N-3 polyunsaturated fatty acids restore Th17 and Treg balance in collagen antibody-induced arthritis

March N-3 polyunsaturated fatty acids restore Th17 and Treg balance in collagen antibody- induced arthritis Ji Young Kim 0 1 Kyu Lim 1 Kyung Hee Kim 1 Jin Hyun Kim 0 1 Jin Sun Choi 0 1 Seung- Cheol Shim 0 1 0 Division of Rheumatology, Daejeon Rheumatoid & Degenerative Arthritis Center, Chungnam National University Hospital , Daejeon , Republic of Korea, 2 Department of Biochemistry and Cancer Research Institute, College of Medicine, Chungnam National University , Daejeon , Republic of Korea, 3 Department of Pathology, Cancer Research Institute, College of Medicine, Chungnam National University , Daejeon , Republic of Korea 1 Editor: Hossam M. Ashour, University of South Florida St Petersburg , UNITED STATES - Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: Ji Young Kim was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (MEST) under Grant number: NRF2013R1A1A2057950 (http://www.nrf.re.kr/nrf_tot_ cms/index.jsp). The funder had no role in study N-3 polyunsaturated fatty acids (PUFA) have anti-inflammatory effects and were considered useful for the treatment of rheumatoid arthritis (RA). Recently, several studies suggested that n-3 PUFAs attenuated arthritis in animal model and human, however the mechanism is still unclear. Interleukin 17 (IL-17) is a pro-inflammatory cytokine mainly produced by T helper 17 (Th17) cells which cause tissue inflammation and bone erosion leading to joint destruction. In contrast, regulatory T (Treg) cells down-regulate various immune responses by suppression of naïve T cells. The imbalance between Th17 cells and Tregs cell is important for the pathogenesis of RA. Here, we investigated whether n-3 PUFAs attenuate arthritis in collagen antibody-induced arthritis (CAIA) model. We used fat-1 transgenic mice expressing the Caenorhabditis elegans fat-1 gene encoding an n-3 fatty acid desaturase that converts n-6 to n-3 fatty acids, leading to abundant n-3 fatty acids without the need of a dietary n-3 supply. Clinical arthritis score was significantly attenuated in fat-1 mice compared to wild type (WT) mice on day 7 (1.6±1.8, p = 0.012) and day 9 (1.5±1.6, p = 0.003). Ankle thickness also decreased significantly in fat-1 mice compared to WT mice (1.82±0.11, p = 0.008). The pathologic finding showed that inflammatory cell infiltration and bone destruction were reduced in fat-1 mice compared to WT. The expression levels of IL-17 and related cytokines including IL-6 and IL-23 decreased in the spleen and ankle joint tissue of fat-1 mice compared to WT mice. Furthermore, Treg cells were expanded in the spleen of fat-1 mice and Treg cell differentiation was significantly higher in fat-1 mice than in wild type (p = 0.038). These data suggest that n-3 PUFAs could attenuate arthritis through increasing the expression of FoxP3 and the differentiation of Treg, while reducing IL-17 production. Therefore, dietary supplementation of n-3 PUFAs could have a therapeutic potential for the treatment of RA. design, data collection and analysis, decision to publish, or preparation of the manuscript. Introduction Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of a joint synovium, leading to progressive bone and cartilage destruction [ 1 ]. Recently, T helper 17 (Th17) cells have been suggested to play key roles in RA induction and maintenance. Th17 cells are pro-inflammatory cells, which produce interleukin 17 (IL-17) and differentiation is dependent on IL-6, IL-23 and TGF-β [ 2,3 ]. IL-17 is raised in synovial fluids of RA patients and in inflamed joints of experimental induced arthritis models. IL-17 induces inflammatory cell infiltration into the synovium and tissue inflammation, leading into bone resorption and erosion [4]. In contrast CD4+CD25+Foxp3+ regulatory T cell (Treg) regulates the immune response to keep peripheral self-tolerance [ 5 ]. Th17 and Treg cells antagonize each other's function, the imbalance between Th17 and Treg cells may be important in the development of RA. N-3 polyunsaturated fatty acid (n-3 PUFA) has shown anti-inflammatory effect through immune cell inhibition [6±8]. N-3 PUFAs are primarily obtained from the diet, only low conversion of α-linolenic acid (ALA) to eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA) [ 9 ]. Recently, experimental animal studies reported that n-3 PUFAs suppress inflammatory cytokine synthesis [ 10 ]. In addition, n-3 PUFAs reduced the number and differentiation of pro-inflammatory Th17 cells [7±8, 11] and increased number of Treg cells in vivo [ 12 ]. A fat-1 transgenic mouse expresses the Caenorhabditis elegans fat-1 gene encoding an n-3 fatty acid desaturase that converts n-6 to n-3 fatty acids (which is absent in mammals), leading to abundant n-3 fatty acids with reduced levels of n-6 fatty acid (...truncated)