title: Phospholipase D enzymes facilitate IL-17- and TNFα-induced expression of proinflammatory genes in rheumatoid arthritis synovial fibroblasts (RASF).
abstract: In rheumatoid arthritis, the synovium exhibits fibroblast hyperplasia and dynamic infiltration of activated T cells. Interaction between rheumatoid arthritis synovial fibroblasts (RASF) and T cell subsets such as Th17 cells can stimulate RASF to express IL-6, IL-8, CCL20, and other proinflammatory mediators of joint destruction. PLD enzymes specifically cleave phosphatidyl choline (PC) producing phosphatidic acid (PA) and choline. Agonist-induced PLD activation results in PA synthesis, which is thought to be involved in a variety of rapid cellular responses such as cytokine secretion. Furthermore, the cellular response to TNF-mediated signaling in myeloid cells is in part mediated by PLD1. However, very few studies have examined the role of PLD enzymes in pro-inflammatory responses of RASF to key pathogenic cytokines such as TNF and IL-17. Microarray analysis of RASF showed that phospholipase D1 (PLD1) is among genes significantly induced by IL-17. We therefore hypothesized that PLD1 might have a role in RASF responses to proinflammatory cytokines. We used 1-butanol, PLD1-specific siRNAs, and small molecule inhibitors specific for PLD1 or PLD2, to investigate the possible role of PLD enzymes in basal, IL-17-, and/or TNFα-evoked expression of proinflammatory cytokines and chemokines by RASF. We studied the in vitro responses of RASF to IL-17A and/or TNFα, with particular attention to effects on IL-6, IL-8 and CCL20 mRNA and secretion as determined by RT-QPCR and ELISA, respectively. Transcriptional and prominent post-transcriptional effects were demonstrated, with robust decreases in RASF secretion of IL-6, IL-8, and CCL20 when both PLD isoforms were inhibited together. Moreover, RA synovial biopsy explants cultured in media containing PLD isoform-specific inhibitors showed significantly reduced constitutive secretion of IL-6 and IL-8. PLD enzymes could be promising targets for controlling proinflammatory gene expression in the treatment of RA in view of roles for PLD in cytokine-evoked transcription and secretion/exocytosis.
authors.affiliation: The University of Michigan, Ann Arbor, USA. Electronic address: fridays@umich.edu.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Friday
authors.affiliation: The University of Michigan, Ann Arbor, USA. Electronic address: dfox@med.umich.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Fox
mesh_terms: D020001:1-Butanol / Q000494:pharmacology; D001172:Arthritis, Rheumatoid / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D001706:Biopsy; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D020381:Interleukin-17 / Q000235:genetics* / Q000378:metabolism; D007527:Isoenzymes; D010739:Phospholipase D / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics* / Q000378:metabolism
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; D020381:Interleukin-17; D007527:Isoenzymes; D014409:Tumor Necrosis Factor-alpha; D020001:1-Butanol; D010739:Phospholipase D
keywords: CAY10593; Fibroblast-like synoviocytes; IL-17; PLD; Rheumatoid arthritis; TNF alpha