Kanematsu M, Sato T, Takai H, Watanabe K, Ikeda K, Yamada Y
Department of Geriatric Research, National Institute for Longevity Sciences, Aichi, Japan.
J Bone Miner Res. 2000 Jul;15(7):1321-9. doi: 10.1359/jbmr.2000.15.7.1321.
Estrogen deficiency causes bone loss as a result of accelerated osteoclastic bone resorption. It also has been reported that estrogen deficiency is associated with an increase in the number of pre-B cells in mouse bone marrow. The present study was undertaken to clarify the role of altered B lymphopoiesis and of the receptor activator of nuclear factor-kappa B ligand (RANKL), a key molecule in osteoclastogenesis, in the bone loss associated with estrogen deficiency. In the presence of prostaglandin E2 (PGE2), the activity to form tartrate-resistant acid phosphatase (TRAP)-positive osteoclast-like cells was significantly greater in bone marrow cells derived from ovariectomized (OVX) mice than in those from sham-operated mice. Northern blot analysis revealed that PGE2 increased the amount of RANKL messenger RNA (mRNA) in bone marrow cells, not only adherent stromal cells but nonadherent hematopoietic cells; among the latter, RANKL mRNA was more abundant in OVX mice than in shamoperated mice and was localized predominantly in B220+ cells. Flow cytometry revealed that most B220+ cells in bone marrow were RANKL positive and that the percentage of RANKL-positive, B220low cells was higher in bone marrow from OVX mice than in that from sham-operated mice. The increase in the expression of RANKL and the percentage of these cells in OVX mice was abolished by the administration of indomethacin in vivo. PGE2 also markedly increased both the level of RANKL mRNA and cell surface expression of RANKL protein in the mouse pre-B cell line 70Z/3. Finally, osteoclastogenic response to PGE2 was reduced markedly by prior depletion of B220+ cells, and it was restored by adding back B220+ cells. Taken together with stimulated cyclo-oxygenase (COX)-2 activity by tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) in estrogen deficiency, these results suggest that an increase in the number of B220+ cells in bone marrow may play an important role in accelerated bone resorption in estrogen deficiency because B220+ cells exhibit RANKL on the cell surface in the presence of PGE2, thereby leading to accelerated osteoclastogenesis.
雌激素缺乏会因破骨细胞骨吸收加速而导致骨质流失。据报道，雌激素缺乏还与小鼠骨髓中前B细胞数量的增加有关。本研究旨在阐明B淋巴细胞生成改变以及核因子κB受体激活剂配体（RANKL，破骨细胞生成中的关键分子）在雌激素缺乏相关骨质流失中的作用。在前列腺素E2（PGE2）存在的情况下，去卵巢（OVX）小鼠骨髓细胞中形成抗酒石酸酸性磷酸酶（TRAP）阳性破骨细胞样细胞的活性显著高于假手术小鼠的骨髓细胞。Northern印迹分析显示，PGE2增加了骨髓细胞中RANKL信使核糖核酸（mRNA）的量，不仅是贴壁基质细胞，还有非贴壁造血细胞；在后者中，OVX小鼠的RANKL mRNA比假手术小鼠更丰富，并且主要定位于B220+细胞中。流式细胞术显示，骨髓中大多数B220+细胞为RANKL阳性，且OVX小鼠骨髓中RANKL阳性、B220low细胞的百分比高于假手术小鼠。体内给予吲哚美辛可消除OVX小鼠中RANKL表达的增加以及这些细胞的百分比。PGE2还显著增加了小鼠前B细胞系70Z/3中RANKL mRNA的水平和RANKL蛋白的细胞表面表达。最后，预先耗尽B220+细胞可显著降低对PGE2的破骨细胞生成反应，通过重新添加B220+细胞可使其恢复。结合雌激素缺乏时肿瘤坏死因子α（TNF-α）和白细胞介素-1（IL-1）对环氧化酶（COX）-2活性的刺激，这些结果表明骨髓中B220+细胞数量的增加可能在雌激素缺乏导致的骨质吸收加速中起重要作用，因为在PGE2存在的情况下，B220+细胞在细胞表面表达RANKL，从而导致破骨细胞生成加速。
