A ligand-receptor pair that triggers a non-apoptotic form of programmed cell death

V. J, Pal S, Nair BG, Kar R, Mishra N. Paraptosis: a unique cell death mode for targeting cancer

Programmed cell death (PCD) is the universal process that maintains cellular homeostasis and regulates all living systems' development, health and disease. Out of all, apoptosis is one of the major PCDs that was found to play a crucial role in many disease conditions, including cancer. The cancer cells acquire the ability to escape apoptotic cell death, thereby increasing their resistance towards current therapies. This issue has led to the need to search for alternate forms of programmed cell death mechanisms. Paraptosis is an alternative cell death pathway characterized by vacuolation and damage to the endoplasmic reticulum and mitochondria. Many natural compounds and metallic complexes have been reported to induce paraptosis in cancer cell lines. Since the morphological and biochemical features of paraptosis are much different from apoptosis and other alternate PCDs, it is crucial to understand the different modulators governing it. In this review, we have highlighted the factors that trigger paraptosis and the role of specific modulators in mediating this alternative cell death pathway. Recent findings include the role of paraptosis in inducing anti-tumour T-cell immunity and other immunogenic responses against cancer. A significant role played by paraptosis in cancer has also scaled its importance in knowing its mechanism. The study of paraptosis in xenograft mice, zebrafish model, 3D cultures, and novel paraptosis-based prognostic model for low-grade glioma patients have led to the broad aspect and its potential involvement in the field of cancer therapy. The co-occurrence of different modes of cell death with photodynamic therapy and other combinatorial treatments in the tumour microenvironment are also summarized here. Finally, the growth, challenges, and future perspectives of paraptosis research in cancer are discussed in this review. Understanding this unique PCD pathway would help to develop potential therapy and combat chemo-resistance in various cancer.

Minireview: What is Known about SUMOylation Among NR4A Family Members?

NR4A receptors, including NUR77 (NR4A1), NURR1 (NR4A2) and NOR-1 (NR4A3), form a family of nuclear receptors that act as transcription factors to regulate many physiological and pathological processes such as cell cycle and apoptosis, lipid metabolism, inflammation, carcinogenesis, vascular and neuronal functions. In the absence of known endogenous ligand modulating their physiological functions, the NR4A family remains a class of orphan receptors. However, several post-translational modifications (PTMs), including SUMOylation, have been shown to regulate the expression and/or activity of these receptors. Addition of Small Ubiquitin-like MOdifier (SUMO) proteins is a dynamic and reversible enzymatic process that regulates multiple essential functions of proteins, including nuclear receptors. This review aims at summarizing what is known about the impact of SUMOylation on NR4A family member transcriptional activities and physiological functions.

Substance P failed to reverse dextran sulfate sodium-induced murine colitis mediated by mitochondrial dysfunction: implications in ulcerative colitis

As controversy exists about the efficacy of substance P (SP) in treating ulcerative colitis (UC) with no previous study highlighting the impact of SP on mitochondrial dysfunction in this diseased condition, it became logical to perform the present study. C57BL/6 J mice were administered with DSS @ 3.5%/gm body weight for 3 cycles of 5 days each followed by i.v. dose of SP @ 5nmole per kg for consecutive 7 days. Histopathological features were noticed in the affected colon along with colonic mitochondrial dysfunction, alterations in mitochondrial stress variables and enhanced colonic cell death. Interestingly, SP failed to reverse colitic features and proved ineffective in inhibiting mitochondrial dysfunction. Unexpectedly SP alone seemed to impart detrimental effects on some of the mitochondrial functions, enhanced lipid peroxidation and increased staining intensities for caspases 3 and 9 in the normal colon. To substantiate in vivo findings and to assess free radical scavenging property of SP, Caco-2 cells were exposed to DSS with or without SP in the presence and absence of specific free radical scavengers and antioxidants. Interestingly, in vitro treatment with SP failed to restore mitochondrial functions and its efficacy proved below par compared to SOD and DMSO indicating involvement of O2 •- and •OH in the progression of UC. Besides, catalase, L-NAME and MEG proved ineffective indicating non-involvement of H2O2, NO and ONOO- in UC. Thus, SP may not be a potent anti-colitogenic agent targeting colonic mitochondrial dysfunction for maintenance of colon epithelial tract as it lacks free radical scavenging property.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

Induction of programmed necrosis: A novel anti-cancer strategy for natural compounds

Cell death plays a critical role in organism development and the pathogenesis of diseases. Necrosis is considered a non-programmed cell death in an extreme environment. Recent advances have provided solid evidence that necrosis could be programmed and quite a few types of programmed necrosis, such as necroptosis, ferroptosis, pyroptosis, paraptosis, mitochondrial permeability transition-driven necrosis, and oncosis, have been identified. The specific biomarkers, detailed signaling, and precise pathophysiological importance of programmed necrosis are yet to be clarified, but these forms of necrosis provide novel strategies for the treatment of various diseases, including cancer. Natural compounds are a unique source of lead compounds for the discovery of anti-cancer drugs. Natural compounds can induce both apoptosis and programmed necrosis. In this review, we summarized the recent progress of programmed necrosis and introduced their natural inducers. Noptosis, which is a novel type of programmed necrosis that is strictly dependent on NAD(P)H: quinone oxidoreductase 1-derived oxidative stress was proposed. Furthermore, the anti-cancer strategies that take advantage of programmed necrosis and the main concerns from the scientific community in this regard were discussed.

The nuclear receptor NR4A1 is regulated by SUMO modification to induce autophagic cell death

NR4A is a nuclear receptor protein family whose members act as sensors of cellular environment and regulate multiple processes such as metabolism, proliferation, migration, apoptosis, and autophagy. Since the ligand binding domains of these receptors have no cavity for ligand interaction, their function is most likely regulated by protein abundance and post-translational modifications. In particular, NR4A1 is regulated by protein abundance, phosphorylation, and subcellular distribution (nuclear-cytoplasmic translocation), and acts both as a transcription factor and as a regulator of other interacting proteins. SUMOylation is a post-translational modification that can affect protein stability, transcriptional activity, alter protein-protein interactions and modify intracellular localization of target proteins. In the present study we evaluated the role of SUMOylation as a posttranslational modification that can regulate the activity of NR4A1 to induce autophagy-dependent cell death. We focused on a model potentially relevant for neuronal cell death and demonstrated that NR4A1 needs to be SUMOylated to induce autophagic cell death. We observed that a triple mutant in SUMOylation sites has reduced SUMOylation, increased transcriptional activity, altered intracellular distribution, and more importantly, its ability to induce autophagic cell death is impaired.

