Abstract 2624: Chronic Hypoxia Increases Bone Marrow-Derived Endothelial Cells of Non-Hematopoietic Stem Cell Origin, as Well as Macrophages of Hematopoietic Stem Cell Origin, in Pulmonary Vascular Lesions in Mice: Differential Roles of Bone Marrow-Derived Hematopoietic and Non-Hematopoietic Stem Cells in Pulmonary Hypertension
Background: Bone marrow (BM) stem cells differentiate into various vascular cells under pathological conditions. However, whether BM-derived cells incorporated into pulmonary vascular diseases (PVD) are of hematopoietic stem cell (HSC) origin or of non-HSC origin, is unknown. We tested the hypothesis that different BM stem cell fractions differentiate into discrete cell lineages in PVD in mice exposed to chronic hypoxia, by using BM chimeric mice transplanted with whole BM cells or a HSC-rich fraction.
Methods: Wild-type mice were lethally irradiated and transplanted with whole BM cells (2 x 106) (TNC study, n=25) or 6,500 cells from c-kit+, Sca-1+, Lin− HSC-rich fraction (KSL study, N=12), sorted by FACSaria sorter, from littermates expressing enhanced green fluorescent protein (eGFP). These animals were exposed to hypobaric hypoxia (380mmHg) for 21 days, or kept in the ambient air. Tissue sections were immunostained and analyzed by using laser scanning confocal microscopy, quantitatively.
Results: In the TNC study, the percentages of CD31+, eGFP+ BM-derived endothelial cells/whole CD31+ cells (4.0±0.5 vs 1.7±0.4 in normoxic mice, p<.05) and of adventitial MOMA2+, eGFP+ BM-derived macrophages/whole MOMA2+ cells (38.4±2.6 vs 20.0±5.0, p<.05) were higher in hypoxic mice than in normoxic mice. However, α-actin+, eGFP+ BM-derived smooth muscle cells were not found in either group investigated. The number of vimentin+, CD31−, eGFP+ BM-derived fibroblast in perivascular adventitia was not increased in hypoxic mice (1.9±0.6 vs 2.6±0.7 cells per vessel, ns). In the KSL study, CD31+, eGFP+ endothelial cells were rarely seen both in hypoxic and normoxic mice (0.5±0.2% vs 0.6±0.2%, ns). In contrast, MOMA2+, eGFP+ cells were more frequently seen in hypoxic mice (47.6±2.2% vs 29.1±3.7%, p<.05). Vimentin+, CD31−, eGFP+ BM-derived fibroblasts were confirmed, but not increased in hypoxic mice (1.9±0.4 vs 1.9±0.2 cells/vessel, ns).
Conclusions: BM-derived macrophages and endothelial cells, which were increased in PVD in mice exposed to chronic hypoxia, mainly originate from a HSC-rich fraction and a non-HSC-rich fraction, respectively. These findings suggest differential roles of BM-derived HSC and non-HSC in the development of pulmonary hypertension.