37 the miR-17~92 cluster and activate its transcription, creating an autoregulatory feedback loop between miR-17~92 cluster members and E2F proteins (Sylvestre Y. Et al., 2007). It has additionally been shown that this cluster regulates cell cycle progression in various cell type by targeting p21 and Rb12 (Wang Q. 2008). In addition to its tumour promoting properties, a recent transgenic overexpression of the miR-17~92 cluster in mice resulted in the development of a fatal lymphoproliferative disease and autoimmunity. The same study also showed that the cluster targets two tumour suppressors, Bim and PTEN, thus favouring increased lymphocyte proliferation and reduced activation-inducedcelldeath in transgenic mice (Xiao C. et al., 2008). In contrast, targeted deletion of the miR-17~92 cluster resulted in the death of mice shortly after birth due to lung hypoplasia and defects in the development of heart. Furthermore, ablation of the miR-17~92 cluster in mice resulted in increased levels of the pro-apoptotic protein Bim and an inhibition of pro-B to pre-B cell transition during B-cell development, due to excessive celldeath (Ventura A. et al., 2008). Furthermore, it has also been shown that three miRNAs, miR-17, miR-20a of the miR-17~92 cluster and miR-106a of the miR-106a~363 cluster are involved in monocyte differentiation and maturation and their reduced expression results in increased levels of their target protein AML-1 (acute myeloid leukaemia-1) (Fontana L. et al., 2007). Recently, it has been found that the miR-17~92 cluster plays a role not only in cell-autonomous tumour survival, but also in tumour evasion from the immune system. Myeloid-derived suppressor cells (MDSCs) are a major component of the immune suppressive network, and expression of the transcription factor STAT3 induces expansion of MDSCs and suppresses activation of CD4 + and CD8 + T cells in
ptotic cells in lymphocytes from aged controls ( ⌬ increase over baseline: old, 6.56 ⫾ 0.86% versus young, 4.33 ⫾ 0.42%; *, P ⫽ 0.014; Fig. 2c). Moreover, when all inves- tigated subjects were pooled for regression analysis, in- creasing age was correlated with percentage of apoptotic cells by regression analysis. Spontaneous apoptosis after 24 h increased 2.1-fold (slope ⫽ 0.061 ⫾ 0.02) between 15 and 93 years of age [Fig. 3, dotted line (- - -)]. There was a significant (***, P ⬍ 0.001, n ⫽ 85) correlation between age and the portion of apoptotic cells. To ascertain that these alterations in apoptotic celldeath were not linked to alter- ations in the distribution of PBMC subpopulations, the same experiments were performed with activated lymphocytes consisting to over 95% of CD3 ⫹ cells. Lymphocytes, which are undergoing proliferation, can be triggered to pro- grammed celldeath by withdrawal of IL-2. IL-2 is the most critical determinant in this process . Activated lympho- cytes have been shown to be more sensitive to apoptosis than nontreated native cells. Basal apoptotic levels of acti- vated T cells correlated significantly with the donor age (*, P ⬍ 0.05, n ⫽ 52; Fig. 4; young, 9.99 ⫾ 1.05%, median 9.87% versus old, 13.29 ⫾ 1.04%, median 12.17%). In addition, spontaneous in vitro apoptosis after 24 h (under these conditions also called AICD: activation-inducedcelldeath, that is triggered by IL-2 treatment followed by with- drawal) did as well significantly correlate with age (*, P ⬍ 0.05, n ⫽ 45; Fig. 4; young, 16.22 ⫾ 1.29%, median 15.23% versus old, 19.58 ⫾ 1.45%, median 19.15%). 3.2. Increased basal levels of ROS in aging
Our data for CD95L demonstrate that caspase-10 shifts the apoptotic celldeath response following DISC formation to the activation of NF- kB and cell survival ( Figure 7 ), both beneficial features for tumor cells. Thus, caspase-10 may have tumorigenic properties. Chronic inflammatory gene expression favors tumor formation and progression ( Chai et al., 2015 ), and CD95 signaling has been shown in several studies to favor tumor growth and invasiveness ( Barnhart et al., 2004; Chen et al., 2010 ). Thus, our data hint at the possibility of modulating cas- pase-10 expression as a therapeutic oncological target; repres- sion of caspase-10 reduces cytokine expression ( Figure 6 ) and favors apoptosis ( Figure 1 ), potentially resulting in impaired tumor growth. Whether DISC-mediated gene induction is responsible for CD95 dependency of cancer cells remains unan- swered. However, we have previously demonstrated that pri- mary keratinocytes activate NF- kB upon stimulation of the TRAIL DISC, and they are 5-fold less sensitive to death-ligand-induced apoptosis than transformed keratinocytes ( Kavuri et al., 2011; Leverkus et al., 2000 ). Thus, gene induction is potentially much more relevant in DISC signaling than currently assumed.
