Physiological functions of autophagy

Microbiota-derived tryptophan metabolism and AMPK/mTOR pathway mediate antidepressant-like effect of Shugan Hewei Decoction

Introduction

Depression is a common psychological disorder, accompanied by a disturbance of the gut microbiota and its metabolites. Recently, microbiota-derived tryptophan metabolism and AMPK/mTOR pathway were found to be strongly linked to the development of depression. Shugan Hewei Decoction (SHD) is a classical anti-depression traditional Chinese medicine formula. Although, we have shown that SHD exerted antidepressant effects via cecal microbiota and cecum NLRP3 inflammasome, the specific mechanism of SHD on metabolism driven by gut microbiota is unknown. In this study, we focus on the tryptophan metabolism and AMPK/mTOR pathway to elucidate the multifaceted mechanisms of SHD.

Methods

Male rats were established to the chronic unpredictable stress (CUS)/social isolation for 6 weeks, and SHD-L (7.34 g/kg/d), SHD-H (14.68 g/kg/d), Fructooligosaccharide (FOS) (3.15 g/kg/d) were given by intragastric administration once daily during the last 2 weeks. Behavioral experiments were carried out to evaluate the model. The colonic content was taken out for shotgun metagenomic sequencing combined with the untargeted metabolomics, the targeted tryptophan metabolomics. ELISA was used to detect the levels of zonula occludens 1 (ZO-1), Occludin in colon, as well as lipopolysaccharide (LPS), diamine oxidase (DAO), D-lactate (DLA) in serum. The expressions of mRNA and proteins of adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway of autophagy were examined using RT-qPCR and Western blot in colon.

Results

SHD modulated gut microbiota function and biological pathways, which were related to tryptophan metabolism. In addition, SHD could regulate microbiota-derived tryptophan production (such as reduction of 3-HK, 3-HAA etc., increment of ILA, IAA etc.), which metabolites belong to kynurenine (KYN) and indole derivatives. Further, SHD reduced intestinal permeability and enhanced the intestinal barrier function. Moreover, SHD could upregulate the levels of AMPK, microtubule associated protein light chain 3 (LC3), autophagy related protein 5 (ATG5) and Beclin1, downregulate the levels of mTOR, p62, promoted autophagy in colon. Spearman's analysis illustrated the close correlation between tryptophan metabolites and intestinal barrier, AMPK/mTOR pathway.

Conclusion

SHD may exert antidepressant-like effects by regulating microbiota-derived tryptophan metabolism, and triggering the AMPK/mTOR pathway of autophagy, enhancing the intestinal barrier function.

UCK2 promotes intrahepatic cholangiocarcinoma progression and desensitizes cisplatin treatment by PI3K/AKT/mTOR/autophagic axis

Intrahepatic cholangiocarcinoma (iCCA) is a highly aggressive tumor with extremely poor prognosis due to the low resection rate, high recurrence rate and drug resistance. Uridine-cytidine kinase 2 (UCK2) is proved to promote progression and drug resistance of various carcinomas by regulating pyrimidine metabolism. However, the role of UCK2 in progression and drug resistance of iCCA was largely unclear. Gene expression matrices were obtained from public database and were verified by qRT-PCR using tumor sample from Sun Yat-sen University Cancer Center. Knockdown and overexpression of UCK2 were used to evaluate the effects of UCK2 on carcinogenesis and cisplatin response in iCCA. CCK8-kit assays and plate clone formation assays were performed to detect the effect of UCK2 on proliferative activity of tumor cells. Western blotting was performed to investigate protein level of UCK2 and the relevant biomarkers of PI3K/AKT/mTOR/autophagic axis. Cell migration and invasion were assessed by using wound-healing and transwell assays. UCK2 expression was detected elevated in iCCA tissues compared with adjacent normal tissues. Biologically, overexpression of UCK2 can promote proliferation of iCCA cells, and desensitizes iCCA to cisplatin in both in vivo and in vitro models. Mechanistically, UCK2 promote iCCA progression and cisplatin resistance through inhibition of autophagy by activating the PI3K/AKT/mTOR signaling pathway. Clinically, higher UCK2 expression in iCCA tumor was associated with aggressive tumor features, poorer survival and lower sensitivity of chemotherapy. UCK2 promotes iCCA progression and desensitizes cisplatin treatment by regulating PI3K/AKT/mTOR/autophagic axis. UCK2 exhibited potential as a biomarker in predicting prognosis and drug sensitivity of iCCA patients.

Unraveling the ultrastructure and dynamics of autophagic vesicles: Insights from advanced imaging techniques

Autophagy, an intracellular self-degradation process, is governed by a complex interplay of signaling pathways and interactions between proteins and organelles. Its fundamental purpose is to efficiently clear and recycle cellular components that are damaged or redundant. Central to this process are autophagic vesicles, specialized structures that encapsulate targeted cellular elements, playing a pivotal role in autophagy. Despite growing interest in the molecular components of autophagic machinery and their regulatory mechanisms, capturing the detailed ultrastructural dynamics of autophagosome formation continues to present significant challenges. However, recent advancements in microscopy, particularly in electron microscopy, have begun to illuminate the dynamic regulatory processes underpinning autophagy. This review endeavors to provide an exhaustive overview of contemporary research on the ultrastructure of autophagic processes. By synthesizing observations from diverse technological methodologies, this review seeks to deepen our understanding of the genesis of autophagic vesicles, their membrane origins, and the dynamic alterations that transpire during the autophagy process. The aim is to bridge gaps in current knowledge and foster a more comprehensive comprehension of this crucial cellular mechanism.

Restraint Stress, Foot Shock and Corticosterone Differentially Alter Autophagy in the Rat Hippocampus, Basolateral Amygdala and Prefrontal Cortex

Autophagy is a conserved lysosomal degradation process that has recently been found to be associated with stress-related psychological diseases. However, previous studies have yielded inconsistent results regarding the effects of various stress patterns on autophagy in different brain regions. This discrepancy may arise from differences in autophagy flux across nuclei, the type of stress experienced, and the timing of autophagy assessment after stress exposure. In this study, we assessed autophagy flux in the rat hippocampus (HPC), medial prefrontal cortex (mPFC), and basal lateral amygdala (BLA) by quantifying protein levels of p-ULK1, LC3-I, LC3-II, and p62 via Western blot analysis at 15 min, 30 min, and 60 min following various stress paradigms: restraint stress, foot shock, single corticosterone injection, and chronic corticosterone treatment. We found that: (1) hippocampal autophagy decreased within 1 h of restraint stress, foot shock, and corticosterone injection, except for a transient increase at 30 min after restraint stress; (2) autophagy increased 1 h after restraint stress and corticosterone injection but decreased 1 h after foot shock in mPFC; (3) In BLA, autophagy increased 1 h after foot shock and corticosterone injection but decreased 1 h after restraint stress; (4) Chronic corticosterone increased autophagy in mPFC and BLA but had no effects in HPC. These findings suggest that stress regulates autophagy in a brain region- and stressor-specific manner within 1 h after stress exposure, which may contribute to the development of stress-related psychological disorders.

The Roles of Autophagy-related miRNAs in Gynecologic Tumors: A Review of Current Knowledge for Possible Targeted Therapy

Gynecological cancers are the leading cause of malignancy-related death and disability in the world. These cancers are diagnosed at end stages, and unfortunately, the standard therapeutic strategies available for the treatment of affected women [including chemotherapy, radiotherapy and surgery] are not safe and effective enough. Moreover, the unwanted side-effects lowering the patients' life quality is another problem for these therapies. Therefore, researchers should search for better alternative/complementary treatments. The involvement of autophagy in the pathogenesis of various cancers has been demonstrated. Recently, a novel crosstalk between microRNAs, small non-coding RNAs with important regulatory functions, and autophagy machinery has been highlighted. In this review, we indicate the importance of this interaction for targeted therapy in the treatment of cancers including gynecological cancers, with a focus on underlying mechanisms.

Regulation of autophagy gene expression and its implications in cancer

Autophagy is a catabolic cellular process that targets and eliminates superfluous cytoplasmic components via lysosomal degradation. This evolutionarily conserved process is tightly regulated at multiple levels as it is critical for the maintenance of homeostasis. Research in the past decade has established that dysregulation of autophagy plays a major role in various diseases, such as cancer and neurodegeneration. However, modulation of autophagy as a therapeutic strategy requires identification of key players that can fine tune the induction of autophagy without complete abrogation. In this Review, we summarize the recent discoveries on the mechanism of regulation of ATG (autophagy related) gene expression at the level of transcription, post transcription and translation. Furthermore, we briefly discuss the role of aberrant expression of ATG genes in the context of cancer.

