Disease Study
editCerebral organoids can be used to study the crucial early stages of brain development, test drugs and, because they can be made from living cells, study diseases of individual patients.[1]
Teratogens
editCerebral organoids have been used to study the effects of certain teratogens on fetal neurological development.[2]
Cerebral organoids have been used in studies in order to understand the process by which Zika virus affects the fetal brain and, in some cases, causes microcephaly.[2][3]Cerebral organoids infected with the Zika virus have been found to be smaller in size than their uninfected counterparts, which is reflective of fetal microcephaly.[2][3] Additionally, lumen size was found to be increased in organoids infected with Zika virus.[2][3]The results found from studying cerebral organoids infected with Zika virus at different stages of maturation suggest that early exposure in developing fetuses can cause greater likelihood of Zika virus-associated neurological birth defects.[3]
Cocaine
editPotential enzyme versions responsible for fetal neurological developmental defects caused by cocaine use during pregnancy have also been identified using cerebral organoids.[2] Cerebral organoids were used to determine the enzyme necessary for development of abnormalities associated with cocaine use. This enzyme was determined to be cytochrome P450 isoform CYP3A5 .[2]
Autism
editCerebral organoids can also be used to study autism spectrum disorders.[4] In a recent study, cerebral organoids were cultured from cells derived from macrocephaly ASD patients.[4] These cerebral organoids were found to reflect characteristics typical of the ASD-related macrocephaly phenotype found in the patients.[4] By cultivating cerebral organoids from ASD patients with macrocephaly, connections could be made between certain gene mutations and phenotypic expression.[4] The field of epigenetics and how DNA methylation might influence development of ASD has also been of interest in recent years. The traditional method of studying post-mortem neural samples from individuals with ASD poses many challenges; cerebral organoids have been proposed as an alternate method of studying the effect of epigenetic mechanisms on the development of autism. This model might provide insight in regards to developmental timelines. However, the conditions in which the organoid is cultured in might affect gene expression. Additionally, there is concern over the variability in cerebral organoids cultured from the same sample.[5] Further research into the extent and accuracy by which cerebral organoids recapitulate epigenetic patterns found in primary samples is also needed.[5]
Other Applications
editA list of potential applications for cerebral organoids is highlighted below. Potential applications include:[6]
Cerebral organoids can be used to study tissue morphogenesis, which, as it relates to cerebral organoids, illuminates how neural organs form in vertebrates. Cerebral organoids can serve as in vitro tools to study the formation, modulate it, and further understand the mechanisms controlling it.[6]
Migration assays
editCerebral organoids can help to study cell migration. Neural glial cells cover a wide variety of neural cells, some of which move around the neurons. The factors that govern their movements can be studied using cerebral organoids.[7]
Clonal lineage tracing
editClonal lineage tracing is part of fate mapping, where the lineage of differentiated tissues is traced to the pluripotent progenitors. The local stimuli released and mechanism of differentiation can be studied using cerebral organoids as a model.[6] Genetic modifications in cerebral organoids might one day serve as a means to accomplish lineage tracing.[8]
Transplantation
editCerebral organoids can be used to grow specific brain regions and transplant them into regions of neurodegeneration as a therapeutic treatment.[9][10] In some cases, the genomes of these cerebral organoids would first have to be edited.[2] The "humanization" of animal models has been raised as a topic of concern in transplantation of human SC derived organoids into other animal models.[11]
Cross species developmental timing
editCerebral organoids provide a unique insight into the timing of development of neural tissues and can be used as a tool to study the differences across species.[6]
Cerebral organoids can be used as simple models of complex brain tissues to study the effects of drugs and to screen them for initial safety and efficacy. Testing new drugs for neurological diseases could also result from this method of applying drugs high-throughput screening methods to cerebral organoids.[2]
