Sang Doo Kim

Serum amyloid A induces CCL2 production via formyl peptide receptor-like 1-mediated signaling in human monocytes.

Although the presence of an elevated level of serum amyloid A (SAA) has been regarded as a cardiovascular risk factor, the role of SAA on the progress of atherosclerosis has not been fully elucidated. In the present study, we investigated the effect of SAA on the production of CCL2, an important mediator of monocyte recruitment, and the mechanism underlying the action of SAA in human monocytes. The stimulation of human monocytes with SAA elicited CCL2 production in a concentration-dependent manner. The production of CCL2 by SAA was found to be mediated by the activation of NF-κB. Moreover, the signaling events induced by SAA included the activation of ERK and the induction of cyclooxygenase-2, which were required for the production of CCL2. Moreover, SAA-induced CCL2 induction was inhibited by a formyl peptide receptor-like 1 (FPRL1) antagonist. We also found that the stimulation of FPRL1-expressing RBL-2H3 cells induced CCL2 mRNA accumulation, but the vector-expressing RBL-2H3 cells combined with SAA did not. Taken together, our findings suggest that SAA stimulates CCL2 production and, thus, contributes to atherosclerosis. Moreover, FPRL1 was found to be engaged in SAA-induced CCL2 induction, and cyclooxygenase-2 induction was found to be essential for SAA-induced CCL2 expression. These results suggest that SAA and FPRL1 offer a developmental starting point for the treatment of atherosclerosis.

Lysophosphatidylethanolamine stimulates chemotactic migration and cellular invasion in SK-OV3 human ovarian cancer cells: involvement of pertussis toxin-sensitive G-protein coupled receptor.

We investigated whether lysophosphatidylethanolamine (LPE) modulates cellular signaling in different cell types. SK‐OV3 ovarian cancer cells and OVCAR‐3 ovarian cancer cells were responsive to LPE. LPE‐stimulated intracellular calcium concentration ([Ca2+]i) increase was inhibited by U‐73122, suggesting that LPE stimulates calcium signaling via phospholipase C activation. Moreover, pertussis toxin (PTX) almost completely inhibited [Ca2+]i increase by LPE, indicating the involvement of PTX‐sensitive G‐proteins. Furthermore, we found that LPE stimulated chemotactic migration and cellular invasion in SK‐OV3 ovarian cancer cells. We examined the role of lysophosphatidic acid receptors on LPE‐stimulated cellular responses using HepG2 cells transfected with different LPA receptors, and found that LPE failed to stimulate nuclear factor kappa B‐driven luciferase. We suggest that LPE stimulates a membrane bound receptor, different from well known LPA receptors, resulting in chemotactic migration and cellular invasion in SK‐OV3 ovarian cancer cells.

The Agonists of Formyl Peptide Receptors Prevent Development of Severe Sepsis after Microbial Infection

Severe sepsis, a principal cause of death in intensive care units, occurs when host immune defenses fail to combat invading microbes. In this paper, we report that the administration of peptide agonists of formyl peptide receptors, including Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm), protected against death by enhanced bactericidal activity and inhibition of vital organ inflammation and immune cell apoptosis in a cecal ligation and puncture (CLP) sepsis mouse model. The administration of WKYMVm also enhanced the production of type 1 (IFN-γ and IL-12) and type 17 (IL-17 and TGF-β) cytokines in CLP mice. In contrast, the administration of WKYMVm inhibited the production of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) in the CLP mice. The therapeutic and bactericidal effects of WKYMVm were partly reversed in IFN-γ–deficient mice, whereas target organ inflammation was not. Meanwhile, the therapeutic and anti-inflammatory effects of WKYMVm were partly reversed in IL-17–deficient mice. In addition, the administration of WKYMVm also enhanced type 1 and type 17 Th cell responses in mice sensitized with LPS plus Ags. These results suggest that the agonists of formyl peptide receptors effectively prevent development of severe sepsis following microbial infection partly via augmentation of type 1 and type 17 immune responses.

Serum Amyloid A Induces Contrary Immune Responses via Formyl Peptide Receptor-Like 1 in Human Monocytes

