title: Heightened induction of proapoptotic signals in response to endoplasmic reticulum stress in primary fibroblasts from a mouse model of longevity.
abstract: Previous work from our laboratory has shown that primary fibroblasts from long-lived Snell dwarf mice display a higher sensitivity to the lethal effects of endoplasmic reticulum (ER) stressors, such as thapsigargin, than cells from normal mice. Here we show that thapsigargin induces higher expression of CHOP, enhanced cleavage of caspase-12, higher caspase-3 activity, and increased phosphorylation of c-JUN, all indicators of enhanced apoptosis, in dwarf fibroblasts. Dwarf and normal fibroblasts show no genotypic difference in up-regulating BiP, GRP94, and ERp72 proteins after exposure to thapsigargin. However, dwarf fibroblasts express lower basal levels of a number of putative XBP1 target genes including Armet, Edem1, Erdj3, p58(IPK) and Sec61a1, as well as Ire1α itself. Furthermore, when exposed to thapsigargin, dwarf fibroblasts display attenuated splicing of Xbp1, but similar phosphorylation of eIF2α, in comparison to normal fibroblasts. These data support the notion that IRE1/XBP1 signaling is set at a lower level in dwarf fibroblasts. Diminished Xbp1 splicing in dwarf-derived fibroblasts may tilt the balance between prosurvival and proapoptotic signals in favor of apoptosis, thereby leading to higher induction of proapoptotic signals in these cells and ultimately their increased sensitivity to ER stressors. These results, together with recent findings in Caenorhabditis elegans daf-2 mutants, point to a potential interplay between insulin/IGF-1 signals and unfolded protein response signaling.
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan 48109. Electronic address: asadighi@umich.edu.
authors.forename: Amir A
authors.initials: AA
authors.lastname: Sadighi Akha
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: James M
authors.initials: JM
authors.lastname: Harper
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Salmon
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Bethany A
authors.initials: BA
authors.lastname: Schroeder
authors.affiliation: Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Tyra
authors.affiliation: Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242.
authors.forename: D Thomas
authors.initials: DT
authors.lastname: Rutkowski
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan 48109; Geriatrics Center, University of Michigan Medical School, Ann Arbor, Michigan 48109; Ann Arbor Veterans Affairs Medical Center, Ann Arbor, Michigan 48105.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Miller
mesh_terms: D000818:Animals; D017209:Apoptosis; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation; D008136:Longevity / Q000235:genetics*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008822:Mice, Transgenic; D009154:Mutation; D010766:Phosphorylation; D010902:Pituitary Gland / Q000378:metabolism; D011489:Protein Denaturation; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction; D051742:Transcription Factor CHOP / Q000378:metabolism
chemical_list: D029742:Caenorhabditis elegans Proteins; D051742:Transcription Factor CHOP; C107483:DAF-2 protein, C elegans; D011972:Receptor, Insulin