[show abstract][hide abstract] ABSTRACT: A growing body of research supports the development of recombinant adeno-associated viral (rAAV) vectors for delivery of gene expression cassettes to striated musculature as a method of treating severe neuromuscular conditions. However, it is unclear whether delivery protocols that achieve extensive gene transfer in mice can be adapted to produce similarly extensive gene transfer in larger mammals and ultimately patients. Consequently, we sought to investigate methodological modifications that would facilitate rAAV-mediated gene transfer to the striated musculature of canines. A simple procedure incorporating acute (i) occlusion of limb blood flow, (ii) exsanguination via compression bandage, and (iii) vector "dwell" time of <20 minutes, markedly enhanced the transduction of limb muscles, compared with a simple bolus limb infusion of vector. A complementary method whereby vector was infused into the jugular vein led to efficient transduction of cardiomyocytes and to a lesser degree the diaphragm. Together these methods can be used to achieve transgene expression in heart, diaphragm, and limb muscles of juvenile dogs using rAAV6 vectors. These results establish that rAAV-mediated gene delivery is a viable approach to achieving systemic transduction of striated musculature in mammals approaching the dimensions of newborn humans.
[show abstract][hide abstract] ABSTRACT: The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.
[show abstract][hide abstract] ABSTRACT: Restoring dystrophin expression in the muscles of patients with Duchenne muscular dystrophy (DMD) may halt or reverse the degenerative wasting and weakness that causes premature death. However, the therapeutic efficacy of an intervention may be limited by the extent of disease progression prior to treatment. In this study, we considered the potential for ameliorating the pathology in a mouse model of advanced-stage muscular dystrophy by systemic administration of recombinant adeno-associated viral (rAAV6) vectors encoding a microdystrophin expression construct. The treatment of 20-month-old mdx mice restored body-wide expression of a dystrophin-based protein in striated musculature. In aged mice that received treatment, the resultant dystrophin expression was associated with improved hindlimb and respiratory muscle morphology and function, concomitant with reduced muscle fiber degeneration. The findings demonstrate that an established dystrophic state remains amenable to improvement with appropriate intervention and, by some measures, may even achieve benefits similar to those observed with intervention early in disease progression. The capacity to ameliorate the pathology in an animal model of advanced-stage muscular dystrophy suggests that interventions ultimately proven to exert a therapeutic effect in young patients may offer benefits to older patients or those with advanced conditions of progressive muscular dystrophy.
[show abstract][hide abstract] ABSTRACT: Skeletal muscles are frequently analyzed for composition of phenotypically distinct myofibers, as a functional determinant. We describe an improved myofiber phenotyping procedure, involving cryosection co-incubation with fluorophore-labeled myosin heavy-chain (MyHC)-isoform-specific antibodies. This technique identifies multiple fiber "types" on a single section, thereby reducing reagents and processing, and offers side-by-side comparison of samples from multiple species including mice. These advances are valuable for studying the physiological attributes of skeletal muscle in health and disease.
[show abstract][hide abstract] ABSTRACT: Adeno-associated virus-based vector (AAV)-mediated gene delivery has been successful in some animal models of human disease such as the mdx mouse model of human Duchenne muscular dystrophy (DMD). However, recent evidence of immune-mediated loss of vector persistence in dogs and humans suggests that immune modulation might be necessary to achieve successful long-term transgene expression in these species. We have previously demonstrated that direct intramuscular injection of AAV2 or AAV6 in wild-type random-bred dogs resulted in a robust immune response to capsid or capsid-associated proteins. We now demonstrate that a brief course of immunosuppression with a combination of anti-thymocyte globulin (ATG), cyclosporine (CSP), and mycophenolate mofetil (MMF) is sufficient to permit long-term and robust expression of a canine micro-dystrophin (c-micro-dys) transgene in the skeletal muscle of a dog model for DMD (canine X-linked muscular dystrophy, or cxmd dog) and that its expression restored localization of components of the dystrophin-associated protein complex at the muscle membrane. This protocol has potential applications to human clinical trials to enhance AAV-mediated therapies.
