Cinnamaldehyde alleviates zearalenone-induced LS174T cell apoptosis, barrier dysfunction and mucin reduction through JNK/NF-κB signaling pathway

As a natural aldehyde organic compound, cinnamaldehyde (CA) is one of the main components of cinnamon essential oil with multiple bioactivities. In this study, we investigated the protective effects of CA on zearalenone (ZEA)-induced apoptosis, barrier dysfunction and mucin reduction, as well as underlying mechanisms in LS174T cells. In the present study, cells pre-treated with or without CA for 24 h were left untreated or subjected to ZEA for indicated time points Our results showed that 10 μM CA significantly prevented ZEA-induced cell viability decline, reversed ZEA-induced increase of the LDH level, cell cycle disruption and apoptosis in LS174T cells. Periodic acid-schiff (PAS) staining analysis showed that CA significantly alleviated the reduction of mucin secretion in LS174T cells caused by ZEA exposure. Western blot analysis showed that CA significantly reversed ZEA-induced reduction of the expression of mucin 2 (MUC2) and tight junction (TJ) proteins (claudin-1, claudin-3, ZO-1 and ZO-2) in LS174T cells. Notably, CA can significantly reduce the upregulation of the main effector of MAPK and NF-κB signaling pathways in LS174T cells. Further study showed that CA protects cells against ZEA-induced cellular damage through JNK/NF-κB signaling pathway in LS174T cells. Supplementation with CA might be an potential strategy to alleviate the damaging effect of ZEA on epithelial cells.

Xenobiotic-induced ribosomal stress compromises dysbiotic gut barrier aging: A one health perspective

Upon exposure to internal or environmental insults, ribosomes stand sentinel. In particular, stress-driven dysregulation of ribosomal homeostasis is a potent trigger of adverse outcomes in mammalians. The present study assessed whether the ribosomal insult affects the aging process via the regulation of sentinel organs such as the gut. Analyses of the human aging dataset demonstrated that elevated features of ribosomal stress are inversely linked to barrier maintenance biomarkers during the aging process. Ribosome-insulted worms displayed reduced lifespan, which was associated with the disruption of gut barriers. Mechanistically, ribosomal stress-activated Sek-1/p38 signaling, a central platform of ribosomal stress responses, counteracted the gut barrier deterioration through the maintenance of the gut barrier, which was consistent with the results in a murine insult model. However, since the gut-protective p38 signaling was attenuated with aging, the ribosomal stress-induced distress was exacerbated in the gut epithelia and mucosa of the aged animals, subsequently leading to increased bacterial exposure. Moreover, the bacterial community-based evaluation predicted concomitant increases in the abundance of mucosal sugar utilizers and mucin metabolic enzymes in response to ribosomal insult in the aged host. All of the present evidence on ribosomal insulting against the gut barrier integrity from worms to mammals provides new insights into organelle-associated translational modulation of biological longevity in a one health perspective.

The Glitazars Paradox: Cardiotoxicity of the Metabolically Beneficial Dual PPARα and PPARγ Activation

The most common complications in patients with type-2 diabetes are hyperglycemia and hyperlipidemia that can lead to cardiovascular disease. Alleviation of these complications constitutes the major therapeutic approach for the treatment of diabetes mellitus. Agonists of peroxisome proliferator-activated receptor (PPAR) alpha and PPARγ are used for the treatment of hyperlipidemia and hyperglycemia, respectively. PPARs belong to the nuclear receptors superfamily and regulate fatty acid metabolism. PPARα ligands, such as fibrates, reduce circulating triglyceride levels, and PPARγ agonists, such as thiazolidinediones, improve insulin sensitivity. Dual-PPARα/γ agonists (glitazars) were developed to combine the beneficial effects of PPARα and PPARγ agonism. Although they improved metabolic parameters, they paradoxically aggravated congestive heart failure in patients with type-2 diabetes via mechanisms that remain elusive. Many of the glitazars, such as muraglitazar, tesaglitazar, and aleglitazar, were abandoned in phase-III clinical trials. The objective of this review article pertains to the understanding of how combined PPARα and PPARγ activation, which successfully targets the major complications of diabetes, causes cardiac dysfunction. Furthermore, it aims to suggest interventions that will maintain the beneficial effects of dual PPARα/γ agonism and alleviate adverse cardiac outcomes in diabetes.

