14-3-3η is a novel mediator associated with the pathogenesis of rheumatoid arthritis and joint damage

Abstract

Introduction: The aim of this study was to investigate whether 14-3-3η, a specific isoform of a family of proteins regulating processes such as cellular signalling, activates cell-signalling pathways and induces factors known to contribute to the pathophysiology of rheumatoid arthritis (RA). We also investigated whether 14-3-3η is associated with more severe disease in both early and established RA.

Methods: We investigated the effect of 14-3-3η on the activation of RA-relevant signalling cascades and induction of proinflammatory mediators that contribute to the joint damage process. 14-3-3η titres from 33 patients with early RA (mean RA duration = 1.8 months) and from 40 patients with established RA were measured in serum drawn at the 3-year time point of the Behandel Strategieën study. The relationship between 14-3-3η titres and standard clinical variables was investigated by correlation analysis. The association with radiographic damage and radiographic progression over at least a 2-year period was investigated using univariate and multivariate regression analyses.

Results: 14-3-3η activated selected members of the mitogen-activated protein kinase (MAPK) family, mainly extracellular regulated kinase 1/2 and c-Jun kinase, but not p38MAPK. Activation by 14-3-3η, using levels spanning the concentration range found in RA patient serum, resulted in the induction of inflammatory transcripts such as interleukin 1 (IL-1) and IL-6 and factors linked to the joint damage process, such as receptor activator of nuclear factor κB ligand and matrix metalloproteinase 1. Serum 14-3-3η correlated significantly with rheumatoid factor (RF) (r = 0.43) and anticitrullinated protein antibodies (ACPAs) (r = 0.31) in the early RA cohort, but not with C-reactive protein (CRP) or the Disease Activity Score in 28 joints in either cohort. Serum 14-3-3η concentrations were significantly higher in patients with radiographically assessed joint damage and in those who had radiographic progression. By multivariate analysis, we show that 14-3-3η complemented markers such as CRP, RF and ACPA in informing RA radiographic status and/or progression.

Conclusions: Extracellular 14-3-3η activates key signalling cascades and induces factors associated with the pathogenesis of RA at concentrations found in patients with RA, and its expression is higher in patients with radiographic damage and RA progression.

Figures

Figure 1

Extracellular 14-3-3η selectively activates extracellular signal-regulated kinase and c-Jun N-terminal kinase/stress-activated protein kinase and potentiates inflammatory and joint damage factors. (A) 14-3-3η leads to the phosphorylation and activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). p-MEK, Phosphorylated mitogen-activated protein kinase kinase; p-SAPK, Phosphorylated stress-activated protein kinase. (B) Equal protein loading. (C) The effects were specific for ERK and JNK because phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) by 14-3-3η was not observed. (D) Similarly to tumour necrosis factor α (TNFα), 14-3-3η leads to the induction of inflammatory and joint damage factors. IL, Interleukin; GAPDH, Glyceraldehyde 3-phosphate dehydrogenase; MMP, Matrix metalloproteinase; RANKL, Receptor activator of nuclear factor κB ligand. (E) 14-3-3η induced effects observed with 14-3-3η concentrations that closely approximated the 14-3-3η median rheumatoid arthritis (RA) serum concentrations.

Figure 2

Scatterplots illustrating serum 14-3-3η concentration according to radiographic progression of rheumatoid arthritis. Radiographic progression of rheumatoid arthritis (RA) was defined as any change in Sharp/van der Heijde score <1 or ≥1 at the end of the follow-up period (30 months for early RA (n = 33) and 2 years for established RA (n = 40)). Triangle = patients with no erosion; Square = patients with erosions; Line = mean levels.