Osmoprotective effects of supplemental epidermal growth factor in an ex vivo multilayered human conjunctival model under hyperosmotic stress

To analyze the effects of supplemental epidermal growth factor (EGF) and the roles of inflammatory cytokines (interleukin [IL]-6) in an ex vivo dry-eye model under hyperosmotic stress using a multilayered culture of human conjunctival epithelial cells (HCECs). Multilayered cultures of HCECs were exposed to hyperosmotic stress (400 mOsm/L) for 24 h in addition to 0.5 ng/mL EGF (low-EGF group) or 25 ng/mL EGF (high-EGF group). Apoptosis was analyzed using the TUNEL assay. Cell proliferation was measured using the [3H]-thymidine incorporation assay. The expression of IL-6, EGF, EGF receptor (EGFR), and phosphorylated extracellular signal-regulated kinase (p-ERK) was measured by western blot analysis. The secretion of IL-6 was measured using ELISA. Western blot analysis was also performed using antibodies against cleaved caspase-3. The percentage of apoptotic cells was lower in the high-EGF group (6.7 %) than in the low-EGF group (10.3 %). The high-EGF group demonstrated increased proliferation (323.7 counts/min in the low-EGF group vs 649.1 counts/min in the high-EGF group). EGF induced higher phosphor-EGFR expression and upregulated p-ERK in HCECs. In addition, EGF significantly decreased the secretion of IL-6 and cleaved caspase-3 in HCECs. The level of IL-6 was increased in the ex vivo HCEC dry-eye model that was under hyperosmotic stress. Supplemental EGF reduces the level of IL-6, decreases apoptosis, and increases proliferation. These findings indicate that EGF has potential as a therapeutic agent for the treatment of dry eyes.