The ER stress factor XBP1s prevents amyloid-β neurotoxicity

Abstract

Alzheimer's disease (AD) is an incurable neurodegenerative disorder clinically characterized by progressive cognitive impairment. A prominent pathologic hallmark in the AD brain is the abnormal accumulation of the amyloid-b 1 -42 peptide (Ab), but the exact pathways mediating Ab neurotoxicity remain enigmatic. Endoplasmic reticulum (ER) stress is induced during AD, and has been indirectly implicated as a mediator of Ab neurotoxicity. We report here that Ab activates the ER stress response factor X-box binding protein 1 (XBP1) in transgenic flies and in mammalian cultured neurons, yielding its active form, the transcription factor XBP1s. XBP1s shows neuroprotective activity in two different AD models, flies expressing Ab and mammalian cultured neurons treated with Ab oligomers. Trying to identify the mechanisms mediating XBP1s neuroprotection, we found that in PC12 cells treated with Ab oligomers, XBP1s prevents the accumulation of free calcium (Ca 21 ) in the cytosol. This protective activity can be mediated by the downregulation of a specific isoform of the ryanodine Ca 21 channel, RyR3. In support of this observation, a mutation in the only ryanodine receptor (RyR) in flies also suppresses Ab neurotoxicity, indicating the conserved mechanisms between the two AD models. These results underscore the functional relevance of XBP1s in Ab toxicity, and uncover the potential of XBP1 and RyR as targets for AD therapeutics.