Autophagy in mammalian cells

Autophagy in cancer immunotherapy: Perspective on immune evasion and cell death interactions

Both the innate and adaptive immune systems work together to produce immunity. Cancer immunotherapy is a novel approach to tumor suppression that has arisen in response to the ineffectiveness of traditional treatments like radiation and chemotherapy. On the other hand, immune evasion can diminish immunotherapy's efficacy. There has been a lot of focus in recent years on autophagy and other underlying mechanisms that impact the possibility of cancer immunotherapy. The primary feature of autophagy is the synthesis of autophagosomes, which engulf cytoplasmic components and destroy them by lysosomal degradation. The planned cell death mechanism known as autophagy can have opposite effects on carcinogenesis, either increasing or decreasing it. It is autophagy's job to maintain the balance and proper functioning of immune cells like B cells, T cells, and others. In addition, autophagy controls whether macrophages adopt the immunomodulatory M1 or M2 phenotype. The ability of autophagy to control the innate and adaptive immune systems is noteworthy. Interleukins and chemokines are immunological checkpoint chemicals that autophagy regulates. Reducing antigen presentation to induce immunological tolerance is another mechanism by which autophagy promotes cancer survival. Therefore, targeting autophagy is of importance for enhancing potential of cancer immunotherapy.

Role of OGDH in Atophagy-IRF3-IFN-β pathway during classical swine fever virus infection

Classical swine fever (CSF) is a severe infectious disease caused by the classical swine fever virus (CSFV) that poses significant challenges to the swine industry. α-ketoglutarate dehydrogenase (OGDH), the first rate-limiting enzyme of the tricarboxylic acid (TCA) cycle, catalyzes α-ketoglutarate (α-KG) to succinyl-CoA, playing a crucial role in glycometabolism. Our previous studies showed that CSFV disrupts the TCA cycle, resulting in α-KG accumulation. However, the interplay between CSFV and OGDH remains unclear. In this study, we found that CSFV significantly reduces OGDH protein levels and promotes α-KG secretion through OGDH in PK-15 cells. Furthermore, we observed CSFV C protein interacts with OGDH and revealed that CSFV utilizes NDP52/NBR1 to target OGDH protein degradation in the autophagy-lysosome pathway. We also unveiled that OGDH overexpression inhibits CSFV proliferation, whereas OGDH knockdown increases CSFV proliferation. Further investigation into the mechanisms of OGDH on CSFV replication revealed that OGDH regulates the AMPK-mTOR-autophagy pathway. Additionally, using the autophagy agonist/inhibitor, rapamycin/3-MA, we observed that OGDH modulates autophagy to regulate the IRF3-IFN-β network and CSFV replication. These findings shed light on the role of OGDH in CSFV infection and host metabolism, promoting the development of innovative strategies for combating CSFV and other viral infections via targeting metabolic pathways.

Impaired Autophagic-Lysosomal Fusion in Parkinson's Patient Midbrain Neurons Occurs through Loss of ykt6 and Is Rescued by Farnesyltransferase Inhibition

Macroautophagy is a catabolic process that coordinates with lysosomes to degrade aggregation-prone proteins and damaged organelles. Loss of macroautophagy preferentially affects neuron viability and is associated with age-related neurodegeneration. We previously found that α-synuclein (α-syn) inhibits lysosomal function by blocking ykt6, a farnesyl-regulated soluble NSF attachment protein receptor (SNARE) protein that is essential for hydrolase trafficking in midbrain neurons. Using Parkinson's disease (PD) patient iPSC-derived midbrain cultures, we find that chronic, endogenous accumulation of α-syn directly inhibits autophagosome-lysosome fusion by impairing ykt6-SNAP-29 complexes. In wild-type (WT) cultures, ykt6 depletion caused a near-complete block of autophagic flux, highlighting its critical role for autophagy in human iPSC-derived neurons. In PD, macroautophagy impairment was associated with increased farnesyltransferase (FTase) activity, and FTase inhibitors restored macroautophagic flux through promoting active forms of ykt6 in human cultures, and male and female mice. Our findings indicate that ykt6 mediates cellular clearance by coordinating autophagic-lysosomal fusion and hydrolase trafficking, and that macroautophagy impairment in PD can be rescued by FTase inhibitors.SIGNIFICANCE STATEMENT The pathogenic mechanisms that lead to the death of neurons in Parkinson's disease (PD) and Dementia with Lewy bodies (LBD) are currently unknown. Furthermore, disease modifying treatments for these diseases do not exist. Our study indicates that a cellular clearance pathway termed autophagy is impaired in patient-derived culture models of PD and in vivo We identified a novel druggable target, a soluble NSF attachment protein receptor (SNARE) protein called ykt6, that rescues autophagy in vitro and in vivo upon blocking its farnesylation. Our work suggests that farnesyltransferase (FTase) inhibitors may be useful therapies for PD and DLB through enhancing autophagic-lysosomal clearance of aggregated proteins.

Role and regulation of autophagy in cancer

Autophagy is an intracellular self-degradative mechanism which responds to cellular conditions like stress or starvation and plays a key role in regulating cell metabolism, energy homeostasis, starvation adaptation, development and cell death. Numerous studies have stipulated the participation of autophagy in cancer, but the role of autophagy either as tumor suppressor or tumor promoter is not clearly understood. However, mechanisms by which autophagy promotes cancer involves a diverse range of modifications of autophagy associated proteins such as ATGs, Beclin-1, mTOR, p53, KRAS etc. and autophagy pathways like mTOR, PI3K, MAPK, EGFR, HIF and NFκB. Furthermore, several researches have highlighted a context-dependent, cell type and stage-dependent regulation of autophagy in cancer. Alongside this, the interaction between tumor cells and their microenvironment including hypoxia has a great potential in modulating autophagy response in favour to substantiate cancer cell metabolism, self-proliferation and metastasis. In this review article, we highlight the mechanism of autophagy and their contribution to cancer cell proliferation and development. In addition, we discuss about tumor microenvironment interaction and their consequence on selective autophagy pathways and the involvement of autophagy in various tumor types and their therapeutic interventions concentrated on exploiting autophagy as a potential target to improve cancer therapy.

Effects of antioxidant on oxidative stress and autophagy in bronchial epithelial cells exposed to particulate matter and cigarette smoke extract

Background

We evaluated the effect of particulate matter (PM) and cigarette smoke extract (CSE) on bronchial epithelial cell survival, as well as oxidative stress and autophagy levels. Moreover, we aimed to assess the effect of the antioxidant N-acetylcysteine (NAC) on the adverse effects of PM and CSE exposure.

Methods

Normal human bronchial epithelial cells (BEAS-2B cells) were exposed to urban PM with or without CSE, after which cytotoxic effects, including oxidative stress and autophagy levels, were measured. After identifying the toxic effects of urban PM and CSE exposure, the effects of NAC treatment on cell damage were evaluated.

Results

Urban PM significantly decreased cell viability in a concentration-dependent manner, which was further aggravated by simultaneous treatment with CSE. Notably, pretreatment with NAC at 10 mM for 1 hour reversed the cytotoxic effects of PM and CSE co-exposure. Treatment with 1, 5, and 10 mM NAC was shown to decrease reactive oxygen species levels induced by exposure to both PM and CSE. Additionally, the autophagy response assessed via LC3B expression was increased by PM and CSE exposure, and this also attenuated by NAC treatment.

Conclusion

The toxic effects of PM and CSE co-exposure on human bronchial epithelial cells, including decreased cell viability and increased oxidative stress and autophagy levels, could be partly prevented by NAC treatment.

Autophagy is required for the promoting effect of angiogenic factor with G patch domain and forkhead-associated domain 1 (AGGF1) in retinal angiogenesis

OBJECTIVE

To investigate the effect of angiogenic factor with G patch domain and forkhead-associated domain 1 (AGGF1) on retinal angiogenesis in ischemic retinopathy and its association with autophagy.

