A novel Atg5-shRNA mouse model enables temporal control of Autophagy in vivo

Autophagy is a novel pathway for neurofilament protein degradation in vivo

How macroautophagy/autophagy influences neurofilament (NF) proteins in neurons, a frequent target in neurodegenerative diseases and injury, is not known. NFs in axons have exceptionally long half-lives in vivo enabling formation of large stable supporting networks, but they can be rapidly degraded during Wallerian degeneration initiated by a limited calpain cleavage. Here, we identify autophagy as a previously unrecognized pathway for NF subunit protein degradation that modulates constitutive and inducible NF turnover in vivo. Levels of NEFL/NF-L, NEFM/NF-M, and NEFH/NF-H subunits rise substantially in neuroblastoma (N2a) cells after blocking autophagy either with the phosphatidylinositol 3-kinase (PtdIns3K) inhibitor 3-methyladenine (3-MA), by depleting ATG5 expression with shRNA, or by using both treatments. In contrast, activating autophagy with rapamycin significantly lowers NF levels in N2a cells. In the mouse brain, NF subunit levels increase in vivo after intracerebroventricular infusion of 3-MA. Furthermore, using tomographic confocal microscopy, immunoelectron microscopy, and biochemical fractionation, we demonstrate the presence of NF proteins intra-lumenally within autophagosomes (APs), autolysosomes (ALs), and lysosomes (LYs). Our findings establish a prominent role for autophagy in NF proteolysis. Autophagy may regulate axon cytoskeleton size and responses of the NF cytoskeleton to injury and disease.

Transient Systemic Autophagy Inhibition Is Selectively and Irreversibly Deleterious to Lung Cancer

Autophagy is a conserved catabolic process that maintains cellular homeostasis. Autophagy supports lung tumorigenesis and is a potential therapeutic target in lung cancer. A better understanding of the importance of tumor cell-autonomous versus systemic autophagy in lung cancer could facilitate clinical translation of autophagy inhibition. Here, we exploited inducible expression of Atg5 shRNA to temporally control Atg5 levels and to generate reversible tumor-specific and systemic autophagy loss mouse models of KrasG12D/+;p53-/- (KP) non-small cell lung cancer (NSCLC). Transient suppression of systemic but not tumor Atg5 expression significantly reduced established KP lung tumor growth without damaging normal tissues. In vivo13C isotope tracing and metabolic flux analyses demonstrated that systemic Atg5 knockdown specifically led to reduced glucose and lactate uptake. As a result, carbon flux from glucose and lactate to major metabolic pathways, including the tricarboxylic acid cycle, glycolysis, and serine biosynthesis, was significantly reduced in KP NSCLC following systemic autophagy loss. Furthermore, systemic Atg5 knockdown increased tumor T-cell infiltration, leading to T-cell-mediated tumor killing. Importantly, intermittent transient systemic Atg5 knockdown, which resembles what would occur during autophagy inhibition for cancer therapy, significantly prolonged lifespan of KP lung tumor-bearing mice, resulting in recovery of normal tissues but not tumors. Thus, systemic autophagy supports the growth of established lung tumors by promoting immune evasion and sustaining cancer cell metabolism for energy production and biosynthesis, and the inability of tumors to recover from loss of autophagy provides further proof of concept that inhibition of autophagy is a valid approach to cancer therapy.

SIGNIFICANCE

Transient loss of systemic autophagy causes irreversible damage to tumors by suppressing cancer cell metabolism and promoting antitumor immunity, supporting autophagy inhibition as a rational strategy for treating lung cancer. See related commentary by Gan, p. 4322.

A Time and Place for Inhibiting Autophagy

Autophagy is an attractive therapeutic target in cancer. Successful autophagy-focused clinical intervention will require a detailed understanding of when and where autophagy is important during tumorigenesis. In this issue of Cancer Research, Khayati and colleagues use state-of-the-art genetically engineered mouse models to demonstrate that transient systemic inhibition of autophagy can irreversibly impair the growth of established lung tumors with a good tolerability in normal tissues, suggesting a therapeutic strategy for cancer treatment. See related article by Khayati et al., p. 4429.

