The optic nerve lamina region is a neural progenitor cell niche.

Retinal ganglion cell axons forming the optic nerve (ON) emerge unmyelinated from the eye and become myelinated after passage through the optic nerve lamina region (ONLR), a transitional area containing a vascular plexus. The ONLR has a number of unusual characteristics: it inhibits intraocular myelination, enables postnatal ON myelination of growing axons, modulates the fluid pressure differences between eye and brain, and is the primary lesion site in the age-related disease open angle glaucoma (OAG). We demonstrate that the human and rodent ONLR possesses a mitotically active, age-depletable neural progenitor cell (NPC) niche, with unique characteristics and culture requirements. These NPCs generate both forms of macroglia: astrocytes and oligodendrocytes, and can form neurospheres in culture. Using reporter mice with SOX2-driven, inducible gene expression, we show that ONLR-NPCs generate macroglial cells for the anterior ON. Early ONLR-NPC loss results in regional dysfunction and hypomyelination. In adulthood, ONLR-NPCs may enable glial replacement and remyelination. ONLR-NPC depletion may help explain why ON diseases such as OAG progress in severity during aging.

Genistein blunts the negative effect of ischaemia to the retina caused by an elevation of intraocular pressure.

AIMS: Deduce whether the isoflavone genistein blunts the effect of ischaemia to the retina. METHODS: Ischaemia was induced in rats by raising the intraocular pressure (120 mm Hg) for 50 min. Genistein (10 mg/kg) was injected intraperitoneally 1 h before and after ischaemia. Seven days after ischaemia, the level of mRNAs for neurofilament light (NF-L), caspase 3, caspase 8, glial fibrillary acidic protein (GFAP), poly-ADP ribose polymerase (PARP), Thy-1 and proteins (GFAP, NF-L, PARP) in whole retinas were determined. NF-L and tubulin proteins in optic nerves were also determined. Retinas were also processed for the localization of choline acetyltransferase (ChAT) and GFAP immunoreactivities. RESULTS: Ischaemia caused a significant reduction in ganglion cell proteins in the optic nerve (NF-L and tubulin) and retina (NF-L). Retinal Thy-1 (mRNA and protein) and NF-L (mRNA) were also reduced while mRNAs of caspase 3, caspase 8, PARP and GFAP (also protein) were increased. Changes in the mRNAs and proteins induced by ischaemia were significantly blunted by genistein with the exception of the increase in GFAP and PARP protein/mRNA levels. Ischaemia-induced changes in the localization of ChAT were also clearly attenuated by genistein treatment. CONCLUSIONS: Genistein blunts most of the damaging effects caused to the retina by ischaemia.

The flavonoid baicalin counteracts ischemic and oxidative insults to retinal cells and lipid peroxidation to brain membranes.

The purpose of the present study was to determine whether the flavonoid, baicalin is effective at blunting the negative influence of ischemia/reperfusion to the rat retina in situ and of various insults to a transformed retinal ganglion cells (RGC-5 cells) in culture. Baicalin was administered intraperitoneally just before and after an ischemic insult to retina of one eye of a rat. Ischemia was delivered by raising the intraocular pressure above the systolic blood pressure for 50min. Seven days after ischemia, retinas were analysed for the localisation of various antigens. Retinal extracts were also analysed for various mRNAs. Moreover, the content of specific proteins was deduced in retinal and optic nerve extracts. Also, RGC-5 cells in culture were given one of three different insults, light (1000lx for 2 days), hydrogen peroxide (200microM H(2)O(2) for 24h) or serum deprivation (48h) where cell survival and reactive oxygen species (ROS) formation was assayed. Moreover, a lipid peroxidation assay was used to compare the antioxidant capacity of baicalin with the flavonoid, epigallocatechin gallate (EGCG). Ischemia/reperfusion to the retina affected the localisation of Thy-1 and choline acetyltransferase (ChAT) and the content of various proteins (optic nerve and retina) and mRNAs (retina). Importantly, baicalin statistically blunted most of the effects induced by ischemia/reperfusion. Only the increase in caspase-8 and caspase-3 mRNAs caused by ischemia/reperfusion were unaffected by baicalin treatment. Baicalin also attenuated significantly the negative insult of light, hydrogen peroxide and serum withdrawal to RGC-5 cells. In the lipid peroxidation studies, baicalin was also found to be equally effective as EGCG to act as an antioxidant. Significantly, the negative insult of serum withdrawal on RGC-5 cell survival was blunted by baicalin but not by EGCG revealing the different properties of the two flavonoids.

Flupirtine attenuates sodium nitroprusside-induced damage to retinal photoreceptors, in situ.

Flupirtine has been shown to function as a neuroprotectant and is presently used in man to treat a number of conditions. The aim of this study was to investigate the specific antioxidant properties of flupirtine in relation to oxidant-induced damage to retinal photoreceptors. Initial in vitro studies on brain membranes showed that flupirtine was approximately 20 times more potent than trolox (vitamin E analogue) and 8 times more potent than metipranolol at attenuating lipid peroxidation caused by the nitric oxide donor, sodium nitroprusside (SNP). Subsequent immunohistochemical studies revealed that following an intraocular injection of SNP, retinal photoreceptors are the only retinal cell types that appear to be clearly affected. This was supported by electroretinogram (ERG) recordings which showed both the a- and b-wave amplitudes to be significantly reduced. Western blotting techniques showed that SNP caused a significant decrease in photoreceptor-specific markers (RET-P1, rhodopsin kinase), an increase in cleaved caspase-3, Bcl-2, and cleaved PARP proteins that are associated with apoptosis and no change in the ganglion cell specific marker, neurofilament (NF-L). This was supported by RT-PCR data where rhodopsin (photoreceptor specific) mRNA was reduced while Thy-1 and NF-L (ganglion cell specific) mRNAs were unaffected. In addition SNP caused an elevation of glial cell response mRNAs primarily associated with Müller cells (GFAP, CNTF, bFGF) as well as caspase-3 and Bcl-2. Importantly, when flupirtine was co-injected, the effects to the retina caused by SNP on retinal proteins and mRNAs were in most cases significantly blunted. The conclusion reached from this study is that flupirtine is a powerful antioxidant and when injected into the eye with SNP attenuates the detrimental influence of SNP to retinal photoreceptors. Since oxidative stress has been implicated in retinal diseases like age-related macular degeneration (AMD) this study provides "proof of principle" for the idea that flupirtine may help individuals suffering from such retinal diseases.