Preformed Vesicle Approach to LNP Manufacturing Enhances Retinal mRNA Delivery

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.

Advancements in pre-clinical development of gene editing-based therapies to treat inherited retinal diseases

One of the major goals in the inherited retinal disease (IRD) field is to develop an effective therapy that can be applied to as many patients as possible. Significant progress has already been made toward this end, with gene editing at the forefront. The advancement of gene editing-based tools has been a recent focus of many research groups around the world. Here, we provide an update on the status of CRISPR/Cas-derived gene editors, promising options for delivery of these editing systems to the retina, and animal models that aid in pre-clinical testing of new IRD therapeutics.

Timed Notch Inhibition Drives Photoreceptor Fate Specification in Human Retinal Organoids

Purpose

Transplanting photoreceptors from human pluripotent stem cell–derived retinal organoids have the potential to reverse vision loss in affected individuals. However, transplantable photoreceptors are only a subset of all cells in the organoids. Hence, the goal of our current study was to accelerate and synchronize photoreceptor differentiation in retinal organoids by inhibiting the Notch signaling pathway at different developmental time-points using a small molecule, PF-03084014 (PF).

Methods

Human induced pluripotent stem cell– and human embryonic stem cells–derived retinal organoids were treated with 10 µM PF for 3 days starting at day 45 (D45), D60, D90, and D120 of differentiation. Organoids were collected at post-treatment days 14, 28, and 42 and analyzed for progenitor and photoreceptor markers and Notch pathway inhibition by immunohistochemistry (IHC), quantitative PCR, and bulk RNA sequencing (n = 3–5 organoids from three independent experiments).

Results

Retinal organoids collected after treatment showed a decrease in progenitor markers (KI67, VSX2, PAX6, and LHX2) and an increase in differentiated pan-photoreceptor markers (OTX2, CRX, and RCVRN) at all organoid stages except D120. PF-treated organoids at D45 and D60 exhibited an increase in cone photoreceptor markers (RXRG and ARR3). PF treatment at D90 revealed an increase in cone and rod photoreceptors markers (ARR3, NRL, and NR2E3). Bulk RNA sequencing analysis mirrored the immunohistochemistry data and quantitative PCR confirmed Notch effector inhibition.

Conclusions

Timing the Notch pathway inhibition in human retinal organoids to align with progenitor competency stages can yield an enriched population of early cone or rod photoreceptors.

Allele-specific gene editing to rescue dominant CRX-associated LCA7 phenotypes in a retinal organoid model

Cases of Leber congenital amaurosis caused by mutations in CRX (LCA7) exhibit an early form of the disease and show signs of significant photoreceptor dysfunction and eventual loss. To establish a translational in vitro model system to study gene-editing-based therapies, we generated LCA7 retinal organoids harboring a dominant disease-causing mutation in CRX. Our LCA7 retinal organoids develop signs of immature and dysfunctional photoreceptor cells, providing us with a reliable in vitro model to recapitulate LCA7. Furthermore, we performed a proof-of-concept study in which we utilize allele-specific CRISPR/Cas9-based gene editing to knock out mutant CRX and saw moderate rescue of photoreceptor phenotypes in our organoids. This work provides early evidence for an effective approach to treat LCA7, which can be applied more broadly to other dominant genetic diseases.

Bulk and single-cell gene expression analyses reveal aging human choriocapillaris has pro-inflammatory phenotype

The human choroidal vasculature is subject to age-related structural and gene expression changes implicated in age-related macular degeneration (AMD). In this study, we performed both bulk and single-cell RNA sequencing on infant (n = 4 for bulk experiments, n = 2 for single-cell experiments) and adult (n = 13 for bulk experiments, n = 6 for single-cell experiments) human donors to characterize how choroidal gene expression changes with age. Differential expression analysis revealed that aged choroidal samples were enriched in genes encoding pro-inflammatory transcription factors and leukocyte transendothelial cell migration adhesion proteins. Such genes were observed to be differentially expressed specifically within choroidal endothelial cells at the single-cell level. Immunohistochemistry experiments support transcriptional findings that CD34 is elevated in infant choriocapillaris endothelial cells while ICAM-1 is enriched in adults. These results suggest several potential drivers of the pro-inflammatory vascular phenotype observed with advancing age.