[show abstract][hide abstract] ABSTRACT: Duchenne muscular dystrophy (DMD) is a fatal disease of striated muscle deterioration resulting from the loss of the cytoskeletal protein dystrophin. Most patients develop significant cardiomyopathy, with heart failure being the second leading cause of death in DMD. Compared with the extensive studies on skeletal muscle defects and potential therapy in DMD, very little attention has been directed at the increasing incidence of heart failure in DMD. Here we show that a single systemic injection of recombinant adeno-associated virus (rAAV2/6) harboring micro-dystrophin leads to extensive cardiac transduction, with micro-dystrophin correctly localized at the periphery of the cardiac myocytes and functionally associated with the sarcolemmal membrane. Significantly, micro-dystrophin gene transfer corrected the baseline end-diastolic volume defect in the mdx mouse heart and prevented cardiac pump failure induced by dobutamine stress testing in vivo, although several parameters of systolic function were not corrected. These results demonstrate that systemic gene delivery of micro-dystrophin can restore ventricular distensibility and protect the mdx myocardium from pump dysfunction during adrenergic stimulation in vivo.
[show abstract][hide abstract] ABSTRACT: Systemic delivery of recombinant adeno-associated virus (rAAV) 6 vectors mediates efficient transduction of the entire striated musculature, making this an attractive strategy for muscle gene therapy. However, owing to widespread transduction of non-muscle tissues, optimization of this method would benefit from the use of muscle-specific promoters. Most such promoters either lack high-level expression in certain muscle types or are too large for inclusion in rAAV vectors encoding microdystrophin. Here, we describe novel regulatory cassettes based on enhancer/promoter regions of murine muscle creatine kinase (CK) and alpha-myosin heavy-chain genes. The strongest cassette, MHCK7 (770 bp), directs high-level expression comparable to cytomegalovirus and Rous sarcoma virus promoters in fast and slow skeletal and cardiac muscle, and low expression in the liver, lung, and spleen following systemic rAAV6 delivery in mice. Compared with CK6, our previous best cassette, MHCK7 activity is approximately 400-, approximately 50-, and approximately 10-fold higher in cardiac, diaphragm, and soleus muscles, respectively. MHCK7 also directs strong microdystrophin expression in mdx muscles. While further study of immune responses to MHCK7-regulated microdystrophin expression is needed, this cassette is not active in dendritic cell lines. MHCK7 is thus a highly improved regulatory cassette for experimental studies of rAAV-mediated transduction of striated muscle.
[show abstract][hide abstract] ABSTRACT: Mice carrying mutations in both the dystrophin and utrophin genes die prematurely as a consequence of severe muscular dystrophy. Here, we show that intravascular administration of recombinant adeno-associated viral (rAAV) vectors carrying a microdystrophin gene restores expression of dystrophin in the respiratory, cardiac and limb musculature of these mice, considerably reducing skeletal muscle pathology and extending lifespan. These findings suggest rAAV vector-mediated systemic gene transfer may be useful for treatment of serious neuromuscular disorders such as Duchenne muscular dystrophy.
Nature Medicine 08/2006; 12(7):787-9. · 22.86 Impact Factor
[show abstract][hide abstract] ABSTRACT: Molecular Therapy (2006) 13, S15|[ndash]|S15; doi: 10.1016/j.ymthe.2006.08.048
35. Systemic Administration of rAAV6-Microdystrophin Preserves Muscle Function and Extends Lifespan in the Dystrophin-/Utrophin- Mouse Model of Severe Muscular Dystrophy
Paul Gregorevic1, Michael J. Blankinship1, Elina Minami2, James M. Allen1, Charles E. Murry2 and Jeffrey S. Chamberlain11Department of Neurology, University of Washington, Seattle, WA2Department of Pathology, University of Washington, Seattle, WA
[show abstract][hide abstract] ABSTRACT: Gene transfer vectors based on adeno-associated virus (AAV) are now widely used in the field of gene therapy. These vectors have been studied for their potential use in treating many diseases, among them the muscular dystrophies, the most common of which is Duchenne muscular dystrophy (DMD). Several recent advances in the areas of AAV serotype analysis, transgene engineering, and vector delivery to muscle, together with novel means of rescuing mutant mRNA transcripts, have yielded impressive results in animal models of DMD. This minireview focuses on these recent advances and their implications for potential treatments for DMD and other neuromuscular disorders.
