Cardiac gene therapy with adeno-associated virus-based vectors

Endovascular transplantation of mRNA-enhanced mesenchymal stromal cells results in superior therapeutic protein expression in swine heart

Heart failure has a poor prognosis and no curative treatment exists. Clinical trials are investigating gene- and cell-based therapies to improve cardiac function. The safe and efficient delivery of these therapies to solid organs is challenging. Herein, we demonstrate the feasibility of using an endovascular intramyocardial delivery approach to safely administer mRNA drug products and perform cell transplantation procedures in swine. Using a trans-vessel wall (TW) device, we delivered chemically modified mRNAs (modRNA) and mRNA-enhanced mesenchymal stromal cells expressing vascular endothelial growth factor A (VEGF-A) directly to the heart. We monitored and mapped the cellular distribution, protein expression, and safety tolerability of such an approach. The delivery of modRNA-enhanced cells via the TW device with different flow rates and cell concentrations marginally affect cell viability and protein expression in situ. Implanted cells were found within the myocardium for at least 3 days following administration, without the use of immunomodulation and minimal impact on tissue integrity. Finally, we could increase the protein expression of VEGF-A over 500-fold in the heart using a cell-mediated modRNA delivery system compared with modRNA delivered in saline solution. Ultimately, this method paves the way for future research to pioneer new treatments for cardiac disease.

Transduction and Genome Editing of the Heart with Adeno-Associated Viral Vectors Loaded onto Electrospun Polydioxanone Nonwoven Fabrics

In this study, we introduce electrospun polydioxanone (PDO) nonwoven fabrics as a platform for the delivery of adeno-associated virus (AAV) vectors for transduction and genome editing by adhering them to organ surfaces, including the heart. AAV vectors were loaded onto the PDO fabrics by soaking the fabrics in a solution containing AAV vectors. In vitro, the amount of AAV vectors loaded onto the fabrics could be adjusted by changing their concentration in the solution, and the number of cells expressing the green fluorescent protein (GFP) encoded by the AAV vectors increased in correlation with the increasing amount of loaded AAV vectors. In vivo, both transduction and genome editing resulted in the observation of GFP expression around AAV vector-loaded PDO fabrics attached to the surfaces of mouse hearts, indicating effective transduction and expression at the target site. These results demonstrate the great potential of electrospun PDO nonwoven fabrics carrying therapeutic AAV vectors for gene therapy.

Gene therapy during ex situ heart perfusion: a new frontier in cardiac regenerative medicine?

Ex situ organ preservation by machine perfusion can improve preservation of organs for transplantation. Furthermore, machine perfusion opens up the possibilities for selective immunomodulation, creation of tolerance to ischemia-reperfusion injury and/or correction of a pathogenic genetic defect. The application of gene modifying therapies to treat heart diseases caused by pathogenic mutations during ex situ heart perfusion seems promising, especially given the limitations related to delivery of vectors that were encountered during clinical trials using in vivo cardiac gene therapy. By isolating the heart in a metabolically and immunologically favorable environment and preventing off-target effects and dilution, it is possible to directly control factors that enhance the success rate of cardiac gene therapy. A literature search of PubMed and Embase databases was performed to identify all relevant studies regarding gene therapy during ex situ heart perfusion, aiming to highlight important lessons learned and discuss future clinical prospects of this promising approach.

Disease modeling of desmosome-related cardiomyopathy using induced pluripotent stem cell-derived cardiomyocytes

Cardiomyopathy is a pathological condition characterized by cardiac pump failure due to myocardial dysfunction and the major cause of advanced heart failure requiring heart transplantation. Although optimized medical therapies have been developed for heart failure during the last few decades, some patients with cardiomyopathy exhibit advanced heart failure and are refractory to medical therapies. Desmosome, which is a dynamic cell-to-cell junctional component, maintains the structural integrity of heart tissues. Genetic mutations in desmosomal genes cause arrhythmogenic cardiomyopathy (AC), a rare inheritable disease, and predispose patients to sudden cardiac death and heart failure. Recent advances in sequencing technologies have elucidated the genetic basis of cardiomyopathies and revealed that desmosome-related cardiomyopathy is concealed in broad cardiomyopathies. Among desmosomal genes, mutations in PKP2 (which encodes PKP2) are most frequently identified in patients with AC. PKP2 deficiency causes various pathological cardiac phenotypes. Human cardiomyocytes differentiated from patient-derived induced pluripotent stem cells (iPSCs) in combination with genome editing, which allows the precise arrangement of the targeted genome, are powerful experimental tools for studying disease. This review summarizes the current issues associated with practical medicine for advanced heart failure and the recent advances in disease modeling using iPSC-derived cardiomyocytes targeting desmosome-related cardiomyopathy caused by PKP2 deficiency.

AAV capsid engineering identified two novel variants with improved in vivo tropism for cardiomyocytes

AAV vectors are promising delivery tools for human gene therapy. However, broad tissue tropism and pre-existing immunity against natural serotypes limit their clinical use. We identified two AAV capsid variants, AAV2-THGTPAD and AAV2-NLPGSGD, by in vivo AAV2 peptide display library screening in a murine model of pressure overload-induced cardiac hypertrophy. Both variants showed significantly improved efficacy in in vivo cardiomyocyte transduction compared with the parental serotype AAV2 as indicated by a higher number of AAV vector episomes in the nucleus and significant improved transduction efficiency. Both variants also outcompeted the reference serotype AAV9 regarding cardiomyocyte tropism, reaching comparable cardiac transduction efficiencies accompanied with liver de-targeting and decreased transduction efficiency of non-cardiac cells. Capsid modification influenced immunogenicity as sera of mice treated with AAV2-THGTPAD and AAV2-NLPGSGD demonstrated a poor neutralization capacity for the parental serotype and the novel variants. In a therapeutic setting, using the long non-coding RNA H19 in low vector dose conditions, novel AAV variants mediated superior anti-hypertrophic effects and revealed a further improved target-to-noise ratio, i.e., cardiomyocyte tropism. In conclusion, AAV2-THGTPAD and AAV2-NLPGSGD are promising novel tools for cardiac-directed gene therapy outperforming AAV9 regarding the specificity and therapeutic efficiency of in vivo cardiomyocyte transduction.

