Inhibitory effect of type 1 collagen gel containing alpha-elastin on proliferation and migration of vascular smooth muscle and endothelial cells

Arterial dissections: Common features and new perspectives

Arterial dissections, which involve an abrupt tear in the wall of a major artery resulting in the intramural accumulation of blood, are a family of catastrophic disorders causing major, potentially fatal sequelae. Involving diverse vascular beds, including the aorta or coronary, cervical, pulmonary, and visceral arteries, each type of dissection is devastating in its own way. Traditionally they have been studied in isolation, rather than collectively, owing largely to the distinct clinical consequences of dissections in different anatomical locations - such as stroke, myocardial infarction, and renal failure. Here, we review the shared and unique features of these arteriopathies to provide a better understanding of this family of disorders. Arterial dissections occur commonly in the young to middle-aged, and often in conjunction with hypertension and/or migraine; the latter suggesting they are part of a generalized vasculopathy. Genetic studies as well as cellular and molecular investigations of arterial dissections reveal striking similarities between dissection types, particularly their pathophysiology, which includes the presence or absence of an intimal tear and vasa vasorum dysfunction as a cause of intramural hemorrhage. Pathway perturbations common to all types of dissections include disruption of TGF-β signaling, the extracellular matrix, the cytoskeleton or metabolism, as evidenced by the finding of mutations in critical genes regulating these processes, including LRP1, collagen genes, fibrillin and TGF-β receptors, or their coupled pathways. Perturbances in these connected signaling pathways contribute to phenotype switching in endothelial and vascular smooth muscle cells of the affected artery, in which their physiological quiescent state is lost and replaced by a proliferative activated phenotype. Of interest, dissections in various anatomical locations are associated with distinct sex and age predilections, suggesting involvement of gene and environment interactions in disease pathogenesis. Importantly, these cellular mechanisms are potentially therapeutically targetable. Consideration of arterial dissections as a collective pathology allows insight from the better characterized dissection types, such as that involving the thoracic aorta, to be leveraged to inform the less common forms of dissections, including the potential to apply known therapeutic interventions already clinically available for the former.

Vascular Endothelial Cell Behavior in Complex Mechanical Microenvironments

The vascular mechanical microenvironment consists of a mixture of spatially and temporally changing mechanical forces. This exposes vascular endothelial cells to both hemodynamic forces (fluid flow, cyclic stretching, lateral pressure) and vessel forces (basement membrane mechanical and topographical properties). The vascular mechanical microenvironment is "complex" because these forces are dynamic and interrelated. Endothelial cells sense these forces through mechanosensory structures and transduce them into functional responses via mechanotransduction pathways, culminating in behavior directly affecting vascular health. Recent in vitro studies have shown that endothelial cells respond in nuanced and unique ways to combinations of hemodynamic and vessel forces as compared to any single mechanical force. Understanding the interactive effects of the complex mechanical microenvironment on vascular endothelial behavior offers the opportunity to design future biomaterials and biomedical devices from the bottom-up by engineering for the cellular response. This review describes and defines (1) the blood vessel structure, (2) the complex mechanical microenvironment of the vascular endothelium, (3) the process in which vascular endothelial cells sense mechanical forces, and (4) the effect of mechanical forces on vascular endothelial cells with specific attention to recent works investigating the influence of combinations of mechanical forces. We conclude this review by providing our perspective on how the field can move forward to elucidate the effects of the complex mechanical microenvironment on vascular endothelial cell behavior.

