Docosahexaenoic acid (DHA) induces autophagy-associated apoptotic cell death in wild-type p53 cancer cells via regulation of p53. The present study investigated the effects of DHA on PC3 and DU145 prostate cancer cell lines harboring mutant p53. Results show that, in addition to apoptosis, DHA increased the expression levels of lipidated form LC3B and potently stimulated the autophagic flux, suggesting that DHA induces both autophagy and apoptosis in cancer cells expressing mutant p53. DHA led to the generation of mitochondrial reactive oxygen species (ROS), as shown by the mitochondrial ROS-specific probe mitoSOX. Similarly, pretreatment with the antioxidant N-acetyl-cysteine (NAC) markedly inhibited both the autophagy and the apoptosis triggered by DHA, indicating that mitochondrial ROS mediate the cytotoxicity of DHA in mutant p53 cells. Further, DHA reduced the levels of phospho-Akt and phospho-mTOR in a concentration-dependent manner, while NAC almost completely blocked that effect. Collectively, these findings present a novel mechanism of ROS-regulated apoptosis and autophagy that involves Akt-mTOR signaling in prostate cancer cells with mutant p53 exposed to DHA.
The docosahexaenoic (DHA), a ω-3 fatty acid, could play a beneficial inhibition of the incidence and progress of a series of human diseases including cancer. It has been report that DHA is involved in cell apoptosis. Recent studies show that the signal transduction pathway links with bcl-2, bax, caspase-3 and MMP-9 molecules. Therefore, we tested the relationship between DHA and cell apoptosis in human hepatocellular carcinoma cells (Bel-7402 cells). We show here that DHA induces Bel-7402 cells apoptosis after pre-treating cells with DHA. DHA down-regulates the protein expression of Bcl-2 and Bim mRNA level, and up-regulates caspase-3 activity and Bax expression level. We also found that DHA inhibits Bel-7402 cells migration. Basic on our studies, DHA may play a role in tumor invasion and survival.
Docosahexaenoic (DHA); Bcl-2; caspase-3; MMP-9
Autophagy is an evolutionarily conserved process to catabolize cytoplasmic proteins and organelles1, 2. During starvation, the target of rapamycin (TOR), a nutrient-responsive kinase, is inhibited, thereby inducing autophagy. In autophagy, double-membrane autophagosomes envelop and sequester intracellular components and then fuse with lysosomes to form autolysosomes which degrade their contents to regenerate nutrients. Current models of autophagy terminate with the degradation of autophagosome cargo in autolysosomes3-5, but the regulation of autophagy in response to nutrients and the subsequent fate of the autolysosome are poorly defined. Here we show that mTOR signaling is inhibited during autophagy initiation, but reactivated with prolonged starvation. mTOR reactivation is autophagy-dependent, and requires the degradation of autolysosomal products. Increased mTOR activity attenuates autophagy and generates proto-lysosomal tubules and vesicles that extrude from autolysosomes and ultimately mature into functional lysosomes, thereby restoring the full complement of lysosomes in the cell – a process we identify in multiple animal species. Thus, an evolutionarily-conserved cycle in autophagy governs nutrient sensing and lysosome homeostasis during starvation.
Docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, is an essential component of membrane phosphatides and has been implicated in cognitive functions. Low levels of circulating or brain DHA are associated with various neurocognitive disorders including Alzheimer’s disease (AD), while laboratory animals, including animal models of AD, can exhibit improved cognitive ability with a diet enriched in DHA. Various cellular mechanisms have been proposed for DHA’s behavioral effects, including increases in cellular membrane fluidity, promotion of neurite extension, and inhibition of apoptosis. However, there is little direct evidence that DHA affects synaptic structure in living animals. Here we show that oral supplementation with DHA substantially increases the number of dendritic spines in adult gerbil hippocampus, particularly when animals are co-supplemented with a uridine source, uridine-5’-monophosphate (UMP), which increases brain levels of the rate-limiting phosphatide precursor CTP. The increase in dendritic spines (> 30%) is accompanied by parallel increases in membrane phosphatides, and in pre- and post-synaptic proteins within the hippocampus. Hence oral DHA may promote neuronal membrane synthesis to increase the number of synapses, particularly when co-administered with UMP. Our findings provide a possible explanation for the effects of DHA on behavior and also suggest a strategy to treat cognitive disorders resulting from synapse loss.
