Fibronectin stimulates migration through lipid raft dependent NHE-1 activation in mouse embryonic stem cells: involvement of RhoA, Ca(2+)/CaM, and ERK

STIM1-dependent store-operated calcium entry mediates sex differences in macrophage chemotaxis and monocyte recruitment

Infiltration of monocyte-derived cells to sites of infection and injury is greater in males than in females, due in part, to increased chemotaxis, the process of directed cell movement toward a chemical signal. The mechanisms governing sexual dimorphism in chemotaxis are not known. We hypothesized a role for the store-operated calcium entry (SOCE) pathway in regulating chemotaxis by modulating leading and trailing edge membrane dynamics. We measured the chemotactic response of bone marrow-derived macrophages migrating toward complement component 5a (C5a). Chemotactic ability was dependent on sex and inflammatory phenotype (M0, M1, and M2), and correlated with SOCE. Notably, females exhibited a significantly lower magnitude of SOCE than males. When we knocked out the SOCE gene, stromal interaction molecule 1 (STIM1), it eliminated SOCE and equalized chemotaxis across both sexes. Analysis of membrane dynamics at the leading and trailing edges showed that STIM1 influences chemotaxis by facilitating retraction of the trailing edge. Using BTP2 to pharmacologically inhibit SOCE mirrored the effects of STIM1 knockout, demonstrating a central role of STIM/Orai-mediated calcium signaling. Importantly, by monitoring the recruitment of adoptively transferred monocytes in an in vivo model of peritonitis, we show that increased infiltration of male monocytes during infection is dependent on STIM1. These data support a model in which STIM1-dependent SOCE is necessary and sufficient for mediating the sex difference in monocyte recruitment and macrophage chemotactic ability by regulating trailing edge dynamics.

Role of Rho GTPases in stem cell regulation

The future of regenerative medicine relies on our understanding of stem cells which are essential for tissue/organ generation and regeneration to maintain and/or restore tissue homeostasis. Rho family GTPases are known regulators of a wide variety of cellular processes related to cytoskeletal dynamics, polarity and gene transcription. In the last decade, major new advances have been made in understanding the regulatory role and mechanism of Rho GTPases in self-renewal, differentiation, migration, and lineage specification in tissue-specific signaling mechanisms in various stem cell types to regulate embryonic development, adult tissue homeostasis, and tissue regeneration upon stress or damage. Importantly, implication of Rho GTPases and their upstream regulators or downstream effectors in the transformation, migration, invasion and tumorigenesis of diverse cancer stem cells highlights the potential of Rho GTPase targeting in cancer therapy. In this review, we discuss recent evidence of Rho GTPase signaling in the regulation of embryonic stem cells, multiple somatic stem cells, and cancer stem cells. We propose promising areas where Rho GTPase pathways may serve as useful targets for stem cell manipulation and related future therapies.

Caveolin1: its roles in normal and cancer stem cells

PURPOSE

Stem cells are characterized by the capability of self-renewal and multi-differentiation. Normal stem cells, which are important for tissue repair and tissue regeneration, can be divided into embryonic stem cells (ESCs) and somatic stem cells (SSCs) depending on their origin. As a subpopulation of cells within cancer, cancer stem cells (CSCs) are at the root of therapeutic resistance. Tumor-initiating cells (TICs) are necessary for tumor initiation. Caveolin1 (Cav1), a membrane protein located at the caveolae, participates in cell lipid transport, cell migration, cell proliferation, and cell signal transduction. The purpose of this review was to explore the relationship between Cav1 and stem cells.

RESULTS

In ESCs, Cav1 is beneficial for self-renewal, proliferation, and migration. In SSCs, Cav1 exhibits positive or/and negative effects on stem cell self-renewal, differentiation, proliferation, migration, and angiogenic capacity. Cav1 deficiency impairs normal stem cell-based tissue repair. In CSCs, Cav1 inhibits or/and promotes CSC self-renewal, differentiation, invasion, migration, tumorigenicity ability, and CSC formation. And suppressing Cav1 promotes chemo-sensitivity in CSCs and TICs.

