Mast cell degranulation damages glymphatic system via PKC/p38MAPK/AQP4 to exacerbate hydrocephalus post intraventricular hemorrhage.

Hydrocephalus following intraventricular hemorrhage (IVH) remains a serious neurological condition with limited treatment options beyond invasive surgical interventions, underscoring the urgent need to elucidate its underlying mechanisms. Emerging evidence implicates impaired glymphatic system function in the pathogenesis of hydrocephalus, particularly through dysregulation of aquaporin-4 (AQP4) expression in astrocytes, which is essential for cerebral waste clearance and fluid homeostasis. Since mast cells are key mediators of neuroinflammation and can influence cerebrospinal fluid (CSF) dynamics, this study investigated their role and underlying mechanisms in hydrocephalus following IVH. An IVH model was established in male Sprague-Dawley (SD) rats by injecting autologous blood into the lateral ventricle. Rats were divided into the following groups: sham operation, IVH, IVH treated with the mast cell stabilizer disodium cromoglycate (DSCG), and IVH treated with DSCG plus the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA). In a rat model of IVH, mast cell degranulation and the release of tryptase and chymase were observed, accompanied by significant impairment of glymphatic influx and efflux. This dysfunction was characterized by reduced penetration of CSF tracers into the brain parenchyma and diminished clearance of interstitial solutes. Pharmacological stabilization of mast cells with DSCG substantially improved glymphatic function, restored glymphatic structural integrity, reduced ventricular enlargement, and ameliorated neurological deficits. Mechanistically, mast cell-derived proteases activated the PKC/p38MAPK signaling pathway, leading to decreased AQP4 expression and altered AQP4 distribution at astrocytic endfeet, thereby disrupting the perivascular polarization critical for glymphatic flow. This mechanism was supported by molecular docking and co-immunoprecipitation (Co-IP), which demonstrated an interaction between p38MAPK and AQP4, and by rescue experiments, which showed that PKC activation reversed DSCG's protective effects. In vitro experiments conducted under indirect co-culture conditions further demonstrated the interaction between mast cells and astrocytes. Our results reveal a novel mast cell-PKC/p38MAPK/AQP4 pathway in the development of hydrocephalus following IVH and identify mast cell stabilization as a promising therapeutic strategy for hydrocephalus post-IVH, offering a potential non-invasive approach to manage this devastating complication.