The vasculature of the central nervous system (CNS) forms a tight barrier, not formed by vessels in non-neural tissues, that limits the movement of molecules and ions from the blood to the brain. This blood-brain barrier (BBB) is critical for the proper function of the CNS, as well as protecting it from toxins and pathogens. The importance of the BBB is highlighted by the severe pathology of diseases in which it is broken down. Many of the symptoms of stroke, edema, brain trauma, and multiple sclerosis are due to a breakdown of the BBB that accompanies the primary insult.
Studying the BBB has two main clinical applications. First, understanding how the BBB is built during development may provide insight into rebuilding the barrier in diseases in which it is broken down. Second, the BBB provides a stubborn obstacle for the treatment of all CNS diseases as it block drug delivery to the brain. Therefore, understanding how to circumvent the BBB may provide methods to deliver therapeutics to the CNS. In this thesis I address both of these issues: In chapters 2–4, aim to elucidate the cellular and molecular interactions that direct the development of the BBB, and in chapter 5, I aim identify a novel target to transiently disrupt the BBB.
All the properties of the BBB are manifested in the endothelial cells that line the blood vessels. Transplantation studies have demonstrated that these properties are not intrinsic to the endothelial cells but induced by the microenvironment of the brain. Despite its importance, the timing of BBB formation and the cellular and molecular interactions that induce the barrier properties in CNS endothelial cells remain unknown.
In chapter 2, I analyze the cellular interactions that direct the development of the BBB. I demonstrate that the BBB is formed during embryonic development prior to gliogenesis. This data reveals that astrocytes, thought to be involved in BBB induction, are not involved in this process. I further explore the role of pericytes in regulating the formation of the BBB. In vitro pericytes regulate the expression of the tight junction molecule occludin by endothelial cells, whereas, in vivo depletion of pericytes increases the permeability of the BBB. Taken together these results implicate pericytes as a modulator of the BBB.
In chapter 3, I generate a molecular characterization of the BBB. Utilizing Affymetrix microarrays I compare the transcriptional profile of purified CNS endothelial with those purified from peripheral tissues, generating a database of transcripts that are enriched at the BBB. This analysis has led to the identification that Wnt and RXRα signaling cascades are specifically enriched at the BBB, implicating these pathways in BBB regulation.
In chapter 4, I further examine the role of Wnt signaling in regulating the formation of CNS vessels. I demonstrate in vivo that Wnt signaling is necessary for CNS angiogenesis, but not angiogenesis in non-neural tissues, and that Wnt signaling regulates the expression of the BBB specific transporter glut-1. These results provide molecular evidence that CNS angiogenesis and BBB formation are tightly coupled.
In chapter 5. I identify Nogo-Receptor 2 (Ngr2) as a molecular target to transiently increase the permeability of the BBB. Binding of this antigen, either through systemic injection of an antibody or its ligand MAG, leads to a rapid and reversible disruption of the BBB.
Taken together these results identify novel cellular and molecular mechanisms that form and maintain the BBB and identify potential molecular targets to modulate the BBB during health and disease.
|School Location:||United States -- California|
|Source:||DAI-B 69/05, Dissertation Abstracts International|
|Subjects:||Molecular biology, Neurology, Cellular biology|
|Keywords:||Angiogenesis, Blood-brain barrier, Central nervous system, Endothelial cells, Pericytes|
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