Acute systemic knockdown of Atg7 is lethal and causes pancreatic destruction in shRNA transgenic mice

The notion that macroautophagy/autophagy is a potentially attractive therapeutic target for a variety of diseases, including cancer, largely stems from pre-clinical mouse studies. Most of these examine the effects of irreversible and organ confined autophagy deletion using site specific Cre-loxP recombination of the essential autophagy regulating genes Atg7 or Atg5. Model systems with the ability to impair autophagy systemically and reversibly at all disease stages would allow a more realistic approach to evaluate the consequences of authophagy inhibition as a therapeutic concept and its potential side effects. Here, we present shRNA transgenic mice that via doxycycline (DOX) regulable expression of a highly efficient miR30-E-based shRNA enabled knockdown of Atg7 simultaneously in the majority of organs, with the brain and spleen being noteable exceptions. Induced animals deteriorated rapidly and experienced profound destruction of the exocrine pancreas, severe hypoglycemia and depletion of hepatic glycogen storages. Cessation of DOX application restored apparent health, glucose homeostasis and pancreatic integrity. In a similar Atg5 knockdown model we neither observed loss of pancreatic integrity nor diminished survival after DOX treatment, but identified histological changes consistent with steatohepatitis and hepatic fibrosis in the recovery period after termination of DOX. Regulable Atg7-shRNA mice are valuable tools that will enable further studies on the role of autophagy impairment at various disease stages and thereby help to evaluate the consequences of acute autophagy inhibition as a therapeutic concept.Abbreviations: ACTB: actin, beta; AMY: amylase complex; ATG4B: autophagy related 4B, cysteine peptidase; ATG5: autophagy related 5; ATG7: autophagy related 7; Cag: CMV early enhancer/chicken ACTB promoter; Col1a1: collagen, type I, alpha 1; Cre: cre recombinase; DOX: doxycycline; GCG: glucagon; GFP: green fluorescent protein; INS: insulin; LC3: microtubule-associated protein 1 light chain 3; miR30-E: optimized microRNA backbone; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; PNLIP: pancreatic lipase; rtTA: reverse tetracycline transactivator protein; SQSTM1/p62: sequestome 1; TRE: tetracycline responsive element.

Autophagy promotes cell survival by maintaining NAD levels

Autophagy is an essential catabolic process that promotes the clearance of surplus or damaged intracellular components. Loss of autophagy in age-related human pathologies contributes to tissue degeneration through a poorly understood mechanism. Here, we identify an evolutionarily conserved role of autophagy from yeast to humans in the preservation of nicotinamide adenine dinucleotide (NAD) levels, which are critical for cell survival. In respiring mouse fibroblasts with autophagy deficiency, loss of mitochondrial quality control was found to trigger hyperactivation of stress responses mediated by NADases of PARP and Sirtuin families. Uncontrolled depletion of the NAD(H) pool by these enzymes ultimately contributed to mitochondrial membrane depolarization and cell death. Pharmacological and genetic interventions targeting several key elements of this cascade improved the survival of autophagy-deficient yeast, mouse fibroblasts, and human neurons. Our study provides a mechanistic link between autophagy and NAD metabolism and identifies targets for interventions in human diseases associated with autophagic, lysosomal, and mitochondrial dysfunction.

Autophagy at the intersection of aging, senescence, and cancer

Autophagy is an evolutionarily conserved cellular process in which macromolecules undergo lysosomal degradation. It fulfills essential roles in quality controlling cellular constituents and in energy homeostasis. Basal autophagy is also widely accepted to provide a protective role in aging and aging-related disorders, and its decline with age might precipitate the onset of a variety of diseases. In this review, we discuss the role of basal autophagy in maintaining homeostasis, in part through the maintenance of stem cell populations and the prevention of cellular senescence. We also consider how stress-induced senescence, for example, during oncogene activation and in premalignant disease, might rely on autophagy, and the possibility that the age-associated decline in autophagy might promote tumour development through a variety of mechanisms. Ultimately, evidence suggests that autophagy is required for malignant cancer progression in a number of settings. Thus, autophagy appears to be tumour-suppressive during the early stages of tumorigenesis and tumour-promoting at later stages.

