Mesquita, Sandro Dá

Abstract Introduction Colony stimulating factor 1 receptor (CSF1R)-related leukoencephalopathy is an early onset neurodegenerative disease characterized by microglial deficits, abnormal glial responses, white matter pathology, and severe motor and cognitive decline. Methods At 8 months, mice lacking two copies of the Csf1r gene Fms-intronic regulatory element (FIRE) recapitulate some of the brain pathological features of CSF1R-related leukoencephalopathy, namely the deficits in microglia, astrogliosis, and demyelination. Of note, we detected deficits in lymphatic vasculature and altered macrophage activation in the meninges of Csf1rΔFIRE/ΔFIRE mice by flow, prior to the appearance of brain gliosis, neuronal dystrophy, and fine motor impairment. Results Eliminating the remainder CSF1R-expressing innate immune cells, including border-associated macrophages (BAMs), with PLX5622 at 2 months reshaped the immune crosstalk at the meningeal dura and restored lymphatic vascular expansion in Csf1rΔFIRE/ΔFIRE mice Conclusion Ongoing experiments in the lab will clarify the exact mechanisms through which dysfunctional innate immunity at the brain-meningeal interface and lack of meningeal lymphatic vasculature contribute to the development of brain pathology and impaired motor behavior in this model of CSF1R-related leukoencephalopathy. This work has unveiled novel molecular insights involving the meningeal lymphatic system that might be of therapeutic relevance to canonical central nervous system white matter diseases. Funding Source n/a Topic Categories Neuroimmunology (NEUR)

Abstract The immune system is a key player in the onset and progression of neurodegenerative disorders. While brain resident immune cell‐mediated neuroinflammation and peripheral immune cell (eg, T cell) infiltration into the brain have been shown to significantly contribute to Alzheimer's disease (AD) pathology, the nature and extent of immune responses in the brain in the context of AD and related dementias (ADRD) remain unclear. Furthermore, the roles of the peripheral immune system in driving ADRD pathology remain incompletely elucidated. In March of 2023, the Alzheimer's Association convened the Alzheimer's Association International Conference (AAIC), Advancements: Immunity, to discuss the roles of the immune system in ADRD. A wide range of topics were discussed, such as animal models that replicate human pathology, immune‐related biomarkers and clinical trials, and lessons from other fields describing immune responses in neurodegeneration. This manuscript presents highlights from the conference and outlines avenues for future research on the roles of immunity in neurodegenerative disorders. Highlights The immune system plays a central role in the pathogenesis of Alzheimer's disease. The immune system exerts numerous effects throughout the brain on amyloid‐beta, tau, and other pathways. The 2023 AAIC, Advancements: Immunity, encouraged discussions and collaborations on understanding the role of the immune system.

Abstract In animal models, brain neurodegeneration biomarkers drain into cervical lymph nodes (CLNs), and this drainage function is reduced with ageing. If this occurred in humans, CLNs may provide a readily accessible measure of this aspect of protein clearance. We tested this hypothesis in people using ultrasound-guided fine needle aspiration. We measured amyloid-beta 40 and 42, phosphorylated tau 181 (pTau181), glial fibrillary acidic protein and neurofilament light using single molecule array in CLN aspirates and plasma from: (i) a discovery cohort of 25 autoimmune patients; and (ii) plasma, CLNs and capillary blood in four healthy volunteers, an optimization cohort. Ultrasound-guided fine needle aspiration was well-tolerated by all participants. In both cohorts, all biomarkers were detected in all plasma and CLN samples, other than neurofilament light (8/17 of discovery cohort). CLN biomarker concentrations were significantly greater than plasma concentrations for all except neurofilament light, most markedly for pTau181 (266-fold; P < 0.02), whose CLN concentrations decreased with age (Spearman r = −0.66, P = 0.001). This study presents the first evidence that neurodegenerative biomarkers are detectable in human CLNs. Raised CLN:plasma biomarker ratios suggest their concentration in CLNs may offer a distinct compartment for minimally-invasive measurement of brain clearance and lymphatic drainage, with potential applicability to study of ageing and future clinical trials.

AbstractBackgroundThe meningeal layers form a unique interface between the central nervous and peripheral immune systems. The lymphatic vasculature that is present in the meningeal dura and drains cerebrospinal fluid (CSF) becomes dysregulated during aging and in models of neurodegenerative disorders such as Alzheimer’s disease (AD). Apolipoprotein E (APOE), and the isoform APOE4 in particular, increases the risk for late‐onset sporadic AD. However, it is still poorly understood whether changes in meningeal lymphatic morphology and drainage are mediating the deleterious effects of APOE4 expression. In the present study, we investigate the effects of human APOE3 or APOE4 on meningeal lymphatic function and immunity.MethodWe evaluated the morphology of lymphatic vessels in dural whole mounts of age‐matched wild type, Apoe‐KO, APOE3, and APOE4 mice at 2‐3, and 11‐12 months. This assessment was performed in both male and female mice. The drainage function of meningeal lymphatics is being assessed in the same mice by in vivo imaging of CSF‐derived fluorescent tracers into the deep cervical lymph nodes. We have also performed RNAscope and protein measurements using murine meningeal tissue to investigate the main cellular source(s) of Apoe, and single‐cell RNA sequencing to explore the cell‐specific transcriptomic signatures linked to the changes in meningeal lymphatic function.ResultLymphatic vessel length is increased in 11‐12‐month‐old APOE4 male mice, when compared to their APOE3 counterparts. Interestingly, the same was not detected in female mice. Dural myeloid cells, expressing Itgam (encoding for CD11b), are the main source of Apoe mRNA transcripts, and one of the main sources of apoE protein in the brain dura mater. APOE4 expression and age markedly alter the transcriptional profile of meningeal myeloid cells, which show overexpression of lysosomal, antigen presentation, and complement genes.ConclusionAPOE4 expression leads to a sex‐dependent meningeal lymphatic vascular remodeling, which is associated with an exacerbated activation of meningeal macrophages. In future studies, we will test whether the changes in meningeal lymphatics observed in mice expressing APOE4 are mediated by myeloid cell derived APOE.

