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Hydrocephalus is a clinical manifestation of cerebrospinal fluid (CSF) accumulation, leading to ventriculomegaly and increased intracranial pressure. Diuretics and other pharmacotherapies have failed to treat hydrocephalus in the human population; therefore, treatment options remain exclusively surgical. The need to develop pharmacotherapies for the treatment of hydrocephalus remains an unmet clinical need and paramount to this need is the study of brain fluid regulation. Previous studies in our laboratory identified the transient receptor potential vanilloid 4 (TRPV4) channel as a potential regulatory hub protein in the choroid plexus responsible, in part, for the regulation of CSF production. Antagonists of the TRPV4 channel were shown to ameliorate hydrocephalus in a genetic rat model. The current studies highlight a novel drug target: serum‐ and glucocorticoid‐induced kinase 1 (SGK1) in the choroid plexus. A specific small molecular weight, membrane permeant inhibitor of SGK1, SI113, has shown promising results in cancer and metabolic research in recent years. In other tissues, SGK1 has been shown to phosphorylate and activate TRPV4 at the membrane, indicating SGK1 as an important upstream regulatory kinase. SI113 blocked TRPV4‐mediated transepithelial ion flux and barrier conductance increases in a cell culture model of human choroid plexus epithelia (HIBCPP line), and ameliorated ventriculomegaly in the genetic rat model. In hydrocephalic animals, there is an increased apical membrane signal in the choroid plexus epithelial cells via immunofluorescent localization of p‐SGK1 and TRPV4, but not of pan‐SGK1. This is not accompanied by a significant increase in either protein or transcript abundance as measured by western blotting or qPCR, respectively. The change in localization is, however, attenuated by treatment with SI113. Animals treated with SI113 show no change in amounts of TRPV4 or total SGK1, but do show significantly reduced levels of p‐SGK1. Thus, phosphorylation of SGK1 appears to be crucial for the activation of TRPV4 which is, in turn, a channel protein that is activated during the development of hydrocephalus. Like Trpv4‐/‐mice, Sgk1‐/‐mice do not show overt phenotypes, indicating pharmacological antagonism of the kinase would have minimal off‐target effects. Overall, these data provide a strong preclinical basis for the use of SGK1 inhibitors in the treatment of hydrocephalus.

Hydrocephalus is a developmental disorder that affects children worldwide with an incidence of approximately 1:1000 births. Multiple causes have been implicated, including a dysfunction of the homeostatic mechanisms of cerebrospinal fluid (CSF) secretion from the choroid plexus, a decreased reabsorption from the subarachnoid granules, or a blockage of CSF circulation, leading to excessive accumulation of CSF within the brain ventricles. One animal model of developmental hydrocephalus involves rats carrying a point mutation on the TMEM67 gene. The homozygous form of this mutation causes a ciliopathy that was originally found in rats with polycystic kidney disease (PKD). Rats homozygous for the TMEM67 mutation show severe hydrocephalus and PKD and do not survive beyond postnatal day (P) 18. Recently we identified a TRPV4 antagonist that appears to protect against the ventriculomegaly in preweaning homozygous rats. We propose that this drug has effects directly on the choroid plexus, and since it is administered intraperitoneally, must gain access to the choroid epithelial cells. Animals heterozygous for the TMEM67 mutation develop a milder degree of hydrocephalus, no renal disease, and live past 1 year. The current study tested the hypothesis that treatment of heterozygous adult animals with the TRPV4 antagonist, RN1734, can limit the extent of hydrocephalus thereby protecting against the associated adverse effects on neurobehavioral function. In the current experiments, the behavioral studies assessed exploration of a complex novel environment called the multivariate concentric square field (MCSF), a 100 x 100 cm arena containing multiple defined zones with a large center area, three dimly‐illuminated perimeter corridors, one brightly illuminated slope and bridge, an enclosed dark corner room (DCR), and a corner hurdle. Video recordings of the single 20‐minute session of each rat are scored by two observers blind to group membership, and quantitative measures of behavioral categories (locomotor activity, exploratory activity, shelter seeking, risk assessment, risk taking) are derived from scores of the type, number and duration of activities in the various zones. MRI's were performed on P300 and P331, and the rats were assigned to either RN1734 or vehicle treatment on P301‐P330, and testing on the MCSF occurred on P315. Several interesting and unexpected results emerged from these studies. Regardless of genotype, the proportion of males that developed hydrocephalus was significantly higher than that of females. Regardless of genotype and drug treatment, the females were more active and engaged in less shelter seeking than males. Because of these sex differences the current studies were underpowered to determine effects of genotype and drug treatment on the behavioral activities.Support or Funding InformationHydrocephalus Association and 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.