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

Molecular Mechanisms of Noncanonical Autophagy

Macroautophagy is a lysosomal catabolic process that maintains the homeostasis of eukaryotic cells, tissues, and organisms. Macroautophagy plays important physiological roles during development and aging processes and also contributes to immune responses. The process of macroautophagy is compromised in diseases, such as cancer, neurodegenerative disorders, and diabetes. The autophagosome, the double-membrane-bound organelle that sequesters cytoplasmic material to initiate macroautophagy, is formed by the hierarchical recruitment of about 15 autophagy-related (ATG) proteins and associated proteins, such as DFCP1, AMBRA1, the class III phosphatidyl-inositol 3-kinase VPS34, and p150/VPS15. Evidence suggests that in addition to the canonical pathway, noncanonical pathways that do not require the entire repertoire of ATGs can also result in formation of autophagosomes. Here we will discuss recent discoveries concerning the molecular regulation of these noncanonical forms of macroautophagy and their potential roles in cellular responses to stressful situations.

Hypoxia promotes noncanonical autophagy in nucleus pulposus cells independent of MTOR and HIF1A signaling

Nucleus pulposus (NP) cells reside in the avascular and hypoxic microenvironment of intervertebral discs. Importantly, many activities related to survival and function of NP cells are controlled by the HIF-family of transcription factors. We hypothesize that NP cells adapt to their hypoxic niche through modulation of macroautophagy/autophagy. In various cell types, hypoxia induces autophagy in a HIF1A-dependent fashion; however, little is known about hypoxic regulation of autophagy in NP cells. Hypoxia increases the number of autophagosomes as seen by TEM analysis and LC3-positive puncta in NP cells. Hypoxic induction of autophagy was also demonstrated by a significantly higher number of autophagosomes and smaller change in autolysosomes in NP cells expressing tandem-mCherry-EGFP-LC3B. Increased LC3-II levels were not accompanied by a concomitant increase in BECN1 or the ATG12-ATG5 complex. In addition, ULK1 phosphorylation at Ser757 and Ser777 responsive to MTOR and AMPK, respectively, was not affected in hypoxia. Interestingly, when MTOR activity was inhibited by rapamycin or Torin1, LC3-II levels did not change, suggesting a novel MTOR-independent regulation. Noteworthy, while silencing of HIF1A affected hypoxic induction of BNIP3, it did not affect LC3-II levels, indicating hypoxia-induced autophagy is HIF1-independent. Importantly, there was no change in the number of LC3-positive autophagosomes in NP-specific Hif1a null mice. Finally, inhibition of autophagic flux did not affect the glycolytic metabolism of NP cells, suggesting a possible nonmetabolic role of autophagy. Taken together, our study for the first time shows that NP cells regulate autophagy in a noncanonical fashion independent of MTOR and HIF1A signaling.

Chronic Iron Overload Results in Impaired Bacterial Killing of THP-1 Derived Macrophage through the Inhibition of Lysosomal Acidification

Iron is essential for living organisms and the disturbance of iron homeostasis is associated with altered immune function. Additionally, bacterial infections can cause major complications in instances of chronic iron overload, such as patients with transfusion-dependent thalassemia. Monocytes and macrophages play important roles in maintaining systemic iron homoeostasis and in defense against invading pathogens. However, the effect of iron overload on the function of monocytes and macrophages is unclear. We elucidated the effects of chronic iron overload on human monocytic cell line (THP-1) and THP-1 derived macrophages (TDM) by continuously exposing them to high levels of iron (100 μM) to create I-THP-1 and I-TDM, respectively. Our results show that iron overload did not affect morphology or granularity of I-THP-1, but increased the granularity of I-TDM. Bactericidal assays for non-pathogenic E. coli DH5α, JM109 and pathogenic P. aeruginosa all revealed decreased efficiency with increasing iron concentration in I-TDM. The impaired P. aeruginosa killing ability of human primary monocyte derived macrophages (hMDM) was also found when cells are cultured in iron contained medium. Further studies on the bactericidal activity of I-TDM revealed lysosomal dysfunction associated with the inhibition of lysosomal acidification resulting in increasing lysosomal pH, the impairment of post-translational processing of cathepsins (especially cathepsin D), and decreased autophagic flux. These findings may explain the impaired innate immunity of thalassemic patients with chronic iron overload, suggesting the manipulation of lysosomal function as a novel therapeutic approach.

Lipid-Induced Endoplasmic Reticulum Stress Impairs Selective Autophagy at the Step of Autophagosome-Lysosome Fusion in Hepatocytes

Blockage of hepatic autophagic degradation system occurs in obesity and is associated with the development of nonalcoholic fatty liver disease. However, the mechanism of this blockage remains unclear. We found a high-fat diet induced accumulation of autophagosomes in the mice livers. However, autophagy substrates such as p62 and ubiquitinated proteins also accumulated in the livers in this model. These findings indicate the possibility that a high-fat diet impairs autophagic flux in the liver. Then, to assess the autophagic flux in more detail, we performed analyses of autophagic flux in cultured hepatocytes exposed to monounsaturated fatty acids (FAs) or saturated FAs (SFAs). SFAs but not monounsaturated FAs suppressed degradation of contents in the autophagosomes. We analyzed each stage of the autophagy pathway (ie, autophagosome formation, autophagosome-lysosome fusion, lysosomal degradation) in cultured hepatocytes treated with monounsaturated FAs or SFAs and found that SFAs impaired autophagosome-lysosome fusion. This impairment occurred in an endoplasmic reticulum stress-dependent manner. Moreover, ubiquitin and p62-positive inclusions observed in high-fat diet-fed mice livers and SFA-treated cells were sequestered within autophagosomes. We also found that SFA-induced accumulation of Ser351-phosphorylated p62, which is indispensable for selective autophagy, further increased on administration of a lysosomal proteinase inhibitor. Although lipid-induced endoplasmic reticulum stress interferes with the autophagosome-lysosome fusion, selective autophagic sequestration of aggregated proteins is not inhibited.

Function of Autophagy in Nonalcoholic Fatty Liver Disease

Autophagy is a lysosomal degradative pathway that functions to promote cell survival by supplying energy in times of stress or by removing damaged organelles and proteins after injury. The involvement of autophagy in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) was first suggested by the finding that this pathway mediates the breakdown of intracellular lipids in hepatocytes and therefore may regulate the development of hepatic steatosis. Subsequent studies have demonstrated additional critical functions for autophagy in hepatocytes and other hepatic cell types such as macrophages and stellate cells that regulate insulin sensitivity, hepatocellular injury, innate immunity, fibrosis, and carcinogenesis. These findings suggest a number of possible mechanistic roles for autophagy in the development of NAFLD and progression to NASH and its complications. The functions of autophagy in the liver, together with findings of decreased hepatic autophagy in association with conditions that predispose to NAFLD such as obesity and aging, suggest that autophagy may be a novel therapeutic target in this disease.

