Alzheimer’s disease (AD) affects tens of millions of people worldwide. Its cause is unknown, with no cure, and disease-modifying treatment options have only recently become available. Emerging research has made a strong case for the involvement of immune cells, such as microglia and T cells, in modulating AD pathology. Newer technologies in RNA-sequencing have detailed specific phenotypic changes to microglia and T cells over the course of neurodegenerative disease. Some researchers have also used whole-genome sequencing to correlate genetic variants with changes in gene expression. However, no studies thus far have conducted this type of genotype-phenotype correlation in immune cells from aged individuals or AD patients. We have collected gene expression data from four sorted T cell subtypes in peripheral blood samples from 96 subjects in ROSMAP, a cohort of AD patients and age-matched controls. 78 of these subjects also have whole-genome sequencing data, which we used to detect genetic variants associated with changes in T cell gene expression. These are known as expression quantitative trait loci (eQTL). We found genes related to T cell cytotoxicity and immunosenescence in gene co-expression modules, among the eQTL, and in correlation with AD neuropathological traits or risk variants for several disease traits. We extended our findings related to disease association by calculating polygenic risk scores (PRSs) in our cohort from whole-genome sequencing data for 19 traits related to immune function and disease, including AD. Genes associated with the PRS for one or more disease traits often were in biological pathways related to downstream cytokine signaling, regulation of T cell receptor signaling, and T cell migration and trafficking. Overall, our findings indicate that the use of aged and AD patients in T cell genotype-phenotype correlation studies highlights genetic variants and differentially expressed genes that are not seen in studies using young, healthy individuals.

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There is ongoing dispute on the question whether CNS neurons possess ATP-sensitive P2X7 receptors (Rs) or whether only non-neuronal cells bear this receptor-type and indirectly signal to the neighboring neurons. We genetically deleted P2X7Rs specifically in astrocytes, oligodendrocytes and microglia, and then recorded current responses in neurons to the prototypic agonist of this receptor, dibenzoyl-ATP (Bz-ATP). These experiments were made in brain slice preparations taken from the indicated variants of the P2X7R KO animals. In hippocampal CA3, but not CA1 pyramidal neurons, the deletion of oligodendrocytic (NG2 glial) P2X7Rs abolished the Bz-ATP-induced current responses. In contrast to the Bz-ATP-induced currents in CA3 pyramidal neurons, current amplitudes evoked by the ionotropic glutamate/GABAAR agonists AMPA/muscimol were not inhibited at all. Whereas in the CA3 area NG2 glia appeared to mediate the P2X7R-mediated stimulation of pyramidal neurons, in the CA1 area, astrocytic P2X7Rs had a somewhat similar effect. This was shown by recording the frequencies and amplitudes of spontaneous excitatory currents (sPSCs) in brain slice preparations. Bz-ATP increased the sPSC frequency in CA1, but not CA3 pyramidal neurons without altering the amplitude, indicating a P2X7R-mediated increase of the neuronal input. Micro-injection of the selective astrocytic toxin L-α-aminoadipate into both hippocampi, or the in vitro application of the GABAAR antagonistic gabazine, completely blocked the frequency increases of sPSCs. Hence, CA1 and CA3 pyramidal neurons of the mouse did not possess P2X7Rs, but were indirectly modulated by astrocytic and oligodendrocytic P2X7Rs, respectively.

No description available.

Despite the immense functional relevance of GPR56 (gene ADGRG1) in highly diverse (patho)physiological processes such as tumorigenesis, immune regulation, and brain development, little is known about its exact tissue localization. Here, we validated antibodies for GPR56-specific binding using cells with tagged GPR56 or eliminated ADGRG1 in immunotechniques. Using the most suitable antibody, we then established the human GPR56 tissue expression profile. Overall, ADGRG1 RNA-sequencing data of human tissues and GPR56 protein expression correlate very well. In the adult brain especially, microglia are GPR56-positive. Outside the central nervous system, GPR56 is frequently expressed in cuboidal or highly prismatic secreting epithelia. High ADGRG1 mRNA, present in the thyroid, kidney, and placenta is related to elevated GPR56 in thyrocytes, kidney tubules, and the syncytiotrophoblast, respectively. GPR56 often appears in association with secreted proteins such as pepsinogen A in gastric chief cells and insulin in islet β-cells. In summary, GPR56 shows a broad, not cell-type restricted expression in humans.

