Enhanced endothelial differentiation of adipose-derived stem cells by substrate nanotopography

How Mechanical and Physicochemical Material Characteristics Influence Adipose-Derived Stem Cell Fate

Adipose-derived stem cells (ASCs) are a subpopulation of mesenchymal stem cells. Compared to bone marrow-derived stem cells, they can be harvested with minimal invasiveness. ASCs can be easily expanded and were shown to be able to differentiate into several clinically relevant cell types. Therefore, this cell type represents a promising component in various tissue engineering and medical approaches (e.g., cell therapy). In vivo cells are surrounded by the extracellular matrix (ECM) that provides a wide range of tissue-specific physical and chemical cues, such as stiffness, topography, and chemical composition. Cells can sense the characteristics of their ECM and respond to them in a specific cellular behavior (e.g., proliferation or differentiation). Thus, in vitro biomaterial properties represent an important tool to control ASCs behavior. In this review, we give an overview of the current research in the mechanosensing of ASCs and current studies investigating the impact of material stiffens, topography, and chemical modification on ASC behavior. Additionally, we outline the use of natural ECM as a biomaterial and its interaction with ASCs regarding cellular behavior.

Micro- and nanotechnology in biomedical engineering for cartilage tissue regeneration in osteoarthritis

Osteoarthritis, which typically arises from aging, traumatic injury, or obesity, is the most common form of arthritis, which usually leads to malfunction of the joints and requires medical interventions due to the poor self-healing capacity of articular cartilage. However, currently used medical treatment modalities have reported, at least in part, disappointing and frustrating results for patients with osteoarthritis. Recent progress in the design and fabrication of tissue-engineered microscale/nanoscale platforms, which arises from the convergence of stem cell research and nanotechnology methods, has shown promising results in the administration of new and efficient options for treating osteochondral lesions. This paper presents an overview of the recent advances in osteochondral tissue engineering resulting from the application of micro- and nanotechnology approaches in the structure of biomaterials, including biological and microscale/nanoscale topographical cues, microspheres, nanoparticles, nanofibers, and nanotubes.

Vascular tissue engineering from human adipose tissue: fundamental phenotype of its resident microvascular endothelial cells and stromal/stem cells

Adipose tissue is an abundant, accessible, and uniquely dispensable source of cells for vascular tissue engineering. Despite its intrinsic endothelial cells, considerable effort is directed at deriving endothelium from its resident stem and progenitor cells. Here, we investigate the composition of human adipose tissue and characterize the phenotypes of its constituent cells in order to help ascertain their potential utility for vascular tissue engineering. Unsupervised clustering based on cell-surface protein signatures failed to detect CD45^-CD31^-VEGFR2⁺ endothelial progenitor cells within adipose tissue, but supported further investigation of its resident CD45^-CD31⁺ microvascular endothelial cells (HAMVECs) and CD45^-CD31^- stromal/stem cells (ASCs). The endothelial differentiation of ASCs altered their proteome, but it remained distinct from that of primary endothelial cell controls - as well as HAMVECs - regardless of their arterial-venous specification or macrovascular-microvascular origin. Rather, ASCs retained a proteome indicative of a perivascular phenotype, which was supported by their ability to facilitate the capillary morphogenesis of HAMVECs. This study supports the use of HAMVECs for the generation of endothelium. It suggests that the utility of ASCs for vascular tissue engineering lies in their capacity to remodel the extracellular matrix and to function as mural cells.

The protective effect of human adiposederived mesenchymal stem cells on cisplatin-induced nephrotoxicity is dependent on their level of expression of heme oxygenase-1

