Capturing instructive cues of tissue microenvironment by silica bioreplication

Silica Replicas Derived from Mammalian Cells as an Innovative Approach to Physically Direct Cell Lineage Decisions of Mesenchymal Stem Cells

By means of a "live-cell" template strategy, silica replicas displaying the same morphology and topography of the mammalian cells used as templates are fabricated. The replicas are used as substrates to direct the differentiation of mesenchymal stem cells (MSCs) to predefined cell lineages. Upregulation of specific genes shows how the silica replica-based substrates have the ability to induce the molecular characteristics of the mature cell types from which they have been derived from. Thus, MSCs cultured in the presence of silica replicas of human osteoblasts (HObs) differentiate into HObs-like cells, as shown by the upregulation of specific osteogenic genes. Likewise, when MSCs are incubated with silica replicas derived from human chondrocytes, an enhanced expression of chondrogenic markers is observed. Importantly, the effects of the silica replicas are cell type-specific since the incubation of MSCs with HObs silica replicas does not result in upregulation of chondrogenic markers and vice versa. What is more, for both cases, the differentiation rate is enhanced when the silica replicas are used in combination with growth factors, suggesting a potential synergistic effect. These results demonstrate the potential of this innovative method as an efficient and cheap approach with the potential to eliminate, or at least reduce, the use of biochemically soluble compounds in stem cells research.

Replication of natural surface topographies to generate advanced cell culture substrates

Surface topographies of cell culture substrates can be used to generate in vitro cell culture environments similar to the in vivo cell niches. In vivo, the physical properties of the extracellular matrix (ECM), such as its topography, provide physical cues that play an important role in modulating cell function. Mimicking these properties remains a challenge to provide in vitro realistic environments for cells. Artificially generated substrates' topographies were used extensively to explore this important surface cue. More recently, the replication of natural surface topographies has been enabling to exploration of characteristics such as hierarchy and size scales relevant for cells as advanced biomimetic substrates. These substrates offer more realistic and mimetic environments regarding the topographies found in vivo. This review will highlight the use of natural surface topographies as a template to generate substrates for in-vitro cell culture. This review starts with an analysis of the main cell functions that can be regulated by the substrate's surface topography through cell-substrate interactions. Then, we will discuss research works wherein substrates for cell biology decorated with natural surface topographies were used and investigated regarding their influence on cellular performance. At the end of this review, we will highlight the advantages and challenges of the use of natural surface topographies as a template for the generation of advanced substrates for cell culture.

The loop of phenotype: Dynamic reciprocity links tenocyte morphology to tendon tissue homeostasis

Cells and their surrounding extracellular matrix (ECM) are engaged in dynamic reciprocity to maintain tissue homeostasis: cells deposit ECM, which in turn presents the signals that define cell identity. This loop of phenotype is obvious for biochemical signals, such as collagens, which are produced by and presented to cells, but the role of biomechanical signals is also increasingly recognised. In addition, cell shape goes hand in hand with cell function and tissue homeostasis. Aberrant cell shape and ECM is seen in pathological conditions, and control of cell shape in micro-fabricated platforms disclose the causal relationship between cell shape and cell function, often mediated by mechanotransduction. In this manuscript, we discuss the loop of phenotype for tendon tissue homeostasis. We describe cell shape and ECM organization in normal and diseased tissue, how ECM composition influences tenocyte shape, and how that leads to the activation of signal transduction pathways and ECM deposition. We further describe the use of technologies to control cell shape to elucidate the link between cell shape and its phenotypical markers and focus on the causal role of cell shape in the loop of phenotype. STATEMENT OF SIGNIFICANCE: The dynamic reciprocity between cells and their surrounding extracellular matrix (ECM) influences biomechanical and biochemical properties of ECM as well as cell function through activation of signal transduction pathways that regulate gene and protein expression. We refer to this reciprocity as Loop of Phenotype and it has been studied and demonstrated extensively by using micro-fabricated platforms to manipulate cell shape and cell fate. In this manuscript, we discuss this concept in tendon tissue homeostasis by giving examples in healthy and pathological tenson tissue. Furthermore, we elaborate this by showing how biomaterials are used to feed this reciprocity to manipulate cell shape and function. Finally, we elucidate the link between cell shape and its phenotypical markers and focus on the activation of signal transduction pathways and ECM deposition.

