Counteracting pulmonary vascular endothelial cell senescence to combat age-related lung dysfunction and pulmonary hypertension

Abstract

Senescent endothelial cells (ECs) represent 30 to 50 % of senescent lung cells during aging and/or development of several lung diseases, including pulmonary hypertension (PH) (Born E et al, Circulation 2023) and emphysema. One potential mechanism is impaired angiogenic vascular endothelial growth factor (VEGF) signalling due to increased production of the soluble form of VEGF receptor 1 (sVEGFR1) via alternative splicing of VEGFR1. sVEGFR1 then acts as a VEGF trap.

The objective is to evaluate the role of impaired VEGF signalling in pulmonary EC senescence during aging and the development of PH and emphysema.

To characterize the lung expression of sVEGFR1 and VEGF receptors in the lung endothelial cells of young and old patients (classified as emphysematous and controls) undergoing lung surgery, 90 patients will be included during the candidate PhD.

In parallel, the lung expression of sVEGFR1 and VEGF receptors will be assessed in young and old mice [developing moderate emphysema and PAH], as well as in mouse models of PH (exposure to chronic hypoxia combined to SUGEN) and emphysema (elastase, elastin± mice), and mice with elimination of senescent cells (ABT senolytic treatment), linked to the rarefaction of the pulmonary capillary network (ICAM-1/CD₃₁labelling) and the accumulation of senescent ECs (measurement of senescence and DNA damage markers p16, p21).

To counter EC senescence during aging and PH development, we generated a new mouse model overexpressing VEGF via a constitutive or tissue-specific inducible system allowing controlled delivery of VEGF from the liver to the lungs (VEGF-TG mice).

The lungs of aged mice compared to young mice have lower capillary density, manifested by a reduction in the number of ECs stained for ICAM1. Treatment of mice with the VEGF receptor inhibitor Sugen amplifies these effects and increases the number of p16-marked senescent ECs, thereby reducing the pulmonary capillary network, impairing pulmonary hemodynamics, and inducing emphysema. Lung expression of sVEGFR1 in mice developing hypoxic PH is increased and worsened by Sugen.

We show in vitro that sVEGFR1 treatment of cultured ECs from patients leads to cellular senescence. Conversely, VEGF treatment reduces endothelial cell senescence and improves proliferation. Senescent endothelial cells produce less sVEGFR1 in both controls and lung emphysema patients. Emphysema patients show higher EC senescence with higher p16 RNA level and B-galactosidase stained cells. ECs from emphysema patients show a lower cumulative PDL level than control patients. Furthermore, in both control and emphysema patients, there is a tendency towards decreased VEGFR1/2 and sVEGFR1 RNA expression in senescent ECs.

The results obtained in old VEGF-TG mice show the preservation of pulmonary microvascular density as well as the suppression of p16-stained cells and protection against pulmonary emphysema. Next, young mice overexpressing VEGF in the liver were exposed to hypoxia to observe whether they are protected from hypoxic pulmonary hypertension compared to control and littermate mice, results are in progress.

Enhanced VEGF signalling protects against pulmonary EC senescence and emphysema during aging, with expected protective effects on the development of PH.