The emerging role of paraptosis in tumor cell biology: Perspectives for cancer prevention and therapy with natural compounds

Standard anti-cancer therapies promote tumor growth suppression mainly via induction of apoptosis. However, in most cases cancer cells acquire the ability to escape apoptotic cell death, thus becoming resistant to current treatments. In this setting, the interest in alternative cell death modes has recently increased. Paraptosis is a new form of programmed cell death displaying endoplasmic reticulum (ER) and/or mitochondria dilation, generally due to proteostasis disruption or redox and ion homeostasis alteration. Recent studies have highlighted that several natural compounds can trigger paraptosis in different tumor cell lines. Here, we review the molecular mechanisms underlying paraptotic cell death, as well as the natural products inducing this kind of cell death program. A better understanding of paraptosis should facilitate the development of new therapeutic strategies for cancer prevention and treatment.

Cytoplasmic vacuolization in cell death and survival

Cytoplasmic vacuolization (also called cytoplasmic vacuolation) is a well-known morphological phenomenon observed in mammalian cells after exposure to bacterial or viral pathogens as well as to various natural and artificial low-molecular-weight compounds. Vacuolization often accompanies cell death; however, its role in cell death processes remains unclear. This can be attributed to studying vacuolization at the level of morphology for many years. At the same time, new data on the molecular mechanisms of the vacuole formation and structure have become available. In addition, numerous examples of the association between vacuolization and previously unknown cell death types have been reported. Here, we review these data to make a deeper insight into the role of cytoplasmic vacuolization in cell death and survival.

Substance P and Antagonists of the Neurokinin-1 Receptor in Neuroinflammation Associated with Infectious and Neurodegenerative Diseases of the Central Nervous System

This review addresses the role that substance P (SP) and its preferred receptor neurokinin-1 (NK1R) play in neuroinflammation associated with select bacterial, viral, parasitic, and neurodegenerative diseases of the central nervous system. The SP/NK1R complex is a key player in the interaction between the immune and nervous systems. A common effect of this interaction is inflammation. For this reason and because of the predominance in the human brain of the NK1R, its antagonists are attractive potential therapeutic agents. Preventing the deleterious effects of SP through the use of NK1R antagonists has been shown to be a promising therapeutic strategy, as these antagonists are selective, potent, and safe. Here we evaluate their utility in the treatment of different neuroinfectious and neuroinflammatory diseases, as a novel approach to clinical management of CNS inflammation.

Antagonist of the neurokinin-1 receptor curbs neuroinflammation in ex vivo and in vitro models of Lyme neuroborreliosis

Background

Lyme neuroborreliosis (LNB) can affect both the peripheral (PNS) and the central nervous systems (CNS); it is caused by the spirochete Borrelia burgdorferi. The neuropeptide substance P (SP) is an important mediator of both neuroinflammation and blood-brain barrier dysfunction, through its NK₁ receptor. Increased levels of SP have been shown to correlate with cell death. The present study used both ex vivo and in vitro models of experimentation to determine if the inflammatory mediator production and concomitant cell death caused by exposure of neural tissues and cells to B. burgdorferi could be attenuated by treatment with a NK₁ receptor antagonist.

Methods

We incubated normal rhesus frontal cortex tissue explants (CNS) and primary cultures of rhesus dorsal root ganglia cells (PNS) with live B. burgdorferi and tested the effectiveness of the NK₁ receptor antagonist L703,606 in attenuating inflammatory immune responses and neuronal and glial damage. Culture supernatants and tissue lysates were subjected to multiplex ELISA to quantify immune mediators, while the cells were evaluated for apoptosis by the in situ TUNEL assay. In addition, we identified immune mediators and producer cells in tissue sections by immunofluorescence staining and confocal microscopy.

Results

Co-incubation of both CNS tissues and PNS cells with the NK₁ receptor antagonist attenuated bacterially induced increases in inflammatory cytokine and chemokine production, particularly, IL-6, CXCL8, and CCL2, and reduced apoptosis levels. Confocal microscopy confirmed that neurons and glial cells are sources of these immune mediators. These results suggest that NK₁R antagonist treatment is able to reduce downstream pro-inflammatory signaling, thereby indicating that its systemic administration may slow disease progression.

Conclusions

We propose that SP contributes to neurogenic inflammation in LNB, and provide data to suggest that an NK₁ receptor antagonist may represent a novel neuroprotective therapy.

An RNA interference screen identifies new avenues for nephroprotection

Acute kidney injury is a major public health problem, which is commonly caused by renal ischemia and is associated with a high risk of mortality and long-term disability. Efforts to develop a treatment for this condition have met with very limited success. We used an RNA interference screen to identify genes (BCL2L14, BLOC1S2, C2ORF42, CPT1A, FBP1, GCNT3, RHOB, SCIN, TACR1, and TNFAIP6) whose suppression improves survival of kidney epithelial cells in in vitro models of oxygen and glucose deprivation. Some of the genes also modulate the toxicity of cisplatin, an anticancer agent whose use is currently limited by nephrotoxicity. Furthermore, pharmacological inhibition of TACR1 product NK1R was protective in a model of mouse renal ischemia, attesting to the in vivo relevance of our findings. These data shed new light on the mechanisms of stress response in mammalian cells, and open new avenues to reduce the morbidity and mortality associated with renal injury.

B-cell receptor-associated protein 31 regulates human embryonic stem cell adhesion, stemness, and survival via control of epithelial cell adhesion molecule

B-Cell receptor-associated protein 31 (BAP31) regulates the export of secreted membrane proteins from the endoplasmic reticulum (ER) to the downstream secretory pathway. Previously, we generated a monoclonal antibody 297-D4 against the surface molecule on undifferentiated human embryonic stem cells (hESCs). Here, we found that 297-D4 antigen was localized to pluripotent hESCs and downregulated during early differentiation of hESCs and identified that the antigen target of 297-D4 was BAP31 on the hESC-surface. To investigate the functional role of BAP31 in hESCs, BAP31 expression was knocked down by small interfering RNA. BAP31 depletion impaired hESC self-renewal and pluripotency and drove hESC differentiation into multicell lineages. BAP31 depletion hindered hESC proliferation by arresting cell cycle at G0/G1 phase and inducing caspase-independent cell death. Interestingly, BAP31 depletion reduced hESC adhesion to extracellular matrix (ECM). Analysis of cell surface molecules showed decreased expression of epithelial cell adhesion molecule (EpCAM) in BAP31-depleted hESCs, while ectopic expression of BAP31 elevated the expression of EpCAM. EpCAM depletion also reduced hESC adhesion to ECM, arrested cell cycle at G0/G1 phase and induced cell death, producing similar effects to those of BAP31 depletion. BAP31 and EpCAM were physically associated and colocalized at the ER and cell surface. Both BAP31 and EpCAM depletion decreased cyclin D1 and E expression and suppressed PI3K/Akt signaling, suggesting that BAP31 regulates hESC stemness and survival via control of EpCAM expression. These findings provide, for the first time, mechanistic insights into how BAP31 regulates hESC stemness and survival via control of EpCAM expression.

