Polyamines and the intestinal tract

Role of polyamines in intestinal mucosal barrier function

The intestinal epithelium is a rapidly self-renewing tissue; the rapid turnover prevents the invasion of pathogens and harmful components from the intestinal lumen, preventing inflammation and infectious diseases. Intestinal epithelial barrier function depends on the epithelial cell proliferation and junctions, as well as the state of the immune system in the lamina propria. Polyamines, particularly putrescine, spermidine, and spermine, are essential for many cell functions and play a crucial role in mammalian cellular homeostasis, such as that of cell growth, proliferation, differentiation, and maintenance, through multiple biological processes, including translation, transcription, and autophagy. Although the vital role of polyamines in normal intestinal epithelial cell growth and barrier function has been known since the 1980s, recent studies have provided new insights into this topic at the molecular level, such as eukaryotic initiation factor-5A hypusination and autophagy, with rapid advances in polyamine biology in normal cells using biological technologies. This review summarizes recent advances in our understanding of the role of polyamines in regulating normal, non-cancerous, intestinal epithelial barrier function, with a particular focus on intestinal epithelial renewal, cell junctions, and immune cell differentiation in the lamina propria.

Effects of Tannin Supplementation in Diet on the Resistance to Ammonia Stress of Pacific White Shrimp Litopenaeus vannamei

Tannin (TA), as a natural phenolic compound with strong antioxidant activity, has been used as a feed additive for various animals. In this study, we fed a diet containing 800 mg/kg of tannin on Litopenaeus vannamei for 56 days and then subjected to acute ammonia stress for 48 hr to investigate the effect of dietary tannin on the ammonia stress response of L. vannamei through transcriptomic and metabolomic analysis. The transcriptome analysis indicated that ammonia stress-induced differential expression of 4,185 genes, while tannin-fed shrimp only had 964 differentially expressed genes. Compared with the TA_0 group, 59 pathways were significantly altered, and the pathways of "starch and sucrose metabolism," "retinol metabolism," "arachidonic acid metabolism," "lysosome," and "amino sugar and nucleotide sugar metabolism" were highly enriched in the TS_0 group. Compared with the TS_0 group, six pathways were significantly altered, and the pathways of "dilated cardiomyopathy," "complement and coagulation cascades," "cardiac muscle contraction," "fructose and mannose metabolism," "cGMP-PKG signaling pathway," and "beta-alanine metabolism" were significantly enriched in the TS_800 group. Metabolomic analysis showed that a total of 107 differential metabolites (DMs) were identified in the TS_0 vs. TA_0 group, while 75 DMs were identified in the TS_800 vs. TS_0 group. Based on KEGG annotation, it was found that a large amount of DM was significantly enriched in amino acid metabolism pathways in the TS_0 group, including "arginine and proline metabolism," "alanine, aspartic acid, and glutamic acid metabolism," "β-Alanine metabolism and tyrosine metabolism" indicated that tannins affect the metabolism of amino acids. The integration of DEGs and DMs indicates that dietary tannins highly alter the digestion and absorption functions of proteins, as well as the biosynthesis and metabolism of amino acids. This study provides new insights into the adaptation of Pacific white shrimp to ammonia stress and the addition of tannins to feed to enhance immune function.

The Roles of Polyamines in Intestinal Development and Function in Piglets

The gastrointestinal tract plays crucial roles in the digestion and absorption of nutrients, as well as in maintenance of a functional barrier. The development and maturation of the intestine is important for piglets to maintain optimal growth and health. Polyamines are necessary for the proliferation and growth of enterocytes, which play a key role in differentiation, migration, remodeling and integrity of the intestinal mucosa after injury. This review elaborates the development of the structure and function of the intestine of piglets during embryonic, suckling and weaning periods, the utilization and metabolism of polyamines in the intestine, as well as the role of polyamines in intestinal development and mucosal repair. The nutritional intervention to improve intestinal development and functions by modulating polyamine metabolism in piglets is also put forward. These results may help to promote the adaption to weaning in pigs and provide useful information for the development and health of piglets.

Lycibarbarspermidine L from the fruit of Lycium barbarum L. recovers intestinal barrier damage via regulating miR-195-3p

ETHNOPHARMACOLOGICAL RELEVANCE

The fruit of Lycium barbarum L. is widely employed with the traditional effect of tonic properties. According to the theory of traditional Chinese medicine, Gou Qi can be distributed in the meridian of stomach, as well as the liver and kidney, indicating its effect on the digestive system. Clinical studies found that Gou Qi enhanced gastrointestinal functions. Pharmacological research showed the extract of Lycium barbarum exhibiting a repaired effect on the intestine barrier. Lycibarbarspermidine L (LBS L), which belongs to polyamines, is separated from the fruit of Lycium barbarum. However, it is unknown whether LBS L can restore damaged intestinal barrier like other polyamines such as spermidine.

AIM OF THE STUDY

To elucidate the recovery effect of LBS L on damaged intestinal epithelium and its miRNA-related mechanism.

MATERIALS AND METHODS

IEC-6 cells were used in vitro to assess the therapeutic effect of LBS L on the injured intestine and the regulation of miR-195-3p. Spermidine (SPD) with intestinal mucosal repair effect was used as a positive control. Sprague Dawley (SD) rats were subjected to 48 h fasting to induce intestinal epithelial atrophy in vivo. To determine the therapeutic effect of LBS L on injured intestinal epithelium and explore the mechanism, the fasting model group rats were treated with LBS L (25 mg/kg) for 4 days.

RESULTS

Results in vitro showed that LBS L (10 μM) promoted cell proliferation and migration, affecting the S phase of the cell cycle. Western blot signals showed that LBS L raised the expression level of occludin. The miR-195-3p levels were decreased following LBS L treatment, which could be inversed by transfecting miR-195-3p mimic, demonstrating that LBS L inhibited miR-195-3p to improve cell growth. Results in vivo showed that LBS L could reverse the atrophic villi and inflammatory cell infiltration in the submucosa and restore miR-195-3p, occludin, and Ki67 levels in the intestine of mice in the fasting group.

CONCLUSIONS

LBS L restores injured intestinal epithelium by reducing the expression of miR-195-3p.

Stabilization of Cx43 mRNA via RNA-binding protein HuR regulated by polyamines enhances intestinal epithelial barrier function

Gut barrier dysfunction occurs commonly in patients with critical disorders, leading to the translocation of luminal toxic substances and bacteria to the bloodstream. Connexin 43 (Cx43) acts as a gap junction protein and is crucial for intercellular communication and the diffusion of nutrients. The levels of cellular Cx43 are tightly regulated by multiple factors, including polyamines, but the exact mechanism underlying the control of Cx43 expression remains largely unknown. The RNA-binding protein HuR regulates the stability and translation of target mRNAs and is involved in many aspects of intestinal epithelial pathobiology. Here we show that HuR directly bound to Cx43 mRNA via its 3'-untranslated region in intestinal epithelial cells (IECs) and this interaction enhanced Cx43 expression by stabilizing Cx43 mRNA. Depletion of cellular polyamines inhibited the [HuR/Cx43 mRNA] complex and decreased the level of Cx43 protein by destabilizing its mRNA, but these changes were prevented by ectopic overexpression of HuR. Polyamine depletion caused intestinal epithelial barrier dysfunction, which was reversed by ectopic Cx43 overexpression. Moreover, overexpression of checkpoint kinase 2 in polyamine-deficient cells increased the [HuR/Cx43 mRNA] complex, elevated Cx43 levels, and promoted barrier function. These findings indicate that Cx43 mRNA is a novel target of HuR in IECs and that polyamines regulate Cx43 mRNA stability via HuR, thus playing a critical role in the maintenance of intestinal epithelial barrier function.NEW & NOTEWORTHY The current study shows that polyamines stabilize the Cx43 mRNA via HuR, thus enhancing the function of the Cx43-mediated gap junction. These findings suggest that induced Cx43 by HuR plays a critical role in the process by which polyamines regulate intestinal epithelial barrier.

