Characterization of the signal that directs Bcl-x(L), but not Bcl-2, to the mitochondrial outer membrane

Serine proteases mediate apoptosis-like cell death and phagocytosis under caspase-inhibiting conditions

Effective execution of apoptosis requires the activation of caspases. However, in many cases, broad-range caspase inhibitors such as Z-VAD.fmk do not inhibit cell death because death signaling continues via basal caspase activities or caspase-independent processes. Although death mediators acting under caspase-inhibiting conditions have been identified, it remains unknown whether they trigger a physiologically relevant cell death that shows typical signs of apoptosis, including phosphatidylserine (PS) exposure and the removal of apoptotic cells by phagocytosis. Here we show that cells treated with ER stress drugs or deprived of IL-3 still show hallmarks of apoptosis such as cell shrinkage, membrane blebbing, mitochondrial release of cytochrome c, PS exposure and phagocytosis in the presence of Z-VAD.fmk. Cotreatment of the stressed cells with Z-VAD.fmk and the serine protease inhibitor Pefabloc (AEBSF) inhibited all these events, indicating that serine proteases mediated the apoptosis-like cell death and phagocytosis under these conditions. The serine proteases were found to act upstream of an increase in mitochondrial membrane permeability as opposed to the serine protease Omi/HtrA2 which is released from mitochondria at a later stage. Thus, despite caspase inhibition or basal caspase activities, cells can still be phagocytosed and killed in an apoptosis-like fashion by a serine protease-mediated mechanism that damages the mitochondrial membrane.

Constitutive association of the proapoptotic protein Bim with Bcl-2-related proteins on mitochondria in T cells

Apoptosis in activated T cells in vivo requires the proapoptotic Bcl-2 family member Bim. We show here that, despite its ability to bind LC8, a component of the microtubule dynein motor complex, most of the Bim in both healthy and apoptotic T cells is associated with mitochondria, not microtubules. In healthy resting T cells Bim is bound to the antiapoptotic proteins Bcl-2 and Bcl-x(L). In activated T cells, levels of Bcl-2 fall, and Bim is associated more with Bcl-x(L) and less with Bcl-2. Our results indicate that, in T cells, Bim function is regulated by interaction with Bcl-2 family members on mitochondria rather than by sequestration to the microtubules.

Bcl-x(L) sequesters its C-terminal membrane anchor in soluble, cytosolic homodimers

Bcl-x(L) is a potent inhibitor of apoptosis. While Bcl-x(L) can be bound to mitochondria, a substantial fraction, depending on the cell type or tissue, is found in the cytosol of healthy cells. Gel filtration and crosslinking experiments reveal that, unlike monomeric Bax, Bcl-x(L) migrates in a complex of approximately 50 kDa in the cytosol. Co-immunoprecipitation experiments indicate that Bcl-x(L) in the cytosol forms homodimers. The C-terminal hydrophobic tails of two Bcl-x(L) molecules are involved in homodimer formation, and analysis of mutants demonstrates that the C-terminal lysine residue and the G138 residue lining the BH3-binding pocket are required for homodimerization. The flexible loop preceding the C-terminal tail in Bcl-x(L) is longer than that of several monomeric Bcl-2 family members and is a requisite for the homodimer formation. Bad binding to Bcl-x(L) dissociates the homodimers and triggers Bcl-x(L) binding to mitochondrial membranes. The C-terminal tail of Bcl-x(L) is also required to mediate Bcl-x(L)/Bax heterodimer formation. Both mitochondrial import and antiapoptotic activity of different Bcl-x(L) mutants correlate with their ability to form homodimers.

Bcl-2 and calcium: controversy beneath the surface

The function of Bcl-2 family members on the endoplasmic reticulum has received increasing attention in recent years. The endoplasmic reticulum is the major organelle involved in intracellular calcium homeostasis and calcium signaling, including calcium signals that mediate apoptosis induction by anticancer drugs. But currently a controversy exists regarding reported effects of Bcl-2 on the calcium concentration within the lumen of the endoplasmic reticulum. Although several prominent reports indicate that Bcl-2 overexpression is associated with a decrease in luminal calcium, there are a large number of reports indicating that Bcl-2 either does not decrease luminal calcium or actually increases luminal calcium. This review summarizes this vast array of conflicting findings, and analyses potential reasons why different conclusions have been reached by different laboratories. Future directions are emphasized that might bring clarity to this important area of apoptosis biology.

