Identification of molecular mechanisms driving hypercapnia-induced downregulation of protein translation in the alveolar epithelium

Hypercapnia is a common complication of acute and chronic lung diseases. Protein synthesis and its key step, protein translation, is one of the crucial determinants of cellular function. Here we investigate how elevated CO2 levels affect protein translation in lung cells and tissues. Exposure of alveolar epithelial cells (AEC) and murine precision-cut lung slices (PCLS) to elevated CO2 concentrations resulted in a significant reduction in global protein translation, as assessed by puromycin incorporation, and was independent of extracellular acidosis. We found that elevated CO2 levels increased the phosphorylation of several kinases involved in the regulation of protein translation, such as eukaryotic initiation factor 2α (eIF2α), cAMP response element-binding protein (CREB), p38 and ribosomal p70 S6. Furthermore, we identified that exposure of AEC to hypercapnia resulted in a rapid increase in eIF2α phosphorylation. Moreover, genetic knockdown by siRNA of four known eIF2α kinases revealed that PKR-like endoplasmic reticulum kinase (PERK) was responsible for the CO2-induced phosphorylation of eIF2α. Neither genetic knockdown of PERK nor chemical inhibition of PERK activity was able to recover protein translation in AEC and PCLS, implying that an alternative pathway may be involved in the hypercapnia-triggered downregulation of protein translation. Elevated CO2 levels reduce global protein translation in AEC and PCLS. Further investigation into the molecular mechanisms underlying these findings could potentially result in the development of novel therapeutic approaches for patients with acute and chronic hypercapnic respiratory failure.