Autophagy in health and disease. 1. Regulation and significance of autophagy: an overview

Interplay of autophagy and innate immunity in Crohn's disease: a key immunobiologic feature

Crohn's disease representing a clinical phenotype of inflammatory bowel disease is a polygenic immune disorder with complex multifactor etiology. Recent genome-wide association studies of susceptibility loci have highlighted on the importance of the autophagy pathway, which previously had not been implicated in disease pathology. Autophagy represents an evolutionarily highly conserved multi-step process of cellular self-digestion due to sequestration of excessive, damaged, or aged proteins and intracellular organelles in double-membranous vesicles of autophagosomes, terminally self-digested in lysosomes. Autophagy is deeply involved in regulation of cell development and differentiation, survival and senescence, and it also fundamentally affects the inflammatory pathways, as well as the innate and adaptive arms of immune responses. Autophagy is mainly activated due to sensors of the innate immunity, i.e., by pattern recognition receptor signaling. The interplay of genes regulating immune functions is strongly influenced by the environment, especially gut resident microbiota. The basic challenge for intestinal immune recognition is the requirement of a simultaneous delicate balance between tolerance and responsiveness towards microbes. On the basis of autophagy-related risk genetic polymorphisms (ATG16L1, IRGM, NOD2, XBP1) impaired sensing and handling of intracellular bacteria by innate immunity, closely interrelated with the autophagic and unfolded protein pathways seem to be the most relevant immunobiologic events. Autophagy is now widely considered as a key regulator mechanism with the capacity to integrate several aspects of Crohn's disease pathogenesis. In this review, recent advances in the exciting crosstalk of susceptibility coding variants-related autophagy and innate immunity are discussed.

The involvement of sphingolipids in chronic obstructive pulmonary diseases

Chronic obstructive pulmonary disease (COPD) includes a spectrum of conditions that have in common varying degrees of airflow obstruction, such as chronic bronchitis and emphysema. There is an increasing evidence of involvement of sphingolipids as key molecular mediators or biomarkers of disease in emphysema, chronic bronchitis, and more recently in asthma, another disease characterized by (reversible) airflow obstruction. Given the recognized central role of oxidative stress and inflammatory stimuli along with involvement of immune responses, apoptosis, and tissue remodeling in the development of chronic obstructive lung diseases, it is not surprising that sphingolipids have been shown to play important role in their pathobiology. In particular the pro-apoptotic effects of ceramide were suspected as events in the lung destruction that occurs as a result of apoptotic loss of structural cells comprising the alveolar walls, such as microvascular endothelial cells and alveolar epithelial cells. In addition, the role of ceramide was investigated in models of larger airway epithelial cell stress responses to cigarette smoke, in the context of ensuing airway remodeling and inflammation. This chapter discusses current evidence of sphingolipid perturbations in experimental models of COPD and relevant links to human disease based on translational and epidemiological data.

Comparative utility of LC3, p62 and TDP-43 immunohistochemistry in differentiation of inclusion body myositis from polymyositis and related inflammatory myopathies

Background

Inclusion body myositis (IBM) is a slowly progressive inflammatory myopathy of the elderly that does not show significant clinical improvement in response to steroid therapy. Distinguishing IBM from polymyositis (PM) is clinically important since PM is steroid-responsive; however, the two conditions can show substantial histologic overlap.

Results

We performed quantitative immunohistochemistry for (1) autophagic markers LC3 and p62 and (2) protein aggregation marker TDP-43 in 53 subjects with pathologically diagnosed PM, IBM, and two intermediate T cell-mediated inflammatory myopathies (polymyositis with COX-negative fibers and possible IBM). The percentage of stained fibers was significantly higher in IBM than PM for all three immunostains, but the markers varied in sensitivity and specificity. In particular, both LC3 and p62 were sensitive markers of IBM, but the tradeoff between sensitivity and specificity was smaller (and diagnostic utility thus greater) for LC3 than for p62. In contrast, TDP-43 immunopositivity was highly specific for IBM, but the sensitivity of this test was low, with definitive staining present in just 67% of IBM cases.

Conclusions

To differentiate IBM from PM, we thus recommend using a panel of LC3 and TDP-43 antibodies: the finding of <14% LC3-positive fibers helps exclude IBM, while >7% of TDP-43-positive fibers strongly supports a diagnosis of IBM. These data provide support for the hypothesis that disruption of autophagy and protein aggregation contribute to IBM pathogenesis.

Scrambled and fried: cigarette smoke exposure causes antral follicle destruction and oocyte dysfunction through oxidative stress

Cigarette smoke is a reproductive hazard associated with pre-mature reproductive senescence and reduced clinical pregnancy rates in female smokers. Despite an increased awareness of the adverse effects of cigarette smoke exposure on systemic health, many women remain unaware of the adverse effects of cigarette smoke on female fertility. This issue is compounded by our limited understanding of the molecular mechanisms behind cigarette smoke induced infertility. In this study we used a direct nasal exposure mouse model of cigarette smoke-induced chronic obstructive pulmonary disease to characterise mechanisms of cigarette-smoke induced ovotoxicity. Cigarette smoke exposure caused increased levels of primordial follicle depletion, antral follicle oocyte apoptosis and oxidative stress in exposed ovaries, resulting in fewer follicles available for ovulation. Evidence of oxidative stress also persisted in ovulated oocytes which escaped destruction, with increased levels of mitochondrial ROS and lipid peroxidation resulting in reduced fertilisation potential. Microarray analysis of ovarian tissue correlated these insults with a complex mechanism of ovotoxicity involving genes associated with detoxification, inflammation, follicular activation, immune cell mediated apoptosis and membrane organisation. In particular, the phase I detoxifying enzyme cyp2e1 was found to be significantly up-regulated in developing oocytes; an enzyme known to cause molecular bioactivation resulting in oxidative stress. Our results provide a preliminary model of cigarette smoke induced sub-fertility through cyp2e1 bioactivation and oxidative stress, resulting in developing follicle depletion and oocyte dysfunction.

How many ways can a podocyte die?

Podocytes are highly specialized epithelial cells that line the urinary surface of the glomerular capillary tuft. To maintain kidney filtration, podocytes oppose the high intraglomerular hydrostatic pressure, form a molecular sieve, secrete soluble factors to regulate other glomerular cell types, and provide synthesis and maintenance of the glomerular basement membrane. Impairment of any of these functions after podocyte injury results in proteinuria and possibly renal failure. Loss of glomerular podocytes is a key feature for the progression of renal diseases, and detached podocytes can be retrieved in the urine of patients with progressive glomerular diseases. Thus, the concept of podocyte loss as a hallmark of progressive glomerular disease has been widely accepted. However, the nature of events that promote podocyte detachment and whether detachment is preceded by any kind of podocyte cell death, such as apoptosis, necroptosis, or necrosis, still remains unclear and is discussed in this review.

