Background/Purpose:   Apoptosis-resistant synovial fibroblasts (SFs) constitute the major cell component of pannus tissues in rheumatoid arthritis (RA). In tumor cells, the binding of inhibitory apoptosis stimulating protein of p53 (iASPP) with transcription factor p53 family members can inhibit the downstream apoptosis signaling. We hypothesized that iASPP molecule is involved in the RA pathogenesis, and examined whether dissociation of such binding can induce SFs apoptosis in the rheumatoid joint.

Methods: Peripheral mononuclear cells (MNCs) from active RA before and after a TNF inhibitor therapy and osteoarthritis (OA) patients were examined for their iASPP expression by real-time RT-PCR. Synovial tissues and purified SFs from RA and OA patients as well as normal and collagen-induced arthritis (CIA) rats were subjected to immunohistochemical (IHC) and immunofluorescent staining for the expression of iASPP and p73, a member of p53 family. SFs transfected with adenoviral vectors encoding 37 amino acid (Ad37AA), a hybrid small peptide corresponding to p53 residues, were subjected to TUNEL assay and real-time RT-PCR for apoptotic status and the expression of p53 upregulated modulator of apoptosis (PUMA), respectively. The association of iASPP with p73 in Ad37AA-transfected SFs was identified by anti-iASPP immunoprecipitation, followed by anti-p73 immunoblotting assay. Therapeutic effects of intra-articular injection of Ad37AA on CIA joints were evaluated by articular index and histological score. Further synovial IHC staining was performed to analyze PUMA and IL-6 expression levels and SFs densities, and in situ apoptotic cells in synovial tissues were detected by the TUNEL assay.

Results: There were reduced iASPP levels by targeting TNF in MNCs from RA patients and increased iASPP levels with co-localized p73 expression in synovial tissues and purified SFs from RA patients and CIA 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 CIA joints with decreased SF densities, increased apoptotic cells, higher PUMA and lower IL-6 expression levels.

Conclusion:   Our results demonstrate a pathogenic role of TNF-mediated up-regulation of iASPP and induction of SFs apoptosis by dissociating the iASPP binding with transcription factor p73 in the rheumatoid joint, implicating iASPP as a potential therapeutic target molecule in RA patients.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/dissociation-of-the-inhibitory-apoptosis-stimulating-protein-of-p53-iaspp-binding-with-transcription-factor-p73-induces-synovial-fibroblast-apoptosis-in-the-rheumatoid-joint/