Looking at the metabolic consequences of the colchicine-based in vivo autophagic flux assay

Chaperone-mediated autophagy protects against hyperglycemic stress

Chaperone-mediated autophagy (CMA) is a major pathway of lysosomal proteolysis critical for cellular homeostasis and metabolism, and whose defects have been associated with several human pathologies. While CMA has been well described in mammals, functional evidence has only recently been documented in fish, opening up new perspectives to tackle this function under a novel angle. Now we propose to explore CMA functions in the rainbow trout (RT, Oncorhynchus mykiss), a fish species recognized as a model organism of glucose intolerance and characterized by the presence of two paralogs of the CMA-limiting factor Lamp2A (lysosomal associated membrane protein 2A). To this end, we validated a fluorescent reporter (KFERQ-PA-mCherry1) previously used to track functional CMA in mammalian cells, in an RT hepatoma-derived cell line (RTH-149). We found that incubation of cells with high-glucose levels (HG, 25 mM) induced translocation of the CMA reporter to lysosomes and/or late endosomes in a KFERQ- and Lamp2A-dependent manner, as well as reduced its half-life compared to the control (5 mM), thus demonstrating increased CMA flux. Furthermore, we observed that activation of CMA upon HG exposure was mediated by generation of mitochondrial reactive oxygen species, and involving the antioxidant transcription factor Nfe2l2/Nrf2 (nfe2 like bZIP transcription factor 2). Finally, we demonstrated that CMA plays an important protective role against HG-induced stress, primarily mediated by one of the two RT Lamp2As. Together, our results provide unequivocal evidence for CMA activity existence in RT and highlight both the role and regulation of CMA during glucose-related metabolic disorders.Abbreviations: AREs: antioxidant response elements; CHC: α-cyano -4-hydroxycinnamic acid; Chr: chromosome; CMA: chaperone-mediated autophagy; CT: control; DMF: dimethyl fumarate; Emi: endosomal microautophagy; HG: high-glucose; HMOX1: heme oxygenase 1; H2O2: hydrogen peroxide; KFERQ: lysine-phenylalanine-glutamate-arginine-glutamine; LAMP1: lysosomal associated membrane protein 1; LAMP2A: lysosomal associated membrane protein 2A; MCC: Manders' correlation coefficient; Manders' correlation coefficient Mo: morpholino oligonucleotide; NAC: N-acetyl cysteine; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; PA-mCherry: photoactivable mCherry; PCC: Pearson's correlation coefficient; ROS: reactive oxygen species; RT: rainbow trout; siRNAs: small interfering RNAs; SOD: superoxide dismutase; Tsg101: tumor susceptibility 101; TTFA: 2-thenoyltrifluoroacetone; WGD: whole-genome duplication.

Precision formulation, a new concept to improve dietary amino acid absorption based on the study of cationic amino acid transporters

Amino acid (AA) transporters (AAT) control AA cellular fluxes across membranes, contributing to maintain cellular homeostasis. In this study, we took advantage of rainbow trout metabolic feature, which highly relies on dietary AA, to explore the cellular and physiological consequences of unbalanced diets on AAT dysregulations with a particular focus on cationic AAs (CAA), frequently underrepresented in plant-based diets. Results evidenced that 24 different CAAT are expressed in various trout tissues, part of which being subjected to AA- and CAA-dependent regulations, with y+LAT2 exchanger being prone to the strongest dysregulations. Moreover, CAA were shown to control two major AA-dependent activation pathways (namely mTOR and GCN2) but at different strength according to the CAA considered. A new feed formulation strategy has been put forward to improve specifically the CAA supplemented absorption in fish together with their growth performance. Such "precision formulation" strategy reveals high potential for nutrition practices, especially in aquaculture.

