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Tristetraprolin (TTP), a negative regulator of many pro-inflammatory genes, is strongly expressed in rheumatoid synovial cells. The mitogen-activated protein kinase (MAPK) p38 pathway mediates the inactivation of TTP via phosphorylation of two serine residues. We wished to test the hypothesis that these phosphorylations contribute to the development of inflammatory arthritis, and that, conversely, joint inflammation may be inhibited by promoting the dephosphorylation and activation of TTP.The expression of TTP and its relationship with MAPK p38 activity were examined in non-inflamed and rheumatoid arthritis (RA) synovial tissue. Experimental arthritis was induced in a genetically modified mouse strain, in which endogenous TTP cannot be phosphorylated and inactivated. In vitro and in vivo experiments were performed to test anti-inflammatory effects of compounds that activate the protein phosphatase 2A (PP2A) and promote dephosphorylation of TTP.TTP expression was significantly higher in RA than non-inflamed synovium, detected in macrophages, vascular endothelial cells and some fibroblasts and co-localised with MAPK p38 activation. Substitution of TTP phosphorylation sites conferred dramatic protection against inflammatory arthritis in mice. Two distinct PP2A agonists also reduced inflammation and prevented bone erosion. In vitro anti-inflammatory effects of PP2A agonism were mediated by TTP activation.The phosphorylation state of TTP is a critical determinant of inflammatory responses, and a tractable target for novel anti-inflammatory treatments.

Original publication

DOI

10.1136/annrheumdis-2016-209424

Type

Journal article

Journal

Annals of the rheumatic diseases

Publication Date

03/2017

Volume

76

Pages

612 - 619

Addresses

Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK.

Keywords

Synovial Membrane, Fibroblasts, Macrophages, Endothelial Cells, Animals, Mice, Inbred C57BL, Humans, Mice, Arthritis, Rheumatoid, Disease Models, Animal, Amino Alcohols, p38 Mitogen-Activated Protein Kinases, Serine, Apolipoproteins E, RNA, Messenger, Cytokines, MAP Kinase Signaling System, Enzyme Activation, Phosphorylation, Tristetraprolin, Protein Phosphatase 2, Molecular Targeted Therapy