The biochemistry of neuronal necrosis: rogue biology?

Necrotic cell death and neurodegeneration: The involvement of endocytosis and intracellular trafficking

Necrosis, one of the two main types of cell death, contributes critically in many devastating pathological conditions in human, including stroke, ischemia, trauma and neurodegenerative diseases. However, unlike apoptosis, the molecular mechanisms underlying necrotic cell death and neurodegeneration are poorly understood. Caenorhabditis elegans offers a powerful platform for a thorough and systematic dissection of the molecular basis of necrotic cell death. Similarly to humans, neuronal necrosis can be induced by several well-characterized genetic lesions and by adverse environmental conditions in the nematode. The availability of precisely-defined C. elegans neurodegeneration models provides a unique opportunity for comprehensive delineation of the cellular and molecular mechanisms mediating necrotic cell death. Through genetic dissection of such models, we recently uncovered an unexpected requirement for specific proteins involved in endocytosis and intracellular trafficking, in the execution of necrosis. Moreover, initiation of necrotic cell death is accompanied by a sharp increase in the formation of early and recycling endosomes, which subsequently disintegrate during the final stage of cell death. These findings implicate endocytic and intracellular trafficking processes in the cellular destruction during necrosis. Indeed, endocytosis synergizes with two other essential cellular processes, autophagy and lysosomal proteolysis to facilitate necrotic neurodegeneration. In this commentary, we consider the contribution of endocytosis and intracellular trafficking to cell injury and discuss the crosstalk between these processes and other molecular mechanisms that mediate necrosis.

Three Ca2+ channel inhibitors in combination limit chronic secondary degeneration following neurotrauma

Following neurotrauma, cells beyond the initial trauma site undergo secondary degeneration, with excess Ca2+ a likely trigger for loss of neurons, compact myelin and function. Treatment using inhibitors of specific Ca2+ channels has shown promise in preclinical studies, but clinical trials have been disappointing and combinatorial approaches are needed. We assessed efficacy of multiple combinations of three Ca2+ channel inhibitors at reducing secondary degeneration following partial optic nerve transection in rat. We used lomerizine to inhibit voltage gated Ca2+ channels; oxidised adenosine-triphosphate (oxATP) to inhibit purinergic P2X7 receptors and/or 2-[7-(1H-imidazol-1-yl)-6-nitro-2,3-dioxo-1,2,3,4-tetrahydro quinoxalin-1-yl]acetic acid (INQ) to inhibit Ca2+ permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Only the three Ca2+ channel inhibitors delivered in combination significantly preserved visual function, as assessed using the optokinetic nystagmus visual reflex, at 3 months after injury. Preservation of retinal ganglion cells was partial and is unlikely to have accounted for differential effects on function. A range of the Ca2+ channel inhibitor combinations prevented swelling of optic nerve vulnerable to secondary degeneration. Each of the treatments involving lomerizine significantly increased the proportion of axons with normal compact myelin. Nevertheless, limiting decompaction of myelin was not sufficient for preservation of function in our model. Multiple combinations of Ca2+ channel inhibitors reduced formation of atypical node/paranode complexes; outcomes were not associated with preservation of visual function. However, prevention of lengthening of the paranodal gap that was only achieved by treatment with the three Ca2+ channel inhibitors in combination was an important additional effect that likely contributed to the associated preservation of the optokinetic reflex using this combinatorial treatment strategy.

Hydrogen peroxide-induced necrotic cell death in cardiomyocytes is independent of matrix metalloproteinase-2

Matrix metalloproteinase-2 (MMP-2) is well known to proteolyse both extracellular and intracellular proteins. Reactive oxygen species activate MMP-2 at both transcriptional and post-translational levels, thus MMP-2 activation is considered an early event in oxidative stress injury. Although hydrogen peroxide is widely used to trigger oxidative stress-induced cell death, the type of cell death (apoptosis vs. necrosis) in cardiomyocytes is still controversial depending on the concentration used and the exposure time. We carefully investigated the mode of cell death in neonatal rat cardiomyocytes induced by different concentrations (50-500 μM) of hydrogen peroxide at various time intervals after exposure and determined whether MMP-2 is implicated in hydrogen peroxide-induced cardiomyocyte death. Treating cardiomyocytes with hydrogen peroxide led to elevated MMP-2 level/activity with maximal effects seen at 200 μM. Hydrogen peroxide caused necrotic cell death by disrupting the plasmalemma as evidenced by the release of lactate dehydrogenase in a concentration- and time-dependent manner as well as the necrotic cleavage of PARP-1. The absence of both caspase-3 cleavage/activation and apoptotic cleavage of PARP-1 illustrated the weak contribution of apoptosis. Pre-treatment with selective MMP inhibitors did not protect against hydrogen peroxide-induced necrosis. In conclusion hydrogen peroxide increases MMP-2 level/activity in cardiomyocytes and induces necrotic cell death, however, the later effect is MMP-2 independent.

Nitric oxide donors as neuroprotective agents after an ischemic stroke-related inflammatory reaction

Cerebral ischemia initiates a cascade of detrimental events including glutamate-associated excitotoxicity, intracellular calcium accumulation, formation of Reactive oxygen species (ROS), membrane lipid degradation, and DNA damage, which lead to the disruption of cellular homeostasis and structural damage of ischemic brain tissue. Cerebral ischemia also triggers acute inflammation, which exacerbates primary brain damage. Therefore, reducing oxidative stress (OS) and downregulating the inflammatory response are options that merit consideration as potential therapeutic targets for ischemic stroke. Consequently, agents capable of modulating both elements will constitute promising therapeutic solutions because clinically effective neuroprotectants have not yet been discovered and no specific therapy for stroke is available to date. Because of their ability to modulate both oxidative stress and the inflammatory response, much attention has been focused on the role of nitric oxide donors (NOD) as neuroprotective agents in the pathophysiology of cerebral ischemia-reperfusion injury. Given their short therapeutic window, NOD appears to be appropriate for use during neurosurgical procedures involving transient arterial occlusions, or in very early treatment of acute ischemic stroke, and also possibly as complementary treatment for neurodegenerative diseases such as Parkinson or Alzheimer, where oxidative stress is an important promoter of damage. In the present paper, we focus on the role of NOD as possible neuroprotective therapeutic agents for ischemia/reperfusion treatment.

