Fibronectin adsorption and arrangement on copolymer surfaces and their significance in cell adhesion

Novel role of homogalacturonan region of pectin in disrupting the interaction between fibronectin and integrin β1

Pectin interacts with fibronectin (FN), a modular protein in the extracellular matrix. This interaction is significant as FN plays a pivotal role by binding to the receptor integrin α5β1. However, the molecular mechanism underlying the pectin-FN interaction and its impact on integrin binding remains unknown. In this study, water-soluble pectins (WSPs) were extracted from three different pectin sources and subsequently characterized. These included Citrus WSP, which primarily comprises the homogalacturonan region, and Kaki and Yuzu WSPs, both of which are rich in rhamnogalacturonan regions. We investigated the molecular interactions between these WSPs and two FN fragments, Anastellin and RetroNectin, using surface plasmon resonance analysis. Citrus WSP exhibited a notable binding affinity to FN, with a dissociation constant (KD) of approximately 10-7 M. In contrast, Kaki and Yuzu WSPs displayed comparatively weaker or negligible binding affinities. The binding reactivity of Citrus WSP with FN was notably diminished following the enzymatic removal of its methyl-ester groups. Additionally, Citrus WSP disrupted the binding of integrin β1 to RetroNectin without altering the affinity, despite its minimal direct binding to integrin itself. This study furthers our understanding of the intricate pectin-FN interaction and sheds light on their potential physiological relevance and impact on cellular responses.

Screening a chemically defined extracellular matrix mimetic substrate library to identify substrates that enhance substrate-mediated transfection

Nonviral gene delivery, though limited by inefficiency, has extensive utility in cell therapy, tissue engineering, and diagnostics. Substrate-mediated gene delivery (SMD) increases efficiency and allows transfection at a cell-biomaterial interface, by immobilizing and concentrating nucleic acid complexes on a surface. Efficient SMD generally requires substrates to be coated with serum or other protein coatings to mediate nucleic acid complex immobilization, as well as cell adhesion and growth; however, this strategy limits reproducibility and may be difficult to translate for clinical applications. As an alternative, we screened a chemically defined combinatorial library of 20 different extracellular matrix mimetic substrates containing combinations of (1) different sulfated polysaccharides that are essential extracellular matrix glycosaminoglycans (GAGs), with (2) mimetic peptides derived from adhesion proteins, growth factors, and cell-penetrating domains, for use as SMD coatings. We identified optimal substrates for DNA lipoplex and polyplex SMD transfection of fibroblasts and human mesenchymal stem cells. Optimal extracellular matrix mimetic substrates varied between cell type, donor source, and transfection reagent, but typically contained Heparin GAG and an adhesion peptide. Multiple substrates significantly increased transgene expression (i.e. 2- to 20-fold) over standard protein coatings. Considering previous research of similar ligands, we hypothesize extracellular matrix mimetic substrates modulate cell adhesion, proliferation, and survival, as well as plasmid internalization and trafficking. Our results demonstrate the utility of screening combinatorial extracellular matrix mimetic substrates for optimal SMD transfection towards application- and patient-specific technologies.

Impact statement

Substrate-mediated gene delivery (SMD) approaches have potential for modification of cells in applications where a cell-material interface exists. Conventional SMD uses ill-defined serum or protein coatings to facilitate immobilization of nucleic acid complexes, cell attachment, and subsequent transfection, which limits reproducibility and clinical utility. As an alternative, we screened a defined library of extracellular matrix mimetic substrates containing combinations of different glycosaminoglycans and bioactive peptides to identify optimal substrates for SMD transfection of fibroblasts and human mesenchymal stem cells. This strategy could be utilized to develop substrates for specific SMD applications in which variability exists between different cell types and patient samples.

Achieving Controlled Biomolecule-Biomaterial Conjugation

The conjugation of biomolecules can impart materials with the bioactivity necessary to modulate specific cell behaviors. While the biological roles of particular polypeptide, oligonucleotide, and glycan structures have been extensively reviewed, along with the influence of attachment on material structure and function, the key role played by the conjugation strategy in determining activity is often overlooked. In this review, we focus on the chemistry of biomolecule conjugation and provide a comprehensive overview of the key strategies for achieving controlled biomaterial functionalization. No universal method exists to provide optimal attachment, and here we will discuss both the relative advantages and disadvantages of each technique. In doing so, we highlight the importance of carefully considering the impact and suitability of a particular technique during biomaterial design.

