Gene editing restores dystrophin expression in a canine model of Duchenne muscular dystrophy

Engineering adeno-associated viral vectors for CRISPR/Cas based in vivo therapeutic genome editing

The recent approval of the first gene editing therapy for sickle cell disease and transfusion-dependent beta-thalassemia by the U.S. Food and Drug Administration (FDA) demonstrates the immense potential of CRISPR (clustered regularly interspaced short palindromic repeats) technologies to treat patients with genetic disorders that were previously considered incurable. While significant advancements have been made with ex vivo gene editing approaches, the development of in vivo CRISPR/Cas gene editing therapies has not progressed as rapidly due to significant challenges in achieving highly efficient and specific in vivo delivery. Adeno-associated viral (AAV) vectors have shown great promise in clinical trials as vehicles for delivering therapeutic transgenes and other cargos but currently face multiple limitations for effective delivery of gene editing machineries. This review elucidates these challenges and highlights the latest engineering strategies aimed at improving the efficiency, specificity, and safety profiles of AAV-packaged CRISPR/Cas systems (AAV-CRISPR) to enhance their clinical utility.

The road toward AAV-mediated gene therapy of Duchenne muscular dystrophy

Forty years after the dystrophin gene was cloned, significant progress has been made in developing gene therapy approaches for Duchenne muscular dystrophy (DMD). The disorder has presented numerous challenges, including the enormous size of the gene (2.2 MB), the need to target muscles body wide, and immunogenic issues against both vectors and dystrophin. Among human genetic disorders, DMD is relatively common, and the genetics are complicated since one-third of all cases arise from a spontaneous new mutation, resulting in thousands of independent lesions throughout the locus. Many approaches have been pursued in the goal of finding an effective therapy, including exon skipping, nonsense codon suppression, upregulation of surrogate genes, gene replacement, and gene editing. Here, we focus specifically on methods using AAV vectors, as these approaches have been tested in numerous clinical trials and are able to target muscles systemically. We discuss early advances to understand the structure of dystrophin, which are crucial for the design of effective DMD gene therapies. Included is a summary of efforts to deliver micro-, mini-, and full-length dystrophins to muscles. Finally, we review current approaches to adapt gene editing to the enormous DMD gene with prospects for improved therapies using all these methods.

Theological and Ethical Perspectives on Gene Editing and the Sanctity of Life: Rare Genetic Diseases in the Philippines as a Model

This paper examines the interplay between the sacredness of life and gene editing in the context of rare genetic diseases. Rare genetic disorders caused by gene mutations often come with limited treatment options. Gene editing techniques present a promising solution by targeting and repairing defective genes. The discussion begins with an overview of the science behind gene editing and its potential applications in treating rare diseases, highlighting three specific genetic conditions affecting Filipinos. It then explores the ethical and theological dimensions of gene editing, emphasizing the Imago Dei doctrine, which underscores human dignity and moral responsibility as well as ethical principles in light of Christian virtues. A comparative analysis between therapeutic somatic gene editing and germline editing is highlighted in the discussions. Using the See-Judge-Act framework, the paper examines the potential of gene editing through the lens of Catholic Church's teachings on human dignity and offers practical insights for applying the theological and ethical considerations in addressing the therapeutic options for rare genetic diseases righteously.

Single-cut gene therapy in a one-step generated rhesus monkey model of Duchenne muscular dystrophy

Progress in Duchenne muscular dystrophy (DMD) treatment is hindered by the lack of animal models that closely replicate human pathology and enable the evaluation of therapy efficacy and safety based on these models. To address this need, we optimize the generation of nonhuman primate DMD models, reducing the development time from 6 to 7 years to under 1 year, enabling the rapid generation of DMD monkey models. These models closely mimic human DMD pathology and motor dysfunction, making them suitable for testing gene therapies. Using these models, we develop a single-cut gene therapy strategy that can be directly applied to humans. This treatment restores dystrophin expression, improves pathological features, and enhances motor abilities in DMD monkeys, with effects lasting at least 1.5 years. In conclusion, we achieve the rapid generation of DMD monkey models and demonstrate that our gene therapy approach is effective and holds significant potential for clinical application.

Innovative Chemical Strategies for Advanced CRISPR Modulation

ConspectusOver the past decade, RNA-guided gene editing technologies, particularly those derived from CRISPR systems, have revolutionized life sciences and opened unprecedented opportunities for therapeutic innovation. Despite their transformative potential, achieving precise control over the activity and specificity of these molecular tools remains a formidable challenge, requiring advanced and innovative regulatory strategies. We and others have developed new approaches that integrate chemical ingenuity with bioorthogonal techniques to achieve remarkable precision in CRISPR regulation. One key innovation lies in the chemical modulation of guide RNA (gRNA), significantly expanding the CRISPR toolkit. Strategies such as CRISPR-ON and CRISPR-OFF switches rely on selective chemical masking and demasking of gRNA. These approaches use either bulky chemical groups to preemptively mask RNA or minor, less obstructive groups to fine-tune its function, followed by bioorthogonal reactions to restore or suppress activity. These methodologies have proven to be pivotal for controlled gene editing and expression, addressing the challenges of precision, reversibility, and dynamic regulation.Parallel to these advances, the development of mesoporous metal-organic frameworks (MOFs) has emerged as a promising solution for RNA deprotection and activation. By serving as catalytic tools, MOFs enhance the versatility and efficiency of CRISPR systems, pushing their applications beyond the conventional boundaries. In addition, the synthesis of novel small molecules for regulating CRISPR-Cas9 activity marks a critical milestone in the evolution of gene therapy protocols. Innovative RNA structural control strategies have also emerged, particularly through the engineering of G-quadruplex (G4) motifs and G-G mismatches. These methods exploit the structural propensities of engineered gRNAs, employing small-molecule ligands to induce specific conformational changes that modulate the CRISPR activity. Whether stabilizing G4 formation or promoting G-G mismatches, these strategies demonstrate the precision and sophistication required for the molecular-level control of gene editing.Further enhancing these innovations, techniques like host-guest chemistry and conditional diacylation cross-linking have been developed to directly alter gRNA structure and function. These approaches provide nuanced, reversible, and safe control over CRISPR systems, advancing both the precision and reliability of gene editing technologies. In conclusion, this body of work highlights the convergence of chemistry, materials science, and molecular biology to create integrative solutions for gene editing. By combination of bioorthogonal chemistry, RNA engineering, and advanced materials, these advancements offer unprecedented accuracy and control for both fundamental research and therapeutic applications. These innovations not only advance genetic research but also contribute to developing safer and more effective gene editing strategies, moving us closer to realizing the full potential of these technologies.

Gene Editing for Duchenne Muscular Dystrophy: From Experimental Models to Emerging Therapies

The CRISPR system has emerged as a ground-breaking gene-editing tool, offering promising therapeutic potential for Duchenne muscular dystrophy (DMD), a severe genetic disorder affecting approximately 1 in 5000 male births globally. DMD is caused by mutations in the dystrophin gene, which encodes a critical membrane-associated protein essential for maintaining muscle structure, function and repair. Patients with DMD experience progressive muscle degeneration, loss of ambulation, respiratory insufficiency, and cardiac failure, with most succumbing to the disease by their third decade of life. Despite the well-characterized genetic basis of DMD, curative treatments- such as exon skipping therapies, micro-dystrophin, and steroids- remain elusive. Recent preclinical studies have demonstrated the promise of CRISPR-based approaches in restoring dystrophin expression across various models, including human cells, murine systems, and large animal models. These advancements highlight the potential of gene editing to fundamentally alter the trajectory of the disease. However, significant challenges persist, including immunogenicity, off-target effects, and limited editing efficiency, which hinder clinical translation. This review provides a comprehensive analysis of the latest developments in CRISPR-based therapeutic strategies for DMD. It emphasizes the need for further innovation in gene-editing technologies, delivery systems, and rigorous safety evaluations to overcome current barriers and harness the full potential of CRISPR/Cas as a durable and effective treatment for DMD.

