Recombinant Human Proteoglycan 4 (rhPRG4) Downregulates TNF alpha-Stimulated NF kappa B Activity and FAT10 Expression in Human Corneal Epithelial Cells

Dry Eye Disease (DED) is a complex pathology affecting millions of people with significant impact on quality of life. Corneal inflammation, including via the nuclear factor kappa B (NF kappa B) pathway, plays a key etiological role in DED. Recombinant human proteoglycan 4 (rhPRG4) has been shown to be a clinically effective treatment for DED that has anti-inflammatory effects in corneal epithelial cells, but the underlying mechanism is still not understood. Our goal was to understand if rhPRG4 affects tumor necrosis factor alpha (TNF alpha)-stimulated inflammatory activity in corneal epithelial cells. We treated hTERT-immortalized corneal epithelial (hTCEpi) cells +/- TNF alpha +/- rhPRG4 and performed Western blotting on cell lysate and RNA sequencing. Bioinformatics analysis revealed that rhPRG4 had a significant effect on TNF alpha-mediated inflammation with potential effects on matricellular homeostasis. rhPRG4 reduced activation of key inflammatory pathways and decreased expression of transcripts for key inflammatory cytokines, interferons, interleukins, and transcription factors. TNF alpha treatment significantly increased phosphorylation and nuclear translocation of p65, and rhPRG4 significantly reduced both these effects. RNA sequencing identified human leukocyte antigen (HLA)-F adjacent transcript 10 (FAT10), a ubiquitin-like modifier protein which has not been studied in the context of DED, as a key pro-inflammatory transcript increased by TNF alpha and decreased by rhPRG4. These results were confirmed at the protein level. In summary, rhPRG4 is able to downregulate NF kappa B activity in hTCEpi cells, suggesting a potential biological mechanism by which it may act as a therapeutic for DED.