Role of a new cytokine IL-34 in occurrence of osteoclast precursors and their movement to bone.

M-CSF和RANKL是从巨噬细胞分化为破骨细胞（OC）的必需细胞因子。IL-34是最近发现的M-CSF受体（M-CSFR）的配体。在这里，我们表明，IL-34是负责OC前体在脾脏中的分布。另一方面，M-CSF负责骨中的分布。我们发现活性维生素D可以诱导M-CSF缺陷op/op小鼠的OC发生。我们以前的研究表明，活性维生素D通过上调骨中RANKL增强体内OC发生。本研究揭示了活性维生素D在卵巢癌发生中的新作用。活性维生素D上调脾血管和骨中IL-34的表达。这导致促进OC前体从脾脏到血流的动员，随后它们沉降到骨。

M-CSF and RANKL are essential cytokines for differentiation from macrophages into osteoclasts (OCs). IL-34 is a recently discovered ligand for M-CSF receptor (M-CSFR). Here we show that IL-34 is responsible for the distribution of OC precursors in spleen. On the other hand, M-CSF is responsible for the distribution in bone. We found that active vitamin D could induce OCgenesis in M-CSF-deficient op/op mice. Our previous study showed that active vitamin D enhanced in vivo OCgenesis through the upregulation of RANKL in bone. In present study, we unveiled new roles of active vitamin D in OCgenesis. Active vitamin D upregulates IL-34 expressions in splenic blood vessels and bone. That results in facilitating the mobilization of OC precursors from spleen to blood stream and subsequent their settlement to bone.