Anti-PDIA6 monoclonal antibody, clone FQS21243(C)

The endoplasmic rcticulum (ER) plays an important role in maintenance of proteostasis through the unfolded protein response (UPR), which is strongly activated in most neurodegencrative disorders. UPR signalling pathways mediated by IRE1 alpha and ATF6 play a crucial role in the maintenance of ER homeostasis through the transactivation of an array of transcription factors. When activated, these transcription factors induce the expression of genes involved in protein folding and degradation with pro-survival effects. However, the specific contribution of these transcription factors to different neurodegenerative diseases remains poorly defined. Here, we characterised 44 target genes strongly influenced by XBP1 and ATF6 and quantified the expression of a subset of genes in the human post-mortem spinal cord from amyotrophic lateral sclerosis (ALS) cases and in the frontal and temporal cortex from frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD) cases and controls. We found that IRE1 alpha-XBP1 and ATF6 pathways were strongly activated both in ALS and AD. In ALS, XBP 1 and ATF6 activation was confirmed by a substantial increase in the expression of both known and novel target genes involved particularly in co-chaperone activity and ER-associated degradation (ERAD) such as DNAJB9, SEL1L and OS9. In AD cases, a distinct pattern emerged, where targets involved in protein folding were more prominent, such as CANX, PDIA3 and PDIA6. These results reveal that both overlapping and disease-specific patterns of IRE1 alpha-XBP1 and ATF6 target genes are activated in AD and ALS, which may be relevant to the development of new therapeutic strategies.

Protein disulfide isomerase A6 (PDIA6) interacts with protein kinase RNA-like endoplasmic reticulum kinase (PERK) and inositol requiring enzyme (IRE)-1 and inhibits their unfolded protein response signaling. In this study, shRNA silencing of PDIA6 expression in insulin-producing mouse cells reduced insulin production (5-fold) and, consequently, glucose-stimulated insulin secretion (3-4-fold). This inhibition of insulin release was independent of the PDIA6-PERK interaction or PERK activity. Acute inhibition of PERK did not change the short-term response of beta cells to glucose. Rather, PDIA6 affected insulin secretion by modulating one of the activities of IRE1. At 11 mM glucose and lower, the regulated IRE1-dependent decay (RIDD) of the mRNA activity of IRE1 was activated, but not its X-box binding protein (XBP)-1 splicing activity. In the absence of PDIA6, RIDD activity toward insulin transcripts was enhanced up to 4-fold, as shown by molecular assays in cultured cells and the use of a fluorescent reporter in intact islets. Such physiologic activation of IRE1 by glucose contrasted with IRE1 activation by chemical stress, when both IRE1 activities were induced. Thus, whereas the stimulus determines the quality of IRE1 signaling, PDIA6 attenuates multiple enzymatic activities of IRE1, maintaining its signaling within a physiologically tolerable range.