Three-dimensional spheroids of mesenchymal stem/stromal cells promote osteogenesis by activating stemness and Wnt/β-catenin

Hydrogel-integrated exosome mimetics derived from osteogenically induced mesenchymal stem cells in spheroid culture enhance bone regeneration

Exosomes derived from mesenchymal stem cells (MSCs) offer a promising alternative to traditional cell-based therapies for tissue repair by mitigating risks associated with the transplantation of living cells. However, insufficient osteogenic capacity of exosomes diminishes their potential in bone tissue regeneration. Here, we report novel osteogenically induced exosome mimetics (EMs) integrated into injectable hydrogel carriers for improved bone regeneration. EMs were produced by a serial extrusion of MSCs cultured as spheroids during osteogenic induction. The prepared EMs were chemically anchored on a self-healing hydrogel assembled by guanidinylated hyaluronic acid and silica-rich nanoclays for sustained release of EMs. The administration of hydrogel-integrated EMs into mouse calvarial defects resulted in robust bone tissue regeneration. miRNA sequencing revealed altered expression of specific miRNAs in the EMs related to Wnt/β-catenin and Notch signaling pathways. Our study provides new insights into the development of advanced exosome-based cell-free therapies for bone tissue engineering.

Mesenchymal stromal cells surface engineering for efficient hematopoietic reconstitution

Mesenchymal stromal cells (MSCs) are believed to migrate to injury sites, release chemical attractants, and either recruit local stem cells or modulate the immune system positively. Although MSCs are highly desired for their potential to reduce inflammation and promote tissue regeneration, their limited lifespan restricts their applications. This study presents a simple approach for protecting MSCs with epigallocatechin-3-gallate (EGCG) and magnesium (Mg) based metal-organic framework coatings (E-Mg@MSC). The layer strengthens MSCs resistant to harmful stresses and creates a favorable microenvironment for repair by providing Mg to facilitate MSCs' osteogenic differentiation and using EGCG to neutralize excessive reactive oxygen species (ROS). E-Mg@MSC serves as a treatment for hematopoietic injury induced by ionizing radiation (IR). Coated MSCs exhibit sustained secretion of hematopoietic growth factors and precise homing to radiation-sensitive tissues. In vivo studies show substantial enhancement in hematopoietic system recovery and multi-organ protection. Mechanistic investigations suggest that E-Mg@MSC mitigates IR-induced ROS, cell apoptosis, and ferroptosis, contributing to reduced radiation damage. The system represents a versatile and compelling strategy for cell-surface engineering with functional materials to advance MSCs therapy.

3D Culture of MSCs for Clinical Application

Mesenchymal stem cells (MSCs) play an important role in regenerative medicine and drug discovery due to their multipotential differentiation capabilities and immunomodulatory effects. Compared with traditional 2D cultures of MSCs, 3D cultures of MSCs have emerged as an effective approach to enhance cell viability, proliferation, and functionality, and provide a more relevant physiological environment. Here, we review the therapeutic potential of 3D-cultured MSCs, highlighting their roles in tissue regeneration and repair and drug screening. We further summarize successful cases that apply 3D MSCs in modeling disease states, enabling the identification of novel therapeutic strategies. Despite these promising applications, we discuss challenges that remain in the clinical translation of 3D MSC technologies, including stability, cell heterogeneity, and regulatory issues. We conclude by addressing these obstacles and emphasizing the need for further research to fully exploit the potential of 3D MSCs in clinical practice.

Lesson on obesity and anatomy of adipose tissue: new models of study in the era of clinical and translational research

Obesity is a serious global illness that is frequently associated with metabolic syndrome. Adipocytes are the typical cells of adipose organ, which is composed of at least two different tissues, white and brown adipose tissue. They functionally cooperate, interconverting each other under physiological conditions, but differ in their anatomy, physiology, and endocrine functions. Different cellular models have been proposed to study adipose tissue in vitro. They are also useful for elucidating the mechanisms that are responsible for a pathological condition, such as obesity, and for testing therapeutic strategies. Each cell model has its own characteristics, culture conditions, advantages and disadvantages. The choice of one model rather than another depends on the specific study the researcher is conducting. In recent decades, three-dimensional cultures, such as adipose spheroids, have become very attractive because they more closely resemble the phenotype of freshly isolated cells. The use of such models has developed in parallel with the evolution of translational research, an interdisciplinary branch of the biomedical field, which aims to learn a scientific translational approach to improve human health and longevity. The focus of the present review is on the growing body of data linking the use of new cell models and the spread of translational research. Also, we discuss the possibility, for the future, to employ new three-dimensional adipose tissue cell models to promote the transition from benchside to bedsite and vice versa, allowing translational research to become routine, with the final goal of obtaining clinical benefits in the prevention and treatment of obesity and related disorders.

