IL-23p19 in osteoarthritic pain and disease.

OBJECTIVE: We have previously reported that the interleukin-23 p19 subunit (IL-23p19) is required for experimental inflammatory arthritic pain-like behaviour and disease. Even though inflammation is often a characteristic feature of osteoarthritis (OA), IL-23 is not usually considered as a therapeutic target in OA. We began to explore the role of IL-23p19 in OA pain and disease utilizing mouse models of OA and patient samples. DESIGN: The role of IL-23p19 in two mouse models of OA, namely collagenase-induced OA and monosodium iodoacetate-induced OA, was investigated using gene-deficient male mice. Pain-like behaviour and arthritis were assessed by relative static weight distribution and histology, respectively. In knee synovial tissues from a small cohort of human OA patients, a correlation analysis was performed between IL-23A gene expression and Oxford knee score (OKS), a validated Patient Reported Outcome Measure. RESULTS: We present evidence that i) IL-23p19 is required for the development of pain-like behaviour and optimal disease, including cartilage damage and osteophyte formation, in two experimental OA models and ii) IL-23A gene expression in OA knee synovial tissues correlates with a lower OKS (r=-0.742, p=0.0057). CONCLUSIONS: The findings support the possible targeting of IL-23 as a treatment for OA pain and disease progression.

IL-23 regulation of myeloid cell biology during inflammation.

Interleukin (IL)-23 is implicated in the pathogenesis of several inflammatory diseases and is usually linked with helper T cell (Th17) biology. However, there is some data linking IL-23 with innate immune biology in such diseases. We therefore examined the effects of IL-23p19 genetic deletion and/or neutralization on in vitro macrophage activation and in an innate immune-driven peritonitis model. We report that endogenous IL-23 was required for maximal macrophage activation by zymosan as determined by pro-inflammatory cytokine production, including a dramatic upregulation of granulocyte-colony stimulating factor (G-CSF). Furthermore, both IL-23p19 genetic deletion and neutralization in zymosan-induced peritonitis (ZIP) led to a specific reduction in the neutrophil numbers, as well as a reduction in the G-CSF levels in exudate fluids. We conclude that endogenous IL-23 can contribute significantly to macrophage activation during an inflammatory response, mostly likely via an autocrine/paracrine mechanism; of note, endogenous IL-23 can directly up-regulate macrophage G-CSF expression, which in turn is likely to contribute to the regulation of IL-23-dependent neutrophil number and function during an inflammatory response, with potential significance for IL-23 targeting particularly in neutrophil-associated inflammatory diseases.

Epigenetic and transcriptional regulation of CCL17 production by glucocorticoids in arthritis.

Glucocorticoids (GCs) are potent anti-inflammatory agents and are broadly used in treating rheumatoid arthritis (RA) patients, albeit with adverse side effects associated with long-term usage. The negative consequences of GC therapy provide an impetus for research into gaining insights into the molecular mechanisms of GC action. We have previously reported that granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced CCL17 has a non-redundant role in inflammatory arthritis. Here, we provide molecular evidence that GCs can suppress GM-CSF-mediated upregulation of IRF4 and CCL17 expression via downregulating JMJD3 expression and activity. In mouse models of inflammatory arthritis, GC treatment inhibited CCL17 expression and ameliorated arthritic pain-like behavior and disease. Significantly, GC treatment of RA patient peripheral blood mononuclear cells ex vivo resulted in decreased CCL17 production. This delineated pathway potentially provides new therapeutic options for the treatment of many inflammatory conditions, where GCs are used as an anti-inflammatory drug but without the associated adverse side effects.

The GM-CSF/CCL17 pathway in obesity-associated osteoarthritic pain and disease in mice.

OBJECTIVES: We have previously identified a granulocyte macrophage-colony stimulating factor (GM-CSF)/C-C motif ligand 17 (CCL17) pathway in monocytes/macrophages, in which GM-CSF regulates the formation of CCL17, and it is important for an experimental osteoarthritis (OA) model. We explore here additional OA models, including in the presence of obesity, such as a requirement for this pathway. DESIGN: The roles of GM-CSF, CCL17, CCR4, and CCL22 in various experimental OA models, including those incorporating obesity (eight-week high-fat diet), were investigated using gene-deficient male mice. Pain-like behavior and arthritis were assessed by relative static weight distribution and histology, respectively. Cell populations (flow cytometry) and cytokine messenger RNA (mRNA) expression (qPCR) in knee infrapatellar fat pad were analyzed. Human OA sera were collected for circulating CCL17 levels (ELISA) and OA knee synovial tissue for gene expression (qPCR). RESULTS: We present evidence that: i) GM-CSF, CCL17, and CCR4, but not CCL22, are required for the development of pain-like behavior and optimal disease in three experimental OA models, as well as for exacerbated OA development due to obesity, ii) obesity alone leads to spontaneous knee joint damage in a GM-CSF- and CCL17-dependent manner, and iii) in knee OA patients, early indications are that BMI correlates with a lower Oxford Knee Score (r = -0.458 and p = 0.0096), with elevated circulating CCL17 levels (r = 0.2108 and p = 0.0153) and with elevated GM-CSF and CCL17 gene expression in OA synovial tissue. CONCLUSIONS: The above findings indicate that GM-CSF, CCL17, and CCR4 are involved in obesity-associated OA development, broadening their potential as targets for possible treatments for OA.

