Role of phosphoinositide 3-kinase in the autophagic death of serum-deprived PC12 cells

Reactive Oxygen Species/Caspase 3 Promotes Autophagy of Nigral Dopaminergic Neuron in Parkinson’s Disease

Parkinson’s disease (PD) is characterized as bradykinesia and sleep disorder, troubling numerous people. In the present study, we aimed to explore whether reactive oxygen species (ROS)/caspase 3 promotes PD to provide a basis for novel treatments of PD. Firstly, we applied 1-methyl-4-phenylpyridinium (MPP+) to stimulate PC12 cell lines to establish a PD cell model. Western blot and qRT-PCR analyses detected protein and mRNA expression of caspase 3, IL-1β, Bax, and BCL2. Finally, ROS detection kit determined ROS content. Compared with the controls, MPP+-treated PC12 exhibited significantly elevated caspase 3, caspase 3, and IL-1β at the protein level (p < 0.001). In addition, MMP + treatment increased Bax protein level in vitro, while decreased Bcl-2 protein expression (p <0.001). Moreover, MPP + induced oxidative stress which contributes to autophagy. The ROS in MPP + group was increased significantly (p < 0.001). ROS and caspase 3 participate in the pathogenesis of PD and enhances autophagy of nigral dopaminergic neuron.

XingNaoJing, prescription of traditional Chinese medicine, prevents autophagy in experimental stroke by repressing p53-DRAM pathway

Background

Xingnaojing (XNJ), a well known prescription in traditional Chinese medicine, has been used for treatment of stroke in China. However, the effects and mechanisms of XNJ on autophagy are not clear. Here, we used the cell models of autophagy induced by serum-free condition and ischemia stroke in rats to further investigate whether the p53-DRAM pathway is involved in the effects of XNJ on autophagy.

Methods

We used the cell model of autophagy induced by serum-free condition and the rat model of ischemia caused by a middle cerebral artery occlusion (MCAO). The effects of XNJ on p53 transcriptional activity of PC12 cells were evaluated by the luciferase activity assay. The mRNA levels and the expression of p53 and its target autophagy gene DRAM (damage-regulated autophagy modulator) were analyzed respectively by Quantitative-RTPCR and Western blot assay. The activation of autophagy was detected by the levels of autophagy markers, microtubule associated protein light chain 3 (LC3) and p62 by Immunofluorescence and Western blot. p53 inhibitor was used to determine whether p53 is responsible for the effects of XNJ on preventing autophagy.

Results

The assay for luciferase activity of p53 promoter indicated that XNJ inhibited p53 transcriptional activity. XNJ reduced the expression of p53 and its target autophagy gene DRAM (damage-regulated autophagy modulator) in serum-free condition PC12 cells and the cortex in MCAO rats. XNJ reduced autophagy of PC12 cells induced by serum-free condition and the cortex in MCAO rats. Furthermore, suppression of p53 by p53 inhibitor significantly reduced the effects of XNJ on the autophagy of PC12 cells in serum-free condition.

Conclusion

XNJ prevents autophagy in experimental stroke by repressing p53/DRAM pathway. Our findings are therefore of considerable therapeutic significance and provide the novel and potential application of XNJ for the treatment of brain diseases.

Multiple interacting cell death mechanisms in the mediation of excitotoxicity and ischemic brain damage: a challenge for neuroprotection

There is currently no approved neuroprotective pharmacotherapy for acute conditions such as stroke and cerebral asphyxia. One of the reasons for this may be the multiplicity of cell death mechanisms, because inhibition of a particular mechanism leaves the brain vulnerable to alternative ones. It is therefore essential to understand the different cell death mechanisms and their interactions. We here review the multiple signaling pathways underlying each of the three main morphological types of cell death--apoptosis, autophagic cell death and necrosis--emphasizing their importance in the neuronal death that occurs during cerebral ischemia and hypoxia-ischemia, and we analyze the interactions between the different mechanisms. Finally, we discuss the implications of the multiplicity of cell death mechanisms for the design of neuroprotective strategies.

