Adipose tissue-derived mesenchymal stem cells acquire bone cell-like responsiveness to fluid shear stress on osteogenic stimulation

Advances in Shear Stress Stimulation of Stem Cells: A Review of the Last Three Decades

Stem cells are widely used in scientific research because of their ability to self-renew and differentiate into a variety of specialized cell types needed for body functions. However, the self-renewal and differentiation of stem cells are regulated by various stimuli, with mechanical stimulation being particularly notable due to its ability to mimic the physical environment in the body. This study systematically collected 2638 research papers published between 1994 and 2024, employing tools such as VOSviewer, CiteSpace, and GraphPad Prism to uncover research hotspots, publication trends, and collaboration networks. The results indicate a yearly increase in global research on the shear stress stimulation of stem cells, with significant contributions from the United States and China in terms of research investment and output. Future research directions include a deeper understanding of the mechanisms underlying mechanical stimulation's effects on stem cell differentiation, the development of new materials and scaffold designs to better replicate the natural cellular environment, and advancements in regenerative medicine. Despite considerable progress, challenges remain in translating basic research findings into clinical applications.

Biomechanics and mechanobiology of the bone matrix

The bone matrix plays an indispensable role in the human body, and its unique biomechanical and mechanobiological properties have received much attention. The bone matrix has unique mechanical anisotropy and exhibits both strong toughness and high strength. These mechanical properties are closely associated with human life activities and correspond to the function of bone in the human body. None of the mechanical properties exhibited by the bone matrix is independent of its composition and structure. Studies on the biomechanics of the bone matrix can provide a reference for the preparation of more applicable bone substitute implants, bone biomimetic materials and scaffolds for bone tissue repair in humans, as well as for biomimetic applications in other fields. In providing mechanical support to the human body, bone is constantly exposed to mechanical stimuli. Through the study of the mechanobiology of the bone matrix, the response mechanism of the bone matrix to its surrounding mechanical environment can be elucidated and used for the health maintenance of bone tissue and defect regeneration. This paper summarizes the biomechanical properties of the bone matrix and their biological significance, discusses the compositional and structural basis by which the bone matrix is capable of exhibiting these mechanical properties, and studies the effects of mechanical stimuli, especially fluid shear stress, on the components of the bone matrix, cells and their interactions. The problems that occur with regard to the biomechanics and mechanobiology of the bone matrix and the corresponding challenges that may need to be faced in the future are also described.

Bio-mimicking Shear Stress Environments for Enhancing Mesenchymal Stem Cell Differentiation

Mesenchymal stem cells (MSCs) are multipotent stromal cells, with the ability to differentiate into mesodermal (e.g., adipocyte, chondrocyte, hematopoietic, myocyte, osteoblast), ectodermal (e.g., epithelial, neural) and endodermal (e.g., hepatocyte, islet cell) lineages based on the type of induction cues provided. As compared to embryonic stem cells, MSCs hold a multitude of advantages from a clinical translation perspective, including ease of isolation, low immunogenicity and limited ethical concerns. Therefore, MSCs are a promising stem cell source for different regenerative medicine applications. The in vitro differentiation of MSCs into different lineages relies on effective mimicking of the in vivo milieu, including both biochemical and mechanical stimuli. As compared to other biophysical cues, such as substrate stiffness and topography, the role of fluid shear stress (SS) in regulating MSC differentiation has been investigated to a lesser extent although the role of interstitial fluid and vascular flow in regulating the normal physiology of bone, muscle and cardiovascular tissues is well-known. This review aims to summarise the current state-of-the-art regarding the role of SS in the differentiation of MSCs into osteogenic, cardiovascular, chondrogenic, adipogenic and neurogenic lineages. We will also highlight and discuss the potential of employing SS to augment the differentiation of MSCs to other lineages, where SS is known to play a role physiologically but has not yet been successfully harnessed for in vitro differentiation, including liver, kidney and corneal tissue lineage cells. The incorporation of SS, in combination with biochemical and biophysical cues during MSC differentiation, may provide a promising avenue to improve the functionality of the differentiated cells by more closely mimicking the in vivo milieu.

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.

Induction of osteogenic differentiation of bone marrow stromal cells on 3D polyester-based scaffolds solely by subphysiological fluidic stimulation in a laminar flow bioreactor

The fatal determination of bone marrow mesenchymal stem/stromal cells (BMSC) is closely associated with mechano-environmental factors in addition to biochemical clues. The aim of this study was to induce osteogenesis in the absence of chemical stimuli using a custom-designed laminar flow bioreactor. BMSC were seeded onto synthetic microporous scaffolds and subjected to the subphysiological level of fluid flow for up to 21 days. During the perfusion, cell proliferation was significantly inhibited. There were also morphological changes, with F-actin polymerisation and upregulation of ROCK1. Notably, in BMSC subjected to flow, mRNA expression of osteogenic markers was significantly upregulated and RUNX2 was localised in the nuclei. Further, under perfusion, there was greater deposition of collagen type 1 and calcium onto the scaffolds. The results confirm that an appropriate level of fluid stimuli preconditions BMSC towards the osteoblastic lineage on 3D scaffolds in the absence of chemical stimulation, which highlights the utility of flow bioreactors in bone tissue engineering.

Scale-Up Technologies for the Manufacture of Adherent Cells

Great importance is being given to the impact our food supply chain and consumers' food habits are having on the environment, human health, and animal welfare. One of the latest developments aiming at positively changing the food ecosystem is represented by cultured meat. This form of cellular agriculture has the objective to generate slaughter-free meat products starting from the cultivation of few cells harvested from the animal tissue of interest. As a consequence, a large number of cells has to be generated at a reasonable cost. Just to give an idea of the scale, there were billions of cells just in a bite of the first cultured-meat burger. Thus, one of the major challenges faced by the scientists involved in this new ambitious and fascinating field, is how to efficiently scale-up cell manufacture. Considering the great potential presented by cultured meat, audiences from different backgrounds are very interested in this topic and eager to be informed of the challenges and possible solutions in this area. In light of this, we will provide an overview of the main existing bioprocessing technologies used to scale-up adherent cells at a small and large scale. Thus, giving a brief technical description of these bioprocesses, with the main associated advantages and disadvantages. Moreover, we will introduce an alternative solution we believe has the potential to revolutionize the way adherent cells are grown, helping cultured meat become a reality.

Advances in human mesenchymal stromal cell-based therapies - Towards an integrated biological and engineering approach

Recent advances of stem cell-based therapies in clinical trials have raised the need for large-scale manufacturing platforms that can supply clinically relevant doses to meet an increasing demand. Promising results have been reported using stirred-tank bioreactors, where human Mesenchymal Stromal Cells (hMSCs) were cultured in suspension on microcarriers (MCs), although the formation of microcarrier-cell-aggregates might still limit mass transfer and determine a heterogeneous distribution of hMSCs. A variety of MCs, bioreactor-impeller configurations, and agitation conditions have been established in an attempt to overcome the trade-off of ensuring good suspension while keeping the stresses to a minimum. While understanding and controlling the fluid flow environment of bioreactors has been initially under-appreciated, it has recently gained in popularity in the mission of providing ideal culture environments across different scales. This review article aims to provide a comprehensive overview of how rigorous engineering characterisation studies improved the outcome of biological process development and scale-up efforts. Reconciling these two disciplines is crucial to propose tailored bioprocessing solutions that can provide improved growth environments across a range of scales for the allogeneic cell therapies of the future.

