Laboratory of Clinical Investigation, National Institute on Aging, Baltimore, MD 21224, USA.
Department of Biology, William Paterson University, Wayne, NJ 07470, USA.
Int J Mol Sci. 2020 Dec 21;21(24):9763. doi: 10.3390/ijms21249763.
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, Dat-Cnr2, and Cx3cr1-Cnr2) of CB1R and CB2R by crossing Cnr1 and Cnr2 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 and Cx3cr1-Cnr2 mice showed genotypic differences in hypomobility, hypothermia, analgesia, and catalepsy induced by the synthetic cannabinoids. Alcohol conditioned place preference was abolished in DAT-Cnr2 mice and remained intact in Cx3cr1-Cnr2 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.
有两种特征明确的大麻素受体（CB1R 和 CB2R 及其他候选受体）：富含中枢神经系统（CNS）的 CB1R 和富含外周组织的 CB2R，在人类组织的不同细胞类型中具有广泛的表达水平动态范围。肝细胞和神经元分别表达低基线 CB1R 和 CB2R，但其细胞类型特异性功能尚未明确界定。在这里，我们报告高脂肪和高糖饮食诱导肝脏 CB1R 的表达，以及安非他命诱导皮质神经元 CB2R 的表达。虽然对于肝细胞 CB1R 存在的争议较少，但迄今为止，功能性神经元 CB2R 的存在仍存在争议。我们通过测量通过荧光激活细胞分选（FACS）分离的神经元中特定异构体 CB2A 的 mRNA 水平和通过胶原酶灌注肝脏分离的肝细胞中 CB1A 的 mRNA 水平，发现神经元 CB2R 的基础表达高于肝细胞 CB1R。对于体内研究，我们通过将 Cnr1 和 Cnr2 株分别与 Abl-Cre、Dat-Cre 和 Cx3cr1-Cre 缺失鼠株杂交，生成肝细胞、多巴胺能神经元和小胶质细胞特异性条件性敲除小鼠（Abl-Cnr1、Dat-Cnr2 和 Cx3cr1-Cnr2）的 CB1R 和 CB2R。我们的数据表明，神经元和小胶质细胞 CB2R 参与混合激动剂 WIN 55212-2、CB1R 选择性激动剂花生四烯酸 2'-氯乙基酰胺（ACEA）和 CB2R 选择性激动剂 JWH133 的“四联”效应。Dat-Cnr2 和 Cx3cr1-Cnr2 小鼠在合成大麻素诱导的运动减少、体温过低、镇痛和僵住方面表现出基因型差异。与 WT 小鼠相比，DAT-Cnr2 小鼠的酒精条件性位置偏好被消除，而 Cx3cr1-Cnr2 小鼠则保持不变。这些 Cre-loxP 重组小鼠系为大麻素研究提供了独特的方法，可用于剖析涉及许多慢性疾病的复杂内源性大麻素系统。
