Elastogenic effects of exogenous hyaluronan oligosaccharides on vascular smooth muscle cells

Elastogenesis in Focus: Navigating Elastic Fibers Synthesis for Advanced Dermal Biomaterial Formulation

Elastin, a fibrous extracellular matrix (ECM) protein, is the main component of elastic fibers that are involved in tissues' elasticity and resilience, enabling them to undergo reversible extensibility and to endure repetitive mechanical stress. After wounding, it is challenging to regenerate elastic fibers and biomaterials developed thus far have struggled to induce its biosynthesis. This review provides a comprehensive summary of elastic fibers synthesis at the cellular level and its implications for biomaterial formulation, with a particular focus on dermal substitutes. The review delves into the intricate process of elastogenesis by cells and investigates potential triggers for elastogenesis encompassing elastin-related compounds, ECM components, and other molecules for their potential role in inducing elastin formation. Understanding of the elastogenic processes is essential for developing biomaterials that trigger not only the synthesis of the elastin protein, but also the formation of a functional and branched elastic fiber network.

Deletion of type VIII collagen reduces blood pressure, increases carotid artery functional distensibility and promotes elastin deposition

Arterial stiffening is a significant predictor of cardiovascular disease development and mortality. In elastic arteries, stiffening refers to the loss and fragmentation of elastic fibers, with a progressive increase in collagen fibers. Type VIII collagen (Col-8) is highly expressed developmentally, and then once again dramatically upregulated in aged and diseased vessels characterized by arterial stiffening. Yet its biophysical impact on the vessel wall remains unknown. The purpose of this study was to test the hypothesis that Col-8 functions as a matrix scaffold to maintain vessel integrity during extracellular matrix (ECM) development. These changes are predicted to persist into the adult vasculature, and we have tested this in our investigation. Through our in vivo and in vitro studies, we have determined a novel interaction between Col-8 and elastin. Mice deficient in Col-8 (Col8^-/-) had reduced baseline blood pressure and increased arterial compliance, indicating an enhanced Windkessel effect in conducting arteries. Differences in both the ECM composition and VSMC activity resulted in Col8^-/- carotid arteries that displayed increased crosslinked elastin and functional distensibility, but enhanced catecholamine-induced VSMC contractility. In vitro studies revealed that the absence of Col-8 dramatically increased tropoelastin mRNA and elastic fiber deposition in the ECM, which was decreased with exogenous Col-8 treatment. These findings suggest a causative role for Col-8 in reducing mRNA levels of tropoelastin and the presence of elastic fibers in the matrix. Moreover, we also found that Col-8 and elastin have opposing effects on VSMC phenotype, the former promoting a synthetic phenotype, whereas the latter confers quiescence. These studies further our understanding of Col-8 function and open a promising new area of investigation related to elastin biology.

Nanoparticle-Assisted Diagnosis and Treatment for Abdominal Aortic Aneurysm

An abdominal aortic aneurysm (AAA) is a localized dilatation of the aorta related to the regional weakening of the wall structure, resulting in substantial morbidity and mortality with the aortic ruptures as complications. Ruptured AAA is a dramatic catastrophe, and aortic emergencies constitute one of the leading causes of acute death in older adults. AAA management has been centered on surgical repair of larger aneurysms to mitigate the risks of rupture, and curative early diagnosis and effective pharmacological treatments for this condition are still lacking. Nanoscience provided a possibility of more targeted imaging and drug delivery system. Multifunctional nanoparticles (NPs) may be modified with ligands or biomembranes to target agents' delivery to the lesion site, thus reducing systemic toxicity. Furthermore, NPs can improve drug solubility, circulation time, bioavailability, and efficacy after systemic administration. The varied judiciously engineered nano-biomaterials can exist stably in the blood vessels for a long time without being taken up by cells. Here, in this review, we focused on the NP application in the imaging and treatment of AAA. We hope to make an overview of NP-assisted diagnoses and therapy in AAA and discussed the potential of NP-assisted treatment.

Quantitative Morphometry of Elastic Fibers in Pelvic Organ Prolapse

Pelvic organ prolapse (POP) is common among older women who have delivered children vaginally. While the pathophysiology is not fully delineated, POP can occur in part from insufficient repair of disrupted elastic matrix fibers. Quantification of structural changes to elastic fibers has not been described previously for POP. The goal of this paper is to present a validated technique for morphometric analysis of elastic fibers in vaginal tissue cultures from lysyl oxidase like-1 knock out (LOXL1 KO) mice with POP. The effect of LOXL1 KO, effect of POP, effect of culture, and effect of elastogenic treatment on the changes in elastin fiber characteristics were tested using vaginal tissues from wild type multiparous (WT), LOXL1 KO multiparous prolapsed (POP) and LOXL1 KO multiparous non-prolapsed (NP) mice. Our results show significantly higher mean aspect ratio, maximum diameter and perimeter length in POP compared to NP after 3 weeks of tissue culture. Further, treatment of POP tissues in culture with growth factors with previously documented elastogenic effects caused a significant increase in the mean area and perimeter length of elastic fibers. This technique thus appears to be useful in quantifying structural changes and can be used to assess the pathophysiology of POP and the effect of elastogenic treatments with potential for POP.

Recent progress on nanoparticles for targeted aneurysm treatment and imaging

An abdominal aortic aneurysm (AAA) is a localized dilatation of the aorta that plagues millions. Its rupture incurs high mortality rates (~80-90%), pressing an urgent need for therapeutic methods to prevent this deadly outcome. Judiciously designed nanoparticles (NPs) have displayed a unique potential to fulfill this need. Aneurysms feature excessive inflammation and extracellular matrix (ECM) degradation. As such, typically inflammatory cells and exposed ECM proteins have been targeted with NPs for therapeutic, diagnostic, or theranostic purposes in experimental models. NPs have been used not only for encapsulation and delivery of drugs and biomolecules in preclinical tests, but also for enhanced imaging to monitor aneurysm progression in patients. Moreover, they can be readily modified with various molecules to improve lesion targeting, detectability, biocompatibility, and circulation time. This review updates on the progress, limitations, and prospects of NP applications in the context of AAA.

Intratumoral fate of functional nanoparticles in response to microenvironment factor: Implications on cancer diagnosis and therapy

The extraordinary growth and progression of tumor require enormous nutrient and energy. Unregulated behaviors of cancer cell progressing and persistently change of tumor microenvironment (TME) which acts as the soil for cancer growth and metastasis are the ubiquitous features. The tumor microenvironment exhibits some unique features which differ with the normal tissues. While the nanoparticles get through the blood vessel leakage, they encounter immediately and interact directly with these microenvironment factors. These factors may inhibit the diffusion of nanoparticles from penetrating through the tumor, or induce the dissociation of nanoparticles. Different nanoparticles encountered with different intratumoral microenvironment factors end up in different way. Therefore, in this review, we first briefly introduced the formations, distributions, features of some intratumoral microenvironment, and their effects on the tumor progression. They include extracellular matrix (ECM), matrix metalloproteinases (MMPs), acidic/hypoxia environment, redox environment, and tumor associated macrophages (TAMs). We then exemplified how these factors interact with nanoparticles and emphasized the potentials and challenges of nanoparticle-based strategies facing in enhancing intratumoral penetration and tumor microenvironment remodeling. We hope to give a simple understanding of the interaction between these microenvironment factors and the nanoparticles, thus, favors the designing and constructing of more ideal functional nanoparticles.

Temporal changes in peritoneal cell phenotype and neoelastic matrix induction with hyaluronan oligomers and TGF-β1 after implantation of engineered conduits

The neoassembly and maturation of elastic matrix is an important challenge for engineering small-diameter grafts for patients with peripheral artery disease. We have previously shown that hyaluronan oligomers and transforming growth factor-β (elastogenic factors or EFs) promote elastogenesis in smooth muscle cell (SMC) culture. However, their combined effects on macrophages and inflammatory cells in vivo are unknown. This information is needed to use the body (e.g., peritoneal cavity) as an "in vivo bioreactor" to recruit autologous cells to implanted EF-functionalized scaffolds. In this study, we determined if peritoneal fluid cells respond to EFs like smooth muscle cells and if these responses differ between cells sourced during different stages of inflammation triggered by scaffold implantation. Electrospun poly(ε-caprolactone)/collagen conduits were implanted in the peritoneal cavity prior to peritoneal fluid collection at 3-42 days postimplantation. Cells from the fluid were cultured in vitro with and without EFs to determine their response. Their phenotype/behaviour was assessed with a DNA assay, quantitative real-time PCR, and immunofluorescence. The EFs reduced peritoneal cell proliferation, maintained cell contractility, and unexpectedly did not exhibit proelastic effects, which we attributed to differences in cell density. We found the greatest elastin deposition in regions containing a high cell density. Further, we found that cells isolated from the peritoneal cavity at longer times after conduit implantation responded better to the EFs and exhibited more CD31 expression than cells at an earlier time point. Overall, this study provides information about the potential use of EFs in vivo and can guide the design of future tissue-engineered vascular grafts.