METHODS

RF/6A cells were divided into the control group, hypoxia group and high-glucose group, and the expression of AGGF1 in cells was detected. C57BL/6 J mice were divided into the control group, oxygen-induced retinopathy (OIR) group and diabetic retinopathy (DR) group, and AGGF1 expression in the retina was observed. RF/6A cells were then divided into the control group and different AGGF1 concentration groups, and the expression of autophagy marker, LC3 was detected. Then, RF/6A cells were divided into the control group, AGGF1 group, 3-methyladenine (3-MA, an early autophagy inhibitor) + AGGF1 group and chloroquine (CQ, a late autophagy inhibitor) + AGGF1 group, and the expression of autophagy markers, LC3 and p62, autophagic flux, as well as was key signaling pathway proteins in autophagy, PI3K, AKT, and mTOR was detected. Finally, the cell proliferation, migration and tube formation were detected in the four groups.

RESULTS

AGGF1 expression in RF/6A cells and in the retinas of OIR and DR mouse model was found to be increased in the state of hypoxic and high glucose condition. AGGF1 treatment led to increased expressions of LC3 and decreased p62; therby induced autophagic flux, and the phosphorylation of PI3K, AKT and mTOR was down-regulated in RF/6A cells. When autophagy was inhibited by 3-MA or CQ, confirmed by corresponding changes of these indicators of autophagy, cellular proliferation, migration and tube formation of RF/6A cells were weakened by AGGF1 treatment when compared with that of AGGF1 treatment alone.

CONCLUSION

This study experimentally revealed that AGGF1 activates autophagy to promote angiogenesis for ischemic retinopathy and inhibition of PI3K/AKT/mTOR pathway may be involved in the activation of autophagy by AGGF1.

The lysosome as an imperative regulator of autophagy and cell death

Lysosomes are single membrane-bound organelles containing acid hydrolases responsible for the degradation of cellular cargo and maintenance of cellular homeostasis. Lysosomes could originate from pre-existing endolysosomes or autolysosomes, acting as a critical juncture between autophagy and endocytosis. Stress that triggers lysosomal membrane permeabilization can be altered by ESCRT complexes; however, irreparable damage to the membrane results in the induction of a selective lysosomal degradation pathway, specifically lysophagy. Lysosomes play an indispensable role in different types of autophagy, including microautophagy, macroautophagy, and chaperone-mediated autophagy, and various cell death pathways such as lysosomal cell death, apoptotic cell death, and autophagic cell death. In this review, we discuss lysosomal reformation, maintenance, and degradation pathways following the involvement of the lysosome in autophagy and cell death, which are related to several pathophysiological conditions observed in humans.

Coffeeberry Activates the CaMKII/CREB/BDNF Pathway, Normalizes Autophagy and Apoptosis Signaling in Nonalcoholic Fatty Liver Rodent Model

Nonalcoholic fatty liver disease (NAFLD) shows extensive liver cell destruction with lipid accumulation, which is frequently accompanied by metabolic comorbidities and increases mortality. This study aimed to investigate the effects of coffeeberry (CB) on regulating the redox status, the CaMKII/CREB/BDNF pathway, autophagy, and apoptosis signaling by a NAFLD rodent model senescence-accelerated mice prone 8 (SAMP8). Three-month-old male SAMP8 mice were divided into a control group and three CB groups (50, 100, and 200 mg/kg BW), and fed for 12 weeks. The results show that CB reduced hepatic malondialdehyde and carbonyl protein levels. CB significantly enhanced Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and brain-derived neurotrophic factor (BDNF) and reduced the phospho-cAMP response element-binding protein (p-CREB)/CREB ratio. In addition, CB increased the silent information regulator T1 level, promoted Beclin 1 and microtubule-associated protein light chain 3 II expressions, and reduced phosphorylated mammalian target of rapamycin and its downstream p-p70s6k levels. CB also inhibited the expressions of apoptosis-related factors poly (ADP-ribose) polymerase-1 and the apoptosis-inducing factor. In conclusion, CB might protect the liver by reducing oxidative stress, activating the CaMKII/CREB/BDNF pathway, and improving autophagic and apoptotic expressions in a dose-dependent manner.

Adding Some "Splice" to Stress Eating: Autophagy, ESCRT and Alternative Splicing Orchestrate the Cellular Stress Response

Autophagy is a widely studied self-renewal pathway that is essential for degrading damaged cellular organelles or recycling biomolecules to maintain cellular homeostasis, particularly under cellular stress. This pathway initiates with formation of an autophagosome, which is a double-membrane structure that envelopes cytosolic components and fuses with a lysosome to facilitate degradation of the contents. The endosomal sorting complexes required for transport (ESCRT) proteins play an integral role in controlling autophagosome fusion events and disruption to this machinery leads to autophagosome accumulation. Given the central role of autophagy in maintaining cellular health, it is unsurprising that dysfunction of this process is associated with many human maladies including cancer and neurodegenerative diseases. The cell can also rapidly respond to cellular stress through alternative pre-mRNA splicing that enables adaptive changes to the cell's proteome in response to stress. Thus, alternative pre-mRNA splicing of genes that are involved in autophagy adds another layer of complexity to the cell's stress response. Consequently, the dysregulation of alternative splicing of genes associated with autophagy and ESCRT may also precipitate disease states by either reducing the ability of the cell to respond to stress or triggering a maladaptive response that is pathogenic. In this review, we summarize the diverse roles of the ESCRT machinery and alternative splicing in regulating autophagy and how their dysfunction can have implications for human disease.

In vivo autophagy quantification: Measuring LC3 and P62 puncta in 3D image system from zebrafish larvae

Autophagy is a central pathway in maintaining cellular homeostasis through the recycling of damaged proteins and organelles. Detection of LC3 protein levels by immunofluorescence or western blot analysis is one of the most common ways to measure autophagy. For quantitative autophagy analysis, LC3 western blot analysis is commonly used, whereas immunostaining is used for qualitative autophagy analysis. However, zebrafish larvae have a lot of proteases that rapidly degrade LC3 protein in samples. P62 is another autophagy marker that bind to damaged proteins and can reflects autophagic status. This study demonstrates a fast and accurate way to quantify autophagy from LC3 and/or P62 immunostaining images. We used a three-dimensional analysis of whole-mount LC3 immunostaining images of zebrafish larvae. Counting LC3 and P62 punctate by two dimensions can be used as a qualitative method for the analysis of autophagy. However, here we demonstrate that 3D image analysis can be used as a quantitative, rapid tool for monitoring autophagy in zebrafish larvae and avoiding drawbacks of LC3 western blot analysis.

Autophagy in Tenebrio molitor Immunity: Conserved Antimicrobial Functions in Insect Defenses

The yellow mealworm beetle (Tenebrio molitor) has been exploited as an experimental model to unravel the intricacies of cellular and humoral immunity against pathogenic infections. Studies on this insect model have provided valuable insights into the phenotypic plasticity of immune defenses against parasites and pathogens. It has thus been possible to characterize the hemocoelic defenses of T. molitor that rely on the recognition of non-self-components of pathogens by pattern recognition receptors (PRRs). The subsequent signaling cascade activating pathways such as the NF-κB controlled by Toll and IMD pathways lead to the synthesis of antimicrobial peptides (AMPs), onset of hemocyte-driven phagocytosis, and activation of the prophenoloxidase cascade regulating the process of melanization. Nevertheless, the activation of autophagy-mediated defenses of T. molitor against the facultative intracellular gram-positive bacterium Listeria monocytogenes provides clear evidence of the existence of a cross-talk between autophagy and the IMD pathway. Moreover, the identification of several autophagy-related genes (Atgs) in T. molitor transcriptome and expressed sequence tag (EST) databases has contributed to the understanding of the autophagy-signaling cascade triggered by L. monocytogenes challenge. Providing further evidence of the cross-talk hypothesis, TmRelish has been shown to be required not only for regulating the synthesis of AMPs through the PGRP-LE/IMD pathway activation but also for the expression of Atgs in T. molitor larvae following L. monocytogenes challenge. Notably, L. monocytogenes can stimulate the T. molitor innate immune system by producing molecules recognized by the multifunctional PRR (TmPGRP-LE), which stimulates intracellular activation of the IMD pathway and autophagy. Considering the conservation of autophagy components involved in combating intracellular pathogens, it will be interesting to extrapolate a dynamic cross-talk model of immune activation. This review summarizes the most significant findings on the regulation of autophagy in T. molitor during L. monocytogenes infection and on the role of the innate immunity machinery, including the NF-κB pathway, in the control of pathogenic load.

