A novel lysophospholipid- and pH-sensitive receptor, GPR4, in brain endothelial cells regulates monocyte transmigration.
Abundant evidence documents the highly proinflammatory actions of lysophosphatidylcholine (LPC). Further, LPC, found in high amounts in oxidized low-density lipoprotein (LDL), is implicated as an atherogenic factor. In endothelial cells, LPC impairs endothelial barrier function through GPR4, a novel receptor hypothesized to be sensitive to LPC and protons. The authors investigated the stimulation by LPC or low pH of GPR4 in human brain microvascular endothelial cells (HBMECs) and whether the activated GPR4 regulates in vitro monocyte transmigration. The results indicated that HBMECs stimulated by LPC (5 microM), but not low pH, showed a twofold increase in monocyte transmigration. Using retroviruses containing siRNA to GPR4, a > 60% reduction of GPR4 expression resulted in blockade of the LPC-stimulated transmigration. The inhibited response was restored by co-expression with an small interference RNA (siRNA)-resistant, but functional, GPR4 mutant construct. To investigate potential signaling mechanisms, the siRNA-mediated knockdown of GPR4 also prevented LPC-induced RhoA activation. C3 transferase, a Rho inhibitor, prevented approximately approximately 65% of the LPC-stimulated transmigration. LPC also increased MLC phosphorylation by 5 min, which was inhibited by the Rho kinase inhibitor, Y-27632 (10 microM) or ML-7 (myosin light chain kinase (MLCK) inhibitor). The findings indicate that the proinflammatory and atherogenic LPC stimulated endothelial GPR4, which promoted monocyte transmigration through a RhoA-dependent pathway.
Huang
Fei
F
Department of Pharmacology, Rush University Medical Center, Chicago, Illinois 60612, USA.
Mehta
Dolly
D
Predescu
Sanda
S
Kim
Kwang S
KS
Lum
Hazel
H
D001921:Brain / Q000098:blood supply*; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008163:Luminescent Measurements; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D009000:Monocytes / Q000378:metabolism*; D009154:Mutation; D034741:RNA, Small Interfering / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D049312:Receptors, Lysophospholipid / Q000235:genetics / Q000378:metabolism*; D012190:Retroviridae / Q000235:genetics
C091670:GPR4 protein, human; D008244:Lysophosphatidylcholines; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled; D049312:Receptors, Lysophospholipid