Article

Spleen serves as a reservoir of osteoclast precursors through vitamin D-induced IL-34 expression in osteopetrotic op/op mice

Division of Hard Tissue Research, Institute for Oral Science, School of Dentistry, Matsumoto Dental University, Nagano 399-0781, Japan.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 06/2012; 109(25):10006-11. DOI: 10.1073/pnas.1207361109
Source: PubMed

ABSTRACT

Osteoclasts are generated from monocyte/macrophage-lineage precursors in response to colony-stimulating factor 1 (CSF-1) and receptor activator of nuclear factor-κB ligand (RANKL). CSF-1-mutated CSF-1(op/op) mice as well as RANKL(-/-) mice exhibit osteopetrosis (OP) caused by osteoclast deficiency. We previously identified RANKL receptor (RANK)/CSF-1 receptor (CSF-1R) double-positive cells as osteoclast precursors (OCPs), which existed in bone in RANKL(-/-) mice. Here we show that OCPs do not exist in bone but in spleen in CSF-1(op/op) mice, and spleen acts as their reservoir. IL-34, a newly discovered CSF-1R ligand, was highly expressed in vascular endothelial cells in spleen in CSF-1(op/op) mice. Vascular endothelial cells in bone also expressed IL-34, but its expression level was much lower than in spleen, suggesting a role of IL-34 in the splenic generation of OCPs. Splenectomy (SPX) blocked CSF-1-induced osteoclastogenesis in CSF-1(op/op) mice. Osteoclasts appeared in aged CSF-1(op/op) mice with up-regulation of IL-34 expression in spleen and bone. Splenectomy blocked the age-associated appearance of osteoclasts. The injection of 2-methylene-19-nor-(20S)-1α,25(OH)(2)D(3) (2MD), a potent analog of 1α,25-dihidroxyvitamin D(3), into CSF-1(op/op) mice induced both hypercalcemia and osteoclastogenesis. Administration of 2MD enhanced IL-34 expression not only in spleen but also in bone through a vitamin D receptor-mediated mechanism. Either splenectomy or siRNA-mediated knockdown of IL-34 suppressed 2MD-induced osteoclastogenesis. These results suggest that IL-34 plays a pivotal role in maintaining the splenic reservoir of OCPs, which are transferred to bone in response to diverse stimuli, in CSF-1(op/op) mice. The present study also suggests that the IL-34 gene in vascular endothelial cells is a unique target of vitamin D.

