Project description:Meningeal lymphatics serve as the primary outlet for cerebrospinal fluid, and their dysfunction is associated with various neurodegenerative conditions. Previous studies have demonstrated that dysfunctional meningeal lymphatics evoke behavioral deficits, but the neural mechanisms underlying those behavioral changes remained elusive. Here, we show that prolonged impairment of meningeal lymphatics alters the balance of cortical excitatory and inhibitory synaptic inputs by reducing inhibitory synapses, accompanied by deficits in novelty recognition tasks. These synaptic and behavioral alterations are mediated by microglia, which exhibit transcriptomic, morphological, and functional alterations as a result of lymphatic dysfunction. Notably, microglial expression of Il6 increases, thereby mediating the reduction in inhibitory synapses via neuronal signaling. Interestingly, improving the function of meningeal lymphatics in aged mice restores the numbers of functional inhibitory synapses and cortical network activity. Our findings suggest that dysfunctional meningeal lymphatics adversely impact cortical circuitry through a microglia−IL-6-dependent mechanism, providing a potential target for the treatment of aging-associated cognitive decline.
Project description:Meningeal lymphatics serve as the primary outlet for cerebrospinal fluid, and their dysfunction is associated with various neurodegenerative conditions. Previous studies have demonstrated that dysfunctional meningeal lymphatics evoke behavioral deficits, but the neural mechanisms underlying those behavioral changes remained elusive. Here, we show that prolonged impairment of meningeal lymphatics alters the balance of cortical excitatory and inhibitory synaptic inputs by reducing inhibitory synapses, accompanied by deficits in novelty recognition tasks. These synaptic and behavioral alterations are mediated by microglia, which exhibit transcriptomic, morphological, and functional alterations as a result of lymphatic dysfunction. Notably, microglial expression of Il6 increases, thereby mediating the reduction in inhibitory synapses via neuronal signaling. Interestingly, improving the function of meningeal lymphatics in aged mice restores the numbers of functional inhibitory synapses and cortical network activity. Our findings suggest that dysfunctional meningeal lymphatics adversely impact cortical circuitry through a microglia−IL-6-dependent mechanism, providing a potential target for the treatment of aging-associated cognitive decline.
Project description:Microglia are thought to originate exclusively from primitive macrophage progenitors in the yolk sac (YS) and persist throughout life without contributions from definitive hematopoiesis. Here, using Ms4a3-Cre lineage tracing, pharmacological manipulation, and RNA-sequencing, we elucidated the presence and unique features of monocyte-derived macrophages (MDMs) in the brain parenchyma at baseline and during microglia repopulation. Using parabiosis and skull transplantation, we show that MDMs derived from both peripheral blood and skull bone marrow can repopulate microglia-depleted brains, and they display distinct transcriptional profiles compared to YS-derived microglia. Blood-derived macrophages possess a disease-associated microglia (DAM)-like phenotype, while skull-derived macrophages mirror injury-responsive microglia (IRM) and exhibit significant interactions with T cells. Repetitive microglia depletion and subsequent MDM engraftment in 5xFAD mice led to increased amyloid burden, suggesting differential responses of resident microglia and MDMs towards amyloid pathology. Our results reveal the heterogeneous origins and functions of microglia during cell turnover and neurodegeneration, offering insights that may guide microglia-targeted immunomodulatory strategies for neurological disorders.
Project description:Major depressive disorder is one of the most common mental health conditions. Meningeal lymphatics are essential for drainage of molecules in the cerebrospinal fluid to the peripheral immune system. Their potential role in depression-like behaviour has not been investigated. Here, we show in mice, sub-chronic variable stress as a model of depression-like behaviour impairs meningeal lymphatics in females but not in males. Manipulations of meningeal lymphatics regulate the sex difference in the susceptibility to stress-induced depression- and anxiety-like behaviors in mice, as well as alterations of the medial prefrontal cortex and the ventral tegmental area, brain regions critical for emotional regulation. Together, our findings suggest meningeal lymphatic impairment contributes to susceptibility to stress in mice, and that restoration of the meningeal lymphatics might have potential for modulation of depression-like behaviour.
Project description:The goal of this study is to use bulk RNA-sequencing of the right brain hemisphere to observe the effects of TBI in the context of pre-existing meningeal lymphatic dysfunction in mice. We find that pre-existing meningeal lymphatic dysfunction potentiates the inflammatory response to TBI, suggesting an important role for the meningeal lymphatics in injury site drainage and proper recovery.