Effects of dietary chloroquine on fish growth, hepatic intermediary metabolism, antioxidant and inflammatory responses in turbot

Autophagy is a conserved cellular self-digestion process and is essential for individual growth, cellular metabolism and inflammatory responses. It was responsive to starvation, pathogens infection and environmental stress. However, the information on the regulation of autophagy in fish hepatic intermediary metabolism, antioxidant system, and immune responses were limited. In the present study, turbot with inhibited autophagy flux was built by dietary chloroquine. The hepatic metabolic response, antioxidant enzymes and immune responses were explored. Results showed that dietary chloroquine induced the expression of Beclin 1, SQSTM and LC-3II, and effectively inhibited autophagy flux. Autophagy dysfunction depressed fish growth and feed utilization, while it induced clusters of liver lipid droplets. The genes involved in lipolysis and fatty acid β-oxidation, as well as the lipogenesis-related genes in chloroquine group were depressed. The phosphorylation of AMPK was activated in chloroquine group, and the genes involved in glycolysis were induced. The hepatic content of malonyldialdehyde and the activities of SOD and CAT were induced when autophagy was inhibited. The content of Complement 3, Complement 4 and Immunoglobulin M, as well as the activity of lysozyme in plasma were depressed in chloroquine group. Dietary chloroquine induced the expression of toll-like receptors and stimulated the expression of myd88 and nf-κb p65, as well as the pro-inflammatory cytokines, such as tnf-α and il-1β. The expression of anti-inflammatory cytokine tgf-β was depressed in the chloroquine group. Our results would extend the knowledge on the role of autophagy in teleost and assist in improving fishery production.

Exposure of zebrafish to a cold environment triggered cellular autophagy in zebrafish liver

Water temperature is the major ecophysiological factor for fish survival in nature and aquaculture. Compared with many homeotherms, fish can survive prolonged periods under the condition of low temperature. However, the metabolic strategies of the liver under a cold environment are still unknown in this species. In our present study, adult zebrafish were exposed to a cold or cold plus starvation environment to analyse the morphological characteristics of hepatocytes by light microscopy and transmission electron microscopy (TEM). The fish livers were dissected and observed under a microscope, and the liver size and shape appeared normal in all groups. Periodic acid-Schiff and TEM analysis showed that hepatic glycogen was significantly lower in zebrafish exposed to cold acclimation (CF group) than that zebrafish at the control water temperature (CT group). Moreover, qPCR and IHC results indicated that the expression of PYGL (a key enzyme involved in glycogenolysis) markedly increased in the CF group. After cold plus starvation treatment (CS group), autophagy activity was significantly enhanced and numerous mitophagic vacuoles were present in the cytoplasm of hepatocytes. In conclusion, hepatic glycogen was first mobilizing to supply energy, and then autophagy, especially mitophagy, played vital roles during nutrient deprivation in fish species.

Are the Main Methionine Sources Equivalent? A Focus on DL-Methionine and DL-Methionine Hydroxy Analog Reveals Differences on Rainbow Trout Hepatic Cell Lines Functions

The replacement of fishmeal by plant proteins in aquafeeds imposes the use of synthetic methionine (MET) sources to balance the amino acid composition of alternative diets and so to meet the metabolic needs of fish of agronomic interest such as rainbow trout (RT-Oncorhynchus mykiss). Nonetheless, debates still exist to determine if one MET source is more efficiently used than another by fish. To address this question, the use of fish cell lines appeared a convenient strategy, since it allowed to perfectly control cell growing conditions notably by fully depleting MET from the media and studying which MET source is capable to restore cell growth/proliferation and metabolism when supplemented back. Thus, results of cell proliferation assays, Western blots, RT-qPCR and liquid chromatography analyses from two RT liver-derived cell lines revealed a better absorption and metabolization of DL-MET than DL-Methionine Hydroxy Analog (MHA) with the activation of the mechanistic Target Of Rapamycin (mTOR) pathway for DL-MET and the activation of integrated stress response (ISR) pathway for MHA. Altogether, the results clearly allow to conclude that both synthetic MET sources are not biologically equivalent, suggesting similar in vivo effects in RT liver and, therefore, questioning the MHA efficiencies in other RT tissues.

The autophagy response during adipogenesis of primary cultured rainbow trout (Oncorhynchus mykiss) adipocytes