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Available from: Yasuhiro Kobayashi
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    • "IL-34 is predominantly expressed in the spleen and not in bone, while M-CSF is expressed in both the bone and spleen. c-Fms+/RANK+ QOPs were not detected in the bone but were detected in the spleen of op/op mice.54 This suggested that QOPs moved from the spleen to the bone in response to M-CSF injections. "
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    ABSTRACT: Vitamin D was discovered as an anti-rachitic agent preventing a failure in bone mineralization, but it is now established that the active form of vitamin D3 (1α,25(OH)2D3) induces bone resorption. Discovery of the receptor activator of nuclear factor -κB ligand (RANKL) uncovered the molecular mechanism by which 1α,25(OH)2D3 stimulates bone resorption. Treating osteoblastic cells with 1α,25(OH)2D3 stimulates RANKL expression, which in turn induces osteoclastogenesis. Nevertheless, active vitamin D compounds such as calcitriol (1α,25(OH)2D3), alfacalcidol (1α(OH)D3) and eldecalcitol (1α,25-dihydroxy-2β-(3-hydroxypropoxy) vitamin D3) have been used as therapeutic drugs for osteoporosis, as they increase bone mineral density (BMD) in osteoporotic patients. Paradoxically, the increase in BMD is caused by the suppression of bone resorption. Several studies have been performed to elucidate the mechanism by which active vitamin D compounds suppress bone resorption in vivo. Our study showed that daily administration of eldecalcitol to mice suppressed neither the number of osteoclast precursors in the bone marrow nor the number of osteoclasts formed in ex vivo cultures. Eldecalcitol administration suppressed RANKL expression in osteoblasts. This review discusses how the difference between in vitro and in vivo effects of active vitamin D compounds on bone resorption is induced.
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    • "CSF-1 and IL-34 exhibit comparable activities in supporting the development, proliferation, and survival of macrophages and osteoclastogenesis in vitro, and the genetic disorders in Csf1 op/op mice are reduced by IL-34 to the same degree as by the secreted glycoprotein isoform of CSF-1 when either cytokine is transgenically expressed with the same CSF-1-spatiotem- poral expression pattern[18]. However, Csf1 op/op mice are not compensated completely by IL-34, which they normally express[18,48], suggesting nonredundant functions of these two cytokines that are determined by their different spatiotemporal expression patterns[18,48]. Thus, it is important to determine how IL-34 and CSF-1 functionally differ in their regulation of a variety of processes in hematopoiesis, immunity, and the brain. "
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    ABSTRACT: With the use of a mouse FDC line, FL-Y, we have been analyzing roles for FDCs in controlling B cell fate in GCs. Beside these regulatory functions, we fortuitously found that FL-Y cells induced a new type of CD11b(+) monocytic cells (F4/80(+), Gr-1(-), Ly6C(-), I-A/E(-/lo), CD11c(-), CD115(+), CXCR4(+), CCR2(+), CX3CR1(-)) when cultured with a Lin(-)c-kit(+) population from mouse spleen cells. The developed CD11b(+) cells shared a similar gene-expression profile to mononuclear phagocytes and were designated as FDMCs. Here, we describe characteristic immunological functions and the induction mechanism of FDMCs. Proliferation of anti-CD40 antibody-stimulated B cells was markedly accelerated in the presence of FDMCs. In addition, the FDMC-activated B cells efficiently acquired GC B cell-associated markers (Fas and GL-7). We observed an increase of FDMC-like cells in mice after immunization. On the other hand, FL-Y cells were found to produce CSF-1 as well as IL-34, both of which are known to induce development of macrophages and monocytes by binding to the common receptor, CSF-1R, expressed on the progenitors. However, we show that FL-Y-derived IL-34, but not CSF-1, was selectively responsible for FDMC generation using neutralizing antibodies and RNAi. We also confirmed that FDMC generation was strictly dependent on CSF-1R. To our knowledge, a CSF-1R-mediated differentiation process that is intrinsically specific for IL-34 has not been reported. Our results provide new insights into understanding the diversity of IL-34 and CSF-1 signaling pathways through CSF-1R.
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    • "Thus, both cytokines support cell growth and survival in cell culture studies (Chihara et al., 2010; Mizuno et al., 2011; Wei et al., 2010) and induce chemokines in human whole blood (Eda et al., 2010). IL-34 can also substitute for MCSF to support RANKL induced osteoclastogenesis (Baud'huin et al., 2010; Chen et al., 2011; Hwang et al., 2012; Nakamichi et al., 2012). The IL- 34 gene, when expressed under the control of the MCSF promoter, can rescue the bone, osteoclast and tissue-macrophage defects of CSF-1 op / op mice (Wei et al., 2010). "
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    ABSTRACT: The mononuclear phagocyte system is composed of monocytes, macrophages and dendritic cells and has crucial roles in inflammation, autoimmunity, infection, cancer, organ transplantation and in maintaining organismal homeostasis. Interleukin-34 (IL-34) and macrophage colony stimulating factor (MCSF), both signalling through the MCSF receptor, regulate the mononuclear phagocyte system. A single IL-34 and MCSF gene are present in tetrapods. Two types of MCSF exist in teleost fish which is resulted from teleost-wide whole genome duplication. In this report, we first identified and sequence analysed six IL-34 genes in five teleost fish, rainbow trout, fugu, Atlantic salmon, catfish and zebrafish. The fish IL-34 molecules had a higher identity within fish group but low identities to IL-34s from birds (27.2-33.8%) and mammals (22.2-31.4%). However, they grouped with tetrapod IL-34 molecules in phylogenetic tree analysis, had a similar 7 exon/6 intron gene organisation, and genes in the IL-34 loci were syntenically conserved. In addition, the regions of the four main helices, along with a critical N-glycosylation site were well conserved. Taken together these data suggest that the teleost IL-34 genes described in this report are orthologues of tetrapod IL-34.
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