Collagen-targeting vascular endothelial growth factor improves cardiac performance after myocardial infarction

Acceleration of wound healing in acute full-thickness skin wounds using a collagen-binding peptide with an affinity for MSCs

Mesenchymal stem cells (MSCs) have been accepted as a promising cell source in tissue repair and regeneration. However, the inability to enrich MSCs in target areas limits their wide application. As a result, it has been a major goal to induce MSCs to be abundantly and specifically recruited to the injury site. In this study, a peptide with a specific affinity for MSCs (E7 peptide) was immobilized to a collagen scaffold via a collagen-binding domain (CBD) to construct a functional collagen scaffold. In addition, the hypothesis that this method could recruit MSCs specifically was evaluated in a porcine model. In vivo investigations indicated that due to the immunore-action, the CBD-MSC-peptide collagen scaffold enhanced MSC adhesion and infiltration and promoted wound healing. At day 7 after surgery, we found more infiltrating cells and capillaries in the Collagen/CBD-E7 peptide group compared to the Scaffold group. At day 14, 21 and 28, a faster healing process was observed in the Collagen/CBD-E7 peptide group, with significant differences compared with the other groups (P < 0.05, P < 0.01). The results demonstrate the potential use of targeted therapy to rapidly heal skin wounds.

Use of natural neural scaffolds consisting of engineered vascular endothelial growth factor immobilized on ordered collagen fibers filled in a collagen tube for peripheral nerve regeneration in rats

The search for effective strategies for peripheral nerve regeneration has attracted much attention in recent years. In this study, ordered collagen fibers were used as intraluminal fibers after nerve injury in rats. Vascular endothelial growth factor (VEGF) plays an important role in nerve regeneration, but its very fast initial burst of activity within a short time has largely limited its clinical use. For the stable binding of VEGF to ordered collagen fibers, we fused a collagen-binding domain (CBD) to VEGF through recombinant DNA technology. Then, we filled the ordered collagen fibers-CBD-VEGF targeting delivery system in a collagen tube to construct natural neural scaffolds, which were then used to bridge transected nerve stumps in a rat sciatic nerve transection model. After transplantation, the natural neural scaffolds showed minimal foreign body reactions and good integration into the host tissue. Oriented collagen fibers in the collagen tube could guide regenerating axons in an oriented manner to the distal, degenerating nerve segment, maximizing the chance of target reinnervation. Functional and histological analyses indicated that the recovery of nerve function in the natural neural scaffolds-treated group was superior to the other grafted groups. The guiding of oriented axonal regeneration and effective delivery systems surmounting the otherwise rapid and short-lived diffusion of growth factors in body fluids are two important strategies in promoting peripheral nerve regeneration. The natural neural scaffolds described take advantage of these two aspects and may produce synergistic effects. These properties qualified the artificial nerve conduits as a putative candidate system for the fabrication of peripheral nerve reconstruction devices.

Scaffold biomaterials for nano-pathophysiology

This review is intended to provide an overview of tissue engineering strategies using scaffold biomaterials to develop a vascularized tissue engineered construct for nano-pathophysiology. Two primary topics are discussed. The first is the biological or synthetic microenvironments that regulate cell behaviors in pathological conditions and tissue regeneration. Second is the use of scaffold biomaterials with angiogenic factors and/or cells to realize vascularized tissue engineered constructs for nano-pathophysiology. These topics are significantly overlapped in terms of three-dimensional (3-D) geometry of cells and blood vessels. Therefore, this review focuses on neovascularization of 3-D scaffold biomaterials induced by angiogenic factors and/or cells. The novel strategy of this approach in nano-pathophysiology is to utilize the vascularized tissue engineered construct as a tissue model to predict the distribution and subsequent therapeutic efficacy of a drug delivery system with different physicochemical and biological properties.

Cardiac Tissue Vascularization: From Angiogenesis to Microfluidic Blood Vessels

Myocardial infarction results from a blockage of a major coronary artery that shuts the delivery of oxygen and nutrients to a region of the myocardium, leading to massive cardiomyocytes death and regression of microvasculature. Growth factor and cell delivery methods have been attempted to revascularize the ischemic myocardium and prevent further cell death. Implantable cardiac tissue patches were engineered to directly revascularize as well as remuscularize the affected muscle. However, inadequate vascularization in vitro and in vivo limits the efficacy of these new treatment options. Breakthroughs in cardiac tissue vascularization will profoundly impact ischemic heart therapies. In this review, we discuss the full spectrum of vascularization approaches ranging from biological angiogenesis to microfluidic blood vessels as related to cardiac tissue engineering.

Cardiac tissue engineering: renewing the arsenal for the battle against heart disease

The development of therapies that lead to the regeneration or functional repair of compromised cardiac tissue is the most important challenge facing translational cardiovascular research today.