Preclinical development of genome editing to treat Duchenne muscular dystrophy by exon skipping

Duchenne muscular dystrophy (DMD) is caused by loss-of-function mutations to the gene encoding dystrophin. Restoring the reading frame of dystrophin by removing internal out-of-frame exons may address symptoms of DMD. Therefore, the principle of exon skipping has been at the center stage in drug development for Duchenne muscular dystrophy (DMD) over the past two decades. Antisense oligonucleotides (AONs) have proven effective in modulating splicing sites for exon skipping, resulting in the FDA approval of several drugs using this technique in recent years. However, due to the temporary nature of AON, researchers are actively exploring genome editing as a potential long-term, single-administration treatment. The advancements in genome-editing technology over the last decade have boosted this transition. While no clinical trials for exon skipping in DMD via genome editing have been conducted as of this writing, preclinical studies show encouraging results. This review describes the preclinical landscape of genome editing for exon skipping in DMD treatment. Along with highlighting the adaptability of genome editing in exon skipping, this review also describes delivery challenges and outlines future research directions that could set a new stage for enhanced therapeutic development in DMD.

Evaluation of a six-minute walk test in the DE50-MD canine model of Duchenne muscular dystrophy and its effect on blood-borne biomarkers

Background

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by mutations in the dystrophin gene resulting in cycles of muscle degeneration, inflammation and regeneration. The 6-minute walk test (6MWT) is a key functional outcome measure for DMD patient clinical trials and has been adapted for use in animal models of the disease. The DE50-MD dog model of DMD closely reflects the DMD patient phenotype prior to loss of ambulation. For pre-clinical trials using this model, functional outcome measures must be established.

Methods

This longitudinal study compared distance walked in a 6MWT by DE50-MD and WT control dogs and assessed the utility of the 6MWT as a functional biomarker. Dogs underwent two 6MWTs conducted approximately 48-hours apart, at 3, 6, 9, 12, 15 and 18 months of age. In addition, we evaluated the stability of selected blood-borne biomarkers in 12-month old DE50-MD and WT dogs 0, 3, 6, 24 and 48 hours following a 6MWT.

Results

DE50-MD dogs exhibited significantly shorter 6-minute walk distance (6MWD) than WT dogs at all timepoints (P<0.05), with no difference in 6MWD between the first and second 6MWT. C-C motif chemokine ligand 2 (CCL2), myomesin-3 (MYOM3) and myostatin (MSTN) were biomarkers of the DE50-MD phenotype that remained unchanged in DE50-MD dogs following the 6MWT, while creatine kinase (CK) activity significantly increased 3-hours following the test in DE50-MD dogs but remained unchanged in WT dogs.

Conclusions

The 6MWT effectively discriminates DE50-MD from WT dogs aged 3-18 months and a single 6MWT is sufficient for future studies. Serum MYOM3, CCL2 and MSTN are good biomarkers of the DE50-MD phenotype that are unaffected by the relatively low level exertion performed in the 6MWT by 12-month-old DE50-MD dogs.

Circulatory CCL2 distinguishes Duchenne muscular dystrophy dogs

To establish a minimally invasive approach to studying body-wide muscle inflammation in the canine Duchenne muscular dystrophy (DMD) model, we evaluated 13 cytokines/chemokines in frozen sera from 90 affected (239 sera) and 73 normal (189 sera) dogs (0.00 to 45.2 months of age). Linear mixed-effects model analysis suggested that ten cytokines/chemokines were significantly elevated in affected dogs, including interleukin (IL)-2, IL-6, IL-7, IL-8, IL-10, IL-15, IL-18, C-C motif chemokine ligand 2 (CCL2), C-X-C motif chemokine ligand 1 (CXCL1) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Further, cytokine/chemokine elevation coincided with the onset of muscle disease. Importantly, only CCL2 showed consistent changes at all ages, with the most pronounced increase occurring between 3 and 9 months. To study the effects of sample storage and type, we compared fresh versus frozen, and serum versus plasma, samples from the same dog. Similar readings were often obtained in fresh and frozen sera. Although plasma readings were significantly lower for many cytokines/chemokines, this did not compromise the robustness of CCL2 as a biomarker. Our study establishes a baseline for using circulatory cytokines/chemokines as biomarkers in canine DMD studies.

The latest developments in synthetic approaches to Duchenne muscular dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a rare X-linked genetic disorder caused by mutations in the dystrophin gene, leading to an almost complete absence of dystrophin, which is essential for muscle cell structure and function. This resulting muscle deterioration and fibrosis, eventually causes respiratory failure and cardiomyopathy. While there is currently no cure, existing therapies aim to prolong survival and alleviate symptoms.

AREAS COVERED

This paper reviews current and emerging therapies for DMD, focusing on their safety and efficacy. Although corticosteroids remain the standard treatment, newly approved drugs such as exon-skipping therapies, vamorolone, delandistrogene moxeparvovec, and givinostat provide new treatment options. Additionally, future therapies, including gene therapy, stem cell treatments, and anti-fibrotic agents, show promise for clinical application.

EXPERT OPINION

Advancements in DMD treatments have expanded patient options. While gene therapy offers potential for correcting the genetic defect and alleviating symptoms, corticosteroids remain the most cost-effective and well-researched treatment. This is partly due to the lack of compelling long-term safety and efficacy data for gene therapies. The accelerated FDA review process has enabled faster approval of new medications; however many have provided minimal clinical benefit to patients. Despite these challenges, continued drug development and innovative research offer hope to patients.

Gene therapy for genetic diseases: challenges and future directions

Genetic diseases constitute the majority of rare human diseases, resulting from abnormalities in an individual's genetic composition. Traditional treatments offer limited relief for these challenging conditions. In contrast, the rapid advancement of gene therapy presents significant advantages by directly addressing the underlying causes of genetic diseases, thereby providing the potential for precision treatment and the possibility of curing these disorders. This review aims to delineate the mechanisms and outcomes of current gene therapy approaches in clinical applications across various genetic diseases affecting different body systems. Additionally, genetic muscular disorders will be examined as a case study to investigate innovative strategies of novel therapeutic approaches, including gene replacement, gene suppression, gene supplementation, and gene editing, along with their associated advantages and limitations at both clinical and preclinical levels. Finally, this review emphasizes the existing challenges of gene therapy, such as vector packaging limitations, immunotoxicity, therapy specificity, and the subcellular localization and immunogenicity of therapeutic cargos, while discussing potential optimization directions for future research. Achieving delivery specificity, as well as long-term effectiveness and safety, will be crucial for the future development of gene therapies targeting genetic diseases.

CRISPR targeting of mmu-miR-21a through a single adeno-associated virus vector prolongs survival of glioblastoma-bearing mice

Glioblastoma (GB), the most aggressive tumor of the central nervous system (CNS), has poor patient outcomes with limited effective treatments available. MicroRNA-21 (miR-21(a)) is a known oncogene, abundantly expressed in many cancer types. miR-21(a) promotes GB progression, and lack of miR-21(a) reduces the tumorigenic potential. Here, we propose a single adeno-associated virus (AAV) vector strategy targeting mmu-miR-21a using the Staphylococcus aureus Cas9 ortholog (SaCas9) guided by a single-guide RNA (sgRNA). Our results demonstrate that AAV8 is a well-suited AAV serotype to express SaCas9-KKH/sgRNA at the tumor site in an orthotopic GB model. The SaCas9-KKH induced a genomic deletion, resulting in lowered mmu-miR-21a levels in the brain, leading to reduced tumor growth and improved overall survival. In this study, we demonstrated that disruption of genomic mmu-miR-21a with a single AAV vector influenced glioma development, resulting in beneficial anti-tumor outcomes in GB-bearing mice.

