In-vivo Imaging of Neuronal Differentiation and Function of Intracranially Implanted Induced Pluripotent Stem Cells (iPSCs) Using A Designer Receptor Exclusively Activated by A Designer Drug (DREADD)

Induced pluripotent stem cells (iPSCs) provide a promising resource for cell replacement therapy in neurological diseases. In the present study, we have applied a designer receptor exclusively activated by a designer drug (DREADD) derived from human M4 muscarinic acetylcholine receptor (hM4D) and its synthetic ligand to in-vivo visualization of neuronal differentiation and function of iPSC-derived grafts implanted into the brain. We successfully captured expression of hM4D driven by neuron-specific Thy-1 promoter in newly-developed hM4D transgenic (hM4D Tg) mice with a 11C-labeled positron emission tomography (PET) ligand for hM4D. We also established iPSCs from a hM4D Tg mouse (hM4D-iPSC), and visualized time course of neuronal differentiation of grafts generated from these iPSCs in the living wild-type mouse brain by longitudinal PET imaging of hM4D with its specific radioligand. Quantitative assessment for cerebral blood flow using arterial spin labeling (ASL) MRI indicated suppression of neuronal activity by clozapine-N-oxide (CNO), an exclusive activator of hM4D, in hM4D Tg but not wild-type mice, in consistency with attenuation of locomotion behaviors. Furthermore, we found CNO-induced reduction of cerebral blood flow in areas associated with implantation of hM4D-iPSC-derived grafts by ASL-MRI of recipient mice. Our results support the utility of hM4D in combination with PET and ASL-MRI for in-vivo longitudinal monitoring of neuronal differentiation and functional manipulation of iPSC-derived implants in the brain. Since this technology is potentially applicable to humans, it would accelerate translational research and development of cell replacement therapy towards clinical trials.Neuroscience meeting 201