The heparin-binding domain confers diverse functions of VEGF-A in development and disease: a structure-function study

Targeting heparan sulfate-protein interactions with oligosaccharides and monoclonal antibodies

Heparan sulfate-binding proteins (HSBPs) are structurally diverse extracellular and membrane attached proteins that interact with HS under normal physiological conditions. Interactions with HS offer an additional level of control over the localization and function of HSBPs, which enables them to behave in a more refined manner. Because all cell signaling events start at the cell membrane, and cell-cell communication relies on translocation of soluble factors across the extracellular matrix, HS occupies an apical position in cellular signal transduction by interacting with hundreds of growth factors, cytokines, chemokines, enzymes, enzyme inhibitors, receptors and adhesion molecules. These extracellular and membrane proteins can play important roles in physiological and pathological conditions. For most HS-binding proteins, the interaction with HS represents an essential element in regulating their normal physiological functions. Such dependence on HS suggests that manipulating HS-protein interactions could be explored as a therapeutic strategy to selectively antagonize/activate HS-binding proteins. In this review, we will discuss current understanding of the diverse nature of HS-HSBP interactions, and the latest advancements in targeting the HS-binding site of HSBPs using structurally-defined HS oligosaccharides and monoclonal antibodies.

Heparin-Induced Changes of Vascular Endothelial Growth Factor (VEGF165) Structure

Vascular endothelial growth factor-A (VEGF-A), a secreted homodimeric glycoprotein, is a critical regulator of angiogenesis in normal and pathological states. The binding of heparin (HE) to VEGF₁₆₅ (the major form of VEGF-A) modulates the angiogenesis-related cascade, but the mechanism of the observed changes at the structural level is still insufficiently explored. In the present study, we examined the effect of HE on the structural and physicochemical properties of recombinant human VEGF₁₆₅ (rhVEGF₁₆₅). The HE binding results in an increase of hydrophobic surface exposure in rhVEGF₁₆₅ without changes in its secondary structure. Differential scanning calorimetry measurements for intact and HE-bound rhVEGF₁₆₅ reveals the absence of any pronounced thermally induced transitions in the protein in the temperature range from 20 to 100 °C. The apolar area increase during the heparin binding explains the pronounced HE-induced oligomerization/aggregation of rhVEGF₁₆₅, as studied by chemical glutaraldehyde cross-linking and dynamic light scattering. Molecular modeling and docking techniques were used to model the full structure of dimeric VEGF₁₆₅ and to reveal putative molecular mechanisms underlying the function of the VEGF₁₆₅/HE system. In general, the results obtained can be a basis for explaining the modulating effect of HE on the biological activity of VEGF-A.

New anti-angiogenic compound based on chemically modified heparin

PURPOSE

The purpose of this study was to measure the anti-angiogenic effect of N-desulfated Re-N-acetylated, a chemically modified heparin (mHep).

METHODS

In vitro assays (cell tube formation, viability, proliferation, and migration) with endothelial cells were performed after 24 h of treatment with mHep at 10, 100, and 1000 ng/mL or saline. In vivo tests were performed after laser-induced choroidal neovascularization (CNV) in rats, followed by an intravitreal injection (5 µL) of mHep (10, 100, 1000 ng/mL) or balanced salt solution. Immunofluorescence analysis of the CNV was performed after 14 days.

RESULTS

mHep produced a statistically significant reduction in cell proliferation, tube formation, and migration, without cell viability changes when compared to saline. Mean measures of CNV area were 54.84 × 10⁶ pixels/mm (± 12.41 × 10⁶), 58.77 × 10⁶ pixels/mm (± 17.52 × 10⁶), and 59.42 × 10⁶ pixels/mm (± 17.33 × 10⁶) in groups 100, 1000, and 10,000 ng/mL, respectively, while in the control group, mean area was 72.23 × 10⁶ (± 16.51 × 10⁶). The P value was 0.0065. Perimeter analysis also demonstrated statistical significance (P = 0.0235) with the mean measure of 93.55 × 10⁴, 94.23 × 10⁴, and 102 × 10⁴ in the 100 ng/mL, 1000 ng/mL, and control groups, respectively.

CONCLUSIONS

These results suggest that mHep N-DRN is a potent anti-angiogenic, anti-proliferative, and anti-migratory compound with negligible anticoagulant or hemorrhagic action and no cytotoxicity for retina cells. This compound may serve as a candidate for treating choroidal neovascularization.

Tissue-engineered vascular patches: comparative characteristics and preclinical test results in a sheep model

Carotid endarterectomy (CEA) with patch angioplasty is the most effective treatment for carotid artery stenosis. However, the use of existing vascular patches is often associated with thrombosis, restenosis, calcification and other complications.

Objective: to develop biodegradable patches for arterial reconstruction, containing vascular endothelial growth factor (VEGF) or arginyl-glycyl-aspartic acid (RGD), and comparatively evaluate their biocompatibility and efficacy in in vitro experiments and during preclinical trials in large laboratory animal models.

Materials and methods. Biodegradable patches, made from a mixture of poly(3-hydroxybutyrate-co-3- hydroxyvalerate (PHBV) and poly(ε-caprolactone) (PCL), were fabricated by electrospinning and modified with VEGF or the peptide sequence RGD in different configurations. In in vitro experiments, the surface structure, physicomechanical and hemocompatibility properties were evaluated. In in vivo experiments, we evaluated the effectiveness of the developed vascular patches for 6 months after implantation into the carotid artery of 12 sheep. The quality of remodeling was assessed using histological and immunofluorescence studies of explanted specimens.

Results. The PHBV/PCL/VEGF patches had physicomechanical characteristics closer to those of native vessels and their biofunctionalization method resulted in the smallest drop in strength characteristics compared with their unmodified PHBV/PCL counterparts. Modification with RGD peptides reduced the strength of the polymer patches by a factor of 2 without affecting their stress-strain behavior. Incorporation of VEGF into polymer fibers reduced platelet aggregation upon contact with the surface of the PHBV/PCL/VEGF patches and did not increase erythrocyte hemolysis. At month 6 of implantation into the carotid artery of sheep, the PHBV/PCL/ VEGF patches formed a complete newly formed vascular tissue without signs of associated inflammation and calcification. This indicates the high efficiency of the VEGF incorporated into the patch. In contrast, the patches modified with different configurations of RGD peptides combined the presence of neointimal hyperplasia and chronic granulomatous inflammation present in the patch wall and developed during bioresorption of the polymer scaffold.

Conclusion. PHBV/PCL/VEGF patches have better biocompatibility and are more suitable for vascular wall reconstruction than PHBV/PCL/RGD patches.

Expression of vascular endothelial growth factor in follicular cell-derived lesions of the thyroid: Is NIFTP benign or precancerous?

Objective: Vascular endothelial growth factor (VEGF) is an angiogenic factor that plays an important role in physiological and pathological angiogenesis of the thyroid. The aim of the current study was to determine the expression characteristics of VEGF in follicular cell-derived lesions of the thyroid and to assess whether a new entity noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is precancerous.

Material and Methods: Patients diagnosed with 33 follicular adenomas (FA), 41 invasive follicular variant papillary thyroid cancer (IN-FVPTC), and 40 NIFTP in surgical resection materials were evaluated retrospectively. Immunostaining was performed on 5-μm paraffin tissue sections. The percentages of immunostaing for VEGF were evaluated on pathological materials. We used a percentage of labeled thyrocytes score (0, no labeling; 1, <30%; 2, 31-60%; 3, >60%) and an intensity score (0, no staining; 1, weak; 2, intermediate; 3, strong). The sum of two scores were accepted as the total score.

