Bioelectric controls of cell proliferation: ion channels, membrane voltage and the cell cycle

The chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) controls cellular quiescence by hyperpolarizing the cell membrane during diapause in the crustacean Artemia

Cellular quiescence, a reversible state in which growth, proliferation, and other cellular activities are arrested, is important for self-renewal, differentiation, development, regeneration, and stress resistance. However, the physiological mechanisms underlying cellular quiescence remain largely unknown. In the present study, we used embryos of the crustacean Artemia in the diapause stage, in which these embryos remain quiescent for prolonged periods, as a model to explore the relationship between cell-membrane potential (V _mem) and quiescence. We found that V _mem is hyperpolarized and that the intracellular chloride concentration is high in diapause embryos, whereas V _mem is depolarized and intracellular chloride concentration is reduced in postdiapause embryos and during further embryonic development. We identified and characterized the chloride ion channel protein cystic fibrosis transmembrane conductance regulator (CFTR) of Artemia (Ar-CFTR) and found that its expression is silenced in quiescent cells of Artemia diapause embryos but remains constant in all other embryonic stages. Ar-CFTR knockdown and GlyH-101-mediated chemical inhibition of Ar-CFTR produced diapause embryos having a high V _mem and intracellular chloride concentration, whereas control Artemia embryos released free-swimming nauplius larvae. Transcriptome analysis of embryos at different developmental stages revealed that proliferation, differentiation, and metabolism are suppressed in diapause embryos and restored in postdiapause embryos. Combined with RNA sequencing (RNA-Seq) of GlyH-101-treated MCF-7 breast cancer cells, these analyses revealed that CFTR inhibition down-regulates the Wnt and Aurora Kinase A (AURKA) signaling pathways and up-regulates the p53 signaling pathway. Our findings provide insight into CFTR-mediated regulation of cellular quiescence and V _mem in the Artemia model.

Ion Channel and Neurotransmitter Modulators as Electroceutical Approaches to the Control of Cancer

The activities of individual cells must be tightly coordinated in order to build and maintain complex 3-dimensional body structures during embryogenesis and regeneration. Thus, one way to view cancer is within systems biology as a network disorder affecting the ability of cells to properly interact with a morphodynamic field of instructive signals that keeps proliferation and migration orchestrated toward the anatomical needs of the host or-ganism. One layer of this set of instructive microenvironmental cues is bioelectrical. Voltage gradients among all somatic cells (not just excitable nerve and muscle) control cell behavior, and the ionic coupling of cells into networks via electrochemical synapses allows them to implement tissue-level patterning decisions. These gradients have been increasingly impli-cated in the induction and suppression of tumorigenesis and metastasis, in the emerging links between developmental bioelectricity to the cancer problem. Consistent with the well-known role of neurotransmitter molecules in transducing electrical activity to downstream cascades in the brain, serotonergic signaling has likewise been implicated in cancer. Here, we review these recent data and propose new approaches for manipulating bioelectric and neurotransmitter pathways in cancer biology based on a bioelectric view of cancer. To sup-port this methodology, we present new data on the effects of the SSRI Prozac and its analog (ZINC ID = ZINC06811610) on survival of both cancer (MCF7) and normal (MCF10A) breast cells exposed to these compounds. We found an IC50 concentration (25 μM for Pro-zac and 100 μM for the Prozac analog) at which these compounds inhibited tumor cell sur-vival and proliferation. Additionally, at these concentrations, we did not observe alterations in a non-tumoral cell line. This constitutes a proof-of-concept demonstration for our hy-pothesis that the use of both existing and novel drugs as electroceuticals could serve as an alternative to highly toxic chemotherapy strategies replacing or augmenting them with less toxic alternatives. We believe this new approach forms an exciting roadmap for future bio-medical advances.

[An integral view of cancer (I). The study, classification and reprogramming of the tumoral microclimate]

The group of diseases that we call cancer share a biological structure formed by a complex ecosystem, with altered intercellular communication, information fields, development and tissue function. Beyond the genetic alterations of the tumor cell, the demonstration of an altered ecosystem, with interconnections at systemic levels, opens up a new perspective on cancer biology and behavior. Different tumor facets, such as morphology, classification, clinical aggressiveness, prognosis and response to treatment now appear under a comprehensive vision that offers a new horizon of study, research and clinical management. The Somatic Mutation Theory in cancer, in force for more than one hundred years, is now completed by the study of the tumor microenvironment, the extracellular matrix, the stromal cells, the immune response, the innervation, the nutrition, the mitochondria, the metabolism, the interstitial fluid, the mechanical and electromagnetic properties of the tissue and many other areas of emerging knowledge; thus opening the door to a reprogramming exercise of the tumor phenotype through the modification of the keys offered by this new paradigm. Its recognition makes it possible to go from considering the oncological process as a cellular problem to a supracellular alteration based on the disorganization of tissues, immersed in the relationships of the complex system of the living being.

Cell Cycle-Dependent Expression of Bk Channels in Human Mesenchymal Endometrial Stem Cells

The study of ion channels in stem cells provides important information about their role in stem cell fate. Previously we have identified the activity of calcium-activated potassium channels of big conductance (BK channels) in human endometrium-derived mesenchymal stem cells (eMSCs). BK channels could have significant impact into signaling processes by modulating membrane potential. The membrane potential and ionic permeability dynamically changes during cycle transitions. Here, we aimed at verification of the role of BK channels as potassium transporting pathway regulating cell cycle passageway of eMSCs. The functional expression of native BK channels was confirmed by patch-clamp and immunocytochemistry. In non-synchronized cells immunofluorescent analysis revealed BK-positive and BK-negative stained eMSCs. Using cell synchronization, we found that the presence of BK channels in plasma membrane was cell cycle-dependent and significantly decreased in G2M phase. However, the study of cell cycle progression in presence of selective BK channel inhibitors showed no effect of pore blockers on cycle transitions. Thus, BK channel-mediated K+ transport is not critical for the fundamental mechanism of passageway through cell cycle of eMSCs. At the same time, the dynamics of the presence of BK channels on plasma membrane of eMSCs can be a novel indicator of cellular proliferation.

Implication of Voltage-Gated Potassium Channels in Neoplastic Cell Proliferation

Voltage-gated potassium channels (Kv) are the largest group of ion channels. Kv are involved in controlling the resting potential and action potential duration in the heart and brain. Additionally, these proteins participate in cell cycle progression as well as in several other important features in mammalian cell physiology, such as activation, differentiation, apoptosis, and cell volume control. Therefore, Kv remarkably participate in the cell function by balancing responses. The implication of Kv in physiological and pathophysiological cell growth is the subject of study, as Kv are proposed as therapeutic targets for tumor regression. Though it is widely accepted that Kv channels control proliferation by allowing cell cycle progression, their role is controversial. Kv expression is altered in many cancers, and their participation, as well as their use as tumor markers, is worthy of effort. There is an ever-growing list of Kv that remodel during tumorigenesis. This review focuses on the actual knowledge of Kv channel expression and their relationship with neoplastic proliferation. In this work, we provide an update of what is currently known about these proteins, thereby paving the way for a more precise understanding of the participation of Kv during cancer development.

