Cells found to use toxic fat droplets to fight infection

Cells found to use toxic fat d...
An electron microscope image of bacteria (blue) being attacked by fat droplets (green)
An electron microscope image of bacteria (blue) being attacked by fat droplets (green)
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An electron microscope image of bacteria (blue) being attacked by fat droplets (green)
An electron microscope image of bacteria (blue) being attacked by fat droplets (green)

Fat is best known for being an energy storage system, but now researchers have discovered that it plays a previously unknown role in defense against infection. A team from the Universities of Queensland and Barcelona found that cells can use fats to fight off bacteria.

Although it’s popularly regarded as an enemy to our health, in the right proportions fat is crucial for our bodies to function. The stuff stores energy in the form of lipid droplets, which are normally located near the mitochondria – the internal cellular structures that convert oxygen into useable chemical energy. When other nutrients run low, the mitochondria turn to lipids as an alternative fuel source.

But now a new study has found a surprising new mechanism. When a cell is invaded by bacteria, lipids migrate from the mitochondria to the parts of the cell where bacteria are present. The attackers often eat the energy-rich lipids – and now it turns out that cells may use this to their advantage, by “poisoning” the lipids before serving them up to the bacteria.

“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,” says Robert Parton, an author of the study. “Fat is part of the cell’s arsenal – cells manufacture toxic proteins, package them into the lipid droplets, then fire them at the intruders.”

The team says that these lipid droplets essentially form a first-line of defense against infection inside cells. In so doing, they actually change the metabolism of the cell.

This process had previously been identified in the cells of fruit flies, so for the new study the team investigated whether it also applied to mammalian cells. Sure enough, electron microscope observations of macrophages (white blood cells) in humans and mice showed that it did. The discovery could lead to new techniques to fight off the emerging threat of bacteria that are developing resistance to antibiotics.

“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,” says Parton. “Our next step is to find out how the lipid droplets target the bacteria. By understanding the body’s natural defenses, we can develop new therapies that don’t rely on antibiotics to fight drug-resistant infections.”

The research was published in the journal Science. The team outlines the work in the video below.

Fats fighting back against bacteria

Source: University of Queensland

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