Adipogenesis is a tightly regulated process, and the involvement of autophagy has been recently proposed in mammalian models. In rainbow trout, two well-defined phases describe the development of primary cultured adipocyte cells: proliferation and differentiation. Nevertheless, information on the transcriptional profile at the onset of differentiation and the potential role of autophagy in this process is scarce. In the present study, the cells showed an early and transient induction of several adipogenic transcription factors genes' expression (i.e., cebpa and cebpb) along with the morphological changes (round shape filled with small lipid droplets) typical of the onset of adipogenesis. Then, the expression of various lipid metabolism-related genes involving the synthesis (fas), uptake (fatp1 and cd36), accumulation (plin2) and mobilization (hsl) of lipids, characteristic of the mature adipocyte, increased. In parallel, several autophagy markers (i.e., atg4b, gabarapl1 and lc3b) mirrored the expression of those adipogenic-related genes, suggesting a role of autophagy during in vitro fish adipogenesis. In this regard, the incubation of preadipocytes with lysosomal inhibitors (Bafilomycin A1 or Chloroquine), described to prevent autophagy flux, delayed the process of adipogenesis (i.e., cell remodelling), thus suggesting a possible relationship between autophagy and adipocyte differentiation in trout. Moreover, the disruption of the autophagic flux altered the expression of some key adipogenic genes such as cebpa and pparg. Overall, this study contributes to improve our knowledge on the regulation of rainbow trout adipocyte differentiation, and highlights for the first time in fish the involvement of autophagy on adipogenesis, suggesting a close-fitting connection between both processes.

Autophagy in farm animals: current knowledge and future challenges

Autophagy (a process of cellular self-eating) is a conserved cellular degradative process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Surprisingly, little attention has been paid to the role of this cellular function in species of agronomical interest, and the details of how autophagy functions in the development of phenotypes of agricultural interest remain largely unexplored. Here, we first provide a brief description of the main mechanisms involved in autophagy, then review our current knowledge regarding autophagy in species of agronomical interest, with particular attention to physiological functions supporting livestock animal production, and finally assess the potential of translating the acquired knowledge to improve animal development, growth and health in the context of growing social, economic and environmental challenges for agriculture.Abbreviations: AKT: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ASC: adipose-derived stem cells; ATG: autophagy-related; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; BVDV: bovine viral diarrhea virus; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CMA: chaperone-mediated autophagy; CTSB: cathepsin B; CTSD: cathepsin D; DAP: Death-Associated Protein; ER: endoplasmic reticulum; GFP: green fluorescent protein; Gln: Glutamine; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; IF: immunofluorescence; IVP: in vitro produced; LAMP2A: lysosomal associated membrane protein 2A; LMS: lysosomal membrane stability; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MDBK: Madin-Darby bovine kidney; MSC: mesenchymal stem cells; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; NBR1: NBR1 autophagy cargo receptor; NDV: Newcastle disease virus; NECTIN4: nectin cell adhesion molecule 4; NOD1: nucleotide-binding oligomerization domain 1; OCD: osteochondritis dissecans; OEC: oviduct epithelial cells; OPTN: optineurin; PI3K: phosphoinositide-3-kinase; PPRV: peste des petits ruminants virus; RHDV: rabbit hemorrhagic disease virus; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy.

PAR2 promotes high-fat diet-induced hepatic steatosis by inhibiting AMPK-mediated autophagy

Protease-activated receptor 2 (PAR2) is a member of G protein-coupled receptors. There are two types of PAR2 signaling pathways: Canonical G-protein signaling and β-arrestin signaling. Although PAR2 signaling has been reported to aggravate hepatic steatosis, the exact mechanism is still unclear, and the role of PAR2 in autophagy remains unknown. In this study, we investigated the regulatory role of PAR2 in autophagy during high-fat diet (HFD)-induced hepatic steatosis in mice. Increased protein levels of PAR2 and β-arrestin-2 and their interactions were detected after four months of HFD. To further investigate the role of PAR2, male and female wild-type (WT) and PAR2-knockout (PAR2 KO) mice were fed HFD. PAR2 deficiency protected HFD-induced hepatic steatosis in male mice, but not in female mice. Interestingly, PAR2-deficient liver showed increased AMP-activated protein kinase (AMPK) activation with decreased interaction between Ca²⁺/calmodulin-dependent protein kinase kinase β (CAMKKβ) and β-arrestin-2. In addition, PAR2 deficiency up-regulated autophagy in the liver. To elucidate whether PAR2 plays a role in the regulation of autophagy and lipid accumulation in vitro, PAR2 was overexpressed in HepG2 cells. Overexpression of PAR2 decreased AMPK activation with increased interaction of CAMKKβ with β-arrestin-2 and significantly inhibited autophagic responses in HepG2 cells. Inhibition of autophagy by PAR2 overexpression further exacerbated palmitate-induced lipid accumulation in HepG2 cells. Collectively, these findings suggest that the increase in the PAR2-β-arrestin-2-CAMKKβ complex by HFD inhibits AMPK-mediated autophagy, leading to the alleviation of hepatic steatosis.