Mucosal ribosomal stress-induced PRDM1 promotes chemoresistance via stemness regulation

The majorities of colorectal cancer (CRC) cases are sporadic in origin and a large proportion of etiologies are associated with environmental stress responses. In response to external and internal stress, the ribosome stands sentinel and stress-driven ribosomal dysfunction triggers the cellular decision pathways via transcriptional reprogramming. In the present study, PR domain zinc finger protein (PRDM) 1, a master transcriptional regulator, was found to be closely associated with ribosomal actions in patients with CRC and the murine models. Stress-driven ribosomal dysfunction enhanced PRDM1 levels in intestinal cancer cells, which contributed to their survival and enhanced cancer cell stemness against cancer treatment. Mechanistically, PRDM1 facilitated clustering modulation of insulin-like growth factor (IGF) receptor-associated genes, which supported cancer cell growth and stemness-linked features. Ribosomal dysfunction-responsive PRDM1 facilitated signaling remodeling for the survival of tumor progenitors, providing compelling evidence for the progression of sporadic CRC.

UPR modulation of host immunity by Pseudomonas aeruginosa in cystic fibrosis

Cystic fibrosis (CF) is a progressive multiorgan autosomal recessive disease with devastating impact on the lungs caused by derangements of the CF transmembrane conductance regulator (CFTR) gene. Morbidity and mortality are caused by the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Pseudomonas aeruginosa is the main respiratory pathogen in individuals with CF infecting most patients in later stages. Despite its recognized clinical impact, molecular mechanisms that underlie P. aeruginosa pathogenesis and the host response to P. aeruginosa infection remain incompletely understood. The nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR) γ (PPARγ), has shown to be reduced in CF airways. In the present study, we sought to investigate the upstream mechanisms repressing PPARγ expression and its impact on airway epithelial host defense. Endoplasmic reticulum-stress (ER-stress) triggered unfolded protein response (UPR) activated by misfolded CFTR and P. aeruginosa infection contributed to attenuated expression of PPARγ. Specifically, the protein kinase RNA (PKR)-like ER kinase (PERK) signaling pathway led to the enhanced expression of the CCAAT-enhancer-binding-protein homologous protein (CHOP). CHOP induction led to the repression of PPARγ expression. Mechanistically, we showed that CHOP induction mediated PPARγ attenuation, impacted the innate immune function of normal and ∆F508 primary airway epithelial cells by reducing expression of antimicrobial peptide (AMP) and paraoxanse-2 (PON-2), as well as enhancing IL-8 expression. Furthermore, mitochondrial reactive oxygen species production (mt-ROS) and ER-stress positive feedforward loop also dysregulated mitochondrial bioenergetics. Additionally, our findings implicate that PPARγ agonist pioglitazone (PIO) has beneficial effect on the host at the multicellular level ranging from host defense to mitochondrial re-energization.

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

Cells have evolved highly specialized sentinels that detect viral infection and elicit an antiviral response. Among these, the stress-sensing protein kinase R, which is activated by double-stranded RNA, mediates suppression of the host translation machinery as a strategy to limit viral replication. Non-translating mRNAs rapidly condensate by phase separation into cytosolic stress granules, together with numerous RNA-binding proteins and components of signal transduction pathways. Growing evidence suggests that the integrated stress response, and stress granules in particular, contribute to antiviral defense. This review summarizes the current understanding of how stress and innate immune signaling act in concert to mount an effective response against virus infection, with a particular focus on the potential role of stress granules in the coordination of antiviral signaling cascades.