Bcl-2 family members: integrators of survival and death signals in physiology and pathology [corrected]

The members of the Bcl-2 family of proteins are crucial regulators of apoptosis. In order to determine cell fate, these proteins must be targeted to distinct intracellular membranes, including the mitochondrial outer membrane (MOM), the membrane of the endoplasmic reticulum (ER) and its associated nuclear envelope. The targeting sequences and mechanisms that mediate the specificity of these proteins for a particular cellular membrane remain poorly defined. Several Bcl-2 family members have been reported to be tail-anchored via their predicted hydrophobic COOH-terminal transmembrane domains (TMDs). Tail-anchoring imposes a posttranslational mechanism of membrane insertion on the already folded protein, suggesting that the transient binding of cytosolic chaperone proteins to the hydrophobic TMD may be an important regulatory event in the targeting process. The TMD of certain family members is initially concealed and only becomes available for targeting and membrane insertion in response to apoptotic stimuli. These proteins either undergo a conformational change, posttranslational modification or a combination of these events enabling them to translocate to sites at which they are functional. Some Bcl-2 family members lack a TMD, but nevertheless localize to the MOM or the ER membrane during apoptosis where they execute their functions. In this review, we will focus on the intracellular targeting of Bcl-2 family members and the mechanisms by which they translocate to their sites of action. Furthermore, we will discuss the posttranslational modifications which regulate these events.

Conformational control of Bax localization and apoptotic activity by Pro168

In healthy cells, Bax resides inactive in the cytosol because its COOH-terminal transmembrane region (TMB) is tucked into a hydrophobic pocket. During apoptosis, Bax undergoes a conformational change involving NH₂-terminal exposure and translocates to mitochondria to release apoptogenic factors. How this process is regulated remains unknown. We show that the TMB of Bax is both necessary and sufficient for mitochondrial targeting. However, its availability for targeting depends on Pro168 located within the preceding loop region. Pro168 mutants of Bax lack apoptotic activity, cannot rescue the apoptosis-resistant phenotype of Bax/Bak double knockout cells, and are retained in the cytosol even in response to apoptotic stimuli. Moreover, the mutants have their NH₂ termini exposed. We propose that Pro168 links the NH₂ and the COOH terminus of Bax and is required for COOH-terminal release and mitochondrial targeting once this link is broken.

Green fluorescent protein causes mitochondria to aggregate in the presence of the Bcl-2 family proteins

Green fluorescent protein (GFP) has been widely used in a variety of experiments in cell biology. When cells were co-transfected with the GFP gene and the bcl-2 family genes bcl-2, bcl-x(L), and bax, mitochondria appeared to aggregate at the periphery of the nucleus specifically where GFP was expressed. Little aggregation was seen in the presence of other members of the GFP family, EGFP (enhanced GFP), ECFP (enhanced cyan variant), and EYFP (enhanced yellow-green variant). GFP but not EGFP seemed to promote cell death induced by pro-apoptotic Bax. Thus, GFP specifically promotes the aggregation of mitochondria when co-expressed with a member of the Bcl-2 family in association with apoptosis.

Apoptosis in cancer--implications for therapy

Resistance towards apoptosis is a key factor for the survival of a malignant cell. Cancer results if there is too little apoptosis and cells grow faster and live longer than normal cells. In addition, defects in apoptosis signaling contribute to drug resistance of tumor cells. Thus, one of the main goals for oncologic treatment is to overcome resistance of tumor cells towards apoptosis. The exciting challenge in oncology is to translate the growing knowledge of apoptotic pathways into clinical applications. In this review we address the role of apoptosis signaling in tumorigenesis and drug resistance of tumor cells and discuss therapeutic approaches interfering with apoptosis pathways.

