Role of mTOR signaling in intestinal cell migration

l-Arginine-Loaded Oxidized Isabgol/Chitosan-Based Biomimetic Composite Scaffold Accelerates Collagen Synthesis, Vascularization, and Re-epithelialization during Wound Healing in Diabetic Rats

Impaired wound healing in diabetic wounds is common due to infection, inflammation, less collagen synthesis, and vascularization. Diabetic wound healing in patients is still a challenge and needs an ideal wound dressing to treat and manage diabetic wounds. Herein, an efficacious wound dressing biomaterial was fabricated by cross-linking oxidized isabgol (Oisab) and chitosan (Cs) via trisodium trimetaphosphate and Schiff base bonds. l-Arginine (l-Arg) was incorporated as a bioactive substance in the Oisab + Cs scaffold to promote cell adhesion, cell proliferation, collagen synthesis, and vascularization. The fabricated scaffolds showed microporous networks in the scanning electron microscopy analysis. The scaffold also possessed excellent hemocompatibility. In vitro studies using fibroblasts (L929 and human dermal fibroblast cells) confirmed the cytocompatibility of these scaffolds. The results of the in vivo chicken chorioallantoic membrane assay confirmed the proangiogenic activity of the Oisab + Cs + l-Arg scaffolds. The wound-healing potential of these scaffolds was studied in streptozotocin-induced diabetic rats. This in vivo study showed that the period of epithelialization in the Oisab + Cs + l-Arg scaffold-treated wounds was 21.67 ± 1.6 days, which was significantly faster than the control (30.33 ± 2.5 days). Histological and immunohistochemical studies showed that the Oisab + Cs + l-Arg scaffolds significantly accelerated the rate of wound contraction by reducing inflammation, improving collagen synthesis, and promoting neovascularization. These findings suggest that the Oisab + Cs + l-Arg scaffolds could be beneficial in treating diabetic wounds in clinical applications.

Dietary glycine supplementation activates mechanistic target of rapamycin signaling pathway in tissues of pigs with intrauterine growth restriction

The mechanistic target of rapamycin (mTOR) cell signaling pathway serves as the central mechanism for the regulation of tissue protein synthesis and growth. We recently reported that supplementing 1% glycine to corn- and soybean meal-based diets enhanced growth performance between weaning and market weights in pigs with intrauterine growth restriction (IUGR). Results of recent studies have revealed an important role for glycine in activating mTOR and protein synthesis in C2C12 muscle cells. Therefore, the present study tested the hypothesis that dietary glycine supplementation enhanced the mTOR cell signaling pathway in skeletal muscle and other tissues of IUGR pigs. At weaning (21 d of age), IUGR pigs and litter mates with normal birth weights (NBW) were assigned randomly to one of the two groups: supplementation with either 1% glycine or 1.19% l-alanine (isonitrogenous control) to a corn- and soybean meal-based diet. Tissues were obtained from the pigs within 1 wk after the feeding trial ended at 188 d of age to determine the abundances of total and phosphorylated forms of mTOR and its two major downstream proteins: eukaryotic initiation factor 4E-binding protein-1 (4EBP1) and ribosomal protein S6 kinase-1 (p70S6K). Results showed that IUGR decreased (P < 0.05) the abundances of both total and phosphorylated mTOR, 4EBP1, and p70S6K in the gastrocnemius muscle and jejunum. In the longissimus lumborum muscle of IUGR pigs, the abundances of total mTOR did not differ (P > 0.05) but those for phosphorylated mTOR and both total and phosphorylated 4EBP1 and p70S6K were downregulated (P < 0.05), when compared to NBW pigs. These adverse effects of IUGR in the gastrocnemius muscle, longissimus lumborum muscle, and jejunum were prevented (P < 0.05) by dietary glycine supplementation. Interestingly, the abundances of total or phosphorylated mTOR, 4EBP1, and p70S6K in the liver were not affected (P > 0.05) by IUGR or glycine supplementation. Collectively, our findings indicate that IUGR impaired the mTOR cell signaling pathway in the tissues of pigs and that adequate glycine intake was crucial for maintaining active mTOR-dependent protein synthesis for the growth and development of skeletal muscle.

Effects of maternal exposure to procymidone on hepatic metabolism in the offspring of mice

As an effective fungicide widely used in agricultural production, the excessive procymidone (PRO) residue has been detected in the environment and food. Our previous study demonstrated that PRO could destroy the intestinal barrier in mice and has a joint toxic effect. To explore the cross-generational impact of maternal exposure, 10-week-old C57BL/6 female mice were orally administrated to 10 and 100 mg/kg body weight/day of PRO during pregnancy and lactation. The offspring obtained nutrients from the maternal through the placenta and breast milk, and PRO residues were detected in the liver, intestine, and feces of F1 generation. Fecal examination found that the residual PRO had been completely metabolized when the offspring mice grew to 35 days. The drug residue of F1 generation male mice was higher than that of female mice. We attributed this result to the difference in cytochrome P450 (CYP450) enzyme expression between male and female mice. The transcriptional levels of CYP1A1, CYP1A2, CYP2D9, and CYP3A4, and CYP450 protein expression levels, were higher in female mice. Furthermore, targeted MS of plasma revealed abnormal amino acid levels. In addition, PRO-induced hepatic metabolite changes in F0 and F1-7w mice. KEGG pathway analysis further showed that PRO jointly changed the amino acid biosynthesis pathway of the maternal and offspring. In summary, these results indicated that maternal exposure to PRO during a special period would interfere with self metabolism, and offspring will also have metabolic disorders.