Endocytic pathway of exogenous iron-loaded ferritin in intestinal epithelial (Caco-2) cells

Ferritin, a food constituent of animal and vegetal origin, is a source of dietary iron. Its hollow central cavity has the capacity to store up to 4,500 atoms of iron, so its potential as an iron donor is advantageous to heme iron, present in animal meats and inorganic iron of mineral or vegetal origin. In intestinal cells, ferritin internalization by endocytosis results in the release of its iron into the cytosolic labile iron pool. The aim of this study was to characterize the endocytic pathway of exogenous ferritin absorbed from the apical membrane of intestinal epithelium Caco-2 cells, using both transmission electron microscopy and fluorescence confocal microscopy. Confocal microscopy revealed that endocytosis of exogenous AlexaFluor 488-labeled ferritin was initiated by its engulfment by clathrin-coated pits and internalization into early endosomes, as determined by codistribution with clathrin and early endosome antigen 1 (EEA1). AlexaFluor 488-labeled ferritin also codistributed with the autophagosome marker microtubule-associated protein 1 light chain 3 (LC3) and the lysosome marker lysosomal-associated membrane protein 2 (LAMP2). Transmission electron microscopy revealed that exogenously added ferritin was captured in plasmalemmal pits, double-membrane compartments, and multivesicular bodies considered as autophagosomes and lysosomes. Biochemical experiments revealed that the lysosome inhibitor chloroquine and the autophagosome inhibitor 3-methyladenine (3-MA) inhibited degradation of exogenously added (131)I-labeled ferritin. This evidence is consistent with a model in which exogenous ferritin is internalized from the apical membrane through clathrin-coated pits, and then follows a degradation pathway consisting of the passage through early endosomes, autophagosomes, and autolysosomes.

Activation of lysosomal function in the course of autophagy via mTORC1 suppression and autophagosome-lysosome fusion

Lysosome is a key subcellular organelle in the execution of the autophagic process and at present little is known whether lysosomal function is controlled in the process of autophagy. In this study, we first found that suppression of mammalian target of rapamycin (mTOR) activity by starvation or two mTOR catalytic inhibitors (PP242 and Torin1), but not by an allosteric inhibitor (rapamycin), leads to activation of lysosomal function. Second, we provided evidence that activation of lysosomal function is associated with the suppression of mTOR complex 1 (mTORC1), but not mTORC2, and the mTORC1 localization to lysosomes is not directly correlated to its regulatory role in lysosomal function. Third, we examined the involvement of transcription factor EB (TFEB) and demonstrated that TFEB activation following mTORC1 suppression is necessary but not sufficient for lysosomal activation. Finally, Atg5 or Atg7 deletion or blockage of the autophagosome-lysosome fusion process effectively diminished lysosomal activation, suggesting that lysosomal activation occurring in the course of autophagy is dependent on autophagosome-lysosome fusion. Taken together, this study demonstrates that in the course of autophagy, lysosomal function is upregulated via a dual mechanism involving mTORC1 suppression and autophagosome-lysosome fusion.

The regulatory role of NF-κB in autophagy-like cell death after focal cerebral ischemia in mice

Autophagy may contribute to ischemia-induced cell death in the brain, but the regulation of autophagic cell death is largely unknown. Nuclear factor kappa B (NF-κB) is a regulator of apoptosis in cerebral ischemia. We examined the hypothesis that autophagy-like cell death could contribute to ischemia-induced brain damage and the process was regulated by NF-κB. In adult wild-type (WT) and NF-κB p50 knockout (p50(-/-)) mice, focal ischemia in the barrel cortex was induced by ligation of distal branches of the middle cerebral artery. Twelve to 24h later, autophagic activity increased as indicated by enhanced expression of Beclin-1 and LC3 in the ischemic core and/or penumbra regions. This increased autophagy contributed to cell injury, evidenced by terminal deoxynucleotidyltransferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) co-staining and a protective effect achieved by the autophagy inhibitor 3-methyladenine. The number of Beclin-1/TUNEL-positive cells was significantly more in p50(-/-) mice than in WT mice. Neuronal and vascular cell death, as determined by TUNEL-positive cells co-staining with NeuN or Collagen IV, was more abundant in p50(-/-) mice. Immunostaining of the endothelial cell tight junction marker occludin revealed more damage to the blood-brain barrier in p50(-/-) mice. Western blotting of the peri-infarct tissue showed a reduction of Akt-the mammalian target of rapamycin (mTOR) signaling in p50(-/-) mice after ischemia. These findings provide the first evidence that cerebral ischemia induced autophagy-like injury is regulated by the NF-κB pathway, which may suggest potential treatments for ischemic stroke.

Autophagy, apoptosis, mitoptosis and necrosis: interdependence between those pathways and effects on cancer

Cell death is a fundamental ingredient of life. Thus, not surprisingly more than one form of cell death exists. Several excellent reviews on various forms of cell death have already been published but manuscripts describing interconnection and interdependence between such processes are uncommon. Here, what follows is a brief introduction on all three classical forms of cell death, followed by a more detailed insight into the role of p53, the master regulator of apoptosis, and other forms of cell death. While discussing p53 and also the role of caspases in cell death forms, we offer insight into the interplay between autophagy and apoptosis, or necrosis, where autophagy may initially serve pro-survival functions. The review moves further to present some details about less researched forms of programmed cell death, namely necroptosis, necrosis and mitoptosis. These "mixed" forms of cell death allow us to highlight the interconnected nature of cell death forms, particularly apoptosis and necrosis. The interdependence between apoptosis, autophagy and necrosis, and their significance for cancer development and treatment are also analyzed in further parts of the review. In the concluding parts, the afore-mentioned issues will be put in perspective for the development of novel anti-cancer therapies.

Lapatinib and obatoclax kill breast cancer cells through reactive oxygen species-dependent endoplasmic reticulum stress

Previous studies showed that lapatinib and obatoclax interact in a greater-than-additive fashion to cause cell death and do so through a toxic form of autophagy. The present studies sought to extend our analyses. Lapatinib and obatoclax killed multiple tumor cell types, and cells lacking phosphatase and tensin homolog (PTEN) function were relatively resistant to drug combination lethality; expression of PTEN in PTEN-null breast cancer cells restored drug sensitivity. Coadministration of lapatinib with obatoclax elicited autophagic cell death that was attributable to the actions of mitochondrial reactive oxygen species. Wild-type cells but not mitochondria-deficient rho-zero cells were radiosensitized by lapatinib and obatoclax treatment. Activation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH(2)-terminal kinase 1/2 (JNK1/2) by the drug combination was enhanced by radiation, and signaling by p38 MAPK and JNK1/2 promoted cell killing. In immunohistochemical analyses, the autophagosome protein p62 was determined to be associated with protein kinase-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme 1, as well as with binding immunoglobulin protein/78-kDa glucose-regulated protein, in drug combination-treated cells. Knockdown of PERK suppressed drug-induced autophagy and protected tumor cells from the drug combination. Knockdown of PERK suppressed the reduction in Mcl-1 expression after drug combination exposure, and overexpression of Mcl-1 protected cells. Our data indicate that mitochondrial function plays an essential role in cell killing by lapatinib and obatoclax, as well as radiosensitization by this drug combination.

Survival features of EBV-stabilized cells from centenarians: morpho-functional and transcriptomic analyses

In the present work, we analyzed the survival features of six different Epstein-Barr virus (EBV)-stabilized lymphoid cell lines obtained from adult subjects and from subjects of more than 95 years. For the first, we found that lymphoid B cells from centenarians were more resistant to apoptosis induction and displayed a more developed lysosomal compartment, the most critical component of phagic machinery, in comparison with lymphoid B cells from adult subjects. In addition, cells from centenarians were capable of engulfing and digesting other cells, i.e., their siblings (even entire cells), whereas lymphoid cells from "control samples", i.e., from adults, did not. This behavior was improved by nutrient deprivation but, strikingly, it was unaffected by the autophagy-modulating drug, rapamycin, an autophagy inducer, and 3-methyladenine, an autophagy inhibitor. Transcriptomic analyses indicated that: (1) aspartyl proteases, (2) cell surface molecules such as integrins and cadherins, and (3) some components of cytoskeletal network could contribute to establish this survival phenotype. Also, Kyoto Encyclopedia of Genes and Genomes pathways such as Wnt signaling pathway, an essential contributor to cell migration and actin cytoskeleton remodeling, appeared as prominent. Although we cannot rule out the possibility that EBV-immortalization could play a role, since we observed this phagic behavior in cells from centenarians but not in those from adults, we hypothesize that it may represent an important survival determinant in cells from centenarians.