The therapeutic efficacy of adipose mesenchymal stem cells (Ad-MSCs) for acute kidney injury (AKI) has been investigated extensively, and the anti-apoptotic, anti-inflammatory, and proangiogenic effects of heme oxygenase-1 (HO-1) reportedly ameliorate AKI. We hypothesized that the therapeutic efficacy of Ad-MSCs is dependent on their expression level of HO-1. The viability and migration ability of cisplatin-treated human renal proximal tubular epithelial cells were assessed. Sprague–Dawley rats were divided into control, cisplatin (10 mg/kg), and cisplatin plus Ad MSCs (with high and low HO-1 expression) groups. The HO-1 expression level in hAd-MSCs increased with increasing passage number, peaking at passage 4 and decreasing thereafter. The viability and migratory ability of hAd-MSCs with high HO-1 expression were greater than those of hAd-MSCs with low HO-1 expression. Renal tubular toxicity in cisplatin-treated rats was ameliorated by administration of hAd-MSCs with high HO-1 expression, although the levels of blood urea nitrogen and serum creatinine did not differ according to the level of HO-1 expression. The magnitude of reactive oxygen species induced DNA damage was lower in hAd-MSCs with high HO-1 expression than in those with low HO-1 expression. Administration of hAd-MSCs significantly suppressed cisplatin induced apoptosis. Also, hAd-MSCs with high HO-1 expression were more resistant to cisplatin-induced apoptosis than were those with low HO-1 expression. hAd MSCs with high HO-1 expression have therapeutic potential for cisplatin induced nephrotoxicity, based on our in vitro and in vivo results. These findings will facilitate the development of novel therapeutic strategies for cisplatin-induced AKI.

Human adipose-derived stem cell spheroids incorporating platelet-derived growth factor (PDGF) and bio-minerals for vascularized bone tissue engineering

Stem cells with mineralized materials have been used for bone regeneration; however, engineering the complex vascularized structure of the natural bone remains a challenge. Here, we developed platelet-derived growth factor (PDGF) and bio-mineral coated fibers which were then assembled with human adipose-derived stem cells (hADSCs) to form spheroids as building blocks for vascularized bone regeneration. The PDGF incorporated within the spheroid increased the proliferation of hADSCs, which was characterized by Ki-67 staining and DNA contents. Furthermore, the PDGF enhanced not only osteogenic differentiation, but also endothelial differentiation of hADSCs; the cells within the spheroids showed significantly greater gene expression by 2.46 ± 0.14 fold for osteocalcin (OCN) and by 12.85 ± 3.36 fold for von Willebrand factor (vWF) than those without PDGF. Finally, at two months following transplantation of PDGF-incorporated spheroids onto in vivo mouse calvarial defect, the regenerated bone area (42.48 ± 10.84%) was significantly enhanced and the greatest number of capillaries and arterioles with indication of transplanted hADSCs were observed. Moreover, millimeter-scale in vitro tissue prepared by fused assembly of the spheroids exhibited greater mRNA expression-associated to endothelial lineage. Taken together, these findings indicate that stem cell spheroids incorporating PDGF and bio-minerals could be used as a module for successful vascularized bone regeneration.

Significance of Cellular Cross-Talk in Stromal Vascular Fraction of Adipose Tissue in Neovascularization

Adult stem cell-based therapy has been regarded as a promising treatment for tissue ischemia because of its ability to promote new blood vessel formation. Bone marrow-derived mesenchymal stem cells are the most used angiogenic cells for therapeutic neovascularization, yet the side effects and low efficacy have limited their clinical application. Adipose stromal vascular fraction is an easily accessible, heterogeneous cell system comprised of endothelial, stromal, and hematopoietic cell lineages, which has been shown to spontaneously form robust, patent, and functional vasculatures in vivo. However, the characteristics of each cell population and their specific roles in neovascularization remain an area of ongoing investigation. In this review, we summarize the functional capabilities of various stromal vascular fraction constituents during the process of neovascularization and attempt to analyze whether the cross-talk between these constituents generates a synergetic effect, thus contributing to the development of new potential therapeutic strategies to promote neovascularization.

Regulating response and leukocyte adhesion of human endothelial cell by gradient nanohole substrate

Understanding signals in the microenvironment that regulate endothelial cell behavior are important in tissue engineering. Although many studies have examined the cellular effects of nanotopography, no study has investigated the functional regulation of human endothelial cells grown on nano-sized gradient hole substrate. We examined the cellular response of human umbilical vein endothelial cells (HUVECs) by using a gradient nanohole substrate (GHS) with three different types of nanohole patterns (HP): which diameters were described in HP1, 120-200 nm; HP2, 200-280 nm; HP3, 280-360 nm. In results, HP2 GHS increased the attachment and proliferation of HUVECs. Also, gene expression of focal adhesion markers in HUVECs was significantly increased on HP2 GHS. In vitro tube formation assay showed the enhancement of tubular network formation of HUVECs after priming on GHS compared to Flat. Furthermore, leukocyte adhesion was also reduced in the HUVECs in a hole-diameter dependent manner. To summarize, optimal proliferations with reduced leukocyte adhesion of HUVECs were achieved by gradient nanohole substrate with 200-280 nm-sized holes.

