New imaging technology set to reveal secret life of virus in cells

Date: Jan-02-2014One of the challenges of unlocking the secret lives of tiny biological agents - like

viruses inside living cells - is how to get close up without disturbing their structure

and behavior.

Now, using high-end imaging, a team from the US has found a way to label and study the

respiratory syncytial virus (RSV) and its activity in living cells that could become a general

method for unlocking the secrets of many important RNA viruses.

With the new approach, Philip Santangelo - associate professor at Wallace H. Coulter Department

of Biomedical Engineering at Georgia Tech and Emory University - and colleagues say scientists

could study how the RSV virion or infective virus particle enters cells, how it replicates, how

many genomes it inserts into its hosts, and perhaps discover why some types of lung cells manage to

avoid infection.

In a recent issue of the journal ACS Nano, they write about how they used the new imaging technique - which brings together multiply-labeled

tetravalent RNA imaging probes (MTRIPS) and direct stochastic optical reconstruction microscopy

(dSTORM) - to probe the life of RSV in living cells.

Prof. Santangelo says:

"We want to develop tools that would allow us to get at how the virus really works. We really

need to be able to follow the infection in a single living cell without affecting how the virus

infects its hosts, and this technology should allow us to do that."

Scientists using such an approach could provide important information for developing new

antiviral drugs and vaccines against severe RSV infections.

Infection with RSV can be severe

RSV causes infections of the lungs and respiratory tract. The virus is so common that by the age

of 2, most children have had it.

In adults and older, healthy children, RSV causes mild symptoms, rather like a common cold, and

self-care is usually enough to relieve them.

But RSV infection can be severe in premature babies and infants who are already sick, as well as adults with weakened immune systems or older people with heart and lung diseases. In these

cases, it can develop into pneumonia and bronchitis, requiring hospitalization and leading to

long-term consequences.

RSV is a slippery character to study

RSV poses some big challenges to scientists. For one thing, it takes on many forms, ranging from 10-micron filaments to ordinary spheres. It can insert more than one genome into the

host cell, and its structure and orientation is disordered, making it difficult to

characterize.

The probe technology the team used, MTRIPS, quickly attaches to RNA within cells. The probe uses

several fluorescent chemicals to show the presence of the viral RNA. This allowed the team to see where it

goes in host cells, and to observe infectious particles leaving the cells to spread infection.

Prof. Santangelo adds:

"Being able to see the genome and the progeny RNA that comes from the genome with the probes we

use really give us much more insight into the replication cycle.

This gives us much more

information about what the virus is really doing. If we can visualize the entry, assembly and

replication of the virus, that would allow us to decide what to go after to fight the virus."

Unlocking secrets of other RNA viruses

Although RSV will be their first target, the team believes their imaging technique could be

used to probe the lives of other RNA viruses, such as influenza and Ebola.

They also hope the technique will help solve another mystery: why certain lung cells become

severely infected with RSV, while others appear to escape relatively unscathed.

Prof. Santangelo says if you look at a field of cells, you can see big differences from cell to

cell. They couldn't understand this at all:

"If we can figure out why some cells are exploding with virus while others are not, perhaps we

can figure out a way to help the bad ones look more like the good ones."

Funds from the National Institute of General Medical Sciences of the National Institutes of

Health helped finance the study.

In a study published recently in the Proceedings of the National Academy of

Sciences, another team of US researchers found that dogs in the home may protect against

infection, including RSV.

Written by Catharine Paddock PhD

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