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|Year : 2018 | Volume
| Issue : 4 | Page : 1208-1210
Cerebral organoids: A new approach to understanding drug resistant epilepsy
Division of Non-Communicable Diseases, Indian Council of Medical Research (ICMR), New Delhi, India
|Date of Web Publication||18-Jul-2018|
Dr. Vikas Dhiman
Division of Non-Communicable Diseases, Indian Council of Medical Research (ICMR), Ansari Nagar, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Dhiman V. Cerebral organoids: A new approach to understanding drug resistant epilepsy. Neurol India 2018;66:1208-10
Epilepsy is the most common serious neurological disorder, affecting approximately 65 million people in the world. In up to 30–40% of people with epilepsy, seizures are not controlled by the available antiepileptic drugs (AEDs). This is often referred to as drug-resistant epilepsy (DRE)., In addition to the debilitating seizures, people with DRE have an increased risk of premature death, injury, psychosocial and cognitive dysfunction, and a reduced quality of life., Surgical resection of the epileptic tissue remains the only viable treatment option for these patients after they have undergone extensive and often costly presurgical investigations. Although surgery is known to positively modulate DRE, 50–80% of patients sustain postoperative seizure freedom.,
Hippocampal sclerosis (HS) and focal cortical dysplasia (FCD) are the most common histopathological findings associated with DRE., HS is characterized by neuronal cell loss and gliosis within the hippocampus and adjacent temporal cortex. The etiology of HS remains enigmatic. There is controversy regarding whether HS is the cause or the effect of seizures. FCDs usually manifest early in the childhood and seizures readily become resistant to the AEDs. FCDs are considered neurodevelopmental disorders, characterized by the disruption in neuronal proliferation, migration, and post-migrational cortical organization; however, how these pathological events lead to the clinical phenotype is not known.
There are various chemoconvulsants (kainic acid and pilocarpine)-induced and electrical stimulation-induced temporal lobe epilepsy animal models but the high mortality among animals, as well as the variability in frequency and severity of induced seizures as well as the high cost of the time consuming procedures limit their widespread use. Recently, studies using human-induced pluripotent stem cell (iPSC)-based epilepsy models and organotypic culture of hippocampal slices from patients who have undergone epilepsy surgery for mesial temporal lobe epilepsy have shown the characteristic morphological and pathological properties of DRE; however, these culture systems lack specificity of the neuronal circuits formed, the cortical laminar organization, and the overall cortical development, which are critical for understanding the pathomechanisms of epilepsy. Hence, it is usually difficult to study DRE using the conventional cell lines and animal models, and current clinical, imaging, and genetic evidences are insufficient and often misleading. There is no rational therapy for HS and FCDs, as there is no concrete explanation for their potent intrinsic ability to cause seizures., DRE is often a devastating condition for the individuals affected and their families. Furthermore, it amounts to a substantial health and socioeconomic burden., Thus, it is the need of the hour to explore novel approaches to unravel the basis of these disorders.
It has been shown that the mature skin cells from humans can be re-programmed under suitable conditions to pluripotent stem cells, which in turn can grow into all types of cells within the body. Similar to human embryonic stem cells, induced pluripotent stem cells (iPS) have unlimited capacity to self-renew and self-organize. Based on these two properties, iPS cells can give rise to an organ-like structure called the “organoid” when grown in a three-dimensional (3D) culture media. These organoids are formed of multiple cell types and can re-organize to grow, similar to the process in vivo. Organoids derived from human iPS cells have been established for gut, liver, kidney, retina, and brain. Adult-derived organoids for gut, kidney, and liver have been even transplanted into mice successfully, which showed human-specific features.,,
“Mini brain”-like structures, called cerebral organoids, can be generated from healthy as well as patient-specific iPS cells. [Figure 1] shows the steps required to generate cerebral (epilepsy) organoids from human skin cells. This protocol is based on the extensive protocols developed for neural differentiation, three-dimensional (3D) tissue culture, and tissue engineering with two main underlying objectives: (i) the establishment of neural identity and differentiation; and, (ii) the recapitulation of the 3D structural organization. The patient-derived iPS cell lines grows to form embryoid bodies (EBs) in appropriate laboratory conditions. Subsequently, on neural induction, a uniform layer of neuroepithelial cells forms on the outer surface of EBs within 8–10 days. These cells expand to form various brain structures in a differentiation medium that supports the growth of neural progenitors and their progeny. EBs with neural epithelium are embedded in the Matrigel ®
droplets, which provides a structural support for proper orientation and continuous development of the neuroepithelium in a 3D environment leading to the rapid formation of large buds of brain tissue with fluid-filled cavities within 15–20 days, indicative of reminiscent brain and ventricles with proper apicobasal orientation.
|Figure 1: Steps required to generate cerebral (epilepsy) organoids from human skin cells (Original)|
Click here to view
Cerebral organoids recapitulate key features of the normal brain development and express molecular markers of different brain regions within individual organoids, suggesting that they show a remarkable degree of regionalization. Recently, cerebral organoids derived from the skin fibroblasts of a patient with microcephaly were shown to recapitulate the clinical phenotype, thus providing new insights into the pathogenic mechanisms of microcephaly. Cerebral organoids have the potential to model neurological disorders that have been difficult or impossible to study using conventional cell lines and animal models.
In view of the widespread structural abnormalities seen in HS and FCDs, the difficulty to obtain live neurons from these patients, and the lack of relevant animal models, the study of cerebral organoids derived from DRE patient-specific iPS cell lines is a promising strategy to assess DRE and is likely to give novel insights into the disease-relevant pathogenic mechanisms. Epilepsy organoid systems can complement in vivo brain development in highly controlled conditions and may contribute to a paradigm shift in our understanding of DRE. In addition, the generation of epilepsy organoids would enable us to generate a platform that can be used for drug testing and discovery of new therapeutic approaches. In addition to possible future ethical issues, the important limitations of the organoid system include the lack of vascularization and essential developmental and patterning clues in the formed organoid, which are necessary for the development of a mature organ. Further improvements in technology and refinement in the laboratory protocols are bound to address these limitations.
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Conflicts of interest
There are no conflicts of interest.
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