Adding Functions to Biomaterial Surfaces through Protein Incorporation

The concept of biomaterials has evolved from one of inert mechanical supports with a long-term, biologically inactive role in the body into complex matrices that exhibit selective cell binding, promote proliferation and matrix production, and may ultimately become replaced by newly generated tissues in vivo. Functionalization of material surfaces with biomolecules is critical to their ability to evade immunorecognition, interact productively with surrounding tissues and extracellular matrix, and avoid bacterial colonization. Antibody molecules and their derived fragments are commonly immobilized on materials to mediate coating with specific cell types in fields such as stent endothelialization and drug delivery. The incorporation of growth factors into biomaterials has found application in promoting and accelerating bone formation in osteogenerative and related applications. Peptides and extracellular matrix proteins can impart biomolecule- and cell-specificities to materials while antimicrobial peptides have found roles in preventing biofilm formation on devices and implants. In this progress report, we detail developments in the use of diverse proteins and peptides to modify the surfaces of hard biomaterials in vivo and in vitro. Chemical approaches to immobilizing active biomolecules are presented, as well as platform technologies for isolation or generation of natural or synthetic molecules suitable for biomaterial functionalization.

Conjugated polymers for the optical control of the electrical activity of living cells

Different conjugated polymers are proposed as bio-optical interfaces. Selected polymers are capable to sustain thermal sterilization but provide different optical coupling with living cells.

Kinetics and isotherm of fibronectin adsorption to three-dimensional porous chitosan scaffolds explored by ¹²⁵I-radiolabelling

In this study, (125)I-radiolabelling was explored to follow the kinetics and isotherm of fibronectin (FN) adsorption to porous polymeric scaffolds, as well as to assess the elution and exchangeability of pre-adsorbed FN following incubation in serum-containing culture medium. Chitosan (CH) porous scaffolds with two different degrees of acetylation (DA 4% and 15%) were incubated in FN solutions with concentrations ranging from 5 to 50 µg/mL. The kinetic and isotherm of FN adsorption to CH were successfully followed using (125)I-FN as a tracer molecule. While on DA 4% the levels of adsorbed FN increased linearly with FN solution concentration, on DA 15% a saturation plateau was attained, and FN adsorbed amounts were significantly lower. These findings were supported by immunofluorescent studies that revealed, for the same FN solution concentration, higher levels of exposed cell-binding domains on DA 4% as compared with DA 15%. Following incubation in serum containing medium, DA 4% also revealed higher ability to exchange pre-adsorbed FN by new FN molecules from serum than DA 15%. In accordance, when assessing the efficacy of passively adsorbed FN to promote endothelial cell (EC) adhesion to CH, ECs were found to adhere at higher levels to DA 4% as compared with DA 15%, 5 µg/mL of FN being already efficient in promoting cell adhesion and cytoskeletal organization on CH with DA 4%. Taken together the results show that protein radiolabelling can be used as an effective tool to study protein adsorption to porous polymeric scaffolds, both from single and complex protein solutions.

Designing nanostructured block copolymer surfaces to control protein adhesion

The profile and conformation of proteins that are adsorbed onto a polymeric biomaterial surface have a profound effect on its in vivo performance. Cells and tissue recognize the protein layer rather than directly interact with the surface. The chemistry and morphology of a polymer surface will govern the protein behaviour. So, by controlling the polymer surface, the biocompatibility can be regulated. Nanoscale surface features are known to affect the protein behaviour, and in this overview the nanostructure of self-assembled block copolymers will be harnessed to control protein behaviour. The nanostructure of a block copolymer can be controlled by manipulating the chemistry and arrangement of the blocks. Random, A-B and A-B-A block copolymers composed of methyl methacrylate copolymerized with either acrylic acid or 2-hydroxyethyl methacrylate will be explored. Using atomic force microscopy (AFM), the surface morphology of these block copolymers will be characterized. Further, AFM tips functionalized with proteins will measure the adhesion of that particular protein to polymer surfaces. In this manner, the influence of block copolymer morphology on protein adhesion can be measured. AFM tips functionalized with antibodies to fibronectin will determine how the surfaces will affect the conformation of fibronectin, an important parameter in evaluating surface biocompatibility.

