Topoisomerase Inhibition Accelerates Gene Expression after Adeno-associated Virus-mediated Gene Transfer to the Mammalian Heart

The Kir2.1E299V mutation increases atrial fibrillation vulnerability while protecting the ventricles against arrhythmias in a mouse model of short QT syndrome type 3

AIMS

Short QT syndrome type 3 (SQTS3) is a rare arrhythmogenic disease caused by gain-of-function mutations in KCNJ2, the gene coding the inward rectifier potassium channel Kir2.1. We used a multidisciplinary approach and investigated arrhythmogenic mechanisms in an in-vivo model of de-novo mutation Kir2.1E299V identified in a patient presenting an extremely abbreviated QT interval and paroxysmal atrial fibrillation.

METHODS AND RESULTS

We used intravenous adeno-associated virus-mediated gene transfer to generate mouse models, and confirmed cardiac-specific expression of Kir2.1WT or Kir2.1E299V. On ECG, the Kir2.1E299V mouse recapitulated the QT interval shortening and the atrial-specific arrhythmia of the patient. The PR interval was also significantly shorter in Kir2.1E299V mice. Patch-clamping showed extremely abbreviated action potentials in both atrial and ventricular Kir2.1E299V cardiomyocytes due to a lack of inward-going rectification and increased IK1 at voltages positive to -80 mV. Relative to Kir2.1WT, atrial Kir2.1E299V cardiomyocytes had a significantly reduced slope conductance at voltages negative to -80 mV. After confirming a higher proportion of heterotetrameric Kir2.x channels containing Kir2.2 subunits in the atria, in-silico 3D simulations predicted an atrial-specific impairment of polyamine block and reduced pore diameter in the Kir2.1E299V-Kir2.2WT channel. In ventricular cardiomyocytes, the mutation increased excitability by shifting INa activation and inactivation in the hyperpolarizing direction, which protected the ventricle against arrhythmia. Moreover, Purkinje myocytes from Kir2.1E299V mice manifested substantially higher INa density than Kir2.1WT, explaining the abbreviation in the PR interval.

CONCLUSION

The first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1E299V mutation. Kir2.1E299V eliminates rectification in both cardiac chambers but protects against ventricular arrhythmias by increasing excitability in both Purkinje-fiber network and ventricles. Consequently, the predominant arrhythmias are supraventricular likely due to the lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1E299V-Kir2.2WT heterotetramer.

Bleomycin promotes rAAV2 transduction via DNA-PKcs/Artemis-mediated DNA break repair pathways

Because it is safe and has a simple genome, recombinant adeno-associated virus (rAAV) is an extremely appealing vector for delivery in in vivo gene therapy. However, its low transduction efficiency for some cells, limits its further application in the field of gene therapy. Bleomycin is a chemotherapeutic agent approved by the FDA whose effect on rAAV transduction has not been studied. In this study, we systematically investigated the effect of Bleomycin on the second-strand synthesis and used CRISPR/CAS9 and RNAi methods to understand the effects of Bleomycin on rAAV vector transduction, particularly the effect of DNA repair enzymes. The results showed that Bleomycin could promote rAAV2 transduction both in vivo and in vitro. Increased transduction was discovered to be a direct result of decreased cytoplasmic rAAV particle degradation and increased second-strand synthesis. TDP1, PNKP, and SETMAR are required to repair the DNA damage gap caused by Bleomycin, TDP1, PNKP, and SETMAR promote rAAV second-strand synthesis. Bleomycin induced DNA-PKcs phosphorylation and phosphorylated DNA-PKcs and Artemis promoted second-strand synthesis. The current study identifies an effective method for increasing the capability and scope of in-vivo and in-vitro rAAV applications, which can amplify cell transduction at Bleomycin concentrations. It also supplies information on combining tumor gene therapy with chemotherapy.

