Sleeper, Margaret M

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Now showing 1 - 10 of 12
  • Publication
    Evaluation of Adeno-Associated Viral Vectors for Liver-Directed Gene Transfer in Dogs
    (2011-08-22) Bell, Peter; Haskins, Mark E; Gao, Guangping; Sleeper, Margaret M; Wang, Lili; Wang, Huan; Calcedo, Roberto; Vandenberghe, Luk H; Chen, Shu-Jen; Weisse, Chick; Withnall, Elanor; Wilson, James M
    This study evaluated six adeno-associated viral (AAV) vectors expressing green fluorescent protein (GFP) from the liver-specific thyroid hormone–binding globulin (TBG) promoter made with novel capsids in canine liver-directed gene transfer. Studies in 1.5-month-old dogs, which were administered vector through a peripheral vein, showed that AAV8 capsid vectors had the most favorable performance profiles. Interestingly, the absolute levels of hepatocyte transduction achieved with AAV8 were lower in dogs compared with what had been achieved in mice and nonhuman primates. Additional studies were performed with AAV8 delivered into the hepatic artery in adult dogs, with higher doses of vector used to assess potential dose-limiting toxicities. These studies showed good transduction on day 7 in one dog that apparently was lost by day 28 in another dog through the generation of GFP-specific T cells. Each adult dog was carefully monitored for any hemodynamic changes associated with vector infusion. Both animals demonstrated mild to moderate hypotension and bradycardia, which appeared to be anesthesia-related, making it difficult to evaluate contributions of the vector.
  • Publication
    Acute Vascular Occlusion in Horses: Effects on Skeletal Muscle Size and Blood Flow
    (2004-11-01) Abe, Takashi; Kearns, Charles F; Manso Filho, Hélio C; Sato, Yoshiaki; Sleeper, Margaret M; McKeever, Kenneth H
    The purpose of this study was to demonstrate whether acute vascular occlusion was safe and if it would result in changes to limb muscle size in horses. Six healthy, unfit Standardbred mares were used. Horses (standing at rest) wore an occlusion cuff at the most proximal position of the left forelimb. The right forelimb was used as control. An occlusion pressure of 200 mmHg was set for 5 min followed by a 2 min recovery. Three sets of occlusions were given to each horse. Muscle thickness was measured using B-mode ultrasound. The circumference of the forelimb and first phalanx was measured using a flexible tape measure. Pulsed-wave Doppler was performed on the radialis artery with a 5–10 MHz mechanical transducer at baseline and at each occlusion. Peak flow velocity (PFV) and the flow velocity integral (FVI) were measured each time. Mid-forelimb, but not first phalanx, girth was increased (P < 0.05) in the occluded but not in the control leg following occlusion. Extensor and flexor muscle thickness was increased (P < 0.05) in the occluded but not in the control leg. There were no changes (P > 0.05) in PFV or FVI at any measurement time point. Acute vascular occlusion may be a suitable and safe model for studying muscle hypertrophy in horses.
  • Publication
    Exploring Human/Animal Intersections: Converging Lines of Evidence in Comparative Models of Aging
    (2008-01-01) Trojanowski, John Q; Aguirre, Gustavo D; Jedrziewski, Kathryn; Johnson, F. Brad; Hess, Rebecka S; Cancro, Michael P; Sleeper, Margaret M; Pignolo, Robert; Lee, Virginia Man-Yee; Hendricks, Joan C; Pack, Allan I; Davies, Peter F; Michel, Kathryn E; Teff, Karen L; Lawler, Dennis F
    At a symposium convened on March 8, 2007 by the Institute on Aging at the University of Pennsylvania, researchers from the University’s Schools of Medicine and Veterinary Medicine explored the convergence of aging research emerging from the two schools. Studies in human patients, animal models, and companion animals have revealed different but complementary aspects of the aging process, ranging from fundamental biologic aspects of aging to the treatment of age-related diseases, both experimentally and in clinical practice. Participants concluded that neither animal nor human research alone will provide answers to most questions about the aging process. Instead, an optimal translational research model supports a bidirectional flow of information from animal models to clinical research.
