Induced Expression of Insulin-like Growth Factor-1 by Amniotic Membrane-Conditioned Medium in Cultured Human Corneal Epithelial Cells

Abstract

PURPOSE: To determine the effect of amniotic membrane-conditioned medium (AMCM), via insulin-like growth factor (IGF)-1 induction, on human corneal epithelial cell (HCEC) proliferation. METHODS: HCECs were cultured from corneal limbal tissue with supplemented hormonal epithelial medium (SHEM). After administration of AMCM, cell proliferation was evaluated with an MTT assay and DNA synthesis with methyl-[(3)H]-thymidine incorporation assay. RT-PCR and Western immunoblot analyses were performed, to determine potential inducible factors that may be associated with AMCM-induced cell proliferation. Neutralizing anti-IGF-1 antibody and small interfering (si)RNA were also used to clarify the role of IGF-1 in AMCM-induced HCEC proliferation. RESULTS: HCEC proliferation increased after AMCM treatment. Of the cytokines known to be associated with HCEC proliferation, only IGF-1 expression was upregulated in response to AMCM in a dose- and time-dependent manner. The IGF-1 induction effect was found on both AMCM from live AM and from cryopreserved AM. HCEC proliferation was also increased by addition of exogenous IGF-1. AMCM-induced HCEC proliferation was inhibited in the presence of neutralizing anti-IGF-1 antibody and IGF-1 siRNA. Finally, Akt phosphorylation was increased in HCECs after AMCM treatment and was inhibited by IGF-1 siRNA. CONCLUSIONS: IGF-1 is induced by AMCM during HCEC proliferation, and this induction may play an important role in the amniotic membrane during HCEC proliferation and migration in several intractable corneal epithelial defects.