μ-Calpain is involved in the postmortem proteolysis of gizzard smooth muscle

Postmortem changes in proteins that have been implicated in affecting muscle integrity were examined in goose (GG) and duck (DG) gizzard smooth muscle stored at 5°C. GG and DG smooth muscles were sampled at 0, 1, 3 and 7 day of storage. The pH was approximately 7 in both GG and DG samples during postmortem storage. Casein zymograms showed that 0-day μ-calpain activity was higher (p<0.05) in GG than in DG samples. As postmortem time progressed, μ-calpain was activated and autolyzed more extensively in GG than in DG samples. However, μ/m-calpain remained relatively stable in both samples. Western blots indicated that postmortem desmin degradation was more rapid in GG than in DG samples. In contrast, α-actinin remained nearly unchanged in both samples. Therefore, our results suggest that μ-calpain has an important role in the postmortem proteolysis of gizzard smooth muscle.

Noninvasive brain stimulation in traumatic brain injury

OBJECTIVE

To review novel techniques of noninvasive brain stimulation (NBS), which may have value in assessment and treatment of traumatic brain injury (TBI).

METHODS

Review of the following techniques: transcranial magnetic stimulation, transcranial direct current stimulation, low-level laser therapy, and transcranial Doppler sonography. Furthermore, we provide a brief overview of TMS studies to date.

MAIN FINDINGS

We describe the rationale for the use of these techniques in TBI, discuss their possible mechanisms of action, and raise a number of considerations relevant to translation of these methods to clinical use. Depending on the stimulation parameters, NBS may enable suppression of the acute glutamatergic hyperexcitability following TBI and/or counter the excessive GABAergic effects in the subacute stage. In the chronic stage, brain stimulation coupled to rehabilitation may enhance behavioral recovery, learning of new skills, and cortical plasticity. Correlative animal models and comprehensive safety trials seem critical to establish the use of these modalities in TBI.

CONCLUSIONS

Different forms of NBS techniques harbor the promise of diagnostic and therapeutic utility, particularly to guide processes of cortical reorganization and enable functional restoration in TBI. Future lines of safety research and well-designed clinical trials in TBI are warranted to determine the capability of NBS to promote recovery and minimize disability.

Small heat-shock proteins protect from heat-stroke-associated neurodegeneration

Heat stroke is a life-threatening condition, characterized by catastrophic collapse of thermoregulation and extreme hyperthermia. In recent years, intensification of heat waves has caused a surge of heat-stroke fatalities. The mechanisms underlying heat-related pathology are poorly understood. Here we show that heat stroke triggers pervasive necrotic cell death and neurodegeneration in Caenorhabditis elegans. Preconditioning of animals at a mildly elevated temperature strongly protects from heat-induced necrosis. The heat-shock transcription factor HSF-1 and the small heat-shock protein HSP-16.1 mediate cytoprotection by preconditioning. HSP-16.1 localizes to the Golgi, where it functions with the Ca(2+)- and Mn(2+)-transporting ATPase PMR-1 to maintain Ca(2+) homeostasis under heat stroke. Preconditioning also suppresses cell death inflicted by diverse insults, and protects mammalian neurons from heat cytotoxicity. These findings reveal an evolutionarily conserved mechanism that defends against diverse necrotic stimuli, and may be relevant to heat stroke and other pathological conditions involving necrosis in humans.

The ubiquitin-proteasome system and the autophagic-lysosomal system in Alzheimer disease

As neurons age, their survival depends on eliminating a growing burden of damaged, potentially toxic proteins and organelles-a capability that declines owing to aging and disease factors. Here, we review the two proteolytic systems principally responsible for protein quality control in neurons and their important contributions to Alzheimer disease pathogenesis. In the first section, the discovery of paired helical filament ubiquitination is described as a backdrop for discussing the importance of the ubiquitin-proteasome system in Alzheimer disease. In the second section, we review the prominent involvement of the lysosomal system beginning with pathological endosomal-lysosomal activation and signaling at the very earliest stages of Alzheimer disease followed by the progressive failure of autophagy. These abnormalities, which result in part from Alzheimer-related genes acting directly on these lysosomal pathways, contribute to the development of each of the Alzheimer neuropathological hallmarks and represent a promising therapeutic target.

Neuronal degeneration and gliosis time-course in the mouse hippocampal formation after pilocarpine-induced status epilepticus

Temporal lobe epilepsy (TLE) is the most common type of human epilepsy and has been related with extensive loss of hippocampal pyramidal and dentate hilar neurons and gliosis. Many characteristics of TLE are reproduced in the pilocarpine model of epilepsy in mice. This study analyzed the neuronal damage, assessed with Fluoro-Jade (FJB) and cresyl violet, and gliosis, investigated with glial fibrilary acidic protein (GFAP) immunohistochemistry, occurring in the hippocampal formation of mice at 3, 6, 12 and 24h, 1 and 3 weeks after the pilocarpine-induced status-epilepticus (SE) onset. The maximum neuronal damage score and the FJB-positive neurons peak were found in the hilus of dentate gyrus 3 and 12 h after SE onset (P<0.05), respectively. At 1 week after SE onset, the greatest neuronal damage score was detected in the CA1 pyramidal cell layer and the greatest numbers of FJB-positive neurons were found both in the CA1 and CA3 pyramidal cell layers (P<0.05). The molecular, CA3 and CA1 pyramidal cell layers expressed highest presence of GFAP immunoreaction at 1 and 3 weeks after SE onset (P<0.05). Our findings show that, depending on the affected area, neuronal death and gliosis can occur within few hours or weeks after SE onset. Our results corroborate previous studies and characterize short time points of temporal evolution of neuropathological changes after the onset of pilocarpine-induced SE in mice and evidences that additional studies of this temporal evolution may be useful to the comprehension of the cellular mechanisms underlying epileptogenesis.

Postmortem role of calpains in Pekin duck skeletal muscles

BACKGROUND

It is generally agreed that calpains are involved in postmortem proteolysis of skeletal muscle and improve meat tenderness. However, little information regarding the postmortem role of calpains in duck skeletal muscle is known. Therefore, the purpose of this study was to examine the role of calpains in Pekin duck postmortem breast muscles (BM) and leg and thigh muscles (LM) muscles at 5 °C.

RESULTS

The postmortem pH was lower (P < 0.05) in BM than in LM. Western blots indicated that postmortem desmin degradation and the 30/32 kDa troponin-T degradation product accumulation were more rapid in BM than in LM. Casein zymograms showed that at-death µ-calpain activity was higher in BM than in LM. As time post mortem increased, µ-calpain was activated and autolyzed more rapidly and extensively in BM than in LM, but µ/m-calpain was activated at a relative slower rate compared with µ-calpain. Correlation results showed that µ-calpain activity, rather than µ/m-calpain activity, in BM samples was highly correlated with the abundance of desmin and the 30/32 kDa troponin-T degradation components across the postmortem period. However, no such correlations were found with LM µ- and µ/m-calpains.

