The effect of substrate microtopography on focal adhesion maturation and actin organization via the RhoA/ROCK pathway.

Recently, a growing number of reports have reported that micro- or nanoscale topography enhances cellular functions such as cell adhesion and stem cell differentiation, but the mechanisms responsible for this topography-mediated cell behavior are not fully understood. In this study, we examine the underlying processes and mechanisms behind specific topography-mediated cellular functions. Formation of focal adhesions (FA) was studied by culturing cells on different kinds of topographies, including a flat surface and surfaces with a micropatterned topography (2 μm lattice pattern with 3 μm intervals). We found that the formation and maturation of focal adhesions were highly dependent on the topography of the substrate although the shape, morphology and spreading of cells on the different substrates were not significantly affected. Focal adhesion maturation and actin polymerization were also promoted in cells cultured on the micropatterned substrate. These differences in cell adhesion led us to focus on the Rho GTPases, RhoA and downstream pathways since a number of reports have demonstrated that RhoA-activated cells have highly enhanced focal adhesions and actin activation such as polymerization. By inhibiting the Rho-associated kinase (ROCK) and downstream myosin II, we found that the FA formation, actin organization, and FAK phosphorylation were dramatically decreased. The topographical dependency of FA formation was also highly decreased. These results show that the FA formation and actin cytoskeleton organization of cells on the microtopography is regulated by the RhoA/ROCK pathway.