Wild-type Retinas Research Articles

Untargeted Metabolomics Reveals the Role of Lipocalin-2 in the Pathological Changes of Lens and Retina in Diabetic Mice.

To identify the role of lipocalin-2 (LCN2) in diabetic cataract (DC) and diabetic retinopathy (DR), diabetes models were established in wild-type (WT) and LCN2 gene knockout (LCN2-/-) mice by streptozotocin (STZ), this study aimed to investigate the metabolic alterations and underlying pathways in the lens and retina. Untargeted metabolomic analysis was performed on the lenses and retinas of WT and LCN2-/- diabetic mice, and relevant pathways were predicted through bioinformatics analysis. LCN2 was notably elevated in the anterior capsules of DC and the vitreous humor of DR. Metabolic profiling of the lenses and retinas of diabetic mice indicated that the differential metabolites were mostly amino acids, fatty acids, carbohydrates, and their derivatives. In the lenses of STZ-induced WT mice, the differential abundance score (DA-score) revealed an increase in metabolites associated with the citrate (or TCA) cycle and glucagon signaling pathway, whereas a decrease was observed in metabolites related to cholesterol metabolism. After the knockout of LCN2, the DA-score indicated that the majority of metabolites involved in cholesterol metabolism, cysteine and methionine metabolism, and tryptophan metabolism were diminished. In the STZ-induced retina, there was an increase in metabolites associated with the mTOR signaling pathway, and this increase was inhibited by the knockout of LCN2. Numerous metabolites exhibited substantial alterations in the lenses and retinas of diabetic mice. Untargeted metabolomics has provided insights into the function of LCN2 in DC and DR. These changes in metabolites, along with their related pathways, could be the mechanisms by which LCN2 modulated DC and DR.

Efficacy, biodistribution and safety comparison of chemically modified antisense oligonucleotides in the retina.

Antisense oligonucleotides (AONs) are a versatile tool for treating inherited retinal diseases. However, little is known about how different chemical modifications of AONs can affect their biodistribution, toxicity, and uptake in the retina. Here, we addressed this question by comparing splice-switching AONs with three different chemical modifications commonly used in a clinical setting (2'O-methyl-phosphorothioate (2-OMe/PS), 2'O-methoxyethyl-phosphoriate (2-MOE/PS), and phosphorodiamidite morpholino oligomers (PMO)).These AONs targeted genes exclusively expressed in certain types of retinal cells. Overall, studies in vitro and in vivo in C57BL/6J wild-type mouse retinas showed that 2-OMe/PS and 2-MOE/PS AONs have comparable efficacy and safety profiles. In contrast, octa-guanidine-dendrimer-conjugated in vivo PMO-oligonucleotides (ivPMO) caused toxicity. This was evidenced by externally visible ocular phenotypes in 88.5% of all ivPMO-treated animals, accompanied by severe alterations at the morphological level. However, delivery of unmodified PMO-AONs did not cause any toxicity, although it clearly reduced the efficacy. We conducted the first systematic comparison of different chemical modifications of AONs in the retina. Our results showed that the same AON sequence with different chemical modifications displayed different splicing modulation efficacies, suggesting the 2'MOE/PS modification as the most efficacious in these conditions. Thereby, our work provides important insights for future clinical applications.

Asymmetric Activation of ON and OFF Pathways in the Degenerated Retina.

Retinal prosthetics are one of the leading therapeutic strategies to restore lost vision in patients with retinitis pigmentosa and age-related macular degeneration. Much work has described patterns of spiking in retinal ganglion cells (RGCs) in response to electrical stimulation, but less work has examined the underlying retinal circuitry that is activated by electrical stimulation to drive these responses. Surprisingly, little is known about the role of inhibition in generating electrical responses or how inhibition might be altered during degeneration. Using whole-cell voltage-clamp recordings during subretinal electrical stimulation in the rd10 and wild-type (wt) retina, we found electrically evoked synaptic inputs differed between ON and OFF RGC populations, with ON cells receiving mostly excitation and OFF cells receiving mostly inhibition and very little excitation. We found that the inhibition of OFF bipolar cells limits excitation in OFF RGCs, and a majority of both pre- and postsynaptic inhibition in the OFF pathway arises from glycinergic amacrine cells, and the stimulation of the ON pathway contributes to inhibitory inputs to the RGC. We also show that this presynaptic inhibition in the OFF pathway is greater in the rd10 retina, compared with that in the wt retina.

