Endothelial Basement Membrane Laminin 511 Contributes to Endothelial Junctional Tightness and Thereby Inhibits Leukocyte Transmigration

Abstract

Endothelial basement membranes constitute barriers to extravasating leukocytes during inflammation, a process where laminin isoforms define sites of leukocyte exit; however, how this occurs is poorly understood. In addition to a direct effect on leukocyte transmigration, we show that laminin 511 affects endothelial barrier function by stabilizing VE-cadherin at junctions and downregulating expression of CD99L2, correlating with reduced neutrophil extravasation. Binding of endothelial cells to laminin 511, but not laminin 411 or non-endothelial laminin 111, enhanced transendothelial cell electrical resistance (TEER) and inhibited neutrophil transmigration. Data suggest that endothelial adhesion to laminin 511 via β1 and β3 integrins mediates RhoA-induced VE-cadherin localization to cell-cell borders, and while CD99L2 downregulation requires integrin β1, it is RhoA-independent. Our data demonstrate that molecular information provided by basement membrane laminin 511 affects leukocyte extravasation both directly and indirectly by modulating endothelial barrier properties.

Regulation of the Immune System by Laminins

“…This suggests that in vivo the laminins do more than just directly affecting leukocyte migration and likely alter endothelial cell properties. This has been confirmed recently by Song and colleagues [7] who showed that laminin 511 via integrins β1 and β3 increased endothelial junctional tightness by stabilizing vascular endothelial-cadherin and downregulating CD99L2, and inhibited leukocyte transmigration. Thus, the modulation of laminin expression or the blocking of laminin interaction with receptors may be an attractive way to regulate leukocyte migration in vivo .…”

“…Laminins 411 and 511 are also present as part of the ECM in the lymph node cortical ridge, a region that is essential to bring T lymphocytes and antigen-presenting cells together [6]. It is also important to note that the laminins regulate endothelial cell phenotype and function [7], so that indirectly they also influence leukocyte–endothelial interactions. Interestingly, most leukocytes express laminin-specific receptors, suggesting that laminins could regulate leukocyte migration.…”

“…Laminin 511 has an important role for the neutrophil migration, and specific regions within the vascular walls show low expression of laminin 511 [7,47]. These sites are preferentially used by transmigrating neutrophils to penetrate the vascular BM.…”

Laminins and their receptors in the CNS

“…Our unpublished result shows that these mutants have no gross defects or BBB breakdown under homeostatic conditions. Consistent with this observation, a similar result was reported by another group using a different endothelium‐specific laminin‐α5 conditional knockout line (Song et al ., , ). Although grossly normal under physiological conditions, these endothelial laminin‐α5 mutants show phenotypes under pathological conditions.…”

“…Similarly, in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis, T‐lymphocyte infiltration into brain parenchyma was significantly decreased in laminin‐α4 −/− mutants, which displayed ubiquitous expression of laminin‐α5 along the vascular tree (Wu et al ., ), suggesting a negative role of laminin‐α5 in T‐lymphocyte extravasation across the BBB. Consistent with these reports, laminin‐511 enhanced vascular integrity under hypoxic and/or inflammatory conditions in in vitro BBB models (Kangwantas, Pinteaux & Penny, ; Song et al ., ). Altogether, these results suggest that laminin‐α4 and ‐α5 exert different functions to maintain BBB integrity.…”