Spontaneous osteogenesis of MSCs cultured on 3D microcarriers through alteration of cytoskeletal tension

Strategies in product engineering of mesenchymal stem cell-derived exosomes: unveiling the mechanisms underpinning the promotive effects of mesenchymal stem cell-derived exosomes

Articular cartilage injuries present a significant global challenge, particularly in the aging population. These injuries not only restrict movement due to primary damage but also exacerbate elderly degenerative lesions, leading to secondary cartilage injury and osteoarthritis. Addressing osteoarthritis and cartilage damage involves overcoming several technical challenges in biological treatment. The use of induced mesenchymal stem cells (iMSCs) with functional gene modifications emerges as a solution, providing a more stable and controllable source of Mesenchymal Stem Cells (MSCs) with reduced heterogeneity. Furthermore, In addition, this review encompasses strategies aimed at enhancing exosome efficacy, comprising the cultivation of MSCs in three-dimensional matrices, augmentation of functional constituents within MSC-derived exosomes, and modification of their surface characteristics. Finally, we delve into the mechanisms through which MSC-exosomes, sourced from diverse tissues, thwart osteoarthritis (OA) progression and facilitate cartilage repair. This review lays a foundational framework for engineering iMSC-exosomes treatment of patients suffering from osteoarthritis and articular cartilage injuries, highlighting cutting-edge research and potential therapeutic pathways.

Microenvironmental Stiffness Directs Chondrogenic Lineages of Stem Cells from the Human Apical Papilla via Cooperation between ROCK and Smad3 Signaling

Cell-based cartilage tissue engineering faces a great challenge in the repair process, partly due to the special physical microenvironment. Human stem cell from apical papilla (hSCAP) shows great potential as seed cells because of its versatile differentiation capacity. However, whether hSCAP has potent chondrogenic differentiation ability in the physical microenvironment of chondroid remains unknown. In this study, we fabricated poly(dimethylsiloxane) (PDMS) substrates with different stiffnesses and investigated the chondrogenic differentiation potential of hSCAPs. First, we found that hSCAPs cultured on soft substrates spread more narrowly accompanied by cortical actin organization, a hallmark of differentiated chondrocytes. On the contrary, stiff substrates were favorable for cell spreading and stress fiber formation. More importantly, the increased chondrogenic differentiation of hSCAPs seeded on soft substrates was confirmed by characterizing increased extracellular proteoglycan aggregation through Alcian blue staining and Safranin O staining and enhanced markers toward chondrogenic differentiation including SRY-box transcription factor 9 (Sox9), type II collagen (Col2), and aggrecan in both normal α-minimum essential medium (αMEM) and specific chondrogenic medium (CM) culture conditions. Then, we investigated the mechanosensing/mechanotransduction governing the chondrogenic differentiation of hSCAPs in response to different stiffnesses and found that stiffness-sensitive integrin β1 and focal adhesion kinase (FAK) were essential for mechanical signal perception and were oriented at the start of mechanotransduction induced by matrix stiffness. We next showed that the increased nuclear accumulation of Smad3 signaling and target Sox9 facilitated the chondrogenic differentiation of hSCAPs on the soft substrates and further verified the importance of Rho-associated protein kinase (ROCK) signaling in regulating chondrogenic differentiation and its driving factors, Smad3 and Sox9. By using SIS3, the specific inhibitor of p-Smad3, and miRNA targeting Rho-associated protein kinase 1 (ROCK-1), we finally confirmed the importance of ROCK/Smad3/Sox9 axis in the chondrogenic differentiation of hSCAPs in response to substrate stiffness. These results help us to increase the understanding of how microenvironmental stiffness directs chondrogenic differentiation from the aspects of mechanosensing, mechanotransduction, and cell fate decision, which will be of great value in the application of hSCAPs in cartilage tissue engineering.

Cascade and Ultrafast Artificial Antioxidases Alleviate Inflammation and Bone Resorption in Periodontitis

Periodontitis, one of the most common, challenging, and rapidly expanding oral diseases, is an oxidative stress-related disease caused by excessive reactive oxygen species (ROS) production. Developing ROS-scavenging materials to regulate the periodontium microenvironments is essential for treating periodontitis. Here, we report on creating cobalt oxide-supported Ir (CoO-Ir) as a cascade and ultrafast artificial antioxidase to alleviate local tissue inflammation and bone resorption in periodontitis. It is demonstrated that the Ir nanoclusters are uniformly supported on the CoO lattice, and there is stable chemical coupling and strong charge transfer from Co to Ir sites. Benefiting from its structural advantages, CoO-Ir presents cascade and ultrafast superoxide dismutase-catalase-like catalytic activities. Notably, it displays distinctly increased Vmax (76.249 mg L-1 min-1) and turnover number (2.736 s-1) when eliminating H2O2, which surpasses most of the by-far-reported artificial enzymes. Consequently, the CoO-Ir not only provides efficient cellular protection from ROS attack but also promotes osteogenetic differentiation in vitro. Furthermore, CoO-Ir can efficiently combat periodontitis by inhibiting inflammation-induced tissue destruction and promoting osteogenic regeneration. We believe that this report will shed meaningful light on creating cascade and ultrafast artificial antioxidases and offer an effective strategy to combat tissue inflammation and osteogenic resorption in oxidative stress-related diseases.

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.

Challenges and strategies: Scalable and efficient production of mesenchymal stem cells-derived exosomes for cell-free therapy

Exosomes are small membrane vesicles secreted by most cell types, and widely exist in cell supernatants and various body fluids. They can transmit numerous bioactive elements, such as proteins, nucleic acids, and lipids, to affect the gene expression and function of recipient cells. Mesenchymal stem cells (MSCs) have been confirmed to be a potentially promising therapy for tissue repair and regeneration. Accumulating studies demonstrated that the predominant regenerative paradigm of MSCs transplantation was the paracrine effect but not the differentiation effect. Exosomes secreted by MSCs also showed similar therapeutic effects as their parent cells and were considered to be used for cell-free regenerative medicine. However, the inefficient and limited production has hampered their development for clinical translation. In this review, we summarize potential methods to efficiently promote the yield of exosomes. We mainly focus on engineering the process of exosome biogenesis and secretion, altering the cell culture conditions, cell expansion through 3D dynamic culture and the isolation of exosomes. In addition, we also discuss the application of MSCs-derived exosomes as therapeutics in disease treatment.