Specific photoreceptor cell fate pathways are differentially altered in NR2E3-associated diseases

Mutations in NR2E3, a gene encoding an orphan nuclear transcription factor, cause two retinal dystrophies with a distinct phenotype, but the precise role of NR2E3 in rod and cone transcriptional networks remains unclear. To dissect NR2E3 function, we performed scRNA-seq in the retinas of wildtype and two different Nr2e3 mouse models that show phenotypes similar to patients carrying NR2E3 mutations. Our results reveal that rod and cone populations are not homogeneous and can be separated into different sub-classes. We identify a previously unreported cone pathway that generates hybrid cones co-expressing both cone- and rod-related genes. In mutant retinas, this hybrid cone subpopulation is more abundant and includes a subpopulation of rods transitioning towards a cone cell fate. Hybrid photoreceptors with high misexpression of cone- and rod-related genes are prone to regulated necrosis. Overall, our results shed light on the role of NR2E3 in modulating photoreceptor differentiation towards cone and rod fates and explain how different mutations in NR2E3 lead to distinct visual disorders in humans.

Knockdown of ChREBP ameliorates retinal microvascular endothelial cell injury and angiogenic responses in diabetic retinopathy

PurposeTo examine whether and how carbohydrate response element-binding protein (ChREBP) plays a role in diabetic retinopathy. MethodsWestern blotting was used to detect ChREBP expression and location following high glucose stimulation of Human Retinal Microvascular Endothelial Cells (HRMECs). Flow cytometry, TUNEL staining, and western blotting were used to evaluate apoptosis following ChREBP siRNA silencing. Cell scratch, transwell migration, and tube formation assays were used to determine cell migration and angiogenesis. Diabetic models for wild-type (WT) and ChREBP knockout (ChKO) mice were developed. Retinas of WT and ChKO animals were cultivated in vitro with vascular endothelial growth factor + high glucose to assess neovascular development. ResultsChREBP gene knockdown inhibited thioredoxin-interacting protein and NOD-like receptor family pyrin domain containing protein 3 expression in HRMECs, which was caused by high glucose stimulation, reduced apoptosis, hindered migration, and tube formation, and repressed AKT/mTOR signaling pathway activation. Compared with WT mice, ChKO mice showed suppressed high glucose-induced alterations in retinal structure, alleviated retinal vascular leakage, and reduced retinal neovascularization. ConclusionsChREBP deficiency decreased high glucose-induced apoptosis, migration, and tube formation in HRMECs as well as structural and angiogenic responses in the mouse retina; thus, it is a potential therapeutic target for diabetic retinopathy.

Dysregulated Arginine Metabolism Is Linked to Retinal Degeneration in Cep250 Knockout Mice.

Degeneration of retinal photoreceptors is frequently observed in diverse ciliopathy disorders, and photoreceptor cilium gates the molecular trafficking between the inner and the outer segment (OS). This study aims to generate a homozygous global Cep250 knockout (KO) mouse and study the resulting phenotype. We used Cep250 KO mice and untargeted metabolomics to uncover potential mechanisms underlying retinal degeneration. Long-term follow-up studies using optical coherence tomography (OCT) and electroretinography (ERG) were performed. OCT and ERG results demonstrated gradual thinning of the outer nuclear layer (ONL) and progressive attenuation of the scotopic ERG responses in Cep250-/- mice. More TUNEL signal was observed in the ONL of these mice. Immunostaining of selected OS proteins revealed mislocalization of these proteins in the ONL of Cep250-/- mice. Interestingly, untargeted metabolomics analysis revealed arginine-related metabolic pathways were altered and enriched in Cep250-/- mice. Mis-localization of a key protein in the arginine metabolism pathway, arginase 1 (ARG1), in the ONL of KO mice further supports this model. Moreover, adeno-associated virus (AAV)-based retinal knockdown of Arg1 led to similar architectural and functional alterations in wild-type retinas. Altogether, these results suggest that dysregulated arginine metabolism contributes to retinal degeneration in Cep250-/- mice. Our findings provide novel insights that increase understanding of retinal degeneration in ciliopathy disorders.

Proteomic analysis of diabetic retinas.

