O colesterol de membrana tem influência na sinalização de insulina e na regeneração hepática

Abstract

Background & Aims: Liver regeneration is a well-coordinated process regulated by many growth factors including insulin. It is known that cholesterol enriched membrane microdomains, known as lipid rafts, play an important role in insulin-mediated cell signaling. However, the role of rafts as regulators of insulin signaling in the liver and hepatic regeneration have not been investigated yet. In this study, we investigated the contribution of the lipid rafts for the hepatic metabolic and mitogenic effects of the insulin. Methods: Insulin receptor (IR) and lipid-rafts were immunolabeled in HepG2 cells and primary rat hepatocytes. To check the effects of lipid-rafts on insulin signaling, membrane cholesterol was depleted in vitro with Metyl-beta-cyclodextrine (MCD) and in vivo with lovastatin. Insulin-induced Ca2+ signals studies were performed in whole liver by intravital confocal imaging. Liver regeneration was evaluated with 70% partial hepatectomy. Results: We observed that a subpopulation of IR is found in membrane microdomains enriched in cholesterol on both HepG2 and hepatocytes. Cholesterol depletion with MCD resulted in reorganization and redistribution of the IR along the cell as well as abolishment of insulin-induced nuclear and cytosolic Ca2+ signaling. In addition, cholesterol removal led to ERK 1/2 hyperphosphorylation and impaired HepG2 proliferation induced by insulin. There was also a reduction of glucose uptake, probably due to an impaired AKT phosphorylation. In vivo cholesterol depletion with lovastatin led to a disruption of the lipid rafts and a decrement in the insulin-induced Ca2+ signaling, imaged in vivo in the liver, that delayed liver regeneration after of partial hepatectomy. Conclusions: Membrane cholesterol and lipid rafts are essential for the metabolic and proliferative effects of insulin in the liver.