Asynchrony and commitment to die during apoptosis

Finding a Direct Method for a Dynamic Process: The DD (Direct and Dynamic) Cell-Tox Method

The main focus of in vitro toxicity assessment methods is to assess the viability of the cells, which is usually based on metabolism changes. Yet, when exposed to toxic substances, the cell triggers multiple signals in response. With this in mind, we have developed a promising cell-based toxicity method that observes various cell responses when exposed to toxic substances (either death, division, or remain viable). Based on the collective cell response, we observed and predicted the dynamics of the cell population to determine the toxicity of the toxicant. The method was tested with two different conformations: In the first conformation, we exposed a monoculture model of blood macrophages to UV light, hydrogen peroxide, nutrient deprivation, tetrabromobisphenol A, fatty acids, and 5-fluorouracil. In the second, we exposed a coculture liver model consisting of hepatocytes, hepatic stellate cells, Kupffer cells, and liver sinusoidal endothelial cells to rifampicin, ibuprofen, and 5-fluorouracil. The method showed good accuracy compared to established toxicity assessment methods. In addition, this approach provided more representative information on the toxic effects of the compounds, as it considers the different cellular responses induced by toxic agents.

A Promising Method for the Determination of Cell Viability: The Membrane Potential Cell Viability Assay

Determining the viability of cells is fraught with many uncertainties. It is often difficult to determine whether a cell is still alive, approaching the point of no return, or dead. Today, there are many methods for determining cell viability. Most rely on an indirect determination of cell death (metabolism, molecular transport, and leakage, to name a few). In contrast, we have developed a promising novel method for a “direct” determination of cell viability. The potential method assesses cell membrane integrity (which is essential for all viable cells) by measuring the electrical potential of the cell membrane. To test the assay, we chose two different cell types, blood macrophages (TLT) and breast cancer epithelial cells (MCF 7). We exposed them to seven different toxic scenarios (arsenic (V), UV light, hydrogen peroxide, nutrient starvation, Tetrabromobisphenol A, fatty acids, and 5-fluorouracil) to induce different cell death pathways. Under controlled test conditions, the assay showed good accuracy when comparing the toxicity assessment with well-established methods. Moreover, the method showed compatibility with live cell imaging. Although we know that further studies are needed to confirm the performance of the assay in other situations, the results obtained are promising for their wider application in the future.

Greek Fire, Poison Arrows, and Scorpion Bombs: How Tumor Cells Defend Against the Siege Weapons of Cytotoxic T Lymphocytes

CD8⁺ cytotoxic T lymphocytes (CTLs) are the main cellular effectors of the adaptive immune response against cancer cells, which in turn have evolved sophisticated cellular defense mechanisms to withstand CTL attack. Herein we provide a critical review of the pertinent literature on early and late attack/defense events taking place at the CTL/target cell lytic synapse. We examine the earliest steps of CTL-mediated cytotoxicity (“the poison arrows”) elicited within seconds of CTL/target cell encounter, which face commensurately rapid synaptic repair mechanisms on the tumor cell side, providing the first formidable barrier to CTL attack. We examine how breach of this first defensive barrier unleashes the inextinguishable “Greek fire” in the form of granzymes whose broad cytotoxic potential is linked to activation of cell death executioners, injury of vital organelles, and destruction of intracellular homeostasis. Herein tumor cells deploy slower but no less sophisticated defensive mechanisms in the form of enhanced autophagy, increased reparative capacity, and dysregulation of cell death pathways. We discuss how the newly discovered supra-molecular attack particles (SMAPs, the “scorpion bombs”), seek to overcome the robust defensive mechanisms that confer tumor cell resistance. Finally, we discuss the implications of the aforementioned attack/defense mechanisms on the induction of regulated cell death (RCD), and how different contemporary RCD modalities (including apoptosis, pyroptosis, and ferroptosis) may have profound implications for immunotherapy. Thus, we propose that understanding and targeting multiple steps of the attack/defense process will be instrumental to enhance the efficacy of CTL anti-tumor activity and meet the outstanding challenges in clinical immunotherapy.

Isolation and culture of murine bone marrow-derived macrophages for nitric oxide and redox biology

Macrophages are mononuclear phagocytes derived from haematopoietic progenitors that are widely distributed throughout the body. These cells participate in both innate and adaptive immune responses and lie central to the processes of inflammation, development, and homeostasis. Macrophage physiology varies depending on the environment in which they reside and they exhibit rapid functional adaption in response to external stimuli. To study macrophages in vitro, cells are typically cultured ex vivo from the peritoneum or alveoli, or differentiated from myeloid bone marrow progenitor cells to form bone marrow-derived macrophages (BMDMs). BMDMs represent an efficient and cost-effective means of studying macrophage biology. However, the inherent sensitivity of macrophages to biochemical stimuli (such as cytokines, metabolic intermediates, and RNS/ROS) makes it imperative to control experimental conditions rigorously. Therefore, the aim of this study was to establish an optimised and standardised method for the isolation and culture of BMDMs. We used classically activated macrophages isolated from WT and nitric oxide (NO)-deficient mice to develop a standardised culture method, whereby the constituents of the culture media are defined. We then methodically compared our standardised protocol to the most commonly used method of BMDM culture to establish an optimal protocol for the study of nitric oxide (NO)-redox biology and immunometabolism in vitro.

Towards a 'resolution limit' for DW-MRI tumor microstructural models: A simulation study investigating the feasibility of distinguishing between microstructural changes

PURPOSE

To determine the feasibility of extracting sufficiently precise estimates of cell radius, R, and intracellular volume fraction, fi , from DW-MRI data in order to distinguish between specific microstructural changes tissue may undergo, specifically focusing on cell death in tumors.

METHODS

Simulations with optimized and non-optimized clinical acquisitions were performed for a range of microstructures, using a two-compartment model. The ability to distinguish between (i) cell shrinkage with cell density constant, mimicking apoptosis, and (ii) cell size constant with cell density decreasing, mimicking loss of cells, was evaluated based on the precision of simulated parameter estimates. Relationships between parameter precision, SNR, and the magnitude of specific parameter changes, were used to infer SNR requirements for detecting changes.

RESULTS

Accuracy and precision depended on microstructural properties, SNR, and the acquisition protocol. The main benefit of optimized acquisitions tended to be improved accuracy and precision of R, particularly for small cells. In most cases considered, higher SNR was required for detecting changes in R than for changes in fi .

CONCLUSIONS

Given the relative changes in R and fi due to apoptosis, simulations indicate that, for a range of microstructures, detecting changes in R require higher SNR than detecting changes in fi , and that such SNR is typically not achieved in clinical data. This suggests that if apoptotic cell size decreases are to be detected in clinical settings, improved SNR is required. Comparing measurement precision with the magnitude of expected biological changes should form part of the validation process for potential biomarkers.

Self-Assembling Multidomain Peptides: Design and Characterization of Neutral Peptide-Based Materials with pH and Ionic Strength Independent Self-Assembly

Self-assembly of peptides is a powerful method of preparing nanostructured materials. These peptides frequently utilize charged groups as a convenient switch for controlling self-assembly in which pH or ionic strength determines the assembly state. Multidomain peptides have been previously designed with charged domains of amino acids, which create molecular frustration between electrostatic repulsion and a combination of supramolecular forces including hydrogen bonding and hydrophobic packing. This frustration is eliminated by the addition of multivalent ions or pH adjustment, resulting in a self-assembled hydrogel. However, these charged functionalities can have profound, unintended effects on the properties of the resulting material. Access to neutral self-assembled nanostructured hydrogels may allow for distinct biological properties that are not available to highly charged analogues. Here, we designed a series of peptides to determine if self-assembly could be mediated by the steric interactions created by neutral hydroxyproline (O) domains, eliminating the need for charged residues and creating a neutral peptide hydrogel. The series of peptides, O _n (SL)₆O _n , was studied to determine the effect of oligo-hydroxyproline on peptide self-assembly and nanostructure. We show that peptide solubility and nanofiber length increase with a higher number of hydroxyproline residues. Within this series, O₅(SL)₆O₅ displayed the optimal properties for self-assembly and hydrogelation. In vitro, this hydrogel supports cell viability of fibroblasts, while in vivo it is infiltrated with cells and easily degraded over time without promoting a strong inflammatory response. This neutral self-assembling peptide hydrogel shows promising properties for biomedical, cell preservation, and tissue regeneration applications.

