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PurposeTo identify Myo/Nog cells in the adult retina and test their role in protecting retinal photoreceptors from light damage.MethodsLight damage was induced by exposing albino rats raised in dim cyclic light to 1000 lux light for 24 hours. In one group of rats, Myo/Nog cells were purified from rat brain tissue by magnetic cell sorting following binding of the G8 monoclonal antibody (mAb). These cells were injected into the vitreous humour of the eye within 2 hours following bright light exposure. Retinal function was assessed using full-field, flash electroretinogram (ERG) before and after treatment. The numbers of Myo/Nog cells, apoptotic photoreceptors, and the expression of glial fibrillary acidic protein (GFAP) in Muller cells were assessed by immunohistochemistry.ResultsMyo/Nog cells were present in the undamaged retina in low numbers. Light induced damage increased their numbers, particularly in the choroid, ganglion cell layer and outer plexiform layer. Intravitreal injection of G8-positive (G8+) cells harvested from brain mitigated all the effects of light damage examined, i.e. loss of retinal function (ERG), death of photoreceptors and the stress-induced expression of GFAP in Muller cells. Some of the transplanted G8+ cells were integrated into the retina from the vitreous.ConclusionsMyo/Nog cells are a subpopulation of cells that are present in the adult retina. They increase in number in response to light induced stress. Intravitreal injection of Myo/Nog cells was protective to the retina, in part, by reducing retinal stress as measured by the Muller cell response. These results suggest that Myo/Nog cells, or the factors they produce, are neuroprotective and may be therapeutic in neurodegenerative retinal diseases.

Introduction Retinopathy of Prematurity (ROP) is the leading cause of blindness in children, affecting 50% of infants born prior to gestational week 32. ROP is the result of postpartum supplemental oxygen administered to compensate for underdeveloped lungs. However, hyperoxia inhibits proper development supplying the retina. When the infants are returned to ambient air, an imbalance is present between the oxygen concentration and metabolic demands of retinal neurons. This leads to a rapid induction of angiogenesis, leaky blood vessels, neovascular tuft formation, and cell death. Myo/Nog cells that express MyoD, Noggin, and brain‐specific angiogenesis inhibitor 1 (BAI1) exhibit neuroprotective properties in the eye and brain and are proposed to play a role in regulating angiogenesis in ROP. Methods An Oxygen‐induced retinopathy (OIR) protocol was implemented in neonatal C57BL/6J mice by exposing them on postnatal days 7‐12 (P7‐P12) to hyperoxia (75% oxygen) and then returning them to normal air (21% oxygen) from P12 until P21. On P15, groups receiving treatments were intravitreally injected with 1 µL of phosphate‐buffered saline (PBS) containing 2000 Myo/Nog cells isolated from the brain with the BAI1 antibody (BAI1+ group), 2000 unsorted brain cells (BAI1‐ group), or PBS alone (PBS group). Electroretinography (ERG) was conducted on P21 to assess retinal function. Eyes were extracted and either dissected for flat‐mount observation of vasculature and tufts, or processed for histology. The thickness of the retina and number of TUNEL+ apoptotic cells were quantified in tissue sections of eyes processed for histology. Adobe Photoshop (Adobe, San Jose, CA) was used to splice together 9 images that made up each whole retina from flat‐mounted eyes. The blood vessels were selected using the “Lasso tool” on photoshop, quantified by number of pixels, and then compared to the total number of pixels in the whole retina. Results OIR induced neovascular tuft formation. Exogenously added Myo/Nog cells normalized the retinopathy induced by the OIR model, reducing the number of tufts and improving the quality of the vasculature. The vasculature was most developed in retinas injected with brain derived Myo/Nog cells. ERG data shows a trend towards improvement of visual function with Myo/Nog cell injection. Conclusion Myo/Nog cell regulation of retinal vascularization may be related to the production of BAI1. Improved visual function seen with injection of Myo/Nog cells may be related to both a reduction of neovascular tufts and direct effects on retinal neurons. Therefore Myo/Nog cells have therapeutic potential in the prevention of ROP by normalizing the vasculature and preventing neuronal cell death.

Background The retina utilizes more oxygen than any other tissue in the body. Photoreceptors located in the retina's outer nuclear layer (ONL) are culled during the “critical period” of eye development when the number of photoreceptors exceeds the supply of oxygen. Retinitis Pigmentosa (RP) is a disease that first affects the rod photoreceptors, causing night blindness and reduced peripheral vision. In mice, RP often starts during the critical period. The objective of this study was to assess the effects of hyperoxia during the critical period on visual function and morphology of the retina in normal mice and mice with RP. Method Thirty five male and female wild‐type (C57BL/6J) mice and 15 mice with an rd1 mutation (C3H/HeJ), which causes a rapidly progressing form of retinitis pigmentosa, were exposed to hyperoxia (75% O₂), hypoxia (12% O₂), and normoxia (21% O₂) from postnatal (P) days 7 to 20. At P26, electroretinography (ERG) was used to assess the visual function of the photoreceptors (A‐wave) and the inner retinal cells (B‐wave). At P27, optical coherence tomography (OCT) and histology were used to observe retinal structure and the effects of the different O₂ groups. For histology, eyes were extracted at P10, P12, P16, and P28. Cell death was evaluated using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Results In ERGs from C57 mice, both A‐wave and B‐wave amplitudes were significantly lower in the hypoxic condition indicating that hypoxia was detrimental to visual function compared to the normoxic group. OCT data showed that the hyperoxic groups of C57 mice had thicker ONLs compared to the other treatment groups. TUNEL cell counts in the ONL and INL indicated a significant decrease in apoptotic cells during the critical period in the hyperoxic group compared to the hypoxic group. In C3H mice, hyperoxia improved the A and B waves compared to untreated mice. Discussion This study suggests that administration of oxygen during the critical period of retinal development reduces the pruning of cells in the retina and increases visual function in both normal mice and mice with an aggressive form of RP. Oxygen treatment during the critical period of retinal development, which occurs from P8 to P16, may slow retinal degeneration in RP. The effects of hyperoxia on the completion of vascular development must be taken into account when considering the use of hyperoxia therapeutically.