As a metabolic disease, diabetes often leads to health complications such as heart failure, nephropathy, neurological disorders, and vision loss. Diabetic retinopathy (DR) affects as many as 100 million people worldwide. The mechanism of DR is complex and known to impact both neural and vascular components in the retina. While recent advances in the field have identified major cellular signaling contributing to DR pathogenesis, little has been reported on the protein post-translational modifications (PTM) - known to define protein localization, function, and activity - in the diabetic retina overall. Protein glycosylation is the enzymatic addition of carbohydrates to proteins, which can influence many protein attributes including folding, stability, function, and subcellular localization. O-linked glycosylation is the addition of sugars to an oxygen atom in amino acids with a free oxygen atom in their side chain (i.e., threonine, serine). To date, more than 100 congenital disorders of glycosylation have been described. However, no studies have identified the retinal O-linked glycoproteome in health or disease. With a critical need to expedite the discovery of PTMomics in diabetic retinas, we identified both global changes in protein levels and the retinal O-glycoproteome of control and diabetic mice. We used liquid chromatography/mass spectrometry-based proteomics and high throughput screening to identify proteins differentially expressed and proteins differentially O-glycosylated in the retinas of wildtype and diabetic mice. Changes in both global expression levels of proteins and proteins differentially glycosylated in the retinas of wild-type and diabetic mice have been identified. We provide evidence that diabetes shifts both global expression levels and O-glycosylation of metabolic and synaptic proteins in the retina. Here we report changes in the retinal proteome of diabetic mice. We highlight alterations in global proteins involved in metabolic processes, maintaining cellular structure, trafficking, and neuronal processes. We then showed changes in O-linked glycosylation of individual proteins in the diabetic retina.

Retinal vascular remodeling in photoreceptor degenerative disease

Abnormal vasculature in the retina, specifically tortuous vessels and capillary degeneration, is common in many of the most prevalent retinal degenerative diseases, currently affecting millions of people across the world. However, the formation and development of abnormal vasculature in the context of retinal degenerative diseases are still poorly understood. The FVB/N (rd1) and rd10 mice are well-studied animal models of retinal degenerative diseases, but how photoreceptor degeneration leads to vascular abnormality in the diseases remains to be elucidated. Here, we used advancements in confocal microscopy, immunohistochemistry, and image analysis software to systematically characterize the pathological vasculature in the FVB/N (rd1) and rd10 mice, known as a chronic, rapid and slower retinal degenerative model, respectively. We demonstrated that there was plexus-specific vascular degeneration in the retinal trilaminar vascular network paralleled to photoreceptor degeneration in the diseased retinas. We also quantitatively analyzed the vascular structural architecture in the wild-type and diseased retinas to provide valuable information on vascular remodeling in retinal degenerative disease.

Using Micro-Electrode-Array Recordings and Retinal Disease Models to Elucidate Visual Functions: Simultaneous Recording of Local Electroretinograms and Ganglion Cell Action Potentials Reveals the Origin of Retinal Oscillatory Potentials.

The electroretinogram (ERG) is an essential diagnostic tool for visual function, both in clinical and research settings. Here, we establish an advanced in vitro approach to assess cell-type-specific ERG signal components. Retinal explant cultures, maintained under entirely controlled conditions, were derived from wild-type mice and rd10 rod- and cpfl1 cone-degeneration mouse models. Local micro-ERG (µERG) and simultaneous ganglion cell (GC) recordings were obtained from the retinal explants using multi-electrode arrays. Band-pass filtering was employed to distinguish photoreceptor, bipolar cell, amacrine cell (AC), and GC responses. Scotopic and photopic stimulation discriminated between rod and cone responses in wild-type and mutant retina. The 25 kHz sampling rate allowed the visualization of oscillatory potentials (OPs) in extraordinary detail, revealing temporal correlations between OPs and GC responses. Pharmacological isolation of different retinal circuits found that OPs are generated by inner retinal AC electrical synapses. Importantly, this AC activity helped synchronise GC activity. Our µERG protocol simultaneously records the light-dependent activities of the first-, second-, and third-order neurons within the native neuronal circuitry, providing unprecedented insights into retinal physiology and pathophysiology. This method now also enables complete in vitro retinal function testing of therapeutic interventions, providing critical guidance for later in vivo investigations.

Proteomics Analysis of R-Ras Deficiency in Oxygen Induced Retinopathy.