Deoxynivalenol Exposure Suppresses Adipogenesis by Inhibiting the Expression of Peroxisome Proliferator-Activated Receptor Gamma 2 (PPARγ2) in 3T3-L1 Cells

Deoxynivalenol (DON)-a type B trichothecene mycotoxin, mainly produced by the secondary metabolism of Fusarium-has toxic effects on animals and humans. Although DON's toxicity in many organs including the adrenal glands, thymus, stomach, spleen, and colon has been addressed, its effects on adipocytes have not been investigated. In this study, 3T3-L1 cells were chosen as the cell model and treated with less toxic doses of DON (100 ng/mL) for 7 days. An inhibition of adipogenesis and decrease in triglycerides (TGs) were observed. DON exposure significantly downregulated the expression of PPARγ2 and C/EBPα, along with that of other adipogenic marker genes in 3T3-L1 cells and BALB/c mice. The anti-adipogenesis effect of DON and the downregulation of the expression of adipogenic marker genes were effectively reversed by PPARγ2 overexpression. The repression of PPARγ2's expression is the pivotal event during DON exposure regarding adipogenesis. DON exposure specifically decreased the di-/trimethylation levels of Histone 3 at lysine 4 in 3T3-L1 cells, therefore weakening the enrichment of H3K4me2 and H3K4me3 at the Pparγ2 promoter and suppressing its expression. Conclusively, DON exposure inhibited PPARγ2 expression via decreasing H3K4 methylation, downregulated the expression of PPARγ2-regulated adipogenic marker genes, and consequently suppressed the intermediate and late stages of adipogenesis. Our results broaden the current understanding of DON's toxic effects and provide a reference for addressing the toxicological mechanism of DON's interference with lipid homeostasis.

Enterocyte-Based Bioassay via Quantitative Combination of Proinflammatory Sentinels Specific to 8-keto-trichothecenes

Type B 8-keto-trichothecenes are muco-active mycotoxins that exist as inevitable contaminants in cereal-based foodstuffs. Gut-associated inflammation is an early frontline response during human and animal exposure to these mycotoxins. Despite various tools for chemical identification, optimized biomonitoring of sentinel response-associated biomarkers is required to assess the specific proinflammatory actions of 8-keto-trichothecenes in the gut epithelial barrier. In the present study, intoxication with 8-keto-trichothecenes in human intestinal epithelial cells was found to trigger early response gene 1 product (EGR-1) that plays crucial roles in proinflammatory chemokine induction. In contrast, epithelial exposure to 8-keto-trichothecenes resulted in downregulated expression of nuclear factor NF-kappa-B p65 protein, a key transcription factor, during general inflammatory responses in the gut. Based on the early molecular patterns of expression, the inflammation-inducing activity of 8-keto-trichothecenes was quantified using intestinal epithelial cells with dual reporters for EGR-1 and p65 proteins. EGR-1-responsive elements were linked to luciferase reporter while p65 promoter was bound to secretory alkaline phosphatase (SEAP) reporter. In response to conventional inflammagens such as endotoxins and cytokines such as TNF-α, both luciferase and SEAP activity were elevated in a dose-dependent manner. However, as expected from the mechanistic evaluation, 8-keto-trichothecene-exposed dual reporters of luciferase and SEAP displayed contrasting expression patterns. Furthermore, 8-keto-trichothecene-elevated EGR-1-responsive luciferase activity was improved by deficiency of PSMA3, an α-type subunit of the 20S proteasome core complex for ubiquitin-dependent EGR-1 degradation. This molecular event-based dual biomonitoring in epithelial cells is a promising supplementary tool for detecting typical molecular inflammatory pathways in response to 8-keto-trichothecenes in the food matrix.