Ginsenoside Rg1 Accelerates Paracrine Activity and Adipogenic Differentiation of Human Breast Adipose-Derived Stem Cells in a Dose-Dependent Manner In Vitro

Augmenting the biological function of adipose-derived stromal cells (ASCs) is a promising approach to promoting tissue remodeling in regenerative medicine. Here, we examined the effect of ginsenoside Rg1 on the paracrine activity and adipogenic differentiation capacity of human breast ASCs (hbASCs) in vitro. hbASCs were isolated and characterized in terms of stromal cell surface markers and multipotency. Third-passage hbASCs were cultured in basic media only or basic media containing different concentrations of G-Rg1 (0.1-100 μM). Cell proliferation was assessed by CCK-8 assay. Paracrine activity was assessed using ELISA. Gene expression was measured by qRT-PCR. Adipogenic differentiation capacity was evaluated by Oil red O staining. We found that hbASCs differentiated into adipocytes, osteoblasts, and chondrocytes in appropriate induction culture medium. hbASCs showed expression of CD29, CD44, CD49d, CD73, CD90, CD105, and CD133 but not CD31 and CD45 surface markers. G-Rg1 increased hbASC proliferation and adipogenic differentiation capacity at lower concentrations (0.1-1 μM) and had the opposite effects at higher concentrations (10-100 μM), while enhanced paracrine activity was observed in all experimental groups compared with control group, and the activation effect of lower concentration G-Rg1 was greater than at higher concentration. These results indicate that G-Rg1 can enhance the proliferation, paracrine activity, and adipogenic differentiation capacity of hbASCs within a certain concentration range. Therefore, the use of G-Rg1 may be beneficial to ASC-assisted fat graft regeneration and soft tissue engineering.

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.

Vascular extracellular matrix and fibroblasts-coculture directed differentiation of human mesenchymal stem cells toward smooth muscle-like cells for vascular tissue engineering

Construction of an artificial vascular graft is widely considered a promising strategy in vascular tissue engineering. However, limited sources of functional vascular smooth muscle cells (VSMCs) remain a major obstacle in vascular tissue engineering. In this study, we innovatively developed an approach to obtain functional VSMCs by onsite differentiating human bone marrow-derived mesenchymal stem cells (MSCs) directed by decellularized extracellular matrix (ECM) and fibroblasts. The resulting cells and ECM-cells constructs were characterized by real time RT-PCR, immunofluorescence staining, cell contractile functions, and migration capacity. Our results showed both ECM and fibroblasts induced MSCs differentiation toward VSMC-like cells with increased transcription of marker genes, upregulated expression of contractile apparatus proteins, and enhanced functional activity of VSMC phenotype. Interestingly, our findings revealed that native ECM and fibroblasts-coculture had a higher potential to promote MSCs differentiation into VSMCs than growth factors cocktail (GFC) supplemented culture, thereby providing a potential source of VSMCs for blood vessel constitution.

Conditioned Medium from Human Umbilical Vein Endothelial Cells Promotes Proliferation, Migration, Invasion and Angiogenesis of Adipose Derived Stem Cells

Preeclampsia (PE) is a pregnancy-specific hypertensive complication, closely related to endothelial dysfunction. Adipose derived stem cells (ADSCs) have the capacity to differentiate into endothelial cells for vascular repair. Therefore, we hypothesized that induced endothelial differentiation of ADSCs might hold great potential for the treatment of PE. In this study, the primary ADSCs and human umbilical vein endothelial cells (HUVECs) were isolated by the collagenase digestion method. The supernatant of HUVECs was collected from the first generation of cells. Then, ADSCs were divided into two groups: ADSCs alone group and induced ADSCs (iADSCs) group. In iADSCs group, ADSCs were induced by HUVECs conditioned medium and ADSCs special culture medium at a ratio of 1:1 over a two-week period. In order to identify the endothelial characteristics of iADSCs, CD31 and CD34 were examined by flow cytometry. The proliferation, migration, invasion and angiogenesis assays were employed to compare the bioactivity of iADSCs and ADSCs. Furthermore, The levels of angiogenic related factors including vascular endothelial growth factor (VEGF) and placenta growth factor (P1GF) were detected by RT-PCR and Western blotting. Results showed conditioned medium from HUVECs promoted ADSCs proliferation, migration, invasion and angiogenesis. In addition, the levels of VEGF and P1GF were significantly enhanced in iADSCs group. This study uncovered the iADSCs application potential in the therapy and intervention of PE.