CONCLUSION

Therefore, our results suggest that BM µ-calpain with a faster and more extensive activation and autolysis would play a relatively dominant role in dictating degradation of desmin and troponin-T in postmortem duck muscle.

Toxicogenomic responses of the model organism Caenorhabditis elegans to gold nanoparticles

We used Au nanoparticles (Au-NPs) as a model for studying particle-specific effects of manufactured nanomaterials (MNMs) by examining the toxicogenomic responses in a model soil organism, Caenorhabditis elegans . Global genome expression for nematodes exposed to 4-nm citrate-coated Au-NPs at the LC(10) level (5.9 mg·L(-1)) revealed significant differential expression of 797 genes. The levels of expression for five genes (apl-1, dyn-1, act-5, abu-11, and hsp-4) were confirmed independently with qRT-PCR. Seven common biological pathways associated with 38 of these genes were identified. Up-regulation of 26 pqn/abu genes from noncanonical unfolded protein response (UPR) pathway and molecular chaperones (hsp-16.1, hsp-70, hsp-3, and hsp-4) were observed and are likely indicative of endoplasmic reticulum stress. Significant increase in sensitivity to Au-NPs in a mutant from noncanonical UPR (pqn-5) suggests possible involvement of the genes from this pathway in a protective mechanism against Au-NPs. Significant responses to Au-NPs in endocytosis mutants (chc-1 and rme-2) provide evidence for endocytosis pathway being induced by Au-NPs. These results demonstrate that Au-NPs are bioavailable and cause adverse effects to C. elegans by activating both general and specific biological pathways. The experiments with mutants further support involvement of several of these pathways in Au-NP toxicity and/or detoxification.

Endocytosis and intracellular trafficking contribute to necrotic neurodegeneration in C. elegans

Unlike apoptosis, necrotic cell death is characterized by marked loss of plasma membrane integrity. Leakage of cytoplasmic material to the extracellular space contributes to cell demise, and is the cause of acute inflammatory responses, which typically accompany necrosis. The mechanisms underlying plasma membrane damage during necrotic cell death are not well understood. We report that endocytosis is critically required for the execution of necrosis. Depletion of the key endocytic machinery components dynamin, synaptotagmin and endophilin suppresses necrotic neurodegeneration induced by diverse genetic and environmental insults in C. elegans. We used genetically encoded fluorescent markers to monitor the formation and fate of specific types of endosomes during cell death in vivo. Strikingly, we find that the number of early and recycling endosomes increases sharply and transiently upon initiation of necrosis. Endosomes subsequently coalesce around the nucleus and disintegrate during the final stage of necrosis. Interfering with kinesin-mediated endosome trafficking impedes cell death. Endocytosis synergizes with autophagy and lysosomal proteolytic mechanisms to facilitate necrotic neurodegeneration. These findings demonstrate a prominent role for endocytosis in cellular destruction during neurodegeneration, which is likely conserved in metazoans.

Deciphering the neuroprotective mechanisms of Bu-yang Huan-wu decoction by an integrative neurofunctional and genomic approach in ischemic stroke mice

ETHNOPHARMACOLOGICAL RELEVANCE

Bu-yang Huan-wu decoction (BHD) is a famous traditional Chinese medicine formula that has been used clinically in Asia to treat stroke-induced disability for centuries, but the underlying neuroprotective mechanisms are not fully understood.

AIM OF THE STUDY

In this study, we aim to investigate the mechanisms of action using an integrative neurofunctional and broad genomics approach.

MATERIALS AND METHODS

Male ICR mice were subjected to an acute ischemic stroke by inducing a middle cerebral ischemic/reperfusion (CI/R) injury. To examine whether BHD could extend the lifespan of mice with a stroke, we used oral administration of BHD (0.5 and 1.0g/kg) twice daily starting from 2h after ischemia and compared this with vehicle control treatments, recombinant tissue-type plasminogen activator (rt-PA, 10mg/kg, i.v.), and MK-801 (0.2mg/kg, i.p.). An integrative neurofunctional and genomic approach was performed to elucidate the underlying molecular mechanisms of BHD.

RESULTS

More than 80% of the mice died within 2 days after stroke induction in the vehicle control treatment group. However, the survival rates and life-spans of mice treated with BHD, rt-PA and MK-801 were significantly enhanced as compared to the vehicle-treated CI/R group in all three cases. Mice treated with BHD (1.0g/kg) showed the greatest protective effect across all groups. BHD successfully restored brain function, ameliorated the cerebral infarction, and significantly improved the neurological deficits of the mice with a stroke. BHD also reduced inflammation, oxidative stress, and apoptosis, as well as improved neurogenesis. The molecular impacts of BHD were assessed by genome-wide transcriptome analysis using brains from the CI/R mice. The results showed a total of 377 ischemia-induced probe-sets that were significantly influenced by BHD including 93 probe-sets that were commonly more abundant in BHD-treated and sham mice, and another 284 ischemia-induced probe sets that were suppressed by BHD. Mining the functional modules and genetic networks of these 377 genes revealed a significant upregulation of neuroprotective genes associated with neurogenesis (6 genes) and nervous system development (9 genes), and a significant down-regulation of destructive genes associated with the induction of inflammation (14 genes), apoptosis (15 genes), angiogenesis (11 genes) and blood coagulation (7 genes) by BHD.

CONCLUSIONS

Our results suggested that BHD is able to protect mice against stroke and extend lifespan primarily through a significant down-regulation of genes involved in inflammation, apoptosis, angiogenesis and blood coagulation, as well as an up-regulation of genes mediating neurogenesis and nervous system development. The changes in expression after treatment with BHD are beneficial after ischemic stroke.

Microscopic optical projection tomography in vivo

We describe a versatile optical projection tomography system for rapid three-dimensional imaging of microscopic specimens in vivo. Our tomographic setup eliminates the in xy and z strongly asymmetric resolution, resulting from optical sectioning in conventional confocal microscopy. It allows for robust, high resolution fluorescence as well as absorption imaging of live transparent invertebrate animals such as C. elegans. This system offers considerable advantages over currently available methods when imaging dynamic developmental processes and animal ageing; it permits monitoring of spatio-temporal gene expression and anatomical alterations with single-cell resolution, it utilizes both fluorescence and absorption as a source of contrast, and is easily adaptable for a range of small model organisms.