Autophagy inhibition of hsa-miR-19a-3p/19b-3p by targeting TGF-β R II during TGF-β1-induced fibrogenesis in human cardiac fibroblasts

Transforming growth factor-β1 (TGF-β1) plays an important role on fibrogenesis in heart disease. MicroRNAs have exhibited as crucial regulators of cardiac homeostasis and remodeling in various heart diseases. MiR-19a-3p/19b-3p expresses with low levels in the plasma of heart failure patients. The purpose of our study is to determine the role of MiR-19a-3p/19b-3p in regulating autophagy-mediated fibrosis of human cardiac fibroblasts. We elucidate our hypothesis in clinical samples and human cardiac fibroblasts (HCF) to provide valuable basic information. TGF-β1 promotes collagen I α2 and fibronectin synthesis in HCF and that is paralleled by autophagic activation in these cells. Pharmacological inhibition of autophagy by 3-methyladenine decreases the fibrotic response, while autophagy induction of rapamycin increases the response. BECN1 knockdown and Atg5 over-expression either inhibits or enhances the fibrotic effect of TGF-β1 in experimental HCF. Furthermore, miR-19a-3p/19b-3p mimics inhibit epithelial mesenchymal transition (EMT) and extracellular matrix (ECM) prodution and invasion of HCF. Functional studies suggest that miR-19a-3p/19b-3p inhibits autophagy of HCF through targeting TGF-β R II mRNA. Moreover, enhancement of autophagy rescues inhibition effect of miR-19a-3p/19b-3p on Smad 2 and Akt phosphorylation through TGF-β R II signaling. Our study uncovers a novel mechanism that miR-19a-3p/19b-3p inhibits autophagy-mediated fibrogenesis by targeting TGF-β R II.

NFκB is a central regulator of protein quality control in response to protein aggregation stresses via autophagy modulation

NFκB is a master regulator of protein quality control. It helps the cells to survive proteotoxicity by modulating autophagy via up-regulation of BAG3 and HspB8 expression, a molecular mechanism relevant to protein conformational diseases.

During cell life, proteins often misfold, depending on particular mutations or environmental changes, which may lead to protein aggregates that are toxic for the cell. Such protein aggregates are the root cause of numerous diseases called “protein conformational diseases,” such as myofibrillar myopathy and familial amyotrophic lateral sclerosis. To fight against aggregates, cells are equipped with protein quality control mechanisms. Here we report that NFκB transcription factor is activated by misincorporation of amino acid analogues into proteins, inhibition of proteasomal activity, expression of the R120G mutated form of HspB5 (associated with myofibrillar myopathy), or expression of the G985R and G93A mutated forms of superoxide dismutase 1 (linked to familial amyotrophic lateral sclerosis). This noncanonical stimulation of NFκB triggers the up-regulation of BAG3 and HspB8 expression, two activators of selective autophagy, which relocalize to protein aggregates. Then NFκB-dependent autophagy allows the clearance of protein aggregates. Thus NFκB appears as a central and major regulator of protein aggregate clearance by modulating autophagic activity. In this context, the pharmacological stimulation of this quality control pathway might represent a valuable strategy for therapies against protein conformational diseases.

Hydrogen sulfide reduces serum triglyceride by activating liver autophagy via the AMPK-mTOR pathway

Autophagy plays an important role in liver triglyceride (TG) metabolism. Inhibition of autophagy could reduce the clearance of TG in the liver. Hydrogen sulfide (H2S) is a potent stimulator of autophagic flux. Recent studies showed H2S is protective against hypertriglyceridemia (HTG) and noalcoholic fatty liver disease (NAFLD), while the mechanism remains to be explored. Here, we tested the hypothesis that H2S reduces serum TG level and ameliorates NAFLD by stimulating liver autophagic flux by the AMPK-mTOR pathway. The level of serum H2S in patients with HTG was lower than that of control subjects. Sodium hydrosulfide (NaHS, H2S donor) markedly reduced serum TG levels of male C57BL/6 mice fed a high-fat diet (HFD), which was abolished by coadministration of chloroquine (CQ), an inhibitor of autophagic flux. In HFD mice, administration of NaSH increased the LC3BII-to-LC3BI ratio and decreased the p62 protein level. Meanwhile, NaSH increased the phosphorylation of AMPK and thus reduced the phosphorylation of mTOR in a Western blot study. In cultured LO2 cells, high-fat treatment reduced the ratio of LC3BII to LC3BI and the phosphorylation of AMPK, which were reversed by the coadministration of NaSH. Knockdown of AMPK by siRNA in LO2 cells blocked the autophagic enhancing effects of NaSH. The same qualitative effect was observed in AMPKα2(-/-) mice. These results for the first time demonstrated that H2S could reduce serum TG level and ameliorate NAFLD by activating liver autophagy via the AMPK-mTOR pathway.

Dysbiotic gut microbiome: A key element of Crohn's disease

Since the first publication on "regional ileitis", the relevance of this chronic inflammatory disease condition termed finally as Crohn's disease is continuously increasing. Although we are beginning to comprehend certain aspects of its pathogenesis, many facets remain unexplored. Host's gut microbiota is involved in a wide range of physiological and pathological processes including immune system development, and pathogen regulation. Further, the microbiome is thought to play a key role in Crohn's disease. The presence of Crohn's-associated variants of NOD2 and ATG16L genes appears to be associated not only with alterations of mucosal barrier functions, and bacterial killing, but the gut microbiota, as well, reflecting a potential relationship between the host's genotype and intestinal dysbiosis, involved in disease etiology. This review aims to characterize some exciting new aspect of Crohn's disease pathology, focusing mainly on the role of intestinal microbes, and their interplay with the immune system of the host.

Oxidative Stress in Placenta: Health and Diseases

During pregnancy, development of the placenta is interrelated with the oxygen concentration. Embryo development takes place in a low oxygen environment until the beginning of the second trimester when large amounts of oxygen are conveyed to meet the growth requirements. High metabolism and oxidative stress are common in the placenta. Reactive oxidative species sometimes harm placental development, but they are also reported to regulate gene transcription and downstream activities such as trophoblast proliferation, invasion, and angiogenesis. Autophagy and apoptosis are two crucial, interconnected processes in the placenta that are often influenced by oxidative stress. The proper interactions between them play an important role in placental homeostasis. However, an imbalance between the protective and destructive mechanisms of autophagy and apoptosis seems to be linked with pregnancy-related disorders such as miscarriage, preeclampsia, and intrauterine growth restriction. Thus, potential therapies to hold oxidative stress in leash, promote placentation, and avoid unwanted apoptosis are discussed.

