Monocyte chemotactic protein-1 (MCP-1): signal transduction and involvement in the regulation of macrophage traffic in normal and neoplastic tissues

Interleukin 17A Promotes Lymphocytes Adhesion and Induces CCL2 and CXCL1 Release from Brain Endothelial Cells

The nature of the interaction between Th17 cells and the blood-brain barrier (BBB) is critical for the development of autoimmune inflammation in the central nervous system (CNS). Tumor necrosis factor alpha (TNF-α) or interleukin 17 (IL-17) stimulation is known to enhance the adherence of Th17 cells to the brain endothelium. The brain endothelial cells (bEnd.3) express Vascular cell adhesion molecule 1 (VCAM-1), the receptor responsible for inflammatory cell adhesion, which binds very late antigen 4 (VLA-4) on migrating effector lymphocytes at the early stage of brain inflammation. The present study examines the effect of the pro-inflammatory cytokines TNF-α and IL-17 on the adherence of Th17 cells to bEnd.3. The bEnd.3 cells were found to increase production of CCL2 and CXCL1 after stimulation by pro-inflammatory cytokines, while CCL2, CCL5, CCL20 and IL17 induced Th17 cell migration through a bEnd.3 monolayer. This observation may suggest potential therapeutic targets for the prevention of autoimmune neuroinflammation development in the CNS.

Interleukin 17A Promotes Lymphocytes Adhesion and Induces CCL2 and CXCL1 Release from Brain Endothelial Cells

The nature of the interaction between Th17 cells and the blood-brain barrier (BBB) is critical for the development of autoimmune inflammation in the central nervous system (CNS). Tumor necrosis factor alpha (TNF-α) or interleukin 17 (IL-17) stimulation is known to enhance the adherence of Th17 cells to the brain endothelium. The brain endothelial cells (bEnd.3) express Vascular cell adhesion molecule 1 (VCAM-1), the receptor responsible for inflammatory cell adhesion, which binds very late antigen 4 (VLA-4) on migrating effector lymphocytes at the early stage of brain inflammation. The present study examines the effect of the pro-inflammatory cytokines TNF-α and IL-17 on the adherence of Th17 cells to bEnd.3. The bEnd.3 cells were found to increase production of CCL2 and CXCL1 after stimulation by pro-inflammatory cytokines, while CCL2, CCL5, CCL20 and IL17 induced Th17 cell migration through a bEnd.3 monolayer. This observation may suggest potential therapeutic targets for the prevention of autoimmune neuroinflammation development in the CNS.

Gomisin N Decreases Inflammatory Cytokine Production in Human Periodontal Ligament Cells

Gomisin N, which is a lignan isolated from Schisandra chinensis, has some pharmacological effects. However, the anti-inflammatory effects of gomisin N on periodontal disease are uncertain. The aim of this study was to examine the effect of gomisin N on inflammatory mediator production in tumor necrosis factor (TNF)-α-stimulated human periodontal ligament cells (HPDLC). Gomisin N inhibited interleukin (IL)-6, IL-8, CC chemokine ligand (CCL) 2, and CCL20 production in TNF-α-stimulated HPDLC in a dose-dependent manner. Moreover, we revealed that gomisin N could suppress extracellular signal-regulated kinase (ERK) and c-Jun N terminal kinase (JNK) phosphorylation in TNF-α-stimulated HPDLC though protein kinase B (Akt) phosphorylation was not suppressed by gomisin N treatment. In summary, gomisin N might exert anti-inflammatory effects by attenuating cytokine production in periodontal ligament cells via inhibiting the TNF-α-stimulated ERK and JNK pathways activation.

Fli-1 controls transcription from the MCP-1 gene promoter, which may provide a novel mechanism for chemokine and cytokine activation

