Involvement of CXC chemokine growth-related oncogene-alpha in monosodium urate crystal-induced arthritis in rabbits

Vigilant keratinocytes trigger pathogen-associated molecular pattern signaling in response to streptococcal M1 protein

The human skin exerts many functions in order to maintain its barrier integrity and protect the host from invading microorganisms. One such pathogen is Streptococcus pyogenes, which can cause a variety of superficial skin wounds that may eventually progress into invasive deep soft tissue infections. Here we show that keratinocytes recognize soluble M1 protein, a streptococcal virulence factor, as a pathogen-associated molecular pattern to release alarming inflammatory responses. We found that this interaction initiates an inflammatory intracellular signaling cascade involving the activation of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK), p38, and Jun N-terminal protein kinase and the subsequent induction and mobilization of the transcription factors NF-κB and AP-1. We also determined the imprint of the inflammatory mediators released, such as interleukin-8 (IL-8), growth-related oncogene alpha, migration inhibitory factor, extracellular matrix metalloproteinase inducer, IL-1α, IL-1 receptor a, and ST2, in response to streptococcal M1 protein. The expression of IL-8 is dependent on Toll-like receptor 2 activity and subsequent activation of the mitogen-activated protein kinases ERK and p38. Notably, this signaling seems to be distinct for IL-8 release, and it is not shared with the other inflammatory mediators. We conclude that keratinocytes participate in a proinflammatory manner in streptococcal pattern recognition and that expression of the chemoattractant IL-8 by keratinocytes constitutes an important protective mechanism against streptococcal M1 protein.

Anti-inflammatory effects of the activation of the angiotensin-(1-7) receptor, MAS, in experimental models of arthritis

Activation of the renin-angiotensin (Ang) system induces inflammation via interaction between Ang II and type 1 receptor on leukocytes. The relevance of the new arm of the renin-Ang system, namely Ang-converting enzyme-2/Ang-(1-7)/Mas receptor, for inflammatory responses is not known and was investigated in this study. For this purpose, two experimental models were used: Ag-induced arthritis (AIA) in mice and adjuvant-induced arthritis (AdIA) in rats. Male C57BL/6 wild-type or Mas(-/-) mice were subjected to AIA and treated with Ang-(1-7), the Mas agonist AVE 0991, or vehicle. AdIA was performed in female rats that were given AVE 0991 or vehicle. In wild-type mice, Mas protein is expressed in arthritic joints. Administration of AVE 0991 or Ang-(1-7) decreased AIA-induced neutrophil accumulation, hypernociception, and production of TNF-α, IL-1β, and CXCL1. Histopathological analysis showed significant reduction of inflammation. Mechanistically, AVE 0991 reduced leukocyte rolling and adhesion, even when given after Ag challenge. Mas(-/-) mice subjected to AIA developed slightly more pronounced inflammation, as observed by greater neutrophil accumulation and cytokine release. Administration of AVE 0991 was without effect in Mas(-/-) mice subjected to AIA. In rats, administration of AVE 0991 decreased edema, neutrophil accumulation, histopathological score, and production of IL-1β and CXCL1 induced by AdIA. Therefore, activation of Mas receptors decreases neutrophil influx and cytokine production and causes significant amelioration of arthritis in experimental models of arthritis in rats and mice. This approach might represent a novel therapeutic opportunity for arthritis.

The chemokine receptor CXCR2 ligand KC (CXCL1) mediates neutrophil recruitment and is critical for development of experimental Lyme arthritis and carditis

Deletion of the chemokine receptor CXCR2 prevents the recruitment of neutrophils into tissues and subsequent development of experimental Lyme arthritis. Following footpad inoculation of Borrelia burgdorferi, the agent of Lyme disease, expression of the CXCR2 ligand KC (CXCL1) is highly upregulated in the joints of arthritis-susceptible mice and is likely to play an important role in the recruitment of neutrophils to the site of infection. To test this hypothesis, we infected C3H KC(-/-) mice with B. burgdorferi and followed the development of arthritis and carditis. Ankle swelling was significantly attenuated during the peak of arthritis in the KC(-/-) mice. Arthritis severity scores were significantly lower in the KC(-/-) mice on days 11 and 21 postinfection, with fewer neutrophils present in the inflammatory lesions. Cardiac lesions were also significantly decreased in KC(-/-) mice at day 21 postinfection. There were, however, no differences between C3H wild-type and KC(-/-) mice in spirochete clearance from tissues. Two other CXCR2 ligands, LIX (CXCL5) and MIP-2 (CXCL2), were not increased to compensate for the loss of KC, and the production of several innate cytokines was unaltered. These results demonstrate that KC plays a critical nonredundant role in the development of experimental Lyme arthritis and carditis via CXCR2-mediated recruitment of neutrophils into the site of infection.

