Characterization of Human Stem Cell-Based Models of Parkinson's Disease and Alzheimer's Disease
Parkinson’s disease (PD) and Alzheimer’s disease (AD) are two most prevalent neurodegenerative disorders in the world. In addition to well-established animal models, human pluripotent stem cell technology has also merged as an innovative approach to model the etiology and pathomechanisms underlying variety of neurodegenerative diseases. Here in this study, we successfully obtained matured human neurons by differentiating two types of human pluripotent stem cell, which are induced pluripotent stem cells (iPSCs) and embryonic stem (ES) cells, to model PD and AD respectively and further investigate their potential mechanisms and therapy mainly by characterizing and comparing their electrophysiological features. (1) Model Parkinson’s disease with DA neurons derived from human iPSC One of the pathological features of Parkinson’s disease is selective degeneration of midbrain DA neurons. These neurons are critical to a broad array of behavioral processes that include cognition, sequence learning, feeding and voluntary movement. A key feature of these neurons is their tonic firing to drive DA release. Meanwhile, the mutation of Parkin, which is an ubiquitin E3 ligase that in human encoded by gene PARK2, is found most frequently in recessively inherited PD. In order to discover the linkage between Parkin and specific loss of DA neurons in this disease, matured midbrain DA neurons were differentiated from iPSCs that were generated from a healthy control and a PD patient with Parkin mutations, respectively. Additionally, CRISPR/Cas9 system was introduced to these two iPS cell lines to further manipulate Parkin expression. We found the loss of Parkin expression will result in significant decreased tonic firing rate of these DA neurons. Correspondingly, Parkin restoration lead to recovery of autonomous firing rate. Thus, our results provided the first experimental evidence to reveal the role of Parkin in DA neurons degeneration pathology of PD. (2) Modeling Alzheimer’s disease with cortical neurons derived from human ES cells Amyloid Beta (Aβ) is one of the major pathological hallmarks of AD. Many studies employing rodent models have identified the synaptic toxicity effect of Abeta, which eventually leads to vast neuron degeneration and cognitive deficits in AD. In our previous study, BIX01294, which is a selective inhibitor of EHMT1/2 histone methyltransferase, has been identified to have rescue effect of both postsynaptic current loss as well as cognition and memory deficits in a familial AD (FAD) mouse model. These findings intrigue us to determine whether we could further examine the effect of BIX01294 in a human AD model. To test this, we first identified rat cortical cultures treated with human Aβ would serve as AD model since it exhibits a reduction of whole-cell AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors) current and AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSC). In addition, BIX01294 successfully rescued both types of current loss. Second, we differentiated human ES cells into matured cortical neurons by modifying a previous protocol. Interestingly, the application of A? on human neurons also induced decreased AMPA current, spontaneous excitatory postsynaptic current (sEPSC) and mEPSC. Furthermore, all three types of current loss were rescued by BIX01294 treatment. Thus, we describe a highly reproducible cellular AD model based on human ES cell-derived cortical neurons that enables the mechanistic analysis of Aβ-induced synaptic toxicity and further confirmed BIX01294 is a promising treatment for human AD.