Micromechanics of elastic lamellae: unravelling the role of structural inhomogeneity in multi-scale arterial mechanics

Microstructural deformation of elastic lamellae plays important roles in maintaining arterial tissue homeostasis and regulating vascular smooth muscle cell fate. Our study unravels the underlying microstructural origin that enables elastic lamellar layers to evenly distribute the stresses through the arterial wall caused by intraluminal distending pressure, a fundamental requirement for tissue and cellular function. A new experimental approach was developed to quantify the spatial organization and unfolding of elastic lamellar layers under pressurization in mouse carotid arteries by coupling physiological extension-inflation and multiphoton imaging. Tissue-level circumferential stretch was obtained from analysis of the deformation of a thick-walled cylinder. Our results show that the unfolding and extension of lamellar layers contribute simultaneously to tissue-level deformation. The inner lamellar layers are wavier and unfold more than the outer layers. This waviness gradient compensates the larger tissue circumferential stretch experienced at the inner surface, thus equalizing lamellar layer extension through the arterial wall. Discoveries from this study reveal the importance of structural inhomogeneity in maintaining tissue homeostasis through the arterial wall, and may have profound implications on vascular remodelling in aging and diseases, as well as in tissue engineering of functional blood vessels.

A Three-Dimensional Collagen-Elastin Scaffold for Heart Valve Tissue Engineering

Since most of the body's extracellular matrix (ECM) is composed of collagen and elastin, we believe the choice of these materials is key for the future and promise of tissue engineering. Once it is known how elastin content of ECM guides cellular behavior (in 2D or 3D), one will be able to harness the power of collagen-elastin microenvironments to design and engineer stimuli-responsive tissues. Moreover, the implementation of such matrices to promote endothelial-mesenchymal transition of primary endothelial cells constitutes a powerful tool to engineer 3D tissues. Here, we design a 3D collagen-elastin scaffold to mimic the native ECM of heart valves, by providing the strength of collagen layers, as well as elasticity. Valve interstitial cells (VICs) were encapsulated in the collagen-elastin hydrogels and valve endothelial cells (VECs) cultured onto the surface to create an in vitro 3D VEC-VIC co-culture. Over a seven-day period, VICs had stable expression levels of integrin β1 and F-actin and continuously proliferated, while cell morphology changed to more elongated. VECs maintained endothelial phenotype up to day five, as indicated by low expression of F-actin and integrin β1, while transformed VECs accounted for less than 7% of the total VECs in culture. On day seven, over 20% VECs were transformed to mesenchymal phenotype, indicated by increased actin filaments and higher expression of integrin β1. These findings demonstrate that our 3D collagen-elastin scaffolds provided a novel tool to study cell-cell or cell-matrix interactions in vitro, promoting advances in the current knowledge of valvular endothelial cell mesenchymal transition.

De Novo Synthesis of Elastin by Exogenous Delivery of Synthetic Modified mRNA into Skin and Elastin-Deficient Cells

Elastin is one of the most important and abundant extracellular matrix (ECM) proteins that provide elasticity and resilience to tissues and organs, including vascular walls, ligaments, skin, and lung. Besides hereditary diseases, such as Williams-Beuren syndrome (WBS), which results in reduced elastin synthesis, injuries, aging, or acquired diseases can lead to the degradation of existing elastin fibers. Thus, the de novo synthesis of elastin is required in several medical conditions to restore the elasticity of affected tissues. Here, we applied synthetic modified mRNA encoding tropoelastin (TE) for the de novo synthesis of elastin and determined the mRNA-mediated elastin synthesis in cells, as well as ex vivo in porcine skin. EA.hy926 cells, human fibroblasts, and mesenchymal stem cells (MSCs) isolated from a patient with WBS were transfected with 2.5 μg TE mRNA. After 24 hr, the production of elastin was analyzed by Fastin assay and dot blot analyses. Compared with untreated cells, significantly enhanced elastin amounts were detected in TE mRNA transfected cells. The delivered synthetic TE mRNA was even able to significantly increase the elastin production in elastin-deficient MSCs. In porcine skin, approximately 20% higher elastin amount was detected after the intradermal delivery of synthetic mRNA by microinjection. In this study, we demonstrated the successful applicability of synthetic TE encoding mRNA to produce elastin in elastin-deficient cells as well as in skin. Thus, this auspicious mRNA-based integration-free method has a huge potential in the field of regenerative medicine to induce de novo elastin synthesis, e.g., in skin, blood vessels, or alveoli.