Cell replacement therapy
editCerebral organoids can be used as a simple model to show how cell replacement therapy would work on brain tissues.[6]
Implantation
editIn addition to being used as tools to study disease pathology and treatments, future application of cerebral organoids include direct implantation into a human host. The organoid can fuse with host tissue in areas of neurodegeneration, being incorporated with the host vasculature and be immunologically silent.[12]
Stroke Therapy
In the future, cerebral organoids with vascularity might provide insight into stroke therapy.[13]
Cell-type specific genome assays
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Culturing Methods
editThe general procedure used to culture a cerebral organoid can be broken down into 5 steps. First, human pluripotent stem cells are cultured. They are then allowed to cultivate into an embryoid
body. Next, the cell culture is induced to form a neuroectoderm. The neuroectoderm is then grown in a matrigel droplet. The matrigel provides nutrients and the neuroectoderm starts to proliferate and grow. However, the lack of vasculature limits the size the organoid can grow. This has been the major limitation in organoid development, however new methods using a spinning bioreactor
have allowed an increase in the availability of nutrients to cells inside the organoid. This last step has been the key breakthrough in organoid development.[14] Spinning bioreactors have been used increasingly in cell culture and tissue growth applications. The reactor is able to deliver faster cell doubling times, increased cell expansion and increased extra-cellular matrix components when compared to statically cultured cells.[15] Some developmental markers include the fact that, after ten days the organoid developed neurons, and after 30 days, it displayed regions similar to parts of brains. Lacking a blood supply, cerebral organoids reach about 4 mm across and can last a year or more.[16] Additionally, while these cells are self organizing, replication of specific brain regions in cerebral organoid counterparts is achieved by the addition of extracellular signals to the organoid environment during different stages of development; these signals were found to create change in cell differentiation patterns, thus leading to recapitulation of the desired brain region.[17] While SMAD inhibition is used in usual cerebral organoid culturing processes, inhibition of this has been shown to generate microglia in cerebral organoids. This adjustment to culturing methods would allow for research into diseases such as ASD.[18]
This was the original method outlined by Madeline Lancaster [19] and has since been developed and refined. Newer methods allow development of cerebrovascular organoids,[20] and micro pumps to provide circulation through them are being developed, as explained in this video by Dr George M. Church.
Assays
editCerebral organoids have the potential to function as a model with which disease and gene expression might be studied.[8] However, diagnostic tools are needed to evaluate cerebral organoid tissue and create organoids modeling the disease or state of development in question.[21]
Genetic Modifications
editCerebral organoids can be used to study gene expression via genetic modifications.[8] The degree to which these genetic modifications are present in the entire organoid depends on what stage of development the cerebral organoid is in when these genetic modifications are made; the earlier these modifications are made, such as when the cerebral organoid is in the single cell stage, the more likely these modifications will affect a greater portion of the cells in the cerebral organoid.[8]
The degree to which these genetic modifications are present within the cerebral organoid also depend on the process by which these genetic modifications are made. If the genetic information is administered into one cerebral organoid cell's genome via machinery, then the genetic modification will remain present in cells resulting from replication.[8] Crispr/Cas 9 is a method by which this long-lasting genetic modification can be made. [8] A system involving use of transposons has also been suggested as a means to generate long-lasting genetic modifications; however, the extent to which transposons might interact with a cell genome might differs on a cell to cell basis, which would create variable expressivity between cells. [8]
If, however, the genetic modification is made via “genetic cargo” insertion (such as through Adeno-associated virus/ electroporation methods) then it has been found that the genetic modification becomes less present with each round of cell division.[8]
