Regulation of Ncbe in the Choroid Plexus of Mice after Hemorrhage-Induced Hydrocephalus.

The choroid plexus (CP) is a small tissue located inside brain ventricles. It is responsible for the production of most of the cerebrospinal fluid (CSF); approximately 500 mL of CSF per day in the adult human [1, 2]. CSF production occurs as a net result of transcellular movement of salt and water, carried out by various cellular transporters. Ncbe is a sodium-coupled bicarbonate transporter located in the basolateral membrane of the choroid plexus epithelial (CPE) cells. It transports Na and HCO into the cell in exchange for Cl . Ncbe is the main sodium loader of the cell and CSF production is probably dependent on this transporter [3]. Posthemorrhagic hydrocephalus (PHH) is a pathological state, caused by an accumulation of CSF in the ventricular system following intraventricular hemorrhage. CSF buildup is caused by a disproportion in CSF production and reabsorption. This leads to an expansion of the brain ventricles. Intraventricular hemorrhage (IVH) is known to cause inflammation in the CP, which is coupled to an over-production of CSF [4-6]. Initially we hypothesized that IVH would stimulate Ncbe in the CPE through increased protein abundance as well as transporter activity. This would lead to increased CSF formation, similar to the response found after treatment with e.g. the cyclic-AMP agonist forskolin [7]. Our preliminary data, however, suggest that Ncbe abundance is reduced by 24% (n=4, p=0.0329) in mice in the initial stages of PHH and then normalizes. The aim of this study is to investigate which role Ncbe plays in PHH and how Ncbe knock down affects CSF production in both healthy mice and a disease model. An adeno-associated virus (AAV) shRNA knockdown vector system has been developed to knock down Ncbe gene expression by intracerebroventricular injections. Our preliminary data shows that the CPE cells incorporate the vector when tagged with GFP. We have established an IVH model and recording of CSF secretion rates in mice. Increased CSF formation rate was validated with ventriculo-cisternal perfusion (data shown in figure). The resulting changes in ventricular volume will be investigated using magnetic resonance imaging (MRI). We propose that Ncbe knock down inhibits CSF production and could potentially target inflammation-dependent hypersecretion by reducing the availability of the sodium supplying the apical transporters in the CP. REFERENCES: 1. Cserr, H.F.,Physiology of the choroid plexus.Physiol Rev, 1971.51(2): p. 273-311. 2. Wright, E.M., Transport processes in the formation of the cerebrospinal fluid. Rev Physiol Biochem Pharmacol, 1978. 83: p. 3-34. 3. Jacobs, S., et al., Mice with targeted Slc4a10 gene disruption have small brain ventricles and show reduced neuronal excitability. Proc Natl Acad Sci U S A, 2008. 105(1): p. 311-6. 4. Tan, X., et al., Prx2 (Peroxiredoxin 2) as a Cause of Hydrocephalus After Intraventricular Hemorrhage. Stroke, 2020. 51(5): p. 1578-1586. 5. Strahle, J.M., et al., Role of hemoglobin and iron in hydrocephalus after neonatal intraventricular hemorrhage.Neurosurgery, 2014. 75(6): p. 696-705; discussion 706. 6. Karimy, J.K., et al., Inflammation-dependent cerebrospinal fluid hypersecretion by the choroid plexus epithelium in posthemorrhagic hydrocephalus. Nat Med, 2017. 23(8): p. 997-1003. 7. Oshio, K., et al., Reduced cerebrospinal fluid production and intracranial pressure in mice lacking choroid plexus water channel Aquaporin-1. FASEB J, 2005. 19(1): p. 76-8.