In vivo adenine base editing ameliorates Rho-associated autosomal dominant retinitis pigmentosa

Mutations in the Rhodopsin (RHO) gene are the main cause of autosomal dominant retinitis pigmentosa (adRP), 84% of which are pathogenic gain-of-function point mutations. Treatment strategies for adRP typically involve silencing or ablating the pathogenic allele, while normal RHO protein replacement has no meaningful therapeutic benefit. Here, we present an adenine base editor (ABE)-mediated therapeutic approach for adRP caused by RHO point mutations in vivo. The correctable pathogenic mutations are screened and verified, including T17M, Q344ter, and P347L. Two adRP animal models are created carrying the class 1 (Q344ter) and class 2 (T17M) mutations, and dual AAV-delivered ABE can effectively repair both mutations in vivo. The early intervention of ABE8e efficiently corrects the Q344ter mutation that causes a severe form of adRP, delays photoreceptor death, and restores retinal function and visual behavior. These results suggest that ABE is a promising alternative to treat RHO mutation-associated adRP. Our work provides an effective spacer-mediated point mutation correction therapy approach for dominantly inherited ocular disorders.

The Role of CRISPR/Cas9 in Revolutionizing Duchenne's Muscular Dystrophy Treatment: Opportunities and Obstacles

Duchenne's muscular dystrophy (DMD) is a severe X-linked disorder characterized by progressive muscle degeneration, leading to loss of ambulation, respiratory failure, and premature death. It affects approximately 1 in 3,500 live male births and is caused by mutations in the dystrophin gene, which impairs muscle fiber stability. Current treatments are limited to managing symptoms and slowing disease progression, with no curative therapies available. The advent of CRISPR/Cas9 gene-editing technology has introduced a promising approach for directly correcting the genetic mutations responsible for DMD. This review explores the potential of CRISPR/Cas9 as a transformative therapy for DMD, highlighting its successes in preclinical models, the challenges associated with its delivery, and the obstacles to its clinical application. While preclinical studies demonstrate the efficacy of CRISPR/Cas9 in restoring dystrophin expression and improving muscle function, significant hurdles remain, including optimizing delivery methods and ensuring long-term safety.

Research hotspots and trends for Duchenne muscular dystrophy: a machine learning bibliometric analysis from 2004 to 2023

Aims

The aim of this study was to conduct a bibliometric analysis of the relevant literature on Duchenne muscular dystrophy (DMD) to ascertain its current status, identify key areas of research and demonstrate the evolution of the field.

Methods

The analysis sourced documents from the Science Citation Index Expanded in the Web of Science core collection, utilizing CiteSpace software and an online bibliometric platform to analyze collaborative networks among authors, institutions and countries, and to map out the research landscape through journal and reference evaluations. Keyword analyses, including clustering and emergent term identification, were conducted, alongside the development of knowledge maps.

Results

The study included 9,277 documents, indicating a rising publication trend in the field. The Institut National de la Santé et de la Recherche Médicale emerged as the top publishing institution, with Francesco Muntoni as the most prolific author. The United States dominated in publication output, showcasing significant leadership. The keyword analysis highlighted 786 key emergent terms, primarily focusing on the mechanisms, diagnostics and treatment approaches in DMD.

Conclusion

The field of DMD research is experiencing robust growth, drawing keen interest globally. A thorough analysis of current research and trends is essential for advancing knowledge and therapeutic strategies in this domain.

DMD mutations in pediatric patients with phenotypes of Duchenne/Becker muscular dystrophy

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are common X-inherited neuromuscular diseases. The genetic diagnosis has been used as the diagnostic choice for DMD/BMD. The study subjects consisted of 37 patients from Southwest China. Peripheral blood was collected for the extraction of genomic DNA. DMD mutation was sequenced using the next-generation sequencing approach. The detected mutation was validated using the multiplex ligation-dependent probe amplification or Sanger sequencing methods. Variation annotation and pathogenicity prediction were performed using the online databases. Pathogenic mutations were identified 3 splicing site, 7 single nucleotide, 1 indel, 23 deletion, and 3 duplication mutations. Novel DMD variants were discovered, including two novel splicing variations (c.1890 + 1G>T; c.1923 + 1G>A), one missense mutation (c.1946G>T), one nonsense mutation (c.7441G>T), one indel mutation (INDEL EX20), and one duplication mutation (DUP EX75-78). The current study provides mutation information of DMD for the genetic diagnosis of DMD/BMD.

Cardiomyopathy: pathogenesis and therapeutic interventions

Cardiomyopathy is a group of disease characterized by structural and functional damage to the myocardium. The etiologies of cardiomyopathies are diverse, spanning from genetic mutations impacting fundamental myocardial functions to systemic disorders that result in widespread cardiac damage. Many specific gene mutations cause primary cardiomyopathy. Environmental factors and metabolic disorders may also lead to the occurrence of cardiomyopathy. This review provides an in-depth analysis of the current understanding of the pathogenesis of various cardiomyopathies, highlighting the molecular and cellular mechanisms that contribute to their development and progression. The current therapeutic interventions for cardiomyopathies range from pharmacological interventions to mechanical support and heart transplantation. Gene therapy and cell therapy, propelled by ongoing advancements in overarching strategies and methodologies, has also emerged as a pivotal clinical intervention for a variety of diseases. The increasing number of causal gene of cardiomyopathies have been identified in recent studies. Therefore, gene therapy targeting causal genes holds promise in offering therapeutic advantages to individuals diagnosed with cardiomyopathies. Acting as a more precise approach to gene therapy, they are gradually emerging as a substitute for traditional gene therapy. This article reviews pathogenesis and therapeutic interventions for different cardiomyopathies.

Gene editing in common cardiovascular diseases

Cardiovascular diseases are the leading cause of morbidity and mortality worldwide, highlighting the high socioeconomic impact. Current treatment strategies like compound-based drugs or surgeries are often limited. On the one hand, systemic administration of substances is frequently associated with adverse side effects; on the other hand, they typically provide only short-time effects requiring daily intake. Thus, new therapeutic approaches and concepts are urgently needed. The advent of CRISPR-Cas9 genome editing offers great promise for the correction of disease-causing hereditary mutations. As such mutations are often very rare, gene editing strategies to correct them are not broadly applicable to many patients. Notably, there is recent evidence that gene editing technology can also be deployed to disrupt common pathogenic signaling cascades in a targeted, specific, and efficient manner, which offers a more generalizable approach. However, several challenges remain to be addressed ranging from the optimization of the editing strategy itself to a suitable delivery strategy up to potential immune responses to the editing components. This review article discusses important CRISPR-Cas9-based gene editing approaches with their advantages and drawbacks and outlines opportunities in their application for treatment of cardiovascular diseases.

