Autophagy

The role of autophagy in the response of human hepatocytes to oxidative stress remains unknown. Understanding this process may have important implications for the understanding of basic liver epithelial cell biology and the responses of hepatocytes during liver disease. To address this we isolated primary hepatocytes from human liver tissue and exposed them ex vivo to hypoxia and hypoxia-reoxygenation (H-R). We showed that oxidative stress increased hepatocyte autophagy in a reactive oxygen species (ROS) and class III PtdIns3K-dependent manner. Specifically, mitochondrial ROS and NADPH oxidase were found to be key regulators of autophagy. Autophagy involved the upregulation of BECN1, LC3A, Atg7, Atg5 and Atg 12 during hypoxia and H-R. Autophagy was seen to occur within the mitochondria of the hepatocyte and inhibition of autophagy resulted in the lowering a mitochondrial membrane potential and onset of cell death. Autophagic responses were primarily observed in the large peri-venular (PV) hepatocyte subpopulation. Inhibition of autophagy, using 3-methyladenine, increased apoptosis during H-R. Specifically, PV human hepatocytes were more susceptible to apoptosis after inhibition of autophagy. These findings show for the first time that during oxidative stress autophagy serves as a cell survival mechanism for primary human hepatocytes.     

Autophagy: a cyto-protective mechanism which prevents primary human hepatocyte apoptosis during oxidative stress

The role of autophagy in the response of human hepatocytes to oxidative stress remains unknown. Understanding this process may have important implications for the understanding of basic liver epithelial cell biology and the responses of hepatocytes during liver disease. To address this we isolated primary hepatocytes from human liver tissue and exposed them ex vivo to hypoxia and hypoxia-reoxygenation (H-R). We showed that oxidative stress increased hepatocyte autophagy in a reactive oxygen species (ROS) and class III PtdIns3K-dependent manner. Specifically, mitochondrial ROS and NADPH oxidase were found to be key regulators of autophagy. Autophagy involved the upregulation of BECN1, LC3A, Atg7, Atg5 and Atg 12 during hypoxia and H-R. Autophagy was seen to occur within the mitochondria of the hepatocyte and inhibition of autophagy resulted in the lowering a mitochondrial membrane potential and onset of cell death. Autophagic responses were primarily observed in the large peri-venular (PV) hepatocyte subpopulation. Inhibition of autophagy, using 3-methyladenine, increased apoptosis during H-R. Specifically, PV human hepatocytes were more susceptible to apoptosis after inhibition of autophagy. These findings show for the first time that during oxidative stress autophagy serves as a cell survival mechanism for primary human hepatocytes.     

Autophagy in hematopoietic stem/progenitor cells exposed to heavy metals: Biological implications and toxicological relevance

The inherent toxicity of many metal compounds, together with their widespread environmental distribution, raises concerns of potential health hazards. Little is known about the impact of these important environmental toxicants on adult stem/progenitor cells, necessary for tissue homeostasis and repair. We recently reported that autophagy is implicated in the response of hematopoietic stem/progenitor cells to toxic concentrations of hexavalent chromium (Cr[VI]) and cadmium (Cd), two well known carcinogenic heavy metal cations. Autophagy may lead to cell death if carried out too extensively, but also acts as a survival pathway in cells under stress. In stem/progenitor cells, an autophagic phenotype could mitigate metal-induced toxicity, contributing to the conservation of tissue renewal capability. Given the key role of toxic damage to adult stem/progenitor cells in cancer, it is necessary to investigate whether autophagic responses modulate the carcinogenic potential of exposure to heavy metals during stem/progenitor cell differentiation.     

Mechanisms of autophagy and apoptosis: Recent developments in breast cancer cells

Autophagy,the pathway whereby cell components are degraded by lysosomes,is involved in the cell response to environmental stresses,such as nutrient deprivation,hypoxia or exposition to chemotherapeutic agents.Under these conditions,which are reminiscent of certain phases of tumor development,autophagy either promotes cell survival or induces cell death. This strengthens the possibility that autophagy could be an important target in cancer therapy,as has been proposed.Here,we describe the regulation of survival and death by autophagy and apoptosis,especially in cultured breast cancer cells.In particular,we discuss whether autophagy represents an apoptosis-independent process and/or if they share common pathways. We believe that understanding in detail the molecular mechanisms that underlie the relationships between autophagy and apoptosis in breast cancer cells could improve the available treatments for this disease.     

