MECHANOTRANSDUCTION DURING CELL ADHESION ANALYZED BY COMPUTATIONAL MODEL

MECHANOTRANSDUCTION DURING CELL ADHESION
ANALYZED BY COMPUTATIONAL MODEL
Jean-Louis MILAN (1), Sandrine LAVENUS (2), Sylvie WENDLING (2), Michel JEAN (3),
Pierre Layrolle (2) and Patrick CHABRAND (2)
1.ISM CNRS Marseille ; LPRO INSERM Nantes ; 3.LMA CNRS Marseille. France
an@univmed.fr
Introduction
Cha nges in cell morphology during cell a dhesion involve mecha notra nsduction. Forces tra nsmitted by the cytoskeleton may deform nuclear membrane nd open ion cha nnels a llowing ca lcium entry inducing associated gene transcription [Itano,2003]. We propose here a mechanical model of cell based on in vitro experiments to a na lyze the rela tion between cell morphology, intern l tension nd nucleus strain during cell adhesion.
Methods
Cell culture
Mesenchyma l stem cells from bone ma rrow were cultured on TCPS fla t substra tes [La venus, 2010]. Morphology of cells nd distribution of foc l a dhesions were reported a fter a ctin a nd vinculin staining.
Computational cell model
The cell model is a mecha nica l multi-intera ction system representing the interconnected structures of cytoskeleton and nucleoskeleton. As a 3D extension of our previous 2D model [Milan,2007], the present model consists of 8500 nodes forming the cell volume a nd intera cting together via compressive and tensile forces. Tensile interactions act as elastic wires between nodes while compressive interactions are computed as contact forces between virtu l spheric l bound ries surrounding nodes. Resulting forces networks are assumed to model the various filamentous lattices of cytoskeleton such as stress fibers, a ctin cortex, microtubules a
nd intermedi a
te fil a ments. Some nodes of cell membra ne, a s integrin receptors do, a re a ble to connect proteins of substrate and form stress fibers between each others.
Intracellular tonus of adherent cell
Some adherent cells were chosen as representative of sprea d (Fig. 1) a nd round morphologies a nd positions of focal adhesions were introduced in the model. The cell model which was originally round with a diameter of 15μm spread until coinciding of foca l a dhesion positions. The intra cellula r tonus wa s computed a s sum of tensile forces through vertical cell section. It was modulated by increasing tensile intera ction stiffness so a s to obta in foca l a dhesion tension of 10-30 nN consistently with experimental studies [Balaban,2001].
Cell adhesion by modeling filopod emission
Cell model was also implemented in free adhesion process. Filopods represented by moving nodes of the membra ne were emitted a t 2 μm a wa y from existing focal points and created remote adhesions.
Results and Discussion
Computations show an intracellular tonus of 58nN a nd a n nucleus shea r stra in of 65 % for a 70 μm-dia meter spread cell (Fig.1), compa red to tonus of 24 nN a nd nucleus stra in of 30 % for 35 μm-
diameter round cell.
Fig. 1: Spread cell and model with coinciding focal adhesions. Tensions (red), deformed nucleus (yellow).
Free adhesion of cell model by filopod emission led to a 75 μm-diameter spread shape with higher tonus of 220 nN due to more foca l a dhesion a nd stress fibers. In tha t ca se nucleus shea r stra in rea ched 52%. This verified previous finding that tonus and nucleus str a in incre a se with cell spre a
ding. Nonetheless depending on spa tia l distribution of foca l a dhesions a nd stress fibers, nucleus ma y deform in a wa y which is not directly coupled to intracellular tonus.
Fig. 2: Model free adhesion. Tensions (red), deformed nucleus (yellow), focal adhesion points (blue) and evolution of tonus and nucleus strain .
REFERENCES
Itano et al ., PNAS 100:5181-6, 2003
Lavenus et al ., Nanomedecine 5(6):937-47, 2010 Milan et al., BMMB 6:373-90, 2007
Balaban et al., Nat. Cell Biol. 3:466-72, 2001
S410Presentation 1019−Topic 31.Mechanobiology and cell biomechanics
Journal of Biomechanics 45(S1)
ESB2012:18th Congress of the European Society of Biomechanics。