High glucose suppresses autophagy through the AMPK pathway while it induces autophagy via oxidative stress in chondrocytes

Diabetes (DB) is a risk factor for osteoarthritis progression. High glucose (HG) is one of the key pathological features of DB and has been demonstrated to induce apoptosis and senescence in chondrocytes. Autophagy is an endogenous mechanism that can protect cells against apoptosis and senescence. The effects of HG on autophagy in cells including chondrocytes have been studied; however, the results have been inconsistent. The current study aimed to elucidate the underlying mechanisms, which could be associated with the contrasting outcomes. The present study revealed that HG can induce apoptosis and senescence in chondrocytes, in addition to regulating autophagy dynamically. The present study demonstrated that HG can cause oxidative stress in chondrocytes and suppress the AMPK pathway in a dose-dependent manner. Elimination of oxidative stress by Acetylcysteine, also called N-acetyl cysteine (NAC), downregulated autophagy and alleviated HG-stimulated apoptosis and senescence, while activation of the AMPK signaling pathway by AICAR not only upregulated autophagy but also alleviated HG-stimulated apoptosis and senescence. A combined treatment of NAC and AICAR was superior to treatment with either NAC or AICAR. The study has demonstrated that HG can suppress autophagy through the AMPK pathway and induce autophagy via oxidative stress in chondrocytes.

Interplay of autophagy and cancer stem cells in hepatocellular carcinoma

Liver cancer is the sixth most common cancer and the fourth leading cause of cancer deaths in the world. The most common type of liver cancers is hepatocellular carcinoma (HCC). Autophagy is the cellular digestion of harmful components by sequestering the waste products into autophagosomes followed by lysosomal degradation for the maintenance of cellular homeostasis. The impairment of autophagy is highly associated with the development and progression of HCC although autophagy may be involved in tumour-suppressing cellular events. In regards to its protecting role, autophagy also shelters the cells from anoikis- a programmed cell death in anchorage-dependent cells detached from the surrounding extracellular matrix which facilitates metastasis in HCC. Liver cancer stem cells (LCSCs) have the ability for self-renewal and differentiation and are associated with the development and progression of HCC by regulating stemness, resistance and angiogenesis. Interestingly, autophagy is also known to regulate normal stem cells by promoting cellular survival and differentiation and maintaining cellular homeostasis. In this review, we discuss the basal autophagic mechanisms and double-faceted roles of autophagy as both tumour suppressor and tumour promoter in HCC, as well as its association with and contribution to self-renewal and differentiation of LCSCs.

Cell Proliferation Is Strongly Associated with the Treatment Conditions of an ER Stress Inducer New Anti-Melanoma Drug in Melanoma Cell Lines

HA15 is a new anti-melanoma drug that triggers endoplasmic reticulum (ER) stress and causes deleterious effects on melanoma cell viability due to autophagy and apoptosis, regardless of driver mutations or drug resistance. In this study, we investigated the effect of HA15 on the viability/proliferation of BRAFV600E-mutant melanoma cells using different culture conditions. In contrast to the published data, we did not detect significant melanoma cell death under normal culture conditions using HA15 treatment. Indeed, only cells that were cultured under long-term starvation conditions were sensitive to the drug. Quantitative measurements of ER stress and autophagy markers showed that the compound HA15 does not trigger stress alone but synergistically enhances ER stress under starvation conditions. Importantly, we observed that the viability of normal melanocytes decreased significantly with treatment, even at low HA15 concentrations. Finally yet importantly, we were able to generate HA15-resistant cell lines, which failed by Cerezo et al. In summary, HA15 only influences the viability of cells that are starved for several hours before and during treatment. However, this in vitro setting is far from the in vivo conditions. In addition, our data clearly show that melanoma cells can acquire HA15 resistance. Further studies are needed to prove that HA15 is an effective anti-cancer agent.

PM2.5-related cell death patterns

With the increasingly serious problem of environmental pollution, the health problems caused by PM2.5 are gradually coming into our line of sight. Previous researches have indicated that air pollution is nearly related to various diseases, but few studies have focused on the exact function mediated by particulate matter less than 2.5 (PM2.5) in these diseases. PM2.5 is known to induce multiple ways of cell death, including autophagy, necrosis, apoptosis, pyroptosis and ferroptosis. Therefore, it is of much importance to understand the different ways of cell death caused by PM2.5 in the pathogenesis and treatment of PM2.5-related diseases. This present review is an insight of multiple ways of PM2.5‑induced cell death in different diseases.

The role of antioxidants in restoring MAPK 14 and a DNA damage marker level following autophagy suppression

Autophagy is a lysosomal degradation mechanism for elimination and recycling of damaged intracellular organelles and proteins. Recent studies have shown that autophagy could help reduce oxidative stress by removing oxidized proteins and damaged mitochondria. Autophagy deficiency is associated with the disruption of many intracellular biological processes. Using bioinformatics tools and fibroblast immunostaining technology, I tried to investigate whether oxidative stress is involved in mediating the effect of autophagy suppression on certain cell biological processes and signalling pathways. Many pharmaceutical components have different modes of action to suppress autophagy. In this study, I performed analysis on autophagy suppression induced by neutralizing lysosomal pH (NH₄Cl and bafilomycin A1). Bioinformatics analysis of GEO data, GSE60570 accession number, revealed that p38 signalling induction and DNA damage response are among the main disrupted signalling pathways in bafilomycin A1-treated RPE-1 cells. Likewise, fibroblast immunostaining showed that autophagy deficiency established by ammonium chloride (NH₄Cl) has significantly increased P38 signalling, DNA damage marker (H2A.X), and oxidative stress marker (dityrosine). I therefore investigated the role of oxidative stress and whether antioxidants treatment could reverse autophagy suppression effects on p38 signalling and DNA damage response. Importantly, antioxidant treatment clearly restored P38 signalling and H2A.X levels in autophagy-suppressed fibroblast cells. Indicating that oxidative stress might be associated with the harmful effect of autophagy suppression.

Pharmacological Inhibition of O-GlcNAc Transferase Promotes mTOR-Dependent Autophagy in Rat Cortical Neurons

O-GlcNAc transferase (OGT) is a ubiquitous enzyme that regulates the addition of β-N-acetylglucosamine (O-GlcNAc) to serine and threonine residues of target proteins. Autophagy is a cellular process of self-digestion, in which cytoplasmic resources, such as aggregate proteins, toxic compounds, damaged organelles, mitochondria, and lipid molecules, are degraded and recycled. Here, we examined how three different OGT inhibitors, alloxan, BXZ2, and OSMI-1, modulate O-GlcNAcylation in rat cortical neurons, and their autophagic effects were determined by immunoblot and immunofluorescence assays. We found that the treatment of cortical neurons with an OGT inhibitor decreased O-GlcNAcylation levels and increased LC3-II expression. Interestingly, the pre-treatment with rapamycin, an mTOR inhibitor, further increased the expression levels of LC3-II induced by OGT inhibition, implicating the involvement of mTOR signaling in O-GlcNAcylation-dependent autophagy. In contrast, OGT inhibitor-mediated autophagy was significantly attenuated by 3-methyladenine (3-MA), a blocker of autophagosome formation. However, when pre-treated with chloroquine (CQ), a lysosomotropic agent and a late-stage autophagy inhibitor, OGT inhibitors significantly increased LC3-II levels along with LC3 puncta formation, indicating the stimulation of autophagic flux. Lastly, we found that OGT inhibitors significantly decreased the levels of the autophagy substrate p62/SQSTM1 while increasing the expression of lysosome-associated membrane protein 1 (LAMP1). Together, our study reveals that the modulation of O-GlcNAcylation by OGT inhibition regulates mTOR-dependent autophagy in rat cortical neurons.

Regulation of Innate Immune Responses by Autophagy: A Goldmine for Viruses

Autophagy is a lysosomal degradation pathway for intracellular components and is highly conserved across eukaryotes. This process is a key player in innate immunity and its activation has anti-microbial effects by directly targeting pathogens and also by regulating innate immune responses. Autophagy dysfunction is often associated with inflammatory diseases. Many studies have shown that it can also play a role in the control of innate immunity by preventing exacerbated inflammation and its harmful effects toward the host. The arms race between hosts and pathogens has led some viruses to evolve strategies that enable them to benefit from autophagy, either by directly hijacking the autophagy pathway for their life cycle, or by using its regulatory functions in innate immunity. The control of viral replication and spread involves the production of anti-viral cytokines. Controlling the signals that lead to production of these cytokines is a perfect way for viruses to escape from innate immune responses and establish successful infection. Published reports related to this last viral strategy have extensively grown in recent years. In this review we describe several links between autophagy and regulation of innate immune responses and we provide an overview of how viruses exploit these links for their own benefit.