Feast or famine: autophagy control and engineering in eukaryotic cell culture

Autophagy is a degradative process playing a role in both cell death and cell survival. Its presence is well conserved both in lower and higher eukaryotes. Recent studies have shown that activation or inhibition of autophagy may be possible in biotechnologically important species including mammalian cells and filamentous fungi using both environmental manipulation and genetic engineering. As our understanding of the autophagic biochemical pathways increases and monitoring methods become more user-friendly, the potential exists to obtain an optimum level of autophagy. This may allow for maximum cell survival and production of proteins and other metabolites in these industrially important eukaryotes.     

Enhanced autophagy as a potential mechanism for the improved physiological function by simvastatin in muscular dystrophy

Autophagy has recently emerged as an important cellular process for the maintenance of skeletal muscle health and function. Excessive autophagy can trigger muscle catabolism, leading to atrophy. In contrast, reduced autophagic flux is a characteristic of several muscle diseases, including Duchenne muscular dystrophy, the most common and severe inherited muscle disorder. Recent evidence demonstrates that enhanced reactive oxygen species (ROS) production by CYBB/NOX2 impairs autophagy in muscles from the dmd/mdx mouse, a genetic model of Duchenne muscular dystrophy. Statins decrease CYBB/NOX2 expression and activity and stimulate autophagy in skeletal muscle. Therefore, we treated dmd/mdx mice with simvastatin and showed decreased CYBB/NOX2-mediated oxidative stress and enhanced autophagy induction. This was accompanied by reduced muscle damage, inflammation and fibrosis, and increased muscle force production. Our data suggest that increased autophagy may be a potential mechanism by which simvastatin improves skeletal muscle health and function in muscular dystrophy.     

Cross-talking between autophagy and viral infection in mammalian cells

Autophagy is a cellular process in degradation of long-lived proteins and organelles in the cytosol for maintaining cellular homeostasis, which has been linked to a wide range of human health and disease states, including viral infection. The viral infected cells exhibit a complicated cross-talking between autophagy and virus. It has been shown that autophagy interacts with both adaptive and innate immunity. For adaptive immunity, viral antigens can be processed in autophagosomes by acidic proteases before major histocompatibility complex (MHC) class II presentation. For innate immunity, autophagy may assist in the delivery of viral nucleic acids to endosomal TLRs and also functions as a part of the TLR-or-PKR-downstream responses. Autophagy was also reported to suppress the magnitude of host innate antiviral immunity in certain cases. On the other hand, viruses has evolved many strategies to combat or utilize the host autophagy for their own benefit. In this review we discussed recent advances toward clarifying the cross-talking between autophagy and viral infection in mammalian cells.     

How autophagy both activates and inhibits cellular senescence

Autophagy and cellular senescence are stress responses essential for homeostasis. While recent studies indicate a genetic relationship between autophagy and senescence, whether autophagy acts positively or negatively on senescence is still subject to debate. Although autophagy was originally recognized as a nonspecific lysosomal degradation pathway (general autophagy), increasing evidence supports a selective form of autophagy that mediates the degradation of specific targets (selective autophagy). Our recent study revealed distinctive roles of selective autophagy and general autophagy in the regulation of senescence, at least in part resolving apparently contradictory reports regarding the relationship between these 2 important homeostatic stress responses.     

Autophagy and plant innate immunity: Defense through degradation

Autophagy is a process of bulk degradation and nutrient sequestration that occurs in all eukaryotes. In plants, autophagy is activated during development, environmental stress, starvation, and senescence. Recent evidence suggests that autophagy is also necessary for the proper regulation of hypersensitive response programmed cell death (HR-PCD) during the plant innate immune response. We review autophagy in plants with emphasis on the role of autophagy during innate immunity. We hypothesize a role for autophagy in the degradation of pro-death signals during HR-PCD, with specific focus on reactive oxygen species and their sources. We propose that the plant chloroplasts are an important source of pro-death signals during HR-PCD, and that the chloroplast itself may be targeted for autophagosomal degradation by a process called chlorophagy.     

