Diabetes Research Group, King's College London, London, UK.
Islets. 2010 Sep-Oct;2(5):293-302. doi: 10.4161/isl.2.5.12729. Epub 2010 Sep 1.
The endocannabinoid system plays a key role in energy homeostasis, with agonists and antagonists of CB1 receptors acting centrally to stimulate and inhibit food intake, respectively. In addition to their established effects on the central nervous system, cannabinoid receptor agonists also exert peripheral effects by modulating cellular cyclic AMP and calcium levels and there have been reports that they regulate β-cell function. However, the few reports to date on islet expression of cannabinoid receptors and effects of agonists on insulin secretion have failed to reach a consensus. We have therefore investigated cannabinoid receptor expression by mouse islet β-and α-cells and the effects of selective receptor agonists on cyclic AMP and calcium levels, and on dynamic insulin secretory responses. CB1 and CB2 mRNA and protein expression by islets was detected by RT-PCR and western blotting respectively, and cellular location of the receptors was identified by immunohistochemistry with insulin and glucagon antibody co-staining. Cyclic AMP generation was quantified by enzyme immunoassay and changes in calcium levels were measured by microfluorimetry of Fura-2-loaded mouse islet cells. Dynamic insulin secretion was quantified by radioimmunoassay after perifusion of isolated islets. We found that mouse islets expressed both CB1 and CB2 receptors, and they were localised to β-cells. Activation of mouse β-cell CB1 and CB2 receptors resulted in decreased cyclic AMP, increased calcium and potentiation of glucose-stimulated insulin secretion. Thus, activation of islet cannabinoid receptors by locally produced endocannabinoids such as 2-aminoglycerol may be another regulatory pathway by which islets stimulate insulin secretion to maintain glucose homeostasis.
内源性大麻素系统在能量平衡中起着关键作用，CB1 受体的激动剂和拮抗剂分别通过中枢作用刺激和抑制食物摄入。除了对中枢神经系统的既定作用外，大麻素受体激动剂还通过调节细胞环 AMP 和钙水平发挥外周作用，并且有报道称它们调节β细胞功能。然而，迄今为止，关于胰岛中大麻素受体的表达以及激动剂对胰岛素分泌的影响的少数报道尚未达成共识。因此，我们研究了选择性受体激动剂对环 AMP 和钙水平以及动态胰岛素分泌反应的影响，以及胰岛 β-和 α-细胞中大麻素受体的表达。通过 RT-PCR 和 Western 印迹分别检测胰岛中 CB1 和 CB2 mRNA 和蛋白的表达，并通过与胰岛素和胰高血糖素抗体共染色的免疫组织化学鉴定受体的细胞定位。通过酶免疫测定定量测定环 AMP 的生成，并通过微荧光法测量 Fura-2 负载的胰岛细胞中钙水平的变化。通过对分离的胰岛进行灌注后，通过放射免疫测定定量测定动态胰岛素分泌。我们发现，胰岛表达 CB1 和 CB2 受体，并且它们定位于β细胞。激活胰岛 CB1 和 CB2 受体导致环 AMP 减少、钙增加和葡萄糖刺激的胰岛素分泌增强。因此，局部产生的内源性大麻素（如 2-氨基甘油）激活胰岛大麻素受体可能是胰岛刺激胰岛素分泌以维持葡萄糖稳态的另一种调节途径。