Arginine transportation mechanism through cationic amino acid transporter 1: insights from molecular dynamics studies

Metabolic and signaling mechanisms in mammalian cells are facilitated by the transportation of L-arginine (Arg) across the plasma membrane through cationic amino acid transporter (CAT) proteins. Due to a lack of argininosuccinate synthase (ASS) activity in various tumor cells such as acute myeloid leukemia, acute lymphocytic leukemia, and chronic lymphocytic leukemia, these tumor entities are arginine-auxotrophic and therefore depend on the uptake of the amino acid arginine. Cationic amino acid transporter-1 (CAT-1) is the leading arginine importer expressed in the aforementioned tumor entities. Hence, in the present study, to investigate the transportation mechanism of arginine in CAT-1, we performed molecular dynamics (MD) simulation methods on the modeled human CAT-1. The MM-PBSA approach was conducted to determine the critical residues interacting with arginine within the corresponding binding site of CAT-1. In addition, we found out that the water molecules have the leading role in forming the transportation channel within CAT-1. The conductive structure of CAT-1 was formed only when the water molecules were continuously distributed across the channel. Steered molecular dynamics (SMD) simulation approach showed various energy barriers against arginine transportation through CAT-1, especially while crossing the bottlenecks of the related channel. These findings at the molecular level might shed light on identifying the crucial amino acids in the binding of arginine to eukaryotic CATs and also provide fundamental insights into the arginine transportation mechanisms through CAT-1. Understanding the transportation mechanism of arginine is essential to developing CAT-1 blockers, which can be potential medications for some types of cancers.Communicated by Ramaswamy H. Sarma.

miR-125b-5p inhibits cell proliferation by targeting ASCT2 and regulating the PI3K/AKT/mTOR pathway in an LPS-induced intestinal mucosa cell injury model

Intestinal barrier injury is an important cause of death in patients with acquired immune deficiency syndrome (AIDS). Therefore, it is of great significance to identify a therapeutic target for intestinal barrier injury to delay the progression of AIDS. microRNA (miRNA/miR)-125b-5p has an extensive role in cancer and controlling intestinal epithelial barrier function, but its role in human immunodeficiency virus-related intestinal mucosal damage remains unknown. The present study was designed to explore the effects of miR-125b-5p on lipopolysaccharide (LPS)-induced intestinal mucosal injury and the underlying mechanism. The expression of miR-125b-5p and ASCT2 mRNA was detected in colon biopsy samples of 10 patients with AIDS and 10 control healthy subjects. Human intestinal embryonic mucosa cells (CCC-HIE-2) were used to establish an LPS-induced intestinal mucosa cell injury model in vitro. Cell proliferation and apoptosis were determined by MTT assays and flow cytometry, respectively. miR-125b-5p levels and ASCT2 mRNA and protein expression levels in the LPS-induced intestinal mucosa cell injury model were detected by reverse transcription-quantitative PCR (RT-qPCR) and western blotting. The interaction between miR-125b-5p and ASCT2 was analyzed using a dual luciferase reporter assay. The results demonstrated that miR-125b-5p levels were increased and ASCT2 mRNA expression levels were decreased in colon samples from patients with AIDS and in LPS-induced intestinal mucosa cells. In the LPS-induced intestinal mucosa cell injury model, transfection with miR-125b-5p mimic inhibited cell proliferation and promoted cell apoptosis, while transfection with a miR-125b-5p inhibitor increased cell proliferation and attenuated cell apoptosis. Furthermore, miR-125b-5p mimic transfection resulted in a decrease of ASCT2 mRNA and protein expression, whereas the inhibitor increased ASCT2 mRNA and protein expression. Dual luciferase reporter assays suggested that ASCT2 was a direct target of miR-125b-5p, and its restoration weakened the effect of miR-125b-5p on LPS-induced intestinal mucosa cell injury. Transfection with the miR-125b-5p mimic also exhibited a suppressive effect on the PI3K/AKT/mTOR pathway in the LPS-induced intestinal mucosal cell injury model. Overall, the present study indicated that miR-125b-5p accelerated LPS-induced intestinal mucosa cell injury by targeting ASCT2 and upregulating the PI3K/AKT/mTOR pathway. The current findings may provide novel targets for the treatment of intestinal barrier injury in patients with AIDS.

Influence of Eimeria spp. infection and dietary inclusion of arginine on intestine histological parameters, serum amino acid profile and ileal amino acids digestibility in broiler chicks

Coccidiosis is considered to be one of the most important challenge in the poultry industry causes economic losses due to the destruction in the digestive tract of chicken. It disturbs amino acids profile and their digestibility, leading to weight lost and economic burden. Using dietary arginine may decrease the adverse effects of coccidiosis on chicken digestive tract. This study aimed to evaluate the effects of dietary inclusion of arginine on intestine histological parameters, serum amino acid concentration and ileal amino acid digestibility of broiler chicks infected with coccidiosis. A total number of 384 one-d-old broiler chicks (Ross 308) of mixed sex with initial weight of 42 ± 2 g was allocated into 8 groups with 8 birds/pen from grower period. At 21 days of age, broiler chicks were infected with a mixture of Eimeria spp. Broiler chicks were divided into infected and un-infected groups and received arginine at recommended levels of 85, 100, 125 and 150 %. Intestinal morphology and lesions, serum amino acid concentration and ileal amino acid digestibility were evaluated. Broiler chicks infected with Eimeria spp. showed lower villus height and villus height: crypt depth ratio and also higher intestinal lesions (P < 0.05). Coccidia infection decreased the ileal amino acid digestibility for all studied amino acids and also reduced serum concentrations of amino acids, except lysine and isoleucine (P < 0.05). Dietary supplementation of arginine especially in higher levels significantly increased villus height and villus height:crypt depth ratio and decreased lesions (P < 0.05). Moreover, dietary supplementing of arginine increased the serum concentration of arginine (P < 0.05), but it did not have any significant effect on its digestibility (P > 0.05). In sum, coccidiosis decreases amino acid digestibility and serum amino acid concentration, but dietary inclusion of higher levels of arginine significantly improved histological parameters of broiler chicks infected with coccidiosis.

Dynamic changes in circulating levels of metabolites in the portal-drained viscera of finishing pigs receiving acute administration of l-arginine

In this study, we examined the effects of acute intravenous administration of l-arginine on circulating levels of metabolites in the portal-drained viscera (PDV) of 12 barrows surgically fitted with chronic catheters in the portal vein. At day 14 post-surgery, the pigs were fasted for 12 hr and then randomly allocated to one of three groups to receive administration of normal saline, l-alanine [103 mg/kg body weight (BW), isonitrogenous control] or l-arginine-HCl (61 mg/kg BW), via the portal vein. Blood samples were obtained from the carotid artery before and at 30-min intervals for 5 hr after the administration of saline or amino acid in order to determine metabolic profiles. The results showed that, compared with the saline treatment, arginine infusion increased plasma concentrations of insulin-like growth factor-I, arginine and cystine in the portal vein plasma, whereas plasma concentrations of threonine, serine, leucine and methionine were reduced. These findings indicate that increasing arginine concentrations in the portal vein alters the metabolic profile in swine, an established animal model for studying human nutrition and metabolism.

Dietary leucine supplementation improves intestinal health of mice through intestinal SIgA secretion

AIMS

Leucine supplementation promotes intestinal health, but the mechanism is largely unknown. This study aimed to elucidate the mechanisms underlying the beneficial effects of leucine on intestinal homeostasis.