Oxidative stress impairs autophagic flux in prion protein-deficient hippocampal cells

We previously reported that autophagy is upregulated in Prnp-deficient (Prnp ( 0/0) ) hippocampal neuronal cells in comparison to cellular prion protein (PrP (C) )-expressing (Prnp (+/+) ) control cells under conditions of serum deprivation. In this study, we determined whether a protective mechanism of PrP (C) is associated with autophagy using Prnp ( 0/0) hippocampal neuronal cells under hydrogen peroxide (H 2O 2)-induced oxidative stress. We found that Prnp ( 0/0) cells were more susceptible to oxidative stress than Prnp (+/+) cells in a dose- and time-dependent manner. In addition, we observed enhanced autophagy by immunoblotting, which detected the conversion of microtubule-associated protein 1 light chain 3 β (LC3B)-I to LC3B-II, and we observed increased punctate LC3B immunostaining in H 2O 2-treated Prnp ( 0/0) cells compared with H 2O 2-treated control cells. Interestingly, this enhanced autophagy was due to impaired autophagic flux in the H 2O 2-treated Prnp ( 0/0) cells, while the H 2O 2-treated Prnp (+/+) cells showed enhanced autophagic flux. Furthermore, caspase-dependent and independent apoptosis was observed when both cell lines were exposed to H 2O 2. Moreover, the inhibition of autophagosome formation by Atg7 siRNA revealed that increased autophagic flux in Prnp (+/+) cells contributes to the prosurvival effect of autophagy against H 2O 2 cytotoxicity. Taken together, our results provide the first experimental evidence that the deficiency of PrP (C) may impair autophagic flux via H 2O 2-induced oxidative stress.

When cytokinin, a plant hormone, meets the adenosine A2A receptor: a novel neuroprotectant and lead for treating neurodegenerative disorders?

It is well known that cytokinins are a class of phytohormones that promote cell division in plant roots and shoots. However, their targets, biological functions, and implications in mammalian systems have rarely been examined. In this study, we show that one cytokinin, zeatin riboside, can prevent pheochromocytoma (PC12) cells from serum deprivation-induced apoptosis by acting on the adenosine A(2A) receptor (A(2A)-R), which was blocked by an A(2A)-R antagonist and a protein kinase A (PKA) inhibitor, demonstrating the functional ability of zeatin riboside by mediating through A(2A)-R signaling event. Since the A(2A)-R was implicated as a therapeutic target in treating Huntington's disease (HD), a cellular model of HD was applied by transfecting mutant huntingtin in PC12 cells. By using filter retardation assay and confocal microscopy we found that zeatin riboside reversed mutant huntingtin (Htt)-induced protein aggregations and proteasome deactivation through A(2A)-R signaling. PKA inhibitor blocked zeatin riboside-induced suppression of mutant Htt aggregations. In addition, PKA activated proteasome activity and reduced mutant Htt protein aggregations. However, a proteasome inhibitor blocked both zeatin riboside-and PKA activator-mediated suppression of mutant Htt aggregations, confirming mediation of the A(2A)-R/PKA/proteasome pathway. Taken together, zeatin riboside might have therapeutic potential as a novel neuroprotectant and a lead for treating neurodegenerative disorders.

The role of autophagy in human endometrium

Autophagy appears to play an important role in the normal development and maintenance of homeostasis in a variety of tissues, including the female reproductive tract. However, the role of autophagy and the association between autophagy and apoptosis in cyclic remodeling of the human endometrium have not been described. Therefore, we investigated the involvement of autophagy during the human endometrial cycle and its association with apoptosis. Endometrial samples were obtained from 15 premenopausal, nonpregnant women who underwent hysterectomies for benign gynecological reasons. The autophagy-associated protein, microtubule-associated protein 1 light chain 3 alpha (MAP1LC3A), was immunolocalized, and its expression level was measured by Western blot analysis. Apoptosis was evaluated by measuring the expression level of cleaved caspase 3 protein. MAP1LC3A protein was primarily expressed within the endometrial glandular cells and increased during the secretory phase. The expression level of the membrane-bound form of MAP1LC3A (MAP1LC3A-II) also increased as the menstrual cycle progressed, reaching a maximum level during the late secretory phase. This pattern coincided with the expression of cleaved caspase 3. Furthermore, expression of MAP1LC3A-II and cleaved caspase 3 increased in the in vitro-cultured endometrial cancer cells when estrogen and/or progesterone were withdrawn from the culture media to mimic physiological hormonal changes. These findings suggest that endometrial cell autophagy is directly involved in the cyclic remodeling of the human endometrium and is correlated with apoptosis. In addition, we inhibited autophagic processes using 3-methyladenine (3-MA) or bafilomycin A1 (Baf A1) to evaluate the role of autophagy in apoptosis induction in endometrial cancer cells. While the inhibition of autophagosome formation using 3-MA did not decrease apoptosis or cell death, the inhibition of autophagosome degradation by fusion with lysosomes using Baf A1 increased apoptosis and cell death, suggesting that the accumulation of autophagosomes induces apoptosis. Furthermore, Baf A1-induced apoptotic cell death was decreased by the apoptosis inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK). In conclusion, these results indicate that autophagy is involved in the endometrial cell cycle affecting apoptosis and is most prominent during the late secretory phase.

