Dynamics and morphology of focal adhesions in complex 3D environment.

Focal adhesions are specific types of cellular adhesion structures through which both mechanical force and regulatory signals are transmitted. Recently, the existence of focal adhesions in 3D environment has been questioned. Using a unique life-like model of dermis-based matrix we analysed the presence of focal adhesions in a complex 3D environment. Although the dermis-based matrix constitutes a 3D environment, the interface of cell-to-matrix contacts on thick bundled fibres within this matrix resembles 2D conditions. We call this a quasi-2D situation. We suggest that the quasi-2D interface of cell-to-matrix contacts constituted in the dermis-based matrix is much closer to in tissue conditions than the meshed structure of mostly uniform thin fibres in the gel-based matrices. In agreement with our assumption, we found that the cell adhesion structures are formed by cells that invade the dermis-based matrix and that these structures are of similar size as focal adhesions formed on fibronectin-coated coverslips (2D). In both 2D situation and the dermis-based matrix, we observed comparable vinculin dynamics in focal adhesions and comparable enlargement of the focal adhesions in response to a MEK inhibitor. We conclude that focal adhesions that are formed in the 3D environment are similar in size and dynamics as those seen in the 2D setting.