Retinoic acid receptor α promotes autophagy to alleviate liver ischemia and reperfusion injury

AIM: To study the role of autophagy and the relationship between retinoic acid receptor α (RARα) and autophagy in liver ischemia and reperfusion (IR) injury.

METHODS: All-trans retinoic acid (ATRA) was administered to mice for two weeks before operation. Reverse transcription-polymerase chain reaction and Western blot were used to detect the expression levels of related factors. To demonstrate the role of RARα, LE540, a RARα inhibitor, was used to treat hepatocytes injured by H₂O₂in vitro.

RESULTS: ATRA pretreatment noticeably diminished levels of serum alanine aminotransferase and aspartate aminotransferase as well as the degree of histopathological changes. Apoptosis was also inhibited, whereas autophagy was promoted. In vitro, RARα was inhibited by LE540, which resulted in decreased autophagy and increased apoptosis. Similarly, the expression of Foxo3a and p-Akt was downregulated, but Foxo1 expression was upregulated.

CONCLUSION: This research provides evidence that ATRA can protect the liver from IR injury by promoting autophagy, which is dependent on Foxo3/p-Akt/Foxo1 signaling.

Disruptive environmental chemicals and cellular mechanisms that confer resistance to cell death

Cell death is a process of dying within biological cells that are ceasing to function. This process is essential in regulating organism development, tissue homeostasis, and to eliminate cells in the body that are irreparably damaged. In general, dysfunction in normal cellular death is tightly linked to cancer progression. Specifically, the up-regulation of pro-survival factors, including oncogenic factors and antiapoptotic signaling pathways, and the down-regulation of pro-apoptotic factors, including tumor suppressive factors, confers resistance to cell death in tumor cells, which supports the emergence of a fully immortalized cellular phenotype. This review considers the potential relevance of ubiquitous environmental chemical exposures that have been shown to disrupt key pathways and mechanisms associated with this sort of dysfunction. Specifically, bisphenol A, chlorothalonil, dibutyl phthalate, dichlorvos, lindane, linuron, methoxychlor and oxyfluorfen are discussed as prototypical chemical disruptors; as their effects relate to resistance to cell death, as constituents within environmental mixtures and as potential contributors to environmental carcinogenesis.

The pan-deacetylase inhibitor panobinostat suppresses the expression of oncogenic miRNAs in hepatocellular carcinoma cell lines

Deacetylase inhibitors (DACi) are a new class of drugs with a broad spectrum of mechanisms that favor their application in cancer therapy. Currently, the exact mechanisms and cellular effects of DACi have not been fully elucidated. In addition to their effects on histone acetylation, DACi can interfere with gene expression via miRNA pathways. Treatment with panobinostat (LBH589), a novel potent DACi, led to the highly aberrant modulation of several miRNAs in hepatocellular carcinoma (HCC) cell lines as shown by miRNA array analysis. Among them, hsa-miR-19a, hsa-miR-19b1 and the corresponding precursors were down-regulated by panobinostat in TP53(-/-) Hep3B and TP53(+/+) HepG2 cell lines; hsa-miR30a-5p mature form only was suppressed in both HCC cell lines, as confirmed by further RT-qPCR analysis. In HCC cell lines, panobinostat caused the upregulation of the predicted miRNA targets APAF1 and Beclin1 protein levels. Transfection with oligonucleotides mimicking these miRNAs led to an increase in the viability rate of both cell lines as analyzed by impedance-based real-time cell analysis. In addition, transfecting miRNA mimicking oligonucleotides resulted in the decrease of APAF1, Beclin1 and PAK6 at the protein level, proving the regulating influence of the investigated miRNAs on gene final products. The overexpression of the above mentioned oncomiRs in Hep3B and HepG2 cell lines leads to cell proliferation and downregulation of cell death associated proteins. In our model, panobinostat exerts its anti-cancer effect by suppressing these miRNAs and restoring the expression of their corresponding tumor suppressor targets.

O-GlcNAc modification is essential for the regulation of autophagy in Drosophila melanogaster

O-GlcNAcylation is a dynamic post-translational modification that takes place on ser/thr residues of nucleocytoplasmic proteins. O-GlcNAcylation regulates almost all cellular events as a nutrient sensor, a transcriptional and translational regulator, and a disease-related factor. Although the role of O-GlcNAcylation in insulin signaling and metabolism are well established, the relationship between O-GlcNAcylation and autophagy is largely unknown. Here, we manipulated O-GlcNAcylation in Drosophila and found that it regulates autophagy through Akt/dFOXO signaling. We demonstrate that O-GlcNAcylation and the levels of O-GlcNAc transferase (OGT) are increased during starvation. Furthermore, Atg proteins and autolysosomes are increased in OGT-reduced flies without fasting. Atg proteins and autophagosomes are reduced in OGT-overexpressing flies. Our results suggest that not only autophagy gene expression but also autophagic structures are regulated by OGT through Akt and dFOXO. These data imply that O-GlcNAcylation is important in modulating autophagy as well as insulin signaling in Drosophila.

Polycation-mediated integrated cell death processes

One of the major challenges in the field of nucleic acid delivery is the design of delivery vehicles with attributes that render them safe as well as efficient in transfection. To this end, polycationic vectors have been intensely investigated with native polyethylenimines (PEIs) being the gold standard. PEIs are highly efficient transfectants, but depending on their architecture and size they induce cytotoxicity through different modes of cell death pathways. Here, we briefly review dynamic and integrated cell death processes and pathways, and discuss considerations in cell death assay design and their interpretation in relation to PEIs and PEI-based engineered vectors, which are also translatable for the design and studying the safety of other transfectants.

Atg8 is involved in endosomal and phagosomal acidification in the parasitic protist Entamoeba histolytica

Autophagy is one of two major bulk protein degradation systems and is conserved throughout eukaryotes. The protozoan Entamoeba histolytica, which is a human intestinal parasite, possesses a restricted set of autophagy‐related (Atg) proteins compared with other eukaryotes and thus represents a suitable model organism for studying the minimal essential components and ancestral functions of autophagy. E. histolytica possesses two conjugation systems: Atg8 and Atg5/12, although a gene encoding Atg12 is missing in the genome. Atg8 is considered to be the central and authentic marker of autophagosomes, but recent studies have demonstrated that Atg8 is not exclusively involved in autophagy per se, but other fundamental mechanisms of vesicular traffic. To investigate this question in E. histolytica, we studied on Atg8 during the proliferative stage. Atg8 was constitutively expressed in both laboratory‐maintained and recently established clinical isolates and appeared to be lipid‐modified in logarithmic growth phase, suggesting a role of Atg8 in non‐stress and proliferative conditions. These findings are in contrast to those for Entamoeba invadens, in which autophagy is markedly induced during an early phase of differentiation from the trophozoite into the cyst. The repression of Atg8 gene expression in En. histolytica by antisense small RNA‐mediated transcriptional gene silencing resulted in growth retardation, delayed endocytosis and reduced acidification of endosomes and phagosomes. Taken together, these results suggest that Atg8 and the Atg8 conjugation pathway have some roles in the biogenesis of endosomes and phagosomes in this primitive eukaryote.

