title: Modulation of apoptosis pathways by oxidative stress and autophagy in β cells.
abstract: Human islets isolated for transplantation are exposed to multiple stresses including oxidative stress and hypoxia resulting in significant loss of functional β cell mass. In this study we examined the modulation of apoptosis pathway genes in islets exposed to hydrogen peroxide, peroxynitrite, hypoxia, and cytokines. We observed parallel induction of pro- and antiapoptotic pathways and identified several novel genes including BFAR, CARD8, BNIP3, and CIDE-A. As BNIP3 is an inducer of autophagy, we examined this pathway in MIN6 cells, a mouse beta cell line and in human islets. Culture of MIN6 cells under low serum conditions increased the levels of several proteins in autophagy pathway, including ATG4, Beclin 1, LAMP-2, and UVRAG. Amino acid deprivation led to induction of autophagy in human islets. Preconditioning of islets with inducers of autophagy protected them from hypoxia-induced apoptosis. However, induction of autophagy during hypoxia exacerbated apoptotic cell death. ER stress led to induction of autophagy and apoptosis in β cells. Overexpression of MnSOD, an enzyme that scavenges free radicals, resulted in protection of MIN6 cells from cytokine-induced apoptosis. Ceramide, a mediator of cytokine-induced injury, reduced the active phosphorylated form of Akt and downregulated the promoter activity of the antiapoptotic gene bcl-2. Furthermore, cytokine-stimulated JNK pathway downregulated the bcl-2 promoter activity which was reversed by preincubation with SP600125, a JNK inhibitor. Our findings suggest that β cell apoptosis by multiple stresses in islets isolated for transplantation is the result of orchestrated gene expression in apoptosis pathway.
authors.affiliation: Section of Endocrinology, Veterans Affairs Medical Center, Denver, CO 80220, USA.
authors.forename: Maorong
authors.initials: M
authors.lastname: Wang
authors.forename: Mia
authors.initials: M
authors.lastname: Crager
authors.forename: Subbiah
authors.initials: S
authors.lastname: Pugazhenthi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics; D002460:Cell Line; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology; D020869:Gene Expression Profiling; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects* / Q000235:genetics; D030421:Peroxynitrous Acid / Q000494:pharmacology
chemical_list: D016207:Cytokines; D030421:Peroxynitrous Acid; D006861:Hydrogen Peroxide