Receptor Protein Tyrosine Phosphatase α–Mediated Enhancement of Rheumatoid Synovial Fibroblast Signaling and Promotion of Arthritis in Mice

Abstract

Objective During rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) critically promote disease pathogenesis by aggressively invading the joint extracellular matrix. The focal adhesion kinase (FAK) signaling pathway is emerging as a contributor to RA FLS anomalous behavior. The receptor protein tyrosine phosphatase α (RPTPα), encoded by the PTPRA gene, is a key promoter of FAK signaling. Here we investigated whether RPTPα mediates FLS aggressiveness and RA pathogenesis. Methods Through RPTPα knockdown, we assessed FLS gene expression by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, invasion and migration in transwell assays, survival by Annexin V and propidium iodide staining, adhesion and spreading by immunofluorescence microscopy, and activation of signaling pathways by Western blotting of FLS lysates. Arthritis development was examined in Ptpra−/− mice using the K/BxN serum transfer model. The contribution of radiosensitive and radioresistant cells to disease was evaluated by reciprocal bone-marrow transplantation. Results RPTPα was enriched in the RA synovial lining. RPTPα knockdown impaired RA FLS survival, spreading, migration, invasiveness and responsiveness to platelet-derived growth factor, tumor necrosis factor and interleukin-1 stimulation. These phenotypes correlated with increased phosphorylation of SRC on inhibitory Y527 and decreased phosphorylation of FAK on stimulatory Y397. Treatment of RA FLS with an inhibitor of FAK phenocopied knockdown of RPTPα. Ptpra-deficient mice were protected from arthritis development, which was due to radioresistant cells. Conclusions By regulating phosphorylation of SRC and FAK, RPTPα mediates pro-inflammatory and pro-invasive signaling in RA FLS, correlating with promotion of disease in an FLS-dependent model of RA.

Abnormal PTPN11 enhancer methylation promotes rheumatoid arthritis fibroblast-like synoviocyte aggressiveness and joint inflammation

“…FAK phosphorylation levels are increased in RA synovial lining cells compared with normal synovial tissue (39), and DNA methylation abnormalities were identified within the FAK pathway in RA FLS (8). Additionally, we recently reported that another tyrosine phosphatase that promotes FAK activation — receptor PTP-α — also mediates the aggressiveness of RA FLS and promotes arthritis in mice (40). …”

“…RA FLS migration was assessed in Transwell chambers (Corning) as previously described (12, 40). Each experiment included 3 membranes per sample, and 4 fields were analyzed per membrane.…”

“…WT and Ptpn11 Het mice were lethally irradiated with 2 doses of 55 Gy and administered bone marrow from gender-matched WT congenic CD45.1 donor mice (40). KBxN pooled sera was administered to induce arthritis (see below) 10 weeks after irradiation.…”

“…Sections were prepared from tissue blocks (HistoTox) and stained with H&E and Safranin-O/Fast Green/Hematoxylin (Sigma-Aldrich). Histopathological scoring for inflammation, bone erosion, and cartilage erosion was performed as previously described (40, 46). Histologic analyses were performed in a blinded manner by 2 operators.…”

PTPN14 phosphatase and YAP promote TGFβ signalling in rheumatoid synoviocytes

“…We previously surveyed the expression of protein tyrosine phosphatases (PTPs) in FLS from patients with RA (RA FLS) and reported that PTPσ, PTPκ and PTPα promote the aggressiveness of RA FLS 5–7. In the same survey, non-receptor protein tyrosine phosphatase 14 (PTPN14, also known as PEZ) was found to be among the most highly expressed PTPs in RA FLS 8…”