The efficient induction of human retinal ganglion-like cells provides a platform for studying optic neuropathies

Retinal ganglion cells (RGCs) are essential for vision perception. In glaucoma and other optic neuropathies, RGCs and their optic axons undergo degenerative change and cell death; this can result in irreversible vision loss. Here we developed a rapid protocol for directly inducing RGC differentiation from human induced pluripotent stem cells (hiPSCs) by the overexpression of ATOH7, BRN3B, and SOX4. The hiPSC-derived RGC-like cells (iRGCs) show robust expression of various RGC-specific markers by whole transcriptome profiling. A functional assessment was also carried out and this demonstrated that these iRGCs display stimulus-induced neuronal activity, as well as spontaneous neuronal activity. Ethambutol (EMB), an effective first-line anti-tuberculosis agent, is known to cause serious visual impairment and irreversible vision loss due to the RGC degeneration in a significant number of treated patients. Using our iRGCs, EMB was found to induce significant dose-dependent and time-dependent increases in cell death and neurite degeneration. Western blot analysis revealed that the expression levels of p62 and LC3-II were upregulated, and further investigations revealed that EMB caused a blockade of lysosome-autophagosome fusion; this indicates that impairment of autophagic flux is one of the adverse effects of that EMB has on iRGCs. In addition, EMB was found to elevate intracellular reactive oxygen species (ROS) levels increasing apoptotic cell death. This could be partially rescued by the co-treatment with the ROS scavenger NAC. Taken together, our findings suggest that this iRGC model, which achieves both high yield and high purity, is suitable for investigating optic neuropathies, as well as being useful when searching for potential drugs for therapeutic treatment and/or disease prevention.

Inhibition of ferroptosis promotes retina ganglion cell survival in experimental optic neuropathies

Retinal ganglion cell (RGC) death is a hallmark of traumatic optic neuropathy, glaucoma, and other optic neuropathies that result in irreversible vision loss. However, therapeutic strategies for rescuing RGC loss still remain challenging, and the molecular mechanism underlying RGC loss has not been fully elucidated. Here, we highlight the role of ferroptosis, a non-apoptotic form of programmed cell death characterized by iron-dependent lethal lipid peroxides accumulation, in RGC death using an experimental model of glaucoma and optic nerve crush (ONC). ONC treatment resulted in significant downregulation of glutathione peroxidase 4 (GPx4) and system xc(-) cystine/glutamate antiporter (xCT) in the rat retina, accompanied by increased lipid peroxide and iron levels. The reduction of GPx4 expression in RGCs after ONC was confirmed by laser-capture microdissection and PCR. Transmission electron microscopy (TEM) revealed alterations in mitochondrial morphology, including increased membrane density and reduced mitochondrial cristae in RGCs after ONC. Notably, the ferroptosis inhibitor ferrostatin-1 (Fer-1) significantly promoted RGC survival and preserved retinal function in ONC and microbead-induced glaucoma mouse models. In addition, compared to the apoptosis inhibitor Z-VAD-FMK, Fer-1 showed better effect in rescuing RGCs death in ONC retinas. Mechanistically, we found the downregulation of GPx4 mainly occurred in the mitochondrial compartment, accompanied by increased mitochondrial reactive oxygen species (ROS) and lipid peroxides. The mitochondria-selective antioxidant MitoTEMPO attenuated RGC loss after ONC, implicating mitochondrial ROS and lipid peroxides as major mechanisms in ferroptosis-induced RGC death in ONC retinas. Notably, administering Fer-1 effectively prevented the production of mitochondrial lipid peroxides, the impairment of mitochondrial adenosine 5'-triphosphate (ATP) production, and the downregulation of mitochondrial genes, such as mt-Cytb and MT-ATP6, in ONC retinas. Our findings suggest that ferroptosis is a major form of regulated cell death for RGCs in experimental glaucoma and ONC models and suggesting targeting mitochondria-dependent ferroptosis as a protective strategy for RGC injuries in optic neuropathies.