Influence of Microenvironment on Mesenchymal Stem Cell Therapeutic Potency: From Planar Culture to Microcarriers

Human mesenchymal stem cells (hMSCs) are a promising candidate in cell therapy as they exhibit multilineage differentiation, homing to the site of injury, and secretion of trophic factors that facilitate tissue healing and/or modulate immune response. As a result, hMSC-derived products have attracted growing interests in preclinical and clinical studies. The development of hMSC culture platforms for large-scale biomanufacturing is necessary to meet the requirements for late-phase clinical trials and future commercialization. Microcarriers in stirred-tank bioreactors have been widely utilized in large-scale expansion of hMSCs for translational applications because of a high surface-to-volume ratio compared to conventional 2D planar culture. However, recent studies have demonstrated that microcarrier-expanded hMSCs differ from dish- or flask-expanded cells in size, morphology, proliferation, viability, surface markers, gene expression, differentiation potential, and secretome profile which may lead to altered therapeutic potency. Therefore, understanding the bioprocessing parameters that influence hMSC therapeutic efficacy is essential for the optimization of microcarrier-based bioreactor system to maximize hMSC quantity without sacrificing quality. In this review, biomanufacturing parameters encountered in planar culture and microcarrier-based bioreactor culture of hMSCs are compared and discussed with specific focus on cell-adhesion surface (e.g., discontinuous surface, underlying curvature, microcarrier stiffness, porosity, surface roughness, coating, and charge) and the dynamic microenvironment in bioreactor culture (e.g., oxygen and nutrients, shear stress, particle collision, and aggregation). The influence of dynamic culture in bioreactors on hMSC properties is also reviewed in order to establish connection between bioprocessing and stem cell function. This review addresses fundamental principles and concepts for future design of biomanufacturing systems for hMSC-based therapy.

A bioengineering approach to Schlemm's canal-like stem cell differentiation for in vitro glaucoma drug screening

Human Schlemm's canal (HSC) cells are critical for understanding outflow physiology and glaucoma etiology. However, primary donor cells frequently used in research are difficult to isolate. HSC cells exhibit both vascular and lymphatic markers. Human adipose-derived stem cells (ADSCs) represent a potential source of HSC due to their capacity to differentiate into both vascular and lymphatic endothelial cells, via VEGF-A and VEGF-C. Shear stress plays a critical role in maintaining HSC integrity, function, and PROX1 expression. Additionally, the human trabecular meshwork (HTM) microenvironment could provide cues for HSC-like differentiation. We hypothesize that subjecting ADSCs to VEGF-A or VEGF-C, shear stress, and co-culture with HTM cells could provide biological, mechanical, and cellular cues necessary for HSC-like differentiation. To test this hypothesis, effects of VEGF-A, VEGF-C, and shear stress on ADSC differentiation were examined and compared to primary HSC cells in terms of cell morphology, and HSC marker expression using qPCR, immunoblotting, and immunocytochemistry analysis. Furthermore, the effect of co-culture with HTM cells on porous scaffolds on ADSC differentiation was studied. Treatment with VEGF-C under shear stress is effective in differentiating ADSCs into PROX1-expressing HSC-like cells. Co-culture with HTM cells on porous scaffolds leads to HTM/ADSC-derived HSC-like constructs that regulate through-flow and respond as expected to dexamethasone. STATEMENT OF SIGNIFICANCE: We successfully generated human Schlemm's canal (HSC) like cells from adipocyte-derived stem cells induced by biochemical and biomechanical cues as well as bioengineered human trabecular meshwork (HTM) on micropatterned, porous SU8 scaffolds. These stem cell-derived HSC-like cells co-cultured with HTM cells on SU8 scaffolds can regulate through-flow, and in particular, are responsive to steroid treatment as expected. These findings show that ADSC-derived HSC-like cells have the potential to recreate the ocular outflow pathway for in vitro glaucoma drug screening. To the best of our knowledge, it is the very first time to demonstrate derivation of Schlemm's canal-like cells from stem cells. It provides an important alternative source to primary Schlemm's canal cells that are very difficult to be isolated and cultured from human donors.

Adenosinergic signalling in chondrogenesis and cartilage homeostasis: Friend or foe?

Chondrocytes and their mesenchymal cell progenitors secrete a variety of bioactive molecules, including adenine nucleotides and nucleosides, but these molecules are not usually highlighted in review papers about the secretome of these cells. Ageing and inflammatory insults compromise chondrocytes ability to keep ATP/adenosine synthesis, release and turnover. Cartilage homeostasis depends on extracellular adenosine levels, which acting via four P1 purinoceptor subtypes modulates the release of pro-inflammatory mediators, including NO, PGE₂ and several cytokines. Native articular cartilage is challenged by synovial fluid flow during normal joint motion transiently increasing ATP release and adenosine formation in the joint microenvironment. Excessive joint motion and shockwave trauma are deleterious to cartilage homeostasis due to HIF-1α overexpression, resulting in disproportionate ecto-5'-nucleotidase/CD73 production, adenosine accumulation and superfluous A_2B receptors activation. Scarcity of data however exists on the putative interplay between coexistent high affinity (A_2A and A₃) and low affinity (A_2B) adenosine receptors activation affecting stem cells fate towards preferential chondrogenic or osteogenic lineages in the human cartilage. Hints gathered in this commentary result mainly from studies using human immortalized cell lines and animal (e.g. rodent, equine, bovine) tissue samples. The available data point towards adenosine A_2A and A₃ receptors having cartilage protective roles, while excessive adenosine accumulation may be detrimental via low affinity A_2B receptors activation, with little reference to the putative role of the adenosine forming enzyme ecto-5'-nucleotidase/CD73. Thus, emphasizing the multiple pathways responsible for controlling adenosine signalling in cartilage will certainly impact on the search for novel therapeutic targets for highly disabling articular disorders.

Short Pretreatment with Calcitriol Is Far Superior to Continuous Treatment in Stimulating Proliferation and Osteogenic Differentiation of Human Adipose Stem Cells

Objective

This study investigated whether short stimulation (30 minutes) of human adipose stem cells (hASCs) with 1,25-dihydroxyvitamin D₃ (calcitriol or 1,25-(OH)₂VitD₃), fitting within the surgical procedure time frame, suffices to induce osteogenic differentiation, and compared this with continuous treatment with 1,25-(OH)₂VitD₃.

