Short-term spheroid formation enhances the regenerative capacity of adipose-derived stem cells by promoting stemness, angiogenesis, and chemotaxis

A new approach to study the sex differences in adipose tissue

Obesity is one of the most invaliding and preventable diseases in the United States. Growing evidence suggests that there are sex differences in obesity in human and experimental animals. However, the specific mechanisms of this disease are unknown. Consequently, there is any particular treatment according to the sex/gender at this time. During the last decade, we observe a rise in the study of adipocyte and the possible mechanisms involved in the different roles of the fat. Furthermore, the effect of sex steroids on the adipocyte is one of the fields that need elucidation. Supporting evidence suggests that sex steroids play an essential role not only in the fat distribution, but also, in its metabolism, proliferation, and function. Thus, using in vitro and in vivo studies will contribute to our fight against this critical health public problem encompassing both sexes. In the present review, we discuss some of the recent advances in the adipocytes and the effect of the sex steroids on the adipose tissue. Also, we propose a new alternative to study the role of sex steroids on adipocyte biology through human adipose-derived stem cells.

Spheroids Spontaneously Generated In Vitro from Sheep Ovarian Cortical Cells Contain Integrating Cells That Exhibit Hallmarks of Neural Stem/Progenitor Cells

Cell spheroids are inducible or spontaneously generated cell aggregates produced in vitro that can provide a valuable model for developmental biology, stem cell biology, and cancer therapy research. This investigation aimed to define the cellular identity of spheroids spontaneously generated in vitro from sheep ovarian cortical cells cultured under specific serum-free conditions. Spheroids were characterized during 21 days of culture by morphometric evaluation, detection of alkaline phosphatase (AP) activity, gene expression analyses of stemness transcription factors and several lineage markers, immunolocalization analyses, as well as assessment of self-renewal and differentiation potential. Cell aggregation, evidenced from day 3 of culture onward, resulted in efficient generation of 65-75 spheroids for every 500,000 cells seeded. The spheroids reached maximum diameter (187 ± 15.9 μm) during the second week of culture and exhibited AP activity. Sox2, Oct4, and Nanog were expressed throughout the culture period, with upregulation of Sox2. Neural lineage specification genes (eg, nestin, vimentin, Pax6, and p75NTR) were expressed from day 10 onward at levels above that of Oct4, Nanog and those for endoderm [alpha-fetoprotein (AFP)], and mesoderm (brachyury) specification. Neural stem cell (NSC)/neural progenitor cell (NPC) markers, nestin, Pax6, p75NTR, and vimentin, were extensively localized in cells on day 10, 15 (44.75% ± 5.84%; 93.54% ± 1.35%; 78.90% ± 4.80%; 73.82% ± 3.40%, respectively), and 21 (49.98% ± 5.30%; 91.84% ± 1.9%; 76.74% ± 11.0%; 95.80% ± 3.60%, respectively). Spheroid cell self-renewal was evidenced by cell proliferation and the generation of new spheroids during two consecutive expansion periods. Culture of spheroid cells under differentiation conditions gave rise to cells showing immunolocalization of the neuron-specific antigen NeuN and the astroglial antigen GFAP (glial fibrillary acidic protein). Our results indicate that spheroids spontaneously generated in this culture system were comprised of cells with molecular characteristics of NSC/NPC that can self-renew and differentiate into neurons and glia, supporting the identity of spheroids as neurospheres.

3D-cultured human placenta-derived mesenchymal stem cell spheroids enhance ovary function by inducing folliculogenesis

Placenta-derived mesenchymal stem cells (PD-MSCs) have numerous advantages over other adult MSCs that make them an attractive cell source for regenerative medicine. Here, we demonstrate the therapeutic effect of PD-MSCs in ovariectomized (Ovx) rats and compare their efficacy when generated via a conventional monolayer culture system (2D, naïve) and a spheroid culture system (3D, spheroid). PD-MSC transplantation significantly increased the estradiol level in Ovx rats compared with the non-transplantation (NTx) group. In particular, the estradiol level in the Spheroid group was significantly higher than that in the Naïve group at 2 weeks. Spheroid PD-MSCs exhibited a significantly higher efficiency of engraftment onto ovarian tissues at 2 weeks. The mRNA and protein expression levels of Nanos3, Nobox, and Lhx8 were also significantly increased in the Spheroid group compared with those in the NTx group at 1 and 2 weeks. These results suggest that PD-MSC transplantation can restore ovarian function in Ovx rats by increasing estrogen production and enhancing folliculogenesis-related gene expression levels and further indicate that spheroid-cultured PD-MSCs have enhanced therapeutic potential via increased engraftment efficiency. These findings improve our understanding of stem-cell-based therapies for reproductive systems and may suggest new avenues for developing efficient therapies using 3D cultivation systems.

Functionalized Scaffold for in Situ Efficient Gene Transfection of Mesenchymal Stem Cells Spheroids toward Chondrogenesis

Multicellular mesenchymal stem cell (MSC) spheroids possess enhanced chondrogenesis ability and limited fibrosis, exhibiting advantage toward hyaline-like cartilage regeneration. However, because of the limited cell surfaces in spheroid exposed to DNA/vector, it is difficult to realize efficient gene transfection, most of which highly rely on cell-substrate interaction. Here, we report a poly(l-glutamic acid)-based porous scaffold with tunable inner surfaces that can sequentially realize cell-scaffold attachment and detachment, as well as the followed in situ spheroid formation. The attachment and detachment of cells from scaffold is achieved by the capture and release of fibronectin (Fn) via reversible imine linkage between aromatic aldehyde groups of scaffold and amino groups of Fn. Together with N, N, N-trimethyl chitosan chloride condensing plasmid DNA encoding transforming growth factor-β1 (pDNA-TGF-β1), cell attachment realizes efficient surface-mediated gene transfection. Conversion of scaffold stiffness can affect the adhesion shape of cells. Stiffer scaffold reinforces the adhesion, leading to the amplification of peripheral focal adhesions and the promotion of cell spreading, as well as the promotion of gene transfection efficiency. After cellular detachment from the scaffold via lysine treatment, the subsequent spheroid formation with extensive cell-cell interaction up-regulates the corresponding protein expression with a prolonged term. With the induction effect of the expressed TGF-β1, significantly enhanced chondrogenesis of MSCs in spheroids is achieved at 10 d in vitro. Well-regenerated cartilage at 8 weeks in vivo indicates that the present gene transfection system is a platform that can be potentially applied toward cartilage tissue engineering.

