Neuroprotective effect of mithramycin against endoplasmic reticulum stress-induced neurotoxicity in organotypic hippocampal slice cultures.

Endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of various neurodegenerative diseases. Although the underlying mechanisms of these diseases have been suggested by many studies, therapeutic drugs have yet to be found. In this study, experiments were performed to examine the effect of mithramycin (MTM), a clinically approved guanosine-cytosine (GC)-rich DNA sequence-binding antitumor antibiotic, on ER stress-induced neurotoxicity in organotypic hippocampal slice cultures (OHCs). Time-dependent induction of the ER chaperones, glucose-regulated protein (GRP) 78 and GRP94, was observed after treatment with tunicamycin (TM) (80 μg/mL). Western blot analysis showed that treatment of OHCs with TM increased the expression of CHOP and the cleaved forms of caspase-12. Simultaneous application of MTM suppressed TM-induced cell death in all areas of OHCs with a concomitant decrease in the level of CHOP. In contrast, MTM had no effect on excitotoxic cell death induced by ibotenic acid, a potent N-methyl-d-aspartate (NMDA) agonist in OHCs. Moreover, RNA interference to CHOP or simultaneous treatment with MTM attenuated TM-induced cell death in primary cultured hippocampal neurons. These results suggest that CHOP plays a critical role in the mechanisms underlying ER-stress-induced neurotoxicity in the hippocampus, and that MTM could be a protective agent against ER stress-induced hippocampal neuronal death through attenuation of ER stress-associated signal proteins.