METHODS AND RESULTS

Female ICR mice (6-week-old) were randomly assigned into three groups: (i) mice received a basal diet; (ii) mice received a dietary 0·5% crystalline l-leucine supplementation; and (iii) mice received a dietary 1·0% crystalline l-leucine supplementation. Our results showed that leucine supplementation stimulated the secretion of SIgA in mice ileum and expression of cytokines related to SIgA production. Moreover, leucine supplementation improved the expression of mTOR and p70S6K1 expression. Further study showed that leucine supplementation markedly decreased microbiota richness and induced a shift in the Firmicutes : Bacteroidetes ratio in favour of Firmicutes.

CONCLUSIONS

Therefore, our data suggested that leucine supplementation could enhance intestinal health through the regulation of mTOR pathway and promoting SIgA secretion in the mouse intestine, which might be associated with intestinal microbiota.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study found that dietary leucine supplementation of mice could improve intestinal health by enhancing intestinal SIgA secretion via a nonexclusive mechanism, which might include T cell-dependent pathway, T cell-independent pathway and gut microbiota.

Protective effects of L-arginine on the intestinal epithelial barrier under heat stress conditions in rats and IEC-6 cell line

Heat stress (HS) and the associated restricted blood flow to the intestine have been proven to destroy intestinal integrity. Considering the beneficial properties of L-arginine on gut function, we investigated the protective effects of L-arginine on the intestine under HS conditions. In vivo, the serum cortisol level and the rectal temperature increased in response to HS. Under HS, the intestinal damage showed obvious morphological changes. Furthermore, HS decreased the mRNA and protein expression levels of Nurr1, ZO-1, occludin, claudin-6 and E-cadherin, increased the mRNA expression of NF-κB and IL-1β, and increased the protein expression of cleaved caspase-3. In contrast, L-arginine supplementation maintained intestinal integrity and increased the villus/crypt ratio. L-arginine also suppressed the expression of inflammation-related genes and the protein expression of cleaved caspase-3, whereas it upregulated the mRNA and protein expression of tight junction proteins and LC3B protein expression. In vitro, L-arginine attenuated HS-induced apoptosis as demonstrated by flow cytometry and decreased cleaved caspase-3 protein expression. L-arginine induced autophagy, which was demonstrated by decreased expression of p62 and p-mTOR/mTOR, and increased expression of LC3B. The protein expression levels of TJ proteins also enhanced by L-arginine in IEC-6 cells. Taken together, these results suggest that L-arginine can alleviate intestinal damage and protect the intestinal integrity by suppressing local inflammation response, promoting the production of TJs and facilitating autophagy under HS conditions.

Influence of starch sources and dietary protein levels on intestinal functionality and intestinal mucosal amino acids catabolism in broiler chickens

Background

There is growing interest in carbohydrate and protein nutrition to enhance the efficiency of animal production. Reduced-crude protein diets depress environmental pollution and feeding cost, but the challenge to their adoption is maintaining digestive function and growth performance of birds. The present study was conducted to evaluate the influence of different dietary starch sources and protein levels on intestinal functionality and mucosal amino acid catabolism.

Methods

Six dietary treatments, based on maize and soybean meal, were offered to 360 AA⁺ male chicks from 6 to 35 d post-hatch as a 3 × 2 factorial array. Either waxy rice or amylose was added to a conventional maize-soy diet to provide three sources of starch with different digestion rates and relatively high and low dietary protein levels. Growth performance, parameters of intestinal functionality and concentrations of free amino acid in the portal circulation were determined.

Results

In the grower phase, starch source influenced (P < 0.02) weight gain as diets containing amylose supported significantly higher weight gains than waxy rice. Significant increase of ileal ATP concentrations and Na⁺/K⁺-ATPase activity were found in amylose treatment. Also, amylose decreased BrdU positive cell numbers and down-regulated mRNA expression for CASP-3. GOT activity in the ileum was higher (P < 0.01) in birds offered low protein diets and there was a trend (P = 0.057) for waxy rice as a starch source to increase ileal GOT activities. There was a significant influence on the concentration of seventeen amino acids in the portal circulation with tryptophan the one exception. Waxy rice as a starch source generated 13.6% and 22.4% numerically higher concentrations of non-essential amino acids than maize and amylose, respectively.

Conclusions

Amino acid catabolism in the gut mucosa is subject to nutritional regulation. Given that amino acids can be spared from catabolism in the gut mucosa by supplementation of amylose, it follows their post-enteral availability would be improved and intestinal energy would be derived more efficiently from glucose.

Arginine affects growth and integrity of grass carp enterocytes by regulating TOR signaling pathway and tight junction proteins

Dietary arginine (Arg) could improve the intestinal structure and absorption of grass carp (Ctenopharyngodon idellus); however, the mechanism of Arg on intestinal morphology improvement was unclear. The present study aimed to explain the possible mechanism of the positive effect of Arg on intestinal epithelial cells of grass carp. An in vitro study was conducted through a primary culture model to assess the growth, cell viability, mRNA expressions of TOR signal pathway, and tight junction proteins of enterocytes after culture in the medium with 6 levels of Arg (0, 0.1, 0.2, 0.5, 1.0, and 2.0 mmol/L). The results showed that 0.5 mmol/L Arg improved the cell number and decreased the lactate dehydrogenase and creatine kinase activities in culture medium (P < 0.05). The alkaline phosphatase activity in cell lysis buffer was depressed by 1 and 2 mmol/L Arg (P < 0.05). The nitric oxide (NO) content showed an increasing trend with the Arg content (P < 0.05), whereas the NO synthase activity showed an opposite trend to NO. TOR expression was higher in 0.2 and 0.5 mmol/L groups, whereas S6K1 expression in 1.0 mmol/L and 2.0 mmol/L groups were lower (P < 0.05). The mRNA expressions of occludin, claudin 3, and claudin c in 0.5 mmol/L group were the highest, while ZO-1 and claudin b expressions were higher in 0.2 and 0.5 mmol/L groups (P < 0.05). This study indicated that Arg enhanced the growth and integrity of intestinal epithelial cells of grass carp through upregulation of mRNA expression of TOR signal pathway and tight junction proteins at an optimal Arg content of 0.2-0.5 mmol/L.

