Programmed death phenomena: from organelle to organism

Inositol 1,4,5-trisphosphate receptor-mediated initial Ca(2+) mobilization constitutes a triggering signal for hydrogen peroxide-induced apoptosis in INS-1 β-cells

Reactive oxygen species, including hydrogen peroxide (H(2)O(2)), are known to induce β-cell apoptosis. The present study investigated the role of Ca(2+) in H(2)O(2)-induced apoptosis of the β-cell line INS-1. Annexin V assay with flow cytometry and DNA ladder assay demonstrated that treatment of INS-1 cells with 100 µM H(2)O(2) for 18 h significantly increased apoptotic cells. A comparable level of apoptosis was also observed after 18 h when the cells were treated with 100 µM H(2)O(2) only for initial 30 min. The H(2)O(2)-induced apoptosis was abolished by 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl)ester (BAPTA/AM), a chelator of intracellular Ca(2+), by 2-aminoethoxydiphenylborate (2-APB), a blocker of inositol 1,4,5-trisphosphate (IP(3)) receptors and cation channels, and by xestospongin D, a blocker of IP(3) receptors, and was partially blocked by SKF-96365, a non-selective cation channel blocker. However, nicardipine, an L-type voltage-dependent Ca(2+) channel blocker, or N-(p-amylcinnamoyl)anthranilic acid (ACA), a TRPM2 blocker, had little effect on the apoptosis. The inhibitory effect of BAPTA/AM or 2-APB on the H(2)O(2)-induced apoptosis was largely attenuated when the drug was added 30 min or 1 h after start of the treatment with H(2)O(2). These results suggest that the initial intracellular Ca(2+) elevation induced by H(2)O(2), which is mediated via IP(3) receptors and store-operated cation channels, plays an obligatory role in the induction of β-cell apoptosis.

Aging is not a process of wear and tear

The idea that bodies wear out with age is so ancient, so pervasive, and so deeply rooted that it affects our thought in unconscious ways. Undeniably, many aspects of aging, e.g., oxidative damage, somatic mutations, and protein cross-linkage are characterized by increased entropy in biomolecules. However, it has been a scientific consensus for more than a century that there is no physical necessity for such damage. Living systems are defined by their capacity to gather order from their environment, concentrate it, and shed entropy with their waste. Organisms in their growth phase become stronger and more robust; no physical law prohibits this progress from continuing indefinitely. Indeed, some animals and many plants are known to grow indefinitely larger and more fertile through their lives. The same conclusion is underscored by experimental findings that various insults and challenges that directly damage the body or increase the rate of wear and tear have the paradoxical effect of extending life span. Hyperactive mice live longer than controls, and worms with their antioxidant systems impaired live longer than wild type. A fundamental understanding of aging must proceed not from physics but from an evolutionary perspective: The body is being permitted to decay because systems of repair and regeneration that are perfectly adequate to build and rebuild a body of ever-increasing resilience are being held back. Regardless of the reason for this retreat, it should be more fruitful to focus on signaling to effect the ongoing activity of systems of repair and regeneration than to attempt repair of the manifold damage left in the wake of their failure.

L-amino acid oxidase activity present in fractions of Bothrops jararaca venom is responsible for the induction of programmed cell death in Trypanosoma cruzi

Bothrops jararaca venom induces programmed cell death in epimastigotes of Trypanosoma cruzi. Here we fractionated the venom and observed that the anti-T. cruzi activity was associated with fractions that present L-amino acid oxidase (L-AAO) activity. L-AAO produces H(2)O(2), which is highly toxic. The addition of catalase to the medium, a H(2)O(2) scavenger, reverted the killing capacity of venom fractions. The anti-T. cruzi activity was also abolished when parasites were cultured in a medium without hydrophobic amino acids that are essential for L-AAO activity. These results were confirmed with a commercial purified L-AAO. Treatment for 24 h with fractions that present L-AAO activity induced parasites cytoplasmic retraction, mitochondrial swelling and DNA fragmentation, all morphological characteristics of programmed cell death. Similar changes were also observed when parasites were treated with H(2)O(2). These results indicate that H(2)O(2), the product of L-AAO reaction, induces programmed cell death explaining the anti-T. cruzi activity of B. jararaca venom.

Mitophagy and mitoptosis in disease processes

Mitochondria play a very important role in cellular function, not only through key metabolic reactions and energy generation, but also by being a major site for production of reactive oxygen species and a key player in cell death. Therefore, mitochondrial dysfunction or damage may have severe consequences. Mitophagy (autophagic degradation of mitochondria) and mitoptosis (programmed destruction of mitochondria) are the processes by which cells can deal with impaired mitochondria. The efficiency of these processes may be a contributing factor to the pathogenesis of various diseases.

BAX/BAK-independent mitoptosis during cell death induced by proteasome inhibition?

Proteasome inhibitors induce rapid death of cancer cells. We show that in epithelial cancer cells, such death is associated with dramatic and simultaneous up-regulation of several BH3-only proteins, including BIK, BIM, MCL-1S, NOXA, and PUMA, as well as p53. Elevated levels of these proteins seem to be the result of direct inhibition of their proteasomal degradation, induction of transcription, and active translation. Subsequent cell death is independent of BAX, and probably BAK, and proceeds through the intrinsic mitochondrial apoptosis pathway. We identify the cascade of molecular events responsible for cell death induced by a prototypical proteasome inhibitor, MG132, starting with rapid accumulation of BH3-only proteins in the mitochondria, proceeding through mitochondrial membrane permeabilization and subsequent loss of DeltaPsi(m), and leading to irreversible changes of mitochondrial ultrastructure, degradation of mitochondrial network, and detrimental impairment of crucial mitochondrial functions. Our results also establish a rationale for the broader use of proteasome inhibitors to kill apoptosis-resistant tumor cells that lack functional BAX/BAK proteins.