Autophagy Blockage Reduces the Incidence of Pancreatic Ductal Adenocarcinoma in the Context of Mutant Trp53

Macroautophagy (hereafter referred to as autophagy) is a homeostatic process that preserves cellular integrity. In mice, autophagy regulates pancreatic ductal adenocarcinoma (PDAC) development in a manner dependent on the status of the tumor suppressor gene Trp53. Studies published so far have investigated the impact of autophagy blockage in tumors arising from Trp53-hemizygous or -homozygous tissue. In contrast, in human PDACs the tumor suppressor gene TP53 is mutated rather than allelically lost, and TP53 mutants retain pathobiological functions that differ from complete allelic loss. In order to better represent the patient situation, we have investigated PDAC development in a well-characterized genetically engineered mouse model (GEMM) of PDAC with mutant Trp53 (Trp53^R172H) and deletion of the essential autophagy gene Atg7. Autophagy blockage reduced PDAC incidence but had no impact on survival time in the subset of animals that formed a tumor. In the absence of Atg7, non-tumor-bearing mice reached a similar age as animals with malignant disease. However, the architecture of autophagy-deficient, tumor-free pancreata was effaced, normal acinar tissue was largely replaced with low-grade pancreatic intraepithelial neoplasias (PanINs) and insulin expressing islet β-cells were reduced. Our data add further complexity to the interplay between Atg7 inhibition and Trp53 status in tumorigenesis.

Magnesium Isoglycyrrhizinate Ameliorates Concanavalin A-Induced Liver Injury by Inhibiting Autophagy

Background and Aims: Acute liver failure (ALF) is a type of liver injury that is caused by multiple factors and leads to severe liver dysfunction; however, current treatments for ALF are insufficient. Magnesium isoglycyrrhizinate (MgIG), a novel glycyrrhizin extracted from the traditional Chinese medicine licorice, has a significant protective effect against concanavalin A (ConA)-induced liver injury, but its underlying therapeutic mechanism is unclear. Hence, this study aims to explore the potential therapeutic mechanism of MgIG against ConA-induced immune liver injury. Methods: ConA (20 mg/kg, i. v.) was administered for 12 h to construct an immune liver injury model, and the treatment group was given MgIG (30 mg/kg, i. p.) injection 1 h in advance. Lethality, liver injury, cytokine levels, and hepatocyte death were evaluated. The level of autophagy was evaluated by electron microscopy, RT-PCR and western blotting, and hepatocyte death was assessed in vitro by flow cytometry. Results: MgIG significantly increased the survival rate of mice and ameliorated severe liver injury mediated by ConA. The decrease in the number of autophagosomes, downregulation of LC3b expression and upregulation of p62 expression indicated that MgIG significantly inhibited ConA-induced autophagy in the liver. Reactivation of autophagy by rapamycin (RAPA) reversed the protective effect of MgIG against ConA-induced liver injury. Compared with MgIG treatment, activation of autophagy by RAPA also promoted the expression of liver inflammation markers (IL-1β, IL-6, TNF-α, CXCL-1, CXCL-2, CXCL-10, etc.) and hepatocyte death. In vitro experiments also showed that MgIG reduced ConA-induced hepatocyte death but did not decrease hepatocyte apoptosis by inhibiting autophagy. Conclusion: MgIG significantly ameliorated ConA-induced immune liver injury in mice by inhibiting autophagy. This study provides theoretical support for the ability of MgIG to protect against liver injury in clinical practice.

