RA RECEPTOR REGULATION ON HEMATOPOIETIC STEM CELLS

全反式维甲酸（ATRA）触发恶性前髓细胞分化，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还没有很好的表征。我们最近积累的证据表明，活化的视黄酸受体增强了相对早期多能造血前体的产生和/或维持，包括放射保护细胞、CFU-S和短期和长期骨髓再生干细胞。这些观察结果表明，维甲酸受体在调节造血过程中具有意想不到且看似矛盾的双重作用，其中一个作用是增强相对较晚的造血祖细胞的承诺和终末分化，另一个作用是刺激原始造血前体细胞/干细胞的增殖和自我更新。维甲酸受体的这种双重作用正是我们希望在目前的应用中探索的。Specific Aim I研究将尝试确定体外培养条件，以优化ATRA对液体悬浮培养中造血干细胞产生/维持的影响。特异性目的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。特异性目的III将解决ATRA是否增强逆转录病毒载体转导造血干细胞的效率的问题。在Specific Aim IV中，我们将尝试确定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。这些研究将深入了解RA受体在调节原始造血前体中的作用，并可能在造血干细胞的体外扩增和基因治疗中具有直接的临床应用。

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.