Collective stability of networks of winner-take-all circuits

The neocortex has a remarkably uniform neuronal organization, suggesting that common principles of processing are employed throughout its extent. In particular, the patterns of connectivity observed in the superficial layers of the visual cortex are consistent with the recurrent excitation and inhibitory feedback required for cooperative-competitive circuits such as the soft winner-take-all (WTA). WTA circuits offer interesting computational properties such as selective amplification, signal restoration, and decision making. But these properties depend on the signal gain derived from positive feedback, and so there is a critical trade-off between providing feedback strong enough to support the sophisticated computations while maintaining overall circuit stability. The issue of stability is all the more intriguing when one considers that the WTAs are expected to be densely distributed through the superficial layers and that they are at least partially interconnected. We consider how to reason about stability in very large distributed networks of such circuits. We approach this problem by approximating the regular cortical architecture as many interconnected cooperative-competitive modules. We demonstrate that by properly understanding the behavior of this small computational module, one can reason over the stability and convergence of very large networks composed of these modules. We obtain parameter ranges in which the WTA circuit operates in a high-gain regime, is stable, and can be aggregated arbitrarily to form large, stable networks. We use nonlinear contraction theory to establish conditions for stability in the fully nonlinear case and verify these solutions using numerical simulations. The derived bounds allow modes of operation in which the WTA network is multistable and exhibits state-dependent persistent activities. Our approach is sufficiently general to reason systematically about the stability of any network, biological or technological, composed of networks of small modules that express competition through shared inhibition.

The contributions of antioxidant activity of lipoic acid in reducing neurogenerative progression of Parkinson's disease: a review

ABSTRACT This work reviews the evidence of the mechanism of neuronal degeneration in Parkinson's disease (PD) and the neuroprotective effect of lipoic acid and its use in the treatment of PD. PD is characterized by slow and progressive degeneration of dopaminergic neurons of the substantia nigra pars compacta, leading to reduction of the striatal dopaminergic terminals. It is known that several factors influence neuronal damage. Among these factors, oxidative stress, immune system activity, microglial cells, and apoptotic mechanisms are of major importance. Currently, several antioxidants have been studied with the aim of reducing/slowing the progression of neurodegenerative processes. Lipoic acid is considered a universal antioxidant because it is an amphipathic substance. Lipoic acid and its reduced form, dihidrolipoic acid, act against reactive oxygen species, reducing oxidative stress. Therefore, this antioxidant has been used in the treatment of many diseases, including a new perspective for the treatment of Parkinson's disease.

Modeling human diseases in Caenorhabditis elegans

Genes linked to human diseases often function in evolutionarily conserved pathways, which can be readily dissected in simple model organisms. Because of its short lifespan and well-known biology, coupled with a completely sequenced genome that shares extensive homology with that of mammals, Caenorhabditis elegans is one of the most versatile and powerful model organisms. Research in C. elegans has been instrumental for the elucidation of molecular pathways implicated in many human diseases. In this review, we introduce C. elegans as a model organism for biomedical research and we survey recent relevant findings that shed light on the basic molecular determinants of human disease pathophysiology. The nematode holds promise of providing clear leads towards the identification of potential targets for the development of new therapeutic interventions against human diseases.

Large-scale in vivo femtosecond laser neurosurgery screen reveals small-molecule enhancer of regeneration

Discovery of molecular mechanisms and chemical compounds that enhance neuronal regeneration can lead to development of therapeutics to combat nervous system injuries and neurodegenerative diseases. By combining high-throughput microfluidics and femtosecond laser microsurgery, we demonstrate for the first time large-scale in vivo screens for identification of compounds that affect neurite regeneration. We performed thousands of microsurgeries at single-axon precision in the nematode Caenorhabditis elegans at a rate of 20 seconds per animal. Following surgeries, we exposed the animals to a hand-curated library of approximately one hundred small molecules and identified chemicals that significantly alter neurite regeneration. In particular, we found that the PKC kinase inhibitor staurosporine strongly modulates regeneration in a concentration- and neuronal type-specific manner. Two structurally unrelated PKC inhibitors produce similar effects. We further show that regeneration is significantly enhanced by the PKC activator prostratin.

Non-apoptotic cell death in Caenorhabditis elegans

The simple nematode worm Caenorhabditis elegans has been instrumental in deciphering the molecular mechanisms underlying apoptosis. Beyond apoptosis, several paradigms of non-apoptotic cell death, either genetically or extrinsically triggered, have also been described in C. elegans. Remarkably, non-apoptotic cell death in worms and pathological cell death in humans share numerous key features and mechanistic aspects. Such commonalities suggest that similarly to apoptosis, non-apoptotic cell death mechanisms are also conserved, and render the worm a useful organism, in which to model and dissect human pathologies. Indeed, the genetic malleability and the sophisticated molecular tools available for C. elegans have contributed decisively to advance our understanding of non-apoptotic cell death. Here, we review the literature on the various types of non-apoptotic cell death in C. elegans and discuss the implications, relevant to pathological conditions in humans.

Lysosomal rupture, necroapoptotic interactions and potential crosstalk between cysteine proteases in neurons shortly after focal ischemia

Ischemic cell death is a complex process and the initial distinction between apoptosis and necrosis appears to be an oversimplification. We previously reported that in ischemic neurons with disrupted plasmalemma, apoptotic mechanisms were also active. In the present study, we investigated cellular co-localization of another necrotic feature, lysosomal rupture, with apoptotic mechanisms in the mouse brain and assessed the potential interactions between cysteine proteases. The lysosomal enzymes were spilled into the cytoplasm 1-4h after ischemia/reperfusion, suggesting that lysosomal membrane integrity was rapidly lost, as occurs in necrosis. The same neurons also exhibited caspase-3 and Bid cleavage, and cytochrome-c release. Caspase-3 activity preceded cathepsin-B leakage in most neurons, and declined by 12h, while lysosomal leakage continued to increase. Concurrent inhibition of cathepsin-B and caspase-3 provided significantly better neuroprotection than obtained with separate use of each inhibitor. These data suggest that necrotic and apoptotic mechanisms may act both in concert as well as independently within the same cell beginning at the onset of ischemia to ensure the demise of damaged neurons. Therefore, combined inhibition of cysteine proteases may abrogate potential shifts between alternative death pathways and improve the success of stroke treatments.

