RESUMO
Hyperhomocysteinemia reduces neurogenesis in the adult mouse brain. Homocysteine (Hcy) inhibits postnatal neural progenitor cell (NPC) proliferation by specifically impairing the fibroblast growth factor receptor (FGFR)-Erk1/2-cyclin E signaling pathway. We demonstrate herein that the inhibition of FGFR-dependent NPC proliferation induced by Hcy is mediated by its capacity to alter the cellular methylation potential. Our results show that this alteration modified the expression pattern and activity of Sprouty2 (Spry2), a negative regulator of the above mentioned pathway. Both elevated concentrations of Hcy and methyltransferase activity inhibition induced Spry2 promoter demethylation in NPC cultures leading to a sustained upregulation of the expression of Spry2 mRNA and protein. In addition, protein levels of two kinases responsible for Spry2 activation/deactivation were altered by Hcy: Spry2 kinase Dyrk1A levels diminished while Spry2 phosphatase PP2A increased, leading to changes in the phosphorylation pattern, activity and stability of Spry2. In conclusion, Hcy inhibits NPC proliferation by indirect mechanisms involving alterations in DNA methylation, gene expression, and Spry2 function, causing FGFR signaling impairment.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Homocisteína/farmacologia , Peptídeos e Proteínas de Sinalização Intracelular/genética , Proteínas de Membrana/genética , Células-Tronco Neurais/efeitos dos fármacos , Proteína Fosfatase 2/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Tirosina Quinases/genética , Animais , Proliferação de Células/efeitos dos fármacos , Ciclina E/genética , Ciclina E/metabolismo , Metilação de DNA/efeitos dos fármacos , Homocisteína/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas de Membrana/metabolismo , Camundongos , Proteína Quinase 1 Ativada por Mitógeno/genética , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/genética , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Células-Tronco Neurais/citologia , Células-Tronco Neurais/metabolismo , Neurogênese/efeitos dos fármacos , Neurogênese/genética , Fosforilação , Regiões Promotoras Genéticas , Proteína Fosfatase 2/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Estabilidade Proteica , Proteínas Tirosina Quinases/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Receptores de Fatores de Crescimento de Fibroblastos/genética , Receptores de Fatores de Crescimento de Fibroblastos/metabolismo , Transdução de Sinais , Esferoides Celulares/citologia , Esferoides Celulares/efeitos dos fármacos , Esferoides Celulares/metabolismo , Quinases DyrkRESUMO
The hippocampus is a brain area characterized by its high plasticity, observed at all levels of organization: molecular, synaptic, and cellular, the latter referring to the capacity of neural precursors within the hippocampus to give rise to new neurons throughout life. Recent findings suggest that promoter methylation is a plastic process subjected to regulation, and this plasticity seems to be particularly important for hippocampal neurogenesis. We have detected the enzyme GNMT (a liver metabolic enzyme) in the hippocampus. GNMT regulates intracellular levels of SAMe, which is a universal methyl donor implied in almost all methylation reactions and, thus, of prime importance for DNA methylation. In addition, we show that deficiency of this enzyme in mice (Gnmt-/-) results in high SAMe levels within the hippocampus, reduced neurogenic capacity, and spatial learning and memory impairment. In vitro, SAMe inhibited neural precursor cell division in a concentration-dependent manner, but only when proliferation signals were triggered by bFGF. Indeed, SAMe inhibited the bFGF-stimulated MAP kinase signaling cascade, resulting in decreased cyclin E expression. These results suggest that alterations in the concentration of SAMe impair neurogenesis and contribute to cognitive decline.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/psicologia , Cognição/fisiologia , Glicina N-Metiltransferase/deficiência , Hipocampo/enzimologia , Proteínas do Tecido Nervoso/fisiologia , Neurogênese/fisiologia , S-Adenosilmetionina/fisiologia , Animais , Ciclina E/biossíntese , Ciclina E/genética , Fator 2 de Crescimento de Fibroblastos/antagonistas & inibidores , Fator 2 de Crescimento de Fibroblastos/farmacologia , Regulação da Expressão Gênica , Glicina N-Metiltransferase/genética , Glicina N-Metiltransferase/fisiologia , Hipocampo/fisiopatologia , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Aprendizagem em Labirinto/fisiologia , Transtornos da Memória/enzimologia , Transtornos da Memória/etiologia , Metionina/metabolismo , Metionina Adenosiltransferase/deficiência , Metionina Adenosiltransferase/genética , Metilação , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas do Tecido Nervoso/deficiência , Proteínas do Tecido Nervoso/genética , Plasticidade Neuronal , Teste de Desempenho do Rota-Rod , S-Adenosilmetionina/biossínteseRESUMO
De novo protein synthesis is required for synapse modifications underlying stable memory encoding. Yet neurons are highly compartmentalized cells and how protein synthesis can be regulated at the synapse level is unknown. Here, we characterize neuronal signaling complexes formed by the postsynaptic scaffold GIT1, the mechanistic target of rapamycin (mTOR) kinase, and Raptor that couple synaptic stimuli to mTOR-dependent protein synthesis; and identify NMDA receptors containing GluN3A subunits as key negative regulators of GIT1 binding to mTOR. Disruption of GIT1/mTOR complexes by enhancing GluN3A expression or silencing GIT1 inhibits synaptic mTOR activation and restricts the mTOR-dependent translation of specific activity-regulated mRNAs. Conversely, GluN3A removal enables complex formation, potentiates mTOR-dependent protein synthesis, and facilitates the consolidation of associative and spatial memories in mice. The memory enhancement becomes evident with light or spaced training, can be achieved by selectively deleting GluN3A from excitatory neurons during adulthood, and does not compromise other aspects of cognition such as memory flexibility or extinction. Our findings provide mechanistic insight into synaptic translational control and reveal a potentially selective target for cognitive enhancement.
