Start codon disruption with CRISPR/Cas9 prevents murine Fuchs' endothelial corneal dystrophy

Elovl4b knockout zebrafish as a model for ocular very-long-chain PUFA deficiency

Very-long-chain PUFAs (VLC-PUFAs) are a group of lipids with chain lengths >24 carbons, and the ELOVL4 (elongation of very-long-chain FA-4) enzyme is responsible for vertebrate VLC-PUFA biosynthesis. Studies on the role of VLC-PUFAs in vision have been hindered because of the need for adequate animal models to capture the global loss of VLC-PUFAs. Since homozygous Elovl4 ablation is lethal in neonatal mice because of catastrophic drying from the loss of their protective skin barrier, we established a zebrafish (Danio rerio) model of Elovl4 ablation. We generated Elovl4b KO zebrafish by creating a 56-bp deletion mutation in exon 2 of the Elovl4b gene using CRISPR-Cas9. We used GC-MS and LC-MS/MS to analyze the VLC-PUFA and lipid profiles from wild-type and Elovl4b KO fish eyes. We also performed histology and visual-behavioral tests. We found that heterozygous and homozygous Elovl4b KO zebrafish eyes had altered lipid profiles and a significantly lower C30 to C36 VLC-PUFA abundance than wild-type fish. Moreover, Elovl4b+/- and Elovl4b-/- KO larvae had significantly lower motor activity in response to light-dark cycles than their age-matched controls. Elovl4b-/- adult fish showed no obvious differences in gross retinal morphology and lamination compared with wild type, except for the presence of lipid droplets within the retinal pigment epithelial cell layer of Elovl4b-/- fish. Our data indicate that the loss of Elovl4b in zebrafish changes ocular lipid profiles and leads to visual abnormalities and subtle retinal changes. These findings highlight the use of zebrafish as a model for VLC-PUFA depletion and ELOVL4-related dysfunction.

Systematic Review of the Diagnostic Criteria and Severity Classification for Fuchs Endothelial Corneal Dystrophy

PURPOSE

There are no defined diagnostic criteria and severity classification for Fuchs endothelial corneal dystrophy (FECD), which are required for objective standardized assessments. Therefore, we performed a systematic literature review of the current diagnosis and severity classification of FECD.

METHODS

We searched the Ovid MEDLINE and Web of Science databases for studies published until January 13, 2021. We excluded review articles, conference abstracts, editorials, case reports with <5 patients, and letters.

RESULTS

Among 468 articles identified, we excluded 173 and 165 articles in the first and second screenings, respectively. Among the 130 included articles, 61 (47%) and 99 (76%) mentioned the diagnostic criteria for FECD and described its severity classification, respectively. Regarding diagnosis, slitlamp microscope alone was the most frequently used device in 31 (51%) of 61 articles. Regarding diagnostic findings, corneal guttae alone was the most common parameter [adopted in 23 articles (38%)]. Regarding severity classification, slitlamp microscopes were used in 88 articles (89%). The original or modified Krachmer grading scale was used in 77 articles (78%), followed by Adami's classification in six (6%). Specular microscopes or Scheimpflug tomography were used in four articles (4%) and anterior segment optical coherence tomography in one (1%).

CONCLUSIONS

FECD is globally diagnosed by the corneal guttae using slitlamp examination, and its severity is predominantly determined by the original or modified Krachmer grading scale. Objective severity grading using Scheimpflug or anterior segment optical coherence tomography can be applied in the future innovative therapies such as cell injection therapy or novel small molecules.

Therapeutic applications of CRISPR/Cas9 gene editing technology for the treatment of ocular diseases

Ocular diseases are a highly heterogeneous group of phenotypes, caused by a spectrum of genetic variants and environmental factors that exhibit diverse clinical symptoms. As a result of its anatomical location, structure and immune privilege, the eye is an ideal system to assess and validate novel genetic therapies. Advances in genome editing have revolutionized the field of biomedical science, enabling researchers to understand the biology behind disease mechanisms and allow the treatment of several health conditions, including ocular pathologies. The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based gene editing facilitates efficient and specific genetic modifications in the nucleic acid sequence, resulting in permanent changes at the genomic level. This approach has advantages over other treatment strategies and is promising for the treatment of various genetic and non-genetic ocular conditions. This review provides an overview of the CRISPR/CRISPR-associated protein 9 (Cas9) system and summarizes recent advances in the therapeutic application of CRISPR/Cas9 for the treatment of various ocular pathologies, as well as future challenges.