Polyurethane and polyurethane/hydroxyapatite scaffold in a three-dimensional culture system

Designing a new scaffold with an optimal ability of osteogenesis differentiation is a significant step bone tissue engineering along with the growing demands for bone craft in recent decades. Herein, we used Polyurethane (PU), a novel biocompatible and flexible polymer, and Hydroxyapatite (HA), the major component of human hard tissues matrix for developing new scaffolds and analyzing the in vitro osteogenic differentiation potential of human adipose-derived mesenchymal stem cells (Ad-MSCs) in basal and induction media. Gene expression analysis was performed to evaluate the expression level of four osteogenic differentiation genes. MTT assays were also done to assess the attachment and proliferation of the cells after 7 and 21 days of seeding to scaffolds. The expression level of RUNX2 was increased in seeded cells on PU/HA scaffolds compared with the PU. Cellular adhesion and proliferation of the Ad-MSCs were higher in PU/HA than PU scaffolds according to the histology analysis. The PU and PU/HA scaffolds supported the attachment, proliferation, and differentiation of Ad-MSCs, and they are suitable candidates for producing constructs in bone regeneration. However, further in-vitro and in-vivo studies on these scaffolds are needed to introduce an appropriate candidate for clinical bone regeneration.

Fabrication and characterization of osteogenic function of progenitor cell-laden gelatin microcarriers

Biomaterial-based bone regeneration strategies often include a cellular component to accelerate healing. Modular approaches have the potential for minimally-invasive delivery and the ability to conformally fill complex defects. In this study, spherical gelatin microparticles were fabricated via water-in-oil emulsification and were subsequently crosslinked with genipin. Microparticle diameter depended on impeller geometry, and increased stirring rates consistently produced smaller particles with narrower size distributions. Increasing the concentration of gelatin resulted in larger particles with a broader size distribution. Viscoelastic characterization showed that increased gelatin concentration produced stiffer matrices, though the mechanical properties at lower gelatin concentration were more stable across strain rate. Microparticles of 6.0% wt/vol gelatin were then applied as microcarriers for packed-bed culture of human mesenchymal stromal cells (MSC) at seeding densities of 5.0 × 10³ , 2.5 × 10⁴ , or 5.0 × 10⁴ cells/cm² of surface area, in either control or osteogenic medium. Cell viability was uniformly high (>90%) across seeding densities over 22 days in culture. MSC number stayed approximately constant in the 5.0 × 10³ and 2.5 × 10⁴  cells/cm² samples, while it dropped over time at 5.0 × 10⁴ cells/cm² . Alkaline phosphatase activity was significantly upregulated in osteogenic conditions relative to controls at day 15, and absolute calcium deposition was strongly induced by days 15 and 22. However, calcium deposition per cell was highest in the lowest cell density, suggesting an inhibitory effect of high cell numbers. These results show that genipin-crosslinked gelatin microcarriers can be reproducibly fabricated and used as microcarriers for progenitor cells, which may have utility in treating large and complex bone defects.

A micro/nano-biomimetic coating on titanium orchestrates osteo/angio-genesis and osteoimmunomodulation for advanced osseointegration

Osseointegration is a sophisticated bone and implant healing process comprising of initial hematoma formation, immediate osteoimmunomodulation, angiogenesis, and osteogenesis. To fulfill rapid and satisfying osseointegration, this study developed a biomimetic implant coating that could confer the intraosseous implants a systematical regulation of the participatory processes. Herein, we shaped dissimilar nano-scale (NS) to form highly biomimetic structures of natural extracellular matrix (ECM) of the host bone and bone healing hematoma with micro/nano-scale (MNS) titania fiber-like network on the surface of titanium (Ti) implants. In vitro experiments revealed that the MNS not only facilitated osteogenic and angiogenic differentiation of bone marrow stromal cells (BMSCs) and endothelial cells, respectively, but also suppressed M1 macrophages (MΦs), whereas, stimulated pro-healing M2 phenotype. Notably, BMSCs on MNS surfaces enabled a significant immunomodulatory effect on MΦs resulting in the downregulation of inflammation-related cell signaling pathways. The favorable osteoimmune microenvironment manipulated by MNS further facilitated osteo-/angio-genesis via the crosstalk of multi-signaling pathways. In vivo evaluation mirrored the aforementioned results, and depicted that MNS induced ameliorative osseointegration when compared with the NS as well as the pristine Ti implant. The study demonstrated the modulatory effect of the multifaceted biomimetic structure on spatiotemporal regulation of the participatory processes during osseointegration.

A Review of the Use of Microparticles for Cartilage Tissue Engineering

Tissue and organ failure has induced immense economic and healthcare concerns across the world. Tissue engineering is an interdisciplinary biomedical approach which aims to address the issues intrinsic to organ donation by providing an alternative strategy to tissue and organ transplantation. This review is specifically focused on cartilage tissue. Cartilage defects cannot readily regenerate, and thus research into tissue engineering approaches is relevant as a potential treatment option. Cells, scaffolds, and growth factors are three components that can be utilized to regenerate new tissue, and in particular recent advances in microparticle technology have excellent potential to revolutionize cartilage tissue regeneration. First, microspheres can be used for drug delivery by injecting them into the cartilage tissue or joint space to reduce pain and stimulate regeneration. They can also be used as controlled release systems within tissue engineering constructs. Additionally, microcarriers can act as a surface for stem cells or chondrocytes to adhere to and expand, generating large amounts of cells, which are necessary for clinically relevant cell therapies. Finally, a newer application of microparticles is to form them together into granular hydrogels to act as scaffolds for tissue engineering or to use in bioprinting. Tissue engineering has the potential to revolutionize the space of cartilage regeneration, but additional research is needed to allow for clinical translation. Microparticles are a key enabling technology in this regard.

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.

[Experimental study on adipose-derived stem cells amplified by silk fibroin/poly- L-lactic acid microcarriers in vitro]

OBJECTIVE

To investigate the effect of silk fibroin-poly- L-lactic acid (SF-PLLA) microcarriers on the expansion and differentiation of adipose-derived stem cells (ADSCs).

METHODS

ADSCs were extracted from adipose tissue donated voluntarily by patients undergoing liposuction by enzymatic digestion. The 3rd generation ADSCs were inoculated on CultiSpher G and SF-PLLA microcarriers (set up as groups A and B, respectively), and cultured in the rotary cell culture system. ADSCs cultured in normal two-dimensional plane were used as the control group (group C). Scanning electron microscope was used to observe the microcarriers structure and cell growth. Live/Dead staining and confocal fluorescence microscope was used to observe the distribution and survival condition of cells on two microcarriers. DNA quantification was used to assess cell proliferation on two microcarriers. Real-time fluorescence quantitative PCR (qRT-PCR) was used to detect chondrogenesis, osteogenesis, and adipogenesis related gene expression of ADSCs in 3 groups cultured for 18 days. Flow cytometry was used to identify the MSCs surface markers of ADSCs in 3 groups cultured for 18 days, and differential experiments were made to identify differentiation ability of the harvested cells.

