Osteogenic Differentiation Potential of iMSCs on GelMA-BG-MWCNT Nanocomposite Hydrogels

The ability of bone biomaterials to promote osteogenic differentiation is crucial for the repair and regeneration of osseous tissue. The development of a temporary bone substitute is of major importance in enhancing the growth and differentiation of human-derived stem cells into an osteogenic lineage. In this study, nanocomposite hydrogels composed of gelatin methacryloyl (GelMA), bioactive glass (BG), and multiwall carbon nanotubes (MWCNT) were developed to create a bone biomaterial that mimics the structural and electrically conductive nature of bone that can promote the differentiation of human-derived stem cells. GelMA-BG-MWCNT nanocomposite hydrogels supported mesenchymal stem cells derived from human induced pluripotent stem cells, hereinafter named iMSCs. Cell adhesion was improved upon coating nanocomposite hydrogels with fibronectin and was further enhanced when seeding pre-differentiated iMSCs. Osteogenic differentiation and mature mineralization were promoted in GelMA-BG-MWCNT nanocomposite hydrogels and were most evidently observed in the 70-30-2 hydrogels, which could be due to the stiff topography characteristic from the addition of MWCNT. Overall, the results of this study showed that GelMA-BG-MWCNT nanocomposite hydrogels coated with fibronectin possessed a favorable environment in which pre-differentiated iMSCs could better attach, proliferate, and further mature into an osteogenic lineage, which was crucial for the repair and regeneration of bone.

Chondroitin Sulphate/Dermatan Sulphate Proteoglycans: Potential Regulators of Corneal Stem/Progenitor Cell Phenotype In Vitro

Chondroitin sulphate (CS) proteoglycans with variable sulphation-motifs along their glycosaminoglycan (GAG) chains are closely associated with the stem cell niche of articular cartilage, where they are believed to influence the characteristics of the resident stem cells. Here, we investigated the immunohistochemical distribution of hybrid CS/dermatan sulphate (DS) GAGs in the periphery of the adult chicken cornea, which is the location of the cornea's stem cell niche in a number of species, using a monoclonal antibody, 6C3, that recognises a sulphation motif-specific CS/DS GAG epitope. This revealed positive labelling that was restricted to the subepithelial corneal stroma, as well as nearby bony structures within the sclera, called ossicles. When cultivated on cell culture dishes coated with 6C3-rich CS/DS, corneal stromal cells (keratocytes) that had been isolated from embryonic chicken corneas formed circular colonies, which took several days to reach confluency. A flow cytometric analysis of these keratocytes revealed changes in their expression levels of the indicative stem cell markers, Connexin 43 (Cx43), Paired Box 6 (PAX6), B-lymphoma Moloney murine leukemia virus insertion region-1 (Bmi-1), and C-X-C Chemokine Receptor 4 (CXCR4) suggestive of a less-differentiated phenotype compared with expression levels in cells not exposed to CS/DS. These findings support the view that CS/DS promotes the retention of a stem cell phenotype in corneal cells, much as it has been proposed to do in other connective tissues.

Assay-ready Cryopreserved Cell Monolayers Enabled by Macromolecular Cryoprotectants

Cell monolayers underpin the discovery and screening of new drugs and allow for fundamental studies of cell biology and disease. However, current cryopreservation technologies do not allow cells to be stored frozen while attached to tissue culture plastic. Hence, cells must be thawed from suspension, cultured for several days or weeks, and finally transferred into multiwell plates for the desired application. This inefficient process consumes significant time handling cells, rather than conducting biomedical research or other value-adding activities. Here, we demonstrate that a synthetic macromolecular cryoprotectant enables the routine, reproducible, and robust cryopreservation of biomedically important cell monolayers, within industry-standard tissue culture multiwell plates. The cells are simply thawed with media and placed in an incubator ready to use within 24 h. Post-thaw cell recovery values were >80% across three cell lines with low well-to-well variance. The cryopreserved cells retained healthy morphology, membrane integrity, proliferative capacity, and metabolic activity; showed marginal increases in apoptotic cells; and responded well to a toxicological challenge using doxorubicin. These discoveries confirm that the cells are “assay-ready” 24 h after thaw. Overall, we show that macromolecular cryoprotectants can address a long-standing cryobiological challenge and offers the potential to transform routine cell culture for biomedical discovery.

