Adipose-derived stem cells (ASCs) as a source of endothelial cells in the reconstruction of endothelialized skin equivalents

The Jagged-1/Notch1 Signaling Pathway Promotes the Construction of Tissue-Engineered Heart Valves

Background: Tissue-engineered heart valves (TEHVs) are promising new heart valve substitutes for valvular heart disease. The Notch signaling pathway plays a critical role in the development of congenital heart valves. Objective: To investigate the role of the Notch signaling pathway in the construction of TEHVs. Methods: The induced endothelial cells, which act as seed cells, were differentiated from adipose-derived stem cells and were treated with Jagged-1 (JAG-1) protein and γ-secretase inhibitor (DAPT, N-[N-(3,5-difluorophenacetyl)-l-alanyl]-s-phenylglycine t-butyl ester), respectively. Cell phenotypic changes, the expression of proteins relating to the epithelial-mesenchymal transition (EMT), and changes in paxillin expression were detected. Decellularized valve scaffolds were produced from decellularized porcine aortic valves. The seed cells were them inoculated into Matrigel-coated flap scaffolds for complex culture and characterization. Results: JAG-1 significantly reduced apoptosis and promoted the seeded cells' proliferation and migration ability, in contrast to the treatment of DAPT. In addition, the expression of EMT-related proteins, E-cadherin and N-cadherin, was significantly increased after treatment with JAG-1 and was reduced after the application of DAPT. Meanwhile, the adhesive-related expression of paxillin and fibronectin proteins was increased after the activation of Notch1 signaling and vice versa. Of interest, activation of the Notch1 signaling pathway resulted in more closely arranged cells on the valve surface after recellularization. Conclusion: Activation of the JAG-1/Notch1 signaling pathway increased seeded cells' proliferation and migratory ability and promoted the EMT and adhesion of seed cells, which was conducive to binding to the matrix, facilitating accelerated endothelialization of TEHVs.

Vascularized 3D Human Skin Models in the Forefront of Dermatological Research

In vitro engineered skin models are emerging as an alternative platform to reduce and replace animal testing in dermatological research. Despite the progress made in recent years, considerable challenges still exist for the inclusion of diverse cell types within skin models. Blood vessels, in particular, are essential in maintaining tissue homeostasis and are one of many primary contributors to skin disease inception and progression. Substantial efforts in the past have allowed the successful fabrication of vascularized skin models that are currently utilized for disease modeling and drugs/cosmetics testing. This review first discusses the need for vascularization within tissue-engineered skin models, highlighting their role in skin grafting and disease pathophysiology. Second, the review spotlights the milestones and recent progress in the fabrication and utilization of vascularized skin models. Additionally, advances including the use of bioreactors, organ-on-a-chip devices, and organoid systems are briefly explored. Finally, the challenges and future outlook for vascularized skin models are addressed.

Characterization of the epidermal-dermal junction in hiPSC-derived skin organoids

Human induced pluripotent stem cell (hiPSC)-derived hair-bearing skin organoids offer exciting new possibilities for modeling diseases like epidermolysis bullosa (EB). These inherited diseases affect 1 in 30,000 people worldwide and result from perturbed expression and/or structure of components of the epidermal-dermal junction (EDJ). To establish whether hiPSC-derived skin organoids might be able to capture salient features of EB, it is thus important to characterize their EDJ. Here, we report successful generation of hair-bearing skin organoids from two hiPSC lines that exhibited fully stratified interfollicular epidermis. Using immunofluorescence and electron microscopy, we showed that basal keratinocytes in organoids adhere to laminin-332 and type IV collagen-rich basement membrane via type I hemidesmosomes and integrin β1-based adhesion complexes. Importantly, we demonstrated that EDJs in organoids are almost devoid of type VII collagen, a fibril that mediates anchorage of the epidermis to dermis. This should be considered when using skin organoids for EB modeling.

Mechano-regulation of vascular network formation without branches in 3D bioprinted cell-laden hydrogel constructs

Restoration of a wound is a common surgical procedure in clinic. Currently, the skin required for clinical use is taken from the patient's own body. However, it can be difficult to obtain enough skin sources for large-sized wounds and thus surgeons have started using commercial skin substitutes. The current commercial skin, which includes epidermis substitute, dermis substitute, and bilateral skin substitute, has been popularized in clinic. However, the application is limited by the occurrence of ischemia necrosis after transplantation. Recent studies suggest the use of pre-vascularized skin substitutes for wound healing is a promising area in the research field of skin tissue engineering. Pre-vascularization can be induced by changes in cultivation periods, exertion of mechanical stimuli, or coculture with endothelial cells and various factors. However, few methods could control the formation of vascular branches in engineering tissue in a self-assembly way. In this study, we use three-dimensional (3D) printing technology to confirm that a mechanical force can control the growth of blood vessels in the direction of mechanical stimulation with no branches, and that Yes-associated protein activity is involved in the regulatory progress. In vivo experiments verified that the blood vessels successfully function for blood circulation, and maintain the same direction. Results provide a theoretical basis for products of pre-vascularized skin tissues and other organs created by 3D bioprinting.

Development of a Peptide Derived from Platelet-Derived Growth Factor (PDGF-BB) into a Potential Drug Candidate for the Treatment of Wounds

Objective: This study evaluated the use of novel peptides derived from platelet-derived growth factor (PDGF-BB) as potential wound healing stimulants. One of the compounds (named PDGF2) was subjected for further research after cytotoxicity and proliferation assays on human skin cells. Further investigation included evaluation of: migration and chemotaxis of skin cells, immunological and allergic safety, the transcriptional analyses of adipose-derived stem cells (ASCs) and dermal fibroblasts stimulated with PDGF2, and the use of dorsal skin wound injury model to evaluate the effect of wound healing in mice. Approach: Colorimetric lactate dehydrogenase and tetrazolium assays were used to evaluate the cytotoxicity and the effect on proliferation. PDGF2 effect on migration and chemotaxis was also checked. Immunological safety and allergic potential were evaluated with a lymphocyte activation and basophil activation test. Transcriptional profiles of ASCs and primary fibroblasts were assessed after stimulation with PDGF2. Eight-week-old BALB/c female mice were used for dorsal skin wound injury model. Results: PDGF2 showed low cytotoxicity, pro-proliferative effects on human skin cells, high immunological safety, and accelerated wound healing in mouse model. Furthermore, transcriptomic analysis of ASCs and fibroblasts revealed the activation of processes involved in wound healing and indicated its safety. Innovation: A novel peptide derived from PDGF-BB was proved to be safe drug candidate in wound healing. We also present a multifaceted in vitro model for the initial screening of new compounds that may be potentially useful in wound healing stimulation. Conclusion: The results show that peptide derived from PDGF-BB is a promising drug candidate for wound treatment.

