Mechanisms Regulating Megakaryocyte Development

描述(申请人提供)：巨核细胞(MK)负责产生血小板，对血液动态平衡有重大影响。在血细胞中，MK在获得多倍体状态方面是独一无二的，这种状态先于血小板的生物生成。不受控制的MK增殖和失控的多倍化是某些血细胞病理的特征。我们最近的研究表明，赖氨酰氧合酶(LOX)参与了MK倍体和增殖的调节。这份修订后的竞争续签申请调查了LOX在这些过程中的作用。LOX是一种已知的纤维化反应的细胞外调节因子，通过交联性基质蛋白发挥作用。虽然MK释放的生长因子，如血小板衍生生长因子-ss(PDGF-ss)，已经在MK白血病相关骨髓纤维化的MK谱系的扩大中得到了证明，但这种情况的许多方面仍然难以捉摸，目前的治疗基本上是无效的。我们的初步发现表明，LOX在正常巨噬细胞池中低水平表达，主要是在低倍体细胞中。然而，LOX在与骨髓纤维化相关的退变巨噬细胞中大量存在，并被PDGF-ss上调。我们发现，抑制LOX酶的活性显著减少了PDGF-ss与细胞的结合以及PDGF-ss诱导的巨噬细胞的扩张。我们还做了一个新的观察，LOX-PP是LOX前处理的产物，它抑制MK多倍化。基于这些发现，我们假设LOX在退变或白血病MK中上调在MK扩张、多倍体抑制和基质沉积中起着关键作用。为了测试这一点，我们提出了三个具体的 目的：1.阐明LOX-PP对MK多倍化的作用机制；2.研究LOX对PDGF-ss诱导的MK增殖的作用机制；3.确定体内LOX表达改变对MK增殖、多倍体和骨髓纤维化的影响。了解LOX和LOX-PP如何调控MK的增殖和多倍化，将为控制这些过程确定新的靶点，为MK相关疾病的新治疗干预措施的发展提供信息，并为MK倍体和增殖的生理控制提供进一步的洞察力。

DESCRIPTION (provided by applicant): Megakaryocytes (MKs) are responsible for the production of platelets, which have a major impact on blood homeostasis. MK is unique among blood cells in attaining states of polyploidy, which precedes platelet biogenesis. Uncontrolled MK proliferation and deregulated polyploidization are hallmarks of some blood cell pathologies. Our recent studies implicate Lysyl Oxidase (LOX) in the regulation of MK ploidy and proliferation. This revised competitive renewal application investigates the role of LOX in these processes. LOX is a known extracellular regulator of the fibrogenic response, acting by cross-linking matrix proteins. Although the role growth factors released by MK, such as Platelet-Derived Growth Factor-ss (PDGF-ss), has been documented in the expansion of the MK lineage in MK leukemia-associated myelofibrosis, many aspects of this condition remain elusive, and current treatments are largely ineffective. Our preliminary findings indicate that LOX is expressed at low levels in a pool of normal MKs, primarily in the low-ploidy cells. However, LOX is abundant in displastic MKs associated with myelofibrosis, and is upregulated by PDGF-ss. We found that inhibition of LOX enzyme activity significantly diminished PDGF-ss binding to cells and PDGF-ss-induced expansion of MKs. We also made the novel observation that LOX-PP, a product of pre- LOX processing, inhibits MK polyploidization. Based on these findings, we hypothesize that upregulated LOX in displastic or leukemic MKs has a pivotal role in MK expansion, inhibition of polyploidy, and matrix deposition. To test this, we propose three specific aims: 1. Elucidate the mechanism of effect of LOX-PP on MK polyploidization; 2. Investigate the mechanism of effect of LOX on PDGF-ss-induced MK expansion; and 3. Determine the consequences of altered LOX expression in vivo on MK expansion, polyploidy and myelofibrosis. Understanding how LOX and LOX-PP regulates MK proliferation and polyploidization will identify new targets for control of these processes, informing the development of new therapeutic interventions for MK-related disorders and providing further insight into the physiological control of MK ploidy and proliferation.