Caveolar communication with xenobiotic-stalled ribosomes compromises gut barrier integrity

In response to internal and external insults, the intestinal lining undergoes various types of epithelial adaptation or pathologic distress via stress-responsive eIF2α kinase signaling and subsequent cellular reprogramming. As a vital platform for growth factor-linked adaptive signaling, caveolae were evaluated for epithelial modulation of the insulted gut. Patients under ulcerative insult displayed enhanced expression of caveolin-1, the main structural component of caveolae, which was positively associated with expression of protein kinase R (PKR), the ribosomal stress-responsive eIF2α kinase. PKR-linked biological responses were simulated in experimental gut models of ribosome-inactivating stress using mice and Caenorhabditis elegans. Caveolar activation counteracted the expression of wound-protective epidermal growth factor receptor (EGFR) and its target genes, such as chemokines that were pivotal for epithelial integrity in the ribosome-inactivated gut. Mechanistic findings regarding ribosomal inactivation-associated disorders in the gut barrier provide crucial molecular evidence for detrimental caveolar actions against EGFR-mediated epithelial protection in patients with IBD.

Protective Ability of Biogenic Antimicrobial Peptide Microcin J25 Against Enterotoxigenic Escherichia Coli-Induced Intestinal Epithelial Dysfunction and Inflammatory Responses IPEC-J2 Cells

Poison of intestinal induce severe health problems in human infants and young animals due to contaminating foods and feedstuffs. With the emergence of public health concerns and high-speed diffuse of drug-opposition of bacteria, the adoption of antimicrobial peptides as potential candidates in treating pathogen infections raised up. Nature Microcin J25 (MccJ25), a class of lasso peptides separated from a fecal strain of E. coli, has been replied to display powerful antimicrobial behavior. Herein, the study was to assess the usefulness of biogenic MccJ25 in the prophylaxis of ETEC K88 infection in IPEC-J2 cells. In vitro antimicrobial activity against ETEC K88 and cytotoxicity of biogenic MccJ25 were determined first. To further understand how biogenic MccJ25 mediates its impact, ETEC K88 adhesion in cells, membrane permeability [as indicated by reduced release of lactate dehydrogenase (LDH)], transepithelial electrical resistance (TEER), barrier function, and proinflammatory cytokines levels were determined in IPEC-J2 cells after treatment with biogenic MccJ25 and challenge with ETEC K88. Biogenic MccJ25 had a minimum inhibitory concentration of 0.25 μg/mL against ETEC K88, decreased ETEC K88 adhesion in cells and did not cause cytotoxicity toward cells. Furthermore, biogenic MccJ25 protects against ETEC-induced barrier dysfunction by increasing the TEER, decreasing the LDH and promoting tight junction proteins (TJPs) by promoting the assembly of occludin and claudin-1 in the tight junction complex. Biogenic MccJ25 was further found to relieve inflammation responses through modulation of interleukine-6, IL-8 and tumor necrosis factor-α levels via inhibition of mitogen-activated protein kinase (MAPK) and nuclear factor κB activation. In summary, biogenic MccJ25 can protects against ETEC K88-induced intestinal damage and inflammatory response, recommend the hidden adoption of biogenic MccJ25 as a novel prophylactic agent to reduce pathogen infection in animals, food or humans.

Dimethyl fumarate reduces the risk of mycotoxins via improving intestinal barrier and microbiota

The effects of dimethyl fumarate (DMF) on mycotoxins and animal growth performance are well documented. However, its mechanism of anti-mildew effects is still unknown. The current study investigated how DMF detoxified the mycotoxin and improved the growth performance using BALB/c mice model, especially its effects on intestinal barrier function and gut micro-ecology. Our study also compared with the ultraviolet radiation (UR) treatment, a traditional anti-mildew control (TC). The results indicated that the DMF treatment had a lower contents of mycotoxin, better growth performance and improved mucosal morphology (P < 0.05), accompanied with the decreased intestinal permeability and the tighter gut barrier. Moreover, the efficiency of DMF was better than TC (P < 0.05). 16S rRNA gene sequence analysis revealed that the richness and diversity of bacteria was increased in DMF treatment. The most abundant OTUs belonged to Firmicutes and Bacteroidetes, and their changes in DMF were more moderate than the TC group, suggesting a more stable micro-ecology and the positive impact of DMF on the biodiversity of intestine. Specifically, the increased abundance of bacteria producing short-chain fatty acids (SCFAs), such as Gemella, Roseburia, Bacillus and Bacteroides in DMF group and prebiotics such as Lactobacillus in TC group, suggested a more healthier microbial composition and distribution. These findings supported that DMF had significant effects on animal's growth performance and intestinal barrier function by modulating the pathway of nutrient absorption and increasing the diversity and balance of gut microbes, which also illuminate that DMF is more efficient than traditional anti-mildew method.

