Aptamers against the Dopamine Transporter (DAT) to Alleviate Symptoms of Parkinson’s Disease

The dopamine transporter (DAT) protein is responsible for controlling the level of dopamine in the body by taking it out of the synapse and putting it back into presynaptic neurons, where the neurotransmitter is then stored and released by vesicles. Returning dopamine to the transmitting neuron terminates the neurotransmitter’s signal (Huang and Zahn 2007). All dopamine-mediated behaviors and motor activities are dependent on DAT and its ability to successfully bind with adequate amounts of the neurotransmitter. Any irregularities in dopamine or DAT concentration could be the result of dopamine related disorders, including Parkinson’s disease, attention deficit hyperactivity disorder (ADHD), Tourette’s syndrome, schizophrenia, and depression. The latter four disorders elevate the amount of DAT, while Parkinson’s usually results in DAT and dopamine depletion over time (Miller and Madras 2002). The direct cause of Parkinson’s is unknown, but is thought be the result of mutations on the DAT and other various genes (Ritz et al. 2009).

To alleviate the more severe symptoms of Parkinson’s, researchers have developed DAT inhibitors. Even though a DAT inhibitor would further decline the amount of dopamine that could be recycled and used, these inhibitors would prevent detrimental neurotoxins from entering transmitting neurons through DAT. Scientists have used rhesus monkeys with the disease to study the effects of inhibitors. Monkey’s treated with inhibitors had reduced bradykinesia, rigidity, and tremor symptoms (Madras et al. 2006). All inhibitors used had a high affinity for the DAT protein, but research with more specific aptamers is needed to draw any concrete conclusions about the potential of DAT inhibitors and what other affects they might cause.

Specific Aim 1: Selection of RNA aptamers against DAT.

Using a high affinity and specific binding nucleic acid aptamer would be an ideal approach to studying DAT inhibitors and their beneficial effects on dopamine related disorders such as Parkinson’s. In its case, inhibiting the protein might improve severe symptoms by preventing neurotoxins from travelling through DAT and slowing, possibly even stopping, the degradation of this transmembrane protein. Using specific amounts of a therapeutic aptamer could also regulate other disorders in which there are high levels of DAT in the body. The possibility at finding a high affinity DAT inhibitor could have a huge and positive impact on the lives of those suffering with dopamine related disorders, specifically Parkinson’s disease.

Figure 1. Using a specific nucleic aptamer to inhibit the dopamine transporter would initially create a buildup of dopamine in the synaptic cleft and increase receptor activity. Over time the amount of dopamine released would decrease, detrimental neurotoxins would be unable to enter presynaptic cells through DAT, and the symptoms of dopamine related disorders may be alleviated. Picture adapted from website http://schizophreniasymptoms.net/dopamine-receptors/.

This transport protein is one of the “available” targets and can be found in the PAI 2.14 -80 freezer. .1 ml of the target can also be purchased at http://www.genwaybio.com for $540. The catalogue number is 20-783-72855 and the Genway phone number is (858)458-0866. An alternate to this is a sodium dependent dopamine transporter on the same website that is $330 and has the catalogue number 18-662-20037.

References

Huang, X. and Zahn, C.G. (2007). “How dopamine transporter interacts with dopamine: insights from molecular modeling and simulation.” Biophysical Journal. 93(10): 3627-3639.

Madras, B.K., Fahey, M.A., Goulet, M., Lin, Z, Bendor, J., Goodrich, C., Meltzer, P.C., Elmaleh, D.R., Livni, E., Bonab, A.A., and Fischman, A.J. (2006). “Dopamine transporter (DAT) inhibitors alleviate specific parkinsonian deficits in monkeys: association with DAT occupancy in vivo.” The Journal Of Pharmacology and Experimental Therapeutics. 319(2): 570-585.

Miller, G.M. and Madras, B.K. (2002). “Polymorphisms in the 3'-untranslated region of human and monkey dopamine transporter genes affect reporter gene expression.” Molecular Psychiatry. 7(1): 44-55.

Ritz, B.R., Manthripragada, A.D., Costello, S., Lincoln, S.J., Farrer, M.J., Cockburn, M., and Bronstein, J. (2009). “Dopamine Transporter Genetic Variants in Pesticides in Parkinson’s Disease.” Environmental Health Perspectives. 117(6): 964-969.