Engineered Cas9 variants bypass Keap1-mediated degradation in human cells and enhance epigenome editing efficiency

As a potent and convenient genome-editing tool, Cas9 has been widely used in biomedical research and evaluated in treating human diseases. Numerous engineered variants of Cas9, dCas9 and other related prokaryotic endonucleases have been identified. However, as these bacterial enzymes are not naturally present in mammalian cells, whether and how bacterial Cas9 proteins are recognized and regulated by mammalian hosts remain poorly understood. Here, we identify Keap1 as a mammalian endogenous E3 ligase that targets Cas9/dCas9/Fanzor for ubiquitination and degradation in an 'ETGE'-like degron-dependent manner. Cas9-'ETGE'-like degron mutants evading Keap1 recognition display enhanced gene editing ability in cells. dCas9-'ETGE'-like degron mutants exert extended protein half-life and protein retention on chromatin, leading to improved CRISPRa and CRISPRi efficacy. Moreover, Cas9 binding to Keap1 also impairs Keap1 function by competing with Keap1 substrates or binding partners for Keap1 binding, while engineered Cas9 mutants show less perturbation of Keap1 biology. Thus, our study reveals a mammalian specific Cas9 regulation and provides new Cas9 designs not only with enhanced gene regulatory capacity but also with minimal effects on disrupting endogenous Keap1 signaling.

Deletion of exons 45 to 55 in the DMD gene: from the therapeutic perspective to the in vitro model

BACKGROUND

Gene editing therapies in development for correcting out-of-frame DMD mutations in Duchenne muscular dystrophy aim to replicate benign spontaneous deletions. Deletion of 45-55 DMD exons (del45-55) was described in asymptomatic subjects, but recently serious skeletal and cardiac complications have been reported. Uncovering why a single mutation like del45-55 is able to induce diverse phenotypes and grades of severity may impact the strategies of emerging therapies. Cellular models are essential for this purpose, but their availability is compromised by scarce muscle biopsies.

METHODS

We introduced, as a proof-of-concept, using CRISPR-Cas9 edition, a del45-55 mimicking the intronic breakpoints harboured by a subset of patients of this form of dystrophinopathy (designing specific gRNAs), into a Duchenne patient's cell line. The edited cell line was characterized evaluating the dystrophin expression and the myogenic status.

RESULTS

Dystrophin expression was restored, and the myogenic defects were ameliorated in the edited myoblasts harbouring a specific del45-55. Besides confirming the potential of CRISPR-Cas9 to create tailored mutations (despite the low cleavage efficiency of our gRNAs) as a useful approach to generate in vitro models, we also generated an immortalized myoblast line derived from a patient with a specific del45-55.

CONCLUSIONS

Overall, we provide helpful resources to deepen into unknown factors responsible for DMD-pathophysiology.

Megabase-scale loss of heterozygosity provoked by CRISPR-Cas9 DNA double-strand breaks

Harnessing DNA double-strand breaks (DSBs) is a powerful approach for gene editing, but it may provoke loss of heterozygosity (LOH), which predisposes to tumorigenesis. To interrogate this risk, we developed a two- color flow cytometry-based system (Flo-LOH), detecting LOH in ∼5% of cells following a DSB. After this initial increase, cells with LOH decrease due to a competitive disadvantage with parental cells, but if isolated, they stably propagate. Segmental loss from terminal deletions with de novo telomere addition and nonreciprocal translocations is observed as well as whole chromosome loss, especially following a centromeric DSB. LOH spans megabases distal from the DSB, but also frequently tens of megabases centromere-proximal. Inhibition of microhomology-mediated end joining massively increases LOH, which is synergistically increased with concomitant inhibition of canonical nonhomologous end joining. The capacity for large-scale LOH must therefore be considered when using DSB-based gene editing, especially in conjunction with end joining inhibition.

Metabolic gene therapy in a canine with pulmonary hypertension secondary to degenerative mitral valve disease

Myxomatous mitral valve disease (MMVD) stands out as the most prevalent acquired canine heart disease. Its occurrence can reach up to 40% in small breed dogs and escalates in geriatric canine populations. MMVD leads to thickening and incomplete coaptation of valve leaflets during systole, resulting in secondary mitral valve regurgitation. Serious complications may arise concurrently with the worsening of mitral valve regurgitation, including left-and right-sided congestive heart failure, and pulmonary hypertension (PH). Ultimately, the PH progression might contribute to the patient's demise or to the owner's decision of euthanasia. Most currently available FDA-approved therapies for PH are costly and aim to address the imbalance between vasoconstriction and vasodilation to restore endothelial cell function. However, none of these medications impact the molecular dysfunction of cells or impede the advancement of pulmonary vascular and right ventricular remodeling. Recent evidence has showcased successful gene therapy approaches in laboratory animal models of PH. In this manuscript, we summarize the latest advancements in gene therapy for the treatment of PH in animals. The manuscript incorporates original data showcasing sample presentations, along with non-invasive hemodynamic assessments. Our findings demonstrate that the use of metabolic gene therapy, combining synthetic adeno-associated virus with acid ceramidase, has the potential to significantly reduce the need for drug treatment and improve spontaneously occurring PH in dogs.

In silico and in cellulo approaches for functional annotation of human protein splice variants

The elegance of pre-mRNA splicing mechanisms continues to interest scientists even after over a half century, since the discovery of the fact that coding regions in genes are interrupted by non-coding sequences. The vast majority of human genes have several mRNA variants, coding structurally and functionally different protein isoforms in a tissue-specific manner and with a linkage to specific developmental stages of the organism. Alteration of splicing patterns shifts the balance of functionally distinct proteins in living systems, distorts normal molecular pathways, and may trigger the onset and progression of various pathologies. Over the past two decades, numerous studies have been conducted in various life sciences disciplines to deepen our understanding of splicing mechanisms and the extent of their impact on the functioning of living systems. This review aims to summarize experimental and computational approaches used to elucidate the functions of splice variants of a single gene based on our experience accumulated in the laboratory of interactomics of proteoforms at the Institute of Biomedical Chemistry (IBMC) and best global practices.

Gene Editing by Ferrying of CRISPR/Cas Ribonucleoprotein Complexes in Enveloped Virus-Derived Particles

The invention of next-generation CRISPR/Cas gene editing tools, like base and prime editing, for correction of gene variants causing disease, has created hope for in vivo use in patients leading to wider clinical translation. To realize this potential, delivery vehicles that can ferry gene editing tool kits safely and effectively into specific cell populations or tissues are in great demand. In this review, we describe the development of enveloped retrovirus-derived particles as carriers of "ready-to-work" ribonucleoprotein complexes consisting of Cas9-derived editor proteins and single guide RNAs. We present arguments for adapting viruses for cell-targeted protein delivery and describe the status after a decade-long development period, which has already shown effective editing in primary cells, including T cells and hematopoietic stem cells, and in tissues targeted in vivo, including mouse retina, liver, and brain. Emerging evidence has demonstrated that engineered virus-derived nanoparticles can accommodate both base and prime editors and seems to fertilize a sprouting hope that such particles can be further developed and produced in large scale for therapeutic applications.

Schnurri-3 inhibition rescues skeletal fragility and vascular skeletal stem cell niche pathology in the OIM model of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a disorder of low bone mass and increased fracture risk due to a range of genetic variants that prominently include mutations in genes encoding type I collagen. While it is well known that OI reflects defects in the activity of bone-forming osteoblasts, it is currently unclear whether OI also reflects defects in the many other cell types comprising bone, including defects in skeletal vascular endothelium or the skeletal stem cell populations that give rise to osteoblasts and whether correcting these broader defects could have therapeutic utility. Here, we find that numbers of skeletal stem cells (SSCs) and skeletal arterial endothelial cells (AECs) are augmented in Col1a2oim/oim mice, a well-studied animal model of moderate to severe OI, suggesting that disruption of a vascular SSC niche is a feature of OI pathogenesis. Moreover, crossing Col1a2oim/oim mice to mice lacking a negative regulator of skeletal angiogenesis and bone formation, Schnurri 3 (SHN3), not only corrected the SSC and AEC phenotypes but moreover robustly corrected the bone mass and spontaneous fracture phenotypes. As this finding suggested a strong therapeutic utility of SHN3 inhibition for the treatment of OI, a bone-targeting AAV was used to mediate Shn3 knockdown, rescuing the Col1a2oim/oim phenotype and providing therapeutic proof-of-concept for targeting SHN3 for the treatment of OI. Overall, this work both provides proof-of-concept for inhibition of the SHN3 pathway and more broadly addressing defects in the stem/osteoprogenitor niche as is a strategy to treat OI.

