Mutation of putative GRK phosphorylation sites in the cannabinoid receptor 1 (CB1R) confers resistance to cannabinoid tolerance and hypersensitivity to cannabinoids in mice.
Daniel J Morgan, Brian J Davis, Chris S Kearn, David Marcus, Alex J Cook, Jim Wager-Miller, Alex Straiker, Michael H Myoga, Jeffrey Karduck, Emma Leishman, Laura J Sim-Selley, Traci A Czyzyk, Heather B. Bradshaw, Dana E Selley, Ken Mackie
Journal of Neuroscience April 9, 2014 DOI: 10.1523/jneurosci.3445-12.2014 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Animal study using a genetic knock-in mouse model Peer reviewed |
|---|---|
| Population | Mice with S426A/S430A mutations in the CB1 receptor, compared with wild-type mice |
| Duration | 7 days of Δ9-THC treatment for desensitization experiments |
| Topics | Cannabis |
| Keywords | Cb1 Gpcr Cannabinoid Desensitization Tolerance |
| Key points | Mutating two CB1R phosphorylation sites (S426 and S430) in mice increased acute sensitivity to Δ9-THC, delayed tolerance, and increased dependence, while eliminating CB1R desensitization in the periaqueductal gray and spinal cord after 7 days of Δ9-THC. The authors argue these sites play major roles in cannabinoid tolerance and dependence and propose the mutant mice as a model for studying excessive endocannabinoid signaling. |
Abstract
For many G-protein-coupled receptors (GPCRs), including cannabinoid receptor 1 (CB1R), desensitization has been proposed as a principal mechanism driving initial tolerance to agonists. GPCR desensitization typically requires phosphorylation by a G-protein-coupled receptor kinase (GRK) and interaction of the phosphorylated receptor with an arrestin. In simple model systems, CB1R is desensitized by GRK phosphorylation at two serine residues (S426 and S430). However, the role of these serine residues in tolerance and dependence for cannabinoids in vivo was unclear. Therefore, we generated mice where S426 and S430 were mutated to nonphosphorylatable alanines (S426A/S430A). S426A/S430A mutant mice were more sensitive to acutely administered delta-9-tetrahydrocannabinol (Δ(9)-THC), have delayed tolerance to Δ(9)-THC, and showed increased dependence for Δ(9)-THC. S426A/S430A mutants also showed increased responses to elevated levels of endogenous cannabinoids. CB1R desensitization in the periaqueductal gray and spinal cord following 7 d of treatment with Δ(9)-THC was absent in S426A/S430A mutants. Δ(9)-THC-induced downregulation of CB1R in the spinal cord was also absent in S426A/S430A mutants. Cultured autaptic hippocampal neurons from S426A/S430A mice showed enhanced endocannabinoid-mediated depolarization-induced suppression of excitation (DSE) and reduced agonist-mediated desensitization of DSE. These results indicate that S426 and S430 play major roles in the acute response to, tolerance to, and dependence on cannabinoids. Additionally, S426A/S430A mice are a novel model for studying pathophysiological processes thought to involve excessive endocannabinoid signaling such as drug addiction and metabolic disease. These mice also validate the approach of mutating GRK phosphorylation sites involved in desensitization as a general means to confer exaggerated signaling to GPCRs in vivo.
Comparable studies
Other preclinical and animal studies on cannabis, most cited first.
Citations in the library
Cited by 2
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