Differential gene expression of proliferating synovial fibroblasts in rheumatoid arthritis

Objective

The aim of this study was to investigate the expression profile of rheumatoid arthritis synovial fibroblasts (RA-SF) during proliferation, and to explore the molecular mechanisms of synovial proliferation in RA.

Methods

Total RNA was extracted from 2 cultures of RA-SF, low-density (LD) proliferating cells and high-density (HD) nonproliferating cells, respectively, and suppression subtractive hybridization (SSH) was performed to compare differential gene expression of these 2 cultures. Subtracted cDNA was subcloned, and nucleotide sequences were analyzed to identify each clone. Differential expression of distinct clones was confirmed by semiquantitative RT-PCR. The expression and distribution of novel genes in synovial tissues was examined by in situ hybridization.

Results

Forty-four clones were upregulated in LD cells, and 44 clones were upregulated in HD cells. Forty-six of the 88 clones were identical to sequences that have previously been characterized. Twenty-nine clones were identical to cDNAs that have been identified, but with unknown functions so far, and 13 clones did not show any significant homology to sequences in the GenBank (NCBI). Differential expression of distinct clones was confirmed by RT-PCR. In situ hybridization showed that specific genes, such as S100 calcium-binding protein A4, nuclear factor of activated T cells 5, upstream of N-ras and F-box only protein 3, were also expressed predominantly in synovial tissues from patients with RA (3/7, 6/7, 5/7, 5/7, respectively), but not from normal individuals (0/3, 0/3, 1/3, 1/3).

Conclusion

SSH was a useful approach to compare the expression profile of cells under different conditions, and we could elucidate that distinct genes, including several novel genes, were differentially expressed in RA-SF during proliferation. Moreover, the expression of these genes could be found in RA synovium, especially at sites of invasion, suggesting that these molecules are involved in synovial activation in RA. It needs to be stressed, that the expression of certain genes in RA-SF depends on the stage of proliferation, and as such this stage needs to be considered in all analysis of differential gene expression in SF.