Down-regulation of Irf8 by Lyz2-cre/loxP accelerates osteoclast differentiation in vitro

Emi Saito, Dai Suzuki, Daisuke Kurotaki, Ayako Mochizuki, Yoko Manome, Tetsuo Suzawa, Yoichi Toyoshima, Takahiro Ichikawa, Takahiro Funatsu, Tomio Inoue, Masamichi Takami, Tomohiko Tamura (+2 others)
2016 Cytotechnology (Dordrecht)  
Interferon regulatory factor 8 (Irf8) is a transcription factor that negatively regulates osteoclast differentiation and Irf8 global knockout (Irf8 -/-) mice have been shown to have reduced bone volume resulting from increased osteoclast numbers. However, detailed analysis of the functions of Irf8 in osteoclast precursors with a monocyte/macrophage linage is difficult, because the population and properties of hematopoietic cells in Irf8 -/mice are severely altered. Therefore, to clearly
more » ... e the functions of Irf8 during osteoclastogenesis, we established myeloid cell-specific Irf8 conditional knockout (Irf8 fl/fl ; Lyz2 cre/? ) mice. We found that trabecular bone volume in the Irf8 fl/fl ;Lyz2 cre/? mice was not significantly affected, while exposure to M-CSF and RANKL significantly increased TRAP activity in vitro in osteoclasts that underwent osteoclastogenesis from bone marrow-derived macrophages (BMMs) induced from bone marrow cells (BMCs) of those mice by addition of M-CSF. Our results also showed that expression of Irf8 mRNA and protein in BMMs obtained from Irf8 fl/fl ;Lyz2 cre/? mice and cultured with M-CSF was reduced. These findings predicted that Lyz2/Lyz2-cre expression is induced when BMCs differentiate into BMMs in cultures with M-CSF. In osteoclast differentiation cultures, Lyz2 was gradually increased by M-CSF during the first 3 days of culture, then rapidly decreased by the addition of RANKL with M-CSF during the next 3 days. Furthermore, BMCs differentiated into osteoclasts while maintaining a low Electronic supplementary material The online version of this article (level of Lyz2 expression when cultured simultaneously with both M-CSF and RANKL from the initiation of culture. These findings suggest that Lyz2-cre expression is induced along with differentiation to BMMs by BMCs obtained from Irf8 fl/fl ;Lyz2 cre/? mice and cultured with M-CSF. In addition, Irf8 was downregulated by activation of the cre/loxP recombination system in BMMs and osteoclastogenesis was accelerated. Based on our results, we propose the existence in vivo of a new lineage of osteoclast precursors among BMCs, which differentiate into osteoclasts without up-regulation of Lyz2 expression.
doi:10.1007/s10616-016-0013-z pmid:27502007 pmcid:PMC5461233 fatcat:wnpeerhrcnbednpjhfeakrx7be