Inquiry into Neurodegeneration: Engrailed Proteins and Parkinson’s Disease

Parkinson’s disease is a devastating neurodegenerative disease that is characterized by the depletion of dopaminergic neurons in the midbrain, leading to a decreased supply of dopamine and involuntary muscle control. An estimated 10 million people worldwide have Parkinson’s disease and approximately 60,000 Americans are newly diagnosed with this disease each year. The United States, like other developed nations, has a growing need for interventions for Parkinson’s disease. The number of patients with Parkinson’s disease (PD) is expected to rise as the average age of the US population is increasing.

In spite of the frequency of this disease, there is little understanding of the cause of Parkinson’s disease, though researchers have reported that genetics and the environment may be significant factors in the etiology of the disease. Studying this disease in vivo is difficult because it would require access to the human midbrain in diseased patients, a feat which at the time is not feasible. Therefore, in vitro techniques such as the use of stem-cell based models can be used to study the disease and find potential treatments. Stem cells derived from the reprogrammed skin cells of PD and non-PD patients can be derived and used to grow dopaminergic neurons in vitro. Previous research has suggested that dopaminergic neurons derived from patients with PD are more sensitive to cytotoxic insult than non-PD derived dopaminergic neurons. While the exact cause of the death of these neurons in patients is unknown, it is postulated that the aggregation of alpha-synuclein (SNCA) is one of the primary culprits. Our research group recently gathered evidence that Engrailed proteins and alpha-synuclein interact physically. The Engrailed homeoproteins (Engrailed-1 (En-1)/ Engrailed-2 (En-2)) are believed to promote differentiation of mesencephalic dopaminergic (mDA) neurons during development and to have a neuroprotective effect throughout the lifetime of the mDA neuron. These proteins have been shown to protect mDA neurons in Parkinson’s disease animal models and enhance dopamine synthesis.

My hypothesis is that Parkinson’s disease may be in part due to high levels of alpha-synuclein having an inhibitory effect on Engrailed proteins. I am exploring the hypothesis to investigate whether Engrailed proteins protect neurons from cell death, which are linked to high levels of alpha-synuclein. To do this, I am creating six genotypes from dopaminergic progenitor cells to test genes and genetic interactions between the two Engrailed proteins and alpha-synuclein. I will then use traditional mDA differentiation models to assess the effects of SNCA and EN proteins on dopaminergic neuron survival, as assayed using a TH-luciferase reporter gene to measure DA-neuron cell number. I expect an increase in dopamine activity from the doubly overexpressed alpha-synuclein and Engrailed protein cell cultures because their overexpressed effects should counteract one another compared to alpha-synuclein overexpression alone. By exploring these combinations of genotypes, I hope to shed light on the genetics behind Parkinson’s disease, and how increased levels of alpha-synuclein may lead to the death of midbrain dopaminergic neurons.