Mechanistic understanding of nanoparticles' interactions with extracellular matrix: the cell and immune system

Extracellular matrix (ECM) is an extraordinarily complex and unique meshwork composed of structural proteins and glycosaminoglycans. The ECM provides essential physical scaffolding for the cellular constituents, as well as contributes to crucial biochemical signaling. Importantly, ECM is an indispensable part of all biological barriers and substantially modulates the interchange of the nanotechnology products through these barriers. The interactions of the ECM with nanoparticles (NPs) depend on the morphological characteristics of intercellular matrix and on the physical characteristics of the NPs and may be either deleterious or beneficial. Importantly, an altered expression of ECM molecules ultimately affects all biological processes including inflammation. This review critically discusses the specific behavior of NPs that are within the ECM domain, and passing through the biological barriers. Furthermore, regenerative and toxicological aspects of nanomaterials are debated in terms of the immune cells-NPs interactions.

Highly aligned core-shell structured nanofibers for promoting phenotypic expression of vSMCs for vascular regeneration

This study was designed to assess the efficacy of hyaluronan (HA) functionalized well-aligned nanofibers of poly-l-lactic acid (PLLA) in modulating the phenotypic expression of vascular smooth muscle cells (vSMCs) for blood vessel regeneration. Highly aligned HA/PLLA nanofibers in core-shell structure were prepared using a novel stable jet electrospinning approach. Formation of a thin HA-coating layer atop each PLLA nanofiber surface endowed the uni-directionally oriented fibrous mats with increased anisotropic wettability and mechanical compliance. The HA/PLLA nanofibers significantly promoted vSMC to elongation, orientation, and proliferation, and also up-regulated the expression of contractile genes/proteins (e.g., α-SMA, SM-MHC) as well as the synthesis of elastin. Six weeks of in vivo scaffold replacement of rabbit carotid arteries showed that vascular conduits made of circumferentially aligned HA/PLLA nanofibers could maintain patency and promoted oriented vSMC regeneration, lumen endothelialization, and capillary formation. This study demonstrated the synergistic effects of nanotopographical and biochemical cues in one biomimetic scaffold design for efficacious vascular regeneration.

Collagen Matrix Remodeling in Stented Pulmonary Arteries after Transapical Heart Valve Replacement

The use of valved stents for minimally invasive replacement of semilunar heart valves is expected to change the extracellular matrix and mechanical function of the native artery and may thus impair long-term functionality of the implant. Here we investigate the impact of the stent on matrix remodeling of the pulmonary artery in a sheep model, focusing on matrix composition and collagen (re)orientation of the host tissue. Ovine native pulmonary arteries were harvested 8 (n = 2), 16 (n = 4) and 24 (n = 2) weeks after transapical implantation of self-expandable stented heart valves. Second harmonic generation (SHG) microscopy was used to assess the collagen (re)orientation of fresh tissue samples. The collagen and elastin content was quantified using biochemical assays. SHG microscopy revealed regional differences in collagen organization in all explants. In the adventitial layer of the arterial wall far distal to the stent (considered as the control tissue), we observed wavy collagen fibers oriented in the circumferential direction. These circumferential fibers were more straightened in the adventitial layer located behind the stent. On the luminal side of the wall behind the stent, collagen fibers were aligned along the stent struts and randomly oriented between the struts. Immediately distal to the stent, however, fibers on both the luminal and the adventitial side of the wall were oriented in the axial direction, demonstrating the stent impact on the collagen structure of surrounding arterial tissues. Collagen orientation patterns did not change with implantation time, and biochemical analyses showed no changes in the trend of collagen and elastin content with implantation time or location of the vascular wall. We hypothesize that the collagen fibers on the adventitial side of the arterial wall and behind the stent straighten in response to the arterial stretch caused by oversizing of the stent. However, the collagen organization on the luminal side suggests that stent-induced remodeling is dominated by contact guidance.

In vitro elastogenesis: instructing human vascular smooth muscle cells to generate an elastic fiber-containing extracellular matrix scaffold

Elastic fibers are essential for the proper function of organs including cardiovascular tissues such as heart valves and blood vessels. Although (tropo)elastin production in a tissue-engineered construct has previously been described, the assembly to functional elastic fibers in vitro using human cells has been highly challenging. In the present study, we seeded primary isolated human vascular smooth muscle cells (VSMCs) onto 3D electrospun scaffolds and exposed them to defined laminar shear stress using a customized bioreactor system. Increased elastin expression followed by elastin deposition onto the electrospun scaffolds, as well as on newly formed fibers, was observed after six days. Most interestingly, we identified the successful deposition of elastogenesis-associated proteins, including fibrillin-1 and -2, fibulin-4 and -5, fibronectin, elastin microfibril interface located protein 1 (EMILIN-1) and lysyl oxidase (LOX) within our engineered constructs. Ultrastructural analyses revealed a developing extracellular matrix (ECM) similar to native human fetal tissue, which is composed of collagens, microfibrils and elastin. To conclude, the combination of a novel dynamic flow bioreactor and an electrospun hybrid polymer scaffold allowed the production and assembly of an elastic fiber-containing ECM.

Nitric oxide stimulates matrix synthesis and deposition by adult human aortic smooth muscle cells within three-dimensional cocultures

Vascular diseases are characterized by the over-proliferation and migration of aortic smooth muscle cells (SMCs), and degradation of extracellular matrix (ECM) within the vessel wall, leading to compromise in cell-cell and cell-matrix signaling pathways. Tissue engineering approaches to regulate SMC over-proliferation and enhance healthy ECM synthesis showed promise, but resulted in low crosslinking efficiency. Here, we report the benefits of exogenous nitric oxide (NO) cues, delivered from S-Nitrosoglutathione (GSNO), to cell proliferation and matrix deposition by adult human aortic SMCs (HA-SMCs) within three-dimensional (3D) biomimetic cocultures. A coculture platform with two adjacent, permeable 3D culture chambers was developed to enable paracrine signaling between vascular cells. HA-SMCs were cultured in these chambers within collagen hydrogels, either alone or in the presence of human aortic endothelial cells (HA-ECs) cocultures, and exogenously supplemented with varying GSNO dosages (0-100 nM) for 21 days. Results showed that EC cocultures stimulated SMC proliferation within GSNO-free cultures. With increasing GSNO concentration, HA-SMC proliferation decreased in the presence or absence of EC cocultures, while HA-EC proliferation increased. GSNO (100 nM) significantly enhanced the protein amounts synthesized by HA-SMCs, in the presence or absence of EC cocultures, while lower dosages (1-10 nM) offered marginal benefits. Multi-fold increases in the synthesis and deposition of elastin, glycosaminoglycans, hyaluronic acid, and lysyl oxidase crosslinking enzyme (LOX) were noted at higher GSNO dosages, and coculturing with ECs significantly furthered these trends. Similar increases in TIMP-1 and MMP-9 levels were noted within cocultures with increasing GSNO dosages. Such increases in matrix synthesis correlated with NO-stimulated increases in endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) expression within EC and SMC cultures, respectively. Results attest to the benefits of delivering NO cues to suppress SMC proliferation and promote robust ECM synthesis and deposition by adult human SMCs, with significant applications in tissue engineering, biomaterial scaffold development, and drug delivery.

Bioengineered vascular scaffolds: the state of the art

To date, there is increasing clinical need for vascular substitutes due to accidents, malformations, and ischemic diseases. Over the years, many approaches have been developed to solve this problem, starting from autologous native vessels to artificial vascular grafts; unfortunately, none of these have provided the perfect vascular substitute. All have been burdened by various complications, including infection, thrombogenicity, calcification, foreign body reaction, lack of growth potential, late stenosis and occlusion from intimal hyperplasia, and pseudoaneurysm formation. In the last few years, vascular tissue engineering has emerged as one of the most promising approaches for producing mechanically competent vascular substitutes. Nanotechnologies have contributed their part, allowing extraordinarily biostable and biocompatible materials to be developed. Specifically, the use of electrospinning to manufacture conduits able to guarantee a stable flow of biological fluids and guide the formation of a new vessel has revolutionized the concept of the vascular substitute. The electrospinning technique allows extracellular matrix (ECM) to be mimicked with high fidelity, reproducing its porosity and complexity, and providing an environment suitable for cell growth. In the future, a better knowledge of ECM and the manufacture of new materials will allow us to "create" functional biological vessels - the base required to develop organ substitutes and eventually solve the problem of organ failure.

