Direct Control of Stem Cell Behavior Using Biomaterials and Genetic Factors. Stem Cells Int. 2018;2018:8642989. [PMID: 29861745 PMCID: PMC5971247 DOI: 10.1155/2018/8642989]

Microfibre-Functionalised Silk Hydrogels

Silk hydrogels have shown potential for tissue engineering applications, but several gaps and challenges, such as a restricted ability to form hydrogels with tuned mechanics and structural features, still limit their utilisation. Here, Bombyx mori and Antheraea mylitta (Tasar) silk microfibres were embedded within self-assembling B. mori silk hydrogels to modify the bulk hydrogel mechanical properties. This approach is particularly attractive because it creates structured silk hydrogels. First, B. mori and Tasar microfibres were prepared with lengths between 250 and 500 μm. Secondary structure analyses showed high beta-sheet contents of 61% and 63% for B. mori and Tasar microfibres, respectively. Mixing either microfibre type, at either 2% or 10% (w/v) concentrations, into 3% (w/v) silk solutions during the solution-gel transition increased the initial stiffness of the resulting silk hydrogels, with the 10% (w/v) addition giving a greater increase. Microfibre addition also altered hydrogel stress relaxation, with the fastest stress relaxation observed with a rank order of 2% (w/v) > 10% (w/v) > unmodified hydrogels for either fibre type, although B. mori fibres showed a greater effect. The resulting data sets are interesting because they suggest that the presence of microfibres provided potential 'flow points' within these hydrogels. Assessment of the biological responses by monitoring cell attachment onto these two-dimensional hydrogel substrates revealed greater numbers of human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) attached to the hydrogels containing 10% (w/v) B. mori microfibres as well as 2% (w/v) and 10% (w/v) Tasar microfibres at 24 h after seeding. Cytoskeleton staining revealed a more elongated and stretched morphology for the cells growing on hydrogels containing Tasar microfibres. Overall, these findings illustrate that hydrogel stiffness, stress relaxation and the iPSC-MSC responses towards silk hydrogels can be tuned using microfibres.

Non-viral gene delivery to human mesenchymal stem cells: a practical guide towards cell engineering

In recent decades, human mesenchymal stem cells (hMSCs) have gained momentum in the field of cell therapy for treating cartilage and bone injuries. Despite the tri-lineage multipotency, proliferative properties, and potent immunomodulatory effects of hMSCs, their clinical potential is hindered by donor variations, limiting their use in medical settings. To address this challenge, gene delivery technologies have emerged as a promising approach to modulate the phenotype and commitment of hMSCs towards specific cell lineages, thereby enhancing osteochondral repair strategies. This review provides a comprehensive overview of current non-viral gene delivery approaches used to engineer MSCs, highlighting key factors such as the choice of nucleic acid or delivery vector, transfection strategies, and experimental parameters. Additionally, it outlines various protocols and methods for qualitative and quantitative evaluation of their therapeutic potential as a delivery system in osteochondral regenerative applications. In summary, this technical review offers a practical guide for optimizing non-viral systems in osteochondral regenerative approaches. hMSCs constitute a key target population for gene therapy techniques. Nevertheless, there is a long way to go for their translation into clinical treatments. In this review, we remind the most relevant transfection conditions to be optimized, such as the type of nucleic acid or delivery vector, the transfection strategy, and the experimental parameters to accurately evaluate a delivery system. This survey provides a practical guide to optimizing non-viral systems for osteochondral regenerative approaches.