Intracellular transport is accelerated in early apoptotic cells

Intracellular transport of cellular proteins and organelles is critical for establishing and maintaining intracellular organization and cell physiology. Apoptosis is a process of programmed cell death with dramatic changes in cell morphology and organization, during which signaling molecules are transported between different organelles within the cells. However, how the intracellular transport changes in cells undergoing apoptosis remains unknown. Here, we study the dynamics of intracellular transport by using the single-particle tracking method and find that both directed and diffusive motions of endocytic vesicles are accelerated in early apoptotic cells. With careful elimination of other factors involved in the intracellular transport, the reason for the acceleration is attributed to the elevation of adenosine triphosphate (ATP) concentration. More importantly, we show that the accelerated intracellular transport is critical for apoptosis, and apoptosis is delayed when the dynamics of intracellular transport is regulated back to the normal level. Our results demonstrate the important role of transport dynamics in apoptosis and shed light on the apoptosis mechanism from a physical perspective.

Modeling Cancer Cell Growth Dynamics In vitro in Response to Antimitotic Drug Treatment

Investigating the role of intrinsic cell heterogeneity emerging from variations in cell-cycle parameters and apoptosis is a crucial step toward better informing drug administration. Antimitotic agents, widely used in chemotherapy, target exclusively proliferative cells and commonly induce a prolonged mitotic arrest followed by cell death via apoptosis. In this paper, we developed a physiologically motivated mathematical framework for describing cancer cell growth dynamics that incorporates the intrinsic heterogeneity in the time individual cells spend in the cell-cycle and apoptosis process. More precisely, our model comprises two age-structured partial differential equations for the proliferative and apoptotic cell compartments and one ordinary differential equation for the quiescent compartment. To reflect the intrinsic cell heterogeneity that governs the growth dynamics, proliferative and apoptotic cells are structured in "age," i.e., the amount of time remaining to be spent in each respective compartment. In our model, we considered an antimitotic drug whose effect on the cellular dynamics is to induce mitotic arrest, extending the average cell-cycle length. The prolonged mitotic arrest induced by the drug can trigger apoptosis if the time a cell will spend in the cell cycle is greater than the mitotic arrest threshold. We studied the drug's effect on the long-term cancer cell growth dynamics using different durations of prolonged mitotic arrest induced by the drug. Our numerical simulations suggest that at confluence and in the absence of the drug, quiescence is the long-term asymptotic behavior emerging from the cancer cell growth dynamics. This pattern is maintained in the presence of small increases in the average cell-cycle length. However, intermediate increases in cell-cycle length markedly decrease the total number of cells and can drive the cancer population to extinction. Intriguingly, a large "switch-on/switch-off" increase in the average cell-cycle length maintains an active cell population in the long term, with oscillating numbers of proliferative cells and a relatively constant quiescent cell number.

An Increased Genotoxic Risk in Lymphocytes from Phototherapy-Treated Hyperbilirubinemic Neonates

BACKGROUND

Phototherapy is believed to be a safe method for the management of hyperbilirubinemia. However, there are some controversial issues regarding the genotoxic effects of phototherapy on DNA. The aim of this study was to investigate morphologically both phototherapy-induced DNA double-strand breaks (DSBs) and apoptosis in lymphocytes derived from jaundiced and non-jaundiced neonates.

METHODS

Newborns were divided into three groups, including phototherapy-treated (PT, n=30) jaundiced newborns with total serum bilirubin (TSB) levels >15 mg/dl, non-treated jaundiced newborns (C+, n=27), as positive, as well as healthy negative (C-, n=30) controls with TSB levels ranging from 10 and 15 mg/dl and less than 5 mg/dl, respectively. Lymphocytes were isolated from whole blood samples by Ficoll-isopaque density gradient centrifugation and then assessed for DNA damage and apoptosis before and 24 hours after incubation at 37°C in 5% CO2 using the neutral comet assay.

RESULTS

DSB levels were significantly much higher in the PT group compared to the controls before incubation but decreased remarkably after the incubation period. As expected, no statistical differences were found between the two control groups before and after incubations. The frequency of apoptotic cells showed no significant differences among all the three groups before incubation; however, it was significantly increased in the PT group after incubation.

CONCLUSION

It seems that phototherapy in jaundiced infants is able not only to induce apoptosis in newborn lymphocytes but also to affect indirectly DNA integrity.

Neuroprotective effects of antibodies on retinal ganglion cells in an adolescent retina organ culture

Glaucoma, a neurodegenerative disease, is characterized by a progressive loss of retinal ganglion cells (rgc). Up- and down-regulated autoantibody immunoreactivities in glaucoma patients have been demonstrated. Previous studies showed protective effects of down-regulated antibodies [gamma (γ)-synuclein and glial fibrillary acidic protein [GFAP]) on neuroretinal cells. The aim of this study was to test these protective antibody effects on rgc in an organ culture model and to get a better understanding of cell-cell interactions of the retina in the context of the protective effect. We used an adolescent retinal organ culture (pig) with an incubation time of up to 4 days. Retinal explants were incubated with different antibodies for 24 h (anti-GFAP, anti-γ-synuclein and anti-myoglobin antibody as a control). Brn3a and TUNEL staining were performed. We also conducted glutamine synthetase staining and quantification of the retinal explants. Mass spectrometry analyses were performed as well as protein analyses via microarray. We detected a continuous decrease of rgc/mm in the retinal explants throughout the 4 days of incubation with increased TUNEL rgc staining. Immunohistochemical analyses showed a protective effect of anti-γ-synuclein (increased rgc/mm of 41%) and anti-GFAP antibodies (increased rgc/mm of 37%). Mass spectrometric, microarray and immunohistochemical analyses demonstrated Müller cell involvement and decreased endoplasmic reticulum stress response in the antibody-treated retinae. We could detect that the tested antibodies have a protective effect on rgc which seems to be the result of reduced stress levels in the retina as well as a shift of glutamine synthetase localization in the endfeet of the Müller cells towards the inner retinal layer. Loss of retinal ganglion cells (rgc) in glaucoma leads to blindness. Several antibodies are down-regulated in glaucoma patients. Our aim was to test if these antibodies have a protective effect of rgc in a retinal organ culture. This could be shown with an increase of rgc numbers. This effect results through reduced stress levels and the shift of glutamine synthetase localization.

Cell death pattern in lens epithelium of cataract patients

PURPOSE

Apoptosis, a type of programmed cell death, is observed in various types of cataract and in cultured lens epithelium subjected to oxidative damage. We have recently described oxidative DNA base damage in epithelium in age-related cataract and cultured cells, and we here aimed to examine such epithelium for markers for proliferation, initiation of apoptosis and morphological patterns of cell damage.

METHODS

Samples (n = 75) were analysed by light microscopy/electron microscopy (LM/EM); immunohistochemistry (IHC) for PCNA and Ki67 (DNA synthesis/proliferation); TUNEL assay (DNA fragmentation/apoptosis); and protein/gene expression of Caspase-3 (apoptotic effector molecule) and BAX/Bcl2 (pro-/anti-apoptotic marker) in fresh/cultured epithelium by IHC and qRT-PCR.

RESULTS

In fresh samples, the majority of cells were Ki67-/PCNA+. BAX/BCL-2-ratio was approximately 1, and Caspase-3 levels were low. TUNEL stained scattered nuclei/nuclear fragments (9/6302 cells). Main morphological signs of cell damage included rupture of cell membranes and hydration of cytoplasm and nuclei. Cultivation increased levels of BAX and Bcl2 by IHC and qRT-PCR (approximately 10-fold upregulation). Caspase-3 levels remained low by IHC with similar expression in fresh and cultured samples by qRT-PCR.

