Stimulated endothelial cell adhesion and angiogenesis with laminin-5 modification of expanded polytetrafluoroethylene

Atg7 Silencing Inhibits Laminin-5 Expression to Suppress Tube Formation by Brain Endothelial Cells

Cerebral angiogenesis is a key event during brain development and recovery from brain injury. We previously demonstrated that Atg7 knockout impaired angiogenesis in the mouse brain. However, the role of Atg7 in angiogenesis is not completely understood. In this study, we used human brain microvascular endothelial cells (HBMECs) to investigate the mechanism of Atg7-regulated cerebral angiogenesis. We found that Atg7 depletion specifically diminished the expression of the β3 and γ2 chains of laminin-5, a major component of the extracellular matrix. In contrast, autophagy inhibitors did not affect laminin-5 expression, suggesting that Atg7-regulated laminin-5 expression is autophagy-independent. We also found that Atg7-regulated laminin-5 expression occurred at the transcriptional level through NF-κB signaling. Exogenous laminin-5 or the NF-κB agonist betulinic acid effectively rescued tube formation by Atg7-deficient HBMECs. Taken together, our study identified a novel mechanism by which Atg7 regulates laminin-5 expression via NF-κB to modulate tube formation by brain endothelial cells during cerebral angiogenesis. Anat Rec, 302:2255-2260, 2019. © 2019 American Association for Anatomy.

Effects of different components of the extracellular matrix on endothelialization

The endothelialization of cardiovascular prostheses is known to improve their haemocompatibility. As such body-foreign materials often do not endothelialize spontaneously. A lot of in vitro studies are ongoing how endothelialization of biomaterials can be improved. In this study the influence of different components of a tissue-typical extracellular matrix (ECM) like laminin, fibronectin or gelatin on the formation of an endothelial cell monolayer and on the shear resistance of adherent cells on these substrates was studied.The study revealed that the density of human venous endothelial cells (HUVEC) monolayers differed markedly between cells grown on a natural ECM and cells grown on singularized components of an ECM (p < 0.001). Only HUVEC grown on laminin showed similar densities and a stress fiber pattern comparable to HUVEC grown on the ECM. HUVEC grown on gelatin- or fibronectin-coated coverslips were less firmly attached to the substrate; frequently individual HUVEC and even groups of cells detached.Concluding it seems that coating of implants with laminin supports the formation of shear resistant endothelial cell (EC) monolayer - superior to other ECM components.

The role of angiogenesis in implant dentistry part II: The effect of bone-grafting and barrier membrane materials on angiogenesis

BACKGROUND

In implant dentistry, bone substitute materials and barrier membranes are used in different treatments including guided bone regeneration (GBR), socket preservation, alveolar ridge augmentation, maxillary sinus elevation, and filling bony defects around the inserted dental implant. One of the most important factors in prognosis of treatments using these materials is the growth of new blood vessels in applied areas. Present review was performed to evaluate the effect of the bone-grafting and barrier membrane materials on angiogenesis events.

MATERIAL AND METHODS

An electronic search was performed in PubMed, MEDLINE, and EMBASE databases via OVID using the keywords mentioned in the PubMed and MeSH headings regarding the role of angiogenesis in implant dentistry from January 2000-April 2014.

RESULTS

Of the 5,622 articles identified in our initial search results, only 33 met the inclusion criteria set for this review. Among bone substitute materials the autogenous bone-grafts, and among the barrier membranes the collagenous membranes, had the highest angiogenic potentials. Other bone-grafting materials or membranes were mostly used with pro-angiogenic factors to enhance their angiogenic properties.

CONCLUSIONS

Angiogenesis is one of the key factors, which plays a critical role in success rate of GBR technique and is seriously considered in manufacturing bone-grafting and barrier membrane materials. However, there is still lack of clinical and in-vivo studies addressing the effect of angiogenesis in treatments using bone-grafting and barrier membrane materials.