Vascularisation for cardiac tissue engineering: the extracellular matrix

Cardiovascular diseases present a major socio-economic burden. One major problem underlying most cardiovascular and congenital heart diseases is the irreversible loss of contractile heart muscle cells, the cardiomyocytes. To reverse damage incurred by myocardial infarction or by surgical correction of cardiac malformations, the loss of cardiac tissue with a thickness of a few millimetres needs to be compensated. A promising approach to this issue is cardiac tissue engineering. In this review we focus on the problem of in vitro vascularisation as implantation of cardiac patches consisting of more than three layers of cardiomyocytes (> 100 μm thick) already results in necrosis. We explain the need for vascularisation and elaborate on the importance to include non-myocytes in order to generate functional vascularised cardiac tissue. We discuss the potential of extracellular matrix molecules in promoting vascularisation and introduce nephronectin as an example of a new promising candidate. Finally, we discuss current biomaterial- based approaches including micropatterning, electrospinning, 3D micro-manufacturing technology and porogens. Collectively, the current literature supports the notion that cardiac tissue engineering is a realistic option for future treatment of paediatric and adult patients with cardiac disease.

Fibrillins in Tendon

Tendons among connective tissue, mainly collagen, contain also elastic fibers (EF) made of fibrillin 1, fibrillin 2 and elastin that are broadly distributed in tendons and represent 1-2% of the dried mass of the tendon. Only in the last years, studies on structure and function of EF in tendons have been performed. Aim of this review is to revise data on the organization of EF in tendons, in particular fibrillin structure and function, and on the clinical manifestations associated to alterations of EF in tendons. Indeed, microfibrils may contribute to tendon mechanics; therefore, their alterations may cause joint hypermobility and contractures which have been found to be clinical features in patients with Marfan syndrome (MFS) and Beals syndrome. The two diseases are caused by mutations in genes FBN1 and FBN2 encoding fibrillin 1 and fibrillin 2, respectively.

Effect of glucose on the biomechanical function of arterial elastin

Elastin is essential to provide elastic support for blood vessels. As a remarkably long-lived protein, elastin can suffer from cumulative effects of exposure to biochemical damages, which can greatly compromise its biomechanical properties. Non-enzymatic glycation is one of the main mechanisms of aging and its effect is magnified in diabetic patients. The purpose of this study is to investigate the effects of glucose on mechanical properties of isolated porcine aortic elastin. Elastin samples were incubated in 2 M glucose solution and were allowed to equilibrate for 4, 7, 14, 21 or 28 days at 37 °C. Equibiaxial tensile tests were performed to study the changes of elastic properties of elastin due to glycation. Significant decreases in tissue dimension were observed after 7 days glucose incubation. Elastin samples treated for 14, 21 or 28 days demonstrate a significant increase in hysteresis in the stress-stretch curves, indicating a greater energy loss due to glucose treatment. Both the longitudinal and the circumferential directions show significant increases in tangent modulus with glucose treatment, however only significant increases are observed after 7 days for the circumferential direction. An eight-chain statistical mechanics based microstructural model was used to study the hyperelastic and orthotropic behavior of the glucose-treated elastin and the material parameters were estimated using a nonlinear least squares method. Material parameters in the model were related to elastin density and fiber orientation, and, hence, the possible microstructural changes in glucose-treated elastin. Estimated material parameters show a general increasing trend in elastin density per unit volume with glucose incubation. The simulation results also indicate that more elastic fibers are aligned in the longitudinal and circumferential directions, rather than in the radial direction.

Elastin is a key regulator of outward remodeling in arteriovenous fistulas

OBJECTIVES

Maturation failure is the major limitation of arteriovenous fistulas (AVFs) as hemodialysis access conduits. Indeed, 30-50% of AVFs fail to mature due to intimal hyperplasia and insufficient outward remodeling. Elastin has emerged as an important determinant of vascular remodeling. Here the role of elastin in AVF remodeling in elastin haplodeficient (eln(+/-)) mice undergoing AVF surgery has been studied.

