SummaryHematopoietic stem cells (HSCs) residing in the bone marrow (BM) accumulate during aging but are functionally impaired. However, the role of HSC-intrinsic and -extrinsic aging mechanisms remains debated. Megakaryocytes promote quiescence of neighboring HSCs. Nonetheless, whether megakaryocyte-HSC interactions change during pathological/natural aging is unclear. Premature aging in Hutchinson-Gilford progeria syndrome recapitulates physiological aging features, but whether these arise from altered stem or niche cells is unknown. Here, we show that the BM microenvironment promotes myelopoiesis in premature/physiological aging. During physiological aging, HSC-supporting niches decrease near bone but expand further from bone. Increased BM noradrenergic innervation promotes β2-adrenergic-receptor(AR)-interleukin-6-dependent megakaryopoiesis. Reduced β3-AR-Nos1 activity correlates with decreased endosteal niches and megakaryocyte apposition to sinusoids. However, chronic treatment of progeroid mice with β3-AR agonist decreases premature myeloid and HSC expansion and restores the proximal association of HSCs to megakaryocytes. Therefore, normal/premature aging of BM niches promotes myeloid expansion and can be improved by targeting the microenvironment.

Atherosclerosis is a chronic disease characterized by vascular lipid retention and inflammation, and pattern recognition receptors (PRRs) are important contributors in early stages of the disease. Given the implication of the intracellular PRR nucleotide‐binding oligomerization domain 1 (NOD1) in cardiovascular diseases, we investigated its contribution to early atherosclerosis. We evidenced NOD1 induction in atherosclerotic human and mouse tissues, predominantly in vascular endothelial cells. Accordingly, NOD1 genetic inactivation in Apoe−/− mice reduced not only atherosclerosis burden, but also monocyte and neutrophil accumulation in atheromata. Of note, in the presence of either peptidoglycan or oxidized LDLs, endothelial NOD1 triggered VCAM‐1 up‐regulation through the RIP2‐NF‐κB axis in an autocrine manner, enhancing firm adhesion of both sets of myeloid cells to the inflamed micro‐ and macro vasculature in vivo. Our data define a major proatherogenic role for endothelial NOD1 in early leukocyte recruitment to the athero‐prone vasculature, thus introducing NOD1 as an innovative therapeutic target and potential prognostic molecule.—González‐Ramos, S., Paz‐García, M., Rius, C., del Monte‐Monge, A., Rodríguez, C., Fernández‐García, V., Andrés, V., Martínez‐González, J., Lasunción, M. A., Martín‐Sanz, P., Soehnlein, O., Boscá, L. Endothelial NOD1 directs myeloid cell recruitment in atherosclerosis through VCAM‐1. FASEB J. 33, 3912–3921 (2019). http://www.fasebj.org