Emulsion electrospun nanofibers as substrates for cardiomyogenic differentiation of mesenchymal stem cells

The potential of cardiomyogenic differentiation of human mesenchymal stem cells (hMSCs) on emulsion electrospun scaffold containing poly(L-lactic acid)-co-poly-(ε-caprolactone), gelatin and vascular endothelial growth factor (PLCL/GV) was investigated in this study. The characterizations of the scaffold were carried out using scanning electron microscope (SEM), transmission electron microscope, water contact angle and porometer. The proliferation of hMSCs showed that 73.4% higher cell proliferation on PLCL/GV scaffolds than that on PLCL scaffold after 20 days of cell culture. Results of 5-chloromethylfluorescein diacetate staining and SEM morphology analysis indicated that hMSCs differentiated on PLCL/GV scaffolds showed irregular morphology of cardiomyocyte phenotype compared to the typical long and thin hMSC phenotype. Immunostaining results showed the expression of alpha actinin and myosin heavy chain. Our studies identified emulsion electrospinning as a method for fabrication of core-shell fibers suitable for the differentiation of stem cells to cardiac cells, with potential application in cardiac regeneration.

Protein engineering for cardiovascular therapeutics: untapped potential for cardiac repair

A number of new and innovative approaches for repairing damaged myocardium are currently undergoing investigation, with several encouraging results. In addition to the progression of stem cell-based approaches and gene therapy/silencing methods, evidence continues to emerge that protein therapeutics may be used to directly promote cardiac repair and even regeneration. However, proteins are often limited in their therapeutic potential by short local half-lives and insufficient bioavailability and bioactivity, and many academic laboratories studying cardiovascular diseases are more comfortable with molecular and cellular biology than with protein biochemistry. Protein engineering has been used broadly to overcome weaknesses traditionally associated with protein therapeutics and has the potential to specifically enhance the efficacy of molecules for cardiac repair. However, protein engineering as a strategy has not yet been used in the development of cardiovascular therapeutics to the degree that it has been used in other fields. In this review, we discuss the role of engineered proteins in cardiovascular therapies to date. Further, we address the promise of applying emerging protein engineering technologies to cardiovascular medicine and the barriers that must be overcome to enable the ultimate success of this approach.

Single-molecule level binding force between collagen and collagen binding domain-growth factor conjugates

Biological studies have shown that collagen/collagen binding domain (CBD)-growth factor composites are effective biomaterials systems for tissue engineering and regeneration. Here we present atomic force spectroscopy (AFM)-based investigations at the single molecule level to address fundamental biophysical questions such as CBD binding sites distribution and the mechanism for controlled release of growth factors from the collagen scaffold. Non-uniformly distributed CBD binding sites on collagen membrane are directly visualized with a quantum dot-based bimodal imaging method. AFM force spectroscopy unbinding experiments reveal that modest unbinding force and dissociation constant of the CBD/collagen interaction could be the key for its successful application in controlled release systems.

Angiogenic therapy for cardiac repair based on protein delivery systems

Cardiovascular diseases remain the first cause of morbidity and mortality in the developed countries and are a major problem not only in the western nations but also in developing countries. Current standard approaches for treating patients with ischemic heart disease include angioplasty or bypass surgery. However, a large number of patients cannot be treated using these procedures. Novel curative approaches under investigation include gene, cell, and protein therapy. This review focuses on potential growth factors for cardiac repair. The role of these growth factors in the angiogenic process and the therapeutic implications are reviewed. Issues including aspects of growth factor delivery are presented in relation to protein stability, dosage, routes, and safety matters. Finally, different approaches for controlled growth factor delivery are discussed as novel protein delivery platforms for cardiac regeneration.

Therapeutic Approaches to the Regulation of Wound Angiogenesis

SIGNIFICANCE

Re-establishment of a functional vascular network is a critical component of successful wound repair. One of the most potent pro-angiogenic agents is vascular endothelial growth factor (VEGF), which, from a basic science and pre-clinical perspective, seems ideal for the therapeutic stimulation of blood vessel growth in non-healing wounds.

CRITICAL ISSUES

Current strategies to improve the dysfunctional angiogenesis that occurs in non-healing wounds are inadequate with regard to the nature and magnitude of the clinical problem. However, VEGF therapy has so far been unsuccessful in promoting healing in the clinic. More effective means of delivery to the wound, which take into account the biochemical and spatio-temporal aspects of angiogenesis, may be necessary to realize VEGF's therapeutic potential. Reviewed approaches for the regulation of wound angiogenesis include: targeting regulators of intracellular VEGF signaling, making use of collagen-binding VEGF fusion proteins for increased retention in the wound, and implantation of heterogeneous scaffold systems for spatial control of angiogenesis with simultaneous use of VEGF and its inhibitor.

