The extracellular microscape governs mesenchymal stem cell fate

Stiffness Mediated-Mechanosensation of Airway Smooth Muscle Cells on Linear Stiffness Gradient Hydrogels

In obstructive airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), the extracellular matrix (ECM) protein amount and composition of the airway smooth muscle (ASM) is often remodelled, likely altering tissue stiffness. The underlying mechanism of how human ASM cell (hASMC) mechanosenses the aberrant microenvironment is not well understood. Physiological stiffnesses of the ASM were measured by uniaxial compression tester using porcine ASM layers under 0, 5 and 10% longitudinal stretch above in situ length. Linear stiffness gradient hydrogels (230 kPa range) were fabricated and functionalized with ECM proteins, collagen I (ColI), fibronectin (Fn) and laminin (Ln), to recapitulate the above-measured range of stiffnesses. Overall, hASMC mechanosensation exhibited a clear correlation with the underlying hydrogel stiffness. Cell size, nuclear size and contractile marker alpha-smooth muscle actin (αSMA) expression showed a strong correlation to substrate stiffness. Mechanosensation, assessed by Lamin-A intensity and nuc/cyto YAP, exhibited stiffness-mediated behaviour only on ColI and Fn-coated hydrogels. Inhibition studies using blebbistatin or Y27632 attenuated most mechanotransduction-derived cell morphological responses, αSMA and Lamin-A expression and nuc/cyto YAP (blebbistatin only). This study highlights the interplay and complexities between stiffness and ECM protein type on hASMC mechanosensation, relevant to airway remodelling in obstructive airway diseases.

Evaluating the ability of cultivated odontoblasts to form dentin-like tissue in vitro using fibroblast growth factor and insulin-like growth factor

Aim

The aim of the study was to evaluate the ability of cultivated odontoblast to form dentin-like tissue using fibroblast growth factor (FGF) and insulin-like growth factor (IGF).

Materials and Methods

Dental pulp stem cells (DPSCs) were extracted from 10 human teeth. They were isolated and cultivated in vitro with the use of stem cell markers. The human DPSCs were characterized for trilineage differentiation. They were then differentiated into odontoblasts. The ability of cultivated odontoblasts to form dentin-like tissue was evaluated using FGF and IGF.

Results

IGF showed superior ability to form dentin-like tissue as compared to FGF. The addition of FGF showed no significant difference in the formation of dentin-like tissue. A combination of FGF and IGF in odontoblast showed an enhanced ability to form dentin-like tissue.

Conclusion

The use of growth factors IGF and FGF with dental stem cells showed a greater potential to form dentin-like tissue. This can profoundly alter the paradigms of conservative vital pulp therapy, which may eventually make it possible to treat dental diseases by regeneration of lost dentine.

Development of Mesoporous Silica Nanoparticle-Based Films with Tunable Arginine-Glycine-Aspartate Peptide Global Density and Clustering Levels to Study Stem Cell Adhesion and Differentiation

Stem cell adhesion is mediated via the binding of integrin receptors to adhesion motifs present in the extracellular matrix (ECM). The spatial organization of adhesion ligands plays an important role in stem cell integrin-mediated adhesion. In this study, we developed a series of biointerfaces using arginine-glycine-aspartate (RGD)-functionalized mesoporous silica nanoparticles (MSN-RGD) to study the effect of RGD adhesion ligand global density (ligand coverage over the surface), spacing, and RGD clustering levels on stem cell adhesion and differentiation. To prepare the biointerface, MSNs were chemically functionalized with RGD peptides via an antifouling poly(ethylene glycol) (PEG) linker. The RGD surface functionalization ratio could be controlled to create MSNs with high and low RGD ligand clustering levels. MSN films with varying RGD global densities could be created by blending different ratios of MSN-RGD and non-RGD-functionalized MSNs together. A computational simulation study was performed to analyze nanoparticle distribution and RGD spacing on the resulting surfaces to determine experimental conditions. Enhanced cell adhesion and spreading were observed when RGD global density increased from 1.06 to 5.32 nmol cm-2 using highly clustered RGD-MSN-based films. Higher RGD ligand clustering levels led to larger cell spreading and increased formation of focal adhesions. Moreover, a higher RGD ligand clustering level promoted the expression of alkaline phosphatase in hMSCs. Overall, these findings indicate that both RGD global density and clustering levels are crucial variables in regulating stem cell behaviors. This study provides important information about ligand-integrin interactions, which could be implemented into biomaterial design to achieve optimal performance of adhesive functional peptides.

