Scarring is a long-lasting problem in higher animals and reductionist approaches could aid in developing treatments. than homogeneously stiff gels. Such differences from bulk-average responses arise because a strong SMA Embramine repressor NKX2.5 slowly exits the nucleus on rigid matrices. NKX2.5 overexpression overrides rigid phenotypes inhibiting SMA and cell spreading while cytoplasm-localized NKX2.5 mutants degrade in well-spread cells. MSCs thus form a ‘mechanical memory’ of rigidity by progressively suppressing NKX2.5 thereby elevating SMA in a scar-like state. in responses (eg. gene expression noise) of cell populations can also be important for understanding and for using cells in therapy especially stem cells that proliferate and differentiate in response to materials. We sought therefore to develop heterogeneous scar-like gel systems in order to compare phenotypes and their cell-to-cell variations to homogeneous materials of different stiffness. Figure 1 A minimal matrix model of scars MMMS Collagen-I is the most abundant protein in mammals but the partially oriented and bundles of crosslinked collagen-I in a scar have been characterized as having an atypical fractal7 micro-architecture the way tree branches fill space. The fiber bundles displace normal tissue and thereby limit tissue function8. In the scarring that occurs in muscle diseases for example collagen-I (gene which produces the ‘scar marker’ smooth muscle actin (SMA) indicates increased cell tension10 and it is expressed many days after injury in Embramine spindle-shaped cells remaining high in scars for a decade or more11. Upregulation of the nuclear structure protein lamin-A (that regulates levels is consistent with recent correlations between lamin-A and collagen-I levels in tissues12 – but kinetics are unclear for this apparent relationship. Large decreases in expression of at least one gene that encodes for a “heart development” transcription factor are also evident in diseased skeletal muscle (Fig. 1c) Embramine which hints at a much broader role than previously considered13 for such a regulatory factor. The complexity of cell types matrix and soluble factors in scars confounds whether any particular cell type responds per such profiles to the fractal heterogeneity of a scar microenvironment. Our reductionist goal here was to develop a controllable minimal matrix model for 2D cultures that possesses a micro-architecture with fractal heterogeneity and inherently variable stiffening observed in scars and that also causes a relevant cell type to respond as if in a 3D scar. For many types of injured and scarred tissues various endogenous cell types including mesenchymal stem cells (MSCs) might impact the collagen at the injured site but therapies are certainly being pursued with MSCs14 15 MSCs are not only multipotent14 but also mechanosensitive16. Whether these cells or derived lineages are ‘plastic’ in changing Embramine phenotype when engrafted into a scar – or even when expanded in culture before injection – is a critical issue for cell therapy. MSCs that are purified from soft marrow (~300 Pa)17 and cultured conventionally on rigid plastic18 or that are derived from embryonic stem cells19 exhibit expression profiles that are similar in Embramine some key ways to those of injured tissues; particularly the progressive increases in and (Fig. 1c). These transcript profiles provide hints of expression changes of possible relevance to scars and motivate the detailed studies here of protein dynamics and mechanisms in MSCs as a suitable cell type on substrates with scar-like features rather than homogeneously rigid plastic. Rigid-on-soft composite substrates have recently been made with Mouse monoclonal to CIB1 micropatterns20 although effects of local elastic modulus were not decoupled from ligand density. Matrix Embramine ligand type and density provide signals complementary to those possible from matrix mechanics in influencing cell behavior such as the differentiation of MSCs21-23. However recent studies in culture of matrix tethering24 topography25 crosslinking and growth in 3D22 23 have also stirred debate on the influence of matrix properties in cell-fate decisions. Indeed the stiffness (of tissues including scars when measured on a macroscopic scale sometimes lead to a far greater stiffness (MPa)26 than when measured on the microscopic.