Levels of human Fis1 at the mitochondrial outer membrane regulate mitochondrial morphology

Mitochondria undergo balanced fission and fusion events that enable their appropriate networking within the cell. In yeast, three factors have been identified that co-ordinate fission events at the mitochondrial outer membrane. Fis1p acts as the outer membrane receptor for recruitment of the dynamin member, Dnm1p and the WD40-repeat-containing protein Mdv1p. In mammals, the Dnm1p counterpart Drp1 has been characterized, but other components have not. Here, we report the characterization of human Fis1 (hFis1). hFis1 is inserted into the mitochondrial outer membrane via a C-terminal transmembrane domain that, along with a short basic segment, is essential for its targeting. Although expression of hFis1 does not complement the phenotype of yeast cells lacking Fis1p, overexpression of hFis1 in tissue culture cells nevertheless causes mitochondrial fragmentation and aggregation. This aggregation could be suppressed by expressing a dominant-negative Drp1 mutant (Drp1K38A). Knockdown of hFis1 in COS-7 cells using RNA interference results in mitochondrial morphology defects with notable extensions in the length of mitochondrial tubules. These results indicate that the levels of hFis1 at the mitochondrial surface influences mitochondrial fission events and hence overall mitochondrial morphology within the cell.

Bcl-w(edding) with mitochondria

Bcl-2-family members (Bcl-2, Bax, Bcl-w and Bcl-x(L)) are crucial integrators of signals for cell survival and death; the pro- or antiapoptotic activities of these proteins are regulated by their subcellular localization. Bcl-2 directly inserts into the membranes, where it acts; however, Bax requires a stimulus-dependent translocation from an inactive cytosolic to an active membrane-inserted state. Recently, a novel mechanism is described for the survival factor Bcl-w, which is active while weakly associated with mitochondria. In apoptotic cells, a BH3-only protein neutralizes the survival activity of Bcl-w by binding to its "hydrophobic pockets", thereby releasing its C-terminal domain and allowing its insertion into the membrane. Here, we discuss the importance of this finding for a better understanding of the action mode of Bcl-w and other Bcl-2-family members.

The Bcl-2 family: roles in cell survival and oncogenesis

Apoptosis, the cell-suicide programme executed by caspases, is critical for maintaining tissue homeostasis, and impaired apoptosis is now recognized to be a key step in tumorigenesis. Whether a cell should live or die is largely determined by the Bcl-2 family of anti- and proapoptotic regulators. These proteins respond to cues from various forms of intracellular stress, such as DNA damage or cytokine deprivation, and interact with opposing family members to determine whether or not the caspase proteolytic cascade should be unleashed. This review summarizes current views of how these proteins sense stress, interact with their relatives, perturb organelles such as the mitochondrion and endoplasmic reticulum and govern pathways to caspase activation. It briefly explores how family members influence cell-cycle entry and outlines the evidence for their involvement in tumour development, both as oncoproteins and tumour suppressors. Finally, it discusses the promise of novel anticancer therapeutics that target these vital regulators.

Bcl-2 on the endoplasmic reticulum: protecting the mitochondria from a distance

Bcl-2 has been described both as an inhibitor of programmed cell death and as an inhibitor of mitochondrial dysfunction during apoptosis. It is still not clear what biochemical activity of Bcl-2 is responsible for its function, but increasing evidence indicates that a functional activity of Bcl-2 on the endoplasmic reticulum (ER) protects mitochondria under diverse circumstances. Indeed, an emerging hypothesis is that, during apoptosis, the Bcl-2 family regulates ER-to-mitochondrion communication by BH3-only proteins and calcium ions and thereby triggers mitochondrial dysfunction and cell death.

