β-Catenin mediates cyclic strain-stimulated cardiomyogenesis in mouse embryonic stem cells through ROS-dependent and integrin-mediated PI3K/Akt pathways

Three-Dimensional Stretchable Sensor-Hydrogel Integrated Platform for Cardiomyocyte Culture and Mechanotransduction Monitoring

Cardiomyocytes are responsible for generating contractile force to pump blood throughout the body and are very sensitive to mechanical forces and can initiate mechano-electric coupling and mechano-chemo-transduction. Remarkable progress has been made in constructing heart tissue by engineered three-dimensional (3D) culture models and in recording the electrical signals of cardiomyocytes. However, it remains a severe challenge for real-time acquiring of the transient biochemical information in cardiomyocyte mechano-chemo-transduction. Herein, we reported a multifunctional platform by integrating a 3D stretchable electrochemical sensor with collagen hydrogel for the culture, electrical stimulation, and electrochemical monitoring of cardiomyocytes. The 3D stretchable electrochemical sensor was prepared by assembling functionalized conductive polymer PEDOT:PSS on an elastic scaffold, which showed excellent electrochemical sensing performance and stability under mechanical deformations. The integration of a 3D stretchable electrochemical sensor with collagen hydrogel provided an in vivo-like microenvironment for cardiomyocyte culture and promoted cell orientation via in situ electrical stimulation. Furthermore, this multifunctional platform allowed real-time monitoring of stretch-induced H2O2 release from cardiomyocytes under their normal and pathological conditions, as well as pharmacological interventions.

Development of a Pneumatic-Driven Fiber-Shaped Robot Scaffold for Use as a Complex 3D Dynamic Culture System

Cells can sense and respond to different kinds of continuous mechanical strain in the human body. Mechanical stimulation needs to be included within the in vitro culture system to better mimic the existing complexity of in vivo biological systems. Existing commercial dynamic culture systems are generally two-dimensional (2D) which fail to mimic the three-dimensional (3D) native microenvironment. In this study, a pneumatically driven fiber robot has been developed as a platform for 3D dynamic cell culture. The fiber robot can generate tunable contractions upon stimulation. The surface of the fiber robot is formed by a braiding structure, which provides promising surface contact and adequate space for cell culture. An in-house dynamic stimulation using the fiber robot was set up to maintain NIH3T3 cells in a controlled environment. The biocompatibility of the developed dynamic culture systems was analyzed using LIVE/DEAD™ and alamarBlue™ assays. The results showed that the dynamic culture system was able to support cell proliferation with minimal cytotoxicity similar to static cultures. However, we observed a decrease in cell viability in the case of a high strain rate in dynamic cultures. Differences in cell arrangement and proliferation were observed between braided sleeves made of different materials (nylon and ultra-high molecular weight polyethylene). In summary, a simple and cost-effective 3D dynamic culture system has been proposed, which can be easily implemented to study complex biological phenomena in vitro.

Dynamic mechanobiology of cardiac cells and tissues: Current status and future perspective

Mechanical forces impact cardiac cells and tissues over their entire lifespan, from development to growth and eventually to pathophysiology. However, the mechanobiological pathways that drive cell and tissue responses to mechanical forces are only now beginning to be understood, due in part to the challenges in replicating the evolving dynamic microenvironments of cardiac cells and tissues in a laboratory setting. Although many in vitro cardiac models have been established to provide specific stiffness, topography, or viscoelasticity to cardiac cells and tissues via biomaterial scaffolds or external stimuli, technologies for presenting time-evolving mechanical microenvironments have only recently been developed. In this review, we summarize the range of in vitro platforms that have been used for cardiac mechanobiological studies. We provide a comprehensive review on phenotypic and molecular changes of cardiomyocytes in response to these environments, with a focus on how dynamic mechanical cues are transduced and deciphered. We conclude with our vision of how these findings will help to define the baseline of heart pathology and of how these in vitro systems will potentially serve to improve the development of therapies for heart diseases.

Wnt 3a Protects Myocardial Injury in Elderly Acute Myocardial Infarction by Inhibiting Serum Cystatin C/ROS-Induced Mitochondrial Damage

Aging represents an independent risk factor affecting the poor prognosis of patients with acute myocardial infarction (AMI). This present research aimed to explore the molecular mechanism of myocardial injury in elderly AMI by animals and cells experiment. Our previous clinical study found the serum Cystatin C (Cys-C) increased in the elderly AMI population, while the mechanism underlying high Cys-C induced myocardial injury of AMI remains unclear. In the in-vitro study, we confirmed that Wnt/β-catenin could significantly reduce the expression of cytoplasmic Cys-C through transnuclear action, and highly attenuate the occurrence of mitochondrial oxidative stress injury induced via Cys-C/reactive oxygen species (ROS). Furthermore, the addition of exogenous Wnt3a and inhibition of Cys-C expression could effectively inhibit mitochondrial oxidative stress injury and relieve the acute myocardial hypoxia injury. These results indicate that Cys-C exerted damaging effects on the hypoxic aging cardiomyocyte through the ROS/mitochondrial signaling pathway. Inhibition of this pathway effectively reduced the apoptosis of aging cardiomyocytes. In the in-vivo study, we also explored the function of the Wnt/Cys-C pathway on the ischemic infarction heart. We confirmed that Wnt/β-catenin served as the upstream protective protein of this pathway, and the promotion of this pathway improved the cardiac structure and function of the elderly AMI mice effectively.

The effect of AKT in extracellular matrix stiffness induced osteogenic differentiation of hBMSCs

Extracellular matrix (ECM) stiffness is an important biophysical factor in human bone marrow mesenchymal stem cells (hBMSCs) differentiation. Although there is evidence that Yes-associated protein (YAP) plays an important role in ECM elasticity induced osteogenesis, but the regulatory mechanism and signaling pathways have not been distinctly uncovered. In this study, hBMSCs were cultured on collagen-coated polydimethylsiloxane hydrogels with stiffness corresponding to Young's moduli of 0.5 kPa and 32 kPa, and gene chip analyses revealed the phosphoinositide 3-kinase (PI3K)-AKT pathway was highly correlated with ECM stiffness. Following western blots indicated that AKT phosphorylation was evidently affected in 5th-7th days after ECM stiffness stimulation, while PI3K showed little difference. The AKT activator SC79 and inhibitor MK2206 were utilized to modulate AKT phosphorylation. SC79 and MK2206 caused alteration in the mRNA expression and protein level of alkaline phosphatase (ALP), collagen type I alpha 1 (COL1A1) and runt related transcription factor 2 (RUNX2). On 32 kPa substrates, YAP enrichment in nucleus were significantly promoted by SC79 and remarkably decreased by MK2206. Besides, the ratio of YAP/p-YAP is upregulated by SC79 on both 32 kPa and 0.5 kPa substrates. In conclusion, these findings suggest that AKT is involved in the modulation of ECM stiffness induced osteogenesis, and AKT phosphorylation also influences the subcellular localization and activation of YAP.

