Effects of cold stress on black porgy tissue injury and apoptosis gene expression

In order to explore the physiological adaptation mechanism of black porgy (Acanthopagrus schlegelii) under low temperature stress, we designed three temperature gradient groups (15, 10 and 5 ℃). Taking 15 ℃ as the control group and with a low temperature stress for 24 h, we studied the tissue structure changes, physiological, biochemical reactions and the expression of apoptosis genes before and after the cold stress. The results show that with the intensification of low temperature stress, the tissue damage such as liver vacuolation, gill lamellae contraction and breakage and muscle fiber breakage were aggravated. The content of triglyceride (TG) in the liver decreased significantly, while the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) as well as the content of total cholesterol (T-CHO) increased significantly, indicating that A. schlegelii had suffered from liver dysfunction and structural damage under cold stress condition. At 10 ℃, the liver reduced the damage of cold stress by decreasing expression levels of apaf-1, bax and caspase-1 genes, increasing expression of caspase-3 and diablo genes so as to reduce the loss of liver cells. When the temperature reached 5 ℃, the temperature exceeded A. schlegelii's physiological regulation threshold, so the degree of liver cell damage was aggravated. The expression of apaf-1, bcl-2 and diablo genes were promoted, while the caspase-3 gene expression was inhibited in order to maintain the homeostasis of liver cells to the greatest extent. It is showed that as the temperature decreased, the liver, gills and muscle damages of A. schlegelii increased. The liver regulated the expression of AST, ALT, T-CHO, TG and apoptotic pathway related genes to reduce the damage caused by tissue damage.