Oscillatory pericellular proteolysis and oxidant deposition during neutrophil locomotion

Self-Organization and Information Processing: From Basic Enzymatic Activities to Complex Adaptive Cellular Behavior

One of the main aims of current biology is to understand the origin of the molecular organization that underlies the complex dynamic architecture of cellular life. Here, we present an overview of the main sources of biomolecular order and complexity spanning from the most elementary levels of molecular activity to the emergence of cellular systemic behaviors. First, we have addressed the dissipative self-organization, the principal source of molecular order in the cell. Intensive studies over the last four decades have demonstrated that self-organization is central to understand enzyme activity under cellular conditions, functional coordination between enzymatic reactions, the emergence of dissipative metabolic networks (DMN), and molecular rhythms. The second fundamental source of order is molecular information processing. Studies on effective connectivity based on transfer entropy (TE) have made possible the quantification in bits of biomolecular information flows in DMN. This information processing enables efficient self-regulatory control of metabolism. As a consequence of both main sources of order, systemic functional structures emerge in the cell; in fact, quantitative analyses with DMN have revealed that the basic units of life display a global enzymatic structure that seems to be an essential characteristic of the systemic functional metabolism. This global metabolic structure has been verified experimentally in both prokaryotic and eukaryotic cells. Here, we also discuss how the study of systemic DMN, using Artificial Intelligence and advanced tools of Statistic Mechanics, has shown the emergence of Hopfield-like dynamics characterized by exhibiting associative memory. We have recently confirmed this thesis by testing associative conditioning behavior in individual amoeba cells. In these Pavlovian-like experiments, several hundreds of cells could learn new systemic migratory behaviors and remember them over long periods relative to their cell cycle, forgetting them later. Such associative process seems to correspond to an epigenetic memory. The cellular capacity of learning new adaptive systemic behaviors represents a fundamental evolutionary mechanism for cell adaptation.

Therapeutic targeting of neutrophil exocytosis

Dysregulation of neutrophil activation causes disease in humans. Neither global inhibition of neutrophil functions nor neutrophil depletion provides safe and/or effective therapeutic approaches. The role of neutrophil granule exocytosis in multiple steps leading to recruitment and cell injury led each of our laboratories to develop molecular inhibitors that interfere with specific molecular regulators of secretion. This review summarizes neutrophil granule formation and contents, the role granule cargo plays in neutrophil functional responses and neutrophil-mediated diseases, and the mechanisms of granule release that provide the rationale for development of our exocytosis inhibitors. We present evidence for the inhibition of granule exocytosis in vitro and in vivo by those inhibitors and summarize animal data indicating that inhibition of neutrophil exocytosis is a viable therapeutic strategy.

Elements of the cellular metabolic structure

A large number of studies have demonstrated the existence of metabolic covalent modifications in different molecular structures, which are able to store biochemical information that is not encoded by DNA. Some of these covalent mark patterns can be transmitted across generations (epigenetic changes). Recently, the emergence of Hopfield-like attractor dynamics has been observed in self-organized enzymatic networks, which have the capacity to store functional catalytic patterns that can be correctly recovered by specific input stimuli. Hopfield-like metabolic dynamics are stable and can be maintained as a long-term biochemical memory. In addition, specific molecular information can be transferred from the functional dynamics of the metabolic networks to the enzymatic activity involved in covalent post-translational modulation, so that determined functional memory can be embedded in multiple stable molecular marks. The metabolic dynamics governed by Hopfield-type attractors (functional processes), as well as the enzymatic covalent modifications of specific molecules (structural dynamic processes) seem to represent the two stages of the dynamical memory of cellular metabolism (metabolic memory). Epigenetic processes appear to be the structural manifestation of this cellular metabolic memory. Here, a new framework for molecular information storage in the cell is presented, which is characterized by two functionally and molecularly interrelated systems: a dynamic, flexible and adaptive system (metabolic memory) and an essentially conservative system (genetic memory). The molecular information of both systems seems to coordinate the physiological development of the whole cell.

Time and Demand are Two Critical Dimensions of Immunometabolism: The Process of Macrophage Activation and the Pentose Phosphate Pathway

A process is a function of time; in immunometabolism, this is reflected by the stepwise adaptation of metabolism to sustain the bio-energetic demand of an immune-response in its various states and shades. This perspective article starts by presenting an early attempt to investigate the physiology of inflammation, in order to illustrate one of the basic concepts of immunometabolism, wherein an adapted metabolism of infiltrating immune cells affects tissue function and inflammation. We then focus on the process of macrophage activation and aim to delineate the factor time within the current molecular context of metabolic-rewiring important for adapting primary carbohydrate metabolism. In the last section, we will provide information on how the pentose phosphate pathway may be of importance to provide both nucleotide precursors and redox-equivalents, and speculate how carbon-scrambling events in the non-oxidative pentose phosphate pathway might be regulated within cells by demand. We conclude that the adapted metabolism of inflammation is specific in respect to the effector-function and appears as a well-orchestrated event, dynamic by nature, and based on a functional interplay of signaling- and metabolic-pathways.

On the dynamics of the adenylate energy system: homeorhesis vs homeostasis

Biochemical energy is the fundamental element that maintains both the adequate turnover of the biomolecular structures and the functional metabolic viability of unicellular organisms. The levels of ATP, ADP and AMP reflect roughly the energetic status of the cell, and a precise ratio relating them was proposed by Atkinson as the adenylate energy charge (AEC). Under growth-phase conditions, cells maintain the AEC within narrow physiological values, despite extremely large fluctuations in the adenine nucleotides concentration. Intensive experimental studies have shown that these AEC values are preserved in a wide variety of organisms, both eukaryotes and prokaryotes. Here, to understand some of the functional elements involved in the cellular energy status, we present a computational model conformed by some key essential parts of the adenylate energy system. Specifically, we have considered (I) the main synthesis process of ATP from ADP, (II) the main catalyzed phosphotransfer reaction for interconversion of ATP, ADP and AMP, (III) the enzymatic hydrolysis of ATP yielding ADP, and (IV) the enzymatic hydrolysis of ATP providing AMP. This leads to a dynamic metabolic model (with the form of a delayed differential system) in which the enzymatic rate equations and all the physiological kinetic parameters have been explicitly considered and experimentally tested in vitro. Our central hypothesis is that cells are characterized by changing energy dynamics (homeorhesis). The results show that the AEC presents stable transitions between steady states and periodic oscillations and, in agreement with experimental data these oscillations range within the narrow AEC window. Furthermore, the model shows sustained oscillations in the Gibbs free energy and in the total nucleotide pool. The present study provides a step forward towards the understanding of the fundamental principles and quantitative laws governing the adenylate energy system, which is a fundamental element for unveiling the dynamics of cellular life.

