Enhanced susceptibility to lipopolysaccharide-induced arthritis and endotoxin shock in interleukin-32 alpha transgenic mice through induction of tumor necrosis factor alpha.

ABSTRACT:

Introduction

The present study assessed the potential functions of interleukin (IL)-32? on inflammatory arthritis and endotoxin shock models using IL-32? transgenic (Tg) mice. The potential signaling pathway for the IL-32-tumor necrosis factor (TNF)? axis was analyzed in vitro.

Methods

IL-32? Tg mice were generated under control of a ubiquitous promoter. Two disease models were used to examine in vivo effects of overexpressed IL-32?: Toll-like receptor (TLR) ligand-induced arthritis developed using a single injection of lipopolysaccharide (LPS) or zymosan into the knee joints; and endotoxin shock induced with intraperitoneal injection of LPS and D-galactosamine. TNF? antagonist etanercept was administered simultaneously with LPS in some mice. Using RAW264.7 cells, in vitro effects of exogenous IL-32? on TNF?, IL-6 or macrophage inflammatory protein 2 (MIP-2) production were assessed with or without inhibitors for nuclear factor kappa B (NF?B) or mitogen-activated protein kinase (MAPK).

Results

Single injection of LPS, but not zymosan, resulted in development of severe synovitis with substantial articular cartilage degradation in knees of the Tg mice. The expression of TNF? mRNA in inflamed synovia was highly upregulated in the LPS-injected Tg mice. Moreover, the Tg mice were more susceptive to endotoxin-induced lethality than the wild-type control mice 48 hours after LPS challenge; but blockade of TNF? by etanercept protected from endotoxin lethality. In cultured bone marrow cells derived from the Tg mice, overexpressed IL-32? accelerated production of TNF? upon stimulation with LPS. Of note, exogenously added IL-32? alone stimulated RAW264.7 cells to express TNF?, IL-6, and MIP-2 mRNAs. Particularly, IL-32? -induced TNF?, but not IL-6 or MIP-2, was inhibited by dehydroxymethylepoxyquinomicin (DHMEQ) and U0126, which are specific inhibitors of nuclear factor kappa B (NF?B) and extracellular signal regulated kinase1/2 (ERK1/2), respectively.

Conclusions

These results show that IL-32? contributed to the development of inflammatory arthritis and endotoxin lethality. Stimulation of TLR signaling with LPS appeared indispensable for activating the IL-32?-TNF? axis in vivo. However, IL-32? alone induced TNF? production in RAW264.7 cells through phosphorylation of inhibitor kappa B (I?B) and ERK1/2 MAPK. Further studies on the potential involvement of IL-32?-TNF? axis will be beneficial in better understanding the pathology of autoimmune-related arthritis and infectious immunity.

SUBMITTER: Nakayama M 

PROVIDER: S-EPMC3446501 | biostudies-literature | 2012 May

REPOSITORIES: biostudies-literature