Bioelectric Properties of Myogenic Progenitor Cells

Modern stem cell research has mainly focused on protein expression and transcriptional networks. However, transmembrane voltage gradients generated by ion channels and transporters have demonstrated to be powerful regulators of cellular processes. These physiological cues exert influence on cell behaviors ranging from differentiation and proliferation to migration and polarity. Bioelectric signaling is a fundamental element of living systems and an untapped reservoir for new discoveries. Dissecting these mechanisms will allow for novel methods of controlling cell fate and open up new opportunities in biomedicine. This review focuses on the role of ion channels and the resting membrane potential in the proliferation and differentiation of skeletal muscle progenitor cells. In addition, findings relevant to this topic are presented and potential implications for tissue engineering and regenerative medicine are discussed.

Membrane potential (Vmem) measurements during mesenchymal stem cell (MSC) proliferation and osteogenic differentiation

Background

Electrochemical signals play an important role in cell communication and behavior. Electrically charged ions transported across cell membranes maintain an electrochemical imbalance that gives rise to bioelectric signaling, called membrane potential or V_mem. V_mem plays a key role in numerous inter- and intracellular functions that regulate cell behaviors like proliferation, differentiation and migration, all playing a critical role in embryonic development, healing, and regeneration.

Methods

With the goal of analyzing the changes in V_mem during cell proliferation and differentiation, here we used direct current electrical stimulation (EStim) to promote cell proliferation and differentiation and simultaneously tracked the corresponding changes in V_mem in adipose derived mesenchymal stem cells (AT-MSC).

Results

We found that EStim caused increased AT-MSC proliferation that corresponded to V_mem depolarization and increased osteogenic differentiation that corresponded to V_mem hyperpolarization. Taken together, this shows that V_mem changes associated with EStim induced cell proliferation and differentiation can be accurately tracked during these important cell functions. Using this tool to monitor V_mem changes associated with these important cell behaviors we hope to learn more about how these electrochemical cues regulate cell function with the ultimate goal of developing new EStim based treatments capable of controlling healing and regeneration.

Arachidonic acid hyperpolarizes mesenchymal stromal cells from the human adipose tissue by stimulating TREK1 K+ channels

The current knowledge of electrogenesis in mesenchymal stromal cells (MSCs) remains scarce. Earlier, we demonstrated that in MSCs from the human adipose tissue, transduction of certain agonists involved the phosphoinositide cascade. Its pivotal effector PLC generates DAG that can regulate ion channels directly or via its derivatives, including arachidonic acid (AA). Here we showed that AA strongly hyperpolarized MSCs by stimulating instantly activating, outwardly rectifying TEA-insensitive K⁺ channels. Among AA-regulated K⁺ channels, K2P channels from the TREK subfamily appeared to be an appropriate target. The expression of K2P channels in MSCs was verified by RT-PCR, which revealed TWIK-1, TREK-1, and TASK-5 transcripts. The TREK-1 inhibitor spadin antagonized the electrogenic action of AA, which was simulated by the channel activator BL 1249. This functional evidence suggested that TREK-1 channels mediated AA-dependent hyperpolarization of MSCs. Being mostly silent at rest, TREK-1 negligibly contributed to the “background” K⁺ current. The dramatic stimulation of TREK-1 channels by AA indicates their involvement in AA-dependent signaling in MSCs.

Cancer-Associated Intermediate Conductance Ca2+-Activated K⁺ Channel KCa3.1

Several tumor entities have been reported to overexpress K_Ca3.1 potassium channels due to epigenetic, transcriptional, or post-translational modifications. By modulating membrane potential, cell volume, or Ca²⁺ signaling, K_Ca3.1 has been proposed to exert pivotal oncogenic functions in tumorigenesis, malignant progression, metastasis, and therapy resistance. Moreover, K_Ca3.1 is expressed by tumor-promoting stroma cells such as fibroblasts and the tumor vasculature suggesting a role of K_Ca3.1 in the adaptation of the tumor microenvironment. Combined, this features K_Ca3.1 as a candidate target for innovative anti-cancer therapy. However, immune cells also express K_Ca3.1 thereby contributing to T cell activation. Thus, any strategy targeting K_Ca3.1 in anti-cancer therapy may also modulate anti-tumor immune activity and/or immunosuppression. The present review article highlights the potential of K_Ca3.1 as an anti-tumor target providing an overview of the current knowledge on its function in tumor pathogenesis with emphasis on vasculo- and angiogenesis as well as anti-cancer immune responses.

Electric field-responsive nanoparticles and electric fields: physical, chemical, biological mechanisms and therapeutic prospects

Electric fields are among physical stimuli that have revolutionized therapy. Occurring endogenously or exogenously, the electric field can be used as a trigger for controlled drug release from electroresponsive drug delivery systems, can stimulate wound healing and cell proliferation, may enhance endocytosis or guide stem cell differentiation. Electric field pulses may be applied to induce cell fusion, can increase the penetration of therapeutic agents into cells, or can be applied as a standalone therapy to ablate tumors. This review describes the main therapeutic trends and overviews the main physical, chemical and biological mechanisms underlying the actions of electric fields. Overall, the electric field can be used in therapeutic approaches in several ways. The electric field can act on drug carriers, cells and tissues. Understanding the multiple effects of this powerful tool will help harnessing its full therapeutic potential in an efficient and safe way.

Evaluation of the anticancer and anti-metastasis effects of novel synthetic sodium channel blockers in prostate cancer cells in vitro and in vivo

BACKGROUND

Voltage-gated sodium channels (VGSCs) are involved in several cellular processes related to cancer cell growth and metastasis, including adhesion, proliferation, apoptosis, migration, and invasion. We here in investigated the effects of S0154 and S0161, two novel synthetic sodium channel blockers (SCBs), on human prostate cancer cells (PC3, DU145, and LnCaP) and a prostate cancer xenograft model.

METHODS

The MTT assay was used to assess the anticancer effects of SCBs in PC3, DU145, and LnCaP cells. Sodium indicator and glucose uptake assays were used to determine the effects of S0154 and S0161 in PC3 cells. The impact of these SCBs on the proliferation, cell cycle, apoptosis, migration, and invasion of PC3 cells were determined using a CFDA-SE cell proliferation assay, cell cycle assay, annexin V-FITC apoptosis assay, transwell cell invasion assay, and wound-healing assay, respectively. The protein expression levels of Nav1.6, Nav1.7, CDK1, cyclin B1, MMP2, MMP9 in PC3 cells were analysis by Western blotting. The in vivo anticancer activity was evaluated using a PC3 xenograft model in nude mice.

