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Decline in IGF1 in CXCL12-Abundant Reticular (CAR) Cells Causes Myeloid-Biased Hematopoiesis Observed During Aging

ABSTRACT: Decline in hematopoietic function in aged individuals is associated with expansion of phenotypic hematopoietic stem cells (HSCs) and a shift in their lineage potential toward production of myeloid cells. Both HSC-intrinsic changes, and extrinsic changes in the bone marrow (BM) microenvironment, have been identified in old mice and humans. However, to extend healthy and robust hematopoietic function from youth into older age, we need to understand and effectively target the processes that initiate functional hematopoietic decline. We recently identified decline in Insulin-Like Growth Factor 1 (IGF1) in the BM microenvironment as early as middle age to be an HSC-extrinsic initiating driver of HSC aging (Young et al., Cell Stem Cell 2021). As systemic IGF1 administration has significant undesirable side effects, we sought to comprehensively interrogate the cell population(s) in the BM microenvironment that are responsible for IGF1 decline, towards the goal of cell type-specific targeted therapy. We performed single cell RNA-seq to comprehensively profile hematopoietic and non-hematopoietic fractions of the BM in young (2-4mo; n = 5 biological replicates) and middle-aged (12-14mo; n = 10) mice. In young mice, we find Igf1 to be nearly entirely detected in the mesenchymal stromal cell populations Adipo-CAR and Osteo-CAR, and Igf1 is significantly reduced in expression in both populations in middle-aged mice. Using two independent mesenchymal stromal cell Cre mouse lines, Lepr-Cre and Prx1-CreERT2, we found that knockout of Igf1 resulted in myeloid-biased hematopoiesis that replicated aging phenotypes. This result was similar to our published work showing that knockout of Igf1 using Nestin-CreER causes myeloid-biased hematopoiesis. While these Cre models generally do not mark similar cell types, it has been shown that Lepr-Cre-expressing perisinusoidal stromal cells include cells that express certain Nestin transgenes. Using fluorescent reporters, we find that all three lines (Lepr-Cre, Prx1-CreERT2, and Nestin-CreER) overlap in expression in the CAR populations that abundantly express Igf1 in young mice. Taken together, our work identifies a new role for Cxcl12-abundant reticular cells in sustaining hematopoietic function through local IGF1 production and suggests that specifically targeting CAR cells to maintain or restore Igf1 expression during aging will have beneficial effects on lymphoid cell production and adaptive immunity.

ORGANISM(S): Mus musculus

PROVIDER: GSE210584 | GEO | 2023/01/01

REPOSITORIES: GEO

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Project description:Hematopoietic stem cells (HSCs) primarily reside in the bone marrow where signals generated by stromal cells regulate their self-renewal, proliferation, and trafficking. Endosteal osteoblasts and perivascular stromal cells including endothelial cells3, CXCL12-abundant reticular (CAR) cells, leptin-receptor positive stromal cells, and nestin-GFP positive mesenchymal progenitors have all been implicated in HSC maintenance. However, it is unclear if specific hematopoietic progenitor cell (HPC) subsets reside in distinct niches defined by the surrounding stromal cells and the regulatory molecules they produce. CXCL12 (stromal-derived factor-1, SDF-1) regulates both HSCs and lymphoid progenitors and is expressed by all of these stromal cell populations. Here, we selectively deleted Cxcl12 from candidate niche stromal cell populations and characterized the effect on HPCs. Deletion of Cxcl12 from mineralizing osteoblasts has no effect on HSCs or lymphoid progenitors. Deletion of Cxcl12 from osterix-expressing stromal cells, which includes CAR cells and osteoblasts, results in constitutive HPC mobilization and a loss of B lymphoid progenitors, but HSC function is normal. Cxcl12 deletion in endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 in nestin-negative mesenchymal progenitors using Prx1-Cre is associated with a marked loss of HSCs, long-term repopulating activity, HSC quiescence, and common lymphoid progenitors. These data suggest that osterix-expressing stromal cells comprise a distinct niche that supports B lymphoid progenitors and retains HPC in the bone marrow, while expression of CXCL12 from stromal cells in the perivascular region, including endothelial cells and mesenchymal progenitors, support HSCs. Total of three samples of two groups analyzed. Replica samples of CXCL12-abundant reticular (CAR) cells from two CXCL12-GFP knock-in mice and a combined sample of PDGFRa+ Sca+ CD45- lineage- cells from three Prx1-Cre Rosa26Ai9/+ Cxcl12gfp/+ mice were used and analyzed.