Topoisomerase Inhibitors Increase Episomal DNA Expression by Inducing the Integration of Episomal DNA in Hepatic Cells

Gene therapy is a promising strategy to treat and cure most inherited metabolic liver disorders. Viral vectors such as those based on adeno-associated viruses (AAVs) and lentiviruses (LVs) are used as vehicles to deliver functional genes to affected hepatocytes. Adverse events associated with the use of high vector doses have motivated the use of small molecules as adjuvants to reduce the dose. In this study, we showed that a one-hour treatment with topoisomerase inhibitors (camptothecin and etoposide) prior to viral transduction is enough to increase AAV and LV reporter expression in non-dividing hepatic cells in culture. Topoisomerase inhibitors increased both integration-competent (ICLV) and integration-deficient (IDLV) LV-derived expression, with a much stronger increase in the IDLV transduction system. In agreement with that, topoisomerase inhibitors increased viral genome integration in both strains, with a greater impact on the IDLV strain, supporting the idea that topoisomerase inhibitors increased episomal DNA integration, especially when viral integrase activity is abolished. These effects correlated with an increase in the DNA damage response produced by the treatments. Our study highlights the need to monitor DNA damage and undesired integration of viral episomal DNAs into the host genome when studying chemical compounds that increase viral transduction.

Autophagic degradation of CCN2 (cellular communication network factor 2) causes cardiotoxicity of sunitinib

Excessive macroautophagy/autophagy is one of the causes of cardiomyocyte death induced by cardiovascular diseases or cancer therapy, yet the underlying mechanism remains unknown. We and other groups previously reported that autophagy might contribute to cardiomyocyte death caused by sunitinib, a tumor angiogenesis inhibitor that is widely used in clinic, which may help to understand the mechanism of autophagy-induced cardiomyocyte death. Here, we found that sunitinib-induced autophagy leads to apoptosis of cardiomyocyte and cardiac dysfunction as the cardiomyocyte-specific Atg7^-/+ heterozygous mice are resistant to sunitinib. Sunitinib-induced maladaptive autophagy selectively degrades the cardiomyocyte survival mediator CCN2 (cellular communication network factor 2) through the TOLLIP (toll interacting protein)-mediated endosome-related pathway and cardiomyocyte-specific knockdown of Ccn2 through adeno-associated virus serotype 9 (AAV9) mimics sunitinib-induced cardiac dysfunction in vivo, suggesting that the autophagic degradation of CCN2 is one of the causes of sunitinib-induced cardiotoxicity and death of cardiomyocytes. Remarkably, deletion of Hmgb1 (high mobility group box 1) inhibited sunitinib-induced cardiomyocyte autophagy and apoptosis, and the HMGB1-specific inhibitor glycyrrhizic acid (GA) significantly mitigated sunitinib-induced autophagy, cardiomyocyte death and cardiotoxicity. Our study reveals a novel target protein of autophagic degradation in the regulation of cardiomyocyte death and highlights the pharmacological inhibitor of HMGB1 as an attractive approach for improving the safety of sunitinib-based cancer therapy.

Microneedle-mediated gene delivery for the treatment of ischemic myocardial disease

Cardiovascular disorders are still the primary cause of mortality worldwide. Although intramyocardial injection can effectively deliver agents to the myocardium, this approach is limited because of its restriction to needle-mediated injection and the minor retention of agents in the myocardium. Here, we engineered phase-transition microneedles (MNs) coated with adeno-associated virus (AAV) and achieved homogeneous distribution of AAV delivery. Bioluminescence imaging revealed the successful delivery and transfection of AAV-luciferase. AAV-green fluorescent protein-transfected cardiomyocytes were homogeneously distributed on postoperative day 28. AAV-vascular endothelial growth factor (VEGF)-loaded MNs improved heart function by enhancing VEGF expression, promoting functional angiogenesis, and activating the Akt signaling pathway. The results indicated the superiority of MNs over direct muscle injection. Consequently, MNs might emerge as a promising tool with great versatility for delivering various agents to treat ischemic myocardial disease.

Neuraminidase-mediated desialylation augments AAV9-mediated gene expression in skeletal muscle

BACKGROUND

Following systemic delivery, AAV9-mediated gene expression is significantly increased in ischemic versus non-ischemic muscle, suggesting that AAV9 is an attractive vector for treating peripheral arterial disease. Potential mechanisms underlying ischemia-augmented expression include: (i) increased vascular permeability and (ii) "unmasking" of endogenous AAV9 receptors. In the present study, we aimed to reconstitute the ischemic induction of AAV9 in vivo, using local injection of histamine (to increase vascular permeability) and neuraminidase (to desialylate cell surface glycans).

