Mechanical strain enhances extracellular matrix-induced gene focusing and promotes osteogenic differentiation of human mesenchymal stem cells through an extracellular-related kinase-dependent pathway

Hydrogels with Reversible Crosslinks for Improved Localised Stem Cell Retention: A Review

Successful stem cell applications could have a significant impact on the medical field, where many lives are at stake. However, the translation of stem cells to the clinic could be improved by overcoming challenges in stem cell transplantation and in vivo retention at the site of tissue damage. This review aims to showcase the most recent insights into developing hydrogels that can deliver, retain, and accommodate stem cells for tissue repair. Hydrogels can be used for tissue engineering, as their flexibility and water content makes them excellent substitutes for the native extracellular matrix. Moreover, the mechanical properties of hydrogels are highly tuneable, and recognition moieties to control cell behaviour and fate can quickly be introduced. This review covers the parameters necessary for the physicochemical design of adaptable hydrogels, the variety of (bio)materials that can be used in such hydrogels, their application in stem cell delivery and some recently developed chemistries for reversible crosslinking. Implementing physical and dynamic covalent chemistry has resulted in adaptable hydrogels that can mimic the dynamic nature of the extracellular matrix.

Adipose and Bone Marrow Derived-Mesenchymal Stromal Cells Express Similar Tenogenic Expression Levels when Subjected to Mechanical Uniaxial Stretching In Vitro

The present study was conducted to determine whether adipose derived mesenchymal stromal cells (AD-MSCs) or bone marrow derived-MSCs (BM-MSCs) would provide superior tenogenic expressions when subjected to cyclical tensile loading. The results for this would indicate the best choice of MSCs source to be used for cell-based tendon repair strategies. Both AD-MSCs and BM-MSCs were obtained from ten adult donors (N = 10) and cultured in vitro. At passaged-2, cells from both groups were subjected to cyclical stretching at 1 Hz and 8% of strain. Cellular morphology, orientation, proliferation rate, protein, and gene expression levels were compared at 0, 24, and 48 hours of stretching. In both groups, mechanical stretching results in similar morphological changes, and the redirection of cell alignment is perpendicular to the direction of stretching. Loading at 8% strain did not significantly increase proliferation rates but caused an increase in total collagen expression and tenogenic gene expression levels. In both groups, these levels demonstrated no significant differences suggesting that in a similar loading environment, both cell types possess similar tenogenic potential. In conclusion, AD-MSCs and BM-MSCs both demonstrate similar tenogenic phenotypic and gene expression levels when subjected to cyclic tensile loading at 1 Hz and 8% strain, thus, suggesting that the use of either cell source may be suitable for tendon repair.

Changes in interstitial fluid flow, mass transport and the bone cell response in microgravity and normogravity

In recent years, our scientific interest in spaceflight has grown exponentially and resulted in a thriving area of research, with hundreds of astronauts spending months of their time in space. A recent shift toward pursuing territories farther afield, aiming at near-Earth asteroids, the Moon, and Mars combined with the anticipated availability of commercial flights to space in the near future, warrants continued understanding of the human physiological processes and response mechanisms when in this extreme environment. Acute skeletal loss, more severe than any bone loss seen on Earth, has significant implications for deep space exploration, and it remains elusive as to why there is such a magnitude of difference between bone loss on Earth and loss in microgravity. The removal of gravity eliminates a critical primary mechano-stimulus, and when combined with exposure to both galactic and solar cosmic radiation, healthy human tissue function can be negatively affected. An additional effect found in microgravity, and one with limited insight, involves changes in dynamic fluid flow. Fluids provide the most fundamental way to transport chemical and biochemical elements within our bodies and apply an essential mechano-stimulus to cells. Furthermore, the cell cytoplasm is not a simple liquid, and fluid transport phenomena together with viscoelastic deformation of the cytoskeleton play key roles in cell function. In microgravity, flow behavior changes drastically, and the impact on cells within the porous system of bone and the influence of an expanding level of adiposity are not well understood. This review explores the role of interstitial fluid motion and solute transport in porous bone under two different conditions: normogravity and microgravity.

Early committed polarization of intracellular tension in response to cell shape determines the osteogenic differentiation of mesenchymal stromal cells

Within the heterogeneous tissue architecture, a comprehensive understanding of how cell shapes regulate cytoskeletal mechanics by adjusting focal adhesions (FAs) signals to correlate with the lineage commitment of mesenchymal stromal cells (MSCs) remains obscure. Here, via engineered extracellular matrices, we observed that the development of mature FAs, coupled with a symmetrical pattern of radial fiber bundles, appeared at the right-angle vertices in cells with square shape. While circular cells aligned the transverse fibers parallel to the cell edge, and moved them centripetally in a counter-clockwise direction, symmetrical bundles of radial fibers at the vertices of square cells disrupted the counter-clockwise swirling and bridged the transverse fibers to move centripetally. In square cells, the contractile force, generated by the myosin IIA-enriched transverse fibers, were concentrated and transmitted outwards along the symmetrical bundles of radial fibers, to the extracellular matrix through FAs, and thereby driving FA organization and maturation. The symmetrical radial fiber bundles concentrated the transverse fibers contractility inward to the linkage between the actin cytoskeleton and the nuclear envelope. The tauter cytoskeletal network adjusted the nuclear-actomyosin force balance to cause nuclear deformability and to increase nuclear translocation of the transcription co-activator YAP, which in turn modulated the switch in MSC commitment. Thus, FAs dynamically respond to geometric cues and remodel actin cytoskeletal network to re-distribute intracelluar tension towards the cell nucleus, and thereby controlling YAP mechanotransduction signaling in regulating MSC fate decision. STATEMENT OF SIGNIFICANCE: We decipher how cellular mechanics is self-organized depending on extracellular geometric features to correlate with mesenchymal stromal cell lineage commitment. In response to geometry constrains on cell morphology, symmetrical radial fiber bundles are assembled and clustered depending on the maturation state of focal adhesions and bridge with the transverse fibers, and thereby establishing the dynamic cytoskeletal network. Contractile force, generated by the myosin-IIA-enriched transverse fibers, is transmitted and dynamically drives the retrograde movement of the actin cytoskeletal network, which appropriately adjusts the nuclear-actomyosin force balance and deforms the cell nucleus for YAP mechano-transduction signaling in regulating mesenchymal stromal cell fate decision.

Mechanical Static Force Negatively Regulates Vitality and Early Skeletal Development in Zebrafish Embryos

Skeletal system development and remodelling is regulated by several different factors, including hormones, cytokines, and mechanical forces. It is known that gravity and pressure stimulate mechanosensors on bone cells which transduce mechanical signals to chemical ones. Nevertheless, few data have been provided about the role of mechanical forces on embryo osteogenesis in vivo. Since the zebrafish is an elective model for developmental studies, in particular on bone formation and tissue mineralization, we analyzed in vivo the effects of a static mechanical force generated by a water column on fertilized zebrafish eggs. The results have shown that an increase in the hydrostatic pressure (HP) of up to 5.9% was lethal for 100% of treated embryos at 48 h post fertilization (hpf). A small decrease in length (−2%) and 49% mortality were found in the +4.4% HP embryos compared with the controls. To analyze skeletal development, we evaluated the number of mineralized vertebral bodies in the trunk at five days post fertilization. The embryos grown under +2.4% HP showed a physiological intramembranous mineralization of vertebral bodies whereas the embryos which grew with +3.4% HP showed a significant decrease in mineralization rate (−54%). Morphological analysis of cartilage and bones in embryos at +3.4% HP revealed a delay of both intramembranous and chondrogenic mineralization, respectively, in axial and head bones, whereas the chondrogenesis appeared normal. These data suggested that developing osteoblasts and different mineralization programs are sensitive to mechanical pressure when applied to early embryogenesis.

