NDP52 acts as a redox sensor in PINK1/Parkin-mediated mitophagy.

Mitophagy, the elimination of mitochondria via the autophagy-lysosome pathway, is essential for the maintenance of cellular homeostasis. The best characterised mitophagy pathway is mediated by stabilisation of the protein kinase PINK1 and recruitment of the ubiquitin ligase Parkin to damaged mitochondria. Ubiquitinated mitochondrial surface proteins are recognised by autophagy receptors including NDP52 which initiate the formation of an autophagic vesicle around the mitochondria. Damaged mitochondria also generate reactive oxygen species (ROS) which have been proposed to act as a signal for mitophagy, however the mechanism of ROS sensing is unknown. Here we found that oxidation of NDP52 is essential for the efficient PINK1/Parkin-dependent mitophagy. We identified redox-sensitive cysteine residues involved in disulphide bond formation and oligomerisation of NDP52 on damaged mitochondria. Oligomerisation of NDP52 facilitates the recruitment of autophagy machinery for rapid mitochondrial degradation. We propose that redox sensing by NDP52 allows mitophagy to function as a mechanism of oxidative stress response.

Adipose tissue depot-specific intracellular and extracellular cues contributing to insulin resistance in obese individuals.

Adipose tissue dysregulation in obesity strongly influences systemic metabolic homeostasis and is often linked to insulin resistance (IR). However, the molecular mechanisms underlying adipose tissue dysfunction in obesity are not fully understood. Herein, a proteomic analysis of subcutaneous (SC) and omental (OM) fat from lean subjects and obese individuals with different degrees of insulin sensitivity was performed to identify adipose tissue biomarkers related to obesity-associated metabolic disease. Our results suggest that dysregulation of both adipose tissue extracellular matrix (ECM) organization and intracellular trafficking processes may be associated with IR in obesity. Thus, abnormal accumulation of the small leucine-rich proteoglycan, lumican, as observed in SC fat of IR obese individuals, modifies collagen I organization, impairs adipogenesis and activates stress processes [endoplasmic reticulum and oxidative stress] in adipocytes. In OM fat, IR is associated with increased levels of the negative regulator of the Rab family of small GTPases, GDI2, which alters lipid storage in adipocytes by inhibiting insulin-stimulated binding of the Rab protein, Rab18, to lipid droplets. Together, these results indicate that lumican and GDI2 might play depot-dependent, pathogenic roles in obesity-associated IR. Our findings provide novel insights into the differential maladaptive responses of SC and OM adipose tissue linking obesity to IR.

Transcriptional block of AMPK-induced autophagy promotes glutamate excitotoxicity in nutrient-deprived SH-SY5Y neuroblastoma cells.

We investigated the role of autophagy, a controlled lysosomal degradation of cellular macromolecules and organelles, in glutamate excitotoxicity during nutrient deprivation in vitro. The incubation in low-glucose serum/amino acid-free cell culture medium synergized with glutamate in increasing AMP/ATP ratio and causing excitotoxic necrosis in SH-SY5Y human neuroblastoma cells. Glutamate suppressed starvation-triggered autophagy, as confirmed by diminished intracellular acidification, lower LC3 punctuation and LC3-I conversion to autophagosome-associated LC3-II, reduced expression of proautophagic beclin-1 and ATG5, increase of the selective autophagic target NBR1, and decreased number of autophagic vesicles. Similar results were observed in PC12 rat pheochromocytoma cells. Both glutamate-mediated excitotoxicity and autophagy inhibition in starved SH-SY5Y cells were reverted by NMDA antagonist memantine and mimicked by NMDA agonists D-aspartate and ibotenate. Glutamate reduced starvation-triggered phosphorylation of the energy sensor AMP-activated protein kinase (AMPK) without affecting the activity of mammalian target of rapamycin complex 1, a major negative regulator of autophagy. This was associated with reduced mRNA levels of autophagy transcriptional activators (FOXO3, ATF4) and molecules involved in autophagy initiation (ULK1, ATG13, FIP200), autophagosome nucleation/elongation (ATG14, beclin-1, ATG5), and autophagic cargo delivery to autophagosomes (SQSTM1). Glutamate-mediated transcriptional repression of autophagy was alleviated by overexpression of constitutively active AMPK. Genetic or pharmacological AMPK activation by AMPK overexpression or metformin, as well as genetic or pharmacological autophagy induction by TFEB overexpression or lithium chloride, reduced the sensitivity of nutrient-deprived SH-SY5Y cells to glutamate excitotoxicity. These data indicate that transcriptional inhibition of AMPK-dependent cytoprotective autophagy is involved in glutamate-mediated excitotoxicity during nutrient deprivation in vitro.

