View Abstract

A2878 - Contrasting Effects of CD117+ Endothelial Cell Injection in Chronic Hypoxic- and Lung Fibrosis-Associated Pulmonary Hypertension
Author Block: D. Farkas1, S. Hultman1, A. R. Bhagwani1, C. Cool2, M. Valentine1, M. R. Kolb3, R. L. Heise4, M. C. Yoder5, M. Clauss6, R. J. Freishtat7, L. Farkas8; 1Virginia Commonwealth University, Richmond, VA, United States, 2University of Colorado Denver, Aurora, CO, United States, 3Mc Master Univ, Hamilton, ON, Canada, 4Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, United States, 5Indiana University School of Medicine, Indianapolis, IN, United States, 6IU School of Medicine, Indianapolis, IN, United States, 7Pediatrics, Children's National Med Ctr, Washington, DC, United States, 8Virginia Commonwealth Univ, Richmond, VA, United States.
Rationale: Subpopulations of the lung endothelial cells (ECs) have gained interest in recent years as to whether they can support vascular regeneration or contribute to the pathobiology of lung diseases, such as Pulmonary Arterial Hypertension (PAH). One particular population that has been attributed a high regenerative potential in mouse lungs are CD117+ ECs. Yet CD117+ cells also seem to contribute to PAH. We hypothesized that the environment in the lung and pulmonary circulation determines whether CD117+ EC promote vascular regeneration or contribute to pathological vascular remodeling.
Methods: CD117+ ECs were isolated from the lungs of rats with ubiquitous expression of enhanced green fluorescent protein (GFP), and enriched via a multi-step clonal selection protocol. These CD117+ EC clones were characterized using flow cytometry and endothelial function tests. Then, CD117+ EC clones were injected into rats that were exposed to chronic hypoxia to induce Pulmonary Hypertension (PH). In a second approach, CD117+ EC clones were given to rats followed by adenovirus-mediated overexpression of transforming growth factor-β (TGF-β), causing Pulmonary Fibrosis and associated PH. At endpoint, invasive right ventricular and pulmonary hemodynamics were obtained. Lung tissue was harvested for molecular biology and histology.
Results: CD117+ EC clones expressed EC markers, bound Griffonia simplicifolia lectin and showed EC function. In chronic hypoxic rats, CD117+ EC clones, but not CD117- control ECs, increased right ventricular systolic pressure (RVSP), associated with occlusion of pulmonary arteries by von Willebrand Factor (vWF)+ cells. However, the changes were at least partially reversible after cessation of chronic hypoxia. Based on analysis of gene expression in CD117+ ECs and lung tissue, we identified bone morphogenic protein 2, vascular endothelial growth factor-C and endothelin-1 as potential driver of CD117+ EC-induced additional vascular remodeling in chronic hypoxic rats. In stark contrast, injection of CD117+ EC clones protected from endothelial injury observed during transgenic overexpression of TGF-β and reduced associated PH. However, delayed administration of ECs after initial EC injury was not protective, indicating a close relationship between protective function and early vascular injury.
Conclusions: CD117+ EC clones have the potential to promote and to protect from vascular remodeling. The direction is determined by the underlying condition. The detailed mechanisms, e.g., shift in the TGF-β/bone morphogenic protein balance, for these divergent effects are currently under investigation.