The roles of retinoids and their receptors in haemopoiesis

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Haemopoietic stem cells (HSCs) are the most widely studied adult somatic stem cell. HSCs have huge potential, sustaining blood cell production throughout an individual's life. Cancers (leukaemias) and other disorders of the blood are largely treated by transplantation of HSCs. However, due to their rare occurrence, it is often difficult to obtain large numbers of HSCs for transplantation, especially from sources of HSCs such as cord blood. Furthermore, protocols requiring manipulation of HSCs, such as gene therapy, have been largely unsuccessful, in part due to the lack of success in growing HSCs outside of the body. In such situations, therefore, determining culture conditions that would enable us to grow HSCs outside of the body are highly desirable. This application is based on the studies of CIA, who recently made the novel discoveries that the vitamin A derivative, all-trans retinoic acid (ATRA) has different effects in the regulation of blood cell production. ATRA is currently used in the treatment of acute promyelocytic leukaemia, as it enhances the maturation of the leukaemic cells. CIA has demonstrated that ATRA has the opposite effect on HSCs, with recent data strongly suggesting that ATRA induces the expansion of HSCs outside of the body. The studies outlined in this proposal seek to further define the mechanisms involved in these effects of ATRA and other vitamin A derivatives (collectively termed retinoids) in the regulation of blood cell production. The first specific aim will determine how retinoids expand HSCs. The second specific aim will explore the roles of the different RARs in the regulation of blood cell production. These studies have direct clinical relevance in improving protocols for transplantation and gene therapy of HSCs. Furthermore, insight gained into the roles of retinoids in blood cell production may also lead to the improvement of treatments of various types of blood disorders.