Enhancement of Bone Regeneration Through the Converse Piezoelectric Effect, A Novel Approach for Applying Mechanical Stimulation

Serious bone injuries have devastating effects on the lives of patients including limiting working ability and high cost. Orthopedic implants can aid in healing injuries to an extent that exceeds the natural regenerative capabilities of bone to repair fractures or large bone defects. Autografts and allografts are the standard implants used, but disadvantages such as donor site complications, a limited quantity of transplantable bone, and high costs have led to an increased demand for synthetic bone graft substitutes. However, replicating the complex physiological properties of biological bone, much less recapitulating its complex tissue functions, is challenging. Extensive efforts to design biocompatible implants that mimic the natural healing processes in bone have led to the investigation of piezoelectric smart materials because the bone has natural piezoelectric properties. Piezoelectric materials facilitate bone regeneration either by accumulating electric charge in response to mechanical stress, which mimics bioelectric signals through the direct piezoelectric effect or by providing mechanical stimulation in response to electrical stimulation through the converse piezoelectric effect. Although both effects are beneficial, the converse piezoelectric effect can address bone atrophy from stress shielding and immobility by improving the mechanical response of a healing defect. Mechanical stimulation has a positive impact on bone regeneration by activating cellular pathways that increase bone formation and decrease bone resorption. This review will highlight the potential of the converse piezoelectric effect to enhance bone regeneration by discussing the activation of beneficial cellular pathways, the properties of piezoelectric biomaterials, and the potential for the more effective administration of the converse piezoelectric effect using wireless control.

Regulation of stem cell fate using nanostructure-mediated physical signals

One of the major issues in tissue engineering is regulation of stem cell differentiation toward specific lineages. Unlike biological and chemical signals, physical signals with adjustable properties can be applied to stem cells in a timely and localized manner, thus making them a hot topic for research in the fields of biomaterials, tissue engineering, and cell biology. According to the signals sensed by cells, physical signals used for regulating stem cell fate can be classified into six categories: mechanical, light, thermal, electrical, acoustic, and magnetic. In most cases, external macroscopic physical fields cannot be used to modulate stem cell fate, as only the localized physical signals accepted by the surface receptors can regulate stem cell differentiation via nanoscale fibrin polysaccharide fibers. However, surface receptors related to certain kinds of physical signals are still unknown. Recently, significant progress has been made in the development of functional materials for energy conversion. Consequently, localized physical fields can be produced by absorbing energy from an external physical field and subsequently releasing another type of localized energy through functional nanostructures. Based on the above concepts, we propose a methodology that can be utilized for stem cell engineering and for the regulation of stem cell fate via nanostructure-mediated physical signals. In this review, the combined effect of various approaches and mechanisms of physical signals provides a perspective on stem cell fate promotion by nanostructure-mediated physical signals. We expect that this review will aid the development of remote-controlled and wireless platforms to physically guide stem cell differentiation both in vitro and in vivo, using optimized stimulation parameters and mechanistic investigations while driving the progress of research in the fields of materials science, cell biology, and clinical research.

Identification osteogenic signaling pathways following mechanical stimulation: A systematic review

INTRODUCTION

It has been shown that mechanical forces can induce or promote osteogenic differentiation as well as remodeling of the new created bone tissues. To apply this characteristic in bone tissue engineering, it is important to know which mechanical stimuli through which signaling pathway has a more significant impact on osteogenesis.

METHODS

In this systematic study, an electronic search was conducted using PubMed and Google Scholar databases. This study has been prepared and organized according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Included studies were first categorized according to the in vivo and in vitro studies.

RESULTS

Six types of mechanical stresses were used in these articles and the most commonly used mechanical force and cell source were tension and bone marrow-derived mesenchymal stem cells (BMMSCs), respectively. These forces were able to trigger twelve signaling pathways in which Wnt pathway was so prominent.

CONCLUSION

1) Although specific signaling pathways are induced through specific mechanical forces, Wnt signaling pathways are predominantly activated by almost all types of force/stimulation, 2) All signaling pathways regulate expression of RUNX2, which is known as a master regulator of osteogenesis, 3) In Tension force, the mode of force administration, i.e, continuous or non-continuous tension is more important than the percentage of elongation.

Mechanical loading and the control of stem cell behavior

OBJECTIVE

Mechanical stimulation regulates many cell responses. The present study describes the effects of different in vitro mechanical stimulation approaches on stem cell behavior.

DESIGN

The narrative review approach was performed. The articles published in English language that addressed the effects of mechanical force on stem cells were searched on Pubmed and Scopus database. The effects of extrinsic mechanical force on stem cell response was reviewed and discussed.

RESULTS

Cells sense mechanical stimuli by the function of mechanoreceptors and further transduce force stimulation into intracellular signaling. Cell responses to mechanical stimuli depend on several factors including type, magnitude, and duration. Further, similar mechanical stimuli exhibit distinct cell responses based on numerous factors including cell type and differentiation stage. Various mechanical applications modulate stemness maintenance and cell differentiation toward specific lineages.

CONCLUSIONS

Mechanical force application modulates stemness maintenance and differentiation. Modification of force regimens could be utilized to precisely control appropriate stem cell behavior toward specific applications.

Sensory nerves in the spotlight of the stem cell niche

Niches are specialized tissue microenvironments that control stem cells functioning. The bone marrow mesenchymal stem cell niche defines a location within the marrow in which mesenchymal stem cells are retained and produce new cells throughout life. Deciphering the signaling mechanisms by which the niche regulates stem cell fate will facilitate the use of these cells for therapy. Recent studies, by using state-of-the-art methodologies, including sophisticated in vivo inducible genetic techniques, such as lineage-tracing Cre/loxP mediated systems, in combination with pharmacological inhibition, provide evidence that sensory neuron is an important component of the bone marrow mesenchymal stem cell niche. Strikingly, knockout of a specific receptor in sensory neurons blocked stem cell function in the bone marrow. The knowledge arising from these discoveries will be crucial for stem cell manipulation in the future. Here, we review recent progress in our understanding of sensory nerves biology in the stem cell niche.

Molecular and Mechanobiological Pathways Related to the Physiopathology of FPLD2

Laminopathies are rare and heterogeneous diseases affecting one to almost all tissues, as in Progeria, and sharing certain features such as metabolic disorders and a predisposition to atherosclerotic cardiovascular diseases. These two features are the main characteristics of the adipose tissue-specific laminopathy called familial partial lipodystrophy type 2 (FPLD2). The only gene that is involved in FPLD2 physiopathology is the LMNA gene, with at least 20 mutations that are considered pathogenic. LMNA encodes the type V intermediate filament lamin A/C, which is incorporated into the lamina meshwork lining the inner membrane of the nuclear envelope. Lamin A/C is involved in the regulation of cellular mechanical properties through the control of nuclear rigidity and deformability, gene modulation and chromatin organization. While recent studies have described new potential signaling pathways dependent on lamin A/C and associated with FPLD2 physiopathology, the whole picture of how the syndrome develops remains unknown. In this review, we summarize the signaling pathways involving lamin A/C that are associated with the progression of FPLD2. We also explore the links between alterations of the cellular mechanical properties and FPLD2 physiopathology. Finally, we introduce potential tools based on the exploration of cellular mechanical properties that could be redirected for FPLD2 diagnosis.