A clear and present danger: endogenous ligands of Toll-like receptors

Neurologic disease promoted by microbial pathogens, sterile injury, or neurodegeneration rapidly induces innate immunity in adjacent healthy tissue, which in turn contributes extensively to neurologic injury. With more recent focus on innate immune processes, it appears that necrotic, but not apoptotic, death mechanisms provoke inflammatory responses likely due to the release or production of endogenous ligands that activate resident immune cells of the central nervous system. These ligands comprise a diverse set of proteins, nucleic acids, and glycosaminoglycans, including heat shock proteins, HMGB1, RNA, DNA, hyaluronan, and heparin sulfate, that stimulate innate immune mechanisms largely through Toll-like receptors (TLRs). The blockade of interactions between endogenous ligands and TLRs may enable neuroprotective therapeutic strategies for a variety of neurologic diseases.

Modulation of BKCa channel gating by endogenous signaling molecules

Large-conductance Ca(2+)- and voltage-activated K(+) (BK(Ca), MaxiK, or Slo1) channels are expressed in almost every tissue in our body and participate in many critical functions such as neuronal excitability, vascular tone regulation, and neurotransmitter release. The functional versatility of BK(Ca) channels owes in part to the availability of a spectacularly wide array of biological modulators of the channel function. In this review, we focus on modulation of BK(Ca) channels by small endogenous molecules, emphasizing their molecular mechanisms. The mechanistic information available from studies on the small naturally occurring modulators is expected to contribute to our understanding of the physiological and pathophysiological roles of BK(Ca) channels.

Neural progenitor cell death is induced by extracellular ATP via ligation of P2X7 receptor

Neural progenitor cells (NPCs) are capable of self-renewal and differentiation into neurons, astrocytes and oligodendrocytes, and have been used to treat several animal models of CNS disorders. In the present study, we show that the P2X7 purinergic receptor (P2X7R) is present on NPCs. In NPCs, P2X7R activation by the agonists extracellular ATP or benzoyl ATP triggers opening of a non-selective cationic channel. Prolonged activation of P2X7R with these nucleotides leads to caspase independent death of NPCs. P2X7R ligation induces NPC lysis/necrosis demonstrated by cell membrane disruption accompanied with loss of mitochondrial membrane potential. In most cells that express P2X7R, sustained stimulation with ATP leads to the formation of a non-selective pore allowing the entry of solutes up to 900 Da, which are reportedly involved in P2X7R-mediated cell lysis. Surprisingly, activation of P2X7R in NPCs causes cell death in the absence of pore formation. Our data support the notion that high levels of extracellular ATP in inflammatory CNS lesions may delay the successful graft of NPCs used to replace cells and repair CNS damage.

Autophagy protects against hypoxic injury in C. elegans

Macroautophagy has been implicated in a variety of pathological processes. Hypoxic/ischemic cellular injury is one such process in which autophagy has emerged as an important regulator. In general, autophagy is induced after a hypoxic/ischemic insult; however, whether the induction of autophagy promotes cell death or recovery is controversial and appears to be context dependent. We have developed C. elegans as a genetically tractable model for the study of hypoxic cell injury. Both necrosis and apoptosis are mechanisms of cell death following hypoxia in C. elegans. However, the role of autophagy in hypoxic injury in C. elegans has not been examined. Here, we found that RNAi knockdown of the C. elegans homologs of beclin 1/Atg6 (bec-1) and LC3/Atg8 (lgg-1, lgg-2), and mutation of Atg1 (unc-51) decreased animal survival after a severe hypoxic insult. Acute inhibition of autophagy by the type III phosphatidylinositol 3-kinase inhibitors, 3-methyladenine and Wortmannin, also sensitized animals to hypoxic death. Hypoxia-induced neuronal and myocyte injury as well as necrotic cellular morphology were increased by RNAi knockdown of BEC-1. Hypoxia increased the expression of a marker of autophagosomes in a bec-1-dependent manner. Finally, we found that the hypoxia hypersensitive phenotype of bec-1(RNAi) animals could be blocked by loss-of-function mutations in either the apoptosis or necrosis pathway. These results argue that inhibition of autophagy sensitizes C. elegans and its cells to hypoxic injury and that this sensitization is blocked or circumvented when either of the two major cell-death mechanisms is inhibited.

Necrotic cell death: From reversible mitochondrial uncoupling to irreversible lysosomal permeabilization

Dictyostelium atg1- mutant cells provide an experimentally and genetically favorable model to study necrotic cell death (NCD) with no interference from apoptosis or autophagy. In such cells subjected to starvation and cAMP, induction by the differentiation-inducing factor DIF or by classical uncouplers led within minutes to mitochondrial uncoupling, which causally initiated NCD. We now report that (1) in this model, NCD included a mitochondrial-lysosomal cascade of events, (2) mitochondrial uncoupling and therefore initial stages of death showed reversibility for a surprisingly long time, (3) subsequent lysosomal permeabilization could be demonstrated using Lysosensor blue, acridin orange, Texas red-dextran and cathepsin B substrate, (4) this lysosomal permeabilization was irreversible, and (5) the presence of the uncoupler was required to maintain mitochondrial lesions but also to induce lysosomal lesions, suggesting that signaling from mitochondria to lysosomes must be sustained by the continuous presence of the uncoupler. These results further characterized the NCD pathway in this priviledged model, contributed to a definition of NCD at the lysosomal level, and suggested that in mammalian NCD even late reversibility attempts by removal of the inducer may be of therapeutic interest.

Neuron and gliocyte death induced by photodynamic treatment: signal processes and neuron-glial interactions

The mechanisms of photodynamic (PD) damage to neurons and gliocytes are discussed. The spike reactions of neurons are described, with stimulation at high concentrations of photosensitizer and inhibition at low concentrations, accompanying necrosis. Glial cells developed both necrosis and apoptosis. Local laser inactivation of neurons increased light-induced apoptosis of gliocytes, i.e., neurons maintained gliocyte survival. Inter-and intracellular signaling plays an important role in the photolesioning of these cells. Studies using inhibitors and activators of signal proteins demonstrated the involvement of the Ca(2+)-dependent, adenylate cyclase, and tyrosine kinase pathways in the responses of neurons and gliocytes to PD treatment. Pharmacological modulation may alter the selectivity of PD neuron and gliocyte damage and the efficacy of PD treatment.

Dantrolene: mechanisms of neuroprotection and possible clinical applications in the neurointensive care unit

Calcium plays a central role in neuronal function and injury. Dantrolene, an inhibitor of the ryanodine receptor, inhibits intracellular calcium release from the sarco-endoplasmic reticulum. We review the available data of dantrolene as a potential neuroprotective agent and briefly summarize its other pharmacologic effects that may have potential applications for patients in the neurointensive care unit (NICU). Areas with the need for continued research are identified.

