RESUMO
Methylmercury (MeHg) is a persistent environmental toxin present in seafood that can compromise the developing nervous system in humans. The effects of MeHg toxicity varies among individuals, despite similar levels of exposure, indicating that genetic differences contribute to MeHg susceptibility. To examine how genetic variation impacts MeHg tolerance, we assessed developmental tolerance to MeHg using the sequenced, inbred lines of the Drosophila melanogaster Genetic Reference Panel (DGRP). We found significant genetic variation in the effects of MeHg on development, measured by eclosion rate, giving a broad sense heritability of 0.86. To investigate the influence of dietary factors, we measured MeHg toxicity with caffeine supplementation in the DGRP lines. We found that caffeine counteracts the deleterious effects of MeHg in the majority of lines, and there is significant genetic variance in the magnitude of this effect, with a broad sense heritability of 0.80. We performed genome-wide association (GWA) analysis for both traits, and identified candidate genes that fall into several gene ontology categories, with enrichment for genes involved in muscle and neuromuscular development. Overexpression of glutamate-cysteine ligase, a MeHg protective enzyme, in a muscle-specific manner leads to a robust rescue of eclosion of flies reared on MeHg food. Conversely, mutations in kirre, a pivotal myogenic gene identified in our GWA analyses, modulate tolerance to MeHg during development in accordance with kirre expression levels. Finally, we observe disruptions of indirect flight muscle morphogenesis in MeHg-exposed pupae. Since the pathways for muscle development are evolutionarily conserved, it is likely that the effects of MeHg observed in Drosophila can be generalized across phyla, implicating muscle as an additional hitherto unrecognized target for MeHg toxicity. Furthermore, our observations that caffeine can ameliorate the toxic effects of MeHg show that nutritional factors and dietary manipulations may offer protection against the deleterious effects of MeHg exposure.
Assuntos
Drosophila melanogaster/crescimento & desenvolvimento , Drosophila melanogaster/genética , Estudo de Associação Genômica Ampla , Compostos de Metilmercúrio/toxicidade , Desenvolvimento Muscular/efeitos dos fármacos , Desenvolvimento Muscular/genética , Sistema Nervoso/crescimento & desenvolvimento , Animais , Drosophila melanogaster/efeitos dos fármacos , Feminino , Ontologia Genética , Redes Reguladoras de Genes/efeitos dos fármacos , Humanos , Larva/efeitos dos fármacos , Larva/genética , Larva/crescimento & desenvolvimento , Sistema Nervoso/efeitos dos fármacos , Fenótipo , Pupa/efeitos dos fármacos , Pupa/genética , Pupa/crescimento & desenvolvimentoRESUMO
Neuroinflammation, through production of proinflammatory molecules and activated glial cells, is implicated in Alzheimer's disease (AD) pathogenesis. One such proinflammatory mediator is tumor necrosis factor α (TNF-α), a multifunctional cytokine produced in excess and associated with amyloid ß-driven inflammation and cognitive decline. Long-term global inhibition of TNF receptor type I (TNF-RI) and TNF-RII signaling without cell or stage specificity in triple-transgenic AD mice exacerbates hallmark amyloid and neurofibrillary tangle pathology. These observations revealed that long-term pan anti-TNF-α inhibition accelerates disease, cautions against long-term use of anti-TNF-α therapeutics for AD, and urges more selective regulation of TNF signaling. We used adeno-associated virus vector-delivered siRNAs to selectively knock down neuronal TNF-R signaling. We demonstrate divergent roles for neuronal TNF-RI and TNF-RII where loss of opposing TNF-RII leads to TNF-RI-mediated exacerbation of amyloid ß and Tau pathology in aged triple-transgenic AD mice. Dampening of TNF-RII or TNF-RI+RII leads to a stage-independent increase in Iba-1-positive microglial staining, implying that neuronal TNF-RII may act nonautonomously on the microglial cell population. These results reveal that TNF-R signaling is complex, and it is unlikely that all cells and both receptors will respond positively to broad anti-TNF-α treatments at various stages of disease. In aggregate, these data further support the development of cell-, stage-, and/or receptor-specific anti-TNF-α therapeutics for AD.