Spatiotemporal mapping of matrix remodelling and evidence of in situ elastogenesis in experimental abdominal aortic aneurysms

Spatiotemporal changes in the extracellular matrix (ECM) were studied within abdominal aortic aneurysms (AAAs) generated in rats via elastase infusion. At 7, 14 and 21 days post-induction, AAA tissues were divided into proximal, mid- and distal regions, based on their location relative to the renal arteries and the region of maximal aortic diameter. Wall thicknesses differed significantly between the AAA spatial regions, initially increasing due to positive matrix remodelling and then decreasing due to wall thinning and compaction of matrix as the disease progressed. Histological images analysed using custom segmentation tools indicated significant differences in ECM composition and structure vs healthy tissue, and in the extent and nature of matrix remodelling between the AAA spatial regions. Histology and immunofluorescence (IF) labelling provided evidence of neointimal AAA remodelling, characterized by presence of elastin-containing fibres. This remodelling was effected by smooth muscle α-actin-positive neointimal cells, which transmission electron microscopy (TEM) showed to differ morphologically from medial SMCs. TEM of the neointima further showed the presence of elongated deposits of amorphous elastin and the presence of nascent, but not mature, elastic fibres. These structures appeared to be deficient in at least one microfibrillar component, fibrillin-1, which is critical to mature elastic fibre assembly. The substantial production of elastin and elastic fibre-like structures that we observed in the AAA neointima, which was not observed elsewhere within AAA tissues, provides a unique opportunity to capitalize on this autoregenerative phenomenon and direct it from the standpoint of matrix organization towards restoring healthy aortic matrix structure, mechanics and function. Copyright © 2014 John Wiley & Sons, Ltd.

Expression of versican V3 by arterial smooth muscle cells alters tumor growth factor β (TGFβ)-, epidermal growth factor (EGF)-, and nuclear factor κB (NFκB)-dependent signaling pathways, creating a microenvironment that resists monocyte adhesion

Monocyte/macrophage accumulation plays a critical role during progression of cardiovascular diseases, such as atherosclerosis. Our previous studies demonstrated that retrovirally mediated expression of the versican V3 splice variant (V3) by arterial smooth muscle cells (ASMCs) decreases monocyte adhesion in vitro and macrophage accumulation in a model of lipid-induced neointimal formation in vivo. We now demonstrate that V3-expressing ASMCs resist monocyte adhesion by altering the composition of the microenvironment surrounding the cells by affecting multiple signaling pathways. Reduction of monocyte adhesion to V3-expressing ASMCs is due to the generation of an extracellular matrix enriched in elastic fibers and depleted in hyaluronan, and reduction of the proinflammatory cell surface vascular cell adhesion molecule 1 (VCAM1). Blocking these changes reverses the protective effect of V3 on monocyte adhesion. The enhanced elastogenesis induced by V3 expression is mediated by TGFβ signaling, whereas the reduction in hyaluronan cable formation induced by V3 expression is mediated by the blockade of epidermal growth factor receptor and NFκB activation pathways. In addition, expression of V3 by ASMCs induced a marked decrease in NFκB-responsive proinflammatory cell surface molecules that mediate monocyte adhesion, such as VCAM1. Overall, these results indicate that V3 expression by ASMCs creates a microenvironment resistant to monocyte adhesion via differentially regulating multiple signaling pathways.

Composition of intraperitoneally implanted electrospun conduits modulates cellular elastic matrix generation

Improving elastic matrix generation is critical to developing functional tissue engineered vascular grafts. Therefore, this study pursued a strategy to grow autologous tissue in vivo by recruiting potentially more elastogenic cells to conduits implanted within the peritoneal cavity. The goal was to determine the impacts of electrospun conduit composition and hyaluronan oligomer (HA-o) modification on the recruitment of peritoneal cells, and their phenotype and ability to synthesize elastic matrix. These responses were assessed as a function of conduit intra-peritoneal implantation time. This study showed that the blending of collagen with poly(ε-caprolactone) (PCL) promotes a faster wound healing response, as assessed by trends in expression of macrophage and smooth muscle cell (SMC) contractile markers and in matrix deposition, compared to the more chronic response for PCL alone. This result, along with the increase in elastic matrix production, demonstrates the benefits of incorporating as little as 25% w/w collagen into the conduit. In addition, PCR analysis demonstrated the challenges in differentiating between a myofibroblast and an SMC using traditional phenotypic markers. Finally, the impact of the tethered HA-o is limited within the inflammatory environment, unlike the significant response found previously in vitro. In conclusion, these results demonstrate the importance of both careful control of implanted scaffold composition and the development of appropriate delivery methods for HA-o.

Nanoparticles for localized delivery of hyaluronan oligomers towards regenerative repair of elastic matrix

Abdominal aortic aneurysms (AAAs) are rupture-prone progressive dilations of the infrarenal aorta due to a loss of elastic matrix that lead to weakening of the aortic wall. Therapies to coax biomimetic regenerative repair of the elastic matrix by resident, diseased vascular cells may thus be useful to slow, arrest or regress AAA growth. Hyaluronan oligomers (HA-o) have been shown to induce elastic matrix synthesis by healthy and aneurysmal rat aortic smooth muscle cells (SMCs) in vitro but only via exogenous dosing, which potentially has side-effects and limitations to in vivo delivery towards therapy. In this paper, we describe the development of HA-o loaded poly(lactide-co-glycolide) nanoparticles (NPs) for targeted, controlled and sustained delivery of HA-o towards the elastogenic induction of aneurysmal rat aortic SMCs. These NPs were able to deliver HA-o over an extended period (>30 days) at previously determined elastogenic doses (0.2-20 μg ml(-1)). HA-o released from the NPs led to dose-dependent increases in elastic matrix synthesis, and the recruitment and activity of lysyl oxidase, the enzyme which cross-links elastin precursor molecules into mature fibers/matrix. Therefore, we were able to successfully develop a nanoparticle-based system for controlled and sustained HA-o delivery for the in vitro elastogenic induction of aneurysmal rat aortic smooth muscle cells.

A cytokine axis regulates elastin formation and degradation

Underlying the dynamic regulation of tropoelastin expression and elastin formation in development and disease are transcriptional and post-transcriptional mechanisms that have been the focus of much research. Of particular importance is the cytokine-governed elastin regulatory axis in which the pro-elastogenic activities of transforming growth factor β-1 (TGFβ1) and insulin-like growth factor-I (IGF-I) are opposed by anti-elastogenic activities of basic fibroblast growth factor (bFGF/FGF-2), heparin-binding epidermal growth factor-like growth factor (HB-EGF), EGF, PDGF-BB, TGFα, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and noncanonical TGFβ1 signaling. A key mechanistic feature of the regulatory axis is that cytokines influence elastin formation through effects on the cell cycle involving control of cyclin-cyclin dependent kinase complexes and activation of the Ras/MEK/ERK signaling pathway. In this article we provide an overview of the major cytokines/growth factors that modulate elastogenesis and describe the underlying molecular mechanisms for their action on elastin production.

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.

Induced Regenerative Elastic Matrix Repair in LOXL1 Knockout Mouse Cell Cultures: Towards Potential therapy for Pelvic Organ Prolapse

Impaired elastic matrix remodeling occurs in reproductive tissues after vaginal delivery. This has been linked to development of pelvic organ prolapse (POP) for which there currently is no pharmacologic therapy. Hyaluronan oligomers and transforming growth factor beta 1 (termed elastogenic factors, EFs) have been shown to significantly enhance tropoelastin synthesis, elastic fiber assembly, and crosslinking by adult vascular smooth muscle cells (SMCs). The goal of this study was to ascertain if these factors similarly improve the quantity and quality of elastic matrix deposition by vaginal SMCs (VSMCs) isolated from lysyl oxidase like-1 knock out (LOXL1 KO) mouse model of POP. Cells isolated from whole vagina of a LOXL1 KO mouse (multiparous, stage 3 prolapse) were cultured and identified as SMCs by their expression of various SMC markers. Passage 2 vaginal SMCs (VSMCs; 3×10⁴/10 cm²) were cultured for 21 days with EFs. Cell layers and spent medium aliquots were assessed for elastin content and quality. EF-treated VSMCs proliferated at a similar rate to untreated controls but synthesized more total elastin primarily in the form of soluble matrix elastin. Elastin mRNA was also increased compared to controls. The elastic matrix was significantly denser in EF-treated cultures, which was composed of more mature, non-interrupted elastic fibers that were absent in controls. The results are promising towards development of a therapy to enhance regenerative elastic matrix repair in post-partum female pelvic floor tissues.

Tissue engineering and regenerative strategies to replicate biocomplexity of vascular elastic matrix assembly

Cardiovascular tissues exhibit architecturally complex extracellular matrices, of which the elastic matrix forms a major component. The elastic matrix critically maintains native structural configurations of vascular tissues, determines their ability to recoil after stretch, and regulates cell signaling pathways involved in morphogenesis, injury response, and inflammation via biomechanical transduction. The ability to tissue engineer vascular replacements that incorporate elastic matrix superstructures unique to cardiac and vascular tissues is thus important to maintaining vascular homeostasis. However, the vascular elastic matrix is particularly difficult to tissue engineer due to the inherently poor ability of adult vascular cells to synthesize elastin precursors and organize them into mature structures in a manner that replicates the biocomplexity of elastic matrix assembly during development. This review discusses current tissue engineering materials (e.g., growth factors and scaffolds) and methods (e.g., dynamic stretch and contact guidance) used to promote cellular synthesis and assembly of elastic matrix superstructures, and the limitations of these approaches when applied to smooth muscle cells, the primary elastin-generating cell type in vascular tissues. The potential application of these methods for in situ regeneration of disrupted elastic matrix at sites of proteolytic vascular disease (e.g., abdominal aortic aneurysms) is also discussed. Finally, the review describes the potential utility of alternative cell types to elastic tissue engineering and regenerative matrix repair. Future progress in the field is contingent on developing a thorough understanding of developmental elastogenesis and then mimicking the spatiotemporal changes in the cellular microenvironment that occur during that phase. This will enable us to tissue engineer clinically applicable elastic vascular tissue replacements and to develop elastogenic therapies to restore homeostasis in de-elasticized vessels.

