Cell therapies for therapeutic angiogenesis: back to the bench

Promoting angiogenesis and diabetic wound healing through delivery of protein transduction domain-BMP2 formulated nanoparticles with hydrogel

Decreased angiogenesis contributes to delayed wound healing in diabetic patients. Recombinant human bone morphogenetic protein-2 (rhBMP2) has also been demonstrated to promote angiogenesis. However, the short half-lives of soluble growth factors, including rhBMP2, limit their use in wound-healing applications. To address this limitation, we propose a novel delivery model using a protein transduction domain (PTD) formulated in a lipid nanoparticle (LNP). We aimed to determine whether a gelatin hydrogel dressing loaded with LNP-formulated PTD-BMP2 (LNP-PTD-BMP2) could enhance the angiogenic function of BMP2 and improve diabetic wound healing. In vitro, compared to the control and rhBMP2, LNP-PTD-BMP2 induced greater tube formation in human umbilical vein endothelial cells and increased the cell recruitment capacity of HaCaT cells. We inflicted large, full-thickness back skin wounds on streptozotocin-induced diabetic mice and applied gelatin hydrogel (GH) cross-linked by microbial transglutaminase containing rhBMP2, LNP-PTD-BMP2, or a control to these wounds. Wounds treated with LNP-PTD-BMP2-loaded GH exhibited enhanced wound closure, increased re-epithelialization rates, and higher collagen deposition than those with other treatments. Moreover, LNP-PTD-BMP2-loaded GH treatment resulted in more CD31- and α-SMA-positive cells, indicating greater neovascularization capacity than rhBMP2-loaded GH or GH treatments alone. Furthermore, in vivo near-infrared fluorescence revealed that LNP-PTD-BMP2 has a longer half-life than rhBMP2 and that BMP2 localizes around wounds. In conclusion, LNP-PTD-BMP2-loaded GH is a viable treatment option for diabetic wounds.

Creation of a vascular inducing device using mesenchymal stem cells to induce angiogenesis

Conventional treatments of peripheral vascular disease and coronary artery disease have partial success but are still limited. Methods to deliver angiogenic factors into ischemic areas using gene, protein and cell therapies are faced with difficult issues such a delivery, effective concentration and duration of action. Tissue engineering offers the possibility of creating a functional self-contained three-dimensional (3D) unit that works as a coordinated biological pump that can secrete a whole range of angiogenic factors. We report a tissue engineering approach using decellularized micro-fragments and mesenchymal stem cells (MSCs) to create a vascular inducing device (VID). Proteomic analysis of the decellularized micro-fragments and of the VIDs reveals a large number of extracellular-matrix (ECM) proteins. Moreover, the VIDs were found to transcribe and secrete a whole repertoire of angiogenic factors in a sustained manner. Furthermore, preliminary results of implantation VIDs into non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice indicate formation of vascular network at the site within a week. We propose that those VIDs could serve as a safe, localized, simple and powerful method for the treatment of certain types of vascular diseases.

Resident vascular endothelial progenitor definition and function: the age of reckoning

The cardiovascular system is composed around the central function of the endothelium that lines the inner surfaces of its vessels. In recent years, the existence of a progenitor population within the endothelium has been validated through the study of endothelial colony-forming cells (ECFCs) in human peripheral blood and certain vascular beds. However, our knowledge on endothelial populations in vivo that can give rise to ECFCs in culture has been limited. In this review we report and analyse recent attempts at describing progenitor populations in vivo from murine studies that reflect the self-renewal and stemness capacity observed in ECFCs. We pinpoint seminal discoveries within the field, which have phenotypically defined, and functionally scrutinised these endothelial progenitors. Furthermore, we review recent publications utilising single-cell sequencing technologies to better understand the endothelium in homeostasis and pathology.

Microvascular Tissue Engineering-A Review

Tissue engineering and regenerative medicine have come a long way in recent decades, but the lack of functioning vasculature is still a major obstacle preventing the development of thicker, physiologically relevant tissue constructs. A large part of this obstacle lies in the development of the vessels on a microscale-the microvasculature-that are crucial for oxygen and nutrient delivery. In this review, we present the state of the art in the field of microvascular tissue engineering and demonstrate the challenges for future research in various sections of the field. Finally, we illustrate the potential strategies for addressing some of those challenges.

Oxygen-release microspheres capable of releasing oxygen in response to environmental oxygen level to improve stem cell survival and tissue regeneration in ischemic hindlimbs

Stem cell transplantation has been extensively explored to promote ischemic limb vascularization and skeletal muscle regeneration. Yet the therapeutic efficacy is low due to limited cell survival under low oxygen environment of the ischemic limbs. Therefore, continuously oxygenating the transplanted cells has potential to increase their survival. During tissue regeneration, the number of blood vessels are gradually increased, leading to the elevation of tissue oxygen content. Accordingly, less exogenous oxygen is needed for the transplanted cells. Excessive oxygen may induce reactive oxygen species (ROS) formation, causing cell apoptosis. Thus, it is attractive to develop oxygen-release biomaterials that are responsive to the environmental oxygen level. Herein, we developed oxygen-release microspheres whose oxygen release was controlled by oxygen-responsive shell. The shell hydrophilicity and degradation rate decreased as the environmental oxygen level increased, leading to slower oxygen release. The microspheres were capable of directly releasing molecular oxygen, which are safer than those oxygen-release biomaterials that release hydrogen peroxide and rely on its decomposition to form oxygen. The released oxygen significantly enhanced mesenchymal stem cell (MSC) survival without inducing ROS production under hypoxic condition. Co-delivery of MSCs and microspheres to the mouse ischemic limbs ameliorated MSC survival, proliferation and paracrine effects under ischemic conditions. It also significantly accelerated angiogenesis, blood flow restoration, and skeletal muscle regeneration without provoking tissue inflammation. The above results demonstrate that the developed microspheres have potential to augment cell survival in ischemic tissues, and promote ischemic tissue regeneration in a safer and more efficient manner.

Therapeutic Angiogenesis Using HGF Plasmid

Hepatocyte growth factor (HGF) is secreted from stromal and mesenchymal cells, and its receptor cMet is expressed on various types of cells such as smooth muscle cells, fibroblast, and endothelial cells. HGF stimulates epithelial and endothelial cell proliferation, motility, and morphogenesis in a paracrine and autocrine manner, organizing multistep of angiogenesis in many organs. In addition, HGF is recognized as a potent anti-inflammatory and anti-fibrotic growth factor, which has been proved in several animal studies, including neointimal hyperplasia and acute myocardial infarction model in rodent. Thus, as compared to other angiogenic growth factors, HGF exerts multiple effects on ischemic tissues, accompanied by the regression of tissue inflammation and fibrosis. These data suggest the therapeutic potential of the HGF for peripheral artery disease as it being accompanied with chronic tissue inflammation and fibrosis. In the present narrative review, the pleiotropic action of the HGF that differentiates it from other angiogenic growth factors is discussed first, and later, outcomes of the human clinical study with gene therapy are overviewed.

