Interactome Analysis Reveals a Link of the Novel ALMS1-CEP70 Complex to Centrosomal Clusters.

Alström syndrome (ALMS) is a very rare autosomal-recessive disorder, causing a broad range of clinical defects most notably retinal degeneration, type 2 diabetes, and truncal obesity. The ALMS1 gene encodes a complex and huge ∼0.5 MDa protein, which has hampered analysis in the past. The ALMS1 protein is localized to the centrioles and the basal body of cilia and is involved in signaling processes, for example, TGF-ß signaling. However, the exact molecular function of ALMS1 at the basal body remains elusive and controversial. We recently demonstrated that protein complex analysis utilizing endogenously tagged cells provides an excellent tool to investigate protein interactions of ciliary proteins. Here, CRISPR/Cas9-mediated endogenously tagged ALMS1 cells were used for affinity-based protein complex analysis. Centrosomal and microtubule-associated proteins were identified, which are potential regulators of ALMS1 function, such as the centrosomal protein 70 kDa (CEP70). Candidate proteins were further investigated in ALMS1-deficient hTERT-RPE1 cells. Loss of ALMS1 led to shortened cilia with no change in structural protein localization, for example, acetylated and É£-tubulin, Centrin-3, or the novel interactor CEP70. Conversely, reduction of CEP70 resulted in decreased ALMS1 at the ciliary basal body. Complex analysis of CEP70 revealed domain-specific ALMS1 interaction involving the TPR-containing C-terminal (TRP-CT) fragment of CEP70. In addition to ALMS1, several ciliary proteins, including CEP135, were found to specifically bind to the TPR-CT domain. Data are available via ProteomeXchange with the identifier PXD046401. Protein interactors identified in this study provide candidate lists that help to understand ALMS1 and CEP70 function in cilia-related protein modification, cell death, and disease-related mechanisms.

Sustained Extracellular Electrical Stimulation Modulates the Permeability of Gap Junctions in rd1 Mouse Retina with Photoreceptor Degeneration.

Neurons build vast gap junction-coupled networks (GJ-nets) that are permeable to ions or small molecules, enabling lateral signaling. Herein, we investigate (1) the effect of blinding diseases on GJ-nets in mouse retinas and (2) the impact of electrical stimulation on GJ permeability. GJ permeability was traced in the acute retinal explants of blind retinal degeneration 1 (rd1) mice using the GJ tracer neurobiotin. The tracer was introduced via the edge cut method into the GJ-net, and its spread was visualized in histological preparations (fluorescent tagged) using microscopy. Sustained stimulation was applied to modulate GJ permeability using a single large electrode. Our findings are: (1) The blind rd1 retinas displayed extensive intercellular coupling via open GJs. Three GJ-nets were identified: horizontal, amacrine, and ganglion cell networks. (2) Sustained stimulation significantly diminished the tracer spread through the GJs in all the cell layers, as occurs with pharmaceutical inhibition with carbenoxolone. We concluded that the GJ-nets of rd1 retinas remain coupled and functional after blinding disease and that their permeability is regulatable by sustained stimulation. These findings are essential for understanding molecular signaling in diseases over coupled networks and therapeutic approaches using electrical implants, such as eliciting visual sensations or suppressing cortical seizures.

CRISPR/Cas9-mediated Genomic Editing of Cluap1/IFT38 Reveals a New Role in Actin Arrangement.

CRISPR/Cas9-mediated gene editing allows manipulation of a gene of interest in its own chromosomal context. When applied to the analysis of protein interactions and in contrast to exogenous expression of a protein, this can be studied maintaining physiological stoichiometry, topology, and context. We have used CRISPR/Cas9-mediated genomic editing to investigate Cluap1/IFT38, a component of the intraflagellar transport complex B (IFT-B). Cluap1 has been implicated in human development as well as in cancer progression. Cluap1 loss of function results in early developmental defects with neural tube closure, sonic hedgehog signaling and left-right defects. Herein, we generated an endogenously tagged Cluap1 for protein complex analysis, which was then correlated to the corresponding interactome determined by ectopic expression. Besides IFT-B complex components, new interacting proteins like Ephrin-B1 and TRIP6, which are known to be involved in cytoskeletal arrangement and protein transport, were identified. With the identification of platelet-derived growth factor A (PDGFA) and coiled-coil domain-containing protein 6 (CCDC6) two new interactions were discovered, which link Cluap1 to ciliogenesis and cancer development. The CRISPR/Cas9-mediated knockout of Cluap1 revealed a new phenotype affecting the actin cytoskeleton. Together, these data provide first evidence for a role of Cluap1 not only for cilia assembly and maintenance but also for cytoskeletal rearrangement and intracellular transport processes.

