Systematic ultrastructural analyses of meningeal and parenchymal vessels of the central nervous system

The direct endothelial contact with adjacent astrocytic end-feet is believed to establish blood-brain barrier (BBB) typical characteristics in endothelial cells of the central nervous system (CNS). However, this contact is only present in capillary vessels of the brain parenchyma and absent in larger veins, arteries and vessels within the meninges. To investigate a potential impact of direct endothelial interactions with adjacent astrocytic end-feet on the molecular tight junction (TJ) composition and ultrastructure, we performed a systematic analysis of endothelial cell contacts within the vascular tree of parenchymal and leptomeningeal vessels. Immunofluorescence labeling for claudin-3, claudin-5, zonula occludens-1 and occludin was used to compare the molecular composition, without showing significant differences in their distribution along the vascular tree of parenchymal and leptomeningeal vessels. Furthermore, electron microscopy in combination with quantitative analyses was performed to investigate the endothelial ultrastructure revealing significant differences within the length of endothelial overlaps between the different vessel types. Here, parenchymal arteries exhibit noticeably longer cell contacts compared to capillaries, which could not be observed in leptomeningeal vessels. It was also observed that arterial vessels regularly contain a higher density of endothelial vesicles throughout the parenchyma and meninges as a sign for transendothelial traffic. Hence, endothelial expression of blood-brain barrier typical TJs is not limited to capillary vessels with an intimate contact to surrounding astrocytes, but is also observed in arteries and veins of the brain parenchyma as well as the meninges, the latter of which are lacking a direct astrocyte-endothelial interaction. These vessel-specific characteristics can now be used to address and compare alterations of the BBB in different settings of CNS pathologies.:Table of Content 1. INTRODUCTION 4 1.1 THE BLOOD-BRAIN BARRIER 4 1.2 HISTORY 5 1.3 STRUCTURE AND COMPOSITION 6 1.4 THE ROLE OF THE MICROENVIRONMENT 8 1.4.1 ASTROCYTES 8 1.4.2 PERICYTES 9 1.5 BLOOD BRAIN BARRIER FUNCTION 10 1.5.1 PHYSIOLOGIC CONDITIONS 10 1. 5.2 PATHOLOGIC CONDITIONS 11 2. OPEN QUESTIONS AND SCIENTIFIC APPROACH 12 3. PUBLICATIONS 13 3.1 DIFFERENT SEGMENTS OF THE CEREBRAL VASCULATURE REVEAL SPECIFIC ENDOTHELIAL SPECIFICATIONS, WHILE TIGHT JUNCTION PROTEINS APPEAR EQUALLY DISTRIBUTED 13 3.2 THE BLOOD-BRAIN BARRIER 28 4. SUMMARY 40 5. REFERENCES 43 6. PROOF OF SIGNIFICANT CONTRIBUTION 48 7. DECLARATION OF ACADEMIC HONESTY 49 8. ACKNOWLEDGMENT 50 9. CURRICULUM VITAE 5