Progress in studies of epidermal stem cells and their application in skin tissue engineering

The epidermis, which is the outermost layer of mammalian skin, provides an essential barrier that is essential for maintenance of life. The epidermis is a stratified epithelium, which is maintained by the proliferation of epidermal stem cells (EPSCs) at the basal layer of the epidermis. As a unique cell population characterized by self-renewal and differentiation capabilities, EPSCs ensure the maintenance of adult skin homeostasis and participate in repair of the epidermis after injury. Recently, the utilization of EPSCs for wound healing and tissue regeneration has been attracting increased attention from researchers. In addition, the advances in tissue engineering have increased the interest in applying EPSCs in tissue-engineered scaffolds to further reconstitute injured tissues. In this review, we introduce research developments related to EPSCs, including methods recently used in the culture and enrichment of EPSCs, as well as advanced tools to study EPSCs. The function and mechanism of the EPSC-dermal units in the development and homeostasis of the skin are also summarized. Finally, the potential applications of EPSCs in skin tissue engineering are discussed.

Structural and Biomechanical Characterization of a Scaffold-Free Skin Equivalent Model via Biophysical Methods

AIMS

Among in vitro skin models, the scaffold-free skin equivalent (SFSE), without exogenous material, is interesting for pharmacotoxicological studies. Our aim was to adapt in vivo biophysical methods to study the structure, thickness, and extracellular matrix of our in vitro model without any chemical fixation needed as for histology.

METHODS

We evaluated 3 batches of SFSE and characterized them by histology, transmission electron microscopy (TEM), and immunofluorescence. In parallel, we investigated 3 biophysical methods classically used for in vivo evaluation, optical coherence tomography (OCT), and laser scanning microscopy (LSM) imaging devices as well as the cutometer suction to study the biomechanical properties.

RESULTS

OCT allowed the evaluation of SFSE total thickness and its different compartments. LSM has a greater resolution enabling an evaluation at the cell scale and the orientation of collagen fibers. The viscoelasticity measurement by cutometry was possible on our thin skin model and might be linked with mature collagen bundles visible in TEM and LSM and with elastic fibers seen in immunofluorescence.

CONCLUSION

Our data demonstrated the simplicity and sensitivity of these different in vivo biophysical devices on our thin skin model. These noninvasive tools allow to study the morphology and the biomechanics of in vitro models.

Human skin equivalents cultured under hypoxia display enhanced epidermal morphogenesis and lipid barrier formation

Human skin equivalents (HSEs) are three-dimensional cell models mimicking characteristics of native human skin (NHS) in many aspects. However, a limitation of HSEs is the altered in vitro morphogenesis and barrier formation. Differences between in vitro and in vivo skin could have been induced by suboptimal cell culture conditions, of which the level of oxygen in vitro (20%) is much higher than in vivo (0.5-8%). Our aim is to study how external oxygen levels affect epidermal morphogenesis and barrier formation in HSEs. In the present study, fibroblast and keratinocyte monocultures, and HSEs were generated under 20% (normoxia) and 3% (hypoxia) oxygen level. In all cultures under hypoxia, expression of hypoxia-inducible factor target genes was increased. Characterization of HSEs generated under hypoxia using immunohistochemical analyses of morphogenesis biomarkers revealed a reduction in epidermal thickness, reduced proliferation, similar early differentiation, and an attenuated terminal differentiation program compared to normoxia, better mimicking NHS. The stratum corneum ceramide composition was studied with liquid chromatography coupled to mass spectrometry. Under hypoxia, HSEs exhibited a ceramide composition that more closely resembles that of NHS. Consequently, the lipid organization was improved. In conclusion, epidermal morphogenesis and barrier formation in HSEs reconstructed under hypoxia better mimics that of NHS.

Wound healing complications in oncological patients: perspectives for cellular therapy

Various types of cancer are nowadays a serious medical and social problem and a great challenge for modern medicine. The majority of anticancer therapy is based on traditional chemotherapy and radiotherapy. Both of these highly non-specific types of treatment have a number of serious side effects including wound healing complications. Radiotherapy and chemotherapy mostly affect rapidly dividing skin cells (e.g. keratinocytes), as well as fibroblasts, melanocytes, endothelial and immune cells. Currently, there are many strategies to improve wound healing in oncological patients, including various types of dressings, biomaterials, growth factors, and cell therapies.

Limited Endothelial Plasticity of Mesenchymal Stem Cells Revealed by Quantitative Phenotypic Comparisons to Representative Endothelial Cell Controls

Considerable effort has been directed toward deriving endothelial cells (ECs) from adipose-derived mesenchymal stem cells (ASCs) since 2004, when it was first suggested that ECs and adipocytes share a common progenitor. While the capacity of ASCs to express endothelial markers has been repeatedly demonstrated, none constitute conclusive evidence of an endothelial phenotype as all reported markers have been detected in other, non-endothelial cell types. In this study, quantitative phenotypic comparisons to representative EC controls were used to determine the extent of endothelial differentiation being achieved with ASCs. ASCs were harvested from human subcutaneous abdominal white adipose tissue, and their endothelial differentiation was induced using well-established biochemical stimuli. Reverse transcription quantitative real-time polymerase chain reaction and parallel reaction monitoring mass spectrometry were used to quantify their expression of endothelial genes and corresponding proteins, respectively. Flow cytometry was used to quantitatively assess their uptake of acetylated low-density lipoprotein (AcLDL). Human umbilical vein, coronary artery, and dermal microvascular ECs were used as positive controls to reflect the phenotypic heterogeneity between ECs derived from different vascular beds. Biochemically conditioned ASCs were found to upregulate their expression of endothelial genes and proteins, as well as AcLDL uptake, but their abundance remained orders of magnitude lower than that observed in the EC controls despite their global proteomic heterogeneity. The findings of this investigation demonstrate the strikingly limited extent of endothelial differentiation being achieved with ASCs using well-established biochemical stimuli, and underscore the importance of quantitative phenotypic comparisons to representative primary cell controls in studies of differentiation. Stem Cells Translational Medicine 2019;8:35-45.