Mitochondrial matrix fragmentation as a protection mechanism of yeast Saccharomyces cerevisiae

It was shown that separate fragments of the inner mitochondrial compartment (mitoplasts) can exist under a single non-fragmented outer membrane. Here we asked whether fragmentation of the inner mitochondria could prevent rupturing of the outer membrane and release of pro-apoptotic molecules from the mitochondrial intermembrane space into the cytoplasm during mitochondrial swelling. First, we showed that in Saccharomyces cerevisiae yeast addition of amiodarone causes formation of electrically separate compartments within mitochondrial filaments. Moreover, amiodarone treatment of Deltaysp2 mutant produced a higher proportion of cells with electrically discontinuous mitochondria than in the wild type, which correlated with the survival of cells. We confirmed the existence of separated mitoplasts under a single outer membrane using electron microscopy. Mitochondria with fragmented matrixes were also detected in cells of the stationary phase. Our data suggest that such fragmentation acts as a cellular protective mechanism against stress.

Brevinin-2R(1) semi-selectively kills cancer cells by a distinct mechanism, which involves the lysosomal-mitochondrial death pathway

Brevinin-2R is a novel non-hemolytic defensin that was isolated from the skin of the frog Rana ridibunda. It exhibits preferential cytotoxicity towards malignant cells, including Jurkat (T-cell leukemia), BJAB (B-cell lymphoma), HT29/219, SW742 (colon carcinomas), L929 (fibrosarcoma), MCF-7 (breast adenocarcinoma), A549 (lung carcinoma), as compared to primary cells including peripheral blood mononuclear cells (PBMC), T cells and human lung fibroblasts. Jurkat and MCF-7 cells overexpressing Bcl2, and L929 and MCF-7 over-expressing a dominant-negative mutant of a pro-apoptotic BNIP3 (DeltaTM-BNIP3) were largely resistant towards Brevinin-2R treatment. The decrease in mitochondrial membrane potential (DeltaPsim), or total cellular ATP levels, and increased reactive oxygen species (ROS) production, but not caspase activation or the release of apoptosis-inducing factor (AIF) or endonuclease G (Endo G), were early indicators of Brevinin-2R-triggered death. Brevinin-2R interacts with both early and late endosomes. Lysosomal membrane permeabilization inhibitors and inhibitors of cathepsin-B and cathepsin-L prevented Brevinin-2R-induced cell death. Autophagosomes have been detected upon Brevinin-2R treatment. Our results show that Brevinin-2R activates the lysosomalmitochondrial death pathway, and involves autophagy-like cell death.

Brain cathepsin B cleaves a caspase substrate

We show that an enzyme exists in rat brain capable of cleaving the caspase-3 specific peptide substrate Ac-DEVD-AMC at low pH. The enzyme shows properties of a cysteine protease and is localized, predominantly, in lysosomes. We have purified this enzyme from rat brain and identified it by MALDI-TOF MS. The enzyme possessing "acidic" DEVDase activity in rat brain appears to be cathepsin B. It remains obscure, whether cathepsin B participates in cleavage of caspase-3 substrates in vivo. We suggest that under certain conditions (e.g. in hypoxia) cathepsin B participates in cleavage of caspase-3 substrates in brain cells.

Longitudinal increases in mitochondrial DNA levels in blood cells are associated with survival in critically ill patients

Background

Mitochondrial dysfunction may be causally related to the pathogenesis of organ failure in critically ill patients. Decreased mitochondrial DNA (mtDNA) levels have been associated with mitochondrial dysfunction and were investigated here in relation to short-term (31-day) survival.

Methods

This was a prospective longitudinal cohort study of 28 mechanically ventilated critically ill adults admitted to a single center tertiary care intensive care unit (ICU) with hypotension secondary to cardiogenic (N = 13), septic (N = 14) or hypovolemic (N = 1) disease processes. Clinical data and blood were collected at baseline and patients were followed until they expired or left the ICU. Blood was collected every Monday, Wednesday and Friday, and the buffycoat relative mtDNA/nuclear DNA (nDNA) ratio was determined. An archived pool of healthy controls was also studied.

Results

At baseline, the patients' mtDNA/nDNA ratio was 30% lower than a pool of 24 healthy controls (0.76 versus 1.09) and was not different between short-term survivors and non-survivors (0.74 ± 0.05 (N = 16) versus 0.79 ± 0.06 (N = 12), p = 0.49). By day 4, the percent mtDNA/nDNA change from baseline in survivors was significantly different from that in non-survivors (+29.5% versus -5.7%, p = 0.03). It also tended to be higher in survivors at last measurement (+38.4% versus +7.1%, p = 0.06). There was a weak correlation between within patient mtDNA/nDNA and platelet count (r = 0.20, p = 0.03) but not with Sequential Organ Failure Assessment (SOFA) scores (r = 0.12, p = 0.23). The mtDNA associations remained after adjustment for platelet.

Conclusion

Blood mtDNA levels appeared initially low, increased over time in patients who ultimately survived, and remained low in those who did not. This is consistent with mitochondrial recovery being associated with survival and warrants further investigation as a marker of mitochondrial alterations and outcome in critical illness.

Program-like aging and mitochondria: instead of random damage by free radicals

As recently suggested, the target of rapamycin (TOR) pathway, rather than molecular damage by free radicals, drives aging and diseases of aging. But may mitochondria nevertheless contribute to aging? Here, I discuss aimless program-like aging (versus altruistic program), conflict between the cell and mitochondria, cell murder (versus cell suicide) and the role of mitochondria in aging. In particular, life-long selection among mitochondria may yield "selfish" (malignant) mitochondria resistant to autophagy. And TOR may create an intra-cellular environment that is permissive for such selfish mitochondria. In theory, pharmacologic inhibitors of the TOR pathway may reverse accumulation of defective mitochondria, while also inhibiting the aging process.

