Macroautophagy and chaperone-mediated autophagy are required for hepatocyte resistance to oxidant stress

Chaperone-Mediated Autophagy Reactivation Protects Against Severe Acute Pancreatitis-Associated Liver Injury Through Upregulating Keap1/Nrf2 Signaling Pathway and Inhibiting NLRP3 Inflammasome Activation

Acute liver injury (ALI) is a vital factor in the early progression of severe acute pancreatitis (SAP). It exacerbates systemic inflammation, impairs the liver's capacity to clear inflammatory mediators and cytokines, and contributes to systemic organ dysfunction syndrome (SODS). However, the mechanisms driving SAP-associated liver injury (SAP-ALI) are poorly understood, and effective therapeutic options remain limited. Chaperone-mediated autophagy (CMA), a selective form of autophagy, plays an essential role in reducing inflammation and oxidative stress by clearing damaged or dysfunctional proteins. This study examines the role of CMA in SAP-ALI and evaluates its therapeutic potential. In a sodium taurocholate-induced SAP-ALI rat model, CMA dysfunction was observed, characterized by reduced LAMP2A expression and the accumulation of CMA substrate proteins in pancreatic and hepatic tissues. The activator AR7 successfully restored CMA function, enhanced anti-inflammatory and antioxidant responses, and mitigated pancreatic and liver damage in SAP rat. In contrast, the CMA inhibitor PPD exacerbated liver injury, underscoring CMA's protective role in SAP-ALI. Mechanistic analyses demonstrated that CMA reactivation activated the Keap1/Nrf2 signaling pathway, leading to increased expression of antioxidant-related genes and suppression of NLRP3 inflammasome activation. Specifically, the protective effects of AR7-induced CMA activation were significantly reversed by the Nrf2 inhibitor ML385, which inhibited Nrf2 signaling and its associated protein levels. These findings show AR7-induced CMA reactivation as a promising therapeutic strategy for SAP-ALI, primarily through its enhancement of Keap1/Nrf2-regulated antioxidant pathways and inhibition of NLRP3 inflammasome activation.

Multiple regulatory mechanisms, functions and therapeutic potential of chaperone-mediated autophagy

Autophagy refers to the proteolytic degradation of cytoplasmic components by lysosomes, and includes three defined types: macroautophagy, chaperone-mediated autophagy (CMA), and microautophagy. Although the regulatory pathways of macroautophagy are well defined, how CMA is accurately regulated remains less understood. In recent years, emerging evidence has suggested that chaperone-mediated autophagy is regulated by multiple mechanisms at nucleic acid and protein levels. In this review, we summarized recent progress on multiple regulatory mechanisms and functions concerning CMA, as well as novel treatments targeting specific regulation sites.

Paraoxonase-2 agonist vutiglabridin promotes autophagy activation and mitochondrial function to alleviate non-alcoholic steatohepatitis

BACKGROUND AND PURPOSE

Only limited therapeutic agents have been developed for non-alcoholic steatohepatitis (NASH). Glabridin, a promising anti-obesity candidate, has only limited druggability due to its low in vivo chemical stability and bioavailability. Therefore, we developed vutiglabridin (VUTI), which is based on a glabridin backbone, and investigated its mechanism of action in treating NASH in animal models.

EXPERIMENTAL APPROACH

Anti-NASH effects of VUTI were determined in in vitro fatty liver models, spheroids of primary human hepatocytes and L02 normal liver cell lines. To identify VUTI possible cellular target/s, biotin-labelled VUTI was synthesized and underwent chemical proteomic analysis. Further, the evaluation of VUTI therapeutic efficacy was carried out using an amylin-NASH and high-fat (HF) diet-induced obese (DIO) mouse models. This was carried out using transcriptomic, lipidomic and proteomic analyses of the livers from the amylin-NASH mouse model.

KEY RESULTS

VUTI treatment markedly reduces hepatic steatosis, fibrosis and inflammation by promoting lipid catabolism, activating autophagy and improving mitochondrial dysfunction, all of which are hallmarks of effective NASH treatment. The cellular target of VUTI was identified as paraoxonase 2 (PON2), a newly proposed protein target for the treatment of NASH, VUTI enhanced PON2 activity. The results using PON2 knockdown cells demonstrated that PON2 is important for VUTI- activation of autophagy, promoting mitochondrial function, decreasing oxidative stress and alleviating lipid accumulation under lipotoxic condition.

CONCLUSION AND IMPLICATIONS

Our data demonstrated that VUTI is a promising therapeutic for NASH. Targeting PON2 may be important for improving liver function in various immune-metabolic diseases including NASH.

Mefunidone ameliorates acute liver failure in mice by inhibiting MKK4-JNK pathway

Acute liver failure (ALF) is a critical condition that can lead to substantial liver dysfunction. It is characterized by complex clinical manifestations and rapid progression, presenting significant challenges in diagnosis and treatment. We investigated the protective effect of mefunidone (MFD), a novel antifibrosis pyridone agent, on ALF in mice, and explored its potential mechanism of action. MFD pretreatment can alleviate lipopolysaccharide (LPS) and d-galactosamine (D-GalN)-induced ALF, reduce hepatocyte apoptosis, and reduce inflammation and oxidative stress. Additionally, MFD alleviated LPS/D-GalN-stimulated reactive oxygen species (ROS) production and cell death in AML12 cells. RNA sequencing enrichment analysis showed that MFD significantly affected the Mitogen-Activated Protein Kinase (MAPK) pathway. In vivo and in vitro experiments showed that MFD inhibited MKK4 and JNK phosphorylation. JNK activation caused by MKK4 and JNK activators could eliminate the therapeutic effect of MFD on AML12. In addition, MFD pretreatment alleviated ConA-induced ALF, reduced inflammation and oxidative stress in mice, and reduced mouse mortality. These results suggest that MFD can potentially protect against ALF, partially by inhibiting the MKK4-JNK pathway, and is a promising new therapeutic drug for ALF.

Lipid droplets, autophagy, and ageing: A cell-specific tale

Lipid droplets are the essential organelle for storing lipids in a cell. Within the variety of the human body, different cells store, utilize and release lipids in different ways, depending on their intrinsic function. However, these differences are not well characterized and, especially in the context of ageing, represent a key factor for cardiometabolic diseases. Whole body lipid homeostasis is a central interest in the field of cardiometabolic diseases. In this review we characterize lipid droplets and their utilization via autophagy and describe their diverse fate in three cells types central in cardiometabolic dysfunctions: adipocytes, hepatocytes, and macrophages.

Nonalcoholic Fatty Liver Disease and Staging of Hepatic Fibrosis

Nonalcoholic fatty liver disease (NAFLD) is in parallel with the obesity epidemic, and it is the most common cause of liver diseases. The patients with severe insulin-resistant diabetes having high body mass index (BMI), high-grade adipose tissue insulin resistance, and high hepatocellular triacylglycerols (triglycerides; TAG) content develop hepatic fibrosis within a 5-year follow-up. Insulin resistance with the deficiency of insulin receptor substrate-2 (IRS-2)-associated phosphatidylinositol 3-kinase (PI3K) activity causes an increase in intracellular fatty acid-derived metabolites such as diacylglycerol (DAG), fatty acyl CoA, or ceramides. Lipotoxicity-related mechanism of NAFLD could be explained still best by the "double-hit" hypothesis. Insulin resistance is the major mechanism in the development and progression of NAFLD/nonalcoholic steatohepatitis (NASH). Metabolic oxidative stress, autophagy, and inflammation induce NASH progression. In the "first hit" the hepatic concentrations of diacylglycerol increase with an increase in saturated liver fat content in human NAFLD. Activities of mitochondrial respiratory chain complexes are decreased in the liver tissue of patients with NASH. Hepatocyte lipoapoptosis is a critical feature of NASH. In the "second hit," reduced glutathione levels due to oxidative stress lead to the overactivation of c-Jun N-terminal kinase (JNK)/c-Jun signaling that induces cell death in the steatotic liver. Accumulation of toxic levels of reactive oxygen species (ROS) is caused at least by two ineffectual cyclical pathways. First is the endoplasmic reticulum (ER) oxidoreductin (Ero1)-protein disulfide isomerase oxidation cycle through the downstream of the inner membrane mitochondrial oxidative metabolism and the second is the Kelch like-ECH-associated protein 1 (Keap1)-nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathways. In clinical practice, on ultrasonographic examination, the elevation of transaminases, γ-glutamyltransferase, and the aspartate transaminase to platelet ratio index indicates NAFLD. Fibrosis-4 index, NAFLD fibrosis score, and cytokeratin18 are used for grading steatosis, staging fibrosis, and discriminating the NASH from simple steatosis, respectively. In addition to ultrasonography, "controlled attenuation parameter," "magnetic resonance imaging proton-density fat fraction," "ultrasound-based elastography," "magnetic resonance elastography," "acoustic radiation force impulse elastography imaging," "two-dimensional shear-wave elastography with supersonic imagine," and "vibration-controlled transient elastography" are recommended as combined tests with serum markers in the clinical evaluation of NAFLD. However, to confirm the diagnosis of NAFLD, a liver biopsy is the gold standard. Insulin resistance-associated hyperinsulinemia directly accelerates fibrogenesis during NAFLD development. Although hepatocyte lipoapoptosis is a key driving force of fibrosis progression, hepatic stellate cells and extracellular matrix cells are major fibrogenic effectors. Thereby, these are pharmacological targets of therapies in developing hepatic fibrosis. Nonpharmacological management of NAFLD mainly consists of two alternatives: lifestyle modification and metabolic surgery. Many pharmacological agents that are thought to be effective in the treatment of NAFLD have been tried, but due to lack of ability to attenuate NAFLD, or adverse effects during the phase trials, the vast majority could not be licensed.