A German study (Engel et al., 2007) monitored a hospital mortality of 55% for severe sepsis which is higher than observed in other studies. The authors explained this fact with the higher median age in their study population which has been shown to be related with increased mortality rates. The extrapolated population based incidence of sepsis in Germany was 76 to 85 cases per 100,000 according to this study. Statistical data for deaths occurring in Austria is unfortunately not available as “Statistik Austria” is sub- suming death causes according to the “International Statistical Classification of Diseases and Related Health Problems”, 10 th revision, (ICD-10 codes) and sepsis is not explicitly stated as a cause of death. The “Wiener Klinische Wochenschrift” published an article by Schmid et al. (2002b) with an estimation of 6,700 to 9,500 patients with severe sepsis annually in Austria. The ICU mortality was 43.2% with a length of stay of 18.1 days and no gender differences. Non-survivors were equally expensive as survivors although their length of stay was shorter. This reflects the attempt to save lives with all possible means. Direct costs of 192 million EUR to 272 million EUR and indirect costs caused by productivity losses due to premature death of 484 million EUR to 686 million EUR were estimated. This would result in total costs of 676 to 958 million EUR annually for the Austrian health care system. However, it is questionable whether a sample size of only 74 patient records is sufficient to justify these assumptions. This objection has not kept these authors from conducting two similar surveys prone to the same criticisms in Ger- many and Switzerland (Schmid et al., 2004, 2002a). The sample size used in the Swiss study was 61 patient records and resulted in an assumption of 3,500 to 8,500 cases of severe sepsis per year. The Swiss severe sepsis patient costs 3,244 CHF (approximately 2,150 EUR) daily which results in an estimated burden of illness from approximately 326.4 to 793.8 million EUR per year.
induced inﬂammation, importantly beyond TNF as the only endogenous inducer of this celldeath.
HOIP and HOIL-1 are essential to maintain skin homeostasis. To understand the role of LUBAC in the skin, we generated mice that lack HOIP or HOIL-1 selectively in epidermal keratinocytes by crossing Hoip- and Hoil-1-ﬂoxed mice with mice expressing the Cre recombinase under the control of the human keratin 14 (K14) promoter. The genotype of the mice was conﬁrmed by PCR (Supplementary Fig. 1a). At the protein level, deletion of HOIP or HOIL-1 in keratinocytes was veriﬁed by western blot and immunohistochemistry (Supplementary Fig. 1b, c). As expected, HOIP deﬁciency abrogated linear ubiquitination at the TNFR1- SC (Supplementary Fig. 1d) and reduced TNFR1-mediated NF- κB activation in primary murine keratinocytes (PMKs) without preventing it (Supplementary Fig. 1e). Mice homozygous for keratinocyte-speciﬁc deletion of HOIP or HOIL-1 (Hoip E-KO and Hoil-1 E-KO mice, respectively) were born at the expected Men- delian frequencies and were macroscopically indistinguishable from littermates up to postnatal day (P) 2 (data not shown). From this day onwards, however, both Hoip E-KO and Hoil-1 E-KO mice developed severely damaged and scaly skin, which, invariably, resulted in the death of these mice between P4 and P6 (Fig. 1 a). No Hoip or Hoil-1 gene dosage effect was observed as Hoip ﬂ/wt K14Cre + and Hoil-1 ﬂ/wt K14Cre + mice developed nor- mally into adulthood without showing any signs of skin disease (data not shown).