Androgens Stimulate EPC-Mediated Neovascularization and Are Associated with Increased Coronary Collateralization

Endothelial progenitor cells (EPCs) play a key role in neovascularization and have been linked to improved cardiovascular outcomes. Although there is a well-established inverse relationship between androgen levels and cardiovascular mortality in men, the role of androgens in EPC function is not fully understood. In this study, we investigated the effects of androgens on 2 subpopulations of EPCs, early EPCs (EEPCs) and late outgrowth EPCs (OECs), and their relationships with coronary collateralization. Early EPCs and OECs were isolated from the peripheral blood of young healthy men and treated with dihydrotestosterone (DHT) with or without androgen receptor (AR) antagonist, hydroxyflutamide, in vitro. Dihydrotestosterone treatment enhanced AR-mediated proliferation, migration, and tubulogenesis of EEPCs and OECs in a dose-dependent manner. Furthermore, DHT augmented EPC sensitivity to extracellular stimulation by vascular endothelial growth factor (VEGF) via increased surface VEGF receptor expression and AKT activation. In vivo, xenotransplantation of DHT pretreated human EPCs augmented blood flow recovery and angiogenesis in BALB/c nude male mice, compared to mice receiving untreated EPCs, following hindlimb ischemia. In particular, DHT pretreated human OECs exhibited higher reparative potential than EEPCs in augmenting postischemic blood flow recovery in mice. Furthermore, whole blood was collected from the coronary sinus of men with single vessel coronary artery disease (CAD) who underwent elective percutaneous intervention (n = 23). Coronary collateralization was assessed using the collateral flow index. Serum testosterone and EPC levels were measured. In men with CAD, circulating testosterone was positively associated with the extent of coronary collateralization and the levels of OECs. In conclusion, androgens enhance EPC function and promote neovascularization after ischemia in mice and are associated with coronary collateralization in men.

An injectable, self-assembled multicellular microsphere with the incorporation of fibroblast-derived extracellular matrix for therapeutic angiogenesis

Decellularized human lung fibroblast-derived matrix (hFDM) has demonstrated its excellent proangiogenic capability. In this study, we propose a self-assembled, injectable multicellular microspheres containing human umbilical vein endothelial cells (HUVECs) and mesenchymal stem cell (MSCs), collagen hydrogel (Col), and hFDM toward therapeutic angiogenesis. Those multicellular microspheres are spontaneously formed by the mixtures of cell and hydrogel after being dropped on the parafilm for several hours. The size of microspheres can be manipulated via adjusting the initial volume of droplets and the culture period. The cells in the microspheres are highly viable. Multicellular microspheres show good capability of cell migration on 2D culture plate and also exhibit active cell sprouting in 3D environment (Col) forming capillary-like structures. We also find that multiple angiogenic-related factors are significantly upregulated with the multicellular microspheres prepared via Col and hFDM (Col/hFDM) than those prepared using Col alone or single cells (harvested from cocultured HUVECs/MSCs in monolayer). For therapeutic efficacy evaluation, three different groups of single cells, Col and Col/hFDM microspheres are injected to a hindlimb ischemic model, respectively, along with PBS injection as a control group. It is notable that Col/hFDM microspheres significantly improve the blood reperfusion and greatly attenuate the fibrosis level of the ischemic regions. In addition, Col/hFDM microspheres show higher cell engraftment level than that of the other groups. The incorporation of transplanted cells with host vasculature is detectable only with the treatment of Col/hFDM. Current results suggest that hFDM plays an important role in the multicellular microspheres for angiogenic cellular functions in vitro as well as in vivo. Taken together, our injectable multicellular microspheres (Col/hFDM) offer a very promising platform for cell delivery and tissue regenerative applications.

Effects of sclerostin on lipopolysaccharide-induced inflammatory phenotype in human odontoblasts and dental pulp cells

Previously we have demonstrated that sclerostin inhibits stress-induced odontogenic differentiation of odontoblasts and accelerates senescence of dental pulp cells (DPCs) Odontoblasts and DPCs are main functioning cells for inflammation resistance and tissue regeneration in dentine-pulp complex. Sclerostin is relevant for systemic inflammation and chronic periodontitis processes, but its effects on dental pulp inflammation remains unclear. In this study, we found that sclerostin expression of odontoblasts was elevated in lipopolysaccharide-induced inflammatory environment, and exogenous sclerostin increased the production of pro-inflammatory cytokines in inflamed odontoblasts. Furthermore, sclerostin activated the NF-κB signaling pathway in inflamed odontoblasts and the NF-κB inhibitor reversed the exaggerative effects of sclerostin on the pro-inflammatory cytokines production. Additionally, sclerostin promoted adhesion and migration of inflamed DPCs, while inhibiting odontoblastic differentiation of inflamed DPCs. Sclerostin also might enhance pulpal angiogenesis. Taken together, it can therefore be inferred that sclerostin is upregulated in inflamed odontoblasts under pulpal inflammatory condition to enhance inflammatory responses in dentine-pulp complex and impair reparative dentinogenesis. This indicates that sclerostin inhibition might be a therapeutic target for anti-inflammation and pro-regeneration during dental pulp inflammation.

Critical limb ischemia: Current and novel therapeutic strategies

Critical limb ischemia (CLI) is the advanced stage of peripheral artery disease spectrum and is defined by limb pain or impending limb loss because of compromised blood flow to the affected extremity. Current conventional therapies for CLI include amputation, bypass surgery, endovascular therapy, and pharmacological approaches. Although these conventional therapeutic strategies still remain as the mainstay of treatments for CLI, novel and promising therapeutic approaches such as proangiogenic gene/protein therapies and stem cell-based therapies have emerged to overcome, at least partially, the limitations and disadvantages of current conventional therapeutic approaches. Such novel CLI treatment options may become even more effective when other complementary approaches such as utilizing proper bioscaffolds are used to increase the survival and engraftment of delivered genes and stem cells. Therefore, herein, we address the benefits and disadvantages of current therapeutic strategies for CLI treatment and summarize the novel and promising therapeutic approaches for CLI treatment. Our analyses also suggest that these novel CLI therapeutic strategies show considerable advantages to be used when current conventional methods have failed for CLI treatment.

