ab22603

Follistatin-related protein gene (FRP) is expressed in the synovial tissues of rheumatoid arthritis, but its polymorphisms are not associated with genetic susceptibility

Y. Ehara¹, D. Sakurai¹, N. Tsuchiya¹, K. Nakano², Y. Tanaka², A. Yamaguchi³, K. Tokunaga¹

¹Department of Human Genetics and ³Department of Allergy and Rheumatology, Graduate School of Medicine, The University of Tokyo, Tokyo; ²The First Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.

ABSTRACT
Objective
To examine the expression level and function of follistatin-related protein gene (FRP, also referred to as FSTL1) in rheumatoid arthritis (RA), and possible association of its polymorphisms with genetic susceptibility to RA.

Methods
FRP mRNA expression levels in the synovial tissues from 10 patients with RA and 5 patients with OA were measured using real-time RT-PCR. Effects on the growth of synovial cells were evaluated by stably introducing FRP cDNA into a rheumatoid synovial cell line, E11. Screening of genomic DNA variations was done using DNA from 12 patients with RA and 12 healthy individuals by direct sequencing. Genotypes at the detected polymorphic sites were determined in 224 patients with RA and 220 healthy individuals using PCR-single strand conformation polymorphism.

Results
FRP mRNA was overexpressed in synovial tissues from RA patients by 2.3-fold as compared with those from OA. A rheumatoid synovial cell line (E11) transfected with FRP exhibited reduced proliferation, probably mediated by secreted FRP molecule. 16 genomic variations were identified, among which 4 were polymorphisms within the promoter region and exons, and the remainder were either rare variations or intronic polymorphisms. Genotyping of 4 polymorphic sites did not reveal statistically significant association with the susceptibility to RA.

Conclusion
FRP mRNA is overexpressed in RA synovium, the product of which exerts inhibitory activity on synovial cell growth. Although new polymorphic sites were identified, they were not associated with susceptibility to RA, suggesting that overexpression of FRP is secondarily caused by synovial environment of RA.

Key words
Rheumatoid arthritis, synovium, gene expression, polymorphism, genetics.

This study was supported by Grant-in-Aid for Scientific Research on Priority Areas (C) "Medical Genome Science", Grant-in-Aid for Scientific Research (B) from the Ministry of Education, Science, Sports and Culture of Japan, and by Health and Labour Sciences Research Grant for Research on Allergic disease and Immunology from the Ministry of Health Labour and Welfare of Japan.
Address correspondence and reprint requests to: Dr. Naoyuki Tsuchiya, Department of Human Genetics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan 113-0033.
E-mail: tsuchiya-tky@umin.ac.jp