ERYTHROPOIETIN AND THE REGULATION OF ERYTHROPOIESIS

本研究的目的是加强对红细胞生成调节的理解，并将这些知识应用于临床贫血。人爆发形成单位-红细胞（BFU- e）和集落形成单位-红细胞（CFU）已经得到了高度纯化，BFU-红细胞生成素（EPO）受体的进化以及对EPO、干细胞因子（SCF）、白细胞介素-3 （IL-3）和胰岛素样生长因子I （IGF-I）的反应已经在无血清培养基中得到了很好的表征。研究表明，Fas （CD95）配体（FasL）组成性地存在于人红细胞祖细胞中，当干扰素（IFNgamma）诱导Fas的存在时，会产生自分泌和/或旁分泌细胞凋亡，这种凋亡可以用高浓度的SCF和EPO来克服。此外，EPO的退出激活Jun n -末端激酶（JNKs）和p38 MAP激酶，它们也会导致细胞凋亡。这些细胞现在将用于进一步研究IFNgamma产生凋亡的机制，通过描绘其对JNKs/p38 MAP激酶激活的影响，以及EPO抑制IFNgamma诱导的凋亡的机制。这将确定IFNgamma诱导的细胞凋亡是如何在人红细胞祖细胞中调控的，以及EPO是如何调节这一过程并防止细胞凋亡的。初步实验表明，IFNgamma激活JNKs和p38 MAP激酶，特异性反义寡核苷酸阻断这一作用，阻断IFNgamma诱导的细胞凋亡。我们还将研究一种死亡抗性途径篡位蛋白（与FLIP、CASH、CASPER相同）的作用。我们发现，篡位蛋白存在于正常的人CFU-E中，但在骨髓异常增生（MDS）骨髓细胞中显著降低，从而增强了细胞凋亡。我们将确定篡位蛋白的高表达是否会减少MDS骨髓细胞的凋亡。我们还证明了EPO和SCF对MAP激酶（ERK1/2）的主要协同激活，这是扩大红细胞生成所必需的，并且SCF和EPO通过不同的途径阻止细胞凋亡。我们将通过确定EPO和SCF刺激的红细胞生成中特定信号分子的作用来进一步研究这些转导系统。这些实验直接应用于了解慢性疾病贫血和MDS中细胞凋亡的增加，使人血细胞明显减少。

The aim of this research is to enhance understanding of the regulation of erythropoiesis and apply this knowledge to clinical anemias. Human burst-forming units-erythroid (BFU-E) and colony-forming units- erythroid (CFU) have been highly purified and the evolution of BFU- erythropoietin (EPO) receptors as well as response to EPO, stem cell factor (SCF), interleukin-3 (IL-3) and insulin-like growth factor I (IGF-I) have been well characterized in a serum-free medium. It has been shown that Fas (CD95) ligand (FasL) is constitutively present in human erythroid progenitors and when interferongamma (IFNgamma) induces the presence of Fas this produces an autocrine and/or paracrine apoptosis which can be overcome with high concentrations of SCF and EPO. In addition, withdrawal of EPO activates the Jun N-terminal kinases (JNKs) and p38 MAP kinase which also produce apoptosis. These cells now will be used to study further the mechanism by which IFNgamma produces apoptosis, by delineating its effect on JNKs/p38 MAP kinase activation, and the mechanism by which EPO inhibits IFNgamma-induced apoptosis. This will determine how IFNgamma- induced apoptosis is regulated in primary human erythroid progenitors and how EPO modulates this process and prevents apoptosis. Preliminary experiments demonstrate that IFNgamma activates JNKs and p38 MAP kinase and that specific antisense oligonucleotides block this and block IFNgamma-induced apoptosis. The role of one death resistance pathway Usurpin (which is the same as FLIP, CASH, CASPER) also will be studied. We have found that Usurpin is present in the normal human CFU-E, but is greatly decreased in myelodysplasia (MDS) marrow cells, which have enhanced apoptosis. We will determine if hyperexpression of Usurpin reduces apoptosis in MDS marrow cells. We also have demonstrated a major synergistic activation of MAP kinase (ERK1/2) by EPO and SCF, which is essential for expanded erythropoiesis, and that SCF and EPO prevent apoptosis through different pathways. We will further investigate these transduction systems by determining the role of specific signaling molecules in EPO- and SCF- stimulated erythropoiesis. These experiments have direct application to understanding the anemia of chronic disease and the increased apoptosis in MDS, which produces a marked decrease in human blood cells.