FUTURE DIRECTIONS
My future directions and primary goal is to discover a new and safer treatment for children with Tourette’s syndrome. These genetic approaches will cover the hypothesis that biological levels of neurotransmitters can be affected by novel compounds to rescue Tourette phenotypes and lead to further studies on this disease.
Tourette syndrome is a non-debilitating disease that affects 1-10 in every 1,000 children worldwide. Although current treatments do exist, the medications do not target any one gene or protein specific to the disease. Medications on today’s market include neuroleptic or antipsychotic medications. These treatments negate motor and vocal tics, attention deficits and compulsive feelings in patients with Tourette’s, however they are not safe for children or for long-term usage.
Modafinil is a current drug on the market that has shown to oppose the biological characteristics of Tourette’s syndrome. Modafinil works by raising the levels of histamine and dopamine in the brain. I propose that Modafinil regulates the expression of Hdc RNA and protein levels. My primary goal is to use a focused chemical genetic screen, similar to Modafinil, to identify drugs that regulate HDC function directly. This compound will potentially negate Hdc mutant phenotypes. |
AIM 1: To determine other cellular targets of HDC function in the brain.
The mutation in the gene Hdc has shown to cause symptoms of Tourette's by altering levels of histamine in the brain. In direct relation with histamine is another neurotransmitter, dopamine. Drug treatments for this disorder could be expanding on by discovering new targets within the brain. After researching function of histidine decarboxylase the brain, similar functions should be easy to find in other genes or cells. Functions that would be valuable in this study include neurotransmitter production of either histamine or dopamine, or the process of increasing sensitivity of channels and binding partners to the already present levels of neurotransmitters.
To test this theory of other HDC targets I would have to choose a model organism. For my experiments I plan to use zebrafish because of their striking similarity in neurotransmitter levels. The Hdc mutant zebrafish has the same phenotype of lower levels of histamine and dopamine in the brain. First, I would perform an RNA seq analysis on wild type zebrafish as well as an Hdc mutant zebrafish. RNA seq analysis will help confirm various cell types that interact with HDC directly. Following the analysis, the data set will be run through GSEA software where these new interacting partners will be grouped into similar categories based on function. My hypothesis is that new found targets will be able to regulate histamine and dopamine levels and can be manipulated through new compounds.
APPROACH
RNA seq analysis will be performed on healthy zebrafish and Hdc mutant zebrafish. Their transcriptomes will be viewed and categorized for interactions with a healthy copy of HDC and the mutated HDC copy.
|
GSEA analysis of the data from RNA seq groups the interacting cell types into categories based on function. Some of these functions can be assumed from GO terms determined earlier in my research. A few are listed here:
1. Histidine metabolic processes 2. Biosynthetic pathways of neurotransmitter production 3. Binding and communication pathways within the brain |
AIM 2: To identify chemical compounds which regulate HDC function
Drugs used on the market today for Tourette syndrome do not eliminate or suppress all symptoms of this disorder. However, during my research I discovered Modafinil. Modafinil is currently a drug used for narcoleptic patients. However, the chemical mechanism relates directly to Tourette's characteristics. This compound raises histamine and dopamine levels in the brains of individuals with sleeping disorders. This, in turn, provides them with an awake and focused yet relaxed state of mind. I believe other compounds such as Modafinil would be able to negate symptoms in Tourette's patients as well, without the many side effects of antipsychotics.
APPROACH
To discover new compounds that target the types of cellular functions listed above I would begin to develop a focused genetic drug screen. A focused library is a collection of compounds that are similar in structure to my chemical of interest, in this case Modafinil. Some R groups may be changed or the number of carbons extended, but the same idea is there because I want to hit similar targets as Modafinil. Each new compound would be incorporated into the water of a small set of Hdc mutant zebrafish. After the dosing period the fish would be screened for increased levels of histamine and dopamine. Compounds that display this positive phenotype will then move on to dosing trials and additional experiments to determine their targets.
To the left is a visual of the process of a screen that will be used to determine the effectiveness of the new compounds on the neurotransmitter levels in the brain.
First, if my target protein (histidine decarboxylase) does not interact at all with my chemical derivative of Modafinil then I will view the wild type phenotype. This would be the case in a non-mutated form of Hdc. Second, if I knock out my gene of interest or mutate the protein product and my interacting chemical binds correctly, I will view a rescued phenotype. Starting with a mutated model, I incorporate the chemical derivative and ultimate treat the discrepancy. In my experiment I would hope to see the an increase in the levels of histamine and dopamine in the brain. Finally, if I start with a mutated gene or protein and my interacting chemical derivative does not bind correctly or influence the brain chemistry, I will view the disease phenotype in my model. This is the model that will correlate with patients of Tourette syndrome who are not being treated. |
FUTURE EXPERIMENTS
In conclusion with my experiments above, a new drug could potentially be discovered that will interact with new interacting partners of HDC and rescue the phenotype associated with Tourette syndrome. These would include common tics and the neurotransmitter levels in the brain. To continue on with this study phase one trials would be put into action. The molecule discovered will be put into different model organisms and tested again for it's restorative functions.
Another area of study that would be interesting to look at are histidine decarboxylase interacting partners with the same protein domain, Peridoxyl_deC. In my STING analysis I found DDC, a protein necessary for the biological process of dopamine and serotonin synthesis. If DDC is not found to be a new target in the RNA seq experiment above, this would be the next step in finding new therapeutic drug targets. Below I have included an image of the STRING association of DDC and HDC.
Another area of study that would be interesting to look at are histidine decarboxylase interacting partners with the same protein domain, Peridoxyl_deC. In my STING analysis I found DDC, a protein necessary for the biological process of dopamine and serotonin synthesis. If DDC is not found to be a new target in the RNA seq experiment above, this would be the next step in finding new therapeutic drug targets. Below I have included an image of the STRING association of DDC and HDC.
PDF copy of Tourette syndrome & HDC gene presentation
hdc_presentation.pdf | |
File Size: | 1274 kb |
File Type: |
University of Wisconsin – Madison
Spring 2014 Genetics 564 |
|