RESUMO
Diverse stress signals including irradiation may trigger cellular senescence. We asked whether irradiation induced senescence in mouse hippocampus, and whether p53 or p21 played a role in this response. Following whole-brain irradiation, polymerase chain reaction (PCR) arrays for senescence-associated genes showed increased expression of CDKN1A (p21) and CDKN2A (p19ARF) in mouse hippocampus at 9 weeks. Upregulation of p21 and p19ARF was confirmed using real-time PCR, which also demonstrated increased CDKN2A/p16INKa expression after irradiation. No altered regulation of another 17 senescence-associated genes was observed after irradiation. Immunohistochemistry revealed increased nuclear expression of p16INK4A, p19ARF, p53, p21, phosphorylated p38 (pp38), 4-hydroxy-2-nonenal, and interleukin-6 (IL6) in granule cells of dentate gyrus after irradiation. Increased p16 nuclear immunoreactivity was further observed in type -1 cells, the putative neural stem cells. γ-phosphorylated-histone-2A nuclear foci were also seen in dentate gyrus 9 weeks postirradiation. In nonirradiated mice knockout of the TRP53 or p21 gene, there was increased p16INK4A, p19ARF, and IL6, but not pp38 in dentate gyrus. We conclude that irradiation induces transcript and protein expression profile alterations in mouse dentate gyrus consistent with the senescence phenotype. Absence of p53 or p21 results in increase in baseline expression of senescence markers with no further increase in expression after irradiation.
Assuntos
Senescência Celular/efeitos da radiação , Inibidor p16 de Quinase Dependente de Ciclina/efeitos da radiação , Inibidor de Quinase Dependente de Ciclina p21/efeitos da radiação , Hipocampo/efeitos da radiação , Animais , Biomarcadores/metabolismo , Núcleo Celular/metabolismo , Núcleo Celular/efeitos da radiação , Inibidor p16 de Quinase Dependente de Ciclina/biossíntese , Inibidor p16 de Quinase Dependente de Ciclina/genética , Inibidor de Quinase Dependente de Ciclina p21/biossíntese , Inibidor de Quinase Dependente de Ciclina p21/genética , Giro Denteado/metabolismo , Giro Denteado/efeitos da radiação , Interleucina-6/biossíntese , Interleucina-6/efeitos da radiação , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Células-Tronco Neurais/metabolismo , Células-Tronco Neurais/efeitos da radiação , Regulação para Cima/efeitos da radiaçãoRESUMO
Mammalian tissue-specific stem cells and progenitors demonstrate differential DNA damage response. Neural progenitors in dentate gyrus of the hippocampus are known to undergo apoptosis after irradiation. Using a mouse model of hippocampal neuronal development, we characterized the apoptosis sensitivity of the different neural progenitor subpopulations in adult mouse dentate gyrus after irradiation. Two different bromodeoxyuridine incorporation paradigms were used for cell fate mapping. We identified two apoptosis sensitive neural progenitor subpopulations after irradiation. The first represented non-proliferative and non-newborn neuroblasts and immature neurons that expressed doublecortin, calretinin or both. The second consisted of proliferative intermediate neural progenitors. The putative radial glia-like neural stem cells or type-1 cells, regardless of proliferation status, were apoptosis resistant after irradiation. There was no evidence of radiation-induced apoptosis in the absence of the Trp53 (p53) gene but absence of Cdkn1a (p21) did not alter the apoptotic response. Upregulation of nuclear p53 was observed in neuroblasts after irradiation. We conclude that adult hippocampal neural progenitors may demonstrate differential p53-dependent apoptosis sensitivity after irradiation.
Assuntos
Apoptose , Hipocampo/efeitos da radiação , Células-Tronco Neurais/efeitos da radiação , Tolerância a Radiação , Animais , Calbindina 2/genética , Calbindina 2/metabolismo , Inibidor de Quinase Dependente de Ciclina p21/genética , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Proteínas do Domínio Duplacortina , Hipocampo/citologia , Hipocampo/crescimento & desenvolvimento , Hipocampo/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Células-Tronco Neurais/citologia , Células-Tronco Neurais/metabolismo , Neurogênese , Neuropeptídeos/genética , Neuropeptídeos/metabolismo , Radiação Ionizante , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
PURPOSE: To assess the influence of aging on hippocampal neuronal development after irradiation (IR). METHODS AND MATERIALS: Male mice, 2, 4, 6, 12, and 18 months of age, were given a single dose of 0 or 5 Gy of IR. A bromodeoxyuridine (BrdU) incorporation study was used to label newborn cells. Neural progenitors, newborn neurons, and microglia in dentate gyrus (DG) were identified by phenotypic markers, and their numbers were quantified by nonbiased stereology 9 weeks after IR. RESULTS: BrdU-positive or newborn cells in DG decreased with aging and after IR. The number of neuroblasts and newborn neurons decreased with aging, and a further significant reduction was observed after IR. Total type 1 cells (the putative neural stem cells), and newborn type 1 cells decreased with aging, and further reduction in total type 1 cells was observed after IR. Aging-associated activation of microglia in hippocampus was enhanced after IR. CONCLUSIONS: The aging-associated decline in hippocampal neurogenesis was further inhibited after IR. Ablation of neural progenitors and activation of microglia may contribute to the inhibition of neuronal development after IR across all ages.
