Duloxetine enhances PAX6 expression and suppresses innate immune responses in murine LPS-induced corneal inflammation

PAX6 is a key regulator of eye development and epithelial homeostasis in the cornea. When deficient, chronic corneal inflammation, neovascularization and limbal stem cell deficiency can occur. Here we investigated the potential of duloxetine, a generic serotonin reuptake inhibitor that can upregulate PAX6 in vitro, for its in vivo activity in the context of corneal inflammation. Duloxetine tolerance was tested in a human limbal stem cell line and isogenic CRISPR-knockout PAX6+/− cells. C57BL/6-Wildtype mice were administered duloxetine eye drops at concentrations of 1 μM - 2 mM and tested for toxicity and corneal PAX6 expression. In LPS-induced corneal inflammation in mice, duloxetine's effect on PAX6 expression, corneal opacification and inflammatory responses were evaluated by in vivo corneal imaging, immunostaining, and whole-transcriptome microarray analysis. No toxicity was observed in vitro for duloxetine concentrations up to 10μΜ. In vivo, duloxetine drops were well-tolerated up to 50 μM. Duloxetine drops at 10μΜ significantly upregulated PAX6 protein levels in the cornea by 30 % within 2 days. In the LPS model, duloxetine resulted in a sustained 33 % PAX6 protein upregulation in the cornea at 7 days, and in reduced opacity within 2 days, accompanied by a significant dampening of IL-17A signaling, neutrophil degranulation, microglial activation, macrophage markers, and MMP expression, despite non-significant changes in total inflammatory cell infiltration. Short-term administration of a repurposed generic drug, duloxetine, upregulates PAX6 protein levels in the cornea of mice and exerts an anti-inflammatory activity by dampening innate immune responses.