Autophagy and intestinal homeostasis

New insights into the interplay between autophagy, gut microbiota and insulin resistance in metabolic syndrome

Metabolic syndrome (MetS) is a widespread and multifactorial disorder, and the study of its pathogenesis and treatment remains challenging. Autophagy, an intracellular degradation system that maintains cellular renewal and homeostasis, is essential for maintaining antimicrobial defense, preserving epithelial barrier integrity, promoting mucosal immune response, maintaining intestinal homeostasis, and regulating gut microbiota and microbial metabolites. Dysfunctional autophagy is implicated in the pathological mechanisms of MetS, involving insulin resistance (IR), chronic inflammation, oxidative stress, and endoplasmic reticulum (ER) stress, with IR being a predominant feature. The study of autophagy represents a valuable field of research with significant clinical implications for identifying autophagy-related signals, pathways, mechanisms, and treatment options for MetS. Given the multifactorial etiology and various potential risk factors, it is imperative to explore the interplay between autophagy and gut microbiota in MetS more thoroughly. This will facilitate the elucidation of new mechanisms underlying the crosstalk among autophagy, gut microbiota, and MetS, thereby providing new insights into the diagnosis and treatment of MetS.

Harnessing autophagy: A potential breakthrough in digestive disease treatment

Autophagy, a conserved cellular degradation process, is crucial for various cellular processes such as immune responses, inflammation, metabolic and oxidative stress adaptation, cell proliferation, development, and tissue repair and remodeling. Dysregulation of autophagy is suspected in numerous diseases, including cancer, neurodegenerative diseases, digestive disorders, metabolic syndromes, and infectious and inflammatory diseases. If autophagy is disrupted, for example, this can have serious consequences and lead to chronic inflammation and tissue damage, as occurs in diseases such as Chron's disease and ulcerative colitis. On the other hand, the influence of autophagy on the development and progression of cancer is not clear. Autophagy can both suppress and promote the progression and metastasis of cancer at various stages. From inflammatory bowel diseases to gastrointestinal cancer, researchers are discovering the intricate role of autophagy in maintaining gut health and its potential as a therapeutic target. Researchers should carefully consider the nature and progression of diseases such as cancer when trying to determine whether inhibiting or stimulating autophagy is likely to be beneficial. Multidisciplinary approaches that combine cutting-edge research with clinical expertise are key to unlocking the full therapeutic potential of autophagy in digestive diseases.

Astragalus polysaccharide protects experimental colitis through an aryl hydrocarbon receptor-dependent autophagy mechanism

BACKGROUND AND PURPOSE

Disruption of intestinal barriers plays a vital role in the pathogenesis of colitis. The aryl hydrocarbon receptor (AhR) is a recognition sensor that mediates intestinal immune homeostasis and minimizes intestinal inflammation. Astragalus polysaccharide (APS) exerts pharmacological actions in colitis; however, the mechanism has not been elucidated. We investigated whether APS protects through AhR-dependent autophagy.

EXPERIMENTAL APPROACH

The symptoms of dextran sulfate sodium (DSS)-induced colitis in mice involving intestinal barrier function and inflammatory injury were evaluated after APS administration. Intestinal-specific Becn1 conditional knockout (Becn1 cKO) mice were constructed and compared with wild-type mice. Autophagy and the effects of APS were investigated after the deactivation of AhRs. The relationship between APS-induced AhRs and autophagic Becn1 was investigated using a dual-luciferase reporter system and chromatin immunoprecipitation (ChIP)-quantitative polymerase chain reaction assay. Caco-2 cells were used to investigate inflammatory responses and AhR-dependent autophagy.

KEY RESULTS

APS improved intestinal barrier function in inflammatory injury in colitis mice. APS triggered autophagic flow; however, knockout of Becn1 in the gut increased susceptibility to colitis, leading to diminished epithelial barrier function and severe intestinal inflammation, impairing the protective effects of APS. Mechanistically, APS-triggered autophagy depends on AhR expression. Activated AhR binds to the promoter Becn1 to operate transcription of genes involved in anti-inflammation and intestinal barrier repair, while deactivation of AhR correlated with intestinal inflammation and the therapeutic function of APS.

CONCLUSIONS AND IMPLICATIONS

APS protects colitis mice by targeting autophagy, especially as the AhR stimulates the repair of damaged intestinal barrier functions.

Malvidin alleviates LPS-induced septic intestinal injury through the nuclear factor erythroid 2-related factor 2/reactive oxygen species/NLRP3 inflammasome pathway

Emerging evidence suggests that the gastrointestinal tract plays a crucial role in the pathophysiology of sepsis, a leading cause of mortality among patients admitted to the intensive care unit (ICU). Malvidin, belonging to the flavonoid family of compounds, exhibits a range of capabilities including anti-inflammatory and antioxidant properties. Studies have demonstrated that Malvidin exhibits a dose-dependent effect in mitigating sepsis-induced intestinal injury. The advantageous impact of Malvidin in safeguarding against sepsis-induced intestinal injury is associated with its capacity to counteract oxidative stress, inhibit cellular apoptosis, diminish the secretion of pro-inflammatory cytokines, and regulate the synthesis of inflammasomes. The findings indicate that Malvidin, a natural compound, exhibits protective effects on the gut by activating the nuclear factor erythroid 2-related factor 2/reactive oxygen species/NLRP3 inflammasome pathway. These results have significant implications for potential clinical applications and offer valuable insights into the treatment of sepsis-induced intestinal injury.

Low-molar-mass oat beta-glucan impacts autophagy and apoptosis in early stages of induced colorectal carcinogenesis in rats

Oat beta-glucan is one of the soluble dietary fibre fractions with a wide spectrum of biological activities such as anti-inflammatory and anti-tumour properties. In the present study, the effect of low-molar-mass oat beta-glucan isolate (OβGl) on the level of autophagy and apoptosis in the colorectum of rats with induced early stages of colorectal cancer was investigated. Forty-five male Sprague-Dawley rats were divided into two main groups: control and azoxymethane-induced early-stage colorectal carcinogenesis (CRC). Both groups were divided into three dietary subgroups fed standard feed without OβGl (OβGl-), with 1 % of OβGl (OβGl+1 %) or with 3 % of OβGl (OβGl+3 %). The expression of autophagy (LC3B, beclin-1) and apoptosis (caspase-3, cleaved caspase-3, BAX, BCL-2 and PARP-1) markers was determined by immunohistochemistry, Western blot and PCR analysis. The obtained results showed that the expression of LC3B, caspase-3 and cleaved caspase-3 in the CRC mucosa, and LC3B-II expression in the CRC wall were higher in the OβGl+3 % compared to the OβGl- rats. A higher BAX/BCL-2 ratio was also observed in the CRC OβGl+1 % rats compared to the other CRC animals. In summary, OβGl+3 % has a modulatory effect, stimulating autophagy and the extrinsic apoptosis pathway, while OβGl+1 % has a stimulatory effect on the intrinsic apoptosis pathway.

Casein-phosphatidylcholine emulsifier remodels LPS-induced intestinal barrier disfunction via regulating ferroptosis and lipid metabolism

Recently, the biosafety of synthetic emulsifier in intestinal barrier has raised significant concerns. Casein- phosphatidylcholine (CP), which is a natural emulsifier, has better emulsification and stability. However, the effect of CP on intestinal barrier remains unknow. Intestinal permeability and lipomics analysis showed that carboxymethyl cellulose (CMC) and CP have no significant effect on intestinal barrier in normal intestinal barrier model, whereas CP increased transmembrane resistance value and remodeled lipid homeostasis in LPS induced intestinal barrier dysfunction model, indicating its superior biosafety. To explore the underlying molecular mechanism of emulsifier on intestinal barrier dysfunction, the bioinformatics analysis of six original microarray datasets including 168 cases in NCBI-Gene Expression Omnibus database showed ferroptosis-related genes showed a significant differential expression. The quantitative polymerase chain reaction analysis demonstrated that CP can repair the imbalance of lipid homeostasis induced by LPS and restore normal intestinal permeability by regulating the expression of ferroptosis-related genes, while CMC could can enhance intestinal permeability by inducing ferroptosis of intestinal epithelial cells through lipid peroxidation. In conclusion, this study highlighted CP could remodel LPS-induced intestinal barrier disfunction via regulating ferroptosis and lipid metabolism. These findings can be used as a new insight for the design of new healthy emulsifier.