Digestibility and Palatability of the Diet and Intestinal Functionality of Dogs Fed a Blend of Yeast Cell Wall and Oregano Essential Oil

Feed additives, such as prebiotics and essential oils, are used in pet foods and can affect digestibility, palatability, and intestinal functionality of dogs. The combined effects of yeast cell wall and oregano essential oil on apparent total tract digestibility (ATTD) and palatability of diet, intestinal fermentation products, and fecal microbiota in dogs were analyzed. Eighteen adult dogs were fed for 20 days with three dry extruded diets for adult dogs: control (without the additive), a diet containing 1.5 kg/ton of yeast cell wall and oregano essential oil (1.5YCO), and a diet containing 3.0 kg/ton of yeast cell wall and oregano essential oil (3.0YCO). The inclusion of both levels of YCO reduced the intake ratio. The addition of 3.0YCO reduced the ATTD of dry matter, compared to the control group (p < 0.05). There were greater putrescine and cadaverine concentrations and lower histamine and ammonia (p < 0.05) in the feces of dogs fed 3.0YCO. In addition, fecal odor of dogs fed YCO was less fetid than the control group (p < 0.05). There was greater fecal bacterial diversity in dogs fed with both dietary concentrations of YCO evaluated (p < 0.05). Dogs fed 1.5YCO and 3.0YCO showed higher relative abundance of Blautia and Faecalibacterium and lower abundance of Streptococcus (p < 0.05) in the feces, in comparison to the control group. Given the modulation of microorganisms considered beneficial and the lower fecal concentrations of histamine, phenols, and ammonia, the YCO blend resulted in indicators of improvement of intestinal functionality in dogs.

Underlying beneficial effects of Rhubarb on constipation-induced inflammation, disorder of gut microbiome and metabolism

Background: Constipation is a common syndrome and a worldwide healthy problem. Constipation patients are becoming younger, with a 29.6% overall prevalence in children, which has captured significant attention because of its epigenetic rejuvenation and recurrent episodes. Despite the usage of rhubarb extract to relieve constipation, novel targets and genes implicated in target-relevant pathways with remarkable functionalities should still be sought for. Materials and methods: We established a reliable constipation model in C57B/6N male mice using intragastric administration diphenoxylate, and the eligible subjects received 600 mg/25 g rhubarb extract to alleviate constipation. Resultant constipation was morphological and genetically compared with the specimen from different groups. Results: Constipation mice exhibited thicker muscle layers, higher levels of cytokines, including IL-17 and IL-23, and lower content of IL-22. Bacterial abundance and diversity varied tremendously. Notably, the alterations were reversed following rhubarb extract treatment. Additionally, Constipation also had a substantial impact on short-chain fatty acids (SCFAs), medium- and long-chain fatty acids (MLCFAs), and the expression of SCFA receptors, GPR41 and GPR43. Conclusion: This thesis has provided insight that rhubarb extract promoted the flexibility of collagen fiber, reduced pro-inflammatory cytokines, enhanced anti-inflammatory cytokines, and maintained gut microflora balance with potential impacts on the fatty acid and polyamine metabolism.

miR-195 Regulates Intestinal Epithelial Restitution after Wounding by altering Actin-Related Protein-2 Translation

Early gut epithelial restitution reseals superficial wounds after acute injury, but the exact mechanism underlying this rapid mucosal repair remains largely unknown. MicroRNA-195 (miR-195) is highly expressed in the gut epithelium and involved in many aspects of mucosal pathobiology. Actin-related proteins (ARPs) are key components essential for stimulation of actin polymerization and regulate cell motility. Here we reported that miR-195 modulates early intestinal epithelial restitution by altering ARP-2 expression at the translation level. MiR-195 directly interacted with the ARP-2 mRNA, and ectopically overexpressed miR-195 decreased ARP-2 protein without effect on its mRNA content. In contrast, miR-195 silencing by transfection with the anti-miR-195 increased ARP-2 protein expression. Decreased ARP-2 levels by miR-195 were associated with an inhibition of early epithelial restitution, as indicated by a decrease in cell migration over the wounded area. Elevation of cellular ARP-2 levels by transfection with its transgene restored cell migration after wounding in cells overexpressing miR-195. Polyamines were found to decrease miR-195 abundance and enhanced ARP-2 translation, thus promoting epithelial restitution after wounding. Moreover, increasing the levels of miR-195 disrupted F-actin cytoskeleton organization, which was prevented by ARP2 overexpression. These results indicate that miR-195 inhibits early epithelial restitution by decreasing ARP-2 translation and that miR-195 expression is negatively regulated by cellular polyamines.

Polyamines in Gut Epithelial Renewal and Barrier Function

Polyamines regulate a variety of physiological functions and are involved in pathogenesis of diverse human diseases. The epithelium of the mammalian gut mucosa is a rapidly self-renewing tissue in the body, and its homeostasis is preserved through well-controlled mechanisms. Here, we highlight the roles of cellular polyamines in maintaining the integrity of the gut epithelium, focusing on the emerging evidence of polyamines in the regulation of gut epithelial renewal and barrier function. Gut mucosal growth depends on the available supply of polyamines to the dividing cells in the crypts, and polyamines are also essential for normal gut epithelial barrier function. Polyamines modulate expression of various genes encoding growth-associated proteins and intercellular junctions via distinct mechanisms involving RNA-binding proteins and noncoding RNAs. With the rapid advance of polyamine biology, polyamine metabolism and transport are promising therapeutic targets in our efforts to protect the gut epithelium and barrier function in patients with critical illnesses.

TRPC1-mediated Ca2+ signaling enhances intestinal epithelial restitution by increasing α4 association with PP2Ac after wounding

Gut epithelial restitution after superficial wounding is an important repair modality regulated by numerous factors including Ca²⁺ signaling and cellular polyamines. Transient receptor potential canonical-1 (TRPC1) functions as a store-operated Ca²⁺ channel in intestinal epithelial cells (IECs) and its activation increases epithelial restitution by inducing Ca²⁺ influx after acute injury. α4 is a multiple functional protein and implicated in many aspects of cell functions by modulating protein phosphatase 2A (PP2A) stability and activity. Here we show that the clonal populations of IECs stably expressing TRPC1 (IEC-TRPC1) exhibited increased levels of α4 and PP2A catalytic subunit (PP2Ac) and that TRPC1 promoted intestinal epithelial restitution by increasing α4/PP2Ac association. The levels of α4 and PP2Ac proteins increased significantly in stable IEC-TRPC1 cells and this induction in α4/PP2Ac complexes was accompanied by an increase in IEC migration after wounding. α4 silencing by transfection with siRNA targeting α4 (siα4) or PP2Ac silencing destabilized α4/PP2Ac complexes in stable IEC-TRPC1 cells and repressed cell migration over the wounded area. Increasing the levels of cellular polyamines by stable transfection with the Odc gene stimulated α4 and PP2Ac expression and enhanced their association, thus also promoting epithelial restitution after wounding. In contrast, depletion of cellular polyamines by treatment with α-difluoromethylornithine reduced α4/PP2Ac complexes and repressed cell migration. Ectopic overexpression of α4 partially rescued rapid epithelial repair in polyamine-deficient cells. These results indicate that activation of TRPC1-mediated Ca²⁺ signaling enhances cell migration primarily by increasing α4/PP2Ac associations after wounding and this pathway is tightly regulated by cellular polyamines.

Health-Promoting Effects of Dietary Polyamines

The purpose of this paper is to summarize the latest information on the various aspects of polyamines and their health benefits. In recent years, attempts to treat cancer by reducing elevated polyamines levels in cancer cells have been made, with some advancing to clinical trials. However, it has been reported since 2009 that polyamines extend the healthy life span of animals by inducing autophagy, protecting the kidneys and liver, improving cognitive function, and inhibiting the progression of heart diseases. As such, there is conflicting information regarding the relationship between polyamines and health. However, attempts to treat cancer by decreasing intracellular polyamines levels are a coping strategy to suppress the proliferation-promoting effects of polyamines, and a consensus is being reached that polyamine intake does not induce cancer in healthy individuals. To provide further scientific evidence for the health-promoting effects of polyamines, large-scale clinical studies involving multiple groups are expected in the future. It is also important to promote basic research on polyamine intake in animals, including elucidation of the polyamine balance between food, intestinal bacteria, and biosynthesis.