The role of microRNAs in the healing of diabetic ulcers

MicroRNAs (miRNAs) are small protected molecules with a length of 18 to 25 nucleotides. Many studies have recently been conducted on miRNAs, illustrating their role in regulating many biological, physiological, and pathological activities, such as maintaining cellular signalling and regulating cellular pathways. The main role of miRNAs is to regulate the expression of genes after translation, which can lead to the destruction or suppression of translation by binding to mRNAs. As any change in the regulation of miRNAs is associated with several physiological abnormalities, such as type 2 diabetes and its complications, these molecules can be used for therapeutic purposes or as biomarkers for the diagnosis of diseases such as diabetes and its complications. In this review article, we will discuss important findings about the miRNAs and the role of these molecules in different phases of the wound-healing process of chronic wounds, especially diabetic ulcer.

Evaluating the efficacy of tissue-engineered human amniotic membrane in the treatment of myocardial infarction

AIM

The aim of this study was to evaluate the efficacy of tissue-engineered amniotic membrane (AM) in the treatment of myocardial infarction lesions.

MATERIALS & METHODS

20 rats were subjected to coronary arterial ligation in order to induce myocardial infarction injury. Decellularized human AMs were seeded with 2 × 10⁵ adipose-derived mesenchymal stem cells and were implanted in the infarcted hearts.

RESULTS & CONCLUSION

Histological and immunohistochemical evaluations indicated the regeneration of cardiomyocytes and reduction of inflammation and fibrosis in the patch-implanted group compared with a control group, 14 days after the surgery. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate biotin nick-end labeling assay was suggestive for apoptosis reduction in the patch-implanted specimens. This study suggested that human AM can be developed into a novel treatment for treating postmyocardial infarction.

Dental pulp stem cells: Novel cell-based and cell-free therapy for peripheral nerve repair

The regeneration of peripheral nerves comprises complicated steps involving a set of cellular and molecular events in distal nerve stumps with axonal sprouting and remyelination. Stem cell isolation and expansion for peripheral nerve repair (PNR) can be achieved using a wide diversity of prenatal and adult tissues, such as bone marrow or brain tissues. The ability to obtain stem cells for cell-based therapy (CBT) is limited due to donor site morbidity and the invasive nature of the harvesting process. Dental pulp stem cells (DPSCs) can be relatively and simply isolated from the dental pulps of permanent teeth, extracted for surgical or orthodontic reasons. DPSCs are of neural crest origin with an outstanding ability to differentiate into multiple cell lineages. They have better potential to differentiate into neural and glial cells than other stem cell sources through the expression and secretion of certain markers and a range of neurotropic factors; thus, they should be considered a good choice for PNR using CBT. In addition, these cells have paracrine effects through the secretion of neurotrophic growth factors and extracellular vesicles, which can enhance axonal growth and remyelination by decreasing the number of dying cells and activating local inhabitant stem cell populations, thereby revitalizing dormant or blocked cells, modulating the immune system and regulating inflammatory responses. The use of DPSC-derived secretomes holds great promise for controllable and manageable therapy for peripheral nerve injury. In this review, up-to-date information about the neurotrophic and neurogenic properties of DPSCs and their secretomes is provided.

Angiogenic Self-Assembling Peptide Scaffolds for Functional Tissue Regeneration

Implantation of acellular biomimetic scaffolds with proangiogenic motifs may have exciting clinical utility for the treatment of ischemic pathologies such as myocardial infarction. Although direct delivery of angiogenic proteins is a possible treatment option, smaller synthetic peptide-based nanostructured alternatives are being investigated due to favorable factors, such as sustained efficacy and high-density epitope presentation of functional moieties. These peptides may be implanted in vivo at the site of ischemia, bypassing the first-pass metabolism and enabling long-term retention and sustained efficacy. Mimics of angiogenic proteins show tremendous potential for clinical use. We discuss possible approaches to integrate the functionality of such angiogenic peptide mimics into self-assembled peptide scaffolds for application in functional tissue regeneration.

Supramolecular hydrogels encapsulating bioengineered mesenchymal stem cells for ischemic therapy

We developed supramolecular hyaluronate (HA) hydrogels to encapsulate genetically engineered mesenchymal stem cells (MSCs) for the treatment of limb ischemia. In vivo angiogenic factors could be produced stably by the bioengineered MSCs (BMSCs) within the supramolecular hydrogels showing effective vascular repair and enhanced blood perfusion.

Potential Roles of Dental Pulp Stem Cells in Neural Regeneration and Repair

This review summarizes current advances in dental pulp stem cells (DPSCs) and their potential applications in the nervous diseases. Injured adult mammalian nervous system has a limited regenerative capacity due to an insufficient pool of precursor cells in both central and peripheral nervous systems. Nerve growth is also constrained by inhibitory factors (associated with central myelin) and barrier tissues (glial scarring). Stem cells, possessing the capacity of self-renewal and multicellular differentiation, promise new therapeutic strategies for overcoming these impediments to neural regeneration. Dental pulp stem cells (DPSCs) derive from a cranial neural crest lineage, retain a remarkable potential for neuronal differentiation, and additionally express multiple factors that are suitable for neuronal and axonal regeneration. DPSCs can also express immunomodulatory factors that stimulate formation of blood vessels and enhance regeneration and repair of injured nerve. These unique properties together with their ready accessibility make DPSCs an attractive cell source for tissue engineering in injured and diseased nervous systems. In this review, we interrogate the neuronal differentiation potential as well as the neuroprotective, neurotrophic, angiogenic, and immunomodulatory properties of DPSCs and its application in the injured nervous system. Taken together, DPSCs are an ideal stem cell resource for therapeutic approaches to neural repair and regeneration in nerve diseases.

Allogeneic transplantation of programmable cells of monocytic origin (PCMO) improves angiogenesis and tissue recovery in critical limb ischemia (CLI): a translational approach

BACKROUND

Employing growth factor-induced partial reprogramming in vitro, peripheral human blood monocytes can acquire a state of plasticity along with expression of various markers of pluripotency. These so-called programmable cells of monocytic origin (PCMO) hold great promise in regenerative therapies. The aim of this translational study was to explore and exploit the functional properties of PCMO for allogeneic cell transplantation therapy in critical limb ischemia (CLI).

METHODS

Using our previously described differentiation protocol, murine and human monocytes were differentiated into PCMO. We examined paracrine secretion of pro-angiogenic and tissue recovery-associated proteins under hypoxia and induction of angiogenesis by PCMO in vitro. Allogeneic cell transplantation of PCMO was performed in a hind limb ischemia mouse model in comparison to cell transplantation of native monocytes and a placebo group. Moreover, we analyzed retrospectively four healing attempts with PCMO in patients with peripheral artery disease (PAD; Rutherford classification, stage 5 and 6). Statistical analysis was performed by using one-way ANOVA, Tukey's test or the Student's t test, p < 0.05.