[show abstract][hide abstract] ABSTRACT: Systemic delivery of rAAV6 vectors can achieve efficient transduction of the entire striated musculature, making this an attractive strategy for gene therapy of Duchenne Muscular Dystrophy. However, this delivery method also transduces cells in many non-muscle tissues, which may cause therapeutic problems including toxicity and a transgene-directed immune response. These problems could be avoided by limiting transgene expression through the use of muscle-specific promoters. Unfortunately, the expression levels of such promoters following systemic delivery of rAAV vectors are lower than viral promoters in most skeletal muscles and negligible in cardiac muscle. The goal of this project is to design regulatory cassettes that drive high levels of skeletal and cardiac muscle-specific transgene expression while also being sufficiently short (
[show abstract][hide abstract] ABSTRACT: Introduction: Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene. Studies in the mdx mouse model of DMD have shown that muscle membrane integrity and function can be improved by AAV-mediated delivery of a functional dystrophin protein. To assess the potential clinical utility of treating human DMD patients with AAV-mediated gene delivery, we performed a series of direct intra-muscular injections in random-bred normal dogs and in dogs with muscular dystrophy caused by a dystrophin mutation (xmd dogs).Methods: AAV serotypes 2 and 6 carrying different promoter-transgene cassettes were produced as previously described for the murine studies and purified either on a heparin column or with a combination of heparin column and cesium chloride gradient. Direct intramuscular injections of virus (1012, 1010, or 108 viral genomes per site) in a total volume of 250 ul were performed. The injection sites were biopsied under anesthesia between 2 and 12 weeks after injection.Results: Injection of either AAV6 or AAV2 expressing CMV-b-galactosidase (b-gal) induced a strong inflammatory response containing both CD8+ and CD4+ T-lymphocytes with peak tissue destruction 4 weeks following viral injection. A similar robust immune response was seen with injection of AAV6-RSV-alkaline-phosphatase, AAV6-CMV-canine-factor-IX (cFIX) and with empty AAV6 capsid alone. Additional purification of the AAV6-CMV-cFIX by centrifugation through a cesium chloride gradient did not diminish the immune response. Continuous immunosuppression with cyclosporine (CSP) and mycophenolate mofetil (MMF) largely prevented the immune response to AAV6-CMV-b-gal in a normal dog for up to four weeks and permitted robust transgene expression. The same immunosuppressive regimen did not prevent an immune response to AAV6-CMV-cFIX or AAV6-CMV-human-micro-dystrophin in an xmd dog, suggesting that a more aggressive immunosuppressive regimen might be necessary in the xmd dog.Conclusions: Taken together, our results suggest that AAV capsid proteins, or proteins associated with the capsid, elicit significant immune responses when directly injected into skeletal muscle of normal random-bred dogs. The combination of CSP and MMF effectively prevents the immune responses in a normal dog, but not in an xmd dog, possibly due to the pre-existing inflammatory nature of the DMD muscle disease or due to genetic variation in a random-bred animal population. The robust immune responses to AAV2 and AAV6 in random-bred dogs contrast with the lack of an immune response in studies by others in inbred mice and dogs. Further studies will be necessary to determine the nature of the immune responses and to develop appropriate immunosuppressive regimen for AAV gene delivery to xmd muscle.