Targeted ablation of the Pde6h gene in mice reveals cross-species differences in cone and rod phototransduction protein isoform inventory.

Phosphodiesterase-6 (PDE6) is a multisubunit enzyme that plays a key role in the visual transduction cascade in rod and cone photoreceptors. Each type of photoreceptor utilizes discrete catalytic and inhibitory PDE6 subunits to fulfill its physiological tasks, i.e. the degradation of cyclic guanosine-3',5'-monophosphate at specifically tuned rates and kinetics. Recently, the human PDE6H gene was identified as a novel locus for autosomal recessive (incomplete) color blindness. However, the three different classes of cones were not affected to the same extent. Short wave cone function was more preserved than middle and long wave cone function indicating that some basic regulation of the PDE6 multisubunit enzyme was maintained albeit by a unknown mechanism. To study normal and disease-related functions of cone Pde6h in vivo, we generated Pde6h knock-out (Pde6h(-/-)) mice. Expression of PDE6H in murine eyes was restricted to both outer segments and synaptic terminals of short and long/middle cone photoreceptors, whereas Pde6h(-/-) retinae remained PDE6H-negative. Combined in vivo assessment of retinal morphology with histomorphological analyses revealed a normal overall integrity of the retinal organization and an unaltered distribution of the different cone photoreceptor subtypes upon Pde6h ablation. In contrast to human patients, our electroretinographic examinations of Pde6h(-/-) mice suggest no defects in cone/rod-driven retinal signaling and therefore preserved visual functions. To this end, we were able to demonstrate the presence of rod PDE6G in cones indicating functional substitution of PDE6. The disparities between human and murine phenotypes caused by mutant Pde6h/PDE6H suggest species-to-species differences in the vulnerability of biochemical and neurosensory pathways of the visual signal transduction system.

A nonsense mutation in PDE6H causes autosomal-recessive incomplete achromatopsia.

Achromatopsia (ACHM) is an autosomal-recessive retinal dystrophy characterized by color blindness, photophobia, nystagmus, and severely reduced visual acuity. Its prevalence has been estimated to about 1 in 30,000 individuals. Four genes, GNAT2, PDE6C, CNGA3, and CNGB3, have been implicated in ACHM, and all encode functional components of the phototransduction cascade in cone photoreceptors. Applying a functional-candidate-gene approach that focused on screening additional genes involved in this process in a cohort of 611 index cases with ACHM or other cone photoreceptor disorders, we detected a homozygous single base change (c.35C>G) resulting in a nonsense mutation (p.Ser12(∗)) in PDE6H, encoding the inhibitory γ subunit of the cone photoreceptor cyclic guanosine monophosphate phosphodiesterase. The c.35C>G mutation was present in three individuals from two independent families with a clinical diagnosis of incomplete ACHM and preserved short-wavelength-sensitive cone function. Moreover, we show through immunohistochemical colocalization studies in mouse retina that Pde6h is evenly present in all retinal cone photoreceptors, a fact that had been under debate in the past. These findings add PDE6H to the set of genes involved in autosomal-recessive cone disorders and demonstrate the importance of the inhibitory γ subunit in cone phototransduction.

Expression of poly(ADP-ribose) glycohydrolase in wild-type and PARG-110 knock-out retina.