A comprehensive systematic review of CSF proteins and peptides that define Alzheimer's disease.

BACKGROUND: During the last two decades, over 100 proteomics studies have identified a variety of potential biomarkers in CSF of Alzheimer's (AD) patients. Although several reviews have proposed specific biomarkers, to date, the statistical relevance of these proteins has not been investigated and no peptidomic analyses have been generated on the basis of specific up- or down- regulation. Herein, we perform an analysis of all unbiased explorative proteomics studies of CSF biomarkers in AD to critically evaluate whether proteins and peptides identified in each study are consistent in distribution; direction change; and significance, which would strengthen their potential use in studies of AD pathology and progression. METHODS: We generated a database containing all CSF proteins whose levels are known to be significantly altered in human AD from 47 independent, validated, proteomics studies. Using this database, which contains 2022 AD and 2562 control human samples, we examined whether each protein is consistently present on the basis of reliable statistical studies; and if so, whether it is over- or under-represented in AD. Additionally, we performed a direct analysis of available mass spectrometric data of these proteins to generate an AD CSF peptide database with 3221 peptides for further analysis. RESULTS: Of the 162 proteins that were identified in 2 or more studies, we investigated their enrichment or depletion in AD CSF. This allowed us to identify 23 proteins which were increased and 50 proteins which were decreased in AD, some of which have never been revealed as consistent AD biomarkers (i.e. SPRC or MUC18). Regarding the analysis of the tryptic peptide database, we identified 87 peptides corresponding to 13 proteins as the most highly consistently altered peptides in AD. Analysis of tryptic peptide fingerprinting revealed specific peptides encoded by CH3L1, VGF, SCG2, PCSK1N, FBLN3 and APOC2 with the highest probability of detection in AD. CONCLUSIONS: Our study reveals a panel of 27 proteins and 21 peptides highly altered in AD with consistent statistical significance; this panel constitutes a potent tool for the classification and diagnosis of AD.

The caveolae-associated coiled-coil protein, NECC2, regulates insulin signalling in Adipocytes.

Adipocyte dysfunction in obesity is commonly associated with impaired insulin signalling in adipocytes and insulin resistance. Insulin signalling has been associated with caveolae, which are coated by large complexes of caveolin and cavin proteins, along with proteins with membrane-binding and remodelling properties. Here, we analysed the regulation and function of a component of caveolae involved in growth factor signalling in neuroendocrine cells, neuroendocrine long coiled-coil protein-2 (NECC2), in adipocytes. Studies in 3T3-L1 cells showed that NECC2 expression increased during adipogenesis. Furthermore, NECC2 co-immunoprecipitated with caveolin-1 (CAV1) and exhibited a distribution pattern similar to that of the components of adipocyte caveolae, CAV1, Cavin1, the insulin receptor and cortical actin. Interestingly, NECC2 overexpression enhanced insulin-activated Akt phosphorylation, whereas NECC2 downregulation impaired insulin-induced phosphorylation of Akt and ERK2. Finally, an up-regulation of NECC2 in subcutaneous and omental adipose tissue was found in association with human obesity and insulin resistance. This effect was also observed in 3T3-L1 adipocytes exposed to hyperglycaemia/hyperinsulinemia. Overall, the present study identifies NECC2 as a component of adipocyte caveolae that is regulated in response to obesity and associated metabolic complications, and supports the contribution of this protein as a molecular scaffold modulating insulin signal transduction at these membrane microdomains.

mTORC1 and Nutrient Homeostasis: The Central Role of the Lysosome.

