Evidence that neurites in human epiretinal membranes express melanopsin, calretinin, rod opsin and neurofilament protein

Aims We have previously identified neurofilament-protein-containing neurites in human epiretinal membranes (ERMs). The aim of this study was to further characterise these neurites by examining the expression of additional specific proteins in human ERMs and to correlate this expression with various retinal disease conditions. Methods Epiretinal membranes originating from 43 patients with proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR) or with no known pathology (idiopathic epiretinal membrane; iERM) were removed during vitrectomy at varying durations after diagnosis and immediately placed in fixative. The membranes were labelled immunohistochemically with different combinations of antibodies to the proteins melanopsin, calretinin and neurofilament (to identify subclasses of ganglion cells), rod opsin (to identify rod photoreceptors), synaptophysin and synaptic vesicle glycoprotein 2A (SV2) (identifies synaptic vesicles) and vimentin (identifies glial cells). Results Anti-melanopsin-, anti-calretinin-, anti-neurofilament- and anti-rod-opsin-labelled neurites were routinely observed in the epiretinal membranes. Their presence did not appear to correlate with a specific disease condition or duration of the membrane. Generally neurites were observed in regions of glial cells. Conclusions Based on the expression of selected markers for neurites, we show neurite processes in human ERMs of various aetiologies originating from rod photoreceptors and different populations of retinal ganglion cells, although there was no obvious correlation with specific disease condition. In addition, synaptophysin and SV2 labelling was observed associated with all types of neurites, indicating the presence of at least one component necessary for synaptic transmission. Our data suggest that the adult human retina retains a significant capacity for neuronal remodelling under various disease conditions.