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Atomic force microscopy-based microrheology reveals significant differences in the viscoelastic response between malign and benign cell lines.

Rother J, Nöding H, Mey I, Janshoff A - Open Biol (2014)

Bottom Line: Mechanical phenotyping of cells by atomic force microscopy (AFM) was proposed as a novel tool in cancer cell research as cancer cells undergo massive structural changes, comprising remodelling of the cytoskeleton and changes of their adhesive properties.In this work, we focused on the mechanical properties of human breast cell lines with different metastatic potential by AFM-based microrheology experiments.Including also other cell lines from different organs shows that the loss tangent (G″/G') increases generally with the metastatic potential from MCF-10A representing benign cells to highly malignant MDA-MB-231 cells.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physical Chemistry, Tammannstrasse 6, 37077 Göttingen, Germany.

ABSTRACT
Mechanical phenotyping of cells by atomic force microscopy (AFM) was proposed as a novel tool in cancer cell research as cancer cells undergo massive structural changes, comprising remodelling of the cytoskeleton and changes of their adhesive properties. In this work, we focused on the mechanical properties of human breast cell lines with different metastatic potential by AFM-based microrheology experiments. Using this technique, we are not only able to quantify the mechanical properties of living cells in the context of malignancy, but we also obtain a descriptor, namely the loss tangent, which provides model-independent information about the metastatic potential of the cell line. Including also other cell lines from different organs shows that the loss tangent (G″/G') increases generally with the metastatic potential from MCF-10A representing benign cells to highly malignant MDA-MB-231 cells.

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Related in: MedlinePlus

Loss tangent η = G″/G′ of the human breast cell lines MCF-10A, MCF-7 and MDA-MB-231 as a function of frequency. Continuous lines represent results of fitting the parameters of the power-law structural damping model to the experimental data.
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RSOB140046F4: Loss tangent η = G″/G′ of the human breast cell lines MCF-10A, MCF-7 and MDA-MB-231 as a function of frequency. Continuous lines represent results of fitting the parameters of the power-law structural damping model to the experimental data.

Mentions: First, we focus on the cell lines MCF-10A, MCF-7 and MDA-MB-231, all from the human mammary gland but with different metastatic potential. Figure 3b compiles the results of the microrheological investigation. Rheological data of the other six cell lines are shown in the electronic supplementary material, figure S4. The presented data are computed from at least two force maps per cell line with a resolution of 32 × 32 pixels. In general, the complex shear modulus of all cell lines followed the typical frequency dependence found for many other cell types, including neutrophils, airway smooth muscle cells, bronchial epithelial cells or pulmonary macrophages with different microrheological methods [14,15]. G′ increases with frequency following a weak power law with exponents α ranging from 0.10 to 0.25 (table 1), while G″ exhibits lower values compared with G′ in the low-frequency regime (less than 50 Hz). In this regime, the cells show a more solid-like behaviour as the loss tangent (η = G″/G′) does not exceed 1 (see also figure 4 and electronic supplementary material, figure S5 for all cell lines). However, the high-frequency domain is dominated by G″, indicating that the cells at high frequencies behave more like a viscous liquid (η > 1). An attempt to explain this power-law behaviour in the microrheological spectra of living cells has been made by Kollmannsberger & Fabry [27]. By describing the cell as an active soft glassy material, some rheological features can be assigned to cytoskeletal organization and remodelling. The model is based on the soft glassy rheology model first described by Sollich [28], and assumes that the cytoskeleton of the cell consists of many disordered elements, which are held together by weak attractive forces between neighbouring elements trapping the elements in energy wells. These weak interactions allow the elements to occasionally jump between the potential wells. A large distribution of energy well depth leads to a scale-free (power-law) behaviour of the lifetime distribution and thus results in a power-law rheological behaviour. The power-law coefficient corresponds to the effective temperature of the material [15]. The material is at the thermal equilibrium if the power-law coefficient becomes 0. The model of active soft glassy rheology also predicts power-law structural damping behaviour, at least at intermediate time scales. The rheological data of all cell lines could be well described by this model (solid lines in figure 3b and electronic supplementary material, figure S4). The obtained fitting parameters of all cell lines according to electronic supplementary material, equation (S8) are summarized in table 1. We found that the measured values of G′ (storage modulus), G0 (scaling factor), α (power-law exponent) or μ (Newton viscosity term) for all cell lines do not show a clear correlation to the malignancy of the cell line. MCF-7, CaKi-1 and MDA-MB-231 cells, three malignant cancer cell lines, show the lowest G′-values at all frequencies, followed by epithelial MDCKII cells with values slightly higher than those of MDA-MB231 cells. Furthermore, malignant A549, NIH 3T3, MCF-10A and NMuMG cells display the highest storage modules. However, considering cells only from one organ (human mammary gland), we can confirm that benign cells are stiffer than malignant ones (figure 3; electronic supplementary material, figure S4). Apart from the obvious stiffness differences that have also been reported by others, we found that the power-law exponent of benign MCF-10A cells is considerably smaller (figure 5). Other than that, no correlation between the various parameters obtained from fitting electronic supplementary material, equation (S8) to the rheological spectra was found (figure 5).Table 1.