Structurally and mechanically tuned macroporous hydrogels for scalable mesenchymal stem cell-extracellular matrix spheroid production

Mesenchymal stem cells (MSCs) are essential in regenerative medicine. However, conventional expansion and harvesting methods often fail to maintain the essential extracellular matrix (ECM) components, which are crucial for their functionality and efficacy in therapeutic applications. Here, we introduce a bone marrow-inspired macroporous hydrogel designed for the large-scale production of MSC-ECM spheroids. Through a soft-templating approach leveraging liquid-liquid phase separation, we engineer macroporous hydrogels with customizable features, including pore size, stiffness, bioactive ligand distribution, and enzyme-responsive degradability. These tailored environments are conducive to optimal MSC proliferation and ease of harvesting. We find that soft hydrogels enhance mechanotransduction in MSCs, establishing a standard for hydrogel-based 3D cell culture. Within these hydrogels, MSCs exist as both cohesive spheroids, preserving their innate vitality, and as migrating entities that actively secrete functional ECM proteins. Additionally, we also introduce a gentle, enzymatic harvesting method that breaks down the hydrogels, allowing MSCs and secreted ECM to naturally form MSC-ECM spheroids. These spheroids display heightened stemness and differentiation capacity, mirroring the benefits of a native ECM milieu. Our research underscores the significance of sophisticated materials design in nurturing distinct MSC subpopulations, facilitating the generation of MSC-ECM spheroids with enhanced therapeutic potential.

Advantages of Using 3D Spheroid Culture Systems in Toxicological and Pharmacological Assessment for Osteogenesis Research

Bone differentiation is crucial for skeletal development and maintenance. Its dysfunction can cause various pathological conditions such as rickets, osteoporosis, osteogenesis imperfecta, or Paget's disease. Although traditional two-dimensional cell culture systems have contributed significantly to our understanding of bone biology, they fail to replicate the intricate biotic environment of bone tissue. Three-dimensional (3D) spheroid cell cultures have gained widespread popularity for addressing bone defects. This review highlights the advantages of employing 3D culture systems to investigate bone differentiation. It highlights their capacity to mimic the complex in vivo environment and crucial cellular interactions pivotal to bone homeostasis. The exploration of 3D culture models in bone research offers enhanced physiological relevance, improved predictive capabilities, and reduced reliance on animal models, which have contributed to the advancement of safer and more effective strategies for drug development. Studies have highlighted the transformative potential of 3D culture systems for expanding our understanding of bone biology and developing targeted therapeutic interventions for bone-related disorders. This review explores how 3D culture systems have demonstrated promise in unraveling the intricate mechanisms governing bone homeostasis and responses to pharmacological agents.

Spheroids as a 3D in vitro model to study bone and bone mineralization

Traumas, fractures, and diseases can severely influence bone tissue. Insight into bone mineralization is essential for the development of therapies and new strategies to enhance bone regeneration. 3D cell culture systems, in particular cellular spheroids, have gained a lot of interest as they can recapitulate crucial aspects of the in vivo tissue microenvironment, such as the extensive cell-cell and cell-extracellular matrix (ECM) interactions found in tissue. The potential of combining spheroids and various classes of biomaterials opens also new opportunities for research within bone tissue engineering. Characterizing cellular organization, ECM structure, and ECM mineralization is a fundamental step for understanding the biological processes involved in bone tissue formation in a spheroid-based model system. Still, many experimental techniques used in this field of research are optimized for use with monolayer cell cultures. There is thus a need to develop new and improving existing experimental techniques, for applications in 3D cell culture systems. In this review, bone composition and spheroids properties are described. This is followed by an insight into the techniques that are currently used in bone spheroids research and how these can be used to study bone mineralization. We discuss the application of staining techniques used with optical and confocal fluorescence microscopy, molecular biology techniques, second harmonic imaging microscopy, Raman spectroscopy and microscopy, as well as electron microscopy-based techniques, to evaluate osteogenic differentiation, collagen production and mineral deposition. Challenges in the applications of these methods in bone regeneration and bone tissue engineering are described. STATEMENT OF SIGNIFICANCE: 3D cell cultures have gained a lot of interest in the last decades as a possible technique that can be used to recreate in vitro in vivo biological process. The importance of 3D environment during bone mineralization led scientists to use this cell culture to study this biological process, to obtain a better understanding of the events involved. New and improved techniques are also required for a proper analysis of this cell model and the process under investigation. This review summarizes the state of the art of the techniques used to study bone mineralization and how 3D cell cultures, in particular spheroids, are tested and analysed to obtain better resolved results related to this complex biological process.

Enhancing Immunomodulatory Function of Mesenchymal Stromal Cells by Hydrogel Encapsulation

Mesenchymal stromal cells (MSCs) showcase remarkable immunoregulatory capabilities in vitro, positioning them as promising candidates for cellular therapeutics. However, the process of administering MSCs and the dynamic in vivo environment may impact the cell-cell and cell-matrix interactions of MSCs, consequently influencing their survival, engraftment, and their immunomodulatory efficacy. Addressing these concerns, hydrogel encapsulation emerges as a promising solution to enhance the therapeutic effectiveness of MSCs in vivo. Hydrogel, a highly flexible crosslinked hydrophilic polymer with a substantial water content, serves as a versatile platform for MSC encapsulation. Demonstrating improved engraftment and heightened immunomodulatory functions in vivo, MSCs encapsulated by hydrogel are at the forefront of advancing therapeutic outcomes. This review delves into current advancements in the field, with a focus on tuning various hydrogel parameters to elucidate mechanistic insights and elevate functional outcomes. Explored parameters encompass hydrogel composition, involving monomer type, functional modification, and co-encapsulation, along with biomechanical and physical properties like stiffness, viscoelasticity, topology, and porosity. The impact of these parameters on MSC behaviors and immunomodulatory functions is examined. Additionally, we discuss potential future research directions, aiming to kindle sustained interest in the exploration of hydrogel-encapsulated MSCs in the realm of immunomodulation.