Mechanomics analysis of hESCs under combined mechanical shear, stretch, and compression

Human embryonic stem cells (hESCs) can differentiate to three germ layers within biochemical and biomechanical niches. The complicated mechanical environments in vivo could have diverse effects on the fate decision and biological functions of hESCs. To globally screen mechanosensitive molecules, three typical types of mechanical stimuli, i.e., tensile stretch, shear flow, and mechanical compression, were applied in respective parameter sets of loading pattern, amplitude, frequency, and/or duration, and then, iTRAQ proteomics test was used for identifying and quantifying differentially expressed proteins in hESCs. Bioinformatics analysis identified 37, 41, and 23 proteins under stretch pattern, frequency, and duration, 13, 18, and 41 proteins under shear pattern, amplitude, and duration, and 4, 0, and 183 proteins under compression amplitude, frequency, and duration, respectively, where distinct parameters yielded the differentially weighted preferences under each stimulus. Ten mechanosensitive proteins were commonly shared between two of three mechanical stimuli, together with numerous proteins identified under single stimulus. More importantly, functional GSEA and WGCNA analyses elaborated the variations of the screened proteins with loading parameters. Common functions in protein synthesis and modification were identified among three stimuli, and specific functions were observed in skin development under stretch alone. In conclusion, mechanomics analysis is indispensable to map actual mechanosensitive proteins under physiologically mimicking mechanical environment, and sheds light on understanding the core hub proteins in mechanobiology.

Mechanotransduction in osteogenesis

Bone is one of the most highly adaptive tissues in the body, possessing the capability to alter its morphology and function in response to stimuli in its surrounding environment. The ability of bone to sense and convert external mechanical stimuli into a biochemical response, which ultimately alters the phenotype and function of the cell, is described as mechanotransduction. This review aims to describe the fundamental physiology and biomechanisms that occur to induce osteogenic adaptation of a cell following application of a physical stimulus. Considerable developments have been made in recent years in our understanding of how cells orchestrate this complex interplay of processes, and have become the focus of research in osteogenesis. We will discuss current areas of preclinical and clinical research exploring the harnessing of mechanotransductive properties of cells and applying them therapeutically, both in the context of fracture healing and de novo bone formation in situations such as nonunion.

Cite this article: Bone Joint Res 2019;9(1):1–14.

Effects of Electrical Stimulation on Stem Cells

Recent interest in developing new regenerative medicine- and tissue engineering-based treatments has motivated researchers to develop strategies for manipulating stem cells to optimize outcomes in these potentially, game-changing treatments. Cells communicate with each other, and with their surrounding tissues and organs via electrochemical signals. These signals originate from ions passing back and forth through cell membranes and play a key role in regulating cell function during embryonic development, healing, and regeneration. To study the effects of electrical signals on cell function, investigators have exposed cells to exogenous electrical stimulation and have been able to increase, decrease and entirely block cell proliferation, differentiation, migration, alignment, and adherence to scaffold materials. In this review, we discuss research focused on the use of electrical stimulation to manipulate stem cell function with a focus on its incorporation in tissue engineering-based treatments.

YAP as a key regulator of adipo-osteogenic differentiation in human MSCs

Background

Mesenchymal stem cells (MSCs) are multipotent stem cells that are able to differentiate into several cell types, including cartilage, fat, and bone. As a common progenitor, MSC differentiation has to be tightly regulated to maintain the balance of their differentiation commitment. It has been reported that the decision process of MSCs into fat and bone cells is competing and reciprocal. Several factors have been suggested as critical factors that affect adipo-osteogenic decision, including melatonin and smad4. Yes-associated protein (YAP) is an important effector protein in the Hippo signaling pathway that acts as a transcriptional regulator by activating the transcription of the genes involved in cell proliferation and anti-apoptosis. The non-canonical role of YAP in regulating bone homeostasis by promoting osteogenesis and suppressing adipogenesis was recently demonstrated in a mouse model. However, it is unclear whether YAP is also crucial for modulating human MSC differentiation to fat and bone.

Methods

The expression level of YAP during MSC differentiation was modulated using pharmaceutical molecule and genetic experiments through gain- and loss-of-function approaches.

Results

We demonstrated for the first time that YAP has a non-canonical role in regulating the balance of adipo-osteogenic differentiation of human MSCs. The result from synchrotron radiation-based Fourier transform infrared (FTIR) microspectroscopy showed unique metabolic fingerprints generated from YAP-targeted differentiated cells that were clearly distinguished from non-manipulated control.

Conclusions

These results, thus, identify YAP as an important effector protein that regulates human MSC differentiation to fat and bone and suggests the use of FTIR microspectroscopy as a promising technique in stem cell research.

Substrate Strain Mitigates Effects of β-Aminopropionitrile-Induced Reduction in Enzymatic Crosslinking

Enzymatic crosslinks stabilize type I collagen and are catalyzed by lysyl oxidase (LOX), a step interrupted through β-aminopropionitrile (BAPN) exposure. This study evaluated dose-dependent effects of BAPN on osteoblast gene expression of type I collagen, LOX, and genes associated with crosslink formation. The second objective was to characterize collagen produced in vitro after exposure to BAPN, and to explore changes to collagen properties under continuous cyclical substrate strain. To evaluate dose-dependent effects, osteoblasts were exposed to a range of BAPN dosages (0-10 mM) for gene expression analysis and cell proliferation. Results showed significant upregulation of BMP-1, POST, and COL1A1 and change in cell proliferation. Results also showed that while the gene encoding LOX was unaffected by BAPN treatment, other genes related to LOX activation and matrix production were upregulated. For the loading study, the combined effects of BAPN and mechanical loading were assessed. Gene expression was quantified, atomic force microscopy was used to extract elastic properties of the collagen matrix, and Fourier Transform infrared spectroscopy was used to assess collagen secondary structure for enzymatic crosslinking analysis. BAPN upregulated BMP-1 in static samples and BAPN combined with mechanical loading downregulated LOX when compared to control-static samples. Results showed a higher indentation modulus in BAPN-loaded samples compared to control-loaded samples. Loading increased the mature-to-immature crosslink ratios in control samples, and BAPN increased the height ratio in static samples. In summary, effects of BAPN (upregulation of genes involved in crosslinking, mature/immature crosslinking ratios, upward trend in collagen elasticity) were mitigated by mechanical loading.

Shape-dependent regulation of differentiation lineages of bone marrow-derived cells under cyclic stretch

Multipotent stem cells are considered as a key material in regenerative medicine, and the understanding of the heterogeneity in the differentiation potentials of bone marrow-derived cells is important in the successful regenerative tissue repair. Therefore, the present study has been performed to investigate how the differentiation of post-harvest, native bone marrow-derived cells is regulated by cyclic stretch in vitro. Bone marrow-derived cells were obtained from mouse femur of both hind limbs and categorized into the following five categories: amebocytes, round cells, spindle cells, stellate cells and others. The cells were seeded on a silicone-made stretch chamber, and subjected to cyclic stretch with an amplitude of 10% at a frequency of 1 Hz for 7 days for cell shape analysis and for 3 days for the analysis of the expression of marker proteins of osteogenic (osteocalcin), vascular smooth muscle (α-smooth muscle actin and smooth muscle myosin heavy chain) and neurogenic (neurofilament) differentiation. When disregarding the differences in the cell shapes, there was an overall trend that the application of 10% cyclic stretch inhibited osteogenic and neurogenic differentiation, but enhanced smooth muscle differentiation. Close examinations revealed that round cells were influenced the most by cyclic stretch (significant up- or down-regulation in all the four marker protein expressions) while amebocytes and spindle cells were only influenced by cyclic stretch for vascular smooth muscle and/or neurogenic differentiation. As far as the authors know, this is the first study reporting the shape-related differences in the fate decision criteria for mechanical strain in bone marrow-derived cells.

