Toll-like receptor 4 is a sensor for autophagy associated with innate immunity

The Role of Autophagy and Autophagy Receptor NDP52 in Microbial Infections

Autophagy is a general protective mechanism for maintaining homeostasis in eukaryotic cells, regulating cellular metabolism, and promoting cell survival by degrading and recycling cellular components under stress conditions. The degradation pathway that is mediated by autophagy receptors is called selective autophagy, also named as xenophagy. Autophagy receptor NDP52 acts as a ‘bridge’ between autophagy and the ubiquitin-proteasome system, and it also plays an important role in the process of selective autophagy. Pathogenic microbial infections cause various diseases in both humans and animals, posing a great threat to public health. Increasing evidence has revealed that autophagy and autophagy receptors are involved in the life cycle of pathogenic microbial infections. The interaction between autophagy receptor and pathogenic microorganism not only affects the replication of these microorganisms in the host cell, but it also affects the host’s immune system. This review aims to discuss the effects of autophagy on pathogenic microbial infection and replication, and summarizes the mechanisms by which autophagy receptors interact with microorganisms. While considering the role of autophagy receptors in microbial infection, NDP52 might be a potential target for developing effective therapies to treat pathogenic microbial infections.

Microglia clear neuron-released α-synuclein via selective autophagy and prevent neurodegeneration

Microglia maintain brain homeostasis by removing neuron-derived components such as myelin and cell debris. The evidence linking microglia to neurodegenerative diseases is growing; however, the precise mechanisms remain poorly understood. Herein, we report a neuroprotective role for microglia in the clearance of neuron-released α-synuclein. Neuronal α-synuclein activates microglia, which in turn engulf α-synuclein into autophagosomes for degradation via selective autophagy (termed synucleinphagy). Synucleinphagy requires the presence of microglial Toll-like receptor 4 (TLR4), which induces transcriptional upregulation of p62/SQSTM1 through the NF-κB signaling pathway. Induction of p62, an autophagy receptor, is necessary for the formation of α-synuclein/ubiquitin-positive puncta that are degraded by autophagy. Finally, disruption of microglial autophagy in mice expressing human α-synuclein promotes the accumulation of misfolded α-synuclein and causes midbrain dopaminergic neuron degeneration. Our study thus identifies a neuroprotective function of microglia in the clearance of α-synuclein via TLR4-NF-κB-p62 mediated synucleinphagy.

The Lipid Virulence Factors of Mycobacterium tuberculosis Exert Multilayered Control over Autophagy-Related Pathways in Infected Human Macrophages

Autophagy is an important innate immune defense mechanism that controls Mycobacterium tuberculosis (Mtb) growth inside macrophages. Autophagy machinery targets Mtb-containing phagosomes via xenophagy after damage to the phagosomal membrane due to the Type VII secretion system Esx-1 or via LC3-associated phagocytosis without phagosomal damage. Conversely, Mtb restricts autophagy-related pathways via the production of various bacterial protein factors. Although bacterial lipids are known to play strategic functions in Mtb pathogenesis, their role in autophagy manipulation remains largely unexplored. Here, we report that the lipid virulence factors sulfoglycolipids (SLs) and phthiocerol dimycocerosates (DIMs) control autophagy-related pathways through distinct mechanisms in human macrophages. Using knock-out and knock-in mutants of Mtb and Mycobacterium bovis BCG (Bacille Calmette Guerin) and purified lipids, we found that (i) Mtb mutants with DIM and SL deficiencies promoted functional autophagy via an MyD88-dependent and phagosomal damage-independent pathway in human macrophages; (ii) SLs limited this pathway by acting as TLR2 antagonists; (iii) DIMs prevented phagosomal damage-independent autophagy while promoting Esx-1-dependent xenophagy; (iv) and DIMs, but not SLs, limited the acidification of LC3-positive Mtb compartments. In total, our study reveals an unexpected and intricate role for Mtb lipid virulence factors in controlling autophagy-related pathways in human macrophages, thus providing further insight into the autophagy manipulation tactics deployed by intracellular bacterial pathogens.

Xenophagy in cancer

Macroautophagy (herein autophagy) is an intracellular pathway in which cytoplasmic components are captured by double-membrane vesicles (autophagosomes) that eventually fuse with lysosomes to degrade the cargo. Basal levels of autophagy in all eukaryotic cells maintain cellular homeostasis and under conditions of stress, organelles and proteins not essential for survival are degraded. Apart from these functions, cargoes like aggregated proteins, damaged organelles and intracellular pathogens, which are otherwise harmful to cells, are also selectively captured by autophagy and are destined for degradation. In terms of infectious diseases, pathogens are cleared by a specific form of autophagy known as xenophagy. This lysosomal mediated degradation of pathogens also increases the antigen presentation of cells thereby inducing a further immune response. The process of xenophagy provides a broad spectrum of defense mechanism to capture bacterial, viral and protozoan pathogens. However, pathogens have developed ingenious mechanisms to modulate xenophagy to enhance their intracellular survival. Meanwhile, certain pathogens also induce deleterious effects such as chronic inflammation and overexpression of oncogenes in the host system. This over time can increase the susceptibility of the host for tumorigenesis. Hence targeting tumor through anti-microbial mechanisms like xenophagy could be a novel strategy for combinatorial anti-cancer therapy. The recent developments in understanding the role of xenophagy in combating cancer causing pathogens will be discussed in this review.

Oral Microbes and Mucosal Dendritic Cells, "Spark and Flame" of Local and Distant Inflammatory Diseases

Mucosal health and disease is mediated by a complex interplay between the microbiota ("spark") and the inflammatory response ("flame"). Pathobionts, a specific class of microbes, exemplified by the oral microbe Porphyromonas gingivalis, live mostly "under the radar" in their human hosts, in a cooperative relationship with the indigenous microbiota. Dendritic cells (DCs), mucosal immune sentinels, often remain undisturbed by such microbes and do not alert adaptive immunity to danger. At a certain tipping point of inflammation, an "awakening" of pathobionts occurs, wherein their active growth and virulence are stimulated, leading to a dysbiosis. Pathobiont becomes pathogen, and commensal becomes accessory pathogen. The local inflammatory outcome is the Th17-mediated degenerative bone disease, periodontitis (PD). In systemic circulation of PD subjects, inflammatory DCs expand, carrying an oral microbiome and promoting Treg and Th17 responses. At distant peripheral sites, comorbid diseases including atherosclerosis, Alzheimer's disease, macular degeneration, chronic kidney disease, and others are reportedly induced. This review will review the immunobiology of DCs, examine the complex interplay of microbes and DCs in the pathogenesis of PD and its comorbid inflammatory diseases, and discuss the role of apoptosis and autophagy in this regard. Overall, the pathophysiological mechanisms of DC-mediated chronic inflammation and tissue destruction will be summarized.

Intestinal Alkaline Phosphatase Exerts Anti-Inflammatory Effects Against Lipopolysaccharide by Inducing Autophagy

Intestinal alkaline phosphatase (IAP) regulates bicarbonate secretion, detoxifies lipopolysaccharide (LPS), regulates gut microbes, and dephosphorylates proinflammatory nucleotides. IAP also exhibits anti-inflammatory effects in a Toll-like Receptor-4 (TLR-4) dependent manner. However, it is not known whether IAP induces autophagy. We tested the hypothesis that IAP may induce autophagy which may mediate the anti-inflammatory effects of IAP. We found that exogenous IAP induced autophagy in intestinal epithelial cells and in macrophages. TLR4INC34 (C34), a TLR4 signaling inhibitor, suppressed IAP-induced autophagy. IAP also inhibited LPS-induced IL-1β mRNA expression and activation of NF-κB. When autophagy was blocked by 3-methyladenine (3MA) or by Atg5 siRNA, IAP failed to block LPS-mediated effects. IAP also upregulated autophagy-related gene expression in small intestine in mice. We administered either vehicle or IAP (100 U/ml) in drinking water for 14 days in C57BL/6 mice. Mice were sacrificed and ileal tissues collected. Increased expression of Atg5, Atg16, Irgm1, Tlr4, and Lyz genes was observed in the IAP treated group compared to the vehicle treated group. Increase in Atg16 protein expression and fluorescence intensity of LC3 was also observed in IAP-treated tissues compared to the vehicle-treated tissues. Thus, our study lays the framework for investigating how IAP and autophagy may act together to control inflammatory conditions.

