p16-3MR: a novel model to study cellular senescence in cigarette smoke-induced lung injuries during aging

Cellular senescence and lung aging are associated with the pathogenesis of Chronic Obstructive Pulmonary Disease (COPD). COPD progresses with aging, and chronic smoking is the key susceptibility factor in lung pathological changes concurrent with biological aging. However, these processes involving cigarette smoke (CS)-mediated lung cellular senescence are difficult to distinguish. One of the impediments to study cellular senescence in relation to age-related lung pathologies is the lack of a suitable in vivo model. In view of this, we provide evidence that supports the suitability of p16-3MR mice to study cellular senescence in CS-mediated and age-related lung pathologies. p16-3MR mice has a trimodal reporter fused to the promoter of p16INK4a gene that enables detection, isolation and selective elimination of senescent cells, thus making it a suitable model to study cellular senescence. To determine its suitability in CS-mediated lung pathologies, we exposed young (12-14 months) and old (17-20 months) p16-3MR mice to 30-day CS exposure and studied the expression of senescent genes (p16, p21 and p53) and SASP-associated markers (MMP9, MMP12, PAI-1, and FN-1) in air- and CS-exposed mouse lungs. Our results showed that this model could detect cellular senescence using luminescence and isolate cells undergoing senescence with the help of tissue fluorescence in CS-challenged young and old mice. Our results from the expression of senescence markers and SASP-associated genes in CS-challenged young and old p16-3MR mice were comparable with increased lung cellular senescence and SASP in COPD. We further showed age-dependent alteration in the (i) tissue luminescence and fluorescence, (ii) mRNA and protein expressions of senescent markers and SASP genes, and (iii) SA-{beta}-gal activity in CS-challenged young and old p16-3MR mice as compared to their air controls. Overall, we showed that p16-3MR is a competent model to study cellular senescence in age-related pathologies and could help understand the pathobiology of cellular senescence in lung conditions like COPD and fibrosis.