Oxidative modifications of the C-terminal domain of tropoelastin prevent cell binding

A dual-vector phospholipid nanosystem of doxorubicin: accumulation and cytotoxic effect in breast cancer cells in vitro

Various chemotherapeutic agents are used to treat breast cancer (BC); one of them is the anthracycline antibiotic doxorubicin (Dox), which, in addition to its cytostatic effect, has serious side effects. In order to reduce its negative impact on healthy organs and tissues and to increase its accumulation in tumors, Dox was incorporated into phospholipid nanoparticles. The additional use of vector molecules for targeted delivery to specific targets can increase the effectiveness of Dox due to higher accumulation of the active substance in the tumor tissue. The integrin αvβ3, which plays an important role in cancer angiogenesis, and the folic acid receptor, which is responsible for cell differentiation and proliferation, have been considered in this study as targets for such vector molecules. Thus, a phospholipid composition of Dox containing two vector ligands, cRGD peptide and folic acid (NPh-Dox-cRGD-Fol(3,4)), was prepared. Study of the physical properties of the developed composition NPh-Dox-cRGD-Fol(3,4) showed that the average particle size was 39.62±4.61 nm, the ζ-potential value was 4.17±0.83 mV. Almost all Dox molecules were incorporated into phospholipid nanoparticles (99.85±0.21%). The simultaneous use of two vectors in the composition led to an increase in the Dox accumulation in MDA-MB-231 BC cells by almost 20% as compared to compositions containing each vector separately (folic acid or the cRGD peptide). Moreover, the degree of Dox internalization was 22% and 24% higher than in the case of separate use of folic acid and cRGD peptide, respectively. The cytotoxic effect on MDA-MB-231 cells was higher during incubations with the compositions containing folic acid as a single vector (NPh-Dox-Fol(3,4)) and together with the RGD peptide (NPh-Dox-cRGD-Fol(3,4)). Experiments on the Wi-38 diploid fibroblast cell line have shown a significantly lower degree of cytotoxic effect of the phospholipid composition, regardless of the presence of the vector molecules in it, as compared to free Dox. The results obtained indicate the potential of using two vectors in one phospholipid composition for targeted delivery of Dox.

Transforming Growth Factor-β-Neutralizing Antibodies Improve Alveolarization in the Oxygen-Exposed Newborn Mouse Lung

Abnormal alveolar formation and excessive disordered elastin accumulation are key pathological features in bronchopulmonary dysplasia. Transforming growth factor (TGF)-β is an important regulator of the extracellular matrix in the developing lung. To determine if increased TGF-β would injure alveolar development by activating TGF-β signaling and by influencing the expression of elastogenesis-related protein, we performed intraperitoneal injection of newborn mice with the TGF-β-neutralizing antibody 1D11 and observed whether 1D11 had a protective role in the oxygen (O₂)-exposed newborn mouse lung. The newborn mice were exposed to 85% O₂ for 14 and 21 days. 1D11 was administered by intraperitoneal injection every day from postnatal days 3 to 20. Alveolar morphology was assessed by hematoxylin and eosin staining. The expression and distribution of elastin were evaluated by immunohistochemistry. The level of TGF-β signaling-related proteins were measured by immunohistochemistry, enzyme-linked immunosorbent assay, and Western blot. The expression levels of elastogenesis-related proteins, including tropoelastin, fibulin-5, and neutrophil elastase (NE), which participate in the synthesis, assembly, and degradation of elastin, were detected by real-time PCR and Western blot. In this research, impaired alveolar development and elastin deposition as well as the excessive activation of TGF-β signaling were observed in the newborn mouse lung exposed to hyperoxia. 1D11 improved alveolarization as well as the distribution of elastin in the newborn lung with hyperoxia exposure. The expression levels of tropoelastin, fibulin-5, and NE, which are important components of elastogenesis, were decreased by treatment with 1D11 in the injured newborn lung. These data demonstrate that 1D11 improved alveolarization by blocking the TGF-β signaling pathway and by reducing the abnormal expression of elastogenesis-related proteins in the O₂-exposed newborn mouse lung. 1D11 may become a new therapeutic method to prevent the development of bronchopulmonary dysplasia.