Extensive Changes in Transcriptomic "Fingerprints" and Immunological Cells in the Large Organs of Patients Dying of Acute Septic Shock and Multiple Organ Failure Caused by Neisseria meningitidis

Background: Patients developing meningococcal septic shock reveal levels of Neisseria meningitidis (10⁶-10⁸/mL) and endotoxin (10¹-10³ EU/mL) in the circulation and organs, leading to acute cardiovascular, pulmonary and renal failure, coagulopathy and a high case fatality rate within 24 h. Objective: To investigate transcriptional profiles in heart, lungs, kidneys, liver, and spleen and immunostain key inflammatory cells and proteins in post mortem formalin-fixed, paraffin-embedded (FFPE) tissue samples from meningococcal septic shock patients. Patients and Methods: Total RNA was isolated from FFPE and fresh frozen (FF) tissue samples from five patients and two controls (acute non-infectious death). Differential expression of genes was detected using Affymetrix microarray analysis. Lung and heart tissue samples were immunostained for T-and B cells, macrophages, neutrophils and the inflammatory markers PAI-1 and MCP-1. Inflammatory mediators were quantified in lysates from FF tissues. Results: The transcriptional profiles showed a complex pattern of protein-coding and non-coding RNAs with significant regulation of pathways associated with organismal death, cell death and survival, leukocyte migration, cellular movement, proliferation of cells, cell-to-cell signaling, immune cell trafficking, and inflammatory responses in an organ-specific clustering manner. The canonical pathways including acute phase response-, EIF2-, TREM1-, IL-6-, HMBG1-, PPAR signaling, and LXR/RXR activation were associated with acute heart, pulmonary, and renal failure. Fewer genes were regulated in the liver and particularly in the spleen. The main upstream regulators were TNF, IL-1β, IL-6, RICTOR, miR-6739-3p, and CD3. Increased numbers of inflammatory cells (CD68+, MPO+, CD3+, and CD20+) were found in lungs and heart. PAI-1 inhibiting fibrinolysis and MCP-1 attracting leukocyte were found significantly present in the septic tissue samples compared to the controls. Conclusions: FFPE tissue samples can be suitable for gene expression studies as well as immunostaining of specific cells or molecules. The most pronounced gene expression patterns were found in the organs with highest levels of Neisseria meningitidis DNA. Thousands of protein-coding and non-coding RNA transcripts were altered in lungs, heart and kidneys. We identified specific biomarker panels both protein-coding and non-coding RNA transcripts, which differed from organ to organ. Involvement of many genes and pathways add up and the combined effect induce organ failure.

TAK-242, a specific inhibitor of Toll-like receptor 4 signalling, prevents endotoxemia-induced skeletal muscle wasting in mice

Circulating lipopolysaccharide (LPS) concentrations are often elevated in patients with sepsis or various endogenous diseases related to bacterial translocation from the gut. Systemic inflammatory responses induced by endotoxemia induce severe involuntary loss of skeletal muscle, termed muscle wasting, which adversely affects the survival and functional outcomes of these patients. Currently, no drugs are available for the treatment of endotoxemia-induced skeletal muscle wasting. Here, we tested the effects of TAK-242, a Toll-like receptor 4 (TLR4)-specific signalling inhibitor, on myotube atrophy in vitro and muscle wasting in vivo induced by endotoxin. LPS treatment of murine C2C12 myotubes induced an inflammatory response (increased nuclear factor-κB activity and interleukin-6 and tumour necrosis factor-α expression) and activated the ubiquitin-proteasome and autophagy proteolytic pathways (increased atrogin-1/MAFbx, MuRF1, and LC-II expression), resulting in myotube atrophy. In mice, LPS injection increased the same inflammatory and proteolytic pathways in skeletal muscle and induced atrophy, resulting in reduced grip strength. Notably, pretreatment of cells or mice with TAK-242 reduced or reversed all the detrimental effects of LPS in vitro and in vivo. Collectively, our results indicate that pharmacological inhibition of TLR4 signalling may be a novel therapeutic intervention for endotoxemia-induced muscle wasting.

Lipopolysaccharide induces neuroinflammation in microglia by activating the MTOR pathway and downregulating Vps34 to inhibit autophagosome formation

Background

Microglial activation is a prominent feature of neuroinflammation, which is present in almost all neurodegenerative diseases. While an initial inflammatory response mediated by microglia is considered to be protective, excessive pro-inflammatory response of microglia contributes to the pathogenesis of neurodegeneration. Although autophagy is involved in the suppression of inflammation, its role and mechanism in microglia are unclear.

Methods

In the present study, we studied the mechanism by which lipopolysaccharide (LPS) affects microglial autophagy and the effects of autophagy on the production of pro-inflammatory factors in microglial cells by western blotting, immunocytochemistry, transfection, transmission electron microscopy (TEM), and real-time PCR. In a mouse model of neuroinflammation, generated by intraventricular injection of LPS (5 μg/animal), we induced autophagy by rapamycin injection and investigated the effects of enhanced autophagy on microglial activation by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry.

Results

We found that autophagic flux was suppressed in LPS-stimulated N9 microglial cells, as evidenced by decreased expression of the autophagy marker LC3-II (lipidated form of MAP1LC3), as well as increased levels of the autophagy adaptor protein SQSTM1. LPS significantly decreased Vps34 expression in N9 microglial cells by activating the PI3KI/AKT/MTOR pathway without affecting the levels of lysosome-associated proteins and enzymes. More importantly, overexpression of Vps34 significantly enhanced the autophagic flux and decreased the accumulation of SQSTM1 in LPS-stimulated N9 microglial cells. Moreover, our results revealed that an LPS-induced reduction in the level of Vps34 prevented the maturation of omegasomes to phagophores. Furthermore, LPS-induced neuroinflammation was significantly ameliorated by treatment with the autophagy inducer rapamycin both in vitro and in vivo.

Conclusions

These data reveal that LPS-induced neuroinflammation in N9 microglial cells is associated with the inhibition of autophagic flux through the activation of the PI3KI/AKT/MTOR pathway, while enhanced microglial autophagy downregulates LPS-induced neuroinflammation. Thus, this study suggests that promoting the early stages of autophagy might be a potential therapeutic approach for neuroinflammation-associated diseases.

Resatorvid protects against hypoxic-ischemic brain damage in neonatal rats

Secondary brain damage caused by hyperactivation of autophagy and inflammatory responses in neurons plays an important role in hypoxic-ischemic brain damage (HIBD). Although previous studies have implicated Toll-like receptor 4 (TLR4) and nuclear factor kappa-B (NF-κB) in the neuroinflammatory response elicited by brain injury, the role and mechanisms of the TLR4-mediated autophagy signaling pathway in neonatal HIBD are still unclear. We hypothesized that this pathway can regulate brain damage by modulating neuron autophagy and neuroinflammation in neonatal rats with HIBD. Hence, we established a neonatal HIBD rat model using the Rice-Vannucci method, and injected 0.75, 1.5, or 3 mg/kg of the TLR4 inhibitor resatorvid (TAK-242) 30 minutes after hypoxic ischemia. Our results indicate that administering TAK-242 to neonatal rats after HIBD could significantly reduce the infarct volume and the extent of cerebral edema, alleviate neuronal damage and neurobehavioral impairment, and decrease the expression levels of TLR4, phospho-NF-κB p65, Beclin-1, microtubule-associated protein l light chain 3, tumor necrosis factor-α, and interleukin-1β in the hippocampus. Thus, TAK-242 appears to exert a neuroprotective effect after HIBD by inhibiting activation of autophagy and the release of inflammatory cytokines via inhibition of the TLR4/NF-κB signaling pathway. This study was approved by the Laboratory Animal Ethics Committee of Affiliated Hospital of Yangzhou University, China (approval No. 20180114-15) on January 14, 2018.