The hegemony of empiricism: The opportunity for theoretical science in medicine

Partly spurred by the rapid emergence of discovery tools, empirical science founded on experimental validation now dominates academic funding, publishing, and recognition while forums for theoretical science have been marginalized. Although this hegemony of empiricism instills useful discipline to the scientific process, it also limits the pace of science to sensor innovation and renders the ontogeny of scientific knowledge path-dependent, concealing potential discontinuities in intellectual trajectories. Theoretical science, founded on intuition, inspiration, and abstraction, can complement empirical science by creating disruptive paradigms that facilitate detection of spurious results and frame new hypotheses. For example, framing the compendium of human diseases as varying manifestations of buffer dysfunctions - insufficient or maladaptive responses to stress - portends new insights into disease mechanisms and treatments. As a specific incarnation of this theory, the "trauma hypothesis" suggests that the coordinated regulation of inflammation, coagulation, vasoconstriction, and fluid retention that evolved as a prehistoric adaptation to predatory stress and environmental injury conspires in modern times to produce acute coronary syndromes, heart failure, renal dysfunction, stroke, and pulmonary embolism. The theory also exposes the paradigmatic flaw behind the half-century detour perfecting balloon-deployed endovascular interventions. As the basis of buffer acquisition shifts from genetic to cognitive, phenoptosis - the theory that adaptive programmed death of organisms yields opportunity to successors - is rendered maladaptive, as an extended lifespan permits more efficient trait acquisition compared with life-death recycling. While forestalling death is a largely unfruitful medical game of "whack-a-mole" today, the recognition that aging and death may be programmed adaptations suggests they may also be amenable to systemic reprogramming. Epitomizing this opportunity are tumor cells, which reprogram themselves to escape their apoptotic fate and assume indefinite persistence. The prevalence and resilience of these cancer cells, and their ability to withstand the protean assaults of toxins, poisons, radiation, and host defenses, presage the potential robustness of life when appropriately programmed. Paradoxical medicine and dynamic range management may represent initial strategies to reprogram the neuroendocrine stress axes to modulate lifespan at the organism level, and many other strategies are anticipated. The key to theoretical science is original insight, but the prevailing pressure to conform to medicine's educational and practice standards dis-incentivizes independent thinking. A scientific future is envisioned when the commoditization of experimental science will enable its outsourcing, liberating health scientists from the tyranny of empiricism to engage in a more balanced process of discovery infused with theoretical considerations.

Ethanol-induced death in yeast exhibits features of apoptosis mediated by mitochondrial fission pathway

Cell death in yeast (Saccharomyces cerevisiae) involves several apoptotic processes. Here, we report the first evidence of the following processes, which are also characteristic of apoptosis, in ethanol-induced cell death in yeast: chromatin condensation and fragmentation, DNA cleavage, and a requirement for de novo protein synthesis. Mitochondrial fission protein, Fis1, appears to mediate ethanol-induced apoptosis and ethanol-induced mitochondrial fragmentation. However, mitochondrial fragmentation in response to elevated ethanol levels was not correlated with cell death. Further, in the presence of ethanol, generation of reactive oxygen species was elevated in mutant fis1Delta cells. Our characterization of ethanol-induced cell death in yeast as being Fis1-mediated apoptosis is likely to pave the way to overcoming limitations in large-scale fermentation processes, such as those employed in the production of alcoholic beverages and ethanol-based biofuels.

ACTX-8, a cytotoxic l-amino acid oxidase isolated from Agkistrodon acutus snake venom, induces apoptosis in Hela cervical cancer cells

ACTX-8 is a protein isolated from Agkistrodon acutus snake venom in our laboratory. It demonstrates cytotoxic activity on various carcinoma cell lines in vitro. However, the mechanism by which ACTX-8 inhibits cell proliferation remains poorly understood. In this study the influence of ACTX-8 on the activation of apoptotic pathway in Hela cells was investigated. We demonstrated that cell death induced by ACTX-8 was concentration- and time-dependent. Apoptotic changes such as phosphatidyl serine externalization and DNA fragmentation were detected in ACTX-8-treated cells. Caspase activation and reactive oxygen species (ROS) production were involved in ACTX-8-induced apoptosis, but pan caspase inhibitor, z-VAD-fmk, could not inhibit cell death induced by ACTX-8 completely, which proved the existence of another pathway for ACTX-8-induced cell death. We found cytochrome c release into cytosol and mitochondrial membrane potential (MMP) dissipation in ACTX-8-treated cells, which indicated that mitochondrial pathway played a role in ACTX-8-induced cell apoptosis. The ratio of expression levels of pro- and anti-apoptotic Bcl-2 family members was not changed by ACTX-8 treatment. However Bad and Bax were translocated from cytosol into mitochondria, and the coimmunoprecipitation result indicated that in mitochondria Bak and Bcl-xL dissociation was followed by the binding of Bad and Bcl-xL. Taken together, the study indicated mitochondrial pathway played an important role in the ACTX-8-induced apoptosis, which was regulated by Bcl-2 family members.

Stress dysfunctions as a unifying paradigm for illness: repairing relationships instead of individuals as a new gateway for medicine

Stress has been implicated as a risk factor for most diseases, but a mechanistic explanation behind such associations remains elusive. As emergent responses to stress, adaptations range from acute responses where extant system capabilities mitigate current stress, to longer-term responses where system plasticity buffers against future stress. The long compendium of human ailments manifests through a much shorter set of symptoms that may operate through the stress axis. We propose a unifying ontology for human illnesses that classifies stress dysfunctions according to types of Darwinian dysfunction - inadequate response with adequate adaptation, inadequate adaptation, inappropriate adaptation, and epiphenomena of adaptation. Examples include cancer as a bystander effect of increased biologic plasticity in response to stress, and infectious illness as a manifestation of mutually escalating stress in an otherwise commensal relationship between hosts and microbes. We explore the contributing role of man-made stresses that have emerged as humans increasingly remodel their environment. Examples include biologic decompensation associated with reliance on technology to buffer stress, and behavioral stress caused by the dislocation of kin networks that promotes illegitimate signaling. Dysfunctional relationships engender stress not only among humans, but also among individual organs; heart failure, renal failure, and carotid stenosis may represent examples of such conditions. If stress dysfunction is the Occam's razor of human illnesses, and derangements in biologic relationships induce stress dysfunctions, then the study of relationships - an incarnation of systems biology - may represent a new gateway for medicine.

Cellular search migrations in normal development and carcinogenesis

This review describes the large group of morphogenetic processes designated as search migrations. Search migrations typically include two stages: i) search, when a group of cells or of the cytoplasmic processes migrate over the cell-free spaces, and ii) choice, the stage when migrating cells reach specific loci where they stop and undergo specific differentiations induced by local factors such as cell-cell contacts and humoral agents. Migrating cells that do not meet their targets usually undergo apoptosis. Numerous examples of search migrations range from gastrulation to formation of axon-muscle connections. Critical stages of carcinogenesis such as acquisition of cell ability for invasion may be regarded as the genetic aberration of normal search migration: cancer cells perform an endless search but cannot make final choice.

