Mechanisms of AIF-mediated apoptotic DNA degradation in Caenorhabditis elegans

Outer membrane vesicles from commensal microbes contribute to the sponge Tedania sp. development by regulating the expression level of apoptosis-inducing factor (AIF)

The transition from the swimming larval stage to the settlement stage represents a significant node in the marine sponge developmental process. Previous research has shown that the outer membrane vesicles (OMVs) from the bacterial species Tenacibaculum mesophilum associated with the sponge Tedania sp. influence larval settlement: low concentrations of OMVs increase the attachment rate, whereas high concentrations decrease the attachment rate. Here, by comparing the transcriptomes of sponge larvae in filtered seawater (FSW group) and in FSW supplemented with OMVs (FSW-OMV group), the results indicated that bacterial OMVs affected larval settlement by modulating the expression levels of apoptosis-inducing factor (AIF) in the host. Subsequently, quantitative real-time PCR revealed a decrease in aif expression near the time of settlement (SE) compared to that in the control group. RNA interference (RNAi) was used to target the aif gene, and the rate of larval settlement was significantly reduced, confirming the inhibitory effect of high concentrations of OMVs. Moreover, small RNA (sRNA) sequencing of OMVs revealed the existence of abundant AIF-sRNAs of 30 nt, further suggesting that one pathway for the involvement of sponge-associated bacteria in host development is the transport of OMVs and the direct function of cargo loading.

Non-apoptotic role of EGL-1 in exopher production and neuronal health in Caenorhabditis elegans

While traditionally studied for their pro-apoptotic functions, recent research suggests BH3-only proteins also have non-apoptotic roles. Here, we find that EGL-1, the BH3-only protein in Caenorhabditis elegans , promotes the cell-autonomous production of exophers in adult neurons. Exophers are large, micron-scale vesicles that are ejected from the cell and contain cellular components such as mitochondria. EGL-1 facilitates exopher production potentially through regulation of mitochondrial dynamics. Moreover, an endogenous, low level of EGL-1 expression appears to benefit dendritic health. Our findings provide insights into the mechanistic role of BH3-only protein in mitochondrial dynamics, downstream exopher production, and ultimately neuronal health.

Significance statement

BH3-only proteins were known for their function in inducing cell death. Their presence in healthy adult neurons, however, suggests additional roles. Our study focused on the BH3-only protein EGL-1 in the nematode Caenorhabditis elegans , where its apoptotic role was discovered. We reveal a new role in cell-autonomously promoting exopher production - a process where neurons extrude large vesicles containing potentially harmful cell contents. EGL-1 appears to promote this by regulating mitochondrial dynamics. We also report that low levels of EGL-1 benefit neuronal health and function. These findings expand our understanding of BH3-only proteins, mitochondrial dynamics, and exopher production in neurons and provide insights for neurodegenerative diseases.

Nicotinamide adenine dinucleotide phosphate oxidase in pancreatic diseases: Mechanisms and future perspectives

Pancreatitis and pancreatic cancer (PC) stand as the most worrisome ailments affecting the pancreas. Researchers have dedicated efforts to unraveling the mechanisms underlying these diseases, yet their true nature continues to elude their grasp. Within this realm, oxidative stress is often believed to play a causal and contributory role in the development of pancreatitis and PC. Excessive accumulation of reactive oxygen species (ROS) can cause oxidative stress, and the key enzyme responsible for inducing ROS production in cells is nicotinamide adenine dinucleotide phosphate hydrogen oxides (NOX). NOX contribute to pancreatic fibrosis and inflammation by generating ROS that injure acinar cells, activate pancreatic stellate cells, and mediate macrophage polarization. Excessive ROS production occurs during malignant transformation and pancreatic carcinogenesis, creating an oxidative microenvironment that can cause abnormal apoptosis, epithelial to mesenchymal transition and genomic instability. Therefore, understanding the role of NOX in pancreatic diseases contributes to a more in-depth exploration of the exact pathogenesis of these diseases. In this review, we aim to summarize the potential roles of NOX and its mechanism in pancreatic disorders, aiming to provide novel insights into understanding the mechanisms underlying these diseases.

Cell death classification: A new insight based on molecular mechanisms

Cells tend to disintegrate themselves or are forced to undergo such destructive processes in critical circumstances. This complex cellular function necessitates various mechanisms and molecular pathways in order to be executed. The very nature of cell death is essentially important and vital for maintaining homeostasis, thus any type of disturbing occurrence might lead to different sorts of diseases and dysfunctions. Cell death has various modalities and yet, every now and then, a new type of this elegant procedure gets to be discovered. The diversity of cell death compels the need for a universal organizing system in order to facilitate further studies, therapeutic strategies and the invention of new methods of research. Considering all that, we attempted to review most of the known cell death mechanisms and sort them all into one arranging system that operates under a simple but subtle decision-making (If \ Else) order as a sorting algorithm, in which it decides to place and sort an input data (a type of cell death) into its proper set, then a subset and finally a group of cell death. By proposing this algorithm, the authors hope it may solve the problems regarding newer and/or undiscovered types of cell death and facilitate research and therapeutic applications of cell death.

Mitochondrial Factors in the Cell Nucleus

The origin of eukaryotic organisms involved the integration of mitochondria into the ancestor cell, with a massive gene transfer from the original proteobacterium to the host nucleus. Thus, mitochondrial performance relies on a mosaic of nuclear gene products from a variety of genomes. The concerted regulation of their synthesis is necessary for metabolic housekeeping and stress response. This governance involves crosstalk between mitochondrial, cytoplasmic, and nuclear factors. While anterograde and retrograde regulation preserve mitochondrial homeostasis, the mitochondria can modulate a wide set of nuclear genes in response to an extensive variety of conditions, whose response mechanisms often merge. In this review, we summarise how mitochondrial metabolites and proteins-encoded either in the nucleus or in the organelle-target the cell nucleus and exert different actions modulating gene expression and the chromatin state, or even causing DNA fragmentation in response to common stress conditions, such as hypoxia, oxidative stress, unfolded protein stress, and DNA damage.

Bone morphogenetic protein inhibitors and mitochondria targeting agents synergistically induce apoptosis-inducing factor (AIF) caspase-independent cell death in lung cancer cells

BACKGROUND

Bone morphogenetic proteins (BMP) are evolutionarily conserved morphogens that are reactivated in lung carcinomas. In lung cancer cells, BMP signaling suppresses AMP activated kinase (AMPK) by inhibiting LKB1. AMPK is activated by mitochondrial stress that inhibits ATP production, which is enhanced 100-fold when phosphorylated by LKB1. Activated AMPK can promote survival of cancer cells but its "hyperactivation" induces cell death. The studies here reveal novel cell death mechanisms induced by BMP inhibitors, together with agents targeting the mitochondria, which involves the "hyperactivation" of AMPK.

METHODS

This study examines the synergistic effects of two BMP inhibitors together with mitochondrial targeting agents phenformin and Ym155, on cell death of lung cancer cells expressing LKB1 (H1299), LKB1 null (A549), and A549 cells transfected with LKB1 (A549-LKB1). Cell death mechanisms evaluated were the activation of caspases and the nuclear localization of apoptosis inducing factor (AIF). A769662 was used to allosterically activate AMPK. Knockdown of BMPR2 and LKB1 using siRNA was used to examine their effects on nuclear localization of AMPK. Validation studies were performed on five passage zero primary NSCLC.

RESULTS

Both BMP inhibitors synergistically suppressed growth when combined with Ym155 or phenformin in cells expressing LKB1. The combination of BMP inhibitors with mitochondrial targeting agents enhanced the activation of AMPK in lung cancer cells expressing LKB1. Allosteric activation of AMPK with A769662 induced cell death in both H1299 and A549 cells. Cell death induced by the combination of BMP inhibitors and mitochondrial-targeting agents did not activate caspases. The combination of drugs induced nuclear localization of AIF in cells expressing LKB1, which was attenuated by knockdown of LKB1. Knockdown of BMPR2 together with Ym155 increased nuclear localization of AIF. Combination therapy also enhanced cell death and AIF nuclear localization in primary NSCLC.