Le troisième trimestre de grossesse est une période-clé du développement cérébelleux. L’extrême prématurité et les lésions cérébelleuses (LCb) associées prédisposent ces enfants à des déficits moteurs, sociaux, comportementaux et cognitifs. Nos objectifs étaient de décrire les déficits neurocomportementaux associés à long-terme aux LCb, et d’explorer le rôle des microglies cérébelleuses dans leur survenue. À 3 jours de vie, des LCb ont expérimentalement et aléatoirement été induites chez des souriceaux transgéniques (B6.129P2(Cg)-Cx3Cr1 CreERT2-EYFP/iDTR), présentant ou non, une déplétion microgliale cérébelleuse transitoire : contrôle, hémorragies cérébelleuses, état inflammatoire systémique précoce et association des deux lésions. Une évaluation neurocomportementale a été réalisée à l’aveugle en période juvénile et à l’âge adulte. En présence de microglies cérébelleuses, les souris mâles adultes ayant souffert de LCb présentaient une diminution des comportements liés à l’anxiété (test du labyrinthe en croix surélevé) et les souris femelles juvéniles ayant souffert de LCb une augmentation des comportements d’investigation sociale (test de reconnaissance sociale) en comparaison des groupes contrôles. Vis-à-vis d’un état inflammatoire systémique précoce, la déplétion microgliale cérébelleuse assurait une récupération fonctionnelle du phénotype anxieux masculin et social féminin. Ce constat suggérait l’implication d’une activation microgliale délétère à la suite de LCb. Des études complémentaires permettront de préciser les sous-domaines neurocomportementaux affectés et d’investiguer les conséquences d’une activation microgliale (altération de l’élagage synaptique et/ou de la myélinogénèse cérébelleuse). / The third trimester of pregnancy is a key period for cerebellar development. Extreme prematurity and cerebellar injuries (CBI) predispose ex-preterm infants to long-term motor, social, behavioral, and cognitive deficits. Our objectives were to describe the long-term neurobehavioral deficits associated with CBI, and to determine if cerebellar microglia play a pathological role in these induced neurobehavioral deficits. At 3 days of life, CBI were experimentally and randomly induced in transgenic mice (B6.129P2(Cg)-Cx3Cr1 CreERT2-EYFP/iDTR), with or without transient cerebellar microglial depletion: control, cerebellar hemorrhages, early systemic inflammatory state, and association of these 2 injuries. A blinded neurobehavioral assessment was performed in juvenile and adult age. In the presence of cerebellar microglial cells, CBI adult male mice exposed to CBI showed a decrease in anxiety-related behaviors (elevated plus maze test), and CBI juvenile female mice exposed to CBI showed an increase in social investigation behaviors (social recognition test) compared to control groups. Cerebellar microglial depletion ensured a functional recovery of these anxiety-related and social investigation behaviors in mice exposed to an early systemic inflammatory state. This finding was consistent with a deleterious role of microglial activation. Further studies will precise the neurobehavioral subdomains affected and investigate the consequences of microglial activation (alteration of synaptic pruning and/or cerebellar myelinogenesis).

Pruning, the elimination of excess synapses is a phenomenon of fundamental importance for correct wiring of the central nervous system. The establishment of the cerebellar climbing fiber (CF)-to-Purkinje cell (PC) synapse provides a suitable model to study pruning and pruning-relevant processes during early postnatal development. Until now, the role of microglia in pruning remains under intense investigation. Here, we analyzed migration of microglia into the cerebellar cortex during early postnatal development and their possible contribution to the elimination of CF-to-PC synapses. Microglia enrich in the PC layer at pruning-relevant time points giving rise to the possibility that microglia are actively involved in synaptic pruning. We investigated the contribution of microglial fractalkine (CX3CR1) signaling during postnatal development using genetic ablation of the CX3CR1 receptor and an in-depth histological analysis of the cerebellar cortex. We found an aberrant migration of microglia into the granule and the molecular layer. By electrophysiological analysis, we show that defective fractalkine signaling and the associated migration deficits neither affect the pruning of excess CFs nor the development of functional parallel fiber and inhibitory synapses with PCs. These findings indicate that CX3CR1 signaling is not mandatory for correct cerebellar circuit formation. Main Points - Ablation of CX3CR1 results in a transient migration defect in cerebellar microglia. - CX3CR1 is not required for functional pruning of cerebellar climbing fibers. - Functional inhibitory and parallel fiber synapse development with Purkinje cells is undisturbed in CX3CR1-deficient mice.

Plant sterols (PSs) cannot be synthesized in mammals and are exclusively diet-derived. PSs cross the blood-brain barrier and may have anti-neuroinflammatory effects. Obesity is linked to lower intestinal uptake and blood levels of PSs, but its effects in terms of neuroinflammation—if any—remain unknown. We investigated the effect of high-fat diet-induced obesity on PSs in the brain and the effects of the PSs campesterol and -sitosterol on in vitro microglia activation. Sterols (cholesterol, precursors, PSs) and polyunsaturated fatty acid-derived lipid mediators were measured in the food, blood, liver and brain of C57BL/6J mice. Under a PSs-poor high-fat diet, PSs levels decreased in the blood, liver and brain (>50%). This effect was reversible after 2 weeks upon changing back to a chow diet. Inflammatory thromboxane B2 and prostaglandin D2 were inversely correlated to campesterol and -sitosterol levels in all brain regions. PSs content was determined post mortem in human cortex samples as well. In vitro, PSs accumulate in lipid rafts isolated from SIM-A9 microglia cell membranes. In summary, PSs levels in the blood, liver and brain were associated directly with PSs food content and inversely with BMI. PSs dampen pro-inflammatory lipid mediators in the brain. The identification of PSs in the human cortex in comparable concentration ranges implies the relevance of our findings for humans.