METHODS

Unilateral AVFs between the branch of the jugular vein and carotid artery in an end to side manner were created in wild-type (WT) C57BL/6 (n = 11) and in eln(+/-) mice (n = 9). Animals were killed at day 21 and the AVFs were analyzed histologically and at an mRNA level using real-time quantitative polymerase chain reaction.

RESULTS

Before AVF surgery, a marked reduction in elastin density in the internal elastic lamina (IEL) of eln(+/-) mice was observed. AVF surgery resulted in fragmentation of the venous internal elastic lamina in both groups while the expression of the tropoelastin mRNA was 53% lower in the eln(+/-) mice than in WT mice (p < .001). At 21 days after AVF surgery, the circumference of the venous outflow tract of the AVF was 21% larger in the eln(+/-) mice than in the WT mice (p = .037), indicating enhanced outward remodeling in the eln(+/-) mice. No significant difference in intimal hyperplasia was observed. The venous lumen of the AVF in the eln(+/-) mice was 53% larger than in the WT mice, although this difference was not statistically significant (eln(+/-), 350,116 ± 45,073 μm(2); WT, 229,405 ± 40,453 μm(2); p = .064).

CONCLUSIONS

In a murine model, elastin has an important role in vascular remodeling following AVF creation, in which a lower amount of elastin results in enhanced outward remodeling. Interventions targeting elastin degradation might be a viable option in order to improve AVF maturation.

Scaffolds in vascular regeneration: current status

An ideal vascular substitute, especially in <6 mm diameter applications, is a major clinical essentiality in blood vessel replacement surgery. Blood vessels are structurally complex and functionally dynamic tissue, with minimal regeneration potential. These have composite extracellular matrix (ECM) and arrangement. The interplay between ECM components and tissue specific cells gives blood vessels their specialized functional attributes. The core of vascular tissue engineering and regeneration relies on the challenges in creating vascular conduits that match native vessels and adequately regenerate in vivo. Out of numerous vascular regeneration concerns, the relevance of ECM emphasizes much attention toward appropriate choice of scaffold material and further scaffold development strategies. The review is intended to be focused on the various approaches of scaffold materials currently in use in vascular regeneration and current state of the art. Scaffold of choice in vascular tissue engineering ranges from natural to synthetic, decellularized, and even scaffold free approach. The applicability of tubular scaffold for in vivo vascular regeneration is under active investigation. A patent conduit with an ample endothelial luminal layer that can regenerate in vivo remains an unanswered query in the field of small diameter vascular tissue engineering. Besides, scaffolds developed for vascular regeneration, should aim at providing functional substitutes for use in a regenerative approach from the laboratory bench to patient bedside.

Distribution and expression of type VI collagen and elastic fibers in human rotator cuff tendon tears

There is increasing evidence for a progressive extracellular matrix change in rotator cuff disease progression. Directly surrounding the cell is the pericellular matrix, where assembly of matrix aggregates typically occurs making it critical in the response of tendon cells to pathological conditions. Studies in animal models have identified type VI collagen, fibrillin-1 and elastin to be located in the pericellular matrix of tendon and contribute in maintaining the structural and biomechanical integrity of tendon. However, there have been no reports on the localization of these proteins in human tendon biopsies. This study aimed to characterize the distribution of these ECM components in human rotator cuffs and gain greater insight into the relationship of pathology to tear size by analyzing the distribution and expression profiles of these ECM components. Confocal microscopy confirmed the localization of these structural molecules in the pericellular matrix of the human rotator cuff. Tendon degeneration led to an increased visibility of these components with a significant disorganization in the distribution of type VI collagen. At the genetic level, an increase in tear size was linked to an increased transcription of type VI collagen and fibrillin-1 with no significant alteration in the elastin levels. This is the first study to confirm the localization of type VI collagen, elastin and fibrillin-1 in the pericellular region of human supraspinatus tendon and assesses the effect of tendon degeneration on these structures, thus providing a useful insight into the composition of human rotator cuff tears which can be instrumental in predicting disease prognosis.