3D bioprinting of skin tissue: From pre-processing to final product evaluation

Bioprinted skin tissue has the potential for aiding drug screening, formulation development, clinical transplantation, chemical and cosmetic testing, as well as basic research. Limitations of conventional skin tissue engineering approaches have driven the development of biomimetic skin equivalent via 3D bioprinting. A key hope for bioprinting skin is the improved tissue authenticity over conventional skin equivalent construction, enabling the precise localization of multiple cell types and appendages within a construct. The printing of skin faces challenges broadly associated with general 3D bioprinting, including the selection of cell types and biomaterials, and additionally requires in vitro culture formats that allow for growth at an air-liquid interface. This paper provides a thorough review of current 3D bioprinting technologies used to engineer human skin constructs and presents the overall pipelines of designing a biomimetic artificial skin via 3D bioprinting from the design phase (i.e. pre-processing phase) through the tissue maturation phase (i.e. post-processing) and into final product evaluation for drug screening, development, and drug delivery applications.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

Therapeutic effects of a recombinant human collagen peptide bioscaffold with human adipose-derived stem cells on impaired wound healing after radiotherapy

Chronic changes following radiotherapy include alterations in tissue-resident stem cells and vasculatures, which can lead to impaired wound healing. In this study, novel recombinant human collagen peptide (rhCP) scaffolds were evaluated as a biomaterial carrier for cellular regenerative therapy. Human adipose-derived stem cells (hASCs) were successfully cultured on rhCP scaffolds. By hASC culture on rhCP, microarray assay indicated that expression of genes related to cell proliferation and extracellular matrix production was upregulated. Pathway analyses revealed that signaling pathways related to inflammatory suppression and cell growth promotion were activated as well as signaling pathways consistent with some growth factors including vascular endothelial growth factor, hepatocyte growth factor, and transforming growth factor beta, although gene expression of these growth factors was not upregulated. These findings suggest the rhCP scaffold showed similar biological actions to cytokines regulating cell growth and immunity. In subsequent impaired wound healing experiments using a locally irradiated (20 Gray) mouse, wound treatment with rhCP sponges combined with cultured hASCs and human umbilical vein endothelial cells accelerated wound closure compared with wounds treated with rhCP with hASCs alone, rhCP only, and control (dressing alone), with better healing observed according to this order. These results indicating the therapeutic value of rhCP scaffolds as a topical biomaterial dressing and a biocarrier of stem cells and vascular endothelial cells for regenerating therapies. The combination of rhCP and functional cells was suggested to be a potential tool for revitalizing stem cell-depleted conditions such as radiation tissue damage.

Recapitulation of Native Dermal Tissue in a Full-Thickness Human Skin Model Using Human Collagens

OBJECTIVE

Full-thickness skin models comprise a three-dimensional dermal equivalent based on an animal-derived collagen matrix that harbors fibroblasts and an epidermal equivalent formed by keratinocytes. The functionality of both equivalents is influenced by many factors, including extracellular matrix composition and resident cell type. Animal-derived collagens differ in amino acid composition and physicochemical properties from human collagens. This composition could alter the functionality of the dermal equivalent and epidermal morphogenesis with the barrier formation in full-thickness models (FTMs). By replacement of animal-derived collagen for human collagen, we generated and characterized the animal material-free human collagen full-thickness models (hC-FTMs) that better mimic native dermal tissue.

MATERIALS AND METHODS

An isolation procedure to obtain soluble collagen from human abdominal dermis was developed. Both FTMs and hC-FTMs were generated with primary human fibroblasts and keratinocytes. Immunohistochemical analyses with biomarkers for the dermal matrix composition, basement membrane (BM) formation, epidermal proliferation, differentiation, and activation were performed. The stratum corneum (SC) lipid composition was studied with liquid chromatography-mass spectrometry. Lipid lamellar organization was determined by small-angle X-ray diffraction.

RESULTS

The FTMs and hC-FTMs exhibit many similarities, including the dermal matrix structure, BM formation, epidermal basal layer proliferation, and execution of differentiation programs. The SC contains a similar number of corneocyte layers and the same level of lipids. The ceramide chain length distribution and ceramide subclass profile showed only minor differences. Subsequently, this led to an unaltered lamellar organization.

CONCLUSION

The animal material-free hC-FTM is generated successfully using collagens isolated from human abdominal dermis. Utilization of human collagens revealed that (epi-)dermal morphogenesis and lipid barrier formation resembled that of original FTMs. The hC-FTMs contain a dermal equivalent that mimics the native stromal tissue to a higher extent. Therefore these in vitro skin models can be used as promising tool for research purposes that contribute to animal-free experimentation.

Skin tissue engineering using 3D bioprinting: An evolving research field

BACKGROUND

Commercially available tissue engineered skin remains elusive despite extensive research because the multi-stratified anisotropic structure is difficult to replicate in vitro using traditional tissue engineering techniques. Bioprinting, involving computer-controlled deposition of cells and scaffolds into spatially controlled patterns, is able to control not only the macro but also micro and nanoarchitecture and could offer the potential to more faithfully replicate native skin.

METHODS

We conducted a literature review using PubMed, EMBASE and Web of Science for studies on skin 3D bioprinting between 2009 and 2016, evaluating the bioprinting technique, cell source, scaffold type and in vitro and in vivo outcomes.