docosahexaenoic acid; uridine; membrane synthesis; spine formation; synaptogenesis; phosphatides
Mitochondria can depolarize and trigger cell death through the opening of the mitochondrial permeability transition pore (MPTP). We recently showed that an increase in the long chain n3 polyunsaturated fatty acids (PUFA) docosahexaenoic acid (DHA; 22:6n3) and depletion of the n6 PUFA arachidonic acid (ARA; 20:4n6) in mitochondrial membranes is associated with a greater Ca2+ load required to induce MPTP opening. Here we manipulated mitochondrial phospholipid composition by supplementing the diet with DHA, ARA or combined DHA+ARA in rats for 10 weeks. There were no effects on cardiac function, or respiration of isolated mitochondria. Analysis of mitochondrial phospholipids showed DHA supplementation increased DHA and displaced ARA in mitochondrial membranes, while supplementation with ARA or DHA+ARA increased ARA and depleted linoleic acid (18:2n6). Phospholipid analysis revealed a similar pattern, particularly in cardiolipin. Tetralinoleoyl cardiolipin was depleted by 80% with ARA or DHA+ARA supplementation, with linoleic acid side chains replaced by ARA. Both the DHA and ARA groups had delayed Ca2+-induced MPTP opening, but the DHA+ARA group was similar to the control diet. In conclusion, alterations in mitochondria membrane phospholipid fatty acid composition caused by dietary DHA or ARA was associated with a greater cumulative Ca2+ load required to induced MPTP opening. Further, high levels of tetralinoleoyl cardiolipin were not essential for normal mitochondrial function if replaced with very-long chain n3 or n6 PUFAs.
Autophagy is a regulated catabolic process triggered in cells deprived of nutrients or growth factors that govern nutrient uptake. Here we report that autophagy is induced by cetuximab, a therapeutic antibody that blocks EGFR function. Cancer cell treatment with cetuximab triggered autophagosome formation, conversion of microtubule-associated protein 1 light chain 3 from its cytoplasmic to membrane-associated form, and increased acidic vesicular organelle formation. Autophagy occurred when cetuximab inhibited the class I PI3K/Akt/mTOR pathway, but not when it inhibited only the MEK/Erk pathway, and it was accompanied by decreased levels of hypoxia inducible factor-1 alpha (HIF-1α) and Bcl-2. Stable overexpression of a HIF-1α mutant prevented cetuximab-induced autophagy and decrease in Bcl-2 levels. Knockdown of autophagy regulator beclin 1 or cell treatment with autophagy inhibitor 3-methyladenine, a class III PI3K (hVps34) inhibitor, also inhibited cetuximab-induced autophagy. Furthermore, knockdown of beclin 1 or Atg7 or treatment with the lysosome inhibitor chloroquine sensitized cancer cells to cetuximab-induced apoptosis. Mechanistic analysis argued that cetuximab acted by promoting an association between beclin 1 and hVps34, which was inhibited by overexpression of Bcl-2. Our findings suggest that the autophagy protects cancer cells from the pro-apoptotic effects of cetuximab.
cetuximab; autophagy; EGFR
The present study investigated the role of autophagy, a cellular self-digestion process, in the cytotoxicity of antileukemic drug cytarabine towards human leukemic cell lines (REH, HL-60, MOLT-4) and peripheral blood mononuclear cells from leukemic patients. The induction of autophagy was confirmed by acridine orange staining of intracellular acidic vesicles, electron microscopy visualization of autophagic vacuoles, as well as by the increase in autophagic proteolysis and autophagic flux, demonstrated by immunoblot analysis of p62 downregulation and LC3-I conversion to autophagosome-associated LC3-II in the presence of proteolysis inhibitors, respectively. Moreover, the expression of autophagy-related genes Atg4, Atg5 and Atg7 was stimulated by cytarabine in REH cells. Cytarabine reduced the phosphorylation of the major negative regulator of autophagy, mammalian target of rapamycin (mTOR), and its downstream target p70S6 kinase in REH cells, which was associated with downregulation of mTOR activator Akt and activation of extracellular signal- regulated kinase. Cytarabine had no effect on the activation of mTOR inhibitor AMP-activated protein kinase. Leucine, an mTOR activator, reduced both cytarabine-induced autophagy and cytotoxicity. Accordingly, pharmacological downregulation of autophagy with bafilomycin A1 and chloroquine, or RNA interference-mediated knockdown of LC3β or p62, markedly increased oxidative stress, mitochondrial depolarization, caspase activation and subsequent DNA fragmentation and apoptotic death in cytarabine-treated REH cells. Cytarabine also induced mTOR-dependent cytoprotective autophagy in HL-60 and MOLT-4 leukemic cell lines, as well as primary leukemic cells, but not normal leukocytes. These data suggest that the therapeutic efficiency of cytarabine in leukemic patients could be increased by the inhibition of the mTOR-dependent autophagic response.
