The Brd4 inhibitor PFI-1 reduces hypergammaglobulinemia, plasma cells and attenuates nephritis in MRL/lpr mice
Hypergammaglobulinemia and the production of high-affinity IgG autoantibodies are important features of SLE, therefore, we first evaluated the effect of the Brd4 inhibitor PFI-1 on serum levels of IgG and its isotypes in MRL/lpr mice. As shown in Fig. 6A, PFI-1 significantly reduced total IgG, IgG1, and IgG2a levels already after 6 weeks of treatment. We further found that serum levels of anti-ANA and anti-dsDNA IgG were decreased in PFI-1-treated mice compared with vehicle-treated mice (Fig. S6). In contrast, serum levels of complement C3 and C4 were increased in PFI-1-treated mice (Fig. S6). PFI-1 treatment markedly decreased glomerular IgG and C3 deposits, and significantly ameliorated mesangial matrix expansion, mesangial cell proliferation and perivascular injuries as well as tubulointerstitial inflammatory cell infiltration and lesions (Fig. 6B and C). This improvement in renal histology was associated with a significant reduction in proteinuria (Fig. 6D) and serum creatinine and BUN levels (Fig. 6E). These findings suggest a critical role of Brd4 in controlling the production of autoantibodies and the progression of lupus nephritis.
To further evaluate the effect of PFI-1 on the frequency of B cell subsets in MRL/lpr mice, B cells were isolated from lymph nodes, PBMCs and spleens of mice. Flow cytometric analysis showed a significant reduction of plasma cells (Fig. 6F and G) but not memory B cells (Fig. S7) from lymph node, spleen and PBMCs of PFI-1-treated MRL/lpr mice compared with DMSO-treated mice. Moreover, as shown in Fig. 6H, PFI-1 treatment also reduced the expression of BLIMP1, a critical transcription factor that regulates plasma cell differentiation. These data provide in vivo evidence for the role of Brd4 in controlling plasma cell differentiation.