Investigation on Intestinal Proteins and Drug Metabolizing Enzymes in Simulated Microgravity Rats by a Proteomics Method

The present study aimed to investigate the change of intestinal mucosa proteins, especially the alteration of intestinal drug metabolizing enzymes (IDMEs) following 14-day simulated microgravity. Morey-Holton tail-suspension analog was used to simulate microgravity. Intestinal mucosa proteins of rats were determined by label-free quantitative proteomic strategy. A total of 335 differentially expressed proteins (DEPs) were identified, 190 DEPs were upregulated, and 145 DEPs were downregulated. According to bioinformatic analysis, most of DEPs exhibited hydrolase, oxidoreductase, transferase, ligase, or lyase catalytic activity. DEPs were mainly enriched in metabolic pathways, including metabolism of amino acid, glucose, and carbon. Moreover, 11 of DEPs were involved in exogenous drug and xenobiotics metabolism. Owing to the importance of IDMEs for the efficacy and safety of oral drugs, the expression of cytochrome P450 1A2 (CYP1A2), CYP2D1, CYP3A2, CYP2E1, alcohol dehydrogenase 1 (ADH1), and glutathione S-transferase mu 5 (GSTM5) in rat intestine mucosa was determined by Western-blot. The activity of ADH, aldehyde dehydrogenase (ALDH) and GST was evaluated. Compared with control rats, the expression of CYP1A2, CYP2D1, CYP3A2, and ADH1 in the simulated microgravity (SMG) group of rats were dramatically decreased by 33.16%, 21.93%, 48.49%, and 22.83%, respectively. GSTM5 was significantly upregulated by 53.14% and CYP2E1 expression did not show a dramatical change in SMG group rats. Moreover, 14-day SMG reduced ADH activity, while ALDH and GST activities was not altered remarkably. It could be concluded that SMG dramatically affected the expression and activity of some IDMEs, which might alter the efficacy or safety of their substrate drugs under microgravity. The present study provided some preliminary information on IDMEs under microgravity. It revealed the potential effect of SMG on intestinal metabolism, which may be helpful to understand the intestinal health of astronauts and medication use.

Polyamines polarized Th2/Th9 cell-fate decision by regulating GATA3 expression

Polyamines produced by both prokaryotes and eukaryotes are bioactive substances with pleiotropic effects. Accumulating evidence has demonstrated that polyamines contribute to anti-inflammatory responses by suppressing the expression of proinflammatory cytokines in mononuclear cells and macrophages. However, the effects of polyamines on CD4⁺ T cell responses remain to be elucidated. Here, we investigated the effect of polyamines on cell fate decisions of naïve CD4⁺ T cells in vitro. We found that endogenously generated polyamines are essential for the development of T helper 2 (Th2) cells. Treatment with DL-2-difluoromethylornithine (DFMO), an inhibitor of polyamine biosynthesis, diminished GATA3 expression in CD4⁺ T cells under Th2-skewed conditions. Supplementation of exogenous polyamines rescued GATA3 downregulation caused by DFMO treatment in CD4⁺ T cells. Transcriptome analysis revealed that deprivation of endogenous polyamines resulted in upregulated Th9-related genes, such as Il9, Irf4, and Batf3, even under the Th2-skewing conditions. Depletion of intracellular polyamines reduced GATA3 expression but increased IL-9-producing CD4⁺ T cells under both Th2 and Th9-skewing conditions. Furthermore, oral administration of DFMO increased IL-9-producing CD4⁺ T cells in small intestine in mice. Thus, our data indicate that polyamines play a critical role in the regulation of the Th2/Th9 balance.

Regulatory role of l-proline in fetal pig growth and intestinal epithelial cell proliferation

l-proline (Pro) is a precursor of ornithine, which is converted into polyamines via ornithine decarboxylase (ODC). Polyamines plays a key role in the proliferation of intestinal epithelial cells. The study investigated the effect of Pro on polyamine metabolism and cell proliferation on porcine enterocytes in vivo and in vitro. Twenty-four Huanjiang mini-pigs were randomly assigned into 1 of 3 groups and fed a basal diet that contained 0.77% alanine (Ala, iso-nitrogenous control), 1% Pro or 1% Pro + 0.0167% α-difluoromethylornithine (DFMO) from d 15 to 70 of gestation. The fetal body weight and number of fetuses per litter were determined, and the small and large intestines were obtained on d 70 ± 1.78 of gestation. The in vitro study was performed in intestinal porcine epithelial (IPEC-J2) cells cultured in Dulbecco's modified Eagle medium-high glucose (DMEM-H) containing 0 μmol/L Pro, 400 μmol/L Pro, or 400 μmol/L Pro + 10 mmol/L DFMO for 4 d. The results showed that maternal dietary supplementation with 1% Pro increased fetal weight; the protein and DNA concentrations of the fetal small intestine; and mRNA levels for potassium voltage-gated channel, shaker-related subfamily, member 1 (Kv1.1) in the fetal small and large intestines (P < 0.05). Supplementing Pro to either gilts or IPEC-J2 cells increased ODC protein abundances and polyamine concentrations in the fetal intestines and IPEC-J2 cells (P < 0.05). In comparison with the Pro group, the combined administration of Pro and DFMO reduced the expression of ODC protein and spermine concentration in the fetal intestine, as well as the concentrations of putrescine, spermidine and spermine in IPEC-J2 cells (P < 0.05). Meanwhile, the percentage of cells in the S-phase and the mRNA levels of proto-oncogenes c-fos and c-myc were increased in response to Pro supplementation, whereas depletion of cellular polyamines with DFMO increased tumor protein p53 (p53) mRNA levels (P < 0.05). Taken together, dietary supplementation with Pro improved fetal pig growth and intestinal epithelial cell proliferation via enhancing polyamine synthesis.

Microbial Metabolites and Intestinal Stem Cells Tune Intestinal Homeostasis

Microorganisms that colonize the gastrointestinal tract, collectively known as the gut microbiota, are known to produce small molecules and metabolites that significantly contribute to host intestinal development, functions, and homeostasis. Emerging insights from microbiome research reveal that gut microbiota-derived signals and molecules influence another key player maintaining intestinal homeostasis-the intestinal stem cell niche, which regulates epithelial self-renewal. In this review, the literature on gut microbiota-host crosstalk is surveyed, highlighting the effects of gut microbial metabolites on intestinal stem cells. The production of various classes of metabolites, their actions on intestinal stem cells are discussed and, finally, how the production and function of metabolites are modulated by aging and dietary intake is commented upon.

The Molecular and Physiological Effects of Protein-Derived Polyamines in the Intestine

Consumption of a high-protein diet increases protein entry into the colon. Colonic microbiota can ferment proteins, which results in the production of protein fermentation end-products, like polyamines. This review describes the effects of polyamines on biochemical, cellular and physiological processes, with a focus on the colon. Polyamines (mainly spermine, spermidine, putrescine and cadaverine) are involved in the regulation of protein translation and gene transcription. In this, the spermidine-derived hypusination modification of EIF5A plays an important role. In addition, polyamines regulate metabolic functions. Through hypusination of EIF5A, polyamines also regulate translation of mitochondrial proteins, thereby increasing their expression. They can also induce mitophagy through various pathways, which helps to remove damaged organelles and improves cell survival. In addition, polyamines increase mitochondrial substrate oxidation by increasing mitochondrial Ca2+-levels. Putrescine can even serve as an energy source for enterocytes in the small intestine. By regulating the formation of the mitochondrial permeability transition pore, polyamines help maintain mitochondrial membrane integrity. However, their catabolism may also reduce metabolic functions by depleting intracellular acetyl-CoA levels, or through production of toxic by-products. Lastly, polyamines support gut physiology, by supporting barrier function, inducing gut maturation and increasing longevity. Polyamines thus play many roles, and their impact is strongly tissue- and dose-dependent. However, whether diet-derived increases in colonic luminal polyamine levels also impact intestinal physiology has not been resolved yet.

