Investigation of active mechanical properties in the cytoplasm of living cells

by Till Moritz Münker
Doctoral thesis
Date of Examination:2024-06-17
Date of issue:2024-07-09
Advisor:Prof. Dr. Timo Betz
Referee:Prof. Dr. Timo Betz
Referee:Prof. Dr. Matthias Krüger
Referee:Prof. Dr. Andreas Janshoff
Referee:Prof. Dr. Jan Huisken
Referee:Prof. Dr. Peter Sollich
Referee:Dr. Robert Mettin
Persistent Address: http://dx.doi.org/10.53846/goediss-10592

 

 

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Abstract

English

Over the past decades, the study of intracellular active mechanical properties has experienced a growth in interest. This is mainly caused by recognizing that vital cellular functions rely on the intricate interplay between the viscoelastic mechanical properties of the cytoplasm and the active force generated by the consumption of metabolic energy. However, quantifying these properties poses significant challenges due to the complexity of the physical quantities and the elaborate and low-throughput experimental methods required for their investigation. In this work, we propose two techniques to meet these challenges. Firstly, we introduce a mechanical fingerprint that reduces the complexity of intracellular active mechanical properties to a set of six parameters. Demonstrated initially on HeLa cells, the fingerprint accurately captured changes in mechanics upon disrupting cytoskeletal components, showcasing its capability to represent intracellular dynamics concisely. The investigation was then expanded to 7 diverse cell types, where their unique fingerprint could identify individual cell types. Further correlational analysis led to the introduction of a three-dimensional phase space comprised of resistance, activity, and fluidity. Here, the positions in phase space correlated with expected cell functions, underlining the fingerprint’s capability of accelerating the investigation of such relations. Secondly, we introduced the Mean Back Relaxation (MBR) as a novel statistical tool to determine the breaking of detailed balance in confined systems. This approach was first established in a well-controlled model system, mimicking the intracellular space. It was then applied to living cells, where we could observe surprising relations between the MBR and intracellular activity. Strikingly, by deploying this relation, we determined the mechanical properties of MDCK cells by purely passive observations. We thus present an alternative approach for the quantification of intracellular active mechanical properties. This will drastically reduce experimental complexity and increase the experimental throughput.
Keywords: Cell mechanics; Optical tweezers; Biophysics; MBR; Mechanical fingerprint; Rheology; Statistical mechanics; Non equilibrium
 
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