Emendation of autophagic dysfuction in neurological disorders: a potential therapeutic target

BACKGROUND

Neurological disorders have been continuously contributing to the global disease burden and affect millions of people worldwide. Researchers strive hard to extract out the ultimate cure and serve for the betterment of the society, and yet the treatments available provide only symptomatic relief. Aging and abnormal mutations seem to be the major culprits responsible for neurotoxicity and neuronal death. One of the major causes of these neurological disorders that has been paid utmost attention recently, is Autophagic Dysfunction.

AIM

The aim of the study was to understand the autophagic process, its impairment in neurological disorders and targeting the impairments as a therapeutic option for the said disorders.

METHODS

For the purpose of review, we carried out an extensive literature study to excerpt the series of steps involved in autophagy and to understand the mechanism of autophagic impairment occurring in a range of neurodegenerative and neuropsychiatric disorders like Parkinson, Alzheimer, Depression, Schizophrenia, Autism etc. The review also involved the exploration of certain molecules that can help in triggering the compromised autophagic members.

RESULTS

We found that, a number of genes, proteins, receptors and transcription factors interplay to bring about autophagy and plethora of neurological disorders are associated with the diminished expression of one or more autophagic member leading to inhibition of autophagy.

CONCLUSION

Autophagy is a significant process for the removal of misfolded, abnormal, damaged protein aggregates and nonfunctional cell organelles in order to suppress neurodegeneration. Therefore, triggering autophagy could serve as an important therapeutic target to treat neurological disorders.

Focus on the Multimodal Role of Autophagy in Rheumatoid Arthritis

Autophagy exerts its dual role in eukaryotic cells and exerts its cytoprotective action through degradation mechanism and by regulating catabolic processes which results in elimination of pathogens. Under suitable conditions, autophagy is associated with recycling of cytoplasmic components which causes regeneration of energy whereas deregulated autophagy exerts its implicated role in development and pathogenesis of auto-immune diseases such as rheumatoid arthritis. The immune, innate, and adaptive responses are regulated through the development, proliferation, and growth of lymphocytes. Such innate and adaptive responses can act as mediator of arthritis; along with this, stimulation of osteoclast-mediated bone resorption takes place via transferring citrullinated peptides towards MHC (major histocompatibility complex) compartments, thereby resulting in degradation of bone. Processes such as apoptosis resistance are also regulated through autophagy. In this review, the current knowledge based on role of autophagy in pathogenesis of rheumatoid arthritis is summarized along with proteins associated.

Metabolic Profiling of Plasma in Different Calving Body Condition Score Cows Using an Untargeted Liquid Chromatography-Mass Spectrometry Metabolomics Approach

This study was undertaken to identify metabolite differences in plasma of dairy cows with a normal or high calving body condition score (CBCS), using untargeted liquid chromatography-mass spectrometry (LC-MS) metabolomics. Sixteen multiparous dairy cows were assigned to one of two groups based on CBCS (0 to 5 scale): Normal group (NBCS, 3.25 ≤ BCS ≤ 3.5, n = 8), and high BCS group (HBCS, BCS ≥ 4, n = 8). Plasma samples were collected for metabolomics analysis and evaluation of biomarkers of lipid metabolism (nonesterified fatty acid (NEFA) and β-hydroxybutyrate (BHB)), and cytokines (leptin, adiponectin, tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6)). A total of 23 differential metabolites were identified, and functional analyses were performed using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Among these metabolites, the concentrations of six lysophosphatidylcholines and one phosphatidylethanolamine, were lower in the HBCS group than in the NBCS group (p < 0.01). Furthermore, these metabolites were involved in these four pathways, among others: glycerophospholipid metabolism, retrograde endocannabinoid signaling, autophagy, and glycosylphosphatidylinositol (GPI)-anchor biosynthesis (p < 0.05). In addition, plasma concentrations of leptin (p = 0.06) and TNF-α (p = 0.08) tended to be greater while adiponectin (p = 0.09) lower in HBCS cows than in NBCS cows. The concentrations of NEFA, BHB, or IL-6 did not differ between NBCS and HBCS groups. More importantly, based on the results of the Spearman's correlation analysis, the seven important metabolites were negatively correlated with indices of lipid metabolisms, proinflammatory cytokines, and leptin, but positively correlated with adiponectin. These results demonstrate that CBCS has a measurable impact on the plasma metabolic profile, even when NEFA and BHB are not different. In addition, the identified differential metabolites were significantly correlated to lipid metabolism and inflammation in the over-conditioned fresh cows, which are expected to render a metabolic basis for the diseases associated with over-conditioned dry cows.

Angiogenic factor with G patch and FHA domains 1 protects retinal vascular endothelial cells under hyperoxia by inhibiting autophagy

Angiogenic factor with G patch and FHA domains 1 (AGGF1) has strong proangiogenic effects on embryonic vascular development and angiogenesis in disease; however, its role in retinopathy has not been elucidated. Retinopathy of prematurity is a serious retinal disorder of premature infants, which is caused by the arrest of immature retinal vascular growth under hyperoxia. This study aims to investigate the effects of AGGF1 on retinal vascular endothelial cells under hyperoxia and the association with autophagy by using rhesus macaque choroid-retinal endothelial (RF/6A) cells. Western blot analysis and immunofluorescence staining were used to detect the expression of AGGF1 in RF/6A cells. Cell Counting Kit-8, flow cytometry, and transwell and matrigel assays were applied to detect the vitality, apoptosis, migration, and tube formation of RF/6A cells, respectively. Western blot analysis was then used to detect the expression of autophagy markers LC3 and Beclin-1, and mCherry-GFP-LC3 adenovirus was used to detect autophagy flux in RF/6A cells. Under hyperoxia, the expression of AGGF1 in RF/6A cells decreased compared with the control. Cell vitality, migration, and tube formation decreased, and apoptosis of RF/6A cells increased under hyperoxia, and these effects of hyperoxia were attenuated by AGGF1. The protein expressions of LC3 and Beclin-1 increased in RF/6A cells and autophagy flux enhanced under hyperoxia. AGGF1 reduced the expression of LC3 and Beclin-1 as well as the autophagy flux stimulated by hyperoxia. The results clearly showed that exogenous AGGF1 can protect retinal vascular endothelial cells and promote angiogenesis under hyperoxia, in which the expression of AGGF1 was inhibited. Inhibition of autophagy by AGGF1 may be one of the mechanisms involved.

Oncogenic BRAF, endoplasmic reticulum stress, and autophagy: Crosstalk and therapeutic targets in cutaneous melanoma

BRAF is a member of the RAF family of serine/threonine-specific protein kinases. Oncogenic BRAF, in particular, BRAF V600E, can disturb the normal protein folding machinery in the endoplasmic reticulum (ER) leading to accumulation of unfolded/misfolded proteins in the ER lumen, a condition known as endoplasmic reticulum (ER) stress. To alleviate such conditions, ER-stressed cells have developed a highly robust and adaptable signaling network known as unfolded protein response (UPR). UPR is ordinarily a cytoprotective response and usually operates through the induction of autophagy, an intracellular lysosomal degradation pathway that directs damaged proteins, protein aggregates, and damaged organelles for bulk degradation and recycling. Both ER stress and autophagy are involved in the progression and chemoresistance of melanoma. Melanoma, which arises as a result of malignant transformation of melanocytes, exhibits exceptionally high therapeutic resistance. Many mechanisms of therapeutic resistance have been identified in individual melanoma patients and in preclinical BRAF-driven melanoma models. Recently, it has been recognized that oncogenic BRAF interacts with GRP78 and removes its inhibitory influence on the three fundamental ER stress sensors of UPR, PERK, IRE1α, and ATF6. Dissociation of GRP78 from these ER stress sensors prompts UPR that subsequently activates cytoprotective autophagy. Thus, pharmacological inhibition of BRAF-induced ER stress-mediated autophagy can potentially resensitize BRAF mutant melanoma tumors to apoptosis. However, the underlying molecular mechanism of how oncogenic BRAF elevates the basal level of ER stress-mediated autophagy in melanoma tumors is not well characterized. A better understanding of the crosstalk between oncogenic BRAF, ER stress and autophagy may provide a rationale for improving existing cancer therapies and identify novel targets for therapeutic intervention of melanoma.

