Global analyses of gene expression in early experimental osteoarthritis

Abstract

Objective. To analyze genome-wide changes in chondrocyte gene expression in a surgically induced model of early osteoarthritis (OA) in rats, to assess the similarity of this model to human OA, and to identify genes and mechanisms leading to OA pathogenesis.Methods. OA was surgically induced in 5 rats by anterior cruciate ligament transection and partial medial meniscectomy. Sham surgery was performed in 5 additional animals, which were used as controls. Both groups underwent 4 weeks of forced mobilization, 3 times per week. RNA was extracted directly from articular chondrocytes in the OA (operated), contralateral, and sham-operated knees. Affymetrix GeneChip expression arrays were used to assess genome-wide changes in gene expression. Expression patterns of selected dysregulated genes, including Col2a1, Mmp13, Adamts5, Ctsc, Ptges, and Cxcr4, were validated by real-time polymerase chain reaction, immunofluorescence, or immunohistochemistry 2, 4, and 8 weeks after surgery.Results. After normalization, comparison of OA and sham-operated samples showed 1,619 differentially expressed probe sets with changes in their levels of expression >1.5-fold, 722 with changes >2-fold, 135 with changes >4-fold, and 20 with changes of 8-fold. Dysregulated genes known to be involved in human OA included Mmp13, Adamts5, and Ptgs2, among others. Several dysregulated genes (e.g., Reln, Phex, and Ltbp2) had been identified in our earlier microarray study of hypertrophic chondrocyte differentiation. Other genes involved in cytokine and chemokine signaling, including Cxcr4 and Ccl2, were identified. Changes in gene expression were also observed in the contralateral knee, validating the sham operation as the appropriate control.Conclusion. Our results demonstrate that the animal model mimics gene expression changes seen in human OA, supporting the relevance of newly identified genes and pathways to early human OA. We propose new avenues for OA pathogenesis research and potential targets for novel OA treatments, including cathepsins and cytokine, chemokine, and growth factor signaling pathways, in addition to factors controlling the progression of chondrocyte differentiation.

Time‐series transcriptional profiling yields new perspectives on susceptibility to murine osteoarthritis

“…Such merging of data from the 2 strains effectively limits any differences attributable solely to strain-specific variation, which might be unrelated to OA, and provides the greatest statistical power. This analysis revealed 390 up-regulated and 272 down-regulated genes in the OA samples (Supplementary Table 2 A significant number of genes described in a recent editorial (7,(18)(19)(20)(21)(22) as being OA targets based on the results of microarray analysis of human OA and a rat model were also identified ( Figure 1I), providing further confirmation of the relevance of our preclinical STR/Ort mouse model to human OA. Among these genes, levels of mRNA for Col2a1, tissue inhibitor of metalloproteinases 1 (TIMP-1), MMP-13, and ADAMTS-4 were further investigated by qPCR and showed increased levels in AC samples from 40-weekold STR/Ort mice as compared to those from age- 3258 POULET ET AL matched CBA mice ( Figure 1H).…”

“…Mice were used in experiments at ages 8-10 weeks (young; 5 CBA and 6 STR/Ort mice), 18-20 weeks (mature; 5 CBA and 7 STR/Ort mice), and 40-42 weeks (aged; 9 CBA and 14 STR/Ort mice). Left knee tibial and femoral surfaces were exposed, and AC from each condyle was isolated using a Friedman-Pearson micro-rongeur (extra-fine tip, 0.7-mm cup width; Fine Science Tools) (7,13), and samples were kept in RNAlater (Qiagen). Right knees were processed for histologic examination.…”

Fibroblast growth factor 2: A new key player in osteoarthritis

“…Studies of the regulation of aggrecanases have shown that the cytokine interleukin-1 (IL-1) induces ADAMTS-5 to a lesser degree than ADAMTS-4, but given the disparity in aggrecanase activity, this may not reflect a lesser importance for ADAMTS-5 (5). Although metalloproteinase expression levels in end-stage OA showed that ADAMTS-5 was among the proteinases that are repressed at this time point (9), recent genome-wide microarray studies of a surgically induced OA in the rat have revealed that Adamts5 is upregulated 4 weeks after surgery (10). These data suggest that ADAMTS-5 is likely to be important in early aggrecan cleavage during the development of OA, but may be repressed, perhaps through a feedback mechanism, during late stages of OA.…”

“…Studies of gene expression in OA, both genome wide (10,24,25) and of specific gene families (9), have revealed important pathways for further study. The article by Chia et al emphasizes the fact that development of OA may well result in modulation of the location and/or function of preexisting proteins in articular cartilage.…”

Proteomics in rheumatology: The beginning of a fairy tale?

“…In addition, well defined animal models (e.g., rats with surgically induced OA by anterior cruciate ligament transaction) may also assist in the discovery of novel disease pathways. Such approach was recently demonstrated at the RNA level to identify genes involved in OA pathogenesis [59]. Moreover, given the continuous growth in commercially available knock-out animals, such models may serve as an excellent tool to validate proteome analysis data.…”