A GH3-like domain in reaper is required for mitochondrial localization and induction of IAP degradation

Reaper is a potent pro-apoptotic protein originally identified in a screen for Drosophila mutants defective in apoptotic induction. Multiple functions have been ascribed to this protein, including inhibition of IAPs (inhibitors of apoptosis); induction of IAP degradation; inhibition of protein translation; and when expressed in vertebrate cells, induction of mitochondrial cytochrome c release. Structure/function analysis of Reaper has identified an extreme N-terminal motif that appears to be sufficient for inhibition of IAP function. We report here that this domain, although required for IAP destabilization, is not sufficient. Moreover, we have identified a small region of Reaper, similar to the GH3 domain of Grim, that is required for localization of Reaper to mitochondria, induction of IAP degradation, and potent cell killing. Although a mutant Reaper protein lacking the GH3 domain was deficient in these properties, these defects could be fully rectified by appending either the C-terminal mitochondrial targeting sequence from Bcl-xL or a homologous region from the pro-apoptotic protein HID. Together, these data strongly suggest that IAP destabilization by Reaper in intact cells requires Reaper localization to mitochondria and that induction of IAP instability by Reaper is important for the potent induction of apoptosis in Drosophila cells.

The Solution Structure of Human Mitochondria Fission Protein Fis1 Reveals a Novel TPR-like Helix Bundle

Fis1 in yeast localizes to the outer mitochondrial membrane and facilitates mitochondrial fission by forming protein complexes with Dnm1 and Mdv1. Fis1 orthologs exist in higher eukaryotes, suggesting that they are functionally conserved. In the present study, we cloned the human Fis1 ortholog that was predicted in a database, and determined the protein structure using NMR spectroscopy. Following a flexible N-terminal tail, six alpha-helices connected with short loops construct a single core domain. The C-terminal tail containing a transmembrane segment appears to be disordered. In the core domain, each of two sequentially adjacent helices forms a hairpin-like conformation, resulting in a six helix assembly forming a slightly twisted slab similar to that of a tandem array of tetratrico-peptide repeat (TPR) motif folds. Within this TPR-like core domain, no significant sequence similarity to the typical TPR motif is found. The structural analogy to the TPR-containing proteins suggests that Fis1 binds to other proteins at its concave hydrophobic surface. A simple composition of Fis1 comprised of a binding domain and a transmembrane segment indicates that the protein may function as a molecular adaptor on the mitochondrial outer membrane. In HeLa cells, however, increased levels in mitochondria-associated Fis1 did not result in mitochondrial translocation of Drp1, a potential binding partner of Fis1 implicated in the regulation of mitochondrial fission, suggesting that the interaction between Drp1 and Fis1 is regulated.

Modulation of synaptic transmission by the BCL-2 family protein BCL-xL

BCL-2 family proteins are known to regulate cell death during development by influencing the permeability of mitochondrial membranes. The anti-apoptotic BCL-2 family protein BCL-xL is highly expressed in the adult brain and localizes to mitochondria in the presynaptic terminal of the adult squid stellate ganglion. Application of recombinant BCL-xL through a patch pipette to mitochondria inside the giant presynaptic terminal triggered multiconductance channel activity in mitochondrial membranes. Furthermore, injection of full-length BCL-xL protein into the presynaptic terminal enhanced postsynaptic responses and enhanced the rate of recovery from synaptic depression, whereas a recombinant pro-apoptotic cleavage product of BCL-xL attenuated postsynaptic responses. The effect of BCL-xL on synaptic responses persisted in the presence of a blocker of mitochondrial calcium uptake and was mimicked by injection of ATP into the terminal. These studies indicate that the permeability of outer mitochondrial membranes influences synaptic transmission, and they raise the possibility that modulation of mitochondrial conductance by BCL-2 family proteins affects synaptic stability.

Modulation of synaptic transmission by the BCL-2 family protein BCL-xL

BCL-2 family proteins are known to regulate cell death during development by influencing the permeability of mitochondrial membranes. The anti-apoptotic BCL-2 family protein BCL-xL is highly expressed in the adult brain and localizes to mitochondria in the presynaptic terminal of the adult squid stellate ganglion. Application of recombinant BCL-xL through a patch pipette to mitochondria inside the giant presynaptic terminal triggered multiconductance channel activity in mitochondrial membranes. Furthermore, injection of full-length BCL-xL protein into the presynaptic terminal enhanced postsynaptic responses and enhanced the rate of recovery from synaptic depression, whereas a recombinant pro-apoptotic cleavage product of BCL-xL attenuated postsynaptic responses. The effect of BCL-xL on synaptic responses persisted in the presence of a blocker of mitochondrial calcium uptake and was mimicked by injection of ATP into the terminal. These studies indicate that the permeability of outer mitochondrial membranes influences synaptic transmission, and they raise the possibility that modulation of mitochondrial conductance by BCL-2 family proteins affects synaptic stability.

