Dynamic expression of mucins and the genes controlling mucin-type O-glycosylation within the mouse respiratory system.

The COVID-19 global pandemic has underscored the need to understand how viruses and other pathogens are able to infect and replicate within the respiratory system. Recent studies have highlighted the role of highly O-glycosylated mucins in the protection of the respiratory system as well as how mucin-type O-glycosylation may be able to modify viral infectivity. Therefore, we set out to identify the specific genes controlling mucin-type O-glycosylation throughout the mouse respiratory system as well as determine how their expression and the expression of respiratory mucins is influenced by infection or injury. Here, we show that certain mucins and members of the Galnt family are abundantly expressed in specific respiratory tissues/cells and demonstrate unique patterns of O-glycosylation across diverse respiratory tissues. Moreover, we find that the expression of certain Galnts and mucins is altered during lung infection and injury in experimental mice challenged with infectious agents, toxins, and allergens. Finally, we examine gene expression changes of Galnts and mucins in a mouse model of SARS-CoV-2 infection. Our work provides foundational knowledge regarding the specific expression of Galnt enzyme family members and mucins throughout the respiratory system, and how their expression is altered upon lung infection and injury.

Detecting residual chemical disinfectant using an atomic Co-N-x-C anchored neuronal-like carbon catalyst modified amperometric sensor

Hydrogen peroxide (H2O2) solution and its aerosols are common disinfectants, especially for urgent reuse of personal protective equipment during the COVID-19 pandemic. Highly sensitive and selective evaluation of the H2O2 concentration is key to customizing the sufficient disinfection process and avoiding disinfection overuse. Amperometric electrochemical detection is an effective means but poses challenges originated from the precarious state of H2O2. Here, an atomic Co-N-x-C site anchored neuronal-like carbon modified amperometric sensor (denoted as the CoSA-N/C@rGO sensor) is designed, which exhibits a broad detection range (from 250 nM to 50 mM), superior sensitivity (743.3 mu A mM(-1) cm(-2), the best among carbon-based amperometric sensors), strong selectivity (no response to interferents), powerful reliability (only 2.86% decay for one week) and fast response (just 5 s) for residual H2O2 detection. We validated the accuracy and practicability of the CoSA-N/C@rGO sensor in the actual H2O2 disinfection process of personal protective equipment. Further characterization verifies that the electrocatalytic activity and selective reduction of H2O2 is determined by the atomically dispersed Co-N-x-C sites and the high oxygen content of CoSA-N/C@rGO, where the response time and reliability of H2O2 detection is determined by the neuronal-like structure with high nitrogen content. Our findings pave the way for developing a sensor with superior sensitivity, selectivity and stability, rendering promising applications such as medical care and environmental treatment.

Furin cleavage of the SARS-CoV-2 spike is modulated by O-glycosylation.

The SARS-CoV-2 coronavirus responsible for the global pandemic contains a novel furin cleavage site in the spike protein (S) that increases viral infectivity and syncytia formation in cells. Here, we show that O-glycosylation near the furin cleavage site is mediated by members of the GALNT enzyme family, resulting in decreased furin cleavage and decreased syncytia formation. Moreover, we show that O-glycosylation is dependent on the novel proline at position 681 (P681). Mutations of P681 seen in the highly transmissible alpha and delta variants abrogate O-glycosylation, increase furin cleavage, and increase syncytia formation. Finally, we show that GALNT family members capable of glycosylating S are expressed in human respiratory cells that are targets for SARS-CoV-2 infection. Our results suggest that host O-glycosylation may influence viral infectivity/tropism by modulating furin cleavage of S and provide mechanistic insight into the role of the P681 mutations found in the highly transmissible alpha and delta variants.

O-glycosylation of the novel SARS-CoV-2 coronavirus spike protein influences furin cleavage

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the pandemic that has affected millions of people worldwide. This virus contains a unique polybasic insertion (PRRA) within the spike protein, resulting in a novel furin cleavage site that has been shown to influence viral infectivity and syncytia formation in cell culture. This insertion also generates novel putative sites of O-glycosylation, a protein modification that has been shown in other proteins to influence furin cleavage. Here, we define the specific members of the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (GALNT) family that are capable of glycosylating the novel SARS-CoV-2 coronavirus spike and examine their presence in human respiratory cells that are targets for SARS-CoV-2 infection. Moreover, we show that O-glycosylation by specific members of the GALNT enzyme family modulates furin cleavage of the spike in vivo. Given the well-established role of O-glycosylation in the regulation of proteolysis, our results suggest that O-glycosylation of SARS-CoV-2 may play roles in aspects of spike stability/processing, which may influence viral infectivity and tropism.

ApoE-Isoform-Dependent SARS-CoV-2 Neurotropism and Cellular Response.

ApoE4, a strong genetic risk factor for Alzheimer disease, has been associated with increased risk for severe COVID-19. However, it is unclear whether ApoE4 alters COVID-19 susceptibility or severity, and the role of direct viral infection in brain cells remains obscure. We tested the neurotropism of SARS-CoV2 in human-induced pluripotent stem cell (hiPSC) models and observed low-grade infection of neurons and astrocytes that is boosted in neuron-astrocyte co-cultures and organoids. We then generated isogenic ApoE3/3 and ApoE4/4 hiPSCs and found an increased rate of SARS-CoV-2 infection in ApoE4/4 neurons and astrocytes. ApoE4 astrocytes exhibited enlarged size and elevated nuclear fragmentation upon SARS-CoV-2 infection. Finally, we show that remdesivir treatment inhibits SARS-CoV2 infection of hiPSC neurons and astrocytes. These findings suggest that ApoE4 may play a causal role in COVID-19 severity. Understanding how risk factors impact COVID-19 susceptibility and severity will help us understand the potential long-term effects in different patient populations.