Cell surface receptors for extracellular matrix components

Hemocyte Clusters Defined by scRNA-Seq in Bombyx mori: In Silico Analysis of Predicted Marker Genes and Implications for Potential Functional Roles

Within the hemolymph, insect hemocytes constitute a heterogeneous population of macrophage-like cells that play important roles in innate immunity, homeostasis and development. Classification of hemocytes in different subtypes by size, morphology and biochemical or immunological markers has been difficult and only in Drosophila extensive genetic analysis allowed the construction of a coherent picture of hemocyte differentiation from pro-hemocytes to granulocytes, crystal cells and plasmatocytes. However, the advent of high-throughput single cell technologies, such as single cell RNA sequencing (scRNA-seq), is bound to have a high impact on the study of hemocytes subtypes and their phenotypes in other insects for which a sophisticated genetic toolbox is not available. Instead of averaging gene expression across all cells as occurs in bulk-RNA-seq, scRNA-seq allows high-throughput and specific visualization of the differentiation status of individual cells. With scRNA-seq, interesting cell types can be identified in heterogeneous populations and direct analysis of rare cell types is possible. Next to its ability to profile the transcriptomes of individual cells in tissue samples, scRNA-seq can be used to propose marker genes that are characteristic of different hemocyte subtypes and predict their functions. In this perspective, the identities of the different marker genes that were identified by scRNA-seq analysis to define 13 distinct cell clusters of hemocytes in larvae of the silkworm, Bombyx mori, are discussed in detail. The analysis confirms the broad division of hemocytes in granulocytes, plasmatocytes, oenocytoids and perhaps spherulocytes but also reveals considerable complexity at the molecular level and highly specialized functions. In addition, predicted hemocyte marker genes in Bombyx generally show only limited convergence with the genes that are considered characteristic for hemocyte subtypes in Drosophila.

Three-dimensional cell-laden collagen scaffolds: From biochemistry to bone bioengineering

The bones can be viewed as both an organ and a material. As an organ, the bones give structure to the body, facilitate skeletal movement, and provide protection to internal organs. As a material, the bones consist of a hybrid organic/inorganic three-dimensional (3D) matrix, composed mainly of collagen, noncollagenous proteins, and a calcium phosphate mineral phase, which is formed and regulated by the orchestrated action of a complex array of cells including chondrocytes, osteoblasts, osteocytes, and osteoclasts. The interactions between cells, proteins, and minerals are essential for the bone functions under physiological loading conditions, trauma, and fractures. The organization of the bone's organic and inorganic phases stands out for its mechanical and biological properties and has inspired materials research. The objective of this review is to fill the gaps between the physical and biological characteristics that must be achieved to fabricate scaffolds for bone tissue engineering with enhanced performance. We describe the organization of bone tissue highlighting the characteristics that have inspired the development of 3D cell-laden collagenous scaffolds aimed at replicating the mechanical and biological properties of bone after implantation. The role of noncollagenous macromolecules in the organization of the collagenous matrix and mineralization ability of entrapped cells has also been reviewed. Understanding the modulation of cell activity by the extracellular matrix will ultimately help to improve the biological performance of 3D cell-laden collagenous scaffolds used for bone regeneration and repair as well as for in vitro studies aimed at unravelling physiological and pathological processes occurring in the bone.

A glance on the role of fibronectin in controlling cell response at biomaterial interface

The bioactivity of biomaterials is closely related to cell response in contact with them. However, shortly after their insertion, materials are soon covered with proteins that constitute the biological fluids, and which render the direct surface recognition by cells almost impossible. The control of protein adsorption at the interface is therefore desirable. Extracellular matrix proteins are of particular interest in this sense, due to their well-known ability to modulate cell behavior. Particularly, fibronectin plays a leading role, being present in both healthy and injured tissues undergoing healing and regeneration. The aim of the present work is to give an overview on fibronectin and on its involvement in the control of cell behavior providing evidence of its pivotal role in the control of cell adhesion, spreading, migration, proliferation and differentiation. A deep insight into methods to enrich biomaterials surface with fibronectin will be then discussed, as well as new cues on the possibility to design tailored platforms able to specifically retain fibronectin from the surrounding extracellular milieu.

Differential effect of platelet-rich plasma fractions on β1-integrin signaling, collagen biosynthesis, and prolidase activity in human skin fibroblasts

The study was conducted to evaluate the effects of platelet-rich plasma (PRP), supernatant of PRP (SPRP) obtained by centrifugation, and supernatant of activated PRP (SActi-PRP) obtained by Ca²⁺ solution-treated PRP on collagen biosynthesis, prolidase activity, and β1-integrin signaling in cultured human skin fibroblasts. Incubation of fibroblasts with 5% PRP for 24 h contributed to ~5-fold increase in collagen biosynthesis compared to the control. In the cells treated with 5% of SPRP or SActi-PRP, collagen biosynthesis showed a 3-fold increase of the control. PRP, SPRP, and SActi-PRP stimulated prolidase activity similar to collagen biosynthesis. Collagen biosynthesis and prolidase activity are regulated by β1-integrin receptor signaling. Incubation of fibroblasts with PRP for 24 h contributed to a dose-dependent increase in the expression of β1-integrin receptor, while SActi-PRP increased the process to a much lower extent. SPRP had no effect on the β1-integrin receptor expression. All the studied fractions of blood increased the expression of FAK as well as the expression of phosphorylated MAP-kinases. However, PRP was found to be the most effective stimulator of expression of these particular kinases. These studies suggest that a complex of factors, including growth factors, adhesion molecules, and prolidase contained in PRP, all evoke growth and collagen-promoting activities in human dermal fibroblasts.

Tissue Engineered Skeletal Muscle: Preparation of Highly Dense, Highly Oriented Hybrid Muscular Tissues

We prepared highly dense, highly oriented hybrid muscular tissues that are composed of C2C12 cells (skeletal muscle myoblast cell line) and type I collagen. A cold mixture of C2C12 cells suspended in DMEM and type I collagen solution was poured into capillary tube molds of two different sizes (inner diameters; 0.90 and 0.53 mm, respectively). One end of each mold was sealed. Upon centrifugation (1000 rpm, 5 min) and subsequent thermal gelation, a rod-shaped gel was obtained. It was cultured in an agarose gel-coated dish for 7 days (first for 3 days in a growth medium and then for 4 days in a differentiation medium), during which time it shrank to become a highly dense tissue. Small-diameter rod-shaped, highly dense cellular assemblages with multinucleated myotubes were formed and only few necrotic cells at the core of the tissue were observed. On the other hand, a ring-shaped tissue prepared using a specially devised agarose gel mold was subjected to cyclic stretching at 60 rpm, resulting in the formation of a highly dense, highly oriented hybrid muscular tissue in which both densely accumulated cells and collagen fiber bundles tended to be aligned in the direction of stretching. The hybrid muscular tissues that were prepared using via sequential procedures of a centrifugal cell packing method and a mechanical stress-loading method became closer to native muscular tissues in terms of cell density and orientation.