Sphingolipids as cell fate regulators in lung development and disease

Sphingolipids are a diverse class of signaling molecules implicated in many important aspects of cellular biology, including growth, differentiation, apoptosis, and autophagy. Autophagy and apoptosis are fundamental physiological processes essential for the maintenance of cellular and tissue homeostasis. There is great interest into the investigation of sphingolipids and their roles in regulating these key physiological processes as well as the manifestation of several disease states. With what is known to date, the entire scope of sphingolipid signaling is too broad, and a single review would hardly scratch the surface. Therefore, this review attempts to highlight the significance of sphingolipids in determining cell fate (e.g. apoptosis, autophagy, cell survival) in the context of the healthy lung, as well as various respiratory diseases including acute lung injury, acute respiratory distress syndrome, bronchopulmonary dysplasia, asthma, chronic obstructive pulmonary disease, emphysema, and cystic fibrosis. We present an overview of the latest findings related to sphingolipids and their metabolites, provide a short introduction to autophagy and apoptosis, and then briefly highlight the regulatory roles of sphingolipid metabolites in switching between cell survival and cell death. Finally, we describe functions of sphingolipids in autophagy and apoptosis in lung homeostasis, especially in the context of the aforementioned diseases.

ER stress and autophagy dysfunction contribute to fatty liver in diabetic mice

Diabetes mellitus and nonalcoholic fatty liver disease (NAFLD) are often identified in patients simultaneously. Recent evidence suggests that endoplasmic reticulum (ER) stress and autophagy dysfunction play an important role in hepatocytes injury and hepatic lipid metabolism, however the mechanistic interaction between diabetes and NAFLD is largely unknown. In this study, we used a diabetic mouse model to study the interplay between ER stress and autophagy during the pathogenic transformation of NAFLD. The coexist of inflammatory hepatic injury and hepatic accumulation of triglycerides (TGs) stored in lipid droplets indicated development of steatohepatitis in the diabetic mice. The alterations of components for ER stress signaling including ATF6, GRP78, CHOP and caspase12 indicated increased ER stress in liver tissues in early stage but blunted in the later stage during the development of diabetes. Likewise, autophagy functioned well in the early stage but suppressed in the later stage. The inactivation of unfolded protein response and suppression of autophagy were positively related to the development of steatohepatitis, which linked to metabolic abnormalities in the compromised hepatic tissues in diabetic condition. We conclude that the adaption of ER stress and impairment of autophagy play an important role to exacerbate lipid metabolic disorder contributing to steatohepatitis in diabetes.

Autophagy is a regulator of TGF-β1-induced fibrogenesis in primary human atrial myofibroblasts

Transforming growth factor-β₁ (TGF-β₁) is an important regulator of fibrogenesis in heart disease. In many other cellular systems, TGF-β₁ may also induce autophagy, but a link between its fibrogenic and autophagic effects is unknown. Thus we tested whether or not TGF-β₁-induced autophagy has a regulatory function on fibrosis in human atrial myofibroblasts (hATMyofbs). Primary hATMyofbs were treated with TGF-β₁ to assess for fibrogenic and autophagic responses. Using immunoblotting, immunofluorescence and transmission electron microscopic analyses, we found that TGF-β₁ promoted collagen type Iα2 and fibronectin synthesis in hATMyofbs and that this was paralleled by an increase in autophagic activation in these cells. Pharmacological inhibition of autophagy by bafilomycin-A1 and 3-methyladenine decreased the fibrotic response in hATMyofb cells. ATG7 knockdown in hATMyofbs and ATG5 knockout (mouse embryonic fibroblast) fibroblasts decreased the fibrotic effect of TGF-β₁ in experimental versus control cells. Furthermore, using a coronary artery ligation model of myocardial infarction in rats, we observed increases in the levels of protein markers of fibrosis, autophagy and Smad2 phosphorylation in whole scar tissue lysates. Immunohistochemistry for LC3β indicated the localization of punctate LC3β with vimentin (a mesenchymal-derived cell marker), ED-A fibronectin and phosphorylated Smad2. These results support the hypothesis that TGF-β₁-induced autophagy is required for the fibrogenic response in hATMyofbs.

Fatty acid signaling: the new function of intracellular lipases

Until recently, intracellular triacylglycerols (TAG) stored in the form of cytoplasmic lipid droplets have been considered to be only passive “energy conserves”. Nevertheless, degradation of TAG gives rise to a pleiotropic spectrum of bioactive intermediates, which may function as potent co-factors of transcription factors or enzymes and contribute to the regulation of numerous cellular processes. From this point of view, the process of lipolysis not only provides energy-rich equivalents but also acquires a new regulatory function. In this review, we will concentrate on the role that fatty acids liberated from intracellular TAG stores play as signaling molecules. The first part provides an overview of the transcription factors, which are regulated by fatty acids derived from intracellular stores. The second part is devoted to the role of fatty acid signaling in different organs/tissues. The specific contribution of free fatty acids released by particular lipases, hormone-sensitive lipase, adipose triacylglycerol lipase and lysosomal lipase will also be discussed.

Post-ovulatory aging of oocytes disrupts kinase signaling pathways and lysosome biogenesis

Post-ovulatory aging of oocytes results in the progressive loss of fertilization and developmental competence. This degradation of oocyte quality has been the object of numerous investigations, primarily focused on individual signaling pathways which provide limited insight into the status of global signaling events. The purpose of the present investigation was to comprehensively assess broad patterns of signaling pathway activity during in vitro aging as an initial step in defining control points that can be targeted to prevent the reduction in oocyte quality during prolonged culture. An antibody microarray-based phospho-proteome analysis performed on oocytes before and after eight hours of culture revealed significant changes in the abundance or activation state of 43 proteins that function in a wide variety of protein kinase-mediated signaling pathways. Several of the most significantly affected kinases were studied by Western blot and confocal immunofluorescence to corroborate the array results. Prolonged culture resulted in global changes in the abundance and activity of protein kinases that regulate the response to calcium, stress, and cell-cycle control. Examination of intracellular structures revealed a previously unrecognized increase in the abundance of large autophogagic lysosomes, which correlates with changes in protein kinase pathways. These results provide insight into the stresses experienced by oocytes during culture and the diversity of responses that results from them. The observed increase in autophagy-related activity, together with the disruptions in calcium signaling, cell-cycle, and stress-response pathways, have the potential to negatively impact oocyte quality by interfering with the normal sequence of biochemical changes that constitute egg activation following fertilization.