Isolation, identification and differentiation of human spermatogonial cells on three-dimensional decellularized sheep testis

Improvement of in vitro culture methods of Spermatogonial Stem Cells (SSCs) is known to be an effective procedure for further study of the process of spermatogenesis and can offer effective therapeutic modality for male infertility. Tissue decellularization by providing natural 3D and extracellular matrix (ECM) conditions for cell growth can be an alternative procedure to enhance in vitro culture conditions. In the present study, the testicular tissues were taken from brain death donors. After enzymatic digestion, the tissue cells were isolated and cultured for four weeks. Then the identity of the SSCs was confirmed using anti-GFRα1 and anti-PLZF antibodies via immunocytochemistry (ICC). The differentiation capacity of SSCs were evaluated by culture of them on a layer of decellularized testicular matrix (DTM) prepared from sheep testis, as well as under two-dimensional (2D) culture with differentiation medium. After four and six weeks of the initiation of differentiation culture, the pre-meiotic, meiotic and post- meiotic genes at the mRNA and protein levels was examined via qPCR and ICC methods, respectively. The results showed that pre-meiotic, meiotic and post-meiotic genes expressions were significantly higher in the cells cultured in DTM substrate (P ≤ 0.01).The present study indicated that, the natural structure of ECM prepare the suitable conditions for further study of the spermatogenesis process in the in vitro and contributes to the maintenance and treatment of male infertility.

Fibroblast feeder layer supports adipogenic differentiation of human adipose stromal/progenitor cells

Adipose stromal/progenitor cells (ASCs) can differentiate into adipocytes in the course of adipogenesis. This process is governed by systemic factors and signals of the adipose stem cell niche. ASCs isolated from fat tissues and amplified in vitro provide an essential and reliable model system to study adipogenesis. However, current cell culture models routinely grow ASCs on plastic surfaces largely missing niche parameters. In the present communication, we employed human foreskin fibroblasts (HFFs) monolayers as feeder cells for ASCs, which were isolated from human subcutaneous white adipose tissue and amplified in vitro. We found that PPARγ2 and several adipocyte markers were significantly higher expressed in differentiated ASCs growing on feeder layers relative to plastic dishes. Moreover, a significant higher number of adipocytes was generated from ASCs cultured on feeder layer and these adipocytes contained larger fat droplets. Insulin strongly stimulated glucose uptake into adipocytes produced on feeder layer suggesting that these cells show characteristic metabolic features of fat cells.  Finally, we show that the HFF feeder layer allows adipogenic differentiation of low-density-seeded ASCs. In conclusion, we demonstrate that the HFF feeder layer increases adipocyte differentiation of ASCs and allows differentiation of low density seeded progenitor cells  into functional adipocytes.

An engineered cell-imprinted substrate directs osteogenic differentiation in stem cells

A cell-imprinted poly(dimethylsiloxane)/hydroxyapatite nanocomposite substrate was fabricated to engage topographical, mechanical, and chemical signals to stimulate and boost stem cell osteogenic differentiation. The physicochemical properties of the fabricated substrates, with nanoscale resolution of osteoblast morphology, were probed using a wide range of techniques including scanning electron microscopy, atomic force microscopy, dynamic mechanical thermal analysis, and water contact angle measurements. The osteogenic differentiation capacity of the cultured stem cells on these substrates was probed by alizarin red staining, ALP activity, osteocalcin measurements, and gene expression analysis. The outcomes revealed that the concurrent roles of the surface patterns and viscoelastic properties of the substrate provide the capability of directing stem cell differentiation toward osteogenic phenotypes. Besides the physical and mechanical effects, we found that the chemical signaling of osteoinductive hydroxyapatite nanoparticles, embedded in the nanocomposite substrates, could further improve and optimize stem cell osteogenic differentiation.

A Contact-Based Method for Differentiation of Human Mesenchymal Stem Cells into an Endothelial Cell-Phenotype

Adult stem cells such as mesenchymal stem cells (MSC) are known to possess the ability to augment neovascularization processes and are thus widely popular as an autologous source of progenitor cells. However there is a huge gap in our current knowledge of mechanisms involved in differentiating MSC into endothelial cells (EC), essential for lining engineered blood vessels. To fill up this gap, we attempted to differentiate human MSC into EC, by culturing the former onto chemically fixed layers of EC or its ECM, respectively. We expected direct contact of MSC when cultured atop fixed EC or its ECM, would coax the former to differentiate into EC. Results showed that human MSC cultured atop chemically fixed EC or its ECM using EC-medium showed enhanced expression of CD31, a marker for EC, compared to other cases. Further in all human MSC cultured using EC-medium, typically characteristic cobble stone shaped morphologies were noted in comparison to cells cultured using MSC medium, implying that the differentiated cells were sensitive to soluble VEGF supplementation present in the EC-medium. Results will enhance and affect therapies utilizing autologous MSC as a cell source for generating vascular cells to be used in a variety of tissue engineering applications.