Utilizing Fibronectin Integrin-Binding Specificity to Control Cellular Responses

Significance: Cells communicate with the extracellular matrix (ECM) protein fibronectin (Fn) through integrin receptors on the cell surface. Controlling integrin-Fn interactions offers a promising approach to directing cell behavior, such as adhesion, migration, and differentiation, as well as coordinated tissue behaviors such as morphogenesis and wound healing. Recent Advances: Several different groups have developed recombinant fragments of Fn that can control epithelial to mesenchymal transition, sequester growth factors, and promote bone and wound healing. It is thought that these physiological responses are, in part, due to specific integrin engagement. Furthermore, it has been postulated that the integrin-binding domain of Fn is a mechanically sensitive switch that drives binding of one integrin heterodimer over another. Critical Issues: Although computational simulations have predicted the mechano-switch hypothesis and recent evidence supports the existence of varying strain states of Fn in vivo, experimental evidence of the Fn integrin switch is still lacking. Future Directions: Evidence of the integrin mechano-switch will enable the development of new Fn-based peptides in tissue engineering and wound healing, as well as deepen our understanding of ECM pathologies, such as fibrosis.

Self-assembly of collagen on flat surfaces: the interplay of collagen-collagen and collagen-substrate interactions

Fibrillar collagens, common tissue scaffolds in live organisms, can also self-assemble in vitro from solution. While previous in vitro studies showed that the pH and the electrolyte concentration in solution largely control the collagen assembly, the physical reasons why such control could be exerted are still elusive. To address this issue and to be able to simulate self-assembly over large spatial and temporal scales, we have developed a microscopic model of collagen with explicit interactions between the units that make up the collagen molecules, as well as between these units and the substrate. We have used this model to investigate assemblies obtained via molecular dynamics deposition of collagen on a substrate at room temperature using an implicit solvent. By comparing the morphologies from our molecular dynamics simulations with those from our atomic-force microscopy experiments, we have found that the assembly is governed by the competition between the collagen-collagen interactions and those between collagen and the substrate. The microscopic model developed here can serve for guiding future experiments that would explore new regions of the parameter space.

The role of mediators of cell invasiveness, motility, and migration in the pathogenesis of silent corticotroph adenomas

Silent corticotroph adenomas (SCAs) represent a distinct subset of clinically non-functioning pituitary adenomas. There are two variants of SCA; type I are densely granulated basophilic tumors and type II are sparsely granulated and chromophobic tumors. SCAs are known to be aggressive than the more common non-functioning gonadotroph adenomas (NFGAs). Cell-matrix interactions play an important role in the pathogenesis of pituitary adenomas. In this study, we compared 19 SCAs and 50 NFGAs with known fibroblast growth factor receptor-4 (FGFR4) status using semi-quantitative immunohistochemistry to localize β1-integrin, osteopontin, and matrix metalloproteinase-1 (MMP-1) as cytoplasmic, membranous, or mixed cytoplasmic-membranous staining to achieve scores of 1-4. Staining for β1-integrin was significantly higher in SCAs (100 %, score 3.3) than in NFGAs (96 %; score 2.6) (p = 0.0482); there was no statistical difference within subgroups of SCA (type II score 3.4; type I score 2.8) (p = 0.2663). Osteopontin immunoreactivity was also higher in SCAs (100 %, score 3.7) than in NFGAs (42 %, score 0.8) (p = 0.0001); there was no statistical difference within subgroups of SCA (type II score 3.6; type I score 3.9) (p = 0.2787). In contrast, MMP-1 immunoreactivity was lower in SCAs (89 %; score 2.5) than in NFGAs (98 %; score 3.6) (p = 0.0005); there was no statistical difference within subgroups of SCA (type II score 2.7; type I score 2.0) (p = 0.30704). The MMP-1 results correlated with FGFR4 expression (NFGA 96 %, type II SCA 71 %, type I SCA 40 %). Our data indicate that the biological aggressivity of SCAs compared with NFGA may be due to high osteopontin expression; in contrast, high MMP-1 is characteristic of NFGAs that also express more FGFR4. Further investigations are warranted to clarify the underlying regulatory mechanisms of these markers. The high osteopontin or FGFR4/MMP-1 expression levels in SCAs and NFGAs, respectively, indicate the potential for therapeutic strategies targeting osteopontin or FGFR4/MMP-1 for inoperable tumors of these types.

Piezoelectric properties of aligned collagen membranes

Electromechanical coupling, a phenomenon present in collagenous materials, may influence cell-extracellular matrix interactions. Here, electromechanical coupling has been investigated via piezoresponse force microscopy in transparent and opaque membranes consisting of helical-like arrays of aligned type I collagen fibrils self-assembled from acidic solution. Using atomic force microscopy, the transparent membrane was determined to contain fibrils having an average diameter of 76 ± 14 nm, whereas the opaque membrane comprised fibrils with an average diameter of 391 ± 99 nm. As the acidity of the membranes must be neutralized before they can serve as cell culture substrates, the structure and piezoelectric properties of the membranes were measured under ambient conditions before and after the neutralization process. A crimp structure (1.59 ± 0.37 µm in width) perpendicular to the fibril alignment became apparent in the transparent membrane when the pH was adjusted from acidic (pH = 2.5) to neutral (pH = 7) conditions. In addition, a 1.35-fold increase was observed in the amplitude of the shear piezoelectricity of the transparent membrane. The structure and piezoelectric properties of the opaque membrane were not significantly affected by the neutralization process. The results highlight the presence of an additional translational order in the transparent membrane in the direction perpendicular to the fibril alignment. The piezoelectric response of both membrane types was found to be an order of magnitude lower than that of collagen fibrils in rat tail tendon. This reduced response is attributed to less-ordered molecular assembly than is present in D-periodic collagen fibrils, as evidenced by the absence of D-periodicity in the membranes.

Effect of CD44 binding peptide conjugated to an engineered inert matrix on maintenance of breast cancer stem cells and tumorsphere formation

INTRODUCTION

As cancer cells are affected by many factors in their microenvironment, a major challenge is to isolate the effect of a specific factor on cancer stem cells (CSCs) while keeping other factors unchanged. We have developed a synthetic inert 3D polyethylene glycol diacrylate (PEGDA) gel culture system as a unique tool to study the effect of microenvironmental factors on CSCs response. We have reported that CSCs formed in the inert PEGDA gel by encapsulation of breast cancer cells maintain their stemness within a certain range of gel stiffness. The objective was to investigate the effect of CD44 binding peptide (CD44BP) conjugated to the gel on the maintenance of breast CSCs.

METHODS

4T1 or MCF7 breast cancer cells were encapsulated in PEGDA gel with CD44BP conjugation. Control groups included dissolved CD44BP and the gel with mutant CD44BP conjugation. Tumorsphere size and density, and expression of CSC markers were determined after 9 days. For in vivo, cell encapsulated gels were inoculated in syngeneic Balb/C mice and tumor formation was determined after 4 weeks. Effect of CD44BP conjugation on breast CSC maintenance was compared with integrin binding RGD peptide (IBP) and fibronectin-derived heparin binding peptide (FHBP).

RESULTS

Conjugation of CD44BP to the gel inhibited breast tumorsphere formation in vitro and in vivo. The ability of the encapsulated cells to form tumorspheres in the peptide-conjugated gels correlated with the expression of CSC markers. Tumorsphere formation in vitro was enhanced by FHBP while it was abolished by IBP.

CONCLUSION

CD44BP and IBP conjugated to the gel abolished tumorsphere formation by encapsulated 4T1 cells while FHBP enhanced tumorsphere formation compared to cells in the gel without peptide. The PEGDA hydrogel culture system provides a novel tool to investigate the individual effect of factors in the microenvironment on CSC maintenance without interference of other factors.