Extracellular matrix structure

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network composed of collagens, proteoglycans/glycosaminoglycans, elastin, fibronectin, laminins, and several other glycoproteins. Matrix components bind each other as well as cell adhesion receptors forming a complex network into which cells reside in all tissues and organs. Cell surface receptors transduce signals into cells from ECM, which regulate diverse cellular functions, such as survival, growth, migration, and differentiation, and are vital for maintaining normal homeostasis. ECM is a highly dynamic structural network that continuously undergoes remodeling mediated by several matrix-degrading enzymes during normal and pathological conditions. Deregulation of ECM composition and structure is associated with the development and progression of several pathologic conditions. This article emphasizes in the complex ECM structure as to provide a better understanding of its dynamic structural and functional multipotency. Where relevant, the implication of the various families of ECM macromolecules in health and disease is also presented.

Laminins: Roles and Utility in Wound Repair

Significance: Laminins are complex extracellular macromolecules that are major players in the control of a variety of core cell processes, including regulating rates of cell proliferation, differentiation, adhesion, and migration. Laminins, and related extracellular matrix components, have essential roles in tissue homeostasis; however, during wound healing, the same proteins are critical players in re-epithelialization and angiogenesis. Understanding how these proteins influence cell behavior in these different conditions holds great potential in identifying new strategies to enhance normal wound closure or to treat chronic/nonhealing wounds. Recent Advances: Laminin-derived bioactive peptides and, more recently, laminin-peptide conjugated scaffolds, have been designed to improve tissue regeneration after injuries. These peptides have been shown to be effective in decreasing inflammation and granulation tissue, and in promoting re-epithelialization, angiogenesis, and cell migration. Critical Issues: Although there is now a wealth of knowledge concerning laminin form and function, there are still areas of some controversy. These include the relative contribution of two laminin-based adhesive devices (focal contacts and hemidesmosomes) to the re-epithelialization process, the impact and implications of laminin proteolytic processing, and the importance of laminin polymer formation on cell behavior. In addition, the roles in wound healing of the laminin-related proteins, netrins, and LaNts are still to be fully defined. Future Directions: The future of laminin-based therapeutics potentially lies in the bioengineering of specific substrates to support laminin deposition for ex vivo expansion of autologous cells for graft formation and transplantation. Significant recent advances suggest that this goal is within sight.

In vivo evaluation of biomimetic fluorosurfactant polymer-coated expanded polytetrafluoroethylene vascular grafts in a porcine carotid artery bypass model

OBJECTIVE

The objective of this study was to evaluate the potential for biomimetic self-assembling fluorosurfactant polymer (FSP) coatings incorporating heptamaltose (M7-FSP) to block nonspecific protein adsorption, the cell adhesive RGD peptide (RGD-FSP), or the endothelial cell-selective CRRETAWAC peptide (cRRE-FSP) to improve patency and endothelialization in small-diameter expanded polytetrafluoroethylene (ePTFE) vascular graft implants.

METHODS

ePTFE vascular grafts (4 mm in diameter, 5 cm in length) were coated with M7-FSP, RGD-FSP, or cRRE-FSP by dissolving FSPs in distilled water and flowing solution through the graft lumen for 24 hours. Coatings were confirmed by receding water contact angle measurements on the lumen surface. RGD-FSP and cRRE-FSP grafts were presodded in vitro with porcine pulmonary artery endothelial cells (PPAECs) using a custom-designed flow system. PPAEC coverage on the lumen surface was visualized with epifluorescent microscopy and quantified. Grafts were implanted as carotid artery interposition bypass grafts in seven pigs for 33 ± 2 days (ePTFE, n = 3; M7-FSP, n = 4; RGD-FSP, n = 3; cRRE-FSP, n = 4). Patency was confirmed immediately after implantation with duplex color flow ultrasound and at explantation with contrast-enhanced angiography. Grafts were sectioned for histology and stained: Movat pentachrome stain to outline vascular layers, immunofluorescent staining to identify endothelial cells (anti-von Willebrand factor antibody), and immunohistochemical staining to identify smooth muscle cells (anti-smooth muscle α-actin antibody). Neointima to lumen area ratio was determined to evaluate neointimal hyperplasia.