Fluid flow-induced modulation of viability and osteodifferentiation of periodontal ligament stem cell spheroids-on-chip

Developing physiologically relevant in vitro models for studying periodontitis is crucial for understanding its pathogenesis and developing effective therapeutic strategies. In this study, we aimed to integrate the spheroid culture of periodontal ligament stem cells (PDLSCs) within a spheroid-on-chip microfluidic perfusion platform and to investigate the influence of interstitial fluid flow on morphogenesis, cellular viability, and osteogenic differentiation of PDLSC spheroids. PDLSC spheroids were seeded onto the spheroid-on-chip microfluidic device and cultured under static and flow conditions. Computational analysis demonstrated the translation of fluid flow rates of 1.2 μl min-1 (low-flow) and 7.2 μl min-1 (high-flow) to maximum fluid shear stress of 59 μPa and 360 μPa for low and high-flow conditions, respectively. The spheroid-on-chip microfluidic perfusion platform allowed for modulation of flow conditions leading to larger PDLSC spheroids with improved cellular viability under flow compared to static conditions. Modulation of fluid flow enhanced the osteodifferentiation potential of PDLSC spheroids, demonstrated by significantly enhanced alizarin red staining and alkaline phosphatase expression. Additionally, flow conditions, especially high-flow conditions, exhibited extensive calcium staining across both peripheral and central regions of the spheroids, in contrast to the predominantly peripheral staining observed under static conditions. These findings highlight the importance of fluid flow in shaping the morphological and functional properties of PDLSC spheroids. This work paves the way for future investigations exploring the interactions between PDLSC spheroids, microbial pathogens, and biomaterials within a controlled fluidic environment, offering insights for the development of innovative periodontal therapies, tissue engineering strategies, and regenerative approaches.

Three-Dimensional Spheroid Culture of Human Mesenchymal Stem Cells: Offering Therapeutic Advantages and In Vitro Glimpses of the In Vivo State

As invaluable as the standard 2-dimensional (2D) monolayer in vitro cell culture system has been, there is increasing evidence that 3-dimensional (3D) non-adherent conditions are more relevant to the in vivo condition. While one of the criteria for human mesenchymal stem cells (MSCs) has been in vitro plastic adherence, such 2D culture conditions are not representative of in vivo cell-cell and cell-extracellular matrix (ECM) interactions, which may be especially important for this progenitor/stem cell of skeletal and connective tissues. The 3D spheroid, a multicellular aggregate formed under non-adherent 3D in vitro conditions, may be particularly suited as an in vitro method to better understand MSC physiological processes, since expression of ECM and other adhesion proteins are upregulated in such a cell culture system. First used in embryonic stem cell in vitro culture to recapitulate in vivo developmental processes, 3D spheroid culture has grown in popularity as an in vitro method to mimic the 3-dimensionality of the native niche for MSCs within tissues/organs. In this review, we discuss the relevance of the 3D spheroid culture for understanding MSC biology, summarize the biological outcomes reported in the literature based on such this culture condition, as well as contemplate limitations and future considerations in this rapidly evolving and exciting area.

Three-dimensional spheroid culture of dental pulp-derived stromal cells enhance their biological and regenerative properties for potential therapeutic applications

Mesenchymal stem/stromal cell (MSC) spheroids generated in a three-dimensional (3D) culture system serve as a surrogate model that maintain stem cell characteristics since these mimic the in vivo behavior of cells and tissue more closely. Our study involved a detailed characterization of the spheroids generated in ultra-low attachment flasks. The spheroids were evaluated and compared for their morphology, structural integrity, viability, proliferation, biocomponents, stem cell phenotype and differentiation abilities with monolayer culture derived cells (2D culture). The in-vivo therapeutic efficacy of DPSCs derived from 2D and 3D culture was also assessed by transplanting them in an animal model of the critical-sized calvarial defect. DPSCs formed compact and well-organized multicellular spheroids when cultured in ultra-low attachment condition with superior stemness, differentiation, and regenerative abilities than monolayer cells. They maintained lower proliferative state and showed marked difference in the cellular biocomponents such as lipid, amide and nucleic acid between DPSCs from 2D and 3D cultures. The scaffold-free 3D culture efficiently preserves DPSCs intrinsic properties and functionality by maintaining them in the state close to the native tissues. The scaffold free 3D culture methods allow easy collection of a large number of multicellular spheroids of DPSCs and therefore, this can be adopted as a feasible and efficient method of generating robust spheroids for various in-vitro and in-vivo therapeutic applications.