Scalable Generation of Mesenchymal Stem Cells from Human Embryonic Stem Cells in 3D

Human embryonic stem cell (hESC) derived mesenchymal stem cells (EMSC) are efficacious in treating a series of autoimmune, inflammatory, and degenerative diseases in animal models. However, all the EMSC derivation methods reported so far rely on two-dimensional (2D) culture systems, which are inefficient, costive and difficult for large-scale production. HESC, as an unlimited source, can be successively propagated in spheroids. Here, we demonstrate that hESC spheroids can directly differentiate into MSC spheroids (EMSC_Sp) within 20 days in one vessel without passaging and the system is scalable to any desired size. EMSC_Sp can further differentiate into osteocytes and chondrocytes in spheres or demineralized bone matrix. EMSC_Sp also retains immune-modulatory effects in vitro and therapeutic effects on two mouse models of colitis after dissociation. Compared to EMSC differentiated in monolayer, EMSC_Sp-derived cells have faster proliferation and higher yield and develop less apoptosis and slower senescence. Thus, the 3D differentiation system allows simple, cost-effective, and scalable production of high-quality EMSC and subsequently bone and cartilage tissues for therapeutic application.

Dynamic Cultivation of Mesenchymal Stem Cell Aggregates

Mesenchymal stem cells (MSCs) are considered as primary candidates for cell-based therapies due to their multiple effects in regenerative medicine. Pre-conditioning of MSCs under physiological conditions—such as hypoxia, three-dimensional environments, and dynamic cultivation—prior to transplantation proved to optimize their therapeutic efficiency. When cultivated as three-dimensional aggregates or spheroids, MSCs display increased angiogenic, anti-inflammatory, and immunomodulatory effects as well as improved stemness and survival rates after transplantation, and cultivation under dynamic conditions can increase their viability, proliferation, and paracrine effects, alike. Only few studies reported to date, however, have utilized dynamic conditions for three-dimensional aggregate cultivation of MSCs. Still, the integration of dynamic bioreactor systems, such as spinner flasks or stirred tank reactors might pave the way for a robust, scalable bulk expansion of MSC aggregates or MSC-derived extracellular vesicles. This review summarizes recent insights into the therapeutic potential of MSC aggregate cultivation and focuses on dynamic generation and cultivation techniques of MSC aggregates.

Effects of three-dimensional spheroid culture on equine mesenchymal stem cell plasticity

Mesenchymal stem cells (MSCs) are useful candidates for tissue engineering and cell therapy fields. We optimize culture conditions of equine adipose tissue-derived MSCs (eAD-MSCs) for treatment of horse fractures. To investigate enhancing properties of three-dimensional (3D) culture system in eAD-MSCs, we performed various sized spheroid formation and determined changes in gene expression levels to obtain different sized spheroid for cell therapy. eAD-MSCs were successfully isolated from horse tailhead. Using hanging drop method, spheroid formation was generated for three days. Quantitative real-time PCR was performed to analyze gene expression. As results, expression levels of pluripotent markers were increased depending on spheroid size and the production of PGE₂ was increased in spheroid formation compared to that in monolayer. Ki-67 showed a remarkable increase in the spheroid formed with 2.0 × 10⁵ cells/drop as compared to that in the monolayer. Expression levels of angiogenesis-inducing factors such as VEGF, IL-6, IL-8, and IL-18 were significantly increased in spheroid formation compared to those in the monolayer. Expression levels of bone morphogenesis-inducing factors such as Cox-2 and TGF-β1 were also significantly increased in spheroid formation compared to those in the monolayer. Expression levels of osteocyte-specific markers such as RUNX2, osteocalcin, and differentiation potential were also significantly increased in spheroid formation compared to those in the monolayer. Therefore, spheroid formation of eAD-MSCs through the hanging drop method can increases the expression of angiogenesis-inducing and bone morphogenesis-inducing factors under optimal culture conditions.

Cell Mimicking Microparticles Influence the Organization, Growth, and Mechanophenotype of Stem Cell Spheroids

Substrate stiffness is known to alter cell behavior and drive stem cell differentiation, though most research in this area has been restricted to traditional, two-dimensional culture systems rather than more physiologically relevant, three-dimensional (3D) platforms. In this study, we utilized polymer-based, cell mimicking microparticles (CMMPs) to deliver distinct, stable mechanical cues to human adipose derived stem cells in 3D spheroid culture to examine changes in adipogenic differentiation response and mechanophenotype. After 21 days of adipogenic induction, spheroids containing CMMPs (composite spheroids) stiffened in accordance with CMMP elasticity such that spheroids containing the stiffest, ~ 10 kPa, CMMPs were over 27% stiffer than those incorporating the most compliant, ~ 0.25 kPa CMMPs. Adipogenically induced, cell-only spheroids were over 180% larger and 50% more compliant than matched controls. Interestingly, composite spheroids cultured without chemical induction factors dissociated when presented with CMMPs stiffer than ~ 1 kPa, while adipogenic induction factors mitigated this behavior. Gene expression for PPARG and FABP4 were upregulated more than 45-fold in adipogenically induced samples compared to controls but were unaffected by CMMP elasticity, attributed to insufficient cell-CMMP contacts throughout the composite spheroid. In summary, mechanically tuned CMMPs influenced whole-spheroid mechanophenotype and stability but minimally affected differentiation response.