Bax/Bak-dependent release of DDP/TIMM8a promotes Drp1-mediated mitochondrial fission and mitoptosis during programmed cell death

Mitochondrial morphology within cells is controlled by precisely regulated rates of fusion and fission . During programmed cell death (PCD), mitochondria undergo extensive fragmentation and ultimately caspase-independent elimination through a process known as mitoptosis . Though this increased fragmentation is due to increased fission through the recruitment of the dynamin-like GTPase Drp1 to mitochondria , as well as to a block in mitochondrial fusion , cellular mechanisms underlying these processes remain unclear. Here, we describe a mechanism for the increased mitochondrial Drp1 levels and subsequent stimulation of mitochondrial fission seen during PCD. We observed Bax/Bak-mediated release of DDP/TIMM8a, a mitochondrial intermembrane space (IMS) protein , into the cytoplasm, where it binds to and promotes the mitochondrial redistribution of Drp1, a mediator of mitochondrial fission. Using both loss- and gain-of-function assays, we also demonstrate that the Drp1- and DDP/TIMM8a-dependent mitochondrial fragmentation observed during PCD is an important step in mitoptosis, which in turn is involved in caspase-independent cell death. Thus, following Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP), IMS proteins released comprise not only apoptogenic factors such as cytochrome c involved in caspase activation but also DDP/TIMM8a, which activates Drp1-mediated fission to promote mitochondrial fragmentation and subsequently elimination during PCD.

Bioenergetic aspects of apoptosis, necrosis and mitoptosis

In this review I summarize interrelations between bioenergetic processes and such programmed death phenomena as cell suicide (apoptosis and necrosis) and mitochondrial suicide (mitoptosis). The following conclusions are made. (I) ATP and rather often mitochondrial hyperpolarization (i.e. an increase in membrane potential, delta psi) are required for certain steps of apoptosis and necrosis. (II) Apoptosis, even if it is accompanied by delta psi and [ATP] increases at its early stage, finally results in a delta psi collapse and ATP decrease. (III) Moderate (about three-fold) lowering of [ATP] for short and long periods of time induces apoptosis and necrosis, respectively. In some types of apoptosis and necrosis, the cell death is mediated by a delta psi-dependent overproduction of ROS by the initial (Complex I) and the middle (Complex III) spans of the respiratory chain. ROS initiate mitoptosis which is postulated to rid the intracellular population of mitochondria from those that are ROS overproducing. Massive mitoptosis can result in cell death due to release to cytosol of the cell death proteins normally hidden in the mitochondrial intermembrane space.

N/A

N/A

Involvement of calcium-mediated apoptotic signals in H2O2-induced MIN6N8a cell death

Reactive oxygen species are believed to be the central mediators of beta-cell destruction that leads to type 1 and 2 diabetes, and calcium has been reported to be an important mediator of beta cell death. In the present study, the authors investigated whether Ca(2+) plays a role in hydrogen peroxide (H(2)O(2))-induced MIN6N8a mouse beta cell death. Treatment with low concentration H(2)O(2) (50 microM) was found to be sufficient to reduce MIN6N8a cell viability by 55%, largely via apoptosis. However, this H(2)O(2)-induced cell death was near completely blocked by pretreatment with BAPTA/AM (5 microM), a chelator of intracellular Ca(2+). Moreover, the intracellular calcium store channel blockers, such as, xestospongin c and ryanodine, significant protected cells from 50 microM H(2)O(2)-induced cell death and under extracellular Ca(2+)-free conditions, 50 microM H(2)O(2) elicited transient [Ca(2+)](i) increases. In addition, pharmacologic inhibitors of calpain, calcineurin, and calcium/calmodulin-dependent protein kinase II were found to have a protective effect on H(2)O(2)-induced death. Moreover, H(2)O(2)-induced apoptotic signals, such as c-JUN N-terminal kinase activation, cytochrome c release, caspase 3 activation, and poly (ADP-ribose) polymerase cleavage were all down-regulated by the intracellular Ca(2+) chelation. These findings show that [Ca(2+)](i) elevation, possibly due to release from intracellular calcium stores and the subsequent activation of Ca(2+)-mediated apoptotic signals, critically mediates low concentration H(2)O(2)-induced MIN6N8a cell death. These findings suggest that a breakdown of calcium homeostasis by low level of reactive oxygen species may be involved in beta cell destruction during diabetes development.

What good is growing old?

Defying evolutionary orthodoxy that aging is a disorderly collapse, some researchers argue that the process is an adaptation. Many of these scientists posit that group selection, a controversial form of natural selection in which the group's interests take precedence over those of the individual, drives the evolution of aging. To support their contention that senescence is genetically programmed, the researchers list evidence such as the existence of mutant organisms that live longer than normal, which suggests that unaltered creatures are "voluntarily" dying. Most evolutionists scoff at programmed aging and group selection, which conflict with the prevailing view that natural selection favors traits that benefit individuals over groups. Other scientists are probing whether aging helps reduce competition between relatives, a less controversial alternative to group selection.

Effect of oxidative stress on dynamics of mitochondrial reticulum

Fission of the mitochondrial reticulum (the thread-grain transition) and following gathering of mitochondria in the perinuclear area are induced by oxidative stress. It is shown that inhibitors of the respiratory chain (piericidin and myxothiazol) cause fission of mitochondria in HeLa cells and fibroblasts, whereas a mitochondria-targeted antioxidant (MitoQ) inhibits this effect. Hydrogen peroxide also induced the fission, which was stimulated by the inhibitors of respiration and suppressed by MitoQ. In untreated cells, the mitochondrial reticulum consisted of numerous electrically-independent fragments. Prolonged treatment with MitoQ resulted in drastic increase in size and decrease in number of these fragments. Local photodamage of mitochondria caused immediate depolarization of a large fraction of the mitochondrial network in MitoQ-treated cells. Our data indicate that the thread-grain transition of mitochondria depends on production of reactive oxygen species (ROS) in initial segments of the respiratory chain and is a necessary step in the process of elimination of mitochondria (mitoptosis).

