Gene Therapy for Alzheimer's Disease
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Imagine that in fifty years, people no longer fear forgetting how to make a sandwich, driving to the store without getting lost, or no longer recognizing loved ones; that's a future people can look forward to when Alzheimer's disease has been eradicated by gene therapy. Alzheimer's is a type of dementia that affects people worldwide as well as those who love them. Gene therapy, the transplantation of normal genes into cells to replace defective ones, is a promising treatment for correcting the underlying causes of the disease instead of just controlling its horrendous symptoms.
Alzheimer's is a disease for which there is currently no cure. Symptoms of the disease include problems remembering newly learned information, confusion, memory loss, behavioral changes and much more (Alzheimer's). Currently available treatments only help to delay the progression of symptoms and improve the quality of life for those it affects. It is imperative that progress be made in treating the disease considering that Alzheimer's is the most common form of dementia, accounting for between sixty to eighty percent of dementia cases, affecting over forty million people worldwide, and being the sixth main cause of death in the United States (Brazier, 2016). However, in order to be effective in combating this degenerative brain disease, researchers must first understand the underlying causes.
Researchers at the Stanford University School of Medicine as well as in the United Kingdom have found a protein fragment that they believe is a factor in causing Alzheimer's: the beta-amyloid protein, AB. AB by itself is not detrimental to the health of the human brain; however, when the concentration of AB in the brain increases, the protein begins destroying synapses before clumping into plaques that ultimately lead to nerve cell death (Goldman, 2013). Scientists at Stanford found that as long as AP is in its soluble form it can travel freely in the brain without negative consequences. However, in its insoluble, clustered form, called plaques, AB can bind to receptors on nerve cells, starting a process that erodes the synaptic connections between cells (Goldman, 2013). AB is generated by the cleavage of the amyloid precursor protein, APP, by the enzyme B-secretase. It was found, in research conducted by S. Herbert, et. al., that the expression of the enzyme B-secretase is Alzheimer's patients than in people without Alzheimer's. B-secretase is the rate determining step in the production of AB, therefore a reduction in the expression of B-secretase is expected to reduce AB concentration in the brain and maintain a harmless, soluble level, and thus destructive plaques will not be created.
Researchers began to develop a new gene therapy that could prevent the accumulation of AB in the brain. The discovery that the PPARy-coactivator-1a, PGC-1a, gene, whose expression is reduced in Alzheimer's patients, regulates the transcription of B-secretase (Katsouri, 2016), allowed researchers to start working on a gene therapy to increase PGC-1a expression, thereby reducing B-secretase in the brain. Using mice as models of Alzheimer's, researchers experimented with creating a lentiviral vector to express PGC-1a and replace damaged genes with healthy ones in patients' brain cells. The mice, called APP23 mice, were bred to develop AB plaques in their brains that increase in size as they age, similar to the way AB plaques in Alzheimer's patients behave (Katsouri, 2016). The similarities between the brains of these mice and those of Alzheimer's patients allowed the researchers to experiment with the lentiviral vector they developed and observed the effect the ehalthy gene had on the brains of the mice. It was found that, four months after the injection of the PGC-1a carrying lentiviral vector, the mice showed remarkable improvement in spatial and recognition memory as well as significant reduction in AB deposition and B-secretase expression (Katsouri, 2016). The researchers also found that the treatment had neuroprotective effects and helped to preserve neurons and synapses that, without treatment, were being destroyed. Based on the results they observed, L. Katsouri, et. al., were able to conclude that selective induction of PGC-1a in specific areas of the brain is effective in targeting Alzheimer's-related neurodegeneration and holds great potential as a therapeutic threatment for this disease.
Unlocking the genetic code has been one of the greatest scientific advancements of this age. Treatments such as gene therapy can be used to treat many of the maladies we face and the importance of research in this field cannot be overstated. Utilizing gene therapy, Alzheimer's may no longer cause trepidation as we age.
Alzheimer's Association. (n.d.). Alzheimer's Disease & Dementia. Retrieved March 01, 2017, from http://www.alz.org/alzheimers_disease_what_is_alzheimers.as
Brazier, Y. (2016, October 11). Gene therapy could prevent Alzheimer's, study suggests. Retrieved March 1, 2017, from http://www.medicalnewstoday.com/articles/313412.php
Herbert, S. S., Horre, K., Nicolai, L., Papadopoulou, A. S., Mandemakers, W., Silahtaroglu, A. N., . . . Strooper, B. D. (2008). Loss of microRNA cluster miR-29a/b-1 in sporadic Alzheimer's disease correlates with increased BACE1/ -secretase expression. Proceedings of the National Academy of Sciences, 105(17), 6415-6420. doi: 10.1073/pnas.0710263105
Goldman, B. (2013, September 19). Scientists reveal how beta-amyloid may cause Alzheimer's. Retrieved March 01, 2017, from http://med.stanford.edu/news/all-news/2013/09/scientists-reveal-how-beta-amyloid-may-cause-alzheimers.html
Katsouri, L., Lim, Y. M., Blondrath, K., Eleftheriadou, I., Lombardero, L., Birch, A.M., . . . Sastre, M. (2016). PPARy-coactivator-1a gene transfer reduces neuronal loss and amyloid-B generation by reducing B-secretase in an Alzheimer's disease model. Proceedings of the National Academy of Sciences, 113(43), 12292-12297. doi: 10.1073/pnas.1606171113
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