A quick signal of starvation induced autophagy: Transcription versus post-translational modification of LC3

Copper-induced Genotoxicity, Oxidative Stress, and Alteration in Transcriptional Level of Autophagy-associated Genes in Snakehead Fish Channa punctatus

Copper (Cu) is an essential and important trace element for some significant life processes for most organisms. However, an excessive amount of Cu can be highly toxic. The present study was conducted to elucidate the oxidative stress-induced alteration in transcriptional level of autophagy-related genes in the liver and kidney tissue of fish Channa punctatus after treatment with three different sublethal concentrations of CuSO₄ for 28 days. All the studied enzymatic and non-enzymatic oxidative stress markers viz. superoxide dismutase-SOD, catalase-CAT, glutathione peroxidase-GPx, glutathione reductase-GR, and glutathione-GSH showed an increase in their activity levels in the treated groups in a dose-dependent manner. Particularly SOD and CAT have shown a significant hike in activity levels. ROS levels in blood cells increased significantly (p < 0.05) in all the treated groups, i.e., Group II-1/20^th of 96 h-LC₅₀ (0.2 mg/L), Group III-1/10^th of 96 h-LC₅₀ (0.4 mg/L), and Group IV-1/5 ^h of 96 h-LC₅₀ (0.8 mg/L) of Cu²⁺ in a dose-dependent manner as compared to control (Group I). The upregulation in mRNA levels of autophagy-related genes Microtubule-associated protein 1 light chain 3 (LC3), Gamma-aminobutyric acid receptor-associated protein precursor (Gabarap), and Golgi-associated ATPase enhancer of 16 kDa (GATE16), autophagy-related 5 (ATG5) was observed while mammalian target of rapamycin (mTOR) showed downregulation in the liver and kidney tissue of fish. The decrease in mTOR and increase in ATG5 gene expression projects autophagic vesicle formation due to oxidative stress. There was significant induction in micronuclei (MN) frequency in all the treated groups. The highest frequency of MN induced by Cu²⁺ was recorded in Group IV after 28 days of the exposure period. Thus, it can be concluded that the available information about Cu²⁺-induced oxidative stress-mediated autophagy in the liver and kidney of fish C. punctatus remains largely unclear to date, so to fill the aforesaid gap, the present study was undertaken, which gives an insight for the mechanisms of autophagy induced by Cu²⁺ in fish.

Altered transcriptional levels of autophagy-related genes, induced by oxidative stress in fish Channa punctatus exposed to chromium

Chromium has been detected in various water bodies as a harmful metallic stressor to aquatic organisms. This study aimed to investigate the mechanism associated with autophagy, oxidative stress, and genotoxicity after chromium (Cr⁶⁺) exposure (1/20th of 96 h-LC50, 1/10th of 96 h-LC50, and 1/5th of 96 h-LC50 of Cr⁶⁺) of common food fish Channa punctatus. The mRNA levels of autophagy-related genes ATG5, LC3, GABARAP, and mTOR were assessed in the liver and kidney tissue of fish. An upregulation of ATG5, LC3, and GABARAP was observed in both liver and kidney tissue samples, while mTOR showed transcriptional downregulation in both the tissue samples. This depicts autophagic vesicle formation due to stress signals. All the studied oxidative stress markers SOD, CAT, GSH, GR, and GPx showed an increase in the activity level of treated groups in a dose-dependent manner. Particularly, SOD and CAT have shown a significant elevation in activity level. ROS levels in blood cells increased significantly (p < 0.05) in all the treated groups (groups II, III, and IV) in a time-dependent manner as compared to the control (group I). There was a significant induction in MN frequency in all the treated groups. The highest frequency of micronuclei induced by Cr⁶⁺ was recorded in group IV after 28 days of exposure period. Collectively, it can be concluded that the information about Cr⁶⁺-induced oxidative stress-mediated autophagy in vital organs of fish Channa punctatus remains largely obscure hitherto; to fill the aforesaid gap, this study was undertaken, which gives a snapshot for the mechanisms of autophagy induced by Cr⁶⁺ in fish. HIGHLIGHTS: • Chronic exposure to Cr⁶⁺ induces eco-toxicological manifestations in a fish Channa punctatus. • Altered transcriptional profile of autophagy-related genes suggests autophagic vesicle formation due to stress signals. • Increased activity levels of oxidative stress biomarkers reveal that Cr⁶⁺ annihilates antioxidative defense system in fish. • Genotoxicity due to chromium exposure is evident by increased frequency of MN in red blood cells of fish. • The information presented in this study is helpful to get an insight into the mechanism of Cr⁶⁺-induced oxidative stress-mediated induction of autophagy in the liver and kidney of Channa punctatus.