Paraptosis cell death induction by the thiamine analog benfotiamine in leukemia cells

Benfotiamine is a synthetic thiamine analogue that stimulates transketolase, a cellular enzyme essential for glucose metabolism. Currently, benfotiamine is used to treat diabetic neuropathy. We recently reported that oral benfotiamine induced a temporary but remarkable recovery from acute myeloid leukemia in an elderly patient who was ineligible for standard chemotherapy due to dementia and renal failure. In the present study we present evidences that benfotiamine possess antitumor activity against leukemia cells. In a panel of nine myeloid leukemia cell lines benfotiamine impaired the viability of HL-60, NB4, K562 and KG1 cells and also inhibited the growing of primary leukemic blasts. The antitumor activity of benfotiamine is not mediated by apoptosis, necrosis or autophagy, but rather occurs though paraptosis cell death induction. Mechanistic studies revealed that benfotiamine inhibited the activity of constitutively active ERK1/2 and concomitantly increased the phosphorylation of JNK1/2 kinase in leukemic cells. In addition, benfotiamine induced the down regulation of the cell cycle regulator CDK3 which resulted in G1 cell cycle arrest in the sensitive leukemic cells. Moreover, combination index studies showed that benfotiamine enhanced the antiproliferative activities of cytarabine against leukemia cells. These findings suggest that benfotiamine has antitumor therapeutic potential.

NK1 tachykinin receptor treatment is superior to capsaicin pre-treatment in improving functional outcome following acute ischemic stroke

Previous results from our laboratory have shown that blockade of the substance P (SP) pathway with an NK1 tachykinin receptor antagonist significantly reduces blood brain barrier breakdown, cerebral edema and functional deficits following ischemic stroke. However, it is unclear whether removal of all neuropeptides is more efficacious than blocking SP alone. As such, the aim of the present study was to determine the effect of neuropeptide depletion with capsaicin pre-treatment on functional outcome following acute ischemic stroke in rats. Animals received 125 mg/kg of capsaicin or equal volume of saline vehicle, administered subcutaneously over a 3-day period. At 14 days following treatment animals were subject to 2h of middle cerebral artery occlusion followed by reperfusion. A subset of animals was treated with an NK1 tachykinin receptor antagonist (NAT) or vehicle at 4h after the onset of stroke only. The functional outcome of animals was assessed for a 7-day period following stroke using a rotarod device, the bilateral asymmetry test, modified neurological severity score, open field and angleboard. Although capsaicin pre-treatment improved outcome, treatment with an NK1 tachykinin receptor antagonist was superior in improving post-stroke functional outcome. This data suggests that some neuropeptides may play a beneficial role following stroke, whilst others such as SP are deleterious.

Involvement of substance P and the NK-1 receptor in human pathology

The peptide substance P (SP) shows a widespread distribution in both the central and peripheral nervous systems, but it is also present in cells not belonging to the nervous system (immune cells, liver, lung, placenta, etc.). SP is located in all body fluids, such as blood, cerebrospinal fluid, breast milk, etc. i.e. it is ubiquitous in human body. After binding to the neurokinin-1 (NK-1) receptor, SP regulates many pathophysiological functions in the central nervous system, such as emotional behavior, stress, depression, anxiety, emesis, vomiting, migraine, alcohol addiction, seizures and neurodegeneration. SP has been also implicated in pain, inflammation, hepatitis, hepatotoxicity, cholestasis, pruritus, myocarditis, bronchiolitis, abortus, bacteria and viral infection (e.g., HIV infection) and it plays an important role in cancer (e.g., tumor cell proliferation, antiapoptotic effects in tumor cells, angiogenesis, migration of tumor cells for invasion, infiltration and metastasis). This means that the SP/NK-1 receptor system is involved in the molecular bases of many human pathologies. Thus, knowledge of this system is the key for a better understanding and hence a better management of many human diseases. In this review, we update the involvement of the SP/NK-1 receptor system in the physiopathology of the above-mentioned pathologies and we suggest valuable future therapeutic interventions involving the use of NK-1 receptor antagonists, particularly in the treatment of emesis, depression, cancer, neural degeneration, inflammatory bowel disease, viral infection and pruritus, in which that system is upregulated.

Safety of neurokinin-1 receptor antagonists

INTRODUCTION

The substance P (SP)/neurokinin (NK)-1 receptor system is involved in many pathological processes. NK-1 receptor antagonists have many promising therapeutic indications. However, the only NK-1 receptor antagonist used in clinical practice is the drug aprepitant and its intravenously administered prodrug, fosaprepitant. In general, NK-1 receptor antagonists are safe and well tolerated.

AREAS COVERED

A search was carried out in Medline using the following terms: adverse events, aprepitant, casopitant, clinical trials, CP-122,721, ezlopitant, fosaprepitant, NK-1 receptor antagonists, randomized, safety, side effects, tolerability and vofopitant.

EXPERT OPINION

Most clinical trials have focused on the antiemetic action of aprepitant in cancer patients treated with chemotherapy. However, the efficacy and safety of aprepitant have not been fully tested in other diseases in which the SP/NK-1 receptor system is involved (e.g., cancer, HIV, alcoholism); thus, clinical trials are required. The use of NK-1 receptor antagonists in oncology therapy is quite promising, but to date pharmacological therapy has not exploited the many possible therapies offered by such antagonists.

The role of substance p in ischaemic brain injury

Stroke is a leading cause of death, disability and dementia worldwide. Despite extensive pre-clinical investigation, few therapeutic treatment options are available to patients, meaning that death, severe disability and the requirement for long-term rehabilitation are common outcomes. Cell loss and tissue injury following stroke occurs through a number of diverse secondary injury pathways, whose delayed nature provides an opportunity for pharmacological intervention. Amongst these secondary injury factors, increased blood-brain barrier permeability and cerebral oedema are well-documented complications of cerebral ischaemia, whose severity has been shown to be associated with final outcome. Whilst the mechanisms of increased blood-brain barrier permeability and cerebral oedema are largely unknown, recent evidence suggests that the neuropeptide substance P (SP) plays a central role. The aim of this review is to examine the role of SP in ischaemic stroke and report on the potential utility of NK1 tachykinin receptor antagonists as therapeutic agents.