Autophagy response: manipulating the mTOR-controlled machinery by amino acids and pathogens

Macroautophagy is a self-degradative process that normally maintains cellular homeostasis via a lysosomal pathway. It is induced by different stress signals, including nutrients and growth factors' restriction as well as pathogen invasions. These stimuli are modulated by the serine/threonine protein kinase mammalian target of rapamycin (mTOR) which control not only autophagy but also protein translation and gene expression. This review focuses on the important role of mTOR as a master regulator of cell growth and the autophagy pathway. Here, we have discussed the role of intracellular amino acid availability and intracellular pH in the redistribution of autophagic structures, which may contribute to mammalian target of rapamycin complex 1 (mTORC1) activity regulation. We have also discussed that mTORC1 complex and components of the autophagy machinery are localized at the lysosomal surface, representing a fascinating mechanism to control the metabolism, cellular clearance and also to restrain invading intracellular pathogens.

Autophagy and microRNA dysregulation in liver diseases

Autophagy is a catabolic process through which organelles and cellular components are sequestered into autophagosomes and degraded via fusion with lysosomes. Autophagy plays a role in many physiological processes, including stress responses, energy homeostasis, elimination of cellular organelles, and tissue remodeling. In addition, autophagy capacity changes in various disease states. A series of studies have shown that autophagy is strictly controlled to maintain homeostatic balance of energy metabolism and cellular organelle and protein turnover. These studies have also shown that this process is post-transcriptionally controlled by small noncoding microRNAs that regulate gene expression through complementary base pairing with mRNAs. Conversely, autophagy regulates the expression of microRNAs. Therefore, dysregulation of the link between autophagy and microRNA expression exacerbates the pathogenesis of various diseases. In this review, we summarize the roles of autophagy and microRNA dysregulation in the course of liver diseases, with the aim of understanding how microRNAs modify key autophagic effector molecules, and we discuss how this dysregulation affects both physiological and pathological conditions. This article may advance our understanding of the cellular and molecular bases of liver disease progression and promote the development of strategies for pharmacological intervention.

Human placenta-derived mesenchymal stem cells promote hepatic regeneration in CCl4 -injured rat liver model via increased autophagic mechanism

Mesenchymal stem cells (MSCs) have great potential for cell therapy in regenerative medicine, including liver disease. Even though ongoing research is dedicated to the goal of bringing MSCs to clinical applications, further understanding of the complex underlying mechanisms is required. Autophagy, a type II programmed cell death, controls cellular recycling through the lysosomal system in damaged cells or tissues. However, it is still unknown whether MSCs can trigger autophagy to enhance regeneration and/or to provide a therapeutic effect as cellular survival promoters. We therefore investigated autophagy's activation in carbon tetrachloride (CCl4 )-injured rat liver following transplantation with chorionic plate-derived MSCs (CP-MSCs) isolated from placenta. The expression markers for apoptosis, autophagy, cell survival, and liver regeneration were analyzed. Whereas caspase 3/7 activities were reduced (p < .05), the expression levels of hypoxia-inducible factor-1α (HIF-1α) and factors for autophagy, survival, and regeneration were significantly increased by CP-MSCs transplantation. Decreased necrotic cells (p < .05) and increased autophagic signals (p < .005) were observed in CCl4 -treated primary rat hepatocytes during in vitro coculture with CP-MSCs. Furthermore, the upregulation of HIF-1α promotes the regeneration of damaged hepatic cells through an autophagic mechanism marked by increased levels of light chain 3 II (LC 3II). These results suggest that the administration of CP-MSCs promotes repair by systemically concomitant mechanisms involving HIF-1α and autophagy. These findings provide further understanding of the mechanisms involved in these processes and will help develop new cell-based therapeutic strategies for regenerative medicine in liver disease.

Autophagy in pancreatic acinar cells and pathogenesis of acute pancreatitis

Acute pancreatitis is an inflammatory disorder of the pancreas, and its pathogenesis remains poorly understood. Autodigestion of the pancreas by its own prematurely activated digestive proteases is a critical event in the onset of acute pancreatitis. Mitochondrial permeability transition results in mitochondrial depolarization and loss of ATP production, which has been found to induce autophagy in several cell types, e.g. cardiomyocytes and hepatocytes and is of vital importance for the fate of cells. Elucidating the relationship between mitochondrial permeability transition and autophagy within pancreatic acinar cells may enlighten the pathogenesis of acute pancreatitis and help provide potential therapeutic targets for this disease.

Inhibition of mTOR affects protein stability of OGT

Autophagy regulates cellular homeostasis through degradation of aged or damaged subcellular organelles and components. Interestingly, autophagy-deficient beta cells, for example Atg7-mutant mice, exhibited hypoinsulinemia and hyperglycemia. Also, autophagy response is diminished in heart of diabetic mice. These results implied that autophagy and diabetes are closely connected and affect each other. Although protein O-GlcNAcylation is up-regulated in hyperglycemia and diabetes, and O-GlcNAcylated proteins play an important role in metabolism and nutrient sensing, little is known whether autophagy affects O-GlcNAc modification and vice versa. In this study, we suppressed the action of mTOR by treatment of mTOR catalytic inhibitors (PP242 and Torin1) to induce autophagic flux. Results showed a decrease in global O-GlcNAcylation, which is due to decreased OGT protein and increased OGA protein. Interestingly, knockdown of ATG genes or blocking of lysosomal degradation enhanced protein stability of OGT. In addition, when proteasomal inhibitor was treated together with mTOR inhibitor, protein level of OGT almost recovered to control level. These data suggest that mTOR inhibition is a more efficient way to reduce protein level of OGT rather than that of CHX treatment. We also showed that not only proteasomal degradation regulated OGT stability but autophagic degradation also affected OGT stability in part. We concluded that mTOR signaling regulates protein O-GlcNAc modification through adjustment of OGT stability.