[show abstract][hide abstract] ABSTRACT: A promising gene therapy approach for treatment of DMD involves systemic delivery of rAAV vectors encoding microdystrophin. This method was shown to mediate efficient transduction of all striated muscles and high-level transgene expression driven by the ubiquitous CMV promoter. However, the use of viral promoters increases the risk of an immune response, largely due to transgene expression in antigen-presenting cells, and may thus be inadequate for long-term therapy. An ideal regulatory cassette for gene therapy of DMD thus needs to direct high-level, tissue-specific expression in skeletal and cardiac muscle and be short enough to package into the rAAV microdystrophin construct.Our lab has developed a series of muscle-specific regulatory cassettes based on the murine muscle creatine kinase (MCK) gene enhancer and promoter regions. The previous “best” small cassette, CK6 (580 bp) drives microdystrophin expression in skeletal muscle following systemic rAAV delivery, at 10% of the level of the CMV promoter. However, expression in heart and diaphragm is very low. To improve expression, we combined the wild type MCK enhancer with a 190 bp enhancer region from the murine alpha myosin heavy chain (MyHC) gene, which is expressed at high levels in cardiac muscle. Addition of the MyHC enhancer increased activity in MM14 skeletal myocytes by 5-fold as assessed by alkaline phosphatase reporter gene activity. Furthermore, high-level expression was detected in skeletal muscle, as well as heart and diaphragm after systemic delivery in mice of rAAV6 vectors encoding these constructs. The activity of the hybrid cassette was 7-fold higher in heart and 3-fold higher in diaphragm and soleus (predominantly slow-twitch muscle fibers) when compared to the wild type MCK cassette, while the activity in tibialis anterioris (predominantly fast-twitch muscle fibers) was unchanged. Expression was restricted to muscle tissue, as evidenced by nearly undetectable levels in the liver, spleen, lung, and aorta. Additional cassettes comprising the MyHC enhancer and various modifications of the minimal MCK cassette have also been tested in MM14 skeletal myocytes. The strongest cassettes were shown to possess 12-fold higher activity than the wild type MCK cassette, and were about 55% as active as the CMV promoter. These contained a 63 bp deletion within the MCK enhancer, addition of a 50 bp region downstream of the transcription initiation site, and a mutation that creates a consensus initiator-binding site from the terminal transferase promoter. We are currently testing activity of these constructs in mouse muscle and non-muscle tissues following systemic delivery of rAAV6 vectors. The strongest tissue-specific cassette will be evaluated for long-term expression of therapeutic levels of microdystrophin in the mdx mouse model for DMD.
[show abstract][hide abstract] ABSTRACT: Recent progress has generated exciting results that are increasing the prospects for gene therapy of a variety of disorders of striated muscle, including the muscular dystrophies and myopathies, acquired and inherited diseases of cardiac muscle, and aging-associated muscle wasting. Numerous viral vector systems are being employed to transfer therapeutic genes to striated muscles, and advances in vector technology are leading to improved gene transfer efficiencies coupled with reduced immunological responses. The current technology in the field of viral vectors as tools for gene delivery to striated muscle is summarized, and recent developments related to gene therapies for skeletal and cardiac muscle disorders are discussed.
Current opinion in molecular therapeutics 10/2004; 6(5):491-8. · 3.42 Impact Factor
[show abstract][hide abstract] ABSTRACT: Vectors based on recombinant adeno-associated viruses (rAAV) have emerged as tools of choice for gene transfer to skeletal muscle. rAAV vectors demonstrate efficient, safe, and stable transduction. Multiple serotypes of AAV exist, but vectors based on serotype 2 (rAAV2) are the most thoroughly characterized and frequently employed. Here, we characterize transduction of the skeletal musculature using rAAV vectors pseudotyped with serotype 6 capsid proteins (rAAV6). We demonstrate that rAAV6 vectors can efficiently transduce the skeletal musculature of mice at levels >500-fold higher than is achievable with rAAV2 vectors and can readily saturate individual muscles following direct injection. Further, rAAV6 vectors are capable of transducing the diaphragm and intercostal muscles of mice after a simple injection into the intrathoracic cavity and are capable of widespread transduction throughout the musculature of mice injected in the intraperitoneal space as newborn pups. These results demonstrate that rAAV6 vectors hold great potential for use in gene delivery protocols targeting the skeletal musculature.
