Rho kinases regulate the renewal and neural differentiation of embryonic stem cells in a cell plating density-dependent manner

Post-Passage rock inhibition induces cytoskeletal aberrations and apoptosis in Human embryonic stem cells

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) are prone to anoikis after single cell dissociation. The small molecule, Y-27632 is known to increase survival of hESCs and hiPSCs by inhibiting the Rho-associated protein kinase (ROCK). However, the underlying mechanisms are still unclear. Here, we thoroughly screened small molecules to investigate the adhesion and survival of hESCs in adherent culture. Y-27632 provided higher adhesion and survival of hESCs by increased cell migration and preventing cell blebbing in single dissociated cells. The combination of Matrigel with poly-d-lysine increased the attachment and survival of dissociated cells via actin filament and microtubule spreading in Y-27632-treated cells. Although Y-27632 prevented apoptosis by suppressing actin filament contraction, microtubule bundling, and blebbing, prolonged Y-27632 treatment presented a different morphology in the attached growing hESC colony. It induced apoptosis of cells by promoting cytoplasmic spread, E-cadherin structural change, and increased detachment. It also induced actin cytoskeleton disruption, combined with microtubule and intermediate filament elongation. For optimal hPSC culture, our research suggests that Y-27632 should be removed shortly after passaging.

Rho-kinase inhibitor Y-27632 facilitates the proliferation, migration and pluripotency of human periodontal ligament stem cells

The selective in vitro expansion and differentiation of multipotent stem cells are critical steps in cell-based regenerative therapies, while technical challenges have limited cell yield and thus affected the success of these potential treatments. The Rho GTPases and downstream Rho kinases are central regulators of cytoskeletal dynamics during cell cycle and determine the balance between stem cells self-renewal, lineage commitment and apoptosis. Trans-4-[(1R)-aminoethyl]-N-(4-pyridinyl)cylohexanecarboxamidedihydrochloride (Y-27632), Rho-associated kinase (ROCK) inhibitor, involves various cellular functions that include actin cytoskeleton organization, cell adhesion, cell motility and anti-apoptosis. Here, human periodontal ligament stem cells (PDLSCs) were isolated by limiting dilution method. Cell counting kit-8 (CCK8), 5-ethynyl-2'-deoxyuridine (EdU) labelling assay, cell apoptosis assay, cell migration assay, wound-healing assay, alkaline phosphatase (ALP) activity assay, Alizarin Red S staining, Oil Red O staining, quantitative real-time polymerase chain reaction (qRT-PCR) were used to determine the effects of Y-27632 on the proliferation, apoptosis, migration, stemness, osteogenic and adipogenic differentiation of PDLSCs. Afterwards, Western blot analysis was performed to elucidate the mechanism of cell proliferation. The results indicated that Y-27632 significantly promoted cell proliferation, chemotaxis, wound healing, fat droplets formation and pluripotency, while inhibited ALP activity and mineral deposition. Furthermore, Y-27632 induced PDLSCs proliferation through extracellular-signal-regulated kinase (ERK) signalling cascade. Therefore, control of Rho-kinase activity may enhance the efficiency of stem cell-based treatments for periodontal diseases and the strategy may have the potential to promote periodontal tissue regeneration by facilitating the chemotaxis of PDLSCs to the injured site, and then enhancing the proliferation of these cells and maintaining their pluripotency.

Synergistic and Superimposed Effect of Bone Marrow-Derived Mesenchymal Stem Cells Combined with Fasudil in Experimental Autoimmune Encephalomyelitis

Bone marrow-derived mesenchymal stem cells (MSCs) are the ideal transplanted cells of cellular therapy for promoting neuroprotection and neurorestoration. However, the optimization of transplanted cells and the improvement of microenvironment around implanted cells are still two critical challenges for enhancing therapeutic effect. In the current study, we observed the therapeutic potential of MSCs combined with Fasudil in mouse model of experimental autoimmune encephalomyelitis (EAE) and explored possible mechanisms of action. The results clearly show that combined intervention of MSCs and Fasudil further reduced the severity of EAE compared with MSCs or Fasudil alone, indicating a synergistic and superimposed effect in treating EAE. The addition of Fasudil inhibited MSC-induced inflammatory signaling TLR-4/MyD88 and inflammatory molecule IFN-γ, IL-1β, and TNF-α but did not convert M1 microglia to M2 phenotype. The delivery of MSCs enhanced the expression of glial cell-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) compared with that of Fasudil. Importantly, combined intervention of MSCs and Fasudil further increased the expression of BDNF and GDNF compared with the delivery of MSCs alone, indicating that combined intervention of MSCs and Fasudil synergistically contributes to the expression of neurotrophic factors which should be related to the expression of increased galactocerebroside (GalC) compared with mice treated with Fasudil and MSCs alone. However, a lot of investigation is warranted to further elucidate the cross talk of MSCs and Fasudil in the therapeutic potential of EAE/multiple sclerosis.