Cathelicidin LL37 Promotes Epithelial and Smooth-Muscle-Like Differentiation of Adipose-Derived Stem Cells through the Wnt/β-Catenin and NF-κB Pathways

Ureter reconstruction is a difficult procedure in urology. Adipose-derived stem cells (ADSCs), along with multipotency and self-renewal capacity, are a preferred choice for tissue engineering-based ureteral reconstruction. We explored the synergic role of cathelicidin LL37 (LL37) in epithelial and smooth-muscle-like differentiation. ADSCs were separated from adipose tissues of mouse and characterized by flow cytometry. The ADSCs were then stably transfected with pGC-FU-GFP (pGC) or pGC containing full-length LL37 (pGC-LL37), respectively. Cell viability and apoptosis were respectively estimated in the stably transfected cells and non-transfected cells. Then, qRT-PCR and Western blot analysis were used for determinations of epithelial marker expressions after induction by all-trans retinoic acid as well as smooth-muscle-like marker expressions after induction by transforming growth factor-β1. Then, possibly involved signaling pathways and extracellular expression of LL37 were detected. Cell viability and apoptosis were not changed after LL37 overexpression. Expression levels of epithelial and smooth-muscle-like markers were significantly upregulated by LL37 overexpression. Moreover, expressions of key kinases involved in the Wnt/β-catenin pathway as well as epithelial marker were upregulated by the LL37 overexpression, while it was reversed by Wnt/β-catenin inhibitor. Likewise, expressions of key kinases involved in the nuclear factor κB (NF-κB) pathway as well as smooth-muscle-like markers were upregulated by LL37 overexpression, which was reversed by NF-κB inhibitor. LL37 was found in the culture medium. LL37, which could be released into the medium, had no impact on cell proliferation and apoptosis of ADSCs. However, LL37 promoted epithelial and smooth-muscle-like differentiation through activating the Wnt/β-catenin and NF-κB pathways, respectively.

Design of Polymeric Culture Substrates to Promote Proangiogenic Potential of Stem Cells

Stem cells are a promising cell source for regenerative medicine due to their differentiation and self-renewal capacities. In the field of regenerative medicine and tissue engineering, a variety of biomedical technologies have been tested to improve proangiogenic activities of stem cells. However, their therapeutic effect is found to be limited in the clinic because of cell loss, senescence, and insufficient therapeutic activities. To address this type of issue, advanced techniques for biomaterial synthesis and fabrication have been approached to mimic proangiogenic microenvironment and to direct proangiogenic activities. This review highlights the types of polymers and design strategies that have been studied to promote proangiogenic activities of stem cells. In particular, scaffolds, hydrogels, and surface topographies, as well as insight into their underlying mechanisms to improve proangiogenic activities are the focuses. The strategy to promote angiogenic activities of hMSCs by controlling substrate repellency is introduced, and the future direction is proposed.

Development of a microfluidic platform integrating high-resolution microstructured biomaterials to study cell-material interactions

Microfluidic screening platforms offer new possibilities for performing in vitro cell-based assays with higher throughput and in a setting that has the potential to closely mimic the physiological microenvironment. Integrating functional biomaterials into such platforms is a promising approach to obtain a deeper insight into the interactions occurring at the cell-material interface. The success of such an approach is, however, largely dependent on the ability to miniaturize the biomaterials as well as on the choice of the assay used to study the cell-material interactions. In this work, we developed a microfluidic device, the main component of which is made of a widely used biocompatible polymer, polylactic acid (PLA). This device enabled cell culture under different fluidic regimes, including perfusion and diffusion. Through a combination of photolithography, two-photon polymerization and hot embossing, it was possible to microstructure the surface of the cell culture chamber of the device with highly defined geometrical features. Furthermore, using pyramids with different heights and wall microtopographies as an example, adhesion, morphology and distribution of human MG63 osteosarcoma cells were studied. The results showed that both the height of the topographical features and the microstructural properties of their walls affected cell spreading and distribution. This proof-of-concept study shows that the platform developed here is a useful tool for studying interactions between cells and clinically relevant biomaterials under controlled fluidic regimes.