αVβ3 Integrin Regulation of Respiratory Burst in Fibrinogen Adherent Human Neutrophils

In response to inflammatory stimuli, microvascular endothelial cells become activated, initiating the capture and exit of neutrophils from the blood vessel and into the extravascular extracellular matrix (ECM). In the extravascular space, neutrophils bind to ECM proteins, regulating cellular functions via signaling through adhesion molecules known as integrins. The αVβ3 integrin is an important mediator of neutrophil adhesion to ECM proteins containing the Arg-Gly-Asp (RGD) peptide sequence, including fibrinogen and fibronectin. Despite the abundance of RGD sequence in the ECM, adhesion molecule-mediated neutrophil activity has been focused on the β2 (Mac-1, CD11b/CD18) and β1 integrin response to matrix proteins. Here we investigated αVβ3 integrin-mediated reactive oxidant suppression as a consequence of human neutrophil adhesion to RGD containing proteins. Using integrin ligand-modified (poly)ethylene glycol hydrogels and reactive oxygen species (ROS) sensitive fluorescent probes (dihydrotetramethylrhosamine, H2TMRos), we evaluated integrin-peptide interactions that effectively regulate ROS generation. This study demonstrates that neutrophil adhesion suppresses ROS production in an αVβ3-dependent manner. Additionally, we determine that p38 mitogen-activated protein kinase in the respiratory burst signaling pathway is interrupted by integrin-mediated adhesion. These data indicate that ECM/integrin interactions can induce αVβ3-mediated adhesion dependent downstream signaling of ROS regulation via a Mac-1 independent mechanism.

The metabolic core and catalytic switches are fundamental elements in the self-regulation of the systemic metabolic structure of cells

BACKGROUND

Experimental observations and numerical studies with dissipative metabolic networks have shown that cellular enzymatic activity self-organizes spontaneously leading to the emergence of a metabolic core formed by a set of enzymatic reactions which are always active under all environmental conditions, while the rest of catalytic processes are only intermittently active. The reactions of the metabolic core are essential for biomass formation and to assure optimal metabolic performance. The on-off catalytic reactions and the metabolic core are essential elements of a Systemic Metabolic Structure which seems to be a key feature common to all cellular organisms.

METHODOLOGY/PRINCIPAL FINDINGS

In order to investigate the functional importance of the metabolic core we have studied different catalytic patterns of a dissipative metabolic network under different external conditions. The emerging biochemical data have been analysed using information-based dynamic tools, such as Pearson's correlation and Transfer Entropy (which measures effective functionality). Our results show that a functional structure of effective connectivity emerges which is dynamical and characterized by significant variations of bio-molecular information flows.

CONCLUSIONS/SIGNIFICANCE

We have quantified essential aspects of the metabolic core functionality. The always active enzymatic reactions form a hub--with a high degree of effective connectivity--exhibiting a wide range of functional information values being able to act either as a source or as a sink of bio-molecular causal interactions. Likewise, we have found that the metabolic core is an essential part of an emergent functional structure characterized by catalytic modules and metabolic switches which allow critical transitions in enzymatic activity. Both, the metabolic core and the catalytic switches in which also intermittently-active enzymes are involved seem to be fundamental elements in the self-regulation of the Systemic Metabolic Structure.

Extracellular ATP induces spikes in cytosolic free Ca(2+) but not in NADPH oxidase activity in neutrophils

In order to establish whether non-mitochondrial oxidase activity in human neutrophils is tightly related to cytosolic Ca(2+) concentration, we simultaneously measured Ca(2+) oscillations induced by ATP and oxidant production in single adherent neutrophils using confocal microscopy. ATP induced fast damped Ca(2+) spikes with a period of 15s and slower irregular spikes with a period greater than 50s. Spikes in Ca(2+) occurred in the absence of Ca(2+) influx, but the amplitude was damped by inhibition of Ca(2+) influx. Using the oxidation of hydroethidine as a cytosolic marker of oxidant production, we show that the generation of reactive oxygen species by neutrophils adherent to glass was accelerated by ATP. The step-up in NADPH oxidase activity followed the first elevation of cytosolic Ca(2+) but, despite subsequent spikes in Ca(2+) concentration, no oscillations in oxidase activity could be detected. ATP induced spikes in Ca(2+) in a very reproducible way and we propose that the Ca(2+) signal is an on-switch for oxidase activity, but the activity is apparently not directly correlated with spiking activity in cytosolic Ca(2+).

Quantitative analysis of cellular metabolic dissipative, self-organized structures

One of the most important goals of the postgenomic era is understanding the metabolic dynamic processes and the functional structures generated by them. Extensive studies during the last three decades have shown that the dissipative self-organization of the functional enzymatic associations, the catalytic reactions produced during the metabolite channeling, the microcompartmentalization of these metabolic processes and the emergence of dissipative networks are the fundamental elements of the dynamical organization of cell metabolism. Here we present an overview of how mathematical models can be used to address the properties of dissipative metabolic structures at different organizational levels, both for individual enzymatic associations and for enzymatic networks. Recent analyses performed with dissipative metabolic networks have shown that unicellular organisms display a singular global enzymatic structure common to all living cellular organisms, which seems to be an intrinsic property of the functional metabolism as a whole. Mathematical models firmly based on experiments and their corresponding computational approaches are needed to fully grasp the molecular mechanisms of metabolic dynamical processes. They are necessary to enable the quantitative and qualitative analysis of the cellular catalytic reactions and also to help comprehend the conditions under which the structural dynamical phenomena and biological rhythms arise. Understanding the molecular mechanisms responsible for the metabolic dissipative structures is crucial for unraveling the dynamics of cellular life.

Global self-regulation of the cellular metabolic structure

BACKGROUND

Different studies have shown that cellular enzymatic activities are able to self-organize spontaneously, forming a metabolic core of reactive processes that remain active under different growth conditions while the rest of the molecular catalytic reactions exhibit structural plasticity. This global cellular metabolic structure appears to be an intrinsic characteristic common to all cellular organisms. Recent work performed with dissipative metabolic networks has shown that the fundamental element for the spontaneous emergence of this global self-organized enzymatic structure could be the number of catalytic elements in the metabolic networks.

METHODOLOGY/PRINCIPAL FINDINGS

In order to investigate the factors that may affect the catalytic dynamics under a global metabolic structure characterized by the presence of metabolic cores we have studied different transitions in catalytic patterns belonging to a dissipative metabolic network. The data were analyzed using non-linear dynamics tools: power spectra, reconstructed attractors, long-term correlations, maximum Lyapunov exponent and Approximate Entropy; and we have found the emergence of self-regulation phenomena during the transitions in the metabolic activities.

CONCLUSIONS/SIGNIFICANCE

The analysis has also shown that the chaotic numerical series analyzed correspond to the fractional Brownian motion and they exhibit long-term correlations and low Approximate Entropy indicating a high level of predictability and information during the self-regulation of the metabolic transitions. The results illustrate some aspects of the mechanisms behind the emergence of the metabolic self-regulation processes, which may constitute an important property of the global structure of the cellular metabolism.

The number of catalytic elements is crucial for the emergence of metabolic cores

Background

Different studies show evidence that several unicellular organisms display a cellular metabolic structure characterized by a set of enzymes which are always in an active state (metabolic core), while the rest of the molecular catalytic reactions exhibit on-off changing states. This self-organized enzymatic configuration seems to be an intrinsic characteristic of metabolism, common to all living cellular organisms. In a recent analysis performed with dissipative metabolic networks (DMNs) we have shown that this global functional structure emerges in metabolic networks with a relatively high number of catalytic elements, under particular conditions of enzymatic covalent regulatory activity.

Methodology/Principal Findings

Here, to investigate the mechanism behind the emergence of this supramolecular organization of enzymes, we have performed extensive DMNs simulations (around 15,210,000 networks) taking into account the proportion of the allosterically regulated enzymes and covalent enzymes present in the networks, the variation in the number of substrate fluxes and regulatory signals per catalytic element, as well as the random selection of the catalytic elements that receive substrate fluxes from the exterior. The numerical approximations obtained show that the percentages of DMNs with metabolic cores grow with the number of catalytic elements, converging to 100% for all cases.