Potential Method of Autophagy Imaging with Cationized Gelatin Nanospheres Incorporating Molecular Beacon

The objective of this research is to develop an imaging method with cationized gelatin nanospheres incorporating molecular beacon (cGNS_MB) to visualize an autophagy activity in living cells. Cationized gelatin nanospheres (cGNS) were prepared by the conventional coacervation method, and then molecular beacon (MB) was incorporated into them. The cGNS_MB prepared were internalized into cells at a high efficiency. In this study, a starvation medium of serum and amino acids-free was used to induce autophagy. The autophagy activity was confirmed by an immunofluorescence staining for microtubule-associated proteins light chain 3B (LC3B) of an autophagy specific protein. With the autophagy induction time, the number of LC3 fluorescent dots increased, which indicated an increased autophagy activity. As the autophagy-related genes, sequestosome 1 (SQSTM1) and cathepsin F (CTSF), which up-regulate after autophagy induction, were chosen as the targets of cGNS_MB. The fluorescence intensity of cGNS_MB targeting to SQSTM1 and CTSF increased with the starvation treatment time, which well corresponded with the gene expression results. When applied to cells in different autophagy conditions, the cGNS_MB visualized the autophagy activity corresponding with the autophagy condition of cells. From the results obtained, it was concluded that the cGNS_MB provide a promising method to visualize the autophagy of cells. The advantage of cGNS_MB visualization is to obtain the temporal and spatial information without destroying sample cells.

Predicting Metabolic Adaptation Under Dynamic Substrate Conditions Using a Resource-Dependent Kinetic Model: A Case Study Using Saccharomyces cerevisiae

Exposed to changes in their environment, microorganisms will adapt their phenotype, including metabolism, to ensure survival. To understand the adaptation principles, resource allocation-based approaches were successfully applied to predict an optimal proteome allocation under (quasi) steady-state conditions. Nevertheless, for a general, dynamic environment, enzyme kinetics will have to be taken into account which was not included in the linear resource allocation models. To this end, a resource-dependent kinetic model was developed and applied to the model organism Saccharomyces cerevisiae by combining published kinetic models and calibrating the model parameters to published proteomics and fluxomics datasets. Using this approach, we were able to predict specific proteomes at different dilution rates under chemostat conditions. Interestingly, the approach suggests that the occurrence of aerobic fermentation (Crabtree effect) in S. cerevisiae is not caused by space limitation in the total proteome but rather an effect of constraints on the mitochondria. When exposing the approach to repetitive, dynamic substrate conditions, the proteome space was allocated differently. Less space was predicted to be available for non-essential enzymes (reserve space). This could indicate that the perceived “overcapacity” present in experimentally measured proteomes may very likely serve a purpose in increasing the robustness of a cell to dynamic conditions, especially an increase of proteome space for the growth reaction as well as of the trehalose cycle that was shown to be essential in providing robustness upon stronger substrate perturbations. The model predictions of proteome adaptation to dynamic conditions were additionally evaluated against respective experimentally measured proteomes, which highlighted the model’s ability to accurately predict major proteome adaptation trends. This proof of principle for the approach can be extended to production organisms and applied for both understanding metabolic adaptation and improving industrial process design.