CONCLUSION

Genomic stress and DNA repair may explain the contrasting expression of Ki67/PCNA in fresh epithelium. Despite low levels of Caspase-3 and similar expression of BAX/Bcl-2, a low incidence of apoptosis may be detected in epithelium in age-related corticonuclear cataract. Epithelium may be transferred to culture without an increase in expression of Caspase-3, one of the central mediators of apoptosis.

Mathematical Modeling Reveals That Changes to Local Cell Density Dynamically Modulate Baseline Variations in Cell Growth and Drug Response

Cell-to-cell variations contribute to drug resistance with consequent therapy failure in cancer. Experimental techniques have been developed to monitor tumor heterogeneity, but estimates of cell-to-cell variation typically fail to account for the expected spatiotemporal variations during the cell growth process. To fully capture the extent of such dynamic variations, we developed a mechanistic mathematical model supported by in vitro experiments with an ovarian cancer cell line. We introduce the notion of dynamic baseline cell-to-cell variation, showing how the emerging spatiotemporal heterogeneity of one cell population can be attributed to differences in local cell density and cell cycle. Manipulation of the geometric arrangement and spatial density of cancer cells revealed that given a fixed global cell density, significant differences in growth, proliferation, and paclitaxel-induced apoptosis rates were observed based solely on cell movement and local conditions. We conclude that any statistical estimate of changes in the level of heterogeneity should be integrated with the dynamics and spatial effects of the baseline system. This approach incorporates experimental and theoretical methods to systematically analyze biologic phenomena and merits consideration as an underlying reference model for cell biology studies that investigate dynamic processes affecting cancer cell behavior. Cancer Res; 76(10); 2882-90. ©2016 AACR.

Temporal Heterogeneity Metrics in Apoptosis Induced by Anticancer Drugs

The apoptotic process is highly heterogeneous and asynchronous. A long-standing question is how many parameters define the time and reversibility of the apoptotic response at a single-cell level. We characterized at the single-cell and population levels the time sequence of apoptotic events in response to anti-cancer drugs using extrinsic and intrinsic apoptotic stimuli. We show that the temporal sequence of major apoptotic events is the same in response to all anti-cancer drugs studied: the apoptotic volume decrease and Na+ influx occur rapidly and are tightly coordinated with mitochondrial outer membrane depolarization (MOMP), mitochondrial inner membrane depolarization and a decrease in the production of reactive oxygen species (ROS). Phosphatidylserine externalization usually starts after MOMP and precedes caspase 3/7 activation. Activation of caspases 3/7 is a slow process that always starts after MOMP, with significant delay. Cell-to-cell variability of the MOMP onset is described by Gaussian distribution, whereas the γ-distribution model describes cellular variability in the duration of MOMP-to-caspase activation stages. Cells from the pre-MOMP stage to the after-caspase 3/7 activation stage coexist for many hours. We demonstrated by FACS that cells in the pre-MOMP stage can recover after apoptotic stimuli, rarely recover after MOMP but before caspase 3/7 activation, and are unable to recover after caspase 3/7 activation. We propose a double-stroke model for apoptosis execution.

Mathematical modeling of growth and death dynamics of mouse embryonic stem cells irradiated with γ-rays

Following ionizing radiation, mouse embryonic stem cells (mESCs) undergo both apoptosis and block at G2/M phase of the cell cycle. The dynamics of cell growth and the transition through the apoptotic phases cannot be directly inferred from experimental data, limiting the understanding of the biological response to the treatment. Here, we propose a semi-mechanistic mathematical model, defined by five compartments, able to describe the time curves of untreated and γ-rays irradiated mESCs and to extract the information therein embedded. To this end, mESCs were irradiated with 2 or 5 Gy γ-rays, collected over a period of 48 h and, at each time point, analyzed for apoptosis by using the Annexin V assay. When compared to unirradiated mESCs, the model estimates an additional 0.2 probability to undergo apoptosis for the 5 Gy-treated cells, and only a 0.07 (not statistically significantly different from zero) when a 2 Gy-irradiation dose is administered. Moreover, the model allows us to estimate the duration of the overall apoptotic process and also the time length of its early, intermediate, and late apoptotic phase.

Overexpression of alpha-synuclein at non-toxic levels increases dopaminergic cell death induced by copper exposure via modulation of protein degradation pathways

Gene multiplications or point mutations in alpha (α)-synuclein are associated with familial and sporadic Parkinson's disease (PD). An increase in copper (Cu) levels has been reported in the cerebrospinal fluid and blood of PD patients, while occupational exposure to Cu has been suggested to augment the risk to develop PD. We aimed to elucidate the mechanisms by which α-synuclein and Cu regulate dopaminergic cell death. Short-term overexpression of wild type (WT) or mutant A53T α-synuclein had no toxic effect in human dopaminergic cells and primary midbrain cultures, but it exerted a synergistic effect on Cu-induced cell death. Cell death induced by Cu was potentiated by overexpression of the Cu transporter protein 1 (Ctr1) and depletion of intracellular glutathione (GSH) indicating that the toxic effects of Cu are linked to alterations in its intracellular homeostasis. Using the redox sensor roGFP, we demonstrated that Cu-induced oxidative stress was primarily localized in the cytosol and not in the mitochondria. However, α-synuclein overexpression had no effect on Cu-induced oxidative stress. WT or A53T α-synuclein overexpression exacerbated Cu toxicity in dopaminergic and yeast cells in the absence of α-synuclein aggregation. Cu increased autophagic flux and protein ubiquitination. Impairment of autophagy by overexpression of a dominant negative Atg5 form or inhibition of the ubiquitin/proteasome system (UPS) with MG132 enhanced Cu-induced cell death. However, only inhibition of the UPS stimulated the synergistic toxic effects of Cu and α-synuclein overexpression. Our results demonstrate that α-synuclein stimulates Cu toxicity in dopaminergic cells independent from its aggregation via modulation of protein degradation pathways.

Modeling intrinsic heterogeneity and growth of cancer cells

Intratumoral heterogeneity has been found to be a major cause of drug resistance. Cell-to-cell variation increases as a result of cancer-related alterations, which are acquired by stochastic events and further induced by environmental signals. However, most cellular mechanisms include natural fluctuations that are closely regulated, and thus lead to asynchronization of the cells, which causes intrinsic heterogeneity in a given population. Here, we derive two novel mathematical models, a stochastic agent-based model and an integro-differential equation model, each of which describes the growth of cancer cells as a dynamic transition between proliferative and quiescent states. These models are designed to predict variations in growth as a function of the intrinsic heterogeneity emerging from the durations of the cell-cycle and apoptosis, and also include cellular density dependencies. By examining the role all parameters play in the evolution of intrinsic tumor heterogeneity, and the sensitivity of the population growth to parameter values, we show that the cell-cycle length has the most significant effect on the growth dynamics. In addition, we demonstrate that the agent-based model can be approximated well by the more computationally efficient integro-differential equations when the number of cells is large. This essential step in cancer growth modeling will allow us to revisit the mechanisms of multidrug resistance by examining spatiotemporal differences of cell growth while administering a drug among the different sub-populations in a single tumor, as well as the evolution of those mechanisms as a function of the resistance level.

Forecasting cell death dose-response from early signal transduction responses in vitro

The rapid pharmacodynamic response of cells to toxic xenobiotics is primarily coordinated by signal transduction networks, which follow a simple framework: the phosphorylation/dephosphorylation cycle mediated by kinases and phosphatases. However, the time course from initial pharmacodynamic response(s) to cell death following exposure can have a vast range. Viewing this time lag between early signaling events and the ultimate cellular response as an opportunity, we hypothesize that monitoring the phosphorylation of proteins related to cell death and survival pathways at key, early time points may be used to forecast a cell's eventual fate, provided that we can measure and accurately interpret the protein responses. In this paper, we focused on a three-phased approach to forecast cell death after exposure: (1) determine time points relevant to important signaling events (protein phosphorylation) by using estimations of adenosine triphosphate production to reflect the relationship between mitochondrial-driven energy metabolism and kinase response, (2) experimentally determine phosphorylation values for proteins related to cell death and/or survival pathways at these significant time points, and (3) use cluster analysis to predict the dose-response relationship between cellular exposure to a xenobiotic and plasma membrane degradation at 24 h post-exposure. To test this approach, we exposed HepG2 cells to two disparate treatments: a GSK-3β inhibitor and a MEK inhibitor. After using our three-phased approach, we were able to accurately forecast the 24 h HepG2 plasma membrane degradation dose-response from protein phosphorylation values as early as 20 min post-MEK inhibitor exposure and 40 min post-GSK-3β exposure.

