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AIMS: According to Braak's hypothesis, it is plausible that Parkinson's disease (PD) originates in the enteric nervous system (ENS) and spreads to the brain through the vagus nerve. In this work, we studied whether inflammatory bowel diseases (IBDs) in humans can progress with the emergence of pathogenic α-synuclein (α-syn) in the gastrointestinal tract and midbrain dopaminergic neurons. METHODS: We have analysed the gut and the ventral midbrain from subjects previously diagnosed with IBD and form a DSS-based rat model of gut inflammation in terms of α-syn pathology. RESULTS: Our data support the existence of pathogenic α-syn in both the gut and the brain, thus reinforcing the potential role of the ENS as a contributing factor in PD aetiology. Additionally, we have analysed the effect of a DSS-based rat model of gut inflammation to demonstrate (i) the appearance of P-α-syn inclusions in both Auerbach's and Meissner's plexuses (gut), (ii) an increase in α-syn expression in the ventral mesencephalon (brain) and (iii) the degeneration of nigral dopaminergic neurons, which all are considered classical hallmarks in PD. CONCLUSION: These results strongly support the plausibility of Braak's hypothesis and emphasise the significance of peripheral inflammation and the gut-brain axis in initiating α-syn aggregation and transport to the substantia nigra, resulting in neurodegeneration.
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Enfermedades Inflamatorias del Intestino , Enfermedad de Parkinson , Humanos , Ratas , Animales , alfa-Sinucleína/metabolismo , Enfermedad de Parkinson/patología , Encéfalo/patología , Inflamación/patología , Neuronas Dopaminérgicas/metabolismo , Enfermedades Inflamatorias del Intestino/patologíaRESUMEN
Adult hippocampal neurogenesis (AHN) is a process involved in numerous neurodegenerative diseases. Many researchers have described microglia as a key component in regulating the formation and migration of new neurons along the rostral migratory stream. Caspase-3 is a cysteine-aspartate-protease classically considered as one of the main effector caspases in the cell death program process. In addition to this classical function, we have identified the role of this protein as a modulator of microglial function; however, its action on neurogenic processes is unknown. The aim of the present study is to identify the role of Caspase-3 in neurogenesis-related microglial functions. To address this study, Caspase-3 conditional knockout mice in the microglia cell line were used. Using this tool, we wanted to elucidate the role of this protein in microglial function in the hippocampus, the main region in which adult neurogenesis takes place. After the reduction of Caspase-3 in microglia, mutant mice showed a reduction of microglia in the hippocampus, especially in the dentate gyrus region, a region inherently associated to neurogenesis. In addition, we found a reduction in doublecortin-positive neurons in conditional Caspase-3 knockout mice, which corresponds to a reduction in neurogenic neurons. Furthermore, using high-resolution image analysis, we also observed a reduction in the phagocytic capacity of microglia lacking Caspase-3. Behavioral analysis using object recognition and Y-maze tests showed altered memory and learning in the absence of Caspase-3. Finally, we identified specific microglia located specifically in neurogenic niche positive for Galectin 3 which colocalized with Cleaved-Caspase-3 in control mice. Taken together, these results showed the essential role of Caspase-3 in microglial function and highlight the relevant role of this specific microglial phenotype in the maintenance of AHN in the hippocampus.
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Caspasa 3 , Hipocampo , Microglía , Animales , Ratones , Caspasa 3/metabolismo , Hipocampo/metabolismo , Ratones Noqueados , Microglía/metabolismo , Neurogénesis/fisiologíaRESUMEN
Molecular diversity of microglia, the resident immune cells in the CNS, is reported. Whether microglial subsets characterized by the expression of specific proteins constitute subtypes with distinct functions has not been fully elucidated. Here we describe a microglial subtype expressing the enzyme arginase-1 (ARG1; that is, ARG1+ microglia) that is found predominantly in the basal forebrain and ventral striatum during early postnatal mouse development. ARG1+ microglia are enriched in phagocytic inclusions and exhibit a distinct molecular signature, including upregulation of genes such as Apoe, Clec7a, Igf1, Lgals3 and Mgl2, compared to ARG1- microglia. Microglial-specific knockdown of Arg1 results in deficient cholinergic innervation and impaired dendritic spine maturation in the hippocampus where cholinergic neurons project, which in turn results in impaired long-term potentiation and cognitive behavioral deficiencies in female mice. Our results expand on microglia diversity and provide insights into microglia subtype-specific functions.