Spheroid-cultured human umbilical cord-derived mesenchymal stem cells attenuate hepatic ischemia-reperfusion injury in rats

Mesenchymal stem cell (MSC) transplantation is a promising treatment for ischemia-reperfusion injury (IRI). However, its effects on hepatic IRI were not consistent in the previous studies. 3D spheroid-cultured MSCs enhance their production of trophic and anti-inflammatory properties, but their effects on hepatic IRI remain unclear. In this study, we compared the 3D spheroid-cultured human umbilical derived MSCs (3D UC-MSCs) with 2D-cultured UC-MSCs (2D UC-MSCs) on treating hepatic IRI. The RNA sequencing data showed that suppression of cell mitosis, response to hypoxia, inflammation, and angiogenesis were the top genetic changes in 3D UC-MSCs compared with 2D UC-MSCs. Although both pro-inflammatory and anti-inflammatory genes were upregulated in the 3D UC-MSCs, the mRNA and protein of an RNase (ZC3H12A), which turnovers the mRNA of pro-inflammatory genes at the post-transcript level, were significantly upregulated in 3D UC-MSCs. 3D UC-MSCs reduced the secretion of many chemokines and growth factors, but increased the secretion of vascular endothelial growth factor. Compared with the vehicle and 2D UC-MSCs, 3D UC-MSCs significantly reduced hepatic IRI in rats, based on the plasma aminotransferase levels, liver damage scores, neutrophil infiltration, hepatocyte apoptosis and expression of inflammation-associated genes. These findings suggest that 3D UC-MSCs therapy is a promising treatment for hepatic IRI.

Concise Review: Fabrication, Customization, and Application of Cell Mimicking Microparticles in Stem Cell Science

Stem and non-stem cell behavior is heavily influenced by the surrounding microenvironment, which includes other cells, matrix, and potentially biomaterials. Researchers have been successful in developing scaffolds and encapsulation techniques to provide stem cells with mechanical, topographical, and chemical cues to selectively direct them toward a desired differentiation pathway. However, most of these systems fail to present truly physiological replications of the in vivo microenvironments that stem cells are typically exposed to in tissues. Thus, cell mimicking microparticles (CMMPs) have been developed to more accurately recapitulate the properties of surrounding cells while still offering ways to tailor what stimuli are presented. This nascent field holds the promise of reducing, or even eliminating, the need for live cells in select, regenerative medicine therapies, and diagnostic applications. Recent, CMMP-based studies show great promise for the technology, yet only reproduce a small subset of cellular characteristics from among those possible: size, morphology, topography, mechanical properties, surface molecules, and tailored chemical release to name the most prominent. This Review summarizes the strengths, weaknesses, and ideal applications of micro/nanoparticle fabrication and customization methods relevant to cell mimicking and provides an outlook on the future of this technology. Moving forward, researchers should seek to combine multiple techniques to yield CMMPs that replicate as many cellular characteristics as possible, with an emphasis on those that most strongly influence the desired therapeutic effects. The level of flexibility in customizing CMMP properties allows them to substitute for cells in a variety of regenerative medicine, drug delivery, and diagnostic systems. Stem Cells Translational Medicine 2018;7:232-240.

Microfluidic Encapsulation Supports Stem Cell Viability, Proliferation, and Neuronal Differentiation

Stem cell encapsulation technology demonstrates much promise for the replacement of damaged tissue in several diseases, including spinal cord injury (SCI). The use of biocompatible microcapsules permits the control of stem cell fate in situ to facilitate the replacement of damaged/lost tissue. In this work, a novel customized microfluidic device was developed for the reproducible encapsulation of neural stem cells (NSCs) and dental pulp stem cells (DPSCs) within monodisperse, alginate-collagen microcapsules. Both cell types survived within the microcapsules for up to 21 days in culture. Stem cells demonstrated retention of their multipotency and neuronal differentiation properties upon selective release from the microcapsules, as demonstrated by high proliferation rates and the production of stem cell and neuronal lineage markers. When cell-laden microcapsules were transplanted into an organotypic SCI model, the microcapsules effectively retained the transplanted stem cells at the site of implantation. Implanted cells survived over a 10 day period in culture after transplantation and demonstrated commitment to a neural lineage. Our device provides a quick, effective, and aseptic method for the encapsulation of two different stem cell types (DPSCs and NSCs) within alginate-collagen microcapsules. Since stem cells were able to retain their viability and neural differentiation capacity within such microcapsules, this method provides a useful technique to study stem cell behavior within three-dimensional environments.

Xeno-free pre-vascularized spheroids for therapeutic applications

Spheroid culture has gained increasing popularity, arising as a promising tool for regenerative medicine applications. Importantly, spheroids may present advantages over single-cell suspensions in cell-based therapies (CT). Unfortunately, most growth media used for spheroid culture contain animal origin-components, such as fetal bovine serum (FBS). The presence of FBS compromises the safety of CT and presents economic and ethical constraints. SCC (supplement for cell culture) is a novel xeno-free (XF) industrial cell culture supplement, derived from well-controlled pooled human plasma and processed under good manufacturing practice rules. Here, we developed a XF SCC-based formulation for 2D-culture of outgrowth endothelial cells (OEC), and then used it for generating co-culture spheroids of OEC and mesenchymal stem cells (MSC). XF MSC-OEC spheroids were characterized in detail and compared to spheroids cultured in FBS-supplemented medium. XF spheroids presented comparable integrity, size and morphology as the reference culture. The use of both media resulted in spheroids with similar structure, abundant extracellular matrix deposition and specific patterns of OEC distribution and organization. Notably, XF spheroids presented significantly enhanced angiogenic potential, both in vitro (fibrin sprouting assay) and in vivo (CAM assay). These findings are particularly promising in the context of potential therapeutic applications.

Differences in the neovascular potential of thymus versus subcutaneous adipose-derived stem cells from patients with myocardial ischaemia

Adipose tissue-derived multipotent mesenchymal cells (ASCs) participate in the information of blood vessels under hypoxic conditions. It is probable that the susceptibility of ASCs to the influence of age and ageing-associated pathologies compromises their therapeutic effectiveness depending on the adipose tissue depot. Our aim was to examine the neovascular potential under hypoxic conditions of ASCs-derived from thymic (thymASCs) and subcutaneous (subASCs) adipose tissue from 39 subjects with and without type 2 diabetes mellitus (T2DM) and of different ages who were undergoing coronary bypass surgery. We confirmed a significant decrease in the percentage of CD34⁺ CD31^- CD45^- subASCs in the cell yield of subASCs and in the survival of cultured endothelial cells in the medium conditioned by the hypox-subASCs with increasing patient age, which was not observed in thymASCs. Whereas the length of the tubules generated by hypox-subASCs tended to correlate negatively with patient age, tubule formation capacity of the hypoxic thymASCs increased significantly. Compared with subASCs, thymASCs from subjects over age 65 and without T2DM showed higher cell yield, tubule formation capacity, vascular endothelial growth factor secretion levels, and ability to promote endothelial cell survival in their conditioned medium. Deterioration in subASCs neovascular potential relative to thymASCs derived from these subjects was accompanied by higher expression levels of NOX4 mRNA and fibrotic proteins. Our results indicate that thymASCs from patients over age 65 and without T2DM have a higher angiogenic potential than those from the other patient groups, suggesting they may be a good candidate for angiogenic therapy in subjects undergoing coronary bypass surgery.