Subcellular Control over Focal Adhesion Anisotropy, Independent of Cell Morphology, Dictates Stem Cell Fate

Although microscale patterning techniques have been used to control cell morphology and shape, they only provide indirect control over the formation of the subcellular cytoskeletal elements that determine contractility. This paper addresses the hypotheses that nanoscale anisotropic features of a patterned matrix can direct the alignment of internal cytoskeletal actin fibers within a confined shape with an unbiased aspect ratio, and that this enhanced control over cytoskeletal architecture directs programmed cell behaviors. Here, large-area polymer pen lithography is used to pattern substrates with nanoscale extracellular matrix protein features and to identify cues that can be used to direct cytoskeletal organization in human mesenchymal stem cells. This nanopatterning approach is used to identify how anisotropic focal adhesions around the periphery of symmetric patterns yield an organized and contractile actin cytoskeleton. This work reports the important finding that anisotropic cues that increase cell contractility within a circular shape redirect cell differentiation from an adipogenic to an osteogenic fate. Together, these experiments introduce a programmable approach for using subcellular spatial cues to control cell behavior within defined geometries.

Polypeptide Thermogels as Three-Dimensional Scaffolds for Cells

BACKGROUND

Thermogel is an aqueous solution that exhibits a sol-to-gel transition as the temperature increases. Stem cells, growth factors, and differentiating factors can be incorporated in situ in the matrix during the sol-to-gel transition, leading to the formation of a three-dimensional (3D) cell-culture scaffold.

METHODS

The uses of thermogelling polypeptides, such as collagen, Matrigel™, elastin-like polypeptides, and synthetic polypeptides, as 3D scaffolds of cells, are summarized in this paper.

RESULTS

The timely supply of growth factors to the cells, cell survival, and metabolite removal is to be insured in the cell culture matrix. Various growth factors were incorporated in the matrix during the sol-to-gel transition of the thermogelling polypeptide aqueous solutions, and preferential differentiation of the incorporated stem cells into specific target cells were investigated. In addition, modulus of the matrix was controlled by post-crosslinking reactions of thermogels or employing composite systems. Chemical functional groups as well as biological factors were selected appropriately for targeted differentiation of the incorporated stem cells.

CONCLUSION

In addition to all the advantages of thermogels including mild conditions for cell-incorporation and controlled supplies of the growth factors, polypeptide thermogels provide neutral pH environments to the cells during the degradation of the gel. Polypeptide thermogels as an injectable scaffold can be a promising system for their eventual in vivo applications in stem cell therapy.

Intramyocardial angiogenetic stem cells and epicardial erythropoietin save the acute ischemic heart

Ischemic heart failure is the leading cause of mortality worldwide. An early boost of intracardiac regenerative key mechanisms and angiogenetic niche signaling in cardiac mesenchymal stem cells (MSCs) could improve myocardial infarction (MI) healing. Epicardial erythropoietin (EPO; 300 U kg^-1) was compared with intraperitoneal and intramyocardial EPO treatments after acute MI in rats (n=156). Real-time PCR and confocal microscopy revealed that epicardial EPO treatment enhanced levels of intracardiac regenerative key indicators (SDF-1, CXCR4, CD34, Bcl-2, cyclin D1, Cdc2 and MMP2), induced transforming growth factor β (TGF-β)/WNT signaling in intramyocardial MSC niches through the direct activation of AKT and upregulation of upstream signals FOS and Fzd7, and augmented intracardiac mesenchymal proliferation 24 h after MI. Cardiac catheterization and tissue analysis showed superior cardiac functions, beneficial remodeling and increased capillary density 6 weeks after MI. Concomitant fluorescence-activated cell sorting, co-cultures with neonatal cardiomyocytes, angiogenesis assays, ELISA, western blotting and RAMAN spectroscopy demonstrated that EPO could promote cardiomyogenic differentiation that was specific of tissue origin and enhance paracrine angiogenetic activity in cardiac CD45^-CD44⁺DDR2⁺ MSCs. Epicardial EPO delivery might be the optimal route for efficient upregulation of regenerative key signals after acute MI. Early EPO-mediated stimulation of mesenchymal proliferation, synergistic angiogenesis with cardiac MSCs and direct induction of TGF-β/WNT signaling in intramyocardial cardiac MSCs could initiate an accelerated healing process that enhances cardiac recovery.

3D uniaxial mechanical stimulation induces tenogenic differentiation of tendon-derived stem cells through a PI3K/AKT signaling pathway

The tendon is a mechanosensitive tissue, but little is known about how mechanical stimulation selectively signals tenogenic differentiation and neo-tendon formation. In this study, we compared the impact of uniaxial and biaxial mechanical loading on tendon-derived stem cells (TDSCs). Our data show that there are variations in cell signaling and cell differentiation of mouse TDSCs in response to uniaxial and biaxial loading in monolayer culture. Whereas uniaxial loading induced TDSCs toward tenogenic and osteogenic differentiation, biaxial loading induced osteogenic, adipogenic, and chondrogenic differentiation of TDSCs. Furthermore, by applying uniaxial loading on 3-dimensional (3D) TDSC constructs, tenogenic-specific differentiation and neo-tendon formation were observed, results that were replicated in human TDSCs. We also showed that uniaxial loading induced PKB (AKT) phosphorylation (pAKT), whereas biaxial loading induced pERK. Most importantly, we found that inhibition of the PI3K/AKT signaling pathway could attenuate tenogenic differentiation and tendon formation in 3D TDSC constructs subjected to uniaxial loading. Taken together, our study highlights the importance of appropriate mechanobiological stimulation in 3D cell niches on tendon-like tissue formation and demonstrates that uniaxial mechanical loading plays an essential role in tenogenic differentiation and tendon formation by activating the PI3K/AKT signaling pathway.-Wang, T., Thien, C., Wang, C., Ni, M., Gao, J., Wang, A., Jiang, Q., Tuan, R. S., Zheng, Q., Zheng, M. H. 3D uniaxial mechanical stimulation induces tenogenic differentiation of tendon-derived stem cells through a PI3K/AKT signaling pathway.

Engineering of an angiogenic niche by perfusion culture of adipose-derived stromal vascular fraction cells

In vitro recapitulation of an organotypic stromal environment, enabling efficient angiogenesis, is crucial to investigate and possibly improve vascularization in regenerative medicine. Our study aims at engineering the complexity of a vascular milieu including multiple cell-types, a stromal extracellular matrix (ECM), and molecular signals. For this purpose, the human adipose stromal vascular fraction (SVF), composed of a heterogeneous mix of pericytes, endothelial/stromal progenitor cells, was cultured under direct perfusion flow on three-dimensional (3D) collagen scaffolds. Perfusion culture of SVF-cells reproducibly promoted in vitro the early formation of a capillary-like network, embedded within an ECM backbone, and the release of numerous pro-angiogenic factors. Compared to static cultures, perfusion-based engineered constructs were more rapidly vascularized and supported a superior survival of delivered cells upon in vivo ectopic implantation. This was likely mediated by pericytes, whose number was significantly higher (4.5-fold) under perfusion and whose targeted depletion resulted in lower efficiency of vascularization, with an increased host foreign body reaction. 3D-perfusion culture of SVF-cells leads to the engineering of a specialized milieu, here defined as an angiogenic niche. This system could serve as a model to investigate multi-cellular interactions in angiogenesis, and as a module supporting increased grafted cell survival in regenerative medicine.

