Huntington’s disease is currently the subject of extensive research which is being carried out to understand the mechanism of the huntingtin (Htt) protein and how exactly its mutation causes brain damage.
Much focus has been placed on identifying how Htt functions and how mutated Htt (mHtt) interrupts this function and causes brain disease. Studies conducted so far have included in vitro studies, animal models and human volunteers. Animal models are essential for elucidating the basic mechanisms of this disease and for the early stages of developing treatments. Originally, these animal models included animals with chemically induced brain damage that led the animals to exhibit symptoms similar to those seen in Huntington’s disease. However, these models could not reflect the progressive nature of the disease.
Since then, identification of the HTT gene, has meant that transgenic animal models could be developed that express the mutated huntingtin and therefore demonstrate neurodegenerative symptoms and other features of the disease as it progresses. Examples of animals in which these models have been achieved include nematode worms, Drosophila fruit flies, pigs, mice, sheep, rats and monkeys.
Currently, research is focused on three main areas to try and understand how the progression of Huntington’s disease can be slowed down. These include how to reduce production of the mutant huntingtin protein, how to improve a cell’s ability to survive the damaging effects, and how to replace neurons that have been lost.
Gene silencing is one area that is being studied as a means of reducing production of the mutated protein. This aims to stop the expression of the one dominant gene that codes for mHtt. In murine models, silencing of mHtt leads to an improvement in symptoms and the safety of gene silencing has now been demonstrated in primates.
Examples of techniques being studied to improve cellular survival of mHtt are modification of transcriptional regulation using histone deacetylase inhibitor; enhancing metabolism and mitochondrial function and rectifying dysfunctional synapses.
With regard to neuronal replacement, stem cell transplantation to replace damaged neurons has proved successful to varying degrees in different studies of animals and humans. Although the future of stem cell therapy as a potential treatment is still undecided, the technique does provide a useful tool for current research into the disease.