CONCLUSIONS

These studies demonstrate that inhibition of BMP signaling together with mitochondrial targeting agents induce AIF caspase-independent cell death, which involves the "hyperactivation" of AMPK. AIF caspase-independent cell death is an evolutionarily conserved cell death pathway that is infrequently studied in cancer. These studies provide novel insight into mechanisms inducing AIF caspase-independent cell death in cancer cells using BMP inhibitors. Video Abstract.

The key players of parthanatos: opportunities for targeting multiple levels in the therapy of parthanatos-based pathogenesis

Parthanatos is a form of regulated cell death involved in the pathogenesis of many diseases, particularly neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. Parthanatos is a multistep cell death pathway cascade that involves poly (ADP-ribose) polymerase 1 (PARP-1) overactivation, PAR accumulation, PAR binding to apoptosis-inducing factor (AIF), AIF release from the mitochondria, nuclear translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and MIF-mediated large-scale DNA fragmentation. All the key players in the parthanatos pathway are pleiotropic proteins with diverse functions. An in-depth understanding of the structure-based activity of the key factors, and the biochemical mechanisms of parthanatos, is crucial for the development of drugs and therapeutic strategies. In this review, we delve into the key players of the parthanatos pathway and reveal the multiple levels of therapeutic opportunities for treating parthanatos-based pathogenesis.

Identification and characterization of an apoptosis-inducing factor 1 involved in apoptosis and immune defense of oyster, Crassostrea gigas

The apoptosis-inducing factor (AIF) is a phylogenetically old protein with classic function of inducing caspase-independent apoptosis, which extensively present in all primary kingdoms. In the present study, an AIF homologue (designated as CgAIF1) was identified from oyster Crassostrea gigas. The open reading frame of CgAIF1 cDNA was of 1836 bp encoding a peptide of 611 amino acid residues. There are a Pyr_redox_2 domain and an AIF_C domain in the predicted CgAIF1 protein. The deduced amino acid sequence of CgAIF1 shared 35.44%-79.22% similarity with AIF1s from other species. In the phylogenetic tree, CgAIF1 firstly clustered with mollusc AIF1s, and then with insect AIF1s, displaying separation from vertebrate AIF1s. The mRNA transcripts of CgAIF1 were constitutively distributed in all the tested oyster tissues, with the highest level in gills (12.98-fold of that in haemocytes, p < 0.05). After LPS and Poly (I:C) stimulation, the mRNA transcripts of CgAIF1 in gills were significantly increased at 6 h and 24 h (5.79-fold, p < 0.001, and 21.96-fold compared to the control group, p < 0.05), respectively. In immunocytochemical assay, the CgAIF1 positive signals were mainly distributed in the cytoplasm of haemocytes, while after Poly (I:C) stimulation, the increased CgAIF1 positive signals were observed in the nucleus. Moreover, in the HEK293T cells transfected with pcDNA3.1-CgAIF1 recombinant plasmid, green signal of CgAIF1 were observed in both the cytoplasm and nucleus. The cell mortality rate, cell shrinking and the phosphatidylserine (PS) ectropion (Annexin V⁺/PI^- cells and Annexin V⁺/PI⁺ cells) of CgAIF1 transfected HEK293T cells were significantly increased, compared to the groups with or without pcDNA3.1 transfection. These results collectively suggested that CgAIF1 was a conserved AIF1 member in oysters, and participated in immune response by inducing cell apoptosis.

Emerging role of PARP-1 and PARthanatos in ischemic stroke

Cell death is a key feature of neurological diseases, including stroke and neurodegenerative disorders. Studies in a variety of ischemic/hypoxic mouse models demonstrate that poly(ADP-ribose) polymerase 1 (PARP-1)-dependent cell death, also named PARthanatos, plays a pivotal role in ischemic neuronal cell death and disease progress. PARthanatos has its unique triggers, processors, and executors that convey a highly orchestrated and programmed signaling cascade. In addition to its role in gene transcription, DNA damage repair, and energy homeostasis through PARylation of its various targets, PARP-1 activation in neuron and glia attributes to brain damage following ischemia/reperfusion. Pharmacological inhibition or genetic deletion of PARP-1 reduces infarct volume, eliminates inflammation, and improves recovery of neurological functions in stroke. Here, we reviewed the role of PARP-1 and PARthanatos in stroke and their therapeutic potential.

Mitophagy in Cerebral Ischemia and Ischemia/Reperfusion Injury

Ischemic stroke is a severe cerebrovascular disease with high mortality and morbidity. In recent years, reperfusion treatments based on thrombolytic and thrombectomy are major managements for ischemic stroke patients, and the recanalization time window has been extended to over 24 h. However, with the extension of the time window, the risk of ischemia/reperfusion (I/R) injury following reperfusion therapy becomes a big challenge for patient outcomes. I/R injury leads to neuronal death due to the imbalance in metabolic supply and demand, which is usually related to mitochondrial dysfunction. Mitophagy is a type of selective autophagy referring to the process of specific autophagic elimination of damaged or dysfunctional mitochondria to prevent the generation of excessive reactive oxygen species (ROS) and the subsequent cell death. Recent advances have implicated the protective role of mitophagy in cerebral ischemia is mainly associated with its neuroprotective effects in I/R injury. This review discusses the involvement of mitochondria dynamics and mitophagy in the pathophysiology of ischemic stroke and I/R injury in particular, focusing on the therapeutic potential of mitophagy regulation and the possibility of using mitophagy-related interventions as an adjunctive approach for neuroprotective time window extension after ischemic stroke.

DNase II mediates a parthanatos-like developmental cell death pathway in Drosophila primordial germ cells

During Drosophila embryonic development, cell death eliminates 30% of the primordial germ cells (PGCs). Inhibiting apoptosis does not prevent PGC death, suggesting a divergence from the conventional apoptotic program. Here, we demonstrate that PGCs normally activate an intrinsic alternative cell death (ACD) pathway mediated by DNase II release from lysosomes, leading to nuclear translocation and subsequent DNA double-strand breaks (DSBs). DSBs activate the DNA damage-sensing enzyme, Poly(ADP-ribose) (PAR) polymerase-1 (PARP-1) and the ATR/Chk1 branch of the DNA damage response. PARP-1 and DNase II engage in a positive feedback amplification loop mediated by the release of PAR polymers from the nucleus and the nuclear accumulation of DNase II in an AIF- and CypA-dependent manner, ultimately resulting in PGC death. Given the anatomical and molecular similarities with an ACD pathway called parthanatos, these findings reveal a parthanatos-like cell death pathway active during Drosophila development.