Methacrylated gelatin/hyaluronan-based hydrogels for soft tissue engineering

In vitro–generated soft tissue could provide alternate therapies for soft tissue defects. The aim of this study was to evaluate methacrylated gelatin/hyaluronan as scaffolds for soft tissue engineering and their interaction with human adipose–derived stem cells (hASCs). ASCs were incorporated into methacrylated gelatin/hyaluronan hydrogels. The gels were photocrosslinked with a lithium phenyl-2,4,6-trimethylbenzoylphosphinate photoinitiator and analyzed for cell viability and adipogenic differentiation of ASCs over a period of 30 days. Additionally, an angiogenesis assay was performed to assess their angiogenic potential. After 24 h, ASCs showed increased viability on composite hydrogels. These results were consistent over 21 days of culture. By induction of adipogenic differentiation, the mature adipocytes were observed after 7 days of culture, their number significantly increased until day 28 as well as expression of fatty acid binding protein 4 and adiponectin. Our scaffolds are promising as building blocks for adipose tissue engineering and allowed long viability, proliferation, and differentiation of ASCs.

Advances, challenges and future directions for stem cell therapy in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative condition where loss of motor neurons within the brain and spinal cord leads to muscle atrophy, weakness, paralysis and ultimately death within 3–5 years from onset of symptoms. The specific molecular mechanisms underlying the disease pathology are not fully understood and neuroprotective treatment options are minimally effective.

In recent years, stem cell transplantation as a new therapy for ALS patients has been extensively investigated, becoming an intense and debated field of study. In several preclinical studies using the SOD1^G93A mouse model of ALS, stem cells were demonstrated to be neuroprotective, effectively delayed disease onset and extended survival. Despite substantial improvements in stem cell technology and promising results in preclinical studies, several questions still remain unanswered, such as the identification of the most suitable and beneficial cell source, cell dose, route of delivery and therapeutic mechanisms. This review will cover publications in this field and comprehensively discuss advances, challenges and future direction regarding the therapeutic potential of stem cells in ALS, with a focus on mesenchymal stem cells. In summary, given their high proliferation activity, immunomodulation, multi-differentiation potential, and the capacity to secrete neuroprotective factors, adult mesenchymal stem cells represent a promising candidate for clinical translation. However, technical hurdles such as optimal dose, differentiation state, route of administration, and the underlying potential therapeutic mechanisms still need to be assessed.

Tunable Surface Repellency Maintains Stemness and Redox Capacity of Human Mesenchymal Stem Cells

Human bone marrow derived mesenchymal stem cells (hMSCs) hold great promise for regenerative medicine due to their multipotent differentiation capacity and immunomodulatory capabilities. Substantial research has elucidated mechanisms by which extracellular cues regulate hMSC fate decisions, but considerably less work has addressed how material properties can be leveraged to maintain undifferentiated stem cells. Here, we show that synthetic culture substrates designed to exhibit moderate cell-repellency promote high stemness and low oxidative stress-two indicators of naïve, healthy stem cells-in commercial and patient-derived hMSCs. Furthermore, the material-mediated effect on cell behavior can be tuned by altering the molar percentage (mol %) and/or chain length of poly(ethylene glycol) (PEG), the repellant block linked to hydrophobic poly(ε-caprolactone) (PCL) in the copolymer backbone. Nano- and angstrom-scale characterization of the cell-material interface reveals that PEG interrupts the adhesive PCL domains in a chain-length-dependent manner; this prevents hMSCs from forming mature focal adhesions and subsequently promotes cell-cell adhesions that require connexin-43. This study is the first to demonstrate that intrinsic properties of synthetic materials can be tuned to regulate the stemness and redox capacity of hMSCs and provides new insight for designing highly scalable, programmable culture platforms for clinical translation.

Hypoxic Three-Dimensional Scaffold-Free Aggregate Cultivation of Mesenchymal Stem Cells in a Stirred Tank Reactor

Extensive expansion of mesenchymal stem cells (MSCs) for cell-based therapies remains challenging since long-term cultivation and excessive passaging in two-dimensional conditions result in a loss of essential stem cell properties. Indeed, low survival rate of cells, alteration of surface marker profiles, and reduced differentiation capacity are observed after in vitro expansion and reduce therapeutic success in clinical studies. Remarkably, cultivation of MSCs in three-dimensional aggregates preserve stem cell properties. Hence, the large scale formation and cultivation of MSC aggregates is highly desirable. Besides other effects, MSCs cultivated under hypoxic conditions are known to display increased proliferation and genetic stability. Therefore, in this study we demonstrate cultivation of adipose derived human MSC aggregates in a stirred tank reactor under hypoxic conditions. Although aggregates were exposed to comparatively high average shear stress of 0.2 Pa as estimated by computational fluid dynamics, MSCs displayed a viability of 78-86% and maintained their surface marker profile and differentiation potential after cultivation. We postulate that cultivation of 3D MSC aggregates in stirred tank reactors is valuable for large-scale production of MSCs or their secreted compounds after further optimization of cultivation parameters.