CXCR2 antagonists for the treatment of pulmonary disease

Chemokines have long been implicated in the initiation and amplification of inflammatory responses by virtue of their role in leukocyte chemotaxis. The expression of one of the receptors for these chemokines, CXCR2, on a variety of cell types and tissues suggests that these receptors may have a broad functional role under both constitutive conditions and in the pathophysiology of a number of acute and chronic diseases. With the development of several pharmacological, immunological and genetic tools to study CXCR2 function, an important role for this CXC chemokine receptor subtype has been identified in chronic obstructive pulmonary disease (COPD), asthma and fibrotic pulmonary disorders. Interference with CXCR2 receptor function has demonstrated different effects in the lungs including inhibition of pulmonary damage induced by neutrophils (PMNs), antigen or irritant-induced goblet cell hyperplasia and angiogenesis/collagen deposition caused by lung injury. Many of these features are common to inflammatory and fibrotic disorders of the lung. Clinical trials evaluating small molecule CXCR2 antagonists in COPD, asthma and cystic fibrosis are currently underway. These studies hold considerable promise for identifying novel and efficacious treatments of pulmonary disorders.

Recent developments in crystal-induced inflammation pathogenesis and management

Crystal-induced inflammation pathogenesis is undergoing a transition with respect to monosodium urate, calcium pyrophosphate dihydrate, and even basic calcium phosphate crystals. It is now recognized that innate immunity could be involved in the earlier pathogenic events and that the inflammasome, along with other signaling pathways, is activated and results in interleukin-1 processing and secretion, ultimately activating cells as a paracrine or autocrine cytokine. Management of acute and chronic monosodium urate crystal-induced inflammation, namely gout, has been critically reviewed by a dedicated European working group, and on the behalf of the European League against Rheumatism, 12 evidence-based recommendations have been reported. Calcium pyrophosphate dihydrate chronic inflammation could benefit from colchicine and from methotrexate as an anti-inflammatory agent.

Innate immunity in triggering and resolution of acute gouty inflammation

Gout has long been recognized as a disease of recurrent bouts of acute inflammation that undergo self-resolution. This inflammation is triggered by the body's response to monosodium urate (MSU) crystals. In this paper, we focus on recent studies that describe how interactions of MSU crystals with the components of the innate immune system trigger acute gouty inflammation as well as mechanisms that are involved in the resolution of this inflammation. Specifically, we describe how toll-like receptors mediate the uptake of MSU crystals involved in the initiation and resolution of gouty inflammation. We also describe recent findings on the role of apoptotic clearance in the resolution of gouty inflammation. In addition, how therapies used to treat gout act on the innate immune system to inhibit MSU crystal-induced inflammation and promote the resolution of inflammation is discussed.

Signaling Events Involved in Macrophage Chemokine Expression in Response to Monosodium Urate Crystals

Chemokine production has been associated with leukocyte infiltration into the joint during gouty arthritis, and monosodium urate (MSU) crystals, the causative agent of this arthropathy, have been shown to modulate their expression. In the present study, we investigated the transductional mechanisms underlying this cellular regulation in the murine macrophage cell line B10R. We report that MSU crystals rapidly and transiently increase mRNA levels of various chemokines in a concentration-dependent manner. Examination of second messenger activation revealed that macrophage exposure to MSU crystals led to MEK1/2, ERK1/2, and inhibitory protein kappaBalpha phosphorylation as well as to NF-kappaB and AP-1 nuclear translocation. Of interest, specific blockage of the ERK1/2 pathway drastically reduced up-modulation of MSU crystal-mediated chemokine production and activation of nuclear factors. Similarly, selective inhibition of NF-kappaB suppressed NF-kappaB DNA binding activity and the induction of all chemokine transcripts. These findings indicate that ERK1/2-dependent signals seem to be required for AP-1 and NF-kappaB activation and subsequent mRNA expression of the various macrophage chemokines. In addition, transcription and stability assays performed in presence of actinomycin D showed that MSU crystal-mediated MIP-1beta mRNA up-regulation resulted solely from transcriptional control, whereas that of MIP-1alpha, MIP-2, and MCP-1 was due to both gene transcription activation and mRNA posttranscriptional stabilization. Overall, the results of this study help to define the molecular events that govern macrophage chemokine regulation in response to MSU crystals, which is of paramount importance to better understand, and eventually to tame, the inflammatory response during acute gout.