Assuntos
Memória/fisiologia , Biossíntese de Proteínas/fisiologia , Receptores de N-Metil-D-Aspartato/metabolismo , Serina-Treonina Quinases TOR/metabolismo , Animais , Feminino , Masculino , Alvo Mecanístico do Complexo 1 de Rapamicina , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Transdução de SinaisRESUMO
Neurodevelopmental disorders (NDDs) are a class of disorders affecting brain development and function and are characterized by wide genetic and clinical variability. In this review, we discuss the multiple factors that influence the clinical presentation of NDDs, with particular attention to gene vulnerability, mutational load, and the two-hit model. Despite the complex architecture of mutational events associated with NDDs, the various proteins involved appear to converge on common pathways, such as synaptic plasticity/function, chromatin remodelers and the mammalian target of rapamycin (mTOR) pathway. A thorough understanding of the mechanisms behind these pathways will hopefully lead to the identification of candidates that could be targeted for treatment approaches.
Assuntos
Transtornos do Neurodesenvolvimento , Humanos , Mutação , Transtornos do Neurodesenvolvimento/genéticaRESUMO
Hyperhomocysteinemia (HHcy)-abnormally elevated plasma levels of homocysteine (Hcy)-has been associated with the development of neurodegenerative dementia and mild cognitive impairment. This association suggests that HHcy might facilitate memory loss in the elderly. As memory loss can occur through a deteriorated neurogenic capacity, we have studied the effects of Hcy on neural progenitor cells (NPCs) both in vitro and in vivo. We show that Hcy exerts an antiproliferative effect on basic fibroblast growth factor (bFGF) -stimulated NPCs isolated from the postnatal subventricular zone (SVZ), accompanied by inactivation of the extracellular signal-regulated kinase (Erk1/2) and inhibition of Erk1/2-dependent expression of cyclin E. Using a mice model we show that, under normal folate conditions, HHcy exerts an inhibitory effect on adult brain neurogenesis. This inhibition occurs in the caudal areas of the dentate gyrus (DG) of the hippocampus, a neurogenic area mainly involved in learning and memory performance, and in the SVZ, recently implicated in olfactory learning performance. In both areas reduced number of proliferative neuroblasts were found. Since neuroblasts are primarily bFGF-responsive progenitors already committed to a neuronal phenotype, our results strongly suggest that excess Hcy inhibits neurogenesis in the DG and SVZ by inhibiting the bFGF-dependent activation of Erk1/2 in these cells.
Assuntos
Células-Tronco Adultas/metabolismo , Ciclina E/biossíntese , Fator 2 de Crescimento de Fibroblastos/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Homocisteína/farmacologia , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Neurônios/enzimologia , Células-Tronco Adultas/patologia , Idoso , Idoso de 80 Anos ou mais , Animais , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Transtornos Cognitivos/enzimologia , Transtornos Cognitivos/patologia , Demência/enzimologia , Demência/patologia , Giro Denteado/enzimologia , Giro Denteado/patologia , Modelos Animais de Doenças , Fator 2 de Crescimento de Fibroblastos/farmacologia , Ácido Fólico/metabolismo , Homocisteína/metabolismo , Humanos , Hiper-Homocisteinemia/enzimologia , Hiper-Homocisteinemia/patologia , Camundongos , Doenças Neurodegenerativas/enzimologia , Doenças Neurodegenerativas/patologia , Núcleo Inferior Caudal do Nervo Trigêmeo/enzimologia , Núcleo Inferior Caudal do Nervo Trigêmeo/patologiaRESUMO
Autism spectrum disorders (ASDs) comprise a group of clinical phenotypes characterized by repetitive behavior and social and communication deficits. Autism is generally viewed as a neurodevelopmental disorder where insults during embryonic or early postnatal periods result in aberrant wiring and function of neuronal circuits. Neurexins are synaptic proteins associated with autism. Here, we generated transgenic ßNrx1ΔC mice in which neurexin function is selectively impaired during late postnatal stages. Whole-cell recordings in cortical neurons show an impairment of glutamatergic synaptic transmission in the ßNrx1ΔC mice. Importantly, mutant mice exhibit autism-related symptoms, such as increased self-grooming, deficits in social interactions, and altered interaction for nonsocial olfactory cues. The autistic-like phenotype of ßNrx1ΔC mice can be reversed after removing the mutant protein in aged animals. The defects resulting from disruption of neurexin function after the completion of embryonic and early postnatal development suggest that functional impairment of mature circuits can trigger autism-related phenotypes.