A druggable signaling hub of choroid plexus immune-secretory function

The choroid plexus (ChP) secretes a half-liter of cerebrospinal fluid (CSF) per day into the cerebral ventricular system and gates immune cell entry into the brain as the blood-CSF barrier. Acquired hydrocephalus, characterized by ventriculomegaly from CSF accumulation, is caused by both brain infection or hemorrhage and is treated by neurosurgical CSF diversion with attendant morbidity and long-term disability. We interrogated novel rat models of post-infectious (PIH) and post-hemorrhagic hydrocephalus (PHH) using a multi-omics, systems biology platform to elucidate mechanisms of disease. Integrated analysis of new genome-level transcriptomic and proteomic ChP datasets demonstrated that lipopolysaccharide in PIH, and blood breakdown products in PHH, trigger highly similar toll-like receptor-4 (TLR4)-dependent immune responses at the ChP-CSF interface. This includes the production of a CSF “cytokine storm” elicited from activated peripherally-derived and border-associated macrophages that accumulate at the ChP. Pro-inflammatory CSF signals stimulate their cognate receptors on ChP epithelial cells in paracrine manner to acutely increase CSF secretion rate via the TNF receptor associated SPAK kinase, which binds and activates a multi-ion transporter and channel complex at the ChP apical membrane. Genetic and pharmacological immunosuppression with repurposed drugs antagonizes SPAK-dependent CSF hypersecretion and prevents acute PIH and PHH. These data expand our understanding of ChP immune-epithelial cell crosstalk, reframe PIH and PHH as related inflammatory disorders vulnerable to systemic immunomodulation, and identify a druggable hub of ChP immune-secretory function that holds promise for other neurological disorders.