Results: Mean ages of the FA, IN-FVPTC, and NIFTP groups were 44.7 ± 11.7 years, 46.9 ± 13.6 years, 43.2 ± 15.4 years, respectively and the mean VEGF immunostaining scores were 44.7 ± 29.3, 50.2 ± 32.54, 4 ± 26.3 respectively. Although there was no statistically significant difference (p= 0.347), the total score of the NIFTPs was higher than the scores of the FA (mean= 3.9 ± 1.8) and IN-FVPTC(mean= 4.3 ± 1.9) groups with a mean value of 4.6 ± 1.7. This result was remarkable. There was no statistically significant difference between tumor diameters and staining percentages (p= 0.750).

Conclusion: Even if there were no statistical differences for VEGF immunostaining, it was high in NIFTPs. Since we know the role of VEGF in tumorigenesis, we can hypothesize that NIPTP can be precancerous. Our argue should be corroborated by a large prospective study.

VEGFA, B, C: Implications of the C-Terminal Sequence Variations for the Interaction with Neuropilins

Vascular endothelial growth factors (VEGFs) are the key regulators of blood and lymphatic vessels’ formation and function. Each of the proteins from the homologous family VEGFA, VEGFB, VEGFC and VEGFD employs a core cysteine-knot structural domain for the specific interaction with one or more of the cognate tyrosine kinase receptors. Additional diversity is exhibited by the involvement of neuropilins–transmembrane co-receptors, whose b1 domain contains the binding site for the C-terminal sequence of VEGFs. Although all relevant isoforms of VEGFs that interact with neuropilins contain the required C-terminal Arg residue, there is selectivity of neuropilins and VEGF receptors for the VEGF proteins, which is reflected in the physiological roles that they mediate. To decipher the contribution made by the C-terminal sequences of the individual VEGF proteins to that functional differentiation, we determined structures of molecular complexes of neuropilins and VEGF-derived peptides and examined binding interactions for all neuropilin-VEGF pairs experimentally and computationally. While X-ray crystal structures and ligand-binding experiments highlighted similarities between the ligands, the molecular dynamics simulations uncovered conformational preferences of VEGF-derived peptides beyond the C-terminal arginine that contribute to the ligand selectivity of neuropilins. The implications for the design of the selective antagonists of neuropilins’ functions are discussed.

Vascular Endothelial Growth Factor as an Immediate-Early Activator of Ultraviolet-Induced Skin Injury

The negative health consequences of acute ultraviolet (UV) exposure are evident, with reports of 30,000 emergency room visits annually to treat the effects of sunburn in the United States alone. The acute effects of sunburn include erythema, edema, severe pain, and chronic overexposure to UV radiation, leading to skin cancer. Whereas the pain associated with the acute effects of sunburn may be relieved by current interventions, existing post-sunburn treatments are not capable of reversing the cumulative and long-term pathological effects of UV exposure, an unmet clinical need. Here we show that activation of the vascular endothelial growth factor (VEGF) pathway is a direct and immediate consequence of acute UV exposure, and activation of VEGF signaling is necessary for initiating the acute pathological effects of sunburn. In UV-exposed human subjects, VEGF signaling is activated within hours. Topical delivery of VEGF pathway inhibitors, targeted against the ligand VEGF-A (gold nanoparticles conjugated with anti-VEGF antibodies) and small-molecule antagonists of VEGF receptor signaling, prevent the development of erythema and edema in UV-exposed mice. These findings collectively suggest targeting VEGF signaling may reduce the subsequent inflammation and pathology associated with UV-induced skin damage, revealing a new postexposure therapeutic window to potentially inhibit the known detrimental effects of UV on human skin. It is essential to emphasize that these preclinical studies must not be construed as suggesting in any way the use of VEGF inhibitors as a sunburn treatment in humans because warranted future clinical studies and appropriate agency approval are essential in that regard.

A crosslinked dextran sulfate-chitosan nanoparticle for delivery of therapeutic heparin-binding proteins

Negatively charged dextran sulfate (DS)-chitosan nanoparticles (DSCS NPs) contain a DS outer shell with binding properties similar to those of heparin and are useful for the incorporation and delivery of therapeutic heparin-binding proteins. These particles, however, are unstable in physiological salt solutions due to their formation through electrostatic interactions. In the present study, a method was developed to covalently crosslink chitosan in the core of the DSCS NP with a short chain dicarboxylic acid (succinate), while leaving the outer shell of the particle untouched. The crosslinked particles, XDSCS NPs, are stable in NaCl solutions up to 3 M. XDSCS NPs were able to incorporate heparin-binding proteins (VEGF and SDF-1α) rapidly and efficiently, and maintain the full biological activity of the proteins. The incorporated proteins were not released from the particles after a 14-day incubation period at 37 °C in PBS, but retained the same activity as those stored at 4 °C. When aerosolized for delivery to the lungs of rats, XDSCS NP-incorporated SDF-1α showed a ∼17-fold greater retention time compared to that of free protein. These properties suggest that XDSCS NPs could be beneficial for the delivery of therapeutic heparin-binding proteins to achieve sustained in vivo effects.

Novel engineered, membrane-tethered VEGF-A variants promote formation of filopodia, proliferation, survival, and cord or tube formation by endothelial cells via persistent VEGFR2/ERK signaling and activation of CDC42/ROCK pathways

Therapeutic angiogenesis would be clinically valuable in situations such as peripheral vascular disease in diabetic patients and tissue reperfusion following ischemia or injury, but approaches using traditional isoforms of vascular endothelial growth factor-A (VEGF) have had little success. The isoform VEGF165 is both soluble and matrix-associated, but can cause pathologic vascular changes. Freely diffusible VEGF121 is not associated with pathologic angiogenesis, but its failure to remain in the vicinity of the targeted area presents therapeutic challenges. In this study, we evaluate the cellular effects of engineered VEGF variants that tether extracellular VEGF121 to the cell membrane with the goal of activating VEGF receptor 2 (VEGFR2) in a sustained, autologous fashion in endothelial cells. When expressed by primary human retinal endothelial cells (hRECs), the engineered, membrane-tethered variants eVEGF-38 and eVEGF-53 provide a lasting VEGF signal that induces cell proliferation and survival, increases endothelial permeability, promotes the formation of a cord/tube network, and stimulates the formation of elongated filopodia on the endothelial cells. The engineered VEGF variants activate VEGFR2, MAPK/ERK, and the Rho GTPase mediators CDC42 and ROCK, activities that are required for the formation of the elongated filopodia. The sustained, pro-angiogenic activities induced by eVEGF-38 and eVEGF-53 support the potential of engineered VEGF variants-overexpressing endothelial cells as a novel combination of gene and cell-based therapeutic strategy for stimulating endothelial cell-autologous therapeutic angiogenesis.

Efficient drug delivery by novel cell-penetrating peptide derived from Midkine, with two heparin binding sites braced by a length-specific helix

Cell-penetrating peptides (CPPs) have been regarded as potential drug carriers for cancer therapy. However, most well-studied CPPs fail to deliver exogenous drugs efficiently and selectively. In this study, a tumour-targeted CPP with high efficiency derived from heparin-binding domain (HBD) of Midkine (named HMD) was discovered. HMD exhibited higher delivery efficiency than classic CPPs (TAT and R9) and manifested selectivity in tumour cells. Normally, the positive charge is the key factor for the transmembrane activity of CPPs such as TAT and R9. Here, the length of α-helix inside CPP was found also important for in the recognition of heparan sulphate proteoglycans (HSPGs). Subsequently, the introduction of HMD enhanced the inhibitory effect of Momordica antiviral protein of 30 kDa (MAP30) on tumour cells, resulting in a 6.07-fold and 5.42-fold increase in HeLa cells and MGC80-3 cells respectively without enhanced cytotoxicity in normal cells. These results show that HMD possesses high efficiency and good tumour specificity and can be utilised as a promising agent for the tumour-targeted delivery of drug. This study is also a supplement to the existing theories about the biological activities of the α-helix in CPPs.