RESULTS

We outline the evolution of biological skin replacements, principles of bioprinting and how they apply to the skin tissue engineering field, potential clinical applications as well the current limitations and future avenues for research. Of the studies analysed, the most common types of bioinks consisted of keratinocytes and fibroblasts combined with collagen, although stem cells are gaining increasing recognition. Laser assisted deposition was the most common printing modality, although ink-jet and pneumatic extrusion have also been tested. Bioprinted skin promoted accelerated wound healing, was able to mimic stratified epidermis but not the thick, elastic, vascular dermis.

CONCLUSIONS

Although 3D bioprinting shows promise in engineering skin, evidenced by large collective investments from the cosmetic industry, the research is still in its infancy. The resolution, vascularity, optimal cell and scaffold combinations and cost of bioprinted skin are hurdles that need to be overcome before the clinical applicability can be realised. Small scale 3D skin tissue models for cosmetics, drug and toxicity testing as well as tumour modelling are likely to be translated first before we see this technology used in reconstructive surgery patients.

Delivery of growth factor-based therapeutics in vascular diseases: Challenges and strategies

Either cardiovascular or peripheral vascular diseases have become the major cause of morbidity and mortality worldwide. Recently, growth factors therapeutics, whatever administrated in form of exogenous growth factors or their relevant genes have been discovered to be an effective strategy for the prevention and therapy of vascular diseases, because of their promoting angiogenesis. Besides, as an alternative, stem cell-based therapy has been also developed in view of their paracrine-mediated effect or ability of differentiation toward angiogenesis-related cells under assistance of growth factors. Despite of being specific and potent, no matter growth factors or stem cells-based therapy, their full clinical transformation is limited from bench to bedside. In this review, the potential choices of therapeutic modes based on types of different growth factors or stem cells were firstly summarized for vascular diseases. The confronted various challenges such as lack of non-invasive delivery method, the physiochemical challenge, the short half-life time, and poor cell survival, were carefully analyzed for these therapeutic modes. Various strategies to overcome these limitations are put forward from the perspective of drug delivery. The expertised design of a suitable delivery form will undoubtedly provide valuable insight into their clinical application in the regenerative medicine.

Evaluation of Three Devices for the Isolation of the Stromal Vascular Fraction from Adipose Tissue and for ASC Culture: A Comparative Study

Adipose-derived stem/stromal cells (ASCs) reside in the stromal vascular fraction (SVF) of adipose tissue (AT) and can be easily isolated. However, extraction of the SVF from lipoaspirate is a critical step in generating ASC, and semiautomated devices have been developed to enhance the efficacy and reproducibility of the outcomes and to decrease manipulation and contamination. In this study, we compared the reference method used in our lab for SVF isolation from lipoaspirate, with three medical devices: GID SVF-1™, Puregraft™, and Stem.pras®. Cell yield and their viability were evaluated as well as their phenotype with flow cytometry. Further on, we determined their proliferative potential using population doublings (PD), PD time (PDT), and clonogenicity assay (CFU-F). Finally, we checked their genetic stability using RT-qPCR for TERT mRNA assay and karyotyping as well as their multilineage potential including adipogenic, chondrogenic, and osteogenic differentiation. Our results demonstrate that all the devices allow the production of SVF cells with consistent yield and viability, in less time than the reference method. Expanded cells from the four methods showed no significant differences in terms of phenotype, proliferation capabilities, differentiation abilities, and genetic stability.

Two-Thirds Lip Defects: A New Combined Reconstructive Technique for Patients With Epithelial Cancer

BACKGROUND

The lips are a common site prone to squamous cell carcinomas, which arise in the facial region. There are different techniques to reconstruct the excised lip region, according to dimensions, area, and position of the tumor. The authors describe a new technique of lip reconstruction born from a combination between a nasolabial flap and adipose tissue transplant.

METHODS

The study was lead in the Plastic and Reconstructive Surgery Department of the University of Catanzaro. It includes 10 patients with squamous and basal cell carcinomas that interested lower or upper lip. The authors used a nasolabial flap to reconstruct two-thirds of the excised lip. All patients were staged and resulted free of disease. As a result of surgery, deformities and depressions persisted in 5 patients. This induced the authors to subject them to transplantation of adipose tissue to maximize results. Aesthetic and functional evaluation was performed with the Patient and Observer Scar Assessment Scale v 2.0 and drooling rating scale questionnaires. Moreover, an anthropometric analysis was performed in patients treated with fat transplant. Data were analyzed using Wilcoxon signed-rank test.

RESULTS

All patients had an acceptable aesthetic and functional outcome. Oral competence, sensation, and movements of the area were adequate and aesthetic was good. Adipose tissue transplant compared with surgery alone, determine a real modification of various parameters, that was statistically significant (P = 0.043) to our analysis.

CONCLUSIONS

The inverted nasolabial flap is versatile and simple. This technique allows to repair large lip defects by maintaining the eurythmia of the face. Autologous fat transplant is a favorable filler. Our data show that surgery alone is unable to restore face eurythmia after a tumor excision. Adipose tissue transplant allows to reach this goal. These 2 techniques, together, may significantly modify the functional and aesthetic result of the lip reconstruction, ensuring an optimal long-term result.

