PURPOSE:This study aimed to compare the neuroprotective effects of subretinally delivered human central nervous system stem cells (HuCNS-SC) and a novel, single-cell suspension formulation, Neubright (NB) in the RCS rat. METHODS:At postnatal day 21, RCS rats were subretinally injected with a 150,000 cell dose of either HuCNS-SC or NB in a 2 μL volume. The contralateral control eye was injected with balanced salt solution. Visual function outcomes were measured using optokinetic tracking and electroretinography. Whole globes were harvested at P60 and P180 for immunofluorescence (IF). To identify cells in the subretinal space, retinal cross-sections were stained with a human specific marker (STEM121). Cell spread, outer nuclear layer (ONL) thickness, and cell migration were quantified using confocal microscopy and image J. RESULTS:IF demonstrated a clear presence of STEM121-positive cells in the subretinal space after delivery of both HuCNS-SC and NB. The ONL was thicker in areas adjacent to the injected cells, whereas a greater degree of degeneration was observed outside of treated areas. The novel NB formulation had significantly increased cell spread and visual performance compared to the original HuCNS-SC formulation. CONCLUSIONS:A novel single-cell suspension of human neural stem cells, NB, with high cell viability was successfully generated. NB improved cell spread in the subretinal space compared to HuCNS-SC improving visual outcomes in the RCS rat. Translational Relevance: This bridging study will be used as an investigational new drug approval enabling study to evaluate NB in clinical trials for macular retinal degeneration.

Photoreceptor (PR) loss causes vision loss in many blinding diseases, and effective therapies to prevent this cell loss are lacking. Aspartate aminotransferases (GOTs), located in the cytosol (GOT1) and mitochondria (GOT2), are key components of the malate-aspartate shuttle, which transfers reducing equivalents from cytosol to mitochondria. Previous work has implicated the GOTs as potential modulators of blinding retinal disease. To determine the roles of GOT1 and GOT2 in rod PRs, we generated rod PR-specific Got1 or Got2 conditional knockout mice (Got1 or Got2 cKO). We previously showed that Got1 cKO causes PR degeneration and is accompanied by NADH accumulation and a decreased retinal NAD+/NADH ratio. Here, we show that NADH oxidation via metabolic or genetic means prolongs PR survival in Got1 cKO animals, implicating NADH accumulation, or reductive stress, as a key driver of PR degeneration. In contrast, Got2 cKO causes minimal PR degeneration and alterations in retinal NADH and the NAD+/NADH ratio that oppose reductive stress. Interestingly, GOT2, but not GOT1, is decreased in multiple models of PR degeneration, including retinal detachment (RD) where the NAD+/NADH ratio favors a reductive state. Notably, loss of Got2 in PRs demonstrates a neuroprotective effect after experimental RD suggesting decreased GOT2 expression may be part of a stress response to promote PR survival. Overall, this study illustrates the differential dependence on the GOTs for PR health, provides evidence that an overly reductive environment is detrimental to PR survival, and identifies GOT2 as a novel therapeutic target with potentially broad application in blinding diseases.

Cell replacement therapy is a promising therapeutic option for dry age-related macular degeneration (AMD). In this study, we outline our design for scalable manufacture with appropriate quality gates and present in vivo data for establishing preclinical safety and efficacy of an induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) product, thus laying the foundation for Phase 1/2a trial approval in India (ClinicalTrials.gov ID: NCT06394232; date of registration: 23rd September 2024). Escalating doses of RPE cell suspension in immunocompromised animals demonstrated absence of tumor formation up to 9 months post-injection. Good Laboratory Practices (GLP) toxicology and tolerability studies in rabbits and non-human primates (NHP) respectively showed no major adverse events. RPE transplanted into immune suppressed RCS rats showed integration, neuroprotection and rescue of visual function. In addition, we provide a detailed description of the modifications in GMP manufacturing protocol to create a final product with a unique composition and Chemistry, Manufacturing and Controls (CMC) studies performed during product development.