While targeted therapy brought a new era in the treatment of BRAF mutant melanoma, therapeu- tic options for non-BRAF mutant cases are still limited. In order to explore the antitumor activity of prenylation inhibition we investigated the response to zoledronic acid treatment in thirteen human melanoma cell lines with known BRAF, NRAS and PTEN mutational status. Effect of zoledronic acid on proliferation, clonogenic potential, apoptosis and migration of melanoma cells as well as the activation of downstream elements of the RAS/RAF pathway were investigated in vitro with SRB, TUNEL and PARP cleavage assays and videomicroscopy and immunoblot measure- ments, respectively. Subcutaneous and spleen-to-liver colonization xenograft mouse models were used to evaluate the influence of zoledronic acid treatment on primary and disseminated tumor growth of melanoma cells in vivo. Zoledronic acid more efficiently decreased short-term in vitro viability in NRAS mutant cells when compared to BRAF mutant and BRAF/NRAS wild-type cells. In line with this finding, following treatment decreased activation of ribosomal protein S6 was found in NRAS mutant cells. Zoledronic acid demonstrated no significant synergism in cell vi- ability inhibition or apoptosis induction with cisplatin or DTIC treatment in vitro. Importantly, zole- dronic acid could inhibit clonogenic growth in the majority of melanoma cell lines except in the three BRAF mutant but PTEN wild-type melanoma lines. A similar pattern was observed in apo- ptosis induction experiments. In vivo zoledronic acid did not inhibit the subcutaneous growth or spleen-to-liver colonization of melanoma cells. Altogether our data demonstrates that prenylation inhibition may be a novel therapeutic approach in NRAS mutant melanoma. Nevertheless, we also demonstrated that therapeutic sensitivity might be influenced by the PTEN status of BRAF mutant melanoma cells. However, further investigations are needed to identify drugs that have appropriate pharmacological properties to efficiently target prenylation in melanoma cells.
Neonates are extremely susceptible to bacterial infections, and evidences suggest that phagocytosis-inducedcelldeath (PICD) is less frequently triggered in neonatal monocytes than in monocytes from adult donors. An insuﬃcient termination of the inﬂammatory response, leading to a prolonged survival of neonatal monocytes with ongoing proin ﬂammatory cytokine release, could be associated with the progression of various in ﬂammatory diseases in neonates. Our previous data indicate that amphiregulin (AREG) is increasingly expressed on the cell surface of neonatal monocytes, resulting in remarkably higher soluble AREG levels after proteolytic shedding. In this study, we found that E. coli-infected neonatal monocytes show an increased phosphorylation of ERK, increased expression of Bcl-2 and Bcl-X L , and reduced levels of cleaved caspase-3 and caspase-9 compared to adult monocytes. In both cell types, additional stimulation with soluble AREG further increased ERK activation and expression of Bcl-2 and Bcl-X L and reduced levels of cleaved caspase-3 and caspase-9 in an EGFR-dependent manner. These data suggest that reduced PICD of neonatal monocytes could be due to reduced intrinsic apoptosis and that AREG can promote protection against PICD. This reduction of the intrinsic apoptosis pathway in neonatal monocytes could be relevant for severely prolonged in ﬂammatory responses of neonates.
Caspase-10 and cFLIP Independently Inhibit Caspase-8- Mediated CellDeath
Interestingly, all cell lines unaffected by the knockdown of cas- pase-10 showed a higher expression level of caspase-10 (exam- ples shown for HaCaT/MC versus HeLa/SK-Mel in Figures 2A and 2B). Remarkably, protein levels after successful knockdown of caspase-10 in HaCaT or MC cells were comparable to endog- enous levels present in HeLa or SK-Mel (Figure 2A). This differen- tial stoichiometry of caspase-10 was also reflected in the DISC (Figure S2). We initially hypothesized that the low levels of cas- pase-10 remaining in these ‘‘high expressors’’ was sufficient to inhibit CD95L-inducedcelldeath. However, a closer look at the expression levels of caspase-10 and cFLIP in HaCaT cells showed a reciprocal counter-regulation of cFLIP after inducible knockdown of caspase-10 (Figures 2C and 2D). Moreover, changes in cFLIP expression were also reflected in the DISC with an increased level of cleaved cFLIP p43 bound to the recep- tor (Figure 2C). In contrast, caspase-8 or FADD levels in the DISC were unchanged (Figure 2C). These data revealed a close rela- tionship between cFLIP and caspase-10 for inhibition of celldeath. To corroborate this assumption, we next combined the knockdown of caspase-10 and cFLIP in HaCaT cells. As shown in Figure 2D, combination of caspase-10 and cFLIP knockdown increased the sensitivity of cells to CD95L (Figures 2D and S3A, dark red columns). As cFLIP expression in HaCaT is very low (Figure 2A), we aimed to extend the data to cell lines with higher cFLIP levels. We thus performed siRNA-mediated knockdown of caspase-10 and cFLIP in HeLa cells. Depletion of either cas- pase-10 (Figure 2E, light red columns) or cFLIP (Figure 2E, black columns) led to a dramatic increase in CD95-inducedcelldeath. Notably, similar to our data in HaCaT cells, combined knock- down of caspase-10 and cFLIP further increased sensitization to CD95L when compared to caspase-10/cFLIP knockdown alone (Figures 2E and S3B, dark red columns). Taken together, our data showed that caspase-10 is a negative regulator of CD95L-inducedcelldeath, independent of cFLIP. However, at least in HaCaT cells, loss of caspase-10 is compensated by increased expression of cFLIP.