A stromal lineage maintains crypt structure and villus homeostasis in the intestinal stem cell niche

BACKGROUND

The nutrient-absorbing villi of small intestines are renewed and repaired by intestinal stem cells (ISCs), which reside in a well-organized crypt structure. Genetic studies have shown that Wnt molecules secreted by telocytes, Gli1+ stromal cells, and epithelial cells are required for ISC proliferation and villus homeostasis. Intestinal stromal cells are heterogeneous and single-cell profiling has divided them into telocytes/subepithelial myofibroblasts, myocytes, pericytes, trophocytes, and Pdgfralow stromal cells. Yet, the niche function of these stromal populations remains incompletely understood.

RESULTS

We show here that a Twist2 stromal lineage, which constitutes the Pdgfralow stromal cell and trophocyte subpopulations, maintains the crypt structure to provide an inflammation-restricting niche for regenerating ISCs. Ablating Twist2 lineage cells or deletion of one Wntless allele in these cells disturbs the crypt structure and impairs villus homeostasis. Upon radiation, Wntless haplo-deficiency caused decreased production of anti-microbial peptides and increased inflammation, leading to defective ISC proliferation and crypt regeneration, which were partially rescued by eradication of commensal bacteria. In addition, we show that Wnts secreted by Acta2+ subpopulations also play a role in crypt regeneration but not homeostasis.

CONCLUSIONS

These findings suggest that ISCs may require different niches for villus homeostasis and regeneration and that the Twist2 lineage cells may help to maintain a microbe-restricted environment to allow ISC-mediated crypt regeneration.

Oat beta-glucan reduces colitis by promoting autophagy flux in intestinal epithelial cells via EPHB6-TFEB axis

Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract, mainly including Crohn's disease and ulcerative colitis. Epidemiological findings suggest that inadequate dietary fibers intake may be a risk factor for IBD. Oat beta-glucan is a type of fermentable dietary fiber and has been proved to reduce experimental colitis. However, the mechanism remains unclear. The aim of this study was to explore the role and possible mechanism of oat beta-glucan in reducing experimental colitis. We used a dextran sulfate sodium (DSS)-induced mice acute colitis model to explore the potential mechanism of oat beta-glucan in reducing experimental colitis. As a result, oat beta-glucan upregulated the expressions of Erythropoietin-producing hepatocyte receptor B6 (EPHB6) and transcription factor EB (TFEB), promoted autophagy flux and downregulated the expressions of interleukin 1 beta (IL-1β), interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) in intestinal epithelial cells (IECs). The role of the EPHB6-TFEB axis was explored using a lipopolysaccharide-induced HT-29 cells inflammation model. The results revealed that EPHB6 regulated the expression of TFEB, and knockdown of EPHB6 decreased the protein level of TFEB. When EPHB6 or TFEB was knocked down, autophagy flux was inhibited, and the anti-inflammatory effect of sodium butyrate, a main metabolite of oat beta-glucan in the gut, was blocked. In summary, our findings demonstrated that oat beta-glucan reduced DSS-induced acute colitis in mice, promoted autophagy flux via EPHB6-TFEB axis and downregulated the expressions of IL-1β, IL-6 and TNF-α in IECs, and this effect may be mediated by butyrate.

From Intestinal Epithelial Homeostasis to Colorectal Cancer: Autophagy Regulation in Cellular Stress

The intestinal epithelium is continuously exposed to abundant stress stimuli, which relies on an evolutionarily conserved process, autophagy, to maintain its homeostasis by degrading and recycling unwanted and damaged intracellular substances. Otherwise, disruption of this balance will result in the development of a wide range of disorders, including colorectal cancer (CRC). Dysregulated autophagy is implicated in the regulation of cellular responses to stress during the development, progression, and treatment of CRC. However, experimental investigations addressing the impact of autophagy in different phases of CRC have generated conflicting results, showing that autophagy is context-dependently related to CRC. Thus, both inhibition and activation of autophagy have been proposed as therapeutic strategies against CRC. Here, we will discuss the multifaceted role of autophagy in intestinal homeostasis and CRC, which may provide insights for future research directions.

Rapamycin administration during an acute heat stress challenge in growing pigs

Study objectives were to determine the effects of rapamycin (Rapa) on biomarkers of metabolism and inflammation during acute heat stress (HS) in growing pigs. Crossbred barrows (n = 32; 63.5 ± 7.2 kg body weight [BW]) were blocked by initial BW and randomly assigned to 1 of 4 environmental-therapeutic treatments: 1) thermoneutral (TN) control (n = 8; TNCon), 2) TN and Rapa (n = 8; TNRapa), 3) HS control (n = 8; HSCon), or 4) HS and Rapa (n = 8; HSRapa). Following 6 d of acclimation to individual pens, pigs were enrolled in two experimental periods (P). During P1 (10 d), pigs were fed ad libitum and housed in TN conditions (21.3 ± 0.2°C). During P2 (24 h), HSCon and HSRapa pigs were exposed to constant HS (35.5 ± 0.4°C), while TNCon and TNRapa pigs remained in TN conditions. Rapamycin (0.15 mg/kg BW) was orally administered twice daily (0700 and 1800 hours) during both P1 and P2. HS increased rectal temperature and respiration rate compared to TN treatments (1.3°C and 87 breaths/min, respectively; P < 0.01). Feed intake (FI) markedly decreased in HS relative to TN treatments (64%; P < 0.01). Additionally, pigs exposed to HS lost BW (4 kg; P < 0.01), while TN pigs gained BW (0.7 kg; P < 0.01). Despite marked changes in phenotypic parameters caused by HS, circulating glucose and blood urea nitrogen did not differ among treatments (P > 0.10). However, the insulin:FI increased in HS relative to TN treatments (P = 0.04). Plasma nonesterified fatty acids (NEFA) increased in HS relative to TN treatments; although this difference was driven by increased NEFA in HSCon compared to TN and HSRapa pigs (P < 0.01). Overall, circulating white blood cells, lymphocytes, and monocytes decreased in HS compared to TN pigs (19%, 23%, and 33%, respectively; P ≤ 0.05). However, circulating neutrophils were similar across treatments (P > 0.31). The neutrophil-to-lymphocyte ratio (NLR) was increased in HS relative to TN pigs (P = 0.02); however, a tendency for reduced NLR was observed in HSRapa compared to HSCon pigs (21%; P = 0.06). Plasma C-reactive protein tended to differ across treatments (P = 0.06) and was increased in HSRapa relative to HSCon pigs (46%; P = 0.03). Circulating haptoglobin was similar between groups. In summary, pigs exposed to HS had altered phenotypic, metabolic, and leukocyte responses; however, Rapa administration had limited impact on outcomes measured herein.