Accumulation of misfolded proinsulin in the β-cell leads to dysfunction induced by endoplasmic reticulum (ER) stress, with diabetes as a consequence. Autophagy helps cellular adaptation to stress via clearance of misfolded proteins and damaged organelles. We studied the effects of proinsulin misfolding on autophagy and the impact of stimulating autophagy on diabetes progression in Akita mice, which carry a mutation in proinsulin, leading to its severe misfolding. Treatment of female diabetic Akita mice with rapamycin improved diabetes, increased pancreatic insulin content, and prevented β-cell apoptosis. In vitro, autophagic flux was increased in Akita β-cells. Treatment with rapamycin further stimulated autophagy, evidenced by increased autophagosome formation and enhancement of autophagosome–lysosome fusion. This was associated with attenuation of cellular stress and apoptosis. The mammalian target of rapamycin (mTOR) kinase inhibitor Torin1 mimicked the rapamycin effects on autophagy and stress, indicating that the beneficial effects of rapamycin are indeed mediated via inhibition of mTOR. Finally, inhibition of autophagy exacerbated stress and abolished the anti-ER stress effects of rapamycin. In conclusion, rapamycin reduces ER stress induced by accumulation of misfolded proinsulin, thereby improving diabetes and preventing β-cell apoptosis. The beneficial effects of rapamycin in this context strictly depend on autophagy; therefore, stimulating autophagy may become a therapeutic approach for diabetes.
The epidermal growth factor receptor (EGFR), which regulates cell growth and survival, is integral to colon tumorigenesis. Lipid rafts play a role in regulating EGFR signaling, and docosahexaenoic acid (DHA) is known to perturb membrane domain organization through changes in lipid rafts. Therefore, we investigated the mechanistic link between EGFR function and DHA. Membrane incorporation of DHA into immortalized colonocytes altered the lateral organization of EGFR. DHA additionally increased EGFR phosphorylation but paradoxically suppressed downstream signaling. Assessment of the EGFR-Ras-ERK1/2 signaling cascade identified Ras GTP binding as the locus of the DHA-induced disruption of signal transduction. DHA also antagonized EGFR signaling capacity by increasing receptor internalization and degradation. DHA suppressed cell proliferation in an EGFR-dependent manner, but cell proliferation could be partially rescued by expression of constitutively active Ras. Feeding chronically-inflamed, carcinogen-injected C57BL/6 mice a fish oil containing diet enriched in DHA recapitulated the effects on the EGFR signaling axis observed in cell culture and additionally suppressed tumor formation. We conclude that DHA-induced alteration in both the lateral and subcellular localization of EGFR culminates in the suppression of EGFR downstream signal transduction, which has implications for the molecular basis of colon cancer prevention by DHA.
Background. Accumulation of free fatty acids leads to lipid-toxicity-associated skeletal muscle atrophy. Palmitate treatment reduces myoblast and myotube growth and causes apoptosis in vitro. It is not known if omega-3 fatty acids will protect muscle cells against palmitate toxicity. Therefore, we examined the effects of docosahexaenoic acid (DHA) on skeletal muscle growth. Methods. Mouse myoblasts (C2C12) were differentiated to myotubes, and then treated with 0 or 0.5 mM palmitic acid or 0 or 0.1 mM DHA. Results. Intramyocellular lipid was increased in palmitate-treated cells but was prevented by DHA-palmitate cotreatment. Total AMPK increased in DHA+ palmitate-treated compared to palmitate only cells. RpS6 phosphorylation decreased after palmitate (−55%) and this was blunted by DHA+ palmitate (−35%) treatment. Palmitate treatment decreased PGC1α protein expression by 69%, but was increased 165% with DHA+ palmitate (P = 0.017) versus palmitate alone. While palmitate induced 25% and 90% atrophy in myotubes (after 48 hours and 96 hours, resp.), DHA+ palmitate treatment caused myotube hypertrophy of ~50% and 100% after 48 and 96 hours, respectively. Conclusion. These data show that DHA is protective against palmitate-induced atrophy. Although DHA did not activate the AMPK pathway, DHA treatment restored growth-signaling (i.e., rpS6) and rescued palmitate-induced muscle atrophy.
