AB0176 MITOGEN- AND STRESS-ACTIVATED PROTEIN KINASE-1 (MSK1) AS THE LINK BETWEEN MIR-130A-DYSREGULATION AND CDC2-ACTIVATION IN SJöGREN’S SYNDROME
Authors: Ana P. Lopes, Joel van Roon, Sofie Blokland, Maojie Wang, Eleni Chouri, Aike A. Kruize, Boudewijn Burgering, Marzia Rossato, Timothy R. Radstake, Maarten Hillen
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by lymphocytic infiltration of the exocrine glands and dryness of mouth and eyes. T and B lymphocytes that infiltrate the salivary glands play a central role in local production of autoantibodies and cytokines, associated with dryness and tissue-damage. Type-2 conventional dendritic cells (cDC2) are very potent antigen-presenting cells and have the ability to produce a variety of cytokines involved in T and B cell activation, germinal centres formation and autoantibody production. <h3>Objectives:</h3> Considering the critical role of microRNAs (miRNAs) in regulation of cell activation, we investigated their potential dysregulation in circulating cDC2s of patients with pSS compared to healthy controls (HC). <h3>Methods:</h3> CD1c-expressing cDC2s were isolated from peripheral blood of pSS patients and controls from two independent cohorts. In the donors from the discovery cohort (15 pSS, 6 HC) the expression of 758 miRNAs was screened; the replication cohort (14 pSS, 11 HC) was used to confirm consistent differential expression of 18 identified miRNAs. A quantitative mass spectrometry-based technique (pSILAC) in HEK-293T cells was used to identify novel targets of the replicated miRNAs. Target-miRNA interaction was replicated in primary cDC2s. Differences in cytokine production between pSS and HC cDC2s were evaluated by FACS. cDC2s were cultured in the presence of different MSK1-inhibitors to examine their effect on cytokine production. <h3>Results:</h3> The expression of miR-130a and miR-708 was consistently decreased in cDC2s from pSS patients compared to HC in both cohorts, and both miRNAs were downregulated upon stimulation via TLR3 and TLR7/8. MSK1 was identified as a novel target of miR-130a and overexpression of miR-130a reduced MSK1 protein expression in both HEK-293T cells and primary cDC2s. In-line with the regulation of MSK1 by miR-130a, MSK1 expression was higher in cDC2s of pSS patients as compared to controls. An increased frequency of cDC2s producing-IL-12 and TNF-α was observed in pSS patients compared to HC, consistent with the central role of MSK1 in regulation of cytokine production. Exposure to either of two different MSK1 inhibitors in vitro reduced cDC2 activation and the production of IL-12, TNF-α and IL-6. <h3>Conclusion:</h3> We here provide the first evidence of molecular dysregulation of cDC2s in pSS, including decreased expression of miR-708 and miR-130a, which can result from TLR activation, and enhanced production of pro-inflammatory cytokines. In view of its central role in NF-κB signalling, inhibition of MSK1 to decrease cell activation and inhibit pro-inflammatory cytokine production represents a novel therapeutic avenue for treatment of Sjögren's Syndrome. <h3>Disclosure of Interests:</h3> None declared