Cell 'quakes' may help cells respond to the outside world

Date:
October 4, 2021
Source:
University of Maryland
Summary:
New computer simulations reveal that sudden restructuring of the
cytoskeleton, or scaffolding, inside animal cells is caused by
the slow buildup and rapid release of mechanical energy. Called
cytoquakes, these disturbances may help the cell respond rapidly
to signals from the outside environment, like chemicals produced
by other cells or hormones in the bloodstream.



FULL STORY ========================================================================== Animal cells get their structural integrity from their cytoskeleton,
a shapeshifting mesh of filaments inside a cell that helps the cell
organize its structure and communicate with its environment. A few years
ago, scientists noticed that parts of the cytoskeleton would occasionally rearrange very rapidly, causing an earthquake-like disturbance in part of
the cell. They named these disturbances cytoquakes, but no one understood
how or why they happened.


==========================================================================
New computer simulations developed by University of Maryland researchers
reveal that these cytoquakes are caused by the slow buildup and sudden
release of mechanical energy within the cell. The researchers believe
the quakes may help the cell respond rapidly to signals from the outside environment, like chemicals produced by other cells or hormones in
the bloodstream.

The research appears in the October 8, 2021, issue of the journal
Proceedings of the National Academy of Sciences. "Cytoquakes represent
a sudden remodeling of a very important component of the cell, but
the physics behind them really wasn't known," said Garegin Papoian, a
co-author of the study who is the Monroe Martin Professor of Chemistry
and Biochemistry with a joint appointment in the Institute for Physical
Science and Technology at the University of Maryland.

"We think these cytoquakes must be biologically important because
the cytoskeleton is involved in so many functions within the
cell. Understanding the physics behind them can provide insight into how
cells work." The cytoskeleton is like an internal scaffolding within
animal cells. It is made of a network of filaments that constantly grow, shrink, attach and detach from one another. In addition to providing
structure to a cell, the filaments also serve as tracks for chemical
signals to flow from one part of a cell to another.

Papoian and his colleagues hypothesized that the sudden rapid
restructuring that happens in cytoquakes was the result of the
cytoskeleton's physical structure being particularly sensitive to its environment. He likens it to the sensitivity of a pile of sand compared
with a brick. Both may be made of the same molecules, but the brick holds
its structure, even under pressure, without collapsing. The pile of sand
may hold its structure for a long while but then suddenly collapses into
an avalanche of sliding sand.

To test the hypothesis, the team created a computer simulation of a model cytoskeleton using a pioneering active matter simulation software that
they developed called MEDYAN for "mechanochemical dynamics of active
networks." The software applies the laws of chemistry and physics to
determine how the molecules within the cytoskeleton interact and behave.

The study revealed that the filaments in a cytoskeleton arrange themselves
a bit like a shape-shifting tensegrity structure. In the macroscopic
world, a tensegrity structure is a kind of geometric toy or sculpture
made of cables and floating rods under tension and compression that
appear to defy gravity.

Analyzing these cellular tensegrity structures helped Papoian and his colleagues understand tension release within the cytoskeleton. They
found that tension applied to one area of the structure can build and
cause tension until it suddenly releases in another area. In other words,
the cytoskeleton behaves more like a pile of sand than a brick.

The physical structure of the cytoskeleton allows tension to build
between some of the filaments like the tension between grains of sand
in a sand pile or between two tectonic plates along a fault line. When
some threshold is met, the tension suddenly releases, the pile of sand collapses, an earthquake rumbles or a cytoquake occurs.

"We postulate that the cytoquake mechanism poises the cell to react
quickly to external signals from its environment compared to a system
without this mechanism," Papoian said.

For example, if a cell involved in repairing injuries must rush to the
site of a wound, the cytoquake mechanism may respond to chemical signals
from the injury site by jolting the cell into motion. When a cell migrates through the body, the leading edge may also use this mechanism to project
or collapse protrusions as the cell probes its local neighborhood.

The team's next step will be to expand on their simulation methods to
include more parts of a cell such as the nucleus. They recently simulated
the outer membrane of a cell and analyzed how the cytoskeleton pushes
against this membrane to form finger-like protrusions.

"This work is showing us that we can use MEDYAN to model
important components of a cell," Papoian said. "Ideally,
we would like to keep going and essentially build the
fundamental model of a whole cell at single molecule resolution." ========================================================================== Story Source: Materials provided by University_of_Maryland. Original
written by Kimbra Cutlip. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Carlos Floyd, Herbert Levine, Christopher Jarzynski, and Garegin A.

Papoian. Understanding cytoskeletal avalanches using mechanical
stability analysis. Proceedings of the National Academy of Science,
October 4, 2021 [abstract] ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211004153738.htm

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