RESULTS

ADSCs could be adhered to and efficiently amplified on the two microcarriers. After 18 days of cultivation, the total increment of ADSCs of the two microcarriers were similar ( P>0.05). qRT-PCR results showed that chondrogenesis related genes (aggrecan, cartilage oligomeric matrix protein, SOX9) were significantly up-regulated for ADSCs on SF-PLLA microcarriers and adipogenesis related genes (peroxisome proliferator-activated receptor γ, lipoprotein lipase, ADIPOQ) were significantly up-regulated for ADSCs on CultiSpher G microcarriers, all showing significant differences ( P<0.05). Flow cytometry and differentiation identification proved that the harvested cells of the two groups were still ADSCs.

CONCLUSION

The ADSCs can be amplified by SF-PLLA microcarriers, and the chondrogenic differential ability of harvested cells was up-regulated while the adipogenic differential was down-regulated.

Collagen type I promotes osteogenic differentiation of amniotic membrane-derived mesenchymal stromal cells in basal and induction media

Collagen has been widely shown to promote osteogenesis of bone marrow mesenchymal stromal cells (BM-MSCs). Due to the invasive procedure of obtaining BM-MSCs, MSCs from other tissues have emerged as a promising alternative for regenerative therapy. MSCs originated from different sources, exhibiting different differentiation potentials. Therefore, the applicability of collagen type I (COL), combining with amniotic membrane (AM)-MSCs was examined through proliferation and differentiation assays together with the expression of surface markers and genes associated with stemness and differentiation under basal or induction conditions. No increase in cell growth was observed because AM-MSCs might be directed toward spontaneous osteogenesis. This was evidenced by the calcium deposition and elevated expression of osteogenic genes when AM-MSCs were cultured in collagen plate with basal media. Under the osteogenic condition, reciprocal expression of OCN and CEBPA suggested a shift toward adipogenesis. Surprisingly, adipogenic genes were not elevated upon adipogenic induction, although oil droplets deposition was observed. In conclusion, our findings demonstrated that collagen causes spontaneous osteogenesis in AM-MSCs. However, the presence of exogenous inductors could shift the direction of adipo-osteogenic gene regulatory network modulated by collagen.

RNA-seq reveals correlations between cytoskeleton-related genes and the osteogenic activity of mesenchymal stem cells on strontium loaded titania nanotube arrays

Strontium loaded titania nanotube arrays (NTSr), as well as titania nanotube arrays (NT), have been regarded as effective coatings to promote bone regeneration on titanium implants, but an understanding of the full extent of early processes affected by such surface modifications is absent. To address this limitation, we performed RNA sequencing (RNA-seq) of Sprague-Dawley rat bone marrow mesenchymal stem cells (rBMMSCs) cultured on unmodified titanium sheets (Con), NT and NTSr specimens. By pairwise comparisons we found that NT and NTSr shared a majority of differentially expressed genes. The Gene Ontology (GO) analysis revealed that NT and NTSr up-regulated a bunch of genes that are annotated to the cytoskeleton. The results were supported by immunofluorescent, transmission electron microscopy (TEM) and western blotting assays. By inhibiting the cytoskeleton through pharmacological agents, the activities of alkaline phosphatase (ALP) on NT and NTSr were also suppressed. Informed by these results, we concluded that NT and NTSr specimens reorganized the cytoskeleton of cultured cells that may play a crucial role in osteogenic lineage commitment.

The Role of the Microenvironment in Controlling the Fate of Bioprinted Stem Cells

The field of tissue engineering and regenerative medicine has made numerous advances in recent years in the arena of fabricating multifunctional, three-dimensional (3D) tissue constructs. This can be attributed to novel approaches in the bioprinting of stem cells. There are expansive options in bioprinting technology that have become more refined and specialized over the years, and stem cells address many limitations in cell source, expansion, and development of bioengineered tissue constructs. While bioprinted stem cells present an opportunity to replicate physiological microenvironments with precision, the future of this practice relies heavily on the optimization of the cellular microenvironment. To fabricate tissue constructs that are useful in replicating physiological conditions in laboratory settings, or in preparation for transplantation to a living host, the microenvironment must mimic conditions that allow bioprinted stem cells to proliferate, differentiate, and migrate. The advances of bioprinting stem cells and directing cell fate have the potential to provide feasible and translatable approach to creating complex tissues and organs. This review will examine the methods through which bioprinted stem cells are differentiated into desired cell lineages through biochemical, biological, and biomechanical techniques.

Biomimetic cues from poly(lactic-co-glycolic acid)/hydroxyapatite nano-fibrous scaffolds drive osteogenic commitment in human mesenchymal stem cells in the absence of osteogenic factor supplements

Mimicking the complex hierarchical architecture of the 'osteon', the functional unit of cortical bone, from the bottom-up offers the possibility of generating mature bone tissue in tissue engineered bone substitutes. In this work, a modular 'bottom-up' approach has been developed to assemble bone niche-mimicking nanocomposite scaffolds composed of aligned electrospun nanofibers of poly(lactic-co-glycolic acid) (PLGA) encapsulating aligned rod-shape nano-sized hydroxyapatite (nHA). By encoding axial orientation of the nHA within these aligned nanocomposite fibers, significant improvements in mechanical properties, surface roughness, hydrophilicity and in vitro simulated body fluid (SBF) mineral deposition were achieved. Moreover, these hierarchical scaffolds induced robust formation of bone hydroxyapatite and osteoblastic maturation of human bone marrow-derived mesenchymal stem cells (hBMSCs) in growth media that was absent of any soluble osteogenic differentiation factors. The results of this investigation confirm that these tailored, aligned nanocomposite fibers, in the absence of media-bone inductive factors, offer the requisite biophysical and biochemical cues to hBMSCs to promote and support their differentiation into mature osteoblast cells and form early bone-like tissue in vitro.

Influence of Microenvironment on Mesenchymal Stem Cell Therapeutic Potency: From Planar Culture to Microcarriers

Human mesenchymal stem cells (hMSCs) are a promising candidate in cell therapy as they exhibit multilineage differentiation, homing to the site of injury, and secretion of trophic factors that facilitate tissue healing and/or modulate immune response. As a result, hMSC-derived products have attracted growing interests in preclinical and clinical studies. The development of hMSC culture platforms for large-scale biomanufacturing is necessary to meet the requirements for late-phase clinical trials and future commercialization. Microcarriers in stirred-tank bioreactors have been widely utilized in large-scale expansion of hMSCs for translational applications because of a high surface-to-volume ratio compared to conventional 2D planar culture. However, recent studies have demonstrated that microcarrier-expanded hMSCs differ from dish- or flask-expanded cells in size, morphology, proliferation, viability, surface markers, gene expression, differentiation potential, and secretome profile which may lead to altered therapeutic potency. Therefore, understanding the bioprocessing parameters that influence hMSC therapeutic efficacy is essential for the optimization of microcarrier-based bioreactor system to maximize hMSC quantity without sacrificing quality. In this review, biomanufacturing parameters encountered in planar culture and microcarrier-based bioreactor culture of hMSCs are compared and discussed with specific focus on cell-adhesion surface (e.g., discontinuous surface, underlying curvature, microcarrier stiffness, porosity, surface roughness, coating, and charge) and the dynamic microenvironment in bioreactor culture (e.g., oxygen and nutrients, shear stress, particle collision, and aggregation). The influence of dynamic culture in bioreactors on hMSC properties is also reviewed in order to establish connection between bioprocessing and stem cell function. This review addresses fundamental principles and concepts for future design of biomanufacturing systems for hMSC-based therapy.

