Hypercapnia impairs protein translation by activating integrated stress response

Introduction:

Elevated levels of CO₂ (hypercapnia) can be often detected in patients with acute and chronic lung diseases. Protein translation is an integral part of protein synthesis which is a major determinant of cellular protein expression and plays a critical role in maintaining homeostasis. In the present study, we investigated how hypercapnia effects on protein translation.

Methods and results:

Exposing human alveolar epithelial A549 cells and N12 lung fibroblasts to elevated CO₂ concentrations (pCO₂ 120 mmHg, pH 7.4) led to a marked and rapid, time- and dose-dependent reduction in global protein translation, as assessed by puromycin incorporation. Additionally, hypercapnia led to an increase in the phosphorylation of eukaryotic initiation factor 2α (eIF2α), the core event of integrated stress response, without altering target of rapamycin or the mitogen-activated protein kinase pathways, other key regulators of protein translation. Furthermore, knockdown of the four known eIF2α kinases by siRNA revealed that PKR-like endoplasmic reticulum kinase (PERK) was responsible for the hypercapnia-induced eIF2α phosphorylation and the decrease in protein translation. Of note, treatment with the endoplasmic reticulum chemical chaperone, 4-phenylbutyric acid, attenuated the phosphorylation of eIF2α and rescued protein translation, suggesting that protein unfolding was potentially involved in the induction of integrated stress response.

Conclusions:

Hypercapnia impairs protein translation in both epithelial and mesenchymal cells. Activation of the integrated stress response pathway, involving increased phosphorylation of eIF2α by PERK may be responsible for the downregulation of global protein translation by elevated CO₂ levels.