Mitochondria-encoded peptide MOTS-c participates in plasma membrane repair by facilitating the translocation of TRIM72 to membrane

Rationale: An impairment of plasma membrane repair has been implicated in various diseases such as muscular dystrophy and ischemia/reperfusion injury. MOTS-c, a short peptide encoded by mitochondria, has been shown to pass through the plasma membrane into the bloodstream. This study determined whether this biological behavior was involved in membrane repair and its underlying mechanism. Methods and Results: In human participants, the level of MOTS-c was positively correlated with the abundance of mitochondria, and the membrane repair molecule TRIM72. In contrast to high-intensity eccentric exercise, moderate-intensity exercise improved sarcolemma integrity and physical performance, accompanied by an increase of mitochondria beneath the damaged sarcolemma and secretion of MOTS-c. Furthermore, moderate-intensity exercise increased the interaction between MOTS-c and TRIM72, and MOTS-c facilitated the trafficking of TRIM72 to the sarcolemma. In vitro studies demonstrated that MOTS-c attenuated membrane damage induced by hypotonic solution, which could be blocked by siRNA-TRIM72, but not AMPK inhibitor. Co-immunoprecipitation study showed that MOTS-c interacted with TRIM72 C-terminus, but not N-terminus. The dynamic membrane repair assay revealed that MOTS-c boosted the trafficking of TRIM72 to the injured membrane. However, MOTS-c itself had negligible effects on membrane repair, which was recapitulated in TRIM72-/- mice. Unexpectedly, MOTS-c still increased the fusion of vesicles with the membrane in TRIM72-/- mice, and dot blot analysis revealed an interaction between MOTS-c and phosphatidylinositol (4,5) bisphosphate [PtdIns (4,5) P2]. Finally, MOTS-c blunted ischemia/reperfusion-induced membrane disruption, and preserved heart function. Conclusions: MOTS-c/TRIM72-mediated membrane integrity improvement participates in mitochondria-triggered membrane repair. An interaction between MOTS-c and plasma lipid contributes to the fusion of vesicles with membrane. Our data provide a novel therapeutic strategy for rescuing organ function by facilitating membrane repair with MOTS-c.

Adenine base editing-mediated exon skipping restores dystrophin in humanized Duchenne mouse model

Duchenne muscular dystrophy (DMD) affecting 1 in 3500-5000 live male newborns is the frequently fatal genetic disease resulted from various mutations in DMD gene encoding dystrophin protein. About 70% of DMD-causing mutations are exon deletion leading to frameshift of open reading frame and dystrophin deficiency. To facilitate translating human DMD-targeting CRISPR therapeutics into patients, we herein establish a genetically humanized mouse model of DMD by replacing exon 50 and 51 of mouse Dmd gene with human exon 50 sequence. This humanized mouse model recapitulats patient's DMD phenotypes of dystrophin deficiency and muscle dysfunction. Furthermore, we target splicing sites in human exon 50 with adenine base editor to induce exon skipping and robustly restored dystrophin expression in heart, tibialis anterior and diaphragm muscles. Importantly, systemic delivery of base editor via adeno-associated virus in the humanized male mouse model improves the muscle function of DMD mice to the similar level of wildtype ones, indicating the therapeutic efficacy of base editing strategy in treating most of DMD types with exon deletion or point mutations via exon-skipping induction.

CRISPR-Based Gene Editing: a Modern Approach for Study and Treatment of Cancer

The development and emergence of clustered regularly interspaced short palindromic repeats (CRISPR) as a genome-editing technology have created a plethora of opportunities in genetic engineering. The ability of sequence-specific addition or removal of DNA in an efficient and cost-effective manner has revolutionized modern research in the field of life science and healthcare. CRISPR is widely used as a genome engineering tool in clinical studies for observing gene expression and metabolic pathway regulations in detail. Even in the case of transgenic research and personalized gene manipulation studies, CRISPR-based technology is used extensively. To understand and even to correct the underlying genetic problem is of cancer, CRISPR-based technology can be used. Various kinds of work is going on throughout the world which are attempting to target different genes in order to discover novel and effective methodologies for the treatment of cancer. In this review, we provide a brief overview on the application of CRISPR gene editing technology in cancer treatment focusing on the key aspects of cancer screening, modelling and therapy techniques.

BREATHE DMD: boosting respiratory efficacy after therapeutic hypoxic episodes in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal genetic neuromuscular disorder, characterised by progressive decline in skeletal muscle function due to the secondary consequences of dystrophin deficiency. Weakness extends to the respiratory musculature, and cardiorespiratory failure is the leading cause of death in men with DMD. Intermittent hypoxia has emerged as a potential therapy to counteract ventilatory insufficiency by eliciting long-term facilitation of breathing. Mechanisms of sensory and motor facilitation of breathing have been well delineated in animal models. Various paradigms of intermittent hypoxia have been designed and implemented in human trials culminating in clinical trials in people with spinal cord injury and amyotrophic lateral sclerosis. Application of therapeutic intermittent hypoxia to DMD is considered together with discussion of the potential barriers to progression owing to the complexity of this devastating disease. Notwithstanding the considerable challenges and potential pitfalls of intermittent hypoxia-based therapies for DMD, we suggest it is incumbent on the research community to explore the potential benefits in pre-clinical models. Intermittent hypoxia paradigms should be implemented to explore the proclivity to express respiratory plasticity with the longer-term aim of preserving and potentiating ventilation in pre-clinical models and people with DMD.

Correction of human nonsense mutation via adenine base editing for Duchenne muscular dystrophy treatment in mouse

Duchenne muscular dystrophy (DMD) is the most prevalent herediatry disease in men, characterized by dystrophin deficiency, progressive muscle wasting, cardiac insufficiency, and premature mortality, with no effective therapeutic options. Here, we investigated whether adenine base editing can correct pathological nonsense point mutations leading to premature stop codons in the dystrophin gene. We identified 27 causative nonsense mutations in our DMD patient cohort. Treatment with adenine base editor (ABE) could restore dystrophin expression by direct A-to-G editing of pathological nonsense mutations in cardiomyocytes generated from DMD patient-derived induced pluripotent stem cells. We also generated two humanized mouse models of DMD expressing mutation-bearing exons 23 or 30 of human dystrophin gene. Intramuscular administration of ABE, driven by ubiquitous or muscle-specific promoters could correct these nonsense mutations in vivo, albeit with higher efficiency in exon 30, restoring dystrophin expression in skeletal fibers of humanized DMD mice. Moreover, a single systemic delivery of ABE with human single guide RNA (sgRNA) could induce body-wide dystrophin expression and improve muscle function in rotarod tests of humanized DMD mice. These findings demonstrate that ABE with human sgRNAs can confer therapeutic alleviation of DMD in mice, providing a basis for development of adenine base editing therapies in monogenic diseases.