  • Publication
    Myostatin Is Upregulated Following Stress in an Erk-Dependent Manner and Negatively Regulates Cardiomyocyte Growth in Culture and in a Mouse Model
    (2010-04-19) Bish, Lawrence T; Sleeper, Margaret M; Sweeney, H. Lee; Morine, Kevin J
    Myostatin is well established as a negative regulator of skeletal muscle growth, but its role in the heart is controversial. Our goal in this study was to characterize myostatin regulation following cardiomyocyte stress and to examine the role of myostatin in the regulation of cardiomyocyte size. Neonatal cardiomyocytes were cultured and stressed with phenylephrine. Adenovirus was used to overexpress myostatin or dominant negative myostatin in culture. Adeno-associated virus was used to overexpress myostatin or dominant negative myostatin in mice. Myostatin is upregulated following cardiomyocyte stress in an Erk-dependent manner that is associated with increased nuclear translocation and DNA binding activity of MEF-2. Myostatin overexpression leads to decreased and myostatin inhibition to increased cardiac growth both in vitro and in vivo due to modulation of Akt and NFAT3 pathways. Myostatin is a negative regulator of cardiac growth, and further studies are warranted to investigate the role of myostatin in the healthy and failing heart.
  • Publication
    Long-Term Systemic Myostatin Inhibition via Liver-Targeted Gene Transfer in Golden Retriever Muscular Dystrophy
    (2011-12-14) Bish, Lawrence T; Sleeper, Margaret M; Forbes, Sean C; Morine, Kevin J; Reynolds, Caryn A; Singletary, Gretchen E.; Trafny, Dennis; Pham, Jennifer; Bogan, Janet; Kornegay, Joe N; Sweeney, H. Lee; Vandenborne, Krista; Walter, Glenn A
    Duchenne muscular dystrophy (DMD) is a lethal, X-linked recessive disease affecting 1 in 3,500 newborn boys for which there is no effective treatment or cure. One novel strategy that has therapeutic potential for DMD is inhibition of myostatin, a negative regulator of skeletal muscle mass that may also promote fibrosis. Therefore, our goal in this study was to evaluate systemic myostatin inhibition in the golden retriever model of DMD (GRMD). GRMD canines underwent liver-directed gene transfer of a self-complementary adeno-associated virus type 8 vector designed to express a secreted dominant-negative myostatin peptide (n =4) and were compared with age-matched, untreated GRMD controls (n =3). Dogs were followed with serial magnetic resonance imaging (MRI) for 13 months to assess cross-sectional area and volume of skeletal muscle, then euthanized so that tissue could be harvested for morphological and histological analysis. We found that systemic myostatin inhibition resulted in increased muscle mass in GRMD dogs as assessed by MRI and confirmed at tissue harvest. We also found that hypertrophy of type IIA fibers was largely responsible for the increased muscle mass and that reductions in serum creatine kinase and muscle fibrosis were associated with long-term myostatin inhibition in GRMD. This is the first report describing the effects of long-term, systemic myostatin inhibition in a large-animal model of DMD, and we believe that the simple and effective nature of our liver-directed gene-transfer strategy makes it an ideal candidate for evaluation as a novel therapeutic approach for DMD patients.