浮游植物细胞自噬作用特点及研究方法

自噬(Autophagy)是真核生物细胞中一类高度保守的、依赖于溶酶体或液泡途径对胞质蛋白和细胞器进行降解的生物学过程。细胞自噬除维持细胞稳态外,在细胞响应各种外界胁迫中也发挥重要作用。近年来,陆续发现浮游植物能够通过细胞自噬应答众多环境胁迫,并在浮游植物细胞中鉴定出了类似于哺乳动物细胞中的核心自噬功能单位。自噬作为一种独特的程序性细胞死亡(PCD)形式,对浮游植物遭受胁迫后的个体存活及种群延续具有至关重要的作用。因此,细胞自噬也将成为浮游植物研究领域的一个新的着力点。主要综述了浮游植物细胞中自噬的保守性、诱导因素、调控机制、自噬与凋亡的交互作用以及浮游植物自噬研究方法等研究进展。     

非编码RNA与细胞自噬调控

细胞自噬是真核生物细胞中高度保守的重要代谢途径。该途径是将细胞内有害或不需要的大分子分解并回收,从而使细胞在生长或环境改变导致的应激和压力条件下获得生存优势。近年越来越多的证据表明,非编码RNA,包括微RNA(microRNA,miRNA)和长非编码RNA(long non-coding RNA,lncRNA),在自噬过程中发挥了重要的作用。本文综述了miRNA和lncRNA在多种细胞环境中对细胞自噬的调控机制,并讨论了这些自噬相关的非编码RNA在疾病分子诊断、分类和预后中的作用,及其作为疾病治疗靶标的可能性。     

Inhibition of autophagy enhances the effects of the AKT inhibitor MK‐2206 when combined with paclitaxel and carboplatin in BRAF wild‐type melanoma

This study investigates the mechanism of action behind the long‐term responses (12–16 months) of two BRAF WT melanoma patients to the AKT inhibitor MK‐2206 in combination with paclitaxel and carboplatin. Although single agent MK‐2206 inhibited phospho‐AKT signaling, it did not impact in vitro melanoma growth or survival. The combination of MK‐2206 with paclitaxel and carboplatin was cytotoxic in long‐term colony formation and 3D spheroid assays, and induced autophagy. Autophagy was initially protective with autophagy inhibitors and deletion of ATG5 found to enhance cytotoxicity. Although prolonged autophagy induction (>6 days) led to caspase‐dependent apoptosis, drug resistant clones still emerged. Autophagy inhibition enhanced the cell death response through reactive oxygen species and could be reversed by anti‐oxidants. We demonstrate for the first time that AKT inhibition in combination with chemotherapy may have clinical activity in BRAF WT melanoma and show that an autophagy inhibitor may prevent resistance to these drugs.     

Autophagy and the integrated stress response

Autophagy is a tightly regulated pathway involving the lysosomal degradation of cytoplasmic organelles or cytosolic components. This pathway can be stimulated by multiple forms of cellular stress, including nutrient or growth factor deprivation, hypoxia, reactive oxygen species, DNA damage, protein aggregates, damaged organelles, or intracellular pathogens. Both specific, stimulus-dependent and more general, stimulus-independent signaling pathways are activated to coordinate different phases of autophagy. Autophagy can be integrated with other cellular stress responses through parallel stimulation of autophagy and other stress responses by specific stress stimuli, through dual regulation of autophagy and other stress responses by multifunctional stress signaling molecules, and/or through mutual control of autophagy and other stress responses. Thus, autophagy is a cell biological process that is a central component of the integrated stress response.     

Redox signaling: Potential arbitrator of autophagy and apoptosis in therapeutic response

Redox signaling plays important roles in the regulation of cell death and survival in response to cancer therapy. Autophagy and apoptosis are discrete cellular processes mediated by distinct groups of regulatory and executioner molecules, and both are thought to be cellular responses to various stress conditions including oxidative stress, therefore controlling cell fate. Basic levels of reactive oxygen species (ROS) may function as signals to promote cell proliferation and survival, whereas increase of ROS can induce autophagy and apoptosis by damaging cellular components. Growing evidence in recent years argues for ROS that below detrimental levels acting as intracellular signal transducers that regulate autophagy and apoptosis. ROS-regulated autophagy and apoptosis can cross-talk with each other. However, how redox signaling determines different cell fates by regulating autophagy and apoptosis remains unclear. In this review, we will focus on understanding the delicate molecular mechanism by which autophagy and apoptosis are finely orchestrated by redox signaling and discuss how this understanding can be used to develop strategies for the treatment of cancer.     