Coordination of spermatogenic processes in the testis: lessons from cystic spermatogenesis

A common observation in the vertebrate testis is that new germ cell clones enter spermatogenesis proper before previously formed clones have completed their development. The extent to which the developmental advance of any given germ cell clone in any phase of spermatogenesis is dependent on that of neighboring clones and/or on the coordinating influence of associated Sertoli cells in the immediate vicinity or of others further away remains unclear. This review presents an overall synthesis of findings in an ancient vertebrate, the spiny dogfish shark and shows that, even at this phyletic level, the developmental advance of a given germ cell clone is the outcome of various processes emanating from its spatiotemporal relationship with (1) its own complement of Sertoli cells in the anatomically distinct spermatocyst and (2) Sertoli cells associated with other germ cell clones that lie upstream or downstream in the spermatogenic progression and that secrete, among others, androgen and estrogen destined for target sites upstream. Analysis of the protracted spermatogenic cycle shows the coordination in space and time of spermatogenic and steroidogenic events. Furthermore, the natural withdrawal of pituitary gonadotropin support in the dogfish causes a distinct and highly ordered gradient of apoptosis among the spermatogonial generations; this in turn is a major contributing factor to the cyclic nature of sperm production observed in this lower vertebrate. Because of the simplicity of their testicular organization, their cystic spermatogenesis and their phylogenetic position, cartilaginous fishes constitute a valid vertebrate reference system for comparative analysis with higher vertebrates.

Inhibition of Akt signaling in hepatoma cells induces apoptotic cell death independent of Akt activation status

The serine/threonine kinase Akt, a downstream effector of phosphatidylinositol 3-kinase (PI3K), is involved in cell survival and anti-apoptotic signaling. Akt has been shown to be constitutively expressed in a variety of human tumors including hepatocellular carcinoma (HCC). In this report we analyzed the status of Akt pathway in three HCC cell lines, and tested cytotoxic effects of Akt pathway inhibitors LY294002, Wortmannin and Inhibitor VIII. In Mahlavu human hepatoma cells Akt was constitutively activated, as demonstrated by its Ser473 phosphorylation, downstream hyperphosphorylation of BAD on Ser136, and by a specific cell-free kinase assay. In contrast, Huh7 and HepG2 did not show hyperactivation when tested by the same criteria. Akt enzyme hyperactivation in Mahlavu was associated with a loss of PTEN protein expression. Akt signaling was inhibited by the upstream kinase inhibitors, LY294002, Wortmannin, as well as by the specific Akt Inhibitor VIII in all three hepatoma cell lines. Cytotoxicity assays with Akt inhibitors in the same cell lines indicated that they were all sensitive, but with different IC50 values as assayed by RT-CES. We also demonstrated that the cytotoxic effect was through apoptotic cell death. Our findings provide evidence for its constitutive activation in one HCC cell line, and that HCC cell lines, independent of their Akt activation status respond to Akt inhibitors by apoptotic cell death. Thus, Akt inhibition may be considered as an attractive therapeutic intervention in liver cancer.

Retinal endothelial cell apoptosis stimulates recruitment of endothelial progenitor cells

PURPOSE

Bone marrow-derived endothelial progenitor cells (EPCs) contribute to vascular repair although it is uncertain how local endothelial cell apoptosis influences their reparative function. This study was conducted to determine how the presence of apoptotic bodies at sites of endothelial damage may influence participation of EPCs in retinal microvascular repair.

METHODS

Microlesions of apoptotic cell death were created in monolayers of retinal microvascular endothelial cells (RMECs) by using the photodynamic drug verteporfin. The adhesion of early-EPCs to these lesions was studied before detachment of the apoptotic cells or after their removal from the wound site. Apoptotic bodies were fed to normal RMECs and mRNA levels for adhesion molecules were analyzed.

RESULTS

Endothelial lesions where apoptotic bodies were left attached at the wound site showed a fivefold enhancement in EPC recruitment (P < 0.05) compared with lesions where the apoptotic cells had been removed. In intact RMEC monolayers exposed to apoptotic bodies, expression of ICAM, VCAM, and E-selectin was upregulated by 5- to 15-fold (P < 0.05-0.001). EPCs showed a characteristic chemotactic response (P < 0.05) to conditioned medium obtained from apoptotic bodies, whereas analysis of the medium showed significantly increased levels of VEGF, IL-8, IL-6, and TNF-alpha when compared to control medium; SDF-1 remained unchanged.

CONCLUSIONS

The data indicate that apoptotic bodies derived from retinal capillary endothelium mediate release of proangiogenic cytokines and chemokines and induce adhesion molecule expression in a manner that facilitates EPC recruitment.

Dynamics of outer mitochondrial membrane permeabilization during apoptosis

Individual cells within a population undergo apoptosis at distinct, apparently random time points. By analyzing cellular mitotic history, we identified that sibling HeLa cell pairs, in contrast to random cell pairs, underwent apoptosis synchronously. This allowed us to use high-speed cellular imaging to investigate mitochondrial outer membrane permeabilization (MOMP), a highly coordinated, rapid process during apoptosis, at a temporal resolution approximately 100 times higher than possible previously. We obtained new functional and mechanistic insight into the process of MOMP: We were able to determine the kinetics of pore formation in the outer mitochondrial membrane from the initiation phase of cytochrome-c-GFP redistribution, and showed differential pore formation kinetics in response to intrinsic or extrinsic apoptotic stimuli (staurosporine, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)). We also detected that the onset of mitochondrial permeabilization frequently proceeded as a wave through the cytosol, and that the frequency of wave occurrence in response to TRAIL was reduced by inhibition of protein kinase CK2. Computational analysis by a partial differential equation model suggested that the spread of permeabilization signals could sufficiently be explained by diffusion-adsorption velocities of locally generated permeabilization inducers. Taken together, our study yielded the first comprehensive analysis of clonal cell-to-cell variability in apoptosis execution and allowed to visualize and explain the dynamics of MOMP in cells undergoing apoptosis.

Real time analysis of tumor necrosis factor-related apoptosis-inducing ligand/cycloheximide-induced caspase activities during apoptosis initiation

Employing fluorescence resonance energy transfer (FRET) imaging, we previously demonstrated that effector caspase activation is often an all-or-none response independent of drug choice or dose administered. We here investigated the signaling dynamics during apoptosis initiation via the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor pathway to investigate how variability in drug exposure can be translated into largely kinetically invariant cell death execution pathways. FRET-based microscopy demonstrated dose-dependent responses of caspase-8 activation and activity within individual living HeLa cells. Caspase-8 on average was activated 45-600 min after TRAIL/cycloheximide addition. Caspase-8-like activities persisted for 15-60 min before eventually inducing mitochondrial outer membrane permeabilization. Independent of the TRAIL concentrations used or the resulting caspase-8-like activities, mitochondrial outer membrane permeabilization was induced when 10% of the FRET substrate was cleaved. In contrast, in Bid-depleted cells, caspase-8-like activity persisted for hours without causing immediate cell death. Our findings provide detailed insight into the intracellular signaling kinetics during apoptosis initiation and describe a threshold mechanism controlling the induction of apoptosis execution.

Is digitalis compound-induced cardiotoxicity, mediated through guinea-pig cardiomyocytes apoptosis?