Computational Methods
editUse of computational methods have been called for as a means to help improve the cerebral organoid cultivation process; development of computational methods has also been called for in order to provide necessary detailed renderings of different components of the cerebral organoid (such as cell connectivity) that current methods are unable to provide.[21] Programming designed to model detailed cerebral organoid morphology does not yet exist.[21]
Transcriptome analysis has also been suggested as a potential assay to examine the pathology of cerebral organoids derived from individual patients. [2]
Apoptotic Markers
TUNEL assays have been used in studies as an evaluative marker of apoptosis in cerebral organoids.[3]
Limitations
editNecrotic Centers
editUntil recently, the central part of organoids have also been found to be necrotic due to oxygen as well as nutrient being unable to reach that innermost area.[13][21]This imposes limitations to cerebral organoids' physiological applicability.[21] However, recent findings suggest that, in the process of culturing a cerebral organoid, a necrotic center could be avoided later on by using fluidic devices to increase the organoid's exposure to media.[21]
Reliability in Generation
editThe structure of cerebral organoids across different cultures has been found to be variable; a standardization procedure to ensure uniformity has yet to become common practice.[13] Future steps in revising cerebral organoid production would include creating methods to ensure standardization of cerebral organoid generation.[13] One such step proposed involves regulating the composition and thickness of the gel in which cerebral organoids are cultured in; this might contribute to greater reliability in cerebral organoid production[21]. Additionally, variability in generation of cerebral organoids is introduced due to differences in stem cells used.[2] These differences can arise from different manufacturing methods or host differences.[2] Increased metabolic stress has also been found within organoids. This metabolic stress has been found to restrict organoid specificity.[18]
Maturity
editAt the moment, the development of mature synapses in cerebral organoids is limited because of the media used.[13] Additionally, while some electrophysiological properties have been shown to develop in cerebral organoids, cultivation of separate and distinct organoid regions has been shown to limit the maturation of these electrophysiological properties. Modeling of electrophysiological neurodevelopmental processes typical of development later in the neurodeveopmental timeline, such as synaptogenesis, is not yet suggested in cerebral organoid models.[22]
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- ^ a b c d e f g h i j k Lee, Chun-Ting; Bendriem, Raphael M.; Wu, Wells W.; Shen, Rong-Fong (2017-08-20). "3D brain Organoids derived from pluripotent stem cells: promising experimental models for brain development and neurodegenerative disorders". Journal of Biomedical Science. 24 (1): 59. doi:10.1186/s12929-017-0362-8. ISSN 1423-0127. PMC 5563385. PMID 28822354.
{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link) - ^ a b c d e Sutarjono, Bayu (2019-02-15). "Can We Better Understand How Zika Leads to Microcephaly? A Systematic Review of the Effects of the Zika Virus on Human Brain Organoids". The Journal of Infectious Diseases. 219 (5): 734–745. doi:10.1093/infdis/jiy572. ISSN 0022-1899.
- ^ a b c d "Drug discovery in psychopharmacology: from 2D models to cerebral organoids". Dialogues in Clinical Neuroscience. doi:10.31887/dcns.2019.21.2/jladewig. PMC 6787544. PMID 31636494. Retrieved 2020-10-04.
{{cite web}}: CS1 maint: PMC format (link) - ^ a b Forsberg, Sheena Louise; Ilieva, Mirolyuba; Maria Michel, Tanja (2018-12). "Epigenetics and cerebral organoids: promising directions in autism spectrum disorders". Translational Psychiatry. 8 (1): 14. doi:10.1038/s41398-017-0062-x. ISSN 2158-3188. PMC 5802583. PMID 29317608.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) - ^ a b c d e Chambers SM, Tchieu J, Studer L (October 2013). "Build-a-brain". Cell Stem Cell. 13 (4): 377–8. doi:10.1016/j.stem.2013.09.010. PMID 24094317.
- ^ Purves D, Augustine GJ, Fitzpatrick D, Hall WC, LaMantia AS, White LE, eds. (2007). Neuroscience (4th ed.). New York: W. H. Freeman. ISBN 978-0-87893-697-7.
- ^ a b c d e f g h Fischer, Jan; Heide, Michael; Huttner, Wieland B. (2019). "Genetic Modification of Brain Organoids". Frontiers in Cellular Neuroscience. 13. doi:10.3389/fncel.2019.00558. ISSN 1662-5102. PMC 6928125. PMID 31920558.