EFFECTS OF EXHAUSTIVE EXERCISE AND CONTUSION ON AUTOPHAGY-RELATED FACTORS IN SKELETAL MUSCLE OF RATS

ABSTRACT Objective: To study the effects of exhaustive exercise and contusion on autophagy-related factors Beclin1, LC3 and PINK1 expression in the skeletal muscle of rats. Methods: Forty-two male SD rats were randomly divided into 7 groups, 6 rats in each group: C, D0, D24, D48, E0, E24, and E48. Each group of rats was killed and dissected at the different respective time points specified above. The whole quadriceps femoris of the left hind limbs were removed and divided into two parts, one for mRNAs of Beclin1, LC3 and PINK1 by real-time fluorescent quantitative PCR, and the other for LC3 protein by Western blotting. Results: Compared with group C, the contents of Beclin1 mRNA, PINK1 mRNA, and LC3 mRNA in the immediate exhaustive exercise group (E0) were significantly reduced p<0.01. However, the levels of PINK1 mRNA, LC3 mRNA, and LC3 protein in skeletal muscle cells increased significantly in the 48 hours after exhaustion (E48) p<0.05, suggesting that cell autophagy had an increasing trend during the recovery period. Meanwhile, compared with the C group, the contents of Beclin1 mRNA, PINK1 mRNA, and LC3 mRNA in the immediate blunt contusion group (D0) increased significantly p<0.01 and were followed by a downward trend. Conclusion: Generally, there were differences between the blunt contusion and exhausted exercise models at each recovery phase. The gene expression of the autophagy-related factors was not high in the early exhaustive exercise recovery phase and subsequently followed an upward trend. But the above factors increased significantly in the immediate and early recovery phases after blunt contusion. Injury from blunt contusion may be more severe than exhaustive exercise-induced-injury, so the autophagy starts earlier according to the changes in autophagy-related factors. Level of evidence III; Therapeutic studies investigating the results of treatment.

First insights into the autophagy machinery of adult Schistosoma mansoni

Schistosomiasis is a disease of global importance caused by parasitic flatworms, schistosomes, which cause pathogenicity through eggs laid by the female worm inside the host's blood vessels. Maintenance of cellular homeostasis is crucial for parasites, as for other organisms, and is quite likely important for schistosome reproduction and vitality. We hypothesize a role for autophagy in these processes, an evolutionarily conserved and essential cellular degradation pathway. Here, for the first known time, we shed light on the autophagy machinery and its involvement in pairing-dependent processes, vitality and reproduction of Schistosoma mansoni. We identified autophagy genes by in silico analyses and determined the influence of in vitro culture on the transcriptional expression in male and female worms using quantitative real-time PCR. Among the identified autophagy genes were Beclin, Ambra1, Vps34, DRAM, DAP1, and LC3B, of which some showed a sex-dependent expression. Specifically, the death-associated protein DAP1 was significantly more highly expressed in females compared with males, while for the damage-regulated autophagy modulator DRAM it was the opposite. Furthermore, in-vitro culture significantly changed the transcript expression level of DAP1 in female worms. Next, worms were treated with an autophagy inducer (rapamycin) or inhibitors (bafilomycin A1, wortmannin and spautin-1) to evaluate effects on autophagy protein expression, worm vitality, and reproduction. The conversion of the key autophagy protein LC3B, a marker for autophagic activity, was increased by rapamycin and blocked by bafilomycin. All inhibitors affected worm fitness, egg production, and negatively affected the morphology of gonads and intestine. In summary, autophagy genes in S. mansoni show an interesting sex-dependent expression pattern and manipulation of autophagy in S. mansoni by inhibitors induced detrimental effects, which encourages subsequent studies to identify antischistosomal targets within the autophagy machinery.