Mitochondrial fission and apoptosis: an ongoing trial

Apoptosis is a form of programmed cell death that is essential for the development and tissue homeostasis in all metazoan animals. Mitochondria play a critical role during apoptosis, since the release of pro-apoptogenic proteins from the organelle is a pivotal event in cell death triggered by many cytotoxic stimuli. A striking morphological change occurring during apoptosis is the disintegration of the semi-reticular mitochondrial network into small punctiform organelles. It is only recently that this event has been shown to require the activity of proteins involved in the physiological processes of mitochondrial fission and fusion. Here, we discuss how this mitochondrial morphological transition occurs during cell death and the role that it may have in apoptosis.

Osteoarthritis: an example of phenoptosis through autonomic dysfunction?

Phenoptosis, the programmed death of organisms akin to cellular apoptosis, constitutes a type of Darwinian selection that enhances inclusive fitness. It provides a means by which senescent and pre-senescent members can self-terminate if they have incurred sufficient cumulative stress such that their continued survival detracts from inclusive fitness. Sepsis, vascular disease, menopause, cancer, and aging all represent examples of phenoptosis at work. We previously proposed that feed-forward autonomic dysfunction fundamentally drives phenoptosis in all its guises. Accordingly, we now postulate that osteoarthritis defines a type of biomechanical phenoptosis, mediated by feed-forward autonomic dysfunction, and manifested through joint destruction associated with fitness disadvantages. Biomechanical capability plays a significant role in evolutionary fitness, and sustained joint insults such as immobility or undue biomechanical stress may serve as proxies for inferior fitness. By both hindering an individual's ability to compete for energy and increasing that individual's vulnerability to predation, feed-forward joint destruction may facilitate adaptive phenoptosis among impaired or senile members. Empirical data suggests that contrary to common belief, heavy joint use does not necessarily cause osteoarthritis, whereas immobility and neuropathy can predispose to the condition. From a Darwinian perspective, another process mediated by sympathetic activity, the alarm cry of attacked prey, simultaneously promotes the escape of kin while attracting predators and scavengers. By effectively enabling the martyrdom of biomechanically-challenged individuals, osteoarthritis may serve to optimize system energy efficiency in a similar fashion. This framework may generalize to other situations where regenerative capacity dissipates in conjunction with maturation, typically leading to fibrosis. By allowing environmental pressure to sort the phenotypes, imperfect repair mechanisms may accelerate adaptation and optimize long-term inclusive fitness for all individuals. As the basis of competition shifts from biomechanical to cognitive skills, and as novel triggers for physical stress emerge, osteoarthritis may now represent a modern maladaptation.

Spend less, live longer. The "thrifty aged" hypothesis

Evolutionary biology has rejected any argument in favour of planned ageing. In this article, the metabolic changes that follow in ageing have been analysed, and in accordance with that, an evolutionary explanation for the senescence program has been proposed. Ageing is characterised by a set of metabolic features all of them designed to reduce energy expenditure and to promote energy storage. Otherwise, the undoubted beneficial effect to fitness that means to live longer could generate a conflict between parents and offspring for energy resources. The solution to that conflict is an adult economical individual, a "thrifty aged". The way to obtain this cheaper individual is through the genetically induced physiological changes that finally lead the process. In conclusion, it is proposed that ageing is the condition, imposed by natural selection, that let organisms to outlast the obligatory reproductive time.

Cancer as a programmed death of an organism

The hypothesis introduces the idea that there is a critical level of mutagenesis that triggers a program of organism death by means of proliferation of killer cells. Similarly to apoptosis, which is an altruistic suicidal act of a faulty cell threatening the stability of a multicellular organism, a malignant tumor is an altruistic suicide of an individual carrier of harmful alleles threatening genetic stability of the population.

A paradigm for viewing biologic systems as scale-free networks based on energy efficiency: Implications for present therapies and the future of evolution

A network constitutes an abstract description of the relationships among entities, respectively termed links and nodes. If a power law describes the probability distribution of the number of links per node, the network is said to be scale-free. Scale-free networks feature link clustering around certain hubs based on preferential attachments that emerge due either to merit or legacy. Biologic systems ranging from sub-atomic to ecosystems represent scale-free networks in which energy efficiency forms the basis of preferential attachments. This paradigm engenders a novel scale-free network theory of evolution based on energy efficiency. As environmental flux induces fitness dislocations and compels a new meritocracy, new merit-based hubs emerge, previously merit-based hubs become legacy hubs, and network recalibration occurs to achieve system optimization. To date, Darwinian evolution, characterized by innovation sampling, variation, and selection through filtered termination, has enabled biologic progress through optimization of energy efficiency. However, as humans remodel their environment, increasing the level of unanticipated fitness dislocations and inducing evolutionary stress, the tendency of networks to exhibit inertia and retain legacy hubs engender maladaptations. Many modern diseases may fundamentally derive from these evolutionary displacements. Death itself may constitute a programmed adaptation, terminating individuals who represent legacy hubs and recalibrating the network. As memes replace genes as the basis of innovation, death itself has become a legacy hub. Post-Darwinian evolution may favor indefinite persistence to optimize energy efficiency. We describe strategies to reprogram or decommission legacy hubs that participate in human disease and death.