Hexavalent chromium-induced apoptosis in Hep3B cells is accompanied by calcium overload, mitochondrial damage, and AIF translocation

Hexavalent chromium [Cr(VI)] is a pervasive environmental pollutant that can enter the body through a variety of routes and cause organ toxicity, genetic damage, and cancer. Cr(VI)-induced apoptosis is a toxicant mechanism of Cr(VI). Studies have shown that Cr(VI) can induce p53-independent apoptosis, but the mechanisms are not fully understood. The intracellular calcium concentration affects cellular life. Apoptosis-inducing factor (AIF), a caspase-independent apoptotic effector, can induce DNA degradation. Using p53-null Hep3B cells, we investigated the effects of cytoplasmic calcium homeostasis and AIF on Cr(VI)-induced apoptosis. We found that 20 µM of Cr(VI) induced DNA damage and mitochondrial permeability transition pore (MPTP) openings, causing calcium overload that was accompanied by decreased Ca²⁺-Mg²⁺-ATPase and Na⁺-K⁺-ATP activities, downregulation of calmodulin (CaM) and Ca²⁺/CaM-dependent protein kinase II (CAMKII) mRNA, and increased expression of p-CaMKII/CaMKII protein. After treatment with calcium chelating agent BAPTA-AM, Cr(VI)-induced DNA damage, calcium overload, and apoptosis were reduced. AIF was released from the mitochondria and translocated into the nuclei. As the Cr(VI) treatment time progressed, the mRNA and protein expression of B cell lymphoma 2 (Bcl-2) and heat-shock protein 70 (HSP70) decreased, whereas the mRNA and protein expression of Bcl-2-associated X (Bax), cyclophilin A (CypA), and endonuclease G (EndoG) were upregulated. These results indicated that Cr(VI)-induced apoptosis of Hep3B cells (p53-null) was closely associated with calcium overload, and was accompanied by the activation of Ca²⁺/CaM/CaMKII signaling pathway. Besides, Cr(VI) triggered AIF nuclear translocation in Hep3B cells, accompanied by the changes in the levels of apoptosis-associated factors. These results provide additional experimental evidence of the molecular mechanisms involved in Cr(VI)-induced p53-independent apoptosis.

Heterogeneous Strategies to Eliminate Intracellular Bacterial Pathogens

Antibiotic tolerance in bacterial pathogens that are genetically susceptible, but phenotypically tolerant to treatment, represents a growing crisis for public health. In particular, the intracellular bacteria-mediated antibiotic tolerance by acting as “Trojan horses” play a critical and underappreciated role in the disease burden of bacterial infections. Thus, more intense efforts are required to tackle this problem. In this review, we firstly provide a brief overview of modes of action of bacteria invasion and survival in macrophage or non-professional phagocytic cells. Furthermore, we summarize our current knowledge about promising strategies to eliminate these intracellular bacterial pathogens, including direct bactericidal agents, antibiotic delivery to infection sites by various carriers, and activation of host immune functions. Finally, we succinctly discuss the challenges faced by bringing them into clinical trials and our constructive perspectives.

Apoptosis inducing factor: Cellular protective function in Dictyostelium discoideum

Apoptosis Inducing Factor (AIF), a nuclear encoded mitochondrial inter-membrane space flavoprotein with intrinsic NADH oxidase activity, plays an important role in inducing cell death mechanisms. In response to cell death signals, it undergoes mitochondrio-nuclear translocation leading to DNA fragmentation. In addition to its role in cell death, AIF has a pro-survival role, wherein it contributes to the maintenance of mitochondrial structure and function in a coordinated manner. However, its exact mechanism of controlling mitochondrial homeostasis is unclear. The current study aims to explore the protective functions of AIF by its downregulation and overexpression in Dictyostelium discoideum. Constitutive AIF downregulated (dR) cells exhibited compromised oxidative phosphorylation along with elevated levels of cellular ROS. Interestingly, constitutive AIF dR cells showed amelioration in the activity of the ETC complexes upon antioxidant treatment, strengthening AIF's role as an ROS regulator, by virtue of its oxidoreductase property. Also, constitutive AIF dR cells showed lower transcript levels of the various subunits of ETC. Moreover, loss of AIF affected mtDNA content and mitochondrial fusion-fission mechanism, which subsequently caused morphometric mitochondrial alterations. Constitutive AIF overexpressed (OE) cells also showed higher cellular ROS and mitochondrial fission genes transcript levels along with reduced mitochondrial fusion genes transcript levels and mtDNA content. Thus, the results of the current study provide a paradigm where AIF is implicated in cell survival by maintaining mitochondrial bioenergetics, morphology and fusion-fission mechanism in D. discoideum, an evolutionarily significant model organism for mitochondrial diseases.

Effect of oxidative stress on AIF-mediated apoptosis and bovine muscle tenderness during postmortem aging

This study aimed to explore the effect exerted by oxidative stress on apoptosis-inducing factors (AIF)-mediated apoptosis and bovine muscle tenderness during postmortem aging. We investigated the reactive oxygen species (ROS) content, mitochondrial membrane permeability, AIF expression level, nucleus apoptosis, shear force, myofibril fragmentation index, pH, and energy level. According to the results, a rise in ROS content was accompanied by the rise in mitochondrial membrane permeability from 6 to 72 hr. In the meantime, the AIF expression in mitochondria was downregulated significantly within 72 hr. However, samples treated with N-acetylcysteine had significantly lower ROS content (6 to 72 hr) and mitochondrial membrane permeability (12 to 72 hr) than the control group. Moreover, during postmortem aging, the variations in AIF levels in mitochondria were closely associated with meat tenderization and nucleus apoptosis. These findings demonstrated that oxidative stress induced by ROS significantly promoted AIF release from mitochondria by enhancing the mitochondrial membrane permeability, and the released AIF mediated nucleus apoptosis that further enhanced bovine muscle tenderness. Besides, results suggest that in the early stage, the environmental factors (ATP content and pH) significantly decreased (0 to 72 hr), whereas ROS-induced oxidative stress had no significant effect on environmental factors. These observations further suggested that during postmortem aging, the decrease of pH and ATP consumption are required by AIF release. We conclude that ROS-induced oxidative stress and internal environment are vital for meat tenderization through the regulation of AIF-mediated apoptosis pathway. PRACTICAL APPLICATION: ROS-induced oxidative stress contributes to bovine muscle tenderization by promoting cell apoptosis. It is likely to lay a theoretical foundation for developing innovative tenderization techniques by altering the internal oxidation environment of postmortem muscles.

Functions of reactive oxygen species in apoptosis and ganoderic acid biosynthesis in Ganoderma lucidum

Ganoderma lucidum is a medicinal fungus that is widely used in traditional medicine. Fungal PacC is recognized as an important transcription factor that functions during adaptation to environmental pH, fungal development and secondary metabolism. Previous studies have revealed that GlPacC plays important roles in mycelial growth, fruiting body development and ganoderic acid (GA) biosynthesis. In this study, using a terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay, we found that the apoptosis level was increased when PacC was silenced. The transcript and activity levels of caspase-like proteins were significantly increased in the PacC-silenced (PacCi) strains compared with the control strains. Silencing PacC also resulted in an increased reactive oxygen species (ROS) levels (∼2-fold) and decreased activity levels of enzymes involved in the antioxidant system. Further, we found that the intracellular ROS levels contributed to apoptosis and GA biosynthesis. Adding N-acetyl-cysteine and vitamin C decreased intracellular ROS and resulted in the inhibition of apoptosis in the PacCi strains. Additionally, the GA biosynthesis was different between the control strains and the PacCi strains after intracellular ROS was eliminated. Taken together, the findings showed that silencing PacC can result in an intracellular ROS burst, which increases cell apoptosis and GA biosynthesis levels. Our study provides novel insight into the functions of PacC in filamentous fungi.

