Abstract 1965: The Identification of Resident Endothelial Stem Cells in the Progression of Pulmonary Arterial Hypertension
Proliferation of myofibroblasts in adult lung diseases such as pulmonary arterial hypertension (PAH) and fibrosis lead to vascular remodeling without functional tissue regeneration. A consequence of vascular hypertrophy and PAH is right heart failure. During pulmonary disease the stem cell differentiation program that normally generates endothelial cells (EC) is altered, leading to the generation of myofibroblasts, which contribute to vascular wall thickening. To identify putative lung stem cells, we performed flow cytometry on single cell lung suspensions to isolate side population (SP) cells, which efflux Hoechst 33342 dye. The SP cell population has been shown to contain stem cells in several mammalian tissues, including epithelial tissues and aorta. Next, we tested whether CD45neg SP stem cells could affect the pathophysiology of PAH. Freshly isolated CD45neg SP cells, CD45pos SP control and whole bone marrow control cells were injected intravenously into mice followed by hypobaric hypoxia, an inducer of PAH.
Results: Stem cell characteristics of the non-hematopoietic CD45neg lung SP cells were demonstrated using label retention assays and telomerase activity assays. We also found that these cells, as mixed or clonal populations, have the capacity to differentiate into several mesenchymal cell lineages, EC and myofibroblasts. In addition, both right ventricular hypertrophy and right ventricular systolic pressure were significantly exacerbated in animals injected with CD45neg SP cells. Our observations support the idea that CD45neg lung SP cells represent multipotent stem cells that have the ability to contribute to disease progression in PAH. The mechanism of action may include engraftment into vascular structures and contribution to remodeling or paracrine mechanisms. Further analysis of abnormal stem cell differentiation during PAH will be essential for the development of therapeutics that target the abnormal stem cell differentiation pathways in PAH.
This research has received full or partial funding support from the American Heart Association, AHA National Center.