Regulation of proinflammatory cytokines and chemokines is a primary role of the innate immune response. MCP-1 is a chemokine that recruits immune cells to sites of inflammation. Expression of MCP-1 is reduced in primary kidney endothelial cells from mice with a heterozygous knockout of the Fli-1 transcription factor. Fli-1 is a member of the Ets family of transcription factors, which are evolutionarily conserved across several organisms including Drosophilla, Xenopus, mouse and human. Ets family members bind DNA through a consensus sequence GGAA/T, or Ets binding site (EBS). Fli-1 binds to EBSs within the endogenous MCP-1 promoter by ChIP assay. In this study, transient transfection assays indicate that the Fli-1 gene actively promotes transcription from the MCP-1 gene promoter in a dose-dependent manner. Mutation of the DNA binding domain of Fli-1 demonstrated that Fli-1 activates transcription of MCP-1 both directly, by binding to the promoter, and indirectly, likely through interactions with other transcription factors. Another Ets transcription factor, Ets-1, was also tested, but failed to promote transcription. While Ets-1 failed to drive transcription independently, a weak synergistic activation of the MCP-1 promoter was observed between Ets-1 and Fli-1. In addition, Fli-1 and the NFκB family member p65 were found to interact synergistically to activate transcription from the MCP-1 promoter, while Sp1 and p50 inhibit this interaction. Deletion studies identified that EBSs in the distal and proximal MCP-1 promoter are critical for Fli-1 activation from the MCP-1 promoter. Together, these results demonstrate that Fli-1 is a novel regulator of the proinflammatory chemokine MCP-1, that interacts with other transcription factors to form a complex transcriptional mechanism for the activation of MCP-1 and mediation of the inflammatory response.

Resolution of central nervous system astrocytic and endothelial sources of CCL2 gene expression during evolving neuroinflammation

BACKGROUND

The chemokine CCL2 is a critical mediator of neuroinflammation in diseases such as multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). CCL2 drives mononuclear cell infiltration into the central nervous system (CNS), alters expression and distribution of microvascular endothelial tight junction proteins, and disrupts the blood-brain and blood-spinal cord barriers. Immunohistochemistry has consistently revealed astrocytes to be a source of this chemokine during neuroinflammation, while providing less uniform evidence that CNS endothelial cells may also express CCL2. Moreover, the relative contributions of these cell types to the CNS pool of CCL2 during MS/EAE are unclear and the aim of this study was to investigate this further.

METHODS

CCL2 gene expression was determined by qRT-PCR in different populations of CNS cells at different times following EAE induced by immunization with MOG35-55 peptide and adjuvants, or after injection with adjuvants alone. CNS cells types were isolated by two different protocols: bulk isolation to yield crude microvascular and parenchymal fractions (containing astrocytes, other glia, and neurons), or laser capture microdissection (LCM) to acquire more precisely microvascular endothelial cells, astrocytes or other parenchymal cells.

RESULTS

Both CNS microvessel and parenchymal populations prepared by crude bulk isolation showed up-regulation of CCL2 mRNA following MOG immunization or injection of adjuvants alone. More exact dissection by LCM revealed microvascular endothelial cells and astrocytes to be the specific sources of CCL2 gene induction following MOG immunization, while only astrocytes showed elevated CCL2 mRNA in response to just adjuvants. Astrocytes displayed the greatest degree of stimulation of CCL2 gene expression following EAE induction.

CONCLUSIONS

High-precision LCM affirmed both microvascular endothelial cells and astrocytes as the major CNS sources of CCL2 gene expression during EAE. Given the high accessibility of the CNS microvascular endothelium, endothelial-derived CCL2 could prove a viable target for therapeutic intervention in neuroinflammatory disease.

Cell-selective knockout and 3D confocal image analysis reveals separate roles for astrocyte-and endothelial-derived CCL2 in neuroinflammation

Background

Expression of chemokine CCL2 in the normal central nervous system (CNS) is nearly undetectable, but is significantly upregulated and drives neuroinflammation during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis which is considered a contributing factor in the human disease. As astrocytes and brain microvascular endothelial cells (BMEC) forming the blood–brain barrier (BBB) are sources of CCL2 in EAE and other neuroinflammatory conditions, it is unclear if one or both CCL2 pools are critical to disease and by what mechanism(s).

Methods

Mice with selective CCL2 gene knockout (KO) in astrocytes (Astro KO) or endothelial cells (Endo KO) were used to evaluate the respective contributions of these sources to neuroinflammation, i.e., clinical disease progression, BBB damage, and parenchymal leukocyte invasion in a myelin oligodendrocyte glycoprotein peptide (MOG_35-55)-induced EAE model. High-resolution 3-dimensional (3D) immunofluorescence confocal microscopy and colloidal gold immuno-electron microscopy were employed to confirm sites of CCL2 expression, and 3D immunofluorescence confocal microscopy utilized to assess inflammatory responses along the CNS microvasculature.

Results

Cell-selective loss of CCL2 immunoreactivity was demonstrated in the respective KO mice. Compared to wild-type (WT) mice, Astro KO mice showed reduced EAE severity but similar onset, while Endo KO mice displayed near normal severity but significantly delayed onset. Neither of the KO mice showed deficits in T cell proliferation, or IL-17 and IFN-γ production, following MOG_35-55 exposure in vitro, or altered MOG-major histocompatibility complex class II tetramer binding. 3D confocal imaging further revealed distinct actions of the two CCL2 pools in the CNS. Astro KOs lacked the CNS leukocyte penetration and disrupted immunostaining of CLN-5 at the BBB seen during early EAE in WT mice, while Endo KOs uniquely displayed leukocytes stalled in the microvascular lumen.