Involvement of lysosomal integral membrane protein-2 in the activation of autophagy

Lysosomal integral membrane protein-2 (LIMP-2) is a type III transmembrane protein that is highly glycosylated and mainly localized to the lysosomal membrane. The diverse functions of LIMP-2 are currently being uncovered; however, its participation in macroautophagy, usually described as autophagy, has not yet been well-investigated. To determine the possible involvement of LIMP-2 in autophagic activity, we examined the intracellular amount of microtubule-associated protein 1 light chain 3 (LC3)-II, which is well-correlated with autophagosome levels, in exogenous rat LIMP-2-expressing COS7 and HEK293 cells. Transient or stable expression of LIMP-2-myc significantly increased the levels of LC3-II. Conversely, knockdown of LIMP-2 decreased the LC3-II levels in NIH3T3 cells. Furthermore, approaches using lysosomal protease inhibitors and mCherry-GFP-LC3 fluorescence suggested that exogenous expression of LIMP-2 increased the biogenesis of autophagosomes rather than decreased the lysosomal turnover of LC3-II. Considering the results of the biochemical assay and the quantitative fluorescence assay together, it is suggested that LIMP-2 has a possible involvement in autophagic activity, especially autophagosome biogenesis.

Investigating AKT activation and autophagy in immunoproteasome-deficient retinal cells

Two major proteolytic systems, the proteasome and the autophagy pathway, are key components of the proteostasis network. The immunoproteasome, a proteasome subtype, and autophagy are upregulated under stress conditions, forming a coordinated unit designed to minimize the effect of cell stress. We investigated how genetic ablation of the LMP2 immunoproteasome subunit affects autophagy in retinal pigment epithelium (RPE) from WT and LMP2 knockout mice. We monitored autophagy regulation by measuring LC3, phosphorylation of AKT (S473), and phosphorylation of S6, a downstream readout of AKT (mTOR) pathway activation. We also evaluated transcription factor EB (TFEB) nuclear translocation, a transcription factor that controls expression of autophagy and lysosome genes. WT and LMP2 KO cells were monitored after treatment with EBSS to stimulate autophagy, insulin to stimulate AKT, or an AKT inhibitor (trehalose or MK-2206). Under basal conditions, we observed hyper-phosphorylation of AKT and S6, as well as lower nuclear-TFEB content in LMP2 KO RPE compared with WT. AKT inhibitors MK-2206 and trehalose significantly inhibited AKT phosphorylation and stimulated nuclear translocation of TFEB. Starvation and AKT inhibition upregulated autophagy, albeit to a lesser extent in LMP2 KO RPE. These data support the idea that AKT hyper-activation is an underlying cause of defective autophagy regulation in LMP2 KO RPE, revealing a unique link between two proteolytic systems and a previously unknown function in autophagy regulation by the immunoproteasome.

ULK1 affects cell viability of goat Sertoli cell by modulating both autophagy and apoptosis

Sertoli cells (SCs) are necessary for proper germ cell development and viability. Unc-51 like autophagy activating kinase (ULK1) protein kinase is an important regulator of autophagy activation. This study aims to investigate the role of autophagy promoter ULK1 on cell viability of goat SCs. Our results showed that ULK1 knockdown in goat SCs decreased autophagy activation, which was confirmed by decreased expression of autophagy-related markers including LC3, Beclin1, Atg5, and Atg7 (P < 0.05). Meanwhile, lower ULK1 levels resulted in decreased expressions of goat SC marker genes ABP, AMH, FASL, and GATA4. However, a reverse trend of these parameters occurred when the goat SCs were transfected with ULK1 overexpression construct; higher ULK1 levels in goat SCs also decreased the ratio of Bax/Bcl-2. Moreover, ULK1 overexpression in goat SCs activated the autophagy levels when cells were exposed to an environmental contaminant bisphenol A (BPA). The above results indicated that ULK1 gene might play important roles in goat SC function by regulating cell viability.

