An integration-free CRISPR platform for genetic dissection of respiratory virus host dependencies in human nasal epithelium
This study establishes an integration-free CRISPR/Cas9 workflow for genetically engineering human nasal basal cells to create gene-edited air-liquid interface cultures, which were used to validate ACE2 and TMPRSS2 as critical host factors for SARS-CoV-2 and hCoV-NL63 infection in a physiologically relevant model.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Viruses that cause respiratory illness, from the common cold to severe pandemics, begin their journey by landing on the lining of the nose. This thin layer of tissue, known as the nasal epithelium, acts as the body's first line of defense, a complex barrier made of many different types of cells working together. To understand how these viruses break through this barrier, scientists need to study the specific tools the virus uses to enter the cells. For decades, researchers have relied on simple, single-layer cell cultures grown in dishes to test which human proteins a virus might need to infect a person. However, these artificial cells often behave differently than the real, multi-layered tissue found in a living human nose. While scientists have recently developed better models that mimic the actual structure of the nasal lining, these realistic models have been difficult to modify genetically. Without the ability to easily turn specific human genes on or off in these realistic models, it has been hard to prove exactly which parts of the human body a virus hijacks to start an infection.
A team of researchers at Duke-NUS Medical School in Singapore has now solved this problem by creating a new method to edit the genes of these realistic nasal cells. They developed a way to use a precise molecular tool, known as CRISPR, to cut out specific genes in the stem cells that grow into the nasal lining. Unlike previous methods that required inserting foreign genetic material into the cells, which could cause unintended changes, this new approach is "integration-free," meaning it leaves no permanent trace of the editing tool behind. The scientists first grew healthy nasal cells from a donor, then used a temporary mixture of the editing tool and a glowing marker to cut out specific genes. They then sorted the cells that had successfully received the editing tool, expanded them, and allowed them to mature into a full, realistic nasal tissue layer. This process allowed them to create a tissue model where specific human genes were missing, letting them see exactly what happened when the virus tried to infect a nose without those specific tools.
Using this new platform, the researchers tested how two different coronaviruses, the one that causes COVID-19 and another common cold virus, infect the human nose. They first removed the gene for a protein called ACE2, which acts as the main door for these viruses to enter the cell. When they infected the edited tissue, the viruses could not get in, confirming that ACE2 is absolutely essential for both viruses to infect the human nose. Next, they investigated a second protein, TMPRSS2, which acts like a key that unlocks the door once the virus is at the surface. Previous studies had suggested that viruses might use different keys depending on the type of cell, but this new research showed that in the realistic nasal tissue, the virus relies almost entirely on TMPRSS2. When the researchers removed the gene for TMPRSS2, the viruses were unable to infect the tissue, proving that this specific protein is the critical key the virus needs to enter human nasal cells.
The study also ruled out other potential pathways the virus might use. The researchers tested whether the viruses could enter the cell through a different route involving internal cellular machinery, but found that blocking this route had no effect on the infection. This confirmed that in the human nose, the virus does not use these alternative entry methods. The findings were consistent across different donors, showing that the reliance on these two proteins is a fundamental feature of how these viruses infect humans. By demonstrating that these viruses depend on specific human proteins to enter the nose, the study provides a clear target for future medical treatments. If scientists can develop drugs that block either the door or the key, they could potentially stop the virus before it ever gets inside the body. This new method of editing realistic nasal tissue opens the door to testing many other viruses and understanding exactly how they infect us, offering a powerful tool for preparing for future respiratory threats.
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