Poly(ADP-ribose) (PAR) turnover is required for many cellular processes, and highly relevant for cell death and survival. This post-translational protein modification is regulated by the synthesizing enzyme poly(ADP)ribose-polymerase (PARP) and the degrading enzyme poly(ADP-ribose) glycohydrolase (PARG). Previously, PARP activity was found to be involved in photoreceptor degeneration in the rd1 mouse and in rd1-like conditions PARP-1 was the main PARP family member contributing to photoreceptor cell death. Despite the manifest role of PARP and PAR accumulation in photoreceptor cell death, the influence of PAR degradation on photoreceptor viability was still unknown. Here, we investigated the role of PARG in photoreceptor degeneration using the PARG-110 knock out mouse and report for the first time on PARG expression in wild-type and knock-out retina.

Paralog-specific TTC30 regulation of Sonic hedgehog signaling.

The intraflagellar transport (IFT) machinery is essential for cilia assembly, maintenance, and trans-localization of signaling proteins. The IFT machinery consists of two large multiprotein complexes, one of which is the IFT-B. TTC30A and TTC30B are integral components of this complex and were previously shown to have redundant functions in the context of IFT, preventing the disruption of IFT-B and, thus, having a severe ciliogenesis defect upon loss of one paralog. In this study, we re-analyzed the paralog-specific protein complexes and discovered a potential involvement of TTC30A or TTC30B in ciliary signaling. Specifically, we investigated a TTC30A-specific interaction with protein kinase A catalytic subunit α, a negative regulator of Sonic hedgehog (Shh) signaling. Defects in this ciliary signaling pathway are often correlated to synpolydactyly, which, intriguingly, is also linked to a rare TTC30 variant. For an in-depth analysis of this unique interaction and the influence on Shh, TTC30A or B single- and double-knockout hTERT-RPE1 were employed, as well as rescue cells harboring wildtype TTC30 or the corresponding mutation. We could show that mutant TTC30A inhibits the ciliary localization of Smoothened. This observed effect is independent of Patched1 but associated with a distinct phosphorylated PKA substrate accumulation upon treatment with forskolin. This rather prominent phenotype was attenuated in mutant TTC30B. Mass spectrometry analysis of wildtype versus mutated TTC30A or TTC30B uncovered differences in protein complex patterns and identified an impaired TTC30A-IFT57 interaction as the possible link leading to synpolydactyly. We could observe no impact on cilia assembly, leading to the hypothesis that a slight decrease in IFT-B binding can be compensated, but mild phenotypes, like synpolydactyly, can be induced by subtle signaling changes. Our systematic approach revealed the paralog-specific influence of TTC30A KO and mutated TTC30A on the activity of PRKACA and the uptake of Smoothened into the cilium, resulting in a downregulation of Shh. This downregulation, combined with interactome alterations, suggests a potential mechanism of how mutant TTC30A is linked to synpolydactyly.

Structural and functional protein network analyses predict novel signaling functions for rhodopsin.

Orchestration of signaling, photoreceptor structural integrity, and maintenance needed for mammalian vision remain enigmatic. By integrating three proteomic data sets, literature mining, computational analyses, and structural information, we have generated a multiscale signal transduction network linked to the visual G protein-coupled receptor (GPCR) rhodopsin, the major protein component of rod outer segments. This network was complemented by domain decomposition of protein-protein interactions and then qualified for mutually exclusive or mutually compatible interactions and ternary complex formation using structural data. The resulting information not only offers a comprehensive view of signal transduction induced by this GPCR but also suggests novel signaling routes to cytoskeleton dynamics and vesicular trafficking, predicting an important level of regulation through small GTPases. Further, it demonstrates a specific disease susceptibility of the core visual pathway due to the uniqueness of its components present mainly in the eye. As a comprehensive multiscale network, it can serve as a basis to elucidate the physiological principles of photoreceptor function, identify potential disease-associated genes and proteins, and guide the development of therapies that target specific branches of the signaling pathway.

A homologous genetic basis of the murine cpfl1 mutant and human achromatopsia linked to mutations in the PDE6C gene.