Effects of Dietary Oat Beta-Glucans on Colon Apoptosis and Autophagy through TLRs and Dectin-1 Signaling Pathways-Crohn's Disease Model Study

Background: Crohn’s disease (CD) is characterized by chronic inflammation of the gastrointestinal tract with alternating periods of exacerbation and remission. The aim of this study was to determine the time-dependent effects of dietary oat beta-glucans on colon apoptosis and autophagy in the CD rat model. Methods: A total of 150 Sprague–Dawley rats were divided into two main groups: healthy control (H) and a TNBS (2,4,6-trinitrobenzosulfonic acid)-induced colitis (C) group, both including subgroups fed with feed without beta-glucans (βG−) or feed supplemented with low- (βGl) or high-molar-mass oat beta-glucans (βGh) for 3, 7, or 21 days. The expression of autophagy (LC3B) and apoptosis (Caspase-3) markers, as well as Toll-like (TLRs) and Dectin-1 receptors, in the colon epithelial cells, was determined using immunohistochemistry and Western blot. Results: The results showed that in rats with colitis, after 3 days of induction of inflammation, the expression of Caspase-3 and LC3B in intestinal epithelial cells did not change, while that of TLR 4 and Dectin-1 decreased. Beta-glucan supplementation caused an increase in the expression of TLR 5 and Dectin-1 with no changes in the expression of Caspase-3 and LC3B. After 7 days, a high expression of Caspase-3 was observed in the colitis-induced animals without any changes in the expression of LC3B and TLRs, and simultaneously, a decrease in Dectin-1 expression was observed. The consumption of feed with βGl or βGh resulted in a decrease in Caspase-3 expression and an increase in TLR 5 expression in the CβGl group, with no change in the expression of LC3B and TLR 4. After 21 days, the expression of Caspase-3 and TLRs was not changed by colitis, while that of LC3B and Dectin-1 was decreased. Feed supplementation with βGh resulted in an increase in the expression of both Caspase-3 and LC3B, while the consumption of feed with βGh and βGl increased Dectin-1 expression. However, regardless of the type of nutritional intervention, the expression of TLRs did not change after 21 days. Conclusions: Dietary intake of βGl and βGh significantly reduced colitis by time-dependent modification of autophagy and apoptosis, with βGI exhibiting a stronger effect on apoptosis and βGh on autophagy. The mechanism of this action may be based on the activation of TLRs and Dectin-1 receptor and depends on the period of exacerbation or remission of CD.

Oxidative Stress in the Pathogenesis of Crohn's Disease and the Interconnection with Immunological Response, Microbiota, External Environmental Factors, and Epigenetics

Inflammatory bowel disease (IBD) is a complex multifactorial disorder in which external and environmental factors have a large influence on its onset and development, especially in genetically susceptible individuals. Crohn’s disease (CD), one of the two types of IBD, is characterized by transmural inflammation, which is most frequently located in the region of the terminal ileum. Oxidative stress, caused by an overabundance of reactive oxygen species, is present locally and systemically in patients with CD and appears to be associated with the well-described imbalanced immune response and dysbiosis in the disease. Oxidative stress could also underlie some of the environmental risk factors proposed for CD. Although the exact etiopathology of CD remains unknown, the key role of oxidative stress in the pathogenesis of CD is extensively recognized. Epigenetics can provide a link between environmental factors and genetics, and numerous epigenetic changes associated with certain environmental risk factors, microbiota, and inflammation are reported in CD. Further attention needs to be focused on whether these epigenetic changes also have a primary role in the pathogenesis of CD, along with oxidative stress.

Interactions between Food Hazards and Intestinal Barrier: Impact on Foodborne Diseases

The intestine is an important digestive organ of the human body, and its barrier is the guardian of the body from the external environment. The impairment of the intestinal barrier is believed to be an important determinant in various foodborne diseases. Food hazards can lead to the occurrence of many foodborne diseases represented by inflammation. Therefore, understanding the mechanisms of the impact of the food hazards on intestinal barriers is essential for promoting human health. This review examined the relationship between food hazards and the intestinal barrier in three aspects: apoptosis, imbalance of gut microbiota, and pro-inflammatory cytokines. The mechanism of dysfunctional gut microbiota caused by food hazards was also discussed. This review discusses the interaction among food hazards, intestinal barrier, and foodborne diseases and, thus, offers a new thought to deal with foodborne disease.

Targeted deletion of Atg5 in intestinal epithelial cells promotes dextran sodium sulfate-induced colitis

Autophagy-associated genes have been identified as susceptible loci for inflammatory bowel disease. We investigated the role of a core autophagy factor, Atg5, in the development of dextran sodium sulfate (DSS)-induced colitis. Intestinal epithelial cell (IEC)-specific Atg5 gene deficient mice (Atg5 ^ΔIEC mice) were generated by cross of Atg5-floxed mice (Atg5 ^fl/fl ) with transgenic mice expressing Cre-recombinase driven by the villin promotor. Mice were given three cycles of 1.5% DSS in drinking water for 5 days and regular water for 14 days over a 60-day period. The dysfunction of autophagy characterized by a marked accumulation of p62 protein, a substrate for autophagy degradation, was detected in epithelial cells in the non-inflamed and inflamed mucosa of inflammatory bowel disease patients. DSS-colitis was exacerbated in Atg5 ^ΔIEC mice compared to control Atg5 ^fl/fl mice. Phosphorylation of inositol-requiring transmembrane kinase/endonuclease1α (IRE1α), a sensor for endoplasmic reticulum stress, and c-Jun N-terminal kinase, a downstream target of IRE1α, were significantly enhanced in IECs in DSS-treated Atg5 ^ΔIEC mice. Accumulation of phosphorylated IRE1α was enhanced by the treatment with chloroquine, an autophagy inhibitor. Apoptotic IECs were more abundant in DSS-treated Atg5 ^ΔIEC mice. These findings suggest that Atg5 suppresses endoplasmic reticulum stress-induced apoptosis of IECs via the degradation of excess p-IRE1α.

Pesticides-induced energy metabolic disorders

Metabolic disorders have become a heavy burden on society. Recently, through excessive use, pesticides have been found to be present in environmental matrixes and sometimes even accumulate in humans or other mammals through the food chain, which then causes health concerns. Evidence has indicated that pesticides have the potential to induce energy metabolic disorders by disturbing the physical process of energy absorption in the intestine and energy storage in the liver, adipose tissue and skeletal muscle in humans or other mammals. In addition, the homeostasis of energy regulation by the pancreas and immune cells is also affected by pesticides. These pesticide-induced disruptions ultimately cause abnormal levels of blood glucose and lipids, which in turn induce the development of related metabolic diseases, including overweight, underweight, insulin resistance and even diabetes. In this review, the results of previous studies focused on the induction of metabolic disorders by pesticides are summarized. We hope that this work will facilitate the discovery of a potential strategy for the treatment of diseases caused by pesticides.

Ganoderma atrum polysaccharide ameliorates intestinal mucosal dysfunction associated with autophagy in immunosuppressed mice

The aim of this study was to investigate the protective effect and underlying mechanisms of Ganoderma atrum polysaccharide (PSG-1) on cyclophosphamide (Cy)-induced intestinal mucosal dysfunction in mice. Results showed that PSG-1 promoted the formation of IgA-secreting cells, modulated sIgA, IgE, IgG, IgM secretion, and improved TLR-2, TLR-4, TLR-6 mRNA levels while these factors were suppressed after Cy treatment. CD4⁺ and CD8⁺ T cell numbers were also elevated by PSG-1. Cytokines including IFN-γ, TNF-α, IL-2, IL-12p70, IL-4, IL-1β, IL-17, IL-21, IL-23, TGF-β3 and transcription factors including T-bet, GATA-3, RORγt, Foxp3 increased after PSG-1 administration. Besides, PSG-1 reversed goblet cell numbers, and upregulated tight junction proteins like ZO-1, occludin and claudin-1 in immunosuppressed mice. Apart from these, the autophagy-related proteins LC3, Beclin-1, Atg5 and Atg7 were enhanced by PSG-1. These findings demonstrated that PSG-1 could ameliorate Cy-induced impairment of intestinal immunity and mucosal integrity, which maybe associated with autophagy in mice.