Neuron-microglia crosstalk up-regulates neuronal FGF-2 expression which mediates neuroprotection against excitotoxicity via JNK1/2

Glial cells and neurons are in constant reciprocal signalling both under physiological and neuropathological conditions. Microglial activation is often associated with neuronal death during inflammation of the CNS, although microglial cells are also known to exert a neuroprotective role. In this work, we investigated the interplay between cerebellar granule neurons (CGN) and microglia in the perspective of CGN survival to an excitotoxic stimulus, quinolinic acid (QA), a catabolite of the tryptophan degradation pathway. We observed that CGN succumb to QA challenge via extracellular signal regulated kinase 1 and 2 (ERK) activation. Our data with transgenic mice expressing the natural inhibitor of calpains, calpastatin, indicate that together with cathepsins they mediate QA-induced toxicity acting downstream of the mitogen-activated protein kinase kinase-ERK pathway. Microglial cells are not only resistant to QA but can rescue neurons from QA-mediated toxicity when they are mixed in culture with neurons or by using mixed culture-conditioned medium (MCCM). This effect is mediated via fibroblast growth factor-2 (FGF-2) present in MCCM. FGF-2 is transcriptionally up-regulated in neurons and secreted in the MCCM as a result of neuron-microglia crosstalk. The neuroprotection is associated with the retention of cathepsins in the lysosomes and with transactivation of inducible heat-shock protein 70 downstream of FGF-2. Furthermore, FGF-2 upon release by neurons activates c-jun N-terminal kinase 1 and 2 pathway which also contributes to neuronal survival. We suggest that FGF-2 plays a pivotal role in neuroprotection against QA as an outcome of neuron-microglia interaction.

Activation of calpain, cathepsin-b and caspase-3 during transient focal cerebral ischemia in rat model

Calpains, cathepsins and caspases play crucial role in mediating cell death. In the present study we observed a cascade of events involving the three proteases during middle cerebral artery occlusion (MCAo) in Wistar rats. The rats were MCA occluded and reperfused at various time points. We observed a maximal increase in the levels of calpains during 1h and 12 h after reperfusion than permanently occluded rats. Further, these levels were reduced by 1st and 3rd day of reperfusion. Similarly the cathepsin-b levels were significantly increased during 1h and 12 h, of reperfusion, followed by activation of caspase-3 which reached maximal levels by 1st and 3rd day of reperfusion. The sequential activation of calpains, cathepsin-b and cleaved caspase-3 is evident by the Western blot analysis which was further confirmed by the cleavage of substrates like PSD-95 and spectrin. The differences in the regional distribution and elevation of these proteases at different reperfusion time periods indicates that differential mode of cell death occur in the brain during cerebral ischemia in rat model.

Physiological characterization of stolon regression in a colonial hydroid

As with many colonial animals, hydractiniid hydroids display a range of morphological variation. Sheet-like forms exhibit feeding polyps close together with short connecting stolons, whereas runner-like forms have more distant polyps and longer connecting stolons. These morphological patterns are thought to derive from rates of stolon growth and polyp formation. Here,stolon regression is identified and characterized as a potential process underlying this variation. Typically, regression can be observed in a few stolons of a normally growing colony. For detailed studies, many stolons of a colony can be induced to regress by pharmacological manipulations of reactive oxygen species (e.g. hydrogen peroxide) or reactive nitrogen species (e.g. nitric oxide). The regression process begins with a cessation of gastrovascular flow to the distal part of the stolon. High levels of endogenous H2O2 and NO then accumulate in the regressing stolon. Remarkably, exogenous treatments with either H2O2 or an NO donor equivalently trigger endogenous formation of both H2O2 and NO. Cell death during regression is suggested by both morphological features, detected by transmission electron microscopy, and DNA fragmentation, detected by TUNEL. Stolon regression may occur when colonies detect environmental signals that favor continued growth in the same location rather than outward growth.

The calpains: modular designs and functional diversity

The eukaryotic calpains are a family of calcium-dependent papain-like proteases and their non-enzymatic relatives whose varied physiological functions are beginning to be fully explored.

The calpain family is named for the calcium dependence of the papain-like, thiol protease activity of the well-studied ubiquitous vertebrate enzymes calpain-1 (μ-calpain) and calpain-2 (m-calpain). Proteins showing sequence relatedness to the catalytic core domains of these enzymes are included in this ancient and diverse eukaryotic protein family. Calpains are examples of highly modular organization, with several varieties of amino-terminal or carboxy-terminal modules flanking a conserved core. Acquisition of the penta-EF-hand module involved in calcium binding (and the formation of heterodimers for some calpains) seems to be a relatively late event in calpain evolution. Several alternative mechanisms for binding calcium and associating with membranes/phospholipids are found throughout the family. The gene family is expanded in mammals, trypanosomes and ciliates, with up to 26 members in Tetrahymena, for example; in striking contrast to this, only a single calpain gene is present in many other protozoa and in plants. The many isoforms of calpain and their multiple splice variants complicate the discussion and analysis of the family, and challenge researchers to ascertain the relationships between calpain gene sequences, protein isoforms and their distinct or overlapping functions. In mammals and plants it is clear that a calpain plays an essential role in development. There is increasing evidence that ubiquitous calpains participate in a variety of signal transduction pathways and function in important cellular processes of life and death. In contrast to relatively promiscuous degradative proteases, calpains cleave only a restricted set of protein substrates and use complex substrate-recognition mechanisms, involving primary and secondary structural features of target proteins. The detailed physiological significance of both proteolytically active calpains and those lacking key catalytic residues requires further study.

