ab22112

Regulation of anabolic and catabolic gene expression in normal and osteoarthritic adult human articular chondrocytes by osteogenic protein-1

Z. Fan¹, S. Chubinskaya², D.C. Rueger³, B. Bau¹, J. Haag¹, T. Aigner¹

¹Cartilage Research, Department of Pathology, University of Erlangen-Nürnberg, Germany; ²Department of Biochemistry and Section of Rheumatology, Rush Medical College at Rush-Presbyterian St. Luke's Medical Center, Chicago, Illinois; ³Stryker Biotech, Hopkinton, Massachusetts, USA.

ABSTRACT
Objective
Osteoarthritis is characterized by dramatic changes in chondrocyte metabolism including the overexpression of catabolic enzymes, but also a lack of anabolic activity. In this respect, osteogenic protein 1 (OP-1) appears to be one of the most potent anabolic factors of chondrocytes. In this study, we were interested in: (1) whether recombinant human OP-1 exerts its anabolic effects also on osteoarthritic chondrocytes, (2) whether OP-1 modulates the expression of catabolic genes, and (3) whether the BMP effects are related to the expression levels of its intracellular mediators (R- and I-Smads).

Methods
Chondrocytes were isolated from cartilage of either normal (n=5) or osteoarthritic (n=8) human knee joints and cultured in short-term high-density monolayer cultures with and without recombinant OP-1. RNA was isolated and analyzed for mRNA expression levels of anabolic (aggrecan, collagen type II), catabolic (MMP-1, -3, -13, ADAMTS-4), and intracellular signaling mediators (Smad 1, 4, 5, 6, 7, and 8) by quantitative online PCR.

Results
After OP-1 stimulation, the anabolic genes were significantly up-regulated in osteoarthritic chondrocytes in comparison to normal chondrocytes. Neither in normal nor osteoarthritic chondrocytes were significant changes observed for the matrix degrading enzymes. Smads were also expressed in both normal and osteoarthritic cells at roughly the same level with and without stimulation with OP-1.

Conclusion
Osteoarthritic chondrocytes are not hypo-responsive to anabolic stimulation by OP-1. Thus, human recombinant OP-1 could be a suitable anabolic activator of osteoarthritic chondrocytes. This might be of particular interest as chondrocytes themselves showed very low levels of OP-1 expression.

Key words
Aggrecan, collagen, MMP, bone morphogenetic protein, chondrocytes.

This work was supported by the German Ministry of Research (BMBF Grant 01GG9824), NIH/NIAMS RO1 grant 47654 (SC); Stryker Biotech (SC).
Please address correspondence and reprint requests to: Thomas Aigner, MD, Cartilage Research, Department of Pathology, University of Erlangen-Nürnberg, Krankenhausstr. 8-10, D-91054 Erlangen, Germany.
E-mail: Thomas.aigner@patho.imed.uni-erlangen.de