A combination of four active compounds alleviates cerebral ischemia-reperfusion injury in correlation with inhibition of autophagy and modulation of AMPK/mTOR and JNK pathways

SMXZF is a combination of Rb1, Rg1, schizandrin, and DT-13 (6:9:5:4) derived from Sheng-mai San, a widely used Chinese traditional medicine for the treatment of cardiovascular and cerebral diseases. The present study explores the inhibitory effects and signaling pathways of SMXZF on autophagy induced by cerebral ischemia-reperfusion injury. Male C57BL/6 mice were subjected to ischemia-reperfusion insult by right middle cerebral artery occlusion (MCAO) for 1 hr with subsequent 24 hr reperfusion. Three doses of SMXZF (4.5, 9, and 18 mg/kg) were administered intraperitoneally (i.p.) after ischemia for 1 hr. An autophagic inhibitor, 3-methyladenine (3-MA; 300 μg/kg), was administered i.p. 20 min before ischemia as a positive drug. We found that SMXZF significantly increased cerebral blood flow and reduced the infarct volume, brain water content, and the neurological deficits in a dose-dependent manner. Similar to the positive control, SMXZF at 18 mg/kg also significantly inhibited autophagosome formation. Immunofluorescence staining and Western blotting demonstrated that SMXZF could significantly decrease the expression levels of beclin1 and microtubule-associated protein 1 light chain 3. SMXZF also remarkably inhibited the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) as well as the expression of c-Jun N-terminal kinase (JNK) and its phosphorylation induced by 24 hr reperfusion. Finally, we demonstrated that the optimal administration time of SMXZF was at the early period of reperfusion. This study reveals that SMXZF displays neuroprotective effect against focal ischemia-reperfusion injury, possibly associated with autophagy inactivation through AMPK/mTOR and JNK pathways.

Mammalian Target of Rapamycin in Inflammatory Skin Conditions

The conserved serine/threonine kinase mammalian target of rapamycin (mTOR) is a major regulator of survival growth, proliferation and motility, in response to mitogens, energy and nutrient levels. Dysregulation of mTOR pathway has been observed in various inflammatory or neoplastic human diseases. To assess the potential involvement of mTOR in some of the most common inflammatory skin diseases, and its interaction with other inflammatory mediators, we investigated mTOR expression in psoriasis, allergic contact dermatitis (ACD) and atopic dermatitis (AD). mTOR gene expression was assessed in the following conditions: i) skin biopsies from 15 patients affected by psoriasis, 5 patients with ACD, 5 patients with AD and 3 patients with EGFR-inhibitor-induced skin rash; ii) in immortalized keratinocytes HaCaT, primary human keratinocytes (KCs) and full thickness skin organ cultures, incubated with tumor necrosis factor (TNF)-α, interleukin (IL) 17A or their combination; iii) in HaCaT cells stimulated with ultraviolet (UV)B; iv) in skin biopsies from 5 psoriatic patients before and after 16 weeks of anti-TNF-α therapy; mTOR expression was also evaluated through immunohistochemistry in lesional and non-lesional skin samples from 5 psoriatic patients. Moreover, mTOR major up-stream and down-stream regulator gene expression was assessed in skin biopsies from 15 patients affected by psoriasis, 5 patients with ACD, 5 patients with AD and 3 patients with EGFR-inhibitor-induced skin rash. All analyzed skin diseases showed an increase of mTOR gene expression whereas mTOR up-stream negative regulators were reduced or not enhanced in all of them. mTOR was strongly expressed in all epidermal layers of lesional and non-lesional psoriatic skin. Conversely, pro-inflammatory conditions, in vitro, were not able to increase mTOR levels, except for UVB. Similarly, anti-TNF-α therapy was not able to reduce mTOR gene expression in patients with psoriasis. Our study provides evidence that mTOR is involved in cutaneous inflammatory process, but through a signalling not directly dependent from Th1-Th17 pathway.

IPF fibroblasts are desensitized to type I collagen matrix-induced cell death by suppressing low autophagy via aberrant Akt/mTOR kinases

Idiopathic pulmonary fibrosis (IPF) is a chronic, lethal interstitial lung disease in which the aberrant PTEN/Akt axis plays a major role in conferring a survival phenotype in response to the cell death inducing properties of type I collagen matrix. The underlying mechanism by which IPF fibroblasts become desensitized to polymerized collagen, thereby eluding collagen matrix-induced cell death has not been fully elucidated. We hypothesized that the pathologically altered PTEN/Akt axis suppresses autophagy via high mTOR kinase activity, which subsequently desensitizes IPF fibroblasts to collagen matrix induced cell death. We found that the autophagosome marker LC3-2 expression is suppressed, while mTOR activity remains high when IPF fibroblasts are cultured on collagen. However, LC3-2 expression increased in response to IPF fibroblast attachment to collagen in the presence of rapamycin. In addition, PTEN over-expression or Akt inhibition suppressed mTOR activity, thereby increasing LC3-2 expression in IPF fibroblasts. Furthermore, the treatment of IPF fibroblasts over-expressing PTEN or dominant negative Akt with autophagy inhibitors increased IPF fibroblast cell death. Enhanced p-mTOR expression along with low LC3-2 expression was also found in myofibroblasts within the fibroblastic foci from IPF patients. Our data show that the aberrant PTEN/Akt/mTOR axis desensitizes IPF fibroblasts from polymerized collagen driven stress by suppressing autophagic activity, which produces a viable IPF fibroblast phenotype on collagen. This suggests that the aberrantly regulated autophagic pathway may play an important role in maintaining a pathological IPF fibroblast phenotype in response to collagen rich environment.

Important role of autophagy in regulation of metabolic processes in health, disease and aging

Autophagy is the basic catabolic mechanism that involves degradation of dysfunctional cellular components through the action of lysosome as well as supplying energy and compounds for the synthesis of essential biomacromolecules. This process enables cells to survive stress from the external environment like nutrient deprivation. Autophagy is important in the breakdown of proteins, carbohydrates and lipids as well. Furthermore, recent studies have shown that autophagy is critical in wide range of normal human physiological processes, and defective autophagy is associated with diverse diseases, including lysosomal storage disease, myopathies, neurodegeneration and various metabolic disorders. This review summarizes the most up-to-date findings on what role autophagy plays in metabolism.

Cardiovascular autophagy: crossroads of pathology, pharmacology and toxicology

Cardiovascular disease (CVD) remains the leading cause of death worldwide, despite the significant advances in medicine. Autophagy, a process of self-cannibalization employed by mammalian cells for the recycling of cellular contents, is altered not only in a number of CVDs, but in other diseases, as well. Many FDA-approved drugs are known to induce autophagy-mediated side effects in the cardiovascular system. In some cases, such drug-induced autophagy could be harnessed and used for treating CVD, greatly reducing the duration and cost of CVD treatments. However, because the induction of autophagy in cardiovascular targets can be both adaptive and maladaptive under specific settings, the challenge is to determine whether the changes stimulated by drug-induced autophagy are, in fact, beneficial. In this review, we surveyed a number of CVDs in which autophagy is known to occur, and we also address the role of FDA-approved drugs for which autophagy-mediated side effects occur within the cardiovascular system. The therapeutic potential of using small molecule modulators of autophagy in the management of CVD progression is discussed.