Response of yeast to the regulated expression of proteins in the Bcl-2 family

The mechanisms by which pro-apoptotic members of the Bcl-2 family of proteins promote the release of mitochondrial factors like cytochrome c, subsequently activating the apoptotic cascade, or by which anti-apoptotic family members block this release, are still not understood. When expressed in yeast, Bcl-2 family members act directly upon conserved mitochondrial components that correspond to their apoptotic substrates in mammalian cells. Here we describe a system in which the levels of representative pro- and anti-apoptotic members of the Bcl-2 family can be regulated independently in yeast. Using this system, we have focused on the action of the anti-apoptotic family member Bcl-x(L), and have defined the quantitative relationships that underlie the antagonistic action of this protein on the lethal consequences of expression of the pro-apoptotic family member Bax. This system has also allowed us to demonstrate biochemically that Bcl-x(L) has two actions at the level of the mitochondrion. Bcl-x(L) is able to inhibit the stable integration of Bax into mitochondrial membranes, as well as hinder the action of Bax that does become stably integrated into these membranes. Taken together, our results suggest that both the functional and biochemical actions of Bcl-x(L) may be based on the ability of this molecule to disrupt the interaction of Bax with a resident mitochondrial target that is required for Bax action. Finally, we confirm that VDAC (voltage-dependent anion channel) is not required for the functional responses observed following the expression of either pro- or anti-apoptotic members of the Bcl-2 family.

Proapoptotic BH3-only proteins trigger membrane integration of prosurvival Bcl-w and neutralize its activity

Prosurvival Bcl-2-like proteins, like Bcl-w, are thought to function on organelles such as the mitochondrion and to be targeted to them by their hydrophobic COOH-terminal domain. We unexpectedly found, however, that the membrane association of Bcl-w was enhanced during apoptosis. In healthy cells, Bcl-w was loosely attached to the mitochondrial membrane, but it was converted into an integral membrane protein by cytotoxic signals that induce binding of BH3-only proteins, such as Bim, or by the addition of BH3 peptides to lysates. As the structure of Bcl-w has revealed that its COOH-terminal domain occupies the hydrophobic groove where BH3 ligands bind, displacement of that domain by a BH3 ligand would displace the hydrophobic COOH-terminal residues, allowing their insertion into the membrane. To determine whether BH3 ligation is sufficient to induce the enhanced membrane affinity, or to render Bcl-w proapoptotic, we mimicked their complex by tethering the Bim BH3 domain to the NH2 terminus of Bcl-w. The chimera indeed bound avidly to membranes, in a fashion requiring the COOH-terminal domain, but neither promoted nor inhibited apoptosis. These results suggest that ligation of a proapoptotic BH3-only protein alters the conformation of Bcl-w, enhances membrane association, and neutralizes its survival function.

p21-Activated kinase 5 (Pak5) localizes to mitochondria and inhibits apoptosis by phosphorylating BAD

Pak5 is the most recently identified and least understood member of the p21-activated kinase (Pak) family. This kinase is known to promote neurite outgrowth in vitro, but its localization, substrates, and effects on cell survival have not been reported. We show here that Pak5 has unique properties that distinguish it from all other members of the Pak family. First, Pak5, unlike Pak1, cannot complement an STE20 mutation in Saccharomyces cerevisiae. Second, Pak5 binds to the GTPases Cdc42 and Rac, but these GTPases do not regulate Pak5 kinase activity, which is constitutive and stronger than any other Pak. Third, Pak5 prevents apoptosis induced by camptothecin and C2-ceramide by phosphorylating BAD on Ser-112 in a protein kinase A-independent manner and prevents the localization of BAD to mitochondria, thereby inhibiting the apoptotic cascade that leads to apoptosis. Finally, we show that Pak5 itself is constitutively localized to mitochondria, and that this localization is independent of kinase activity or Cdc42 binding. These features make Pak5 unique among the Pak family and suggest that it plays an important role in apoptosis through BAD phosphorylation.