Updates on congenital hereditary endothelial dystrophy

Congenital hereditary endothelial dystrophy (CHED) is a rare genetic corneal disorder causing progressive cornea clouding and significant visual impairment. CHED remains a leading indication for pediatric corneal transplantation despite its infrequency, particularly in regions with high consanguinity rates like Southeast Asia. Identifying the Solute Carrier Family 4 Member 11 (SLC4A11) gene as the genetic basis of CHED has led to the discovery of it's various genetic variations. However, a comprehensive understanding of its clinical-genetic correlation, pathophysiology, and optimal management is ongoing. This review aims to consolidate current knowledge about CHED, covering its genetic origins, pathophysiological mechanisms, clinical presentation, and management strategies. Surgical intervention, such as penetrating keratoplasty (PK), Descemet stripping automated endothelial keratoplasty (DSAEK), and Descemet membrane endothelial keratoplasty (DMEK), remains the primary treatment. DSAEK and DMEK offer advantages over PK, including quicker visual recovery, reduced complications, and longer graft survival, especially in the pediatric age group. The timing of surgical interventions depends on disease severity, age at presentation, comorbidities, and visual potential. Elevated oxidative stress in CHED corneal tissue suggests potential benefits from anti-inflammatory drugs to rescue mutated endothelial cells. Considering the limitations of corneal graft surgeries, exploring novel gene-based molecular therapies are essential for future management. Early diagnosis, appropriate surgical interventions, amblyopia control, and genetic counseling for predictive analysis are pivotal for optimizing CHED management. A multidisciplinary approach involving ophthalmologists, researchers, and genetic counselors is essential for precise diagnosis and optimal care for CHED patients.

Diagnostic implications of pitfalls in causal variant identification based on 4577 molecularly characterized families

Despite large sequencing and data sharing efforts, previously characterized pathogenic variants only account for a fraction of Mendelian disease patients, which highlights the need for accurate identification and interpretation of novel variants. In a large Mendelian cohort of 4577 molecularly characterized families, numerous scenarios in which variant identification and interpretation can be challenging are encountered. We describe categories of challenges that cover the phenotype (e.g. novel allelic disorders), pedigree structure (e.g. imprinting disorders masquerading as autosomal recessive phenotypes), positional mapping (e.g. double recombination events abrogating candidate autozygous intervals), gene (e.g. novel gene-disease assertion) and variant (e.g. complex compound inheritance). Overall, we estimate a probability of 34.3% for encountering at least one of these challenges. Importantly, our data show that by only addressing non-sequencing-based challenges, around 71% increase in the diagnostic yield can be expected. Indeed, by applying these lessons to a cohort of 314 cases with negative clinical exome or genome reports, we could identify the likely causal variant in 54.5%. Our work highlights the need to have a thorough approach to undiagnosed diseases by considering a wide range of challenges rather than a narrow focus on sequencing technologies. It is hoped that by sharing this experience, the yield of undiagnosed disease programs globally can be improved.

Novel Mechanisms Guide Innovative Molecular-Based Therapeutic Strategies for Fuchs Endothelial Corneal Dystrophy

ABSTRACT

Major advances in genomics have dramatically increased our understanding of Fuchs endothelial corneal dystrophy (FECD) and identified diverse genetic causes and associations. Biomarkers derived from these studies have the potential to inform both clinical treatment and yield novel therapeutics for this corneal dystrophy.

Genome editing in the treatment of ocular diseases

Genome-editing technologies have ushered in a new era in gene therapy, providing novel therapeutic strategies for a wide range of diseases, including both genetic and nongenetic ocular diseases. These technologies offer new hope for patients suffering from previously untreatable conditions. The unique anatomical and physiological features of the eye, including its immune-privileged status, size, and compartmentalized structure, provide an optimal environment for the application of these cutting-edge technologies. Moreover, the development of various delivery methods has facilitated the efficient and targeted administration of genome engineering tools designed to correct specific ocular tissues. Additionally, advancements in noninvasive ocular imaging techniques and electroretinography have enabled real-time monitoring of therapeutic efficacy and safety. Herein, we discuss the discovery and development of genome-editing technologies, their application to ocular diseases from the anterior segment to the posterior segment, current limitations encountered in translating these technologies into clinical practice, and ongoing research endeavors aimed at overcoming these challenges.