Although the level of serum amyloid A has been reported to be up-regulated during inflammatory response, the role of serum amyloid A on the regulation of inflammation and immune response has not been elucidated. We found that serum amyloid A stimulated the production of tumor necrosis factor (TNF)-α and interleukin (IL)-10, which are proinflammatory and anti-inflammatory cytokines, respectively, in human monocytes. Low concentrations of serum amyloid A stimulated TNF-α production with maximal activity at 6 h after stimulation, whereas high concentrations of serum amyloid A stimulated IL-10 production with maximal activity at 12 h. The activations of the two cytokines by serum amyloid A occurred at both the transcription and translational levels. Signaling events induced by serum amyloid A included the activation of two mitogen-activated protein kinases (extracellular signal-regulated kinase and p38 kinase), which were found to be required for TNF-α and IL-10 production, respectively. The stimulation of formyl peptide receptor-like-1-expressing RBL-2H3 cells, but not of vector-expressing RBL-2H3 cells with serum amyloid A, induced mitogen-activated protein kinases activation and the accumulation of the RNAs of these two cytokines. Together, our findings suggest that serum amyloid A modulates contrary immune responses via formyl peptide receptor-like 1, by inducing TNF-α or IL-10, and demonstrate that extracellular signal-regulated kinase and p38 kinase play counteracting roles in this process.

Functional Expression of Formyl Peptide Receptor Family in Human NK Cells

We determined the expression of the formyl peptide receptor (FPR) family and the functional roles of the FPR family in NK cells. All tested human NK cells express two members of the FPR family (FPR1 and FPR2). The expression of FPR3 was noted to occur in a donor-specific manner. The stimulation of NK cells with FPR family-selective agonists (fMLF (N-formyl-Met-Leu-Phe), MMK-1, F2L, and WKYMVm (Trp-Lys-Tyr-Met-Val-d-Met)) elicited cytolytic activity in resting NK cells, but not in IL-2-activated NK cells; the cytolytic activity was not inhibited by pertussis toxin. The FPR family agonists also stimulated chemotactic migration of IL-2-activated NK cells, but not resting NK cells; the chemotactic migration was completely inhibited by pertussis toxin. WKYMVm stimulates ERK, p38 MAPK, and JNK activities in both resting and IL-2-activated NK cells. WKYMVm-induced chemotactic migration was partially inhibited by PD98059 (2′-amino-3′-methoxyflavone); however, the inhibition of JNK by its selective inhibitor (SP600125, anthra[1,9-cd]pyrazol-6(2H)-one) dramatically inhibited the WKYMVm-induced cytolytic activity. Furthermore, WKYMVm-induced chemotactic migration and cytolytic activity were partly inhibited by FPR family-selective antagonists (cyclosporin H and WRWWWW). Taken together, our findings indicate that human NK cells express functional members of the FPR family, and in turn the activation of the three members of the FPR receptor family elicit cytolytic activity in NK cells, thus suggesting that the receptors are potentially important therapeutic targets for the modulation of NK cell-mediated immune responses.

Activation of CXCR2 by Extracellular Matrix Degradation Product Acetylated Pro-Gly-Pro Has Therapeutic Effects against Sepsis

RATIONALE Acetylated Pro-Gly-Pro (Ac-PGP) is an endogenous degradation product of extracellular collagen that binds to leukocyte-expressed chemoattractant receptor CXCR2. Although certain agents that block CXCR2-mediated signaling protect against experimental sepsis, the roles of Ac-PGP and CXCR2 in sepsis are unclear. OBJECTIVES To investigate the role of Ac-PGP and its receptor, CXCR2, in murine models of cecal ligation and puncture (CLP)-induced polymicrobial sepsis and organ injury. METHODS The impact of in vivo Ac-PGP treatment on animal survival after induction of experimental sepsis was assessed. Vital organ inflammation and immune cell apoptosis were evaluated by histology, and the modulation of proinflammatory cytokine production and bactericidal activity by Ac-PGP in mouse and human blood leukocytes was measured. MEASUREMENTS AND MAIN RESULTS The activation of CXCR2 by tripeptide agonist Ac-PGP dramatically improved survival in three experimental sepsis models. Ac-PGP elicited bactericidal activity via the generation of hydrogen peroxide, inhibited lung inflammation, and reduced immune cell apoptosis. Fluorescein isothiocyanate-labeled PGP bound directly to CXCR2, and the protective effect of Ac-PGP in sepsis was abolished in CXCR2-deficient mice. Ac-PGP treatment enhanced the production of type 1 cytokines (IFN-γ and IL-12) but inhibited the production of proinflammatory cytokines (tumor necrosis factor [TNF]-α, IL-1β, and IL-6) in vivo. In vitro, Ac-PGP directly increased IFN-γ production and decreased the LPS-stimulated production of TNF-α by mouse splenocytes and human leukocytes. Furthermore, direct treatment of LPS-stimulated splenocytes with IFN-γ resulted in diminished secretion of TNF-α and IL-6. CONCLUSIONS CXCR2 and Ac-PGP are thus novel target and starting molecules, respectively, for the development of therapeutic agents against sepsis.

