The influence of "yin and yang" of purinergic receptors of the P2X and P1 type on the hematopoietic stem cell compartment

Purinergic signaling has emerged as a crucial regulatory network in hematopoiesis that affects the migration and proliferation of hematopoietic stem/progenitor cells (HSPCs). The central purinergic mediator is adenosine triphosphate (ATP), which, after releasing from the cells into the hematopoietic microenvironment as extracellular ATP (eATP), binds as a signaling ligand to the family of P2X purinergic receptors and promotes migration and proliferation of HSPCs. Subsequently, eATP is degraded in extracellular space by two cell surface-expressed ectonucleotidases CD39 and CD73 to its metabolite extracellular adenosine (eAdo), which in the negative feedback mechanism inhibits the positive effects of eATP. We found that murine and human HSPCs express at a high level three eATP binding functional P2X receptors - P2X1, P2X4, and P2X7, and at the same time, they express highly two P1 receptors for eAdo – A2A and A2B. Based on our preliminary data, we hypothesize that while eATP engaging P2X receptors stimulates intracellular pattern recognition receptor (PPR) Nlrp3 inflammasome (Nlrp3), eAdo signaling through P1 receptors has an opposite inhibitory effect on this PRR. Our novel data demonstrated that within the beneficial physiological range of activation in the so-called “hormetic zone,” Nlrp3 stimulates the trafficking and proliferation of HSPCs. It becomes activated by reactive oxygen species (ROS) and inhibited by heme oxygenase-1 (HO-1). While the intracellular level of ROS increases in cells stimulated by eATP, the intracellular level of HO-1 in cytosol increases in response to eAdo. Therefore, in this proposal, we would like to investigate in detail the positive (“yin”) P2 receptor-mediated and negative (“yang”) P1 receptor-mediated signaling effects on Nlrp3 inflammasome mediated HSPCs trafficking. We will perform our experiments using murine and human HSPCs, murine strains deficient in purinergic receptors, and employ small molecular modulators of investigated pathways. In parallel, we will analyze in-depth molecular changes at the mRNA and protein level by using state-of-the-art OMICS strategies. These studies will lead to the development of better stem cell mobilization and homing protocols and lead to more efficient ex vivo expansion of HSPCs.

This work was supported by the National Science Centre, Poland OPUS grant UMO- 2022/45/B/NZ3/00476.