Electrical control of calcium oscillations in mesenchymal stem cells using microsecond pulsed electric fields

BACKGROUND

Human mesenchymal stem cells are promising tools for regenerative medicine due to their ability to differentiate into many cellular types such as osteocytes, chondrocytes and adipocytes amongst many other cell types. These cells present spontaneous calcium oscillations implicating calcium channels and pumps of the plasma membrane and the endoplasmic reticulum. These oscillations regulate many basic functions in the cell such as proliferation and differentiation. Therefore, the possibility to mimic or regulate these oscillations might be useful to regulate mesenchymal stem cells biological functions.

METHODS

One or several electric pulses of 100 μs were used to induce Ca2+ spikes caused by the penetration of Ca2+ from the extracellular medium, through the transiently electropermeabilized plasma membrane, in human adipose mesenchymal stem cells from several donors. Attached cells were preloaded with Fluo-4 AM and exposed to the electric pulse(s) under the fluorescence microscope. Viability was also checked.

RESULTS

According to the pulse(s) electric field amplitude, it is possible to generate a supplementary calcium spike with properties close to those of calcium spontaneous oscillations, or, on the contrary, to inhibit the spontaneous calcium oscillations for a very long time compared to the pulse duration. Through that inhibition of the oscillations, Ca2+ oscillations of desired amplitude and frequency could then be imposed on the cells using subsequent electric pulses. None of the pulses used here, even those with the highest amplitude, caused a loss of cell viability.

CONCLUSIONS

An easy way to control Ca2+ oscillations in mesenchymal stem cells, through their cancellation or the addition of supplementary Ca2+ spikes, is reported here. Indeed, the direct link between the microsecond electric pulse(s) delivery and the occurrence/cancellation of cytosolic Ca2+ spikes allowed us to mimic and regulate the Ca2+ oscillations in these cells. Since microsecond electric pulse delivery constitutes a simple technology available in many laboratories, this new tool might be useful to further investigate the role of Ca2+ in human mesenchymal stem cells biological processes such as proliferation and differentiation.

The extracellular microscape governs mesenchymal stem cell fate

Each cell forever interacts with its extracellular matrix (ECM); a stem cell relies on this interaction to guide differentiation. The stiffness, nanotopography, protein composition, stress and strain inherent to any given ECM influences stem cell lineage commitment. This interaction is dynamic, multidimensional and reciprocally evolving through time, and from this concerted exchange the macroscopic tissues that comprise living organisms are formed. Mesenchymal stem cells can give rise to bone, cartilage, tendon and muscle; thus attempts to manipulate their differentiation must heed the physical properties of incredibly complex native microenvironments to realize regenerative goals.

Synchrotron FTIR microspectroscopy reveals early adipogenic differentiation of human mesenchymal stem cells at single-cell level

Human mesenchymal stem cells (hMSCs) have been used as an ideal in vitro model to study human adipogenesis. However, little knowledge of the early stage differentiation greatly hinders our understanding on the mechanism of the adipogenesis processes. In this study, synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy was applied to track the global structural and compositional changes of lipids, proteins and nucleic acids inside individual hMSCs along the time course. The multivariate analysis of the SR-FTIR spectra distinguished the dynamic and significant changes of the lipids and nucleic acid at early differentiation stage. Importantly, changes of lipid structure during early days (Day 1-3) of differentiation might serve as a potential biomarker in identifying the state in early differentiation at single cell level. These results proved that SR-FTIR is a powerful tool to study the stem cell fate determination and early lipogenesis events.

Canonical FGFs Prevent Osteogenic Lineage Commitment and Differentiation of Human Bone Marrow Stromal Cells Via ERK1/2 Signaling

Controlling the adipo-osteogenic lineage decision of trabecular human bone marrow stromal cells (hBMSCs) in favor of osteogenesis represents a promising approach for osteoporosis therapy and prevention. Previously, Fibroblast Growth Factor 1 (FGF1) and its subfamily member FGF2 were scored as leading candidates to exercise control over skeletal precursor commitment and lineage decision albeit literature results are highly inconsistent. We show here that FGF1 and 2 strongly prevent the osteogenic commitment and differentiation of hBMSCs. Mineralization of extracellular matrix (ECM) and mRNA expression of osteogenic marker genes Alkaline Phosphatase (ALP), Collagen 1A1 (COL1A1), and Integrin-Binding Sialoprotein (IBSP) were significantly reduced. Furthermore, master regulators of osteogenic commitment like Runt-Related Transcription Factor 2 (RUNX2) and Bone Morphogenetic Protein 4 (BMP4) were downregulated. When administered under adipogenic culture conditions, canonical FGFs did not support osteogenic marker expression. Moreover despite the presence of osteogenic differentiation factors, FGFs even disabled the pro-osteogenic lineage decision of pre-differentiated adipocytic cells. In contrast to FGF Receptor 2 (FGFR2), FGFR1 was stably expressed throughout osteogenic and adipogenic differentiation and FGF addition. Moreover, FGFR1 and Extracellular Signal-Regulated Kinases 1 and 2 (ERK1/2) were found to be responsible for underlying signal transduction using respective inhibitors. Taken together, we present new findings indicating that canonical FGFR-ERK1/2 signaling entrapped hBMSCs in a pre-committed state and arrested further maturation of committed precursors. Our results might aid in unraveling and controlling check points relevant for ageing-associated aberrant adipogenesis with consequences for the treatment of degenerative diseases such as osteoporosis and for skeletal tissue engineering strategies. J. Cell. Biochem. 118: 263-275, 2017. © 2016 Wiley Periodicals, Inc.

Use of nanoscale mechanical stimulation for control and manipulation of cell behaviour

The ability to control cell behaviour, cell fate and simulate reliable tissue models in vitro remains a significant challenge yet is crucial for various applications of high throughput screening e.g. drug discovery. Mechanotransduction (the ability of cells to convert mechanical forces in their environment to biochemical signalling) represents an alternative mechanism to attain this control with such studies developing techniques to reproducibly control the mechanical environment in techniques which have potential to be scaled. In this review, the use of techniques such as finite element modelling and precision interferometric measurement are examined to provide context for a novel technique based on nanoscale vibration, also known as "nanokicking". Studies have shown this stimulus to alter cellular responses in both endothelial and mesenchymal stem cells (MSCs), particularly in increased proliferation rate and induced osteogenesis respectively. Endothelial cell lines were exposed to nanoscale vibration amplitudes across a frequency range of 1-100 Hz, and MSCs primarily at 1 kHz. This technique provides significant potential benefits over existing technologies, as cellular responses can be initiated without the use of expensive engineering techniques and/or chemical induction factors. Due to the reproducible and scalable nature of the apparatus it is conceivable that nanokicking could be used for controlling cell behaviour within a wide array of high throughput procedures in the research environment, within drug discovery, and for clinical/therapeutic applications.

STATEMENT OF SIGNIFICANCE

The results discussed within this article summarise the potential benefits of using nanoscale vibration protocols for controlling cell behaviour. There is a significant need for reliable tissue models within the clinical and pharma industries, and the control of cell behaviour and stem cell differentiation would be highly beneficial. The full potential of this method of controlling cell behaviour has not yet been realised.

Optimisation of conductive polymer biomaterials for cardiac progenitor cells

The characterisation of biomaterials for cardiac tissue engineering applications is vital for the development of effective treatments for the repair of cardiac function.