Perspectives on the Therapeutic Benefits of Arginine Supplementation in Cancer Treatment

BACKGROUND

Arginine is considered a semi-essential amino acid in healthy adults and the elderly. This amino acid seems to improve the immune system, stimulate cell growth and differentiation, and increase endothelial permeability, among other effects. For those reasons, it has been theorized that arginine supplementation may be used as an adjuvant to conventional cancer therapy treatments.

OBJECTIVE

This review aims to evaluate the existing knowledge of the scientific community on arginine supplementation in order to improve the efficacy of current cancer treatment.

RESULTS

Despite the continued efforts of science to improve treatment strategies, cancer remains one of the greatest causes of death on the planet in adults and elderly people. Chemo and radiotherapy are still the most effective treatments but at the cost of significant side effects.

CONCLUSION

Thus, new therapeutic perspectives have been studied in recent years, to be used in addition to traditional treatments or not, seeking to treat or even cure the various types of cancer with fewer side effects.

Interleukin-2 induces the in vitro maturation of human pluripotent stem cell-derived intestinal organoids

Human pluripotent stem cell (hPSC)-derived intestinal organoids (hIOs) form 3D structures organized into crypt and villus domains, making them an excellent in vitro model system for studying human intestinal development and disease. However, hPSC-derived hIOs still require in vivo maturation to fully recapitulate adult intestine, with the mechanism of maturation remaining elusive. Here, we show that the co-culture with human T lymphocytes induce the in vitro maturation of hIOs, and identify STAT3-activating interleukin-2 (IL-2) as the major factor inducing maturation. hIOs exposed to IL-2 closely mimic the adult intestinal epithelium and have comparable expression levels of mature intestinal markers, as well as increased intestine-specific functional activities. Even after in vivo engraftment, in vitro-matured hIOs retain their maturation status. The results of our study demonstrate that STAT3 signaling can induce the maturation of hIOs in vitro, thereby circumventing the need for animal models and in vivo maturation.

Molecular cloning, polymorphism, and expression analysis of the LKB1/STK11 gene and its association with non-specific digestive disorder in rabbits

Liver kinase B1 (LKB1, also called STK11) encodes a serine/threonine kinase mutated in Peutz-Jeghers cancer syndrome characterized by gastrointestinal polyposis. Although LKB1 plays an important role in regulating energy homeostasis, cell growth, and metabolism via activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), nothing is known about its molecular characteristics and possible involvement in non-specific digestive disorder (NSDD) of rabbits. In the present study, we first cloned the coding sequence (CDS) of rabbit LKB1, which consisted of 1317 bp encoding 438 amino acids (AAs) and contained a highly conserved S_TKc kinase domain. Its deduced AA sequence showed 87.93-91.10% similarities with that of other species. In order to determine its involvement in NSDD, a NSDD rabbit model was built by a dietary fiber deficiency. The polymorphic site of LKB1 was then investigated in both healthy and NSDD groups using directing sequencing. Our results suggested that a synonymous variant site (840 c. G > C, CCC→CCG) existed in its S_TKc domain, which was associated with susceptibility to NSDD. Furthermore, qPCR was utilized to examine the mRNA levels of LKB1 and its downstream targets (i.e., PRKAA2, mTOR and NF-kβ) in several intestinal-related tissues from both healthy and NSDD groups. Significant changes in their expression levels between two groups indicated that impaired LKB1 signaling contributed to the intestinal abnormality in NSDD rabbits. Taken together, it could be concluded that LKB1 might be a potential candidate gene affecting the occurrence of rabbit NSDD. This information may serve as a basis for further investigations on rabbit digestive diseases.

Structural basis for amino acid transport by the CAT family of SLC7 transporters

Amino acids play essential roles in cell biology as regulators of metabolic pathways. Arginine in particular is a major signalling molecule inside the cell, being a precursor for both l-ornithine and nitric oxide (NO) synthesis and a key regulator of the mTORC1 pathway. In mammals, cellular arginine availability is determined by members of the solute carrier (SLC) 7 family of cationic amino acid transporters. Whereas CAT-1 functions to supply cationic amino acids for cellular metabolism, CAT-2A and -2B are required for macrophage activation and play important roles in regulating inflammation. Here, we present the crystal structure of a close homologue of the mammalian CAT transporters that reveals how these proteins specifically recognise arginine. Our structural and functional data provide a model for cationic amino acid transport in mammalian cells and reveals mechanistic insights into proton-coupled, sodium-independent amino acid transport in the wider APC superfamily.

Cationic amino acid transporters (CATs) belong to the physiologically important solute carrier (SLC) 7 family. Here, the authors present the structure of the mammalian CAT transporter homologue Geobacillus kaustophilus GkApcT, which reveals how arginine is recognized, and propose a model for proton-coupled amino acid transport.

Role of the gut, melanocortin system and malonyl-CoA in control of feed intake in non-ruminant animals

Regulation of feed intake is under complex control, involving physical, chemical, hormonal and neuronal responses. Understanding the regulation of feed intake in farm animals is key to optimisation of intake to meet production and profitability goals. Fundamental mechanisms regulating feed intake include constraints imposed by the gut, systems monitoring current and long-term energy status to increase or decrease intake, and hedonic, reward-related drives. Feed intake is closely related to the rate of passage of digesta and the capacity of the gastrointestinal tract. Indigestible fibre increases the rate of digesta passage and feed intake until excess distension sends signals of satiety to the brain. The presence of partially digested nutrients and products of microbial fermentation in the distal intestines releases peptides (PYY, OXM, GPL-1, Apo A-IV, amylin) from gut and pancreas to activate the intestinal brake, which slows the rate of passage and reduces feed intake. These peptides also act on orexigenic (NPY, AgRP) and anorexigenic (POMC, CART) peptides of the melanocortin system of the hypothalamus to reduce intake over the long term. Immediate energy status of the animal is monitored through the ratio of AMP : ATP via adenosine monophosphate-activated kinase and mammalian target of rapamycin, whereas the overall animal energy status is monitored by insulin, leptin and ghrelin. These energy-monitoring systems control short- and long-term intakes through the melanocortin system of the hypothalamus, primarily via malonyl-CoA, to alter the relative expression of orexigenic and anorexigenic peptides. Gut and hypothalamic control of feed intake can be over-ridden by hedonic, reward-related centres of the brain, predominantly through the release of dopamine. These hedonic responses can lead to over-consumption and obesity under some circumstances or reduced feed intake under stressful or other negative environmental situations. Knowledge of these mechanisms can be used to identify practical strategies for either increasing or decreasing voluntary intake in pigs.