In vitro biomimetic platforms featuring a perfusion system and 3D spheroid culture promote the construction of tissue-engineered corneal endothelial layers

Corneal endothelial cells (CECs) are very important for the maintenance of corneal transparency. However, in vitro, CECs display limited proliferation and loss of phenotype via endothelial to mesenchymal transformation (EMT) and cellular senescence. In this study, we demonstrate that continuous supplementary nutrition using a perfusion culture bioreactor and three-dimensional (3D) spheroid culture can be used to improve CEC expansion in culture and to construct a tissue-engineered CEC layer. Compared with static culture, perfusion-derived CECs exhibited an increased proliferative ability as well as formed close cell-cell contact junctions and numerous surface microvilli. We also demonstrated that the CEC spheroid culture significantly down-regulated gene expression of the proliferation marker Ki67 and EMT-related markers Vimentin and α-SMA, whereas the gene expression level of the CEC marker ATP1A1 was significantly up-regulated. Furthermore, use of the perfusion system in conjunction with a spheroid culture on decellularized corneal scaffolds and collagen sheets promoted the generation of CEC monolayers as well as neo-synthesized ECM formation. This study also confirmed that a CEC spheroid culture on a curved collagen sheet with controlled physiological intraocular pressure could generate a CEC monolayer. Thus, our results show that the use of a perfusion system and 3D spheroid culture can promote CEC expansion and the construction of tissue-engineered corneal endothelial layers in vitro.

3D culture increases pluripotent gene expression in mesenchymal stem cells through relaxation of cytoskeleton tension

Three‐dimensional (3D) culture has been shown to improve pluripotent gene expression in mesenchymal stem cells (MSCs), but the underlining mechanisms were poorly understood. Here, we found that the relaxation of cytoskeleton tension of MSCs in 3D culture was critically associated with the expressional up‐regulation of Nanog. Cultured in spheroids, MSCs showed decreased integrin‐based cell–matrix adhesion but increased cadherin‐based cell–cell interaction. Different from that in 2D culture, where MSCs exhibited branched and multiple‐directed F‐actin stress bundles at the cell edge and strengthened stress fibres transversing the cell body, MSCs cultured in spheroids showed compact cell body, relaxed cytoskeleton tension with very thin cortical actin filament outlining the cell, and increased expression of Nanog along with reduced levels of Suv39h1 (H3K9 methyltransferase) and H3K9me3. Notably, pharmaceutical inhibition of actin polymerization with cytochalasin D or silencing Suv39h1 expression with siRNA in 2D‐cultured MSCs elevated the expression of Nanog via H3K9 demethylation. Thus, our data suggest that 3D culture increases the expression of Nanog through the relaxation of actin cytoskeleton, which mediates reduced Suv39h1 and H3K9me3 levels.

Purification and differentiation of human adipose-derived stem cells by membrane filtration and membrane migration methods

Human adipose-derived stem cells (hADSCs) are easily isolated from fat tissue without ethical concerns, but differ in purity, pluripotency, differentiation ability, and stem cell marker expression, depending on the isolation method. We isolated hADSCs from a primary fat tissue solution using: (1) conventional culture, (2) a membrane filtration method, (3) a membrane migration method where the primary cell solution was permeated through membranes, adhered hADSCs were cultured, and hADSCs migrated out from the membranes. Expression of mesenchymal stem cell markers and pluripotency genes, and osteogenic differentiation were compared for hADSCs isolated by different methods using nylon mesh filter membranes with pore sizes ranging from 11 to 80 μm. hADSCs isolated by the membrane migration method had the highest MSC surface marker expression and efficient differentiation into osteoblasts. Osteogenic differentiation ability of hADSCs and MSC surface marker expression were correlated, but osteogenic differentiation ability and pluripotent gene expression were not.

Physiologically Low Oxygen Enhances Biomolecule Production and Stemness of Mesenchymal Stem Cell Spheroids

Multicellular human mesenchymal stem cell (hMSC) spheroids have been demonstrated to be valuable in a variety of applications, including cartilage regeneration, wound healing, and neoangiogenesis. Physiological relevant low oxygen culture can significantly improve in vitro hMSC expansion by preventing cell differentiation. We hypothesize that hypoxia-cultured hMSC spheroids can better maintain the regenerative properties of hMSCs. In this study, hMSC spheroids were fabricated using hanging drop method and cultured under 2% O2 and 20% O2 for up to 96 h. Spheroid diameter and viability were examined, as well as extracellular matrix (ECM) components and growth factor levels between the two oxygen tensions at different time points. Stemness was measured among the spheroid culture conditions and compared to two-dimensional cell cultures. Spheroid viability and structural integrity were studied using different needle gauges to ensure no damage would occur when implemented in vivo. Spheroid attachment and integration within a tissue substitute were also demonstrated. The results showed that a three-dimensional hMSC spheroid cultured at low oxygen conditions can enhance the production of ECM proteins and growth factors, while maintaining the spheroids' stemness and ability to be injected, attached, and potentially be integrated within a tissue.

Dual-crosslinked hydrogel microwell system for formation and culture of multicellular human adipose tissue-derived stem cell spheroids

Three-dimensional (3D) multicellular spheroids of human adipose tissue-derived stem cells (hASCs) are an attractive system for basic science studies and tissue engineering applications, as they can resemble cellular condensations present in developmental and healing processes. The purpose of this study was to engineer a hydrogel-based microwell platform by capitalizing on the differential swelling behavior of micropatterned dual-crosslinked oxidized, methacrylated alginate (OMA)/multi-arm polyethylene glycol (PEG) hydrogels for rapid formation of uniform multicellular hASC spheroids with controllable size and evaluation of the capacity of the system to be used to drive osteogenic differentiation of the spheroids. By changing the micropattern size, the size of the hydrogel microwells was easily controllable. Microwell-seeded hASCs generated spheroids of relatively uniform size and high cell viability. hASC spheroids exhibited rapid mineralization in osteogenic media, which was faster than that of conventional two-dimensionally cultured hASCs. This new hydrogel microwell system has great potential for controlled multicellular spheroid formation and defined signal presentation from the hydrogel material to the cell aggregates to regulate tissue formation.