Starvation, detoxification, and multidrug resistance in cancer therapy

The selection of chemotherapy drugs is based on the cytotoxicity to specific tumor cell types and the relatively low toxicity to normal cells and tissues. However, the toxicity to normal cells poses a major clinical challenge, particularly when malignant cells have acquired resistance to chemotherapy. This drug resistance of cancer cells results from multiple factors including individual variation, genetic heterogeneity within a tumor, and cellular evolution. Much progress in the understanding of tumor cell resistance has been made in the past 35 years, owing to milestone discoveries such as the identification and characterization of ABC transporters. Nonetheless, the complexity of the genetic and epigenetic rewiring of cancer cells makes drug resistance an equally complex phenomenon that is difficult to overcome. In this review, we discuss how the remarkable changes in the levels of glucose, IGF-I, IGFBP-1 and in other proteins caused by fasting have the potential to improve the efficacy of chemotherapy against tumors by protecting normal cells and tissues and possibly by diminishing multidrug resistance in malignant cells.

Neuronal autophagy as a mediator of life and death: contrasting roles in chronic neurodegenerative and acute neural disorders

Autophagy is a cellular mechanism for degrading proteins and organelles. It was first described as a physiological process essential for cellular health and survival, and this is its role in most cells. However, it can also be a mediator of cell death, either by the triggering of apoptosis or by an independent "autophagic" cell death mechanism. This duality is important in the central nervous system, where the activation of autophagy has recently been shown to be protective in certain chronic neurodegenerative diseases but deleterious in acute neural disorders such as stroke and hypoxic/ischemic injury. The authors here discuss these distinct roles of autophagy in the nervous system with a focus on the role of autophagy in mediating neuronal death. The development of new therapeutic strategies based on the manipulation of autophagy will need to take into account these opposing roles of autophagy.

A systems level strategy for analyzing the cell death network: implication in exploring the apoptosis/autophagy connection

The mammalian cell death network comprises three distinct functional modules: apoptosis, autophagy and programmed necrosis. Currently, the field lacks systems level approaches to assess the extent to which the intermodular connectivity affects cell death performance. Here, we developed a platform that is based on single and double sets of RNAi-mediated perturbations targeting combinations of apoptotic and autophagic genes. The outcome of perturbations is measured both at the level of the overall cell death responses, using an unbiased quantitative reporter, and by assessing the molecular responses within the different functional modules. Epistatic analyses determine whether seemingly unrelated pairs of proteins are genetically linked. The initial running of this platform in etoposide-treated cells, using a few single and double perturbations, identified several levels of connectivity between apoptosis and autophagy. The knock down of caspase3 turned on a switch toward autophagic cell death, which requires Atg5 or Beclin-1. In addition, a reciprocal connection between these two autophagic genes and apoptosis was identified. By applying computational tools that are based on mining the protein-protein interaction database, a novel biochemical pathway connecting between Atg5 and caspase3 is suggested. Scaling up this platform into hundreds of perturbations potentially has a wide, general scope of applicability, and will provide the basis for future modeling of the cell death network.

The role of autophagy in follicular development and atresia in rat granulosa cells

OBJECTIVE

To investigate the involvement of autophagy in folliculogenesis and its correlation with apoptosis.

DESIGN

Animal model-based study.

SETTING

University medical center.

ANIMAL(S)

Twenty-one day-old female Sprague-Dawley rats.

INTERVENTION(S)

Ovaries obtained from established immature rat models primed with pregnant mare serum gonadotropin (PMSG) were used for the induction of follicular development and atresia. Granulosa cells isolated from developing follicles were cultured in serum-free condition with or without follicle-stimulating hormone.

MAIN OUTCOME MEASURE(S)

Microtubule-associated light-chain protein 3 (LC3) and autophagic vacuoles were used as autophagic markers, and cleaved caspase-3 was used as an apoptotic marker in ovaries and/or granulosa cells.

RESULT(S)

The LC3 protein was expressed mainly in granulosa cells during all developmental stages. In granulosa cells isolated from PMSG-primed immature rat ovaries, LC3-II expression showed a similar expression pattern to cleaved caspase-3. In addition, granulosa cells of atretic follicles that showed intense cleaved caspase-3 staining also showed intense LC3 immunoreactivity. An in vitro culture experiment revealed that the levels of LC3-II and cleaved caspase-3 proteins were gonadotropin-dependent. The induction and the gonadotropin dependency of granulosa cell autophagy were confirmed by the observation of autophagic vacuoles under transmission electron microscopy.