Human pluripotent stem cell (PSC)-derived mesenchymal stem cells (MSCs) show potent neurogenic capacity which is enhanced with cytoskeletal rearrangement

Mesenchymal stem cells (MSCs) are paraxial mesodermal progenitors with potent immunomodulatory properties. Reports also indicate that MSCs can undergo neural-like differentiation, offering hope for use in neurodegenerative diseases. However, ex vivo expansion of these rare somatic stem cells for clinical use leads to cellular senescence. A newer source of MSCs derived from human pluripotent stem cells (PSC) can offer the 'best-of-both-worlds' scenario, abrogating the concern of teratoma formation while preserving PSC proliferative capacity. PSC-derived MSCs (PSC-MSCs) also represent MSCs at the earliest developmental stage, and we found that these MSCs harbor stronger neuro-differentiation capacity than post-natal MSCs. PSC-MSCs express higher levels of neural stem cell (NSC)-related genes and transcription factors than adult bone marrow MSCs at baseline, and rapidly differentiate into neural-like cells when cultured in either standard neurogenic differentiation medium (NDM) or when the cytoskeletal modulator RhoA kinase (ROCK) is inhibited. Interestingly, when NDM is combined with ROCK inhibition, PSC-MSCs undergo further commitment, acquiring characteristics of post-mitotic neurons including nuclear condensation, extensive dendritic growth, and neuron-restricted marker expression including NeuN, β-III-tubulin and Doublecortin. Our data demonstrates that PSC-MSCs have potent capacity to undergo neural differentiation and also implicate the important role of the cytoskeleton in neural lineage commitment.

Neural crest specification by inhibition of the ROCK/Myosin II pathway

Neural crest is a population of multipotent progenitor cells that form at the border of neural and non-neural ectoderm in vertebrate embryos, and undergo epithelial-mesenchymal transition and migration. According to the traditional view, the neural crest is specified in early embryos by signaling molecules including BMP, FGF, and Wnt proteins. Here, we identify a novel signaling pathway leading to neural crest specification, which involves Rho-associated kinase (ROCK) and its downstream target nonmuscle Myosin II. We show that ROCK inhibitors promote differentiation of human embryonic stem cells (hESCs) into neural crest-like progenitors (NCPs) that are characterized by specific molecular markers and ability to differentiate into multiple cell types, including neurons, chondrocytes, osteocytes, and smooth muscle cells. Moreover, inhibition of Myosin II was sufficient for generating NCPs at high efficiency. Whereas Myosin II has been previously implicated in the self-renewal and survival of hESCs, we demonstrate its role in neural crest development during ESC differentiation. Inhibition of this pathway in Xenopus embryos expanded neural crest in vivo, further indicating that neural crest specification is controlled by ROCK-dependent Myosin II activity. We propose that changes in cell morphology in response to ROCK and Myosin II inhibition initiate mechanical signaling leading to neural crest fates.

Neuronal differentiation of human iPS cells induced by baicalin via regulation of bHLH gene expression

Efficient differentiation is important for regenerative medicine based on pluripotent stem cells, including treatment of neurodegenerative disorders and trauma. Baicalin promotes neuronal differentiation of neural stem/progenitor cells of rats and mice. To evaluate the suitability of baicalin for neuronal differentiation of human iPS cells, we investigated whether it promotes neuronal differentiation in human iPS cells and monitored basic helix-loop-helix (bHLH) gene expression during neuronal differentiation. Baicalin promoted neuronal differentiation and inhibited glial differentiation, suggesting that baicalin can influence the neuronal fate decision in human iPS cells. Notch signaling, which is upstream of bHLH proteins, was not involved in baicalin-induced neuronal differentiation. Baicalin treatment did not down-regulate Hes1 gene expression, but it reduced Hes1 protein levels and up-regulated Ascl1 gene expression. Thus, baicalin promoted neuronal differentiation via modulation of bHLH transcriptional factors. Therefore, baicalin has potential to be used as a small-molecule drug for regenerative treatment of neurodegenerative disorders.

