Adipose-derived endothelial and mesenchymal stem cells enhance vascular network formation on three-dimensional constructs in vitro

Oscillatory Strain Promotes Vessel Stabilization and Alignment through Fibroblast YAP-Mediated Mechanosensitivity

Endothelial cells form the interior layer of blood vessels and, as such, are constantly exposed to shear stress and mechanical strain. While the impact of shear stress on angiogenesis is widely studied, the role of mechanical strain is less understood. To this end, endothelial cells and fibroblasts are cocultured under oscillatory strain to create a vessel network. The two cell types show distinctly different sensitivities to the mechanical stimulation. The fibroblasts, sense the stress directly, and respond by increased alignment, proliferation, differentiation, and migration, facilitated by YAP translocation into the nucleus. In contrast, the endothelial cells form aligned vessels by tracking fibroblast alignment. YAP inhibition in constructs under mechanical strain results in vessel destruction whereas less damage is observed in the YAP-inhibited static control. Moreover, the mechanical stimulation enhances vessel development and stabilization. Additionally, vessel orientation is preserved upon implantation into a mouse dorsal window chamber and promotes the invading host vessels to orient in the same manner. This study sheds light on the mechanisms by which mechanical strain affects the development of blood vessels within engineered tissues. This can be further utilized to engineer a more organized and stable vasculature suitable for transplantation of engineered grafts.

Induction of Expression of CD271 and CD34 in Mesenchymal Stromal Cells Cultured as Spheroids

Cultured mesenchymal stromal cells (MSCs) are cells that can be used for tissue engineering or cell therapies owing to their multipotency and ability to secrete immunomodulatory and trophic molecules. Several studies suggest that MSCs can become pericytes when cocultured with endothelial cells (ECs) but failed to use pericyte markers not already expressed by MSCs. We hypothesized ECs could instruct MSCs to express the molecules CD271 or CD34, which are expressed by pericytes in situ but not by MSCs. CD271 is a marker of especial interest because it is associated with multipotency, a characteristic that wanes in MSCs as they are culture expanded. Consequently, surface expression of CD271 and CD34 was detected in roughly half of the MSCs cocultured with ECs as spheroids in the presence of insulin-like growth factor 1 (IGF-1). Conversely, expression of CD271 and CD34 was detected in a similar proportion of MSCs cultured under these conditions without ECs, and expression of these markers was low or absent when no IGF-1 was added. These findings indicate that specific culture conditions including IGF-1 can endow cultured MSCs with expression of CD271 and CD34, which may enhance the multipotency of these cells when they are used for therapeutic purposes.

CD140b (PDGFRβ) signaling in adipose-derived stem cells mediates angiogenic behavior of retinal endothelial cells

Adipose-derived stem cells (ASCs) are multipotent mesenchymal progenitor cells that have functional and phenotypic overlap with pericytes lining microvessels in adipose tissue. The role of CD140b [platelet-derived growth factor receptor- β (PDGFR-β)], a constitutive marker expressed by ASCs, in the angiogenic behavior of human retinal endothelial cells (HREs) is not known. CD140b was knocked down in ASCs using targeted siRNA and lipofectamine transfection protocol. Both CD140b+ and CD140b- ASCs were tested for their proliferation (WST-1 reagent), adhesion (laminin-1 coated plates), and migration (wound-scratch assay). Angiogenic effect of CD140b+ and CD140b- ASCs on HREs was examined by co-culturing ASCs:HREs in 12:1 ratio for 6 days followed by visualization of vascular network by Isolectin B4 staining. The RayBio® Membrane-Based Antibody Array was used to assess differences in human cytokines released by CD140b+ or CD140b- ASCs. Knockdown of CD140b in ASCs resulted in a significant 50% decrease in proliferation rate, 25% decrease in adhesion ability to Laminin-1, and 50% decrease in migration rate, as compared to CD140b+ ASCs. Direct contact of ASCs expressing CD140b+ with HREs resulted in robust vascular network formation that was significantly reduced with using CD140b- ASCs. Of the 80 proteins tested, 45 proteins remained unchanged (>0.5-<1.5 fold), 6 proteins including IL-10 downregulated (<0.5 fold) and 29 proteins including IL-16 & TNF-β were upregulated (>1.5 fold) in CD140b- ASCs compared to CD140b+ ASCs. Our data demonstrate a substantial role for CD140b in the intrinsic abilities of ASCs and their angiogenic influence on HREs. Future studies are needed to fully explore the signaling of CD140b in ASCs in vivo for retinal regeneration.