MANF delivery improves retinal homeostasis and cell replacement therapies in ageing mice

Ageing is a major risk factor for vision loss, and inflammation is an important contributor to retinal disease in the elderly. Regenerative medicine based on cell replacement strategies has emerged in recent years as a promising approach to restore vision. However, how the ageing process affects retinal homeostasis and inflammation in the retina and how this may impose a limitation to the success of such interventions remains unknown. Here we report that, in mice and humans, retinal ageing is associated with a reduction in MANF protein levels, specifically in the choroid, where increased densities of activated macrophages can be detected. We further show that the retina of old wild type mice, in the absence of any other genetic alteration, has limited homeostatic capacity after damage imposed by light exposure and reduced engraftment efficiency of exogenously supplied photoreceptors. Finally, we show that supplementation of MANF recombinant protein can improve retinal homeostasis and repair capacity in both settings, correlating with reduced numbers of activated macrophages in the old retina. Our work identifies age-related alterations in retinal homeostasis, independent of genetic alterations, leading to age-related retinal inflammation and damage susceptibility. We suggest that MANF therapy is a potential intervention to maintain retinal homeostasis in the elderly and improve the success of retinal regenerative therapies applied to aged individuals.

Immunological Considerations for Retinal Stem Cell Therapy

There is an increasing effort toward generating replacement cells for neuronal application due to the nonregenerative nature of these tissues. While much progress has been made toward developing methodologies to generate these cells, there have been limited improvements in functional restoration. Some of these are linked to the degenerative and often nonreceptive microenvironment that the new cells need to integrate into. In this chapter, we will focus on the status and role of the immune microenvironment of the retina during homeostasis and disease states. We will review changes in both innate and adaptive immunity as well as the role of immune rejection in stem cell replacement therapies. The chapter will end with a discussion of immune-modulatory strategies that have helped to ameliorate these effects and could potentially improve functional outcome for cell replacement therapies for the eye.

Imidazole Compounds for Protecting Choroidal Endothelial Cells from Complement Injury

Age-related macular degeneration (AMD) is a common, blinding disease associated with increased complement system activity. Eyes with AMD show elevated accumulation of the membrane attack complex (MAC) in the choriocapillaris and degeneration of macular choriocapillaris endothelial cells (ECs). Thus, one could reasonably conclude that the endothelial cell death that occurs in AMD is due to injury by the MAC. We therefore sought to identify strategies for protecting ECs against MAC lysis. RF/6A endothelial cells were pre-incubated with a library of FDA-approved small molecules, followed by incubation with complement intact human serum quantification of cell death. Two closely related molecules identified in the screen, econazole nitrate and miconazole nitrate, were followed in validation and mechanistic studies. Both compounds reduced lysis of choroidal ECs treated with complement-intact serum, across a range of doses from 1 to 100 µM. Cell rescue was confirmed in mouse primary choroidal ECs. Both exosome release and cell surface roughness (assessed using a Holomonitor system) were reduced by drug pretreatment in RF/6A cells, whereas endosome formation increased with both drugs, consistent with imidazole-mediated alterations of cell surface dynamics. The results in the current study provide further proof of principle that small molecules can protect choroidal ECs from MAC-induced cell death and suggest that FDA approved compounds may be beneficial in reducing vascular loss and progression of AMD.

CRISPR-Cas9 genome engineering: Treating inherited retinal degeneration

Gene correction is a valuable strategy for treating inherited retinal degenerative diseases, a major cause of irreversible blindness worldwide. Single gene defects cause the majority of these retinal dystrophies. Gene augmentation holds great promise if delivered early in the course of the disease, however, many patients carry mutations in genes too large to be packaged into adeno-associated viral vectors and some, when overexpressed via heterologous promoters, induce retinal toxicity. In addition to the aforementioned challenges, some patients have sustained significant photoreceptor cell loss at the time of diagnosis, rendering gene replacement therapy insufficient to treat the disease. These patients will require cell replacement to restore useful vision. Fortunately, the advent of induced pluripotent stem cell and CRISPR-Cas9 gene editing technologies affords researchers and clinicians a powerful means by which to develop strategies to treat patients with inherited retinal dystrophies. In this review we will discuss the current developments in CRISPR-Cas9 gene editing in vivo in animal models and in vitro in patient-derived cells to study and treat inherited retinal degenerative diseases.

C-Reactive Protein As a Mediator of Complement Activation and Inflammatory Signaling in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a devastating neurodegenerative disease affecting millions worldwide. Complement activation, inflammation, and the loss of choroidal endothelial cells have been established as key factors in both normal aging and AMD; however, the exact mechanisms for these events have yet to be fully uncovered. Herein, we provide evidence that the prototypic acute phase reactant, C-reactive protein (CRP), contributes to AMD pathogenesis. We discuss serum CRP levels as a risk factor for disease, immunolocalization of distinct forms of CRP in the at-risk and diseased retina, and direct effects of CRP on ocular tissue. Furthermore, we discuss the complement system as it relates to AMD pathophysiology, provide a model for the role of CRP in this disease, and outline current therapies being developed and tested to treat AMD patients.