Our aim in performing this study was to analyze in vivo the cell death mechanism induced by toxic doses of digitalis compounds on guinea-pig cardiomyocytes. We analyzed three study groups of five male guinea pigs each. Guinea pigs were intoxicated under anesthesia with ouabain or digoxin (at a 50-60% lethal dose); the control group did not receive digitalis. A 5-hours period elapsed before guinea pig hearts were extracted to obtain left ventricle tissue. We carried out isolation of mitochondria and cytosol, cytochrome c and caspase-3 and -9 determination, and electrophoretic analysis of nuclear DNA. TdT-mediated DUTP-X nick end labeling (TUNEL) reaction was performed in histologic preparations to identify in situ apoptotic cell death. Ultrastructural analysis was performed by electron microscopy. Electrophoretic analysis of DNA showed degradation into fragments of 200-400 base pairs in digitalis-treated groups. TUNEL reaction demonstrated the following: in the control group, <10 positive nuclei per field; in the digoxin-treated group, 2-14 positive nuclei per field, while in the ouabain-treated group counts ranged from 9-30 positive nuclei per field. Extracts from ouabain-treated hearts had an elevation of cytochrome c in cytosol and a corresponding decrease in mitochondria; this release of cytochrome c provoked activation of caspase-9 and -3. Electron microscopy revealed presence of autophagic vesicles in cytoplasm of treated hearts. Toxic dosages of digitalis at 50-60% of the lethal dose are capable of inducing cytochrome c release from mitochondria, processing of procaspase-9 and -3, and DNA fragmentation; these observations are mainly indicative of apoptosis, although a mixed mechanism of cell death cannot be ruled out.

Epithelial cell density in cataractous lenses of patients with diabetes: association with erythrocyte aldose reductase

In the present study we evaluated the cell density of lens epithelium and its relation to the degree of erythrocyte aldose reductase (AR) in patients with type 2 diabetes. This prospective clinical study included 46 eyes of patients with type 2 diabetes and 48 eyes of patients without diabetes mellitus (DM). Flat preparations of lens epithelial cells (LECs) attached to the anterior capsule were studied. Multiple regression analysis was performed to evaluate the association between lens cell density and age, gender, type of cataract, duration of diabetes, diabetic retinopathy (DR), the levels of glycosylated hemoglobin (HbA1c) and erythrocyte AR. The mean density of LECs of patients with type 2 diabetes was 4,141+/-508cells/mm(2), which was significantly lower than that of patients without DM (4,560+/-458cells/mm(2); p<0.0001). Multiple regression analysis revealed that the level of erythrocyte AR was correlated with the reduction of LECs in the eyes of patients with type 2 diabetes. The correlation between the density of LECs and the amount of erythrocyte AR was significant in the diabetic group with a high value of HbA1c (>6.5%) or with DR. These results suggest that the polyol pathway via AR may be associated with the reduction of epithelial cell density in the eyes of patients with DM.

Automated laser scanning cytometry: a powerful tool for multi-parameter analysis of drug-induced apoptosis

BACKGROUND

Simultaneous analysis of multiple intracellular events is critical for assessing the effect of biological response modifiers, including the efficacy of chemotherapy. Here we used the automated laser scanning cytometry (LSC) for multi-parameter analysis of drug-induced tumor cell apoptosis.

MATERIALS

Using 2-mercaptopyridine-N-oxide-hydrate sodium salt, or the commonly used chemotherapeutic agents etoposide and camptothecin, we performed simultaneous analyses of apoptosis-related morphological features as well as fluorescence-based biochemical changes in a 96-well format.

RESULTS

We demonstrate the scope of LSC as a platform for comparing multiple variables between different cell populations, distinguishing unique events at a single cell level within a sample population, and enabling simultaneous screenings in a single assay at multiple dosages and time-points.

CONCLUSION

These data underscore the power of LSC for simultaneous multi-parameter analysis, which could have implications for screening or assessing the efficacy of drug responses in heterogeneous cell populations and at the single cell level.

Ischaemic injury to femoral head induces apoptotic and oncotic cell death

AIMS

The mechanism of cell death in ischaemic osteonecrosis of the femoral head is not clear. Therefore, this study was designed to clarify the mode of cell death following ischaemic osteonecrosis of the femoral head in an established pig model.

METHODS

Morphological assessment, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL) assay, detection of DNA laddering and transmission electron microscopy studies were performed to determine whether apoptosis is one of the pathways of cell death following ischaemic osteonecrosis of the femoral head.

RESULTS

Mode of cell death was investigated from 2 to 14 days following the surgical induction of ischaemia. Ischaemic femoral heads showed morphological evidence of cell death by oncotic and apoptotic pathways in earlier stages of osteonecrosis. TUNEL positive cells were seen from 2 to 14 days following the induction of ischaemia. DNA samples obtained from ischaemic femoral heads following the induction of ischaemia showed nucleosomal ladders indicating apoptotic cell death. Electron micrographs also showed morphological changes associated with apoptosis.

CONCLUSIONS

This study demonstrates that oncosis is not the sole mechanism of cell death following ischaemic injury of the femoral head. Both apoptosis and oncosis are involved as a result of ischaemic injury to the femoral head.

Neuronal apoptosis linked to EglN3 prolyl hydroxylase and familial pheochromocytoma genes: developmental culling and cancer

Germline NF1, c-RET, SDH, and VHL mutations cause familial pheochromocytoma. Pheochromocytomas derive from sympathetic neuronal precursor cells. Many of these cells undergo c-Jun-dependent apoptosis during normal development as NGF becomes limiting. NF1 encodes a GAP for the NGF receptor TrkA, and NF1 mutations promote survival after NGF withdrawal. We found that pheochromocytoma-associated c-RET and VHL mutations lead to increased JunB, which blunts neuronal apoptosis after NGF withdrawal. We also found that the prolyl hydroxylase EglN3 acts downstream of c-Jun and is specifically required among the three EglN family members for apoptosis in this setting. Moreover, EglN3 proapoptotic activity requires SDH activity because EglN3 is feedback inhibited by succinate. These studies suggest that failure of developmental apoptosis plays a role in pheochromocytoma pathogenesis.

Rat hepatocyte invasion by Listeria monocytogenes and analysis of TNF-alpha role in apoptosis

Listeria monocytogenes, etiological agent of severe human foodborne infection, uses sophisticated mechanisms of entry into host cytoplasm and manipulation of the cellular cytoskeleton, resulting in cell death. The host cells and bacteria interaction may result in cytokine production as Tumor Necrosis Factor (TNF) alpha. Hepatocytes have potential to produce pro-inflammatory cytokines as TNF-alpha when invaded by bacteria. In the present work we showed the behavior of hepatocytes invaded by L. monocytogenes by microscopic analysis, determination of TNF-alpha production by bioassay and analysis of the apoptosis through TUNEL technique. The presence of bacterium, in ratios that ranged from 5 to 50,000 bacteria per cell, induced the rupture of cellular monolayers. We observed the presence of internalized bacteria in the first hour of incubation by electronic microscopy. The levels of TNF-alpha increased from first hour of incubation to sixth hour, ranging from 0 to 3749 pg/mL. After seven and eight hours of incubation non-significant TNF-alpha levels decrease occurred, indicating possible saturation of cellular receptors. Thus, the quantity of TNF-alpha produced by hepatocytes was dependent of the incubation time, as well as of the proportion between bacteria and cells. The apoptosis rate increased in direct form with the incubation time (1 h to 8 + 24 h), ranging from 0 to 43%, as well as with the bacteria : cells ratio. These results show the ability of hepatocyte invasion by non-hemolytic L. monocytogenes, and the main consequences of this phenomenon were the release of TNF-alpha by hepatocytes and the induction of apoptosis. We speculate that hepatocytes use apoptosis induced by TNF-alpha for release bacteria to extracellular medium. This phenomenon may facilitate the bacteria destruction by the immune system.

Neuroprotection of edaravone on hypoxic-ischemic brain injury in neonatal rats

Edaravone has an inhibitory effect on lipid peroxidation by scavenging free radicals and prevents vascular endothelial cell injury. We examined whether edaravone was effective on hypoxic-ischemic (HI) brain injury in immature brain or not using the Rice-Vannucci model. The initial dose, 3 mg/kg (0.05 ml) of edaravone, was injected intraperitoneally just before hypoxic exposure. Subsequently, the same dose was injected every 12 h until the animals were killed. Controls received saline injection as the same protocol. Macroscopic evaluation of brain injury revealed that the neuroprotective effect of edaravone on HI brain after 48 h post HI. TUNEL showed that edaravone injection decreased neurodegeneration. Quantitative analysis of cell death using H&E-stained 2.5 microm sections showed that there was a trend for both necrotic and apoptotic cells to decrease in edaravone injection group. Edaravone injection inhibited the release of cytochrome c from mitochondria to cytosol and caspase-3 activation in cortex and hippocampus between 24 and 168 h post HI. Our results suggest that edaravone is protective after HI insult in the immature brain by decreasing both apoptosis and necrosis and also by inhibiting mitochondrial injury.