Self-Sustained Regulation or Self-Perpetuating Dysregulation: ROS-dependent HIF-YAP-Notch Signaling as a Double-Edged Sword on Stem Cell Physiology and Tumorigenesis

Organ development, homeostasis, and repair often rely on bidirectional, self-organized cell-niche interactions, through which cells select cell fate, such as stem cell self-renewal and differentiation. The niche contains multiplexed chemical and mechanical factors. How cells interpret niche structural information such as the 3D topology of organs and integrate with multiplexed mechano-chemical signals is an open and active research field. Among all the niche factors, reactive oxygen species (ROS) have recently gained growing interest. Once considered harmful, ROS are now recognized as an important niche factor in the regulation of tissue mechanics and topology through, for example, the HIF-YAP-Notch signaling pathways. These pathways are not only involved in the regulation of stem cell physiology but also associated with inflammation, neurological disorder, aging, tumorigenesis, and the regulation of the immune checkpoint molecule PD-L1. Positive feedback circuits have been identified in the interplay of ROS and HIF-YAP-Notch signaling, leading to the possibility that under aberrant conditions, self-organized, ROS-dependent physiological regulations can be switched to self-perpetuating dysregulation, making ROS a double-edged sword at the interface of stem cell physiology and tumorigenesis. In this review, we discuss the recent findings on how ROS and tissue mechanics affect YAP-HIF-Notch-PD-L1 signaling, hoping that the knowledge can be used to design strategies for stem cell-based and ROS-targeting therapy and tissue engineering.

The Oxidative Balance Orchestrates the Main Keystones of the Functional Activity of Cardiomyocytes

This review is aimed at providing an overview of the key hallmarks of cardiomyocytes in physiological and pathological conditions. The main feature of cardiac tissue is the force generation through contraction. This process requires a conspicuous energy demand and therefore an active metabolism. The cardiac tissue is rich of mitochondria, the powerhouses in cells. These organelles, producing ATP, are also the main sources of ROS whose altered handling can cause their accumulation and therefore triggers detrimental effects on mitochondria themselves and other cell components thus leading to apoptosis and cardiac diseases. This review highlights the metabolic aspects of cardiomyocytes and wanders through the main systems of these cells: (a) the unique structural organization (such as different protein complexes represented by contractile, regulatory, and structural proteins); (b) the homeostasis of intracellular Ca²⁺ that represents a crucial ion for cardiac functions and E-C coupling; and (c) the balance of Zn²⁺, an ion with a crucial impact on the cardiovascular system. Although each system seems to be independent and finely controlled, the contractile proteins, intracellular Ca²⁺ homeostasis, and intracellular Zn²⁺ signals are strongly linked to each other by the intracellular ROS management in a fascinating way to form a "functional tetrad" which ensures the proper functioning of the myocardium. Nevertheless, if ROS balance is not properly handled, one or more of these components could be altered resulting in deleterious effects leading to an unbalance of this "tetrad" and promoting cardiovascular diseases. In conclusion, this "functional tetrad" is proposed as a complex network that communicates continuously in the cardiomyocytes and can drive the switch from physiological to pathological conditions in the heart.

The role of statins in the differentiation and function of bone cells

BACKGROUND

Statins are 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors blocking cholesterol biosynthesis in hepatic cells, thereby causing an increase in low-density lipoprotein (LDL) receptors resulting in enhanced uptake and clearance of atherogenic LDL-cholesterol (LDL-C) from the blood. Accordingly, statins decrease the risk of developing atherosclerosis and its acute complications, such as acute myocardial infarction and ischaemic stroke. Besides the LDL-C-lowering impact, statins also have other so-called pleiotropic effects. Among them, the ability to modulate differentiation and function of bone cells and exert direct effects on osteosynthesis factors. Specifically, earlier studies have shown that statins cause in vitro and in vivo osteogenic differentiation.

DESIGN

The most relevant papers on the bone-related 'pleiotropic' effects of statins were selected following literature search in databases and were reveiwed.

RESULTS

Statins increase the expression of many mediators involved in bone metabolism including bone morphogenetic protein-2 (BMP-2), glucocorticoids, transforming growth factor-beta (TGF-β), alkaline phosphatase (ALP), type I collagen and collagenase-1. As a result, they enhance bone formation and improve bone mineral density by modulating osteoblast and osteoclast differentiation.

CONCLUSION

This review summarizes the literature exploring bone-related 'pleiotropic' effects of statins and suggests an anabolic role in the bone tissue for this drug class. Accordingly, current knowledge encourages further clinical trials to assess the therapeutic potential of statins in the treatment of bone disorders, such as arthritis and osteoporosis.

Multifunctional Conductive Biomaterials as Promising Platforms for Cardiac Tissue Engineering

Adult cardiomyocytes are terminally differentiated cells that result in minimal intrinsic potential for the heart to self-regenerate. The introduction of novel approaches in cardiac tissue engineering aims to repair damages from cardiovascular diseases. Recently, conductive biomaterials such as carbon- and gold-based nanomaterials, conductive polymers, and ceramics that have outstanding electrical conductivity, acceptable mechanical properties, and promoted cell-cell signaling transduction have attracted attention for use in cardiac tissue engineering. Nevertheless, comprehensive classification of conductive biomaterials from the perspective of cardiac cell function is a subject for discussion. In the present review, we classify and summarize the unique properties of conductive biomaterials considered beneficial for cardiac tissue engineering. We attempt to cover recent advances in conductive biomaterials with a particular focus on their effects on cardiac cell functions and proposed mechanisms of action. Finally, current problems, limitations, challenges, and suggested solutions for applications of these biomaterials are presented.

Roles of Reactive Oxygen Species in Cardiac Differentiation, Reprogramming, and Regenerative Therapies

Reactive oxygen species (ROS) have been implicated in mechanisms of heart development and regenerative therapies such as the use of pluripotent stem cells. The roles of ROS mediating cell fate are dependent on the intensity of stimuli, cellular context, and metabolic status. ROS mainly act through several targets (such as kinases and transcription factors) and have diverse roles in different stages of cardiac differentiation, proliferation, and maturation. Therefore, further detailed investigation and characterization of redox signaling will help the understanding of the molecular mechanisms of ROS during different cellular processes and enable the design of targeted strategies to foster cardiac regeneration and functional recovery. In this review, we focus on the roles of ROS in cardiac differentiation as well as transdifferentiation (direct reprogramming). The potential mechanisms are discussed in regard to ROS generation pathways and regulation of downstream targets. Further methodological optimization is required for translational research in order to robustly enhance the generation efficiency of cardiac myocytes through metabolic modulations. Additionally, we highlight the deleterious effect of the host's ROS on graft (donor) cells in a paracrine manner during stem cell-based implantation. This knowledge is important for the development of antioxidant strategies to enhance cell survival and engraftment of tissue engineering-based technologies. Thus, proper timing and level of ROS generation after a myocardial injury need to be tailored to ensure the maximal efficacy of regenerative therapies and avoid undesired damage.