Eukaryotic translation initiation factor 4E binding protein 1 (4EBP-1) function is suppressed by Src and protein phosphatase 2A (PP2A) on extracellular matrix

Human lung fibroblasts utilize integrins to attach and proliferate on type I collagen. β1 integrin is the major integrin subunit for this attachment. Integrins coordinate cellular responses to cell-cell and cell-extracellular matrix interactions that regulate a variety of biological processes. Although β1 integrin-mediated signaling pathways in lung fibroblasts have been studied, a detailed molecular mechanism regulating translational control of gene expression by 4EBP-1 is not understood. 4EBP-1 inhibits cap-dependent translation by binding to the eIF4E translation initiation factor. We found that when lung fibroblasts attach to collagen via β1 integrin, high Src activity suppresses 4EBP-1 expression via PP2A, and the decrease of 4EBP-1 is due to protein degradation. The inhibition of Src activity dramatically increases PP2A and 4EBP-1 expression. Furthermore ectopic expression of PP2A, or PP2A silencing using PP2A siRNA confirmed that 4EBP-1 is regulated by PP2A. In addition, we found that 4EBP-1 inhibition by fibroblast attachment to collagen increases cap-dependent translation. Our study showed that when lung fibroblasts are attached to collagen matrix, the β1 integrin/Src/PP2A-mediated 4EBP-1 regulatory pathway is activated. We suggest that β1 integrin-mediated signaling pathway may be a crucial event in regulating fibroblast translational control machinery on collagen matrix.

Biotechnological applications of recombinant microbial prolidases

Prolidase is a metallopeptidase that is ubiquitous in nature and has been isolated from mammals, bacteria and archaea. Prolidase specifically hydrolyzes dipeptides with a prolyl residue in the carboxy terminus (NH(2)-X-/-Pro-COOH). Currently, the only solved structure of prolidase is from the hyperthermophilic archaeon Pyrococcus furiosus. This enzyme is of particular interest because it can be used in many biotechnological applications. Prolidase is able to degrade toxic organophosphorus (OP) compounds, namely, by cleaving the P-F and P-O bonds in the nerve agents, sarin and soman. Applications using prolidase to detoxify OP nerve agents include its incorporation into fire-fighting foams and as biosensors for OP compound detection. Prolidases are also employed in the cheese-ripening process to improve cheese taste and texture. In humans, prolidase deficiency (PD) is a rare autosomal recessive disorder that affects the connective tissue. Symptoms of PD include skin lesions, mental retardation and recurrent respiratory infections. Enzyme replacement therapies are currently being studied in an effort to optimize enzyme delivery and stability for this application. Previously, prolidase has been linked to collagen metabolism and more recently is being associated with melanoma. Increased prolidase activity in melanoma cell lines has lead investigators to create cancer prodrugs targeting this enzyme. Thus, there are many biotechnological applications using recombinant and native forms of prolidase and this review will describe the biochemical and structural properties of prolidases as well as discuss their most current applications.

Prolidase-dependent regulation of collagen biosynthesis

Prolidase [EC.3.4.13.9] is a cytosolic imidodipeptidase, which specifically splits imidodipeptides with C-terminal proline or hydroxyproline. The enzyme plays an important role in the recycling of proline from imidodipeptides (mostly derived from degradation products of collagen) for resynthesis of collagen and other proline-containing proteins. The enzyme activity is up-regulated by beta(1)-integrin receptor stimulation. The increase in the enzyme activity is due to its phosphorylation on serine/threonine residues. Collagen is not only structural component of extracellular matrix. It has been recognized as a ligand for integrin receptors, which play an important role in signaling that regulate ion transport, lipid metabolism, kinase activation and gene expression. Therefore, changes in the quantity, structure and distribution of collagens in tissues may affect cell signaling, metabolism and function. Several line of evidence suggests that prolidase activity may be a step-limiting factor in the regulation of collagen biosynthesis. It has been shown in different physiologic and pathologic conditions. It is of great importance during wound healing, inflammation, aging, tissue fibrosis and possibly skeletal abnormalities seen in Osteogenesis Imperfecta. The mechanism of prolidase-dependent regulation of collagen biosynthesis was found at both transcriptional and post-transcriptional levels. In this study, we provide evidence for prolidase-dependent transcriptional regulation of collagen biosynthesis. The mechanism was found at the level of NF-kB, known inhibitor of type I collagen gene expression. Modulation of integrin-dependent signaling by stimulatory (i.e. thrombin) or inhibitory (i.e. echistatin) beta(1)-integrin ligands or by nitric oxide donors (i.e. DETA/NO) affect prolidase at post-transcriptional level. All those factors may represent novel approach to pharmacotherapy of connective tissue disorders.

Enhanced prolidase activity and decreased collagen content in breast cancer tissue

Adherent interactions between integrins and extracellular matrix (ECM) proteins play an important role in tumorigenicity and invasiveness. The major component of ECM is collagen that plays a central role in the interaction with integrins. The expression of certain collagenases (gelatinases) by tumour cells is one of the characteristic features of the so-called metastatic phenotype, presumably by breaking down ECM barriers as well by altering the ECM-cell interaction. Although extracellular collagenases initiate the breakdown of collagen, the final step of collagen degradation is catalysed by intracellular prolidase. Collagen deposition, gelatinolytic and prolidase activities, expression of beta(1)-integrin receptor and their possible relationships were studied in seven operable breast cancer cases. In breast cancer tissue, we have found significant decrease in the amount of collagen. The decrease in collagen deposition in breast cancer tissue was accompanied by increase in the tissue gelatinolytic and prolidase activities. Simultaneously, a slight decrease in the expression of beta(1)-integrin receptor in breast cancer tissue was observed. These results suggest that alteration in collagen metabolism in breast cancer tissue may reflect tissue remodelling, characteristic for invasive phenotype of cancer cells. Increased gelatinolytic and prolidase activities in breast cancer tissue may enhance stromal matrix degradation and thus may promote metastatic dissemination. On the basis of the data, it seems that compounds endowed with gelatinolytic and prolidase inhibitory activities may be considered as a potential drug candidates for breast cancer therapy.

Observing growth steps of collagen self-assembly by time-lapse high-resolution atomic force microscopy

Insights into molecular mechanisms of collagen assembly are important for understanding countless biological processes and at the same time a prerequisite for many biotechnological and medical applications. In this work, the self-assembly of collagen type I molecules into fibrils could be directly observed using time-lapse atomic force microscopy (AFM). The smallest isolated fibrillar structures initiating fibril growth showed a thickness of approximately 1.5 nm corresponding to that of a single collagen molecule. Fibrils assembled in vitro established an axial D-periodicity of approximately 67 nm such as typically observed for in vivo assembled collagen fibrils from tendon. At given collagen concentrations of the buffer solution the fibrils showed constant lateral and longitudinal growth rates. Single fibrils continuously grew and fused with each other until the supporting surface was completely covered by a nanoscopically well-defined collagen matrix. Their thickness of approximately 3 nm suggests that the fibrils were build from laterally assembled collagen microfibrils. Laterally the fibrils grew in steps of approximately 4 nm, indicating microfibril formation and incorporation. Thus, we suggest collagen fibrils assembling in a two-step process. In a first step, collagen molecules assemble with each other. In the second step, these molecules then rearrange into microfibrils which form the building blocks of collagen fibrils. High-resolution AFM topographs revealed substructural details of the D-band architecture of the fibrils forming the collagen matrix. These substructures correlated well with those revealed from positively stained collagen fibers imaged by transmission electron microscopy.