RESULTS

S0154 and S0161 both showed anticancer and anti-metastatic effects against prostate cancer cells and significantly inhibited cell viability, with IC₅₀ values in the range of 10.51-26.60 μmol/L (S0154) and 5.07-11.92 μmol/L (S0161). Both compounds also increased the intracellular level of sodium, inhibited the protein expression of two α subunits of VGSCs (Nav1.6 and Nav1.7), and caused G2/M phase cell cycle arrest, with no or minor effects on cell apoptosis. Concentrations of 5 and 10 μmol/L of S0154 and S0161 significantly decreased the glucose uptake of PC3 cells. The compounds also inhibited the proliferation of PC3 cells and decreased their invasion in transwell assays. Furthermore, S0161 exerted antitumor activity in an in vivo PC3 xenograft model in nude mice, inhibiting the growth of the tumors by about 51% compared to the control group.

CONCLUSIONS

These results suggest that S0154 and S0161 have anticancer and anti-metastasis effects in prostate cancer cells both in vitro and in vivo, supporting their further development as potential therapeutic agents for prostate cancer.

Extracellular Surface Potential Mapping by Scanning Ion Conductance Microscopy Revealed Transient Transmembrane Pore Formation Induced by Conjugated Polymer Nanoparticles

In-depth understanding of the biophysicochemical interactions at the nano-bio interface is important for basic cell biology and applications in nanomedicine and nanobiosensors. Here, the extracellular surface potential and topography changes of live cell membranes interacting with polymeric nanomaterials using a scanning ion conductance microscopy-based potential imaging technique are investigated. Two structurally similar amphiphilic conjugated polymer nanoparticles (CPNs) containing different functional groups (i.e., primary amine versus guanidine) are used to study incubation time and functional group-dependent extracellular surface potential and topographic changes. Transmembrane pores, which induce significant changes in potential, only appear transiently in the live cell membranes during the initial interactions. The cells are able to self-repair the damaged membrane and become resilient to prolonged CPN exposure. This study provides an important observation on how the cells interact with and respond to extracellular polymeric nanomaterials at the early stage. This study also demonstrates that extracellular surface potential imaging can provide a new insight to help understand the complicated interactions at the nano-bio interface and the following cellular responses.

Perspective: The promise of multi-cellular engineered living systems

Recent technological breakthroughs in our ability to derive and differentiate induced pluripotent stem cells, organoid biology, organ-on-chip assays, and 3-D bioprinting have all contributed to a heightened interest in the design, assembly, and manufacture of living systems with a broad range of potential uses. This white paper summarizes the state of the emerging field of "multi-cellular engineered living systems," which are composed of interacting cell populations. Recent accomplishments are described, focusing on current and potential applications, as well as barriers to future advances, and the outlook for longer term benefits and potential ethical issues that need to be considered.

Ion Channels in Cancer: Are Cancer Hallmarks Oncochannelopathies?

Genomic instability is a primary cause and fundamental feature of human cancer. However, all cancer cell genotypes generally translate into several common pathophysiological features, often referred to as cancer hallmarks. Although nowadays the catalog of cancer hallmarks is quite broad, the most common and obvious of them are 1) uncontrolled proliferation, 2) resistance to programmed cell death (apoptosis), 3) tissue invasion and metastasis, and 4) sustained angiogenesis. Among the genes affected by cancer, those encoding ion channels are present. Membrane proteins responsible for signaling within cell and among cells, for coupling of extracellular events with intracellular responses, and for maintaining intracellular ionic homeostasis ion channels contribute to various extents to pathophysiological features of each cancer hallmark. Moreover, tight association of these hallmarks with ion channel dysfunction gives a good reason to classify them as special type of channelopathies, namely oncochannelopathies. Although the relation of cancer hallmarks to ion channel dysfunction differs from classical definition of channelopathies, as disease states causally linked with inherited mutations of ion channel genes that alter channel's biophysical properties, in a broader context of the disease state, to which pathogenesis ion channels essentially contribute, such classification seems absolutely appropriate. In this review the authors provide arguments to substantiate such point of view.

Progenitor Hyperpolarization Regulates the Sequential Generation of Neuronal Subtypes in the Developing Neocortex

During corticogenesis, ventricular zone progenitors sequentially generate distinct subtypes of neurons, accounting for the diversity of neocortical cells and the circuits they form. While activity-dependent processes are critical for the differentiation and circuit assembly of postmitotic neurons, how bioelectrical processes affect nonexcitable cells, such as progenitors, remains largely unknown. Here, we reveal that, in the developing mouse neocortex, ventricular zone progenitors become more hyperpolarized as they generate successive subtypes of neurons. Experimental in vivo hyperpolarization shifted the transcriptional programs and division modes of these progenitors to a later developmental status, with precocious generation of intermediate progenitors and a forward shift in the laminar, molecular, morphological, and circuit features of their neuronal progeny. These effects occurred through inhibition of the Wnt-beta-catenin signaling pathway by hyperpolarization. Thus, during corticogenesis, bioelectric membrane properties are permissive for specific molecular pathways to coordinate the temporal progression of progenitor developmental programs and thus neocortical neuron diversity.

Staying in shape: Planarians as a model for understanding regenerative morphology

A key requirement of tissue/organ regeneration is the ability to induce appropriate shape in situ. Regenerated structures need to be integrated with pre-existing ones, through the combined regulation of new tissue growth and the scaling of surrounding tissues. This requires a tightly coordinated control of individual cell functions such as proliferation and stem cell differentiation. While great strides have been made in elucidating cell growth and differentiation mechanisms, how overall shape is generated during regeneration remains unknown. This is because a significant gap remains in our understanding of how cell behaviors are coordinated at the level of tissues and organs. The highly regenerative planarian flatworm has emerged as an important model for defining and understanding regenerative shape mechanisms. This review provides an overview of the main processes known to regulate tissue and animal shape during planarian regeneration: adult stem cell regulation, the reestablishment of body axes, tissue remodeling in pre-existing structures, organ scaling and the maintenance of body proportion, and the bioelectrical regulation of animal morphology. In order for the field to move forward, it will be necessary to identify shape mutants as a means to uncover the molecular mechanisms that synchronize all these separate processes to produce the worm's final regenerative shape. This knowledge will also aid efforts to define the mechanisms that control the termination of regenerative processes.

Roles of pH in control of cell proliferation

Precise spatiotemporal regulation of intracellular pH (pH_i ) is a prerequisite for normal cell function, and changes in pH_i or pericellular pH (pH_e ) exert important signalling functions. It is well established that proliferation of mammalian cells is dependent on a permissive pH_i in the slightly alkaline range (7.0-7.2). It is also clear that mitogen signalling in nominal absence of HCO3- is associated with an intracellular alkalinization (~0.3 pH unit above steady-state pH_i ), which is secondary to activation of Na⁺ /H⁺ exchange. However, it remains controversial whether this increase in pH_i is part of the mitogenic signal cascade leading to cell cycle entry and progression, and whether it is relevant under physiological conditions. Furthermore, essentially all studies of pH_i in mammalian cell proliferation have focused on the mitogen-induced G0-G1 transition, and the regulation and roles of pH_i during the cell cycle remain poorly understood. The aim of this review is to summarize and critically discuss the possible roles of pH_i and pH_e in cell cycle progression. While the focus is on the mammalian cell cycle, important insights from studies in lower eukaryotes are also discussed. We summarize current evidence of links between cell cycle progression and pH_i and discuss possible pH_i - and pH_e sensors and signalling pathways relevant to mammalian proliferation control. The possibility that changes in pH_i during cell cycle progression may be an integral part of the checkpoint control machinery is explored. Finally, we discuss the relevance of links between pH and proliferation in the context of the perturbed pH homoeostasis and acidic microenvironment of solid tumours.

