Glutamate-mediated autophagy inhibition intensifies excitotoxic death of nutrient-deprived SH-SY5Y neuroblastoma cells

Abstract

We investigated the role of autophagy in glutamate excitotoxicity during nutrient deprivation in vitro. Lack of serum, amino acids, and glucose markedly increased the sensitivity of SH-SY5Y human neuroblastoma cell line to glutamate-induced excitotoxic necrosis. Glutamate suppressed starvation-triggered autophagic response, as confirmed by diminished intracellular acidification, lower LC3 punctuation and conversion of LC3I to autophagosome associated LC3II, reduced levels of autophagy activators beclin-1 and ATG5, increased levels of the selective autophagic target NBR1, and reduced appearance of autophagic vesicles observed by transmission electron microscopy. Glutamate reduced starvation-triggered phosphorylation of the intracellular energy sensor AMP-activated protein kinase (AMPK), without affecting the activity of mammalian target of rapamycin complex1 as a major negative regulator of autophagy. Similar results were shown on PC12 cells, which are often exploited as a model for excitotoxicity. We also detected reduced mRNA expression of autophagy transcription factors FOXO3 and ATF4, as well as molecules involved in autophagy initiation (ULK1, ATG13, FIP200), autophagosome nucleation/elongation (ATG14, beclin 1, ATG5, ATG12), and the autophagy cargo delivery to autophagosmes (SQSTM1/p62). Genetic or pharmacological AMPK activation by AMPK overexpression or metformin, reduced the sensitivity of nutrient-deprived SH-SY5Y cells to glutamate dependent autophagy is involved in glutamate-mediated excitotoxicity during nutrient deprivation in vitro.