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Dynamic modeling of cell migration and spreading behaviors on fibronectin coated planar substrates and micropatterned geometries.

Kim MC, Neal DM, Kamm RD, Asada HH - PLoS Comput. Biol. (2013)

Bottom Line: The integrative model of this paper successfully reproduced these experimental results and indicates the mechanism of cell migration and spreading.In addition, the integrated model is validated by showing persistent high stress concentrations at sharp geometrically patterned edges.This model will be used as a predictive model to assist in design and data processing of upcoming microfluidic cell migration assays.

View Article: PubMed Central - PubMed

Affiliation: BioSystem & Micromechanics IRG, Singapore MIT Alliance Research Technology, Singapore. mincheol@mit.edu

ABSTRACT
An integrative cell migration model incorporating focal adhesion (FA) dynamics, cytoskeleton and nucleus remodeling, actin motor activity, and lamellipodia protrusion is developed for predicting cell spreading and migration behaviors. This work is motivated by two experimental works: (1) cell migration on 2-D substrates under various fibronectin concentrations and (2) cell spreading on 2-D micropatterned geometries. These works suggest (1) cell migration speed takes a maximum at a particular ligand density (∼1140 molecules/µm(2)) and (2) that strong traction forces at the corners of the patterns may exist due to combined effects exerted by actin stress fibers (SFs). The integrative model of this paper successfully reproduced these experimental results and indicates the mechanism of cell migration and spreading. In this paper, the mechanical structure of the cell is modeled as having two elastic membranes: an outer cell membrane and an inner nuclear membrane. The two elastic membranes are connected by SFs, which are extended from focal adhesions on the cortical surface to the nuclear membrane. In addition, the model also includes ventral SFs bridging two focal adhesions on the cell surface. The cell deforms and gains traction as transmembrane integrins distributed over the outer cell membrane bond to ligands on the ECM surface, activate SFs, and form focal adhesions. The relationship between the cell migration speed and fibronectin concentration agrees with existing experimental data for Chinese hamster ovary (CHO) cell migrations on fibronectin coated surfaces. In addition, the integrated model is validated by showing persistent high stress concentrations at sharp geometrically patterned edges. This model will be used as a predictive model to assist in design and data processing of upcoming microfluidic cell migration assays.

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Actin motor activity in the model.A) An example of simulated cell migration on the plate showing that two types of stress fibers connected to the nucleus are anchored at both leading and trailing edges, and a schematic in the inset representing distributions of SFs in the cell in a top view. B) A scatter plot showing the lifetime of SFs at both leading and trailing edges. black and blue colored bold lines indicate averages values of 32.00 s and 24.91 s at the leading and trailing edges, respectively. Statistical data were acquired from 266 focal adhesions sites at the leading edge and 245 focal adhesions sites at the trailing edge during 3 hours of simulated cell migration on the plate.
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pcbi-1002926-g005: Actin motor activity in the model.A) An example of simulated cell migration on the plate showing that two types of stress fibers connected to the nucleus are anchored at both leading and trailing edges, and a schematic in the inset representing distributions of SFs in the cell in a top view. B) A scatter plot showing the lifetime of SFs at both leading and trailing edges. black and blue colored bold lines indicate averages values of 32.00 s and 24.91 s at the leading and trailing edges, respectively. Statistical data were acquired from 266 focal adhesions sites at the leading edge and 245 focal adhesions sites at the trailing edge during 3 hours of simulated cell migration on the plate.

Mentions: It has been reported that nascent adhesions (smaller than ∼0.25 µm) initiate the adhesion of protrusions of the leading edge of the cell, followed by the disassembly of a subpopulation of nascent adhesions within a minute and growth of the remainder into focal complexes (∼0.5 µm in size) and then focal adhesions (1–5 µm in size) within 5 minutes [44]. Afterwards, focal adhesions either disassemble or mature within the ventral surface of the cell membrane within 10–20 minutes [45], [46]. Furthermore, it is known that the maturation and turnover of focal adhesions involves protein recruitment and elongation, followed by protein disengagement and shrinkage [46]. In the current integrative cell migration model, the disengagement of actin stress fibers from integrins bound to the ECM is assumed to occur when a force-transmitting structural linkage ruptures ( = 0) (see Figure 2-B). With the onset of motor activity after actin polymerization, the generated force is transmitted to the focal adhesions, and receptor-ligand bonds at the focal adhesions are subsequently stretched, resulting in an increases in both traction force and rupture probability for a receptor-ligand bond according to Bell's law [39]. As shown in Figure 5-A, the situation differs at the leading and trailing edges, in large part due to the location of the nucleus closer to the rear of the cell. Note that the angle between the inclined stress fiber and the horizontal plane of the substrate at the trailing edge is higher than that at the leading edge of the cell. If we assume that the stress fibers all exert comparable levels of force then the normal force component will be larger at the trailing edge and therefore have a higher probability of rupture, thereby allowing forward motion of the cell. To test this hypothesis, 266 stress fibers connected to the nucleus at the leading edge and 245 stress fibers connected to the nucleus at the trailing edge were monitored and statistically analysed during three hours of simulated cell migration on the plate with fibronectin density of 200 molecules/µm2 (Figure 5-A, Video S9). Consistent with this hypothesis, we found the lifetime of stress fibers at the trailing edge to be less than that at the leading edge of the cell; 32.00±2.78 s at the leading edge and 24.92±2.17 s at the trailing edge (Figure 5-B). Therefore, we propose that increased magnitude of normal force on the adhesion site at the trailing edge plays a key role in accelerating the rupture of receptor-ligand bonds, leading to an increase in cell migration speed.