Fungal Deoxynivalenol-Induced Enterocyte Distress Is Attenuated by Adulterated Adlay: In Vitro Evidences for Mucoactive Counteraction

Adlay is a cereal crop that has long been used as traditional herbal medicine and as a highly nourishing food. However, deoxynivalenol (DON), the most prevalent trichothecene mycotoxin worldwide, frequently spoils grains, including adlay, via fungal infection. On the basis of an assumption that the actions of DON in the gut could be modified by adlay consumption, we simulated the impacts of co-exposure in enterocytes and investigated the effectiveness of treatment with adlay for reducing the risk of DON-induced inflammation and epithelia barrier injury. In particular, adlay suppressed DON-induced pro-inflammatory signals such as mitogen-activated kinase transduction and the epidermal growth factor receptor-linked pathway. In addition to regulation of pro-inflammatory responses, adlay treatment interfered with DON-induced disruption of the epithelial barrier. Mechanistically, adlay could boost the activation of protein kinase C (PKC) and cytosolic translocation of human antigen R (HuR) protein, which played critical roles in the epithelial restitution, resulting in protection against disruption of enterocyte barrier integrity. Notably, DON abrogated the Ras homolog gene family member A GTPase-mediated actin cytoskeletal network, which was diminished by adlay treatment in PKC and HuR-dependent ways. Taken together, this study provides evidences for adlay-based attenuation of trichothecene-induced gut distress, implicating potential use of a new gut protector against enteropathogenic insults in diets.

Epithelial Cholesterol Deficiency Attenuates Human Antigen R-linked Pro-inflammatory Stimulation via an SREBP2-linked Circuit

Patients with chronic intestinal ulcerative diseases, such as inflammatory bowel disease, tend to exhibit abnormal lipid profiles, which may affect the gut epithelial integrity. We hypothesized that epithelial cholesterol depletion may trigger inflammation-checking machinery via cholesterol sentinel signaling molecules whose disruption in patients may aggravate inflammation and disease progression. In the present study, sterol regulatory element-binding protein 2 (SREBP2) as the cholesterol sentinel was assessed for its involvement in the epithelial inflammatory responses in cholesterol-depleted enterocytes. Patients and experimental animals with intestinal ulcerative injuries showed suppression in epithelial SREBP2. Moreover, SREBP2-deficient enterocytes showed enhanced pro-inflammatory signals in response to inflammatory insults, indicating regulatory roles of SREBP2 in gut epithelial inflammation. However, epithelial cholesterol depletion transiently induced pro-inflammatory chemokine expression regardless of the well known pro-inflammatory nuclear factor-κB signals. In contrast, cholesterol depletion also exerts regulatory actions to maintain epithelial homeostasis against excessive inflammation via SREBP2-associated signals in a negative feedback loop. Mechanistically, SREBP2 and its induced target EGR-1 were positively involved in induction of peroxisome proliferator-activated receptor γ (PPARγ), a representative anti-inflammatory transcription factor. As a crucial target of the SREBP2-EGR-1-PPARγ-associated signaling pathways, the mRNA stabilizer, human antigen R (HuR) was retained in nuclei, leading to reduced stability of pro-inflammatory chemokine transcripts. This mechanistic investigation provides clinical insights into protective roles of the epithelial cholesterol deficiency against excessive inflammatory responses via the SREBP2-HuR circuit, although the deficiency triggers transient pro-inflammatory signals.