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Arginasa , Microglía , Animales , Femenino , Ratones , Arginasa/genética , Arginasa/metabolismo , Hipocampo/metabolismo , Microglía/metabolismoRESUMEN
The advent of high-throughput single-cell transcriptomic analysis of microglia has revealed different phenotypes that are inherently associated with disease conditions. A common feature of some of these activated phenotypes is the upregulation of galectin-3. Representative examples of these phenotypes include disease-associated microglia (DAM) and white-associated microglia (WAM), whose role(s) in neuroprotection/neurotoxicity is a matter of high interest in the microglia community. In this review, we summarise the main findings that demonstrate the ability of galectin-3 to interact with key pattern recognition receptors, including, among others, TLR4 and TREM2 and the importance of galectin-3 in the regulation of microglia activation. Finally, we discuss increasing evidence supporting the involvement of this lectin in the main neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, traumatic brain injury, and stroke.
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Enfermedad de Alzheimer , Enfermedad de Parkinson , Enfermedad de Alzheimer/genética , Galectina 3/genética , Humanos , MicroglíaRESUMEN
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread around the globe causing coronavirus disease 2019 (COVID-19). Because it affects the respiratory system, common symptoms are cough and breathing difficulties with fever and fatigue. Also, some cases progress to acute respiratory distress syndrome (ARDS). The acute phase of COVID-19 has been also related to nervous system symptoms, including loss of taste and smell as well as encephalitis and cerebrovascular disorders. However, it remains unclear if neurological complications are due to the direct viral infection of the nervous system, or they appear as a consequence of the immune reaction against the virus in patients who presented pre-existing deficits or had a certain detrimental immune response. Importantly, the medium and long-term consequences of the infection by SARS-CoV-2 in the nervous system remain at present unknown. This review article aims to give an overview of the current neurological symptoms associated with COVID-19, as well as attempting to provide an insight beyond the acute affectation.
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Apoptotic caspases are thought to play critical roles in elimination of excessive and non-functional synapses and removal of extra cells during early developmental stages. Hence, an impairment of this process may thus constitute a basis for numerous neurological and psychiatric diseases. This view is especially relevant for dopamine due to its pleiotropic roles in motor control, motivation and reward processing. Here, we have analysed the effect of caspase-3 depletion on the development of catecholaminergic neurons and performed a wide array of neurochemical, ultrastructural and behavioural assays. To achieve this, we performed selective deletion of the Casp3 gene in tyrosine hydroxylase (TH)-expressing cells using Cre-loxP-mediated recombination. Histological evaluation of most relevant catecholaminergic nuclei revealed the ventral mesencephalon as the most affected region. Stereological analysis demonstrated an increase in the number of TH-positive neurons in both the substantia nigra and ventral tegmental area along with enlarged volume of the ventral midbrain. Analysis of main innervating tissues revealed a rather contrasting profile. In striatum, basal extracellular levels and potassium-evoked DA release were significantly reduced in mice lacking Casp3, a clear indication of dopaminergic hypofunction in dopaminergic innervating tissues. This view was sustained by analysis of TH-labelled dopaminergic terminals by confocal and electron microscopy. Remarkably, at a behavioural level, Casp3-deficient mice exhibited impaired social interaction, restrictive interests and repetitive stereotypies, which are considered the core symptoms of autism spectrum disorder (ASD). Our study revitalizes the potential involvement of dopaminergic transmission in ASD and provides an excellent model to get further insights in ASD pathogenesis.