Inhibition of gastric cancer cell adhesion in nude mice by inraperitoneal phospholipids

Adhesion of tumor cells to mesothelial cells or extracellular matrix components is a pivotal step in developing peritoneal dissemination after gastric cancer. As phospholipids were found to reduce adhesion formation, especially at sites of peritoneal lesions, we assessed the inhibition of attachment of NUGC-4 gastric cancer cells by local treatment with phospholipids to the peritoneum in nude mice. Gastric cancer cells (1xl0(6)) suspended in either normal saline (controls) or phospholipid suspension 75 mg/kg body weight (PL75) or 150 mg/kg (PL150) were injected intraperitoneally into 90 female BALB/c nu/nu mice. The treatment groups were subdivided into animals with defined peritoneal lesions and animals without lesions. After 30 days the extent of peritoneal carcinosis and the Peritoneal Cancer Index were evaluated. Statistical analysis was performed with two factorial ANOVAs. The level of significance was adjusted according to Bonferrorni (alpha = 0.00278). During a 90-day observation period the survival rate was determined using the log rank test. After 30 days the intraperitoneal tumor volume was reduced by PL150 up to 0.6 ml (SEM 0.16) and 0.48 ml (SEM 0.09) in mice with peritoneal lesions compared to 0.9 ml (SEM 0.2) and 0.9 ml (SEM 0.1) in the control group (P = 0.04). The mean area of tumor adhesion amounted to 145 mm(2) (SEM 17) (P = 0.08) and 164 mm(2) (SEM 32.8) (P = 0.049) with peritoneal lesions after treatment with PL150 [controls: 216 mm(2) (SEM 28.5) and 245 mm(2) (SEM 29.3)]. The peritoneal cancer index was 16.4 (SEM 1.7) in the control group and 9 (SEM 1.68) with PL150 (P = 0.0002). In the subgroup with peritoneal lesions, the respective values were as follows: controls: 20.8 (SEM 0.85); PL 150:14.3 (SEM 1.07) (P = 0.0001). We found a prolonged survival rate after treatment with PL150. However, this effect was not significantly different to that seen in the control group. Treatment with PL75 had no significant influence. Phospholipids may be an efficacious and economic tool for reducing peritoneal tumor cell adhesion and consequently the development of peritoneal carcinosis after resection of gastric cancer.

Insulin-like growth factor-I attenuates the inhibitory effect of type I collagen through β1 integrin receptor

Extracellular matrix and growth factors are the crucial factors that regulate healing and regenerating processes in human periodontal ligament cells. The purpose of this study was to examine the effects of type I collagen and insulin-like growth factor-I (IGF-I) on osteopontin (OPN) expression. The data showed that OPN expression was significantly decreased when cells were cultured on collagen-coated plates. Addition of IGF-I obviously induced OPN expression only in a collagen-coated condition, suggesting an attenuating effect of IGF-I on the decrease of OPN expression. Cells treated with a combination of inhibitory antibody to beta1 integrin and IGF-I showed the same level of OPN expression as those treated with either inhibitory antibody to beta1 integrin or IGF-I alone. These results indicate that IGF-I counteracts with the inhibitory signal from type I collagen through beta1 integrin receptor.

A selective cyclic integrin antagonist blocks the integrin receptors alphavbeta3 and alphavbeta5 and inhibits retinal pigment epithelium cell attachment, migration and invasion

Background

Proliferative vitreoretinopathy (PVR) is a leading cause of blindness after failed retinal reattachment surgery. PVR is characterized by the proliferation, migration and contraction of retinal pigmented epithelial cells (RPE), and these cellular responses are influenced by the expression and function of integrin receptors. The effect of a cyclic integrin antagonist containing the amino acid sequence Arg-Gly-Asp-D-Phe-Val (RGDfV), specific for the integrin receptors α_vβ₃ and α_vβ₅, was investigated on basic fibroblast growth factor (bFGF), platelet derived growth factor-BB (PDGF-BB), and serum induced human RPE proliferation, migration, invasion and attachment to the extracellular matrix. Furthermore, the effects of bFGF and PDGF-BB regulated expression of integrins α_vβ₃ and α_vβ₅ on RPE cells was examined.

Methods

The effect of a cyclic integrin antagonist and a control peptide (0.01 μg/ml to 300 μg/ml) was investigated on serum or cytokine (bFGF or PDGF-BB pretreatment) induced human fetal RPE cell proliferation by H³-thymidine uptake. The effect of the cyclic integrin antagonist on RPE cell attachment onto different extracellular matrices (laminin, collagen IV, fibronectin), RPE cell invasion stimulated by PDGF-BB or serum, and migration stimulated by PDGF-BB, vascular endothelial growth factor (VEGF) or serum was explored. PDGF-BB and bFGF modulation of the integrin receptors α_vβ₃ and α_vβ₅ was evaluated by flow cytometry.

Results

The integrin antagonist did not inhibit DNA synthesis stimulated by serum, bFGF, or PDGF-BB treatment. RPE attachment onto fibronectin was inhibited in a concentration range of 1–10 μg/ml (p < 0.05). Attachment of the RPE cells onto collagen IV and laminin was inhibited in a range of 3–10 μg/ml (p < 0.05). Serum and PDGF-BB stimulated migration was inhibited by the cyclic integrin antagonist in a concentration range of 1–10 μg/ml (p < 0.05). Furthermore, the cyclic integrin antagonist inhibited PDGF-BB stimulated RPE cell invasion through fibronectin (3μg/ml: 66% inhibition, p < 0.001). In each of these experiments, the control peptides had no significant effects. PDGF-BB and bFGF pretreatment of RPE cells increased the expression of integrin receptors α_vβ₃ (bFGF: 1.9 fold, PDGF-BB: 2.3 fold) and α_vβ₅ (bFGF: 2.9 fold, PDGF-BB: 1.5 fold).

Conclusion

A selective inhibition of the integrin receptors α_vβ₃ and α_vβ₅ through a cyclic integrin antagonist is able to inhibit RPE cell attachment, migration and invasion. Since these steps are of importance for the progression of PVR, a cyclic integrin antagonist should be further evaluated for the treatment of this disease.

Involvement of integrin-linked kinase in capillary/tube-like network formation of human vascular endothelial cells

Angiogenesis is a complex process involving an ECM and vascular endothelial cells (EC), and is regulated by various angiogenic factors including VEGF. The ability to form a capillary/tube-like network is a specialized function of EC. Therefore, in vitro angiogenesis was assessed by a capillary/tube-like network formation assay. There are three angiogenic parameters: capillary length, number of capillaries, and relative capillary area per field. We evaluated capillary length per field in the assay. VEGF promoted capillary/tube-like network formation of EC in a type I collagen gel matrix in vitro. Moreover, we demonstrated the involvement of ILK in a VEGF signaling pathway mediating capillary/tube-like network formation of EC using dominant-negative, kinase deficient ILK. This is a straightforward assay to monitor responses of human vascular endothelial cells.

