Background In rheumatoid arthritis (RA), apoptosis-resistant synovial fibroblasts (SFs) constitute the major cell component of pannus tissues [1]. 37 amino acid (37AA), a hybrid small peptide corresponding to p53 residues, inhibits the binding of p53 family members with inhibitory apoptosis stimulating protein of p53 (iASPP), thus activating the downstream apoptosis signaling pathway in tumor cells [2].

Objectives We hypothesized that iASPP is involved in the RA pathogenesis, and examined whether dissociating the binding of p53 family members with this molecule can ameliorate experimental arthritis.

Methods Synovial tissues and SFs from RA and osteoarthritis patients were subjected to immunohistochemical (IHC) and immunofluorescent staining, respectively, for expression of iASPP and p73, a p53 family member molecule. Synovial tissues from male Sprague-Dawley rats immunized with type II collagen, were analyzed by IHC staining and real-time RT-PCR for expression of iASPP and p73. SFs transfected with adenoviral vectors encoding 37AA (Ad37AA), were subjected to TUNEL assay for apoptotic status and real-time RT-PCR for expression of p53 upregulated modulator of apoptosis (PUMA), a downstream apoptosis signaling molecule. The association of iASPP with p73 in Ad37AA-transfected SFs was identified by immunoprecipitation with anti-iASPP, followed by immunoblot with anti-p73. Therapeutic effects of intra-articular (i.a.) injection with Ad37AA on arthritis rats were evaluated by articular index and histological score. IHC staining was performed to analyze synovial expression of cadherin-11 (a specific SF marker), PUMA and IL-6, and apoptotic cells were detected by the TUNEL assay.

Results There were increased levels of iASPP with co-localized p73 expression in synovial lining layers and purified SFs from RA patients and arthritis rats. Enhanced cell apoptosis and increased PUMA expression were identified in Ad37AA-transfected SFs with lower iASPP-associated p73 levels. Articular indexes and histologic scores were reduced in Ad37AA-injected joints with decreased SF densities, increased apoptotic cells, higher PUMA expression and lower IL-6 levels.

Conclusions Our results demonstrate amelioration of experimental arthritis by dissociating the i.a. binding of p53 family members with iASPP to induce apoptosis in SFs, implicating this molecule as a potential therapeutic target in RA patients.

1. Bottini N et al. Nat Rev Rheumatol 2013;9:24–33.

2. Bell HS et al. J Clin Invest 2007;117:1008–18.

Acknowledgement We thank Dr. Kevin M. Ryan (Cancer Research UK Beatson Institute, Glasgow, UK) for providing pShuttleCMV-37AA adenoviral plasmids.

Disclosure of Interest None declared