Abstract 508: Endothelial Cell Telomerase Promotes Aberrant Cell Proliferation in Pulmonary Hypertension

Abstract

Background: Pulmonary arterial hypertension (PAH) is a progressive, severe disease with high morbidity and mortality. Mechanistically, early pulmonary vasoconstriction promotes cell proliferation and extensive vascular remodeling. Mammalian cell proliferation is dependent on telomerase expression; however, a mechanistic link between endothelial cell telomerase reverse transcriptase (TERT) and the control of mitogenic responses during the development of PAH has never been established. Hypothesis: Elevated telomerase levels in the diseased pulmonary endothelium induce proliferation of endothelial and smooth muscle cells in the pulmonary vasculature. Methods: We first received isolated pulmonary arterial endothelial cells from control subjects and patients with PAH. Autopsy sections obtained from patients were stained for endothelial cells, mitogenic markers, and TERT. Pooled primary pulmonary endothelial cells were used for in vitro experiments. Results: TERT expression was increased in the endothelium of pulmonary artery specimens of patients with PAH. Co-staining for the mitogenic marker PCNA confirmed high TERT expression specifically in proliferating cells. Key mechanistic stimuli causally involved in PAH, including hypoxia, inflammation, and vascular injury, increased mRNA and protein expression of TERT in pulmonary artery endothelial cells. TERT expression is necessary and sufficient for endothelial cell proliferation, as demonstrated through genetic TERT depletion and overexpression. Mechanistically, TERT supports the transcription of key endothelial growth factors, including vascular endothelial growth factor and epidermal growth factor, an effect that is mediated through TERT-dependent regulation of the transcription factor HIF1α. Conclusions: These data support the hypothesis that TERT promotes a proliferative phenotype of endothelial cells in PAH. Future experiments will investigate the cell-specific role of TERT in endothelial cell function and proliferation during the development of PAH using Cre/loxP recombination in mice harboring floxed TERT alleles.