The roles of RGD and grooved topography in the adhesion, morphology, and differentiation of C2C12 skeletal myoblasts

Both chemical and topographic cues are crucial for the development of skeletal muscle. In this study, the relative roles of both signals in regard to cell adhesion, morphology, and differentiation of C2C12 skeletal myoblasts were investigated. Grooved polystyrene substrates containing grooves with approximately 900 nm in width with 600 nm ridge spans and 665 nm in depth were conjugated with the cell adhesion peptide arginine-glycine-aspartic acid (RGD). RGD conjugation significantly enhanced the adhesion, growth and differentiation of C2C12 cells. On the other hand, anisotropic topography primarily directed the direction and alignment of myoblasts and myotubes. The results in this study provide information regarding the relative roles of chemical and topographic cues in musculoskeletal myogenesis, and are of interest to applications in muscle tissue engineering.

Block copolymer arrangement and composition effects on protein conformation using atomic force microscope-based antigen-antibody adhesion

The conformational changes of fibronectin (FN) deposited on various block copolymers where one block is composed of poly(methyl methacrylate) (PMMA) and the other block is either poly(acrylic acid) (PAA) or poly(2-hydroxyethyl methacrylate) (PHEMA) were investigated using a functionalized atomic force microscope (AFM) tip. The tip was modified with an antibody sensitive to the exposure of the arginine-glycine-aspartic acid (RGD) groups in FN. By studying the adhesive interactions between the antibody and the proteins adsorbed on the block copolymer surface and phase imaging, it was found that the triblock copolymers PAA-b-PMMA-b-PAA and PMMA-b-PHEMA-b-PMMA, which both have large domain sizes, are conducive to the exposure of the FN RGD groups on the surface. On the basis of these results, it is concluded that the surface chemistry as well as the nanomorphology dictated by the block copolymer arrangement could both tune protein conformation and orientation and optimize cell adhesion to the biomaterial surface.

Protein conformation changes on block copolymer surfaces detected by antibody-functionalized atomic force microscope tips

Conformational changes of fibronectin (Fn) deposited on poly(methyl methacrylate) and poly(acrylic acid) block copolymers with identical chemical compositions were detected using an antibody-functionalized atomic force microscope (AFM) tip. Based on the antibody-protein adhesive force maps and phase imaging, it was found that the nanomorphology of the triblock copolymer is conducive to the exposure of the arginine-glycine-aspartic acid (RGD) groups in Fn. For the first time, X-ray photoelectron spectroscopy was used to elucidate surface chemical composition and confirm AFM results. The findings demonstrate that block copolymer nanomorphology can be used to regulate protein conformation and potentially cellular response.

Atomic force microscopy evidence for conformational changes of fibronectin adsorbed on unmodified and sulfonated polystyrene surfaces

The effect of polystyrene surface polarity on the conformation of adsorbed fibronectin (FN) has been studied with atomic force microscopy. We demonstrated that bare sulfonated and nonsulfonated polystyrene surfaces featured similar topographies. After the FN adsorption, direct comparison of both types of substrata revealed drastically different topographies, roughness values, and also cell-adhesive properties. This was interpreted in terms of FN conformational changes induced by the surface polarity. At high-solute FN concentrations the multilayer FN adsorption took place resulting, for the sulfonated substratum, in an increase of surface roughness, whereas for the nonsulfonated one the roughness was approximately stable. Conversely, the FN conformation characteristic for the first saturative layer tended to be conserved in the consecutive layers, as evidenced by height histograms. The height of individual FN molecules indicated, consonantly with the derived thickness of the adsorbed protein layer (the latter value being 1.4 nm and 0.6 nm, respectively, for an unmodified and sulfonated polystyrene surface), that molecules are flattened on polar surfaces and more compact on nonsulfonated ones. It was also demonstrated that the FN adsorption and conformation on polymeric substrata, and hence the resultant cell-adhesive properties, depended on the chemistry of the original surface rather than on its topography. Our results also demonstrated the ability of surface polarity to influence the protein conformation and its associated biological activity.