Acquisition of Chemoresistance and Other Malignancy-related Features of Colorectal Cancer Cells Are Incremented by Ribosome-inactivating Stress

Colorectal cancer (CRC) as an environmental disease is largely influenced by accumulated epithelial stress from diverse environmental causes. We are exposed to ribosome-related insults, including ribosome-inactivating stress (RIS), from the environment, dietary factors, and medicines, but their physiological impacts on the chemotherapy of CRC are not yet understood. Here we revealed the effects of RIS on chemosensitivity and other malignancy-related properties of CRC cells. First, RIS led to bidirectional inhibition of p53-macrophage inhibitory cytokine 1 (MIC-1)-mediated death responses in response to anticancer drugs by either enhancing ATF3-linked antiapoptotic signaling or intrinsically inhibiting MIC-1 and p53 expression, regardless of ATF3. Second, RIS enhanced the epithelial-mesenchymal transition and biogenesis of cancer stem-like cells in an ATF3-dependent manner. These findings indicate that gastrointestinal exposure to RIS interferes with the efficacy of chemotherapeutics, mechanistically implying that ATF3-linked malignancy and chemoresistance can be novel therapeutic targets for the treatment of environmentally aggravated cancers.

PPARs: Protectors or Opponents of Myocardial Function?

Over 5 million people in the United States suffer from the complications of heart failure (HF), which is a rapidly expanding health complication. Disorders that contribute to HF include ischemic cardiac disease, cardiomyopathies, and hypertension. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family. There are three PPAR isoforms: PPARα, PPARγ, and PPARδ. They can be activated by endogenous ligands, such as fatty acids, as well as by pharmacologic agents. Activators of PPARs are used for treating several metabolic complications, such as diabetes and hyperlipidemia that are directly or indirectly associated with HF. However, some of these drugs have adverse effects that compromise cardiac function. This review article aims to summarize the current basic and clinical research findings of the beneficial or detrimental effects of PPAR biology on myocardial function.

Ribosomal alteration-derived signals for cytokine induction in mucosal and systemic inflammation: noncanonical pathways by ribosomal inactivation

Ribosomal inactivation damages 28S ribosomal RNA by interfering with its functioning during gene translation, leading to stress responses linked to a variety of inflammatory disease processes. Although the primary effect of ribosomal inactivation in cells is the functional inhibition of global protein synthesis, early responsive gene products including proinflammatory cytokines are exclusively induced by toxic stress in highly dividing tissues such as lymphoid tissue and epithelia. In the present study, ribosomal inactivation-related modulation of cytokine production was reviewed in leukocyte and epithelial pathogenesis models to characterize mechanistic evidence of ribosome-derived cytokine induction and its implications for potent therapeutic targets of mucosal and systemic inflammatory illness, particularly those triggered by organellar dysfunctions.

Novel regulatory action of ribosomal inactivation on epithelial Nod2-linked proinflammatory signals in two convergent ATF3-associated pathways

In response to excessive nucleotide-binding oligomerization domain-containing protein 2 (Nod2) stimulation caused by mucosal bacterial components, gut epithelia need to activate regulatory machinery to maintain epithelial homeostasis. Activating transcription factor 3 (ATF3) is a representative regulator in the negative feedback loop that modulates TLR-associated inflammatory responses. In the current study, the regulatory effects of ribosomal stress-induced ATF3 on Nod2-stimulated proinflammatory signals were assessed. Ribosomal inactivation caused persistent ATF3 expression that in turn suppressed proinflammatory chemokine production facilitated by Nod2. Decreased chemokine production was due to attenuation of Nod2-activated NF-κB and early growth response protein 1 (EGR-1) signals by ATF3. However, the underlying molecular mechanisms involve two convergent regulatory pathways. Although ATF3 induced by ribosomal inactivation regulated Nod2-induced EGR-1 expression epigenetically through the recruitment of histone deacetylase 1, NF-κB regulation was associated with posttranscriptional regulation by ATF3 rather than epigenetic modification. ATF3 induced by ribosomal inactivation led to the destabilization of p65 mRNA caused by nuclear entrapment of transcript-stabilizing human Ag R protein via direct interaction with ATF3. These findings demonstrate that ribosomal stress-induced ATF3 is a critical regulator in the convergent pathways between EGR-1 and NF-κB, which contributes to the suppression of Nod2-activated proinflammatory gene expression.

