Quantitative measurement of cell adhesion using centrifugal force

Adhesion, proliferation and differentiation of human mesenchymal stem cell on chitosan/collagen composite scaffold

In vitro tissue engineering requires a progenitor cell source and a porous scaffold providing three dimensional (3D) supports for growth and differentiation to attain tissue architectures. This research focused on fabrication and characterization of 3D porous scaffolds using chitosan (CS), collagen (CG) and chitosan-collagen (CS-CG) composite to investigate their influence on human mesenchymal stem cell (hMSC) adhesion, proliferation and differentiation. Material dependent variations in porous morphology and mechanical behavior of the fabricated CS, CG and CS-CG scaffold showed significant impact on hMSC adhesion, proliferation and differentiation. The maximum hMSC adhesion and proliferation was reported on CS-CG scaffold among all fabricated scaffold groups. Interconnectivity of pores structure in CS-CG scaffold was considered as preferable attribute for such enhanced growth and distribution throughout the scaffold. Besides, CS scaffold with well interconnected pores showed poor adhesion and proliferation because of inadequate adhesion motifs. In case of CG scaffold, optimum growth and distribution of hMSC occurs only at the surface because of the absence of interconnectivity in their pore structures. Likewise, osteogenic differentiation of hMSC occurs most preferably in CS-CG composite scaffold among all scaffold groups. Such enhanced hMSC proliferation and differentiation in CS-CG scaffold significantly influenced on mechanical behavior of scaffold which is essential for in vivo application of a bone tissue implant. Thus CS-CG composite scaffold holds promise to be a suitable platform for in vitro engineering of bone tissue implant.

Engineered chitosan for improved 3D tissue growth through Paxillin-FAK-ERK activation

Scaffold engineering has attracted significant attention for three-dimensional (3D) growth, proliferation and differentiation of stem cells in vitro. Currently available scaffolds suffer from issues such as poor ability for cell adhesion, migration and proliferation. This paper addresses these issues with 3D porous chitosan scaffold, fabricated and functionalized with cysteine-terminated Arg-Gly-Asp (Cys-RGD) tri-peptide on their walls. The study reveals that the compressive moduli of the scaffold is independent to RGD functionalization but shows dependence on the applied freezing temperature (TM) during the fabrication process. The low freezing TM (-80°C) produces scaffold with high compressive moduli (14.64 ± 1.38 kPa) and high TM (-30°C) produces scaffold with low compressive moduli (5.6 ± 0.38 kPa). The Cys-RGD functionalized scaffolds lead to significant improvements in adhesion (150%) and proliferation (300%) of human mesenchymal stem cell (hMSC). The RGD-integrin coupling activates the focal adhesion signaling (Paxillin-FAK-ERK) pathways, as confirmed by the expression of p-Paxillin, p-FAK and p-ERK protein, and results in the observed improvement of cell adhesion and proliferation. The proliferation of hMSC on RGD functionalized surface was evaluated with scanning electron microscopy imaging and distribution though pore was confirmed by histochemistry of transversely sectioned scaffold. The hMSC adhesion and proliferation in scaffold with high compressive moduli showed a constant enhancement (with a slope value 9.97) of compressive strength throughout the experimental period of 28 days. The improved cell adhesion and proliferation with RGD functionalized chitosan scaffold, together with their mechanical stability, will enable new interesting avenues for 3D cell growth and differentiation in numerous applications including regenerative tissue implants.

Dual-functioning peptides discovered by phage display increase the magnitude and specificity of BMSC attachment to mineralized biomaterials