Lipid nanoparticles (LNPs) have shown great potential in the field of gene therapy for retinal diseases. To expand on this application, we investigated LNP-mediated mRNA delivery to the anterior chamber of the eye via the intracameral (IC) route of administration. Here, we show that IC injections of LNPs facilitated protein expression and gene editing in the trabecular meshwork (TM). Administration of Cre-mRNA LNPs to Ai9 mice resulted in robust tdTomato expression in the angle and corneal endothelium. In C57BL/6 mice, mCherry-mRNA LNPs demonstrated localized protein expression in the TM, which peaked at 72 h and subsequently declined over 120 h. Additionally, LNPs encapsulating Cas9 mRNA with sgAi9 enabled in vivo gene editing in Ai9 mice, with up to 14.3 % editing efficiency. This induced tdTomato expression in the iridocorneal angle, validating the potential of LNPs for gene editing applications. Importantly, no ocular toxicity was observed, indicating the safety of the IC LNP administration. Our findings highlight the use of LNPs for targeted gene therapy and editing, paving the path for the treatment of diseases such as glaucoma in the anterior eye.

The number of retinal pigment epithelium (RPE) transplantation clinical trials for dry age-related macular degeneration (AMD) is increasing quickly, with groups using different stem cell sources, delivery approaches, and immune suppression. We discuss the recent success in a phase 1/2a clinical trial1 evaluating allogeneic RPE stem cell-derived RPE cells isolated from the RPE layer of human cadaveric eyes.

Pantothenate kinase-associated neurodegeneration (PKAN) is an autosomal recessive movement and vision disorder in the neurodegeneration with brain iron accumulation family of diseases. PKAN is caused by mutations in PANK2, encoding pantothenate kinase 2, causing an inborn error of coenzyme A metabolism and leading to iron accumulation in the basal ganglia. Peripheral pigmentary retinopathy is common in people with PKAN. The knockout murine model of the orthologous Pank2 gene is known to manifest retinal degeneration through electroretinography, pupillary response and histology analyses. Our longitudinal characterization of the retinopathy in this model reveals reduced visual performance and reduced photoreceptor thickness compared to wild-type mice. Additionally, retinal perturbations in coenzyme A metabolism and dopamine metabolism pathways mimic those previously observed in the brain. These data extend the murine ocular phenotype associated with loss of function of Pank2. With a measurable behavioral, structural and mechanistic retinal phenotype, this mouse model is an ideal pre-clinical model that can be used to evaluate therapeutics for PKAN.

Gene therapy has become a successful tool for treating inherited retinal diseases (IRDs). To date, recombinant adeno-associated virus (rAAV)- mediated delivery is the preferred method for gene transfer; however, its limited payload capacity restricts its use for treatment to causative loci under 5 kb. Recent advances in gene therapy tools have demonstrated the success of non-viral delivery vectors with lipid-based nanoparticles (LNPs) at the forefront. Owing to the SARS-CoV-2 vaccine, LNPs have already demonstrated clinical safety, however in regard to IRDs, the LNPs are limited to RPE and Muller glia cells, and their application has been limited to transient RNA delivery. Previously, we have reported that the introduction of N-Hydroxysuccinamide (NHS) functionalized PEG lipid (DSPE-PEG2K-NHS) to the LNPs (called LNPx) improved their overall transfection rate and widened their transfection efficiency to include not only RPE but photoreceptor cells. Taken together, this could expand LNP utility and allow for the treatment of many prevalent IRDs. Herein, we utilized LNPx to demonstrate the feasibility and safety of dsDNA delivery after subretinal injection into the murine retina, through a combination of multimodal in vivo imaging and post-mortem histology.