METHODS

Bioassays were performed to optimize the effects of histamine and neuraminidase after intramuscular injection. Histamine and/or neuraminidase were then injected intramuscularly shortly before intravenous injection of an AAV9 vector expressing luciferase. Luciferase expression was serially assessed with bioluminescence imaging. At the end of the study, tissues were harvested for assays of luciferase activity and AAV9 genome copy number aiming to assess AAV-mediated gene expression and transduction, respectively.

RESULTS

Intramuscular injection of either neuraminidase or neuraminidase plus histamine significantly increased both transduction and gene expression, whereas histamine alone had little effect. Pre-injection with neuraminidase increased AAV9-mediated gene delivery by four- to nine-fold and luciferase activity by 60-100-fold. Luciferase activity in neuraminidase-injected muscle was > 100-fold higher than in any off-target tissue (including heart, liver and brain).

CONCLUSIONS

The ischemic induction of AAV9-mediated gene expression in muscle can largely be reconstituted by pre-injecting neuraminidase intranmuscularly. This strategy may prove useful in future human gene therapy protocols as a quick and efficient means to selectively target systemically injected AAV9 to localized regions of muscle, thus decreasing the potential for adverse effects in off-target tissues.

Recombinant adeno-associated virus serotype 9 in a mouse model of atherosclerosis: Determination of the optimal expression time in vivo

Adeno-associated virus 9 (AAV9) has been identified as one of the optimal gene transduction carriers for gene therapy. The aim of the present study was to determine the gene transfection efficiency and safety of an AAV9 vector produced using a recombinant baculovirus (rBac)‑based system. AAV9‑cytomegalovirus (CMV)-green fluorescent protein was produced using an rBac system and the resulting vector particles were injected intravenously into mice. Animals were sacrificed at 14, 21, 28, 35, 60, 90 and 120 days following injection. GFP expression in aortic vasculature and aortic plaques in C57/6B and apolipoprotein E‑/‑ mice was analyzed by fluorescence imaging and western blotting. In vivo analyses of biological markers of liver and heart damage, and renal function, as well as in vitro terminal deoxynucleotidyl transferase dUTP nick end labeling analysis were used to determine the toxicity of the AAV9 carrier. The findings of the present study demonstrated that AAV9 viral vectors packaged using the rBac system functioned appropriately in arteriosclerosis plaques. The CMV promoter significantly induced GFP expression in the vascular plaque in a time-dependent manner. AAV9‑CMV viral particles did not lead to heart, liver or renal damage and no change in apoptotic rate was identified. These findings indicated that AAV9-CMV may be effectively and safely used to transfect genes into atherosclerotic plaques.

Direct interaction of human serum proteins with AAV virions to enhance AAV transduction: immediate impact on clinical applications

Recent hemophilia B clinical trials using adeno-associated virus (AAV) gene delivery have demonstrated much lower FIX production in patients compared to the high levels observed in animal models and AAV capsid specific CTLs response elicited at high doses of AAV vectors. These results emphasize the necessity to explore effective approaches for enhancement of AAV transduction. Initially, we found that incubation of all AAV vectors with human serum enhanced AAV transduction. Complementary analytical experiments demonstrated that human serum albumin (HSA) directly interacted with the AAV capsid and augmented AAV transduction. The enhanced transduction was observed with clinical grade HSA. Mechanistic studies suggest that HSA increases AAV binding to target cells and that the interaction of HSA with AAV doesn’t interfere with the AAV infection pathway. Importantly, HSA incubation during vector dialysis also increased transduction. Finally, HSA enhancement of AAV transduction in a model of hemophilia B displayed greater than a 5-fold increase in vector derived circulating FIX, which improved the bleeding phenotype correction. In conclusion, incubation of HSA with AAV vectors supports a universal augmentation of AAV transduction and more importantly, this approach can be immediately transitioned to the clinic for the treatment of hemophilia and other diseases.