Tendon Tissue Engineering: Mechanism and Effects of Human Tenocyte Coculture With Adipose-Derived Stem Cells

PURPOSE

Adipose-derived stem cells (ASCs) are a potential candidate for cell-based therapy targeting tendon injury; however, their therapeutic benefit relies on their ability to interact with native tenocytes. This study examines the mechanism and effects of coculturing human tenocytes and ASCs.

METHODS

Tenocytes (T) were directly cocultured with either ASCs (A) or fibroblasts (F) (negative control) in the following ratios: 50% T/50% A or F; 25% T/75% A or F; and 75% T/25% A or F. Cells were indirectly cocultured using a transwell insert that allowed for exchange of soluble factors only. Proliferation and collagen I production were measured and compared with monoculture controls. Synergy was quantified using the interaction index (II), which normalizes measured values by the expected values assuming no interaction (no synergy when II = 1). The ability of ASCs to elicit tenocyte migration was examined in vitro using a transwell migration assay and ex vivo using decellularized human flexor tendon explants.

RESULTS

Compared with monoculture controls, II of proliferation was greater than 1 for all tenocyte and ASC direct coculture ratios, but not for tenocyte and fibroblast direct coculture ratios or for tenocyte and ASC indirect coculture. The ASCs elicited greater tenocyte migration in vitro and ex vivo. The II of collagen I production was greater than 1 for direct coculture groups with 25% T/75% A and 75% T/25% A.

CONCLUSIONS

Direct coculture of ASCs and tenocytes demonstrated synergistic proliferation and collagen I production, and ASCs elicited tenocyte migration in vitro and ex vivo. These interactions play a key role in tendon healing and were absent when ASCs were replaced with fibroblasts, supporting the use of ASCs for cell-based therapy targeting tendon injuries.

CLINICAL RELEVANCE

When ASCs are delivered for cell-based therapy, they directly interact with native tenocytes to increase cell proliferation, collagen I production, and tenocyte migration, which may enhance tendon healing.

Localization of Engineered Vasculature within 3D Tissue Constructs

Today, in vitro vessel network systems frequently serve as models for investigating cellular and functional mechanisms underlying angiogenesis and vasculogenesis. Understanding the cues triggering the observed cell migration, organization, and differentiation, as well as the time frame of these processes, can improve the design of engineered microvasculature. Here, we present first evidence of the migration of endothelial cells into the depths of the scaffold, where they formed blood vessels surrounded by extracellular matrix and supporting cells. The supporting cells presented localization-dependent phenotypes, where cells adjacent to blood vessels displayed a more mature phenotype, with smooth muscle cell characteristics, whereas cells on the scaffold surface showed a pericyte-like phenotype. Yes-associated protein (YAP), a transcription activator of genes involved in cell proliferation and tissue growth, displayed spatially dependent expression, with cells on the surface showing more nuclear YAP than cells situated deeper within the scaffold.

Scaffold Composition Determines the Angiogenic Outcome of Cell-Based Vascular Endothelial Growth Factor Expression by Modulating Its Microenvironmental Distribution

