Novel Evidence That the P2X1 Purinergic Receptor - Nlrp3 Inflammasome Axis Orchestrates Optimal Trafficking of Hematopoietic Stem Progenitors Cells (HSPCs)

Background. Extracellular adenosine triphosphate (eATP) and P2X family of purinergic receptors were for many years understudied and not fully appreciated as regulators of hematopoiesis. Nevertheless, our previous research demonstrated P2X purinergic receptors as important extracellular adenosine triphosphate (eATP) sensing receptors that promote migration, mobilization, and homing of hematopoietic stem progenitor cells (HSPCs) (Leukemia 2022;36(1):23-32;Stem Cell Rev Rep. 2020 16(5):954-967). Accordingly, mice deficient in expression of P2X4 and P2X7 receptors turned out to mobilize poorly HSPCs as well, as defective expression of these receptors on transplanted HSPCs or in bone marrow (BM) microenvironment of graft recipient mice led to defective homing, engraftment, and delayed hematopoietic reconstitution. We explained these defects as a result of an impaired activation of the downstream target from P2X4 and P2X7 receptors, that is, an intracellular pattern recognition receptor Nlrp3 inflammasome (Leukemia. 2018;32(9):1920-1931 andLeukemia 2022;36(1):248-256). The P2X receptor family consists of seven purinergic receptors (P2X1-7). We noticed that one of the members of this receptor family - the P2X1 receptor, which is the most sensitive to eATP receptor from P2X receptor family, is highly expressed on HSPCs. Aim of the study. This prompted us to investigate the potential novel, the underappreciated role of P2X1 in the trafficking of HSPCs. We also become interested if P2X1 receptor-mediated trafficking of HSPCs, also occurs similarly as P2X4 and P2X7 in Nlrp3 inflammasome-dependent manner. Materials and Methods. We employed mice with perturbed expression of P2X1 receptor and evaluated the migration of HSPCs to primary bone marrow (BM) chemoattractants, including SDF-1, S1P, and eATP. Subsequently, we assessed the role of P2X1 in G-CSF and AMD3100 mediated mobilization of HSPCs and homing and engraftment of these cells in wild-type (WT) animals. Finally, we evaluated the effect of P2X1 receptor stimulation on activation of Nlrp3 inflammasome by employing a Glow assay. Results. We report for the first time that the ion-gated P2X1 purinergic receptor is a novel regulator of migration, mobilization, homing, and engraftment of HSPCs. We also demonstrate that this most sensitive receptor from the P2X receptor family activates Nlrp3 inflammasome in HSPCs as a mediator as of its biological function. Conclusions. This study sheds light on the novel role of the P2X1 receptor in normal hematopoiesis. Our data demonstrates a novel role of P2X1 receptor in eATP mediated trafficking of HSPCs that occurs in Nlrp3 inflammasome-dependent manner. Therefore, this study sheds more light on the underappreciated role of P2X1 receptor in normal hematopoiesis and further supports a vital function of purinergic signaling in the mobilization, homing, and engraftment of HSPCs. It also demonstrates a regulatory link between purinergic signaling and innate immunity and the role of Nlrp3 inflammasome being an important novel orchestrator in these processes.

No relevant conflicts of interest to declare.