Freie Universität Berlin
Claudins and tight junction-associated MARVEL proteins at the blood-brain barrier – contribution to paracellular barrier formation
Abstract
dc:description.abstractClaudin (Cldn)-5 is thought to dominate the tight junctions (TJs) of the blood-brain barrier (BBB) with minor contribution of Cldn3, -12 and occludin (Ocln). However, in Cldn5 knockout mice the BBB appears ultrastructurally normal (Nitta et al., 2003). Therefore, the involvement of further Cldns and TJ-associated MARVEL proteins (TAMPs) can be hypothesized. Laser-dissected brain capillaries exhibit a high expression of Cldn1, -5, -11, -12, -25 and Ocln, as well as Cldn20 and -26 in mice or Cldn9 and -27 in human. Below one percent of total Cldn/ TAMP mRNA, tricellulin and 10 further Cldns in mice and 9 partially different Cldns in human are found. mRNA values correlate with protein expression, quantified by a novel epitope dilution assay. In brain sections, Cldn3, -4, -5, -11, -12, -20 and -25 are enriched at TJs of capillaries. Cldn25 with ~50% of total Cldn/ TAMP mRNA, the strongest expressed TJ protein at the human BBB, neither tightens the paracellular barrier nor interconnects opposing cells through loop interactions. But a contribution to the proper TJ strand morphology, possibly through interactions with other TJ associated proteins is found. Despite lack of the typical PDZ binding motif, interaction of Cldn25 with the PDZ1 domain of zonula occludens protein 1 is as pronounced as for classic Cldns. Besides, glycosylation of the extracellular loop of Cldn25 is found to be crucial for the localization at the plasma membrane. During post ischemic reperfusion Cldn5 is transcriptionally up-regulated, supporting a re-establishment of TJs at the BBB. Cldn1, -3, -12 and Ocln are down-regulated in the early phase of reperfusion associated with disassembly of TJs due to ischemia. Inversely, Cldn1 expression is strongly up-regulated in brain endothelial cells upon silencing of Cldn5. Collectively, in the first complete Cldn/ TAMP profile, in addition to Cldn5, seven high and eleven low abundant TJ proteins in the brain endothelium become evident and new insights in their interdependent regulation are found. Human and mouse share a common profile ex vivo but differ substantially in quantity. Moreover, in vitro BBB models of isolated endothelial cells are missing ex vivo-complexity and hence, are of limiting informational value. A misconception of the complexity of BBB TJs with respect to Cldn expression was revealed. Furthermore new potential drug targets to modulate the permeability of the BBB were identified.
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Berndt, Philipp
Subjects
dc:subject × 5Rights
- Licence dc:rights.uri
- Language dc:language
- eng
Identifiers
dc:identifier.*- Identifier URI
- http://dx.doi.org/10.17169/refubium-12348