Mechanisms Regulating Megakaryocyte Development

描述（由申请人提供）：巨核细胞（mk）负责血小板的产生，血小板对血液稳态有重大影响。MK在获得多倍体状态的血细胞中是独一无二的，它先于血小板的生物发生。不受控制的MK增殖和不受控制的多倍体化是一些血细胞病理的标志。我们最近的研究表明赖氨酸氧化酶（LOX）参与了MK倍性和增殖的调控。修订后的竞争性更新申请调查了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剂，通过交联基质蛋白起作用。虽然MK释放的生长因子，如血小板衍生生长因子-ss (PDGF-ss)，在MK白血病相关骨髓纤维化的MK谱系扩展中发挥了重要作用，但这种疾病的许多方面仍然难以捉摸，目前的治疗在很大程度上是无效的。我们的初步研究结果表明，LOX在正常mk中表达水平较低，主要在低倍体细胞中表达。然而，LOX在与骨髓纤维化相关的非塑性mk中含量丰富，并被PDGF-ss上调。我们发现LOX酶活性的抑制显著降低了PDGF-ss与细胞的结合以及PDGF-ss诱导的mk的扩增。我们还观察到LOX- pp，一个LOX预处理的产物，抑制MK多倍体化。基于这些发现，我们假设在非塑性或白血病MK中上调的LOX在MK扩增、多倍体抑制和基质沉积中起关键作用。为了验证这一点，我们提出三个具体的

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.