Systemic injection of AAV9 carrying a periostin promoter targets gene expression to a myofibroblast-like lineage in mouse hearts after reperfused myocardial infarction

Adeno-associated virus (AAV) has been used to direct gene transfer to a variety of tissues, including heart, liver, skeletal muscle, brain, kidney and lung, but it has not previously been shown to effectively target fibroblasts in vivo, including cardiac fibroblasts. We constructed expression cassettes using a modified periostin promoter to drive gene expression in a cardiac myofibroblast-like lineage, with only occasional spillover into cardiomyocyte-like cells. We compared AAV serotypes 6 and 9 and found robust gene expression when the vectors were delivered by systemic injection after myocardial infarction (MI), with little expression in healthy, non-infarcted mice. AAV9 provided expression in a greater number of cells than AAV6, with reporter gene expression visible in the cardiac infarct and border zones from 5 to 62 days post MI, as assessed by luciferase and Cre-activated green fluorescent protein expression. Although common myofibroblast markers were expressed in low abundance, most of the targeted cells expressed myosin IIb, an embryonic form of smooth muscle myosin heavy chain that has previously been associated with myofibroblasts after reperfused MI. This study is the first to demonstrate AAV-mediated expression in a potentially novel myofibroblast-like lineage in mouse hearts post MI and may open new avenues of gene therapy to treat patients surviving MI.

Systemic delivery of shRNA by AAV9 provides highly efficient knockdown of ubiquitously expressed GFP in mouse heart, but not liver

AAV9 is a powerful gene delivery vehicle capable of providing long-term gene expression in a variety of cell types, particularly cardiomyocytes. The use of AAV-delivery for RNA interference is an intense area of research, but a comprehensive analysis of knockdown in cardiac and liver tissues after systemic delivery of AAV9 has yet to be reported. We sought to address this question by using AAV9 to deliver a short-hairpin RNA targeting the enhanced green fluorescent protein (GFP) in transgenic mice that constitutively overexpress GFP in all tissues. The expression cassette was initially tested in vitro and we demonstrated a 61% reduction in mRNA and a 90% reduction in GFP protein in dual-transfected 293 cells. Next, the expression cassette was packaged as single-stranded genomes in AAV9 capsids to test cardiac GFP knockdown with several doses ranging from 1.8×10(10) to 1.8×10(11) viral genomes per mouse and a dose-dependent response was obtained. We then analyzed GFP expression in both heart and liver after delivery of 4.4×10(11) viral genomes per mouse. We found that while cardiac knockdown was highly efficient, with a 77% reduction in GFP mRNA and a 71% reduction in protein versus control-treated mice, there was no change in liver expression. This was despite a 4.5-fold greater number of viral genomes in the liver than in the heart. This study demonstrates that single-stranded AAV9 vectors expressing shRNA can be used to achieve highly efficient cardiac-selective knockdown of GFP expression that is sustained for at least 7 weeks after the systemic injection of 8 day old mice, with no change in liver expression and no evidence of liver damage despite high viral genome presence in the liver.

Mechanistic insights into the enhancement of adeno-associated virus transduction by proteasome inhibitors

Proteasome inhibitors (e.g., bortezomib, MG132) are known to enhance adeno-associated virus (AAV) transduction; however, whether this results from pleotropic proteasome inhibition or off-target serine and/or cysteine protease inhibition remains unresolved. Here, we examined recombinant AAV (rAAV) effects of a new proteasome inhibitor, carfilzomib, which specifically inhibits chymotrypsin-like proteasome activity and no other proteases. We determined that proteasome inhibitors act on rAAV through proteasome inhibition and not serine or cysteine protease inhibition, likely through positive changes late in transduction.

Plectin-1 Targeted AAV Vector for the Molecular Imaging of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is highly malignant disease that is the fourth leading cause of cancer-related death in the US. Gene therapy using AAV vectors to selectively deliver genes to PDAC cells is an attractive treatment option for pancreatic cancer. However, most AAV serotypes display a broad spectrum of tissue tropism and none of the existing serotypes specifically target PDAC cells. This study tests the hypothesis that AAV2 can be genetically re-engineered to specifically target PDAC cells by modifying the capsid surface to display a peptide that has previously been shown to bind plectin-1. Toward this end, a Plectin-1 Targeting Peptide (PTP) was inserted into the loop IV region of the AAV2 capsid, and the resulting capsid (AAV-PTP) was used in a series of in vitro and in vivo experiments. In vitro, AAV-PTP was found to target all five human PDAC cell lines tested (PANC-1, MIA PaCa-2, HPAC, MPanc-96, and BxPC-3) preferentially over two non-neoplastic human pancreatic cell lines (human pancreatic ductal epithelial and human pancreatic stellate cells). In vivo, mice bearing subcutaneous tumor xenografts were generated using the PANC-1 cell line. Once tumors reached a size of ∼1-2 mm in diameter, the mice were injected intravenously with luciferase reporter vectors packaged in the either AAV-PTP or wild type AAV2 capsids. Luciferase expression was then monitored by bioluminescence imaging on days 3, 7, and 14 after vector injection. The results indicate that the AAV-PTP capsid displays a 37-fold preference for PANC-1 tumor xenographs over liver and other tissues; whereas the wild type AAV2 capsid displays a complementary preference for liver over tumors and other tissues. Together, these results establish proof-of-principle for the ability of PTP-modified AAV capsids to selectively target gene delivery to PDAC cells in vivo, which opens promising new avenues for the early detection, diagnosis, and treatment of pancreatic cancer.

