GENETIC DELETION OF NATURAL KILLER CELL TRANSFORMING GROWTH FACTOR-β SIGNALING PROTECTS MICE FROM HYPOXIA-INDUCED PULMONARY HYPERTENSION

Abstract

<h3>BACKGROUND</h3> Pulmonary arterial hypertension (PAH) is a disease of obstructive vascular remodeling that is strongly linked to immune dysfunction. Natural killer (NK) cells are cytotoxic innate lymphoid cells that are known to contribute to vascular remodeling in pregnancy and cancer. Previous work has shown that NK cells from PAH patients exhibit an impaired phenotype that is linked to elevated transforming growth factor (TGF)-β signaling and that NK-deficient mice also develop pulmonary hypertension spontaneously. While these findings support a critical role for NK cell impairment in disease pathogenesis, the molecular mechanisms underlying this contribution are unknown. We hypothesize that TGFβ drives NK cell impairment in PAH, and that the selective deletion of TGFβ signaling in NK cells will protect against pathological vascular remodeling in disease. <h3>METHODS AND RESULTS</h3> NK cells from Tgfbr2NK-/- mice, bearing an NK-conditional deletion of the TGFβ type II receptor, exhibited insensitivity to TGFβ stimulation in vitro relative to cells from Tgfbr2NK+/+ littermate controls, as measured by flow cytometry for phosphorylated Smad2/3. Exposure of Tgfbr2NK-/- and Tgfbr2NK+/+ mice to chronic hypoxia (10% O2) for 21 days as a model of PAH caused an equivalent reduction in peripheral NK cell numbers in mice of both genotypes. However, assessment of right ventricular systolic pressure by closed-chest cardiac catheterization indicated that Tgfbr2NK-/- mice are partially protected from developing pulmonary hypertension relative to Tgfbr2NK+/+ controls (n= 11-13, p=0.056). Transthoracic echocardiography of the right ventricular outflow tract also demonstrated preserved RV ejection velocity in hypoxic Tgfbr2NK-/- mice relative to controls, indicating preserved right heart and pulmonary artery compliance in mice possessing NK cells that are insensitive to TGFβ. Immunofluorescent imaging of pulmonary arterioles for von Willebrand factor and a-smooth muscle actin revealed a hypoxia-induced muscularization of vessels in mice of both genotypes. Tgfbr2NK-/- mice also appear to have a developmentally altered pulmonary vascular tree, as indicated by a decrease in the total number of vessels per mm2 of distal lung tissue relative to Tgfbr2NK+/+ controls. <h3>CONCLUSION</h3> The genetic deletion of Tgfbr2 in NK cells was sufficient to protect mice from hypoxia-induced PAH. Further work is underway to understand how this conditional deletion affects the development of the pulmonary vasculature and the potential of targeting NK cell TGFβ signaling as a novel therapeutic strategy for PAH.