Retinal cone photoreceptors mediate fine visual acuity, daylight vision, and color vision. Congenital hereditary conditions in which there is a lack of cone function in humans cause achromatopsia, an autosomal recessive trait, characterized by low vision, photophobia, and lack of color discrimination. Herein we report the identification of mutations in the PDE6C gene encoding the catalytic subunit of the cone photoreceptor phosphodiesterase as a cause of autosomal recessive achromatopsia. Moreover, we show that the spontaneous mouse mutant cpfl1 that features a lack of cone function and rapid degeneration of the cone photoreceptors represents a homologous mouse model for PDE6C associated achromatopsia.

In vivo imaging reveals novel aspects of retinal disease progression in Rs1h(-/Y) mice but no therapeutic effect of carbonic anhydrase inhibition.

PURPOSE: X-linked juvenile retinoschisis (XLRS) is the most common juvenile maculopathy in men and is caused by mutations in the gene encoding retinoschisin (RS1). Evidence in the literature on the therapeutic effect of carboanhydrase inhibitors (CAIs) to treat schisis formation in the retina has remained equivocal. Here, we evaluate the effect of the CAI dorzolamide on the structural and functional disease progression in the mouse model for XLRS (Rs1h(-/y)). METHODS: Rs1h (-/y) mice were treated unilaterally with dorzolamide eye drops (Trusopt(®) 20 mg/mL) every 12 h for 2 weeks starting on postnatal day 14 (n = 27). Changes of retinal structure were monitored by confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography 12 h, 14 days, 4 weeks, 2 months, and 6 months after completion of the treatment. RESULTS: Schisis formation (peak at 3 months) preceded photoreceptor degeneration and hyper-fluorescence (peak at 7 months). Structural pathology was most severe in the superior hemi-retina with previously unreported hyper-fluorescent lesions. Quantitative analysis showed no significant differences regarding the inner or outer retinal thickness of the treated vs. untreated eyes 12 h after the completion of treatment (IRT(12 h) = -1.29 ± 1.89 µm; ORT(12 h) = 0.61 ± 2.08 µm; mean ± 95%CI) or at any later time point. CONCLUSION: Time line analysis after short-term treatment with CAI failed to show short-, intermediate-, or long-term evidence of structural improvement in Rs1h(-/y) mice. Schisis formation in the inner retina peaked at the age of 3 months and was followed by photoreceptor degeneration predominantly in the superior hemi-retina. Previously unreported hyper-fluorescent lesions co-register with structural retinal pathologies.

TTC30A and TTC30B Redundancy Protects IFT Complex B Integrity and Its Pivotal Role in Ciliogenesis.

Intraflagellar transport (IFT) is a microtubule-based system that supports the assembly and maintenance of cilia. The dysfunction of IFT leads to ciliopathies of variable severity. Two of the IFT-B components are the paralogue proteins TTC30A and TTC30B. To investigate whether these proteins constitute redundant functions, CRISPR/Cas9 was used to generate single TTC30A or B and double-knockout hTERT-RPE1 cells. Ciliogenesis assays showed the redundancy of both proteins while the polyglutamylation of cilia was affected in single knockouts. The localization of other IFT components was not affected by the depletion of a single paralogue. A loss of both proteins led to a severe ciliogenesis defect, resulting in no cilia formation, which was rescued by TTC30A or B. The redundancy can be explained by the highly similar interaction patterns of the paralogues; both equally interact with the IFT-B machinery. Our study demonstrates that a loss of one TTC30 paralogue can mostly be compensated by the other, thus preventing severe ciliary defects. However, cells assemble shorter cilia, which are potentially limited in their function, especially because of impaired polyglutamylation. A complete loss of both proteins leads to a deficit in IFT complex B integrity followed by disrupted IFT and subsequently no cilia formation.

Caspase inhibitors protect against NMDA-mediated retinal ganglion cell death.