β-Catenin Preserves the Stem State of Murine Bone Marrow Stromal Cells Through Activation of EZH2

During bone marrow stromal cell (BMSC) differentiation, both Wnt signaling and the development of a rigid cytoskeleton promote commitment to the osteoblastic over adipogenic lineage. β-catenin plays a critical role in the Wnt signaling pathway to facilitate downstream effects on gene expression. We show that β-catenin was additive with cytoskeletal signals to prevent adipogenesis, and β-catenin knockdown promoted adipogenesis even when the actin cytoskeleton was depolymerized. β-catenin also prevented osteoblast commitment in a cytoskeletal-independent manner, with β-catenin knockdown enhancing lineage commitment. Chromatin immunoprecipitation (ChIP)-sequencing demonstrated binding of β-catenin to the promoter of enhancer of zeste homolog 2 (EZH2), a key component of the polycomb repressive complex 2 (PRC2) complex that catalyzes histone methylation. Knockdown of β-catenin reduced EZH2 protein levels and decreased methylated histone 3 (H3K27me3) at osteogenic loci. Further, when EZH2 was inhibited, β-catenin's anti-differentiation effects were lost. These results indicate that regulating EZH2 activity is key to β-catenin's effects on BMSCs to preserve multipotentiality. © 2020 American Society for Bone and Mineral Research.

Modular microcarrier technologies for cell-based bone regeneration

A variety of materials-based approaches to accelerate the regeneration of damaged bone have been developed to meet the important clinical need for improved bone fillers. This comprehensive review covers the materials and technologies used in modular microcarrier-based methods for delivery of progenitor cells in orthopaedic repair applications. It provides an overview of the field and the rationale for using microcarriers combined with osteoprogenitor cells for bone regeneration in particular. The general concepts and methods used in microcarrier-based cell culture and delivery are described, and methods for fabricating and characterizing microcarriers designed for specific indications are presented. A comprehensive review of the current literature on the use of microcarriers in bone regeneration is provided, with emphasis on key developments in the field and their impact. The studies reviewed are organized according to the broad classes of materials that are used for fabricating microcarriers, including polysaccharides, proteins and peptides, ceramics, and synthetic polymers. In addition, composite microcarriers that incorporate multiple material types or that are mineralized biomimetically are included. In each case, the fabrication, processing, characterization, and resulting function of the microcarriers is described, with an emphasis on their ability to support osteogenic differentiation of progenitor cells in vitro, and their effectiveness in healing bone defects in vivo. In addition, a summary of the current state of the field is provided, as are future perspectives on how microcarrier technologies may be enhanced to create improved cell-based therapies for bone regeneration.

Biological Considerations in Scaling Up Therapeutic Cell Manufacturing

Cell therapeutics - using cells as living drugs - have made advances in many areas of medicine. One of the most clinically studied cell-based therapy products is mesenchymal stromal cells (MSCs), which have shown promising results in promoting tissue regeneration and modulating inflammation. However, MSC therapy requires large numbers of cells, the generation of which is not feasible via conventional planar tissue culture methods. Scale-up manufacturing methods (e.g., propagation on microcarriers in stirred-tank bioreactors), however, are not specifically tailored for MSC expansion. These processes may, in principle, alter the cell secretome, a vital component underlying the immunosuppressive properties and clinical effectiveness of MSCs. This review outlines our current understanding of MSC properties and immunomodulatory function, expansion in commercial manufacturing systems, and gaps in our knowledge that need to be addressed for effective up-scaling commercialization of MSC therapy.

3D Culture of Bone Marrow-Derived Mesenchymal Stem Cells (BMSCs) Could Improve Bone Regeneration in 3D-Printed Porous Ti6Al4V Scaffolds

Mandibular bone defect reconstruction is an urgent challenge due to the requirements for daily eating and facial aesthetics. Three-dimensional- (3D-) printed titanium (Ti) scaffolds could provide patient-specific implants for bone defects. Appropriate load-bearing properties are also required during bone reconstruction, which makes them potential candidates for mandibular bone defect reconstruction implants. However, in clinical practice, the insufficient osteogenesis of the scaffolds needs to be further improved. In this study, we first encapsulated bone marrow-derived mesenchymal stem cells (BMSCs) into Matrigel. Subsequently, the BMSC-containing Matrigels were infiltrated into porous Ti6Al4V scaffolds. The Matrigels in the scaffolds provided a 3D culture environment for the BMSCs, which was important for osteoblast differentiation and new bone formation. Our results showed that rats with a full thickness of critical mandibular defects treated with Matrigel-infiltrated Ti6Al4V scaffolds exhibited better new bone formation than rats with local BMSC injection or Matrigel-treated defects. Our data suggest that Matrigel is able to create a more favorable 3D microenvironment for BMSCs, and Matrigel containing infiltrated BMSCs may be a promising method for enhancing the bone formation properties of 3D-printed Ti6Al4V scaffolds. We suggest that this approach provides an opportunity to further improve the efficiency of stem cell therapy for the treatment of mandibular bone defects.

The Effect of Cell Morphology on the Permeability of the Nuclear Envelope to Diffusive Factors

A recent advance in understanding stem cell differentiation is that the cell is able to translate its morphology, i.e., roundish or spread, into a fate decision. We hypothesize that strain states in the nuclear envelope (NE) cause changes in the structure of the nuclear pore complexes. This induces significant changes in the NE's permeability to the traffic of the transcription factors involved in stem cell differentiation which are imported into the nucleus by passive diffusion. To demonstrate this, we set up a numerical model of the transport of diffusive molecules through the nuclear pore complex (NPC), on the basis of the NPC deformation. We then compared the prediction of the model for two different cell configurations with roundish and spread nuclear topologies with those measured on cells cultured in both configurations. To measure the geometrical features of the NPC, using electron tomography we reconstructed three-dimensional portions of the envelope of cells cultured in both configurations. We found non-significant differences in both the shape and size of the transmembrane ring of single pores with envelope deformation. In the numerical model, we thus assumed that the changes in pore complex permeability, caused by the envelope strains, are due to variations in the opening configuration of the nuclear basket, which in turn modifies the porosity of the pore complex mainly on its nuclear side. To validate the model, we cultured cells on a substrate shaped as a spatial micro-grid, called the “nichoid,” which is nanoengineered by two-photon laser polymerization, and induces a roundish nuclear configuration in cells adhering to the nichoid grid, and a spread configuration in cells adhering to the flat substrate surrounding the grid. We then measured the diffusion through the nuclear envelope of an inert green-fluorescent protein, by fluorescence recovery after photobleaching (FRAP). Finally, we compared the diffusion times predicted by the numerical model for roundish vs. spread cells, with the measured times. Our data show that cell stretching modulates the characteristic time needed for the nuclear import of a small inert molecule, GFP, and the model predicts a faster import of diffusive molecules in the spread compared to roundish cells.