Neuroimaging in Leber Hereditary Optic Neuropathy: State-of-the-art and future prospects

Leber Hereditary Optic Neuropathy (LHON) is an inherited mitochondrial retinal disease that causes the degeneration of retinal ganglion cells and leads to drastic loss of visual function. In the last decades, there has been a growing interest in using Magnetic Resonance Imaging (MRI) to better understand mechanisms of LHON beyond the retina. This is partially due to the emergence of gene-therapies for retinal diseases, and the accompanying expanded need for reliably quantifying and monitoring visual processing and treatment efficiency in patient populations. This paper aims to draw a current picture of key findings in this field so far, the challenges of using neuroimaging methods in patients with LHON, and important open questions that MRI can help address about LHON disease mechanisms and prognoses, including how downstream visual brain regions are affected by the disease and treatment and why, and how scope for neural plasticity in these pathways may limit or facilitate recovery.

[Clinical and paraclinical examination of non-traumatic optic neuropathy in the adult population]

Optic neuropathies (ON) occur in a variety of clinical presentations depending on their pattern of occurrence, their topography and the amount of functional visual impairment. Management of an ON requires a sequence of steps: confirm its existence (positive diagnosis): the diagnosis of ON is usually clinical and must be considered in the case of decreased visual acuity, change in color vision, visual field defect, relative afferent pupillary defect (RAPD), and absence of macular pathology; rule out differential diagnoses: determine the cause; etiologic diagnosis is sometimes complex and takes shape from clinical and paraclinical building blocks. The etiology may be vascular, inflammatory or demyelinating, infectious, toxic, vitamin-deficient, compressive (neoplastic or non-neoplastic), hereditary, congenital, traumatic or even pressure-related (glaucoma or advanced intracranial hypertension). Cerebral and orbital imaging with fine cuts of the optic nerves is often a mandatory examination, which is sometimes useful to repeat; identify therapeutic emergencies.

Peripapillary vessel density in pediatric cases with buried optic disk drusen

BACKGROUND

To evaluate the retinal nerve fiber layer (RNFL) and peripapillary vascular density (VD) changes in the pediatric group with optic disk drusen (ODD).

METHODS

Sixty eyes of 30 patients with buried ODD referred by the pediatric or neurology physicians to ophthalmology clinic with a preliminary diagnosis of papillary edema were included in this retrospective study. Sixty eyes of 30 healthy children were included as the control group. Thickness of RNFL (micrometer) and VD percentages (%) of the superior, inferior, nasal, and temporal quadrants of the peripapillary region of all cases were evaluated with optical coherence tomography angiography (OCT-A) device.

RESULTS

The study and control groups were homogeneous in terms of age and gender. VD values were significantly lower in the study group for all four quadrants, when compared to controls (p < 0.001, p < 0.001, p = 0.003, and p < 0.001, for inferior, superior, nasal, and temporal quadrants, respectively. For RFNL thickness measurements, a significant difference between groups was only evident for the nasal quadrant, where the study group had significantly higher nasal RFNL thickness (p = 0.001).

CONCLUSION

This study detected decreases in peripapillary VD values in all quadrants and peripapillary RNFL thickening in nasal quadrant in pediatric cases with buried drusen compared to healthy controls. Further studies are necessary to reveal the effects of drusen pathogenesis on optic nerve head perfusion and to understand the underlying mechanisms of related complications.

Advances in the Differentiation of Retinal Ganglion Cells from Human Pluripotent Stem Cells

Human pluripotent stem cell (hPSC) technology has revolutionized the field of biology through the unprecedented ability to study the differentiation of human cells in vitro. In the past decade, hPSCs have been applied to study development, model disease, develop drugs, and devise cell replacement therapies for numerous biological systems. Of particular interest is the application of this technology to study and treat optic neuropathies such as glaucoma. Retinal ganglion cells (RGCs) are the primary cell type affected in these diseases, and once lost, they are unable to regenerate in adulthood. This necessitates the development of strategies to study the mechanisms of degeneration as well as develop translational therapeutic approaches to treat early- and late-stage disease progression. Numerous protocols have been established to derive RGCs from hPSCs, with the ability to generate large populations of human RGCs for translational applications. In this review, the key applications of hPSCs within the retinal field are described, including the use of these cells as developmental models, disease models, drug development, and finally, cell replacement therapies. In greater detail, the current report focuses on the differentiation of hPSC-derived RGCs and the many unique characteristics associated with these cells in vitro including their genetic identifiers, their electrophysiological activity, and their morphological maturation. Also described is the current progress in the use of patient-specific hPSCs to study optic neuropathies affecting RGCs, with emphasis on the use of these RGCs for studying disease mechanisms and pathogenesis, drug screening, and cell replacement therapies in future studies.