Clinical Outcome and Glenoid Morphology After Arthroscopic Repair of Chronic Osseous Bankart Lesions: A Five to Eight-Year Follow-up Study

BACKGROUND

Arthroscopic osseous Bankart repair for shoulders with chronic recurrent anterior instability has been reported as an effective procedure with promising short-term outcomes. However, to date, we know of no report describing longer-term outcomes and glenoid morphologic change. The purpose of the present study was to report intermediate to long-term outcomes and glenoid morphologic change after arthroscopic osseous Bankart repair in patients with substantial glenoid bone loss.

METHODS

A consecutive series of eighty-five patients with traumatic anterior glenohumeral instability associated with a chronic osseous Bankart lesion underwent arthroscopic repair from January 2005 through December 2006. Forty-six patients with bone loss of >15% of the inferior glenoid diameter relative to the assumed inferior circle regardless of the fragment size were selected as candidates for this study. Thirty-eight patients (83%), including thirty-four male and four female patients, with a mean age of 23.4 years (range, fifteen to thirty-six years) at the time of surgery, were available for final follow-up at a mean of 6.2 years (range, 5.0 to 8.1 years) after surgery.

RESULTS

One patient had a redislocation during a traffic accident five months after surgery before obtaining an osseous union. The mean Rowe score and the mean Western Ontario Shoulder Instability Index improved significantly from 30.7 points preoperatively to 95.4 points postoperatively and from 26.5% to 81.5%, respectively. Although the mean preoperative fragment size was measured as only 4.7%, the mean glenoid bone loss improved from 20.4% preoperatively to -1.1% postoperatively.

CONCLUSIONS

Arthroscopic osseous Bankart repair is an effective primary treatment for shoulders with substantial glenoid bone loss as it provides successful outcomes without recurrence of instability once osseous union is obtained. Glenoid morphology can be normalized during the intermediate to long-term postoperative period, even in shoulders with a smaller fragment.

MiR-154-5p regulates osteogenic differentiation of adipose-derived mesenchymal stem cells under tensile stress through the Wnt/PCP pathway by targeting Wnt11

Mechanical stress is a well-acknowledged positive regulatory factor for osteogenic differentiation of adipose- derived mesenchymal stem cells (ADSCs). However, the molecular mechanisms associated with micro-RNAs (miRNAs) whereby ADSCs respond to mechanical stimuli remain elusive. We investigated the mechanism of mechanotransduction from the miRNA perspective in the osteogenic differentiation of ADSCs under tensile stress. Microarray analysis showed that miR-154-5p was remarkably downregulated when ADSCs were subjected to mechanical tension. Bioinformatics analysis with luciferase reporter assays demonstrated that Wnt11 3'UTR was a new direct target of miR-154-5p. Under tensile stress, lentivirus-mediated gain- or loss-of-function studies revealed that forced expression of miR-154-5p inhibited osteogenic differentiation of ADSCs, whereas inhibition of endogenous miR-154-5p with its antisense oligonucleotide (ASO-154-5p) obviously promoted osteogenic differentiation. Furthermore, miR-154-5p overexpression decreased activity of the non-canonical Wnt/PCP (RhoA-ROCK) pathway, as indicated by lower expression of Wnt11, active RhoA and ROCKII in miR-154-5p-treated ADSCs. By contrast, miR-154-5p inhibition activated the Wnt/PCP signals. Taken together, these results demonstrate that, under tensile stress, miR-154-5p negatively regulates ADSCs osteogenic differentiation through the Wnt/PCP pathway by directly targeting Wnt11. This novel regulatory pathway provides new insights into the molecular mechanism of mechanotransduction in osteogenic differentiation of ADSCs.

Physical, Spatial, and Molecular Aspects of Extracellular Matrix of In Vivo Niches and Artificial Scaffolds Relevant to Stem Cells Research

Extracellular matrix can influence stem cell choices, such as self-renewal, quiescence, migration, proliferation, phenotype maintenance, differentiation, or apoptosis. Three aspects of extracellular matrix were extensively studied during the last decade: physical properties, spatial presentation of adhesive epitopes, and molecular complexity. Over 15 different parameters have been shown to influence stem cell choices. Physical aspects include stiffness (or elasticity), viscoelasticity, pore size, porosity, amplitude and frequency of static and dynamic deformations applied to the matrix. Spatial aspects include scaffold dimensionality (2D or 3D) and thickness; cell polarity; area, shape, and microscale topography of cell adhesion surface; epitope concentration, epitope clustering characteristics (number of epitopes per cluster, spacing between epitopes within cluster, spacing between separate clusters, cluster patterns, and level of disorder in epitope arrangement), and nanotopography. Biochemical characteristics of natural extracellular matrix molecules regard diversity and structural complexity of matrix molecules, affinity and specificity of epitope interaction with cell receptors, role of non-affinity domains, complexity of supramolecular organization, and co-signaling by growth factors or matrix epitopes. Synergy between several matrix aspects enables stem cells to retain their function in vivo and may be a key to generation of long-term, robust, and effective in vitro stem cell culture systems.

Ligand-Modified Human Serum Albumin Nanoparticles for Enhanced Gene Delivery

The development of nonviral gene delivery systems is a great challenge to enable safe gene therapy. In this study, ligand-modified nanoparticles based on human serum albumin (HSA) were developed and optimized for an efficient gene therapy. Different glutaraldehyde cross-linking degrees were investigated to optimize the HSA nanoparticles for gene delivery. The peptide sequence arginine-glycine-aspartate (RGD) and the HIV-1 transactivator of transduction sequence (Tat) are well-known as promising targeting ligands. Plasmid DNA loaded HSA nanoparticles were covalently modified on their surface with these different ligands. The transfection potential of the obtained plasmid DNA loaded RGD- and Tat-modified nanoparticles was investigated in vitro, and optimal incubation conditions for these preparations were studied. It turned out that Tat-modified HSA nanoparticles with the lowest cross-linking degree of 20% showed the highest transfection potential. Taken together, ligand-functionalized HSA nanoparticles represent promising tools for efficient and safe gene therapy.

Mechanical strain regulates osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells

This study examined the effects of mechanical strain on osteogenic and adipogenic differentiation of cultured MSCs by stimulating MSCs cultured in general and adipogenic differentiation media using a mechanical strain device. Markers of osteogenic (Runx2, Osx, and I-collagen) and adipogenic (PPARγ-2, C/EBPα, and lipid droplets) differentiation were examined using real-time PCR, western blot, immunocytochemical, or histochemical stain analyses. Levels of Runx2 and Osx gradually increased in MSC groups in general medium subject to strain stimulation, as compared with in unstrained groups. After adding the stress signal, I-collagen protein levels of expression were obviously promoted in cells in comparison to the controls. The levels of PPARγ-2 and C/EBPα were decreased, and the emergence of lipid droplets was delayed in MSCs groups in adipogenic differentiation medium subject to strain stimulation, as compared with in unstrained groups. Mechanical strain can promote differentiation of MSCs into osteoblasts and can impede differentiation into adipocytes. These results clarify the mechanisms underlying the effects of exercise on bone repair and reconstruction and provide a more adequate scientific basis for the use of exercise therapy in the treatment of obesity and metabolic osteoporosis.

