Among PDF's research awards of $5 million in 2013, we awarded $1 million for 14 novel investigator-initiated research project. The projects are supported via two core programs that encourage early-career scientists to test out their most daring ideas – International Research Grants and Research Fellowships.
Abstracts of these projects appear below.
[+] Epigenetic Dysregulation in Levodopa-Induced Dyskinesia
David Anderson, Ph.D., and Jay Schneider, Ph.D., Thomas Jefferson University, Philadelphia, PA
After long-term treatment with levodopa, some people with Parkinson’s disease experience a side effect called levodopa-induced dyskinesia (LID). Scientists are uncertain what causes these involuntary twisting and writhing movements, but certain brain cells could be responsible. Perhaps levodopa triggers a key event that controls multiple types of brain cells, which together cause LID. We wondered if a cellular event called DNA methylation could be this key event. The body uses DNA methylation to turn genes on or off. Researchers have already shown that taking levodopa can change DNA methylation levels in people with PD. We will study animals with PD-like symptoms. About half of the animals take levodopa and experience LID. We will compare DNA methylation in animals with and without LID, looking for genes in the brain that are methylated differently between the two groups. In this way, we may identify genes linked to LID, which could provide new clues to how this side effect develops and suggest new strategies to prevent or treat it.
[+] Stability of Tetrameric Alpha-synuclein as a Biomarker in Parkinson’s Disease*
Tim Bartels, M.Sc., Ph.D., and Dennis J. Selkoe, M.D. Harvard Medical School and Brigham and Women’s Hospital, Boston, MA
A hallmark of Parkinson’s is the clumping together of a protein known as alpha-synuclein in certain cells of the brain. Although scientists don’t know exactly how or why alpha-synuclein forms clumps, abnormally shaped forms of the protein may be to blame. Our laboratory recently discovered that in normal cells, four copies of the alpha-synuclein protein associate with each other to form a structure that is called a tetramer. In people with PD, however, the alpha-synuclein tetramer doesn’t assemble properly, which may make the protein more vulnerable to clumping. Currently, we do not have a method for detecting these abnormal forms of alpha-synuclein in the blood or brains of people with PD. Therefore, we plan to develop a test, known as an Enzyme-linked Immunosorbant Assay (ELISA), to detect different forms of alpha-synuclein. The ELISA will use antibodies that can discriminate between normal and abnormal alpha-syuclein forms to determine which forms of alpha-synuclein are present in blood or brain tissue samples. We will use this ELISA to characterize alpha-synuclein forms in many blood samples and brains of humans and mice with PD. Being able to do so may help us better understand how alpha-synuclein forms clumps, as well as aid PD diagnosis and the search for more effective therapies.
[+] Elucidation of the Role of Cholinergic Interneurons in Levodopa-Induced Dyskinesias Using Transgenic Rats and AAV-mediated Overexpression of Modulatable Receptors
Tomas Björklund, Ph.D., Lund University, Lund, Sweden
After long-term treatment with levodopa, some people with Parkinson’s disease experience a side effect called levodopa-induced dyskinesia (LID). Scientists are uncertain what causes these involuntary twisting and writhing movements. But there is suspicion that brain cells called cholinergic interneurons are involved. Our research aims to better understand how these cells contribute to LID. We will work with rats with PD-like symptoms that are receiving levodopa treatment. We will observe what happens when we first activate and then quiet cholinergic interneurons. In this way, we can find out whether signaling these cells really worsens LID, as we hypothesize. In another set of experiments, we will compare the actual cholinergic interneurons from the brains of rats with and without LID, looking at which genes are turned on and off in the cells. These experiments may provide clues as to which genes scientists should target to treat LID in people. Thus, this project is expected to provide new insights into the role of cholinergic interneurons in LID and suggest new targets for therapy to control this debilitating side effect.