Materials and Methods

In this experimental study, hASCs were pretreated with/without 10 nM calcitriol for 30 minutes, seeded on biphasic calcium phosphate (BCP), and cultured for 3 weeks with/without 1,25-(OH)₂VitD₃. Cell attachment was determined 30 minutes after cell seeding. AlamarBlue assay, alkaline phosphatase (ALP) assay, ALP staining, real-time polymerase chain reaction (PCR), and protein assay were used to evaluate the effect of short calcitriol pretreatment on proliferation and osteogenic differentiation of hASCs up to 3 weeks.

Results

Pretreatment with 1,25-(OH)₂VitD₃ enhanced the attachment of hASCs to BCP by 1.5-fold compared to nontreated cells and increased the proliferation by 3.5-fold at day 14, and 2.6-fold at day 21. In contrast, continuous treatment increased the proliferation by 1.7-fold only at day 14. After 2 weeks, ALP activity was increased by 18.5-fold when hASCs were pretreated with 1,25-(OH)₂VitD₃ for 30 minutes but increased only 2.6-fold when compared with its continuous counterpart. Moreover, after 14 days, pretreatment resulted in significant upregulation of the osteogenic markers RUNX2 and SPARC by 3.6-fold and 2.2-fold, respectively, while this was not observed upon continuous treatment. Finally, 30 minutes pretreatment of hASCs with 1,25-(OH)₂VitD₃ increased VEGF₁₈₉ expression, which may contribute to the process of angiogenesis.

Conclusion

This study is the first research showing that 30 minutes pretreatment of hASCs with 1,25-(OH)₂VitD₃, not only enhanced cell attachment to the scaffold at seeding time, but also promoted the proliferation and osteogenic differentiation of hASCs more strongly than continuous treatment, suggesting that short pre-treatment with 1,25-(OH)₂VitD₃ is a promising approach for the regeneration of bones in a one-step surgical procedure.

ECM in Differentiation: A Review of Matrix Structure, Composition and Mechanical Properties

Stem cell regenerative potential owing to the capacity to self-renew as well as differentiate into other cell types is a promising avenue in regenerative medicine. Stem cell niche not only provides physical scaffolding but also possess instructional capacity as it provides a milieu of biophysical and biochemical cues. Extracellular matrix (ECM) has been identified as a major dictator of stem cell lineage, thus understanding the structure of in vivo ECM pertaining to specific tissue differentiation will aid in devising in vitro strategies to improve the differentiation efficiency. In this review, we summarize details about the native architecture, composition and mechanical properties of in vivo ECM of the early embryonic stages and the later adult stages. Native ECM from adult tissues categorized on their origin from respective germ layers are discussed while engineering techniques employed to facilitate differentiation of stem cells into particular lineages are noted. Overall, we emphasize that in vitro strategies need to integrate tissue specific ECM biophysical cues for developing accurate artificial environments for optimizing stem cell differentiation.

Validation of a novel 3D flow model for the optimization of construct perfusion in radial-flow packed-bed bioreactors (rPBBs) for long-bone tissue engineering

Osteogenic cell culture in three-dimensional (3D) hollow cylindrical porous scaffolds in radial-flow packed-bed bioreactors (rPBBs) may overcome the transport limitations of static and axial perfusion bioreactors in the engineering of long-bone substitutes. Flow models of rPBBs help optimize radial flux distribution of medium and tissue maturation in vitro. Only a 2D model is available for steady flow transport in rPBBs with axisymmetric inlet and outlet accounting for the fluid dynamics of void spaces, assessed against literature information. Here, a novel 3D model is proposed for steady flow transport in the three compartments of rPBBs with a more practical lateral outlet. A 3D model of transient tracer transport was developed based on the flow model to predict bioreactor residence time distribution (RTD). Model-predicted flow patterns were validated in terms of RTD against tracer experiments performed with bioreactor prototypes equipped with commercial scaffolds for bone tissue engineering. Bioreactors were challenged with a step change in entering tracer concentration in an optimized set-up under conditions promoting uniform radial flux distribution and typical shunt flows. Model-predicted RTDs agreed well with those experimentally determined. In conclusion, tracer experiments validate the use of the 3D flow model for optimizing construct perfusion in rPBBs to engineer long-bone substitutes.

Primary Cilia Exhibit Mechanosensitivity to Cyclic Tensile Strain and Lineage-Dependent Expression in Adipose-Derived Stem Cells

Non-motile primary cilia are dynamic cellular sensory structures and are expressed in adipose-derived stem cells (ASCs). We have previously shown that primary cilia are involved in chemically-induced osteogenic differentiation of human ASC (hASCs) in vitro. Further, we have reported that 10% cyclic tensile strain (1 Hz, 4 hours/day) enhances hASC osteogenesis. We hypothesize that primary cilia respond to cyclic tensile strain in a lineage dependent manner and that their mechanosensitivity may regulate the dynamics of signaling pathways localized to the cilium. We found that hASC morphology, cilia length and cilia conformation varied in response to culture in complete growth, osteogenic differentiation, or adipogenic differentiation medium, with the longest cilia expressed in adipogenically differentiating cells. Further, we show that cyclic tensile strain both enhances osteogenic differentiation of hASCs while it suppresses adipogenic differentiation as evidenced by upregulation of RUNX2 gene expression and downregulation of PPARG and IGF-1, respectively. This study demonstrates that hASC primary cilia exhibit mechanosensitivity to cyclic tensile strain and lineage-dependent expression, which may in part regulate signaling pathways localized to the primary cilium during the differentiation process. We highlight the importance of the primary cilium structure in mechanosensing and lineage specification and surmise that this structure may be a novel target in manipulating hASC for in tissue engineering applications.

Biomechanical studies on biomaterial degradation and co-cultured cells: mechanisms, potential applications, challenges and prospects

This review provides a comprehensive overview of biomechanical studies on biomaterial degradation and co-cultured cells as well as valuable biomechanical ideas on how to design or optimize cell biomaterial co-culture system.

Transplantation of Adipose-derived Cells for Periodontal Regeneration: A Systematic Review

This systematic review evaluated the transplantation of cells derived from adipose tissue for applications in dentistry. SCOPUS, PUBMED and LILACS databases were searched for in vitro studies and pre-clinical animal model studies using the keywords "ADIPOSE", "CELLS", and "PERIODONTAL", with the Boolean operator "AND". A total of 160 titles and abstracts were identified, and 29 publications met the inclusion criteria, 14 in vitro and 15 in vivo studies. In vitro studies demonstrated that adipose- derived cells stimulate neovascularization, have osteogenic and odontogenic potential; besides adhesion, proliferation and differentiation on probable cell carriers. Preclinical studies described improvement of bone and periodontal healing with the association of adipose-derived cells and the carrier materials tested: Platelet Rich Plasma, Fibrin, Collagen and Synthetic polymer. There is evidence from the current in vitro and in vivo data indicating that adipose-derived cells may contribute to bone and periodontal regeneration. The small quantity of studies and the large variation on study designs, from animal models, cell sources and defect morphology, did not favor a meta-analysis. Additional studies need to be conducted to investigate the regeneration variability and the mechanisms of cell participation in the processes. An overview of animal models, cell sources, and scaffolds, as well as new perspectives are provided for future bone and periodontal regeneration study designs.