Conclusions/Significance

The results show evidence that the fundamental factor for the spontaneous emergence of this global self-organized enzymatic structure is the number of catalytic elements in the metabolic networks. Our analysis corroborates and expands on our previous studies illustrating a crucial property of the global structure of the cellular metabolism. These results also offer important insights into the mechanisms which ensure the robustness and stability of living cells.

Global self-organization of the cellular metabolic structure

BACKGROUND

Over many years, it has been assumed that enzymes work either in an isolated way, or organized in small catalytic groups. Several studies performed using "metabolic networks models" are helping to understand the degree of functional complexity that characterizes enzymatic dynamic systems. In a previous work, we used "dissipative metabolic networks" (DMNs) to show that enzymes can present a self-organized global functional structure, in which several sets of enzymes are always in an active state, whereas the rest of molecular catalytic sets exhibit dynamics of on-off changing states. We suggested that this kind of global metabolic dynamics might be a genuine and universal functional configuration of the cellular metabolic structure, common to all living cells. Later, a different group has shown experimentally that this kind of functional structure does, indeed, exist in several microorganisms.

METHODOLOGY/PRINCIPAL FINDINGS

Here we have analyzed around 2.500.000 different DMNs in order to investigate the underlying mechanism of this dynamic global configuration. The numerical analyses that we have performed show that this global configuration is an emergent property inherent to the cellular metabolic dynamics. Concretely, we have found that the existence of a high number of enzymatic subsystems belonging to the DMNs is the fundamental element for the spontaneous emergence of a functional reactive structure characterized by a metabolic core formed by several sets of enzymes always in an active state.

CONCLUSIONS/SIGNIFICANCE

This self-organized dynamic structure seems to be an intrinsic characteristic of metabolism, common to all living cellular organisms. To better understand cellular functionality, it will be crucial to structurally characterize these enzymatic self-organized global structures.

Oxidant release is dramatically increased by elevated glucose concentrations in neutrophils from pregnant women

OBJECTIVE

To evaluate the mechanism of oxidative stress at glucose levels accompanying diabetic pregnancy. Specifically, we hypothesize that elevated glucose overwhelms hexose monophosphate shunt (HMS) down-regulation observed during pregnancy.

METHODS

Peripheral blood cells from normal healthy pregnant women were exposed to heightened glucose levels to provide an in vitro model of the effects of diabetic pregnancy. Changes in NAD(P)H, reactive oxygen species (ROS) and nitric oxide (NO) production were evaluated in single cells.

RESULTS

Altered metabolic dynamics, as judged by NAD(P)H autofluorescence of neutrophils from both pregnant and non-pregnant women, were observed during incubation with 14 mM glucose, a pathophysiologic level. In parallel, increased production of ROS and NO was observed. The ROS and NO levels attained in cells from pregnant women were greater than those observed in cells from non-pregnant women. Inhibitors of the HMS and NAD(P)H oxidase blocked these effects. These metabolic and oxidant changes required approximately one minute, suggesting that transient glucose spikes during pregnancy could trigger this response.

CONCLUSIONS

Elevated glucose levels enhance HMS activity and oxidant production in cells from pregnant women. This mechanism may be generally applicable in understanding the role of diabetes in materno-fetal health.

Elevated glucose concentrations promote receptor-independent activation of adherent human neutrophils: an experimental and computational approach

Neutrophil activation plays integral roles in host tissue damage and resistance to infectious diseases. As glucose uptake and NADPH availability are required for reactive oxygen metabolite production by neutrophils, we tested the hypothesis that pathological glucose levels (>or=12 mM) are sufficient to activate metabolism and reactive oxygen metabolite production in normal adherent neutrophils. We demonstrate that elevated glucose concentrations increase the neutrophil's metabolic oscillation frequency and hexose monophosphate shunt activity. In parallel, substantially increased rates of NO and superoxide formation were observed. However, these changes were not observed for sorbitol, a nonmetabolizable carbohydrate. Glucose transport appears to be important in this process as phloretin interferes with the glucose-specific receptor-independent activation of neutrophils. However, LY83583, an activator of glucose flux, promoted these changes at 1 mM glucose. The data suggest that at pathophysiologic concentrations, glucose uptake by mass action is sufficient to activate neutrophils, thus circumventing the normal receptor transduction mechanism. To enable us to mechanistically understand these dynamic metabolic changes, mathematical simulations were performed. A model for glycolysis in neutrophils was created. The results indicated that the frequency change in NAD(P)H oscillations can result from the activation of the hexose monophosphate shunt, which competes with glycolysis for glucose-6-phosphate. Experimental confirmation of these simulations was performed by measuring the effect of glucose concentrations on flavoprotein autofluorescence, an indicator of the rate of mitochondrial electron transport. Moreover, after prolonged exposure to elevated glucose levels, neutrophils return to a "nonactivated" phenotype and are refractile to immunologic stimulation. Our findings suggest that pathologic glucose levels promote the transient activation of neutrophils followed by the suppression of cell activity, which may contribute to nonspecific tissue damage and increased susceptibility to infections, respectively.

IFN-gamma primes RAW264 macrophages and human monocytes for enhanced oxidant production in response to CpG DNA via metabolic signaling: roles of TLR9 and myeloperoxidase trafficking

Macrophages and monocytes are activated by CpG DNA motifs to produce NO, which is enhanced dramatically by IFN-gamma. We hypothesize that synergistic cellular responses to IFN-gamma and CpG DNA are due to cross-talk between metabolic signaling pathways of leukocytes. Adherent RAW264.7 macrophages and human monocytes exhibited NAD(P)H autofluorescence oscillation periods of approximately 20 s. IFN-gamma increased the oscillatory amplitude, which was required for CpG DNA-mediated metabolic changes. These alterations in metabolic dynamics required the appropriate combinations of murine/human TLR9 and murine/human-specific CpG DNA. Other factors that also promoted an increase in metabolic oscillatory amplitude could substitute for IFN-gamma. Because recent studies have shown that the metabolic frequency is coupled to the hexose monophosphate shunt, and the amplitude is coupled to the peroxidase cycle, we tested the hypothesis that myeloperoxidase (MPO) participates in IFN-gamma priming for oxidant production. MPO inhibitors blocked cell responses to IFN-gamma and CpG DNA. In the absence of IFN-gamma exposure, the effects of CpG DNA could be duplicated by MPO addition to cell samples. Moreover, monocytes from MPO knockout mice were metabolically unresponsive to IFN-gamma and CpG DNA. NAD(P)H frequency doubling responses due to CpG DNA were blocked by an inhibitor of the hexose monophosphate shunt. Because NAD(P)H participates in electron trafficking to NO and superoxide anions, we tested oxidant production. Although CpG DNA alone had no effect, IFN-gamma plus CpG enhanced NO and reactive oxygen metabolite release compared with IFN-gamma treatment alone. We suggest that amplitude and frequency modulation of cellular metabolic oscillations contribute to intracellular signaling synergy.

Trophoblast contact deactivates human neutrophils

Trophoblasts are fetal epithelial cells that form an interface between mother and offspring. To evaluate their anti-inflammatory capacity, we tested the hypothesis that trophoblasts deactivate neutrophils using single-cell assays. Several biophysical (Ca2+ and NAD(P)H oscillation frequency) and physiological (oxidant production) markers of activated neutrophils revert to a nonactivated phenotype as activated cells make contact with trophoblasts. Indistinguishable results were obtained using syncytiotrophoblasts and in experiments using trophoblasts and neutrophils from the same mother to recapitulate the semiallogeneic system. These changes suggest reduced hexose monophosphate shunt (HMS) activity. We discovered that two metabolic regulatory points, glucose transport and HMS enzyme trafficking, are affected by trophoblasts. This restriction in HMS activity deactivates neutrophils, thereby limiting oxidative DNA damage within trophoblasts.