Autophagy in the brains of young patients with poorly controlled T1DM and fatal diabetic ketoacidosis

Semi-quantitative neuroradiologic studies, quantitative neuron density studies and immunocytochemistry markers of oxidative stress and neuroinflammation indicate neuronal injury and deficits in young patients with chronic poorly controlled type 1 diabetes mellitus (T1DM). Present data suggest that pathogenesis of the neuronal deficits in young patients, who die as the result of diabetic ketoacidosis (DKA) and brain edema (BE), does not involve apoptosis, a prominent form of regulated cell death in many disease states. To further address this we studied mediators of macroautophagy, endoplasmic reticulum (ER) stress and apoptosis. In all areas studied we demonstrated increased levels of macroautophagy-associated proteins including light chain-3 (LC3) and autophagy related protein-4 (Atg4), as well as increased levels of the ER-associated glucose-regulated protein78/binding immunoglobulin protein (GRP78/BiP) in T1DM. In contrast, cleaved caspase-3 was rarely detected in any T1DM brain regions. These results suggest that chronic metabolic instability and oxidative stress may cause alterations in the autophagy-lysosomal pathway but not apoptosis, and macroautophagy-associated molecules may serve as useful candidates for further study in the pathogenesis of early neuronal deficits in T1DM.

Autophagy induction by silver nanowires: a new aspect in the biocompatibility assessment of nanocomposite thin films

Nanomaterials and their enabled products have increasingly been attracting global attention due to their unique physicochemical properties. Among these emerging products, silver nanowire (AgNW)-based thin films are being developed for their promising applications in next generation nanoelectronics and nanodevices. However, serious concerns remain about possible health and safety risks they may pose. Here, we employed a multi-modal systematic biocompatibility assessment of thin films incorporating AgNW. To represent the possible routes of nanomaterial entry during occupational or environmental exposure, we employed four different cell lines of epithelial, endothelial, gastric, and phagocytic origin. Utilizing a cell-based automated image acquisition and analysis procedure in combination with real-time impedance sensing, we observed a low level of cytotoxicity of AgNW, which was dependent on cell type, nanowire lengths, doses and incubation times. Similarly, no major cytotoxic effects were induced by AgNW-containing thin films, as detected by conventional cell viability and imaging assays. However, transmission electron microscopy and Western immunoblotting analysis revealed AgNW-induced autophasosome accumulation together with an upregulation of the autophagy marker protein LC3. Autophagy represents a crucial mechanism in maintaining cellular homeostasis, and our data for the first time demonstrate triggering of such mechanism by AgNW in human phagocytic cells. Finally, atomic force microscopy revealed significant changes in the topology of cells attaching and growing on these films as substrates. Our findings thus emphasize the necessity of comprehensive biohazard assessment of nanomaterials in modern applications and devices and a thorough analysis of risks associated with their possible contact with humans through occupational or environmental exposure.

Lapatinib and obatoclax kill tumor cells through blockade of ERBB1/3/4 and through inhibition of BCL-XL and MCL-1

Prior studies in breast cancer cells have shown that lapatinib and obatoclax interact in a greater than additive fashion to cause cell death and do so through a toxic form of autophagy. The present studies sought to extend our analyses to the central nervous system (CNS) tumor cells and to further define mechanisms of drug action. Lapatinib and obatoclax killed multiple CNS tumor isolates. Cells lacking PTEN (phosphatase and tensin homolog on chromosome 10) function were relatively resistant to drug combination lethality; expression of PTEN in PTEN-null cells restored drug sensitivity, and knockdown of PTEN promoted drug resistance. On the basis of knockdown of ERBB1-4 (erythroblastic leukemia viral oncogene homolog 1-4), we discovered that the inhibition of ERBB1/3/4 receptors were most important for enhancing obatoclax lethality rather than ERBB2. In parallel, we noted in CNS tumor cells that knockdown of BCL-xL (B-cell lymphoma-extra large)and MCL-1 (myeloid cell leukemia-1) interacted in an additive fashion to facilitate lapatinib lethality. Pretreatment of tumor cells with obatoclax enhanced the lethality of lapatinib to a greater extent than concomitant treatment. Treatment of animals carrying orthotopic CNS tumor isolates with lapatinib- and obatoclax-prolonged survival. Altogether, our data show that lapatinib and obatoclax therapy could be of use in the treatment of tumors located in the CNS.

Clinical utility of LC3 and p62 immunohistochemistry in diagnosis of drug-induced autophagic vacuolar myopathies: a case-control study

Background

Some patients treated with chloroquine, hydroxychloroquine, or colchicine develop autophagic vacuolar myopathy, the diagnosis of which currently requires electron microscopy. The goal of the current study was to develop an immunohistochemical diagnostic marker for this pathologic entity.

Methodology

Microtubule-associated protein light chain 3 (LC3) has emerged as a robust marker of autophagosomes. LC3 binds p62/SQSTM1, an adapter protein that is selectively degraded via autophagy. In this study, we evaluated the utility of immunohistochemical stains for LC3 and p62 as diagnostic markers of drug-induced autophagic vacuolar myopathy. The staining was performed on archival muscle biopsy material, with subject assignment to normal control, drug-treated control, and autophagic myopathy groups based on history of drug use and morphologic criteria.

Principal Findings

In all drug-treated subjects, but not in normal controls, LC3 and p62 showed punctate staining characteristic of autophagosome buildup. In the autophagic myopathy subjects, puncta were coarser and tended to coalesce into linear structures aligned with the longitudinal axis of the fiber, often in the vicinity of vacuoles. The percentage of LC3- and p62-positive fibers was significantly higher in the autophagic myopathy group compared to either the normal control (p<0.001) or the drug-treated control group (p<0.05). With the diagnostic threshold set between 8% and 15% positive fibers (depending on the desired level of sensitivity and specificity), immunohistochemical staining for either LC3 or p62 could be used to identify subjects with autophagic vacuolar myopathy within the drug-treated subject group (p≤0.001).

Significance

Immunohistochemistry for LC3 and p62 can facilitate tissue-based diagnosis of drug-induced autophagic vacuolar myopathies. By limiting the need for electron microscopy (a time consuming and costly technique with high specificity, but low sensitivity), clinical use of these markers will improve the speed and accuracy of diagnosis, resulting in significantly improved clinical care.

Beclin 1-mediated autophagy in hepatocellular carcinoma cells: implication in anticancer efficiency of oroxylin A via inhibition of mTOR signaling

Autophagy is a tightly-regulated catabolic process that involves the degradation of intracellular components via lysosomes. Although the pivotal role of autophagy in cell growth, development, and homeostasis has been well understood, its function in cancer prevention and intervention remains to be delineated. The aim of this study was to investigate the function and mechanism of autophagy induced by oroxylin A, a natural mono-flavonoid extracted from Scutellariae radix. We found for the first time that oroxylin A induced Beclin 1-mediated autophagy in human hepatocellular carcinoma HepG2 cells. Time-lapse video microscopy and western blotting studies showed that treatment of cells with 80 μM oroxylin A resulted in the conversion of water soluble MAP-LC3 (LC3-I) to the lipidated and autophagosome-associated form (LC3-II) after 12hours; then autophagosome-lysosome fusion and lysosome degradation after 24 hours was required in oroxylin A-mediated cell death. This induction was associated with the suppressing of PI3K-PTEN-Akt-mTOR signaling pathway by oroxylin A. Our results also showed that autophagy took place before noticeable apoptosis can be observed. It was further demonstrated that oroxylin A-triggered autophagy contributed to cell death using over-expression of autophagy-related gene (Atg5 and Atg7) and inhibition of autophagy by siBeclin 1 and 3-methyladenine (3-MA). In vivo study, oroxylin A inhibited xenograft tumor growth and induced obvious autophagy in tumors. Taken together, we conclude that oroxylin A exhibits autophagy-mediated antitumor activity in a dose and time-dependent manner in vivo and in vitro. These findings define and support a novel function of autophagy in promoting death of hepatocellular carcinoma cells.