Extensive Characterization and Comparison of Endothelial Cells Derived from Dermis and Adipose Tissue: Potential Use in Tissue Engineering

Tissue-engineered constructs need to become quickly vascularized in order to ensure graft take. One way of achieving this is to incorporate endothelial cells (EC) into the construct. The adipose tissue stromal vascular fraction (adipose-SVF) might provide an alternative source for endothelial cells as adipose tissue can easily be obtained by liposuction. Since adipose-EC are now gaining more interest in tissue engineering, we aimed to extensively characterize endothelial cells from adipose tissue (adipose-EC) and compare them with endothelial cells from dermis (dermal-EC). The amount of endothelial cells before purification varied between 4–16% of the total stromal population. After MACS selection for CD31 positive cells, a >99% pure population of endothelial cells was obtained within two weeks of culture. Adipose- and dermal-EC expressed the typical endothelial markers PECAM-1, ICAM-1, Endoglin, VE-cadherin and VEGFR2 to a similar extent, with 80–99% of the cell population staining positive. With the exception of CXCR4, which was expressed on 29% of endothelial cells, all other chemokine receptors (CXCR1, 2, 3, and CCR2) were expressed on less than 5% of the endothelial cell populations. Adipose-EC proliferated similar to dermal-EC, but responded less to the mitogens bFGF and VEGF. A similar migration rate was found for both adipose-EC and dermal-EC in response to bFGF. Sprouting of adipose-EC and dermal-EC was induced by bFGF and VEGF in a 3D fibrin matrix. After stimulation of adipose-EC and dermal-EC with TNF-α an increased secretion was seen for PDGF-BB, but not uPA, PAI-1 or Angiopoietin-2. Furthermore, secretion of cytokines and chemokines (IL-6, CCL2, CCL5, CCL20, CXCL1, CXCL8 and CXCL10) was also upregulated by both adipose- and dermal-EC. The similar characteristics of adipose-EC compared to their dermal-derived counterpart make them particularly interesting for skin tissue engineering. In conclusion, we show here that adipose tissue provides for an excellent source of endothelial cells for tissue engineering purposes, since they are readily available, and easily isolated and amplified.

Skin Diseases Modeling using Combined Tissue Engineering and Microfluidic Technologies

In recent years, both tissue engineering and microfluidics have significantly contributed in engineering of in vitro skin substitutes to test the penetration of chemicals or to replace damaged skins. Organ-on-chip platforms have been recently inspired by the integration of microfluidics and biomaterials in order to develop physiologically relevant disease models. However, the application of organ-on-chip on the development of skin disease models is still limited and needs to be further developed. The impact of tissue engineering, biomaterials and microfluidic platforms on the development of skin grafts and biomimetic in vitro skin models is reviewed. The integration of tissue engineering and microfluidics for the development of biomimetic skin-on-chip platforms is further discussed, not only to improve the performance of present skin models, but also for the development of novel skin disease platforms for drug screening processes.

Hydrogels for therapeutic cardiovascular angiogenesis

Acute myocardial infarction (MI) caused by ischemia is the most common cause of cardiac dysfunction. While growth factor or cell therapy is promising, the retention of bioactive agents in the highly vascularized myocardium is limited and prevents sustained activation needed for adequate cellular responses. Various types of biomaterials with different physical and chemical properties have been developed to improve the localized delivery of growth factor and/or cells for therapeutic angiogenesis in ischemic tissues. Hydrogels are particularly advantageous as carrier systems because they are structurally similar to the tissue extracellular matrix (ECM), they can be processed under relatively mild conditions and can be delivered in a minimally invasive manner. Moreover, hydrogels can be designed to degrade in a timely fashion that coincides with the angiogenic process. For these reasons, hydrogels have shown great potential as pro-angiogenic matrices. This paper reviews a few of the hydrogel systems currently being applied together with growth factor delivery and/or cell therapy to promote therapeutic angiogenesis in ischemic tissues, with emphasis on myocardial applications.

Tracing behavior of endothelial cells promotes vascular network formation

The in vitro formation of network structures derived from endothelial cells in grafts before transplantation contributes to earlier engraftment. In a previous study, endothelial cells migrated to form a net-shaped structure in co-culture. However, the specific network formation behavior of endothelial cells during migration remains unclear. In this study, we demonstrated the tracing behavior and cell cycle of endothelial cells using Fucci-labeled (Fluorescent Ubiquitination-based Cell Cycle Indicator) endothelial cells. Here, we observed the co-culture of Fucci-labeled human umbilical vein endothelial cells (HUVECs) together with normal human dermal fibroblasts (NHDFs) using time-lapse imaging and analyzed by multicellular concurrent tracking. In the G0/G1 period, HUVECs migrate faster than in the S/G2/M period, because G0/G1 is the mobile phase and S/G2/M is the proliferation phase in the cell cycle. When HUVECs are co-cultured, they tend to move randomly until they find existing tracks that they then follow to form clusters. Extracellular matrix (ECM) staining showed that collagen IV, laminin and thrombospondin deposited in accordance with endothelial cell networks. Therefore the HUVECs may migrate on the secreted ECM and exhibit tracing behavior, where the HUVECs migrate toward each other. These results suggested that ECM and a cell phase contributed to form a network by accelerating cell migration.

In vitro and in vivo biocompatibility, bioavailability and tolerance of an injectable vehicle for adipose-derived stem/stromal cells for plastic surgery indications

Soft tissue reconstruction is a challenge in plastic surgery, when replacing lost materials and correcting contour defects. Many permanent and temporary fillers have been used to restore the volume of these lesions, but often with poor results and even complications. Adipose-derived stem/stromal cells (ASCs) and adipose tissue engineering have been suggested as valuable alternatives. In order to inject these cultured cells, it was essential to find a suitable vehicle. The purpose of this study was to evaluate Cytocare(®), an injectable medical device, composed of hyaluronic acid plus amino acids, vitamins and mineral salts. First, ASC viability and bioavailability in the 3 different available Cytocare(®) formulations using the MTT test were assessed; then an animal experiment, testing the tolerance after intradermal injections of both Cytocare(®) alone and with ASCs was carried out. Our in vitro results demonstrate a high biocompatibility of Cytocare(®) resulting in a better viability of ASCs when cultured in Cytocare(®) compared to culture medium (p < 0.05, Mann and Whitney). Cytocare(®) also permits their bioavailability and proliferation, making it a potential transfer vehicle that can retain the cells before their integration around the recipient site. Finally, our animal experiment shows that the ASC + Cytocare(®) combination is well tolerated. In conclusion, Cytocare(®) can be used as a biocompatible scaffold for cultured ASCs in therapeutic treatments, ensuring ASC bioavailability, as well as evidence of excellent tolerance in nude mice.