CLINICOPATHOLOGICAL CORRELATION IN A PATIENT WITH PREVIOUSLY TREATED BIRDSHOT CHORIORETINOPATHY

PURPOSE

Birdshot chorioretinopathy (BCR) is a bilateral, chronic uveitis primarily involving the posterior segment that often results in progressive vision loss. Histopathology on eyes with BCR has been limited, but we had the rare opportunity to study the eyes of a donor with BCR. We sought to compare immunolabeling in the eyes of this donor who was treated with immunosuppression for over 30 years to age-matched controls.

METHODS

From each eye, a macular punch and superotemporal regions were used for cryostat sectioning, and immunohistochemistry was performed on the sections using antibodies directed against CD45, intercellular adhesion molecule-1, IBA1, and GFAP. The vasculature-binding lectin, Ulex europaeus agglutinin-I (UEA-I), was also used to perform lectin histochemistry.

RESULTS

At death, her visual acuity was 20/25 right eye, 20/250 left eye with extensive chorioretinal atrophy, vascular attenuation, and disk pallor. Compared with controls, the BCR donor had extensive degeneration of the outer nuclear layer and retinal pigment epithelium as well as choroidal thinning with inner retinal preservation. Loss of UEA-I+ choroidal endothelial cells was extensive, and atypical intercellular adhesion molecule-1 labeling and IBA+ microglia/macrophages were present along with widespread GFAP labeling throughout the retina.

CONCLUSION

The BCR may cause progressive chorioretinal and optic atrophy with long-standing increased leukocyte abundance throughout the retina and microglial activation especially at the retina-choroid interface.

Evaluation of sFLT1 protein levels in human eyes with the FLT1 rs9943922 polymorphism

PURPOSE

Age-related macular degeneration (AMD) is a devastating disease characterized by central vision impairment in individuals with advanced age. Neovascular AMD is a form of end-stage disease in which choroidal vessel outgrowth occurs beneath the retina. While many hypotheses have been raised as to what triggers the formation of pathological choroidal neovascular membranes, the exact mechanism for their initiation remains unresolved. Polymorphisms in the FLT1 gene have previously been associated with neovascular AMD risk, including the rs9943922 single nucleotide polymorphism (SNP). Here, we aimed to determine the association between the high-risk FLT1 genotype and FLT1 protein levels in human retina or retinal pigment epithelium (RPE)/choroid tissue.

METHODS

Retina and RPE/choroid tissue from 10 human donor eyes was selected from a collection of eyes genotyped for the rs9943922 SNP. Differences in soluble and membrane bound FLT1 protein levels were assessed for retina versus RPE/choroid donor tissue using ELISA and Western blotting analyses. Genotype-associated changes in FLT1 protein levels were also evaluated.

RESULTS

We found soluble FLT1 levels in the RPE/choroid tissue to be approximately three times higher than that of the retina (p < 0.001), while both samples have similar levels of the membrane bound form. When tissue with the rs9943922 SNP was compared with controls, no significant genotypic differences in FLT1 protein levels were observed.

CONCLUSIONS

Based on these data, we conclude that the rs9943922 SNP in the FLT1 gene does not result in a large difference in FLT1 protein levels, regardless of whether it is the soluble or the membrane bound form.

Preparation and evaluation of human choroid extracellular matrix scaffolds for the study of cell replacement strategies

Endothelial cells (ECs) of the choriocapillaris are one of the first cell types lost during age-related macular degeneration (AMD), and cell replacement therapy is currently a very promising option for patients with advanced AMD. We sought to develop a reliable method for the production of human choroidal extracellular matrix (ECM) scaffolds, which will allow for the study of choroidal EC (CEC) replacement strategies in an environment that closely resembles the native tissue. Human RPE/choroid tissue was treated sequentially with Triton X-100, SDS, and DNase to remove all native cells. While all cells were successfully removed from the tissue, collagen IV, elastin, and laminin remained, with preserved architecture of the acellular vascular tubes. The ECM scaffolds were then co-cultured with exogenous ECs to determine if the tissue can support cell growth and allow EC reintegration into the decellularized choroidal vasculature. Both monkey and human ECs took up residence in the choriocapillary tubes of the decellularized tissue. Together, these data suggest that our decellularization methods are sufficient to remove all cellular material yet gentle enough to preserve tissue structure and allow for the optimization of cell replacement strategies.

