title: Sequential activation of caspases and synergistic beta-cell cytotoxicity by palmitate and anti-Fas antibodies.
abstract: To assess the mechanism of beta-cell lipotoxicity in comparison with Fas-mediated cell death, we used a mouse beta-cell clone stably transfected with human Fas. Palmitate induced beta-cell death in correlation with medium glucose levels between 5 and 20 mmol/l, while Fas-mediated cytotoxicity was observed irrespective of glucose concentration. At the glucose level of 10 mmol/l, palmitate induced caspase-6 activity within 3 h, and caspase-3 activity after a lag period of 6 h. The activities of caspases were correlated with glucose concentration. A caspase-6 inhibitor attenuated caspase-3 activation and cell death induced by palmitate. Oxfenicine, an inhibitor of carnitine palmitoyltransferase-1, attenuated both palmitate-induced cytotoxicity and activation of caspases. Finally, beta-cell cytotoxicity caused by the combination of anti-Fas and palmitate at 25 mmol/l of glucose was greater than the sum of those induced by each. These observations suggest that palmitate induces sequential activation of caspase-6 and caspase-3 through a mitochondrial signal(s), and caspase-6 plays a primary role in the mechanism. Fas-mediated beta-cell death and lipotoxicity may share common mechanisms involving caspase activation, and thereby synergistically inducing beta-cell death, although upstream signaling pathways are distinct.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, Kurume University School of Medicine, 67 Asahimachi, Kurume, 830-0011, Japan.
authors.forename: Naotoshi
authors.initials: N
authors.lastname: Hirota
authors.forename: Shuichi
authors.initials: S
authors.lastname: Otabe
authors.forename: Hitomi
authors.initials: H
authors.lastname: Nakayama
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Yuan
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yamada
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology*; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism; D053148:Caspase 3; D053178:Caspase 6; D020169:Caspases / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects*; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D050417:Insulin-Secreting Cells / Q000187:drug effects*; D051379:Mice; D010168:Palmitates / Q000633:toxicity*; D020239:Receptor Cross-Talk / Q000187:drug effects; D019014:fas Receptor / Q000276:immunology*
chemical_list: D000906:Antibodies; D010168:Palmitates; D019014:fas Receptor; C023010:4-hydroxyphenylglycine; D002334:Carnitine O-Palmitoyltransferase; C505407:CASP3 protein, human; C505514:CASP6 protein, human; C505409:Casp3 protein, mouse; C505516:Casp6 protein, mouse; D053148:Caspase 3; D053178:Caspase 6; D020169:Caspases; D005998:Glycine