Besides histones, another abundant component of NET is neutrophil elastase (Urban et al., 2009), which has an important role in clearing invading pathogens. Moreover, elastase is able to mediate neutrophil-induced tissue damage and can degrade extracellular matrix efficiently (Perl et al., 2008). Neutrophil elastase activity in NET increased after digestion of DNA. These data support the presence of NET in BAL fluid after LPS induction, as they also showed increase in elastase activity after DNA digestion. However, inhibition of neutrophil elastase in DNase-digested or non-digested NET did not reduce NET-mediated cytotoxicity. Presence of more cytotoxic components of NET (such as histones) can explain this effect so that inhibition of neutrophil elastase is not sufficient to suppress NET-mediated cytotoxicity. MPO, another granular protein with anti-microbial activity, was also investigated for NET- mediated cytotoxicity in the present study. MPO has an important role in defence against bacteria by conversion of hydrogen peroxide to HOCl. Nevertheless, MPO activity can also provoke damage to adjacent tissue and, therefore contribute to the pathogenesis of several inflammatory diseases including pulmonary injuty (Klebanoff, 1999; Van Der Vliet et al., 2000). It has been reported that MPO can provoke caspase-3 activation and apoptosis in HL- 60 human leukemia cells (Myzak and Carr, 2002). Moreover, MPO can induce DNA strand breakage in lung epithelial cells (Haegens et al., 2008). Pre-incubation of NET with MPO inhibitor decreased NET-mediated cytotoxicity of epithelial cells, indicating that besides histones MPO is also responsible for the cell damaging capacity of NET.
Membrane trafficking of Kv2.1 is regulated by multiple phosphorylation events (Figure 4). For example, activation of the mitogen-activated protein (MAP) kinase p38 is necessary for the induction of neuronal apoptosis after oxidative injury. By phosphorylating a serine residue at the C-terminal of the channel protein (S800), active p38 leads to membrane insertion of Kv2.1 and the potassium current surge that initiates celldeath, possibly by changing the association of Kv2.1 with other proteins (such as syntaxin) ( Redman et al., 2007 ). p38 activation, in turn, depends on an intracellular zinc increase caused by oxidants such as peroxynitrite ( Zhang et al., 2004 ). Intracellular zinc leads, in addition to p38 activation, also to inhibition of the phosphatase Cyt-PTP ε that in standard conditions dephosphorylates Kv2.1 at a tyrosine residue at the N-terminal (Y124). Src kinase is responsible for phosphorylation of the channel at Y124, enhancing the Kv2.1-mediated current at the onset of apoptosis ( Redman et al., 2009 ). Phosphorylation at S800 and Y124 mutually co-regulate each other, with P-Y124 facilitating the action of p38 on S800 and vice versa ( He et al., 2015 ). Additionally, serum deprivation, which induces apoptosis of cortical neurons in a model of excitotoxicity, leads to N-Methyl- d-aspartate (NMDA) receptor activation and enhanced plasma membrane expression of Kv2.1 due to dephosphorylation of the channel protein by the Protein Phosphatase 1 (PP1) and/or 2A (PP2A) ( Yao et al., 2009 ). It was further shown that activation of Protein Kinase A (PKA) following an increase in cyclic AMP protects cerebellar granular neurons from celldeathinduced by potassium-low and serum-free medium ( Jiao et al., 2007 ). In this study, PKA activation decreased the Kv2.1- dependent outgoing potassium current upon application of the pro-apoptotic stimulus, likely by reducing Kv2.1 expression. Cleavage of Kv2.1 can also affect celldeath induction. Liu et al. recently showed that beta-secretase 2 (BACE2), a protease that frequently shows increased expression in Alzheimer’s disease, cleaves Kv2.1 at three different sites, reducing the current surge at the onset of apoptosis and protecting neurons from celldeath ( Liu et al., 2018 ).