Astragaloside II promotes intestinal epithelial repair by enhancing L-arginine uptake and activating the mTOR pathway

Astragaloside II (AS II) extracted from Astragalus membranaceus has been reported to promote tissue wound repair. However, the effect of AS II on inflammatory bowel disease is unknown. We investigated the effects and mechanism of AS II on intestinal wound healing in both in vitro and in vivo models. Human intestinal Caco-2 cells were treated with multiple concentrations of AS II to assess cell proliferation, scratch wound closure, L-arginine uptake, cationic amino acid transporter activity, and activation of the mTOR signaling pathway. These effects were also measured in a mouse model of colitis. AS II promoted wound closure and increased cell proliferation, L-arginine uptake, CAT1 and CAT2 protein levels, total protein synthesis, and phosphorylation of mTOR, S6K, and 4E-BP1 in Caco-2 cells. These effects were suppressed by lysine or rapamycin treatment, suggesting that the enhanced arginine uptake mediates AS II-induced wound healing. Similar results were also observed in vivo. Our findings indicate that AS II can contribute to epithelial barrier repair following intestinal injury, and may offer a therapeutic avenue in treating irritable bowel disease.

MicroRNA-7-5p regulates the proliferation and migration of intestinal epithelial cells by targeting trefoil factor 3 via inhibiting the phosphoinositide 3-kinase/Akt signalling pathway

Trefoil factor 3 (TFF3) reconstructs the epithelial barrier by stimulating epithelial cell migration and proliferation, and significantly contributes to intestinal mucosal damage and healing. In a previous study, TFF3 was identified as a novel target of microRNA-7-5p (miR-7-5p). The aim of the present study was to investigate the roles and mechanisms of miR-7-5p in the proliferation and migration of intestinal epithelial cells. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to determine the expression level of miR-7-5p in the experimental groups. In addition, western blot analysis was performed to examine the expression levels of TFF3, phosphoinositide 3-kinase (PI3K), Akt and phosphorylated (p)-AKT when miR-7-5p or TFF3 was overexpressed, and the effects of miR-7-5p and TFF3 on LS174T cell proliferation and migration were simultaneously investigated. miR-7-5p was demonstrated to decrease the expression level of TFF3, and inhibit LS174T cell proliferation and migration, which was accompanied by decreased expression levels of PI3K and p-Akt. miR-7-5p was decreased following combined treatment with the TFF3 plasmid and miR‑7-5p mimics, compared with treatment with miR-7-5p mimics alone, which was accompanied by increased expression levels of TFF3, PI3K and p-Akt, and enhanced LS174T cell proliferation and migration effects. The expression levels of miR-7-5p in the miRNA negative control (NC) + LY294002 group, the miR‑7-5p mimic + LY294002 group, and the miR-7-5p mimic + TFF3 plasmid + LY294002 group were higher than those in the NC group, the miR-7-5p mimic group and the miR-7-5p mimic + TFF3 plasmid group, respectively. Accordingly, the expression level of TFF3 was downregulated and the proliferation and migration ability of the cells was downregulated. The present study demonstrates that overexpressed miR-7-5p may inhibit the proliferation and migration of LS174T cells by targeting the expression of TFF3 via inhibiting the PI3K/Akt signalling pathway. The PI3K/Akt signalling pathway may exert a feedback regulation effect on miR-7-5p, inhibiting the activity of this signalling pathway, which increases the miR-7-5p expression levels and further enhances the effects of miR-7-5p on cell proliferation and migration.

Recombinant Thrombomodulin Exerts Anti-autophagic Action in Endothelial Cells and Provides Anti-atherosclerosis Effect in Apolipoprotein E Deficient Mice

Stress-induced alteration in endothelial cells (ECs) integrity precedes the development of atherosclerosis. Previous studies showed that the soluble recombinant thrombomodulin (rTM) not only increases ECs proliferation but also exerts anti-apoptotic activity in ECs. However, the functional significance of soluble rTM on autophagy-related apoptosis in ECs is still undetermined. Implicating a cytoprotective role for rTM in persistent serum starvation (SS)-induced autophagy in cultured ECs, we found that treatment of rTM decreased the expression of SS-induced autophagy-related proteins, ATG5 and LC3, and the formation of autophagosomes through activation of AKT/mTOR pathway. In addition, treatment of rTM decreased SS-induced EC apoptosis, but this effect of rTM could not be recapitulated by co-treatment with a potent autophagy inducer, rapamycin and in ECs with ATG5 knockdown. In human atherosclerosis specimens, expression of autophagy markers, ATG13 and LC3, were more abundant in aortic intimal ECs with severe atherosclerosis than those without atherosclerosis. Moreover, compared to saline treatment group, administration of rTM reduced LC3 and ATG13 expression, intimal EC apoptosis, and atherosclerotic lesion severity in the aorta of apolipoprotein E deficient mice. In conclusion, treatment with rTM suppressed stress-induced autophagy overactivation in ECs, provided ECs protective effects, and decreased atherosclerosis in apolipoprotein E deficient mice.

L-Arginine promotes protein synthesis and cell growth in brown adipocyte precursor cells via the mTOR signal pathway

L-Arginine has been reported to enhance brown adipose tissue developments in fetal lambs of obese ewes, but the underlying mechanism is unknown. The present study tested the hypothesis that L-arginine stimulates growth and development of brown adipocyte precursor cells (BAPCs) through activation of mammalian target of rapamycin cell signaling. BAPCs isolated from fetal lambs at day 90 of gestation were incubated   for 6 h in arginine-free DMEM, and then cultured in DMEM with concentrations of 50, 100, 200, 500 or 1000 μmol L-arginine/L for 24-96 h. Cell proliferation, protein turnover, the mammalian target of rapamycin (mTOR) signaling pathway and pre-adipocyte differentiation markers were determined. L-arginine treatment enhanced (P < 0.05) BAPC growth and protein synthesis, while inhibiting proteolysis in a dose-dependent manner. Compared with 50 and 100 μmol/L (the concentrations of arginine in the maternal plasma of obese ewes), 200 μmol L-arginine/L (the concentrations of arginine in the maternal plasma of obese ewes receiving arginine supplementation) increased (P < 0.05) the abundances of phosphorylated mTOR, P70^S6K and 4EBP1, as well as the abundances of PGC1α, UCP1, BMP7 and PRDM16. These novel findings indicate that increasing extra-cellular arginine concentration from 50 to 200 µmol/L activates mTOR cell signaling in BAPCs and enhances their growth and development in a dose-dependent manner. Our results provide a mechanism for arginine supplementation to enhance the development of brown adipose tissue in fetal lambs.