A bicellular fluorescent ductal carcinoma in situ (DCIS)-like tumoroid to study the progression of carcinoma: practical approaches and optimization

Recently, many types of 3D culture systems have been developed to preserve the physicochemical environment and biological characteristics of the original tumors better than the conventional 2D monolayer culture system. There are various types of models belonging to this culture, such as the culture based on non-adherent and/or scaffold-free matrices to form the tumors. Agarose mold has been widely used to facilitate tissue spheroid assembly, as it is essentially non-biodegradable, bio-inert, biocompatible, low-cost, and low-attachment material that can promote cell spheroidization. As no studies have been carried out on the development of a fluorescent bicellular tumoroid mimicking ductal carcinoma in situ (DCIS) using human cell lines, our objective was to detail the practical approaches developed to generate this model, consisting of a continuous layer of myoepithelial cells (MECs) around a previously formed in situ breast tumor. The practical approaches developed to generate a bi-cellular tumoroid mimicking ductal carcinoma in situ (DCIS), consisting of a continuous layer of myoepithelial cells (MECs) around a previously formed in situ breast tumoroid. Firstly, the optimal steps and conditions of spheroids generation using a non-adherent agarose gel were described, in particular, the appropriate medium, seeding density of each cell type and incubation period. Next, a lentiviral transduction approach to achieve stable fluorescent protein expression (integrative system) was used to characterize the different cell lines and to track tumoroid generation through immunofluorescence, the organization of the two cell types was validated, specific merits and drawbacks were compared to lentiviral transduction. Two lentiviral vectors expressing either EGFP (Enhanced Green Fluorescent Protein) or m-Cherry (Red Fluorescent Protein) were used. Various rates of a multiplicity of infection (MOI) and multiple types of antibodies (anti-p63, anti-CK8, anti-Maspin, anti-Calponin) for immunofluorescence analysis were tested to determine the optimal conditions for each cell line. At MOI 40 (GFP) and MOI 5 (m-Cherry), the signals were almost homogeneously distributed in the cells which could then be used to generate the DCIS-like tumoroids. Images of the tumoroids in agarose molds were captured with a confocal microscope Micro Zeiss Cell Observer Spinning Disk or with IncuCyte® to follow the progress of the generation. Measurement of protumoral cytokines such as IL-6, IL8 and leptin confirmed their secretion in the supernatants, indicating that the properties of our cells were not altered. Finally the advantages and disadvantages of each fluorescent approach were discussed. This model could also be used for other solid malignancies to study the complex relationship between different cells such as tumor and myoepithelial cells in various microenvironments (inflammatory, adipose and tumor, obesity, etc.). Although, this new model is well established to monitor drug screening applications and perform pharmacokinetic and pharmacodynamic analyses.

Recent methods of droplet microfluidics and their applications in spheroids and organoids

Droplet microfluidic techniques have long been known as a high-throughput approach for cell manipulation. The capacity to compartmentalize cells into picolitre droplets in microfluidic devices has opened up a range of new ways to extract information from cells. Spheroids and organoids are crucial in vitro three-dimensional cell culture models that physiologically mimic natural tissues and organs. With the aid of developments in cell biology and materials science, droplet microfluidics has been applied to construct spheroids and organoids in numerous formats. In this article, we divide droplet microfluidic approaches for managing spheroids and organoids into three categories based on the droplet module format: liquid droplet, microparticle, and microcapsule. We discuss current advances in the use of droplet microfluidics for the generation of tumour spheroids, stem cell spheroids, and organoids, as well as the downstream applications of these methods in high-throughput screening and tissue engineering.

Effect of spheroid size on gene expression profiles of a mouse mesenchymal stem cell line in spheroid culture

BACKGROUND

Mesenchymal stem cell (MSC)-based therapies offer potential for bone repair. MSC spheroid cultures may harbor enhanced therapeutic potential over MSC monolayers through increased secretion of trophic factors. However, the impact of spheroid size on trophic factor expression is unclear.

OBJECTIVE

We investigated the effect of spheroid size on trophic factor-related gene expression.

METHODS

KUM10, a murine MSC line was used. RNA-seq was used to screen the transcriptional profiles of MSC monolayer and spheroid cultures. Differentially expressed genes identified in RNA-seq were evaluated by q-PCR in cultures of 5 × 104 (S group), 5 × 105 (M group), 5 × 106 (L group) cells/well.

RESULTS

Comparison of expression levels between KUM10 monolayer and spheroid cultures identified 2140 differentially expressed genes, of which 1047 were upregulated and 1093 were downregulated in KUM10 spheroids. Among these, 12 upregulated genes (Bmp2, Fgf9, Fgf18, Ngf, Pdgfa, Pdgfb, Tgfb1, Vegfa, Vegfc, Wnt4, Wnt5a, Wnt10a) were associated with secretory growth factors. Of these, expression of Fgf9, Fgf18, Vegfa and Vegfc was elevated in the L group, and Pdgfb and Tgfb1 was elevated in the S group.

CONCLUSIONS

Spheroid size may impact trophic factor expression. Our results will be useful for future studies assessing the utility of MSC spheroids for treating bone injury.