Lipo-Xenopeptide Polyplexes for CRISPR/Cas9 based Gene editing at ultra-low dose

Double pH-responsive xenopeptide carriers containing succinoyl tetraethylene pentamine (Stp) and lipo amino fatty acids (LAFs) were evaluated for CRISPR/Cas9 based genome editing. Different carrier topologies, variation of LAF/Stp ratios and LAF types as Cas9 mRNA/sgRNA polyplexes were screened in three different reporter cell lines using three different genomic targets (Pcsk9, eGFP, mdx exon 23). One U-shaped and three bundle (B2)-shaped lipo-xenopeptides exhibiting remarkable efficiencies were identified. Genome editing potency of top carriers were observed at sub-nanomolar EC50 concentrations of 0.4 nM sgRNA and 0.1 nM sgRNA for the top U-shape and top B2 carriers, respectively, even after incubation in full (≥ 90%) serum. Polyplexes co-delivering Cas9 mRNA/sgRNA with a single stranded DNA template for homology directed gene editing resulted in up to 38% conversion of eGFP to BFP in reporter cells. Top carriers were formulated as polyplexes or lipid nanoparticles (LNPs) for subsequent in vivo administration. Formulations displayed long-term physicochemical and functional stability upon storage at 4 °C. Importantly, intravenous administration of polyplexes or LNPs mediated in vivo editing of the dystrophin gene, triggering mRNA exon 23 splicing modulation in dystrophin-expressing cardiac muscle, skeletal muscle and brain tissue.

CRISPR-Based Gene Therapies: From Preclinical to Clinical Treatments

In recent years, clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) protein have emerged as a revolutionary gene editing tool to treat inherited disorders affecting different organ systems, such as blood and muscles. Both hematological and neuromuscular genetic disorders benefit from genome editing approaches but face different challenges in their clinical translation. The ability of CRISPR/Cas9 technologies to modify hematopoietic stem cells ex vivo has greatly accelerated the development of genetic therapies for blood disorders. In the last decade, many clinical trials were initiated and are now delivering encouraging results. The recent FDA approval of Casgevy, the first CRISPR/Cas9-based drug for severe sickle cell disease and transfusion-dependent β-thalassemia, represents a significant milestone in the field and highlights the great potential of this technology. Similar preclinical efforts are currently expanding CRISPR therapies to other hematologic disorders such as primary immunodeficiencies. In the neuromuscular field, the versatility of CRISPR/Cas9 has been instrumental for the generation of new cellular and animal models of Duchenne muscular dystrophy (DMD), offering innovative platforms to speed up preclinical development of therapeutic solutions. Several corrective interventions have been proposed to genetically restore dystrophin production using the CRISPR toolbox and have demonstrated promising results in different DMD animal models. Although these advances represent a significant step forward to the clinical translation of CRISPR/Cas9 therapies to DMD, there are still many hurdles to overcome, such as in vivo delivery methods associated with high viral vector doses, together with safety and immunological concerns. Collectively, the results obtained in the hematological and neuromuscular fields emphasize the transformative impact of CRISPR/Cas9 for patients affected by these debilitating conditions. As each field suffers from different and specific challenges, the clinical translation of CRISPR therapies may progress differentially depending on the genetic disorder. Ongoing investigations and clinical trials will address risks and limitations of these therapies, including long-term efficacy, potential genotoxicity, and adverse immune reactions. This review provides insights into the diverse applications of CRISPR-based technologies in both preclinical and clinical settings for monogenic blood disorders and muscular dystrophy and compare advances in both fields while highlighting current trends, difficulties, and challenges to overcome.

Myospreader improves gene editing in skeletal muscle by myonuclear propagation

Successful CRISPR/Cas9-based gene editing in skeletal muscle is dependent on efficient propagation of Cas9 to all myonuclei in the myofiber. However, nuclear-targeted gene therapy cargos are strongly restricted to their myonuclear domain of origin. By screening nuclear localization signals and nuclear export signals, we identify "Myospreader," a combination of short peptide sequences that promotes myonuclear propagation. Appending Myospreader to Cas9 enhances protein stability and myonuclear propagation in myoblasts and myofibers. AAV-delivered Myospreader dCas9 better inhibits transcription of toxic RNA in a myotonic dystrophy mouse model. Furthermore, Myospreader Cas9 achieves higher rates of gene editing in CRISPR reporter and Duchenne muscular dystrophy mouse models. Myospreader reveals design principles relevant to all nuclear-targeted gene therapies and highlights the importance of the spatial dimension in therapeutic development.

Advanced cell and gene therapies in cardiology

We review the evidence for the presence of stem/progenitor cells in the heart and the preclinical and clinical data using diverse cell types for the therapy of cardiac diseases. We highlight the failure of adult stem/progenitor cells to ameliorate heart function in most cardiac diseases, with the possible exception of refractory angina. The use of pluripotent stem cell-derived cardiomyocytes is analysed as a viable alternative therapeutic option but still needs further research at preclinical and clinical stages. We also discuss the use of direct reprogramming of cardiac fibroblasts into cardiomyocytes and the use of extracellular vesicles as therapeutic agents in ischemic and non-ischemic cardiac diseases. Finally, gene therapies and genome editing for the treatment of hereditary cardiac diseases, ablation of genes responsible for atherosclerotic disease, or modulation of gene expression in the heart are discussed.

Recent Therapeutic Gene Editing Applications to Genetic Disorders

Recent years have witnessed unprecedented progress in therapeutic gene editing, revolutionizing the approach to treating genetic disorders. In this comprehensive review, we discuss the progression of milestones leading to the emergence of the clustered regularly interspaced short palindromic repeats (CRISPR)-based technology as a powerful tool for precise and targeted modifications of the human genome. CRISPR-Cas9 nuclease, base editing, and prime editing have taken center stage, demonstrating remarkable precision and efficacy in targeted ex vivo and in vivo genomic modifications. Enhanced delivery systems, including viral vectors and nanoparticles, have further improved the efficiency and safety of therapeutic gene editing, advancing their clinical translatability. The exploration of CRISPR-Cas systems beyond the commonly used Cas9, such as the development of Cas12 and Cas13 variants, has expanded the repertoire of gene editing tools, enabling more intricate modifications and therapeutic interventions. Outstandingly, prime editing represents a significant leap forward, given its unparalleled versatility and minimization of off-target effects. These innovations have paved the way for therapeutic gene editing in a multitude of previously incurable genetic disorders, ranging from monogenic diseases to complex polygenic conditions. This review highlights the latest innovative studies in the field, emphasizing breakthrough technologies in preclinical and clinical trials, and their applications in the realm of precision medicine. However, challenges such as off-target effects and ethical considerations remain, necessitating continued research to refine safety profiles and ethical frameworks.

Gene editing in small and large animals for translational medicine: a review

The CRISPR/Cas9 system is a simpler and more versatile method compared to other engineered nucleases such as Zinc Finger Nucleases (ZFNs) and Transcription Activator-Like Effector Nucleases (TALENs), and since its discovery, the efficiency of CRISPR-based genome editing has increased to the point that multiple and different types of edits can be made simultaneously. These advances in gene editing have revolutionized biotechnology by enabling precise genome editing with greater simplicity and efficacy than ever before. This tool has been successfully applied to a wide range of animal species, including cattle, pigs, dogs, and other small animals. Engineered nucleases cut the genome at specific target positions, triggering the cell's mechanisms to repair the damage and introduce a mutation to a specific genomic site. This review discusses novel genome-based CRISPR/Cas9 editing tools, methods developed to improve efficiency and specificity, the use of gene-editing on animal models and translational medicine, and the main challenges and limitations of CRISPR-based gene-editing approaches.