Whole-mount in situ TUNEL method revealed ectopic pattern of apoptosis in cadmium treated naupliar larvae of barnacle (Balanus amphitrite Darwin)

The effect of cadmium on stage II naupliar larvae of barnacle (Balanus amphitrite Darwin) was investigated. Barnacle larvae were exposed to 0-15 microM CdCl(2) for 24 h. Apoptotic cells were stained by the terminal deoxyribonucleotidyl transferase mediated dUTP nick end labelling (TUNEL) method. Incidence of apoptosis, as measured by numbers of animals with ectopic pattern of apoptosis as well as numbers of apoptotic cells per animal, was assessed using confocal microscopy. An increase in incidence of apoptosis was observed in the experimental animals with an increase in cadmium concentration. Mortality increased, and motility decreased, when barnacle larvae were exposed to an increasing concentration of cadmium. The relationship between the occurrence of apoptosis and swimming behaviour was investigated in larvae exposed to 10 microM CdCl(2). Significant increases in apoptosis were detected in the non-motile and dead nauplii. This study suggested that whole-mount in situ TUNEL method may be used to study increased occurrence of apoptotic cells in crustacean larvae.

Development of a postnatal 3-day-old rat model of mild hypoxic-ischemic brain injury

Improvements in both obstetric and paediatric care have been responsible for a continuing reduction in mortality in extremely premature infants. However, higher survival rates have been at the expense of more long-term neurological damage. Various animal models have been developed to study the effect of hypoxic-ischemic insults on the brain. However, established models like the postnatal day 7 rat model represent damage found in term infants rather than in preterm infants of 24-28 weeks' gestation, and produce a severe form of injury resulting in high mortality rates. In this study we developed a reliable model of minor hypoxic-ischemic brain injury in postnatal day 3 rats. At this maturity, the pattern of damage represents that expected in a preterm infant suffering a non-lethal perinatal insult. We found that minor changes in duration of insult and both temperature and humidity produced wide fluctuations in the degree of injury observed. By maintaining strict control over experimental conditions including duration of insult, temperature and humidity, we produced a reliable model of minor injury primarily affecting all five areas of the cerebral cortex, and also the thalamus (area 7) and basal ganglia (area 8). Differences were significant compared to normal controls and sham-operated animals (p<0.05). These areas represent the primary motor, insular, visual and temporal cortices. The overall mortality rate in this study was 12.3%.

Resetting the problem of cell death following muscle-derived cell transplantation: detection, dynamics and mechanisms

We conducted a study in mice to reevaluate and clarify many aspects of the early survival of muscle cells following transplantation. Male mouse muscle cells (primary-cultures and T-antigen-immortalized clones) labeled with [14C]thymidine and beta-galactosidase were injected into female muscles. Each label was detected in the muscles after different time periods. TUNEL, alizarin red, and immunodetection of active caspase-3 were done in muscle sections. The donor cell labels disappeared from the muscles following donor cell death, but this was not instantaneous and even if the donor cells were killed before transplantation, the first 6 hours were not enough to clear [14C]thymidine and Y chromosome. Using the cell pellet before injection as the 100% baseline for cells injected to evaluate cell death can lead to misinterpretations: the Y-chromosome band was 5-fold stronger than that of a muscle injected with cells, irrespective of whether the cells were previously killed or not. There was no evidence of an immediate massive donor cell death. Necrosis (detected by alizarin red) and apoptosis (detected by active caspase-3) were present among the donor myoblasts following transplantation. Necrosis seemed to be the most important mechanism during the first hours. T-antigen immortalized cells died earlier and more massively than primary-cultured cells, but the surviving cells proliferated more. Indeed, they seemed to exhibit more apoptosis and they triggered a more rapid CD8+ cell infiltration. As a result of our findings, many concepts concerning the early donor cell death following myoblast transplantation must be reconsidered.

Apoptotic cell death in the lens epithelium of rat sugar cataract

Apoptosis of lens epithelial cells (LECs) is implicated in the pathogenesis of several types of cataract formation. The high intracellular levels of polyol induce histological change in the LECs, which is considered the earliest event in sugar cataractogenesis. This study was designed to investigate whether high galactose exposure induces apoptosis in LECs during the development of sugar cataract. The effect of an aldose reductase inhibitor, SNK-860, was also examined. We induced sugar cataract in Sprague-Dawley rats by feeding them a 50% galactose-containing diet with or without SNK-860. The percentage of LECs undergoing apoptosis was measured by the terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL) method, and DNA fragmentation analyses were performed. Galactitol levels in the lens epithelium were quantified by gas chromatography. The number of TUNEL-positive cells gradually increased throughout the period of galactose exposure, up to 5 days. DNA fragmentation analysis in LECs of rats fed a galactose-rich diet demonstrated an apparent ladder pattern. SNK-860 reduced the percentage of TUNEL-positive cells, the amount of intracellular galactitol, and the levels of DNA laddering. To explore the mechanism of the apoptotic process, the expression of p53, a potent mediator of apoptosis, was examined. Based on Western blot and real-time reverse transcription-polymerase chain reaction results, the amount of p53-expression increased at both the protein and mRNA levels after galactose exposure, and the increase in p53-expression was inhibited by SNK-860. Based on these results, we concluded that apoptosis occurs in rat lens epithelial cells following galactose exposure. Furthermore, the reduction of apoptosis by aldose reductase inhibitor suggests that this apoptosis is associated with the accumulation of sugar alcohols. It is probable that the mechanism of apoptosis during sugar cataract formation involves the increased expression of p53.

Expression of the low affinity neurotrophin receptor p75 in spinal motoneurons in a transgenic mouse model for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a lethal neurodegenerative disorder involving motoneuron loss in the cortex, brainstem and spinal cord, resulting in progressive paralysis. Aberrant neurotrophin signalling via the low affinity neurotrophin receptor p75 has been suggested to be involved in the motoneuron death by the activation of apoptotic pathways. In order to investigate the involvement of neurotrophin receptor p75 in the amyotrophic lateral sclerosis related motoneuron degeneration process, we have studied the expression of this receptor in the spinal cord of transgenic mice carrying a mutated human Cu, Zn superoxide dismutase gene. Mutations in the superoxide dismutase gene are one of the genetic causes for familiar amyotrophic lateras sclerosis and human superoxide dismutase-1 transgenic mice develop symptoms and pathology similar to those in human amyotrophic lateras sclerosis. Our study shows that in these mice, spinal motoneurons, which normally do not contain the neurotrophin receptor p75 receptor, express this receptor during the progress of the disease. Expression of the neurotrophin receptor p75 receptor coincides with the expression of activating transcription factor 3, a member of the activating transcription factor/cyclic AMP family of stress transcription factors. Only a minority of these spinal motoneurons actually showed co-expression of neurotrophin receptor p75 with caspase-3 activity, suggesting that expression of the neurotrophin receptor p75 receptor is not directly related to the execution phase of the apoptosis process.

Temporal and sequential analysis of microglia in the substantia nigra following medial forebrain bundle axotomy in rat

Dopaminergic neurons in the substantia nigra pars compacta undergo apoptosis after transection of the medial forebrain bundle. We have assessed the temporal and sequential activities of microglia in these events by examining the complement-3 (OX-42), major histocompatibility complex class II antigen presentation (OX-6) and phagocytic activity (ED1), and correlating these indicators with dopaminergic neuronal loss. Microglia in the ipsilateral substantia nigra pars reticulata evinced activation morphology at 12 h postaxotomy. Phagocytic microglia apposed dying dopaminergic neurons in the pars compacta starting at 3 days postlesion; their number increased through 14 days and slowly decreased. Nuclear chromatin condensation and significant loss of tyrosine hydroxylase-positive dopaminergic neurons occurred around 7 days postlesion. In contrast to microglial expression of interleukin-1beta and inducible nitric oxide synthase at the axotomy site, nigral microglia were interleukin-1beta and inducible nitric oxide synthase-negative. Consistently, RNase protection assays showed that interleukin-1beta and inducible nitric oxide synthase transcripts in nigra were equivocal. The present data support the idea that phagocytosis of axotomized neurons by activated microglia is not limited to dead neurons but includes dying neurons probably without cytotoxic effects of inflammatory substances, such as interleukin-1beta or nitric oxide.

