The Role of Neuropilin-1 in SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) facilitates entry into the host cell via an association between its viral spike (S) protein and the angiotensin-converting enzyme 2 (ACE2) cell membrane-bound receptor. While it is known that other coronaviruses, such as severe acute respiratory syndrome coronavirus (SARS-CoV) exploit the same mechanism of entry, the infectivity of SARS-CoV-2 appears far superior. It is thought that a specific furin-like cleavage site located in the S protein may potentiate SARS-CoV-2’s ability to spread. The cleavage site processes the S protein, generating a sequence in the resulting peptide that appears to be a recognition and activation motif for another cellular receptor called neuropilin-1 (Nrp1).

Dr. Maria Anastasina from the University of Helsinki and colleagues have been investigating the involvement of Nrp1 in SARS-CoV-2 cell entry and infectivity. Technology Networks had the pleasure of speaking with Anastasina to learn more about this work, which was presented as part of The European Laboratory Research & Innovation Group (ELRIG)'s Drug Discovery 2021 meeting.

Laura Lansdowne (LL): Despite SARS-CoV and SARS-CoV-2 both using ACE2 as a receptor, their tissue tropism differs – what is the consequence of this variation?

Maria Anastasina (MA): Differences in tissue tropism of SARS-CoV and SARS-CoV-2 are reflected in different pathogenesis of these viruses and hence in different symptoms experienced during COVID-19. A striking example is a loss of sense of smell experienced by many COVID-19-affected individuals – a symptom we haven’t observed during infections caused by other coronaviruses. This symptom is most likely a consequence of SARS-CoV-2 infection of the olfactory nerves and supporting olfactory epithelial cells.

LL: Could you tell me more about the distinctive feature of SARS-CoV-2’s S protein (the cleavage site for host protease furin). What is the function of the furin site and what is its relationship with Nrp1?

MA: Our data suggest that the proteolytic processing of SARS-CoV-2’s S protein by furin results in an arginine-rich C-terminal peptide on S1. This peptide follows a so-called C-end rule, i.e., contains a recognition sequence for Nrp1. Therefore, we propose that furin processing of SARS-CoV-2’s S protein renders the virus capable of interacting with Nrp1, an additional entry receptor for the virus that facilitates its spread to different tissues.

LL: You mentioned that you initially used a pseudovirus expressing S protein to investigate Nrp1’s role in infectivity. What were the benefits of using this rather than SARS-CoV-2?

MA: S-pseudotyped lentivirus is relatively easy to generate and can be handled within a biosafety level 2 laboratory, whereas live SARS-CoV-2 must be handled within a much stricter biosafety level 3 laboratory. We used pseudotyped lentivirus at the initial stages of our work, while in parallel obtaining SARS-CoV-2 isolates and establishing conditions to handle them.

LL: How did you investigate the interaction in vivo?

MA: We took advantage of gold nanoparticles coated with peptides identical to those produced after S protein cleavage by furin. Such nanoparticles interact with Nrp1 expressed in animal tissues and are internalized by relevant cells the same way as the virus would be. Gold particles are relatively easy to detect in animal cells and are therefore a useful model to study how Nrp1 could drive SARS-CoV-2 entry.

LL: Was Nrp1 expression higher in certain cell types, and if so, could you tell us more about each of these and the potential clinical implications associated?

MA: Nrp1 expression was high, for example, in cells of respiratory and olfactory epithelia, as well as in olfactory neurons progenitors. The potential associated clinical implication is that SARS-CoV-2 could infect these types of cells and may account for the relevant COVID-19 symptoms, such as breathing difficulties and loss of smell.

LL: Your work suggests that the S protein–Nrp1 interaction could be targeted therapeutically, are you planning to investigate this further?

MA: We are currently working to determine the structure of the S protein–Nrp1 complex, which will provide atomic-resolution details of how this interaction occurs and inform the design of potential therapeutics.

Reference: Cantuti-Castelvetri L, Ojha R, Pedro LD, et al. Neuropilin-1 facilitates SARS-CoV-2 cell entry and infectivity. Science. 2020;370(6518):856–860. doi: 10.1126/science.abd2985.

Maria Anastasina was speaking to Laura Elizabeth Lansdowne, Managing Editor for Technology Networks.