Protective effect of natural products in the metabolic-associated kidney diseases via regulating mitochondrial dysfunction

Metabolic syndrome (MS) is a complex group of metabolic disorders syndrome with hypertension, hyperuricemia and disorders of glucose or lipid metabolism. As an important organ involved in metabolism, the kidney is inevitably attacked by various metabolic disorders, leading to abnormalities in kidney structure and function. Recently, an increasing number of studies have shown that mitochondrial dysfunction is actively involved in the development of metabolic-associated kidney diseases. Mitochondrial dysfunction can be used as a potential therapeutic strategy for the treatment of metabolic-associated kidney diseases. Many natural products have been widely used to improve the treatment of metabolic-associated kidney diseases by inhibiting mitochondrial dysfunction. In this paper, by searching several authoritative databases such as PubMed, Web of Science, Wiley Online Library, and Springer Link. We summarize the Natural Products Protect Against Metabolic-Associated Kidney Diseases by Regulating Mitochondrial Dysfunction. In this review, we sought to provide an overview of the mechanisms by which mitochondrial dysfunction impaired metabolic-associated kidney diseases, with particular attention to the role of mitochondrial dysfunction in diabetic nephropathy, gouty nephropathy, hypertensive kidney disease, and obesity-related nephropathy, and then the protective role of natural products in the kidney through inhibition of mitochondrial disorders, thus providing a systematic understanding of the targets of mitochondrial dysfunction in metabolic-associated kidney diseases, and finally a review of promising therapeutic targets and herbal candidates for metabolic-associated kidney diseases through inhibition of mitochondrial dysfunction.

Role of autophagy in lung diseases and ageing

The lungs face ongoing chemical, mechanical, biological, immunological and xenobiotic stresses over a lifetime. Advancing age progressively impairs lung function. Autophagy is a "housekeeping" survival strategy involved in numerous physiological and pathological processes in all eukaryotic cells. Autophagic activity decreases with age in several species, whereas its basic activity extends throughout the lifespan of most animals. Dysregulation of autophagy has been proven to be closely related to the pathogenesis of several ageing-related pulmonary diseases. This review summarises the role of autophagy in the pathogenesis of pulmonary diseases associated with or occurring in the context of ageing, including acute lung injury, chronic obstructive pulmonary disease, asthma and pulmonary fibrosis, and describes its potential as a therapeutic target.

The interplay between oxidative stress and autophagy in chronic obstructive pulmonary disease

Autophagy is a highly conserved process that is indispensable for cell survival, embryonic development, and tissue homeostasis. Activation of autophagy protects cells against oxidative stress and is a major adaptive response to injury. When autophagy is dysregulated by factors such as smoking, environmental insults and aging, it can lead to enhanced formation of aggressors and production of reactive oxygen species (ROS), resulting in oxidative stress and oxidative damage to cells. ROS activates autophagy, which in turn promotes cell adaptation and reduces oxidative damage by degrading and circulating damaged macromolecules and dysfunctional cell organelles. The cellular response triggered by oxidative stress includes changes in signaling pathways that ultimately regulate autophagy. Chronic obstructive pulmonary disease (COPD) is the most common lung disease among the elderly worldwide, with a high mortality rate. As an induced response to oxidative stress, autophagy plays an important role in the pathogenesis of COPD. This review discusses the regulation of oxidative stress and autophagy in COPD, and aims to provide new avenues for future research on target-specific treatments for COPD.

Corosolic Acid Protects Rat Chondrocytes Against IL-1β-Induced ECM Degradation by Activating Autophagy via PI3K/AKT/mTOR Pathway and Ameliorates Rat Osteoarthritis

Purpose

Osteoarthritis (OA) is an age-related degenerative disease associated with enhanced degradation of extracellular matrix (ECM) and decreased autophagy. Our study is aimed to explore how corosolic acid (CRA) affect cartilage ECM metabolism and the potential mechanism.

Methods

Rat chondrocytes were pretreated with different concentrations of CRA (0, 2.5, 5, and 10 μM), and were stimulated with IL-1β (10ng/mL) for 24 h, subsequently. RT-qPCR, Western blot, and immunofluorescence were used to detect the expression of genes related to ECM metabolism and explore the potential molecular mechanism. The effect of CRA on articular cartilage was observed in the surgically induced OA rat model with the method of Safranin O/Fast green and immunohistochemical staining.

Results

Results showed that CRA reversed the IL-1β-induced degradation of aggrecan and type II collagen and the high expression of MMP13 and ADAMTS5. Mechanistically, CRA enhanced autophagy through inhibiting the classical PI3K/AKT/mTOR signaling pathway. Furthermore, inhibition of autophagy partly abolished the protective effects of CRA on ECM synthesis in IL-1β-treated chondrocytes. Correspondingly, the protective effect of CRA was also confirmed in a rat OA model.

Conclusion

Herein, we demonstrate that CRA can enhance autophagy by inhibiting PI3K/AKT/mTOR signaling pathway, prevent IL-1β-induced cartilage ECM degradation, and may be a potentially applicable candidate for the treatment of OA.

Significance of the association between early embryonic development and endocytosis

Fertilization triggers a process called maternal-to-zygotic transition, in which the oocyte undergoes oocyte-to-embryo transition, leading to massive intracellular remodeling toward early embryogenesis. This transition requires the degradation of oocyte-derived components; however, the significance and mechanism of degradation of cell surface components remain unknown. In this review, we focused on the dynamics of plasma membrane proteins and investigated the relationship between embryonic development and endocytosis. Our survey of the extant literature on the topic led to the conclusion that clathrin-mediated endocytosis is essential for the progression of early embryogenesis and selective degradation of oocyte-derived plasma membrane proteins in mouse embryos, as reported by studies analyzing maternal cellular surface proteins, including a glycine transporter, GlyT1a. Evaluation of such endocytic activity in individual embryos may allow the selection of embryos with higher viability in assisted reproductive technologies, and it is important to select viable embryos to increase the rates of successful pregnancy and live birth. Although the early embryonic developmental abnormalities are mainly accompanied with chromosomal aneuploidy, other causes and mechanisms remain unclear. This review summarizes molecular biological approaches to early embryonic developmental abnormalities and their future prospects.

Therapeutic effects of apocynin on ovarian ischemia-reperfusion induced lung injury

Ovarian ischemia-reperfusion (I-R) injury may damage remote organs, including the lungs. We investigated whether apocynin, a NADPH oxidase inhibitor, might protect against ovarian I-R induced apoptosis in the lungs of rats. Bilateral ovarian I-R was induced for 3 h, then apocynin was applied at two concentrations. Lung tissue was evaluated using spectrophotometric and immunohistochemical methods. We found that I-R increased total oxidant status (TOS), oxidative stress index (OSI) and myeloperoxidase (MPO) levels, and immunostaining of nuclear factor kappa-B (NF-κB), light chain 3B (LC3B), interleukin 1-beta (IL-1β), caspase-3 and tumor necrosis factor-alpha (TNF-α), but decreased superoxide dismutase (SOD) values. Apocynin application to I-R injured rats enhanced recovery of lung tissue oxidants and improved both histology and frequency of apoptosis.

Exosomes Immunity Strategy: A Novel Approach for Ameliorating Intervertebral Disc Degeneration

Low back pain (LBP), which is one of the most severe medical and social problems globally, has affected nearly 80% of the population worldwide, and intervertebral disc degeneration (IDD) is a common musculoskeletal disorder that happens to be the primary trigger of LBP. The pathology of IDD is based on the impaired homeostasis of catabolism and anabolism in the extracellular matrix (ECM), uncontrolled activation of immunologic cascades, dysfunction, and loss of nucleus pulposus (NP) cells in addition to dynamic cellular and biochemical alterations in the microenvironment of intervertebral disc (IVD). Currently, the main therapeutic approach regarding IDD is surgical intervention, but it could not considerably cure IDD. Exosomes, extracellular vesicles with a diameter of 30–150 nm, are secreted by various kinds of cell types like stem cells, tumor cells, immune cells, and endothelial cells; the lipid bilayer of the exosomes protects them from ribonuclease degradation and helps improve their biological efficiency in recipient cells. Increasing lines of evidence have reported the promising applications of exosomes in immunological diseases, and regarded exosomes as a potential therapeutic source for IDD. This review focuses on clarifying novel therapies based on exosomes derived from different cell sources and the essential roles of exosomes in regulating IDD, especially the immunologic strategy.

The Role of Macroautophagy and Chaperone-Mediated Autophagy in the Pathogenesis and Management of Hepatocellular Carcinoma

Simple Summary

Hepatocellular carcinoma (HCC) is a major health problem with the second highest mortality among all cancers and a continuous increase worldwide. HCC is highly resistant to available chemotherapeutic agents, leaving patients with no effective therapeutic option and a poor prognosis. Although an increasing number of studies have elucidated the potential role of autophagy underlying HCC, the complete regulation is far from understood. The different forms of autophagy constitute important cell survival mechanisms that could prevent hepatocarcinogenesis by limiting hepatocyte death and the associated hepatitis and fibrosis at early stages of chronic liver diseases. On the other hand, at late stages of hepatocarcinogenesis, they could support the malignant transformation of (pre)neoplastic cells by facilitating their survival.