Autophagy-related genes in rainbow trout Oncorhynchus mykiss (Walbaum) gill epithelial cells and their role in nutrient restriction

Autophagy is primarily an adaptive response to provide nutrients and energy following exposure to stress and starvation but can also regulate muscle mass and impact infectious disease susceptibility. Expression of 10 autophagy-related (Atg) genes in rainbow trout was monitored throughout the autophagosome formation cycle. The Atg gene sequences of rainbow trout were compared to other species to identify highly conserved regions and to generate primers. Phylogeny trees created with rainbow trout and 14 other species demonstrate that rainbow trout Atg gene sequences have greatest similarity to Atlantic salmon and other fish species. RTgill-W1 cells were subjected to nutrient restriction and compared to cells in normal nutrient conditions using quantitative reverse transcriptase polymerase chain reaction to assess changes in Atg gene expression. Nutrient restriction had a direct impact on Atg gene expression, with atg4, atg9, atg12, lc3, gabarap and becn1 undergoing the greatest differential expression (p < 0.05), most dramatically on Day 3. This was corroborated by Western blot detection of LC3, which also showed a peak of autophagy activity at Day 3 post-nutrient restriction. Atg gene expression revealed autophagy flux in RTgill-W1, as well as, those genes that were most significantly altered by nutrient restriction.

Studying the Role of AMPK in Autophagy

AMPK is an energy-sensing kinase and is required for the induction and progression of the autophagy process. In this chapter, we describe experimental approaches to study the steady state and flux of autophagy in response to AMPK activation. For this purpose, we provide detailed protocols for the measurement of general as well as AMPK-specific autophagy markers by immunoblot and immunofluorescence analysis.

Transcriptional and epigenetic profiling of nutrient-deprived cells to identify novel regulators of autophagy

Macroautophagy (hereafter autophagy) is a lysosomal degradation pathway critical for maintaining cellular homeostasis and viability, and is predominantly regarded as a rapid and dynamic cytoplasmic process. To increase our understanding of the transcriptional and epigenetic events associated with autophagy, we performed extensive genome-wide transcriptomic and epigenomic profiling after nutrient deprivation in human autophagy-proficient and autophagy-deficient cells. We observed that nutrient deprivation leads to the transcriptional induction of numerous autophagy-associated genes. These transcriptional changes are reflected at the epigenetic level (H3K4me3, H3K27ac, and H3K56ac) and are independent of autophagic flux. As a proof of principle that this resource can be used to identify novel autophagy regulators, we followed up on one identified target: EGR1 (early growth response 1), which indeed appears to be a central transcriptional regulator of autophagy by affecting autophagy-associated gene expression and autophagic flux. Taken together, these data stress the relevance of transcriptional and epigenetic regulation of autophagy and can be used as a resource to identify (novel) factors involved in autophagy regulation.

TSC1 and TSC2 regulate cilia length and canonical Hedgehog signaling via different mechanisms

Primary cilia are sensory organelles that coordinate multiple cellular signaling pathways, including Hedgehog (HH), Wingless/Int (WNT) and Transforming Growth Factor-β (TGF-β) signaling. Similarly, primary cilia have been implicated in regulation of mTOR signaling, in which Tuberous Sclerosis Complex proteins 1 and 2 (TSC1/2) negatively regulate protein synthesis by inactivating the mTOR complex 1 (mTORC1) at energy limiting states. Here we report that TSC1 and TSC2 regulate Smoothened (SMO)-dependent HH signaling in mouse embryonic fibroblasts (MEFs). Reduced SMO-dependent expression of Gli1 was demonstrated in both Tsc1-/- and Tsc2-/- cells, and we found that Tsc1 is required for TGF-β induced phosphorylation of SMAD2/3 and subsequent expression of the HH signaling effector and transcription factor GLI2. Hedgehog signaling was restored in Tsc1-/- cells after exogenous expression of Gli2, whereas rapamycin restored HH signaling in Tsc2-/- cells. Furthermore, we observed that Tsc1-/- MEFs display significantly elongated cilia, whereas cilia in Tsc2-/- MEFs were shorter than normal. The elongated cilium phenotype of Tsc1-/- MEFs is likely due to increased mTORC1-dependent autophagic flux observed in these cells, as both the autophagic flux and the cilia length phenotype was restored by rapamycin. In addition, ciliary length control in Tsc1-/- MEFs was also influenced by reduced expression of Gli2, which compromised expression of Wnt5a that normally promotes cilia disassembly. In summary, our results support distinct functions of Tsc1 and Tsc2 in cellular signaling as the two genes affect ciliary length control and HH signaling via different mechanisms.

