Cannabinoid receptor 2
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Location (UCSC) | Chr 1: 23.87 – 23.91 Mb | Chr 4: 135.62 – 135.65 Mb | |||||||
PubMed search | [3] | [4] |
View/Edit Human | View/Edit Mouse |
The cannabinoid receptor 2 (CB2), is a
CB2 was
Structure
The CB2 receptor is encoded by the CNR2 gene.
As is commonly seen in G protein-coupled receptors, the CB2 receptor has seven transmembrane spanning domains,
The human CB1 and the CB2 receptors possess approximately 44% amino acid similarity.
Mechanism
Like the CB1 receptors, CB2 receptors inhibit the activity of
Five recognized
Expression
Dispute
Originally it was thought that the CB2 receptor was only expressed in peripheral tissue while the CB1 receptor is the endogenous receptor on neurons. Recent work with immunohistochemical staining has shown expression within neurons. Subsequently, it was shown that CB2 knock out mice produced the same immunohistochemical staining, indicating the presence of the CB2 receptor where none was expressed. This has created a long history of debate as to whether the CB2 receptor is expressed in the CNS. A new mouse model was described in 2014 that expresses a fluorescent protein whenever CB2 is expressed within a cell. This has the potential to resolve questions about the expression of CB2 receptors in various tissues.[20]
Immune system
Initial investigation of CB2 receptor expression patterns focused on the presence of CB2 receptors in the peripheral tissues of the
Brain
Further investigation into the expression patterns of the CB2 receptors revealed that CB2 receptor gene transcripts are also expressed in the brain, though not as densely as the CB1 receptor and located on different cells.[22] Unlike the CB1 receptor, in the brain, CB2 receptors are found primarily on microglia.[21][23] The CB2 receptor is expressed in some neurons within the central nervous system (e.g.; the brainstem), but the expression is very low.[24][25] CB2s are expressed on some rat retinal cell types.[26] Functional CB2 receptors are expressed in neurons of the ventral tegmental area and the hippocampus, arguing for a widespread expression and functional relevance in the CNS and in particular in neuronal signal transmission.[27][28]
Gastrointestinal system
CB2 receptors are also found throughout the
Peripheral nervous system
Application of CB2-specific antagonists has found that these receptors are also involved in mediating analgesic effects in the peripheral nervous system. However, these receptors are not expressed by nociceptive sensory neurons, and at present are believed to exist on an undetermined, non-neuronal cell. Possible candidates include mast cells, known to facilitate the inflammatory response. Cannabinoid mediated inhibition of these responses may cause a decrease in the perception of noxious-stimuli.[8]
Function
Immune system
Primary research on the functioning of the CB2 receptor has focused on the receptor's effects on the immunological activity of
Later studies examining the effect of synthetic cannabinoid agonist JWH-015 on CB2 receptors revealed that changes in cAMP levels result in the phosphorylation of leukocyte receptor tyrosine kinase at Tyr-505, leading to an inhibition of T cell receptor signaling. Thus, CB2 agonists may also be useful for treatment of inflammation and pain, and are currently being investigated, in particular for forms of pain that do not respond well to conventional treatments, such as neuropathic pain.[37] Consistent with these findings are studies that demonstrate increased CB2 receptor expression in the spinal cord, dorsal root ganglion, and activated microglia in the rodent neuropathic pain model, as well as on human hepatocellular carcinoma tumor samples.[38]
CB2 receptors have also been implicated in the regulation of homing and retention of
Clinical applications
CB2 receptors may have possible therapeutic roles in the treatment of neurodegenerative disorders such as
Changes in endocannabinoid levels and/or CB2 receptor expressions have been reported in almost all diseases affecting humans,[43] ranging from cardiovascular, gastrointestinal, liver, kidney, neurodegenerative, psychiatric, bone, skin, autoimmune, lung disorders to pain and cancer. The prevalence of this trend suggests that modulating CB2 receptor activity by either selective CB2 receptor agonists or inverse agonists/antagonists depending on the disease and its progression holds unique therapeutic potential for these pathologies [43]