Abstract

Hepatocarcinogenesis is a long process with a complex pathophysiology. The current therapeutic options for HCC management, during the advanced stage, provide short-term survival ranging from 10–14 months. Autophagy acts as a double-edged sword during this process. Recently, two main autophagic pathways have emerged to play critical roles during hepatic oncogenesis, macroautophagy and chaperone-mediated autophagy. Mounting evidence suggests that upregulation of macroautophagy plays a crucial role during the early stages of carcinogenesis as a tumor suppressor mechanism; however, it has been also implicated in later stages promoting survival of cancer cells. Nonetheless, chaperone-mediated autophagy has been elucidated as a tumor-promoting mechanism contributing to cancer cell survival. Moreover, the autophagy pathway seems to have a complex role during the metastatic stage, while induction of autophagy has been implicated as a potential mechanism of chemoresistance of HCC cells. The present review provides an update on the role of autophagy pathways in the development of HCC and data on how the modulation of the autophagic pathway could contribute to the most effective management of HCC.

Alterations of the 70 kDa heat shock protein (HSP70) and sequestosome-1 (p62) in women with breast cancer

Peripheral blood mononuclear cells (PBMCs) respond to altered physiological conditions to alleviate the threat. Production of the 70 kDa heat shock protein (HSP70) is up-regulated to protect proteins from degradation. Sequestosome-1 (p62) binds to altered proteins and the p62-protein complex is degraded by autophagy. P62 is also a regulator of intracellular kinase activity and cell differentiation. We hypothesized that the PBMC response to a malignant breast mass involves elevated production of HSP70 and a decrease in intracellular p62. In this study 46 women had their breast mass excised. PBMCs were isolated and intracellular levels of HSP70 and p62 were quantitated by ELISA. Differences between women with a benign or malignant breast mass were determined. A breast malignancy was diagnosed in 38 women (82.6%) while 8 had a benign lesion. Mean intracellular HSP70 levels were 79.3 ng/ml in PBMCs from women with a malignant lesion as opposed to 44.2 ng/ml in controls (p = 0.04). The mean PBMC p62 level was 2.3 ng/ml in women with a benign breast lesion as opposed to 0.6 ng/ml in those with breast cancer (p < 0.001). Mean p62 levels were lowest in women with invasive carcinoma and a positive lymph node biopsy when compared to those with in-situ carcinoma or absence of lymphadenopathy, respectively. Intracellular HSP70 and p62 levels in PBMCs differ between women with a malignant or benign breast lesion. These measurements may be of value in the preoperative triage of women with a breast mass.

Crosstalk between autophagy inhibitors and endosome-related secretory pathways: a challenge for autophagy-based treatment of solid cancers

Autophagy is best known for its role in organelle and protein turnover, cell quality control, and metabolism. The autophagic machinery has, however, also adapted to enable protein trafficking and unconventional secretory pathways so that organelles (such as autophagosomes and multivesicular bodies) delivering cargo to lysosomes for degradation can change their mission from fusion with lysosomes to fusion with the plasma membrane, followed by secretion of the cargo from the cell. Some factors with key signalling functions do not enter the conventional secretory pathway but can be secreted in an autophagy-mediated manner.Positive clinical results of some autophagy inhibitors are encouraging. Nevertheless, it is becoming clear that autophagy inhibition, even within the same cancer type, can affect cancer progression differently. Even next-generation inhibitors of autophagy can have significant non-specific effects, such as impacts on endosome-related secretory pathways and secretion of extracellular vesicles (EVs). Many studies suggest that cancer cells release higher amounts of EVs compared to non-malignant cells, which makes the effect of autophagy inhibitors on EVs secretion highly important and attractive for anticancer therapy. In this review article, we discuss how different inhibitors of autophagy may influence the secretion of EVs and summarize the non-specific effects of autophagy inhibitors with a focus on endosome-related secretory pathways. Modulation of autophagy significantly impacts not only the quantity of EVs but also their content, which can have a deep impact on the resulting pro-tumourigenic or anticancer effect of autophagy inhibitors used in the antineoplastic treatment of solid cancers.

Autophagy-activated nucleus pulposus cells deliver exosomal miR-27a to prevent extracellular matrix degradation by targeting MMP-13

Although autophagy may be beneficial for maintaining the metabolic balance of the extracellular matrix (ECM) in the nucleus pulposus (NP) and its vitality under inflammation, the underlying mechanism still remains unclear. A previous study found that autophagy activation stimulated the release of exosomes in normal chondrocytes, which are located in a similar avascular environment and share many common features with those of nucleus pulposus cells (NPCs). This study explored the protective effect on matrix degradation in the NP by exosomes derived from autophagy-activated NPCs and exosomal microRNAs. NPCs-derived exosomes (NPCs-Exos) were isolated from culture medium of either normal NPCs or rapamycin-treated NPCs and quantified by nanoparticle tracking analysis. The effect of rapamycin-treated NPC-derived exosomes on NPCs were assessed by coculture with interleukin 1β (IL-1β)-stimulated NPCs. After examination of six major proteinases of the ECM, matrix metalloproteinase 13 (MMP-13) was chosen for further study. miR-27a, which targets MMP-13, was investigated through previous studies and bioinformatics tool. The levels of miR-27a were upregulated in both rapamycin-treated NPCs and their exosomes, compared to the control. When exosomal miR-27a was transferred into NPCs, it alleviated IL-1β-induced degradation of the NPC ECM by targeting MMP-13. Autophagy activation may promote the release of NPCs-derived exosomes and thereby prevent the NPC matrix from degradation. Autophagy activation also alleviates intervertebral disc degeneration (IDD), at least partly via exosomal miR-27a, which restrains MMP-13 expression under IL-1β stimulation. Our work elucidates a new mechanism for how autophagy may participate in preventing IDD, which may be a promising therapeutic strategy.

Aberrant Autophagy Impacts Growth and Multicellular Development in a Dictyostelium Knockout Model of CLN5 Disease

Mutations in CLN5 cause a subtype of neuronal ceroid lipofuscinosis (NCL) called CLN5 disease. While the precise role of CLN5 in NCL pathogenesis is not known, recent work revealed that the protein has glycoside hydrolase activity. Previous work on the Dictyostelium discoideum homolog of human CLN5, Cln5, revealed its secretion during the early stages of development and its role in regulating cell adhesion and cAMP-mediated chemotaxis. Here, we used Dictyostelium to examine the effect of cln5-deficiency on various growth and developmental processes during the life cycle. During growth, cln5^– cells displayed reduced cell proliferation, cytokinesis, viability, and folic acid-mediated chemotaxis. In addition, the growth of cln5^– cells was severely impaired in nutrient-limiting media. Based on these findings, we assessed autophagic flux in growth-phase cells and observed that loss of cln5 increased the number of autophagosomes suggesting that the basal level of autophagy was increased in cln5^– cells. Similarly, loss of cln5 increased the amounts of ubiquitin-positive proteins. During the early stages of multicellular development, the aggregation of cln5^– cells was delayed and loss of the autophagy genes, atg1 and atg9, reduced the extracellular amount of Cln5. We also observed an increased amount of intracellular Cln5 in cells lacking the Dictyostelium homolog of the human glycoside hydrolase, hexosaminidase A (HEXA), further supporting the glycoside hydrolase activity of Cln5. This observation was also supported by our finding that CLN5 and HEXA expression are highly correlated in human tissues. Following mound formation, cln5^– development was precocious and loss of cln5 affected spore morphology, germination, and viability. When cln5^– cells were developed in the presence of the autophagy inhibitor ammonium chloride, the formation of multicellular structures was impaired, and the size of cln5^– slugs was reduced relative to WT slugs. These results, coupled with the aberrant autophagic flux observed in cln5^– cells during growth, support a role for Cln5 in autophagy during the Dictyostelium life cycle. In total, this study highlights the multifaceted role of Cln5 in Dictyostelium and provides insight into the pathological mechanisms that may underlie CLN5 disease.

Spatio-Temporal Autophagy Tracking with a Cell-Permeable, Water-Soluble, Peptide-Based, Autophagic Vesicle-Targeted Sensor

Autophagy is an essential cellular degradation process. Impaired autophagy has been linked to multiple disorders, including cancer and neurodegeneration. Tracking the autophagic flux in living cells will provide mechanistic insights into autophagy and will allow rapid screening of autophagy modulators as potential therapeutics. Imaging autophagy to track the autophagic flux demands a cell-permeable probe that can specifically target autophagic vesicles and report on the extent of autophagy. Existing fluorescent protein-based probes for imaging autophagy target autophagic vesicles but are cell-impermeable and degrade with the progress of autophagy resulting in ambiguous information on the later stages of autophagy. Although small-molecule-based autophagy probes can be cell-permeable, they are mostly water-insoluble and often target lysosomes instead of autophagic vesicles leading to incomplete evidence of the early stages of the process. Hence, there is a major gap in the ability to link the imaging data obtained by applying fluorescent sensors to the real extent of autophagy in living cells. To address these challenges, we have combined the desirable features of targetability and cell permeability to develop a novel water-soluble, cell-permeable, visible-light excitable, peptide-based, fluorescent sensor, HCFP, for imaging autophagy and tracking the autophagic flux. The probe readily enters living cells within 30 min of incubation, distinctly targets autophagic vesicles, and spatio-temporally tracks the entire autophagy pathway in living cells via a ratiometric pH-sensitive detection scheme. The salient features of the probe combining targetability with cell permeability should provide an edge in high-throughput screening of autophagy modulators by tracking autophagy live.