Strategies for MSC expansion and MSC-based microtissue for bone regeneration

Mesenchymal stem cells (MSCs) have gained increasing attention as a potential approach for the treatment of bone injuries due to their multi-lineage differentiation potential and also their ability to recognize and home to damaged tissue sites, secreting bioactive factors that can modulate the immune system and enhance tissue repair. However, a wide gap between the number of MSCs obtainable from the donor site and the number required for implantation, as well as the lack of understanding of MSC functions under different in vitro and in vivo microenvironment, hinders the progression of MSCs toward clinical settings. The clinical translation of MSCs pre-requisites a scalable expansion process for the biomanufacturing of therapeutically qualified cells. This review briefly introduces the features of implanted MSCs to determine the best strategies to optimize their regenerative capacity, as well as the current MSC implantation for bone diseases. Current achievements for expansion of MSCs using various culturing methods, bioreactor technologies, biomaterial platforms, as well as microtissue-based expansion strategies are also discussed, providing new insights into future large-scale MSC expansion and clinical applications.

An Integrated Bioprocess for the Expansion and Chondrogenic Priming of Human Periosteum-Derived Progenitor Cells in Suspension Bioreactors

The increasing use of microcarrier-based suspension bioreactors for scalable expansion of adult progenitor cells in recent years reveals the necessity of such approaches to address bio manufacturing challenges of advanced therapeutic medicinal products. However, the differentiation of progenitor cells within suspension bioreactors for the production of tissue modules is of equal importance but not well investigated. This study reports on the development of a bioreactor-based integrated process for expansion and chondrogenic priming of human periosteum-derived stem cells (hPDCs) using Cultispher S microcarriers. Spinner flask-based expansion and priming of hPDCs were carried out over 12 days for expansion and 14 days for priming. Characterization of the cells were carried out every 3rd day. Our study showed that hPDCs were able to expand till confluency with fold increase of 3.2±0.64 and to be subsequently primed toward a chondrogenic state within spinner flasks. During expansion, the cells maintained their phenotypic markers, trilineage differentiation capabilities and viability. Upon switching to TGF-β containing media the cells were able to differentiate toward chondrogenic lineage by clustering into mm-sized macrotissues containing hundreds of microcarriers. Chondrogenic priming was further evidenced by the expression of relevant markers at the mRNA level while maintaining their viability. Ectopic implantation of macrotissues highlighted that they were able to sustain their chondrogenic properties for 8 weeks in vivo. The method indicated here, suggests that expansion and relevant priming of progenitor cells can be carried out in an integrated bioprocess using spinner flasks and as such could be potentially extrapolated to other stem and progenitor cell populations.

Fabrication of Innovative Silk/Alginate Microcarriers for Mesenchymal Stem Cell Delivery and Tissue Regeneration

The aim of this study was to exploit silk fibroin’s properties to develop innovative composite microcarriers for mesenchymal stem cell (MSCs) adhesion and proliferation. Alginate microcarriers were prepared, added to silk fibroin solution, and then treated with ethanol to induce silk conformational transition. Microcarriers were characterized for size distribution, coating stability and homogeneity. Finally, in vitro cytocompatibility and suitability as delivery systems for MSCs were investigated. Results indicated that our manufacturing process is consistent and reproducible: silk/alginate microcarriers were stable, with spherical geometry, about 400 μm in average diameter, and fibroin homogeneously coated the surface. MSCs were able to adhere rapidly onto the microcarrier surface and to cover the surface of the microcarrier within three days of culture; moreover, on this innovative 3D culture system, stem cells preserved their metabolic activity and their multi-lineage differentiation potential. In conclusion, silk/alginate microcarriers represent a suitable support for MSCs culture and expansion. Since it is able to preserve MSCs multipotency, the developed 3D system can be intended for cell delivery, for advanced therapy and regenerative medicine applications.

Combined treatment with platelet-rich plasma and insulin favours chondrogenic and osteogenic differentiation of human adipose-derived stem cells in three-dimensional collagen scaffolds

Osteochondral lesions due to injury or other pathology commonly result in the development of osteoarthritis and progressive joint destruction. Bioengineered scaffolds are widely studied for regenerative surgery strategies in osteochondral defect management, also combining the use of stem cells, growth factors and hormones. The utility in tissue engineering of human adipose-derived stem cells (ASCs) isolated from adipose tissue has been widely noted. Autologous platelet-rich plasma (PRP) represents an alternative strategy in regenerative medicine for the local release of endogenous growth factors and hormones. Here we compared the effects of three-dimensional (3D) collagen type I scaffold culture and combined treatment with PRP and human recombinant insulin on the chondro-/osteogenic differentiation of ASCs. Histochemical and biomolecular analyses demonstrated that chondro-/osteogenic differentiation was increased in ASC-populated 3D collagen scaffolds compared with two-dimensional (2D) plastic dish culture. Chondro-/osteogenic differentiation was further enhanced in the presence of combined PRP (5% v/v) and insulin (100 nm) treatment. In addition, chondro-/osteogenic differentiation associated with the contraction of ASC-populated 3D collagen scaffold and increased β1/β3-integrin expression. Inhibition studies demonstrated that PRP/insulin-induced chondro-/osteogenic differentiation is independent of insulin-like growth factor 1 receptor (IGF-1R) and mammalian target of rapamycin (mTOR) signalling; IGF-R1/mTOR inhibition even enhanced ASC chondro-/osteogenic differentiation. Our findings underline that 3D collagen scaffold culture in association with platelet-derived growth factors and insulin favour the chondro-/osteogenic differentiation of ASCs, suggesting new translational applications in regenerative medicine for the management of osteochondral defects. Copyright © 2016 John Wiley & Sons, Ltd.