Reactive Oxygen Species (ROS): Pathogens or Sources of Vital Energy? Part 2. Bioenergetic and Bioinformational Functions of ROS

In Part 1 of the review of experimental data concerning reactive oxygen species (ROS) production and use, their indispensable role in regulation of multiple physiologic processes is examined. Part 2 considers the unique property of reactions in which ROS participates, the generation of energy of electronic excitation (EEE). Because of incessant ROS cycling, EEE is continuously produced in aerobic organisms. It may be used as an energy activator for multiple biochemical reactions and also may function as a specific signaling factor. This approach allows the perception of the beneficial effects of hydrogen peroxide, ozone, other ROS therapy, and foods rich in antioxidants. Both insufficient production of ROS and distortions in their use may cause anomalies in coordination of ROS generation and use, resulting in the deranged operation of biochemical and physiologic processes and the development of pathology.

Human, but not bovine, photoreceptor outer segments prime human retinal pigment epithelial cells for metabolic activation and massive oxidant release in response to lipopolysaccharide and interferon-gamma

Reactive oxygen metabolites (ROMs) may contribute to several eye diseases, such as age-related macular degeneration, although the underlying mechanisms are unclear. The present study shows that human photoreceptor outer segments (POS) prime human retinal pigment epithelial (RPE) cells for massive ROM release in response to lipopolysaccharide (LPS) and interferon-gamma. However, no ROM priming of human RPE cells is observed for bovine POS. ROM production appears to be linked with underlying metabolic oscillations involving the hexose monophosphate shunt.

6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase form a supramolecular complex in human neutrophils that undergoes retrograde trafficking during pregnancy

Neutrophils from pregnant women display reduced neutrophil-mediated effector functions, such as reactive oxygen metabolite (ROM) release. Because the NADPH oxidase and NO synthase produce ROMs and NO, the availability of their substrate NADPH is a potential regulatory factor. NADPH is produced by glucose-6-phosphate dehydrogenase (G-6-PDase) and 6-phosphogluconate dehydrogenase (6-PGDase), which are the first two steps of the hexose monophosphate shunt (HMS). Using immunofluorescence microscopy, we show that 6-PGDase, like G-6-PDase, undergoes retrograde transport to the microtubule-organizing centers in neutrophils from pregnant women. In contrast, 6-PGDase is found in an anterograde distribution in cells from nonpregnant women. However, lactate dehydrogenase distribution is unaffected by pregnancy. Cytochemical studies demonstrated that the distribution of 6-PGDase enzymatic activity is coincident with 6-PGDase Ag. The accumulation of 6-PGDase at the microtubule-organizing centers could be blocked by colchicine, suggesting that microtubules are important in this enzyme's intracellular distribution. In situ kinetic studies reveal that the rates of 6-gluconate turnover are indistinguishable in samples from nonpregnant and pregnant women, suggesting that the enzyme is functionally intact. Resonance energy transfer experiments showed that 6-PGDase and G-6-PDase are in close physical proximity within cells, suggesting the presence of supramolecular enzyme complexes. We suggest that the retrograde trafficking of HMS enzyme complexes during pregnancy influences the dynamics of NADPH production by separating HMS enzymes from glucose-6-phosphate generation at the plasma membrane and, in parallel, reducing ROM and NO production in comparison with fully activated neutrophils from nonpregnant women.

Toll-like receptor 4 (TLR4) of retinal pigment epithelial cells participates in transmembrane signaling in response to photoreceptor outer segments

Retinal pigment epithelial (RPE) cells mediate the recognition and clearance of effete photoreceptor outer segments (POS), a process central to the maintenance of normal vision. Given the emerging importance of Toll-like receptors (TLRs) in transmembrane signaling in response to invading pathogens as well as endogenous substances, we hypothesized that TLRs are associated with RPE cell management of POS. TLR4 clusters on human RPE cells in response to human, but not bovine, POS. However, TLR4 clustering could be inhibited by saturating concentrations of an inhibitory anti-TLR4 mAb. Furthermore, human POS binding to human RPE cells elicited transmembrane metabolic and calcium signals within RPE cells, which could be blocked by saturating doses of an inhibitory anti-TLR4 mAb. However, the heterologous combination of bovine POS and human RPE did not trigger these signals. The pattern recognition receptor CD36 collected at the POS-RPE cell interface for both homologous and heterologous samples, but human TLR4 only collected at the human POS-human RPE cell interface. Kinetic experiments of human POS binding to human RPE cells revealed that CD36 arrives at the POS-RPE interface followed by TLR4 accumulation within 2 min. Metabolic and calcium signals immediately follow. Similarly, the production of reactive oxygen metabolites (ROMs) was observed for the homologous human system, but not the heterologous bovine POS-human RPE cell system. As (a) the bovine POS/human RPE combination did not elicit TLR4 accumulation, RPE signaling, or ROM release, (b) TLR4 arrives at the POS-RPE cell interface just before signaling, (c) TLR4 blockade with an inhibitory anti-TLR4 mAb inhibited TLR4 clustering, signaling, and ROM release in the human POS-human RPE system, and (d) TLR4 demonstrates similar clustering and signaling responses to POS in confluent RPE monolayers, we suggest that TLR4 of RPE cells participates in transmembrane signaling events that contribute to the management of human POS.

Signal processing times in neutrophil activation: dependence on ligand concentration and the relative phase of metabolic oscillations

Intracellular NAD(P)H oscillations exhibited by polarized neutrophils display congruent with 20 s periods, which are halved to congruent with 10 s upon stimulation with chemotactic peptides such as FNLPNTL (N-formyl-nle-leu-phe-nle-tyr-lys). By monitoring this frequency change, we have measured accurately the time interval between stimulus and metabolic frequency changes. A microscope flow chamber was designed to allow rapid delivery of FNLPNTL to adherent cells. Using fluorescein as a marker, we found delivery to be complete and stable throughout the chamber within approximately 400 ms. Peptides were injected into the chamber at concentrations ranging from 10(-6) to 10(-9) M. Injections also varied with respect to the relative phase of a cell's NAD(P)H oscillations. The time interval between injection of 10(-6) M FNLPNTL and the acquisition of congruent with 10 s period metabolic oscillations was found to be 12.2+/-3.3 s when injections occurred at the NAD(P)H oscillation peak whereas the lag time was 22.5+/-4.8 s when coinciding with a trough. At 10(-8) M FNLPNTL, lag times were found to be 26.1+/-5.2 and 30.5+/-7.3 s for injections at NAD(P)H peaks and troughs, respectively. FNLPNTL at 10(-9) M had no effect on metabolic oscillations, consistent with previous studies. Our experiments show that the kinetics of transmembrane signal processing, in contrast to a simple transmembrane chemical reaction, can depend upon both ligand dose and its temporal relationship with intracellular metabolic oscillations.