Recent studies have revealed that crosstalk between glioma cells and the brain microenvironment is a crucial regulator of cancer initiation and progression. A vast majority of glioma patients suffer from seizures, and this pathological neuronal activity has been proposed to contribute to increased glioma cell proliferation. Glioma patients also suffer from additional neurological symptoms, including deficits in attention, concentration, memory, and language. These neurological effects of gliomas along with the limited therapeutic options underscore the need for novel therapies. This thesis investigates the neuronal alterations at the margins of glioma which contribute to the neurological symptoms (Chapter 2), and on the effect of sensory stimulation on the glioma cells and microglia in the glioma microenvironment (Chapter 3). The work describes the development of new mouse models in which glioma cells are infiltrating the somatosensory cortex in mice that express GCaMP in neurons or microglia. Methodologies include a combination of in vivo two-photon calcium imaging and tissue-based analysis to determine the glioma-induced alteration on whisker stimulation-evoked responses of these different cell types. This work also tests the effects of pharmacologically inhibiting mTOR signaling on neuronal responses (Chapter 2) or purinergic signaling on microglial responses (Chapter 3). Together these studies demonstrate that glioma infiltration induces local effects in functionally-responsive cortex, and that many of these glioma-induced effects on neurons and microglia are ameliorated by pharmacological inhibition of mTOR or purinergic signaling. This reveals a highly dynamic and plastic nature of the glioma-induced alterations, and points towards new strategies to treat glioma-associated neurological symptoms while potentially slowing tumor progression.

Myeloid cells of the innate immune system have been strongly implicated in the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD). Similarly, several lines of evidence call on the adaptive immune system as a critical driver of disease, particularly in PD. The immune dynamics in both of these diseases are complex, and span across not only the innate and adaptive immune systems, but also across the periphery local action in the central nervous system (CNS). This thesis aims to address critical gaps in our knowledge regarding molecular and functional alterations of immune cells in AD and PD. We apply tools including single nucleus RNA – and ATAC – sequencing as well as protein – level and functional studies to advance our understanding of molecular pathways involved in the innate and adaptive immune dysfunction in these diseases, including both immune cells in the CNS as well as in the periphery. Chapter 1 provides an overview of the evidence implicating myeloid cell dysfunction in AD and PD, including microglia as well as peripheral myeloid cells such as monocytes. It also describes the features of immune dysregulation in both diseases, and evidence implicating the adaptive immune system in PD. Chapter 2 aims to address our currently limited understanding of microglial molecular phenotypes and diversity in PD, by characterizing microglial transcriptomic and chromatin signatures in disease. We demonstrate microglial subpopulation-specific effects, including the focal depletion of a microglial population in the substantia nigra in PD, which open novel avenues for targeted neuroimmune interventions in PD. Chapter 3 aims to identify interactions regulating the infiltration and retention of peripheral immune cells into the CNS in PD; a process which is implicated in the progression of this disease, but the mechanisms of which are not fully understood. We characterized transcriptomic signatures of infiltrating lymphocytes and blood brain barrier cells, and found increased T cell infiltration in PD as well as fibroblast and endothelial populations associated with disease. We further identified transcriptional shifts suggestive of a proinflammatory and profibrotic milieu in disease, in which chemokines and extracellular matrix elements produced by fibroblasts may influence T cell trafficking and retention in the substantia nigra in PD. Chapter 4 aims to address the gap in our knowledge of how myeloid dysfunction in the periphery contributes to AD. While genetics implicate all myeloid cells in AD and PD, contributions of peripheral myeloid cells, such as monocytes, have been largely overlooked in place of microglia, which are resident in the CNS. We evaluate the convergence of the AD genetic risk loci on functional outcomes in monocytes, in the context of Aβ as an immune stimulus. We identified functional convergence of the CD33 and SPI1 AD risk variants in the context of Aβ stress, including reduced phagocytosis and loss of surface TREM2 expression, demonstrating an interaction between genetics and environment to reduce myeloid cell fitness. Finally, Chapter 5 concludes with a summary of key findings from this work, and discusses future directions for modulating innate and adaptive immune populations, both in the CNS and in the periphery, as therapeutic approaches for these neurodegenerative diseases.