Structural mechanism for the arginine sensing and regulation of CASTOR1 in the mTORC1 signaling pathway

The mTOR complex I (mTORC1) signaling pathway controls many metabolic processes and is regulated by amino acid signals, especially arginine. CASTOR1 has been identified as the cytosolic arginine sensor for the mTORC1 pathway, but the molecular mechanism of how it senses arginine is elusive. Here, by determining the crystal structure of human CASTOR1 in complex with arginine, we found that an exquisitely tailored pocket, carved between the NTD and the CTD domains of CASTOR1, is employed to recognize arginine. Mutation of critical residues in this pocket abolished or diminished arginine binding. By comparison with structurally similar aspartate kinases, a surface patch of CASTOR1-NTD on the opposite side of the arginine-binding site was identified to mediate direct physical interaction with its downstream effector GATOR2, via GATOR2 subunit Mios. Mutation of this surface patch disrupted CASTOR1’s recognition and inhibition of GATOR2, revealed by in vitro pull-down assay. Normal mode (NM) analysis revealed an ‘open’-to-‘closed’ conformational change for CASTOR1, which is correlated to the switching between the exposing and concealing of its GATOR2-binding residues, and is most likely related to arginine binding. Interestingly, the GATOR2-binding sites on the two protomers of CASTOR1 dimer face the same direction, which prompted us to propose a model for how dimerization of CASTOR1 relieves the inhibition of GATOR1 by GATOR2. Our study thus provides a thorough analysis on how CASTOR1 recognizes arginine, and describes a possible mechanism of how arginine binding induces the inter-domain movement of CASTOR1 to affect its association with GATOR2.

The Effect of l-Arginine on Dural Healing After Experimentally Induced Dural Defect in a Rat Model

BACKGROUND

Incomplete repair of the dura mater may result in numerous complications such as cerebrospinal fluid leakage and meningitis. For this reason, accurate repair of the dura mater is essential. In this study, the effect of systemic and local supplementation of l-arginine on dural healing was evaluated.

METHODS

Thirty male Wistar rats were used and divided into control, local, and systemic l-arginine groups, with 10 rats in each. In each group, a 5-mm experimental incision was made at the lumbar segment of the dura mater and cerebrospinal fluid leakage was induced. Each group was divided into 2 subgroups and at the end of the first and sixth weeks, the rats were killed and the damaged segments of the dura were separated, histologically evaluated and the dural healing indicators including cell types, granulation tissue formation, collagen deposit, and vascularization were compared between groups.

RESULTS

The systematic supplementation of l-arginine showed a significant effect in dural healing compared with the control group. After the first week, granulation formation increased considerably (P < 0.031), and after 6 weeks, collagen deposition and neovascularization were significantly different compared with the control group (P < 0.030; P < 0.009). In comparison between different groups at the end of the first and sixth weeks, maximum changes in healing indicators were observed in the systemic group and the least variations were related to the control group.

CONCLUSIONS

The systemic supplementation of l-arginine may accelerate dural healing by increasing the level of granulation tissue formation, collagen deposition, and vascularization.

The CASTOR Proteins Are Arginine Sensors for the mTORC1 Pathway

Amino acids signal to the mTOR complex I (mTORC1) growth pathway through the Rag GTPases. Multiple distinct complexes regulate the Rags, including GATOR1, a GTPase activating protein (GAP), and GATOR2, a positive regulator of unknown molecular function. Arginine stimulation of cells activates mTORC1, but how it is sensed is not well understood. Recently, SLC38A9 was identified as a putative lysosomal arginine sensor required for arginine to activate mTORC1 but how arginine deprivation represses mTORC1 is unknown. Here, we show that CASTOR1, a previously uncharacterized protein, interacts with GATOR2 and is required for arginine deprivation to inhibit mTORC1. CASTOR1 homodimerizes and can also heterodimerize with the related protein, CASTOR2. Arginine disrupts the CASTOR1-GATOR2 complex by binding to CASTOR1 with a dissociation constant of ~30 μM, and its arginine-binding capacity is required for arginine to activate mTORC1 in cells. Collectively, these results establish CASTOR1 as an arginine sensor for the mTORC1 pathway.

The preclinical evaluation of the dual mTORC1/2 inhibitor INK-128 as a potential anti-colorectal cancer agent

The colorectal cancer is the leading contributor of cancer-related mortality. Mammalian target of rapamycin (mTOR), existing in 2 complexes (mTORC1/2), is frequently dysregulated and constitutively activated in colorectal cancers. It represents an important drug target. Here we found that INK-128, the novel ATP-competitive kinase inhibitor of mTOR, blocked both mTORC1 and mTORC2 activation in colorectal cancer cells (both primary and transformed cells). The immunoprecipitation results showed that the assembly of mTORC1 (mTOR-Raptor association) and mTORC2 (mTOR-Rictor-Sin1 association) was also disrupted by INK-128. INK-128 inhibited colorectal cancer cell growth and survival, and induced both apoptotic and non-apoptotic cancer cell death. Further, INK-128 showed no effect on Erk/MAPK activation, while MEK/Erk inhibition by MEK-162 enhanced INK-128-induced cytotoxicity in colorectal cancer cells. Meanwhile, INK-128 downregulated Fascin1 (FSCN1)/E-Cadherin expressions and inhibited HT-29 cell in vitro migration. In vivo, daily INK-128 oral administration inhibited HT-29 xenograft growth in mice, which was further enhanced by MEK-162 administration. Finally, we found that INK-128 sensitized 5-fluorouracil-(5-FU)-mediated anti-HT-29 activity in vivo and in vitro. Thus, our preclinical studies strongly suggest that INK-128 might be investigated for colorectal cancer treatment in clinical trials.

Autophagy inhibits endothelial progenitor cells migration via the regulation of MMP2, MMP9 and uPA under normoxia condition

OBJECTIVE

The aim of this study was to explore the role of autophagy on the regulation of endothelial progenitor cells (EPCs) migration under normoxic condition.

METHODS

After EPCs were isolated and characterized in vitro, we employed Atg5 knocking down and rapamycin to monitor the autophagy, and performed wound healing and transwell assay to assess the cell migration. On the mechanism, the expression of matrix metalloproteinases (MMPs) and urokinase type plasminogen activator (uPA) was evaluated.