FGF21 alleviates acute liver injury by inducing the SIRT1-autophagy signalling pathway

Liver injury can lead to different hepatic diseases, which are the mainly causes of high global mortality and morbidity. Autophagy and Sirtuin type 1 (SIRT1) have been shown protective effects in response to liver injury. Previous studies have showed that Fibroblast growth factor 21 (FGF21) could alleviate acute liver injury (ALI), but the mechanism remains unclear. Here, we verified the relationship among FGF21, autophagy and SIRT1 in carbon tetrachloride (CCl₄)‐induced ALI. We established CCl₄‐induced ALI models in C57BL/6 mice and the L02 cell line. The results showed that FGF21 was robustly induced in response to stress during the development of ALI. After exogenous FGF21 treatment in ALI models, liver damage in ALI mice was significantly reduced, as well as serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Consistently, FGF21 also greatly reduced the levels of ALT, AST, pro‐inflammatory cytokines interleukin 6 (IL6) and tumour necrosis factor‐alpha (TNFα) in ALI cell lines. Mechanistically, exogenous FGF21 treatment efficiently upregulated the expression of autophagy marker microtubule‐associated protein light chain‐3 beta (LC3 II) and autophagy key molecule coiled‐coil myosin‐like BCL2‐interacting protein (Beclin1), which was accompanied by alleviating hepatotoxicity in CCl₄‐treated wild‐type mice. Then, we examined how FGF21 induced autophagy expression and found that SIRT1 was also upregulated by FGF21 treatment. To further verify our results, we constructed an anti‐SIRT1 lentit‐RNAi to inhibit SIRT1 expression in mice and L02 cells, which reversed the protective effect of FGF21 on ALI. In summary, these results indicate that FGF21 alleviates ALI by enhancing SIRT1‐mediated autophagy.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Gene Manipulation Protocols in Autophagy

Macroautophagy (referred to as autophagy hereafter) is a highly conserved catabolic process in eukaryotic cells. Autophagy is essential for cellular homeostasis through elimination and recycling of large cytoplasmic components, such as abnormal protein aggregates and damaged organelles, via lysosomal degradation. Since being originally identified by genetic screening in yeast, autophagy-related (ATG) genes have played a central role in autophagy research in different organisms, including plants, worms, flies, and mammals. Mouse models for monitoring autophagic activity or clarifying its biological functions have also been established. These mice are powerful tools to investigate roles of autophagy in vivo. Owing to the rapid technological advances in molecular biology, it is ever more efficient and simpler to manipulate autophagy-associated genes. Herein, we will introduce some commonly used approaches of gene silencing in mammalian cells, including CRIPSR/Cas9-mediated gene knockout and siRNA- and shRNA-mediated gene knockdown. We also summarized the common mouse models used for assessing autophagy. We hope to bring the researchers some useful information as they study autophagy.

The role of autophagy in hepatic fibrosis

Hepatic fibrosis is a chronic liver injury process, and its continuous development can lead to cirrhosis, hepatic failure and even hepatocellular carcinoma (HCC). Autophagy has attracted much attention because of its controversial role in the course of hepatic fibrosis. In this review, we introduce the mechanism related to noncoding RNAs and some of the signaling pathways that promote or inhibit fibrosis by affecting autophagy. Finally, we list some targets related to autophagy that enable hepatic fibrosis therapy and forecast its prospect in hepatic fibrosis. This review will provide new ideas in diagnosing and treating hepatic fibrosis, which will be helpful to reduce the incidence of cirrhosis and its complications.

Autophagy in liver diseases: A review

The liver is a highly dynamic metabolic organ that plays critical roles in plasma protein synthesis, gluconeogenesis and glycogen storage, cholesterol metabolism and bile acid synthesis as well as drug/xenobiotic metabolism and detoxification. Research from the past decades indicate that autophagy, the cellular catabolic process mediated by lysosomes, plays an important role in maintaining cellular and metabolic homeostasis in the liver. Hepatic autophagy fluctuates with hormonal cues and the availability of nutrients that respond to fed and fasting states as well as circadian activities. Dysfunction of autophagy in liver parenchymal and non-parenchymal cells can lead to various liver diseases including non-alcoholic fatty liver diseases, alcohol associated liver disease, drug-induced liver injury, cholestasis, viral hepatitis and hepatocellular carcinoma. Therefore, targeting autophagy may be a potential strategy for treating these various liver diseases. In this review, we will discuss the current progress on the understanding of autophagy in liver physiology. We will also discuss several forms of selective autophagy in the liver and the molecular signaling pathways in regulating autophagy of different cell types and their implications in various liver diseases.