Effect of equiaxial cyclic strain on cardiomyogenic induction in mesenchymal stem cells

Differentiation of stem cells and functionality of target cells are regulated by microenvironmental stimuli to which the cells are exposed. Chemical agents such as growth factors and physical parameters including mechanical loadings are among major stimuli. In this study, equiaxial cyclic strain with two amplitudes was applied on rat adipose-derived mesenchymal stem cells (rAMSCs) with or without 5-azacytidine. The mRNA expression of cardiac-related genes was investigated through RT-PCR (polymerase chain reaction) method. Moreover, morphological features and the actin structure of the cells were studied. Results were indications of significant increase in mRNA expression among four target genes, which marked the increase in two principal cardiac markers of GATA4 and α-cardiac actin, and lesser increase in two other genes (NKX2-5, βMHC) in all experimental groups treated chemically and/or mechanically. Such effect was maximal when both treatments were applied describing the synergistic effect of combined stimuli. All treatments caused significant increase in cell area and cell shape index. The well spreading of cells was accompanied by enhanced actin structure, especially among samples subjected to mechanical stimulus. Both effects were among required features for functional muscle cells such as cardiac cells. It was concluded that the cyclic equiaxial strain enhanced cardiomyogenic induction among rat adipose-derived mesenchymal stem cells and such effect was strengthened when it was accompanied by application of chemical factor. Results can be considered among strategies for cardiomyogenic differentiation and can be employed in cardiac tissue engineering for production of functional cardiomyocytes to repair of damaged myocardium.

Cancer-adipose tissue interaction and fluid flow synergistically modulate cell kinetics, HER2 expression, and trastuzumab efficacy in gastric cancer

BACKGROUND

Early local tumor invasion in gastric cancer results in likely encounters between cancer cells and submucosal and subserosal adipose tissue, but these interactions remain to be clarified. Microenvironmental mechanical forces, such as fluid flow, are known to modulate normal cell kinetics, but the effects of fluid flow on gastric cancer cells are poorly understood. We analyzed the cell kinetics and chemosensitivity in gastric cancer using a simple in vitro model that simultaneously replicated the cancer-adipocyte interaction and physical microenvironment.

METHODS

Gastric cancer cells (MKN7 and MKN74) were seeded on rat adipose tissue fragment-embedded discs or collagen discs alone. To generate fluid flow, samples were placed on a rotatory shaker in a CO₂ incubator. Proliferation, apoptosis, invasion, and motility-related molecules were analyzed by morphometry and immunostaining. Proteins were evaluated by western blot analysis. Chemosensitivity was investigated by trastuzumab treatment.

RESULTS

Adipose tissue and fluid flow had a positive synergistic effect on the proliferative potential and invasive capacity of gastric cancer cells, and adipose tissue inhibited apoptosis in these cells. Adipose tissue upregulated ERK1/2 signaling in gastric cancer cells, but downregulated p38 signaling. Notably, adipose tissue and fluid flow promoted membranous and cytoplasmic HER2 expression and modulated chemosensitivity to trastuzumab in gastric cancer cells.

CONCLUSION

We have demonstrated that cancer-adipocyte interaction and physical microenvironment mutually modulate gastric cancer cell kinetics. Further elucidation of the microenvironmental regulation in gastric cancer will be very important for the development of strategies involving molecular targeted therapy.

Eminent Sources of Adult Mesenchymal Stem Cells and Their Therapeutic Imminence

In the recent times, stem cell biology has garnered the attention of the scientific fraternity and the general public alike due to the immense therapeutic potential that it holds in the field of regenerative medicine. A breakthrough in this direction came with the isolation of stem cells from human embryo and their differentiation into cell types of all three germ layers. However, the isolation of mesenchymal stem cells from adult tissues proved to be advantageous over embryonic stem cells due to the ethical and immunological naivety. Mesenchymal Stem Cells (MSCs) isolated from the bone marrow were found to differentiate into multiple cell lineages with the help of appropriate differentiation factors. Furthermore, other sources of stem cells including adipose tissue, dental pulp, and breast milk have been identified. Newer sources of stem cells have been emerging recently and their clinical applications are also being studied. In this review, we examine the eminent sources of Mesenchymal Stem Cells (MSCs), their immunophenotypes, and therapeutic imminence.

Physical stimulations and their osteogenesis-inducing mechanisms

Physical stimulations such as magnetic, electric and mechanical stimulation could enhance cell activity and promote bone formation in bone repair process via activating signal pathways, modulating ion channels, regulating bonerelated gene expressions, etc. In this paper, bioeffects of physical stimulations on cell activity, tissue growth and bone healing were systematically summarized, which especially focused on their osteogenesis-inducing mechanisms. Detailedly, magnetic stimulation could produce Hall effect which improved the permeability of cell membrane and promoted the migration of ions, especially accelerating the extracellular calcium ions to pass through cell membrane. Electric stimulation could induce inverse piezoelectric effect which generated electric signals, accordingly up-regulating intracellular calcium levels and growth factor synthesis. And mechanical stimulation could produce mechanical signals which were converted into corresponding biochemical signals, thus activating various signaling pathways on cell membrane and inducing a series of gene expressions. Besides, bioeffects of physical stimulations combined with bone scaffolds which fabricated using 3D printing technology on bone cells were discussed. The equipments of physical stimulation system were described. The opportunities and challenges of physical stimulations were also presented from the perspective of bone repair.

Establishment and characterization of a primary murine adipose tissue-chip

Better experimental models are needed to enhance our understanding of metabolic regulation which is seen in obesity and metabolic disorders, such as type 2 diabetes. In vitro models based on microfluidics enable physiological representations of tissues with several advantages over conventional culture systems, such as perfused flow to better mimic the physiological environment. Although cell lines such as 3T3-L1 have been incorporated in microfluidic devices, murine primary preadipocytes have not been differentiated and maintained for long-term monitoring in these culture systems. We describe the differentiation of these cells into white adipose depots on a perfused microfluidic chip. We compare the effects of shear flow on these cells, and show with a direct comparison of high/low shear conditions that direct shear is detrimental to the viability of preadipocytes. We further develop a dual-chamber microfluidic chip that enables perfusion while at the same time protects the cells from direct fluidic shear. We show that the dual-layer microfluidic device enables long-term culture of cells and allows stimulation of cells through perfusion-we can culture, differentiate, and maintain the differentiated adipose tissue for over multiple weeks in the device. Both triglycerides and lipolytic glycerol production increased significantly by several folds during differentiation. After successful differentiation, the adipocytes had upregulated expression of leptin and adiponectin, which are important makers of the final stage of adipogenic differentiation. In conclusion, the dual-layer microfluidic device incorporated with primary adipocytes improves the understanding of adipose differentiation under dynamic conditions and is positioned to serve as a disease model for studying obesity and other metabolic disorders.

