| The mechanism of liver's unique regenerative capacity is a hotspot as well as a complicated issue in liver research. Determining the molecular base is crucial to understand this multi-stage pathophysiological process involving complex networks. The comparative proteomic approach is a powerful tool to investigate molecular changes and has been employed to elucidate crucial information about liver regeneration in recent years. Among them, subcellular proteomics is a valuable addition to the commonly used proteomic approaches in liver regeneration for providing subcellular compartments information which facilitates understand proteins' functional roles in the regulating system of regeneration.Lipd droplets (LDs), the central organelles regulating lipid synthesis and metabolism, are volved in multiple physiological processes. Studies revealed universal interaction between LDs and other organelles, as well as LDs' roles in regulating lipid homeostasis that function in specific cellular condition. A recent work reported LDs accumulated in hepatocytes in early and middle stages of liver regeneration, and correlated with regeneration process. Wheras the mechanism remains undetermined.In the present study, comparative proteomic analysis in rat liver regeneration after 2/3 hepatectomy (PH) was performed using 8-plex iTRAQ technology coupled with 2D LC-MS/MS for the first time. Differentially expressed proteins in the early stage (6h,12h), middle stage (24h,48h) and late stage (72h,120h) were profiled, using normal and sham operated liver as control.4 main results were achieved as follows.Firstly, the data from 2D LC-MS/MS were analyzed against IPI database and 248 distinct proteins, matching 200 genes, were identified in total.158 out of 200 genes were newly detected on LDs. The outcome from functional analysis with GO annotation system suggested LDs proteins might regulate intracellular lipid homeostasis, through which LDs function as stable energy supplier for cell proliferation and repository for substrates of membrane synthesis. LDs, together with their surface proteins, could further adjust intracellular oxidative stress and prevent cytotoxicity caused by excessive lipid.Secondly, hierarchical clustering analysis of the proteins expression patterns demonstrated correlation between LDs proteome changes and liver regeneration progress:proteins expression at 6h and 12h after PH hold a like pattern, which of 24h was similar to those of 6h and 12h, that of 48h similar to 72h, and that of 120h was more close to sham than any other time points.Thirdly, we employed significance analysis using ProteinPilot, and found 29 proteins with notable changes (p<0.05) at one time point or more, of which 14 were up-regulated and 15 were down-regulated. Some of these proteins, for instance L-FABP,17-βHSD 11/13 and ACSL, might be directly linked to cell proliferation and other reponses following stimulus by modulating intracellular lipid transport, synthesis and metabolism.In conclusion, this study figured out a dynamically quantitative expression pattern of LD proteins during liver regeneration for the first time, and detected some protential key factors. These findings indicated the possible roles of LDs in liver regeneration as follows:1. regulating intracellular oxidation level responding to the stimulus; 2. storing lipid and buffering cells from the toxic effects of excessive amounts of lipid,3. regulating lipid homestasis, providing energy for cell proliferation and building blocks for biological membranes, such as phospholipids and sterols; 4. recruiting and delivering proteins, crosstalking with the other organelles; 5. sequestrating abnormal proteins before degradation, maintaining intracellular microenviroment. Our results provided useful clues for further research on this issue. |
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