Glymphatic System Is Enhanced in Anti-NMDAR Encephalitis and Facilitates Antibody Influx and Clearance in the Brain

Abstract

ABSTRACT Background: Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is an antibody-mediated neuroinflammatory disease. How pathogenic autoantibodies enter and are cleared from the brain parenchyma remains poorly understood. The glymphatic system (GS) mediates cerebrospinal fluid (CSF)-interstitial fluid (ISF) exchange and waste removal, yet its role in anti-NMDAR encephalitis is undefined. Methods: We used polypeptides GluN1356-385 induced active-immunization anti-NMDAR encephalitis mouse model. Glymphatic influx and efflux were evaluated via fluorescent tracer delivery combined with real-time imaging and ex-vivo quantification. Perivascular aquaporin-4 (AQP4) polarization, brain IgG deposition, NMDAR levels and blood-brain barrier (BBB) integrity were analyzed. GS function was pharmacologically modulated with AER-271 (an AQP4 inhibitor) or dexmedetomidine (Dex), and deep cervical lymphatic vessels (dCLV) were ligated in a passive-transfer model (PTM). Behavioral performance was characterized by multiple neurobehavioral tests. Results: Both glymphatic influx and efflux were enhanced in anti-NMDAR encephalitis mice, accompanied by upregulated antibody entry into and clearance from the brain. However, the cerebral IgG deposition was increased. These changes were associated with increased perivascular AQP4 polarization, with no alterations in overall AQP4 abundance or BBB tight-junction integrity. AQP4 inhibition with AER-271 attenuated glymphatic influx and efflux, reduced hippocampus IgG deposition, and partially ameliorated behavioral deficits without restoring hippocampus NMDAR levels. Conversely, dCLV ligation in the PTM mice increased brain retention of patient-derived IgG and exacerbated anxiety-like behavior. Dex enhanced antibody clearance and reduced hippocampus IgG deposition but did not improve behavioral outcomes. Conclusion: The GS is dynamically upregulated in anti-NMDAR encephalitis, driven by increased perivascular AQP4 polarization. The enhanced glymphatic influx facilitates antibody entry into the brain parenchyma and exacerbates neuronal injury, whereas enhanced efflux provides a compensatory route for antibody clearance. Rather than broadly enhancing glymphatic activity, precise tuning of this pathway may present a promising non-immunological therapeutic strategy for autoimmune encephalitis. Keywords: anti-NMDAR encephalitis; antibody influx and clearance; glymphatic system; AQP4 polarization; AER-271; dexmedetomidine