RA RECEPTOR REGULATION ON HEMATOPOIETIC STEM CELLS

全反式维甲酸(ATRA)可诱导恶性前髓细胞分化，现已成为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，全反式维甲酸对其他造血祖细胞的影响还没有得到很好的描述。我们最近积累的证据表明，激活的维甲酸受体可以促进相对早期的多潜能造血祖细胞的产生和/或维持，包括辐射防护细胞、CFU-S和短期和长期的骨髓再生干细胞。这些观察表明，维甲酸受体在调节造血方面具有意想不到且似乎自相矛盾的双重作用，一个作用是促进相对较晚的造血祖细胞的承诺和终末分化，第二个作用是刺激原始造血祖细胞/干细胞的增殖和自我更新。正是这种维甲酸受体的双重作用，我们希望在目前的应用中进行探索。我研究的具体目的将试图确定体外培养条件，以优化ATRA在液体悬浮培养中对造血干细胞生成/维持的影响。具体目标II将直接确定全反式维甲酸在体外和体内是否增强造血干细胞的自我更新。《特定目的III》将解决ATRA是否能提高逆转录病毒载体转导造血干细胞的效率的问题。在特定的目的IV中，我们将试图确定原始造血前体中可能受全反式维甲酸调控的靶基因，重点是HOX基因的表达。这些研究将有助于深入了解RA受体在调节原始造血祖细胞中的作用，并可能对造血干细胞的体外扩增和基因治疗具有直接的临床应用价值。

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.