Induction of mesenchymal stem cell differentiation in the absence of soluble inducer for cutaneous wound regeneration by a chitin nanofiber-based hydrogel

Transplantation of bone marrow mesenchymal stem cells (BMSCs) has been considered to be a promising strategy for wound healing. However, poor viability of engrafted BMSCs and limited capabilities of differentiation into the desired cell types in wounds often hinder its application. Few studies report the induction of BMSC differentiation into the skin regeneration-related cell types using natural biopolymer, e.g. chitin and its derivative. Here we utilized a chitin nanofiber (CNF) hydrogel as a directive cue to induce BMSC differentiation for enhancing cutaneous wound regeneration in the absence of cell-differentiating factors. First, a 'green' fabrication of CNF hydrogels encapsulating green fluorescence protein (GFP)-transfected rat BMSCs was performed via in-situ physical gelation without chemical cross-linking. Without soluble differentiation inducers, CNF hydrogels decreased the expression of BMSC transcription factors (Oct4 and Klf4) and concomitantly induced their differentiation into the angiogenic cells and fibroblasts, which are indispensable for wound regeneration. In vivo, rat full-thickness cutaneous wounds treated with BMSC hydrogel exhibited better viability of the cells than did local BMSC injection-treated wounds. Similar to that of the in vitro result, CNF hydrogels induced BMSCs to differentiate into beneficial cell types, resulting in accelerated wound repair characterized by granulation tissue formation. Our data suggest that three-dimensional CNF hydrogel may not only serve as a 'protection' to improve the viability of exogenous BMSCs, but also provide a functional scaffold capable of enhancing BMSC regenerative potential to promote wound healing. This may help to overcome the current limitations to stem cell therapy that are faced in the field of wound regeneration. Copyright © 2017 John Wiley & Sons, Ltd.

Critical attributes of human early mesenchymal stromal cell-laden microcarrier constructs for improved chondrogenic differentiation

Background

Microcarrier cultures which are useful for producing large cell numbers can act as scaffolds to create stem cell-laden microcarrier constructs for cartilage tissue engineering. However, the critical attributes required to achieve efficient chondrogenic differentiation for such constructs are unknown. Therefore, this study aims to elucidate these parameters and determine whether cell attachment to microcarriers throughout differentiation improves chondrogenic outcomes across multiple microcarrier types.

Methods

A screen was performed to evaluate whether 1) cell confluency, 2) cell numbers, 3) cell density, 4) centrifugation, or 5) agitation are crucial in driving effective chondrogenic differentiation of human early mesenchymal stromal cell (heMSC)-laden Cytodex 1 microcarrier (heMSC-Cytodex 1) constructs.

Results

Firstly, we found that seeding 10 × 10³ cells at 70% cell confluency with 300 microcarriers per construct resulted in substantial increase in cell growth (76.8-fold increase in DNA) and chondrogenic protein generation (78.3- and 686-fold increase in GAG and Collagen II, respectively). Reducing cell density by adding empty microcarriers at seeding and indirectly compacting constructs by applying centrifugation at seeding or agitation throughout differentiation caused reduced cell growth and chondrogenic differentiation. Secondly, we showed that cell attachment to microcarriers throughout differentiation improves cell growth and chondrogenic outcomes since critically defined heMSC-Cytodex 1 constructs developed larger diameters (2.6-fold), and produced more DNA (13.8-fold), GAG (11.0-fold), and Collagen II (6.6-fold) than their equivalent cell-only counterparts. Thirdly, heMSC-Cytodex 1/3 constructs generated with cell-laden microcarriers from 1-day attachment in shake flask cultures were more efficient than those from 5-day expansion in spinner cultures in promoting cell growth and chondrogenic output per construct and per cell. Lastly, we demonstrate that these critically defined parameters can be applied across multiple microcarrier types, such as Cytodex 3, SphereCol and Cultispher-S, achieving similar trends in enhancing cell growth and chondrogenic differentiation.

Conclusions

This is the first study that has identified a set of critical attributes that enables efficient chondrogenic differentiation of heMSC-microcarrier constructs across multiple microcarrier types. It is also the first to demonstrate that cell attachment to microcarriers throughout differentiation improves cell growth and chondrogenic outcomes across different microcarrier types, including biodegradable gelatin-based microcarriers, making heMSC-microcarrier constructs applicable for use in allogeneic cartilage cell therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0538-x) contains supplementary material, which is available to authorized users.

Development of demineralized bone matrix-based implantable and biomimetic microcarrier for stem cell expansion and single-step tissue-engineered bone graft construction

Tissue engineered bone grafts (TEBG) using mesenchymal stem cells (MSCs) demonstrate great potential for bone defect treatment.

Enhanced Osteogenesis of ADSCs by the Synergistic Effect of Aligned Fibers Containing Collagen I

The topographical features and material composition of scaffolds have a powerful influence on cell behaviors such as proliferation and differentiation. Here, scaffolds consisting of aligned fibers with incorporated bioactive collagen I were tested for their ability to enhance osteogenesis in vitro. Rat adipose-derived mesenchymal stem cells (ADSCs) were seeded on the scaffolds and their morphology, proliferation, and osteogenic differentiation were examined. Aligned scaffolds with collagen I showed the best osteogenic properties. Also, adhesion-related genes showed the higher expression on aligned scaffolds with collagen I. Our findings indicate that fiber alignment combined with incorporation of collagen I increases the capacity of electrospun scaffolds to induce enhanced and directed osteogenesis. Such scaffolds may, therefore, have potential for improving guided oral bone regeneration.

c-Maf regulates pluripotency genes, proliferation/self-renewal, and lineage commitment in ROS-mediated senescence of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are therapeutically relevant multilineage and immunomodulatory progenitors. Ex vivo expansion of these rare cells is necessary for clinical application and can result in detrimental senescent effects, with mechanisms still largely unknown. We found that vigorous ex vivo expansion of human adipose tissue-derived MSCs (hAMSCs) results in proliferative decline, cell cycle arrest, and altered differentiation capacity. This senescent phenotype was associated with reactive oxygen species (ROS) accumulation, and with increased expression of G1 cell -cycle inhibitors— p15^INK4b and p16^INK4a — but decreased expression of pluripotency genes—Oct-4, Sox-2, Nanog, and c-Myc—as well as c-Maf a co-factor of MSC lineage-specific transcription factor and sensitive to oxidative stress. These global changes in the transcriptional and functional programs of proliferation, differentiation, and self-renewal were all mediated by ROS-induced suppression of c-Maf, as evidenced by binding of c-Maf to promoter regions of multiple relevant genes in hAMSCs which could be reduced by exogenous ROS. Our findings implicate the strong effects of ROS on multiple stem cell functions with a central role for c-Maf in stem cell senescence.

