Department of Biochemistry, University of Alberta, Edmonton, AB, Canada.
Instituto de Fisiología Experimental (IFISE), Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, UNR, Rosario, Argentina; Área Morfología, Facultad de Ciencias Bioquímicas y Farmacéuticas, UNR, Rosario, Argentina.
J Proteomics. 2018 Jun 15;181:213-224. doi: 10.1016/j.jprot.2018.04.024. Epub 2018 Apr 23.
During fasting, the liver increases lipid storage as a mean to reserve and provide energy for vital cellular functions. After re-feeding, hepatocytes rapidly decrease the amount of triacylglycerol that is stored in lipid droplets (LDs), visible as the size of hepatic LDs significantly decreases after re-feeding. Little is known about the changes in the liver LD proteome that occur during the fasting/re-feeding transition. This study aimed to investigate the hepatic LD proteome in fasted and re-fed conditions in the mouse. Using label-free LC-MS/MS analysis the relative abundance of 817 proteins was determined in highly purified LDs. Comparative analysis for differential protein abundance with respect to feeding states revealed 130 with higher abundance in LDs from fasted mice and 31 in LDs from re-fed mice. Among proteins observed to have higher abundance on LDs in the fasted state we found perilipin-5, and several mitochondrial and peroxisomal marker proteins, supporting the role of LDs in the provision of substrates for fatty acid oxidation. Proteins of higher abundance upon re-feeding included several peroxisomal and mitochondrial marker proteins and expand our understanding of the dynamic nature of the hepatic LD proteome according to the energetic requirements of the cell.
Proteomic investigations have been revealing the complexities and dynamics of cellular LDs from a variety of cell types. As these sub-cellular structures are truly dynamic in nature, our investigations reveal that simply the feeding state of an animal leads to significant changes to the protein composition of LDs and suggest a variety of dynamic interactions with other cellular organelles, such as the mitochondria and peroxisomes. As such, the experimental design for investigations of this cellular structure must consider this dynamic baseline. Lastly our analysis on global protein abundance has revealed the unforeseen high abundance of murine major urinary proteins associated with hepatic lipid droplets, which warrants further investigations.
在禁食期间，肝脏会增加脂质储存，以储备和提供能量用于重要的细胞功能。重新进食后，肝细胞会迅速减少储存在脂质滴（LD）中的三酰甘油量，这可以从重新进食后肝 LD 的大小明显减小看出。关于在禁食/再进食过渡期间肝脏 LD 蛋白质组发生的变化知之甚少。本研究旨在研究禁食和再进食条件下小鼠肝脏 LD 蛋白质组。使用无标签 LC-MS/MS 分析，在高度纯化的 LD 中确定了 817 种蛋白质的相对丰度。对与喂养状态有关的差异蛋白丰度进行比较分析，发现 130 种在禁食小鼠 LD 中丰度较高，31 种在再进食小鼠 LD 中丰度较高。在禁食状态下 LD 中丰度较高的蛋白质中，我们发现了 perilipin-5 和几种线粒体和过氧化物酶体标记蛋白，这支持了 LD 为脂肪酸氧化提供底物的作用。再进食时丰度较高的蛋白质包括几种过氧化物酶体和线粒体标记蛋白，这扩展了我们对根据细胞能量需求动态肝脏 LD 蛋白质组的理解。
蛋白质组学研究从多种细胞类型揭示了细胞 LD 的复杂性和动态性。由于这些亚细胞结构本质上是动态的，我们的研究表明，动物的进食状态仅导致 LD 蛋白质组成发生重大变化，并表明与其他细胞细胞器（如线粒体和过氧化物酶体）之间存在各种动态相互作用。因此，对这种细胞结构的研究的实验设计必须考虑到这种动态基线。最后，我们对全局蛋白质丰度的分析揭示了与肝脂滴相关的鼠主要尿蛋白的意外高丰度，这值得进一步研究。