Small GTPase R-Ras regulates vascular permeability in angiogenesis. In the eye, abnormal angiogenesis and hyperpermeability are the leading causes of vision loss in several ischemic retinal diseases such as proliferative diabetic retinopathy (PDR), retinal vein occlusion (RVO), and retinopathy of prematurity (ROP). Oxygen-induced retinopathy (OIR) is the most widely used experimental model for these ischemic retinopathies. To shed more light on how the R-Ras regulates vascular permeability in pathological angiogenesis, we performed a comprehensive (>2900 proteins) characterization of OIR in R-Ras knockout (KO) and wild-type (WT) mice by sequential window acquisition of all theoretical mass spectra (SWATH-MS) proteomics. OIR and age-matched normoxic control retinas were collected at P13, P17, and P42 from R-Ras KO and WT mice and were subjected to SWATH-MS and data analysis. The most significant difference between the R-Ras KO and WT retinas was an accumulation of plasma proteins. The pathological vascular hyperpermeability during OIR in the R-Ras KO retina took place very early, P13. This led to simultaneous hypoxic cell injury/death (ferroptosis), glycolytic metabolism as well compensatory mechanisms to counter the pathological leakage from angiogenic blood vessels in the OIR retina of R-Ras deficient mice.

Ocular permeability, intraocular biodistribution of lipid nanocapsule formulation intended for retinal drug delivery

Recently, cGMP analogues have been investigated for the treatment of inherited retinal degenerations (IRD) using intravitreal injections. However, higher vitreous elimination rates limit the possibility to treat the retina with small molecule drugs. Here, we investigated the potential of lipid nanocapsules (LNCs) as vehicles to reduce clearance and prolong the delivery of cGMP analogue, CN03 to the retinal photoreceptors. Initially LNCs were investigated for both topical/periocular and intravitreal administration routes. While LNC-mediated drug permeation through the cornea proved to be too low for clinical applications, intravitreal application showed significant promise. Intravitreally administered LNCs containing fluorescent tracer in ex vivo porcine eyes showed complete intravitreal dispersal within 24 h. Ocular bio-distribution on histological sections showed that around 10 % of the LNCs had reached the retina, and 40 % accumulated in the ciliary body. For comparison, we used fluorescently labeled liposomes and these showed a different intraocular distribution with 48 % accumulated in the retina, and almost none were in the ciliary body. LNCs were then tested in retinal explants prepared from wild-type (WT) and rd1 mouse. In WT retina LNCs showed no significant toxic effects up to a concentration of 5 mg/mL. In rd1 retina, the LNC/CN03 formulation protected rd1 photoreceptors with similar efficacy to that of free CN03, demonstrating the usefulness of LNC/CN03 formulation in the treatment of IRD. Overall, our results indicate the suitability of LNCs for intraocular administration and drug delivery to both the retina and the ciliary body.

Azithromycin and Sildenafil May Have Protective Effects on Retinal Ganglion Cells via Different Pathways: Study in a Rodent Microbead Model.

Decreased blood flow to the optic nerve (ON) and neuroinflammation are suggested to play an important role in the pathophysiology of glaucoma. This study investigated the potential neuroprotective effect of azithromycin, an anti-inflammatory macrolide, and sildenafil, a selective phosphodiesterase-5 inhibitor, on retinal ganglion cell survival in a glaucoma model, which was induced by microbead injection into the right anterior chamber of 50 wild-type (WT) and 30 transgenic toll-like receptor 4 knockout (TLR4KO) mice. Treatment groups included intraperitoneal azithromycin 0.1 mL (1 mg/0.1 mL), intravitreal sildenafil 3 µL, or intraperitoneal sildenafil 0.1 mL (0.24 μg/3 µL). Left eyes served as controls. Microbead injection increased intraocular pressure (IOP), which peaked on day 7 in all groups and on day 14 in azithromycin-treated mice. Furthermore, the retinas and ON of microbead-injected eyes showed a trend of increased expression of inflammatory- and apoptosis-related genes, mainly in WT and to a lesser extent in TLR4KO mice. Azithromycin reduced the BAX/BCL2 ratio, TGFβ, and TNFα levels in the ON and CD45 expression in WT retina. Sildenafil activated TNFα-mediated pathways. Both azithromycin and sildenafil exerted a neuroprotective effect in WT and TLR4KO mice with microbead-induced glaucoma, albeit via different pathways, without affecting IOP. The relatively low apoptotic effect observed in microbead-injected TLR4KO mice suggests a role of inflammation in glaucomatous damage.

Electrically-evoked responses for retinal prostheses are differentially altered depending on ganglion cell types in outer retinal neurodegeneration caused by Crb1 gene mutation.

