Mechanics of blebbing cell motility – BlebMechanics

The first measurements of the bleb mechanics was possibly by using a new optical technique developed by our group. We use the special optical properties of laser light to detect the position of the cell membrane with the accuracy of a molecule and the time resolution that is 10 times faster than the blink of an eye. The fluctuations allow to directly determine the rigidity of the cell wall.

In the first 6 month of the project we started to build a new experimental setup that will allow us to manipulate living cells in 3D environments using highly focused laser beams, and to even cut structures within the cells using pulsed UV lasers.
The first experimental results on a currently working setup show that the measurement of the membrane fluctuation allows to directly determine the mechanical properties of the cells edge, such as the tension. This is important to understand how cancer cells can move through a body to eventually form new metastasis. The forces and the mechanisms involved in this translocation are not very well understood, and might provide a way to prevent or to reduce the formation of metastasis.

After finishing the setup we will have the unique opportunity to manipulate cancer cells in 3D with a yet unknown precision. This will be coupled to modern 3D confocal microscopy and precise particle position detection systems to better understand the forces, dynamics and movement of cancer cells in 3D. While we are constructing this new setup, we will continue to measure the mechanical properties of cell blebs on current experimental setups. Hopefully this work will allow to understand how the dynamic polymerization of the cytoskeleton changes the mechanical properties of the cell cortex.

The first scientific results of this work show that the membrane tension is changing during the lifetime of a cell bleb, and that the recruitment of the actin cytoskeleton increases the rigidity of the cells. These first results are currently combined in a scientific paper that will be submitted before end of the year.

Cell motility is at the heart of many fundamental biological processes ranging from development over the immune response to the metastatic potential of cancer cells. Cell motility is divided in two different types, the mesenchymal, or gliding motility type, and the amoeboid, or blebbing motility type. While mesenchymal motility has been extensively studied, the knowledge on blebbing motility is limited. Blebbing motility is characterized by a fast growing membrane bulge, called a bleb, where the leading edge cell membrane growths into the surrounding medium, probably driven by hydrostatic pressure. Hence, the leading edge invades new area, and subsequently, contractile forces squeeze the whole cell volume in this new compartment. Blebbing motility is commonly found in amoebae, in leukocytes and in many metastatic cancer cells. Despite the recent advances in the understanding of blebbing cell motility, the direct measurement and in depth quantitative modeling of the mechanical principles have yet not been achieved. We propose to study the mechanics of bleb-forming cell motility by combining biomimetic approaches with the investigation of blebbing in cancerous cells. This poses a combination of a bottom up (reconstitution) and top down (living cells) approach. We will probe the mechanical characteristics using optical tweezers, laser-based active and passive micro-rheology, which will be combined with 3D traction force and 3D speckle microscopy. The aim of the project is to identify the fundamental physical process involved in the full cycle of a cell bleb, which ranges from formation, stabilization and bleb retraction. This will allow to define quantitative model of bleb formation, that will be applied to blebbing cell motility, finally explaining the mechanical differences between the different motility types.