The impact of proteostasis dysfunction secondary to environmental and genetic causes on neurodegenerative diseases progression and potential therapeutic intervention

Aggregation of particular proteins in the form of inclusion bodies or plaques followed by neuronal death is a hallmark of neurodegenerative proteopathies such as primary Parkinsonism, Alzheimer's disease, Lou Gehrig's disease, and Huntington's chorea. Complex polygenic and environmental factors implicated in these proteopathies. Accumulation of proteins in these disorders indicates a substantial disruption in protein homeostasis (proteostasis). Proteostasis or cellular proteome homeostasis is attained by the synchronization of a group of cellular mechanisms called the proteostasis network (PN), which is responsible for the stability of the proteome and achieves the equilibrium between synthesis, folding, and degradation of proteins. In this review, we will discuss the different types of PN and the impact of PN component dysfunction on the four major neurodegenerative diseases mentioned earlier. Graphical abstract.

Role of autophagy during the replication and pathogenesis of common mosquito-borne flavi- and alphaviruses

Arboviruses that are transmitted to humans by mosquitoes represent one of the most important causes of febrile illness worldwide. In recent decades, we have witnessed a dramatic re-emergence of several mosquito-borne arboviruses, including dengue virus (DENV), West Nile virus (WNV), chikungunya virus (CHIKV) and Zika virus (ZIKV). DENV is currently the most common mosquito-borne arbovirus, with an estimated 390 million infections worldwide annually. Despite a global effort, no specific therapeutic strategies are available to combat the diseases caused by these viruses. Multiple cellular pathways modulate the outcome of infection by either promoting or hampering viral replication and/or pathogenesis, and autophagy appears to be one of them. Autophagy is a degradative pathway generally induced to counteract viral infection. Viruses, however, have evolved strategies to subvert this pathway and to hijack autophagy components for their own benefit. In this review, we will focus on the role of autophagy in mosquito-borne arboviruses with emphasis on DENV, CHIKV, WNV and ZIKV, due to their epidemiological importance and high disease burden.

Japanese flounder pol-miR-3p-2 suppresses Edwardsiella tarda infection by regulation of autophagy via p53

MicroRNAs (miRNAs) are post-transcriptional regulators that play vital roles in diverse physiological processes including immunity. In this study, we investigated the regulatory mechanism and function of a novel Japanese flounder (Paralichthys olivaceus) miRNA, pol-miR-3p-2. pol-miR-3p-2 was responsive in expression to the infection of the bacterial pathogen Edwardsiella tarda. pol-miR-3p-2 negatively regulated the expression of p53 through interaction with the 3'UTR of p53. Overexpression of pol-miR-3p-2 promoted autophagy, resulting in augmented production of LC3-II, while knockdown of p53 increased the level of beclin, a key factor of autophagy. In vivo and in vitro studies showed that E. tarda infection induced autophagy in flounder, and pol-miR-3p-2 inhibited the infectivity of E. tarda. Together these results indicate that pol-miR-3p-2 regulates autophagy through the target gene p53, thus revealing a regulatory link between p53 and autophagy in teleost, and that pol-miR-3p-2 plays an important role in the immune defense against E. tarda.

Regulation of immune response by S-1-propenylcysteine through autophagy-mediated protein degradation

Autophagy is a key event in cellular recycling processes due to its involvement in the intracellular degradation of proteins. It has been demonstrated that S−1-propenylcysteine (S1PC), a characteristic sulfur compound in aged garlic extract, induces the activation of autophagy. S1PC degrades the adaptor protein myeloid differentiation response protein 88 (MyD88) of downstream of Toll-like receptor (TLR) by activating autophagy in vitro and in vivo. The degradation of MyD88 inhibits the TLR signaling pathway, including the phosphorylation of interleukin 1 receptor associated kinase 4 (IRAK4) and nuclear factor (NF)-κB p65 in vitro, and eventually leads to the inhibition of interleukin (IL)-6 production in vitro and C-C motif chemokine ligand 2 (Ccl2) mRNA expression in vivo. S1PC also increases the level of intestinal immunoglobulin A (IgA) and the number of IgA-producing cells in Peyer's patches in vivo. In addition, S1PC triggers the mRNA expression of X-box binding protein 1 (Xbp1), an inducer of IgA-producing cell differentiation via the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and the degradation of paired box protein 5 (Pax5), a suppressor of Xbp1 mRNA expression. The present review summarizes the mechanisms through which the activation of autophagy by S1PC modulates the immune response.

Modulation of O-GlcNAcylation Regulates Autophagy in Cortical Astrocytes

The addition of O-linked β-N-acetylglucosamine (O-GlcNAcylation) to serine and threonine residues is a common posttranslational modification of intracellular proteins which modulates protein functions and neurodegenerative diseases, controlled by a single pair of enzymes, O-GlcNAcase (OGA), and O-GlcNAcylation transferase (OGT). Autophagy is a cellular recycling pathway activated by stress and nutrient signaling; however, the mechanism by which O-GlcNAcylation modification regulates autophagy in cortical astrocytes is poorly understood. Here, we report that increased O-GlcNAcylation by the suppression of OGA activity using thiamet-G and OGA siRNA did not affect autophagy, whereas decreased O-GlcNAcylation caused by OGT inhibition by alloxan and OGT siRNA increased autophagy. OGT inhibitor and siRNA accumulated LC3 puncta, and cotreatment with chloroquine (CQ), an autophagy inhibitor, significantly increased LC3 puncta and LC3-II protein, confirming that decreased O-GlcNAcylation promotes autophagic flux. In particular, we found that OGT knockdown increases the fusion between autophagosomes as well as lysosomes and stimulates autophagy to promote lysosomal-associated membrane protein 1 (LAMP-1). Additionally, decreasing O-GlcNAcylation by treatment with alloxan, OGT siRNA, and OGA overexpression significantly decreased the level of autophagy substrate SQSTM1/p62, indicating that autophagic degradation was activated. Together, our study reveals a mechanism by which the modulation of O-GlcNAcylation modification regulates autophagy in mouse cortical astrocytes.

Glutamine protects both transcellular and paracellular pathways of chick intestinal calcium absorption under oxidant conditions

Glutamine (GLN) avoids the inhibition of the intestinal Ca²⁺ absorption caused by menadione (MEN) through oxidative stress. The purpose of this study was to elucidate whether molecules of transcellular and/or paracellular pathways of intestinal Ca²⁺ absorption are involved in the GLN action and underlying mechanisms. One-month old chicks were divided in four groups: 1) controls, 2) MEN treated, 3) GLN treated and 4) GLN + MEN treated. The morphology of intestinal villi, the intestinal Ca²⁺ absorption and the molecules involved in the transcellular and paracellular pathways were analyzed. Markers of autophagy and inflammation were also evaluated. The data demonstrated that GLN protected both transcellular and paracellular pathways. GLN avoided morphological changes in the intestine caused by MEN. GLN protected the gene expression of transporters involved in the transcellular pathway and the gene and protein expression of molecules belonging to the paracellular pathways altered by MEN. GLN increased the LC3-II protein expression and the number of acidic vesicular organelles, markers of autophagy, and blocked an increase in the NFkB protein expression in the nuclei and in the IL-6 gene expression caused by MEN. In conclusion, GLN protects both transcellular and paracellular pathways of intestinal Ca²⁺ absorption by increasing autophagy and blocking inflammation.

