Abstract 277: The Lung Side Population Contains a Multipotent Vascular Stem Cell which Contributes to the Pathology of Pulmonary Arterial Hypertension
Rationale: Pulmonary arterial hypertension (PAH) occurs as the result of a combination of vasoconstriction and vascular remodeling. Side population (SP) cells were named for their lateral location in Hoechst 33342 red vs. blue cytometric dot plot, and are enriched for multipotential stem cells found resident in many tissues including lung. Two recent breakthroughs in understanding the pathogenesis of pulmonary arterial hypertension (PAH) include, the recognition of the potential role of stem cells to contribute to vascular remodeling and platelet derived growth factor B (PDGFBB) as a co-factor in disease progression have led us to hypothesize that the lung side population (lung SP) contains multipotent endothelial (EC) progenitors that differentiate abnormally into myofibroblasts in response to PDGFBB and thereby contribute to the progression of PAH.
Methods: We identified the adult lung SP in vitro as a novel source of resident lung vascular endothelial progenitors by FACS of collagenase digested, Hoechst 33342 and CD45 stained adult mouse lung cell suspensions. Additionally, a murine model of hypobaric hypoxia induced PAH was used to test the effects of lung SP given intravenously on right ventricular hypertrophy and right ventricular systolic pressure.
Results: Studies in vitro demonstrated the stem cell characteristics of lung SP and their ability to typically differentiate into EC, as assessed by clonal analysis, a series of protein markers and angiogenic function. However, the differentiation of clonal lung SP in the presence of PDGFBB resulted in a phenotype switch of the lung SP cells into myofibroblast-like cells that did not express EC markers, but instead produced elastin and were contractile. Additional studies in vivo confirmed the ability of lung SP to augment the hypertensive response via increasing right ventricular hypertrophy as well as right ventricular systolic pressures.
Conclusions: These observations support the idea that lung SP cells are indeed multipotent EC progenitors and that they have the ability to exacerbate PAH. These studies provide a link between hypoxic PAH and the inability of stem cells to repair local vascular tissue, possibly due to abnormal myofibroblast differentiation at the expense of EC.