Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials , Campinas, Sao Paulo , Brazil.
Department of Physiology and Biophysics, Federal University of Minas Gerais , Belo Horizonte, Minas Gerais , Brazil.
Am J Physiol Gastrointest Liver Physiol. 2018 Jul 1;315(1):G80-G94. doi: 10.1152/ajpgi.00008.2018. Epub 2018 Feb 22.
Hepatocyte proliferation during liver regeneration is a well-coordinated process regulated by the activation of several growth factor receptors, including the insulin receptor (IR). The IR can be localized in part to cholesterol-enriched membrane microdomains, but the role of such domains in insulin-mediated events in hepatocytes is not known. We investigated whether partitioning of IRs into cholesterol-enriched membrane rafts is important for the mitogenic effects of insulin in the hepatic cells. IR and lipid rafts were labeled in HepG2 cells and primary rat hepatocytes. Membrane cholesterol was depleted in vitro with metyl-β-cyclodextrin (MβCD) and in vivo with lovastatin. Insulin-induced calcium (Ca) signals studies were examined in HepG2 cells and in freshly isolated rat hepatocytes as well as in whole liver in vivo by intravital confocal imaging. Liver regeneration was studied by 70% partial hepatectomy (PH), and hepatocyte proliferation was assessed by PCNA staining. A subpopulation of IR was found in membrane microdomains enriched in cholesterol. Depletion of cholesterol from plasma membrane resulted in redistribution of the IR along the cells, which was associated with impaired insulin-induced nuclear Ca signals, a signaling event that regulates hepatocyte proliferation. Cholesterol depletion also led to ERK1/2 hyper-phosphorylation. Lovastatin administration to rats decreased hepatic cholesterol content, disrupted lipid rafts and decreased insulin-induced Ca signaling in hepatocytes, and delayed liver regeneration after PH. Therefore, membrane cholesterol content and lipid rafts integrity showed to be important for the proliferative effects of insulin in hepatic cells. NEW & NOTEWORTHY One of insulin's actions is to stimulate liver regeneration. Here we show that a subpopulation of insulin receptors is in a specialized cholesterol-enriched region of the cell membrane and this subfraction is important for insulin's proliferative effects.
肝细胞再生过程中的增殖是一个受到多种生长因子受体（包括胰岛素受体）激活的协调过程。胰岛素受体（IR）可以部分定位于富含胆固醇的膜微区，但这种结构域在肝细胞中胰岛素介导的事件中的作用尚不清楚。我们研究了胰岛素受体（IR）在富含胆固醇的膜筏中的分区是否对肝细胞有丝分裂效应重要。在 HepG2 细胞和原代大鼠肝细胞中标记 IR 和脂质筏。用甲基-β-环糊精（MβCD）体外和洛伐他汀体内耗竭膜胆固醇。用共聚焦活体成像研究胰岛素诱导的 HepG2 细胞和新鲜分离的大鼠肝细胞以及整体肝脏中的钙（Ca）信号。通过 70%部分肝切除术（PH）研究肝再生，并用 PCNA 染色评估肝细胞增殖。发现一部分胰岛素受体（IR）存在于富含胆固醇的膜微区中。质膜胆固醇的耗竭导致 IR 在细胞中重新分布，这与胰岛素诱导的核 Ca 信号受损有关，这是调节肝细胞增殖的信号事件。胆固醇耗竭还导致 ERK1/2 过度磷酸化。洛伐他汀给药可降低大鼠肝脏胆固醇含量，破坏脂质筏，并减少胰岛素诱导的肝细胞内 Ca 信号，延迟 PH 后肝脏再生。因此，膜胆固醇含量和脂质筏完整性对于肝细胞中胰岛素的增殖作用很重要。
新的和值得注意的是胰岛素的作用之一是刺激肝脏再生。在这里，我们发现胰岛素受体的一个亚群位于细胞膜的一个特殊的富含胆固醇的区域，这个亚群对于胰岛素的增殖作用很重要。