An overview of substrate stiffness guided cellular response and its applications in tissue regeneration

Cell-matrix interactions play a critical role in tissue repair and regeneration. With gradual uncovering of substrate mechanical characteristics that can affect cell-matrix interactions, much progress has been made to unravel substrate stiffness-mediated cellular response as well as its underlying mechanisms. Yet, as a part of cell-matrix interaction biology, this field remains in its infancy, and the detailed molecular mechanisms are still elusive regarding scaffold-modulated tissue regeneration. This review provides an overview of recent progress in the area of the substrate stiffness-mediated cellular responses, including 1) the physical determination of substrate stiffness on cell fate and tissue development; 2) the current exploited approaches to manipulate the stiffness of scaffolds; 3) the progress of recent researches to reveal the role of substrate stiffness in cellular responses in some representative tissue-engineered regeneration varying from stiff tissue to soft tissue. This article aims to provide an up-to-date overview of cell mechanobiology research in substrate stiffness mediated cellular response and tissue regeneration with insightful information to facilitate interdisciplinary knowledge transfer and enable the establishment of prognostic markers for the design of suitable biomaterials.

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Substrate stiffness physically determines cell fate and tissue development.

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Rational design of scaffolds requires the understanding of cell-matrix interactions.

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Substrate stiffness depends on scaffold molecular-constituent-structure interaction.

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Substrate stiffness-mediated cellular responses vary in different tissues.

Dentin Particulate for Bone Regeneration: An In Vitro Study

The aim of this in vitro study was to investigate the commitment and behavior of dental pulp stem cells (DPSCs) seeded onto two different grafting materials, human dentin particulate (DP) and deproteinized bovine bone matrix (BG), with those cultured in the absence of supplements. Gene expression analyses along with epigenetic and morphological tests were carried out to examine odontogenic and osteogenic differentiation and cell proliferation. Compressive testing of the grafting materials seeded with DPSCs was performed as well. DPSC differentiation into odontoblast-like cells was identified from the upregulation of odontogenic markers (DSPP and MSX) and osteogenic markers (RUNX2, alkaline phosphatase, osteonectin, osteocalcin, collagen type I, bmp2, smad5/8). Epigenetic tests confirmed the presence of miRNAs involved in odontogenic or osteogenic commitment of DPSCs cultured for up to 21 days on DP. Compressive strength values obtained from extracellular matrix (ECM) synthesized by DPSCs showed a trend of being higher when seeded onto DP than onto BG. High expression of VEGF factor, which is related to angiogenesis, and of dentin sialoprotein was observed only in the presence of DP. Morphological analyses confirmed the typical phenotype of adult odontoblasts. In conclusion, the odontogenic and osteogenic commitment of DPSCs and their respective functions can be achieved on DP, which enables exceptional dentin and bone regeneration.

Towards an understanding of the mechanoreciprocity process in adipocytes and its perturbation with aging

Adipose tissue (AT) is a complex organ, with multiple functions that are essential for maintaining metabolic health. A feature of AT is its capability to expand in response to physiological challenges, such as pregnancy and aging, and during chronic states of positive energy balance occurring throughout life. AT grows through adipogenesis and/or an increase in the size of existing adipocytes. One process that is required for healthy AT growth is the remodeling of the extracellular matrix (ECM), which is a necessary step to restore mechanical homeostasis and maintain tissue integrity and functionality. While the relationship between mechanobiology and adipogenesis is now well recognized, less is known about the role of adipocyte mechanosignaling pathways in AT growth. In this review article, we first summarize evidence linking ECM remodelling to AT expansion and how its perturbation is associated to a metabolically unhealthy phenotype. Subsequently, we highlight findings suggesting that molecules involved in the dynamic, bidirectional process (mechanoreciprocity) enabling adipocytes to sense changes in the mechanical properties of the ECM are interconnected to pathways regulating lipid metabolism. Finally, we discuss processes through which aging may influence the ability of adipocytes to appropriately respond to alterations in ECM composition.

Hyaluronic acid bioinspired polymers for the regulation of cell chondrogenic and osteogenic differentiation

As the simplest glycosaminoglycan (GAG) in extracellular matrix, hyaluronic acid (HA) takes part in several important biological processes, such as regulating cell proliferation, differentiation, and migration. In this work, a series of HA-inspired polymers with different saccharide and carboxylate units (HA-analogue polymers) are synthesized by free radical polymerization, and characterized using Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC) and nuclear magnetic resonance spectrometer (NMR), Moreover, cell experiments demonstrate that HA-analogue polymers with a certain proportion of saccharide and carboxylate (PM₁G₁) units shows a positive effect on the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs). Furthermore, HA-analogue polymers have prominent cartilage inductive capacity in chondrogenic induction medium (CIM) and brilliant bone inductive capacity in osteogenic induction medium (OIM) toward BMSCs. Therefore, it is confirmed that the HA-analogue polymers can effectively mimic the functions of HA and have broad potential application prospects in the biomedical and clinical fields.