Mechanistic Illustration: How Newly-Formed Blood Vessels Stopped by the Mineral Blocks of Bone Substitutes Can Be Avoided by Using Innovative Combined Therapeutics

One major limitation for the vascularization of bone substitutes used for filling is the presence of mineral blocks. The newly-formed blood vessels are stopped or have to circumvent the mineral blocks, resulting in inefficient delivery of oxygen and nutrients to the implant. This leads to necrosis within the implant and to poor engraftment of the bone substitute. The aim of the present study is to provide a bone substitute currently used in the clinic with suitably guided vascularization properties. This therapeutic hybrid bone filling, containing a mineral and a polymeric component, is fortified with pro-angiogenic smart nano-therapeutics that allow the release of angiogenic molecules. Our data showed that the improved vasculature within the implant promoted new bone formation and that the newly-formed bone swapped the mineral blocks of the bone substitutes much more efficiently than in non-functionalized bone substitutes. Therefore, we demonstrated that our therapeutic bone substitute is an advanced therapeutical medicinal product, with great potential to recuperate and guide vascularization that is stopped by mineral blocks, and can improve the regeneration of critical-sized bone defects. We have also elucidated the mechanism to understand how the newly-formed vessels can no longer encounter mineral blocks and pursue their course of vasculature, giving our advanced therapeutical bone filling great potential to be used in many applications, by combining filling and nano-regenerative medicine that currently fall short because of problems related to the lack of oxygen and nutrients.

Interaction of vascular endothelial growth factor and heparin quantified by single molecule force spectroscopy

Heparin, as an effective anticoagulant, has been increasingly used in clinical practice, but the binding characteristics and influence of exogenous heparin on heparin-affinity proteins in the body are still unclear. Vascular endothelial growth factor A (VEGF-A) is a kind of protein with heparin affinity involved in the pathogenesis and progression of many angiogenesis-dependent diseases including cancer. As an important step in the angiogenesis-related cascade, it is necessary to clarify the interaction between VEGF165 (the major form of VEGF-A) and heparin. In this work, we investigated this interaction based on single molecule force spectroscopy (SMFS) and molecular dynamics (MD) simulation. From the SMFS study, binding forces between VEGF165 and heparin at different loading rates were quantified under near-physiological conditions. Meanwhile, the kinetic and thermodynamic parameters of the VEGF165/heparin complex dissociation process were also obtained. Results of MD simulation visually displayed the most likely binding conformation of VEGF165/heparin* complex, indicating that hydrogen bonding and hydrophobic interaction play a positive role in the binding between the two molecules. This work provides a new insight into the binding between VEGF165 and heparin and offers a research framework to study the interaction between heparin and multiple heparin affinity proteins, which is helpful for guiding the safe application of heparin in the clinic.

Long-term reversal of diabetes by subcutaneous transplantation of pancreatic islet cells and adipose-derived stem cell sheet using surface-immobilized heparin and engineered collagen scaffold

OBJECTIVE

Esterified collagen (EC) can be functionalized with heparin to enhance islet graft stability. Growth factors secreted by human adipose-derived stem cells (hADSCs) can bind efficiently to EC-heparin (EC-Hep), which enhances revascularization and cell protection. We investigated the therapeutic potential of a combined heparin-esterified collagen-hADSC (HCA)-islet sheet to enhance islet engraftment.

RESEARCH DESIGN AND METHODS

This study was designed to assess the efficiency of using EC-Hep as a scaffold for subcutaneous islet transplantation in diabetic athymic mice. After the hADSC-cocultured islets were seeded in the EC-Hep scaffold, islet function was measured by glucose-stimulated insulin secretion test and growth factors in the culture supernatants were detected by protein array. Islet transplantation was performed in mice, and graft function and survival were monitored by measuring the blood glucose levels. β-Cell mass and vascular densities were assessed by immunohistochemistry.

RESULTS

The EC-Hep composite allowed sustained release of growth factors. Secretion of growth factors and islet functionality in the HCA-islet sheet were significantly increased compared with the control groups of islets alone or combined with native collagen. In vivo, stable long-term glucose control by the graft was achieved after subcutaneous transplantation of HCA-islet sheet due to enhanced capillary network formation around the sheet.

CONCLUSIONS

The findings indicate the potential of the HCA-islet sheet to enhance islet revascularization and engraftment in a hADSC dose-dependent manner, following clinical islet transplantation for the treatment of diabetes mellitus.

A Single Intraventricular Injection of VEGF Leads to Long-Term Neurotrophic Effects in Axotomized Motoneurons

Vascular endothelial growth factor (VEGF) has been recently demonstrated to induce neuroprotective and synaptotrophic effects on lesioned neurons. Hitherto, the administration of VEGF in different animal models of lesion or disease has been conducted following a chronic protocol of administration. We questioned whether a single dose of VEGF, administered intraventricularly, could induce long-term neurotrophic effects on injured motoneurons. For this purpose, we performed in cats the axotomy of abducens motoneurons and the injection of VEGF into the fourth ventricle in the same surgical session and investigated the discharge characteristics of axotomized and treated motoneurons by single-unit extracellular recordings in the chronic alert preparation. We found that injured motoneurons treated with a single VEGF application discharged with normal characteristics, showing neuronal eye position (EP) and velocity sensitivities similar to control, thereby preventing the axotomy-induced alterations. These effects were present for a prolonged period of time (50 d) after VEGF administration. By confocal immunofluorescence we also showed that the synaptic stripping that ensues lesion was not present, rather motoneurons showed a normal synaptic coverage. Moreover, we demonstrated that VEGF did not lead to any angiogenic response pointing to a direct action of the factor on neurons. In summary, a single dose of VEFG administered just after motoneuron axotomy is able to prevent for a long time the axotomy-induced firing and synaptic alterations without any associated vascular sprouting. We consider that these data are of great relevance due to the potentiality of VEGF as a therapeutic agent in neuronal lesions and diseases.

Construction and evaluation of an antibody phage display library targeting heparan sulfate

Heparan sulfate (HS) is a linear polysaccharide with high structural diversity. Different HS epitopes have been detected and localized using single chain variable fragment (scFv) antibodies from a ‘single pot’ phage display library containing a randomized complementarity determining region of the heavy chain (CDR3). In this study, we created a new library containing anti-HS scFvs that all harbor a dp-38 heavy chain segment where the CDR3 region was engineered to contain the XBBXBX heparin binding consensus site (X = any amino acid, B = R, K or H). The library contained ~1.73 × 10⁶ unique antibodies and was biopanned against HS from several sources. The selected antibodies were sequenced and chemically/immunohistologically characterized. A number of 67 anti-HS scFv antibodies were selected, of which 31 contained a XBBXBX CDR3 sequence. There was a clear preference for glycine at the first and proline at the fourth position of the CDR3. The sequence GZZP(R/K)X (Z = R, K or H, but may also contain N, S, or Q) was unusually overrepresented. Selected antibodies reacted with HS/heparin, but not with other glycosaminoglycans. Antibodies reacted differentially with respect to N-, 2-O, or 6-O-desulfated heparin preparations, and showed distinct topologies of HS epitopes in rat kidney sections. The library may be instrumental in the selection of a large pool of HS epitope-specific antibodies, and - since all antibodies differ only in their 6 amino acid CDR region - may be a tool for a rational design of antibodies recognizing specific HS sulfation patterns.

