Universal Kinetics of the Onset of Cell Spreading on Substrates of Different Stiffness

Abstract

When plated onto substrates, cell morphology and even stem cell differentiation are influenced by the stiffness of their environment. Stiffer substrates give strongly spread (eventually polarized) cells with strong focal adhesions, and stress fibers; very soft substrates give a less developed cytoskeleton, and much lower cell spreading. The kinetics of this process of cell spreading is studied extensively, and important universal relationships are established on how the cell area grows with time. Here we study the population dynamics of spreading cells, investigating the characteristic processes involved in cell response to the substrate. We show that unlike the individual cell morphology, this population dynamics does not depend on the substrate stiffness. Instead, a strong activation temperature dependence is observed. Different cell lines on different substrates all have long-time statistics controlled by the thermal activation over a single energy barrier ∆G ≈ 19 kcal/mol, while the early-time kinetics follows a power law ∼ t 5 . This implies that the rate of spreading depends on an internal process of adhesion complex assembly and activation: the operational complex must have 5 component proteins, and the last process in the sequence (which we believe is the activation of focal adhesion kinase) is controlled by the binding energy ∆G.

Progesterone receptor expression contributes to gemcitabine resistance at higher ECM stiffness in breast cancer cell lines

“…When cultured on the PAA gels, MCF-7 breast cancer cells showed different morphology between the stiffnesses ( Fig 1B ). Immunofluorescent staining of the actin cytoskeleton and DNA ( Fig 1C ) determined that cells had an increase in cytoplasmic and nuclear area at 4 kPa, compared to 500 Pa ( Fig 1D ), consistent with the literature [ 7 ]. Staining of mature focal adhesions (vinculin) also showed a change in the staining pattern ( Fig 1C ).…”

Development of Nascent Focal Adhesions in Spreading Cells

“…The fully-assembled mechanosensing complex would then positively signal for Rho/Rac signalling and lead to an activation of F-actin polymerisation. An adaptation of the mechanism of Bell et al (39) to account for this behaviour is shown in Fig. 2.…”

“…The component proteins of a mechanosensor complex take a characteristic time to be recruited to the membrane sites, depending on a (fast) diffusion time, and a (much slower) binding time. By examining population dynamics of the time at which the cell becomes hemispherical in shape, Bell et al (39) found that a 5 th order power law determined the number of spread cells at a particular early spreading time, suggesting 5 slow thermally-activated steps Figure 2: Sketch of a possible mechanism for the 5-step assembly of a mechanosensing protein complex Bell et al (39). α-actinin is suggested as a possible basis for nearestneighbour interactions between complexes.…”

“…The duration of these processes depends heavily on temperature, i.e. the internal thermally-activated processes, as shown by Bell et al (39).…”

Magnetic Nanocomposite Hydrogels for Directing Myofibroblast Activity in Adipose‐Derived Stem Cells

“…Cell size and morphology are influenced by matrix stiffness. [ 14–16 ] On a stiff surface, cells can adopt robust focal adhesions with an organized cytoskeleton, thereby facilitating a dynamic push and pull, whereas on soft surface, cells fail to develop this contractile network. In addition to cell morphology, stiffness also influences cellular functions such a proliferation [ 17–19 ] and differentiation.…”