Lipid Nanoparticles for Nucleic Acid Delivery to Endothelial Cells

Endothelial cells play critical roles in circulatory homeostasis and are also the gateway to the major organs of the body. Dysfunction, injury, and gene expression profiles of these cells can cause, or are caused by, prevalent chronic diseases such as diabetes, cardiovascular disease, and cancer. Modulation of gene expression within endothelial cells could therefore be therapeutically strategic in treating longstanding disease challenges. Lipid nanoparticles (LNP) have emerged as potent, scalable, and tunable carrier systems for delivering nucleic acids, making them attractive vehicles for gene delivery to endothelial cells. Here, we discuss the functions of endothelial cells and highlight some receptors that are upregulated during health and disease. Examples and applications of DNA, mRNA, circRNA, saRNA, siRNA, shRNA, miRNA, and ASO delivery to endothelial cells and their targets are reviewed, as well as LNP composition and morphology, formulation strategies, target proteins, and biomechanical factors that modulate endothelial cell targeting. Finally, we discuss FDA-approved LNPs as well as LNPs that have been tested in clinical trials and their challenges, and provide some perspectives as to how to surmount those challenges.

Nucleic Acid Delivery to the Vascular Endothelium

This Review examines the state-of-the-art in the delivery of nucleic acid therapies that are directed to the vascular endothelium. First, we review the most important homeostatic functions and properties of the vascular endothelium and summarize the nucleic acid tools that are currently available for gene therapy and nucleic acid delivery. Second, we consider the opportunities available with the endothelium as a therapeutic target and the experimental models that exist to evaluate the potential of those opportunities. Finally, we review the progress to date from investigations that are directly targeting the vascular endothelium: for vascular disease, for peri-transplant therapy, for angiogenic therapies, for pulmonary endothelial disease, and for the blood-brain barrier, ending with a summary of the future outlook in this field.

Autophagy in the normal and diseased cornea

The cornea and covering tear film are together the 'objective lens' of the eye through which 80% of light is refracted. Despite exposure to a physically harsh and at times infectious or toxic environment, transparency essential for sight is in most cases maintained. Such resiliency makes the avascular cornea a superb model for the exploration of autophagy in the regulation of homeostasis with relevancy to all organs. Nonetheless, missense mutations and inflammation respectively clog or apparently overwhelm autophagic flux to create dystrophies much like in neurodegenerative diseases or further exacerbate inflammation. Here there is opportunity to generate novel topical therapies towards the restoration of homeostasis with potential broad application.

LNP-mediated delivery of CRISPR RNP for wide-spread in vivo genome editing in mouse cornea

CRISPR/Cas9-based genome-editing therapies are poised to change the clinical outcome for many diseases with validated therapeutic targets awaiting an appropriate delivery system. Recent advances in lipid nanoparticle (LNP) technology make them an attractive platform for the delivery of various forms of CRISPR/Cas9, including the efficient and transient Cas9/gRNA ribonucleoprotein (RNP) complexes. In this study, we initially tested our novel LNP platform by delivering pre-complexed RNPs and template DNA to cultured mouse cortical neurons, and obtained successful ex vivo genome editing. We then directly injected LNP-packaged RNPs and DNA template into the mouse cornea to evaluate in vivo delivery. For the first time, we demonstrated wide-spread genome editing in the cornea using our LNP-RNPs. The ability of our LNPs to transfect the cornea highlights the potential of our novel delivery platform to be used in CRISPR/Cas9-based genome editing therapies of corneal diseases.

Identification and in silico analysis of a spectrum of SLC4A11 variations in Indian familial and sporadic cases of congenital hereditary endothelial dystrophy

Background

Congenital hereditary endothelial dystrophy (CHED) is a rare form of corneal dystrophy caused by SLC4A11 gene variations. This study aims to find the genetic alterations in SLC4A11, in two Indian familial CHED cases with affected members n = 3 and n = 2 respectively and five sporadic CHED cases using direct sequencing, followed by in silico analysis and characterization of the identified variants.

Results

All three affected members of the first CHED family were identified with a novel homozygous c.1514C > G (p.Ser489Trp) variation while second family showed presence of a compound heterozygous variation c.529A > C (p.Arg161Arg) + c.2461insT (p.Val805fs). Among five sporadic cases, two showed novel changes, homozygous c.1487G > T (p.Ser480Ile) and c.620-2A > G, while the other one had previously reported homozygous c.2653C > T (p.Arg869Cys) variation. The remaining two cases did not reveal the presence of SLC4A11-related pathogenic variations. The identified variations were excluded from the Indian control (n = 80). In silico analysis using homology-based protein modeling and pathogenicity prediction tools, which revealed these alterations as pathogenic, changing their protein stability, local flexibility, residue contact clashes, and the hydrogen bond interactions.