CONCLUSION

Cav1 shows dual roles in stem cell biology. Targeting the Cav1-stem cell axis would be a new way for tissue repair and cancer drug resistance.

Transient receptor potential vanilloid-3 (TRPV3) channel induces dermal fibrosis via the TRPV3/TSLP/Smad2/3 pathways in dermal fibroblasts

BACKGROUND

Excessive wound healing can lead to hypertrophic scars, which are not only a cosmetic issue but could also be itchy or painful. Previously, we reported that, in comparison with normal tissue, thymic stromal lymphopoietin (TSLP) expression was increased in skin burn scars when the activation of transient receptor potential vanilloid-3 (TRPV3) of keratinocytes was increased. However, the functional role of TRPV3 in dermal fibrosis remains unclear.

OBJECTIVE

We aimed to determine whether TRPV3 affects the collagen production of human primary dermal fibroblasts (HPDFs) and to investigate the mechanism involved.

METHOD

Human primary dermal fibroblasts were cultured and transformed into myofibroblasts using TSLP and carvacrol. Expression levels of α-SMA, fibronectin, and COL1A1 were determined using qPCR, western blotting, and immunofluorescence staining. Ca²⁺ influx was measured using a calcium-sensitive fluorescent dye, Fura3-AM. Nuclear factor of activated T-cells (NFAT) and phosphorylated-Smad2/3 were determined by western blotting. Silencing of TRPV3 with TRPV3-specific small interference RNA was evaluated using qPCR and western blotting.

RESULTS

The expression levels of α-SMA, fibronectin, COL1A1, and TSLP were significantly increased in carvacrol-treated HPDFs. The expression levels of α-SMA, fibronectin, and COL1A1 were significantly increased by TSLP. The expression levels of TSLP and COL1A1 were significantly blocked by TRPV3 silencing in HPDFs. Regulation of Ca²⁺ influx and the expression levels of NFAT and p-Smad2/3 were significantly increased in carvacrol-treated HPDFs. ECM productions induced via the TRPV3/TSLP/Smad2/3 pathways.

CONCLUSIONS

The activation of the TRPV3 channels regulates dermal fibrosis by reducing extracellular matrix production via the TRPV3/TSLP/Smad2/3 pathways in dermal fibroblasts.

A steroid alkaloid derivative 02F04 upregulates thymic stromal lymphopoietin expression slowly and continuously through a novel Gq/11-ROCK-ERK1/2 signaling pathway in mouse keratinocytes

Thymic stromal lymphopoietin (TSLP), a master switch of allergic inflammation, plays an important role in the pathogenesis of allergic diseases. Although many compounds upregulate TSLP expression in vivo or in vitro, most of them are pollutants or toxicants. In the previous study, for the first time, we found that a steroid alkaloid derivative 02F04, which has a unique skeletal structure compared with other TSLP-inducing chemicals, significantly induced TSLP production in mouse keratinocytes. However, it is not investigated thoroughly that how 02F04 produces TSLP and why. In this study, we did a detailed investigation on the inducible effect and underlying molecular mechanism of 02F04 on TSLP production. We found that the peak time of TSLP mRNA level induced by 02F04 at 48 h led to a slow and continuous TSLP production in PAM212 cells. Besides, 02F04-induced TSLP production was significantly suppressed by inhibitors of Rho-associated protein kinase (ROCK), guanine nucleotide-binding protein subunit alpha q/11 (Gq/11) and extracellular signal-regulated kinase 1/2 (ERK1/2) at not only protein but also mRNA levels, and by siRNA-mediated knockdown of Gq or G11. This suggested that ROCK, Gq/11 and ERK1/2 signaling pathways were involved in 02F04-induced TSLP production. Increase in the level of p-ERK1/2 induced by 02F04 was suppressed by both inhibitors of ROCK and Gq/11, indicating that ROCK and Gq/11 molecules were located at the upstream of ERK1/2 to regulate 02F04-induced TSLP production. Gq/11 was located at the upstream of ROCK because the specific Gq/11 inhibitor of YM-254890 significantly reduced 02F04-induced actin stress fiber formation. Taken together, 02F04 upregulates a slow and continuous TSLP production through a novel Gq/11-ROCK-ERK1/2 signaling pathway. The thorough understanding the effect and mechanism of 02F04 on TSLP production is expected to supply it as a novel TSLP-regulating compound and a potential new tool for investigating the role of TSLP in allergic disorders.

