Department of Atherosclerosis Research, Children's Hospital Oakland Research Institute, Oakland, California, United States of America.
PLoS One. 2011;6(11):e26415. doi: 10.1371/journal.pone.0026415. Epub 2011 Nov 4.
Endocannabinoids regulate energy balance and lipid metabolism by stimulating the cannabinoid receptor type 1 (CB1). Genetic deletion and pharmacological antagonism have shown that CB1 signaling is necessary for the development of obesity and related metabolic disturbances. However, the sufficiency of endogenously produced endocannabinoids to cause hepatic lipid accumulation and insulin resistance, independent of food intake, has not been demonstrated. Here, we show that a single administration of isopropyl dodecylfluorophosphonate (IDFP), perhaps the most potent pharmacological inhibitor of endocannabinoid degradation, increases hepatic triglycerides (TG) and induces insulin resistance in mice. These effects involve increased CB1 signaling, as they are mitigated by pre-administration of a CB1 antagonist (AM251) and in CB1 knockout mice. Despite the strong physiological effects of CB1 on hepatic lipid and glucose metabolism, little is known about the downstream targets responsible for these effects. To elucidate transcriptional targets of CB1 signaling, we performed microarrays on hepatic RNA isolated from DMSO (control), IDFP and AM251/IDFP-treated mice. The gene for the secreted glycoprotein lipocalin 2 (lcn2), which has been implicated in obesity and insulin resistance, was among those most responsive to alterations in CB1 signaling. The expression pattern of IDFP mice segregated from DMSO mice in hierarchal cluster analysis and AM251 pre-administration reduced (>50%) the majority (303 of 533) of the IDFP induced alterations. Pathway analysis revealed that IDFP altered expression of genes involved in lipid, fatty acid and steroid metabolism, the acute phase response, and amino acid metabolism in a CB1-dependent manner. PCR confirmed array results of key target genes in multiple independent experiments. Overall, we show that acute IDFP treatment induces hepatic TG accumulation and insulin resistance, at least in part through the CB1 receptor, and identify novel cannabinoid responsive genes.
内源性大麻素通过刺激大麻素受体 1（CB1）来调节能量平衡和脂质代谢。基因缺失和药理学拮抗作用表明，CB1 信号对于肥胖和相关代谢紊乱的发展是必要的。然而，尚未证明内源性产生的内源性大麻素足以引起肝脂质积累和胰岛素抵抗，而与食物摄入无关。在这里，我们表明，单次给予异丙基十二烷基氟膦酸酯（IDFP），可能是最有效的内源性大麻素降解的药理学抑制剂，可增加小鼠肝甘油三酯（TG）并诱导胰岛素抵抗。这些作用涉及 CB1 信号的增加，因为它们可以通过预先给予 CB1 拮抗剂（AM251）和 CB1 敲除小鼠来减轻。尽管 CB1 对肝脂质和葡萄糖代谢有很强的生理作用，但对于负责这些作用的下游靶标知之甚少。为了阐明 CB1 信号的转录靶标，我们对来自 DMSO（对照）、IDFP 和 AM251/IDFP 处理的小鼠的肝 RNA 进行了微阵列分析。在肥胖和胰岛素抵抗中起作用的分泌糖蛋白脂蛋白 2（lcn2）的基因是对 CB1 信号改变反应最敏感的基因之一。IDFP 小鼠的表达模式在层次聚类分析中与 DMSO 小鼠分离，并且 AM251 预处理减少了（>50%）大多数（IDFP 诱导的 303 个中的 533 个）改变。通路分析表明，IDFP 以 CB1 依赖的方式改变了与脂质、脂肪酸和类固醇代谢、急性期反应和氨基酸代谢相关的基因的表达。PCR 在多个独立实验中证实了关键靶基因的阵列结果。总的来说，我们表明急性 IDFP 处理会导致肝 TG 积累和胰岛素抵抗，至少部分通过 CB1 受体，并且确定了新的大麻素反应基因。
