New light on cellular hydration

Why do we get hangovers? “They’re caused by a water imbalance within our bodies,” says Sylvie Roke, the head of EPFL’s Laboratory for Fundamental BioPhotonics. “Our cells become dehydrated as they eliminate alcohol through osmosis.” This process takes place in our bodies every day without us even knowing. The wrinkles that appear in our fingers when we stay in the bathtub too long are another example – that’s the result of water penetrating our body and then our cells.

“Osmosis occurs when two liquids with different concentrations of a given solute come into contact through a semi-permeable membrane,” says Aurélien Roux, a biochemistry professor at the University of Geneva. “The water passes from the lower-concentration liquid to the higher-concentration one, until an equilibrium is established between the two.”

It’s all about tension

Roke and Roux are studying the molecular mechanisms involved in cell membrane tension – still largely unknown on a nanometric and microscopic scale – in a project that has just received a Synergy Grant from the European Research Council.

Osmosis takes place through our cell membranes because they’re semi-permeable: they let water through but not ions. The membranes protect cells from their environment and, by regulating the cells’ electrical activity and the exchange of compounds with surrounding fluids, they keep cells healthy and stable.

When osmosis occurs across a cell membrane, the cell’s volume can expand or contract – like a balloon – thereby increasing or decreasing the tension in the membrane. The same changes in membrane tension can be seen during cell migration. “Controlling this tension is just as important as controlling our body temperature,” says Roux. “First, because if the tension gets too high, the cell membrane can rupture. Second, this tension plays an important role in regulating many cellular processes.”

Innovative methods

Many studies have already been conducted on cell membrane tension, but the methods they use don’t provide enough spatial and temporal resolution to thoroughly examine the underlying molecular interactions.

Roke and Roux therefore plan to develop new systems for non-linear imaging and optical spectroscopy, drawing on technology developed in the EPFL lab. Roke says: “We will build two microscopes: one that uses probes to observe how water molecules interact with the lipids making up a cell membrane, and another that lets us examine membrane tension with unprecedented spatial-temporal resolution. That will require a lot of calibration work, which we’ll do using Aurélien’s biophysics and cellular-biology resources.”

Water and biology

“Around 60% of the human body is water. So it’s important to understand how our cells control the flow of this fluid,” says Roke. “And to do that, we need to investigate the molecular interactions and dynamics of how water molecules interact with cell membranes.”

The systems she and Roux will develop will provide fundamental information about how cells respond to osmotic shocks – a response that plays an important role in infections and in kidney and intestine function. They will also learn more about cell migration, which is essential to many cell processes such as the healing of wounds, the spreading of cancer cells and the immunological response.