Chaperone-Mediated Autophagy in the Light of Evolution: Insight from Fish

Chaperone-mediated autophagy (CMA) is a major pathway of lysosomal proteolysis recognized as a key player of the control of numerous cellular functions, and whose defects have been associated with several human pathologies. To date, this cellular function is presumed to be restricted to mammals and birds, due to the absence of an identifiable lysosome-associated membrane protein 2A (LAMP2A), a limiting and essential protein for CMA, in nontetrapod species. However, the recent identification of expressed sequences displaying high homology with mammalian LAMP2A in several fish species challenges that view and suggests that CMA likely appeared earlier during evolution than initially thought. In the present study, we provide a comprehensive picture of the evolutionary history of the LAMP2 gene in vertebrates and demonstrate that LAMP2 indeed appeared at the root of the vertebrate lineage. Using a fibroblast cell line from medaka fish (Oryzias latipes), we further show that the splice variant lamp2a controls, upon long-term starvation, the lysosomal accumulation of a fluorescent reporter commonly used to track CMA in mammalian cells. Finally, to address the physiological role of Lamp2a in fish, we generated knockout medaka for that specific splice variant, and found that these deficient fish exhibit severe alterations in carbohydrate and fat metabolisms, in consistency with existing data in mice deficient for CMA in liver. Altogether, our data provide the first evidence for a CMA-like pathway in fish and bring new perspectives on the use of complementary genetic models, such as zebrafish or medaka, for studying CMA in an evolutionary perspective.

Analysis of hepatic transcriptome modulation exerted by γ-conglutin from lupins in a streptozotocin-induced diabetes model

Lupinus albus γ-conglutin is proposed to positively affect glucose metabolism through inhibition of hepatic glucose production and insulin-mimetic activity; however, the action mechanism is not entirely known. Besides, most studies had focused on its effect on molecular targets directly related to glucose metabolism, and few studies have investigated how γ-conglutin may affect the liver gene expression or if it plays a role in other metabolic processes. Therefore, we investigated the influence of γ-conglutin on the liver transcriptome of streptozotocin-induced diabetic rats using DNA microarrays, ontological analyses, and quantitative PCR. Of the 22,000 genes evaluated, 803 and 173 were downregulated and upregulated, respectively. The ontological analyses of the differentially expressed genes revealed that among others, the mitochondria, microtubules, cytoskeleton, and oxidoreductase activity terms were enriched, implying a possible role of γ-conglutin on autophagy. To corroborate the microarray results, we selected and quantified, by PCR, the expression of two genes associated with autophagy (Atg7 and Snx18) and found their expression augmented two and threefold, respectively; indicating a higher autophagy activity in animals treated with γ-conglutin. Although complementary studies are required, our findings indicate for the first time that the hypoglycaemic effects of γ-conglutin may involve an autophagy induction mechanism, a pivotal process for the preservation of cell physiology and glucose homeostasis.

RTH-149 Cell Line, a Useful Tool to Decipher Molecular Mechanisms Related to Fish Nutrition

Nowadays, aquaculture provides more than 50% of fish consumed worldwide but faces new issues that challenge its sustainability. One of them relies on the replacement of fish meal (FM) in aquaculture feeds by other protein sources without deeply affecting the whole organism's homeostasis. Multiple strategies have already been tested using in vivo approaches, but they hardly managed to cope with the multifactorial problems related to the complexities of fish biology together with new feed formulations. In this context, rainbow trout (RT) is particularly concerned by these problems, since, as a carnivorous fish, dietary proteins provide the amino acids required to supply most of its energetic metabolism. Surprisingly, we noticed that in vitro approaches considering RT cell lines as models to study RT amino acid metabolism were never previously used. Therefore, we decided to investigate if, and how, three major pathways described, in other species, to be regulated by amino acid and to control cellular homeostasis were functional in a RT cell line called RTH-149-namely, the mechanistic Target Of Rapamycin (mTOR), autophagy and the general control nonderepressible 2 (GCN2) pathways. Our results not only demonstrated that these three pathways were functional in RTH-149 cells, but they also highlighted some RT specificities with respect to the time response, amino acid dependencies and the activation levels of their downstream targets. Altogether, this article demonstrated, for the first time, that RT cell lines could represent an interesting alternative of in vivo experimentations for the study of fish nutrition-related questions.