The tale of tail-anchored proteins: coming from the cytosol and looking for a membrane

A group of integral membrane proteins, known as C-tail anchored, is defined by the presence of a cytosolic NH2-terminal domain that is anchored to the phospholipid bilayer by a single segment of hydrophobic amino acids close to the COOH terminus. The mode of insertion into membranes of these proteins, many of which play key roles in fundamental intracellular processes, is obligatorily posttranslational, is highly specific, and may be subject to regulatory processes that modulate the protein's function. Although recent work has elucidated structural features in the tail region that determine selection of the correct target membrane, the molecular machinery involved in interpreting this information, and in modulating tail-anchored protein localization, has not been identified yet.

The regulatory domain of protein kinase Ctheta localises to the Golgi complex and induces apoptosis in neuroblastoma and Jurkat cells

This study investigates apoptotic effects of protein kinase C (PKC) delta and theta in neuroblastoma cells. 12-O-tetradecanoylphorbol-13-acetate induces apoptosis in SK-N-BE(2) neuroblastoma cells overexpressing PKCdelta or PKCtheta, but not PKC epsilon. The PKC inhibitor GF109203X does not suppress this apoptotic effect, suggesting that it is independent of the catalytic activity of PKC. The isolated catalytic domains of PKCdelta and PKCtheta or the regulatory domain (RD) of PKCtheta also induce apoptosis in neuroblastoma cells. The apoptotic responses are suppressed by caspase inhibition and by Bcl-2 overexpression. The PKCtheta RD induced apoptosis also in Jurkat cells. Colocalisation analysis revealed that the PKCtheta RD primarily localises to the Golgi complex. The C1b domain is required for this localisation and removal of the C1b domain results in a PKCtheta construct that does not induce apoptosis. This suggests that the PKCtheta RD has apoptotic activity and that Golgi localisation may be important for this effect.

Inhibition of Bid-induced apoptosis by Bcl-2. tBid insertion, Bax translocation, and Bax/Bak oligomerization suppressed

Bcl-2 family proteins are important regulators of apoptosis. They can be pro-apoptotic (e.g. Bid, Bax, and Bak) or anti-apoptotic (e.g. Bcl-2 and Bcl-x(L)). The current study examined Bid-induced apoptosis and its inhibition by Bcl-2. Transfection of Bid led to apoptosis in HeLa cells. In these cells, Bid was processed into active forms of truncated Bid or tBid. Following processing, tBid translocated to the membrane-bound organellar fraction. Bcl-2 co-transfection inhibited Bid-induced apoptosis but did not prevent Bid processing or tBid translocation. On the other hand, Bcl-2 blocked the release of mitochondrial cytochrome c in Bid-transfected cells, suggesting actions at the mitochondrial level. Alkaline treatment stripped off tBid from the membrane-bound organellar fraction of Bid plus Bcl-2-co-transfected cells, but not from cells transfected with only Bid, suggesting inhibition of tBid insertion into mitochondrial membranes by Bcl-2. Bcl-2 also prevented Bid-induced Bax translocation from cytosol to the membrane-bound organellar fraction. Finally, Bcl-2 diminished Bid-induced oligomerization of Bax and Bak within the membrane-bound organellar fraction, shown by cross-linking experiments. In conclusion, Bcl-2 inhibited Bid-induced apoptosis at the mitochondrial level by blocking cytochrome c release, without suppressing Bid processing or activation. Critical steps blocked by Bcl-2 included tBid insertion, Bax translocation, and Bax/Bak oligomerization in the mitochondrial membranes.