The mechanistic target of rapamycin complex 1 (mTORC1) coordinates cellular growth and metabolism with environmental inputs to ensure that cells grow only under favourable conditions. When active, mTORC1 stimulates biosynthetic pathways including protein, lipid and nucleotide synthesis and inhibits cellular catabolism through repression of the autophagic pathway, thereby promoting cell growth and proliferation. The recruitment of mTORC1 to the lysosomal surface has been shown to be essential for its activation. This finding has significantly enhanced our knowledge of mTORC1 regulation and has focused the attention of the field on the lysosome as a signalling hub which coordinates several homeostatic pathways. The intriguing localisation of mTORC1 to the cellular organelle that plays a crucial role in catabolism enables mTORC1 to feedback to autophagy and lysosomal biogenesis, thus leading mTORC1 to enact precise spatial and temporal control of cell growth. This review will cover the signalling interactions which take place on the surface of lysosomes and the cross-talk which exists between mTORC1 activity and lysosomal function.

The cytoskeletal protein septin 11 is associated with human obesity and is involved in adipocyte lipid storage and metabolism.

AIMS/HYPOTHESIS: Septins are newly identified members of the cytoskeleton that have been proposed as biomarkers of a number of diseases. However, septins have not been characterised in adipose tissue and their relationship with obesity and insulin resistance remains unknown. Herein, we characterised a member of this family, septin 11 (SEPT11), in human adipose tissue and analysed its potential involvement in the regulation of adipocyte metabolism. METHODS: Gene and protein expression levels of SEPT11 were analysed in human adipose tissue. SEPT11 distribution was evaluated by immunocytochemistry, electron microscopy and subcellular fractionation techniques. Glutathione S-transferase (GST) pull-down, immunoprecipitation and yeast two-hybrid screening were used to identify the SEPT11 interactome. Gene silencing was used to assess the role of SEPT11 in the regulation of insulin signalling and lipid metabolism in adipocytes. RESULTS: We demonstrate the expression of SEPT11 in human adipocytes and its upregulation in obese individuals, with SEPT11 mRNA content positively correlating with variables of insulin resistance in subcutaneous adipose tissue. SEPT11 content was regulated by lipogenic, lipolytic and proinflammatory stimuli in human adipocytes. SEPT11 associated with caveolae in mature adipocytes and interacted with both caveolin-1 and the intracellular fatty acid chaperone, fatty acid binding protein 5 (FABP5). Lipid loading of adipocytes caused the association of the three proteins with the surface of lipid droplets. SEPT11 silencing impaired insulin signalling and insulin-induced lipid accumulation in adipocytes. CONCLUSIONS/INTERPRETATION: Our findings support a role for SEPT11 in lipid traffic and metabolism in adipocytes and open new avenues for research on the control of lipid storage in obesity and insulin resistance.

Adiponectin receptors form homomers and heteromers exhibiting distinct ligand binding and intracellular signaling properties.

