COUNTER-REGULATORY MECHANISMS IN BONE MINERALIZATION

通过基因敲除模型，已经确定了存在于成骨细胞中的三种分子，它们影响骨矿物质的受控沉积，即碱性磷酸酶（TNAP）；PC-1（或Npps，核苷三磷酸焦磷酸水解酶同工酶，NTPPPH）和基因产物。我们的初步结果表明，来自TNAP-/-低磷酸症小鼠的原代成骨细胞在其基质囊泡（mv）中增加了无机焦磷酸盐（PPi）的水平，无机焦磷酸盐（PPi）是一种已知的矿化抑制剂。PPi是由ANK蛋白作用产生的。本研究的中心假设是TNAP在骨降解PPi去除矿化抑制剂中的关键作用。我们进一步假设PC-1是TNAP功能的直接拮抗剂，但ANK也可能拮抗TNAP依赖性基质钙化。此外，我们提出两种不同的骨骼TNAP拮抗剂PC-1和ANK的功能丧失将改善体内TNAP缺乏相关的骨软化症。相反，我们提出PC-1缺失小鼠和ank/ank缺失小鼠相关的高骨化将通过体内TNAP功能的丧失而得到改善。因此，我们的具体目标是：1 .验证PC-1和TNAP缺陷通过杂交相互挽救的假设；2。验证ank/ank和TNAP缺失小鼠也可以通过杂交相互拯救的假设；3。为了验证细胞内和细胞外PPi水平是调节PPi产生、降解和分泌的基因（PC-1、TNAP和ANK）表达的中心调节因子的假设。该提案将定义TNAP和PC-1/ANK通过影响PPi代谢作为反调控因子控制骨矿化的潜力，从而也解决了PPi代谢影响对TNAP、PC-1和ANK调节骨矿化能力的相对贡献。这些研究的完成将有可能为基质矿化减少和增加的疾病提供治疗方法。

Three molecules present in osteoblasts have been identified, by means of gene knock-out models, as affecting the controlled deposition of bone mineral i.e., alkaline phosphatase (TNAP); PC-1 (or Npps, a nucleoside triphosphate pyrophosphate hydrolase isozyme, NTPPPH) and the and gene product. Our preliminary results indicate that primary osteoblasts from TNAP-/- hyphosphastasia mice have increased levels of inorganic pyrophosphate (PPi), a known inhibitor of mineralization, in their matrix vesicles (MVs). PPi is produced by the action of the ANK protein. The central hypotheses to be tested in this proposal are that TNAP's key function in bone degradation of PPi to remove the mineralization inhibitor. We further hypothesize that PC-1 is a direct antagonist of TNAP function but also that ANK may antagonize TNAP-dependent matrix calcification. Furthermore, we propose that loss of function of two distinct skeletal TNAP antagonists, PC-1 and ANK, will ameliorate TNAP deficiency-associated osteomalacia in vivo. Conversely, we propose that the hyperossification associated with both PC-1 null mice and ANK-deficient (ank/ank) mice will be ameliorated by loss of function of TNAP in vivo. Thus, our Specific Aims are: I. To test the hypothesis that the PC-1 and TNAP deficiencies are mutually rescued by cross-breeding; II. To test the hypothesis that ank/ank and TNAP null mice are also mutually rescued by cross breeding; III. To test the hypothesis that levels of intracellular and extracellular PPi are central regulators of the expression of the genes (PC-1, TNAP, and ANK) that regulate PPi production, degradation and secretion. The proposal will define the potential for TNAP and PC-1/ANK to serve as counter-regulatory factors controlling bone mineralization through effects on PPi metabolism, and thereby also address the relative contribution of the effects on PPi metabolism to the ability of TNAP, PC-1 and ANK to regulate bone mineralization. Completion of these studies will potentially provide therapeutic approaches to disorders of both decreased and increased matrix mineralization.