Retinoschisin deficiency induces persistent aberrant waves of activity affecting neuroglial signaling in the retina.

Genetic disorders which present during development make treatment strategies particularly challenging because there is a need to disentangle primary pathophysiology from downstream dysfunction caused at key developmental stages. To provide a deeper insight into this question, we studied a mouse model of X-linked juvenile retinoschisis (XLRS), an early-onset inherited condition caused by mutations in the Rs1 gene encoding retinoschisin (RS1) and characterized by cystic retinal lesions and early visual deficits. Using an unbiased approach in expressing the fast intracellular calcium indicator GCaMP6f in neuronal, glial, and vascular cells of the retina of RS1-deficient male mice, we found that initial cyst formation is paralleled by the appearance of aberrant spontaneous neuro-glial signals as early as postnatal day 15, when eyes normally open. These presented as glutamate-driven wavelets of neuronal activity and sporadic radial bursts of activity by Müller glia, spanning all retinal layers and disrupting light-induced signaling. This study confers a role to RS1 beyond its function as an adhesion molecule, identifies an early onset for dysfunction in the course of disease, establishing a potential window for disease diagnosis and therapeutic intervention.Significance StatementDevelopmental disorders make it difficult to distinguish pathophysiology due to ongoing disease from pathophysiology due to disrupted development. Here, we investigated a mouse model for X-linked retinoschisis (XLRS), a well-defined monogenic degenerative disease caused by mutations in the Rs1 gene, which codes for the protein retinoschisin. We evaluated the spontaneous activity of explanted retinas lacking retinoschisin at key stages of development using the unbiased approach of ubiquitously expressing GCaMP6f in all retinal neurons, vasculature and glia. In mice lacking RS1, we found an array of novel phenotypes which present around eye-opening, are linked to glutamatergic neurotransmission, and affect visual processing. These data identify novel pathophysiology linked to RS1, and define a window where treatments might be best targeted.

HDAC6 inhibition promotes α-tubulin acetylation and ameliorates CMT2A peripheral neuropathy in mice.

Charcot-Marie-Tooth type 2A (CMT2A) peripheral neuropathy, the most common axonal form of CMT, is caused by dominantly inherited point mutations in the Mitofusin 2 (Mfn2) gene. It is characterized by progressive length-dependent degeneration of motor and sensory nerves with corresponding clinical features of motor and sensory impairment. There is no cure for CMT, and therapeutic approaches are limited to physical therapy, orthopedic devices, surgery, and analgesics. In this study we focus on histone deacetylase 6 (HDAC6) as a therapeutic target in a mouse model of mutant MFN2 (MFN2R94Q)-induced CMT2A. We report that these mice display progressive motor and sensory dysfunction as well as a significant decrease in α-tubulin acetylation in distal segments of long peripheral nerves. Treatment with a new, highly selective HDAC6 inhibitor, SW-100, was able to restore α-tubulin acetylation and ameliorate motor and sensory dysfunction when given either prior to or after the onset of symptoms. To confirm HDAC6 is the target for ameliorating the CMT2A phenotype, we show that genetic deletion of Hdac6 in CMT2A mice prevents the development of motor and sensory dysfunction. Our findings suggest α-tubulin acetylation defects in distal parts of nerves as a pathogenic mechanism and HDAC6 as a therapeutic target for CMT2A.

The Developmental Stage of Adult Human Stem Cell-Derived Retinal Pigment Epithelium Cells Influences Transplant Efficacy for Vision Rescue.

Age-related macular degeneration (AMD) is a common cause of central visual loss in the elderly. Retinal pigment epithelial (RPE) cell loss occurs early in the course of AMD and RPE cell transplantation holds promise to slow disease progression. We report that subretinal transplantation of RPE stem cell (RPESC)-derived RPE cells (RPESC-RPE) preserved vision in a rat model of RPE cell dysfunction. Importantly, the stage of differentiation that RPESC-RPE acquired prior to transplantation influenced the efficacy of vision rescue. Whereas cells at all stages of differentiation tested rescued photoreceptor layer morphology, an intermediate stage of RPESC-RPE differentiation obtained after 4 weeks of culture was more consistent at vision rescue than progeny that were differentiated for 2 weeks or 8 weeks of culture. Our results indicate that the developmental stage of RPESC-RPE significantly influences the efficacy of RPE cell replacement, which affects the therapeutic application of these cells for AMD.

Melanopsin-expressing retinal ganglion-cell photoreceptors: cellular diversity and role in pattern vision.

Using the photopigment melanopsin, intrinsically photosensitive retinal ganglion cells (ipRGCs) respond directly to light to drive circadian clock resetting and pupillary constriction. We now report that ipRGCs are more abundant and diverse than previously appreciated, project more widely within the brain, and can support spatial visual perception. A Cre-based melanopsin reporter mouse line revealed at least five subtypes of ipRGCs with distinct morphological and physiological characteristics. Collectively, these cells project beyond the known brain targets of ipRGCs to heavily innervate the superior colliculus and dorsal lateral geniculate nucleus, retinotopically organized nuclei mediating object localization and discrimination. Mice lacking classical rod-cone photoreception, and thus entirely dependent on melanopsin for light detection, were able to discriminate grating stimuli from equiluminant gray and had measurable visual acuity. Thus, nonclassical retinal photoreception occurs within diverse cell types and influences circuits and functions encompassing luminance as well as spatial information.

Maximizing functional photoreceptor differentiation from adult human retinal stem cells.