Assembly of collagen into microribbons: effects of pH and electrolytes

Collagen represents the major structural protein of the extracellular matrix. Elucidating the mechanism of its assembly is important for understanding many cell biological and medical processes as well as for tissue engineering and biotechnological approaches. In this work, conditions for the self-assembly of collagen type I molecules on a supporting surface were characterized. By applying hydrodynamic flow, collagen assembled into ultrathin ( approximately 3 nm) highly anisotropic ribbon-like structures coating the entire support. We call these novel collagen structures microribbons. High-resolution atomic force microscopy topographs show that subunits of these microribbons are built by fibrillar structures. The smallest units of these fibrillar structures have cross-sections of approximately 3 x 5nm, consistent with current models of collagen microfibril formation. By varying the pH and electrolyte of the buffer solution during the self-assembly process, the microfibril density and contacts formed within this network could be controlled. Under certain electrolyte compositions the microribbons and microfibers display the characteristic D-periodicity of approximately 65 nm observed for much thicker collagen fibrils. In addition to providing insight into the mechanism of collagen assembly, the ultraflat collagen matrices may also offer novel ways to bio-functionalize surfaces.

Inhibition of breast cancer cell extracellular matrix degradative activity by chemically modified tetracyclines

BACKGROUND

Inhibition of tumour cell proliferation, invasion and metastasis by chemically modified tetracyclines has been ascribed to inhibition of matrix metalloproteinase (MMP) activity.

METHODS

Exposure of the human breast carcinoma cell line MDA-MB-231 or its MMP-9-overproducing transfected clone (E-10) to 6-demethyl, 6-deoxy, 4-de [dimethylamino]-tetracycline (CMT-3), a chemically modified non-antimicrobial tetracycline followed by analysis using gelatinase activity assay, zymography, degradation of radiolabelled extracellular matrix (ECM), Western blotting, TNF-alpha ELISA and cell viability assays.

RESULTS

CMT-3 treatment results in diminution in extracellular MMP-9 protein levels as well as inhibition of gelatinase activity. This prevents cell-mediated ECM degradation without inducing general cytostasis or cytotoxicity. Culturing E-10 cells in 10 or 20 microM CMT-3 diminished secreted MMP-9 levels by 45% or 60%, respectively, but did not affect levels of most other secreted proteins, including tissue inhibitor of Metalloproteinases (TIMP-1). ECM degradation by E-10 cells or their conditioned medium was inhibited by approximately 20%-30% in the presence of 20 microM CMT-3, reflecting inhibition of MMP-9 activity in addition to diminution of released MMP-9 levels. TNF-alpha levels were also diminished in E-10 conditioned medium in the presence of CMT-3, but cell viability, measured by MTS reduction and cytosolic LDH retention, was unaffected.

CONCLUSIONS

It is proposed that the reduction in ECM-degradative activity reflects diminished levels of expression as well as inhibition of enzymatic activity of MMPs released by cells in the presence of CMT-3. These multiple effects of CMT-3 may offer promise for use in suppressing tumour invasion, and if used in conjunction with other chemotherapy agents, may lead to more successful treatment of cancer.

Supramolecular assemblies of adsorbed collagen affect the adhesion of endothelial cells

The behavior of endothelial cells (HUVECs) in contact with thin collagen films presenting different supramolecular organizations was investigated. Collagen was adsorbed on polystyrene (PS) and plasma-oxidized PS (PSox) in conditions ensuring the formation of continuous layers presenting an increasing density of fibrillar structures. Discontinuous collagen layers were also prepared on PS by adsorption followed by dewetting. The morphology of the obtained collagen films was checked by using atomic force microscopy. HUVECs adhesion was evaluated in terms of cell number, cell area, cell shape, and actin structure after 4 h of contact with the prepared collagen layers. In the presence of serum, no adhesion was observed on PS, whereas a substantial adhesion was found on PSox. This is explained by the competition for adsorption, which turns in favor of adhesive proteins secreted by the cells on the hydrophilic PSox, but turns in favor of serum albumin on the hydrophobic PS. The progressive coating of PS by smooth collagen films increased cell adhesion and spreading. However, cell spreading and cytoskeleton organization were adversely affected by the appearance of a high density of collagen fibrillar structures. This latter trend was similarly observed on PSox. On the other hand, HUVECs spreading and cytoskeleton organization were clearly enhanced on discontinuous collagen layers compared with continuous ones. A possible explanation for these observations lies in the modification of exposure and/or spatial distribution of recognition sequences due to spontaneous collagen self-assembly on fibril formation or to collagen aggregation on dewetting.

Phospholipids reduce gastric cancer cell adhesion to extracellular matrix in vitro

Background

Nidation of floating tumour cells initiates peritoneal carcinosis and limits prognosis of gastro-intestinal tumours. Adhesion of tumour cells to extracellular matrix components is a pivotal step in developing peritoneal dissemination of intraabdominal malignancies. Since phospholipids efficaciously prevented peritoneal adhesion formation in numerous animal studies we investigated their capacity to reduce adhesions of gastric cancer cells to extracellular matrix components (ECM).

Methods

Human gastric cancer cells (NUGC-4, Japanese Cancer Research Resources Bank, Tokyo, Japan) were used in this study. Microtiter plates were coated with collagen IV (coll), laminin (ln) and fibronectin (fn). Non-specific protein binding of the coated wells was blocked by adding 1% (w/v) BSA (4°C, 12 h) and rinsing the wells with Hepes buffer. 50.000 tumour cells in 100 μl medium were seeded into each well. Beside the controls, phospholipids were added in concentrations of 0.05, 0.1, 0.5, 0.75 and 1.0/100 μl medium. After an incubation interval of 30 min, attached cells were fixed and stained with 0.1% (w/v) crystal violet. The dye was resuspended with 50 μl of 0.2% (v/v) Triton X-100 per well and colour yields were then measured by an ELISA reader at 590 nm. Optical density (OD) showed a linear relationship to the amount of cells and was corrected for dying of BSA/polystyrene without cells.

Results

The attachment of gastric cancer cells to collagen IV, laminin, and fibronectin could be significantly reduced up to 53% by phospholipid concentrations of 0.5 mg/100 μl and higher.

Conclusion

These results, within the scope of additional experimental studies on mice and rats which showed a significant reduction of peritoneal carcinosis, demonstrated the capacity of phospholipids in controlling abdominal nidation of tumour cells to ECM components. Lipid emulsions may be a beneficial adjunct in surgery of gastrointestinal malignancies.

Role of Ascorbic Acid in Periodontal Ligament Cell Differentiation

BACKGROUND

Periodontal ligament (PDL) cells form mineralized nodules in vitro. Ascorbic acid is known to be required in this process, although its effect on osteoblastic differentiation of PDL cells remains unclear. The purpose of this study was to determine the role of ascorbic acid on the early osteoblastic differentiation of PDL cells, with regard to alkaline phosphatase (ALP) activity, type I collagen production and integrin expression.

METHODS

Cultured PDL cells were stimulated at confluence with ascorbic acid in the presence or absence of type I collagen inhibitor and blocking antibodies to integrins. After stimulation, the cells and culture supernatants were examined for ALP activity, type I collagen production, and integrin expression. The ALP activity was measured using a colorimetric assay with p-nitrophenyl phosphate and ALP staining. Enzyme-linked immunosorbent assay (ELISA) was used to determine type I collagen production, and ELISA and flow cytometric analysis were employed for assessment of integrin expression.

