Tumor necrosis factor alpha, citrullination, and peptidylarginine deiminase 4 in lung and joint inflammation

Thomas F. Warner,Anthony P. Nicholas,Mandar Bawadekar,Lennart K. A. Lundblad,Daeun Shim,Annette Gendron-Fitzpatrick,Paul R. Thompson,Miriam A. Shelef,Ryan Rebernick

doi:10.1186/s13075-016-1068-0

Abstract

BackgroundThe relationship between lung and joint inflammation in rheumatoid arthritis is poorly understood. Lung inflammation with resultant protein citrullination may trigger anti-citrullinated protein antibodies, inflammation, and arthritis. Alternatively, lung and joint inflammation may be two manifestations of a single underlying pathology. The lung has increased citrullination and TNF-α levels are high in rheumatoid arthritis; however, it is unknown if TNF-α can induce lung protein citrullination. The citrullinating enzyme peptidylarginine deiminase 4 (PAD4) exacerbates TNF-α-induced arthritis, but a role for PAD4 in lung citrullination and TNF-α-induced lung inflammation has not been explored. Our aim was to use TNF-α-overexpressing mice to clarify the intersection of TNF-α, citrullination, PAD4, arthritis, and lung inflammation.MethodsLung protein citrullination in wild-type mice, mice that overexpress TNF-α systemically (TNF+), TNF+PAD4+/+, and TNF+PAD4-/- mice was quantified by both gel electrophoresis using a citrulline probe and western blot. Hematoxylin and eosin (H&E)-stained lung sections from TNF+PAD4+/+ and TNF+PAD4-/- mice were scored for lung inflammation. H&E-stained ankle joint sections from mice that overexpress TNF-α only in the lungs were assessed for arthritis.ResultsTNF+ mice have increased lung protein citrullination. TNF+PAD4-/- mice do not have significantly reduced lung protein citrullination, but do have decreased lung inflammation compared to TNF+PAD4+/+ mice. Mice that overexpress TNF-α only in the lungs do not develop arthritis.ConclusionsPAD4 exacerbates lung inflammation downstream of TNF-α without having a major role in generalized protein citrullination in inflamed lungs. Also, TNF-α-induced lung inflammation is not sufficient to drive murine arthritis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-016-1068-0) contains supplementary material, which is available to authorized users.

Highlights

The relationship between lung and joint inflammation in rheumatoid arthritis is poorly understood
Additional studies are needed to better characterize the role of peptidylarginine deiminase 4 (PAD4) in immune cells, clarify the role of PAD2 in citrullination and arthritis, and Conclusions We have shown that PAD4 contributes to lung inflammation, but is not critical for gross protein citrullination in the inflamed lung
These findings suggest that PAD4 exacerbates inflammation apart from antigen citrullination and that peptidylarginine deiminase (PAD) other than PAD4 are responsible for the majority of inflammation-dependent protein citrullination in the lung

Summary

Introduction

The relationship between lung and joint inflammation in rheumatoid arthritis is poorly understood. The lung has increased citrullination and TNF-α levels are high in rheumatoid arthritis; it is unknown if TNF-α can induce lung protein citrullination. The citrullinating enzyme peptidylarginine deiminase 4 (PAD4) exacerbates TNF-α-induced arthritis, but a role for PAD4 in lung citrullination and TNF-α-induced lung inflammation has not been explored. Our aim was to use TNF-α-overexpressing mice to clarify the intersection of TNF-α, citrullination, PAD4, arthritis, and lung inflammation. PAD4 is interesting in rheumatoid arthritis for several reasons It is expressed in immune cells and is increased in the rheumatoid joint [1, 2]. Mice deficient in PAD4 have reduced TNF-αinduced [9] and glucose-6-phosphate isomerase-induced arthritis [10], but it is not known if PAD4 impacts lung citrullination or inflammation

Objectives

Methods

Results

Discussion

Conclusion