Elastin is heterogeneously cross-linked

Elastin is an essential vertebrate protein responsible for the elasticity of force-bearing tissues such as those of the lungs, blood vessels, and skin. One of the key features required for the exceptional properties of this durable biopolymer is the extensive covalent cross-linking between domains of its monomer molecule tropoelastin. To date, elastin's exact molecular assembly and mechanical properties are poorly understood. Here, using bovine elastin, we investigated the different types of cross-links in mature elastin to gain insight into its structure. We purified and proteolytically cleaved elastin from a single tissue sample into soluble cross-linked and noncross-linked peptides that we studied by high-resolution MS. This analysis enabled the elucidation of cross-links and other elastin modifications. We found that the lysine residues within the tropoelastin sequence were simultaneously unmodified and involved in various types of cross-links with different other domains. The Lys-Pro domains were almost exclusively linked via lysinonorleucine, whereas Lys-Ala domains were found to be cross-linked via lysinonorleucine, allysine aldol, and desmosine. Unexpectedly, we identified a high number of intramolecular cross-links between lysine residues in close proximity. In summary, we show on the molecular level that elastin formation involves random cross-linking of tropoelastin monomers resulting in an unordered network, an unexpected finding compared with previous assumptions of an overall beaded structure.

Exposure of tropoelastin to peroxynitrous acid gives high yields of nitrated tyrosine residues, di-tyrosine cross-links and altered protein structure and function

Elastin is an abundant extracellular matrix protein in elastic tissues, including the lungs, skin and arteries, and comprises 30-57% of the aorta by dry mass. The monomeric precursor, tropoelastin (TE), undergoes complex processing during elastogenesis to form mature elastic fibres. Peroxynitrous acid (ONOOH), a potent oxidising and nitrating agent, is formed in vivo from superoxide and nitric oxide radicals. Considerable evidence supports ONOOH formation in the inflamed artery wall, and a role for this species in the development of human atherosclerotic lesions, with ONOOH-damaged extracellular matrix implicated in lesion rupture. We demonstrate that TE is highly sensitive to ONOOH, with this resulting in extensive dimerization, fragmentation and nitration of Tyr residues to give 3-nitrotyrosine (3-nitroTyr). This occurs with equimolar or greater levels of oxidant and increases in a dose-dependent manner. Quantification of Tyr loss and 3-nitroTyr formation indicates extensive Tyr modification with up to two modified Tyr per protein molecule, and up to 8% conversion of initial ONOOH to 3-nitroTyr. These effects were modulated by bicarbonate, an alternative target for ONOOH. Inter- and intra-protein di-tyrosine cross-links have been characterized by mass spectrometry. Examination of human atherosclerotic lesions shows colocalization of 3-nitroTyr with elastin epitopes, consistent with TE or elastin modification in vivo, and also an association of 3-nitroTyr containing proteins and elastin with lipid deposits. These data suggest that exposure of TE to ONOOH gives marked chemical and structural changes to TE and altered matrix assembly, and that such damage accumulates in human arterial tissue during the development of atherosclerosis.

Targeted Modulation of Tropoelastin Structure and Assembly

Tropoelastin, as the monomer unit of elastin, assembles into elastic fibers that impart strength and resilience to elastic tissues. Tropoelastin is also widely used to manufacture versatile materials with specific mechanical and biological properties. The assembly of tropoelastin into elastic fibers or biomaterials is crucially influenced by key submolecular regions and specific residues within these domains. In this work, we identify the functional contributions of two rarely occurring negatively charged residues, glutamate 345 in domain 19 and glutamate 414 in domain 21, in jointly maintaining the native conformation of the tropoelastin hinge, bridge and foot regions. Alanine substitution of E345 and/or E414 variably alters the positioning and interactive accessibility of these regions, as illustrated by nanostructural studies and detected by antibody and cell probes. These structural changes are associated with a lower propensity for monomer coacervation, cross-linking into morphologically and functionally atypical hydrogels, and markedly impaired and abnormal elastic fiber formation. Our work indicates the crucial significance of both E345 and E414 residues in modulating specific local structure and higher-order assembly of human tropoelastin.

