35 research outputs found
Thermorheology of living cells: impact of temperature variations on cell mechanics
Upon temperature changes, we observe a systematic shift of creep
compliance curves J (t) for single living breast epithelial cells. We use a
dual-beam laser trap (optical stretcher) to induce temperature jumps within
milliseconds, while simultaneously measuring the mechanical response of whole
cells to optical force. The cellular mechanical response was found to differ
between sudden temperature changes compared to slow, long-term changes
implying adaptation of cytoskeletal structure. Interpreting optically induced cell
deformation as a thermorheological experiment allows us to consistently explain
data on the basis of time–temperature superposition, well known from classical
polymer physics. Measured time shift factors give access to the activation
energy of the viscous flow of MCF-10A breast cells, which was determined
to be 80 kJ mol−1. The presented measurements highlight the fundamental
role that temperature plays for the deformability of cellular matter. We propose
thermorheology as a powerful concept to assess the inherent material properties
of living cells and to investigate cell regulatory responses upon environmental
changes
Predicting disordered regions driving phase separation of proteins under variable salt concentration
We determine the intrinsically disordered regions (IDRs) of phase separating proteins and investigate their impact on liquid-liquid phase separation (LLPS) with a random-phase approx- imation (RPA) that accounts for variable salt concentration. We focus on two proteins, PGL-3 and FUS, known to undergo LLPS. For PGL-3 we predict that an IDR near the C-terminus pro- motes LLPS, which we validate through direct comparison with in vitro experimental results. For the structurally more complex protein FUS the role of the low complexity (LC) domain in LLPS is not as well understood. Apart from the LC domain we here identify two IDRs, one near the N-terminus and another near the C-terminus. Our RPA analysis of these domains predict that, surprisingly, the IDR at the N-terminus (aa 1-285) and not the LC domain promotes LLPS of FUS by comparison to in vitro experiments under physiological temperature and salt conditions
Thermal instability of cell nuclei
DNA is known to be a mechanically and thermally stable structure. In its double
stranded form it is densely packed within the cell nucleus and is thermo-resistant
up to 70 °C. In contrast, we found a sudden loss of cell nuclei integrity at
relatively moderate temperatures ranging from 45 to 55 °C. In our study, suspended
cells held in an optical double beam trap were heated under controlled
conditions while monitoring the nuclear shape. At specific critical temperatures,
an irreversible sudden shape transition of the nuclei was observed. These temperature
induced transitions differ in abundance and intensity for various normal
and cancerous epithelial breast cells, which clearly characterizes different cell
types. Our results show that temperatures slightly higher than physiological
conditions are able to induce instabilities of nuclear structures, eventually
leading to cell death. This is a surprising finding since recent thermorheological
cell studies have shown that cells have a lower viscosity and are thus more
deformable upon temperature increase. Since the nucleus is tightly coupled to
the outer cell shape via the cytoskeleton, the force propagation of nuclear
reshaping to the cell membrane was investigated in combination with the
application of cytoskeletal drugs
Complex thermorheology of living cells
Temperature has a reliable and nearly instantaneous influence onmechanical responses of cells.As recently
published, MCF-10Anormal epithelial breast cells follow the time–temperature superposition (TTS)
principle. Here,wemeasured thermorheological behaviour of eightcommoncell types within
physiologically relevant temperatures and appliedTTS to creep compliance curves.Our results showed that
superposition is not universal and was seen in four of the eight investigated cell types. For the other cell
types, transitions of thermorheological responses were observed at 36 °C.Activation energies (EA)were
calculated for all cell types and ranged between 50 and 150 kJmol−1.The scaling factors of the superposition
of creep curves were used to group the cell lines into three categories. They were dependent on relaxation
processes aswell as structural composition of the cells in response tomechanical load and temperature
increase.This study supports the view that temperature is a vital parameter for comparing cell rheological
data and should be precisely controlledwhen designing experiments
Complex thermorheology of living cells
Temperature has a reliable and nearly instantaneous influence on mechanical responses of cells. As recently published, MCF-10A normal epithelial breast cells follow the time-temperature superposition (TTS) principle. Here, we measured thermorheological behaviour of eight common cell types within physiologically relevant temperatures and applied TTS to creep compliance curves. Our results showed that superposition is not universal and was seen in four of the eight investigated cell types. For the other cell types, transitions of thermorheological responses were observed at 36 °C. Activation energies (EA) were calculated for all cell types and ranged between 50 and 150 kJ mol-1. The scaling factors of the superposition of creep curves were used to group the cell lines into three categories. They were dependent on relaxation processes as well as structural composition of the cells in response to mechanical load and temperature increase. This study supports the view that temperature is a vital parameter for comparing cell rheological data and should be precisely controlled when designing experiments