Inhibition of extracellular signal regulated kinase (ERK) leads to apoptosis inducing factor (AIF) mediated apoptosis in epithelial breast cancer cells: the lack of effect of ERK in p53 mediated copper induced apoptosis

Recent studies have shown that MEK/ERK-mediated signals play a major role in regulation of activity of p53 tumor suppressor protein. In this study, we investigated whether or not there is functional interaction between p53 and MEK/ERK pathways in epithelial breast cancer cells exposed to copper or zinc. We demonstrated that expression of wild-type p53 induced by copper or zinc significantly reduced phosphorylation of extracellular signal regulated kinase (ERK) in epithelial breast cancer MCF7 cells. Mutation or suppression of p53 in MDA-MB231 and MCF7-E6 cells, respectively, resulted in a strong ERK phosphorylation in the presence of metals. Weak ERK phosphorylation in MCF7 cells induced by copper or zinc was linked to mitochondrial disruption and apoptosis. Furthermore, inhibition of ERK through addition of PD98059 stimulated p53 activation in MCF7 cells and also led to upregulation of p53 downstream targets, p21 and Bax, which is a proapototic member of Bcl-2 family triggering mitochondrial pore opening. Moreover, blockage of the MEK/ERK pathway caused a breakdown of the mitochondrial membrane potential accompanied by an elevation in the ROS production. Disruption of p53 expression attenuated the depolarization of the mitochondrial membrane and ROS generation. Furthermore, PD98059 initiated apoptosis inducing factor (AIF) translocation from mitochondria to the nucleus in MCF7 cells; which are depleted in caspase 3. Interestingly, repression of MEK/ERK pathway did not intensify the cell stress caused by metal toxicity. Therefore, these findings demonstrate that MEK/ERK pathway plays an important role in downregulation of p53 and cell survival. Inhibition of ERK can lead to apoptosis via nuclear relocation of AIF. However, metal-induced activation of p53 and mitochondrial depolarization appears to be independent of ERK. Our data suggest that copper induces apoptosis through depolarization of mitochondrial membrane with release of AIF, and this process is MEK/ERK independent.

Bud selection and apoptosis-like degradation of nuclei in yeast heterokaryons: a KAR1 effect

It has been shown that defects in cell fusion during mating can trigger programmed cell death in the yeast Saccharomyces cerevisiae. We wished to test whether defects in nuclear migration during cell fusion have the same effect. A partial pedigree analysis of nine kar1 x KAR1 crosses of two different types (four alpha KAR1 x a kar1 and five alpha kar1 x a KAR1 crosses) was carried out, and quantitative estimates of the frequencies of different mother/daughter (m/d) classes were obtained. The kar1 mutation affects nuclear congression and delays nuclear fusion. In each cross tested, the nucleus that entered the first bud tended to be the one contributed by the cell that carried the wild-type allele of KAR1. If budding was delayed by nutrient limitation, the kar1 nucleus could be rescued, indicating that the primary effect of the kar1 mutation is that it slows spindle action. Many m/d classes appear as a result of the degradation of one of the nuclei in the heterokaryon. Loss of nuclei in heterokaryons was accompanied by an accumulation of reactive oxygen species (ROS), and by abnormalities in nuclear structure revealed by TUNEL (terminal transferase-mediated dUTP nick end-labeling) analysis, DAPI staining and by histone-GFP fluorescence patterns which suggested an apoptosis-like process. Often only one nucleus was degraded, and ROS accumulation was restricted to one half of the zygote. We therefore suggest that the data obtained can be explained by apoptosis-like death of a half-cell (cell body).

Molecular pathology of aging and its implications for senescent coronary atherosclerosis

PURPOSE OF REVIEW

This review highlights common mechanisms of organismal aging and inflammatory coronary atherosclerosis.

RECENT FINDINGS

A substantial body of evidence now indicates that aging is largely due to molecular damage inflicted by reactive oxygen species, electrophiles, and other reactive endobiotic and xenobiotic metabolites. Our understanding of genetic pathways regulating longevity began 12 years ago with the discovery that a developmental-arrest program in the nematode Caenorhabditis elegans also has marked effects on adult lifespan. This pathway, closely related to the insulin and insulinlike growth factor-signaling pathways of mammals, modulates longevity and stress resistance in several model organisms. Insulin-like signaling also has an impact on redox signaling, antioxidant defenses, and metabolic generation of oxidative stress. Recently, additional signaling pathways--involving Sirtuins, AMP kinase, Jun N-terminal kinase 1, and other master regulatory proteins--have been implicated in longevity and stress-resistance mechanisms. The inflammatory process involves acute production of reactive oxygen species by specialized cells responding to infection, exposure to toxins or allergens, cell damage, hypoxia, ischemia/reperfusion, and other factors, initiating signaling through several of these pathways. Free radical chain reactions arise from lipid oxidation and generate oxidized low-density lipoprotein, a powerful inflammatory signal and potentiator of atherosclerosis. Oxidized low-density lipoprotein accumulates in atherosclerotic arteries, particularly in rupture-prone regions. Inflammation involving oxidative stress, by way of the production of reactive oxygen species, is a hallmark of coronary atherosclerosis.

SUMMARY

Common pathways underlie both organismal aging and tissue-autonomous senescent pathologic processes, such as coronary atherosclerosis. The mechanisms discovered in model organisms may lead to pharmacotherapeutic interventions.

SLE—a disease of clearance deficiency?

Systemic lupus erythematosus (SLE) is a multifactorial disease and its pathogenesis and precise aetiology remain unknown. Under physiological conditions, neither apoptotic nor necrotic cell material is easily found in tissues because of its quick removal by a highly efficient scavenger system. Autoantigens are found in apoptotic and necrotic material and they are recognized by autoimmune sera from SLE patients. The clearance of dying cells is finely regulated by a highly redundant system of receptors on phagocytic cells and bridging molecules, which detect molecules specific for dying cells. Changes on apoptotic and necrotic cell surfaces are extremely important for their recognition and further disposal. Some SLE patients seem to have an impaired ability to clear such apoptotic material from tissues, and this could cause the breakdown of central and peripheral mechanisms of tolerance against self-antigens. In this article, we address the cells, receptors and molecules involved in the clearance process and show how deficiencies in this process may contribute to the aetiopathogenesis of SLE.

The role of the mitochondrion in trauma and shock

The mitochondrion of the eukaryotic cell is well known as a "power plant" whose energy is made available via the high-energy phosphate bonds of ATP. This indispensable and superbly adapted organelle appears to have originated as an endosymbiotic bacterium rather than as a eukaryotic creation per se. However, under the dangerous conditions of trauma and shock, the mitochondrion can become destabilized and harm its host cell in a variety of ways. These contrary traits may be, in part, vestiges from the bacterial origins of mitochondria. The mitochondrion can respond to the stress of trauma and shock by opening pores that leak contents into the host cell's cytoplasm, an event that can trigger programmed cell death or necrosis. In addition, the enormous oxygen consumption by mitochondria presents a two-edged sword in that a deranged mitochondrion can produce reactive oxygen species that damage genes and gene products, inflicting considerable harm to the mitochondrion and its host cell. However, although trauma and shock can cause the mitochondrion to wreak havoc in many ways, an adjuvant intervention with exogenous ATP-MgCl2 after trauma and shock appears useful for reducing cell and organ damage under those conditions.

