Tyrosine hydroxylase-positive cells and dopaminergic neuronal function in human embryonic stem cells An electrophysiological validation*

BACKGROUND: Induced differentiation strategies and cytochemical properties of human embryonic stem cells (hESCs) have been investigated. However, the electrophysiological functions of tyrosine hydroxylase (TH)-positive cells derived from hESCs remain unclear. OBJECTIVE: To investigate the differentiation efficiency of TH-positive cells from hESCs in vitro using modified four-step culture methods, including embryoid body formation, and to examine the functional characteristics of the differentiated TH-positive cells using electrophysiological techniques. DESIGN, TIME AND SETTING: Neuroelectrophysiology was performed at the Reproductive Medicine Center and Stem Cell Research Center, Peking University Third Hospital, and the Neuroscience Research Institute and Department of Neurobiology, Peking University, from September 2004 to August 2008. MATERIALS: The hESC line, PKU-1.1, a monoclonal cell line derived from a pre-implantation human blastocyst in the Reproductive Medical Center of Peking University Third Hospital. The patch clamp recording system was provided by the Neuroscience Research Institute and Department of Neurobiology, Peking University. METHODS: The hESC line was induced to differentiate into TH-positive cells in vitro using a modified four-step culture method, including the formation of embryoid body, as well as the presence of sonic hedgehog and fibroblast growth factor 8. The cell karyotype was assessed by G-banding karyotype analysis techniques and specific markers were detected immunocytochemically. Whole-cell configuration was obtained after obtaining a tight seal of over 1 GΩ. Ionic currents were detected by holding the cells at -70 mV and stepping to test voltages between -80 and 40 mV in 10-mV increments in voltage-clamp configuration. MAIN OUTCOME MEASURES: We measured the cell karyotype, specific cell markers, and the electrophysiological properties of the voltage-gated ion channels on the cell membrane of TH-positive dopaminergic cells differentiated from our hESCs line in vitro. RESULTS: The differentiated cells had a consistent appearance, and the majority of cells (> 90%) expressed TH and β-tubulion, as well as the neural progenitor marker, nestin. Cell karyotype analysis demonstrated that all of the hESCs had a stable and normal karyotype (46, XX) after differentiation. In addition, patch clamp recording showed that the 10 recorded TH-positive cells exhibited a fast inward current when the test voltage depolarized to -30 mV, and a delayed outward current when the test voltage depolarized to -10 mV. The peak of inward current was obtained at voltage between -10 mV and 0 mV, while the peak of outward current was obtained at 40 mV. The average peak of inward current density was (-50.05 ± 15.50) pA/pF, and the average peak of outward current density was (41.98 ± 13.55) pA/pF. CONCLUSION: More than 90% of the differentiated hESC-derived cells induced by the modified four-step culture method exhibit dopaminergic neuronal properties, including general electrophysiological functional properties, such as functional potassium and sodium channels.