RESULTS

Cell culture experiments revealed good resilience of PCMO under hypoxia, enhanced paracrine release of pro-angiogenic and tissue recovery-associated proteins and induction of angiogenesis in vitro by PCMO. Animal experiments demonstrated significantly enhanced SO₂ saturation, blood flow, neoangiogenesis and tissue recovery after treatment with PCMO compared to treatment with native monocytes and placebo. Finally, first therapeutic application of PCMO in humans demonstrated increased vascular collaterals and improved wound healing in patients with chronic CLI without exaggerated immune response, malignant processes or extended infection after 12 months. In all patients minor and/or major amputations of the lower extremity could be avoided.

CONCLUSIONS

In summary, PCMO improve angiogenesis and tissue recovery in chronic ischemic muscle and first clinical results promise to provide an effective and safe treatment of CLI.

Gene-Therapeutic Strategies Targeting Angiogenesis in Peripheral Artery Disease

The World Health Organization announced that cardiovascular disease is the number one cause of death globally, representing 31% of all global deaths. Coronary artery disease (CAD) affects approximately 5% of the US population aged 40 years and older. With an age-adjusted prevalence of approximately 12%, peripheral artery disease (PAD) affects at least 8 to 12 million Americans. Both CAD and PAD are caused by mainly atherosclerosis, the hardening and narrowing of arteries over the years by lipid deposition in the vascular bed. Despite the significant advances in interventions for revascularization and intensive medical care, patients with CAD or PAD who undergo percutaneous transluminal angioplasty have a persistent high rate of myocardial infarction, amputation, and death. Therefore, new therapeutic strategies are urgently needed for these patients. To overcome this unmet need, therapeutic angiogenesis using angiogenic growth factors has evolved in an attempt to stimulate the growth of new vasculature to compensate for tissue ischemia. After nearly 20 years of investigation, there is growing evidence of successful or unsuccessful gene therapy for ischemic heart and limb disease. This review will discuss basic and clinical data of therapeutic angiogenesis studies employing angiogenic growth factors for PAD patients and will draw conclusions on the basis of our current understanding of the biological processes of new vascularization.

Noninvasive evaluation of the migration effect of transplanted endothelial progenitor cells in ischemic muscle using a multimodal imaging agent

Background

Endothelial progenitor cells (EPCs) play an important role in repairing ischemia tissues. However, the survival, migration and therapeutic efficacy of EPCs after transplantation need to be better understood for further cell therapy.

Purpose

This study investigated the migration effect of EPCs labeled with a multimodal imaging agent in a murine ischemic hindlimb model, using magnetic resonance imaging (MRI) and optical imaging after transplantation.

Methods

EPCs derived from mouse bone marrow were labeled with a multimodal imaging agent and were administered through intracardiac delivery to mice with ischemic hindlimbs. The injected EPCs and their migration effect were observed via MRI and optical imaging in vivo, and then compared to a reference standard based on histological data. The quantification of gadolinium in tissue samples was done using inductively coupled plasma mass spectrometry (ICP-MS).

Results

Using in vivo MRI and optical imaging, the labeled EPCs were observed to migrate to ischemic muscle on days 3-5 after injection, while ex vivo, the EPCs were observed in the capillary vessels of the injured tissue. There were significant linear correlations between the Gd contents measured using ICP-MS in samples from the ischemic hindlimbs and livers and T₁ relaxation times calculated using MRI, as well as the average fluorescence signal intensities recorded in optical images (T₁ relaxation time: r=0.491; average signal from optical imaging: r=0.704, P<0.01). EPC treatment upregulated the levels of C-X-C chemokine receptor 4 and vascular endothelial growth factor (VEGF) receptor 2 and enhanced the expression of stromal cell-derived factor-1 and VEGF.

Conclusion

Transplanted EPCs can be monitored with noninvasive MRI and optical imaging in vivo and were found to enhance the paracrine secretion of angiogenic factors.

Human dental pulp stromal cell conditioned medium alters endothelial cell behavior

Background

Angiogenesis is of utmost importance for tissue regeneration and repair. Human dental pulp stromal cells (hDPSCs) possess angiogenic potential, as they secrete paracrine factors that may alter the host microenvironment. However, more insight into how hDPSCs guide endothelial cells (ECs) in a paracrine fashion is yet to be obtained. Therefore, the current study aimed to investigate the effect(s) of conditioned medium derived from hDPSCs (hDPSC-CM) on EC behavior in vitro.

Methods

hDPSCs were harvested from third molars scheduled for surgical removal under informed consent. The angiogenic profile of hDPSC-CM was identified using human angiogenesis antibody array and enzyme-linked immunosorbent assay (ELISA). Using real-time reverse transcription-polymerase chain reaction (RT-PCR) and ELISA, the mRNA and protein expression level of specific angiogenic biomarkers was determined in human umbilical vein endothelial cells (HUVECs) exposed to hDPSC-CM. The effect of hDPSC-CM on HUVEC attachment, proliferation and migration was evaluated by crystal violet staining, MTT, transwell migration along with real-time cell monitoring assays (xCELLigence; ACEA Biosciences, Inc.). A Matrigel assay was included to examine the influence of hDPSC-CM on HUVEC network formation. Endothelial growth medium (EGM-2) and EGM-2 supplemented with hDPSC-CM served as experimental groups, whereas endothelial basal medium (EBM-2) was set as negative control.

Results

A wide range of proangiogenic and antiangiogenic factors, including vascular endothelial growth factor, tissue inhibitor of metalloproteinase protein 1, plasminogen activator inhibitor (serpin E1), urokinase plasminogen activator and stromal cell-derived factor 1, was abundantly detected in hDPSC-CM by protein profiling array and ELISA. hDPSC-CM significantly accelerated the adhesion phases, from sedimentation to attachment and spreading, the proliferation rate and migration of HUVECs as shown in both endpoint assays and real-time cell analysis recordings. Furthermore, Matrigel assay demonstrated that hDPSC-CM stimulated tubulogenesis, affecting angiogenic parameters such as the number of nodes, meshes and total tube length.

Conclusions

The sustained proangiogenic and promaturation effects of hDPSC-CM shown in this in vitro study strongly suggest that the trophic factors released by hDPSCs are able to trigger pronounced angiogenic responses, even beyond EGM-2 considered as an optimal culture condition for ECs.