Lysosomes are acidic organelles that have a crucial role in degrading intracellular macromolecules and organelles during the final stage of autophagy. Tetrandrine (Tet), a bisbenzylisoquinoline alkaloid, was reported as an autophagy activator. Here, in contrast with previous studies, we show that Tet is a potent lysosomal deacidification agent and is able to block autophagic flux in the degradation stage. Single-agent Tet induces significant apoptosis both in vitro and in xenograft models. In the presence of Tet, apoptosis was preceded by a robust accumulation of autophagosomes and an increased level of microtubule-associated protein 1 light chain 3, type II (LC3-II). However, Tet increased the level of sequestosome 1 and decreased the turnover of LC3, indicating the blockade of autophagic flux in the degradation stage. As blockade of autophagic flux decreases the recycling of cellular fuels, Tet reduces the uptake of glucose in cancer cells. These effects lead to insufficient substrates for tricarboxylic acid (TCA) cycle and impaired oxidative phosphorylation. Blunting autophagosome formation using 3-methyladenine or genetic knockdown of Beclin-1 failed to rescue cells upon Tet treatment. By contrast, addition of methyl pyruvate to supplement TCA substrates protected Tet-treated tumor cells. These results demonstrate that energetic impairment is required in Tet-induced apoptosis. Tet, as a potent lysosomal inhibitor, is translatable to the treatment of malignant tumor patients.
tetrandrine; autophagy; lysosomes; apoptosis; metabolism
The role of autophagy in oncogenesis remains ambiguous, and mechanisms that induce autophagy and regulate its outcome in human cancers are poorly understood. The maternally imprinted Ras-related tumor suppressor gene aplasia Ras homolog member I (ARHI; also known as DIRAS3) is downregulated in more than 60% of ovarian cancers, and here we show that re-expression of ARHI in multiple human ovarian cancer cell lines induces autophagy by blocking PI3K signaling and inhibiting mammalian target of rapamycin (mTOR), upregulating ATG4, and colocalizing with cleaved microtubule-associated protein light chain 3 (LC3) in autophagosomes. Furthermore, ARHI is required for spontaneous and rapamycin-induced autophagy in normal and malignant cells. Although ARHI re-expression led to autophagic cell death when SKOv3 ovarian cancer cells were grown in culture, it enabled the cells to remain dormant when they were grown in mice as xenografts. When ARHI levels were reduced in dormant cells, xenografts grew rapidly. However, inhibition of ARHI-induced autophagy with chloroquine dramatically reduced regrowth of xenografted tumors upon reduction of ARHI levels, suggesting that autophagy contributed to the survival of dormant cells. Further analysis revealed that autophagic cell death was reduced when cultured human ovarian cancer cells in which ARHI had been re-expressed were treated with growth factors (IGF-1, M-CSF), angiogenic factors (VEGF, IL-8), and matrix proteins found in xenografts. Thus, ARHI can induce autophagic cell death, but can also promote tumor dormancy in the presence of factors that promote survival in the cancer microenvironment.