Baseline demographics, clinical features, and treatment protocols of 240 patients with optic neuropathy: experiences from a neuro-ophthalmological clinic in the Aegean region of Turkey

PURPOSE

To analyze the demographic patterns, clinical characteristics, and treatment protocols of optic neuropathies.

MATERIALS AND METHODS

The hospital data of patients with optic neuropathy admitted to the Department of Neuro-ophthalmology in a tertiary referral center in Turkey between January 2010 to January 2017 were retrospectively analyzed. Demographic patterns, clinical features, treatment protocols, and the natural disease courses were assessed.

RESULTS

The total number of patients with optic neuropathy seen over this period was 240, which consist of 43 with idiopathic optic neuritis (17.9%), 40 with multiple sclerosis-related optic neuritis (16.7%), 12 with chronic relapsing inflammatory optic neuritis (5.0%), 12 with atypical optic neuritis (5.0%), 11 with neuromyelitis optica spectrum disorders-related optic neuritis (4.6%), 90 with non-arteritic ischemic optic neuropathy (37.5%), 4 with arteritic ischemic optic neuropathy (1.7%), 10 with traumatic optic neuropathy (4.1%), 6 with compressive optic neuropathy (2.5%), and 12 with mitochondrial optic neuropathy [9 with toxic optic neuropathy (3.7%) and 3 with Leber's hereditary optic neuropathy (1.2%)]. There were 101 males (42%) and 139 females (58%). The mean age was 43.34 ± 15.86 years.

CONCLUSION

This study reported the demographics, clinical characteristics, and treatment protocols of optic neuropathies in a neuro-ophthalmology specialty clinic at a tertiary referral center in Turkey during the past decade. The data may be useful in assessing the global status of optic neuropathies.

Mitochondrial dynamics, transport, and quality control: A bottleneck for retinal ganglion cell viability in optic neuropathies

Retinal ganglion cells, the neurons that selectively die in glaucoma and other optic neuropathies, are endowed with an exceedingly active metabolism and display a particular vulnerability to mitochondrial dysfunction. Mitochondria are exquisitely dynamic organelles that are continually responding to endogenous and environmental cues to readily meet the energy demand of neuronal networks. The highly orchestrated regulation of mitochondrial biogenesis, fusion, fission, transport and degradation is paramount for the maintenance of energy-expensive synapses at RGC dendrites and axon terminals geared for optimal neurotransmission. The present review focuses on the progress made to date on understanding the biology of mitochondrial dynamics and quality control and how dysregulation of these processes can profoundly affect retinal ganglion cell viability and function in optic nerve diseases.

Characterization of two novel intronic OPA1 mutations resulting in aberrant pre-mRNA splicing

BACKGROUND

We report two novel splice region mutations in OPA1 in two unrelated families presenting with autosomal-dominant optic atrophy type 1 (ADOA1) (ADOA or Kjer type optic atrophy). Mutations in OPA1 encoding a mitochondrial inner membrane protein are a major cause of ADOA.

METHODS

We analyzed two unrelated families including four affected individuals clinically suspicious of ADOA. Standard ocular examinations were performed in affected individuals of both families. All coding exons, as well as exon-intron boundaries of the OPA1 gene were sequenced. In addition, multiplex ligation-dependent probe amplification (MLPA) was performed to uncover copy number variations in OPA1. mRNA processing was monitored using RT-PCR and subsequent cDNA analysis.

RESULTS

We report two novel splice region mutations in OPA1 in two unrelated individuals and their affected relatives, which were previously not described in the literature. In one family the heterozygous insertion and deletion c.[611-37_611-38insACTGGAGAATGTAAAGGGCTTT;611-6_611-16delCATATTTATCT] was found in all investigated family members leading to the activation of an intronic cryptic splice site. In the second family sequencing of OPA1 disclosed a de novo heterozygous deletion c.2012+4_2012+7delAGTA resulting in exon 18 and 19 skipping, which was not detected in healthy family members.

CONCLUSION

We identified two novel intronic mutations in OPA1 affecting the correct OPA1 pre-mRNA splicing, which was confirmed by OPA1 cDNA analysis. This study shows the importance of transcript analysis to determine the consequences of unclear intronic mutations in OPA1 in proximity to the intron-exon boundaries.