Chloroquine Downregulation of Intestinal Autophagy to Alleviate Biological Stress in Early-Weaned Piglets

Simple Summary

Weaning is one of the biggest challenges in a pig’s life. Autophagy is a catabolic process aimed at recycling cellular components and damaged organelles in response to diverse stress conditions. There are two autophagy-modifying agents, rapamycin (RAPA) and chloroquine (CQ), that are often used in vitro and in vivo to regulate this process. We speculated that the regulation of autophagy may have some effect on weaning pressure. In this study, we try to understand the role of autophagy in intestinal barrier function and inflammation during the first week after weaning. We examined the effects of modulation of autophagy via RAPA and CQ on growth performance, immunity, inflammation profile, and the intestinal barrier to find potential value for CQ as a feed additive agent for ameliorating weaning stress.

Abstract

Early weaning stress impairs the development of gastrointestinal barrier function, causing immune system dysfunctions, reduction in feed intake, and growth retardation. Autophagy was hypothesized to be a key underlying cellular process in these dysfunctions. We conjectured that rapamycin (RAPA) and chloroquine (CQ), as two autophagy-modifying agents, regulate the autophagy process and may produce deleterious or beneficial effects on intestinal health and growth. To explore the effect of autophagy on early weaning stress in piglets, 18 early-weaned piglets were assigned to three treatments (each treatment of six piglets) and treated with an equal volume of RAPA, CQ, or saline. The degree of autophagy and serum concentrations of immunoglobulins and cytokines, as well as intestinal morphology and tight junction protein expression, were evaluated. Compared with the control treatment, RAPA-treated piglets exhibited activated autophagy and had decreased final body weight (BW) and average daily gain (ADG) (p < 0.05), impaired intestinal morphology and tight junction function, and higher inflammatory responses. The CQ-treated piglets showed higher final BW, ADG, jejuna and ileal villus height, and lower autophagy and inflammation, compared with control piglets (p < 0.05). Throughout the experiment, CQ treatment was beneficial to alleviate early weaning stress and intestinal and immune system dysfunction.

Autophagy Dysfunction and mTOR Hyperactivation Is Involved in Surgery: Induced Behavioral Deficits in Aged C57BL/6J Mice

Autophagy is crucial for cell survival, development, division, and homeostasis. The mammalian target of rapamycin (mTOR), which is the foremost negative controller of autophagy, plays a key role in many endogenous processes. The present study investigated whether rapamycin can ameliorate surgery-induced cognitive deficits by inhibiting mTOR and activating autophagy in the hippocampus. Both adult and aged C57BL/6J mice received an intraperitoneal injection of rapamycin (10 mg/kg/day) for 5 days per week for one and a half months. Mice were then subjected to partial hepatectomy under general anesthesia. Behavioral performance was assessed on postoperative days 3, 7, and 14. Hippocampal autophagy-related (Atg)-5, phosphorylated mTOR, and phosphorylated p70S6K were examined at each time point. Brain derived neurotrophic factor (BDNF), synaptophysin, and tau hyperphosphorylation (T396) in the hippocampus were also examined. Surgical trauma and anesthesia exacerbated spatial learning and memory impairment in aged mice on postoperative days 3 and 7. Following partial hepatectomy, the levels of phosphorylated mTOR, phosphorylated 70S6K, and phosphorylated tau were all increased in the hippocampus. A corresponding decline in BDNF and synaptophysin were observed. Rapamycin treatment restored autophagy function, attenuated phosphorylation of tau protein, and increased BDNF and synaptophysin expression in the hippocampus of surgical mice. Furthermore, surgery and anesthesia induced spatial learning and memory impairments were also reversed by rapamycin treatment. Autophagy impairments and mTOR hyperactivation were detected along with surgery-induced behavioral deficits. Inhibiting the mTOR signaling pathway with rapamycin successfully ameliorated surgery-related cognitive impairments by sustaining autophagic degradation, inhibiting tau hyperphosphorylation, and increasing synaptophysin and BDNF expression.

Punicalagin Reversed the Hepatic Injury of Tetrachloromethane by Antioxidation and Enhancement of Autophagy

Hepatic injury is significant in the pathogenesis and development of many types of liver diseases. Punicalagin (PU) is a bioactive antioxidant polyphenol found in pomegranates. To explore its protective effect against carbon tetrachloride (CCl₄)-induced liver injury and the mechanism, Institute of Cancer Research (ICR) mice and L02 cells were used to observe the changes of serum biochemical indicators, histopathological liver structure, cell viability, antioxidative indices, and autophagy-related proteins were assessed. In ICR mice, PU ameliorated the CCl₄-induced increase of the serum aspartate aminotransferase, alanine aminotransferase, the activity of liver lactate dehydrogenase, and the damage of histopathological structure, and exhibited a hepatoprotective effect against CCl₄. PU attenuated oxidative stress by decreasing the liver malondialdehyde level and increasing the activities of liver superoxide dismutase, glutathione peroxidase, and the expression of the liver nuclear factor E2-related factor (Nrf2) protein. Furthermore, according to the vivo and vitro experiments, PU might activate autophagy through the mediation of the Akt/FOXO3a and P62/Nrf2 signaling pathway. Taken together, these results suggest that PU may protect against CCl₄-induced liver injury through the upregulation of antioxidative activities and autophagy.

Inhibition of Autophagy Attenuated Intestinal Injury After Intestinal I/R via mTOR Signaling

BACKGROUND

Intestinal ischemia/reperfusion (I/R) is a grave condition related to high morbidity and mortality. Autophagy, which can induce a new cell death named type II programmed cell death, has been reported in some intestinal diseases, but little is known in I/R-induced intestinal injury. In this study, we aimed to explore the role of autophagy in intestinal injury induced by I/R and its potential mechanisms.

MATERIALS AND METHODS

The rats pretreated with rapamycin or 3-methyladenine had intestinal I/R injury. After reperfusion, intestinal injury was measured by Chiu's score, intestinal mucosal wet-to-dry ratio, and lactic acid level. Intestinal mucosal oxidative stress level was measured by malondialdehyde and superoxide dismutase. Autophagosome, LC3, and p62 were detected to evaluate autophagy level. Mammalian target of rapamycin (mTOR) was detected to explore potential mechanism.

RESULTS

Chiu's score, intestinal mucosal wet-to-dry ratio, lactic acid level, malondialdehyde level, autophagosomes, and LC3-II/LC3-I were significantly increased, and superoxide dismutase level and expression of p62 were significantly decreased in intestinal mucosa after intestinal ischemia/reperfusion. Pretreatment with rapamycin significantly aggravated intestinal injury evidenced by increased Chiu's score, intestinal mucosal wet-to-dry ratio and lactic acid level, increased autophagy level evidenced by increased autophagosomes and LC3-II/LC3-I and decreased expression of p62, and downregulated expression of p-mTOR/mTOR. On the contrary, pretreatment with 3-methyladenine significantly attenuated intestinal injury and autophagy level and upregulated expression of p-mTOR/mTOR.

CONCLUSIONS

In summary, autophagy was significantly enhanced in intestinal mucosa after intestinal ischemia/reperfusion, and inhibition of autophagy attenuated intestinal injury induced by I/R through activating mTOR signaling.