Dimemorfan protects rats against ischemic stroke through activation of sigma-1 receptor-mediated mechanisms by decreasing glutamate accumulation

Dimemorfan, an antitussive and a sigma-1 (sigma(1)) receptor agonist, has been reported to display neuroprotective properties. We set up an animal model of ischemic stroke injury by inducing cerebral ischemia (for 1 h) followed by reperfusion (for 24 h) (CI/R) in rats to examine the protective effects and action mechanisms of dimemorfan against stroke-induced damage. Treatment with dimemorfan (1.0 microg/kg and 10 microg/kg, i.v.) either 15 min before ischemia or at the time of reperfusion, like the putative sigma(1) receptor agonist, PRE084 (10 microg/kg, i.v.), ameliorated the size of the infarct zone by 67-72% or 51-52%, respectively, which was reversed by pre-treatment with the selective sigma(1) receptor antagonist, BD1047 (20 microg/kg, i.v.). Major pathological mechanisms leading to CI/R injury including excitotoxicity, oxidative/nitrosative stress, inflammation, and apoptosis are all downstream events initiated by excessive accumulation of extracellular glutamate. Dimemorfan treatment (10 microg/kg, i.v., at the time of reperfusion) inhibited the expressions of monocyte chemoattractant protein-1 and interleukin-1beta, which occurred in parallel with decreases in neutrophil infiltration, activation of inflammation-related signals (p38 mitogen-activated protein kinase, nuclear factor-kappaB, and signal transducer and activator of transcription-1), expression of neuronal and inducible nitric oxide synthase, oxidative/nitrosative tissue damage (lipid peroxidation, protein nitrosylation, and 8-hydroxy-guanine formation), and apoptosis in the ipsilateral cortex after CI/R injury. Dimemorfan treatment at the time of reperfusion, although did not prevent an early rise of glutamate level, significantly prevented subsequent glutamate accumulation after reperfusion. This inhibitory effect was lasted for more than 4 h and was reversed by pre-treatment with BD1047. These results suggest that dimemorfan activates the sigma(1) receptor to reduce glutamate accumulation and then suppresses initiation of inflammation-related events and signals as well as induction of oxidative and nitrosative stresses, leading to reductions in tissue damage and cell death. In conclusion, our results demonstrate for the first time that dimemorfan exhibits protective effects against ischemic stroke in CI/R rats probably through modulation of sigma(1) receptor-dependent signals to prevent subsequent glutamate accumulation and its downstream pathologic events.

Early necrosis and apoptosis of Schwann cells transplanted into the injured rat spinal cord

Poor survival of cells transplanted into the CNS is a widespread problem and limits their therapeutic potential. Whereas substantial loss of transplanted cells has been described, the extent of acute cell loss has not been quantified previously. To assess the extent and temporal profile of transplanted cell death, and the contributions of necrosis and apoptosis to this cell death following spinal cord injury, different concentrations of Schwann cells (SCs), lentivirally transduced to express green fluorescent protein (GFP), were transplanted into a 1-week-old moderate contusion of the adult rat thoracic spinal cord. In all cases, transplanted cells were present from 10 min to 28 days. There was a 78% reduction in SC number within the first week, with no significant decrease thereafter. Real-time polymerase chain reaction showed a similar 80% reduction in GFP-DNA within the first week, confirming that the decrease in SC number was due to death rather than decreased GFP transgene expression. Cells undergoing necrosis and apoptosis were identified using antibodies against the calpain-mediated fodrin breakdown product and activated caspase 3, respectively, as well as ultrastructurally. Six times more SCs died during the first week after transplantation by necrosis than apoptosis, with the majority of cell death occurring within the first 24 h. The early death of transplanted SCs indicates that factors present, even 1 week after a moderate contusion, are capable of inducing substantial transplanted cell death. Intervention by strategies that limit necrosis and/or apoptosis should be considered for enhancing acute survival of transplanted cells.

Autophagy is required for necrotic cell death in Caenorhabditis elegans

Autophagy is the main process for bulk protein and organelle recycling in cells under extracellular or intracellular stress. Deregulation of autophagy has been associated with pathological conditions such as cancer, muscular disorders and neurodegeneration. Necrotic cell death underlies extensive neuronal loss in acute neurodegenerative episodes such as ischemic stroke. We find that excessive autophagosome formation is induced early during necrotic cell death in C. elegans. In addition, autophagy is required for necrotic cell death. Impairment of autophagy by genetic inactivation of autophagy genes or by pharmacological treatment suppresses necrosis. Autophagy synergizes with lysosomal catabolic mechanisms to facilitate cell death. Our findings demonstrate that autophagy contributes to cellular destruction during necrosis. Thus, interfering with the autophagic process may protect neurons against necrotic damage in humans.

A homogeneous assay to measure live and dead cells in the same sample by detecting different protease markers

A method to simultaneously determine the relative numbers of live and dead cells in culture by introducing a combination of two fluorogenic substrates or a fluorogenic and a luminogenic protease substrate into the sample is described. The method is based on detection of differential ubiquitous proteolytic activities associated with intact viable cells and cells that have lost membrane integrity. A cell-permeable peptide aminofluorocoumarin substrate detects protease activity restricted to intact viable cells. Upon cell death, the viable cell protease marker becomes inactive. An impermeable peptide rhodamine 110 (or aminoluciferin) conjugated substrate detects protease activity from nonviable cells that have lost membrane integrity. The multiplex assay can detect 200 dead cells in a population of 10,000 viable cells. The protease substrate reagents do not damage viable cells over the course of the assay, thus the method can be multiplexed further with other assays in a homogeneous format. Ratiometric measurement of viable and dead cells in the same sample provides an internal control that can be used to normalize data from other cell-based assays.

Involvement of Ca2+- and cyclic adenosine monophosphate-mediated signaling pathways in photodynamic injury of isolated crayfish neuron and satellite glial cells

To investigate the mechanisms of oxidative injury of neurons and glia, we studied the photodynamic effect on isolated stretch receptor that consists of only two sensory neurons enwrapped by satellite glial cells. Photodynamic therapy (PDT), a potent inducer of oxidative stress, is a prospective method for destruction of brain tumors. PDT induced functional inactivation and necrosis of neurons, necrosis, apoptosis, and proliferation of glial cells. The roles of calmodulin, calmodulin-dependent kinase II, phospholipase C, protein kinases A and C, and phosphodiesterase in these processes were studied by using their inhibitors: fluphenazine, KN-93, D-609, H89, staurosporine, and papaverine, respectively. PDT-induced firing abolishment was enhanced by H89 or papaverine, whereas staurosporine acted oppositely. Fluphenazine or KN-93 reduced necrosis of neurons and glial cells. H89 enhanced necrosis of neurons, whereas staurosporine enhanced necrosis of glial cells. Inhibition of protein kinases A and C enhanced PDT-induced glial apoptosis. Photodynamic gliosis was prevented by KN-93 or staurosporine. These data indicate possible involvement of calmodulin and calmodulin-dependent kinase II in photoinduced necrosis of neurons and glia. Protein kinase C could protect glial cells from necrosis and apoptosis and participate in photoinduced gliosis and loss of neuronal activity. Protein kinase A maintained neuronal firing and protected neurons from photoinduced necrosis and glial cells from apoptosis. Phosphodiesterase reduced necrosis of photosensitized neurons and glia. Thus, Ca(2+)- and cAMP-mediated signaling pathways were involved in photooxidative injury of neurons and glia. Their pharmacological modulation may differently change the efficacy of photodynamic injury of neurons and glial cells.

