Loss of endothelial miR-126 drives age-related decline in hematopoiesis

Aging profoundly alters the bone marrow (BM) microenvironment and impairs hematopoietic stem cell (HSC) function. Here, we identify decrease of miR-126 derived from arteriolar endothelial cells (EC) as a key mechanism of impaired HSC self-renewal capacity during aging. In young BM, arteriolar EC express high levels of miR-126, which is transferred to HSC and supports these cells' homeostasis and functional integrity. Using young and aged wild-type, endothelial-specific miR-126 knockout (EC-miR-126 KO), EC-Spred1 knockout (a functional model of EC-miR-126 upregulation), and EC/Sca-1 dual fluorescent reporter mice, we show that age-related increase in inflammatory cytokines (such as TNFα) reduces EC miR-126 expression and in turn drives loss of miR-126high CD31+Sca-1high EC-lined arterioles in the aging BM niche. Loss of arterioles in turn decreases the EC miR-126 supply to HSC, leading to expansion of HSC with limited self-renewal capacity. Remarkably, administration of a synthetic miR-126 mimic oligonucleotide restores EC-HSC communication and rescues aging-related HSC dysfunction. Our findings uncover a novel, non-cell-autonomous mechanism of HSC aging and highlight EC-derived miR-126 as a promising therapeutic target to rejuvenate hematopoiesis.