Autophagy and senescence

Autophagy and senescence share a number of characteristics, which suggests that both responses could serve to collaterally protect the cell from the toxicity of external stress such as radiation and chemotherapy and internal forms of stress such as telomere shortening and oncogene activation. Studies of oncogene activation in normal fibroblasts as well as exposure of tumor cells to chemotherapy have indicated that autophagy and senescence are closely related but not necessarily interdependent responses; specifically, interference with autophagy delays but does not abrogate senescence. The literature relating to this topic is inconclusive, with some reports appearing to be consistent with a direct relationship between autophagy and senescence and others indicative of an inverse relationship. Before this question can be resolved, additional studies will be necessary where autophagy is clearly inhibited by genetic silencing and where the temporal responses of both autophagy and senescence are monitored, preferably in cells that are intrinsically incapable of apoptosis or where apoptosis is suppressed. Understanding the nature of this relationship may provide needed insights relating to cytoprotective as well as potential cytotoxic functions of both autophagy and senescence.     

Autophagy as a defense strategy against stress: focus on Paracentrotus lividus sea urchin embryos exposed to cadmium

Autophagy is used by organisms as a defense strategy to face environmental stress. This mechanism has been described as one of the most important intracellular pathways responsible for the degradation and recycling of proteins and organelles. It can act as a cell survival mechanism if the cellular damage is not too extensive or as a cell death mechanism if the damage/stress is irreversible; in the latter case, it can operate as an independent pathway or together with the apoptotic one. In this review, we discuss the autophagic process activated in several aquatic organisms exposed to different types of environmental stressors, focusing on the sea urchin embryo, a suitable system recently included into the guidelines for the use and interpretation of assays to monitor autophagy. After cadmium (Cd) exposure, a heavy metal recognized as an environmental toxicant, the sea urchin embryo is able to adopt different defense mechanisms, in a hierarchical way. Among these, autophagy is one of the main responses activated to preserve the developmental program. Finally, we discuss the interplay between autophagy and apoptosis in the sea urchin embryo, a temporal and functional choice that depends on the intensity of stress conditions.     

Role of plant autophagy in stress response

Autophagy is a conserved pathway for the bulk degradation of cytoplasmic components in all eukaryotes. This process plays a critical role in the adaptation of plants to drastic changing environmental stresses such as starvation, oxidative stress, drought, salt, and pathogen invasion. This paper summarizes the current knowledge about the mechanism and roles of plant autophagy in various plant stress responses.     

Reactive oxygen species and nitric oxide regulate mitochondria-dependent apoptosis and autophagy in evodiamine-treated human cervix carcinoma HeLa cells

The redox environment of the cell is currently thought to be extremely important to control either apoptosis or autophagy. This study reported that reactive oxygen species (ROS) and nitric oxide (NO) generations were induced by evodiamine time-dependently; while they acted in synergy to trigger mitochondria-dependent apoptosis by induction of mitochondrial membrane permeabilization (MMP) through increasing the Bax/Bcl-2 or Bcl-x(L) ratio. Autophagy was also stimulated by evodiamine, as demonstrated by the positive autophagosome-specific dye monodansylcadaverine (MDC) staining as well as the expressions of autophagy-related proteins, Beclin 1 and LC3. Pre-treatment with 3-MA, the specific inhibitor for autophagy, dose-dependently decreased cell viability, indicating a survival function of autophagy. Importantly, autophagy was found to be promoted or inhibited by ROS/NO in response to the severity of oxidative stress. These findings could help shed light on the complex regulation of intracellular redox status on the balance of autophagy and apoptosis in anti-cancer therapies.     

Autophagy and Alzheimer’s Disease

Autophagy is an essential degradation pathway in clearing abnormal protein aggregates in mammalian cells and is responsible for protein homeostasis and neuronal health. Several studies have shown that autophagy deficits occurred in early stage of Alzheimer’s disease (AD). Autophagy plays an important role in generation and metabolism of β-amyloid (Aβ), assembling of tau and thus its malfunction may lead to the progress of AD. By considering the above evidences, autophagy may be a new target in developing drugs for AD. So far, a number of mammalian target of rapamycin (mTOR)-dependent and independent autophagy modulators have been identified to have positive effects in AD treatment. In this review, we summarized the latest progress supporting the role for autophagy deficits in AD and the potential therapeutic effects of autophagy modulators in AD.