Cell transfer technology for tissue engineering

We recently developed novel cell transplantation method “cell transfer technology” utilizing photolithography. Using this method, we can transfer ex vivo expanded cells onto scaffold material in desired patterns, like printing of pictures and letters on a paper. We have investigated the possibility of this novel method for cell-based therapy using several disease models. We first transferred endothelial cells in capillary-like patterns on amnion. The transplantation of the endothelial cell-transferred amnion enhanced the reperfusion in mouse ischemic limb model. The fusion of transplanted capillary with host vessel networks was also observed. The osteoblast- and periodontal ligament stem cell-transferred amnion were next transplanted in bone and periodontal defects models. After healing period, both transplantations improved the regeneration of bone and periodontal tissues, respectively. This method was further applicable to transfer of multiple cell types and the transplantation of osteoblasts and periodontal ligament stem cell-transferred amnion resulted in the improved bone regeneration compared with single cell type transplantation. These data suggested the therapeutic potential of the technology in cell-based therapies for reperfusion of ischemic limb and regeneration of bone and periodontal tissues. Cell transfer technology is applicable to wide range of regenerative medicine in the future.

Strategies to develop endogenous stem cell-recruiting bioactive materials for tissue repair and regeneration

A leading strategy in tissue engineering is the design of biomimetic scaffolds that stimulate the body's repair mechanisms through the recruitment of endogenous stem cells to sites of injury. Approaches that employ the use of chemoattractant gradients to guide tissue regeneration without external cell sources are favored over traditional cell-based therapies that have limited potential for clinical translation. Following this concept, bioactive scaffolds can be engineered to provide a temporally and spatially controlled release of biological cues, with the possibility to mimic the complex signaling patterns of endogenous tissue regeneration. Another effective way to regulate stem cell activity is to leverage the inherent chemotactic properties of extracellular matrix (ECM)-based materials to build versatile cell-instructive platforms. This review introduces the concept of endogenous stem cell recruitment, and provides a comprehensive overview of the strategies available to achieve effective cardiovascular and bone tissue regeneration.

The Aortic Ring Co-culture Assay: A Convenient Tool to Assess the Angiogenic Potential of Mesenchymal Stromal Cells In Vitro

Angiogenesis is a complex, highly regulated process responsible for providing and maintaining adequate tissue perfusion. Insufficient vasculature maintenance and pathological malformations can result in severe ischemic diseases, while overly abundant vascular development is associated with cancer and inflammatory disorders. A promising form of pro-angiogenic therapy is the use of angiogenic cell sources, which can provide regulatory factors as well as physical support for newly developing vasculature. Mesenchymal Stromal Cells (MSCs) are extensively investigated candidates for vascular regeneration due to their paracrine effects and their ability to detect and home to ischemic or inflamed tissues. In particular, first trimester human umbilical cord perivascular cells (FTM HUCPVCs) are a highly promising candidate due to their pericyte-like properties, high proliferative and multilineage potential, immune-privileged properties, and robust paracrine profile. To effectively evaluate potentially angiogenic regenerative cells, it is a requisite to test them in reliable and "translatable" pre-clinical assays. The aortic ring assay is an ex vivo angiogenesis model that allows for easy quantification of tubular endothelial structures, provides accessory supportive cells and extracellular matrix (ECM) from the host, excludes inflammatory components, and is fast and inexpensive to set up. This is advantageous when compared to in vivo models (e.g., corneal assay, Matrigel plug assay); the aortic ring assay can track the administered cells and observe intercellular interactions while avoiding xeno-immune rejection. We present a protocol for a novel application of the aortic ring assay, which includes human MSCs in co-cultures with developing rat aortic endothelial networks. This assay allows for the analysis of the MSC contribution to tube formation and development through physical pericyte-like interactions and of their potency for actively migrating to sites of angiogenesis, and for evaluating their ability to perform and mediate ECM processing. This protocol provides further information on changes in MSC phenotype and gene expression following co-culture.

Angiogenic potency evaluation of cell therapy candidates by a novel application of the in vitro aortic ring assay

Background

Due to limitations of current angiogenesis assays, we aimed to develop a novel application of the rat aortic ring assay to assess the angiogenic potential of mesenchymal stromal cells (MSCs). First-trimester human umbilical cord-derived perivascular cells (FTM HUCPVCs) have multipotent characteristics and previously demonstrated angiogenic potential. We compared the effect of this young source of MSCs and adult bone marrow stromal cells (BMSCs) on ex vivo aortic endothelial network formation.

Methods

Thoracic segments of adult rat aortas were isolated, sectioned and embedded into Matrigel™. Fluorophore-labeled FTM HUCPVC lines and BMSCs (N = 3) were cocultured with developing endothelial networks (day 0). MSC integration, tube formation and endothelial network growth were monitored daily using phase-contrast and fluorescence microscopy. Quantification of endothelial networks was performed using ImageJ network analysis software on day 5 of coculture.

Results

FTM HUCPVCs from two umbilical cord samples migrated toward and integrated with developing aortic ring tubular networks while displaying elongated morphologies (day 1). In contrast, BMSCs did not show targeted migration and maintained spherical morphologies with limited physical interactions. Within 1 week of coculture, FTM HUCPVC lines contributed to significantly greater radial network growth and network loop formation when compared to BMSCs and untreated networks.

Conclusions

We have developed a novel potency assay to assess the angiogenic potential of cell therapy candidates. Favorable properties of FTM HUCPVCs over BMSCs that we observed with this assay and which merit further study include chemotaxis, affinity for developing vasculature, and physical supportive interactions contributing to the development of endothelial networks.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0631-1) contains supplementary material, which is available to authorized users.

Profiling the Secretome of Human Stem Cells from Dental Apical Papilla

Recent studies have shown that secretion of bioactive factors from mesenchymal stem cells (MSCs) plays a primary role in MSC-mediated therapy; especially for bone marrow-derived MSCs (BMSCs). MSCs from dental apical papilla (SCAPs) are involved in root development and may play a critical role in the formation of dentin and pulp. Bioactive factors secreted from SCAPs actively contribute to their environment; however, the SCAPs secretome remains unclear. To address this and gain a deeper understanding of the relevance of SCAPs secretions in a clinical setting, we used isobaric chemical tags and high-performance liquid chromatography with tandem mass spectrometry to profile the secretome of human SCAPs and then compared it to that of BMSCs. A total of 2,046 proteins were detected from the conditioned medium of SCAPs, with a false discovery rate of less than 1.0%. Included were chemokines along with angiogenic, immunomodulatory, antiapoptotic, and neuroprotective factors and extracellular matrix (ECM) proteins. The secreted levels of 151 proteins were found to differ by at least twofold when BMSCs and SCAPs were compared. Relative to BMSCs, SCAPs exhibited increased secretion of proteins that are involved in metabolic processes and transcription and lower levels of those associated with biological adhesion, developmental processes, and immune function. In addition, SCAPs secreted significantly larger amounts of chemokines and neurotrophins than BMSCs, whereas BMSCs secreted more ECM proteins and proangiogenic factors. These results may provide important clues regarding the molecular mechanisms associated with tissue regeneration and how they differ between cell sources.