Cell-instructive high-resolution micropatterned polylactic acid surfaces

Micro and nanoscale topographical structuring of biomaterial surfaces has been a valuable tool for influencing cell behavior, including cell attachment, proliferation and differentiation. However, most fabrication techniques for surface patterning of implantable biomaterials suffer from a limited resolution, not allowing controlled generation of sub-cellular three-dimensional features. Here, a direct laser lithography technique based on two-photon absorption was used to construct several patterns varying in size between 500 nm and 15 μm. Through replication via an intermediate mold, the patterns were transferred into polylactic acid (PLA), a widely used biomedical polymer, while retaining the original geometry. An osteoblast-like cell line, MG-63 was used for characterizing the morphological response to the topographical patterns. The results indicated that semi-continuous (dashed) lines, with a height of 1 μm were able to induce cell elongation in the direction of the lines. However, when dashes with a height of 0.5 μm were combined with perpendicularly crossing continuous lines (rails) with a height of 8 μm, the contact guidance effect of the dashes was lost and elongation of the cells was observed in the direction of the larger features. A second pattern, consisting of different arrays of pillars showed that, depending on the pillar height, the cells were either able to spread over the pattern or were confined between the pattern features. These differences in the ability of cells to spread further resulted in the formation of tension forces through stress fibers and displacement of vimentin. The method for high-resolution micropatterning of PLA as presented here can also be applied to other biomedical polymers, making it useful both for fundamental studies and for designing new biomaterials with improved functionality.

[Research progress of adipose-derived stem cells in skin wound healing]

Objective

To review the research progress of adipose-derived stem cells (ADSCs) in skin wound healing.

Methods

The recent experiments and clinical studies on the role of ADSCs in skin wound healing were extensively retrieved and analyzed. Additionally, possible mechanisms and novel application strategies were proposed.

Results

As confirmed by in vitro and in vivo experiments and clinical studies, ADSCs promote skin wound healing mainly by two mechanisms: differentiation to target cells that participate in skin wound healing and cytokines paracrine to promote proliferation and migration of various cell lines that are mandatory to promote skin wound healing. Moreover, scaffold materials and cell sheet technology may further add to the potency of ADSCs in promoting skin wound healing.

Conclusion

Remarkable progress has been made in the application of ADSCs in skin wound healing. Further studies are needed to explore the application methods of ADSCs.

Silicon microgrooves for contact guidance of human aortic endothelial cells

Background: Micro- and nanoscale substrates have been fabricated in order to study the influence of the topography on the cellular response. The aim of this work was to prepare different collagen-coated silicon substrates displaying grooves and ridges to mimic the aligned and elongated endothelium found in linear vessels, and to use them as substrates to study cell growth and behaviour. Results: The influence of groove-shaped substrates on cell adhesion, morphology and proliferation were assessed, by comparing them to flat silicon substrates, used as control condition. Using human aortic endothelial cells, microscopy images demonstrate that the cellular response is different depending on the silicon surface, when it comes to cell adhesion, morphology (alignment, circularity and filopodia presence) and proliferation. Moreover, these structures exerted no cytotoxic effect. Conclusion: The results suggest that topographical patterning influences cell response. Silicon groove substrates can be used in developing medical devices with microscale features to mimic the endothelium in lineal vessels.

Adipose-derived stem cells in cartilage regeneration: current perspectives

Repair of cartilage injuries represents a musculoskeletal medicine criticism because of the poor ability to self-renewal of adult cartilage. Therefore, research focuses on developing new regenerative strategies combining chondrocytes or stem cells, scaffolds and growth factors. Because of the low proliferation capability of explanted chondrocytes, new chondrogenesis models, employing human adipose-derived stem cells (ASCs), have been investigated. ASCs are readily accessible with no morbidity and display the capability to differentiate into several cell lineages, including the spontaneous chondrogenic differentiation when entrapped in collagen gel scaffolds. Recent studies also defined some biomolecular mechanisms involved in ASC chondrogenesis in vitro, and their regenerative properties in bioengineered scaffolds and in the presence of growth factors. However, further investigations are required to validate these exciting preclinical results for the application of bioenginereed ASCs in the clinical practice.