Ectopic transient overexpression of OCT-4 facilitates BMP4-induced osteogenic transdifferentiation of human umbilical vein endothelial cells

Limitation in cell sources for autologous cell therapy has been a recent focus in stem cell therapy and tissue engineering. Among various research advances, direct conversion, or transdifferentiation, is a notable and feasible strategy for the generation and acquirement of wanted cell source. So far, utilizing cell transdifferentiation technology in tissue engineering was mainly restricted at achieving single wanted cell type from diverse cell types with high efficiency. However, regeneration of a complete tissue always requires multiple cell types which poses an intrinsic complexity. In this study, enhanced osteogenic differentiation was achieved by transient ectopic expression of octamer-binding transcription factor 4 (OCT-4) gene followed by bone morphogenetic protein 4 treatment on human umbilical vein endothelial cells. OCT-4 transfection and bone morphogenetic protein 4 treatment resulted in enhanced expression of osteogenic markers such as core-binding factor alpha 1, alkaline phosphatase, and collagen 1 compared with bone morphogenetic protein 4 treatment alone. Furthermore, we employed gelatin-heparin cryogel in cranial defect model for in vivo bone formation. Micro-computed tomography and histological analysis of in vivo samples showed that OCT-4 transfection followed by bone morphogenetic protein 4 treatment resulted in efficient transdifferentiation of endothelial cells to osteogenic cells. These results suggest that the combination of OCT-4 and bone morphogenetic protein 4 on endothelial cells would be a reliable multicellular transdifferentiation model which could be applied for bone tissue engineering.

Dual Action of Sulfated Hyaluronan on Angiogenic Processes in Relation to Vascular Endothelial Growth Factor-A

Pathological healing characterized by abnormal angiogenesis presents a serious burden to patients’ quality of life requiring innovative treatment strategies. Glycosaminoglycans (GAG) are important regulators of angiogenic processes. This experimental and computational study revealed how sulfated GAG derivatives (sGAG) influence the interplay of vascular endothelial growth factor (VEGF)₁₆₅ and its heparin-binding domain (HBD) with the signaling receptor VEGFR-2 up to atomic detail. There was profound evidence for a HBD-GAG-HBD stacking configuration. Here, the sGAG act as a “molecular glue” leading to recognition modes in which sGAG interact with two VEGF₁₆₅-HBDs. A 3D angiogenesis model demonstrated the dual regulatory role of high-sulfated derivatives on the biological activity of endothelial cells. While GAG alone promote sprouting, they downregulate VEGF₁₆₅-mediated signaling and, thereby, elicit VEGF₁₆₅-independent and -dependent effects. These findings provide novel insights into the modulatory potential of sGAG derivatives on angiogenic processes and point towards their prospective application in treating abnormal angiogenesis.

TRF2 positively regulates SULF2 expression increasing VEGF-A release and activity in tumor microenvironment

The telomeric protein TRF2 is overexpressed in several human malignancies and contributes to tumorigenesis even though the molecular mechanism is not completely understood. By using a high-throughput approach based on the multiplexed Luminex X-MAP technology, we demonstrated that TRF2 dramatically affects VEGF-A level in the secretome of cancer cells, promoting endothelial cell-differentiation and angiogenesis. The pro-angiogenic effect of TRF2 is independent from its role in telomere capping. Instead, TRF2 binding to a distal regulatory element promotes the expression of SULF2, an endoglucosamine-6-sulfatase that impairs the VEGF-A association to the plasma membrane by inducing post-synthetic modification of heparan sulfate proteoglycans (HSPGs). Finally, we addressed the clinical relevance of our findings showing that TRF2/SULF2 expression is a worse prognostic biomarker in colorectal cancer (CRC) patients.

Poly(ε-caprolactone)/keratin/heparin/VEGF biocomposite mats for vascular tissue engineering

Vascular endothelial growth factor (VEGF) is an effective growth and angiogenic cytokine, which stimulates proliferation and survival of endothelial cells, and promotes angiogenesis and vascular permeability. Binding VEGF with heparin could protect it from rapid degradation, subsequently allowing it to be controlled release. Primarily, poly(ε-caprolactone) (PCL) and keratin were coelectrospun, followed by conjugating with heparin and subsequently binding VEGF. The loaded heparin and VEGF on these mats were quantified, respectively. The surface characteristics of mats were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The VEGF delivery results indicated these mats could sustainably release VEGF for 2 weeks. Cell viability assays suggested these mats were valid to accelerate human umbilical vein endothelial cells (HUVECs) proliferation, while inhibit human umbilical arterial smooth muscle cells (HUASMCs) growth under the combined actions of VEGF and heparin. The results tested by blood clotting times (APTT, PT, and TT), hemolysis, and platelet adhesion indicated the mats were blood compatible. To sum up, these biocomposite mats are ideal scaffolds for vascular tissue engineering.

Three-dimensional cryogels for biomedical applications

Cryogels are a subset of hydrogels synthesized under sub-zero temperatures: initially solvents undergo active freezing, which causes crystal formation, which is then followed by active melting to create interconnected supermacropores. Cryogels possess several attributes suited for their use as bioscaffolds, including physical resilience, bio-adaptability, and a macroporous architecture. Furthermore, their structure facilitates cellular migration, tissue-ingrowth, and diffusion of solutes, including nano- and micro-particle trafficking, into its supermacropores. Currently, subsets of cryogels made from both natural biopolymers such as gelatin, collagen, laminin, chitosan, silk fibroin, and agarose and/or synthetic biopolymers such as hydroxyethyl methacrylate, poly-vinyl alcohol, and poly(ethylene glycol) have been employed as 3D bioscaffolds. These cryogels have been used for different applications such as cartilage, bone, muscle, nerve, cardiovascular, and lung regeneration. Cryogels have also been used in wound healing, stem cell therapy, and diabetes cellular therapy. In this review, we summarize the synthesis protocol and properties of cryogels, evaluation techniques as well as current in vitro and in vivo cryogel applications. A discussion of the potential benefit of cryogels for future research and their application are also presented.

The heparin binding domain of von Willebrand factor binds to growth factors and promotes angiogenesis in wound healing

During wound healing, the distribution, availability, and signaling of growth factors (GFs) are orchestrated by their binding to extracellular matrix components in the wound microenvironment. Extracellular matrix proteins have been shown to modulate angiogenesis and promote wound healing through GF binding. The hemostatic protein von Willebrand factor (VWF) released by endothelial cells (ECs) in plasma and in the subendothelial matrix has been shown to regulate angiogenesis; this function is relevant to patients in whom VWF deficiency or dysfunction is associated with vascular malformations. Here, we show that VWF deficiency in mice causes delayed wound healing accompanied by decreased angiogenesis and decreased amounts of angiogenic GFs in the wound. We show that in vitro VWF binds to several GFs, including vascular endothelial growth factor-A (VEGF-A) isoforms and platelet-derived growth factor-BB (PDGF-BB), mainly through the heparin-binding domain (HBD) within the VWF A1 domain. VWF also binds to VEGF-A and fibroblast growth factor-2 (FGF-2) in human plasma and colocalizes with VEGF-A in ECs. Incorporation of the VWF A1 HBD into fibrin matrices enables sequestration and slow release of incorporated GFs. In vivo, VWF A1 HBD-functionalized fibrin matrices increased angiogenesis and GF retention in VWF-deficient mice. Treatment of chronic skin wounds in diabetic mice with VEGF-A165 and PDGF-BB incorporated within VWF A1 HBD-functionalized fibrin matrices accelerated wound healing, with increased angiogenesis and smooth muscle cell proliferation. Therefore, the VWF A1 HBD can function as a GF reservoir, leading to effective angiogenesis and tissue regeneration.

