Comparative impact of AAV and enzyme replacement therapy on respiratory and cardiac function in adult Pompe mice

Abstract

Pompe disease is an autosomal recessive genetic disorder characterized by a deficiency of the enzyme responsible for degradation of lysosomal glycogen (acid α-glucosidase (GAA)). Cardiac dysfunction and respiratory muscle weakness are primary features of this disorder. To attenuate the progressive and rapid accumulation of glycogen resulting in cardiorespiratory dysfunction, adult Gaa (-/-) mice were administered a single systemic injection of rAAV2/9-DES-hGAA (AAV9-DES) or bimonthly injections of recombinant human GAA (enzyme replacement therapy (ERT)). Assessment of cardiac function and morphology was measured 1 and 3 months after initiation of treatment while whole-body plethysmography and diaphragmatic contractile function was evaluated at 3 months post-treatment in all groups. Gaa (-/-) animals receiving either AAV9-DES or ERT demonstrated a significant improvement in cardiac function and diaphragmatic contractile function as compared to control animals. AAV9-DES treatment resulted in a significant reduction in cardiac dimension (end diastolic left ventricular mass/gram wet weight; EDMc) at 3 months postinjection. Neither AAV nor ERT therapy altered minute ventilation during quiet breathing (eupnea). However, breathing frequency and expiratory time were significantly improved in AAV9-DES animals. These results indicate systemic delivery of either strategy improves cardiac function but AAV9-DES alone improves respiratory parameters at 3 months post-treatment in a murine model of Pompe disease.

Figure 1

Effects of AAV9-DES or continuous enzyme replacement therapy (ERT) on animal weight gain and cardiac characteristics at 1 and 3 months. (a) AAV9-DES or ERT did not significantly improve animals’ weights until 3 months after study initiation (P > 0.05). (b) Detection of ejection fraction (EF%) and (c) end diastolic cardiac mass/gram wet weight (EDM/c) at 4.7-T were not significantly altered compared to Gaa^–/– following 1 month of therapy. (b) ERT and AAV9-DES resulted in a significant increase in EF% at 3 months. (c) EDM/c was significantly reduced at 3 months in AAV9-DES-treated animals. (d) Elongation of PR interval was significant following AAV9-DES at 3 months post-treatment. Values indicated are the mean ± SEM. *P ≤ 0.05. **P ≤ 0.01. ***P ≤ 0.001. ****P ≤ 0.0001. θ = wild-type at 6 months.

Figure 2

Whole-body plethysmography during eupnea. AAV9-DES resulted in significant changes in (a) breathing frequency when compared to Gaa^–/– or enzyme replacement therapy (ERT). No significant change was detected in (b) minute ventilation, (c) tidal volume, or (d) inspiratory time. AAV9-DES treatment significantly decreases (e) expiratory time and increased the (f) total respiratory cycle time. Values indicated are the mean ± SEM. *P ≤ 0.05. **P ≤ 0.01.

Figure 3

Diaphragmatic force-frequency response (in vitro) of costal diaphragm. AAV9-DES and enzyme replacement therapy (ERT) groups demonstrated a significant increase in force generating capacity of diaphragm myofibers ≥ 60 Hz when compared to Gaa^–/–. AAV9-DES and ERT remained significantly lower than wild-type samples ≥ 60 Hz. Values indicated are the mean ± SEM. *WT = P ≤ 0.05 versus AAV9-DES or ERT. **AAV9-DES = P ≤ 0.01 versus Gaa^–/–. ***AAV9-DES or ERT = P ≤ 0.001 versus Gaa^–/–. ****AAV9-DES = P ≤ 0.0001 versus Gaa^–/–. ^####ERT = P ≤ 0.0001 versus Gaa^–/–. n.s., not significant.

Figure 4

GAA antibody titers following systemic AAV9-DES or continuous ERT therapy. Continuous enzyme replacement therapy (ERT) administration resulted in significant elevation of GAA antibody titers at 3 weeks, 2 months, and 3 months when compared to naive Gaa^–/–. ERT-generated GAA antibody titers were significantly increased at 2 months when compared to AAV9-DES treated Gaa^–/– animals. Values indicated are the mean ± SEM. ^#ERT = P ≤ 0.05 versus Gaa^–/–. ^##ERT = P ≤ 0.01 versus Gaa^–/–. ****AAV9-DES = P ≤ 0.0001 versus Gaa^–/–. ^####ERT = P ≤ 0.0001 versus Gaa^–/–. n.s., not significant; GAA, acid α-glucosidase.

Figure 5

Vector genome quantification of AAV9 following systemic injection. Detection of vector copy number was significantly increased in cardiac, diaphragm, and spinal cord following AAV9 administration. Values indicated are the mean ± SEM. **AAV9-DES = P ≤ 0.01 versus Gaa^–/–.

Figure 6

GAA enzymatic activity following systemic AAV9-DES or continuous enzyme replacement therapy (ERT) therapy. GAA activity in the heart, diaphragm, and costal muscle 3 months following AAV9-DES or ERT (2 weeks after final ERT administration). AAV9-DES administration resulted in significant detection of GAA in lysates of the heart, diaphragm, and costal muscle compared to Gaa^–/–. Values indicated are the mean ± SEM. * = P ≤ 0.05. ** = P ≤ 0.01. **** = P ≤ 0.001. n.s., not significant; GAA, acid α-glucosidase.

Figure 7

Glycogen accumulation in the myocardium and diaphragm. At 6 months of age, significant accumulation of glycogen is apparent in the Gaa^–/– (b) myocardium and (f) diaphragm when compared to control (a) and (e), ERT (d) and (h), respectively. Reduction of glycogen in the myocardium and diaphragm of AAV9-DES (c and g, respectively) was not significantly elevated compared to WT. Quantification of glycogen content in the fraction of region of interest is presented for the myocardium (i) and diaphragm (j). Inset = 2× magnification. *WT = P ≤ 0.05 versus Gaa^–/– or ERT. **WT = P ≤ 0.01 versus ERT. ERT, enzyme replacement therapy; WT, wild type.