Precise genomic editing of pathogenic mutations in RBM20 rescues dilated cardiomyopathy

Mutations in RNA binding motif protein 20 (RBM20) are a common cause of familial dilated cardiomyopathy (DCM). Many RBM20 mutations cluster within an arginine/serine-rich (RS-rich) domain, which mediates nuclear localization. These mutations induce RBM20 mis-localization to form aberrant ribonucleoprotein (RNP) granules in the cytoplasm of cardiomyocytes and abnormal alternative splicing of cardiac genes, contributing to DCM. We used adenine base editing (ABE) and prime editing (PE) to correct pathogenic p.R634Q and p.R636S mutations in the RS-rich domain in human isogenic induced pluripotent stem cell (iPSC)-derived cardiomyocytes. Using ABE to correct RBM20^R634Q human iPSCs, we achieved 92% efficiency of A-to-G editing, which normalized alternative splicing of cardiac genes, restored nuclear localization of RBM20, and eliminated RNP granule formation. In addition, we developed a PE strategy to correct the RBM20^R636S mutation in iPSCs and observed A-to-C editing at 40% efficiency. To evaluate the potential of ABE for DCM treatment, we also created Rbm20^R636Q mutant mice. Homozygous (R636Q/R636Q) mice developed severe cardiac dysfunction, heart failure, and premature death. Systemic delivery of ABE components containing ABEmax-VRQR-SpCas9 and single-guide RNA by adeno-associated virus serotype 9 in these mice restored cardiac function as assessed by echocardiography and extended life span. As seen by RNA sequencing analysis, ABE correction rescued the cardiac transcriptional profile of treated R636Q/R636Q mice, compared to the abnormal gene expression seen in untreated mice. These findings demonstrate the potential of precise correction of genetic mutations as a promising therapeutic approach for DCM.

Long-term amelioration of an early-onset familial atrial fibrillation model with AAV-mediated in vivo gene therapy

Atrial fibrillation (AF) is a common cardiac disease with high prevalence in the general population. Despite a mild manifestation at the onset stage, it causes serious consequences, including sudden death, when the disease progresses to the late stage. Most available treatments of AF focus on symptom management or alleviation, due to a lack of fundamental knowledge and the fact that considerable variations of AF exist. With the popularisation of the next-generation sequencing technology, several causal genetic factors, including MYL4, have been discovered to contribute to AF, giving hope to developing its gene therapies. In this study, we attempted to treat a previously established rat AF model, which carried Myl4E11K/E11K loss of function mutation, via overexpression of exogenous wild-type Myl4 by AAV9 vectors. Our results showed that delivery of Myl4 expressing AAV9 to postnatal rat models rescued the symptoms of AF, indicating the therapeutic potential that early gene therapy intervention can achieve long-term effects in treating cardiac arrhythmias caused by gene mutations.

High-throughput optical action potential recordings in hiPSC-derived cardiomyocytes with a genetically encoded voltage indicator in the AAVS1 locus

Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) represent an excellent in vitro model in cardiovascular research. Changes in their action potential (AP) dynamics convey information that is essential for disease modeling, drug screening and toxicity evaluation. High-throughput optical AP recordings utilizing intramolecular Förster resonance energy transfer (FRET) of the voltage-sensitive fluorescent protein (VSFP) have emerged as a substitute or complement to the resource-intensive patch clamp technique. Here, we functionally validated our recently generated voltage indicator hiPSC lines stably expressing CAG-promoter-driven VSFP in the AAVS1 safe harbor locus. By combining subtype-specific cardiomyocyte differentiation protocols, we established optical AP recordings in ventricular, atrial, and nodal CMs in 2D monolayers using fluorescence microscopy. Moreover, we achieved high-throughput optical AP measurements in single hiPSC-derived CMs in a 3D context. Overall, this system greatly expands the spectrum of possibilities for high-throughput, non-invasive and long-term AP analyses in cardiovascular research and drug discovery.

Cell-Based and Selected Cell-Free Therapies for Myocardial Infarction: How Do They Compare to the Current Treatment Options?

Because of cardiomyocyte death or dysfunction frequently caused by myocardial infarction (MI), heart failure is a leading cause of morbidity and mortality in modern society. Paradoxically, only limited and non-curative therapies for heart failure or MI are currently available. As a result, over the past two decades research has focused on developing cell-based approaches promoting the regeneration of infarcted tissue. Cell-based therapies for myocardial regeneration include powerful candidates, such as multipotent stem cells (mesenchymal stem cells (MSCs), bone-marrow-derived stem cells, endothelial progenitor cells, and hematopoietic stem cells) and induced pluripotent stem cells (iPSCs). These possess unique properties, such as potency to differentiate into desired cell types, proliferation capacity, and patient specificity. Preclinical and clinical studies have demonstrated modest improvement in the myocardial regeneration and reduced infarcted areas upon transplantation of pluripotent or multipotent stem cells. Another cell population that need to be considered as a potential source for cardiac regeneration are telocytes found in different organs, including the heart. Their therapeutic effect has been studied in various heart pathologies, such as MI, arrhythmias, or atrial amyloidosis. The most recent cell-free therapeutic tool relies on the cardioprotective effect of complex cargo carried by small membrane-bound vesicles—exosomes—released from stem cells via exocytosis. The MSC/iPSC-derived exosomes could be considered a novel exosome-based therapy for cardiovascular diseases thanks to their unique content. There are also other cell-free approaches, e.g., gene therapy, or acellular cardiac patches. Therefore, our review provides the most recent insights into the novel strategies for myocardial repair based on the regenerative potential of different cell types and cell-free approaches.