Myalgia and chronic fatigue syndrome following immunization: macrophagic myofasciitis and animal studies support linkage to aluminum adjuvant persistency and diffusion in the immune system

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a multifactorial and poorly undersood disabling disease. We present epidemiological, clinical and experimental evidence that ME/CFS constitutes a major type of adverse effect of vaccines, especially those containing poorly degradable particulate aluminum adjuvants. Evidence has emerged very slowly due to the multiplicity, lack of specificity, delayed onset, and frequent medical underestimation of ME/CFS symptoms. It was supported by an epidemiological study comparing vaccinated vs unvaccinated militaries that remained undeployed during Gulf War II. Affected patients suffer from cognitive dysfunction affecting attention, memory and inter-hemispheric connexions, well correlated to brain perfusion defects and associated with a stereotyped and distinctive pattern of cerebral glucose hypometabolism. Deltoid muscle biopsy performed to investigate myalgia typically yields macrophagic myofasciitis (MMF), a histological biomarker assessing longstanding persistency of aluminum agglomerates within innate immune cells at site of previous immunization. MMF is seemingly linked to altered mineral particle detoxification by the xeno/autophagy machinery. Comparing toxicology of different forms of aluminum and different types of exposure is misleading and inadequate and small animal experiments have turned old dogma upside down. Instead of being rapidly solubilized in the extracellular space, injected aluminum particles are quickly captured by immune cells and transported to distant organs and the brain where they elicit an inflammatory response and exert selective low dose long-term neurotoxicity. Clinical observations and experiments in sheep, a large animal like humans, confirmed both systemic diffusion and neurotoxic effects of aluminum adjuvants. Post-immunization ME/CFS represents the core manifestation of "autoimmune/inflammatory syndrome induced by adjuvants" (ASIA).

Deficiency in intestinal epithelial O-GlcNAcylation predisposes to gut inflammation

Post-translational modifications in intestinal epithelial cells (IECs) allow for precise control in intestinal homeostasis, the breakdown of which may precipitate the pathological damage and inflammation in inflammatory bowel disease. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification on intracellular proteins controls diverse biological processes; however, its roles in intestinal homeostasis are still largely unexplored. Here, we found that levels of protein O-GlcNAcylation and the expression of O-GlcNAc transferase (OGT), the enzyme adding the O-GlcNAc moiety, were reduced in IECs in human IBD patients. Deletion of OGT specifically in IECs resulted in disrupted epithelial barrier, microbial dysbiosis, Paneth cell dysfunction, and intestinal inflammation in mice. Using fecal microbiota transplantation in mice, we demonstrated that microbial dysbiosis although was insufficient to induce spontaneous inflammation but exacerbated chemical-induced colitis. Paneth cell-specific deletion of OGT led to Paneth cell dysfunction, which might predispose mice to chemical-induced colitis. On the other hand, the augmentation of O-GlcNAc signaling by inhibiting O-GlcNAcase, the enzyme removing O-GlcNAcylation, alleviated chemical-induced colitis. Our data reveal that protein O-GlcNAcylation in IECs controls key regulatory mechanisms to maintain mucosal homeostasis.

Autophagy: roles in intestinal mucosal homeostasis and inflammation

The intestinal mucosa is a site of multiple stressors and forms the barrier between the internal and external environment. In the intestine, a complex interplay between the microbiota, epithelial barrier and the local immune system maintains homeostasis and promotes a healthy gut. One of the major cellular catabolic processes that regulate this homeostasis is autophagy. Autophagy is required to maintain anti-microbial defense, epithelial barrier integrity and mucosal immune response. Dysregulation of the autophagy process causes disruption of several aspects of the intestinal epithelium and the immune system that can lead to an inappropriate immune response and subsequent inflammation. Genome-wide association studies have found an association between several risk loci in autophagy genes and inflammatory bowel disease. The aim of the current review is to provide an update on the role of autophagy in intestinal mucosal physiology and in the control of inappropriate inflammation.

Resveratrol-Induced Xenophagy Promotes Intracellular Bacteria Clearance in Intestinal Epithelial Cells and Macrophages

Autophagy is a lysosomal degradation process that contributes to host immunity by eliminating invasive pathogens and the modulating inflammatory response. Several infectious and immune disorders are associated with autophagy defects, suggesting that stimulation of autophagy in these diseases should be beneficial. Here, we show that resveratrol is able to boost xenophagy, a selective form of autophagy that target invasive bacteria. We demonstrated that resveratrol promotes in vitro autophagy-dependent clearance of intracellular bacteria in intestinal epithelial cells and macrophages. These results were validated in vivo using infection in a transgenic GFP-LC3 zebrafish model. We also compared the ability of resveratrol derivatives, designed to improve the bioavailability of the parent molecule, to stimulate autophagy and to induce intracellular bacteria clearance. Together, our data demonstrate the ability of resveratrol to stimulate xenophagy, and thereby enhance the clearance of two invasive bacteria involved life-threatening diseases, Salmonella Typhimurium and Crohn's disease-associated Adherent-Invasive Escherichia coli. These findings encourage the further development of pro-autophagic nutrients to strengthen intestinal homeostasis in basal and infectious states.

A broad-spectrum antibiotic, DCAP, reduces uropathogenic Escherichia coli infection and enhances vorinostat anticancer activity by modulating autophagy

The cellular recycling pathway of autophagy plays a fundamental role in adaptive responses to nutrient deprivation and other forms of stress under physiological and pathological conditions. However, autophagy can also be a double-edge sword during certain bacterial infections (such as urinary tract infections) and in cancer, where it can be hijacked by the pathogens and cancer cells, respectively, to promote their own survival. Thus, autophagy modulation can potentially have multiple effects in multiple contexts and this property can be leveraged to improve outcomes. In this report, we identify that a broad-spectrum antibiotic, 2-((3-(3, 6-dichloro-9H-carbazol-9-yl)-2-hydroxypropyl) amino)-2-(hydroxymethyl) propane-1, 3-diol (DCAP) modulates autophagy. We employed combined biochemical, fluorescence microscopy and correlative light electron microscopy approaches to demonstrate that DCAP treatment blocks autophagy at the late stages by preventing autophagolysosome maturation and interrupting the autophagic flux. We further show that, DCAP significantly reduces UPEC infection in urinary tract epithelial cells via inhibition of autophagy. Finally, we reveal that DCAP enhances the anticancer activity of the histone acetyltransferase (HDAC) inhibitor, vorinostat, which has been reported to increase susceptibility to bacterial infections as a common adverse effect. Collectively, our data support the concept that DCAP represents a valuable chemical scaffold for the development of an innovative class of bactericidal autophagy inhibitors for treatment of urinary tract infections and/or for adjuvant therapy in cancer treatment.

The independence of and associations among apoptosis, autophagy, and necrosis

Cell death is an essential biological process for physiological growth and development. Three classical forms of cell death-apoptosis, autophagy, and necrosis-display distinct morphological features by activating specific signaling pathways. With recent research advances, we have started to appreciate that these cell death processes can cross-talk through interconnecting, even overlapping, signaling pathways, and the final cell fate is the result of the interplay of different cell death programs. This review provides an insight into the independence of and associations among these three types of cell death and explores the significance of cell death under the specific conditions of human diseases, particularly neurodegenerative diseases and cancer.

CK1α suppresses lung tumour growth by stabilizing PTEN and inducing autophagy

The contribution of autophagy to cancer development remains controversial, largely owing to the fact that autophagy can be tumour suppressive or oncogenic in different biological contexts. Here, we show that in non-small-cell lung cancer (NSCLC), casein kinase 1 alpha 1 (CK1α) suppresses tumour growth by functioning as an autophagy inducer to activate an autophagy-regulating, tumour-suppressive PTEN/AKT/FOXO3a/Atg7 axis. Specifically, CK1α bound the C-terminal tail of PTEN and enhanced both PTEN stability and activity by competitively antagonizing NEDD4-1-induced PTEN polyubiquitination and abrogating PTEN phosphorylation, thereby inhibiting AKT activity and activating FOXO3a-induced transcription of Atg7. Notably, blocking CK1α-induced Atg7-dependent autophagy cooperates with oncogenic HRasV12 to initiate tumorigenesis of lung epithelial cells. An association of a CK1α-modulated autophagic program with the anti-neoplastic activities of the CK1α/PTEN/FOXO3a/Atg7 axis was demonstrated in xenografted tumour models and human NSCLC specimens. This provides insights into the biological and potentially clinical significance of autophagy in NSCLC.