Accumulating evidence suggests that the pathophysiology of depression might be associated with neuroinflammation, which could be attenuated by pharmacological treatment for depression. Omega-3 polyunsaturated fatty acids (PUFAs) are anti-inflammatory and exert antidepressant effects. The aim of this study was to identify the molecular mechanisms through which docosahexaenoic acid (DHA), the main omega-3 PUFA in the brain, modulates oxidative reactions and inflammatory cytokine production in microglial and neuronal cells. The results of this study showed that DHA reduced expressions of tumor necrosis factor-α, interleukin-6, nitric oxide synthase, and cyclo-oxygenase-2, induced by interferon-γ, and induced upregulation of heme oxygenase-1 (HO-1) in BV-2 microglia. The inhibitory effect of DHA on nitric oxide production was abolished by HO-1 inhibitor zinc protoporphyrin IX. In addition, DHA caused AKT and ERK activation in a time-dependent manner, and the DHA-induced HO-1 upregulation could be attenuated by PI-3 kinase/AKT and MEK/ERK inhibitors. DHA also increased IKKα/β phosphorylation, IκBα phosphorylation, and IκBα degradation, whereas both nuclear factor-κB and IκB protease inhibitors could inhibit DHA-induced HO-1 expressions. The other major n-3 PUFA, eicosapentaenoic acid, showed similar effects of DHA on inflammation and HO-1 in repeated key experiments. In connecting with inflammation hypothesis of depression and clinical studies supporting the antidepressant effects of omega-3 PUFAs, this study provides a novel implication of the antidepressant mechanisms of DHA.
omega-3 fatty acids; docosahexaenoic acid (DHA); heme oxygenase-1 (HO-1); antidepressant; microglia; inflammation; biological psychiatry; depression, unipolar/bipolar; molecular & cellular neurobiology; psychopharmacology; omega-3 fatty acids; docosahexaenoic acid (DHA); heme oxygenase-1 (HO-1); antidepressant; microglia, inflammation
The apoptotic effects of docosahexaenoic acid (DHA) and other ω-3 polyunsaturated fatty acids (PUFAs) have been documented in cell and animal studies. The molecular mechanism by which DHA induces apoptosis is unclear. Although there is no direct evidence, some studies have suggested that DNA damage generated through lipid peroxidation may be involved. Our previous studies showed that DHA, because it is high degree of unsaturation, can give rise to the acrolein-derived 1,N2-propanodeoxyguanosine (Acr-dG) as a major class of DNA adducts via lipid oxidation. As a first step to investigate the possible role of oxidative DNA damage in apoptosis induced by DHA, we examined the relationships between oxidative DNA damage and apoptosis caused by DHA in human colon cancer HT-29 cells. The apoptosis and oxidative DNA damage, including Acr-dG and 8-oxo-deoxyguanosine (8-oxo-dG) formation, in cells treated with DHA and ω-6 PUFAs, including arachidonic acid (AA) and linoleic acid (LA), were measured. DHA induced apoptosis in a dose- and time-dependent manner with a concentration range from 0 to 300 µM as indicated by increased caspase-3 activity and PARP cleavage. In contrast, AA and LA had little or no effect at these concentrations. The Acr-dG levels were increased in HT-29 cells treated with DHA at 240 and 300µM, and the increases were correlated with the induction of apoptosis at these concentrations, while no significant changes were observed for 8-oxo-dG. Because proteins may compete with DNA to react with Acr, we then examined the effects of BSA on the DHA induced apoptosis and oxidative DNA damage. The addition of BSA to HT-29 cell culture media significantly decreases Acr-dG levels with a concomitant decrease in the apoptosis induced by DHA. The reduced Acr-dG formation is attributed to the reaction of BSA with acrolein as indicated by increased levels of total protein carbonyls. Similar correlations between Acr-dG formation and apoptosis were observed in HT-29 cells directly incubated with 0 to 200µM of acrolein. Additionally, DHA treatment increased level of DNA strand breaks and caused cell cycle arrested at G1 phase. Taken together, these results demonstrate the parallel relationships between the Acr-dG level and apoptosis in HT-29 cells, suggesting that the formation of Acr-dG in cellular DNA may contribute to apoptosis induced by DHA.