Gene profile of soluble growth factors involved in angiogenesis, in an adipose-derived stromal cell/endothelial cell co-culture, 3D gel model

OBJECTIVES

The aim of this study was to investigate gene expressions of growth factors for angiogenesis, in a three-dimensional (3D) gel populated with adipose-derived stromal cells (ASCs) and endothelial cells (ECs) in co-culture.

MATERIALS AND METHODS

The 3D gel, mixed with green fluorescent protein (GFP)-positive ASCs and DsRed-Express-positive ECs, 1:1 ratio, was established in vitro. The phenomenon of angiogenesis was observed using confocal microscopy. To detect gene expressions for growth factor proteins in both ASCs and ECs, transwell co-culture was used, and cell lysate samples were collected at 1, 3, 5 and 7 days. Semi-quantitative polymerase chain reaction (PCR) was conducted to quantify mRNA expressions of the growth factors.

RESULTS

Angiogenesis was first observed in the gels by 7 days post-implantation. Over this time in ECs, genes coding for VEGFA/B, IGF-1, HIF-1α, FGF-1/-2 and BMP-5/-7 significantly increased. Meanwhile in ASCs, genes coding for VEGFA/B, IGF-1, HIF-1α, FGF-1/-2 and BMP-6 also were significantly enhanced. In particular, increased amounts of IGF-1 and HIF-1α in both ECs and ASCs were prominent relative to other factors.

CONCLUSIONS

Contact co-culture with ASCs and ECs at 1:1 ratio, in the 3D gel promoted angiogenesis; non-contact co-culture further confirmed gene expressions for growth factors, VEGFA/B, IGF-1, HIF-1α and FGF-1/-2 in both ASCs and ECs; BMP-5/-7 in ECs and BMP-6 in ASCs were also confirmed. This establishment of growth factor expression seemed to be responsible for enhancement of angiogenesis. This indicates that these factors could be utilized as targets for engineered angiogenesis.

Elastin-based biomaterials and mesenchymal stem cells

Elastin is the dominant mammalian elastic protein found in soft tissue. Elastin-based biomaterials have the potential to repair elastic tissues by improving local elasticity and providing appropriate cellular interactions and signaling. Studies that combine these biomaterials with mesenchymal stem cells have demonstrated their capacity to also regenerate non-elastic tissue. Mesenchymal stem cell differentiation can be controlled by their immediate environment, and their sensitivity to elasticity makes them an ideal candidate for combining with elastin-based biomaterials. With the growing accessibility of the elastin precursor, tropoelastin, and elastin-derived materials, the amount of research interest in combining these two fields has increased and, subsequently, is leading to the realization of a potentially new strategy for regenerative medicine.

Gellan gum-hyaluronic acid spongy-like hydrogels and cells from adipose tissue synergize promoting neoskin vascularization

Currently available substitutes for skin wound healing often result in the formation of nonfunctional neotissue. Thus, urgent care is still needed to promote an effective and complete regeneration. To meet this need, we proposed the assembling of a construct that takes advantage of cell-adhesive gellan gum-hyaluronic acid (GG-HA) spongy-like hydrogels and a powerful cell-machinery obtained from adipose tissue, human adipose stem cells (hASCs), and microvascular endothelial cells (hAMECs). In addition to a cell-adhesive character, GG-HA spongy-like hydrogels overpass limitations of traditional hydrogels, such as reduced physical stability and limited manipulation, due to improved microstructural arrangement characterized by pore wall thickening and increased mean pore size. The proposed constructs combining cellular mediators of the healing process within the spongy-like hydrogels that intend to recapitulate skin matrix aim to promote neoskin vascularization. Stable and off-the-shelf dried GG-HA polymeric networks, rapidly rehydrated at the time of cell seeding then depicting features of both sponges and hydrogels, enabled the natural cell entrapment/encapsulation and attachment supported by cell-polymer interactions. Upon transplantation into mice full-thickness excisional wounds, GG-HA spongy-like hydrogels absorbed the early inflammatory cell infiltrate and led to the formation of a dense granulation tissue. Consequently, spongy-like hydrogel degradation was observed, and progressive wound closure, re-epithelialization, and matrix remodelling was improved in relation to the control condition. More importantly, GG-HA spongy-like hydrogels promoted a superior neovascularization, which was enhanced in the presence of human hAMECs, also found in the formed neovessels. These observations highlight the successful integration of a valuable matrix and prevascularization cues to target angiogenesis/neovascularization in skin full-thickness excisional wounds.

The use of skin models in drug development

Three dimensional (3D) tissue models of the human skin are probably the most developed and understood in vitro engineered constructs. The motivation to accomplish organotypic structures was driven by the clinics to enable transplantation of in vitro grown tissue substitutes and by the cosmetics industry as alternative test substrates in order to replace animal models. Today a huge variety of 3D human skin models exist, covering a multitude of scientific and/or technical demands. This review summarizes and discusses different approaches of skin model development and sets them into the context of drug development. Although human skin models have become indispensable for the cosmetics industry, they have not yet started their triumphal procession in pharmaceutical research and development. For drug development these tissue models may be of particular interest for a) systemically acting drugs applied on the skin, and b) drugs acting at the site of application in the case of skin diseases or disorders. Although quite a broad spectrum of models covering different aspects of the skin as a biologically acting surface exists, these are most often single stand-alone approaches. In order to enable the comprehensive application into drug development processes, the approaches have to be synchronized to allow a cross-over comparison. Besides the development of biological relevant models, other issues are not less important in the context of drug development: standardized production procedures, process automation, establishment of significant analytical methods, and data correlation. For the successful routine use of engineered human skin models in drug development, major requirements were defined. If these requirements can be accomplished in the next few years, human organotypic skin models will become indispensable for drug development, too.

The year in burns 2012

Approximately 2457 research articles were published with burns in the title, abstract, and/or keyword in 2012. This number continues to rise through the years; this article reviews those selected by the Editor of one of the major journals in the field (Burns) and his colleague that are most likely to have the greatest likelihood of affecting burn care treatment and understanding. As done previously, articles were found and divided into these topic areas: epidemiology of injury and burn prevention, wound and scar characterization, acute care and critical care, inhalation injury, infection, psychological considerations, pain and itching management, rehabilitation, long-term outcomes, and burn reconstruction. Each selected article is mentioned briefly with comment from the authors; readers are referred to the full papers for further details.