Autophagy is essential for maintaining the growth of a human (mini-)organ: Evidence from scalp hair follicle organ culture

Autophagy plays a crucial role in health and disease, regulating central cellular processes such as adaptive stress responses, differentiation, tissue development, and homeostasis. However, the role of autophagy in human physiology is poorly understood, highlighting a need for a model human organ system to assess the efficacy and safety of strategies to therapeutically modulate autophagy. As a complete, cyclically remodelled (mini-)organ, the organ culture of human scalp hair follicles (HFs), which, after massive growth (anagen), spontaneously enter into an apoptosis-driven organ involution (catagen) process, may provide such a model. Here, we reveal that in anagen, hair matrix keratinocytes (MKs) of organ-cultured HFs exhibit an active autophagic flux, as documented by evaluation of endogenous lipidated Light Chain 3B (LC3B) and sequestosome 1 (SQSTM1/p62) proteins and the ultrastructural visualization of autophagosomes at all stages of the autophagy process. This autophagic flux is altered during catagen, and genetic inhibition of autophagy promotes catagen development. Conversely, an anti-hair loss product markedly enhances intrafollicular autophagy, leading to anagen prolongation. Collectively, our data reveal a novel role of autophagy in human hair growth. Moreover, we show that organ-cultured scalp HFs are an excellent preclinical research model for exploring the role of autophagy in human tissue physiology and for evaluating the efficacy and tissue toxicity of candidate autophagy-modulatory agents in a living human (mini-)organ.

Loss of Paneth Cell Autophagy Causes Acute Susceptibility to Toxoplasma gondii-Mediated Inflammation

The protozoan parasite Toxoplasma gondii triggers severe small intestinal immunopathology characterized by IFN-γ- and intestinal microbiota-mediated inflammation, Paneth cell loss, and bacterial dysbiosis. Paneth cells are a prominent secretory epithelial cell type that resides at the base of intestinal crypts and releases antimicrobial peptides. We demonstrate that the microbiota triggers basal Paneth cell-specific autophagy via induction of IFN-γ, a known trigger of autophagy, to maintain intestinal homeostasis. Deletion of the autophagy protein Atg5 specifically in Paneth cells results in exaggerated intestinal inflammation characterized by complete destruction of the intestinal crypts resembling that seen in pan-epithelial Atg5-deficient mice. Additionally, lack of functional autophagy in Paneth cells within intestinal organoids and T. gondii-infected mice causes increased sensitivity to the proinflammatory cytokine TNF along with increased intestinal permeability, leading to exaggerated microbiota- and IFN-γ-dependent intestinal immunopathology. Thus, Atg5 expression in Paneth cells is essential for tissue protection against cytokine-mediated immunopathology during acute gastrointestinal infection.

Erbin exerts a protective effect against inflammatory bowel disease by suppressing autophagic cell death

The pathogenesis and key functional molecules involved in inflammatory bowel disease (IBD) including Crohn's disease (CD) and ulcerative colitis (UC) remain unclear. Here, we reported that Erbin, a protein required for the polarity of epithelial cells, is conserved across species and highly expressed in the intestinal mucosa in mice and zebrafish. Pathologically, Erbin expression in the intestinal mucosa was significantly decreased in DSS induced acute colitis mice, IL-10 deficient mice and clinical biopsy specimens from patients with ulcerative colitis. Moreover, Erbin deficient mice are more susceptible to experimental colitis, exhibiting more severe intestinal barrier disruption, with increased histological scores and excessive production of proinflammatory cytokines. Mechanistically, Erbin deficiency or knockdown significantly exacerbated activation of autophagic program and autophagic cell death in vivo and in vitro. And, inhibition of autophagy by Chloroquine attenuates excessive inflammatory response in the DSS-induced colitis mouse model of Erbin deletion. Generally, our study uncovers a crucial role of Erbin in autophagic cell death and IBD, giving rise to a new strategy for IBD therapy by inhibiting excessive activation of autophagy and autophagic cell death.

The Roles of Glutamine in the Intestine and Its Implication in Intestinal Diseases

Glutamine, the most abundant free amino acid in the human body, is a major substrate utilized by intestinal cells. The roles of glutamine in intestinal physiology and management of multiple intestinal diseases have been reported. In gut physiology, glutamine promotes enterocyte proliferation, regulates tight junction proteins, suppresses pro-inflammatory signaling pathways, and protects cells against apoptosis and cellular stresses during normal and pathologic conditions. As glutamine stores are depleted during severe metabolic stress including trauma, sepsis, and inflammatory bowel diseases, glutamine supplementation has been examined in patients to improve their clinical outcomes. In this review, we discuss the physiological roles of glutamine for intestinal health and its underlying mechanisms. In addition, we discuss the current evidence for the efficacy of glutamine supplementation in intestinal diseases.

Protective effects of ethyl pyruvate on lipopolysaccharide‑induced acute lung injury through inhibition of autophagy in neutrophils

Among a number of clinical factors, bacterial infection is one of the most common causes of acute lung injury (ALI), a serious complication that carries a high risk of mortality (~40%). During the process of ALI, intense local and systemic inflammation is elicited, which exacerbates the injury. Neutrophil infiltration into airspace is observed in early stage of ALI, and is required for the full development of ALI through an array of mechanisms, including the release of granule contents and the production of pro‑inflammatory cytokines, due to the overactivation of complement and cytokines. The present study noted that ethyl pyruvate alleviated ALI in lipopolysaccharide (LPS)‑induced ALI mice. Increased autophagy in neutrophils from ALI mice was observed, while ethyl pyruvate diminished autophagy in neutrophils and constrained granule release, and therefore myeloperoxidase (MPO) in bronchoalveolar lavage fluid and the production of proinflammatory cytokines. Using neutrophil cells, it was identified that autophagy was required for neutrophil activation and granule release, and that ethyl pyruvate caused neutrophil autophagy, leading to the restriction of granule release, and thus contributing to the mitigation of ALI. If autophagy was obviated through knockdown of key regulator of autophagy Atg5, the effects of ethyl pyruvate on granule release by neutrophils disappeared. Taken together, the results demonstrated that ethyl pyruvate alleviates ALI through inhibition of autophagy‑induced granule release by neutrophils, and this mechanism suggested a novel potential therapeutic target in autophagy regulation for ALI.

β-Conglycinin enhances autophagy in porcine enterocytes

β-Conglycinin (β-CG) is well known for inducing intestinal allergies and dysfunction in neonates and young pigs. However, the underlying mechanisms are largely unknown. In this study, to clarify the role of autophagy in β-CG-induced cytotoxicity, we investigated the effects of β-CG on cell viability and autophagy activity in porcine enterocytes (IPEC-1 cells). The results indicated that the cell viability was decreased with the increasing levels of β-CG. β-CG treatment enhanced the eGFP-LC3 puncta per cells and LC3-II/LC3-I, and the latter was further increased in IPEC-1 cells cultured with bafilomycin A1. We conclude that β-CG enhances autophagy activity in enterocytes.

Understanding the regulation of pattern recognition receptors in inflammatory diseases - a 'Nod' in the right direction

Nucleotide-binding oligomerization domain (NOD) -like receptors (NLRs) are a family of 23 receptors known as pattern recognition receptors; they are expressed in many cell types and play a key role in the innate immune response. The NLRs are activated by pathogen-associated molecular patterns, which include structurally conserved molecules present on the surfaces of bacteria. The activation of these NLRs by pathogens results in the downstream activation of signalling kinases and transcription factors, culminating in the transcription of genes coding for pro-inflammatory factors. Expression of NLR is altered in many cellular, physiological and disease states. There is a lack of understanding of the mechanisms by which NLR expression is regulated, particularly in chronic inflammatory states. Genetic polymorphisms and protein interactions are included in such mechanisms. This review seeks to examine the current knowledge regarding the regulation of this family of receptors and their signalling pathways as well as how their expression changes in disease states with particular focus on NOD1 and NOD2 in inflammatory bowel diseases among others.