The Role of Oxidative Stress in Cardiac Disease: From Physiological Response to Injury Factor

Reactive oxygen species (ROS) are highly reactive chemical species containing oxygen, controlled by both enzymatic and nonenzymatic antioxidant defense systems. In the heart, ROS play an important role in cell homeostasis, by modulating cell proliferation, differentiation, and excitation-contraction coupling. Oxidative stress occurs when ROS production exceeds the buffering capacity of the antioxidant defense systems, leading to cellular and molecular abnormalities, ultimately resulting in cardiac dysfunction. In this review, we will discuss the physiological sources of ROS in the heart, the mechanisms of oxidative stress-related myocardial injury, and the implications of experimental studies and clinical trials with antioxidant therapies in cardiovascular diseases.

Pkm2 Regulates Cardiomyocyte Cell Cycle and Promotes Cardiac Regeneration

BACKGROUND

The adult mammalian heart has limited regenerative capacity, mostly attributable to postnatal cardiomyocyte cell cycle arrest. In the last 2 decades, numerous studies have explored cardiomyocyte cell cycle regulatory mechanisms to enhance myocardial regeneration after myocardial infarction. Pkm2 (Pyruvate kinase muscle isoenzyme 2) is an isoenzyme of the glycolytic enzyme pyruvate kinase. The role of Pkm2 in cardiomyocyte proliferation, heart development, and cardiac regeneration is unknown.

METHODS

We investigated the effect of Pkm2 in cardiomyocytes through models of loss (cardiomyocyte-specific Pkm2 deletion during cardiac development) or gain using cardiomyocyte-specific Pkm2 modified mRNA to evaluate Pkm2 function and regenerative affects after acute or chronic myocardial infarction in mice.

RESULTS

Here, we identify Pkm2 as an important regulator of the cardiomyocyte cell cycle. We show that Pkm2 is expressed in cardiomyocytes during development and immediately after birth but not during adulthood. Loss of function studies show that cardiomyocyte-specific Pkm2 deletion during cardiac development resulted in significantly reduced cardiomyocyte cell cycle, cardiomyocyte numbers, and myocardial size. In addition, using cardiomyocyte-specific Pkm2 modified RNA, our novel cardiomyocyte-targeted strategy, after acute or chronic myocardial infarction, resulted in increased cardiomyocyte cell division, enhanced cardiac function, and improved long-term survival. We mechanistically show that Pkm2 regulates the cardiomyocyte cell cycle and reduces oxidative stress damage through anabolic pathways and β-catenin.

CONCLUSIONS

We demonstrate that Pkm2 is an important intrinsic regulator of the cardiomyocyte cell cycle and oxidative stress, and highlight its therapeutic potential using cardiomyocyte-specific Pkm2 modified RNA as a gene delivery platform.

Rolling-sliding load decreases the loss of chondrocyte viability and the mechanical properties of cartilage explants preserved in vitro

The viability of cartilage explants preserved in vitro decreases with time, which limits its use for transplantation. The effect of mechanical stimulation to cartilage explants in vitro is unknown. In this study, we observed the effects of mechanical stimulation on chondrocyte viability and the mechanical properties of cartilage explants preserved in vitro using a rolling-sliding loading device designed by us, and the optimal stimulation protocol was established. A cylindrical osteochondral mass drilled on the femoral condyle of a healthy pig was divided into two groups (loading group and control group), and changes in the chondrocyte survival rate, matrix composition and cartilage biomechanical properties was observed at different time points. Additionally, the mRNA expression of the apoptosis-related proteins caspase-3/Bax/Bcl-2, the cytoskeletal proteins actin/vimentin, and the matrix-related protein MMP13 were detected. The loading group exhibited delayed collagen and aggrecan degeneration and improved chondrocyte viability for three days. Protein and mRNA detection showed that apoptotic factors such as caspase-3 and Bax decreased rapidly in cartilage tissue after loading. The cytoskeletal proteins actin and vimentin showed no significant changes in mRNA expression in the control group, but was significantly higher in the loading group. MMP-13 mRNA expression was significantly higher in both the control group and loading group. Overall, this study suggests that suitable mechanical stimulation decreases the loss of chondrocyte viability and the mechanical properties of cartilage explants in vitro and improves cartilage preservation.

Comparative study of variations in mechanical stress and strain of human blood vessels: mechanical reference for vascular cell mechano-biology

The diseases of human blood vessels are closely associated with local mechanical variations. A better understanding of the quantitative correlation in mechanical environment between the current mechano-biological studies and vascular physiological or pathological conditions in vivo is crucial for evaluating numerous existing results and exploring new factors for disease discovery. In this study, six representative human blood vessels with known experimental measurements were selected, and their stress and strain variations in vessel walls under different blood pressures were analyzed based on nonlinear elastic theory. The results suggest that conventional mechano-biological experiments seeking the different biological expressions of cells at high/low mechanical loadings are ambiguous as references for studying vascular diseases, because distinct "site-specific" characteristics appear in different vessels. The present results demonstrate that the inner surface of the vessel wall does not always suffer the most severe stretch under high blood pressures comparing to the outer surface. Higher tension on the outer surface of aortas supports the hypothesis of the outside-in inflammation dominated by aortic adventitial fibroblasts. These results indicate that cellular studies at different mechanical niches should be "disease-specific" as well. The present results demonstrate considerable stress gradients across the wall thickness, which indicate micro-scale mechanical variations existing around the vascular cells, and imply that the physiological or pathological changes are not static processes confined within isolated regions, but are coupled with dynamic cell behaviors such as migration. The results suggest that the stress gradients, as well as the mechanical stresses and strains, are key factors constituting the mechanical niches, which may shed new light on "factor-specific" experiments of vascular cell mechano-biology.

