PLK1-activating IFI16-STING-TBK1 pathway induces apoptosis of intestinal epithelial cells in patients with intestinal Behçet's syndrome

Inflammatory signals from immunological cells may cause damage to intestinal epithelial cells (IECs), resulting in intestinal inflammation and tissue impairment. Interferon-γ-inducible protein 16 (IFI16) was reported to be involved in the pathogenesis of Behçet's syndrome (BS). This study aimed to investigate how inflammatory cytokines released by immunological cells and IFI16 participate in the pathogenesis of intestinal BS. RNA sequencing and real-time quantitative PCR (qPCR) showed that the positive regulation of tumor necrosis factor-α (TNF-α) production in peripheral blood mononuclear cells (PBMCs) of intestinal BS patients may be related to the upregulation of polo like kinase 1 (PLK1) in PBMCs (P = 0.012). The plasma TNF-α protein level in intestinal BS was significantly higher than in healthy controls (HCs; P = 0.009). PBMCs of intestinal BS patients and HCs were co-cultured with human normal IECs (NCM460) to explore the interaction between immunological cells and IECs. Using IFI16 knockdown, PBMC-NCM460 co-culture, TNF-α neutralizing monoclonal antibody (mAb), stimulator of interferon genes (STING) agonist 2'3'-cGAMP, and the PLK1 inhibitor SBE 13 HCL, we found that PLK1 promotes the secretion of TNF-α from PBMCs of intestinal BS patients, which causes overexpression of IFI16 and induces apoptosis of IECs via the STING-TBK1 pathway. The expressions of IFI16, TNF-α, cleaved caspase 3, phosphorylated STING (pSTING) and phosphorylated tank binding kinase 1 (pTBK1) in the intestinal ulcer tissue of BS patients were significantly higher than that of HCs (all P < 0.05). PLK1 in PBMCs of intestinal BS patients increased TNF-α secretion, inducing IEC apoptosis via activation of the IFI16-STING-TBK1 pathway. PLK1 and the IFI16-STING-TBK1 pathway may be new therapeutic targets for intestinal BS.

Iguratimod inhibits osteoclastogenesis by modulating the RANKL and TNF-α signaling pathways

BACKGROUND

Iguratimod, a small molecular drug, has been proven to have effective bone protection for treatment of patients with bone loss-related diseases, such as rheumatoid arthritis (RA). However, the exact bone protective mechanism of iguratimod remains to be determined. The purpose of this study was to better explore the underlying mechanism of bone protection of iguratimod.

METHODS

Bone marrow monocytes from C57/BL6 mice were stimulated with either RANKL or TNF-α plus M-CSF. The effects of iguratimod on morphology and function of osteoclasts were confirmed by TRAP staining and bone resorption assay, respectively. The expression of osteoclast related genes was detected by RT-PCR and the activation of signal pathway was detected by Western blotting. We used rodent models of osteoporosis (ovariectomy) and of arthritis (modified TNF-α-induced osteoclastogenesis) to evaluate the osteoprotective effect of iguratimod in vivo.

RESULTS

Iguratimod potently inhibited osteoclast formation in a dose-dependent manner at the early stage of RANKL-induced osteoclastogenesis, whereas iguratimod had no effect on M-CSF-induced proliferation and RANK expression in bone marrow monocytes. Bone resorption was significantly reduced by both early and late addition of iguratimod. Administration of iguratimod prevented bone loss in ovariectomized mice. The blockage of osteoclastogenesis elicited by iguratimod results from abrogation of the p38、ERK and NF-κB pathways induced by RANKL. Importantly, Iguratimod also dampened TNF-α-induced osteoclastogenesis in vitro and attenuated osteoclasts generation in vivo through disrupting NF-κB late nuclear translocation without interfering with IκBα degradation.

CONCLUSIONS

Iguratimod not only suppresses osteoclastogenesis by interfering with RANKL and TNF-α signals, but also inhibits the bone resorption of mature osteoclasts. These results provided promising evidence for the therapeutic application of iguratimod as a unique treatment option against RA and especially in prevention of bone loss.