Pathogenicity and Virulence of Legionella: Intracellular replication and host response

Bacteria of the genus Legionella are natural pathogens of amoebae that can cause a severe pneumonia in humans called Legionnaires’ Disease. Human disease results from inhalation of Legionella-contaminated aerosols and subsequent bacterial replication within alveolar macrophages. Legionella pathogenicity in humans has resulted from extensive co-evolution with diverse genera of amoebae. To replicate intracellularly, Legionella generates a replication-permissive compartment called the Legionella-containing vacuole (LCV) through the concerted action of hundreds of Dot/Icm-translocated effector proteins. In this review, we present a collective overview of Legionella pathogenicity including infection mechanisms, secretion systems, and translocated effector function. We also discuss innate and adaptive immune responses to L. pneumophila, the implications of Legionella genome diversity and future avenues for the field.

FGF21 facilitates autophagy in prostate cancer cells by inhibiting the PI3K-Akt-mTOR signaling pathway

Fibroblast growth factor 21 (FGF21) plays an important role in regulating glucose and lipid metabolism, but its role in cancer is less well-studied. We aimed to investigate the action of FGF21 in the development of prostate cancer (PCa). Herein, we found that FGF21 expression was markedly downregulated in PCa tissues and cell lines. FGF21 inhibited the proliferation and clone formation of LNCaP cells (a PCa cell line) and promoted apoptosis. FGF21 also inhibited PCa cell migration and invasiveness. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that FGF21 was related to autophagy and the phosphatidylinositol 3-kinase–Akt kinase–mammalian target of rapamycin (PI3K–Akt–mTOR) pathway. Mechanistically, FGF21 promoted autophagy in LNCaP cells by inhibiting the PI3K–Akt–mTOR–70S6K pathway. In addition, FGF21 inhibited PCa tumorigenesis in vivo in nude mice. Altogether, our findings show that FGF21 inhibits PCa cell proliferation and promoted apoptosis in PCa cells through facilitated autophagy. Therefore, FGF21 might be a potential novel target in PCa therapy.

IL-17 deficiency aggravates the streptozotocin-induced diabetic nephropathy through the reduction of autophagosome formation in mice

BACKGROUND

Diabetic nephropathy (DN) is one of the most important medical complications of diabetes mellitus. Autophagy is an important mediator of pathological response and plays a critical role in inflammation during the progression of diabetic nephropathy. Interleukin (IL)-17A favorably modulates inflammatory disorders including DN. In this study, we examined whether IL-17A deficiency affected the autophagy process in the kidneys of mice with streptozotocin (STZ)-induced DN.

METHODS

The autophagic response of IL-17A to STZ-induced nephrotoxicity was evaluated by analyzing STZ-induced functional and histological renal injury in IL-17A knockout (KO) mice.

RESULTS

IL-17A KO STZ-treated mice developed more severe nephropathy than STZ-treated wild-type (WT) mice, with increased glomerular damage and renal interstitial fibrosis at 12 weeks. IL-17A deficiency also increased the up-regulation of proinflammatory cytokines and fibrotic gene expression after STZ treatment. Meanwhile, autophagy-associated proteins were induced in STZ-treated WT mice. However, IL-17A KO STZ-treated mice displayed a significant decrease in protein expression. Especially, the levels of LC3 and ATG7, which play crucial roles in autophagosome formation, were notably decreased in the IL-17A KO STZ-treated mice compared with their WT counterparts.

CONCLUSIONS

IL-17 deficiency aggravates of STZ-induced DN via attenuation of autophagic response. Our study demonstrated that IL-17A mediates STZ-induced renal damage and represents a potential therapeutic target in DN.

The biological pathways of Alzheimer disease: a review

Alzheimer disease is a progressive neurodegenerative disorder, mainly affecting older people, which severely impairs patients' quality of life. In the recent years, the number of affected individuals has seen a rapid increase. It is estimated that up to 107 million subjects will be affected by 2050 worldwide. Research in this area has revealed a lot about the biological and environmental underpinnings of Alzheimer, especially its correlation with β-Amyloid and Tau related mechanics; however, the precise molecular events and biological pathways behind the disease are yet to be discovered. In this review, we focus our attention on the biological mechanics that may lie behind Alzheimer development. In particular, we briefly describe the genetic elements and discuss about specific biological processes potentially associated with the disease.

Autophagy regulates levels of tumor suppressor enzyme protein phosphatase 6

Protein phosphatase 6 (PP6) is an essential serine/threonine protein phosphatase that acts as an important tumor suppressor. However, increased protein levels of PP6 have been observed in some cancer types, and they correlate with poor prognosis in glioblastoma. This raises a question about how PP6 protein levels are regulated in normal and transformed cells. In this study, we show that PP6 protein levels increase in response to pharmacologic and genetic inhibition of autophagy. PP6 associates with autophagic adaptor protein p62/SQSTM1 and is degraded in a p62-dependent manner. Accordingly, protein levels of PP6 and p62 fluctuate in concert under different physiological and pathophysiological conditions. Our data reveal that PP6 is regulated by p62-dependent autophagy and suggest that accumulation of PP6 protein in tumor tissues is caused at least partially by deficiency in autophagy.

Autophagy regulates trophoblast invasion by targeting NF-κB activity

Preeclampsia is one of the most serious complications of pregnancy, affecting 5-10% of parturients worldwide. Recent studies have suggested that autophagy is involved in trophoblast invasion and may be associated with defective placentation underlying preeclampsia. We thus aimed to understand the mechanistic link between autophagy and trophoblast invasion. Using the two most commonly used trophoblast cell lines, JEG-3 and HTR-8/SVneo, we inhibited autophagy by ATG5 and beclin-1 shRNA. Conversion of LC3-II was evaluated in ATG5 and beclin-1 knock-down cells in the presence of the lysosomal protease inhibitors E-64d and pepstatin A, to detect the efficiency of autophagy inhibition. Upon autophagy inhibition, we measured cell invasion, activity of NF-κB and related signaling pathways, MMP-2, MMP-9, sFlt-1, and TNF-α levels. Autophagy inhibition increased the invasiveness of these trophoblastic cell lines and increased Akt and NF-κB activity as well as p65 expression. Of note, an NF-κB inhibitor significantly attenuated the trophoblast invasion induced by autophagy inhibition. Autophagy inhibition was also associated with increased MMP-2 and MMP-9 levels and decreased the production of sFlt-1 and TNF-α. Collectively, our results indicate that autophagy regulates trophoblast invasiveness in which the NF-κB pathway and MMP-2, MMP-9, sFlt-1 and TNF-α levels are affected.

Propofol-induced MiR-20b expression initiates endogenous cellular signal changes mitigating hypoxia/re-oxygenation-induced endothelial autophagy in vitro

Certain miRNAs can attenuate hypoxia/re-oxygenation-induced autophagic cell death reported in our previous studies, but how these miRNAs regulate the autophagy-related cellular signaling pathway in preventing cell death is largely unknown. In the current study, the autophagy-related miRNAs of hsa-miR-20b were investigated in an in vitro model of hypoxia/re-oxygenation-induced endothelial autophagic cell death. Of these, miR-20b was found to be the most important miRNA which targeted on the key autophagy kinase ULK1 and inhibited hypoxia/re-oxygenation injury-induced autophagy by decreasing both autophagosomes and LC3I to II transition rate and P62 degradation. These processes were reversed by the transfection of an miR-20b inhibitor. Re-expression of ULK1 restores miR-20b-inhibited autophagy. Propofol, a commonly used anesthetic, promoted miR-20b and METTL3 expression and attenuated endothelial autophagic cell death. The inhibited endogenous expression of miR-20b or silenced METTL3 diminished the protective effect of propofol and accentuated autophagy. Additionally, METTL3 knockdown significantly inhibited miR-20b expression but up-regulated pri-miR-20b expression. Together, our data shows that propofol protects against endothelial autophagic cell death induced by hypoxia/re-oxygenation injury, associated with activation of METTL3/miR-20b/ULK1 cellular signaling.