polyunsaturated fatty acids; apoptosis; chemoprevention; colon cancer; docosahexaenoic acid (DHA); arachidonic acid (AA); linoleic (LA); acrolein; 4-hydroxy-2-nonenal; cyclic deoxyguanosine adducts; oxidative DNA damage; 32P-postlabeling
Liver cancer ranks in prevalence and mortality among top five cancers worldwide. Accumulating interests have been focused in developing new strategies for liver cancer treatment. We have previously showed that dihydroartemisinin (DHA) exhibited antitumor activity towards liver cancer. In this study, we demonstrated that histone deacetylase inhibitors (HDACi) significantly augmented the antineoplastic effect of DHA via increasing apoptosis in vitro and in vivo. Inhibition of ERK phosphorylation contributed to DHA-induced apoptosis, due to the fact that inhibitor of ERK phosphorylation (PD98059) increased DHA-induced apoptosis. Compared with DHA alone, the combined treatment with DHA and HDACi reduced mitochondria membrane potential, released cytochrome c into cytoplasm, increased p53 and Bak, decreased Mcl-1 and p-ERK, activated caspase 3 and PARP, and induced apoptotic cells. Furthermore, we showed that HDACi pretreatment facilitated DHA-induced apoptosis. In Hep G2-xenograft carrying nude mice, the intraperitoneal injection of DHA and SAHA resulted in significant inhibition of xenograft tumors. Results of TUNEL and H&E staining showed more apoptosis induced by combined treatment. Immunohistochemistry data revealed the activation of PARP, and the decrease of Ki-67, p-ERK and Mcl-1. Taken together, our data suggest that the combination of HDACi and DHA offers an antitumor effect on liver cancer, and this combination treatment should be considered as a promising strategy for chemotherapy.
Apoptotic cell death is mediated by caspase activation. Autophagy involves the sequestration of cytoplasmic contents into autophagosomes for traffic to lysosomes for degradation. While autophagy is antiapoptotic, increased numbers of autophagosomes have been associated with forms of non-apoptotic cell death. Apoptosis and autophagy may be co-regulated in the same directions, as the anti-apoptotic Bcl-2 and Bcl-xL proteins negatively regulate autophagy by binding to Beclin 1 (mammalian Atg6), and pro-apoptotic BH3-only proteins may reverse this effect by displacing these interactions. Here we show that apoptosis can suppress autophagy. Apoptosis induced by the pro-apoptotic protein Bax reduced autophagy by enhancing caspase-mediated cleavage of Beclin 1 at D149. After cleavage, both N and C-terminal Beclin 1 fragments change their localisations and these fragments do not interact normally with Vps34, which is required for autophagy. The cleavage of Beclin 1 is a critical event whereby caspases inhibit autophagy, as a non-cleavable Beclin 1 mutant restored autophagy in cells overexpressing Bax.
apoptosis; autophagy; cleavage; caspase
Dietary intake of long-chain n-3 polyunsaturated fatty acids (n-3 PUFA) has been reported to decrease several markers of lymphocyte activation and modulate monocyte susceptibility to apoptosis. However most human studies examined the combined effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) using relatively high daily amounts of n-3 PUFA. The present study investigated the effects of increasing doses of DHA added to the regular diet of human healthy volunteers on lymphocyte response to tetradecanoylphorbol acetate (TPA) plus ionomycin activation, and on monocyte apoptosis induced by oxidized LDL (oxLDL). Eight subjects were supplemented with increasing daily doses of DHA (200, 400, 800 and 1600mg) in a triacylglycerol form containing DHA as the only PUFA, for two weeks each dose. DHA intake dose-dependently increased the proportion of DHA in mononuclear cell phospholipids, the augmentation being significant after 400mg DHA/day. The TPA plus ionomycin-stimulated IL-2 mRNA level started to increase after ingestion of 400mg DHA/day, with a maximum after 800mg intake, and was positively correlated (P<0.003) with DHA enrichment in cell phospholipids. The treatment of monocytes by oxLDL before DHA supplementation drastically reduced mitochondrial membrane potential as compared with native LDL treatment. OxLDL apoptotic effect was significantly attenuated after 400mg DHA/day and the protective effect was maintained throughout the experiment, although to a lesser extent at higher doses. The present results show that supplementation of the human diet with low DHA dosages improves lymphocyte activability. It also increases monocyte resistance to oxLDL-induced apoptosis, which may be beneficial in the prevention of atherosclerosis.