Conclusions

This study contributed to the CHED mutational spectrum, adding four novel variations and confirming a previously reported one. It demonstrates different type of variations in CHED cases, including coding, non-coding, homozygous, synonymous, and compound heterozygous variations. The identified variations revealed different degrees of pathogenic effects in silico. Moreover, two sporadic cases could not be identified with pathogenic variation emphasizing the involvement of other genes or genetic mechanisms.

Rescue of the Congenital Hereditary Endothelial Dystrophy Mouse Model by Adeno-Associated Viruse-Mediated Slc4a11 Replacement

Purpose

Congenital hereditary endothelial dystrophy (CHED) is a rare condition that manifests at an early age showing corneal edema, increased oxidative stress, mitochondrial dysfunction, and eventually apoptosis of the endothelium due to loss of function of the membrane transport protein SLC4A11. This project tested whether replacing Slc4a11 into the Slc4a11 -/- CHED mouse model can reverse the disease-associated phenotypes.

Design

Experimental study.

Participants

Five-week-old or 11-week-old Slc4a11 -/- mice. Age- and gender-matched Slc4a11 +/+ animals were used as controls. A total of 124 animals (62 female, and 62 male) were used in this study. Fifty-three animals of the genotype Slc4a11 +/+ were used as age- and gender-matched noninjected controls. Seventy-one Slc4a11 -/- mice were administered anterior chamber injections of adeno-associated virus (AAV).

Methods

Anterior chambers of young (5 weeks old) or older (11 weeks old) Slc4a11 -/- mice were injected once with adeno-associated virus serotype 9 (AAV9) mouse Slc4a11 or AAV9-Null vectors. Corneal thickness was measured using OCT. End point analysis included corneal endothelial cell density, mitochondrial oxidative stress, and corneal lactate concentration.

Main Outcome Measures

Corneal thickness, endothelial cell loss, lactate levels, and mitochondrial oxidative stress.

Results

In the young animals, AAV9-Slc4a11 reversed corneal edema, endothelial cell loss, mitochondrial oxidative stress, lactate transporter expression, and corneal lactate concentration to the levels observed in wild-type animals. In the older animals, gene replacement did not reverse the phenotype but prevented progression.

Conclusions

Functional rescue of CHED phenotypes in the Slc4a11 -/- mouse is possible; however, early intervention is critical.

Current approaches in CRISPR-Cas9 mediated gene editing for biomedical and therapeutic applications

A single gene mutation can cause a number of human diseases that affect quality of life. Until the development of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein (Cas) systems, it was challenging to correct a gene mutation to avoid disease by reverting phenotypes. The advent of CRISPR technology has changed the field of gene editing, given its simplicity and intrinsic programmability, surpassing the limitations of both zinc-finger nuclease and transcription activator-like effector nuclease and becoming the method of choice for therapeutic gene editing by overcoming the bottlenecks of conventional gene-editing techniques. Currently, there is no commercially available medicinal cure to correct a gene mutation that corrects and reverses the abnormality of a gene's function. Devising reprogramming strategies for faithful recapitulation of normal phenotypes is a crucial aspect for directing the reprogrammed cells toward clinical trials. The CRISPR-Cas9 system has been promising as a tool for correcting gene mutations in maladies including blood disorders and muscular degeneration as well as neurological, cardiovascular, renal, genetic, stem cell, and optical diseases. In this review, we highlight recent developments and utilization of the CRISPR-Cas9 system in correcting or generating gene mutations to create model organisms to develop deeper insights into diseases, rescue normal gene functionality, and curb the progression of a disease.

Start codon disruption with CRISPR/Cas9 prevents murine Fuchs' endothelial corneal dystrophy

A missense mutation of collagen type VIII alpha 2 chain (COL8A2) gene leads to early-onset Fuchs' endothelial corneal dystrophy (FECD), which progressively impairs vision through the loss of corneal endothelial cells. We demonstrate that CRISPR/Cas9-based postnatal gene editing achieves structural and functional rescue in a mouse model of FECD. A single intraocular injection of an adenovirus encoding both the Cas9 gene and guide RNA (Ad-Cas9-Col8a2gRNA) efficiently knocked down mutant COL8A2 expression in corneal endothelial cells, prevented endothelial cell loss, and rescued corneal endothelium pumping function in adult Col8a2 mutant mice. There were no adverse sequelae on histology or electroretinography. Col8a2 start codon disruption represents a non-surgical strategy to prevent vision loss in early-onset FECD. As this demonstrates the ability of Ad-Cas9-gRNA to restore the phenotype in adult post-mitotic cells, this method may be widely applicable to adult-onset diseases, even in tissues affected with disorders of non-reproducing cells.