Dense distribution of macrophages in flexor aspects of the hand and foot of mid-term human fetuses

In the developing human musculoskeletal system, cell death with macrophage accumulation occurs in the thigh muscle and interdigital area. To comprehensively clarify the distribution of macrophages, we immunohistochemically examined 16 pairs of upper and lower extremities without the hip joint (left and right sides) obtained from 8 human fetuses at approximately 10-15 weeks of gestation. Rather than in muscles, CD68-positive macrophages were densely distributed in loose connective tissues of the flexor aspects of the extremities, especially in the wrist, hand and foot. In contrast, no or fewer macrophages were evident in the shoulder and the extensor aspects of the extremities. The macrophages were not concentrated at the enthesis of the tendon and ligament, but tended to be arranged along other connective tissue fibers. Deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling revealed apoptosis in the hand lumbricalis muscles, but not in the area of macrophage accumulation. Likewise, podoplanin-positive lymphatic vessels were not localized to areas of macrophage accumulation. Re-organization of the connective tissue along and around the flexor tendons of the hand and foot, such as development of the bursa or tendon sheath at 10-15 weeks, might require the phagocytotic function of macrophages, although details of the mechanism remain unknown.

The nuclear receptor NR4A1 induces a form of cell death dependent on autophagy in mammalian cells

The control of cell death is a biological process essential for proper development, and for preventing devastating pathologies like cancer and neurodegeneration. On the other hand, autophagy regulation is essential for protein and organelle degradation, and its dysfunction is associated with overlapping pathologies like cancer and neurodegeneration, but also for microbial infection and aging. In the present report we show that two evolutionarily unrelated receptors--Neurokinin 1 Receptor (NK(1)R,) a G-protein coupled receptor, and Insulin-like Growth Factor 1 Receptor (IGF1R), a tyrosine kinase receptor--both induce non-apoptotic cell death with autophagic features and requiring the activity of the autophagic core machinery proteins PI3K-III, Beclin-1 and Atg7. Remarkably, this form of cell death occurs in apoptosis-competent cells. The signal transduction pathways engaged by these receptors both converged on the activation of the nuclear receptor NR4A1, which has previously been shown to play a critical role in some paradigms of apoptosis and in NK(1)R-induced cell death. The activity of NR4A1 was necessary for IGF1R-induced cell death, as well as for a canonical model of cell death by autophagy induced by the presence of a pan-caspase inhibitor, suggesting that NR4A1 is a general modulator of this kind of cell death. During cell death by autophagy, NR4A1 was transcriptionally competent, even though a fraction of it was present in the cytoplasm. Interestingly, NR4A1 interacts with the tumor suppressor p53 but not with Beclin-1 complex. Therefore the mechanism to promote cell death by autophagy might involve regulation of gene expression, as well as protein interactions. Understanding the molecular basis of autophagy and cell death mediation by NR4A1, should provide novel insights and targets for therapeutic intervention.

Transient Appearance of Tyrosine Hydroxylase Immunoreactive Cells in the Midline Epithelial Seam of the Human Fetal Secondary Palate

Objective

Transient immunoreactivity for tyrosine hydroxylase, which mediates the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine, in the midline epithelial seam between the bilateral palatal shelves was investigated in human fetuses.

Materials and Methods

Horizontal or frontal paraffin sections of two human fetuses at 9 and 15 weeks of gestation were used to examine the distribution of tyrosine hydroxylase–immunoreactive cells in regions of the entire head other than the brain. Immunohistochemical staining for S100 protein, calretinin, cytokeratin 14, and vimentin was examined using adjacent or near sections.

Results

Tyrosine hydroxylase–immunoreactive cells were large and densely distributed in the midline epithelial seam at the site of palatal fusion in fetuses at 9 weeks but not in fetuses at 15 weeks, in which the midline epithelial seam had already disappeared. No expression of S100 protein, calretinin, or vimentin was detected, but the midline epithelial seam was positive for cytokeratin 14. Tyrosine hydroxylase immunoreactivity was not detected in epithelia during the process of palatal fusion in mice from E 14.0 to 15.0.

Conclusions

These findings indicate that tyrosine hydroxylase–immunoreactive cells in the midline epithelial seams are nonneural epithelial cells and suggest that the tyrosine hydroxylase is a novel factor involved in normal palatal formation, especially the fate of the midline epithelial seam in humans.

Singapore grouper iridovirus, a large DNA virus, induces nonapoptotic cell death by a cell type dependent fashion and evokes ERK signaling

Virus induced cell death, including apoptosis and nonapoptotic cell death, plays a critical role in the pathogenesis of viral diseases. Singapore grouper iridovirus (SGIV), a novel iridovirus of genus Ranavirus, causes high mortality and heavy economic losses in grouper aquaculture. Here, using fluorescence microscopy, electron microscopy and biochemical assays, we found that SGIV infection in host (grouper spleen, EAGS) cells evoked nonapoptotic programmed cell death (PCD), characterized by appearance of cytoplasmic vacuoles and distended endoplasmic reticulum, in the absence of DNA fragmentation, apoptotic bodies and caspase activation. In contrast, SGIV induced typical apoptosis in non-host (fathead minnow, FHM) cells, as evidenced by caspase activation and DNA fragmentation, suggesting that SGIV infection induced nonapoptotic cell death by a cell type dependent fashion. Furthermore, viral replication was essential for SGIV induced nonapoptotic cell death, but not for apoptosis. Notably, the disruption of mitochondrial transmembrane potential (ΔΨm) and externalization of phosphatidylserine (PS) were not detected in EAGS cells but in FHM cells after SGIV infection. Moreover, the extracellular signal-regulated kinase (ERK) signaling was involved in SGIV infection induced nonapoptotic cell death and viral replication. This is a first demonstration of ERK-mediated nonapoptotic cell death induced by a DNA virus. These findings contribute to understanding the mechanisms of iridovirus pathogenesis.