7 DED containing proteins per FADD molecule are recruited and form DED chains. Procaspases-8 and -10 are activated by dimerization according to the induced proximity model. Short c-FLIP isoforms in these chains block activation of procaspase-8/10 by forming heterodimer, while long c-FLIP isoform can also have activating functions in the heterodimer depending on their concentration in the chains. Active caspase-8 cleaves executioner caspases and Bid. Truncated Bid (tBid) induces Bax and Bak oligomerization and formation of pores in the outer mitochondrial membrane. This allows cytochrome C and SMAC/DIABLO to be released from the mitochondrial intermembrane room into the cytosol. Cytochrome C binds to APAF1, which recruits procaspase-9 into the resulting high molecular weight complex, the apoptosome. Here, procaspase-9 is activated and cleaves executioner caspases, which results in the caspase cascade and apoptotic celldeath. The mitochondrial protein SMAC/DIABLO blocks XIAP, the inhibitor of caspase-9 and the executioner caspases-3 and -7. From (Walczak et al., 2013)
low TNF-α secretion and diminished TNFR1 internalization. Downstream of TNF/TNFR1 internalization caspase-8 and consecutively caspase-3 activation was reduced in CBMO, lead- ing to their diminished apoptosis.
Reduced levels of TNF-α in neonatal monocytes after infection or challenge with bacteria ( Fig 1A ) or bacterial PAMPs (such as LPS) are a matter of debate with most studies indicating a bias towards reduced TH1 cytokine production in CBMO. In response to most TLR ligands, most reports found neonatal innate immune cells, including monocytes, conventional and plasmacytoid dendritic cells producing less IL-12p70 and IFN-ɣ, moderately less TNF-α but as much or even more IL-1ß, IL-6, IL-23, and IL-10 than adult cells [ 18 ].In concurrence with our study, reduced extracellular TNF-α levels in E. coli-infected purified monocytes have been described [ 19 ] [ 20 – 22 ]. Dampening inflammation is thought to be essential for the fetal immune system to avoid rejection by the mother and termination of pregnancy [ 23 ]. There- fore reduced secretion of TNF-α could be beneficial for the fetal environment, albeit bearing the risk of reduced capacity to fight of infection and of prolonged activation of immune effec- tor cells by due to missing pro-apoptotic signaling. In this regard, the isolation of PBMO and CBMO via depletion of granulocytes and removal of serum factors could be limiting factors of our model. However, comparison of our published results to the whole blood assays ( S1 Fig ), showed that basic results, such as phagocytic activity, TNF-α secretion and induction of apo- ptosis were similar in both experimental setups.
prognosis for many of these childhood cancers is good, with high survival rates [ 130 ], but the consequences can be very severe [ 131 , 132 ], and currently, the only option is the surgical removal of (parts of) the ovaries, cryostorage and re-implantation after the end of the therapy [ 133 , 134 ]. However, this procedure bears the risk of also re-introducing tumor cells and surgery might not be possible before the start of chemotherapy, necessitating the search for alternatives to preserve the primary oocyte pool. With the elucidation of the mechanism of inhibition and the activation pathway of TAp63α, pharmacological approaches to inhibit the induction of oocyte death have become possible. At the center of such approaches are the three kinases, ATM, CHK1/2 and CK1, that play essential roles in this activation process. Inhibitor studies in mouse ovaries have indeed shown that using inhibitors for one of these kinases suppresses activation of TAp63α [ 64 , 135 ], allowing oocytes to survive [ 72 , 136 ].
