Single cell RNA-seq of liver cells from B6J mice fed a chow or a high-fat-and-high-sucrose diet

Cannabinoid receptor-1 (CB-1) blockage in brain is responsible for weight loss, many of the metabolic benefits associated with CB-1 blockade have been attributed to inhibition of CB-1 signaling in the periphery. We produced mice that lacked CB-1 receptors in hepatocytes or stellate cells to determine if CB-1 signaling contributes to the development of NAFLD or liver fibrosis. Deletion of CB-1 receptors in hepatocytes did not alter the development of NAFLD in mice fed a high sucrose high fat diet (HSD) or high fat diet (HFD). Similarly, deletion of CB-1 deletion specifically in stellate cells also did not prevent the development of NAFLD in mice fed the HFD nor did it protect mice for carbon tetrachloride-induced fibrosis. To determine if a small population of cells in liver express CB-1 at high levels either before and/or after HSD feeding, here we performed single cell RNA-sequencing of livers from wild-type mice fed chow or a HSD for 17 weeks and analyzed CB-1 expression. Single-cell sequencing of hepatocytes and stellate cells reveals low Cnr1 expression in livers of mice fed a chow or HSD. Combined, these studies do not support a direct role for hepatocyte or stellate cell CB-1 signaling in the development of NAFLD or liver fibrosis. Two pairs of mice (one pair fed a chow, one pair fed a high-fat-and-high-sucrose diet for 17 weeks) were used for single cell sequencing. For each pair, one mouse was perfused for hepatocyte preparation, and the other for stellate cells preparation. All cells were collected as single cell suspension.

脑内大麻素受体1（Cannabinoid receptor-1, CB-1）的阻断可引发体重减轻，既往研究多将CB-1阻断所带来的诸多代谢益处归因于外周组织中CB-1信号通路的抑制。本研究构建了肝细胞或肝星状细胞（stellate cells）缺失CB-1受体的小鼠模型，旨在探究CB-1信号通路是否参与非酒精性脂肪性肝病（Non-Alcoholic Fatty Liver Disease, NAFLD）及肝纤维化的发生发展。
在高蔗糖高脂饮食（High Sucrose High Fat Diet, HSD）或高脂饮食（High Fat Diet, HFD）喂养的小鼠中，肝细胞CB-1受体的敲除并未改变NAFLD的病程进展。同样，仅在肝星状细胞中特异性敲除CB-1受体，既无法阻止高脂饮食喂养小鼠的NAFLD进展，也不能保护小鼠免受四氯化碳（carbon tetrachloride, CCl4）诱导的肝纤维化。
为明确肝脏中是否存在少量细胞在HSD喂养前后均高表达CB-1，本研究对喂食普通饲料或HSD达17周的野生型小鼠肝脏开展了单细胞RNA测序（single cell RNA-sequencing, scRNA-seq），并分析了CB-1的表达情况。对肝细胞与肝星状细胞的单细胞测序结果显示，无论喂食普通饲料还是HSD，小鼠肝脏中Cnr1基因的表达水平均较低。
综合而言，本研究结果并不支持肝细胞或肝星状细胞的CB-1信号通路直接参与NAFLD及肝纤维化的发生发展。本研究共使用两对小鼠：一对喂食普通饲料，另一对喂食高蔗糖高脂饮食达17周，用于单细胞测序。每对小鼠中，1只通过灌流法制备肝细胞，另1只用于分离肝星状细胞。所有细胞均以单细胞悬液的形式收集。