Low-density expansion protects human synovium-derived stem cells from replicative senescence: a preliminary study

Our hypothesis in this study is that low seeding density expansion could retain human synovium-derived stem cell (hSDSC) "stemness", defined as higher proliferation and multi-differentiation capacity; retention of "stemness" probably occurs through the mitogen-activated protein kinase (MAPK) signaling pathway. hSDSCs were expanded in conventional plastic flasks for two consecutive passages at either low or high density (30 or 3,000 cells/cm(2)). Expanded cells were assessed for the effect of seeding density on their morphology, proliferation, apoptosis, stem cell surface markers, and multi-lineage differentiation capacity (chondrogenic, adipogenic, and osteogenic differentiation) using flow cytometry, biochemical analysis, histology, immunostaining, and real-time polymerase chain reaction. The MAPK signaling pathway (Erk1/2, p38, and JNK) and senescence-associated markers (p21 and caveolin) were also evaluated for their role in cell density-based monolayer expansion using western blot. Our data suggested that low seeding density expansion yielded hSDSCs with enhanced proliferation and multi-differentiation capacity compared to those grown at high seeding density, despite the fact that the cells expanded at both high and low density had lower osteogenic capacity. Low seeding density also down-regulated Erk1/2 and JNK expression and up-regulated p38 expression, which might be responsible for the retained "stemness" in the cells expanded at low density. Low seeding density expansion could retain hSDSC proliferation and multi-differentiation capacity and protect cells from replicative senescence.

Rho kinase inhibitor Y-27632 promotes the differentiation of human bone marrow mesenchymal stem cells into keratinocyte-like cells in xeno-free conditioned medium

INTRODUCTION

Bone marrow mesenchymal stem cells (BMSCs), which have the ability to self-renew and to differentiate into multiple cell types, have recently become a novel strategy for cell-based therapies. The differentiation of BMSCs into keratinocytes may be beneficial for patients with burns, disease, or trauma. However, the currently available cells are exposed to animal materials during their cultivation and induction. These xeno-contaminations severely limit their clinical outcomes. Previous studies have shown that the Rho kinase (ROCK) inhibitor Y-27632 can promote induction efficiency and regulate the self-renewal and differentiation of stem cells. In the present study, we attempted to establish a xeno-free system for the differentiation of BMSCs into keratinocytes and to investigate whether Y-27632 can facilitate this differentiation.

METHODS

BMSCs isolated from patients were cultured by using a xeno-free system and characterised by using flow cytometric analysis and adipogenic and osteogenic differentiation assays. Human primary keratinocytes were also isolated from patients. Then, the morphology, population doubling time, and β-galactosidase staining level of these cells were evaluated in the presence or absence of Y-27632 to determine the effects of Y-27632 on the state of the keratinocytes. Keratinocyte-like cells (KLCs) were detected at different time points by immunocytofluorescence analysis. Moreover, the efficiency of BMSC differentiation under different conditions was measured by quantitative real-time-polymerase chain reaction (RT-PCR) and Western blot analyses.

RESULTS

The ROCK inhibitor Y-27632 promoted the proliferation and lifespan of human primary keratinocytes. In addition, we showed that keratinocyte-specific markers could be detected in BMSCs cultured in a xeno-free system using keratinocyte-conditioned medium (KCM) independent of the presence of Y-27632. However, the efficiency of the differentiation of BMSCs into KLCs was significantly higher in the presence of Y-27632 using immunofluorescence, quantitative RT-PCR, and Western blot analyses.

CONCLUSIONS

This study demonstrated that Y-27632 could promote the proliferation and survival of human primary keratinocytes in a xeno-free culture system. In addition, we found that BMSCs have the ability to differentiate into KLCs in KCM and that Y-27632 can facilitate this differentiation. Our results suggest that BMSCs are capable of differentiating into KLCs in vitro and that the ROCK pathway may play a critical role in this process.