BACKGROUND: Apoptosis is a major mechanism of cell death in glutamate-induced excitotoxicity and caspases as the executors of apoptosis play an important role in the development of various central nervous system and eye diseases. We studied the involvement of certain caspases in excitotoxic retinal ganglion cell death, which was experimentally induced in Brown Norway Rats by application of the glutamate receptor agonist N-methyl-D-aspartate (NMDA). METHODS: Animals were injected intravitreally with one of six caspase inhibitors (against caspases 1, 3, 4, 6, 8 and 9). Seven hours later, NMDA or phosphate-buffered saline as a control was injected intravitreally into the respective eyes. The neuroprotective potential against NMDA toxicity was assessed by retinal ganglion cell quantification. Additionally, wholemount TUNEL was performed. RESULTS: Statistical analysis revealed significant neuroprotective effects for the inhibitors of caspases 3, 6, 8 and 9, but not for those of caspases 1 and 4. The inhibitors of caspases 6 and 9 showed greater neuroprotective potential than those of caspases 3 and 8, although cell death was not entirely averted in any case. Results of ganglion cell counts were confirmed for the most pronounced treatment groups using wholemount TUNEL. CONCLUSION: Excitotoxic retinal ganglion cell death after NMDA injection is mediated mainly through apoptosis, whereby extrinsic as well as intrinsic pathways of caspase activation play a role.

Pharmacological Inhibition of the VCP/Proteasome Axis Rescues Photoreceptor Degeneration in RHOP23H Rat Retinal Explants.

Rhodopsin (RHO) misfolding mutations are a common cause of the blinding disease autosomal dominant retinitis pigmentosa (adRP). The most prevalent mutation, RHOP23H, results in its misfolding and retention in the endoplasmic reticulum (ER). Under homeostatic conditions, misfolded proteins are selectively identified, retained at the ER, and cleared via ER-associated degradation (ERAD). Overload of these degradation processes for a prolonged period leads to imbalanced proteostasis and may eventually result in cell death. ERAD of misfolded proteins, such as RHOP23H, includes the subsequent steps of protein recognition, targeting for ERAD, retrotranslocation, and proteasomal degradation. In the present study, we investigated and compared pharmacological modulation of ERAD at these four different major steps. We show that inhibition of the VCP/proteasome activity favors cell survival and suppresses P23H-mediated retinal degeneration in RHOP23H rat retinal explants. We suggest targeting this activity as a therapeutic approach for patients with currently untreatable adRP.

Pharmacokinetics of Pullulan-Dexamethasone Conjugates in Retinal Drug Delivery.

The treatment of retinal diseases by intravitreal injections requires frequent administration unless drug delivery systems with long retention and controlled release are used. In this work, we focused on pullulan (≈67 kDa) conjugates of dexamethasone as therapeutic systems for intravitreal administration. The pullulan-dexamethasone conjugates self-assemble into negatively charged nanoparticles (average size 326 ± 29 nm). Intravitreal injections of pullulan and pullulan-dexamethasone were safe in mouse, rat and rabbit eyes. Fluorescently labeled pullulan particles showed prolonged retention in the vitreous and they were almost completely eliminated via aqueous humor outflow. Pullulan conjugates also distributed to the retina via Müller glial cells when tested in ex vivo retina explants and in vivo. Pharmacokinetic simulations showed that pullulan-dexamethasone conjugates may release free and active dexamethasone in the vitreous humor for over 16 days, even though a large fraction of dexamethasone may be eliminated from the eye as bound pullulan-dexamethasone. We conclude that pullulan based drug conjugates are promising intravitreal drug delivery systems as they may reduce injection frequency and deliver drugs into the retinal cells.

Loss of Complement Factor H impairs antioxidant capacity and energy metabolism of human RPE cells.

Polymorphisms in the Complement Factor H (CFH) gene, coding for the Factor H protein (FH), can increase the risk for age-related macular degeneration (AMD). AMD-associated CFH risk variants, Y402H in particular, impair FH function leading to complement overactivation. Whether this alone suffices to trigger AMD pathogenesis remains unclear. In AMD, retinal homeostasis is compromised due to the dysfunction of retinal pigment epithelium (RPE) cells. To investigate the impact of endogenous FH loss on RPE cell balance, we silenced CFH in human hTERT-RPE1 cells. FH reduction led to accumulation of C3, at both RNA and protein level and increased RPE vulnerability toward oxidative stress. Mild hydrogen-peroxide exposure in combination with CFH knock-down led to a reduction of glycolysis and mitochondrial respiration, paralleled by an increase in lipid peroxidation, which is a key aspect of AMD pathogenesis. In parallel, cell viability was decreased. The perturbations of energy metabolism were accompanied by transcriptional deregulation of several glucose metabolism genes as well as genes modulating mitochondrial stability. Our data suggest that endogenously produced FH contributes to transcriptional and metabolic homeostasis and protects RPE cells from oxidative stress, highlighting a novel role of FH in AMD pathogenesis.