Recruiting endogenous stem cells: a novel therapeutic approach for erectile dysfunction

Transplanted stem cells (SCs), owing to their regenerative capacity, represent one of the most promising methods to restore erectile dysfunction (ED). However, insufficient source, invasive procedures, ethical and regulatory issues hamper their use in clinical applications. The endogenous SCs/progenitor cells resident in organ and tissues play critical roles for organogenesis during development and for tissue homeostasis in adulthood. Even without any therapeutic intervention, human body has a robust self-healing capability to repair the damaged tissues or organs. Therefore, SCs-for-ED therapy should not be limited to a supply-side approach. The resident endogenous SCs existing in patients could also be a potential target for ED therapy. The aim of this review was to summarize contemporary evidence regarding: (1) SC niche and SC biological features in vitro; (2) localization and mobilization of endogenous SCs; (3) existing evidence of penile endogenous SCs and their possible mode of mobilization. We performed a search on PubMed for articles related to these aspects in a wide range of basic studies. Together, numerous evidences hold the promise that endogenous SCs would be a novel therapeutic approach for the therapy of ED.

The Neurovascular Properties of Dental Stem Cells and Their Importance in Dental Tissue Engineering

Within the field of tissue engineering, natural tissues are reconstructed by combining growth factors, stem cells, and different biomaterials to serve as a scaffold for novel tissue growth. As adequate vascularization and innervation are essential components for the viability of regenerated tissues, there is a high need for easily accessible stem cells that are capable of supporting these functions. Within the human tooth and its surrounding tissues, different stem cell populations can be distinguished, such as dental pulp stem cells, stem cells from human deciduous teeth, stem cells from the apical papilla, dental follicle stem cells, and periodontal ligament stem cells. Given their straightforward and relatively easy isolation from extracted third molars, dental stem cells (DSCs) have become an attractive source of mesenchymal-like stem cells. Over the past decade, there have been numerous studies supporting the angiogenic, neuroprotective, and neurotrophic effects of the DSC secretome. Together with their ability to differentiate into endothelial cells and neural cell types, this makes DSCs suitable candidates for dental tissue engineering and nerve injury repair.

Transplanted Endothelial Progenitor Cells Improve Ischemia Muscle Regeneration in Mice by Diffusion Tensor MR Imaging

Endothelial progenitor cells (EPCs) play an important role in repairing ischemia tissues. Diffusion tensor imaging (DTI) was applied to detect the architectural organization of skeletal muscle. This study investigated the feasibility and accuracy of using the DTI to evaluate effectiveness of EPCs treatment. Mouse bone marrow-derived EPCs were isolated, cultured, characterized, and transplanted to hindlimb ischemia mice model. DTI was performed on the hindlimb at postischemia time points. The edema regions of diffusion restriction (high signal in diffusion weighted imaging) were decreased in the ischemic muscle of EPCs treated mice after 14 days compared with the controls. These results from DTI show the lower apparent diffusion coefficient and eigenvalues (λ1, λ2, and λ3) and the higher fractional anisotropy and fiber counts of ischemic muscle on 7 and 14 days after EPCs treatment compared to the controls. There was a significant correlation between fiber counts calculated by DTI and survival fibers evaluated by histological section (r = 0.873, P < 0.01). Our study demonstrated that the time frame for muscle fiber regeneration after EPCs transplantation was significantly shortened in vivo. DTI could be a useful tool for noninvasive evaluation of muscle tissue damage and repair in animal models and patient with ischemic diseases.

Poly-ADP-ribose polymerase inhibition enhances ischemic and diabetic wound healing by promoting angiogenesis

OBJECTIVE

Chronic nonhealing wounds are a major health problem for patients in the United States and worldwide. Diabetes and ischemia are two major risk factors behind impaired healing of chronic lower extremity wounds. Poly-ADP-ribose polymerase (PARP) is found to be overactivated with both ischemic and diabetic conditions. This study seeks a better understanding of the role of PARP in ischemic and diabetic wound healing, with a specific focus on angiogenesis and vasculogenesis.

METHODS

Ischemic and diabetic wounds were created in FVB/NJ mice and an in vitro scratch wound model. PARP inhibitor PJ34 was delivered to the animals at 10 mg/kg/d through implanted osmotic pumps or added to the culture medium, respectively. Animal wound healing was assessed by daily digital photographs. Animal wound tissues, peripheral blood, and bone marrow cells were collected at different time points for further analysis with Western blot and flow cytometry. Scratch wound migration and invasion angiogenesis assays were performed using human umbilical vein endothelial cells (HUVECs). Measurements were reported as mean ± standard deviation. Continuous measurements were compared by t-test. P < .05 was considered statistically significant.

RESULTS

A significant increase in PARP activity was observed under ischemic and diabetic conditions that correlated with delayed wound healing and slower HUVEC migration. The beneficial effect of PARP inhibition with PJ34 on ischemic and diabetic wound healing was observed in both animal and in vitro models. In the animal model, the percentage of wound healing was significantly enhanced from 43% ± 6% to 71% ± 9% (P < .05) by day 7 with the addition of PJ34. PARP inhibition promoted angiogenesis at the ischemic and diabetic wound beds as evidenced by significantly higher levels of endothelial cell markers (vascular endothelial growth factor receptor 2 [VEGFR2] and endothelial nitric oxide synthase) in mice treated with PJ34 compared with controls. Flow cytometry analysis of peripheral blood mononuclear cells showed that PARP inhibition increased mobilization of endothelial progenitor cells (VEGFR2⁺/CD133⁺ and VEGFR2⁺/CD34⁺) into the systemic circulation. Furthermore, under in vitro hyperglycemia and hypoxia conditions, PARP inhibition enhanced HUVEC migration and invasion in Boyden chamber assays by 80% and 180% (P < .05), respectively.

CONCLUSIONS

Delayed healing in ischemic and diabetic wounds is caused by PARP hyperactivity, and PARP inhibition significantly enhanced ischemic and diabetic wound healing by promoting angiogenesis.

Early outgrowth cells versus endothelial colony forming cells functions in platelet aggregation

Background

Endothelial progenitor cells (EPCs) have been implicated in neoangiogenesis, endothelial repair and cell-based therapies for cardiovascular diseases. We have previously shown that the recruitment of EPCs to sites of vascular lesions is facilitated by platelets where EPCs, in turn, modulate platelet function and thrombosis. However, EPCs encompass a heterogeneous population of progenitor cells that may exert different effects on platelet function. Recent evidence suggests the existence of two EPC subtypes: early outgrowth cells (EOCs) and endothelial colony-forming cells (ECFCs). We aimed at characterizing these two EPC subtypes and at identifying their role in platelet aggregation.