Soluble bioactive microbial mediators regulate proteasomal degradation and autophagy to protect against inflammation-induced stress

Bifidobacterium breve and other Gram-positive gut commensal microbes protect the gastrointestinal epithelium against inflammation-induced stress. However, the mechanisms whereby these bacteria accomplish this protection are poorly understood. In this study, we examined soluble factors derived from Bifidobacterium breve and their impact on the two major protein degradation systems within intestinal epithelial cells, proteasomes and autophagy. Conditioned media from gastrointestinal Gram-positive, but not Gram-negative, bacteria activated autophagy and increased expression of the autophagy proteins Atg5 and Atg7 along with the stress response protein heat shock protein 27. Specific examination of media conditioned by the Gram-positive bacterium Bifidobacterium breve (Bb-CM) showed that this microbe produces small molecules (<3 kDa) that increase expression of the autophagy proteins Atg5 and Atg7, activate autophagy, and inhibit proteasomal enzyme activity. Upregulation of autophagy by Bb-CM was mediated through MAP kinase signaling. In vitro studies using C2BBe1 cells silenced for Atg7 and in vivo studies using mice conditionally deficient in intestinal epithelial cell Atg7 showed that Bb-CM-induced cytoprotection is dependent on autophagy. Therefore, this work demonstrates that Gram-positive bacteria modify protein degradation programs within intestinal epithelial cells to promote their survival during stress. It also reveals the therapeutic potential of soluble molecules produced by these microbes for prevention and treatment of gastrointestinal disease.

An overview of the bacterial contribution to Crohn disease pathogenesis

Crohn disease (CD) is a chronic inflammatory condition primarily affecting the gastro-intestinal tract and is characterized by reduced bacterial diversity. The exact cause of disease is unknown; however, evidence suggests that several components, including microbiota, may contribute to the underlying pathology and disease development. Perturbation of the host-microbe commensal relationship is considered the main driving force of tissue destruction and pathological changes seen in CD. Several putative bacterial pathogens including species from Mycobacterium, Campylobacter and Helicobacter are postulated in the aetiology of CD. However, to date, no strong evidence supports a single bacterium contributing overall to CD pathogenesis. Alternatively, dysbiosis or bacterial imbalance is more widely accepted as a leading factor in the disrupted host-immune system cross-talk resulting in subsequent intestinal inflammation. Depletion of symbiont microbes including Firmicutes, Bifidobacterium and Clostridia, in conjunction with an increase in pathobiont microbes from Bacteroidetes and Enterobacteria, is a striking feature observed in CD. No single factor has been identified as driving this dysbiosis, although diet, antibiotic exposure and possible early life events in presence of underlying genetic susceptibility may contribute. The aim of this review is to highlight the current accumulating literature on the proposed role of bacteria in the pathogenesis of CD.

The role of barrier function, autophagy, and cytokines in maintaining intestinal homeostasis

Intestinal homeostasis is maintained through the interplay of the intestinal mucosa, local and systemic immune factors, and the microbial content of the gut. The cellular processes of autophagy, endoplasmic reticulum stress, the unfolded protein response and regulation of reactive oxygen species production are required to maintain a balance between pro-inflammatory responses against potential pathogens and a tolerogenic response towards commensal bacteria. Intestinally active cytokines regulate innate immune pathways and cellular pathways within the gut mucosa. Disruption of these processes, or alterations in the cytokine milieu, can result in an improper response to the commensal gut microbial community leading to inappropriate inflammation characteristic of conditions such as inflammatory bowel disease.

Effect of liposome-encapsulated hemoglobin resuscitation on proteostasis in small intestinal epithelium after hemorrhagic shock

Gut barrier dysfunction is the major trigger for multiorgan failure associated with hemorrhagic shock (HS). Although the molecular mediators responsible for this dysfunction are unclear, oxidative stress-induced disruption of proteostasis contributes to the gut pathology in HS. The objective of this study was to investigate whether resuscitation with nanoparticulate liposome-encapsulated hemoglobin (LEH) is able to restore the gut proteostatic mechanisms. Sprague-Dawley rats were recruited in four groups: control, HS, HS+LEH, and HS+saline. HS was induced by withdrawing 45% blood, and isovolemic LEH or saline was administered after 15 min of shock. The rats were euthanized at 6 h to collect plasma and ileum for measurement of the markers of oxidative stress, unfolded protein response (UPR), proteasome function, and autophagy. HS significantly increased the protein and lipid oxidation, trypsin-like proteasome activity, and plasma levels of IFNγ. These effects were prevented by LEH resuscitation. However, saline was not able to reduce protein oxidation and plasma IFNγ in hemorrhaged rats. Saline resuscitation also suppressed the markers of UPR and autophagy below the basal levels; the HS or LEH groups showed no effect on the UPR and autophagy. Histological analysis showed that LEH resuscitation significantly increased the villus height and thickness of the submucosal and muscularis layers compared with the HS and saline groups. Overall, the results showed that LEH resuscitation was effective in normalizing the indicators of proteostasis stress in ileal tissue. On the other hand, saline-resuscitated animals showed a decoupling of oxidative stress and cellular protective mechanisms.

The Mucosal Immune System and Its Regulation by Autophagy

The gastrointestinal tract presents a unique challenge to the mucosal immune system, which has to constantly monitor the vast surface for the presence of pathogens, while at the same time maintaining tolerance to beneficial or innocuous antigens. In the intestinal mucosa, specialized innate and adaptive immune components participate in directing appropriate immune responses toward these diverse challenges. Recent studies provide compelling evidence that the process of autophagy influences several aspects of mucosal immune responses. Initially described as a “self-eating” survival pathway that enables nutrient recycling during starvation, autophagy has now been connected to multiple cellular responses, including several aspects of immunity. Initial links between autophagy and host immunity came from the observations that autophagy can target intracellular bacteria for degradation. However, subsequent studies indicated that autophagy plays a much broader role in immune responses, as it can impact antigen processing, thymic selection, lymphocyte homeostasis, and the regulation of immunoglobulin and cytokine secretion. In this review, we provide a comprehensive overview of mucosal immune cells and discuss how autophagy influences many aspects of their physiology and function. We focus on cell type-specific roles of autophagy in the gut, with a particular emphasis on the effects of autophagy on the intestinal T cell compartment. We also provide a perspective on how manipulation of autophagy may potentially be used to treat mucosal inflammatory disorders.

FoxO1-mediated autophagy is required for NK cell development and innate immunity

Natural killer (NK) cells exert a crucial role in early immune responses as a major innate effector component. However, the underlying mechanisms of NK cell development remain largely elusive. Here we show that robust autophagy appears in the stage of immature NK cells (iNKs), which is required for NK cell development. Autophagy defects result in damaged mitochondria and accumulation of reactive oxygen species (ROS) that leads to apoptosis of NK cells. Autophagy protects NK cell viability during development through removal of damaged mitochondria and intracellular ROS. Phosphorylated Forkhead box O (FoxO)1 is located to the cytoplasm of iNKs and interacts with Atg7, leading to induction of autophagy. FoxO1 deficiency or an inactive FoxO1^AAA mutant abrogates autophagy initiation in iNKs and impairs NK cell development and viral clearance. Therefore we conclude that FoxO1-mediated autophagy is required for NK cell development and NK cell-induced innate immunity.

Natural killer cells are a major component of the innate immune response. Here, Wang et al. show that natural killer cell development requires robust activation of autophagy at the immature stage where it acts to remove damaged mitochondria and reduces levels of reactive oxygen species.