Vascular wall extracellular matrix proteins and vascular diseases

Extracellular matrix proteins form the basic structure of blood vessels. Along with providing basic structural support to blood vessels, matrix proteins interact with different sets of vascular cells via cell surface integrin or non-integrin receptors. Such interactions induce vascular cell de novo synthesis of new matrix proteins during blood vessel development or remodeling. Under pathological conditions, vascular matrix proteins undergo proteolytic processing, yielding bioactive fragments to influence vascular wall matrix remodeling. Vascular cells also produce alternatively spliced variants that induce vascular cell production of different matrix proteins to interrupt matrix homeostasis, leading to increased blood vessel stiffness; vascular cell migration, proliferation, or death; or vascular wall leakage and rupture. Destruction of vascular matrix proteins leads to vascular cell or blood-borne leukocyte accumulation, proliferation, and neointima formation within the vascular wall; blood vessels prone to uncontrolled enlargement during blood flow diastole; tortuous vein development; and neovascularization from existing pathological tissue microvessels. Here we summarize discoveries related to blood vessel matrix proteins within the past decade from basic and clinical studies in humans and animals - from expression to cross-linking, assembly, and degradation under physiological and vascular pathological conditions, including atherosclerosis, aortic aneurysms, varicose veins, and hypertension.

A fibronectin-fibrinogen-tropoelastin coating reduces smooth muscle cell growth but improves endothelial cell function

Reendothelialization of the stent surface after percutaneous coronary intervention (PCI) is known to be an important determinant of clinical outcome. We compared the effects of biological stent coatings, fibronectin, fibrinogen and tropoelastin, on human umbilical vein endothelial cell (HUVEC) and vascular smooth muscle cell (VSMC) characteristics. Umbilical cord arterial segments were cultured on coated surfaces and VSMC outgrowth (indicating proliferation and migration) was measured after 12 days. mRNA was isolated from HUVEC and VSMC cultured on these coatings and gene expression was profiled by QPCR. Procoagulant properties of HUVEC were determined by an indirect chromogenic assay which detects tissue factor activity. The varying stent coatings influence VSMC outgrowth: 31.2 ± 4.0 mm² on fibronectin, 1.6 ± 0.3 mm² on tropoelastin and 8.1 ± 1.5 mm² on a mixture of fibronectin/fibrinogen/tropoelastin, although HUVEC migration remains unaffected. Culturing HUVEC on tropoelastin induces increased expression of VCAM-1 (13.1 ± 4.4 pg/ml), ICAM-1 (5.1 ± 1.3 pg/ml) and IL-8 (11.6 ± 3.1 pg/ml) compared to fibronectin (0.7 ± 0.2, 0.8 ± 0.2, 2.3 ± 0.5 pg/ml, respectively), although expression levels on fibronectin/fibrinogen/tropoelastin remain unaltered. No significant differences in VCAM-1, ICAM-1 and IL-8 mRNA expression are found in VSMC. Finally, HUVEC cultured on tropoelastin display a fivefold increased tissue factor activity (511.6 ± 26.7%), compared to cells cultured on fibronectin (100 ± 3.9%) or fibronectin/fibrinogen/tropoelastin (76.3 ± 25.0%). These results indicate that tropoelastin inhibits VSMC migration but leads to increased inflammatory and procoagulant markers on endothelial cells. Fibronectin/fibrinogen/tropoelastin inhibits VSMCs while compensating the inflammatory and procoagulant effects. These data suggest that coating a mixture of fibronectin/fibrinogen/tropoelastin on a stent may promote reendothelialization, while keeping unfavourable processes such as restenosis and procoagulant activity limited.

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.