Adeno-associated virus 9 vector-mediated cardiac-selective expression of human secretory leukocyte protease inhibitor attenuates myocardial ischemia/reperfusion injury

Protease enzymes contribute to the initiation of cardiac remodeling and heart failure after myocardial ischemic/reperfusion (I/R) injury. Protease inhibitors attenuate protease activity and limit left ventricular dysfunction and remodeling. Previous studies showed the cardioprotective effect of secretory leukocyte protease inhibitor (SLPI) against I/R injury. However, overexpression of SLPI gene in cardiovascular diseases has only been investigated in an in vitro experiment. Here, cardiac-selective expression of the human secretory leukocyte protease inhibitor (hSLPI) gene and its effect on I/R injury were investigated. Adeno-associated virus (AAV) serotype 9 carrying hSLPI under the control of cardiac-selective expression promoter (cardiac troponin, cTn) was intravenously administered to Sprague–Dawley rats for 4 weeks prior to coronary artery ligation. The results showed that myocardial-selective expression of hSLPI significantly reduced infarct size, cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and myoglobin levels that all served to improve cardiac function. Moreover, overexpression of hSLPI showed a reduction in inflammatory cytokines, oxidatively modified protein carbonyl (PC) content, ischemia-modified albumin (IMA), and necrosis and cardiac tissue degeneration. In conclusion, this is the first study to demonstrate cardiac-selective gene delivery of hSLPI providing cardioprotection against myocardial I/R injury in an in vivo model.

Recombinant Adeno-Associated Viral Vector-Mediated Gene Transfer of hTBX18 Generates Pacemaker Cells from Ventricular Cardiomyocytes

Sinoatrial node dysfunction can manifest as bradycardia, leading to symptoms of syncope and sudden cardiac death. Electronic pacemakers are the current standard of care but are limited due to a lack of biological chronotropic control, cost of revision surgeries, and risk of lead- and device-related complications. We therefore aimed to develop a biological alternative to electronic devices by using a clinically relevant gene therapy vector to demonstrate conversion of cardiomyocytes into sinoatrial node-like cells in an in vitro context. Neonatal rat ventricular myocytes were transduced with recombinant adeno-associated virus vector 6 encoding either hTBX18 or green fluorescent protein and maintained for 3 weeks. At the endpoint, qPCR, Western blot analysis and immunocytochemistry were used to assess for reprogramming into pacemaker cells. Cell morphology and Arclight action potentials were imaged via confocal microscopy. Compared to GFP, hTBX18-transduced cells showed that hTBX18, HCN4 and Cx45 were upregulated. Cx43 was significantly downregulated, while sarcomeric α-actinin remained unchanged. Cardiomyocytes transduced with hTBX18 acquired the tapering morphology of native pacemaker cells, as compared to the block-like, striated appearance of ventricular cardiomyocytes. Analysis of the action potentials showed phase 4 depolarization and a significant decrease in the APD50 of the hTBX18-transduced cells. We have demonstrated that rAAV-hTBX18 gene transfer to ventricular myocytes results in morphological, molecular, physiological, and functional changes, recapitulating the pacemaker phenotype in an in vitro setting. The generation of these induced pacemaker-like cells using a clinically relevant vector opens new prospects for biological pacemaker development.

Targeted Delivery for Cardiac Regeneration: Comparison of Intra-coronary Infusion and Intra-myocardial Injection in Porcine Hearts

BACKGROUND

The optimal delivery route to enhance effectiveness of regenerative therapeutics to the human heart is poorly understood. Direct intra-myocardial (IM) injection is the gold standard, however, it is relatively invasive. We thus compared targeted IM against less invasive, catheter-based intra-coronary (IC) delivery to porcine myocardium for the acute retention of nanoparticles using cardiac magnetic resonance (CMR) imaging and viral vector transduction using qPCR.

METHODS

Ferumoxytol iron oxide (IO) nanoparticles (5 ml) were administered to Yorkshire swine (n = 13) by: (1) IM via thoracotomy, (2) catheter-based IC balloon-occlusion (BO) with infusion into the distal left anterior descending (LAD) coronary artery, (3) IC perforated side-wall (SW) infusion into the LAD, or (4) non-selective IC via left main (LM) coronary artery infusion. Hearts were harvested and imaged using at 3T whole-body MRI scanner. In separate Yorkshire swine (n = 13), an adeno-associated virus (AAV) vector was similarly delivered, tissue harvested 4-6 weeks later, and viral DNA quantified from predefined areas at risk (apical LV/RV) vs. not at risk in a potential mid-LAD infarct model. Results were analyzed using pairwise Student's t-test.

RESULTS

IM delivery yielded the highest IO retention (16.0 ± 4.6% of left ventricular volume). Of the IC approaches, BO showed the highest IO retention (8.7 ± 2.2% vs. SW = 5.5 ± 4.9% and LM = 0%) and yielded consistent uptake in the porcine distal LAD territory, including the apical septum, LV, and RV. IM delivery was limited to the apex and anterior wall, without septal retention. For the AAV delivery, the BO was most efficient in the at risk territory (Risk: BO = 6.0 × 10-9, IM = 1.4 × 10-9, LM = 3.2 × 10-10 viral copies per μg genomic DNA) while all delivery routes were comparable in the non-risk territory (BO = 1.7 × 10-9, IM = 8.9 × 10-10, LM = 1.2 × 10-9).

CONCLUSIONS

Direct IM injection has the highest local retention, while IC delivery with balloon occlusion and distal infusion is the most effective IC delivery technique to target therapeutics to a heart territory most in risk from an infarct.

