Interactions between mesenchymal stem cells, adipocytes, and osteoblasts in a 3D tri-culture model of hyperglycemic conditions in the bone marrow microenvironment.

Recent studies have found that uncontrolled diabetes and consequential hyperglycemic conditions can lead to an increased incidence of osteoporosis. Osteoblasts, adipocytes, and mesenchymal stem cells (MSCs) are all components of the bone marrow microenvironment and thus may have an effect on diabetes-related osteoporosis. However, few studies have investigated the influence of these three cell types on each other, especially in the context of hyperglycemia. Thus, we developed a hydrogel-based 3D culture platform engineered to allow live-cell retrieval in order to investigate the interactions between MSCs, osteoblasts, and adipocytes in mono-, co-, and tri-culture configurations under hyperglycemic conditions for 7 days of culture. Gene expression, histochemical analysis of differentiation markers, and cell viability were measured for all cell types, and MSC-laden hydrogels were degraded to retrieve cells to assess their colony-forming capacity. Multivariate models of gene expression data indicated that primary discrimination was dependent on the neighboring cell type, validating the need for co-culture configurations to study conditions modeling this disease state. MSC viability and clonogenicity were reduced when mono- and co-cultured with osteoblasts at high glucose levels. In contrast, MSCs showed no reduction of viability or clonogenicity when cultured with adipocytes under high glucose conditions, and the adipogenic gene expression indicates that cross-talk between MSCs and adipocytes may occur. Thus, our unique culture platform combined with post-culture multivariate analysis provided a novel insight into cellular interactions within the MSC microenvironment and highlights the necessity of multi-cellular culture systems for further investigation of complex pathologies such as diabetes and osteoporosis.

Development of 3D hydrogel culture systems with on-demand cell separation.

Recently there has been an increased interest in the effects of paracrine signaling between groups of cells, particularly in the context of better understanding how stem cells contribute to tissue repair. Most current 3D co-culture methods lack the ability to effectively separate two cell populations after the culture period, which is important for simultaneously analyzing the reciprocal effects of each cell type on the other. Here, we detail the development of a 3D hydrogel co-culture system that allows us to culture different cell types for up to 7 days and subsequently separate and isolate the different cell populations using enzyme-sensitive glues. Separable 3D co-culture laminates were prepared by laminating PEG-based hydrogels with enzyme-degradable hydrogel adhesives. Encapsulated cell populations exhibited good segregation with well-defined interfaces. Furthermore, constructs can be separated on-demand upon addition of the appropriate enzyme, while cell viability remains high throughout the culture period, even after laminate separation. This platform offers great potential for a variety of basic cell signaling studies as the incorporation of an enzyme-sensitive adhesive interface allows the on-demand separation of individual cell populations for immediate analysis or further culture to examine persistence of co-culture effects and paracrine signaling on cell populations.

Three-dimensional in vitro tri-culture platform to investigate effects of crosstalk between mesenchymal stem cells, osteoblasts, and adipocytes.

The bone marrow niche for mesenchymal stem cells (MSCs) contains different amounts of bone and fat that vary with age and certain pathologies. How this dynamic niche environment may affect their differentiation potential and/or healing properties for clinical applications remains unknown, largely due to the lack of physiologically relevant in vitro models. We developed an enabling platform to isolate and study effects of signaling interactions between tissue-scale, laminated hydrogel modules of multiple cell types in tandem. We applied this platform to co- and tri-culture of primary human MSCs, osteoblasts, and adipocytes over 18 days in vitro. Each cell type was analyzed separately with quantitative polymerase chain reaction (qPCR) and histochemistry for several mesenchymal lineage markers. Distinct expression dynamics for osteogenic, adipogenic, chondrogenic, and myogenic transcriptional regulators resulted within each cell type depending on its culture setting. Incorporating this data into multivariate models produced latent identifiers of each emergent cell type dependent on its co- or tri-culture setting. Histological staining showed sustained triglyceride storage in adipocytes regardless of culture condition, but transient alkaline phosphatase activity in both osteoblasts and MSCs. Taken together, our results suggest novel emergent phenotypes for MSCs, osteoblasts, and adipocytes in bone marrow that are dependent on and result in part from paracrine interactions with their neighboring cell types.

Development of nano- and microscale chondroitin sulfate particles for controlled growth factor delivery.

Size scale plays an important role in the release properties and cellular presentation of drug delivery vehicles. Because negatively charged chondroitin sulfate (CS) is capable of electrostatically sequestering positively charged growth factors, CS-derived nanoscale micelles and microscale spheroids were synthesized as potential growth factor carriers to enhance differentiation of stem cells. Particles were characterized for morphology, size distribution, surface charge and cytocompatibility, as well as release of transforming growth factor-ß1 (TGF-ß1) and tumor necrosis factor-α (TNF-α). CS micelles were spherical and negatively charged with a bimodal distribution of 324.1±8.5 and 73.2±4.4 nm diameters, and CS microspheres possessed a rounded morphology and a diameter of 4.3±0.93 µm. Positively charged TGF-ß1 demonstrated minimal release after loading in CS microspheres, while negatively charged TNF-α exhibited substantial release over the first 15 h, suggesting that TGF-ß1 electrostatically complexed with CS. The micelles and microparticles were found to be cytocompatible at moderate concentrations with marrow stromal cell monolayers and within embryonic stem cell embryoid bodies. These synthesis techniques, which allow the formation of CS-based carriers over a variety of nano- and microscale sizes, offer versatility for tailored release of positively charged growth factors and controlled CS presentation for a variety of stem cell-based applications in tissue engineering and regenerative medicine.

Long-term spatially defined coculture within three-dimensional photopatterned hydrogels.

Spatially controlled coculture in three-dimensional environments that appropriately mimic in vivo tissue architecture is a highly desirable goal in basic scientific studies of stem cell physiological processes (e.g., proliferation, matrix production, and tissue repair) and in enhancing the development of novel stem-cell-based clinical therapies for a variety of ailments. This study describes a novel fabrication system for photopatterning and assembling cell-laden oligo(polyethylene glycol)-fumarate:poly(ethylene glycol)-diacrylate hydrogels with high spatial fidelity and thickness using a controlled, inert nitrogen environment without the need for expensive precision equipment. Cross-linking was performed using Irgacure-2959 photoinitiator and 365-nm light (∼7 mW/cm²) to form gels ranging from 0.9 to 3 mm in width. Employing a nitrogen environment increased gel thickness up to 240%, generating gels > 1 mm thick before swelling. This technique was further applied for spatially controlled patterning of primary tendon/ligament fibroblasts and marrow stromal cells in a single 1.5-mm-thick laminated hydrogel construct. Cells encapsulated using this technique maintained viability over 14 days in culture. This system potentially enables better understanding of paracrine effects on a range of stem cell functions and therefore may be useful as an in vitro model system for a wide array of regenerative medicine applications.