HGF regulation of RPE proliferation in an IL-1β/retinal hole-induced rabbit model of PVR

Purpose: To understand molecular events that lead to retinal pigment epithelial (RPE) cell proliferation and migration during the early phases of proliferative vitreoretinopathy (PVR) in a rabbit model. Methods: Retinal holes were created and interleukin-1β(IL-1β) was injected intravitreally. Eyes were examined by indirect ophthalmoscopy and eyecup pieces containing retinal holes were analyzed at different times after the surgery up to 4 weeks. RPE proliferation and migration were examined by immunohistochemistry. Tyrosine phosphorylation of extracellular signal regulated kinase (ERK) and hepatocyte growth factor receptor (HGFR or c-met) was determined by immunoprecipitation and western blot analysis. Tyrosine phosphorylation of c-met and morphological studies was performed on vitreous treated ARPE-19 cells. Expression of c-jun was determined by Northern blot analysis. Matrix metalloproteinase (MMP) content in vitreous was assessed by zymography. Results: Indirect ophthalmoscopy identified formation of epiretinal membrane and immunohistochemistry identified proliferative and migratory RPE and other cells in the posterior segment containing retinal holes at 4 weeks post-surgery. Tyrosine phosphorylation of ERK and c-met occurred in this segment within 30 min of surgery. ARPE-19 cells treated with vitreous from the 24 h post-surgical eyes, but not with control vitreous or IL-1β, showed morphological changes and tyrosine phosphorylation of c-met. Northern blot analysis in this segment identified upregulation of c-jun within 30 min of surgery and the expression peaked at 72 h. Zymographic analysis of vitreous identified MMP-9 in 12-72 h post-surgery. Conclusions: These data suggest that the presence of retinal holes and IL-1β may lead to activation of HGF, mitogen activated protein kinases (MAPK), c-jun and extracellular matrix remodeling, resulting in proliferative and migratory cells in the wounded retina.