Design of biomaterials for cell-based therapies requires presentation of specific physical and chemical cues to cells, analogous to cues provided by native extracellular matrices (ECM). We previously identified a peptide sequence with high affinity towards apatite (VTKHLNQISQSY, VTK) using phage display. The aims of this study were to identify a human MSC-specific peptide sequence through phage display, combine it with the apatite-specific sequence, and verify the specificity of the combined dual-functioning peptide to both apatite and human bone marrow stromal cells. In this study, a combinatorial phage display identified the cell binding sequence (DPIYALSWSGMA, DPI) which was combined with the mineral binding sequence to generate the dual peptide DPI-VTK. DPI-VTK demonstrated significantly greater binding affinity (1/K_D) to apatite surfaces compared to VTK, phosphorylated VTK (VTK_phos), DPI-VTK_phos, RGD-VTK, and peptide-free apatite surfaces (p < 0.01), while significantly increasing hBMSC adhesion strength (τ₅₀, p < 0.01). MSCs demonstrated significantly greater adhesion strength to DPI-VTK compared to other cell types, while attachment of MC3T3 pre-osteoblasts and murine fibroblasts was limited (p < 0.01). MSCs on DPI-VTK coated surfaces also demonstrated increased spreading compared to pre-osteoblasts and fibroblasts. MSCs cultured on DPI-VTK coated apatite films exhibited significantly greater proliferation compared to controls (p < 0.001). Moreover, early and late stage osteogenic differentiation markers were elevated on DPI-VTK coated apatite films compared to controls. Taken together, phage display can identify non-obvious cell and material specific peptides to increase human MSC adhesion strength to specific biomaterial surfaces and subsequently increase cell proliferation and differentiation. These new peptides expand biomaterial design methodology for cell-based regeneration of bone defects. This strategy of combining cell and material binding phage display derived peptides is broadly applicable to a variety of systems requiring targeted adhesion of specific cell populations, and may be generalized to the engineering of any adhesion surface.

The cytoskeleton regulates cell attachment strength

Quantitative information about adhesion strength is a fundamental part of our understanding of cell-extracellular matrix (ECM) interactions. Adhesion assays should measure integrin-ECM bond strength, but reports now suggest that cell components remain behind after exposure to acute force for radial shear assays in the presence of divalent cations that increase integrin-ECM affinity. Here, we show that focal adhesion proteins FAK, paxillin, and vinculin but not the cytoskeletal protein actin remain behind after shear-induced detachment of HT1080 fibrosarcoma cells. Cytoskeletal stabilization increased attachment strength by eightfold, whereas cross-linking integrins to the substrate only caused a 1.5-fold increase. Reducing temperature-only during shear application-also increased attachment strength eightfold, with detachment again occurring between focal adhesion proteins and actin. Detachment at the focal adhesion-cytoskeleton interface was also observed in mouse and human fibroblasts and was ligand-independent, highlighting the ubiquity of this mode of detachment in the presence of divalent cations. These data show that the cytoskeleton and its dynamic coupling to focal adhesions are critically important for cell adhesion in niche with divalent cations.

Monitoring of TGF-β 1-Induced Human Lung Adenocarcinoma A549 Cells Epithelial-Mesenchymal Transformation Process by Measuring Cell Adhesion Force with a Microfluidic Device

The epithelial-mesenchymal transition (EMT) is a process in which epithelial cells lose their cell polarity and cell-cell adhesion, and gain migratory and invasive properties. It is believed that EMT is associated with initiation and completion of the invasion-metastasis cascade. In this study, an economic approach was developed to fabricate a microfluidic device with less instrumentation requirement for the investigation of EMT by quantifying cell adhesion force. Fluid shear force was precisely controlled by a homemade microfluidic perfusion apparatus and interface. The adhesion capability of the human lung adenocarcinoma cell line A549 on different types of extracellular matrix protein was studied. In addition, effects of transforming growth factor-β (TGF-β) on EMT in A549 cells were investigated by characterizing the adhesion force changes and on-chip fluorescent staining. The results demonstrate that the microfluidic device is a potential tool to characterize the epithelial-mesenchymal transition process by measuring cell adhesion force.

Dual-functioning phage-derived peptides encourage human bone marrow cell-specific attachment to mineralized biomaterials

Cell instructive mineralized biomaterials are a promising alternative to conventional auto-, allo-, and xenograft therapies for the reconstruction of critical sized defects. Extracellular matrix proteins, peptide domains, and functional motifs demonstrating cell and mineral binding activity have been used to improve cell attachment. However, these strategies vary in their tissue regeneration outcomes due to lack of specificity to both regenerative cell populations and the material substrates. In order to mediate cell-specific interactions on apatite surfaces, we identified peptide sequences with high affinity towards apatite (VTKHLNQISQSY, VTK) and clonally derived human bone marrow stromal cells (DPIYALSWSGMA, DPI) using phage display. The primary aims of this study were to measure apatite binding affinity, human bone marrow stromal cell (hBMSC) adhesion strength, and peptide specificity to hBMSCs when the apatite and cell-specific peptides are combined into a dual-functioning peptide. To assess binding affinity to hydroxyapatite (HA), binding isotherms were constructed and peptide binding affinity (K1) determined. HBMSC, MC3T3 and mouse dermal fibroblast (MDF) adhesion strength on biomimetic apatite functionalized with single- and dual-functioning peptide sequences were evaluated using a centrifugation assay. DPI-VTK had the highest binding strength towards hBMSCs (p < 0.01). DPI-VTK, while promoting strong initial attachment to hBMSCs, did not encourage strong adhesions to MC3T3s or fibroblasts (p < 0.01). Taken together, phage display is a promising strategy to identify preferential cell and material binding peptide sequences that can tether specific cell populations onto specific biomaterial chemistries.