Adeno-associated virus serotype 9 efficiently targets ischemic skeletal muscle following systemic delivery

Targeting therapeutic gene expression to the skeletal muscle following intravenous (IV) administration is an attractive strategy for treating peripheral arterial disease (PAD), except that vector access to the ischemic limb could be a limiting factor. As adeno-associated virus serotype 9 (AAV-9) transduces skeletal muscle at high efficiency following systemic delivery, we employed AAV-9 vectors bearing luciferase or enhanced green fluorescent protein (eGFP) reporter genes to test the hypothesis that increased desialylation of cell-surface glycans secondary to hindlimb ischemia (HLI) might help offset the reduction in tissue perfusion that occurs in mouse models of PAD. The utility of the creatine kinase-based (CK6) promoter for restricting gene expression to the skeletal muscle was also examined by comparing it with the cytomegalovirus (CMV) promoter after systemic administration following surgically induced HLI. Despite reduced blood flow to the ischemic limbs, CK6 promoter-driven luciferase activities in the ischemic gastrocnemius (GA) muscles were ∼34-, ∼28- and ∼150-fold higher than in the fully perfused contralateral GA, heart and liver, respectively, 10 days after IV administration. Furthermore, luciferase activity from the CK6 promoter in the ischemic GA muscles was ∼twofold higher than with CMV, while in the liver CK6-driven activity was ∼42-fold lower than with CMV, demonstrating that the specificity of ischemic skeletal muscle transduction can be further improved with the muscle-specific promoters. Studies with Evans blue dye and fluorescently labeled lectins revealed that vascular permeability and desialylation of the cell-surface glycans were increased in the ischemic hindlimbs. Furthermore, AAV9/CK6/Luc vector genome copy numbers were ∼sixfold higher in the ischemic muscle compared with the non-ischemic muscle in the HLI model, whereas this trend was reversed when the same genome was packaged in the AAV-1 capsid (which binds sialylated, as opposed to desialylated glycans), further underscoring the importance of desialylation in the ischemic enhancement of transduction displayed by AAV-9. Taken together, these findings suggest two complementary mechanisms contributing to the preferential transduction of ischemic muscle by AAV-9: increased vascular permeability and desialylation. In conclusion, ischemic muscle is preferentially targeted following systemic administration of AAV-9 in a mouse model of HLI. Unmasking of the primary AAV-9 receptor as a result of ischemia may contribute importantly to this effect.

Cardiac-selective expression of extracellular superoxide dismutase after systemic injection of adeno-associated virus 9 protects the heart against post-myocardial infarction left ventricular remodeling

BACKGROUND

Cardiac magnetic resonance imaging has not been used previously to document the attenuation of left ventricular (LV) remodeling after systemic gene delivery. We hypothesized that targeted expression of extracellular superoxide dismutase (EcSOD) via the cardiac troponin-T promoter would protect the mouse heart against both myocardial infarction (MI) and subsequent LV remodeling.