The Role of Reactive Oxygen Species in In Vitro Cardiac Maturation

Recent advances in developmental biology and biomedical engineering have significantly improved the efficiency and purity of cardiomyocytes (CMs) generated from pluripotent stem cells (PSCs). Regardless of the protocol used to derive CMs, these cells exhibit hallmarks of functional immaturity. In this Opinion, we focus on reactive oxygen species (ROS), signaling molecules that can potentially modulate cardiac maturation. We outline how ROS impacts nearly every aspect associated with cardiac maturation, including contractility, calcium handling, metabolism, and hypertrophy. Though the precise role of ROS in cardiac maturation has yet to be elucidated, ROS may provide a valuable perspective for understanding the molecular mechanisms for cardiac maturation under various conditions.

Met-enkephalin inhibits ROS production through Wnt/β-catenin signaling in the ZF4 cells of zebrafish

Opioid neuropeptides are developed early in the course of a long evolutionary process. As the endogenous messengers of immune system, opioid neuropeptides participate in regulating immune response. In this study, the mechanism that Met-enkephalin (M-ENK) inhibits ROS production through Wnt/β-catenin signaling was investigated in the ZF4 cells of zebrafish. ZF4 cells were exposed to 0, 10, 20, 40, 80, and 160 μM Met-enkephalin (M-ENK) for 24 h, and the cell viability was detected with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. The cell viability was significantly increased by 10, 20, 40, 80, and 160 μM M-ENK. After ZF4 cells were exposed to 0, 20, 40, and 80 μM M-ENK for 24 h, the mRNA expression of Wnt10b, β-catenin, and CCAAT/enhancer binding protein α (C/EBPα) was significantly increased by 40 and 80 μM M-ENK. However, the mRNA and protein expression of GSK-3β was significantly decreased by 40 and 80 μM M-ENK. The protein expression of β-catenin was significantly induced by 40 and 80 μM M-ENK, while the protein expression of p-β-catenin was significantly decreased by 20, 40, and 80 μM M-ENK. In addition, the mRNA expression of CAT, SOD, and GSH-PX was significantly increased by 40 and 80 μM M-ENK. The levels of H₂O₂, ·OH, and O₂^·- were significantly decreased, but the activity of CAT, SOD, and GSH-PX was significantly increased by 40 and 80 μM M-ENK. The fluorescence intensity of reactive oxygen species (ROS) was decreased, and that of mitochondrial membrane potential (MMP) was increased with the increase of M-ENK concentration in ZF4 cells. The results showed that M-ENK could induce Wnt/β-catenin signaling, which further inhibited ROS production through the induction of C/EBPα, MMP, and the activities of antioxidant enzymes.

Overexpression of miR-27b-3p Targeting Wnt3a Regulates the Signaling Pathway of Wnt/β-Catenin and Attenuates Atrial Fibrosis in Rats with Atrial Fibrillation

MicroRNAs (miRNAs) are regarded as a potential method for the treatment of atrial fibrillation (AF) although its molecular mechanism remains unknown. We found in our previous study that the level of peripheral blood miR-27b-3p and the expression of atrial tissue CX43 were both significantly downregulated in AF patients. In the present study, we propose and test this hypothesis that overexpression of miR-27b-3p attenuates atrial fibrosis, increases CX43 expression, and regulates the signaling pathway of Wnt/β-Catenin by targeting Wnt3a. miR-27b-3p overexpression was induced by rat tail vein injection of adeno-associated virus. Two weeks after transfection of adeno-associated virus, the rat AF model was established by tail vein injection of acetylcholine- (ACh-) CaCl₂ for 7 days, and 1 ml/kg was injected daily. The incidence and duration of AF were recorded with an electrocardiogram. Cardiac function was monitored by cardiac ultrasound. Serum cardiac enzyme was detected by ELISA. The expression of atrial miR-27b-3 and Wnt3a was assayed by quantitative RT-PCR. Atrial fibrosis was determined by Masson's trichrome staining. Expression of atrial Collagen-I and Collagen-III was tested by the immunohistochemical method. Expression of CX43 was measured by immunofluorescence. The expression of Collagen-I, a-SMA, Collagen-III, TGF-β1, CX43, Wnt3a, β-Catenin, and p-β-Catenin was assayed by western blot. Our results showed that miR-27b-3p overexpression could reduce the incidence and duration of AF, alleviate atrial fibrosis, increase atrial CX43 expression, and decrease the expression of Collagen-I, a-SMA, Collagen-III, TGF-β1, Wnt3a, and p-β-Catenin. In addition, the results of luciferase activity assay showed that Wnt3a is a validated miR-27b-3p target in HEK 293T cells. Our results provide a new evidence that miR-27b-3p regulates the signaling pathway of Wnt/β-Catenin by targeting Wnt3a, which may play an important role in the development of atrial fibrosis and AF.

Gap Junctions and Wnt Signaling in the Mammary Gland: a Cross-Talk?

Connexins (Cxs), the building blocks of gap junctions (GJs), exhibit spatiotemporal patterns of expression and regulate the development and differentiation of the mammary gland, acting via channel-dependent and channel-independent mechanisms. Impaired Cx expression and localization are reported in breast cancer, suggesting a tumor suppressive role for Cxs. The signaling events that mediate the role of GJs in the development and tumorigenesis of the mammary gland remain poorly identified. The Wnt pathways, encompassing the canonical or the Wnt/β-catenin pathway and the noncanonical β-catenin-independent pathway, also play important roles in those processes. Indeed, aberrant Wnt signaling is associated with breast cancer. Despite the coincident roles of Cxs and Wnt pathways, the cross-talk in the breast tissue is poorly defined, although this is reported in a number of other tissues. Our previous studies revealed a channel-independent role for Cx43 in inducing differentiation or suppressing tumorigenesis of mammary epithelial cells by acting as a negative regulator of the Wnt/β-catenin pathway. Here, we provide a brief overview of mammary gland development, with emphasis on the role of Cxs in development and tumorigenesis of this tissue. We also discuss the role of Wnt signaling in similar contexts, and review the literature illustrating interplay between Cxs and Wnt pathways.

Ablation of a Single N-Glycosylation Site in Human FSTL 1 Induces Cardiomyocyte Proliferation and Cardiac Regeneration

Adult mammalian hearts have a very limited regeneration capacity, due largely to a lack of cardiomyocyte (CM) proliferation. It was recently reported that epicardial, but not myocardial, follistatin-like 1 (Fstl1) activates CM proliferation and cardiac regeneration after myocardial infarction (MI). Furthermore, bacterially synthesized human FSTL 1 (hFSTL1) was found to induce CM proliferation, whereas hFSTL1 synthesized in mammals did not, suggesting that post-translational modifications (e.g., glycosylation) of the hFSTL1 protein affect its regenerative activity. We used modified mRNA (modRNA) technology to investigate the possible role of specific hFSTL1 N-glycosylation sites in the induction, by hFSTL1, of CM proliferation and cardiac regeneration. We found that the mutation of a single site (N180Q) was sufficient and necessary to increase the proliferation of rat neonatal and mouse adult CMs in vitro and after MI in vivo, respectively. A single administration of the modRNA construct encoding the N180Q mutant significantly increased cardiac function, decreased scar size, and increased capillary density 28 days post-MI. Overall, our data suggest that the delivery of N180Q hFSTL1 modRNA to the myocardium can mimic the beneficial effect of epicardial hFSTL1, triggering marked CM proliferation and cardiac regeneration in a mouse MI model.