Mesenchymal Stem Cells in Chronic Wounds: The Spectrum from Basic to Advanced Therapy

Significance: Almost 7 million Americans have chronic cutaneous wounds and billions of dollars are spent on their treatment. The number of patients with nonhealing wounds keeps increasing worldwide due to an ever-aging population, increasing number of obese and diabetic patients, and cardiovascular disease. Recent Advances: Advanced treatments for difficult wounds are needed. Therapy with mesenchymal stem cells (MSCs) is attractive due to their differentiating potential, their immunomodulating properties, and their paracrine effects. Critical Issues: New technologies (including growth factors and skin substitutes) are now widely used for stimulating wound healing. However, in spite of these advances, the percentage of complete wound closure in most clinical situations is around 50-60%. Moreover, there is a high rate of wound recurrence. Future Directions: Recently, it has been demonstrated that MSCs speed up wound healing by decreasing inflammation, by promoting angiogenesis, and by decreasing scarring. However, there are some potential limitations to successful MSC therapy. These limitations include the need to improve cell delivery methods, cell viability, heterogeneity in MSC preparations, and suboptimal wound bed preparation. Further large, controlled clinical trials are needed to establish the safety of MSCs before widespread clinical application.

Soft Elasticity-Associated Signaling and Bone Morphogenic Protein 2 Are Key Regulators of Mesenchymal Stem Cell Spheroidal Aggregates

Cell therapy with adult mesenchymal stem cells (MSCs) is a promising approach to regenerative medicine and autoimmune diseases. There are various approaches to improve the efficacy of MSC-based therapeutics, and MSC preparation as spheroidal aggregates, or MSC spheroids, is a novel preparatory and delivery method. Spheroid formation induces a dramatic change in the gene expression profile of MSCs. Self-activation of interleukin-1 (IL1) signaling was shown to be upstream of both pro- and anti-inflammatory genes in MSC spheroids, but the molecular pathways that initiate IL1 signaling remain unknown. As bone morphogenic protein (BMP)2 upregulation precedes that of IL1B expression during spheroid formation, we hypothesized that BMP2 signaling triggers IL1 signaling in MSC spheroids. Contrary to expectations, BMP2 signaling decreased expression of IL1B and downstream genes in a SMAD6-dependent manner. Conversely, IL1B signaling enhanced BMP2 expression. Another major difference between two-dimensional (2D) monolayer culture and three-dimensional (3D) spheroid culture is the Young's elasticity modulus, or stiffness, of the materials surrounding the cells, as there is a million-fold difference between a plastic surface for standard 2D culture (GPa) and 3D spheroidal aggregates (0.1 kPa). We tested another hypothesis that soft elasticity-associated mechano-signaling initiates the gene expression change during spheroid formation. Results showed that both BMP2 expression and inflammatory signaling are upregulated in an elasticity-associated signaling-dependent manner in MSCs. Lastly, BMP2 signaling enhanced cell survival and cell spreading of MSC spheroids. In summary, our study suggests that soft elasticity and BMP2 signaling are critical for MSC spheroids.

High glucose-induced reactive oxygen species generation promotes stemness in human adipose-derived stem cells

BACKGROUND AIMS

Adipose-derived stem cells (ASCs) represent an important source of cell therapy to treat diabetic complications. However, hyperglycemia may alter several cellular functions, so the present study aimed to investigate the influence of a diabetic environment on the stemness and differentiation capabilities of ASCs.

METHODS

Human ASCs were obtained from subcutaneous adipose tissues of diabetic (dASCs) and nondiabetic donors (nASCs) and characterized. To reproduce an in vitro hyperglycemia environment, the nASCs were also cultured under prolonged high-glucose (HG; 4.5 g/L) or low-glucose (LG; 1.0 g/L) conditions.

RESULTS

The expression of cell surface markers in dASCs and nASC was similar and characteristic of mesenchymal stem cells. Although dASCs or HG-treated nASCs exhibited decreased proliferation, enhanced expression of the pluripotent markers Sox-2, Oct-4, and Nanog was observed. Moreover, HG-treated nASCs exhibited decreased cell migration, enhanced senescence, and significantly higher intracellular reactive oxygen species (ROS), whereas their adipogenic and osteogenic differentiation capacities remained comparable to LG-treated cells. With antioxidant treatment, HG-treated nASCs showed improved cell proliferative activity without stemness enhancement. This HG-induced biological response was associated with ROS-mediated AKT attenuation. When cultured in an appropriate induction medium, the HG-treated nASCs and dASCs exhibited enhanced potential of transdifferentiation into neuron-like cells.

DISCUSSION

Despite lower proliferative activity and higher senescence in a diabetic environment, ASCs also exhibit enhanced stemness and neurogenic transdifferentiation potential via a ROS-mediated mechanism. The information is important for future application of autologous ASCs in diabetic patients.

Hypoxia Inhibits De Novo Vascular Assembly of Adipose-Derived Stromal/Stem Cell Populations, but Promotes Growth of Preformed Vessels

Vascularization is critical for cell survival within tissue-engineered grafts. Adipose-derived stromal/stem cells (ASCs) are widely used in tissue engineering applications as they are a clinically relevant source of stem cells and endothelial progenitor cells. ASCs have previously been shown to self-assemble into pericyte-stabilized vascular networks in normoxic (20% O2) cultures. This capacity for de novo vascular assembly may accelerate graft vascularization in vivo rather than relying solely on angiogenic ingrowth. However, oxygen depletion within large cell-seeded grafts will be rapid, and it is unclear how this worsening hypoxic environment will impact the vascular assembly of the transplanted cells. The objectives of this study were to determine whether ASC-derived vessels could grow in hypoxia and to assess whether the vessel maturity (i.e., individual cells vs. preformed vessels) influenced this hypoxic response. Utilizing an in vitro vascularization model, ASCs were encapsulated within fibrin gels and cultured in vitro for up to 6 days in either normoxia (20% O2) or hypoxia (0.2% or 2% O2). In a subsequent experiment, vessels were allowed to preform in normoxia for 6 days before an additional 6 days of either normoxia or hypoxia. Viability, vessel growth, pericyte coverage, proliferation, metabolism, and angiogenic factor expression were assessed for each experimental approach. Vessel growth was dramatically inhibited in both moderate and severe hypoxia (47% and 11% total vessel length vs. normoxia, respectively), despite maintaining high cell viability and upregulating endogenous expression of vascular endothelial growth factor in hypoxia. Bromodeoxyuridine labeling indicated significantly reduced proliferation of endothelial cells in hypoxia. In contrast, when vascular networks were allowed to preform for 6 days in normoxia, vessels not only survived but also continued to grow more in hypoxia than those maintained in normoxia. These findings demonstrate that vascular assembly and growth are tightly regulated by oxygen tension and may be differentially affected by hypoxic conditions based on the maturity of the vessels. Understanding this relationship is critical to developing effective approaches to engineer viable tissue-engineered grafts in vivo.