Bioprinting and Differentiation of Stem Cells

The 3D bioprinting of stem cells directly into scaffolds offers great potential for the development of regenerative therapies; in particular for the fabrication of organ and tissue substitutes. For this to be achieved; the lineage fate of bioprinted stem cell must be controllable. Bioprinting can be neutral; allowing culture conditions to trigger differentiation or alternatively; the technique can be designed to be stimulatory. Such factors as the particular bioprinting technique; bioink polymers; polymer cross-linking mechanism; bioink additives; and mechanical properties are considered. In addition; it is discussed that the stimulation of stem cell differentiation by bioprinting may lead to the remodeling and modification of the scaffold over time matching the concept of 4D bioprinting. The ability to tune bioprinting properties as an approach to fabricate stem cell bearing scaffolds and to also harness the benefits of the cells multipotency is of considerable relevance to the field of biomaterials and bioengineering.

Hypoxia Suppresses Spontaneous Mineralization and Osteogenic Differentiation of Mesenchymal Stem Cells via IGFBP3 Up-Regulation

Hypoxia has diverse stimulatory effects on human adipose-derived stem cells (ASCs). In the present study, we investigated whether hypoxic culture conditions (2% O₂) suppress spontaneous mineralization and osteogenic differentiation of ASCs. We also investigated signaling pathways and molecular mechanisms involved in this process. We found that hypoxia suppressed spontaneous mineralization and osteogenic differentiation of ASCs, and up-regulated mRNA and protein expression of Insulin-like growth factor binding proteins (IGFBPs) in ASCs. Although treatment with recombinant IGFBPs did not affect osteogenic differentiation of ASCs, siRNA-mediated inhibition of IGFBP3 attenuated hypoxia-suppressed osteogenic differentiation of ASCs. In contrast, overexpression of IGFBP3 via lentiviral vectors inhibited ASC osteogenic differentiation. These results indicate that hypoxia suppresses spontaneous mineralization and osteogenic differentiation of ASCs via intracellular IGFBP3 up-regulation. We determined that reactive oxygen species (ROS) generation followed by activation of the MAPK and PI3K/Akt pathways play pivotal roles in IGFBP3 expression under hypoxia. For example, ROS scavengers and inhibitors for MAPK and PI3K/Akt pathways attenuated the hypoxia-induced IGFBP3 expression. Inhibition of Elk1 and NF-κB through siRNA transfection also led to down-regulation of IGFBP3 mRNA expression. We next addressed the proliferative potential of ASCs with overexpressed IGFBP3, but IGFBP3 overexpression reduced the proliferation of ASCs. In addition, hypoxia reduced the osteogenic differentiation of bone marrow-derived clonal mesenchymal stem cells. Collectively, our results indicate that hypoxia suppresses the osteogenic differentiation of mesenchymal stem cells via IGFBP3 up-regulation.

Restoration of a Critical Mandibular Bone Defect Using Human Alveolar Bone-Derived Stem Cells and Porous Nano-HA/Collagen/PLA Scaffold

Periodontal bone defects occur in a wide variety of clinical situations. Adult stem cell- and biomaterial-based bone tissue regeneration are a promising alternative to natural bone grafts. Recent evidence has demonstrated that two populations of adult bone marrow mesenchymal stromal cells (BMSCs) can be distinguished based on their embryonic origins. These BMSCs are not interchangeable, as bones preferentially heal using cells that share the same embryonic origin. However, the feasibility of tissue engineering using human craniofacial BMSCs was unclear. The goal of this study was to explore human craniofacial BMSC-based therapy for the treatment of localized mandibular defects using a standardized, minimally invasive procedure. The BMSCs' identity was confirmed. Scanning electron microscopy, a cell proliferation assay, and supernatant detection indicated that the nHAC/PLA provided a suitable environment for aBMSCs. Real-time PCR and electrochemiluminescence immunoassays demonstrated that osteogenic markers were upregulated by osteogenic preinduction. Moreover, in a rabbit critical-size mandibular bone defect model, total bone formation in the nHAC/PLA + aBMSCs group was significantly higher than in the nHAC/PLA group but significantly lower than in the nHAC/PLA + preinduced aBMSCs. These findings demonstrate that this engineered bone is a valid alternative for the correction of mandibular bone defects.

Manufacturing of Human Umbilical Cord Mesenchymal Stromal Cells on Microcarriers in a Dynamic System for Clinical Use

The great properties of human mesenchymal stromal cells (hMSCs) make these cells an important tool in regenerative medicine. Because of the limitations of hMSCs derived from the bone marrow during isolation and expansion, hMSCs derived from the umbilical cord stroma are a great alternative to overcome these issues. For a large expansion of these cells, we performed a process transfer from static culture to a dynamic system. For this reason, a microcarrier selection out of five microcarrier types was made to achieve a suitable growth surface for the cells. The growth characteristics and metabolite consumption and production were used to compare the cells growth in 12-well plate and spinner flask. The goal to determine relevant process parameters to transfer the expansion process into a stirred tank bioreactor was achieved.

Dynamic Bioreactor Culture of High Volume Engineered Bone Tissue

Within the field of tissue engineering and regenerative medicine, the fabrication of tissue grafts of any significant size--much less a whole organ or tissue--remains a major challenge. Currently, tissue-engineered constructs cultured in vitro have been restrained in size primarily due to the diffusion limit of oxygen and nutrients to the center of these grafts. Previously, we developed a novel tubular perfusion system (TPS) bioreactor, which allows the dynamic culture of bead-encapsulated cells and increases the supply of nutrients to the entire cell population. More interestingly, the versatility of TPS bioreactor allows a large range of engineered tissue volumes to be cultured, including large bone grafts. In this study, we utilized alginate-encapsulated human mesenchymal stem cells for the culture of a tissue-engineered bone construct in the size and shape of the superior half of an adult human femur (∼ 200 cm(3)), a 20-fold increase over previously reported volumes of in vitro engineered bone grafts. Dynamic culture in TPS bioreactor not only resulted in high cell viability throughout the femur graft, but also showed early signs of stem cell differentiation through increased expression of osteogenic genes and proteins, consistent with our previous models of smaller bone constructs. This first foray into full-scale bone engineering provides the foundation for future clinical applications of bioengineered bone grafts.