Autophagy releases lipid that promotes fibrogenesis by activated hepatic stellate cells in mice and in human tissues

BACKGROUND & AIMS

The pathogenesis of liver fibrosis involves activation of hepatic stellate cells, which is associated with depletion of intracellular lipid droplets. When hepatocytes undergo autophagy, intracellular lipids are degraded in lysosomes. We investigated whether autophagy also promotes loss of lipids in hepatic stellate cells to provide energy for their activation and extended these findings to other fibrogenic cells.

METHODS

We analyzed hepatic stellate cells from C57BL/6 wild-type, Atg7(F/F), and Atg7(F/F)-GFAP-Cre mice, as well as the mouse stellate cell line JS1. Fibrosis was induced in mice using CCl(4) or thioacetamide (TAA); liver tissues and stellate cells were analyzed. Autophagy was blocked in fibrogenic cells from liver and other tissues using small interfering RNAs against Atg5 or Atg7 and chemical antagonists. Human pulmonary fibroblasts were isolated from samples of lung tissue from patients with idiopathic pulmonary fibrosis or from healthy donors.

RESULTS

In mice, induction of liver injury with CCl(4) or TAA increased levels of autophagy. We also observed features of autophagy in activated stellate cells within injured human liver tissue. Loss of autophagic function in cultured mouse stellate cells and in mice following injury reduced fibrogenesis and matrix accumulation; this effect was partially overcome by providing oleic acid as an energy substrate. Autophagy also regulated expression of fibrogenic genes in embryonic, lung, and renal fibroblasts.

CONCLUSIONS

Autophagy of activated stellate cells is required for hepatic fibrogenesis in mice. Selective reduction of autophagic activity in fibrogenic cells in liver and other tissues might be used to treat patients with fibrotic diseases.

Relationship of low plasma klotho with poor grip strength in older community-dwelling adults: the InCHIANTI study

Handgrip strength is a strong indicator of total body muscle strength and is a predictor of poor outcomes in older adults. The aging suppressor gene klotho encodes a single-pass transmembrane protein that is secreted as a circulating hormone. In mice, disruption of klotho expression results in a syndrome that includes sarcopenia, atherosclerosis, osteoporosis, and shortened lifespan, and conversely, overexpression of klotho leads to a greater longevity. The objective was to determine whether plasma klotho levels are related to skeletal muscle strength in humans. We measured plasma klotho in 804 adults, ≥65 years, in the InCHIANTI study, a longitudinal population-based study of aging in Tuscany, Italy. Grip strength was positively correlated with plasma klotho at threshold <681 pg/mL. After adjusting for age, sex, education, smoking, physical activity, cognition, and chronic diseases, plasma klotho (per 1 standard deviation increase) was associated with grip strength (beta = 1.20, standard error = 0.35, P = 0.0009) in adults with plasma klotho <681 pg/mL. These results suggest that older adults with lower plasma klotho have poor skeletal muscle strength.

Endoplasmic reticulum stress, the unfolded protein response, autophagy, and the integrated regulation of breast cancer cell fate

How breast cancer cells respond to the stress of endocrine therapies determines whether they will acquire a resistant phenotype or execute a cell-death pathway. After a survival signal is successfully executed, a cell must decide whether it should replicate. How these cell-fate decisions are regulated is unclear, but evidence suggests that the signals that determine these outcomes are highly integrated. Central to the final cell-fate decision is signaling from the unfolded protein response, which can be activated following the sensing of stress within the endoplasmic reticulum. The duration of the response to stress is partly mediated by the duration of inositol-requiring enzyme-1 activation following its release from heat shock protein A5. The resulting signals appear to use several B-cell lymphoma-2 family members to both suppress apoptosis and activate autophagy. Changes in metabolism induced by cellular stress are key components of this regulatory system, and further adaptation of the metabolome is affected in response to stress. Here we describe the unfolded protein response, autophagy, and apoptosis, and how the regulation of these processes is integrated. Central topologic features of the signaling network that integrate cell-fate regulation and decision execution are discussed.

Prohibitin 1 modulates mitochondrial stress-related autophagy in human colonic epithelial cells

Introduction

Autophagy is an adaptive response to extracellular and intracellular stress by which cytoplasmic components and organelles, including damaged mitochondria, are degraded to promote cell survival and restore cell homeostasis. Certain genes involved in autophagy confer susceptibility to Crohn's disease. Reactive oxygen species and pro-inflammatory cytokines such as tumor necrosis factor α (TNFα), both of which are increased during active inflammatory bowel disease, promote cellular injury and autophagy via mitochondrial damage. Prohibitin (PHB), which plays a role in maintaining normal mitochondrial respiratory function, is decreased during active inflammatory bowel disease. Restoration of colonic epithelial PHB expression protects mice from experimental colitis and combats oxidative stress. In this study, we investigated the potential role of PHB in modulating mitochondrial stress-related autophagy in intestinal epithelial cells.

Methods

We measured autophagy activation in response to knockdown of PHB expression by RNA interference in Caco2-BBE and HCT116 WT and p53 null cells. The effect of exogenous PHB expression on TNFα- and IFNγ-induced autophagy was assessed. Autophagy was inhibited using Bafilomycin A₁ or siATG16L1 during PHB knockdown and the affect on intracellular oxidative stress, mitochondrial membrane potential, and cell viability were determined. The requirement of intracellular ROS in siPHB-induced autophagy was assessed using the ROS scavenger N-acetyl-L-cysteine.

Results

TNFα and IFNγ-induced autophagy inversely correlated with PHB protein expression. Exogenous PHB expression reduced basal autophagy and TNFα-induced autophagy. Gene silencing of PHB in epithelial cells induces mitochondrial autophagy via increased intracellular ROS. Inhibition of autophagy during PHB knockdown exacerbates mitochondrial depolarization and reduces cell viability.

Conclusions

Decreased PHB levels coupled with dysfunctional autophagy renders intestinal epithelial cells susceptible to mitochondrial damage and cytotoxicity. Repletion of PHB may represent a therapeutic approach to combat oxidant and cytokine-induced mitochondrial damage in diseases such as inflammatory bowel disease.

Autophagy is a survival force via suppression of necrotic cell death

Macroautophagy or autophagy is a self-digesting mechanism that the cellular contents are engulfed by autophagosomes and delivered to lysosomes for degradation. Although it has been well established that autophagy is an important protective mechanism for cells under stress such as starvation via provision of nutrients and removal of protein aggregates and damaged mitochondria, there is a very complex relation between autophagy and cell death. At present, the molecular cross-talk between autophagy and apoptosis has been well discussed, while the relationship between autophagy and programmed necrotic cell death is less understood. In this review we focus on the role of autophagy in necrotic cell death by detailed discussion on two important forms of necrotic cell death: (i) necroptosis and (ii) poly-(ADP-ribose) polymerase (PARP)-mediated cell death. It is believed that one important aspect of the pro-survival function of autophagy is achieved via its ability to block various forms of necrotic cell death.

