RESUMO
In order to further investigate the molecular mechanisms that regulate oligodendrocyte (OC) survival, we utilized microarrays to characterize changes in OC gene expression after exposure to the cytokines neurotrophin3, insulin, or leukemia inhibitory factor (LIF) in vitro. We identified and validated the induction and secretion of the neuropeptide galanin in OCs, specifically in response to LIF. We next established that galanin is an OC survival factor and showed that autocrine or paracrine galanin secretion mediates LIF-induced OC survival in vitro. We also revealed that galanin is up-regulated in OCs in the cuprizone model of central demyelination, and that oligodendroglial galanin expression is significantly regulated by endogenous LIF in this context. We also showed that knock-out of galanin reduces OC survival and exacerbates callosal demyelination in the cuprizone model. These findings suggest a potential role for the use of galanin agonists in the treatment of human demyelinating diseases.
Assuntos
Galanina/metabolismo , Fator Inibidor de Leucemia/metabolismo , Bainha de Mielina/fisiologia , Oligodendroglia/fisiologia , Animais , Astrócitos/patologia , Astrócitos/fisiologia , Encéfalo/patologia , Encéfalo/fisiopatologia , Sobrevivência Celular/fisiologia , Células Cultivadas , Cuprizona , Doenças Desmielinizantes/patologia , Doenças Desmielinizantes/fisiopatologia , Modelos Animais de Doenças , Galanina/genética , Expressão Gênica , Sistema de Sinalização das MAP Quinases/fisiologia , Camundongos Endogâmicos C57BL , Camundongos Knockout , Bainha de Mielina/patologia , Células-Tronco Neurais/patologia , Células-Tronco Neurais/fisiologia , Oligodendroglia/patologia , Nervo Óptico/patologia , Nervo Óptico/fisiologia , RNA Mensageiro/metabolismo , Ratos Sprague-DawleyRESUMO
OBJECTIVES: Microsatellite instability (MSI) is an established marker of good prognosis in colorectal cancer (CRC). Chromosomal instability (CIN) is strongly negatively associated with MSI and has been shown to be a marker of poor prognosis in a small number of studies. However, a substantial group of "double-negative" (MSI-/CIN-) CRCs exists. The prognosis of these patients is unclear. Furthermore, MSI and CIN are each associated with specific molecular changes, such as mutations in KRAS and BRAF, that have been associated with prognosis. It is not known which of MSI, CIN, and the specific gene mutations are primary predictors of survival. METHODS: We evaluated the prognostic value (disease-free survival, DFS) of CIN, MSI, mutations in KRAS, NRAS, BRAF, PIK3CA, FBXW7, and TP53, and chromosome 18q loss-of-heterozygosity (LOH) in 822 patients from the VICTOR trial of stage II/III CRC. We followed up promising associations in an Australian community-based cohort (N=375). RESULTS: In the VICTOR patients, no specific mutation was associated with DFS, but individually MSI and CIN showed significant associations after adjusting for stage, age, gender, tumor location, and therapy. A combined analysis of the VICTOR and community-based cohorts showed that MSI and CIN were independent predictors of DFS (for MSI, hazard ratio (HR)=0.58, 95% confidence interval (CI) 0.36-0.93, and P=0.021; for CIN, HR=1.54, 95% CI 1.14-2.08, and P=0.005), and joint CIN/MSI testing significantly improved the prognostic prediction of MSI alone (P=0.028). Higher levels of CIN were monotonically associated with progressively poorer DFS, and a semi-quantitative measure of CIN was a better predictor of outcome than a simple CIN+/- variable. All measures of CIN predicted DFS better than the recently described Watanabe LOH ratio. CONCLUSIONS: MSI and CIN are independent predictors of DFS for stage II/III CRC. Prognostic molecular tests for CRC relapse should currently use MSI and a quantitative measure of CIN rather than specific gene mutations.
Assuntos
Neoplasias Colorretais/genética , Neoplasias Colorretais/mortalidade , Instabilidade de Microssatélites , Mutação , Idoso , Idoso de 80 Anos ou mais , Proteínas de Ciclo Celular/genética , Aberrações Cromossômicas , Classe I de Fosfatidilinositol 3-Quinases , Neoplasias Colorretais/patologia , Análise Mutacional de DNA , Intervalo Livre de Doença , Proteínas F-Box/genética , Proteína 7 com Repetições F-Box-WD , Feminino , GTP Fosfo-Hidrolases/genética , Humanos , Perda de Heterozigosidade , Masculino , Proteínas de Membrana/genética , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Fosfatidilinositol 3-Quinases/genética , Prognóstico , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas B-raf/genética , Proteínas Proto-Oncogênicas p21(ras) , Taxa de Sobrevida , Proteína Supressora de Tumor p53/genética , Ubiquitina-Proteína Ligases/genética , Proteínas ras/genéticaRESUMO
Enhancement of oligodendrocyte survival through activation of leukemia inhibitory factor receptor (LIFR) signaling is a candidate therapeutic strategy for demyelinating disease. However, in other cell types, LIFR signaling is under tight negative regulation by the intracellular protein suppressor of cytokine signaling 3 (SOCS3). We, therefore, postulated that deletion of the SOCS3 gene in oligodendrocytes would promote the beneficial effects of LIFR signaling in limiting demyelination. By studying wild-type and LIF-knockout mice, we established that SOCS3 expression by oligodendrocytes was induced by the demyelinative insult, that this induction depended on LIF, and that endogenously produced LIF was likely to be a key determinant of the CNS response to oligodendrocyte loss. Compared with wild-type controls, oligodendrocyte-specific SOCS3 conditional-knockout mice displayed enhanced c-fos activation and exogenous LIF-induced phosphorylation of signal transducer and activator of transcription 3. Moreover, these SOCS3-deficient mice were protected against cuprizone-induced oligodendrocyte loss relative to wild-type animals. These results indicate that modulation of SOCS3 expression could facilitate the endogenous response to CNS injury.
