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A7633 - Targeting Cellular Senescence Prevents Cigarette Smoke-Induced Pulmonary Emphysema
Author Block: T. Cottage1, J. Kearley2, A. Berlin1, N. Peterson1, J. Connor1, R. Lemaire1; 1RIA, Medimmune, Gaithersburg, MD, United States, 2RIA, MedImmune, Gaithersburg, MD, United States.
Rationale - Senescent cell accumulation is a consequence of aging and plays a critical role in tissue remodeling following injury by depleting the stem cell pool and by secreting profibrotic factors. The pathophysiology of chronic obstructive pulmonary disease (COPD) resembles that of early aging and senescence. COPD lungs have cells with shortened telomeres and mitochondrial dysfunction, as well as diminished stem cell populations. Short telomeres and DNA damage from environmental toxins like cigarette smoke (CS) induces senescence at least in part by activating the cell cycle inhibitor CDK2NA (p16) pathway. This study evaluates the contribution of the p16 senescent pathway to CS-induced lung pathologies. Methods - p16 expression were assessed in human COPD lungs by immunohistochemistry (IHC). For mouse studies, we used a transgenic knockin/knockout mouse model where Luciferase gene (Luc) replaces the p16 coding sequence, combining p16 deletion and p16-promoter driven Luc activity in senescent cells (p16 KO). Wild type and p16 KO mice were exposed to CS for four months, then lungs evaluated for alterations in alveolar structure (histology) and function (Flexivent). Cytokine expression was evaluated using Luminex and ELISA assays. Alveolar Type II (ATII) were identified by Surfactant C IHC, together with EdU incorporation to identify proliferating cells. Results - p16 was prominent in COPD lungs and absent in normal. CS-exposed lungs of wild-type mice showed impaired pulmonary function that was associated with alveolar destruction, increased senescence (Luc activity and p21 expression), diminished cell proliferation, and fibrosis (collagen 3 and TGF1β). In comparison, CS-exposed lungs of p16 KO mice exhibited normal pulmonary function that associated with senescence and emphysema protection. Specifically, p16 KO lungs had 3-fold less air space enlargement, increased cell proliferation (46% Edu increase), and reduced fibrosis markers. Expression of cytokines known to be upregulated in COPD, MMP-12, IL-33, and TGF1β were downregulated in p16 KO lungs, likely contributing to structure preservation of CS-exposed alveoli. In addition, ATII cells were abundant in p16KO lungs, most likely contributing to alveolar maintenance and repair. Deletion of p16 diminished CS-induced senescence associated secretory factors (SASPs) and prevented a pro-inflammatory cytokine response. Conclusions- Taken together these data suggest that targeting senescence improves healthspan by preventing lung structure and functional alteration typically associated with lung CS exposure.