Background Systemic juvenile idiopathic arthritis (SJIA) is an autoinflammatory disease of childhood, characterized by a predominance of mononuclear phagocytic effector cells, compared to the lymphocyte driven pathogenesis seen in other autoimmune JIA subtypes. Monocytes respond to their local cytokine milieu by adopting specific polarization phenotypes with distinct functions. These phenotypes include M1 (classical) activation as well as several forms of alternative activation, including M2b and M2c which have potent immunoregulatory properties. Previous data has shown that monocytes in SJIA patients have a novel phenotype, with features of both classical activation and immunoregulatory phenotypes. Controlling factors of monocyte/macrophage differentiation in SJIA are unknown. MicroRNA serve as transcriptional negative regulators which fine-tune gene expression programs, and have been implicated in the differentiation of monocytes/macrophages. However, miRNA expression in SJIA has not been examined.
Methods CD14+ monocytes were isolated from children with active SJIA and clinically inactive disease (CID), and quantified miRNA expression using TaqMan MicroRNA Array (Life technologies). Freshly isolated human monocytes or THP1 macrophage-like cells were polarized in vitro using LPS and interferon-γ (M1), IL-4 (M2a), LPS plus immune complexes (M2b), and IL-10 or TGF-β (M2c). For experiments modulating expression of mir125a-5p, THP1 cells were treated with either mir125a-5p-specific or negative control antagomir (RiboBio) or transfected with miR125a-5p or negative control mimic (Dharmacon) prior to polarization with the indicated conditions. Gene expression was determined using real-time PCR or TaqMan assays.
Results We identified mir125a-5p as the most highly upregulated microRNA in monocytes from children with active SJIA compared to those with CID (relative expression 16.8 vs. 3.0, p<0.05). In addition, expression of mir-125a-5p significantly correlated with markers of disease activity, including ferritin (R=0.73, p<0.001) and the presence of systemic features such as rash and hepatomegaly. Expression of mir125a-5p was significantly increased in both primary human monocytes and THP1 macrophage-like cells after polarization with M2b or M2c conditions, but was not altered by M1 polarization. Interestingly, we found that mir125a-5p was dispensable for M1 polarization, as treatment with a specific microRNA antagomir did not alter expression of MIG, I-TAC, TNF-α or IL-6. However, mir125a-5p was essential for M2b polarization, as antagomir treatment significantly reduced expression of the M2b-specific chemokine CCL1 by 56%. Conversely, transfection of a mir125a-5p mimic into THP1 cells resulted in enhanced M2b polarization with increased expression of CCL1, IL-6, as well as of the M2c marker CD163. Transfection of mir125a-5p mimic also altered M1 polarization by increasing production of CCL1.
Conclusions Our data demonstrated increased levels of mir125a-5p in active SJIA and correlation with disease activity. We also showed that mir125a-5p serves as a key regulator of the polarization of immunomodulatory macrophages. Taken together, these data suggest that mir125a-5p could serve as an important diagnostic and therapeutic target in SJIA.
Disclosure of Interest G. Schulert: None declared, N. Fall: None declared, N. Shen: None declared, S. Thornton: None declared, A. Grom Grant/research support from: Novartis, NovImmune, Consultant for: Novartis, Roche