Rapid Self-Assembly of Tubular Arterial Media Layer from Smooth Muscle Cells in Transient Fibrin Gel

BACKGROUND: Tissue engineered blood vessels could address the large clinical need for small caliber vascular grafts. Self-assembly approaches that employ transient scaffolds to form tissues from only cells and secreted matrix could form completely autologous vascular grafts that rapidly remodel and integrate with host tissue in vivo. The objective of this study was to develop a simple and rapid method to self-assemble vascular cells into vascular grafts. HYPOTHESIS: We hypothesized that entrapment in rapidly degrading fibrin gels could facilitate self-assembly of vascular smooth muscle cells into a tubular tissue comprised mainly of SMCs and secreted matrix. METHODS: Baboon SMCs were entrapped in fibrin around a silicone tube and cultured for 14 days without fibrinolysis inhibitor. Spontaneous delamination from the inner tube allowed for simple isolation of constructs with forceps. RESULTS: Engineered tissues are tubular, handleable, and highly cellular, with substantial collagen deposition. Fibrin is largely degraded within 14 days. Tensile elastic modulus of ring segments is 36.2 kPa and 1.60 MPa for the toe and heel regions of the stress-strain relation, respectively. CONCLUSION: Fibrin entrapment without fibrinolysis inhibitor can facilitate rapid self-assembly of SMCs into tubular tissues. Future work will focus on mechanical conditioning and co-culture with vascular endothelial cells to improve mechanical strength and impart antithrombogenicity.

Aligned electrospun scaffolds and elastogenic factors for vascular cell-mediated elastic matrix assembly

Strategies to enhance the production of organized elastic matrix by smooth muscle cells (SMCs) are critical in engineering functional vascular conduits. Therefore, the goal of this study was to determine the effect of different surfaces, i.e. random and aligned electrospun poly(ε-caprolactone) meshes and two-dimensional (2D) controls, and exogenous elastogenic factors on the cultured rat aortic SMC phenotype and production of extracellular matrix. This study demonstrated that aligned electrospun fibres guide cell alignment, induce a more elongated cell morphology and promote a more synthetic phenotype. Importantly, these cells produced greater amounts of elastin-rich matrix per cell on the electrospun scaffolds. In addition, exogenous elastogenic factors severely limited rat aortic smooth muscle cells (RASMCs) proliferation and promoted a more synthetic SMC phenotype on electrospun meshes, but they had less effect on 2D controls. Finally, the elastogenic factors induced the SMCs to generate more matrix collagen and elastin on a per cell basis. Together, these results demonstrate the elastogenic benefits of electrospun meshes.

Induced elastic matrix deposition within three-dimensional collagen scaffolds

The structural stability of a cyclically distending elastic artery and the healthy functioning of vascular smooth muscle cells (SMCs) within are maintained by the presence of an intact elastic matrix and its principal protein, elastin. The accelerated degradation of the elastic matrix, which occurs in several vascular diseases, coupled with the poor ability of adult SMCs to regenerate lost elastin, can therefore adversely impact vascular homeostasis. Similarly, efforts to tissue engineer elastic matrix structures are constrained by our inability to induce adult cells to synthesize tropoelastin precursors and to crosslink them into architectural mimics of native elastic matrices, especially within engineered constructs where SMCs/fibroblasts primarily deposit collagen in abundance. In this study, we have shown that transforming growth factor-beta1 (TGF-β1) and hyaluronan oligomers (HA-o) synergistically enhance elastic matrix deposition by adult rat aortic SMCs (RASMCs) seeded within nonelastogenic, statically loaded three-dimensional gels, composed of nonelastogenic type-I collagen. While there was no substantial increase in production of tropoelastin within experimental cases compared to the nonadditive control cultures over 3 weeks, we observed significant increases in matrix elastin deposition; soluble matrix elastin in constructs that received the lowest doses of TGF-β1 with respective doses of HA-o, and insoluble matrix at the highest doses that corresponded with elevated lysyl-oxidase protein quantities. However, despite elastogenic induction, overall matrix yields remained poor in all experimental cases. At all provided doses, the factors reduced the production of matrix metalloproteinases (MMP)-9, especially the active enzyme, though MMP-2 levels were lowered only in constructs cultured with the higher doses of TGF-β1. Immuno-fluorescence showed elastic fibers within the collagen constructs to be discontinuous, except at the edges of the constructs. Von Kossa staining revealed no calcific deposits in any of the cases. This study confirms the benefits of utilizing TGF-β1 and HA-o in inducing matrix elastin synthesis by adult RASMCs over nonadditive controls, within a collagenous environment, that is not inherently conducive to elastogenesis.

The effects of covalently immobilized hyaluronic acid substrates on the adhesion, expansion, and differentiation of embryonic stem cells for in vitro tissue engineering

We investigated the in vitro effects of the molecular weight (MW) of hyaluronic acid (HA) on the maintenance of the pluripotency and proliferation of murine embryonic stem (ES) cells. High (1000 kDa) or low (4-8 kDa) MW HA was derivatized using an ultraviolet-reactive compound, 4-azidoaniline, and the derivative was immobilized onto cell culture cover slips. Murine ES cells were cultured on these HA surfaces for 5 days. High-MW HA interacted with murine ES cells via CD44, whereas low-MW HA interacted with these cells mostly via CD168. ES cells grown on both high- and low-MW HA appeared undifferentiated after 3 days. However, more cells adhered, proliferated, and exhibited greater amounts of phospho-p42/44 mitogen-activated-protein-kinase on low- compared with high-MW HA. Expression of Oct-3/4 and phosphorylation of STAT3 were enhanced by ES cells on low-MW HA, not on high-MW HA. After release from HA, cells cultured on low-MW HA in the presence of differentiating medium showed enhanced expression of α-SMA or CD31 compared with cells cultured on high-MW HA. It was concluded that low-MW HA substrates were effective in maintaining murine ES cells in a viable and undifferentiated state, which favors their use in the propagation of ES cells for tissue engineering.

Evaluating smooth muscle cells from CaCl2-induced rat aortal expansions as a surrogate culture model for study of elastogenic induction of human aneurysmal cells

Regression of abdominal aortic aneurysms (AAAs) via regeneration of new elastic matrix is constrained by poor elastin synthesis by adult vascular cells and absence of methods to stimulate the same. We recently showed hyaluronan oligomers (HA-o) and TGF-β1 (termed elastogenic factors) to enhance elastin synthesis and matrix formation by healthy rat aortic smooth muscle cells (RASMCs). We also determined that these factors could likewise elastogenically induce aneurysmal RASMCs isolated from periadventitial CaCl(2)-injury induced rat AAAs (aRASMCs). However, the factor doses should be increased for these diseased cell types, as even when induced, elastic matrix amounts are roughly one order of magnitude lower than those produced by healthy RASMCs. We presently investigate the dose-specific elastogenic effects of HA-o (0-20  μg/mL) and TGF-β1 (0-10  ng/mL) factors on aRASMCs and compare their phenotype and elastogenic responses to those of human AAA-derived SMCs (aHASMCs); we seek to determine whether aRASMCs are appropriate surrogate cell types to study in the context of inducing elastic matrix regeneration within human AAAs. The periadventitial CaCl(2)-injury model of AAAs exhibits many of the pathological characteristics of human AAAs, including similarities in terms of decreased SMC contractile activity, enhanced proliferation, and reduced elastogenic capacity of aneurysmal SMCs (relative to healthy SMCs) when isolated and expanded in culture. Both aRASMCs and aHASMCs can be elastogenically stimulated by HA-o and TGF-β1 and show broadly similar trends in their dose-specific responses to these factors. However, compared with aHASMCs, aRASMCs appear to be far less elastogenically inducible. This may be due to differences in maturity of the AAAs studied, with the CaCl(2)-injury induced aortal expansion barely qualifying as an aneurysm and the human AAA representing a more well-developed condition. Further study of SMCs from stage-matched CaCl(2)-injury induced rat aortal expansions and human AAAs will be necessary to more rigorously evaluate their basal and induced elastogenic responses.

