RESUMO
ERp57 (also known as grp58 and PDIA3) is a protein disulfide isomerase that catalyzes disulfide bonds formation of glycoproteins as part of the calnexin and calreticulin cycle. ERp57 is markedly upregulated in most common neurodegenerative diseases downstream of the endoplasmic reticulum (ER) stress response. Despite accumulating correlative evidence supporting a neuroprotective role of ERp57, the contribution of this foldase to the physiology of the nervous system remains unknown. Here we developed a transgenic mouse model that overexpresses ERp57 in the nervous system under the control of the prion promoter. We analyzed the susceptibility of ERp57 transgenic mice to undergo neurodegeneration. Unexpectedly, ERp57 overexpression did not affect dopaminergic neuron loss and striatal denervation after injection of a Parkinson's disease-inducing neurotoxin. In sharp contrast, ERp57 transgenic animals presented enhanced locomotor recovery after mechanical injury to the sciatic nerve. These protective effects were associated with enhanced myelin removal, macrophage infiltration and axonal regeneration. Our results suggest that ERp57 specifically contributes to peripheral nerve regeneration, whereas its activity is dispensable for the survival of a specific neuronal population of the central nervous system. These results demonstrate for the first time a functional role of a component of the ER proteostasis network in peripheral nerve regeneration.
Assuntos
Axônios/fisiologia , Isomerases de Dissulfetos de Proteínas/genética , Isomerases de Dissulfetos de Proteínas/metabolismo , Regeneração , Animais , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/genética , Corpo Estriado/metabolismo , Denervação , Neurônios Dopaminérgicos/efeitos dos fármacos , Neurônios Dopaminérgicos/metabolismo , Neurônios Dopaminérgicos/patologia , Feminino , Expressão Gênica , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Modelos Animais , Atividade Motora/genética , Degeneração Neural/genética , Degeneração Neural/patologia , Fenômenos Fisiológicos do Sistema Nervoso , Oxidopamina/farmacologia , Traumatismos dos Nervos Periféricos/genética , Traumatismos dos Nervos Periféricos/fisiopatologia , Traumatismos dos Nervos Periféricos/reabilitaçãoRESUMO
Parkinson disease (PD) is characterized by the selective loss of dopaminergic neurons of the substantia nigra pars compacta (SNpc). Although growing evidence indicates that endoplasmic reticulum (ER) stress is a hallmark of PD, its exact contribution to the disease process is not well understood. Here we report that developmental ablation of X-Box binding protein 1 (XBP1) in the nervous system, a key regulator of the unfolded protein response (UPR), protects dopaminergic neurons against a PD-inducing neurotoxin. This survival effect was associated with a preconditioning condition that resulted from induction of an adaptive ER stress response in dopaminergic neurons of the SNpc, but not in other brain regions. In contrast, silencing XBP1 in adult animals triggered chronic ER stress and dopaminergic neuron degeneration. Supporting this finding, gene therapy to deliver an active form of XBP1 provided neuroprotection and reduced striatal denervation in animals injected with 6-hydroxydopamine. Our results reveal a physiological role of the UPR in the maintenance of protein homeostasis in dopaminergic neurons that may help explain the differential neuronal vulnerability observed in PD.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Neurônios Dopaminérgicos/citologia , Neurônios Dopaminérgicos/metabolismo , Fatores de Transcrição/metabolismo , Animais , Sobrevivência Celular , Proteínas de Ligação a DNA/deficiência , Proteínas de Ligação a DNA/genética , Neurônios Dopaminérgicos/efeitos dos fármacos , Estresse do Retículo Endoplasmático , Técnicas de Silenciamento de Genes , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Degeneração Neural , Neurotoxinas/toxicidade , Oxidopamina/toxicidade , Doença de Parkinson/etiologia , Doença de Parkinson/metabolismo , Doença de Parkinson/patologia , Fatores de Transcrição de Fator Regulador X , Substância Negra/metabolismo , Fatores de Transcrição/deficiência , Fatores de Transcrição/genética , Resposta a Proteínas não Dobradas , Proteína 1 de Ligação a X-BoxRESUMO
Parkinson's disease (PD) is the second most common neurodegenerative disease and is characterized by the selective loss of dopaminergic neurons of the substantia nigra pars compacta and the accumulation of intracellular inclusions containing α-synuclein (αSyn). Growing evidence from studies in human PD brain, in addition to genetic and toxicological models, indicates that endoplasmic reticulum (ER) stress is a common feature of the disease and contributes to neurodegeneration. Recent reports place ER dysfunction as an early component of PD pathogenesis, and in this article we review the impact of ER stress in PD models and discuss the multiple mechanisms underlying the perturbation of secretory pathway function. Possible therapeutic strategies to mitigate ER stress in the context of PD are also discussed.