Apoptosis and autophagy induced by pyropheophorbide-α methyl ester-mediated photodynamic therapy in human osteosarcoma MG-63 cells

Pyropheophorbide-α methyl ester (MPPa) was a second-generation photosensitizer with many potential applications. Here, we explored the impact of MPPa-mediated photodynamic therapy (MPPa-PDT) on the apoptosis and autophagy of human osteosarcoma (MG-63) cells as well as the relationships between apoptosis and autophagy of the cells, and investigated the related molecular mechanisms. We found that MPPa-PDT demonstrated the ability to inhibit MG-63 cell viability in an MPPa concentration- and light dose-dependent manner, and to induce apoptosis via the mitochondrial apoptosis pathway. Additionally, MPPa-PDT could also induce autophagy of MG-63 cell. Meanwhile, the ROS scavenger N-acetyl-l-cysteine (NAC) and the Jnk inhibitor SP600125 were found to inhibit the MPPa-PDT-induced autophagy, and NAC could also inhibit Jnk phosphorylation. Furthermore, pretreatment with the autophagy inhibitor 3-methyladenine or chloroquine showed the potential in reducing the apoptosis rate induced by MPPa-PDT in MG-63 cells. Our results indicated that the mitochondrial pathway was involved in MPPa-PDT-induced apoptosis of MG-63 cells. Meanwhile the ROS-Jnk signaling pathway was involved in MPPa-PDT-induced autophagy, which further promoted the apoptosis in MG-63 cells.

Effect and proposed mechanism of vitamin C modulating amino acid regulation of autophagic proteolysis

Autophagy is an intracellular bulk degradation process, induced under nutrient starvation. Failure of autophagy has been recognized as a contributor to aging and multiple age related neurodegenerative diseases. Improving autophagy is a beneficial anti-aging strategy, however very few physiological regulators have been identified. Here, we demonstrate that vitamin C is a nutritional stimulator of autophagy. Supplementation of fresh hepatocytes with vitamin C increased autophagic proteolysis significantly in the presence of amino acids in a dose- and time-dependent manner, although no effect was observed in the absence of amino acids. In addition, inhibitor studies with 3-methyladenine, chloroquine, leupeptin and β-lactone confirmed that vitamin C is active through the lysosomal autophagy and not the proteasome pathway. Furthermore, the autophagy marker LC3 protein was significantly increased by vitamin C, suggesting its possible site of action is at the formation step. Both the reduced (ascorbic acid, AsA) and oxidized form (dehydroascorbic acid, DHA) of vitamin C exhibited equal enhancing effect, indicating that the effect does not depend on the anti-oxidation functionality of vitamin C. To understand the mechanism, we established that the effective dose (50 μM) was 15× lower than the intracellular content suggesting these would be only a minor influx from the extracellular pool. Moreover, transporter inhibitor studies in an AsA deficient ODS model rat revealed more accurately that the enhancing effect on autophagic proteolysis still existed, even though the intracellular influx of AsA was blocked. Taken together, these results provide evidence that vitamin C can potentially act through extracellular signaling.

Induction of apoptosis and autophagy by calcifying nanoparticles in human bladder cancer cells

Calcifying nanoparticles have been linked to various types of human disease, but how they contribute to disease processes is unclear. Here, we examined whether and how calcifying nanoparticles isolated from patients with kidney stones are cytotoxic to human bladder cancer cells. Calcifying nanoparticles were isolated from midstream urine of patients with renal calcium oxalate stones and examined by electron microscopy. Human bladder cancer cells (EJ cells) were cultured in the presence of calcifying nanoparticles or nanohydroxyapatites for 12 and 72 h and examined for toxicity using the Cell Counting Kit-8, for autophagy using transmission electron microscopy and confocal microscopy, and for apoptosis using fluorescence microscopy, transmission electron microscopy, and flow cytometry. Changes in protein expression were analyzed by Western blotting. The results showed that the size and shape of the isolated calcifying nanoparticles were as expected. Calcifying nanoparticles were cytotoxic to EJ cells, more so than nanohydroxyapatites, and this was due, at least in part, to the production of intracellular reactive oxygen species. Transmission electron microscopy showed that calcifying nanoparticles were packaged into vesicles and autolysosomes. Calcifying nanoparticles induced greater autophagy and apoptosis than nanohydroxyapatites. Our findings demonstrate that calcifying nanoparticles can trigger bladder cancer cell injury by boosting reactive oxygen species production and stimulating autophagy and apoptosis.