CONCLUSION(S)

These preliminary results suggest that autophagy is induced mainly in granulosa cells during folliculogenesis and shows good correlation with apoptosis.

Lysosome dysfunction triggers Atg7-dependent neural apoptosis

Macroautophagy (autophagy) is a process wherein bulk cytosolic proteins and damaged organelles are sequestered and degraded via the lysosome. Alterations in autophagy-associated proteins have been shown to cause neural tube closure defects, neurodegeneration, and tumor formation. Normal lysosome function is critical for autophagy completion and when altered may lead to an accumulation of autophagic vacuoles (AVs) and caspase activation. The tumor suppressor p53 is highly expressed in neural precursor cells (NPCs) and has an important role in the regulation of both autophagy and apoptosis. We hypothesized that altered lysosome function would lead to NPC death via an interaction between autophagy- and apoptosis-associated proteins. To test our hypothesis, we utilized FGF2-expanded NPCs and the neural stem cell line, C17.2, in combination with the lysosomotropic agent chloroquine (CQ) and the vacuolar ATPase inhibitor bafilomycin A1 (Baf A1). Both CQ and Baf A1 caused concentration- and time-dependent AV accumulation, p53 phosphorylation, increased damage regulator autophagy modulator levels, caspase-3 activation, and cell death. Short hairpin RNA knockdown of Atg7, but not Beclin1, expression significantly inhibited CQ- and Baf A1-induced cell death, indicating that Atg7 is an upstream mediator of lysosome dysfunction-induced cell death. Cell death and/or caspase-3 activation was also attenuated by protein synthesis inhibition, p53 deficiency, or Bax deficiency, indicating involvement of the intrinsic apoptotic death pathway. In contrast to lysosome dysfunction, starvation-induced AV accumulation was inhibited by either Atg7 or Beclin1 knockdown, and Atg7 knockdown had no effect on starvation-induced death. These findings indicate that Atg7- and Beclin1-induced autophagy plays a cytoprotective role during starvation but that Atg7 has a unique pro-apoptotic function in response to lysosome dysfunction.

Lipid droplets: their role in nanoparticle-induced oxidative stress

Lipid droplets are cytoplasmic organelles found in almost all cells under physiological or pathological conditions. Certain nanoparticles can induce lipid droplet formation under oxidative stress conditions. Small metallic nanoparticles such as cadmium telluride (CdTe) nanoparticles, particularly those with incompletely protected surfaces, induce oxidative stress and may inflict damages to several intracellular organelles. The objective of this study was to assess formation of lipid droplets in cells treated with CdTe nanoparticles and relate their status to cell function (mitochondrial activity and cell viability). Multicolor labeling of cellular organelles (lipid droplets and lysosomes) showed that lipid droplets formed in pheochromocytoma (PC12) cells following nanoparticle or oleic acid treatment. Some lipid droplets were found closely apposed to lysosomes suggesting possible communication between these organelles during severe oxidative stress. Combination of microscopy of living cells with cell viability assays showed that oleic acid-induced lipid droplets not only serve as intracellular lipid storage sites but also play a protective role in starving stressed cells. Results from these studies suggest that oleic acid-induced LD in PC12 cells are dynamic and adaptive organelles, which provide energy to starving cells and facilitate their rescue under starvation and exposure to metallic nanoparticles.

The flavonoid fisetin promotes nerve cell survival from trophic factor withdrawal by enhancement of proteasome activity

To explore the possibility that specific flavonoids can substitute for neurotrophic factors, we examined the ability of the flavonol fisetin and several related flavonoids to support the survival of low density, serum-free cultures of rat cortical neurons. Normally these cells die within 24h in the absence of trophic factors but in the presence of fisetin and several related flavonoids the cells survive and produce long neurites. While the survival-promoting effect of several of the fisetin-related flavonoids was partially dependent on ERK activation, the effect of fisetin was not. Fisetin can enhance glutathione synthesis but the survival-promoting effect of fisetin was also not dependent on glutathione. However, proteasome inhibitors almost completely blocked the ability of fisetin to promote survival. Consistent with this observation, fisetin increased proteasome activity. Together these results demonstrate a new activity for fisetin and tie this activity to its neurotrophic effects.

