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Cellular senescence and senescence-associated secretory phenotype: comparison of idiopathic pulmonary fibrosis, connective tissue disease-associated interstitial lung disease, and chronic obstructive pulmonary disease.

Background
The senescence-associated secretory phenotype (SASP) develops due to cellular senescence during conditions such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). However, studies comparing the degree of cellular senescence and SASP between COPD and IPF are limited. Furthermore, to the best of our knowledge, no study has examined cellular senescence and/or SASP in connective tissue disease-associated interstitial lung disease (CTD-ILD).


Methods
To compare the degree of cellular senescence among COPD, IPF, and CTD-ILD, tissue samples from surgical lung biopsies or noncancerous tissue from lobectomy specimens of patients with lung cancer were subjected to immunostaining for p16 and p21. Double-staining for p16 and phosphorylated NF-κB was performed to verify the relationship between cellular senescence and SASP.


Results
There was a greater degree of enhancement of p16 and p21 expression in patients with IPF than in those with COPD and controls. Immunostaining for p16 revealed an enhanced expression of this marker in patients with COPD compared with that in controls. No significant differences were observed in the phosphorylated NF-κB expression rate of p16-positive and p16-negative cells among patients with IPF, CTD-ILD, and COPD.


Conclusions
Epithelial cells in patients with IPF express higher levels of both cellular senescence and SASP than those in patients with COPD or controls.