Spheroid Culture of Mesenchymal Stem Cells

Compared with traditional 2D adherent cell culture, 3D spheroidal cell aggregates, or spheroids, are regarded as more physiological, and this technique has been exploited in the field of oncology, stem cell biology, and tissue engineering. Mesenchymal stem cells (MSCs) cultured in spheroids have enhanced anti-inflammatory, angiogenic, and tissue reparative/regenerative effects with improved cell survival after transplantation. Cytoskeletal reorganization and drastic changes in cell morphology in MSC spheroids indicate a major difference in mechanophysical properties compared with 2D culture. Enhanced multidifferentiation potential, upregulated expression of pluripotency marker genes, and delayed replicative senescence indicate enhanced stemness in MSC spheroids. Furthermore, spheroid formation causes drastic changes in the gene expression profile of MSC in microarray analyses. In spite of these significant changes, underlying molecular mechanisms and signaling pathways triggering and sustaining these changes are largely unknown.

Therapeutic Potential of Human Adipose-Derived Stem/Stromal Cell Microspheroids Prepared by Three-Dimensional Culture in Non-Cross-Linked Hyaluronic Acid Gel

Three-dimensional culture of mesenchymal stem/stromal cells for spheroid formation is known to enhance their therapeutic potential for regenerative medicine. Spheroids were prepared by culturing human adipose-derived stem/stromal cells (hASCs) in a non-cross-linked hyaluronic acid (HA) gel and compared with dissociated hASCs and hASC spheroids prepared using a nonadherent dish. Preliminary experiments indicated that a 4% HA gel was the most appropriate for forming hASC spheroids with a relatively consistent size (20-50 µm) within 48 hours. Prepared spheroids were positive for pluripotency markers (NANOG, OCT3/4, and SOX-2), and 40% of the cells were SSEA-3-positive, a marker of the multilineage differentiating stress enduring or Muse cell. In contrast with dissociated ASCs, increased secretion of cytokines such as hepatocyte growth factor was detected in ASC spheroids cultured under hypoxia. On microarray ASC spheroids showed upregulation of some pluripotency markers and downregulation of genes related to the mitotic cell cycle. After ischemia-reperfusion injury to the fat pad in SCID mice, local injection of hASC spheroids promoted tissue repair and reduced the final atrophy (1.6%) compared with that of dissociated hASCs (14.3%) or phosphate-buffered saline (20.3%). Part of the administered hASCs differentiated into vascular endothelial cells. ASC spheroids prepared in a HA gel contain undifferentiated cells with therapeutic potential to promote angiogenesis and tissue regeneration after damage.

SIGNIFICANCE

This study shows the therapeutic value of human adipose-derived stem cell spheroids prepared in hyarulonic acid gel. The spheroids have various benefits as an injectable cellular product and show therapeutic potential to the stem cell-depleted conditions such as diabetic chronic skin ulcer.

Qualitative and quantitative differences of adipose-derived stromal cells from superficial and deep subcutaneous lipoaspirates: a matter of fat

BACKGROUND AIMS

Subcutaneous fat represents a valuable reservoir of adipose-derived stem cells (ASCs) in the stromal vascular fraction (SVF), widely exploited in regenerative medicine applications, being easily harvested through lipoaspiration. The lack of standardized procedures for autologous fat grafting guided research efforts aimed at identifying possible differences related to the harvesting site, which may affect cell isolation yield, cell growth properties and clinical outcomes. Subcutaneous fat features a complex architecture: the superficial fascia separates superficial adipose tissue (SAT) from deep layer tissue (DAT). We aimed to unravel the differences between SAT and DAT, considering morphological structure, SVF composition, and ASC properties.

METHODS

SAT and DAT were collected from female donors and comparatively analyzed to evaluate cellular yield and viability, morphology, immunophenotype and molecular profile. ASCs were isolated in primary culture and used for in vitro differentiation assays. SAT and DAT from cadaver donors were also analyzed through histology and immunohistochemistry to assess morphology and cell localization within the hypoderm.

RESULTS

Liposuctioned SAT contained a higher stromal tissue compound, along with a higher proportion of CD105-positive cells, compared with DAT from the same harvesting site. Also, cells isolated from SAT displayed increased multipotency and stemness features. All differences were mainly evidenced in specimens harvested from the abdominal region. According to our results, SAT features overall increased stem properties.

CONCLUSIONS

Given that subcutaneous adipose tissue is currently exploited as the gold standard source for high-yield isolation of adult stem cells, these results may provide precious hints toward the definition of standardized protocols for microharvesting.

Applicability of Adipose-Derived Stem Cells in Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) is a form of early onset diabetes mellitus characterized by the autoimmune destruction of insulin-producing cells (IPCs), resulting in hyperglycemia and abnormal glucose metabolism. There are currently no treatments available capable of completely curing the symptoms associated with the loss or functional defects of IPCs. Nonetheless, stem cell therapy has demonstrated considerable promise in the replacement of IPCs with immunomodulatory functions to overcome the defects caused by T1DM. Adipose-derived stem cells (ADSCs) are particularly suitable for use in cell transplantation therapy, especially when seeking to avoid the ethical issues and tumorigenic complications commonly associated with embryos or induced pluripotent stem cells. Cell-based treatments have demonstrated therapeutic advantages and clinical applicability of ADSCs in T1DM, ensuring their suitability for transplantation therapy. This manuscript focuses on the benefits and possible mechanisms in a T1DM-relevant model and displays positive results from finished or ongoing human clinical trials. We also discuss and hypothesize potential methods to further enhance the therapeutic efficacy of these efforts, such as a humanized rodent model and gene therapies for IPC clusters, to meet the clinical applicability of the standard.