RESULTS

Atg5 knocking down and rapamycin could respectively inhibit and enhance autophagy, which could result in significantly increased and decreased cell migration in wound healing and transwell assay under normoxic condition. Moreover, Atg5 knocking down could significantly increase the expression of MMP2, MMP9 and uPA in EPCs while rapamycin could decrease the expression of uPA and MMP9. In addition, the mTOR-P70 S6K pathway was also involved in EPCs migration regulation.

CONCLUSIONS

These results demonstrated that autophagy could regulate the EPCs migration through mTOR-P70 S6K pathway, and MMP2, MMP9 and uPA may also involve in the regulation mechanism.

l-Tryptophan Activates Mammalian Target of Rapamycin and Enhances Expression of Tight Junction Proteins in Intestinal Porcine Epithelial Cells

BACKGROUND

Besides serving as a substrate for protein synthesis, L-tryptophan (L-Trp) is used via serotonin-, kynurenine-, and niacin-synthetic pathways to produce bioactive compounds crucial for whole-body homeostasis. It is unknown whether L-Trp itself can regulate metabolic pathways in animal cells.

OBJECTIVE

This study tested the hypothesis that L-Trp may activate mammalian target of rapamycin (mTOR) complex 1 and enhance expression of tight junction (TJ) proteins in intestinal porcine epithelial cells.

METHODS

Jejunal enterocytes, intestinal porcine epithelial cell line 1 (IPEC-1) isolated from newborn pigs, were cultured in customized Dulbecco's modified Eagle medium (DMEM) supplemented with or without L-Trp for the indicated time periods. Cell proliferation, L-Trp metabolism, protein turnover, mRNA abundance for L-Trp transporters [solute carrier family 3 member 1 (SLC3A1), solute carrier family 6 member 14 (SLC6A14), solute carrier family 6 member 19 (SLC6A19), and Na(+)/K(+) ATPase subunit-α1 (ATP1A1)], abundance of proteins involved in mTOR signaling, and TJ proteins were determined.

RESULTS

L-Trp was not degraded in IPEC-1 cells. Compared with basal medium containing 0.04 mmol/L L-Trp, 0.4 and 0.8 mmol/L L-Trp enhanced (P < 0.05) protein synthesis by 45-52% and cell growth by 17% and 25% on day 1 and 72% and 51% on day 2, respectively, while reducing (P < 0.05) protein degradation by 12% and 22%, respectively. These effects of L-Trp were associated with mTOR activation and increased (P < 0.05) mRNA abundance for L-Trp transporters (SLC6A19, SLC6A14, and SLC3A1) by 1.5-2.7 fold and ATP1A1 by 3 fold. L-Trp also upregulated (P < 0.05) the abundance of occludin, claudin-4, zonula occludens (ZO) 1 and 2 by 0.5-2 fold but did not affect expression of claudin-1 or ZO-3 in IPEC-1 cells.

CONCLUSION

L-Trp is not catabolized by pig small intestinal epithelial cells but can regulate intracellular protein turnover and expression of TJ proteins in these cells.

L-arginine upregulates the gene expression of target of rapamycin signaling pathway and stimulates protein synthesis in chicken intestinal epithelial cells

L-arginine (Arg) is an indispensable amino acid in avians and is required for growth. The aim of this study was to investigate the effects of L-Arg on protein synthesis and genes expression involved in target of rapamycin (TOR) signaling pathway in chicken enterocytes. Cells were cultured for 4 days in L-Arg-free Dulbecco's modified Eagle's medium containing 10, 100, 200, 400, or 600 μM L-Arg. Cell growth, cell cycle, protein synthesis, and protein degradation as well as mRNA expression levels of TOR, ribosomal protein S6 kinase 1 (S6K1), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) were determined. The results showed that cell viability was enhanced by L-Arg with a maximal response at 10 to 400 μM. Increasing extracellular concentrations of L-Arg from 10 to 400 μM increased the cells in S and G2/M phase to a significant extent and decreased cell numbers in G0/G1 phase. Further more, addition of 100, 200, or 400 μM L-Arg to culture medium increased protein synthesis and reduced protein degradation in chicken intestinal epithelial cells. Consistent with the data on cell growth and protein turnover, supplementation of 100, 200, or 400 μM L-Arg increased the mRNA abundances of TOR, 4E-BP1, and S6K1. It was concluded the action of L-Arg involves in upregulating the genes expression of TOR cell signaling pathway which increases protein synthesis and reduces protein degradation.

Glycine stimulates protein synthesis and inhibits oxidative stress in pig small intestinal epithelial cells

Glycine has recently been classified as a nutritionally essential amino acid for maximal growth in young pigs. Currently, little is known about the metabolism or function of glycine in the neonatal intestine. This work was conducted to test the hypothesis that glycine has a protective effect against oxidative stress in intestinal epithelial cells. Jejunal enterocytes isolated from newborn pigs were cultured in the presence of 0.0-2 mmol/L glycine for measurements of glycine metabolism, cell proliferation, protein turnover, apoptosis, and antioxidative response. Compared with 0.0-0.5 mmol/L glycine, 1.0 mmol/L glycine enhanced (P < 0.05) cell growth (by 8-24% on day 2 and by 34-224% on day 4, respectively) and protein synthesis (by 36-419%) while reducing (P < 0.05) protein degradation (by 7-28%). This effect of glycine was associated with activation of the mammalian target of rapamycin signaling pathway in enterocytes. By using a model of oxidative stress induced by 30 μmol/L 4-hydroxynonenal (4-HNE), which was assessed by flow cytometry analysis, 1.0 mmol/L glycine inhibited (P < 0.05) activation of caspase 3 by 25% and attenuated (P < 0.05) 4-HNE-induced apoptosis by 38% in intestinal porcine epithelial cell line 1 cells through promotion of reduced glutathione synthesis and expression of glycine transporter 1 while reducing the activation of extracellular signal-regulated kinases, c-Jun amino-terminal kinases, and p38 protein in the mitogen-activated protein kinase signaling pathway. These novel findings provide a biochemical mechanism for the use of dietary glycine to improve intestinal health in neonates under conditions of oxidative stress and glycine deficiency.