ATP-induced Ca2+-signalling mechanisms in the regulation of mesenchymal stem cell migration

The ability of cells to migrate to the destined tissues or lesions is crucial for physiological processes from tissue morphogenesis, homeostasis and immune responses, and also for stem cell-based regenerative medicines. Cytosolic Ca²⁺ is a primary second messenger in the control and regulation of a wide range of cell functions including cell migration. Extracellular ATP, together with the cognate receptors on the cell surface, ligand-gated ion channel P2X receptors and a subset of G-protein-coupled P2Y receptors, represents common autocrine and/or paracrine Ca²⁺ signalling mechanisms. The P2X receptor ion channels mediate extracellular Ca²⁺ influx, whereas stimulation of the P2Y receptors triggers intracellular Ca²⁺ release from the endoplasmic reticulum (ER), and activation of both type of receptors thus can elevate the cytosolic Ca²⁺ concentration ([Ca²⁺]_c), albeit with different kinetics and capacity. Reduction in the ER Ca²⁺ level following the P2Y receptor activation can further induce store-operated Ca²⁺ entry as a distinct Ca²⁺ influx pathway that contributes in ATP-induced increase in the [Ca²⁺]_c. Mesenchymal stem cells (MSC) are a group of multipotent stem cells that grow from adult tissues and hold promising applications in tissue engineering and cell-based therapies treating a great and diverse number of diseases. There is increasing evidence to show constitutive or evoked ATP release from stem cells themselves or mature cells in the close vicinity. In this review, we discuss the mechanisms for ATP release and clearance, the receptors and ion channels participating in ATP-induced Ca²⁺ signalling and the roles of such signalling mechanisms in mediating ATP-induced regulation of MSC migration.

Differential Effects of Coating Materials on Viability and Migration of Schwann Cells

Synthetic nerve conduits have emerged as an alternative to guide axonal regeneration in peripheral nerve gap injuries. Migration of Schwann cells (SC) from nerve stumps has been demonstrated as one essential factor for nerve regeneration in nerve defects. In this experiment, SC viability and migration were investigated for various materials to determine the optimal conditions for nerve regeneration. Cell viability and SC migration assays were conducted for collagen I, laminin, fibronectin, lysine and ornithine. The highest values for cell viability were detected for collagen I, whereas fibronectin was most stimulatory for SC migration. At this time, clinically approved conduits are based on single-material structures. In contrast, the results of this experiment suggest that material compounds such as collagen I in conjunction with fibronectin should be considered for optimal nerve healing.

Reactive oxygen species induce MMP12-dependent degradation of collagen 5 and fibronectin to promote the motility of human umbilical cord-derived mesenchymal stem cells

BACKGROUND AND PURPOSE

Reactive oxygen species (ROS) are potent regulators of stem cell behaviour; however, their physiological significance as regards MMP-mediated regulation of the motility of human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) has not been characterized. In the present study, we investigated the role of hydrogen peroxide (H2O2 ) and associated signalling pathways in promoting UCB-MSCs motility.

EXPERIMENTAL APPROACH

The regulatory effects of H2O2 on the activation of PKC, MAPKs, NF-κB and β-catenin were determined. The expressions of MMP and extracellular matrix proteins were examined. Pharmacological inhibitors and gene-specific siRNA were used to identify the signalling pathways of H2O2 that affect UCB-MSCs motility. An experimental skin wound-healing model was used to confirm the functional role of UCB-MSCs treated with H2O2 in ICR mice.