Defects in the disposal of dying cells lead to autoimmunity

The fast and efficient uptake of dying cells is of main importance to prevent contact of the immune system with intracellular autoantigens. Insufficient clearance of the latter is discussed to drive the humoral autoimmune response in systemic lupus erythematosus. Many adaptor molecules and receptors are involved in the recognition of dying cells. In this paper we focus on the involvement of phosphatidylserine, glycoproteins, and complement and DNaseI in the clearance of apoptotic and necrotic cells, respectively. Furthermore, extracellular danger signals released from necrotic cells are discussed and the uptake process of primary necrotic cells is investigated in detail. Last but not least, the character and origin of clearance defects observed in some systemic lupus erythematosus patients is presented.

On evolutionary origin of cancer

BACKGROUND: The necessary and sufficient capabilities of cancer cell have been identified. Strikingly, this list does not include one that would seem to be a key property, namely the ability of cancer cells to kill their "host". This is believed to be a self-evident consequence of the other capabilities (e.g., metastasis), although the available evidence suggests a distinct killer function. Taking into account this unlisted property can significantly affect the current paradigm of carcinogenesis. PRESENTATION OF THE HYPOTHESIS: On the assumption that killer function is a key capability of the cancer cell, it is suggested that cancer has evolved as a mechanism of negative selection of mutant alleles of vitally important genes present in population. Similarly to apoptosis, which is an altruistic suicidal act of a damaged cell, cancer is an altruistic suicidal act of an individual who carries dangerous alleles and presents a hazard for genetic stability of the population. From this point of view, apoptosis is not a protection means against cancer as generally believed, but rather they are the first and second lines of defense against genome instability, respectively. TESTING THE HYPOTHESIS: The modern DNA array technology is capable of revealing gene expression profiles responsible for killer function of cancer cell as well as those specific targets in the body that are most strongly affected by the tumor growth. IMPLICATIONS OF THE HYPOTHESIS: This hypothesis suggests new avenues of cancer research as well as principally new therapeutic strategies.

Downregulation of the human Lon protease impairs mitochondrial structure and function and causes cell death

Lon now emerges as a major regulator of multiple mitochondrial functions in human beings. Lon catalyzes the degradation of oxidatively modified matrix proteins, chaperones the assembly of inner membrane complexes, and participates in the regulation of mitochondrial gene expression and genome integrity. An early result of Lon downregulation in WI-38 VA-13 human lung fibroblasts is massive caspase 3 activation and extensive (although not universal) apoptotic death. At a later stage, the surviving cells fail to divide, display highly abnormal mitochondrial function and morphology, and rely almost exclusively on anaerobic metabolism. In a selected subpopulation of cells, the mitochondrial mass decreases probably as a result of mitochondrial inability to divide. At this final point the Lon-deficient cells are not engaged anymore in apoptosis, and are lost by necrosis or "mitoptosis." Our results indicate that mitochondrial Lon is required for normal survival and proliferation; a clear impetus for Lon's evolutionary conservation.

Reactive oxygen and nitrogen species: Friends or foes?

Chemical and physiological functions of molecular oxygen and reactive oxygen species (ROS) and existing equilibrium between pools of pro-oxidants and anti-oxidants providing steady state ROS level vital for normal mitochondrial and cell functioning are reviewed. The presence of intracellular oxygen and ROS sensors is postulated and few candidates for this role are suggested. Possible involvement of ROS in the process of fragmentation of mitochondrial reticulum made of long mitochondrial filaments serving in the cell as "electric cables", as well as the role of ROS in apoptosis and programmed mitochondrial destruction (mitoptosis) are reviewed. The critical role of ROS in destructive processes under ischemia/reoxygenation and ischemic preconditioning is discussed. Mitochondrial permeability transition gets special consideration as a possible component of the apoptotic cascade, resulting in excessive "ROS-induced ROS release".

Persister cells and the riddle of biofilm survival

This review addresses a long-standing puzzle in the life and death of bacterial populations--the existence of a small fraction of essentially invulnerable cells. Bacterial populations produce persisters, cells that neither grow nor die in the presence of bactericidal agents, and thus exhibit multidrug tolerance (MDT). The mechanism of MDT and the nature of persisters, which were discovered in 1944, have remained elusive. Our research has shown that persisters are largely responsible for the recalcitrance of infections caused by bacterial biofilms. The majority of infections in the developed world are caused by biofilms, which sparked a renewed interest in persisters. We developed a method to isolate persister cells, and obtained a gene expression profile of Escherichia coli persisters. The profile indicated an elevated expression of toxin-antitoxin modules and other genes that can block important cellular functions such as translation. Bactericidal antibiotics kill cells by corrupting the target function, such as translation. For example, aminoglycosides interrupt translation, producing toxic peptides. Inhibition of translation leads to a shutdown of other cellular functions as well, preventing antibiotics from corrupting their targets, which will give rise to tolerant persister cells. Overproduction of chromosomally-encoded "toxins" such as RelE, an inhibitor of translation, or HipA, causes a sharp increase in persisters. Deletion of the hipBA module produces a sharp decrease in persisters in both stationary and biofilm cells. HipA is thus the first validated persister/MDT gene. We conclude that the function of "toxins" is the exact opposite of the term, namely, to protect the cell from lethal damage. It appears that stochastic fluctuations in the levels of MDT proteins lead to formation of rare persister cells. Persisters are essentially altruistic cells that forfeit propagation in order to ensure survival of kin cells in the presence of lethal factors.