FUTURE DIRECTIONS

To maximize efficacy of therapeutic VEGF, it may be necessary to also target its intracellular inhibitory mechanisms. Immobilizing VEGF to the wound matrix may increase its bioavailability and therapeutic efficacy. Gaining spatial control of angiogenesis opens up possibilities for advanced directed therapy. The reviewed studies present innovative approaches to in vivo directed modulation of angiogenesis utilizing VEGF biology which can, if taken further and validated in human subjects, have significant impact on clinical wound care in the future.

Ultrasound-mediated stimulation of microbubbles after acute myocardial infarction and reperfusion ameliorates left-ventricular remodelling in mice via improvement of borderzone vascularization

AIMS

Post-infarction remodelling (PIR) determines left-ventricular (LV) function and prognosis after myocardial infarction. The aim of this study was to evaluate transthoracic ultrasound-mediated microbubble stimulation (UMS) as a novel gene- and cell-free therapeutic option after acute myocardial infarction and reperfusion (AMI/R) in mice.

METHODS AND RESULTS

For myocardial delivery of UMS, a novel therapeutic ultrasound-system (TIPS, Philips Medical) and commercially available microbubbles (BR1, Bracco Suisse SA) were utilized in a closed-chest mouse model. UMS was performed as myocardial post-conditioning (PC) on day four after 30 minutes of coronary occlusion and reperfusion. LV-morphology, as well as global and regional function were measured repeatedly with reconstructive 3-dimensional echocardiography applying an additional low-dose dobutamine protocol after two weeks. Scar size was quantified by means of histomorphometry. A total of 41 mice were investigated; 17 received PC with UMS. Mean ejection fraction (EF) prior UMS was similar in both groups 53%±10 (w/o UMS) and 53%±14 (UMS, p = 0.5), reflecting comparable myocardial mass at risk 17%±8 (w/o UMS), 16%±13 (UMS, p = 0.5). Two weeks after AMI/R, mice undergoing UMS demonstrated significantly better global LV-function (EF = 53%±7) as compared to the group without PC (EF = 39%±11, p<0.01). The fraction of akinetic myocardial mass was significantly lower among mice undergoing UMS after AMI/R [27%±10 (w/o UMS), 13%±8 (UMS), p<0.001)]. Our experiments showed a fast onset of transient, UMS-induced upregulation of vascular-endothelial and insulin-like growth factor (VEGF-a, IGF-1), as well as caveolin-3 (Cav-3). The mice undergoing PC with UMS after AMI/R showed a significantly lower scar size. In addition, the microvascular density was significantly higher in the borderzone of UMS-treated animals.

CONCLUSION

UMS following AMI/R ameliorates PIR in mice via up-regulation of VEGF-a, IGF-1 and Cav-3, and consecutive improvement of myocardial borderzone vascularization.

In vivo cardiac cellular reprogramming efficacy is enhanced by angiogenic preconditioning of the infarcted myocardium with vascular endothelial growth factor

BACKGROUND

In situ cellular reprogramming offers the possibility of regenerating functional cardiomyocytes directly from scar fibroblasts, obviating the challenges of cell implantation. We hypothesized that pretreating scar with gene transfer of the angiogenic vascular endothelial growth factor (VEGF) would enhance the efficacy of this strategy.

METHODS AND RESULTS

Gata4, Mef2c, and Tbx5 (GMT) administration via lentiviral transduction was demonstrated to transdifferentiate rat fibroblasts into (induced) cardiomyocytes in vitro by cardiomyocyte marker studies. Fisher 344 rats underwent coronary ligation and intramyocardial administration of an adenovirus encoding all 3 major isoforms of VEGF (AdVEGF-All6A(+)) or an AdNull control vector (n=12/group). Lentivirus encoding GMT or a GFP control was administered to each animal 3 weeks later, followed by histologic and echocardiographic analyses. GMT administration reduced the extent of fibrosis by half compared with GFP controls (12 ± 2% vs 24 ± 3%, P<0.01) and reduced the number of myofibroblasts detected in the infarct zone by 4-fold. GMT-treated animals also demonstrated greater density of cardiomyocyte-specific marker beta myosin heavy chain 7(+) cells compared with animals receiving GFP with or without VEGF (P<0.01). Ejection fraction was significantly improved after GMT vs GFP administration (12 ± 3% vs -7 ± 3%, P<0.01). Eight (73%) GFP animals but no GMT animals demonstrated decreased ejection fraction during this interval (P<0.01). Also, improvement in ejection fraction was 4-fold greater in GMT/VEGF vs GMT/null animals (17 ± 2% vs 4 ± 1%, P<0.05).

CONCLUSIONS

VEGF administration to infarcted myocardium enhances the efficacy of GMT-mediated cellular reprogramming in improving myocardial function and reducing the extent of myocardial fibrosis compared with the use of GMT or VEGF alone.

