B Cell OPG Production in Bone Homeostasis

描述（由申请方提供）：从未报道过B细胞在生理性骨转换中的体内作用。我们对B细胞敲除（KO）小鼠的生理性骨转换的初步研究表明，B细胞的消融导致骨吸收增强，从而导致骨质减少。我们的初步数据表明，驱动这种骨质减少的机制是骨保护素（OPG）骨髓缺陷的结果，骨保护素是NF-κ B配体受体激活剂（RANKL）的生理性诱饵受体，也是破骨细胞形成的强效抑制剂。尽管骨髓OPG的主要来源通常被认为是来自成骨细胞，但我们的初步数据表明，骨髓B细胞是骨髓微环境中骨保护素的一个重要且以前未被认识的来源，可能占骨中总OPG水平的一半。此外，我们还发现，由于B细胞OPG产生减少，CD 40和CD 40 L以及T细胞缺陷的小鼠同样遭受骨髓OPG缺陷。这表明，T细胞和B细胞是通过调节B细胞OPG产生的基础条件下的骨量的预示性保护者。基于这些数据，我们假设B细胞衍生的OPG对于体内生理骨量的稳定是必不可少的，并且在基础生理条件下，淋巴细胞是体内骨量的关键保护者。本R21申请的具体目的是提供明确和确定的证据，证明B细胞是体内生理性骨稳态的关键维持者，因为它们能够分泌大量浓度的OPG。具体目标1：Floxed OPG转基因小鼠的产生，以及条件B细胞特异性和成骨细胞特异性OPG缺失小鼠的产生。特定目的2：表征a）条件性B细胞特异性和B）条件性成骨细胞特异性OPG KO小鼠的骨表型。

DESCRIPTION (provided by applicant): An in vivo role for B cells in physiological bone turnover has never been reported. Our preliminary investigations into physiological bone turnover in B cell knock out (KO) mice demonstrate that ablation of B cells results in enhanced bone resorption leading to osteopenia. Our preliminary data suggests that the mechanism driving this osteopenia is the result of a bone marrow deficit in Osteoprotegerin (OPG), the physiological decoy receptor of Receptor Activator of NF-kB Ligand (RANKL) and a potent inhibitor of osteoclast formation. Although the major source of bone marrow OPG has generally been considered to be from osteoblasts, our preliminary data suggests that bone marrow B cells represent a considerable and previously unrecognized source of osteoprotegerin in the bone marrow microenvironment and may account for up to half of the total OPG levels in bone. Furthermore we show that mice deficient in CD40 and CD40L, and in T cells likewise suffer a deficit in bone marrow OPG, due to decreased B cell OPG production. This suggests that T cells and B cells are portent protectors of bone mass under basal conditions, through regulation of B cell OPG production. Based on this data we hypothesize that B cell derived OPG is essential for the stabilization of physiological bone mass in vivo and that under basal physiological conditions lymphocytes are critical protectors of bone mass in vivo. The Specific Aims of this R21 application are to provide an unambiguous and definitive demonstration that B cells are critical preservers of physiological bone homeostasis in vivo by virtue of their capacity to secrete copious concentrations of OPG. Specific Aim 1: The generation of a Floxed OPG transgenic mouse, and the production of conditional B cell specific, and Osteoblast specific, OPG null mice. Specific Aim 2: Characterization of the bone phenotypes of a) conditional B cell specific and b) conditional osteoblast specific, OPG KO mice.