Kainic acid induces early and transient autophagic stress in mouse hippocampus

Abstract

Kainic acid (KA) treatment is a well-established model of hippocampal neuron death mediated in large part by KA receptor-induced excitotoxicity. KA-induced, delayed neuron death has been shown previously to follow the induction of seizures and exhibit characteristics of both apoptosis and necrosis. Growing evidence supports a role of autophagic stress-induced death of neurons in several in vitro and in vivo models of neuron death and neurodegeneration. However, whether autophagic stress also plays a role in KA-induced excitotoxicity has not been previously investigated. To examine whether KA alters the levels of proteins associated with or known to regulate the formation of autophagic vacuoles, we isolated hippocampal extracts from control mice and in mice following 2–16h KA injection. KA induced a significant increase in the amount of LC3-II, a specific marker of autophagic vacuoles, at 4–6h following KA, which indicates a transient induction of autophagic stress. Levels of autophagy-associated proteins including ATG5 (conjugated to ATG12), ATG6 and ATG7 did not change significantly after treatment with KA. However, ratios of phospho-mTOR/mTOR were elevated from 6 to 16h, and ratios of phospho-Akt/Akt were elevated at 16h following KA treatment, suggesting a potential negative feedback loop to inhibit further stimulation of autophagic stress. Together these data indicate the transient induction of autophagic stress by KA which may serve to regulate excitotoxic death in mouse hippocampus.