Endoplasmic reticulum stress implication in fibroblast senescence in COPD.

<b>Background</b>: Senescence is a critical cellular process involved in COPD progression. The molecular mechanisms that trigger&nbsp;senescence in small airways fibroblasts (SAF) are not clearly identified. These cells secrete proinflammatory cytokines and resist to apoptosis. <i>In vitro</i> studies suggest endoplasmic reticulum (ER) stress is important in COPD pathogenesis but whether this is linked to senescence is unknown. <b>Aim</b>: Assess the role of ER stress and the related unfolded protein response (UPR) pathways in fibroblast senescence in COPD. <b>Methods</b>: SAF were isolated from peripheral lung tissue from COPD patients and age-matched non-smokers (NS). Expression of senescence markers p21, p16, p-γH2AX and UPR pathway actors p-IRE1, p-PERK, p-eIF2α, ATF4, ATF6α were evaluated by Western blotting or immunocytochemistry. To link ER stress to senescence, protein expression of senescence markers was evaluated in SAF treated with ISRIB, a specific inhibitor of p-eiF2α. Apoptosis was measured using a caspase 3 activity assay in SAF exposed to cigarette smoke extract (CSE) (5%) treated with or without ISRIB. <b>Results</b>: p21, p16 and p-γH2AX were increased in COPD SAF (n=6, 57%, 27% and 62%) as well as UPR markers p-IRE1, p-PERK and p-eIF2α (n=6, 53%, 65% and 63%). COPD SAF showed also an elevated nuclear localization of the UPR transcription factors ATF4 and ATF6α (n=4). ISRIB treatment decreased expression of p21, p16 and p-γH2AX in COPD SAF (n=6). CSE induced more active caspase 3 positive cells in NS (n=2, 43%) than in COPD (n=2, 14%), ISRIB treatment restored the apoptotic effect of CSE in COPD SAF (n=2, 35%). <b>Conclusion</b>: ER stress, especially the p-eIF2α pathway, may play a role in primary SAF senescence in COPD suggesting that this molecular pathway could be targeted for new therapeutic strategies