Induction of rat facial nerve regeneration by functional collagen scaffolds

Nerve conduit provides a promising strategy for nerve regeneration, and the proper microenvironment in the lumen could improve the regeneration. Our previous work had demonstrated that linear ordered collagen scaffold (LOCS) could effectively guide the oriented growth of axons. Laminin is known as an important nerve growth promoting factor and can facilitate the growth cone formation. In addition, ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) can effectively improve the nerve regeneration after nerve injuries. However, in practice, diffusion caused by the body fluids is the major obstacle in their applications. To retain CNTF or BDNF on the scaffolds, we produced collagen binding CNTF (CBD-CNTF), collagen binding BDNF (CBD-BDNF) and laminin binding CNTF (LBD-CNTF), laminin binding BDNF (LBD-BDNF) respectively. In this work, we developed laminin modified LOCS fibers (L × LOCS) by chemical cross-linking LOCS fibers with laminin. Collagen binding or laminin binding neurotrophic factors were combined with LOCS or L × LOCS, and then filled them into the collagen nerve conduit. They were found to guide the ordered growth of axons, and improve the nerve functional recovery in the rat facial nerve transection model. The combination of CNTF and BDNF greatly enhanced the facial nerve regeneration and functional recovery.

Therapeutic angiogenesis: controlled delivery of angiogenic factors

Therapeutic angiogenesis aims at treating ischemic diseases by generating new blood vessels from existing vasculature. It relies on delivery of exogenous factors to stimulate neovasculature formation. Current strategies using genes, proteins and cells have demonstrated efficacy in animal models. However, clinical translation of any of the three approaches has proved to be challenging for various reasons. Administration of angiogenic factors is generally considered safe, according to accumulated trials, and offers off-the-shelf availability. However, many hurdles must be overcome before therapeutic angiogenesis can become a true human therapy. This article will highlight protein-based therapeutic angiogenesis, concisely review recent progress and examine critical challenges. We will discuss growth factors that have been widely utilized in promoting angiogenesis and compare their targets and functions. Lastly, since bolus injection of free proteins usually result in poor outcomes, we will focus on controlled release of proteins.

Thrombopoietin improved ventricular function and regulated remodeling genes in a rat model of myocardial infarction

BACKGROUND

Thrombopoietin (TPO) protects against heart damages by doxorubicin-induced cardiomyopathy in animal models. We aimed to investigate the therapeutic efficacy of TPO for treatment of myocardial infarction (MI) in a rat model and explored the mechanisms in terms of the genome-wide transcriptional profile, TPO downstream protein signals, and bone marrow endothelial progenitor cells (EPCs).

METHODS

Sprague-Dawley rats were divided into 3 groups: Sham-operated, MI (permanent ligation of the left coronary artery) and MI+TPO. Three doses of TPO were administered weekly for 2 weeks, and outcomes were assessed at 4 or 8 weeks post-injury.

RESULTS AND CONCLUSIONS

TPO treatment significantly improved left ventricular function, hemodynamic parameters, myocardium morphology, neovascularization and infarct size. MI damage upregulated a large cohort of gene expressions in the infarct border zone, including those functioned in cytoskeleton organization, vascular and matrix remodeling, muscle development, cell cycling and ion transport. TPO treatment significantly reversed these modulations. While phosphorylation of janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3) and protein kinase B (AKT) was modified in MI animals, TPO treatment regulated phosphorylation of STAT3 and extracellular signal-regulated kinases (ERK), and bone morphogenetic protein 1 (BMP1) protein level. TPO also increased EPC colonies in the bone marrow of MI animals. Our data showed that TPO alleviated damages of heart tissues from MI insults, possibly mediated by multi-factorial mechanisms including suppression of over-reacted ventricular remodeling, regulation of TPO downstream signals and mobilization of endothelial progenitor cells. TPO could be developed for treatment of cardiac damages.

Sustained delivery of VEGF from designer self-assembling peptides improves cardiac function after myocardial infarction

Poor vascularization and insufficient oxygen supply are detrimental to the survival of residual cardiomyocytes or transplanted stem cells after myocardial infarction. To prolong and slow the release of angiogenic factors, which stimulate both angiogenesis and vasculogenesis, we constructed a novel self-assembling peptide by attaching the heparin-binding domain sequence LRKKLGKA to the self-assembling peptide RADA16. This designer self-assembling peptide self-assembled into nanofiber scaffolds under physiological conditions, as observed by atomic force microscopy. The injection of designer self-assembling peptides can efficiently provide the sustained delivery of VEGF for at least 1 month. At 4 weeks after transplantation, cardiac function was improved, and scar size and collagen deposition were markedly reduced in the group receiving VEGF with the LRKKLGKA scaffolds compared with groups receiving VEGF alone, LRKKLGKA scaffolds alone or VEGF with RADA16 scaffolds. The microvessel density in the VEGF with LRKKLGKA group was higher than that in the VEGF with RADA16 group. TUNEL and cleaved caspase-3 expression assays showed that the transplantation of VEGF with LRKKLGKA enhanced cell survival in the infarcted heart. These results present the tailor-made peptide scaffolds as a new generation of sustained-release biomimetic biomaterials and suggest that the use of angiogenic factors along with designer self-assembling peptides can lead to myocardial protection, sufficient angiogenesis, and improvement in cardiac function.