Extracellular matrix molecules facilitating vascular biointegration

All vascular implants, including stents, heart valves and graft materials exhibit suboptimal biocompatibility that significantly reduces their clinical efficacy. A range of biomolecules in the subendothelial space have been shown to play critical roles in local regulation of thrombosis, endothelial growth and smooth muscle cell proliferation, making these attractive candidates for modulation of vascular device biointegration. However, classically used biomaterial coatings, such as fibronectin and laminin, modulate only one of these components; enhancing endothelial cell attachment, but also activating platelets and triggering thrombosis. This review examines a subset of extracellular matrix molecules that have demonstrated multi-faceted vascular compatibility and accordingly are promising candidates to improve the biointegration of vascular biomaterials.

The profile of the extracellular matrix changes in the aorta after sympathectomy in the hypercholesterolemic rats

We previously showed that sympathectomy induces thickened intima and decreases the expression of cytoskeletal proteins associated with a differentiated smooth muscle cell (SMC) phenotype in hypercholesterolemic rats. In the present study, we sought to determine the effect of sympathectomy on various components of the extracellular matrix (ECM) in the aorta from these animals, since the state of SMC differentiation depends on the nature of ECM components. Collagen types I and III, previously reported to be associated with SMC dedifferentiation, and collagen VI, elastin, laminin and elastin-laminin receptor (E/L-R), previously reported to be associated with SMC differentiation, were analyzed by western immunoblot and confocal microscopy in abdominal aortae from sham rats and hypercholesterolemic rats sympathectomized with guanethidine. Both western immunoblot and immunohistological analysis showed an increase in collagens I and III (more for collagen I), with abundant labeling in the media, adventitia and thickened intima in sympathectomized aortae. Collagen IV labeling was decreased in the media and adventitia and was weak in the thickened intima in sympathectomised aortae. The E/L-R increased and was abundantly labeled in the media and weakly in the thickened intima in sympathectomized aortae. Elastin and laminin decreased and appeared less labeled in the media in the sympathectomised aortae. In the thickened intima, laminin was slightly labeled while elastin was not obviously labeled. These data show that sympathectomy favors the ECM features reported in association with a dedifferentiated/immature SMC phenotype and intimal thickening, probably by actions on both SMCs and fibroblasts.

The organisation of elastin and fibrillins 1 and 2 in the cruciate ligament complex

Although elastin fibres and oxytalan fibres (bundles of microfibrils) have important mechanical, biochemical and cell regulatory functions, neither their distribution nor their function in cruciate ligaments has been investigated. Twelve pairs of cruciate ligaments (CLs) were obtained from 10 adult dogs with no evidence of knee osteoarthritis. Elastic fibres were identified using Verhoeff's and Miller's staining. Fibrillins 1 and 2 were immunolocalised and imaged using confocal laser scanning microscopy. Hydrated, unfixed tissue was analysed using Nomarski differential interference microscopy (NDIC), allowing structural and mechanical analysis. Microfibrils and elastin fibres were widespread in both CLs, predominantly within ligament fascicles, parallel to collagen bundles. Although elastin fibres were sparse, microfibrils were abundant. We described abundant fibres composed of both fibrillin 1 and fibrillin 2, which had a similar pattern of distribution to oxytalan fibres. NDIC demonstrated complex interfascicular and interbundle anatomy in the CL complex. The distribution of elastin fibres is suggestive of a mechanical role in bundle reorganisation following ligament deformation. The presence and location of fibrillin 2 in oxytalan fibres in ligament differs from the solely fibrillin 1-containing oxytalan fibres previously described in tendon and may demonstrate a fundamental difference between ligament and tendon.

Elastin-based materials

Elastin is a versatile elastic protein that dominates flexible tissues capable of recoil, and facilitates commensurate cell interactions in these tissues in all higher vertebrates. Elastin's persistence and insolubility hampered early efforts to construct versatile biomaterials. Subsequently the field has progressed substantially through the adapted use of solubilized elastin, elastin-based peptides and the increasing availability of recombinant forms of the natural soluble elastin precursor, tropoelastin. These interactions allow for the formation of a sophisticated range of biomaterial constructs and composites that benefit from elastin's physical properties of innate assembly and elasticity, and cell interactive properties as discussed in this tutorial review.

