AUTHOR=Kang Hui , Yang Kai , Xiao Lianbo , Guo Lei , Guo Changjun , Yan Yufei , Qi Jin , Wang Fei , Ryffel Bernhard , Li Changwei , Deng Lianfu 

TITLE=Osteoblast Hypoxia-Inducible Factor-1α Pathway Activation Restrains Osteoclastogenesis via the Interleukin-33-MicroRNA-34a-Notch1 Pathway

JOURNAL=Frontiers in Immunology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2017.01312

DOI=10.3389/fimmu.2017.01312

ISSN=1664-3224

ABSTRACT=<p>Functional cross-talk between osteoblasts and osteoclasts is a key process for bone homeostasis. Although osteoblast hypoxia-inducible factor-1α (HIF-1α) pathway activation results in impaired osteoclastogenesis <italic>via</italic> the direct regulation of osteoprotegerin (OPG), it is unclear whether there are other efficient mediators are involved in osteoblast HIF-1α pathway activation-restrained osteoclast formation. In addition to upregulated OPG, we observed that osteoblast HIF-1α activation led to increased interleukin-33 (IL-33) expression, which was found to inhibit osteoclastogenesis. Mechanistically, HIF-1α facilitates IL-33 expression by binding to −1,504/−1,500 bp on the <italic>Il-33</italic> promoter. IL-33, thereby, acts on bone marrow-derived monocytes (BMMs) to reduce their osteoclastic differentiation. Moreover, microRNA-34a-5p (miR-34a-5p)-inhibited Notch1 activation was observed to play a central role in this process. Thereby, the identification of IL-33-miR-34a-5p-Notch1 pathway in the inhibitory effect of osteoblast HIF-1α pathway on osteoclastogenesis uncovers a new mechanism for understanding the effects of HIF-1α on bone remodeling.</p>