Dural effects of oxidative stress on cardiomyogenesis via Gata4 transcription and protein ubiquitination

Oxidative stress generates reactive oxygen species (ROS) that can promote or inhibit cardiac differentiation of stem cells dependent on the intensity of stimuli as well as cellular context in redox and differentiation status. In the current study, we confirmed that suitable intensity of hydrogen peroxide at the formation stage of embryoid bodies (EBs) effectively favored the formation of spontaneously beating cardiomyocytes from P19 embryonal carcinoma cells. Mechanistic studies implicated that extrinsic ROS enhanced the Caspase-mediated degradation of Oct4 and Nanog, two factors that governing pluripotent property. Further experiments suggested that a cohort of Nanog together with histone deacetylase 4 (Hdac4) played a critical role in establishing and maintaining the silent transcriptional status of Gata4 and Nkx2.5 in undifferentiated cells. Thus, an impulse of hydrogen peroxide depleted Nanog and Hdac4 via a caspase-dependent manner to ameliorate the repression on Gata4 and Nkx2.5 promoters, thereby generating a persistent activation on cardiac differentiation program. Meanwhile, we found that excessive ROS-activated JNK cascade to facilitate the ubiquitination and subsequent degradation of Gata4 protein. Overall, our results indicate that suitable ROS promotes the activation of Gata4 in transcription, while excessive ROS targets Gata4 protein for proteasome-dependent degradation. Gata4 is an important modulator balancing the promoting and inhibitory effects of oxidative stress on differentiation program of cardiomyogenesis.

Understanding the extracellular forces that determine cell fate and maintenance

Stem cells interpret signals from their microenvironment while simultaneously modifying the niche through secreting factors and exerting mechanical forces. Many soluble stem cell cues have been determined over the past century, but in the past decade, our molecular understanding of mechanobiology has advanced to explain how passive and active forces induce similar signaling cascades that drive self-renewal, migration, differentiation or a combination of these outcomes. Improvements in stem cell culture methods, materials and biophysical tools that assess function have improved our understanding of these cascades. Here, we summarize these advances and offer perspective on ongoing challenges.

Nox, Reactive Oxygen Species and Regulation of Vascular Cell Fate

The generation of reactive oxygen species (ROS) and an imbalance of antioxidant defence mechanisms can result in oxidative stress. Several pro-atherogenic stimuli that promote intimal-medial thickening (IMT) and early arteriosclerotic disease progression share oxidative stress as a common regulatory pathway dictating vascular cell fate. The major source of ROS generated within the vascular system is the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes (Nox), of which seven members have been characterized. The Nox family are critical determinants of the redox state within the vessel wall that dictate, in part the pathophysiology of several vascular phenotypes. This review highlights the putative role of ROS in controlling vascular fate by promoting endothelial dysfunction, altering vascular smooth muscle phenotype and dictating resident vascular stem cell fate, all of which contribute to intimal medial thickening and vascular disease progression.

Molecular and Cellular Mechanisms of Cardiovascular Disorders in Diabetes

The clinical correlations linking diabetes mellitus with accelerated atherosclerosis, cardiomyopathy, and increased post-myocardial infarction fatality rates are increasingly understood in mechanistic terms. The multiple mechanisms discussed in this review seem to share a common element: prolonged increases in reactive oxygen species (ROS) production in diabetic cardiovascular cells. Intracellular hyperglycemia causes excessive ROS production. This activates nuclear poly(ADP-ribose) polymerase, which inhibits GAPDH, shunting early glycolytic intermediates into pathogenic signaling pathways. ROS and poly(ADP-ribose) polymerase also reduce sirtuin, PGC-1α, and AMP-activated protein kinase activity. These changes cause decreased mitochondrial biogenesis, increased ROS production, and disturbed circadian clock synchronization of glucose and lipid metabolism. Excessive ROS production also facilitates nuclear transport of proatherogenic transcription factors, increases transcription of the neutrophil enzyme initiating NETosis, peptidylarginine deiminase 4, and activates the NOD-like receptor family, pyrin domain-containing 3 inflammasome. Insulin resistance causes excessive cardiomyocyte ROS production by increasing fatty acid flux and oxidation. This stimulates overexpression of the nuclear receptor PPARα and nuclear translocation of forkhead box O 1, which cause cardiomyopathy. ROS also shift the balance between mitochondrial fusion and fission in favor of increased fission, reducing the metabolic capacity and efficiency of the mitochondrial electron transport chain and ATP synthesis. Mitochondrial oxidative stress also plays a central role in angiotensin II-induced gap junction remodeling and arrhythmogenesis. ROS contribute to sudden death in diabetics after myocardial infarction by increasing post-translational protein modifications, which cause increased ryanodine receptor phosphorylation and downregulation of sarco-endoplasmic reticulum Ca(++)-ATPase transcription. Increased ROS also depress autonomic ganglion synaptic transmission by oxidizing the nAch receptor α3 subunit, potentially contributing to the increased risk of fatal cardiac arrhythmias associated with diabetic cardiac autonomic neuropathy.

Dual effect of fetal bovine serum on early development depends on stage-specific reactive oxygen species demands in pigs

Despite the application of numerous supplements to improve in vitro culture (IVC) conditions of mammalian cells, studies regarding the effect of fetal bovine serum (FBS) on mammalian early embryogenesis, particularly in relation to redox homeostasis, are lacking. Herein, we demonstrated that early development of in vitro-produced (IVP) porcine embryos highly depends on the combination of FBS supplementation timing and embryonic reactive oxygen species (ROS) requirements. Interestingly, FBS significantly reduced intracellular ROS levels in parthenogenetically activated (PA) embryos regardless of the developmental stage. However, the beneficial effect of FBS on early embryogenesis was found only during the late phase (IVC 4-6 days) treatment group. In particular, developmental competence parameters, such as blastocyst formation rate, cellular survival, total cell number and trophectoderm proportion, were markedly increased by FBS supplementation during the late IVC phase. In addition, treatment with FBS elevated antioxidant transcript levels during the late IVC phase. In contrast, supplementation with FBS during the entire period (1-6 days) or during the early IVC phase (1-2 days) greatly impaired the developmental parameters. Consistent with the results from PA embryos, the developmental competence of in vitro fertilization (IVF) or somatic cell nuclear transfer (SCNT) embryos were markedly improved by treatment with FBS during the late IVC phase. Moreover, the embryonic stage-specific effects of FBS were reversed by the addition of an oxidant and were mimicked by treatment with an antioxidant. These findings may increase our understanding of redox-dependent early embryogenesis and contribute to the large-scale production of high-quality IVP embryos.