A substance P antagonist improves outcome when administered 4 h after onset of ischaemic stroke

Previous studies have suggested that substance P (SP) plays a critical role in the development of brain oedema and functional deficits following traumatic brain injury and that SP receptor antagonism may improve outcome. No studies have described such a role in ischemic stroke. The present study characterized the effects of the NK1 tachykinin receptor antagonist, n-acetyl-L-tryptophan (NAT), on blood-brain barrier (BBB) breakdown, oedema formation, infarct volume and functional outcome following reversible ischemic stroke in rats. Ischemia was induced using a reversible thread model of middle cerebral artery occlusion where occlusion was maintained for 2 h before reperfusion. Animals received either NAT or equal volume saline vehicle intravenously at 2 h post-reperfusion. Ischaemic stroke resulted in increased perivascular SP immunoreactivity at 24 h. Administration of NAT significantly reduced oedema formation and BBB permeability at 24 h post-ischemia and significantly improved functional outcome as assessed over 7 days. There was no effect on infarct volume. We conclude that inhibition of SP activity with a NK1 tachykinin receptor antagonist is effective in reducing cerebral oedema, BBB permeability and functional deficits following reversible ischemia and may therefore represent a novel therapeutic approach to the treatment of ischaemic stroke.

Identification of new modulators and protein alterations in non-apoptotic programmed cell death

This study describes the first proteomic analysis of paraptosis--a non-apoptotic form of programmed cell death. As with apoptosis, the first description of paraptosis was based on morphological criteria. Since there are no known markers for paraptosis, the purpose of this study was to dissect changes in the proteome profile occurring during paraptosis. Using one- and two-dimensional SDS-PAGE, Western analysis, and mass spectrometry, we show that during paraptosis, alterations occur mainly in cytoskeletal proteins, signal transduction proteins, mitochondrial proteins, and some metabolic proteins. We also report the identification of: (1) a paraptosis inhibitor, phosphatidylethanolamine binding protein (PEBP-1), and (2) a candidate mediator of paraptosis, prohibitin. Identification of specific paraptotic changes will ultimately lead to tools to detect this type of programmed cell death in in vivo systems and allow for its further characterization.

False positive reactivity of a substance P-antibody in the ectodermal/epithelial plug of the nose, ear, eye and perineum of the human and mouse fetuses

Epithelial/ectodermal plug formation in the developing nose, ear, and eye regions is followed by canalization/recanalization mediated by cell death. However, the mechanism is not well understood. Recently, substance P (SP)-mediated cell death, rather than cell apoptosis, has been reported in neuronal and non-neuronal cells. Horizontal paraffin sections of 5 human fetuses at 15-16 weeks of gestation were used to examine the entire area of the nose, ear, eye and perineum with immunohistochemistry for SP and its receptor neurokinin-1 (NK-1), and protein gene product (PGP) 9.5 and S100 protein to identify whether the positive cells had neural origins. The deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) method was also conducted to identify apoptosis. Four SP antibodies were commercially obtained and compared the results. In addition, using the same antibodies for SP, those results were compared with fetal mouse heads (E14-17). Substance P immunoreactivity of one of the 4 antibodies (sc9758) was clearly found in the nasal plug, the epithelium of the anterior nasal cavity, the entire excretory tear duct, the marginal palpebral conjunctiva, the auditory meatal plug, the parotid duct, the external urethral orifice and, the preputial lamella along the future prepuce. Immunoreactivity was usually seen in enlarged round cells in humans. In fetal mouse heads, in spite of negative reaction in all these sites, the midline epithelial seam at the palate fusion and the oral epithelium especially at and near the tooth germ specifically reacted with the sc9758. Nevertheless, the other 3 antibodies did not react at any of those sites both in human and mouse fetuses. NK-1 receptor-positive cells were seen in the nose and meatal plugs and preputial lamella, but not in the tear duct. S100 protein, PGP 9.5, and TUNEL method all demonstrated negative reactivity at any sc9758-positive sites. Consequently, the present immunoreactivity of the sc9758 antibody seemed to be false positive, but it was likely to react with a specific substance in the epithelial or ectodermal cell because of the clearly restricted staining. Which substance it crossed remains unknown.

Oligomer procyanidins from grape seeds induce a paraptosis-like programmed cell death in human glioblastoma U-87 cells

CONTEXT

We recently reported that F2, an oligomer procyanidin fraction isolated from grape seeds, triggered an original form of cell death in U-87 human glioblastoma cells with a phenotype resembling morphological characteristics of paraptosis. However, the specific death mode induced by F2 and the mechanism of its action have not been assessed so far.

OBJECTIVE

In the present work, we therefore further investigated the death mode of human glioblastoma cells induced by F2 and gained insight into the nature of the signaling pathways activated by F2 in glioblastoma cells.

MATERIALS AND METHODS

Cell viability assay using MTT, (AO/EB) double staining, Western blot analysis, and Ca2+ assay using fura-2.

RESULTS

Morphology studies revealed extensive cytoplasmic vacuolization in dying cells and no apoptotic body formation, membrane bleb formation, or nuclear fragmentation, though some was accompanied by MAPK activation and new protein synthesis, and was independent of caspase activation. Moreover, we demonstrated the involvement of calcium mobilization in F2-induced U-87 cell signaling.

DISCUSSION AND CONCLUSION

Altogether we showed that F2 induced a kind of cell death resembling paraptosis in U-87 cells. The current report complements previous studies on the characterization of F2-induced U-87 cell death, enhances our understanding of the action mechanism of F2 on glioma, and helps in the development of novel antitumor therapeutics.

Taxol induces paraptosis independent of both protein synthesis and MAPK pathway

Our recent studies have shown that high concentration of taxol induced a caspase-independent paraptosis-like cell death and cytoplasmic vacuolization derived predominantly from endoplasmic reticulum (ER) swelling in human lung carcinoma cell lines (ASTC-a-1). In this report, we further explored the relationship between taxol-induced cell death and vacuolization, and the roles of protein synthesis, mitogen-activated protein kinase kinases (MEK), c-jun N-terminal kinase (JNK) and P38 in taxol-induced paraptosis. Enhanced green fluorescent protein (EGFP) was used to probe the cell morphological change, while ER-targeted red fluorescent protein (er-RFP) was used to probe ER spatial distribution. Real-time monitoring of the ER swelling dynamics during the formation of vacuolization inside single living cells co-expressing EGFP and er-RFP further demonstrated that taxol-induced cytoplasmic vacuolization was from the ER restructuring due to fusion and swelling. PI staining showed that taxol-induced vacuolization was not necrosis. These results further demonstrated that the taxol-induced cell death was neither apoptosis nor necrosis, and fitted the criteria of paraptosis characterized by cytoplasmic vacuolization, caspase-independence, lack of apoptotic morphology and insensitivity to broad caspase inhibitor. Our data further indicated that taxol-induced paraptosis required neither protein synthesis nor the participation of MEK, JNK, and P38, which was different from the insulin-like growth factor I receptor (IGFIR)-induced paraptosis. These results suggest that high concentration of taxol activates an alternative paraptotic cell death pathway.