Cell cycle synchronization of porcine fetal fibroblasts by serum deprivation initiates a nonconventional form of apoptosis

The success of somatic nuclear transfer depends upon the cell cycle stage of the donor nucleus and the recipient cytoplast. Recently, we established efficient cell cycle synchronization protocols for porcine fetal fibroblasts and found that serum withdrawal leads to cell death. Here, we examined whether the specific cell death induced by serum deprivation follows the conventional apoptotic pathway in porcine fibroblasts. Terminal deoxynucleotidyl transferase mediated dUTP nick end-labeling analysis revealed that serum deprivation induced DNA fragmentation in a concentration and time dependent manner. Semiquantitative RT-PCR and Western blotting revealed activation of cell death-related genes Bak and Bax of the Bcl-2 family. However, electrophoretic analysis of genomic DNA from serum deprived cells did not provide evidence for the internucleosomal DNA cleavage which is characteristic of conventional apoptosis. Thus, serum deprivation triggers initial steps in the apoptotic pathway, but does not lead to the typical oligonucleosome-sized DNA ladder. These findings contribute to a better understanding of apoptotic pathways and aid to define essential parameters of the donor nucleus for successful somatic cloning.

Ras stimulates aberrant cell cycle progression and apoptosis in rat thyroid cells

Abundant evidence supports the ability of Ras to stimulate thyroid cell proliferation. Stable expression of activated Ras enhances the sensitivity of thyroid cells to apoptosis. We report that apoptosis is a primary and general response of rat thyroid cells to acute expression of activated Ras in the absence or presence of thyrotropin, insulin, and serum, survival factors for thyroid cells. Ras induced apoptosis in quiescent and cycling cells. Concomitantly, Ras stimulated S phase entry in quiescent cells and enhanced G1/S transition in cycling cells. Ras effects on the cell cycle were characterized by delayed progression through S phase and an apparent failure to proceed through G2/M phase. Unlike thyroid cell mitogens, Ras markedly decreased cyclin D1 expression. Although acute expression of Ras decreased cyclin D1 protein levels, cells selected to survive chronic Ras expression exhibited a selective increase in cyclin D1 expression. In summary, thyroid cells harbor an apoptotic program activated by Ras that outstrips the protective effects of thyrotropin, insulin, and serum. Apoptosis is accompanied by dysregulated cell cycle progression, suggesting that cell death may arise, at least in part, as a consequence of inappropriate proliferative cues.

Phagocytosis of apoptotic cells by macrophages induces novel signaling events leading to cytokine-independent survival and inhibition of proliferation: activation of Akt and inhibition of extracellular signal-regulated kinases 1 and 2

Recent evidence indicates that phagocytic clearance of apoptotic cells, initially thought to be a silent event, can modulate macrophage (M phi) function. We show in this work that phagocytic uptake of apoptotic cells or bodies, in the absence of serum or soluble survival factors, inhibits apoptosis and maintains viability of primary cultures of murine peritoneal and bone marrow M phi with a potency approaching that of serum-supplemented medium. Apoptotic uptake also profoundly inhibits the proliferation of bone marrow M phi stimulated to proliferate by M-CSF. While inhibition of proliferation is an unusual property for survival factors, the combination of increased survival and decreased proliferation may aid the M phi in its role as a scavenger during resolution of inflammation. The ability of apoptotic cells to promote survival and inhibit proliferation appears to be the result of simultaneous activation of Akt and inhibition of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1 and ERK2 (ERK1/2). While several activators of the innate immune system, or danger signals, also inhibit apoptosis and proliferation, danger signals and necrotic cells differ from apoptotic cells in that they activate, rather than inhibit, ERK1/2. These signaling differences may underlie the opposing tendencies of apoptotic cells and danger signals in promoting tolerance vs immunity.

Gamma-tocopheryl quinone stimulates apoptosis in drug-sensitive and multidrug-resistant cancer cells

Chemotherapy-induced cell death is linked to apoptosis, and there is increasing evidence that multidrug-resistance in cancer cells may be the result of a decrease in the ability of a cell to initiate apoptosis in response to cytotoxic agents. In previous studies, we synthesized two classes of electrophilic tocopheryl quinones (TQ), nonarylating alpha-TQ and arylating gamma- and delta-TQ, and found that gamma- and delta-TQ, but not alpha-TQ, were highly cytotoxic in human acute lymphoblastic leukemia cells (CEM) and multidrug-resistant (MDR) CEM/VLB100. We have now extended these studies on tumor biology with CEM, HL60 and MDR HL60/MX2 human promyelocytic leukemia, U937 human monocytic leukemia, and ZR-75-1 breast adenocarcinoma cells. gamma-TQ, but not alpha-TQ or tocopherols, showed concentration and incubation time-dependent effects on loss of plasma membrane integrity, diminished viable cell number, and stimulation of apoptosis. Its cytotoxicity exceeded that of doxorubicin in HL60/MX2 cells, which express MRP, an MDR-associated protein. Apoptosis was confirmed by TEM, TUNEL, and DNA gel electrophoresis. Kinetic studies showed that an induction period was required to initiate an irreversible multiphase process. Gamma-TQ released mitochondrial cytochrome c to the cytosol, induced the cleavage of poly(ADP-ribose)polymerase, and depleted intracellular glutathione. Unlike xenobiotic electrophiles, gamma-TQ is a highly cytotoxic arylating electrophile that stimulates apoptosis in several cancer cell lines including cells that express MDR through both P-glycoprotein and MRP-associated proteins. The biological properties of arylating TQ electrophiles are closely associated with cytotoxicity and may contribute to other biological effects of these highly active agents.

Kinetics of apoptotic markers in exogeneously induced apoptosis of EL4 cells

We investigated the time-dependence of apoptotic events in EL4 cells by monitoring plasma membrane changes in correlation to DNA fragmentation and cell shrinkage. We applied three apoptosis inducers (staurosporine, tubericidine and X-rays) and we looked at various markers to follow the early-to-late apoptotic events: phospholipid translocation (identified through annexin V-fluorescein assay and propidium iodide), lipid package (via merocyanine assay), membrane fluidity and anisotropy (via fluorescent measurements), DNA fragmentation by the fluorescence-labeling test and cell size measurements. The different apoptotic inducers caused different reactions of the cells: staurosporine induced apoptosis most rapidly in a high number of cells, tubercidine triggered apoptosis only in the S phase cells, while X-rays caused a G2/M arrest and subsequently apoptosis. Loss of lipid asymmetry is promptly detectable after one hour of incubation time. The phosphatidylserine translocation, decrease of lipid package and anisotropy, and the increase of membrane fluidity appeared to be based on the same process of lipid asymmetry loss. Therefore, the DNA fragmentation and the cell shrinkage appear to be parallel and independent processes running on different time scales but which are kinetically inter-related. The results indicate different signal steps to apoptosis dependent on inducer characteristics but the kinetics of "early-to-late" apoptosis appears to be a fixed program.

A population of PC12 cells that is initiating apoptosis can be rescued by nerve growth factor

Programmed cell death, or apoptosis, occurs asynchronously in neuronal cells. To overcome this asynchrony, rat pheochromocytoma (PC12) cells were separated at different stages of apoptosis on the basis of cell density. Live cells that exhibited no apoptotic features floated to the top of density gradients. The most dense cells showed extensive loss of cytochrome c from mitochondria, caspase activation, chromatin condensation, and DNA fragmentation. These cells were committed to apoptosis and could not be rescued by reculturing in with nerve growth factor (NGF). Cells of intermediate density displayed no DNA fragmentation, but had begun to show cytochrome c loss, caspase activation, and chromatin condensation. This population displayed upregulation of the prodeath factor, c-Jun, and downregulation of prosurvival kinase, Akt. Importantly, apoptosis was reversible by NGF in this population. These studies suggest that increased cell density correlates with an initial step in the apoptosis mechanism that precedes irreversible commitment to suicide.