Promotion of mesenchymal-to-epithelial transition by Rac1 inhibition with small molecules accelerates hepatic differentiation of mesenchymal stromal cells

In vitro differentiation of stem cells into specific cell lineages provides a stable cell supply for cell therapy and tissue engineering. Therefore, understanding the mechanisms underlying such differentiation processes is critical for generating committed lineage-specific cell progenies effectively. We previously developed a two-step protocol to differentiate mesenchymal stromal cells (MSCs) into hepatocyte-like cells. Since hepatic differentiation involves mesenchymal-epithelial transition (MET), we hypothesize that promoting MET could further accelerate the differentiation process. Ras-related C3 botulinum toxin substrate 1 (Rac1) is involved in actin polymerization and its role in MET was investigated in the study. Our results showed that inhibition of Rac1 activation by Rac1-specific inhibitor, NSC23766, led to cells favoring epithelial morphology and being more packed during hepatic differentiation. In addition, Rac1 inhibition accelerated the upregulation of hepatic marker genes accompanied by more mature hepatic functions. Taken together, promotion of MET by inhibiting Rac1 accelerates the hepatic differentiation of MSCs. Our findings open a new prospect of directing the commitment of MSCs by manipulating cell morphology and cytoskeleton arrangement through small molecules. The results provide further insight into scaffold design for rapid production of MSC-differentiated hepatocytes.

Mechanical regulation of mesenchymal stem cell differentiation

Biophysical cues play a key role in directing the lineage commitment of mesenchymal stem cells or multipotent stromal cells (MSCs), but the mechanotransductive mechanisms at play are still not fully understood. This review article first describes the roles of both substrate mechanics (e.g. stiffness and topography) and extrinsic mechanical cues (e.g. fluid flow, compression, hydrostatic pressure, tension) on the differentiation of MSCs. A specific focus is placed on the role of such factors in regulating the osteogenic, chondrogenic, myogenic and adipogenic differentiation of MSCs. Next, the article focuses on the cellular components, specifically integrins, ion channels, focal adhesions and the cytoskeleton, hypothesized to be involved in MSC mechanotransduction. This review aims to illustrate the strides that have been made in elucidating how MSCs sense and respond to their mechanical environment, and also to identify areas where further research is needed.

In search of the pivot point of mechanotransduction: mechanosensing of stem cells

Stem cells are undifferentiated cells with the ability to self-renew and to differentiate into diverse specialized cell types; hence, they have great potential in tissue engineering and cell therapies. In addition to biochemical regulation, the physical properties of the microenvironments, such as scaffold topography, substrate stiffness, and mechanical forces, including fluid shear stress, compression, and tensile strain, can also regulate the proliferation and differentiation of stem cells. Upon physical stimuli, cytoskeleton rearrangements are expected to counterbalance the extracellular mechanical forces, trigger signaling cascades, and eventually cause epigenetic modifications. This article mainly focuses on the mechanosensing, which is the upstream event of stem cell mechanotransduction and the downstream one of physical stimuli. Putative mechanosensors such as ion channels, integrins, and cell membrane as well as primary cilia are discussed. Because mechanical environment is an important stem cell niche, identification of mechanosensors not only can elucidate the mechanisms of mechanotransduction and fate commitments but also bring new prospects of the mechanical control as well as drug development for clinical application.

Mechanically induced osteogenic lineage commitment of stem cells

Bones adapt to accommodate the physical forces they experience through changes in architecture and mass. Stem cells differentiate into bone-forming osteoblasts, and mechanical stimulation is involved in this process. Various studies have applied controlled mechanical stimulation to stem cells and investigated the effects on osteogenic lineage commitment. These studies demonstrate that physical stimuli can induce osteogenic lineage commitment. Tension, fluid shear stress, substrate material properties, and cell shape are all factors that influence osteogenic differentiation. In particular, the level of tension is important. Also, rigid substrates with stiffness similar to collagenous bone induce osteogenic differentiation, while softer substrates induce other lineages. Finally, cells allowed to adhere over a larger area are able to differentiate towards the osteogenic lineage while cells adhering to a smaller area are restricted to the adipogenic lineage. Stem cells are able to sense their mechanical environments through various mechanosensors, including the cytoskeleton, focal adhesions, and primary cilia. The cytoskeleton provides a structural frame for the cell, and myosin interacts with actin to generate cytoskeletal tension, which is important for mechanically induced osteogenesis of stem cells. Adapter proteins link the cytoskeleton to integrins, which attach the cell to the substrate, forming a focal adhesion. A variety of signaling proteins are also associated with focal adhesions. Forces are transmitted to the substrate at these sites, and an intact focal adhesion is important for mechanically induced osteogenesis. The primary cilium is a single, immotile, antenna-like structure that extends from the cell into the extracellular space. It has emerged as an important signaling center, acting as a microdomain to facilitate biochemical signaling. Mechanotransduction is the process by which physical stimuli are converted into biochemical responses. When potential mechanosensors are disrupted, the activities of components of mechanotransduction pathways are also inhibited, preventing mechanically induced osteogenesis. Calcium, mitogen-activated protein kinase/extracellular signal-regulated kinase, Wnt, Yes-associated protein/transcriptional coactivator with PDZ-binding motif and RhoA/Rho kinase signaling are some of the mechanotransduction pathways proposed to be important. In this review, types of mechanical stimuli, mechanosensors, and key pathways involved in mechanically induced osteogenesis of stem cells are discussed.

Osteogenic differentiation of amniotic epithelial cells: synergism of pulsed electromagnetic field and biochemical stimuli

BACKGROUND

Pulsed electromagnetic field (PEMF) is a non-invasive physical therapy used in the treatment of fracture nonunion or delayed healing. PEMF can facilitate the osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Amniotic epithelial cells (AECs) have been proposed as a potential source of stem cells for cell therapy. However, whether PEMF could modulate the osteogenic differentiation of AECs is unknown. In the present study, the effects of PEMF on the osteogenic differentiation of AECs were investigated.

METHODS

AECs were isolated from amniotic membrane of human placenta by trypsin digestion and were induced by PEMF and/or osteo-induction medium. After 21 days we used real time RT-PCR and immunocytochemistry to study the expression of osteoblast markers. The signal transduction of osteogenesis was further investigated.

RESULTS

The PEMF stimulation, or osteo-induction medium alone could induce osteogenic differentiation of AECs, as shown by expression of osteoblast specific genes and proteins including alkaline phosphatase and osteocalcin. Furthermore, a combination of PEMF and osteo-induction medium had synergy effects on osteogenic differentiation. In our study, the gene expression of BMP-2, Runx2, β-catenin, Nrf2, Keap1 and integrinβ1 were up-regulated in the osteogenic differentiation of AECs induced by PEMF and/or osteo-induction medium.

CONCLUSIONS

Combined application of PEMF and osteo-induction medium is synergistic for the osteogenic differentiation of AECs. It might be a novel approach in the bone regenerative medicine.

Mechanomics: an emerging field between biology and biomechanics

Cells sense various in vivo mechanical stimuli, which initiate downstream signaling to mechanical forces. While a body of evidences is presented on the impact of limited mechanical regulators in past decades, the mechanisms how biomechanical responses globally affect cell function need to be addressed. Complexity and diversity of in vivo mechanical clues present distinct patterns of shear flow, tensile stretch, or mechanical compression with various parametric combination of its magnitude, duration, or frequency. Thus, it is required to understand, from the viewpoint of mechanobiology, what mechanical features of cells are, why mechanical properties are different among distinct cell types, and how forces are transduced to downstream biochemical signals. Meanwhile, those in vitro isolated mechanical stimuli are usually coupled together in vivo, suggesting that the different factors that are in effect individually could be canceled out or orchestrated with each other. Evidently, omics analysis, a powerful tool in the field of system biology, is advantageous to combine with mechanobiology and then to map the full-set of mechanically sensitive proteins and transcripts encoded by its genome. This new emerging field, namely mechanomics, makes it possible to elucidate the global responses under systematically-varied mechanical stimuli. This review discusses the current advances in the related fields of mechanomics and elaborates how cells sense external forces and activate the biological responses.

