Oscillatory pericellular proteolysis and oxidant deposition during neutrophil locomotion

Amplitude and Frequency Modulation of Metabolic Signals in Leukocytes: Synergistic Role of IFN-γ in IL-6- and IL-2-Mediated Cell Activation

Many stimuli cause intracellular concentration oscillations of second messengers or metabolites, which, in turn, may encode information in their amplitudes and frequencies. We now test the hypothesis that synergistic cellular responses to dual cytokine exposure correlate with cross-talk between metabolic signaling pathways of leukocytes. Polarized RAW264.7 macrophages and human neutrophils and monocytes exhibited NAD(P)H autofluorescence oscillation periods of ≅20 s. IFN-γ tripled the NAD(P)H oscillatory amplitude for these cells. Although IL-6 had no effect, incubation of cells with IFN-γ and IL-6 increased both oscillatory amplitude and frequency. Parallel changes were noted after treatment with IFN-γ and IL-2. However, IL-1β and TNF-α did not display frequency doubling with or without IFN-γ exposure. To determine whether frequency doubling required complete IFN-γ signaling or simply metabolic amplitude modulation, an electric field was applied to cells at NAD(P)H troughs, which has been shown to enhance NAD(P)H amplitudes. Electric field application led to frequency doubling in the presence of IL-6 or IL-2 alone, suggesting that amplitude modulation is crucial to synergism. Because NADPH participates in electron trafficking to NO, we tested NO production during cytokine exposure. Although IL-6 and IL-2 alone had no effect, IFN-γ plus IL-6 and IFN-γ plus IL-2 enhanced NO release in comparison to IFN-γ treatment alone. When NO production was examined for single cells, it incrementally increased with the same phase and period as NAD(P)H. We suggest that amplitude and frequency modulation of cellular metabolic oscillations contribute to intracellular signaling synergy and entrain NO production.

Oscillatory behavior of a simple kinetic model for proteolysis during cell invasion

Extracellular proteolysis during cell invasion is thought to be tightly organized, both temporally and spatially. This work presents a simple kinetic model that describes the interactions between extracellular matrix (ECM) proteins, proteinases, proteolytic fragments, and integrins. Nonmonotonous behavior arises from enzyme de novo synthesis consecutive to integrin binding to fragments or entire proteins. The model has been simulated using realistic values for kinetic constants and protein concentrations, with fibronectin as the ECM protein. The simulations show damped oscillations of integrin-complex concentrations, indicating alternation of maximal adhesion periods with maximal mobility periods. Comparisons with experimental data from the literature confirm the similarity between this system behavior and cell invasion. The influences on the system of cryptic functions of ECM proteins, proteinase inhibitors, and soluble antiadhesive peptides were examined. The first critical parameter for oscillation is the discrepancy between integrin affinity for intact ECM proteins and the respective proteolytic fragments, thus emphasizing the importance of cryptic functions of ECM proteins in cell invasion. Another critical parameter is the ratio between proteinase and the initial ECM protein concentration. These results suggest new insights into the organization of the ECM degradation during cell invasion.

Complement deposition on immune complexes reduces the frequencies of metabolic, proteolytic, and superoxide oscillations of migrating neutrophils