Substance P immunoreactivity increases following human traumatic brain injury

Recent experimental evidence suggests that neuropeptides, and in particular substance P (SP), are released following traumatic brain injury (TBI) and may play a significant role in the aetiology of cerebral edema and increased intracranial pressure. Whether SP may play a similar role in clinical TBI remains unknown and was investigated in the current study. Archival post-mortem material was selected from patients who had sustained TBI, had died and had undergone post-mortem and detailed neuropathological examination (n = 13). A second cohort of patients who had died, but who showed no neuropathological abnormality (n = 10), served as case controls. Changes in SP immunoreactivity were examined in the cerebral cortex directly beneath the subdural haematoma in 7 TBI cases and in proximity to contusions in the other 6 cases. Increased SP perivascular immunoreactivity was observed after TBI in 10/13 cases, cortical neurones in 12/13 and astrocytes in 10/13 cases. Perivascular axonal injury was observed by amyloid precursor protein (APP) immunoreactivity in 6/13 TBI cases. Co-localization of SP and APP in a small subset of perivascular fibres suggests perivascular axonal injury could be a mechanism of release of this neuropeptide. The abundance of SP fibres around the human cerebral microvasculature, particularly post capillary venules, together with the changes observed following TBI in perivascular axons, cortical neurones and astrocytes suggest a potentially important role for substance P in neurogenic inflammation following human TBI.

Smooth-to-striated muscle transition in human esophagus: an immunohistochemical study using fetal and adult materials

BACKGROUND

A craniocaudal transition from smooth to striated muscle occurs in the fetal mouse esophagus muscularis propria, until finally the entire muscle component becomes striated. Although no such investigation has been conducted using human fetuses, the transition appears to be incomplete.

METHODS

In horizontal sections of 10 human fetuses between 9 and 16 weeks of gestation, we identified immunoreactivity for smooth muscle actin (SMA), striated muscle myosin heavy chain (MyH), desmin, PGP9.5, S100 protein, c-kit, and CD68 in the thoracic esophagus. The TUNEL method was used to identify apoptosis. For comparison, the same immunohistochemistry was conducted using 10 adult esophaguses.

RESULTS

In fetuses at all stages examined, a transition zone was found in the upper thoracic esophagus that was attached to the middle one-third of the trachea. In the transition zone, the MyH-positive longitudinal muscle fibers were surrounded by flat, SMA-positive cells, whereas the MyH-positive circular fibers were sometimes located adjacent to the SMA-positive fibers. However, in adults, smooth muscle tended to be clearly separated from striated muscle. The distribution of cells showing immunoreactivity for PGP9.5, S100 or c-kit did not differ between the oral and anal sides of the transition zone. Desmin was positive in the muscularis propria, but negative in the muscularis mucosae. Neither CD68-positive macrophages nor TUNEL-positive cells were present in the esophagus.

CONCLUSIONS

In the human esophagus, the smooth-to-striated muscle transition appears to stop at the mid-thoracic level. Cell death or transdifferentiation of smooth muscle appears unlikely, but phenotypic transformation into desmin-positive myofibroblasts is a possibility.

ERK and cell death: ERK1/2 in neuronal death

Extracellular signal-regulated kinase (ERK) is a versatile protein kinase that regulates many cellular functions. Growing evidence suggests that ERK1/2 plays a crucial role in promoting cell death in a variety of neuronal systems, including neurodegenerative diseases. It is believed that the magnitude and the duration of ERK1/2 activity determine its cellular function. In this review, we summarize recent evidence for a role of ERK1/2 in neuronal death. Furthermore, we discuss the mechanisms involved in ERK1/2 mediating neuronal death.

Exogenous application of persephin influences phosphatidylinositol-3 kinase and MAPK/ERK signalling and enhances proliferation during early development in retinospheres

Persephin (PSPN), a member of the glial cell line-derived neurotrophic factor family, and its implication in the retina is not well understood but might be an interesting therapeutic target for degenerative diseases. Although, PSPN is lost in the chicken during evolution, its target, the GDNF family receptor alpha 4 (GFRalpha4), is still expressed in a temporal and spatial pattern in the developing retina. We used this "knockout-precondition" to study the bioactivity and the effect of exogenous PSPN application and subsequent GFRalpha activation during retinal development in vitro without impairments of endogenous PSPN. Retinospheres, derived from dissociated chicken retina of embryonic day 6, were treated with PSPN and intracellular signalling was monitored. Additionally, PSPN was added during cultivation of the retinospheres and immunhistochemical stainings and Western blotting were performed to evaluate changes in proliferation, apoptosis and differentiation. Exogenous applied PSPN enhanced phosphatidylinositol-3-kinase (PI-3K) signalling and decreased signalling of mitogen-activated protein kinases (MAPK). Most importantly early retinal proliferation was enhanced and glutamine synthetase expression was decreased whereas differentiation of major retinal cell types was not changed. In contrast to GDNF, PSPN is exclusively influencing early progenitors whereas differentiation is not effected and seems to be regulated through PSPN-independent mechanisms. Since the binding site of PSPN and therefore the target of potential therapeuticals, is well conserved among species and is with high probability not able to bind other members of the GDNF-family, these results might be assigned to other species including mammals and humans.

Absence of Bax switched MG132-induced apoptosis to non-apoptotic cell death that could be suppressed by transcriptional or translational inhibition

Targeting to the ubiquitin proteasome degradation pathway has become a promising approach for treating cancer. Previous studies showed that inhibition of the proteasome can induce apoptosis in various cancer cells. However, whether and how the inhibition of the proteasome induces other forms of cell death is not quite known. We previously showed that proteasome inhibitors including MG132 and Bortezomib could induce apoptosis in a Bax- and caspase-dependent way. In the present study, we found that in the absence of Bax and caspase activation, inhibition of the proteasome could also kill cancer cells by an alternative, non-apoptotic form of cell death. We further demonstrated that proteasome inhibitors, such as MG132, could induce intracellular accumulation of polyubiquitinated proteins and extensive cellular vacuolization likely due to ER stress. Translational or transcriptional inhibitors suppressed MG132-induced polyubiquitinated protein accumulation, and in turn inhibited MG132-induced ER stress, cellular vacuolization and cell death. These findings thus suggested that non-apoptotic cell death was resulted from misfolded protein accumulation and ER stress. Furthermore, our study indicated that proteasome inhibitors could be favorable chemotherapeutic agents because they could induce non-apoptotic cell death in addition to apoptosis, which could overcome resistance due to compromised apoptotic machinery.

