Changes in human mesenchymal stem cell behaviors on dendrimer-immobilized surfaces due to mediation of fibronectin adsorption and assembly

Novel approach to enhance aggregate migration-driven epigenetic memory which induces cardiomyogenic differentiation on a dendrimer-immobilized surface

The dynamic migratory behavior of human mesenchymal stem cells (hMSCs) has a significant impact on the epigenetic profiles that determine fate choice and lineage commitment during differentiation. Here we report a novel approach to enhance repeated migration-driven epigenetic memory which induces cardiomyogenic differentiation on a dendrimer surface with fifth generation (G5). Cells exhibited the formation of cell aggregates on the G5 surface through active migration with morphological changes, and these aggregates showed strong expression of the cardiac-specific marker cardiac troponin T (cTnT) at 10 days. When cell aggregates were passaged onto a fresh G5 surface over three passages of 40 days, the expression levels of the multiple cardiac-specific markers including GATA4, NKX2.5, MYH7, and TNNT2 were higher compared to those passaged as single cells. To investigate whether cardiomyogenic differentiation of hMSCs was enhanced by repeated aggregate migration-driven epigenetic memory, cells on the G5 surface were reseeded onto a fresh G5 surface during three passages using aggregate-based and single cell-based passage methods. Analyses of global changes in H3 histone modifications exhibited pattern of increased H3K9ac and H3K27me3, and decreased H3K9me3 in aggregate-based passage cultures during three passages. However, the pattern of their histone modification on the PS surface was repeated after the initialization and reformation during three passages in single cell-based passage cultures. Thus, repetitive aggregate migratory behavior during aggregate-based passage led to a greater degree of histone modification, as well as gene expression changes suggestive of cardiomyogenic differentiation.

Muscle lineage switching by migratory behaviour-driven epigenetic modifications of human mesenchymal stem cells on a dendrimer-immobilized surface

Understanding of the fundamental mechanisms of epigenetic modification in the migration of human mesenchymal stem cells (hMSCs) provides surface design strategies for controlling self-renewal and lineage commitment. We investigated the mechanism underlying muscle lineage switching of hMSCs by cellular and nuclear deformation during cell migration on polyamidoamine dendrimer surfaces. With an increase in the dendrimer generation number, cells exhibited increased nuclear deformation and decreased lamin A/C and lamin B1 expression. Analysis of two repressive modifications (H3K9me3 and H3K27me3) and one activating modification (H3K9ac) revealed that H3K9me3 was suppressed, and H3K9ac and H3K27me3 were upregulated in the cultures on a higher-generation dendrimer surface. This induced significant hMSC lineage switching to smooth, skeletal, and cardiac muscle lineages. Thus, reorganizations of the nuclear lamina and cytoskeleton related to migration changes on dendrimer surfaces are responsible for the integrated regulation of histone modifications in hMSCs, thereby shifting the cells from the multipotent state to muscle lineages. These findings improve our understanding of the role of epigenetic modification in cell migration and provide new insights into how designed surfaces can be applied as cell-instructive materials in the field of biomaterial-guided differentiation of hMSCs to different cell types. STATEMENT OF SIGNIFICANCE: Stem cell engineering strategies currently applied the mechanical cues that emerge from cellular microenvironment to regulate stem cell behaviour. This study significantly improved our understanding of the mechanotransduction mechanism involving cell-ECM and cytoskeleton-nucleoskeleton interactions, and of nuclear genome regulation based on cellular responses to biomaterial modifications. The new insights into how the physical environment on a culture surface influences cell behaviour improve our understanding of mechanical control mechanisms of the interactions of cells with the extracellular environment. Our findings are also expected to contribute to and play an essential role in the development of future material strategies for creating artificial cell-instructive niches.

Maintenance of Neurogenic Differentiation Potential in Passaged Bone Marrow-Derived Human Mesenchymal Stem Cells Under Simulated Microgravity Conditions