Engineering surfaces for substrate-mediated gene delivery using recombinant proteins

Immobilized fibronectin and other natural proteins have been utilized to enhance substrate-mediated gene delivery, with apparent contributions from the intrinsic bioactivity and also physical properties of the immobilized proteins. In this report, we investigated the use of recombinant proteins, compared to the full-length fibronectin protein, as surface coatings for gene delivery to investigate the mechanisms by which fibronectin enhances gene transfer. The recombinant fibronectin fragment FNIII(7-10) (FNIII) contains the alpha(5)beta(1) binding domain of fibronectin and supports cell adhesion, whereas the recombinant protein polymer PP-12 is also negatively charged and has a molecular weight similar to FNIII, but lacks cell binding domains. Transfection was compared on surfaces modified with FNIII, full-length fibronectin, or PP-12. The full-length fibronectin provided the greatest extent of transgene expression relative to FNIII or PP-12, which was consistent with the amount of DNA that associated with cells. FNIII had 4.2-fold or 4.7-fold lower expression levels relative to fibronectin for polyplexes and lipoplexes, respectively. PP-12 produced expression levels that were 317-fold and 12.0-fold less than fibronectin for polyplexes and lipoplexes, respectively. Although expression was greater on FNIII relative to PP-12, the levels of DNA associated per cell with FNIII were similar to or less than those with PP-12, suggesting that the bioactive sequences may contribute to an enhanced intracellular trafficking. For lipoplexes delivered on FNIII, the efficiency of intracellular trafficking and levels of caveolar DNA were greater than that observed with either the full-length fibronectin or PP-12. For polyplexes, fibronectin fragment resulted in greater intracellular trafficking efficiency compared to PP-12 protein polymer. Recombinant proteins can be employed in place of full-length extracellular matrix proteins for substrate-mediated gene delivery, and bioactive sequences can influence one or more steps in the gene delivery process to maximize transfection.

Substrate-induced assembly of fibronectin into networks: influence of surface chemistry and effect on osteoblast adhesion

The influence of surface chemistry-substrates with controlled surface density of -OH groups-on fibronectin (FN) conformation and distribution is directly observed by atomic force microscopy (AFM). FN fibrillogenesis, which is known to be a process triggered by interaction with integrins, is shown in our case to be induced by the substrate (in absence of cells), which is able to enhance FN-FN interactions leading to the formation of a protein network on the material surface. This phenomenon depends both on surface chemistry and protein concentration. The level of the FN fibrillogenesis was quantified by calculating the fractal dimension of the adsorbed protein from image analysis of the AFM results. The total amount of adsorbed FN is obtained by making use of a methodology that employs Western blotting combined with image analysis of the corresponding protein bands, with the lowest sensitivity threshold equal to 15 ng of adsorbed protein. Further, FN adsorption is correlated to human osteoblast adhesion through morphology and actin cytoskeleton formation. Actin polymerization is in need of the formation of the protein network on the substrate's surface. Cell morphology is more rounded (as quantified by calculating the circularity of the cells by image analysis) when the degree of FN fibrillogenesis on the substrate is lower.

Biological activity of the substrate-induced fibronectin network: insight into the third dimension through electrospun fibers

Fibronectin (FN) fibrillogenesis is a cell-mediated process involving integrin activation that results in conformational changes of FN molecules and the organization of actin cytoskeleton. A similar process can be induced by some chemistries in the absence of cells, e.g., poly(ethyl acrylate) (PEA), which enhance FN-FN interactions leading to the formation of a biologically active network. Atomic force microscopy images of single FN molecules, at the early stages of adsorption on plane PEA, allow one to rationalize the process. Further, the role of the spatial organization of the FN network on the cellular response is investigated through its adsorption on electrospun fibers. Randomly oriented and aligned PEA fibers were prepared to mimic the three-dimensional organization of the extracellular matrix. The formation of the FN network on the PEA fibers but not on the supporting coverglass was confirmed. Fibroblasts aligned with oriented fibers, displayed extended morphology, developed linearly organized focal adhesion complexes, and matured actin filaments. Conversely, on random PEA fibers, cells acquired polygonal morphology with altered actin cytoskeleton but well-developed focal adhesions. Late FN matrix formation was also influenced: spatially organized FN matrix fibrils along the oriented PEA fibers and an altered arrangement on random ones.