Light-controlled scaffold- and serum-free hard palatal-derived mesenchymal stem cell aggregates for bone regeneration

Cell aggregates that mimic in vivo cell-cell interactions are promising and powerful tools for tissue engineering. This study isolated a new, easily obtained, population of mesenchymal stem cells (MSCs) from rat hard palates named hard palatal-derived mesenchymal stem cells (PMSCs). The PMSCs were positive for CD90, CD44, and CD29 and negative for CD34, CD45, and CD146. They exhibited clonogenicity, self-renewal, migration, and multipotent differentiation capacities. Furthermore, this study fabricated scaffold-free 3D aggregates using light-controlled cell sheet technology and a serum-free method. PMSC aggregates were successfully constructed with good viability. Transplantation of the PMSC aggregates and the PMSC aggregate-implant complexes significantly enhanced bone formation and implant osseointegration in vivo, respectively. This new cell resource is easy to obtain and provides an alternative strategy for tissue engineering and regenerative medicine.

Physiological Mineralization during In Vitro Osteogenesis in a Biomimetic Spheroid Culture Model

Bone health-targeting drug development strategies still largely rely on inferior 2D in vitro screenings. We aimed at developing a scaffold-free progenitor cell-based 3D biomineralization model for more physiological high-throughput screenings. MC3T3-E1 pre-osteoblasts were cultured in α-MEM with 10% FCS, at 37 °C and 5% CO₂ for up to 28 days, in non-adherent V-shaped plates to form uniformly sized 3D spheroids. Osteogenic differentiation was induced by 10 mM β-glycerophosphate and 50 µg/mL ascorbic acid. Mineralization stages were assessed through studying expression of marker genes, alkaline phosphatase activity, and calcium deposition by histochemistry. Mineralization quality was evaluated by Fourier transformed infrared (FTIR) and scanning electron microscopic (SEM) analyses and quantified by micro-CT analyses. Expression profiles of selected early- and late-stage osteoblast differentiation markers indicated a well-developed 3D biomineralization process with strongly upregulated Col1a1, Bglap and Alpl mRNA levels and type I collagen- and osteocalcin-positive immunohistochemistry (IHC). A dynamic biomineralization process with increasing mineral densities was observed during the second half of the culture period. SEM–Energy-Dispersive X-ray analyses (EDX) and FTIR ultimately confirmed a native bone-like hydroxyapatite mineral deposition ex vivo. We thus established a robust and versatile biomimetic, and high-throughput compatible, cost-efficient spheroid culture model with a native bone-like mineralization for improved pharmacological ex vivo screenings.

Changes of cell membrane fluidity for mesenchymal stem cell spheroids on biomaterial surfaces

BACKGROUND

The therapeutic potential of mesenchymal stem cells (MSCs) in the form of three-dimensional spheroids has been extensively demonstrated. The underlying mechanisms for the altered cellular behavior of spheroids have also been investigated. Cell membrane fluidity is a critically important physical property for the regulation of cell behavior, but it has not been studied for the spheroid-forming cells to date.

AIM

To explore the association between cell membrane fluidity and the morphological changes of MSC spheroids on the surface of biomaterials to elucidate the role of membrane fluidity during the spheroid-forming process of MSCs.

METHODS

We generated three-dimensional (3D) MSC spheroids on the surface of various culture substrates including chitosan (CS), CS-hyaluronan (CS-HA), and polyvinyl alcohol (PVA) substrates. The cell membrane fluidity and cell morphological change were examined by a time-lapse recording system as well as a high-resolution 3D cellular image explorer. MSCs and normal/cancer cells were pre-stained with fluorescent dyes and co-cultured on the biomaterials to investigate the exchange of cell membrane during the formation of heterogeneous cellular spheroids.

RESULTS

We discovered that vesicle-like bubbles randomly appeared on the outer layer of MSC spheroids cultured on different biomaterial surfaces. The average diameter of the vesicle-like bubbles of MSC spheroids on CS-HA at 37 °C was approximately 10 μm, smaller than that on PVA substrates (approximately 27 μm). Based on time-lapse images, these unique bubbles originated from the dynamic movement of the cell membrane during spheroid formation, which indicated an increment of membrane fluidity for MSCs cultured on these substrates. Moreover, the membrane interaction in two different types of cells with similar membrane fluidity may further induce a higher level of membrane translocation during the formation of heterogeneous spheroids.

CONCLUSION

Changes in cell membrane fluidity may be a novel path to elucidate the complicated physiological alterations in 3D spheroid-forming cells.

Bioengineered 3D microfibrous-matrix modulates osteopontin release from MSCs and facilitates the expansion of hematopoietic stem cells

The osteopontin released from mesenchymal stem cells (MSC) undergoing lineage differentiation can negatively influence the expansion of hematopoietic stem cells (HSCs) in co-culture systems developed for expanding HSCs. Therefore, minimising the amount of osteopontin in the co-culture system is important for the successful ex vivo expansion of HSCs. Towards this goal, a bioengineered 3D microfibrous-matrix that can maintain MSCs in less osteopontin-releasing conditions has been developed, and its influence on the expansion of HSCs has been studied. The newly developed 3D matrix significantly decreased the release of osteopontin, depending on the MSC culture conditions used during the priming period before HSC seeding. The culture system with the lowest amount of osteopontin facilitated a more than 24-fold increase in HSC number in 1 week time period. Interestingly, the viability of expanded cells and the CD34+ pure population of HSCs were found to be the highest in the low osteopontin-containing system. Therefore, bioengineered microfibrous 3D matrices seeded with MSCs, primed under suitable culture conditions, can be an improved ex vivo expansion system for HSC culture. This article is protected by copyright. All rights reserved.