Atg7- and Keap1-dependent autophagy protects breast cancer cell lines against mitoquinone-induced oxidative stress

The interplay between oxidative stress and autophagy is critical for determining the fate of cancer cells exposed to redox-active and cytotoxic chemotherapeutic agents. Mitoquinone (MitoQ), a mitochondrially-targeted redox-active ubiquinone conjugate, selectively kills breast cancer cells over healthy mammary epithelial cells. We reported previously that MitoQ, although a derivative of the antioxidant ubiquinone, can generate excess ROS and trigger the Keap1-Nrf2 antioxidant response in the MDA-MB-231 cell line. Following MitoQ treatment, a greater number of cells underwent autophagy than apoptosis. However, the relationship between MitoQ-induced oxidative stress and autophagy as a primary cellular response was unclear. In this report, we demonstrate that MitoQ induces autophagy related gene 7 (Atg7)-dependent, yet Beclin-1-independent, autophagy marked by an increase in LC3-II. Both the ATG7-deficient human MDA-MB-231 cells and Atg7-knockout mouse embryonic fibroblasts exhibited lower levels of autophagy following MitoQ treatment than their respective wild-type counterparts. Increased apoptosis was confirmed in these autophagy-deficient isogenic cell line pairs, indicating that autophagy was attempted for survival in wild type cell lines. Furthermore, we observed higher levels of ROS in Atg7-deficient cells, as measured by hydroethidine oxidation. In Atg7-deficient cells, redox-sensitive Keap1 degradation was decreased, suggesting autophagy- and Atg7-dependent degradation of Keap1. Conversely, downregulation of Keap1 decreased autophagy levels, increased Nrf2 activation, upregulated cytoprotective antioxidant gene expression, and caused accumulation of p62, suggesting a feedback loop between ROS-regulated Keap1-Nrf2 and Atg7-regulated autophagy. Our data indicate that excessive ROS causes the upregulation of autophagy, and autophagy acts as an antioxidant feedback response triggered by cytotoxic levels of MitoQ.

Development of a novel method for quantification of autophagic protein degradation by AHA labeling

Autophagy is a catabolic process during which cellular components including protein aggregates and organelles are degraded via a lysosome-dependent process to sustain metabolic homeostasis during nutrient or energy deprivation. Measuring the rate of proteolysis of long-lived proteins is a classical assay for measurement of autophagic flux. However, traditional methods, such as a radioisotope labeling assay, are technically tedious and have low sensitivity. Here, we report a novel method for quantification of long-lived protein degradation based on L-azidohomoalanine (AHA) labeling in mouse embryonic fibroblasts (MEFs) and in human cancer cells. AHA is a surrogate for L-methionine, containing a bio-orthogonalazide moiety. When added to cultured cells, AHA is incorporated into proteins during active protein synthesis. After a click reaction between an azide and an alkyne, the azide-containing proteins can be detected with an alkyne-tagged fluorescent dye, coupled with flow cytometry. Induction of autophagy by starvation or mechanistic target of rapamycin (MTOR) inhibitors was able to induce a significant reduction of the fluorescence intensity, consistent with other autophagic markers. Coincidently, inhibition of autophagy by pharmacological agents or by Atg gene deletion abolished the reduction of the fluorescence intensity. Compared with the classical radioisotope pulse-labeling method, we think that our method is sensitive, quantitative, nonradioactive, and easy to perform, and can be applied to both human and animal cell culture systems.

Acute hyperglycemia together with hematoma of high-glucose blood exacerbates neurological injury in a rat model of intracerebral hemorrhage

Recent evidence suggests that admission hyperglycemia has deleterious effects on the survival and functional outcome of patients with intracerebral hemorrhage (ICH). In this study, we first induced acute hyperglycemia in male adult Sprague-Dawley rats by intraperitoneal injection of 50% glucose (6 mL/kg), and created the ICH model thereafter by delivering autologous whole blood or homologous normal-glucose blood into the right basal ganglia. Twenty-four hours later, we assessed the neurological injury, evaluated the hematoma and brain water content, and investigated autophagy. We found elevations of neurological deficit scores, brain water content, and microtubule-associated protein light chain-3 (LC3) and beclin-1 protein levels, and decreased SQSTM1/ p62 levels after ICH with normal-glucose blood (without hyperglycemia). Acute hyperglycemia with ICH of high-glucose blood hematoma was associated with significantly increased forelimb-use asymmetry test scores, brain water content and SQSTM1/p62 protein levels, and evident decreases in the ratio of LC3-II/LC3-I and beclin-1 protein levels. On the other hand, acute hyperglycemia and ICH with normal-glucose blood hematoma only slightly increased the neurological deficit scores and brain water content (P >0.05). In conclusion, the autophagy pathway was activated after ICH, and acute hyperglycemia with hematoma of high-glucose blood exacerbates the neurological injury, and reduces autophagy around the hematoma.

Autophagy and pancreatic β-cells

Autophagy plays a key role in maintaining pancreatic β-cell homeostasis. Deregulation of this process is associated with loss of β-cell mass and function, and it is likely to be involved in type 2 diabetes development and progression. Evidence that modulation of autophagy may be beneficial to preserve β-cell mass and function is beginning to accumulate although the complexity of this process, the intricate link between autophagy and apoptosis, and the fine balance between the protective and the disruptive role of autophagy make it very difficult to develop interventional strategies. This chapter provides an overview of the role of constitutive and adaptive autophagy in pancreatic β-cell and in the context of type 2 diabetes.

Purinergic receptor X7 is a key modulator of metabolic oxidative stress-mediated autophagy and inflammation in experimental nonalcoholic steatohepatitis

Recent studies indicate that metabolic oxidative stress, autophagy, and inflammation are hallmarks of nonalcoholic steatohepatitis (NASH) progression. However, the molecular mechanisms that link these important events in NASH remain unclear. In this study, we investigated the mechanistic role of purinergic receptor X7 (P2X7) in modulating autophagy and resultant inflammation in NASH in response to metabolic oxidative stress. The study uses two rodent models of NASH. In one of them, a CYP2E1 substrate bromodichloromethane is used to induce metabolic oxidative stress and NASH. Methyl choline-deficient diet feeding is used for the other NASH model. CYP2E1 and P2X7 receptor gene-deleted mice are used to establish their roles in regulating metabolic oxidative stress and autophagy. Autophagy gene expression, protein levels, confocal microscopy based-immunolocalization of lysosome-associated membrane protein (LAMP)2A and histopathological analysis were performed. CYP2E1-dependent metabolic oxidative stress induced increases in P2X7 receptor expression and chaperone-mediated autophagy markers LAMP2A and heat shock cognate 70 but caused depletion of light chain 3 isoform B (LC3B) protein levels. P2X7 receptor gene deletion significantly decreased LAMP2A and inflammatory indicators while significantly increasing LC3B protein levels compared with wild-type mice treated with bromodichloromethane. P2X7 receptor-deleted mice were also protected from NASH pathology as evidenced by decreased inflammation and fibrosis. Our studies establish that P2X7 receptor is a key regulator of autophagy induced by metabolic oxidative stress in NASH, thereby modulating hepatic inflammation. Furthermore, our findings presented here form a basis for P2X7 receptor as a potential therapeutic target in the treatment for NASH.