METHODS AND RESULTS

Using reporter genes, we first compared the specificity, time course, magnitude, and distribution of gene expression from adeno-associated virus (AAV) 1, 2, 6, 8, and 9 after intravenous injection. The troponin-T promoter restricted gene expression largely to the heart for all AAV serotypes tested. AAV1, 6, 8, and 9 provided early-onset gene expression that approached steady-state levels within 2 weeks. Gene expression was highest with AAV9, which required only 3.15×10(11) viral genomes per mouse to achieve an 84% transduction rate. AAV9-mediated, cardiac-selective gene expression elevated EcSOD enzyme activity in heart by 5.6-fold (P=0.015), which helped protect the heart against both acute MI and subsequent LV remodeling. In acute MI, infarct size in EcSOD-treated mice was reduced by 40% compared with controls (P=0.035). In addition, we found that cardiac-selective expression of EcSOD increased myocardial capillary fractional area and decreased neutrophil infiltration after MI. In a separate study of LV remodeling, after a 60-minute coronary occlusion, cardiac magnetic resonance imaging revealed that LV volumes at days 7 and 28 post-MI were significantly lower in the EcSOD group compared with controls.

CONCLUSIONS

Cardiac-selective expression of EcSOD from the cardiac troponin-T promoter after systemic administration of AAV9 provides significant protection against both acute MI and LV remodeling.

Arsenic trioxide stabilizes accumulations of adeno-associated virus virions at the perinuclear region, increasing transduction in vitro and in vivo

Interactions with cellular stress pathways are central to the life cycle of many latent viruses. Here, we utilize adeno-associated virus (AAV) as a model to study these interactions, as previous studies have demonstrated that cellular stressors frequently increase transduction of recombinant AAV (rAAV) vectors and may even substitute for helper virus functions. Since several chemotherapeutic drugs are known to increase rAAV transduction, we investigated the effect of arsenic trioxide (As(2)O(3)), an FDA-approved chemotherapeutic agent with known effects on several other virus life cycles, on the transduction of rAAV. In vitro, As(2)O(3) caused a dose-dependent increase in rAAV2 transduction over a broad range of cell lines from various cell types and species (e.g., HEK-293, HeLa, HFF hTERT, C-12, and Cos-1). Mechanistically, As(2)O(3) treatment acted to prevent loss of virions from the perinuclear region, which correlated with increased cellular vector genome retention, and was distinguishable from proteasome inhibition. To extend our investigation of the cellular mechanism, we inhibited reactive oxygen species formation and determined that the As(2)O(3)-mediated increase in rAAV2 transduction was dependent upon production of reactive oxygen species. To further validate our in vitro data, we tested the effect of As(2)O(3) on rAAV transduction in vivo and determined that treatment initiated transgene expression as early as 2 days posttransduction and increased reporter expression by up to 10-fold. Moreover, the transduction of several other serotypes of rAAV was also enhanced in vivo, suggesting that As(2)O(3) affects a pathway used by several AAV serotypes. In summary, our data support a model wherein As(2)O(3) increases rAAV transduction both in vitro and in vivo and maintains perinuclear accumulations of capsids, facilitating productive nuclear trafficking.

Adeno-associated virus serotype 9 administered systemically after reperfusion preferentially targets cardiomyocytes in the infarct border zone with pharmacodynamics suitable for the attenuation of left ventricular remodeling

BACKGROUND

Adeno-associated virus serotype 9 (AAV9) vectors provide efficient and uniform gene expression to normal myocardium following systemic administration, with kinetics that approach steady-state within 2-3 weeks. However, as a result of the delayed onset of gene expression, AAV vectors have not previously been administered intravenously after reperfusion for post-infarct gene therapy applications. The present study evaluated the therapeutic potential of post-myocardial infarction gene delivery using intravenous AAV9.

METHODS

AAV9 vectors expressing firefly luciferase, enhanced green fluorescent protein (eGFP) or extracellular superoxide dismutase genes from the cardiac troponin-T (cTnT) promoter (AcTnTLuc, AcTnTeGFP, AcTnTEcSOD) were employed. AcTnTLuc was administered intravenously at 10 min and at 1, 2 and 3 days post-ischemia/reperfusion (IR), and the kinetics of luciferase expression were assessed with bioluminescence imaging. AcTnTeGFP was used to evaluate the distribution of eGFP expression. High-resolution echocardiography was used to evaluate the effects of AcTnTEcSOD on left ventricular (LV) remodeling when injected 10 min post-IR.

RESULTS

Compared to sham animals, luciferase expression at 2 days after vector administration was elevated by four-, 24-, 210- and 213-fold in groups injected at 10 min, 1 day, 2 days and 3 days post-IR, respectively. The expression of cTnT-driven eGFP was strongest in cardiomyocytes bordering the infarct zone. In the efficacy study of EcSOD, post-infarct LV end-systolic and end-diastolic volumes at days 14 and 28 were significantly smaller in the EcSOD group compared to the control.