Cell-Based Determination of Neutralizing Antibodies Against Adeno-Associated Virus in Cardiac Gene Therapy

The field of cardiac gene therapy has seen the rising use of adeno-associated viral (AAV) vectors as a promising therapeutic option for cardiac diseases and heart failure. To achieve intended results of AAV delivery, a majority of clinical studies screen patients for existing neutralizing antibodies that could inhibit the effects of the administered AAV and confound treatment efficacy. The cell-based neutralizing antibody assay offers a method of quantifying and identifying a patient's existing neutralizing antibodies against specific serotypes. Combined with the luciferase assay, the neutralizing antibody assay tests the ability of patient antibodies in the blood to prevent gene transduction of AAV-encoded luciferase gene at ranging serial dilutions. This chapter provides a protocol and experimental techniques to determine the presence of neutralizing antibodies against AAV in the blood.

Updates on Cardiac Gene Therapy Research and Methods: Overview of Cardiac Gene Therapy

Gene therapy has made a significant progress in clinical translation over the past few years with several gene therapy products currently approved or anticipating approval for clinical use. Cardiac gene therapy lags behind that of other areas of diseases, with no application of cardiac gene therapy yet approved for clinical use. However, several clinical trials for gene therapy targeting the heart are underway, and innovative research studies are being conducted to close the gap. The second edition of Cardiac Gene Therapy in Methods in Molecular Biology provides protocols for cutting-edge methodologies used in these studies. In this chapter, we discuss recent updates on cardiac gene therapy studies and provide an overview of the chapters in the book.

Combination Therapy with STAT3 Inhibitor Enhances SERCA2a-Induced BMPR2 Expression and Inhibits Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a devastating lung disease characterized by the progressive obstruction of the distal pulmonary arteries (PA). Structural and functional alteration of pulmonary artery smooth muscle cells (PASMC) and endothelial cells (PAEC) contributes to PA wall remodeling and vascular resistance, which may lead to maladaptive right ventricular (RV) failure and, ultimately, death. Here, we found that decreased expression of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) in the lung samples of PAH patients was associated with the down-regulation of bone morphogenetic protein receptor type 2 (BMPR2) and the activation of signal transducer and activator of transcription 3 (STAT3). Our results showed that the antiproliferative properties of SERCA2a are mediated through the STAT3/BMPR2 pathway. At the molecular level, transcriptome analysis of PASMCs co-overexpressing SERCA2a and BMPR2 identified STAT3 amongst the most highly regulated transcription factors. Using a specific siRNA and a potent pharmacological STAT3 inhibitor (STAT3i, HJC0152), we found that SERCA2a potentiated BMPR2 expression by repressing STAT3 activity in PASMCs and PAECs. In vivo, we used a validated and efficient model of severe PAH induced by unilateral left pneumonectomy combined with monocrotaline (PNT/MCT) to further evaluate the therapeutic potential of single and combination therapies using adeno-associated virus (AAV) technology and a STAT3i. We found that intratracheal delivery of AAV1 encoding SERCA2 or BMPR2 alone or STAT3i was sufficient to reduce the mean PA pressure and vascular remodeling while improving RV systolic pressures, RV ejection fraction, and cardiac remodeling. Interestingly, we found that combined therapy of AAV1.hSERCA2a with AAV1.hBMPR2 or STAT3i enhanced the beneficial effects of SERCA2a. Finally, we used cardiac magnetic resonance imaging to measure RV function and found that therapies using AAV1.hSERCA2a alone or combined with STAT3i significantly inhibited RV structural and functional changes in PNT/MCT-induced PAH. In conclusion, our study demonstrated that combination therapies using SERCA2a gene transfer with a STAT3 inhibitor could represent a new promising therapeutic alternative to inhibit PAH and to restore BMPR2 expression by limiting STAT3 activity.

Detailed Protocol for the Novel and Scalable Viral Vector Upstream Process for AAV Gene Therapy Manufacturing

Recombinant adeno-associated viral (rAAV) vector-based gene therapy has been adapted for use in more than 100 clinical trials. This is mainly because of its excellent safety profile, ability to target a wide range of tissues, stable transgene expression, and significant clinical benefit. However, the major challenge is to produce a high-titer, high-potency vector to achieve a better therapeutic effect. Even though the three plasmid-based transient transfection method is currently being used for AAV production in many clinical trials, there are complications associated with scalability and it is not cost-effective. Other methods require either large-scale production of two herpes simplex viruses, rHSV-RepCap and rHSV-GOI (gene of interest), with high titers, or a stable cell line with high titer wild-type adenovirus infection. Both of these options make the process even more complex. To address this issue, we have developed a stable cell line-based production with the use of only one rHSV-RepCap virus. Using this new methodology in small-scale production, we achieved ∼1-6 E + 04 vg/cell of AAV9 in the top producer clones. Large-scale production in 10-CS (10-Cell Stack) of one of the top producing clones resulted in ∼1-2 E + 13 vg/10-CS with 50% of full capsid ratio after purification. This method could potentially be adapted to suspension cells. The major advantage of this novel methodology is that by using the rHSV-RepCap virus, high titer AAV can be produced with any GOI containing a stable adherent or suspension producer cell line. The use of this AAV production platform could be beneficial for the treatment of many diseases.

Transduction of rat and human adipose-tissue derived mesenchymal stromal cells by adeno-associated viral vector serotype DJ

Ex vivo, gene therapy is a powerful approach holding great promises for the treatment of both genetic and acquired diseases. Adeno-associated virus (AAV) vectors are a safe and efficient delivery system for modification of mesenchymal stem cells (MSC) that could maximize their therapeutic benefits. Assessment of MSC viability and functional activity after infection with new AAV serotypes is necessary, due to AAV tropism to specific cell types. We infected human and rat adipose-tissue MSC with hybrid AAV-DJ serotype vectors carrying GFP and SCF genes. GFP expression from AAV-DJ was about 1.5-fold superior to that observed with AAV-2 and lasted for at least 21 days as was evaluated by flow cytometry and fluorescence microscopy. AAV-DJ proves to be suitable for the infection of rat and human MSC with a similar efficiency. Infected MSC were still viable but showed a 25-30% growth-rate slowdown. Moreover, we found an increase of SERPINB2 mRNA expression in human MSC while expression of other oxidative stress markers and extracellular matrix proteins was not affected. These results suggest that there is a differential cellular response in MSC infected with AAV viral vectors, which should be taken into account as it can affect the expected outcome for the therapeutic application.

