Human iPSC-derived neural stem Cells from an epilepsy patient

Epilepsy Neural Stem Cells (ax0411) cultured on Sure Bond+ (ax0041+). Image taken after 3 days of spontaneous differentiation in Neural Expansion-XF Medium (ax0030-500). nestin (R) - FOXG1 (G)

Understanding epilepsy

Epilepsy is one of the most common neurological disorders. The age of onset is typically early with potentially serious neurocognitive residuals apparent in later life [1]. Symptoms can include recurring aggressive electrical activity, seizures, behavioral, neurological and cognitive difficulties, and may result in early death [2].

Genetic factors are thought to play a role in at least 70% of patients [1]. For example, the SLC25A22 gene encodes a mitochondrial glutamate transporter and is associated with early-onset epileptic encephalopathies (OMIM #609304) such as early myoclonic encephalopathy. Several mutations in this gene (rs121918334, rs121918335, rs587777243) have already been identified in epilepsy patients. The prognosis for individuals with epilepsy can be poor [3] hence, a model system is needed to determine the effects of epilepsy-associated mutations such as these on human neurons and to help identify more effective treatments.

Human cells are needed for effective disease modeling & drug discovery

For many years, understanding development, learning and memory in brain function has relied heavily upon the use of animal models. While these have elucidated a number of mechanisms in brain function, the need for a human model in which to validate and further evaluate these findings remains and can often be difficult to obtain. Human induced pluripotent stem cells (hiPSCs) however, can be differentiated into neural cells and used to study network formation and electrical conductivity in vitro [4]. These can be derived from a single donor and are available on an industrial scale, providing an isogenic source of cells from the same individual for consistency throughout the experimental process. Furthermore, it is possible to derive these cells from both healthy and patient donors and as such, this has led to an increase in the uptake of these cells in drug discovery and helped further our understanding of disease mechanisms underlying conditions such as epilepsy and neurodegenerative conditions (e.g. Alzheimer’s, Huntington’s and Parkinson’s diseases).

Using human induced pluripotent stem cells to study epileptiform phenomena

Human iPSC-derived neurons are a potentially powerful in vitro model for evaluating disease mechanisms and drug responses. A paper published by Odawara et al. (2015) co-cultured astrocytes with Axol’s Human iPSC-Derived Cerebral Cortical Neurons on a multi-electrode array (MEA) platform for over 100 days in order to study plasticity such as long-term potentiation (LTP) and long-term potentiation depression (LTD) in neuronal networks. They then went on to maintain these cells for 400 days and investigate the spontaneous electrical activity and pharmacological responses in cultured human iPSC-derived cortical neurons using MEA. They conducted several pharmacological studies to determine the properties of evoked responses upon administration of synapse antagonists bicuculline, CNQX and AP5, and the agonist, L-glutamate, a kainic acid, which induced significant changes in firing rates and synchronised burst firing activity. They also induced epileptiform activity in these cells with pentylentetrazole (PTZ) and observed the suppressive effects of clinical anti-epilepsy drugs such as phenytoin at various concentrations over several weeks.

Future potential for human iPSC-derived neural cells in epilepsy research

Additional work is required in order to standardise cell culture protocols for these cells and establish functional evaluation methods. Furthermore, the cells used here are derived from a healthy individual and iPSCs derived patient donors are an essential requirement if future studies are to conduct a comparison across disease-relevant genetic backgrounds and controls.

Human iPSC-derived neural cells offer great potential to further our understanding of new biological pathways and clarify human neuronal network function. These systems might be used for disease modeling to help identify the mechanisms behind alternate firing patterns in conditions such epilepsy. Additionally, they are of significant value for drug screening applications as they provide a relevant cell type to investigate novel compounds for the effective treatment of such conditions.

References

[1] Hildebrand MS, et al., Recent advances in the molecular genetics of epilepsy. J. Med. Genet. 50:271-279, 2013.

[2] Epilepsy Foundation. Epileptic Encephalopathies in Infancy and Childhood. http://www.epilepsy.com/information/professionals/about-epilepsy-seizures/epileptic-encephalopathies-infancy-and-childhood

[3] Molinari, F, et al., Impaired mitochondrial glutamate transport in autosomal recessive neonatal myoclonic epilepsy. Am. J. Hum. Genet. 76: 334-339, 2005

[4] Odawara A, et al., Induction of long-term potentiation and depression phenomena in human induced pluripotent stem cell-derived cortical neurons. Biochemical and Biophysical Research Communications, 2015


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