Development of mechano-responsive polymeric scaffolds using functionalized silica nano-fillers for the control of cellular functions

We demonstrate an efficient method to produce mechano-responsive polymeric scaffolds which can alter cellular functions using two different functionalized (OH and NH2) silica nano-fillers. Fumed silica-hydroxyl and fumed silica-amine nano-fillers were mixed with a biocompatible polymer (POSS-PCU) at various wt% to produce scaffolds. XPS and mechanical testing demonstrate that bulk mechanical properties are modified without changing the scaffold's surface chemistry. Mechanical testing showed significant change in bulk properties of POSS-PCU scaffolds with an addition of silica nanofillers as low as 1% (P<0.01). Scaffolds modified with NH2 silica showed significantly higher bulk mechanical properties compared to the one modified with the OH group. Enhanced cell adhesion, proliferation and collagen production over 14days were observed on scaffolds with higher bulk mechanical properties (NH2) compared to those with lower ones (unmodified and OH modified) (P<0.05) during in vitro analysis. This study provides an effective method of manufacturing mechano-responsive polymeric scaffolds, which can help to customize cellular responses for biomaterial applications.

Enhanced renoprotective effect of HIF-1α modified human adipose-derived stem cells on cisplatin-induced acute kidney injury in vivo

Current therapeutic options for acute kidney injury (AKI) are limited to the use of supportive measures and dialysis. A recent approach that has sparked great interest and gained enormous popularity is the implantation of stem cells to repair acutely damaged kidney organ. Hypoxia inducible factor-1α (HIF-1α) is effective in protecting the kidney from ischemia and nephrotoxicity. In this study, we investigated whether HIF-1α-modified adipose-derived stem cells (ASCs) had an enhanced protective effect on cisplatin-induced kidney injury in vivo. Cisplatin-induced AKI was established in nude mice. Our study demonstrated that HIF-1α-modified ASCs obviously promoted the recovery of renal function, ameliorated the extent of histologic injury and reduced renal apoptosis and inflammation, but HIF-1α-modified ASCs homed to kidney tissues at very low levels after transplantation. In addition, we also found that HIF-1α-modified ASCs significantly increased HO-1 expression in cisplatin-induced AKI in vivo. Thus, our study indicated HIF-1α-modified ASCs implantation could provide advanced benefits in the protection again AKI, which will contribute to developing a new therapeutic strategy for the treatment of AKI.

Endothelial Differentiation of Human Adipose-Derived Stem Cells on Polyglycolic Acid/Polylactic Acid Mesh

Adipose-derived stem cell (ADSC) is considered as a cell source potentially useful for angiogenesis in tissue engineering and regenerative medicine. This study investigated the growth and endothelial differentiation of human ADSCs on polyglycolic acid/polylactic acid (PGA/PLA) mesh compared to 2D plastic. Cell adhesion, viability, and distribution of hADSCs on PGA/PLA mesh were observed by CM-Dil labeling, live/dead staining, and SEM examination while endothelial differentiation was evaluated by flow cytometry, Ac-LDL/UEA-1 uptake assay, immunofluorescence stainings, and gene expression analysis of endothelial related markers. Results showed hADSCs gained a mature endothelial phenotype with a positive ratio of 21.4 ± 3.7% for CD31+/CD34- when induced in 3D mesh after 21 days, which was further verified by the expressions of a comprehensive range of endothelial related markers, whereas hADSCs in 2D induced and 2D/3D noninduced groups all failed to differentiate into endothelial cells. Moreover, compared to 2D groups, the expression for α-SMA was markedly suppressed in 3D cultured hADSCs. This study first demonstrated the endothelial differentiation of hADSCs on the PGA/PLA mesh and pointed out the synergistic effect of PGA/PLA 3D culture and growth factors on the acquisition of mature characteristic endothelial phenotype. We believed this study would be the initial step towards the generation of prevascularized tissue engineered constructs.