Adiponectin binds to two widely expressed receptors (AdipoR1 and AdipoR2) that contain seven transmembrane domains but, unlike G-protein coupled receptors, present an extracellular C terminus and a cytosolic N terminus. Recently, AdipoR1 was found to associate in high order complexes. However, it is still unknown whether AdipoR2 may also form homomers or heteromers with AdipoR1 or if such interactions may be functionally relevant. Herein, we have analyzed the oligomerization pattern of AdipoRs by FRET and immunoprecipitation and evaluated both the internalization of AdipoRs in response to various adiponectin isoforms and the effect of adiponectin binding to different AdipoR combinations on AMP-activated protein kinase phosphorylation and peroxisome proliferator-activated receptor α activation. Transfection of HEK293AD cells with AdipoR1 and AdipoR2 showed that both receptors colocalize at both the plasma membrane and the endoplasmic reticulum. Co-transfection with the different AdipoR pairs yielded high FRET efficiencies in non-stimulated cells, which indicates that AdipoR1 and AdipoR2 form homo- and heteromeric complexes under resting conditions. Live FRET imaging suggested that both homo- and heteromeric AdipoR complexes dissociate in response to adiponectin, but heteromers separate faster than homomers. Finally, phosphorylation of AMP-activated protein kinase in response to adiponectin was delayed in cells wherein heteromer formation was favored. In sum, our findings indicate that AdipoR1 and AdipoR2 form homo- and heteromers that present unique interaction behaviors and signaling properties. This raises the possibility that the pleiotropic, tissue-dependent functions of adiponectin depend on the expression levels of AdipoR1 and AdipoR2 and, therefore, on the steady-state proportion of homo- and heteromeric complexes.

Olive leaf protein: Extraction optimization, in vitro digestibility, structural and techno-functional properties.

Olive leaf, as an important by-product of olive farming, is generated from the pruning and harvesting of olive trees and represents >10 % of the total olive weight. The present study was conducted to evaluate the composition, functional and structural characterizations, as well as the in vitro digestibility of olive leaf proteins isolated from ultrasonic-assisted extraction, comparing to classical and industrial techniques. The ultrasound-assisted extraction of olive leaf protein was optimized by the simultaneous maximization of the yield and purity of protein using a Box-Behnken design (BBD) of response surface methodology (RSM). The results indicated that the optimal extraction conditions were as follows: pH of 10.99, temperature of 40.48 °C, sonication time of 47.25 min, and solvent/solid ratio of 24.08 mL/g. Under these conditions, the extraction yield and protein content were 11.67 and 51.2 %, respectively, which were significantly higher than those obtained by the conventional techniques. Regarding the functionality of protein, extraction technique had significant impacts on the structural and functional properties of proteins. In general, ultrasound assisted extraction had higher solubility, and better foaming and thermal properties and in vitro digestibility but lower emulsifying stability and fluid binding capacity compared to conventional ones. Ultrasound-assisted alkaline extraction has great potential to produce edible olive leaf protein with modified functional properties that can be used for various aims in the food applications.

The Golgi-associated long coiled-coil protein NECC1 participates in the control of the regulated secretory pathway in PC12 cells.

Golgi-associated long coiled-coil proteins, often referred to as golgins, are involved in the maintenance of the structural organization of the Golgi apparatus and the regulation of membrane traffic events occurring in this organelle. Little information is available on the contribution of golgins to Golgi function in cells specialized in secretion such as endocrine cells or neurons. In the present study, we characterize the intracellular distribution as well as the biochemical and functional properties of a novel long coiled-coil protein present in neuroendocrine tissues, NECC1 (neuroendocrine long coiled-coil protein 1). The present study shows that NECC1 is a peripheral membrane protein displaying high stability to detergent extraction, which distributes across the Golgi apparatus in neuroendocrine cells. In addition, NECC1 partially localizes to post-Golgi carriers containing secretory cargo in PC12 cells. Overexpression of NECC1 resulted in the formation of juxtanuclear aggregates together with a slight fragmentation of the Golgi and a decrease in K+-stimulated hormone release. In contrast, NECC1 silencing did not alter Golgi architecture, but enhanced K+-stimulated hormone secretion in PC12 cells. In all, the results of the present study identify NECC1 as a novel component of the Golgi matrix and support a role for this protein as a negative modulator of the regulated trafficking of secretory cargo in neuroendocrine cells.