STATEMENT OF SIGNIFICANCE

Age-related macular degeneration (AMD) is a devastating disease affecting more than 600 million people worldwide. Endothelial cells of the choriocapillaris (CECs) are among the first cell types lost in early AMD, and cell replacement therapy is currently the most promising option for restoring vision in patients with advanced AMD. In order to study CEC replacement strategies we have generated a 3D choroid scaffold using a novel decellularization method in human RPE/choroid tissue. To our knowledge, this is the first report describing decellularization of human RPE/choroid, as well as recellularization of a choroid scaffold with CECs. This work will aid in our development and optimization of cell replacement strategies using a tissue scaffold that is similar to the in vivo environment.

Connective Tissue Growth Factor Promotes Efficient Generation of Human Induced Pluripotent Stem Cell-Derived Choroidal Endothelium

Age‐related macular degeneration (AMD) is a leading cause of irreversible blindness in the Western world. Although, the majority of stem cell research to date has focused on production of retinal pigment epithelial (RPE) and photoreceptor cells for the purpose of evaluating disease pathophysiology and cell replacement, there is strong evidence that the choroidal endothelial cells (CECs) that form the choriocapillaris vessels are the first to be lost in this disease. As such, to accurately evaluate disease pathophysiology and develop an effective treatment, production of patient‐specific, stem cell‐derived CECs will be required. In this study, we report for the first time a stepwise differentiation protocol suitable for generating human iPSC‐derived CEC‐like cells. RNA‐seq analysis of the monkey CEC line, RF/6A, combined with two statistical screens allowed us to develop media comprised of various protein combinations. In both screens, connective tissue growth factor (CTGF) was identified as the key component required for driving CEC development. A second factor tumor necrosis factor (TNF)‐related weak inducer of apoptosis receptor was also found to promote iPSC to CEC differentiation by inducing endogenous CTGF secretion. CTGF‐driven iPSC‐derived CEC‐like cells formed capillary tube‐like vascular networks, and expressed the EC‐specific markers CD31, ICAM1, PLVAP, vWF, and the CEC‐restricted marker CA4. In combination with RPE and photoreceptor cells, patient‐specific iPSC derived CEC‐like cells will enable scientists to accurately evaluate AMD pathophysiology and develop effective cell replacement therapies. Stem Cells Translational Medicine2017;6:1533–1546

Structural and molecular changes in the aging choroid: implications for age-related macular degeneration

Age-related macular degeneration (AMD) is a devastating disease-causing vision loss in millions of people around the world. In advanced stages of disease, death of photoreceptor cells, retinal pigment epithelial cells, and choroidal endothelial cells (CECs) are common. Loss of endothelial cells of the choriocapillaris is one of the earliest detectable events in AMD, and, because the outer retina relies on the choriocapillaris for metabolic support, this loss may be the trigger for progression to more advanced stages. Here we highlight evidence for loss of CECs, including changes to vascular density within the choriocapillaris, altered abundance of CEC markers, and changes to overall thickness of the choroid. Furthermore, we review the key components and functions of the choroid, as well as Bruch's membrane, both of which are vital for healthy vision. We discuss changes to the structure and molecular composition of these tissues, many of which develop with age and may contribute to AMD pathogenesis. For example, a crucial event that occurs in the aging choriocapillaris is accumulation of the membrane attack complex, which may result in complement-mediated CEC lysis, and may be a primary cause for AMD-associated choriocapillaris degeneration. The actions of elevated monomeric C-reactive protein in the choriocapillaris in at-risk individuals may also contribute to the inflammatory environment in the choroid and promote disease progression. Finally, we discuss the progress that has been made in the development of AMD therapies, with a focus on cell replacement.

MMP19 expression in the human optic nerve

PURPOSE

The defining feature of glaucoma is excavation of the optic nerve head; however, the mechanism of this loss of tissue is not well understood. We recently discovered a copy number variation upstream of matrix metalloproteinase 19 (MMP19) in a large, autosomal dominant pedigree with a congenital malformation of the optic disc called cavitary optic disc anomaly (CODA). Patients with CODA have abnormal optic discs that exhibit an excavated shape similar to cupping seen in glaucoma. The goal of this study is to characterize the localization of MMP19 within the human optic nerve.

METHODS

The MMP19 protein in the optic nerve was evaluated with western blot analysis and with immunohistochemistry in sagittal and en face/cross sections of optic nerves obtained from healthy human donor eyes.

