January 31, 2020 | On occasion of the «GCB Symposium 2020», held on January 30, 2020, at the Department of Chemistry and Biochemistry and the Department of Physiology, University of Bern, the «GCB Award for Best PhD Thesis» for the year 2019 was conferred on Mariana Mota Castro Dias, PhD in Neuroscience, for her PhD thesis entitled «The role of the brain-barrier tight junctions in neuroinflammation».

GCB Award for Best PhD Thesis 2019

Mariana Mota Castro Dias, PhD, performed her research work in the group of Prof. Dr. Britta Engelhardt, Theodor Kocher Institute, within the framework of the PhD program of the Graduate School for Cellular and Biomedical Sciences, University of Bern. She received her PhD in Neuroscience in October 2019.

Our warmest congratulations and best wishes for her future career go to Mariana Dias, PhD.

After completing her contract with the Theodor Kocher Institute last December, Mariana is taking up a new position as Scientific Communicator at Roche Diagnostics in Rotkreuz, Switzerland in February 2020.

Abstract of the PhD Thesis:

«The role of the brain-barrier tight junctions in neuroinflammation»

by Mariana Mota Castro Dias, Theodor Kocher Institute, University of Bern

The homeostasis of the central nervous system (CNS) is ensured by the blood-brain barrier (BBB), which strictly controls the passage of molecules, solutes and immune cells from the bloodstream into the CNS parenchyma. Paracellular diffusion of molecules across the BBB is ensured by complex and continuous tight junctions (TJs) between brain microvascular endothelial cells. However, during neurological disorders, such as in multiple sclerosis (MS), immune cell infiltration into the CNS and BBB breakdown associated with alterations in TJs are described.

In addition to claudin-5, expression of claudin-3 and claudin-12 has been described in TJs of brain endothelial cells and, despite being suggested to be involved in regulating BBB TJ integrity, the precise role of claudin-3 and claudin-12 have remained unknown. Thus, this prompted us to study the role of claudin-3 and claudin-12 in the regulation of BBB TJ integrity in health and in inflammation, by establishing claudin-3 knockout and claudin-12- lacZ knock in C57BL/6J mice. Surprisingly, RNA sequencing and direct comparative qRT-PCR analysis of brain microvascular samples from WT and claudin-3-/- mice showed beyond doubt that brain endothelial cells do not express claudin-3 mRNA.  On the other hand, our study confirmed expression and junctional localization of claudin-3 at the blood-cerebrospinal-fluid barrier (BCSFB) of the choroid plexus, but its absence did not impair BCSFB properties during health and neuroinflammation. Making use of our reporter claudin-12lacZ/+ C57BL/6J mouse we observed that claudin-12 expression is not limited to blood vessels, but it is mainly expressed by CNS parenchymal cells. Moreover, claudin-12lacZ/lacZ C57BL/6J mouse, which lacked claudin-12, displayed an intact BBB and thus we conclude that claudin-12 is not essential in establishing or maintaining BBB TJs integrity.

Besides BBB TJ alterations in the context of autoimmune neuroinflammation, autoaggressive T cells cross the BBB and enter the CNS parenchyma, which can occur paracellular, through the endothelial junctions, or transcellular, via a pore through the endothelial cell body. However, the precise mechanisms underlying paracellular versus transcellular CD4+TEM cell diapedesis across the BBB remain unknown. By combining serial block face scanning electron scanning microscopy (SBF-SEM) with in vitro live cell imaging, we analyzed, in a 3D ultrastructural level, the interactions between CD4+TEM cell and mouse brain microvascular endothelial cells that favor paracellular versus transcellular diapedesis under physiological flow. Here, we describe that junctional modifications by targeting protein components of paracellular junctions in BBB endothelial cells reduced paracellular T cell diapedesis while favoring transcellular diapedesis under low inflammatory conditions, with no effects on barrier integrity.

Taken together, our studies suggest that claudin-5 is the only critical TJ claudin known to date that contributes to the mouse BBB function. Moreover, we argue that the BBB endothelium and specifically its junctional complexes act as an active player in the regulation of the extravasation of T-cells across the BBB, during immunosurveillance and in inflammatory conditions.