Rheumatoid arthritis (RA) is a chronic, symmetric, systemic autoimmune disease. Because insufficient apoptosis of fibroblast-like synoviocytes (FLS) is an important characteristic of RA, promoting apoptosis is considered a potential therapeutic tool for treating RA. We have previously found that daphnetin (7,8-dihydroxycoumarin, DAP) has a pro-apoptotic effect on fibroblast-like synoviocytes from collagen-induced arthritis (CIA) rats. In the present study, we further investigated the mechanisms of DAP-induced apoptosis in CIA-FLS. CIA-FLS were incubated with DAP for 48 h in the presence or absence of caspase inhibitors, including inhibitors of caspase-3, caspase-8, or caspase-9 or a pan-caspase inhibitor; then, a series of experiments were performed to evaluate the mechanisms of DAP-induced apoptosis. Our results showed that DAP markedly decreased cell viability and induced the apoptosis of CIA-FLS along with typical morphological and ultrastructural changes; moreover, DAP increased FasL, cytochrome c (Cyt-c), Bax, caspase-3, caspase-8, and caspase-9 mRNA expression and Bax, caspase-3, caspase-8, and caspase-9 protein expression. In contrast, DAP decreased Bcl-2 mRNA and protein expression and promoted the release of Cyt-c from the mitochondria into the cytosol; these effects were attenuated to varying degrees by pre-treatment with caspase inhibitors, especially with caspase-3 or caspase-9 inhibitors or a pan-caspase inhibitor. In conclusion, the current findings demonstrate that the DAP-induced apoptosis of CIA-FLS occurred mainly via a caspase-dependent pathway, in particular the mitochondrial pathway, and that the Bax/Bcl-2 ratio was involved in this process. Thus, DAP may be a potential therapeutic agent for RA.
Keywords: Apoptosis; Daphnetin; FLS; Mitochondrial pathway.
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