The current study employed a well-established model using DEN as initiator and PB as promoting agent of hepatocarcinogenesis in mice. The carcinogenic capacity of DEN is related to its ability to alkylate DNA following hydroxylation by cytochrome P450 and to oxidative stress from ROS production. PB enhances the effect of DEN through induction of cytochrome P450 and causes hypermethylation of promoter regions in tumor suppressor genes influencing cellular proliferation . The oncogenic potential of DEN/PB was significantly reduced in Bcl-3 overexpressing animals at 40 weeks of age. Bcl-3 reduced the number and especially the size of tumor nodules. Hepatocellular injury at this late time point was not affected by Bcl-3 expression and the predominant type of celldeath was apoptosis. Interestingly, the number of dysplastic nodules and small tumors at week 40 was comparable in both genotypes. This suggests that HCC formation was reduced primarily due to effects that are occurring early following tumor initiation and that over
labeling might thus indicate that they are relatively unstable and constantly refilled from the bone marrow. It is in contrast to CD19 -/- B cells that exhibit a similar decline to CD19 +/- B cells, albeit it has been shown that they have a slight survival disadvantage that is revealed after long times of labeling and tracking (Otero et al., 2003). Hence, LMP1/CD40-expressing B cells in vivo are highly susceptible to the loss of CD19. Interestingly, this survival defect is not as prominent in vitro, arguing for a role of the microenvironment in the induction of celldeath of LMP1/CD40//CD19 -/- B cells in vivo. Astonishingly, LMP1/CD40//CD19 +/- B cells show a higher percentage of BrdU labeled B cells in the spleen but not in the peripheral blood and show enhanced survival in the blood but not in the spleen. This phenotype might be due to a defect in negative selection of LMP1/CD40-expressing B cells at the T1/ T2 B cell stage, induced by the abnormally high noncanonical NF-B signaling, resulting in more BrdU labeled B cells passing the transitional stage. However, since this selection defect would result in an accumulation of non-selected, autoreactive B cells in the spleen, these cells might become anergic and die. The non-autoreactive B cells passing this stage on the other hand survive and are able to recirculate to the blood and lymph nodes. These might indeed have a prolonged life span which is detected by the BrdU assay in the blood but masked in the spleen. To finally prove this hypothesis, blockage of BM influx will be applied to exclude newly emerging cells from the bone marrow that have to pass the transitional stage. This requires treatment of mice with a -IL7 receptor antibody that blocks B cell development in the bone marrow (Sudo et al., 1993).
Defence responses in cell cultures from grapevine had been examined previously (Chang & Nick, 2012). In this system, PTI can be induced by a synthetic 22-amino- acid peptide (flg22) from a conserved flagellin domain, whereas the bacterial elicitor harpin induced an ETI-like immunity culminating in celldeath. In the same system, it has been shown that flg22 induced the accumulation of jasmonic acid and its bioactive isoleucine conjugate JA-Ile, whereas harpin did not, assigning the activation of jasmonate synthesis clearly to basal, but not to cell-death related defence (Chang et al., 2016). This led to the question, whether the bifurcation of the oxylipin pathway produced by the duplication into the CYP74A (AOS) jasmonate generating branch and the CYP74B (HPL) volatile generating branch might be linked with the bifurcation of defence signalling that either leads to basal immunity (AOS, jasmonate pathway) or a cell-death related immunity (HPL, volatile pathway). Therefore, in this study HPL was isolated from the Vitis vinifera cultivar Müller-Thurgau and overexpressed in the tobacco cell line BY-2 wanting to understand the swithch between basal and cell-death related defense.
