Characterizing the role of primary cilia in neural progenitor cell development and neonatal hydrocephalus

Neonatal hydrocephalus is a common neurological disorder leading to expansion of the cerebral ventricles. This disease is associated with significant morbidity and mortality and is often fatal if left untreated. Hydrocephalus was first described over 2500 years ago by Hippocrates, the father of medicine, and remains poorly understood today. Current therapies still rely on invasive procedures developed over 60 years ago that are associated with high failure and complication rates. Thus, the identification of molecular mechanisms and the development of non-invasive medical treatments for neonatal hydrocephalus are high priorities for the medical and scientific communities. The prevailing doctrine in the field is that hydrocephalus is strictly a "plumbing problem" caused by impaired cerebrospinal fluid (CSF) flow. Recently, animal models with impaired cilia have provided insight into the mechanisms involved in communicating (non-obstructive) hydrocephalus. However, as a result of a poor understanding of hydrocephalus, no animal studies to date have identified an effective non-invasive treatment.

The goal of this thesis project is to investigate the molecular mechanisms underlying this disease and to identify a non-invasive, highly effective treatment strategy.

In Chapter 2, we utilize a novel animal model with idiopathic hydrocephalus, mimicking the human ciliopathy Bardet-Biedl Syndrome (BBS), to examine the role of cilia in hydrocephalus. We find that these mice develop communicating hydrocephalus prior to the development of ependymal "motile" cilia, suggesting that this phenotype develops as a result of dysfunctional "primary" cilia. Primary cilia are non-motile and play a role in cellular signaling. These results challenge the current dogma that dysfunctional motile cilia underlies neonatal hydrocephalus and implicate a novel role for primary cilia and cellular signaling in this disease.

Chapter 3 focuses on identifying the link between primary cilia and neonatal hydrocephalus. In this chapter, we report that disrupting the molecular machinery within primary cilia leads to faulty PDGFRα signaling and the loss of a particular class of neural progenitor cells called oligodendrocyte precursor cells (OPCs). We find that the loss of OPCs leads to neonatal hydrocephalus. Importantly, we identify the molecular mechanism underlying both the loss of OPCs and the pathogenesis of neonatal hydrocephalus.

Chapter 4 explores the therapeutic potential of targeting the defective cellular signaling pathways to treat neonatal hydrocephalus. By targeting the faulty signaling, we restore normal development of oligodendrocyte precursor cells, and curtail the development of hydrocephalus. This work challenges the predominant view of hydrocephalus being strictly a "plumbing problem" treatable solely by surgical diversion of CSF. Here, we propose that hydrocephalus is a neurodevelopmental disorder that can be ameliorated by non-invasive means. Importantly, we introduce novel molecular targets and a non-invasive treatment strategy for this devastating disorder. To our knowledge, we are the first to successfully treat neonatal hydrocephalus in any model organism by targeting neural progenitor cells.