The effect of pharmacological inhibition of mitogen- and stress-activated protein kinase-1 (MSK1) on chemokine-induced neutrophil recruitment
Neutrophil recruitment to the site of acute inflammation is a multistep process regulated by specific signaling molecules. The signaling mechanisms that regulate neutrophil-endothelial cell interactions remain incompletely understood. p38 mitogen-activated protein kinase (MAPK) signalling was shown to regulate different steps of neutrophil migration in response to inflammatory stimuli. The mitogen- and stress-activated protein kinase-1 (MSK1) can be activated by either extracellular-signal-regulated kinase (ERK) 1/2 or p38 MAPK. The aim of the present study is to investigate the effects of pharmacological suppression of MSK1 by its specific inhibitor, SB747651A, on various steps of neutrophil recruitment. In vivo studies were conducted using real-time and time-lapsed intravital video microscopy of the cremaster microcirculation to determine the dynamic leukocyte-endothelial cell interactions. Intrascrotal injection of macrophage inflammatory protein-2 (MIP-2, 0.2 μg/mouse) decreased leukocyte rolling velocity which was significantly reversed by pre-treatment with SB747651A (intrascrotal injection of 3 mg/kg). SB747651A pre-treatment enhanced MIP-2-induced increase in neutrophil adhesion and emigration. To better understand the effect of SB747651A on different steps of neutrophil recruitment, we placed a small piece of MIP-2-containing agarose gel on the exposed cremaster muscle and studied directed migration of neutrophils in the postcapillary venule and in the tissue. Superfusion of SB747651A (5 μM) on cremaster muscle subjected to MIP-2 gradient significantly increased rolling velocity and adhesion, but decreased emigration of neutrophils in comparison to superfusion of normal saline III without SB747651A. SB747651A treatment significantly affected transmigration time, detachment time, intravascular crawling and the velocity of migration, but not the directionality of migrating neutrophils in tissue. The expression of intercellular adhesion molecule-1 (ICAM-1) in cultured endothelial cells was up-regulated by co-treatment with SB747651A and MIP-2 but not by MIP-2 alone. Flow cytometry analysis showed that co-treatment of bone marrow neutrophils with SB747651A and MIP-2 significantly decreased macrophage antigen-1 (Mac-1) but not lymphocyte function associated antigen-1 (LFA-1) expression as compared with MIP-2 treatment alone. Collectively, our findings demonstrate that pharmacological suppression of MSK1 by SB747651A affects multiple steps of MIP-2-induced neutrophil recruitment in vivo.
Neutrophil recruitment, MSK1, SB747651A, MIP-2
Master of Science (M.Sc.)