Going after Parkinson’s disease with iPS cells

TOKYO—A joint research group centered around Dr. Hideyuki Okano and Dr. Jun Kohyama—a professor and associate professor, respectively, at the Department of Physiology of the Keio University School of Medicine—together with a research group of Eisai Co. Ltd., has identified a compound that has the potential to be a treatment for Parkinson’s disease by using dopaminergic neurons differentiated from induced pluripotent stem (iPS) cells from patients with familial Parkinson’s disease.

Aiming to develop treatments for Parkinson’s disease, this research group utilized neural progenitor cells induced from iPS cells derived from patients with familial Parkinson’s disease and established a differentiation protocol for the stable supply of a large number of dopaminergic neurons. Furthermore, the research group screened an existing drug library as an indicator of susceptibility to stress observed in dopaminergic neurons derived from Parkinson’s disease patients, and identified compounds that inhibit calcium channels. Further detailed analysis conducted by the research group revealed higher expression of T-type calcium channels in dopaminergic neurons derived from patients with the PARK2 gene associated with Parkinson’s disease. It was also found that apoptosis of dopaminergic neurons derived from Parkinson’s disease patients could be reduced by inhibiting calcium influx via T-type calcium channels.

From these results, it is suggested that combining disease-specific iPS cells and existing drug libraries has potential for both the development of treatments and clarification of disease pathology. The results of this research were published in the online version of Stem Cell Reports on Oct. 18.

Parkinson’s disease is the second most common neurodegenerative disorder after Alzheimer’s disease, and causes motor symptoms such as tremor, bradykinesia, rigidity and postural instability and autonomic dysfunction due to a preferential loss of dopaminergic neurons in the substantia nigra. For 90 percent of Parkinson’s disease patients, symptoms are idiopathic and it is difficult to understand the relationship between various factors, including those associated with the environment and the disease mechanism. However, approximately 10 percent of patients show the familial incidence of Parkinson’s disease; as such, understanding the disease mechanism for familial Parkinson’s disease may also link with the understanding of idiopathic Parkinson’s disease as well as drug development.

Through the use of iPS cell technologies developed by Prof. Shinya Yamanaka of Kyoto University in 2006, research has made great advances even in diseases that were difficult to be investigated by conventional methods. In 2012, the Keio University School of Medicine became the first research facility in Japan to create iPS cells from patients with familial Parkinson’s disease, and was successful in replicating the disease mechanism. Currently, research into neurological diseases has become very active throughout the world, and the understanding of diseases and development of new treatments is highly anticipated.

In April 2013, the Keio University School of Medicine and Eisai initiated the “Innovative Drug Discovery Project for Refractory Neurological Diseases Using iPS Cell Technologies,” and since then this drug discovery project has been progressing as an industry-academia collaboration, making full use of the Keio University School of Medicine’s iPS cell and related technologies as well as Eisai’s drug discovery techniques. Through this research, dopaminergic neurons which are thought to be damaged in Parkinson’s disease patients are created efficiently and easily using iPS cells derived from Parkinson’s disease patients, and an experimental system for conducting screening for drug discovery was established. In this research, Keio University School of Medicine’s library of over 1,000 existing drugs was screened to find compounds preventing increased susceptibility to stress in dopaminergic neurons derived from Parkinson’s disease patients.

In this research, neural progenitor cells induced from iPS cells established from two familial Parkinson’s disease (PARK2) patients were used to efficiently generate dopaminergic neurons. In patient-derived neurons, reduced neurite length as well as elevated oxidative stress and apoptosis were observed compared to neurons derived from healthy controls. Furthermore, it was revealed that these disease-relevant phenotypes were also observed in dopaminergic neurons derived from isogenic PARK2 null iPS cells obtained by genome editing.

In addition, since patient-derived dopaminergic neurons showed high susceptibility to rotenone, a mitochondrial respiratory chain complex I inhibitor, an existing drug library was screened with vulnerability to this drug-induced stress as the target. From phenotypic screening with an existing drug library, several compounds that suppressed stress-induced apoptosis were identified. Furthermore, it was found that T-type calcium channel antagonists effectively reduced stress-induced apoptosis. Importantly, these compounds demonstrated similar reduction in stress-induced apoptosis in dopaminergic neurons derived from another type of familial Parkinson’s disease (PARK6)—such patients ossess a genetic abnormality which is different from PARK2.

Further detailed analysis conducted by the research group revealed higher expression of T-type calcium channels in dopaminergic neurons derived from PARK2 patients. It was also found that apoptosis of dopaminergic neurons derived from Parkinson’s disease patients could be reduced by inhibiting calcium influx via T-type calcium channels.

From these results, using iPS cells derived from patients enabled the establishment of in-vitro disease models that reflect human biology, and by further combining with existing drug library, suggested efficacy for drug screening. By promoting the understanding of disease pathology through this method, it is hoped that this will lead to application in the development of a fundamental treatment for Parkinson’s disease. Going forward, this research will continue, the knowledge gained will be further developed and experimental systems closely reflecting the brain environment in vivo, such as co-cultured neurons with glial cells, will be utilized in an effort to verify the validity of targets for Parkinson’s disease.