Exosomes derived from dental pulp stem cells accelerate cutaneous wound healing by enhancing angiogenesis via the Cdc42/p38 MAPK pathway

Skin wound healing is a common challenging clinical issue which requires advanced treatment strategies. The present study investigated the therapeutic effects of exosomes derived from dental pulp stem cells (DPSC‑Exos) on cutaneous wound healing and the underlying mechanisms. The effects of DPSC‑Exos on cutaneous wound healing in mice were examined by measuring wound closure rates, and using histological and immunohistochemical analysis. A series of functional assays were performed to evaluate the effects of DPSC‑Exos on the angiogenic activities of human umbilical vein endothelial cells (HUVECs) <i>in vitro</i>. Tandem mass tag‑based quantitative proteomics analysis of DPSCs and DPSC‑Exos was performed. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were used to evaluate the biological functions and pathways for the differentially expressed proteins in DPSC‑Exos. Western blot analysis was used to assess the protein levels of cell division control protein 42 (Cdc42) and p38 in DPSC‑Exos and in HUVECs subjected to DPSC‑Exos‑induced angiogenesis. SB203580, a p38 mitogen‑activated protein kinase (MAPK) signaling pathway inhibitor, was employed to verify the role of the p38 MAPK pathway <i>in vitro</i> and <i>in vivo</i>. Histological and immunohistochemical staining revealed that the DPSC‑Exos accelerated wound healing by promoting neovascularization. The DPSC‑Exos promoted the migration, proliferation and capillary formation capacity of HUVECs. Proteomics data demonstrated that proteins contained in DPSC‑Exos regulated vasculature development and angiogenesis. Pathway analysis revealed that proteins expressed in DPSC‑Exos were involved in several pathways, including MAPK pathway. Western blot analysis demonstrated that the DPSC‑Exos increased the protein levels of Cdc42 and phosphorylation of p38 in HUVECs. SB203580 suppressed the angiogenesis induced by DPSC‑Exos. On the whole, the present study demonstrates that DPSC‑Exos accelerate cutaneous wound healing by enhancing the angiogenic properties of HUVECs via the Cdc42/p38 MAPK signaling pathway.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

Biomaterials as a Vital Frontier for Stem Cell-Based Tissue Regeneration

Biomaterials and tissue regeneration represent two fields of intense research and rapid advancement. Their combination allowed the utilization of the different characteristics of biomaterials to enhance the expansion of stem cells or their differentiation into various lineages. Furthermore, the use of biomaterials in tissue regeneration would help in the creation of larger tissue constructs that can allow for significant clinical application. Several studies investigated the role of one or more biomaterial on stem cell characteristics or their differentiation potential into a certain target. In order to achieve real advancement in the field of stem cell-based tissue regeneration, a careful analysis of the currently published information is critically needed. This review describes the fundamental description of biomaterials as well as their classification according to their source, bioactivity and different biological effects. The effect of different biomaterials on stem cell expansion and differentiation into the primarily studied lineages was further discussed. In conclusion, biomaterials should be considered as an essential component of stem cell differentiation strategies. An intense investigation is still required. Establishing a consortium of stem cell biologists and biomaterial developers would help in a systematic development of this field.

Vitamin D3 Stimulates Proliferation Capacity, Expression of Pluripotency Markers, and Osteogenesis of Human Bone Marrow Mesenchymal Stromal/Stem Cells, Partly through SIRT1 Signaling

The biology of vitamin D3 is well defined, as are the effects of its active metabolites on various cells, including mesenchymal stromal/stem cells (MSCs). However, the biological potential of its precursor, cholecalciferol (VD3), has not been sufficiently investigated, although its significance in regenerative medicine—mainly in combination with various biomaterial matrices—has been recognized. Given that VD3 preconditioning might also contribute to the improvement of cellular regenerative potential, the aim of this study was to investigate its effects on bone marrow (BM) MSC functions and the signaling pathways involved. For that purpose, the influence of VD3 on BM-MSCs obtained from young human donors was determined via MTT test, flow cytometric analysis, immunocytochemistry, and qRT-PCR. Our results revealed that VD3, following a 5-day treatment, stimulated proliferation, expression of pluripotency markers (NANOG, SOX2, and Oct4), and osteogenic differentiation potential in BM-MSCs, while it reduced their senescence. Moreover, increased sirtuin 1 (SIRT1) expression was detected upon treatment with VD3, which mediated VD3-promoted osteogenesis and, partially, the stemness features through NANOG and SOX2 upregulation. In contrast, the effects of VD3 on proliferation, Oct4 expression, and senescence were SIRT1-independent. Altogether, these data indicate that VD3 has strong potential to modulate BM-MSCs’ features, partially through SIRT1 signaling, although the precise mechanisms merit further investigation.

