In Vivo Base Editing of Scn5a Rescues Type 3 Long QT Syndrome in Mice

Gene therapy for cardiac arrhythmias

Cardiovascular diseases are the leading cause of death globally, with cardiac arrhythmias contributing substantially to this burden. Gene therapy, which directly targets the underlying disease pathobiology, offers an appealing treatment strategy for cardiac arrhythmias owing to its potential as a one-time, curative solution. Over the past two decades, substantial efforts have been made to develop new gene therapy approaches that overcome the limitations of conventional treatments. In this Review, we describe the rationale for gene therapy to treat cardiac arrhythmias; discuss advantages and disadvantages of gene silencing, gene replacement, gene suppression-and-replacement and gene editing technologies; summarize vector modalities and delivery approaches used in the field; present examples of gene therapy strategies used for atrial and ventricular arrhythmias; and highlight the current challenges and limitations in the gene therapy field.

SCN10A-short gene therapy to restore conduction and protect against malignant cardiac arrhythmias

BACKGROUND AND AIMS

Life-threatening arrhythmias are a well-established consequence of reduced cardiac sodium current (INa). Gene therapy approaches to increase INa have demonstrated potential benefits to prevent arrhythmias. However, the development of such therapies is hampered by the large size of sodium channels. In this study, SCN10A-short (S10s), a short transcript encoding the carboxy-terminal domain of the human neuronal sodium channel, was evaluated as a gene therapy target to increase INa and prevent arrhythmias.

METHODS

Adeno-associated viral vector overexpressing S10s was injected into wild type and Scn5a-haploinsufficient mice on which patch-clamp studies, optical mapping, electrocardiogram analyses, and ischaemia reperfusion were performed. In vitro and in silico studies were conducted to further explore the effect of S10s gene therapy in the context of human hearts.

RESULTS

Cardiac S10s overexpression increased cellular INa, maximal action potential upstroke velocity, and action potential amplitude in Scn5a-haploinsufficient cardiomyocytes. S10s gene therapy rescues conduction slowing in Scn5a-haploinsufficient mice and prevented ventricular tachycardia induced by ischaemia-reperfusion in wild type mice. S10s overexpression increased maximal action potential upstroke velocity in human inducible pluripotent stem cell-derived cardiomyocytes and prevented inducible arrhythmias in simulated human heart models.

CONCLUSIONS

S10s gene therapy may be effective to treat cardiac conduction abnormalities and associated arrhythmias.

CRISPR-dependent base editing as a therapeutic strategy for rare monogenic disorders

Rare monogenic disorders are caused by mutations in single genes and have an incidence rate of less than 0.5%. Due to their low prevalence, these diseases often attract limited research and commercial interest, leading to significant unmet medical needs. In a therapeutic landscape where treatments are targeted to manage symptoms, gene editing therapy emerges as a promising approach to craft curative and lasting treatments for these patients, often referred to as "one-and-done" therapeutics. CRISPR-dependent base editing enables the precise correction of genetic mutations by direct modification of DNA bases without creating potentially deleterious DNA double-strand breaks. Base editors combine a nickase version of Cas9 with cytosine or adenine deaminases to convert C·G to T·A and A·T to G·C, respectively. Together, cytosine (CBE) and adenine (ABE) base editors can theoretically correct ∼95% of pathogenic transition mutations cataloged in ClinVar. This mini-review explores the application of base editing as a therapeutic approach for rare monogenic disorders. It provides an overview of the state of gene therapies and a comprehensive compilation of preclinical studies using base editing to treat rare monogenic disorders. Key considerations for designing base editing-driven therapeutics are summarized in a user-friendly guide for researchers interested in applying this technology to a specific rare monogenic disorder. Finally, we discuss the prospects and challenges for bench-to-bedside translation of base editing therapies for rare monogenic disorders.

Living myocardial slices as a model for testing cardiac pro-reparative gene therapies

Available models currently adopted for preclinical studies in the cardiovascular field either fail to recapitulate human cardiac physiology or are extremely expensive and time-consuming. Translational research would greatly benefit from the development of novel models that reflect the native mature phenotype of the human heart while being cost and time effective. Living myocardial slices (LMSs) have emerged as a novel, powerful ex vivo tool for translational research. Although the number of studies adopting LMSs is rapidly increasing, this model remains largely under-characterized. In this study, we make use of LMSs and compare them to a murine model to deliver the cardioprotective factor zinc finger E box-binding homeobox 2 (ZEB2), a transcription factor known to exert cardioprotective effects after ischemic injury and promote the secretion of pro-angiogenetic factors thymosin beta-4 (TMSB4) and prothymosin alpha (PTMA). Our data show that viral-mediated delivery of these factors induced similar cardiomyocyte gene expression changes in LMS and mouse models. We also show that the delivery of these pro-angiogenic factors enhances an angiogenic response in both models, indicating that LMSs are a suitable alternative to mice for studying the effects of gene transfer in various cardiac cell types.

The Genetic Basis of Sudden Cardiac Death: From Diagnosis to Emerging Genetic Therapies

Sudden cardiac death (SCD) is an abrupt, tragic manifestation of a number of cardiovascular diseases, primarily ion channelopathies and heritable cardiomyopathies. Because these diseases are heritable, genetics play a key role in the diagnosis and management of SCD-predisposing diseases. Historically, genetics have been used to confirm a diagnosis and identify at-risk family members, but a deeper understanding of the genetic causes of SCD could pave the way for individualized therapy, early risk detection, and a transformative shift toward genetically informed therapies. This review focuses on the evolving genetic landscape of SCD-predisposing diseases, the current state of gene therapy and therapeutic development, and the promise of using predictive genetics to identify individuals at risk of SCD.