RESULTS

Both ALP activity and type I collagen production were upregulated when PDL cells were cultured in the presence of ascorbic acid (200 microM). Inhibitor of the formation of collagen triple helices and blocking antibodies to alpha2beta1 integrin inhibited ALP activity by 50% in ascorbic acid-stimulated PDL cells. Furthermore, ascorbic acid increased the cell surface expression of alpha2beta1 integrin.

CONCLUSIONS

Our findings indicated that ascorbic acid increases the ALP activity of PDL cells via type I collagen production and also enhances the expression of alpha2beta1 integrin, which is a major receptor of type I collagen. These results suggest that ascorbic acid promotes the osteoblastic differentiation of PDL cells by modulating type I collagen-alpha2beta1 integrin interaction.

Integrin-linked kinase regulates vascular morphogenesis induced by vascular endothelial growth factor

Integrin-linked kinase (ILK) is one of the signaling moieties that interact with the cytoplasmic domains of integrin beta1 and beta3 subunits. Integrin-mediated outside-in signals cooperate with vascular endothelial growth factor (VEGF) receptor to promote morphological changes, cell proliferation and motility in endothelial cells. In this report we demonstrate that VEGF-induced vessel morphogenesis of human umbilical vein endothelial cells (HUVEC) was inhibited by the transfection of a dominant negative, kinase-deficient ILK (ILK-KD), as well as by treatment with the phosphatidylinositol 3-kinase inhibitor LY294002. VEGF induced phosphorylation of protein kinase B (PKB/Akt), a regulator of cell survival and apoptosis, on serine 473, but not on threonine 308, in an ILK-dependent manner. Furthermore, transfection of antisense ILK (ILK-AS) blocked the survival effect of VEGF in annexin-V binding assays, and a VEGF-mediated decrease in caspase activity was reversed by both ILK-KD and ILK-AS as measured by a homogeneous caspase-3/7 assay. We also demonstrate that both chemotactic migration and cell proliferation of HUVEC induced by VEGF were suppressed by the inhibition of ILK. We conclude that ILK plays an important role in vascular morphogenesis mediated by VEGF.

Relaxin increases ubiquitin-dependent degradation of fibronectin in vitro and ameliorates renal fibrosis in vivo

Fibronectin, a large adhesive glycoprotein, is a prominent constituent of the extracellular matrix. Abnormalities in fibronectin homeostasis occur in numerous disease states, ranging from primary fibrosing conditions to neoplastic transformation. We demonstrate that fibronectin is a target protein substrate for ubiquitin-dependent degradation. Coimmunoprecipitation experiments and confocal microscopy demonstrated ubiquitin-fibronectin interaction. In an in vitro model of renal fibrosis, relaxin, an insulin-like growth factor, increased ubiquitin-dependent fibronectin degradation. Relaxin also was evaluated in an anti-glomerular basement membrane model of renal fibrosis. Animals treated with relaxin experienced renoprotection, manifested by decreased serum creatinine and proteinuria. Histological evaluation of kidney sections from animals treated with relaxin showed decreased glomerulosclerosis and interstitial fibrosis. We conclude that relaxin might be developed as a useful agent for the treatment of renal fibrosis.

Fibronectin in malignancy

Fibronectin (Fn) was the first 'structural' glycoprotein intensively studied as an ubiquitous matrix component of early phylogenetic appearance. Its age-dependent increase in plasma and tissues may be accompanied in pathological states, especially in tumor growth, by its proteolytic breakdown by a number of neutral proteases. It was also shown that several of its proteolytic breakdown products exhibit unexpected and mostly harmful biological activities. The first of these effects was a potentiation of malignant transformation. Some fragments had proteolytic activity, others behaved as proinflammatory agents stimulating IL-1 and collagenolytic MMP up-regulation. This matricryptic potential of Fn was followed by several other examples of proteolytic production of biologically active peptides. The study of solid human tumors showed among the early signs of malignant transformation the fragmentation of pericellular Fn, concommitent with the increase of its production by the peritumoral stroma. These results should encourage further investigations concerning the potential importance of Fn production and breakdown during cancer progression.

Integrin expression is upregulated during early healing in a canine intrasynovial flexor tendon repair and controlled passive motion model

To explore crucial early molecular events involved in contact healing of the intrasynovial flexor tendon, integrin expression was evaluated at the transcriptional and post-transcriptional levels during the first two weeks following injury, repair and controlled passive motion in a canine model. Specifically, immunohistochemical and reverse transcription polymerase chain reaction (RT-PCR) techniques were employed to evaluate expression of the fibronectin, vitronectin and endothelial cell binding integrin receptor subunits alpha5, alphav and alpha6, along with the common beta1 subunit. The two techniques revealed increasing expression of the four subunits over the two week post-repair period. Immunohistochemistry revealed that beta1 and alpha5 expression was concentrated in the epitenon layer near the repair site and interiorly within the wound area, while alpha6 was associated with capillary-forming endothelial cells near the wound. RT-PCR and quantitation by NIH image analysis demonstrated peak messenger RNA expression of beta1 and alpha5 at ten days post-repair and peak expression of alpha6 and alphav at 15 days. The results in this study correlate well with previous results demonstrating increased fibronectin deposition and angiogenesis during the same time period in a similar injury/repair model.

Role of Proteoglycans in Tumor Progression

Data is now starting to accumulate on the differential expression of PGs in tumor cells of various invasive/metastatic potential. This is not so surprising if one considers the key functions that PGs play in the regulation of cell proliferation, adhesion and motility. However, characterization of PG expression in individual tumor types still awaits further detailed studies. Data on melanomas clearly indicate that PG phenotype is both specific and also promiscuous in a sense that ectopic expression of certain tissue specific PGs can occur in various tumors. Expression of a metastatic phenotype-specific splice variants of CD44 provides an example for the possible marker-function of PG. This also raises the hope that some PGs could be used as diagnostic/prognostic tools in pathology or even as a therapeutic targets against tumor dissemination. On the other hand, specific glycanation inhibitors may also be used for the modulation of tumor PG exist and the invasive phenotype.

Integrins as mediators of epithelial cell-matrix interactions in the human small intestinal mucosa

The intestinal epithelium is a highly dynamic tissue, which depends on a variety of factors for the regulation of its rapid renewal and expression of digestive functions. Over the last 10 years, it has become evident that among these factors are cell interactions with the extracellular matrix, more specifically with the underlying basement membrane, through a series of specific cell membrane receptors, many of which are integrins. Integrins regulate the assembly of adhesive junctions as well as the activation of various signaling pathways, leading to the modulation of gene expression. The analysis of the integrin repertoire along the crypt-villus axis in the human small intestinal epithelium identifies a number of beta1 and beta4 integrins, showing differential patterns of expression relative to its two functional compartments. Among them are the integrins alpha3beta1, alpha7Bbeta1 and the functional form of alpha6beta4 that appear to be related, in concert with the distribution of their ligands, to the process of intestinal cell differentiation, and the integrins alpha2beta1, alpha1beta1, alpha5beta1, and the non-functional form of alpha6beta4 that seem to be coupled with the undifferentiated/proliferative status of crypt cells. These observations delineate the potential complexity of the organization of epithelial cell-matrix interactions involved in the maintenance of the human intestinal crypt-villus axis.