Differentiation patterns of mouse embryonic stem cells and induced pluripotent stem cells into neurons

Mouse embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have the ability to differentiate in vitro into various cell lineages including neurons. The differentiation of these cells into neurons has potential applications in regenerative medicine. Previously, we reported that a chick dorsal root ganglion (DRG)-conditioned medium (CM) promoted the differentiation of mouse ES and iPS cells into neurons. Here, we used real-time PCR to investigate the differentiation patterns of ES and iPS cells into neurons when DRG-CM was added. DRG-CM promoted the expression levels of βIII-tubulin gene (a marker of postmitotic neurons) in ES and iPS cells. ES cells differentiated into neurons faster than iPS cells, and the maximum peaks of gene expression involved in motor, sensory, and dopaminergic neurons were different. Rho kinase (ROCK) inhibitors could be very valuable at numerous stages in the production and use of stem cells in basic research and eventual cell-based therapies. Thus, we investigated whether the addition of a ROCK inhibitor Y-27632 and DRG-CM on the basis of the differentiation patterns promotes the neuronal differentiation of ES cells. When the ROCK inhibitor was added to the culture medium at the initial stages of cultivation, it stimulated the neuronal differentiation of ES cells more strongly than that stimulated by DRG-CM. Moreover, the combination of the ROCK inhibitor and DRG-CM promoted the neuronal differentiation of ES cells when the ROCK inhibitor was added to the culture medium at day 3. The ROCK inhibitor may be useful for promoting neuronal differentiation of ES cells.

Promotion of mouse embryonic stem cell differentiation by Rho kinase inhibitor Y-27632

Rho kinase (ROCK) is one of the major downstream mediators of Rho. Rho plays crucial regulatory roles in the cellular proliferation and differentiation. Because a ROCK inhibitor, Y-27632, is known to inhibit the dissociation-induced cell death in human embryonic stem (ES) cells, we investigated the effects of this ROCK inhibitor on the differentiation of the mouse ES cells. The ROCK inhibitor promoted the differentiation of the ES cells into neurons, particularly motor and sensory neurons. The addition of both ROCK inhibitor and nerve growth factor (NGF) strongly stimulated the differentiation of the ES cells into neurons. Moreover, the ROCK inhibitor promoted the differentiation of the ES cells into muscle cells. The ES cells primarily differentiated into neurons rather than muscle cells. We found that the ROCK inhibitor may promote the neuronal differentiation of the ES cells by activating the extracellular signal-regulated kinase (ERK) signaling pathway. These results suggest that the ROCK inhibitor has a significant potential to regulate the differentiation of the ES cells.

Hippo/YAP-mediated rigidity-dependent motor neuron differentiation of human pluripotent stem cells

Our understanding of the intrinsic mechanosensitive properties of human pluripotent stem cells (hPSCs), in particular the effects that the physical microenvironment has on their differentiation, remains elusive. Here, we show that neural induction and caudalization of hPSCs can be accelerated by using a synthetic microengineered substrate system consisting of poly(dimethylsiloxane) micropost arrays (PMAs) with tunable mechanical rigidities. The purity and yield of functional motor neurons derived from hPSCs within 23 days of culture using soft PMAs were improved more than fourfold and tenfold, respectively, compared with coverslips or rigid PMAs. Mechanistic studies revealed a multi-targeted mechanotransductive process involving Smad phosphorylation and nucleocytoplasmic shuttling, regulated by rigidity-dependent Hippo/YAP activities and actomyosin cytoskeleton integrity and contractility. Our findings suggest that substrate rigidity is an important biophysical cue influencing neural induction and subtype specification, and that microengineered substrates can thus serve as a promising platform for large-scale culture of hPSCs.

The effects of artificial E-cadherin matrix-induced embryonic stem cell scattering on paxillin and RhoA activation via α-catenin

Mechanical forces have been shown to affect stem cell behavior in a large array of ways. However, our understanding of how these mechanical cues may regulate the behavior of embryonic stem cells (ESCs) remains in its infancy. Here, we aim to clarify the effect of cell scattering on the regulation of Rho family GTPases Rac1 and RhoA as well as paxillin. Allowing ESCs to spread and scatter on a synthetically designed E-cadherin substratum causes phosphorylation of paxillin on consensus phosphorylation sites leading to activation of Rac1 and inactivation of RhoA. By culturing cells in presence of RhoA activator or growing cells to a highly confluent state reverses the effect of cell scattering phenotype. Knockdown of E-cadherin-adapter protein α-catenin revealed that it negatively affects paxillin phosphorylation and up-regulates RhoA activity in compact cellular aggregates. Collectively these results indicate that cell scattering might cause a conformational change of α-catenin limiting its capacity to inhibit paxillin phosphorylation that causes an increase in Rac1 activation and RhoA deactivation. Understanding how synthetically designed extracellular matrix affect ESC signaling through mechanical cues brings a new aspect for stem cell engineers to develop technologies for controlling cell function.