Differential effect of MLC kinase in TNF-alpha-induced endothelial cell apoptosis and barrier dysfunction

Tumor necrosis factor (TNF)-alpha is released in acute inflammatory lung syndromes linked to the extensive vascular dysfunction associated with increased permeability and endothelial cell apoptosis. TNF-alpha induced significant decreases in transcellular electrical resistance across pulmonary endothelial cell monolayers, reflecting vascular barrier dysfunction (beginning at 4 h and persisting for 48 h). TNF-alpha also triggered endothelial cell apoptosis beginning at 4 h, which was attenuated by the caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone. Exploring the involvement of the actomyosin cytoskeleton in these important endothelial cell responses, we determined that TNF-alpha significantly increased myosin light chain (MLC) phosphorylation, with prominent stress fiber and paracellular gap formation, which paralleled the onset of decreases in transcellular electrical resistance and enhanced apoptosis. Reductions in MLC phosphorylation by the inhibition of either MLC kinase (ML-7, cholera toxin) or Rho kinase (Y-27632) dramatically attenuated TNF-alpha-induced stress fiber formation, indexes of apoptosis, and caspase-8 activity but not TNF-alpha-induced barrier dysfunction. These studies indicate a central role for the endothelial cell cytoskeleton in TNF-alpha-mediated apoptosis, whereas TNF-alpha-induced vascular permeability appears to evolve independently of contractile tension generation.

Effect of antioxidants on L-glutamate and N-methyl-4-phenylpyridinium ion induced-neurotoxicity in PC12 cells

The neuropathology associated with Parkinson's disease within and around the substantia nigra is thought to involve excessive production of free radicals, dopamine autoxidation, defects in the expression of glutathione peroxidase, attenuated levels of reduced glutathione, altered calcium homeostasis, excitotoxicity and genetic defects in mitochondrial complex I activity. While the neurotoxic mechanisms are vastly different for excitotoxins and N-methyl-4-phenylpyridinium ion (MPP+), both are thought to involve free radical production, compromised mitochondrial activity and excessive lipid peroxidation. In the present study, several dietary antioxidant compounds, monoamine oxidase inhibitors and ergogenic compounds were examined for protective action against neurotoxicity induced by L-glutamate (15 mM) or MPP+-HCl (5 mM) in a plastic adhering variant of murine pheochromocytoma cells. The results show no significant protective effects exhibited by azulene, (+)-catechin, curcrumin, (-)-epigallocatechin gallate, green tea, morin, pygnogenol, silymarin, clove oil, garlic oil or rosemary, extract. Compounds, which were effective in providing protection against L-glutamate-induced cell death, were coenzyme Q-0, coenzyme Q-10, L-deprenyl and N-acetyl-L-cysteine. Compounds, which provided protection against MPP+-HCl toxicity, were allopurinol, coenzyme Q-10, L-deprenyl, N-acetyl-L-cysteine and sesame oil. In both models, significant protection was achieved in the presence of coenzyme Q-10, L-deprenyl and N-acetyl-L-cysteine. These results indicate that the mechanism of cell death in both of these toxicity models is most likely not related to the destructive effects of free radicals.

Role of programmed cell death in development

Programmed cell death (PCD) is an integral part of both animal and plant development. In animals, model systems such as Caenorhabditis elegans, Drosophila melanogaster, and mice have shown a general cell death profile of induction, caspase mediation, cell death, and phagocytosis. Tremendous strides have been made in cell death research in animals in the past decade. The ordering of the C. elegans genes Ced-3, 4 and 9, identification of caspase-activated DNase that degrades nuclear DNA during PCD, identification of signal transduction modules involving caspases as well as the caspase-independent pathway, and the involvement of mitochondria are some of the findings of immense value in understanding animal PCDs. Similarly, the caspase inactivation mechanisms of infecting viruses to stall host cell death give a new dimension to the viral infection process. However, plant cell death profiles provide an entirely different scenario. The presence of a cell wall that cannot be phagocytosed, absence of the hallmarks of animal PCDs such as DNA laddering, formation of apoptotic bodies, a cell-death-specific nuclease, a biochemical machinery of killer enzymes such as caspases all point to novel ways of cell elimination. Large gaps in our understanding of plant cell death have prompted speculative inferences and comparisons with animal cell death mechanisms. This paper deals with both animals and plants for a holistic view on cell death in eukaryotes.

Apoptosis has a prolonged role in the neurodegeneration after hypoxic ischemia in the newborn rat

Birth asphyxia can cause moderate to severe brain injury. It is unclear to what degree apoptotic or necrotic mechanisms of cell death account for damage after neonatal hypoxia-ischemia (HI). In a 7-d-old rat HI model, we determined the contributions of apoptosis and necrosis to neuronal injury in adjacent Nissl-stained, hematoxylin and eosin-stained, and terminal deoxynucleotidyl transferase-mediated UTP nick end-labeled sections. We found an apoptotic-necrotic continuum in the morphology of injured neurons in all regions examined. Eosinophilic necrotic neurons, typical in adult models, were rarely observed in neonatal HI. Electron microscopic analysis showed "classic" apoptotic and necrotic neurons and "hybrid" cells with intermediate characteristics. The time course of apoptotic injury varied regionally. In CA3, dentate gyrus, medial habenula, and laterodorsal thalamus, the density of apoptotic cells was highest at 24-72 hr after HI and then declined. In contrast, densities remained elevated from 12 hr to 7 d after HI in most cortical areas and in the basal ganglia. Temporal and regional patterns of neuronal death were compared with expression of caspase-3, a cysteine protease involved in the execution phase of apoptosis. Immunocytochemical and Western blot analyses showed increased caspase-3 expression in damaged hemispheres 24 hr to 7 d after HI. A p17 peptide fragment, which results from the proteolytic activation of the caspase-3 precursor, was detected in hippocampus, thalamus, and striatum but not in cerebral cortex. The continued expression of activated caspase-3 and the persistence of cells with an apoptotic morphology for days after HI suggests a prolonged role for apoptosis in neonatal hypoxic ischemic brain injury.

Two waves of programmed cell death occur during formation and development of somatic embryos in the gymnosperm, Norway spruce

In the animal life cycle, the earliest manifestations of programmed cell death (PCD) can already be seen during embryogenesis. The aim of this work was to determine if PCD is also involved in the elimination of certain cells during plant embryogenesis. We used a model system of Norway spruce somatic embryogenesis, which represents a multistep developmental pathway with two broad phases. The first phase is represented by proliferating proembryogenic masses (PEMs). The second phase encompasses development of somatic embryos, which arise from PEMs and proceed through the same sequence of stages as described for their zygotic counterparts. Here we demonstrate two successive waves of PCD, which are implicated in the transition from PEMs to somatic embryos and in correct embryonic pattern formation, respectively. The first wave of PCD is responsible for the degradation of PEMs when they give rise to somatic embryos. We show that PCD in PEM cells and embryo formation are closely interlinked processes, both stimulated upon withdrawal or partial depletion of auxins and cytokinins. The second wave of PCD eliminates terminally differentiated embryo-suspensor cells during early embryogeny. During the dismantling phase of PCD, PEM and embryo-suspensor cells exhibit progressive autolysis, resulting in the formation of a large central vacuole. Autolytic degradation of the cytoplasm is accompanied by lobing and budding-like segmentation of the nucleus. Nuclear DNA undergoes fragmentation into both large fragments of about 50 kb and multiples of approximately 180 bp. The tonoplast rupture is delayed until lysis of the cytoplasm and organelles, including the nucleus, is almost complete. The protoplasm then disappears, leaving a cellular corpse represented by only the cell wall. This pathway of cell dismantling suggests overlapping of apoptotic and autophagic types of PCD during somatic embryogenesis in Norway spruce.