Inhibition of pSTAT1 by tofacitinib accounts for the early improvement of experimental chronic synovitis

Sandra Pérez-Baos,Paula Gratal,Juan I Barrasa,Ana Lamuedra,Gabriel Herrero-Beaumont,Olga Sánchez-Pernaute,Raquel Largo

doi:10.1186/s12950-019-0206-2

Abstract

BackgroundIn order to gain insight into the early effects drawn by JAK inhibitors on intra-joint JAK/STAT-dependent signaling, we sought synovial activation of STATs and their end-products, along with their modification with tofacitinib (TOFA), at flare-up in antigen induced arthritis (AIA). New Zealand rabbits were randomly assigned to four groups –healthy controls, AIA, TOFA-treated AIA, or TOFA-treated controls–. AIA was induced with 4 weekly intra-articular ovalbumin injections in sensitized animals. TOFA (10 mg·kg− 1·day− 1) was administered for the last 2 weeks. Animals were euthanized 24 h after the last injection.ResultsAIA animals showed high-grade synovitis, which was partially improved by TOFA. No effects of the treatment were found on serum C-reactive protein or on the synovial macrophage infiltration at this stage. Synovial MMP-1,-3 and -13 expression levels in treated AIA rabbits were found to drop to those of controls, while a downregulation of IL6, IFNγ and TNF was evident in treated versus untreated AIA rabbits. Concurrently, a reduction in pSTAT1 and SOCS1, but not in pSTAT3, SOCS3 or active NFκB-p65, was noted with TOFA.ConclusionsStudying the mechanism of action of immunomodulatory drugs represents a major challenge in vivo, since drug-dependent decreases in inflammation very likely mask direct effects on disease mechanisms. This study design allowed us to prevent any confounding effect resulting from reductions in the overall inflammatory status, hence assessing the true pharmacological actions of TOFA in a very severe synovitis. Our findings point to pSTAT1 and MMPs as early molecular readouts of response to this JAK inhibitor.

Highlights

In order to gain insight into the early effects drawn by Janus kinase (JAK) inhibitors on intra-joint JAK/STATdependent signaling, we sought synovial activation of Signal Transducer and Activator of Transcription (STAT) and their end-products, along with their modification with tofacitinib (TOFA), at flare-up in antigen induced arthritis (AIA)
In a rabbit model of chronic antigen induced arthritis (AIA) which faithfully reproduces rheumatoid synovitis, we studied the earliest modifications drawn by TOFA at joints during flare-up reactions, in order to explore the changes induced by this inhibitor on phosphorylated STATs and their end products in the short term
Effect of TOFA on serum C-reactive protein and body weight gain of AIA rabbits The high inflammatory status evoked by the experimental disease led to a decreased weight gain, already evident in arthritic animals from the first intra-articular challenge and continuing thereafter until the end of the study (Fig. 1 b)

Summary

Introduction

In order to gain insight into the early effects drawn by JAK inhibitors on intra-joint JAK/STATdependent signaling, we sought synovial activation of STATs and their end-products, along with their modification with tofacitinib (TOFA), at flare-up in antigen induced arthritis (AIA). The synovial membrane is the primary site of inflammation in rheumatoid arthritis (RA) It is organized as an interstitial tissue overlaid by an intimal lining of 1 to 3 rows of cells. Activation of the Janus kinase (JAK) and Signal Transducer and Activator of Transcription (STAT) pathway by type I/II cytokines is currently regarded as a major contributor to the sustained inflammatory response of RA [7, 8]. This pathway has become a promising target of RA therapeutics [9]. There are 7 isoforms of STATs –namely STAT1 to 6, with STAT5 subtypes A and B– which display a cell and tissue dependent distribution and account for the production of cytokines, proteases and growth factors in response to environmental stressors [8]

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Conclusion