A Local and Low-Dose Chemotherapy/Autophagy-Enhancing Regimen Treatment Markedly Inhibited the Growth of Established Solid Tumors Through a Systemic Antitumor Immune Response

Chemotherapy is one of the main options for the treatment of a variety of malignant tumors. However, the severe side effects resulting from the killing of normal proliferating cells limit the application of cancer-targeting chemotherapeutic drugs. To improve the efficacy of classic systemic chemotherapy, the local delivery of high-dose chemotherapeutic drugs was developed as a method to enhance local drug concentrations and minimize systemic toxicity. Studies have demonstrated that chemotherapy is often accompanied by cancer-associated immunogenic cell death (ICD) and that autophagy is involved in the induction of ICD. To improve the efficacy of local cancer chemotherapy, we hypothesized that the local delivery of chemotherapeutic plus autophagy-enhancing agents would enhance the promotive effects of ICD on the antitumor immune response. Here, we report that a low-dose chemotherapy/autophagy enhancing regimen (CAER) not only resulted in the increased death of B16F10 and 4T1 tumor cells, but also induced higher levels of autophagy in vitro. Importantly, the local delivery of the CARE drugs significantly inhibited tumor growth in B16F10 and 4T1 tumor-bearing mice. Systemic antitumor T-cell immunity was observed in vivo, including neoantigen-specific T-cell responses. Furthermore, bioinformatic analysis of human breast cancer and melanoma tissues showed that autophagy-associated gene expression was upregulated in tumor samples. Increased autophagy and immune cell infiltration in tumor tissues were positively correlated with good prognosis of tumor patients. This work highlights a new approach to improve the effects of local chemotherapy and enhance systemic antitumor immunity.

Autophagy and senescence, converging roles in pathophysiology as seen through mouse models

Both senescence and autophagy have been strongly linked to aging and also cancer development. Numerous molecular, cellular, and physiological changes are known to correlate with an increasing age, yet our understanding of what underlies these changes or how they combine to give rise to the various pathologies associated with aging is still unclear. Levels of autophagy activity are known to decrease with advancing age, in a variety of organisms including mammals. Whereas senescent cells are known to accumulate in our bodies with age. Herein we review evidence from some elegant genetic mouse models linking senescence and also autophagy to aging and cancer. It is especially interesting to note the convergence in the pathological phenotypes of these two processes, senescence and autophagy, in these mouse models.

Autophagy in the cancer-immunity dialogue

Autophagy is quintessential for the maintenance of cellular homeostasis in all eukaryotic cells, explaining why both normal and malignant cells benefit from proficient autophagic responses. Moreover, autophagy is intimately involved in the immunological control of malignant transformation, tumor progression and response to therapy. However, the net effect of autophagy activation or inhibition on the natural growth or therapeutic response of tumors evolving in immunocompetent hosts exhibits a considerable degree of context dependency. Here, we discuss the complex cross-talk between autophagy and immuno-oncology as delineated by genetic and pharmacological approaches in mouse models of cancer.