Tropomyosins induce neuritogenesis and determine neurite branching patterns in B35 neuroblastoma cells

BACKGROUND

The actin cytoskeleton is critically involved in the regulation of neurite outgrowth.

RESULTS

The actin cytoskeleton-associated protein tropomyosin induces neurite outgrowth in B35 neuroblastoma cells and regulates neurite branching in an isoform-dependent manner.

CONCLUSIONS

Our data indicate that tropomyosins are key regulators of the actin cytoskeleton during neurite outgrowth.

SIGNIFICANCE

Revealing the molecular machinery that regulates the actin cytoskeleton during neurite outgrowth may provide new therapeutic strategies to promote neurite regeneration after nerve injury.

SUMMARY

The formation of a branched network of neurites between communicating neurons is required for all higher functions in the nervous system. The dynamics of the actin cytoskeleton is fundamental to morphological changes in cell shape and the establishment of these branched networks. The actin-associated proteins tropomyosins have previously been shown to impact on different aspects of neurite formation. Here we demonstrate that an increased expression of tropomyosins is sufficient to induce the formation of neurites in B35 neuroblastoma cells. Furthermore, our data highlight the functional diversity of different tropomyosin isoforms during neuritogenesis. Tropomyosins differentially impact on the expression levels of the actin filament bundling protein fascin and increase the formation of filopodia along the length of neurites. Our data suggest that tropomyosins are central regulators of actin filament populations which drive distinct aspects of neuronal morphogenesis.

Matrix-specified differentiation of human decidua parietalis placental stem cells

To create suitable biological scaffolds for tissue engineering and cell therapeutics, it is essential to understand the matrix-mediated specification of stem cell differentiation. To this end, we studied the effect of collagen type I on stem cell lineage specification. We altered the properties of collagen type I by incorporating carbon nanotubes (CNT). The collagen-CNT composite material was stiffer with thicker fibers and longer D-period. Human decidua parietalis stem cells (hdpPSC) were found to differentiate exclusively and rapidly towards neural cells on the collagen-CNT matrix. We attribute this accelerated neural differentiation to the enhanced structural and mechanical properties of collagen-CNT material. Strikingly, the collagen-CNT matrix, unlike collagen, imposes the neural fate by an alternate mechanism that may be independent of beta-1 integrin and beta-catenin. The study demonstrates the sensitivity of stem cells to subtle changes in the matrix and the utilization of a novel biocomposite material for efficient and directed differentiation of stem cells.

Surface bound amine functional group density influences embryonic stem cell maintenance

Gradient surfaces are highly effective tools to screen and optimize cell- surface interactions. Here, the response of embryonic stem (ES) cell colonies to plasma polymer gradient surfaces is investigated. Surface chemistry ranged from pure allylamine (AA) plasma polymer on one end of the gradient to pure octadiene (OD) plasma polymer on the other end. Optimal surface chemistry conditions for retention of pluripotency were identified. Expression of the stem cell markers alkaline phosphatase (AP) and Oct4 varied with the position of the ES cell colonies across the OD-AA plasma polymer gradient. Both markers were more strongly retained on the OD plasma polymer rich regions of the gradients. The observed variation of expression across the plasma polymer gradient increased with duration of stem cell culture. While maximum cell adhesion to the gradient substrate occurred at a nitrogen- to-carbon (N/C ratio) of approximately 0.1, Oct4 and AP expression was best retained at an N/C ratio < 0.04. Stem cell marker expression correlated with colony size and morphology: more compact, multilayered colonies with prominent F-actin staining arose as the N/C ratio decreased. Disruption of actin polymerization using Y-27632 ROCK inhibitor resulted in a collapse of the multilayer colony structure into monolayers with limited cell-cell contact. A corresponding decrease in expression of AP and Oct4 was observed. Oct4 expression along with 3D colony morphology was partially rescued on the OD plasma polymer rich regions of the gradient.