The role of sex differences in autophagy in the heart during coxsackievirus B3-induced myocarditis

Under normal conditions, autophagy maintains cardiomyocyte health and integrity through turnover of organelles. During stress, oxygen and nutrient deprivation, or microbial infection, autophagy prolongs cardiomyocyte survival. Sex differences in induction of cell death may to some extent explain the disparity between the sexes in many human diseases. However, sex differences in gene expression, which regulate cell death and autophagy, were so far not taken in consideration to explain the sex bias of viral myocarditis. Coxsackievirus B3 (CVB3)-induced myocarditis is a sex-biased disease, with females being substantially less susceptible than males and sex hormones largely determine this bias. CVB3 was shown to induce and subvert the autophagosome for its optimal viral RNA replication. Gene expression analysis on mouse and human, healthy and CVB3-infected, cardiac samples of both sexes, suggests sex differences in autophagy-related gene expression. This review discusses the aspects of sex bias in autophagy induction in cardiomyocytes.

Crosstalk between autophagy and inflammasomes

A variety of cellular stresses activate the autophagy pathway, which is fundamentally important in protection against injurious stimuli. Defects in the autophagy process are associated with a variety of human diseases, including inflammatory and metabolic diseases. The inflammasomes are emerging as key signaling platforms directing the maturation and secretion of interleukin-1 family cytokines in response to pathogenic and sterile stimuli. Recent studies have identified the critical role of inflammasome activation in host defense and inflammation. Delineation of the relationship between autophagy and inflammasome activation is now being greatly facilitated by the use of mice models of autophagy gene deficiency and clinical studies. We surveyed the recent research regarding the contribution of autophagy to the control of inflammation, in particular the association between autophagy and inflammasomes. Understanding the mechanisms by which autophagy balances inflammation might facilitate the development of autophagy-based therapeutic modalities for infectious and inflammatory diseases.

Impaired leukocytes autophagy in chronic kidney disease patients

BACKGROUND

Proteins and cytoplasmic organelles undergo degradation and recycling via autophagy; its role in patients with chronic kidney disease (CKD) is still unclear. We hypothesize that impaired kidney function causes autophagy activation failure.

METHODS

We included 60 patients with stage 5 CKD and 30 age- and sex-matched healthy subjects as controls. Patients with conditions that could affect autophagy were excluded. Leukocytes were isolated and analyzed from peripheral blood samples collected after overnight fasting and 2 h after breakfast.

RESULTS

Overnight fasting induced conversion of microtubule-associated protein-1 light chain 3 I to II (γLC3) and increased mRNA levels of the autophagy-related gene 5 (Atg5) and Beclin-1 in healthy subjects, which were nearly absent in CKD patients (p = 0.0001). Moreover, no significant difference in autophagy activation was observed between CKD patients with or without hemodialysis. Correlation studies showed that γLC3 was negatively associated with the left atrium size. Changes in Atg5 transcript levels were negatively associated with the left ventricular end-diastolic diameter, and changes in Beclin-1 transcript levels were negatively associated with the mitral inflow E- and A-wave sizes.

CONCLUSION

These data suggest that CKD patients have impaired autophagy activation, which cannot be reversed with hemodialysis and is closely related to their cardiac abnormalities.

Autophagy modulates cell migration and β1 integrin membrane recycling

Cell migration is dependent on a series of integrated cellular events including the membrane recycling of the extracellular matrix receptor integrins. In this paper, we investigate the role of autophagy in regulating cell migration. In a wound-healing assay, we observed that autophagy was reduced in cells at the leading edge than in cells located rearward. These differences in autophagy were correlated with the robustness of MTOR activity. The spatial difference in the accumulation of autophagic structures was not detected in rapamycin-treated cells, which had less migration capacity than untreated cells. In contrast, the knockdown of the autophagic protein ATG7 stimulated cell migration of HeLa cells. Accordingly, atg3(-/-) and atg5(-/-) MEFs have greater cell migration properties than their wild-type counterparts. Stimulation of autophagy increased the co-localization of β1 integrin-containing vesicles with LC3-stained autophagic vacuoles. Moreover, inhibition of autophagy slowed down the lysosomal degradation of internalized β1 integrins and promoted its membrane recycling. From these findings, we conclude that autophagy regulates cell migration, a central mechanism in cell development, angiogenesis, and tumor progression, by mitigating the cell surface expression of β1 integrins.

New insights into the pathology of podocyte loss: mitotic catastrophe

Podocytes represent an essential component of the kidney's glomerular filtration barrier. They stay attached to the glomerular basement membrane via integrin interactions that support the capillary wall to withstand the pulsating filtration pressure. Podocyte structure is maintained by a dynamic actin cytoskeleton. Terminal differentiation is coupled with permanent exit from the cell cycle and arrest in a postmitotic state. Postmitotic podocytes do not have an infinite life span; in fact, physiologic loss in the urine is documented. Proteinuria and other injuries accelerate podocyte loss or induce death. Mature podocytes are unable to replicate and maintain their actin cytoskeleton simultaneously. By the end of mitosis, cytoskeletal actin forms part of the contractile ring, rendering a round shape to podocytes. Therefore, when podocyte mitosis is attempted, it may lead to aberrant mitosis (ie, mitotic catastrophe). Mitotic catastrophe implies that mitotic podocytes eventually detach or die; this is a previously unrecognized form of podocyte loss and a compensatory mechanism for podocyte hypertrophy that relies on post-G1-phase cell cycle arrest. In contrast, local podocyte progenitors (parietal epithelial cells) exhibit a simple actin cytoskeleton structure and can easily undergo mitosis, supporting podocyte regeneration. In this review we provide an appraisal of the in situ pathology of mitotic catastrophe compared with other proposed types of podocyte death and put experimental and renal biopsy data in a unified perspective.