TRPM2 ion channel is involved in the aggravation of cognitive impairment and down regulation of epilepsy threshold in pentylenetetrazole-induced kindling mice

Epilepsy is one of the most common neurological conditions. Recent findings suggest that one of the mechanisms promoting its existence is calcium influx. The transient receptor potential melastatin type 2 channel (TRPM2) is a Ca²⁺-permeable cation channel that contributes to cell apoptosis; its possible signaling pathway is the PARP1/BNIP3/AIF/Endo G pathway that may be related to epilepsy. The aim of this study was to investigate the TRPM2 channel's involvement in epilepsy and how it works. We also explored the possible role of the TRPM2 channel on cognitive ability and emotion in epilepsy. To accomplish our goals, we used different animal epilepsy models to study the effect of the TRPM2 channel on epilepsy. The results showed that the knockout (KO) of the TRPM2 gene might play a protective role in epilepsy. Considering the advantages attributed to pentylenetetrazole (PTZ)-induced kindling mouse model, we used the model for the following assessments: 1. to observe changes in cognition and anxiety between wild type (WT) mice and TRPM2-KO mice with the recognition of new things trial and elevated plus-maze; 2. to determine the expression of apoptosis-associated proteins (PARP1, BNIP3, AIF, and Endo G) using Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot; 3. to observe neurons pathologic damages and astrocyte activation in each group. The main findings of our study were: (a) TRPM2-KO had a protective effect on epilepsy; (b) TRPM2-KO improved spatial memory deficits overtime during epilepsy, but it did not improve anxiety; (c) the protective effect probably occurred via the PARP1 downstream signaling pathway; (d) TRPM2-KO could ameliorate epilepsy-induced hippocampal pathological damages and weaken astrocyte activation. These findings may provide a new approach for the treatment of epilepsy and early intervention.

AEBP1 down regulation induced cell death pathway depends on PTEN status of glioma cells

Glioblastoma (GBM) is the most common aggressive form of brain cancer with overall dismal prognosis (10–12 months) despite all current multimodal treatments. Previously we identified adipocyte enhancer binding protein 1 (AEBP1) as a differentially regulated gene in GBM. On probing the role of AEBP1 over expression in glioblastoma, we found that both cellular proliferation and survival were affected upon AEBP1 silencing in glioma cells, resulting in cell death. In the present study we report that the classical caspase pathway components are not activated in cell death induced by AEBP1 down regulation in PTEN-deficient (U87MG and U138MG) cells. PARP-1 was not cleaved but over-activated under AEBP1 down regulation which leads to the synthesis of PAR in the nucleus triggering the release of AIF from the mitochondria. Subsequently, AIF translocates to the nucleus along with MIF causing chromatinolysis. AEBP1 positively regulates PI3KinaseCβ by the binding to AE-1 binding element in the PI3KinaseCβ promoter. Loss of PI3KinaseCβ expression under AEBP1 depleted condition leads to excessive DNA damage and activation of PARP-1. Furthermore, over expression of PIK3CB (in trans) in U138MG cells prevents DNA damage in these AEBP1 depleted cells. On the contrary, AEBP1 down regulation induces caspase-dependent cell death in PTEN-proficient (LN18 and LN229) cells. Ectopic expression of wild-type PTEN in PTEN-deficient U138MG cells results in the activation of canonical caspase and Akt dependent cell death. Collectively, our findings define AEBP1 as a potential oncogenic driver in glioma, with potential implications for therapeutic intervention.

TRPM2 channel regulates cytokines production in astrocytes and aggravates brain disorder during lipopolysaccharide-induced endotoxin sepsis

Sepsis is one of the most significant challenges in intensive care units, which is associated with increased morbidity and mortality. Sepsis-associated encephalopathy (SAE) is a severe complication which can cause death and serious disabilities. Calcium signaling in astrocyte is essential for cellular activation and the potential resolution of infection or inflammation in SAE patients. The transient receptor potential melastatin 2 (TRPM2) channel has been identified as a unique fusion of a Ca2+-permeable nonselective cation channel, which plays an important role in inflammation and immune response. Because of its role as an oxidative stress sensor in astrocytes, we investigated the function of TRPM2 in inflammation mediators (interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α) release, Bcl-2/E1B-19 K-interacting protein 3 (BNIP3), apoptosis inducing factor (AIF) and Endonuclease G (Endo G) expression. We showed that TRPM2-KO mice, when intraperitoneally (i.p) injected with LPS, exhibited better neurologic assessment scores and decreased inflammatory injury in hippocampal neurons compared with wild-type (WT) mice. The absence of TRPM2 triggered less production of inflammatory mediators (IL-1β, IL-6, TNF-α) and decreased apoptosis related proteins (BNIP3, AIF, Endo G) expressions in response to LPS induced sepsis. Furthermore, TRPM2-deficient astrocytes (transfected with TRPM2 siRNA) upon LPS stimulation also induced decreased IL-1β, IL-6 and TNF-α level. Our data suggested that decreased production of inflammatory cytokines and apoptosis related proteins with TRPM2 deletion could regulate inflammatory stress and decrease inflammatory injury in hippocampal neurons, and consequently, ameliorate brain disorder.

Organochlorinated pesticides expedite the enzymatic degradation of DNA

Extracellular DNA in the environment may play important roles in genetic diversity and biological evolution. However, the influence of environmental persistent organic contaminants such as organochlorinated pesticides (e.g., hexachlorocyclohexanes [HCHs]) on the enzymatic degradation of extracellular DNA has not been elucidated. In this study, we observed expedited enzymatic degradation of extracellular DNA in the presence of α-HCH, β-HCH and γ-HCH. The HCH-expedited DNA degradation was not due to increased deoxyribonuclease I (DNase I) activity. Our spectroscopic and computational results indicate that HCHs bound to DNA bases (most likely guanine) via Van der Waals forces and halogen bonds. This binding increased the helicity and accumulation of DNA base pairs, leading to a more compact DNA structure that exposed more sites susceptible to DNase I and thus expedited DNA degradation. This study provided insight into the genotoxicity and ecotoxicity of pesticides and improved our understanding of DNA persistence in contaminated environments.

p53- and ROS-mediated AIF pathway involved in TGEV-induced apoptosis

We previously demonstrated that transmissible gastroenteritis virus (TGEV) could induce apoptosis through caspase signaling. However, apoptosis was not completely prevented by caspases inhibitors, suggesting that there may be a caspase-independent pathway involved in TGEV-induced cell apoptosis. In this study, we investigated the regulation of apoptosis-inducing factor (AIF) on TGEV-induced apoptotic pathway. Results indicated that AIF translocated from the mitochondria to nucleus during TGEV infection, and the AIF inhibitor, N-phenylmaleimide (NP), significantly attenuated the apoptosis. In addition, the translocation of AIF was inhibited by Veliparib (ABT-888), an inhibitor of poly (ADP-ribose) polymerase (PARP). And the reactive oxygen species (ROS) scavenger, pyrrolidinedithiocarbamic (PDTC), redistributed AIF in the mitochondria and nucleus in TGEV-infected cells. Moreover, the protein levels in nucleus and the mRNA levels of AIF were inhibited in the presence of the p53 inhibitor, pifithrin-α (PFT-α) or in TGEV-infected p53-/-cells. Furthermore, TGEV-induced apoptosis was blocked by combination of three or more inhibitors, such as pan caspase inhibitor Z-VAD-FMK, NP, ABT-888, PDTC, PFT-α, to treat PK-15 cells. Taken together, these results suggest that the p53- and ROS-mediated AIF pathway and caspase-dependent pathway were involved in TGEV-induced apoptosis.

Study on the apoptosis mediated by apoptosis-inducing-factor and influencing factors of bovine muscle during postmortem aging

This study investigated the apoptosis pathway mediated by apoptosis-inducing factors (AIF) and internal factors that influence the release of AIF. The results indicated that the AIF expression was decreased in mitochondria and increased in nucleus (P < 0.05). However, no significant differences were observed in the AIF expression in mitochondria with caspase inhibitor treatment. The optical density of nucleus and mitochondrial swelling was significant increased (P < 0.05). Reactive oxygen species (ROS) fell gradually within the first 6 h and increased in the next 24 h. Calpain I activity was decreased, Ca²⁺ concentration, cathepsin B and D activities was increased (P < 0.05). The results demonstrated that AIF-mediated caspase-dependent pathway was a new mitochondrial apoptosis pathway and that mitochondrial swelling, ROS content, Ca²⁺ concentration, calpain I, cathepsin B and cathepsin D activities are the key influencing factors in apoptosis in postmortem bovine muscle.