Modulation of cocaine reward
Researchers investigated the effects of CB2 agonists on cocaine self-administration in mice. Systemic administration of JWH-133 reduced the number of self-infusions of cocaine in mice, as well as reducing locomotor activity and the break point (maximum amount of level presses to obtain cocaine). Local injection of JWH-133 into the nucleus accumbens was found to produce the same effects as systemic administration. Systemic administration of JWH-133 also reduced basal and cocaine-induced elevations of extracellular dopamine in the nucleus accumbens. These findings were mimicked by another, structurally different CB2 agonist, GW-405,833, and were reversed by the administration of a CB2 antagonist, AM-630.[44]
Ligands
Many selective ligands for the CB2 receptor are now available.[45]
Agonists
Partial agonists
Unspecified efficacy agonists
Herbal
Inverse agonists
Binding affinities
CB1 affinity (Ki) | Efficacy towards CB1 | CB2 affinity (Ki) | Efficacy towards CB2 | Type | References | |
---|---|---|---|---|---|---|
Anandamide | 78 nM | Partial agonist | 370 nM | Partial agonist | Endogenous | |
N-Arachidonoyl dopamine | 250 nM | Agonist | 12000 nM | ? | Endogenous | [48] |
2-Arachidonoylglycerol | 58.3 nM | Full agonist | 145 nM | Full agonist | Endogenous | [48] |
2-Arachidonyl glyceryl ether | 21 nM | Full agonist | 480 nM | Full agonist | Endogenous | |
Tetrahydrocannabinol | 10 nM | Partial agonist | 24 nM | Partial agonist | Phytogenic | [49] |
EGCG
|
33.6 μM | Agonist | >50 μM | ? | Phytogenic | [50] |
EGC | 35.7 μM | Agonist | >50 μM | ? | Phytogenic | [50] |
ECG | 47.3 μM | Agonist | >50 μM | ? | Phytogenic | [50] |
N-alkylamide | - | - | <100 nM | Partial agonist | Phytogenic | [51] |
β-Caryophyllene | - | - | <200 nM | Full agonist | Phytogenic | [51] |
Falcarinol | <1 μM | Inverse agonist | ? | ? | Phytogenic | [51] |
Rutamarin | - | - | <10 μM | ? | Phytogenic | [51] |
3,3'-Diindolylmethane | - | - | 1 μM | Partial Agonist | Phytogenic | [51] |
AM-1221 | 52.3 nM | Agonist | 0.28 nM | Agonist | Synthetic | [52] |
AM-1235 | 1.5 nM | Agonist | 20.4 nM | Agonist | Synthetic | [53] |
AM-2232 | 0.28 nM | Agonist | 1.48 nM | Agonist | Synthetic | [53] |
UR-144 | 150 nM | Full agonist | 1.8 nM | Full agonist | Synthetic | [54] |
JWH-007 | 9.0 nM | Agonist | 2.94 nM | Agonist | Synthetic | [55] |
JWH-015 | 383 nM | Agonist | 13.8 nM | Agonist | Synthetic | [55] |
JWH-018 | 9.00 ± 5.00 nM | Full agonist | 2.94 ± 2.65 nM | Full agonist | Synthetic | [55] |
Evolution
Paralogues
Source:[56]
- CNR1
- GPR12
- GPR6
- S1PR1
- S1PR4
- S1PR3
- S1PR5
- S1PR2
- LPAR1
- GPR3
- LPAR3
- LPAR2
- MC4R
- MC5R
- GPR119
- MC1R
- MC3R
- MC2R
References
- ^ a b c GRCh38: Ensembl release 89: ENSG00000188822 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000062585 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
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- ^ PMID 22048769.
- ^ "Entrez Gene: CNR2 cannabinoid receptor 2 (macrophage)".
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- PMID 18289088. Archived from the originalon 2013-01-12. Retrieved 2018-11-19.
- PMID 23960212.
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- ^ PMID 21079038.
- ^ "PDSP Database - UNC". Archived from the original on 8 November 2013. Retrieved 11 June 2013.
- ^ PMID 19897346.
- ^ PMID 20590562.
- ^ WO patent 200128557, Makriyannis A, Deng H, "Cannabimimetic indole derivatives", granted 2001-06-07
- ^ a b US patent 7241799, Makriyannis A, Deng H, "Cannabimimetic indole derivatives", granted 2007-07-10
- PMID 19921781.
- ^ PMID 10940540.
- ^ "GeneCards®: The Human Gene Database".
External links
- "Cannabinoid Receptors: CB2". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Archived from the original on 2012-03-05. Retrieved 2008-11-25.
- Cannabinoid Receptor 2 (CNR2) Human Protein Atlas
This article incorporates text from the United States National Library of Medicine, which is in the public domain.