Transformation of adult retina from the regenerative to the axonogenesis state activates specific genes in various subsets of neurons and glial cells

Abstract

The purpose of this study was to identify the gene expression profile of the regenerating retina in vitro. To achieve this goal, three experimental groups were studied: (1) an injury control group (OC-LI group) that underwent open crush (OC) of the optic nerve and lens injury (LI) in vivo; (2) an experimental group (OC-LI-R group) that comprised animals treated like those in the OC-LI group except that retinal axons were allowed to regenerate (R) in vitro; and (3) an experimental group (OC-LI-NR group) that comprised animals treated as those in the OC-LI group, except that the retinas were cultured in vitro with the retinal ganglion cell (RGC) layer facing upwards to prevent axonal regeneration (NR). Gene expression in each treatment group was compared to that of untreated controls. Immunohistochemistry was used to examine whether expression of differentially regulated genes also occurred at the protein level and to localize these proteins to the respective retinal cells. Genes that were regulated belonged to different functional categories such as antioxidants, antiapoptotic molecules, transcription factors, secreted signaling molecules, inflammation-related genes, and others. Comparison of changes in gene expression among the various treatment groups revealed a relatively small cohort of genes that was expressed in different subsets of cells only in the OC-LI-R group; these genes can be considered to be regeneration-specific. Our findings demonstrate that axonal regeneration of RGC involves an orchestrated response of all retinal neurons and glia, and could provide a platform for the development of therapeutic strategies for the regeneration of injured ganglion cells.

RGMA and neogenin protein expression are influenced by lens injury following optic nerve crush in the rat retina

“…Outer and inner segments of photoreceptors were never RGMA+. Upregulation of GFAP including an activation of the Müller cells in the retina after LI or optic nerve trauma has been reported by many groups [33,[35][36][37][38][39][40]. Furthermore, it has been reported that LI-induced upregulation of astrocytederived CNTF switches RGC into a regenerative state [41].…”

Traumatology of the optic nerve and contribution of crystallins to axonal regeneration

“…The addition of crystallin βb2 (crybb2) to the culture medium enhances the growth of axons in retinal explants, in the RGC-5 cell line and in primary hippocampal neurons. These results suggest that some crystallins constitute a new group of factors that operate either directly or indirectly on neurons and promote axon outgrowth (Liedtke et al 2007a(Liedtke et al , 2007b.…”

“…Activated macrophages have recently been suggested to be the source of factors mediating these effects (Yin et al 2003). However, next to macrophage-derived factors, lens-derived factors have also been previously shown to facilitate axon regrowth of RGCs in culture, suggesting that lens-derived factors either directly or indirectly exert additional effects on retinal neurons, effects that are triggered by a macrophage-independent mechanism (Liedtke et al 2007a(Liedtke et al , 2007bLorber et al 2008;Stupp et al 2005). Lens injury effects have also been shown to occur in the absence or presence of low numbers of macrophages ) and that astrocytederived CNTF, which is upregulated in retinal glia and released after lens injury or zymosan injection, is a keycontributing factor mediating the beneficial effects of intraocular inflammation (Müller et al 2007).…”

“…The exceptional stability of these proteins is attributable to their relationship to stress proteins. Some members of this superfamily are also expressed outside the lens and, in particular, within retinal and hippocampal neurons (Liedtke et al 2007a(Liedtke et al , 2007b. Their functional role in these neurons is still unknown.…”

“…Their functional role in these neurons is still unknown. Several β-crystallin isoforms are secreted by cultured retinas during axonal regeneration and seem to be involved in the elongation process of RGC axons (Liedtke et al 2007a(Liedtke et al , 2007b. The addition of crystallin βb2 (crybb2) to the culture medium enhances the growth of axons in retinal explants, in the RGC-5 cell line and in primary hippocampal neurons.…”