Serum amyloid A stimulates macrophage foam cell formation via lectin-like oxidized low-density lipoprotein receptor 1 upregulation

Elevated levels of serum amyloid A (SAA) is a risk factor for cardiovascular diseases, however, the role of SAA in the pathophysiology of atherosclerosis remains unclear. Here we show that SAA induced macrophage foam cell formation. SAA-stimulated foam cell formation was mediated by c-jun N-terminal kinase (JNK) signaling. Moreover, both SAA and SAA-conjugated high density lipoprotein stimulated the expression of the important scavenger receptor lectin-like oxidized low-density lipoprotein receptor 1 (LOX1) via nuclear factor-κB (NF-κB). A LOX1 antagonist carrageenan significantly blocked SAA-induced foam cell formation, indicating that SAA promotes foam cell formation via LOX1 expression. Our findings therefore suggest that SAA stimulates foam cell formation via LOX1 induction, and thus likely contributes to atherogenesis.

Lysophosphatidylserine stimulates chemotactic migration in U87 human glioma cells.

Lysophosphatidylserine (LPS) was found to stimulate intracellular calcium increase in U87 human glioma cells. LPS also stimulated chemotactic migration of U87 human glioma cells, which was completely inhibited by pertussis toxin (PTX). Moreover, LPS was also found to stimulate ERK, p38 MAPK, JNK, and Akt activities in U87 cells. We observed that LPS-induced U87 chemotaxis was mediated by PI3K, p38 MAPK, and JNK. LPS-induced chemotactic migration in U87 cells was inhibited by Ki16425, an LPA(1/3) receptor-selective antagonist, which suggested that the Ki16425-sensitive G-protein coupled receptor (GPCR) played a role in this process. Moreover, U87 cells were found to uniquely express LPA(1) but not LPA(2-5). In addition, LPS failed to stimulate the NF-kappaB-driven luciferase activity in exogenously LPA(1)-transfected HepG2 cells. Taken together, we propose that LPS stimulates GPCR, which is in contrast to the well-known LPA receptors, thus resulting in the chemotactic migration in U87 human glioma cells.

N-Formyl-Methionyl-Leucyl-Phenylalanine (fMLP) Promotes Osteoblast Differentiation via the N-Formyl Peptide Receptor 1-mediated Signaling Pathway in Human Mesenchymal Stem Cells from Bone Marrow

Binding of N-formyl-methionyl-leucyl-phenylalanine (fMLP) to its specific cell surface receptor, N-formyl peptide receptor (FPR), triggers different cascades of biochemical events, eventually leading to cellular activation. However, the physiological role of fMLP and FPR during differentiation of mesenchymal stem cells is unknown. In this study, we attempted to determine whether fMLP regulates differentiation of mesenchymal stem cells derived from bone marrow. Analysis by quantitative-PCR and flow cytometry showed significantly increased expression of FPR1, but not FPR2 and FPR3, during osteoblastic differentiation. fMLP, a specific ligand of FPR1, promotes osteoblastic commitment and suppresses adipogenic commitment under differentiation conditions. Remarkably, fMLP-stimulated osteogenesis is associated with increased expression of osteogenic markers and mineralization, which were blocked by cyclosporine H, a selective FPR1 antagonist. In addition, fMLP inhibited expression of peroxisome proliferator-activated receptor-γ1, a major regulator of adipocytic differentiation. fMLP-stimulated osteogenic differentiation was mediated via FPR1-phospholipase C/phospholipase D-Ca2+-calmodulin-dependent kinase II-ERK-CREB signaling pathways. Finally, fMLP promoted bone formation in zebrafish and rabbits, suggesting its physiological relevance in vivo. Collectively, our findings provide novel insight into the functional role of fMLP in bone biology, with important implications for its potential use as a therapeutic agent for treatment of bone-related disorders.

Wnt5a stimulates chemotactic migration and chemokine production in human neutrophils

Wnt5a is a ligand that activates the noncanonical Wnt signaling pathways (β-catenin-independent pathways). Human neutrophils expressed several Wnt5a receptors, such as Frizzled 2, 5 and 8. Stimulation of human neutrophils with Wnt5a caused chemotactic migration and the production of two important chemokines, CXCL8 and CCL2. CCL2 production by Wnt5a was mediated by a pertussis toxin-sensitive G-protein-dependent pathway. Wnt5a also stimulated the phosphorylation of three mitogen-activated protein kinases (MAPKs: ERK, p38 MAPK and JNK) and Akt. Inhibition of ERK, p38 MAPK or JNK by specific inhibitors induced a dramatic reduction in Wnt5a-induced CCL2 production. Supernatant collected from lipopolysaccharide-stimulated macrophages induced neutrophil chemotaxis, which was significantly inhibited by anti-Wnt5a antibody. Our results suggested that Wnt5a may contribute to neutrophil recruitment, mediating the inflammation response.