Assuntos
Doença de Alzheimer/metabolismo , Neurônios/metabolismo , Receptores do Fator de Necrose Tumoral/biossíntese , Adenoviridae/genética , Envelhecimento/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/metabolismo , Animais , Encéfalo/patologia , Progressão da Doença , Regulação para Baixo/fisiologia , Técnicas de Silenciamento de Genes , Vetores Genéticos , Masculino , Camundongos , Camundongos Transgênicos , Microglia/metabolismo , Placa Amiloide/metabolismo , RNA Interferente Pequeno/genética , Receptores do Fator de Necrose Tumoral/deficiência , Receptores do Fator de Necrose Tumoral/genética , Receptores Tipo I de Fatores de Necrose Tumoral/biossíntese , Receptores Tipo I de Fatores de Necrose Tumoral/deficiência , Receptores Tipo I de Fatores de Necrose Tumoral/genética , Receptores Tipo II do Fator de Necrose Tumoral/biossíntese , Receptores Tipo II do Fator de Necrose Tumoral/deficiência , Receptores Tipo II do Fator de Necrose Tumoral/genética , Transdução de Sinais/fisiologiaRESUMO
Alterations in adult hippocampal neurogenesis have been observed in numerous neurological diseases that contain a neuroinflammatory component. Interleukin-1ß (IL-1ß) is a pro-inflammatory cytokine that contributes to neuroinflammation in many CNS disorders. Our previous results reveal a severe reduction in adult hippocampal neurogenesis due to focal and chronic expression of IL-1ß in a transgenic mouse model, IL-1ß(XAT), that evokes a complex neuroinflammatory response. Other investigators have shown that IL-1ß can bind directly to neural precursors to cause cell cycle arrest in vitro. In order to observe if IL-1 signaling is necessary in vivo, we conditionally knocked out MyD88, an adapter protein essential for IL-1 signaling, in nestin(+) neural precursor cells (NPCs) in the presence of IL-1ß-dependent inflammation. Our results show that conditional knockout of MyD88 does not prevent IL-1ß-induced reduction in neuroblasts using a genetic fate mapping model. Interestingly, MyD88 deficiency in nestin(+) NPCs causes an increase in the number of astrocytes in the presence of IL-1ß, suggesting that MyD88-dependent signaling is important in limiting astroglial differentiation due to inflammation. MyD88 deficiency does not alter the fate of NPCs in the absence of inflammation. Furthermore, the inflammatory milieu due to IL-1ß is not affected by the absence of MyD88 in nestin(+) NPCs. These results show that sustained IL-1ß causes a reduction in adult hippocampal neurogenesis that is independent of MyD88-dependent signaling in nestin(+) NPCs, suggesting an indirect negative effect of IL-1ß on neurogenesis.
Assuntos
Hipocampo/crescimento & desenvolvimento , Interleucina-1beta/biossíntese , Nestina/fisiologia , Células-Tronco Neurais/fisiologia , Neurogênese/fisiologia , Animais , Antineoplásicos Hormonais/toxicidade , Astrócitos/efeitos dos fármacos , Astrócitos/fisiologia , Dependovirus/genética , Feminino , Citometria de Fluxo , Hipocampo/citologia , Imuno-Histoquímica , Masculino , Camundongos , Camundongos Knockout , Fator 88 de Diferenciação Mieloide/biossíntese , Fator 88 de Diferenciação Mieloide/genética , Nestina/genética , Células-Tronco Neurais/metabolismo , RNA/biossíntese , RNA/isolamento & purificação , Reação em Cadeia da Polimerase em Tempo Real , Receptores de Interleucina-1/biossíntese , Transdução de Sinais/fisiologia , Tamoxifeno/toxicidadeRESUMO
Tumor Necrosis Factor-alpha (TNF-α) is a prototypic pro-inflammatory cytokine involved in the innate immune response. TNF-α ligation and downstream signaling with one of its cognate receptors, TNF-RI or TNF-RII, modulates fundamental processes in the brain including synapse formation and regulation, neurogenesis, regeneration, and general maintenance of the central nervous system (CNS). During states of chronic neuroinflammation, extensive experimental evidence implicates TNF-α as a key mediator in disease progression, gliosis, demyelination, inflammation, blood-brain-barrier deterioration, and cell death. This review explores the complex roles of TNF-α in the CNS under normal physiologic conditions and during neurodegeneration. We focus our discussion on Multiple Sclerosis, Parkinson's disease, and Alzheimer's disease, relaying the outcomes of preclinical and clinical testing of TNF-α directed therapeutic strategies, and arguing that despite the wealth of functions attributed to this central cytokine, surprisingly little is known about the cell type- and stage-specific roles of TNF-α in these debilitating disorders.
Assuntos
Doença de Alzheimer/imunologia , Homeostase/imunologia , Esclerose Múltipla/imunologia , Doença de Parkinson/imunologia , Fator de Necrose Tumoral alfa/imunologia , Doença de Alzheimer/metabolismo , Animais , Sistema Nervoso Central/imunologia , Humanos , Esclerose Múltipla/metabolismo , Neurogênese/imunologia , Doença de Parkinson/metabolismo , Transdução de Sinais/imunologia , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by severe memory loss and cognitive impairment. Neuroinflammation, including the extensive production of pro-inflammatory molecules and the activation of microglia, has been implicated in the disease process. Tumor necrosis factor (TNF)-α, a prototypic pro-inflammatory cytokine, is elevated in AD, is neurotoxic, and colocalizes with amyloid plaques in AD animal models and human brains. We previously demonstrated that the expression of TNF-α is increased in AD mice at ages preceding the development of hallmark amyloid and tau pathological features and that long-term expression of this cytokine in these mice leads to marked neuronal death. Such observations suggest that TNF-α signaling promotes AD pathogenesis and that therapeutics suppressing this cytokine's activity may be beneficial. To dissect TNF-α receptor signaling requirements in AD, we generated triple-transgenic AD mice (3xTg-AD) lacking both TNF-α receptor 1 (TNF-RI) and 2 (TNF-RII), 3xTg-ADxTNF-RI/RII knock out, the cognate receptors of TNF-α. These mice exhibit enhanced amyloid and tau-related pathological features by the age of 15 months, in stark contrast to age-matched 3xTg-AD counterparts. Moreover, 3xTg-ADxTNF-RI/RII knock out-derived primary microglia reveal reduced amyloid-ß phagocytic marker expression and phagocytosis activity, indicating that intact TNF-α receptor signaling is critical for microglial-mediated uptake of extracellular amyloid-ß peptide pools. Overall, our results demonstrate that globally ablated TNF receptor signaling exacerbates pathogenesis and argues against long-term use of pan-anti-TNF-α inhibitors for the treatment of AD.