Metformin Mitigates Cartilage Degradation by Activating AMPK/SIRT1-Mediated Autophagy in a Mouse Osteoarthritis Model

Chondrocyte dysfunction is a key mechanism underlying osteoarthritis. Metformin has shown protective effects in many diseases. The present study aimed to investigate the effects of metformin on autophagy and apoptosis in the process of osteoarthritis. A mouse osteoarthritis model was set up by surgically destabilizing medial meniscus in the knee. Intraarticular injection of metformin or vehicle was applied in the right knee for eight weeks. Mouse articular chondrocytes were isolated and passaged for in vitro experiments. Small interfering RNA (siRNA) transfection was used to silence target genes. Western blotting, immunohistochemistry, transmission electron microscopy were used. After eight weeks, metformin restored surgery-induced upregulation of MMP13 and downregulation of type II collagen in the joint cartilage. In cultured primary murine chondrocytes, IL-1β aggravated apoptosis and catabolic response in a dose-dependent manner. In the presence of IL-1β, metformin increased phosphorylated levels of AMPKα and upregulated SIRT1 protein expression, leading to an increase in autophagy as well as a decrease in catabolism and apoptosis. Inactivating AMPKα or inhibiting SIRT1 prevented the augmented autophagy in the presence of metformin. Silencing AMPKα2, but not AMPKα1, reduced SIRT1 expression and downregulated autophagy in cultured chondrocytes. Metformin protects against IL-1β-induced extracellular matrix (ECM) degradation in cultured chondrocytes and in mouse osteoarthritis model through activating AMPKα/SIRT1 signaling. Metformin shed light on the treatment of osteoarthritis.

Baicalin Protects Human OA Chondrocytes Against IL-1β-Induced Apoptosis and ECM Degradation by Activating Autophagy via MiR-766-3p/AIFM1 Axis

Background

Osteoarthritis (OA) is one of the most prevalent and degenerative diseases with complicated pathology including articular cartilage degradation, subchondral sclerosis and synovitis. Chondrocytes play a crucial role in maintaining cartilage integrity.

Methods

Primary chondrocytes were treated with 10 ng/mL IL-1β alone, or pre-treated with 20 μM baicalin for 5 h followed by co-treatment with 20 μM baicalin and 10 ng/mL IL-1β. CCK-8 assay was used to assess cell viability, and cell apoptosis was analyzed by both PI/FITC-Annexin V staining and quantitating apoptosis-related Bcl-2, Bax and cleaved-caspase-3 expression at both protein and mRNA level by Western blotting and qRT-PCR, respectively. Chondrocytes were transfected with miRNA-766-3p mimic and autophagy flux was examined by LC3, Beclin and p62 Western blotting and by Cyto-ID assay to quantify autophagic vacuoles.

Results

Baicalin treatment decreased the apoptosis rate and the expressions of pro-apoptotic proteins induced by IL-1β, up-regulated anti-apoptotic Bcl-2 expression, and inhibited the degradation of ECM. Baicalin increased autophagy through up-regulating the autophagy markers Beclin-1 expression and LC3 Ⅱ/LC3 Ⅰ ratio and promoting autophagic flux. Contrarily, autophagy inhibition partially alleviated the beneficial effects of baicalin on ECM synthesis and anti-apoptosis in the chondrocytes treated with L-1β. Furthermore, the differential expressional profiles of miR-766-3p and apoptosis-inducing factor mitochondria-associated 1 (AIFM1) were determined in IL-1β and IL-1β + baicalin-treated chondrocytes, and we confirmed AIFM1 was a target of miR-766-3p. MiR-766-3p overexpression suppressed apoptosis and facilitated autophagy and ECM synthesis in the chondrocytes through decreasing AIFM1. Contrarily, silencing of miR-766-3p inhibited chondrocyte autophagy and promoted apoptosis, and this effect could be reversed by AIFM1 silence.

Conclusion

Baicalin protects human OA chondrocytes against IL-1β-induced apoptosis and the degradation of ECM through activating autophagy via miR-766-3p/AIFM1 axis and serves as a potential therapeutic candidate for OA treatment.

Mechanisms governing autophagosome biogenesis

Autophagosomes are double-membrane vesicles newly formed during autophagy to engulf a wide range of intracellular material and transport this autophagic cargo to lysosomes (or vacuoles in yeasts and plants) for subsequent degradation. Autophagosome biogenesis responds to a plethora of signals and involves unique and dynamic membrane processes. Autophagy is an important cellular mechanism allowing the cell to meet various demands, and its disruption compromises homeostasis and leads to various diseases, including metabolic disorders, neurodegeneration and cancer. Thus, not surprisingly, the elucidation of the molecular mechanisms governing autophagosome biogenesis has attracted considerable interest. Key molecules and organelles involved in autophagosome biogenesis, including autophagy-related (ATG) proteins and the endoplasmic reticulum, have been discovered, and their roles and relationships have been investigated intensely. However, several fundamental questions, such as what supplies membranes/lipids to build the autophagosome and how the membrane nucleates, expands, bends into a spherical shape and finally closes, have proven difficult to address. Nonetheless, owing to recent studies with new approaches and technologies, we have begun to unveil the mechanisms underlying these processes on a molecular level. We now know that autophagosome biogenesis is a highly complex process, in which multiple proteins and lipids from various membrane sources, supported by the formation of membrane contact sites, cooperate with biophysical phenomena, including membrane shaping and liquid-liquid phase separation, to ensure seamless segregation of the autophagic cargo. Together, these studies pave the way to obtaining a holistic view of autophagosome biogenesis.

Virus-Induced Cytoplasmic Aggregates and Inclusions are Critical Cellular Regulatory and Antiviral Factors

RNA granules, aggresomes, and autophagy are key players in the immune response to viral infections. They provide countermeasures that regulate translation and proteostasis in order to rewire cell signaling, prevent viral interference, and maintain cellular homeostasis. The formation of cellular aggregates and inclusions is one of the strategies to minimize viral infections and virus-induced cell damage and to promote cellular survival. However, viruses have developed several strategies to interfere with these cellular processes in order to achieve productive replication within the host cells. A review on how these mechanisms could function as modulators of cell signaling and antiviral factors will be instrumental in refining the current scientific knowledge and proposing means whereby cellular granules and aggregates could be induced or prevented to enhance the antiviral immune response in mammalian cells.

Interplay Between Mitochondrial Oxidative Disorders and Proteostasis in Alzheimer's Disease

Although the basis of Alzheimer’s disease (AD) etiology remains unknown, oxidative stress (OS) has been recognized as a prodromal factor associated to its progression. OS refers to an imbalance between oxidant and antioxidant systems, which usually consist in an overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which overwhelms the intrinsic antioxidant defenses. Due to this increased production of ROS and RNS, several biological functions such as glucose metabolism or synaptic activity are impaired. In AD, growing evidence links the ROS-mediated damages with molecular targets including mitochondrial dynamics and function, protein quality control system, and autophagic pathways, affecting the proteostasis balance. In this scenario, OS should be considered as not only a major feature in the pathophysiology of AD but also a potential target to combat the progression of the disease. In this review, we will discuss the role of OS in mitochondrial dysfunction, protein quality control systems, and autophagy associated to AD and suggest innovative therapeutic strategies based on a better understanding of the role of OS and proteostasis.

Autophagy and autophagy-related proteins in cancer

Autophagy, as a type II programmed cell death, plays crucial roles with autophagy-related (ATG) proteins in cancer. Up to now, the dual role of autophagy both in cancer progression and inhibition remains controversial, in which the numerous ATG proteins and their core complexes including ULK1/2 kinase core complex, autophagy-specific class III PI3K complex, ATG9A trafficking system, ATG12 and LC3 ubiquitin-like conjugation systems, give multiple activities of autophagy pathway and are involved in autophagy initiation, nucleation, elongation, maturation, fusion and degradation. Autophagy plays a dynamic tumor-suppressive or tumor-promoting role in different contexts and stages of cancer development. In the early tumorigenesis, autophagy, as a survival pathway and quality-control mechanism, prevents tumor initiation and suppresses cancer progression. Once the tumors progress to late stage and are established and subjected to the environmental stresses, autophagy, as a dynamic degradation and recycling system, contributes to the survival and growth of the established tumors and promotes aggressiveness of the cancers by facilitating metastasis. This indicates that regulation of autophagy can be used as effective interventional strategies for cancer therapy.

Enhanced expression of HNF4α during intestinal epithelial differentiation is involved in the activation of ER stress

Intestinal epithelial cells are derived from stem cells at the crypts that undergo differentiation into transit-amplifying cells, which in turn form terminally differentiated enterocytes as these cells reach the villus. Extensive alterations in both transcriptional and translational programs occur during differentiation, which can induce the activation of cellular stress responses such as ER stress-related unfolded protein response (UPR) and autophagy, particularly in the cells that are already committed to becoming absorptive cells. Using an epithelial cell model of enterocyte differentiation, we report a mechanistic study connecting enterocyte differentiation to UPR and autophagy. We report that differentiated colon epithelial cells showed increased cytosolic Ca²⁺ levels and activation of all three pathways of UPR: inositol-requiring enzyme 1 (IRE1), protein kinase RNA-like ER kinase, and activating transcription factor 6 (ATF6) compared to the undifferentiated cells. Enhanced UPR in the differentiated cells was accompanied by the induction of autophagy as evidenced by increased ratio of light chain 3 II/I, upregulation of Beclin-1, and downregulation of p62. We show for the first time that mechanistically, the upregulation of hepatocyte nuclear factor 4α (HNF4α) during differentiation led to increased promoter binding and transcriptional upregulation of two major proteins of UPR: X-box binding protein-1 and ATF6, implicating HNF4α as a key regulator of UPR response during differentiation. Integrating wet-lab with in silico analyses, the present study links differentiation to cellular stress responses, and highlights the importance of transcription factor signaling and cross-talk between the cellular events in the regulation of intestinal cell differentiation.