Retinal stem cells (RSCs) are present in the ciliary margin of the adult human eye and can give rise to all retinal cell types. Here we show that modulation of retinal transcription factor gene expression in human RSCs greatly enriches photoreceptor progeny, and that strong enrichment was obtained with the combined transduction of OTX2 and CRX together with the modulation of CHX10. When these genetically modified human RSC progeny are transplanted into mouse eyes, their retinal integration and differentiation is superior to unmodified RSC progeny. Moreover, electrophysiologic and behavioral tests show that these transplanted cells promote functional recovery in transducin mutant mice. This study suggests that gene modulation in human RSCs may provide a source of photoreceptor cells for the treatment of photoreceptor disease.

Intraocular CNTF reduces vision in normal rats in a dose-dependent manner.

PURPOSE: CNTF is a neuroprotective agent for retinal degenerations that can cause reduced electroretinogram (ERG) amplitudes. The goal of the present study was to determine the effects of intraocular delivery of CNTF on normal rat visual function. METHODS: Full-field scotopic and photopic ERG amplitudes and spatial frequency thresholds of the optokinetic response (OKR) of adult Long-Evans rats were measured before and after intravitreous injection of CNTF or subretinal delivery of adenoassociated virus-vectored CNTF (AAV-CNTF) into one eye. Visual acuity was also measured by using the Visual Water Task in AAV-CNTF-injected animals. Multiunit luminance thresholds were recorded in the superior colliculus after CNTF injection, and the eyes were examined histologically. RESULTS: In eyes injected with a high dose of CNTF, ERG amplitudes and OKR thresholds measured through CNTF-injected eyes were decreased by 45% to 70% within 6 days after injection. ERG amplitudes had begun to recover by 21 days, whereas OKR thresholds only began to recover after 56 days. Neither OKR thresholds nor ERG amplitudes fully recovered until 90 to 100 days. When measured in the superior colliculus at 2 weeks after CNTF injection, luminance thresholds were elevated by 0.35 log units. In AAV-CNTF-injected eyes, OKR thresholds, and visual acuity were reduced by approximately 50% for at least 6 months, and scotopic and photopic ERG b-waves were reduced by 30% to 50%. Photoreceptor loss occurred in the injected regions in some of the eyes. By contrast, comparison of dose-response analysis with a dose-response study of light damage strongly suggests that therapeutic doses of CNTF exist that do not suppress ERG responses. CONCLUSIONS: Intraocular delivery of CNTF, which preserves photoreceptors in animal models of retinal degeneration, impairs visual function in normal rats at very high doses, but not at lower doses that still provide protection from constant light damage.

Enhancement of vision by monocular deprivation in adult mice.

Plasticity of vision mediated through binocular interactions has been reported in mammals only during a "critical" period in juvenile life, wherein monocular deprivation (MD) causes an enduring loss of visual acuity (amblyopia) selectively through the deprived eye. Here, we report a different form of interocular plasticity of vision in adult mice in which MD leads to an enhancement of the optokinetic response (OKR) selectively through the nondeprived eye. Over 5 d of MD, the spatial frequency sensitivity of the OKR increased gradually, reaching a plateau of approximately 36% above pre-deprivation baseline. Eye opening initiated a gradual decline, but sensitivity was maintained above pre-deprivation baseline for 5-6 d. Enhanced function was restricted to the monocular visual field, notwithstanding the dependence of the plasticity on binocular interactions. Activity in visual cortex ipsilateral to the deprived eye was necessary for the characteristic induction of the enhancement, and activity in visual cortex contralateral to the deprived eye was necessary for its maintenance after MD. The plasticity also displayed distinct learning-like properties: Active testing experience was required to attain maximal enhancement and for enhancement to persist after MD, and the duration of enhanced sensitivity after MD was extended by increasing the length of MD, and by repeating MD. These data show that the adult mouse visual system maintains a form of experience-dependent plasticity in which the visual cortex can modulate the normal function of subcortical visual pathways.

Rapid quantification of adult and developing mouse spatial vision using a virtual optomotor system.

PURPOSE: To develop a simple, rapid method of quantifying the spatial vision of mice. METHODS: A rotating cylinder covered with a vertical sine wave grating was calculated and drawn in virtual three-dimensional (3-D) space on four computer monitors facing to form a square. C57BL/6 mice standing unrestrained on a platform in the center of the square tracked the grating with reflexive head and neck movements. The spatial frequency of the grating was clamped at the viewing position by repeatedly recentering the cylinder on the head. Acuity was quantified by increasing the spatial frequency of the grating until an optomotor response could not be elicited. Contrast sensitivity was measured at spatial frequencies between 0.03 and 0.35 cyc/deg. RESULTS: Grating acuity was measurable on the day of eye opening (postnatal day [P]15: mean acuity, 0.031 cyc/deg) and reached a maximum (approximately 0.4 cyc/deg) by P24. A peak in the contrast sensitivity function emerged on P16 (4.7, or 21% contrast at 0.064 cyc/deg). The peak remained at 0.064 cyc/deg and climbed to a maximum sensitivity of 24.5, or 4% contrast, by P29. Acuity was obtained in each mouse in <10 minutes, and a detailed contrast sensitivity curve was generated in approximately 30 minutes. CONCLUSIONS: The virtual optomotor system provides a simple and precise method for rapidly quantifying mouse vision. Behavioral measures of vision in mice are essential for interpreting the results of experiments designed to reveal the cellular and molecular mechanisms of vision and visual development and for evaluating potential treatments for visual diseases.