An Overlooked Bone Metabolic Disorder: Cigarette Smoking-Induced Osteoporosis

Cigarette smoking (CS) leads to significant bone loss, which is recognized as an independent risk factor for osteoporosis. The number of smokers is continuously increasing due to the addictive nature of smoking. Therefore it is of great value to effectively prevent CS-induced osteoporosis. However, there are currently no effective interventions to specifically counteract CS-induced osteoporosis, owing to the fact that the specific mechanisms by which CS affects bone metabolism are still elusive. This review summarizes the latest research findings of important pathways between CS exposure and bone metabolism, with the aim of providing new targets and ideas for the prevention of CS-induced osteoporosis, as well as providing theoretical directions for further research in the future.

Three-dimensional spheroids of dedifferentiated fat cells enhance bone regeneration

Introduction

Mesenchymal stromal/stem cells (MSCs) are multipotent, self-renewing cells that are extensively used in tissue engineering. Dedifferentiated fat (DFAT) cells are derived from adipose tissues and are similar to MSCs. Three-dimensional (3D) spheroid cultures comprising MSCs mimic the biological microenvironment more accurately than two-dimensional cultures; however, it remains unclear whether DFAT cells in 3D spheroids possess high osteogenerative ability. Furthermore, it is unclear whether DFAT cells from 3D spheroids transplanted into calvarial bone defects are as effective as those from two-dimensional (2D) monolayers in promoting bone regeneration.

Methods

We compared the in vitro osteogenic potential of rat DFAT cells cultured under osteogenic conditions in 3D spheroids with that in 2D monolayers. Furthermore, to elucidate the ability of 3D spheroid DFAT cells to promote bone healing, we examined the in vivo osteogenic potential of transplanting DFAT cells from 3D spheroids or 2D monolayers into a rat calvarial defect model.

Results

Osteoblast differentiation stimulated by bone morphogenetic protein-2 (BMP-2) or osteogenesis-inducing medium upregulated osteogenesis-related molecules in 3D spheroid DFAT cells compared with 2D monolayer DFAT cells. BMP-2 activated phosphorylation in the canonical Smad 1/5 pathways in 3D spheroid DFAT cells but phosphorylated ERK1/2 and Smad2 in 2D monolayer DFAT cells. Regardless of osteogenic stimulation, the transplantation of 3D DFAT spheroid cells into rat calvarial defects promoted new bone formation at a greater extent than that of 2D DFAT cells.

Conclusions

Compared with 2D DFAT cells, 3D DFAT spheroid cells promote osteoblast differentiation and new bone formation via canonical Smad 1/5 signaling pathways. These results indicate that transplantation of DFAT cells from 3D spheroids, but not 2D monolayers, accelerates bone healing.

Construction of Hybrid Cell Spheroids Using Cell-Sized Cross-Linked Nanogel Microspheres as an Artificial Extracellular Matrix

The introduction of functional material supports or spacers into cell spheroids increases the free volume, allowing oxygen, nutrients, and waste products to diffuse in and out more freely. Here, a biocompatible polysaccharide spacer material was investigated. Microspheres were prepared by cross-linking cholesterol-modified pullulan (CHP) nanogels with poly(ethylene glycol) (PEG). The ratio of modified CHP nanogel to PEG cross-linker was optimized to give uniform microspheres with an average diameter of approximately 14 μm. Rhodamine B-labeled microspheres showed a homogeneous assembly with bone marrow-derived mesenchymal stem cells (1:1 ratio) to create hybrid cell spheroids. The addition of the cross-linked nanogel spacers did not affect the cell viability, indicating that the microspheres provided a biocompatible scaffold that supported cell proliferation. In addition, the microspheres were stable under culture conditions over 14 days. The hybrid cell spheroids were scaled up to millimeter size to demonstrate their potential as a transplantable treatment, and the cells were found to maintain their high viability. The hybrid cell spheroids are expected to support the production of organoids.

Self-Organization Provides Cell Fate Commitment in MSC Sheet Condensed Areas via ROCK-Dependent Mechanism

Multipotent mesenchymal stem/stromal cells (MSC) are one of the crucial regulators of regeneration and tissue repair and possess an intrinsic program from self-organization mediated by condensation, migration and self-patterning. The ability to self-organize has been successfully exploited in tissue engineering approaches using cell sheets (CS) and their modifications. In this study, we used CS as a model of human MSC spontaneous self-organization to demonstrate its structural, transcriptomic impact and multipotent stromal cell commitment. We used CS formation to visualize MSC self-organization and evaluated the role of the Rho-GTPase pathway in spontaneous condensation, resulting in a significant anisotropy of the cell density within the construct. Differentiation assays were carried out using conventional protocols, and microdissection and RNA-sequencing were applied to establish putative targets behind the observed phenomena. The differentiation of MSC to bone and cartilage, but not to adipocytes in CS, occurred more effectively than in the monolayer. RNA-sequencing indicated transcriptional shifts involving the activation of the Rho-GTPase pathway and repression of SREBP, which was concordant with the lack of adipogenesis in CS. Eventually, we used an inhibitory analysis to validate our findings and suggested a model where the self-organization of MSC defined their commitment and cell fate via ROCK1/2 and SREBP as major effectors under the putative switching control of AMP kinase.