From the gut to the brain: journey and pathophysiological effects of the food-associated trichothecene mycotoxin deoxynivalenol

Mycotoxins are fungal secondary metabolites contaminating food and causing toxicity to animals and humans. Among the various mycotoxins found in crops used for food and feed production, the trichothecene toxin deoxynivalenol (DON or vomitoxin) is one of the most prevalent and hazardous. In addition to native toxins, food also contains a large amount of plant and fungal derivatives of DON, including acetyl-DON (3 and 15ADON), glucoside-DON (D3G), and potentially animal derivatives such as glucuronide metabolites (D3 and D15GA) present in animal tissues (e.g., blood, muscle and liver tissue). The present review summarizes previous and very recent experimental data collected in vivo and in vitro regarding the transport, detoxification/metabolism and physiological impact of DON and its derivatives on intestinal, immune, endocrine and neurologic functions during their journey from the gut to the brain.

Integrated stress response-altered pro-inflammatory signals in mucosal immune-related cells

Various cells are associated with the integrated stress response (ISR) that leads to translation arrest via phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2. Pathogenic insults or nutritional imbalance in the mucosal tissues including the intestinal, airway, and genitourinary epithelia can cause ISRs, which have been linked to different mucosal inflammatory responses and subsequent systemic diseases. In particular, translational arrest caused by the early recognition of luminal microbes as well as nutritional status allows the human body to mount appropriate responses and maintain homeostasis both at the cellular and systemic levels. However, an over- or reduced ISR can create pathogenic conditions such as inflammation and carcinogenesis. This present review explores the association between eIF2α kinase-linked pathways and mucosal or systemic pro-inflammatory signals activated by xenobiotic insults (such as ones caused by microbes or nutritional abnormalities). Understanding ISR-modulated cellular alterations will provide progressive insights into approaches for treating human mucosal inflammatory and metabolic disorders.

Two in-and-out modulation strategies for endoplasmic reticulum stress-linked gene expression of pro-apoptotic macrophage-inhibitory cytokine 1

Excessive and persistent insults during endoplasmic reticulum (ER) stress lead to apoptotic cell death that is implicated in a range of chronic inflammatory diseases and cancers. Macrophage inhibitory cytokine 1 (MIC-1), a member of the transforming growth factor-β superfamily, is diversely linked to the pathogenesis of cancer. To investigate the precise molecular mechanisms of MIC-1 gene regulation, ER stress and its related signals were studied in human colon cancer cells. Functionally, MIC-1 played pivotal roles in ER stress-linked apoptotic death, which was also influenced by C/EBP homologous protein, a well known apoptotic mediator of ER stress. ER stress enhanced MIC-1 mRNA stability instead of transcriptional activation, and there were two mechanistic translocations critical for mRNA stabilization. First, C/EBP homologous protein triggered protein kinase C-linked cytosolic translocation of the HuR/ELAVL1 (Elav-like RNA-binding protein 1) RNA-binding protein, which bound to and stabilized MIC-1 transcript. As the second critical in-and-out regulation, ER stress-activated ERK1/2 signals contributed to enhanced stabilization of MIC-1 transcript by controlling the extended holding of the nucleated mRNA in the stress granules fusing with the mRNA-decaying processing body. We propose that these two sequential in-and-out modulations can account for stabilized transcription and subsequent translation of pro-apoptotic MIC-1 gene in human cancer cells under ER stress.