Protein kinases: The key contributors in pathogenesis and treatment of nonalcoholic fatty liver disease-derived hepatocellular carcinoma

Protein kinases (PKs), one of the largest protein families, can be further divided into different groups based on their substrate or structure and function. PKs are important signaling messengers in numerous life activities, including cell metabolism, proliferation, division, differentiation, senescence, death, and disease. Among PK-related diseases, nonalcoholic fatty liver disease (NAFLD) has been recognized as a major contributor to hepatocellular carcinoma (HCC) and liver transplantation. Unfortunately, NAFLD-derived HCC (NAFLD-HCC) has poor prognosis because it is typically accompanied by older age, multiple metabolic syndromes, obstacles in early-stage diagnosis, and limited licensed drugs for treatment. Accumulating evidence suggests that PKs are implicated in the pathogenic process of NAFLD-HCC, via aberrant metabolism, hypoxia, autophagy, hypoxia, gut microbiota dysbiosis, and/or immune cell rearrangement. The present review aims to summarize the latest research advances and emphasize the feasibility and effectiveness of therapeutic strategies that regulate the expression and activities of PKs. This might yield clinically significant effects and lead to the design of novel PK-targeting therapies. Furthermore, we discuss emerging PK-based strategies for the treatment of other malignant diseases similar to NAFLD-HCC.

Chaperone-mediated autophagy: Molecular mechanisms, biological functions, and diseases

Chaperone-mediated autophagy (CMA) is a lysosomal degradation pathway that eliminates substrate proteins through heat-shock cognate protein 70 recognition and lysosome-associated membrane protein type 2A-assisted translocation. It is distinct from macroautophagy and microautophagy. In recent years, the regulatory mechanisms of CMA have been gradually enriched, including the newly discovered NRF2 and p38-TFEB signaling, as positive and negative regulatory pathways of CMA, respectively. Normal CMA activity is involved in the regulation of metabolism, aging, immunity, cell cycle, and other physiological processes, while CMA dysfunction may be involved in the occurrence of neurodegenerative disorders, tumors, intestinal disorders, atherosclerosis, and so on, which provides potential targets for the treatment and prediction of related diseases. This article describes the general process of CMA and its role in physiological activities and summarizes the connection between CMA and macroautophagy. In addition, human diseases that concern the dysfunction or protective role of CMA are discussed. Our review deepens the understanding of the mechanisms and physiological functions of CMA and provides a summary of past CMA research and a vision of future directions.

Higher pNRF2, SOCS3, IRF3, and RIG1 Tissue Protein Expression in NASH Patients versus NAFL Patients: pNRF2 Expression Is Concomitantly Associated with Elevated Fasting Glucose Levels

Non-alcoholic fatty liver disease (NAFLD) embraces simple steatosis in non-alcoholic fatty liver (NAFL) to advanced non-alcoholic steatohepatitis (NASH) associated with inflammation, fibrosis, and cirrhosis. NAFLD patients often have metabolic syndrome and high risks of cardiovascular and liver-related mortality. Our aim was to clarify which proteins play a role in the progression of NAFL to NASH. The study investigates paraffin-embedded samples of 22 NAFL and 33 NASH patients. To detect potential candidates, samples were analyzed by immunohistochemistry for the proteins involved in innate immune regulation, autophagy, apoptosis, and antioxidant defense: IRF3, RIG-1, SOCS3, pSTAT3, STX17, SGLT2, Ki67, M30, Caspase 3, and pNRF2. The expression of pNRF2 immunopositive nuclei and SOCS3 cytoplasmic staining were higher in NASH than in NAFL (p = 0.001); pNRF2 was associated with elevated fasting glucose levels. SOCS3 immunopositivity correlated positively with RIG1 (r = 0.765; p = 0.001). Further, in NASH bile ducts showed stronger IRF3 immunostaining than in NAFL (p = 0.002); immunopositive RIG1 tissue was higher in NASH than in NAFL (p = 0.01). Our results indicate that pNRF2, SOCS3, IRF3, and RIG1 are involved in hepatic lipid metabolism. We suggest that they may be suitable for further studies to assess their potential as therapeutics.

Defective chaperone-mediated autophagy is a hallmark of joint disease in patients with knee osteoarthritis

OBJECTIVE

Defects in autophagy contribute to joint aging and Osteoarthritis (OA). Identifying specific autophagy types could be useful for developing novel treatments for OA.

DESIGN

An autophagy-related gene array was performed in blood from non-OA and knee OA subjects from the Prospective Cohort of A Coruña (PROCOAC). The differential expression of candidate genes was confirmed in blood and knee cartilage and a regression analysis was performed adjusting for age and BMI. HSP90A, a chaperone mediated autophagy (CMA) marker was validated in human knee joint tissues, as well as, in mice with aging-related and surgically-induced OA. The consequences of HSP90AA1 deficiency were evaluated on OA pathogenesis. Finally, the contribution of CMA to homeostasis was studied by assessing the capacity to restore proteostasis upon ATG5-mediated macroautophagy deficiency and genetic HSP90AA1 overexpression.

RESULTS

16 autophagy-related genes were significantly down-regulated in blood from knee OA subjects. Validation studies showed that HSP90AA1 was down-regulated in blood and human OA cartilage and correlated with risk incidence of OA. Moreover, HSP90A was reduced in human OA joints tissues and with aging and OA in mice. HSP90AA1 knockdown was linked to defective macroautophagy, inflammation, oxidative stress, senescence and apoptosis. However, macroautophagy deficiency increased CMA, highlighting the CMA-macroautophagy crosstalk. Remarkably, CMA activation was sufficient to protect chondrocytes from damage.

CONCLUSIONS

We show that HSP90A is a key chaperone for chondrocyte homeostasis, while defective CMA contributes to joint damage. We propose that CMA deficiency is a relevant disease mechanism and could represent a therapeutic target for OA.

Autophagy: A Key Regulator of Homeostasis and Disease: An Overview of Molecular Mechanisms and Modulators

Autophagy is a highly conserved lysosomal degradation pathway active at basal levels in all cells. However, under stress conditions, such as a lack of nutrients or trophic factors, it works as a survival mechanism that allows the generation of metabolic precursors for the proper functioning of the cells until the nutrients are available. Neurons, as post-mitotic cells, depend largely on autophagy to maintain cell homeostasis to get rid of damaged and/or old organelles and misfolded or aggregated proteins. Therefore, the dysfunction of this process contributes to the pathologies of many human diseases. Furthermore, autophagy is highly active during differentiation and development. In this review, we describe the current knowledge of the different pathways, molecular mechanisms, factors that induce it, and the regulation of mammalian autophagy. We also discuss its relevant role in development and disease. Finally, here we summarize several investigations demonstrating that autophagic abnormalities have been considered the underlying reasons for many human diseases, including liver disease, cardiovascular, cerebrovascular diseases, neurodegenerative diseases, neoplastic diseases, cancers, and, more recently, infectious diseases, such as SARS-CoV-2 caused COVID-19 disease.

Identification of Hub Genes Associated With Non-alcoholic Steatohepatitis Using Integrated Bioinformatics Analysis

Background and aims: As a major cause of liver disease worldwide, non-alcoholic fatty liver disease (NAFLD) comprises non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH). Due to the high prevalence and poor prognosis of NASH, it is critical to understand its mechanisms. However, the etiology and mechanisms remain largely unknown. In addition, the gold standard for the diagnosis of NASH is liver biopsy, which is an invasive procedure. Therefore, there is a pressing need to develop noninvasive tests for NASH diagnosis. The goal of the study is to discover key genes involved in NASH development and investigate their value as noninvasive biomarkers.

