Abstract
SDF-1/CXCR4 axis plays a principle role in the homing and engraftment of hematopoietic stem/progenitor cells (HSPCs), a process that defines cells ability to reach and seed recipient bone marrow niche following their intravenous infusion. However, the proper functioning of CXCR4 downstream signaling depends upon consistent optimal expression of both SDF-1 ligand and its receptor CXCR4, which in turn is variable and regulated by several factors. The constitutive active mutants of CXCR4 (N119A and N119S) being able to induce autonomous downstream signaling, overcome the limitation of ligand-receptor interaction for induction of CXCR4 signaling. Therefore, we intended to explore their potential in Chemotaxis; a key cellular process which crucially regulates cells homing to bone marrow. In present study, Tet-on inducible gene expression vector system was used for doxycycline inducible regulated transgene expression of CXCR4 active mutants in hematopoietic stem progenitor cell line K-562. Both of these mutants revealed significantly enhanced Chemotaxis to SDF-1 gradient as compared to wild type. Furthermore, gene expression profiling of these genetically engineered cells as assessed by microarray analysis revealed the up-regulation of group of genes that are known to play a crucial role in CXCR4 mediated cells homing and engraftment. Hence, this study suggest the potential prospects of CXCR4 active mutants in research and development aimed to improve the efficiency of cells in the mechanism of homing and engraftment process.
Highlights
Hematopoietic stem cell transplantation (HSCT) success primarily depends on the ability of intravenously transfused hematopoietic stem/progenitor cells (HSPCs) in circulation to cross the blood-bone marrow endothelial cell barrier and reach their niche in recipient bone marrow (BM), where they lodge and repopulate in order to resume hematopoiesis, a process termed as homing and engraftment [1,2]
SDF-1 binding to its receptor CXCR4 expressed on HSPCs, induces the active conformation of receptor resulting in G protein mediated downstream signaling that regulate cellular and molecular events which elicit cell homing and engraftment
The homing and engraftment efficiency appears to be dependent on the response of HSPCs to SDF-1, which in turn depends upon CXCR4 availability/expression on HSPCs [11,12]
Summary
Hematopoietic stem cell transplantation (HSCT) success primarily depends on the ability of intravenously transfused hematopoietic stem/progenitor cells (HSPCs) in circulation to cross the blood-bone marrow endothelial cell barrier and reach their niche in recipient bone marrow (BM), where they lodge and repopulate in order to resume hematopoiesis, a process termed as homing and engraftment [1,2]. The low homing and engraftment efficiency especially in context of low availability of donor CD34+ HSPCs is a major challenge ahead which limits the clinical applications of HSCT [3,4]. Specific modification or modulation of key molecular player of homing and engraftment may serve as a possible approach to make the limited number of available HSPCs more efficient in homing and engraftment. Pivotal role of SDF-1/CXCR4 axis has been well established in HSPCs homing and engraftment to BM. SDF-1 binding to its receptor CXCR4 expressed on HSPCs, induces the active conformation of receptor resulting in G protein mediated downstream signaling that regulate cellular and molecular events which elicit cell homing and engraftment. Autonomous signaling of CXCR4 without SDF-1 binding can be a possible approach to overcome the necessity of consistent optimal expression of both ligand and receptor in induction of CXCR4 downstream signaling cascade
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