The Study On The Injury Of Liver In The Acute Cold Exposure And Its Possible Mechanisms

Background:People usually expose to cold environment in out-door activities in the cold winter. And workers who engage in the low temperature environment work and soldiers who execute special environment military missions will commonly expose to harsh weather. The mechanism of healthy effects caused by cold exposure and the method of preventing cold exposure relative diseases is of great interest to scientist and is of great importance.Being at the important military status, the mechanism of cold relative injuries is hardly to be seen in the open press. Up to now, the experimental models used by the study on mechanisms of cold exposure induced healthy effects are mostly the long lasting chronic ones, while the acute cold exposure models are rarely adopted. Soldiers who execute border patrolling or sentry duty will expose to the low tempareture environment in cold winter, and when they were insufficiently prevented, they will easily get acute cold injuries. The studies on acute cold injury are mainly focusing on the frostbite of skin and superficial structures, while the cold effects on the internal organs and the potential functions of the internal organs during cold exposure is rarely studied or reported. When exposed to the cold environment, adult mammals will sponsor the thermogenic activities to maintain body temperature. Although liver is less efficient on calorification than muscle, as one of the largest clycogen storage organ and the dominant thermogenic organ in the resting status, liver may participate in the response to acute cold stressing. Human and rat liver can form a number of binuclear hepatocytes during development. Under some pathological situations, the formation of binuclear hepatocyte may be relative with the liver injury and generative ability changing. The hepatocyte mitosis will be failure under energy stressing or other injurious status and then the binuclear hepatocyte formed. The PI3K-Akt-mTOR signaling is an important pathway that participates in the regulative progression of metabolism, differentiation, development and survival. The potential functions of the pathway in cold exposure have been studied in the chronic cold exposure model, while its role in the acute cold exposure circumstances is still to be illustrating.As expected, using the acute cold exposure animal model, we attempt to explain whether liver could get any physiological or pathological changes during acute cold exposure, and to explain whether and what role the PI3K-Akt-mTOR pathway participates in the responsive reactivities. This will be of great importance to find more effective biomarkers and targets of prevention in acute cold exposure situations.Aims:1. To observe the physiological and pathological changes of liver during acute cold exposure: The changes of number of mitotic hepatocytes and binuclear hepatocytes and the changes of energy level in the hepatocytes during cold exposure as well as the activity changing of the PI3K-Akt-mTOR pathway and its relative potential functions.2. By the utility of inhibitor, explores whether the PI3K-Akt-mTOR pathway participates in the regulation of liver ATP level during acute cold exposure. And whether this change can affect the process of promoting hepatocyte enter into the mitosis phase and the formation of binuclear hepatocyte.Methods:1. Adult male rats weighing 220-230 g are exposed to the cold environment at﹣15℃for 0.5, 1, 2 and 4 hours.2. To observe the pathological changes of liver during acute cold exposure by HE staining and immuno-histochemistry detecting.3. To observe the ultramicrostructure changes of the hepatocytes during acute cold exposure.4. To observe the changes of activities of the PI3K-Akt-mTOR pathway by western blot method.Results:1. Acute cold exposure could injure the liver by a time dependent manner. After 4 hours exposure, the rat hepatocytes were vacuolate degeneration and there were an increasing number of mitosis hepatocytes and binuclear hepatocytes, as well as some apoptosis hepatocytes. 4 hours exposure also caused the microstructure injuries such as the swollen of mitochondria and the depletion of clycogen.2. The ATP level elevated rapidly and peaked at the 0.5 hours during cold exposure and then declined as the exposure time prolonged.3. The activity of the PI3K-Akt-mTOR pathway paralleled with the changes of ATP level. And the AMPK activated in a time dependent manner.4. After injecting of inhibitor wortmannin intraperitoneally, the ATP level declined magnificently and the binuclear hepatocyte increased. Conclution:1. 4 hours acute cold exposure causes rat liver injury and an abnormally transiently increasing in the ATP level, and promotes the liver entering into the mitosis phase as well as forming an increasing number of binuclear hepatocytes.2. PI3K-Akt-mTOR pathway participates in the progression of liver injury during acute cold exposure that regulates the ATP genesis and promotes the hepatocyte getting into the M phase and forming the binuclear hepatocyte.