Tissue transglutaminase, coagulation factor XIII, and the pro-polypeptide of von Willebrand factor are all ligands for the integrins alpha 9beta 1 and alpha 4beta 1

We previously reported that MOLT-3 human lymphocyte-like leukemia cells adhere to tissue-type transglutaminase (tTG) through the integrin alpha(4)beta(1). We now report that G-361 human melanoma cells also adhere to tTG, although they do not express alpha(4)beta(1). G-361 cells utilize two additional integrins, alpha(9)beta(1) and alpha(5)beta(1) to adhere to tTG. Furthermore, blood coagulation factor XIII (FXIII), another member of the transglutaminase family that is highly homologous to tTG, and propolypeptide of von Willebrand factor (pp-vWF) also promoted cell adhesion through alpha(9)beta(1) or alpha(4)beta(1) in G-361 or MOLT-3 cells, respectively. In the case of pp-vWF, alpha(9)beta(1) and alpha(4)beta(1) both bind to the same site, comprised of 15 amino acid residues and designated T2-15. Moreover, SW480 human colon cancer cells stably transfected to express alpha(9)beta(1), but not mock transfectants, adhered to tTG, FXIII, pp-vWF, and T2-15/bovine serum albumin conjugate. These data identify tTG, FXIII, and pp-vWF as shared ligands for the integrins alpha(9)beta(1) and alpha(4)beta(1). This report is the first to unambiguously show that these two integrins share the same cell adhesion site within one protein and provides strong support for classifying alpha(9)beta(1-) and alpha(4)-integrins as functionally related members of an integrin subfamily.

[Cortex-wall connections in the apical cell of Sphacelaria]

The apical cell of Sphacelaria (Fucophyceae) exhibits a permanent polarized organization throughout asymmetric divisions. The apex organization was studied by immunolocalization of tubulin, vitronectin, alpha-actinin and beta 1 integrin. Microfilaments were stained directly by fluorescein phalloidin. The apex was highly organized around a patch of microfilaments densely packed at the tip, where vitronectin-like and alpha-actinin-like proteins colocalized. In the same area, an actin-dependent targeted secretion of sulfated polysaccharides was shown. The permanent localization of these components throughout cell elongation suggests that a cortical site involving transmembrane connections between the cytoskeleton and the extracellular matrix is required for cell polarity. A model of the organization of the tip is proposed.

Regulation of alpha(v)beta3 and alpha5beta1 integrin receptors by basic fibroblast growth factor and platelet-derived growth factor-BB in intrasynovial flexor tendon cells

Integrins are important players in soft tissue healing as molecules that mediate communication between cells and extracellular matrix. Thus, the regulation of the expression of these molecules would be important during wound repair. To explore the regulatory roles of specific growth factors on integrin expression by intrasynovial flexor tendon cells, the present study assessed the in vitro effects of basic fibroblast growth factor and platelet derived growth factor-BB on expression of the alpha5beta1 and alpha(v)beta3 integrins in these cells. Analyses were carried out at the transcriptional (reverse transcription-polymerase chain reaction) and translational (immunohistochemistry) levels of cellular metabolism. Both types of analyses revealed increased expression of alpha5beta1 and alpha(v)beta3 by tendon cells exposed to either basic fibroblast growth factor or platelet-derived growth factor-BB over a wide range of growth factor concentrations employed in the study. Semiquantitative reverse transcription-polymerase chain reaction showed that, relative to control, basic fibroblast growth factor and platelet-derived growth factor-BB increased the expression of alpha(v) mRNA by 2-and 3-fold, respectively. Alpha 5 mRNA expression was also increased 3-fold by basic fibroblast growth factor, and 2-fold by platelet-derived growth factor-BB. We believe the results of this study are significant because the specific integrins affected are intimately involved in two events that have been shown to be important to intrasynovial flexor tendon healing, namely fibronectin deposition (alpha5beta1) as part of the provisional matrix and angiogenesis/revascularization (alpha(v)beta3).

The electrostatics of lipid surfaces

Charged lipids constitute a substantial fraction of all membrane lipids. Their charges vary in quantity and distribution within their headgroup regions. In long range interactions, their charges' value and electrostatic potential in the vicinity of the membrane surface can be approximated by the Guy-Chapman theory. This theory treats the interface as a charged structureless plain surrounded by uniform environments. However, if one considers intermolecular interactions, such assumptions need to be revised. The interface is in reality a thick region containing the residual charges of lipid headgroups. Their arrangement depends on the type of lipid present in the membrane. The variety of lipids and their biological functions suggests that charge distribution determines the extent and type of interaction with surface associated molecules. Numerous examples show that protein behavior at the lipid bilayer surface is determined by the type of lipid present, indicating protein specificity towards certain surface locations and local properties (determined by lipid composition) of a particular type. Such specificity is achieved by a combination of electrostatic, hydrophobic and enthropic effects. Comparing lipid biological activity, it can be stated that residual charge distribution is one of the factors of intermolecular recognition leading to the specific interaction of lipid molecules and selected proteins in various processes, particularly those involved with signal transduction pathways. Such specificity enables a variety of processes occurring simultaneously on the same membrane surface to function without cross-reaction interference.

Integrin subunits responsible for adhesion of human osteoblast-like cells to biomimetic peptide surfaces

We have identified the integrin subunits responsible for the initial adhesion of human osteoblast-like cells to peptide-modified surfaces. Biomimetic peptide surfaces containing homogenous RGD (Arg-Gly-Asp), homogenous FHRRIKA (Phe-His-Arg-Arg-Ile-Lys-Ala), and a mixed ratio of FHRRIKA:RGD (25:75) were used to assess integrin-mediated adhesion. The RGD and FHRRIKA peptides were selected from the cell-binding and putative heparin-binding domains of bone sialoprotein. A panel of monoclonal antibodies against human alpha1, alpha2, alpha3, alpha4, alpha5, beta1, alpha(v), and alpha(v)beta3 was used to identify the subunits most dominant in mediating short-term (10 or 30 minutes) and long-term (4 hours) cell adhesion to the peptide surfaces. Anti-alpha2, anti-beta1, and anti-alpha(v) significantly (p < 0.05) diminished cell attachment to homogenous RGD surfaces following 30 minutes of incubation. After 4 hours of incubation on RGD-grafted surfaces, immunostaining of these integrin subunits revealed discrete localization of the alpha(v) subunit at the periphery of the cell (similar to focal contact points), whereas the alpha2 and beta1 subunits stained very diffusely throughout the cell. A radial-flow apparatus was used to determine the effect of anti-integrin antibodies on strength of cell detachment following 10 minutes of incubation on peptide-grafted surfaces. The strength of detachment from surfaces containing RGD was significantly reduced (p < 0.05) in the presence of anti-alpha2, anti-alpha(v), or anti-beta1 compared with controls (presence of preimmune mouse IgG). None of the antibodies significantly influenced cell attachment to homogenous FHRRIKA-grafted surfaces. These results demonstrate that initial (30 minutes) attachment of human osteoblast-like cells to homogenous RGD surfaces was mediated by the collagen receptor alpha2beta1 and the vitronectin receptor alpha(v)beta3, whereas only the vitronectin receptor governed longer term (longer than 30 minutes) adhesion (localization to focal contacts). The importance of distinct integrins in mediating the attachment of bone cells to RGD-immobilized surfaces indicates a strategy for engineering orthopaedic implants with a built-in surface specificity for cell adhesion.

