Amazing stuff! What other pathogens can we now watch in action? This could be a breakthrough!
Will we soon have even better flu vaccinations?
"... On the surface of the influenza virus are two molecular "keys": hemagglutinin (HA) and neuraminidase (NA). They are the virus's lockpicks, the tools that let it slip into our cells and spread from one host to another.
The flu virus attacks much like a thief looking for unlocked doors. Its HA and NA proteins grab onto tiny molecules called sialic acids on the surface of cells. Once attached, the virus slides along the surface until the cell reshapes itself and swallows the virus inside. This process is called endocytosis.
But watching how the flu virus sneaks into cells has been difficult because standard microscopes can't capture these fast, tiny steps clearly.
In a breakthrough study, scientists from Switzerland and Japan built a new kind of "super microscope" by blending two powerful imaging tools: atomic force microscopy (AFM) and fluorescence microscopy, creating a new method called virus-view dual confocal and AFM (ViViD-AFM). This hybrid system lets researchers zoom in on living human cells with incredible detail. This offers a new real time insight into how the flu virus operates.
For the first time, researchers could actually see the nanoscale drama of influenza invading a cell. But what surprised them most was the target cell's role in this process. Instead of sitting quietly and letting the virus in, the cell seemed to fight back: stretching, shifting, and even trying to grab hold of the virus as if to control the encounter. "The infection of our body cells is like a dance between virus and cell," ...
With their new system, the team watched how single flu virus particles move across the surface of a cell under different conditions, like when specific viral proteins were blocked, when fewer binding sites were available on the cell, or when different virus types were tested. They also studied how the cell's membrane changes shape before and during the virus's entry. ..."
From the significance and abstract:
"Significance
Influenza A viruses (IAVs) continue to cause epidemics worldwide due to their high mutability. Nevertheless, the initial step of infection, viral uptake into cells, has been challenging to observe directly with conventional microscopy techniques. Here, we developed a hybrid imaging system combining atomic force microscopy and confocal microscopy with enhanced mechanical functionality and minimal invasiveness to directly visualize nanoscale dynamics of IAV and cell membranes during viral uptake into living cells. This system enables the analysis of IAV lateral diffusion resulting from IAV–membrane interactions and characteristic membrane morphological changes induced by IAV during endocytosis. Our approach offers a method to rapidly assess the impact of viral mutations on host cell entry, which is critical for understanding emerging IAV variants.
Abstract
Influenza A virus (IAV) entry into host cells begins with interactions between the viral envelope proteins hemagglutinin (HA)/neuraminidase (NA) and sialic acid moieties on the cell plasma membrane.
These interactions drive IAV’s lateral diffusion along the cell membrane and trigger membrane morphological changes required for endocytosis. However, directly visualizing these dynamic processes, which are crucial for IAV entry, has been challenging using conventional microscopy techniques.
In this study, we enabled live-cell observation of nanoscale morphological dynamics of IAV and the cell membrane by reducing the mechanical invasiveness of atomic force microscopy (AFM).
A customised cantilever with less than half the spring constant of conventional cantilevers enabled virus-view AFM imaging that preserved IAV–membrane interactions.
By combining virus-view AFM with confocal microscopy, we performed correlative morphological and fluorescence observations of IAV lateral diffusion and endocytosis in living cells.
Variations in diffusion coefficients of single virions suggested heterogeneity in sialic acid density on the cell membrane. NA inhibition decreased diffusion coefficients, while reduced sialic acid density increased them.
The timing of clathrin accumulation at virion binding sites coincided with a decrease in diffusion coefficients, a relationship that was maintained independent of NA activity or sialic acid density. As clathrin assembly progressed, ~100-nm-high membrane bulges emerged adjacent to the virus, culminating in the complete membrane envelopment of the virus at peak clathrin accumulation.
Our virus-view AFM will deepen our understanding of various virus–cell interactions, facilitate the evaluation of drug effects and promote future translational research."
How influenza viruses enter our cells (original news release) "For the first time, researchers have observed live and in high resolution how influenza viruses infect living cells. This was possible thanks to a new microscopy technique, which could now help to develop antiviral therapies in a more targeted manner. "
Enhanced visualization of influenza A virus entry into living cells using virus-view atomic force microscopy (open access)
Fig. 4 Membrane bulges cover virus particles during IAV CME.
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