A Hybrid Chalcone Combining the Trimethoxyphenyl and Isatinyl Groups Targets Multiple Oncogenic Proteins and Pathways in Hepatocellular Carcinoma Cells

Small molecule inhibitors that can simultaneously inhibit multiple oncogenic proteins in essential pathways are promising therapeutic chemicals for hepatocellular carcinoma (HCC). To combine the anticancer effects of combretastatins, chalcones and isatins, we synthesized a novel hybrid molecule 3’,4’,5’-trimethoxy-5-chloro-isatinylchalcone (3MCIC). 3MCIC inhibited proliferation of cultured HepG2 cells, causing rounding-up of the cells and massive vacuole accumulation in the cytoplasm. Paxillin and focal adhesion plaques were downregulated by 3MCIC. Surprisingly, unlike the microtubule (MT)-targeting agent CA-4 that inhibits tubulin polymerization, 3MCIC stabilized tubulin polymers both in living cells and in cell lysates. 3MCIC treatment reduced cyclin B1, CDK1, p-CDK1/2, and Rb, but increased p53 and p21. Moreover, 3MCIC caused GSK3β degradation by promoting GSK3β-Ser9 phosphorylation. Nevertheless, 3MCIC inhibited the Wnt/β-catenin pathway by downregulating β-catenin, c-Myc, cyclin D1 and E2F1. 3MCIC treatment not only activated the caspase-3-dependent apoptotic pathway, but also caused massive autophagy evidenced by rapid and drastic changes of LC3 and p62. 3MCIC also promoted cleavage and maturation of the lysosomal protease cathepsin D. Using ligand-affinity chromatography (LAC), target proteins captured onto the Sephacryl S1000-C₁₂-3MCIC resins were isolated and analyzed by mass spectrometry (MS). Some of the LAC-MS identified targets, i.e., septin-2, vimentin, pan-cytokeratin, nucleolin, EF1α1/2, EBP1 (PA2G4), cyclin B1 and GSK3β, were further detected by Western blotting. Moreover, both septin-2 and HIF-1α decreased drastically in 3MCIC-treated HepG2 cells. Our data suggest that 3MCIC is a promising anticancer lead compound with novel targeting mechanisms, and also demonstrate the efficiency of LAC-MS based target identification in anticancer drug development.

Autophagy: A double-edged sword in intervertebral disk degeneration

Autophagy is a homeostatic mechanism through which intracellular damaged organelles and proteins are degraded and recycled in response to increased metabolic demands or stresses. Although primarily cytoprotective, dysfunction of autophagy is often associated with many degenerative diseases, including intervertebral disc (IVD) degeneration (IDD). As a main contributing factor to low back pain, IDD is the pathological basis for various debilitating spinal diseases. Either higher or lower levels of autophagy are observed in degenerative IVD cells. Despite the precise role of autophagy in disc degeneration that is still controversial, with difference from protection to aggravation, targeting autophagy has shown promise for mitigating disc degeneration. In the current review, we summarize the changes of autophagy in degenerative IVD cells and mainly discuss the relationship between autophagy and IDD. With continued efforts, modulation of the autophagic process could be a potential and attractive therapeutic strategy for degenerative disc disease.

Dose-dependent autophagic effect of titanium dioxide nanoparticles in human HaCaT cells at non-cytotoxic levels

BACKGROUND

Interactions between nanoparticles and cells are now the focus of a fast-growing area of research. Though many nanoparticles interact with cells without any acute toxic responses, metal oxide nanoparticles including those composed of titanium dioxide (TiO2-NPs) may disrupt the intracellular process of macroautophagy. Autophagy plays a key role in human health and disease, particularly in cancer and neurodegenerative diseases. We herein investigated the in vitro biological effects of TiO2-NPs (18 nm) on autophagy in human keratinocytes (HaCaT) cells at non-cytotoxic levels.