Dual growth factor-immobilized bioactive injection material for enhanced treatment of glottal insufficiency

With increasing demand for treatment of glottal insufficiency, several injection materials have been examined. However, biological resorption, degradation of injected materials, and the subsequent need to perform multiple injections still remain major clinical problems. In this study, we fabricated two different growth factor (GF) [single basic fibroblast growth factor (bFGF), single hepatocyte growth factor (HGF), or dual bFGF/HGF]-immobilized polycaprolactone (PCL)/Pluronic F127 microspheres. These materials were investigated for their potential use as bioactive injection laryngoplasty agents. HGF was found to be continuously released over 20 days and the bFGF was found to be continuously released over 25 days, as demonstrated by ELISA assay. Human vocal fold fibroblasts (hVFFs) showed significantly higher proliferative ability on dual GF-immobilized microspheres. GF-immobilized microspheres (bFGF, HGF, and dual GF) were injected into paralyzed vocal folds of New Zealand white rabbits. Through endoscopic observation and H&E staining, we identified that the microspheres remained localized at the injection site, resulting in constant volume augmentation of the paralyzed vocal fold without significant loss of the initial volume after 4 weeks. The expression of genes related to the extracellular matrix (ECM) in the vocal fold was upregulated by dual GF-immobilized microspheres. Furthermore, dual GF-immobilized microspheres inhibited muscle degeneration and upregulation of myogenic-related genes. In conclusion, dual GF-immobilized microspheres passively augmented the volume of the paralyzed vocal fold while actively inducing ECM synthesis at the injected vocal fold and preserving muscle tissue. Dual GF-immobilized microspheres could be a new and promising injection material for paralyzed vocal folds. STATEMENT OF SIGNIFICANCE: Limitation of prolonged augmentation of vocal fold and degeneration of vocal fold tissue still remain as major clinical problems in the treatment of vocal fold paralysis. Herein, we fabricated the polycaprolactone (PCL)/Pluronic F127 microspheres to augment volume of paralyzed vocal folds. On top of that, we additionally immobilized the growth factors (bFGF, HGF, or dual bFGF/HGF) on the surface of these microspheres. We highlight the efficacy of the dual GF-immobilized microspheres which augmented the volume of the paralyzed vocal fold passively, induced ECM synthesis actively at the injected vocal fold and preserved laryngeal muscle tissue. Our results suggest that the dual GF-immobilized microsphere could be a new promising injection material for injection laryngoplasty to treat paralyzed vocal fold.

Heparin impairs angiogenic signaling and compensatory lung growth after left pneumonectomy

Children with hypoplastic lung diseases, such as congenital diaphragmatic hernia, can require life support via extracorporeal membrane oxygenation and systemic anticoagulation, usually in the form of heparin. The role of heparin in angiogenesis and organ growth is inconclusive, with conflicting data reported in the literature. This study aimed to investigate the effects of heparin on lung growth in a model of compensatory lung growth (CLG). Compared to the absence of heparin, treatment with heparin decreased the vascular endothelial growth factor (VEGF)-mediated activation of VEGFR2 and mitogenic effect on human lung microvascular endothelial cells in vitro. Compared to non-heparinized controls, heparinized mice demonstrated impaired pulmonary mechanics, decreased respiratory volumes and flows, and reduced activity levels after left pneumonectomy. They also had lower lung volume, pulmonary septal surface area and alveolar density on morphometric analyses. Lungs of heparinized mice displayed decreased phosphorylation of VEGFR2 compared to the control group, with consequential downstream reduction in markers of cellular proliferation and survival. The use of bivalirudin, an alternative anticoagulant that does not interact with VEGF, preserved lung growth and pulmonary mechanics. These results demonstrated that heparin impairs CLG by reducing VEGFR2 activation. These findings raise concern for the clinical use of heparin in the setting of organ growth or regeneration.

Heparin Functionalized Injectable Cryogel with Rapid Shape-Recovery Property for Neovascularization

Cryogel based scaffolds have high porosity with interconnected macropores that may provide cell compatible microenvironment. In addition, cryogel based scaffolds can be utilized in minimally invasive surgery due to its sponge-like properties, including rapid shape recovery and injectability. Herein, we developed an injectable cryogel by conjugating heparin to gelatin as a carrier for vascular endothelial growth factor (VEGF) and fibroblasts in hindlimb ischemic disease. Our gelatin/heparin cryogel showed gelatin concentration-dependent mechanical properties, swelling ratios, interconnected porosities, and elasticities. In addition, controlled release of VEGF led to effective angiogenic responses both in vitro and in vivo. Furthermore, its sponge-like properties enabled cryogels to be applied as an injectable carrier system for in vivo cells and growth factor delivery. Our heparin functionalized injectable cryogel facilitated the angiogenic potential by facilitating neovascularization in a hindlimb ischemia model.

Molecularly Imprinted Nanocavities Capable of Ligand-Binding Domain and Size/Shape Recognition for Selective Discrimination of Vascular Endothelial Growth Factor Isoforms

Vascular endothelial growth factor 165 (VEGF165) is known to be predominantly expressed in the first stage of vascularization; therefore, the detection of VEGF165 is important in the stage diagnosis of cancers. Molecularly imprinted nanocavities, capable of the selective discrimination of VEGF165 from other VEGF isoforms, were prepared by surface-initiated atom transfer radical polymerization. VEGF165 was immobilized on a gold-coated glass substrate by anchored heparin moieties, where the immobilized heparin was able to capture VEGF165 by binding with the heparin-binding domain (HBD) on VEGF165. Molecular imprinting was conducted on the immobilized VEGF165 by using methacrylic acid (MAA) as a functional monomer to interact with basic amino acids outside of the HBD of VEGF165 by electrostatic interaction. After the removal of VEGF165 from the obtained polymer thin layer (ca. 7 nm), VEGF165-imprinted nanocavities remained, in which the heparin moiety and MAA residues were located in suitable positions for VEGF165 recognition. The molecularly imprinted polymer (MIP) thin layer showed a binding affinity for VEGF165 (dissociation constant: 3.4 nM) that was ten times higher than that of the substrate before polymerization (heparin-immobilized substrate). A much lower binding affinity for VEGF121, which contains no heparin-binding domain, was observed. Moreover, the MIP thin layer distinguished VEGF165 from VEGF189, which possesses a larger molecular size than VEGF165, an amino acid sequence homology of 87%, and contains HBDs, whereas the heparin-immobilized substrate showed almost no selectivity. These results suggested that the heparin moiety within the nanocavity provided HBD selectivity and the polymer matrix composed of the molecularly imprinted nanocavity provided size/shape selectivity, which resulted in the highly selective discrimination of VEGF isoforms.

A macroporous heparin-releasing silk fibroin scaffold improves islet transplantation outcome by promoting islet revascularisation and survival

Islet transplantation is considered the most promising therapeutic option with the potential to cure diabetes. However, efficacy of current clinical islet transplantation is limited by long-term graft dysfunction and attrition. We have investigated the therapeutic potential of a silk fibroin macroporous (SF) scaffold for syngeneic islet transplantation in diabetic mice. The SF scaffold was prepared via lyophilisation, which enables incorporation of active compounds including cytokines, peptide and growth factors without compromising their biological activity. For the present study, a heparin-releasing SF scaffold (H-SF) in order to evaluate the versatility of the SF scaffold for biological functionalisation. Islets were then co-transplanted with H-SF or SF scaffolds in the epididymal fat pad of diabetic mice. Mice from both H-SF and SF groups achieved 100% euglycaemia, which was maintained for 1year. More importantly, the H-SF-islets co-transplantation led to more rapid reversal of hyperglycaemia, complete normalisation of glucose responsiveness and lower long-term blood glucose levels. This superior transplantation outcome is attributable to H-SF-facilitated islet revascularisation and cell proliferation since significant increase of islet endocrine and endothelial cells proliferation was shown in grafts retrieved from H-SF-islets co-transplanted mice. Better intra-islet vascular reformation was also evident, accompanied by VEGF upregulation. In addition, when H-SF was co-transplanted with islets extracted from vegfr2-luc transgenic mice in vivo, sustained elevation of bioluminescent signal that corresponds to vegfr2 expression was collected, implicating a role of heparin-dependent activation of endogenous VEGF/VEGFR2 pathway in promoting islet revascularisation and proliferation. In summary, the SF scaffolds provide an open platform as scaffold development for islet transplantation. Furthermore, given the pro-angiogenic, pro-survival and minimal post-transplantation inflammatory reactions of H-SF, our data also support the feasibility of clinical implementation of H-SF to improve islet transplantation outcome.