Testing the differential adhesion hypothesis across the epithelial− mesenchymal transition
Weanalyze the mechanical properties of three epithelial/mesenchymal cell lines (MCF-10A, MDAMB-
231, MDA-MB-436) that exhibit a shift in E-, N- and P-cadherin levels characteristic of an
epithelial−mesenchymal transition associated with processes such as metastasis, to quantify the role of
cell cohesion in cell sorting and compartmentalization. Wedevelop a unique set of methods to
measure cell–cell adhesiveness, cell stiffness and cell shapes, and compare the results to predictions
from cell sorting in mixtures of cell populations.Wefind that the final sorted state is extremely robust
among all three cell lines independent of epithelial or mesenchymal state, suggesting that cell sorting
may play an important role in organization and boundary formation in tumours.Wefind that surface
densities of adhesive molecules do not correlate with measured cell–cell adhesion, but do correlate
with cell shapes, cell stiffness and the rate at which cells sort, in accordance with an extended version of
the differential adhesion hypothesis (DAH). Surprisingly, theDAHdoes not correctly predict the final
sorted state. This suggests that these tissues are not behaving as immiscible fluids, and that dynamical
effects such as directional motility, friction and jamming may play an important role in tissue
compartmentalization across the epithelial−mesenchymal transition
Cell membrane softening in human breast and cervical cancer cells
Biomechanical properties are key to many cellular functions such as cell division and cell motility and
thus are crucial in the development and understanding of several diseases, for instance cancer. The
mechanics of the cellular cytoskeleton have been extensively characterized in cells and artificial
systems. The rigidity of the plasma membrane, with the exception of red blood cells, is unknown and
membrane rigidity measurements only exist for vesicles composed of a few synthetic lipids. In this
study, thermal fluctuations of giant plasma membrane vesicles (GPMVs) directly derived from the
plasma membranes of primary breast and cervical cells, as well as breast cell lines, are analyzed. Cell
blebs or GPMVs were studied via thermal membrane fluctuations and mass spectrometry. It will be
shown that cancer cell membranes are significantly softer than their non-malignant counterparts. This
can be attributed to a loss of fluid raft forming lipids in malignant cells. These results indicate that the
reduction of membrane rigidity promotes aggressive blebbing motion in invasive cancer cells
Thermorheology of living cells: impact of temperature variations on cell mechanics
Upon temperature changes, we observe a systematic shift of creep
compliance curves J (t) for single living breast epithelial cells. We use a
dual-beam laser trap (optical stretcher) to induce temperature jumps within
milliseconds, while simultaneously measuring the mechanical response of whole
cells to optical force. The cellular mechanical response was found to differ
between sudden temperature changes compared to slow, long-term changes
implying adaptation of cytoskeletal structure. Interpreting optically induced cell
deformation as a thermorheological experiment allows us to consistently explain
data on the basis of time–temperature superposition, well known from classical
polymer physics. Measured time shift factors give access to the activation
energy of the viscous flow of MCF-10A breast cells, which was determined
to be 80 kJ mol−1. The presented measurements highlight the fundamental
role that temperature plays for the deformability of cellular matter. We propose
thermorheology as a powerful concept to assess the inherent material properties
of living cells and to investigate cell regulatory responses upon environmental
changes
Thermorheology of living cells: impact of temperature variations on cell mechanics
Upon temperature changes, we observe a systematic shift of creep
compliance curves J (t) for single living breast epithelial cells. We use a
dual-beam laser trap (optical stretcher) to induce temperature jumps within
milliseconds, while simultaneously measuring the mechanical response of whole
cells to optical force. The cellular mechanical response was found to differ
between sudden temperature changes compared to slow, long-term changes
implying adaptation of cytoskeletal structure. Interpreting optically induced cell
deformation as a thermorheological experiment allows us to consistently explain
data on the basis of time–temperature superposition, well known from classical
polymer physics. Measured time shift factors give access to the activation
energy of the viscous flow of MCF-10A breast cells, which was determined
to be 80 kJ mol−1. The presented measurements highlight the fundamental
role that temperature plays for the deformability of cellular matter. We propose
thermorheology as a powerful concept to assess the inherent material properties
of living cells and to investigate cell regulatory responses upon environmental
changes