The nitric oxide pathway modulates hemangioblast activity of adult hematopoietic stem cells

Abstract

We have previously established a model inducing hematopoietic stem cell (HSC) production of circulating endothelial progenitor cells (EPCs) to revascularize ischemic injury in adult mouse retina. The unique vascular environment of the retina results in new blood vessel formation primarily from HSC-derived EPCs. Using mice deficient (؊/؊) in inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS), we show that vessel phenotype resulting from hemangioblast activity can be altered by modulation of the NO/NOS pathway. iNOS ؊/؊ or eNOS ؊/؊ animals were engrafted with wild-type (WT) HSCs expressing green fluorescence protein (gfp ؉ ) and subjected to our adult retinal ischemia model. WT hemangioblast activity in adult iNOS ؊/؊ recipients resulted in the formation of highly branched blood vessels of donor origin, which were readily perfused indicating functionality. In contrast, eNOS ؊/؊ recipients produced relatively unbranched blood vessels with significant donor contribution that were difficult to perfuse, indicating poor functionality. Furthermore, eNOS ؊/؊ chimeras had extensive gfp ؉ HSC contribution throughout their vasculature without additional injury. This neovascularization, via EPCs derived from the transplanted HSCs, reveals that the NO pathway can modulate EPC activity and plays a critical role in both blood vessel formation in response to injury and normal endothelial cell maintenance. ( IntroductionDuring embryogenesis, the hematopoietic and endothelial lineages arise from a common progenitor termed the hemangioblast. 1 We recently demonstrated that hemangioblast activity persists into adulthood by showing that adult hematopoietic stem cells (HSCs) produce both blood and blood vessels. 2 In adults, the relatively short lifespan of most blood cells necessitates replacement in large quantities each day to maintain homeostasis. Conversely, the endothelial vasculature in the eye can have up to a 4-year half-life in humans. When these vessels are replaced, it has been traditionally believed that the new endothelial cells (ECs) were derived solely from local EC proliferation. However, both ECs and endothelial progenitor cells (EPCs) were found in the circulation, posing the question whether cells of the vasculature can be formed from remote sources. 3,4 Multiple studies demonstrate the bone marrow (BM) origin of EPCs in a variety of ischemic and wound repair models. [5][6][7][8] In these models new vessel formation appears to be a combination of EC and EPC contributions, with ECs forming the majority of each new vessel. In contrast, ischemia or injury alone is not sufficient to induce neovascularization of the adult murine retina. Induction of retinal neovascularization requires both exogenous administration of vascular endothelial growth factor (VEGF) and ischemic injury. Providing both stimuli resulted in a highly proliferative retinopathy including new vessels protruding into the vitreous of the eye. 2 The pathology of our model is very similar to the proliferative stage of hum...

Role of MAdCAM-1 and Its Ligand on the Homing of Transplanted Hematopoietic Cells in Irradiated Mice

“…GFP blood chimeric mice have frequently been used for the study of hematopoietic stem cell plasticity [1,6,17]. HSPCs are believed to differentiate into blood vessels and replace injured ECs.…”

Vascular endothelial growth factor in eye disease

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Deficiency of Endothelial Nitric-Oxide Synthase Confers Susceptibility to Diabetic Nephropathy in Nephropathy-Resistant Inbred Mice

“…Because compensatory up-regulation of NOS isoforms has been demonstrated in retinal vasculature in eNOS KO mice, 29,30 we next asked whether glomerular lesions in diabetic eNOS KO mice were the result of reduced glomerular NO synthesis. Glomerular NO synthesis and NOS isoform expression were evaluated in isolated glomeruli as described in Materials and Methods.…”