Dynamic modeling of cell migration and spreading behaviors on fibronectin coated planar substrates and micropatterned geometries.

Kim MC, Neal DM, Kamm RD, Asada HH - PLoS Comput. Biol. (2013)

Actin motor activity in the model.A) An example of simulated cell migration on the plate showing that two types of stress fibers connected to the nucleus are anchored at both leading and trailing edges, and a schematic in the inset representing distributions of SFs in the cell in a top view. B) A scatter plot showing the lifetime of SFs at both leading and trailing edges. black and blue colored bold lines indicate averages values of 32.00 s and 24.91 s at the leading and trailing edges, respectively. Statistical data were acquired from 266 focal adhesions sites at the leading edge and 245 focal adhesions sites at the trailing edge during 3 hours of simulated cell migration on the plate.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585413&req=5

pcbi-1002926-g005: Actin motor activity in the model.A) An example of simulated cell migration on the plate showing that two types of stress fibers connected to the nucleus are anchored at both leading and trailing edges, and a schematic in the inset representing distributions of SFs in the cell in a top view. B) A scatter plot showing the lifetime of SFs at both leading and trailing edges. black and blue colored bold lines indicate averages values of 32.00 s and 24.91 s at the leading and trailing edges, respectively. Statistical data were acquired from 266 focal adhesions sites at the leading edge and 245 focal adhesions sites at the trailing edge during 3 hours of simulated cell migration on the plate.
Mentions: It has been reported that nascent adhesions (smaller than ∼0.25 µm) initiate the adhesion of protrusions of the leading edge of the cell, followed by the disassembly of a subpopulation of nascent adhesions within a minute and growth of the remainder into focal complexes (∼0.5 µm in size) and then focal adhesions (1–5 µm in size) within 5 minutes [44]. Afterwards, focal adhesions either disassemble or mature within the ventral surface of the cell membrane within 10–20 minutes [45], [46]. Furthermore, it is known that the maturation and turnover of focal adhesions involves protein recruitment and elongation, followed by protein disengagement and shrinkage [46]. In the current integrative cell migration model, the disengagement of actin stress fibers from integrins bound to the ECM is assumed to occur when a force-transmitting structural linkage ruptures ( = 0) (see Figure 2-B). With the onset of motor activity after actin polymerization, the generated force is transmitted to the focal adhesions, and receptor-ligand bonds at the focal adhesions are subsequently stretched, resulting in an increases in both traction force and rupture probability for a receptor-ligand bond according to Bell's law [39]. As shown in Figure 5-A, the situation differs at the leading and trailing edges, in large part due to the location of the nucleus closer to the rear of the cell. Note that the angle between the inclined stress fiber and the horizontal plane of the substrate at the trailing edge is higher than that at the leading edge of the cell. If we assume that the stress fibers all exert comparable levels of force then the normal force component will be larger at the trailing edge and therefore have a higher probability of rupture, thereby allowing forward motion of the cell. To test this hypothesis, 266 stress fibers connected to the nucleus at the leading edge and 245 stress fibers connected to the nucleus at the trailing edge were monitored and statistically analysed during three hours of simulated cell migration on the plate with fibronectin density of 200 molecules/µm2 (Figure 5-A, Video S9). Consistent with this hypothesis, we found the lifetime of stress fibers at the trailing edge to be less than that at the leading edge of the cell; 32.00±2.78 s at the leading edge and 24.92±2.17 s at the trailing edge (Figure 5-B). Therefore, we propose that increased magnitude of normal force on the adhesion site at the trailing edge plays a key role in accelerating the rupture of receptor-ligand bonds, leading to an increase in cell migration speed.

Bottom Line: The integrative model of this paper successfully reproduced these experimental results and indicates the mechanism of cell migration and spreading.In addition, the integrated model is validated by showing persistent high stress concentrations at sharp geometrically patterned edges.This model will be used as a predictive model to assist in design and data processing of upcoming microfluidic cell migration assays.

View Article: PubMed Central - PubMed

Affiliation: BioSystem & Micromechanics IRG, Singapore MIT Alliance Research Technology, Singapore. mincheol@mit.edu

ABSTRACT
An integrative cell migration model incorporating focal adhesion (FA) dynamics, cytoskeleton and nucleus remodeling, actin motor activity, and lamellipodia protrusion is developed for predicting cell spreading and migration behaviors. This work is motivated by two experimental works: (1) cell migration on 2-D substrates under various fibronectin concentrations and (2) cell spreading on 2-D micropatterned geometries. These works suggest (1) cell migration speed takes a maximum at a particular ligand density (∼1140 molecules/µm(2)) and (2) that strong traction forces at the corners of the patterns may exist due to combined effects exerted by actin stress fibers (SFs). The integrative model of this paper successfully reproduced these experimental results and indicates the mechanism of cell migration and spreading. In this paper, the mechanical structure of the cell is modeled as having two elastic membranes: an outer cell membrane and an inner nuclear membrane. The two elastic membranes are connected by SFs, which are extended from focal adhesions on the cortical surface to the nuclear membrane. In addition, the model also includes ventral SFs bridging two focal adhesions on the cell surface. The cell deforms and gains traction as transmembrane integrins distributed over the outer cell membrane bond to ligands on the ECM surface, activate SFs, and form focal adhesions. The relationship between the cell migration speed and fibronectin concentration agrees with existing experimental data for Chinese hamster ovary (CHO) cell migrations on fibronectin coated surfaces. In addition, the integrated model is validated by showing persistent high stress concentrations at sharp geometrically patterned edges. This model will be used as a predictive model to assist in design and data processing of upcoming microfluidic cell migration assays.

Show MeSH
Related in: MedlinePlus