DRP-1-mediated apoptosis induces muscle degeneration in dystrophin mutants

Mitochondria are double-membrane subcellular organelles with highly conserved metabolic functions including ATP production. Mitochondria shapes change continually through the combined actions of fission and fusion events rendering mitochondrial network very dynamic. Mitochondria are largely implicated in pathologies and mitochondrial dynamics is often disrupted upon muscle degeneration in various models. Currently, the exact roles of mitochondria in the molecular mechanisms that lead to muscle degeneration remain poorly understood. Here we report a role for DRP-1 in regulating apoptosis induced by dystrophin-dependent muscle degeneration. We found that: (i) dystrophin-dependent muscle degeneration was accompanied by a drastic increase in mitochondrial fragmentation that can be rescued by genetic manipulations of mitochondrial dynamics (ii) the loss of function of the fission gene drp-1 or the overexpression of the fusion genes eat-3 and fzo-1 provoked a reduction of muscle degeneration and an improved mobility of dystrophin mutant worms (iii) the functions of DRP-1 in apoptosis and of others apoptosis executors are important for dystrophin-dependent muscle cell death (iv) DRP-1-mediated apoptosis is also likely to induce age-dependent loss of muscle cell. Collectively, our findings point toward a mechanism involving mitochondrial dynamics to respond to trigger(s) of muscle degeneration via apoptosis in Caenorhabditis elegans.

Apoptosis-Inducing Factor (AIF) in Physiology and Disease: The Tale of a Repented Natural Born Killer

Apoptosis-inducing factor (AIF) is a mitochondrial oxidoreductase that contributes to cell death programmes and participates in the assembly of the respiratory chain. Importantly, AIF deficiency leads to severe mitochondrial dysfunction, causing muscle atrophy and neurodegeneration in model organisms as well as in humans. The purpose of this review is to describe functions of AIF and AIF-interacting proteins as regulators of cell death and mitochondrial bioenergetics. We describe how AIF deficiency induces pathogenic processes that alter metabolism and ultimately compromise cellular homeostasis. We report the currently known AIFM1 mutations identified in humans and discuss the variability of AIFM1-related disorders in terms of onset, organ involvement and symptoms. Finally, we summarize how the study of AIFM1-linked pathologies may help to further expand our understanding of rare inherited forms of mitochondrial diseases.

•

AIF is a mitochondrial NADH-dependent oxidoreductase.

•

Nuclear translocation of AIF occurs during cell death and has been associated with human disorders.

•

Under physiological settings, AIF participates to the biogenesis of the respiratory complexes.

•

AIFM1 mutations have been identified in patients with impaired mitochondrial bioenergetics.

•

Inherited AIFM1 mutations lead to a variety of clinical manifestations, including severe childhood-onset mitochondrial diseases.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

WAH-1/AIF regulates mitochondrial oxidative phosphorylation in the nematode Caenorhabditis elegans

Impaired mitochondrial energy metabolism contributes to a wide range of pathologic conditions, including neurodegenerative diseases. Mitochondrial apoptosis-inducing factor (AIF) is required for the correct maintenance of mitochondrial electron transport chain. An emerging body of clinical evidence indicates that several mutations in the AIFM1 gene are causally linked to severe forms of mitochondrial disorders. Here we investigate the consequence of WAH-1/AIF deficiency in the survival of the nematode Caenorhabditis elegans. Moreover, we assess the survival of C. elegans strains expressing a disease-associated WAH-1/AIF variant. We demonstrate that wah-1 downregulation compromises the function of the oxidative phosphorylation system and reduces C. elegans lifespan. Notably, the loss of respiratory subunits induces a nuclear-encoded mitochondrial stress response independently of an evident increase of oxidative stress. Overall, our data pinpoint an evolutionarily conserved role of WAH-1/AIF in the maintenance of proper mitochondrial activity.

Flavonoids of Rosa roxburghii Tratt Exhibit Anti-Apoptosis Properties by Regulating PARP-1/AIF

Radioprotection is an important approach to reduce the side-effects of radiotherapy. The radioprotective effect of the flavonoids of Rosa roxburghii Tratt (FRT) has been confirmed, and the mechanism has been identified as theBcl-2/caspase-3/PARP-1 signaling pathway. In this study, we investigated the effects of FRT on the intercellular adhesion molecule (ICAM), and vascular cell adhesion protein (VCAM) in addition to apoptosis-related proteins such as Bax/Bcl-2, p-ERK/ERK, p-p53/p53, and p-p38/p38. In the present study, we focused on the effect of FRT on PARP-1/AIF. Ionizing radiation triggered the activation of PARP-1 and AIF translocation from the mitochondrion to the nucleus. The inhibition of PARP-1/AIF signaling pathway by FRT was investigated. Our results showed that the expressions of Bax/Bcl-2, p-ERK/ ERK, p-p53/p53, and p-p38/p38 were decreased after FRT treatment compared with the radiation-treated group. FRT inhibited PARP-1 activation to inhibit AIF translocation from mitochondrion to nucleus. Pretreatment with FRT diminished the comet's tail and reduced fragments in six Gy-irradiated thymocytes compared with the irradiated cells without FRT treatment. We conclude that FRT enhanced radioprotection at least partially by regulating PARP-1/AIF to reduce apoptosis. J. Cell. Biochem. 118: 3943-3952, 2017. © 2017 Wiley Periodicals, Inc.

Pro-Inflammatory CXCR3 Impairs Mitochondrial Function in Experimental Non-Alcoholic Steatohepatitis

Mitochondrial dysfunction plays a crucial role in the development of non-alcoholic steatohepatitis (NASH). However, the regulator of mitochondrial dysfunction in the pathogenesis of NASH is still largely unclear. CXCR3 is an essential pro-inflammatory factor in chronic liver diseases. We explored the significance of CXCR3 in regulating mitochondrial function during NASH development in animal models and cultured hepatocytes.

METHODS

The effects of CXCR3 on mitochondrial function were evaluated by genetic knockout or pharmacological inhibition in mouse models and in vitro. The ultrastructural changes of mitochondria were assessed by transmission electron microscopy (TEM). Hepatic levels of mitochondrial reactive oxygen species (ROS), DNA damage, membrane potential and ATP were examined.

RESULTS

CXCR3 ablation by genetic knockout or pharmacological inhibition in mice protected against NASH development by influencing mitochondrial function. Similarly, depletion of CXCR3 reduced steatohepatitis injury in cultured hepatocytes. TEM analysis revealed that liver mitochondrial integrity was much improved in CXCR3 knockout (CXCR3^-/-) compared to wildtype (WT) mice. In agreement with this, impaired mitochondrial function was pronounced in WT mice compared to CXCR3^-/- mice, evidenced by increased protein expression of dynamic-related protein-1 (DRP1) and fission-1 (FIS1) and decreased protein expression of mitofusin-1 (MFN1). Mitochondrial dysfunction was induced in AML-12 hepatocytes by methionine and choline deficient medium and in HepG2 cells by palmitic acid. The impaired mitochondrial function in both cell lines was evidenced by reduced membrane potential and ATP content, and by increased mitochondrial ROS accumulation and DNA damage. However, CXCR3 knockdown by siCXCR3 significantly diminished the mitochondrial dysfunction in both AML-12 and HepG2 hepatocytes. In addition, inhibition of CXCR3 by CXCR3 specific antagonists SCH546738 and AMG487 restored mitochondrial function and inhibited mitochondrial-dependent apoptosis in the liver of WT mice fed with methionine and choline deficient diet.

CONCLUSION

CXCR3 induces mitochondrial dysfunction, which contributes to the pathogenesis of steatohepatitis. Pharmacologic blockade of CXCR3 prevents mitochondrial dysfunction and restores the severity of steatohepatitis, indicating a potential clinical impact for controlling the disease.

