Team:Austin UTexas LASA/Description
Description
What is Parkinson's Disease?
Parkinson’s disease is a neurodegenerative disorder characterized by the destruction of dopaminergic (dopamine producing) neurons in the substantia nigra in the brain. Dopamine acts as a neurotransmitter, a chemical messenger, between two brain areas, substantia nigra and the corpus striatum, to produce controlled movements. When there is a shortage of dopamine, the communication between the two areas becomes ineffective and the movement becomes impaired. In short, the greater the loss of dopamine, the worst the movement-related symptoms. These motor symptoms include shaking, rigidity, slowness of movement, impaired balance, and difficulty in walking. As symptoms get worse, talking, chewing, speaking, or swallowing may be difficult for an individual. Additionally, non-motor symptoms associated with Parkinson’s Disease include loss of sense of smell, cognitive impairment, and constipation. Emotional symptoms may include depression, apathy, and anxiety.
What are the current Treatments?
There are various ways to treat the symptoms of Parkinson’s disease. Deep brain stimulation surgery can stimulate parts of the brain that control movement. Tolcapone drugs inhibit the COMT enzyme that degrades dopamine. Dopamine agonists are less effective at controlling motor symptoms than Levodopa, but they are usually able to manage the symptoms in the first year of the treatment. MAO-B inhibitors increase the amount of dopamine in the basal ganglia by inhibiting the activity of monoamine oxidase B, an enzyme that breaks down dopamine (Jankovic and Aguilar). Regular exercise with or without physical therapy is another method that can improve mobility, flexibility, strength, gait speed, and quality life. In general, aerobic and learning-based exercises can be neuroprotective in aging individuals. Anything that requires large, rhythmical movements will decrease rigidity and will help to decrease bradykinesia, and combat Parkinson’s disease without the use of medication (Keus et. al.).
Presently, the most common and effective treatment for severe cases of Parkinson’s disease is Levodopa (L-DOPA) therapy, which increases dopamine levels by introducing dopamine’s chemical precursor, L-DOPA, into the bloodstream, often achieved using an oral capsule. Once in the bloodstream, L-DOPA can diffuse through the blood-brain barrier and be converted to Dopamine by L-DOPA Decarboxylase in the brain. Despite its efficacy, the prescription of L-DOPA therapy is often offset because after the “honeymoon” phase, in which certain symptoms are significantly reduced, the effectiveness of L-DOPA wears off over time, leading to “dopa resistant” motor symptoms. Furthermore, with oral capsules, additional side effects can result from fluctuating concentrations of L-DOPA in the bloodstream throughout the day before peak dosage, and after peak dosage due to the “wearing off effect.” These symptoms include bradykinesia, slowness of movement, other dyskinesias, involuntary movements, motor fluctuation, and nausea. Continuous dopaminergic stimulation (CDS), the constant release of L-DOPA, is sometimes used for very severe cases to prevent further symptoms resulting from the “wearing off effect” (Jankovic and Aguilar). A common application of CDS is Duodopa, a portable pump that administers a continuous mixture of L-DOPA and Carbidopa, an L-amino acid decarboxylase inhibitor, directly into the duodenum or jejunum (part of the small intestine) via a surgically implanted tube (Karlsborg et. al.).
What is our project?
The goal of our project is to develop a bacteria-based method of L-DOPA dosage by using E. coli as a chassis for a genetic circuit that both produces and self-regulates the production of L-DOPA. This bacterial treatment method would ideally provide a less invasive method of continuous dopaminergic stimulation than a jejunal pump while bypassing the “wearing off symptoms associated with oral treatment. To achieve this goal we constructed a multigene plasmid that served two primary purposes: Produce L-DOPA and detect the produced L-DOPA and produce an indicator in response. The production portion of the plasmid consists of the genes HpaB and HpaC (4-hydroxyphenylacetate 3-hydroxylase) from E. Coli with the pA3 promoter and the rpoC terminator. HpaB and HpaC produce two monomeric subunits of a protein complex responsible for the production of L-DOPA in E. coli by catalyzing the addition of a hydroxyl group to the amino acid Tyrosine. The sensing circuit consists of the fluorescent protein Venus which is regulated by the promoter ppddc, and the gene PP2551, which encodes the transcription factor that binds to ppddc (Thyer). PP2551 is regulated by the CP25 promoter with LacO to prevent expression prior to initiation during experimentation with IPTG. When the transcription factor encoded by PP2551 binds to ppddc it increases the transcription of the downstream gene, leading to increased production of Venus fluorescent protein which is measured using a plate reader.
While our project currently only produces and detects L-DOPA it tests this circuit’s efficacy as a method of using L-DOPA to regulate its own production in order to supply a constant and consistent supply of L-DOPA in a non-invasive manner. With that goal in mind future improvements include adding a genetic “kill switch” for safety and containment purposes and having the transcription factor coded for by PP2551 directly control L-DOPA production by HpaB and HpaC.
References
"Genetics and Parkinson's Disease." The Michael J. Fox Foundation for Parkinson's Research | Parkinson's Disease. N.p., n.d. Web.
Heyn, PhD Sietske N. "Parkinson's Disease: 17 Early Signs, Symptoms & Treatment." MedicineNet. N.p., n.d. Web.
Jankovic, Joseph, and L. Giselle Aguilar. "Current Approaches to the Treatment of Parkinson’s Disease." Neuropsychiatric Disease and Treatment. Dove Medical Press, Aug. 2008. Web.
Karlsborg, Merete, Lise Korbo, Lisbeth Regeur, and Arne Arne Glad. "Duodopa Pump Treatment in Patients with Advanced Parkinson‘s Disease." Danish Medical Bulletin (2010): 1-6. Danish Medical Journal. Web.
Keus, Samyra H.J., Bastiaan R. Bloem, Erik J.M. Hendriks, Alexandra B. Bredero‐Cohen, and Marten Munneke. "Evidence‐based Analysis of Physical Therapy in Parkinson's Disease with Recommendations for Practice and Research." Movement Disorders. Wiley Subscription Services, Inc., A Wiley Company, 28 Nov. 2006. Web.
"Parkinson's Disease | PD | MedlinePlus." MedlinePlus Trusted Health Information for You. N.p., n.d. Web.
"What Is Parkinson's?" Parkinson's Foundation. N.p., 18 Oct. 2017. Web.
iGEM teams are encouraged to record references you use during the course of your research. They should be posted somewhere on your wiki so that judges and other visitors can see how you thought about your project and what works inspired you.
