title: Inhibition of autophagic turnover in β-cells by fatty acids and glucose leads to apoptotic cell death.
abstract: Autophagy, a cellular recycling process responsible for turnover of cytoplasmic contents, is critical for maintenance of health. Defects in this process have been linked to diabetes. Diabetes-associated glucotoxicity/lipotoxicity contribute to impaired β-cell function and have been implicated as contributing factors to this disease. We tested the hypothesis that these two conditions affect β-cell function by modulating autophagy. We report that exposure of β-cell lines and human pancreatic islets to high levels of glucose and lipids blocks autophagic flux and leads to apoptotic cell death. EM analysis showed accumulation of autophagy intermediates (autophagosomes), with abundant engulfed cargo in palmitic acid (PA)- or glucose-treated cells, indicating suppressed autophagic turnover. EM studies also showed accumulation of damaged mitochondria, endoplasmic reticulum distention, and vacuolar changes in PA-treated cells. Pulse-chase experiments indicated decreased protein turnover in β-cells treated with PA/glucose. Expression of mTORC1, an inhibitor of autophagy, was elevated in β-cells treated with PA/glucose. mTORC1 inhibition, by treatment with rapamycin, reversed changes in autophagic flux, and cell death induced by glucose/PA. Our results indicate that nutrient toxicity-induced cell death occurs via impaired autophagy and is mediated by activation of mTORC1 in β-cells, contributing to β-cell failure in the presence of metabolic stress.
authors.affiliation: From the Department of Surgery and the Holland Regenerative Medicine Program, University Nebraska Medical Center, Omaha, Nebraska 68198-5965.
authors.forename: Shakeel U R
authors.initials: SU
authors.lastname: Mir
authors.affiliation: From the Department of Surgery and the Holland Regenerative Medicine Program, University Nebraska Medical Center, Omaha, Nebraska 68198-5965.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: George
authors.affiliation: From the Department of Surgery and the Holland Regenerative Medicine Program, University Nebraska Medical Center, Omaha, Nebraska 68198-5965.
authors.forename: Lubna
authors.initials: L
authors.lastname: Zahoor
authors.affiliation: From the Department of Surgery and the Holland Regenerative Medicine Program, University Nebraska Medical Center, Omaha, Nebraska 68198-5965.
authors.forename: Robert
authors.initials: R
authors.lastname: Harms
authors.affiliation: From the Department of Surgery and the Holland Regenerative Medicine Program, University Nebraska Medical Center, Omaha, Nebraska 68198-5965.
authors.forename: Zachary
authors.initials: Z
authors.lastname: Guinn
authors.affiliation: From the Department of Surgery and the Holland Regenerative Medicine Program, University Nebraska Medical Center, Omaha, Nebraska 68198-5965 noras@unmc.edu.
authors.forename: Nora E
authors.initials: NE
authors.lastname: Sarvetnick
mesh_terms: D000328:Adult; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001343:Autophagy / Q000235:genetics*; D000071193:Autophagy-Related Protein 7; D002460:Cell Line; D003920:Diabetes Mellitus / Q000235:genetics* / Q000473:pathology; D005227:Fatty Acids / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000473:pathology; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000235:genetics*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000235:genetics*; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D046912:Multiprotein Complexes; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; D044764:Ubiquitin-Activating Enzymes; D005947:Glucose
keywords: ATP; Apoptosis; Autophagy; Autophagy-related Protein 7 (ATG7); Beta Cell (B-cell)