Application and perspective of CRISPR/Cas9 genome editing technology in human diseases modeling and gene therapy

The Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) mediated Cas9 nuclease system has been extensively used for genome editing and gene modification in eukaryotic cells. CRISPR/Cas9 technology holds great potential for various applications, including the correction of genetic defects or mutations within the human genome. The application of CRISPR/Cas9 genome editing system in human disease research is anticipated to solve a multitude of intricate molecular biology challenges encountered in life science research. Here, we review the fundamental principles underlying CRISPR/Cas9 technology and its recent application in neurodegenerative diseases, cardiovascular diseases, autoimmune related diseases, and cancer, focusing on the disease modeling and gene therapy potential of CRISPR/Cas9 in these diseases. Finally, we provide an overview of the limitations and future prospects associated with employing CRISPR/Cas9 technology for diseases study and treatment.

Preclinical Models of Cardiac Disease: A Comprehensive Overview for Clinical Scientists

For recent decades, cardiac diseases have been the leading cause of death and morbidity worldwide. Despite significant achievements in their management, profound understanding of disease progression is limited. The lack of biologically relevant and robust preclinical disease models that truly grasp the molecular underpinnings of cardiac disease and its pathophysiology attributes to this stagnation, as well as the insufficiency of platforms that effectively explore novel therapeutic avenues. The area of fundamental and translational cardiac research has therefore gained wide interest of scientists in the clinical field, while the landscape has rapidly evolved towards an elaborate array of research modalities, characterized by diverse and distinctive traits. As a consequence, current literature lacks an intelligible and complete overview aimed at clinical scientists that focuses on selecting the optimal platform for translational research questions. In this review, we present an elaborate overview of current in vitro, ex vivo, in vivo and in silico platforms that model cardiac health and disease, delineating their main benefits and drawbacks, innovative prospects, and foremost fields of application in the scope of clinical research incentives.

CRISPR-Based Gene Editing Techniques in Pediatric Neurological Disorders

The emergence of gene editing technologies offers a unique opportunity to develop mutation-specific treatments for pediatric neurological disorders. Gene editing systems can potentially alter disease trajectory by correcting dysfunctional mutations or therapeutically altering gene expression. Clustered regularly interspaced short palindromic repeats (CRISPR)-based approaches are attractive gene therapy platforms to personalize treatments because of their specificity, ease of design, versatility, and cost. However, many such approaches remain in the early stages of development, with ongoing efforts to optimize editing efficiency, minimize unintended off-target effects, and mitigate pathologic immune responses. Given the rapid evolution of CRISPR-based therapies, it is prudent for the clinically based child neurologist to have a conceptual understanding of what such therapies may entail, including both benefits and risks and how such therapies may be clinically applied. In this review, we describe the fundamentals of CRISPR-based therapies, discuss the opportunities and challenges that have arisen, and highlight preclinical work in several pediatric neurological diseases.

Preclinical evaluation of CRISPR-based therapies for Noonan syndrome caused by deep-intronic LZTR1 variants

Gene variants in LZTR1 are implicated to cause Noonan syndrome associated with a severe and early-onset hypertrophic cardiomyopathy. Mechanistically, LZTR1 deficiency results in accumulation of RAS GTPases and, as a consequence, in RAS-MAPK signaling hyperactivity, thereby causing the Noonan syndrome-associated phenotype. Despite its epidemiological relevance, pharmacological as well as invasive therapies remain limited. Here, personalized CRISPR-Cas9 gene therapies might offer a novel alternative for a curative treatment in this patient cohort. In this study, by utilizing a patient-specific screening platform based on iPSC-derived cardiomyocytes from two Noonan syndrome patients, we evaluated different clinically translatable therapeutic approaches using small Cas9 orthologs targeting a deep-intronic LZTR1 variant to cure the disease-associated molecular pathology. Despite high editing efficiencies in cardiomyocyte cultures transduced with lentivirus or all-in-one adeno-associated viruses, we observed crucial differences in editing outcomes in proliferative iPSCs vs. non-proliferative cardiomyocytes. While editing in iPSCs rescued the phenotype, the same editing approaches did not robustly restore LZTR1 function in cardiomyocytes, indicating critical differences in the activity of DNA double-strand break repair mechanisms between proliferative and non-proliferative cell types and highlighting the importance of cell type-specific screens for testing CRISPR-Cas9 gene therapies.

Past, present, and future of CRISPR genome editing technologies

Genome editing has been a transformative force in the life sciences and human medicine, offering unprecedented opportunities to dissect complex biological processes and treat the underlying causes of many genetic diseases. CRISPR-based technologies, with their remarkable efficiency and easy programmability, stand at the forefront of this revolution. In this Review, we discuss the current state of CRISPR gene editing technologies in both research and therapy, highlighting limitations that constrain them and the technological innovations that have been developed in recent years to address them. Additionally, we examine and summarize the current landscape of gene editing applications in the context of human health and therapeutics. Finally, we outline potential future developments that could shape gene editing technologies and their applications in the coming years.

Duchenne Muscular Dystrophy Gene Therapy

Duchenne and Becker muscular dystrophies are allelic X-linked recessive neuromuscular diseases affecting both skeletal and cardiac muscles. Therefore, owing to their single X chromosome, the affected boys receive pathogenic gene mutations from their unknowing carrier mothers. Current pharmacological drugs are palliative that address the symptoms of the disease rather than the genetic cause imbedded in the Dystrophin gene DNA sequence. Therefore, alternative therapies like gene drugs that could address the genetic cause of the disease at its root are crucial, which include gene transfer/implantation, exon skipping, and gene editing. Presently, it is possible through genetic reprogramming to engineer AAV vectors to deliver certain therapeutic cargos specifically to muscle or other organs regardless of their serotype. Similarly, it is possible to direct the biogenesis of exosomes to carry gene editing constituents or certain therapeutic cargos to specific tissue or cell type like brain and muscle. While autologous exosomes are immunologically inert, it is possible to camouflage AAV capsids, and lipid nanoparticles to evade the immune system recognition. In this review, we highlight current opportunities for Duchenne muscular dystrophy gene therapy, which has been known thus far as an incurable genetic disease. This article is a part of Gene Therapy of Rare Genetic Diseases thematic issue.

Precision medicine using whole genome sequencing identifies a novel dystrophin (DMD) variant for X-linked muscular dystrophy in a cat

BACKGROUND

Muscular dystrophies (MDs) are a large, heterogeneous group of degenerative muscle diseases. X-linked dystrophin-deficient MD in cats is the first genetically characterized cat model for a human disease and a few novel forms have been identified.

HYPOTHESIS/OBJECTIVES

Muscular dystrophy was suspected in a young male domestic shorthair cat. Clinical, molecular, and genetic techniques could provide a definitive diagnosis.

ANIMALS

A 1-year-old male domestic shorthair cat presented for progressive difficulty walking, macroglossia and dysphagia beginning at 6 months of age. The tongue was thickened, protruded with constant ptyalism, and thickening and rigidity of the neck and shoulders were observed.

METHODS

A complete neurological examination, baseline laboratory evaluation and biopsies of the trapezius muscle were performed with owner consent. Indirect immunofluorescence staining of muscle cryosections was performed using several monoclonal and polyclonal antibodies against dystrophy-associated proteins. DNA was isolated for genomic analyses by whole genome sequencing and comparison to DNA variants in the 99 Lives Cat Genome Sequencing dataset.

RESULTS AND CLINICAL IMPORTANCE

Aspartate aminotransferase (687 IU/L) and creatine kinase (24 830 IU/L) activities were increased and mild hypokalemia (3.7 mmol/L) was present. Biopsy samples from the trapezius muscle confirmed a degenerative and regenerative myopathy and protein alterations identified by immunohistochemistry resulted in a diagnosis of a in dystrophin-deficient form of X-linked MD. A stop gain variant (c.4849C>T; p.Gln1617Ter) dystrophin was identified by genome sequencing. Precision/genomic medicine efforts for the domestic cat and in veterinary medicine support disease variant and animal model discovery and provide opportunities for targeted treatments for companion animals.