Identification of a novel interaction between corticotropin releasing hormone (Crh) and macroautophagy

In inflammatory bowel disease (IBD), compromised restitution of the epithelial barrier contributes to disease severity. Owing to the complexity in the pathogenesis of IBD, a variety of factors have been implicated in its progress. In this study, we report a functional interaction between macroautophagy and Corticotropin Releasing Hormone (Crh) in the gut. For this purpose we used DSS colitis model on Crh -/- or wild-type (wt) with pharmacological inhibition of autophagy. We uncovered sustained basal autophagy in the gut of Crh -/- mice, which persisted over the course of DSS administration. Autophagy inhibition resulted in partial rescue of Crh -/- mice, while it increased the expression of Crh in the wt gut. Similarly, Crh deficiency was associated with sustained activation of base line autophagy. In vitro models of amino acid deprivation- and LPS-induced autophagy confirmed the in vivo findings. Our results indicate a novel role for Crh in the intestinal epithelium that involves regulation of autophagy, while suggesting the complementary action of the two pathways. These data suggest the intriguing possibility that targeting Crh stimulation in the intestine may provide a novel therapeutic approach to support the integrity of the epithelial barrier and to protect from chronic colitis.

MicroRNAs in colorectal carcinoma--from pathogenesis to therapy

Background

Acting as inflammatory mediators, tumor oncogenes or suppressors, microRNAs are involved in cell survival, death, epithelial–mesenchymal transition and metastasis, etc. Investigating the communication between microRNAs and tumorigenesis is critical to our understanding of the pathogenesis of multiple disease states.

Main body

Currently, colorectal carcinoma (CRC), one of the most common malignancies worldwide, has a poor prognosis due to lack of an effective therapeutic option. Increasing evidence has identified altered profiles and regulatory potential of microRNAs in conditions related to environmentally-caused colorectal inflammation and colitis-associated cancer. Many studies have shed light on a more thorough understanding of the function and distribution of microRNAs in CRC initiation and emergence. However, the molecular mechanisms by which microRNAs modulate cellular processes still need to be further elucidated and may offer a foundation for evaluating microRNA-based therapeutic potential for CRC in both animal models and clinical trials.

Conclusion

In this review, the roles and mechanisms of microRNAs involved in CRC from pathogenesis to therapy are summarized and discussed, which may provide more useful hints for CRC prevention and therapy.

Autophagy protects intestinal epithelial cells against deoxynivalenol toxicity by alleviating oxidative stress via IKK signaling pathway

Autophagy is an intracellular process of homeostatic degradation that promotes cell survival under various stressors. Deoxynivalenol (DON), a fungal toxin, often causes diarrhea and disturbs the homeostasis of the intestinal system. To investigate the function of intestinal autophagy in response to DON and associated mechanisms, we firstly knocked out ATG5 (autophagy-related gene 5) in porcine intestinal epithelial cells (IPEC-J2) using CRISPR-Cas9 technology. When treated with DON, autophagy was induced in IPEC-J2 cells but not in IPEC-J2.Atg5ko cells. The deficiency in autophagy increased DON-induced apoptosis in IPEC-J2.atg5ko cells, in part, through the generation of reactive oxygen species (ROS). The cellular stress response can be restored in IPEC-J2.atg5ko cells by overexpressing proteins involved in protein folding. Interestingly, we found that autophagy deficiency downregulated the expression of endoplasmic reticulum folding proteins BiP and PDI when IPEC-J2.atg5ko cells were treated with DON. In addition, we investigated the molecular mechanism of autophagy involved in the IKK, AMPK, and mTOR signaling pathway and found that Bay-117082 and Compound C, specific inhibitors for IKK and AMPK, respectively, inhibited the induction of autophagy. Taken together, our results suggest that autophagy is pivotal for protection against DON in pig intestinal cells.

Streptococcus pneumoniae induces autophagy through the inhibition of the PI3K-I/Akt/mTOR pathway and ROS hypergeneration in A549 cells

The present study focused on the action mechanism of S. pneumoniae (Sp) in inducing autophagy in human alveolar epithelial cells. Sp, a gram-positive extracellular bacterium, activates autophagy with considerably increased microtuble-associated protein light chain 3 (LC3) punctation in A549 cells. The accumulation of typical autophagosomes and conjugation of LC3 to phosphatidylethanolamine were observed in Sp-infected cells as an indication of autophagy. Using the pneumolysin (PLY) mutant, we successfully demonstrated that PLY is involved in initiating autophagy without affecting the expression levels of PI3K-III and Beclin1. PLY-mediated autophagy depends on the inhibition of the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway. Furthermore, Sp could also lead to the reactive oxygen species (ROS) hypergeneration in A549 cells. Taken together, Sp infection-induced autophagy is PLY-mediated through ROS hypergeneration and mTOR inhibition. PI3K-I and rapamycin (autophagy inducers) enhanced bacterial clearance, whereas wortmannin (autophagy inhibitor) and acetylcysteine (ROS inhibitor) reduced intracellular bacteria clearance. Thus, Sp-induced autophagy represents a host-protective mechanism, providing new insight into the pathogenesis of respiratory tract Sp infection.

Functional impacts of the intestinal microbiome in the pathogenesis of inflammatory bowel disease

: The human intestinal microbiome plays a critical role in human health and disease, including the pathogenesis of inflammatory bowel disease (IBD). Numerous studies have identified altered bacterial diversity and abundance at varying taxonomic levels through biopsies and fecal samples of patients with IBD and diseased model animals. However, inconsistent observations regarding the microbial compositions of such patients have hindered the efforts in assessing the etiological role of specific bacterial species in the pathophysiology of IBD. These observations highlight the importance of minimizing the confounding factors associated with IBD and the need for a standardized methodology to analyze well-defined microbial sampling sources in early IBD diagnosis. Furthermore, establishing the linkage between microbiota compositions with their function within the host system can provide new insights on the pathogenesis of IBD. Such research has been greatly facilitated by technological advances that include functional metagenomics coupled with proteomic and metabolomic profiling. This review provides updates on the composition of the microbiome in IBD and emphasizes microbiota dysbiosis-involved mechanisms. We highlight functional roles of specific bacterial groups in the development and management of IBD. Functional analyses of the microbiome may be the key to understanding the role of microbiota in the development and chronicity of IBD and reveal new strategies for therapeutic intervention.

Four types of Bifidobacteria trigger autophagy response in intestinal epithelial cells

OBJECTIVES

To investigate the influence of gut microbiota on autophagy activation in intestinal epithelial cells (IEC) and to evaluate the IEC autophagy response to different types of Bifidobacteria.

METHODS

IEC-18 cells were treated with lipopolysaccharide (LPS) derived from enteropathogenic Escherichia coli (EPEC) O127:B8 and culture medium supernatants of four types of Bifidobacteria. Transepithelial electrical resistance (TEER) was measured using an epithelial voltohmmeter. Autophagy was determined by transmission electron microscopy (TEM), the ratio of LC3-II to LC3-I and the persistence of both green fluorescent protein (GFP) and mCherry signals using a tandem mCherry-GFP-LC3 construct. The expression of Atg12-Atg5-Atg16 complex was measured by quantitative real-time polymerase chain reaction.

RESULTS

EPEC-LPS significantly diminished the TEER of IEC compared with untreated controls by 45-55%. This reduction was not observed after treated with Bifidobacteria at all time points. Bifidobacteria could initiate the activation of autophagy in IEC, based on both the ratio of LC3-II to LC3-I and TEM. There was no difference in the influence of the four types of Bifidobacteria on the autophagy response. Compared with Bifidobacteria, IEC reacted to EPEC-LPS much more intensively by autophagy accumulation. More mCherry(+) LC3 autophagic puncta and increased expressions of autophagy genes Atg5, Atg12 and Atg16 could be detected after being treated with Bifidobacteria and EPEC-LPS.

CONCLUSIONS

Bifidobacteria initiate autophagy activation in IEC. The Atg12-Atg5-Atg16 multimeric complex might participate in the activation of Bifidobacteria-induced cell autophagy.