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Logo of annrheumdAnnals of the Rheumatic DiseasesVisit this articleSubmit a manuscriptReceive email alertsContact usBMJ
Ann Rheum Dis. 2004 October; 63(10): 1205–1211.
PMCID: PMC1754744

Discrepancy between mRNA and protein expression of tumour suppressor maspin in synovial tissue may contribute to synovial hyperplasia in rheumatoid arthritis


Objective: To investigate the expression of maspin in RA synovial tissue and compare it with the expression in osteoarthritis (OA) and normal synovial tissue (NS).

Methods: Using specific primers for maspin, a 237 bp fragment was amplified from cDNA obtained from cultured RA, OA, and normal synovial fibroblasts (SF) by RT-PCR. Additionally, mRNA expression levels were determined quantitatively by real time PCR. mRNA expression of maspin was investigated on snap frozen and paraffin embedded synovial tissue sections by in situ hybridisation. Immunohistochemistry was used to identify the cell type expressing maspin. SDS-PAGE and western blotting were performed to evaluate the protein expression in cultured SF. To confirm protein synthesis in situ, immunohistochemistry with specific anti-maspin antibodies was performed in synovial tissue sections of patients with RA.

Results: RT-PCR showed expression of maspin in all cDNA samples from cultured SF. Maspin mRNA was found to be decreased in RA SF twofold and 70-fold compared with OA SF and NS SF, respectively. Maspin mRNA was expressed in RA, OA, and normal synovial tissue. Importantly, maspin transcripts were also found at sites of invasion into cartilage and bone. At the protein level, maspin could be detected in RA and, less prominently, OA SF. In RA synovial tissue, maspin protein was detected in only a few synovial lining cells.

Conclusion: Maspin is expressed intensively in RA SF at the mRNA level, but only slightly at the protein level, possibly owing to down regulation of maspin; this may contribute to the hyperplasia of synovial tissue in RA.

Figure 1
 RT-PCR using maspin-specific primers spanning a 237 bp fragment showed expression of maspin in all synovial fibroblast RNA samples examined (representative RA, OA, normal synovial tissue samples).
Figure 2
 SF from seven patients with RA, four with OA, and one trauma patient were examined by real time PCR with maspin-specific primers and probe (TaqMan system, PE Biosystems). Less maspin was expressed in RA samples than in OA and normal synovial ...
Figure 3
 In situ hybridisation on paraffin embedded synovial tissue sections showed maspin mRNA expression in RA, OA, and normal synovial tissue. Whereas the expression of maspin was restricted to SF in lining and sublining in normal and OA synovial ...
Figure 4
 To further characterise the cell type expressing maspin, double labelling with anti-CD68 (A, C) and anti-CD3 antibodies (B, D) was performed after in situ hybridisation with maspin probes on paraffin embedded RA synovial tissue samples. Predominantly, ...
Figure 5
 Maspin mRNA expression was additionally investigated in RA synovial tissue at sites of cartilage and bone destruction. Maspin positive cells with both fibroblast-like (A) and macrophage-like as well as osteoclast-like morphology (C) were found. ...
Figure 6
 To examine the protein expression of maspin in RA SF, SDS-PAGE and western blot with anti-maspin antibodies was performed in SF of seven patients with RA and four with OA. A positive band of the correct size (42 kDa) was detected in all RA SF ...

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