RESUMO
The Huntington's disease gene product, huntingtin, is indispensable for neural tube formation, but its role is obscure. We studied neurulation in htt-null embryonic stem cells and htt-morpholino zebrafish embryos and found a previously unknown, evolutionarily recent function for this ancient protein. We found that htt was essential for homotypic interactions between neuroepithelial cells; it permitted neurulation and rosette formation by regulating metalloprotease ADAM10 activity and Ncadherin cleavage. This function was embedded in the N terminus of htt and was phenocopied by treatment of htt knockdown zebrafish with an ADAM10 inhibitor. Notably, in htt-null cells, reversion of the rosetteless phenotype occurred only with expression of evolutionarily recent htt heterologues from deuterostome organisms. Conversely, all of the heterologues that we tested, including htt from Drosophila melanogaster and Dictyostelium discoideum, exhibited anti-apoptotic activity. Thus, anti-apoptosis may have been one of htt's ancestral function(s), but, in deuterostomes, htt evolved to acquire a unique regulatory activity for controlling neural adhesion via ADAM10-Ncadherin, with implications for brain evolution and development.
Assuntos
Proteínas ADAM/metabolismo , Secretases da Proteína Precursora do Amiloide/metabolismo , Evolução Biológica , Caderinas/metabolismo , Adesão Celular/fisiologia , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Células Neuroepiteliais/fisiologia , Neurônios/fisiologia , Proteínas Nucleares/metabolismo , Proteínas ADAM/antagonistas & inibidores , Proteínas ADAM/genética , Proteína ADAM10 , Secretases da Proteína Precursora do Amiloide/antagonistas & inibidores , Secretases da Proteína Precursora do Amiloide/genética , Análise de Variância , Animais , Animais Geneticamente Modificados , Apoptose/efeitos dos fármacos , Apoptose/genética , Padronização Corporal/efeitos dos fármacos , Padronização Corporal/genética , Encéfalo/citologia , Encéfalo/efeitos dos fármacos , Encéfalo/embriologia , Encéfalo/metabolismo , Caderinas/genética , Adesão Celular/efeitos dos fármacos , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/genética , Células Cultivadas , Ventrículos Cerebrais/citologia , Ventrículos Cerebrais/embriologia , Dictyostelium , Dipeptídeos/farmacologia , Proteína 1 Homóloga a Discs-Large , Drosophila melanogaster , Embrião de Mamíferos , Embrião não Mamífero , Células-Tronco Embrionárias/efeitos dos fármacos , Células-Tronco Embrionárias/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Regulação da Expressão Gênica no Desenvolvimento/genética , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Guanilato Quinases/genética , Guanilato Quinases/metabolismo , Proteínas Hedgehog/genética , Proteínas Hedgehog/metabolismo , Proteína Huntingtina , Ácidos Hidroxâmicos/farmacologia , Imunoprecipitação , Proteínas de Filamentos Intermediários/genética , Proteínas de Membrana/antagonistas & inibidores , Proteínas de Membrana/genética , Camundongos , Morfolinas/farmacologia , Mutação/genética , Fatores de Transcrição NFI/metabolismo , Proteínas do Tecido Nervoso/genéticaRESUMO
Reduced Brain-Derived Neurotrophic Factor (BDNF) levels have been described in a number of patho-physiological conditions, most notably, in Huntington's disease (HD), a progressive neurodegenerative disorder. Since BDNF is also produced in blood, we have undertaken the measurement of its peripheral levels in the attempt to identify a possible link with HD prognosis and/or its progression. Here we evaluated BDNF level in 398 blood samples including 138 controls, 56 preHD, and 204 HD subjects. We found that BDNF protein levels were not reliably different between groups, whether measured in plasma (52 controls, 26 preHD, 105 HD) or serum (39 controls, 5 preHD, 29 HD). Our experience, and a re-analysis of the literature highlighted that intra-group variability and methodological aspects affect this measurement, especially in serum. We also assessed BDNF mRNA levels in blood samples from 47 controls, 25 preHD, and 70 HD subjects, and found no differences among the groups. We concluded that levels of BDNF in human blood were not informative (mRNA levels or plasma protein level) nor reliable (serum protein levels) as HD biomarkers. We also wish to warn the scientific community in interpreting the significance of changes measured in BDNF protein levels in serum from patients suffering from different conditions.