Grain free diets for utility dogs during training work: Evaluation of the nutrient digestibility and faecal characteristics

Two different diets characterized by the absence of cereals or by the presence of conventional cereals were evaluated on the nutrient digestibility and faecal characteristics and faecal fermentative end-product concentrations of 8 neutered adult Labrador retrievers housed at the Regional Centre Helen Keller (Messina, Italy) during the training work for the service guide for the blind. Dogs (age = 17 ± 1 months, initial body weight [BW] = 26.3 ± 1 kg, and body condition score [BCS] = 4.5 ± 0.11) were divided into 2 homogeneous groups for sex (half males and half females). Dogs in the grain free (GF) group were fed a commercial diet characterized by the absence of grain cereals, and dogs in the control (CTR) group were fed a super-premium pet food characterized by conventional grains as the carbohydrate source. The trial lasted 84 d, preceded by a 7-d of adaption period. Physical examination, digestibility, and faecal characteristics were studied. The statistical model included the effects of diet (GF vs. CTR), time (from d 0 to 84, end of the trial) and the interaction (diet × time). The high-protein, low-carbohydrate dry diet (GF) offered higher apparent nutrient digestibility of protein (+10%; P = 0.002) and fat (+7%; P < 0.001) and more stable large intestinal fermentation of carbohydrate compared to the commercial high-carbohydrate dry diet, enabling dogs to use nutrients from the diet more efficiently and thus requiring less food (-13%) to satisfy their nutrient requirements, producing less excrement (-33%; P = 0.033), and reaching a higher final BW (+8%; P < 0.0001) and a higher final BCS (+15%; P = 0.003). Therefore, the GF diet appears the nutritional plan most suitable for these animals taking due account not only of the training work done by animals with their increased nutrient and energy needs, but also of the gastrointestinal disorders consequent to stress coming from work and life in kennels, which cause in the Labrador retrievers an unusual weight loss.

miR-222 represses expression of zipcode binding protein-1 and phospholipase C-γ1 in intestinal epithelial cells

Both zipcode binding protein-1 (ZBP1) and phospholipase C-γ1 (PLCγ1) are intimately involved in many aspects of early intestinal mucosal repair after acute injury, but the exact mechanisms that control their cellular abundances remain largely unknown. The present study shows that microRNA-222 (miR-222) interacts with the mRNAs encoding ZBP1 and PLCγ1 and regulates ZBP1 and PLCγ1 expression in intestinal epithelial cells (IECs). The biotinylated miR-222 bound specifically to the ZBP1 and PLCγ1 mRNAs in IECs. Ectopically expressed miR-222 precursor destabilized the ZBP1 and PLCγ1 mRNAs and consequently lowered the levels of cellular ZBP1 and PLCγ1 proteins. Conversely, decreasing the levels of cellular miR-222 by transfection with its antagonism increased the stability of the ZBP1 and PLCγ1 mRNAs and increased the levels of ZBP1 and PLCγ1 proteins. Overexpression of miR-222 also inhibited cell migration over the wounded area, which was partially abolished by overexpressing ZBP1 and PLCγ1. Furthermore, prevention of the increased levels of ZBP1 and PLCγ1 in the miR-222-silenced cells by transfection with specific small interfering RNAs targeting ZBP1 or PLCγ1 mRNA inhibited cell migration after wounding. These findings indicate that induced miR-222 represses expression of ZBP1 and PLCγ1 at the posttranscriptional level, thus inhibiting IEC migration during intestinal epithelial restitution after wounding.

What We Know and What We Need to Know about Aromatic and Cationic Biogenic Amines in the Gastrointestinal Tract

Biogenic amines derived from basic and aromatic amino acids (B/A-BAs), polyamines, histamine, serotonin, and catecholamines are a group of molecules playing essential roles in many relevant physiological processes, including cell proliferation, immune response, nutrition and reproduction. All these physiological effects involve a variety of tissue-specific cellular receptors and signalling pathways, which conforms to a very complex network that is not yet well-characterized. Strong evidence has proved the importance of this group of molecules in the gastrointestinal context, also playing roles in several pathologies. This work is based on the hypothesis that integration of biomedical information helps to reach new translational actions. Thus, the major aim of this work is to combine scientific knowledge on biomolecules, metabolism and physiology of the main B/A-BAs involved in the pathophysiology of the gastrointestinal tract, in order to point out important gaps in information and other facts deserving further research efforts in order to connect molecular information with pathophysiological observations.

Chemotaxis of Escherichia coli to major hormones and polyamines present in human gut

The microorganisms in the gastrointestinal (GI) tract can influence the metabolism, immunity, and behavior of animal hosts. Increasing evidence suggests that communication between the host and the microbiome also occurs in the opposite direction, with hormones and other host-secreted compounds being sensed by microorganisms. Here, we addressed one key aspect of the host–microbe communication by studying chemotaxis of a model commensal bacterium, Escherichia coli, to several compounds present abundantly in the GI tract, namely catecholamines, thyroid hormones, and polyamines. Our results show that E. coli reacts to five out of ten analyzed chemicals, sensing melatonin, and spermidine as chemorepellents and showing mixed responses to dopamine, norepinephrine and 3,4-dihydroxymandelic acid. The strongest repellent response was observed for the polyamine spermidine, and we demonstrate that this response involves the low-abundance chemoreceptor Trg and the periplasmic binding protein PotD of the spermidine uptake system. The chemotactic effects of the tested compounds apparently correlate with their influence on growth and their stability in the GI tract, pointing to the specificity of the observed behavior. We hypothesize that the repellent responses observed at high concentrations of chemoeffective compounds might enable bacteria to avoid harmful levels of hormones and polyamines in the gut and, more generally, antimicrobial activities of the mucous layer.

β-PIX plays an important role in regulation of intestinal epithelial restitution by interacting with GIT1 and Rac1 after wounding

Early gut mucosal restitution is a process by which intestinal epithelial cells (IECs) migrate over the wounded area, and its defective regulation occurs commonly in various critical pathological conditions. This rapid reepithelialization is mediated by different activating small GTP-binding proteins, but the exact mechanism underlying this process remains largely unknown. Recently, it has been reported that interaction between p21-activated kinase-interacting exchange factor (β-PIX) and G protein-coupled receptor kinase-interacting protein 1 (GIT1) activates small GTPases and plays an important role in the regulation of cell motility. Here, we show that induced association of β-PIX with GIT1 is essential for the stimulation of IEC migration after wounding by activating Rac1. Levels of β-PIX and GIT1 proteins and their association in differentiated IECs (line of IEC-Cdx2L1) were much higher than those observed in undifferentiated IECs (line of IEC-6), which was associated with an increase in IEC migration after wounding. Decreased levels of endogenous β-PIX by its gene-silencing destabilized β-PIX/GIT1 complexes, repressed Rac1 activity and inhibited cell migration over the wounded area. In contrast, ectopic overexpression of β-PIX increased the levels of β-PIX/GIT1 complexes, stimulated Rac1 activity, and enhanced intestinal epithelial restitution. Increased levels of cellular polyamines also stimulated β-PIX/GIT1 association, increased Rac1 activity, and promoted the epithelial restitution. Moreover, polyamine depletion decreased cellular abundances of β-PIX/GIT1 complex and repressed IEC migration after wounding, which was rescued by ectopic overexpression of β-PIX or GIT1. These results indicate that β-PIX/GIT1/Rac1 association is necessary for stimulation of IEC migration after wounding and that this signaling pathway is tightly regulated by cellular polyamines. NEW & NOTEWORTHY Our current study demonstrates that induced association of β-PIX with GIT1 is essential for the stimulation of intestinal epithelial restitution by activating Rac1, and this signaling pathway is tightly regulated by cellular polyamines.

Microbiota in anorexia nervosa: The triangle between bacterial species, metabolites and psychological tests

Anorexia nervosa (AN) is a psychiatric disease with devastating physical consequences, with a pathophysiological mechanism still to be elucidated. Metagenomic studies on anorexia nervosa have revealed profound gut microbiome perturbations as a possible environmental factor involved in the disease. In this study we performed a comprehensive analysis integrating data on gut microbiota with clinical, anthropometric and psychological traits to gain new insight in the pathophysiology of AN. Fifteen AN women were compared with fifteen age-, sex- and ethnicity-matched healthy controls. AN diet was characterized by a significant lower energy intake, but macronutrient analysis highlighted a restriction only in fats and carbohydrates consumption. Next generation sequencing showed that AN intestinal microbiota was significantly affected at every taxonomic level, showing a significant increase of Enterobacteriaceae, and of the archeon Methanobrevibacter smithii compared with healthy controls. On the contrary, the genera Roseburia, Ruminococcus and Clostridium, were depleted, in line with the observed reduction in AN of total short chain fatty acids, butyrate, and propionate. Butyrate concentrations inversely correlated with anxiety levels, whereas propionate directly correlated with insulin levels and with the relative abundance of Roseburia inulinivorans, a known propionate producer. BMI represented the best predictive value for gut dysbiosis and metabolic alterations, showing a negative correlation with Bacteroides uniformis (microbiota), with alanine aminotransferase (liver function), and with psychopathological scores (obsession-compulsion, anxiety, and depression), and a positive correlation with white blood cells count. In conclusion, our findings corroborate the hypothesis that the gut dysbiosis could take part in the AN neurobiology, in particular in sustaining the persistence of alterations that eventually result in relapses after renourishment and psychological therapy, but causality still needs to be proven.