Exploring microenvironment strategies to delay mesenchymal stem cell senescence

Mesenchymal stem cells (MSCs) have recently emerged as an important candidate for cell therapy and tissue regeneration. However, some limitations in translational research and therapies still exist, such as insufficient cell supply, inadequate differentiation potential, and decreased immune capacity, all of which result from replicative senescence during long-term in vitro culture. In vitro, stem cells lack a protective microenvironment owing to the absence of physical and biochemical cues compared with the in vivo niche, which provides dynamic physicochemical and biological cues. This difference results in accelerated aging after long-term in vitro culture. Therefore, it remains a great challenge to delay replicative senescence in culture. Constructing a microenvironment to delay replicative senescence of MSCs by maintaining their phenotypes, properties, and functions is a feasible strategy to solve this problem and has made measurable progress both in preclinical studies and clinical trials. Here, we review the current knowledge on the characteristics of senescent MSCs, explore the molecular mechanisms of MSCs senescence, describe the niche of MSCs, and discuss some current microenvironment strategies to delay MSCs replicative senescence that can broaden their range of therapeutic applications.

Compounded topographical and physicochemical cueing by micro-engineered chitosan substrates on rat dorsal root ganglion neurons and human mesenchymal stem cells

Given the intertwined physicochemical effects exerted in vivo by both natural and synthetic (e.g., biomaterial) interfaces on adhering cells, the evaluation of structure-function relationships governing cellular response to micro-engineered surfaces for applications in neuronal tissue engineering requires the use of in vitro testing platforms which consist of a clinically translatable material with tunable physiochemical properties. In this work, we micro-engineered chitosan substrates with arrays of parallel channels with variable width (20 and 60 μm). A citric acid (CA)-based crosslinking approach was used to provide an additional level of synergistic cueing on adhering cells by regulating the chitosan substrate's stiffness. Morphological and physicochemical characterization was conducted to unveil the structure-function relationships which govern the activity of rat dorsal root ganglion neurons (DRGs) and human mesenchymal stem cells (hMSCs), ultimately singling out the key role of microtopography, roughness and substrate's stiffness. While substrate's stiffness predominantly affected hMSC spreading, the modulation of the channels' design affected the neuronal architecture's complexity and guided the morphological transition of hMSCs. Finally, the combined analysis of tubulin expression and cell morphology allowed us to cast new light on the predominant role of the microtopography over substrate's stiffness in the process of hMSCs neurogenic differentiation.

Magnetic nanoparticle loaded human adipose derived mesenchymal cells spheroids in levitated culture

Magnetic nanoparticles (MNP) are intensely scrutinized for biomedical applications due to their excellent biocompatibility and adjustable magnetic field (MF) responsiveness. Three-dimensional spheroid culture of ADSC improves stem cell proliferation and differentiation, increasing their potential for clinical applications. In this study we aimed to detect if MF levitated culture of ADSC loaded with proprietary MNP maintain the properties of ADSC and improve their performances. Levitated ADSC-MNP formed aggregates with increased volume and reduced number compared to nonlevitated ones. ADSC-MNP from levitated spheroid displayed higher viability, proliferation and mobility compared to nonlevitated and 2D culture. Levitated and nonlevitated ADSC-MNP spheroids underwent three lineage differentiation, demonstrating preserved ADSC stemness. Quantitative osteogenesis showed similar values in MNP-loaded levitated and nonlevitated spheroids. Significant increases in adipogenic conversion was observed for all 3D formulation. Chondrogenic conversion in levitated and nonlevitated spheroids produced comparable ratio glucosaminoglycan (GAG)/DNA. Increased chondrogenesis could be observed for ADSC-MNP in both levitated and nonlevitated condition. Taken together, ADSC-MNP levitated spheroids retain stemness and display superior cell viability and migratory capabilities. Furthermore, the method consistently increases spheroid maneuverability, potentially facilitating large scale manufacturing and automation. Levitated spheroid culture of ADSC-MNP can be further tested for various application in regenerative medicine and organ modeling.

