Peng Jun, Yu Jingwei, Xu Hu, Kang Chen, Shaul Philip W, Guan Youfei, Zhang Xiaoyan, Su Wen
Department of Pathology, Shenzhen University Medical Center, Shenzhen University Health Science Center, Shenzhen, China.
Department of Biology, Guangdong Pharmaceutical University, Guangzhou, China.
Cell Physiol Biochem. 2018;47(2):784-799. doi: 10.1159/000490030. Epub 2018 May 22.
BACKGROUND/AIMS: Transient lipid accumulation within hepatocytes preceding the peak proliferative process is a characteristic feature of liver regeneration. However, molecular mediators responsible for this lipid accumulation and their functions are not well defined. Sterol regulatory element-binding proteins-1c (SREBP-1c) are critical transcriptional factors that regulate lipid homeostasis in the liver. We hypothesized that SREBP-1c deficiency induced alterations of lipid metabolism may influence hepatocyte proliferation and liver regeneration.
2/3 partial hepatectomy (PH) was performed in wild type C57BL/6J (WT) and Srebp-1c-/- mice. The lipid contents in serum and liver were measured by enzymatic colorimetric methods. Hepatic lipid droplets were detected by Oil Red O staining and immunohistological staining. Hepatic expression of genes involved in lipid metabolism and cellular proliferation was determined by real-time PCR and/or immunoblot. Hepatocyte proliferation and liver regeneration were assessed by BrdU staining and the weight of remanent liver lobes in Srebp-1c-/- mice, respectively.
Srebp-1c-/- mice displayed reduced triglyceride and fatty acids but increased cholesterol in the liver before PH. In response to PH, hepatocellular DNA synthesis was elevated and cell cycle progression was prolonged in Srebp-1c-/- mice, which was associated with enhanced liver regeneration. However, Srebp-1c-/- mice had comparable triglyceride and fatty acid contents and expressions of related genes compared with WT mice during the liver regeneration. In contrast, SREBP-1c-deficiency-induced alteration of cholesterol metabolism was retained during the liver regeneration after PH. Srebp-1c-/- mice exhibited higher cholesterol contents and enhanced expression of SREBP-2 and 3-hydroxy-3-methylglutaryl-Coenzyme A reductase (HMGCR) in the liver than WT mice after PH. Moreover, downregulation of genes involved in cholesterol elimination was observed after PH in Srebp-1c-/- mice.
SREBP-1c deficiency in mice did not interfere with triglyceride and fatty acid metabolism but was associated with significant changes in cholesterol profiles during liver regeneration after PH. These results suggest that increased hepatocellular cholesterol storage and cholesterol availability with the enhanced liver regeneration are identified in Srebp-1c-/- mice. This study also shows that providing requisite cholesterol levels to proliferating hepatocytes and keeping appropriate cholesterol metabolism are required for normal liver regeneration.
背景/目的：在肝脏再生的高峰增殖过程之前，肝细胞内出现短暂的脂质积累是肝脏再生的一个特征。然而，负责这种脂质积累的分子介质及其功能尚未明确。固醇调节元件结合蛋白-1c（SREBP-1c）是调节肝脏脂质稳态的关键转录因子。我们假设SREBP-1c缺乏诱导的脂质代谢改变可能影响肝细胞增殖和肝脏再生。
对野生型C57BL/6J（WT）小鼠和Srebp-1c基因敲除小鼠进行2/3肝部分切除术（PH）。采用酶比色法测定血清和肝脏中的脂质含量。通过油红O染色和免疫组织化学染色检测肝脏脂质滴。通过实时PCR和/或免疫印迹法测定参与脂质代谢和细胞增殖的基因在肝脏中的表达。分别通过BrdU染色和Srebp-1c基因敲除小鼠剩余肝叶的重量评估肝细胞增殖和肝脏再生情况。
在进行PH之前，Srebp-1c基因敲除小鼠肝脏中的甘油三酯和脂肪酸含量降低，但胆固醇含量增加。对PH的反应中，Srebp-1c基因敲除小鼠的肝细胞DNA合成增加，细胞周期进程延长，这与肝脏再生增强有关。然而，在肝脏再生过程中，Srebp-1c基因敲除小鼠的甘油三酯和脂肪酸含量以及相关基因的表达与WT小鼠相当。相反，PH后肝脏再生过程中，SREBP-1c缺乏诱导的胆固醇代谢改变仍然存在。PH后，Srebp-1c基因敲除小鼠肝脏中的胆固醇含量更高，SREBP-2和3-羟基-3-甲基戊二酰辅酶A还原酶（HMGCR）的表达增强。此外，在Srebp-1c基因敲除小鼠PH后，观察到参与胆固醇清除的基因下调。
小鼠中SREBP-1c缺乏并不干扰甘油三酯和脂肪酸代谢，但与PH后肝脏再生过程中胆固醇谱的显著变化有关。这些结果表明，在Srebp-1c基因敲除小鼠中，肝细胞胆固醇储存增加以及胆固醇可用性增加与肝脏再生增强有关。本研究还表明，为增殖的肝细胞提供必需的胆固醇水平并维持适当的胆固醇代谢是正常肝脏再生所必需的。