Autophagy and Gastrointestinal Diseases

Normal gastrointestinal physiology is fundamental for all the living beings. Gastrointestinal diseases mainly include gastrointestinal motility disorders, infectious inflammation (such as Helicobacter pylori infection, cholera, and intestinal parasites), non-infectious inflammation (such as chronic gastritis and Crohn's disease), and gastrointestinal cancers. In addition, intestinal microbial disorder is also an important cause of intestinal diseases, so intestinal microecological treatment (fecal microbiota transplantation) is an important mean of treating gastrointestinal diseases. In recent years, the role of autophagy in gastrointestinal diseases has been studied extensively. Autophagy is observed under various pathological processes of the gastrointestinal tract. For example, it has been demonstrated that autophagy plays an important role in maintaining the homeostasis and integrity of intestinal epithelium. Additionally, autophagy regulates host response to H. pylori infection and development of gastrointestinal cancers. Therefore, we will discuss pivotal roles of autophagy in various gastrointestinal diseases and analyze the underlying molecular mechanisms, which may provide new therapeutic targets applicable for the treatment of gastrointestinal diseases.

Contrasting and emerging roles of autophagy in plant immunity

Autophagy is a conserved eukaryotic process that mediates degradation and relocation of cellular material to maintain homeostasis and cope with cellular stress. Remarkably, this ancient catabolic machinery has been co-opted to eliminate invading pathogens in a variety of ways. Plant autophagy not only mediates selective destruction of viruses but also limits infection by extracellular bacterial and filamentous pathogens. The emerging paradigm is that autophagy adaptors, responsible for selective cargo sorting, have been appointed to counteract pathogen infection, while adapted pathogens have evolved to subvert the immune functions of the autophagic machinery. In this review, we discuss recent findings that contribute to understanding the role of autophagy in plant immunity and highlight key questions to address in the field moving forward.

Inhibitory effects of berberine on proinflammatory M1 macrophage polarization through interfering with the interaction between TLR4 and MyD88

BACKGROUNDS

Inflammation is recognized as the key pathological mechanism of type 2 diabetes. The hypoglyceamic effects of berberine (BBR) are related to the inhibition of the inflammatory response, but the mechanism is not completely clear.

METHODS

The inflammatory polarization of Raw264.7 cells and primary peritoneal macrophages were induced by LPS, and then effects and underlying mechanisms of BBR were explored. An inflammatory model was established by LPS treatment at different concentrations for different treatment time. An ELISA assay was used to detect the secretions of TNF-α. RT-PCR was applied to detect M1 inflammatory factors. The F4/80+ ratio and CD11c+ ratio of primary peritoneal macrophages were determined by flow cytometry. The expressions of p-AMPK and TLR4 were detected by Western blot. The cytoplasmic and nuclear distributions of NFκB p65 were observed by confocal microscopy. The binding of TLR4 to MyD88 was tested by CoIP, and the affinity of BBR for TLR4 was assessed by molecular docking.

RESULTS

Upon exposure to LPS, the secretion of TNF-α and transcription of inflammatory factors in macrophages increased, cell morphology changed and protrusions appeared gradually, the proportion of F4/80+CD11c+ M1 macrophages increased, and the nuclear distribution of NFκB p65 increased. BBR pretreatment partially inhibited the changes mentioned above. However, the expression of TLR4 and p-AMPK did not change significantly after LPS intervention for 3 h. Meanwhile, CoIP showed that the interaction between TLR4 and MyD88 increased, and BBR inhibited the binding. Molecular docking suggested that BBR might interact with TLR4.

CONCLUSIONS

Inflammatory changes were induced in macrophages after LPS stimulation for 3 h, and BBR pretreatment inhibited inflammatory polarization. BBR might interact with TLR4 and disturb TLR4/MyD88/NFκB signalling pathway, and it might be the mechanism by which BBR attenuated inflammation in the early phase.

Deciphering the Role Played by Autophagy in Leishmania Infection

In recent decades, studies have shown that, depending on parasite species and host background, autophagy can either favor infection or promote parasite clearance. To date, relatively few studies have attempted to assess the role played by autophagy in Leishmania infection. While it has been consistently shown that Leishmania spp. induce autophagy in a variety of cell types, published results regarding the effects of autophagic modulation on Leishmania survival are contradictory. The present review, after a short overview of the general aspects of autophagy, aims to summarize the current body of knowledge surrounding how Leishmania spp. adaptively interact with macrophages, the host cells mainly involved in controlling leishmaniasis. We then explore the scarce studies that have investigated interactions between these parasite species and the autophagic pathway, and finally present a critical perspective on how autophagy influences infection outcome.

Lactobacillus reuteri ZJ617 Culture Supernatant Attenuates Acute Liver Injury Induced in Mice by Lipopolysaccharide

BACKGROUND

Lactobacillus rhamnosus GG culture supernatant (LGGs) promotes intestinal integrity and ameliorates acute liver injury induced by alcohol in mice.

OBJECTIVES

The aim of this study was to investigate the protective effects and molecular mechanisms of Lactobacillus reuteri ZJ617 culture supernatant (ZJ617s) on acute liver injury induced by lipopolysaccharide (LPS) in mice.

METHODS

Male C57BL/6 mice (20 ± 2 g, 8 wk old) were randomly divided into 4 groups (6 mice/group): oral inoculation with phosphate-buffered saline (control), intraperitoneal injection of LPS (10 mg/kg body weight) (LPS), oral inoculation with ZJ617s 2 wk before intraperitoneal injection of LPS (ZJ617s + LPS), or oral inoculation with LGGs 2 wk before intraperitoneal injection of LPS (LGGs + LPS). Systemic inflammation, intestinal integrity, biomarkers of hepatic function, autophagy, and apoptosis signals in the liver were determined.

RESULTS

Twenty-four hours after LPS injection, the activities of serum alanine transaminase and aspartate transaminase were 32.2% and 30.3% lower in the ZJ617s + LPS group compared with the LPS group, respectively (P < 0.05). The ZJ617s + LPS group exhibited higher intestinal expression of claudin 3 (62.5%), occludin (60.1%), and zonula occludens 1 (60.5%) compared with the LPS group (P < 0.05). The concentrations of hepatic interleukin-6 and tumor necrosis factor-α were 21.4% and 27.3% lower in the ZJ617s + LPS group compared with the LPS group, respectively (P < 0.05). However, the concentration of interleukin-10 was 22.2% higher in the ZJ617s + LPS group. LPS increased the expression of Toll-like receptor 4 (TLR4; by 50.5%), phosphorylation p38 mitogen-activated protein kinase (p38MAPK; by 57.1%), extracellular signal-regulated kinase (by 77.8%), c-Jun N-terminal kinase (by 42.9%), and nuclear factor-κB (NF-κB; by 36.0%) compared with the control group. Supplementation with ZJ617s or LGGs ameliorated these effects (P < 0.05). Moreover, the hepatic expression of active caspase-3 and microtubule-associated protein 1 light chain 3 II was 23.8% and 28.6% lower in the ZJ617s + LPS group compared with the LPS group, respectively (P < 0.05).

CONCLUSIONS

ZJ617s exerts beneficial effects on the mouse liver through suppression of hepatic TLR4/MAPK/NF-κB activation, apoptosis, and autophagy. This trial was registered at Zhejiang University (http://www.lac.zju.edu.cn) as NO.ZJU20170529.

Sepsis roadmap: What we know, what we learned, and where we are going

Sepsis is a life-threatening condition originating as a result of systemic blood infection causing, one or more organ damage due to the dysregulation of the immune response. In 2017, the world health organization (WHO) declared sepsis as a disease of global health priority, needing special attention due to its high prevalence and mortality around the world. Most of the therapeutics targeting sepsis have failed in the clinics. The present review highlights the history of the sepsis, its immunopathogenesis, and lessons learned after the failure of previously used immune-based therapies. The subsequent section, where to go describes in details the importance of the complement system (CS), autophagy, inflammasomes, and microbiota along with their targeting to manage sepsis. These systems are interconnected to each other, thus targeting one may affect the other. We are in an urgent need for a multi-targeting therapeutic approach for sepsis.

iNOS Interacts with Autophagy Receptor p62 and is Degraded by Autophagy in Macrophages

Nitric oxide (NO) is an important mediator of inflammation response and the production of NO has been linked to a variety of diseases, including tumors, inflammation and central nervous system diseases. In macrophages, a high level of NO is generated by iNOS during inflammatory responses triggered by cytokines or pathogens. Autophagy, a cellular bulk degradation process via lysosome, has been implicated in many disease conditions including inflammation. In this study, we have reported the previously unknown role of autophagy in regulating iNOS levels in macrophages, both under basal and Lipopolysaccharides (LPS)-induced conditions. Our data showed that iNOS levels accumulated upon autophagy inhibition and decreased upon autophagy induction. iNOS interacted and co-localized with autophagy receptor p62/SQSTM1, especially under LPS-stimulated condition in macrophages. Moreover, the immunostaining data revealed that iNOS also co-localizes with the autophagosome marker LC3 and lysosome marker LAMP1, especially under lysosomal inhibition conditions, indicating iNOS is an autophagy substrate. Finally, we showed that autophagy negatively regulated the generation of NO in macrophages, which is consistent with the changes of iNOS levels. Collectively, our study revealed a previously unknown mechanism by which autophagy regulates iNOS levels to modulate NO production during inflammation.

