Using the Electroretinogram to Assess Function in the Rodent Retina and the Protective Effects of Remote Limb Ischemic Preconditioning

Optimal Efficacy and Safety of Humanized Anti-Scg3 Antibody to Alleviate Oxygen-Induced Retinopathy

The retinopathy of prematurity (ROP), a neovascular retinal disorder presenting in premature infants, is the leading causes of blindness in children. Currently, there is no approved drug therapy for ROP in the U.S., highlighting the urgent unmet clinical need for a novel therapeutic to treat the disease. Secretogranin III (Scg3) was recently identified as a disease-selective angiogenic factor, and Scg3-neutralizing monoclonal antibodies were reported to alleviate pathological retinal neovascularization in mouse models. In this study, we characterized the efficacy and safety of a full-length humanized anti-Scg3 antibody (hAb) to ameliorate retinal pathology in oxygen-induced retinopathy (OIR) mice, a surrogate model of ROP, by implementing histological and functional analyses. Our results demonstrate that the anti-Scg3 hAb outperforms the vascular endothelial growth factor inhibitor aflibercept in terms of efficacy and safety to treat OIR mice. Our findings support the development of anti-Scg3 hAb for clinical application.

α-synuclein overexpression in the retina leads to vision impairment and degeneration of dopaminergic amacrine cells

The presence of α-synuclein aggregates in the retina of Parkinson's disease patients has been associated with vision impairment. In this study we sought to determine the effects of α-synuclein overexpression on the survival and function of dopaminergic amacrine cells (DACs) in the retina. Adult mice were intravitreally injected with an adeno-associated viral (AAV) vector to overexpress human wild-type α-synuclein in the inner retina. Before and after systemic injections of levodopa (L-DOPA), retinal responses and visual acuity-driven behavior were measured by electroretinography (ERG) and a water maze task, respectively. Amacrine cells and ganglion cells were counted at different time points after the injection. α-synuclein overexpression led to an early loss of DACs associated with a decrease of light-adapted ERG responses and visual acuity that could be rescued by systemic injections of L-DOPA. The data show that α-synuclein overexpression affects dopamine neurons in the retina. The approach provides a novel accessible method to model the underlying mechanisms implicated in the pathogenesis of synucleinopathies and for testing novel treatments.

Effect of sevoflurane preconditioning on light-induced retinal damage in diabetic rats

Hyperglycemia and bright light are powerful stress agents that produce an enhanced retinal damage, when simultaneously acting on retina. Previous studies have shown that preconditioning with sevoflurane anesthesia offers a certain degree of protection to retinal cells against light damage. The objective of this study was to explore the effect of sevoflurane anesthetic preconditioning on a model of light-induced retinal degeneration in diabetic rats. Wistar rats that were randomly divided into four groups: control (rats exposed to photostress), group 1 (rats exposed to photostress and sevoflurane preconditioning), group 2 (diabetic rats exposed to photostress), group 3 (diabetic rats exposed to photostress and sevoflurane preconditioning) were used for this experiment. We recorded basal electroretinogram (ERG), at 36 h and 14 days after photostress and performed histological analysis of the retina. Results showed that sevoflurane has a protective effect on light-induced neuroretinal degeneration proved by significantly less variations of the ERG before and after photostress. Diabetes appears to increase the damaging effect of photostress on retina and attenuate the protection provided by sevoflurane preconditioning.

Role of Myo/Nog Cells in Neuroprotection: Evidence from the Light Damaged Retina

PURPOSE

To identify Myo/Nog cells in the adult retina and test their role in protecting retinal photoreceptors from light damage.

METHODS

Light 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.

RESULTS

Myo/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.

CONCLUSIONS

Myo/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.