SPAK as a candidate mediator of TRPV4-induced NKCC1 activation and a possible pharmacological entry point in posthemorrhagic hydrocephalus

Hydrocephalus arises from pathological disturbances in cerebrospinal fluid (CSF) homeostasis, yet current treatment relies almost exclusively on neurosurgical diversion procedures that frequently require surgical revision. No specific and efficient pharmacological alternative is available as a complement to the invasive neurosurgery due to our lack of understanding of the molecular regulators of CSF secretion. By in vivo determination of CSF dynamics in rats and in vitro quantification of choroid plexus transporter activity, we demonstrate that the STE20-proline-alanine-rich kinase (SPAK) is a critical modulator of CSF secretion via its regulation of the Na ⁺ /K ⁺ /2Cl ^- cotransporter 1 (NKCC1) and the Na⁺/K⁺-ATPase. Systemic administration of a SPAK inhibitor after a mimicked hemorrhagic event attenuated posthemorrhagic hydrocephalus formation 24h post-hemorrhage. Activation of the choroid plexus transient receptor potential vanilloid 4 (TRPV4) ion channel induced hydrocephalus through CSF hypersecretion. This TRPV4-mediated hypersecretion occurred via activation of NKCC1, not the Na ⁺ /K ⁺ -ATPase, and required SPAK activity as a molecular link. Together, these findings identify SPAK as a central integrator of TRPV4-dependent signaling and choroid plexus transporter activity, positioning the TRPV4-SPAK axis as a potential pharmacological target for modulating CSF dynamics in hydrocephalus and other pressure-related pathologies.