Expression of Neurotrophins and Their Receptors in Primary and Transformed Rat Retinal Ganglion Cells (RGC–5) and Adult Rat Retina: A Double Immunofluorescent Confocal Study

Abstract

Abstract: : Purpose: To determine the expression profile of neurotrophins and their receptors in primary adult rat retinal ganglion cells (RGCs), transformed rat retinal ganglion cells (RGC–5), and adult rat retinas. Methods: Immunofluorescent confocal microscopy using double–labeling with Thy–1 as a marker for RGCs was used to demonstrate expression of neurotrophins and their receptors by cultured RGCs and in adult rat retinas. Enzyme–linked immunosorbent assays (ELISA) were used to demonstrate secretion of neurotrophins by RGC–5 cells. Results: Immunofluorescent confocal microscopy showed that primary RGCs and RGC–5 cells co–expressed Thy–1 with brain–derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin–3 (NT–3), neurotrophin–4 (NT–4), receptors TrkA and p75 respectively. However, very little expression of TrkB or TrkC was demonstrated by these cells. RGC–5 cells also secreted NT–3 (1311pg/ml), BDNF (92.2pg/ml), NGF (86.1pg/ml), and NT–4 (21.0pg/ml) into the condition media. In the adult rat retina, BDNF and NGF were expressed by RGCs and cells of the inner nuclear layer (INL). NT–3 was demonstrated in RGCs and some cells of the INL. NT–4 was also expressed in RGCs, cells of the INL, and photoreceptor cell outer segments (OS). The p75 receptor was expressed by RGCs and components of the nerve fiber layer (NFL). TrkA was shown in the RGCs, NFL, inner plexiform layer, and retinal pigment epithelium (RPE). TrkB and TrkC were not localized to RGCs, but were expressed by components of the NFL and in OS. Similar to RGCs in vitro, the RGCs of adult rat retina co–expressed Thy–1 with BDNF, NGF, NT–3, NT–4, p75, and TrkA respectively with little or no expression of TrkB and TrkC. Conclusions: These results demonstrated that neurotrophins and TrkA and p75 receptors are expressed by rat retinas and primary cultures of adult rat RGCs and RGC–5 cells. The RGC–5 cells were shown to secrete neurotrophins in vitro. Specific neurotrophins acting through TrkA and p75 receptors within the RGCs may be involved in the maintenance and/or apoptosis of the RGCs in glaucoma with a minimum involvement of TrkB and TrkC. Thus, paracrine and/or autocrine signaling pathways may play a significant role in RGC death during glaucoma. Furthermore, NT–4 and Trk receptors may also play a role in survival of photoreceptor cells in retinal dystrophies.

Keywords: growth factors/growth factor receptors • neuroprotection • cell death/apoptosis