Summary: Adeno-associated viral vectors are widely used for gene delivery but their impact on the different cell types varies greatly and is not well understood. We describe effects of two most popular AAV serotypes on mesenchymal stromal cells of rat and human origin.

Targeted delivery of therapeutic agents to the heart

For therapeutic materials to be successfully delivered to the heart, several barriers need to be overcome, including the anatomical challenges of access, the mechanical force of the blood flow, the endothelial barrier, the cellular barrier and the immune response. Various vectors and delivery methods have been proposed to improve the cardiac-specific uptake of materials to modify gene expression. Viral and non-viral vectors are widely used to deliver genetic materials, but each has its respective advantages and shortcomings. Adeno-associated viruses have emerged as one of the best tools for heart-targeted gene delivery. In addition, extracellular vesicles, including exosomes, which are secreted by most cell types, have gained popularity for drug delivery to several organs, including the heart. Accumulating evidence suggests that extracellular vesicles can carry and transfer functional proteins and genetic materials into target cells and might be an attractive option for heart-targeted delivery. Extracellular vesicles or artificial carriers of non-viral and viral vectors can be bioengineered with immune-evasive and cardiotropic properties. In this Review, we discuss the latest strategies for targeting and delivering therapeutic materials to the heart and how the knowledge of different vectors and delivery methods could successfully translate cardiac gene therapy into the clinical setting.

Optimizing delivery for efficient cardiac reprogramming

Following heart injury, cardiomyocytes, are lost and are not regenerated. In their place, fibroblasts invade the dead tissue where they generate a scar, which reduces cardiac function. We and others have demonstrated that combinations of specific miRNAs (miR combo) or transcription factors (GMT), delivered by individual lenti-/retro-viruses in vivo, can convert fibroblasts into cardiomyocytes and improve cardiac function. However, the effects are relatively modest due to the low efficiency of delivery of miR combo or GMT. We hypothesized that efficiency would be improved by optimizing delivery. In the first instance, we developed a multicistronic system to express all four miRNAs of miR combo from a single construct. The order of each miRNA in the multicistronic construct gave rise to different levels of miRNA expression. A combination that resulted in equivalent expression levels of each of the four miRNAs of miR combo showed the highest reprogramming efficiency. Further efficiency can be achieved by directly targeting fibroblasts. Screening of several AAV serotypes indicated that AAV1 displayed tropism towards cardiac fibroblasts. Combining multicistronic expression with AAV1 delivery robustly reprogrammed cardiac fibroblasts into cardiomyocytes in vivo.

Large Animal Models of Cell-Free Cardiac Regeneration

The adult mammalian heart lacks the ability to sufficiently regenerate itself, leading to the progressive deterioration of function and heart failure after ischemic injuries such as myocardial infarction. Thus far, cell-based therapies have delivered unsatisfactory results, prompting the search for cell-free alternatives that can induce the heart to repair itself through cardiomyocyte proliferation, angiogenesis, and advantageous remodeling. Large animal models are an invaluable step toward translating basic research into clinical applications. In this review, we give an overview of the state-of-the-art in cell-free cardiac regeneration therapies that have been tested in large animal models, mainly pigs. Cell-free cardiac regeneration therapies involve stem cell secretome- and extracellular vesicles (including exosomes)-induced cardiac repair, RNA-based therapies, mainly regarding microRNAs, but also modified mRNA (modRNA) as well as other molecules including growth factors and extracellular matrix components. Various methods for the delivery of regenerative substances are used, including adenoviral vectors (AAVs), microencapsulation, and microparticles. Physical stimulation methods and direct cardiac reprogramming approaches are also discussed.

Translating genomic insights into cardiovascular medicine: Opportunities and challenges of CRISPR-Cas9

The growing appreciation of human genetics and genomics in cardiovascular disease (CVD) accompanied by the technological breakthroughs in genome editing, particularly the CRISPR-Cas9 technologies, has presented an unprecedented opportunity to explore the application of genome editing in cardiovascular medicine. The ever-growing genome editing toolbox includes an assortment of CRISPR-Cas systems with increasing efficiency, precision, flexibility, and targeting capacity. Over the past decade, the advent of large-scale genotyping technologies and genome-wide association studies (GWAS) has provided numerous genotype-phenotype associations for diseases with complex traits. Notably, a growing number of loss-of-function mutations have been associated with favorable CVD risk-factor profiles that may confer protection. Combining the newly gained insights of human genetics with recent breakthrough technologies, such as the CRISPR-Cas9 technologies, holds great promise in elucidating novel disease mechanisms and transforming genes into medicines. Nonetheless, translating genetic insights into novel therapeuties remains challenging. Applications of "in body" genome editing for CVD treatment and engineering cardioprotection remain mostly theoretical. Here we highlight the recent advances of the CRISPR-based genome editing toolbox and discuss the potential and challenges of CRISPR-based technologies for translating GWAS findings into genomic medicines.

Two-variable nullcline analysis of ionic general equilibrium predicts calcium homeostasis in ventricular myocytes

Ventricular contraction is roughly proportional to the amount of calcium released from the Sarcoplasmic Reticulum (SR) during systole. While it is rather straightforward to measure calcium levels and contractibility under different physiological conditions, the complexity of calcium handling during systole and diastole has made the prediction of its release at steady state impossible. Here we approach the problem analyzing the evolution of intracellular and extracellular calcium fluxes during a single beat which is away from homeostatic balance. Using an in-silico subcellular model of rabbit ventricular myocyte, we show that the high dimensional nonlinear problem of finding the steady state can be reduced to a two-variable general equilibrium condition where pre-systolic calcium level in the cytosol and in the SR must fulfill simultaneously two different equalities. This renders calcium homeostasis as a problem that can be studied in terms of its equilibrium structure, leading to precise predictions of steady state from single-beat measurements. We show how changes in ion channels modify the general equilibrium, as shocks would do in general equilibrium macroeconomic models. This allows us to predict when an enhanced entrance of calcium in the cell reduces its contractibility and explain why SERCA gene therapy, a change in calcium handling to treat heart failure, might fail to improve contraction even when it successfully increases SERCA expression.