c-Jun enhances intestinal epithelial restitution after wounding by increasing phospholipase C-γ1 transcription

c-Jun is an activating protein 1 (AP-1) transcription factor and implicated in many aspects of cellular functions, but its exact role in the regulation of early intestinal epithelial restitution after injury remains largely unknown. Phospholipase C-γ1 (PLCγ1) catalyzes hydrolysis of phosphatidylinositol 4,5 biphosphate into the second messenger diacylglycerol and inositol 1,4,5 triphosphate, coordinates Ca²⁺ store mobilization, and regulates cell migration and proliferation in response to stress. Here we reported that c-Jun upregulates PLCγ1 expression and enhances PLCγ1-induced Ca²⁺ signaling, thus promoting intestinal epithelial restitution after wounding. Ectopically expressed c-Jun increased PLCγ1 expression at the transcription level, and this stimulation is mediated by directly interacting with AP-1 and CCAAT-enhancer-binding protein (C/EBP) binding sites that are located at the proximal region of the rat PLCγ1 promoter. Increased levels of PLCγ1 by c-Jun elevated cytosolic free Ca²⁺ concentration and stimulated intestinal epithelial cell migration over the denuded area after wounding. The c-Jun-mediated PLCγ1/Ca²⁺ signal also plays an important role in polyamine-induced cell migration after wounding because increased c-Jun rescued Ca²⁺ influx and cell migration in polyamine-deficient cells. These findings indicate that c-Jun induces PLCγ1 expression transcriptionally and enhances rapid epithelial restitution after injury by activating Ca²⁺ signal.

Health relevance of intestinal protein fermentation in young pigs

The physiological role of the gastrointestinal microbiota has become an important subject of nutrition research in pigs in the past years, and the importance of intestinal microbial activity in the etiology of disease is doubtless. This review summarizes the recent knowledge related to the microbial ecology of protein fermentation and the appearance of protein-derived metabolites along the pig intestine. The amount of fermentable protein depends on factors such as dietary protein concentration, protein digestibility due to secondary or tertiary structure, the interaction with dietary compounds or anti-nutritional factors, and the secretion of endogenous proteins into the gut lumen. High protein diets increase the luminal concentrations and epithelial exposure to putatively toxic metabolites and increase the risk for post-weaning diarrhea, but the mechanisms are not yet clarified. Although the use of fermentable carbohydrates to reduce harmful protein-derived metabolites in pigs is well-established, recent studies suggest that the inclusion of fermentable carbohydrates into diets with low protein digestibility or high dietary protein level may not ameliorate all negative effects with regard to epithelial response. Based on the current knowledge, the use of diets with low levels of high-quality protein may help to reduce the risk for intestinal disease in young pigs.

Oral administration of putrescine and proline during the suckling period improves epithelial restitution after early weaning in piglets

Polyamines are necessary for normal integrity and the restitution after injury of the gastrointestinal epithelium. The objective of this study was to investigate the effects of oral administration of putrescine and proline during the suckling period on epithelial restitution after early weaning in piglets. Eighteen neonatal piglets (Duroc × Landrace × Large Yorkshire) from 3 litters (6 piglets per litter) were assigned to 3 groups, representing oral administration with an equal volume of saline (control), putrescine (5 mg/kg BW), and proline (25 mg/kg BW) twice daily from d 1 to weaning at 14 d of age. Plasma and intestinal samples were obtained 3 d after weaning. The results showed that oral administration of putrescine or proline increased the final BW and ADG of piglets compared with the control (P < 0.05). Proline treatment decreased plasma D-lactate concentration but increased the villus height in the jejunum and ileum, as well as the percentage of proliferating cell nuclear antigen (PCNA) positive cells and alkaline phosphatase (AKP) activity in the jejunal mucosa (P < 0.05). The protein expressions for zonula occludens (ZO-1), occludin, and claudin-3 (P < 0.05) but not mRNA were increased in the jejunum of putrescine- and proline-treated piglets compared with those of control piglets. The voltage-gated K+ channel (Kv) 1.1 protein expression in the jejunum of piglets administrated with putrescine and the Kv1.5 mRNA and Kv1.1 protein levels in the ileum of piglets administrated with proline were greater than those in control piglets (P < 0.05). These findings indicate that polyamine or its precursor could improve mucosal proliferation, intestinal morphology, as well as tight junction and potassium channel protein expressions in early-weaned piglets, with implications for epithelial restitution and barrier function after stress injury.

RhoA enhances store-operated Ca2+ entry and intestinal epithelial restitution by interacting with TRPC1 after wounding

Early mucosal restitution occurs as a consequence of epithelial cell migration to resealing of superficial wounds after injury. Our previous studies show that canonical transient receptor potential-1 (TRPC1) functions as a store-operated Ca(2+) channel (SOC) in intestinal epithelial cells (IECs) and plays an important role in early epithelial restitution by increasing Ca(2+) influx. Here we further reported that RhoA, a small GTP-binding protein, interacts with and regulates TRPC1, thus enhancing SOC-mediated Ca(2+) entry (SOCE) and epithelial restitution after wounding. RhoA physically associated with TRPC1 and formed the RhoA/TRPC1 complexes, and this interaction increased in stable TRPC1-transfected IEC-6 cells (IEC-TRPC1). Inactivation of RhoA by treating IEC-TRPC1 cells with exoenzyme C3 transferase (C3) or ectopic expression of dominant negative RhoA (DNMRhoA) reduced RhoA/TRPC1 complexes and inhibited Ca(2+) influx after store depletion, which was paralleled by an inhibition of cell migration over the wounded area. In contrast, ectopic expression of wild-type (WT)-RhoA increased the levels of RhoA/TRPC1 complexes, induced Ca(2+) influx through activation of SOCE, and promoted cell migration after wounding. TRPC1 silencing by transfecting stable WT RhoA-transfected cells with siRNA targeting TRPC1 (siTRPC1) reduced SOCE and repressed epithelial restitution. Moreover, ectopic overexpression of WT-RhoA in polyamine-deficient cells rescued the inhibition of Ca(2+) influx and cell migration induced by polyamine depletion. These findings indicate that RhoA interacts with and activates TRPC1 and thus stimulates rapid epithelial restitution after injury by inducing Ca(2+) signaling.

The effects of polyamines on human colonic mucosal function

Electrogenic ion transport in human colon is a surrogate marker for colonic mucosal function, and may be manipulated by a variety of hormonal, neural, immune and paracrine mediators. Polyamines are present in vast quantities in the colonic lumen and appear to be integral to cellular function. This study explores some of the mechanisms of polyamine action on colonic tissue through study of their effects on differential secretory pathways, as well as examining their actions on intracellular cAMP and Ca(2+) accumulation. Human colonic mucosa was mounted in Ussing chambers and treated with polyamines (spermine, spermidine and putrescine) with changes in ion transport recorded. In separate experiments colonic crypts were treated with polyamines and intracellular cAMP levels determined by ELISA and intracellular calcium concentrations were quantified by fluorescent imaging. Polyamines at physiological concentrations (1mM) exert no effects on basal mucosal chloride secretion or transepithelial electrical resistance. Polyamines inhibit electrogenic ion secretion as stimulated by forskolin (cAMP-mediated), but not carbachol (Ach-mediated). All the polyamines used in this study inhibited intracellular cAMP accumulation, according to potency (spermine>spermidine>putrescine). Spermine increased intracellular Ca(2+) in a PKC-dependent manner, likely due to its effects on the extracellular calcium-sensing receptor (CaSR). Polyamines act to prevent cAMP-mediated Cl(-) hypersecretion in the colon, acting through CaSR to inhibit PKC-mediated [Ca(2+)]i release from intracellular stores.

Modulation by miR-29b of intestinal epithelium homoeostasis through the repression of menin translation

Menin regulates distinct cellular functions by regulating gene transcription through its interaction with partner transcription factors, but the exact mechanisms that control menin levels remain largely unknown. In the present study we report that Men1 mRNA, encoding menin, is a novel target of miR-29b and that miR-29b/Men1 mRNA association regulates menin expression post-transcriptionally in rat intestinal epithelial cells (IECs). Overexpression of a miR-29b precursor lowered the levels of Men1 mRNA modestly, but reduced new synthesis of menin robustly; conversely, antagonism of miR-29b enhanced menin protein synthesis and steady-state levels. The repressive effect of miR-29b on menin expression was mediated through a single binding site in the coding region of Men1 mRNA, because point mutation of this site prevented miR-29b-induced repression of menin translation. Increasing cellular polyamines due to overexpression of ornithine decarboxylase (ODC) enhanced menin translation by reducing miR-29b, whereas polyamine depletion by inhibiting ODC increased it, thus suppressing menin expression. Moreover, an increase in menin abundance in an miR-29b-silenced population of IECs led to increased sensitivity to apoptosis, which was prevented by silencing menin. These findings indicate that miR-29b represses translation of Men1 mRNA, in turn affecting intestinal epithelial homoeostasis by altering IEC apoptosis.