Cellular response to nanoscale elastin-like polypeptide polyelectrolyte multilayers

Ionic elastin-like polypeptide (ELP) conjugates are a new class of biocompatible, self-assembling biomaterials. ELPs composed of the repeat unit (GVGVP)(n) are derived from the primary sequence of mammalian elastin and produced in Escherichia coli. These biopolymers exhibit an inverse transition temperature that renders them extremely useful for applications in cell-sheet engineering. Cationic and anionic conjugates were synthesized by the chemical coupling of ELP to polyethyleneimine (PEI) and polyacrylic acid (PAA). The self-assembly of ELP-PEI and ELP-PAA using the layer-by-layer deposition of alternately charged polyelectrolytes is a simple, versatile technique to generate bioactive and biomimetic surfaces with the ability to modulate cell-substratum interactions. Our studies are focused on cellular response to self-assembled multilayers of ionic (GVGVP)(40) incorporated within the polymeric sequence H(2)N-MVSACRGPG-(GVGVP)(40)-WP-COOH. Angle-dependent XPS studies indicated a difference in the chemical composition at the surface ( approximately 10A below the surface) and subsurface regions. These studies provided additional insight into the growth of the nanoscale multilayer assembly as well as the chemical environment that the cells can sense. Overall, cellular response was enhanced on glass substrata coated with ELP conjugates compared with uncoated surfaces. We report significant differences in cell proliferation, focal adhesions and cytoskeletal organization as a function of the number of bilayers in each assembly. These multilayer assemblies have the potential to be successfully utilized in the rational design of coatings on biomaterials to elicit a desired cellular response.

Macromolecular biomaterials for scaffold-based vascular tissue engineering

Cardiovascular diseases are increasingly becoming the main cause of death all over the world, which has led to an increase in the economic and social burden of such diseases. Vascular tissue engineering (VTE) is providing a route towards interesting applications, mainly focussing on the in vitro, in vivo, or combined in vitro/in vivo regeneration of small-diameter blood vessels (<6 mm) for coronary or peripheral vascular substitutions. Although different approaches have been investigated in the past two decades to achieve this aim, the most common method uses a macromolecular-based structure to scaffold cells during the regeneration process. Therefore, the aim of this work is to comprehensively review macromolecular biomaterials that were designed, developed, fabricated, and tested for scaffolding VTE. In an effort to provide a comprehensive overview, this review will mainly focus on the mechanical properties of the construct and its biological performance that results from the scaffold colonization during cell growth.

Negative regulation of monocyte adhesion to arterial elastic laminae by signal regulatory protein alpha and Src homology 2 domain-containing protein-tyrosine phosphatase-1

Elastic laminae are extracellular matrix constituents that not only contribute to the stability and elasticity of arteries but also play a role in regulating arterial morphogenesis and pathogenesis. We demonstrate here that an important function of arterial elastic laminae is to prevent monocyte adhesion, which is mediated by the inhibitory receptor signal regulatory protein (SIRP) alpha and Src homology 2 domain-containing protein-tyrosine phosphatase (SHP)-1. In a matrix-based arterial reconstruction model in vivo, elastic laminae were resistant to leukocyte adhesion and transmigration compared with the collagen-dominant arterial adventitia. The density of leukocytes within the elastic lamina-dominant media was about 58-70-fold lower than that within the adventitia from 1 to 30 days. An in vitro assay confirmed the inhibitory effect of elastic laminae on monocyte adhesion. The exposure of monocytes to elastic laminae induced activation of SIRP alpha, which in turn activated SHP-1. Elastic lamina degradation peptides extracted from arterial specimens could also activate SIRP alpha and SHP-1. The knockdown of SIRP alpha and SHP-1 by specific small interfering RNA diminished the inhibitory effect of elastic laminae, resulting in a significant increase in monocyte adhesion. These observations suggest that SIRP alpha and SHP-1 potentially mediate the inhibitory effect of elastic laminae on monocyte adhesion.