Calcium as a signal integrator in developing epithelial tissues

Decoding how tissue properties emerge across multiple spatial and temporal scales from the integration of local signals is a grand challenge in quantitative biology. For example, the collective behavior of epithelial cells is critical for shaping developing embryos. Understanding how epithelial cells interpret a diverse range of local signals to coordinate tissue-level processes requires a systems-level understanding of development. Integration of multiple signaling pathways that specify cell signaling information requires second messengers such as calcium ions. Increasingly, specific roles have been uncovered for calcium signaling throughout development. Calcium signaling regulates many processes including division, migration, death, and differentiation. However, the pleiotropic and ubiquitous nature of calcium signaling implies that many additional functions remain to be discovered. Here we review a selection of recent studies to highlight important insights into how multiple signals are transduced by calcium transients in developing epithelial tissues. Quantitative imaging and computational modeling have provided important insights into how calcium signaling integration occurs. Reverse-engineering the conserved features of signal integration mediated by calcium signaling will enable novel approaches in regenerative medicine and synthetic control of morphogenesis.

Electromechanics and Volume Dynamics in Nonexcitable Tissue Cells

Cell volume regulation is fundamentally important in phenomena such as cell growth, proliferation, tissue homeostasis, and embryogenesis. How the cell size is set, maintained, and changed over a cell's lifetime is not well understood. In this work we focus on how the volume of nonexcitable tissue cells is coupled to the cell membrane electrical potential and the concentrations of membrane-permeable ions in the cell environment. Specifically, we demonstrate that a sudden cell depolarization using the whole-cell patch clamp results in a 50% increase in cell volume, whereas hyperpolarization results in a slight volume decrease. We find that cell volume can be partially controlled by changing the chloride or the sodium/potassium concentrations in the extracellular environment while maintaining a constant external osmotic pressure. Depletion of external chloride leads to a volume decrease in suspended HN31 cells. Introducing cells to a high-potassium solution causes volume increase up to 50%. Cell volume is also influenced by cortical tension: actin depolymerization leads to cell volume increase. We present an electrophysiology model of water dynamics driven by changes in membrane potential and the concentrations of permeable ions in the cells surrounding. The model quantitatively predicts that the cell volume is directly proportional to the intracellular protein content.

Promoter CpG island methylation in ion transport mechanisms and associated dietary intakes jointly influence the risk of clear-cell renal cell cancer

Background

Sodium intake, but not potassium or fluid intake, has been associated with higher renal cell cancer (RCC) risk. However, risk factors may differ by molecular subtypes of the tumour. In renal physiology, electrolyte and water homeostasis is facilitated by ion transport mechanisms (ITM). Aberrant regulation of ITM genes, for example by promoter CpG island methylation, may modify associations between sodium, potassium and fluid intake and RCC risk.

Methods

We identified ARHGDIG , ATP1A1 , SCNN1B and SLC8A3 as ITM genes exhibiting RCC-specific promoter methylation and down-regulation. Methylation-specific polymerase chain reaction (PCR) was used to analyse promoter CpG island methylation in tumour DNA of 453 RCC cases from the Netherlands Cohort Study ( n = 120 852) after 20.3 years of follow-up. Diet was measured at baseline using food-frequency questionnaires. Cox regression analyses were restricted to clear-cell (cc)RCC ( n = 306) and stratified by tumours with no, low (1 gene) and high (≥ 2 genes) methylation.

Results

Sodium intake (high vs low) increased ccRCC risk particularly in tumours with a high methylation index: hazard ratio (HR) [95% confidence interval (CI)]: 2.04 (1.16-3.58), whereas heterogeneity across the methylation index was not significant ( P -heterogeneity = 0.26). Potassium intake was differentially associated with ccRCC risk ( P -heterogeneity = 0.008); the risk for high (vs low) potassium intake was low for unmethylated tumours [HR (95% CI): 0.60 (0.36-1.01)], but high for tumours with a high methylation index [HR (95% CI): 1.60 (0.96-2.65)]. Risks similarly differed for fluid intake, though not significantly ( P -heterogeneity = 0.54).

Conclusions

Our findings suggest for the first time that dietary intakes are differentially associated with ccRCC risk according to molecular subtypes defined by ITM gene-specific promoter methylation.

Comparing Plant and Animal Glutamate Receptors: Common Traits but Different Fates?

Animal ionotropic glutamate receptors (iGluRs) are ligand-gated channels whose evolution is intimately linked to the one of the nervous system, where the agonist glutamate and co-agonists glycine/D-serine act as neuro-transmitters or -modulators. While iGluRs are specialized in neuronal communication, plant glutamate receptor-like (GLR) homologues have evolved many plant-specific physiological functions, such as sperm signaling in moss, pollen tube growth, root meristem proliferation, innate immune and wound responses. GLRs have been associated with Ca2+ signaling by directly channeling its extracellular influx into the cytosol. Nevertheless, very limited information on functional properties of GLRs is available, and we mostly rely on structure/function data obtained for animal iGluRs to interpret experimental results obtained for plant GLRs. Yet, a deeper characterization and better understanding of plant GLRs is progressively unveiling original and different mode of functions when compared to their mammalian counterparts. Here, we review the function of plant GLRs comparing their predicted structure and physiological roles to the well-documented ones of iGluRs. We conclude that interpreting GLR function based on comparison to their animal counterparts calls for caution, especially when presuming physiological roles and mode of action for plant GLRs from comparison to iGluRs in peripheral, non-neuronal tissues.

Involvement of AMP-activated Protein Kinase (AMPK) in Regulation of Cell Membrane Potential in a Gastric Cancer Cell Line

Membrane potential (V_mem) is a key bioelectric property of non-excitable cells that plays important roles in regulating cell proliferation. However, the regulation of V_mem itself remains largely unexplored. We found that, under nutrient starvation, during which cell division is inhibited, MKN45 gastric cancer cells were in a hyperpolarized state associated with a high intracellular chloride concentration. AMP-activated protein kinase (AMPK) activity increased, and expression of cystic fibrosis transmembrane conductance regulator (CFTR) decreased, in nutrient-starved cells. Furthermore, the increase in intracellular chloride concentration level and V_mem hyperpolarization in nutrient-starved cells was suppressed by inhibition of AMPK activity. Intracellular chloride concentrations and hyperpolarization increased after over-activation of AMPK using the specific activator AICAR or suppression of CFTR activity using specific inhibitor GlyH-101. Under these conditions, proliferation of MKN45 cells was inhibited. These results reveal that AMPK controls the dynamic change in V_mem by regulating CFTR and influencing the intracellular chloride concentration, which in turn influences cell-cycle progression. These findings offer new insights into the mechanisms underlying cell-cycle arrest regulated by AMPK and CFTR.