STATEMENT OF SIGNIFICANCE

1) The silk fibroin scaffold presented in the present study provides an open platform for scaffold development in islet transplantation, with heparinisation as an example. 2) Both heparin and silk fibroin have been used clinically. The excellent in vivo therapeutic outcome reported here may therefore be clinically relevant and provide valuable insights for bench to bed translation. 3) Compared to conventional clinical islet transplantation, during which islets are injected via the hepatic portal vein, the physical/mechanical properties of silk fibroin scaffolds create a more accessible transplantation site (i.e., within fat pad), which significantly reduces discomfort. 4) Islet implantation into the fat pad also avoids an instant blood mediated inflammatory response, which occurs upon contact of islet with recipient's blood during intraportal injection, and prolongs survival and function of implanted islets.

Targeting heparin and heparan sulfate protein interactions

Heparin and heparan sulfate glycosaminoglycans are long, linear polysaccharides that are made up of alternating dissacharide sequences of sulfated uronic acid and amino sugars. Unlike heparin, which is only found in mast cells, heparan sulfate is ubiquitously expressed on the cell surface and in the extracellular matrix of all animal cells. These negatively-charged glycans play essential roles in important cellular functions such as cell growth, adhesion, angiogenesis, and blood coagulation. These biomolecules are also involved in pathophysiological conditions such as pathogen infection and human disease. This review discusses past and current methods for targeting these complex biomolecules as a novel therapeutic strategy to treating disorders such as cancer, neurodegenerative diseases, and infection.

High heparin content surface-modified polyurethane discs promote rapid and stable angiogenesis in full thickness skin defects through VEGF immobilization

Three-dimensional scaffolds have the capacity to serve as an architectural framework to guide and promote tissue regeneration. Parameters such as the type of material, growth factors, and pore dimensions are therefore critical in the scaffold's success. In this study, heparin has been covalently bound to the surface of macroporous polyurethane (PU) discs via two different loading methods to determine if the amount of heparin content had an influence on the therapeutic affinity loading and release of (VEGF₁₆₅ ) in full thickness skin defects. PU discs (5.4 mm diameter, 300 µm thickness, and interconnected pore size of 150 µm) were produced with either a low (2.5 mg/g) or high (6.6 mg/g) heparin content (LC and HC respectively), and were implanted into the modified dorsal skin chamber (MDSC) of C57BL/6 J mice with and without VEGF. Both low- and high-content discs with immobilized VEGF₁₆₅ (LCV and HCV, respectively) presented accelerated neovascularization and tissue repair in comparison to heparin discs alone. However, the highest angiogenetic peak was on day 7 with subsequent stabilization for HCV, whereas other groups displayed a delayed peak on day 14. We therefore attribute the superior performance of HCV due to its ability to hold more VEGF_165, based on its increased heparin surface coverage, as also demonstrated in VEGF elution dynamics. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2543-2550, 2017.

Sulfated Hyaluronan Alters Endothelial Cell Activation in Vitro by Controlling the Biological Activity of the Angiogenic Factors Vascular Endothelial Growth Factor-A and Tissue Inhibitor of Metalloproteinase-3

Several pathologic conditions such as rheumatoid arthritis, ocular neovascularization, cancer, or atherosclerosis are often associated with abnormal angiogenesis, which requires innovative biomaterial-based treatment options to control the activity of angiogenic factors. Here, we studied how sulfated hyaluronan (sHA) and oversulfated chondroitin sulfate derivatives as potential components of functional biomaterials modulate vascular endothelial growth factor-A (VEGF-A) signaling and endothelial cell activity in vitro. Tissue inhibitor of metalloproteinase-3 (TIMP-3), an effective angiogenesis inhibitor, exerts its activity by competing with VEGF-A for binding to VEGF receptor-2 (VEGFR-2). However, even though TIMP-3 and VEGF-A are known to interact with glycosaminoglycans (GAGs), the potential role and mechanism by which GAGs alter the VEGF-A/TIMP-3 regulated VEGFR-2 signaling remains unclear. Combining surface plasmon resonance, immunobiochemical analysis, and molecular modeling, we demonstrate the simultaneous binding of VEGF-A and TIMP-3 to sHA-coated surfaces and identified a novel mechanism by which sulfated GAG derivatives control angiogenesis: GAG derivatives block the binding of VEGF-A and TIMP-3 to VEGFR-2 thereby reducing their biological activity in a defined, sulfation-dependent manner. This effect was stronger for sulfated GAG derivatives than for native GAGs. The simultaneous formation of TIMP-3/sHA complexes partially rescues the sHA inhibited VEGF-A/VEGFR-2 signaling and endothelial cell activation. These results provide novel insights into the regulation of angiogenic factors by GAG derivatives and highlight the potential of sHA derivatives for the treatment of diseases associated with increased VEGF-A and VEGFR-2 levels.

Branching Analysis of Multivalent Conjugates Using Size Exclusion Chromatography-Multiangle Light Scattering

Multivalent conjugates (MVCs) (conjugation of multiple proteins to a linear polymer chain) are powerful for improving the bioactivity and pharmacokinetics of a bioactive molecule. Since this effect is highly dependent upon the valency of the conjugated proteins, it is imperative to have a technique for analysis of the conjugation ratio. Studies of MVCs have used size exclusion chromatography-multiangle light scattering (SEC-MALS), which allows for the separate and individual analysis of the protein and biopolymer components based on their specific refractive index increment and UV extinction coefficient constants to determine the number of proteins bound per biopolymer molecule. In this work, we have applied traditional branching analysis to the SEC-MALS data, with the primary assumption that the polymer backbone can be used as the linear counterpart. We demonstrated good agreement between the branching values and the valency determined by traditional analysis, demonstrating that branching analysis can be used as an alternative technique to approximate the valency of MVCs. The branching analysis method also provides a more complete picture of the distribution of the measured values, provides important branching information about the molecules, and lowers the cost and complexity of the characterization. However, since MVC molecules are both conjugate molecules and branched molecules, the most powerful approach to their characterization would be to use both traditional multivalent conjugate analysis and branching analysis in conjunction.

An Overview of VEGF-Mediated Signal Transduction

Vascular endothelial growth factor (VEGF) plays a fundamental role in angiogenesis and endothelial cell biology, and has been the subject of intense study as a result. VEGF acts via a diverse and complex range of signaling pathways, with new targets constantly being discovered. This review attempts to summarize the current state of knowledge regarding VEGF cell signaling in endothelial and cardiovascular biology, with a particular emphasis on its role in angiogenesis.

Vascular endothelial growth factor A: just one of multiple mechanisms for sex-specific vascular development within the testis?

Testis development from an indifferent gonad is a critical step in embryogenesis. A hallmark of testis differentiation is sex-specific vascularization that occurs as endothelial cells migrate from the adjacent mesonephros into the testis to surround Sertoli-germ cell aggregates and induce seminiferous cord formation. Many in vitro experiments have demonstrated that vascular endothelial growth factor A (VEGFA) is a critical regulator of this process. Both inhibitors to VEGFA signal transduction and excess VEGFA isoforms in testis organ cultures impaired vascular development and seminiferous cord formation. However, in vivo models using mice which selectively eliminated all VEGFA isoforms: in Sertoli and germ cells (pDmrt1-Cre;Vegfa(-/-)); Sertoli and Leydig cells (Amhr2-Cre;Vegfa(-/-)) or Sertoli cells (Amh-Cre;Vegfa(-/-) and Sry-Cre;Vegfa(-/-)) displayed testes with observably normal cords and vasculature at postnatal day 0 and onwards. Embryonic testis development may be delayed in these mice; however, the postnatal data indicate that VEGFA isoforms secreted from Sertoli, Leydig or germ cells are not required for testis morphogenesis within the mouse. A Vegfa signal transduction array was employed on postnatal testes from Sry-Cre;Vegfa(-/-) versus controls. Ptgs1 (Cox1) was the only upregulated gene (fivefold). COX1 stimulates angiogenesis and upregulates, VEGFA, Prostaglandin E2 (PGE2) and PGD2. Thus, other gene pathways may compensate for VEGFA loss, similar to multiple independent mechanisms to maintain SOX9 expression. Multiple independent mechanism that induce vascular development in the testis may contribute to and safeguard the sex-specific vasculature development responsible for inducing seminiferous cord formation, thus ensuring appropriate testis morphogenesis in the male.