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Trastorno Autístico/genética , Trastorno Autístico/metabolismo , Caspasa 3/deficiencia , Caspasa 3/genética , Dopamina/metabolismo , Eliminación de Gen , Animales , Locomoción/fisiología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
The pro-inflammatory immune response driven by microglia is a key contributor to the pathogenesis of several neurodegenerative diseases. Though the research of microglia spans over a century, the last two decades have increased our understanding exponentially. Here, we discuss the phenotypic transformation from homeostatic microglia towards reactive microglia, initiated by specific ligand binding to pattern recognition receptors including toll-like receptor-4 (TLR4) or triggering receptors expressed on myeloid cells-2 (TREM2), as well as pro-inflammatory signaling pathways triggered such as the caspase-mediated immune response. Additionally, new research disciplines such as epigenetics and immunometabolism have provided us with a more holistic view of how changes in DNA methylation, microRNAs, and the metabolome may influence the pro-inflammatory response. This review aimed to discuss our current knowledge of pro-inflammatory microglia from different angles, including recent research highlights such as the role of exosomes in spreading neuroinflammation and emerging techniques in microglia research including positron emission tomography (PET) scanning and the use of human microglia generated from induced pluripotent stem cells (iPSCs). Finally, we also discuss current thoughts on the impact of pro-inflammatory microglia in neurodegenerative diseases.
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Sistema Nervioso Central/patología , Inflamación/patología , Microglía/patología , Animales , Caspasas/metabolismo , Epigénesis Genética , Humanos , Microglía/enzimología , Modelos BiológicosRESUMEN
In neurodegenerative diseases, microglia-mediated neuroinflammation and oxidative stress are central events. Recent genome-wide transcriptomic analyses of microglial cells under different disease conditions have uncovered a new subpopulation named disease-associated microglia (DAM). These studies have challenged the classical view of the microglia polarization state's proinflammatory M1 (classical activation) and immunosuppressive M2 (alternative activation). Molecular signatures of DAM and proinflammatory microglia (highly pro-oxidant) have shown clear differences, yet a partial overlapping gene profile is evident between both phenotypes. The switch activation of homeostatic microglia into reactive microglia relies on the selective activation of key surface receptors involved in the maintenance of brain homeostasis (a.k.a. pattern recognition receptors, PRRs). Two relevant PRRs are toll-like receptors (TLRs) and triggering receptors expressed on myeloid cells-2 (TREM2), whose selective activation is believed to generate either a proinflammatory or a DAM phenotype, respectively. However, the recent identification of endogenous disease-related ligands, which bind to and activate both TLRs and TREM2, anticipates the existence of rather complex microglia responses. Examples of potential endogenous dual ligands include amyloid ß, galectin-3, and apolipoprotein E. These pleiotropic ligands induce a microglia polarization that is more complicated than initially expected, suggesting the possibility that different microglia subtypes may coexist. This review highlights the main microglia polarization states under disease conditions and their leading role orchestrating oxidative stress.
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Neuroinflammation is a common feature shared by neurodegenerative disorders, such as Parkinson's disease (PD), and seems to play a key role in their development and progression. Microglia cells, the principal orchestrators of neuroinflammation, can be polarized in different phenotypes, which means they are able to have anti-inflammatory, pro-inflammatory, or neurodegenerative effects. Increasing evidence supports that the traditional Mediterranean dietary pattern is related to the reduction of cognitive decline in neurodegenerative diseases. A considerable intake of plant foods, fish, and extra virgin olive oil (EVOO), as well as a moderate consumption of red wine, all characteristic of the Mediterranean diet (MD), are behind these effects. These foods are especially rich in polyphenols, being the most relevant in the MD hydroxytyrosol (HT) and their derivatives present in EVOO, which have demonstrated a wide array of biological activities. Here, we demonstrate that HT is able to reduce the inflammation induced by two different stimuli: lipopolysaccharide and α-synuclein. We also study the possible molecular mechanisms involved in the anti-inflammatory effect of HT, including the study of nuclear factor kappa B (NF-кB), mitogen-activated protein kinases (MAPKs), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and inflammasome. Our data support the use of HT to prevent the inflammation associated with PD and shed light into the relationship between MD and this neurological disorder.
