ATF6 and neurodegenerative disease: ER stress occurring in neurodegenerative diseases activates all three pathways of the mammalian unfolded protein response (UPR), each represented by its unique UPR sensor: PKR-like ER kinase (PERK) [8], inositol-requiring transmembrane kinase/endoribonuclease-1α (IRE1α) [9] and activating transcription factor 6 (ATF6) [10].