Microelectronic prostheses for artificial vision stimulate neurons surviving outer retinal neurodegeneration such as retinitis pigmentosa (RP). Yet, the quality of prosthetic vision substantially varies across subjects, maybe due to different levels of retinal degeneration and/or distinct genotypes. Although the RP genotypes are remarkably diverse, prosthetic studies have primarily used retinal degeneration (rd) 1 and 10 mice, which both have Pde6b gene mutation. Here, we report the electric responses arising in retinal ganglion cells (RGCs) of the rd8 mouse model which has Crb1 mutation. We first investigated age-dependent histological changes of wild-type (wt), rd8, and rd10 mice retinas by H&E staining. Then, we used cell-attached patch clamping to record spiking responses of ON, OFF and direction selective (DS) types of RGCs to a 4-ms-long electric pulse. The electric responses of rd8 RGCs were analyzed in comparison with those of wt RGCs in terms of individual RGC spiking patterns, populational characteristics, and spiking consistency across trials. In the histological examination, the rd8 mice showed partial retinal foldings, but the outer nuclear layer thicknesses remained comparable to those of the wt mice, indicating the early-stage of RP. Although spiking patterns of each RGC type seemed similar to those of the wt retinas, correlation levels between electric vs. light response features were different across the two mouse models. For example, in comparisons between light vs. electric response magnitudes, ON/OFF RGCs of the rd8 mice showed the same/opposite correlation polarity with those of wt mice, respectively. Also, the electric response spike counts of DS RGCs in the rd8 retinas showed a positive correlation with their direction selectivity indices (r = 0.40), while those of the wt retinas were negatively correlated (r = -0.90). Lastly, the spiking timing consistencies of late responses were largely decreased in both ON and OFF RGCs in the rd8 than the wt retinas, whereas no significant difference was found across DS RGCs of the two models. Our results indicate the electric response features are altered depending on RGC types even from the early-stage RP caused by Crb1 mutation. Given the various degeneration patterns depending on mutation genes, our study suggests the importance of both genotype- and RGC type-dependent analyses for retinal prosthetic research.

Using cGMP analogues to modulate photoreceptor light sensitivity.

For many hereditary degenerative diseases, like retinitis pigmentosa, the primary degeneration of rod photoreceptors leads to a secondary loss of cones and eventually to blindness. The pathophysiological mechanism is very often characterized by an increase of cGMP level in rods. Thus, rod degeneration is mainly triggered by an over-activation of cyclic nucleotide-gated (CNG) channels and excessive Ca2+ influx. While targeting of CNG channels was already proposed for therapeutic purposes, thus far, it has not been possible to selectively inhibit rod CNG channels without compromising cone function. Here, we present a novel strategy, based on a combination of cGMP analogues, which enables the selective modulation of rod photoreceptor activity. This approach was first tested by means of the patch-clamp technique on retinal CNG channels, heterologously expressed in Xenopus oocytes and further confirmed by micro-electroretinography recordings on wild-type mouse retina. The cGMP-analogues mixture contained a CNG-channel inhibitor (Rp-8-Br-PET-cGMPS) and a CNG-channel activator (8-pCPT-cGMP). While Rp-8-Br-PET-cGMPS, when applied alone, behaved as a partial agonist and inhibited both cone and rod CNG channels equally, 8-pCPT-cGMP behaved as a very potent agonist and showed a strong concentration-dependent cone selectivity. Co-application of both compounds inhibited rod CNG channels and preserved cone functionality under both physiological and pathological cGMP levels. While the kinetics of rod channels was not influenced by this treatment, the deactivation of cone channels was slowed down. Surprisingly, this aspect did not affect the physiological cone responsiveness to light, indicating possible intracellular compensatory mechanisms. In conclusion, by delaying primary rods degeneration, this strategy shields the healthy cones and thus may either postpone the onset or slow down the disease development. Beyond the treatment of retinal diseases, using cGMP analogues with desired properties may elegantly address the isoform-specificity problem in future pharmacological therapies of related diseases.

High amplitude pulses on the same charge condition efficiently elicit bipolar cell-mediated retinal ganglion cell responses in the degenerate retina.

