title: Regulation of methylglyoxal-elicited leukocyte recruitment by endothelial SGK1/GSK3 signaling.
abstract: Excessive levels of the glycolysis metabolite methylglyoxal (MG) elicit enhanced expression of adhesion molecules which foster leukocyte-endothelial cell interactions. The signaling mechanisms involved remain elusive. To address this, we investigated the signal transduction of leukocyte- and endothelial-expressed phosphoinositide 3-kinase (PI3K) effector kinases glycogen synthase kinase 3 (GSK3) and serum- and glucocorticoid-inducible kinase 1 (SGK1) in the regulation of MG-elicited leukocyte recruitment. Using intravital microscopy of mouse cremasteric microvasculature, we demonstrate that GSK3 inhibitors lithium and SB216763 mitigate MG-elicited leukocyte recruitment and microvascular hyperpermeability. In SVEC4-10EE2 endothelial cells, but not in neutrophils, MG transiently activates GSK3 by reducing inhibitory phospho-GSK3α/β (Ser21/9) which parallels decrease of phospho-Akt at early time points (<30min). At later time points (≥1h), MG induces GSK3 deactivation which is dissipated by siRNA silencing of SGK. MG treatment potentiates endothelial SGK1 mRNA, total SGK1, phospho-SGK1 and phospho-NDRG1. The SGK1 inhibitor GSK650394 attenuates MG-elicited leukocyte recruitment. Pharmacological inhibition or silencing endothelial GSK3 or SGK attenuates MG-triggered nuclear factor (NF)-κB activity. Furthermore, silencing SGK blunts MG-triggered redox-sensitive phosphorylation of endothelial transcription factor CREB. Inhibition of SGK1 or GSK3 mitigates the expression of endothelial adhesion molecules P- and E-selectins and ICAM-1. Moreover, SGK1-dependent CREB activation participates in MG-elicited ICAM-1 upregulation. We conclude that temporal activation of endothelial SGK1 and GSK3 is decisive in MG-elicited upregulation of transcription factors, adhesion molecule expression, and leukocyte-vascular endothelium interactions. This novel signaling pathway may link excessive MG levels in vivo to inflammation, thus, unraveling potential therapeutic targets.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Yang
authors.initials: Y
authors.lastname: Su
authors.affiliation: Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Syed M
authors.initials: SM
authors.lastname: Qadri
authors.affiliation: Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Francisco S
authors.initials: FS
authors.lastname: Cayabyab
authors.affiliation: Department of Health Sciences, Lakehead University, Thunder Bay, Ontario, Canada; Thunder Bay Regional Research Institute, Thunder Bay, Ontario, Canada.
authors.forename: Lingyun
authors.initials: L
authors.lastname: Wu
authors.affiliation: Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Electronic address: lixin.liu@usask.ca.
authors.forename: Lixin
authors.initials: L
authors.lastname: Liu
keywords: Endothelial cell; GSK3; Inflammation; Leukocyte recruitment; Methylglyoxal; SGK1