Differential response to ischemia in adjacent hippocampalsectors: neuronal death in CA1versus neurogenesis in dentate gyrus

Two hippocampal sectors show distinct responses to transient ischemia: the cornu Ammonis (CA)1 sector undergoes a delayed neuronal death followed by a lack of neuronal generation, while the dentate gyrus (DG) shows slight postischemic damage followed by an increased neurogenesis. Using the monkey experimental paradigm of transient whole brain global ischemia, the 'calpain-cathepsin hypothesis' was formulated in 1998. This hypothesis proposes that following ischemia calpain compromises the integrity of lysosomal membrane, causing a leakage of degrading hydrolytic enzymes--cathepsins--into the cytoplasm. Ischemia induces Ca(2+) mobilization, calpain activation, lysosomal membrane disruption, and cathepsin release, which all occur specifically in the CA1 sector and cause neuronal death. In the postischemic DG, a vascular niche has been implicated in adult neurogenesis, in that adventitial cells of the DG microvascular environment provoke postischemic up-reguation of neurogenesis with the aid of brain-derived neurotrophic factor and polysialylated form of the neural cell adhesion molecule. In parallel, Down's syndrome cell adhesion molecule has recently been shown to be expressed specifically in the neural progenitor cells of DG. In this review, we focus on the monkey experimental paradigm to reveal the remarkable contrasts between CA1 and DG in response to the ischemic insult.

Cardiomyocyte necrosis: alternative mechanisms, effective interventions

Necrotic death of cardiac myocytes is a major contributor to heart failure associated with several cardiac pathologies such as ischemia and reperfusion injury. Preventing cardiomyocyte necrosis is an important challenge towards the development of effective strategies, aiming to battle cardiovascular disorders. While, necrotic cell death was traditionally considered a passive and chaotic process, emerging evidence indicates that specific molecular mechanisms underlie cellular destruction during necrosis. Elucidation of these mechanisms will facilitate therapeutic intervention against heart failure.

Calpain regulation of AMPA receptor channels in cortical pyramidal neurons

AMPA receptors (AMPARs) are the principal glutamate receptors mediating fast excitatory synaptic transmission in neurons. Aberrant extracellular glutamate has long been recognized as a hallmark phenomenon during neuronal excitotoxicity. Excessive glutamate triggers massive Ca(2+) influx through NMDA receptors (NMDARs), which in turn can activate Ca(2+)-dependent protease, calpain. In the present study, we found that prolonged NMDA treatment (100 microM, 10 min) caused a sustained and irreversible suppression of AMPAR-mediated currents in cortical pyramidal neurons, which was largely blocked by selective calpain inhibitors. Biochemical and immunocytochemical studies demonstrated that in cortical cultures, prolonged glutamate or NMDA treatment reduced the level of surface and total GluR1, but not GluR2, subunits in a calpain-dependent manner. Consistent with the in vitro data, in animals exposed to transient ischaemic insults, calpain was strongly activated, and the AMPAR current density and GluR1 expression level were substantially reduced. Moreover, calpain inhibitors blocked the ischaemia-induced depression of AMPAR currents, and the NMDAR-induced, calpain-mediated depression of AMPA responses was occluded in ischaemic animals. Taken together, our studies show that overstimulation of NMDARs reduces AMPAR functions in cortical pyramidal neurons through activation of endogenous calpain, and calpain mediates the ischaemia-induced synaptic depression. The down-regulation of AMPARs by calpain provides a negative feedback to dampen neuronal excitability in excitotoxic conditions like ischaemia and epilepsy.

Mechanosensitive Ion Channels in Caenorhabditis elegans

Caenorhabditis elegans depends critically on mechanosensory perception to negotiate its natural habitat, the soil. The worm displays a rich repertoire of mechanosensitive behaviors, which can be easily examined in the laboratory. This, coupled with the availability of sophisticated genetic and molecular biology tools, renders C. elegans a particularly attractive model organism to study the transduction of mechanical stimuli to biological responses. Systematic genetic analysis has facilitated the dissection of the molecular mechanisms that underlie mechanosensation in the nematode. Studies of various worm mechanosensitive behaviors have converged to identify highly specialized plasma membrane ion channels that are required for the conversion of mechanical energy to cellular signals. Strikingly, similar mechanosensitive ion channels appear to function at the core of the mechanotransduction apparatus in higher organisms, including humans. Thus, the mechanisms responsible for the detection of mechanical stimuli are likely conserved across metazoans. The nematode offers a powerful platform for elucidating the fundamental principles that govern the function of metazoan mechanotransducers. This chapter evaluates the current understanding of mechanotransduction in C. elegans and focuses on the role of mechanosensitive ion channels in specific mechanosensory behavioral responses. The chapter also outlines potential unifying themes, common to mechanosensory transduction in diverse species.

Non-developmentally programmed cell death in Caenorhabditis elegans

The simple nematode worm Caenorhabditis elegans has played a pivotal role in deciphering the molecular mechanisms of apoptosis. Precisely 131 somatic cells undergo programmed apoptotic death during development to contour the 959-cell adult organism. In addition to developmental cell death, specific genetic manipulations and extrinsic factors can trigger non-programmed cell death that is morphologically and mechanistically distinct from apoptosis. Here, we survey paradigms of cell death that is not developmentally programmed in C. elegans and review the molecular mechanisms involved. Furthermore, we consider the potential of the nematode as a platform to investigate pathological cell death. The striking extent of conservation between apoptotic pathways in worms and higher organisms including humans, holds promise that similarly, studies of non-programmed cell death in C. elegans will yield significant new insights, highly relevant to human pathology.

Necrotic death without mitochondrial dysfunction-delayed death of cardiac myocytes following oxidative stress

Oxidative stress has been implicated in cell death in range of disease states including ischemia/reperfusion injury of the heart and heart failure. Here we have investigated the mechanisms of cell death following chronic exposure of cardiac myocytes to oxidative stress initiated by hydrogen peroxide. This exposure induced a delayed form of cell death with ultrastructural changes typical of necrosis, and that was accompanied by the release of lactate dehydrogenase and increased lipid peroxidation. However, this delayed death was not accompanied by the loss of mitochondrial membrane potential or caspase-3 activation. Furthermore, we could demonstrate that this delayed necrosis was at least partially prevented by pre-treatment with the hypertrophic stimuli endothelin-1 or leukemic inhibitory factor. Our results suggest that this delayed form necrosis may also comprise an ordered series of events involving pathways amenable to therapeutic modulation.