Delivery of genetically modified cells overexpressing Vascular Endothelial Growth Factor (VEGF) is a promising approach to induce therapeutic angiogenesis in ischemic tissues. The effect of the protein is strictly modulated by its interaction with the components of the extracellular matrix. Its therapeutic potential depends on a sustained but controlled release at the microenvironmental level in order to avoid the formation of abnormal blood vessels. In this study, it is hypothesized that the composition of the scaffold plays a key role in modulating the binding, hence the therapeutic effect, of the VEGF released by 3D-cell constructs. It is found that collagen sponges, which poorly bind VEGF, prevent the formation of localized hot spots of excessive concentration, therefore, precluding the development of aberrant angiogenesis despite uncontrolled expression by a genetically engineered population of adipose tissue-derived stromal cells. On the contrary, after seeding on VEGF-binding egg-white scaffolds, the same cell population caused aberrantly enlarged vascular structures after 14 d. Collagen-based engineered tissues also induced a safe and efficient angiogenesis in both the patch itself and the underlying myocardium in rat models. These findings open new perspectives on the control and the delivery of proangiogenic stimuli, and are fundamental for the vascularization of engineered tissues/organs.

Biological Interaction Between Human Gingival Fibroblasts and Vascular Endothelial Cells for Angiogenesis: A Co-culture Perspective

Advancement in cell culture protocols, multidisciplinary research approach, and the need of clinical implication to reconstruct damaged or diseased tissues has led to the establishment of three-dimensional (3D) test systems for regeneration and repair. Regenerative therapies, including dental tissue engineering, have been pursued as a new prospect to repair and rebuild the diseased/lost oral tissues. Interactions between the different cell types, growth factors, and extracellular matrix components involved in angiogenesis are vital in the mechanisms of new vessel formation for tissue regeneration. In vitro pre-vascularization is one of the leading scopes in the tissue-engineering field. Vascularization strategies that are associated with co-culture systems have proved that there is communication between different cell types with mutual beneficial effects in vascularization and tissue regeneration in two-dimensional or 3D cultures. Endothelial cells with different cell populations, including osteoblasts, smooth muscle cells, and fibroblasts in a co-culture have shown their ability to advocate pre-vascularization. In this review, a co-culture perspective of human gingival fibroblasts and vascular endothelial cells is discussed with the main focus on vascularization and future perspective of this model in regeneration and repair.

Adipose-derived perivascular mesenchymal stromal/stem cells promote functional vascular tissue engineering for cardiac regenerative purposes

Cardiac tissue engineering approaches have the potential to regenerate functional myocardium with intrinsic vascular networks. This study compared the relative effects of human adipose-derived stem/stromal cells (hASCs) and human dermal fibroblasts (hDFs) in cocultures with neonatal rat ventricular cardiomyocytes (NRVCMs) and human umbilical vein endothelial cells (HUVECs). At the same ratios of NRVCM:hASC and NRVCM:hDF, the hASC cocultures displayed shorter action potentials and maintained capture at faster pacing rates. Similarly, in coculture with HUVECs, hASC:HUVEC exhibited superior ability to support vascular capillary network formation relative to hDF:HUVEC. Based on these studies, a range of suitable cell ratios were determined to develop a triculture system. Six seeding ratios of NRVCM:hASC:HUVEC were tested and it was found that a ratio of 500:50:25 cells (i.e. 250,000:25,000:12,500 cells/cm² ) resulted in the formation of robust vascular networks while retaining action potential durations and propagation similar to pure NRVCM cultures. Tricultures in this ratio exhibited an average conduction velocity of 20 ± 2 cm/s, action potential durations at 80% repolarization (APD₈₀ ) and APD₃₀ of 122 ± 5 ms and 59 ± 4 ms, respectively, and maximum capture rate of 7.4 ± 0.6 Hz. The NRVCM control groups had APD₈₀ and APD₃₀ of 120 ± 9 ms and 51 ± 5 ms, with a maximum capture rate of 7.3 ± 0.2 Hz. In summary, the combination of hASCs in the appropriate ratios with NRVCMs and HUVECs can facilitate the formation of densely vascularized cardiac tissues that appear not to impact the electrophysiological function of cardiomyocytes negatively. Copyright © 2017 John Wiley & Sons, Ltd.

