Fibronectin fibrillogenesis is a cell-mediated, step-wise process that converts soluble fibronectin into insoluble fibronectin matrix. The deposition of fibronectin fibrils occurs at specific sites on the cell surface and depends on the unfolding of the fibronectin dimer. Fibronectin matrix provides positional information for cell migration during early embryogenesis and plays an important role in cell growth, differentiation, survival, and oncogenic transformation. Here we present simple techniques, based on the use of fluorescently labeled fibronectin and species-specific antifibronectin antibodies that allow determination of the fibronectin fibril growth in conventional in vitro cell cultures and in three-dimensional matrix environment.
"In fixed tissues or fibrillar matrices, extracellular matrix proteins such as fibronectin or fibrin can be also be fluorescently labeled and imaged using standard wide-field or confocal microscopy   . For dynamic studies of cell-induced ECM organization, pre-labeled ECM proteins can be used, such as Rhodamine-conjugated fibronectin  . However, as detailed below, the most powerful methods for visualizing collagen matrix fibrils are differential interference contrast (DIC), confocal reflection microscopy and second harmonic generation imaging. "
[Show abstract][Hide abstract] ABSTRACT: Cellular interactions with extracellular matrices (ECM) through the application of mechanical forces mediate numerous biological processes including developmental morphogenesis, wound healing and cancer metastasis. They also play a key role in the cellular repopulation and/or remodeling of engineered tissues and organs. While 2-D studies can provide important insights into many aspects of cellular mechanobiology, cells reside within 3-D ECMs in vivo, and matrix structure and dimensionality have been shown to impact cell morphology, protein organization and mechanical behavior. Global measurements of cell-induced compaction of 3-D collagen matrices can provide important insights into the regulation of overall cell contractility by various cytokines and signaling pathways. However, to understand how the mechanics of cell spreading, migration, contraction and matrix remodeling are regulated at the molecular level, these processes must also be studied in individual cells. Here we review the evolution and application of techniques for imaging and assessing local cell-matrix mechanical interactions in 3-D culture models, tissue explants and living animals.
Experimental Cell Research 06/2013; 319(16). DOI:10.1016/j.yexcr.2013.06.018 · 3.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fibronectin (FN) is a plasma glycoprotein that circulates in the near micromolar concentration range and is deposited along with locally produced FN in the extracellular matrices of many tissues. The control of FN deposition is tightly controlled by cells. Agents that modulate FN assembly may be useful therapeutically in conditions characterized by excessive FN deposition, such as fibrosis, inflammatory diseases, and malignancies. To identify such agents by high throughput screening (HTS), we developed a microtiter assay of FN deposition by human fibroblasts. The assay provides a robust read-out of FN assembly. Alexa 488-FN (A488-FN) was added to cell monolayers, and the total fluorescence intensity of deposited A488-FN was quantified. The fluorescence intensity of deposited A488-FN correlated with the presence of FN fibrils visualized by fluorescence microscopy. The assay Z' values were 0.67 or 0.54, respectively, when using background values of fluorescence either with no added A488-FN or with A488-FN added together with a known inhibitor of FN deposition. The assay was used to screen libraries comprising 4160 known bioactive compounds. Nine compounds were identified as non- or low-cytotoxic inhibitors of FN assembly. Four (ML-9, HA-100, tyrphostin and imatinib mesylate) are kinase inhibitors, a category of compounds known to inhibit FN assembly; two (piperlongumine and cantharidin) are promoters of cancer cell apoptosis; and three (maprotiline, CGS12066B, and aposcopolamine) are modulators of biogenic amine signaling. The latter six compounds have not been recognized heretofore as affecting FN assembly. The assay is straight-forward, adapts to 96- and 384-well formats, and should be useful for routine measurement of FN deposition and HTS. Screening of more diverse chemical libraries and identification of specific and efficient modulators of FN fibrillogenesis may result in therapeutics to control excessive connective tissue deposition.
Matrix biology: journal of the International Society for Matrix Biology 08/2012; 31(6). DOI:10.1016/j.matbio.2012.07.003 · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mena is an Ena/VASP family actin regulator with roles in cell migration, chemotaxis, cell–cell adhesion, tumor cell invasion,
and metastasis. Although enriched in focal adhesions, Mena has no established function within these structures. We find that
Mena forms an adhesion-regulated complex with α5β1 integrin, a fibronectin receptor involved in cell adhesion, motility, fibronectin
fibrillogenesis, signaling, and growth factor receptor trafficking. Mena bound directly to the carboxy-terminal portion of
the α5 cytoplasmic tail via a 91-residue region containing 13 five-residue “LERER” repeats. In fibroblasts, the Mena–α5 complex
was required for “outside-in” α5β1 functions, including normal phosphorylation of FAK and paxillin and formation of fibrillar
adhesions. It also supported fibrillogenesis and cell spreading and controlled cell migration speed. Thus, fibroblasts require
Mena for multiple α5β1-dependent processes involving bidirectional interactions between the extracellular matrix and cytoplasmic
focal adhesion proteins.
The Journal of Cell Biology 08/2012; 198(4):657-676. DOI:10.1083/jcb.201202079 · 9.83 Impact Factor
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