Neutrophils exhibit intrinsic sinusoidal metabolite concentration oscillations of 3 min in resting cells and an additional approximately 10- or 20-s oscillation in migrating/adhering cells. To better understand immune complex (IC)-mediated leukocyte activation, we have studied neutrophil metabolic oscillations in the presence of ICs either with or without fixed complement. Using a microscope photometer we quantitated NAD(P)H autofluorescence oscillations. Cells exposed to ICs exhibited metabolic oscillation periods of approximately 12 s in the absence of complement and approximately 22 s in the presence of complement opsonization. To determine if the effects could be associated with C3 deposition, we used ICs opsonized with only C3 or only C1 and C4. Untreated ICs, heat-inactivated complement-treated ICs, and C1,C4-treated ICs trigger rapid metabolic oscillations, as do fMLP and yeast; in contrast, ICs treated with full complement or C3 alone did not affect NAD(P)H oscillations in comparison to controls. The induction of higher frequency (approximately 10 s) NAD(P)H oscillations by ICs could be blocked by addition of anti-FcgammaRII, but not FcgammaRIII mAb fragments, suggesting the participation of FcgammaRII in cellular metabolic responses to ICs. Parallel changes in the frequencies of oxidant release and pericellular proteolysis were found for all of these stimuli. Thus, immune complex composition affects both intracellular metabolic signals and extracellular functional oscillations. We suggest that complement attenuates the phlogistic potential of ICs by reducing the frequency of cytoplasmic NAD(P)H oscillations.

Early Membrane Rupture Events During Neutrophil-Mediated Antibody-Dependent Tumor Cell Cytolysis

Although cell-mediated cytolysis is a fundamental immune effector response, its mechanism remains poorly understood at the cellular level. In this report, we image for the first time transient ruptures, as inferred by cytoplasmic marker release, in tumor cell membranes during Ab-dependent cellular cytolysis. The cytosol of IgG-opsonized YAC tumor cells was labeled with tetramethylrhodamine diacetate followed by the formation of tumor cell-neutrophil conjugates. We hypothesized that tumor cell cytolysis proceeds via a series of discrete membrane rupture/resealing events that contribute to marker release. To test this hypothesis, we occluded the fluorescence image of the labeled tumor cells by passing an opaque disk into a field-conjugated plane between the light source and the sample. Multiple small bursts of fluorescent label release from tumor cells could be detected using a photomultiplier tube. Similarly, multiple fluorescent plumes were observed at various sites around the perimeter of a target. These findings support a multihit model of target cytolysis and suggest that cytolytic release is not focused at specific sites. Cytolytic bursts were generally observed at 20-s intervals, which match the previously described reduced nicotinamide-adenine dinucleotide phosphate and superoxide release oscillation periods for neutrophils; we speculate that metabolic oscillations of the effector cell drive the membrane damage of the target.

How organisms do the right thing: The attractor hypothesis

Neo-Darwinian theory is highly successful at explaining the emergence of adaptive traits over successive generations. However, there are reasons to doubt its efficacy in explaining the observed, impressively detailed adaptive responses of organisms to day-to-day changes in their surroundings. Also, the theory lacks a clear mechanism to account for both plasticity and canalization. In effect, there is a growing sentiment that the neo-Darwinian paradigm is incomplete, that something more than genetic structure, mutation, genetic drift, and the action of natural selection is required to explain organismal behavior. In this paper we extend the view of organisms as complex self-organizing entities by arguing that basic physical laws, coupled with the acquisitive nature of organisms, makes adaptation all but tautological. That is, much adaptation is an unavoidable emergent property of organisms' complexity and, to some a significant degree, occurs quite independently of genomic changes wrought by natural selection. For reasons that will become obvious, we refer to this assertion as the attractor hypothesis. The arguments also clarify the concept of "adaptation." Adaptation across generations, by natural selection, equates to the (game theoretic) maximization of fitness (the success with which one individual produces more individuals), while self-organizing based adaptation, within generations, equates to energetic efficiency and the matching of intake and biosynthesis to need. Finally, we discuss implications of the attractor hypothesis for a wide variety of genetical and physiological phenomena, including genetic architecture, directed mutation, genetic imprinting, paramutation, hormesis, plasticity, optimality theory, genotype-phenotype linkage and puncuated equilibrium, and present suggestions for tests of the hypothesis. (c) 1998 American Institute of Physics.

