Brain pericytes increase the lipopolysaccharide-enhanced transcytosis of HIV-1 free virus across the in vitro blood–brain barrier: evidence for cytokine-mediated pericyte-endothelial cell crosstalk

Shinya Dohgu,William A Banks

doi:10.1186/2045-8118-10-23

Abstract

BackgroundHuman immunodeficiency virus-1 (HIV-1) enters the brain by crossing the blood–brain barrier (BBB) as both free virus and within infected immune cells. Previous work showed that activation of the innate immune system with lipopolysaccharide (LPS) enhances free virus transport both in vivo and across monolayer monocultures of brain microvascular endothelial cells (BMECs) in vitro.MethodsHere, we used monocultures and co-cultures of brain pericytes and brain endothelial cells to examine the crosstalk between these cell types in mediating the LPS-enhanced permeation of radioactively-labeled HIV-1 (I-HIV) across BMEC monolayers.ResultsWe found that brain pericytes when co-cultured with BMEC monolayers magnified the LPS-enhanced transport of I-HIV without altering transendothelial electrical resistance, indicating that pericytes affected the transcytotic component of HIV-1 permeation. As LPS crosses the BBB poorly if at all, and since pericytes are on the abluminal side of the BBB, we postulated that luminal LPS acts indirectly on pericytes through abluminal secretions from BMECs. Consistent with this, we found that the pattern of secretion of cytokines by pericytes directly exposed to LPS was different than when the pericytes were exposed to the abluminal fluid from LPS-treated BMEC monolayers.ConclusionThese results are evidence for a cellular crosstalk in which LPS acts at the luminal surface of the brain endothelial cell, inducing abluminal secretions that stimulate pericytes to release substances that enhance the permeability of the BMEC monolayer to HIV.

Highlights

Human immunodeficiency virus-1 (HIV-1) enters the brain by crossing the blood–brain barrier (BBB) as both free virus and within infected immune cells
These results show that monolayers with or without pericytes are more permeable to HIV-1 than the much smaller albumin, demonstrating that HIV-1 is crossing brain microvascular endothelial cells (BMECs) by a process other than leakage
The results show that pericytes have differing effects on the three mechanisms of permeability illustrated in this table: increasing TEER and decreasing HIV permeability, but not affecting albumin permeability

Summary

Introduction

Human immunodeficiency virus-1 (HIV-1) enters the brain by crossing the blood–brain barrier (BBB) as both free virus and within infected immune cells. Free virus entry is a multi-step transcytotic process [15,18,19] that is JNKindependent but does depend on p38 mitogen-activated protein kinase [20] and glycoprotein interactions [21] with the mannose-6-phosphate receptor [22] Both of these mechanisms, diapedesis of infected immune cells and free virus transcytosis, are enhanced by inflammation. Diapedesis of infected immune cells and free virus transcytosis, are enhanced by inflammation This is relevant as HIV-1 and its viral proteins gp120 and TAT can activate the immune system and the cells that form the BBB [23,24,25]. To further study the mechanisms by which neuroinflammation can enhance viral permeability across the BBB

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Discussion

Conclusion