Spatially Assembled Bilayer Cell Sheets of Stem Cells and Endothelial Cells Using Thermosensitive Hydrogels for Therapeutic Angiogenesis

Although the coculture of multiple cell types has been widely employed in regenerative medicine, in vivo transplantation of cocultured cells while maintaining the hierarchical structure remains challenging. Here, a spatially assembled bilayer cell sheet of human mesenchymal stem cells and human umbilical vein endothelial cells on a thermally expandable hydrogel containing fibronectin is prepared and its effect on in vitro proangiogenic functions and in vivo ischemic injury is investigated. The expansion of hydrogels in response to a temperature change from 37 to 4 °C allows rapid harvest and delivery of the bilayer cell sheet to two different targets (an in vitro model glass surface and in vivo tissue). The in vitro study confirms that the bilayer sheet significantly increases proangiogenic functions such as the release of nitric oxide and expression of vascular endothelial cell genes. In addition, transplantation of the cell sheet from the hydrogels into a hindlimb ischemia mice model demonstrates significant retardation of necrosis particularly in the group transplated with the bilayer sheet. Collectively, the bilayer cell sheet is readily transferrable from the thermally expandable hydrogel and represents an alternative approach for recovery from ischemic injury, potentially via improved cell-cell communication.

The Adipose Stromal Vascular Fraction as a Complex Cellular Source for Tissue Engineering Applications

A major challenge in tissue engineering is the generation of sufficient volumes of viable tissue for organ transplant. The development of a stable, mature vasculature is required to sustain the metabolic and functional activities of engineered tissues. Adipose stromal vascular fraction (SVF) cells are an easily accessible, heterogeneous cell system comprised of endothelial cells, macrophages, pericytes, and various stem cell populations. Collectively, SVF has been shown to spontaneously form vessel-like networks in vitro and robust, patent, and functional vasculatures in vivo. Capitalizing on this ability, we and others have demonstrated adipose SVF's utility in generating and augmenting engineered liver, cardiac, and vascular tissues, to name a few. This review highlights the scientific origins of SVF, the use of SVF as a clinically relevant vascular source, various SVF constituents and their roles, and practical considerations associated with isolating SVF for various tissue engineering applications.

Elderly Patient-Derived Endothelial Cells for Vascularization of Engineered Muscle

In vitro prevascularization of engineered tissue constructs promises to enhance their clinical applicability. We hypothesize that adult endothelial cells (ECs), isolated from limb veins of elderly patients, bear the vasculogenic properties required to form vascular networks in vitro that can later integrate with the host vasculature upon implantation. Here, we show that adult ECs formed vessel networks that were more developed and complex than those formed by human umbilical vein endothelial cells (HUVECs) seeded with various supporting cells on three-dimensional (3D) biodegradable polymer scaffolds. In parallel, secreted levels of key proangiogenic cytokines were significantly higher in adult EC-bearing scaffolds as compared to HUVEC scaffolds. As a proof of concept for applicability of this model, adult ECs were co-seeded with human myoblasts as well as supporting cells and successfully formed a branched network, which was surrounded by aligned human myotubes. The vascularized engineered muscle tissue implanted into a full-thickness defect in immunodeficient mice remained viable and anastomosed with the host vasculature within 9 days of implantation. Functional "chimeric" blood vessels and various types of anastomosis were observed. These findings provide strong evidence of the applicability of adult ECs in construction of clinically relevant autologous vascularized tissue.

Mesenchymal Stem and Progenitor Cells in Regeneration: Tissue Specificity and Regenerative Potential

It has always been an ambitious goal in medicine to repair or replace morbid tissues for regaining the organ functionality. This challenge has recently gained momentum through considerable progress in understanding the biological concept of the regenerative potential of stem cells. Routine therapeutic procedures are about to shift towards the use of biological and molecular armamentarium. The potential use of embryonic stem cells and invention of induced pluripotent stem cells raised hope for clinical regenerative purposes; however, the use of these interventions for regenerative therapy showed its dark side, as many health concerns and ethical issues arose in terms of using these cells in clinical applications. In this regard, adult stem cells climbed up to the top list of regenerative tools and mesenchymal stem cells (MSC) showed promise for regenerative cell therapy with a rather limited level of risk. MSC have been successfully isolated from various human tissues and they have been shown to offer the possibility to establish novel therapeutic interventions for a variety of hard-to-noncurable diseases. There have been many elegant studies investigating the impact of MSC in regenerative medicine. This review provides compact information on the role of stem cells, in particular, MSC in regeneration.