Increasing β-catenin/Wnt3A activity levels drive mechanical strain-induced cell cycle progression through mitosis

Mechanical force and Wnt signaling activate β-catenin-mediated transcription to promote proliferation and tissue expansion. However, it is unknown whether mechanical force and Wnt signaling act independently or synergize to activate β-catenin signaling and cell division. We show that mechanical strain induced Src-dependent phosphorylation of Y654 β-catenin and increased β-catenin-mediated transcription in mammalian MDCK epithelial cells. Under these conditions, cells accumulated in S/G2 (independent of DNA damage) but did not divide. Activating β-catenin through Casein Kinase I inhibition or Wnt3A addition increased β-catenin-mediated transcription and strain-induced accumulation of cells in S/G2. Significantly, only the combination of mechanical strain and Wnt/β-catenin activation triggered cells in S/G2 to divide. These results indicate that strain-induced Src phosphorylation of β-catenin and Wnt-dependent β-catenin stabilization synergize to increase β-catenin-mediated transcription to levels required for mitosis. Thus, local Wnt signaling may fine-tune the effects of global mechanical strain to restrict cell divisions during tissue development and homeostasis.

DOI:http://dx.doi.org/10.7554/eLife.19799.001

Tissues and organs can both produce and respond to physical forces. For example, the lungs expand and contract; the heart pumps blood; and bones and muscles grow or shrink depending on how much they are used. These responses are possible because cells contain proteins that can respond to physical forces. One of the best studied of these is a protein called β-catenin, which increases the activity of genes that trigger cells to divide to promote the expansion of tissues. β-catenin is over-active in many types of cancer cells where it contributes to tumor growth. In addition to being switched on by mechanical force, β-catenin is also activated when cells detect a signal molecule called Wnt.

Cells cycle through a series of stages known as the cell cycle to ensure that they only divide when they are fully prepared to do so. Benham-Pyle et al. investigated if physical force and Wnt activate β-catenin in the same way or if they have different effects on cell division. The experiments were conducted on dog kidney cells that had left the cell cycle and had therefore temporarily stopped dividing. Physical forces, such as stretching, resulted in β-catenin being modified by an enzyme called SRC kinase, which allowed the cells to re-enter the cell cycle. On the other hand, Wnt stabilized β-catenin and temporarily increased the number of cell divisions.

When mechanical stretch and Wnt signaling were combined, the cells were more likely to re-enter the cell cycle and divide compared to either stimulus alone. These data suggest that physical force and Wnt signaling affect β-catenin differently and that they can therefore have a greater effect on cell or tissue growth when they act together than on their own.

The findings of Benham-Pyle et al. show that β-catenin is not simply switched on or off, but can have different levels of activity depending on the input the cells are receiving. Future experiments will test whether these mechanisms also exist in three-dimensional tissues, which will help us understand how organs develop.

DOI:http://dx.doi.org/10.7554/eLife.19799.002

Mechanical Forces Reshape Differentiation Cues That Guide Cardiomyogenesis

Soluble morphogen gradients have long been studied in the context of heart specification and patterning. However, recent data have begun to challenge the notion that long-standing in vivo observations are driven solely by these gradients alone. Evidence from multiple biological models, from stem cells to ex vivo biophysical assays, now supports a role for mechanical forces in not only modulating cell behavior but also inducing it de novo in a process termed mechanotransduction. Structural proteins that connect the cell to its niche, for example, integrins and cadherins, and that couple to other growth factor receptors, either directly or indirectly, seem to mediate these changes, although specific mechanistic details are still being elucidated. In this review, we summarize how the wingless (Wnt), transforming growth factor-β, and bone morphogenetic protein signaling pathways affect cardiomyogenesis and then highlight the interplay between each pathway and mechanical forces. In addition, we will outline the role of integrins and cadherins during cardiac development. For each, we will describe how the interplay could change multiple processes during cardiomyogenesis, including the specification of undifferentiated cells, the establishment of heart patterns to accomplish tube and chamber formation, or the maturation of myocytes in the fully formed heart.

Gene-Specific Assessment of Guanine Oxidation as an Epigenetic Modulator for Cardiac Specification of Mouse Embryonic Stem Cells

Epigenetics have essential roles in development and human diseases. Compared to the complex histone modifications, epigenetic changes on mammalian DNA are as simple as methylation on cytosine. Guanine, however, can be oxidized as an epigenetic change which can undergo base-pair transversion, causing a genetic difference. Accumulating evidence indicates that reactive oxygen species (ROS) are important signaling molecules for embryonic stem cell (ESC) differentiation, possibly through transient changes on genomic DNA such as 7,8-dihydro-8-oxoguanine (8-oxoG). Technical limitations on detecting such DNA modifications, however, restrict the investigation of the role of 8-oxoG in ESC differentiation. Here, we developed a Hoogsteen base pairing-mediated PCR-sequencing assay to detect 8-oxoG lesions that can subsequently cause G to T transversions during PCR. We then used this assay to assess the epigenetic and transient 8-oxoG formation in the Tbx5 gene of R1 mouse ESCs subjected to oxidative stress by removing 2-mercaptoethanol (2ME) from the culture media. To our surprise, significantly higher numbers of 8-oxoG-mediated G∙C to C∙G transversion, not G∙C to T∙A, were detected at 7th and 9th base position from the transcription start site of exon 1 of Tbx5 in ESCs in the (-)2ME than (+)2ME group (p < 0.05). This was consistent with the decrease in the amount of amplifiable of DNA harboring the 8-oxoG lesions at the Tbx5 promoter region in the oxidative stressed ESCs. The ESCs responded to oxidative stress, possibly through the epigenetic effects of guanine oxidation with decreased proliferation (p < 0.05) and increased formation of beating embryoid bodies (EBs; p < 0.001). Additionally, the epigenetic changes of guanine induced up-regulation of Ogg1 and PolB, two base excision repairing genes for 8-oxoG, in ESCs treated with (-)2ME (p < 0.01). Together, we developed a gene-specific and direct quantification assay for guanine oxidation. Using oxidative stressed mouse ESCs, we validated this assay and assessed the epigenetic effects of 8-oxoG by studying expression of DNA repair genes, ESC proliferation, and EB formation.