Agarose and polyacrylamide gel electrophoresis methods for molecular mass analysis of 5- to 500-kDa hyaluronan

Agarose and polyacrylamide gel electrophoresis systems for the molecular mass-dependent separation of hyaluronan (HA) in the size range of approximately 5-500 kDa were investigated. For agarose-based systems, the suitability of different agarose types, agarose concentrations, and buffer systems was determined. Using chemoenzymatically synthesized HA standards of low polydispersity, the molecular mass range was determined for each gel composition over which the relationship between HA mobility and logarithm of the molecular mass was linear. Excellent linear calibration was obtained for HA molecular mass as low as approximately 9 kDa in agarose gels. For higher resolution separation, and for extension to molecular masses as low as approximately 5 kDa, gradient polyacrylamide gels were superior. Densitometric scanning of stained gels allowed analysis of the range of molecular masses present in a sample as well as calculation of weight-average and number-average values. The methods were validated for polydisperse HA samples with viscosity-average molecular masses of 112, 59, 37, and 22 kDa at sample loads of 0.5 μg (for polyacrylamide) to 2.5 μg (for agarose). Use of the methods for electrophoretic mobility shift assays was demonstrated for binding of the HA-binding region of aggrecan (recombinant human aggrecan G1-IGD-G2 domains) to a 150-kDa HA standard.

Elastogenic inductability of smooth muscle cells from a rat model of late stage abdominal aortic aneurysms

Although abdominal aortic aneurysms (AAA) can be potentially stabilized by inhibiting inflammatory cell recruitment and their release of proteolytic enzymes, active AAA regression is not possible without regeneration of new elastic matrix structures. Unfortunately, postneonatal vascular smooth muscle cells (SMCs), healthy, and likely more so, diseased cells, poorly synthesize or remodel elastic fibers, impeding any effort directed at regenerative AAA treatment. Previously, we determined the eleastogenic benefits of oligomers (HA-o; 4-6 mers) of the glycosaminoglycan, hyaluronan (HA) and transforming growth factor-β1 (TGF-β1) to healthy SMCs. Since AAAs are often diagnosed only late in development when matrix disruption is severe, we now determine if elastogenic upregulation of SMCs from late-stage AAAs (>100% diameter increase) is possible. AAAs were induced by perfusion of rat infrarenal aortae with porcine pancreatic elastase. Elastic matrix degradation, vessel expansion (∼120%), inflammatory cell infiltration, and enhanced activity of matrix-metalloproteases (MMPs) 2 and 9 resulted, paralleling human AAAs. Aneurysmal SMCs (EaRASMCs) maintained a diseased phenotype in 2D cell culture and exhibited patterns of gene expression different from healthy rat aortic SMCs (RASMCs). Relative to passage-matched healthy RASMCs, unstimulated EaRASMCs produced far less tropoelastin and matrix elastin. Exogenous TGF-β and HA-o (termed "factors") significantly decreased EaRASMC proliferation and enhanced tropoelastin synthesis, though only at the highest provided dose combination (20 mg/mL of HA-o, 10 ng/mL of TGF-β); despite such enhancement, tropoelastin amounts were only ∼40% of amounts synthesized by healthy RASMC cultures. Differently, elastic matrix synthesis was enhanced beyond amounts synthesized by healthy RASMCs (112%), even at lower doses of factors (2 mg/mL of HA-o and 5 ng/mL of TGF-β). The factors also enhanced elastic fiber deposition over untreated EaRASMC cultures and restored several genes whose expression was altered in EaRASMC cultures back to levels expressed by healthy RASMCs. However, the activity of MMPs 2 and 9 generated by EaRASMC cultures was unaffected by the factors/factor dose. The study confirms that SMCs from advanced AAAs can be elastogenically induced, although much higher doses of elastogenic factors are required for induction relative to healthy SMCs. Also, the factors do not appear to inhibit MMP activity, vital to preserve existing elastic matrix structures that serve as nucleation sites for new elastic fiber deposition. Thus, to enhance net accumulation of newly regenerated elastic matrix, toward possibly regressing AAAs, codelivery of MMP inhibitors may be necessitated.

Impact of pre-existing elastic matrix on TGFβ1 and HA oligomer-induced regenerative elastin repair by rat aortic smooth muscle cells

Regenerating elastic matrices lost to disease (e.g. in aneurysms) is vital to re-establishing vascular homeostasis but is challenged by the poor elastogenicity of post-neonatal cells. We previously showed that exogenous hyaluronan oligomers (HA-o) and TGFβ1 synergistically enhance tropo- and matrix elastin deposition by healthy adult rat aortic SMCs (RASMCs). Towards treating aortic aneurysms (AAs), which exhibit cause- and site-specific heterogeneity in matrix content/structure and contain proteolytically-injured SMCs, we investigated the impact of pre-existing elastic matrix degeneration on elastogenic induction of injured RASMCs. Elastin-rich RASMC layers at 21 days of culture were treated with 0.15 U/ml (PPE15) and 0.75 U/ml (PPE75) porcine pancreatic elastase to degrade the elastic matrix variably, or left uninjured (control). One set of cultures was harvested at 21 days, before and after injury, to quantify viable cell count, matrix elastin loss. Other injured cell layers were cultured to 42 days with or without factors (0.2 µg/ml HA oligomers, 1 ng/ml TGFβ1). We showed that: (a) the ability of cultures to self-repair and regenerate elastic matrices following proteolysis is limited when elastolysis is severe; (b) HA oligomers and TGFβ1 elastogenically stimulate RASMCs in mildly-injured (i.e. PPE15) cultures to restore both elastic matrix amounts and elastic fibre deposition to levels in healthy cultures; and (c) in severely injured (i.e. PPE75) cultures, the factors stimulate matrix elastin synthesis and crosslinking, although not to control levels. The outcomes underscore the need to enhance elastogenic factor doses based on the severity of elastin loss. This study will help in customizing therapies for elastin regeneration within AAs, based on cause and location.

Three-dimensional topography of synthetic scaffolds induces elastin synthesis by human coronary artery smooth muscle cells

Due to the important structural and signaling roles of elastin in vascular stability, engineered human vascular tissues must incorporate elastin. However, despite considerable progress toward engineering of elastin-containing vascular tissues from animal cells, currently engineered vascular tissues using human cells largely lack elastin. In this study, we evaluated the effect of scaffold topography (two dimensional [2D] vs. three dimensional [3D]) on elastogenesis in adult human coronary artery smooth muscle cells (HCASMCs). We report that elastin gene expression by HCASMCs was increased by twofold after 4 days of culture in porous 3D polyurethane scaffolds. Transforming growth factor β1 (TGF-β1) further increased elastin gene expression in 3D cultures but not in 2D cultures. To evaluate if gene expression is translated into elastin synthesis, both 2D and 3D cultures were analyzed using Western blots. We show that only HCASMCs in 3D scaffolds produced elastin, suggesting that scaffold geometry itself is an important cue for elastogenesis. Moreover, TGF-β1 enhanced elastin synthesis in 3D, but had no effect on cells grown on 2D surfaces. TGF-β1, known to induce vascular smooth muscle cells (VSMC) differentiation, upregulated contractile VSMC marker proteins smooth muscle-α-actin and calponin in cells on 2D surfaces. Interestingly, in 3D scaffolds, TGF-β1 failed to upregulate these differentiation marker proteins for at least 7 days, but did so in cells cultured for 14 days, whereas elastin synthesis was not affected. To our knowledge this study is the first to successfully demonstrate that adult human VSMC can produce elastin when seeded on 3D scaffolds and to directly compare the effect of scaffold topography on elastin synthesis. Knowledge about the conditions required to regulate the phenotype of human VSMCs is paramount to engineer elastin-containing autologous human vascular substitutes.

Biocompatible, detachable, and free-standing polyelectrolyte multilayer films

Self-assembled polyelectrolyte multilayers have gained tremendous popularity over the past decade and have been incorporated in diverse applications. However, the fabrication of detachable and free-standing polyelectrolyte multilayers (PEMs) has proven to be difficult. We report the design of detachable, free-standing, and biocompatible PEMs comprised of hyaluronic acid (anionic PE) and chitosan (cationic PE). These PEMs can be detached from an underlying inert substrate without any postprocessing steps. Our approach enables the fabrication of detachable PEMs from a wide range of polyelectrolytes. Cross-linked PEMs exhibited greater than 95% weight retention when maintained in phosphate buffered saline at 37 °C over a seven day period. The PEM thickness was approximately 3 μm for dried films and increased 2-fold under hydration. A unique feature of the detachable, free-standing PEMs is their optical transparency in the 400-900 nm range under hydrated conditions. The Young's modulus of the cross-linked films ranged from 300-400 MPa, rendering these detachable free-standing multilayers ideal for biomaterial applications. BALB/c 3T3 fibroblasts adhered on the PEMs and colonized the entire surface over a six day period. The cellular responses, as well as the physical properties, demonstrate that the detachable PEM films exhibit tremendous potential for applications in biomaterials and tissue engineering.

