Cell senescence in chronic lung disease – SENEC

Cellular senescence – defined by a stable arrest of the cell cycle coupled to stereotyped phenotypic changes – might play a causal role in a variety of lung pathologies, among which chronic obstructive pulmonary disease (COPD), predicted to be the third cause of death worldwide in 2020. COPD is characterized by slowly progressive airflow obstruction and emphysema due to destruction of the lung parenchyma, and is often associated with pulmonary hypertension (PH). No curative treatment is available for this disease. Senescent cells are increased in lungs from COPD patients and express a robust senescence-associated secretory phenotype (SASP), which is pro-inflammatory.
Our goal is to critically test the hypothesis that senescent cells drive the lung alterations seen in COPD, to understand the mechanisms, and to develop therapeutic interventions able to slow or delay the cell senescence process in vitro and the lung alterations in vivo.
Aim 1- To test the hypothesis that cellular senescence is CAUSAL in lung pathology.
Two ways to test this hypothesis:
a) Take advantage of a new mouse model that allows induction of senescence in targeted cells and see if this mimicks disease alterations observed in COPD or in PH. We will test the hypothesis that conditional deletion of the specific p53 ubiquitin-ligase Mdm2 (or its homologue Mdm4) in pulmonary endothelial cells (P-EC), alveolar epithelial cells (AEC), or fibroblasts in mice induces cell senescence, lung emphysema, and PH in the absence of lung aggression, or leads to an exaggerated phenotype during exposure to cigarette smoke (CS) or to chronic hypoxia.
b) Take advantage of a new mouse model that allows the elimination of senescent cells by combining mouse models of lung pathology with mice expressing a killer gene construct driven by the p16 promoter (p16-INK-ATTAC mice). We will test the hypothesis that treatment of p16-INK-ATTAC mice with AP20187 (which activates caspase 8 in p16 expressing cells), by eliminating p16 positive senescent cells: i) prevents the development of smoke-induced emphysema or reverses it; ii) prevents and reverses PH induced by chronic hypoxia exposure. Parallel studies will be performed with p16-luciferase mice to follow senescent cell appearance.
Aim 2- To understand the mechanisms underlying the replicative or premature cell senescence process in COPD and evaluate therapeutic interventions.
Two major pathways altered in COPD lungs will be explored:
a) Over-activation of the mTOR signaling pathway. We will test the hypothesis that activation of the mTOR complex 1 (mTORC1) is central to the cell senescence process in COPD, and that treatment of cells with mTORC1 inhibitors (low doses of rapamycin and metformin) delays the onset of cell senescence and suppresses the hyper-functional secretory phenotype of lung cells from COPD patients. We will question whether mTOR activation (by deleting TSC1 in targeted cells) in mice increases lung cell senescence and replicates lung alterations seen in patients with COPD and test pharmacological interventions in vivo that inhibit mTOR and suppress the SASP.
b) Altered telomere dependent and independent functions of telomerase in COPD and PH.
We will question whether mice with deletion of TERT or TERC (protein and RNA components of telomerase, respectively), exhibiting different telomere length, show various emphysema severity in response to CS, whether transgenic mice expressing TERT under the control of the p16 promoter (p16-TERT+ mice) are protected and investigate the modulation of TERT expression in the setting of COPD.
We will test the hypothesis that: -TERT overexpression drives pulmonary artery smooth muscle cell growth and PH development through independent telomere elongation function of TERT, - genetic or pharmacological inactivation of TERT protects against hypoxic PH in mice and, - p16-TERT+ mice develop an exaggerated PH phenotype.