Activation of TLR7 increases CCND3 expression via the downregulation of miR-15b in B cells of systemic lupus erythematosus

Systemic lupus erythematosus （SLE） is an autoimmune disease characterized by B-cell hyperreactivity. The Toll-like receptor 7 （TLR7） signaling pathway is abnormally activated in SLE B cells. CyclinD3 （CCND3） plays an important role in B-cell proliferation, development, and differentiation. Although previous studies focused on the B cell-intrinsic role of TLR7 for the development of spontaneous germinal centers, the influence of TLR7 on CCND3 in SLE B cells is still not clear. Here, we used a B-cell profiling chip and found that CCND3 was related to SLE and significantly elevated in SLE B cells. Moreover, we determined that the expression level of CCND3 was higher, while miR-15b was significantly lower in the B cells from SLE patients and B6.MRL-Faslpr/J lupus mice compared to normal subjects. Furthermore, we demonstrated that the activation of TLR7 dramatically increased CCND3 expression but significantly decreased miR-15b in B cells in vitro and we identified that CCND3 is a direct target of miR-15b. To further confirm our results, we established another lupus model by topically treating C57BL/6 （B6） mice with the TLR-7 agonist imiquimod （IMQ） for 8 weeks according to the previously described protocol. Expectedly, topical treatment with I MQ also significantly increased CCND3 and decreased miR-15b in B cells of B6 mice. Taken together, our results identified that the activation of TLR7 increased CCND3 expression via the downregulation of miR-15b in B cells; thus, these findings suggest that extrinsic factor-induced CCND3 expression may contribute to the abnormality of B cell in SLE.

Ligation of CD180 inhibits IFN-α signaling in a Lyn-PI3K-BTK-dependent manner in B cells

A hallmark of systemic lupus erythematosus （SLE） is the consistent production of various auto-antibodies by auto-reactive B cells. Interferon-α（IFN-α） signaling is highly activated in SLE B cells and plays a vital role in the antibody response by B cells. Previous studies have shown that CD180-negative B cells, which are dramatically increased in SLE patients, are responsible for the production of auto-antibodies. However, the association between CD180 and IFN-αsignaling remains unknown. In the present study, we explored the effect of CD180 on regulating the activation of IFN-α signaling in B cells. We found that the number of CD180-negative B cells was increased in MRIJMp-Fas（Ipr/Ipr） lupus-prone mice compared with wild-type mice. Phenotypic analysis showed that CD180-negative B cells comprised CD138＋ plasmablast/plasma cells and GL-7＋ germinal center （GC） B cells. Notably, ligation of CD180 significantly inhibited the I FN-α-induced phosphorylation of signal transducer and activator of transcription 2 （STAT-2） and expression of IFN-stimulated genes （ISGs） in a Lyn-PI3K-BTK-dependent manner in vitro. Moreover, ligation of CD180 could also inhibit IFN-α-induced ISG expression in B cells in vivo. Furthermore, the Toll-like receptor 7 and Toll-like receptor 9 signaling pathways could significantly downregulate CD180 expression and modulate the inhibitory effect of CD180 signaling on the activation of I FN-a signaling. Collectively, our results highlight the close association between the increased proportion of CD180-negative B cells and the activation of IFN-α signaling in SLE. Our data provide molecular insight into the mechanism of IFN-α signaling activation in SLE B cells and a potential therapeutic approach for SLE treatment.