Regulation of osteoclast biology by anion exchanger SLC4A2 in mouse and human sys

描述（由申请人提供）：骨是一种动态组织，可以重塑生长，适应压力并保持完整性。两种细胞类型控制这一过程，成骨细胞（OB）和破骨细胞（OC），分别合成和降解骨。骨重塑中的病理不平等倾向于吸收而不是形成，导致骨质疏松症、类风湿关节炎和转移性骨癌等疾病。目前，超过3000万美国人骨量低，近1%的人患有类风湿性关节炎。这些疾病每年的医疗费用负担是巨大的。目前批准的针对OCs的治疗方法不足，需要发现新的靶点。为了吸收骨头，破骨细胞分泌盐酸。为了防止细胞质碱的相互积累，碳酸氢盐通过阴离子交换器进行氯离子的电中性交换。这种交换剂的身份一直无法确定，直到我们最近的报告显示，溶质载体家族4，阴离子交换剂，成员2 （Slc4a2, Ae2）在发育过程中对破骨细胞活性是绝对必需的。在缺乏它的情况下，小鼠会患上严重的骨质疏松症。最近发表的一篇文章已经在缺乏SLC4A2的牛身上发现了一种几乎相同的表型。迄今为止，只有少数突变被发现能如此显著地削弱破骨细胞吸收钙化组织的能力。我们的初步数据表明，SCL4A2在OC生理中起着意想不到的复杂作用。我们发现SLC4A2缺乏不仅会阻碍细胞正常分泌酸和进行阴离子交换，还会严重影响细胞骨架的组织。关于SLC4A2在OC中的生物学作用仍有许多重要的问题有待解决。我们不知道SLC4A2是否在发育后的骨重塑或炎症性骨骼疾病的发病机制中起重要作用。SLC4A2的细胞质和跨膜结构域对破骨细胞生物学调节的相对贡献尚不清楚。此外，人类破骨细胞是否利用SLC4A2尚不清楚。我们提出了四个具体目标来回答这些问题：1)确立SLC4A2的oc -内在作用，并解决骨硬化对SLC4A2 -/-小鼠致死表型的贡献；2)建立小鼠炎性关节炎模型对SLC4A2的需求；3)对SLC4A2在OCs中的结构-功能进行分析，4)确认SLC4A2在人类OCs中的作用。我将利用波士顿独特的环境来促进这些研究。与当地专家在阴离子交换生理学、OC细胞生物学、RA小鼠模型和RNA干扰方面建立了合作关系。通过分析一个如此深刻影响骨肉瘤生物学的基因的功能，该资助将促进对骨骼重塑的基本理解，对一般细胞生物学和信号转导做出重要贡献，最重要的是，确定抑制病理性骨质流失的新靶点。

DESCRIPTION (provided by applicant): Bone is a dynamic tissue that remodels to grow, adapt to stress and maintain integrity. Two cell types control this process, the osteoblast (OB) and the osteoclast (OC), which synthesize and degrade bone, respectively. Pathologic inequality in bone remodeling favoring resorption over formation leads to diseases such as osteoporosis, rheumatoid arthritis and metastatic bone cancer. Currently, over 30 million Americans have low bone mass and nearly 1% of our population suffers from rheumatoid arthritis. The yearly health care cost burden of these diseases is immense. Currently approved therapeutics targeting OCs are inadequate, necessitating the discovery of new targets. To resorb bone, osteoclasts secrete hydrochloric acid. To prevent a reciprocal build up of cytoplasmic base, electroneutral exchange of bicarbonate for chloride occurs through an anion exchanger. The identity of this exchanger eluded identification until our recent report showing Solute carrier family 4, anion exchanger, member 2 (Slc4a2, Ae2) is absolutely required for osteoclast activity during development. In its absence, mice develop profound osteopetrosis. A recent publication has identified a nearly identical phenotype in cattle that lack SLC4A2. To date, only a handful of mutations have been identified that so dramatically curtail the ability of osteoclasts to resorb calcified tissue. Our preliminary data suggest that SCL4A2 plays an unexpected complex role in OC physiology. We have found that SLC4A2 deficiency not only prevents OCs from properly secreting acid and performing anion exchange, but also profoundly affects the organization of their cytoskeleton. Many important questions remain regarding the biology of SLC4A2 in the OC. We do not know whether SLC4A2 is important in bone remodeling beyond the developmental period or in the pathogenesis of inflammatory skeletal disease. The relative contribution of the cytoplasmic and transmembrane domains of SLC4A2 to the regulation of osteoclast biology is unknown. Moreover, whether human osteoclasts utilize SLC4A2 is undefined. Four specific aims are proposed to answer these questions: 1) Establish the OC-intrinsic role of SLC4A2 and resolve the contribution of osteopetrosis to the lethal phenotype of Slc4a2-/- mice; 2) Establish the requirement of SLC4A2 in a mouse model of inflammatory arthritis; 3) Perform a structure-function analysis of SLC4A2 in OCs and 4) Confirm a role for SLC4A2 in human OCs. I will take advantage of the unique environment in Boston to facilitate these studies. Collaborations have been established with local experts in anion exchange physiology, OC cell biology, mouse models of RA and RNA interference. By analyzing the function of a gene that so profoundly affects OC biology, this grant will advance basic understanding of skeletal remodeling, make important contributions to general cell biology and signal transduction and, most importantly, define a new target to suppress pathologic bone loss.