RESULTS

Receding water contact angle measurements on graft luminal surfaces were significantly lower (P < .05) on FSP-coated ePTFE surfaces (M7-FSP, 40 ± 16 degrees; RGD-FSP, 25 ± 10 degrees; cRRE-FSP, 33 ± 16 degrees) compared with uncoated ePTFE (126 ± 2 degrees), confirming presence of the FSP layer. In vitro sodding of PPAECs on RGD-FSP and cRRE-FSP grafts resulted in a confluent monolayer of PPAECs on the luminal surface, with a similar cell population on RGD-FSP (1200 ± 187 cells/mm(2)) and cRRE-FSP (1134 ± 153 cells/mm(2)) grafts. All grafts were patent immediately after implantation, and one of three uncoated, two of three RGD-FSP, two of four M7-FSP, and two of four cRRE-FSP grafts remained patent after 1 month. PPAEC coverage of the lumen surface was seen in all patent grafts. RGD-FSP grafts had a slightly higher neointima to lumen area ratio (0.53 ± 0.06) compared with uncoated (0.29 ± 0.15), M7-FSP (0.20 ± 0.15), or cRRE-FSP (0.17 ± 0.09) grafts.

CONCLUSIONS

Biomimetic FSP-coated ePTFE grafts can be used successfully in vivo and have potential to support endothelialization. Grafts modified with the M7-FSP and cRRE-FSP showed lower intimal hyperplasia compared with RGD-FSP grafts.

In vivo effects of tailored laminin-332 α3 conjugated scaffolds enhances wound healing: a histomorphometric analysis

Surface modification techniques have been used to develop biomimetic scaffolds by incorporating cell adhesion peptides. In our previous work, we have shown the tethering of laminin-332 α3 chain to type I collagen scaffold using microbial transglutaminase (mTGase), promotes cell adhesion, migration, and proliferation. In this study, we evaluated the wound healing properties of tailored laminin-332 α3 chain (peptide A: PPFLMLLKGSTR) tethered to a type I collagen scaffold using mTGase by incorporating transglutaminase substrate peptide sequences containing either glutamine (peptide B: PPFLMLLKGSTREAQQIVM) or lysine (peptide C: PPFLMLLKGSTRKKKKG) in rat full-thickness wound model at two different time points (7 and 21 days). Histological evaluations were assessed for wound closure, epithelialization, angiogenesis, inflammatory, fibroblastic cellular infiltrations, and quantified using stereological methods (p < 0.05). Peptide A and B tethered to collagen scaffold using mTGase stimulated neovascularization, decreased the inflammatory cell infiltration and prominently enhanced the fibroblast proliferation which significantly accelerated the wound healing process. We conclude that surface modification by incorporating motif of laminin-332 α3 chain (peptide A: PPFLMLLK GSTR) domain and transglutaminase substrate to the laminin-332 α3 chain (peptide B: PPFLMLLKGSTREAQQIVM) using mTGase may be a potential candidate for tissue engineering applications and skin regeneration.

Encapsulation of ePTFE in prevascularized collagen leads to peri-implant vascularization with reduced inflammation

During the typical healing response to an implanted biomaterial, vascular-rich granulation tissue forms around the implant and later resolves into a relatively avascular, fibrous capsule. We have previously shown that a microvascular construct (MVC) consisting of isolated microvessel fragments suspended in a collagen I gel forms a persistent microcirculation in lieu of avascular scar when implanted. The current study evaluated the potential for microvascular constructs to maintain a vascularized tissue environment around an implanted biomaterial. An analysis of the peri-implant tissue around bare expanded polytetrafluoroethylene (ePTFE), ePTFE embedded within a microvascular construct, or ePTFE embedded within collagen alone revealed that the presence of the MVC, but not collagen alone, promoted vascular densities comparable to that of the granulation tissue formed around bare ePTFE. The vessels within the microvascular construct surrounding the ePTFE were perfusion competent, as determined by India ink perfusion casting, and extended into the interstices of the polymer. In contrast to bare ePTFE, the presence of the MVC or collagen alone significantly reduced the number of activated macrophages in association with ePTFE. Similar results were observed for ePTFE modified to increase cellularity and prevent the formation of an avascular scar. The microvascular construct may prove effective in forming vascularized tissue environments and limiting the number of activated macrophages around implanted polymers thereby leading to effective implant incorporation.