Design and synthesis of binding growth factors

Growth factors play important roles in tissue regeneration. However, because of their instability and diffusible nature, improvements in their performance would be desirable for therapeutic applications. Conferring binding affinities would be one way to improve their applicability. Here we review techniques for conjugating growth factors to polypeptides with particular affinities. Conjugation has been designed at the level of gene fusion and of polypeptide ligation. We summarize and discuss the designs and applications of binding growth factors prepared by such conjugation approaches.

Increased expression of integrin-linked kinase improves cardiac function and decreases mortality in dilated cardiomyopathy model of rats

Aims

Integrin-linked kinase (ILK) is a multifunctional kinase linking the extracellular matrix to intracellular signaling pathways, whose activation in the heart gives rise to a number of functional consequences. The aim of this study is to demonstrate the therapeutic and survival benefit of cardiac ILK overexpression in a rat model of dilated cardiomyopathy.

Methods and Results

The dilated cardiomyopathy model was generated in rats by intraperitoneal administration of six equal doses of doxorubicin over a 2 week period. Five weeks after the first injection, echocardiographic analysis demonstrated impaired cardiac function and, at that point, recombinant adenoviral vector harboring ILK cDNA or vehicle was injected into the myocardium, and the rats re-studied 4 weeks later. Compared with vehicle injection, ILK treatment ameliorated inflammatory cell infiltration and cardiomyocyte degeneration, as well as left ventricular dilation and dysfunction. ILK treatment was also associated with a reduction in apoptosis and an increase in proliferation of cardiomyocytes, as well as decreased oxidative stress and autophagic vacuole accumulation. Importantly, mortality was lower in rats following ILK treatment than in those following vehicle injection. In cultured neonatal rat cardiomyocytes, we also found that ILK overexpression protected against doxorubicin-induced apoptosis, giving rise to an increase in their proliferation.

Conclusions

These data demonstrate for the first time that ILK gene therapy improves cardiac function and survival in a model of dilated cardiomyopathy, and this may be mediated through suppression of inflammation, prevention of ventricular remodeling, inhibition of cardiomyocyte apoptosis and autophagy, and stimulation of cardiomyocyte proliferation.

The effect of collagen-binding vascular endothelial growth factor on the remodeling of scarred rat uterus following full-thickness injury

Serious injuries of uterine which lead to scar formation will finally result in infertility or pregnancy complications. There are few effective methods to treat such damages because of the shortage of native tissues. Vascular endothelial growth factor (VEGF) is important for the formation of new vessels and re-epithelialization of endometrium. Here we produced a collagen-binding VEGF by fusing a collagen-binding domain to the N-terminal of native VEGF. After injection into a rat scarred uterus model (partial of rat uterine horn was excised and left for scar formation) the collagen targeting VEGF promoted remodeling of the scarred uterus including the regeneration of endometrium, muscular cells, and vascularization and improved pregnancy outcomes. Thus, collagen-binding VEGF may be a pragmatic solution for the treatment of severe uterine damages.

Nestin+ cells and healing the infarcted heart

Scar formation following an ischemic insult to the heart is referred to as reparative fibrosis and represents an essential physiological response to heal the damaged myocardium. The biological events of reparative fibrosis include inflammation, the deposition of collagen by myofibroblasts, sympathetic innervation, and angiogenesis. Several studies have further reported that scar formation was associated with the recruitment of neural crest-derived cardiac resident nestin(+) cells that display characteristics consistent with a neural progenitor/stem cell phenotype. During the reparative fibrotic response, these nestin(+) cells participate in neural remodeling and represent a novel cellular substrate of angiogenesis. In addition, a subpopulation of nestin(+) cells identified in the normal heart expressed cardiac progenitor transcriptional factors and may directly contribute to myocardial regeneration following ischemic damage. Nestin protein was also detected in endothelial cells of newly formed blood vessels in the scar and may represent a marker of revascularization. Lastly, nestin was induced in a subpopulation of smooth muscle α-actin(+) scar-derived myofibroblasts, and the expression of the intermediate filament protein may provide a proliferative advantage. Collectively, these data demonstrate that diverse populations of nestin(+) cells participate in cardiac wound healing.

Regeneration of uterine horns in rats by collagen scaffolds loaded with collagen-binding human basic fibroblast growth factor

Severe damages of uterine endometrium which prevent embryos from implantation and placentation finally often result in infertility or pregnant complications. There is lack of effective treatments due to the limitation of native materials available and complexity of the function and internal environment of uterus. In the present study, a collagen targeting basic fibroblast growth factor (bFGF) delivery system was constructed by a collagen membrane loaded with bFGF fused a collagen-binding domain (CBD) to the N-terminal which limits the diffusion of bFGF from collagen. We tested the bFGF delivery system in rats under the severe uterine damage model (partial rat uterine horn excision/reconstruction), and found this delivery system improved regeneration abilities of uterine endometrium and muscular cells, improved vascularization, as well as better pregnancy outcomes in rats. Therefore, this targeting delivery system may be an effective strategy for uterine tissue regeneration.

