Choroid plexus mast cells drive tumor-associated hydrocephalus

Tumor-associated hydrocephalus (TAH) is a common and lethal complication of brain metastases. Although other factors beyond mechanical obstructions have been suggested, the exact mechanisms are unknown. Using single-nucleus RNA-sequencing and spatial transcriptomics, we find that a distinct population of mast cells locate in the choroid plexus and dramatically increase during TAH. Genetic fate-tracing and intracranial mast cell-specific tryptase knockout showed that choroid plexus mast cells (CPMCs) disrupt cilia of choroid plexus epithelia via the tryptase-PAR2-FoxJ1 pathway and consequently increase cerebrospinal fluid production. Mast cells are also found in the human choroid plexus. Levels of tryptase in cerebrospinal fluid are closely associated with clinical severity of TAH. BMS-262084, an inhibitor of tryptase, can cross blood-brain-barrier, inhibits TAH in vivo and alleviates mast cell-induced damage of epithelial cilia in a human pluripotent stem cell-derived choroid plexus organoid model. Collectively, we uncover the function of CPMCs and provide an attractive therapy for TAH. Overall design: 1. sn-seq: two exprimental groups: normal and EO771-VM-bearing mice, 3 independent replicates with 5 mice per group in each replicate. 2. ST, 3 brain sections from 3 EO771-VM mice. 3.RNA-seq: human choroid plexus epithelial cell line (HCPEpiC) treated with or without tryptase (3 independent replicates per group).