Effect of nerve growth factor on the in vitro induction of apoptosis of human conjunctival epithelial cells by hyperosmolar stress.

PURPOSE: To evaluate the effects of nerve growth factor (NGF), which is activated during inflammatory episodes of ocular diseases, on the apoptotic response in cultured human primary conjunctival epithelial cells (pHCECs).

METHODS: Levels of NGF transcripts and NGF protein in pHCEC grown in medium with normal osmolarity (307 mOsm/L) or hyperosmolar medium (350, 400, and 450 mOsm/L) were determined using RT-PCR or ELISA, respectively. To assess apoptosis, pHCEC were cultured in normal or 400 mOsm/L hyperosmolar medium with neutralizing anti-NGF antibody or recombinant human NGF for 6 hours before analysis by flow cytometry. Levels of Bcl-xL, Bax, phosphorylated JNK, and cleaved caspase-3 were detected using Western blotting. Levels of the inflammatory cytokine IL-6 was analyzed using ELISA.

RESULTS: Hyperosmolar conditions increased NGF levels in cultured pHCECs. Hyperosmolarity and exposure to neutralizing anti-NGF antibody significantly increased the number of apoptotic cells. Addition of recombinant human NGF to 400 mOsm/L medium decreased the number of apoptotic cells, reduced the expression of phosphorylated JNK, Bax, and cleaved caspase-3 and increased the expression of Bcl-xL. Levels of IL-6 were increased by hyperosmotic stress but decreased by exposure to recombinant human NGF.

CONCLUSIONS: Hyperosmolarity induces apoptosis of pHCECs by activating JNK signaling. Increased levels of NGF under hyperosmolar conditions may contribute, at least in part, to the reduced apoptosis of pHCECs and may be beneficial in recovering conjunctival damage due to chronic hyperosmolar stress.