The potential immunotoxicity of fine particulate matter based on SD rat spleen

Health risks have been closely related to increased exposure of fine particulate matter (PM_2.5) in general population. Immune system is considered to be a most vulnerable target for airborne pollutants. PM_2.5 could make some serious damages to the body organs by inducing immunotoxicity. However, the underlying molecular mechanisms are still unclear. The purpose of this study is aimed to elucidate the possible mechanisms of PM_2.5-mediated immunotoxicity on spleen organ by using SD rat models. This research demonstrated that the spleen structure damage induced by PM_2.5 treatment was more pronounced in winter than in summer. Mechanistically, TUNEL staining show a considerable increase in spleen apoptosis by summer and winter PM_2.5 exposures compared with control. However, winter PM_2.5 exposure caused more toxicity in the spleen than summer PM_2.5 exposure. Furthermore, our results illustrated that PM_2.5 triggered oxidative stress and ERS in spleen tissues of SD rats, and lead to apoptosis via upregulation of CHOP and caspase-12. Likewise, the protein levels of LC3 were significantly increased and p62 was decreased by PM_2.5 exposure, thereby activated the autophagy of spleen in SD rats in a concentration-dependent manner. In conclusion, this study supported that PM_2.5 mediated the immunotoxicity by the occurrence of stimulation of ERS and autophagy in SD rats. Taken together, these findings suggest PM_2.5 as potential agent of immunotoxicity that needs an urgent attention. Graphical abstract Graphical abstract contains poor quality of text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.Thanks you attention. We will provide tiff format image.

PARP1 and Poly(ADP-ribosyl)ation Signaling during Autophagy in Response to Nutrient Deprivation

Autophagy is considered to be the primary degradative pathway that takes place in all eukaryotic cells. Morphologically, the autophagy pathway refers to a process by which cytoplasmic portions are delivered to double-membrane organelles, called autophagosomes, to fuse with lysosomes for bulk degradation. Autophagy, as a prosurvival mechanism, can be stimulated by different types of cellular stress such as nutrient deprivation, hypoxia, ROS, pH, DNA damage, or ER stress, promoting adaptation of the cell to the changing and hostile environment. The functional relevance of autophagy in many diseases such as cancer or neurodegenerative diseases remains controversial, preserving organelle function and detoxification and promoting cell growth, although in other contexts, autophagy could suppress cell expansion. Poly(ADP-ribosyl)ation (PARylation) is a covalent and reversible posttranslational modification (PTM) of proteins mediated by Poly(ADP-ribose) polymerases (PARPs) with well-described functions in DNA repair, replication, genome integrity, cell cycle, and metabolism. Herein, we review the current state of PARP1 activation and PARylation in starvation-induced autophagy.

Autophagy: a new mechanism for regulating VEGF and PEDF expression in retinal pigment epithelium cells

AIM

To investigate the regulation of vascular endothelial growth factors (VEGF) and pigment epithelium-derived factor (PEDF) expression by autophagy in retinal pigment epithelium (RPE) cells on exposure to hypoxia.

METHODS

ARPE-19, an RPE cell line, was treated as following: the control group was kept in a normoxic incubator; the hypoxia group was incubated in a hypoxic incubator with 1% O₂/5% CO₂/94% N₂ for 24h; the hypoxia + 3-methyladenine (3-MA) group was pretreated with 10 mmol/L 3-MA for 1h and then in the hypoxic incubator for 24h; and the hypoxia + chloroquine (CQ) group was pretreated with 50 µmol/L CQ for 1h and then in the hypoxic incubator for 24h. The morphology and ultrastructure of the cells was observed by an inverted microscope or a transmission electronic microscope (TEM). Western blot was performed to assay the expression of autophagy-associated markers, including microtubule associated protein 1 light chain 3 B (LC3B), Beclin-1, Atg5 and p62. The concentration of VEGF and PEDF in the culture supernatant was determined by ELISA, and the ratio of VEGF/PEDF was calculated.

RESULTS

There were no obvious differences in cell morphology among different groups and autolysosomes could be observed in the cytoplasm in all groups. Compared to the control cells, the LC3B-II/I ratio and levels of Beclin-1 and Atg5 were significantly increased and p62 level was significantly decreased in the hypoxia group. With the increase of VEGF and decrease of PEDF concentration, the VEGF/PEDF ratio was significantly increased in the hypoxia group compared to the control cells. The LC3B-II/I ratio was significantly reduced by 3-MA treatment and increased by CQ treatment. The expressions of Beclin-1 and Atg5 were significantly reduced by 3-MA or CQ treatment, while expression of p62 was increased in the 3-MA or CQ treated cells. The concentration of VEGF was significantly decreased and PEDF increased, thereby the VEGF/PEDF ratio was decreased in the hypoxia + 3-MA group and hypoxia + CQ group compared with that in the hypoxia group.

CONCLUSION

Hypoxia leads to elevated autophagy in RPE cells, and expression of VEGF and PEDF might be regulated by autophagy on exposure to hypoxia to further participate in regulating the formation of retinal neovascularization.

Influence of Normal Aging on Brain Autophagy: A Complex Scenario

Misfolded proteins are pathological findings in some chronic neurodegenerative disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Aging is a major risk factor for these disorders, suggesting that the mechanisms responsible for clearing misfolded proteins from the brain, the ubiquitin-proteasome system and the autophagy-lysosomal pathway, may decline with age. Although autophagic mechanisms have been found to decrease with age in many experimental models, whether they do so in the brain is unclear. This review examines the literature with regard to age-associated changes in macroautophagy and chaperone-mediated autophagy (CMA) in the central nervous system (CNS). Beclin 1, LC3-II, and the LC3-II/LC3-I ratio have frequently been used to examine changes in macroautophagic activity, while lamp2a and HSPA8 (also known as hsc70) have been used to measure CMA activity. Three gene expression analyses found evidence for an age-related downregulation of macroautophagy in human brain, but no published studies were found of age-related changes in CMA in human brain, although cerebrospinal fluid concentrations of HSPA8 were reported to decrease with age. Most studies of age-related changes in brain autophagy in experimental animals have found age-related declines in macroautophagy, and macroautophagy is necessary for normal lifespan in Caenorhabditis elegans, Drosophila, and mice. However, the few studies of age-related changes in brain CMA in experimental animals have produced conflicting results. Investigations of the influence of aging on macroautophagy in experimental animals in systems other than the CNS have generally found an age-related decrease in Beclin 1, but conflicting results for LC3-II and the LC3-II/LC3-I ratio, while CMA decreases with age in most models. CONCLUSION: while indirect evidence suggests that brain autophagy may decrease with normal aging, this issue has not been investigated sufficiently, particularly in human brain. Measuring autophagic activity in the brain can be challenging because of differences in basal autophagic activity between experimental models, and the inability to include lysosomal inhibitors when measuring the LC3-II/LC3-I ratio in postmortem specimens. If autophagy does decrease in the brain with aging, then pharmacological interventions and/or lifestyle alterations to slow this decline could reduce the risk of developing age-related neurodegenerative disorders.

Autophagy in cardiomyopathies

Autophagy (greek auto: self; phagein: eating) is a highly conserved process within eukaryotes that degrades long-lived proteins and organelles within lysosomes. Its accurate and constant operation in basal conditions ensures cellular homeostasis by degrading damaged cellular components and thereby acting not only as a quality control but as well as an energy supplier. An increasing body of evidence indicates a major role of autophagy in the regulation of cardiac homeostasis and function. In this review, we describe the different forms of mammalian autophagy, their regulations and monitoring with a specific emphasis on the heart. Furthermore, we address the role of autophagy in several forms of cardiomyopathy and the options for therapy.

Alpha-lipoic acid attenuates p-cresyl sulfate-induced renal tubular injury through suppression of apoptosis and autophagy in human proximal tubular epithelial cells

The p-cresyl sulfate accumulates in kidney disease and may be involved in renal injury. α-Lipoic acid (α-LA) acts as an antioxidant in cell injury. We investigated the effects of α-LA treatment on p-cresyl sulfate-induced renal tubular injury. p-Cresyl sulfate induced cell death, and increased Bax/Bcl-2, cleaved caspase-3, Beclin-1, and LC3BII/LC3BI in human renal proximal tubular epithelial (HK-2) cells, which was counteracted by α-LA treatment. p-Cresyl sulfate-induced apoptosis was reduced by autophagy inhibitor 3-methyladenine, and p-cresyl sulfate induced autophagy was reduced by pan-caspase inhibitor Z-VAD-FMK. Moreover, p-cresyl sulfate treatment increased the expression of ER stress proteins and decreased the expression of baculoviral IAP repeat-containing proteins 6; these effects were prevented by α-LA treatment. Apoptosis and autophagy were associated with the phosphorylation of mitogen-activated protein kinase and nuclear translocation of the nuclear factor-κB p65 subunit. Pretreatment inhibitors of p38 and JNK, and knockdown of ATF4 gene reduced apoptosis- and autophagy-related protein expressions in p-cresyl sulfate treated HK-2 cells. These results demonstrate that α-lipoic acid attenuated p-cresyl sulfate-induced cell death by suppression of apoptosis and autophagy via regulation of ER stress in HK-2 cells.