Atomic force microscopy-based microrheology reveals significant differences in the viscoelastic response between malign and benign cell lines.

Rother J, Nöding H, Mey I, Janshoff A - Open Biol (2014)

Loss tangent η = G″/G′ of the human breast cell lines MCF-10A, MCF-7 and MDA-MB-231 as a function of frequency. Continuous lines represent results of fitting the parameters of the power-law structural damping model to the experimental data.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4042852&req=5

RSOB140046F4: Loss tangent η = G″/G′ of the human breast cell lines MCF-10A, MCF-7 and MDA-MB-231 as a function of frequency. Continuous lines represent results of fitting the parameters of the power-law structural damping model to the experimental data.
Mentions: First, we focus on the cell lines MCF-10A, MCF-7 and MDA-MB-231, all from the human mammary gland but with different metastatic potential. Figure 3b compiles the results of the microrheological investigation. Rheological data of the other six cell lines are shown in the electronic supplementary material, figure S4. The presented data are computed from at least two force maps per cell line with a resolution of 32 × 32 pixels. In general, the complex shear modulus of all cell lines followed the typical frequency dependence found for many other cell types, including neutrophils, airway smooth muscle cells, bronchial epithelial cells or pulmonary macrophages with different microrheological methods [14,15]. G′ increases with frequency following a weak power law with exponents α ranging from 0.10 to 0.25 (table 1), while G″ exhibits lower values compared with G′ in the low-frequency regime (less than 50 Hz). In this regime, the cells show a more solid-like behaviour as the loss tangent (η = G″/G′) does not exceed 1 (see also figure 4 and electronic supplementary material, figure S5 for all cell lines). However, the high-frequency domain is dominated by G″, indicating that the cells at high frequencies behave more like a viscous liquid (η > 1). An attempt to explain this power-law behaviour in the microrheological spectra of living cells has been made by Kollmannsberger & Fabry [27]. By describing the cell as an active soft glassy material, some rheological features can be assigned to cytoskeletal organization and remodelling. The model is based on the soft glassy rheology model first described by Sollich [28], and assumes that the cytoskeleton of the cell consists of many disordered elements, which are held together by weak attractive forces between neighbouring elements trapping the elements in energy wells. These weak interactions allow the elements to occasionally jump between the potential wells. A large distribution of energy well depth leads to a scale-free (power-law) behaviour of the lifetime distribution and thus results in a power-law rheological behaviour. The power-law coefficient corresponds to the effective temperature of the material [15]. The material is at the thermal equilibrium if the power-law coefficient becomes 0. The model of active soft glassy rheology also predicts power-law structural damping behaviour, at least at intermediate time scales. The rheological data of all cell lines could be well described by this model (solid lines in figure 3b and electronic supplementary material, figure S4). The obtained fitting parameters of all cell lines according to electronic supplementary material, equation (S8) are summarized in table 1. We found that the measured values of G′ (storage modulus), G0 (scaling factor), α (power-law exponent) or μ (Newton viscosity term) for all cell lines do not show a clear correlation to the malignancy of the cell line. MCF-7, CaKi-1 and MDA-MB-231 cells, three malignant cancer cell lines, show the lowest G′-values at all frequencies, followed by epithelial MDCKII cells with values slightly higher than those of MDA-MB231 cells. Furthermore, malignant A549, NIH 3T3, MCF-10A and NMuMG cells display the highest storage modules. However, considering cells only from one organ (human mammary gland), we can confirm that benign cells are stiffer than malignant ones (figure 3; electronic supplementary material, figure S4). Apart from the obvious stiffness differences that have also been reported by others, we found that the power-law exponent of benign MCF-10A cells is considerably smaller (figure 5). Other than that, no correlation between the various parameters obtained from fitting electronic supplementary material, equation (S8) to the rheological spectra was found (figure 5).Table 1.

Bottom Line: Mechanical phenotyping of cells by atomic force microscopy (AFM) was proposed as a novel tool in cancer cell research as cancer cells undergo massive structural changes, comprising remodelling of the cytoskeleton and changes of their adhesive properties.In this work, we focused on the mechanical properties of human breast cell lines with different metastatic potential by AFM-based microrheology experiments.Including also other cell lines from different organs shows that the loss tangent (G″/G') increases generally with the metastatic potential from MCF-10A representing benign cells to highly malignant MDA-MB-231 cells.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physical Chemistry, Tammannstrasse 6, 37077 Göttingen, Germany.

ABSTRACT
Mechanical phenotyping of cells by atomic force microscopy (AFM) was proposed as a novel tool in cancer cell research as cancer cells undergo massive structural changes, comprising remodelling of the cytoskeleton and changes of their adhesive properties. In this work, we focused on the mechanical properties of human breast cell lines with different metastatic potential by AFM-based microrheology experiments. Using this technique, we are not only able to quantify the mechanical properties of living cells in the context of malignancy, but we also obtain a descriptor, namely the loss tangent, which provides model-independent information about the metastatic potential of the cell line. Including also other cell lines from different organs shows that the loss tangent (G″/G') increases generally with the metastatic potential from MCF-10A representing benign cells to highly malignant MDA-MB-231 cells.

Show MeSH
Related in: MedlinePlus