CXCR4 signaling strength regulates hematopoietic multipotent progenitor fate through extrinsic and intrinsic mechanisms
How cell-extrinsic niche-related and cell-intrinsic cues drive lineage specification of hematopoietic multipotent progenitors (MPPs) in the bone marrow (BM) is partly understood. We show that CXCR4 signaling strength regulates localization and fate of MPPs. In mice phenocopying the BM myeloid skewing of patients with WHIM Syndrome (WS), a rare immunodeficiency caused by gain-of-function CXCR4 mutations, enhanced mTOR signaling and overactive Oxphos metabolism were associated with myeloid rewiring of lymphoid-primed MPPs (or MPP4). Fate decision of MPP4 was also affected by molecular changes established at the MPP1 level. Mutant MPP4 displayed altered BM localization relative to peri-arteriolar structures, suggesting that extrinsic cues contribute to their myeloid skewing. Chronic treatment with CXCR4 antagonist AMD3100 or mTOR inhibitor Rapamycin rescued lymphoid capacities of mutant MPP4, demonstrating a pivotal role for the CXCR4-mTOR axis in regulating MPP4 fate. Our study thus provides mechanistic insights into how CXCR4 signaling regulates the lymphoid potential of MPPs.