Caenorhabditis elegans ATPase inhibitor factor 1 (IF1) MAI-2 preserves the mitochondrial membrane potential (Δψm) and is important to induce germ cell apoptosis

When the electrochemical proton gradient is disrupted in the mitochondria, IF1 (Inhibitor Factor-1) inhibits the reverse hydrolytic activity of the F1Fo-ATP synthase, thereby allowing cells to conserve ATP at the expense of losing the mitochondrial membrane potential (Δψm). The function of IF1 has been studied mainly in different cell lines, but these studies have generated contrasting results, which have not been helpful to understand the real role of this protein in a whole organism. In this work, we studied IF1 function in Caenorhabditis elegans to understand IF1´s role in vivo. C. elegans has two inhibitor proteins of the F1Fo-ATPase, MAI-1 and MAI-2. To determine their protein localization in C. elegans, we generated translational reporters and found that MAI-2 is expressed ubiquitously in the mitochondria; conversely, MAI-1 was found in the cytoplasm and nuclei of certain tissues. By CRISPR/Cas9 genome editing, we generated mai-2 mutant alleles. Here, we showed that mai-2 mutant animals have normal progeny, embryonic development and lifespan. Contrasting with the results previously obtained in cell lines, we found no evident defects in the mitochondrial network, dimer/monomer ATP synthase ratio, ATP concentration or respiration. Our results suggest that some of the roles previously attributed to IF1 in cell lines could not reflect the function of this protein in a whole organism and could be attributed to specific cell lines or methods used to silence, knockout or overexpress this protein. However, we did observe that animals lacking IF1 had an enhanced Δψm and lower physiological germ cell apoptosis. Importantly, we found that mai-2 mutant animals must be under stress to observe the role of IF1. Accordingly, we observed that mai-2 mutant animals were more sensitive to heat shock, oxidative stress and electron transport chain blockade. Furthermore, we observed that IF1 is important to induce germ cell apoptosis under certain types of stress. Here, we propose that MAI-2 might play a role in apoptosis by regulating Δψm. Additionally, we suggest that IF1 function is mainly observed under stress and that, under physiological conditions, this protein does not play an essential role.

Programmed Cell Death During Caenorhabditis elegans Development

Programmed cell death is an integral component of Caenorhabditis elegans development. Genetic and reverse genetic studies in C. elegans have led to the identification of many genes and conserved cell death pathways that are important for the specification of which cells should live or die, the activation of the suicide program, and the dismantling and removal of dying cells. Molecular, cell biological, and biochemical studies have revealed the underlying mechanisms that control these three phases of programmed cell death. In particular, the interplay of transcriptional regulatory cascades and networks involving multiple transcriptional regulators is crucial in activating the expression of the key death-inducing gene egl-1 and, in some cases, the ced-3 gene in cells destined to die. A protein interaction cascade involving EGL-1, CED-9, CED-4, and CED-3 results in the activation of the key cell death protease CED-3, which is tightly controlled by multiple positive and negative regulators. The activation of the CED-3 caspase then initiates the cell disassembly process by cleaving and activating or inactivating crucial CED-3 substrates; leading to activation of multiple cell death execution events, including nuclear DNA fragmentation, mitochondrial elimination, phosphatidylserine externalization, inactivation of survival signals, and clearance of apoptotic cells. Further studies of programmed cell death in C. elegans will continue to advance our understanding of how programmed cell death is regulated, activated, and executed in general.

GOP-1 promotes apoptotic cell degradation by activating the small GTPase Rab2 in C. elegans

Rab2 regulates multiple membrane traffic processes, but how it is recruited to and activated on the target membrane remains unclear. Here, Yin et al. identify a conserved protein, GOP-1, that activates UNC-108/Rab2 to promote phagosome, endosome, and DCV maturation.

Apoptotic cells generated by programmed cell death are engulfed by phagocytes and enclosed within plasma membrane–derived phagosomes. Maturation of phagosomes involves a series of membrane-remodeling events that are governed by the sequential actions of Rab GTPases and lead to formation of phagolysosomes, where cell corpses are degraded. Here we identified gop-1 as a novel regulator of apoptotic cell clearance in Caenorhabditis elegans. Loss of gop-1 affects phagosome maturation through the RAB-5–positive stage, causing defects in phagosome acidification and phagolysosome formation, phenotypes identical to and unaffected by loss of unc-108, the C. elegans Rab2. GOP-1 transiently associates with cell corpse–containing phagosomes, and loss of its function abrogates phagosomal association of UNC-108. GOP-1 interacts with GDP-bound and nucleotide-free UNC-108/Rab2, disrupts GDI-UNC-108 complexes, and promotes activation and membrane recruitment of UNC-108/Rab2 in vitro. Loss of gop-1 also abolishes association of UNC-108 with endosomes, causing defects in endosome and dense core vesicle maturation. Thus, GOP-1 is an activator of UNC-108/Rab2 in multiple processes.

Visualization and Inhibition of Mitochondria-Nuclear Translocation of Apoptosis Inducing Factor by a Graphene Oxide-DNA Nanosensor

High concentrations of oxidized low density lipoprotein (oxLDL) induce aberrant apoptosis of vascular smooth muscle cells (VSMCs) in atherosclerotic plaques. This apoptosis cannot be blocked completely by the inhibition of caspase, and it eventually potentiates plaque disruption and risk for cardiovascular disease. Given the important role of apoptosis inducing factor (AIF) in caspase-independent apoptosis, here we develop an AIF-targeting nanosensor by the assembly of graphene oxide (GO) nanosheets and dye-labeled DNA hybrid structures. This nanosensor selectively localizes in the cytosol of VSMCs, where it exhibits a "turn-off" fluorescence signal. Under oxLDL stimuli, the release of AIF from mitochondria into cytosol liberates the DNA hybrid structures from the surface of GO and results in a "turn-on" fluorescence signal. This nanosensor is shown to possess rapid response, high sensitivity, and selectivity for AIF that enables real-time imaging of AIF translocation in VSMCs. Using this novel nanosensor, a better assessment of the apoptotic level of VSMCs and a more accurate evaluation of the extent of atherosclerotic lesions can be obtained. More importantly, the abundant binding between DNA hybrid structures and AIF inhibits the translocation of AIF into the nucleus and subsequent apoptosis in VSMCs. This inhibition may help stabilize plaque and reduce the risk of heart attack and stroke.

Lanatoside C, a cardiac glycoside, acts through protein kinase Cδ to cause apoptosis of human hepatocellular carcinoma cells

Recent studies have revealed that cardiac glycosides, such as digitalis and digoxin, have anticancer activity and may serve as lead compounds for the development of cancer treatments. The poor prognosis of hepatocellular carcinoma (HCC) patients reflects the development of resistance to current chemotherapeutic agents, highlighting the need for discovering new small-molecule therapeutics. Here, we found that lanatoside C, an anti-arrhythmic agent extracted from Digitalis lanata, inhibited the growth of HCC cells and dramatically decreased tumor volume as well as delayed tumor growth without obvious body weight loss. Moreover, lanatoside C triggered mitochondrial membrane potential (MMP) loss, activation of caspases and translocation of apoptosis-inducing factor (AIF) into the nucleus, which suggests that lanatoside C induced apoptosis through both caspase-dependent and -independent pathways. Furthermore, we discovered that lanatoside C activated protein kinase delta (PKCδ) via Thr505 phosphorylation and subsequent membrane translocation. Inhibition of PKCδ reversed lanatoside C-induced MMP loss and apoptosis, confirming that lanatoside C caused apoptosis through PKCδ activation. We also found that the AKT/mTOR pathway was negatively regulated by lanatoside C through PKCδ activation. In conclusion, we provide the first demonstration that the anticancer effects of lanatoside C are mainly attributable to PKCδ activation.