Characterization and angiogenic potential of human neonatal and infant thymus mesenchymal stromal cells

Resident mesenchymal stromal cells (MSCs) are involved in angiogenesis during thymus regeneration. We have previously shown that MSCs can be isolated from enzymatically digested human neonatal and infant thymus tissue that is normally discarded during pediatric cardiac surgical procedures. In this paper, we demonstrate that thymus MSCs can also be isolated by explant culture of discarded thymus tissue and that these cells share many of the characteristics of bone marrow MSCs. Human neonatal thymus MSCs are clonogenic, demonstrate exponential growth in nearly 30 population doublings, have a characteristic surface marker profile, and express pluripotency genes. Furthermore, thymus MSCs have potent proangiogenic behavior in vitro with sprout formation and angiogenic growth factor production. Thymus MSCs promote neoangiogenesis and cooperate with endothelial cells to form functional human blood vessels in vivo. These characteristics make thymus MSCs a potential candidate for use as an angiogenic cell therapeutic agent and for vascularizing engineered tissues in vitro.

Digital microfluidics for automated hanging drop cell spheroid culture

Cell spheroids are multicellular aggregates, grown in vitro, that mimic the three-dimensional morphology of physiological tissues. Although there are numerous benefits to using spheroids in cell-based assays, the adoption of spheroids in routine biomedical research has been limited, in part, by the tedious workflow associated with spheroid formation and analysis. Here we describe a digital microfluidic platform that has been developed to automate liquid-handling protocols for the formation, maintenance, and analysis of multicellular spheroids in hanging drop culture. We show that droplets of liquid can be added to and extracted from through-holes, or "wells," and fabricated in the bottom plate of a digital microfluidic device, enabling the formation and assaying of hanging drops. Using this digital microfluidic platform, spheroids of mouse mesenchymal stem cells were formed and maintained in situ for 72 h, exhibiting good viability (>90%) and size uniformity (% coefficient of variation <10% intraexperiment, <20% interexperiment). A proof-of-principle drug screen was performed on human colorectal adenocarcinoma spheroids to demonstrate the ability to recapitulate physiologically relevant phenomena such as insulin-induced drug resistance. With automatable and flexible liquid handling, and a wide range of in situ sample preparation and analysis capabilities, the digital microfluidic platform provides a viable tool for automating cell spheroid culture and analysis.

The effects of spheroid formation of adipose-derived stem cells in a microgravity bioreactor on stemness properties and therapeutic potential

Adipose-derived stem cells (ADSCs) represent a valuable source of stem cells for regenerative medicine, but the loss of their stemness during in vitro expansion remains a major roadblock. We employed a microgravity bioreactor (MB) to develop a method for biomaterial-free-mediated spheroid formation to maintain the stemness properties of ADSCs. ADSCs spontaneously formed three-dimensional spheroids in the MB. Compared with monolayer culture, the expression levels of E-cadherin and pluripotent markers were significantly upregulated in ADSC spheroids. Spheroid-derived ADSCs exhibited increased proliferative ability and colony-forming efficiency. By culturing the spheroid-derived ADSCs in an appropriate induction medium, we found that the multipotency differentiation capacities of ADSCs were significantly improved by spheroid culture in the MB. Furthermore, when ADSCs were administered to mice with carbon tetrachloride-induced acute liver failure, spheroid-derived ADSCs showed more effective potentials to rescue liver failure than ADSCs derived from constant monolayer culture. Our results suggest that spheroid formation of ADSCs in an MB enhances their stemness properties and increases their therapeutic potential. Therefore, spheroid culture in an MB can be an efficient method to maintain stemness properties, without the involvement of any biomaterials for clinical applications of in vitro cultured ADSCs.

Three-dimensional aggregates of mesenchymal stem cells: cellular mechanisms, biological properties, and applications

Mesenchymal stem cells (MSCs) are primary candidates in cell therapy and tissue engineering and are being tested in clinical trials for a wide range of diseases. Originally isolated and expanded as plastic adherent cells, MSCs have intriguing properties of in vitro self-assembly into three-dimensional (3D) aggregates reminiscent of skeletal condensation in vivo. Recent studies have shown that MSC 3D aggregation improved a range of biological properties, including multilineage potential, secretion of therapeutic factors, and resistance against ischemic condition. Hence, the formation of 3D MSC aggregates has been explored as a novel strategy to improve cell delivery, functional activation, and in vivo retention to enhance therapeutic outcomes. This article summarizes recent reports of MSC aggregate self-assembly, characterization of biological properties, and their applications in preclinical models. The cellular and molecular mechanisms underlying MSC aggregate formation and functional activation are discussed, and the areas that warrant further investigation are highlighted. These analyses are combined to provide perspectives for identifying the controlling mechanisms and refining the methods of aggregate fabrication and expansion for clinical applications.

A role of cell adhesion molecules and gelatinases in human serum-induced aggregation of human eyelid-derived stem cells in vitro

Human serum (HS) has been reported to induce aggregation of human eyelid adipose-derived stem cells (HEACs) during high-density culture in vitro. The present study focused on the role of cell adhesion molecules and gelatinases during HS-induced aggregation of HEACs. HS-induced aggregation occurred between 9-15 days of culture. Cells aggregated by HS medium (HS-agg) showed stronger expression of α2, α2B, αX, and CEACAM1 genes compared to non-aggregated cells in HS medium (HS-ex) or in control FBS-cultured cells. HS-agg were distinctly labeled with antibodies against α2, α2B, and αX proteins. Western blot results demonstrated that the two integrin proteins were greatly expressed in HS-agg compared to HS-ex and control FBS-cultured cells. Treatment of HEACs with anti-integrin α2 antibody during culture in HS medium delayed aggregation formation. HS-agg exhibited strong expression of MMP1 and MMP9 compared to HS-ex or FBS-cultured cells. Conditioned media from HS-culture showed remarkable increase of MMP9 gelatinolytic activity in comparison to those from FBS-culture. However, there was no change of TIMP mRNA expression in relation to the HS-induced aggregation. Based on these results, it is suggested that integrin α2, α2B, and αX, and MMP9 might play an important role in the HS-induced aggregation of HEACs.