Redox signaling-mediated S-glutathionylation of protein disulfide isomerase A1 initiates intrinsic apoptosis and contributes to accelerated aging

Abstract

Identifying factors that contribute to the age-related onset of chronic obstructive pulmonary disease (COPD) is crucial for its prevention and treatment. The multifunctional endoplasmic reticulum (ER) chaperone protein disulfide isomerase A1 (PDIA1) shows a protective increase in expression levels in human and mouse non-COPD smokers. However, this increase slows with aging and disease progression, while increase in glutathione S-transferase π1 (GSTP1) does not. PDI has redox sensitive cysteine residues that can become S-glutathionylated (PDI-SSG) which compromise both isomerase and chaperone activity. Oxidized PDIA1 levels progressively rise with age in the lungs of murine non-smokers, with an even greater increase in smokers. To investigate whether an increased oxidized-to-native PDIA1 ratio (PDI-SSG/PDI-SH) contributes to the depletion of alveolar epithelial type 2 progenitor cells in COPD, we used the type-2-like cell line MLE12. High doses of cigarette smoke (CS) induced elevated oxidized PDIA1 levels, while a redox-refractory PDIA1 variant maintained a lower PDI-SSG/PDI-SH. Upon CS exposure, PDIA1 was S-glutathionylated by GSTP1 and predominantly localized at the ER–mitochondria interface. This mitochondrial proximity was prevented by pharmacological or genetic GSTP1 inhibition. When localized at the ER–mitochondria interface, S-glutathionylated PDIA1 decreased mitochondrial membrane potential (MMP), facilitated mitochondrial permeability transition pore opening, decreased mitochondrial respiration and triggered cytochrome c (Cyt c) release, followed by caspase-3 activation. Isolated mitochondrial studies confirmed that PDI-SSG trigger these apoptotic signals whereas native PDI does not. Our findings indicate that GSTP1-mediated S-glutathionylation of PDIA1 drives pro-apoptotic intraorganellar signaling by altering its ER distribution. Overexpression of a redox-refractory PDIA1 variant restored MMP and reduced Cyt c release, suggesting that a lower S-glutathionylated-to-native PDIA1 ratio is protective. These findings highlight a threshold-dependent regulation of PDIA1-SSG/PDIA1-SH redox signaling. We propose that the simultaneous inability to maintain high PDIA1 levels and the age-associated increase in its S-glutathionylated form in smokers accelerates AEC2 depletion and exhaustion, thereby contributing to emphysema progression.