  • Publication
    Chronic Losartan Administration Reduces Mortality and Preserves Cardiac but Not Skeletal Muscle Function in Dystrophic Mice
    (2011-06-22) Bish, Lawrence T; Sleeper, Margaret M; Yarchoan, Mark; Barton, Elisabeth R; Gazzara, Jeffrey; Sweeney, H. Lee; Morine, Kevin J; Acosta, Pedro
    Duchenne muscular dystrophy (DMD) is a degenerative disorder affecting skeletal and cardiac muscle for which there is no effective therapy. Angiotension receptor blockade (ARB) has excellent therapeutic potential in DMD based on recent data demonstrating attenuation of skeletal muscle disease progression during 6–9 months of therapy in the mdx mouse model of DMD. Since cardiac-related death is major cause of mortality in DMD, it is important to evaluate the effect of any novel treatment on the heart. Therefore, we evaluated the long-term impact of ARB on both the skeletal muscle and cardiac phenotype of the mdx mouse. Mdx mice received either losartan (0.6 g/L) (n = 8) or standard drinking water (n = 9) for two years, after which echocardiography was performed to assess cardiac function. Skeletal muscle weight, morphology, and function were assessed. Fibrosis was evaluated in the diaphragm and heart by Trichrome stain and by determination of tissue hydroxyproline content. By the study endpoint, 88% of treated mice were alive compared to only 44% of untreated (p = 0.05). No difference in skeletal muscle morphology, function, or fibrosis was noted in losartan-treated animals. Cardiac function was significantly preserved with losartan treatment, with a trend towards reduction in cardiac fibrosis. We saw no impact on the skeletal muscle disease progression, suggesting that other pathways that trigger fibrosis dominate over angiotensin II in skeletal muscle long term, unlike the situation in the heart. Our study suggests that ARB may be an important prophylactic treatment for DMD-associated cardiomyopathy, but will not impact skeletal muscle disease.
  • Publication
    Overexpression of SERCA1a in the mdx Diaphragm Reduces Susceptibility to Contraction-Induced Damage
    (2010-12-10) Sleeper, Margaret M; Barton, Elisabeth R; Morine, Kevin J; Sweeney, H. Lee
    Although the precise pathophysiological mechanism of muscle damage in dystrophin-deficient muscle remains disputed, calcium appears to be a critical mediator of the dystrophic process. Duchenne muscular dystrophy patients and mouse models of dystrophin deficiency exhibit extensive abnormalities of calcium homeostasis, which we hypothesized would be mitigated by increased expression of the sarcoplasmic reticulum calcium pump. Neonatal adeno-associated virus gene transfer of sarcoplasmic reticulum ATPase 1a to the mdx diaphragm decreased centrally located nuclei and resulted in reduced susceptibility to eccentric contraction-induced damage at 6 months of age. As the diaphragm is the mouse muscle most representative of human disease, these results provide impetus for further investigation of therapeutic strategies aimed at enhanced cytosolic calcium removal.
  • Publication
    Systemic Myostatin Inhibition via Liver-Targeted Gene Transfer in Normal and Dystrophic Mice
    (2010-02-11) Bish, Lawrence T; Sleeper, Margaret M; Morine, Kevin J; Barton, Elisabeth R; Sweeney, H. Lee; Pendrak, Klara
    Background: Myostatin inhibition is a promising therapeutic strategy to maintain muscle mass in a variety of disorders, including the muscular dystrophies, cachexia, and sarcopenia. Previously described approaches to blocking myostatin signaling include injection delivery of inhibitory propeptide domain or neutralizing antibodies. Methodology/Principal Findings: Here we describe a unique method of myostatin inhibition utilizing recombinant adeno-associated virus to overexpress a secretable dominant negative myostatin exclusively in the liver of mice. Systemic myostatin inhibition led to increased skeletal muscle mass and strength in control C57 Bl/6 mice and in the dystrophin-deficient mdx model of Duchenne muscular dystrophy. The mdx soleus, a mouse muscle more representative of human fiber type composition, demonstrated the most profound improvement in force production and a shift toward faster myosin-heavy chain isoforms. Unexpectedly, the 11-month-old mdx diaphragm was not rescued by long-term myostatin inhibition. Further, mdx mice treated for 11 months exhibited cardiac hypertrophy and impaired function in an inhibitor dose–dependent manner. Conclusions/Significance: Liver-targeted gene transfer of a myostatin inhibitor is a valuable tool for preclinical investigation of myostatin blockade and provides novel insights into the long-term effects and shortcomings of myostatin inhibition on striated muscle.
