The pro-fibrogenic effect of nerve growth factor on conjunctival fibroblasts is mediated by transforming growth factor-β

BACKGROUND: Nerve growth factor (NGF) and nerve growth factor receptor (NGFR) expressions have been found to be increased in sub-conjunctival scarring. OBJECTIVE: The aim of this study was to investigate the in vitro effects of NGF on some pro-fibrogenic properties of human conjunctival fibroblasts. METHODS: Expression of NGF, trkA(NGFR) and p75NTR on human fibroblasts grown from conjunctival biopsies and incubated for 2 or 6 days with NGF were evaluated by immunofluorescence, RT-PCR, flow cytometry and ELISA. The fibrogenic effect of NGF on conjunctival fibroblasts was investigated by evaluating their migration (wound model), proliferation ([3H]-thymidine incorporation), collagen production (3H]-proline incorporation), expression of alpha-smooth muscle actin (alpha-SMA) (cell surface ELISA) and contraction of 3D collagen gels. RESULTS: NGF induced the expression of p75NTR in the fibroblasts that constitutively expressed only trkA(NGF) and increased the migration of wounded fibroblasts, but not their proliferation and collagen production. NGF induced the conversion of fibroblasts into myofibroblasts expressing alpha-SMA, and enhanced their contraction of a collagen matrix. Interestingly, chronic NGF treatment induced transforming growth factor-beta1 (TGF-beta1) production by fibroblasts, and following specific TGF-beta neutralization, all the NGF-induced effects were completely abrogated. CONCLUSION: Our findings indicate that NGF, via TGF-beta induction, is likely to be involved in the healing or fibrotic processes occurring in conjunctiva during some pathological conditions.