A nuclease that mediates cell death induced by DNA damage and poly(ADP-ribose) polymerase-1

Inhibition or genetic deletion of poly(ADP-ribose) (PAR) polymerase-1 (PARP-1) is protective against toxic insults in many organ systems. The molecular mechanisms underlying PARP-1-dependent cell death involve release of mitochondrial apoptosis-inducing factor (AIF) and its translocation to the nucleus, which results in chromatinolysis. We identified macrophage migration inhibitory factor (MIF) as a PARP-1-dependent AIF-associated nuclease (PAAN). AIF was required for recruitment of MIF to the nucleus, where MIF cleaves genomic DNA into large fragments. Depletion of MIF, disruption of the AIF-MIF interaction, or mutation of glutamic acid at position 22 in the catalytic nuclease domain blocked MIF nuclease activity and inhibited chromatinolysis, cell death induced by glutamate excitotoxicity, and focal stroke. Inhibition of MIF's nuclease activity is a potential therapeutic target for diseases caused by excessive PARP-1 activation.

Apoptosis-inducing factor (AIF) nuclear translocation mediated caspase-independent mechanism involves in X-ray-induced MCF-7 cell death

PURPOSE

Breast cancer is the most common cancer among women and radiotherapy is a conventional therapy following surgery. Previous studies have demonstrated that except the caspase-dependent pathway, caspase-independent pathway is also involved in the cell death responding to irradiation, despite the unclear mechanism. The purpose of the present study was to observe the role of apoptosis-inducing factor (AIF), the first identified caspase-independent molecule, in X-ray-induced breast cancer cell (MCF-7) cell death.

MATERIALS AND METHODS

In this study, WST-1 assay, DAPI nuclear staining and clonogenic survival assay were used to test the cell response to different treatments; Western blot was used to detect the protein expression; RT-PCR and plasmid transfection were used to observe the role of AIF.

RESULTS

X-ray-induced AIF transferred from the mitochondrion to the nucleus. Inhibition of AIF expression reduced X-ray-induced MCF-7 cell death. Further, AIF nuclear translocation is in a caspase-independent manner in this process, but not caspase-dependent manner.

CONCLUSIONS

The present study revealed that AIF nuclear translocation proceeded in X-ray-induced MCF-7 cell death in a caspase-independent manner.

Caspase-Dependent and Caspase-Independent Pathways Are Involved in Cadmium-Induced Apoptosis in Primary Rat Proximal Tubular Cell Culture

We designed this study to investigate whether cadmium induces caspase-independent apoptosis and to investigate the relationship between the caspase-dependent and caspase-independent apoptotic pathways. Cadmium (1.25-2.5 μM) induced oxidative stress in rat proximal tubular (rPT) cells, as seen in the reactive oxygen species levels; N-acetylcysteine prevented this. Cyclosporin A (CsA) prevented mitochondrial permeability transition pore opening and apoptosis; there was mitochondrial ultrastructural disruption, mitochondrial cytochrome c (cyt c) translocation to the cytoplasm, and subsequent caspase-9 and caspase-3 activation. Z-VAD-FMK prevented caspase-3 activation and apoptosis and decreased BNIP-3 (Bcl-2/adenovirus E1B 19-kDa interacting protein 3) expression levels and apoptosis-inducing factor/endonuclease G (AIF/Endo G) translocation. Simultaneously, cadmium induced prominent BNIP-3 expression in the mitochondria and cytoplasmic AIF/Endo G translocation to the nucleus. BNIP-3 silencing significantly prevented AIF and Endo G translocation and decreased the apoptosis rate, cyt c release, and caspase-9 and caspase-3 activation. These results suggest that BNIP-3 is involved in the caspase-independent apoptotic pathway and is located upstream of AIF/Endo G; both the caspase-dependent and caspase-independent pathways are involved in cadmium-induced rPT cell apoptosis and act synergistically.

Crystal structure of endonuclease G in complex with DNA reveals how it nonspecifically degrades DNA as a homodimer

Endonuclease G (EndoG) is an evolutionarily conserved mitochondrial protein in eukaryotes that digests nucleus chromosomal DNA during apoptosis and paternal mitochondrial DNA during embryogenesis. Under oxidative stress, homodimeric EndoG becomes oxidized and converts to monomers with diminished nuclease activity. However, it remains unclear why EndoG has to function as a homodimer in DNA degradation. Here, we report the crystal structure of the Caenorhabditis elegans EndoG homologue, CPS-6, in complex with single-stranded DNA at a resolution of 2.3 Å. Two separate DNA strands are bound at the ββα-metal motifs in the homodimer with their nucleobases pointing away from the enzyme, explaining why CPS-6 degrades DNA without sequence specificity. Two obligatory monomeric CPS-6 mutants (P207E and K131D/F132N) were constructed, and they degrade DNA with diminished activity due to poorer DNA-binding affinity as compared to wild-type CPS-6. Moreover, the P207E mutant exhibits predominantly 3′-to-5′ exonuclease activity, indicating a possible endonuclease to exonuclease activity change. Thus, the dimer conformation of CPS-6 is essential for maintaining its optimal DNA-binding and endonuclease activity. Compared to other non-specific endonucleases, which are usually monomeric enzymes, EndoG is a unique dimeric endonuclease, whose activity hence can be modulated by oxidation to induce conformational changes.

Kinetics and specificity of paternal mitochondrial elimination in Caenorhabditis elegans

In most eukaryotes, mitochondria are inherited maternally. The autophagy process is critical for paternal mitochondrial elimination (PME) in Caenorhabditis elegans, but how paternal mitochondria, but not maternal mitochondria, are selectively targeted for degradation is poorly understood. Here we report that mitochondrial dynamics have a profound effect on PME. A defect in fission of paternal mitochondria delays PME, whereas a defect in fusion of paternal mitochondria accelerates PME. Surprisingly, a defect in maternal mitochondrial fusion delays PME, which is reversed by a fission defect in maternal mitochondria or by increasing maternal mitochondrial membrane potential using oligomycin. Electron microscopy and tomography analyses reveal that a proportion of maternal mitochondria are compromised when they fail to fuse normally, leading to their competition for the autophagy machinery with damaged paternal mitochondria and delayed PME. Our study indicates that mitochondrial dynamics play a critical role in regulating both the kinetics and the specificity of PME.

Autophagy mediates the degradation of paternal mitochondria after fertilization in C. elegans to ensure that mitochondria are inherited maternally. Here the authors show that mitochondrial dynamics is critical for the selectivity and kinetics of paternal mitochondrial elimination.

Mitochondrial endonuclease G mediates breakdown of paternal mitochondria upon fertilization

Mitochondria are inherited maternally in most animals, but the mechanisms of selective paternal mitochondrial elimination (PME) are unknown. While examining fertilization in Caenorhabditis elegans, we observed that paternal mitochondria rapidly lose their inner membrane integrity. CPS-6, a mitochondrial endonuclease G, serves as a paternal mitochondrial factor that is critical for PME. We found that CPS-6 relocates from the intermembrane space of paternal mitochondria to the matrix after fertilization to degrade mitochondrial DNA. It acts with maternal autophagy and proteasome machineries to promote PME. Loss of cps-6 delays breakdown of mitochondrial inner membranes, autophagosome enclosure of paternal mitochondria, and PME. Delayed removal of paternal mitochondria causes increased embryonic lethality, demonstrating that PME is important for normal animal development. Thus, CPS-6 functions as a paternal mitochondrial degradation factor during animal development.