Amoeboid shape change and contact guidance: T-lymphocyte crawling through fibrillar collagen is independent of matrix remodeling by MMPs and other proteases

The passage of leukocytes through basement membranes involves proteolytic degradation of extracellular matrix (ECM) components executed by focalized proteolysis. We have investigated whether the migration of leukocytes through 3-dimensional collagenous tissue scaffolds requires similar ECM breakdown. Human T blasts and SupT1 lymphoma cells expressed mRNA of MMP-9, MT1-MMP, MT4-MMP, cathepsin L, uPA, and uPAR as well as ADAM-9, -10, -11, -15, and -17. Upon long-term migration within 3-dimensional collagen matrices, however, no in situ collagenolysis was obtained by sensitive fluorescein isothiocyanate-collagen fragmentation analysis and confocal fluorescence/backscatter microscopy. Consistent with nonproteolytic migration, T-cell crawling and path generation were not impaired by protease inhibitor cocktail targeting MMPs, serine proteases, cysteine proteases, and cathepsins. Dynamic imaging of cell-ECM interactions showed T-cell migration as an amoeba-like process driven by adaptive morphology, crawling along collagen fibrils (contact guidance) and squeezing through pre-existing matrix gaps by vigorous shape change. The concept of nonproteolytic amoeboid migration was confirmed for multicomponent collagen lattices containing hyaluronan and chondroitin sulfate and for other migrating leukocytes including CD8+ T blasts, monocyte-derived dendritic cells, and U937 monocytic cells. Together, amoeboid shape change and contact guidance provide constitutive protease-independent mechanisms for leukocyte trafficking through interstitial tissues that are insensitive toward pharmacologic protease inhibitors.

Human RPE cell lysis of extracellular matrix: functional urokinase plasminogen activator receptor (uPAR), collagenase and elastase

Age-related macular degeneration (ARMD), proliferative vitreoretinopathy (PVR) and uveitis are characterized by RPE motility through the ECM of retinal lesions. The purpose of this study was to test the hypothesis that multiple proteolytic systems are functionally intact at the HRPE surface and peri-cellular region and that these activities are differentially modulated by IL-1beta. HRPE cells were evaluated: (1). as individual cells or cell extracts, (2). during migration across three-dimensional ECM-like layers and (3). in tissue sections. The urokirase plasminogen activator receptor (uPAR; CD87) was detected on HRPE cells as well as its functional activity. Although uPAR was associated with CD11b (CR3) on live resting cells, polarized migratory HRPE cells were found to dissociate uPAR from CR3; uPAR then translocated to anterior pole of the cell, where it enhanced PAI-1-inhibitable local proteolytic activity. The relative contribution of uPAR and collagenase in HRPE migration was evaluated using three-dimensional gelatin matrices. Interestingly, uPAR/uPA was found to play a key role in migration across these layers. IL-1 upregulated uPAR, collagenase, and elastase activities, suggesting that cytokines may affect the invasive program of HRPE cells in vivo. Immunohistochemistry for uPAR was performed in sections of human retina. Immunoreactive uPAR was present along the HRPE basolateral membrane in retinal sections and in sections of diseased retinal tissue at an enhanced level. Our results suggest that multiple proteolytic systems are present in association with HRPE and that the uPAR/uPA system may be particularly important.

Pregnancy alters glucose-6-phosphate dehydrogenase trafficking, cell metabolism, and oxidant release of maternal neutrophils

Pregnancy is associated with changes in host susceptibility to infections and inflammatory disease. We hypothesize that metabolic enzyme trafficking affects maternal neutrophil activation. Specifically, immunofluorescence microscopy has shown that glucose-6-phosphate dehydrogenase (G-6-PDase), the rate-controlling step of the hexose monophosphate shunt (HMS), is located near the cell periphery in control neutrophils but is found near the microtubule-organizing centers in cells from pregnant women. Cytochemical studies confirmed that the distribution of the G-6-PDase antigen is coincident with functional G-6-PDase activity. Metabolic oscillations within activated pregnancy neutrophils are higher in amplitude, though lower in frequency, than activated control neutrophils, suggesting limited HMS activity. Analysis of radioisotope-labeled carbon flux from glucose to CO(2) indicates that the HMS is intact in leukocytes from pregnant women, but its level is not enhanced by cell stimulation. Using extracellular fluorescent markers, activated pregnancy neutrophils were found to release reactive oxygen metabolites (ROMs) at a lower rate than activated control neutrophils. However, basal levels of ROM production in polarized pregnancy neutrophils were greater than in control neutrophils. Microtubule-disrupting agents reversed the observed changes in G-6-PDase trafficking, metabolic oscillations, and ROM production by maternal neutrophils. G-6-PDase trafficking appears to be one mechanism regulating ROM production by maternal neutrophils.

A model of the oscillatory metabolism of activated neutrophils

We present a two-compartment model to explain the oscillatory behavior observed experimentally in activated neutrophils. Our model is based mainly on the peroxidase-oxidase reaction catalyzed by myeloperoxidase with melatonin as a cofactor and NADPH oxidase, a major protein in the phagosome membrane of the leukocyte. The model predicts that after activation of a neutrophil, an increase in the activity of the hexose monophosphate shunt and the delivery of myeloperoxidase into the phagosome results in oscillations in oxygen and NAD(P)H concentration. The period of oscillation changes from >200 s to 10-30 s. The model is consistent with previously reported oscillations in cell metabolism and oxidant production. Key features and predictions of the model were confirmed experimentally. The requirement of the hexose monophosphate pathway for 10 s oscillations was verified using 6-aminonicotinamide and dexamethasone, which are inhibitors of glucose-6-phosphate dehydrogenase. The role of the NADPH oxidase in promoting oscillations was confirmed by dose-response studies of the effect of diphenylene iodonium, an inhibitor of the NADPH oxidase. Moreover, the model predicted an increase in the amplitude of NADPH oscillations in the presence of melatonin, which was confirmed experimentally. Successful computer modeling of complex chemical dynamics within cells and their chemical perturbation will enhance our ability to identify new antiinflammatory compounds.

Pregnancy alters glucose-6-phosphate dehydrogenase trafficking, cell metabolism, and oxidant release of maternal neutrophils

Pregnancy is associated with changes in host susceptibility to infections and inflammatory disease. We hypothesize that metabolic enzyme trafficking affects maternal neutrophil activation. Specifically, immunofluorescence microscopy has shown that glucose-6-phosphate dehydrogenase (G-6-PDase), the rate-controlling step of the hexose monophosphate shunt (HMS), is located near the cell periphery in control neutrophils but is found near the microtubule-organizing centers in cells from pregnant women. Cytochemical studies confirmed that the distribution of the G-6-PDase antigen is coincident with functional G-6-PDase activity. Metabolic oscillations within activated pregnancy neutrophils are higher in amplitude, though lower in frequency, than activated control neutrophils, suggesting limited HMS activity. Analysis of radioisotope-labeled carbon flux from glucose to CO(2) indicates that the HMS is intact in leukocytes from pregnant women, but its level is not enhanced by cell stimulation. Using extracellular fluorescent markers, activated pregnancy neutrophils were found to release reactive oxygen metabolites (ROMs) at a lower rate than activated control neutrophils. However, basal levels of ROM production in polarized pregnancy neutrophils were greater than in control neutrophils. Microtubule-disrupting agents reversed the observed changes in G-6-PDase trafficking, metabolic oscillations, and ROM production by maternal neutrophils. G-6-PDase trafficking appears to be one mechanism regulating ROM production by maternal neutrophils.