Neointima formation on vascular elastic laminae and collagen matrices scaffolds implanted in the rat aortae

Synthetic polymers, including polytetrafluoroethylene and Dacron, and biomatrix proteins, including collagen and fibrin, have been used for the construction of vascular substitutes. However, these materials induce inflammatory reactions, contributing to thrombosis, smooth muscle cell (SMC) proliferation, and neointima formation, processes leading to the failure of vascular substitutes. Thus, a pressing issue in vascular reconstruction is to construct vascular substitutes with surface materials that are inflammation-resistant. Here, we demonstrate that the vascular elastic laminae exhibit such a property. Aortic specimens from donor rats were treated with 0.1M NaOH for various times, resulting in elastic lamina-collagen matrix scaffolds with and without the basal lamina. Matrix scaffolds were implanted into the host aorta with three different surface materials, including the elastic lamina, basal lamina, and adventitial collagen, and observed for leukocyte adhesion, endothelial migration, cell proliferation, and neointimal formation on these surfaces. It was found that the elastic lamina was associated with significantly lower leukocyte adhesion, BrdU incorporation, and neointima formation than the basal lamina and adventitial collagen, while the migration of endothelial cells was comparable on all three surfaces. The adventitial collagen matrix was associated with leukocyte infiltration from blood and subsequent SMC migration from the host aorta, whereas the elastic laminae were resistant to such processes. The morphology of the implanted elastic laminae appeared normal at all times. These observations suggest that the vascular elastic laminae exhibit inflammation-resistant properties and inhibit SMC mitogenic activities compared with collagen-containing matrices and may be considered a potential surface material for vascular reconstruction.

Effect of coacervated alpha-elastin on proliferation of vascular smooth muscle and endothelial cells

The arterial wall injury associated with arterial graft implantation causes smooth muscle cells (SMCs) in the media to migrate and proliferate in the intima at the graft-artery junction resulting in anastomotic intimal hyperplasia (AIH). An important step in developing a small-diameter prosthesis may be to stimulate endothelialization and thereby inhibit AIH. In this study, we investigated the effect of coacervated and crosslinked alpha-elastin on proliferation of SMCs and endothelial cells (ECs) in vitro. Coacervation is an important step in the conversion of proelastin to make an elastin fiber in vivo. SMCs and ECs were prepared from porcine aortic media and endothelium, respectively. SMCs and ECs (three to five passages, 4 x 10[4] cells/well) were seeded onto 12 well plates, coated and crosslinked with 0 or 10 mg/mL of coacervated alpha-elastin. After the 1st, 2nd, or 3rd day of cultivation, proliferation was assayed by scintillation counting of [3H]-thymidine incorporation. For the 4th day only, 0, 0.1, 1, 10 mg/mL concentration of coacervated alpha-elastin was coated and crosslinked. SMC proliferation (1st, 2nd day: p<0.005; 3rd, 4th day: p<0.0001) was significantly inhibited over time and dose dependently, eg, 0.1 mg/mL (45.7+/-2.3%: % of control p<0.005), 1 mg/mL (5.9+/-0.7%, p<0.0005), 10 mg/mL (2.8+/-0.4%, p<0.0005). EC proliferation was inhibited over time by 10 mg/mL of coacervated alpha-elastin (2nd, 3rd day: p<0.005; 4th day: p<0.0001), but proliferation (132.8+/-9.9%: % of control p=NS) was stimulated by 0.1 mg/mL of coacervated alpha-elastin. These results suggest that coating and crosslinking a coacervated alpha-elastin into the structure of arterial prosthesis may inhibit AIH and stimulate endothelialization.