AbstractBackgroundInter‐cellular communication within the gliovascular unit (GVU) is critical for cerebral blood flow regulation, and maintenance of the blood‐brain‐barrier (BBB) properties. The breakdown of BBB in Alzheimer’s disease (AD) is well‐established, but precise underlying molecular changes remain unclear. Additionally, whether GVU molecular alterations observed in AD brains are also detected in blood from living patients is unknown. Further, these GVU molecular perturbations require further investigation in different model systems to identify both human brain‐specific and cross‐species conserved alterations. In this study, we investigated prioritized GVU molecules altered in AD brains for their conservation in blood and cross‐species model systems.MethodsWe performed single nucleus RNA sequencing (snRNAseq) of temporal cortex tissue in AD and control brains. We analyzed this data to detect cell‐specific GVU molecular perturbations and their interactions. We investigated molecular interactions between vascular and astrocyte clusters, the major cell types of the GVU of the BBB. To determine whether GVU transcriptional alterations detected in the brain are preserved in the blood, existing blood expression, genetic, and neuroimaging data from two longitudinal antemortem cohorts were analyzed. Using model systems, including mouse, drosophila, and zebrafish, we evaluated the cross‐species conservation of the top GVU alterations detected in AD brains.ResultsBrain snRNAseq revealed transcriptional profiles of 6,541 astrocytes and 2,210 vascular cells. The latter formed three distinct vascular clusters characterized as pericytes, endothelia and perivascular fibroblasts. We identified differentially expressed genes and their enriched pathways within these clusters and observed the highest levels of transcriptional changes within pericytes. Vascular targets that interact with astrocytic ligands have biological functions in cell signaling, angiogenesis, amyloid ß metabolism, and cytoskeletal architecture. We discovered that genetic variants influencing blood expression levels of some of the prioritized GVU genes were associated with neuroimaging burden of cerebrovascular disease in living human cohorts. Our ongoing studies in model systems revealed conservation of some of the top prioritized molecular perturbations across species.ConclusionOur findings prioritized by multiscale, cross‐tissue human data revealed GVU perturbations within interacting pericyte and astrocyte molecules, which are conserved across multiple cross‐species models. These results nominate new molecular targets and mechanistic insights for BBB disruptions in AD.

AbstractBackgroundAlzheimer’s disease (AD) is the most prevalent form of dementia. We have recently shown that proper meningeal lymphatic drainage is important for brain fluid flow, learning and memory in aging and for brain amyloid beta (Aβ) clearance in mouse models of AD. Interestingly, genetic factors that increased the risk for AD are also linked to altered meningeal lymphatic function.MethodMeningeal lymphatic function was evaluated in mouse models of AD at different ages by RNA sequencing of sorted meningeal lymphatic endothelial cells (LECs) and by assessing of lymphatic vessel morphology and drainage capacity. Meningeal lymphatic dysfunction was induced by photoablation, whereas enhancement of meningeal lymphatic drainage was achieved by increasing the levels of VEGF‐C. The transcriptional signatures of brain blood endothelial cells and microglia were determined by single‐cell RNA sequencing upon manipulation of meningeal lymphatic drainage. Changes in Aβ plaque clearance by monoclonal antibodies were assessed upon prolonged manipulation of meningeal lymphatic drainage. Integrated analysis was performed using murine and human cell RNA‐seq data, as well as AD summary statistics.ResultWe show that a progressive deposition of meningeal Aβ with aging leads to gene expression changes in meningeal lymphatic endothelial cells and an accelerated reduction in meningeal lymphatic vessel coverage in the 5xFAD mouse model. Interestingly, modulating meningeal lymphatic function in AD transgenic mice affects the clearance of Aβ by monoclonal antibodies, a feature that is closely associated with the activation signatures in brain blood endothelial cells and microglia. Furthermore, genes that are highly expressed in lymphatic vasculature are associated with increased risk for AD and altered levels of Aβ in the CSF of AD patients. Integrated analysis of murine and human microglia transcriptomes revealed an association between the signatures of activated microglia from mice with defective meningeal lymphatic function and activated microglia isolated from the AD brain. We are now turning our attention to the interaction between the main genetic risk factor for AD, expression of the apolipoprotein E4, and changes in brain drainage by the meningeal lymphatic vascular system.ConclusionCollectively, our data underline the notion that a dysfunctional meningeal lymphatic vasculature may impact on AD pathophysiology and therapeutic outcome.

A genuine network of lymphatic vessels can be found in the dural layer of the meninges that ensheathe the brain and spinal cord of mammalians. In this issue, Jacob et al. (2022. J. Exp. Med.https://doi.org/10.1084/jem.20220035) employ light sheet fluorescence imaging of intact mouse heads to provide a more comprehensive chart of the meningeal lymphatic vasculature and draw a parallel between lymphatic drainage of cerebrospinal fluid in mice and humans.