Cutting edge: fever-associated temperatures enhance neutrophil responses to lipopolysaccharide: a potential mechanism involving cell metabolism

Although much progress has been made in elucidating the mechanisms underlying the physiological regulation of fever, there is little understanding of the biological utility of fever's thermal component. Considering the evolutionary co-conservation of fever and innate immunity, we hypothesize that fever's thermal component might in general augment innate immune function and, in particular, neutrophil activation. Accordingly, we have evaluated the effect of febrile temperatures on neutrophil function at the single-cell level. We find that reactive oxygen intermediates and NO release are greatly enhanced at febrile temperatures for unstimulated as well as LPS-stimulated adherent human neutrophils. Furthermore, our studies suggest that these changes in oxidant release are linked to upstream changes in NADPH dynamics. Inasmuch as reactive oxygen intermediates and NO production are important elements in innate immune responses to bacterial pathogens, we suggest that the febrile rise in core temperature is a broad-based systemic signaling mechanism to enhance innate immunity.

Interactions of integrins with their partner proteins in leukocyte membranes

Integrins participate in many aspects of immunologic and inflammatory responses, especially those involving cell migration, adherence, and activation. Although leukocyte integrins such as complement receptor type 3 (CR3) are known to carry out certain functions without the intervention of other plasma membrane receptors, many plasma membrane proteins are now known to physically interact and functionally cooperate with integrins. Several of these interactions are highly dynamic within cell membranes; thus integrin-partner protein interactions change during certain physiological processes. This allows an extraordinary adaptability of the system to prime and promote proinflammatory signaling. Since our discovery of the CR3-FcgammaRIIIB interaction, the plasma membrane protein repertoire of beta1, beta2, and beta3 integrins has grown to include: FcgammaRIIA (CD32), uPAR (urokinase-type plasminogen activator receptor; CD87), CD14, voltage-gated K+channels (Kv1.3), integrin-associated protein (IAP), CD98, tetraspans (TM4SF), insulin receptors, and PDGFbeta receptors. In this article we will highlight certain features of this growing field of research, especially with regard to their relevance in immunology and inflammation.

Phorbol ester induces elevated oxidative activity and alkalization in a subset of lysosomes

BACKGROUND

Lysosomes are acidic organelles that play multiple roles in various cellular oxidative activities such as the oxidative burst during cytotoxic killing. It remains to be determined how lysosomal lumen oxidative activity and pH interact and are regulated. Here, I report the use of fluorescent probes to measure oxidative activity and pH of lysosomes in live macrophages upon treatment with the tumor promotor phorbol 12-myristate 13-acetate (PMA), and providing new insight on regulation mechanism of oxidative activity and pH.

RESULTS

The substrate used to measure oxidative activity was bovine serum albumin covalently coupled to dihydro-2',4,5,6,7,7'-hexafluorofluorescein (OxyBURST Green H2HFF BSA). During pulse-chase procedures with live macrophages, this reduced dye was internalized through an endocytic pathway and accumulated in the lysosomes. Oxidation of this compound, which results in fluorescence increases, depends on the redox potential in the lysosomal lumen. By using low-light level fluorescence microscopy, I determined that phorbol ester treatment results in increased oxidative activity and pH elevation in different subsets of lysosomes. Furthermore, lysosomes with stronger oxidative activity tend to exclude an acidotropic lysosomal indicator, and thus exhibit higher alkalinity.

CONCLUSION

Results indicate that there is a regulatory mechanism between lysosomal oxidative activity and pH. Activation of lysosomal Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase by phorbol ester may result in increase of intralysosomal O2- and H2O2, concurrent with pH elevation due to consumption of H+ and generation of OH-. Furthermore, effect of phorbol ester on elevated oxidative activity and pH is heterogeneous among total lysosomal population. Higher oxidative activity and/or pH are only observed in subsets of lysosomes.

Apparent role of traveling metabolic waves in oxidant release by living neutrophils

Cell metabolism self-organizes into two types of dissipative structures: chemical oscillations and traveling metabolic waves. In the present study we test the hypothesis that traveling NAD(P)H waves within neutrophils are associated spatially and temporally with the release of reactive oxygen metabolites (ROMs). Using high-speed optical microscopy and taking advantage of the autofluorescence of NAD(P)H, we have observed the propagation of NAD(P)H waves within cells. When NAD(P)H waves reach the lamellipodium of morphologically polarized neutrophils, a diffusing plume of superoxide is released as evidenced by the conversion of hydroethidine in the extracellular environment to ethidium bromide. Parallel results were obtained by using high-speed emission microspectrophotometry. These experiments indicate that the spatial and temporal properties of NAD(P)H waves are transformed into ROM pulses in the extracellular environment. Propagating NAD(P)H waves allow neutrophils to specifically deliver substrate to the lamellipodium at high concentrations, thus facilitating the local and periodic release of ROMs in the direction of cell movement and/or a target.

Modeling extracellular matrix degradation balance with proteinase/transglutaminase cycle

Extracellular matrix mass balance is implied in many physiological and pathological events, such as metastasis dissemination. Widely studied, its destructive part is mainly catalysed by extracellular proteinases. Conversely, the properties of the constructive part are less obvious, cellular neo-synthesis being usually considered as its only element. In this paper, we introduce the action of transglutaminase in a mathematical model for extracellular matrix remodeling. This extracellular enzyme, catalysing intermolecular protein cross-linking, is considered here as a reverse proteinase as far as the extracellular matrix physical state is concerned. The model is based on a proteinase/transglutaminase cycle interconverting insoluble matrix and soluble proteolysis fragments, with regulation of cellular proteinase expression by the fragments. Under "closed" (batch) conditions, i.e. neglecting matrix influx and fragment efflux from the system, the model is bistable, with reversible hysteresis. Extracellular matrix proteins concentration abruptly switches from low to high levels when transglutaminase activity exceeds a threshold value. Proteinase concentration usually follows the reverse complementary kinetics, but can become apparently uncoupled from extracellular matrix concentration for some parameter values. When matrix production by the cells and fragment degradation are taken into account, the dynamics change to sustained oscillations because of the emergence of a stable limit cycle. Transitions out of and into oscillation areas are controlled by the model parameters. Biological interpretation indicates that these oscillations could represent the normal homeostatic situation, whereas the other exhibited dynamics can be related to pathologies such as tumor invasion or fibrosis. These results allow to discuss the insights that the model could contribute to the comprehension of these complex biological events.

Hexokinase translocation during neutrophil activation, chemotaxis, and phagocytosis: disruption by cytochalasin D, dexamethasone, and indomethacin

Neutrophils expend large amounts of energy to perform demanding cell functions. To better understand energy production and flow during cell activation, immunofluorescence microscopy was employed to determine the location of the key metabolic enzyme hexokinase during various conditions. Hexokinase is translocated from the neutrophil's cytosol to its periphery in response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) and other activating stimuli, but not during exposure to the formyl peptide receptor antagonist N-tert-BOC-phe-leu-phe-leu-phe (Boc-PLPLP). Translocation was observed from 10(-6) to 10(-9)M fMLP. However, fMLP did not affect the intracellular distribution of lactate dehydrogenase. Hexokinase accumulated at the lamellipodium of cells exposured to an fMLP gradient whereas it localized to the phagosome after latex bead uptake. Thus, hexokinase is differentially translocated within cells depending upon the prevailing physiological conditions. Further studies noted that cytochalasin D, dexamethasone, and indomethacin blocked hexokinase translocation. Parallel regulation of reactive oxygen metabolite (ROM) production was shown. We speculate that hexokinase translocation participates in neutrophil activation.