Conclusions

These results point to astrocyte and endothelial pools of CCL2 each regulating different stages of neuroinflammation in EAE, and carry implications for drug delivery in neuroinflammatory disease.

Toll-like receptor cross-talk in human monocytes regulates CC-chemokine production, antigen uptake and immune cell recruitment

Chemokines production in monocytes/macrophages is crucial in modulating immune responses generated through Toll-like receptor (TLR)-mediated recognition of microbes. During microbial onset, multiple pathogen-associated structures can be present at infection sites, and simultaneously trigger different TLRs. We report here that TLR3, TLR4 and TLR8 engagement induce CCL1, CCL2 and CCL4 production in freshly isolated monocytes. While differentiating cells maintain the capacity to secrete CCL2 and CCL4, CCL1 is no longer induced at later differentiation stages. Although different pairs of TLR agonists have been described to synergistically induce cytokine production in different cell types, agonist combinations cooperate in reducing CCL1 and CCL2, but not CCL4 secretion in freshly isolated monocytes, and fail to rescue CCL1 production at later differentiation stages. The effects of single, but not combined, TLR engagement on chemokine expression mostly occur at transcriptional level, and are IL-10 independent. Conversely, inhibition of CCL1 secretion upon combined TLR engagement is partially rescued by blocking IL-23. A different chemotactic activity of monocyte-conditioned medium on blood mononuclear cells as well as antigen uptake capacity of TLR agonist activated monocytes parallel the regulated production of chemokines. Overall, these findings indicate that simultaneous engagement of TLRs may lead to different patterns of chemokine expression depending on cellular differentiation state, chemokine, and TLR agonist combination. These different responses may be relevant for the distinct but complementary functions of monocytes and macrophages in the immune response, and may have important implications for the therapeutic manipulation of the innate immune system.

Distinct granuloma responses in C57BL/6J and BALB/cByJ mice in response to pristane

Granuloma formation is an inflammatory response of the host against invading pathogens or indigestible substances. We generated mesenteric oil granulomas by injecting pristane into the peritoneal cavity (PC) of mice, and compared oil granuloma formation in the C57BL/6J and BALB/cByJ strains of mice. The formation and kinetics of oil granulomas were distinct between the two strains. In C57BL/6J mice, injected pristane induced oil granuloma formation at both the mesenteric centers (MG) and margins (SG). MG was resolving by 11 weeks, and SG persisted. In BALB/cByJ mice, MG developed slower but persisted longer than in C57BL/6J mice, and SG resolved sooner than in C57BL/6J mice. Injection of India ink revealed that phagocytes were localised mainly to the SG in C57BL/6J mice, but were located diffusely in both MG and SG of BALB/cByJ mice. SG cells expressed more monocyte chemotactic protein-1 (MCP-1) mRNA than MG cells in C57BL/6J mice, but there was no difference in MCP-1 expression between the MG and SG in BALB/cByJ mice. These observations suggest that the recruitment of inflammatory leucocytes under the direction of chemokines differentiates the patterns of granuloma responses to pristane in C57BL/6J and BALB/cByJ mice.

Predominant expression of CCL2 at the tumor site of prostate cancer patients directs a selective loss of immunological tolerance to CCL2 that could be amplified in a beneficial manner

We have previously shown that, during inflammatory autoimmune diseases in humans, the immune system develops a neutralizing auto-Ab-based response to a very limited number of inflammatory mediators, and that amplification of each response could be beneficial for the host. Our working hypothesis has been that this selective breakdown of immunological tolerance is due to a predominant expression of an inflammatory mediator at an immune-restricted site undergoing a destructive process. All three conditions also take place in cancer diseases. In this study, we delineate this hypothesis for the first time in a human cancer disease and then explore its clinical implications. We show that in primary tumor sections of prostate cancer subjects, CCL2 is predominantly expressed at the tumor site over other chemokines that have been associated with tumor development, including: CXCL12, CXCL10, CXCL8, CCL3, and CCL5. Subsequently, the immune response selectivity mounts an Ab-based response to CCL2. These Abs are neutralizing Abs. These findings hold diagnostic and therapeutic implications. The current diagnosis of prostate cancer is based on prostate-specific Ag measurements that do not distinguish benign hypertrophy from malignancy. We show in this study that development of anti-CCL2 Abs is selective to the malignant stage. From a clinically oriented perspective, we show, in an experimental model of the disease, that DNA-based amplification of this response suppresses disease, which has implications for a novel way of therapy in humans.