Silk-tropoelastin protein films for nerve guidance

Peripheral nerve regeneration may be enhanced through the use of biodegradable thin film biomaterials as highly tuned inner nerve conduit liners. Dorsal root ganglion neuron and Schwann cell responses were studied on protein films comprising silk fibroin blended with recombinant human tropoelastin protein. Tropoelastin significantly improved neurite extension and enhanced Schwann cell process length and cell area, while the silk provided a robust biomaterial template. Silk-tropoelastin blends afforded a 2.4-fold increase in neurite extension, when compared to silk films coated with poly-d-lysine. When patterned by drying on grooved polydimethylsiloxane (3.5 μm groove width, 0.5 μm groove depth), these protein blends induced both neurite and Schwann cell process alignment. Neurons were functional as assessed using patch-clamping, and displayed action potentials similar to those cultured on poly(lysine)-coated glass. Taken together, silk-tropoelastin films offer useful biomaterial interfacial platforms for nerve cell control, which can be considered for neurite guidance, disease models for neuropathies and surgical peripheral nerve repairs.

A negatively charged residue stabilizes the tropoelastin N-terminal region for elastic fiber assembly

Tropoelastin is an extracellular matrix protein that assembles into elastic fibers that provide elasticity and strength to vertebrate tissues. Although the contributions of specific tropoelastin regions during each stage of elastogenesis are still not fully understood, studies predominantly recognize the central hinge/bridge and C-terminal foot as the major participants in tropoelastin assembly, with a number of interactions mediated by the abundant positively charged residues within these regions. However, much less is known about the importance of the rarely occurring negatively charged residues and the N-terminal coil region in tropoelastin assembly. The sole negatively charged residue in the first half of human tropoelastin is aspartate 72. In contrast, the same region comprises 17 positively charged residues. We mutated this aspartate residue to alanine and assessed the elastogenic capacity of this novel construct. We found that D72A tropoelastin has a decreased propensity for initial self-association, and it cross-links aberrantly into denser, less porous hydrogels with reduced swelling properties. Although the mutant can bind cells normally, it does not form elastic fibers with human dermal fibroblasts and forms fewer atypical fibers with human retinal pigmented epithelial cells. This impaired functionality is associated with conformational changes in the N-terminal region. Our results strongly point to the role of the Asp-72 site in stabilizing the N-terminal segment of human tropoelastin and the importance of this region in facilitating elastic fiber assembly.

A novel cell adhesion region in tropoelastin mediates attachment to integrin αVβ5

Tropoelastin protein monomers assemble to form elastin. Cellular integrin αVβ3 binds RKRK at the C-terminal tail of tropoelastin. We probed cell interactions with tropoelastin by deleting the RKRK sequence to identify other cell-binding interactions within tropoelastin. We found a novel human dermal fibroblast attachment and spreading site on tropoelastin that is located centrally in the molecule. Inhibition studies demonstrated that this cell adhesion was not mediated by either elastin-binding protein or glycosaminoglycans. Cell interactions were divalent cation-dependent, indicating integrin dependence. Function-blocking monoclonal antibodies revealed that αV integrin(s) and integrin αVβ5 specifically were critical for cell adhesion to this part of tropoelastin. These data reveal a common αV integrin-binding theme for tropoelastin: αVβ3 at the C terminus and αVβ5 at the central region of tropoelastin. Each αV region contributes to fibroblast attachment and spreading, but they differ in their effects on cytoskeletal assembly.

Elastic fibres in health and disease

Elastic fibres are insoluble components of the extracellular matrix of dynamic connective tissues such as skin, arteries, lungs and ligaments. They are laid down during development, and comprise a cross-linked elastin core within a template of fibrillin-based microfibrils. Their function is to endow tissues with the property of elastic recoil, and they also regulate the bioavailability of transforming growth factor β. Severe heritable elastic fibre diseases are caused by mutations in elastic fibre components; for example, mutations in elastin cause supravalvular aortic stenosis and autosomal dominant cutis laxa, mutations in fibrillin-1 cause Marfan syndrome and Weill–Marchesani syndrome, and mutations in fibulins-4 and -5 cause autosomal recessive cutis laxa. Acquired elastic fibre defects include dermal elastosis, whereas inflammatory damage to fibres contributes to pathologies such as pulmonary emphysema and vascular disease. This review outlines the latest understanding of the composition and assembly of elastic fibres, and describes elastic fibre diseases and current therapeutic approaches.