The degradation of apolipoprotein B100: multiple opportunities to regulate VLDL triglyceride production by different proteolytic pathways

Very low density lipoproteins (VLDL) are a major secretory product of the liver. They serve to transport endogenously synthesized lipids, mainly triglycerides (but also some cholesterol and cholesteryl esters) to peripheral tissues. VLDL is also the precursor of LDL. ApoB100 is absolutely required for VLDL assembly and secretion. The amount of VLDL triglycerides secreted by the liver depends on the amount loaded onto each lipoprotein particle, as well as the number of particles. Each VLDL has one apoB100 molecule, making apoB100 availability a key determinant of the number of VLDL particles, and hence, triglycerides, that can be secreted by hepatic cells. Surprisingly, the pool of apoB100 in the liver is typically regulated not by its level of synthesis, which is relatively constant, but by its level of degradation. It is now recognized that there are multiple opportunities for the hepatic cell to intercept apoB100 molecules and to direct them to distinct degradative processes. This mini-review will summarize progress in understanding these processes, with an emphasis on autophagy, the most recently described pathway of apoB100 degradation, and the one with possibly the most physiologic relevance to common metabolic perturbations affecting VLDL production. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

NF-κB regulates protein quality control after heat stress through modulation of the BAG3-HspB8 complex

We previously found that the NF-κB transcription factor is activated during the recovery period after heat shock; moreover, we demonstrated that NF-κB is essential for cell survival after heat shock by activating autophagy, a mechanism that probably helps the cell to cope with hyperthermic stress through clearance of damaged proteins. In this study, we analyze the involvement of NF-κB in basal and heat-stress-induced protein quality control, by comparing the level of multiubiquitylated and/or aggregated proteins, and proteasome and autophagic activity in NF-κB-competent and NF-κB-incompetent cells. We show that NF-κB has only a minor role in basal protein quality control, where it modulates autophagosome maturation. By contrast, NF-κB is shown to be a key player in protein quality control after hyperthermia. Indeed, NF-κB-incompetent cells show highly increased levels of multiubiquitylated and/or aggregated proteins and aggresome clearance defects; a phenotype that disappears when NF-κB activity is restored to normal. We demonstrate that during heat shock recovery NF-κB activates selective removal of misfolded or aggregated proteins--a process also called 'aggrephagy'--by controlling the expression of BAG3 and HSPB8 and by modulating the level of the BAG3-HspB8 complex. Thus NF-κB-mediated increase in the level of the BAG3-HspB8 complex leads to upregulation of aggrephagy and clearance of irreversibly damaged proteins and might increase cell survival in conditions of hyperthermia.

E Platinum, a newly synthesized platinum compound, induces autophagy via inhibiting phosphorylation of mTOR in gastric carcinoma BGC-823 cells

A tightly regulated catabolic process named autophagy involves the degradation of intracellular components via lysosomes. Here we investigate the antitumor effect of E Platinum, a newly synthesized derivative of oxaliplatin, in vivo and in vitro. E Platinum exhibits growth inhibition of various tumor cells in a dose-dependent manner, but the mechanism underlying it is unclear. Based on theory introducing autophagy, we preliminarily investigate whether autophagy could contribute to the antitumor activity of E Platinum. Our results showed that autophagy induced by 12.5 μM E Platinum in gastric carcinoma BGC-823 cells was significantly characterized by the FITC-fluorescent microtubule associated protein 1 light chain 3 (MAP-LC3), lysosomal-rich/acidic compartments visualized with Lysotracker red (LTR-red) and an accumulation of numerous large autophagic vesicles within the cytoplasm, but not in the control cells. Meanwhile treatment of cells with 12.5 μM E Platinum resulted in conversion of water soluble LC3 (LC3-I) to lipidated and autophagosome-associated form (LC3-II) as well as increasing expression of autophagy protein Beclin 1. Activation of predominant lysosomal aspartic protease, LAMP-1 and cathepsin D, was demonstrated. Moreover, RNA interference targeting Beclin 1, inhibition of autophagy by 3-methyladenine (3-MA) and chloroquine significantly suppressed the above process as well as the BGC-823 cells growth inhibition triggered by 12.5 μM E Platinum. Studies of mechanism revealed that E Platinum suppressed activation of mTOR and p70S6K by decreasing phosphorylation of Akt, ERK1/2, JNK and p38 involved in mitogen-activated protein kinase signaling. We supported new evidences for E Platinum as a promising antitumor agent, involving with autophagy induction.

TRIM13 regulates ER stress induced autophagy and clonogenic ability of the cells

Autophagy is one of the cellular adaptive processes that provide protection against many pathological conditions like infection, cancer, neurodegeneration, and aging. Recent evidences suggest that ubiquitination plays an important role in degradation of proteins or defective organelle either through proteasome or autophagy. In this study, we describe the role of TRIM13, ER resident ubiquitin E3 ligase in induction of autophagy and its role during ER stress. The ectopic expression of TRIM13 in HEK-293 cells induces autophagy. Domain mapping showed that coiled-coil (CC) domain is required for induction of autophagy. TRIM13 is stabilized during ER stress, interacts with p62/SQSTM1 and co-localizes with DFCP1. TRIM13 regulates initiation of autophagy during ER stress and decreases the clonogenic ability of the cells. This study for the first time demonstrates the role of TRIM13 in induction of autophagy which may play an important role in regulation of ER stress and may act as tumor suppressor.

Role of autophagy in the pathogenesis of liver diseases

Autophagy is a self-digestion process that plays an important role in the development, differentiation and homeostasis of cells, helping their survival during starvation and hypoxia. Accumulated mutant proteins in the endoplasmic reticulum can be degraded by autophagy in alpha-1 antitrypsin deficiency. Hepatitis C and B virus may exploit the autophagy pathway to escape the innate immune response and to promote their own replication. Autophagy is decreased in response to chronic alcohol consumption, likely due to a decrease in 5’-adenosine monophosphate-activated protein kinase, increase in mTOR activity and due to an alteration in vesicle transport in hepatocytes. In obesity and alcoholic liver disease the decreased function of autophagy causes formation of Mallory-Denk bodies and cell death. The deficient autophagy can contribute to liver steatosis, to endoplasmic reticulum stress, and to progression of liver disease. Autophagy defect in hepatocellular carcinoma suggests that it can serve a tumor-suppressor function. The autophagy protein Beclin-1 levels have prognostic significance in liver tumors. Understanding of the molecular mechanism and the role of autophagy may lead to more effective therapeutic strategies in liver diseases in the future. Orv. Hetil., 2011, 152, 1955–1961.

Autophagic activity in cortical neurons under acute oxidative stress directly contributes to cell death

Primary neurons undergo insult-dependent programmed cell death. We examined autophagy as a process contributing to cell death in cortical neurons after treatment with either hydrogen peroxide (H(2)O(2)) or staurosporine. Although caspase-9 activation and cleavage of procaspase-3 were significant following staurosporine treatment, neither was observed following H(2)O(2) treatment, indicating a non-apoptotic death. Autophagic activity increased rapidly with H(2)O(2), but slowly with staurosporine, as quantified by processing of endogenous LC3. Autophagic induction by both stressors increased the abundance of fluorescent puncta formed by GFP-LC3, which could be blocked by 3-methyladenine. Significantly, such inhibition of autophagy blocked cell death induced by H(2)O(2) but not staurosporine. Suppression of Atg7 inhibited cell death by H(2)O(2), but not staurosporine, whereas suppression of Beclin 1 prevented cell death by both treatments, suggesting it has a complex role regulating both apoptosis and autophagy. We conclude that autophagic mechanisms are activated in an insult-dependent manner and that H(2)O(2) induces autophagic cell death.

