Bari Monica, Paradisi Andrea, Pasquariello Nicoletta, Maccarrone Mauro
Department of Biomedical Sciences, University of Teramo, Teramo, Italy.
J Neurosci Res. 2005 Jul 15;81(2):275-83. doi: 10.1002/jnr.20546.
Type 1 cannabinoid receptors (CB1R) are G-protein-coupled receptors that mediate several actions of the endocannabinoid anandamide (N-arachidonoylethanolamine; AEA) in the central nervous system. Here we show that cholesterol enrichment of rat C6 glioma cell membranes reduces by approximately twofold the binding efficiency (i.e., the ratio between maximum binding and dissociation constant) of CB1R and that activation of CB1R by AEA leads to approximately twofold lower [(35)S]GTPgammaS binding in cholesterol-treated cells than in controls. In addition, we show that CB1R-dependent signaling via adenylate cyclase and p42/p44 mitogen-activated protein kinase is almost halved by cholesterol enrichment. Unlike CB1R, the other AEA-binding receptor TRPV1, the AEA synthetase NAPE-PLD, and the AEA hydrolase FAAH are not modulated by cholesterol, whereas the catalytic efficiency (i.e., the ratio between maximal velocity and Michaelis-Menten constant) of the AEA membrane transporter AMT is almost doubled compared with control cells. These data demonstrate that, among the proteins of the "endocannabinoid system," only CB1R and AMT critically depend on membrane cholesterol content. This observation may have important implications for the role of CB1R in protecting nerve cells against (endo)cannabinoid-induced apoptosis.
1型大麻素受体（CB1R）是G蛋白偶联受体，可介导内源性大麻素花生四烯酸乙醇胺（N-花生四烯酰乙醇胺；AEA）在中枢神经系统中的多种作用。在此我们表明，大鼠C6胶质瘤细胞膜的胆固醇富集使CB1R的结合效率（即最大结合与解离常数之比）降低了约两倍，并且AEA对CB1R的激活导致胆固醇处理细胞中的[³⁵S]GTPγS结合比对照细胞低约两倍。此外，我们表明，通过腺苷酸环化酶和p42/p44丝裂原活化蛋白激酶的CB1R依赖性信号传导因胆固醇富集而几乎减半。与CB1R不同，另一种AEA结合受体TRPV1、AEA合成酶NAPE-PLD和AEA水解酶FAAH不受胆固醇调节，而与对照细胞相比，AEA膜转运蛋白AMT的催化效率（即最大速度与米氏常数之比）几乎增加了一倍。这些数据表明，在“内源性大麻素系统”的蛋白质中，只有CB1R和AMT严重依赖于膜胆固醇含量。这一观察结果可能对CB1R在保护神经细胞免受（内源性）大麻素诱导的细胞凋亡中的作用具有重要意义。
