Cell microstructural mechanical modeling and biomechanics analysis based on cell manipulation with optical tweezers

Abstract

Cells are the basic units of all living organisms, having various functions closely related to biomechanics. Studies on cell mechanics not only contribute to the knowledge on how healthy cells respond to mechanical stimuli, but also provide an insight into the pathogenesis of specific diseases by examining the mechanical response of diseased cells. Structural changes in the actin cytoskeleton during the progression of diseases may change cell mechanics. Therefore, cell mechanical properties are regarded as effective biomarkers to distinguish healthy cells from abnormal ones and monitor the physiological developmental stages of cells. However, the study of the link between cell functions and cell biomechanics remains challenging. A particular demand exists for the quantification of the underlying actin remodeling profile that reflects the relationship between the cell mechanical behavior and alterations in cell functions. This study combines optical tweezers technology with the cell microstructural mechanical model to probe quantitatively how changes in the actin cytoskeleton associated with various pathological cellular conditions mediate cell mechanical behavior. First, a study platform for cell biomechanics is set up with combined optical tweezers technology and cell microstructural modeling. The cell microstructural model focuses on the influence of the actin cytoskeleton on cell mechanical behavior. The semiflexibility of the actin cytoskeleton is considered in the cell model, and the framework of the model is developed. The optical trap is calibrated to establish the relationship between stretching force and laser power. Experiments on hematopoietic cells with distinct primitiveness from the umbilical cord blood and bone marrow of patients with acute myeloid leukemia are performed with optical tweezers at the single cell level. The experimental results demonstrate the effectiveness of optical tweezers manipulation. Second, with the established cell manipulation system, a cell microsctructural model is developed to predict the mechanical response of cells. A three-dimensional actin cytoskeleton network is generated through Delaunay triangulation. The model is validated by fitting with the experimental data on hematopoietic cells. The influence of the structural properties of the actin cytoskeleton, such as prestress conditions, density of cross-links, and actin concentration, on the cell mechanical behavior is characterized based on the proposed model. The model indicated that increasing prestress conditions, actin concentration, and density of cross-links reduced cell deformation, and that the cell exhibited strain stiffening behavior with increasing stretching force. Third, based on the cell microstructural model and optical tweezers manipulation, the underlying mechanism by which actin filaments (F-actin) affect the mechanical behavior of leukemia cells associated with chemotherapy treatment is examined quantitatively. Doxorubicin (DOX) is a typical chemotherapy drug widely used for cancer treatment. The mechanical behavior of DOX-treated Jurkat and K562 cells is obtained via optical tweezers stretching manipulation. DOX made the Jurkat and K562 cells stiffer than their control counterparts. Remarkable differences in the architecture of the actin cytoskeleton of the DOX-treated leukemia cells are observed using a confocal microscope. The proposed cell microstructural model is utilized to extract the structural parameters of F-actin. The stiffening of DOX-treated Jurkat and K562 cells is interpreted based on these extracted parameters. This study is expected to benefit the monitoring of the progression of leukemia cells for more effective chemotherapy. In summary, the proposed optical tweezers technology and cell microstructural modeling provide a novel solution to reveal further the in-depth link between cell biomechanics and cell functions. Based on the proposed method, F-actin mediation of the mechanical behavior of leukemia cells under the treatment of a chemotherapy drug is illustrated quantitatively. This study potentially provides a solid ground for further investigation of targeted abnormal cellular functions for therapeutic and diagnostic purposes from the perspective of biophysics.

Date of Award	15 Jul 2013
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Dong SUN (Supervisor)