Le rôle des microglies et de l'inflammation dans l'ischémie cérébrale

L'ischémie cérébrale induit une réponse inflammatoire aiguë et prolongée caractérisée par la production de cytokines, l'infiltration de leukocytes dans le cerveau, ainsi que l'activation des cellules gliales résidentes dont les microglies. Les microglies sont impliquées dans l'élimination des débris cellulaires, la production de cytokines proinflammatoires et de facteurs trophiques. Un rôle neuroprotecteur des microglies suite à une dégénérescence du SNC est proposé dans la littérature. Cependant, l'activation des cellules microgliales est aussi associée avec la sécrétion de molécules toxiques et l'atténuation de l'activation microgliale est bénéfique dans certaines maladies neurodegeneratives. Dans l'ischémie cérébrale, le rôle de la prolifération microgliale et de la dynamique de la réponse inflammatoire reste méconnu. L'analyse de la souris CDllb-TKmut³⁰ après l'ischémie cérébrale, a permis de montrer que l'élimination sélective des microglies en prolifération amplifie la réponse inflammatoire après l'ischémie cérébrale et augmente la taille de la lésion ischémique. La caractérisation de cette population a permis de déterminer que les premières cellules microgliales à proliférer sont les cellules résidentes exprimant le marqueur d'activation galectine-3. De plus, après l'ischémie cérébrale, cette population sert de source endogène d'IGF-1, une molécule neurotrophique. L'inactivation génétique de la galectine 3 chez la souris a permis de confirmer le rôle bénéfique de cette population microgliale ainsi que de lien potentiel entre la galectine 3 et l'induction de la réponse mitogénique d'IGF-1. De plus, l'étude longitudinale de l'activation des microglies à l'aide la souris transgénique TLR2-Fluc-GFP a permis de montrer que l'activation microgliale après l'ischémie cérébrale est biphasique et perdure plusieurs mois après l'attaque initiale. Deux sites majeurs d'activation ont pu aussi être détectés : la région ischémique et le bulbe olfactif. D'ailleurs, l'augmentation de signal au site de la lésion ischémique est toujours précédée par une augmentation significative du signal TLR2 dans le bulbe olfactif. Par leur position anatomique particulière, les cellules microgliales du bulbe olfactif sont plus sensibles aux signaux provenant autant de l'environnement que de l'intérieur du cerveau et pourraient servir de senseurs et/ou modulateurs de l'inflammation cérébrale. Les résultats obtenus par l'étude de différents modèles de souris transgéniques ont permis de montrer la dynamique de la réponse inflammatoire, le rôle neuroprotecteur des microglies en prolifération et le lien potentiel entre la galectine 3 et le facteur neuroprotecteur IGF-

Gender-specific associations between functional autonomy and physical capacities in independent older adults: Results from the NuAge study

Abstract : Background: Even with healthy and active aging, many older adults will experience a decrease in physical capacities. This decrease might be associated with diminished functional autonomy. However, little is known about the physical capacities associated with functional autonomy in older women and men. Objective: This study aimed to examine gender-specific associations between functional autonomy and physical capacities in independent older women and men. Methods: Secondary analyses were carried out using cross-sectional data from 652 women and 613 men who participated in the NuAge longitudinal study. The "functional autonomy measurement system" (SMAF) was used to evaluate functional autonomy. The physical capacities measured (tests used) were: biceps and quadriceps strength (Microfet dynamometer), grip strength (Martin vigorimeter), unipodal balance, changing position & walking (timed up and go), normal & fast walking (four-meter walking speed) and changing position (chair stand). Correlation and multiple linear regression analyses adjusted for age, depressive symptoms and body composition were performed. Results: On average, participants were aged 73 years and had mild to moderate functional autonomy loss. In women, after controlling for age, depressive symptoms and body composition, greater functional autonomy was best explained by faster changing position & walking skills and superior biceps strength (R2 = 0.46; p < 0.001). After controlling for depressive symptoms, faster changing position & walking skills and better unipodal balance best explained greater functional autonomy in men (R2 = 0.21; p < 0.001). Conclusion: According to these results, physical capacities are moderately associated with functional autonomy among independent older adults, especially women

Microglia-Secreted Galectin-3 Acts as a Toll-like Receptor 4 Ligand and Contributes to Microglial Activation.

Inflammatory response induced by microglia plays a critical role in the demise of neuronal populations in neuroinflammatory diseases. Although the role of toll-like receptor 4 (TLR4) in microglia's inflammatory response is fully acknowledged, little is known about endogenous ligands that trigger TLR4 activation. Here, we report that galectin-3 (Gal3) released by microglia acts as an endogenous paracrine TLR4 ligand. Gal3-TLR4 interaction was further confirmed in a murine neuroinflammatory model (intranigral lipopolysaccharide [LPS] injection) and in human stroke subjects. Depletion of Gal3 exerted neuroprotective and anti-inflammatory effects following global brain ischemia and in the neuroinflammatory LPS model. These results suggest that Gal3-dependent-TLR4 activation could contribute to sustained microglia activation, prolonging the inflammatory response in the brain