Agarose-based spheroid culture enhanced stemness and promoted odontogenic differentiation potential of human dental follicle cells in vitro

Human dental follicle cells (HDFCs) are an ideal cell source of stem cells for dental tissue repair and regeneration and they have great potential for regenerative medicine applications. However, the conventional monolayer culture usually reduces cell proliferation and differentiation potential due to the continuous passage during in vitro expansion. In this study, primary HDFC spheroids were generated on 1% agarose, and the HDFCs spontaneously formed cell spheroids in the agarose-coated dishes. Compared with monolayer culture, the spheroid-derived HDFCs exhibited increased proliferative ability for later passage HDFCs as analysed by Cell Counting Kit-8 (CCK-8). The transcription-quantitative polymerase chain reaction (qRT-PCR), western blot and immunofluorescence assay showed that the expression of stemness marker genes Sox2, Oct4 and Nanog was increased significantly in the HDFC spheroids. Furthermore, we found that the odontogenic differentiation capability of HDFCs was significantly improved by spheroid culture in the agarose-coated dishes. On the other hand, the osteogenic differentiation capability was weakened compared with monolayer culture. Our results suggest that spheroid formation of HDFCs in agarose-coated dishes partially restores the proliferative ability of HDFCs at later passages, enhances their stemness and improves odontogenic differentiation capability in vitro. Therefore, spheroid formation of HDFCs has great therapeutic potential for stem cell clinical therapy.

Specificity of 3D MSC Spheroids Microenvironment: Impact on MSC Behavior and Properties

Mesenchymal stem cells (MSC) have been considered the promising candidates for the regenerative and personalized medicine due to their self-renewal potential, multilineage differentiation and immunomodulatory capacity. Although these properties have encouraged profound MSC studies in recent years, the majority of research has been based on standard 2D culture utilization. The opportunity to resemble in vivo characteristics of cells native niche has been provided by implementation of 3D culturing models such as MSC spheroid formation assesed through cells self-assembling. In this review, we address the current literature on physical and biochemical features of 3D MSC spheroid microenvironment and their impact on MSC properties and behaviors. Starting with the reduction in the cells' dimensions and volume due to the changes in adhesion molecules expression and cytoskeletal proteins rearrangement resembling native conditions, through the microenvironment shifts in oxygen, nutrients and metabolites gradients and demands, we focus on distinctive and beneficial features of MSC in spheroids compared to cells cultured in 2D conditions. By summarizing the data for 3D MSC spheroids regarding cell survival, pluripotency, differentiation, immunomodulatory activities and potential to affect tumor cells growth we highlighted advantages and perspectives of MSC spheroids use in regenerative medicine. Further detailed analyses are needed to deepen our understanding of mechanisms responsible for modified MSC behavior in spheroids and to set future directions for MSC clinical application.

Three-dimensional Spheroid Culture Enhances Multipotent Differentiation and Stemness Capacities of Human Dental Pulp-derived Mesenchymal Stem Cells by Modulating MAPK and NF-kB Signaling Pathways

BACKGROUND

Three-dimensional (3D) culture of mesenchymal stem cells has become an important research and development topic. However, comprehensive analysis of human dental pulp-derived mesenchymal stem cells (DPSCs) in 3D-spheroid culture remains unexplored. Thus, we evaluated the cellular characteristics, multipotent differentiation, gene expression, and related-signal transduction pathways of DPSCs in 3D-spheroid culture via magnetic levitation (3DM), compared with 2D-monolayer (2D) and 3D-aggregate (3D) cultures.

METHODS

The gross morphology and cellular ultrastructure were observed in the 2D, 3D, and 3DM experimental groups using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Surface markers and trilineage differentiation were evaluated using flow cytometry and staining analysis. Quantitative reverse transcription-polymerase chain reaction and immunofluorescence staining (IF) were performed to investigate the expression of differentiation and stemness markers. Signaling transduction pathways were evaluated using western blot analysis.

RESULTS

The morphology of cell aggregates and spheroids was largely influenced by the types of cell culture plates and initial cell seeding density. SEM and TEM experiments confirmed that the solid and firm structure of spheroids was quickly formed in the 3DM-medium without damaging cells. In addition, these three groups all expressed multilineage differentiation capabilities and surface marker expression. The trilineage differentiation capacities of the 3DM-group were significantly superior to the 2D and 3D-groups. The osteogenesis, angiogenesis, adipogenesis, and stemness-related genes were significantly enhanced in the 3D and 3DM-groups. The IF analysis showed that the extracellular matrix expression, osteogenesis, and angiogenesis proteins of the 3DM-group were significantly higher than those in the 2D and 3D-groups. Finally, 3DM-culture significantly activated the MAPK and NF-kB signaling transduction pathways and ameliorated the apoptosis effects of 3D-culture.

CONCLUSIONS

This study confirmed that 3DM-spheroids efficiently enhanced the therapeutic efficiency of DPSCs.