Hessian fly larval feeding triggers enhanced polyamine levels in susceptible but not resistant wheat

BACKGROUND

Hessian fly (Mayetiola destructor), a member of the gall midge family, is one of the most destructive pests of wheat (Triticum aestivum) worldwide. Probing of wheat plants by the larvae results in either an incompatible (avirulent larvae, resistant plant) or a compatible (virulent larvae, susceptible plant) interaction. Virulent larvae induce the formation of a nutritive tissue, resembling the inside surface of a gall, in susceptible wheat. These nutritive cells are a rich source of proteins and sugars that sustain the developing virulent Hessian fly larvae. In addition, on susceptible wheat, larvae trigger a significant increase in levels of amino acids including proline and glutamic acid, which are precursors for the biosynthesis of ornithine and arginine that in turn enter the pathway for polyamine biosynthesis.

RESULTS

Following Hessian fly larval attack, transcript abundance in susceptible wheat increased for several genes involved in polyamine biosynthesis, leading to higher levels of the free polyamines, putrescine, spermidine and spermine. A concurrent increase in polyamine levels occurred in the virulent larvae despite a decrease in abundance of Mdes-odc (ornithine decarboxylase) transcript encoding a key enzyme in insect putrescine biosynthesis. In contrast, resistant wheat and avirulent Hessian fly larvae did not exhibit significant changes in transcript abundance of genes involved in polyamine biosynthesis or in free polyamine levels.

CONCLUSIONS

The major findings from this study are: (i) although polyamines contribute to defense in some plant-pathogen interactions, their production is induced in susceptible wheat during interactions with Hessian fly larvae without contributing to defense, and (ii) due to low abundance of transcripts encoding the rate-limiting ornithine decarboxylase enzyme in the larval polyamine pathway the source of polyamines found in virulent larvae is plausibly wheat-derived. The activation of the host polyamine biosynthesis pathway during compatible wheat-Hessian fly interactions is consistent with a model wherein the virulent larvae usurp the polyamine biosynthesis machinery of the susceptible plant to acquire nutrients required for their own growth and development.

Dietary fibre and crude protein: impact on gastrointestinal microbial fermentation characteristics and host response

The role of the gastrointestinal tract microbiota in animal health and nutrition has become the subject of intensive research. Carbohydrates and crude protein are major components of swine diets and numerous studies have been performed looking at the effect of inclusion of dietary fibre with possible functional properties. In recent years, our understanding of the diversity and functionality of the gastrointestinal tract microbiota has increased further enabling the possibility for their targeted modulation. However, favouring potential beneficial bacteria, inhibiting possible pathogens or promotion of the formation of desired metabolites, is complex and underlies many factors and uncertainties. Approaches targeting this complex ecosystem (and discussed in this review) include the utilisation of fermentable carbohydrates such as resistant starch, cereal 1–3/1–4 β-glucans, arabinoxylans, inulin or other sources from legumes and industrial by-products. In addition, strategies regarding protein level and the protein : carbohydrate ratio are discussed briefly. Results are both promising and sometimes rather disillusioning considering the dietary concentrations needed to show biologically relevant effects. Deriving recommendations for an optimal inclusion rate of dietary fibre for weaning, growing pigs and sows and maximum levels for dietary crude protein may be one of the main challenges in the near future in the swine industry.

Caveolin-1 enhances rapid mucosal restitution by activating TRPC1-mediated Ca2+ signaling

Early rapid mucosal restitution occurs as a consequence of epithelial cell migration to reseal superficial wounds, a process independent of cell proliferation. Our previous studies revealed that the canonical transient receptor potential-1 (TRPC1) functions as a store-operated Ca(2+) channel (SOCs) in intestinal epithelial cells (IECs) and regulates epithelial restitution after wounding, but the exact mechanism underlying TRPC1 activation remains elusive. Caveolin-1 (Cav1) is a major component protein that is associated with caveolar lipid rafts in the plasma membrane and was recently identified as a regulator of store-operated Ca(2+) entry (SOCE). Here, we showed that Cav1 plays an important role in the regulation of mucosal restitution by activating TRPC1-mediated Ca(2+) signaling. Target deletion of Cav1 delayed gastric mucosal repair after exposure to hypertonic NaCl in mice, although it did not affect total levels of TRPC1 protein. In cultured IECs, Cav1 directly interacted with TRPC1 and formed Cav1/TRPC1 complex as measured by immunoprecipitation assays. Cav1 silencing in stable TRPC1-transfected cells by transfection with siCav1 reduced SOCE without effect on the level of resting [Ca(2+)]cyt. Inhibition of Cav1 expression by siCav1 and subsequent decrease in Ca(2+) influx repressed epithelial restitution, as indicated by a decrease in cell migration over the wounded area, whereas stable ectopic overexpression of Cav1 increased Cav1/TRPC1 complex, induced SOCE, and enhanced cell migration after wounding. These results indicate that Cav1 physically interacts with and activates TRPC1, thus stimulating TRPC1-mediated Ca(2+) signaling and rapid mucosal restitution after injury.

Association of germ-free mice with a simplified human intestinal microbiota results in a shortened intestine

Genetic, nutritional, and gut microbiota-derived factors have been proposed to play a role in the development of the whole intestine that is around 40% longer in PRM/Alf mice compared with other mouse strains. The PRM/Alf genotype explains 60% of this length difference. The remaining 40% are due to a maternal effect that could depend on the gut microbiota transmitted by the mother to their pups. Germ-free PRM/Alf mice and C3H/He mice were associated with a simplified human microbiota (SIHUMI) to study its impact on gut length. The small intestines of the SIHUMI-associated mice were 16.4% (PRM/Alf) and 9.7% (C3H/He) shorter than those of the corresponding germ-free counterparts. Temporal temperature gradient gel electrophoresis and quantitative real-time PCR revealed differences in microbiota composition between both SIHUMI-associated mouse strains. Anaerostipes caccae was one log lower in PRM/Alf mice than in C3H/He mice. Since polyamines and short-chain fatty acids (SCFAs) are important intestinal growth factors, their concentrations were explored. Cecal concentrations of putrescine, spermine, spermidine, and N-acetylspermine were 1.5-fold, 3.7-fold, 2.2-fold, and 1.4-fold higher, respectively, in the SIHUMI-C3H/He mice compared with the SIHUMI-PRM/Alf mice. In addition, cecal acetate, propionate, and butyrate concentrations in SIHUMI-C3H/He mice were 1.4-fold, 1.1-fold, and 2.1-fold higher, respectively, than in SIHUMI-PRM/Alf mice. These results indicate that polyamines and SCFAs did not promote gut lengthening in any of the two mouse strains. This suggests that as yet unknown factors provided by the SIHUMI prevented gut lengthening in the SIHUMI-associated mice compared with the germfree mice.

Inhibition of Smurf2 translation by miR-322/503 modulates TGF-β/Smad2 signaling and intestinal epithelial homeostasis

Smurf2 is an E3 ubiquitin ligase that regulates TGF-β/Smad signaling and is implicated in a wide variety of cellular responses. miR-322 and miR-503 repress Smurf2 translation and thus modulate TGF-β/Smad2 signaling and intestinal epithelial homeostasis.

Smad ubiquitin regulatory factor 2 (Smurf2) is an E3 ubiquitin ligase that regulates transforming growth factor β (TGF-β)/Smad signaling and is implicated in a wide variety of cellular responses, but the exact mechanisms that control Smurf2 abundance are largely unknown. Here we identify microRNA-322 (miR-322) and miR-503 as novel factors that regulate Smurf2 expression posttranscriptionally. Both miR-322 and miR-503 interact with Smurf2 mRNA via its 3′-untranslated region (UTR) and repress Smurf2 translation but do not affect total Smurf2 mRNA levels. Studies using heterologous reporter constructs reveal a greater repressive effect of miR-322/503 through a single binding site in the Smurf2 3′-UTR, whereas point mutation of this site prevents miR-322/503–induced repression of Smurf2 translation. Increased levels of endogenous Smurf2 via antagonism of miR-322/503 inhibits TGF-β–induced Smad2 activation by increasing degradation of phosphorylated Smad2. Furthermore, the increase in Smurf2 in intestinal epithelial cells (IECs) expressing lower levels of miR-322/503 is associated with increased resistance to apoptosis, which is abolished by Smurf2 silencing. These findings indicate that miR-322/503 represses Smurf2 translation, in turn affecting intestinal epithelial homeostasis by altering TGF-β/Smad2 signaling and IEC apoptosis.

