FATE OF THE OSTEOCLAST

骨质疏松症，随着年龄的增长骨骼质量的损失，是一个主要的健康问题 在美国这一过程在女性中加速， 由于雌激素的破骨细胞刺激作用引起的绝经 缺陷雌激素缺乏增加的确切机制 对骨吸收了解甚少。虽然有说服力 有证据表明，雌激素戒断增加破骨细胞 形成，破骨细胞寿命也增加的可能性， 没有被调查。破骨细胞活性增加后， 绝经似乎是由细胞因子介导的，如白细胞介素6（IL-6）。 6），白细胞介素1（IL-1）和肿瘤坏死因子（TNF），虽然 这些细胞因子的作用是否仅在破骨细胞上介导 产生或也对破骨细胞损失（例如，通过凋亡）的影响是 未知我们发现这些因素中的每一个都可以增加破骨细胞 在体外和体内产生，我们有间接证据表明， IL-1促进破骨细胞存活。人们普遍认为 破骨细胞是相对短寿命的细胞， 在骨重建的逆转阶段， 停止和形成开始。破骨细胞在逆转部位的命运 是未知的，但显然加速或延迟他们的消失是一个 骨吸收的潜在控制机制，并可能参与 骨质疏松症的发病机制。我们假设破骨细胞 在骨重建单位中经历程序性细胞死亡（凋亡）。我们 已经检查了正常小鼠的颅骨切片， 骨吸收由IL-1启动，并观察到破骨细胞凋亡 在骨重建单位中，主要在逆转部位。我们还 报道了表达SV 40 T抗原的转基因小鼠中的破骨细胞， 由抗酒石酸酸性磷酸酶（TRAP）启动子驱动， 凋亡从那以后我们重新检查了 正常小鼠，其中骨吸收由IL-1启动， 在骨重建单位中观察到破骨细胞凋亡，主要在 逆转位点。最近，我们已经修改了体外小鼠骨 骨髓源性破骨细胞培养系统，并检测凋亡 在细胞离心器制备的上清液中的破骨细胞进一步 培养24或48小时。在这个模型的初步实验中，我们 已经发现雌二醇和转化生长因子β（TGF β） 似乎促进破骨细胞凋亡，而1，25（OH）2维生素D3和 我们现在计划1）开发并充分描述一种 体外模型，以检查参与的调节和分子机制， 破骨细胞凋亡，2）确定凋亡是否是一个决定因素 体外和体内破骨细胞功能的影响，3）确定 雌二醇和细胞因子抗体，如IL-6，对破骨细胞 卵巢切除小鼠体内的细胞凋亡和存活，以及4）确定 细胞存活基因功能的丧失，如Bcl-2蛋白， 抑制骨吸收。如果凋亡是一个重要的决定因素， 破骨细胞活性和骨重建，那么这些研究可能 为调节骨重建速率提供新的分子靶点 与药理学试剂。

Osteoporosis, loss of skeletal mass with aging, is a major health problem in the United States. This process is accelerated in women after the menopause due to the osteoclast stimulating effects of estrogen deficiency. The precise mechanism by which estrogen deficiency increases bone resorption is poorly understood. Although there is convincing evidence to suggest that estrogen withdrawal increases osteoclast formation, the possibility that osteoclast life span is also increased has not been investigated. The increased osteoclast activity seen after the menopause appears to be mediated by cytokines, such as interleukin 6 (IL- 6), interleukin 1 (IL-1), and tumor necrosis factor (TNF), although whether the effects of these cytokines are mediated only on osteoclast generation or also on osteoclast loss (for example, by apoptosis) is unknown. We have found that each of these factors can increase osteoclast generation in vitro and in vivo,, and we have indirect evidence to suggest that IL-1 promotes osteoclast survival. It is generally accepted that osteoclasts are relatively short-lived cells that disappear from the bone surface during the reversal phase of bone remodeling when resorption ceases and formation commences. The fate of osteoclasts at reversal sites is unknown, but clearly acceleration or delay of their disappearance is a potential control mechanism for bone resorption, and could be involved in the pathogenesis of osteoporosis. We have hypothesized that osteoclasts undergo programmed cell death (apoptosis) in bone remodelling units. We have examined sections of calvarial bone from normal mice in which bone resorption was initiated by IL-1 and have observed apoptotic osteoclasts in bone remodelling units, predominantly at reversal sites. We have also reported that osteoclasts in transgenic mice expressing SV40 T antigen driven by the tartrate-resistant acid phosphatase (TRAP) promoter undergo apoptosis. We have since re-examined sections of calvarial bone from normal mice in which bone resorption was initiated by IL-1 and have observed apoptotic osteoclasts in bone remodelling units, predominantly at reversal sites. More recently, we have modified the in vitro mouse bone marrow-derived osteoclast culture system and have detected apoptotic osteoclasts in cytospin preparations of the supernatants after a further 24 or 48 hours of culture. In preliminary experiments with this model, we have found that estradiol and transforming growth factor-beta (TGFbeta) appear to promote osteoclast apoptosis, while 1,25 (OH)2 vitamin D3 and IL-1 prevent it. We now plan 1) to develop and fully characterize an in vitro model to examine the regulation and molecular mechanisms involved in osteoclast apoptosis, 2) to establish whether apoptosis is a determinant of osteoclast function in vitro and in vivo, 3) to determine the effects of estradiol and antibodies to cytokines, such as IL-6, on osteoclast apoptosis and survival in vivo in ovariectomized mice and 4) to determine whether loss of function of cell survival genes, such as Bcl-2 protein, inhibits bone resorption. If apoptosis is an important determinant of osteoclast activity and of bone remodelling, then these studies may provide new molecular targets for regulating rates of bone remodelling with pharmacologic agents.