Shear Conditioning of Adipose Stem Cells for Reduced Platelet Binding to Engineered Vascular Grafts

Conferring antithrombogenicity to tissue-engineered vascular grafts remains a major challenge, especially for urgent bypass grafting that excludes approaches based on expanding autologous endothelial cells (ECs) that requires weeks of cell culture. Adipose-derived stem cells (ASCs) are available from most patients in sufficient number for coronary bypass graft seeding and may be effective as allogeneic cells. We thus compared the adhesion and platelet binding of human ASCs that were shear conditioned with constant and pulsatile shear stress (SS) after seeding the cells on a biologically engineered matrix suitable for arterial grafts. A monolayer of cells was maintained up to 15 dyn/cm² constant SS and up to 15 dyn/cm² mean pulsatile SS for 6 days of shear flow. Platelet binding was reduced from 83% to 6% of surface area and nitric oxide production was increased 23-fold with 7.5-15 dyn/cm² constant SS, but not pulsatile SS, relative to cells cultured statically on the matrix for 6 days. The reduction in platelet binding varied from no reduction to maximum reduction over a constant shear range of ∼2 to 4 dyn/cm², respectively. Collectively, the study supports the potential use of ASCs to seed the luminal surface of a vascular graft made from this biologically engineered matrix to confer an antithrombogenic surface during the development of an endothelium from the seeded cells or the surrounding blood and tissue.

MAPK signaling has stage-dependent osteogenic effects on human adipose-derived stem cells in vitro

OVERVIEW

The use of pro-osteogenic growth factors, such as BMP2, in human adipose-derived stem cell (ASC) osteogenesis is well described. Because these growth factors work via signal transduction pathways, such as the mitogen-activated protein kinase (MAPK) cascade, a study of the relationship between MAPK signaling and ASC osteogenesis was conducted.

MATERIALS AND METHODS

ERK, JNK, and p38MAPK activation were measured in ASCs osteo-induced using either dexamethasone or vitamin D3 and correlated with mineralization. Activation and mineralization were also measured without dexamethasone or using the glucocorticoid, cortisone. The expression of the MAPK phosphatase, MKP1, and its relationship to mineralization was also assessed. The effect of decreasing MAPK activation on mineralization through the use of exogenous inhibitors was examined along with siRNA-knockdown and adenoviral overexpression of ERK1/2. Finally, the effect of ERK1/2 overexpression on ASCs induced on PLGA scaffolds was assessed.

RESULTS

ASC mineralization in dexamethasone or vitamin D3-induced ASCs correlated with both increased ERK1/2 and JNK1/2 activation. ASCs induced without dexamethasone also mineralized, with JNK1/2 signaling possibly mediating this event. No link between cortisone induction and MAPK signaling could be ascertained. ASCs treated with ERK, JNK, or p38MAPK inhibitors showed decreased osteogenic gene expression and diminished mineralization. Mineralization levels were also affected by viruses designed to inhibit or augment ERK1/2 expression and activity. Finally, ASC mineralization appeared to be a balance between the MAPK kinase activity and MKP1.

CONCLUSIONS

It is likely that MAPK signaling plays a significant role in ASC osteogenesis, affecting differentiation in kinase- and stage-specific manners.

Three-Dimensional Graphene-RGD Peptide Nanoisland Composites That Enhance the Osteogenesis of Human Adipose-Derived Mesenchymal Stem Cells

Graphene derivatives have immense potential in stem cell research. Here, we report a three-dimensional graphene/arginine-glycine-aspartic acid (RGD) peptide nanoisland composite effective in guiding the osteogenesis of human adipose-derived mesenchymal stem cells (ADSCs). Amine-modified silica nanoparticles (SiNPs) were uniformly coated onto an indium tin oxide electrode (ITO), followed by graphene oxide (GO) encapsulation and electrochemical deposition of gold nanoparticles. A RGD–MAP–C peptide, with a triple-branched repeating RGD sequence and a terminal cysteine, was self-assembled onto the gold nanoparticles, generating the final three-dimensional graphene–RGD peptide nanoisland composite. We generated substrates with various gold nanoparticle–RGD peptide cluster densities, and found that the platform with the maximal number of clusters was most suitable for ADSC adhesion and spreading. Remarkably, the same platform was also highly efficient at guiding ADSC osteogenesis compared with other substrates, based on gene expression (alkaline phosphatase (ALP), runt-related transcription factor 2), enzyme activity (ALP), and calcium deposition. ADSCs induced to differentiate into osteoblasts showed higher calcium accumulations after 14–21 days than when grown on typical GO-SiNP complexes, suggesting that the platform can accelerate ADSC osteoblastic differentiation. The results demonstrate that a three-dimensional graphene–RGD peptide nanoisland composite can efficiently derive osteoblasts from mesenchymal stem cells.

Mechanoresponsiveness of human adipose stem cells on nanocomposite and micro-hybrid composite

Resin-based composites are used for bone repair applications and comprise resin matrix and different sized filler particles. Nanometer-sized filler particles improve composite's mechanical properties compared with micrometer-sized filler particles, but whether differences exist in the biological response to these composites is unknown. Natural bone comprises a nanocomposite structure, and nanoscale interactions with extracellular matrix components influence stem cell differentiation. Therefore we hypothesized that nanometer-sized filler particles in resin-based composites enhance osteogenic differentiation of stem cells showing a more bone cell-like response to mechanical loading compared with micrometer-sized filler particles. Pulsating fluid flow (PFF; 5 Hz, mean shear stress: 0.7 Pa; 1 h) rapidly, within 5 min, increased nitric oxide production in human adipose stem cells (hASCs) on nanocomposite, but not on micro-hybrid composite. PFF increased RUNX2 expression in hASCs on micro-hybrid composite, but not on nanocomposite after 2 h post-incubation. PFF did not affect mean cell orientation and shape index of hASCs on both composites. In conclusion, the PFF-increased nitric oxide production in hASCs on nanocomposite, and increased osteogenic differentiation of hASCs on micro-hybrid composite suggest different responses to mechanical loading of hASCs on composite with nanometer-sized and micrometer-sized filler particles. This might have important implications for bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2986-2994, 2017.

Biomechanical Forces Promote Immune Regulatory Function of Bone Marrow Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) are believed to mobilize from the bone marrow in response to inflammation and injury, yet the effects of egress into the vasculature on MSC function are largely unknown. Here we show that wall shear stress (WSS) typical of fluid frictional forces present on the vascular lumen stimulates antioxidant and anti-inflammatory mediators, as well as chemokines capable of immune cell recruitment. WSS specifically promotes signaling through NFκB-COX2-prostaglandin E2 (PGE2 ) to suppress tumor necrosis factor-α (TNF-α) production by activated immune cells. Ex vivo conditioning of MSCs by WSS improved therapeutic efficacy in a rat model of traumatic brain injury, as evidenced by decreased apoptotic and M1-type activated microglia in the hippocampus. These results demonstrate that force provides critical cues to MSCs residing at the vascular interface which influence immunomodulatory and paracrine activity, and suggest the potential therapeutic use of force for MSC functional enhancement. Stem Cells 2017;35:1259-1272.

