Congenital hydrocephalus (CH), featuring enlarged brain ventricles, has been classically attributed to failed cerebrospinal fluid (CSF) homeostasis and treated with surgical CSF shunting with high morbidity and failure rates. Significant gaps in our understanding of the molecular mechanisms of human CH impede development of preventive measures and targeted therapies. Using whole exome sequencing (WES), we recently demonstrated de novo mutations (DNMs) in four different neural stem cell (NSC) regulators cause >10% of sporadic human CH (Neuron, 2018). All four genes regulate NSC fate, implicating dysregulated neural stem cell development rather than primary CSF over-accumulation in a subset of CH patients, with potentially paradigm-changing ramifications. In subsequent WES studies >200 CH patients, we have identified the PTEN- PI3K-mTOR signaling pathway as the most commonly mutated gene module in sporadic human CH to date, with multiple loss-of-function (LoF) DNMs in PTEN. Nonetheless, the physiological, cellular, and developmental mechanisms by which PTEN LoF causes CH is unknown. Corroborating our human genetic findings, we now find that embryonic conditional deletion of Pten in a discrete subset of NSCs is sufficient to cause lethal, postnatal CH in mice.
Aim 1 of this study will use detailed histological examination and advanced imaging to characterize the ventricular morphology and cerebrospinal spinal fluid dynamics of hydrocephalic Pten cKO mice. Successful completion of this Aim will help further our understanding of the pathophysiology of human PTEN-associated CH.
Aim 2 of this study will use immunofluorescent confocal microscopy imaging and immunoblot analysis of the ventricular epithelium to examine neural stem cell differentiation and development into mature ependymal cells and mTor pathway activation, underlying the development of hydrocephalus in Pten cKO mice. Based on promising preliminary data, we will also use delivery of rapamycin, an FDA- approved mTOR inhibitor, to attenuate the progression of CH in Pten cKO mice. Successful completion of this Aim will provide insight into the cellular and molecular mechanisms of PTEN-mutated human CH, setting the stage for near-term pre-clinical and translational studies. In addition, this application details research mentorship, clinical experiences, advanced coursework, training of new techniques, and development of the needed skills in scientific grantsmanship, writing, and presentation. This F31 fellowship will serve as an important training tool in the applicant?s development of a patient-driven research program as an independent investigator and neurosurgeon.
Congenital hydrocephalus (CH) is a disorder that causes an excessive accumulation of fluid within the brain, and neurosurgical shunting is currently the only available treatment for CH patients. PTEN has been identified as a candidate CH gene, and studying its function using a genetic mouse model will address significant gaps in our understanding of CH. In the future, this may lead to enhanced treatment options for CH patients, reducing the need for invasive neurosurgical procedures.