Bcl-XL and Mcl-1 upregulation by calreticulin promotes apoptosis resistance of fibroblast-like synoviocytes via activation of PI3K/Akt and STAT3 pathways in rheumatoid arthritis.

OBJECTIVES: Fibroblast-like synoviocytes (FLS) play key roles in synovium hyperplasia and pannus formation in rheumatoid arthritis (RA). The present study was undertaken to explore the mechanisms that calreticulin (CRT) promoted anti-apoptosis of RA FLS. METHODS: The expression of CRT and anti-apoptotic proteins Bcl-XL and Mcl-1 in RA synovium were detected by immunohistochemistry. The expression of Bcl-XL and Mcl-1 in RA FLS by CRT were determined. The phosphorylation of Akt and STAT3 was detected by western blot. The effect of CRT on proliferation of RA FLS was examined by MTT assay. The ability of CRT to inhibit RA FLS apoptosis was assessed by flow cytometry. RESULTS: Increased expressions of CRT, Bcl-XL and Mcl-1 were detected in RA synovium compared with osteoarthritis (OA). Moreover, CRT expression correlated positively with Bcl-XL and Mcl-1 in RA, respectively. In vitro, CRT induced upregulation of Bcl-XL and Mcl-1 protein levels in RA FLS, in dose/time dependent manners. Upregulated expression of Bcl-XL and Mcl-1 induced by CRT were inhibited by PI3K/Akt or STAT3 pathways inhibitors in RA FLS, respectively. The increased phosphorylation levels of Akt and STAT3 were also detected with CRT incubation, in dose/time dependent manners. Additionally, CRT rescued apoptosis of RA FLS mediated by FasL. CONCLUSIONS: This study showed that upregulation of Bcl-XL and Mcl-1 expression in RA FLS by CRT were PI3K/Akt and STAT3 signal pathways dependent, and promoted the anti-apoptosis of RA FLS. Therefore, this may represent a therapeutic target for the treatment of RA.

STAT3/HIF-1α/fascin-1 axis promotes RA FLSs migration and invasion ability under hypoxia.

Rheumatoid arthritis (RA) synovium was identified as "tumor-like" tissues because of the hypoxic microenvironment, significant cell proliferation, and invasion phenotypes. It was reported that hypoxia promoted tumor aggressiveness via up-regulated expression of fascin-1 in cancer. However, the role of fascin-1 in RA synovial hyperplasia and joint injury progression remains unknown. In the current study, we first identified that both fascin-1 and HIF-1α were highly expressed in the RA synovium, in which they were widely colocalized, compared to osteoarthritis(OA). As well, levels of fascin-1 in RA fibroblast-like synoviocytes(FLSs) were found significantly higher than those in OA FLSs. Further, it was demonstrated that the mRNA and protein levels of fascin-1 in RA FLSs were up-regulated in hypoxia (3 % O2) and experimental hypoxia induced by cobalt chloride. Mechanistically, the HIF-1α-mediated hypoxia environment activated the gene expression of the fascin-1 protein, which in turn promoted the migration and invasion of RA FLSs. Accordingly, the restoration of FLSs migration and invasion was observed following siRNA-mediated silencing of fascin-1 and HIF-1α expression. Notably, under the experimental hypoxia, we found that the expression levels of fascin-1, HIF-1α, and p-STAT3 were increased in a time-dependent manner, and fascin-1and HIF-1α expressions were dependent on p-STAT3. Our results indicated that hypoxia-induced fascin-1 up-regulation promoted RA FLSs migration and invasion through the STAT3/HIF-1α/fascin-1 axis, which might represent a novel therapeutic target for the treatment of RA.