Characterization of glycidyl methacrylate - crosslinked hyaluronan hydrogel scaffolds incorporating elastogenic hyaluronan oligomers

Prior studies on two-dimensional cell cultures suggest that hyaluronic acid (HA) stimulates cell-mediated regeneration of extracellular matrix structures, specifically those containing elastin, though such biologic effects are dependent on HA fragment size. Towards being able to regenerate three-dimensional (3-D) elastic tissue constructs, the present paper studies photo-crosslinked hydrogels containing glycidyl methacrylate (GM)-derivatized bio-inert high molecular weight (HMW) HA (1 × 10(6)Da) and a bioactive HA oligomer mixture (HA-o: MW ∼0.75 kDa). The mechanical (rheology, degradation) and physical (apparent crosslinking density, swelling ratio) properties of the gels varied as a function of incorporated HA oligomer content; however, overall, the mechanics of these hydrogels were too weak for vascular applications as stand-alone materials. Upon in vivo subcutaneous implantation, only a few inflammatory cells were evident around GM-HA gels, however their number increased as HA-o content within the gels increased, and the collagen I distribution was uniform. Smooth muscle cells (SMC) were encapsulated into GM hydrogels, and calcein acetoxymethyl detection revealed that the cells were able to endure twofold the level of UV exposure used to crosslink the gels. After 21 days of culture, SMC elastin production, measured by immunofluorescence quantification, showed HA-o to increase cellular deposition of elastic matrix twofold relative to HA-o-free GM-HA gels. These results demonstrate that cell response to HA/HA-o is not altered by their methacrylation and photo-crosslinking into a hydrogel, and that HA-o incorporation into cell-encapsulating hydrogel scaffolds can be useful for enhancing their production of elastic matrix structures in a 3-D space, important for regenerating elastic tissues.

Hydrostatic pressure independently increases elastin and collagen co-expression in small-diameter engineered arterial constructs

Prior studies have demonstrated that smooth muscle cell (SMC) proliferation, migration, and extracellular matrix production increase with hydrostatic pressure in vitro. We have engineered highly compliant small-diameter arterial constructs by culturing primary adult baboon arterial SMCs under pulsatile perfusion on tubular, porous, elastomeric scaffolds composed of poly(glycerol sebacate) (PGS). This study investigates the effect of hydrostatic pressure on the biological and mechanical properties of PGS-based engineered arterial constructs. Pressure was raised using a downstream needle valve during perfusion while preserving flow rate and pulsatility, and constructs were evaluated by pressure-diameter testing and biochemical assays for collagen and elastin. Pressurized constructs contained half as much insoluble elastin as baboon common carotid arteries but were significantly less compliant, while constructs cultured at low hydrostatic pressure contained one-third as much insoluble elastin as baboon carotids and were similar in compliance. Hydrostatic pressure significantly increased construct burst pressure, collagen and insoluble elastin content, and soluble elastin concentration in culture medium. All arteries and constructs exhibited elastic recovery during pressure cycling. Hydrostatic pressure did not appear to affect radial distribution of SMCs, collagens I and III, and elastin. These results provide insights into the control of engineered smooth muscle tissue properties using hydrostatic pressure.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

The design of in vitro liver sinusoid mimics using chitosan-hyaluronic acid polyelectrolyte multilayers

Interactions between hepatocytes and liver sinusoidal endothelial cells (LSECs) are essential for the development and maintenance of hepatic phenotypic functions. We report the assembly of three-dimensional liver sinusoidal mimics comprised of primary rat hepatocytes, LSECs, and an intermediate chitosan-hyaluronic acid polyelectrolyte multilayer (PEM). The height of the PEMs ranged from 30 to 55 nm and exhibited a shear modulus of approximately 100 kPa. Hepatocyte-PEM cellular constructs exhibited stable urea and albumin production over a 7-day period, and these values were either higher or similar to cells cultured in a collagen sandwich. This is of significance because the thickness of a collagen gel is approximately 1000-fold higher than the height of the chitosan-hyaluronic acid PEM. In the hepatocyte-PEM-LSEC liver-mimetic cellular constructs, LSEC phenotype was maintained, and these cultures exhibited stable urea and albumin production. CYP1A1/2 activity measured over a 7-day period was significantly higher in the hepatocyte-PEM-LSEC constructs than in collagen sandwich cultures. A 16-fold increase in CYP1A1/2 activity was observed for hepatocyte-PEM-10,000 LSEC samples, thereby suggesting that interactions between hepatocytes and LSECs are critical in enhancing the detoxification capability in hepatic cultures in vitro.

3D hepatic cultures simultaneously maintain primary hepatocyte and liver sinusoidal endothelial cell phenotypes

Developing in vitro engineered hepatic tissues that exhibit stable phenotype is a major challenge in the field of hepatic tissue engineering. However, the rapid dedifferentiation of hepatic parenchymal (hepatocytes) and non-parenchymal (liver sinusoidal endothelial, LSEC) cell types when removed from their natural environment in vivo remains a major obstacle. The primary goal of this study was to demonstrate that hepatic cells cultured in layered architectures could preserve or potentially enhance liver-specific behavior of both cell types. Primary rat hepatocytes and rat LSECs (rLSECs) were cultured in a layered three-dimensional (3D) configuration. The cell layers were separated by a chitosan-hyaluronic acid polyelectrolyte multilayer (PEM), which served to mimic the Space of Disse. Hepatocytes and rLSECs exhibited several key phenotypic characteristics over a twelve day culture period. Immunostaining for the sinusoidal endothelial 1 antibody (SE-1) demonstrated that rLSECs cultured in the 3D hepatic model maintained this unique feature over twelve days. In contrast, rLSECs cultured in monolayers lost their phenotype within three days. The unique stratified structure of the 3D culture resulted in enhanced heterotypic cell-cell interactions, which led to improvements in hepatocyte functions. Albumin production increased three to six fold in the rLSEC-PEM-Hepatocyte cultures. Only rLSEC-PEM-Hepatocyte cultures exhibited increasing CYP1A1/2 and CYP3A activity. Well-defined bile canaliculi were observed only in the rLSEC-PEM-Hepatocyte cultures. Together, these data suggest that rLSEC-PEM-Hepatocyte cultures are highly suitable models to monitor the transformation of toxins in the liver and their transport out of this organ. In summary, these results indicate that the layered rLSEC-PEM-hepatocyte model, which recapitulates key features of hepatic sinusoids, is a potentially powerful medium for obtaining comprehensive knowledge on liver metabolism, detoxification and signaling pathways in vitro.

The bladder extracellular matrix. Part I: architecture, development and disease

From the earliest studies with epithelial cells implanted into detrusor muscle to later experiments on smooth muscle in defined collagen gels, cell niche and extracellular matrix (ECM) have been clearly shown to orchestrate cellular behavior and fate whether quiescent, migratory, or proliferative. Normal matrix can revert transformed cells to quiescence, and damaged matrix can trigger malignancy or dedifferentiation. ECM influence in disease, development, healing and regeneration has been demonstrated in many other fields of study, but a thorough examination of the roles of ECM in bladder cell activity has not yet been undertaken. Structural ECM proteins, in concert with adhesive proteins, provide crucial structural support to the bladder. Both structural and nonstructural components of the bladder have major effects on smooth muscle function, through effects on matrix rigidity and signaling through ECM receptors. While many ECM components and receptors identified in the bladder have specific known functions in the vascular smooth musculature, their function in the bladder is often less well defined. In cancer and obstructive disease, the ECM has a critical role in pathogenesis. The challenge in these settings will be to find therapies that prevent hyperproliferation and encourage proper differentiation, through an understanding of matrix effects on cell biology and susceptibility to therapeutics.

Utility of hyaluronan oligomers and transforming growth factor-beta1 factors for elastic matrix regeneration by aneurysmal rat aortic smooth muscle cells

The progression of aortic aneurysms (AAs) is typically associated with an activated smooth muscle cell (SMC) phenotype, diminished density of mature medial elastic fibers, and an elevated presence of matrix-degrading enzymes, which ultimately leads to vessel rupture. Currently, no surgical or nonsurgical methods are available to regress aneurysms via regeneration of new elastic matrices, particularly because of inherently poor elastin synthesis by adult vascular cells and absence of tools to stimulate the same. We seek to address this void in this study. We recently showed 0.2 microg/mL of hyaluronan oligomers and 1 ng/mL of transforming growth factor-beta1 (termed elastogenic factors) to dramatically enhance elastin synthesis and matrix formation by healthy aortic SMCs. In this study, the effect of these factors, alone or together, on suppressing procalcific and elastolytic activities of aneurysmal vascular cells, and improving their elastin matrix synthesis and assembly is examined. Periadventitial injury with calcium chloride was used to induce AAs in rats, and approximately 45% increase in aortic diameter was observed after 4 weeks. Aneurysmal SMCs isolated from these AA segments produced higher levels of inflammatory markers matrix metalloproteinases-2 and 9 elastase activity and calcific deposits, while synthesizing significantly less collagen, tropoelastin, and matrix elastin proteins over a 3-week culture period, relative to healthy SMCs. While hyaluronan oligomers alone significantly suppressed aneurysmal cell proliferation and promoted 20-50% increases in collagen and elastin synthesis (p < 0.01), transforming growth factor-beta1 alone had no effect on cellular proliferation and elastin synthesis. However, provision of factors together resulted in significantly higher amounts of collagen/elastin protein synthesis and crosslinking, by upregulating lysyl oxidase and desmosine. Compared to their individual contributions, the factors together were highly effective in minimizing the release of inflammatory enzymes, and encouraging elastic fiber formation. Since elastic matrix amounts were one order of magnitude lower than that observed with healthy cells, even upon elastogenic stimulation at doses optimized previously for healthy cells, increased doses are likely required and must be reoptimized for diseased cells. Despite this, the results point to the potential utility of these elastogenic factors in regenerating elastic matrices within AAs.