Identification of regulatory Hck and PAI-2 proteins in the monocyte response to PEG-containing matrices

Mass spectrometry is a powerful proteomic tool enabling researchers to survey the global proteome of a cell. This technique has only recently been employed to investigate cell-material interactions. We had previously identified material scarcity and limited adherent cells as challenges facing mass spectrometric analysis of cell-material interactions. U937 adherent to tissue culture poly(styrene) was used as a model system for identifying proteins expressed by adherent monocytes and analyzed by HPLC coupled offline to MALDI-ToF/ToF (LC-MALDI). We identified 645 proteins from two cation fractions of crude U937 monocyte cell lysate. Forty three proteins of interest from the 645 were chosen based on literature searches for relevance to monocyte-material inflammation and wound healing. Proteins such as 40S ribosomal protein S19 and tyrosyl tRNA synthetase highlight the ability of LC-MALDI to identify proteins relevant to monocyte-material interactions that are currently unexplored. We used PEG-based semi-interpenetrating polymer networks and PEG-only hydrogels to investigate surface dependent effects on the Src family kinase Hck and plasminogen activator inhibitor-2 (PAI-2) using the pyrazolo pyrimidine small molecule inhibitor PP2 and exogenous urokinase plasminogen activator addition, respectively. Hck is well researched in cell adhesion while PAI-2 is virtually unknown in cell-material interactions. U937 on TCPS and PEG-only hydrogels secreted similar levels of inflammatory cytokines and gelatinase MMP-9. MCP-1 secretion from monocytes on PEG-only hydrogels was Hck independent in contrast to Hck-dependent MCP-1 secretion in U937 on TCPS. Overall, U937 adherent to sIPNs secrete low levels of soluble gelatinase MMP-9, IL-1beta, TNF-alpha, IL-6, and MCP-1 independent of Hck and PAI-2. This work demonstrates significant changes in surface dependent expression of proteins from monocytes adherent to PEG-based materials compared to TCPS.

Activation of MCP-1/CCR2 axis promotes prostate cancer growth in bone

Prostate cancer (PCa) frequently metastasizes to bone resulting in a mixture of osteolytic and osteoblastic lesions. We have previously reported that monocyte chemotactic protein-1 (MCP-1) is chemotactic for PCa cells, and its receptor, CCR2 expression, correlates with pathological stages. However, the role of MCP-1/CCR2 axis on PCa progression in bone remains unclear. We first evaluated the serum levels of MCP-1 in patients with bone metastases or localized PCa by enzyme-linked immunosorbent assay. We found that MCP-1 levels were elevated in patients with bone metastases compared to localized PCa. We further determined the effects of knockdown CCR2 or MCP-1 on PCa cell invasion and the tumor cell-induced osteoclast activity in vitro, respectively. PCa C4-2B and PC3 cells were transfected stably with either CCR2 short hairpin RNA (shRNA) or a scrambled RNA. CCR2 knockdown significantly diminished the MCP-1-induced PCa cell invasion. In addition, the MCP-1 production was knocked down by MCP-1 shRNA in C4-2B and PC3 cells. Conditioned media (CM) was collected and determined for the CM-induced osteoclast formation in vitro. MCP-1 knockdown significantly decreased the PCa CM-induced osteoclast formation. Finally, MCP-1 knockdown PC3 cells were implanted into the tibia of SCID mice for 4 weeks. Tumor volume was determined by histopathology and bone histomorphometry. MCP-1 knockdown diminished PC3 tumor growth in bone. We concluded that activation of MCP-1/CCR2 axis promotes PCa growth in bone. This study suggests that MCP-1 may be a target for PCa progression.

Evidence that lipopolysaccharide-induced anorexia depends upon central, rather than peripheral, inflammatory signals