Ulinastatin Protects Against LPS-Induced Acute Lung Injury By Attenuating TLR4/NF-κB Pathway Activation and Reducing Inflammatory Mediators

Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome, remain the leading causes of morbidity and mortality in intensive care units. Ulinastatin (UTI), a serine protease inhibitor, possesses anti-inflammatory properties and has been suggested to modulate lipopolysaccharide (LPS)-induced sepsis; thus, it is now widely used in the treatment of pancreatitis, sepsis, and septic shock. Toll-like receptor 4 (TLR4), an essential LPS signaling receptor, plays a critical role in the activation of innate immunity. The aim of this study was to investigate whether UTI alleviates ALI by attenuating TLR4 expression and to explore the underlying molecular mechanisms involved. Male C56BL/6 mice were administered UTI intravenously 1 h before and 6 h after exposure to LPS by intratracheal instillation. Human lung epithelial (BEAS-2B) cells were incubated with LPS in the presence or absence of UTI. An enzyme-linked immunosorbent assay was used to detect levels of inflammatory cytokines. Western blot analysis was performed to detect changes in TLR4 expression and nuclear factor-κB (NF-κB) activation. UTI significantly protected animals from LPS-induced ALI, decreasing the lung wet/dry weight ratio, ALI score, total cells, neutrophils, macrophages, myeloperoxidase activity, and malondialdehyde content, factors associated with lung histological damage. UTI treatment also markedly attenuated levels of TLR4 and other proinflammatory cytokines. Furthermore, UTI significantly attenuated LPS-induced increases in TLR4 protein expression and NF-κB activation in lung tissues. Similarly, UTI markedly attenuated TLR4 expression and NF-κB activation in LPS-stimulated BEAS-2B cells. These findings indicate that UTI ameliorates LPS-induced ALI by attenuating the TLR4/NF-κB pathway activation.

Lipopolysaccharide enhances DNA-induced IFN-β expression and autophagy by upregulating cGAS expression in A549 cells

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is a newly identified cytosolic DNA sensor, but its function in lung epithelial cells is relatively unknown. In the present study, the effects of lipopolysaccharide (LPS) on the expression and function of cGAS in the A549 lung epithelial cell line was investigated. The cells were treated with LPS at different concentrations (e.g., 100, 200, 400 and 800 ng/ml), and the cGAS expression levels were examined via western blot analysis and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The cells were pretreated with LPS, followed by E. coli DNA transfection using Lipofectamine^® 3000. After 24 h, interferon (IFN)-β production was measured using ELISA and the expression of the autophagic markers, microtubule-associated proteins 1A/1B light chain 3 and sequestosome-1, were determined using western blot analysis. The cells were also pretreated with either a toll-like receptor (TLR) 4 inhibitor, a serine/threonine-protein kinase TBK1 (TBK1) inhibitor or an nuclear factor (NF)-κB inhibitor, followed by LPS treatment, and the cGAS expression levels were examined via western blot analysis and RT-qPCR. The result showed that LPS treatment upregulated cGAS expression in a dose-dependent manner. E. coli DNA treatment could induce IFN-β production and autophagy via cGAS, which was enhanced by LPS pretreatment. The effect of LPS on cGAS expression was suppressed by treatment with a TLR4 inhibitor, a TBK1 inhibitor and an NF-κB inhibitor. In conclusion, LPS enhances DNA-induced IFN-β production and autophagy by upregulating cGAS expression through the myeloid differentiation primary response protein MyD88-independent TLR4 signaling pathway in A549 cells.

Induction of autophagy through CLEC4E in combination with TLR4: an innovative strategy to restrict the survival of Mycobacterium tuberculosis

Host-directed therapies are gaining considerable impetus because of the emergence of drug-resistant strains of pathogens due to antibiotic therapy. Therefore, there is an urgent need to exploit alternative and novel strategies directed at host molecules to successfully restrict infections. The C-type lectin receptor CLEC4E and Toll-like receptor TLR4 expressed by host cells are among the first line of defense in encountering pathogens. Therefore, we exploited signaling of macrophages through CLEC4E in association with TLR4 agonists (C₄.T₄) to control the growth of Mycobacterium tuberculosis (Mtb). We observed significant improvement in host immunity and reduced bacterial load in the lungs of Mtb-infected mice and guinea pigs treated with C₄.T₄ agonists. Further, intracellular killing of Mtb was achieved with a 10-fold lower dose of isoniazid or rifampicin in conjunction with C₄.T₄ than the drugs alone. C₄.T₄ activated MYD88, PtdIns3K, STAT1 and RELA/NFKB, increased lysosome biogenesis, decreased Il10 and Il4 gene expression and enhanced macroautophagy/autophagy. Macrophages from autophagy-deficient (atg5 knockout or Becn1 knockdown) mice showed elevated survival of Mtb. The present findings also unveiled the novel role of CLEC4E in inducing autophagy through MYD88, which is required for control of Mtb growth. This study suggests a unique immunotherapeutic approach involving CLEC4E in conjunction with TLR4 to restrict the survival of Mtb through autophagy.

ABBREVIATIONS

3MA: 3 methyladenine; AO: acridine orange; Atg5: autophagy related 5; AVOs: acidic vesicular organelles; BECN1: beclin 1, autophagy related; BMDMs: bone marrow derived macrophages; bw: body weight; C₄.T₄: agonists of CLEC4E (C₄/TDB) and TLR4 (T₄/ultra-pure-LPS); CFU: colony forming unit; CLEC4E/Mincle: C-type lectin domain family 4, member e; CLR: c-type lectin receptor; INH: isoniazid; LAMP1: lysosomal-associated membrane protein 1; Mφ^C4.T4: Mtb-infected C₄.T₄ stimulated macrophages; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MDC: monodansylcadaverine; MTOR: mechanistic target of rapamycin kinase; MYD88: myeloid differentiation primary response 88; NFKB: nuclear factor of kappa light polypeptide gene enhance in B cells; NLR: NOD (nucleotide-binding oligomerization domain)-like receptors; PFA: paraformaldehyde; PPD: purified protein derivative; PtdIns3K: class III phosphatidylinositol 3-kinase; RELA: v-rel reticuloendotheliosis viral oncogene homolog A (avian); RIF: rifampicin; RLR: retinoic acid-inducible gene-I-like receptors; TDB: trehalose-6,6´-dibehenate; TLR4: toll-like receptor 4; Ultra-pure-LPS: ultra-pure lipopolysaccharide-EK; V-ATPase: vacuolar-type H⁺ ATPase.

TAK1 converts Sequestosome 1/p62 from an autophagy receptor to a signaling platform

The protein p62/Sequestosome 1 (p62) has been described as a selective autophagy receptor and independently as a platform for pro-inflammatory and other intracellular signaling. How these seemingly disparate functional roles of p62 are coordinated has not been resolved. Here, we show that TAK1, a kinase involved in immune signaling, negatively regulates p62 action in autophagy. TAK1 reduces p62 localization to autophagosomes, dampening the autophagic degradation of both p62 and p62-directed autophagy substrates. TAK1 also relocalizes p62 into dynamic cytoplasmic bodies, a phenomenon that accompanies the stabilization of TAK1 complex components. On the other hand, p62 facilitates the assembly and activation of TAK1 complexes, suggesting a connection between p62's signaling functions and p62 body formation. Thus, TAK1 governs p62 action, switching it from an autophagy receptor to a signaling platform. This ability of TAK1 to disable p62 as an autophagy receptor may allow certain autophagic substrates to accumulate when needed for cellular functions.