DHA enrichment; interleukin-2; mitochondrial membrane potential; oxidized LDL
Autophagy is a highly regulated intracellular process involved in the turnover of most cellular constituents and in the maintenance of cellular homeostasis. In this study, we show that the activity of autophagy increases in H2O2 or RasV12-induced senescent fibroblasts. Inhibiting autophagy promotes cell apoptosis in senescent cells, suggesting that autophagy activation plays a cytoprotective role. Furthermore, our data indicate that the increase of autophagy in senescent cells is linked to the activation of transcription factor FoxO3A, which blocks ATP generation by transcriptionally up-regulating the expression of PDK4, an inhibitor of pyruvate dehydrogenase complex, thus leading to AMPK activation and mTOR inhibition. These findings suggest a novel mechanism by which FoxO3A factors can activate autophagy via metabolic alteration.
autophagy; senescent cells; apoptosis; FoxO3A; AMPK; fibroblasts
Diets enriched in n-3 polyunsaturated fatty acids (n-3 PUFA) may protect against breast cancer but biochemical mechanisms are unclear. Our studies showed that the n-3 fatty acid, docosahexaenoic acid (DHA) up-regulated syndecan-1 (SDC-1) in human breast cancer cells and we tested the hypothesis that DHA-mediated up-regulation of SDC-1 induces apoptosis. DHA was delivered to MCF-7 cells by n-3 PUFA-enriched low density lipoproteins (LDL) or by albumin in the presence or absence of SDC-1 siRNA. The n-3 PUFA induced apoptosis, which was blocked by SDC-1 silencing. We also confirmed that SDC-1 up-regulation and apoptosis promotion by n-3 PUFA was mediated by PPARγ. Using a luciferase gene driven either by a PPAR response element (PPRE) or a DR-1 site present in the SDC-1 promoter, reporter activities were enhanced by n-3 LDL, DHA and PPARγ agonist, whereas activity of a luciferase gene placed downstream of a mutant DR-1 site was unresponsive. Co-transfection with dominant negative PPARγ DNA eliminated the increase in luciferase activity. These data provide strong evidence that SDC-1 is a molecular target of n-3 PUFA in human breast cancer cells through activation of PPARγ, and that n-3 PUFA-induced apoptosis is mediated by SDC-1. This provides a novel mechanism for the chemo-preventive effects of n-3 PUFA in breast cancer.
During the lipid peroxidation reaction, lipid hydroperoxides are formed as primary products. Several lines of evidence suggest that lipid hydroperoxides can trigger cell death in many cell types, including neurons. In a screening of lipid hydroperoxides which can induce toxicity in neuronal cells, we found docosahexaenoic acid hydroperoxides (DHA-OOH) induced much severe levels of reactive oxygen species generation and cell death in human neuroblastoma SH-SY5Y cells compared to the hydroperoxides of linoleic acid and arachidonic acid. Therefore, we focused on DHA-OOH, and demonstrated that DHA-OOH apparently induced an apoptosis in the neuronal cells through several apoptotic hallmarks including nuclei condensation, DNA fragmentation, poly (ADP-ribose) polymerase cleavage and increased activity of caspase-3. We also found the signaling changes in mitochondria-mediated apoptosis, such as cytochrome c release and increased expression of Bcl-2, as well as a dose-dependent attenuation of mitochondrial membrane potential in the DHA-OOH treated cells. These data indicated DHA hydroperoxide as a potential inducer of apoptosis in human neuroblastoma SH-SY5Y cells, which may be mediated by mitochondria dysfunction pathway.
lipid peroxidation; DHA hydroperoxides; apoptosis; mitochondria dysfunction; neurodegeneration
Docosahexaenoic acid (DHA), a long-chain omega-3 polyunsaturated fatty acid, has been used to treat a range of different conditions, including periodontal disease (PD) and inflammatory bowel disease (IBD). That DHA helps with these oral and gastrointestinal diseases in which inflammation and bacterial dysbiosis play key roles, raises the question of whether DHA may assist in the prevention or treatment of other inflammatory conditions, such as the metabolic syndrome, which have also been linked with inflammation and alterations in normal host microbial populations. Here we review established and investigated associations between DHA, PD, and IBD. We conclude that by beneficially altering cytokine production and macrophage recruitment, the composition of intestinal microbiota and intestinal integrity, lipopolysaccharide- and adipose-induced inflammation, and insulin signaling, DHA may be a key tool in the prevention of metabolic syndrome.
