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

描述(申请人提供)：骨骼是一种动态组织，它可以重塑以生长、适应压力并保持完整性。有两种细胞控制着这一过程，成骨细胞(OB)和破骨细胞(OC)，它们分别合成和降解骨骼。骨重建中的病理不平等倾向于吸收而不是形成，会导致骨质疏松症、类风湿性关节炎和转移性骨癌等疾病。目前，超过3000万美国人患有低骨量，我国近1%的人口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的疗法是不够的，需要发现新的靶点。对于骨吸收，破骨细胞分泌盐酸。为了防止细胞质碱基的相互堆积，重碳酸盐通过阴离子交换器进行电中和交换以换取氯化物。直到我们最近的报告显示，溶质载体家族4，阴离子交换器，成员2(SLC4a2，AE2)对于发育过程中的破骨细胞活动是绝对必要的，这种交换器的身份一直没有确定。在缺乏它的情况下，小鼠会患上严重的骨化症。最近的一篇文章发现，在缺乏SLC4A2的牛中发现了几乎相同的表型。到目前为止，只发现了少数突变，这些突变极大地削弱了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生理学中发挥着意想不到的复杂作用。我们发现SLC4A2缺乏不仅阻碍OCS正常分泌酸和进行阴离子交换，而且还深刻地影响其细胞骨架的组织。关于SLC4A2在OC中的生物学，仍有许多重要的问题。我们不知道SLC4A2在发育期以后的骨重建中是否重要，或者在炎症性骨骼疾病的发病机制中是否重要。SLC4A2的细胞质和跨膜结构域对破骨细胞生物学调控的相对贡献尚不清楚。此外，人类破骨细胞是否利用SLC4A2还不确定。提出了四个具体的目标来回答这些问题：1)建立SLC4A2的OC内在作用，并解决骨化病对SLC4a2-/-小鼠致死表型的贡献；2)在炎性关节炎小鼠模型中建立SLC4A2的需求；3)进行SLC4A2在OCS中的结构和功能分析；4)确认SLC4A2在人类OCS中的作用。我将利用波士顿独特的环境为这些学习提供便利。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地影响OC生物学的基因的功能，这项资助将促进对骨骼重塑的基本理解，对普通细胞生物学和信号转导做出重要贡献，最重要的是，定义一个新的靶点来抑制病理性骨丢失。

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.