Engineering Embryonic Stem Cell Microenvironments for Tailored Cellular Differentiation

The rapid progress of embryonic stem cell (ESCs) research offers great promise for drug discovery, tissue engineering, and regenerative medicine. However, a major limitation in translation of ESCs technology to pharmaceutical and clinical applications is how to induce their differentiation into tailored lineage commitment with satisfactory efficiency. Many studies indicate that this lineage commitment is precisely controlled by the ESC microenvironment in vivo. Engineering and biomaterial-based approaches to recreate a biomimetic cellular microenvironment provide valuable strategies for directing ESCs differentiation to specific lineages in vitro. In this review, we summarize and examine the recent advances in application of engineering and biomaterial-based approaches to control ESC differentiation. We focus on physical strategies (e.g., geometrical constraint, mechanical stimulation, extracellular matrix (ECM) stiffness, and topography) and biochemical approaches (e.g., genetic engineering, soluble bioactive factors, coculture, and synthetic small molecules), and highlight the three-dimensional (3D) hydrogel-based microenvironment for directed ESC differentiation. Finally, future perspectives in ESCs engineering are provided for the subsequent advancement of this promising research direction.

Controlling Redox Status for Stem Cell Survival, Expansion, and Differentiation

Reactive oxygen species (ROS) have long been considered as pathological agents inducing apoptosis under adverse culture conditions. However, recent findings have challenged this dogma and physiological levels of ROS are now considered as secondary messengers, mediating numerous cellular functions in stem cells. Stem cells represent important tools for tissue engineering, drug screening, and disease modeling. However, the safe use of stem cells for clinical applications still requires culture improvements to obtain functional cells. With the examples of mesenchymal stem cells (MSCs) and pluripotent stem cells (PSCs), this review investigates the roles of ROS in the maintenance of self-renewal, proliferation, and differentiation of stem cells. In addition, this work highlights that the tight control of stem cell microenvironment, including cell organization, and metabolic and mechanical environments, may be an effective approach to regulate endogenous ROS generation. Taken together, this paper indicates the need for better quantification of ROS towards the accurate control of stem cell fate.

Mechanical Stress Promotes Maturation of Human Myocardium From Pluripotent Stem Cell-Derived Progenitors

Recent advances in pluripotent stem cell biology and directed differentiation have identified a population of human cardiovascular progenitors that give rise to cardiomyocytes, smooth muscle, and endothelial cells. Because the heart develops from progenitors in 3D under constant mechanical load, we sought to test the effects of a 3D microenvironment and mechanical stress on differentiation and maturation of human cardiovascular progenitors into myocardial tissue. Progenitors were derived from embryonic stem cells, cast into collagen hydrogels, and left unstressed or subjected to static or cyclic mechanical stress. Compared to 2D culture, the unstressed 3D environment increased cardiomyocyte numbers and decreased smooth muscle numbers. Additionally, 3D culture suppressed smooth muscle α-actin content, suggesting diminished cell maturation. Cyclic stress-conditioning increased expression of several cardiac markers, including β-myosin heavy chain and cardiac troponin T, and the tissue showed enhanced calcium dynamics and force production. There was no effect of mechanical loading on cardiomyocyte or smooth muscle specification. Thus, 3D growth conditions favor cardiac differentiation from cardiovascular progenitors, whereas 2D conditions promote smooth muscle differentiation. Mechanical loading promotes cardiomyocyte structural and functional maturation. Culture in 3-D facilitates understanding how cues such as mechanical stress affect the differentiation and morphogenesis of distinct cardiovascular cell populations into organized, functional human cardiovascular tissue. Stem Cells 2015;33:2148-2157.

Paramagnetic beads and magnetically mediated strain enhance cardiomyogenesis in mouse embryoid bodies

Mechanical forces play an important role in proper embryologic development, and similarly such forces can directly impact pluripotency and differentiation of mouse embryonic stem cells (mESC) in vitro. In addition, manipulation of the embryoid body (EB) microenvironment, such as by incorporation of microspheres or microparticles, can similarly influence fate determination. In this study, we developed a mechanical stimulation regimen using permanent neodymium magnets to magnetically attract cells within an EB. Arginine-Glycine-Aspartic Acid (RGD)-conjugated paramagnetic beads were incorporated into the interior of the EBs during aggregation, allowing us to exert force on individual cells using short-term magnetization. EBs were stimulated for one hour at different magnetic field strengths, subsequently exerting a range of force intensity on the cells at different stages of early EB development. Our results demonstrated that following exposure to a 0.2 Tesla magnetic field, ESCs respond to magnetically mediated strain by activating Protein Kinase A (PKA) and increasing phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) expression. The timing of stimulation can also be tailored to guide ESC differentiation: the combination of bone morphogenetic protein 4 (BMP4) supplementation with one hour of magnetic attraction on Day 3 enhances cardiomyogenesis by increasing contractile activity and the percentage of sarcomeric α-actin-expressing cells compared to control samples with BMP4 alone. Interestingly, we also observed that the beads alone had some impact on differentiation by increasingly slightly, albeit not significantly, the percentage of cardiomyocytes. Together these results suggest that magnetically mediated strain can be used to enhance the percentage of mouse ESC-derived cardiomyocytes over current differentiation protocols.

Graphene-regulated cardiomyogenic differentiation process of mesenchymal stem cells by enhancing the expression of extracellular matrix proteins and cell signaling molecules

The potential of graphene as a mesenchymal stem cell (MSC) culture substrate to promote cardiomyogenic differentiation is demonstrated. Graphene exhibits no sign of cytotoxicity for stem cell culture. MSCs are committed toward cardiomyogenic lineage by simply culturing them on graphene. This may be attributed, at least partially, to the regulation of expression levels of extracellular matrix and signaling molecules.

Reactive oxygen species mediate Cr(VI)-induced carcinogenesis through PI3K/AKT-dependent activation of GSK-3β/β-catenin signaling

Cr(VI) compounds are known human carcinogens that primarily target the lungs. Cr(VI) produces reactive oxygen species (ROS), but the exact effects of ROS on the signaling molecules involved in Cr(VI)-induced carcinogenesis have not been extensively studied. Chronic exposure of human bronchial epithelial cells to Cr(VI) at nanomolar concentrations (10-100nM) for 3months not only induced cell transformation, but also increased the potential of these cells to invade and migrate. Injection of Cr(VI)-stimulated cells into nude mice resulted in the formation of tumors. Chronic exposure to Cr(VI) increased levels of intracellular ROS and antiapoptotic proteins. Transfection with catalase or superoxide dismutase (SOD) prevented Cr(VI)-mediated increases in colony formation, cell invasion, migration, and xenograft tumors. While chronic Cr(VI) exposure led to activation of signaling cascades involving PI3K/AKT/GSK-3β/β-catenin and PI3K/AKT/mTOR, transfection with catalase or SOD markedly inhibited Cr(VI)-mediated activation of these signaling proteins. Inhibitors specific for AKT or β-catenin almost completely suppressed the Cr(VI)-mediated increase in total and active β-catenin proteins and colony formation. In particular, Cr(VI) suppressed autophagy of epithelial cells under nutrition deprivation. Furthermore, there was a marked induction of AKT, GSK-3β, β-catenin, mTOR, and carcinogenic markers in tumor tissues formed in mice after injection with Cr(VI)-stimulated cells. Collectively, our findings suggest that ROS is a key mediator of Cr(VI)-induced carcinogenesis through the activation of PI3K/AKT-dependent GSK-3β/β-catenin signaling and the promotion of cell survival mechanisms via the inhibition of apoptosis and autophagy.