Methods

EOCs and ECFCs were generated from human peripheral blood mononuclear cells (PBMCs) seeded in conditioned media on fibronectin and collagen, respectively. The morphological, phenotypical and functional characteristics of EOCs and ECFCs were assessed by optical and confocal laser scanning microscopes, cell surface markers expression, and Matrigel tube formation. The impact of EOCs and ECFCs on platelet aggregation was monitored in collagen-induced optical aggregometry and compared with PBMCs and human umbilical vein endothelial cells (HUVECs). The levels of the anti-platelet agents’ nitric oxide (NO) and prostacyclin (PGI₂) released from cultured cells as well as the expression of their respective producing enzymes NO synthases (NOS) and cyclooxygenases (COX) were also assessed.

Results

We showed that EOCs display a monocytic-like phenotype whereas ECFCs have an endothelial-like phenotype. We demonstrated that both EOCs and ECFCs and their supernatants inhibited platelet aggregation; however ECFCs were more efficient than EOCs. This could be related to the release of significantly higher amounts of NO and PGI₂ from ECFCs, in comparison to EOCs. Indeed, ECFCs, like HUVECs, constitutively express the endothelial (eNOS)—and inducible (iNOS)—NOS isoforms, and COX-1 and weakly express COX-2, whereas EOCs do not constitutively express these NO and PGI₂ producing enzymes.

Conclusion

The different morphological, phenotypic and more importantly the release of the anti-aggregating agents PGI₂ and NO in each EPC subtype are implicated in their respective roles in platelet function and thus, may be linked to the increased efficiency of ECFCs in inhibiting platelet aggregation as compared to EOCs.

Muscle weakness during aging: a deficiency state involving declining angiogenesis

This essay begins by proposing that muscle weakness of old age from sarcopenia is due in large part to reduced capillary density in the muscles, as documented in 9 reports of aged persons and animals. Capillary density (CD) is determined by local levels of various angiogenic factors, which also decline in muscles with aging, as reported in 7 studies of old persons and animals. There are also numerous reports of reduced CD in the aged brain and other studies showing reduced CD in the kidney and heart of aged animals. Thus a waning angiogenesis throughout the body may be a natural occurrence in later years and may account significantly for the lesser ailments (physical and cognitive) of elderly people. Old age is regarded here as a deficiency state which may be corrected by therapeutic angiogenesis, much as a hormonal deficiency can be relieved by the appropriate hormone therapy. Such therapy could employ recombinant angiogenic factors which are now commercially available.

Generating induced pluripotent stem cell derived endothelial cells and induced endothelial cells for cardiovascular disease modelling and therapeutic angiogenesis

Standard therapy for atherosclerotic coronary and peripheral arterial disease is insufficient in a significant number of patients because extensive disease often precludes effective revascularization. Stem cell therapy holds promise as a supplementary treatment for these patients, as pre-clinical and clinical research has shown transplanted cells can promote angiogenesis via direct and paracrine mechanisms. Induced pluripotent stem cells (iPSCs) are a novel cell type obtained by reprogramming somatic cells using exogenous transcription factor cocktails, which have been introduced to somatic cells via viral or plasmid constructs, modified mRNA or small molecules. IPSCs are now being used in disease modelling and drug testing and are undergoing their first clinical trial, but despite recent advances, the inefficiency of the reprogramming process remains a major limitation, as does the lack of consensus regarding the optimum transcription factor combination and delivery method and the uncertainty surrounding the genetic and epigenetic stability of iPSCs. IPSCs have been successfully differentiated into vascular endothelial cells (iPSC-ECs) and, more recently, induced endothelial cells (iECs) have also been generated by direct differentiation, which bypasses the pluripotent intermediate. IPSC-ECs and iECs demonstrate endothelial functionality in vitro and have been shown to promote neovessel growth and enhance blood flow recovery in animal models of myocardial infarction and peripheral arterial disease. Challenges remain in optimising the efficiency, safety and fidelity of the reprogramming and endothelial differentiation processes and establishing protocols for large-scale production of clinical-grade, patient-derived cells.

Retinal Angiogenesis Effects of TGF-β1 and Paracrine Factors Secreted From Human Placental Stem Cells in Response to a Pathological Environment

Abnormal angiogenesis is a primary cause of many eye diseases, including diabetic retinopathy, age-related macular degeneration, and retinopathy of prematurity. Mesenchymal stem cells (MSCs) are currently being investigated as a treatment for several such retinal diseases based on their neuroprotective and angiogenic potentials. In this study, we evaluated the role of systemically injected human placental amniotic membrane-derived MSCs (AMSCs) on pathological neovascularization of proliferative retinopathy. We determined that AMSCs secrete higher levels of transforming growth factor-β (TGF-β1) than other MSCs, and the secreted TGF-β1 directly suppresses the proliferation of endothelial cells under pathological conditions in vitro. Moreover, in a mouse model of oxygen-induced retinopathy, intraperitoneally injected AMSCs migrated into the retina and suppressed excessive neovascularization of the vasculature via expression of TGF-β1, and the antineovascular effect of AMSCs was blocked by treatment with TGF-β1 siRNA. These findings are the first to demonstrate that TGF-β1 secreted from AMSCs is one of the key factors to suppress retinal neovascularization in proliferative retinopathy and further elucidate the therapeutic function of AMSCs for the treatment of retinal neovascular diseases.

Role of angiogenesis in endodontics: contributions of stem cells and proangiogenic and antiangiogenic factors to dental pulp regeneration

INTRODUCTION

Dental pulp regeneration is a part of regenerative endodontics, which includes isolation, propagation, and re-transplantation of stem cells inside the prepared root canal space. The formation of new blood vessels through angiogenesis is mandatory to increase the survival rate of re-transplanted tissues. Angiogenesis is defined as the formation of new blood vessels from preexisting capillaries, which has great importance in pulp regeneration and homeostasis. Here the contribution of human dental pulp stem cells and proangiogenic and antiangiogenic factors to angiogenesis process and regeneration of dental pulp is reviewed.

METHODS

A search was performed on the role of angiogenesis in dental pulp regeneration from January 2005 through April 2014. The recent aspects of the relationship between angiogenesis, human dental pulp stem cells, and proangiogenic and antiangiogenic factors in regeneration of dental pulp were assessed.

RESULTS

Many studies have indicated an intimate relationship between angiogenesis and dental pulp regeneration. The contribution of stem cells and mechanical and chemical factors to dental pulp regeneration has been previously discussed.

CONCLUSIONS

Angiogenesis is an indispensable process during dental pulp regeneration. The survival of inflamed vital pulp and engineered transplanted pulp tissue are closely linked to the process of angiogenesis at sites of application. However, the detailed regulatory mechanisms involved in initiation and progression of angiogenesis in pulp tissue require investigation.