Rabbit neutrophil chemotactic protein (NCP) activates both CXCR1 and CXCR2 and is the functional homologue for human CXCL6

Neutrophil chemotactic protein (NCP) is a rabbit CXC chemokine with activating and chemotactic properties on neutrophilic granulocytes. Although its selective activity on neutrophils is demonstrated, its interactions with specific chemokine receptors are not defined. For further functional characterization, NCP was chemically synthesized and was found to be equipotent as natural NCP in neutrophil chemotaxis. To identify its human homologue, we separately expressed two potential rabbit NCP receptors (CXCR1 and CXCR2) in Jurkat cells. Pure synthetic NCP was equally efficient to promote chemotaxis through either rabbit CXCR1 or CXCR2. Moreover, chemotaxis assays on rabbit CXCR1 and CXCR2 transfectants showed that NCP uses the same receptors as interleukin-8 (IL-8), a major rabbit CXC chemokine, but not rabbit GROalpha, which only recognized CXCR2. In addition, specific inhibitors for CXCR1 or CXCR2 reduced rabbit neutrophil chemotaxis induced by NCP and rabbit IL-8. Furthermore, NCP and the structurally related human CXCR1/CXCR2 agonist CXCL6/GCP-2 (granulocyte chemotactic protein-2) cross-desensitized each other in intracellular calcium release assays on human neutrophils, further indicating that both chemokines share the same receptors. The inflammatory role of NCP was also evidenced by its potent granulocytosis inducing capacity in rabbits upon systemic administration. This study provides in vitro and in vivo evidences that NCP is the functional rabbit homologue for human CXCL6/GCP-2 rather than the most related CXCR2 agonist CXCL5/ENA-78 (epithelial cell-derived neutrophil activating peptide-78). It is concluded that the rabbit is a better model to study human neutrophil activation compared to mice, which lack CXCL8/IL-8.

Inhibition of monosodium urate monohydrate crystal-induced acute inflammation by retrovirally transfected prostaglandin D synthase

OBJECTIVE

Hematopoietic prostaglandin D synthase (H-PGDS) is a key enzyme in the production of prostaglandin D and its J series metabolites. We evaluated the antiinflammatory effect of retrovirally transfected H-PGDS in order to investigate the role of H-PGDS in monosodium urate monohydrate (MSU) crystal-induced acute inflammation.

METHODS

Expression of endogenous PGDS in a murine air-pouch model of MSU crystal-induced acute inflammation was determined by real-time polymerase chain reaction. H-PGDS complementary DNA (cDNA) was retrovirally transfected into C57BL/6J fibroblasts, and the cells were designated as C57-PGDS cells. Production of prostaglandins by C57-PGDS cells was measured by enzyme immunoassay. The effect of C57-PGDS cells on crystal-induced inflammation was investigated.

RESULTS

Injection of the crystals caused a rapid decrease in H-PGDS expression by infiltrating cells and by the soft tissues around the air pouches. In contrast, expression of interleukin-1beta (IL-1beta) and macrophage inflammatory protein 2 (MIP-2) as well as cellular infiltration were significantly increased during the early stage of inflammation. C57-PGDS cells, but not control cells, produced an increased amount of PGD(2) in vitro, but suppressed production of PGE(2). Injection of C57-PGDS cells into air pouches inhibited cellular infiltration and MIP-2 and IL-1beta expression.

CONCLUSION

In this murine air-pouch model of MSU crystal-induced inflammation, retrovirally transfected H-PGDS cDNA could reduce cellular infiltration, at least partly by inhibiting MIP-2 and IL-1beta. These findings suggest that gene therapy with H-PGDS may be useful for treating inflammatory diseases.