Induction of predominant tenogenic phenotype in human dermal fibroblasts via synergistic effect of TGF-β and elongated cell shape

Micropattern topography is widely investigated for its role in mediating stem cell differentiation, but remains unexplored for phenotype switch between mature cell types. This study investigated the potential of inducing tenogenic phenotype in human dermal fibroblasts (hDFs) by artificial elongation of cultured cells. Our results showed that a parallel microgrooved topography could convert spread hDFs into an elongated shape and induce a predominant tenogenic phenotype as the expression of biomarkers was significantly enhanced, such as scleraxis, tenomodulin, collagens I, III, VI, and decorin. It also enhanced the expression of transforming growth factor (TGF)-β1, but not α-smooth muscle actin. Elongated hDFs failed to induce other phenotypes, such as adiopogenic, chondrogenic, neurogenic, and myogenic lineages. By contrast, no tenogenic phenotype could be induced in elongated human chondrocytes, although chondrogenic phenotype was inhibited. Exogenous TGF-β1 could enhance the tenogenic phenotype in elongated hDFs at low dose (2 ng/ml), but promoted myofibroblast transdifferentiation of hDFs at high dose (10 ng/ml), regardless of cell shape. Elongated shape also resulted in decreased RhoA activity and increased Rho-associated protein kinase (ROCK) activity. Antagonizing TGF-β or inhibiting ROCK activity with Y27632 or depolymerizing actin with cytochalasin D could all significantly inhibit tenogenic phenotype induction, particularly in elongated hDFs. In conclusion, elongation of cultured dermal fibroblasts can induce a predominant tenogenic phenotype likely via synergistic effect of TGF-β and cytoskeletal signaling.

Enhanced in vitro osteogenic differentiation of human fetal MSCs attached to 3D microcarriers versus harvested from 2D monolayers

BACKGROUND

Mesenchymal stem cells (MSCs) are of great interest in bone regenerative medicine due to their osteogenic potential and trophic effects. However, challenges to large-scale production of MSCs can hinder the translation of MSC therapies. 3D Microcarrier (MC)-based MSC culture presents a scalable and cost-effective alternative to conventional methods of expansion in 2D monolayers. Furthermore, biodegradable MCs may allow for MC-bound MSC delivery without enzymatic harvest for selected applications such as bone healing. However, the effects of cell expansion on microcarriers and enzymatic cell harvest on MSC phenotype and osteogenic differential potential are not well understood. In this study, we characterized human fetal MSCs (hfMSCs) after expansion in 3D microcarrier spinner or 2D monolayer cultures. Following expansion, we compared osteogenic differentiation of cultures seeded with 3D MC-harvested, 3D MC-bound and conventional 2D monolayer (MNL)-harvested cells when cultured in osteogenic induction media on collagen-coated plates.

RESULTS

Fetal MSCs expanded on both 3D agitated Microcarriers (MC) and 2D Plastic static monolayer (MNL) cultures express high levels of MSC surface markers. MC-harvested hfMSCs displayed higher expression of early osteogenic genes but slower mineralization kinetics compared to MNL-harvested MSCs during osteogenic induction. However, in the comparison between MC-bound and MC-harvested hfMSCs, osteogenic genes were upregulated and mineralization kinetics was accelerated in the former condition. Importantly, 3D MC-bound hfMSCs expressed higher levels of osteogenic genes and displayed either higher or equivalent levels of mineralization, depending on the cell line, compared to the classical monolayer cultures use in the literature (MNL-harvested hfMSCs).

CONCLUSION

Beyond the processing and scalability advantages of the microcarrier culture, hfMSCs attached to MCs undergo robust osteogenic differentiation and mineralization compared to enzymatically harvested cells. Thus biodegradable/biocompatible MCs which can potentially be used for cell expansion as well as a scaffold for direct in vivo delivery of cells may have advantages over the current methods of monolayer-expansion and delivery post-harvest for bone regeneration applications.

Recent advances in serum-free microcarrier expansion of mesenchymal stromal cells: Parameters to be optimized

Mesenchymal stromal cells (MSCs) are being investigated for a variety of therapeutic indications. However, current 2D planar technology cannot meet the anticipated demand and a shift to serum-free microcarrier cultures is needed in order to meet the quality and quantity of cells required. Here we summarize several recent attempts to grow cells in such conditions, and identify several variables that affect cell expansion, including tissue source, serum-free medium formulation, microcarrier type and matrix, and agitation regime (continuous versus intermittent). Optimization of these culture conditions will be necessary to ensure success in bioreactor-scale production of MSCs for cell therapies.

Comparison of Mesenchymal Stem Cell Source Differentiation Toward Human Pediatric Aortic Valve Interstitial Cells within 3D Engineered Matrices

Living tissue-engineered heart valves (TEHV) would be a major benefit for children who require a replacement with the capacity for growth and biological integration. A persistent challenge for TEHV is accessible human cell source(s) that can mimic native valve cell phenotypes and matrix remodeling characteristics that are essential for long-term function. Mesenchymal stem cells derived from bone marrow (BMMSC) or adipose tissue (ADMSC) are intriguing cell sources for TEHV, but they have not been compared with pediatric human aortic valve interstitial cells (pHAVIC) in relevant 3D environments. In this study, we compared the spontaneous and induced multipotency of ADMSC and BMMSC with that of pHAVIC using different induction media within three-dimensional (3D) bioactive hybrid hydrogels with material modulus comparable to that of aortic heart valve leaflets. pHAVIC possessed some multi-lineage differentiation capacity in response to induction media, but limited to the earliest stages and much less potent than either ADMSC or BMMSC. ADMSC expressed cell phenotype markers more similar to pHAVIC when conditioned in basic fibroblast growth factor (bFGF) containing HAVIC growth medium, while BMMSC generally expressed similar extracellular matrix remodeling characteristics to pHAVIC. Finally, we covalently attached bFGF to PEG monoacrylate linkers and further covalently immobilized in the 3D hybrid hydrogels. Immobilized bFGF upregulated vimentin expression and promoted the fibroblastic differentiation of pHAVIC, ADMSC, and BMMSC. These findings suggest that stem cells retain a heightened capacity for osteogenic differentiation in 3D culture, but can be shifted toward fibroblast differentiation through matrix tethering of bFGF. Such a strategy is likely important for utilizing stem cell sources in heart valve tissue engineering applications.

Influence of culture conditions and extracellular matrix alignment on human mesenchymal stem cells invasion into decellularized engineered tissues

The variables that influence the in vitro recellularization potential of decellularized engineered tissues, such as cell culture conditions and scaffold alignment, have yet to be explored. The goal of this work was to explore the influence of insulin and ascorbic acid and extracellular matrix (ECM) alignment on the recellularization of decellularized engineered tissue by human mesenchymal stem cells (hMSCs). Aligned and non-aligned tissues were created by specifying the geometry and associated mechanical constraints to fibroblast-mediated fibrin gel contraction and remodelling using circular and C-shaped moulds. Decellularized tissues (matrices) of the same alignment were created by decellularization with detergents. Ascorbic acid promoted the invasion of hMSCs into the matrices due to a stimulated increase in motility and proliferation. Invasion correlated with hyaluronic acid secretion, α-smooth muscle actin expression and decreased matrix thickness. Furthermore, hMSCs invasion into aligned and non-aligned matrices was not different, although there was a difference in cell orientation. Finally, we show that hMSCs on the matrix surface appear to differentiate toward a smooth muscle cell or myofibroblast phenotype with ascorbic acid treatment. These results inform the strategy of recellularizing decellularized engineered tissue with hMSCs.