Assessment of the intimal response to a protein-modified stent in a tissue-engineered blood vessel mimic

Protein-coated intravascular stents have emerged as potential pro-healing modifications for or alternatives to anti-proliferative drug-eluting stents. To support the development of these devices, preclinical testing is required to evaluate the intimal response to new coatings and modifications. The purpose of this work was to implement a tissue-engineered blood vessel as an in vitro testing system to evaluate extracellular matrix-modified stents with regard to endothelialization of the stent surface. Stents were modified by submersion in a protein-enriched medium and were subsequently deployed within tissue-engineered blood vessels and cultivated in vitro under flow to assess the intimal response. Scanning electron microscopy, fluorescent nuclear staining with en face imaging, and histological assessments were performed 7 or 14 days postdeployment. Results illustrated accelerated cellular regeneration over protein-modified stent strut surfaces, with increased coverage and increased tissue thickness atop protein-modified stent struts. In addition, the intimal response to modified stents differed significantly from bare metal stents. Conclusions from this work support the use of a tissue-engineered blood vessel mimic system for evaluation of modified stent surfaces. These findings are important to stent researchers as well as laboratories developing tissue-engineered constructs.

Deposition of Functional Polymer Thin Films Using Atmospheric Pressure Plasma for Biomedical Applications – Endothelialization of Vascular Prostheses

Functionalized plasma polymer thin films were obtained in a dielectric barrier discharge at atmospheric pressure in an atmosphere of N2 and C2H4. The coatings were hydrophilic, adherent, chemically stable and presented a surface concentration of NH2 suitable for further biomolecule conjugation. Covalent grafting of a linking arm (glutaric anhydride) and subsequent conjugation of fibronectin, a protein of the extracellular matrix, were successful. Finally, endothelial cell adhesion experiments were performed directly on the functionalized thin films as well as on the conjugated coatings. Effects on cell adhesion were observed as a function of the plasma thin film deposition parameters.

In vitro biocompatibility of degradable biopolymers in cell line cultures from various ocular tissues: extraction studies

In vitro biocompatibility of 50:50 PDLGA, 85:15 PDLGA, and Inion GTR(TM) membrane was evaluated in cell line cultures from various ocular tissues, in human corneal epithelial cells (HCE), rabbit stromal fibroblasts (SIRC), bovine corneal endothelial cells (BCE), human conjunctival epithelial cells (IOBA-NHC), and human retinal pigment epithelial cells (ARPE-19). To study the toxicity of degradation products, the biomaterials were extracted in phosphate buffered saline at 70 degrees C for 24 h. The cell cultures were exposed to biomaterial extract diluted in medium (1:1-1:8) and the biocompatibility was evaluated by the WST-1 cytotoxicity/cell proliferation test. In all experiments without pH neutralization, cell viability increased with decreasing biomaterial extract volume. The highest extraction ratio 1:1 of PDLGA 50:50 decreased viability from 5-20%, from the control level, depending on the cell type. The corresponding cell viability values for PDLGA 85:15 and Inion GTR membrane ranged from 47-87% and 66-92%, respectively. When the pH of biomaterial extract was neutralized, Inion GTR membrane and PDLGA 85:15 had no effect on viability. BCE, HCE, and IOBA-NHC appeared to the most sensitive cell types, while SIRC and ARPE-19 were more resistant. The results of our in vitro studies suggest that the polymers tested are satisfactorily biocompatible.

Covalent grafting of fibronectin onto plasma-treated PTFE: influence of the conjugation strategy on fibronectin biological activity

Surface coating of synthetic materials is often considered to improve biomedical devices biocompatibility. In this study, we covalently bound fibronectin (FN) onto ammonia plasma-treated PTFE via two crosslinkers, namely glutaric anhydride (GA) and sulfosuccinimidyl-4-(p-maleimidophenyl)butyrate (sulfo-SMPB). With respect to clean PTFE, cell adhesion increased markedly on both FN grafted surfaces, although it was twice higher on PTFE-GA-FN than on PTFE-SMPB-FN. ELISA experiments performed with a polyclonal antibody revealed that the amount of FN is identical on both surfaces while monoclonal antibody specific to the RGD binding site clearly demonstrated a greater availability when FN is surface grafted through GA. These results provide evidence of a variation in protein conformation correlated with the surface conjugation strategy.