The effect of equiaxial stretching on the osteogenic differentiation and mechanical properties of human adipose stem cells

Although mechanical cues are known to affect stem cell fate and mechanobiology, the significance of such stimuli on the osteogenic differentiation of human adipose stem cells (hASCs) remains unclear. In this study, we investigated the effect of long-term mechanical stimulation on the attachment, osteogenic differentiation and mechanical properties of hASCs. Tailor-made, pneumatic cell stretching devices were used to expose hASCs to cyclic equiaxial stretching in osteogenic medium. Cell attachment and focal adhesions were visualised using immunocytochemical vinculin staining on days 3 and 6, and the proliferation and alkaline phosphatase activity, as a sign of early osteogenic differentiation, were analysed on days 0, 6 and 10. Furthermore, the mechanical properties of hASCs, in terms of apparent Young's modulus and normalised contractility, were obtained using a combination of atomic force microscopy based indentation and computational approaches. Our results indicated that cyclic equiaxial stretching delayed proliferation and promoted osteogenic differentiation of hASCs. Stretching also reduced cell size and intensified focal adhesions and actin cytoskeleton. Moreover, cell stiffening was observed during osteogenic differentiation and especially under mechanical stimulation. These results suggest that cyclic equiaxial stretching modifies cell morphology, focal adhesion formation and mechanical properties of hASCs. This could be exploited to enhance osteogenic differentiation.

Biomimetic Approaches for Bone Tissue Engineering

Although autologous bone grafts are considered a gold standard for the treatment of bone defects, they are limited by donor site morbidities and geometric requirements. We propose that tissue engineering technology can overcome such limitations by recreating fully viable and biological bone grafts. Specifically, we will discuss the use of bone scaffolds and autologous cells with bioreactor culture systems as a tissue engineering paradigm to grow bone in vitro. We will also discuss emergent vascularization strategies to promote graft survival in vivo, as well as the role of inflammation during bone repair. Finally, we will highlight some recent advances and discuss new solutions to bone repair inspired by endochondral ossification.

Isolation of autologous adipose tissue-derived mesenchymal stem cells for bone repair

INTRODUCTION

Adipose tissue represents an abundant and accessible source of adult stem cells that can differentiate into cells and tissues of mesodermal origin, including osteogenic cells.

METHODS

This paper describes the procedure to obtain a 5-cm³ saline sample, containing the adipose-derived stem cells (ASCs) pellet, starting from lipoaspirate obtained from a conventional abdominal liposuction.

RESULTS

A mean of 2.5×10⁶ cells is isolated for each procedure; 35% (875000) of these are CD34+/CD45- cells, which express a subset of both positive (CD10, CD13, CD44, CD59, CD73, CD90, HLAABC) and negative (CD33, CD39, CD102, CD106, CD146, HLADR) cell-associated surface antigens, characterizing them as ASCs.

CONCLUSIONS

This procedure is easy, effective, economic and safe. It allows the harvesting of a significant number of ASCs that are ready for one-step bony regenerative surgical procedures.

Fabrication of novel high surface area mushroom gilled fibers and their effects on human adipose derived stem cells under pulsatile fluid flow for tissue engineering applications

The fabrication and characterization of novel high surface area hollow gilled fiber tissue engineering scaffolds via industrially relevant, scalable, repeatable, high speed, and economical nonwoven carding technology is described. Scaffolds were validated as tissue engineering scaffolds using human adipose derived stem cells (hASC) exposed to pulsatile fluid flow (PFF). The effects of fiber morphology on the proliferation and viability of hASC, as well as effects of varied magnitudes of shear stress applied via PFF on the expression of the early osteogenic gene marker runt related transcription factor 2 (RUNX2) were evaluated. Gilled fiber scaffolds led to a significant increase in proliferation of hASC after seven days in static culture, and exhibited fewer dead cells compared to pure PLA round fiber controls. Further, hASC-seeded scaffolds exposed to 3 and 6dyn/cm(2) resulted in significantly increased mRNA expression of RUNX2 after one hour of PFF in the absence of soluble osteogenic induction factors. This is the first study to describe a method for the fabrication of high surface area gilled fibers and scaffolds. The scalable manufacturing process and potential fabrication across multiple nonwoven and woven platforms makes them promising candidates for a variety of applications that require high surface area fibrous materials.

STATEMENT OF SIGNIFICANCE

We report here for the first time the successful fabrication of novel high surface area gilled fiber scaffolds for tissue engineering applications. Gilled fibers led to a significant increase in proliferation of human adipose derived stem cells after one week in culture, and a greater number of viable cells compared to round fiber controls. Further, in the absence of osteogenic induction factors, gilled fibers led to significantly increased mRNA expression of an early marker for osteogenesis after exposure to pulsatile fluid flow. This is the first study to describe gilled fiber fabrication and their potential for tissue engineering applications. The repeatable, industrially scalable, and versatile fabrication process makes them promising candidates for a variety of scaffold-based tissue engineering applications.

Concise Review: Primary Cilia: Control Centers for Stem Cell Lineage Specification and Potential Targets for Cell-Based Therapies

Directing stem cell lineage commitment prevails as the holy grail of translational stem cell research, particularly to those interested in the application of mesenchymal stem cells and adipose-derived stem cells in tissue engineering. However, elucidating the mechanisms underlying their phenotypic specification persists as an active area of research. In recent studies, the primary cilium structure has been intimately associated with defining cell phenotype, maintaining stemness, as well as functioning in a chemo, electro, and mechanosensory capacity in progenitor and committed cell types. Many hypothesize that the primary cilium may indeed be another important player in defining and controlling cell phenotype, concomitant with lineage-dictated cytoskeletal dynamics. Many of the studies on the primary cilium have emerged from disparate areas of biological research, and crosstalk amongst these areas of research is just beginning. To date, there has not been a thorough review of how primary cilia fit into the current paradigm of stem cell differentiation and this review aims to summarize the current cilia work in this context. The goal of this review is to highlight the cilium's function and integrate this knowledge into the working knowledge of stem cell biologists and tissue engineers developing regenerative medicine technologies. Stem Cells 2016;34:1445-1454.

Advances in Adipose-Derived Stem Cells Isolation, Characterization, and Application in Regenerative Tissue Engineering

Obesity is a complex, multifactorial disease that has been extensively researched in recent times. Obesity is characterized by excess deposition of adipose tissue in response to surplus energy. Despite the negative connotations of adipose tissue (AT), it serves as a critical endocrine organ. Adipose tissue is a source of several adipokines and cytokines which have been deemed important for both normal metabolic function and disease formation. The discoveries of metabolically active brown AT in adult humans and adipose tissue derived stem cells (ADSC) have been key findings in the past decade with potential therapeutic implications. ADSCs represent an enticing pool of multipotent adult stem cells because of their noncontroversial nature, relative abundance, ease of isolation, and expandability. A decade and a half since the discovery of ADSCs, the scientific community is still working to uncover their therapeutic potential in a wide range of diseases. In this review, we provide an overview of the recent developments in the field of ADSCs and examine their potential use in transplantation and cell-based therapies for the regeneration of diseased organs and systems. We also hope to provide perspective on how to best utilize this readily available, powerful pool of stem cells in the future.