Methods: The Gene Expression Omnibus (GEO) database was used to obtain two datasets encompassing NASH patients and healthy controls. We used weighted gene co-expression network analysis (WGCNA) and differential expression analysis in order to investigate the association between gene sets and clinical features, as well as to discover co-expression modules. A protein-protein interaction (PPI) network was created to extract hub genes. The results were validated using another publicly available dataset and mice treated with a high-fat diet (HFD) and carbon tetrachloride (CCl4).

Results: A total of 24 differentially co-expressed genes were selected by WGCNA and differential expression analysis. KEGG analysis indicated most of them were enriched in the focal adhesion pathway. GO analysis showed these genes were mainly enriched in circadian rhythm, aging, angiogenesis and response to drug (biological process), endoplasmic reticulum lumen (cellular component), and protein binding (molecular function). As a result, eight genes (JUN, SERPINE1, GINS2, TYMS, HMMR, IGFBP2, BIRC3, TNFRSF12A) were identified as hub genes. Finally, three genes were found significantly changed in both the validation dataset and the mouse model.

Conclusion: Our research discovered genes that have the potential to mediate the process of NASH and might be useful diagnostic biomarkers for the disorder.

Combination of Ascorbic Acid and Menadione Induces Cytotoxic Autophagy in Human Glioblastoma Cells

We investigated the ability of the ascorbic acid (AA) and menadione (MD) combination, the well-known reactive oxidative species- (ROS-) generating system, to induce autophagy in human U251 glioblastoma cells. A combination of AA and MD (AA+MD), in contrast to single treatments, induced necrosis-like cell death mediated by mitochondrial membrane depolarization and extremely high oxidative stress. AA+MD, and to a lesser extent MD alone, prompted the appearance of autophagy markers such as autophagic vacuoles, autophagosome-associated LC3-II protein, degradation of p62, and increased expression of beclin-1. While both MD and AA+MD increased phosphorylation of AMP-activated protein kinase (AMPK), the well-known autophagy promotor, only the combined treatment affected its downstream targets, mechanistic target of rapamycin complex 1 (mTORC1), Unc 51-like kinase 1 (ULK1), and increased the expression of several autophagy-related genes. Antioxidant N-acetyl cysteine reduced both MD- and AA+MD-induced autophagy, as well as changes in AMPK/mTORC1/ULK1 activity and cell death triggered by the drug combination. Pharmacological and genetic autophagy silencing abolished the toxicity of AA+MD, while autophagy upregulation enhanced the toxicity of both AA+MD and MD. Therefore, by upregulating oxidative stress, inhibiting mTORC1, and activating ULK1, AA converts MD-induced AMPK-dependent autophagy from nontoxic to cytotoxic. These results suggest that AA+MD or MD treatment in combination with autophagy inducers could be further investigated as a novel approach for glioblastoma therapy.

The regulation, function, and role of lipophagy, a form of selective autophagy, in metabolic disorders

Autophagy is a conserved method of quality control in which cytoplasmic contents are degraded via lysosomes. Lipophagy, a form of selective autophagy and a novel type of lipid metabolism, has recently received much attention. Lipophagy is defined as the autophagic degradation of intracellular lipid droplets (LDs). Although much remains unknown, lipophagy appears to play a significant role in many organisms, cell types, metabolic states, and diseases. It participates in the regulation of intracellular lipid storage, intracellular free lipid levels (e.g., fatty acids), and energy balance. However, it remains unclear how intracellular lipids regulate autophagy. Impaired lipophagy can cause cells to become sensitive to death stimuli and may be responsible for the onset of a variety of diseases, including nonalcoholic fatty liver disease and metabolic syndrome. Like autophagy, the role of lipophagy in cancer is poorly understood, although analysis of specific autophagy receptors has helped to expand the diversity of chemotherapeutic targets. These studies have stimulated increasing interest in the role of lipophagy in the pathogenesis and treatment of cancer and other human diseases.

The Role of Chaperone-Mediated Autophagy in Bortezomib Resistant Multiple Myeloma

Background: Multiple myeloma (MM) remains incurable despite high-dose chemotherapy, autologous stem cell transplants and novel agents. Even with the improved survival of MM patients treated with novel agents, including bortezomib (Bz), the therapeutic options in relapsed/refractory MM remain limited. The majority of MM patients eventually develop resistance to Bz, although the mechanisms of the resistance are poorly understood. Methods: Lysosomal associated membrane protein 2A (LAMP2A) mRNA and protein expression levels were assessed in ex vivo patient samples and a Bz-resistant MM cell line model by in real-rime PCR, western blotting and immunohistochemistry. In vitro modelling of chaperone-mediated autophagy (CMA) activity in response to ER stress were assessed by western blotting and confocal microscopy. The effects of CMA inhibition on MM cell viability and Bz sensitivity in MM cells were assessed by Annexin V/7AAD apoptosis assays using flow cytometry. Results: In this study, there is evidence that CMA, a chaperone-mediated protein degradation pathway, is upregulated in Bz-resistant MM and the inhibition of CMA sensitises resistant cells to Bz. The protein levels of LAMP2A, the rate-limiting factor of the CMA pathway, are significantly increased in MM patients resistant to Bz and within our Bz-resistant cell line model. Bz-resistant cell lines also possessed higher basal CMA activity than the Bz-sensitive parent cell line. In MM cell lines, CMA activity was upregulated in response to ER stress induced by Bz. The inhibition of CMA sensitises Bz-resistant cells to Bz and the combination of CMA inhibition and Bz in vitro had a more cytotoxic effect on myeloma cells than Bz alone. Conclusion: In summary, the upregulation of CMA is a potential mechanism of resistance to Bz and a novel target to overcome Bz-resistant MM.

A Decade of Mighty Lipophagy: What We Know and What Facts We Need to Know?

Lipids are integral cellular components that act as substrates for energy provision, signaling molecules, and essential constituents of biological membranes along with a variety of other biological functions. Despite their significance, lipid accumulation may result in lipotoxicity, impair autophagy, and lysosomal function that may lead to certain diseases and metabolic syndromes like obesity and even cell death. Therefore, these lipids are continuously recycled and redistributed by the process of selective autophagy specifically termed as lipophagy. This selective form of autophagy employs lysosomes for the maintenance of cellular lipid homeostasis. In this review, we have reviewed the current literature about how lipid droplets (LDs) are recruited towards lysosomes, cross-talk between a variety of autophagy receptors present on LD surface and lysosomes, and lipid hydrolysis by lysosomal enzymes. In addition to it, we have tried to answer most of the possible questions related to lipophagy regulation at different levels. Moreover, in the last part of this review, we have discussed some of the pathological states due to the accumulation of these LDs and their possible treatments under the light of currently available findings.

Natural Products in Therapeutic Management of Multineurodegenerative Disorders by Targeting Autophagy

Autophagy is an essential cellular process that involves the transport of cytoplasmic content in double-membraned vesicles to lysosomes for degradation. Neurons do not undergo cytokinesis, and thus, the cell division process cannot reduce levels of unnecessary proteins. The primary cause of neurodegenerative disorders (NDs) is the abnormal deposition of proteins inside neuronal cells, and this could be averted by autophagic degradation. Thus, autophagy is an important consideration when considering means of developing treatments for NDs. Various pharmacological studies have reported that the active components in herbal medicines exhibit therapeutic benefits in NDs, for example, by inhibiting cholinesterase activity and modulating amyloid beta levels, and α-synuclein metabolism. A variety of bioactive constituents from medicinal plants are viewed as promising autophagy controllers and are revealed to recover the NDs by targeting the autophagic pathway. In the present review, we discuss the role of autophagy in the therapeutic management of several NDs. The molecular process responsible for autophagy and its importance in various NDs and the beneficial effects of medicinal plants in NDs by targeting autophagy are also discussed.

Celecoxib Analogues for Cancer Treatment: An Update on OSU-03012 and 2,5-Dimethyl-Celecoxib

Cyclooxygenase-2 (COX-2) is an important enzyme involved in prostaglandins biosynthesis from arachidonic acid. COX-2 is frequently overexpressed in human cancers and plays a major tumor promoting function. Accordingly, many efforts have been devoted to efficiently target the catalytic site of this enzyme in cancer cells, by using COX-2 specific inhibitors such as celecoxib. However, despite their potent anti-tumor properties, the myriad of detrimental effects associated to the chronic inhibition of COX-2 in healthy tissues, has considerably limited their use in clinic. In addition, increasing evidence indicate that these anti-cancerous properties are not strictly dependent on the inhibition of the catalytic site. These findings have led to the development of non-active COX-2 inhibitors analogues aiming at preserving the antitumor effects of COX-2 inhibitors without their side effects. Among them, two celecoxib derivatives, 2,5-Dimethyl-Celecoxib and OSU-03012, have been developed and suggested for the treatment of viral (e.g., recently SARS-CoV-2), inflammatory, metabolic diseases and cancers. These molecules display stronger anti-tumor properties than celecoxib and thus may represent promising anti-cancer molecules. In this review, we discuss the impact of these two analogues on cancerous processes but also their potential for cancer treatment alone or in combination with existing approaches.