Induced elastin regeneration by chronically activated smooth muscle cells for targeted aneurysm repair

Elastin breakdown in vascular aneurysms is mediated by cytokines such as tumor necrosis factor alpha (TNF-alpha, which induces vascular smooth muscle cell (SMC) activation and regulates their deposition of matrix. We previously demonstrated that exogenous supplementation with TGF-beta1 (1 ng ml(-1)) and hyaluronan oligomers (0.786 kDa, 0.2 microg ml(-1)) cues the upregulation of elastin matrix synthesis by healthy cultured SMCs. Here, we determine whether these cues likewise enhance elastin matrix synthesis and assembly by TNF-alpha-stimulated SMCs, while restoring their healthy phenotype. Adult rat aortic SMCs were treated with TNF-alpha alone or together with TGF-beta1/hyaluronan oligomeric cues and the release of inflammatory markers were monitored during over a 21 day culture. Biochemical analysis was used to quantify cell proliferation, matrix protein synthesis and cross-linking efficiency, while immunofluorescence and electron microscopy were used to analyze the elastin matrix quality. It was observed that SMC activation with TNF-alpha (10 ng ml(-1)) induced matrix calcification and promoted production of elastolytic MMP-2 and MMP-9. However, these effects were attenuated by the addition of TGF-beta1 and HA oligomer cues to TNF-alpha-stimulated cultures, which also enhanced tropoelastin and collagen production, improved elastin matrix yield and cross-linking, promoted elastin fiber formation and suppressed elastase activity, although the release of MMP-2 and MMP-9 was not affected. Overall, the results suggest that TGF-beta1 and HA oligomers are potentially useful in suppressing SMC activation and inducing regenerative elastin repair within aneurysms.

Physiologic compliance in engineered small-diameter arterial constructs based on an elastomeric substrate

Compliance mismatch is a significant challenge to long-term patency in small-diameter bypass grafts because it causes intimal hyperplasia and ultimately graft occlusion. Current engineered grafts are typically stiff with high burst pressure but low compliance and low elastin expression. We postulated that engineering small arteries on elastomeric scaffolds under dynamic mechanical stimulation would result in strong and compliant arterial constructs. This study compares properties of engineered arterial constructs based on biodegradable polyester scaffolds composed of either rigid poly(lactide-co-glycolide) (PLGA) or elastomeric poly(glycerol sebacate) (PGS). Adult baboon arterial smooth muscle cells (SMCs) were cultured in vitro for 10 days in tubular, porous scaffolds. Scaffolds were significantly stronger after culture regardless of material, but the elastic modulus of PLGA constructs was an order of magnitude greater than that of porcine carotid arteries and PGS constructs. Deformation was elastic in PGS constructs and carotid arteries but plastic in PLGA constructs. Compliance of arteries and PGS constructs were equivalent at pressures tested. Altering scaffold material from PLGA to PGS significantly decreased collagen content and significantly increased insoluble elastin content in constructs without affecting soluble elastin concentration in the culture medium. PLGA constructs contained no appreciable insoluble elastin. This research demonstrates that: (1) substrate stiffness directly affects in vitro tissue development and mechanical properties; (2) rigid materials likely inhibit elastin incorporation into the extracellular matrix of engineered arterial tissues; and (3) grafts with physiologic compliance and significant elastin content can be engineered in vitro after only days of cell culture.

Probing vocal fold fibroblast response to hyaluronan in 3D contexts

A number of treatments are being investigated for vocal fold (VF) scar, including designer implants. The aim of the present study was to validate a 3D model system for probing the effects of various bioactive moieties on VF fibroblast (VFF) behavior toward rational implant design. We selected poly(ethylene glycol) diacrylate (PEGDA) hydrogels as our base-scaffold due to their broadly tunable material properties. However, since cells encapsulated in PEGDA hydrogels are generally forced to take on rounded/stellate morphologies, validation of PEGDA gels as a 3D VFF model system required that the present work directly parallel previous studies involving more permissive scaffolds. We therefore chose to focus on hyaluronan (HA), a polysaccharide that has been a particular focus of the VF community. Toward this end, porcine VFFs were encapsulated in PEGDA hydrogels containing consistent levels of high Mw HA (HA(HMW)), intermediate Mw HA (HA(IMW)), or the control polysaccharide, alginate, and cultured for 7 and 21 days. HA(HMW) promoted sustained increases in active ERK1/2 relative to HA(IMW). Furthermore, VFFs in HA(IMW) gels displayed a more myofibroblast-like phenotype, higher elastin production, and greater protein kinase C (PkC) levels at day 21 than VFFs in HA(HMW) and alginate gels. The present results are in agreement with a previous 3D study of VFF responses to HA(IMW) relative to alginate in collagen-based scaffolds permissive of cell elongation, indicating that PEGDA hydrogels may serve as an effective 3D model system for probing at least certain aspects of VFF behavior.

Glycosaminoglycans restrained in a fibrin matrix improve ECM remodelling by endothelial cells grown for vascular tissue engineering

The success of a biocompatible vascular graft depends upon its mechanical attributes and post-implantation healing responses. Mechanical strength is a paramount issue because grafts placed in the arterial circulation must be capable of withstanding long-term haemodynamic stress without graft failure. Extracellular matrix (ECM) proteins that are deposited by the cells to remodel the environment play a major role in determining the construct stability and strength. A suitable scaffold that stimulates ECM deposition and remodelling by cells grown in vitro may generate tissues with normal function. The objective of this study was to prove that fibrin matrix composition can be modified with growth factors (GFs) and glycosaminoglycans (GAGs) to promote ECM remodelling coupled with endothelial cell (EC) growth. Effect of GFs and GAGs on ECM production and remodelling was studied separately and in combination. Matrices recovered after EC cultures were analysed after immunochemical staining and it was observed that GFs and GAGs influence collagen IV and elastin deposition. Quantitative PCR analysis of mRNA after specific periods of culture demonstrated significant upregulation of elastin and collagen expression in EC by combination of GFs and GAGS when compared to their individual effects. The results of experiments conducted with various combinations of GFs and GAGs show that a biomimetic approach of immobilization of signalling molecules in fibrin can upregulate ECM remodelling with simultaneous degradation of the fibrin matrix and deposition of collagen IV and elastin. Hence, this combination may be suitable for cardiovascular tissue generation in vitro.

Biomimetic regeneration of elastin matrices using hyaluronan and copper ion cues

Current efforts to tissue engineer elastin-rich vascular constructs and grafts are limited because of the poor elastogenesis of adult vascular smooth muscle cells (SMCs) and the unavailability of appropriate cues to upregulate and enhance cross-linking of elastin precursors (tropoelastin) into organized, mature elastin fibers. We earlier showed that hyaluronan (HA) fragments greatly enhance tropo- and matrix-elastin synthesis by SMCs, although the yield of matrix elastin is low. To improve matrix yields, here we investigate the benefits of adding copper (Cu(2+)) ions (0.01 M and 0.1 M), concurrent with HA (756-2000 kDa), to enhance lysyl oxidase (LOX)-mediated elastin cross-linking machinery. Although absolute elastin amounts in test groups were not different from those in controls, on a per-cell basis, 0.1 M of Cu(2+) ions slowed cell proliferation (5.6 +/- 2.3-fold increase over 21 days vs 22.9 +/- 4.2-fold for non-additive controls), stimulated synthesis of collagen (4.1 +/- 0.4-fold), tropoelastin (4.1 +/- 0.05-fold) and cross-linked matrix elastin (4.2 +/- 0.7-fold). LOX protein synthesis increased 2.5 times in the presence of 0.1 M of Cu(2+) ions, and these trends were maintained even in the presence of HA fragments, although LOX functional activity remained unchanged in all cases. The abundance of elastin and LOX in cell layers cultured with 0.1 M of Cu(2+) ions and HA fragments was qualitatively confirmed using immunoflourescence. Scanning electron microscopy images showed that SMC cultures supplemented with 0.1 M of Cu(2+) ions and HA oligomers and large fragments exhibited better deposition of mature elastic fibers ( approximately 1 mum diameter). However, 0.01 M of Cu(2+) ions did not have any beneficial effect on elastin regeneration. In conclusion, the results suggest that supplying 0.1 M of Cu(2+) ions to SMCs to concurrently (a) enhance per-cell yield of elastin matrix while allowing cells to remain viable and synthetic and not density-arrested in long-term culture because of their moderating effects on otherwise rapid cell proliferation and (b) provide additional benefits of enhanced elastin fiber formation and cross-linking within these tissue-engineered constructs.

