RA RECEPTOR REGULATION ON HEMATOPOIETIC STEM CELLS

全反式维甲酸（ATRA）触发恶性早幼粒细胞的分化，现在是急性早幼粒细胞白血病（APL）患者标准缓解诱导/维持方案的一部分。然而，ATRA对其他造血前体的影响并没有得到很好的表征。我们最近积累的证据表明，活化的视黄酸受体增强相对早期的多能造血前体的产生和/或维持，所述造血前体包括辐射防护细胞、CFU-S以及短期和长期骨髓再生干细胞。这些观察结果表明，一个意想不到的和看似矛盾的双重作用，视黄酸受体在调节造血，其中一个作用是提高相对较晚的造血祖细胞的承诺和终末分化，但第二个作用是刺激增殖，也许自我更新的原始造血前体/干细胞。我们希望在本申请中探索的正是视黄酸受体的这种双重作用。特定目标I研究将尝试确定优化ATRA对液体悬浮培养物中造血干细胞生成/维持的影响的体外培养条件。特异性目标II将涉及直接确定ATRA是否在体外和体内增强造血干细胞的自我更新。具体目标III将解决的问题，是否ATRA增强与逆转录病毒载体转导造血干细胞的效率。在具体目标IV中，我们将试图确定在原始造血前体中可能受ATRA调控的靶基因，特别强调Hox基因的表达。这些研究将提供洞察RA受体在调节原始造血前体细胞的作用，也可能有直接的临床应用，体外扩增和造血干细胞的基因治疗。

All-trans retinoic acid (ATRA) triggers the differentiation of malignant pro-myelocytes and is now part of the standard remission induction/maintenance regimen for patients presenting with acute promyelocytic leukemia (APL). However, the effects of ATRA on other hematopoietic precursors is not as well characterized. We have recently accumulated evidence indicating that activated retinoic acid receptors enhance the generation and/or maintenance of relatively early multi- potent hematopoietic precursors including radioprotective cells, CFU-S, and short and long-term marrow repopulating stem cells. These observations suggest an unexpected and seemingly paradoxical dual role for retinoic acid receptors in regulating hematopoiesis, with one role being to enhance the commitment and terminal differentiation of relatively late hematopoietic progenitors but a second role being to stimulate the proliferation and perhaps self-renewal of primitive hematopoietic precursors/stem cells. It is this dual role of retinoic acid receptors that we wish to explore in the present application. The Specific Aim I studies will attempt to identify the in vitro culture conditions that optimize the ATRA effects on the generation/maintenance of hematopoietic stem cells in liquid suspension cultures. Specific Aim II will involve directly determining whether ATRA enhances the self- renewal of hematopoietic stem cells both in vitro and in vivo. Specific Aim III will address the question of whether ATRA enhances the efficiency of transducing hematopoietic stem cells with retroviral vectors. In Specific Aim IV we will attempt to identify the target genes that may be regulated by ATRA in primitive hematopoietic precursor with particular emphasis on Hox gene expression. These studies will provide insight into the roles of RA receptors in regulating primitive hematopoietic precursors and may also have direct clinical application to the ex vivo expansion and gene therapy of hematopoietic stem cells.