UC Irvine

In this thesis I will discuss my work on two distinct projects, one of which is the main focus of my work and this thesis, and, as reflected in the title, aims to find non-dopaminergic systems that can act as targets for treating PD. The other project investigates the impact of intergenerational trauma, specifically, how prenatal stress exposure affects the offspring in mice. Parkinson’s disease is a neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons. After sufficient degeneration has occurred, many motor and non-motor symptoms begin to appear. This study focuses on treating the motor symptoms, which include tremors, bradykinesia, rigidity and postural instability. In mice, this manifests itself as a decrease in overall locomotor activity. Currently, we cannot stop the degeneration that occurs, so the motor symptoms are usually what is treated in an attempt to improve the quality of life for the patient. Typically, Parkinson’s disease is treated with various forms of dopamine replacement therapy, most commonly through the use of levodopa (L-DOPA), which gets converted to dopamine via the enzyme dopa decarboxylase. Despite its ability to improve motor function, after continual use, its effectiveness begins to decline and it has the very high potential of causing other motor complications such as dyskinesias. Because of this, there is a considerable need to find alternative treatments that are able to treat the motor symptoms, while not losing effectiveness or causing other complications. We were able to characterize a bit of the promiscuity of L-DOPA as many other studies have observed a similar characteristic of L-DOPA binding to many different things in the brain. L-DOPA frequently binds to iron in the brain, but what happens to this complex is fairly unknown. We found that L-DOPA was able to form a stable complex with iron and siderocalin and in doing so, we speculate that this may be one of the reasons why L-DOPA efficacy is reduced as the amount of free L-DOPA available decreases due to forming these complexes. In this study, we were able to induce locomotor activity in our Parkinson’s disease modeled mice to much greater effect than what is currently used. After inducing the Parkinson’s disease model in the mice, we treated the mice with L-DOPA and NSD1015, a central acting dopa decarboxylase inhibitor. In doing so, we are preventing the conversion of L-DOPA to dopamine. After a brief delay, we see that the animals display locomotor activity at a level significantly higher than that of animals treated with just L-DOPA which gets converted to dopamine. Not only this, but we were also able to confirm that our treatment does not involve the dopamine system as there is no dopamine at all in the animals when the locomotor activity is induced. Because of this, we are able to design a treatment around this new system and won’t see the same complications that other dopamine-related treatments may have. After performing a metabolomic study, we were able to identify different metabolites and observed how they changed after our new treatment. In doing so, we observed one metabolite experience a significant fold change vastly greater than the rest. This metabolite was ophthalmic acid and had experienced an approximated 20-fold increase in the animals treated with L-DOPA and NSD1015 compared to those just treated with L-DOPA. Very little research has been done on this tripeptide analog of glutathione and what little has been done has no links to motor function. What we found was that ophthalmic acid when administered via intraperitoneal injection showed no improvements in the animals locomotor activity, but that was because we later found that it does not cross the blood-brain barrier. After that discovery, we administered ophthalmic acid via intracerebroventricular injection and were able to induce locomotor activity in the disease modeled animals. Although we found the non-dopaminergic compound responsible for inducing locomotor activity, we wanted to understand the mechanism of action for this compound. In this study, we identified that the target for ophthalmic acid is the calcium sensing receptor. Interestingly, many studies have shown the calcium sensing receptor to be expressed in many regions of the brain that are involved in the regulation of movement, such as the basal ganglia. Here we show that ophthalmic acid is able to bind and activate the calcium sensing receptor and is able to do so with a respectable affinity. Lastly, we were able to show that the hyperactivity induced via ophthalmic acid injection was able to be blocked using a calcium sensing receptor antagonist. That, alongside the rest of the evidence presented in this paper, prove that ophthalmic acid is able to induce locomotor activity in Parkinson’s disease modeled mice through its interactions with the calcium sensing receptor. This study not only identifies some of the potential problems with L-DOPA being used as a treatment for Parkinson’s disease, but also suggests the calcium sensing receptor as a potential therapeutic target as an alternative to the very problematic system that is the dopamine system. As part of a separate study, we investigated the effects of intergenerational trauma on offspring. Stress during pregnancy has been shown many times to have negative effects on the child, such as increased lifetime susceptibility to depression and other psychiatric disorders. Despite that, whether the trauma that is passed down is a consequence of in-utero development or early mother-infant interactions isn’t well known. In our study, we are able to demonstrate that the trauma exposure during pregnancy induces social deficits and depressive-like behavior. We also show that good caregiving by normal mothers via cross-fostering was unable to reverse prenatal trauma-induced deficits. This suggests that there is a two-hit mechanism, with both in-utero abnormalities and poor parenting both playing a role in the developmental deficits. We noticed significant increases in mitochondria hypoxia marker and epigenetic modifier 2-hydroxyglutaric acid in the brains of neonates and adults exposed to prenatal stress. Bioinformatics analyses revealed long-lasting alterations in mitochondrial energy metabolism and epigenetic processes. Lastly, we were able to show that early intervention with acetyl-L-carnitine supplements produced long-lasting protection against the intergenerational trauma-induced depression.