CCL17/TARC in autoimmunity and inflammation-not just a T-cell chemokine.

Chemokine (C-C) ligand 17 (CCL17) was first identified as thymus- and activation-regulated chemokine when it was found to be constitutively expressed in the thymus and identified as a T-cell chemokine. This chemoattractant molecule has subsequently been found at elevated levels in a range of autoimmune and inflammatory diseases, as well as in cancer. CCL17 is a C-C chemokine receptor type 4 (CCR4) ligand, with chemokine (C-C) ligand 22 being the other major ligand and, as CCR4 is highly expressed on helper T cells, CCL17 can play a role in T-cell-driven diseases, usually considered to be via its chemotactic activity on T helper 2 cells; however, given that CCR4 is also expressed by other cell types and there is elevated expression of CCL17 in many diseases, a broader CCL17 biology is suggested. In this review, we summarize the biology of CCL17, its regulation and its potential contribution to the pathogenesis of various preclinical models. Reference is made, for example, to recent literature indicating a role for CCL17 in the control of pain as part of a granulocyte macrophage-colony-stimulating factor/CCL17 pathway in lymphocyte-independent models and thus not as a T-cell chemokine. The review also discusses the potential for CCL17 to be a biomarker and a therapeutic target in human disorders.

Type I interferon antagonism of the JMJD3-IRF4 pathway modulates macrophage activation and polarization.

Metabolic adaptations can directly influence the scope and scale of macrophage activation and polarization. Here we explore the impact of type I interferon (IFNß) on macrophage metabolism and its broader impact on cytokine signaling pathways. We find that IFNß simultaneously increased the expression of immune-responsive gene 1 and itaconate production while inhibiting isocitrate dehydrogenase activity and restricting α-ketoglutarate accumulation. IFNß also increased the flux of glutamine-derived carbon into the tricarboxylic acid cycle to boost succinate levels. Combined, we identify that IFNß controls the cellular α-ketoglutarate/succinate ratio. We show that by lowering the α-ketoglutarate/succinate ratio, IFNß potently blocks the JMJD3-IRF4-dependent pathway in GM-CSF and IL-4 activated macrophages. The suppressive effects of IFNß on JMJD3-IRF4-dependent responses, including M2 polarization and GM-CSF-induced inflammatory pain, were reversed by supplementation with α-ketoglutarate. These results reveal that IFNß modulates macrophage activation and polarization through control of the cellular α-ketoglutarate/succinate ratio.

Epigenetic and transcriptional regulation of IL4-induced CCL17 production in human monocytes and murine macrophages.

Interleukin 4 (IL4) is generally viewed as a Th2 cytokine capable of polarizing macrophages into an anti-inflammatory phenotype, whereas granulocyte macrophage-colony-stimulating factor (GM-CSF) is often viewed as a proinflammatory cytokine with part of this function due to its action on monocytes/macrophages. Paradoxically, these two cytokines act additively to enhance the in vitro differentiation of dendritic cells from precursors such as monocytes. One up-regulated marker of an IL4-polarized M2 macrophage is the chemokine (C-C motif) ligand 17 (CCL17), which we have recently reported to be induced by GM-CSF in monocytes/macrophages in an interferon regulatory factor 4 (IRF4)-dependent manner. In this study, we report that IL4 also induces CCL17 production by acting through IRF4 in human monocytes and murine macrophages. Furthermore, evidence is presented that IL4 up-regulates IRF4 expression at the epigenetic level by enhancing the expression and activity of jumonji domain-containing protein 3 (JMJD3) demethylase. Intriguingly, silencing the signal transducer and activator of transcription 6 (STAT6) gene led to a decrease in not only CCL17 formation, but also in that of its upstream regulators, JMJD3 and IRF4. Moreover, IL4 treatment of human monocytes resulted in an increased association of STAT6 to the promoter regions of the CCL17, IRF4, and JMJD3 genes. Thus, despite their vastly different functions, IL4 and GM-CSF appear to share elements of a common signaling pathway in regulating CCL17 production in human monocytes and murine macrophages.