Generation of human epidermis-derived mesenchymal stem cell-like pluripotent cells (hEMSCPCs)

We isolated human epidermis-derived mesenchymal stem cell-like pluripotent cells (hEMSCPCs) and demonstrate efficient harvesting, maintenance in vitro for at least 30 passages, reprogramming into multiple phenotypes in vivo, and integration into adult host tissues after injection into the mouse blastocyst to create chimeras. Cell phenotype was examined by karyotyping, immunostaining, immunofluorescence, and flow cytometry. A nested PCR protocol using primers specific for human SRY genes was designed to detect hEMSCPC-derived cells in female chimeric mice. FISH was used to validate the results of nested PCR. Results indicated that hEMSCPCs were derived from epidermis but were distinct from epidermal cells; they resembled mesenchymal stem cells (MSCs) morphologically and expressed the main markers of MSCs. About half of all female offspring of mice implanted with embryos injected with hEMSCPCs at the blastocyst stage harbored the human Y chromosome and tissue-specific human protein, thereby demonstrating the transdifferentiation of hEMSCPCs.

Effects of Vitamin C on Cytotherapy-Mediated Muscle Regeneration

Skeletal muscles are the largest organs in the human body, and several therapeutic trials have been conducted that included stem cell transplantation to regenerate damaged or wasted muscles. It is well known that it is essential to make a favorable microenvironment (stem cell niche) to induce the proper differentiation of the transplanted stem cells. Some drugs, such as losartan (angiotensin II type I blocker), enhance the therapeutic effects of transplanted stem cells by inhibiting fibrosis. In this study, we hypothesized that another substance, vitamin C (ascorbic acid), might improve the niche for stem cell transplantation based on its potent antioxidant effects. In both gross and microscopic observations, vitamin C-depleted mice exhibited more incomplete regeneration of damaged muscles than those treated with vitamin C. Carbonylated protein groups, which are the end products of oxidative stress, were detected in all experimental groups; however, the vitamin C-depleted groups exhibited a more potent positive reaction than that of the vitamin C-supplied groups. The difference is clearer in the presence of transplanted stem cells. Moreover, the serum total vitamin C level and the ascorbic acid (AA) to dehydroascorbic acid (DHA) ratio also were decreased in the presence of transplanted adipose-derived stem cells (ASCs). Taken together, these data can be considered as proof of vitamin C utilization by cells in vivo. The vitamin C-supplied groups displayed more severe fibrosis than that of the vitamin C-depleted groups. Since vitamin C is a major cofactor for the collagen synthesis, its deficiency resulted in reduced fibrosis. In conclusion, we demonstrated that vitamin C not only has a positive effect on adjusting the stem cell niche to boost muscle regeneration but also has an adverse aspect due to its profibrotic effect.

Cellularized microcarriers as adhesive building blocks for fabrication of tubular tissue constructs

To meet demands of vascular reconstruction, there is a need for prosthetic alternatives to natural blood vessels. Here we explored a new conduit fabrication approach. Macroporous, gelatin microcarriers laden with human umbilical vein endothelial cells and aortic smooth muscle cells were dispensed into tubular agarose molds and found to adhere to form living tubular tissues. The ability of cellularized microcarriers to adhere to one another involved cellular and extracellular matrix bridging that included the formation of epithelium-like cell layers lining the lumenal and ablumenal surfaces of the constructs and the deposition of collagen and elastin fibers. The tubular tissues behaved as elastic solids, with a uniaxial mechanical response that is qualitatively similar to that of native vascular tissues and consistent with their elastin and collagen composition. Linearized measures of the mechanical response of the fabricated tubular tissues at both low and high strains were observed to increase with duration of static culture, with no significant loss of stiffness following decellularization. The findings highlight the utility of cellularized macroporous gelatin microcarriers as self-adhering building blocks for the fabrication of living tubular structures.

Adipose tissue-derived stem cells in clinical applications

INTRODUCTION

In the past decade human adipose tissue has been identified as a source of multipotent stem cells. Adipose tissue derived stem cells (ASCs) are characterised by immunosuppressive properties and low immunogenicity. Therefore, they can be used in regenerative medicine, as well as applied to induce graft tolerance or prevent autoimmunity. ASCs can be easily harvested with low morbidity, which is their main advantage over mesenchymal stem cells (MSCs) derived from other sources.

AREAS COVERED

The review focuses on reported clinical applications of ASCs and discusses technical approaches of their isolation and processing. The differences in phenotype and differentiation preferences between ASCs and other MSCs that may affect the choice of a particular cell type for the future therapy are also described.

EXPERT OPINION

ASCs seem to be the perfect tool for regenerative medicine and immunosuppressive cellular therapies. Nevertheless, there are some tasks that should be addressed by the future studies: i) ASCs require better characterisation; a set of markers determining ASCs should be clearly defined; ii) there is need for more studies on safety of reconstructive therapies with ASCs in cancer patients (e.g., after mastectomy); iii) release criteria should be determined for freshly isolated and ex vivo expanded ASCs designed for clinical applications.

Stem cell therapy in veterinary dermatology

BACKGROUND

Adult stem cells come from many sources and have the capacity to differentiate into many cell types, including those of the skin. The most commonly studied stem cells are those termed mesenchymal stem cells (MSCs), which are easily isolated from bone marrow and adipose tissue. Mesenchymal stem cells are known to produce a wide array of cytokines that modulate the regeneration process. The ease of collection, propagation and use of these MSCs in therapy of traumatic, ischaemic and immune-mediated skin conditions is emerging.