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- ^ Daviaud, Nicolas; Friedel, Roland H.; Zou, Hongyan (November 2018). "Vascularization and Engraftment of Transplanted Human Cerebral Organoids in Mouse Cortex". eNeuro. 5 (6): ENEURO.0219–18.2018. doi:10.1523/ENEURO.0219-18.2018. ISSN 2373-2822. PMC 6243198. PMID 30460331.
- ^ Chen, H. Isaac; Wolf, John A.; Blue, Rachel; Song, Mingyan Maggie; Moreno, Jonathan D.; Ming, Guo-li; Song, Hongjun (2019-10). "Transplantation of Human Brain Organoids: Revisiting the Science and Ethics of Brain Chimeras". Cell Stem Cell. 25 (4): 462–472. doi:10.1016/j.stem.2019.09.002. ISSN 1934-5909. PMC 7180006. PMID 31585092.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) - ^ Lelkes PI, Unsworth BR (2002). "Neuroectodermal Cell Culture: Endocrine Cells". In Atala A, Lanza R (eds.). Methods of tissue engineering (1st ed.). San Diego, CA: Academic Press. p. 381. ISBN 978-0-12-436636-7.
- ^ a b c d e Kelava, Iva; Lancaster, Madeline A. (2016-12). "Dishing out mini-brains: Current progress and future prospects in brain organoid research". Developmental Biology. 420 (2): 199–209. doi:10.1016/j.ydbio.2016.06.037. PMC 5161139. PMID 27402594.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) - ^ Vogel G (August 2013). "Neurodevelopment. Lab dishes up mini-brains". Science. 341 (6149): 946–7. doi:10.1126/science.341.6149.946. PMID 23990534.
- ^ Reichardt A, Polchow B, Shakibaei M, Henrich W, Hetzer R, Lueders C (14 June 2013). "Large scale expansion of human umbilical cord cells in a rotating bed system bioreactor for cardiovascular tissue engineering applications". The Open Biomedical Engineering Journal. 7 (1): 50–61. doi:10.2174/1874120701307010050. PMC 3706833. PMID 23847691.
- ^ "Growing model brains: An embryonic idea". The Economist. 2013-08-31. Retrieved 2013-09-07.
- ^ Di Lullo, Elizabeth; Kriegstein, Arnold R. (2017-10). "The use of brain organoids to investigate neural development and disease". Nature Reviews Neuroscience. 18 (10): 573–584. doi:10.1038/nrn.2017.107. ISSN 1471-0048. PMC 5667942. PMID 28878372.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) - ^ a b Chan, Wai Kit; Griffiths, Rosie; Price, David J.; Mason, John O. (2020-12). "Cerebral organoids as tools to identify the developmental roots of autism". Molecular Autism. 11 (1): 58. doi:10.1186/s13229-020-00360-3. ISSN 2040-2392. PMC 7359249. PMID 32660622.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link) - ^ Lancaster MA, Renner M, Martin CA, Wenzel D, Bicknell LS, Hurles ME, Homfray T, Penninger JM, Jackson AP, Knoblich JA (September 2013). "Cerebral organoids model human brain development and microcephaly". Nature. 501 (7467): 373–9. Bibcode:2013Natur.501..373L. doi:10.1038/nature12517. PMC 3817409. PMID 23995685.
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- ^ a b c d e f g Poli, Daniele; Magliaro, Chiara; Ahluwalia, Arti (2019). "Experimental and Computational Methods for the Study of Cerebral Organoids: A Review". Frontiers in Neuroscience. 13. doi:10.3389/fnins.2019.00162. ISSN 1662-453X. PMC 6411764. PMID 30890910.
{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link) - ^ Chan, Wai Kit; Griffiths, Rosie; Price, David J.; Mason, John O. (2020-12). "Cerebral organoids as tools to identify the developmental roots of autism". Molecular Autism. 11 (1): 58. doi:10.1186/s13229-020-00360-3. ISSN 2040-2392. PMC 7359249. PMID 32660622.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)