Extended criteria grafts and emerging therapeutics strategy in liver transplantation. The unstable balance between damage and repair

Due to increasing demand for donor organs, "extended criteria" donors are increasingly considered for liver transplantation, including elderly donors and donors after cardiac death. The grafts of this subgroup of donors share a major risk to develop significant features of ischemia reperfusion injury, that may eventually lead to graft failure. Ex-situ machine perfusion technology has gained much interest in liver transplantation, because represents both a useful tool for improving graft quality before transplantation and a platform for the delivery of therapeutics directly to the organ. In this review, we survey ongoing clinical evidences supporting the use of elderly and DCD donors in liver transplantation, and the underlying mechanistic aspects of liver aging and ischemia reperfusion injury that influence graft quality and transplant outcome. Finally, we highlight evidences in the field of new therapeutics to test in MP in the context of recent findings of basic and translational research.

Lipotoxicity reduces DDX58/Rig-1 expression and activity leading to impaired autophagy and cell death

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease globally. NAFLD is a consequence of fat accumulation in the liver leading to lipotoxicity. Increasing evidence has demonstrated the critical role of autophagy in NAFLD. This study uncovers the unexpected role of immune surveillance protein DDX58/Rig-1 (DExD/H box helicase 58) in activating macroautophagy/autophagy and protecting from lipotoxicity associated with NAFLD. Here we show for the first time that DDX58 protein is significantly reduced in nonalcoholic steatohepatitis (NASH) mouse model, an aggressive form of NAFLD characterized by inflammation and fibrosis of the liver. In addition to decreased expression of DDX58, we found that DDX58 activity can be attenuated by treatments with palmitic acid (PA), a saturated fatty acid. To investigate whether PA inhibition of DDX58 is harmful to the cell, we characterized DDX58 function in hepatocytes when exposed to high doses of PA in the presence and/or absence of DDX58. We show that siRNA knockdown of DDX58 promotes apoptosis. Importantly, we show that stable overexpression of DDX58 is protective against toxic levels of PA and stimulates autophagy. This study begins to demonstrate the regulation of the autophagy receptor protein SQSTM1/p62 through DDX58. DDX58 expression directly influences SQSTM1 mRNA and protein levels. This work proposes a model in which activating DDX58 increases an autophagic response and this aids in clearing toxic lipid inclusion bodies, which leads to inflammation and apoptosis. Activating a DDX58-induced autophagy response may be a strategy for treating NAFLD.Abbreviations:5'pppdsRNA: 5' triphosphate double-stranded RNA; CDAHFD: choline-deficient, L-amino acid defined high-fat diet; CEBPB: CCAAT/enhancer binding protein (C/EBP), beta; CQ: chloroquine; DDX58/retinoic acid inducible gene 1/Rig-1: DExD/H box helicase 58; h: hours; IFIH1/MDA5: interferon induced with helicase C domain 1; IFNB/IFN-β: interferon beta 1, fibroblast; KO: knockout; MAVS: mitochondrial antiviral signaling protein; NAFLD: nonalcoholic fatty liver disease; NASH: nonalcoholic steatohepatitis; NFKB/NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; PA: palmitic acid; poly:IC: polyinosinic:polycytidylic acid; PRR: pattern recognition receptors; PSR: picrosirus red; RAP: rapamycin; RLR: RIG-I-like receptor; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK-binding kinase 1.

Dexmedetomidine Protects Against Septic Liver Injury by Enhancing Autophagy Through Activation of the AMPK/SIRT1 Signaling Pathway

Background: Liver injury is one of the serious complications of sepsis. Previous studies suggested that dexmedetomidine (DEX) could alleviate cecal ligation and puncture (CLP)-induced liver injury. However, it is unclear whether the protective effect of DEX on sepsis-induced liver injury is related to autophagy.

Methods: Mice (n = 105) were randomly divided into the following groups: (i) CON group (Sham); (ii) CLP group (CLP-induced liver injury + saline); (iii) CLP + DEX group (CLP-induced liver injury + DEX). Mouse models of sepsis-induced liver injury were established using CLP. DEX or normal saline was administered by intraperitoneal injection at 0, 2, and 4 h after CLP surgery. The mortality rate within 120 h was calculated. The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and inflammatory cytokines were measured at 6, 12, and 24 h in each group. Hematoxylin and eosin staining assay was carried out to detect the morphological changes of mouse liver cells in each group. The levels of autophagy-associated proteins LC3II, Beclin-1, p62, and LAMP-2 were detected in three groups of mice using western blotting. The expression of LC3II was detected using immunofluorescence. Transmission electron microscopy (TEM) of liver tissue was used to observe autophagosomes and autophagosome–lysosomes. Lastly, the effect of DEX on the AMPK/SIRT1 pathway-associated protein levels were detected using western blotting. Meanwhile, we used L0-2 cells infected with mRFP-GFP-LC3 adenovirus to further analyze the role of SIRT1 in DEX-induced autophagy in liver injury model in vitro.

Results: DEX significantly improved the survival rate of septic mice at the early stage and ameliorated the pathology of sepsis-induced liver injury. The level of autophagy-associated proteins, phosphorylated (p)-AMPK/AMPK, and SIRT1 in the liver of CLP-induced sepsis mice peaked at 12 h post-CLP and decreased significantly at 24 h. In the CLP + DEX group, the levels of autophagy-associated proteins, p-AMPK/AMPK, and SIRT1 increased, whereas inflammatory cytokines decreased at 24 h. The autophagosome structure was clearly observed at different time points in the CLP + DEX group. In the in vitro hepatocyte injury model, the SIRT1 inhibitor significantly increased intracellular ROS levels and reversed the effect of DEX on autophagy flux.

Conclusion: We demonstrated a novel mechanism in which DEX protects against CLP-induced liver injury. DEX enhances autophagy, which alleviates the inflammatory responses in CLP-induced liver injury by regulating the SIRT1/AMPK pathway.

Autophagy and Liver Diseases

Autophagy plays an important role in the physiology and pathology of the liver. It is involved in the development of many liver diseases such as α-1-antitrypsin deficiency, chronic hepatitis virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, and liver cancer. Autophagy has thus become a new target for the treatment of liver diseases. How to treat liver diseases by regulating autophagy has been a hot topic.

Autophagy alleviates amiodarone-induced hepatotoxicity

Amiodarone is a widely used antiarrhythmic drug that can cause the development of steatohepatitis as well as liver fibrosis and cirrhosis. The molecular mechanisms of amiodarone-mediated liver injury remain largely unknown. We therefore analyzed amiodarone-mediated hepatocellular injury in patients with chronic heart failure, in primary hepatocytes and HepG2 cells. We found that amiodarone-treated patients with chronic heart failure revealed significantly higher serum levels of caspase-cleaved keratin-18, an apoptosis biomarker, compared to healthy individuals or patients not receiving amiodarone. Furthermore, amiodarone treatment of hepatocytes resulted in apoptosis associated with lipid accumulation and ER-stress induction. Liver cell steatosis was accompanied by enhanced de novo lipogenesis which, after reaching peak levels, declined together with decreased activation of ER stress. The decline of amiodarone-mediated lipotoxicity was associated with protective autophagy induction. In contrast, in hepatocytes treated with the autophagy inhibitor chloroquine as well as in autophagy gene (ATG5 or ATG7)-deficient hepatocytes, amiodarone-triggered toxicity was increased. In conclusion, we demonstrate that amiodarone induces lipid accumulation associated with ER stress and apoptosis in hepatocytes, which is mirrored by increased keratin-18 fragment serum levels in amiodarone-treated patients. Autophagy reduces amiodarone-mediated lipotoxicity and could provide a therapeutic strategy for protection from drug-induced liver injury.