Surface energy of hydroxyapatite and beta-tricalcium phosphate ceramics driving serum protein adsorption and osteoblast adhesion

The main objective of this work was to evaluate the specific role of calcium phosphates surface energy on serum protein adsorption and human osteoblast adhesion, by isolating chemical effects from those caused by topography. Highly dense phosphate ceramics (single-phase hydroxyapatite HA and beta-tricalcium phosphates beta-TCP) presenting two distinct nano roughnesses were produced. Some samples were gold-sputter coated in order to conveniently mask the surface chemical effects (without modification of the original roughness) and to study the isolated effect of surface topography on cellular behavior. The results indicated that the nano topography of calcium phosphates strongly affected the protein adsorption process, being more important than surface chemistry. The seeding efficacy of osteoblasts was not affected nor by the topography neither by the calcium phosphate chemistries but the beta-TCP chemistry negatively influenced cell spreading. We observed that surface hydrophobicity is another way to change protein adsorption on surfaces. The decrease of the polar component of surface energy on gold-coated samples leaded to a decreased albumin and fibronectin adsorption but to an increased cell adhesion. Overall, this work contributes to better understand the role of topography and surface chemistry of calcium phosphates in serum protein adsorption and osteoblast adhesion.

Bovine serum albumin adsorption on nano-rough platinum surfaces studied by QCM-D

The adsorption of bovine serum albumin (BSA) on platinum surfaces with a root-mean-square roughness ranging from 1.49nm to 4.62nm was investigated using quartz crystal microbalance with dissipation (QCM-D). Two different BSA concentrations, 50microg/ml and 1mg/ml, were used, and the adsorption studies were complemented by monitoring the antibody interaction with the adsorbed BSA layer. The adsorption process was significantly influenced by the surface nano-roughness, and it was observed that the surface mass density of the adsorbed BSA layer is enhanced in a non-trivial way with the surface roughness. From a close examination of the energy dissipation vs. frequency shift plot obtained by the QCM-D technique, it was additionally observed that the BSA adsorption on the roughest surface is subject to several distinct adsorption phases revealing the presence of structural changes facilitated by the nano-rough surface morphology during the adsorption process. These changes were in particular noticeable for the adsorption at the low (50microg/ml) BSA concentration. The results confirm that the nano-rough surface morphology has a significant influence on both the BSA mass uptake and the functionality of the resulting protein layer.

Adhesion of eukaryotic cells andStaphylococcus aureus to silicon model surfaces

Silicon wafers modified by silanisation with different functional groups are used to study the bioactivity of surfaces with varying physicochemical properties. Oxidation of the wafers created very hydrophilic surfaces, and moderately wettable surfaces were produced by coating with poly(ethylene glycol) (PEG). Immobilization of hydrocarbon chains to the wafers produced hydrophobic surfaces, and hydrophobicity was further increased by fluorocarbon coatings. The oxidized and the hydrocarbon-modified surfaces supported the adhesion of human MG-63 osteoblasts and 3T3 mouse fibroblasts as well as Staphylococcus aureus 8325-4. Adhesion of osteoblasts and fibroblasts, however, was decreased on highly hydrophobic fluorocarbon surfaces, whereas adhesion of S. aureus was supported. Coating of the fluorocarbon surface with fibronectin increased the number of attached eukaryotic cells, but the accumulation of bacteria remained unchanged. In contrast, surface coatings with PEG-groups inhibited the binding of S. aureus; however, the adhesion of the eukaryotic cells was high. The number of S. aureus on PEG-modified surfaces covered with fibronectin increased about twofold, yet it was still decreased to 25-30% related to the number of bacteria on other surfaces. These findings provide evidence that the PEG-modified surfaces showed selective bioactivity, preventing the attachment of a microbial pathogen but supporting the adhesion of eukaryotic cells.

Gene expression and internalization following vector adsorption to immobilized proteins: dependence on protein identity and density

BACKGROUND

Gene delivery by non-specific adsorption of non-viral vectors to protein-coated surfaces can reduce the amount of DNA required, and also increase transgene expression and the number of cells expressing the transgene. The protein on the surface mediates cell adhesion and vector immobilization, and functions to colocalize the two to enhance gene delivery. This report investigates the mechanism and specificity by which the protein coating enhances gene transfer, and determines if the protein coating targets the vector for internalization by a specific pathway.

METHODS

Proteins (FBS, BSA, fibronectin, collagen I, and laminin) were dried onto culture dishes, followed by PEI/DNA complex adsorption for surface delivery. Reporter genes were employed to characterize transfection as a function of the protein identity and density. Vector immobilization was measured using radiolabeled plasmid, and internalization was quantified in the presence and absence of the endocytosis inhibitors chlorpromazine and genistein.