Combinatorial approach for improving the outcome of angiogenic therapy in ischemic tissues

Two major populations of endothelial progenitor cells (EPC), namely endothelial colony forming cells (ECFC, or late outgrowth EPC) and circulating angiogenic cells (CAC, or early outgrowth EPC) have been reported to play important roles in vasculogenesis in numerous pathological conditions. However, the poor retention of cells into the ischemic tissue and neovessel fragility are two major flaws that need to be overcome for successful angiogenic therapy. The objective of this study was to explore and exploit the functional properties of EPC populations in order to increase the effectiveness of post-ischemic cell therapy. The results indicate different, still complementary, effects of the two EPC populations on adherence and proliferation of vascular endothelial cells. Matrigel plug assay and mouse hind limb ischemia model showed that concomitant administration of CAC-secreted factors and ECFC resulted in three-fold increase in local cell retention and improved muscle perfusion, vessel maturation and hind limb regeneration, in comparison to either treatment alone. By concluding, factors secreted by CAC co-administered at the time of ECFC transplantation improve tissue regeneration and vascular repair through stabilization of newly-derived blood vessels.

Cell-based therapy for therapeutic lymphangiogenesis

Lymphedema is a medically irreversible condition for which currently conservative and surgical therapies are either ineffective or impractical. The potential use of progenitor and stem cell-based therapies has offered a paradigm that may provide alternative treatment options for lymphatic disorders. Moreover, basic research, preclinical studies, as well as clinical trials have evaluated the therapeutic potential of various cell therapies in the field of lymphatic regeneration medicine. Among the available cell approaches, mesenchymal stem cells (MSCs) seem to be the most promising candidate mainly due to their abundant sources and easy availability as well as evitable ethical and immunological issues confronted with embryonic stem cells and induced pluripotent stem cells. In this context, the purpose of this review is to summarize various cell-based therapies for lymphedema, along with strengths and weaknesses of these therapies in the clinical application for lymphedema treatment. Particularly, we will highlight the use of MSCs for lymphatic regeneration medicine. In addition, the future perspectives of MSCs in the field of lymphatic regeneration will be discussed.

The Role of MicroRNAs in Diabetic Complications-Special Emphasis on Wound Healing

Overweight and obesity are major problems in today’s society, driving the prevalence of diabetes and its related complications. It is important to understand the molecular mechanisms underlying the chronic complications in diabetes in order to develop better therapeutic approaches for these conditions. Some of the most important complications include macrovascular abnormalities, e.g., heart disease and atherosclerosis, and microvascular abnormalities, e.g., retinopathy, nephropathy and neuropathy, in particular diabetic foot ulceration. The highly conserved endogenous small non-coding RNA molecules, the micro RNAs (miRNAs) have in recent years been found to be involved in a number of biological processes, including the pathogenesis of disease. Their main function is to regulate post-transcriptional gene expression by binding to their target messenger RNAs (mRNAs), leading to mRNA degradation, suppression of translation or even gene activation. These molecules are promising therapeutic targets and demonstrate great potential as diagnostic biomarkers for disease. This review aims to describe the most recent findings regarding the important roles of miRNAs in diabetes and its complications, with special attention given to the different phases of diabetic wound healing.

Diabetes-associated macrovascular complications: cell-based therapy a new tool?

Diabetes mellitus and its ongoing macrovascular complications represent one of the major health problems around the world. Rise in obesity and population ages correlate with the increased incidence of diabetes. This highlights the need for novel approaches to prevent and treat this pandemic. The discovery of a reservoir of stem/progenitors in bone marrow and in mesenchymal tissue has attracted interest of both biologists and clinicians. A number of preclinical and clinical trials were developed to explore their potential clinical impact, as target or vehicle, in different clinical settings, including diabetes complications. Currently, bone marrow, peripheral blood, mesenchymal, and adipose tissues have been used as stem/progenitor cell sources. However, evidences have been provided that both bone marrow and circulating progenitor cells are dysfunctional in diabetes. These observations along with the growing advantages in genetic manipulation have spurred researchers to exploit ex vivo manipulated cells to overcome these hurdles. In this article, we provide an overview of data relevant to stem-progenitors potential clinical application in revascularization and/or vascular repair. Moreover, the hurdles at using progenitor cells in diabetic patients will be also discussed.

Angiogenic properties of human dental pulp stem cells

Angiogenesis, the formation of capillaries from pre-existing blood vessels, is a key process in tissue engineering. If blood supply cannot be established rapidly, there is insufficient oxygen and nutrient transport and necrosis of the implanted tissue will occur. Recent studies indicate that the human dental pulp contains precursor cells, named dental pulp stem cells (hDPSC) that show self-renewal and multilineage differentiation capacity. Since these cells can be easily isolated, cultured and cryopreserved, they represent an attractive stem cell source for tissue engineering. Until now, only little is known about the angiogenic abilities and mechanisms of the hDPSC. In this study, the angiogenic profile of both cell lysates and conditioned medium of hDPSC was determined by means of an antibody array. Numerous pro-and anti-angiogenic factors such as vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1), plasminogen activator inhibitor-1 (PAI-1) and endostatin were found both at the mRNA and protein level. hDPSC had no influence on the proliferation of the human microvascular endothelial cells (HMEC-1), but were able to significantly induce HMEC-1 migration in vitro. Addition of the PI3K-inhibitor LY294002 and the MEK-inhibitor U0126 to the HMEC-1 inhibited this effect, suggesting that both Akt and ERK pathways are involved in hDPSC-mediated HMEC-1 migration. Antibodies against VEGF also abolished the chemotactic actions of hDPSC. Furthermore, in the chicken chorioallantoic membrane (CAM) assay, hDPSC were able to significantly induce blood vessel formation. In conclusion, hDPSC have the ability to induce angiogenesis, meaning that this stem cell population has a great clinical potential, not only for tissue engineering but also for the treatment of chronic wounds, stroke and myocardial infarctions.

Binding of pro-migratory serum factors to electrospun PLLA nano-fibers

Architecture of the poly(l-lactic acid) (PLLA) scaffolds is known to affect protein affinity and binding strength. Here, we demonstrate that nanofibrous electrospun PLLA scaffolds reversibly absorb the pro-migratory serum factors that stimulate migration of vascular smooth muscle via an NFkB-dependent mechanism. Further, we demonstrate that mesenchymal stem cells seeded on the PLLA scaffolds do not enhance muscle migration but may maintain the ability of induced cells to migrate in an NFkB-independent manner. These findings further support the promising application of PLLA scaffolds for therapeutic angiogenesis and vascular graft engineering.