Human mesenchymal stem cells (hMSCs) are considered to be able to adapt to environmental changes induced by gravity during cell expansion. In this study, we investigated neurogenic differentiation potential of passaged hMSCs under conventional gravity and simulated microgravity conditions. Immunostaining, quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR), and western blot analysis of neurogenic differentiation markers, neurofilament heavy (NF-H), and microtubule-associated protein 2 (MAP2) revealed that differentiated cells from the cells cultured under simulated microgravity conditions expressed higher neurogenic levels than those from conventional gravity conditions. The levels of NF-H and MAP2 in the cells from simulated microgravity conditions were consistent during passage culture, whereas cells from conventional gravity conditions exhibited a reduction of the neurogenic levels against an increase of their passage number. In growth culture, cells under simulated microgravity conditions showed less apical stress fibers over their nucleus with fewer cells having a polarization of lamin A/C than those under conventional gravity conditions. The ratio of lamin A/C to lamin B expression in the cells under simulated microgravity conditions was constant; however, cells cultured under conventional gravity conditions showed an increase in the lamin ratio during passages. Furthermore, analysis of activating H3K4me3 and repressive H3K27me3 modifications at promoters of neuronal lineage genes indicated that cells passaged under simulated microgravity conditions sustained the methylation during serial cultivation. Nevertheless, the enrichment of H3K27me3 significantly increased in the passaged cells cultured under conventional gravity conditions. These results demonstrated that simulated microgravity-coordinated cytoskeleton-lamin reorganization leads to suppression of histone modification associated with neurogenic differentiation capacity of passaged hMSCs.

Alterations in Nuclear Lamina and the Cytoskeleton of Bone Marrow-Derived Human Mesenchymal Stem Cells Cultured Under Simulated Microgravity Conditions

Cells sense and respond to environmental changes induced by gravity. Although reactions to conventional culture have been intensively studied, little is known about the cellular reaction to simulated microgravity conditions. Thus, in this study, we investigated the effects of simulated microgravity on human mesenchymal stem cells using a three-dimensional clinostat (Gravite^®), a recently developed device used to generate simulated microgravity condition in vitro. Our time-lapse analysis shows that cells cultured under conventional culture conditions have a stretched morphology and undergo unidirectional migration, whereas cells cultured under simulated microgravity conditions undergo multidirectional migration with directional changes of cell movement. Furthermore, cells cultured under conventional culture conditions maintained their spindle shape through fibronectin fibril formation in their bodies and focal adhesion stabilization with enriched stress fibers. However, cells cultured under simulated microgravity conditions were partially contracted and the fibril structures were degraded in the cell bodies. Additionally, paxillin phosphorylation in the cells cultured under simulated microgravity conditions was more intense at the cell periphery in regions near the leading and trailing edges, but was less expressed in the cell bodies compared with that observed in cells cultured under conventional culture conditions. Furthermore, lamin A/C, a major component of the nuclear lamina, was mainly located on the apical side in cells cultured under conventional culture conditions, indicating basal-to-apical polarization. However, cells cultured under simulated microgravity conditions showed lamin A/C localization on both the apical and basal sides. Taken together, these results demonstrate that simulated microgravity-driven fibronectin assembly affects nuclear lamina organization through the spatial reorganization of the cytoskeleton.

Maintenance of human chondrogenic phenotype on a dendrimer-immobilized surface for an application of cell sheet engineering

BACKGROUND

Dedifferentiation of chondrocytes during cell expansion is one of the barriers in tissue construction for cartilage repair. To understand chondrocyte behavior and improve cell expansion in monolayer culture, this study investigated the effects of morphological changes and cellular aggregation on the maintenance of chondrogenic capacity by observing the expression patterns of chondrogenic (collagen type II and aggrecan) and dedifferentiation (collagen type I) markers. Primary human chondrocytes were cultured on either a polystyrene surface (PS) or a polyamidoamine dendrimer surface with a fifth-generation (G5) dendron structure to create a one-step process of cell expansion and the maintenance of chondrogenic activities prior to the construction of cell sheets.

RESULTS

During the first two passages (P0 - P2), the relative mRNA level of collagen type II decreased in all cultures, while that of collagen type I increased. Remarkably, the level of collagen type II was higher and aggrecan was retained in the chondrocytes, forming cell aggregates and showing some round-shaped cells with less production of stress fibers on the G5 surface compared to fibroblast-like chondrocytes with abundant stress fibers on the PS surface. The numbers of P2 chondrocytes on the G5 and PS surfaces were nearly the same and sufficient for construction of chondrocyte sheets using a temperature-responsive plate. Without a supporting material during cell sheet manipulation, chondrocyte sheets spontaneously detached and exhibited a honeycomb-like structure of stress fibers. Unlike the chondrocyte sheets constructed from cells on the PS surface, the chondrocyte sheets from cells on the G5 surface had higher chondrogenic activities, as evidenced by the high expression of chondrogenic markers and the low expression of dedifferentiation markers.

CONCLUSIONS

The one-step process of cell expansion and maintenance of chondrogenic activity could be obtained using the G5 surface. Human chondrocyte sheets were successfully constructed with high chondrogenic activity. These findings may lead to an alternative cultivation technique for human chondrocytes that offers high clinical potential in autologous chondrocyte implantation.