Sirtuins: molecular traffic lights in the crossroad of oxidative stress, chromatin remodeling, and transcription

Transcription is regulated by acetylation/deacetylation reactions of histone and nonhistone proteins mediated by enzymes called KATs and HDACs, respectively. As a major mechanism of transcriptional regulation, protein acetylation is a key controller of physiological processes such as cell cycle, DNA damage response, metabolism, apoptosis, and autophagy. The deacetylase activity of class III histone deacetylases or sirtuins depends on the presence of NAD⁺ (nicotinamide adenine dinucleotide), and therefore, their function is closely linked to cellular energy consumption. This activity of sirtuins connects the modulation of chromatin dynamics and transcriptional regulation under oxidative stress to cellular lifespan, glucose homeostasis, inflammation, and multiple aging-related diseases including cancer. Here we provide an overview of the recent developments in relation to the diverse biological activities associated with sirtuin enzymes and stress responsive transcription factors, DNA damage, and oxidative stress and relate the involvement of sirtuins in the regulation of these processes to oncogenesis. Since the majority of the molecular mechanisms implicated in these pathways have been described for Sirt1, this sirtuin family member is more extensively presented in this paper.

ULK1 inhibits mTORC1 signaling, promotes multisite Raptor phosphorylation and hinders substrate binding

Protein synthesis and autophagy work as two opposing processes to control cell growth in response to nutrient supply. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway, which acts as a master regulator to control protein synthesis, has recently been shown to inhibit autophagy by phosphorylating and inactivating ULK1, an autophagy regulatory protein. ULK1 also inhibits phosphorylation of a mTORC1 substrate, S6K1, indicating that a complex signaling interplay exists between mTORC1 and ULK1. Here, we demonstrate that ULK1 induces multisite phosphorylation of Raptor in vivo and in vitro. Using phospho-specific antibodies we identify Ser855 and Ser859 as being strongly phosphorylated by ULK1, with moderate phosphorylation of Ser792 also observed. Interestingly, ULK1 overexpression also increases phosphorylation of Raptor Ser863 and the mTOR autophosphorylation site, Ser2481 in a mTORC1-dependent manner. Despite this evidence for heightened mTORC1 kinase activity following ULK1 overexpresssion, mTORC1-mediated phosphorylation of S6K1 and 4E-BP1 is significantly inhibited. ULK1 expression has no effect on protein-protein interactions between the components of mTORC1, but does reduce the ability of Raptor to bind to the substrate 4E-BP1. Furthermore, shRNA knockdown of ULK1 leads to increased phosphorylation of mTORC1 substrates and decreased phosphorylation of Raptor at Ser859 and Ser792. We propose a new mechanism whereby ULK1 contributes to mTORC1 inhibition through hindrance of substrate docking to Raptor. This is a novel negative feedback loop that occurs upon activation of autophagy to maintain mTORC1 inhibition when nutrient supplies are limiting.

Antidepressant drugs diversely affect autophagy pathways in astrocytes and neurons--dissociation from cholesterol homeostasis

In the search for antidepressants' (ADs') mechanisms of action beyond their influence on monoaminergic neurotransmission, we analyzed the effects of three structurally and pharmacologically different ADs on autophagic processes in rat primary astrocytes and neurons. Autophagy has a significant role in controlling protein turnover and energy supply. Both, the tricyclic AD amitriptyline (AMI) and the selective serotonin re-uptake inhibitor citalopram (CIT) induced autophagy as mirrored by pronounced upregulation and cellular redistribution of the marker LC3B-II. Redistribution was characterized by formation of LC3B-II-positive structures indicative of autophagosomes, which associated with AVs in a time-dependent manner. Deletion of Atg5, representing a central mediator of autophagy in MEFs, led to abrogation of AMI-induced LC3B-I/II conversion. By contrast, VEN, a selective serotonin and noradrenaline reuptake inhibitor, did not promote autophagic processes in either cell type. The stimulatory impact of AMI on autophagy partly involved class-III PI3 kinase-dependent pathways as 3-methyladenine slightly diminished the effects of AMI. Autophagic flux as defined by autophagosome turnover was vastly undisturbed, and degradation of long-lived proteins was augmented upon AMI treatment. Enhanced autophagy was dissociated from drug-induced alterations in cholesterol homeostasis. Subsequent to AMI- and CIT-mediated autophagy induction, neuronal and glial viability decreased, with neurons showing signs of apoptosis. In conclusion, we report that distinct ADs promote autophagy in neural cells, with important implications on energy homeostasis.

Secrets of a successful pathogen: legionella resistance to progression along the autophagic pathway

To proliferate within phagocytes, Legionella pneumophila relies on Type IV secretion to modulate host cellular pathways. Autophagy is an evolutionarily conserved degradative pathway that captures and transfers a variety of microbes to lysosomes. Biogenesis of L. pneumophila-containing vacuoles and autophagosomes share several features, including endoplasmic reticulum (ER)-derived membranes, contributions by the host GTPases Rab1, Arf1 and Sar1, and a final destiny in lysosomes. We discuss morphological, molecular genetic, and immunological data that support the model that, although A/J mouse macrophages efficiently engulf L. pneumophila within autophagosomal membranes, the Type IV effector proteins DrrA/SidM, LidA, and RalF prolong association with the ER. By inhibiting immediately delivery to lysosomes, the bacteria persist in immature autophagosomal vacuoles for a period sufficient to differentiate into an acid-resistant, replicative form. Subsequent secretion of the Type IV effector LepB releases the block to autophagosome maturation, and the adapted progeny continue to replicate within autophagolysosomes. Accordingly, L. pneumophila can be exploited as a genetic tool to analyze the recruitment and function of the macrophage autophagy pathway.

Proteolysis in illness-associated skeletal muscle atrophy: from pathways to networks

Improvements in health in the past decades have resulted in increased numbers of the elderly in both developed and developing regions of the world. Advances in therapy have also increased the prevalence of patients with chronic and degenerative diseases. Muscle wasting, a feature of most chronic diseases, is prominent in the elderly and contributes to both morbidity and mortality. A major research goal has been to identify the proteolytic system(s) that is responsible for the degradation of proteins that occurs in muscle atrophy. Findings over the past 20 years have clearly confirmed an important role of the ubiquitin proteasome system in mediating muscle proteolysis, particularly that of myofibrillar proteins. However, recent observations have provided evidence that autophagy, calpains and caspases also contribute to the turnover of muscle proteins in catabolic states, and furthermore, that these diverse proteolytic systems interact with each other at various levels. Importantly, a number of intracellular signaling pathways such as the IGF1/AKT, myostatin/Smad, PGC1, cytokine/NFκB, and AMPK pathways are now known to interact and can regulate some of these proteolytic systems in a coordinated manner. A number of loss of function studies have identified promising therapeutic approaches to the prevention and treatment of wasting. However, additional biomarkers and other approaches to improve early identification of patients who would benefit from such treatment need to be developed. The current data suggests a network of interacting proteolytic and signaling pathways in muscle. Future studies are needed to improve understanding of the nature and control of these interactions and how they work to preserve muscle function under various states of growth and atrophy.

LC3 and GATE-16 N termini mediate membrane fusion processes required for autophagosome biogenesis

Autophagy is a unique membrane trafficking pathway describing the formation and targeting of double membrane autophagosomes to the vacuole/lysosome. The biogenesis of autophagosomes and their delivery to the vacuole/lysosome depend on multiple membrane fusion events. Using a cell-free system, we have investigated the ability of LC3 and GATE-16, two mammalian Atg8 orthologs, to mediate membrane fusion. We found that both proteins promote tethering and membrane fusion, mediated by the proteins' N-terminal α helices. We further show that short, 10 amino acid long synthetic peptides derived from the N terminus of LC3 or GATE-16 are sufficient to promote membrane fusion. Our data indicate that the fusion activity of LC3 is mediated by positively charged amino acids, whereas the activity of GATE-16 is mediated by hydrophobic interactions. Finally, we demonstrate that LC3 and GATE-16 N termini in general and specific residues needed for the fusion activity are essential for the proteins role in autophagosome biogenesis.