Spatial and Temporal Protein Modules Signatures Associated with Alzheimer Disease in 3xTg-AD Mice Are Restored by Early Ubiquinol Supplementation.

Despite its robust proteopathic nature, the spatiotemporal signature of disrupted protein modules in sporadic Alzheimer's disease (AD) brains remains poorly understood. This considered oxidative stress contributes to AD progression and early intervention with coenzyme Q10 or its reduced form, ubiquinol, delays the progression of the disease. Using MALDI-MSI and functional bioinformatic analysis, we have developed a protocol to express how deregulated protein modules arise from hippocampus and cortex in the AD mice model 3xTG-AD in an age-dependent manner. This strategy allowed us to identify which modules can be efficiently restored to a non-pathological condition by early intervention with ubiquinol. Indeed, an early deregulation of proteostasis-related protein modules, oxidative stress and metabolism has been observed in the hippocampus of 6-month mice (early AD) and the mirrored in cortical regions of 12-month mice (middle/late AD). This observation has been validated by IHC using mouse and human brain sections, suggesting that these protein modules are also affected in humans. The emergence of disrupted protein modules with AD signature can be prevented by early dietary intervention with ubiquinol in the 3xTG-AD mice model.

Revisiting the regulated secretory pathway: from frogs to human.

The regulated secretory pathway is a hallmark of endocrine and neuroendocrine cells. This process comprises different sequential steps, including ER-associated protein synthesis, ER-to-Golgi protein transport, Golgi-associated posttranslational modification, sorting and packing of secretory proteins into carrier granules, cytoskeleton-based granule transport towards the plasma membrane and tethering, docking and fusion of granules with specialized releasing zones in the plasma membrane. Each one of these steps is tightly regulated by a large number of factors that function in a spatially and temporarily coordinated fashion. During the past three decades, much effort has been devoted to characterize the precise role of the yet-known proteins participating in the different steps of this process and to identify new regulatory factors in order to obtain a unifying picture of the secretory pathway. In spite of this and given the enormous complexity of the process, certain steps are not fully understood yet and many players remain to be identified. In this review, we offer a summary of the current knowledge on the main molecular mechanisms that govern and ensure the correct release of secretory proteins. In addition, we have integrated the advance on the field made possible by studies carried out in non-mammalian vertebrates, which, although not very numerous, have substantially contributed to acquire a mechanistic understanding of the regulated secretory pathway.

Genomic targets and selective inhibition of DNA methyltransferase isoforms.

BACKGROUND: DNA methylation in the human genome is established and maintained by DNA methyltransferases (DNMTs). DNMT isoforms show differential expression by cell lineage and during development, but much remains to be elucidated about their shared and unique genomic targets. RESULTS: We examined changes in the epigenome following overexpression of 13 DNMT isoforms in HEK293T cells. We observed increased methylation (Δß > 0.2) at 43,405 CpG sites, with expression of DNMT3A2, DNMTΔ3B4 and DNMTΔ3B2 associated with the greatest impact. De novo methylation occurred primarily within open sea regions and at loci with intermediate methylation levels (ß: 0.2-0.6). 53% of differentially methylated loci showed specificity towards a single DNMT subfamily, primarily DNMTΔ3B and DNMT3A and 39% towards a single isoform. These loci were significantly enriched for pathways related to neuronal development (DNMTΔ3B4), calcium homeostasis (DNMTΔ3B3) and ion transport (DNMT3L). Repetitive elements did not display differential sensitivity to overexpressed DNMTs, but hypermethylation of Alu elements was associated with their evolutionary age following overexpression of DNMT3A2, DNMT3B1, DNMT3B2 and DNMT3L. Differential methylation (Δß > 0.1) was observed at 121 of the 353 loci associated with the Horvath 'epigenetic clock' model of ageing, with 51 showing isoform specificity, and was associated with reduction of epigenetic age by 5-15 years following overexpression of seven isoforms. Finally, we demonstrate the potential for dietary constituents to modify epigenetic marks through isoform-specific inhibition of methylation activity. CONCLUSIONS: Our results provide insight into regions of the genome methylated uniquely by specific DNMT isoforms and demonstrate the potential for dietary intervention to modify the epigenome.

