Zooming in on viruses

Respiratory disease represents the most important cause of mortality worldwide, of which a significant portion is due to infectious agents. My lab mainly conducts research on respiratory-borne viruses, with a current focus on respiratory syncytial virus (RSV), human metapneumovirus (HMPV), and human and avian influenza viruses.

In collaboration with local hospitals and diagnostic laboratories in Singapore, which provide critical access to clinical and veterinary virus isolates, my research aims to identify and characterise essential pathogen-host interactions that occur during viral infection. Due to the complex nature of these questions, the projects undertaken involve a significant degree of multidisciplinary work, including imaging, functional genomics and bioinformatics, proteomics and standard molecular and cell biology techniques.

Respiratory syncytial virus—a global health concern

Epidemiological data from the World Health Organisation indicates that RSV is responsible for 64 million infections per year and 160,000 deaths, mainly involving young children. It is the leading cause of viral pneumonia in young children, and this situation is exacerbated by the absence of licensed vaccines and the limited availability of cost-effective drugs.

A better understanding of RSV’s replication cycle could help identify novel drug targets and aid in vaccine development. Therefore, my research focuses on the identification and characterisation of essential pathogen-host interactions that occur during RSV maturation and transmission. Using light microscopy (Figure 1), we can identify virus filaments—special filamentous projections generated by virus particles to attach to and assemble at specific surface regions of cells in the respiratory tract. Another structure, known as inclusion body, contains the virus nucleocapsid—a complex of the virus genome and associated viral proteins including the nucleoprotein, phosphoprotein and large polymerase protein.

Figure 1: Images obtained by confocal microscopy of a virus-infected cell labelled using antibodies to the virus phosphoprotein (green) and virus fusion glycoprotein (red), highlighting the association of virus filaments and inclusion bodies in virus-infected cells. (A) Two-dimensional micrograph of the cell obtained at a single focal plane. (B) A series of images of a region near the surface of the same cell at different focal planes—processed and visualised in 3D—showing inclusion bodies (IB) labelled by anti-phosphoprotein and virus filaments (VF) labelled by both anti-phosphoprotein and anti-fusion glycoprotein. (C) A rotated and tilted projection of the cell’s interior at higher magnification, showing an individual inclusion body and its associated virus filaments. Credit: Reproduced from Molecular & Cellular Proteomics (2010), DOI: 10.1074/mcp.M110.001651.

Virus filaments as targets for antivirals

To examine RSV replication, we used a nasal epithelial organoid cell model, which closely resembles the cells in the nasal airways that are the primary site of viral infection in humans. Use of this cell model has allowed us to demonstrate virus filament formation during RSV infection (Figure 2), highlighting the physiological relevance of these structures in the development of antivirus strategies.

The formation of virus filaments also correlates with the degradation and dysfunction of cilia—projections of epithelial cells in the respiratory tract that clear mucus and dirt out of the airways. Destruction of the cilia contributes to the damage caused by the virus in our lungs.

Figure 2:  Scanning electron microscopy of mock-infected and RSV-infected cells. Cilia, microvilli (mv) on non-ciliated cells, and virus particles (VF) are labelled. Credit: Richard Sugrue.

New avenues to prevent virus particle binding                                     

My lab was able to demonstrate that an enzyme called 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) is highly expressed during RSV particle formation. HMGCR is a key enzyme in the mevalonate pathway, which regulates the formation of small hydrophobic molecules. These molecules are important in the anchoring of certain cellular proteins to membranes where they are exploited by the virus to build virus particles.

We also demonstrated that a cardiovascular drug—lovastatin—is able to block virus filament formation and virus transmission. The antiviral activity of lovastatin supports our hypothesis that the mevalonate pathway is involved in the assembly and formation of virus particles on the surface of infected cells.

Our findings of virus-induced changes in cellular signalling and metabolic activities underline the complexity of the virus particle formation process. Understanding this process in greater detail may lead to the development of novel drugs to treat infection with RSV and related virus species.

Author: Richard Sugrue
Assoc Prof Richard Sugrue of NTU’s School of Biological Sciences is an expert on the infection biology of respiratory viruses. More details on the research described here can be found in Virology (2018), DOI: 10.1016/j.virol.2018.05.012; Virology (2015), DOI: 10.1016/j.virol.2015.05.014; Antiviral Research (2013), DOI: 10.1016/j.antiviral.2013.08.012; and Molecular & Cellular Proteomics (2010), DOI: 10.1074/mcp.M110.001651.
The article appeared first in NTU’s research & innovation magazine Pushing Frontiers (issue #17, August 2020).

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