Merging organoid and organ-on-a-chip technology to generate complex multi-layer tissue models in a human retina-on-a-chip platform.

The devastating effects and incurable nature of hereditary and sporadic retinal diseases such as Stargardt disease, age-related macular degeneration or retinitis pigmentosa urgently require the development of new therapeutic strategies. Additionally, a high prevalence of retinal toxicities is becoming more and more an issue of novel targeted therapeutic agents. Ophthalmologic drug development, to date, largely relies on animal models, which often do not provide results that are translatable to human patients. Hence, the establishment of sophisticated human tissue-based in vitro models is of upmost importance. The discovery of self-forming retinal organoids (ROs) derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) is a promising approach to model the complex stratified retinal tissue. Yet, ROs lack vascularization and cannot recapitulate the important physiological interactions of matured photoreceptors and the retinal pigment epithelium (RPE). In this study, we present the retina-on-a-chip (RoC), a novel microphysiological model of the human retina integrating more than seven different essential retinal cell types derived from hiPSCs. It provides vasculature-like perfusion and enables, for the first time, the recapitulation of the interaction of mature photoreceptor segments with RPE in vitro. We show that this interaction enhances the formation of outer segment-like structures and the establishment of in vivo-like physiological processes such as outer segment phagocytosis and calcium dynamics. In addition, we demonstrate the applicability of the RoC for drug testing, by reproducing the retinopathic side-effects of the anti-malaria drug chloroquine and the antibiotic gentamicin. The developed hiPSC-based RoC has the potential to promote drug development and provide new insights into the underlying pathology of retinal diseases.

A Cleared View on Retinal Organoids.

Human induced pluripotent stem cell (hiPSC)-derived organoids mimicking tissues and organs in vitro have advanced medical research, as they opened up new possibilities for in-depth basic research on human organ development as well as providing a human in vitro model for personalized therapeutic approaches. hiPSC-derived retinal organoids have proven to be of great value for modeling the human retina featuring a very similar cellular composition, layering, and functionality. The technically challenging imaging of three-dimensional structures such as retinal organoids has, however, raised the need for robust whole-organoid imaging techniques. To improve imaging of retinal organoids we optimized a passive clearing technique (PACT), which enables high-resolution visualization of fragile intra-tissue structures. Using cleared retinal organoids, we could greatly enhance the antibody labeling efficiency and depth of imaging at high resolution, thereby improving the three-dimensional microscopy output. In that course, we were able to identify the spatial morphological shape and organization of, e.g., photoreceptor cells and bipolar cell layers. Moreover, we used the synaptic protein CtBP2/Ribeye to visualize the interconnection points of photoreceptor and bipolar cells forming the retinal-specific ribbon synapses.

A retinal model of cerebral malaria.

Malaria is a causative factor in about 500.000 deaths each year world-wide. Cerebral malaria is a particularly severe complication of this disease and thus associated with an exceedingly high mortality. Malaria retinopathy is an ocular manifestation often associated with cerebral malaria, and presumably shares a substantial part of its pathophysiology. Here, we describe that indeed murine malaria retinopathy reproduced the main hallmarks of the corresponding human disease. In the living animal, we were able to follow the circulation and cellular localization of malaria parasites transgenically labelled with GFP via non-invasive in vivo retinal imaging. We found that malaria parasites cross the blood-retinal-barrier and infiltrate the neuroretina, concomitant with an extensive, irreversible, and long-lasting retinal neurodegeneration. Furthermore, anti-malarial treatment with dihydroartemisinin strongly diminished the load of circulating parasites but resolved the symptoms of the retinopathy only in part. In summary, we introduce here a novel preclinical model for human cerebral malaria that is much more directly accessible for studies into disease pathophysiology and development of novel treatment approaches. In vivo retinal imaging may furthermore serve as a valuable tool for the early diagnosis of the human disease.