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The oral antidiabetic drug metformin is known to exhibit anti-inflammatory properties through activation of AMP kinase, thus protecting various brain tissues as cortical neurons, for example. However, the effect of metformin on the substantia nigra (SN), the main structure affected in Parkinson's disease (PD), has not yet been studied in depth. Inflammation is a key feature of PD and it may play a central role in the neurodegeneration that takes place in this disorder. The aim of this work was to determine the effect of metformin on the microglial activation of the SN of rats using the animal model of PD based on the injection of the pro-inflammogen lipopolysaccharide (LPS). In vivo and in vitro experiments were conducted to study the activation of microglia at both the cellular and molecular levels. Our results indicate that metformin overall inhibits microglia activation measured by OX-6 (MHCII marker), IKKß (pro-inflammatory marker) and arginase (anti-inflammatory marker) immunoreactivity. In addition, qPCR experiments reveal that metformin treatment minimizes the expression levels of several pro- and anti-inflammatory cytokines. Mechanistically, the drug decreases the phosphorylated forms of mitogen-activated protein kinases (MAPKs) as well as ROS generation through the inhibition of the NADPH oxidase enzyme. However, metformin treatment fails to protect the dopaminergic neurons of SN in response to intranigral LPS. These findings suggest that metformin could have both beneficial and harmful pharmacological effects and raise the question about the potential use of metformin for the prevention and treatment of PD.
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The impact of systemic inflammation in nigral dopaminergic cell loss remains unclear. Here, we have investigated the role of peripheral inflammation induced by systemic lipopolysaccharide (LPS) administration in the MPTP-based model of Parkinson's disease. Brain inflammation, microglia and astroglia activation, disruption of the blood-brain barrier (BBB) and integrity of the nigrostriatal dopaminergic system were evaluated in response to i.p. injection of LPS, MPTP or the combination of both. Our results showed that combinative treatment exacerbates microglia activation and enhances (i) the appearance of galectin-3-positive microglia, recently identified as microglial disease-associated phenotypic marker, (ii) the up-regulation of pro-inflammatory cytokines, (iii) the occurrence of A1 neurotoxic astrocytes, (iv) the breakdown of the BBB, and (v) the loss of dopaminergic neurons in the substantia nigra. Microglia activation was triggered earlier than other degenerative events, suggesting that over-activation of microglia (including different polarization states) may induce dopaminergic neuron loss by itself, initiating the endless cycle of inflammation/degeneration. Our study revitalizes the importance of peripheral inflammation as a potential risk factor for Parkinson's disease and raises the possibility of using new anti-inflammatory therapies to improve the course of neurodegenerative diseases, including those directly aimed at modulating the deleterious activity of disease-associated microglia.
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Ischemic stroke (caused by thrombosis, embolism or vasoconstriction) lead to the recruitment and activation of immune cells including resident microglia and infiltrating peripheral macrophages, which contribute to an inflammatory response involved in regulation of the neuronal damage. We showed earlier that upon pro-inflammatory stimuli, the orderly activation of caspase-8 and caspase-3/7 regulates microglia activation through a protein kinase C-δ dependent pathway. Here, we present in vivo evidence for the activation of caspase-8 and caspase-3 in microglia/macrophages in post-mortem tissue from human ischemic stroke subjects. Indeed, CD68-positive microglia/macrophages in the ischemic peri-infarct area exhibited significant expression of the cleaved and active form of caspase-8 and caspase-3. The temporal and spatial activation of caspase-8 was further investigated in a permanent middle cerebral artery occlusion mouse model of ischemic stroke. Increasing levels of active caspase-8 was found in Iba1-positive cells over time in the peri-infarct area, at 6, 24 and 48 h after artery occlusion. Analysis of post-mortem brain tissue from human subject who suffered two stroke events, referred as recent and old stroke, revealed that expression of cleaved caspase-8 and -3 in CD68-positive cells could only be found in the recent stroke area. Analysis of cleaved caspase-8 and -3 expressions in a panel of human stroke cases arranged upon days-after stroke and age-matched controls suggested that the expression of these caspases correlated with the time of onset of stroke. Collectively, these data illustrate the temporal and spatial activation of caspase-8 and -3 in microglia/macrophages occurring upon ischemic stroke and suggest that the expression of these caspases could be used in neuropathological diagnostic work.