Cell Death Mechanisms in Esophageal Squamous Cell Carcinoma Induced by Vesicular Stomatitis Virus Matrix Protein

Objectives

Vesicular stomatitis virus (VSV) is under development as an oncolytic virus due to its preferential replication in cancer cells and oncolytic activity, however the viral components responsible have not yet been determined. In this study the effects of VSV wild-type (wt) and M51R-mutant matrix proteins (M51R-mMP) on apoptosis, pyroptosis, necroptosis, and autophagy pathways, in an esophagus cancer cell line (KYSE-30) were investigated.

Methods

The KYSE-30 cells were transfected with pcDNA3.1 plasmids encoding wt or M51R-mMP, and apoptosis, pyroptosis, necroptosis, and autophagy were evaluated 48 and 72 hours after transfection.

Results

KYSE-30 cells transfected with VSV wt and M51R-mMPs significantly reduced cell viability to < 50% at 72 hours post-transfection. M51R-MP significantly increased the concentration of caspase-8 and caspase-9 at 48 and 72 hours post-transfection, respectively ( p < 0.05). In contrast, no significant changes were detected following transfection with the VSV wt plasmid. Moreover, VSV wt and M51R-mMP transfected cells did not change the expression of caspase-3. VSV wt and M51R-mMPs did not mMP change caspase-1 expression (a marker of pyroptosis) at 48 and 72 hours post-transfection. However, M51R-mMP and VSV wt transfected cells significantly increased RIP-1 (a marker of necroptosis) expression at 72 hours post-infection ( p < 0.05). Beclin-1, a biomarker of autophagy, was also induced by transfection with VSV wt or M51R-mMPs at 48 hours post-transfection.

Conclusion

The results in this study indicated that VSV exerts oncolytic activity in KYSE-30 tumor cells through different cell death pathways, suggesting that M51R-mMP may potentially be used to enhance oncolysis.

The metabolic regulator Lamtor5 suppresses inflammatory signaling via regulating mTOR-mediated TLR4 degradation

Comprehensive immune responses are essential for eliminating pathogens but must be tightly controlled to avoid sustained immune activation and potential tissue damage. The engagement of TLR4, a canonical pattern recognition receptor, has been proposed to trigger inflammatory responses with different magnitudes and durations depending on TLR4 cellular compartmentalization. In the present study, we identify an unexpected role of Lamtor5, a newly identified component of the amino acid-sensing machinery, in modulating TLR4 signaling and controlling inflammation. Specifically, Lamtor5 associated with TLR4 via their LZ/TIR domains and facilitated their colocalization at autolysosomes, preventing lysosomal tethering and the activation of mTORC1 upon LPS stimulation and thereby derepressing TFEB to promote autophagic degradation of TLR4. The loss of Lamtor5 was unable to trigger the TFEB-driven autolysosomal pathway and delay degradation of TLR4, leading to sustained inflammation and hence increased mortality among Lamtor5 haploinsufficient mice during endotoxic shock. Intriguingly, nutrient deprivation, particularly leucine deprivation, blunted inflammatory signaling and conferred protection to endotoxic mice. This effect, however, was largely abrogated upon Lamtor5 deletion. We thus propose a homeostatic function of Lamtor5 that couples pathogenic insults and nutrient availability to optimize the inflammatory response; this function may have implications for TLR4-associated inflammatory and metabolic disorders.

Accelerated and Severe Lupus Nephritis Benefits From M1, an Active Metabolite of Ginsenoside, by Regulating NLRP3 Inflammasome and T Cell Functions in Mice

Chinese herbal medicines used in combination have long-term been shown to be mild remedies with “integrated effects.” However, our study provides the first demonstration that M1, an active metabolite of ginsenoside, exerted its dramatic therapeutic effects on accelerated and severe lupus nephritis (ASLN) mice, featuring acute renal function impairment, heavy proteinuria, high serum levels of anti-dsDNA, and high-grade, diffuse proliferative renal lesions. In the present study, NZB/WF1 mice were given injections of lipopolysaccharide to induce the ASLN model. M1 (30 mg/kg) was then administered to the mice by gavage daily, and the mice were sacrificed on week 3 and week 5 after the induction of disease. To identify the potential mechanism of action for the pure compound, levels of NLRP3 inflammasome activation in bone marrow-derived dendritic cells (BMDCs), podocytes and macrophages, and antigen-specific T cell activation in BMDCs were determined in addition to mechanistic experiments in vivo. Treatment with M1 dramatically improved renal function, albuminuria and renal lesions and reduced serum levels of anti-dsDNA in the ASLN mice. These beneficial effects with M1 treatment involved the following cellular and molecular mechanistic events: [1] inhibition of NLRP3 inflammasome associated with autophagy induction, [2] modulation of T help cell activation, and [3] induction of regulatory T cell differentiation. M1 improved the ASLN mice by blunting NLRP3 inflammasome activation and differentially regulating T cell functions, and the results support M1 as a new therapeutic candidate for LN patients with a status of abrupt transformation of lower-grade (mesangial) to higher-grade (diffuse proliferative) nephritis.

An autophagy-inducing and TLR-2 activating BCG vaccine induces a robust protection against tuberculosis in mice

Mycobacterium bovis BCG is widely used as a vaccine against tuberculosis due to M. tuberculosis (Mtb), which kills millions of people each year. BCG variably protects children, but not adults against tuberculosis. BCG evades phagosome maturation, autophagy, and reduces MHC-II expression of antigen-presenting cells (APCs) affecting T-cell activation. To bypass these defects, an autophagy-inducing, TLR-2 activating C5 peptide from Mtb-derived CFP-10 protein was overexpressed in BCG in combination with Ag85B. Recombinant BCG85C5 induced a robust MHC-II-dependent antigen presentation to CD4 T cells in vitro, and elicited stronger TH1 cytokines (IL-12, IL-1β, and TNFα) from APCs of C57Bl/6 mice increasing phosphorylation of p38MAPK and ERK. BCG85C5 also enhanced MHC-II surface expression of MΦs by inhibiting MARCH1 ubiquitin ligase that degrades MHC-II. BCG85C5 infected APCs from MyD88 or TLR-2 knockout mice showed decreased antigen presentation. Furthermore, BCG85C5 induced LC3-dependent autophagy in macrophages increasing antigen presentation. Consistent with in vitro effects, BCG85C5 markedly expanded both effector and central memory T cells in C57Bl/6 mice protecting them against both primary aerosol infection with Mtb and reinfection, but was less effective among TLR-2 knockout mice. Thus, BCG85C5 induces stronger and longer lasting immunity, and is better than BCG against tuberculosis of mice.

Therapeutic Effect of Modulating TREM-1 via Anti-inflammation and Autophagy in Parkinson's Disease

Parkinson’s disease (PD) is one of the most common age-related neurodegenerative diseases, and neuroinflammation has been identified as one of its key pathological characteristics. Triggering receptors expressed on myeloid cells-1 (TREM-1) amplify the inflammatory response and play a role in sepsis and cancer. Recent studies have demonstrated that the attenuation of TREM-1 activity produces cytoprotective and anti-inflammatory effects in macrophages. However, no study has examined the role of TREM-1 in neurodegeneration. We showed that LP17, a synthetic peptide blocker of TREM-1, significantly inhibited the lipopolysaccharide (LPS)-induced upregulation of proinflammatory cascades of inducible nitric oxide synthase (iNOS), cyclooxygenase-2, and nuclear factor-kappa B. Moreover, LP17 enhanced the LPS-induced upregulation of autophagy-related proteins such as light chain-3 and histone deacetylase-6. We also knocked down TREM-1 expression in a BV2 cell model to further confirm the role of TREM-1. LP17 inhibited 6-hydroxydopamine-induced locomotor deficit and iNOS messenger RNA expression in zebrafish. We also observed therapeutic effects of LP17 administration in 6-hydroxydopamine-induced PD syndrome using a rat model. These data suggest that the attenuation of TREM-1 could ameliorate neuroinflammatory responses in PD and that this neuroprotective effect might occur via the activation of autophagy and anti-inflammatory pathways.

