Genetic ablation of p16 leads to pulmonary remodeling, pro-senescence response, and immune modulation in mice exposed to low-dose, Sub-chronic, environmental tobacco smoke

OBJECTIVE: Cyclin-dependent kinase inhibitor 2 A, CDKN2A/p16INK4a (p16), is a gene involved in regulating the cell cycle, cellular senescence, and inflammatory responses. The role of p16 in pulmonary immune-inflammatory and cellular senescence responses to low-dose, sub-chronic environmental tobacco smoke (ETS) is not known. We hypothesized that p16-deficient (knockout, KO) mice would exhibit adverse lung responses compared to wild-type (WT) mice, characterized by a decline in lung function, impaired immune responses, lung remodeling, and dysregulated inflammatory responses at low-level ETS exposure. MATERIALS AND METHODS: C57BL/6J (WT) and p16 knockout, p16-/-, were exposed to low dose ETS [10 mg/m³ total particulate matter (TPM)] for 3 months. Bronchoalveolar fluid (BALF) and lung tissue were used in subsequent analyses. RESULTS: Histological analysis revealed mild alveolar simplification in p16 KO mice compared to WT mice. CDKN2A/p16 KO BALF did not have the same immune cell infiltration or cytokine response as the WT counterparts, where IL-17A, TNF-α, and GM-CSF were significantly elevated, indicating impaired immune response with p16 deficiency. Proteomic analysis revealed significantly elevated proteins related to inflammation, extracellular matrix remodeling, cellular metabolism, pro-senescence, and oxidative stress in p16 KO mice (Kynu, Col5a3, Lamtor3). NLRP3 and PTGS2 (COX-2) activation z-scores were lower in p16 KO mice, while IL33 and CCR5 activation z-scores were higher compared to WT mice. DISCUSSION: Thus, p16 deficiency amplifies ETS-induced alveolar architecture, impaired immune responses, and altered inflammatory pathways, contributing to heightened susceptibility to emphysema-like changes compared to WT mice even at low ETS levels. This study revealed that p16 deletion alters response to low-level ETS, not necessarily by amplifying the classic 'damage response' but by modifying immune and senescence signaling in the lungs. CONCLUSION: Overall, p16 has a complex and nuanced protective role in lung health, and careful targeting p16-related pathways could offer therapeutic strategies for mitigating chronic lung diseases.