Cardiomyocytes, upon voltage excitation, release calcium, which leads to cell contraction. However, under some pathological conditions, calcium handling is impaired. Recently, SERCA gene therapy, whose aim is to improve Ca²⁺ sequestration by the Sarcoplasmic Reticulum (SR), has failed to improve the prognosis of patients with Heart Failure. This, together with recent counterintuitive results in calcium handling, has highlighted the need for a framework to understand calcium homeostasis across species and pathologies. We show here that the proper framework is a general equilibrium approach of two independent variables. The development of this framework allows us to find a possible mechanism for the failure of SERCA gene therapy even when it manages to increase Ca SERCA expression.

Combining Nanomaterials and Developmental Pathways to Design New Treatments for Cardiac Regeneration: The Pulsing Heart of Advanced Therapies

The research for heart therapies is challenged by the limited intrinsic regenerative capacity of the adult heart. Moreover, it has been hampered by the poor results obtained by tissue engineering and regenerative medicine attempts at generating functional beating constructs able to integrate with the host tissue. For this reason, organ transplantation remains the elective treatment for end-stage heart failure, while novel strategies aiming to promote cardiac regeneration or repair lag behind. The recent discovery that adult cardiomyocytes can be ectopically induced to enter the cell cycle and proliferate by a combination of microRNAs and cardioprotective drugs, like anti-oxidant, anti-inflammatory, anti-coagulants and anti-platelets agents, fueled the quest for new strategies suited to foster cardiac repair. While proposing a revolutionary approach for heart regeneration, these studies raised serious issues regarding the efficient controlled delivery of the therapeutic cargo, as well as its timely removal or metabolic inactivation from the site of action. Especially, there is need for innovative treatment because of evidence of severe side effects caused by pleiotropic drugs. Biocompatible nanoparticles possess unique physico-chemical properties that have been extensively exploited for overcoming the limitations of standard medical therapies. Researchers have put great efforts into the optimization of the nanoparticles synthesis and functionalization, to control their interactions with the biological milieu and use as a viable alternative to traditional approaches. Nanoparticles can be used for diagnosis and deliver therapies in a personalized and targeted fashion. Regarding the treatment of cardiovascular diseases, nanoparticles-based strategies have provided very promising outcomes, in preclinical studies, during the last years. Efficient encapsulation of a large variety of cargos, specific release at the desired site and improvement of cardiac function are some of the main achievements reached so far by nanoparticle-based treatments in animal models. This work offers an overview on the recent nanomedical applications for cardiac regeneration and highlights how the versatility of nanomaterials can be combined with the newest molecular biology discoveries to advance cardiac regeneration therapies.

AAV Vector Immunogenicity in Humans: A Long Journey to Successful Gene Transfer

Gene therapy with adeno-associated virus (AAV) vectors has demonstrated safety and long-term efficacy in a number of trials across target organs, including eye, liver, skeletal muscle, and the central nervous system. Since the initial evidence that AAV vectors can elicit capsid T cell responses in humans, which can affect the duration of transgene expression, much progress has been made in understanding and modulating AAV vector immunogenicity. It is now well established that exposure to wild-type AAV results in priming of the immune system against the virus, with development of both humoral and T cell immunity. Aside from the neutralizing effect of antibodies, the impact of pre-existing immunity to AAV on gene transfer is still poorly understood. Herein, we review data emerging from clinical trials across a broad range of gene therapy applications. Common features of immune responses to AAV can be found, suggesting, for example, that vector immunogenicity is dose-dependent, and that innate immunity plays an important role in the outcome of gene transfer. A range of host-specific factors are also likely to be important, and a comprehensive understanding of the mechanisms driving AAV vector immunogenicity in humans will be key to unlocking the full potential of in vivo gene therapy.

Optogenetics: Background, Methodological Advances and Potential Applications for Cardiovascular Research and Medicine

Optogenetics is an elegant approach of precisely controlling and monitoring the biological functions of a cell, group of cells, tissues, or organs with high temporal and spatial resolution by using optical system and genetic engineering technologies. The field evolved with the need to precisely control neurons and decipher neural circuity and has made great accomplishments in neuroscience. It also evolved in cardiovascular research almost a decade ago and has made considerable progress in both in vitro and in vivo animal studies. Thus, this review is written with an objective to provide information on the evolution, background, methodical advances, and potential scope of the field for cardiovascular research and medicine. We begin with a review of literatures on optogenetic proteins related to their origin, structure, types, mechanism of action, methods to improve their performance, and the delivery vehicles and methods to express such proteins on target cells and tissues for cardiovascular research. Next, we reviewed historical and recent literatures to demonstrate the scope of optogenetics for cardiovascular research and regenerative medicine and examined that cardiac optogenetics is vital in mimicking heart diseases, understanding the mechanisms of disease progression and also in introducing novel therapies to treat cardiac abnormalities, such as arrhythmias. We also reviewed optogenetics as promising tools in providing high-throughput data for cardiotoxicity screening in drug development and also in deciphering dynamic roles of signaling moieties in cell signaling. Finally, we put forth considerations on the need of scaling up of the optogenetic system, clinically relevant in vivo and in silico models, light attenuation issues, and concerns over the level, immune reactions, toxicity, and ectopic expression with opsin expression. Detailed investigations on such considerations would accelerate the translation of cardiac optogenetics from present in vitro and in vivo animal studies to clinical therapies.

