Novel tools for molecular analysis in synovium

Objective

Current approaches to analyze and track disease-related genes and proteins in synovium or in animal models for arthritis including gene transfer models are based on RNA isolated either from cultured synovial cells or from synovial biopsies. This strategy does neither allow one to distinguish between specific gene expression of cells originating from different synovial compartments due to a potential mixture of different expression profiles nor to track these genes or gene products in the synovium. Therefore, we established laser-mediated microdissection (LMM) and differential display for analysis of gene expression profiles of histologically defined areas in rheumatoid synovium, and established novel molecular imaging techniques to track the molecules associated with pathogenic synovial processes.

Methods

Synovial cryosections derived from different human arthritides were used to obtain cell samples from distinct synovial areas using LMM. RNA was isolated and analyzed using differential display fingerprinting. Differential expression of identified sequences was confirmed by in situ hybridization and immunohistochemistry. Molecular imaging using different fluorescence-based techniques was performed to track molecules of interest such as human serum albumin-coupled molecules and circulating cells such as T-cell hybridomas and dendritic cells following adoptive cellular gene transfer within the synovium.

Results

Microdissected synovial tissue sections containing about 600 cells yield enough RNA for a stable, reproducible RNA fingerprint. Several genes – known and unknown ones with regard to rheumatoid arthritis pathophysiology – could be identified as being expressed differentially between the synovial lining, the sublining, and the microvasculature (e.g. thrombospondin-4 in the lining layer, ciz-1 in the sublining, and CD82 around the microvasculature). In addition, molecular bioluminescence-based imaging revealed that T-cell hybridomas and dendritic cells home to the synovium. It was found that the arthritic joint is the primary target of adoptive cellular gene transfer and that the synovial fibroblasts are the target of albumin-coupled molecules.

Conclusion

High-sensitivity molecular analysis methods such as LMM and differential display, in combination with molecular imaging of 'vehicle' cells, genes and proteins of interest, present a valuable tool to obtain novel insights into compartment-dependent synovial pathways. In addition, the results also demonstrate the potential of these novel analytic strategies in a nonmalignant multifactorial inflammatory disease.