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.

Soft Polymeric Matrix as a Macroscopic Cage for Magnetically Modulating Reversible Nanoscale Ligand Presentation

A physical, noninvasive, and reversible means of controlling the nanoscale presentation of bioactive ligands is highly desirable for regulating and investigating the time-dependent responses of cells, including stem cells. Herein we report a magnetically actuated dynamic cell culture platform consisting of a soft hydrogel substrate conjugated with RGD-bearing magnetic nanoparticle (RGD-MNP). The downward/upward magnetic attraction conceals/promotes the presentation of the RGD-MNP in/on the soft hydrogel matrix, thereby inhibiting/enhancing the cell adhesion and mechanosensing-dependent differentiation. Meanwhile, the lateral magnetic attraction promotes the unidirectional migration of cells in the opposite direction on the hydrogel. Furthermore, cyclic switching between the "Exposed" and "Hidden" conditions induces the repeated cycles of differentiation/dedifferentiation of hMSCs which significantly enhances the differentiation potential of hMSCs. Our design approach capitalizes on the bulk biomaterial matrix as the macroscopic caging structure to enable dynamic regulation of cell-matrix interactions reversibly, which is hard to achieve by using conventional cell culture systems.

Generation of mesenchymal stem-like cells for producing extracellular vesicles

Mesenchymal stem cells (MSCs) are multipotent progenitor cells with therapeutic potential against autoimmune diseases, inflammation, ischemia, and metabolic disorders. Contrary to the previous conceptions, recent studies have revealed that the tissue repair and immunomodulatory functions of MSCs are largely attributed to their secretome, rather than their potential to differentiate into desired cell types. The composition of MSC secretome encompasses cytokines and growth factors, in addition to the cell-derived structures known as extracellular vesicles (EVs). EVs are membrane-enclosed nanoparticles that are capable of delivering biomolecules, and it is now believed that MSC-derived EVs are the major players that induce biological changes in the target tissues. Based on these EVs’ characteristics, the potential of EVs derived from MSC (MSC-EV) in terms of tissue regeneration and immune modulation has grown during the last decade. However, the use of MSCs for producing sufficient amount of EVs has not been satisfactory due to limitations in the cell growth and large variations among the donor cell types. In this regard, pluripotent stem cells (PSCs)-derived MSC-like cells, which can be robustly induced and expanded in vitro, have emerged as more accessible cell source that can overcome current limitations of using MSCs for EV production. In this review, we have highlighted the methods of generating MSC-like cells from PSCs and their therapeutic outcome in preclinical studies. Finally, we have also discussed future requirements for making this cell-free therapy clinically feasible.

Adipose-derived stem cell-secreted factors promote early stage follicle development in a biomimetic matrix

Development of primary follicles in vitro benefits from a three-dimensional matrix that is enriched with paracrine factors secreted from feeder cells and mimics the in vivo environment. In this study, we investigated the role of paracrine signaling from adipose-derived stem cells (ADSCs) in supporting primary follicle development in a biomimetic poly(ethylene glycol) (PEG)-based matrix. Follicles co-cultured with ADSCs and follicles cultured in conditioned medium from ADSCs encapsulated in gels (3D CM) exhibited significantly (p < 0.01 and p = 0.09, respectively) improved survival compared to follicles cultured in conditioned medium collected from ADSCs cultured in flasks (2D CM) and follicles cultured without paracrine support. The gene expression of ADSCs suggested that the stem cells maintained their multipotency in the 3D PEG environment over the culture period, regardless of the presence of the follicles, while under 2D conditions the multipotency markers were downregulated. The differences in cytokine signatures of follicles exposed to 3D and 2D ADSC paracrine factors suggest that early cytokine interactions are key for follicle survival. Taken together, the biomimetic PEG scaffold provides a three-dimensional, in vivo-like environment to induce ADSCs to secrete factors which promote early stage ovarian follicle development and survival.