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Isquemia Encefálica/enzimología , Encéfalo/enzimología , Caspasa 8/metabolismo , Células Mieloides/enzimología , Accidente Cerebrovascular/enzimología , Enfermedad Aguda , Anciano , Animales , Antígenos CD/metabolismo , Antígenos de Diferenciación Mielomonocítica/metabolismo , Encéfalo/patología , Isquemia Encefálica/patología , Proteínas de Unión al Calcio/metabolismo , Caspasa 3/metabolismo , Proteínas de Unión al ADN/metabolismo , Modelos Animales de Enfermedad , Femenino , Humanos , Masculino , Ratones Endogámicos C57BL , Proteínas de Microfilamentos/metabolismo , Microglía/enzimología , Microglía/patología , Células Mieloides/patología , Accidente Cerebrovascular/patología , Factores de TiempoRESUMEN
The molecular mechanisms underlying the negative effects of psychological stress on cellular stress during aging and neurodegenerative diseases are poorly understood. The main objective of this study was to test the effect of chronic psychological stress, and the consequent increase of circulating glucocorticoids, on several hippocampal genes involved in longevity. Sirtuin-1, p53, thioredoxin-interacting protein, and heat shock protein 70 were studied at the mRNA and protein levels in stressed and non-stressed animals. Stress treatment for 10 days decreased sirtuin-1 and heat shock protein 70 levels, but increased levels of p53, thioredoxin-interacting protein and the NADPH oxidase enzyme. Examination of protein expression following two months of stress treatment indicated that sirtuin-1 remained depressed. In contrast, an increase was observed for thioredoxin-interacting protein, heat shock protein 70, p53 and the NADPH oxidase enzyme. The effect of stress was reversed by mifepristone, a glucocorticoid receptor antagonist. These data suggest that chronic stress could contribute to aging in the hippocampus.
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Hipocampo/metabolismo , Longevidad/fisiología , Estrés Oxidativo/fisiología , Estrés Psicológico/genética , Estrés Psicológico/metabolismo , Animales , Enfermedad Crónica , Expresión Génica , Masculino , Ratas , Ratas Wistar , Sirtuina 1/biosíntesis , Sirtuina 1/genética , Estrés Psicológico/psicologíaRESUMEN
Metformin is a widely used oral antidiabetic drug with known anti-inflammatory properties due to its action on AMPK protein. This drug has shown a protective effect on various tissues, including cortical neurons. The aim of this study was to determine the effect of metformin on the dopaminergic neurons of the substantia nigra of mice using the animal model of Parkinson's disease based on the injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, an inhibitor of the mitochondrial complex I. In vivo and in vitro experiments were used to study the activation of microglia and the damage of the dopaminergic neurons. Our results show that metformin reduced microglial activation measured both at cellular and molecular levels. Rather than protecting, metformin exacerbated dopaminergic damage in response to MPTP. Our data suggest that, contrary to other brain structures, metformin treatment could be deleterious for the dopaminergic system. Hence, metformin treatment may be considered as a risk factor for the development of Parkinson's disease.
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Antiinflamatorios/toxicidad , Cuerpo Estriado/efectos de los fármacos , Neuronas Dopaminérgicas/efectos de los fármacos , Metformina/toxicidad , Trastornos Parkinsonianos , Sustancia Negra/efectos de los fármacos , Animales , Antiinflamatorios/farmacología , Apoptosis/efectos de los fármacos , Apoptosis/inmunología , Técnicas de Cultivo de Célula , Línea Celular , Cuerpo Estriado/metabolismo , Cuerpo Estriado/patología , Dopamina/metabolismo , Neuronas Dopaminérgicas/metabolismo , Neuronas Dopaminérgicas/patología , Inmunohistoquímica , Masculino , Metformina/farmacología , Ratones Endogámicos C57BL , Microglía/efectos de los fármacos , Microglía/inmunología , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/inmunología , Trastornos Parkinsonianos/inducido químicamente , Trastornos Parkinsonianos/patología , Especies Reactivas de Oxígeno/metabolismo , Reacción en Cadena en Tiempo Real de la Polimerasa , Sustancia Negra/metabolismo , Sustancia Negra/patologíaRESUMEN
This review is aimed to highlight the importance of stress and glucocorticoids (GCs) in modulating the inflammatory response of brain microglia and hence its potential involvement in Parkinson's disease (PD). The role of inflammation in PD has been reviewed extensively in the literature and it is supposed to play a key role in the course of the disease. Historically, GCs have been strongly associated as anti-inflammatory hormones. However, accumulating evidence from the peripheral and central nervous system have clearly revealed that, under specific conditions, GCs may promote brain inflammation including pro-inflammatory activation of microglia. We have summarized relevant data linking PD, neuroinflamamation and chronic stress. The timing and duration of stress response may be critical for delineating an immune response in the brain thus probably explain the dual role of GCs and/or chronic stress in different animal models of PD.
