Investigating the Heterogeneous Intercellular Signaling of Hematopoietic Stem and Progenitor Cells and its Changes around the Circadian Clock - PROJECT SUMMARY Blood regeneration must constantly adapt to bleeding, infection, injury, and disease. These processes rely on cell-cell communication to hematopoietic stem cells, HSCs, that are responsible for maintaining the homeostasis of the blood and immune systems. To fulfill this role, HSCs must engage in cell-cell communication with the surrounding cells in the bone marrow. Previous studies have demonstrated that some of these cells, including mesenchymal cells, vascular cells, and osteoblasts, referred to as their niche, play significant roles in regulating and maintaining HSCs via signaling pathways like KIT, CXCL, and VCAM. In these pathways, HSCs play the role of receiver by expressing the receptors for the ligands the niche cells produce. Several studies have suggested that HSCs play active roles in signaling within the bone marrow as well. Not only do they express the receptors for the ligands their niche produces, but they also secrete ligands to their microenvironment. However, individual HSCs do not have even access to these ligands in the dense, semi-fluid, heterogeneous bone marrow environment. This observation, coupled with the fact that gene expression within HSPC populations is heterogeneous, suggest significant signaling heterogeneity in the bone marrow. From my preliminary studies, HSCs exhibit heterogeneous signaling patterns with their niche, immune cells, and other hematopoietic progenitor cells (HPCs), some of which significantly correlate across individual cells. Further, it has been shown that HSPC homing to the bone marrow niche significantly alters with the circadian clock and preliminary data suggests circadian rhythms modulate gene expression and signaling in a lineage-specific manner. Given these preliminary findings, I hypothesize that individual HSPCs are engaged in diverse intercellular signaling pathways in the bone marrow that coordinate with each other and alternate around the circadian clock. The goal of this project is to better understand cell-cell signaling in the bone marrow between HSPCs and their microenvironment and how these signals influence their cell fate decisions and change around the circadian clock in the following three Specific Aims. Aim 1. To use single-cell RNA-sequencing data from HSPCs, their niche, and mature immune cells paired with single-cell spatial data from bone marrow to predict cell-cell signaling pathways. Aim 2. Determine intercellular signaling correlations to construct cell-cell signaling networks. Aim 3. Determine the impact of the circadian clock on HSPC’s intercellular signaling and production of blood and immune cells. In doing so, I will establish a compendium of potential pathways that influence HSPC fate decisions and elucidate the impact of circadian rhythms on HSPC signaling and blood and immune production.