Structural properties of scaffolds: Crucial parameters towards stem cells differentiation

Tissue engineering is a multidisciplinary field that applies the principles of engineering and life-sciences for regeneration of damaged tissues. Stem cells have attracted much interest in tissue engineering as a cell source due to their ability to proliferate in an undifferentiated state for prolonged time and capability of differentiating to different cell types after induction. Scaffolds play an important role in tissue engineering as a substrate that can mimic the native extracellular matrix and the properties of scaffolds have been shown to affect the cell behavior such as the cell attachment, proliferation and differentiation. Here, we focus on the recent reports that investigated the various aspects of scaffolds including the materials used for scaffold fabrication, surface modification of scaffolds, topography and mechanical properties of scaffolds towards stem cells differentiation effect. We will present a more detailed overview on the effect of mechanical properties of scaffolds on stem cells fate.

Accelerating in situ endothelialisation of cardiovascular bypass grafts

The patency of synthetic cardiovascular grafts in the long run is synonymous with their ability to inhibit the processes of intimal hyperplasia, thrombosis and calcification. In the human body, the endothelium of blood vessels exhibits characteristics that inhibit such processes. As such it is not surprising that research in tissue engineering is directed towards replicating the functionality of the natural endothelium in cardiovascular grafts. This can be done either by seeding the endothelium within the lumen of the grafts prior to implantation or by designing the graft such that in situ endothelialisation takes place after implantation. Due to certain difficulties identified with in vitro endothelialisation, in situ endothelialisation, which will be the focus of this article, has garnered interest in the last years. To promote in situ endothelialisation, the following aspects can be taken into account: (1) Endothelial progenital cell mobilization, adhesion and proliferation; (2) Regulating differentiation of progenitor cells to mature endothelium; (3) Preventing thrombogenesis and inflammation during endothelialisation. This article aims to review and compile recent developments to promote the in situ endothelialisation of cardiovascular grafts and subsequently improve their patency, which can also have widespread implications in the field of tissue engineering.

Mesenchymal stem cells: roles and relationships in vascularization

One of the primary challenges in translating tissue engineering to clinical applicability is adequate, functional vascularization of tissue constructs. Vascularization is necessary for the long-term viability of implanted tissue expanded and differentiated in vitro. Such tissues may be derived from various cell sources, including mesenchymal stem cells (MSCs). MSCs, able to differentiate down several lineages, have been extensively researched for their therapeutic capabilities. In addition, MSCs have a variety of roles in the vascularization of tissue, both through direct contact and indirect signaling. The studied relationships between MSCs and vascularization have been utilized to further the necessary advancement of vascularization in tissue engineering concepts. This review aims to provide a summary of relevant relationships between MSCs, vascularization, and other relevant cell types, along with an overview discussing applications and challenges related to the roles and relationships of MSCs and vascular tissues.

Isolation and characterization of a spontaneously immortalized multipotent mesenchymal cell line derived from mouse subcutaneous adipose tissue

The emerging field of tissue engineering and regenerative medicine is a multidisciplinary science that is based on the combination of a reliable source of stem cells, biomaterial scaffolds, and cytokine growth factors. Adult mesenchymal stem cells are considered important cells for applications in this field, and adipose tissue has revealed to be an excellent source of them. Indeed, adipose-derived stem cells (ASCs) can be easily isolated from the stromal vascular fraction (SVF) of adipose tissue. During the isolation and propagation of murine ASCs, we observed the appearance of a spontaneously immortalized cell clone, named m17.ASC. This clone has been propagated for more than 180 passages and stably expresses a variety of stemness markers, such as Sca-1, c-kit/CD117, CD44, CD106, islet-1, nestin, and nucleostemin. Furthermore, these cells can be induced to differentiate toward osteogenic, chondrogenic, adipogenic, and cardiogenic phenotypes. m17.ASC clone displays a normal karyotype and stable telomeres; it neither proliferates when plated in soft agar nor gives rise to tumors when injected subcutaneously in NOD/SCID-γ (null) mice. The analysis of gene expression highlighted transcriptional traits of SVF cells. m17.ASCs were genetically modified by lentiviral vectors carrying green fluorescent protein (GFP) as a marker transgene and efficiently engrafted in the liver, when injected in the spleen of NOD/SCID-γ (null) monocrotaline-treated mice. These results suggest that this non-tumorigenic spontaneously immortalized ASC line may represent a useful tool (cell model) for studying the differentiation mechanisms involved in tissue repair as well as a model for pharmacological/toxicological studies.