Focal Adhesion Kinase Signaling Mediated the Enhancement of Osteogenesis of Human Mesenchymal Stem Cells Induced by Extracorporeal Shockwave

Extracorporeal shockwave (ESW) has been shown of great potential in promoting the osteogenesis of bone marrow mesenchymal stem cells (BMSCs), but it is unknown whether this osteogenic promotion effect can also be achieved in other MSCs (i.e., tendon-derived stem cells (TDSCs) and adipose-derived stem cells (ADSCs)). In the current study, we aimed not only to compare the osteogenic effects of BMSCs induced by ESW to those of TDSCs and ADSCs; but also to investigate the underlying mechanisms. We show here that ESW (0.16 mj/mm(2)) significantly promoted the osteogenic differentiation in all the tested types of MSCs, accompanied with the downregulation of miR-138, but the activation of FAK, ERK1/2, and RUNX2. The enhancement of osteogenesis in these MSCs was consistently abolished when the cells were pretreated with one of the following conditions: overexpression of miR-138, FAK knockdown using specific siRNA, and U0126, implying that all of these elements are indispensable for mediating the effect of ESW. Moreover, our study provides converging genetic and molecular evidence that the miR-138-FAK-ERK1/2-RUNX2 machinery can be generally activated in ESW-preconditioned MSCs, suggesting that ESW may be a promising therapeutic strategy for the enhancement of osteogenesis of MSCs, regardless of their origins.

Advances in Adipose-Derived Stem Cells Isolation, Characterization, and Application in Regenerative Tissue Engineering

Obesity is a complex, multifactorial disease that has been extensively researched in recent times. Obesity is characterized by excess deposition of adipose tissue in response to surplus energy. Despite the negative connotations of adipose tissue (AT), it serves as a critical endocrine organ. Adipose tissue is a source of several adipokines and cytokines which have been deemed important for both normal metabolic function and disease formation. The discoveries of metabolically active brown AT in adult humans and adipose tissue derived stem cells (ADSC) have been key findings in the past decade with potential therapeutic implications. ADSCs represent an enticing pool of multipotent adult stem cells because of their noncontroversial nature, relative abundance, ease of isolation, and expandability. A decade and a half since the discovery of ADSCs, the scientific community is still working to uncover their therapeutic potential in a wide range of diseases. In this review, we provide an overview of the recent developments in the field of ADSCs and examine their potential use in transplantation and cell-based therapies for the regeneration of diseased organs and systems. We also hope to provide perspective on how to best utilize this readily available, powerful pool of stem cells in the future.

A single short session of media perfusion induces osteogenesis in hBMSCs cultured in porous scaffolds, dependent on cell differentiation stage

Perfusing culture media through porous cell-seeded scaffolds is now a common approach within many tissue engineering strategies. Human bone-marrow derived mesenchymal stem cells (hBMSC) are a clinically valuable source of osteoprogenitors that respond to mechanical stimuli. However, the optimal mechanical conditions for their osteogenic stimulation in vitro have not been defined. Whereas the effects of short durations of media fluid flow have been studied in monolayers of osteoblastic cells, in 3D culture continuous or repeated perfusion is usually applied. Here, we investigated whether a short, single perfusion session applied to hBMSCs cultured in 3D would enhance their osteogenesis in vitro. We cultured hBMSCs on gelatine-coated, porous polyurethane scaffolds with osteogenic supplements and stimulated them with a single 2-h session of unidirectional, steady, 2.5 mL/min media perfusion, at either early or late stages of culture in 3D. Some cells were pre-treated in monolayer with osteogenic supplements to advance cell differentiation, followed by 3D culture also with the osteogenic supplements. We report that this single, short session of media perfusion can markedly enhance the expression of bone-related transcription and growth factors, and matrix components, by hBMSCs but that it is more effective when cells reach the pre-osteoblast or osteoblast differentiation stage. These findings could aid in the optimization of 3D culture protocols for efficient bone tissue engineering. Biotechnol. Bioeng. 2016;113: 1814-1824. © 2016 Wiley Periodicals, Inc.

Osteogenic performance of donor-matched human adipose and bone marrow mesenchymal cells under dynamic culture

Adipose-derived mesenchymal cells (ACs) and bone marrow-derived mesenchymal cells (BMCs) have been widely used for bone regeneration and can be seeded on a variety of rigid scaffolds. However, to date, a direct comparison of mesenchymal cells (MC) harvested from different tissues from the same donor and cultured in identical osteogenic conditions has not been investigated. Indeed, it is unclear whether marrow-derived or fat-derived MC possess intrinsic differences in bone-forming capabilities, since within-patient comparisons have not been previously done. This study aims at comparing ACs and BMCs from three donors ranging in age from neonatal to adult. Matched cells from each donor were studied in three distinct bioreactor settings, to determine the best method to create a viable osseous engineered construct. Human ACs and BMCs were isolated from each donor, cultured, and seeded on decellularized porcine bone (DCB) constructs. The constructs were then subjected to either static or dynamic (stirring or perfusion) bioreactor culture conditions for 7-21 days. Afterward, the constructs were analyzed for cell adhesion and distribution and osteogenic differentiation. ACs demonstrated higher seeding efficiency than BMCs. However, static and dynamic culture significantly increased BMCs proliferation more than ACs. In all conditions, BMCs demonstrated stronger osteogenic activity as compared with ACs, through higher alkaline phosphatase activity and gene expression for various bony markers. Conversely, ACs expressed more collagen I, which is a nonspecific matrix molecule in most connective tissues. Overall, dynamic bioreactor culture conditions enhanced osteogenic gene expression in both ACs and BMCs. Scaffolds seeded with BMCs in dynamic stirring culture conditions exhibit the greatest osteogenic proliferation and function in vitro, proving that marrow-derived MC have superior bone-forming potential as compared with adipose-derived cells.

Adipose-Derived Stromal Vascular Fraction Differentially Expands Breast Progenitors in Tissue Adjacent to Tumors Compared to Healthy Breast Tissue

Supplemental Digital Content is available in the text.

Background:

Autologous fat grafts supplemented with adipose-derived stromal vascular fraction are used in reconstructive and cosmetic breast procedures. Stromal vascular fraction contains adipose-derived stem cells that are thought to encourage wound healing, tissue regeneration, and graft retention. Although use of stromal vascular fraction has provided exciting perspectives for aesthetic procedures, no studies have yet been conducted to determine whether its cells contribute to breast tissue regeneration. The authors examined the effect of these cells on the expansion of human breast epithelial progenitors.

Methods:

From patients undergoing reconstructive breast surgery following mastectomies, abdominal fat, matching tissue adjacent to breast tumors, and the contralateral non–tumor-containing breast tissue were obtained. Ex vivo co-cultures using breast epithelial cells and the stromal vascular fraction cells were used to study the expansion potential of breast progenitors. Breast reduction samples were collected as a source of healthy breast cells.

