Advances in gene-based therapy for heart failure

Role of Purine-Rich Regions in Mason-Pfizer Monkey Virus (MPMV) Genomic RNA Packaging and Propagation

A distinguishing feature of the Mason-Pfizer monkey virus (MPMV) packaging signal RNA secondary structure is a single-stranded purine-rich sequence (ssPurines) in close vicinity to a palindromic stem loop (Pal SL) that functions as MPMV dimerization initiation site (DIS). However, unlike other retroviruses, MPMV contains a partially base-paired repeat sequence of ssPurines (bpPurines) in the adjacent region. Both purine-rich sequences have earlier been proposed to act as potentially redundant Gag binding sites to initiate the process of MPMV genomic RNA (gRNA) packaging. The objective of this study was to investigate the biological significance of ssPurines and bpPurines in MPMV gRNA packaging by systematic mutational and biochemical probing analyses. Deletion of either ssPurines or bpPurines individually had no significant effect on MPMV gRNA packaging, but it was severely compromised when both sequences were deleted simultaneously. Selective 2′ hydroxyl acylation analyzed by primer extension (SHAPE) analysis of the mutant RNAs revealed only mild effects on structure by deletion of either ssPurines or bpPurines, while the structure was dramatically affected by the two simultaneous deletions. This suggests that ssPurines and bpPurines play a redundant role in MPMV gRNA packaging, probably as Gag binding sites to facilitate gRNA capture and encapsidation. Interestingly, the deletion of bpPurines revealed an additional severe defect on RNA propagation that was independent of the presence or absence of ssPurines or the gRNA structure of the region. These findings further suggest that the bpPurines play an additional role in the early steps of MPMV replication cycle that is yet to be identified.

An attenuated coxsackievirus b3 vector: a potential tool for viral tracking study and gene delivery

Cardiomyocytes are quite resistant to gene transfer using standard techniques. We developed an expression vector carrying an attenuated but infectious and replicative coxsackievirus B3 (CVB3) genome, and unique ClaI-StuI cloning sites for an exogenous gene, whose product can be released from the nascent viral polyprotein by 2A(pro) cleavage. This vector was tested as an expression vehicle for green fluorescent protein (GFP). The vector transiently expressed GFP in cell cultures for at least ten passages and delivered functional GFP to the infected cardiomyocytes for at least 6 days. Moreover, the recombinant viruses showed virulence attenuation in vitro and in vivo. The findings suggest that the recombinant CVB3 vector could be a useful tool for viral tracking study and delivering exogenous proteins to cardiomyocytes.

AAV-microdystrophin therapy improves cardiac performance in aged female mdx mice

Dystrophin deficiency leads to lethal dilated Duchenne cardiomyopathy. A promising therapy is to deliver a highly abbreviated microdystrophin gene to the heart using adeno-associated virus (AAV). Microdystrophin has been shown to mitigate dystrophin-deficient skeletal muscle disease. However, it is not clear whether microdystrophin is equally effective in treating Duchenne cardiomyopathy. To evaluate microdystrophin therapy in the heart, we injected 5 × 10(12) viral genome particles/mouse of AAV-9 ΔR4-23/ΔC microdystrophin vector via tail vein to ~16-20-month-old (average 18.7-month-old) female mdx mice, a manifesting model of Duchenne cardiomyopathy. Cardiac transduction and heart function were examined at 2-8 months after gene transfer. We observed robust myocardial microdystrophin expression. Electrocardiography (ECG) and left ventricular catheter hemodynamic assays also revealed significant improvement. Furthermore, AAV-microdystrophin therapy prevented dobutamine-stress induced acute cardiac death. We demonstrate for the first time that AAV microdystrophin therapy significantly ameliorates functional deficiency in a phenotypic model of Duchenne cardiomyopathy. Our results support further exploration of microdystrophin therapy to treat Duchenne cardiomyopathy.