Using Lifeline Cell Systems to Study Coronavirus Infection
As the world is coping with the COVID-19 pandemic, researchers around the world are studying this novel virus to discover how it works, how it could be treated, and how it might be targeted with a vaccine.
COVID-19 is a respiratory disease caused by the severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2. SARS-CoV-2 is a member of the coronavirus family, which also includes human coronaviruses 229E, NL63, OC43, and HKU1 viruses. According to the US Centers for Disease Control (CDC), these four common coronaviruses (unlike SARS-CoV-2) “usually cause mild to moderate upper respiratory illnesses, like the common cold.”
The human coronavirus family also includes MERS-CoV and SARS-CoV, which cause Middle East Respiratory Syndrome (MERS) and severe acute respiratory syndrome (SARS), respectively.
Due to its novelty, SARS-CoV-2 has not yet been widely studied. However, for those studying SARS-CoV-2, or other human respiratory viruses, Lifeline® cell systems are a great place to start. As summarized below, Lifeline human bronchial/tracheal epithelial cells (HBTECs) are an excellent model system in which to study the human airway epithelium and its response to infection by coronaviruses and other respiratory pathogens.
In addition to HBTECs themselves, Lifeline also offers Air-Liquid Interface Epithelial Differentiation Medium for the optimal mucocilliary differentiation of HBTECs in an air-liquid interface. To more effectively model airway biology and dynamics in vitro, researchers often use air-liquid interface culture, a specialized culture system in which HBTECs become polarized, contacting medium at their basolateral surface and air at their apical surface, mimicking the orientation and contacts that occur in vivo. For more on how air-liquid interface culture systems work, check out one of our previous blog posts here.
Lifeline HBTECs in Respiratory Viral Infection Research
Characterization of HKU1 coronavirus: In a 2014 study, Dominguez et al. set out to further characterize the HKU1 coronavirus following successful isolation of clinical specimens and development of a system to propagate HKU1 strains in vitro. Using Lifeline HBTECs in an air-liquid interface, the authors isolated clinical specimens of HKU1 and sequenced their respective genomes, which enabled them to classify HKU1 strains using phylogenetic analysis.
Mechanisms of human coronavirus infection: In a 2017 study, Shirato and colleagues investigated how human coronavirus enters human airway epithelial cells to cause respiratory infections. Using Lifeline HBTECs cultured in an air-liquid interface system, the authors tested the infectivity and cell entry method of clinical isolates of HCoV-OC43 and HCoV-HKU1. They found that these viral strains entered cell via transmembrane protease serine 2, a membrane protease.
Evolution of HCoV-229E over time in culture: In a 2016 study, Shirato et al. studied how long-term propagation of HCoV-229E in culture has changed its behavior. Using Lifeline HBTECs cultured in an air-liquid interface, the group found that clinical isolates of HCoV-229E had reduced replicative capacity over time. The authors found that this reduced replication was likely due to a point mutation in the spike (S) protein of the virus (a key molecule used in viral entry) that reduced its ability to infect cells.
Mapping the HKU1 S protein receptor-binding domain: In a 2015 study, Qian and colleagues set out to identify the receptor-binding domain of the HCoV-HKU1 group A S protein, which mediates viral infection. Using Lifeline HBTECs grown in an air-liquid interface, the authors used monoclonal antibody binding assays to determine that the receptor-binding domain of HCoV-HKU1 was located in the C domain of the S protein.
Crystal structure of the HKU1 S protein: In a 2017 study, Ou and colleagues solved the crystal structure of the human CoV-HKU1 S protein C-terminal domain to better understand how the S protein binds its receptor to infect cells. Using Lifeline HBTECs in an air-liquid interface, the authors demonstrated that S protein residues W515 and R517 were required for receptor binding, providing insight into how the CoV-HKU1 S protein infects cells.
Mechanisms of adenovirus infection and regulation of host cell gene expression: In a 2018 study, Hsu and colleagues used Lifeline HBTECs to study the early stages of adenovirus infection and viral protein transcription by the host cell. Using Lifeline HBTECs, the authors found that inhibition of p300 ( a histone acetyltransferase) by the viral E1A protein epigenetically regulated host cell gene expression through histone acetylation following E1A-p300 binding.
Influenza reassortment: In a 2013 study, Hauser and colleagues set out to study how the influenza virus reassorts in swine, which can be infected with influenza viruses from humans and birds and following reassortment, can transmit reassorted avian flu to humans. Using Lifeline HBTECs in an air-liquid interface culture system, the authors concluded that in contrast to human respiratory epithelial cells, swine respiratory epithelial cells exhibit less antiviral response, which may explain why avian and human viruses more readily reassort in swine.
During this pandemic, we hope you stay well and healthy. For more about Lifeline cell systems, visit our blog for regular posts every other week!