The role of Nox2-ROS-Nlrp3 interactions in the processes of hematopoietic stem cell engraftment

Delayed engraftment of hematopoietic stem/progenitor cells (HSPCs), or even failure to engraft, is still a significant clinical problem, mainly if the number of HSPCs is limited. The mechanisms that direct homing and engraftment of HSPCs after transplantation to BM are still not well understood. We propose that these processes could be enhanced by employing some safe, innovative, and efficient approaches. We will shed more light on these processes and propose new innovative strategies by i) improving the responsiveness of infused HSPCs so that they can better migrate toward a gradient of the main BM chemoattractant, stromal-derived factor 1 (SDF-1), and the two supporting BM chemoattractants, sphingosine-1-phosphate (S1P) and extracellular adenosine triphosphate (eATP), and ii) we will manipulate in BM microenvironment of transplant recipient a state of “sterile inflammation” induced by myeloablative condition for transplantation, to promote better homing and engraftment. Our pioneering data indicate that receptors for HSPCs chemoattractants, including CXCR4 for SDF-1, S1P1R for S1P, and P2X7 for eATP, have to be included in membrane lipid rafts (MLRs) for optimal migration and BM homing. These MLRs are assembled on the cell surface in response to NADPH oxidase 2 (Nox2) that generates reactive oxygen species (ROS) to trigger activation of Nlrp3 inflammasome. Thus, we propose that the Nox2-ROS-Nlrp3 inflammasome axis regulates the migration of HSPCs and their homing properties. Similarly, our data indicate that the same axis facilitates the homing response of the BM microenvironment after myeloablative conditioning before transplantation. Therefore, based on our intriguing published and preliminary evidence, we propose three interrelated specific aims. Specific Aim 1. To enhance the Nox2–ROS–Nlrp3 inflammasome-mediated MLRs formation to increase migration of HSPCs to BM chemoattractants. We will test strategies to improve the responsiveness of transplanted HSPCs to BM chemoattractants by increasing the formation of MLRs on HSPCs in Nox2–ROS–Nlrp3 inflammasome-dependent manner. Specific Aim 2. To enhance homing of HSPCs by modulating Nox2-ROS-Nlrp3 inflammasome mediated sterile inflammation in the recipient BM microenvironment after myeloablative conditioning for transplantation. Since myeloablative conditioning for transplantation fuels a state of “sterile inflammation” in the BM microenvironment that directs the homing of transplanted HSPCs, we will manipulate the state of sterile inflammation in the BM microenvironment to promote better homing and engraftment. Specific Aim 3. To explain at the cellular and molecular level, the role of the Nox2-ROS-Nlrp3 inflammasome axis in migration, homing, and engraftment of HSPCs. We will employ state of the art strategies to analyze cellular and molecular effects that regulate i) optimal MLRs-dependent migration of HSPCs and ii) sterile inflammation induced BM microenvironment that facilitates homing and expansion of transplanted HSPCs.