"Wages of fear": transient threefold decrease in intracellular ATP level imposes apoptosis

In HeLa cells, complete inhibition of oxidative phosphorylation by oligomycin, myxothiazol or FCCP combined with partial inhibition of glycolysis by DOG resulted in a steady threefold decrease in the intracellular ATP level. The ATP level recovers when the DOG-containing medium was replaced by that with high glucose. In 48 h after a transient (3 h) [ATP] lowering followed by recovery of the ATP level, the majority of the cells commits suicide by means of apoptosis. The cell death does not occur if DOG or an oxidative phosphorylation inhibitor was added separately, treatments resulting in 10-35% lowering of [ATP]. Apoptosis is accompanied by Bax translocation to mitochondria, cytochrome c release into cytosol, caspase activation, reactive oxygen species (ROS) generation, and reorganization and decomposition of chromatin. Apoptosis appears to be sensitive to oncoprotein Bcl-2 and a pancaspase inhibitor zVADfmk. In the latter case, necrosis is shown to develop instead of apoptosis. The cell suicide is resistant to cyclosporine A, a phospholipase inhibitor trifluoroperazine, the JNK and p38 kinase inhibitors, oligomycin, N-acetyl cysteine and mitoQ, differing in these respects from the tumor necrosis factor (TNF)- and H(2)O(2)-induced apoptoses. It is suggested that the ATP concentration in the cell is monitored by intracellular "ATP-meter(s)" generating a cell suicide signal when ATP decreases, even temporarily, below some critical level (around 1 mM).

Actions of thermal stress in two-cell bovine embryos: oxygen metabolism, glutathione and ATP content, and the time-course of development

The mechanism by which heat shock disrupts development of the two-cell bovine embryo was examined. The reduction in the proportion of embryos that became blastocysts caused by heat shock was not exacerbated when embryos were cultured in air (20.95% O(2)) as compared with 5% O(2). In addition, heat shock did not reduce embryonic content of glutathione, cause a significant alteration in oxygen consumption, or change embryonic ATP content. When embryos were heat-shocked at the two-cell stage and allowed to continue development until 72 h post insemination, heat-shocked embryos had fewer total nuclei and a higher percentage of them were condensed. Moreover, embryos became blocked in development at the eight-cell stage. The lack of effect of the oxygen environment on the survival of embryos exposed to heat shock, as well as the unchanged content of glutathione, suggest that free radical production is not a major cause for the inhibition in development caused by heat shock at the two-cell stage. In addition, heat shock appears to have no immediate effect on oxidative phosphorylation since no differences in ATP content were observed. Finally, the finding that heat shock causes a block to development at the eight-cell stage implies that previously reported mitochondrial damage caused by heat shock or other heat shock-induced alterations in cellular physiology render the embryo unable to proceed past the eight-cell stage.

Does the glucose-dependent insulin secretion mechanism itself cause oxidative stress in pancreatic beta-cells?

Glucose-dependent insulin secretion (GDIS), reactive oxygen species (ROS) production, and oxidative stress in pancreatic beta-cells may be tightly linked processes. Here we suggest that the same pathways used in the activation of GDIS (increased glycolytic flux, ATP-to-ADP ratio, and intracellular Ca2+ concentration) can dramatically enhance ROS production and manifestations of oxidative stress and, possibly, apoptosis. The increase in ROS production and oxidative stress produced by GDIS activation itself suggests a dual role for metabolic insulin secretagogues, as an initial sharp increase in insulin secretion rate can be accompanied by progressive beta-cell injury. We propose that therapeutic strategies targeting enhancement of GDIS should be carefully considered in light of possible loss of beta-cell function and mass.

Escherichia coli mazEF-mediated cell death is triggered by various stressful conditions

mazEF is an Escherichia coli suicide module specific for a stable toxin and a labile antitoxin. Inhibiting mazEF expression appeared to activate the module to cause cell death. Here we show that several stressful conditions, including high temperatures, DNA damage, and oxidative stress, also induce mazEF-mediated cell death. We also show that this process takes place only during logarithmic growth and requires an intact relA gene.

The Evolution of Programmed Death in a Spatially Structured Population

Recent studies have identified a number of genes that regulate life span. When these genes are inactivated, organisms live longer, but suffer no obvious adverse effects. These results have generated considerable debate, largely because current evolutionary theory is unable to explain them. In this article, I report results from an individual-based spatial model in which a programmed age of death is allowed to evolve. In a freely mixing population with global dispersal, evolution selects for individuals with ever-increasing life span. However, in a spatially structured population with localized dispersal, a programmed age of death evolves. The exact age of death that evolves depends critically on the scale of dispersal. Within this model, individuals are genetically programmed to die, even though they are still able to reproduce. These results suggest that death can be adaptive and offer an explanation for the evolution of "death genes."

Apoptosis in plants: specific features of plant apoptotic cells and effect of various factors and agents

Apoptosis is an integral part of plant ontogenesis; it is controlled by cellular oxidative status, phytohormones, and DNA methylation. In wheat plants apoptosis appears at early stages of development in coleoptile and initial leaf of 5- to 6-day-old seedlings. Distinct ultrastructural features of apoptosis observed are (1). compaction and vacuolization of cytoplasm in the apoptotic cell, (2). specific fragmentation of cytoplasm and appearance in the vacuole of unique single-membrane vesicles containing active organelles, (3). cessation of nuclear DNA synthesis, (4). condensation and margination of chromatin in the nucleus, (5). internucleosomal fragmentation of nuclear DNA, and (6). intensive synthesis of mitochondrial DNA in vacuolar vesicles. Peroxides, abscisic acid, ethylene releaser ethrel, and DNA methylation inhibitor 5-azacytidine induce and stimulate apoptosis. Modulation of the reactive oxygen species (ROS) level in seedling by antioxidants and peroxides results in tissue-specific changes in the target date for the appearance and the intensity of apoptosis. Antioxidant butylated hydroxytoluene (BHT) reduces the amount of ROS and prevents apoptosis in etiolated seedlings, prolongs coleoptile life span, and prevents the appearance of all apoptotic features mentioned. Besides, BHT induces large structural changes in the organization of all cellular organelles and the formation of new unusual membrane structures in the cytoplasm. BHT distorts mitosis and this results in the appearance of multiblade polyploid nuclei and multinuclear cells. In roots of etiolated wheat seedlings, BHT induces differentiation of plastids with the formation of chloro(chromo)plasts. Therefore, ROS controlled by BHT seems to regulate mitosis, trigger apoptosis, and control plastid differentiation and the organization of various cellular structures formed by endocytoplasmic reticulum.