Structural and cellular biology of adeno-associated virus attachment and entry

Adeno-associated virus (AAV) is a nonenveloped, ssDNA virus in the parvovirus family, which has become one of the leading candidate vectors for human gene therapy. AAV has been studied extensively to identify host cellular factors involved in infection, as well as to identify capsid variants that confer clinically favorable transduction profiles ex vivo and in vivo. Recent advances in technology have allowed for direct genetic approaches to be used to more comprehensively characterize host factors required for AAV infection and allowed for identification of a critical multi-serotype receptor, adeno-associated virus receptor (AAVR). In this chapter, we will discuss the interactions of AAV with its glycan and proteinaceous receptors and describe the host and viral components involved in AAV entry, which requires cellular attachment, endocytosis, trafficking to the trans-Golgi network and nuclear import. AAV serves as a paradigm for entry of nonenveloped viruses. Furthermore, we will discuss the potential of utilizing our increased understanding of virus-host interactions during AAV entry to develop better AAV-based therapeutics, with a focus on host factors and capsid interactions involved in in vivo tropism.

Analysis of recombinant adeno-associated viral vector shedding in sheep following intracoronary delivery

Differences between mouse and human hearts pose a significant limitation to the value of small animal models when predicting vector behavior following recombinant adeno-associated viral (rAAV) vector-mediated cardiac gene therapy. Hence, sheep have been adopted as a preclinical animal, as they better model the anatomy and cardiac physiological processes of humans. There is, however, no comprehensive data on the shedding profile of rAAV in sheep following intracoronary delivery, so as to understand biosafety risks in future preclinical and clinical applications. In this study, sheep received intracoronary delivery of rAAV serotypes 2/6 (2 × 10¹² vg), 2/8, and 2/9 (1 × 10¹³ vg) at doses previously administered in preclinical and clinical trials. This was followed by assessment over 96 h to examine vector shedding in urine, feces, nasal mucus, and saliva samples. Vector genomes were detected via real-time quantitative PCR in urine and feces up to 48 and 72 h post vector delivery, respectively. Of these results, functional vector particles were only detected via a highly sensitive infectious replication assay in feces samples up to 48 h following vector delivery. We conclude that rAAV-mediated gene transfer into sheep hearts results in low-grade shedding of non-functional vector particles for all excreta samples, except in the case of feces, where functional vector particles are present up to 48 h following vector delivery. These results may be used to inform containment and decontamination guidelines for large animal dealings, and to understand the biosafety risks associated with future preclinical and clinical uses of rAAV.

EHRA White Paper: knowledge gaps in arrhythmia management—status 2019

Clinicians accept that there are many unknowns when we make diagnostic and therapeutic decisions. Acceptance of uncertainty is essential for the pursuit of the profession: bedside decisions must often be made on the basis of incomplete evidence. Over the years, physicians sometimes even do not realize anymore which the fundamental gaps in our knowledge are. As clinical scientists, however, we have to halt and consider what we do not know yet, and how we can move forward addressing those unknowns. The European Heart Rhythm Association (EHRA) believes that scanning the field of arrhythmia / cardiac electrophysiology to identify knowledge gaps which are not yet the subject of organized research, should be undertaken on a regular basis. Such a review (White Paper) should concentrate on research which is feasible, realistic, and clinically relevant, and should not deal with futuristic aspirations. It fits with the EHRA mission that these White Papers should be shared on a global basis in order to foster collaborative and needed research which will ultimately lead to better care for our patients. The present EHRA White Paper summarizes knowledge gaps in the management of atrial fibrillation, ventricular tachycardia/sudden death and heart failure.

AAV Vectors for Efficient Gene Delivery to Rodent Hearts

Currently, gene therapy is one of the most promising fields in biomedicine, with great therapeutic potential for an array of inherited and acquired diseases. Adeno-associated viral (AAV) vectors have emerged as promising tools to deliver selectively a therapeutic payload to target organs, including the heart. In this chapter, we describe the production and quality control of recombinant AAV (rAAV) vectors of the serotype 9, the most cardiotropic AAV serotype when delivered systemically in rodents. We also describe the systemic administration of rAAV vectors and the local delivery of rAAV vectors by direct intramyocardial injection. Taken together, the methods described in this chapter will allow the reader to deliver efficiently therapeutic genes to the rodent heart, both globally and regionally.

Gene Therapy Approaches to Biological Pacemakers

Bradycardia arising from pacemaker dysfunction can be debilitating and life threatening. Electronic pacemakers serve as effective treatment options for pacemaker dysfunction. They however present their own limitations and complications. This has motivated research into discovering more effective and innovative ways to treat pacemaker dysfunction. Gene therapy is being explored for its potential to treat various cardiac conditions including cardiac arrhythmias. Gene transfer vectors with increasing transduction efficiency and biosafety have been developed and trialed for cardiovascular disease treatment. With an improved understanding of the molecular mechanisms driving pacemaker development, several gene therapy targets have been identified to generate the phenotypic changes required to correct pacemaker dysfunction. This review will discuss the gene therapy vectors in use today along with methods for their delivery. Furthermore, it will evaluate several gene therapy strategies attempting to restore biological pacing, having the potential to emerge as viable therapies for pacemaker dysfunction.

Efficient Gene Transfer to the Central Nervous System by Single-Stranded Anc80L65

Adeno-associated viral vectors (AAVs) have demonstrated potential in applications for neurologic disorders, and the discovery that some AAVs can cross the blood-brain barrier (BBB) after intravenous injection has further expanded these opportunities for non-invasive brain delivery. Anc80L65, a novel AAV capsid designed from in silico reconstruction of the viral evolutionary lineage, has previously demonstrated robust transduction capabilities after local delivery in various tissues such as liver, retina, or cochlea, compared with conventional AAVs. Here, we compared the transduction efficacy of Anc80L65 with conventional AAV9 in the CNS after intravenous, intracerebroventricular (i.c.v.), or intraparenchymal injections. Anc80L65 was more potent at targeting the brain and spinal cord after intravenous injection than AAV9, and mostly transduced astrocytes and a wide range of neuronal subpopulations. Although the efficacy of Anc80L65 and AAV9 is similar after direct intraparenchymal injection in the striatum, Anc80L65's diffusion throughout the CNS was more extensive than AAV9 after i.c.v. infusion, leading to widespread EGFP expression in the cerebellum. These findings demonstrate that Anc80L65 is a highly efficient gene transfer vector for the murine CNS. Systemic injection of Anc80L65 leads to notable expression in the CNS that does not rely on a self-complementary genome. These data warrant further testing in larger animal models.