Complete encapsulation of nucleic acids by lipid-based nanoparticles (LNPs) is often thought to be one of the main prerequisites for successful nucleic acid delivery, as the lipid environment protects mRNA from degradation by external nucleases and assists in initiating delivery processes. However, delivery of mRNA via a preformed vesicle approach (PFV-LNPs) defies this precondition. Unlike traditional LNPs, PFV-LNPs are formed via a solvent-free mixing process, leading to a superficial mRNA localization. While demonstrating low encapsulation efficiency in the RiboGreen assay, PFV-LNPs improved delivery of mRNA to the retina by up to 50% compared to the LNP analogs across several benchmark formulations, suggesting the utility of this approach regardless of the lipid composition. Successful mRNA and gene editors' delivery is observed in the retinal pigment epithelium and photoreceptors and validated in mice, non-human primates, and human retinal organoids. Deploying PFV-LNPs in gene editing experiments result in a similar extent of gene editing compared to analogous LNP (up to 3% on genomic level) in the Ai9 reporter mouse model; but, remarkably, retinal tolerability is significantly improved for PFV-LNP treatment. The study findings indicate that the LNP formulation process can greatly influence mRNA transfection and gene editing outcomes, improving LNP treatment safety without sacrificing efficacy.

Purpose: Recent studies have shown that the retinal pigment epithelium (RPE) relies on fatty acid oxidation (FAO) for energy, however, its role in overall retinal health is unknown. The only FAO disorder that presents with chorioretinopathy is long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). Studying the molecular mechanisms can lead to new treatments for patients and elucidate the role of FAO in the RPE. This paper characterizes the chorioretinopathy progression in a recently reported LCHADD mouse model. Methods: Visual assessments, such as optokinetic tracking and fundus imaging, were performed in wildtype (WT) and LCHADD mice at 3, 6, 10, and 12 months of age. Retinal morphology was analyzed in 12-month retinal cross-sections using hematoxylin and eosin (H&E), RPE65, CD68, and TUNEL staining, whereas RPE structure was assessed using transmission electron microscopy (TEM). Acylcarnitine profiles were measured in isolated RPE/sclera samples to determine if FAO was blocked. Bulk RNA-sequencing of 12 month old male WT mice and LCHADD RPE/sclera samples assessed gene expression changes. Results: LCHADD RPE/sclera samples had a 5- to 7-fold increase in long-chain hydroxyacylcarnitines compared to WT, suggesting an impaired LCHAD step in long-chain FAO. LCHADD mice have progressively decreased visual performance and increased RPE degeneration starting at 6 months. LCHADD RPE have an altered structure and a two-fold increase in macrophages in the subretinal space. Finally, LCHADD RPE/sclera have differentially expressed genes compared to WT, including downregulation of genes important for RPE function and angiogenesis. Conclusions: Overall, this LCHADD mouse model recapitulates early-stage chorioretinopathy seen in patients with LCHADD and is a useful model for studying LCHADD chorioretinopathy.

Lipid nanoparticles (LNPs) largely rely on ionizable lipids to yield successful nucleic acid delivery via electrostatic disruption of the endosomal membrane. Here, we report the identification and evaluation of ionizable lipids containing a thiophene moiety (Thio-lipids). The Thio-lipids can be readily synthesized via the Gewald reaction, allowing for modular lipid design with functional constituents at various positions of the thiophene ring. Through the rational design of ionizable lipid structure, we prepared 47 Thio-lipids and identified some structural criteria required in Thio-lipids for efficient mRNA (messenger RNA) encapsulation and delivery in vitro and in vivo. Notably, none of the tested lipids have a pH-response profile like traditional ionizable lipids, potentially due to the electron delocalization in the thiophene core. Placement of the tails and localization of the ionizable headgroup in the thiophene core can endow the nanoparticles with the capability to reach various tissues. Using high-throughput formulation and barcoding techniques, we optimized the formulations to select two top lipids— 20b and 29d —and investigated their biodistribution in mice. Lipid 20b enabled LNPs to transfect the liver and spleen, and 29d LNP transfected the lung and spleen. Unexpectedly, LNP with lipid 20b was especially potent in mRNA delivery to the retina with no acute toxicity, leading to the successful delivery to the photoreceptors and retinal pigment epithelium in non-human primates.