Metformin is widely used to suppress certain functions of the cells found in diseases including diabetes and obesity. In this study, the effects of metformin on downregulating IL-17-producing T (Th17) cells, activating and upregulating regulatory T (Treg) cells, suppressing osteoclastogenesis, and clinically scoring collagen-induced arthritis (CIA) were investigated. To evaluate the effect of metformin on CIA, mice were orally fed with either metformin or saline as control three times a week for nine weeks. Histological analysis of the joints was performed using immunohistochemistry and Th17 cells and Treg cells of the spleen tissue were examined by confocal microscopy staining. Metformin mitigated the severity of CIA, reduced serum immunoglobulin concentrations, and reciprocally regulated Th17/Treg axis. Also, metformin treatment of normal cells cultured in Th17 conditions decreased the number of Th17 cells and increased the number of Treg cells. Metformin decreased gene expression and osteoclastogenic activity in CIA and normal mice. These results indicate that metformin had immunomodulatory actions influencing anti-inflammatory action on CIA through the inhibition of Th17 cell differentiation and the upregulation of Treg cell differentiation along with the suppression of osteoclast differentiation. Our results suggest that metformin may be a potential therapeutic for rheumatoid arthritis.

Circulating autoantibodies and immune complex deposition are pathological hallmarks of systemic lupus erythematosus (SLE). B cell differentiation into plasma cells (PCs) and some T cell subsets that function as B cell helpers can be therapeutic targets of SLE. Mechanistic target of rapamycin (mTOR) signaling is implicated in the formation of B cells and germinal centers (GCs). We assessed the effect of metformin, which inhibits mTOR, on the development of autoimmunity using Roquinsan/san mice. Oral administration of metformin inhibited the formation of splenic follicles and inflammation in kidney and liver tissues. It also decreased serum levels of anti-dsDNA Abs without affecting serum glucose levels. Moreover, metformin inhibited CD21highCD23low marginal zone B cells, B220+GL7+ GC B cells, B220−CD138+ PCs, and GC formation. A significant reduction in ICOS+ follicular helper T cells was found in the spleens of the metformin-treated group compared with the vehicle-treated group. In addition, metformin inhibited Th17 cells and induced regulatory T cells. These alterations in B and T cell subsets by metformin were associated with enhanced AMPK expression and inhibition of mTOR–STAT3 signaling. Furthermore, metformin induced p53 and NF erythroid-2–related factor-2 activity in splenic CD4+ T cells. Taken together, metformin-induced alterations in AMPK–mTOR–STAT3 signaling may have therapeutic value in SLE by inhibiting B cell differentiation into PCs and GCs.

IntroductionFibroblast-like synoviocytes (FLSs) are a major cell population of the pannus that invades adjacent cartilage and bone in rheumatoid arthritis (RA). The study was undertaken to determine the effect of interleukin-17 (IL-17) on the survival and/or proliferation of FLSs from RA patients and to investigate whether signal tranducer and activator of transcription 3 (STAT3) is implicated in this process.MethodsBcl-2 and Bax expression in FLSs was determined using the real-time PCR and western blot analysis. The expression of Bcl-2 and phosphoSTAT3 in synovial tissues was investigated by confocal microscope. Apoptosis of FLSs was detected by Annexin V/propidium iodide staining and/or phase contrast microscopy. The proliferation of FLSs was determined by CCK-8 ELISA assay.ResultsThe pro-apoptotic Bax is decreased and anti-apoptotic Bcl-2 is increased in FLSs from RA patients compared with those from patients with osteoarthritis (OA). IL-17 upregulated the expression of Bcl-2 in FLSs from RA patients, but not in FLSs from OA patients. STAT3 was found to mediate IL-17-induced Bcl-2 upregulation in FLSs from RA patients. Additionally, IL-17 promoted the survival and proliferation of FLSs from RA patients. Most importantly, treatment with STAT3 inhibitor reversed the protective effect of IL-17 on FLSs apoptosis induced by sodium nitroprusside (SNP).ConclusionsOur data demonstrate that STAT3 is critical in IL-17-induced survival of FLS from RA patients. Therefore, therapeutic strategies that target the IL-17/STAT3 pathway might be strong candidates for RA treatment modalities.

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The green tea polyphenol epigallocatechin-3-gallate is a potent antioxidant. Here, we describe the effects of epigallocatechin-3-gallate on T cell differentiation and osteoclast differentiation in an animal model of arthritis. Mice with collagen-induced arthritis were injected intraperitoneally with epigallocatechin-3-gallate, 3 times/wk after the primary immunization. Surface markers of T helper 17 cells and regulatory T cells were analyzed by flow cytometry. Flow cytometry, Western blotting, and enzyme-linked immunosorbent assays were used to evaluate the effect of epigallocatechin-3-gallate on cell signaling in the collagen-induced arthritis model. Epigallocatechin-3-gallate decreased the arthritis index and showed protective effects against joint destruction in collagen-induced arthritis mice. The expression of cytokines, oxidative stress proteins, and phosphorylated-signal transducer and activator of transcription-3, 705 and 727, were significantly less in mice treated with epigallocatechin-3-gallate than it was in controls. Epigallocatechin-3-gallate reduced the expression of osteoclast markers in vitro and in vivo relative to the control, and the antiosteoclastic activity was observed in epigallocatechin-3-gallate-treated, interferon-γ knockout mice. The proportion of forkhead box protein 3-positive regulatory T cells was increased in the spleens of mice treated with epigallocatechin-3-gallate compared with control mice, whereas the proportion of T helper 17 cells was reduced. In vitro, the expression of nuclear respiratory factor 2, heme oxygenase-1, and extracellular signal-regulated kinase was increased significantly by epigallocatechin-3-gallate. We demonstrated that the administration of epigallocatechin-3-gallate attenuated the symptoms of arthritis, inhibited osteoclastogenesis and T helper 17 cell activation, and increased the number of regulatory T cells. At the molecular level, the antiarthritic effects of epigallocatechin-3-gallate may be due to induction of phosphorylated-extracellular signal-regulated kinase, nuclear respiratory factor 2, and heme oxygenase-1 and inhibition of signal transducer and activator of transcription-3 activation.