Substance P up-regulates matrix metalloproteinase-1 and down-regulates collagen in human lung fibroblast

Substance P is involved in inflammatory processes, but its effect on extracellular matrix metabolism has not been studied; therefore, the authors evaluated its effect on collagen synthesis and degradation, expression of pro-alpha1(I) collagen, matrix metalloproteinase-1 and -2, and tissue inhibitor of metalloproteinase-1 and -2 in normal human lung fibroblast strains. Substance P induced a decrease in collagen biosynthesis, concomitant to a down-regulation of pro-alpha1(I) collagen mRNA. In contrast, an increase in collagen degradation was observed, accompanied with an up-regulation of matrix metalloproteinase-1. Substance P did not influence tissue inhibitor of metalloproteinase-1 and -2 or matrix metalloproteinase-2 expression. The results suggest that substance P participates in extracellular matrix metabolism.

Apoptosis-inducing factor: A matter of neuron life and death

The mitochondrial flavoprotein apoptosis-inducing factor (AIF) is the main mediator of caspase-independent apoptosis-like programmed cell death. Upon pathological permeabilization of the outer mitochondrial membrane, AIF is translocated to the nucleus, where it participates in chromatin condensation and is associated to large-scale DNA fragmentation. Heavy down-regulation of AIF expression in mutant mice or reduced AIF expression achieved with small interfering RNA (siRNA) provides neuroprotection against acute neurodegenerative insults. Paradoxically, in addition to its pro-apoptotic function, AIF likely plays an anti-apoptotic role by regulating the production of reactive oxygen species (ROS) via its putative oxidoreductase and peroxide scavenging activities. In this review, we discuss accumulating evidence linking AIF to both acute and chronic neurodegenerative processes by emphasising mechanisms underlying the dual roles apparently played by AIF in these processes.

Direct phosphorylation and regulation of poly(ADP-ribose) polymerase-1 by extracellular signal-regulated kinases 1/2

Sustained activation of poly(ADP-ribose) polymerase-1 (PARP-1) and extracellular signal-regulated kinases 1/2 (ERK1/2) both promote neuronal death. Here we identify a direct link between these two cell death pathways. In a rat model of hypoglycemic brain injury, neuronal PARP-1 activation and subsequent neuronal death were blocked by the ERK1/2 inhibitor 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059). In neuron cultures, PARP-1-mediated neuronal death induced by N-methyl-d-aspartate, peroxynitrite, or DNA alkylation was similarly blocked by ERK1/2 pathway inhibitors. These inhibitors also blocked PARP-1 activation and PARP-1-mediated death in astrocytes. siRNA down-regulation of ERK2 expression in astrocytes also blocked PARP-1 activation and cell death. Direct effects of ERK1/2 on PARP-1 were evaluated by using isolated recombinant enzymes. The activity of recombinant human PARP-1 was reduced by incubation with alkaline phosphatase and restored by incubation with active ERK1 or ERK2. Putative ERK1/2 phosphorylation sites on PARP-1 were identified by mass spectrometry. Using site-directed mutagenesis, these sites were replaced with alanine (S372A and T373A) to block phosphorylation, or with glutamate (S372E and T373E) to mimic constitutive phosphorylation. Transfection of PARP-1 deficient mouse embryonic fibroblasts with the mutant PARP-1 species showed that the S372A and T373A mutations impaired PARP-1 activation, whereas the S372E and T373E mutations increased PARP-1 activity and eliminated the effect of ERK1/2 inhibitors on PARP-1 activation. These results suggest that PARP1 phosphorylation by ERK1/2 is required for maximal PARP-1 activation after DNA damage.

A novel paraptosis pathway involving LEI/L-DNaseII for EGF-induced cell death in somato-lactotrope pituitary cells

We have recently reported that EGF triggers an original form of cell death in pituitary cell line (GH4C1) with a phenotype sharing some characteristics of both apoptosis (internucleosomal DNA fragmentation) and paraptosis (caspase-independence and cytoplasmic vacuolization). However, the endonuclease involved in EGF-induced DNA fragmentation has not been assessed so far. In the present work we therefore further explored the putative paraptosis involvement in EGF-induced cell death and asked whether L-DNaseII might be involved. Indeed, this endonuclease is known to mediate internucleosomal DNA fragmentation in caspase independent manner. Our Western blot, immunocytochemistry and enzymatic measurement assays show that EGF triggers a cleavage of Leukocyte Elastase Inhibitor (LEI) precursor into L-DNaseII, its subsequent enzymatic activation and nuclear translocation thus pointing to the involvement of this endonuclease pathway in caspase-independent DNA fragmentation. In addition, EGF-induced cell death can be blocked by paraptosis inhibitor AIP-1/Alix, but not with its anti-apoptotic C-terminal fragment (Alix-CT). Altogether these data suggest that EGF-induced cell death defines a novel, L-DNaseII-mediated form of paraptosis.

Extracellular signal-regulated kinase as an inducer of non-apoptotic neuronal death

Extracellular signal-regulated kinase (ERK) is a versatile protein kinase, which has been implicated in signaling numerous biological functions ranging from embryonic development to memory formation. Recent reports, including ours, indicate that ERK plays a central role in promoting neuronal degeneration in various neuronal systems including neurodegenerative diseases. Mechanisms involved in ERK-induced neuronal degeneration are beginning to emerge. In this review, we summarize evidence suggesting ERK to be a predominant inducer of a non-apoptotic mode of neuronal death. Further, we discuss the mechanisms and the putative molecular inter-players associated with ERK-mediated neuronal death.

Mechanisms of neural cell death: implications for development of neuroprotective treatment strategies

It has been increasingly recognized that cell death phenotypes and their molecular mechanisms are highly diverse. Necrosis is no longer considered a single entity, passively mediated by energy failure. Moreover, caspase-dependent apoptosis is not the only pathway involved in programmed cell death or even the only apoptotic mechanism. Recent experimental work emphasizes the diverse and interrelated nature of cell death mechanisms. Thus, there are both caspase-dependent and caspase-independent forms of apoptosis, which may differ morphologically as well as mechanistically. There are also necrotic-like phenotypes that require de novo protein synthesis and are, therefore, forms of programmed cell death. In addition, forms of cell death showing certain morphological features of both necrosis and apoptosis have been identified, leading to the term aponecrosis. Considerable experimental evidence also shows that modulation of one form of cell death may lead to another. Together, these observations underscore the need to substantially revise our conceptions about neuroprotection strategies. Use of multiple treatments that target different cell death cascades, or single agents that moderate multiple cell death pathways, is likely to lead to more effective neuroprotection for clinical disorders.