Fell-Muir Lecture: Heparan sulphate and the art of cell regulation: a polymer chain conducts the protein orchestra

Heparan sulphate (HS) sits at the interface of the cell and the extracellular matrix. It is a member of the glycosaminoglycan family of anionic polysaccharides with unique structural features designed for protein interaction and regulation. Its client proteins include soluble effectors (e.g. growth factors, morphogens, chemokines), membrane receptors and cell adhesion proteins such as fibronectin, fibrillin and various types of collagen. The protein-binding properties of HS, together with its strategic positioning in the pericellular domain, are indicative of key roles in mediating the flow of regulatory signals between cells and their microenvironment. The control of transmembrane signalling is a fundamental element in the complex biology of HS. It seems likely that, in some way, HS orchestrates diverse signalling pathways to facilitate information processing inside the cell. A dictionary definition of an orchestra is 'a large group of musicians who play together on various instruments …' to paraphrase, the HS orchestra is 'a large group of proteins that play together on various receptors'. HS conducts this orchestra to ensure that proteins hit the right notes on their receptors but, in the manner of a true conductor, does it also set 'the musical pulse' and create rhythm and harmony attractive to the cell? This is too big a question to answer but fun to think about as you read this review.

Long-Term Expansion in Platelet Lysate Increases Growth of Peripheral Blood-Derived Endothelial-Colony Forming Cells and Their Growth Factor-Induced Sprouting Capacity

Introduction

Efficient implementation of peripheral blood-derived endothelial-colony cells (PB-ECFCs) as a therapeutical tool requires isolation and generation of a sufficient number of cells in ex vivo conditions devoid of animal-derived products. At present, little is known how the isolation and expansion procedure in xenogeneic-free conditions affects the therapeutical capacity of PB-ECFCs.

Results

The findings presented in this study indicate that human platelet lysate (PL) as a serum substitute yields twice more colonies per mL blood compared to the conventional isolation with fetal bovine serum (FBS). Isolated ECFCs displayed a higher proliferative ability in PL supplemented medium than cells in FBS medium during 30 days expansion. The cells at 18 cumulative population doubling levels (CPDL) retained their proliferative capacity, showed higher sprouting ability in fibrin matrices upon stimulation with FGF-2 and VEGF-A than the cells at 6 CPDL, and displayed low β-galactosidase activity. The increased sprouting of PB-ECFCs at 18 CPDL was accompanied by an intrinsic activation of the uPA/uPAR fibrinolytic system. Induced deficiency of uPA (urokinase-type plasminogen activator) or uPAR (uPA receptor) by siRNA technology completely abolished the angiogenic ability of PB-ECFCs in fibrin matrices. During the serial expansion, the gene induction of the markers associated with inflammatory activation such as VCAM-1 and ICAM-1 did not occur or only to limited extent. While further propagation up to 31 CPDL proceeded at a comparable rate, a marked upregulation of inflammatory markers occurred in all donors accompanied by a further increase of uPA/uPAR gene induction. The observed induction of inflammatory genes at later stages of long-term propagation of PB-ECFCs underpins the necessity to determine the right time-point for harvesting of sufficient number of cells with preserved therapeutical potential.

Conclusion

The presented isolation method and subsequent cell expansion in platelet lysate supplemented culture medium permits suitable large-scale propagation of PB-ECFC. For optimal use of PB-ECFCs in clinical settings, our data suggest that 15–20 CPDL is the most adequate maturation stage.

Heparin/Heparan sulfate proteoglycans glycomic interactome in angiogenesis: biological implications and therapeutical use

Angiogenesis, the process of formation of new blood vessel from pre-existing ones, is involved in various intertwined pathological processes including virus infection, inflammation and oncogenesis, making it a promising target for the development of novel strategies for various interventions. To induce angiogenesis, angiogenic growth factors (AGFs) must interact with pro-angiogenic receptors to induce proliferation, protease production and migration of endothelial cells (ECs). The action of AGFs is counteracted by antiangiogenic modulators whose main mechanism of action is to bind (thus sequestering or masking) AGFs or their receptors. Many sugars, either free or associated to proteins, are involved in these interactions, thus exerting a tight regulation of the neovascularization process. Heparin and heparan sulfate proteoglycans undoubtedly play a pivotal role in this context since they bind to almost all the known AGFs, to several pro-angiogenic receptors and even to angiogenic inhibitors, originating an intricate network of interaction, the so called "angiogenesis glycomic interactome". The decoding of the angiogenesis glycomic interactome, achievable by a systematic study of the interactions occurring among angiogenic modulators and sugars, may help to design novel antiangiogenic therapies with implications in the cure of angiogenesis-dependent diseases.

Conjugation of proteins to polymer chains to create multivalent molecules

The activation of cellular signaling cascades, critical for regulating cell function and fate, often involves changes in the organization of receptors in the cell membrane. Using synthetic multivalent ligands to control the nanoscale organization of cellular receptors into clusters is an attractive approach to elicit desired downstream cellular responses, since multivalent ligands can be significantly more potent than their corresponding monovalent ligands. Synthetic multivalent ligands can serve as both versatile biological tools and potent nanoscale therapeutics, for example in applications to harness them to control stem cell fate in vitro and in vivo. Here we describe the use of recombinant protein expression and bioconjugate chemistry to synthesize multivalent ligands that have the potential to regulate cell signaling in a variety of cell types.

Contrasting biofunctionalization strategies for the enhanced endothelialization of biodegradable vascular grafts

Surface modification of biodegradable vascular grafts is an important strategy to improve the in situ endothelialization of tissue engineered vascular grafts (TEVGs) and prevent major complications associated with current synthetic grafts. Important strategies for improving endothelialization include increasing endothelial cell mobilization and increased endothelial cell capture through biofunctionalization of TEVGs. The objective of this study was to assess two biofunctionalization strategies for improving endothelialization of biodegradable polyester vascular grafts. These techniques consisted of cross-linking heparin to graft surfaces to immobilize vascular endothelial growth factor (VEGF) or antibodies against CD34 (anti-CD34Ab). To this end, heparin, VEGF, and anti-CD34Ab attachment and quantification assays confirmed the efficacy of the modification strategy. Cell attachment and proliferation on these groups were compared to unmodified grafts in vitro and in vivo. To assess in vivo graft functionality, the grafts were implanted as inferior vena cava interpositional conduits in mice. Modified vascular grafts displayed increased endothelial cell attachment and activity in vivo, according to microscopy techniques, histological results, and eNOS expression. Inner lumen diameter of the modified grafts was also better maintained than controls. Overall, while both functionalized grafts outperformed the unmodified control, grafts modified with anti-CD34Ab appeared to yield the most improved results compared to VEGF-loaded grafts.

Discovering aptamers by cell-SELEX against human soluble growth factors ectopically expressed on yeast cell surface

SELEX, the process of selecting aptamers, is often hampered by the difficulty of preparing target molecules in their native forms and by a lack of a simple yet quantitative assay for monitoring enrichment and affinity of reactive aptamers. In this study, we sought to discover DNA aptamers against human serum markers for potential therapeutic and diagnostic applications. To circumvent soluble expression and immobilization for performing SELEX, we ectopically expressed soluble growth factors on the surface of yeast cells to enable cell-SELEX and devised a flow cytometry-based method to quantitatively monitor progressive enrichment of specific aptamers. High-throughput sequencing of selected pools revealed that the emergence of highly enriched sequences concurred with the increase in the percentage of reactive aptamers shown by flow cytometry. Particularly, selected DNA aptamers against VEGF were specific and of high affinity (K(D)  = ∼ 1 nM) and demonstrated a potent inhibition of capillary tube formation of endothelial cells, comparable to the effect of a clinically approved anti-VEGF antibody drug, bevacizumab. Considering the fact that many mammalian secretory proteins have been functionally expressed in yeast, the strategy of implementing cell-SELEX and quantitative binding assay can be extended to discover aptamers against a broad array of soluble antigens.

