Adeno-Associated Serotype 5 -Gene Vector Therapy for Huntington’s Disease

Riti Kotamarti

Introduction. HD is a chronic and progressive neurodegenerative condition in which there is no known cure, and results in an early death. The prevalence of this disease is 10.6-13.7 cases per 100,000 people6. The disease pathology is due purely to a CAG trinucleotide repeat on chromosome 4. The trinucleotide repeat is translated into a polyglutamine structure in the N-terminus of the mutant HTT protein. This results in misfolding of the protein and aggregation, which disrupts the integrity of important neuronal pathways and can consequentially result in neuronal death, specifically in GABAergic medium spiny neurons10.  HD is shows a higher penetrance in clinical presentation with CAG repeats of 36-40 in length. Increased CAG repeats increases the manifestation of symptoms, which include motor dysfunction such as chorea, apathy, depression, and poor executive function6, 7,10. MiRNA has been used in a variety of gene therapy settings to target pathogenic mRNA9. Since HD pathology is due to a single genetic mutation, miRNA using an AAV-5 vector has been hypothesized to target HD mRNA and reduce protein aggregations7. Methods. Rats were injected with Lentivirus vectors recombined with polyglutamine genes to mimic the pathology of HD through protein aggregations7. Four separate miRNA constructs were created and recombined with AAV-5 vectors:  (injection1) miHTT-451 and miSNP67, (injection 2) miHTT-451 and miSN50T7. These miRNAs were chosen due to in vitro studies that showed miHTT constructs bound to and reduced the HD mRNA, while the miSNP constructs targeted specific SNPs seen in HD. 2 months post injection, cortical striatal sections were examined in order to see the efficacy of the miRNAs in reducing the polyglutamine aggregates7. Results: First injection (2-months post): saline control showed 2.4 × 106±0.4 × 106  number of aggregates. With use of the AAV5-miHT-155 vector, aggregates decreased from that number to 0.4 × 106±0.2 × 106. With use of AAV5-miSNP67T, aggregates decreased to 0.8 × 106±0.3 × 106. Second injection (2-months post):  similar results were seen with aggregate reduction of 98.1% for miHTT-451, and 77.3% for miSNP50T, compared to saline7. Conclusions. All four miRNA-AAV5 constructs were seen to reduce the number of protein aggregates in rats. This indicates that that the AAV5 vector was successful in both delivery and transduction of the miRNA. Further studies can examine the efficacy of this vector in primate models, and eventually develop a safe delivery method for human models to potentially reverse the pathogenesis of this disease.

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