Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


TNF-Driven IL-32 Expression in Rheumatoid Arthritis Synovial Tissue Amplifies an Inflammatory Cascade.

Heinhuis4,  Bas, Koenders4,  Marije I., van Riel2,  Piet L., Dinarello3,  Charles A., Netea1,  Mihai G., van den Berg4,  Wim B., Joosten1,  Leo A. B.

Department of Medicine, Radboud University Nijmegen Medical Centre, Nijmegen the Netherlands
Department of Rheumatology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
Division of Infectious Diseases, University of Colorado Denver, Aurora, CO
Rheumatology Research & Advanced Therapeutics, Department of Rheumatology, Radboud University Nijmegen Medical Centre, Nijmegen the Netherlands

Statement of Purpose:

To investigate the interplay between IL-32 and TNFa in chronic inflamed synovial tissue and to assess whether anti-TNFa treatment of RA patients modulates synovial IL-32 expression.

Methods:

To study the interplay between IL-32 and TNFa, we first investigated the induction of IL-32g by TNFa stimulation in human synovial fibroblasts donated by arthritis patients and compared it with other stimuli such as TLR ligands or IL-1b. Second, we investigated the production of TNFa through intracellular overexpression of IL-32g followed by LPS stimulation in human THP1 cells. Additionally, we determined the induction of IL-1b, IL-6, and CXCL8. Third, the role of endogenous IL-32 was studied by silencing IL-32g in human synovial fibroblasts and subsequently IL-6 and CXCL8 levels were determined. Fourth, overexpression of intracellular IL-32g using an adenovirus expressing human IL-32g followed by TNFa stimulation was done in synovial fibroblasts to investigate induction of proinflammatory cytokines. Fifth, modulation of TNFa mRNA stability was investigated in human THP1 cells transduced with an adenoviral vector expressing human IL-32g. IL-1b, IL-6, and CXCL8 mRNA stability was determined. Finally, immunohistochemistry was applied to study IL-32 expression in synovial biopsies from RA patients.

Summary of the Results:

Synovial fibroblasts stimulated with TNFa showed potent induction of IL-32g expression when compared to IL-1b, TLR ligands or medium. Moreover, TNFa induced IL-32g expression is specific since IL-1b stimulation induced primarily IL-6 and CXCL8. Of high interest, overexpression of intracellular IL-32g in human THP1 cells followed by LPS exposure resulted in significant production of TNFa, IL-1b, IL-6, and CXCL8. Furthermore, silencing of endogenous IL-32g showed potent downregulation of IL-6 and CXCL8 whereas overexpression of IL-32g resulted in enhanced production of IL-6 and CXCL8 in human synovial fibroblasts. To investigate the mechanism how IL-32g is capable of amplifying the inflammatory cascade resulting in a self perpetuating loop between IL-32g and TNFa, we studied mRNA stability. Enhanced expression of intracellular IL-32g resulted in delayed TNFa, IL-1b, and CXCL8 mRNA decay. In contrast, IL-6 mRNA stability was not regulated by IL-32g. Of high interest, treatment of RA patients with anti-TNFa resulted in significant reduction of IL-32 protein expression in synovial tissue.

Conclusions:

TNFa is a potent specific inducer of endogenous IL-32 expression and IL-32 itself contributes to a prolonged TNFa production. This results in a self perpetuating loop between IL-32g and TNFa resulting in potent induction of several proinflammatory cytokines and chemokines. This auto-inflammatory loop can potentially be intervened by silencing IL-32 or anti-TNFa treatment. Targeting IL-32 might be a novel therapy to counteract the auto-inflammatory cascade of TNFa-IL-371-TNFa present in chronic inflamed synovial tissue of RA patients.

To cite this abstract, please use the following information:
Heinhuis, Bas, Koenders, Marije I., van Riel, Piet L., Dinarello, Charles A., Netea, Mihai G., van den Berg, Wim B., et al; TNF-Driven IL-32 Expression in Rheumatoid Arthritis Synovial Tissue Amplifies an Inflammatory Cascade. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :371
DOI: 10.1002/art.28140

Abstract Supplement

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2010 ACR/ARHP