The Use of Coenzyme Q10 in Cardiovascular Diseases.

CoQ10 is an endogenous antioxidant produced in all cells that plays an essential role in energy metabolism and antioxidant protection. CoQ10 distribution is not uniform among different organs, and the highest concentration is observed in the heart, though its levels decrease with age. Advanced age is the major risk factor for cardiovascular disease and endothelial dysfunction triggered by oxidative stress that impairs mitochondrial bioenergetic and reduces NO bioavailability, thus affecting vasodilatation. The rationale of the use of CoQ10 in cardiovascular diseases is that the loss of contractile function due to an energy depletion status in the mitochondria and reduced levels of NO for vasodilatation has been associated with low endogenous CoQ10 levels. Clinical evidence shows that CoQ10 supplementation for prolonged periods is safe, well-tolerated and significantly increases the concentration of CoQ10 in plasma up to 3-5 µg/mL. CoQ10 supplementation reduces oxidative stress and mortality from cardiovascular causes and improves clinical outcome in patients undergoing coronary artery bypass graft surgery, prevents the accumulation of oxLDL in arteries, decreases vascular stiffness and hypertension, improves endothelial dysfunction by reducing the source of ROS in the vascular system and increases the NO levels for vasodilation.

The Protective Effect of Ubiquinone against the Amyloid Peptide in Endothelial Cells Is Isoprenoid Chain Length-Dependent.

Vascular brain pathology constitutes a common feature in neurodegenerative diseases that could underlie their development. Indeed, vascular dysfunction acts synergistically with neurodegenerative changes to exacerbate the cognitive impairment found in Alzheimer's disease. Different injuries such as hypertension, high glucose, atherosclerosis associated with oxidized low-density lipoprotein or inflammation induce NADPH oxidase activation, overproduction of reactive oxygen species, and apoptosis in endothelial cells. Since it has been shown that pretreatment of cultured endothelial cells with the lipophilic antioxidant coenzyme Q10 (CoQ10) displays a protective effect against the deleterious injuries caused by different agents, this study explores the cytoprotective role of different CoQs homologues against Aß25-35-induced damage and demonstrates that only pretreatment with CoQ10 protects endothelial brain cells from Aß25-35-induced damage. Herein, we show that CoQ10 constitutes the most effective ubiquinone in preventing NADPH oxidase activity and reducing both reactive oxygen species generation and the increase in free cytosolic Ca2+ induced by Aß25-35, ultimately preventing apoptosis and necrosis. The specific cytoprotective effect of CoQ with a side chain of 10 isoprenoid units could be explained by the fact that CoQ10 is the only ubiquinone that significantly reduces the entry of Aß25-35 into the mitochondria.

Biological Significance of the Protein Changes Occurring in the Cerebrospinal Fluid of Alzheimer's Disease Patients: Getting Clues from Proteomic Studies.

The fact that cerebrospinal fluid (CSF) deeply irrigates the brain together with the relative simplicity of sample extraction from patients make this biological fluid the best target for biomarker discovery in neurodegenerative diseases. During the last decade, biomarker discovery has been especially fruitful for the identification new proteins that appear in the CSF of Alzheimer's disease (AD) patients together with amyloid-ß (Aß42), total tau (T-tau), and phosphorylated tau (P-tau). Thus, several proteins have been already stablished as important biomarkers, due to an increase (i.e., CHI3L1) or a decrease (i.e., VGF) in AD patients' CSF. Notwithstanding this, only a deep analysis of a database generated with all the changes observed in CSF across multiple proteomic studies, and especially those using state-of-the-art methodologies, may expose those components or metabolic pathways disrupted at different levels in AD. Deep comparative analysis of all the up- and down-regulated proteins across these studies revealed that 66% of the most consistent protein changes in CSF correspond to intracellular proteins. Interestingly, processes such as those associated to glucose metabolism or RXR signaling appeared inversely represented in CSF from AD patients in a significant manner. Herein, we discuss whether certain cellular processes constitute accurate indicators of AD progression by examining CSF. Furthermore, we uncover new CSF AD markers, such as ITAM, PTPRZ or CXL16, identified by this study.

mTORC1 activity is supported by spatial association with focal adhesions.