Development of a dynamic stem cell culture platform for mesenchymal stem cell adhesion and evaluation

The importance of providing a physiologically relevant environment for cell culture is well recognized. The combination of proper environmental cues which are provided in vivo by the bloodstream and extracellular matrix must be reproduced to properly examine cell response in vitro, and cannot be recapitulated using traditional culture on polystyrene. Here, we have developed a device, the dynamic stem cell culture platform (DSCCP), consisting of a biomimetic scaffold cultured within the dynamic environment of a perfusion bioreactor. By varying scaffold parameters including stiffness and protein inclusion at the material surface, we found that human mesenchymal stem cells (hMSCs) were able to adhere to modified substrates, while still maintaining multipotency. Culture in a perfusion bioreactor showed cell survival and proliferation, particularly on modified substrates. The DSCCP represents a complete platform for cell adhesion and subsequent evaluation, including the response of a cell population to drug treatment.

Human Sprouty1 suppresses growth, migration, and invasion in human breast cancer cells

Breast cancer is the most common cancer and the leading cause of cancer death in women worldwide. Expression of human Sprouty1 (hSpry1) gene is downregulated in most breast cancer patients, implicating it as an important tumor suppressor gene. So, we hypothesized that overexpression of hSpry1 gene may suppress breast cancer cell growth, migration, and invasion. Here, we demonstrate that in breast cancer cell lines, MDA-MB-231 and T47D, transfection-induced overexpression of hSpry1 reduced cell population, proliferation, and colony formation in vitro without affecting cell apoptosis. Adhesion molecules act as both positive and negative modulators of cellular migration and invasion. Here, we found that overexpression of hSpry1 enhances the initial establishment events in breast cancer cell adhesion to type IV collagen and vitronectin. Moreover, the overexpression of hSpry1 in the highly invasive MDA-MB-231 breast cancer cells causes a significant reduction in cellular migration and invasion through Matrigel membranes. In addition, we showed that hSpry1 overexpression prevents VEGF secretion. VEGF is essential for primary tumor growth, migration, and invasion. Thus, our study provides a novel mechanism of tumor suppression activity of hSpry1.

Recombinant fibronectin matrix mimetics specify integrin adhesion and extracellular matrix assembly

Tissue engineering seeks to create functional tissues and organs by integrating natural or synthetic scaffolds with bioactive factors and cells. Creating biologically active scaffolds that support key aspects of tissue regeneration, including the re-establishment of a functional extracellular matrix (ECM), is a challenge currently facing this field. During tissue repair, fibronectin is converted from an inactive soluble form into biologically active ECM fibrils through a cell-dependent process. ECM fibronectin promotes cell processes critical to tissue regeneration and regulates the deposition and organization of other ECM proteins. We previously developed biomimetics of ECM fibronectin by directly coupling the heparin-binding fragment of the first type III repeat of fibronectin (FNIII1H) to the integrin-binding repeats (FNIII8-10). As adhesive substrates, fibronectin matrix mimetics promote cell growth, migration, and contractility through a FNIII1H-dependent mechanism. Here, we analyzed fibronectin matrix mimetic variants designed to include all or part of the integrin-binding domain for their ability to support new ECM assembly. We found that specific modifications of the integrin-binding domain produced adhesive substrates that selectively engage different integrin receptors to, in turn, regulate the amount of fibronectin and collagen deposited into the ECM. The ability of fibronectin matrix mimetics to direct cell-substrate interactions and regulate ECM assembly makes them promising candidates for use as bioactive surfaces, where precise control over integrin-binding specificity and ECM deposition are required.