Elastin signaling in wound repair

Skin is an important organ to the human body as it functions as an interface between the body and environment. Cutaneous injury elicits a complex wound healing process, which is an orchestration of cells, matrix components, and signaling factors that re-establishes the barrier function of skin. In adults, an unavoidable consequence of wound healing is scar formation. However, in early fetal development, wound healing is scarless. This phenomenon is characterized by an attenuated inflammatory response, differential expression of signaling factors, and regeneration of normal skin architecture. Elastin endows a range of mechanical and cell interactive properties to skin. In adult wound healing, elastin is severely lacking and only a disorganized elastic fiber network is present after scar formation. The inherent properties of elastin make it a desirable inclusion to adult wound healing. Elastin imparts recoil and resistance and induces a range of cell activities, including cell migration and proliferation, matrix synthesis, and protease production. The effects of elastin align with the hallmarks of fetal scarless wound healing. Elastin synthesis is substantial in late stage in utero and drops to a trickle in adults. The physical and cell signaling advantages of elastin in a wound healing context creates a parallel with the innate features of fetal skin that can allow for scarless healing.

Tropoelastin--a multifaceted naturally smart material

Tropoelastin dominates the physical performance of human elastic tissue as it is assembled to make elastin. Tropoelastin is increasingly appreciated as a protein monomer with a defined solution shape comprising modular, bridged regions that specialize in elasticity and cell attachment, which collectively participate in macromolecular assembly. This modular, multifaceted molecule is being exploited to enhance the physical performance and biological presentation of engineered constructs to augment and repair human tissues. These tissues include skin and vasculature, and emphasize how growing knowledge of tropoelastin can be powerfully adapted to add value to pre-existing devices like stents and novel, multi-featured biological implants.

Effect of ProNectin F derivatives on cell attachment and proliferation

ProNectin F (PnF) was chemically modified by introducing some functional groups to prepare various derivatives of primary amino (PnF-N₁), tertiary amino (PnF-N₃), quaternary ammonium (PnF-N₄), carboxyl (PnF-COOH) and sulfonyl groups (PnF-SO₃H). When C3H10T1/2 cells were cultured on non-treated dishes coated with the derivatives, the number of mesenchymal cells attached to the culture dishes increased for the coating with PnF-COOH and PnF-SO₃H, even at their low adsorption amount. The cytotoxicity was high for the coating of PnF-N₁ and PnF-N₄ compared with that of the PnF-N₃, PnF-COOH and PnF-SO₃H. The treatment with integrin α5 and αV antibodies suppressed the cell attachment to the dishes coated with PnF-COOH and PnF-SO₃H. The phosphorylation of extracellular signal-regulated kinase (ERK) was upregulated for cells attached to the dishes coated with PnF-COOH and PnF-SO₃H, indicating their enhanced proliferation. It is concluded that the chemical derivatization of PnF enhanced the ability of cell attachment and proliferation.

Cell patterning via linker-free protein functionalization of an organic conducting polymer (polypyrrole) electrode

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of the conducting polymer, polypyrrole, which possesses electrical properties. PIII treatment enabled persistent, covalent binding of the cell adhesive protein, tropoelastin, without employing chemical linking molecules. In contrast tropoelastin was readily eluted from the untreated surface. Through this differential persistence of binding, surface bound tropoelastin supported cell adhesion and spreading on the PIII treated but not the untreated polypyrrole surface. The application of a steel shadow mask during PIII treatment allowed for spatial definition of tropoelastin exclusively to PIII treated regions. The general applicability of this approach to other extracellular matrix proteins was illustrated using collagen I, which displayed similar results to tropoelastin but required extended washing conditions. This approach allowed fine patterning of cell adhesion and spreading to tropoelastin and collagen, specifically on PIII treated polypyrrole regions. We therefore present a methodology to alter the functionality of polypyrrole surfaces, generating surfaces that can spatially control cellular interactions through protein functionalization with the potential for electrical stimulation.

