28. rAAV2/9 Mediated Gene Delivery of Acid α-Glucosidase Corrects the Cardiac Phenotype in a Mouse Model of Pompe Disease

Abstract

Top of pageAbstract The long term goal of this project is to develop a clinically relevant gene therapy approach for the treatment of Pompe Disease. Pompe Disease is a form of muscular dystrophy and metabolic myopathy caused by mutations in the acid alpha glucosidase (GAA) gene. An insufficient amount of GAA leads to the accumulation of glycogen in lysosomes and consequent cellular dysfunction. Cardio-respiratory failure typically occurs in the early onset patients within the first year of life. We have characterized the cardiac phenotype in our mouse model (gaa-/-) at various ages. Through ECG analysis we observe a shortened PR interval by 3 months of age (gaa-/-33.41|[plusmn]|1.35ms, cont 44.95|[plusmn]|1.58ms) mimicking the conduction phenotype in the human Pompe population. Abnormal amounts of glycogen are observed in lysosomes as demonstrated by the periodic acid shift (PAS) stain. MRI analysis shows a decrease in stroke volume (SV)(gaa-/-36.13|[plusmn]|1.19ul, cont 51.84|[plusmn]|3.59ul) and a decrease in cardiac output (CO)(gaa-/-7.95|[plusmn]|0.26ml/min, cont 11.40|[plusmn]|0.79ml/ min) at 3 months and an increase in mass (gaa-/-181.99|[plusmn]|10.7mg, cont 140.79|[plusmn]|5.12mg) by 12 months. This model of cardiac dysfunction is being used to develop a cardiac gene delivery technique which can be applied to many genetically inherited cardiomyopathies. Previously, we have shown that intra-venous (IV) delivery of recombinant adeno-associated virus type 1 (rAAV2/1) pseudotype capsid carrying the CMV-hgaa construct to 1 day old gaa-/- neonates restores GAA activity in mice. Also, LacZ transgene delivery using the IV administration route and rAAV2/9 pseudotype capsid resulted in 200 fold higher levels of expression in cardiac tissue than rAAV2/1. Additional experiments showed transduction following delivery to adults. We have now combined rAAV2/9 with the clinically relevant IV administration route in order to deliver the human GAA (hgaa) gene to gaa-/- mice. Neonates treated with rAAV2/9-CMV-hgaa at a range of doses (4|[times]|105vg 4|[times]|108vg 4|[times]|1010vg) have demonstrated sustained PR interval correction (39.38|[plusmn]|2.42 ms). PAS stains as well as NMR analysis have shown less glycogen accumulation in cardiac tissue of treated gaa-/- mice as compared to untreated mice. MRI analysis shows an increase in SV and CO. Adult gaa-/- mice have also been treated using this strategy and are being assessed in order to determine if we have the ability to reverse the effects of Pompe Disease in mice already presenting the cardiac phenotype. While the focus of this project is on correction of the cardiac phenotype of Pompe Disease, our systemic delivery route, use of the CMV promoter and the fact that GAA is a secreted enzyme all promote correction throughout the body. GAA activity is observed in other tissues of treated mice including skeletal muscles and liver. These studies have demonstrated the ability of rAAV2/9 to be administered systemically using the IV delivery route, transcend the vasculature, transduce tissues throughout the body and ultimately prevent presentation of the cardiac phenotypes of Pompe Disease.