Cyclic stretch increases glucose uptake and pro-inflammatory response in rat alveolar epithelial type II cells

Mechanical ventilation (MV) is used to improve gas exchange but can exacerbate lung inflammation by increasing alveolar cell stretch, leading to ventilator-induced lung injury (VILI). Alveolar epithelial stretching promotes cytokine release, but its effects on glucose uptake remain unclear. In vitro studies suggest that high tidal volume ventilation corresponds to cyclic stretch levels of approximately 18%, whereas larger deformations represent supraphysiological and injurious conditions. Therefore, 30% cyclic stretch was used to reproduce severe alveolar deformation associated with volutrauma. We investigated the modulation of inflammation and glucose uptake in alveolar epithelial type II cells exposed to excessive cyclic stretch. We hypothesized that cells exposed to an overstretch of 30% at 1 and 4 hours would increase glucose uptake and pro-inflammatory responses.

Rat alveolar epithelial type II cells (L2 AECs) treated and untreated with lipopolysaccharide (LPS) were exposed to 1 or 4 hours of 30% cyclic stretch. Non-stretched cells, stimulated or not with LPS, served as a control. Glucose oxidase activity was measured using a colorimetric/fluorometric assay, while glucose uptake was assessed by immunofluorescence using the fluorescent glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG). Gene expression and secretion were measured by real-time polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Statistical analyses were performed using one-way ANOVA followed by Šidák's multiple comparisons test, with significance set at p < 0.05.

30% cyclic stretch significantly increased glucose uptake and glucose oxidase activity in both LPS-treated and untreated cells. Inflammatory gene expression and mediator secretion were predominantly increased in LPS-primed cells, although the effects varied according to the marker and time point.

Overall, excessive cyclic stretch increased the glucose-related readouts assessed in AECs L2 cells, whereas inflammatory responses were more strongly influenced by LPS stimulation and varied among mediators and time points.