Gene therapy strategies in the treatment of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited myocardial disease with an estimated prevalence of 1:200 caused by mutations in sarcomeric proteins. It is associated with hypertrophy of the left ventricle, increased interstitial fibrosis, and diastolic dysfunction for heterozygous mutation carriers. Carriers of double heterozygous, compound heterozygous, and homozygous mutations often display more severe forms of cardiomyopathies, ultimately leading to premature death. So far, there is no curative treatment against HCM, as current therapies are focused on symptoms relief by pharmacological intervention and not on the cause of HCM. In the last decade, several strategies have been developed to remove genetic defects, including genome editing, exon skipping, allele-specific silencing, spliceosome-mediated RNA trans-splicing, and gene replacement. Most of these technologies have already been tested for efficacy and efficiency in animal- or human-induced pluripotent stem cell models of HCM with promising results. We will summarize recent technological advances and their implication as gene therapy options in HCM with a special focus on treating MYBPC3 mutations and its potential for being a successful bench to bedside example.

A Calsequestrin Cis-Regulatory Motif Coupled to a Cardiac Troponin T Promoter Improves Cardiac Adeno-Associated Virus Serotype 9 Transduction Specificity

Adeno-associated virus serotype 9 (AAV9) is an efficient vector for gene transfer to the myocardium. However, the use of ubiquitous promoters, such as the cytomegalovirus (CMV) promoter, can result in expression of the transgene in organs other than the heart. This study tested if the efficiency and specificity of cardiac transcription from a chicken cardiac troponin T (TnT) promoter could be further increased by incorporating a cardiomyocyte-specific transcriptional cis-regulatory motif from human calsequestrin 2 (CS-CRM4) into the expression cassette (Enh.TnT). The efficiency of luciferase expression from the TnT and Enh.TnT constructs was compared to expression of luciferase under the control of the CMV promoter in both adult and neonatal mice. Overall, expression levels of luciferase in the heart were similar in mice injected with AAV9.TnT.Luc, AAV9.Enh.TnT.Luc and AAV9.CMV.Luc. In contrast, expression levels of luciferase activity in nontarget organs, including the liver and muscle, was lower in mice injected with the AAV9.TnT.Luc compared to AAV9.CMV.Luc and was negligible with AAV9.Enh.TnT. In neonates, in organs other than the heart, luciferase expression levels were too low to be quantified for all constructs. Taken together, the data show that the AAV9 Enh.TnT constructs drives high levels of expression of the transgene in the myocardium, with insignificant expression in other organs. These properties reduce the risks associated with the AAV9-mediated expression of the therapeutic protein of interest in nontarget organs. The excellent cardiac specificity should allow for the use of higher vector doses than are currently used, which might be essential to achieve the levels of transgene expression necessary for therapeutic benefits. Taken together, the findings suggest that the Enh.TnT transcription unit is a potentially attractive tool for clinical cardiac gene therapy in adults.

Adeno-associated Virus (AAV) Serotypes Have Distinctive Interactions with Domains of the Cellular AAV Receptor

Adeno-associated virus (AAV) entry is determined by its interactions with specific surface glycans and a proteinaceous receptor(s). Adeno-associated virus receptor (AAVR) (also named KIAA0319L) is an essential cellular receptor required for the transduction of vectors derived from multiple AAV serotypes, including the evolutionarily distant serotypes AAV2 and AAV5. Here, we further biochemically characterize the AAV-AAVR interaction and define the domains within the ectodomain of AAVR that facilitate this interaction. By using a virus overlay assay, it was previously shown that the major AAV2 binding protein in membrane preparations of human cells corresponds to a glycoprotein with a molecular mass of 150 kDa. By establishing a purification procedure, performing further protein separation by two-dimensional electrophoresis, and utilizing mass spectrometry, we now show that this glycoprotein is identical to AAVR. While we find that AAVR is an N-linked glycosylated protein, this glycosylation is not a strict requirement for AAV2 binding or functional transduction. Using a combination of genetic complementation with deletion constructs and virus overlay assays with individual domains, we find that AAV2 functionally interacts predominantly with the second Ig-like polycystic kidney disease (PKD) repeat domain (PKD2) present in the ectodomain of AAVR. In contrast, AAV5 interacts primarily through the first, most membrane-distal, PKD domain (PKD1) of AAVR to promote transduction. Furthermore, other AAV serotypes, including AAV1 and -8, require a combination of PKD1 and PKD2 for optimal transduction. These results suggest that despite their shared dependence on AAVR as a critical entry receptor, different AAV serotypes have evolved distinctive interactions with the same receptor.

IMPORTANCE Over the past decade, AAV vectors have emerged as leading gene delivery tools for therapeutic applications and biomedical research. However, fundamental aspects of the AAV life cycle, including how AAV interacts with host cellular factors to facilitate infection, are only partly understood. In particular, AAV receptors contribute significantly to AAV vector transduction efficiency and tropism. The recently identified AAV receptor (AAVR) is a key host receptor for multiple serotypes, including the most studied serotype, AAV2. AAVR binds directly to AAV2 particles and is rate limiting for viral transduction. Defining the AAV-AAVR interface in more detail is important to understand how AAV engages with its cellular receptor and how the receptor facilitates the entry process. Here, we further define AAV-AAVR interactions, genetically and biochemically, and show that different AAV serotypes have discrete interactions with the Ig-like PKD domains of AAVR. These findings reveal an unexpected divergence of AAVR engagement within these parvoviruses.