CONCLUSIONS

Systemic administration of AAV9 vectors after IR both elevates and accelerates gene expression that preferentially targets cardiomyocytes in the border zone with pharmacodynamics suitable for the attenuation of LV remodeling.

AAV vectors for cardiac gene transfer: experimental tools and clinical opportunities

Since the first demonstration of in vivo gene transfer into myocardium there have been a series of advancements that have driven the evolution of cardiac gene delivery from an experimental tool into a therapy currently at the threshold of becoming a viable clinical option. Innovative methods have been established to address practical challenges related to tissue-type specificity, choice of delivery vehicle, potency of the delivered material, and delivery route. Most importantly for therapeutic purposes, these strategies are being thoroughly tested to ensure safety of the delivery system and the delivered genetic material. This review focuses on the development of recombinant adeno-associated virus (rAAV) as one of the most valuable cardiac gene transfer agents available today. Various forms of rAAV have been used to deliver "pre-event" cardiac protection and to temper the severity of hypertrophy, cardiac ischemia, or infarct size. Adeno-associated virus (AAV) vectors have also been functional delivery tools for cardiac gene expression knockdown studies and successfully improving the cardiac aspects of several metabolic and neuromuscular diseases. Viral capsid manipulations along with the development of tissue-specific and regulated promoters have greatly increased the utility of rAAV-mediated gene transfer. Important clinical studies are currently underway to evaluate AAV-based cardiac gene delivery in humans.

Adeno-associated virus serotype 9-mediated overexpression of extracellular superoxide dismutase improves recovery from surgical hind-limb ischemia in BALB/c mice

OBJECTIVE

Neovascularization is a physiologic repair process that partly depends on nitric oxide. Extracellular superoxide dismutase (EcSOD) is the major scavenger of superoxide. It is an important regulator of nitric oxide bioavailability and thus protects against vascular dysfunction. We hypothesized that overexpression of EcSOD in skeletal muscle would improve recovery from hind-limb ischemia.

METHODS

Adeno-associated virus serotype 9 (AAV9) vectors expressing EcSOD or luciferase (control) from the cytomegalovirus promoter were cross-packaged into AAV9 capsids and injected intramuscularly into the hind-limb muscles (1 × 10(11) viral genomes/limb) of 12-week-old mice. Ischemia was induced after intramuscular injections. Laser Doppler was used to measure limb perfusion on days 0, 7, and 14 after injection. Values were expressed as a ratio relative to the nonischemic limb. EcSOD expression was measured by Western blotting. Capillary density was documented by immunohistochemical staining for platelet endothelial cell adhesion molecule. Apoptosis was assessed by terminal deoxynucleotide transferase-mediated biotin-deoxy uridine triphosphate nick-end labeling and necrosis was visually evaluated daily.

RESULTS

EcSOD expression was twofold upregulated in EcSOD treated vs control ischemic muscles at day 14. Capillary density (capillaries/fiber) was 1.9-fold higher in treated (1.65 ± 0.02) vs control muscle (0.78 ± 0.17, P < .05). Recovery of perfusion ratio at day 14 after ischemia was 1.5-fold greater in EcSOD vs control mice (P < .05). The percentage of apoptotic nuclei was 1.3% ± 0.4% in EcSOD-treated mice compared with 4.2% ± 0.2% in controls (P < .001). Limb necrosis was also significantly lower in EcSOD vs control mice.

CONCLUSION

AAV9-mediated overexpression of EcSOD in skeletal muscle significantly improves recovery from hind-limb ischemia in mice, consistent with improved capillary density and perfusion ratios in treated mice.

A single direct injection into the left ventricular wall of an adeno-associated virus 9 (AAV9) vector expressing extracellular superoxide dismutase from the cardiac troponin-T promoter protects mice against myocardial infarction

BACKGROUND

Localized administration of a highly efficient gene delivery system in combination with a cardiac-selective promoter may provide a favorable biosafety profile in clinical applications such as coronary artery bypass graft surgery, where regions of myocardium can be readily injected to protect them against the potential threat of future ischemic events.

