Bats are carriers of natural viruses. Why do they carry a large number of viruses without being harmed? Can humans seek a universal idea against multiple viruses from here?
On March 31, research teams from Tsinghua University's High-Tech Innovation Center for Structural Biology, Duke-National University of Singapore School of Medicine, China Centers for Disease Control and Prevention, Institute of Zoology, Chinese Academy of Sciences, and Duke University jointly published a preprinted website BioRxiv published a new study online, "Orthogonal genome-wide screenings in bat cells identify MTHFD1 as a target of broad antiviral therapy".
The study has not been peer-reviewed.
The team conducted a comprehensive screening of more than 20,000 genes in bat cells, identified dozens of key bat genes on which virus replication depends, and discovered a common new host gene, MTHFD1.
Further research found that MTHFD1 expression levels in bat cells were much lower than those in human corresponding tissues, which may be related to the physiological changes in bats' adaptation to flight life.
The research team finally found that carolacton, an inhibitor of the host protein MTHFD1, was effective in inhibiting the replication of the new coronavirus.
They believe that the research results will not only help the development of new coronavirus drugs, effectively fight the epidemic but also lay the foundation for future humans to fight the sudden virus epidemic.
Researcher Tan Xu from Tsinghua University's High-Tech Innovation Center for Structural Biology and Professor Wang Linfa from Duke-NUS Medical School are co-corresponding authors.
Jin Cui, a Ph.D. candidate in the School of Pharmacy, Tsinghua University, Ye Qian, postdoc, Danielle Anderson, Duke-NUS Medical School, and Dr. Huang Baoying, Chinese Center for Disease Control and Prevention are the co-first authors.
The study was also helped by Researcher Tan Wenjie of the Chinese Center for Disease Control and Prevention, Researcher Zhou Xuming of the Institute of Zoology, Chinese Academy of Sciences, and Professor So Young Kim of Duke University.
In addition, the work of Tan Xu Lab was co-funded by Tsinghua University's special project for epidemic prevention and control technology, Beijing High-Tech Innovation Center for Structural Biology, Tsinghua-Peking University Life Science Joint Center, and National Natural Science Foundation of China Youth Fund.
Humans need broad-spectrum antiviral drugs
From SARS and Ebola to new coronavirus pneumonia (COVID-19) in 2019, infectious diseases caused by the virus have been one of the major diseases that seriously endanger global health.
The history of the epidemic situation has made us deeply realize that the urgent task is the research and development of broad-spectrum antiviral drugs.
The emergency treatment of broad-spectrum antiviral drugs for newly emerged viral infections can save critically ill patients in danger and has an inestimable effect on reducing mortality and alleviating the epidemic situation.
However, traditional antiviral drugs use viral proteins as targets, and they are difficult to play a role in coping with the emergence of many different types of viruses, and viruses can easily develop resistance by mutating their own genes.
In contrast, since multiple viruses require many common host proteins to replicate in the cell to complete the replication cycle, new antiviral drugs targeting viral replication-dependent host proteins may have the advantages of broad-spectrum and resistance to drug resistance.
The paper mentions that bats are natural hosts for viruses such as Ebola virus, SARS-CoV, MERS-CoV, Hannibal virus genus, and novel coronaviruses.
The research team tried to start with bat genome analysis, use leading functional genomics methods to systematically search for host factors that depend on the life cycle of the virus, and find new antiviral drug targets by understanding the molecular mechanism of virus-host factor interactions.
Why are bats immune to viruses?
Bats belong to the order Merophysalis and are the only mammals that can truly fly. In recent years, many large-scale lethal outbreaks have been inextricably linked with bats, and bats have been recognized as the most important natural "reservoir" for emerging viruses.
The authors mention that SARS in 2003, Ebola in 2014, and the new coronavirus pneumonia that began to erupt at the end of 2019 have brought huge economic losses and psychological panic around the world.
Much evidence supports that bats are the common natural host for these disease-causing viruses. The spread of the virus from bats to some intermediate host eventually led to a large-scale outbreak.
However, it is puzzling that although bats can carry a variety of disease-causing viruses, these viruses do not cause obvious symptoms in bats. Bats' high tolerance to viruses may also be an important reason for their ability to carry and spread multiple viruses.