Manipulation of autophagy for host-directed tuberculosis therapy

Mycobacterium tuberculosis (M. tb) is one of the world’s most successful human pathogens, infecting ~2 billion people worldwide. Although there are effective drugs against M. tb., the disease remains out of control owing to prolonged and toxic treatment. Shorter regimens are urgently required to control TB. Drug-resistant TB (DR-TB) also threatens to derail TB control. These unfulfilled needs could be addressed by the identification and development of host-directed therapeutic agents for TB. Manipulation of the innate immune response, including autophagy, may lead to the identification of cellular pathways that could be exploited to develop host-directed therapeutic interventions. Host-directed therapies (HDTs) aim to augment immune mechanisms against M. tb infection and/or reduce excess inflammation, thus preventing end-organ tissue damage, preserving lung function and/or enhancing the effectiveness of TB drug therapy in eliminating infection. HDTs may also have additional advantages for patients with TB/HIV co-infection, as HDTs may reduce the risk of interaction with antiretroviral drugs and the risk of developing immune reconstitution inflammatory syndrome (IRIS) and death. In this review, we discuss the role of autophagy as a potential pathway that could be exploited as a host-directed TB therapeutic agent.

Mammalian Target of Rapamycin (mTOR) and the Proteasome Attenuates IL-1β Expression in Primary Mouse Cardiac Fibroblasts

Background: IL-1β is a highly potent pro-inflammatory cytokine and its secretion is tightly regulated. Inactive pro-IL-1β is transcribed in response to innate immune receptors activating NFκB. If tissue damage occurs, danger signals released from necrotic cells, such as ATP, can activate NLRP3-inflammasomes (multiprotein complexes consisting of NLRP3, ASC, and active caspase-1) which cleaves and activates pro-IL-1β. NLRP3 activation also depends on NEK7 and mitochondrial ROS-production. Thus, IL-1β secretion may be regulated at the level of each involved component. We have previously shown that NLRP3-dependent IL-1β release can be induced in cardiac fibroblasts by pro-inflammatory stimuli. However, anti-inflammatory mechanisms targeting IL-1β release in cardiac cells have not been investigated. mTOR is a key regulator of protein metabolism, including autophagy and proteasome activity. In this study we explored whether autophagy or proteasomal degradation are regulators of NLRP3 inflammasome activation and IL-1β release from cardiac fibroblasts. Methods and Results: Serum starvation selectively reduced LPS/ATP-induced IL-1β secretion from cardiac fibroblasts. However, no other inflammasome components, nor mitochondrial mass, were affected. The mTOR inhibitor rapamycin restored pro-IL-1β protein levels as well as LPS/ATP-induced IL-1β release from serum starved cells. However, neither serum starvation nor rapamycin induced autophagy in cardiac fibroblasts. Conversely, chloroquine and bafilomycin A (inhibitors of autophagy) and betulinic acid (a proteasome activator) effectively reduced LPS-induced pro-IL-1β protein levels. Key findings were reinvestigated in human monocyte-derived macrophages. Conclusion: In cardiac fibroblasts, mTOR inhibition selectively favors pro-IL-1β synthesis while proteasomal degradation and not autophagy is the major catabolic anti-inflammatory mechanism for degradation of this cytokine.

Dexmedetomidine alleviates LPS-induced apoptosis and inflammation in macrophages by eliminating damaged mitochondria via PINK1 mediated mitophagy

The macrophage is an innate immune response cell that plays an important role in the development of sepsis. Dexmedetomidine (DEX) is a sedation drug, which have anti-oxidative, anti-inflammatory and anti-apoptosis effects and can be used on sepsis patients in the ICU. However, its mechanisms of action remain poorly understood. PTEN-induced putative kinase 1 (PINK1) is a mitochondrial serine/threonine protein kinase that recognizes damaged mitochondria and leads to mitophagy. This study investigated the effects of DEX on Lipopolysaccharides(LPS)-induced macrophage injury and explained the underlying mechanisms. The results showed that LPS treatment caused mitochondrial damage, mitochondria-dependent apoptosis and PINK1-mediated mitophagy; at the same time, PINK1 has a protective effect on LPS-induced macrophage apoptosis and inflammation by mitophagy that eliminates dysfunctional mitochondria. DEX could promote the clearance of damaged mitochondria characterized by low Mitochondrial membrane potential (MMP) and high reactive oxygen species(ROS), thus exerting a protective effect in LPS treated macrophages, and PINK1 mediated mitophagy is required for this protective effect.

Beclin-1 is involved in the regulation of antimicrobial peptides expression in Chinese mitten crab Eriocheir sinensis

Beclin-1, the mammalian ortholog of yeast Atg6, plays essential roles in the regulation of various processes, including autophagy, apoptosis, embryonic development and immune responses in vertebrates. However, the information about Beclin-1 in invertebrates especially in crustaceans is still very limited. In the present study, a novel Beclin-1 (designated as EsBeclin-1) was identified from Chinese mitten crab Eriocheir sinensis. The open reading frame of EsBeclin-1 cDNA was of 1,275 bp, encoding a typical APG6 domain. The deduced amino acid sequence of EsBeclin-1 shared high similarity ranging from 42.9% to 63.6% with the previously identified Beclins. In the phylogenetic tree, EsBeclin-1 was firstly clustered with Drosophila melanogaster Atg6 and then assigned into the branch of invertebrate Beclin-1. The mRNA transcripts of EsBeclin-1 were highly expressed in hepatopancreas, hemocytes and gill. After lipopolysaccharide (LPS) and Aeromonas hydrophila stimulations, the relative mRNA expression of EsBeclin-1 in hemocytes was significantly increased from 3 to 24 h with the peak level of 4.70-fold (p < 0.01) and 2.91-fold (p < 0.01) at 6 h, respectively. EsBeclin-1 protein was diffusely distributed in the cytoplasm of crab hemocytes under normal conditions, whereas it displayed predominantly punctuate distribution after LPS stimulation. After EsBeclin-1 was interfered with specific EsBeclin-1-dsRNA, the mRNA transcripts of some antimicrobial peptides, including EsALF2, EsLYZ, EsCrus and EsCrus2 in crab hemocytes were significantly decreased at 6 h post LPS stimulation. These results implicated that EsBeclin-1 played a role in regulating the antimicrobial peptides expressions in the immune responses of E. sinensis.

Toll-Like Receptor 4 as an Immune Receptor Against Mycobacterium tuberculosis: A Systematic Review

OBJECTIVE

To review the main Mycobacterium tuberculosis (Mtb) pathogen-associated molecular patterns (PAMPs) and the roles played by toll-like receptor (TLR)4 in determination of Mtb infection outcome.

METHODS

Several scientific databases, including Scopus, PubMed, and Google Scholar, were used for searching appropriate research articles from the literature for information on our topic.

RESULTS

TLR4 plays positive roles in induction of immune responses against Mtb and participates in eradication of the infection. Some limited investigations approved the roles of TLR4 in induction of apoptosis in macrophages during tuberculosis (TB) and attenuation of immune responses in some situations.

CONCLUSIONS

TB outcome appears to be dependent on TLR4/Mtb interaction and several factors, including bacterial load and immune or nonimmune cells, as hosts. Also, other TLR/Mtb interactions can affect TLR4 responses.

Iron oxide nanoparticles promote macrophage autophagy and inflammatory response through activation of toll-like Receptor-4 signaling

Nanoparticle-induced autophagy is crucial for its metabolism, cytotoxicity and therapy potency, but little is known about how the host immune system would respond to it. In this study, we demonstrated that two clinically used superparamagnetic iron oxide nanoparticles (SPIONs) specifically induced macrophage autophagy through activation of TLR4, followed by phosphorylation of p38 and nucleus translocation of Nrf2, leading to upregulation of p62/SQSTM1 and macrophage scavenger receptor SR-AI mRNA expression. Overexpressed p62 conjugated with LC3 to form aggresome-like induced structures (ALIS) and then fused with SPIONs containing endosomes and lysosomes to form autolysosomes for degradation of endocytosed nanoparticles. More importantly, SPIONs also could promote macrophage autophagy in mouse liver which is their imaging target. We also discovered that SPIONs could stimulate the expression of inflammatory cytokines through activation of TLR4 signaling in macrophage. In general, our findings indicate that SPIONs would interact with TLR4 on the macrophage membrane and trigger its downstream signaling pathway, independent of the classic autophagic p62 reduction pathway. The observed autophagy and induced inflammatory responses in macrophages provide unique and novel perspectives in optimizing imaging/therapy nanoparticle performance in addition to analysis by traditional biochemical evaluation methods. It also enriches our understanding of NP/macrophage interaction mechanisms in reticular endothelial system (RES) organs.