Acetyl-CoA Derived from Hepatic Peroxisomal β-Oxidation Inhibits Autophagy and Promotes Steatosis via mTORC1 Activation

Autophagy is activated by prolonged fasting but cannot overcome the ensuing hepatic lipid overload, resulting in fatty liver. Here, we describe a peroxisome-lysosome metabolic link that restricts autophagic degradation of lipids. Acyl-CoA oxidase 1 (Acox1), the enzyme that catalyzes the first step in peroxisomal β-oxidation, is enriched in liver and further increases with fasting or high-fat diet (HFD). Liver-specific Acox1 knockout (Acox1-LKO) protected mice against hepatic steatosis caused by starvation or HFD due to induction of autophagic degradation of lipid droplets. Hepatic Acox1 deficiency markedly lowered total cytosolic acetyl-CoA levels, which led to decreased Raptor acetylation and reduced lysosomal localization of mTOR, resulting in impaired activation of mTORC1, a central regulator of autophagy. Dichloroacetic acid treatment elevated acetyl-CoA levels, restored mTORC1 activation, inhibited autophagy, and increased hepatic triglycerides in Acox1-LKO mice. These results identify peroxisome-derived acetyl-CoA as a key metabolic regulator of autophagy that controls hepatic lipid homeostasis.

Hepatitis C Virus Proteins Core and NS5A Are Highly Sensitive to Oxidative Stress-Induced Degradation after eIF2α/ATF4 Pathway Activation

Hepatitis C virus (HCV) infection is accompanied by increased oxidative stress and endoplasmic reticulum stress as a consequence of viral replication, production of viral proteins, and pro-inflammatory signals. To overcome the cellular stress, hepatocytes have developed several adaptive mechanisms like anti-oxidant response, activation of Unfolded Protein Response and autophagy to achieve cell survival. These adaptive mechanisms could both improve or inhibit viral replication, however, little is known in this regard. In this study, we investigate the mechanisms by which hepatocyte-like (Huh7) cells adapt to cellular stress in the context of HCV protein overexpression and oxidative stress. Huh7 cells stably expressing individual HCV (Core, NS3/4A and NS5A) proteins were treated with the superoxide anion donor menadione to induce oxidative stress. Production of reactive oxygen species and activation of caspase 3 were quantified. The activation of the eIF2α/ATF4 pathway and changes in the steady state levels of the autophagy-related proteins LC3 and p62 were determined either by quantitative polymerase chain reaction (qPCR) or Western blotting. Huh7 cells expressing Core or NS5A demonstrated reduced oxidative stress and apoptosis. In addition, phosphorylation of eIF2α and increased ATF4 and CHOP expression was observed with subsequent HCV Core and NS5A protein degradation. In line with these results, in liver biopsies from patients with hepatitis C, the expression of ATF4 and CHOP was confirmed. HCV Core and NS5A protein degradation was reversed by antioxidant treatment or silencing of the autophagy adaptor protein p62. We demonstrated that hepatocyte-like cells expressing HCV proteins and additionally exposed to oxidative stress adapt to cellular stress through eIF2a/ATF4 activation and selective degradation of HCV pro-oxidant proteins Core and NS5A. This selective degradation is dependent on p62 and results in increased resistance to apoptotic cell death induced by oxidative stress. This mechanism may provide a new key for the study of HCV pathology and lead to novel clinically applicable therapeutic interventions.

Hepatitis C virus core or NS3/4A protein expression preconditions hepatocytes against oxidative stress and endoplasmic reticulum stress

Objectives: The occurrence of oxidative stress and endoplasmic reticulum (ER) stress in hepatitis C virus (HCV) infection has been demonstrated and play an important role in liver injury. During viral infection, hepatocytes must handle not only the replication of the virus, but also inflammatory signals generating oxidative stress and damage. Although several mechanisms exist to overcome cellular stress, little attention has been given to the adaptive response of hepatocytes during exposure to multiple noxious triggers.

Methods: In the present study, Huh-7 cells and hepatocytes expressing HCV Core or NS3/4A proteins, both inducers of oxidative and ER stress, were additionally challenged with the superoxide anion generator menadione to mimic external oxidative stress. The production of reactive oxygen species (ROS) as well as the response to oxidative stress and ER stress were investigated.

Results: We demonstrate that hepatocytes diminish oxidative stress through a reduction in ROS production, ER-stress markers (HSPA5 [GRP78], sXBP1) and apoptosis (caspase-3 activity) despite external oxidative stress. Interestingly, the level of the autophagy substrate protein p62 was downregulated together with HCV Core degradation, suggesting that hepatocytes can overcome excess oxidative stress through autophagic degradation of one of the stressors, thereby increasing cell survival.

Duscussion: In conclusion, hepatocytes exposed to direct and indirect oxidative stress inducers are able to cope with cellular stress associated with viral hepatitis and thus promote cell survival.

Hepatocyte Injury and Hepatic Stem Cell Niche in the Progression of Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease characterized by lipid accumulation in hepatocytes in the absence of excessive alcohol consumption. The global prevalence of NAFLD is constantly increasing. NAFLD is a disease spectrum comprising distinct stages with different prognoses. Non-alcoholic steatohepatitis (NASH) is a progressive condition, characterized by liver inflammation and hepatocyte ballooning, with or without fibrosis. The natural history of NAFLD is negatively influenced by NASH onset and by the progression towards advanced fibrosis. Pathogenetic mechanisms and cellular interactions leading to NASH and fibrosis involve hepatocytes, liver macrophages, myofibroblast cell subpopulations, and the resident progenitor cell niche. These cells are implied in the regenerative trajectories following liver injury, and impairment or perturbation of these mechanisms could lead to NASH and fibrosis. Recent evidence underlines the contribution of extra-hepatic organs/tissues (e.g., gut, adipose tissue) in influencing NASH development by interacting with hepatic cells through various molecular pathways. The present review aims to summarize the role of hepatic parenchymal and non-parenchymal cells, their mutual influence, and the possible interactions with extra-hepatic tissues and organs in the pathogenesis of NAFLD.

The Jun N-terminal kinases signaling pathway plays a "seesaw" role in ovarian carcinoma: a molecular aspect

Ovarian cancer is the most common gynecological malignancy that causes cancer-related deaths in women today; this being the case, developing an understanding of ovarian cancer has become one of the major driving forces behind cancer research overall. Moreover, such research over the last 20 years has shown that the Jun N-terminal kinase (JNK) signaling pathway plays an important role in regulating cell death, survival, growth and proliferation in the mitogen-activated protein kinases (MAPK) signaling pathway, an important pathway in the formation of cancer. Furthermore, the JNK signaling pathway is often regulated by an abnormal activation in human tumors and is frequently reported in the literature for its effect on the progression of ovarian cancer. Although the FDA has approved some JNK inhibitors for melanoma, the agency has not approved JNK inhibitors for ovarian cancer. However, there are some experimental data on inhibitors and activators of the JNK signaling pathway in ovarian cancer, but related clinical trials need to be further improved. Although the Jun N-terminal kinase (JNK) signaling pathway is implicated in the formation of cancer in general, research has also indicated that it has a role in suppressing cancer as well. Here, we summarize this seemingly contradictory role of the JNK signaling pathway in ovarian cancer, that ‘seesaws’ between promoting and suppressing cancer, as well as summarizing the application of several JNK pathway inhibitors in cancer in general, and ovarian cancer in particular.

Sulfuretin protects hepatic cells through regulation of ROS levels and autophagic flux

Palmitate (PA) exposure induces stress conditions featuring ROS accumulation and upregulation of p62 expression, resulting in autophagic flux blockage and cell apoptosis. Sulfuretin (Sul) is a natural product isolated from Rhus verniciflua Stokes; the cytoprotective effect of Sul on human hepatic L02 cells and mouse primary hepatocytes under PA-induced stress conditions was investigated in this study. Sul induced mitophagy by activation of p-TBK1 and LC3 and produced a concomitant decline in p62 expression. Autophagosome formation and mitophagy were assessed by the sensitive dual fluorescence reporter mCherry-EGFP-LC3B, and mitochondrial fragmentation was analyzed using MitoTracker Deep Red FM. A preliminary structure-activity relationship (SAR) for Sul was also investigated, and the phenolic hydroxyl group was found to be pivotal for maintaining the cytoprotective bioactivity of Sul. Furthermore, experiments using flow cytometry and western blots revealed that Sul reversed the cytotoxic effect stimulated by the autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ), and its cytoprotective effect was almost eliminated when the autophagy-related 5 (Atg5) gene was knocked down. These studies suggest that, in addition to its antioxidative effects, Sul stimulates mitophagy and restores impaired autophagic flux, thus protecting hepatic cells from apoptosis, and that Sul has potential future medical applications for hepatoprotection.

