Human brain cells successfully transplanted into mouse heads… Ethical issues remain

Mice transplanted with organ analogue ‘organoid’, brain neurons grow and function

input 2022.10.18 11:54
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input 2022.10.18 11:54
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An experiment in which ‘brain organoids’, which are analogs of human brains, were implanted into the brains of mice recently succeeded. [사진=unoL/게티이미지뱅크]

As a result of transplanting human brain cells into the brains of baby mice, it was found that the cells settle and grow and connect with the mouse brain cells.

Animal experiments like this are controversial from an ethical point of view, but the research team requested that scientists look at them as efforts to study diseases that occur in the brain, the most complex organ of the human being.

“Autism and schizophrenia may be diseases unique to humans,” said a research team at Stanford University in the United States, who led this study. “But the human brain is not an easily accessible institution for research.” The need for research subjects to replace the human brain.

For this purpose, scientists are using ‘organoids’. Organoids are organ analogues made by culturing or recombining stem cells to have structures and functions similar to those of human organs, such as the brain, liver, and kidneys. To create brain organoids, the research team reverse-differentiated human skin cells into stem cells and then proliferated them to become organisms resembling the cerebral cortex of the brain, which plays the role of memory, thinking, learning, reasoning, and emotions.

When these brain organoids were transplanted into two or three-day-old mice, the organoids gradually grew and took up a third of the mouse brain. In addition, as the nerve cells of the organoids were connected to each other, it was shown that the mouse brain circuit worked.

Human neurons have been transplanted into rodents before, but usually into adult animals. The research team said that it was the first time that organoids made using human skin cells were transplanted into the brains of young mice, and that they were able to prove how human cells affect the growth of mice.

The research team transplanted organoids made using cells from healthy people and cells from patients with Timothy’s syndrome, a disease related to autism spectrum disorder, to both sides of the mouse brain.

After 5-6 months, the neurons formed in the brain were examined. As a result, it was confirmed that much fewer nerve cells were formed at the site of transplantation of organoids in patients with Timothy’s syndrome. The research team believes that transplanting organoids made using cells from patients with autism or schizophrenia might also confirm the various potential effects of the disease on the brain.

However, these experiments have ethical issues. It is regarding the extent to which experiments can be conducted on mice and whether these experiments can be applied to primates such as monkeys. The researchers say it is not yet time to apply the experiment to primates. Although unlikely at this time, some ethicists are also concerned regarding the threatening situation when brain organoids acquire human cognitive abilities. For this reason, some scientists, including a research team in Zurich, Switzerland, are conducting research on brain organoids without transplanting them into animals.

This study was recently published in the international academic journal Nature.