Age‐related alterations in meningeal immunity drive impaired central nervous system waste removal

Abstract

AbstractBackgroundThe meningeal lymphatic network enables the drainage of cerebrospinal fluid (CSF) and facilitates the removal of central nervous system (CNS) waste. During aging and in Alzheimer’s disease, impaired meningeal lymphatic drainage promotes the buildup of toxic misfolded proteins in the CNS. Reversing this age‐related dysfunction represents a promising strategy to augment CNS waste clearance, however, the mechanisms underlying this decline remain elusive.MethodYoung (2‐3 month old) and aged (20‐24 month old) C57BL/6J mice were used to study age‐related meningeal phenotypes by single‐cell RNA‐sequencing (scRNA‐seq), high dimensional flow cytometry, and immunohistochemistry. Lymphatic drainage to deep cervical lymph nodes was determined by CSF‐delivery of ovalbumin‐A594. CSF‐delivery of AAVs or antibodies were used to model age‐related deficits in young mice. Peripheral chronic neutralizing antibody administration was utilized to attenuate age‐related alterations in aged mice. 3D in vitro microfluidic devices of human lymphatic endothelial cells were used to model physiological flow parameters.ResultscRNA‐seq of meningeal lymphatic endothelial cells from aged mice revealed a response signature to the inflammatory cytokine IFNγ, which was increased in the aged meninges due to T cell accumulation. Chronic elevation of meningeal IFNγ in young mice via AAV‐mediated over‐expression attenuated CSF drainage—comparable to the deficits observed in aged mice. Mechanistically, this occurred through disruption of lymphatic adherans junctions which was confirmed in 3D in vitro microfluidic systems, and through antibody‐mediated VE‐Cadherin disruption. Therapeutically, IFNγ neutralization alleviated age‐related impairments in meningeal lymphatic function.ConclusionHere we demonstrate that alterations in meningeal immunity underlie the age‐related lymphatic impairment and impaired CNS waste removal. These data suggest manipulation of meningeal immunity as a viable approach to normalize CSF drainage and alleviate the neurological deficits associated with impaired waste removal in neurodegenerative disease.