Although little is known about the signalling cascade during PCD in plants, recent studies have shown that activation of phospholipase C (PLC) and phospholipase D (PLD) is required during camptothecin- and cadmium- induced PCD in tomato suspension cells (Yakimova et al., 2006; Woltering et al., 2007). As PLD and PLC have also been described to be activated during salt stress caused by NaCl or KCl in the unicellular green alga Chlamydomonas moewusii (Munnik et al., 2000; Meijer et al., 2002; Arisz et al., 2003) a similar signalling mechanism could play a pivotal role during salt stress-iduced PCD in Micrasterias. In summary, it has been demonstrated that Micrasterias shows PCD hallmarks like autophagy, vacuolization, ultra- structural changes, and DNA laddering upon salt stress. As the iso-osmotic sorbitol treatment does not result in these effects, the ionic, rather than the osmotic component of salt stress seems to lead to PCD in Micrasterias. The ap- pearance of these changes was accompanied by an active metabolism measured by viability assay, pigment composi- tion, photosynthesis, and respiration pointing towards a programmed celldeath and not to a necrotic, accidental celldeath event. Our data also reveal that KCl has more pronounced effects on viability and on ultrastructural changes when compared to NaCl. This suggests that Micrasterias can cope better with NaCl than with KCl. A possible explanation could be that salt stress in nature is usually caused by NaCl and not by KCl (Ramos et al., 2004). The physiological, biochemical, and ultrastructural changes observed in Micrasterias cells during salt stress- induced PCD differ in several features from those described after H 2 O 2 induction (see Dahrehshouri et al., 2008). As Morel and Dangle (1997) suggested, the diversity of morphologies during celldeath (including PCD) probably reflects different ways in which cells may die. In addition, our results show that different inducers may lead to dif- ferent celldeath pathways in one and the same organism.
Various crystallopathies share certain common pathomechanisms, i.e. mechanical obstruction due to crystal deposits, cytotoxicity of cells that interact with crystals, and crystal induced inflammatory responses and activation of immune system. Various examples of crystallopathies include kidney stones that are formed as a result of hyperoxaluria or hypercalcuria leading to nephrocalcinosis. In the urinary tract, crystallization usually starts in the renal tubules where supersaturation is a consequence of stepwise concentrating the glomerular filtrate and of the active secretion of calcium, uric acid, oxalate, phosphate or drug metabolites (Table 1) 136,137 and this eventually hinder normal kidney functions. Furthermore, crystal masses may also cause vascular obstruction but through mechanisms other than stone formation. For example, atherosclerosis is a consequence of an accumulation of cholesterol crystals in the tunica intima of the arteria wall, the atheroma 138 . In gouty arthritis, non- aggregating crystal masses of MSU form creamy tophi in subcutaneous layer of skin. Particles like silica and asbestos are known to induce silicosis and asbestosis, diseases associated with lung inflammation.
11 and Na + , metabolites such as ATP, ADP, NAD(P), glutathione, lipid second messengers and multiple proteins including kinases and phosphatases (K ROEMER et al., 2007). These signals lead to the permeabilization of the mitochondrial membrane resulting in a release of intermembrane space proteins. For instance, cytochrome c, has a vital function in the respiration chain, once released into the cytosol it promotes the formation of the apoptosome. This molecular complex activates caspase-9 and the APAF-1 under ATP usage. Finally it results in activation of effector caspasis (Z EISS , 2003). The caspase independent celldeath effectors AIF and EndoG translocate to the nucleus and induce DNA fragmentation.
Since Bid is apparently a key regulator in glutamate-induced neuronal apoptosis further experiments focused on the activation of Bid after the glutamate challenge. As outlined above, a direct involvement of Omi/HtrA2 in Bid cleavage could be excluded. Similar negative results were obtained when addressing other prominent candidates that have been linked to Bid cleavage and activation: Caspase-8 and caspase-2 have been shown to cleave Bid mediating apoptosis induced by Fas/TNF or TRAIL receptor stimuli, respectively [118, 119]. Increases in intracellular calcium levels activate Calpain I, which is also suggested to cleave Bid thereby triggering tBid mediated mitochondrial damage . In addition, calpain has been identified to mediate cleavage and release of AIF from isolated mitochondria, after entering the mitochondrial intermembrane space through the tBid-generated pore in the mitochondrial outer membrane . The lysosomal involvement in neuronal apoptosis triggered by oxidative stress is being increasingly recognized and may involve mitochondrial membrane permeabilization either directly through activation of phospholipases or indirectly through cleavage of Bid. For example, the lysosomal cysteine proteases such as Cathepsin B, D, H and L have been reported to mediate Bid cleavage, subsequent activation of Bax by tBid, and mitochondrial release of cytochrome c, AIF, and Smac/Diablo . The findings of this work, however, strongly suggest that none of these factors that may act upstream of Bid cleavage and mitochondrial AIF release are involved in glutamate-induced apoptosis of HT-22 neurons: Inhibition of caspase-8 or caspase-2, calpains or cathepsins failed to prevent glutamate-inducedcelldeath in HT-22 neurons.