A recent paper published in the journal Science Advances described that tunneling nanotubes (TNTs) provide a pathway for neuronal spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Study: Tunneling nanotubes provide route for spread of SARS-CoV-2. Image credit: 2020 Timelapse/Shutterstock
background
Although patients with Coronavirus disease 2019 (COVID-19) usually have severe respiratory symptoms and SARS-CoV-2 mainly affects the respiratory system, it also affects other organs such as the liver, intestine, kidneys, brain and the heart There have also been reports of different neurological manifestations of severity during COVID-19. In addition, the neurological effects of SARS-CoV-2 infection are a major long-term problem of COVID.
Since several types of coronaviruses (CoVs) have been documented to invade and survive in the central nervous system (CNS) (e.g. Middle East respiratory syndrome CoV). [MERS-CoV] and SARS-CoV), the ability of SARS-CoV-2 to penetrate the CNS is predicted. In addition, case studies have shown that SARS-CoV-2 ribonucleic acid (RNA) was present in the brain tissue of people who died after having COVID-19.
However, it is not clear how SARS-CoV-2 enters the brain or how infection causes neurological symptoms, as the main route of viral entry by endocytosis, angiotensin-converting enzyme 2 (ACE2) receptors ), are hardly detected in the brain.
About the study
In the current research, the scientists examined the neuroinvasive ability of SARS-CoV-2. They determined whether TNTs may play a role in the intercellular transmission of the virus.
TNTs are thin, actin-rich membrane channels that allow the direct traffic of elements such as viral particles, organelles, and amyloid proteins across different cells. Numerous viruses, such as herpes simplex virus and influenza virus, can communicate directly with naïve cells by using TNT to transfer their genomes, preventing drug targeting and bypassing protection of the guest
The team proposed that SARS-CoV-2 could use TNT to spread from permissive cells to less permissive cells that lack the membrane receptor for virus entry to spread pathogenicity viral and evade immune control. Furthermore, since the Vero E6 cell line has been widely used for the propagation, isolation, and antiviral evaluation of SARS-CoV-2, they used it as an epithelial model to test this theory.
The SH-SY5Y cell line, a human cell type that is frequently used as a neuronal model and whose TNTs have also been broadly defined and can be recognized with considerable precision, was chosen by researchers as a neuronal paradigm of non-permissive cells. Primary neurons were preferred, but it was substantially difficult to distinguish between TNT-like structures in them. In addition, it was also difficult to use the state-of-the-art cryo-electron tomography (cryo-ET) and cryocorrelative light and electron microscopy (cryo-CLEM) technologies that the team developed while using primary neural models.
results
The authors noted that SH-SY5Y human neuronal cells were not permissive to SARS-CoV-2 via exocytosis- or endocytosis-dependent pathways. However, they showed that it can be infected by SARS-CoV-2 via a TNT-induced route when co-cultured with permissive Vero E6 epithelial cells previously infected with SARS-CoV-2 by using confocal microscopy and establishing of cryo-ET and cryo of cellulose. – CLEM. The team found that SARS-CoV-2 creates TNTs and then uses them to spread to uninfected cells.
Correlative cryo-ET and cellulosic fluorescence demonstrate that TNTs among permissive cells were connected to SARS-CoV-2. The results indicated that TNTs across permissive and nonpermissive cells contain viral replication sites and numerous vesicular structures, including double-membrane vesicles.
In addition, data obtained using remdesivir and immunostaining for the viral replicative markers nonstructural protein 3 (nsp3) and J2 represented that SARS-CoV-2 can multiply once in neuronal cells . The researchers further demonstrated that SARS-CoV-2 could spread between permissive cells via an autonomous secretion channel by suppressing ACE2-facilitated virus entry using a neutralizing antibody. They postulate that TNTs accelerate the spread of infection, even between permissive cells.
Conclusions
Overall, the data from the study point to a hitherto unidentified mode of transmission of SARS-CoV-2, which is likely used to enter non-permissive cells and intensify infection in permissive ones. The current findings elucidate the molecular basis of SARS-CoV-2 infection and transmission and the structure of viral particles bound to TNTs.
In particular, the results of the study suggest the function of TNTs in viral transmission, possibly increasing the effectiveness of viral spread throughout the body, within the limitations of an in vitro investigation. Available studies mainly focus on blocking SARS-CoV-2 peak receptor (S) interactions. The present study, together with existing reports, paves the way for further investigations into the involvement of cell-to-cell interaction in the spread of SARS-CoV-2 in the brain in more physiological settings and in surrogate therapeutic strategies to impair viral spread.
In summary, the present work illustrated that SARS-CoV-2 could exploit TNTs to spread between linked cells, suggesting that the intercellular route may play a role in the pathogenesis of COVID- 19 and the spread of the virus to cells that are not susceptible. , such as neuronal cells.