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) signaling 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 signaling in pulmonary EC senescence during aging and the development of PH and emphysema.

To do this, differents points will be addressed:

The lung expression of sVEGFR1 and VEGF receptors characterized in the lung and ECs of young and old patients undergoing lung surgery, classified as emphysematous and non-emphysematous (Costemcells study). The effects of VEGF and/or sVEGFR1 treatment on human lung ECs studied (B-galactosidase staining and senescence markers). The lung expression of sVEGR1 and VEGF receptors assessed in young and old mice, as well as in mouse models of PH (exposure to chronic hypoxia) and emphysema (administration of elastase, elastin ± mice). The effects of sVEGFR1 overexpression selectively in the lung and the consequences studied on pulmonary emphysema and PAH, using mice overexpressing sVEGFR1 according to a tissue-specific and inducible Tet-on system.

Plasma sVEGFR1 levels are increased in patients with PAH (plasma Quebec Cohort), and this level is correlated with disease severity measured using different parameters such as pulmonary vascular resistance or cardiac index. Plasma sVEGFR1 is also increased with age in control patients.

We show in vitro that sVEGFR1 treatment of cultured ECs from patients (Costemcells study) leads to cellular senescence measured by B-galactosidase activity. Conversely, VEGF treatment reduces endothelial cell senescence and improves proliferation. Senescent ECs produce less sVEGFR1 in both controls and lung emphysema patients, with no differences between the two groups. Regarding VEGFR2 activity measured by pVEGFR2/VEGFR2 protein ratio, we did not observe any decrease with senescence. Also, no differences were found between controls and emphysema patients in both lung tissue and lung ECs.

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.

Next, to see if sVEGFR1 contribute to lung dysfunction during aging or the development of several diseases, another transgenic mice overexpressing sVEGFR1 in the lungs using SPC promoter was generated. These mice were studied under normoxia or hypoxia exposition. We expected to see an aggravation of hypoxic PH and/or the development of lung emphysema compared to control and littermate mice, results are in progress.

Enhanced VEGF signaling protects against pulmonary EC senescence while sVEGFR1 induces EC senescence with expected worsening effects on the development of PH.