KEY RESULTS

H2O2 increased the motility of UCB-MSCs by activating PKCα via a calcium influx mechanism. H2O2 activated ERK and p38 MAPK, which are responsible for the distinct activation of transcription factors NF-κB and β-catenin. UCB-MSCs expressed eight MMP genes, but only MMP12 expression was uniquely regulated by NF-κB and β-catenin activation. H2O2 increased the MMP12-dependent degradation of collagen 5 (COL-5) and fibronectin (FN) associated with UCB-MSCs motility. Finally, topical transplantation of UCB-MSCs treated with H2O2 enhanced skin wound healing in mice.

CONCLUSIONS AND IMPLICATIONS

H2O2 stimulated UCB-MSCs motility by increasing MMP12-dependent degradation of COL-5 and FN through the activation of NF-κB and glycogen synthase kinase-3β/β-catenin, which is critical for providing a suitable microenvironment for MSCs transplantation and re-epithelialization of skin wounds in mice.

Upregulation of NHE1 protein expression enables glioblastoma cells to escape TMZ-mediated toxicity via increased H⁺ extrusion, cell migration and survival

Sodium-hydrogen exchanger isoform 1 (NHE1) plays a role in survival and migration/invasion of several cancers and is an emerging new therapeutic target. However, the role of NHE1 in glioblastoma and the interaction of NHE1 expression and function in glioblastoma cells with cytotoxic temozolomide (TMZ) therapy remain unknown. In this study, we detected high levels of NHE1 protein only in primary human glioma cells (GC), glioma xenografts and glioblastoma, but not in human neural stem cells or astrocytes. GC exhibited an alkaline resting pHi (7.46±0.04) maintained by robust NHE1-mediated H(+) extrusion. GC treatment with TMZ for 2-24h triggered a transient decrease in pHi, which recovered by 48h and correlated with concurrent upregulation of NHE1 protein expression. NHE1 protein was colocalized with ezrin at lamellipodia and probably involved in GC migration. The TMZ-treated GC exhibited increased migration and invasion, which was attenuated by addition of NHE1 inhibitor HOE-642. Most importantly, NHE1 inhibition prevented prosurvival extracellular signal-regulated kinase activation and accelerated TMZ-induced apoptosis. Taken together, our study provides the first evidence that GC upregulate NHE1 protein to maintain alkaline pHi. Combining TMZ therapy with NHE1 inhibition suppresses GC migration and invasion, and also augments TMZ-induced apoptosis. These findings strongly suggest that NHE1 is an important cytoprotective mechanism in GC and presents a new therapeutic strategy of combining NHE1 inhibition and TMZ chemotherapy.

Galectin-1 stimulates motility of human umbilical cord blood-derived mesenchymal stem cells by downregulation of smad2/3-dependent collagen 3/5 and upregulation of NF-κB-dependent fibronectin/laminin 5 expression

Galectin-1 (Gal-1) belongs to a family of endogenous lectins with conserved carbohydrate recognition domains binding β-galactosidase sugars and plays a vital role in regulating stem cell functions including determination of cell fate. However, our understanding of the functional roles of Gal-1 in human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) is still fragmentary and incomplete. Gal-1 significantly increased motility after a 24-h incubation, and this effect was inhibited by β-lactose. We analyzed 17 extracellular matrix (ECM) genes in UCB-MSCs. Gal-1 decreased the expression of collagen genes COL3A1 (COL-3) and COL5A1 (COL-5) but increased the expression of fibronectin (FN) and laminin 5 (LM-5), that were reversed by β-lactose. Gal-1 increased protein kinase C (PKC), c-Src, and caveolin-1 (Cav-1) phosphorylation that was attenuated by β-lactose and the Src inhibitor PP2. In addition, pretreatment with the lipid raft disruptor Mβ-CD and the PKC inhibitors inhibited Gal-1-induced UCB-MSC motility. In addition, Gal-1 reduced smad2/3 phosphorylation and induced nuclear factor (NF)-κB phosphorylation. Pretreatment with Mβ-CD attenuated Gal-1-reduced smad2/3 phosphorylation, COL-3, and COL-5 expression but did not affect NF-κB phosphorylation, FN, or LM-5 expression. In contrast, PKC inhibitors only attenuated NF-κB phosphorylation, FN, and LM-5 expression. Reconstructing Gal-1-induced genetic changes by replacing it with siRNA specific for COL-3 or COL-5, or treatment of the cells with FN and LM-5 proteins, increased motility and its related proteins such as focal adhesion kinase, Akt, Erk, integrins, and matrix metalloproteinase-2. A combined treatment with COL-3/COL-5 siRNA or FN/LM-5 compared with that of single treatments was synergistic. However, a single Gal-1 treatment maximally stimulated motility and related protein phosphorylation/expression. These results demonstrate that Gal-1 stimulated human UCB-MSC motility by decreasing COL-3/COL-5 expression and increasing FN/LM-5 expression through a PKC-dependent NF-κB and c-Src/Cav-1-dependent smad2/3 pathway that was critical for governing the activation of FAK, Akt, Erk, integrins, and MMP2.