Autophagy Is a Tolerance-Avoidance Mechanism that Modulates TCR-Mediated Signaling and Cell Metabolism to Prevent Induction of T Cell Anergy

Mocholi et al. show that, following T cell activation, activation of autophagy constitutes a tolerance-avoidance mechanism that, through modulation of cell metabolism and specific signaling pathways, allows T cells to engage in effector responses and avoid anergy. In vivo inhibition of autophagy in T cells induces tolerance and prevents autoimmunity.

In response to activation, CD4⁺ T cells upregulate autophagy. However, the functional consequences of that upregulation have not been fully elucidated. In this study, we identify autophagy as a tolerance-avoidance mechanism. Our data show that inhibition of autophagy during CD4⁺ T cell activation induces a long-lasting state of hypo-responsiveness that is accompanied by the expression of an anergic gene signature. Cells unable to induce autophagy after T cell receptor (TCR) engagement show inefficient mitochondrial respiration and decreased turnover of the protein tyrosine phosphatase PTPN1, which translates into defective TCR-mediated signaling. In vivo, inhibition of autophagy during antigen priming induces T cell anergy and decreases the severity of disease in an experimental autoimmune encephalomyelitis mouse model. Interestingly, CD4⁺ T cells isolated from the synovial fluid of juvenile idiopathic arthritis patients, while resistant to suboptimal stimulation-induced anergy, can be tolerized with autophagy inhibitors. We propose that autophagy constitutes a tolerance-avoidance mechanism, which determines CD4⁺ T cell fate.

Intra-articular Injection of Chloramphenicol Reduces Articular Cartilage Degeneration in a Rabbit Model of Osteoarthritis

BACKGROUND

Osteoarthritis (OA) is characterized by degeneration of articular cartilage. Studies have found that enhancement of autophagy, an intracellular catabolic process, may limit the pathologic progression of OA. Chloramphenicol is a potent activator of autophagy; however, the effects of chloramphenicol on articular cartilage are unknown.

QUESTIONS/PURPOSES

Using human OA knee chondrocytes in vitro, we asked, does chloramphenicol (1) activate autophagy in chondrocytes; (2) protect chondrocytes from IL-1β-induced apoptosis; and (3) reduce the expression of matrix metallopeptidase (MMP)-13 and IL-6 (markers associated with articular cartilage degradation and joint inflammation). Using an in vivo rabbit model of OA, we asked, does an intra-articular injection of chloramphenicol in the knee (4) induce autophagy; (5) reduce OA severity; and (6) reduce MMP-13 expression?

METHODS

Human chondrocytes were extracted from 10 men with OA undergoing TKA. After treatment with 25 μg/mL, 50 μg/mL, or 100μg/mL chloramphenicol, the autophagy of chondrocytes was detected with Western blotting, transmission electron microscopy, or an autophagy detection kit. There were four groups in our study: one group was untreated, one was treated with 100 μg/mL chloramphenicol, another was treated with 10 ng/mL of IL-1β, and the final group was treated with 10 ng/mL of IL-1β and 100 μg/mL of chloramphenicol. All groups were treated for 48 hours; cell apoptosis was detected with Western blotting and flow cytometry. Inflammation marker IL-6 in the cell culture supernatant was detected with an ELISA. Articular cartilage degradation-related enzyme MMP-13 was analyzed with Western blotting. A rabbit model of OA was induced by intra-articular injection of type II collagenase in 20 male 3-month-old New Zealand White rabbits' right hind leg knees; the left hind leg knees served as controls. Rabbits were treated by intra-articular injection of saline or chloramphenicol once a week for 8 weeks. Autophagy of the articular cartilage was detected with Western blotting and transmission electron microscopy. Degeneration of articular cartilage was analyzed with Safranin O-fast green staining and the semi-quantitative index Osteoarthritis Research Society International (OARSI) grading system. Degeneration of articular cartilage was evaluated using the OARSI grading system. The expression of MMP-13 in articular cartilage was detected with immunohistochemistry.

RESULTS

Chloramphenicol activated autophagy in vitro in the chondrocytes of humans with OA and in an in vivo rabbit model of OA. Chloramphenicol inhibited IL-1-induced apoptosis (flow cytometry results with chloramphenicol, 25.33 ± 3.51%, and without chloramphenicol, 44.00 ± 3.61%, mean difference, 18.67% [95% CI 10.60 to 26.73]; p = 0.003) and the production of proinflammatory cytokine IL-6 (ELISA results, with chloramphenicol, 720.00 ± 96.44 pg/mL, without chloramphenicol, 966.67 ± 85.05 pg/mL; mean difference 74.24 pg/mL [95% CI 39.28 to 454.06]; p = 0.029) in chondrocytes. After chloramphenicol treatment, the severity of cartilage degradation was reduced in the treatment group (OARSI 6.80 ± 2.71) compared with the control group (12.30 ± 2.77), (mean difference 5.50 [95% CI 1.50 to 9.50]; p = 0.013). Furthermore, chloramphenicol treatment also decreased the production of MMP-13 in vitro and in vivo.

CONCLUSIONS

Chloramphenicol reduced the severity of cartilage degradation in a type II collagen-induced rabbit model of OA, which may be related to induction of autophagy and inhibition of MMP-13 and IL-6.

CLINICAL RELEVANCE

Our study suggests that an intra-articular injection of chloramphenicol may reduce degeneration of articular cartilage and that induction of autophagy may be a method for treating OA. The animal model we used was type II collagen-induced OA, which was different from idiopathic OA and post-traumatic OA. Therefore, we need to use other types of OA models (idiopathic OA or a surgically induced OA model) to further verify its effect, and the side effects of chloramphenicol also need to be considered, such as myelosuppression.

Transcriptome analysis reveals autophagy as regulator of TGFβ/Smad-induced fibrogenesis in trabecular meshwork cells

The trabecular meshwork (TM) is a specialized ocular tissue, which is responsible, together with the Schlemm’s canal (SC), for maintaining appropriate levels of intraocular pressure. Dysfunction of these tissues leads to ocular hypertension and increases the risk for developing glaucoma. Previous work by our laboratory revealed dysregulated autophagy in aging and in glaucomatous TM cells. In order to gain more insight in the role of autophagy in the TM pathophysiology, we have conducted transcriptome and functional network analyses of TM primary cells with silenced expression of the autophagy genes Atg5 and Atg7. Atg5/7-deficient TM cells showed changes in transcript levels of several fibrotic genes, including TGFβ2, BAMBI, and SMA. Furthermore, genetic and pharmacological inhibition of autophagy was associated with a parallel reduction in TGFβ-induced fibrosis, caused by a BAMBI-mediated reduced activation of Smad2/3 signaling in autophagy-deficient cells. At the same time, TGFβ treatment led to Smad2/3-dependent dysregulation of autophagy in TM cells, characterized by increased LC3-II levels and autophagic vacuoles content. Together, our results indicate a cross-talk between autophagy and TGFβ signaling in TM cells.

Sestrins as a Therapeutic Bridge between ROS and Autophagy in Cancer

The regulation of Reactive Oxygen Species (ROS) levels and the contribution therein from networks regulating cell metabolism, such as autophagy and the mTOR-dependent nutrient-sensing pathway, constitute major targets for selective therapeutic intervention against several types of tumors, due to their extensive rewiring in cancer cells as compared to healthy cells. Here, we discuss the sestrin family of proteins—homeostatic transducers of oxidative stress, and drivers of antioxidant and metabolic adaptation—as emerging targets for pharmacological intervention. These adaptive regulators lie at the intersection of those two priority nodes of interest in antitumor intervention—ROS control and the regulation of cell metabolism and autophagy—therefore, they hold the potential not only for the development of completely novel compounds, but also for leveraging on synergistic strategies with current options for tumor therapy and classification/stadiation to achieve personalized medicine.