Zhou Peng, a researcher at the Wuhan Institute of Virology of the Chinese Academy of Sciences, said in an interview with thepapr.cn, "From the perspective of immunology, the bat's immune system is still unique. It is the only mammal that can fly continuously. Many of its genes are different from those of humans or other mammals. Many of these different genes are related to the antiviral and immune systems. "
Zhou Peng and others have previously confirmed that a certain amount of interferon expression is always maintained in bats. Interferon is a key antiviral protein. If it is always kept "low" in the body, it is equivalent to the animal having a "weather protection" defense mechanism.
"Our preliminary conclusion now is that its immune pathway will maintain a certain amount of defense, but it will not be overexposed. Viruses such as SARS infection in humans will eventually die of excessive inflammation, but the inflammatory response and innate immunity of bats will not. Excessive, so it won't be damaged. "
Zhou Peng and others have previously mentioned similar ideas, studying the uniqueness of carrying viruses without disease in bats, which is expected to allow humans to learn how to fight the virus.
The authors believe that the results of bat physiology and genome sequencing provide multiple explanations for its ability to tolerate the virus, and functional genomic screening can help us further understand the host factors required by the virus to infect bat cells.
Difference between the virus infection mechanism of bats and humans
Based on the above background, the research team established the first genomic genome CRISPR knockout library of the bat (Pteropus Alecto) and completed the genome-wide CRISPR screening for influenza virus infection in the black demon fox kidney epithelial cells (PaKi cells). From them, more than 20 host factors that virus replication depends on were found (Figure 1).
At the same time, Wang Linfa's group at Duke-NUS Medical School used RNA interference (RNAi) to screen bat cells for mumps virus infection and found dozens of virus-dependent host factors.
By comparing the screening results of the two research groups, the research team found that they include important genes for cell endocytosis and protein secretion pathways, which are similar to viral infections in human cells, indicating that viral infections in bat cells and human cells Reliance on these pathways is conservative.
In addition, both sets of screenings revealed a common new host gene, MTHFD1.
MTHFD1 encodes methylenetetrahydrofolate dehydrogenase and is an important metabolic enzyme for de novo synthesis of purine bases from DNA and RNA.
It is very interesting that MTHFD1 was not found in the previous genome-wide screening of viral host factors in human cells.
Further research found that MTHFD1 expression levels in bat cells were much lower than those in human corresponding tissues, which may be related to the physiological changes in bats' adaptation to flight life.
Overall, the research team identified dozens of key bat genes that virus replication depends on through a comprehensive screening of more than 20,000 genes in bat cells.
These genes are functionally conserved in bats and humans, but species differences in gene expression levels may determine different pathological outcomes of viral infections.
Carolacton
The research team further found that RNA viruses, including mumps virus, Malacca virus, Zika virus, etc., are very sensitive to the loss of MTHFD1, and MTHFD1 inhibitor carolacton has a very strong inhibitory effect on the replication of these viruses.
This phenomenon is significant in both bats and human cells.
Carolacton is a natural product that has been used as a candidate for antibiotics to inhibit the production of bacterial membranes.
Encouragingly, through cooperation with the Chinese Centers for Disease Control and Prevention, the research team found that carolacton can also effectively inhibit the replication of new coronavirus in human cells, and the effective concentration of antivirus is far lower than the cytotoxic concentration, showing a good Medicine.
Genetic screening of bats has led to the discovery of MTHFD1, a new antiviral drug target and the small antiviral molecule carolacton.
This result also suggests that we can learn how to deal with virus infection by studying the mechanism of bat virus infection.
Genome-wide CRISPR screening of bat cells found a key host factor for RNA virus replication, MTHFD1, and its inhibitor carolacton effectively inhibited the replication of the new coronavirus in primate cell lines.
The research team will further conduct preclinical tests on the antiviral function of carolacton and its derivatives in animal infection models in the hope that it can be used as a broad-spectrum antiviral drug as soon as possible.
The study of the effects of MTHFD1-related genes on the virus and its drug targeting is also expected to provide more candidate drug molecules.
In addition, the genome-wide screening system established earlier by the research team will also play a huge role in the research of other tissue cells, especially immune cells, to help researchers continue to explore more of the mysteries of bats.
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