Functions of autophagy in hepatic and pancreatic physiology and disease

Autophagy is a lysosomal pathway that degrades and recycles intracellular organelles and proteins to maintain energy homeostasis during times of nutrient deprivation and to remove damaged cell components. Recent studies have identified new functions for autophagy under basal and stressed conditions. In the liver and pancreas, autophagy performs the standard functions of degrading mitochondria and aggregated proteins and regulating cell death. In addition, autophagy functions in these organs to regulate lipid accumulation in hepatic steatosis, trypsinogen activation in pancreatitis, and hepatitis virus replication. This review discusses the effects of autophagy on hepatic and pancreatic physiology and the contribution of this degradative process to diseases of these organs. The discovery of novel functions for this lysosomal pathway has increased our understanding of the pathophysiology of diseases in the liver and pancreas and suggested new possibilities for their treatment.

GIV/Girdin is a rheostat that fine-tunes growth factor signals during tumor progression

GIV/Girdin is a multidomain signaling molecule that enhances PI3K-Akt signals downstream of both G protein-coupled and growth factor receptors. We previously reported that GIV triggers cell migration via its C-terminal guanine-nucleotide exchange factor (GEF) motif that activates Gαi. Recently we discovered that GIV's C-terminus directly interacts with the epidermal growth factor receptor (EGFR), and when its GEF function is intact, a Gαi-GIV-EGFR signaling complex assembles. By coupling G proteins to growth factor receptors, GIV is uniquely poised to intercept the incoming receptor-initiated signals and modulate them via G protein intermediates. Subsequent work has revealed that expression of the highly specialized C-terminus of GIV undergoes a bipartite dysregulation during oncogenesis-full length GIV with an intact C-terminus is expressed at levels ~20-50-fold above normal in highly invasive cancer cells and metastatic tumors, but its C-terminus is truncated by alternative splicing in poorly invasive cancer cells and non-invasive tumors. The consequences of such dysregulation on graded signal transduction and cellular phenotypes in the normal epithelium and its implication during tumor progression are discussed herein. Based on the fact that GIV grades incoming signals initiated by ligand-activated receptors by linking them to cyclical activation of G proteins, we propose that GIV is a molecular rheostat for signal transduction.

Autophagy in nonalcoholic steatohepatitis

Autophagy is a critical pathway for the degradation of intracellular components by lysosomes. Established functions for both macroautophagy and chaperone-mediated autophagy in hepatic lipid metabolism, insulin sensitivity and cellular injury suggest a number of potential mechanistic roles for autophagy in nonalcoholic steatohepatitis (NASH). Decreased autophagic function in particular may promote the initial development of hepatic steatosis and progression of steatosis to liver injury. Additional functions of autophagy in immune responses and carcinogenesis may also contribute to the development of NASH and its complications. The impairment in autophagy that occurs with cellular lipid accumulation, obesity and aging may therefore have an important impact on this disease, and agents to augment hepatic autophagy have therapeutic potential in NASH.

Autophagy in protists

Autophagy is the degradative process by which eukaryotic cells digest their own components using acid hydrolases within the lysosome. Originally thought to function almost exclusively in providing starving cells with nutrients taken from their own cellular constituents, autophagy is in fact involved in numerous cellular events including differentiation, turnover of macromolecules and organelles, and defense against parasitic invaders. During the last 10-20 years, molecular components of the autophagic machinery have been discovered, revealing a complex interactome of proteins and lipids, which, in a concerted way, induce membrane formation to engulf cellular material and target it for lysosomal degradation. Here, our emphasis is autophagy in protists. We discuss experimental and genomic data indicating that the canonical autophagy machinery characterized in animals and fungi appeared prior to the radiation of major eukaryotic lineages. Moreover, we describe how comparative bioinformatics revealed that this canonical machinery has been subject to moderation, outright loss or elaboration on multiple occasions in protist lineages, most probably as a consequence of diverse lifestyle adaptations. We also review experimental studies illustrating how several pathogenic protists either utilize autophagy mechanisms or manipulate host-cell autophagy in order to establish or maintain infection within a host. The essentiality of autophagy for the pathogenicity of many parasites, and the unique features of some of the autophagy-related proteins involved, suggest possible new targets for drug discovery. Further studies of the molecular details of autophagy in protists will undoubtedly enhance our understanding of the diversity and complexity of this cellular phenomenon and the opportunities it offers as a drug target.

MODULATION OF AUTOPHAGY AND ITS POTENTIAL FOR CANCER THERAPY

Autophagy is a process in which cellular contents are captured in specialized, membrane-bounded vesicles and delivered to lysosomes for final degradation. Most studies support an inherent connection between autophagy and survival, but increasing evidence also suggests an association between autophagy and cell death. The therapeutic potential of targeting the autophagy pathway in cancer seems clear, but specific strategies for achieving successful eradication of cancer cells are less obvious. Recent developments in the fields of autophagy and programmed cell death, nevertheless, have shed light on therapeutic strategies with significant potential. In this review, we provide an overview of the autophagy process, pathways that modulate autophagy, and promising autophagy-based therapeutic strategies for cancer.

The complex interplay of NOD-like receptors and the autophagy machinery in the pathophysiology of Crohn disease

Several coding variants of NOD2 and ATG16L1 are associated with increased risk of Crohn disease (CD). NOD2, a cytosolic receptor of the innate immune system activates pro-inflammatory signalling cascades upon recognition of bacterial muramyl dipeptide, but seems also to be involved in antiviral and anti-parasitic defence programs. The CD associated variant L1007fsinsC leads to impaired pro-inflammatory signalling and diminished bacterial clearance. ATG16L1 is a protein essential for autophagosome formation at the phagophore assembly site. The CD associated T300A variant is located in the c-terminal WD40 domain, whose function is still unknown. Basal autophagy is not affected by the T300A variant, but antibacterial autophagy (xenophagy) is impaired, a finding that relates ATG16L1 as well as NOD2 to pathogen defence. Notably, combination of disease-associated alleles of ATG16L1 and NOD2/CARD15 leads to synergistically increased susceptibility for CD, indicating a possible crosstalk between NOD2- and ATG16L1-mediated processes in the pathogenesis of CD. This review surveys current research results and discusses the functional models of potential interplay between NLR-pathways and xenophagy. Interaction between pathways is discussed in the context of reactive oxygen species (ROS), membrane co-localisation, antigen processing and implications of disturbed Paneth cell vesicle export. These effects on pathogen response might imbalance the intestinal barrier epithelia towards chronic inflammation and promote development of Crohn disease. Further elucidation of NOD2/ATG16L1 interplay in xenophagy is relevant for understanding the aetiology of chronic intestinal inflammation and host-microbe interaction in general and could lead to principal new insights to xenophagy induction.

Autophagy in liver diseases

Autophagy, or cellular self-digestion, is a cellular pathway crucial for development, differentiation, survival, and homeostasis. Its implication in human diseases has been highlighted during the last decade. Recent data show that autophagy is involved in major fields of hepatology. In liver ischemia reperfusion injury, autophagy mainly has a prosurvival activity allowing the cell for coping with nutrient starvation and anoxia. During hepatitis B or C infection, autophagy is also increased but subverted by viruses for their own benefit. In hepatocellular carcinoma, the autophagy level is decreased. In this context, autophagy has an anti-tumor role and therapeutic strategies increasing autophagy, as rapamycin, have a beneficial effect in patients. Moreover, in hepatocellular carcinoma, Beclin-1 level, an autophagy protein, has a prognostic significance. In α-1-antitrypsin deficiency, the aggregation-prone ATZ protein accumulates in the endoplasmic reticulum. This activates the autophagic response which aims at degrading mutant ATZ. Some FDA-approved drugs which enhance autophagy and the disposal of aggregation-prone proteins may be useful in α-1-antitrypsin deficiency. Following alcohol consumption, autophagy is decreased in liver cells, likely due to a decrease in intracellular 5'-AMP-activated protein kinase (AMPk) and due to an alteration in vesicle transport in hepatocytes. This decrease in autophagy contributes to the formation of Mallory-Denk bodies and to liver cell death. Hepatic autophagy is defective in the liver in obesity and its upregulation improves insulin sensitivity.

