Gene Therapy Rescues Cardiac Dysfunction in Duchenne Muscular Dystrophy Mice by Elevating Cardiomyocyte Deoxy-Adenosine Triphosphate

Figures

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  Figure 1. Overview of Experimental Design for the Treatment of Aged (22-24 Month) mdx4cv Mice (A) Graphic representation of rAAV6 vectors used in the present study. The ribonucleotide reductase vector contains the human cDNA for the RRM1 and RRM2 subunits whose expression is driven by the cardiac specific (cTnT455) regulatory cassette (RC). The human microdystrophin (ΔR2-R15/ΔR18-R22/ΔCT) vector has expression driven by the CK8 muscle-specific RC. The control vector used in the present study carries the firefly luciferase transgene whose CMV early promoter/enhancer RC has been deleted. (B) Outline of animal enrollment, vector administration, and experimental protocols implemented following a treatment period of 5 months. cDNA = complementary DNA; CMV = cytomegalovirus; ITR = inverted terminal repeat; dATP = deoxy-adenosine triphosphate; p2A = porcine teschovirus-1 2A; pA = poly-adenylation; qPCR = quantitative polymerase chain reaction; rAAV6 = recombinant adeno-associated viral vector 6; RC = regulatory cassette; WT = wild-type.

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  Figure 2. Pressure-Volume Relationships in Isolated Perfused Hearts From Vector-Treated mdx4cv Mice Hearts were isolated from mdx4cv mice treated with control vector (mdx4cv, n = 6), ribonucleotide reductase (mdx4cv+ RNR, n = 6), or microdystrophin (mdx4cv+ μDys, n = 5). Age-matched, nondiseased, nontreated wild-type (WT) mice were used as control subjects (n = 8). The pressure-volume relationship (i.e., Frank-Starling mechanism) was evaluated by gradually increasing the volume of the left ventricular (LV) balloon. Hearts were paced at 450 beats/min throughout the protocol. (A) Left ventricular systolic pressure (LVSP). (B) LV end-diastolic pressure (LVEDP). (C) LV developed pressure (LVDevP, the difference between systolic and diastolic pressures). (D) Positive (pos) rate of pressure change was calculated by the first derivative of the ascending LV pressure wave (+dP/dt), and is used as an index of ventricular contractility. (E) Negative (neg) rate of pressure change calculated by the first derivative of the descending LV pressure wave (–dP/dt), and is used as an index of ventricular relaxation. * p < 0.05 mdx4cv versus WT; # p < 0.05 mdx4cv+ RNR versus mdx4cv; † p < 0.05 mdx4cv+ μDys…

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  Figure 3. The Response of Vector-Treated mdx4cv Mice to High Workload Challenge in Langendorff Isolated Heart Preparations Hearts were isolated from mdx4cv mice treated with control vector (mdx4cv, n = 6), ribonucleotide reductase (mdx4cv+ RNR, n = 6), or microdystrophin (mdx4cv+ μDys, n = 5). Age-matched, nondiseased, nontreated wild-type (WT) mice were used as control subjects (n = 4). All hearts were perfused with a glucose-pyruvate buffer containing high calcium (4.0 mmol/l) to simulate a high workload challenge for 20 min. Hearts were paced at 450 beats per minute throughout the protocol. (A) LVDevP (the difference between systolic and diastolic pressures). (B) Rate pressure product (RPP, the product of LVDevP and HR). (C) Positive rate of pressure change calculated by the first derivative of the ascending LV pressure wave (+dP/dt), is used as an index of ventricular contractility. (D) Negative rate of pressure change calculated by the first derivative of the descending LV pressure wave (–dP/dt), is used as an index of ventricular relaxation. * p < 0.05 mdx4cv versus WT; # p < 0.05 mdx4cv+ RNR versus mdx4cv; † p < 0.05 mdx4cv+ μDys versus mdx4cv. Abbreviations as in Figures 1 and 2.

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  Figure 4. Cardiac Transduction Following Intravenous Delivery of Ribonucleotide Reductase or Microdystrophin At 5 months after vector administration, cryosections were prepared and immunostained with antisera against dystrophin or ribonucleotide reductase. A considerable level of protein is detected for each ribonucleotide reductase subunit-1 (human specific) as indicated by immunofluorescent staining (red) localized primarily within the cytoplasm of cardiomyocytes with occasional perinuclear accumulation (upper panel). On the lower panel, the robust level of expression for dystrophin in WT and in aged mdx4cv mice treated with AAV6-CK8-μDys (laminin staining, inset image). Abbreviations as in Figures 1 and 2.

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  Figure 5. Heart Histologic Staining of mdx4cv Mice Suggests No Morphologic Alterations From RNR Therapy Representative full-view photomicrographs of Masson trichrome staining of the hearts from mdx4cv mice displaying control vector (ΔCMV), and rAAV6-treated with either RNR or μDys from mdx4cv mice. Similarly, a 20× enlarged view of the corresponding images (*) is shown. Abbreviations as in Figures 1 and 2.

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  Figure 6. Protein Expression Levels for μDys, RNR, and Resultant Vector Genomes Due to rAAV6-Mediated Gene Transfer (A) RNR and μDys protein expression detection as revealed by immunoblotting of cardiac whole tissue lysates using either RRM1, RRM2, or antidystrophin antibody. (B) HPLC-MS/MS intracellular [dNTP] quantification from methanol extracted cardiac tissue. (C) qPCR analysis of vector genomes from cardiac tissue revealed similar vector genomes being represented for all treated cohorts. dNTP = deoxynucleotide triphosphate; HPLC-MS/MS = high-performance liquid chromatography–tandem mass spectrometry; qPCR = quantitative polymerase chain reaction; other abbreviations as in Figures 1 and 2.