Genetic and adenoviral ablation of the choroid plexus reduces postnatal hippocampal neurogenesis

Abstract

BackgroundChoroid plexus (ChP) produces cerebrospinal fluid (CSF) and regulates brain development and adult subventricular zone (SVZ) neurogenesis, but its role in postnatal hippocampal subgranular zone (SGZ) neurogenesis is not well understood. Neonatal hydrocephalus, a devastating neurological condition characterized by excessive accumulation of CSF in the brain, is sometimes treated in conjunction with partial ChP cauterization in the lateral ventricles, which results in the resolution of clinical symptoms without large reductions in ventricular volumes. To both understand the roles of the ChP/CSF system in normal CNS function and the impact of ChP ablation or cauterization in hydrocephalus, novel tools for the manipulation of CSF volume and production by ChP are urgently needed. MethodsWe first discovered specific "leaky" expression of diphtheria toxin receptors (DTR) in the ChP of adult ROSA26-iDTR mice, which resulted in a robust and permanent ablation of ChP and reduction of ventricular CSF volume after diphtheria toxin (Dtx) administration. In this study, we first tested the effectiveness of this genetic approach for ChP ablation at neonatal ages. We then generated a novel AAV5-CMV-DTR vector with high ChP tropism to more effectively reduce ventricular volume in these neonatal mice. Genetic (ROSA26-iDTR) and gene therapy (AAV5-DTR) approaches were compared for their extent of ChP ablation, reduction of ventricular CSF volume as assessed by MRI, and impact on postnatal hippocampal neurogenesis at neonatal and young adult ages. Lastly, we tested the therapeutic potential of AAV-mediated ChP ablation using an intracisternal kaolin model of hydrocephalus. ResultsIn our genetic model, ChP ablation and CSF volume reduction was robust at postnatal day (P)10-12, but ineffective at P3-5 with standard Dtx dosing (20 ng/g/day for 3 consecutive days). A higher dose of Dtx (40 ng/g/day) at P3-5 generated a mild reduction of CSF volume but was associated with higher subsequent neonatal mortality. In contrast, AAV5 CMV-DTR virus shows high tropism for ChP epithelial cells and leads to near-complete loss of ventricular CSF in neonates. ChP/CSF loss in neonates or young adult mice leads to a substantial reduction of DCX+ cells within the SVZ, but only a moderate reduction of DCX+ neuroblasts in the SGZ, without altering the number of proliferating or apoptotic cells. In the cisternal kaolin model of hydrocephalus, AAV-mediated ChP ablation within 10 hrs after the onset of hydrocephalus profoundly reduced parenchymal edema and corpus callosum hyperintensity without causing ventricular collapse. ConclusionsThis study reports a novel role of the ChP/CSF in maintaining the neuroblast pool in the neurogenic niches in both early postnatal and adult stages. ROSA26-iDTR-mediated ChP ablation is inefficient before P10, suggesting that this mouse line may be of limited utility in the early postnatal period. In contrast, our novel AAV vector efficiently targets the ChP and CSF production at both neonatal and adult ages, and demonstrates the therapeutic potential of AAV-mediated ChP ablation for the treatment of hydrocephalus. The limited radiographic changes in the kaolin mouse model mirror the clinical findings following choroid plexus cauterization in humans.