Tissue-engineered vascular grafts as in vitro blood vessel mimics for the evaluation of endothelialization of intravascular devices

The accelerating use of minimally invasive procedures for the treatment of cardiovascular disease, and the commensurate development of intravascular devices such as stents, has lead to a high demand for preclinical assessment techniques. A 3-dimensional in vitro blood vessel mimic (BVM) would be ideal for device testing before animal or clinical studies. This is possible based on current capabilities for the creation of tissue-engineered vascular grafts (TEVGs). Using an established method of pressure-sodding human endothelial cells onto a polymer scaffold, a BVM was created in an in vitro bioreactor system under flow. Scanning electron microscopy and immunohistochemistry verified a cellular lining and revealed a luminal monolayer of endothelial cells. After BVM development, bare metal stents were deployed. Stented and unstented BVMs were evaluated using fluorescent nuclear staining and optical coherence tomography (OCT). En face and cross-sectional evaluation of bisbenzimide-stained nuclei revealed cellular coverage of the stent surfaces. Cross-sectional evaluation using OCT also illustrated a cellular layer developing over the stent struts. These data support the use of TEVGs as in vitro BVMs for pre-clinical evaluation of the endothelial cell response to stents and endovascular devices.

Tissue-engineered vascular grafts as in vitro blood vessel mimics for the evaluation of endothelialization of intravascular devices

The accelerating use of minimally invasive procedures for the treatment of cardiovascular disease, and the commensurate development of intravascular devices such as stents, has lead to a high demand for preclinical assessment techniques. A 3-dimensional in vitro blood vessel mimic (BVM) would be ideal for device testing before animal or clinical studies. This is possible based on current capabilities for the creation of tissue-engineered vascular grafts (TEVGs). Using an established method of pressure-sodding human endothelial cells onto a polymer scaffold, a BVM was created in an in vitro bioreactor system under flow. Scanning electron microscopy and immunohistochemistry verified a cellular lining and revealed a luminal monolayer of endothelial cells. After BVM development, bare metal stents were deployed. Stented and unstented BVMs were evaluated using fluorescent nuclear staining and optical coherence tomography (OCT). En face and cross-sectional evaluation of bisbenzimide-stained nuclei revealed cellular coverage of the stent surfaces. Cross-sectional evaluation using OCT also illustrated a cellular layer developing over the stent struts. These data support the use of TEVGs as in vitro BVMs for pre-clinical evaluation of the endothelial cell response to stents and endovascular devices.

Enhancement of cell attachment and tissue integration by a IKVAV containing multi-domain peptide

Laminin contains a number of cell binding motifs including IKVAV and some that bind heparin. We developed a multi-domain synthetic peptide, LA2, which combines IKVAV sequences with a heparin-binding domain with the goal of improving cell attachment to otherwise non-adherent substrates. LA2 was used to coat polystyrene, ethyl vinyl acetate (EVA), expanded polytetrafluoroethylene (ePTFE), polycarbonate, titanium and stainless steel. In cell attachment studies, LA2 dramatically increased cell attachment to polystyrene and EVA compared to uncoated counterparts or those coated with SIKVAV. Similar increases were observed on ePTFE and titanium. On polystyrene, LA2 enhanced the attachment of endothelial cells, smooth muscle cells, epithelial cells, myoblasts, and osteoblast progenitor cells. Following adhesion, the cells underwent proliferation to form confluent monolayers with phenotypic morphologies. Using osteoblast progenitor cells (MC3T3 cells) grown on LA2/polystyrene, the cells exhibited an increased production of a differentiation marker, alkaline phosphatase. In vivo, LA2 improved tissue integration into ePTFE when implanted subcutaneously in rats. After 2 weeks, cells had penetrated deep into the LA2 coated ePTFE implant whereas little cell penetration was found in uncoated grafts. The implant sites exhibited little inflammation or other untoward effects. The results indicated that the LA2 peptide improved cell adhesion and tissue integration and might be useful in a number of tissue engineering applications.