RESULTS

Fibronectin coating yielded the greatest expression for PEI/DNA polyplexes, with maximal expression at intermediate protein densities. Expression in control studies with bolus delivery was independent of the protein identity. Substrate binding was independent of the protein identity; however, internalization was greatest on surfaces coated with fibronectin and collagen I. Inhibition of caveolae-mediated endocytosis reduced gene expression more than clathrin-mediated endocytosis. Similarly, inhibition of caveolae-mediated endocytosis significantly reduced the intracellular levels of DNA.

CONCLUSIONS

Fibronectin at intermediate densities mediated the highest levels of transgene expression, potentially by targeting internalization through caveolae-mediated endocytosis. Substrate modifications, such as the identity and density of proteins, provide an opportunity for modification of biomaterials for enhancing gene expression.

Antiadenoviral Effect of the α5β1 Integrin Receptor Ligand, GRGDSP Peptide, in Serotypes That Cause Acute Keratoconjunctivitis

BACKGROUND/AIMS

In adenoviral conjunctivitis, the infection process starts by the attachment of adenoviral fibers to conjunctival epithelial cells that contain the receptor for the adenovirus. The alpha 5 beta 1 integrin receptor ligand, GRGDSP peptide, contains the arginine-glycine-aspartate-binding motif which is common to the Coxsackie adenovirus receptor and integrins that are known to be adenoviral receptors. We evaluated the antiadenoviral effect of an expected adenoviral receptor inhibitor, GRGDSP peptide,in vitro.

METHODS

Adenovirus types 3, 4, 8, 19 and 37 were used. After calculating the 50% cytotoxic concentration of GRGDSP peptide, the adenovirus was cultivated with the agent for 7 days under serial dilution. Adenoviral DNA was qualitatively measured by real-time PCR.

RESULTS

GRGDSP peptide showed an inhibitory effect against adenoviral proliferation in all serotypes except type 4 in a dose-dependent manner.

CONCLUSION

This result suggests that the alpha 5 beta 1 integrin receptor ligand, GRGDSP peptide, has antiadenoviral activity in vitro, and the possibility of being used for local treatment of epidemic keratoconjunctivitis.

Presentation of RGDS epitopes on self-assembled nanofibers of branched peptide amphiphiles

Branched peptide amphiphile (PA) molecules bearing biological epitopes were designed and synthesized using orthogonal protecting group chemistry on amine groups at lysine residues. These molecules self-assemble into high-aspect-ratio cylindrical nanofibers, and their branched architecture enhances accessibility of epitopes for protein binding and also allows the presentation of more than one epitope in a single molecule. The RGDS cell adhesion epitope was used as a model bioactive signal on PA molecules for potential biomedical applications. Aggregation of the branched PA molecules into nanofibers was demonstrated by TEM and through shifts in the protonation profiles of peripheral amines. These systems also formed self-supporting gels in the presence of physiological fluids and other biologically relevant macromolecules such as synovial fluid and DNA, an important property for their potential use in medicine. Fluorescence anisotropy measurements on the PAs with tryptophan residues were performed to examine the effect of branching on packing and mobility of the peptides in the self-assembled nanofibers. The mobility of tryptophan residues was observed to be restricted upon packing of PA molecules into nanofibers. However, relative to linear analogues, branched molecules retain more mobility in the supramolecular aggregates.

Fibronectin terminated multilayer films: protein adsorption and cell attachment studies