[+] Dissecting the Different Properties of Human Alpha-synuclein Between Dopamine and Non-dopamine Neurons in Vivo*
Linan Chen, M.D., Ph.D., and Xiaoxi Zhuang, Ph.D., University of Chicago, Chicago, IL
Recently, scientists discovered that alpha-synuclein — a protein that when damaged forms clumps called Lewy bodies in the brains of people with Parkinson’s disease — exists in cells as a complex of four alpha-synuclein proteins bound together, known as a tetramer. In people with PD, this tetramer may fall apart into four single alpha-synuclein proteins, which are then more prone to clumping. We don’t know why certain brain cells, called dopamine neurons, are more vulnerable to Lewy body formation than other cell types. One possibility is that dopamine neurons contain fewer alpha-synuclein tetramers and more single alpha-synuclein proteins than other brain cells. However, comparing the levels of alpha-synuclein tetramer in different cell types is very difficult: when we purify alpha-synuclein from dissected brain tissue, we can’t tell which alpha-synuclein proteins came from dopamine neurons and which came from non-dopamine neurons. Therefore, we have genetically engineered mice to produce large amounts of human alpha-synuclein specifically in dopamine neurons. When we isolate human alpha-synuclein from the brains of these mice, we will know that it was produced exclusively by dopamine neurons. Likewise, we generated mice that produce high amounts of human alpha-synuclein in non-dopamine neurons. We will compare the forms of human alpha-synuclein in the brains of these two groups of mice. These experiments may shed light on the vulnerability of dopamine neurons to Lewy bodies and how alpha-synuclein is toxic for these neurons.
[+] The Cellular Mechanisms of Semaphorin 3E-Plexin-D1 Signaling in Basal Ganglia Circuitry Formation and Neurodegenerative Diseases*
Chenghua Gu, D.V.M., Ph.D., Harvard Medical School, Boston, MA
People with neurological diseases such as Parkinson’s often suffer from uncoordinated, involuntary body movements. This impaired motor function may result from an imbalance in the transmission of nerve signals within the brain. If one set of neurons are too stimulated or, alternatively, too inactive, they could cause either involuntary or impaired muscle movement. An important part of achieving the correct balance requires proper “wiring” of brain circuits during development. Currently, we don’t know exactly how neurons make specific connections with other neurons to achieve the proper balance in the brain regions affected by Parkinson’s. Recently, however, my colleagues and I discovered that a protein called semaphorin 3E (Sema3E) that is secreted by certain neurons helps guide circuit formation. We found that Sema3E interacts with another protein called Plexin-D1. This interaction between these two proteins helps determine how neurons connect to each other. We plan to further explore the importance of the Sema3E–Plexin-D1 interaction in maintaining the proper balance between stimulatory and inhibitory circuits that control movement. By understanding how neuronal circuits maintain the proper balance, we hope to use this information to help find ways to rebuild neural circuits that have been destroyed by cell death in PD, thereby improving the motor control of people affected by PD.
[+] Identification and Characterization of a Novel Gene for Parkinsonism*
Paul Lockhart, Ph.D., and Gabrielle Wilson, Ph.D., Bruce Lefroy Centre, Murdoch Childrens Research Institute, Royal Children's Hospital Parkville, Victoria, Australia
Parkinson’s disease is a common neurodegenerative disorder with symptoms that predominantly result from the loss of a specific type of neuron, called dopamine neurons, within the brain. These neurons make up less than one percent of the more than 50 million neurons in the brain, and scientists do not know why they are the ones lost during disease development. Therefore, identifying what causes dopaminergic neurons to die is a crucial step in understanding PD. Genetic studies and modern genomic technologies provide a powerful approach to identify genes and disease-causing events associated with PD. We have studied two families with early onset parkinsonism and identified a shared underlying genetic cause. We will now characterize the gene responsible and determine what role the gene plays in PD. This study will help to understand what causes dopamine neurons to die and may identify new therapies to prevent PD or slow its onset and progression.
[+] Interaction of LRRK2 and Tau in Mediating Neurodegeneration in Mouse Models of Parkinson's Disease
Darren J. Moore, Ph.D., Swiss Federal Institute of Technology in Lausanne (EPFL), Lausanne, Switzerland
Cases of inherited Parkinson’s disease are rare. But when they occur, mutations in the LRRK2 gene are one of the most common causes. Autopsies have shown that the brains of people with LRRK2 mutations contain abnormal clumps of various proteins, including alpha-synuclein and tau. In addition, recent studies have revealed that tau accumulates in the brains of rodents with LRRK2 mutations. Most prior research has focused on the contribution of alpha-synuclein clumps, or Lewy bodies to PD. But we wondered whether tau might cooperate with mutated LRRK2 to harm dopamine neurons in Parkinson’s disease. To answer this question, we will study mutated LRRK2 in cell cultures and in rats, observing whether tau is required for the neuron death. Also, we will examine whether normal LRRK2 is required for the neurodegeneration observed in mice that produce mutated tau. These studies may uncover interactions between LRRK2 and tau that contribute to neurodegeneration in PD. Understanding these interactions could help develop new drugs that interfere with the actions of either or both proteins to prevent or treat PD.