Results:

The authors observed that progenitors present in healthy breast tissue or contralateral non–tumor-containing breast tissue showed significant and robust expansion in the presence of stromal vascular fraction (5.2- and 4.8-fold, respectively). Whereas the healthy progenitors expanded up to 3-fold without the stromal vascular fraction cells, the expansion of tissue adjacent to breast tumor progenitors required the presence of stromal vascular fraction cells, leading to a 7-fold expansion, which was significantly higher than the expansion of healthy progenitors with stromal vascular fraction.

Conclusions:

The use of stromal vascular fraction might be more beneficial to reconstructive operations following mastectomies compared with cosmetic corrections of the healthy breast. Future studies are required to examine the potential risk factors associated with its use.

CLINICAL QUESTION/LEVEL OF EVIDENCE:

Therapeutic, V.

Evaluation of the effect of adipose tissue-derived stem cells on the quality of bone healing around implants

PURPOSE/AIM

This study evaluates the efficacy of grafted adipose-derived stem cells (ADSCs) on blade-type implants in improving osseointegration in rat femurs using a low-density bone model.

MATERIALS AND METHODS

After isolating and expanding ADSCs, twice-passaged cells were seeded on blade-type implants on culture plates. Osteogenic induction of grafted cells began after attaching cells to the prepared titanium surfaces and it continued for 4 days. The scaffolds were then implanted in the femurs of Wistar rats. Osteogenic differentiation of these cells was confirmed using polymerase chain reaction (PCR) and alizarin red staining of the mineralized extracellular matrix. After 8 weeks, histological and histomorphometric evaluations of undecalcified resin sections (bone-implant contact [BIC] % and bone mineral index [BMI]) were performed using light microscopy and scanning electron microscopy.

RESULTS

Alizarin red staining in conjunction with gene expression results confirmed osteogenic differentiation. Histomorphometric assessment using scanning electron microscopy demonstrated improved BIC% and BMI near the treated surface compared with the untreated surface.

CONCLUSIONS

The complex of differentiated grafted ADSCs and extracellular matrix and the macrodesign and microdesign of the implant can improve osseointegration in low-density bone.

Oscillatory shear stress mediates directional reorganization of actin cytoskeleton and alters differentiation propensity of mesenchymal stem cells

Shear stress stimuli differentially regulate cellular functions based on the pattern, magnitude as well as duration of the flow. Shear stress can modify intracellular kinase activities and cytoskeleton reorganization to result in changes of cell behavior. Mesenchymal stem cells (MSCs) are mechano-sensitive cells, but little is known about the effects of oscillatory shear stress (OS). In this study, we demonstrate that OS of 0.5 ± 4 dyn/cm(2) induces directional reorganization of F-actin to mediate the fate choice of MSCs through the regulation of β-catenin. We also found that intercellular junction molecules are the predominant mechanosensors of OS in MSCs to deliver the signals that result in directional rearrangement of F-actin, as well as the increase of phosphorylated β-catenin (pβ-catenin) after 30 minutes of OS stimulation. Depolymerization of F-actin and increase in pβ-catenin also lead to the upregulation of Wnt inhibitory factors sclerostin and dickkopf-1. Inhibition of β-catenin/Wnt signaling pathway is accompanied by the upregulation of sex determining region Y-box2 and NANOG to control self-renewal. In conclusion, the reorganization of actin cytoskeleton and increase in β-catenin phosphorylation triggered by OS regulate the expression of pluripotency genes via the β-catenin/Wnt signaling pathway to differentially direct fate choices of MSCs at different time points. Results from this study have provided new information regarding how MSCs respond to mechanical cues from their microenvironment in a time-dependent fashion, and such biophysical stimuli could be administered to guide the fate and differentiation of stem cells in addition to conventional biochemical approaches.

Comprehensive Review of Adipose Stem Cells and Their Implication in Distraction Osteogenesis and Bone Regeneration

Bone is one of the most dynamic tissues in the human body that can heal following injury without leaving a scar. However, in instances of extensive bone loss, this intrinsic capacity of bone to heal may not be sufficient and external intervention becomes necessary. Several techniques are available to address this problem, including autogenous bone grafts and allografts. However, all these techniques have their own limitations. An alternative method is the technique of distraction osteogenesis, where gradual and controlled distraction of two bony segments after osteotomy leads to induction of new bone formation. Although distraction osteogenesis usually gives satisfactory results, its major limitation is the prolonged duration of time required before the external fixator is removed, which may lead to numerous complications. Numerous methods to accelerate bone formation in the context of distraction osteogenesis have been reported. A viable alternative to autogenous bone grafts for a source of osteogenic cells is mesenchymal stem cells from bone marrow. However, there are certain problems with bone marrow aspirate. Hence, scientists have investigated other sources for mesenchymal stem cells, specifically adipose tissue, which has been shown to be an excellent source of mesenchymal stem cells. In this paper, the potential use of adipose stem cells to stimulate bone formation is discussed.

Biomechanical Screening of Cell Therapies for Vocal Fold Scar

Candidate cell sources for vocal fold scar treatment include mesenchymal stromal cells from bone marrow (BM-MSC) and adipose tissue (AT-MSC). Mechanosensitivity of MSC can alter highly relevant aspects of their behavior, yet virtually nothing is known about how MSC might respond to the dynamic mechanical environment of the larynx. Our objective was to evaluate MSC as a potential cell source for vocal fold tissue engineering in a mechanically relevant context. A vibratory strain bioreactor and cDNA microarray were used to evaluate the similarity of AT-MSC and BM-MSC to the native cell source, vocal fold fibroblasts (VFF). Posterior probabilities for each of the microarray transcripts fitting into specific expression patterns were calculated, and the data were analyzed for Gene Ontology (GO) enrichment. Significant wound healing and cell differentiation GO terms are reported. In addition, proliferation and apoptosis were evaluated with immunohistochemistry. Results revealed that VFF shared more GO terms related to epithelial development, extracellular matrix (ECM) remodeling, growth factor activity, and immune response with BM-MSC than with AT-MSC. Similarity in glycosaminoglycan and proteoglycan activity dominated the ECM analysis. Analysis of GO terms relating to MSC differentiation toward osteogenic, adipogenic, and chondrogenic lineages revealed that BM-MSC expressed fewer osteogenesis GO terms in the vibrated and scaffold-only conditions compared to polystyrene. We did not evaluate if vibrated BM-MSC recover osteogenic expression markers when returned to polystyrene culture. Immunostaining for Ki67 and cleaved caspase 3 did not vary with cell type or mechanical condition. We conclude that VFF may have a more similar wound healing capacity to BM-MSC than to AT-MSC in response to short-term vibratory strain. Furthermore, BM-MSC appear to lose osteogenic potential in the vibrated and scaffold-only conditions compared to polystyrene, potentially attenuating the risk of osteogenesis for in vivo applications.