THU0243 ROLE OF METHIONINE AND ITS TRANSPORTER CD98 IN HUMAN B CELL DIFFERENTIATION AND THE RELEVANCE TO PATHOLOGICAL PROCESSES OF SLE
Authors: Mingzeng Zhang, Shigeru Iwata, Maiko Hajime, Naoaki Ohkubo, Yasuyuki Todoroki, Hiroko Miyata, Shingo Nakayamada, Yamagata Kaoru, Yoshiya Tanaka
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> B cells play an important role in systemic lupus erythematosus (SLE). Several research protocols have focused in recent years on the topic of immunometabolism. Activation of immunocompetent cells depends on rapid synthesis of cell structure components and biomolecules, which requires enormous amounts of energy, nucleic acids and lipids. Amino acids are important ingredients of many metabolic processes. However, the role of amino acids in plasmablast differentiation and their relevance to the pathogenesis of SLE remain elusive. <h3>Objectives:</h3> To determine the role of essential amino acids in human B cell differentiation and relevance to the pathogenesis of SLE. <h3>Methods:</h3> In the <i>in vitro</i> arm of the study, purified CD19<sup>+</sup> B cells from healthy donors were cultured with TLR7/9 ligand (LOX or CpG), IFN-α and B cell receptor (BCR) cross-linking, in the presence or absence of amino acids. We determined 1) the types of amino acids that are important for PB differentiation, 2) the amino acid transporters that are important for PB differentiation, 3) the main signaling pathway(s) involved in the presence of amino acids, 4) the transcriptional factors used in the presence of amino acids. In the clinical arm of the study, peripheral blood mononuclear cells (PBMCs) were obtained from 24 patients with RA, 35 patients with SLE, and 28 age-matched healthy controls, and subjected to flow cytometric analysis to determine the expression of amino acids-related markers. <h3>Results:</h3> 1) Stimulation with the combination of BCR, IFN-α and TLR7/9 ligand induced PB differentiation accompanied by uptake of amino acids. PB differentiation was abrogated in the absence of essential amino acid methionine, and to a lesser extent leucine, but not in non-essential amino acid cystine. 2) LAT1 and CD98 are known amino acid transporters. Stimulation with BCR, IFN-α and TLR7/9 ligand induced CD98 expression but suppressed LAT1 expression. CD98 expression was higher in CD27<sup>hi</sup>CD38<sup>hi</sup> PB than in CD27<sup>-</sup>CD38<sup>-</sup> non-PB. 3) Previous studies reported that amino acids were perceived by the sensor, leading to mTORC1 phosphorylation. However, the mechanism by which amino acids activate other intracellular signaling pathways in B cells remains elusive. We found that methionine facilitated both the BCR and mTORC1 signals. In addition, the two signals synergistically induced EZH2 expression, which is well known as a transcriptional factor for histone modification via induction of H3K27me3, in the presence of methionine. 4) Methionine induced EZH2 expression, leading to suppression of BACH2, induction of BLIMP1, XBP1 and PB differentiation. These results indicate that EZH2 is a critical factor for PB differentiation in the presence of methionine. Assessment of the expression of amino acid transporters CD98, LAT1 and EZH2 in B cells in RA and SLE patients showed overexpression of CD98 and EZH2, but not LAT1, in SLE, compared with RA and control. In SLE patients, EZH2 expression level correlated with that of CD98 in B cells. EZH2 expression also correlated with ESR and disease activity scores, such as of SLEDAI and BILAG, in SLE patients. <h3>Conclusion:</h3> The results indicate that essential amino acid methionine plays an important role in PB differentiation through the CD98-EZH2-axis. The pathological process of SLE seems to involve essential amino acids and their metabolic/activation pathways throughout the process of PB differentiation. <h3>Disclosure of Interests:</h3> Mingzeng Zhang: None declared, Shigeru Iwata: None declared, Maiko Hajime: None declared, Naoaki Ohkubo: None declared, Yasuyuki Todoroki: None declared, Hiroko Miyata: None declared, Shingo Nakayamada Grant/research support from: Mitsubishi-Tanabe, Takeda, Novartis and MSD, Speakers bureau: Bristol-Myers, Sanofi, Abbvie, Eisai, Eli Lilly, Chugai, Asahi-kasei and Pfizer, Yamagata Kaoru: None declared, Yoshiya Tanaka Grant/research support from: Abbvie, Astellas, Bristol-Myers Squibb, Chugai, Daiichi-Sankyo, Eisai, Mitsubishi-Tanabe, MSD, Ono, Taisho-Toyama, Takeda, Speakers bureau: Abbvie, Asahi-kasei, Astellas, Bristol-Myers Squibb, Chugai, Daiichi-Sankyo, Eli Lilly, Eisai, Glaxo-Smithkline, Janssen, Mitsubishi-Tanabe, Novartis, Pfizer Japan Inc, Sanofi, Takeda, UCB, YL Biologics