Ischemia-induced programmed cell death in astrocytes

Astrocytes are essential for neuronal survival and function, neurogenesis, and neural repair. Although astrocytes are more resistant than neurons to most stress conditions in vitro, certain astrocyte subtypes, such as the glial fibrillary acidic protein (GFAP)-negative protoplasmic astrocytes that predominate in gray matter structures, may be equally or more sensitive than neurons to ischemia in vivo. Programmed cell death differs from passive, necrotic death in that cell constituents actively participate in cell demise. Like neurons, astrocytes undergo programmed cell death during normal development. Cell culture studies have shown that astrocytes can be induced to undergo apoptosis and other forms of programmed cell death by many factors relevant to ischemia, including acidosis, oxidative stress, substrate deprivation, and cytokines. Animal models of cerebral ischemia have confirmed nuclear condensation and upregulation of Bax and caspases in a subset of astrocytes exposed to ischemia, especially in immature brain. A causal role for these events in astrocyte death is supported by improved astrocyte survival after inhibition of caspase-dependent cell death pathways. Astrocyte survival is also improved by blocking the poly(ADP-ribose)-1 cell death pathway. Markers of programmed cell death are generally less evident and less widespread in astrocytes than in neighboring neurons. However, most studies to date have relied only on markers of classical apoptosis. In addition, these studies have relied almost exclusively on GFAP to identify astrocytes. Since most protoplasmic astrocytes are poorly immunoreactive for GFAP, the extent of ischemia-induced programmed cell death in this cell type remains uncertain.

Growth arrest and non-apoptotic programmed cell death associated with the up-regulation of c-myc mRNA expression in T-47D breast tumor cells following exposure to Epipremnum pinnatum (L.) Engl. hexane extract

Epipremnum pinnatum (L.) Engl. hexane extract produced a significant growth inhibition against T-47D breast carcinoma cells and analysis of cell death mechanisms indicated that the extract elicited a non-apoptotic programmed cell death. T-47D cells exposed to the extract at EC(50) concentration (72 h) for 24 h failed to demonstrate typical DNA fragmentation associated with apoptosis, as carried out using a modified TUNEL assay. In addition, acute exposure to the extract produced an insignificant regulation of caspase-3 and p53 mRNA expression but increased in the c-myc mRNA expression. Ultrastructural analysis using transmission electron microscope demonstrated distinct vacuolated cells, which strongly indicated a Type II non-apoptotic cell death although the changes in chromatin were also detected. The presence of non-apoptotic programmed cell death was then reconfirmed with annexin-V and propidium iodide staining. These findings suggested that up-regulation of c-myc mRNA expression may have contributed to the growth arrest and Type II non-apoptotic programmed cell death in the Epipremnum pinnatum (L.) Engl. hexane extract-treated T-47D cells.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

An alternative form of paraptosis-like cell death, triggered by TAJ/TROY and enhanced by PDCD5 overexpression

Accumulating reports demonstrate that apoptosis does not explain all the forms of programmed cell death (PCD), particularly in individual development and neurodegenerative disease. Recently, a novel type of PCD, designated 'paraptosis', was described. Here, we show that overexpression of TAJ/TROY, a member of the tumor necrosis factor receptor superfamily, induces non-apoptotic cell death with paraptosis-like morphology in 293T cells. Transmission electron microscopy studies reveal extensive cytoplasmic vacuolation and mitochondrial swelling in some dying cells and no condensation or fragmentation of the nuclei. Characteristically, cell death triggered by TAJ/TROY was accompanied by phosphatidylserine externalization, loss of the mitochondrial transmembrane potential and independent of caspase activation. In addition, TAJ/TROY suppressed clonogenic growth of HEK293 and HeLa cells. Interestingly, overexpression of Programmed cell death 5 (PDCD5), an apoptosis-promoting protein, enhanced TAJ/TROY-induced paraptotic cell death. Moreover, cellular endogenous PDCD5 protein was significantly upregulated in response to TAJ/TROY overexpression. These results provide novel evidence that TAJ/TROY activates a death pathway distinct from apoptosis and that PDCD5 is an important regulator in both apoptotic and non-apoptotic PCD.

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.

Growth factor deprivation induces an alternative non-apoptotic death mechanism that is inhibited by Bcl2 in cells derived from neural precursor cells

Although apoptosis has been considered the typical mechanism for physiological cell death, presently alternative mechanisms need to be considered. We previously showed that fibroblast growth factor-2 (FGF2) could act as a survival factor for neural precursor cells. To study the death mechanism activated by the absence of this growth factor, we followed the changes in cell morphology and determined cell viability by staining with several dyes after FGF2 removal from mesencephalic neural-progenitor-cell cultures. The changes observed did not correspond to those associated with apoptosis. After 48 h in the absence of FGF2, cells began to develop vacuoles in their cytoplasm, a phenotype that became very obvious 3-5 days later. Double-membrane vacuoles containing cell debris were observed. Vacuolated cells did not stain with either ethidium bromide or trypan Blue, and did not show chromatin condensations. Nonetheless, during the course of culture, vacuolated cells formed aggregates with highly condensed chromatin and detached from the plate. Neural progenitor cells grown in the presence of FGF2 did not display any of those characteristics. The vacuolated phenotype could be reversed by the addition of FGF2. Typical autophagy inhibitors such as 3-MA and LY294002 inhibited vacuole development, whereas a broad-spectrum caspase inhibitor did not. Interestingly, Bcl-2 overexpression retarded vacuole development. In conclusion, we identified a death autophagy-like mechanism activated by the lack of a specific survival factor that can be inhibited by Bcl2. We propose that anti-apoptotic Bcl2 family members are key molecules controlling death activation independently of the cell degeneration mechanism used.

Paraptosis: mediation by MAP kinases and inhibition by AIP-1/Alix

Programmed cell death (pcd) may take the form of apoptotic or nonapoptotic pcd. Whereas cysteine aspartyl-specific proteases (caspases) mediate apoptosis, the mediators of nonapoptotic cell death programs are much less well characterized. Here, we report that paraptosis, an alternative, nonapoptotic cell death program that may be induced by the insulin-like growth factor I receptor (among other inducers), is mediated by mitogen-activated protein kinases (MAPKs) and inhibited by AIP-1/Alix. The inhibition by AIP-1/Alix is specific for paraptosis since apoptosis was not inhibited. Caspases were not activated in this paradigm, nor were caspase inhibitors effective in blocking cell death. However, insulin-like growth factor I receptor (IGFIR)-induced paraptosis was inhibited by MEK-2-specific inhibitors and by antisense oligonucleotides directed against c-jun N-terminal kinase-1 (JNK-1). These results suggest that IGFIR-induced paraptosis is mediated by MAPKs, and inhibited by AIP-1/Alix.