Single cell studies: Lean survive better than fat cells

Amoeba: Being slim has a drastic effect on cell health
Larger fat reserves are considered a tried and tested means in the animal world to survive periods when there is less food. Or it serves as an insulating layer, as with whales or bears, to protect the body from the cold. However, fat appears to have health disadvantages for amoebas, as a team of researchers from the Institute of Biology at the University of Kassel found.

Body fat fulfills many useful functions for living organisms. Biologists from the University of Kassel have now discovered the surprising effects of storage fat on a primitive protozoa. The results of the experiments show that lean cells cope with starvation better than fat cells.

The single cell Dictyostelium discoideum normally lives as an amoeba in the forest floor and feeds on bacteria. When there is a lack of food, several hundred thousand cells cluster together and form a tiny mushroom-shaped fruiting body in which they can survive as spores. So far it has not been known whether fat reserves are beneficial for survival.

For warm-blooded marine mammals such as whales, body fat forms an insulating layer under the skin to protect the animal from heat loss. It serves as an energy store for bears during hibernation. Because fat does not bind water, it weighs little and takes up little space, which is an advantage for migratory birds when crossing the Alps. Even plants equip their seeds with fat because it provides more energy. Overall, fat storage under natural conditions appears to be an advantageous property.

"Because crossing the Alps, hibernation and increased body temperature are out of the question for unicellular organisms," says Prof. Dr. Markus Maniak, cell biologist from the Institute of Biology at the University of Kassel, "the experimental procedure was quite obvious". In an experiment, his doctoral student Jessica Kornke mixed amoebas that had fat reserves with those that were slim. The mixture was then starved until fruiting bodies formed. The cells were marked in different colors, which made it easy to see which cells mastered the direct competitive situation more easily. To the great surprise of the scientists, the slim amoebas prevailed against the fat cells. In fact, around 80% of the fat cells died prematurely within the 24 hours necessary for fruiting.

The researchers were spurred on by the result that slimming has a drastic effect on cell health to conduct further experiments. Kornke and Maniak, for example, examined a number of Dictyostelium mutants in which genes are defective that also lead to metabolic disorders and a lack of fat in humans. Despite an oversupply of food, the amoebas were just as unable to build up fat reserves as people with a genetic defect. In keeping with the previous finding, these "genetically slim" cells did not suffer any damage on the way through Lent and contributed to the normal formation of fruiting bodies.

"We are very surprised," explains Prof. Maniak, "that these primitive unicellular organisms show problems, as are common for over-nourished civilizations, and we urgently need to find out which molecular causes are behind the drastically shortened life expectancy of the fat cells."

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