RESULTS

The MMP19 protein was detected in the human optic nerve, retina, and RPE/choroid with western blot analysis, with highest expression in the retina and the optic nerve. Using immunohistochemistry, MMP19 was localized within the optic nerve to the extracellular space within the septa that separate bundles of optic nerve axons into fascicles. The presence of MMP19 within the optic nerve septa was further confirmed by the colocalization of MMP19 to this structure with type IV collagen. Strong labeling of MMP19 was also detected in the arachnoid layer of the optic nerve sheath. Finally, immunohistochemistry of the optic nerve cross sections demonstrated that MMP19 shows a peripheral to central gradient, with more abundant labeling along the edges of the optic nerve and in the arachnoid layer than in the center of the nerve.

CONCLUSIONS

Abundant MMP19 was detected in the optic nerve head, the primary site of pathology in patients with CODA. The localization of MMP19 to the optic nerve septa is consistent with its predicted secretion and accumulation within the extracellular spaces of this tissue. Moreover, the lateral localization of MMP19 observed in the optic nerve cross sections suggests that it might have a role in regulating adhesion to the optic nerve to the scleral canal and remodeling the extracellular matrix that provides the structural integrity of the optic disc. Dysregulation of MMP19 production might, therefore, undermine the connections between the optic nerve and the scleral canal and cause a collapse of the optic disc and the development of CODA. Similar processes might also be at work in the formation of optic disc cupping in glaucoma.

Monomeric C-reactive protein and inflammation in age-related macular degeneration

Age-related macular degeneration (AMD) is a devastating disease characterized by central vision loss in elderly individuals. Previous studies have suggested a link between elevated levels of total C-reactive protein (CRP) in the choroid, CFH genotype, and AMD status; however, the structural form of CRP present in the choroid, its relationship to CFH genotype, and its functional consequences have not been assessed. In this report, we studied genotyped human donor eyes (n = 60) and found that eyes homozygous for the high-risk CFH (Y402H) allele had elevated monomeric CRP (mCRP) within the choriocapillaris and Bruch's membrane, compared to those with the low-risk genotype. Treatment of choroidal endothelial cells in vitro with mCRP increased migration rate and monolayer permeability compared to treatment with pentameric CRP (pCRP) or medium alone. Organ cultures treated with mCRP exhibited dramatically altered expression of inflammatory genes as assessed by RNA sequencing, including ICAM-1 and CA4, both of which were confirmed at the protein level. Our data indicate that mCRP is the more abundant form of CRP in human choroid, and that mCRP levels are elevated in individuals with the high-risk CFH genotype. Moreover, pro-inflammatory mCRP significantly affects endothelial cell phenotypes in vitro and ex vivo, suggesting a role for mCRP in choroidal vascular dysfunction in AMD. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Selective accumulation of the complement membrane attack complex in aging choriocapillaris

The complement membrane attack complex (MAC) shows increased abundance in the choriocapillaris during normal aging and is especially prevalent in age-related macular degeneration (AMD). While perivascular MAC accumulation occurs in the choroid, it is not well understood whether similar deposition occurs in other aging tissues. In this study we examined the abundance of MAC across multiple human tissues. For studies on fixed tissues, paraffin sections were obtained from six human donor eyes and a commercially available tissue array containing 19 different tissues. Immunohistochemical labeling was performed using antibodies directed against the MAC and intercellular adhesion molecule-1 (ICAM-1), as well as the lectin Ulex europaeus agglutinin-I (UEA-I). The choriocapillaris was the only tissue with high levels of the MAC, which was not detected in any of the 38 additional samples from 19 tissues. ICAM-1 was abundantly expressed in the majority of tissues evaluated, and UEA-I labeled the vasculature in all tissues. A second experiment was performed using unfixed frozen sections of RPE-choroid and 7 extraocular tissues, which confirmed the relatively limited localization of the MAC to the choriocapillaris. In comparison to other tissues assessed, the restricted accumulation of MAC in the choriocapillaris may, in part, explain the specificity of AMD to the neural retina, RPE and choroid, and the relative absence of systemic pathology in this disease.

Complement activation and choriocapillaris loss in early AMD: implications for pathophysiology and therapy

Age-related macular degeneration (AMD) is a common and devastating disease that can result in severe visual dysfunction. Over the last decade, great progress has been made in identifying genetic variants that contribute to AMD, many of which lie in genes involved in the complement cascade. In this review we discuss the significance of complement activation in AMD, particularly with respect to the formation of the membrane attack complex in the aging choriocapillaris. We review the clinical, histological and biochemical data that indicate that vascular loss in the choroid occurs very early in the pathogenesis of AMD, and discuss the potential impact of vascular dropout on the retinal pigment epithelium, Bruch's membrane and the photoreceptor cells. Finally, we present a hypothesis for the pathogenesis of early AMD and consider the implications of this model on the development of new therapies.