Glycosaminoglycan-based hydrogels to modulate heterocellular communication in in vitro angiogenesis models

Angiogenesis, the outgrowth of blood vessels, is crucial in development, disease and regeneration. Studying angiogenesis in vitro remains challenging because the capillary morphogenesis of endothelial cells (ECs) is controlled by multiple exogenous signals. Therefore, a set of in situ-forming starPEG-heparin hydrogels was used to identify matrix parameters and cellular interactions that best support EC morphogenesis. We showed that a particular type of soft, matrix metalloproteinase-degradable hydrogel containing covalently bound integrin ligands and reversibly conjugated pro-angiogenic growth factors could boost the development of highly branched, interconnected, and lumenized endothelial capillary networks. Using these effective matrix conditions, 3D heterocellular interactions of ECs with different mural cells were demonstrated that enabled EC network modulation and maintenance of stable vascular capillaries over periods of about one month in vitro. The approach was also shown to permit in vitro tumor vascularization experiments with unprecedented levels of control over both ECs and tumor cells. In total, the introduced 3D hydrogel co-culture system could offer unique options for dissecting and adjusting biochemical, biophysical, and cell-cell triggers in tissue-related vascularization models.

Demystifying heparan sulfate-protein interactions

Numerous proteins, including cytokines and chemokines, enzymes and enzyme inhibitors, extracellular matrix proteins, and membrane receptors, bind heparin. Although they are traditionally classified as heparin-binding proteins, under normal physiological conditions these proteins actually interact with the heparan sulfate chains of one or more membrane or extracellular proteoglycans. Thus, they are more appropriately classified as heparan sulfate-binding proteins (HSBPs). This review provides an overview of the various modes of interaction between heparan sulfate and HSBPs, emphasizing biochemical and structural insights that improve our understanding of the many biological functions of heparan sulfate.

Isolating single stranded DNA using a microfluidic dialysis device

Isolating a particular strand of DNA from a double stranded DNA duplex is an important step in aptamer generation as well as many other biotechnology applications. Here we describe a microfluidic, flow-through, dialysis device for isolating single-stranded DNA (ssDNA) from double-stranded DNA (dsDNA). The device consists of two channels fabricated in polydimethylsiloxane (PDMS) separated by a track etched polycarbonate membrane (800 nm pore size). To isolate ssDNA, dual-biotin labelled dsDNA was immobilized onto streptavidin-coated polystyrene beads. Alkaline treatment was used to denature dsDNA, releasing the non-biotinylated ssDNA. In the flow-through dialysis device the liberated ssDNA was able to cross the membrane and was collected in an outlet channel. The complementary sequence bound to the bead was unable to cross the membrane and was directed to a waste channel. The effect of NaOH concentration and flow rate on purity and yield were compared. >95% ssDNA purity was achieved at 25 mM NaOH. However, lower flow rates were necessary to achieve ssDNA yields approaching the 50% theoretical maximum of the concurrent-flow device. Under optimized conditions the microfluidic isolation achieved even higher purity ssDNA than analogous manual procedures.

Shifts in the vascular endothelial growth factor isoforms result in transcriptome changes correlated with early neural stem cell proliferation and differentiation in mouse forebrain

Regulation of neural stem cell (NSC) fate decisions is critical during the transition from a multicellular mammalian forebrain neuroepithelium to the multilayered neocortex. Forebrain development requires coordinated vascular investment alongside NSC differentiation. Vascular endothelial growth factor A (Vegf) has proven to be a pleiotrophic gene whose multiple protein isoforms regulate a broad range of effects in neurovascular systems. To test the hypothesis that the Vegf isoforms (120, 164, and 188) are required for normal forebrain development, we analyzed the forebrain transcriptome of mice expressing specific Vegf isoforms, Vegf120, VegfF188, or a combination of Vegf120/188. Transcriptome analysis identified differentially expressed genes in embryonic day (E) 9.5 forebrain, a time point preceding dramatic neuroepithelial expansion and vascular investment in the telencephalon. Meta-analysis identified gene pathways linked to chromosome-level modifications, cell fate regulation, and neurogenesis that were altered in Vegf isoform mice. Based on these gene network shifts, we predicted that NSC populations would be affected in later stages of forebrain development. In the E11.5 telencephalon, we quantified mitotic cells [Phospho-Histone H3 (pHH3)-positive] and intermediate progenitor cells (Tbr2/Eomes-positive), observing quantitative and qualitative shifts in these populations. We observed qualitative shifts in cortical layering at P0, particularly with Ctip2-positive cells in layer V. The results identify a suite of genes and functional gene networks that can be used to further dissect the role of Vegf in regulating NSC differentiation and downstream consequences for NSC fate decisions.

Multivalent ligands control stem cell behaviour in vitro and in vivo

There is broad interest in designing nanostructured materials that can interact with cells and regulate key downstream functions. In particular, materials with nanoscale features may enable control over multivalent interactions, which involve the simultaneous binding of multiple ligands on one entity to multiple receptors on another and are ubiquitous throughout biology. Cellular signal transduction of growth factor and morphogen cues (which have critical roles in regulating cell function and fate) often begins with such multivalent binding of ligands, either secreted or cell-surface-tethered to target cell receptors, leading to receptor clustering. Cellular mechanisms that orchestrate ligand-receptor oligomerization are complex, however, so the capacity to control multivalent interactions and thereby modulate key signalling events within living systems is currently very limited. Here, we demonstrate the design of potent multivalent conjugates that can organize stem cell receptors into nanoscale clusters and control stem cell behaviour in vitro and in vivo. The ectodomain of ephrin-B2, normally an integral membrane protein ligand, was conjugated to a soluble biopolymer to yield multivalent nanoscale conjugates that potently induce signalling in neural stem cells and promote their neuronal differentiation both in culture and within the brain. Super-resolution microscopy analysis yielded insights into the organization of the receptor-ligand clusters at the nanoscale. We also found that synthetic multivalent conjugates of ephrin-B1 strongly enhance human embryonic and induced pluripotent stem cell differentiation into functional dopaminergic neurons. Multivalent bioconjugates are therefore powerful tools and potential nanoscale therapeutics for controlling the behaviour of target stem cells in vitro and in vivo.

Functional porous hydrogels to study angiogenesis under the effect of controlled release of vascular endothelial growth factor

Angiogenesis occurs through a cascade of events controlled by complex multiple signals that are orchestrated according to specific spatial patterns and temporal sequences. Vascularization is a central issue in most tissue engineering applications. However, only a better insight into spatio-temporal signal presentation can help in controlling and guiding angiogenesis in vivo. To this end, versatile and accessible material platforms are required in order to study angiogenic events in a systematic way. In this work we report a three-dimensional porous polyethylene glycol (PEG) diacrylate hydrogel bioactivated with heparin that is able to deliver vascular endothelial growth factor (VEGF) in a sustained and controlled manner. The efficiency of the material has been tested both in vitro and in vivo. In particular, the VEGF released from the hydrogel induces cell proliferation when tested on HUVECs, retains its bioactivity up to 21days, as demonstrated by Matrigel assay, and, when implanted on a chorion allantoic membrane, the hydrogel shows superior angiogenic potential in stimulating new vessel formation compared with unfunctionalized hydrogels. Moreover, in the light of potential tissue regeneration studies, the proposed hydrogel has been modified with adhesion peptides (RGD) to enable cell colonization. The porous hydrogel reported here can be used as a valid tool to characterize angiogenesis, and, possibly, other biological processes, in different experimental set-ups.