[+] Identifying Connectivity Changes with Deep Brain Stimulation in Parkinson’s Disease
Matthias L. Schroeter, M.D., M.A., Ph.D., and Karsten Mueller, Ph.D., Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Sachsen, Germany
In recent years, deep brain stimulation (DBS) has been established as a successful surgical method for treating some people with Parkinson’s disease. DBS provides a small electric current to structures of the brain in order to block motor symptoms of PD. The technique involves the surgical insertion of tiny electrodes deep into the basal ganglia region of the brain and the implantation of an impulse generator (similar to a pacemaker) under the person’s collarbone to provide an electrical impulse to their brain. However, it is still unknown how DBS improves motor symptoms. One idea is that the treatment may alter connections among circuits of neurons, or neural networks, in the brain. We plan to investigate how neural networks change with DBS and compare these changes with those caused by Parkinson’s medications. We will use a brain scan called functional magnetic resonance imaging (fMRI) to study resting state brain activity before and after taking PD medications, and with and without DBS. By examining a person’s brain images before treatment, we may be able to predict their response to the treatment. In this way, we could identify people who would benefit from DBS before they undergo surgery. We expect this research project to advance our knowledge of PD and our understanding of therapeutic approaches.
[+] Imaging Impulsive Control Disorders in PD
Antonio Strafella, M.D., Ph.D., FRCPC, Toronto Western Hospital, Toronto, Ontario, Canada
Some people who take dopamine agonists to treat motor symptoms of Parkinson’s disease (PD) develop side effects such as compulsive eating, gambling, shopping, or sexual activity. Together, these side effects are called impulse control disorders (ICDs). Scientists suspect that dopamine agonists may change the way some people’s brains perceive risks and rewards. As a result, some people who take dopamine agonists may have trouble controlling harmful behaviors that produce temporary feelings of pleasure or “highs.” We plan to use a type of brain scan – positron emission tomography (PET) scanning – to examine the brains of people with PD, with and without ICDs. Each participant will be injected with a small amount of a radioactive “tracer” that will allow us to observe dopamine levels in the brain. By comparing the scans of people with PD who suffer from ICDs to scans of people with PD who do not have an ICD, we may be able to determine brain differences that cause some people to develop ICDs. Understanding these differences may help better diagnose and treat ICDs in people with PD.
[+] Cyclic GMP Signaling and Experimental Parkinsonism*
Anthony R. West, Ph.D., and Kuei-Yuan Tseng, M.D., Ph.D., Rosalind Franklin University, North Chicago, IL
We plan to identify new strategies to treat Parkinson’s disease by interfering with specific signaling pathways inside brain cells. Like a signal to turn on a light switch can illuminate an entire room, these pathways take small signals and turn them into large responses. The pathway we are investigating is called the soluble guanylyl cyclase (sGC) – cyclic GMP (cGMP) signaling pathway, where sGC is the switch and cGMP is the light. Mice and rats with PD-like conditions have elevated levels of cGMP in cells of the striatum of the brain. We recently found that a drug that can block activation of the sGC switch can reverse various cellular and behavioral abnormalities in animal models of PD. Now we will determine the effects of administering the drug for a long period of time to rats with a PD-like condition. We hypothesize that selectively blocking the sGC–cGMP activity with the drug will ease the rats’ symptoms and enhance their response to levodopa therapy. These studies will provide valuable information on the effects of this signaling pathway in the brain and may reveal promising new therapies for PD that could be used alone or in combination with levodopa treatment.
[+] Optogenetic Characterization of the Pallidostriatal Synapse in Parkinsonian Mice
Kelly Glajch, Ph.D., mentor C. Savio Chan, Ph.D., Northwestern University, Chicago, IL
Neurons in the brain form complex, interconnected circuits that help control movement. Under normal conditions, a balance exists between two circuits – one that allows us to perform voluntary movements and another circuit that prevents involuntary movements. This balance allows us to contract our muscles and move when we wish, but it suppresses contraction when we don’t want to move. In Parkinson’s disease, the loss of the neurotransmitter dopamine disrupts this balance, causing the brain to focus more on preventing involuntary contractions than on allowing voluntary ones. As a result, people with PD often have trouble initiating movements, leading to the motor problems characteristic of PD. We plan to study in detail how two areas of the brain, the globus pallidus external segment (GPe) and the dorsal striatum (dStr), communicate to control voluntary and involuntary movements, and how this communication changes in PD. For these studies, we will compare nerve signaling in healthy mice with that in a mouse model of PD by using a light to modulate neurons' activity. These experiments should increase our understanding of the brain circuits that control movement and how they become impaired in PD, enabling the design of therapies to better control motor symptoms.