Glial Cell Line-Derived Neurotrophic Factor Enhances Autophagic Flux in Mouse and Rat Hepatocytes and Protects Against Palmitate Lipotoxicity

Glial cell line-derived neurotrophic factor (GDNF) is a protein that is required for the development and survival of enteric, sympathetic, and catecholaminergic neurons. We previously reported that GDNF is protective against high fat diet (HFD)-induced hepatic steatosis in mice through suppression of hepatic expression of peroxisome proliferator activated receptor-γ and genes encoding enzymes involved in de novo lipogenesis. We also reported that transgenic overexpression of GDNF in mice prevented the HFD-induced liver accumulation of the autophagy cargo-associated protein p62/sequestosome 1 characteristic of impaired autophagy. Here we investigated the effects of GDNF on hepatic autophagy in response to increased fat load, and on hepatocyte mitochondrial fatty acid β-oxidation and cell survival. GDNF not only prevented the reductions in the liver levels of some key autophagy-related proteins, including Atg5, Atg7, Beclin-1 and LC3A/B-II, seen in HFD-fed control mice, but enhanced their levels after 12 weeks of HFD feeding. In vitro, GDNF accelerated autophagic cargo clearance in primary mouse hepatocytes and a rat hepatocyte cell line, and reduced the phosphorylation of the mechanistic target of rapamycin complex downstream-target p70S6 kinase similar to the autophagy activator rapamycin. GDNF also enhanced mitochondrial fatty acid β-oxidation in primary mouse and rat hepatocytes, and protected against palmitate-induced lipotoxicity. Conclusion: We demonstrate a role for GDNF in enhancing hepatic autophagy and in potentiating mitochondrial function and fatty acid oxidation. Our studies show that GDNF and its receptor agonists could be useful for enhancing hepatocyte survival and protecting against fatty acid-induced hepatic lipotoxicity.

Molecular pathways of nonalcoholic fatty liver disease development and progression

Nonalcoholic fatty liver disease (NAFLD) is a main hepatic manifestation of metabolic syndrome. It represents a wide spectrum of histopathological abnormalities ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with or without fibrosis and, eventually, cirrhosis and hepatocellular carcinoma. While hepatic simple steatosis seems to be a rather benign manifestation of hepatic triglyceride accumulation, the buildup of highly toxic free fatty acids associated with insulin resistance-induced massive free fatty acid mobilization from adipose tissue and the increased de novo hepatic fatty acid synthesis from glucose acts as the "first hit" for NAFLD development. NAFLD progression seems to involve the occurrence of "parallel, multiple-hit" injuries, such as oxidative stress-induced mitochondrial dysfunction, endoplasmic reticulum stress, endotoxin-induced, TLR4-dependent release of inflammatory cytokines, and iron overload, among many others. These deleterious factors are responsible for the triggering of a number of signaling cascades leading to inflammation, cell death, and fibrosis, the hallmarks of NASH. This review is aimed at integrating the overwhelming progress made in the characterization of the physiopathological mechanisms of NAFLD at a molecular level, to better understand the factor influencing the initiation and progression of the disease.

The cellular stress response in hepatitis C virus infection: A balancing act to promote viral persistence and host cell survival

Oxidative- and endoplasmic reticulum (ER)-stress are common events during hepatitis C virus (HCV) infection and both regulate cell survival and determine clinical outcome. In response to intrinsic and extrinsic cellular stress, different adaptive mechanisms have evolved in hepatocytes to restore cellular homeostasis like the anti-oxidant response, the unfolded protein response (UPR) and the integrated stress response (ISR). In this review, we focus on the cellular stress response in the context of acute and chronic HCV infection. The mechanisms of induction and modulation of oxidative- and ER-stress are reviewed and analyzed from both perspectives: viral persistence and cell survival. Besides, we delve into the activation of the eIF2α/ATF4 pathway and selective autophagy induction; pathways involved in the elimination of harmful viral proteins after oxidative stress induction. For this, the negative role of autophagy upon HCV infection or negative regulation of viral replication is analyzed. Finally, we hypothesize that the cellular stress response in hepatocytes plays a major role for HCV control thus acting as an important host-factor for virus clearance during the early stages of HCV infection.

Lipid Droplets in Cancer: Guardians of Fat in a Stressful World

Cancer cells possess remarkable abilities to adapt to adverse environmental conditions. Their survival during severe nutrient and oxidative stress depends on their capacity to acquire extracellular lipids and the plasticity of their mechanisms for intracellular lipid synthesis, mobilisation, and recycling. Lipid droplets, cytosolic fat storage organelles present in most cells from yeast to men, are emerging as major regulators of lipid metabolism, trafficking, and signalling in various cells and tissues exposed to stress. Their biogenesis is induced by nutrient and oxidative stress and they accumulate in various cancers. Lipid droplets act as switches that coordinate lipid trafficking and consumption for different purposes in the cell, such as energy production, protection against oxidative stress or membrane biogenesis during rapid cell growth. They sequester toxic lipids, such as fatty acids, cholesterol and ceramides, thereby preventing lipotoxic cell damage and engage in a complex relationship with autophagy. Here, we focus on the emerging mechanisms of stress-induced lipid droplet biogenesis; their roles during nutrient, lipotoxic, and oxidative stress; and the relationship between lipid droplets and autophagy. The recently discovered principles of lipid droplet biology can improve our understanding of the mechanisms that govern cancer cell adaptability and resilience to stress.

SNX10 mediates alcohol-induced liver injury and steatosis by regulating the activation of chaperone-mediated autophagy

BACKGROUND & AIMS

Alcoholic liver disease (ALD) is a major cause of morbidity and mortality worldwide. However, the cellular defense mechanisms underlying ALD are not well understood. Recent studies highlighted the involvement of chaperone-mediated autophagy (CMA) in regulating hepatic lipid metabolism. Sorting nexin (SNX)-10 has a regulatory function in endolysosomal trafficking and stabilisation. Here, we investigated the roles of SNX10 in CMA activation and in the pathogenesis of alcohol-induced liver injury and steatosis.

METHODS

Snx10 knockout (Snx10 KO) mice and their wild-type (WT) littermates fed either the Lieber-DeCarli liquid alcohol diet or a control liquid diet, and primary cultured WT and Snx10 KO hepatocytes stimulated with ethanol, were used as in vivo and in vitro ALD models, respectively. Activation of CMA, liver injury parameters, inflammatory cytokines, oxidative stress and lipid metabolism were measured.

RESULTS

Compared with WT littermates, Snx10 KO mice exhibited a significant amelioration in ethanol-induced liver injury and hepatic steatosis. Both in vivo and in vitro studies showed that SNX10 deficiency upregulated lysosome-associated membrane protein type 2A (LAMP-2A) expression and CMA activation, which could be reversed by SNX10 overexpression in vitro. LAMP-2A interference confirmed that the upregulation of Nrf2 and AMPK signalling pathways induced by SNX10 deficiency relied on CMA activation. Pull-down assays revealed an interaction between SNX10 and cathepsin A (CTSA), a key enzyme involved in LAMP-2A degradation. Deficiency in SNX10 inhibited CTSA maturation and increased the stability of LAMP-2A, resulting in an increase in CMA activity.

CONCLUSIONS

SNX10 controls CMA activity by mediating CTSA maturation, and, thus, has an essential role in alcohol-induced liver injury and steatosis. Our results provide evidence for SNX10 as a potential promising therapeutic target for preventing or ameliorating liver injury in ALD.

LAY SUMMARY

Alcoholic liver disease is a major cause of morbidity and mortality worldwide. Recent studies highlight the involvement of chaperone-mediated autophagy (CMA) in regulating hepatic lipid metabolism. Our study reveals that deficiency of sorting nexin (SNX) 10 increases the stability of LAMP-2A by inhibiting cathepsin A maturation, resulting in the increase of CMA activity and, thus, alleviates alcohol-induced liver injury and steatosis.

Autophagy, NAFLD and NAFLD-Related HCC

Non-alcoholic fatty liver disease (NAFLD) will become a dominant cause of hepatocellular carcinoma (HCC) in the coming decade. Whereas the exact molecular mechanisms underlying the progression from simple steatosis, through steatohepatitis, to HCC remains largely unclear, emerging evidence has supported a central role of defective autophagy in the pathogenesis of NAFLD and its complications. Autophagy not only regulates lipid metabolism and insulin resistance, but also protects hepatocytes from injury and cell death. Nevertheless, in inflammation and tumorigenesis, the role of autophagy is more paradoxical. In NAFLD, defective hepatic autophagy occurs at multiple levels through numerous mechanisms and is causally linked to NAFLD-related HCC. In this chapter, we summarize the regulation and function of autophagy in NAFLD and highlight recent identification of potential pharmacological agents for restoring autophagic flux in NAFLD.