[show abstract][hide abstract] ABSTRACT: A major obstacle limiting gene therapy for diseases of the heart and skeletal muscles is an inability to deliver genes systemically to muscles of an adult organism. Systemic gene transfer to striated muscles is hampered by the vascular endothelium, which represents a barrier to distribution of vectors via the circulation. Here we show the first evidence of widespread transduction of both cardiac and skeletal muscles in an adult mammal, after a single intravenous administration of recombinant adeno-associated virus pseudotype 6 vectors. The inclusion of vascular endothelium growth factor/vascular permeability factor, to achieve acute permeabilization of the peripheral microvasculature, enhanced tissue transduction at lower vector doses. This technique enabled widespread muscle-specific expression of a functional micro-dystrophin in the skeletal muscles of dystrophin-deficient mdx mice, which model Duchenne muscular dystrophy. We propose that these methods may be applicable for systemic delivery of a wide variety of genes to the striated muscles of adult mammals.
Nature Medicine 09/2004; 10(8):828-34. · 22.86 Impact Factor
[show abstract][hide abstract] ABSTRACT: Molecular Therapy (2004) 9, S274–S274; doi: 10.1016/j.ymthe.2004.06.624
718. Systemic Gene Transfer to Striated Muscles Using rAAV6 Vectors
Paul Gregorevic1, Michael J. Blankinship1, James M. Allen1, Leonard Meuse1, Jay Han1, Suzanne Oakley1 and Jeffrey S. Chamberlain11Muscular Dystrophy Co-Operative Research Center, Department of Neurology, University of Washington, Seattle, WA
[show abstract][hide abstract] ABSTRACT: Vectors based on recombinant adeno-associated virus (rAAV) have garnered significant interest in gene replacement therapies for Duchenne muscular dystrophy. Several serotypes of rAAV have been shown to transduce skeletal muscle with high efficiency and low toxicity. These vectors suggest a possible therapeutic approach where dystrophin expression cassettes could be delivered to the striated musculature of an affected individual. However, a significant constraint inherent in rAAV vectors is their relatively small packaging capacity of approximately 5 kb. This packaging capacity is of great concern in attempting to deliver dystrophin via rAAV as the dystrophin cDNA is approximately 14 kb. This limitation has been overcome by engineering dystrophin proteins encompassing large deletions, which nonetheless remain highly functional. An additional concern in gene replacement therapies is the possibility of a patient's immune system viewing the therapeutic protein as a foreign antigen and raising a detrimental immune response, as the patient may not normally express the therapeutic protein. In Duchenne muscular dystrophy, a possible alternative to dystrophin replacement is utrophin over-expression. Utrophin is an autosommal homologue of dystrophin that is expressed in patients and should be viewed as a self antigen. Utrophin over-expression has been shown to functionally rescue a dystrophin deficient mouse model of muscular dystrophy, though the utrophin cDNA is also too large to be packaged into rAAV vectors without modification. Here we report and characterize a micro-utrophin protein based precisely on our previously reported, highly functional micro-dystrophin (ΔR4-R23/ ΔCT). Despite high, uniform expression and proper localization to the sarcolemma, this protein is not as efficient as micro-dystrophin in rescuing the dystrophic phenotype. Significant pathology is seen on a gross histological level despite restoration of DGC proteins to the sarcolemma. These findings highlight potential difficulties in micro-utrophin based therapies for Duchenne muscular dystrophy via rAAV, and suggest that domain engineering may be required to enable generation of a functional micro-utrophin/dystrophin hybrid.