Chidamide, a histone deacetylase inhibitor, inhibits autophagy and exhibits therapeutic implication in chronic lymphocytic leukemia

Novel agents have made the management of chronic lymphocytic leukemia (CLL) more promising and personalized. However, long-term treatment is still warranted which may result in toxicity and resistance. Thus, new combination therapy may help achieve deeper remission and limited-duration therapy. Histone deacetylase inhibitors (HDACi) can affect many tumors by modulating key biological functions including autophagy. Studies have shown that some novel targeted agents including ibrutinib induce autophagy. This study aimed to explore the effect of oral HDAC inhibitor, chidamide, on CLL cells as well as the role of autophagy in this process. Here, we showed that autophagy flux in CLL cells was inhibited by chidamide via post-transcriptional modulation and chidamide had cytostatic and cytotoxic effects on CLL cells. Besides, the pro-survival role of autophagy in CLL cells was validated by using autophagy inhibitor and knocking down critical autophagy gene. Notably, a combination of chidamide and ibrutinib showed significant synergism and downregulated ibrutinib-induced autophagy. This work highlights the therapeutic potential of chidamide via its effect on autophagy, especially in combination with ibrutinib.

Self-eating: friend or foe? The emerging role of autophagy in fibrotic diseases

Fibrosis occurs in most human organs including the liver, lung, heart and kidney, and is crucial for the progression of most chronic diseases. As an indispensable catabolic process for intracellular quality control and homeostasis, autophagy occurs in most mammalian cells and is implicated in many biological processes including fibrogenesis. Although advances have been made in understanding autophagy process, the potential role of autophagy in fibrotic diseases remains controversial and has recently attracted a great deal of attention. In the current review, we summarize the commonalities of autophagy affecting different types of fibrosis in different organs, including the liver, lung, heart, and kidney as well as in cystic fibrosis, systematically outline the contradictory results and highlight the distinct role of autophagy during the various stages of fibrosis. In summary, the exact role autophagy plays in fibrogenesis depends on specific cell types and different stimuli, and identifying and evaluating the pathogenic contribution of autophagy in fibrogenesis will promote the discovery of novel therapeutic strategies for the clinical management of these fibrotic diseases.

Dynamic modulation of autophagy: implications for aging and cancer

Reduced autophagy has been implicated in aging, yet whether its loss can promote aging phenotypes and pathologies in mammals, and how reversible this process is, has never been fully explored. Using inducible short hairpin RNA (shRNA) mouse models, we have recently shown that autophagy inhibition accelerates aging, and that even a temporary block in autophagy can create irreversible damage that increases a cancer risk.

COX-2 in liver fibrosis

As a vital inducible sensor, cyclooxygenase-2 (COX-2) plays an important role in the progress of hepatic fibrogenesis. Activation of hepatic stellate cells (HSCs) in the liver can significantly accelerate the onset and development of liver fibrosis. COX-2 overexpression triggers inflammation that is an important inducer in hepatic fibrosis. Increasing evidence indicates that COX-2 is involved in the main pathogenesis of liver fibrosis, such as inflammation, apoptosis, and cell senescence. Moreover, COX-2 expression is altered in patients and animal models with non-alcoholic fatty liver disease or cirrhosis. These findings suggest that COX-2 has a broad and critical role in the development of liver fibrosis. In this review, we summarize the latest advances in the regulation and signal transduction of COX-2 and its impact on liver fibrosis.

Temporal inhibition of autophagy reveals segmental reversal of ageing with increased cancer risk

Autophagy is an important cellular degradation pathway with a central role in metabolism as well as basic quality control, two processes inextricably linked to ageing. A decrease in autophagy is associated with increasing age, yet it is unknown if this is causal in the ageing process, and whether autophagy restoration can counteract these ageing effects. Here we demonstrate that systemic autophagy inhibition induces the premature acquisition of age-associated phenotypes and pathologies in mammals. Remarkably, autophagy restoration provides a near complete recovery of morbidity and a significant extension of lifespan; however, at the molecular level this rescue appears incomplete. Importantly autophagy-restored mice still succumb earlier due to an increase in spontaneous tumour formation. Thus, our data suggest that chronic autophagy inhibition confers an irreversible increase in cancer risk and uncovers a biphasic role of autophagy in cancer development being both tumour suppressive and oncogenic, sequentially.