Electrostatically driven layer-by-layer (LbL) assembly is a simple and robust method for producing structurally tailored thin film biomaterials, of thickness ca. 10nm, containing biofunctional ligands. We investigate the LbL formation of multilayer films composed of polymers of biological origin (poly(L-lysine) (PLL) and dextran sulfate (DS)), the adsorption of fibronectin (Fn)--a matrix protein known to promote cell adhesion--onto these films, and the subsequent spreading behavior of human umbilical vein endothelial cells (HUVEC). We employ optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microgravimetry with dissipation (QCMD) to characterize multilayer assembly in situ, and find adsorbed Fn mass on PLL-terminated films to exceed that on DS terminated films by 40%, correlating with the positive charge and lower degree of hydration of PLL terminated films. The extent and initial rate of Fn adsorption to both PLL and DS-terminated films exceed those onto the bare substrate, indicating the important role of electrostatic complexation between negatively charged protein and positively charged PLL at or near the film surface. We use phase-contrast optical microscopy to investigate the time-dependent morphological changes of HUVEC as a function of layer number, charge of terminal layer, and the presence of Fn. We observe HUVEC to attach, spread, and lose circularity on all surfaces. Positively charged PLL-terminated films exhibit a greater extent of cell spreading than do (negatively charged) DS-terminated films, and spreading is enhanced while circularity loss is suppressed by the presence of adsorbed Fn. The number of layers plays a significant role only for DS-terminated films with Fn, where spreading on a bilayer greatly exceeds that on a multilayer, and PLL-terminated films without Fn, where initial spreading is significantly higher on a monolayer. We observe initial cell spreading to be followed by retraction (i.e. decreased cell area and circularity with time) for films without Fn, and for DS-terminated films with Fn. Overall, the Fn-coated PLL monolayer and the Fn-coated PLL-terminated multilayer are the best performing films in promoting cell spreading. We conclude the presence of Fn to be an important factor (more so than film charge or layer number) in controlling the interaction between multilayer films and living cells, and thus to represent a promising strategy toward in vivo applications such as tissue engineering.

Minute changes in composition of polymer substrates produce amplified differences in cell adhesion and motility via optimal ligand conditioning

We explored the interplay between substratum chemistry of polymeric materials and surface-adsorbed ligand concentration (human plasma fibronectin) in the control of cell adhesion and cell motility. We found that small changes in the chemical composition of a polymeric substratum had different effects on cellular motility--depending on the concentration of preadsorbed fibronectin. We used two tyrosine-derived polyarylates, poly(DTD diglycolate) and poly(DTD glutarate), as substrata for the seeding of NIH-3T3 fibroblasts. The only compositional difference between the two test polymers was that one single oxygen atom in the polymer backbone of poly(DTD diglycolate) had been substituted by a methylene group in the backbone of poly(DTD glutarate), The two polymers had closely matched hydrophobicity and physical properties. Flat, spin-coated surfaces of these polymers were pretreated with different concentrations of human plasma fibronectin (0-20 microg/ml). After seeding with NIH-3T3 fibroblasts, we examined the adhesion and motility behavior of these cells. We found that NIH-3T3 fibroblasts migrated significantly faster on poly(DTD diglycolate), but only when the polymer surfaces were pretreated with intermediate concentrations of fibronectin. Only at these intermediate levels of ligand conditioning, did the presence of an extra oxygen atom in the backbone of poly(DTD diglycolate) relative to poly(DTD glutarate) (i) alter the overall organization/concentration of the fibronectin; (ii) weaken cell attachment strength and inhibited excessive cell spreading; and (iii) promote cell motility kinetics. These findings indicate that the biological effect of minute changes in substratum chemistry is critically dependent on the level of surface-adsorbed cell-binding ligands.

Elements in the C terminus of apolipoprotein [a] responsible for the binding to the tenth type III module of human fibronectin

In previous studies, we showed that the C-terminal domain, F2, but not the N-terminal domain, F1, is responsible for the binding of apolipoprotein [a] (apo[a]) to human fibronectin (Fn). To pursue those observations, we prepared, by both elastase digestion and recombinant technology, subsets of F2 of a different length containing either kringle (K) V or the protease domain (PD). We also studied rhesus monkey apo[a], which is known to contain PD but not KV. In the case of Fn, we used both an intact product and its tenth type III module (10FN-III) expressed in Escherichia coli. The binding studies carried out on microtiter plates showed that the affinity of F2 for immobilized 10FN-III was approximately 6-fold higher than that for Fn (dissociation constants = 1.75 +/- 0.31 nM and 10.25 +/- 1.62 nM, respectively). The binding was also exhibited by rhesus apo[a] and by an F2 subset containing the PD linked to an upstream microdomain comprising KIV-8 to KIV-10 and KV, inactive by itself. Competition experiments on microtiter plates showed that both Fn and 10FN-III, when in solution, are incompetent to bind F2. Together, our results indicate that F2 binds to immobilized 10FN-III more efficiently than whole Fn and that the binding can be sustained by truncated forms of F2 that contain the catalytically inactive PD linked to an upstream four K microdomain.