Loss of BRUCE reduces cellular energy level and induces autophagy by driving activation of the AMPK-ULK1 autophagic initiating axis

Autophagy is an intracellular catabolic system. It delivers cellular components to lysosomes for degradation and supplies nutrients that promote cell survival under stress conditions. Although much is known regarding starvation-induced autophagy, the regulation of autophagy by cellular energy level is less clear. BRUCE is an ubiquitin conjugase and ligase with multi-functionality. It has been reported that depletion of BRUCE inhibits starvation-induced autophagy by blockage of the fusion step. Herein we report a new function for BRUCE in the dual regulation of autophagy and cellular energy. Depletion of BRUCE alone (without starvation) in human osteosarcoma U2OS cells elevated autophagic activity as indicted by the increased LC3B-II protein and its autophagic puncta as well as further increase of both by chloroquine treatment. Such elevation results from enhanced induction of autophagy since the numbers of both autophagosomes and autolysosomes were increased, and recruitment of ATG16L onto the initiating membrane structure phagophores was increased. This concept is further supported by elevated lysosomal enzyme activities. In contrast to starvation-induced autophagy, BRUCE depletion did not block fusion of autophagosomes with lysosomes as indicated by increased lysosomal cleavage of the GFP-LC3 fusion protein. Mechanistically, BRUCE depletion lowered the cellular energy level as indicated by both a higher ratio of AMP/ATP and the subsequent activation of the cellular energy sensor AMPK (pThr-172). The lower energy status co-occurred with AMPK-specific phosphorylation and activation of the autophagy initiating kinase ULK1 (pSer-555). Interestingly, the higher autophagic activity by BRUCE depletion is coupled with enhanced cisplatin resistance in human ovarian cancer PEO4 cells. Taken together, BRUCE depletion promotes induction of autophagy by lowering cellular energy and activating the AMPK-ULK1-autophagy axis, which could contribute to ovarian cancer chemo-resistance. This study establishes a BRUCE-AMPK-ULK1 axis in the regulation of energy metabolism and autophagy, as well as provides insights into cancer chemo-resistance.

The negative effect of lipid challenge on autophagy inhibits T cell responses

Obesity is associated with changes in the immune system that significantly hinder its ability to mount efficient immune responses. Previous studies have reported a dysregulation of immune responses caused by lipid challenge; however, the mechanisms underlying that dysregulation are still not completely understood. Autophagy is an essential catabolic process through which cellular components are degraded by the lysosomal machinery. In T cells, autophagy is an actively regulated process necessary to sustain homeostasis and activation. Here, we report that CD4⁺ T cell responses are inhibited when cells are challenged with increasing concentrations of fatty acids. Furthermore, analysis of T cells from diet-induced obese mice confirms that high lipid load inhibits activation-induced responses in T cells. We have found that autophagy is inhibited in CD4⁺ T cells exposed in vitro or in vivo to lipid stress, which causes decreased autophagosome formation and degradation. Supporting that inhibition of autophagy caused by high lipid load is a key mechanism that accounts for the effects on T cell function of lipid stress, we found that ATG7 (autophagy-related 7)-deficient T cells, unable to activate autophagy, did not show additional inhibitory effects on their responses to activation when subjected to lipid challenge. Our results indicate, thus, that increased lipid load can dysregulate autophagy and cause defective T cell responses, and suggest that inhibition of autophagy may underlie some of the characteristic obesity-associated defects in the T cell compartment.Abbreviations: ACTB: actin, beta; ATG: autophagy-related; CDKN1B: cyclin-dependent kinase inhibitor 1B; HFD: high-fat diet; IFNG: interferon gamma; IL: interleukin; MAPK1/ERK2: mitogen-activated protein kinase 1; MAPK3/ERK1: mitogen-activated protein kinase 3; MAPK8/JNK: mitogen-activated protein kinase 8; LC3-I: non-conjugated form of MAP1LC3B; LC3-II: phosphatidylethanolamine-conjugated form of MAP1LC3B; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; MS: mass spectrometry; MTOR: mechanistic target of rapamycin kinase; NFATC2: nuclear factor of activated T cells, cytoplasmic, calcineurin dependent 2; NLRP3: NLR family, pyrin domain containing 3; OA: oleic acid; PI: propidium iodide; ROS: reactive oxygen species; STAT5A: signal transducer and activator of transcription 5A; TCR: T cell receptor; T_H1: T helper cell type 1.

Mitophagy regulates mitochondrial network signaling, oxidative stress, and apoptosis during myoblast differentiation

Macroautophagy/autophagy is a degradative process essential for various cellular processes. We previously demonstrated that autophagy-deficiency causes myoblast apoptosis and impairs myotube formation. In this study, we continued this work with particular emphasis on mitochondrial remodelling and stress/apoptotic signaling. We found increased (p < 0.05) autophagic (e.g., altered LC3B levels, increased ATG7, decreased SQSTM1) and mitophagic (e.g., BNIP3 upregulation, mitochondrial localized GFP-LC3 puncta, and elevated mitochondrial LC3B-II) signaling during myoblast differentiation. shRNA-mediated knockdown of ATG7 (shAtg7) decreased these autophagic and mitophagic responses, while increasing CASP3 activity and ANXA5/annexin V staining in differentiating myoblasts; ultimately resulting in dramatically impaired myogenesis. Further confirming the importance of mitophagy in these responses, CRISPR-Cas9-mediated knockout of Bnip3 (bnip3^-/-) resulted in increased CASP3 activity and DNA fragmentation as well as impaired myoblast differentiation. In addition, shAtg7 myoblasts displayed greater endoplasmic reticulum (e.g., increased CAPN activity and HSPA) and mitochondrial (e.g., mPTP formation, reduced mitochondrial membrane potential, elevated mitochondrial 4-HNE) stress. shAtg7 and bnip3^-/- myoblasts also displayed altered mitochondria-associated signaling (e.g., PPARGC1A, DNM1L, OPA1) and protein content (e.g., SLC25A4, VDAC1, CYCS). Moreover, shAtg7 myoblasts displayed CYCS and AIFM1 release from mitochondria, and CASP9 activation. Similarly, bnip3^-/- myoblasts had significantly higher CASP9 activation during differentiation. Importantly, administration of a chemical inhibitor of CASP9 (Ac-LEHD-CHO) or dominant-negative CASP9 (ad-DNCASP9) partially recovered differentiation and myogenesis in shAtg7 myoblasts. Together, these data demonstrate an essential role for autophagy in protecting myoblasts from mitochondrial oxidative stress and apoptotic signaling during differentiation, as well as in the regulation of mitochondrial network remodelling and myogenesis. Abbreviations: 3MA: 3-methyladenine; 4-HNE: 4-hydroxynonenal; ACT: actin; AIFM1/AIF: apoptosis-inducing factor, mitochondrion-associated 1; ANXA5: annexin V; ATG7: autophagy related 7; AU: arbitrary units; BAX: BCL2-associated X protein; BCL2: B cell leukemia/lymphoma 2; BECN1: beclin 1, autophagy related; BNIP3: BCL2/adenovirus E1B interacting protein 3; CAPN: calpain; CASP: caspase; CASP3: caspase 3; CASP8: caspase 8; CASP9: caspase 9; CASP12: caspase 12; CAT: catalase; CQ: chloroquine; CYCS: cytochrome c, somatic; DCF; 2',7'-dichlorofluorescein; DNM1L/DRP1: dynamin 1-like; DM: differentiation media; DMEM: Dulbecco's modified Eagle's medium; ER: endoplasmic reticulum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; GM: growth media; p-H2AFX: phosphorylated H2A histone family, member X; H2BFM: H2B histone family, member M; HBSS: Hanks balanced salt solution; HSPA/HSP70: heat shock protein family A; JC-1: tetraethylbenzimidazolylcarbocyanine iodide; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mPTP: mitochondrial permeability transition pore; MYH: myosin heavy chain; MYOG: myogenin; OPA1: OPA1, mitochondrial dynamin like GTPase; PI: propidium iodide; PINK1: PTEN induced putative kinase 1; PPARGC1A/PGC1α: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; ROS: reactive oxygen species; SLC25A4/ANT1: solute carrier family 25 (mitochondrial carrier, adenine nucleotide translocator), member 4; SOD1: superoxide dismutase 1, soluble; SOD2: superoxide dismutase 2, mitochondrial; SQSTM1/p62: sequestosome 1; VDAC1: voltage-dependent anion channel 1.

Targeting autophagy using metallic nanoparticles: a promising strategy for cancer treatment

Despite the extensive genetic and phenotypic variations present in the different tumors, they frequently share common metabolic alterations, such as autophagy. Autophagy is a self-degradative process in response to stresses by which damaged macromolecules and organelles are targeted by autophagic vesicles to lysosomes and then eliminated. It is known that autophagy dysfunctions can promote tumorigenesis and cancer development, but, interestingly, its overstimulation by cytotoxic drugs may also induce cell death and chemosensitivity. For this reason, the possibility to modulate autophagy may represent a valid therapeutic approach to treat different types of cancers and a variety of clinical trials, using autophagy modulators, are currently employed. On the other hand, recent progress in nanotechnology offers plenty of tools to fight cancer with innovative and efficient therapeutic agents by overcoming obstacles usually encountered with traditional drugs. Interestingly, nanomaterials can modulate autophagy and have been exploited as therapeutic agents against cancer. In this article, we summarize the most recent advances in the application of metallic nanostructures as potent modulators of autophagy process through multiple mechanisms, stressing their therapeutic implications in cancer diseases. For this reason, we believe that autophagy modulation with nanoparticle-based strategies would acquire clinical relevance in the near future, as a complementary therapy for the treatment of cancers and other diseases.