Gene therapy for cardiac diseases: methods, challenges, and future directions

Gene therapy is advancing at an unprecedented pace, and the recent success of clinical trials reinforces optimism and trust among the scientific community. Recently, the cardiac gene therapy pipeline, which had progressed more slowly than in other fields, has begun to advance, overcoming biological and technical challenges, particularly in treating genetic heart pathologies. The primary rationale behind the focus on monogenic cardiac diseases is the well-defined molecular mechanisms driving their phenotypes, directly linked to the pathogenicity of single genetic mutations. This aspect makes these conditions a remarkable example of 'genetically druggable' diseases. Unfortunately, current treatments for these life-threatening disorders are few and often poorly effective, underscoring the need to develop therapies to modulate or correct their molecular substrates. In this review we examine the latest advancements in cardiac gene therapy, discussing the pros and cons of different molecular approaches and delivery vectors, with a focus on their therapeutic application in cardiac inherited diseases. Additionally, we highlight the key factors that may enhance clinical translation, drawing insights from previous trials and the current prospects of cardiac gene therapy.

Targeting the IKs Channel PKA Phosphorylation Axis to Restore Its Function in High-Risk LQT1 Variants

BACKGROUND

The KCNQ1+KCNE1 (IKs) potassium channel plays a crucial role in cardiac adaptation to stress, in which β-adrenergic stimulation phosphorylates the IKs channel through the cyclic adenosine monophosphate (cAMP)/PKA (protein kinase A) pathway. Phosphorylation increases the channel current and accelerates repolarization to adapt to an increased heart rate. Variants in KCNQ1 can cause long-QT syndrome type 1 (LQT1), and those with defective cAMP effects predispose patients to the highest risk of cardiac arrest and sudden death. However, the molecular connection between IKs channel phosphorylation and channel function, as well as why high-risk LQT1 mutations lose cAMP sensitivity, remain unclear.

METHODS

Regular patch clamp and voltage clamp fluorometry techniques were utilized to record pore opening and voltage sensor movement of wild-type and mutant KCNQ1/IKs channels. The clinical phenotypic penetrance of each LQT1 mutation was analyzed as a metric for assessing their clinical risk. The patient-specific-induced pluripotent stem-cell model was used to test mechanistic findings in physiological conditions.

RESULTS

By systematically elucidating mechanisms of a series of LQT1 variants that lack cAMP sensitivity, we identified molecular determinants of IKs channel regulation by phosphorylation. These key residues are distributed across the N-terminus of KCNQ1 extending to the central pore region of IKs. We refer to this pattern as the IKs channel PKA phosphorylation axis. Next, by examining LQT1 variants from clinical databases containing 10 579 LQT1 carriers, we found that the distribution of the most high-penetrance LQT1 variants extends across the IKs channel PKA phosphorylation axis, demonstrating its clinical relevance. Furthermore, we found that a small molecule, ML277, which binds at the center of the phosphorylation axis, rescues the defective cAMP effects of multiple high-risk LQT1 variants. This finding was then tested in high-risk patient-specific induced pluripotent stem cell-derived cardiomyocytes, where ML277 remarkably alleviates the beating abnormalities.

CONCLUSIONS

Our findings not only elucidate the molecular mechanism of PKA-dependent IKs channel phosphorylation but also provide an effective antiarrhythmic strategy for patients with high-risk LQT1 variants.

Characterization of NiCas12b for In Vivo Genome Editing

The RNA-guided clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12b system represents the third family of CRISPR-Cas systems that are harnessed for genome editing. However, only a few nucleases have demonstrated activity in human cells, and their in vivo therapeutic potential remains uncertain. In this study, a green fluorescent protein (GFP)-activation assay is conducted to screen a panel of 15 Cas12b orthologs, and four of them exhibited editing activity in mammalian cells. Particularly noteworthy is the NiCas12b derived from Nitrospira sp., which recognizes a "TTN" protospacer adjacent motif (PAM) and facilitates efficient genome editing in various cell lines. Importantly, NiCas12b also exhibits a high degree of specificity, rendering it suitable for therapeutic applications. As proof of concept, the adeno-associated virus (AAV) is employed to introduce NiCas12b to target the cholesterol regulatory gene proprotein convertase subtilisin/ kexin type 9 (Pcsk9) in the mouse liver. After 4 weeks of injections, an impressive is observed over 16.0% insertion/deletion (indel) efficiency, resulting in a significant reduction in serum cholesterol levels. NiCas12b provides a novel option for both basic research and clinical applications.

Advances in base editing: A focus on base transversions

Single nucleotide variants (SNVs) constitute the most frequent variants that cause human genetic diseases. Base editors (BEs) comprise a new generation of CRISPR-based technologies, which are considered to have a promising future for curing genetic diseases caused by SNVs as they enable the direct and irreversible correction of base mutations. Two of the early types of BEs, cytosine base editor (CBE) and adenine base editor (ABE), mediate C-to-T, T-to-C, A-to-G, and G-to-A base transition mutations. Together, these represent half of all the known disease-associated SNVs. However, the remaining transversion (i.e., purine-pyrimidine) mutations cannot be restored by direct deamination and so these require the replacement of the entire base. Recently, a variety of base transversion editors were developed and so these add to the currently available BEs enabling the correction of all types of point mutation. However, compared to the base transition editors (including CBEs and ABEs), base transversion editors are still in the early development stage. In this review, we describe the basics and advances of the various base transversion editors, highlight their limitations, and discuss their potential for treating human diseases.