Oxidative Stress Impairs Cell Death by Repressing the Nuclease Activity of Mitochondrial Endonuclease G

Endonuclease G (EndoG) is a mitochondrial protein that is released from mitochondria and relocated into the nucleus to promote chromosomal DNA fragmentation during apoptosis. Here, we show that oxidative stress causes cell-death defects in C. elegans through an EndoG-mediated cell-death pathway. In response to high reactive oxygen species (ROS) levels, homodimeric CPS-6-the C. elegans homolog of EndoG-is dissociated into monomers with diminished nuclease activity. Conversely, the nuclease activity of CPS-6 is enhanced, and its dimeric structure is stabilized by its interaction with the worm AIF homolog, WAH-1, which shifts to disulfide cross-linked dimers under high ROS levels. CPS-6 thus acts as a ROS sensor to regulate the life and death of cells. Modulation of the EndoG dimer conformation could present an avenue for prevention and treatment of diseases resulting from oxidative stress.

Programmed cell death and clearance of cell corpses in Caenorhabditis elegans

Programmed cell death is critical to the development of diverse animal species from C. elegans to humans. In C. elegans, the cell death program has three genetically distinguishable phases. During the cell suicide phase, the core cell death machinery is activated through a protein interaction cascade. This activates the caspase CED-3, which promotes numerous pro-apoptotic activities including DNA degradation and exposure of the phosphatidylserine "eat me" signal on the cell corpse surface. Specification of the cell death fate involves transcriptional activation of the cell death initiator EGL-1 or the caspase CED-3 by coordinated actions of specific transcription factors in distinct cell types. In the cell corpse clearance stage, recognition of cell corpses by phagocytes triggers several signaling pathways to induce phagocytosis of apoptotic cell corpses. Cell corpse-enclosing phagosomes ultimately fuse with lysosomes for digestion of phagosomal contents. This article summarizes our current knowledge about programmed cell death and clearance of cell corpses in C. elegans.

PtdIns(4,5)P₂ and PtdIns3P coordinate to regulate phagosomal sealing for apoptotic cell clearance

A coincidence detection mechanism regulates phagosomal sealing and couples it with phosphoinositide conversion from PtdIns(4,5)P₂ enrichment on unsealed phagosomes to PtdIns3P enrichment on fully sealed phagosomes.

Phagocytosis requires phosphoinositides (PIs) as both signaling molecules and localization cues. How PIs coordinate to control phagosomal sealing and the accompanying switch of organelle identity is unclear. In this study, we followed dynamic changes in PIs during apoptotic cell clearance in Caenorhabditis elegans. We found that phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P₂) and phosphatidylinositol-3-phosphate (PtdIns3P), which accumulate transiently on unsealed and fully sealed phagosomes, respectively, are both involved in phagosome closure. We identified PtdIns3P phosphatase MTM-1 as an effector of PtdIns(4,5)P₂ to promote phagosomal sealing. MTM-1 coordinates with the class II PI3 kinase PIKI-1 to control PtdIns3P levels on unsealed phagosomes. The SNX9 family protein LST-4 is required for sealing, and its association with unsealed phagosomes is regulated by PtdIns(4,5)P₂, PIKI-1, and MTM-1. Loss of LST-4 or its retention on phagosomes disrupts sealing and suppresses PtdIns3P accumulation, indicating close coupling of the two events. Our findings support a coincidence detection mechanism by which phagosomal sealing is regulated and coupled with conversion from PtdIns(4,5)P₂ enrichment on unsealed phagosomes to PtdIns3P enrichment on fully sealed phagosomes.

Basal metabolic state governs AIF-dependent growth support in pancreatic cancer cells

Background

Apoptosis-inducing factor (AIF), named for its involvement in cell death pathways, is a mitochondrial protein that regulates metabolic homeostasis. In addition to supporting the survival of healthy cells, AIF also plays a contributory role to the development of cancer through its enzymatic activity, and we have previously shown that AIF preferentially supports advanced-stage prostate cancer cells. Here we further evaluated the role of AIF in tumorigenesis by exploring its function in pancreatic cancer, a disease setting that most often presents at an advanced stage by the time of diagnosis.

Methods

A bioinformatics approach was first employed to investigate AIF mRNA transcript levels in pancreatic tumor specimens vs. normal tissues. AIF-deficient pancreatic cancer cell lines were then established via lentiviral infection. Immunoblot analysis was used to determine relative protein quantities within cells. Cell viability was measured by flow cytometry; in vitro and Matrigel™ growth/survival using Coulter™ counting and phase contrast microscopy; and glucose consumption in the absence and presence of Matrigel™ using spectrophotometric methods.

Results

Archival gene expression data revealed a modest elevation of AIF transcript levels in subsets of pancreatic tumor specimens, suggesting a possible role in disease progression. AIF expression was then suppressed in a panel of five pancreatic cancer cell lines that display diverse metabolic phenotypes. AIF ablation selectively crippled the growth of cells in vitro in a manner that directly correlated with the loss of mitochondrial respiratory chain subunits and altered glucose metabolism, and these effects were exacerbated in the presence of Matrigel™ substrate. This suggests a critical metabolic role for AIF to pancreatic tumorigenesis, while the spectrum of sensitivities to AIF ablation depends on basal cellular metabolic phenotypes.

Conclusions

Altogether these data indicate that AIF supports the growth and survival of metabolically defined pancreatic cancer cells and that this metabolic function may derive from a novel mechanism so far undocumented in other cancer types.

Xyloketal-derived small molecules show protective effect by decreasing mutant Huntingtin protein aggregates in Caenorhabditis elegans model of Huntington's disease

Huntington's disease is an autosomal-dominant neurodegenerative disorder, with chorea as the most prominent manifestation. The disease is caused by abnormal expansion of CAG codon repeats in the IT15 gene, which leads to the expression of a glutamine-rich protein named mutant Huntingtin (Htt). Because of its devastating disease burden and lack of valid treatment, development of more effective therapeutics for Huntington's disease is urgently required. Xyloketal B, a natural product from mangrove fungus, has shown protective effects against toxicity in other neurodegenerative disease models such as Parkinson's and Alzheimer's diseases. To identify potential neuroprotective molecules for Huntington's disease, six derivatives of xyloketal B were screened in a Caenorhabditis elegans Huntington's disease model; all six compounds showed a protective effect. Molecular docking studies indicated that compound 1 could bind to residues GLN369 and GLN393 of the mutant Htt protein, forming a stable trimeric complex that can prevent the formation of mutant Htt aggregates. Taken together, we conclude that xyloketal derivatives could be novel drug candidates for treating Huntington's disease. Molecular target analysis is a good method to simulate the interaction between proteins and drug compounds. Further, protective candidate drugs could be designed in future using the guidance of molecular docking results.

A microfluidic device for automated, high-speed microinjection of Caenorhabditis elegans

The nematode worm Caenorhabditis elegans has been widely used as a model organism in biological studies because of its short and prolific life cycle, relatively simple body structure, significant genetic overlap with human, and facile/inexpensive cultivation. Microinjection, as an established and versatile tool for delivering liquid substances into cellular/organismal objects, plays an important role in C. elegans research. However, the conventional manual procedure of C. elegans microinjection is labor-intensive and time-consuming and thus hinders large-scale C. elegans studies involving microinjection of a large number of C. elegans on a daily basis. In this paper, we report a novel microfluidic device that enables, for the first time, fully automated, high-speed microinjection of C. elegans. The device is automatically regulated by on-chip pneumatic valves and allows rapid loading, immobilization, injection, and downstream sorting of single C. elegans. For demonstration, we performed microinjection experiments on 200 C. elegans worms and demonstrated an average injection speed of 6.6 worm/min (average worm handling time: 9.45 s/worm) and a success rate of 77.5% (post-sorting success rate: 100%), both much higher than the performance of manual operation (speed: 1 worm/4 min and success rate: 30%). We conducted typical viability tests on the injected C. elegans and confirmed that the automated injection system does not impose significant adverse effect on the physiological condition of the injected C. elegans. We believe that the developed microfluidic device holds great potential to become a useful tool for facilitating high-throughput, large-scale worm biology research.