Project description:Alzheimer's disease (AD) is the most prevalent cause of dementia1. Although there is no effective treatment for AD, passive immunotherapy with monoclonal antibodies against amyloid beta (Aβ) is a promising therapeutic strategy2,3. Meningeal lymphatic drainage has an important role in the accumulation of Aβ in the brain4, but it is not known whether modulation of meningeal lymphatic function can influence the outcome of immunotherapy in AD. Here we show that ablation of meningeal lymphatic vessels in 5xFAD mice (a mouse model of amyloid deposition that expresses five mutations found in familial AD) worsened the outcome of mice treated with anti-Aβ passive immunotherapy by exacerbating the deposition of Aβ, microgliosis, neurovascular dysfunction, and behavioural deficits. By contrast, therapeutic delivery of vascular endothelial growth factor C improved clearance of Aβ by monoclonal antibodies. Notably, there was a substantial overlap between the gene signature of microglia from 5xFAD mice with impaired meningeal lymphatic function and the transcriptional profile of activated microglia from the brains of individuals with AD. Overall, our data demonstrate that impaired meningeal lymphatic drainage exacerbates the microglial inflammatory response in AD and that enhancement of meningeal lymphatic function combined with immunotherapies could lead to better clinical outcomes.
Project description:Neuroinflammatory diseases, such as multiple sclerosis, are characterized by invasion of the brain by autoreactive T cells. The mechanism for how T cells acquire their encephalitogenic phenotype and trigger disease remains, however, unclear. The existence of lymphatic vessels in the meninges indicates a relevant link between the CNS and peripheral immune system, perhaps affecting autoimmunity. Here we demonstrate that meningeal lymphatics fulfill two critical criteria: they assist in the drainage of cerebrospinal fluid components and enable immune cells to enter draining lymph nodes in a CCR7-dependent manner. Unlike other tissues, meningeal lymphatic endothelial cells do not undergo expansion during inflammation, and they express a unique transcriptional signature. Notably, the ablation of meningeal lymphatics diminishes pathology and reduces the inflammatory response of brain-reactive T cells during an animal model of multiple sclerosis. Our findings demonstrate that meningeal lymphatics govern inflammatory processes and immune surveillance of the CNS and pose a valuable target for therapeutic intervention.
Project description:Aging is a major risk factor for many neurological pathologies, including Alzheimer’s disease (AD). However, the mechanisms underlying brain aging and cognitive decline remain elusive. Body tissues are perfused by interstitial fluid (ISF), which is locally reabsorbed via the lymphatic vascular network. In contrast, the parenchyma of the central nervous system (CNS) is devoid of lymphatic vasculature; in the brain, removal of cellular debris and toxic molecules, such as amyloid beta (A) peptides, is mediated by a combination of transcellular mechanisms of transport across the blood−brain and blood−cerebrospinal fluid (CSF) barriers, phagocytosis and digestion by resident microglia and recruited monocytes/macrophages, and CSF influx and ISF efflux through a paravascular route. The recent characterization of meningeal lymphatic vessels prompted a reassessment of the conventional pathways of CNS waste clearance. The role of this vasculature in brain function, specifically in the context of aging and AD, is still poorly understood. Here we show that meningeal lymphatic vessels play an essential role in maintaining brain homeostasis by draining macromolecules from the CNS (CSF and ISF) into the cervical lymph nodes. Using pharmacological, surgical, and genetic models we show that impairment of meningeal lymphatic function in adult mice slows paravascular influx of CSF macromolecules and efflux of ISF macromolecules, and induces cognitive impairment. Treatment with a lymphangiogenic factor, vascular endothelial growth factor C (VEGF-C), enhances meningeal lymphatic drainage of CSF macromolecules, improving brain perfusion and learning and memory performance in aged mice. Disruption of meningeal lymphatic vessels in transgenic mouse models of AD promotes amyloid deposition in the meninges, which closely correlates with human meningeal pathology, and aggravates overall disease severity. Our findings suggest that meningeal lymphatic dysfunction may be an aggravating factor in AD pathology and in age-associated cognitive decline. Thus, augmentation of meningeal lymphatic function might be a promising therapeutic target for preventing or delaying age-associated neurological diseases.