Endothelial cells derived from embryonic stem cells respond to cues from topographical surface patterns

The generation of micro- and nano-topography similar to those found in the extra cellular matrix of three-dimensional tissues is one technique used to recapitulate the cell-tissue physiology found in the native tissues. Despite the fact that ample studies have been conducted on the physiological significance of endothelial cells alignment parallel to shear stress, as this is the normal physiologic arrangement for healthy arterial EC, very few studies have examined the use of topographical signals to initiate endothelial cell alignment. Here, we have examined the ability for our mouse embryonic stem cell-derived endothelial cells (ESC-EC) to align on various microchip topographical systems. Briefly, we generated metal molds with 'wrinkled' topography using 1) 15 nm and 2) 30 nm of gold coating on the pre-strained polystryene (PS) sheets. After thermal-induced shrinkage of the PS sheets, polydimethylsiloxane (PDMS) microchips were then generated from the wrinkled molds. Using similar Shrink™-based technology, 3) larger selectively crazed acetone-etched lines in the PS sheets, and 4) fully crazed acetone-treated PS sheets of stochastic topographical morphology were also generated. The 15 nm and 30 nm gold coating generated 'wrinkles' of uniaxial anisotropic channels at nano-scaled widths while the crazing generated micron-sized channels. The ESC-EC were able to respond and align on the 320 nm, 510 nm, and the acetone-etched 10.5 μm channels, but not on the fully 'crazed' topographies. Moreover, the ESC-EC aligned most robustly on the wrinkles, and preferentially to ridge edges on the 10.5 μm-sized channels. The ability to robustly align EC on topographical surfaces enables a variety of controlled physiological studies of EC-EC and EC-ECM contact guidance, as well as having potential applications for the rapid endothelialization of stents and vascular grafts.

Strategies and techniques to enhance the in situ endothelialization of small-diameter biodegradable polymeric vascular grafts

Due to the lack of success in small-diameter (<6 mm) prosthetic vascular grafts, a variety of strategies have evolved utilizing a tissue-engineering approach. Much of this work has focused on enhancing the endothelialization of these grafts. A healthy, confluent endothelial layer provides dynamic control over homeo-stasis, influencing and preventing thrombosis and smooth muscle cell proliferation that can lead to intimal hyperplasia. Strategies to improve endothelialization of biodegradable polymeric grafts have encompassed both chemical and physical modifications to graft surfaces, many focusing on the recruitment of endothelial and endothelial progenitor cells. This review aims to provide a compilation of current and developing strategies that utilize in situ endothelialization to improve vascular graft outcomes, providing a context for the future directions of vascular tissue-engineering strategies that do not require preprocedural cell seeding.

Proangiogenic features of Wharton's jelly-derived mesenchymal stromal/stem cells and their ability to form functional vessels

Mesenchymal stromal/stem cells derived from human Wharton's jelly (WJ-MSC) have emerged as a favorable source for autologous and allogenic cell therapy. Here, we characterized the proangiogenic features of WJ-MSCs and examined their ability to form functional vessels in in vivo models. First, we examined whether WJ-MSCs express endothelial and smooth muscle cell specific markers after culture in endothelial growth media. WJ-MSCs expressed an endothelial specific marker, VEGFR1, at mRNA and protein levels, but did not express other specific markers (VEGFR2, Tie2, vWF, CD31, and VE-cadherin). Rather, WJ-MSCs expressed smooth muscle cell specific markers, α-SMA, PDGFR-β and calponin, and were unable to form tube-like structures with lumen on Matrigel. WJ-MSCs secreted growth factors including angiogenin, IGFBP-3, MCP-1, and IL-8, which stimulated endothelial proliferation, migration, and tube formation. When WJ-MSCs suspended in Matrigel were implanted into nude mice, it led to formation of functional vessels containing erythrocytes after 7 days. However, implantation of endothelial cell-suspended Matrigel resulted in no perfused vessels. The implanted WJ-MSCs were stained positively for calponin or PDGFR-β and were located adjacent to the lining of mouse endothelial cells that were stained with labeled BS-lectin B4. In a murine hindlimb ischemia model, the transplantation of MSCs (5×10(5)cells) into the ischemic limbs improved perfusion recovery and neovascularization of the limbs compared to control group. Therefore, the results suggest that WJ-MSCs promote neovascularization and perfusion by secreting paracrine factors and by functioning as perivascular precursor cells, and that WJ-MSCs can be used efficiently for cell therapy of ischemic disease.