Chaperone Mediated Autophagy in the Crosstalk of Neurodegenerative Diseases and Metabolic Disorders

Chaperone Mediated Autophagy (CMA) is a lysosomal-dependent protein degradation pathway. At least 30% of cytosolic proteins can be degraded by this process. The two major protein players of CMA are LAMP-2A and HSC70. While LAMP-2A works as a receptor for protein substrates at the lysosomal membrane, HSC70 specifically binds protein targets and takes them for CMA degradation. Because of the broad spectrum of proteins able to be degraded by CMA, this pathway has been involved in physiological and pathological processes such as lipid and carbohydrate metabolism, and neurodegenerative diseases, respectively. Both, CMA, and the mentioned processes, are affected by aging and by inadequate nutritional habits such as a high fat diet or a high carbohydrate diet. Little is known regarding about CMA, which is considered a common regulation factor that links metabolism with neurodegenerative disorders. This review summarizes what is known about CMA, focusing on its molecular mechanism, its role in protein, lipid and carbohydrate metabolism. In addition, the review will discuss how CMA could be linked to protein, lipids and carbohydrate metabolism within neurodegenerative diseases. Furthermore, it will be discussed how aging and inadequate nutritional habits can have an impact on both CMA activity and neurodegenerative disorders.

Cytosolic lipolysis and lipophagy: two sides of the same coin

Fatty acids are the most efficient substrates for energy production in vertebrates and are essential components of the lipids that form biological membranes. Synthesis of triacylglycerols from non-esterified free fatty acids (FFAs) combined with triacylglycerol storage represents a highly efficient strategy to stockpile FFAs in cells and prevent FFA-induced lipotoxicity. Although essentially all vertebrate cells have some capacity to store and utilize triacylglycerols, white adipose tissue is by far the largest triacylglycerol depot and is uniquely able to supply FFAs to other tissues. The release of FFAs from triacylglycerols requires their enzymatic hydrolysis by a process called lipolysis. Recent discoveries thoroughly altered and extended our understanding of lipolysis. This Review discusses how cytosolic 'neutral' lipolysis and lipophagy, which utilizes 'acid' lipolysis in lysosomes, degrade cellular triacylglycerols as well as how these pathways communicate, how they affect lipid metabolism and energy homeostasis and how their dysfunction affects the pathogenesis of metabolic diseases. Answers to these questions will likely uncover novel strategies for the treatment of prevalent metabolic diseases.

Kinases Involved in Both Autophagy and Mitosis

Both mitosis and autophagy are highly regulated dynamic cellular processes and involve various phosphorylation events catalysed by kinases, which play vital roles in almost all physiological and pathological conditions. Mitosis is a key event during the cell cycle, in which the cell divides into two daughter cells. Autophagy is a process in which the cell digests its own cellular contents. Although autophagy regulation has mainly been studied in asynchronous cells, increasing evidence indicates that autophagy is in fact tightly regulated in mitosis. Here in this review, we will discuss kinases that were originally identified to be involved in only one of either mitosis or autophagy, but were later found to participate in both processes, such as CDKs (cyclin-dependent kinases), Aurora kinases, PLK-1 (polo-like kinase 1), BUB1 (budding uninhibited by benzimidazoles 1), MAPKs (mitogen-activated protein kinases), mTORC1 (mechanistic target of rapamycin complex 1), AMPK (AMP-activated protein kinase), PI3K (phosphoinositide-3 kinase) and protein kinase B (AKT). By focusing on kinases involved in both autophagy and mitosis, we will get a more comprehensive understanding about the reciprocal regulation between the two key cellular events, which will also shed light on their related therapeutic investigations.

Activation of PERK-Nrf2 oncogenic signaling promotes Mdm2-mediated Rb degradation in persistently infected HCV culture

The mechanism of how chronic hepatitis C virus (HCV) infection leads to such a high rate of hepatocellular carcinoma (HCC) is unknown. We found that the PERK axis of endoplasmic reticulum (ER) stress elicited prominent nuclear translocation of Nrf2 in 100% of HCV infected hepatocytes. The sustained nuclear translocation of Nrf2 in chronically infected culture induces Mdm2-mediated retinoblastoma protein (Rb) degradation. Silencing PERK and Nrf2 restored Mdm2-mediated Rb degradation, suggesting that sustained activation of PERK/Nrf2 axis creates oncogenic stress in chronically infected HCV culture model. The activation of Nrf2 and its nuclear translocation were prevented by ER-stress and PERK inhibitors, suggesting that PERK axis is involved in the sustained activation of Nrf2 signaling during chronic HCV infection. Furthermore, we show that HCV clearance induced by interferon-α based antiviral normalized the ER-stress response and prevented nuclear translocation of Nrf2, whereas HCV clearance by DAAs combination does neither. In conclusion, we report here a novel mechanism for how sustained activation of PERK axis of ER-stress during chronic HCV infection activates oncogenic Nrf2 signaling that promotes hepatocyte survival and oncogenesis by inducing Mdm2-mediated Rb degradation.

The Perilipins: Major Cytosolic Lipid Droplet-Associated Proteins and Their Roles in Cellular Lipid Storage, Mobilization, and Systemic Homeostasis

The discovery by Dr. Constantine Londos of perilipin 1, the major scaffold protein at the surface of cytosolic lipid droplets in adipocytes, marked a fundamental conceptual change in the understanding of lipolytic regulation. Focus then shifted from the enzymatic activation of lipases to substrate accessibility, mediated by perilipin-dependent protein sequestration and recruitment. Consequently, the lipid droplet became recognized as a unique, metabolically active cellular organelle and its surface as the active site for novel protein-protein interactions. A new area of investigation emerged, centered on lipid droplets' biology and their role in energy homeostasis. The perilipin family is of ancient origin and has expanded to include five mammalian genes and a growing list of evolutionarily conserved members. Universally, the perilipins modulate cellular lipid storage. This review provides a summary that connects the perilipins to both cellular and whole-body homeostasis.

Lipid Droplets in Health and Disease

Lipids are essential building blocks synthesized by complex molecular pathways and deposited as lipid droplets (LDs) in cells. LDs are evolutionary conserved organelles found in almost all organisms, from bacteria to mammals. They are composed of a hydrophobic neutral lipid core surrounding by a phospholipid monolayer membrane with various decorating proteins. Degradation of LDs provide metabolic energy for divergent cellular processes such as membrane synthesis and molecular signaling. Lipolysis and autophagy are two main catabolic pathways of LDs, which regulate lipid metabolism and, thereby, closely engaged in many pathological conditons. In this review, we first provide an overview of the current knowledge on the structural properties and the biogenesis of LDs. We further focus on the recent findings of their catabolic mechanism by lipolysis and autophagy as well as their connection ragarding the regulation and function. Moreover, we discuss the relevance of LDs and their catabolism-dependent pathophysiological conditions.

Relevance of autophagy to fatty liver diseases and potential therapeutic applications

Autophagy is an evolutionarily conserved lysosome-mediated cellular degradation program. Accumulating evidence shows that autophagy is important to the maintenance of liver homeostasis. Autophagy involves recycling of cellular nutrients recycling as well as quality control of subcellular organelles. Autophagy deficiency in the liver causes various liver pathologies. Fatty liver disease (FLD) is characterized by the accumulation of lipids in hepatocytes and the dysfunction in energy metabolism. Autophagy is negatively affected by the pathogenesis of FLD and the activation of autophagy could ameliorate steatosis, which suggests a potential therapeutic approach to FLD. In this review, we will discuss autophagy and its relevance to liver diseases, especially FLD. In addition, we will discuss recent findings on potential therapeutic applications of autophagy modulators for FLD.

Dysfunctional autophagy in RPE, a contributing factor in age-related macular degeneration

Age-related macular degeneration (AMD) is a devastating neurodegenerative disease and a major cause of blindness in the developed world. Owing to its complexity and the lack of an adequate human model that recapitulates key aspects of the disease, the molecular mechanisms of AMD pathogenesis remain poorly understood. Here we show that cultured human retinal pigment epithelium (RPE) from AMD donors (AMD RPE) are functionally impaired and exhibit distinct phenotypes compared with RPE cultured from normal donors (normal RPE). Accumulation of lipid droplets and glycogen granules, disintegration of mitochondria, and an increase in autophagosomes were observed in AMD RPE cultures. Compared with normal RPE, AMD RPE exhibit increased susceptibility to oxidative stress, produce higher levels of reactive oxygen species (ROS) under stress conditions, and showed reduced mitochondrial activity. Measurement of the ratio of LC3-II/ LC3-I, revealed impaired autophagy in AMD RPE as compared with normal RPE. Autophagic flux was also reduced in AMD RPE as compared with normal RPE, as shown by inability of AMD RPE to downregulate p62 levels during starvation. Impaired autophagic pathways were further shown by analyzing late autophagic vesicles; immunostaining with lysosome-associated membrane protein 1 (LAMP-1) antibody revealed enlarged and annular LAMP-1-positive organelles in AMD RPE as opposed to smaller discrete puncta observed in normal RPE. Our study provides insights into AMD cellular and molecular mechanisms, proposes dysfunctional autophagy as an underlying mechanism contributing to the pathophysiology of the disease, and opens up new avenues for development of novel treatment strategies.

