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Open Access Research article

Biomechanical signals and the C-type natriuretic peptide counteract catabolic activities induced by IL-1β in chondrocyte/agarose constructs

Manoj Ramachandran2, Prim Achan2, Donald M Salter3, Dan L Bader1 and Tina T Chowdhury1*

Author affiliations

1 School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK

2 Department of Trauma and Orthopaedics, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Whitechapel Road, London E1 1BB, UK

3 Molecular Medicine Centre, Western General Hospital, University of Edinburgh, Crew Road, Edinburgh EH4 2XU, UK

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Citation and License

Arthritis Research & Therapy 2011, 13:R145  doi:10.1186/ar3459

Published: 13 September 2011

Abstract

Introduction

The present study examined the effect of C-type natriuretic peptide (CNP) on the anabolic and catabolic activities in chondrocyte/agarose constructs subjected to dynamic compression.

Methods

Constructs were cultured under free-swelling conditions or subjected to dynamic compression with low (0.1 to 100 pM) or high concentrations (1 to 1,000 nM) of CNP, interleukin-1β (IL-1β), and/or KT-5823 (inhibits cyclic GMP-dependent protein kinase II (PKGII)). Anabolic and catabolic activities were assessed as follows: nitric oxide (NO) and prostaglandin E2 (PGE2) release, and [3H]-thymidine and 35SO4 incorporation were quantified by using biochemical assays. Gene expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), aggrecan, and collagen type II were assessed with real-time quantitative PCR (qPCR). Two-way ANOVA and the post hoc Bonferroni-corrected t tests were used to examine data.

Results

CNP reduced NO and PGE2 release and partially restored [3H]-thymidine and 35SO4 incorporation in constructs cultured with IL-1β. The response was dependent on the concentration of CNP, such that 100 pM increased [3H]-thymidine incorporation (P < 0.001). This is in contrast to 35SO4 incorporation, which was enhanced with 100 or 1000 nM CNP in the presence and absence of IL-1β (P < 0.001). Stimulation by both dynamic compression and CNP and/or the PKGII inhibitor further reduced NO and PGE2 release and restored [3H]-thymidine and 35SO4 incorporation. In the presence and absence of IL-1β, the magnitude of stimulation for [3H]-thymidine and 35SO4 incorporation by dynamic compression was dependent on the concentration of CNP and the response was inhibited with the PKGII inhibitor. In addition, stimulation by CNP and/or dynamic compression reduced IL-1β-induced iNOS and COX-2 expression and restored aggrecan and collagen type II expression. The catabolic response was not further influenced with the PKGII inhibitor in IL-1β-treated constructs.

Conclusions

Treatment with CNP and dynamic compression increased anabolic activities and blocked catabolic effects induced by IL-1β. The anabolic response was PKGII mediated and raises important questions about the molecular mechanisms of CNP with mechanical signals in cartilage. Therapeutic agents like CNP could be administered in conjunction with controlled exercise therapy to slow the OA disease progression and to repair damaged cartilage. The findings from this research provide the potential for developing novel agents to slow the pathophysiologic mechanisms and to treat OA in the young and old.