Strategies for tissue engineering cardiac constructs to affect functional repair following myocardial infarction

Tissue-engineered cardiac constructs are a high potential therapy for treating myocardial infarction. These therapies have the ability to regenerate or recreate functional myocardium following the infarction, restoring some of the lost function of the heart and thereby preventing congestive heart failure. Three key factors to consider when developing engineered myocardial tissue include the cell source, the choice of scaffold, and the use of biomimetic culture conditions. This review details the various biomaterials and scaffold types that have been used to generate engineered myocardial tissues as well as a number of different methods used for the fabrication and culture of these constructs. Specific bioreactor design considerations for creating myocardial tissue equivalents in vitro, such as oxygen and nutrient delivery as well as physical stimulation, are also discussed. Lastly, a brief overview of some of the in vivo studies that have been conducted to date and their assessment of the functional benefit in repairing the injured heart with engineered myocardial tissue is provided.

A myocardial patch made of collagen membranes loaded with collagen-binding human vascular endothelial growth factor accelerates healing of the injured rabbit heart

Tissue-engineered myocardial patches could be useful in the repair of myocardial injuries. The aim of the present study was to evaluate a collagen targeting delivery system for myocardial repair. A specific peptide collagen-binding domain (CBD) was fused to human vascular endothelial growth factor (VEGF) to enhance the binding of VEGF to collagen. In this study, collagen membranes loaded with CBD-VEGF, natural VEGF, or phosphate-buffered saline are used as cardiac patches to repair the infarcted myocardium in a rabbit model. CBD-VEGF/collagen group could effectively induce more cells to penetrate into the collagen membrane after 4 weeks and promote more vascularization in infarcted myocardium after 12 weeks compared with the other two control groups. Echocardiography and hemodynamic studies both show cardiac function improvement in the CBD-VEGF/collagen group. These results reveal that implantation of CBD-VEGF collagen membrane patch into the infarcted myocardium could effectively improve left ventricle cardiac function and increase the vascular density.

Portal vein infusion of recombinant vascular endothelial growth factor 165 mitigates liver fibrosis in cirrhotic rats

AIM: To evaluate the effect of portal vein infusion of recombinant vascular endothelial growth factor (VEGF) 165 on liver fibrosis in rats with cirrhosis.

METHODS: Fifty male SD rats were randomly divided into normal group (n = 10) and model group (n = 40). The model group was used to induce cirrhosis using the thioacetamide approach. After 10 wk, 25 cirrhotic rats were randomly divided into experimental group (n = 15) and model control group (n = 10). The experimental group was intubated for implantation of an Alzet osmotic pump, which was used to infuse recombinant VEGF165 via the portal vein for 2 wk. The normal group and model control group underwent sham operation. All rats were killed after 2 wk, and HE staining was used to observe the pathological changes in liver tissue. Serum hyaluronic acid and laminin were measured using radioimmunoassay method. Immunohistochemistry was used to detect the expression of type I and type IV collagen in the liver.

RESULTS: Degeneration and necrosis of liver cells, diffuse proliferation of fibrous connective tissue and formation of pseudo lobules occurred in the model control group. In the experimental group, degeneration and necrosis of liver cells were milder and the rate of liver fibrosis was improved significantly compared to the model control group (P < 0.01). Compared to the normal group, serum hyaluronic acid and laminin concentrations increased significantly in the model control group (P < 0.01). However, serum concentrations of hyaluronic acid and laminin was significantly lower in the experimental group than in the model control group (412.63 μg/L ± 85.18 μg/L vs 741.60 μg/L ± 72.83 μg/L; 58.87 μg/L ± 5.46 μg/L vs 92.80 μg/L ± 8.41 μg/L; both P < 0.01). The expression levels of type I and type IV collagen in the liver was significantly lower in the experimental group than in the model control group (6.84 ± 0.96, 8.25 ± 0.82 vs 18.38 ± 1.86, 20.86 ± 2.48, all P < 0.01).

CONCLUSION: Portal vein infusion of VEGF165 can relieve liver fibrosis in rats with cirrhosis.