Neutrophil oscillations: temporal and spatiotemporal aspects of cell behavior

Neutrophil activation is an essential event in inflammatory responses. How cells coordinate, integrate, manage, and distribute information on physiologically-relevant timescales are not well understood. Although neutrophil oscillators have been known for many years, their biological roles have not been identified. We suggest that intracellular oscillators (such as NAD(P)H, pH, calcium, and so on) account for functional oscillations (e.g., superoxide and NO production, cytolytic marker release, pericellular proteolysis, and actin assembly). In addition to these well-known temporal oscillations, we have recently discovered self-organized traveling chemical waves in neutrophils; these waves respond to extracellular signals and have distinct origins that coincide with a cell's uropod, lamellipodium, or adherence site. The fundamental physico-chemical features of cell chemistry will have an increasing role in our understanding of leukocyte function.

Human retinal pigment epithelial lysis of extracellular matrix: functional urokinase plasminogen activator receptor, collagenase, and elastase

PURPOSE

To show (1) human retinal pigment epithelial (HRPE) expression of functional urokinase plasminogen activator receptor (uPAR; CD87), (2) HRPE secretion of collagenase and elastase, (3) uPAR-dependent HRPE migration, and (4) uPAR expression in diseased human retinal tissue.

METHODS

Immunohistochemistry for uPAR was performed on cultured HRPE cells and in sections of human retina. Double-immunofluorescent staining of live human RPE cells with anti-CR3 antibody (CD11b) was performed to demonstrate the physical proximity of this beta 2 integrin with uPAR and determine whether associations were dependent on RPE confluence and polarity. Extracellular proteolysis by HRPE uPAR was evaluated using fluorescent bodipy-BSA and assessed for specificity by plasminogen activator inhibitor-1 (PAI-1) inhibition. The effect of interleukin-1 beta (IL-1 beta) on uPAR expression was assessed. Collagenase and elastase secretion by unstimulated and IL-1-stimulated HRPE cells was measured by 3H-labelled collagen and elastin cleavage. HRPE-associated collagenase was also assessed by cleavage of fluorescent DQ-collagen and inhibited by phenanthroline. Using an extracellular matrix assay, the roles of uPAR and collagenase in HRPE migration were assessed.

RESULTS

Immunoreactive uPAR was detected on cultured HRPE cells and increased by IL-1. On elongated, live HRPE cells, uPAR dissociated from CD11b (CR3) and translocated to anterior poles of migrating cells. Extracellular proteolysis was concentrated at sites of uPAR expression and specifically inhibited by PAI-1. Cultured HRPE cells secreted substantial, functional collagenase and elastase. IL-1 upregulated uPAR, collagenase, and elastase activities. Specific inhibition of uPAR, and to a lesser degree collagenase, reduced HRPE migration in matrix/gel assays. Immunoreactive uPAR was present along the HRPE basolateral membrane in retinal sections and in sections of diseased retinal tissue.

CONCLUSIONS

HRPE cells express functional uPAR, collagenase, and elastase, which may permit HRPE proteolysis and migration. uPAR polarization may concentrate proteolysis at the leading edge of migrating HRPE cells.

Identification of colchicine in placental blood from patients using herbal medicines

While characterizing natural antiinflammatory substances in human placental blood, we discovered a factor that affected human neutrophils and their adherence. Rigorous chemical and stereochemical analyses revealed this factor to be the well-known alkaloid, colchicine. When samples from individual patients were analyzed, significant levels (49-763 microg/L) of colchicine could be found in placental blood of patients using nonprescription herbal dietary supplements during pregnancy. We confirmed the presence of colchicine in commercially available ginkgo biloba. Due to its potential harmful effects, it would appear that such supplements should be avoided by women who are pregnant or are trying to conceive.

Pulsed DC electric fields couple to natural NAD(P)H oscillations in HT-1080 fibrosarcoma cells

Previously, we have demonstrated that NAD(P)H levels in neutrophils and macrophages are oscillatory. We have also found that weak ultra low frequency AC or pulsed DC electric fields can resonate with, and increase the amplitude of, NAD(P)H oscillations in these cells. For these cells, increased NAD(P)H amplitudes directly signal changes in behavior in the absence of cytokines or chemotactic factors. Here, we have studied the effect of pulsed DC electric fields on HT-1080 fibrosarcoma cells. As in neutrophils and macrophages, NAD(P)H levels oscillate. We find that weak (~10(-)(5) V/m), but properly phased DC (pulsed) electric fields, resonate with NAD(P)H oscillations in polarized and migratory, but not spherical, HT-1080 cells. In this instance, electric field resonance signals an increase in HT-1080 pericellular proteolytic activity. Electric field resonance also triggers an immediate increase in the production of reactive oxygen metabolites. Under resonance conditions, we find evidence of DNA damage in HT-1080 cells in as little as 5 minutes. Thus the ability of external electric fields to effect cell function and physiology by acting on NAD(P)H oscillations is not restricted to cells of the hematopoietic lineage, but may be a universal property of many, if not all polarized and migratory eukaryotic cells.

Membrane raft microdomains in chemokine receptor function

Cell chemotaxis requires the acquisition and maintenance of both spatial and functional asymmetry between initially equivalent cell parts. In leukocytes one becomes the leading edge and the other, the rear edge or uropod. The acquisition of this cell polarity is controlled by an array of chemoattractants, including those of the chemokine family. We propose that chemokine receptor activation in highly organized lipid raft domains is a major determinant for the correct localization of the signaling pathways leading to the cell asymmetries required for migration. The lateral organization imposed by membrane raft microdomains is discussed in the context of other chemokine receptor activities, such as its role as a human immunodeficiency virus (HIV) coreceptor.

Tumor cell invasion of model 3-dimensional matrices: demonstration of migratory pathways, collagen disruption, and intercellular cooperation

We report a novel 3-dimensional model for visualizing tumor cell migration across a nylon mesh-supported gelatin matrix. To visualize migration across these model barriers, cell proteolytic activity of the pericellular matrix was detected using Bodipy-BSA (fluorescent upon proteolysis) and DQ collagen (fluorescent upon collagenase activity). For 3-dimensional image reconstruction, multiple optical images at sequential z axis positions were deconvoluted by computer analysis. Specificity was indicated using well-known inhibitors. Using these fluorescent proteolysis markers and imaging methods, we have directly demonstrated proteolytic and collagenolytic activity during tumor cell invasion. Moreover, it is possible to visualize migratory pathways followed by tumor cells during matrix invasion. Using cells of differing invasive potentials (uPAR-negative T-47D wild-type and uPAR-positive T-47D A2--1 cells), we show that the presence of the T-47D-A2--1 cells facilitates the entry of T-47D wild-type cells into the matrix. In some cases, wild-type cells follow T-47D A2--1 cells into the matrix whereas other T-47D-wild-type cells appear to enter without the direct intervention of T-47D A2--1 cells. Thus, we have developed a new 3-dimensional model of tumor cell invasion, demonstrated protein and collagen disruption, mapped the pathways followed by tumor cells during migration through an extracellular matrix, and illustrated cross-talk among tumor cell populations during invasion.

Dissipative metabolic patterns respond during neutrophil transmembrane signaling

Self-organization is a common theme in biology. One mechanism of self-organization is the creation of chemical patterns by the diffusion of chemical reactants and their nonlinear interactions. We have recently observed sustained unidirectional traveling chemical redox [NAD(P)H - NAD(P)(+)] waves within living polarized neutrophils. The present study shows that an intracellular metabolic wave responds to formyl peptide receptor agonists, but not antagonists, by splitting into two waves traveling in opposite directions along a cell's long axis. Similar effects were noted with other neutrophil-activating substances. Moreover, when cells were exposed to an N-formyl-methionyl-leucyl-phenylalanine (FMLP) gradient whose source was perpendicular to the cell's long axis, cell metabolism was locally perturbed with reorientation of the pattern in a direction perpendicular to the initial cellular axis. Thus, extracellular activating signals and the signals' spatial cues are translated into distinct intracellular dissipative structures.

