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）是加速骨丢失和骨质疏松症的常见原因。尽管进行了广泛的研究，但PTH的骨分解代谢作用机制尚未完全阐明。PHP也是骨转换增加的重要原因，骨转换是骨折的独立危险因素。在4个体内和5个体外模型中的研究表明，T细胞通过膜结合共刺激分子CD 40 L向骨髓（BM）基质细胞（SC）提供存活、增殖和促破骨细胞生成信号。因此，T细胞缺陷型小鼠可免受PTH诱导的骨丢失。这是由于来源于T细胞缺陷型小鼠的BM SC数量较少，产生的破骨细胞生成细胞因子量较低，并且缺乏支持PTH诱导的破骨细胞（OC）形成的能力。T细胞上调SC数量和破骨细胞生成活性的能力通过T细胞中PTH受体PPR的沉默而消除。因此，我们推测，PTH直接刺激T细胞，以促进SC破骨细胞的活性，通过PTH受体PPR的信号传导，和T细胞调节SC的数量和活性，通过CD 40 L。本申请的目的是确定T细胞介导PTH的骨分解代谢活性的机制。在具体目标1中，我们将确定由PTH调节并介导PTH诱导的骨丢失的T淋巴细胞的表型。这将通过评估缺乏特异性T细胞亚群的小鼠中连续PTH治疗的效果来实现。在目的2中，我们将确定T细胞中的直接PPR信号传导在PTH诱导的OC形成和骨丢失中的作用。这将通过利用T细胞中缺乏PTH受体的条件性KO小鼠的T细胞来实现。我们还将确定T细胞中的PPR信号是否通过产生上调SC的破骨细胞生成活性的T细胞信号来刺激OC形成，以及T细胞中的PPR信号是否增加它们的RANKL、TNF和IL-1的产生以及它们的CD 40 L表达。在目标3中，我们将确定是否以自发方式调节SC破骨细胞生成活性的能力（而不是响应于PTH刺激），以及体内CD 40 L沉默是否阻止SC破骨细胞生成活性、OC形成和PTH诱导的骨丢失的增加。新的PTH作用机制的发现与公共卫生相关，因为它可能导致鉴定PHP、骨质疏松症和与终末期肾病相关的骨病的新治疗靶点。我们的研究也可以提供关于增强间歇性PTH治疗的合成代谢活性的策略的见解。一种这样的策略可能是拮抗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.