Systemic inflammatory stimuli cause anorexia and weight loss by disrupting the physiological regulation of energy balance. Mice lacking MyD88, an intracellular mediator of signal transduction activated by Toll-like receptor 4 or IL-1beta receptors, are resistant to anorexia induced by the bacterial endotoxin lipopolysaccharide (LPS), despite a significant circulating cytokine response. Thus, we hypothesized that induction of a peripheral inflammatory response is insufficient to cause LPS-induced anorexia when MyD88 signaling in the central nervous system and other tissues is absent. To test this hypothesis, we used bone marrow transplantation (BMT) to determine if LPS-induced anorexia can be restored to MyD88-deficient mice by reconstituting their bone marrow with wild-type (WT) immune cells. We found that restoring WT circulating immune cells to mice lacking MyD88 conferred only a mild, short-lived anorexia in response to LPS, such that food intake was fully normalized by 20 h post injection (LPS 4.1 +/- 0.5 g vs. vehicle 4.3 +/- 0.3 g), whereas LPS-induced anorexia was profound and sustained in WT controls after either autologous BMT or sham BMT. Similarly, LPS-mediated induction of hypothalamic mRNA encoding IL-1beta and TNFalpha was robust in both WT control groups but was absent in chimeric MyD88 mice, despite comparable peripheral inflammatory responses across the three groups. We conclude that LPS reduces food intake via a mechanism dependent on MyD88 signaling within brain and/or other tissues and that in the absence of this effect, robust stimulation of circulating immune cells cannot induce sustained anorexia.

Endogenous CCL2 (monocyte chemotactic protein-1) modulates human immunodeficiency virus type-1 replication and affects cytoskeleton organization in human monocyte-derived macrophages

CC chemokine ligand 2 (CCL2) is constitutively expressed at high levels in human peripheral blood monocytes, and its expression is further up-modulated during their differentiation into macrophages as well as in the course of HIV infection. To investigate the role of endogenous CCL2 on HIV replication and macrophage function, CCL2's activity was neutralized by specific antibodies. Infection of monocyte-derived macrophages with laboratory-adapted HIV-1 or primary viral isolates in the continuous presence of anti-CCL2 antibody resulted in significantly lower p24 Gag antigen release with respect to control cultures. Interestingly, CCL2 neutralization did not affect the early steps of the HIV life cycle but resulted in the intracellular accumulation of p24 Gag antigen. Simultaneously, remarkable changes in cell morphology and size occurred in cell cultures maintained in the presence of anti-CCL2 antibody. These results suggest that CCL2 may represent an autocrine factor important for enhancing virion production likely by affecting the macrophage cytoskeleton.

Site A of the MCP-1 distal regulatory region functions as a transcriptional modulator through the transcription factor NF1

The monocyte chemoattractant protein-1 (MCP-1) functions to recruit monocytes and macrophages to areas of inflammation and is a prototypic chemokine subjected to coordinate regulation by immunomodulatory agents. TNF mediated regulation of MCP-1 occurs through a distal regulatory region located 2.5 kb upstream of the transcriptional start site. Within this region are two NF-kB motifs that are each critical for function. Site A, located within the distal regulatory region and upstream of the kappaB elements is required for maximal induction by TNF. However, unlike the kappaB elements and other MCP-1 regulatory elements, Site A is constitutively occupied by factors in vivo. To better understand the nature of Site A function, this report identified a Site A binding protein and provides a functional analysis of the element in driving transcription. The results showed that the transcription factor NF1/CTF binds to Site A both in vitro and in vivo. While Site A has no transcriptional activity on its own, it was found to augment the transcriptional activity of a GAL4-VP16 reporter system in an orientation and position independent manner. Because NF1 is known to interact with factors that modify nucleosomes, these results suggest a unique role for Site A in regulating MCP-1 expression.

Chemokines: a superfamily of chemotactic cytokines

Chemokines are a bipartite family of chemotactic proteins that bear the structural hallmark of four cysteine residues, the first two of which are in tandem. The spectrum of action of chemokines encompasses a large number of leukocyte populations, including monocytes, granulocytes, lymphocytes, NK and dendritic cells. Although the spectrum of action of chemokines largely overlaps, clear differences are still present. Chemokines play an important role in the recruitment of leukocytes at the site of inflammation, allergic reaction and tumors. Available information on receptor usage by MCP-1 and related chemokines and signal transduction pathways is reviewed. The better understanding of signaling mechanisms will provide a new basis for the development of therapeutic strategies.

TNF regulates the in vivo occupancy of both distal and proximal regulatory regions of the MCP-1/JE gene

In vivo genomic footprinting (IVGF) was used to examine regulatory site occupancy during the activation of the murine inflammatory response gene MCP-1/JE by TNF. In response to TNF, both promoter distal and proximal regulatory regions became occupied in vivo. EMSA analysis showed that while some of the factors involved in expression, including NF-kappa B, were translocated to the nucleus following TNF treatment, others were already present and able to bind DNA in vitro. Protein kinase inhibitor studies showed that protein phosphorylation was required for TNF activation but not factor assembly. These studies provide evidence for a multistep model of TNF-mediated gene regulation involving chromatin accessibility, transcription factor complex assembly, and protein phosphorylation.