On ATG4B as Drug Target for Treatment of Solid Tumours-The Knowns and the Unknowns

Autophagy is an evolutionary conserved stress survival pathway that has been shown to play an important role in the initiation, progression, and metastasis of multiple cancers; however, little progress has been made to date in translation of basic research to clinical application. This is partially due to an incomplete understanding of the role of autophagy in the different stages of cancer, and also to an incomplete assessment of potential drug targets in the autophagy pathway. While drug discovery efforts are on-going to target enzymes involved in the initiation phase of the autophagosome, e.g., unc51-like autophagy activating kinase (ULK)1/2, vacuolar protein sorting 34 (Vps34), and autophagy-related (ATG)7, we propose that the cysteine protease ATG4B is a bona fide drug target for the development of anti-cancer treatments. In this review, we highlight some of the recent advances in our understanding of the role of ATG4B in autophagy and its relevance to cancer, and perform a critical evaluation of ATG4B as a druggable cancer target.

Ursodeoxycholic acid alleviates experimental liver fibrosis involving inhibition of autophagy

AIMS

Ursodeoxycholic acid (UDCA) has been widely used in the treatment of primary biliary cholangitis (PBC) with chronic liver fibrosis, but its detailed mechanism remains unclear. This study was aimed to determine whether autophagic signaling is involved in the therapeutic effect of UDCA on liver fibrosis.

METHODS

By using hepatic stellate cell (HSC) line LX2 and CCl₄-induced fibrotic rat model, autophagy signaling was investigated by western blotting and mRFP-EGFP-LC3 tandem fluorescent tagged plasmid (ptfLC3) transfection technique. Anti-fibrotic profile was determined by western blotting, qRT-PCR, MTT assay, trypan blue, hydroxyproline assay and Masson staining.

KEY FINDINGS

TGFβ1 treatment decreased P62 accumulation and increased both autophagosomes and autolysosomes in LX2 cells, thereby elevated autophagic flux. Hydroxychloroquine (HCQ), antagonist of autophagy, was found to dramatically inhibit COL1A2 mRNA expression and cell proliferation in a dose-dependent manner. This coincides with the effect of UDCA intervention on collagen aggradation and cell viability. Meanwhile, UDCA inhibited TGFβ1-induced autophagy flux. And rapamycin, agonist of autophagy, was found to impair the anti-fibrotic effect of UDCA. Moreover, study in vivo showed that UDCA alone or in combination with HCQ restored the CCl₄-induced liver fibrosis in rodent models with autophagy inhibited profile.

SIGNIFICANCE

Taken together, our study revealed that UDCA displays anti-fibrotic role by protecting HSC against production of collagen and inhibiting cellular viability involving autophagy inhibition and provide a new insight into the pharmacological basis of UDCA treatment for hepatic fibrosis.

Artificial tethering of LC3 or p62 to organelles is not sufficient to trigger autophagy

The retention using selective hooks (RUSH) system allows to retain a target protein fused to green fluorescent protein (GFP) and a streptavidin-binding peptide (SBP) due to the interaction with a molar excess of streptavidin molecules ("hooks") targeted to selected subcellular compartments. Supplementation of biotin competitively disrupts the interaction between the SBP moiety and streptavidin, liberating the chimeric target protein from its hooks, while addition of avidin causes the removal of biotin from the system and reestablishes the interaction. Based on this principle, we engineered two chimeric proteins involved in autophagy, namely microtubule-associated proteins 1A/1B light chain 3B (MAP1LC3B, best known as LC3) and sequestosome-1 (SQSTM1, best known as p62) to move them as SBP-GFP-LC3 and p62-SBP-GFP at will between the cytosol and two different organelles, the endoplasmic reticulum (ER) and the Golgi apparatus. Although both proteins were functional in thus far that SBP-GFP-LC3 and p62-SBP-GFP could recruit their endogenous binding partners, p62 and LC3, respectively, their enforced relocation to the ER or Golgi failed to induce organelle-specific autophagy. Hence, artificial tethering of LC3 or p62 to the surface of the ER and the Golgi is not sufficient to trigger autophagy.

