Protein kinase R-like endoplasmic reticulum kinase is a mediator of stretch in ventilator-induced lung injury

Abstract

BackgroundAcute respiratory distress syndrome (ARDS) is a severe form of lung injury characterized by damage to the epithelial barrier with subsequent pulmonary edema and hypoxic respiratory failure. ARDS is a significant medical problem in intensive care units with associated high care costs. There are many potential causes of ARDS; however, alveolar injury associated with mechanical ventilation, termed ventilator-induced lung injury (VILI), remains a well-recognized contributor. It is thus critical to understand the mechanism of VILI. Based on our published preliminary data, we hypothesized that the endoplasmic reticulum (ER) stress response molecule Protein Kinase R-like Endoplasmic Reticulum Kinase (PERK) plays a role in transmitting mechanosensory signals the alveolar epithelium.MethodsER stress signal responses to mechanical stretch were studied in ex-vivo ventilated pig lungs. To explore the effect of PERK inhibition on VILI, we ventilated live rats and compared lung injury parameters to non-ventilated controls. The effect of stretch-induced epithelial ER Ca2+ signaling on PERK was studied in stretched alveolar epithelial monolayers. To confirm the activation of PERK in human disease, ER stress signaling was compared between ARDS and non-ARDS lungs.ResultsOur studies revealed increased PERK-specific ER stress signaling in response to overstretch. PERK inhibition resulted in dose-dependent improvement of alveolar inflammation and permeability. Our data indicate that stretch-induced epithelial ER Ca2+ release is an activator of PERK. Experiments with human lung tissue confirmed PERK activation by ARDS.ConclusionOur study provides evidences that PERK is a mediator stretch signals in the alveolar epithelium.

Hidden Microatelectases Increase Vulnerability to Ventilation-Induced Lung Injury

“…Dolinay and co-workers demonstrated in a primary alveolar epithelial cell culture model that a bi-axial strain of 25%, which corresponds to ventilation with 15 ml/kg bodyweight (Tschumperlin and Margulies, 1999), the unfolded protein response is activated in a Ca 2+ dependent manner. These findings could be reproduced in vivo in a rat model ventilated with a tidal volume of 20 ml/kg bodyweight and an ex vivo porcine model ventilated with a tidal volume of 15 ml/kg bodyweight (Dolinay et al, 2017(Dolinay et al, , 2018. The investigators suggested that a stretch-induced cytosolic increase in Ca 2+ concentration resulted in an autophosphorylation of Perk which in a further step phosphorylated EIF-2α.…”

“…In vitro models of increased epithelial stretch demonstrated that the integrated stress response is activated by mechanical stress of primary alveolar epithelial cells ( Dolinay et al, 2017 , 2018 ). Therefore, we performed immunohistochemical staining of p-Perk and p-EIF-2α in four sections per experimental group.…”

“…Phosphorylated Perk (p-Perk) moreover phosphorylates eukaryotic translation initiating factor 2α (EIF-2α), a step critical to switch off the protein biosynthesis machinery of the cell (Harding et al, 2000). If the ISR lingers on then cell death is initiated by selective expression of CCAAT/Enhancer binding Protein homologous Protein (CHOP) (Günther et al, 2012;Dolinay et al, 2018).…”

“…Ruptures of the plasma membrane of alveolar epithelial cells increase cytoplasmic Ca 2+ levels which are responsible for activation of the cellular integrated stress response (ISR) ( Dolinay et al, 2017 , 2018 ). Stretch-induced ISR is initiated by Ca 2+ dependent auto-phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (Perk).…”

The integrated stress response in pulmonary disease

“…In cell models of alveolar epithelial stretch, or if the lung is hyperinflated mechanically in vivo, PERK-dependent ISR signalling is triggered, possibly via stretch-induced release of calcium from the ER. This may mediate some of the toxicity of barotrauma, since pharmacological inhibition of PERK limits alveolar permeability and production of IL-8 during acute inflammation induced by cyclic strain [126,127].…”