Stem Cell Dopamine

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Dr. Kwang-Soo Kim
Harvard Medical School
Massachusetts

Abstract

In the brain of Parkinson’s disease (PD) patients, midbrain dopaminergic (DA) neurons are selectively degenerated. The clinical limitation of pharmacological treatment for idiopathic PD and other neurodegenerative conditions has resulted in the development of cell transplantation therapies. At present, fetal cell transplantation is the only well-accepted cell replacement procedure for PD treatment. Based on recent progress of signaling molecules (e.g., Shh and FGF8) and transcription factors (e.g., Nurr1) that are critical for differentiation of DA neurons, there are compelling research opportunities to develop blastula-derived embryonic stem (ES) cells as potentially optimal and unlimited source of donor cells for transplantation. We have previously shown that ES cells, when grated into the DA-denervated striatum in a rat model of PD, extended axonal processes into appropriate regions of the host brain and spontaneously differentiated into tyrosine hydroxylase (TH)+ neurons in vivo. Furthermore, our preliminary studies showed the Nurr1 directly transactivates the TH, but not the dopamine beta-hydroxylase promoter activity, indicating that it may directly control DA neurotransmitter phenotype. In this application, we propose to establish transgenic ES cell lines that exogenously express Nurr1. We will optimize in vitro (e.g., signaling molecules) and in vivo parameters (e.g., cell number and graft size) for the efficient survival and differentiation of naïve and transgenic ES cell lines into DA cell fate. We will examine expression of various marker proteins of DA neurons such as dopamine transporter (DAT), aromatic amino acid decarboxylase( AADC), and vesicular monoamine transporter 2 (VMAT2) in ES-derived TH+ neurons. Cells derived from grafted ES cells will be distinguished from host cells using the green fluorescent proteins expressed by ES cells. The functional effects of these optimized ES cell grafts will be determined in rate, and eventually primate models of PD (in collaboration with PD Center Project 2). By comparing the behavioral efficacy of the ES cell grafts versus fetal ventral mesencephalic (VM) cell grafts in both rodent and primate models, we will access the potential of ES cells to serve as a cell source for transplantation therapies in PD. In addition, we propose to explore and identify novel genes specifically induced during differentiation of ES cells to DA cell fate by DNA chip technology. Identification of novel DA neuron-specific genes will facilitate the understanding of DA neuron differentiation and provide opportunities for further genetic modification of ES cells and development of ES cell therapy for PD.

Progress Report (as of 8/2002)

We demonstrated in a rat model of Parkinson’s that mimics the dopamine loss and movement deficits seen in the disease that it is possible to obtain a high expansion and differentiation of naïve mouse embryonic stem cells into normal midbrain dopaminergic neurons by direct placement in the brain. There was a gradual restoration of abnormal motor signs consistent with the development of a new dopamine system in the rat brain. Brain scanning and functional MRI provided parallell evidence of new dopamine transmitter function. Expansion of embryonic stem cells into dopamine neurons with functional effects in an animal model of Parkinson’s is the first step towards a restorative stem cell therapy. (Bjorklund, LM et al. 2002).

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