Feasibility study for a glutamate driven subretinal prosthesis: local subretinal application of glutamate on blind retina evoke network-mediated responses in different types of ganglion cells.

OBJECTIVE: A feasibility study for a transmitter based subretinal prosthesis, generating visual responses in blind mouse retina is presented. APPROACH: Degenerated rd1 mouse retina were stimulated in subretinal configuration by local glutamate (Glu) or NMDA application via micropipettes (~1.5 µm) and thereby the outer retinal activity was recorded by calcium-imaging or the ganglion cell (GC) activity was recorded by the multi-electrode array system. The network mediated activation of GC via bipolar cells was approved by the administration of Glu receptor blockers. MAIN RESULTS: Data of the degenerated and blind rd1 mouse retina reveals that the outer retina is Glu sensitive and that the subretinal Glu stimulation promotes network mediated GC responses. Analysis of the spatial activity-spread indicates that the Glu induced cell activation radius in the outer retina (~12.5 µm) and postsynaptically activated GC (~40 µm) is focal to the stimulation pipette tip. Moreover, the application of NMDA in subretinal space also evoked network mediated GC responses. The Glu-activated GC were identified as ON-OFF, OFF and two ON cells types. SIGNIFICANCE: This study evaluates the prerequisite for the function of a transmitter based implant, that after the loss of the photoreceptors, the remnant blind retinal network is Glu sensitive and functional, positively. The differential activation of ON (hyperpolarisation) and OFF (depolarisation) bipolar cells by transmitter Glu is a unique feature and of high interest for retinal implants. Therefore, the respective bipolar cell types could only be driven by glutamatergic stimulation accurately and not by electrical stimulation. The preserved functionality of the blind retina at the onset of complete blindness is motivating to continue research on a transmitter-based prosthesis. Since the artificial Glu stimulation mimics the natural retinal input, early implantation of a Glu-prosthesis might delay the devastating retinal remodelling positively, due to the neuronal-plasticity.

Evaluation of polyesteramide (PEA) and polyester (PLGA) microspheres as intravitreal drug delivery systems in albino rats.

PURPOSE: To study the suitability of injectable microspheres based on poly(ester amide) (PEA) or poly lactic-co-glycolic acid (PLGA) as potential vehicles for intravitreal drug delivery in rat eyes. Dexamethasone-loaded PEA microspheres (PEA + DEX) were also evaluated. METHODS: Forty male Sprague Dawley rats were divided into four groups that received different intravitreally injected microspheres: PEA group (n = 12); PLGA group (n = 12); PEA + DEX group (n = 8); and control group (no injection, n = 8). Electroretinography (ERG), fundus autofluorescence (FAF), and spectral domain optical coherence tomography (sdOCT) were performed at baseline, weeks 1 and 2, and months 1, 2, and 3 after intravitreal injection. Eyes were histologically examined using light microscopy and transmission electron microscopy at the end of the in vivo study. RESULTS: There were no statistically significant changes in ERG among the groups. Abnormal FAF pattern and abnormal deposits in OCT were observed after injection but almost completely disappeared between week 2 and month 3 in all injected groups. GFAP staining showed that Müller glia cell activation was most pronounced in PLGA-injected eyes. Increased cell death was not observed by TUNEL staining at month 1. In electron microscopy at month 3, the remnants of microparticles were found in the retinal cells of all injected groups, and loss of plasma membrane was seen in the PLGA group. CONCLUSIONS: Although morphological changes such as mild glial activation and material remnants were observed histologically 1 month and 3 months after injection in all injected groups, minor cell damage was noted only in the PLGA group at 3 months after injection. No evidence of functional abnormality relative to untreated eyes could be detected by ERG 3 months after injection in all groups. Changes observed in in vivo imaging such as OCT and FAF disappeared after 3 months in almost all cases.