Two transcription factors PU.1a and PU.1b have different functions in the immune system of teleost ayu

Transcription factor PU.1 is a regulator of macrophage function, however, the specific function of PU.1 in teleost monocytes/macrophages (MO/MФ) remains unknown. We determined the cDNA sequence of two PU.1 genes from ayu (Plecoglossus altivelis; PaPU.1a and PaPU.1b). Sequence comparisons showed that PaPU.1 were most closely related to the PU.1 of rainbow smelt (Osmerus mordax). The PU.1 transcripts were mainly expressed in the spleen, and their expression was altered in various tissues upon infection with Vibrio anguillarum. PaPU.1a and PaPU.1b proteins were upregulated in MO/MФ, after infection. RNA interference was employed to knockdown PaPU.1a and PaPU.1b to investigate their function in MO/MФ. The expression of inflammatory cytokines was regulated by PaPU.1a, but not PaPU.1b, in ayu MO/MФ upon V. anguillarum infection. Both PaPU.1a and PaPU.1b knockdown lowered the phagocytic activity of MO/MФ. Furthermore, PaPU.1b knockdown attenuated MO/MФ bacterial killing capability. Our results indicate that two PaPU.1 genes differentially modulate the immune response in ayu MO/MФ against bacterial infection.

N16 suppresses RANKL-mediated osteoclatogenesis by down-regulating RANK expression

N16 is an active protein existing in Pinctada martensi. Our previous studies have demonstrated that N16 inhibited osteoclast differentiation in vitro. To better understand how N16 regulates osteoclast differentiation, RAW264.7 cells, a murine monocytic cell line and murine bone marrow-derived macrophages (BMMs) were adopted. Treatment of RAW264.7 cells with RANKL activated osteoclastogenesis and N16 inhibited the formation of multinucleated osteoclasts and TRAP activity. The suppression occurred at the early stage of osteoclastogenesis. Moreover, we found that N16 inhibited PU.1 and MITF expressions, mirroring the inhibition of RANK expressions, indicating that N16 inhibited RANK expression by down-regulating the expressions of MITF and PU.1, thus preventing osteoclastogenesis.