Retinal pigmentosa (RP) patients lose vision due to the loss of photoreceptors. Retinal prostheses bypass the dead photoreceptors by electrically stimulating surviving retinal neurons, such as bipolar cells or retinal ganglion cells (RGCs). In previous studies, stimulus charge has been mainly optimized to maximize the RGC response to electrical stimulation. This study aimed to investigate the effect of amplitude and duration even under the same charge condition on eliciting RGC spikes in the wild-type and degenerate retinas. Wild-type (WT) Sprague-Dawley rats were used as the normal retinal model, and Pde6b knockout rats were used as a retinal degeneration (RD) model. Electrically-evoked RGC spikes were recorded from isolated rat retinas using an 8 8 multielectrode array. The same charge was maintained (10 or 20 nC), and electrical stimulation was applied to WT and RD retinas, adjusting the amplitude and duration of the 1st phase of biphasic pulses. In the pulse modulation of the 1st phase, high amplitude (short duration) pulses induced more RGC spikes than low amplitude (long duration) pulses. Both WT and RD retinas showed a significant reduction in the number of RGC spikes upon stimulation with lower amplitude (longer duration) pulses. In clinical trials where stimulus charges are delivered to the degenerate retina of blind patients, high amplitude (short duration) pulses would help elicit more RGC spikes.

Measuring the Release of Lactate from Wild-Type and rd1 Mouse Retina.

The retina has the highest energy consumption of any tissue in the human body. Remarkably, to satisfy its energy demand, the retina appears to rely mostly on aerobic glycolysis, which results in the production and release of large amounts of lactate. In the present study, we compared two different methods to assess lactate release from in vitro organotypic retinal explants cultured under entirely controlled, serum-free conditions. We used a standard lactate assay kit and 1H-nuclear magnetic resonance(NMR) spectroscopy-based analysis. We found that during the culturing of retinal explants derived from wild-type mice, lactate was released in large amounts and that the two different methods agreed well with each other. When comparing wild-type retina with degenerating rd1 mouse retina, we found the latter to release significantly higher amounts of lactate. Hence, degenerating retina may have an even higher energy demand and metabolic rate compared to healthy retina. We conclude that the use of lactate measurement can be a reliable and simple readout to evaluate ongoing retinal metabolism.

Transducin-Deficient Rod Photoreceptors Evaluated With Optical Coherence Tomography and Oxygen Consumption Rate Energy Biomarkers.

To test the hypothesis that rod energy biomarkers in light and dark are similar in mice without functional rod transducin (Gnat1rd17). Gnat1rd17 and wildtype (WT) mice were studied in canonically low energy demand (light) and high energy demand (dark) conditions. We measured rod inner segment ellipsoid zone (ISez) profile shape, external limiting membrane-retinal pigment epithelium (ELM-RPE) thickness, and magnitude of a hyporeflective band (HB) intensity dip located between photoreceptor tips and apical RPE; antioxidants were given in a subset of mice. Oxygen consumption rate (OCR) and visual performance indexes were also measured. The lower energy demand expected in light-adapted wildtype retinas was associated with an elongated ISez, thicker ELM-RPE, and higher HB magnitude, and lower OCR compared to high energy demand conditions in the dark. Gnat1rd17 mice showed a wildtype-like ISez profile shape at 20 minutes of light that became rounder at 60 minutes; at both times, ELM-RPE was smaller than wildtype values, and the HB magnitude was unmeasurable. OCR was higher than in the dark. Light-adapted Gnat1rd17 mice biomarkers were unaffected by anti-oxidants. Gnat1rd17 mice showed modest outer nuclear layer thinning and no reduction in visual performance indexes. Light-stimulated changes in all biomarkers in WT mice are consistent with the established light-induced decrease in net energy demand. In contrast, biomarker changes in Gnat1rd17 mice raise the possibility that light increases net energy demand in the absence of rod phototransduction.

Rapamycin Inhibits Light-Induced Necrosome Activation Occurring in Wild-Type, but not RPE65-Null, Mouse Retina.