Subretinal adipose tissue-derived mesenchymal stem cell implantation in advanced stage retinitis pigmentosa: a phase I clinical safety study

BACKGROUND

This prospective clinical case series aimed to investigate the safety of subretinal adipose tissue-derived mesenchymal stem cell (ADMSC) implantation in advanced stage retinitis pigmentosa (RP).

METHODS

This study included 11 patients with end-stage RP who received subretinal implantation of ADMSCs. All patients had a total visual field defect and five of them only had light perception. The best corrected visual acuity (BCVA) in the study was 20/2000. All patients had undetectable electroretinography (ERG). The worst eye of the patient was operated on and, after total vitrectomy with a 23 gauge, ADMSCs were injected subretinally. Patients were evaluated at day 1, at weeks 1-4, and then once a month for 6 months, postoperatively. BCVA, anterior segment and fundus examination, color photography, and optical coherence tomography (OCT) were carried out at each visit. Fundus fluorescein angiography (FFA), perimetry, and ERG recordings were performed before treatment and at the end of month 6, and anytime if necessary during the follow-up.

RESULTS

All 11 patients completed the 6-month follow-up. None of them had systemic complications. Five patients had no ocular complications. One of the patients experienced choroidal neovascular membrane (CNM) at the implantation site and received an intravitreal anti-vascular endothelial growth factor drug once. Five patients had epiretinal membrane around the transplantation area and at the periphery, and received a second vitrectomy and silicon oil injection. There was no statistically significant difference in BCVA and ERG recordings from baseline. Only one patient experienced an improvement in visual acuity (from 20/2000 to 20/200), visual field, and ERG. Three patients mentioned that the light and some colors were brighter than before and there was a slight improvement in BCVA. The remaining seven patients had no BCVA improvement (five of them only had light perception before surgery).

CONCLUSIONS

Stem cell treatment with subretinal implantation of ADMSCs seems to have some ocular complications and should be applied with caution. The results of this study provide the first evidence of the short-term safety of ADMSCs in humans, and clarifies the complications of the therapy which would be beneficial for future studies. To optimize the cell delivery technique and to evaluate the effects of this therapy on visual acuity and the quality of life of these patients, future studies with a larger number of cases will be necessary.

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.

Ultrathin Metal Films with Defined Topographical Structures as In Vitro Cell Culture Platforms for Unveiling Vascular Cell Behaviors

Implanted material surfaces make direct contact with body tissues to work on its own purpose. Therefore, studies of the surface properties of implantable materials that determine cell fate are very important for successful implantation. Although numerous studies have addressed the relationship between cells and material surfaces, nonmetallic surfaces and metallic surfaces likely produce different cellular responses because of their intrinsic differences in surface energy, roughness, and chemical composition. Moreover, given the nontransparent property of metal materials, which hampers the real-time imaging of cellular behavior, a detailed cellular-level analysis at the metal-tissue interface has not been performed. In this study, metal-based cell culture platforms (MCPs) with defined microscale topographical patterns are developed using a combination of photolithography and direct current magnetron sputtering techniques. The MCPs allow to observe vascular cells on metals in real time and identify the selective regulation of human aortic smooth muscle cells and Human umbilical vein endothelial cells (HUVECs) by metallic surface topography. Additionally, atomic force microscopy, contact angles, and energy-dispersive X-ray spectroscopy analyses show that the MCPs exhibit nearly identical chemical properties with their bulk counterparts, demonstrating that MCPs can be utilized as an in vitro cell culture platform system for understanding the cellular behavior on metal substrates.

Fluorescence light-up AIE probe for monitoring cellular alkaline phosphatase activity and detecting osteogenic differentiation

Three phosphorylated tetraphenylethylene (TPE) probes were synthesized for monitoring ALP activity in living stem cells and detecting osteogenic differentiation.