IL-1b-mediated Immunometabolic Adaptation in Corneal Epithelial Cells

Abstract

Purpose: As an external mucosal surface, the corneal epithelium is subject to a barrage of stressors that are known to trigger inflammation. IL-1b, a master regulator of inflammation, is secreted into the preocular tear film by ocular surface epithelial cells and infiltrating immune cells. While increased levels of IL-1b have been associated with corneal disease, the effects of IL-1b on mitochondrial function in corneal epithelial cells (CECs) is unknown. Methods: To investigate the effects of IL-1b on mitochondrial function, telomerase immortalized human CECs were cultured in either 50 ng/mL or 100 ng/mL IL-1b for short term (24 hours) or prolonged (72 hours) time periods. Cells were assessed for ROS, inflammatory cytokine production, mitochondrial polarization and ultrastructure, mitophagy, and changes in the metabolite composition. Lipid drops were examined using light and fluorescent microscopy. Results: Short term exposure to IL-1b triggered an increase in IL-8 and ROS levels that corresponded to a reduction in mitochondrial membrane potential. Long term exposure also showed increased levels of IL-8 and IL-6 and further increased ROS. After long term exposure however, there was a paradoxical increase in mitochondrial membrane potential that was associated an increase in spare respiratory capacity and mitochondrial hyperfusion. Metabolomics confirmed an upregulation of the pentose phosphate pathway and the TCA cycle. Fumarate was also increased, suggesting an increase in flux through complex II. Changes in lipid metabolism included an upregulation in cardiolipin and de novo triacylglyceride biosynthesis, along with increasing numbers of lipid droplets. Conclusion: Prolonged exposure to IL-1b induces metabolic rewiring in CECs that results in an increase in spare respiratory capacity. These findings suggest that the corneal epithelium is able to adapt to certain levels of chronic inflammation and may have important implications in our understanding of immune tone and cellular stress responses in ocular surface epithelia.