Redox signaling in cardiac physiology and pathology

Redox signaling refers to the specific and usually reversible oxidation/reduction modification of molecules involved in cellular signaling pathways. In the heart, redox signaling regulates several physiological processes (eg, excitation-contraction coupling) and is involved in a wide variety of pathophysiological and homoeostatic or stress response pathways. Reactive oxygen species involved in cardiac redox signaling may derive from many sources, but NADPH oxidases, as dedicated sources of signaling reactive oxygen species, seem to be especially important. An increasing number of specific posttranslational oxidative modifications involved in cardiac redox signaling are being defined, along with the reactive oxygen species sources that are involved. Here, we review current knowledge on the molecular targets of signaling reactive oxygen species in cardiac cells and their involvement in cardiac physiopathology. Advances in this field may allow the development of targeted therapeutic strategies for conditions such as heart failure as opposed to the general antioxidant approaches that have failed to date.

Cadmium induces carcinogenesis in BEAS-2B cells through ROS-dependent activation of PI3K/AKT/GSK-3β/β-catenin signaling

Cadmium has been widely used in industry and is known to be carcinogenic to humans. Although it is widely accepted that chronic exposure to cadmium increases the incidence of cancer, the mechanisms underlying cadmium-induced carcinogenesis are unclear. The main aim of this study was to investigate the role of reactive oxygen species (ROS) in cadmium-induced carcinogenesis and the signal transduction pathways involved. Chronic exposure of human bronchial epithelial BEAS-2B cells to cadmium induced cell transformation, as evidenced by anchorage-independent growth in soft agar and clonogenic assays. Chronic cadmium treatment also increased the potential of these cells to invade and migrate. Injection of cadmium-stimulated cells into nude mice resulted in the formation of tumors. In contrast, the cadmium-mediated increases in colony formation, cell invasion and migration were prevented by transfection with catalase, superoxide dismutase-1 (SOD1), or SOD2. In particular, chronic cadmium exposure led to activation of signaling cascades involving PI3K, AKT, GSK-3β, and β-catenin and transfection with each of the above antioxidant enzymes markedly inhibited cadmium-mediated activation of these signaling proteins. Inhibitors specific for AKT or β-catenin almost completely suppressed the cadmium-mediated increase in total and active β-catenin proteins and colony formation. Moreover, there was a marked induction of AKT, GSK-3β, β-catenin, and carcinogenic markers in tumor tissues formed in mice after injection with cadmium-stimulated cells. Collectively, our findings suggest a direct involvement of ROS in cadmium-induced carcinogenesis and implicate a role of AKT/GSK-3β/β-catenin signaling in this process.

Continuously generated H2O2 stimulates the proliferation and osteoblastic differentiation of human periodontal ligament fibroblasts

Numerous studies have shown that hydrogen peroxide (H(2)O(2)) inhibits proliferation and osteoblastic differentiation in bone-like cells. Human periodontal ligament fibroblasts (PLF) are capable of differentiating into osteoblasts and are exposed to oxidative stress during periodontal inflammation. However, the cellular responses of PLF to H(2)O(2) have not been identified. In this study, we examined how H(2)O(2) affects the viability and proliferation of PLF by exposing the cells to glucose oxidase (GO) or direct addition of H(2)O(2). We also explored the effects of GO on the osteoblastic differentiation of PLF and the mechanisms involved. The viability and proliferation in PLF were increased with the addition of 10 mU/ml GO but not by volumes greater than 15 mU/ml or by H(2)O(2) itself. GO-stimulated DNA synthesis was correlated with the increase in cyclin E protein levels in the cells. Osteoblastic differentiation of PLF was also augmented by combined treatment with GO, as evidenced by the increases in alkaline phosphatase activity, mineralization, collagen synthesis, and osteocalcin content in the cells. The inductions of runt-related transcription factor 2 and osterix mRNA and proteins were further increased in PLF incubated in combination with GO compared to those in untreated cells. These results demonstrate that the continuous presence of H(2)O(2) stimulates the proliferation of PLF and augments their potential to differentiate into osteoblasts through the up-regulation of bone-specific transcription factors. Collectively, we suggest that H(2)O(2) may elicit the functions of PLF in maintaining the dimensions of the periodontal ligament and in mediating a balanced metabolism in alveolar bone.

Simvastatin promotes osteogenic differentiation of mouse embryonic stem cells via canonical Wnt/β-catenin signaling

Simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, has been known to reduce cholesterol biosynthesis. However, recent studies demonstrate that simvastatin shows diverse cholesterol-independent functions including cellular differentiation. In this study, we investigated the stimulatory effect of simvastatin on the osteogenic differentiation of mouse embryonic stem cells (ESCs). The osteogenic effect of simvastatin was observed at relatively low doses (ranging from 1 nM to 200 nM). Incubation of ESCs in simvastatin-supplemented osteogenic medium significantly increased alkaline phosphatase (ALP) activity at day 7. The matrix mineralization was also augmented and demonstrated pivotal levels after 14 days incubation of simvastatin. Osteogenic differentiation of ESCs by simvastatin was determined by upregulation of the mRNA expression of runtrelated gene 2 (Runx2), osterix (OSX), and osteocalcin (OCN) as osteogenic transcription factors. Moreover, the increased protein expression of OCN, osteopontin (OPN), and collagen type I (Coll I) was assessed using Western blot analysis and immunocytochemistry. However, the blockage of canonical Wnt signaling by DKK-1 downregulated simvastatin-induced ALP activity and the mRNA expression of each osteogenic transcription factor. Furthermore, the β-catenin specific siRNA transfection decreased the protein levels of OCN, OPN, and Coll I. Collectively, these findings suggest that simvastatin enhances the differentiation of ESCs toward osteogenic lineage through activation of canonical Wnt/β-catenin signaling.