Autophagy in Pulmonary Innate Immunity

Autophagy is a major intracellular digestion system that delivers cytoplasmic components for degradation and recycling. In this capacity, autophagy plays an important role in maintaining cellular homeostasis by mediating the degradation of cellular macromolecules and dysfunctional organelles and regeneration of nutrients for cell growth. Autophagy is important in innate immunity, as it is responsible for the clearance of various pathogens. Deficiency of intracellular autophagy can result in exaggerated activation of the inflammasome. The latter is an innate immune complex that senses diverse pathogen-associated or danger-associated molecular patterns and activates the expression of inflammatory cytokines. In autophagy-deficient cells, accumulation of damaged organelles, misfolded proteins, and reactive oxygen species contribute to inflammasome activation. The lung is continuously exposed to pathogens from the environment, rendering it vulnerable to infection. The lung innate immune cells act as a crucial initial barrier against the continuous threat from pathogens. In this review, we will summarize recent findings on the regulation of autophagy and its inter-action with innate immunity, focusing on the lung.

ELMO1 Regulates Autophagy Induction and Bacterial Clearance During Enteric Infection

Macrophages are specialized phagocytic cells involved in clearing invading pathogens. Previously we reported that engulfment and cell motility protein 1 (ELMO1) in macrophages mediates bacterial internalization and intestinal inflammation. Here we studied the role of ELMO1 in the fate of internalized targets. ELMO1 is present in the intracellular vesicles and enhances accumulation of the protein LC3B following engulfment of Salmonella or treatment with autophagy-inducing rapamycin. The protein ATG5 and the kinase ULK1 are involved in classical autophagy, while LC3-associated phagocytosis is ULK1 independent. ATG5 but not ULK1 cooperated with ELMO1 in LC3 accumulation after infection, suggesting the ELMO1 preferentially regulated LC3-associated phagocytosis. Because LC3-associated phagocytosis delivers cargo for degradation, the contribution of ELMO1 to the lysosome degradation pathways was evaluated by studying pH and cathepsin B activity. ELMO1-depleted macrophages showed a time-dependent increase in pH and a decrease in cathepsin B activity associated with bacterial survival. Together, ELMO1 regulates LC3B accumulation and antimicrobial responses involved in the clearance of enteric pathogens. This paper investigated how innate immune pathways involving ELMO1 work in a coordinated fashion to eliminate bacterial threats. ELMO1 is present in the phagosome and enhances bacterial clearance by differential regulation of lysosomal acidification and enzymatic activity.

Autophagy in regulatory T cells: A double-edged sword in disease settings

Autophagy is an evolutionarily conserved catabolic process that directs cytoplasmic proteins, organelles and microbes to lysosomes for degradation. It not only represents an essential cell-intrinsic mechanism to protect against internal and external stresses but also shapes both innate and adaptive immunity. Regulatory T cells (Tregs) are a developmentally and functionally distinct T cell subpopulation engaged in sustaining immunological self-tolerance and homeostasis. There is compelling evidence that autophagy is actively regulated in Tregs and serves as a central signal-dependent controller for Tregs by restraining excessive apoptotic and metabolic activities. In this review, we discuss how autophagy modulates the stability and functionality of Tregs in different disease settings, and provide a perspective on how manipulation of autophagy enables better control of immune response by targeting the generation of Tregs and the maintenance of their stability.

Expression of autophagy‑associated proteins in rat dental irreversible pulpitis

Autophagy serves an important role in numerous diseases, as well as in infection and inflammation. Irreversible pulpitis (IP) is one of the most common inflammatory endodontic diseases, and autophagy has been reported to regulate IP in vitro. However, the level of autophagy in the IP pathogenic process in vivo remains unknown. The aim of the current study was, thus, to investigate the levels of autophagy-associated proteins in rats with IP in vivo. A rat dental IP model was successfully constructed, and five different time points (0, 1, 3, 5 and 7 days) were investigated. The levels of the autophagy-related 5 (ATG5), ATG7, light chain 3 (LC3) and Beclin-1 proteins exhibited a time-dependent increase in rats with IP, whereas the levels of mammalian target of rapamycin and p62/sequestosome 1 were decreased. In addition, the levels of ATG proteins were specifically increased in odontoblasts and microvascular endothelial cells in pulpitis tissue. Based on these findings, autophagy may serve an important role in IP, and the present study data provide a new insight into the IP pathogenesis and treatment.

Neisseria gonorrhoeae evades autophagic killing by downregulating CD46-cyt1 and remodeling lysosomes

The Gram-negative human pathogen N. gonorrhoeae (Ngo) quickly attaches to epithelial cells, and large numbers of the bacteria remain on the cell surface for prolonged periods. Ngo invades cells but few viable intracellular bacteria are recovered until later stages of infection, leading to the assumption that Ngo is a weak invader. On the cell surface, Ngo quickly recruits CD46-cyt1 to the epithelial cell cortex directly beneath the bacteria and causes its cleavage by metalloproteinases and Presenilin/γSecretease; how these interactions affect the Ngo lifecycle is unknown. Here, we show Ngo induces an autophagic response in the epithelial cell through CD46-cyt1/GOPC, and this response kills early invaders. Throughout infection, the pathogen slowly downregulates CD46-cyt1 and remodeling of lysosomes, another key autophagy component, and these activities ultimately promote intracellular survival. We present a model on the dynamics of Ngo infection and describe how this dual interference with the autophagic pathway allows late invaders to survive within the cell.

Regulation of the innate immune system by autophagy: monocytes, macrophages, dendritic cells and antigen presentation

Autophagy is well equipped functionally to isolate microbial pathogens in autophagosomes and to carry out their clearance by dismemberment in the course of catabolic processes in the lysosome. Clearly, this is a non-metabolic function of autophagy that impacts strongly on the immune system. While in a preceding article on neutrophils, eosinophils, mast cells, and natural killer cells our focus was on the role of autophagy in regulating innate immune cell differentiation, degranulation, phagocytosis and extracellular trap formation, here we discuss monocytes/macrophages and dendritic cells, specifically, the influence of autophagy on functional cellular responses, such as phagocytosis, antigen presentation, cytokine production, control of inflammasome activation, tolerance and the consequences for overall host defense.

Autophagy induction and PDGFR-β knockdown by siRNA-encapsulated nanoparticles reduce chlamydia trachomatis infection

C. trachomatis is the most common sexually transmitted bacterial infection in the world. Although the infection can be easily controlled by the use of antibiotics, several reports of clinical isolates that are resistant to antibiotics have prompted us to search for alternative strategies to manage this disease. In this paper, we developed a nanoparticle formulation (PDGFR-β siRNA-PEI-PLGA-PEG NP) that can simultaneously induce autophagy in human cells and knock down PDGFR-β gene expression, an important surface binding protein for C. trachomatis, as a strategy to reduce vaginal infection of C. trachomatis. PDGFR-β siRNA-PEI-PLGA-PEG NP significantly induced autophagy in human vaginal epithelial cells (VK2/E6E7) 48 hr post treatment by improving autophagic degradation activity without causing inflammation, apoptosis or any decrease in cell viability. Beclin-1, VPS34 (markers for initiation stage of autophagy), UVRAG, TECPR-1 (markers for degradation stage of autophagy) were found to be significantly upregulated after treatment with PDGFR-β siRNA-PEI-PLGA-PEG NP. Furthermore, PDGFR-β siRNA-PEI-PLGA-PEG NP decreased PDGFR-β mRNA expression by 50% and protein expression by 43% in VK2/E6E7 cells 48 hr post treatment. Treatment of cells with PDGFR-β siRNA-PEI-PLGA-PEG NP significantly decreased the intracellular C. trachomatis and extracellular release of C. trachomatis by approximately 65% and 67%, respectively, in vitro through augmenting autophagic degradation pathways and reducing bacterial binding simultaneously.