Assuntos
Estresse do Retículo Endoplasmático/fisiologia , Doença de Parkinson/fisiopatologia , Animais , Modelos Animais de Doenças , Humanos , Desdobramento de Proteína , Substância Negra/metabolismo , Substância Negra/fisiopatologia , Resposta a Proteínas não Dobradas , alfa-Sinucleína/metabolismoRESUMO
Hepcidin (Hepc) is considered a key mediator in iron trafficking. Although the mechanism of Hepc action in macrophages is fairly well established, much less is known about its action in intestinal cells, one of the main targets of Hepc. The current study investigated the effects of physiologically generated Hepc on iron transport in Caco-2 cell monolayers and rat duodenal segments compared with the effects on the J774 macrophage cell line. Addition of Hepc to Caco-2 cells or rat duodenal segments strongly inhibited apical (55)Fe uptake without apparent effects on the transfer of (55)Fe from the cells to the basolateral medium. Concurrently, the levels of divalent metal transporter 1 (DMT1) mRNA and protein in Caco-2 cells decreased while the mRNA and protein levels of the iron export transporter ferroportin did not change. Plasma membrane localization of ferroportin was studied by selective biotinylation of apical and basolateral membrane domains; Hepc induced rapid internalization of ferroportin in J774 cells but not in Caco-2 cells These results indicate that the effect of Hepc is cell dependent: in macrophages it inhibits iron export by inducing ferroportin degradation, whereas in enterocytes it inhibits apical iron uptake by inhibiting DMT1 transcription. Our results highlight the crucial role of Hepc in the control of intestinal iron absorption.
Assuntos
Peptídeos Catiônicos Antimicrobianos/metabolismo , Duodeno/metabolismo , Enterócitos/metabolismo , Absorção Intestinal , Ferro/metabolismo , Neoplasias Hepáticas/metabolismo , Macrófagos/metabolismo , Animais , Peptídeos Catiônicos Antimicrobianos/genética , Células CACO-2 , Proteínas de Transporte de Cátions/genética , Proteínas de Transporte de Cátions/metabolismo , Membrana Celular/metabolismo , Meios de Cultivo Condicionados/metabolismo , Hepcidinas , Humanos , Radioisótopos de Ferro , Neoplasias Hepáticas/genética , Masculino , RNA Mensageiro/metabolismo , Ratos , Ratos Endogâmicos F344 , Fatores de Tempo , Transcrição Gênica , TransfecçãoRESUMO
Reactive iron is an important prooxidant factor, whereas GSH is a crucial component of a long-term adaptive system that allows cells to function during extended periods of high oxidative stress. In this work, the adaptive response of the GSH system to prolonged iron loads was characterized in human dopaminergic SH-SY5Y neuroblastoma cells. After the initial death of a substantial portion of the cell population, the surviving cells increased their GSH content by up to fivefold. This increase was traced to increased expression of the catalytic and modulatory subunits of gamma-glutamate-cysteine ligase. Under conditions of high iron load, cells maintained a low GSSG content through two mechanisms: 1) GSSG reductase-mediated recycling of GSSG to GSH and 2) multidrug resistant protein 1-mediated extrusion of GSSG. Increased GSH synthesis and low GSSG levels contributed to recover the cell reduction potential from -290 mV at the time of cell death to about -320 mV. These results highlight the fundamental role of GSH homeostasis in the antioxidant response to cellular iron accumulation and provide novel insights into the adaptive mechanisms of neurons subjected to increased iron loads, such as those observed in Parkinson's disease.