Aberrant neutrophil trafficking and metabolic oscillations in severe pyoderma gangrenosum

Having previously associated metabolic oscillations with cell locomotion, we hypothesized that patients with abnormalities in neutrophil trafficking may display aberrant intracellular oscillations. A pyoderma gangrenosum patient exhibiting aberrant leukocyte trafficking in vivo and skin ulceration without infection was identified. This patient's neutrophils constitutively overexpressed and clustered the leukocyte integrins CR3 and CR4 and failed to display appropriate integrin-to-GPI receptor interactions. Increased levels of tyrosine phosphorylation were observed. NAD(P)H oscillations, which are sinusoidal in normals, were chaotic with multiple frequency components in this patient's neutrophils. Normal cell shape and sinusoidal NAD(P)H oscillations were restored by providing a pulsed electric field to drive metabolic oscillations and by temperature reduction. N-acetyl-D-glucosamine disrupted CR3 clusters and sinusoidal NAD(P)H oscillations returned. Anecdotal reports suggest that local hypothermia is clinically useful for this patient. These data define the first metabolic oscillation-associated disease and suggest that pyoderma gangrenosum can be classified as a dynamical disease at the cellular level.

Aberrant integrin (CR4; alpha(x)beta2; CD11c/CD18) oscillations on neutrophils in a mild form of pyoderma gangrenosum

We have previously shown that the beta2 integrins CR3 and CR4 physically and functionally interact with urokinase receptors (uPAR) on neutrophil plasma membranes in an oscillatory fashion. In this study we have analyzed neutrophils from patient SC, a 34 y old African American female, with aberrant skin window results and recurrent perianal abscesses and pretibial lesions diagnosed as pyoderma gangrenosum. Although untreated migrating normal neutrophils exhibited 20 s sinusoidal oscillations in CR4-uPAR proximity, neutrophils from SC demonstrated a faster oscillation (10 s) in the form of a flyback sawtooth wave. This waveform mimicked that observed for normal neutrophils treated with subsaturating doses of the kinase inhibitors staurosporine, genistein, and erbstatin. As beta2 integrins are regulated by phosphorylation, we tested the hypothesis that the aberrant CR4-uPAR proximity oscillations seen in SC's neutrophils are due to defective kinase activity that might be balanced by a decrease in phosphatase activity. When SC's cells are exposed to subsaturating concentrations of the phosphatase inhibitor pervanadate, this caused the CR4-uPAR oscillations to become sinusoidal in shape with a 20 s period, as seen in normal migrating neutrophils. Although SC's neutrophils were deficient in spontaneous and N-formyl-methionyl-leucyl-phenylalanine-induced polarization, 0.5 microM pervanadate returned cell polarization to nearly normal levels, thus paralleling the acquisition of normal receptor interactions. Inasmuch as SC's cellular phenotype is mimicked by kinase inhibitors and corrected by phosphatase inhibitors, we suggest that a mutation(s) affecting the kinetics of intracellular signaling enzymes, but not blocking the pathway per se, may be responsible for this clinical state.

Cellular memory: neutrophil orientation reverses during temporally decreasing chemoattractant concentrations

Cell directional orientation or shape polarization is the first cellular step in neutrophil locomotion. To better understand how chemoattractants interact with cells, we studied neutrophil polarization (or shape changes) during exposure to a temporally decreasing chemoattractant signal of N-formyl-methionyl-leucyl-phenylalanine (FMLP) in the absence of a spatial concentration gradient. To accomplish this objective, we used a manifold of differing FMLP concentrations attached to a stopped-flow microscope chamber. Spatial gradients of a fluorescent chemotactic peptide could not be detected in the chamber by using microfluorometry. When FMLP was injected at continually increasing concentrations at 10-s intervals, the shape and relative direction of the neutrophil persisted. However, when temporally decreasing FMLP concentrations were injected, approximately 80% of the cells changed their direction with 44% of the total cells swinging about to 180 degrees +/- 15 degrees. Most of these directional changes involved dissolution of both the lamellipodium and uropod and reformation of these structures 180 degrees from their original positions. This research suggests that neutrophils reverse their morphological polarity when exposed to temporally decreasing ligand concentrations by "remembering" their ligand exposure history and relative direction.