Mitochondrial oxygen consumption inhibition importance for TMT-dependent cell death in undifferentiated PC12 cells

The evolving role of mitochondria as a target for different death-inducing noxae prompted us to investigate trimethyltin (TMT)-dependent effects on mitochondrial functionality. For this purpose, we used a homogeneous cell culture model represented by undifferentiated PC12 cells. Mitochondria isolated from PC12 cells treated with TMT for 6, 12 and 24h, showed a time-dependent inhibition of ADP-stimulated oxygen consumption using succinate or glutamate/malate as substrate. Using a fluorescent assay, the effect of TMT on mitochondrial membrane potential (delta Psi) in PC12 cells was also determined. After 24h in culture, a strong loss of mitochondrial membrane potential (delta Psi) was observed in TMT-treated cells. Collapse of mitochondrial membrane potential correlated with an increased expression of bax/bcl-2 ratio, as evaluated by polymerase chain reaction. Western blotting and spectrophotometric analysis showed that cytochrome c release and activation of caspase 3 were concurrently induced. Our findings suggest that inhibition of mitochondrial respiration represents the early toxic event for cell death in PC12 due to trimethyltin.

Hypoxia-like transcriptional activation in TMT-induced degeneration: microarray expression analysis on PC12 cells

To more clearly elucidate the complete network of molecular mechanisms induced by trimethyltin (TMT) toxicity, we used a homogeneous cell culture model represented by PC12 cells treated with 1 and 5 micromol/L TMT for 24 h. The gene expression profile was performed by microarray analysis, enabling us to identify 189 genes that were significantly modulated in treated cells, compared with controls. The main effects of TMT on gene expression seem to be related to the activation of metabolic processes (glycolysis and lipogenesis) along with cell death pathways, membrane remodeling and intracellular biomolecules trafficking. These alterations are triggered by the neurotoxicant earlier than a strong decrease in cell viability, which occurs at higher TMT concentrations or at later time points. Some aspects of the transcriptional modulation observed in this study resemble the gene activation known to occur during cell response to hypoxia. Other cell toxicants have also been reported to exert similar effects on gene expression. Therefore, our data help to delineate general basic adaptive mechanisms possibly shared by cells responding to different death-inducing noxae, such as TMT.

Initiation of apoptosis and autophagy by photodynamic therapy

BACKGROUND AND OBJECTIVES

This study was designed to examine modes of cell death after photodynamic therapy (PDT).

STUDY DESIGN

Murine leukemia L1210 cells and human prostate Bax-deficient DU145 cells were examined after PDT-induced photodamage to the endoplasmic reticulum (ER). Phase contrast, fluorescence and electron microscopy were used to identify changes in cellular morphology, chromatin condensation, loss of mitochondrial membrane potential, and formation of phagolysosomes. Western blots were used to assess the processing of LC3-I to LC3-II, a marker for autophagy. Inhibitors of apoptosis and/or autophagy were used to delineate the contributions of the two pathways to the effects of PDT.

RESULTS

Both apoptosis and autophagy occurred in L1210 after ER photodamage with the latter predominating after 24 hours. In DU145 cells, PDT conditions causing comparable cytotoxicity only initiated autophagy. PI3-kinase inhibitors suppressed autophagy in both cell lines as indicated by inhibition of vacuolization and LC3 processing.

CONCLUSIONS

Both autophagy and apoptosis were observed in L1210 cells following ER photodamage. In the Bax-deficient DU145 cell line only autophagy was observed. Current information suggests that autophagy can function as either a survival or death pathway. We propose that in the context of PDT, this may also be true.

Initiation of apoptosis and autophagy by photodynamic therapy

This study was designed to examine modes of cell death after photodynamic therapy (PDT). Murine leukemia L1210 cells and human prostate Bax-deficient DU-145 cells were examined after PDT-induced photodamage to the endoplasmic reticulum (ER). Previous studies indicated that this treatment resulted in a substantial loss of Bcl-2 function. Both apoptosis and autophagy occurred in L1210 cells after ER photodamage with the latter predominating after 24 hr. These processes were characterized by altered cellular morphology, chromatin condensation, loss of mitochondrial membrane potential and formation of vacuoles containing cytosolic components. Western blots demonstrated processing of LC3-I to LC3-II, a marker for autophagy. In DU145 cells, PDT initiated only autophagy. Phosphatidylinositol (PI) 3-kinase inhibitors suppressed autophagy in both cell lines as indicated by inhibition of vacuolization and LC3 processing. Inhibitors of apoptosis and/or autophagy were then used to delineate the contributions of the two pathways to the effects of PDT. Given the ability of autophagy to upregulate MHC-11 peptide presentation, autophagy may play a role in the ability of photodynamic therapy to stimulate immunologic recognition of target cells.