Transforming growth factor beta 1 and hyaluronan oligomers synergistically enhance elastin matrix regeneration by vascular smooth muscle cells

Elastin is a vital structural and regulatory matrix protein that plays an important role in conferring elasticity to blood vessel wall. Previous tissue engineering approaches to regenerate elastin in situ or within tissue engineering constructs are curtailed by innate poor elastin synthesis potential by adult vascular smooth muscle cells (SMCs). Currently, we seek to develop cellular cues to enhance tropoelastin synthesis and improve elastin matrix yield, stability, and ultrastructure. Our earlier studies attest to the elastogenic utility of hyaluronan (HA)-based cellular cues, though their effects are fragment size dependent and dose dependent, with HA oligomers deemed most elastogenic. We presently show transforming growth factor beta 1 (TGF-beta1) and HA oligomers, when provided concurrently, to synergistically and dramatically improve elastin matrix regeneration by adult vascular SMCs. Together, these cues suppress SMC proliferation, enhance synthesis of tropoelastin (8-fold) and matrix elastin protein (5.5-fold), and also improve matrix elastin yield (45% of total elastin vs. 10% for nonadditive controls), possibly by more efficient recruitment of tropoelastin for crosslinking. The density of desmosine crosslinks within the elastin matrix was itself attenuated, although the cues together modestly increased production and activity of the elastin crosslinking enzyme, lysyl oxidase. TGF-beta1 and HA oligomers together induced much greater assembly of mature elastin fibers than they did separately, and did not induce matrix calcification. The present outcomes might be great utility to therapeutic regeneration of elastin matrix networks in situ within elastin-compromised vessels, and within tissue-engineered vascular graft replacements.

Copper nanoparticle cues for biomimetic cellular assembly of crosslinked elastin fibers

Elastin, a structural protein distributed in the extracellular matrix of vascular tissues, is critical to maintaining the elastic stability and mechanical properties of blood vessels, as well as regulating cell-signaling pathways involved in vascular injury response and morphogenesis. Pathological degradation of vascular elastin or its malformation within native vessels and the poor ability to tissue-engineer elastin-rich vascular replacements due to innately poor elastin synthesis by adult vascular cells can compromise vascular homeostasis, and must thus be addressed. Our recent studies attest to the utility of hyaluronan (HA) oligomers for elastin synthesis and organization by adult vascular smooth muscle cells (SMCs), though the elastin matrix yields in these cases were quite low relative to total elastin produced. Thus, in this study, we investigated the utility of copper (Cu(2+)) ions to enhance cellular elastin deposition, crosslinking and maturation into structural fibers. Copper nanoparticles (CuNPs; 80-100 nm) in the dose range of 1-100 ng ml(-1) were tested for Cu(2+) ion release, and based on mathematical modeling of their release profiles, CuNPs (1, 10, and 400 ng ml(-1)) were chosen for supplementation to adult SMC cultures. The 400 ng ml(-1) dose of CuNPs cumulatively delivered Cu(2+) doses in the range of 0.1 M, over the 21 day culture period. It was observed that while exogenous CuNP supplements do not up-regulate tropoelastin production by vascular SMCs, they promoted formation of crosslinked elastin matrices. The deposition of crosslinked matrix elastin was further improved by the additional presence of HA oligomers in these cultures. Immunofluorescence imaging and structural analysis of the isolated elastin matrices indicate that amorphous elastin clumps were formed within non-additive control cultures, while aggregating elastin fibrils were observed within SMC cultures treated with CuNPs (1-10 ng ml(-1)) alone or together with HA oligomers. The presence of 400 ng ml(-1) of CuNPs concurrent with HA oligomers furthered aggregation of these elastin fibrils into mature fibers with diameters ranging from 200 to 500 nm. Ultrastructural analysis of elastin matrix within cultures treated with HA oligomers and 400 ng ml(-1) of CuNPs suggest that elastin matrix deposition as stimulated by Cu(2+) ions proceeds via a fibrillin-mediated assembly process, with enhanced crosslinking occurring via stimulation of lysyl oxidase. Overall, the data suggest that CuNPs and HA oligomers are highly useful for regenerating crosslinked, fibrillar elastin matrices by adult vascular SMCs. These results have immense utility in tissue-engineering vascular replacements.

Benefits of concurrent delivery of hyaluronan and IGF-1 cues to regeneration of crosslinked elastin matrices by adult rat vascular cells

Elastin, a major component of vascular matrices, critically determines vascular mechanics and maintains the quiescence of smooth muscle cells (SMCs). Attempts to regenerate elastin in elastin-compromised blood vessels using tissue-engineering approaches is limited by the unavailability of elastogenic cues to upregulate poor elastin output and matrix assembly by adult vascular cells. We previously showed that hyaluronan (HA) elastogenically stimulates aortic SMCs, although these effects are highly specific to HA fragment size. The elastogenic response of SMCs can also be modulated with growth factors such as insulin-like growth factor (IGF-1). Here, we evaluate the benefits of concurrent delivery of HA fragments (0.76-2000 kDa) and IGF-1 (500 ng/ml) to elastin synthesis, organization and crosslinking. The study outcomes show that, relative to supplement-free cultures, IGF-1 and long-chain HA/large HA fragments, but not HA oligomers, together induce multifold increases in the synthesis of elastin precursors, structural elastin matrix yields and crosslink densities within cell layers, and encourage elastic fibre formation. These outcomes are not all obtained when either of the cues is provided separately. IGF-1 and large HA fragments (>20 kDa) also together inhibit cell proliferation, a concern in elastin-compromised vessels, where SMC hyperproliferation is common. The results will benefit efforts to provide exogenous or scaffold-based elastogenic cues (IGF-1 + HMW HA/large HA fragments) to enable robust and faithful regeneration of elastin matrix structures in vivo or in vitro. The present outcomes may be used to restore elastin matrix homeostasis in de-elasticized vessels and tissue-engineered constructs that may be grafted as a substitute.

Neoarteries grown in vivo using a tissue-engineered hyaluronan-based scaffold

Vascular tissue engineering has emerged as a promising technology for the design of an ideal, responsive, living conduit with properties similar to that of native tissue. The missing link in tissue-engineered blood vessels is elastin biosynthesis. Several biomaterials are currently used but few support elastin biosynthesis in a 3-D array. In previous studies, we demonstrated that a hyaluronan-based scaffold (HYAFF-11) grafted in the infrarenal rat aorta successfully guided the complete regeneration of a well-functioning small-diameter (2 mm) neoartery. The aim of the present study was to test the ability of HYAFF-11 biodegradable grafts to develop into neovessels of larger size (4 mm) in a porcine model, focusing on extracellular matrix (ECM) remodeling and elastin biosynthesis. HYAFF-11 tubes (diameter 4 mm, length 5 cm) were implanted in an end-to-end fashion in the common carotid artery. Grafts were analyzed for patency with a Duplex scan every 15 days. ECM components were evaluated by histological and molecular biological methods. All the animals survived the observation period without complications. Intimal hyperplasia (initiating at the anastomotic site) and graft thrombosis led to 3 cases of partial or complete occlusion, as demonstrated by histological examination. There were no signs of stenoses or aneurysms in the remaining grafts. After 5 months, the biomaterial was almost completely degraded and replaced by a neoartery segment composed of mature smooth muscle cells, collagen, and elastin fibers organized in layers and was completely covered on the luminal surface by endothelial cells (vWF(+)). Whereas in previous small animal studies, patency rates were not optimal, those obtained in the present study using hyaluronan-based grafts of larger size confirmed the ability of these constructs to guide the development of a well-functioning neoartery, with the remarkable additional attribute of facilitating the formation of organized layers of elastin fibers.

Hyaluronan-dependent pericellular matrix

Hyaluronan is a multifunctional glycosaminoglycan that forms the structural basis of the pericellular matrix. Hyaluronan is extruded directly through the plasma membrane by one of three hyaluronan synthases and anchored to the cell surface by the synthase or cell surface receptors such as CD44 or RHAMM. Aggregating proteoglycans and other hyaluronan-binding proteins, contribute to the material and biological properties of the matrix and regulate cell and tissue function. The pericellular matrix plays multiple complex roles in cell adhesion/de-adhesion, and cell shape changes associated with proliferation and locomotion. Time-lapse studies show that pericellular matrix formation facilitates cell detachment and mitotic cell rounding. Hyaluronan crosslinking occurs through various proteins, such as tenascin, TSG-6, inter-alpha-trypsin inhibitor, pentraxin and TSP-1. This creates higher order levels of structured hyaluronan that may regulate inflammation and other biological processes. Microvillous or filopodial membrane protrusions are created by active hyaluronan synthesis, and form the scaffold of hyaluronan coats in certain cells. The importance of the pericellular matrix in cellular mechanotransduction and the response to mechanical strain are also discussed.

The many ways to cleave hyaluronan

Hyaluronan is being used increasingly as a component of artificial matrices and in bioengineering for tissue scaffolding. The length of hyaluronan polymer chains is now recognized as informational, involving a wide variety of size-specific functions. Inadvertent scission of hyaluronan can occur during the process of preparation. On the other hand, certain size-specific hyaluronan fragments may be desirable, endowing the finished bioengineered product with specific properties. In this review, the vast arrays of reactions that cause scission of hyaluronan polymers is presented, including those on an enzymatic, free radical, and chemical basis.