Role of the Inflammation-Autophagy-Senescence Integrative Network in Osteoarthritis

Osteoarthritis is the most common musculoskeletal disease causing chronic disability in adults. Studying cartilage aging, chondrocyte senescence, inflammation, and autophagy mechanisms have identified promising targets and pathways with clinical translatability potential. In this review, we highlight the most recent mechanistic and therapeutic preclinical models of aging with particular relevance in the context of articular cartilage and OA. Evidence supporting the role of metabolism, nuclear receptors and transcription factors, cell senescence, and circadian rhythms in the development of musculoskeletal system degeneration assure further translational efforts. This information might be useful not only to propose hypothesis and advanced models to study the molecular mechanisms underlying joint degeneration, but also to translate our knowledge into novel disease-modifying therapies for OA.

Titanium dioxide nanoparticles induce in vitro autophagy

Aim:

Concerns about the possible toxicity to environment and human health of titanium dioxide nanoparticles (TiO2 NPs) are increasing. The aim of this study was to investigate the relationship between toxicology and autophage in vitro.

Methods:

RAW 264.7 cells were exposed to five concentrations (50, 100, 200, 300, and 400 μg/mL) and two particle size of TiO2 NPs (30 and 100 nm) for 24 h.

Results:

The results showed that TiO2 NPs decreased cell viability, phagocytic rate, and phagocytic index in a concentration-dependent manner, thereby inducing autophagy. TiO2 NPs-induced autophagy was indicated by monodansyl cadaverine staining and transmission electron microscopy. TiO2 NPs-induced messenger RNA expression of autophagy-related proteins LC3 and Beclin-1 was also significantly increased compared with those of the unexposed control cells. LC3 and Beclin-1 protein expression levels were markedly increased with the increase of TiO2 NPs concentrations.

Conclusion:

These results suggest the possibility that TiO2 NPs-induced toxicology probably plays a key role in autophagy in RAW 264.7 cells, and further exhaustive research on the harmful effects of these NPs in relevant organisms is needed for their safe application.

Manipulation of autophagy: a novelly potential therapeutic strategy for retinal neovascularization

BACKGROUND

The relationship between the role of VEGF and autophagy in the process of retinal angiogenesis is still unclear. In this study, we explored this issue by using the mouse retinal vascular endothelial cell (RVEC) as a model.

METHODS

RVECs were divided into the following groups: control, hypoxia (H), 3-methyladenine (3-MA) + H, VEGF + H, 3-MA + VEGF+H, anti-VEGF antibody + H, 3-MA+ anti-VEGF antibody + H. We then examined activation of autophagy by detecting formation of autophagosomes with transmission electron microscopy (TEM) and by counting the number of green fluorescent protein-positive (GFP+) puncta in RVECs. The turnover of microtubule associated protein 1 light chain 3 B (LC3B) and VEGF were examined by western blot. Cell migratory capacity was measured with wound healing assay and transwell assay. The capillary formation assay was performed to investigate the angiogenic capacity.

RESULTS

Hypoxia led to an increased number of autophagosome and of the GFP+ puncta, an increased ratio of LC3B-II/I and enhanced migratory and capillary-formation capacities of RVECs. Pre-treatment with 3-MA attenuated activation of autophagy and abrogated the enhanced cell migration and capillary formation under hypoxia. Exposure to VEGF significantly increased migratory and capillary formation capacities of RVECs under hypoxia and 3-MA decreased VEGF-induced angiogenesis without its expression. Formation of autophagosome, the number of GFP+ puncta of RVECs and expression of LC3B-II/I were both elevated in cells treated with anti-VEGF antibody and these effects were partially inhibited by 3-MA pretreatment.

CONCLUSION

Our present data may identify autophagic response as a novel target for enhancing the therapeutic efficacy of angiogenesis inhibitors.

Autophagy activation and the mechanism of retinal microvascular endothelial cells in hypoxia

AIM

To explore the state of autophagy and related mechanisms in the murine retinal microvascular endothelial cells (RMECs) under hypoxia stimulation.

METHODS

The murine RMECs were primarily cultured and randomly divided into three groups: hypoxia group (cultured in 1% O₂ environment), hypoxia+autophagy inhibition group [pretreated with 5 mmol/L 3-methyladenine (3-MA) for 4h followed by incubation in 1% O₂] and control group (cultured under normoxic condition). The state of autophagy in RMECs was examined by assaying the turnover of light chain 3B (LC3BB) and expression of Beclin-1, Atg3 and Atg5 proteins with Western blotting, by detecting formation of autophagosomes with transmission electron microscopy (TEM) and by counting the number of GFP+ puncta in RMECs. The protein levels of AMPK, P-AMPK, Akt, P-Akt, m-TOR and P-mTOR were also assayed by Western blotting.

RESULTS

Primary murine RMECs were successfully cultured. Under hypoxic conditions, the ratio of LC3BB-II/I and the expression of Beclin-1, Atg3 and Atg5 proteins were increased when compared with the control group. In addition, the numbers of autophagosome and the GFP+ puncta were also increased under hypoxia. However, pre-treatment with 3-MA obviously attenuated these changes in autophagy in RMECs under hypoxia. Protein expression of P-Akt and P-AMPK was increased but P-mTOR level was decreased in cells exposed to hypoxia.

CONCLUSION

In murine RMECs autophagy is activated under hypoxia possibly through activation of the AMPK/mTOR signaling pathway.

Autophagy and Autophagic Cell Death: Uncovering New Mechanisms Whereby Dehydroepiandrosterone Promotes Beneficial Effects on Human Health

Dehydroepiandrosterone (DHEA) is the most abundant steroid hormone in human serum and a precursor of sexual hormones. Its levels, which are maximum between the age of 20 and 30, dramatically decline with aging thus raising the question that many pathological conditions typical of the elderly might be associated with the decrement of circulating DHEA. Moreover, since its very early discovery, DHEA and its metabolites have been shown to be active in many pathophysiological contexts, including cardiovascular disease, brain disorders, and cancer. Indeed, treatment with DHEA has beneficial effects for the cure of these and many other pathologies in vitro, in vivo, and in patient studies. However, the molecular mechanisms underlying DHEA effects have been only partially elucidated. Autophagy is a self-digestive process, by which cell homeostasis is maintained, damaged organelles removed, and cell survival assured upon stress stimuli. However, high rate of autophagy is detrimental and leads to a form of programmed cell death known as autophagic cell death (ACD). In this chapter, we describe the process of autophagy and the morphological and biochemical features of ACD. Moreover, we analyze the beneficial effects of DHEA in several pathologies and the molecular mechanisms with particular emphasis on its regulation of cell death processes. Finally, we review data indicating DHEA and structurally related steroid hormones as modulators of both autophagy and ACD, a research field that opens new avenues in the therapeutic use of these compounds.

Involvement of autophagy in the beneficial effects of resveratrol in hepatic steatosis treatment. A comparison with energy restriction

Involvement of autophagy in the liver delipidating effects of resveratrol and energy restriction.

Cell death pathways of particulate matter toxicity

Humans are exposed to various complex mixtures of particulate matter (PM) from different sources. Long-term exposure to high levels of these particulates has been linked to a diverse range of respiratory and cardiovascular diseases that have resulted in hospital admission. The evaluation of the effects of PM exposure on the mechanisms related to cell death has been a challenge for many researchers. Therefore, in this review, we have discussed the effects of airborne PM exposure on mechanisms related to cell death. For this purpose, we have compiled literature data on PM sources, the effects of exposure, and the assays and models used for evaluation, in order to establish comparisons between various studies. The analysis of this collected data suggested divergent responses to PM exposure that resulted in different cell death types (apoptosis, autophagy, and necrosis). In addition, PM induced oxidative stress within cells, which appeared to be an important factor in the determination of cell fate. When the levels of reactive oxygen species were overpowering, the cellular fate was directed toward cell death. This may be the underlying mechanism of the development or exacerbation of respiratory diseases, such as emphysema and chronic obstructive pulmonary diseases. In addition, PM was shown to cause DNA damage and the resulting mutations increased the risk of cancer. Furthermore, several conditions should be considered in the assessment of cell death in PM-exposed models, including the cell culture line, PM composition, and the interaction of the different cells types in in vivo models.