Tendon-Derived Biomimetic Surface Topographies Induce Phenotypic Maintenance of Tenocytes In Vitro

The tenocyte niche contains biochemical and biophysical signals that are needed for tendon homeostasis. The tenocyte phenotype is correlated with cell shape in vivo and in vitro, and shape-modifying cues are needed for tenocyte phenotypical maintenance. Indeed, cell shape changes from elongated to spread when cultured on a flat surface, and rat tenocytes lose the expression of phenotypical markers throughout five passages. We hypothesized that tendon gene expression can be preserved by culturing cells in the native tendon shape. To this end, we reproduced the tendon topographical landscape into tissue culture polystyrene, using imprinting technology. We confirmed that the imprints forced the cells into a more elongated shape, which correlated with the level of Scleraxis expression. When we cultured the tenocytes for 7 days on flat surfaces and tendon imprints, we observed a decline in tenogenic marker expression on flat but not on imprints. This research demonstrates that native tendon topography is an important factor contributing to the tenocyte phenotype. Tendon imprints therefore provide a powerful platform to explore the effect of instructive cues originating from native tendon topography on guiding cell shape, phenotype, and function of tendon-related cells.

Extracellular Matrix-Derived Hydrogels as Biomaterial for Different Skeletal Muscle Tissue Replacements

Recently, skeletal muscle represents a complex and challenging tissue to be generated in vitro for tissue engineering purposes. Several attempts have been pursued to develop hydrogels with different formulations resembling in vitro the characteristics of skeletal muscle tissue in vivo. This review article describes how different types of cell-laden hydrogels recapitulate the multiple interactions occurring between extracellular matrix (ECM) and muscle cells. A special attention is focused on the biochemical cues that affect myocytes morphology, adhesion, proliferation, and phenotype maintenance, underlining the importance of topographical cues exerted on the hydrogels to guide cellular orientation and facilitate myogenic differentiation and maturation. Moreover, we highlight the crucial role of 3D printing and bioreactors as useful platforms to finely control spatial deposition of cells into ECM based hydrogels and provide the skeletal muscle native-like tissue microenvironment, respectively.

Deconstructing, Replicating, and Engineering Tissue Microenvironment for Stem Cell Differentiation

One of the most crucial components of regenerative medicine is the controlled differentiation of embryonic or adult stem cells into the desired cell lineage. Although most of the reported protocols of stem cell differentiation involve the use of soluble growth factors, it is increasingly evident that stem cells also undergo differentiation when cultured in the appropriate microenvironment. When cultured in decellularized tissues, for instance, stem cells can recapitulate the morphogenesis and functional specialization of differentiated cell types with speed and efficiency that often surpass the traditional growth factor-driven protocols. This suggests that the tissue microenvironment (TME) provides stem cells with a holistic "instructive niche" that harbors signals for cellular reprogramming. The translation of this into medical applications requires the decoding of these signals, but this has been hampered by the complexity of TME. This problem is often addressed by a reductionist approach, in which cells are exposed to substrates decorated with simple, empirically designed geometries, textures, and chemical compositions ("bottom-up" approach). Although these studies are invaluable in revealing the basic principles of mechanotransduction mechanisms, their physiological relevance is often uncertain. This review examines the recent progress of an alternative, "top-down" approach, in which the TME is treated as a holistic biological entity. This approach is made possible by recent advances in systems biology and fabrication technologies that enable the isolation, characterization, and reconstitution of TME. It is hoped that these new techniques will elucidate the nature of niche signals so that they can be extracted, replicated, and controlled. This review summarizes these emerging techniques and how the data they generated are changing our view on TME. Impact statement This review summarizes the current state of art of the understanding of instructive niche in the field of tissue microenvironment. Not only did we survey the use of different biochemical preparations as stimuli of stem cell differentiation and summarize the recent effort in dissecting the biochemical composition of these preparations, through the application of extracellular matrix (ECM) arrays and proteomics, but we also introduce the use of open-source, high-content immunohistochemistry projects in contributing to the understanding of tissue-specific composition of ECM. We believe this review would be highly useful for our peer researching in the same field. "Mr. Tulkinghorn is always the same… so oddly out of place and yet so perfectly at home." -Charles Dickens, Bleak House.