RESULTS

TiO2-NPs were characterized by transmission electron microscopy (TEM) and dynamic light scattering techniques. Cellular uptake, as evaluated by TEM and NanoSIMS revealed that NPs internalization led to the formation of autophagosomes. TiO2-NPs treatment did not reduce cell viability of HaCaT cells nor increased oxidative stress. Cellular autophagy was additionally evaluated by confocal microscopy using eGFP-LC3 keratinocytes, western blotting of autophagy marker LC3I/II, immunodetection of p62 and NBR1 proteins, and gene expression of LC3II, p62, NBR1, beclin1 and ATG5 by RT-qPCR. We also confirmed the formation and accumulation of autophagosomes in NPs treated cells with LC3-II upregulation. Based on the lack of degradation of p62 and NBR1 proteins, autophagosomes accumulation at a high dose (25.0 μg/ml) is due to blockage while a low dose (0.16 μg/ml) promoted autophagy. Cellular viability was not affected in either case.

CONCLUSIONS

The uptake of TiO2-NPs led to a dose-dependent increase in autophagic effect under non-cytotoxic conditions. Our results suggest dose-dependent autophagic effect over time as a cellular response to TiO2-NPs. Most importantly, these findings suggest that simple toxicity data are not enough to understand the full impact of TiO2-NPs and their effects on cellular pathways or function.

Effects of Atrazine and Chlorpyrifos on Autophagy-Related Genes in the Brain of Common Carp: Health-Risk Assessments

This study assessed the impacts of atrazine (ATR), chlorpyrifos (CPF), and a combined ATR/CPF exposure on the brain of common carp (Cyprinus carpio L.). The carp were sampled after a 40-days exposure to CPF and ATR, individually or in combination, followed by a 40-days recovery period to measure autophagy and antioxidant activity. The results indicate that the anti-superoxide anion and anti-hydroxy radical activities decreased upon exposure to ATR, CPF, and the ATR/CPF combination but increased after a subsequent 40-days recovery period. Quantitative real-time PCR and Western blot analyses revealed that the mRNA and protein levels of LC3B and dynein in common carp decreased significantly after exposure to ATR and CPF alone or in combination. Moreover, the mRNA and protein levels of beclin1 gene decreased significantly only in the 116 and 11.3 μg/L treatment groups. However, the mRNA and protein levels of all tested genes increased significantly after a 40-days recovery. Transmission electron microscope demonstrated the occurrence of autolysosomes in the recovery groups but not in the exposure groups. These results suggest that exposure to ATR, CPF, or their combination promotes oxidative stress and autophagic responses in the brain of common carp.

Low dietary protein content alleviates motor symptoms in mice with mutant dynactin/dynein-mediated neurodegeneration

Mutations in components of the molecular motor dynein/dynactin lead to neurodegenerative diseases of the motor system or atypical parkinsonism. These mutations are associated with prominent accumulation of vesicles involved in autophagy and lysosomal pathways, and with protein inclusions. Whether alleviating these defects would affect motor symptoms remain unknown. Here, we show that a mouse model expressing low levels of disease linked-G59S mutant dynactin p150(Glued) develops motor dysfunction >8 months before loss of motor neurons or dopaminergic degeneration is observed. Abnormal accumulation of autophagosomes and protein inclusions were efficiently corrected by lowering dietary protein content, and this was associated with transcriptional upregulations of key players in autophagy. Most importantly this dietary modification partially rescued overall neurological symptoms in these mice after onset. Similar observations were made in another mouse strain carrying a point mutation in the dynein heavy chain gene. Collectively, our data suggest that stimulating the autophagy/lysosomal system through appropriate nutritional intervention has significant beneficial effects on motor symptoms of dynein/dynactin diseases even after symptom onset.