LOC66273 isoform 2, a novel protein highly expressed in white adipose tissue, induces adipogenesis in 3T3-L1 cells

Obesity results in part from altered adipocyte metabolism and enhanced adipogenesis. However, the factors that influence insulin-independent differentiation of preadipocytes in response to excess intake of dietary energy remain poorly understood. Based on our recent finding that LOC66273 isoform 2 (LI2), a gene that encodes a novel Mth938 domain-containing protein, is highly expressed in white adipose tissues, we hypothesized that LI2 plays an important role in adipogenesis. Plasmid pcDNA3.1-LI2 was electroporated into 3T3-L1 preadipocytes to overexpress the LI2 protein. Synthetic siRNA was transfected into 3T3-L1 cells to knockdown endogenous LI2. Using constitutively active and potent siRNA against LI2, we determined cell morphology, cell viability, and adipocytic factors in 3T3-L1 preadipocytes. Our results indicated that LI2 was sufficient to drive preadipocyte differentiation via modulating the phosphorylation level and transcriptional activity of CREB, coincident with expression of several adipogenic regulators and mature adipocyte markers, without insulin treatment. In addition, overexpression of the LI2 protein inhibited preadipocyte growth, whereas knockdown of the LI2 protein resulted in preadipocyte apoptosis via caspase-3 activation during adipogenesis. These results indicated that LI2 might function to switch preadipocytes from proliferation to differentiation and to maintain the viability of preadipocytes during adipogenesis by regulating the caspase-3 pathway. Our findings highlight the importance of LI2 in the formation of new adipocytes, thus helping understand the mechanisms responsible for insulin-independent adipogenesis in mammals.

Mucosal injuries due to ribosome-inactivating stress and the compensatory responses of the intestinal epithelial barrier

Ribosome-inactivating (ribotoxic) xenobiotics are capable of using cleavage and modification to damage 28S ribosomal RNA, which leads to translational arrest. The blockage of global protein synthesis predisposes rapidly dividing tissues, including gut epithelia, to damage from various pathogenic processes, including epithelial inflammation and carcinogenesis. In particular, mucosal exposure to ribotoxic stress triggers integrated processes that are important for barrier regulation and re-constitution to maintain gut homeostasis. In the present study, various experimental models of the mucosal barrier were evaluated for their response to acute and chronic exposure to ribotoxic agents. Specifically, this review focuses on the regulation of epithelial junctions, epithelial transporting systems, epithelial cytotoxicity, and compensatory responses to mucosal insults. The primary aim is to characterize the mechanisms associated with the intestinal epithelial responses induced by ribotoxic stress and to discuss the implications of ribotoxic stressors as chemical modulators of mucosa-associated diseases such as ulcerative colitis and epithelial cancers.

Chronic Nod2 stimulation potentiates activating transcription factor 3 and paradoxical superinduction of epithelial proinflammatory chemokines by mucoactive ribotoxic stressors via RNA-binding protein human antigen R

Chronic exposure to gut bacteria and bacterial products including Nod2 ligands triggers homeostatic regulation in response to various mucosal insults. Activating transcription factor 3 (ATF3) is a negative regulator of proinflammatory cytokines via bacterial pattern recognition. On the assumption that ATF3 can be a critical modulator of epithelial inflammation, chronic stimulation of Nod2 was assessed for its effects on ATF3 and proinflammatory signals in response to mucosal ribotoxic insult, which is a critical etiological factor of human intestinal inflammatory disease. Muramyl dipeptide, the minimal moiety of bacterial peptidoglycan, is the Nod2 ligand, and pre-exposure to it enhanced ATF3 expression in ribotoxic stress-exposed human enterocytes. In terms of gene regulation, Nod2 preactivation potentiated ATF3 induction by enhancing stability of the ATF3 transcript, which was particularly linked to the regulation of the 3'-untranslated region of the human ATF3 gene. Moreover, chronic stimulation of Nod2 enhanced both the basal and the ribotoxic stress-stimulated cytoplasmic translocation of the HuR protein, which bound to and stabilized ATF3 messenger RNA (mRNA). Functionally, chronic stimulation of Nod2 also led to superinduction of proinflammatory chemokine genes by the mucoactive ribotoxic stress. However, the chemokine superinduction was not affected by ATF3 gene regulation although Nod2-triggered ATF3 had suppressive effects on the proinflammatory nuclear factor kappa B (NF-κB) signal. This paradoxical superinduction of chemokines was also mediated by enhanced mRNA stabilization by HuR protein in spite of ATF3-mediated suppression of NF-κB signal in human intestinal epithelial cells.