Vet Comp Orthop Traumatol 2007; 20(03): 185-191
DOI: 10.1160/VCOT-06-07-0061
Original Research
Schattauer GmbH

Phenotypic maintenance of articular chondrocytes in vitro requires BMP activity

A. O. Oshin
1  Department of Clinical Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
,
E. Caporali
1  Department of Clinical Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
,
C. R. Byron
1  Department of Clinical Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
,
A. A. Stewart
1  Department of Clinical Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
,
M. C. Stewart
1  Department of Clinical Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
› Author Affiliations
Further Information

Publication History

Received 29 August 2006

Accepted 29 July 2006

Publication Date:
21 December 2017 (online)

Summary

Articular chondrocytes are phenotypically unique cells that are responsible for the maintenance of articular cartilage. The articular chondrocytic phenotype is influenced by a range of soluble factors. In particular, members of the bone morphogenetic protein (BMP) family support the articular chondrocytic phenotype and stimulate synthesis of cartilaginous matrix. This study was carried out to determine the importance of BMPs in supporting the differentiated phenotype of articular chondrocytes in vitro. Exogenous BMP-2 supported expression of collagen type II and aggrecan in monolayer chondrocyte cultures, slowing the dedifferentiation process that occurs under these conditions. In contrast, BMP-2 had little effect on expression of these genes in three-dimensional aggregate cultures. Endogenous BMP-2 expression was lost in monolayer cultures, coincident with the down-regulation of collagen type II and aggrecan mRNAs, whereas BMP-2 mRNA levels were stable in aggregate cultures. Antagonism of endogenous BMP activity in aggregate cultures by Noggin or a soluble form of the BMP receptor resulted in reduced expression of collagen type II and aggrecan mRNAs, reduced collagen type II protein and sulfated glycosaminoglycan (GAG) deposition into the aggregate matrices and reduced secretion of GAGs into the culture media. These results indicate that endogenous BMPs are required for maintenance of the differentiated articular chondrocytic phenotype in vitro. These findings are of importance to cell-based strategies designed to repair articular cartilage. Articular chondrocytes require conditions that will support endogenous expression of BMPs to maintain the specialized phenotype of these cells.