Progress in bioengineering of myotropic Adeno-associated viral (AAV) gene therapy vectors

Functional benefit of CRISPR-Cas9-induced allele deletion for RYR1 dominant mutation

More than 700 pathogenic or probably pathogenic variations have been identified in the RYR1 gene causing various myopathies collectively known as "RYR1-related myopathies." There is no treatment for these myopathies, and gene therapy stands out as one of the most promising approaches. In the context of a dominant form of central core disease due to a RYR1 mutation, we aimed at showing the functional benefit of inactivating specifically the mutated RYR1 allele by guiding CRISPR-Cas9 cleavages onto frequent single-nucleotide polymorphisms (SNPs) segregating on the same chromosome. Whole-genome sequencing was used to pinpoint SNPs localized on the mutant RYR1 allele and identified specific CRISPR-Cas9 guide RNAs. Lentiviruses encoding these guide RNAs and the SpCas9 nuclease were used to transduce immortalized patient myoblasts, inducing the specific deletion of the mutant RYR1 allele. The efficiency of the deletion was assessed at DNA and RNA levels, and at the functional level after monitoring calcium release induced by the stimulation of the RyR1-channel. This study provides in cellulo proof of concept regarding the benefits of mutant RYR1 allele deletion, in the case of a dominant RYR1 mutation, from both a molecular and functional perspective, and could apply potentially to 20% of all patients with a RYR1 mutation.

On RNA-programmable gene modulation as a versatile set of principles targeting muscular dystrophies

The repurposing of RNA-programmable CRISPR systems from genome editing into epigenome editing tools is gaining pace, including in research and development efforts directed at tackling human disorders. This momentum stems from the increasing knowledge regarding the epigenetic factors and networks underlying cell physiology and disease etiology and from the growing realization that genome editing principles involving chromosomal breaks generated by programmable nucleases are prone to unpredictable genetic changes and outcomes. Hence, engineered CRISPR systems are serving as versatile DNA-targeting scaffolds for heterologous and synthetic effector domains that, via locally recruiting transcription factors and chromatin remodeling complexes, seek interfering with loss-of-function and gain-of-function processes underlying recessive and dominant disorders, respectively. Here, after providing an overview about epigenetic drugs and CRISPR-Cas-based activation and interference platforms, we cover the testing of these platforms in the context of molecular therapies for muscular dystrophies. Finally, we examine attributes, obstacles, and deployment opportunities for CRISPR-based epigenetic modulating technologies.

Artificial viruses: A nanotechnology based approach

OBJECTIVES

The main objective of this work was to review and summarise the detailed literature available on viral nanoparticle and the strategies utilised for their manufacture along with their applications as therapeutic agents.

DATA ACQUISITION

The reported literature related to development and application of virus nanoparticles have been collected from electronic data bases like ScienceDirect, google scholar, PubMed by using key words like "viral nanoparticles", "targeted drug delivery" and "vaccines" and related combinations.

RESULT

From the detailed literature survey, virus nanoparticles were identified as carriers for the targeted delivery. Due to the presence of nanostructures in virus nanoparticles, these protect the drugs from the degradation in the gastrointestinal tract and in case of the delivery of gene medicine, they carry the nucleic acids to the target/susceptible host cells. Thus, artificial viruses are utilised for targeted delivery to specific organ in biomedical and biotechnological areas.

CONCLUSION

Thus, virus nanoparticles can be considered as viable option as drug/gene carrier in various healthcare sectors especially drug delivery and vaccine and can be explored further in future for the development of better drug delivery techniques.

Molecular regulation of myocyte fusion

Myocyte fusion is a pivotal process in the development and regeneration of skeletal muscle. Failure during fusion can lead to a range of developmental as well as pathological consequences. This review aims to comprehensively explore the intricate processes underlying myocyte fusion, from the molecular to tissue scale. We shed light on key players, such as the muscle-specific fusogens - Myomaker and Myomixer, in addition to some lesser studied molecules contributing to myocyte fusion. Conserved across vertebrates, Myomaker and Myomixer play a crucial role in driving the merger of plasma membranes of fusing myocytes, ensuring the formation of functional muscle syncytia. Our multiscale approach also delves into broader cell and tissue dynamics that orchestrate the timing and positioning of fusion events. In addition, we explore the relevance of muscle fusogens to human health and disease. Mutations in fusogen genes have been linked to congenital myopathies, providing unique insights into the molecular basis of muscle diseases. We conclude with a discussion on potential therapeutic avenues that may emerge from manipulating the myocyte fusion process to remediate skeletal muscle disorders.

Redirecting AAV vectors to extrahepatic tissues

Recombinant adeno-associated viral (AAV) vectors are the current benchmark for systemic delivery of gene therapies to multiple organs in vivo. Despite clinical successes, safe and effective gene delivery to extrahepatic tissues has proven challenging due to dose limiting toxicity arising from high liver uptake of AAV vectors. Deeper understanding of AAV structure, receptor biology, and pharmacology has enabled the design and engineering of liver-de-targeted capsids ushering in several new vector candidates. This next generation of AAVs offers significant promise for extrahepatic gene delivery to cardiovascular, musculoskeletal, and neurological tissues with improved safety profiles.

Lethal immunotoxicity in high-dose systemic AAV therapy

High-dose systemic gene therapy with adeno-associated virus (AAV) is in clinical trials to treat various inherited diseases. Despite remarkable success in spinal muscular atrophy and promising results in other diseases, fatality has been observed due to liver, kidney, heart, or lung failure. Innate and adaptive immune responses to the vector play a critical role in the toxicity. Host factors also contribute to patient death. This mini-review summarizes clinical findings and calls for concerted efforts from all stakeholders to better understand the mechanisms underlying lethality in AAV gene therapy and to develop effective strategies to prevent/treat high-dose systemic AAV-gene-therapy-induced immunotoxicity.

Duchenne Muscular Dystrophy Gene Therapy in 2023: Status, Perspective, and Beyond

Duchenne muscular dystrophy (DMD) was named more than 150 years ago. About four decades ago, the DMD gene was discovered, and the reading frame shift was determined as the genetic underpinning. These pivotal findings significantly changed the landscape of DMD therapy development. Restoration of dystrophin expression with gene therapy became a primary focus. Investment in gene therapy has led to the approval of exon skipping by regulatory agencies, multiple clinical trials of systemic microdystrophin therapy using adeno-associated virus vectors, and revolutionary genome editing therapy using the CRISPR technology. However, many important issues surfaced during the clinical translation of DMD gene therapy (such as low efficiency of exon skipping, immune toxicity-induced serious adverse events, and patient death). In this issue of Human Gene Therapy, several research articles highlighted some of the latest developments in DMD gene therapy. Importantly, a collection of articles from experts in the field reviewed the progress, major challenges, and future directions of DMD gene therapy. These insightful discussions have significant implications for gene therapy of other neuromuscular diseases.