Most biological cells have a fixed place in an organism. However, cells can become mobile and move around the body. This happens, for example, during wound healing or when cancer cells divide uncontrollably and migrate through the body. Mobile and stationary cells differ in different ways, including their cytoskeleton.
This structure of protein filaments makes cells stable, extensible, and resistant to external forces. In this context, “intermediate threads” play an important role. Interestingly, two different types of intermediate filaments are present in stationary and mobile cells.
Researchers at the University of Göttingen and ETH Zurich have succeeded in accurately measuring and describing the mechanical properties of these two filaments. In the process, they discovered similarities to non-biological materials. The results are published in Theme.
The scientists used optical tweezers to investigate how filaments behave under tension. They attached the ends of the threads to small plastic pellets, then moved them in a controlled manner with the help of a laser beam. This tightened two different types of strands, which are known as vimentin and keratin. The researchers worked out the forces that were necessary for the stretching and how different threads behave when stretched multiple times.
Surprisingly, different filaments behave in different ways upon repeated stretching: vimentin filaments become softer and retain their length, keratin filaments become longer and retain their stiffness. The experimental results match computer simulations of molecular interactions: in the vimentine strands, the researchers hypothesize, the structures open up, similar to gels made of several components; In keratin strands, they suppose the structures shift against each other, as in minerals.
Both mechanisms demonstrate that networks of intermediate filaments in the cytoskeleton can be severely deformed without being damaged. However, this protection factor is explained by fundamentally different physical principles.
“These findings expand our understanding of why different types of cells have such different mechanical properties,” explains Dr. Charlotta Lorenz, first author of the study.
Professor Sarah Koster, from the University of Göttingen’s Institute for X-ray Physics and lead study, adds, “We can learn from nature and think about designing new, sustainable, transferable materials whose properties can be chosen or designed to suit exact requirements.”
Charlotta Lorenz et al., Keratin filament mechanics and energy dissipation are determined by metal-like plasticity, Theme (2023). doi: 10.1016/j.matt.2023.04.014
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