inflammation; periodontal disease; inflammatory bowel disease; metabolic syndrome; bacterial dysbiosis; microbiome; DHA; docosahexaenoic acid; omega-3; fattyacid
The goal of the study is to examine the relationship between the sensor molecules, Hypoxia Inducible Factor-1 (HIF-1), AMP activated Protein Kinase (AMPK) and mammalian Target of Rapamycin (mTOR) in chondrocyte survival and autophagy. We showed that chondrocytes expressed the energy sensor AMPK-1 and that activation increased with maturation. In addition, we showed that thapsigargin treatment activated AMPK and autophagy in a HIF-1 dependent manner. Using serum-starved AMPK-silenced cells, we demonstrated that AMPK was required for the induction of the autophagic response. We also noted a change in chondrocyte sensitivity to apoptogens, due to activation of caspase-8 and cleavage and activation of the pro-apoptotic protein, BID. To test the hypothesis that AMPK signaling directly promoted autophagy, we inhibited AMPK activity in mTOR silenced cells and showed that while mTOR suppression induced autophagy, AMPK inhibition did not block this activity. Based on these findings, it is concluded that due to the micro-environmental changes experienced by the chondrocyte, autophagy is activated by AMPK in a HIF-1 dependent manner.
AMPK; mTOR; HIF-1; autophagy; chondrocyte
Epigallocatechin gallate (EGCG) is a major polyphenol in green tea that has been shown to have anti-inflammatory, anti-cancer, anti-steatotic effects on the liver. Autophagy also mediates similar effects; however, it is not currently known whether EGCG can regulate hepatic autophagy. Here, we show that EGCG increases hepatic autophagy by promoting the formation of autophagosomes, increasing lysosomal acidification, and stimulating autophagic flux in hepatic cells and in vivo. EGCG also increases phosphorylation of AMPK, one of the major regulators of autophagy. Importantly, siRNA knockdown of AMPK abrogated autophagy induced by EGCG. Interestingly, we observed lipid droplet within autophagosomes and autolysosomes and increased lipid clearance by EGCG, suggesting it promotes lipid metabolism by increasing autophagy. In mice fed with high-fat/western style diet (HFW; 60% energy as fat, reduced levels of calcium, vitamin D3, choline, folate, and fiber), EGCG treatment reduces hepatosteatosis and concomitantly increases autophagy. In summary, we have used genetic and pharmacological approaches to demonstrate EGCG induction of hepatic autophagy, and this may contribute to its beneficial effects in reducing hepatosteatosis and potentially some other pathological liver conditions.
Autophagy and apoptosis control the turnover of organelles and proteins within cells, and of cells within organisms, respectively, and many stress pathways sequentially elicit autophagy, and apoptosis within the same cell. Generally autophagy blocks the induction of apoptosis, and apoptosis-associated caspase activation shuts off the autophagic process. However, in special cases, autophagy or autophagy-relevant proteins may help to induce apoptosis or necrosis, and autophagy has been shown to degrade the cytoplasm excessively, leading to ‘autophagic cell death’. The dialogue between autophagy and cell death pathways influences the normal clearance of dying cells, as well as immune recognition of dead cell antigens. Therefore, the disruption of the relationship between autophagy and apoptosis has important pathophysiological consequences.
Calcium can play an important role in the regulation of autophagy. We previously reported that exogenously introduced calcium in the form of calcium phosphate precipitates (CPP) induces autophagy. Here we showed that CPP-induced autophagy required the classical autophagic machinery, including the autophagosome initiating molecules FIP200 and Beclin 1, as well as molecules involved in the autophagosome membrane extension, Atg4, Atg5 and Atg3. On the other hand, Atg9 seemed to place a restriction on CPP-induced autophagy. Loss of Atg9 led to enhanced LC3 punctation and enhanced p62 degradation. CPP-induced autophagy was independent of mTOR and reactive oxygen species. It also did not affect MAP kinase activation and ER stress. DFCP1 is an ER-resident molecule that binds to phosphatidylinositol 3-phosphate. CPP activated DFCP1 punctation in a class III phosphatidylinositol-3-kinase and calcium dependent manner, and caused the association of DFCP1 puncta with the autophagosomes. Consistently, ER membranes, but not Golgi or mitochondrial membranes, colocalized with CPP-induced LC3 positive autophagosomes. These data suggest that CPP-induced autophagosome formation involves the interaction with the ER membrane.