Both photodamage and aberrant visual cycle contribute to disease progress of many retinal degenerative disorders, whereas the signaling pathways causing photoreceptor death remain unclear. Here we investigated the effects of intense photo-stress on (1) necrosome activation in wild-type and RPE65-null mice, (2) interaction of p62/Sequestosome-1 with the necrosome proteins, and (3) the effects of rapamycin on photodamage-induced necrosome activation and retinal degeneration in wild-type mice. Dark-adapted rd12 mice and 129S2/Sv mice with or without rapamycin treatment were exposed to 15,000 lux light for different times. Expression levels and subcellular localization of proteins were determined through immunoblot and immunohistochemical analyses. Cone sheaths were stained with peanut agglutinin. Correlation between photoreceptor degeneration and receptor-interacting protein kinase-1 (RIPK1) expression was assessed with Spearman's correlation analysis. Protein-protein interaction was analyzed by immunoprecipitation. Intense light caused rod and cone degeneration accompanied by a significant increase in RIPK1-RIPK3 expressions, mixed lineage kinase domain-like protein phosphorylation, damage-associated molecular patterns protein release, and inflammatory responses in wild-type mouse retina. The same intense light did not induce the necrosome activation in rd12 retina, but it did in rd12 mice that received 9-cis-retinal supply. RIPK1 expression levels are positively correlated with the degrees of rod and cone degeneration. Photodamage upregulated expression and interaction of the p62 autophagosome cargo protein with the necrosome proteins, whereas rapamycin treatment attenuated the light-induced necrosome activation and photoreceptor degeneration. Necrosome activation contributed to photodamage-induced rod and cone degeneration. The visual cycle and autophagy are the important therapeutic targets to alleviate light-induced retinal necroptosis.

Deletion of POMT2 in Zebrafish Causes Degeneration of Photoreceptors.

Mutations in the extracellular matrix protein eyes shut homolog (EYS) are a common cause of retinitis pigmentosa, a blinding disease characterized by photoreceptor degeneration. EYS binds to matriglycan, a carbohydrate modification on O-mannosyl glycan substitutions of the cell-surface glycoprotein α-dystroglycan. Patients with mutations in enzymes required for the biosynthesis of matriglycan exhibit syndromic retinal atrophy, along with brain malformations and congenital muscular dystrophy. Protein O-mannosyltransferase 2 (POMT2) is an enzyme required for the synthesis of O-mannosyl glycans. To evaluate the roles of O-mannosyl glycans in photoreceptor health, we generated protein O-mannosyltransferase 2 (pomt2) mutant zebrafish by CRISPR. pomt2 mutation resulted in a loss of matriglycan and abolished binding of EYS protein to α-dystroglycan. Mutant zebrafish presented with hydrocephalus and hypoplasia of the cerebellum, as well as muscular dystrophy. EYS protein was enriched near photoreceptor connecting cilia in the wild-type, but its presence and proper localization was significantly reduced in mutant animals. The mutant retina exhibited mis-localization of opsins and increased apoptosis in both rod and cone photoreceptors. Immunofluorescence intensity of G protein subunit alpha transducin 2 (GNAT2) antibody (a general cone marker) and 1D4 antibody (a long double cone marker) in mutant retinas did not differ from wild-type retinas at 1-month post fertilization, but was reduced at 6 months post fertilization, indicating significant cone degeneration. These data suggest that POMT2-mediated O-mannosyl glycosylation is required for EYS protein localization to the connecting cilium region and photoreceptor survival.

Quantitative characterisation of ipRGCs in retinal degeneration using a computation platform for extracting and reconstructing single neurons in 3D from a multi-colour labeled population.

Light has a profound impact on mammalian physiology and behavior. Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin, rendering them sensitive to light, and are involved in both image-forming vision and non-image forming responses to light such as circadian photo-entrainment and the pupillary light reflex. Following outer photoreceptor degeneration, the death of rod and cone photoreceptors results in global re-modeling of the remnant neural retina. Although ipRGCs can continue signaling light information to the brain even in advanced stages of degeneration, it is unknown if all six morphologically distinct subtypes survive, or how their dendritic architecture may be affected. To answer these questions, we generated a computational platform-BRIAN (Brainbow Analysis of individual Neurons) to analyze Brainbow labeled tissues by allowing objective identification of voxels clusters in Principal Component Space, and their subsequent extraction to produce 3D images of single neurons suitable for analysis with existing tracing technology. We show that BRIAN can efficiently recreate single neurons or individual axonal projections from densely labeled tissue with sufficient anatomical resolution for subtype quantitative classification. We apply this tool to generate quantitative morphological information about ipRGCs in the degenerate retina including soma size, dendritic field size, dendritic complexity, and stratification. Using this information, we were able to identify cells whose characteristics match those reported for all six defined subtypes of ipRGC in the wildtype mouse retina (M1-M6), including the rare and complex M3 and M6 subtypes. This indicates that ipRGCs survive outer retinal degeneration with broadly normal morphology. We additionally describe one cell in the degenerate retina which matches the description of the Gigantic M1 cell in Humans which has not been previously identified in rodent.