The pathogenesis of neurological diseases can be difficult to model due to the complexities or specificities associated with them. This leaves scientists with having to use animal models or other in vitro methods that may not entirely represent the human brain. However, recent studies have shown that 3-D human cerebral organoid models can be derived from human stem cells, and can be used toward researching otherwise difficult to observe diseases in the human brain.
In the article “Dynamic Characterization of Structural, Molecular, and Electrophysiological Phenotypes of Human-Induced Pluripotent Stem Cell-Derived Cerebral Organoids, and Comparison with Fetal and adult Gene Profiles,” Dr. Thiago Arzua et. al explored the development of a 3-D cerebral organoid model, over a two month time period, using human induced pluripotent stem cells (iPSCs) to be compared with activity in adult and fetal brains. This was accomplished through staining important biomarkers in the cerebral organoids and preparing cDNAs using extracted RNA. Reverse transcriptase PCR (qRT-PCR) was then used to create multiple copies of the extracted RNA. Electrophysiological analysis of the cerebral organoid was also performed, using patch-clamp amplifiers, to measure the voltage potential at specific ion concentrations. The researchers then used microarray analysis to compare the gene expression between the cerebral organoid, fetal brain tissue, and adult brain tissue. They were able to identify that neural cells and glial cells formed in the cerebral organoid using gene expression. Additionally, it was observed that the cerebral organoids showed a decrease in the number of pluripotent stem cells, meaning that the stem cells were changing into neural/glial cells. The cerebral organoids were also reported to show synaptic activity, postsynaptic GABA channel reaction to a GABA agonist, and action potential generation. They were able to conclude that the cerebral organoid model more closely represented fetal brain activity compared to adult brain activity.
The usage of 3-D cerebral organoid models also proved to be useful in the study, “Modeling Human Cytomegalovirus-Induced Microcephaly in Human iPSC-Derived Brain Organoids” by Dr. Guoqiang Son et. al. The Human Cytomegalovirus (HCMV) has not been well understood in the past due to its species-specific neuropathogenesis. Because of this, animal models have been rendered useless, with in vitro models being the only plausible method of studying the pathogen. This is where the researchers resorted to using iPSC cerebral organoid models to observe HCMV and test potential antiviral methods. They first created an HCMV strain called TB40/E which was shown to reduce the organoid size. This accurately represents the microcephaly in infants which occurs as a result of HCMV. Once they were able to determine the TB40/E strain can depict HCMV, they began testing treatments for the prevention of the virus. Neutralizing antibodies (NAbs) have been shown to be important in the prevention of HCMV. However, there is still ambiguity with its capabilities to interfere with an HCMV in a developing brain. The researchers tested this by infecting the human brain organoids with the GFP labeled TB40/E strain at day 45 of differentiation, introducing the NAbs to the organoids, then measuring the organoid size and GFP fluorescence intensity. They also had a control model where they introduced IgG (immunoglobulin G) to a TB40/E infected organoid. Results showed that the organoids treated with the NAbs were larger and displayed less GFP fluorescence intensity than the IgG treated organoids. From this, the researchers were able to determine that NAbs are capable of interfering with and inhibiting HCMV infection in a developing human brain organoid.
These studies both observed the abilities of human cerebral organoids in researching neuropathology. Dr. Thiago Arzua used human iPSC derived organoid models to study their similarities with adult and fetal brains. Dr. Guoqiang Son and his lab used the human cerebral organoids to study the effects of HCMV along with uncovering the grey-areas associated with the preventative effects of neutralizing antibodies on HCMV in a developing brain. The functionality of the brain can be very complicated and there are still several aspects that have yet to be explained. If perfected, these human cerebral organoids will allow us to gain a much better understanding of the neural circuitry of the brain and the pathology of neural diseases.
Citations
Logan, Sarah, et al. “Dynamic Characterization of Structural, Molecular, and Electrophysiological Phenotypes of Human-Induced Pluripotent Stem Cell-Derived Cerebral Organoids, and Comparison with Fetal and Adult Gene Profiles.” Cells, vol. 9, no. 5, 2020, p. 1301., doi:10.3390/cells9051301.
Sun, Guoqiang, et al. “Modeling Human Cytomegalovirus-Induced Microcephaly in Human IPSC-Derived Brain Organoids.” 25 Mar. 2020
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