Keratin 18-deficiency results in steatohepatitis and liver tumors in old mice: A model of steatohepatitis-associated liver carcinogenesis

Backround: Steatohepatitis (SH)-associated liver carcinogenesis is an increasingly important issue in clinical medicine. SH is morphologically characterized by steatosis, hepatocyte injury, ballooning, hepatocytic cytoplasmic inclusions termed Mallory-Denk bodies (MDBs), inflammation and fibrosis.

RESULTS

17-20-months-old Krt18-/- and Krt18+/- mice in contrast to wt mice spontaneously developed liver lesions closely resembling the morphological spectrum of human SH as well as liver tumors. The pathologic alterations were more pronounced in Krt18-/- than in Krt18+/- mice. The frequency of liver tumors with male predominance was significantly higher in Krt18-/- compared to age-matched Krt18+/- and wt mice. Krt18-deficient tumors in contrast to wt animals displayed SH features and often pleomorphic morphology. aCGH analysis of tumors revealed chromosomal aberrations in Krt18-/- liver tumors, affecting loci of oncogenes and tumor suppressor genes.

MATERIALS AND METHODS

Livers of 3-, 6-, 12- and 17-20-months-old aged wild type (wt), Krt18+/- and Krt18-/- (129P2/OlaHsd background) mice were analyzed by light and immunofluorescence microscopy as well as immunohistochemistry. Liver tumors arising in aged mice were analyzed by array comparative genomic hybridization (aCGH).

CONCLUSIONS

Our findings show that K18 deficiency of hepatocytes leads to steatosis, increasing with age, and finally to SH. K18 deficiency and age promote liver tumor development in mice, frequently on the basis of chromosomal instability, resembling human HCC with stemness features.

Regulation and Functions of Autophagic Lipolysis

The selective breakdown by autophagy of lipid droplet (LD)-stored lipids, termed lipophagy, is a lysosomal lipolytic pathway that complements the actions of cytosolic neutral lipases. The physiological importance of lipophagy has been demonstrated in multiple mammalian cell types, as well as in lower organisms, and this pathway has many functions in addition to supplying free fatty acids to maintain cellular energy stores. Recent studies have begun to delineate the molecular mechanisms of the selective recognition of LDs by the autophagic machinery, as well as the intricate crosstalk between the different forms of autophagy and neutral lipases. These studies have led to increased interest in the role of lipophagy in both human disease pathogenesis and therapy.

Lipids, lysosomes, and autophagy

Lipids are essential components of a cell providing energy substrates for cellular processes, signaling intermediates, and building blocks for biological membranes. Lipids are constantly recycled and redistributed within a cell. Lysosomes play an important role in this recycling process that involves the recruitment of lipids to lysosomes via autophagy or endocytosis for their degradation by lysosomal hydrolases. The catabolites produced are redistributed to various cellular compartments to support basic cellular function. Several studies demonstrated a bidirectional relationship between lipids and lysosomes that regulate autophagy. While lysosomal degradation pathways regulate cellular lipid metabolism, lipids also regulate lysosome function and autophagy. In this review, we focus on this bidirectional relationship in the context of dietary lipids and provide an overview of recent evidence of how lipid-overload lipotoxicity, as observed in obesity and metabolic syndrome, impairs lysosomal function and autophagy that may eventually lead to cellular dysfunction or cell death.

Macrophage autophagy protects against liver fibrosis in mice

Autophagy is a lysosomal degradation pathway of cellular components that displays antiinflammatory properties in macrophages. Macrophages are critically involved in chronic liver injury by releasing mediators that promote hepatocyte apoptosis, contribute to inflammatory cell recruitment and activation of hepatic fibrogenic cells. Here, we investigated whether macrophage autophagy may protect against chronic liver injury. Experiments were performed in mice with mutations in the autophagy gene Atg5 in the myeloid lineage (Atg5(fl/fl) LysM-Cre mice, referred to as atg5(-/-)) and their wild-type (Atg5(fl/fl), referred to as WT) littermates. Liver fibrosis was induced by repeated intraperitoneal injection of carbon tetrachloride. In vitro studies were performed in cultures or co-cultures of peritoneal macrophages with hepatic myofibroblasts. As compared to WT littermates, atg5(-/-) mice exposed to chronic carbon tetrachloride administration displayed higher hepatic levels of IL1A and IL1B and enhanced inflammatory cell recruitment associated with exacerbated liver injury. In addition, atg5(-/-) mice were more susceptible to liver fibrosis, as shown by enhanced matrix and fibrogenic cell accumulation. Macrophages from atg5(-/-) mice secreted higher levels of reactive oxygen species (ROS)-induced IL1A and IL1B. Moreover, hepatic myofibroblasts exposed to the conditioned medium of macrophages from atg5(-/-) mice showed increased profibrogenic gene expression; this effect was blunted when neutralizing IL1A and IL1B in the conditioned medium of atg5(-/-) macrophages. Finally, administration of recombinant IL1RN (interleukin 1 receptor antagonist) to carbon tetrachloride-exposed atg5(-/-) mice blunted liver injury and fibrosis, identifying IL1A/B as central mediators in the deleterious effects of macrophage autophagy invalidation. These results uncover macrophage autophagy as a novel antiinflammatory pathway regulating liver fibrosis.

LRP1 Protein Deficiency Exacerbates Palmitate-induced Steatosis and Toxicity in Hepatocytes

LRP1 (LDL receptor-related protein-1) is a ubiquitous receptor with both cell signaling and ligand endocytosis properties. In the liver, LRP1 serves as a chylomicron remnant receptor and also participates in the transport of extracellular cathepsin D to the lysosome for prosaposin activation. The current study showed that in comparison with wild type mice, hepatocyte-specific LRP1 knock-out (hLrp1(-/-)) mice were more susceptible to fasting-induced lipid accumulation in the liver. Primary hepatocytes isolated from hLrp1(-/-) mice also accumulated more intracellular lipids and experienced higher levels of endoplasmic reticulum (ER) stress after palmitate treatment compared with similarly treated hLrp1(+/+) hepatocytes. Palmitate-treated hLrp1(-/-) hepatocytes displayed similar LC3-II levels, but the levels of p62 were elevated in comparison with palmitate-treated hLrp1(+/+) hepatocytes, suggesting that the elevated lipid accumulation in LRP1-defective hepatocytes was not due to defects in autophagosome formation but was due to impairment of lipophagic lipid hydrolysis in the lysosome. Additional studies showed increased palmitate-induced oxidative stress, mitochondrial and lysosomal permeability, and cell death in hLrp1(-/-) hepatocytes. Importantly, the elevated cell death and ER stress observed in hLrp1(-/-) hepatocytes were abrogated by E64D treatment, whereas inhibiting ER stress diminished cell death but not lysosomal permeabilization. Taken together, these results documented that LRP1 deficiency in hepatocytes promotes lipid accumulation and lipotoxicity through lysosomal-mitochondrial permeabilization and ER stress that ultimately result in cell death. Hence, LRP1 dysfunction may be a major risk factor in fatty liver disease progression.

Intravenous Administration of Multiwalled Carbon Nanotubes Aggravates High-Fat Diet-Induced Nonalcoholic Steatohepatitis in Sprague Dawley Rats

Multiwalled carbon nanotubes (MWCNTs) have been explored in pharmaceutical applications such as tumor targeting and delivery of drugs, in which MWCNTs are given through intravenous injection. However, the biosafety of MWCNTs is of concern for such application. Therefore, in the current study, we used a fatty liver model to investigate the possible toxicity of MWCNTs to the liver, as MWCNTs were retained mainly in the liver of mice after intravenous injection. Male Sprague Dawley rats were used to generate the fatty liver model, and the effects of intravenous administration of MWCNTs on fatty liver were studied. Hematoxylin and eosin staining for hepatocellular anatomy and Masson trichrome staining for hepatic fibrosis were conducted. Histologically, MWCNTs aggravated steatohepatitis with higher nonalcoholic fatty liver disease scores. Analysis of liver injury markers indicated that MWCNTs administration resulted in chronic hepatitis, along with increased liver fat and altered liver oxidation, including the increase of P6 protein and the depletion of glutathione. In conclusion, our results suggest that MWCNTs can aggravate nonalcoholic steatohepatitis in Sprague Dawley rats, and oxidative injury may be involved in this process.