The role of NF-kB triggered inflammation in cerebral ischemia

Cerebral ischemia is a devastating disease that affects many people worldwide every year. The neurodegenerative damage as a consequence of oxygen and energy deprivation, to date, has no known effective treatment. The ischemic insult is followed by an inflammatory response that involves a complex interaction between inflammatory cells and molecules which play a role in the progression towards cell death. However, there is presently a matter of controversy over whether inflammation could either be involved in brain damage or be a necessary part of brain repair. The inflammatory response is triggered by inflammasomes, key multiprotein complexes that promote secretion of pro-inflammatory cytokines. An early event in post-ischemic brain tissue is the release of certain molecules and reactive oxygen species (ROS) from injured neurons which induce the expression of the nuclear factor-kappaB (NF-kB), a transcription factor involved in the activation of the inflammasome. There are conflicting observations related to the role of NF-kB. While some observe that NF-kB plays a damaging role, others suggest it to be neuroprotective in the context of cerebral ischemia, indicating the need for additional investigation. Here we discuss the dual role of the major inflammatory signaling pathways and provide a review of the latest research aiming to clarify the relationship between NF- kB mediated inflammation and neuronal death in cerebral ischemia

Minocycline reduces microgliosis and improves subcortical white matter function in a model of cerebral vascular disease

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.Chronic cerebral hypoperfusion is a key mechanism associated with white matter disruption in cerebral vascular disease and dementia. In a mouse model relevant to studying cerebral vascular disease, we have previously shown that cerebral hypoperfusion disrupts axon-glial integrity and the distribution of key paranodal and internodal proteins in subcortical myelinated axons. This disruption of myelinated axons is accompanied by increased microglia and cognitive decline. The aim of the present study was to investigate whether hypoperfusion impairs the functional integrity of white matter, its relation with axon-glial integrity and microglial number, and whether by targeting microglia these effects can be improved. We show that in response to increasing durations of hypoperfusion, the conduction velocity of myelinated fibres in the corpus callosum is progressively reduced and that paranodal and internodal axon-glial integrity is disrupted. The number of microglial cells increases in response to hypoperfusion and correlates with disrupted paranodal and internodal integrity and reduced conduction velocities. Further minocycline, a proposed anti-inflammatory and microglia inhibitor, restores white matter function related to a reduction in the number of microglia. The study suggests that microglial activation contributes to the structural and functional alterations of myelinated axons induced by cerebral hypoperfusion and that dampening microglia numbers/proliferation should be further investigated as potential therapeutic benefit in cerebral vascular disease.We gratefully acknowledge the support of Alzheimer's Research UK (ARUK) in funding this project and for providing a small grant via the ARUK Scotland Network Centre. SS is funded by an ARUK PhD studentship. Funding support from the Alzheimer's Society is also gratefully acknowledged. BMcC was funded by grants from the BBSRC and MRC. We would also like to acknowledge Abcam for the supply of TMEM119 antibody and technical support

Microglial brain region−dependent diversity and selective regional sensitivities to aging

Microglia play critical roles in neural development, homeostasis and neuroinflammation and are increasingly implicated in age-related neurological dysfunction. Neurodegeneration often occurs in disease-specific spatially-restricted patterns, the origins of which are unknown. We performed the first genome-wide analysis of microglia from discrete brain regions across the adult lifespan of the mouse and reveal that microglia have distinct region-dependent transcriptional identities and age in a regionally variable manner. In the young adult brain, differences in bioenergetic and immunoregulatory pathways were the major sources of heterogeneity and suggested that cerebellar and hippocampal microglia exist in a more immune vigilant state. Immune function correlated with regional transcriptional patterns. Augmentation of the distinct cerebellar immunophenotype and a contrasting loss in distinction of the hippocampal phenotype among forebrain regions were key features during ageing. Microglial diversity may enable regionally localised homeostatic functions but could also underlie region-specific sensitivities to microglial dysregulation and involvement in age-related neurodegeneration

Genomic programming of human neonatal dendritic cells in congenital systemic and in vitro cytomegalovirus infection reveal plastic and robust immune pathway biology responses

Neonates and especially premature infants are highly susceptible to infection but still can have a remarkable resilience that is poorly understood. The view that neonates have an incomplete or deficient immune system is changing. Human neonatal studies are challenging, and elucidating host protective responses and underlying cognate pathway biology, in the context of viral infection in early life, remains to be fully explored. In both resource rich and poor settings, human cytomegalovirus (HCMV) is the most common cause of congenital infection. By using unbiased systems analyses of transcriptomic resources for HCMV neonatal infection, we find the systemic response of a preterm congenital HCMV infection, involves a focused IFN regulatory response associated with dendritic cells. Further analysis of transcriptional-programming of neonatal dendritic cells in response to HCMV infection in culture revealed an early dominant IFN-chemokine regulatory subnetworks, and at later times the plasticity of pathways implicated in cell-cycle control and lipid metabolism. Further, we identify previously unknown suppressed networks associated with infection, including a select group of GPCRs. Functional siRNA viral growth screen targeting 516-GPCRs and subsequent validation identified novel GPCR-dependent antiviral (ADORA1) and proviral (GPR146, RGS16, PTAFR, SCTR, GPR84, GPR85, NMUR2, FZ10, RDS, CCL17, and SORT1) roles. By contrast a gene family cluster of protocadherins is significantly differentially induced in neonatal cells, suggestive of possible immunomodulatory roles. Unexpectedly, programming responses of adult and neonatal dendritic cells, upon HCMV infection, demonstrated comparable quantitative and qualitative responses showing that functionally, neonatal dendritic cell are not overly compromised. However, a delay in responses of neonatal cells for IFN subnetworks in comparison with adult-derived cells are notable, suggestive of subtle plasticity differences. These findings support a set-point control mechanism rather than immaturity for explaining not only neonatal susceptibility but also resilience to infection. In summary, our findings show that neonatal HCMV infection leads to a highly plastic and functional robust programming of dendritic cells in vivo and in vitro. In comparison with adults, a minimal number of subtle quantitative and temporal differences may contribute to variability in host susceptibility and resilience, in a context dependent manner