Talking to cells: semiconductor nanomaterials at the cellular interface

The interface of biological components with semiconductors is a growing field with numerous applications. For example, the interfaces can be used to sense and modulate the electrical activity of single cells and tissues. From the materials point of view, silicon is the ideal option for such studies due to its controlled chemical synthesis, scalable lithography for functional devices, excellent electronic and optical properties, biocompatibility and biodegradability. Recent advances in this area are pushing the bio-interfaces from the tissue and organ level to the single cell and sub-cellular regimes. In this progress report, we will describe some fundamental studies focusing on miniaturizing the bioelectric and biomechanical interfaces. Additionally, many of our highlighted examples involve freestanding silicon-based nanoscale systems, in addition to substrate-bound structures or devices; the former offers new promise for basic research and clinical application. In this report, we will describe recent developments in the interfacing of neuronal and cardiac cells and their networks. Moreover, we will briefly discuss the incorporation of semiconductor nanostructures for interfacing non-excitable cells in applications such as probing intracellular force dynamics and drug delivery. Finally, we will suggest several directions for future exploration.

Oligodendrocytes control potassium accumulation in white matter and seizure susceptibility

The inwardly rectifying K⁺ channel K_ir4.1 is broadly expressed by CNS glia and deficits in K_ir4.1 lead to seizures and myelin vacuolization. However, the role of oligodendrocyte K_ir4.1 channels in controlling myelination and K⁺ clearance in white matter has not been defined. Here, we show that selective deletion of K_ir4.1 from oligodendrocyte progenitors (OPCs) or mature oligodendrocytes did not impair their development or disrupt the structure of myelin. However, mice lacking oligodendrocyte K_ir4.1 channels exhibited profound functional impairments, including slower clearance of extracellular K⁺ and delayed recovery of axons from repetitive stimulation in white matter, as well as spontaneous seizures, a lower seizure threshold, and activity-dependent motor deficits. These results indicate that K_ir4.1 channels in oligodendrocytes play an important role in extracellular K⁺ homeostasis in white matter, and that selective loss of this channel from oligodendrocytes is sufficient to impair K⁺ clearance and promote seizures.

miR-497-5p inhibits cell proliferation and invasion by targeting KCa3.1 in angiosarcoma

Angiosarcoma is a rare malignant mesenchymal tumor with poor prognosis. We aimed to identify malignancy-associated miRNAs and their target genes, and explore biological functions of miRNA and its target in angiosarcoma. By miRNA microarrays and reverse transcription polymerase chain reaction, we identified 1 up-regulated miRNA (miR-222-3p) and 3 down-regulated miRNAs (miR-497-5p, miR-378-3p and miR-483-5p) in human angiosarcomas compared with human capillary hemangiomas. The intermediate-conductance calcium activated potassium channel KCa3.1 was one of the putative target genes of miR-497-5p, and marked up-regulation of KCa3.1 was detected in angiosarcoma biopsy specimens by immunohistochemistry. The inverse correlation of miR-497-5p and KCa3.1 also was observed in the ISO-HAS angiosarcoma cell line at the mRNA and protein levels. The direct targeting of KCa3.1 by miR-497-5p was evidenced by reduced luciferase activity due to complementary binding of miR-497-5p to KCa3.1 mRNA 3′ untranslated region. For the functional role of miR-497-5p/KCa3.1 pair, we showed that application of TRAM-34, a specific KCa3.1 channel blocker, or transfection of ISO-HAS cells with KCa3.1 siRNA or miR-497-5p mimics inhibited cell proliferation, cell cycle progression, and invasion by down-regulating cell-cycle related proteins including cyclin D1, surviving and P53 and down-regulating matrix metallopeptidase 9. In an in vivo angiosarcoma xenograft model, TRAM-34 or miR-497-5p mimics both inhibited tumor growth. In conclusion, the tumor suppressor miR-497-5p down-regulates KCa3.1 expression and contributes to the inhibition of angiosarcoma malignancy development. The miR-497-5p or KCa3.1 might be potential new targets for angiosarcoma treatment.

The Antiarrhythmic Drug, Amiodarone, Decreases AKT Activity and Sensitizes Human Acute Myeloid Leukemia Cells to Apoptosis by ABT-263

BACKGROUND

Successful treatment of leukemia requires new medications to combat drug resistance, but the development of novel therapies is an arduous and risky endeavor. Repurposing currently approved drugs or those already in clinical development to treat other indications is a more practical approach. Moreover, combinatorial therapeutics are often more efficacious than single agent therapeutics because the former can simultaneously target multiple pathways that mitigate tumor aggressiveness and induce cancer cell death.

MATERIAL AND METHODS

In this study, we combined the class III antiarrhythmic agent amiodarone and the BH3 mimetic ABT-263 based on data from a prior drug screen to assess the degree of apoptotic induction in 2 human leukemia cell lines.

RESULTS

The combination yielded statistically significant increases in apoptosis in both cell lines by downregulating AKT activity and increasing cleaved caspase-3.

CONCLUSIONS

Overall, our findings suggest that combining K⁺ channel blockers with prosurvival Bcl-2 family inhibitors is a promising therapeutic approach in treating leukemia.

Manipulation of the sodium-potassium ratio as a lever for controlling cell growth and improving cell specific productivity in perfusion CHO cell cultures

Perfusion processes typically require removal of a continuous or semi-continuous volume of cell culture in order to maintain a desired target cell density. For fast growing cell lines, the product loss from this stream can be upwards of 35%, significantly reducing the overall process yield. As volume removed is directly proportional to cell growth, the ability to modulate growth during perfusion cell culture production thus becomes crucial. Leveraging existing media components to achieve such control without introducing additional supplements is most desirable because it decreases process complexity and eliminates safety and clearance concerns. Here, the impact of extracellular concentrations of sodium (Na) and potassium (K) on cell growth and productivity is explored. High throughput small-scale models of perfusion revealed Na:K ratios below 1 can significantly suppress cell growth by inducing cell cycle arrest in the G0/1 phase. A concomitant increase in cell specific productivity was also observed, reaching as high as 115 pg/cell/day for one cell line studied. Multiple recombinant Chinese hamster ovary (CHO) cell lines demonstrated similar responses to lower Na:K media, indicating the universal applicability of such an approach. Product quality attributes were also assessed and revealed that effects were cell line specific, and can be acceptable or manageable depending on the phase of the drug development. Drastically altering Na and K levels in perfusion media as a lever to impact cell growth and productivity is proposed.

Preclinical study of a Kv11.1 potassium channel activator as antineoplastic approach for breast cancer

Potassium ion (K⁺) channels have been recently found to play a critical role in cancer biology. Despite that pharmacologic manipulation of ion channels is recognized as an important therapeutic approach, very little is known about the effects of targeting of K⁺ channels in cancer. In this study, we demonstrate that use of the Kv11.1 K⁺ channel activator NS1643 inhibits tumor growth in an in vivo model of breast cancer.

