Sphingosine 1-phosphate receptor 5 mediates the immune quiescence of the human brain endothelial barrier.
BACKGROUND
The sphingosine 1-phosphate (S1P) receptor modulator FTY720P (Gilenya®) potently reduces relapse rate and lesion activity in the neuroinflammatory disorder multiple sclerosis. Although most of its efficacy has been shown to be related to immunosuppression through the induction of lymphopenia, it has been suggested that a number of its beneficial effects are related to altered endothelial and blood-brain barrier (BBB) functionality. However, to date it remains unknown whether brain endothelial S1P receptors are involved in the maintenance of the function of the BBB thereby mediating immune quiescence of the brain. Here we demonstrate that the brain endothelial receptor S1P5 largely contributes to the maintenance of brain endothelial barrier function.


METHODS
We analyzed the expression of S1P5 in human post-mortem tissues using immunohistochemistry. The function of S1P5 at the BBB was assessed in cultured human brain endothelial cells (ECs) using agonists and lentivirus-mediated knockdown of S1P5. Subsequent analyses of different aspects of the brain EC barrier included the formation of a tight barrier, the expression of BBB proteins and markers of inflammation and monocyte transmigration.


RESULTS
We show that activation of S1P5 on cultured human brain ECs by a selective agonist elicits enhanced barrier integrity and reduced transendothelial migration of monocytes in vitro. These results were corroborated by genetically silencing S1P5 in brain ECs. Interestingly, functional studies with these cells revealed that S1P5 strongly contributes to brain EC barrier function and underlies the expression of specific BBB endothelial characteristics such as tight junctions and permeability. In addition, S1P5 maintains the immunoquiescent state of brain ECs with low expression levels of leukocyte adhesion molecules and inflammatory chemokines and cytokines through lowering the activation of the transcription factor NFκB.


CONCLUSIONS
Our findings demonstrate that S1P5 in brain ECs contributes to optimal barrier formation and maintenance of immune quiescence of the barrier endothelium.
Department of Molecular Cell Biology and Immunology, VU University Medical Center, 1007 MB, Amsterdam, The Netherlands.
Ruben
R
van Doorn
Melissa A
MA
Lopes Pinheiro
Gijs
G
Kooij
Kim
K
Lakeman
Bert
B
van het Hof
Susanne M A
SM
van der Pol
Dirk
D
Geerts
Jack
J
van Horssen
Paul
P
van der Valk
Elizabeth
E
van der Kam
Eric
E
Ronken
Arie
A
Reijerkerk
Helga E
HE
de Vries
D000369:Aged, 80 and over; D001812:Blood-Brain Barrier / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D007111:Immunity, Cellular / Q000235:genetics; D016086:Lentivirus / Q000235:genetics; D008297:Male; D049349:Receptors, Lysosphingolipid / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D049349:Receptors, Lysosphingolipid