Biomaterials that regulate growth factor activity via bioinspired interactions

Growth factor activity is localized within the natural extracellular matrix (ECM) by specific non-covalent interactions with core ECM biomolecules, such as proteins and proteoglycans. Recently, these interactions have inspired us and others to develop synthetic biomaterials that can non-covalently regulate growth factor activity for tissue engineering applications. For example, biomaterials covalently or non-covalently modified with heparin glycosaminoglycans can augment growth factor release strategies. In addition, recent studies demonstrate that biomaterials modified with heparin-binding peptides can sequester cell-secreted heparin proteoglycans and, in turn, sequester growth factors and regulate stem cell behavior. Another set of studies show that modular versions of growth factor molecules can be designed to interact with specific components of natural and synthetic ECMs, including collagen and hydroxyapatite. In addition, layer-by-layer assemblies of GAGs and other natural polyelectrolytes retain growth factors at a cell-material interface via specific non-covalent interactions. This review will detail the various bioinspired strategies being used to non-covalently localize growth factor activity within biomaterials, and will highlight in vivo examples of the efficacy of these materials to promote tissue regeneration.

Engineered cardiac tissues

Cardiac tissue engineering offers the promise of creating functional tissue replacements for use in the failing heart or for in vitro drug screening. The last decade has seen a great deal of progress in this field with new advances in interdisciplinary areas such as developmental biology, genetic engineering, biomaterials, polymer science, bioreactor engineering, and stem cell biology. We review here a selection of the most recent advances in cardiac tissue engineering, including the classical cell-scaffold approaches, advanced bioreactor designs, cell sheet engineering, whole organ decellularization, stem cell-based approaches, and topographical control of tissue organization and function. We also discuss current challenges in the field, such as maturation of stem cell-derived cardiac patches and vascularization.

Improved cellularization and angiogenesis using collagen scaffolds chemically conjugated with vascular endothelial growth factor

Much research has focused on developing vascular endothelial growth factor (VEGF) delivery systems to enhance angiogenesis in wound repair and in tissue engineering. Collagen can be used as a delivery system because of its biocompatibility, but its fast degradation rate and limited affinity with growth factors are disadvantageous for maintaining a sufficient growth factor concentration at injury sites. To enhance VEGF binding to collagen scaffolds and reduce the collagen degradation rate we found a simple way to modify porous collagen scaffolds by chemical addition of sulfhydryl groups, which then allow both cross-linking of the collagen fibers with each other and the immobilization of more VEGF in the scaffold after treatment with sulfo-SMCC. We demonstrated that cross-linking led to a slower degradation rate of the collagen scaffolds, while cellularization was improved by both cross-linking and the presence of VEGF. On the other hand, angiogenesis was increased only moderately by cross-linking, but significantly more by the presence of immobilized VEGF. We conclude that collagen scaffolds chemically conjugated to VEGF by Traut's reagent and sulfo-SMCC is an effective delivery system in wound repair and tissue engineering.

Renalase deficiency in heart failure model of rats--a potential mechanism underlying circulating norepinephrine accumulation

Background

Sympathetic overactivity and catecholamine accumulation are important characteristic findings in heart failure, which contribute to its pathophysiology. Here, we identify a potential mechanism underlying norepinephrine accumulation in a rat model of heart failure.

Methodology/Principal Findings

Initially, we constructed a rat model of unilateral renal artery stenosis (n = 16) and found that the expression of renalase, a previously identified secreted amine oxidase, was markedly reduced in the ischemic compared to the non-ischemic kidney (protein: 0.295±0.085 versus 0.765±0.171, p<0.05). Subsequently, we utilized an isolated perfused rat kidney model to demonstrate that the clearance rate of norepinephrine decreased with reduction of perfusion flow. On the basis of these findings, we hypothesized the reduced renal blood supply which occurs in heart failure would result in impaired synthesis of renalase by the kidney and consequently reduced degradation of circulating norepinephrine. To verify this, we used a rat model of infarction-induced heart failure (n = 12 per group). In these rats, the flow velocity of renal artery, when measured at four weeks, is obviously lower in the operation group. Renal expression of renalase was reduced (protein: 0.476±0.043 for control, 0.248±0.029 for operation versus 0.636±0.151 for sham-operation) and this was associated with an increase in circulating norepinephrine (0.168±0.016 ng/mL for control, 0.203±0.019 ng/mL for operation versus 0.138±0.008 ng/mL for sham-operation).

Conclusions/Significance

Renalase expression is influenced by renal blood flow and impaired synthesis of renalase by the kidney may represent a potential mechanism underlying circulating norepinephrine accumulation in heart failure.

The impact of vascular endothelial growth factor and basic fibroblast growth factor on cardiac fibroblasts grown under altered gravity conditions

BACKGROUND

Myocardium is very sensitive to gravitational changes. During a spaceflight cardiovascular atrophy paired with rhythm problems and orthostatic intolerance can occur. The aim of this study was to investigate the impact of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) on cardiac fibroblasts (CF) grown under altered gravity conditions.

METHODS

We examined the influence of exposure to a Random Positioning Machine (RPM) on CF, derived from porcine hearts. We focused on growth, extracellular matrix protein (ECMP) synthesis and apoptosis.