Application of Rho-associated protein kinase (ROCK) inhibitor to human pluripotent stem cells

Susceptibility of human pluripotent stem cells (hPSCs), such as human iPS and embryonic stem (ES) cells, to single-cell dissociation has been a large obstacle to develop the efficient manipulation techniques required for stem cell research. When hPSCs are completely dissociated into single cells, programmed cell death (apoptosis) is immediately induced. A specific inhibitor of Rho-associated protein kinase (ROCK inhibitor), Y-27632, is of particular interest as a useful reagent that allows hPSCs to escape the dissociation-induced apoptosis. ROCK inhibitor has been used in a variety of applications associated with cell dissociation in the process of stem cell research, such as passaging, expansion, cryopreservation, gene transfer, differentiation induction, and cell sorting, suggesting that it may be a crucial reagent for the handling of hPSCs. This article reviews the current applications of ROCK inhibitors to stem cell research from the viewpoint of quality control of hPSCs.

14-3-3σ regulates β-catenin-mediated mouse embryonic stem cell proliferation by sequestering GSK-3β

BACKGROUND

Pluripotent embryonic stem cells are considered to be an unlimited cell source for tissue regeneration and cell-based therapy. Investigating the molecular mechanism underlying the regulation of embryonic stem cell expansion is thus important. 14-3-3 proteins are implicated in controlling cell division, signaling transduction and survival by interacting with various regulatory proteins. However, the function of 14-3-3 in embryonic stem cell proliferation remains unclear.

METHODOLOGY AND PRINCIPAL FINDINGS

In this study, we show that all seven 14-3-3 isoforms were detected in mouse embryonic stem cells. Retinoid acid suppressed selectively the expression of 14-3-3σ isoform. Knockdown of 14-3-3σ with siRNA reduced embryonic stem cell proliferation, while only 14-3-3σ transfection increased cell growth and partially rescued retinoid acid-induced growth arrest. Since the growth-enhancing action of 14-3-3σ was abrogated by β-catenin knockdown, we investigated the influence of 14-3-3σ overexpression on β-catenin/GSK-3β. 14-3-3σ bound GSK-3β and increased GSK-3β phosphorylation in a PI-3K/Akt-dependent manner. It disrupted β-catenin binding by the multiprotein destruction complex. 14-3-3σ overexpression attenuated β-catenin phosphorylation and rescued the decline of β-catenin induced by retinoid acid. Furthermore, 14-3-3σ enhanced Wnt3a-induced β-catenin level and GSK-3β phosphorylation. DKK, an inhibitor of Wnt signaling, abolished Wnt3a-induced effect but did not interfere GSK-3β/14-3-3σ binding.

SIGNIFICANCE

Our findings show for the first time that 14-3-3σ plays an important role in regulating mouse embryonic stem cell proliferation by binding and sequestering phosphorylated GSK-3β and enhancing Wnt-signaled GSK-3β inactivation. 14-3-3σ is a novel target for embryonic stem cell expansion.

Guided migration of neural stem cells derived from human embryonic stem cells by an electric field

Small direct current (DC) electric fields (EFs) guide neurite growth and migration of rodent neural stem cells (NSCs). However, this could be species dependent. Therefore, it is critical to investigate how human NSCs (hNSCs) respond to EF before any possible clinical attempt. Aiming to characterize the EF-stimulated and guided migration of hNSCs, we derived hNSCs from a well-established human embryonic stem cell line H9. Small applied DC EFs, as low as 16 mV/mm, induced significant directional migration toward the cathode. Reversal of the field polarity reversed migration of hNSCs. The galvanotactic/electrotactic response was both time and voltage dependent. The migration directedness and distance to the cathode increased with the increase of field strength. (Rho-kinase) inhibitor Y27632 is used to enhance viability of stem cells and has previously been reported to inhibit EF-guided directional migration in induced pluripotent stem cells and neurons. However, its presence did not significantly affect the directionality of hNSC migration in an EF. Cytokine receptor [C-X-C chemokine receptor type 4 (CXCR4)] is important for chemotaxis of NSCs in the brain. The blockage of CXCR4 did not affect the electrotaxis of hNSCs. We conclude that hNSCs respond to a small EF by directional migration. Applied EFs could potentially be further exploited to guide hNSCs to injured sites in the central nervous system to improve the outcome of various diseases.