Anti-apoptosis and cell survival: a review

Type I programmed cell death (PCD) or apoptosis is critical for cellular self-destruction for a variety of processes such as development or the prevention of oncogenic transformation. Alternative forms, including type II (autophagy) and type III (necrotic) represent the other major types of PCD that also serve to trigger cell death. PCD must be tightly controlled since disregulated cell death is involved in the development of a large number of different pathologies. To counter the multitude of processes that are capable of triggering death, cells have devised a large number of cellular processes that serve to prevent inappropriate or premature PCD. These cell survival strategies involve a myriad of coordinated and systematic physiological and genetic changes that serve to ward off death. Here we will discuss the different strategies that are used to prevent cell death and focus on illustrating that although anti-apoptosis and cellular survival serve to counteract PCD, they are nevertheless mechanistically distinct from the processes that regulate cell death.

Oxidative stress, apoptosis, and proteolysis in skeletal muscle repair after unloading

Although several lines of evidence link muscle-derived oxidants and inflammation to skeletal muscle wasting via regulation of apoptosis and proteolysis, little information is currently available on muscle repair. The present work was designed to study oxidative stress response, inflammatory cytokines, apoptotic, or proteolytic pathways during the early (1 and 5 days) and later (14 days) stages of the regrowth process subsequent to 14 days of hindlimb unloading. During the early stages of reloading, muscle mass recovery ( day 5) was facilitated by transcriptional downregulation ( day 1) of pathways involved in muscle proteolysis [μ-calpain, atrogin-1/muscle atrophy F-box (MAFbx), and muscle RING finger-1/(MuRF1) mRNA] and upregulation of an autophagy-related protein Beclin-1 ( day 5). At the same time, oxidative stress (glutathione vs. glutathione disulfide ratio, superoxide dismutase, catalase activities) remained still enhanced, whereas the increased uncoupling protein 3 gene expression recovered. Increased caspase-9 (mitochondrial-driven apoptosis) and decreased caspase-12 (sarcoplasmic reticulum-mediated apoptosis) activation was also normalized at early stages ( day 5). Conversely, the receptor-mediated apoptotic pathway initiated by ligand-induced (tumor necrosis factor-α, TNF-α) binding and promoting the activation of caspase-8 remained elevated until 14 days. Our data suggest that at early stages, muscle repair is mediated via the modulation of mitochondrial-driven apoptosis and muscle proteolysis. Despite full muscle mass recovery, oxidative stress and TNF-α-mediated apoptotic pathway are still activated till later stages of muscle remodeling.

Starvation-induced hyperacetylation of tubulin is required for the stimulation of autophagy by nutrient deprivation

The molecular mechanisms underlying microtubule participation in autophagy are not known. In this study, we show that starvation-induced autophagosome formation requires the most dynamic microtubule subset. Upon nutrient deprivation, labile microtubules specifically recruit markers of autophagosome formation like class III-phosphatidylinositol kinase, WIPI-1, the Atg12-Atg5 conjugate, and LC3-I, whereas mature autophagosomes may bind to stable microtubules. We further found that upon nutrient deprivation, tubulin acetylation increases both in labile and stable microtubules and is required to allow autophagy stimulation. Tubulin hyperacetylation on lysine 40 enhances kinesin-1 and JIP-1 recruitment on microtubules and allows JNK phosphorylation and activation. JNK, in turn, triggers the release of Beclin 1 from Bcl-2-Beclin 1 complexes and its recruitment on microtubules where it may initiate autophagosome formation. Finally, although kinesin-1 functions to carry autophagosomes in basal conditions, it is not involved in motoring autophagosomes after nutrient deprivation. Our results show that the dynamics of microtubules and tubulin post-translational modifications play a major role in the regulation of starvation-induced autophagy.

Ca2+ overload and mitochondrial permeability transition pore activation in living delta-sarcoglycan-deficient cardiomyocytes

Muscular dystrophies are often associated with significant cardiac disease that can be the prominent feature associated with gene mutations in sarcoglycan. Cardiac cell death is a main feature of cardiomyopathy in sarcoglycan deficiency and may arise as a cardiomyocyte intrinsic process that remains unclear. Deficiency of delta-sarcoglycan (delta-SG) induces disruption of the dystrophin-associated glycoprotein complex, a known cause of membrane instability that may explain cardiomyocytes cytosolic Ca2+ increase. In this study we assessed the hypothesis that cytosolic Ca2+ increase triggers cardiomyocyte death through mitochondrial Ca2+ overload and dysfunction in the delta-SG-deficient CHF147 hamster. We showed that virtually all isolated CHF147 ventricular myocytes exhibited elevated cytosolic and mitochondrial Ca2+ levels by the use of the Fura-2 and Rhod-2 fluorescent probes. Observation of living cells with Mito-Tracker red lead to the conclusion that approximately 15% of isolated CHF147 cardiomyocytes had disorganized mitochondria. Transmission electron microscope imaging showed mitochondrial swelling associated with crest and membrane disruption. Analysis of the mitochondrial permeability transition pore (MPTP) activity using calcein revealed that mitochondria of CHF147 ventricular cells were twofold leakier than wild types, whereas reactive oxygen species production was unchanged. Bax, Bcl-2, and LC3 expression analysis by Western blot indicated that the intrinsic apoptosis and the cell death associated to autophagy pathways were not significantly activated in CHF147 hearts. Our results lead to conclusion that cardiomyocytes death in delta-SG-deficient animals is an intrinsic phenomenon, likely related to Ca2+-induced necrosis. In this process Ca2+ overload-induced MPTP activation and mitochondrial disorganization may have an important role.

The Bcl-2 homology domain 3 mimetic gossypol induces both Beclin 1-dependent and Beclin 1-independent cytoprotective autophagy in cancer cells

Gossypol, a natural Bcl-2 homology domain 3 mimetic compound isolated from cottonseeds, is currently being evaluated in clinical trials. Here, we provide evidence that gossypol induces autophagy followed by apoptotic cell death in both the MCF-7 human breast adenocarcinoma and HeLa cell lines. We first show that knockdown of the Bcl-2 homology domain 3-only protein Beclin 1 reduces gossypol-induced autophagy in MCF-7 cells, but not in HeLa cells. Gossypol inhibits the interaction between Beclin 1 and Bcl-2 (B-cell leukemia/lymphoma 2), antagonizes the inhibition of autophagy by Bcl-2, and hence stimulates autophagy. We then show that knockdown of Vps34 reduces gossypol-induced autophagy in both cell lines, and consistent with this, the phosphatidylinositol 3-phosphate-binding protein WIPI-1 is recruited to autophagosomal membranes. Further, Atg5 knockdown also reduces gossypol-mediated autophagy. We conclude that gossypol induces autophagy in both a canonical and a noncanonical manner. Notably, we found that gossypol-mediated apoptotic cell death was potentiated by treatment with the autophagy inhibitor wortmannin or with small interfering RNA against essential autophagy genes (Vps34, Beclin 1, and Atg5). Our findings support the notion that gossypol-induced autophagy is cytoprotective and not part of the cell death process induced by this compound.