T CELLS AND PTH INDUCED BONE LOSS

描述（由申请人提供）：原发性甲状旁腺功能亢进（PHP）是加速骨质流失和骨质疏松症的常见原因。尽管有广泛的研究，甲状旁腺激素骨分解代谢作用的机制尚未完全阐明。PHP也是骨转换增加的重要原因，这是骨折的独立危险因素。4个体内和5个体外模型的研究表明，T细胞通过膜结合的共刺激分子CD40L向骨髓（BM）基质细胞（SCs）提供存活、增殖和促破骨细胞生成信号。因此，T细胞缺陷小鼠可以防止甲状旁腺激素引起的骨质流失。这是由于来自T细胞缺陷小鼠的骨髓干细胞数量较少，产生的破骨细胞因子量较低，并且缺乏支持PTH诱导的破骨细胞（OC）形成的能力。T细胞通过沉默PTH受体PPR来消除T细胞上调SCs数量和破骨活性的能力。因此，我们假设PTH通过PTH受体PPR直接刺激T细胞促进SC破骨活性，T细胞通过CD40L调节SC数量和活性。本应用的目的是确定T细胞介导甲状旁腺激素骨分解代谢活性的机制。在特异性目标1中，我们将确定受甲状旁腺激素调节的T淋巴细胞的表型，并介导甲状旁腺激素诱导的骨质流失。这将通过评估在缺乏特异性T细胞亚群的小鼠中持续PTH治疗的效果来完成。在Aim 2中，我们将确定T细胞中直接PPR信号在PTH诱导的OC形成和骨质流失中的作用。这将通过利用T细胞中缺乏PTH受体的条件性KO小鼠的T细胞来完成。我们还将确定T细胞中的PPR信号是否通过产生上调SCs破骨活性的T细胞信号来刺激OC的形成，以及T细胞中的PPR信号是否增加RANKL、TNF和IL-1的产生以及CD40L的表达。在Aim 3中，我们将确定自发调节SC破骨活性的能力（而不是对PTH刺激的反应），以及体内CD40L的沉默是否能阻止PTH诱导的SC破骨活性的增加、OC形成和骨质流失。甲状旁腺激素的新作用机制的发现与公共卫生相关，因为它可能导致PHP，骨质疏松症和终末期肾脏疾病相关的骨病的新治疗靶点的确定。我们的研究也可能为增强间歇性甲状旁腺激素治疗的合成代谢活性的策略提供见解。其中一种策略可能是拮抗T细胞产生破骨细胞因子。

DESCRIPTION (provided by applicant): Primary hyperparathyroidism (PHP) is a common cause of accelerated bone loss and osteoporosis. In spite of extensive investigation the mechanism of the bone catabolic action of PTH has not been not been completely elucidated. PHP is also an important cause of increased bone turnover, which is an independent risk factor for fractures. Studies in 4 in vivo and 5 in vitro models suggest that T cells provide survival, proliferative and pro-osteoclastogenic signals to bone marrow (BM) stromal cells (SCs) through the membrane-bound costimulatory molecule CD40L. As a result, T cell deficient mice are protected against PTH induced bone loss. This is due to the fact that BM SCs derived from T cell deficient mice are fewer in number, produce lower amounts of osteoclastogenic cytokines, and lack the capacity to support PTH induced osteoclast (OC) formation. The capacity of T cells to upregulate both the number and the osteoclastogenic activity of SCs is abolished by silencing of the PTH receptor PPR in T cells. We thus hypothesize that PTH directly stimulates T cells to promote SC osteoclastogenic activity by signaling through the PTH receptor PPR, and that T cells regulate SC number and activity through CD40L. The goal of this application is to determine the mechanism by which T cells mediate the bone catabolic activity of PTH. In Specific Aim 1 we will determine the phenotype of the T lymphocytes which are regulated by PTH, and mediate PTH induced bone loss. This will be accomplished by evaluating the effect of continuous PTH treatment in mice lacking specific T cell subsets. In Aim 2 we will determine the role of direct PPR signaling in T cells in PTH induced OC formation and bone loss. This will be accomplished by utilizing T cells from conditional KO mice which lack the PTH receptor in T cells. We will also determine if PPR signaling in T cells stimulate OC formation by generating T cell signals which upregulate the osteoclastogenic activity of SCs, and if PPR signaling in T cells increases their production of RANKL, TNF and IL-1, and their expression of CD40L. In Aim 3 we will determine if the capacity to regulate SC osteoclastogenic activity in a spontaneous fashion (as opposed to in response to PTH stimulation) and if in vivo silencing of CD40L prevent the increase in SC osteoclastogenic activity, OC formation and bone loss induced by PTH. The discovery of new mechanisms of action of PTH is relevant to public health as it may lead to the identification of novel therapeutic targets for PHP, osteoporosis and the bone disease associated with end stage renal disease. Our studies may also provide insights on strategies for augmenting the anabolic activity of intermittent PTH treatment. One such strategy could be that of antagonizing T cell production of osteoclastogenic factors.