Evaluating Oxygen Tensions Related to Bone Marrow and Matrix for MSC Differentiation in 2D and 3D Biomimetic Lamellar Scaffolds

The physiological O2 microenvironment of mesenchymal stem cells (MSCs) and osteoblasts and the dimensionality of a substrate are known to be important in regulating cell phenotype and function. By providing the physiologically normoxic environments of bone marrow (5%) and matrix (12%), we assessed their potential to maintain stemness, induce osteogenic differentiation, and enhance the material properties in the micropatterned collagen/silk fibroin scaffolds that were produced in 2D or 3D. Expression of osterix (OSX) and vascular endothelial growth factor A (VEGFA) was significantly enhanced in the 3D scaffold in all oxygen environments. At 21% O2, OSX and VEGFA expressions in the 3D scaffold were respectively 13,200 and 270 times higher than those of the 2D scaffold. Markers for assessing stemness were significantly more pronounced on tissue culture polystyrene and 2D scaffold incubated at 5% O2. At 21% O2, we measured significant increases in ultimate tensile strength (p < 0.0001) and Young's modulus (p = 0.003) of the 3D scaffold compared to the 2D scaffold, whilst 5% O2 hindered the positive effect of cell seeding on tensile strength. In conclusion, we demonstrated that the 3D culture of MSCs in collagen/silk fibroin scaffolds provided biomimetic cues for bone progenitor cells toward differentiation and enhanced the tensile mechanical properties.

The Duo of Osteogenic and Angiogenic Differentiation in ADSC-Derived Spheroids

Bone formation during embryogenesis is driven by interacting osteogenesis and angiogenesis with parallel endothelial differentiation. Thence, all in vitro bioengineering techniques are aimed at pre-vascularization of osteogenic bioequivalents to provide better regeneration outcomes upon transplantation. Due to appearance of cell-cell and cell-matrix interactions, 3D cultures of adipose-derived stromal cells (ADSCs) provide a favorable spatial context for the induction of different morphogenesis processes, including vasculo-, angio-, and osteogenesis and, therefore, allow modeling their communication in vitro. However, simultaneous induction of multidirectional cell differentiation in spheroids from multipotent mesenchymal stromal cells (MMSCs) was not considered earlier. Here we show that arranging ADSCs into spheroids allows rapid and spontaneous acquiring of markers of both osteo- and angiogenesis compared with 2D culture. We further showed that this multidirectional differentiation persists in time, but is not influenced by classical protocols for osteo- or angio-differentiation. At the same time, ADSC-spheroids retain similar morphology and microarchitecture in different culture conditions. These findings can contribute to a better understanding of the fundamental aspects of autonomous regulation of differentiation processes and their cross-talks in artificially created self-organizing multicellular structures. This, in turn, can find a wide range of applications in the field of tissue engineering and regeneration.

Three-Dimensional Culture of Umbilical Cord Mesenchymal Stem Cells Effectively Promotes Platelet Recovery in Immune Thrombocytopenia

Mesenchymal stem cells (MSCs) can effectively regulate immune cell functions and therefore are promising for the treatment of autoimmune disorders, such as immune thrombocytopenia (ITP). Recent research has shown that three-dimensional (3D) culture method have many advantages over conventional culture with respect to MSC secretion and immunogenicity. In this study, 2D and 3D cultured MSCs were used to evaluate cytokine secretion, extracellular matrix (ECM) gene expression, immune regulatory activity, and therapeutic effects in a mouse model of ITP. MSCs cultured on scaffolds had higher expression levels of immune regulatory genes, such as IDO1, HLA-G, and PTGS2, and greater inhibitory activity against lymphocyte activation that those of 2D-MSCs. In addition, 3D-MSCs exhibited higher ECM expression and greater protection against interferon-γ (IFN-γ)-induced apoptosis. In a mouse study, ITP was induced by guinea pig anti-mouse platelet serum injections. Based on enzyme-linked immunosorbent assays, serum levels of the suppressive cytokine interleukin (IL)-10 were higher and IFN-γ levels were lower after intravenous injection with 3D-MSCs and with 2D-MSCs. Additionally, 3D-MSCs improved the body weight, spleen index, and platelet index relative to those for 2D-MSCs. Bone marrow homing was also significantly enhanced in the 3D group. Therefore, the 3D culture of MSCs is an effective technique for the treatment of ITP.

Growth Factor Gene-Modified Mesenchymal Stem Cells in Tissue Regeneration

There have been marked changes in the field of stem cell therapeutics in recent years, with many clinical trials having been conducted to date in an effort to treat myriad diseases. Mesenchymal stem cells (MSCs) are the cell type most frequently utilized in stem cell therapeutic and tissue regenerative strategies, and have been used with excellent safety to date. Unfortunately, these MSCs have limited ability to engraft and survive, reducing their clinical utility. MSCs are able to secrete growth factors that can support the regeneration of tissues, and engineering MSCs to express such growth factors can improve their survival, proliferation, differentiation, and tissue reconstructing abilities. As such, it is likely that such genetically modified MSCs may represent the next stage of regenerative therapy. Indeed, increasing volumes of preclinical research suggests that such modified MSCs expressing growth factors can effectively treat many forms of tissue damage. In the present review, we survey recent approaches to producing and utilizing growth factor gene-modified MSCs in the context of tissue repair and discuss its prospects for clinical application.