Huntington’s disease is caused by the presence of an expanded CAG repeat region in the Huntingtin gene. Inheritance of a single copy of the mutant Huntingtin is sufficient to cause disease. The presence of mutant Huntingtin disrupts a large number of cellular pathways, causing neuronal disfunction and cell death. RNA interference provides a method for preventing the toxic effects of Huntingtin by reducing its expression. We are developing RNAi therapeutics to reduce Huntingtin in the brain. These include molecules which target the mutant Huntingtin specifically (allele-specific silencing) and those that aim to reduce total Huntingtin (gene-specific silencing).
One of the main challenges for RNAi therapeutics in the brain is delivery. We are working in close collaboration with faculty in the RNA therapeutics institutes to develop new technologies for delivering RNAi to the brain including novel siRNAs which enter the cell without transfection reagents. We are investigating the distribution and spread of various AAV serotypes and exploring ways to improve cellular uptake of recombinant AAVs.
Recent work has indicated that microvesicles called exosomes can be used to deliver siRNA through the blood brain barrier . We are investigating the use of exosomes for less invasive delivery of highly potent (hyperfunctional) siRNA.
In collaboration with Dr. Steve Miller, we are developing an in vivo reporter system to monitor RNA silencing in the brain. We use a virally delivered firefly luciferase reporter gene and in vivo imaging to visualize silencing in the living animal. This allows us to answer questions about dosing and activity over time and may allow us to compare different silencing molecules in the same animal.
We are investigating the distribution and spread of various AAV serotypes in a large animal (sheep) brain and exploring ways to improve entry of the virus into cells. In parallel we are exploring the safety and potency of AAV-delivered miRNAs in sheep models of Huntington’s disease.
In addition to our extensive work on RNA silencing of Huntingtin, we are investigating alternative methods for reducing Huntingtin protein. This might include methods to increase degradation of the mutant huntingtin protein, methods to inhibit translation of the mutant huntingtin mRNA and modifiers of mutant huntingtin toxicity.