Abstract
Physiological regulation of blood flow in bone marrow is important to maintain oxygen and glucose supplies but also the physiological hypoxic state of the hematopoietic stem cell (HSC) niche. However, regulatory mechanisms underlying microcirculation in the bone marrow (BM) niche remain unclear. Here, we identify vessels functioning in control of blood flow in bone marrow and assess their contractility. To evaluate contractile potential of Alexa Fluor 633 (AF633; an arterial marker)-positive vessels, we performed immunohistochemistry for α-smooth muscle actin (α-SMA) and found it expressed around AF633+ vessels in the femoral and calvarial marrow. To validate AF633+ vessel contractility, we developed a simple system to locally administer vasoactive agents that penetrate BM through transcalvarial vessels. After exposure of the calvarial surface to FITC-dextran (70 kDa), FITC intensity in calvarial bone marrow gradually increased. When we evaluated the effect of transcalvarial administration (TCA) of norepinephrine (NE) on vascular tone of AF633+ arteries and behavior of transplanted blood cells, NE administration decreased artery diameter and transendothelial migration of transplanted cells, suggesting that adrenergic signaling regulates the HSC niche microcirculation and blood cell migration into the BM via effects on BMarteries. We conclude that TCA is a useful tool for bone marrow research.
Highlights
Physiological regulation of blood flow in bone marrow is important to maintain oxygen and glucose supplies and the physiological hypoxic state of the hematopoietic stem cell (HSC) niche
To determine whether Alexa Fluor 633 (AF633)+ vessels were surrounded by vascular smooth muscle cells (VSMCs), we stained sections obtained from femoral and calvarial bone marrow (BM) of AF633-injected mice with antibodies against α-smooth muscle actin (α-SMA) and CD31
Our findings further indicate that adrenergic signals from sympathetic nerves regulate local blood flow by inducing arterial vasoconstriction in BM
Summary
Physiological regulation of blood flow in bone marrow is important to maintain oxygen and glucose supplies and the physiological hypoxic state of the hematopoietic stem cell (HSC) niche. Much of our current understanding of homeostasis in many organs has emerged following use of multi-photon microscopy to visualize tissue-resident cells in vivo, a methodology that originated in the field of physiology[11,12]. Others have extended this technology to analysis of the murine calvarium to assess migratory behavior of osteoclasts and spatiotemporal intercellular interactionsofliving osteoblasts and osteoclasts[13,14,15]. We conclude that TCA allows detailed manipulation of the microcirculation during intravital imaging
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