  • Publication
    Adeno-Assocated Virus (AAV) Serotype 9 Provides Global Cardiac Gene Transfer Superior to AAV1, AAV6, AAV7, and AAV8 in the Mouse and Rat
    (2008-12-01) Bish, Lawrence T; Sleeper, Margaret M; Morine, Kevin J; Sanmiguel, Julio; Wu, Di; Sweeney, H. Lee; Gao, Guangping; Wilson, James M
    Heart disease is the leading cause of morbidity and mortality. Cardiac gene transfer may serve as a novel therapeutic approach. This investigation was undertaken to compare cardiac tropisms of adeno-associated virus (AAV) serotypes 1, 6, 7, 8, and 9. Neonatal mice were injected with 2.5 × 1011 genome copies (GC) of AAV serotype 1, 6, 7, 8, or 9 expressing LacZ under the control of the constitutive chicken β-actin promoter with cytomegalovirus enhancer promoter via intrapericardial injection and monitored for up to 1 year. Adult rats were injected with 5 × 1011 GC of the AAV vectors via direct cardiac injection and monitored for 1 month. Cardiac distribution of LacZ expression was assessed by X-Gal histochemistry, and β-galactosidase activity was quantified in a chemiluminescence assay. Cardiac functional data and biodistribution data were also collected in the rat. AAV9 provided global cardiac gene transfer stable for up to 1 year that was superior to other serotypes. LacZ expression was relatively cardiac specific, and cardiac function was unaffected by gene transfer. AAV9 provides high-level, stable expression in the mouse and rat heart and may provide a simple alternative to the creation of cardiac-specific transgenic mice. AAV9 should be used in rodent cardiac studies and may be the vector of choice for clinical trials of cardiac gene transfer.
  • Publication
    Transcendocardinal Delivery of AAV6 Results in Highly Efficient and Global Cardiac Gene Transfer in Rhesus Macaques
    (2011-08-22) Bish, Lawrence T; Sleeper, Margaret M; Gao, Guangping; Mu, Xin; Sun, Lan; Lou, You; Duan, Jiachuan; Sweeney, H. Lee; Hu, Chunyan; Wang, Li
    Heart disease is the leading cause of morbidity and mortality, and cardiac gene transfer has potential as a novel therapeutic approach. We previously demonstrated safe and efficient gene transfer to the canine heart using a percutaneous transendocardial injection procedure to deliver self-complementary (sc) adeno-associated virus 6 (AAV6) vector. In the present study, we proceed with our vertical translation study to evaluate cardiac gene transfer in nonhuman primates (NHPs). We screened approximately 30 adult male rhesus macaques for the presence of neutralizing antibodies against AAV6, AAV8, and AAV9, and then selected seven monkeys whose antibody titers against these three serotypes were lower than 1/5. The animals were then randomized to receive either scAAV6 (n =3), scAAV8 (n =1), or scAAV9 (n =3) vector expressing the enhanced green fluorescent protein (EGFP) reporter gene at a dose of 5.4×1012 genome copies/kg, which was administered according to a modified version of our previously developed transendocardial injection procedure. One animal treated with scAAV6 died secondary to esophageal intubation. The remaining animals were euthanized 7 days after gene transfer, at which time tissue was collected for analysis of EGFP expression, histopathology, and biodistribution of the vector genome. We found that (i) transendocardial delivery of AAV is safe in the NHP, (ii) AAV6 and AAV8 provide efficient cardiac gene transfer at similar levels and are superior to AAV9, and (iii) AAV6 is more cardiac-specific than AAV8 and AAV9. The results of this NHP study may help guide the development AAV vectors for the treatment of cardiovascular disease in humans.