Leukemia Inhibitory Factor Participates in the Formation of Stress Adaptation via Hippocampal Myelination in Mice

Abstract

Leukemia inhibitory factor (LIF) has been shown to be involved in myelination. The present study investigated whether LIF plays a significant role in the formation of stress adaptation using stress-adaptive and -maladaptive mice, and also attempted to confirm whether there was any difference in myelination between these animal models. A single exposure to restraint stress for 1 h induced a decrease in head-dipping behavior in the hole-board test. This stress response was not seen in mice that had been exposed to restraint stress for 1 h/day for 14 days, which is referred to as stress adaptation. In contrast, repeated exposure to restraint stress for 4 h/day for 14 days did not lead to the development of stress adaptation, and was still associated with a decrease in head-dipping behaviors. Under these conditions, LIF protein was found to be increased with astrocyte activation in the hippocampus of stress-adaptive mice, whereas no change was observed in stress-maladaptive mice. On the other hand, major myelin proteins including myelin-associated glycoprotein and myelin basic protein, as well as mature oligodendrocytes, were decreased in the hippocampus of stress-maladaptive, but not stress-adaptive, mice. Furthermore, while the levels of phosphorylated-extracellular signal-regulated kinase (p-ERK) were increased in the hippocampus of stress-adaptive, this change did not occur in stress-maladaptive mice. Taken together, the present findings suggest that LIF, which may be derived from activated astrocytes, plays a critical role in the maintenance of hippocampal myelination via an ERK signaling pathway, and contributes to the development of stress adaptation.

Keywords: astrocyte; emotional behavior; leukemia inhibitory factor; myelin; restraint stress; stress adaptation.