Pre-culture of mesenchymal stem cells within RGD-modified hyaluronic acid hydrogel improves their resilience to ischaemic conditions

The incorporation of the RGD peptide (arginine-glycine-aspartate) into biomaterials has been proposed to promote cell adhesion to the matrix, which can influence and control cell behaviour and function. While many studies have utilised RGD modified biomaterials for cell delivery, few have examined its effect under the condition of reduced oxygen and nutrients, as found at ischaemic injury sites. Here, we systematically examine the effect of RGD on hMSCs in hyaluronic acid (HA) hydrogel under standard and ischaemic culture conditions, to elucidate under what conditions RGD has beneficial effects over unmodified HA and its effectiveness in improving cell viability. Results demonstrate that under standard culture conditions, RGD significantly increased hMSC spreading and the release of vascular endothelial factor-1 (VEGF) and monocyte chemoattractant factor-1 (MCP-1), compared to unmodified HA hydrogel. As adhesion is known to influence cell survival, we hypothesised that cells in RGD hydrogels would exhibit increased cell viability under ischaemic culture conditions. However, results demonstrate that cell viability and protein release was comparable in both RGD modified and unmodified HA hydrogels. Confocal imaging revealed cellular morphology indicative of weak cell adhesion. Subsequent investigations found that RGD was could exert positive effects on encapsulated cells under ischaemic conditions but only if hMSCs were pre-cultured under standard conditions to allow strong adhesion to RGD before exposure. Together, these results provide novel insight into the value of RGD introduction and suggest that the adhesion of hMSCs to RGD prior to delivery could improve survival and function at ischaemic injury sites. STATEMENT OF SIGNIFICANCE: The development of a biomaterial scaffold capable of maintaining cell viability while promoting cell function is a major research goal in the field of cardiac tissue engineering. This study confirms the suitability of a modified HA hydrogel whereby stem cells in the modified hydrogel showed significantly greater cell spreading and protein secretion compared to cells in the unmodified HA hydrogel. A pre-culture period allowing strong adhesion of the cells to the modified hydrogel was shown to improve cell survival under conditions that mimic the myocardium post-MI. This finding may have a significant impact on the use and timelines of modifications to improve stem cell survival in harsh environments like the injured heart.

Early hMSC morphology and proliferation on model polyelectrolyte multilayers

Polyelectrolyte multilayers (PEMs) are a category of materials commonly used as coatings on surfaces that interact with cells. The properties of PEMs have been established to be controlled by not only polyelectrolyte choice, but by the identity of the initially applied (bottom) layer. In this work, 5-bilayer PEMs consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) were coated on gold-sputtered quartz substrates with different first layer materials. A final poly-l-lysine (PLL) layer was added to all PEMs to provide identical top layers conducive to cell growth. As in previous work, initial layer selection affected PEM roughness. All coated surfaces, including the PLL-only control, showed increased dispersive surface energy but decreased polar surface energy, as compared to uncoated surfaces. When human mesenchymal stem cells (hMSCs) were cultured on these surfaces, analysis through lateral cell imaging for the first 90 min and fluorescent staining after 1 day showed improved attachment on surfaces with a PDADMAC bottom layer. However, after 4 days, a higher cell density was observed on the PLL-only and uncoated control surfaces, indicating that the PEMs negatively affected hMSC proliferation. Both the long and short time period results did not correlate to any of the roughness and surface energy trends, indicating more complex interactions between the cells and the surface relating to charge distribution and functional group density.

Biological Activation of Bioinert Medical High-Performance Oxide Ceramics by Hydrolytically Stable Immobilization of c(RGDyK) and BMP-2

High-performance oxide ceramics (HPOC), such as alumina, zirconia, and dispersion ceramics thereof are successfully used as articulating components in joint arthroplasty. HPOC exhibit excellent wear resistance, high strength, and cytocompatible behavior; however, they lack sufficient tissue bonding capability. Thus, they are primarily deployed as low-wear-bearing articulating components in arthroplasty without direct tissue contact, although proper cellular stimulation would hold significant advantages. Here, we describe a surface modification approach for HPOC, enabling hydrolytically stable interfacial binding of c(RGDyK) peptides and BMP-2 proteins to significantly improve the adhesion and osteogenic differentiation of human mesenchymal stem cells (hMSCs) without altering the mechanical properties of the underlying ceramic substrates. Analyses of cellular attachment of murine fibroblasts (L929), human alveolar basal epithelial cells (A549), hMSCs on c(RGDyK), and osteogenic differentiation of hMSCs on BMP-2-coated interfaces demonstrate significant improvements of cell adhesion and an enhanced osteogenic differentiation potential in vitro. The presented approach provides a strategy for the development of a novel class of bioactive HPOC with osseointegration potential that could lead to novel therapeutic solutions for biomedical applications. Furthermore, the developed surface modification is designed in a way to be readily translated to other medically employed bioinert materials in the future.