METHODS

Adeno-associated virus (AAV) vectors expressing luciferase or enhanced green fluorescent protein (eGFP) packaged into AAV serotypes 1, 2, 6, 8 and 9 were injected into the left ventricular (LV) wall of adult mice to determine the time course, magnitude and distribution of gene expression. An AAV9 vector expressing extracellular superoxide dismutase (EcSOD) from the cardiac troponin T (cTnT) promoter was then directly injected into the LV wall of adult mice. Myocardial infarction was induced 4 weeks after injection and infarct size was determined by triphenyltetrazolium chloride and phthalo blue staining.

RESULTS

Serotypes AAV 9, 8, 1 and 6 provided early onset of gene expression in the heart with minimal extra-cardiac gene expression. AAV9 provided the highest magnitude of gene expression. Immunostaining for eGFP showed expression spanning the anterior to posterior walls from the mid ventricle to the apex. A single direct injection of the AAV9 vector bearing EcSOD ( n  = 5) decreased the mean infarct size by 50% compared to the eGFP control group (n = 8) (44 ± 7% versus 22 ± 5%; p = 0.04).

CONCLUSIONS

AAV serotype 9 is highly efficient for cardiac gene delivery, as evidenced by early onset and high-level gene expression. AAV9-mediated, cardiac selective overexpression of EcSOD from the cTnT promoter significantly reduced infarct size in mice.

Generation of novel reporter stem cells and their application for molecular imaging of cardiac-differentiated stem cells in vivo

Stem cell therapies offer the potential for repair and regeneration of cardiac tissue. To facilitate evaluation of stem cell activity in vivo, we created novel dual-reporter mouse embryonic stem (mES) cell lines that express the firefly luciferase (LUC) reporter gene under the control of the cardiac sodium-calcium exchanger-1 (Ncx-1) promoter in the background of the 7AC5-EYFP mES cell line that constitutively expresses the enhanced yellow fluorescent protein (EYFP). We compared the ability of recombinant clonal cell lines to express LUC before and after induction of cardiac differentiation in vitro. In particular, one of the clonal cell lines (Ncx-1-43LUC mES cells) showed markedly enhanced LUC expression (45-fold increase) upon induction of cardiac differentiation in vitro. Further, cardiac differentiation in these cells was perpetuated over a period of 2-4 weeks after transplantation in a neonatal mouse heart model, as monitored by noninvasive bioluminescence imaging (BLI) and confirmed via postmortem immunofluorescence and histological assessments. In contrast, transplantation of undifferentiated pluripotent Ncx-1-43LUC mES cells in neonatal hearts did not result in detectable levels of cardiac differentiation in these cells in vivo. These results suggest that prior induction of cardiac differentiation in vitro enhances development and maintenance of a cardiomyocyte-like phenotype for mES cells following transplantation into neonatal mouse hearts in vivo. We conclude that the Ncx-1-43LUC mES cell line is a novel tool for monitoring early cardiac differentiation in vivo using noninvasive BLI.

Robust cardiomyocyte-specific gene expression following systemic injection of AAV: in vivo gene delivery follows a Poisson distribution

Newly-isolated serotypes of AAV readily cross the endothelial barrier to provide efficient transgene delivery throughout the body. However, tissue-specific expression is preferred in most experimental studies and gene therapy protocols. Previous efforts to restrict gene expression to the myocardium often relied on direct injection into heart muscle or intracoronary perfusion. Here, we report an AAV vector system employing the cardiac troponin T promoter (cTnT). Using luciferase and eGFP, the efficiency and specificity of cardiac reporter gene expression using AAV serotype capsids: AAV-1, 2, 6, 8 or 9 were tested after systemic administration to 1 week old mice. Luciferase assays showed that the cTnT promoter worked in combination with each of the AAV serotype capsids to provide cardiomyocyte-specific gene expression, but AAV-9 followed closely by AAV-8 was the most efficient. AAV9-mediated gene expression from the cTnT promoter was 640-fold greater in the heart compared to the next highest tissue (liver). eGFP fluorescence indicated a transduction efficiency of 96% using AAV-9 at a dose of only 3.15×10¹⁰ viral particles per mouse. Moreover, the intensity of cardiomyocyte eGFP fluorescence measured on a cell-by-cell basis revealed that AAV-mediated gene expression in the heart can be modeled as a Poisson distribution; requiring an average of nearly two vector genomes per cell to attain an 85% transduction efficiency.