Early feeding of rainbow trout (Oncorhynchus mykiss) with methionine-deficient diet over a 2 week period: consequences for liver mitochondria in juveniles

Methionine is a key factor in modulating the cellular availability of the main biological methyl donor S-adenosylmethionine (SAM), which is required for all biological methylation reactions including DNA and histone methylation. As such, it represents a potential critical factor in nutritional programming. Here, we investigated whether early methionine restriction at first feeding could have long-term programmed metabolic consequences in rainbow trout. For this purpose, trout fry were fed with either a control diet (C) or a methionine-deficient diet (MD) for 2 weeks from the first exogenous feeding. Next, fish were subjected to a 5 month growth trial with a standard diet followed by a 2 week challenge (with the MD or C diet) to test the programming effect of the early methionine restriction. The results showed that, whatever the dietary treatment of fry, the 2 week challenge with the MD diet led to a general mitochondrial defect associated with an increase in endoplasmic reticulum stress, mitophagy and apoptosis, highlighting the existence of complex cross-talk between these different functions. Moreover, for the first time, we also observed that fish fed the MD diet at the first meal later exhibited an increase in several critical factors of mitophagy, hinting that the early nutritional stimulus with methionine deficiency resulted in long-term programming of this cell function. Together, these data extend our understanding of the role of dietary methionine and emphasize the potential for this amino acid in the application of new feeding strategies, such as nutritional programming, to optimize the nutrition and health of farmed fish.

Profiling the rainbow trout hepatic miRNAome under diet-induced hyperglycemia

Carnivorous rainbow trout exhibit prolonged postprandial hyperglycemia when fed a diet exceeding 20% carbohydrate content. This poor capacity to utilize carbohydrates has led to rainbow trout being classified as "glucose-intolerant" (GI). The metabolic phenotype has spurred research to identify the underlying cellular and molecular mechanisms of glucose intolerance, largely because carbohydrate-rich diets provide economic and ecological advantages over traditionally used fish meal, considered unsustainable for rainbow trout aquaculture operations. Evidence points to a contribution of hepatic intermediary carbohydrate and lipid metabolism, as well as upstream insulin signaling. Recently, microRNAs (miRNAs), small noncoding RNAs acting as negative posttranscriptional regulators affecting target mRNA stability and translation, have emerged as critical regulators of hepatic control of glucose-homeostasis in mammals, revealing that dysregulated hepatic miRNAs might play a role in organismal hyperglycemia in metabolic disease. To determine whether hepatic regulatory miRNA networks may contribute to GI in rainbow trout, we induced prolonged postprandial hyperglycemia in rainbow trout by using a carbohydrate-rich diet and profiled genome-wide hepatic miRNAs in hyperglycemic rainbow trout compared with fasted trout and trout fed a diet devoid of carbohydrates. Using small RNA next-generation sequencing and real-time RT-PCR validation, we identified differentially regulated hepatic miRNAs between these groups and used an in silico approach to predict bona fide mRNA targets and enriched pathways. Diet-induced hyperglycemia resulted in differential regulation of hepatic miRNAs compared with fasted fish. Some of the identified miRNAs, such as miRNA-27b-3p and miRNA-200a-3p, are known to be responsive to hyperglycemia in the liver of hyperglycemic glucose-tolerant fish and mammals, suggesting an evolutionary conserved regulation. Using Gene Ontology term-based enrichment analysis, we identify intermediate carbohydrate and lipid metabolism and insulin signaling as potential targets of posttranscriptional regulation by hyperglycemia-regulated miRNAs and provide correlative expression analysis of specific predicted miRNA-target pairs. This study identifies hepatic miRNAs in rainbow trout that exhibit differential postprandial expression in response to diets with different carbohydrate content and predicts posttranscriptionally regulated target mRNAs enriched for pathways involved in glucoregulation. Together, these results provide a framework for testable hypotheses of functional involvement of specific hepatic miRNAs in GI in rainbow trout.

