This article is the original of translational medicine network, please indicate the source when reprinting
Author: Daisy
Various pathogens, such as Ebola virus, Marburg virus, Nipah virus, Hendra virus, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV) and SARS-CoV-2, are threatening human global health. The natural hosts of these pathogens are thought to be bats. Now, researchers have grown organoids from the gut cells of a fruit bat, the brown fruit bat. The established organoids successfully summarized the characteristics of the structure and morphology of the intestinal epithelium and identified the appropriate supplements necessary for long-term stable culture. In experimental inoculation, organoids showed susceptibility to PRV but not to SARS-CoV-2. This is the first report on the establishment of a scalable organoid culture system for fruit bat gut organoids and their sensitivity to bat-associated viruses, PRV and SARS-CoV-2. This organoid is a useful tool for elucidating the mechanisms of tolerance of emerging fruit bat-related viruses such as Ebola and Marburg virus.
Experiments trying to explain why bats can infect many viruses at once without dying from diseases like COVID-19 — knowledge that can help us reduce the threat of infectious diseases to humans — has been working on it until now, because live wild bats are not good subjects for study. To overcome this obstacle, the researchers for the first time bred an "organoid" of bats that can multiply their intestines in vitro.
A paper describing bat organoid growth techniques was published in the International Journal of Molecular Sciences.
https://www.mdpi.com/1422-0067/22/19/10763
Bats are a natural source of a large number of human pathogens (or, in epidemiological parlance, "hosts"—hosts in which pathogens survive without causing disease). These viruses include viruses that cause many diseases such as Ebola, Marburg, Nipah, Hendra, SARS, MERS and novel coronavirus pneumonia. In fact, a bat can carry these viruses without getting sick. Why bats are able to live with so many viruses without getting sick themselves remains one of the great mysteries of virology and its neighboring disciplines. There are limitations to the detailed analysis of viral tolerance mechanisms in vivo using individual bats. The current COVID-19 pandemic makes it all the more urgent to solve this mystery.
Bats, however, are wild animals, not domesticated experimental animal subjects. It is more difficult to conduct reproducible studies on bats than on more common experimental animals such as mice or pigs. Therefore, most experiments must be performed on cell lines taken from bats, not on the bats themselves or on bat organs.
"If this experimental obstacle can be overcome, the relationship between viruses and bats can be understood, thereby reducing human illness and death." Tsutomu Omatsu, one of the paper's authors and an associate professor at the Center for Infectious Disease Epidemiology and Prevention at Tokyo University of Agriculture and Technology, said.
As a result, the researchers developed bat organoids that could be used in such experiments. An organoid is a three-dimensional tissue structure grown from stem cells "in vitro" (in a petri dish or other laboratory device) that mimics the organs of living animals. The intestine is known to be one of the passages through which pathogens enter and leave the body along with the lungs. In this case, they grew organoids from the gut cells of a fruit bat, the brown fruit bat (a species of fruit bat, also known as fruit bats).
Why fruit bats? Fruit bats are giant bats that are thought to be natural hosts to a family of viruses, including Ebola and Marburg. Brown fruit bats were chosen because in previous studies, experimental vaccination with SARS-CoV-2 (the virus that causes COVID-19) has been shown to cause a brief but not intense infection, while cell lines from the brown fruit bat gut have not been infected at all. Several species of fox bats in Southeast Asia and Australia have also been found to be hosts for the PRV virus that causes respiratory diseases in humans.
Researchers must first find an optimal medium for bat gut cell growth. They did this by experimenting with culturing organoids with nine different growth supplements (nutrients and other molecules that promote cell proliferation), including Wnt 3a, Noggin, R-spondin (WNR), EGF, FGF2, FGF7, FGF10, IGF, or TGF-α. The effects of different supplements on the growth and proliferation of fruit bat organoids vary significantly. After seven days, the rate of cell growth and proliferation in three of these groups (WNR, TGF-α, EGF) increased significantly. However, FGF2, FGF7, FGF10, and IGF had no significant effect compared to the control group.
Identification of suitable intestinal organoid culture supplements from fruit bats
Based on these results, the researchers found that WNR, EGF, and TGF-α were critical for the culture of gut organoids in fruit bats. In addition, fruit bat intestinal organoids grown with these three supplements have a long lifespan and are able to remain active for proliferation for up to ten generations (up to 10 times more organoids than the previous organoids composed of isolated cells). Organoids that are long-term cryopreserved (essentially frozen) can also grow normally once thawed.
To confirm that organoids mimic the epithelial (external) tissue of bat intestines— the first part of bat organs to encounter viral particles— and therefore have special scientific implications, the researchers deployed two techniques. First, they used transmission electron microscopy to study the cellular anatomy (histology) of organoids. Second, they used immunofluorescence staining, a common method for detecting and visualizing molecules in biological samples— to look for molecular markers that showed that the tissues studied came from the guts of bats. The combination of these two techniques tells the researchers that organoids are indeed rebuilding the typical cellular components of fruit bat gut tissue.
Organoids reproduce the cellular composition of intestinal tissue
Preliminary tests using organoids to study viral relationships were also conducted. In experimental inoculation, they show sensitivity to PRV but not to SARS-CoV-2.
After successfully creating bat organoids for the first time, the researchers now want to repeat their technique on other fruit bat organs, such as the lungs, liver and kidneys. The researchers will then infect a large number of bats "in vivos" with highly pathogenic viruses, analyzing their gene expression in detail (turning genes on and off), thus being able to elucidate the mechanisms by which bats are able to host these pathogens without getting sick.
Resources:
https://medicalxpress.com/news/2021-12-intestine-organoid-grown-lab-viruses.html
Note: This article is intended to introduce the progress of medical research and cannot be used as a reference for treatment options. For health guidance, please visit a regular hospital.