Research article

Transcriptional profiling differences for articular cartilage and repair tissue in equine joint surface lesions

Michael J Mienaltowski^1,4 , Liping Huang² , David D Frisbie³ , C Wayne McIlwraith³ , Arnold J Stromberg² , Arne C Bathke² and James N MacLeod¹

¹University of Kentucky, Department of Veterinary Science, Maxwell H. Gluck Equine Research Center, Lexington, KY, 40546-0099, USA

²University of Kentucky, Department of Statistics, 817 Patterson Office Tower, Lexington, KY, 40506-0027, USA

³Colorado State University, College of Veterinary Medicine, Gail Holmes Equine Orthopaedic Research Center, Ft. Collins, CO, 80523-1678, USA

⁴University of South Florida, College of Medicine, Department of Orthopaedics & Sports Medicine, 12901 Bruce B. Downs Blvd, MDC Box 11, Tampa, FL, 33612, USA

author email corresponding author email

BMC Medical Genomics 2009, 2:60doi:10.1186/1755-8794-2-60

Published:	14 September 2009

Abstract

Background

Full-thickness articular cartilage lesions that reach to the subchondral bone yet are restricted to the chondral compartment usually fill with a fibrocartilage-like repair tissue which is structurally and biomechanically compromised relative to normal articular cartilage. The objective of this study was to evaluate transcriptional differences between chondrocytes of normal articular cartilage and repair tissue cells four months post-microfracture.

Methods

Bilateral one-cm² full-thickness defects were made in the articular surface of both distal femurs of four adult horses followed by subchondral microfracture. Four months postoperatively, repair tissue from the lesion site and grossly normal articular cartilage from within the same femorotibial joint were collected. Total RNA was isolated from the tissue samples, linearly amplified, and applied to a 9,413-probe set equine-specific cDNA microarray. Eight paired comparisons matched by limb and horse were made with a dye-swap experimental design with validation by histological analyses and quantitative real-time polymerase chain reaction (RT-qPCR).

Results

Statistical analyses revealed 3,327 (35.3%) differentially expressed probe sets. Expression of biomarkers typically associated with normal articular cartilage and fibrocartilage repair tissue corroborate earlier studies. Other changes in gene expression previously unassociated with cartilage repair were also revealed and validated by RT-qPCR.

Conclusion

The magnitude of divergence in transcriptional profiles between normal chondrocytes and the cells that populate repair tissue reveal substantial functional differences between these two cell populations. At the four-month postoperative time point, the relative deficiency within repair tissue of gene transcripts which typically define articular cartilage indicate that while cells occupying the lesion might be of mesenchymal origin, they have not recapitulated differentiation to the chondrogenic phenotype of normal articular chondrocytes.