The mammalian target of rapamycin complex 1 (mTORC1) integrates mitogenic and stress signals to control growth and metabolism. Activation of mTORC1 by amino acids and growth factors involves recruitment of the complex to the lysosomal membrane and is further supported by lysosome distribution to the cell periphery. Here, we show that translocation of lysosomes toward the cell periphery brings mTORC1 into proximity with focal adhesions (FAs). We demonstrate that FAs constitute discrete plasma membrane hubs mediating growth factor signaling and amino acid input into the cell. FAs, as well as the translocation of lysosome-bound mTORC1 to their vicinity, contribute to both peripheral and intracellular mTORC1 activity. Conversely, lysosomal distribution to the cell periphery is dispensable for the activation of mTORC1 constitutively targeted to FAs. This study advances our understanding of spatial mTORC1 regulation by demonstrating that the localization of mTORC1 to FAs is both necessary and sufficient for its activation by growth-promoting stimuli.

Interplay Between Mitochondrial Oxidative Disorders and Proteostasis in Alzheimer's Disease.

Although the basis of Alzheimer's disease (AD) etiology remains unknown, oxidative stress (OS) has been recognized as a prodromal factor associated to its progression. OS refers to an imbalance between oxidant and antioxidant systems, which usually consist in an overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which overwhelms the intrinsic antioxidant defenses. Due to this increased production of ROS and RNS, several biological functions such as glucose metabolism or synaptic activity are impaired. In AD, growing evidence links the ROS-mediated damages with molecular targets including mitochondrial dynamics and function, protein quality control system, and autophagic pathways, affecting the proteostasis balance. In this scenario, OS should be considered as not only a major feature in the pathophysiology of AD but also a potential target to combat the progression of the disease. In this review, we will discuss the role of OS in mitochondrial dysfunction, protein quality control systems, and autophagy associated to AD and suggest innovative therapeutic strategies based on a better understanding of the role of OS and proteostasis.

mTORC1 as the main gateway to autophagy.

Cells and organisms must coordinate their metabolic activity with changes in their environment to ensure their growth only when conditions are favourable. In order to maintain cellular homoeostasis, a tight regulation between the synthesis and degradation of cellular components is essential. At the epicentre of the cellular nutrient sensing is the mechanistic target of rapamycin complex 1 (mTORC1) which connects environmental cues, including nutrient and growth factor availability as well as stress, to metabolic processes in order to preserve cellular homoeostasis. Under nutrient-rich conditions mTORC1 promotes cell growth by stimulating biosynthetic pathways, including synthesis of proteins, lipids and nucleotides, and by inhibiting cellular catabolism through repression of the autophagic pathway. Its close signalling interplay with the energy sensor AMP-activated protein kinase (AMPK) dictates whether the cell actively favours anabolic or catabolic processes. Underlining the role of mTORC1 in the coordination of cellular metabolism, its deregulation is linked to numerous human diseases ranging from metabolic disorders to many cancers. Although mTORC1 can be modulated by a number of different inputs, amino acids represent primordial cues that cannot be compensated for by any other stimuli. The understanding of how amino acids signal to mTORC1 has increased considerably in the last years; however this area of research remains a hot topic in biomedical sciences. The current ideas and models proposed to explain the interrelationship between amino acid sensing, mTORC1 signalling and autophagy is the subject of the present review.