neuroscience
- Molecular Biology
Background:
- Tolerance to cannabinoid drugs, like those targeting G protein-coupled receptors (GPCRs) such as the cannabinoid type-1 receptor (CB1R), is partly mediated by receptor desensitization.
- CB1R desensitization involves phosphorylation at S426 and S430 residues by a GPCR kinase, followed by beta-arrestin2 recruitment.
- Previous studies indicated reduced tolerance in S426A/S430A mutant and beta-arrestin2 knockout mice, but the role of these specific sites in overall beta-arrestin2-mediated desensitization remained unclear due to other phosphorylatable residues.
Purpose of the Study:
- To investigate whether phosphorylation of CB1R residues S426 and S430 fully accounts for beta-arrestin2-mediated desensitization and tolerance.
- To assess the acute response and tolerance to cannabinoids delta-9-tetrahydrocannabinol (Δ9-THC) and CP55,940 in double-mutant mice lacking both S426/S430 phosphorylation and beta-arrestin2.
Main Methods:
- Generation and analysis of S426A/S430A x beta-arrestin2 knockout double-mutant mice.
- Assessment of acute antinociceptive and hypothermic responses to cannabinoids (Δ9-THC and CP55,940) in wild-type, single-mutant, and double-mutant mice.
- Evaluation of cannabinoid tolerance development following chronic dosing in different mouse models.
Main Results:
- Male S426A/S430A single- and double-mutant mice exhibited delayed tolerance and increased sensitivity to CP55,940's antinociceptive and hypothermic effects compared to wild-type mice.
- Female S426A/S430A single- and double-mutant mice showed increased sensitivity to acute antinociception (CP55,940 and Δ9-THC) and hypothermia (CP55,940 only) after chronic dosing, but no difference in tolerance development.
- Double-mutant mice did not differ from S426A/S430A single-mutant mice regarding cannabinoid tolerance and sensitivity, suggesting S426/S430 phosphorylation is critical for beta-arrestin2-mediated desensitization.
Conclusions:
- Phosphorylation of CB1R residues S426 and S430 is likely the primary mechanism for beta-arrestin2-mediated desensitization and subsequent cannabinoid tolerance.
- Further deletion of beta-arrestin2 does not enhance the tolerance delay observed in CB1R S426A/S430A mutant mice.
- Cannabinoid effects, including antinociception and hypothermia, are dependent on sex, specific agonist, and duration of treatment.
