Functional studies of TRPV4 in Choroid Plexus Epithelial Cells

Abstract

Cerebrospinal fluid (CSF) is produced by the choroid plexus epithelial (CPe) cells, and is moved throughout the brain ventricular system in coordinated waves that are generated by ependymal cilia lining the ventricles and subsequently absorbed by the subarachnoid granulations. CSF is moved in a pulsatile motion which is thought to be influenced by multiple factors like blood pressure and circadian rhythms. Hydrocephalus is a blanket disease description which covers clinical manifestations from CSF over‐production to decreased absorption and can occur at any age. Patients with pediatric hydrocephalus have enlarged ventricles, failure to thrive, sleepiness, sunsetting of the eyes, and vomiting. The current treatment paradigm for hydrocephalus is exclusively surgical and includes CSF diversion by shunt or endoscopic third ventriculostomy. These surgeries have known morbidity and mortality rates, and variable patient outcomes. In order to study pediatric hydrocephalus, the lab has two mouse lines which develop hydrocephalus postnatally. These models have been backcrossed to different genetic backgrounds in order to characterize disease severity, and to select the models with the most viability to undergo further studies. Disease severity is characterized by ventricular area as a function of total brain area in Nissl stained brain slices at specific points from the bregma. Additional characterization is being performed by utilizing intracranial pressure (ICP) monitoring using a small probe inserted into the brain parenchyma. The models that are the most stable and have disease severity similar to pediatric hydrocephalus will be used to test a class of drugs known as Transient Receptor Potential Vanilloid 4 (TRPV4) antagonists. TRPV4 is a widely expressed, widely translated protein which functions in many epithelial tissues as well as in the vasculature, and several neuronal cell types. TRPV4 can function as an osmosensor, mechanosensor, or thermosensor, and can be activated by a number of different metabolites. Activation of TRPV4 results in cation influx into the epithelial cells which can secondarily affect other transporters. TRPV4 antagonists have been shown to ameliorate hydrocephalus in the rat model of pediatric hydrocephalus, the WPK rat. To further understand the in vivo mechanism of TRPV4, a CPe line (Porcine Choroid Plexus – Riems) was used to characterize the effects of pressure (both chronic and acute), and shear force on the TRPV4‐mediated ion flux and conductance. TRPV4‐mediated ion flux is potentiated by acute pressure on the apical side of the CPe cells. In addition, both chronic and acute pressure and shear stress increase TRPV4‐mediated conductance. Successfully completing drug studies in the mouse models of hydrocephalus, as well as characterizing the mechanism of action of the TRPV4 antagonist drugs in vivo will provide a solid basis for further preclinical pharmacology studies.Support or Funding InformationGrants from the Hydrocephalus Association and the Department of Defense Office of the Congressionally Directed Medical Research Programs (CDMRP).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.