Effect of tryptase on mouse brain microvascular endothelial cells via protease-activated receptor 2

Abstract

BackgroundMast cells (MCs), the ‘first responders’ in brain injury, are able to disrupt the blood–brain barrier (BBB), but the underlying mechanism is not well understood. Tryptase is the most abundant MC secretory product. Protease-activated receptor 2 (PAR-2) has been identified as a specific receptor for tryptase, which is abundantly expressed in brain microvascular endothelial cells. The BBB comprises brain microvascular endothelial cells that display specialised molecular properties essential for BBB function and integrity. Therefore, the purpose of the present study was to investigate the effects of tryptase on mouse brain microvascular endothelial cell line bEnd3 and its potential mechanisms of action.MethodsInduction of mouse brain microvascular endothelial cell activation by tryptase was examined. Then, mouse brain microvascular endothelial cells were pretreated with a PAR-2 antagonist and stimulated with tryptase. Cellular activation, proinflammatory cytokine production, expression of PAR-2, Toll-like receptors (TLRs) and mitogen-activated protein kinases (MAPK), nuclear factor kappa B (NF-kappa B) phosphorylation were assessed.ResultsTryptase upregulated the production of VCAM-1, MMPs (MMP9 and MMP2), TLR4 and TNF-α and downregulated the expression of the tight junction proteins occludin and claudin-5 in mouse brain microvascular endothelial cell. Among the MAPK and NF-kappa B pathway, ERK and NF-kappa B were activated by tryptase. All of these effects could be eliminated by the PAR-2 inhibitor.ConclusionBased on our findings, we conclude that tryptase can trigger brain microvascular endothelial cell activation and proinflammatory mediator release. These findings may further clarify the involvement and mechanism of tryptase in BBB disruption.

Inhibition of mast cell tryptase attenuates neuroinflammation via PAR-2/p38/NFκB pathway following asphyxial cardiac arrest in rats

“…Thus, our results were in line with previous data indicating the MC-tryptase-dependent expression of PAR-2 [37,49]. In addition to the evidence suggesting linked expression of PAR-2 to MC-tryptase [37], the ability of MC-tryptase to upregulate the protein expression of PAR-2 [49] as well as a positive correlation between their expression levels were proposed in earlier studies [37,[55][56][57]. However, despite our extensive research, we could not encounter literature evidence unveiling how MC-tryptase acts as a regulator on PAR-2 protein expression [49].…”

“…We also provided in vivo evidence demonstrating that PAR-2 expression in the brain was linked to MC-tryptase given the attenuated PAR-2 expression in response to the selective inhibition of MC-tryptase with APC366 following CA. Thus, our results were in line with previous data indicating the MC-tryptase-dependent expression of PAR-2 [37,49]. In addition to the evidence suggesting linked expression of PAR-2 to MC-tryptase [37], the ability of MC-tryptase to upregulate the protein expression of PAR-2 [49] as well as a positive correlation between their expression levels were proposed in earlier studies [37,[55][56][57].…”

“…The activator effect of PAR-2 on microglia and astrocytes, resulting in a neuroinflammatory response has been demonstrated in earlier in vitro studies [17,48]. In addition to its contribution to the activation of microglia and astrocytes, the activation of PAR-2 leading to neuronal death and blood brain barrier disruption has been proposed as well [49,50]. However, evidence regarding PAR-2 expression in response to cerebral ischemia is limited and controversial as well.…”

The Mast Cell Is an Early Activator of Lipopolysaccharide-Induced Neuroinflammation and Blood-Brain Barrier Dysfunction in the Hippocampus

“…Further, MCs are powerful and fast sensors of brain injury [15][16][17] by releasing cytoplasmic secretory granules filled with immune and inflammatory mediators including histamine, β-tryptase, tumor necrosis factor-alpha (TNF-α), and interleukin-(IL-) 1β [18]. MCs also express receptors and ligands of various inflammatory pathways, including protease-activated receptor-2-(PAR2-) MAPK-NF-kappa B, histamine receptor 1 (H1R)/H4R-MAPK, and PI3K/AKT-NF-kappa B pathways [19,20].…”

“…Studies showed that MC β-tryptase could activate proteinase-activated receptor 2 receptors, which contribute to the degradation of tight junction proteins, in brain microvascular endothelial cells [20]. Furthermore, microglia express all four histamine receptors (H1R, H2R, H3R, and H4R), and stimulation of mitogen-activated protein kinases (MAPK), PI3K/AKT, and nuclear factor kappa B (NF-kappa B) signaling pathways through H1R and H4R leads to the production of TNF-α and IL-6 [19,34,35].…”