Increased bacterial putrescine has no impact on gut morphology and physiology in gnotobiotic adolescent mice

Gut bacteria influence host anatomy and physiology. It has been proposed that bacterial metabolites including polyamines are responsible for intestinal maturation and mucosal growth. We have hypothesised that bacterially produced polyamines act as trophic factors and thereby influence large intestinal crypt depth and thickness of the different gut layers. For that purpose, germ-free mice were associated with two different microbial consortia. One group was colonised with a simplified human microbiota (SIHUMI). The second group was associated with SIHUMI + Fusobacterium varium (SIHUMI + Fv), which is known to produce high amounts of polyamines. Polyamine concentrations were measured by HPLC and morphological parameters were determined microscopically. Germ-free and conventional mice served as controls. The caecal putrescine concentration of the SIHUMI + Fv was 61.8 μM (47.6-75.5 μM), whereas that of conventional and SIHUMI mice was 28.8 μM (1.3-41.7 μM) and 24.5 μM (16.8-29.1 μM), respectively. The caecal putrescine concentration of germ-free mice was only 0.6 μM (0-1.0 μM). Caecal crypt depth and thickness of the different caecal layers revealed no significant differences between SIHUMI and SIHUMI + Fv mice. However, the crypt depth in the caeca of conventional, SIHUMI and SIHUMI + Fv mice was increased by 48.6% (P<0.001), 39.7% (P<0.001) and 28.5% (P<0.05), respectively, compared to germ-free mice. These findings indicate that increased intestinal putrescine concentrations do not influence gut morphology in our gnotobiotic adolescent mice.

Resembling breast milk: influence of polyamine-supplemented formula on neonatal BALB/cOlaHsd mouse microbiota

Infant microbiota is influenced by numerous factors, such as delivery mode, environment, prematurity and diet (breast milk or formula). In addition to its nutritional value, breast milk contains bioactive substances that drive microbial colonisation and support immune system development, which are usually not present in infant formulas. Among these substances, polyamines have been described to be essential for intestinal and immune functions in newborns. However, their effect on the establishment of microbiota remains unclear. Therefore, the aim of the present study was to ascertain whether an infant formula supplemented with polyamines has an impact on microbial colonisation by modifying it to resemble that in breast-fed neonatal BALB/c mice. In a 4 d intervention, a total of sixty pups (14 d old) were randomly assigned to the following groups: (1) breast-fed group; (2) non-enriched infant formula-fed group; (3) three different groups fed an infant formula enriched with increasing concentrations of polyamines (mixture of putrescine, spermidine and spermine), following the proportions found in human milk. Microbial composition in the contents of the oral cavity, stomach and small and large intestines was analysed by quantitative PCR targeted at fourteen bacterial genera and species. Significantly different (P< 0·05) microbial colonisation patterns were observed in the entire gastrointestinal tract of the breast-fed and formula-fed mice. In addition, our findings demonstrate that supplementation of polyamines regulates the amounts of total bacteria,Akkermansia muciniphila,Lactobacillus,Bifidobacterium,Bacteroides–PrevotellaandClostridiumgroups to levels found in the breast-fed group. Such an effect requires further investigation in human infants, as supplementation of an infant formula with polyamines might contribute to healthy gastrointestinal tract development.

Aliphatic polyamines in physiology and diseases

Aliphatic polyamines are a family of polycationic molecules derived from decarboxylation of the amino acid ornithine that classically comprise three molecules: putrescine, spermidine and spermine. In-cell polyamine homeostasis is tightly controlled at key steps of cell metabolism. Polyamines are involved in an array of cellular functions from DNA stabilization, and regulation of gene expression to ion channel function and, particularly, cell proliferation. As such, aliphatic polyamines play an essential role in rapidly dividing cells such as in the immune system and digestive tract. Because of their role in cell proliferation, polyamines are also involved in carcinogenesis, prompting intensive research into polyamine metabolism as a target in cancer therapy. More recently, another aliphatic polyamine, agmatine, the decarboxylated derivative of arginine, has been identified as a neurotransmitter in mammals, and investigations have focused on its effects in the CNS, notably as a neuroprotector in brain injury.

Effects of polyamines on Vibrio cholerae virulence properties

Vibrio cholerae is the causative agent of the severe enteric disease cholera. To cause cholera the bacterium must be able to synthesize both cholera toxin (CT) and toxin-coregulated pilus (TCP) which mediates autoagglutination and is required for colonization of the small intestine. Only a few environmental signals have been shown to regulate V. cholerae virulence gene expression. Polyamines, which are ubiquitous in nature, and have been implicated in regulating virulence gene expression in other bacteria, have not been extensively studied for their effect on V. cholerae virulence properties. The objective of this study was to test the effect of several polyamines that are abundant in the human intestine on V. cholerae virulence properties. All of the polyamines tested inhibited autoagglutination of V. cholerae O1 classical strain in a concentration dependent manner. Putrescine and cadaverine decreased the synthesis of the major pilin subunit, TcpA, spermidine increased its production, and spermine had no effect. Putrescine and spermidine led to a decrease and increase, respectively, on the relative abundance of TCP found on the cell surface. Spermine led to a small reduction in cholera toxin synthesis whereas none of the other polyamines had an effect. The polyamines did not affect pili bundling morphology, but caused a small reduction in CTXφ transduction, indicating that the TCP present on the cell surface may not be fully functional. We hypothesize the inhibition of autoagglutination is likely to be caused by the positively charged amine groups on the polyamines electrostatically disrupting the pili-pili interactions which mediate autoagglutination. Our results implicate that polyamines may have a protective function against colonization of the small intestine by V. cholerae.

Polyamines regulate intestinal epithelial restitution through TRPC1-mediated Ca²+ signaling by differentially modulating STIM1 and STIM2

Early epithelial restitution occurs as a consequence of intestinal epithelial cell (IEC) migration after wounding, and its defective regulation is implicated in various critical pathological conditions. Polyamines stimulate intestinal epithelial restitution, but their exact mechanism remains unclear. Canonical transient receptor potential-1 (TRPC1)-mediated Ca(2+) signaling is crucial for stimulation of IEC migration after wounding, and induced translocation of stromal interaction molecule 1 (STIM1) to the plasma membrane activates TRPC1-mediated Ca(2+) influx and thus enhanced restitution. Here, we show that polyamines regulate intestinal epithelial restitution through TRPC1-mediated Ca(2+) signaling by altering the ratio of STIM1 to STIM2. Increasing cellular polyamines by ectopic overexpression of the ornithine decarboxylase (ODC) gene stimulated STIM1 but inhibited STIM2 expression, whereas depletion of cellular polyamines by inhibiting ODC activity decreased STIM1 but increased STIM2 levels. Induced STIM1/TRPC1 association by increasing polyamines enhanced Ca(2+) influx and stimulated epithelial restitution, while decreased formation of the STIM1/TRPC1 complex by polyamine depletion decreased Ca(2+) influx and repressed cell migration. Induced STIM1/STIM2 heteromers by polyamine depletion or STIM2 overexpression suppressed STIM1 membrane translocation and inhibited Ca(2+) influx and epithelial restitution. These results indicate that polyamines differentially modulate cellular STIM1 and STIM2 levels in IECs, in turn controlling TRPC1-mediated Ca(2+) signaling and influencing cell migration after wounding.