Tumors exposed to NS1643 had reduced levels of proliferation markers, high expression levels of senescence markers, increased production of ROS and DNA damage compared to tumors of untreated mice. Importantly, mice treated with NS1643 did not exhibit significant cardiac dysfunction. In conclusion, pharmacological stimulation of Kv11.1 activity produced arrested TNBC-derived tumor growth by generating DNA damage and senescence without significant side effects. We propose that use of Kv11.1 channels activators could be considered as a possible pharmacological strategy against breast tumors.

The interaction between electromagnetic fields at megahertz, gigahertz and terahertz frequencies with cells, tissues and organisms: risks and potential

Since regular radio broadcasts started in the 1920s, the exposure to human-made electromagnetic fields has steadily increased. These days we are not only exposed to radio waves but also other frequencies from a variety of sources, mainly from communication and security devices. Considering that nearly all biological systems interact with electromagnetic fields, understanding the affects is essential for safety and technological progress. This paper systematically reviews the role and effects of static and pulsed radio frequencies (100-109 Hz), millimetre waves (MMWs) or gigahertz (109-1011 Hz), and terahertz (1011-1013 Hz) on various biomolecules, cells and tissues. Electromagnetic fields have been shown to affect the activity in cell membranes (sodium versus potassium ion conductivities) and non-selective channels, transmembrane potentials and even the cell cycle. Particular attention is given to millimetre and terahertz radiation due to their increasing utilization and, hence, increasing human exposure. MMWs are known to alter active transport across cell membranes, and it has been reported that terahertz radiation may interfere with DNA and cause genomic instabilities. These and other phenomena are discussed along with the discrepancies and controversies from published studies.

Use of genetically encoded, light-gated ion translocators to control tumorigenesis

It has long been known that the resting potential of tumor cells is depolarized relative to their normal counterparts. More recent work has provided evidence that resting potential is not just a readout of cell state: it regulates cell behavior as well. Thus, the ability to control resting potential in vivo would provide a powerful new tool for the study and treatment of tumors, a tool capable of revealing living-state physiological information impossible to obtain using molecular tools applied to isolated cell components. Here we describe the first use of optogenetics to manipulate ion-flux mediated regulation of membrane potential specifically to prevent and cause regression of oncogene-induced tumors. Injection of mutant-KRAS mRNA induces tumor-like structures with many documented similarities to tumors, in Xenopus tadpoles. We show that expression and activation of either ChR2^D156A, a blue-light activated cation channel, or Arch, a green-light activated proton pump, both of which hyperpolarize cells, significantly lowers the incidence of KRAS tumor formation. Excitingly, we also demonstrate that activation of co-expressed light-activated ion translocators after tumor formation significantly increases the frequency with which the tumors regress in a process called normalization. These data demonstrate an optogenetic approach to dissect the biophysics of cancer. Moreover, they provide proof-of-principle for a novel class of interventions, directed at regulating cell state by targeting physiological regulators that can over-ride the presence of mutations.

Unraveling the mechanistic effects of electric field stimulation towards directing stem cell fate and function: A tissue engineering perspective

Electric field (EF) stimulation can play a vital role in eliciting appropriate stem cell response. Such an approach is recently being established to guide stem cell differentiation through osteogenesis/neurogenesis/cardiomyogenesis. Despite significant recent efforts, the biophysical mechanisms by which stem cells sense, interpret and transform electrical cues into biochemical and biological signals still remain unclear. The present review critically analyses the variety of EF stimulation approaches that can be employed to evoke appropriate stem cell response and also makes an attempt to summarize the underlying concepts of this notion, placing special emphasis on stem cell based tissue engineering and regenerative medicine. This review also discusses the major signaling pathways and cellular responses that are elicited by electric stimulation, including the participation of reactive oxygen species and heat shock proteins, modulation of intracellular calcium ion concentration, ATP production and numerous other events involving the clustering or reassembling of cell surface receptors, cytoskeletal remodeling and so on. The specific advantages of using external electric stimulation in different modalities to regulate stem cell fate processes are highlighted with explicit examples, in vitro and in vivo.

The Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels: from Biophysics to Pharmacology of a Unique Family of Ion Channels

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels are important members of the voltage-gated pore loop channels family. They show unique features: they open at hyperpolarizing potential, carry a mixed Na/K current, and are regulated by cyclic nucleotides. Four different isoforms have been cloned (HCN1-4) that can assemble to form homo- or heterotetramers, characterized by different biophysical properties. These proteins are widely distributed throughout the body and involved in different physiologic processes, the most important being the generation of spontaneous electrical activity in the heart and the regulation of synaptic transmission in the brain. Their role in heart rate, neuronal pacemaking, dendritic integration, learning and memory, and visual and pain perceptions has been extensively studied; these channels have been found also in some peripheral tissues, where their functions still need to be fully elucidated. Genetic defects and altered expression of HCN channels are linked to several pathologies, which makes these proteins attractive targets for translational research; at the moment only one drug (ivabradine), which specifically blocks the hyperpolarization-activated current, is clinically available. This review discusses current knowledge about HCN channels, starting from their biophysical properties, origin, and developmental features, to (patho)physiologic role in different tissues and pharmacological modulation, ending with their present and future relevance as drug targets.

The secret life of ion channels: Kv1.3 potassium channels and proliferation

Kv1.3 channels are involved in the switch to proliferation of normally quiescent cells, being implicated in the control of cell cycle in many different cell types and in many different ways. They modulate membrane potential controlling K⁺ fluxes, sense changes in potential, and interact with many signaling molecules through their intracellular domains. From a mechanistic point of view, we can describe the role of Kv1.3 channels in proliferation with at least three different models. In the "membrane potential model," membrane hyperpolarization resulting from Kv1.3 activation provides the driving force for Ca²⁺ influx required to activate Ca²⁺-dependent transcription. This model explains most of the data obtained from several cells from the immune system. In the "voltage sensor model," Kv1.3 channels serve mainly as sensors that transduce electrical signals into biochemical cascades, independently of their effect on membrane potential. Kv1.3-dependent proliferation of vascular smooth muscle cells (VSMCs) could fit this model. Finally, in the "channelosome balance model," the master switch determining proliferation may be related to the control of the Kv1.3 to Kv1.5 ratio, as described in glial cells and also in VSMCs. Since the three mechanisms cannot function independently, these models are obviously not exclusive. Nevertheless, they could be exploited differentially in different cells and tissues. This large functional flexibility of Kv1.3 channels surely gives a new perspective on their functions beyond their elementary role as ion channels, although a conclusive picture of the mechanisms involved in Kv1.3 signaling to proliferation is yet to be reached.

