Impact And Significance Of Hypoxia Preconditioning On The Expression Of Bcl-2 Protein In Orthopotic Liver Autotransplantation Of Rats

OBJECTIVE:Hepatic ischemia–reperfusion injury (HIRI) is an important clinical problem that affects liver transplantation. Previously, it was thought that necrosis was the only form of hepatocyte death after HIRI. However, recent research has shown that apoptosis is more severe and common after HIRI. Therefore, it is very important to establish how to relieve apoptosis after HIRI.Bcl-2 protein is considered to be one of the most ordinary and definite modulins in apoptosis. Several experiments have indicated that HIRI can down-regulate expression of Bcl-2 protein, and thus induce hepatocyte apoptosis. Therefore, Bcl-2 protein has been widely used in apoptosis research. It is a type of regulatory factor expressed by the Bcl-2 inhibiting gene, which resides in the mitochondrial membrane. Thus, Bcl-2 protein may relieve apoptosis by regulating mitochondrial function. Since 1986, hypoxic preconditioning (HP) has previously been considered likely to alleviate reperfusion injury. During that time, our laboratory has found that HP has some protective effects on HIRI, by alleviating injury to sinusoidal endothelial cells. In the present study, we used an upgraded model, which precluded the influence of immunological agents. Thus, it is ideal for studying HIRI in liver transplantation. Finally, we investigated the Bcl-2 signaling pathway of HP in apoptosis and its possible mechanism during orthotopic liver autotransplantation.METHODS:A modified orthotopic liver autotransplantation model was used to simulate HIRI, Sprague-Dawley rats were randomly divided into normal control, autotransplantation (AT) and HP groups. The HP group was subjected to an 8% oxygen atmosphere for 90 minutes before surgery. At 1, 6 and 24 h after surgery,the rats were killed and their liver tissue was sampled to assess the expression of Bcl-2 protein; The samples were subjected to blood chemistry study, morphological study under a light or transmission electron microscopy, and quantitative study of mitochondria.RESULTS:The Serum levels of ALT and AST in the HP group were lower than those in the AT group at 1, 6 and 24 h after orthotopic liver autotransplantation. Bcl-2 protein expression was increased in the HP group at each measurement point. Light microscopy showed that hepatic injury in the AT group was much more severe than in the HP group. Hepatocytes in the AT group showed typical apoptosis signs under a transmission electron microscopy. The ultrastructural appearance of hepatocytes in the HP group was much better than that in the AT group, and the area, perimeter and diameter of the mitochondria were smaller in the HP group than in the AT group (P<0.05).CONCLUTION:Hepatocytes sense and respond to decreased tissue oxygenation. Stimulation by HP relieves apoptosis by upregulating expression of Bcl-2 protein and its protection of mitochondria after orthotopic liver autotransplantation.