APPROACH AND EVIDENCE

In traumatic and ischaemic skin damage, MSCs are used in tissue-engineered skin and by direct injection into damaged tissue. For immune-mediated diseases, systemic administration of stem cells can modulate the immune system. The earliest clinical work has been with autologous stem cell sources, such as adipose tissue and bone marrow. In immune-mediated diseases, the MSCs are used to downregulate production of inflammatory cytokines and to block T-cell activation. Cells are generally given intravenously. Multiple sclerosis, rheumatoid arthritis and lupus have been successfully treated in human clinical trials. Mesenchymal stem cells can also stimulate resident local cells, such as keratinocytes and progenitor cells, to proliferate, migrate and repair skin injury and disease.

LOOKING AHEAD

The discovery of the MSC in adipose tissue has spawned a global effort to utilize these cells in therapy of a wide range of diseases of the skin. Reconstructive surgery, scar blocking and resolution and skin regeneration have all been shown to be possible in human and animal studies.

Adipose tissue angiogenesis: impact on obesity and type-2 diabetes

The growth and function of tissues are critically dependent on their vascularization. Adipose tissue is capable of expanding many-fold during adulthood, therefore requiring the formation of new vasculature to supply growing and proliferating adipocytes. The expansion of the vasculature in adipose tissue occurs through angiogenesis, where new blood vessels develop from those pre-existing within the tissue. Inappropriate angiogenesis may underlie adipose tissue dysfunction in obesity, which in turn increases type-2 diabetes risk. In addition, genetic and developmental factors involved in vascular patterning may define the size and expandability of diverse adipose tissue depots, which are also associated with type-2 diabetes risk. Moreover, the adipose tissue vasculature appears to be the niche for pre-adipocyte precursors, and factors that affect angiogenesis may directly impact the generation of new adipocytes. Here we review recent advances on the basic mechanisms of angiogenesis, and on the role of angiogenesis in adipose tissue development and obesity. A substantial amount of data points to a deficit in adipose tissue angiogenesis as a contributing factor to insulin resistance and metabolic disease in obesity. These emerging findings support the concept of the adipose tissue vasculature as a source of new targets for metabolic disease therapies. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Human adipose tissue stem cells: relevance in the pathophysiology of obesity and metabolic diseases and therapeutic applications

Stem cells are unique cells exhibiting self-renewing properties and the potential to differentiate into multiple specialised cell types. Totipotent or pluripotent stem cells are generally abundant in embryonic or fetal tissues, but the use of discarded embryos as sources of these cells raises challenging ethical problems. Adult stem cells can also differentiate into a wide variety of cell types. In particular, adult adipose tissue contains a pool of abundant and accessible multipotent stem cells, designated as adipose-derived stem cells (ASCs), that are able to replicate as undifferentiated cells, to develop as mature adipocytes and to differentiate into multiple other cell types along the mesenchymal lineage, including chondrocytes, myocytes and osteocytes, and also into cells of endodermal and neuroectodermal origin, including beta-cells and neurons, respectively. An impairment in the differentiation potential and biological functions of ASCs may contribute to the development of obesity and related comorbidities. In this review, we summarise different aspects of the ASCs with special reference to the isolation and characterisation of these cell populations, their relation to the biochemical features of the adipose tissue depot of origin and to the metabolic characteristics of the donor subject and discuss some prospective therapeutic applications.

Exogenous endothelial cells as accelerators of hematopoietic reconstitution

Despite the successes of recombinant hematopoietic-stimulatory factors at accelerating bone marrow reconstitution and shortening the neutropenic period post-transplantation, significant challenges remain such as cost, inability to reconstitute thrombocytic lineages, and lack of efficacy in conditions such as aplastic anemia. A possible means of accelerating hematopoietic reconstitution would be administration of cells capable of secreting hematopoietic growth factors. Advantages of this approach would include: a) ability to regulate secretion of cytokines based on biological need; b) long term, localized production of growth factors, alleviating need for systemic administration of factors that possess unintended adverse effects; and c) potential to actively repair the hematopoietic stem cell niche. Here we overview the field of hematopoietic growth factors, discuss previous experiences with mesenchymal stem cells (MSC) in accelerating hematopoiesis, and conclude by putting forth the rationale of utilizing exogenous endothelial cells as a novel cellular therapy for acceleration of hematopoietic recovery.

Development of a vascularized skin construct using adipose-derived stem cells from debrided burned skin

Large body surface area burns pose significant therapeutic challenges. Clinically, the extent and depth of burn injury may mandate the use of allograft for temporary wound coverage while autografts are serially harvested from the same donor areas. The paucity of donor sites in patients with burns involving large surface areas highlights the need for better skin substitutes that can achieve early and complete coverage and retain normal skin durability with minimal donor requirements. We have isolated autologous stem cells from the adipose layer of surgically debrided burned skin (dsASCs), using a point-of-care stem cell isolation device. These cells, in a collagen—polyethylene glycol fibrin-based bilayer hydrogel, differentiate into an epithelial layer, a vascularized dermal layer, and a hypodermal layer. All-trans-retinoic acid and fenofibrate were used to differentiate dsASCs into epithelial-like cells. Immunocytochemical analysis showed a matrix- and time-dependent change in the expression of stromal, vascular, and epithelial cell markers. These results indicate that stem cells isolated from debrided skin can be used as a single autologous cell source to develop a vascularized skin construct without culture expansion or addition of exogenous growth factors. This technique may provide an alternative approach for cutaneous coverage after extensive burn injuries.

Autologous stromal vascular fraction therapy for rheumatoid arthritis: rationale and clinical safety

Advancements in rheumatoid arthritis (RA) treatment protocols and introduction of targeted biological therapies have markedly improved patient outcomes, despite this, up to 50% of patients still fail to achieve a significant clinical response. In veterinary medicine, stem cell therapy in the form of autologous stromal vascular fraction (SVF) is an accepted therapeutic modality for degenerative conditions with 80% improvement and no serious treatment associated adverse events reported. Clinical translation of SVF therapy relies on confirmation of veterinary findings in targeted patient populations. Here we describe the rationale and preclinical data supporting the use of autologous SVF in treatment of RA, as well as provide 1, 3, 6, and 13 month safety outcomes in 13 RA patients treated with this approach.