The effects of extracellular matrix proteins on neutrophil-endothelial interaction--a roadway to multiple therapeutic opportunities

Polymorphoneuclear leukocytes or neutrophils, a major component of white blood cells, contribute to the innate immune response in humans. Upon sensing changes in the microenvironment, neutrophils adhere to the vascular wall, migrate through the endothelial cell (EC)-pericyte bilayer, and subsequently through the extracellular matrix to reach the site of inflammation. These cells are capable of destroying microbes, cell debris, and foreign proteins by oxidative and non-oxidative processes. While primarily mediators of tissue homeostasis, there are an increasing number of studies indicating that neutrophil recruitment and transmigration can also lead to host-tissue injury and subsequently inflammation-related diseases. Neutrophil-induced tissue injury is highly regulated by the microenvironment of the infiltrated tissue, which includes cytokines, chemokines, and the provisional extracellular matrix, remodeled through increased vascular permeability and other cellular infiltrates. Thus, investigation of the effects of matrix proteins on neutrophil-EC interaction and neutrophil transmigration may help identify the proteins that induce pro- or anti-inflammatory responses. This area of research presents an opportunity to identify therapeutic targets in inflammation-related diseases. This review will summarize recent literature on the role of neutrophils and the effects of matrix proteins on neutrophil-EC interactions, with focus on three different disease models: 1) atherosclerosis, 2) COPD, and 3) tumor growth and progression. For each disease model, inflammatory molecules released by neutrophils, important regulatory matrix proteins, current anti-inflammatory treatments, and the scope for further research will be summarized.

Colocalization in vivo and association in vitro of perlecan and elastin

We have colocalized elastin and fibrillin-1 with perlecan in extracellular matrix of tensional and weight-bearing connective tissues. Elastin and fibrillin-1 were identified as prominent components of paraspinal blood vessels, and posterior longitudinal ligament in the human fetal spine and outer annulus fibrosus of the fetal intervertebral disc. We also colocalized perlecan with a synovial elastic basal lamina, where the attached synovial cells were observed to produce perlecan. Elastin, fibrillin-1 and perlecan were co-localized in the intima and media of small blood vessels in the synovium and in human fetal paraspinal blood vessels. Elastic fibers were observed at the insertion point of the anterior cruciate ligament to bone in the ovine stifle joint where they colocalized with perlecan. Elastin has not previously been reported to be spatially associated with perlecan in these tissues. Interactions between the tropoelastin and perlecan heparan sulfate chains were demonstrated using quartz crystal microbalance with dissipation solid phase binding studies. Electrostatic interactions through the heparan sulfate chains of perlecan and core protein mediated the interactions with tropoelastin, and were both important in the coacervation of tropoelastin and deposition of elastin onto perlecan immobilized on the chip surface. This may help us to understand the interactions which are expected to occur in vivo between the tropoelastin and perlecan to facilitate the deposition of elastin and formation of elastic microfibrils in situ and would be consistent with the observed distributions of these components in a number of connective tissues.

Binding of the cell adhesive protein tropoelastin to PTFE through plasma immersion ion implantation treatment

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of polytetrafluorethylene (PTFE), enabling the covalent binding of a cell adhesive protein, tropoelastin, without employing chemical linking molecules. Tropoelastin coating of untreated or PIII treated PFTE simultaneously promoted and blocked cell interactions respectively, i.e. PIII treatment of the PTFE surface completely inverses the cell interactive properties of bound tropoelastin. This activity persisted over long term storage of the PIII treated surfaces. The integrin binding C-terminus of tropoelastin was markedly less solvent exposed when bound to PIII treated PTFE than untreated PTFE, accounting for the modulation of cell adhesive activity. This presents a new methodology to specifically modulate cell behavior on a polymer surface using a simple one step treatment process, by adjusting the adhesive activity of a single extracellular matrix protein.