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Open Access Research article

Regulation of chondrocyte gene expression by osteogenic protein-1

Susan Chubinskaya123*, Lori Otten1, Stephan Soeder4, Jeffrey A Borgia15, Thomas Aigner4, David C Rueger6 and Richard F Loeser7

Author Affiliations

1 Department of Biochemistry, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612, USA

2 Department of Orthopedic Surgery, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612, USA

3 Section of Rheumatology, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612, USA

4 Klinikum Coburg GmbH, Ketschendorfer Str. 33, D - 96450 Coburg, Germany

5 Department of Pathology, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612, USA

6 Stryker Biotech, 35 South Street, Hopkinton, MA 01748, USA

7 Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157, USA

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Arthritis Research & Therapy 2011, 13:R55  doi:10.1186/ar3300

Published: 29 March 2011

Abstract

Introduction

The objective of this study was to investigate which genes are regulated by osteogenic protein-1 (OP-1) in human articular chondrocytes using Affimetrix gene array, in order to understand the role of OP-1 in cartilage homeostasis.

Methods

Chondrocytes enzymatically isolated from 12 normal ankle cartilage samples were cultured in high-density monolayers and either transfected with OP-1 antisense oligonucleotide in the presence of lipofectin or treated with recombinant OP-1 (100 ng/ml) for 48 hours followed by RNA isolation. Gene expression profiles were analyzed by HG-U133A gene chips from Affimetrix. A cut-off was chosen at 1.5-fold difference from controls. Selected gene array results were verified by real-time PCR and by in vitro measures of proteoglycan synthesis and signal transduction.

Results

OP-1 controls cartilage homeostasis on multiple levels including regulation of genes responsible for chondrocyte cytoskeleton (cyclin D, Talin1, and Cyclin M1), matrix production, and other anabolic pathways (transforming growth factor-beta (TGF-β)/ bone morphogenetic protein (BMP), insulin-like growth factor (IGF), vascular endothelial growth factor (VEGF), genes responsible for bone formation, and so on) as well as regulation of cytokines, neuromediators, and various catabolic pathways responsible for matrix degradation and cell death. In many of these cases, OP-1 modulated the expression of not only the ligands, but also their receptors, mediators of downstream signaling, kinases responsible for an activation of the pathways, binding proteins responsible for the inhibition of the pathways, and transcription factors that induce transcriptional responses.

Conclusions

Gene array data strongly suggest a critical role of OP-1 in human cartilage homeostasis. OP-1 regulates numerous metabolic pathways that are not only limited to its well-documented anabolic function, but also to its anti-catabolic activity. An understanding of OP-1 function in cartilage will provide strong justification for the application of OP-1 protein as a therapeutic treatment for cartilage regeneration and repair.