RESUMO
Redox-mediated posttranslational modifications represent a molecular switch that controls major mechanisms of cell function. Nitric oxide (NO) can mediate redox reactions via S-nitrosylation, representing transfer of an NO group to a critical protein thiol. NO is known to modulate neurogenesis and neuronal survival in various brain regions in disparate neurodegenerative conditions. However, a unifying molecular mechanism linking these phenomena remains unknown. Here, we report that S-nitrosylation of myocyte enhancer factor 2 (MEF2) transcription factors acts as a redox switch to inhibit both neurogenesis and neuronal survival. Structure-based analysis reveals that MEF2 dimerization creates a pocket, facilitating S-nitrosylation at an evolutionally conserved cysteine residue in the DNA binding domain. S-Nitrosylation disrupts MEF2-DNA binding and transcriptional activity, leading to impaired neurogenesis and survival in vitro and in vivo. Our data define a molecular switch whereby redox-mediated posttranslational modification controls both neurogenesis and neurodegeneration via a single transcriptional signaling cascade.
Assuntos
Apoptose , Fatores de Transcrição MEF2/metabolismo , Células-Tronco Neurais/metabolismo , Neurogênese , Óxido Nítrico/metabolismo , Processamento de Proteína Pós-Traducional , Ativação Transcricional , Animais , Sítios de Ligação , Células Cultivadas , DNA/metabolismo , Células HEK293 , Humanos , Fatores de Transcrição MEF2/química , Fatores de Transcrição MEF2/genética , Camundongos , Células-Tronco Neurais/citologia , Oxirredução , Ligação ProteicaRESUMO
X-linked inhibitor of apoptosis (XIAP) is a potent antagonist of caspase apoptotic activity. XIAP also functions as an E3 ubiquitin ligase, targeting caspases for degradation. However, molecular pathways controlling XIAP activities remain unclear. Here, we report that nitric oxide (NO) reacts with XIAP by S-nitrosylating its RING domain (forming SNO-XIAP), thereby inhibiting E3 ligase and antiapoptotic activity. NO-mediated neurotoxicity and caspase activation have been linked to several neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases. We find significant SNO-XIAP formation in brains of patients with these diseases, implicating this reaction in the etiology of neuronal damage. Conversely, S-nitrosylation of caspases is known to inhibit apoptotic activity. Unexpectedly, we find that SNO-caspase transnitrosylates (transfers its NO group) to XIAP, forming SNO-XIAP, and thus promotes cell injury and death. These findings provide insights into the regulation of caspase activation in neurodegenerative disorders mediated, at least in part, by nitrosative stress.
Assuntos
Apoptose , Caspases/metabolismo , Óxido Nítrico/metabolismo , Processamento de Proteína Pós-Traducional , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismo , Caspases/genética , Ativação Enzimática/genética , Humanos , Doenças Neurodegenerativas/genética , Doenças Neurodegenerativas/metabolismo , Óxido Nítrico/genética , Estrutura Terciária de Proteína , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/genéticaRESUMO
Huntington's disease is caused by an expanded CAG repeat in the gene encoding huntingtin (HTT), resulting in loss of striatal and cortical neurons. Given that the gene product is widely expressed, it remains unclear why neurons are selectively targeted. Here we show the relationship between synaptic and extrasynaptic activity, inclusion formation of mutant huntingtin protein (mtHtt) and neuronal survival. Synaptic N-methyl-D-aspartate-type glutamate receptor (NMDAR) activity induces mtHtt inclusions via a T complex-1 (TCP-1) ring complex (TRiC)-dependent mechanism, rendering neurons more resistant to mtHtt-mediated cell death. In contrast, stimulation of extrasynaptic NMDARs increases the vulnerability of mtHtt-containing neurons to cell death by impairing the neuroprotective cyclic AMP response element-binding protein (CREB)-peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) cascade and increasing the level of the small guanine nucleotide-binding protein Rhes, which is known to sumoylate and disaggregate mtHtt. Treatment of transgenic mice expressing a yeast artificial chromosome containing 128 CAG repeats (YAC128) with low-dose memantine blocks extrasynaptic (but not synaptic) NMDARs and ameliorates neuropathological and behavioral manifestations. By contrast, high-dose memantine, which blocks both extrasynaptic and synaptic NMDAR activity, decreases neuronal inclusions and worsens these outcomes. Our findings offer a rational therapeutic approach for protecting susceptible neurons in Huntington's disease.
Assuntos
Mutação , Proteínas do Tecido Nervoso/fisiologia , Proteínas Nucleares/fisiologia , Receptores de N-Metil-D-Aspartato/fisiologia , Sinapses/fisiologia , Animais , Morte Celular/fisiologia , Cromossomos Artificiais de Levedura , Proteína Huntingtina , Memantina/farmacologia , Camundongos , Camundongos Transgênicos , Proteínas do Tecido Nervoso/genética , Neurônios/citologia , Neurônios/efeitos dos fármacos , Proteínas Nucleares/genética , Técnicas de Patch-Clamp , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Transativadores/fisiologia , Fatores de TranscriçãoRESUMO
Impaired adult neurogenesis has been observed in several neurodegenerative diseases, including human immunodeficiency virus (HIV-1)-associated dementia (HAD). Here we report that the HIV-envelope glycoprotein gp120, which is associated with HAD pathogenesis, inhibits proliferation of adult neural progenitor cells (aNPCs) in vitro and in vivo in the dentate gyrus of the hippocampus of HIV/gp120-transgenic mice. We demonstrate that HIV/gp120 arrests cell-cycle progression of aNPCs at the G1 phase via a cascade consisting of p38 mitogen-activated protein kinase (MAPK) --> MAPK-activated protein kinase 2 (a cell-cycle checkpoint kinase) --> Cdc25B/C. Our findings define a molecular mechanism that compromises adult neurogenesis in this neurodegenerative disorder.