The Autophagic Flux Inhibitor Bafilomycine A1 Affects the Expression of Intermediary Metabolism-Related Genes in Trout Hepatocytes

Autophagy is an evolutionarily conserved process of cellular self-eating which emerged these last years as a major adaptive metabolic response to various stresses such as fasting, hypoxia, or environmental pollutants. However, surprisingly very few data is currently available on its role in fish species which are directly exposed to frequent environmental perturbations. Here, we report that the treatment of fasted trout hepatocytes with the autophagy inhibitor Bafilomycine A1 lowered the mRNA levels of many of the gluconeogenesis-related genes and increased those of genes involved in intracellular lipid stores. Concurrently, intracellular free amino acid levels dropped and the expression of the main genes involved in the endoplasmic reticulum (ER) stress exhibited a sharp increase in autophagy inhibited cells. Together these results highlight the strong complexity of the crosstalk between ER, autophagy and metabolism and support the importance of considering this function in future studies on metabolic adaptation of fish to environmental stresses.

New Insights on Intermediary Metabolism for a Better Understanding of Nutrition in Teleosts

The rapid development of aquaculture production throughout the world over the past few decades has led to the emergence of new scientific challenges to improve fish nutrition. The diet formulations used for farmed fish have been largely modified in the past few years. However, bottlenecks still exist in being able to suppress totally marine resources (fish meal and fish oil) in diets without negatively affecting growth performance and flesh quality. A better understanding of fish metabolism and its regulation by nutrients is thus mandatory. In this review, we discuss four fields of research that are highly important for improving fish nutrition in the future: ( a) fish genome complexity and subsequent consequences for metabolism, ( b) microRNAs (miRNAs) as new actors in regulation of fish metabolism, ( c) the role of autophagy in regulation of fish metabolism, and ( d) the nutritional programming of metabolism linked to the early life of fish.

Autophagy in Human Health and Disease: Novel Therapeutic Opportunities

SIGNIFICANCE

In eukaryotes, autophagy represents a highly evolutionary conserved process, through which macromolecules and cytoplasmic material are degraded into lysosomes and recycled for biosynthetic or energetic purposes. Dysfunction of the autophagic process has been associated with the onset and development of many human chronic pathologies, such as cardiovascular, metabolic, and neurodegenerative diseases as well as cancer. Recent Advances: Currently, comprehensive research is being carried out to discover new therapeutic agents that are able to modulate the autophagic process in vivo. Recent evidence has shown that a large number of natural bioactive compounds are involved in the regulation of autophagy by modulating several transcriptional factors and signaling pathways.

CRITICAL ISSUES

Critical issues that deserve particular attention are the inadequate understanding of the complex role of autophagy in disease pathogenesis, the limited availability of therapeutic drugs, and the lack of clinical trials. In this context, the effects that natural bioactive compounds exert on autophagic modulation should be clearly highlighted, since they depend on the type and stage of the pathological conditions of diseases.

FUTURE DIRECTIONS

Research efforts should now focus on understanding the survival-supporting and death-promoting roles of autophagy, how natural compounds interact exactly with the autophagic targets so as to induce or inhibit autophagy and on the evaluation of their pharmacological effects in a more in-depth and mechanistic way. In addition, clinical studies on autophagy-inducing natural products are strongly encouraged, also to highlight some fundamental aspects, such as the dose, the duration, and the possible synergistic action of these compounds with conventional therapy.

Analysis of Time-Series Gene Expression Data to Explore Mechanisms of Chemical-Induced Hepatic Steatosis Toxicity

Non-alcoholic fatty liver disease (NAFLD) represents a wide spectrum of disease, ranging from simple fatty liver through steatosis with inflammation and necrosis to cirrhosis. One of the most challenging problems in biomedical research and within the chemical industry is to understand the underlying mechanisms of complex disease, and complex adverse outcome pathways (AOPs). Based on a set of 28 steatotic chemicals with gene expression data measured on primary hepatocytes at three times (2, 8, and 24 h) and three doses (low, medium, and high), we identified genes and pathways, defined as molecular initiating events (MIEs) and key events (KEs) of steatosis using a combination of a time series and pathway analyses. Among the genes deregulated by these compounds, the study highlighted OSBPL9, ALDH7A1, MYADM, SLC51B, PRDX6, GPAT3, TMEM135, DLGDA5, BCO2, APO10LA, TSPAN6, NEURL1B, and DUSP1. Furthermore, pathway analysis indicated deregulation of pathways related to lipid accumulation, such as fat digestion and absorption, linoleic and linolenic acid metabolism, calcium signaling pathway, fatty acid metabolism, peroxisome, retinol metabolism, and steroid metabolic pathways in a time dependent manner. Such transcription profile analysis can help in the understanding of the steatosis evolution over time generated by chemical exposure.

