Decreased expression of mitochondrial aldehyde dehydrogenase-2 induces liver injury via activation of the mitogen-activated protein kinase pathway

The aim of this study was to determine the role of ALDH2 in the injury of liver from brain-dead donors. Using brain-dead rabbit model and hypoxia model, levels of ALDH2 and apoptosis in tissues and cell lines were determined by Western blot, flow cytometry (FCM), and transferase (TdT)-mediated biotin-16-dUTP nick-end labeling (TUNEL) assays. After the expression of ALDH2 during hypoxia had been inhibited or activated, the accumulations of 4-hydroxynonenal (4-HNE) and molecules involved in mitogen-activated protein kinase (MAPK) signaling pathway were analyzed using ELISA kit and Western blot. The low expression of phosphorylated ALDH2 in liver was time-dependent in the brain-dead rabbit model. Immunohistochemistry showed ALDH2 was primarily located in endothelial, and the rates of cell apoptosis in the donation after brain-death (DBD) rabbit groups significantly increased with time. Following the treatment of inhibitor of ALDH2, daidzein, in combination with hypoxia for 8 h, the apoptosis rate and the levels of 4-HNE, P-JNK, and cleaved caspase-3 significantly increased in contrast to that in hypoxic HUVECs; however, they all decreased after treatment with Alda-1 and hypoxia compared with that in hypoxic HUVECs (P < 0.05). Instead, the levels of P-P38, P-ERK, P-JNK, and cleaved caspase-3 decreased and the ratio of bcl-2/bax increased with ad-ALDH2 (10(6) pfu/ml) in combination with hypoxia for 8 h, which significantly alleviated in contrast to that in hypoxic HUVECs. We found low expression of ALDH2 and high rates of apoptosis in the livers of brain-dead donor rabbits. Furthermore, decreased ALDH2 led to apoptosis in HUVECs through MAPK pathway.