Interferon-gamma and sinusoidal electric fields signal by modulating NAD(P)H oscillations in polarized neutrophils

Metabolic activity in eukaryotic cells is known to naturally oscillate. We have recently observed a 20-s period NAD(P)H oscillation in neutrophils and other polarized cells. Here we show that when polarized human neutrophils are exposed to interferon-gamma or to ultra-low-frequency electric fields with periods double that of the NAD(P)H oscillation, the amplitude of the NAD(P)H oscillations increases. Furthermore, increases in NAD(P)H amplitude, whether mediated by interferon-gamma or by an oscillating electric field, signals increased production of reactive oxygen metabolites. Hence, amplitude modulation of NAD(P)H oscillations suggests a novel signaling mechanism in polarized cells.

Clustering of urokinase receptors (uPAR; CD87) induces proinflammatory signaling in human polymorphonuclear neutrophils

Leukocytes use urokinase receptors (uPAR; CD87) in adhesion, migration, and proteolysis of matrix proteins. Typically, uPAR clusters at cell-substratum interfaces, at focal adhesions, and at the leading edges of migrating cells. This study was undertaken to determine whether uPAR clustering mediates activation signaling in human polymorphonuclear neutrophils. Cells were labeled with fluo-3/AM to quantitate intracellular Ca2+ ([Ca2+]i) by spectrofluorometry, and uPAR was aggregated by Ab cross-linking. Aggregating uPAR induced a highly reproducible increase in [Ca2+]i (baseline to peak) of 295 +/- 37 nM (p = 0.0002). Acutely treating cells with high m.w. urokinase (HMW-uPA; 4000 IU/ml) produced a response of similar magnitude but far shorter duration. Selectively aggregating uPA-occupied uPAR produced smaller increases in [Ca2+]i, but saturating uPAR with HMW-uPA increased the response to approximate that of uPAR cross-linking. Cross-linking uPAR induced rapid and significant increases in membrane expression of CD11b and increased degranulation (release of beta-glucuronidase and lactoferrin) to a significantly greater degree than cross-linking control Abs. The magnitude of degranulation correlated closely with the difference between baseline and peak [Ca2+]i, but was not dependent on the state of uPA occupancy. By contrast, selectively cross-linking uPA-occupied uPAR was capable of directly inducing superoxide release as well as enhancing FMLP-stimulated superoxide release. These results could not be duplicated by preferentially cross-linking unoccupied uPAR. We conclude that uPAR aggregation initiates activation signaling in polymorphonuclear neutrophils through at least two distinct uPA-dependent and uPA-independent pathways, increasing their proinflammatory potency (degranulation and oxidant release) and altering expression of CD11b/CD18 to favor a firmly adherent phenotype.

Reaction-diffusion waves of actin filament polymerization/depolymerization in Dictyostelium pseudopodium extension and cell locomotion

Cell surface movements and the intracellular spatial patterns and dynamics of actin filament (F-actin) were investigated in living and formalin-fixed cells of Dictyostelium discoideum by confocal microscopy. Excitation waves of F-actin assembly developed and propagated several micrometers at up to 26 microm/min in cells which had been intracellularly loaded with fluorescently labeled actin monomer. Wave propagation and extinction corresponded with the initiation and attenuation of pseudopodium extension and cell advance, respectively. The identification of chemical waves was supported by the ring, sphere, spiral and scroll wave patterns, which were observed in the extensions of fixed cells stained with phalloidin-rhodamine, and by the similar, asymmetrical [F-actin] distribution in wavefronts in living and fixed cells. These F-actin patterns and dynamics in Dictyostelium provide evidence for a new supramolecular state of actin, which propagates as a self-organized, reaction-diffusion wave of reversible F-actin assembly and affects pseudopodium extension. Actin's properties of oscillation and self-organization might also fundamentally determine the nature of the eukaryotic cell's reactions of adaptation, timing and signal response.

Extremely low frequency pulsed DC electric fields promote neutrophil extension, metabolic resonance and DNA damage when phase-matched with metabolic oscillators

Application of extremely low frequency pulsed DC electric fields that are frequency- and phase-matched with endogenous metabolic oscillations leads to greatly exaggerated neutrophil extension and metabolic resonance wherein oscillatory NAD(P)H amplitudes are increased. In the presence of a resonant field, migrating cell length grows from 10 to approximately 40 microm, as does the overall length of microfilament assemblies. In contrast, cells stop locomotion and become spherical when exposed to phase-mismatched fields. Although cellular effects were not found to be dependent on electrode type and buffer, they were sensitive to temporal constraints (phase and pulse length) and cell surface charge. We suggest an electromechanical coupling hypothesis wherein applied electric fields and cytoskeletal polymerization forces act together to overcome the surface/cortical tension of neutrophils, thus promoting net cytoskeletal assembly and heightened metabolic amplitudes. Metabolic resonance enhances reactive oxygen metabolic production by neutrophils. Furthermore, cellular DNA damage was observed after prolonged metabolic resonance using both single cell gel electrophoresis ('comet' assay) and 3'-OH DNA labeling using terminal deoxynucleotidyl transferase. These results provide insights into transmembrane signal processing and cell interactions with weak electric fields.

Periodic formation of nascent lamellae is driven by changes in the stable F-actin pool of polymorphonuclear neutrophils after stimulation with chemotactic peptide and cross-linking of CD18 or CD61

Cell motility and changes in cell shape are largely powered by actin polymerization and depolymerization. Eight to ten second periodic changes in human polymorphonuclear neutrophil (PMN) shape were detected by video-image analysis of PMN crawling on a surface and by right angle light scattering (RALS) in suspended PMN. However, sustained RALS oscillations in suspended PMN requires pre-treatment with an inhibitor of phosphatidylinositol 3-kinase or an activator of protein kinase C. Here, we show that cross-linking of the beta(2) (CD18) or beta(3) (CD61), but not beta(1) (CD 29) integrins in the presence of a low dose of formyl-Methionyl-Leucyl-Phenylalanine (fMLP) enables similar 8-s periodic RALS oscillations in suspended PMN in response to stimulation with two consecutive doses of chemoattractants. This effect did not appear to be due to increased surface expression of CD18 or CD61. RALS oscillations occurred in phase with 8-s oscillations in the stable F-actin pool and peaks in F-actin correlated with predominance of cells exhibiting a nascent lamella. Thus, simulation of surface attachment by CD18 and CD61 cross-linking after exposure to fMLP in suspended cells supports shape oscillations that are the result of actin-driven cyclic extension/retraction of nascent lamellae at the same frequency as the shape changes previously observed in crawling PMN.

Developmental Instability as a Means of Assessing Stress in Plants: A Case Study Using Electromagnetic Fields and Soybeans

Developmental instability is often assessed using deviations from perfect bilateral symmetry. Here, we review the literature describing previous studies, suggest mechanisms that may account for both the generation and disruption of bilateral symmetry, and examine the influence of electromagnetic fields on the asymmetry of soybean leaves. Leaves from plants under high-voltage power lines generating pulsed magnetic fields of <3 to >50 mG were more asymmetrical for two parameters (the terminal leaflet widths and lateral rachilla lengths) than leaves of plants even 50 or 100 m away from power lines. This asymmetry could not be attributed to either size scaling or measurement error.