Autophagy blockade sensitizes human head and neck squamous cell carcinoma towards CYT997 through enhancing excessively high reactive oxygen species-induced apoptosis

The functional relationship between apoptosis and autophagy in anticancer drug treatment is extremely complex, and the molecular machinery is obscure. This study aims to investigate the efficacy of CYT997, a novel microtubule-disrupting agent, in head and neck squamous cell carcinomas (HNSCCs) and complete the autophagy-apoptosis puzzle involved in drug action. We report here that CYT997 exhibits anticancer activity by triggering oxidative stress-associated apoptosis in HNSCC cells. Interestingly, upregulation of autophagy by mTOR-dependent pathways appears to have a cytoprotective role in preventing apoptosis by inhibiting CYT997-induced excessively high levels of reactive oxygen species (ROS). Blockade of autophagy by ATG7 depletion or addition of autophagy inhibitor hydroxychloroquine (HCQ) sensitizes HNSCC cells to CYT997 as evidenced by enhanced ROS-associated apoptosis. Moreover, HCQ exhibits a good synergism with CYT997 on induction of apoptosis in HNSCC xenografts without cytotoxicity, suggesting combined treatment of CYT997 with autophagy inhibitors would increase the anticancer efficacy of CYT997. These findings unveil the importance of ROS in crosstalk between autophagy and apoptosis in CYT997 treatment, raising concerns that genetic or pharmacologic blockade of autophagy should be considered in the design of new therapeutics for HNSCC.

KEY MESSAGES

• CYT997 exhibits anticancer activity by induction of ROS-associated apoptosis. • mTOR-dependent cytoprotective autophagy prevents CYT997-induced apoptosis. • Blockade of autophagy augments CYT997 efficacy by enhanced ROS-associated apoptosis. • Combination of autophagy inhibitors with CYT997 is more effective against HNSCC.

Dietary methionine deficiency affects oxidative status, mitochondrial integrity and mitophagy in the liver of rainbow trout (Oncorhynchus mykiss)

The low levels of methionine in vegetable raw materials represent a limit to their use in aquafeed. Methionine is considered as an important factor in the control of oxidative status. However, restriction of dietary methionine has been shown to reduce generation of mitochondrial oxygen radicals and thus oxidative damage in liver. Here, we aim to evaluate the effect of dietary methionine deficiency in hepatic oxidative status in rainbow trout and identify the underlying mechanisms. Fish were fed for 6 weeks diets containing two different methionine concentrations: deficient (MD, Methionine Deficient diet) or adequate (CTL, control diet). At the end of the experiment, fish fed the MD diet showed a significantly lower body weight and feed efficiency compared to fish fed the CTL diet. Growth reduction of the MD group was associated to a general mitochondrial defect and a concomitant decrease of the oxidative status in the liver. The obtained results also revealed a sharp increase of mitochondrial degradation through mitophagy in these conditions and emphasized the involvement of the PINK1/PARKIN axis in this event. Collectively, these results provide a broader understanding of the mechanisms at play in the reduction of oxidant status upon dietary methionine deficiency.

Tetrahydrohyperforin prevents articular cartilage degeneration and affects autophagy in rats with osteoarthritis

Osteoarthritis (OA) is a highly prevalent disease, which is associated with extracellular matrix degradation and cell death in articular cartilage. The aim of the present study was to identify whether tetrahydrohyperforin (IDN5706) ameliorates the degeneration of articular cartilage and affects autophagy in OA. The rat model of experimental OA was induced by intra-articular injection of collagenase solution. IDN5706 was administered intragastrically to rats for 6 weeks. Histopathological changes in articular cartilage were examined using hematoxylin and eosin (H&E) and safranin O staining, and Mankin scoring systems. The effect of IDN5706 on autophagy was examined using western blotting. ELISA was performed to detect cartilage inflammation. H&E and safranin O staining, Mankin scores, and electron microscopy indicated that IDN5706 could lessen the degeneration of articular cartilage in OA rats. In addition, western blotting revealed that IDN5706 treatment may activate the suppressed autophagy in OA rats. In conclusion, the present study demonstrated that IDN5706 was able to reduce the severity of experimental OA, alleviate the degeneration of articular cartilage, and affect autophagy in OA model rats.

