Novel drugs targeting TNF-alpha are available for treatment of RA. Fibroblast-like synoviocytes (FLSs) play a fundamental role in RA progression, through their expansion caused in part by resistance to cell death induction. The aim of our study was to determine the effects of different anti-TNF-alpha agents on FLS apoptosis.
FLS from patients with either RA or OA were co-cultured with peripheral blood mononuclear cells (PBMCs), and incubated with various drugs for 6 days. Subsequently, apoptosis induction was detected by Nucleosome ELISA and terminal deoxynucleotidyl transferase dUTP nick end labeling. Western blot was used to determine the activation of the phosphatase and tensin homologue deleted on chromosome 10 (PTEN)-focal adhesion kinase (FAK) pathway as well as Bax and Bcl-2 levels. Immunoprecipitation was used for studying phosphorylation of transmembrane TNF-alpha (tmTNF-alpha).
All the tested drugs induced apoptosis of FLSs in the presence of PBMCs obtained from the same patient only when the two cell populations were in direct contact by activating the PTEN-FAK pathway and increasing Bax levels. This effect was not due to antibody-dependent cell-mediated cytotoxicity. Only the two antibodies infliximab and adalimumab were able to up-regulate Bcl-2.
Etanercept is more effective in inducing FLS apoptosis compared with the other drugs tested. This induction is dependent on the presence of PBMCs, and involves the activation of PTEN-FAK pathway. Bcl-2 increase induced by the monoclonal antibodies infliximab and adalimumab may play a protective role and thus counteract their pro-apoptotic effect on FLSs.