RESULTS

When cultured on a RPM, CF began to form 3D spheroids within 24h, irrespective of growth factor treatment. Exposure to RPM induced an increased synthesis of ECMP and also resulted in elevated apoptosis in adherent CF as measured by terminal deoxynucleotidyl transferase-mediated dUTP digoxigenin nick end labeling (TUNEL) analysis, 4',6-diamidino-2-phenylindole (DAPI) staining, and caspase-3 detection. bFGF and VEGF significantly decreased the amount of ECMP (collagen type I, III, chondroitin sulfate) in 1g and RPM cultures, and also significantly reduced the amount of apoptotic CF as well as caspase-3.

CONCLUSIONS

Altered gravity conditions on a RPM induced 3D growth, elevated ECMP synthesis and apoptosis in cardiac fibroblasts. Growth factor treatment attenuated programmed cell death and ECMP secretion.

Acceleration of diabetic wound healing by collagen-binding vascular endothelial growth factor in diabetic rat model

AIMS

Vascular endothelial growth factor (VEGF) is an important active protein for the induction of angiogenesis and plays an important role in the tissue regeneration of diabetic wounds. In this study, we used collagen-binding VEGF in a diabetic rat model to investigate the effects of this new method.

METHODS

We produced a fusion protein (CBD-VEGF) consisting of VEGF and a collagen-binding domain (CBD), which allowed VEGF to bind to collagen. The diabetic rat models were made by injected streptozocin (STZ) peritoneally and removed full thickness skin on the back. All the rats were randomly divided into 3 groups: PBS group (n=24), NAT-VEGF group (n=24), and CBD-VEGF group (n=24). After model establishment, the dissolved drugs were evenly given on the wounds using syringe. The healing rates were calculated and compared among the groups and the tissues of the wound were taken and evaluated for histological analysis.

RESULTS

The CBD-VEGF group showed better result in wound healing rate, better vascularization and higher amount of VEGF in the wound granulation tissue compared with NAT-VEGF group and control.

CONCLUSIONS

Topical application of CBD-VEGF can promote diabetic wound healing in rat model, which could potentially provide a better therapeutic option for diabetic wounds.

Loading of VEGF to the heparin cross-linked demineralized bone matrix improves vascularization of the scaffold

Deficient vascularization is one of the prominent shortcomings of porous tissue-engineering scaffolds, which results in insufficient oxygen and nutrients transportation. Here, heparin cross-linked demineralized bone matrices (HC-DBM) pre-loaded with vascular endothelial growth factor (VEGF) were designed to promote cells and new microvessels invasion into the matrices. After being chemical crosslinked with heparin by N-hydroxysuccinimide and N-(3-di-methylaminopropyl)-N'-ethylcarbodiimide, the scaffold could bind more VEGF than the non-crosslinked one and achieve localized and sustained delivery. The biological activity of VEGF binding on heparinized collagen was demonstrated by promoting endothelial cells proliferation. Evaluation of the angiogenic potential of heparinized DBM loaded with VEGF was further investigated by subcutaneous implantation. Improved angiogenesis of heparinized DBM loaded with VEGF was observed from haematoxylin-eosin staining and immunohistochemistry examination. The results demonstrated that heparin cross-linked DBM binding VEGF could be a useful strategy to stimulate cells and blood vessels invasion into the scaffolds.

Altered hepatic gene expression profiles associated with myocardial ischemia

BACKGROUND

Acute coronary syndrome is sometimes accompanied by accelerated coagulability, lipid metabolism, and inflammatory responses, which are not attributable to the cardiac events alone. We hypothesized that the liver plays a pivotal role in the pathophysiology of acute coronary syndrome. We simultaneously analyzed the gene expression profiles of the liver and heart during acute myocardial ischemia in mice.

METHODS AND RESULTS

-Mice were divided into 3 treatment groups: sham operation, ischemia/reperfusion, and myocardial infarction. Mice with liver ischemia/reperfusion were included as additional controls. Marked changes in hepatic gene expression were observed after 24 hours, despite the lack of histological changes in the liver. Genes related to tissue remodeling, adhesion molecules, and morphogenesis were significantly upregulated in the livers of mice with myocardial ischemia/reperfusion or infarction but not in those with liver ischemia/reperfusion. Myocardial ischemia, but not changes in the hemodynamic state, was postulated to significantly alter hepatic gene expression. Moreover, detailed analysis of the signaling pathway suggested the presence of humoral factors that intervened between the heart and liver. To address these points, we used isolated primary hepatocytes and showed that osteopontin released from the heart actually altered the signaling pathways of primary hepatocytes to those observed in the livers of mice under myocardial ischemia. Moreover, osteopontin stimulated primary hepatocytes to secrete vascular endothelial growth factor-A, which is important for tissue remodeling.

CONCLUSIONS

Hepatic gene expression is potentially regulated by cardiac humoral factors under myocardial ischemia. These results provide new insights into the pathophysiology of acute coronary syndrome.