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Neurodegenerative diseases are characterized by a progressive deterioration of brain function, with a consequent significant decline in the quality of life of patients and their families. Due to the concurrent increase in life expectancy, the incidence of these diseases has been increasing over the last years and thus there is a growing interest in finding potential risk factors. This review focuses on the correlation between peripheral inflammatory diseases and neurodegeneration, in particular on the relationship between gastrointestinal disorders and Parkinson's disease, especially through the so called gut-brain axis.
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Enfermedades Gastrointestinales/fisiopatología , Inflamación/fisiopatología , Enfermedades Neurodegenerativas/fisiopatología , Enfermedad de Parkinson/fisiopatología , Enfermedad de Alzheimer/fisiopatología , Animales , Enfermedad Crónica , Suplementos Dietéticos , Encefalitis/fisiopatología , Humanos , Enfermedades Inflamatorias del Intestino/fisiopatología , Proteína 2 Quinasa Serina-Treonina Rica en Repeticiones de Leucina , Microglía/patología , Microglía/fisiología , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismoRESUMEN
The study of monocyte activation and differentiation has great applications in sepsis, chronic inflammatory diseases, and cancer studies. However, despite the existence of well-established protocols for monocyte purification from human blood, the isolation of murine monocytes that can be subsequently activated has not yet been fully optimized. Here we evaluate a recently developed commercial procedure for obtaining monocytes from the bone marrow based on immunomagnetic depletion of non-monocytic cells. Moreover, we compare the advantages and disadvantages of this approach relative to other existing procedures. We found that monocytes isolates generated using this technique had equal purity to those attained via depletion from peripheral blood; however, higher yields were achieved. Furthermore, isolates from this technique have lower levels of macrophage contamination than those reported in samples generated by culturing bone marrow extracts with macrophage colony-stimulating factor (M-CSF). In addition, we demonstrate that the purified monocytes are sensitive to lipopolysaccharide (LPS)-mediated activation and, therefore, are useful for studies aimed at elucidating the molecular mechanisms involved in monocyte activation and differentiation.
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Células de la Médula Ósea , Separación Celular , Monocitos/citología , Animales , Células de la Médula Ósea/efectos de los fármacos , Lipopolisacáridos/farmacología , Ratones , Ratones Endogámicos C57BL , Monocitos/efectos de los fármacosRESUMEN
Alzheimer's disease is the most common cause of dementia in the elderly. Although the primary cause of the disease is presently unknown, to date several risk factors have been described. Evidence suggests that one of these risk factors could be chronic stress. The aim of this work is to demonstrate that chronic stress is able to induce Alzheimer's disease features after the administration of nontoxic doses of sodium azide. We found that chronic stress increases the levels of several proteins involved in Alzheimer's disease pathogenesis, such as presenilin 1, presenilin 2, and S100ß, besides inducing the aggregation of Tau, ubiquitin, and ß-amyloid proteins in the hippocampus. More important, our work shows a synergistic effect of stress and sodium azide treatment leading to significant neuronal death in the mouse hippocampus. Our results point out that chronic stress is a risk factor contributing to amplify and accelerate Alzheimer's disease features in the hippocampus.
