Characterization of Cell Mechanobiological Behavior: From Mechanical Property Change to Biological Function Alternation

Abstract

Changes in cell mechanical properties influence various cellular processes, such as differentiation, aging, apoptosis, and migration. In specific, changes in cell stiffness through cytoskeleton structure reorganization can alter cell biological properties. Previous research reported about the relationship between cell mechanical properties and different cellular processes. However, quantitative studies on how changes in cell mechanical properties influence cell biological properties remain lacking. This thesis utilizes optical tweezers (OT) and dielectrophoresis (DEP) and microstructural mechanical models to analyze the mechanical properties of cells and investigates quantitatively how changes in cell mechanical properties alter cell biological properties.

First, OT and DEP-based cell stretching platforms are introduced and calibrated. Leukemia NB4 cells of the control group and those after chemotherapy treatment with DOX are tested, and the cell deformation behavior under these two stretching methods is compared. Structural parameters of the cytoskeleton are extracted using the actin cytoskeleton microstructural model. This study showed that the DEP method combined with the actin cytoskeleton modeling analysis can provide a simple and cost-effective engineering tool to characterize the biomechanical properties of cells

Second, a quantitative study on how changes in cell mechanical properties influence cell biological functions was performed. Electric field with voltages of 5, 10, and 20 V/cm was applied to NB4 cells as mechanical stimuli. Variation in the mechanical properties of these electric field treated cells in comparison with the control group was examined by stretching the single cells using an OT manipulation system. Gene expression was tested through real time-PCR. Immunofluorescence microscopy was used to observe the variations in F-actin cytoskeleton structures and an actin microstructural model was utilized to extract the cytoskeleton structural parameters. Cell stiffness decreased after electric field treatment, which corresponded to the change in the cytoskeleton structure F-actin concentration of cells. This study, although still limiting, opens up a new and reasonable direction for further exploration.

Third, the interrelationship between cell mechanical and biological properties was characterized quantitatively. Changes in the biological properties of hMSCs during adipogenesis and of leukemia NB4 cell lines during electric field stimulation were particularly investigated. The deformation of the stretched cells was measured by OT. The experimental data were fitted into the actin cytoskeleton model to extract actin cytoskeleton parameters. Actin related gene expression was measured to understand this phenomenon. The expressions of β-actin in the two cases agree with the cell stretching results, suggesting that β-actin is a main indicator of changes in cell biological properties in relation to changes in actin cytoskeleton mechanical properties. This finding reveals how the actin cytoskeleton remodeling profile and the actin-based gene expression reflect the quantitative interrelationship between cell mechanical and biological properties.

In summary, this thesis presents a quantitative investigation on how changes in cell mechanical properties affect cell biological properties. The study of this interrelationship is of great value for disease diagnosis and treatment. This study lays a solid foundation for further exploration of the targeted alternation of cell biological behavior by inducing specific changes in cell mechanical properties.

Date of Award	12 Feb 2019
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Dong SUN (Supervisor)