Assessing autophagy in murine skeletal muscle: current findings to modulate and quantify the autophagic flux

PURPOSE OF REVIEW

In addition to the currently available lysosomotropic drugs and autophagy whole-body knockout mouse models, we provide alternative methods that enable the modulation and detection of autophagic flux in vivo, discussing advantages and disadvantages of each method.

RECENT FINDINGS

With the autophagosome-lysosome fusion inhibitor colchicine in skeletal muscle and temporal downregulation of autophagy using a novel Autophagy related 5-short hairpin RNA (Atg5-shRNA) mouse model we mention two models that directly modulate autophagy flux in vivo. Furthermore, methods to quantify autophagy flux, such as mitophagy transgenic reporters, in situ immunofluorescent staining and multispectral imaging flow cytometry, in mature skeletal muscle and cells are addressed.

SUMMARY

To achieve clinical benefit, less toxic, temporary and cell-type-specific modulation of autophagy should be pursued further. A temporary knockdown as described for the Atg5-shRNA mice could provide a first insight into possible implications of autophagy inhibition. However, it is also important to take a closer look into the methods to evaluate autophagy after harvesting the tissue. In particular caution is required when experimental conditions can influence the final measurement and this should be pretested carefully.

RAB18 modulates autophagy in human stellate cells

BACKGROUND

Macroautophagy (or autophagy) is a conserved degradative pathway that breaks down sequestered cytoplasmic proteins and organelles in specialized double-membrane compartments called autophagosomes that fuse with lysosomes. Several proteins orchestrate this process, specifically Rab GTPases that are master regulators of molecular trafficking. RAB18 GTPase, a known mediator of stellate cell activation, is known to modulate autophagic flux in fibroblasts. However, its role in autophagy is unexplored in hepatic stellate cells.

OBJECTIVE

The aim of this study was to investigate the role of RAB18 in modulating autophagy in hepatic stellate cells.

METHODS

Role of RAB18 was determined by genetic depletion, pharmacologic inhibition, and overexpression studies to monitor autophagy flux and proteostasis in human LX2 stellate cell line.

RESULTS

RAB18 knockdown increases autophagy flux and regulates proteostasis. LX2 cells stimulated with transforming growth factor-beta robustly increases expression of profibrotic genes such as COL1A1 and ACTA2 along with RAB18 and its guanine nucleotide exchange factor, RAB3GAP1.

CONCLUSION

The study elucidates a role for RAB18 in autophagy and regulation of proteostasis in human stellate cells. Molecular insights into this process can provide therapeutic opportunities for intervention in liver fibrosis.

Autophagy in liver diseases: Time for translation?

Autophagy is a self-eating catabolic pathway that contributes to liver homeostasis through its role in energy balance and in the quality control of the cytoplasm, by removing misfolded proteins, damaged organelles and lipid droplets. Autophagy not only regulates hepatocyte functions but also impacts on non-parenchymal cells, such as endothelial cells, macrophages and hepatic stellate cells. Deregulation of autophagy has been linked to many liver diseases and its modulation is now recognized as a potential new therapeutic strategy. Indeed, enhancing autophagy may prevent the progression of a number of liver diseases, including storage disorders (alpha-1 antitrypsin deficiency, Wilson's disease), acute liver injury, non-alcoholic steatohepatitis and chronic alcohol-related liver disease. Nevertheless, in some situations such as fibrosis, targeting specific liver cells must be considered, as autophagy displays opposing functions depending on the cell type. In addition, an optimal therapeutic time-window should be identified, since autophagy might be beneficial in the initial stages of disease, but detrimental at more advanced stages, as in the case of hepatocellular carcinoma. Finally, identifying biomarkers of autophagy and methods to monitor autophagic flux in vivo are important steps for the future development of personalized autophagy-targeting strategies. In this review, we provide an update on the regulatory role of autophagy in various aspects of liver pathophysiology, describing the different strategies to manipulate autophagy and discussing the potential to modulate autophagy as a therapeutic strategy in the context of liver diseases.