Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects
There are two well-characterized cannabinoid receptors (CB1R and CB2R and other candidates): the central nervous system (CNS) enriched CB1R and peripheral tissue enriched CB2R with a wide dynamic range of expression levels in different cell types of human tissues. Hepatocytes and neurons express low...
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MDPI AG
2020-12-01
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| Series: | International Journal of Molecular Sciences |
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| author | Qing-Rong Liu Ana Canseco-Alba Ying Liang Hiroki Ishiguro Emmanuel S. Onaivi |
| author_facet | Qing-Rong Liu Ana Canseco-Alba Ying Liang Hiroki Ishiguro Emmanuel S. Onaivi |
| author_sort | Qing-Rong Liu |
| collection | DOAJ |
| description | There are two well-characterized cannabinoid receptors (CB1R and CB2R and other candidates): the central nervous system (CNS) enriched CB1R and peripheral tissue enriched CB2R with a wide dynamic range of expression levels in different cell types of human tissues. Hepatocytes and neurons express low baseline CB1R and CB2R, respectively, and their cell-type-specific functions are not well defined. Here we report inducible expression of CB1R in the liver by high-fat and high sugar diet and CB2R in cortical neurons by methamphetamine. While there is less controversy about hepatocyte CB1R, the presence of functional neuronal CB2R is still debated to date. We found that neuron CB2R basal expression was higher than that of hepatocyte CB1R by measuring mRNA levels of specific isoform CB2A in neurons isolated by fluorescence-activated cell sorting (FACS) and CB1A in hepatocytes isolated by collagenase perfusion of liver. For in vivo studies, we generated hepatocyte, dopaminergic neuron, and microglia-specific conditional knockout mice (Abl-Cnr1<sup>Δ</sup>, Dat-Cnr2<sup>Δ</sup>, and Cx3cr1-Cnr2<sup>Δ</sup>) of CB1R and CB2R by crossing Cnr1<sup>f/f</sup> and Cnr2<sup>f/f</sup> strains to Abl-Cre, Dat-Cre, and Cx3cr1-Cre deleter mouse strains, respectively. Our data reveals that neuron and microglia CB2Rs are involved in the “tetrad” effects of the mixed agonist WIN 55212-2, CB1R selective agonist arachidonyl-2′-chloroethylamide (ACEA), and CB2R selective agonist JWH133. Dat-Cnr2<sup>Δ</sup> and Cx3cr1-Cnr2<sup>Δ</sup> mice showed genotypic differences in hypomobility, hypothermia, analgesia, and catalepsy induced by the synthetic cannabinoids. Alcohol conditioned place preference was abolished in DAT-Cnr2<sup>Δ</sup> mice and remained intact in Cx3cr1-Cnr2<sup>Δ</sup> mice in comparison to WT mice. These Cre-loxP recombinant mouse lines provide unique approaches in cannabinoid research for dissecting the complex endocannabinoid system that is implicated in many chronic disorders. |
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| spelling | doaj.art-32aa7a4da0334d529fe741f461d0b4a12023-11-21T01:53:29ZengMDPI AGInternational Journal of Molecular Sciences1661-65961422-00672020-12-012124976310.3390/ijms21249763Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad EffectsQing-Rong Liu0Ana Canseco-Alba1Ying Liang2Hiroki Ishiguro3Emmanuel S. Onaivi4Laboratory of Clinical Investigation, National Institute on Aging, Baltimore, MD 21224, USADepartment of Biology, William Paterson University, Wayne, NJ 07470, USACollege of Food Science and Engineering, Central South University of Forestry and Technology, Changsha 410004, Hunan, ChinaDepartment of Neuropsychiatry, Graduate School of Medical Science, University of Yamanashi, Chuo, Yamanashi 409-3898, JapanDepartment of Biology, William Paterson University, Wayne, NJ 07470, USAThere are two well-characterized cannabinoid receptors (CB1R and CB2R and other candidates): the central nervous system (CNS) enriched CB1R and peripheral tissue enriched CB2R with a wide dynamic range of expression levels in different cell types of human tissues. Hepatocytes and neurons express low baseline CB1R and CB2R, respectively, and their cell-type-specific functions are not well defined. Here we report inducible expression of CB1R in the liver by high-fat and high sugar diet and CB2R in cortical neurons by methamphetamine. While there is less controversy about hepatocyte CB1R, the presence of functional neuronal CB2R is still debated to date. We found that neuron CB2R basal expression was higher than that of hepatocyte CB1R by measuring mRNA levels of specific isoform CB2A in neurons isolated by fluorescence-activated cell sorting (FACS) and CB1A in hepatocytes isolated by collagenase perfusion of liver. For in vivo studies, we generated hepatocyte, dopaminergic neuron, and microglia-specific conditional knockout mice (Abl-Cnr1<sup>Δ</sup>, Dat-Cnr2<sup>Δ</sup>, and Cx3cr1-Cnr2<sup>Δ</sup>) of CB1R and CB2R by crossing Cnr1<sup>f/f</sup> and Cnr2<sup>f/f</sup> strains to Abl-Cre, Dat-Cre, and Cx3cr1-Cre deleter mouse strains, respectively. Our data reveals that neuron and microglia CB2Rs are involved in the “tetrad” effects of the mixed agonist WIN 55212-2, CB1R selective agonist arachidonyl-2′-chloroethylamide (ACEA), and CB2R selective agonist JWH133. Dat-Cnr2<sup>Δ</sup> and Cx3cr1-Cnr2<sup>Δ</sup> mice showed genotypic differences in hypomobility, hypothermia, analgesia, and catalepsy induced by the synthetic cannabinoids. Alcohol conditioned place preference was abolished in DAT-Cnr2<sup>Δ</sup> mice and remained intact in Cx3cr1-Cnr2<sup>Δ</sup> mice in comparison to WT mice. These Cre-loxP recombinant mouse lines provide unique approaches in cannabinoid research for dissecting the complex endocannabinoid system that is implicated in many chronic disorders.https://www.mdpi.com/1422-0067/21/24/9763cannabinoidsCre-loxP systemin situ hybridizationCB1 receptorCB2 receptorhepatocytes |
| spellingShingle | Qing-Rong Liu Ana Canseco-Alba Ying Liang Hiroki Ishiguro Emmanuel S. Onaivi Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects International Journal of Molecular Sciences cannabinoids Cre-loxP system in situ hybridization CB1 receptor CB2 receptor hepatocytes |
| title | Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects |
| title_full | Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects |
| title_fullStr | Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects |
| title_full_unstemmed | Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects |
| title_short | Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects |
| title_sort | low basal cb2r in dopamine neurons and microglia influences cannabinoid tetrad effects |
| topic | cannabinoids Cre-loxP system in situ hybridization CB1 receptor CB2 receptor hepatocytes |
| url | https://www.mdpi.com/1422-0067/21/24/9763 |
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