Mesenchymal stem cell differentiation: Control by calcium-activated potassium channels

Mesenchymal stem cells (MSCs) are widely used in modern medicine for which understanding the mechanisms controlling their differentiation is fundamental. Ion channels offer novel insights to this process because of their role in modulating membrane potential and intracellular milieu. Here, we evaluate the contribution of calcium-activated potassium (K_Ca ) channels to the three main components of MSC differentiation: initiation, proliferation, and migration. First, we demonstrate the importance of the membrane potential (V_m ) and the apparent association of hyperpolarization with differentiation. Of K_Ca subtypes, most evidence points to activity of big-conductance channels in inducing initiation. On the other hand, intermediate-conductance currents have been shown to promote progression through the cell cycle. While there is no information on the role of K_Ca channels in migration of MSCs, work from other stem cells and cancer cells suggest that intermediate-conductance and to a lesser extent big-conductance channels drive migration. In all cases, these effects depend on species, tissue origin and lineage. Finally, we present a conceptual model that demonstrates how K_Ca activity could influence differentiation by regulating V_m and intracellular Ca²⁺ oscillations. We conclude that K_Ca channels have significant involvement in MSC differentiation and could potentially enable novel tissue engineering approaches and therapies.

Endogenous bioelectric currents promote differentiation of the mammalian lens

The functional roles of bioelectrical signals (ES) created by the flow of specific ions at the mammalian lens equator are poorly understood. We detected that mature, denucleated lens fibers expressed high levels of the α1 and β1 subunits of Na⁺/K⁺‐ATPase (ATP1A1 and ATP1B1 of the sodium pump) and had a hyperpolarized membrane potential difference (V_mem). In contrast, differentiating, nucleated lens fiber cells had little ATP1A1 and ATP1B1 and a depolarized V_mem. Mimicking the natural equatorial ES with an applied electrical field (EF) induced a striking reorientation of lens epithelial cells to lie perpendicular to the direction of the EF. An EF also promoted the expression of β‐crystallin, aquaporin‐0 (AQP0) and the Beaded Filament Structural Protein 2 (BFSP2) in lens epithelial cells (LECs), all of which are hallmarks of differentiation. In addition, applied EF activated the AKT and CDC2 and inhibition of AKT reduced the activation of CDC2. Our results indicate that the endogenous bioelectrical signal at the lens equator promotes differentiation of LECs into denucleated lens fiber cells via depolarization of V_mem. Development of methods and devices of EF application or amplification in vivo may supply a novel treatment for lens diseases and even promote regeneration of a complete new lens following cataract surgery.

Different patterns of neuronal activity trigger distinct responses of oligodendrocyte precursor cells in the corpus callosum

In the developing and adult brain, oligodendrocyte precursor cells (OPCs) are influenced by neuronal activity: they are involved in synaptic signaling with neurons, and their proliferation and differentiation into myelinating glia can be altered by transient changes in neuronal firing. An important question that has been unanswered is whether OPCs can discriminate different patterns of neuronal activity and respond to them in a distinct way. Here, we demonstrate in brain slices that the pattern of neuronal activity determines the functional changes triggered at synapses between axons and OPCs. Furthermore, we show that stimulation of the corpus callosum at different frequencies in vivo affects proliferation and differentiation of OPCs in a dissimilar way. Our findings suggest that neurons do not influence OPCs in “all-or-none” fashion but use their firing pattern to tune the response and behavior of these nonneuronal cells.

Oligodendrocytes are glial cells of the central nervous system. One of their major tasks is to enwrap neuronal axons with myelin, providing electrical insulation of axons and a dramatic increase in the speed of nerve impulse propagation. Oligodendrocytes develop from oligodendrocyte precursor cells (OPCs). Self-renewal of OPCs, their differentiation into oligodendrocytes, and the process of myelin synthesis are influenced by neuronal activity. Furthermore, OPCs receive glutamatergic synaptic input from neurons. Neuronal activity in vivo is highly variable depending on the brain region, input stimulus, and/or behavioral task that an animal or human has to perform in everyday life. Therefore, it is important to understand whether different types of neuronal activity affect development and function of oligodendrocyte lineage cells in a distinct way. In this study, we demonstrate that the amount and the timing of glutamate release at synapses between neurons and OPCs, the properties of the subsequent ionic current through glutamate receptors in OPC membrane, as well as the extent of OPCs’ self-renewal and differentiation into oligodendrocytes differ depending on the frequency and duration of neuronal activity. Hence, the pattern of neuronal activity rather than just presence or absence of activity is an important parameter that determines development and function of oligodendroglial cells.

Controlling the Resting Membrane Potential of Cells with Conducting Polymer Microwires

All cells have a resting membrane potential resulting from an ion gradient across the plasma membrane. The resting membrane potential of cells is tightly coupled to regeneration and differentiation. The ability to control this parameter provides the opportunity for both biomedical advances and the probing of fundamental bioelectric pathways. The use of poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) conducting polymer microwires to depolarize cells is tested using E. coli cells loaded with a fluorescent dye that is pumped out of the cells in response to depolarization; a more positive membrane potential. Fluorescence imaging of the cells in response to a conducting-polymer-microwire applied voltage confirms depolarization and shows that the rate of depolarization is a function of the applied voltage and frequency. Microwire activity does not damage the cells, demonstrated with a propidium iodide assay of membrane integrity. The conducting polymer microwires do not penetrate the cell, or even come into contact with the cell; they only need to generate a minimum electric field, controlled by the placement of the wires. It is expected that these microwires will provide a new, noninvasive, cellular-scale tool for the control of resting membrane potential with high spatial precision.

Endogenous Bioelectric Signaling Networks: Exploiting Voltage Gradients for Control of Growth and Form

Living systems exhibit remarkable abilities to self-assemble, regenerate, and remodel complex shapes. How cellular networks construct and repair specific anatomical outcomes is an open question at the heart of the next-generation science of bioengineering. Developmental bioelectricity is an exciting emerging discipline that exploits endogenous bioelectric signaling among many cell types to regulate pattern formation. We provide a brief overview of this field, review recent data in which bioelectricity is used to control patterning in a range of model systems, and describe the molecular tools being used to probe the role of bioelectrics in the dynamic control of complex anatomy. We suggest that quantitative strategies recently developed to infer semantic content and information processing from ionic activity in the brain might provide important clues to cracking the bioelectric code. Gaining control of the mechanisms by which large-scale shape is regulated in vivo will drive transformative advances in bioengineering, regenerative medicine, and synthetic morphology, and could be used to therapeutically address birth defects, traumatic injury, and cancer.

Bioelectric regulation of innate immune system function in regenerating and intact Xenopus laevis

Two key inputs that regulate regeneration are the function of the immune system, and spatial gradients of transmembrane potential (Vmem). Endogenous bioelectric signaling in somatic tissues during regenerative patterning is beginning to be understood, but its role in the context of immune response has never been investigated. Here, we show that Vmem levels modulate innate immunity activity in Xenopus laevis embryos. We developed an assay in which X. laevis embryos are infected with a uropathogenic microorganism, in the presence or absence of reagents that modify Vmem, prior to the ontogenesis of the adaptive immune system. General depolarization of the organism's Vmem by pharmacological or molecular genetic (ion channel misexpression) methods increased resistance to infection, while hyperpolarization made the embryos more susceptible to death by infection. Hyperpolarized specimens harbored a higher load of infectious microorganisms when compared to controls. We identified two mechanisms by which Vmem mediates immune function: serotonergic signaling involving melanocytes and an increase in the number of primitive myeloid cells. Bioinformatics analysis of genes whose transcription is altered by depolarization revealed a number of immune system targets consistent with mammalian data. Remarkably, amputation of the tail bud potentiates systemic resistance to infection by increasing the number of peripheral myeloid cells, revealing an interplay of regenerative response, innate immunity, and bioelectric regulation. Our study identifies bioelectricity as a new mechanism by which innate immune response can be regulated in the context of infection or regeneration. Vmem modulation using drugs already approved for human use could be exploited to improve resistance to infections in clinical settings.

