Novel imaging approach offers insights into HIV’s lifecycle

A team of scientists have used a novel live-cell fluorescent imaging system that has allowed them for the first time to identify individual particles associated with HIV.

The researchers at Northwestern Medicine were able to monitor how the HIV capsid uncoats in the cell at the individual particle level. They demonstrated that uncoating leading to infection occurs early in the cytoplasm, around 30 minutes after cell fusion. The finding is just one example of novel discoveries about HIV that might now be possible with the imaging system.

“Being able to connect infectivity of individual particles and how they behave in the cell to infection — which is what we really care about — is going to have a big impact on the field,” said principal investigator Dr Thomas Hope, Professor of Cell and Molecular Biology “The system can now be used to resolve other controversies in HIV biology and to determine which potential targets for drug development are most relevant.”

The study has implications in the wider field of virology research as well.

“Theoretically, you could apply this technique to the study of any fluorescently-tagged virus,” explained first author Dr João Mamede, Post-Doctoral Fellow in Dr Hope’s laboratory.

“We want to understand all the details, from when the virus fuses, to the point where it integrates and starts to make new viruses, to the last phase,” explained Dr Hope, “We need to understand what’s going on, so we can find the Achilles’ heel of the virus and use it as a drug target.”

It has become routine to visualise the movement and progression of individual virions in cells, but the relevance of these observations was previously unclear, as many virions are defective or do not progress to make further copies of themselves.

During the course of infection, HIV fuses onto a target immune cell and delivers its capsid — a cone that holds the genetic material of the virus — into the cell’s cytoplasm. From there, the capsid disassembles through a process called “uncoating,” which is crucial to the synthesis of viral DNA from its RNA genome and the hijacking of the cell’s functions.

But the specific details of uncoating have been controversial, with two groups of thought. One believed that uncoating takes place late at pores, allowing factors to enter the nucleus. A second camp showed data suggesting that uncoating takes place early and in the cytoplasm.