Macrophage-Specific Hypoxia-Inducible Factor-1α Contributes to Impaired Autophagic Flux in Nonalcoholic Steatohepatitis

Inflammatory cell activation drives diverse cellular programming during hepatic diseases. Hypoxia-inducible factors (HIFs) have recently been identified as important regulators of immunity and inflammation. In nonalcoholic steatohepatitis (NASH), HIF-1α is upregulated in hepatocytes, where it induces steatosis; however, the role of HIF-1α in macrophages under metabolic stress has not been explored. In this study, we found increased HIF-1α levels in hepatic macrophages in methionine-choline-deficient (MCD) diet-fed mice and in macrophages of patients with NASH compared with controls. The HIF-1α increase was concomitant with elevated levels of autophagy markers BNIP3, Beclin-1, LC3-II, and p62 in both mouse and human macrophages. LysM^Cre HIF^dPA fl/fl mice, which have HIF-1α levels stabilized in macrophages, showed higher steatosis and liver inflammation compared with HIF^dPA fl/fl mice on MCD diet. In vitro and ex vivo experiments reveal that saturated fatty acid, palmitic acid (PA), both induces HIF-1α and impairs autophagic flux in macrophages. Using small interfering RNA-mediated knock-down and overexpression of HIF-1α in macrophages, we demonstrated that PA impairs autophagy via HIF-1α. We found that HIF-1α mediates NF-κB activation and MCP-1 production and that HIF-1α-mediated impairment of macrophage autophagy increases IL-1β production, contributing to MCD diet-induced NASH. Conclusion: Palmitic acid impairs autophagy via HIF-1α activation in macrophages. HIF-1α and impaired autophagy are present in NASH in vivo in mouse macrophages and in human blood monocytes. We identified that HIF-1α activation and decreased autophagic flux stimulate inflammation in macrophages through upregulation of NF-κB activation. These results suggest that macrophage activation in NASH involves a complex interplay between HIF-1α and autophagy as these pathways promote proinflammatory overactivation in MCD diet-induced NASH.

The relationship between autophagy and the immune system and its applications for tumor immunotherapy

Autophagy is a genetically well-controlled cellular process that is tightly controlled by a set of core genes, including the family of autophagy-related genes (ATG). Autophagy is a “double-edged sword” in tumors. It can promote or suppress tumor development, which depends on the cell and tissue types and the stages of tumor. At present, tumor immunotherapy is a promising treatment strategy against tumors. Recent studies have shown that autophagy significantly controls immune responses by modulating the functions of immune cells and the production of cytokines. Conversely, some cytokines and immune cells have a great effect on the function of autophagy. Therapies aiming at autophagy to enhance the immune responses and anti-tumor effects of immunotherapy have become the prospective strategy, with enhanced antigen presentation and higher sensitivity to CTLs. However, the induction of autophagy may also benefit tumor cells escape from immune surveillance and result in intrinsic resistance against anti-tumor immunotherapy. Increasing studies have proven the optimal use of either ATG inducers or inhibitors can restrain tumor growth and progression by enhancing anti-tumor immune responses and overcoming the anti-tumor immune resistance in combination with several immunotherapeutic strategies, indicating that induction or inhibition of autophagy might show us a prospective therapeutic strategy when combined with immunotherapy. In this article, the possible mechanisms of autophagy regulating immune system, and the potential applications of autophagy in tumor immunotherapy will be discussed.

The Interplay Between Pattern Recognition Receptors and Autophagy in Inflammation

Pattern recognition receptors (PRRs) are sensors of exogenous and endogenous "danger" signals from pathogen-associated molecular patterns (PAMPs), and damage associated molecular patterns (DAMPs), while autophagy can respond to these signals to control homeostasis. Almost all PRRs can induce autophagy directly or indirectly. Toll-like receptors (TLRs), Nod-like receptors (NLRs), retinoic acid-inducible gene-I-like receptors (RLRs), and cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) pathway can induce autophagy directly through Beclin-1 or LC3-dependent pathway, while the interactions with the receptor for advanced glycation end products (RAGE)/high mobility group box 1 (HMGB1), CD91/Calreticulin, and TLRs/HSPs are achieved by protein, Ca2⁺, and mitochondrial homeostasis. Autophagy presents antigens to PRRs and helps to clean the pathogens. In addition, the induced autophagy can form a negative feedback regulation of PRRs-mediated inflammation in cell/disease-specific manner to maintain homeostasis and prevent excessive inflammation. Understanding the interaction between PRRs and autophagy in a specific disease will promote drug development for immunotherapy. Here, we focus on the interactions between PRRs and autophagy and how they affect the inflammatory response.

TLR4 (toll-like receptor 4) activation suppresses autophagy through inhibition of FOXO3 and impairs phagocytic capacity of microglia

Macroautophagy/autophagy is a lysosome-dependent catabolic process for the turnover of proteins and organelles in eukaryotes. Autophagy plays an important role in immunity and inflammation, as well as metabolism and cell survival. Diverse immune and inflammatory signals induce autophagy in macrophages through pattern recognition receptors, such as toll-like receptors (TLRs). However, the physiological role of autophagy and its signaling mechanisms in microglia remain poorly understood. Microglia are phagocytic immune cells that are resident in the central nervous system and share many characteristics with macrophages. Here, we show that autophagic flux and expression of autophagy-related (Atg) genes in microglia are significantly suppressed upon TLR4 activation by lipopolysaccharide (LPS), in contrast to their stimulation by LPS in macrophages. Metabolomics analysis of the levels of phosphatidylinositol (PtdIns) and its 3-phosphorylated form, PtdIns3P, in combination with bioinformatics prediction, revealed an LPS-induced reduction in the synthesis of PtdIns and PtdIns3P in microglia but not macrophages. Interestingly, inhibition of PI3K, but not MTOR or MAPK1/3, restored autophagic flux with concomitant dephosphorylation and nuclear translocation of FOXO3. A constitutively active form of FOXO3 also induced autophagy, suggesting FOXO3 as a downstream target of the PI3K pathway for autophagy inhibition. LPS treatment impaired phagocytic capacity of microglia, including MAP1LC3B/LC3-associated phagocytosis (LAP) and amyloid β (Aβ) clearance. PI3K inhibition restored LAP and degradation capacity of microglia against Aβ. These findings suggest a unique mechanism for the regulation of microglial autophagy and point to the PI3K-FOXO3 pathway as a potential therapeutic target to regulate microglial function in brain disorders. Abbreviations: Atg: autophagy-related gene; Aβ: amyloid-β; BafA1: bafilomycin A₁; BECN1: beclin 1, autophagy related; BMDM: bone marrow-derived macrophage; CA: constitutively active; CNS: central nervous system; ZFYVE1/DFCP1: zinc finger, FYVE domain containing 1; FOXO: forkhead box O; ELISA:enzyme-linked immunosorbent assay; HBSS: Hanks balanced salt solution; LAP: LC3-associated phagocytosis; MAP1LC3B: microtubule-associated protein 1 light chain 3; LPS: lipopolysaccharide; LY: LY294002; MTOR: mechanistic target of rapamycin kinase; Pam₃CSK₄: N-palmitoyl-S-dipalmitoylglyceryl Cys-Ser-(Lys)₄; PtdIns: phosphatidylinositol; PtdIns3P: phosphatidylinositol-3-phosphate; PLA: proximity ligation assay; Poly(I:C): polyinosinic-polycytidylic acid; qRT-PCR: quantitative real-time polymerase chain reaction; RPS6KB1: ribosomal protein S6 kinase, polypeptide 1; TLR: Toll-like receptor; TNF: tumor necrosis factor; TFEB: transcription factor EB; TSPO: translocator protein.

Inflammasomes: Pandora's box for sepsis

Sepsis was known to ancient Greeks since the time of great physician Hippocrates (460-377 BC) without exact information regarding its pathogenesis. With time and medical advances, it is now considered as a condition associated with organ dysfunction occurring in the presence of systemic infection as a result of dysregulation of the immune response. Still with this advancement, we are struggling for the development of target-based therapeutic approach for the management of sepsis. The advancement in understanding the immune system and its working has led to novel discoveries in the last 50 years, including different pattern recognition receptors. Inflammasomes are also part of these novel discoveries in the field of immunology which are <20 years old in terms of their first identification. They serve as important cytosolic pattern recognition receptors required for recognizing cytosolic pathogens, and their pathogen-associated molecular patterns play an important role in the pathogenesis of sepsis. The activation of both canonical and non-canonical inflammasome signaling pathways is involved in mounting a proinflammatory immune response via regulating the generation of IL-1β, IL-18, IL-33 cytokines and pyroptosis. In addition to pathogens and their pathogen-associated molecular patterns, death/damage-associated molecular patterns and other proinflammatory molecules involved in the pathogenesis of sepsis affect inflammasomes and vice versa. Thus, the present review is mainly focused on the inflammasomes, their role in the regulation of immune response associated with sepsis, and their targeting as a novel therapeutic approach.