title: Alleviation of autophagy by knockdown of Beclin-1 enhances susceptibility of hippocampal neurons to proapoptotic signals induced by amino acid starvation.
abstract: Autophagy has been described as a cellular response to stressful stimuli like starvation. One of its primary functions is to recycle amino acids from degraded proteins for cellular survival under nutrient deprived conditions. Autophagy is characterized by double membrane cytosolic vesicles called autophagosomes and prolonged autophagy is known to result in autophagic (Type II) cell death. Beclin-1 is involved in the regulation of autophagy in mammalian cells. This study examined the potential impact of knockdown of beclin-1 in an autophagic response in HT22 neurons challenged with amino acid starvation (AAS). AAS exposure induced light chain-3 (LC-3)-immunopositive and monodansylcadaverine (MDC) fluorescent dye-labeled autophagosome formation in cell bodies as early as 3 h post-AAS in wild type cells. Elevated levels of the autophagosome-targeting LC3-II were also observed following AAS. In addition, neuronal death induced by AAS in HT22-cells led to a moderate activation of caspase-3, a slight upregulation of AIF and did not alter the HtrA2 levels. Autophagy inhibition by a knockdown of beclin-1 significantly reduced AAS-induced LC3-II increase, reduced accumulation of autophagosomes, and potentiated AAS-mediated neuronal death. Collectively, this study shows that the both apoptotic and autophagic machineries are inducible in cultured hippocampal HT22 neurons subjected to AAS. Our data further show that attenuation of autophagy by a knockdown of beclin-1 enhanced neurons susceptibility to proapoptotic signals induced by AAS and underlines that autophagy is per se a protective than a deleterious mechanism.
authors.affiliation: Dr. Senckenbergische Anatomie, Institute of Cellular and Molecular Anatomy, Wolfgang Goethe-University, Anatomie III, Universitätsklinikum, Theodor-Stern-Kai 7, 60590 Frankfurt/Main, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Kim
authors.forename: J
authors.initials: J
authors.lastname: Fekadu
authors.forename: E
authors.initials: E
authors.lastname: Maronde
authors.forename: A
authors.initials: A
authors.lastname: Rami
mesh_terms: D000596:Amino Acids / Q000172:deficiency*; D000818:Animals; D017209:Apoptosis; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy; D000071186:Beclin-1; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D055785:Gene Knockdown Techniques; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006624:Hippocampus / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D034622:RNA Interference; D012697:Serine Endopeptidases / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
chemical_list: D000596:Amino Acids; D051033:Apoptosis Inducing Factor; D051017:Apoptosis Regulatory Proteins; D000071186:Beclin-1; C115010:Becn1 protein, mouse; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D024101:Mitochondrial Proteins; C494830:AIFM1 protein, mouse; D012697:Serine Endopeptidases; D000074923:High-Temperature Requirement A Serine Peptidase 2; C000615915:Htra2 protein, mouse; C505409:Casp3 protein, mouse; D053148:Caspase 3