Dystrophin- and Utrophin-Based Therapeutic Approaches for Treatment of Duchenne Muscular Dystrophy: A Comparative Review

Duchenne muscular dystrophy is a devastating disease that leads to progressive muscle loss and premature death. While medical management focuses mostly on symptomatic treatment, decades of research have resulted in first therapeutics able to restore the affected reading frame of dystrophin transcripts or induce synthesis of a truncated dystrophin protein from a vector, with other strategies based on gene therapy and cell signaling in preclinical or clinical development. Nevertheless, recent reports show that potentially therapeutic dystrophins can be immunogenic in patients. This raises the question of whether a dystrophin paralog, utrophin, could be a more suitable therapeutic protein. Here, we compare dystrophin and utrophin amino acid sequences and structures, combining published data with our extended in silico analyses. We then discuss these results in the context of therapeutic approaches for Duchenne muscular dystrophy. Specifically, we focus on strategies based on delivery of micro-dystrophin and micro-utrophin genes with recombinant adeno-associated viral vectors, exon skipping of the mutated dystrophin pre-mRNAs, reading through termination codons with small molecules that mask premature stop codons, dystrophin gene repair by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9)-mediated genetic engineering, and increasing utrophin levels. Our analyses highlight the importance of various dystrophin and utrophin domains in Duchenne muscular dystrophy treatment, providing insights into designing novel therapeutic compounds with improved efficacy and decreased immunoreactivity. While the necessary actin and β-dystroglycan binding sites are present in both proteins, important functional distinctions can be identified in these domains and some other parts of truncated dystrophins might need redesigning due to their potentially immunogenic qualities. Alternatively, therapies based on utrophins might provide a safer and more effective approach.

Clinical applications of the CRISPR/Cas9 genome-editing system: Delivery options and challenges in precision medicine

CRISPR/Cas9 is an effective gene editing tool with broad applications for the prevention or treatment of numerous diseases. It depends on CRISPR (clustered regularly interspaced short palindromic repeats) as a bacterial immune system and plays as a gene editing tool. Due to the higher specificity and efficiency of CRISPR/Cas9 compared to other editing approaches, it has been broadly investigated to treat numerous hereditary and acquired illnesses, including cancers, hemolytic diseases, immunodeficiency disorders, cardiovascular diseases, visual maladies, neurodegenerative conditions, and a few X-linked disorders. CRISPR/Cas9 system has been used to treat cancers through a variety of approaches, with stable gene editing techniques. Here, the applications and clinical trials of CRISPR/Cas9 in various illnesses are described. Due to its high precision and efficiency, CRISPR/Cas9 strategies may treat gene-related illnesses by deleting, inserting, modifying, or blocking the expression of specific genes. The most challenging barrier to the in vivo use of CRISPR/Cas9 like off-target effects will be discussed. The use of transfection vehicles for CRISPR/Cas9, including viral vectors (such as an Adeno-associated virus (AAV)), and the development of non-viral vectors is also considered.

Precision therapy in dilated cardiomyopathy: Pipedream or paradigm shift?

Precision medicine for cardiomyopathies holds great promise to improve patient outcomes costs by shifting the focus to patient-specific treatment decisions, maximising the use of therapies most likely to lead to benefit and minimising unnecessary intervention. Dilated cardiomyopathy (DCM), characterised by left ventricular dilatation and impairment, is a major cause of heart failure globally. Advances in genomic medicine have increased our understanding of the genetic architecture of DCM. Understanding the functional implications of genetic variation to reveal genotype-specific disease mechanisms is the subject of intense investigation, with advanced cardiac imaging and mutliomics approaches playing important roles. This may lead to increasing use of novel, targeted therapy. Individualised treatment and risk stratification is however made more complex by the modifying effects of common genetic variation and acquired environmental factors that help explain the variable expressivity of rare genetic variants and gene elusive disease. The next frontier must be expanding work into early disease to understand the mechanisms that drive disease expression, so that the focus can be placed on disease prevention rather than management of later symptomatic disease. Overcoming these challenges holds the key to enabling a paradigm shift in care from the management of symptomatic heart failure to prevention of disease.

CRISPR/Cas9 Landscape: Current State and Future Perspectives

CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 is a unique genome editing tool that can be easily used in a wide range of applications, including functional genomics, transcriptomics, epigenetics, biotechnology, plant engineering, livestock breeding, gene therapy, diagnostics, and so on. This review is focused on the current CRISPR/Cas9 landscape, e.g., on Cas9 variants with improved properties, on Cas9-derived and fusion proteins, on Cas9 delivery methods, on pre-existing immunity against CRISPR/Cas9 proteins, anti-CRISPR proteins, and their possible roles in CRISPR/Cas9 function improvement. Moreover, this review presents a detailed outline of CRISPR/Cas9-based diagnostics and therapeutic approaches. Finally, the review addresses the future expansion of genome editors' toolbox with Cas9 orthologs and other CRISPR/Cas proteins.

Elimination of CaMKIIδ Autophosphorylation by CRISPR-Cas9 Base Editing Improves Survival and Cardiac Function in Heart Failure in Mice

BACKGROUND

Cardiovascular diseases are the main cause of worldwide morbidity and mortality, highlighting the need for new therapeutic strategies. Autophosphorylation and subsequent overactivation of the cardiac stress-responsive enzyme CaMKIIδ (Ca2+/calmodulin-dependent protein kinase IIδ) serves as a central driver of multiple cardiac disorders.

METHODS

To develop a comprehensive therapy for heart failure, we used CRISPR-Cas9 adenine base editing to ablate the autophosphorylation site of CaMKIIδ. We generated mice harboring a phospho-resistant CaMKIIδ mutation in the germline and subjected these mice to severe transverse aortic constriction, a model for heart failure. Cardiac function, transcriptional changes, apoptosis, and fibrosis were assessed by echocardiography, RNA sequencing, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, and standard histology, respectively. Specificity toward CaMKIIδ gene editing was assessed using deep amplicon sequencing. Cellular Ca2+ homeostasis was analyzed using epifluorescence microscopy in Fura-2-loaded cardiomyocytes.

RESULTS

Within 2 weeks after severe transverse aortic constriction surgery, 65% of all wild-type mice died, and the surviving mice showed dramatically impaired cardiac function. In contrast to wild-type mice, CaMKIIδ phospho-resistant gene-edited mice showed a mortality rate of only 11% and exhibited substantially improved cardiac function after severe transverse aortic constriction. Moreover, CaMKIIδ phospho-resistant mice were protected from heart failure-related aberrant changes in cardiac gene expression, myocardial apoptosis, and subsequent fibrosis, which were observed in wild-type mice after severe transverse aortic constriction. On the basis of identical mouse and human genome sequences encoding the autophosphorylation site of CaMKIIδ, we deployed the same editing strategy to modify this pathogenic site in human induced pluripotent stem cells. It is notable that we detected a >2000-fold increased specificity for editing of CaMKIIδ compared with other CaMKII isoforms, which is an important safety feature. While wild-type cardiomyocytes showed impaired Ca2+ transients and an increased frequency of arrhythmias after chronic β-adrenergic stress, CaMKIIδ-edited cardiomyocytes were protected from these adverse responses.

CONCLUSIONS

Ablation of CaMKIIδ autophosphorylation by adenine base editing may offer a potential broad-based therapeutic concept for human cardiac disease.