Parkinson’s disease (PD) is currently the most common neurodegenerative movement disorder, severely debilitating approximately 1-2% of the US population. The disease is caused by a selective loss of dopamine-producing neurons located in a specific region of the brain. This loss leads to significant motor function impairment and age-dependent tremors. Unfortunately there is currently no cure for PD, however a synthetic dopamine treatment (L-DOPA), temporarily alleviates symptoms.
The mechanism of PD progression is currently unknown. However, genetic studies have identified that mutations (changes) in multiple genes, including α-synuclein, LRRK2, uchL1, parkin, PINK1, DJ-1 and ATP13A2 cause familial PD. Although the familial form of PD only affects a small portion of PD cases, uncovering the function of these genes may provide insight into the mechanisms that lead to the majority of PD cases.
One of the best strategies to study PD mechanisms is to generate experimental models that mimic the initiation and progression of PD. A number of cellular and animal models have been developed for PD research. However, a model, which closely resembles the human degeneration process of PD, is currently not available because human neurons are unable to continuously propagate (grow) in culture. Human stem cells provide an opportunity to fulfill this task because these cells can grow and be programmed to generate dopamine nerve cells (the neurons under assault in PD patients).
In this study, we propose to create stem cell lines that either have the genetic background of sporadic PD patients or possess PD-associated mutations using cultured patient fibroblasts. These cell lines will in effect, represent a model of human PD degeneration of dopaminergic neurons. Our working hypothesis is that the degeneration of stem cell-derived dopaminergic neurons and dopaminergic neurons in vivo via the same mechanism. We will fulfill three tasks in this study; 1/ To generate the PD-stem cell (PD-SCs) line which either have the genetic background of sporadic PD patients or harbor PD specific gene mutantions; 2/ To determine the whether the PD-SCs cell lines can form into midbrain dopaminergic nerve cells; 3/ To determine whether mutations in parkin and PINK1 effect the survival of dopaminergic neurons which are derived from the PD-SCs cells. Successful completion of this study will yield novel cellular models for studying the mechanisms involved in PD initiation and progression, and further screening remedies for PD treatment.
During last year, we have finished to develop 15 lines of iPSCs. These include 5 lines from normal control individuals, 5 lines from sporadic Parkinson disease patients, and 5 lines from Parkinson disease patients harboring disease related mutations of PINK1, DJ-1 and PLA2G6 genes. These lines provide an unique opportunity to systematically study comparative pathophysiology of Parkinson disease using sporadic and genetic cases. Moreover, we indeed spent more than a year in optimizing the condition for differentiation of these lines. It is recognized that iPSCs are more difficult to differentiate than the hESCs. We are now able to finalize the protocols to have all lines be differentiated in vitro. Therefore, we will be able to compare differences among the controls, sporadic PD and genetic PD at the level of cell biology and molecular biology.
During the next report year, we will differentiate all lines into DA neurons and carefully the functional changes of these cells. We hope that the results will reveal some molecular basis of PD pathogenesis from these human neurons.