Modeling of autophagy-related gene expression dynamics during long term fasting in European eel (Anguilla anguilla)

Autophagy is an evolutionary conserved cellular self-degradation process considered as a major energy mobilizing system in eukaryotes. It has long been considered as a post-translationally regulated event, and the importance of transcriptional regulation of autophagy-related genes (atg) for somatic maintenance and homeostasis during long period of stress emerged only recently. In this regard, large changes in atg transcription have been documented in several species under diverse types of prolonged catabolic situations. However, the available data primarily concern atg mRNA levels at specific times and fail to capture the dynamic relationship between transcript production over time and integrated phenotypes. Here, we present the development of a statistical model describing the dynamics of expression of several atg and lysosomal genes in European glass eel (Anguilla anguilla) during long-term fasting at two temperatures (9 °C and 12 °C) and make use of this model to infer the effect of transcripts dynamics on an integrated phenotype – here weight loss. Our analysis shows long-term non-random fluctuating atg expression dynamics and reveals for the first time a significant contribution of atg transcripts production over time to weight loss. The proposed approach thus offers a new perspective on the long-term transcriptional control of autophagy and its physiological role.

The critical role played by endotoxin-induced liver autophagy in the maintenance of lipid metabolism during sepsis

Macroautophagy/autophagy is a central mechanism by which cells maintain integrity and homeostasis, and endotoxin-induced autophagy plays important roles in innate immunity. Although TLR4 stimulation mediated by lipopolysaccharide (LPS) also upregulates autophagy in hepatocytes and liver, its physiological role remains elusive. The objective of this study was to determine the role of LPS-induced autophagy in the regulation of liver lipid metabolism. LPS treatment (5 mg/kg) increased autophagy, as detected by LC3 conversion and transmission electron microscopy (TEM) analysis in C57BL6 mouse livers. AC2F hepatocytes also showed increased autophagic flux after LPS treatment (1 μg/ml). To investigate the role of LPS-induced autophagy further, liver lipid metabolism changes in LPS-treated mice and fasted controls were compared. Interestingly, LPS-treated mice showed less lipid accumulation in liver than fasted mice despite increased fatty acid uptake and lipid synthesis-associated genes. In vitro analysis using AC2F hepatocytes demonstrated LPS-induced autophagy influenced the degradation of lipid droplets. Inhibition of LPS-induced autophagy using bafilomycin A₁ or Atg7 knockdown significantly increased lipid accumulation in AC2F hepatocytes. In addition, pretreatment with chloroquine aggravated LPS-induced lipid accumulation and inflammation in C57BL6 mouse livers. The physiological importance of autophagy was verified in LPS-treated young and aged rats. Autophagic response was diminished in LPS-treated aged rats and lipid metabolism was impaired during sepsis, indicating autophagy response is important for regulating lipid metabolism after endotoxin challenge. Our findings demonstrate endotoxin-induced autophagy is important for the regulation of lipid metabolism, and suggest that autophagy helps maintain lipid metabolism homeostasis during sepsis.

An Autophagic Flux Probe that Releases an Internal Control

Macroautophagy is an intracellular degradation system that utilizes the autophagosome to deliver cytoplasmic components to the lysosome. Measuring autophagic activity is critically important but remains complicated and challenging. Here, we have developed GFP-LC3-RFP-LC3ΔG, a fluorescent probe to evaluate autophagic flux. This probe is cleaved by endogenous ATG4 proteases into equimolar amounts of GFP-LC3 and RFP-LC3ΔG. GFP-LC3 is degraded by autophagy, while RFP-LC3ΔG remains in the cytosol, serving as an internal control. Thus, autophagic flux can be estimated by calculating the GFP/RFP signal ratio. Using this probe, we re-evaluated previously reported autophagy-modulating compounds, performed a high-throughput screen of an approved drug library, and identified autophagy modulators. Furthermore, we succeeded in measuring both induced and basal autophagic flux in embryos and tissues of zebrafish and mice. The GFP-LC3-RFP-LC3ΔG probe is a simple and quantitative method to evaluate autophagic flux in cultured cells and whole organisms.