Calcium signaling and apoptosis

Ca(2+) is one of the key regulators of cell survival, but Ca(2+) can also induce apoptosis in response to a variety of pathological conditions. The pro-apoptotic effects of Ca(2+) are mediated by a diverse range of Ca(2+)-sensitive factors that are compartmentalized in various intracellular organelles including the ER, cytoplasm, and mitochondria. The Ca(2+) dynamics of these organelles appear to be modulated by the apoptosis-regulating Bcl-2 family proteins. In this paper, the recent progress of research on the mechanisms mediating the apoptosis-regulating effects of Ca(2+) and the interactions of Bcl-2 family proteins with the Ca(2+) storage organelles are discussed.

Cellular distribution of Bcl-2 family proteins

Proteins synthesized in the cytosol can be inserted into or across organellar membranes depending on the signals present in their primary sequences. Proteins of the Bcl-2 family, which includes proteins that promote programmed cell death (apoptosis) and proteins that inhibit apoptosis, have signals that can target particular members to either the mitochondria or the endoplasmic reticulum (ER) or both. Germain and Shore discuss evidence for a role for the anti-apoptotic members of the family at the ER and describe an interaction with the FK506 binding protein, FKBP38, that may regulate the relative distribution of Bcl-2 proteins at the ER or mitochondria. This interaction may control the cell's sensitivity to apoptotic stimuli.

Effect of Nilvadipine on the Cerebral Ischemia-Induced Impairment of Spatial Memory and Hippocampal Apoptosis in Rats

We investigated the effects of nilvadipine and amlodipine on the cerebral ischemia-induced impairment of spatial memory in 8-arm radial maze performance and hippocampal CA1 apoptosis in rats. Single cerebral ischemia impaired memory without inducing apoptosis. In these rats, neither nilvadipine nor amlodipine at 3.2 mg/kg, i.p. improved the impaired memory. On the other hand, repeated cerebral ischemia (10 min ischemia x 2, 1 h interval) impaired spatial memory and induced hippocampal apoptosis 7 days after the final occlusion/reperfusion. Moreover, repeated ischemia increased the apoptotic cell number, an effect observed after 3 days and peaked after 7 days. However, mRNA expression of the apoptosis-related early oncogene bax and CPP 32 (caspase-3) was observed after 24 h. In these rats, nilvadipine, but not amlodipine, significantly improved memory, concomitantly decreased hippocampal apoptosis, and suppressed both bax and CPP 32 expression. These results suggest that nilvadipine improved the memory impairment in repeated ischemia by reducing bax and CPP 32 expression and suppressing the induction of apoptosis in the hippocampus. Nilvadipine may have a neuroprotective effect and could be a useful pharmacotherapeutic agent for cerebrovascular dementia.

Programmed death phenomena: from organelle to organism

Programmed death phenomena appear to be inherent not only in living cells (apoptosis), but also in subcellular organelles (e.g., self-elimination of mitochondria, called mitoptosis), organs (organoptosis), and even whole organisms (phenoptosis). In all these cases, the "Samurai law of biology"--it is better to die than to be wrong--seems to be operative. The operation of this law helps complicated living systems avoid the risk of ruin when a system of lower hierarchic position makes a significant mistake. Thus, mitoptosis purifies a cell from damaged and hence unwanted mitochondria; apoptosis purifies a tissue from unwanted cells; and phenoptosis purifies a community from unwanted individuals. Defense against reactive oxygen species (ROS) is probably one of the primary evolutionary functions of programmed death mechanisms. So far, it seems that ROS play a key role in the mito-, apo-, organo-, and phenoptoses, which is consistent with Harman's theory of aging. Here a concept is described that tries to unite Weismann's hypothesis of aging as an adaptive programmed death mechanism and the generally accepted alternative point of view that considers aging as an inevitable result of accumulation in an organism of occasional injuries. It is suggested that injury accumulation is monitored by a system(s) actuating a phenoptotic death program when the number of injuries reaches some critical level. The system(s) in question are organized in such a way that the lethal case appears to be a result of phenoptosis long before the occasional injuries make impossible the functioning of the organism. It is stressed that for humans these cruel regulations look like an atavism that, if overcome, might dramatically prolong the human life span.