Chondrogenic differentiation of BMSCs encapsulated in chondroinductive polysaccharide/collagen hybrid hydrogels

Although BMSC-based therapy is one of the most front-line technologies for cartilage repair, it is still a big challenge to attain ideal niches for BMSC chondrogenic differentiation. In this study, we developed hyaluronate and chondroitin sulfate derivatives to prepare covalently crosslinked polysaccharide hydrogels. Based on these binary hydrogels, collagen was added to prepare ternary hybrid hydrogels and its effect on encapsulated BMSCs was studied. After culturing with different cell densities in vitro without the addition of growth factors for 3 weeks, the chondrogenesis of BMSCs was evaluated by CLSM, mechanical testing, histological staining, immunohistochemical staining and gene expression. The results indicated that BMSCs in high cell density (50 million per mL) cell-laden constructs had a more obvious chondrogenic phenotype than those in low cell density ones (5 million per mL). However, the components of hydrogels had a significant influence on chondrogenic differentiation. With the addition of collagen, the BMSCs in ternary hybrid hydrogels showed more significant chondrogenesis, possessing with more amounts of secreted glycosaminoglycans (GAGs) and type II collagen deposition, higher mechanical properties and chondrogenic gene expression over 3 weeks of culture in vitro. It can be concluded that the bioactive collagen is beneficial to the chondrogenesis of BMSCs. This hybrid hydrogels deserve further studies to have a prospective application in tissue engineering for cartilage defect repair.

Decellularized Extracellular Matrix as an In Vitro Model to Study the Comprehensive Roles of the ECM in Stem Cell Differentiation

Stem cells are a promising cell source for regenerative medicine. Stem cell differentiation must be regulated for applications in regenerative medicine. Stem cells are surrounded by extracellular matrix (ECM) in vivo. The ECM is composed of many types of proteins and glycosaminoglycans that assemble into a complex structure. The assembly of ECM molecules influences stem cell differentiation through orchestrated intracellular signaling activated by many ECM molecules. Therefore, it is important to understand the comprehensive role of the ECM in stem cell differentiation as well as the functions of the individual ECM molecules. Decellularized ECM is a useful in vitro model for studying the comprehensive roles of ECM because it retains a native-like structure and composition. Decellularized ECM can be obtained from in vivo tissue ECM or ECM fabricated by cells cultured in vitro. It is important to select the correct decellularized ECM because each type has different properties. In this review, tissue-derived and cell-derived decellularized ECMs are compared as in vitro ECM models to examine the comprehensive roles of the ECM in stem cell differentiation. We also summarize recent studies using decellularized ECM to determine the comprehensive roles of the ECM in stem cell differentiation.

The significance of membrane fluidity of feeder cell-derived substrates for maintenance of iPS cell stemness

The biological activity of cell-derived substrates to maintain undifferentiated murine-induced pluripotent stem (iPS) cells was correlated to membrane fluidity as a new parameter of cell culture substrates. Murine embryonic fibroblasts (MEFs) were employed as feeder cells and their membrane fluidity was tuned by chemical fixation using formaldehyde (FA). Membrane fluidity was evaluated by real-time single-molecule observations of green fluorescent protein-labeled epidermal growth factor receptors on chemically fixed MEFs. Biological activity was monitored by colony formation of iPS cells. Treatment with a low concentration of FA sustained the membrane fluidity and biological activity, which were comparable to those of mitomycin C-treated MEFs. The biological activity was further confirmed by sustained expression of alkaline phosphatase, SSEA-1, and other pluripotency markers in iPS cells after 3-5 days of culture on FA-fixed MEFs. Chemical fixation of feeder cells has several advantages such as providing ready-to-use culture substrates without contamination by proliferating feeder cells. Therefore, our results provide an important basis for the development of chemically fixed culture substrates for pluripotent stem cell culture as an alternative to conventional treatment by mitomycin C or x-ray irradiation.