Melatonin-mediated regulation of autophagy: Making sense of double-edged sword in cancer

Much research has been conducted to discover novel techniques to reverse the process of tumorigenesis and, cure already stablished malignancies. One well-stablished approach has been the use of organic compounds and naturally found agents such as melatonin whose anticancer effects have been shown in multiple studies, signaling a unique opportunity regarding cancer prevention and treatment. Various agents use a variety of methods to exert their anticancer effects. Two of the most important of these methods are interfering with cell signaling pathways and changing cellular functions, such as autophagy, which is essential in maintaining cellular stability against multiple exogenous and endogenous sources of stress, and is a major tool to evade early cell death. In this study, the importance of melatonin and autophagy are discussed, and the effects of melatonin on autophagy, and its contribution in the process of tumorigenesis are then noted.

Biogenesis of Autophagosome in Trichomonas vaginalis during Macroautophagy Induced by Rapamycin-treatment and Iron or Glucose Starvation Conditions

Autophagy is an adaptive response for cell survival in which cytoplasmic components and organelles are degraded in bulk under normal and stress conditions. Trichomonas vaginalis is a parasite highly adaptable to stress conditions such as iron (IR) and glucose restriction (GR). Autophagy can be traced by detecting a key autophagy protein (Atg8) anchored to the autophagosome membrane by a lipid moiety. Our goal was to perform a morphological and cellular study of autophagy in T. vaginalis under GR, IR, and Rapamycin (Rapa) treatment using TvAtg8 as a putative autophagy marker. We cloned tvatg8a and tvatg8b and expressed and purified rTvAtg8a and rTvAtg8b to produce specific polyclonal antibodies. Autophagy vesicles were detected by indirect immunofluorescence assays and confirmed by ultrastructural analysis. The biogenesis of autophagosomes was detected, showing intact cytosolic cargo. TvAtg8 was detected as puncta signal with the anti-rTvAtg8b antibody that recognized soluble and lipid-associated TvAtg8b by Western blot assays in lysates from stress-inducing conditions. The TvAtg8b signal co-localized with the CytoID and lysotracker labeling (autolysosomes) that accumulated after E-64d treatment in GR parasites. Our data suggest that autophagy induced by starvation in T. vaginalis results in the formation of autophagosomes for which TvAtg8b could be a putative autophagy marker.

Elevated arterial shear rate increases indexes of endothelial cell autophagy and nitric oxide synthase activation in humans

Continuous laminar shear stress increases the process of autophagy, activates endothelial nitric oxide (NO) synthase phosphorylation at serine 1177 (p-eNOSS1177), and generates NO in bovine and human arterial endothelial cells (ECs) compared with static controls. However, the translational relevance of these findings has not been explored. In the current study, primary ECs were collected from the radial artery of 7 men using sterile J-wires before (Pre) and after (Post) 60 min of rhythmic handgrip exercise (HG) performed with the same arm. After ECs were identified by positive costaining for vascular endothelial cadherin and 4',6'-diamidino-2-phenylindole, immunofluorescent antibodies were used to assess indices of autophagy, NO generation, and superoxide anion (O2·-) production. Commercially available primary human arterial ECs were stained and processed in parallel to serve as controls. All end points were evaluated using 75 ECs from each subject. Relative to Pre-HG, HG elevated arterial shear rate ( P < 0.05) ~3-fold, whereas heart rate, arterial pressure, and cardiac output were not altered. Compared with values obtained from ECs Pre-HG, Post-HG ECs displayed increased ( P < 0.05) expression of p-eNOSS1177, NO generation, O2·- production, BECLIN1, microtubule-associated proteins 1A/1B light chain 3B, autophagy-related gene 3, and lysosomal-associated membrane protein 2A and decreased ( P < 0.05) expression (i.e., enhanced degradation) of the adaptor protein p62/sequestosome-1. These novel findings provide evidence that elevated arterial shear rate associated with functional hyperemia initiates autophagy, activates p-eNOSS1177, and increases NO and O2·- generation in primary human ECs. NEW & NOTEWORTHY Previously, our group reported in bovine arterial and human arterial endothelial cells (ECs) that shear stress initiates trafficking of the autophagosome to the lysosome and increases endothelial nitric oxide (NO) synthase phosphorylation at serine 1177, NO generation, and O2·- production. Here, the translational relevance of these findings is documented. Specifically, functional hyperemia induced by rhythmic handgrip exercise elevates arterial shear rate to an extent that increases indices of autophagy, NO generation, and O2·- production in primary arterial ECs collected from healthy men.

Ozone induces autophagy in rat chondrocytes stimulated with IL-1β through the AMPK/mTOR signaling pathway

Background

Ozone injection is generally used for the management of pain in diseases such as osteoarthritis (OA). Recent studies have shown that reduced autophagy in chondrocytes plays an important role in the development of OA. The purpose of this study was to determine whether ozone treats OA by inducing autophagy in OA chondrocytes.

Materials and methods

In this study, primary chondrocytes were stimulated with IL-1β for 24 hours to simulate an OA chondrocyte model, followed by treatment with ozone (30 µg/ mL) or pretreatment with 3-methyladenine or compound C before ozone treatment. Then, cell viability was detected by a CCK-8 kit, and the AMPK/mTOR signaling pathway and autophagy were detected by Western blotting and immunofluorescence. The mRNA expression levels of IL-6, TNF-α, MMP-13 and TIMP-1 were measured by quantitative real-time PCR. Finally, autophagosomes in chondrocytes were observed by transmission electron microscopy.

Results

Ozone improved cell viability in chondrocytes stimulated by IL-1β. The decreased level of autophagy in IL-1β-stimulated chondrocytes improved with ozone treatment through activation of the AMPK/mTOR signaling pathway. In addition, the mRNA expression levels of IL-6 and TNF-α were suppressed by ozone treatment in chondrocytes stimulated with IL-1β. Ozone increased the mRNA level of TIMP-1 and decreased the mRNA level of MMP-13 in chondrocytes stimulated with IL-1β.

Conclusion

These results suggested that ozone improved the decreased level of autophagy in chondrocytes stimulated with IL-1β through activation of the AMPK/mTOR signaling pathway. Moreover, ozone treatment suppressed inflammation and helped maintain metabolic balance in chondrocytes stimulated with IL-1β.

The Role of Autophagy in Subarachnoid Hemorrhage: An Update

BACKGROUND

Autophagy is an extensive self-degradation process for the disposition of cytosolic aggregated or misfolded proteins and defective organelles which executes the functions of pro-survival and pro-death to maintain cellular homeostasis. The pathway plays essential roles in several neurological disorders. Subarachnoid Hemorrhage (SAH) is a devastating subtype of hemorrhagic stroke with high risk of neurological deficit and high mortality. Early brain injury (EBI) plays a role in the poor clinical course and outcome after SAH. Recent studies have paid attention on the role of the autophagy pathway in the development of EBI after SAH. We aim to update the multifaceted roles of autophagy pathway in the pathogenesis of SAH, especially in the phase of EBI.

METHODS

We reviewed early researches related to autophagy and SAH. The following three aspects of contents will be mainly discussed: the process of the autophagy pathway, the role of the autophagy in SAH and the interaction between organelle dysfunction and autophagy pathway after SAH.

RESULTS

Accumulating evidence shows an increased autophagy reaction in response to early stages of SAH. However, others suggest inadequate or excessive autophagy activation can result in cell injury and death. In addition to autophagy, apoptosis and necrosis can occur in neurons simultaneously after SAH, leading to mixed features of cell death morphologies. And it is also known that there is extensive crosstalk between autophagy and apoptosis pathway. Subcellular organelles of neural cells generally participate in the formation and functional parts of autophagy process.

CONCLUSION

Autophagy plays an important role in the SAH-induced brain injury. A better understanding of the interrelationship among autophagy, apoptosis, and necrosis might provide us better therapeutic targets for the treatment of SAH.

Recent trends in mucopolysaccharidosis research

Mucopolysaccharidosis (MPS) is a group of inherited conditions involving metabolic dysfunction. Lysosomal enzyme deficiency leads to the accumulation of glycosaminoglycan (GAG) resulting in systemic symptoms, and is categorized into seven types caused by deficiency in one of eleven different enzymes. The pathophysiological mechanism of these diseases has been investigated, indicating impaired autophagy in neuronal damage initiation, association of activated microglia and astrocytes with the neuroinflammatory processes, and involvement of tauopathy. A new inherited error of metabolism resulting in a multisystem disorder with features of the MPS was also identified. Additionally, new therapeutic methods are being developed that could improve conventional therapies, such as new recombinant enzymes that can penetrate the blood brain barrier, hematopoietic stem cell transplantation with reduced intensity conditioning, gene therapy using a viral vector system or gene editing, and substrate reduction therapy. In this review, we discuss the recent developments in MPS research and provide a framework for developing strategies.