N,N'-dinitrosopiperazine-mediated ezrin protein phosphorylation via activation of Rho kinase and protein kinase C is involved in metastasis of nasopharyngeal carcinoma 6-10B cells

N,N'-Dinitrosopiperazine (DNP) is a carcinogen for nasopharyngeal carcinoma (NPC), which shows organ specificity to nasopharyngeal epithelium. Herein, we demonstrate that DNP induces fiber formation of NPC cells (6-10B) and also increases invasion and motility of 6-10B cells. DNP-mediated NPC metastasis also was confirmed in nude mice. Importantly, DNP induced the expression of phosphorylated ezrin (phos-ezrin) at threonine 567 (Thr-567) dose- and time-dependently but had no effect on the total ezrin expression at these concentrations. Furthermore, DNP-induced phos-ezrin expression was dependent on increased Rho kinase and protein kinase C (PKC) activity. DNP may activate Rho kinase through binding to its pleckstrin homology and may activate PKC through promoting its translocation to the plasma membrane in vivo. DNP-induced phos-ezrin was associated with induction of fiber growth in 6-10B cells. However, DNP could not induce motility and invasion of NPC cells containing ezrin mutated at Thr-567. Similarly, DNP could not induce motility and invasion of the cells containing siRNAs against Rho or PKC. These results indicate that DNP induces ezrin phosphorylation at Thr-567, increases motility and invasion of cells, and promotes tumor metastasis. DNP may be involved in NPC metastasis through regulation of ezrin phosphorylation at Thr-567.

Spatio-temporal dependence of the signaling response in immune-receptor trafficking networks regulated by cell density: a theoretical model

Cell signaling processes involve receptor trafficking through highly connected networks of interacting components. The binding of surface receptors to their specific ligands is a key factor for the control and triggering of signaling pathways. In most experimental systems, ligand concentration and cell density vary within a wide range of values. Dependence of the signal response on cell density is related with the extracellular volume available per cell. This dependence has previously been studied using non-spatial models which assume that signaling components are well mixed and uniformly distributed in a single compartment. In this paper, a mathematical model that shows the influence exerted by cell density on the spatio-temporal evolution of ligands, cell surface receptors, and intracellular signaling molecules is developed. To this end, partial differential equations were used to model ligand and receptor trafficking dynamics through the different domains of the whole system. This enabled us to analyze several interesting features involved with these systems, namely: a) how the perturbation caused by the signaling response propagates through the system; b) receptor internalization dynamics and how cell density affects the robustness of dose-response curves upon variation of the binding affinity; and c) that enhanced correlations between ligand input and system response are obtained under conditions that result in larger perturbations of the equilibrium . Finally, the results are compared with those obtained by considering that the above components are well mixed in a single compartment.

Effective vitrification of human induced pluripotent stem cells using carboxylated ε-poly-l-lysine

Derivation of human induced pluripotent stem (iPS) cells could enable their widespread application in future. Establishment of highly efficient and reliable methods for their preservation is a prerequisite for these applications. In this study, we developed a vitrification solution comprising ethylene glycol (EG) and sucrose as well as carboxylated ε-poly-l-lysine (PLL); this solution inhibited devitrification. Human iPS cells were vitrified in 200-μL vitrification solutions comprised 6.5M EG, 0.75 M sucrose and 0 or 10%w/v carboxylated PLL with 65 mol% of the amino groups converted to carboxyl groups [PLL (0.65)] in a cryovial by directly immersing in liquid nitrogen. After warming, attached colony and recovery rates of human iPS cells vitrified by adding PLL (0.65) were significantly higher than those for cells without PLL (0.65) and vitrification solution (DAP213: 2M dimethyl sulfoxide, 1M acetamide and 3M propylene glycol). Furthermore, even after warming at room temperature, attached colony and recovery rates of iPS cells vitrified with PLL (0.65) were reduced to a lesser extent than those vitrified with either DAP213 or EG and sucrose without PLL (0.65). This could be attributed to inhibition of devitrification by PLL (0.65), as differential scanning calorimetry indicated less damage after vitrification with PLL (0.65). In addition, human iPS cells vitrified in the solution with PLL (0.65) had normal karyotypes and maintained undifferentiated states and pluripotency as determined by immunohistochemistry and teratoma formation. Addition of PLL (0.65) successfully vitrified human iPS cells with high efficiency. We believe that this method could aid future applications and increase utility of human iPS cells.