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Hipocampo/efectos de los fármacos , Azida Sódica/farmacología , Estrés Fisiológico , Enfermedad de Alzheimer/fisiopatología , Animales , Hipocampo/fisiopatología , Masculino , Ratones , Ratones Endogámicos C57BLRESUMEN
BACKGROUND: We have uncovered a caspase-dependent (caspase-8/caspase-3/7) signaling governing microglia activation and associated neurotoxicity. Importantly, a profuse non-nuclear activation of cleaved caspases 8 and 3 was found in reactive microglia in the ventral mesencephalon from subjects with Parkinson's disease, thus supporting the existence of endogenous factors activating microglia through a caspase-dependent mechanism. One obvious candidate is neuromelanin, which is an efficient proinflammogen in vivo and in vitro and has been shown to have a role in the pathogenesis of Parkinson's disease. Consequently, the goal of this study is to test whether synthetic neuromelanin activates microglia in a caspase-dependent manner. RESULTS: We found an in-vivo upregulation of CD16/32 (M1 marker) in Iba1-immunolabeled microglia in the ventral mesencephalon after neuromelanin injection. In vitro experiments using BV2 cells, a microglia-derived cell line, demonstrated that synthetic neuromelanin induced a significant chemotactic response to BV2 microglial cells, along with typical morphological features of microglia activation, increased oxidative stress and induction of pattern-recognition receptors including Toll-like receptor 2, NOD2, and CD14. Analysis of IETDase (caspase-8) and DEVDase (caspase-3/7) activities in BV2 cells demonstrated a modest but significant increase of both activities in response to neuromelanin treatment, in the absence of cell death. CONCLUSIONS: Caspase-8 inhibition prevented typical features of microglia activation, including morphological changes, a high rate of oxidative stress and expression of key proinflammatory cytokines and iNOS.
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Caspasa 8/metabolismo , Citocinas/metabolismo , Melaninas/farmacología , Microglía/efectos de los fármacos , Animales , Apoptosis/efectos de los fármacos , Encéfalo/citología , Caspasa 3/metabolismo , Línea Celular Transformada , Citocinas/genética , Lipopolisacáridos/farmacología , Ratones , Ratones Endogámicos C57BL , Óxido Nítrico/metabolismo , Proteína Adaptadora de Señalización NOD1/genética , Proteína Adaptadora de Señalización NOD1/metabolismo , Proteína Adaptadora de Señalización NOD2/genética , Proteína Adaptadora de Señalización NOD2/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Receptor para Productos Finales de Glicación Avanzada/genética , Receptor para Productos Finales de Glicación Avanzada/metabolismo , Transducción de Señal/efectos de los fármacos , Receptor Toll-Like 2/genética , Receptor Toll-Like 2/metabolismo , Receptor Toll-Like 4/genética , Receptor Toll-Like 4/metabolismoRESUMEN
BACKGROUND: Parkinson's disease is an irreversible neurodegenerative disease linked to progressive movement disorders and is accompanied by an inflammatory reaction that is believed to contribute to its pathogenesis. Since sensitivity to inflammation is not the same in all brain structures, the aim of this work was to test whether physiological conditions as stress could enhance susceptibility to inflammation in the substantia nigra, where death of dopaminergic neurons takes place in Parkinson's disease. METHODS: To achieve our aim, we induced an inflammatory process in nonstressed and stressed rats (subject to a chronic variate stress) by a single intranigral injection of lipopolysaccharide, a potent proinflammogen. The effect of this treatment was evaluated on inflammatory markers as well as on neuronal and glial populations. RESULTS: Data showed a synergistic effect between inflammation and stress, thus resulting in higher microglial activation and expression of proinflammatory markers. More important, the higher inflammatory response seen in stressed animals was associated with a higher rate of death of dopaminergic neurons in the substantia nigra, the most characteristic feature seen in Parkinson's disease. This effect was dependent on glucocorticoids. CONCLUSIONS: Our data demonstrate that stress sensitises midbrain microglia to further inflammatory stimulus. This suggests that stress may be an important risk factor in the degenerative processes and symptoms of Parkinson's disease.