Endoplasmic reticulum stress implication in senescence of small airway fibroblasts from COPD patients

<b>Background:</b> In COPD, senescence of small airway fibroblasts (SAF) is closely related to the oxidative imbalance. The SAF secretome is characterised by a pro-inflammatory pattern that may drive small airway fibrosis. Molecular events leading to senescence are not clearly defined but <i>in vitro</i> studies suggest endoplasmic reticulum (ER) stress may be a key event in COPD pathogenesis. <b>Aim:</b> Assess the role of ER stress in SAF senescence. <b>Methods:</b> SAF were isolated from COPD lung tissue and age-matched non-smokers (NS) (n=6). Senescence (p21, γ-H2AX) and ER stress markers (p-IRE1, p-PERK, p-eIF2α, XBP1) were evaluated by Western blot. CXCL-8 and PAI-1 release were measured by ELISA. Co-expression of XBP1 and p21 was studied by immunochemistry. To link ER stress and senescence, SAF were exposed to ISRIB, a selective inhibitor of P-eIF2α and modification of senescence markers as well as the level of antioxidant markers (NRF2 stabilisation, <i>SOD3</i> expression, catalase activity) were evaluated. <b>Results:</b> At baseline, the expression of p21, γ-H2AX and CXCL-8 were increased in COPD SAF compared to NS (2.6, 3.2 and 2.7-fold-change). Phosphorylation of PERK and eIF2α was only observed in COPD SAF. XBP1 and p21 were co-expressed in the nucleus of ~35% of COPD SAF. ISRIB reduced expression of p21 and γ-H2AX (47% and 63% decrease, p&lt;0.01) as well as CXCL-8 and PAI-1 in COPD SAF supernatant compared to non-treated cells (29% and 22% decrease, p&lt;0.05). ISRIB also reduced NRF2 protein, <i>SOD3</i> mRNA expression and catalase activity in COPD SAF (47%, 53% and 63% decrease). <b>Conclusion:</b> These data imply a role for ER stress in SAF senescence in COPD and suggest p-eIF2α as a new target for therapeutic strategy.