Minimal platelet deposition and activation in models of injured vessel wall ensure optimal neutrophil adhesion under flow conditions

Platelets at injured vessel wall form an adhesive surface for leukocyte adhesion. The precise relation between platelet adhesion and activation and leukocyte adhesion, however, is not known. We therefore used various models of injured vessel wall to form different patterns of platelet adhesion. The interaction of polymorphonuclear neutrophils (PMNs) was subsequently studied under flow conditions. In the absence of platelets, not only endothelial cell, smooth muscle cell, and fibroblast matrices but also purified matrix proteins (fibrinogen, collagen, and fibronectin) barely support PMN adhesion. The presence of platelets, however, strongly enhances PMN adhesion. PMN adhesion shows a proportional increase with platelet coverage up to 15%. Although PMNs roll over the scarcely scattered platelets, they speed up again when encountering surfaces without platelets. This "hopping" interaction of PMNs vanishes with platelet coverage >15%. Unobstructed rolling of PMNs is than observed and soon leads to a maximal adhesion of 1000 to 1200 cells/mm2. The mean rolling velocity of PMNs continues to decrease with higher platelet coverage. Platelet aggregate formation is an accepted indicator of platelet activation. The presence of platelet aggregates instead of contact or spread platelets, however, does not increase PMN adhesion. Also, additional stimulation of surface-associated platelets by thrombin fails to influence PMN adhesion. Moreover, indomethacin as an inhibitor of platelet activation and aggregation does not change the subsequent PMN interaction. In conclusion, approximately 15% of platelet coverage is sufficient for optimal PMN adhesion. Increasing platelet coverage increases the availability of platelet-associated receptors that lower PMN rolling velocity. Additional activation of adherent platelets makes no difference in the expression of relevant adhesion receptors. Therefore, minimal vascular damage in vivo and only scarce platelet adhesion will already evoke significant colocalization of leukocytes.

Metal-catalyzed oxidation of extracellular matrix increases macrophage nitric oxide generation

BACKGROUND

Oxygen radicals are believed to play a significant role in glomerular disease. In part this may be due to oxidation of lipids, but protein oxidation may play a contributory role as well. We have demonstrated that the mesangial extracellular matrix is susceptible to metal-catalyzed oxidation and that this increases scavenger receptor-mediated adhesion of macrophages, cells which appear to be important participants in glomerular injury via their secretory products. As other scavenger receptor ligands can increase macrophage nitric oxide generation, we examined whether oxidation of matrix could increase the activity of macrophage inducible nitric oxide synthase (iNOS).

METHODS

Extracellular matrix was oxidized using a metal-catalyzed oxidation system. Matrix oxidation was measured using carbonyl analysis, and iNOS activity in macrophages seeded onto the matrix was measured by nitrite determination and Western and Northern analyses for iNOS.

RESULTS

Macrophages exposed to oxidized matrix demonstrated a significant enhancement of iNOS activity. This enhancement could be antagonized by cotreatment of matrix with the radical spin trap N-tert-butyl-a-phenylnitrone, resulting in a corresponding decrease in protein carbonyl content, a measure of protein oxidation. Seeding macrophages onto oxidized matrix and adding the scavenger receptor ligand polyinosinic acid further augmented iNOS activity, suggesting that additional scavenger receptors were available to bind ligand and that further augmentation of iNOS activity did not require an additional change in cell shape. Western blot analysis revealed an increase in iNOS protein expression as a consequence of interaction with the oxidized matrix, but there was no difference in iNOS mRNA expression by Northern analysis suggesting a post-transcriptional mechanism for enhanced iNOS activity.

CONCLUSION

These data demonstrate that oxidation of extracellular matrix enhances macrophage nitric oxide generation, and suggest a previously undescribed role for extracellular matrix modification in the regulation of cellular function and possibly the mediation of glomerular injury.

Hepatocyte attachment on biodegradable modified chitosan membranes: in vitro evaluation for the development of liver organoids

Extracellular matrix structures including glycosaminoglycans play a critical role in cell attachment, differentiation, and morphogenesis. We evaluated chitosan ([1-->4] linked 2-amino-2-deoxy-beta-D-glucan) as a biomaterial for hepatocyte attachment because of its structural similarity to glycosaminoglycans. Freshly isolated rat and fetal porcine hepatocytes were seeded on chitosan membranes that had been previously blended with collagen, gelatin, or albumin to improve biocompatibility and surface roughness. The optimal cell density and attachment kinetics were quantified. The metabolic activity was investigated by measuring daily urea and total protein secretion by the cells for 2 weeks. While collagen blended-chitosan membranes provided a good attachment surface for rat hepatocytes, albumin and gelatin blended chitosan membranes were superior for fetal porcine hepatocyte attachment. The optimal attachment was maintained with membranes of medium molecular weight (Mr = 750,000 daltons) chitosan, at 3-4 x 10(4) cells/cm2 after 3 h of incubation. In vitro experiments demonstrated that fetal porcine hepatocytes survived at least 14 days when seeded on the chitosan-albumin matrix, demonstrating that this biomaterial can provide suitable cell attachment scaffolds for creating liver tissue organoids.

Muskelin, a novel intracellular mediator of cell adhesive and cytoskeletal responses to thrombospondin-1

We have used an expression cloning strategy based on a cell-attachment assay screen to seek identification of molecules required in cellular responses to thrombospondin-1, a regulated macromolecular component of extracellular matrix. We report the identification and functional characterization of a novel, widely expressed, intracellular protein, named muskelin, which contains dispersed motifs with homology to the tandem repeats first identified in the Drosophila kelch ORF1 protein. In adherent C2C12 cells, muskelin localizes in the cytoplasm and at cell margins. Over-expression of muskelin in C2C12 cells promotes cell attachment to the thrombospondin-1 C-terminal domain, alters the mechanisms of attachment to intact thrombospondin-1 and correlates with decreased formation of fascin microspikes and increased assembly of focal contacts by cells adherent on thrombospondin-1. Reciprocally, cell attachment, spreading and cytoskeletal organization are specifically reduced in TSP-1-adherent cells after antisense depletion of muskelin. These results establish a requirement for muskelin in cell responses to thrombospondin-1 and demonstrate that such responses involve a novel process which is integrated into the regulation of cell-adhesive behaviour and cytoskeletal organization.

The extracellular matrix in balloon arterial injury: a novel target for restenosis prevention

The role of the extracellular matrix (ECM) in the pathobiology of restenosis has not been fully appreciated. Recent discoveries have shown the ECM to be a complex, heterogeneous structure whose components are dynamically altered in response to vascular injury. This report reviews the structure and function of vascular ECM and the importance of the matrix in modulating the vascular response to arterial injury such as balloon angioplasty and atherosclerosis.

Fibronectin-binding peptides. I. Isolation and characterization of two unique fibronectin-binding peptides from gelatin

Gelatin binds to fibronectin with a high affinity although the fibronectin-binding components have not been located. Fibronectin plays an important role in tumor cell metastasis and gelatin may have a profound effect on the metastatic process. In this study, fractionated acid-washed gelatin was cleaved with trypsin and resultant peptides fractionated by fibronectin-Sepharose affinity chromatography. After further purification using size exclusion HPLC and then reverse-phase HPLC, two unique peptides were obtained and sequenced. The binding affinities of these two peptides to fibronectin were evaluated by an ELISA method developed during this study and compared with the gelatin. Both possessed significantly higher binding affinities to fibronectin than gelatin alone.