[+] Characterization of a Novel Component That Functions Upstream of PINK1 Linking Mitochondrial Unfolded Protein Stress to Mitophagy
Yi-Fan Lin, Ph.D., mentor Cole Haynes, Ph.D., Sloan-Kettering Institute, New York, NY
Mitochondria are vital energy-producing structures found inside all cells of the body. However, when mitochondria become damaged, they can release toxic chemicals into the cell. The body has a mechanism in place to rid itself of toxic mitochondria, but in Parkinson’s disease, this mechanism appears to malfunction in dopamine neurons. There is then a build-up of damaged mitochondria that may contribute to the death of neurons, leading to PD. In fact, genetic mutations in the two genes that lead to young-onset PD, PINK1 and Parkin, are involved in this process. Studying nematodes, a type of roundworm, we plan to investigate how the degradation process is carried out in response to various types of mitochondrial damage. Furthermore, we will investigate how PINK1, Parkin, and other proteins cooperate to remove damaged mitochondria. Hopefully, these studies will lead to new therapeutic strategies that can delay or prevent PD.
[+] Role of Parkin in the Clearance of Defective Mitochondria with Deleted mtDNA. A New Mouse Model of Parkinson's Disease.
Milena Pinto, Ph.D., mentor Carlos Moraes, Ph.D., University of Miami, Miami, FL
Cases of inherited Parkinson’s disease are rare, but can help us understand the disease generally. For example, mutations in the PARK2 gene, which encodes a protein called Parkin, can cause Parkinson's disease. The normal function of Parkin is to help clear damaged cellular structures called mitochondria from the cell. Mitochondria produce energy for the cell, but when they become damaged, they can release toxic chemicals. Parkin helps protect cells by targeting damaged mitochondria for degradation. In previous studies, scientists have studied mice without the gene to understand its role in PD. Unexpectedly, however, these mice show only mild motor symptoms, slightly reduced dopamine levels, and no signs of neurodegeneration—in marked contrast to people with PARK2 mutations. We wondered if these differences could be explained by a lack of harmful events that damage mitochondria in the mice. Mitochondria carry their own DNA, and in people, PD and aging can cause mutations in this mitochondrial DNA that signal Parkin and other proteins to degrade the damaged mitochondria. To test this idea, we will create new mouse models that both lack Parkin and are genetically engineered to accumulate different forms of mitochondrial DNA damage. We will study motor behavior, dopamine levels and neurodegeneration in these mice to see if their condition better resembles PD in people with PARK2 mutations. This project will shed new light on the role of Parkin and mitochondrial DNA mutations in PD. In addition, the new mouse models should prove useful for testing new drugs to prevent or treat PD.
[+] Clearing Defective Mitochondria: How is Parkin Recruited and Activated?
Evgeny Shlevklov, Ph.D., mentor Thomas Schwarz, Ph.D., Children’s Hospital Boston, Boston, MA
Cases of inherited Parkinson’s disease are rare, but studying them helps us to understand the disease generally. For example, the proteins PINK1 and Parkin are mutated in many cases of inherited PD. Both proteins help clear damaged mitochondria (an important cell structure that produces energy) from the cell. When they are mutated, defective mitochondria accumulate and release toxic chemicals. PINK1 and Parkin help protect cells by targeting the damaged mitochondria. We know that when a mitochondrion is damaged, PINK1 accumulates on its surface and activates Parkin to help out. Parkin then sends signals to other proteins that result in recycling of the mitochondrion by a cellular compartment. How PINK1 recruits and activates Parkin is unclear. We aim to understand how PINK1 and Parkin cooperate with each other and with other proteins to mark the damaged mitochondrion for destruction. We will study these interactions among isolated proteins and mitochondria in the test tube, as well as in cultured human cells. Understanding the interactions may help researchers design drugs that stimulate this important quality control process in people with PD.
*Denotes second year of funding