Imaging of vascular bone marrow niche in cardiovascular disease

Hematopoietic stem cells at the bone marrow (BM) niche generate excess inflammatory leukocytes harming the heart after a myocardial infarction (MI). Whether MI affects the hematopoietic organ’s microvasculature is unknown. Next, we performed intravital microscopy at the skull before and after MI to examine structural and functional changes, specifically (i) angiogenesis, (ii) integrin activation, (iii) vascular leakage and (iv) blood flow. (i) We imaged AplnCreER;Rosa26ZsGreen/+ reporter mice5, in which sprouting endothelial cells and their progeny express ZsGreen. We visualized (ii) fluorescent RGD probe that binds to integrin αVβ3. We studied (iii) endothelial barrier function with intravital time lapse imaging after labeling the blood pool with fluorescent albumin6. We assayed (iv) blood velocity in the skull BM. Next, we translated our microscopy studies towards non-invasive whole mouse imaging, enabling system-wide in vivo assessment of all hematopoietic sites. Using 68Ga-RGD PET and a gadolinium-labeled albumin, which relied on imaging agents corresponding to the fluorescent companions used for intravital microscopy, indicated increased integrin binding and higher vascular permeability in the femur after MI. Thus, MI triggers bone marrow endothelial dysfunction, leakage leading to systemic leukocytosis. Introducing a tool set to image bone marrow vascular changes, either with cellular resolution or noninvasively within the entire skeleton, allowed us to quantify remodeling of the vascular bone marrow niche, which stimulates hematopoiesis and production of inflammatory leukocytes after MI. Understanding and monitoring bone marrow vasculature in cardiovascular disease may provide a key to unlock therapeutic targets.