Droplets of fat help us fight infection

An international research team has discovered that droplets of fat inside our cells are helping the body’s defence system fight back against infection, with scientists finding that these fat droplets serve as both a food source for and a weapon against bacterial invaders. Their discovery has been published in the journal Science.

“It was previously thought that bacteria were merely using the lipid droplets to feed on, but we have discovered these fatty droplets are involved in the battle between the pathogens and our cells,” said Professor Robert Parton from The University of Queensland (UQ), who co-led the research with Professor Albert Pol from the University of Barcelona.

“Fat is part of the cell’s arsenal — cells manufacture toxic proteins, package them into the lipid droplets, then fire them at the intruders.

“This is a new way that cells are protecting themselves, using fats as a covert weapon, and giving us new insights into ways of fighting infection.”

With antibiotic-resistant superbugs on the rise, researchers are determined to find alternative ways to fight infection. One possibility is ramping up the body’s natural defences.

“We showed that upon infection of white blood cells called macrophages, lipid droplets move to the part of the macrophage where the bacteria are present,” said Professor Matthew Sweet, also from UQ.

The bacterial infection also changed the way that white blood cells used energy. Prof Sweet noted, “Lipid droplets can be used as a fuel source for mitochondria when there aren’t enough other nutrients.

“During an infection, lipid droplets move away from the mitochondria and attack the bacteria instead, altering metabolism of the cell.”

Prof Parton said he was inspired to research this phenomenon after it was observed in fruit flies. He said, “Most people thought the lipid droplets were ‘blobs of fat’, only useful for energy storage, but now we are seeing that they act as metabolic switches in the cell, defend against infection and much more — there are now entire scientific conferences of researchers working on them.

“Our next step is to find out how the lipid droplets target the bacteria.

“By understanding the body’s natural defences, we can develop new therapies that don’t rely on antibiotics to fight drug-resistant infections.”

Image caption: Electron micrograph of a macrophage with bacteria (green) surrounded by lipid droplets (pink).

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