Mechanoregulation of stem cell fate via micro-/nano-scale manipulation for regenerative medicine

Recent developments in the field of mechanobiology have renewed the call for a better understanding of the role of mechanical forces as potent regulators and indicators of stem cell fate. Although it is well established that mechanical forces play a crucial role in guiding tissue development, little is known about how submicroscopic biomechanical forces can influence key stem cell behaviors. This review will detail the use of micro-/nano-technologies that are advancing our current understanding of stem cell mechanobiology, and mechanoregulation of stem cell fate using engineered surface topographies and small-scale patterning techniques. The involvement of focal adhesions and the cytoskeleton systems as a common biophysical impetus through which these mechanical signals are transduced via distinct signaling pathways will also be discussed. These insights are envisioned to provide the basis for the rational design of future biocompatible materials and may inspire alternative drug-free therapeutic strategies to manage diseased sites via biomechanical management.

Imaging horse tendons using multimodal 2-photon microscopy

Injuries and damage to tendons plague both human and equine athletes. At the site of injuries, various cells congregate to repair and re-structure the collagen. Treatments for collagen injury range from simple procedures such as icing and pharmaceutical treatments to more complex surgeries and the implantation of stem cells. Regardless of the treatment, the level of mechanical stimulation incurred by the recovering tendon is crucial. However, for a given tendon injury, it is not known precisely how much of a load should be applied for an effective recovery. Both too much and too little loading of the tendon could be detrimental during recovery. A mapping of the complex local environment imparted to any cell present at the site of a tendon injury may however, convey fundamental insights related to their decision making as a function of applied load. Therefore, fundamentally knowing how cells translate mechanical cues from their external environment into signals regulating their functions during repair is crucial to more effectively treat these types of injuries. In this paper, we studied systems of tendons with a variety of 2-photon-based imaging techniques to examine the local mechanical environment of cells in both normal and injured tendons. These tendons were chemically treated to instigate various extents of injury and in some cases, were injected with stem cells. The results related by each imaging technique distinguish with high contrast and resolution multiple morphologies of the cells' nuclei and the alignment of the collagen during injury. The incorporation of 2-photon FLIM into this study probed new features in the local environment of the nuclei that were not apparent with steady-state imaging. Overall, this paper focuses on horse tendon injury pattern and analysis with different 2-photon confocal modalities useful for wide variety of application in damaged tissues.

Blueberry consumption prevents loss of collagen in bone matrix and inhibits senescence pathways in osteoblastic cells

Ovariectomy (OVX)-induced bone loss has been linked to increased bone turnover and higher bone matrix collagen degradation as the result of osteoclast activation. However, the role of degraded collagen matrix in the fate of resident bone-forming cells is unclear. In this report, we show that OVX-induced bone loss is associated with profound decreases in collagen 1 and Sirt1. This was accompanied by increases in expression and activity of the senescence marker collagenase and expression of p16/p21 in bone. Feeding a diet supplemented with blueberries (BB) to pre-pubertal rats throughout development or only prior to puberty [postnatal day 21 (PND21) to PND34] prevents OVX-induced effects on expression of these molecules at PND68. In order to provide more evidence and gain a better understanding on the association between bone collagen matrix and resident bone cell fate, in vitro studies on the cellular senescence pathway using primary calvarial cells and three cell lines (ST2 cells, OB6, and MLO-Y4) were conducted. We found that senescence was inhibited by collagen in a dose-response manner. Treatment of cells with serum from OVX rats accelerated osteoblastic cell senescence pathways, but serum from BB-fed OVX rats had no effect. In the presence of low collagen or treatment with OVX rat serum, ST2 cells exhibited higher potential to differentiate into adipocytes. Finally, we demonstrated that bone cell senescence is associated with decreased Sirt1 expression and activated p53, p16, and p21. These results suggest that (1) a significant prevention of OVX-induced bone cell senescence from adult rats can occur after only 14 days consumption of a BB-containing diet immediately prior to puberty, and (2) the molecular mechanisms underlying this effect involves, at least in part, prevention of collagen degradation.

A generic micropatterning platform to direct human mesenchymal stem cells from different origins towards myogenic differentiation

Human mesenchymal stem cells (MSCs) derived from various origins show varied differentiation capability. Recent work shows that cell shape manipulation via micropatterning can modulate the differentiation of bone-marrow-derived MSCs. Herein, the effect of micropatterning on the myogenesis of MSCs isolated from three different sources (bone marrow, fetal tissue, and adipose) is reported. All the well-aligned cells, regardless of source, predominantly commit to myogenic lineage, as shown by the significant upregulation of myogenic gene markers and positive myosin heavy chain staining. It is demonstrated that our novel micropattern can be used as a generic platform for inducing myogenesis of MSCs from different sources and may also have the potential to be extended to induce other lineage commitment.

Osteogenesis of mesenchymal stem cells by nanoscale mechanotransduction

It is likely that mesenchymal stem cells will find use in many autologous regenerative therapies. However, our ability to control cell stem growth and differentiation is presently limited, and this is a major hurdle to the clinical use of these multipotent cells especially when considering the desire not to use soluble factors or complex media formulations in culture. Also, the large number of cells required to be clinically useful is currently a hurdle to using materials-based (stiffness, chemistry, nanotopography, etc.) culture substrates. Here we give a first demonstration of using nanoscale sinusoidal mechanotransductive protocols (10-14 nm displacements at 1 kHz frequency), "nanokicking", to promote osteoblastogenesis in human mesenchymal stem cell cultures. On the basis of application of the reverse piezo effect, we use interferometry to develop the optimal stem cell stimulation conditions, allowing delivery of nanoscale cues across the entire surface of the Petri dishes used. A combination of immunofluorescence, PCR, and microarray has then been used to demonstrate osteoblastogenesis, and the arrays implicate RhoA as central to osteoblastic differentiation in agreement with materials-based strategies. We validate this with pharmacological inhibition of RhoA kinase. It is easy to envisage such stimulation protocols being up-scaled to form large-scale osteoblast bioreactors as standard cell culture plates and incubators are used in the protocol.

Chip-based comparison of the osteogenesis of human bone marrow- and adipose tissue-derived mesenchymal stem cells under mechanical stimulation

Adipose tissue-derived stem cells (ASCs) are considered as an attractive stem cell source for tissue engineering and regenerative medicine. We compared human bone marrow-derived mesenchymal stem cells (hMSCs) and hASCs under dynamic hydraulic compression to evaluate and compare osteogenic abilities. A novel micro cell chip integrated with microvalves and microscale cell culture chambers separated from an air-pressure chamber was developed using microfabrication technology. The microscale chip enables the culture of two types of stem cells concurrently, where each is loaded into cell culture chambers and dynamic compressive stimulation is applied to the cells uniformly. Dynamic hydraulic compression (1 Hz, 1 psi) increased the production of osteogenic matrix components (bone sialoprotein, oateopontin, type I collagen) and integrin (CD11b and CD31) expression from both stem cell sources. Alkaline phosphatase and Alrizarin red staining were evident in the stimulated hMSCs, while the stimulated hASCs did not show significant increases in staining under the same stimulation conditions. Upon application of mechanical stimulus to the two types of stem cells, integrin (β1) and osteogenic gene markers were upregulated from both cell types. In conclusion, stimulated hMSCs and hASCs showed increased osteogenic gene expression compared to non-stimulated groups. The hMSCs were more sensitive to mechanical stimulation and more effective towards osteogenic differentiation than the hASCs under these modes of mechanical stimulation.