The impact of genetic stress by ATGL deficiency on the lipidome of lipid droplets from murine hepatocytes

We showed earlier that nutritional stress like starvation or high fat diet resulted in phenotypic changes in the lipidomes of hepatocyte lipid droplets (LDs), representative for the pathophysiological status of the mouse model. Here we extend our former study by adding genetic stress due to knock-out (KO) of adipocyte triglyceride lipase (ATGL), the rate limiting enzyme in LD lipolysis. An intervention trial for 6 weeks with male wild-type (WT) and ATGL-KO mice was carried out; both genotypes were fed lab chow or were exposed to short-time starvation. Isolated LDs were analyzed by LC-MS/MS. Triacylglycerol, diacylglycerol and phosphatidylcholine lipidomes, in that order, provided best phenotypic signatures characteristic for respective stresses applied to the animals. This was evidenced at lipid species level by principal component analysis, calculation of average values for chain-lengths and numbers of double bonds, and by visualization in heat maps. Structural backgrounds for analyses and metabolic relationships were elaborated at lipid molecular species level. Relating our lipidomic data to non-alcoholic fatty liver diseases of nutritional and genetic etiologies with or without accompanying insulin resistance, phenotypic distinction in hepatocyte LDs dependent on insulin status emerged. Taken together, lipidomes of hepatocyte lipid droplets are sensitive responders to nutritional and genetic stress.我们此前的研究表明，饥饿或高脂饮食这类营养应激会导致肝细胞脂滴（lipid droplets, LDs）的脂质组发生表型变化，该变化可作为小鼠模型病理生理状态的代表性特征。本研究在此前工作的基础上，引入了由脂肪细胞甘油三酯脂肪酶（adipocyte triglyceride lipase, ATGL）基因敲除（knock-out, KO）所引发的遗传应激——ATGL是脂滴脂解过程中的限速酶。我们对雄性野生型（wild-type, WT）和ATGL-KO小鼠开展了为期6周的干预实验：两类基因型小鼠均喂食标准实验室饲料，或接受短期饥饿处理。通过液相色谱-串联质谱法（LC-MS/MS）对分离得到的脂滴进行分析。按三酰甘油、二酰甘油、磷脂酰胆碱的顺序得到的脂质组，可最为精准地反映对应应激处理下动物的表型特征。该结论可通过脂质物种层面的主成分分析、脂酰链长度与双键数目平均值计算，以及热图可视化得到证实。研究还在脂质分子物种层面阐明了分析的结构背景与代谢关联。将本研究的脂质组数据与伴有或不伴胰岛素抵抗的营养性、遗传性病因非酒精性脂肪性肝病（non-alcoholic fatty liver diseases）相关联时，我们发现肝细胞脂滴的表型区分依赖于胰岛素状态。综上，肝细胞脂滴的脂质组可作为营养应激与遗传应激的敏感响应指标。