Polyamines inhibit the assembly of stress granules in normal intestinal epithelial cells regulating apoptosis

Polyamines regulate multiple signaling pathways and are implicated in many aspects of cellular functions, but the exact molecular processes governed by polyamines remain largely unknown. In response to environmental stress, repression of translation is associated with the assembly of stress granules (SGs) that contain a fraction of arrested mRNAs and are thought to function as mRNA storage. Here we show that polyamines modulate the assembly of SGs in normal intestinal epithelial cells (IECs) and that induced SGs following polyamine depletion are implicated in the protection of IECs against apoptosis. Increasing the levels of cellular polyamines by ectopic overexpression of the ornithine decarboxylase gene decreased cytoplasmic levels of SG-signature constituent proteins eukaryotic initiation factor 3b and T-cell intracellular antigen-1 (TIA-1)-related protein and repressed the assembly of SGs induced by exposure to arsenite-induced oxidative stress. In contrast, depletion of cellular polyamines by inhibiting ornithine decarboxylase with α-difluoromethylornithine increased cytoplasmic eukaryotic initiation factor 3b and TIA-1 related protein abundance and enhanced arsenite-induced SG assembly. Polyamine-deficient cells also exhibited an increase in resistance to tumor necrosis factor-α/cycloheximide-induced apoptosis, which was prevented by inhibiting SG formation with silencing SG resident proteins Sort1 and TIA-1. These results indicate that the elevation of cellular polyamines represses the assembly of SGs in normal IECs and that increased SGs in polyamine-deficient cells are crucial for increased resistance to apoptosis.

Cellular diamine levels in cancer chemoprevention: modulation by ibuprofen and membrane plasmalogens

Background

To develop effective strategies in cancer chemoprevention, an increased understanding of endogenous biochemical mediators that block metastatic processes is critically needed. Dietary lipids and non-steroidal anti-inflammatory drugs (NSAIDs) have a published track record of providing protection against gastrointestinal malignancies. In this regard, we examined the effects of membrane plasmalogens and ibuprofen on regulation of cellular levels of diamines, polyamine mediators that are augmented in cancer cells. For these studies we utilized Chinese hamster ovary (CHO) cells and NRel-4 cells, a CHO cell line with defective plasmalogen synthesis.

Results

NRel-4 cells, which possess cellular plasmalogen levels that are 10% of control CHO cells, demonstrated 2- to 3-fold increases in cellular diamine levels. These diamine levels were normalized by plasmalogen replacement and significantly reduced by ibuprofen. In both cases the mechanism of action appears to mainly involve increased diamine efflux via the diamine exporter. The actions of ibuprofen were not stereospecific, supporting previous studies that cyclooxygenase (COX) inhibition is unlikely to be involved in the ability of NSAIDs to reduce intracellular diamine levels.

Conclusions

Our data demonstrate that ibuprofen, a drug known to reduce the risk of colorectal cancer, reduces cellular diamine levels via augmentation of diamine efflux. Similarly, augmentation of membrane plasmalogens can increase diamine export from control and plasmalogen-deficient cells. These data support the concept that membrane transporter function may be a therapeutic point of intervention for dietary and pharmacological approaches to cancer chemoprevention.

miR-503 represses CUG-binding protein 1 translation by recruiting CUGBP1 mRNA to processing bodies

This study shows that microRNA-503 interacts with the CUG-binding protein 1 (CUGBP1) mRNA and represses its translation by recruiting the CUGBP1 mRNA to processing bodies.

microRNAs (miRNAs) and RNA-binding proteins (RBPs) jointly regulate gene expression at the posttranscriptional level and are involved in many aspects of cellular functions. The RBP CUG-binding protein 1 (CUGBP1) destabilizes and represses the translation of several target mRNAs, but the exact mechanism that regulates CUGBP1 abundance remains elusive. In this paper, we show that miR-503, computationally predicted to associate with three sites of the CUGBP1 mRNA, represses CUGBP1 expression. Overexpression of an miR-503 precursor (pre-miR-503) reduced the de novo synthesis of CUGBP1 protein, whereas inhibiting miR-503 by using an antisense RNA (antagomir) enhanced CUGBP1 biosynthesis and elevated its abundance; neither intervention changed total CUGBP1 mRNA levels. Studies using heterologous reporter constructs revealed a greater repressive effect of miR-503 through the CUGBP1 coding region sites than through the single CUGBP1 3′-untranslated region target site. CUGBP1 mRNA levels in processing bodies (P-bodies) increased in cells transfected with pre-miR-503, while silencing P-body resident proteins Ago2, RCK, or LSm4 decreased miR-503–mediated repression of CUGBP1 expression. Decreasing the levels of cellular polyamines reduced endogenous miR-503 levels and promoted CUGBP1 expression, an effect that was prevented by ectopic miR-503 overexpression. Repression of CUGBP1 by miR-503 in turn altered the expression of CUGBP1 target mRNAs and thus increased the sensitivity of intestinal epithelial cells to apoptosis. These findings identify miR-503 as both a novel regulator of CUGBP1 expression and a modulator of intestinal epithelial homoeostasis.

Regulation of cyclin-dependent kinase 4 translation through CUG-binding protein 1 and microRNA-222 by polyamines

The amino acid-derived polyamines are organic cations that are essential for growth in all mammalian cells, but their exact roles at the molecular level remain largely unknown. Here we provide evidence that polyamines promote the translation of cyclin-dependent kinase 4 (CDK4) by the action of CUG-binding protein 1 (CUGBP1) and microRNA-222 (miR-222) in intestinal epithelial cells. Both CUGBP1 and miR-222 were found to bind the CDK4 mRNA coding region and 3'-untranslated region and repressed CDK4 translation synergistically. Depletion of cellular polyamines increased cytoplasmic CUGBP1 abundance and miR-222 levels, induced their associations with the CDK4 mRNA, and inhibited CDK4 translation, whereas increasing the levels of cellular polyamines decreased CDK4 mRNA interaction with CUGBP1 and miR-222, in turn inducing CDK4 expression. Polyamine-deficient cells exhibited an increased colocalization of tagged CDK4 mRNA with processing bodies; this colocalization was abolished by silencing CUGBP1 and miR-222. Together, our findings indicate that polyamine-regulated CUGBP1 and miR-222 modulate CDK4 translation at least in part by altering the recruitment of CDK4 mRNA to processing bodies.

Posttranscriptional regulation of gene expression in epithelial cells by polyamines

In addition to regulating gene transcription, polyamines also potently modulate gene expression posttranscriptionally. Posttranscriptional gene regulation, which includes processes such as mRNA transport, turnover, and translation, involves specific mRNA sequences (cis-element) that interact with transacting factors such as RNA-binding proteins (RBPs) and microRNAs. U- or AU-rich elements (ARE) are the best characterized cis-acting sequences located in the 3'-untranslated regions of many labile mRNAs. Several RBPs, including AUF1, BRF1, TTP, and KSRP, promote ARE-mRNA decay through the recruitment of the ARE-bearing mRNA to sites of mRNA degradation, whereas RBPs such as HuR, HuB, HuC, and HuD stabilize target mRNAs and stimulate their translation. HuR is one of the best-studied RBPs and has emerged as a key regulator of posttranscriptional control of gene expression and its activity is tightly regulated by cellular polyamines. Ribonucleoprotein immunoprecipitation assays and biotin pull-down assays are two major methods used extensively in experiments investigating the roles and mechanisms of cellular polyamines in the posttranscriptional regulation and are described in detail in this chapter.

Post-transcriptional regulation of MEK-1 by polyamines through the RNA-binding protein HuR modulating intestinal epithelial apoptosis

MEK-1 [MAPK (mitogen-activated protein kinase) kinase-1] is an important signal transducing enzyme that is implicated in many aspects of cellular functions. In the present paper, we report that cellular polyamines regulate MEK-1 expression at the post-transcriptional level through the RNA-binding protein HuR (Hu-antigen R) in IECs (intestinal epithelial cells). Decreasing the levels of cellular polyamines by inhibiting ODC (ornithine decarboxylase) stabilized MEK-1 mRNA and promoted its translation through enhancement of the interaction between HuR and the 3'-untranslated region of MEK-1 mRNA, whereas increasing polyamine levels by ectopic ODC overexpression destabilized the MEK-1 transcript and repressed its translation by reducing the abundance of HuR-MEK-1 mRNA complex; neither intervention changed MEK-1 gene transcription via its promoter. HuR silencing rendered the MEK-1 mRNA unstable and inhibited its translation, thus preventing increases in MEK-1 mRNA and protein in polyamine-deficient cells. Conversely, HuR overexpression increased MEK-1 mRNA stability and promoted its translation. Inhibition of MEK-1 expression by MEK-1 silencing or HuR silencing prevented the increased resistance of polyamine-deficient cells to apoptosis. Moreover, HuR overexpression did not protect against apoptosis if MEK-1 expression was silenced. These results indicate that polyamines destabilize the MEK-1 mRNA and repress its translation by inhibiting the association between HuR and the MEK-1 transcript. Our findings indicate that MEK-1 is a key effector of the HuR-elicited anti-apoptotic programme in IECs.