The role of anti-apoptotic BCL-XL protein in the maintenance of human hematopoiesis

Abstract: Depletion of hematopoietic progenitor cells (HPCs) and their mature descendants by the use of conventional chemo/radiotherapies often leads to acute myelosuppression. In this condition, the primary hematopoietic stem cells (HSCs) can undergo differentiation and self-renewal to repopulate the peripheral hematopoietic system. Nevertheless, if the self-renewing ability of HSCs is compromised, then a fatal and irreversible damage to the hematopoietic system can occur. This damage to HSCs can be due to the use of anti-cancer therapies that are particularly toxic to them. To avoid the complete depletion of HSCs during chemotherapy or radiotherapy, there is a need to understand and investigate the pathways and mechanisms which are involved in the survival and regeneration of these early hematopoietic cells. The aim of this project was to determine whether BCL-XL is necessary for the survival of human hematopoietic stem and progenitor cells (HSPCs) and their descendants.
BCL-2 protein family members have been demonstrated to play an important role with regards to apoptosis. Cell death takes place when the BH3 domain of upstream pro-apoptotic BCL-2 family proteins (BH3-only proteins) binds to the anti-apoptotic BCL-2 proteins (i.e. BCL-2, MCL-1, A1, BCL-XL), thereby blocking their anti-apoptotic activity. Subsequently, other members of the pro-apoptotic BCL-2 protein subgroup (i.e. BAX and BAK) are activated and lead to disruption of outer mitochondrial membrane, followed by caspase activation.
Preclinical studies on murine models have shown that the depletion of BCL-2 pro-survival proteins increases vulnerability of HSPCs to cell death. Veis et al demonstrated that BCL-2 is essential for the survival of melanocytes, and mature lymphatic cells in mice. Similarly, depletion of the pro-survival BCL-XL protein has been reported to cause defects in neural tube closure, highly elevated apoptosis of HSCs in fetal liver, and even embryonic mortality in mice. Conditional deletion of BCL-X gene in murine hematopoietic system results in hemolytic anemia. Loss of BCL-XL in murine leads to their reduction in size and disruption of their morphology.
Based on these pre-clinical findings, it was expected BCL-XL might have important roles in the survival of human HSPCs as well. To test its role in the survival of human cord blood derived CD34+ HSPCs, Green Fluorescent Protein (GFP) expressing lentivirus system- based RNA interference technology was used. Knockdown of BCL-XL strongly reduced engraftment potential of human HSPCs in rag2-/-γc-/- immune compromised juvenile xenograft mice. Further, these cells exhibited severely compromised ability to give rise to and maintain erythroid populations. Megakaryocytes were also affected. Human erythroid massive amplification assays (HEMA) confirmed the loss of erythroid cells upon BCL-XL knockdown. Further, it was speculated whether overexpression of BCL-2 pro-survival protein or inhibition of its antagonist, BH3-only protein BIM, is able to rescue human HSPCs with BCL-XL knockdown phenotype. While the knockdown of BIM had no rescue effect, overexpression of BCL-2 compensated for the loss of human erythroid cells with BCL-XL knockdown. Therefore, it is reported here for the first time that BCL-XL is necessary for the successful engraftment of human HSPCs and their differentiation into erythroid and megakaryocytic lineage. Finally, BCL-2 overexpression but not inhibition of BIM can compensate for the loss of BCL-XL in human HSPCs

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2018

Classification and Topics

• Keyword: Hematopoiesis ; Maintenance

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2019
• Creator: Afreen, Sehar
• Contributor: Borner, Christoph ; Erlacher, Miriam ; Albert-Ludwigs-Universität Freiburg. Fakultät für Biologie

Further information

• DOI: 10.6094/UNIFR/17109
• URN: urn:nbn:de:bsz:25-freidok-171095
• Rights: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 10:54 AM CEST