Long-Term, Stochastic Editing of Regenerative Anatomy via Targeting Endogenous Bioelectric Gradients

We show that regenerating planarians' normal anterior-posterior pattern can be permanently rewritten by a brief perturbation of endogenous bioelectrical networks. Temporary modulation of regenerative bioelectric dynamics in amputated trunk fragments of planaria stochastically results in a constant ratio of regenerates with two heads to regenerates with normal morphology. Remarkably, this is shown to be due not to partial penetrance of treatment, but a profound yet hidden alteration to the animals' patterning circuitry. Subsequent amputations of the morphologically normal regenerates in water result in the same ratio of double-headed to normal morphology, revealing a cryptic phenotype that is not apparent unless the animals are cut. These animals do not differ from wild-type worms in histology, expression of key polarity genes, or neoblast distribution. Instead, the altered regenerative bodyplan is stored in seemingly normal planaria via global patterns of cellular resting potential. This gradient is functionally instructive, and represents a multistable, epigenetic anatomical switch: experimental reversals of bioelectric state reset subsequent regenerative morphology back to wild-type. Hence, bioelectric properties can stably override genome-default target morphology, and provide a tractable control point for investigating cryptic phenotypes and the stochasticity of large-scale epigenetic controls.

Nanoscale silicon for subcellular biointerfaces

Semiconductor nanomaterials are emerging as a class of materials that can push the fundamental limits of current biomedical devices and possibly revolutionize healthcare. In particular, silicon nanostructures have been proven to be attractive systems for integrating nanoscale machines in biology because of their tunable electronic and optical properties, low cytotoxicity, and the vast microfabrication toolbox available for silicon. Studies have demonstrated that the implementation of next-generation silicon-based biomedical devices can benefit from the rational design of their nanoscale components. In this review, we will discuss some recent progress in this area, with a particular focus on the chemical synthesis of new silicon nanostructures and their emerging applications ranging from fundamental biophysical studies to clinical relevance.

Ion channel expression patterns in glioblastoma stem cells with functional and therapeutic implications for malignancy

Ion channels and transporters have increasingly recognized roles in cancer progression through the regulation of cell proliferation, migration, and death. Glioblastoma stem-like cells (GSCs) are a source of tumor formation and recurrence in glioblastoma multiforme, a highly aggressive brain cancer, suggesting that ion channel expression may be perturbed in this population. However, little is known about the expression and functional relevance of ion channels that may contribute to GSC malignancy. Using RNA sequencing, we assessed the enrichment of ion channels in GSC isolates and non-tumor neural cell types. We identified a unique set of GSC-enriched ion channels using differential expression analysis that is also associated with distinct gene mutation signatures. In support of potential clinical relevance, expression of selected GSC-enriched ion channels evaluated in human glioblastoma databases of The Cancer Genome Atlas and Ivy Glioblastoma Atlas Project correlated with patient survival times. Finally, genetic knockdown as well as pharmacological inhibition of individual or classes of GSC-enriched ion channels constrained growth of GSCs compared to normal neural stem cells. This first-in-kind global examination characterizes ion channels enriched in GSCs and explores their potential clinical relevance to glioblastoma molecular subtypes, gene mutations, survival outcomes, regional tumor expression, and experimental responses to loss-of-function. Together, the data support the potential biological and therapeutic impact of ion channels on GSC malignancy and provide strong rationale for further examination of their mechanistic and therapeutic importance.

Electrically Controlled "Sponge Effect" of PEDOT:PSS Governs Membrane Potential and Cellular Growth

PSS is a highly conductive material with good thermal and chemical stability and enhanced biocompatibility that make it suitable for bioengineering applications. The electrical control of the oxidation state of PEDOT:PSS films allows modulation of peculiar physical and chemical properties of the material, such as topography, wettability, and conductivity, and thus offers a possible route for controlling cellular behavior. Through the use of (i) the electrophysiological response of the plasma membrane as a biosensor of the ionic availability; (ii) relative abundance around the cells via X-ray spectroscopy; and (iii) atomic force microscopy to monitor PEDOT:PSS film thickness relative to its oxidation state, we demonstrate that redox processes confer to PEDOT:PSS the property to modify the ionic environment at the film-liquid interface through a "sponge-like" effect on ions. Finally, we show how this property offers the capability to electrically control central cellular properties such as viability, substrate adhesion, and growth, paving the way for novel bioelectronics and biotechnological applications.

Energy transduction and signal averaging of fluctuating electric fields by a single protein ion channel

A biological ion channel is used to charge a conventional capacitor from an external fluctuating electrical noise.

Ca2+ involvement in activation of extracellular-signal-regulated-kinase 1/2 and m-calpain after axotomy of the sciatic nerve

Detailed mechanisms behind regeneration after nerve injury, in particular signal transduction and the fate of Schwann cells (SCs), are poorly understood. Here, we investigated axotomy-induced activation of extracellular-signal-regulated kinase-1/2 (ERK1/2; important for proliferation) and m-calpain in vitro, and the relation to Ca²⁺ deletion and Schwann cell proliferation and death after rat sciatic nerve axotomy. Nerve segments were cultured for up to 72 hours with and without ethylene glycol-bis(β-aminoethyl ether)-N, N, N’, N’-tetraacetic acid (EGTA). In some experiments, 5-bromo-2’-deoxyuridine (BrdU) was added during the last 24 hours to detect proliferating cells and propidium iodide (PI) was added at the last hour to detect dead and/or dying cells. Immunohistochemistry of sections of the cultured nerve segments was performed to label m-calpain and the phosphorylated and activated form of ERK1/2. The experiments revealed that immunoreactivity for p-ERK1/2 increased with time in organotypically cultured SCs. p-ERK1/2 and m-calpain were also observed in axons. A significant increase in the number of dead or dying SCs was observed in nerve segments cultured for 24 hours. When deprived of Ca²⁺, activation of axonal m-calpain was reduced, whereas p-ERK1/2 was increased in SCs. Ca²⁺ deprivation also significantly reduced the number of proliferating SCs, and instead increased the number of dead or dying SCs. Ca²⁺ seems to play an important role in activation of ERK1/2 in SCs and in SC survival and proliferation. In addition, extracellular Ca²⁺ levels are also required for m-calpain activation and up-regulation in axons. Thus, regulation of Ca²⁺ levels is likely to be a useful method to promote SC proliferation.