Structural dynamics and regulation of the mammalian SLC9A family of Na⁺/H⁺ exchangers

Mammalian Na⁺/H⁺ exchangers of the SLC9A family are widely expressed and involved in numerous essential physiological processes. Their primary function is to mediate the 1:1 exchange of Na⁺ for H⁺ across the membrane in which they reside, and they play central roles in regulation of body, cellular, and organellar pH. Their function is tightly regulated through mechanisms involving interactions with multiple protein and lipid-binding partners, phosphorylations, and other posttranslational modifications. Biochemical and mutational analyses indicate that the SLC9As have a short intracellular N-terminus, 12 transmembrane (TM) helices necessary and sufficient for ion transport, and a C-terminal cytoplasmic tail region with essential regulatory roles. No high-resolution structures of the SLC9As exist; however, models based on crystal structures of the bacterial NhaAs support the 12 TM organization and suggest that TMIV and XI may form a central part of the ion-translocation pathway, whereas pH sensing may involve TMII, TMIX, and several intracellular loops. Similar to most ion transporters studied, SLC9As likely exist as coupled dimers in the membrane, and this appears to be important for the well-studied cooperativity of H⁺ binding. The aim of this work is to summarize and critically discuss the currently available evidence on the structural dynamics, regulation, and binding partner interactions of SLC9As, focusing in particular on the most widely studied isoform, SLC9A1/NHE1. Further, novel bioinformatic and structural analyses are provided that to some extent challenge the existing paradigm on how ions are transported by mammalian SLC9As.

The less-often-traveled surface of stem cells: caveolin-1 and caveolae in stem cells, tissue repair and regeneration

Stem cells are an important resource for tissue repair and regeneration. While a great deal of attention has focused on derivation and molecular regulation of stem cells, relatively little research has focused on how the subcellular structure and composition of the cell membrane influences stem cell activities such as proliferation, differentiation and homing. Caveolae are specialized membrane lipid rafts coated with caveolin scaffolding proteins, which can regulate cholesterol transport and the activity of cell signaling receptors and their downstream effectors. Caveolin-1 is involved in the regulation of many cellular processes, including growth, control of mitochondrial antioxidant levels, migration and senescence. These activities are of relevance to stem cell biology, and in this review evidence for caveolin-1 involvement in stem cell biology is summarized. Altered stem and progenitor cell populations in caveolin-1 null mice suggest that caveolin-1 can regulate stem cell proliferation, and in vitro studies with isolated stem cells suggest that caveolin-1 regulates stem cell differentiation. The available evidence leads us to hypothesize that caveolin-1 expression may stabilize the differentiated and undifferentiated stem cell phenotype, and transient downregulation of caveolin-1 expression may be required for transition between the two. Such regulation would probably be critical in regenerative applications of adult stem cells and during tissue regeneration. We also review here the temporal changes in caveolin-1 expression reported during tissue repair. Delayed muscle regeneration in transgenic mice overexpressing caveolin-1 as well as compromised cardiac, brain and liver tissue repair and delayed wound healing in caveolin-1 null mice suggest that caveolin-1 plays an important role in tissue repair, but that this role may be negative or positive depending on the tissue type and the nature of the repair process. Finally, we also discuss how caveolin-1 quiescence-inducing activities and effects on mitochondrial antioxidant levels may influence stem cell aging.