Autophagy: The spotlight for cellular stress responses

Autophagy is an essential cellular mechanism which plays "housekeeping" role in normal physiological processes including removing of long lived, aggregated and misfolded proteins, clearing damaged organelles, growth regulation and aging. Autophagy is also involved in a variety of biological functions like development, cellular differentiation, defense against pathogens and nutritional starvation. The integration of autophagy into these biological functions and other stress responses is determined by the transcriptional factors that undertake the regulatory mechanism. This review discusses the machinery of autophagy, the molecular web that connects autophagy to various stress responses like inflammation, hypoxia, ER stress, and various other pathologic conditions. Defects in autophagy regulation play a central role in number of diseases, including neurodegenerative diseases, cancer, pathogen infection and metabolic diseases. Similarly, inhibiting autophagy would contribute in the treatment of cancer. However, understanding the biology of autophagy regulation requires pharmacologically active compounds which modulate the autophagy process. Inducers of autophagy are currently receiving considerable attention as autophagy upregulation may be a therapeutic benefit for certain neurodegenerative diseases (via removal of protein aggregates) while the inhibitors are being investigated for the treatment of cancers. Both induction and inhibition of autophagy have been proven to be beneficial in the treatment of cancer. This dual role of autophagy in cancers is now getting uncovered by the advancement in the research findings and development of effective autophagy modulators.

Mitophagy: a balance regulator of NLRP3 inflammasome activation

The NLRP3 inflammasome is activated by a variety of external or host-derived stimuli and its activation initiates an inflammatory response through caspase-1 activation, resulting in inflammatory cytokine IL-1β maturation and secretion. The NLRP3 inflammasome activation is a kind of innate immune response, most likely mediated by myeloid cells acting as a host defense mechanism. However, if this activation is not properly regulated, excessive inflammation induced by overactivated NLRP3 inflammasome can be detrimental to the host, causing tissue damage and organ dysfunction, eventually causing several diseases. Previous studies have suggested that mitochondrial damage may be a cause of NLRP3 inflammasome activation and autophagy, which is a conserved self-degradation process that negatively regulates NLRP3 inflammasome activation. Recently, mitochondria-selective autophagy, termed mitophagy, has emerged as a central player for maintaining mitochondrial homeostasis through the elimination of damaged mitochondria, leading to the prevention of hyperinflammation triggered by NLRP3 inflammasome activation. In this review, we will first focus on the molecular mechanisms of NLRP3 inflammasome activation and NLRP3 inflammasome-related diseases. We will then discuss autophagy, especially mitophagy, as a negative regulator of NLPP3 inflammasome activation by examining recent advances in research. [BMB Reports 2016; 49(10): 529-535]

Diabetes-accelerated experimental osteoarthritis is prevented by autophagy activation

OBJECTIVE

Type 2 Diabetes (T2D) is a risk factor for osteoarthritis (OA). Autophagy, an essential homeostasis mechanism in articular cartilage, is defective in T2D and OA. However, how T2D may influence OA progression is still unknown. We aimed to determine how diabetes affects cartilage integrity and whether pharmacological activation of autophagy has efficacy in diabetic mice (db/db mice) with OA.

DESIGN

Experimental OA was performed in the right knee of 9 weeks-old C57Bl/6J male mice (Lean group, N = 8) and of 9 weeks-old B6.BKS (D)-Leprdb male mice (db/db group, N = 16) by transection of medial meniscotibial and medial collateral ligaments. Left knee was employed as control knee. Rapamycin (2 mg/kg weight/day) or Vehicle (dimethyl sulfoxide) were administered intraperitoneally three times a week for 10 weeks. Histopathology of articular cartilage and synovium was evaluated by using semiquantitative scoring and synovitis grading systems, respectively. Immunohistochemistry was employed to evaluate the effect of diabetes and Rapamycin on cartilage integrity and OA biomarkers.

RESULTS

Cartilage damage was increased in db/db mice compared to Lean mice after experimental OA, while no differences are observed in the control knee. Cartilage damage and synovium inflammation were reduced by Rapamycin treatment of OA-db/db mice. This protection was accompanied with a decrease in MMP-13 expression and decreased interleukin 12 (IL-12) levels. Furthermore, autophagy was increased and cartilage cellularity was maintained, suggesting that mammalian target of rapamycin (mTOR) targeting prevents joint physical harm.

CONCLUSION

Our findings indicate that diabetic mice exhibit increased joint damage after experimental OA, and that autophagy activation might be an effective therapy for diabetes-accelerated OA.

Autophagy and its implication in human oral diseases

Macroautophagy/autophagy is a conserved lysosomal degradation process essential for cell physiology and human health. By regulating apoptosis, inflammation, pathogen clearance, immune response and other cellular processes, autophagy acts as a modulator of pathogenesis and is a potential therapeutic target in diverse diseases. With regard to oral disease, autophagy can be problematic either when it is activated or impaired, because this process is involved in diverse functions, depending on the specific disease and its level of progression. In particular, activated autophagy functions as a cytoprotective mechanism under environmental stress conditions, which regulates tumor growth and mediates resistance to anticancer treatment in established tumors. During infections and inflammation, activated autophagy selectively delivers microbial antigens to the immune systems, and is therefore connected to the elimination of intracellular pathogens. Impaired autophagy contributes to oxidative stress, genomic instability, chronic tissue damage, inflammation and tumorigenesis, and is involved in aberrant bacterial clearance and immune priming. Hence, substantial progress in the study of autophagy provides new insights into the pathogenesis of oral diseases. This review outlines the mechanisms of autophagy, and highlights the emerging roles of this process in oral cancer, periapical lesions, periodontal diseases, and oral candidiasis.

Role of Autophagy in Hypoxia-Induced Angiogenesis of RF/6A Cells in vitro

PURPOSE

Autophagy plays a role in the pathogenesis of tumor angiogenesis and cardiovascular diseases. The autophagy level in mammalian cells was found to increase in the state of hypoxia or ischemia reperfusion. However, the role of autophagy in ocular angiogenesis has not yet been elucidated. The aim of this study was to investigate the effects of autophagy on hypoxia-induced choroidal and retinal angiogenesis in vitro using a rhesus macaque choroid-retinal endothelial (RF/6A) cell line.

MATERIALS AND METHODS

RF/6A cells were cultured and randomly divided into three groups according to the different culture media: control, hypoxia model[adding 125μMcobalt chloride (CoCl₂) to the culture medium], and hypoxia with an autophagy inhibition group [pretreatment with 5 mmol/L 3-methyladenine (3-MA) for 1.5 h and then adding125μmol/LCoCl₂ to the culture medium]. The impact of 3-MA's effect on the level of autophagy proteins (Beclin-1 and LC3) was tested by Western blot analysis. The cell proliferation was assessed using the chromogenicmethylthiazol tetrazolium bromide (MTT) dye after 24 and 48 hours. Cell migration was investigated by wound assay. The tube formation was measured on Matrigel.

RESULTS

Under chemical hypoxia conditions, Beclin-1 and LC3 levels increased and this change can be inhibited by 3-MA. Cell viability was decreased in cells treated with CoCl₂ for 24 and 48 h compared with the control, and pretreatment with 3-MA slightly promoted CoCl₂-inhibited cell proliferation. Cell migration and tube formation were increased in cells treated with CoCl₂ for 24 and 48 h compared with the control. Pretreatment with 3-MA significantly inhibited CoCl₂-induced cell migration and tube formation.

CONCLUSIONS

Hypoxia-induced autophagy decreased the cell viability and increased the cell migration and tube formation of RF/6A cells. 3-MA can inhibit hypoxia-induced angiogenesis of RF/6A cells in vitro. The present study suggests that autophagy plays a role in retinal and choroidal angiogenesis and the autophagy inhibitor can be a potential candidate for the treatment of choroidal or retinal neovascularization.