Parkinson's disease (PD) is a devastating movement disorder caused by the death of dopaminergic neurons (a type of neurons in the central nervous system) present in the midbrain. These neurons secrete dopamine (a signaling molecule) and are a critical component of the motor circuit that ensures movements are smooth and coordinated.
All current treatments attempt to overcome the loss of these neurons by either replacing the lost dopamine, or modulating other parts of the circuit to balance this loss or attempting to halt or delay the loss of dopaminergic neurons. Cell replacement therapy attempts to use cells as small pumps of dopamine that will be secreted locally and in a regulated way and has been evaluated as a potential therapy for PD. Small molecules (e.g., GDNF) have also been tested to determine their efficacy in prolonging the survival or promoting sprouting of dopaminergic neurons in PD patients. Work in these fields has been limited however, partially due to the limited availability of cells for transplantation (e.g. 6-10 fetuses of 6-10 weeks post-conception are required for a single patient) and for high throughput drug screening.
We believe that human embryonic stem cells (hESCs) may offer a potentially unlimited source of the right kind of cell required for cell replacement therapy. The fact that hESCs can be expanded and directed to produce specific cell types such as dopaminergic neuron makes it possible to develop cell-based screening models for drug discovery, for example, drugs that are protective to dopaminergic neurons.
In this proposal we seek to understand how hESCs differentiate into authentic dopaminergic neurons using a culture method that we have tested. We believe that this differentiation can be broken into several stages and each of which is regulated by growth factors and other molecules. We also believe that these stages can be understood by selecting cells at each stage and comparing their properties using molecular tools and by examining their behavior after transplanting the cells into a rodent model of the disease. We also believe dopaminergic neurons produced from hESCs offer an unprecedented opportunity to develop screening models for assessing small molecule drugs and to clarify the mechanisms of disease. Indeed, we have shown in our preliminary studies that sufficient numbers of cells can be generated from hESCs to run such screening. Finally, we will need to develop a non invasive method of following cells after transplantation and we propose to develop a reporter line carrying a magnetic resonance imaging (MRI) label (and can be detected by MRI) based on previous successful work in mice to monitor dopaminergic neurons in animal models and possibly in future clinical trials. We believe that these experiments are critical to enhancing our understanding of the disease and providing the tools that will be necessary to move cell therapy to the clinic.
We have proposed three aims in this proposal to identify factors that regulate the process of dopaminergic development and to develop reporter lines that allow us to screen large chemical libraries for drugs that promote dopaminergic differentiation or prolong the survival of dopaminergic neurons. We have also proposed to assess the long-term integration and differentiation of transplanted cells non-invasively in animal models that mimic the human disease using a magnetic resonance imaging (MRI)-based labeling system.
We believe these experiments not only provide a proof-of-principle for moving Parkinson’s disease towards the clinic for people suffering with the disorder but also a generalized plan for the development of stem cell therapy and stem cell based drug discovery for multiple degenerative disorders. The tools and reagents that we develop will be made widely available to Californian researchers and we will select California-based companies for commercialization of such therapies. We hope that California-based physicians will be at the forefront of developing this promising avenue of research. We expect that the money expended on this research will benefit the Californian research community and the tools and reagents we develop will help accelerate the research of our colleagues in both California and worldwide.