Date of Completion

8-17-2015

Embargo Period

8-31-2017

Keywords

Blood-Brain Barrier, Neuroinflammation, Central Nervous System, Multiple Sclerosis, Neurovascular unit, Endothelial heterogeneity, CCL2, Extracellular vesicles, Claudin 5, Transendothelial migration

Major Advisor

Joel S. Pachter

Associate Advisor

Ann E. Cowan

Associate Advisor

Donald L. Kreutzer

Associate Advisor

Robert E. Cone

Field of Study

Biomedical Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Leukocyte infiltration into the central nervous system (CNS) underlies the pathology in a wide spectrum of neuroinflammatory and neurodegenerative diseases like multiple sclerosis (MS), stroke, meningitis, and neuroAIDS. While the steps that mediate the initial adhesion of activated leukocytes to the endothelial wall has been well-characterized, not much is known about their subsequent transendothelial migration (TEM) across the blood-brain barrier (BBB), a highly restrictive paracellular barrier established by the specialized CNS endothelial cells, thus severely limiting the treatment options.

In Multiple Sclerosis (MS) ‘focal’ leukocyte infiltration into the CNS parenchyma early in disease is thought to be critical for the inflammatory response, and eventual neurodegeneration. Therefore, to explore the cues that regulate leukocyte TEM across the BBB in a neuroinflmmatory milieu, in this dissertation, we evaluated the role of three factors- endothelial heterogeneity, chemokine CCL2 from CNS sources, and extracellular vesicles (EVs) from endothelial cells containing a major tight-junction (TJ) protein, Claudin-5 (CLN-5), in CNS leukocyte infiltration, in an animal model of MS called Experimental Autoimmune Encephalomyelitis (EAE).

Using a novel high-resolution three-dimensional confocal image analysis approach, existence of a functional heterogeneity in microvascular response was found during neuroinflammation in EAE. Specifically BBB damage and leukocyte extravasation in EAE was restricted to venules only. Furthermore, Chemokine CCL2, which only surges in a neuroinflammatory milieu to detectable levels and released predominantly from endothelium and astrocytes in the CNS, was shown to uniquely guide leukocytes across the 'respective' (endothelial and astrocyte) basement membranes. Interestingly, leukocytes invading the CNS early in EAE were found to be coated with TJ protein CLN-5. Brain microvascular endothelial cells (BMECs) were seen to release extracellular vesicles (EVs) in neuroinflammation that contained CLN-5, and could bind to the adherent leukocytes possibly for conveying the TJ protein cargo. These CLN-5+ leukocytes were found to transmigrate more efficiently across cultured BMECs. The obtained results from these studies have shed significant light on previously uncharacterized cues and mechanisms that guide circulating leukocytes across the BBB in disease, and holds the key for novel therapeutic strategies to treat a myriad of neurologic disorders and vasculopathies that display immune infiltration in the CNS.

Download

Share

COinS