Research Papers: Autophagy and Cell Death:

ABSTRACT

Unlike the role of autophagy in continuous hypoxia, the role of autophagy in intermittent hypoxia is unclear. To investigate whether autophagy is involved in intermittent hypoxia- caused hippocampal neuronal apoptosis, we studied the activity and action of autophagy in hippocampal neurons after exposure to intermittent hypoxia. We found the expression of autophagy-related proteins and the autolysosome formation were upregulated, and exposure to intermittent hypoxia led to a significant increase in light chain 3 (LC3) turnover and a decrease in SQSTM1/p62 level in hippocampal neurons. Furthermore, accompanying autophagy activation, the level of hypoxia inducible factor-1α (HIF-1α) was increased. Conversely, inhibition of HIF-1α by chemical inhibitor or small interfering RNA (siRNA) downregulated the expression of autophagy-related proteins and blocked autophagy activation. We also found reactive oxygen species (ROS) increased after exposure to intermittent hypoxia, and inhibition of ROS by antioxidants decreased LC3-II expression. What’s more, activation of autophagy by rapamycin exacerbated the apoptosis induced by intermittent hypoxia, whereas inhibition of autophagy by chloroquine or autophagy-related genes siRNA (Beclin1, Atg5 and Atg7) ameliorated intermittent hypoxia-induced apoptosis. Additionally, X-linked inhibitor of apoptosis protein (XIAP), an apoptosis inhibitor protein, was decreased significantly after autophagy activation. Taken together, HIF-1α and ROS-mediated autophagy activation aggravated hippocampal neuronal apoptosis caused by intermittent hypoxia, and the decrease of XIAP might be one of the mechanisms of hippocampal neuronal apoptosis caused by autophagy activation.