Keenan Walker

 The highly conserved unfolded protein response (UPR) acts under endoplasmic reticulum (ER) stress as one of the main cellular signaling pathways to restore protein homeostasis and maintain cell and organismal survival through three signaling pathways: inositol-requiring enzyme 1 (IRE1), PKR-like ER kinase (PERK), and activating transcription factor 6. The UPR is especially crucial in secretory cell types. Interplay exists between arms of the UPR, but the crosstalk between PERK and IRE1 is not robustly characterized in neurons, and current findings support both antagonistic and perpetuating relationships. PERK is implicated in various diseases with neurological phenotypes, including neurodegenerative tauopathies and the genetic disorder, Wolcott-Rallison Syndrome, where a loss-of-function mutation in the PERK encoding gene can generate neurodegenerative phenotypes in young children. IRE1 is similarly implicated in neurodegeneration. These pathways are additionally pertinent in other disease models, including metabolic diseases and cancers. Here, we examine how neurons derived from iPSCs that exhibit CRISPR-Cas9-induced PERK variants affect the IRE1 signaling pathway by evaluating expression of pathway genes, protein, and cell death. Investigated cell lines include an isogenic PERK knock-out (PERK KO) and a GWAS-derived haplotype-bearing line homozygous for tauopathy-associated risk variants (TPM). To do so, we assessed UPR gene expression and apoptosis in the iPSC-derived neurons under pharmacologically-induced ER stress. Although we observed some differences in XBP1 splicing in the TPM and PERK KO via qPCR, respectively, these and downstream-IRE1 signaling were not consistent, and analysis of splicing via gel did not recapitulate the results.