Activation of Peroxisome Proliferator-Activated Receptor γ (PPARγ) Suppresses Rho GTPases in Human Brain Microvascular Endothelial Cells and Inhibits Adhesion and Transendothelial Migration of HIV-1 Infected Monocytes

Abstract

Under inflammatory conditions (including HIV-1 encephalitis and multiple sclerosis), activated brain endothelium enhances the adhesion and transmigration of monocytes across the blood-brain barrier (BBB). Synthetic ligands that activate the peroxisome proliferator-activated receptors (PPARs) have anti-inflammatory properties, and PPAR stimulation prevents the interaction of leukocytes with cytokine stimulated-endothelium. However, the mechanism underlying these effects of PPAR ligands and their ability to intervene with leukocyte adhesion and migration across brain endothelial cells has yet to be explored. For the first time, using primary human brain endothelial cells (BMVEC), we demonstrated that monocyte adhesion and transendothelial migration across inflamed endothelium were markedly reduced by PPARγ activation. In contrast to non-brain-derived endothelial cells, PPARα activation in the BMVEC had no significant effect on monocyte-endothelial interaction. Previously, our work indicated a critical role of Rho GTPases (like RhoA) in BMVEC to control migration of HIV-1 infected monocytes across BBB. In this study, we show that in the BMVEC PPARγ stimulation prevented activation of two GTPases, Rac1 and RhoA, which correlated with decreased monocyte adhesion to and migration across brain endothelium. Relevant to HIV-1 neuropathogenesis, enhanced adhesion and migration of HIV-1 infected monocytes across the BBB were significantly reduced when BMVEC were treated with PPARγ agonist. These findings indicate that Rac1 and RhoA inhibition by PPARγ agonists could be a new approach for treatment of neuroinflammation by preventing monocyte migration across the BBB.

Inhibition of Glycogen Synthase Kinase 3β (GSK3β) Decreases Inflammatory Responses in Brain Endothelial Cells

“…34 Our experiments showed that interactions of monocytes with TNF␣-stimulated BMVECs resulted in diminished barrier function (TEER decrease); GSK3␤ inactivation significantly protected the barrier from injury. We have previously shown that engagement of BMVECs by monocytes results in activation of Rho GTPases (like RhoA, Rac) 16 inducing an increase in barrier permeability and phosphorylation of tight junction proteins (occludin, claudin-5); consequently, inhibition of RhoA/Rho kinase prevented these effects. 19 Whether GSK3␤ inhibition prevents tight junction modifications or interferes with GTPase activity that lead to barrier dysfunction remains to be determined.…”

“…Michael Bernas and Marlys Witte, University of Arizona, Tucson, AZ) were isolated from microvessels derived from temporal or hippocampal tissue removed during operative treatment of epilepsy as described. 16 Tissue used for BMVEC isolation was outside epileptogenic foci. The procedures were approved by the Temple University Institutional Review Board.…”

“…16 FluoroBlok (BD Falcon) cell culture inserts, designed to block the transmission of fluorescent light between 490 and 700 nm, were used in the assay to allow for continuous detection of fluorescently labeled monocytes migrating across en-dothelial monolayers. Briefly, BMVECs were plated at a density of 2.5 ϫ 10 4 cells per insert on type I collagencoated FluoroBlok inserts.…”

“…16 Briefly, BMVECs were plated at a density of 2.5 ϫ 10 4 cells per well on 96-well plates. After formation of monolayers, the BMVECs were activated with TNF␣ (20 ng/ml) or simultaneously treated with the indicated test compounds for 24 hours.…”

Adding Fuel to the Fire: Methamphetamine Enhances HIV Infection

“…35 Furthermore, strategies to prevent activation of two GTPases, Rac1 and RhoA, in the brain microvascular endothelial cells resulted in decreased adhesion and migration of HIV-1-infected monocytes across the brain endothelium. 36 It is plausible that the combined effects of methamphetamine and HIV-1 central nervous system infection could be attributable to activation of transcription factors and GTPases leading to BBB dysfunction secondary to oxidative stress.…”