Substrate Rigidity Regulates the Formation and Maintenance of Tissues

Abstract

The ability of cells to form tissues represents one of the most fundamental issues in biology. However, it is unclear what triggers cells to adhere to one another in tissues and to migrate once a piece of tissue is planted on culture surfaces. Using substrates of identical chemical composition but different flexibility, we show that this process is controlled by substrate rigidity: on stiff substrates, cells migrate away from one another and spread on surfaces, whereas on soft substrates they merge to form tissue-like structures. Similar behavior was observed not only with fibroblastic and epithelial cell lines but also explants from neonatal rat hearts. Cell compaction on soft substrates involves a combination of weakened adhesions to the substrate and myosin II-dependent contractile forces that drive cells toward one another. Our results suggest that tissue formation and maintenance is regulated by differential mechanical signals between cell-cell and cell-substrate interactions, which in turn elicit differential contractile forces and adhesions to determine the preferred direction of cell migration and association.

Retrograde Fluxes of Focal Adhesion Proteins in Response to Cell Migration and Mechanical Signals

“…This structural shear mechanism also explains the different degrees of correlated movements with actin flux for different focal adhesion proteins (Brown et al, 2006;Hu et al, 2007), and they may serve as a feedback mechanism that adjusts structural assembly, possibly coupled with the generation of contractile forces, in response to the needs of cell migration. The mechanism will provide the strongest propulsive forces for slow-moving cells on stiff substrates, which are known to induce strong resistive adhesions as well as traction forces (Guo et al, 2006). A second potential function of a regulated flux at focal adhesions is to serve as a slippage clutch for cell migration (Smilenov et al, 1999;Hu et al, 2007).…”

“…Adherent cells seem capable of both responding to applied mechanical forces (Tzima et al, 2005) and applying contractile forces to probe mechanical properties of the environment (Discher et al, 2005). The downstream responses include changes in migration (Pelham and Wang, 1997;Sheetz et al, 1998;Lo et al, 2000), cell-cell interactions (Guo et al, 2006), proliferation Nelson et al, 2005), differentiation (Engler et al, 2004(Engler et al, , 2006, and apoptosis . For cultured adherent cells, focal adhesions are thought to mediate mechanosensing through integrin-mediated anchorage to the extracellular matrix (Larsen et al, 2006).…”

Polyelectrolyte Multilayer Films of Controlled Stiffness Modulate Myoblast Cell Differentiation

“…For soft films, the absence of well organized adhesion structures may lead to a deregulated myofibril assembly, which may hinder further myotubes growth. Myosin II, a molecular motor known to play an important role in the generation of traction forces and in contractility [17,50] might also be involved in the cell clumping observed on soft films. Another hypothesis is that film stiffness might affect myoblast motility, a parameter that was recently shown to be very important in the growth of myotubes after their initial formation [51] and which is currently under study.…”

“…For the attachment experiments, cells were labeled with rhodamine-phalloidin (1:800, Sigma, France) and monoclonal mouse antivinculin (1:400, Sigma, France). The number density of focal adhesions was calculated as the number of focal adhesions divided by the total cell area [50] . For the differentiation experiments, cells were labeled with monoclonal mouse anti-troponin T (1:100), mouse anti-myosin heavy chain (MHC, 1:500) (both from Sigma, France), rabbit anti-myogenin (1:60), or rabbit antiMyf-5 (1:300) (both from Santa Cruz Biotechnology, Tebu-Bio, France) [58] .…”

Focal adhesion kinase as a regulator of cell tension in the progression of cancer

“…For example, cells plated on rigid substrates have more robust adhesions than those on more flexible substrates [15][16][17], presumably because rigid substrates are more capable of resisting the contractile forces from the cell. Likewise, cells treated with agents that increase actinomyosin contractility such as Lysophosphatidic acid (LPA), thrombin, or bombesin also lead to a further increase in FA size in cells plated on rigid substrates [18,19].…”