Supplemental dietary L-arginine attenuates intestinal mucosal disruption during a coccidial vaccine challenge in broiler chickens

The present study investigated the effects of dietary arginine (Arg) supplementation on intestinal structure and functionality in broiler chickens subjected to coccidial challenge. The present study was a randomised complete block design employing a 3 × 2 factorial arrangement (n 8) with three dietary concentrations of Arg (11·1, 13·3 and 20·2 g/kg) with or without coccidial vaccine challenge (unchallenged and coccidial challenge). On day 14, birds were orally administered with coccidial vaccine or saline. On day 21, birds were killed to obtain jejunal tissue and mucosal samples for histological, gene expression and mucosal immunity measurements. Within 7 d of the challenge, there was a decrease in body-weight gain and feed intake, and an increase in the feed:gain ratio (P< 0·05). Jejunal inflammation was evidenced by villus damage, crypt dilation and goblet cell depletion. Coccidial challenge increased mucosal secretory IgA concentration and inflammatory gene (iNOS, IL-1β, IL-8 and MyD88) mRNA expression levels (P< 0·05), as well as reduced jejunal Mucin-2, IgA and IL-1RI mRNA expression levels (P< 0·05). Increasing Arg concentration (1) increased jejunal villus height (P< 0·05) and linearly increased jejunal crypt depth (P< 0·05); (2) quadratically increased mucosal maltase activity (P< 0·05) and linearly decreased mucosal secretory IgG concentration (P< 0·05) within the coccidiosis-challenged groups; and (3) linearly decreased jejunal Toll-like receptor 4 (TLR4) mRNA expression level (P< 0·05) within the coccidiosis-challenged groups. The mRNA expression of mechanistic target of rapamycin (mTOR) complex 1 pathway genes (mTOR and RPS6KB1) and the anti-apoptosis gene Bcl-2 quadratically responded to increasing dietary Arg supplementation (P< 0·05). These results indicate that dietary Arg supplementation attenuates intestinal mucosal disruption in coccidiosis-challenged chickens probably through suppressing TLR4 and activating mTOR complex 1 pathways.

L-arginine stimulates fibroblast proliferation through the GPRC6A-ERK1/2 and PI3K/Akt pathway

l-Arginine is considered a conditionally essential amino acid and has been shown to enhance wound healing. However, the molecular mechanisms through which arginine stimulates cutaneous wound repair remain unknown. Here, we evaluated the effects of arginine supplementation on fibroblast proliferation, which is a key process required for new tissue formation. We also sought to elucidate the signaling pathways involved in mediating the effects of arginine on fibroblasts by evaluation of extracellular signal-related kinase (ERK) 1/2 activation, which is important for cell growth, survival, and differentiation. Our data demonstrated that addition of 6 mM arginine significantly enhanced fibroblast proliferation, while arginine deprivation increased apoptosis, as observed by enhanced DNA fragmentation. In vitro kinase assays demonstrated that arginine supplementation activated ERK1/2, Akt, PKA and its downstream target, cAMP response element binding protein (CREB). Moreover, knockdown of GPRC6A using siRNA blocked fibroblast proliferation and decreased phosphorylation of ERK1/2, Akt and CREB. The present experiments demonstrated a critical role for the GPRC6A-ERK1/2 and PI3K/Akt signaling pathway in arginine-mediated fibroblast survival. Our findings provide novel mechanistic insights into the positive effects of arginine on wound healing.

MicroRNA-451 regulates AMPK/mTORC1 signaling and fascin1 expression in HT-29 colorectal cancer

The earlier studies have shown that Fascin1 (FSCN1), the actin bundling protein, is over-expressed in colorectal cancers, and is associated with cancer cell progression. Here, we aimed to understand the molecular mechanisms regulating FSCN1 expression by focusing on mammalian target of rapamycin (mTOR) signaling and its regulator microRNA-451. We found that microRNA-451 was over-expressed in multiple colorectal cancer tissues, and its expression was correlated with mTOR complex 1 (mTORC1) activity and FSCN1 expression. In cultured colorectal cancer HT-29 cells, knockdown of FSCN1 by RNAi inhibited cell migration and proliferation. Activation of mTORC1 was required for FSCN1 expression, HT-29 cell migration and proliferation, as RAD001 and rapamycin, two mTORC1 inhibitors, suppressed FSCN1 expression, HT-29 cell migration and proliferation. Meanwhile, forced activation of AMP-activated protein kinase (AMPK), the negative regulator of mTORC1, by its activators or by the genetic mutation, inhibited mTORC1 activation, FSCN1 expression, cell migration and proliferation. In HT-29 cells, we found that over-expression of microRNA-451 inhibited AMPK activation, causing mTORC1 over-activation and FSCN1 up-regulation, cells were with high migration ability and proliferation rate. Significantly, these effects by microRNA-451 were largely inhibited by mTORC1 inhibitors or the AMPK activator AICAR. On the other hand, knockdown of miRNA-451 by the treatment of HT-29 cells with miRNA-451 antagomir inhibited mTORC1 activation and FSCN1 expression. The proliferation and migration of HT-29 cells after miRNA-45 knockdown were also inhibited. Our results suggested that the over-expressed microRNA-451 in colon cancer cells might inhibit AMPK to activate mTORC1, which mediates FSCN1 expression and cancer cell progression.

Regulation of the mTOR-Rac1 axis in platelet function

Small GTPase proteins regulate cytoskeletal dynamics to orchestrate diverse cellular functions in organismal physiology, development and disease. The Rho GTPase family member Rac1 is central to actin-driven processes in a number of cell types, particularly platelets, where Rac1 serves as an essential mediator of lamellipodia formation and thrombus stability. Despite the importance of Rac1 to platelet function, little is known about how Rac1 activity is regulated in platelets. We recently defined the tyrosine-kinase based signaling cascade that activates mTOR to regulate Rac1 activation downstream of platelet integrin and glycoprotein receptors. We demonstrated a critical role for the mTOR-Rac1 axis in regulating platelet spreading, aggregation and aggregate stability under shear. These studies suggest that in addition to cancer and transplant medicine, intervention of the mTOR system may have implications for hemostatic and thrombotic processes as well as immunotherapies and intravascular stent design.

Role of specific dietary amino acids in clinical conditions

In a variety of chronic and acute disease states, alterations in protein synthesis, breakdown and protein turnover rates occur that are related to the loss of body protein and skeletal muscle wasting. A key observation is the stimulation of protein breakdown in muscle and the stimulation of protein synthesis in the splanchnic area; mainly liver. An altered splanchnic extraction of amino acids as well as an anabolic resistance to dietary protein, related to stress, disuse and aging play a key role in the pathogenesis of muscle wasting in these conditions. To overcome these factors, specific dietary protein and amino acid diets have been introduced. The main focus of these diets is the quantity and quality of dietary proteins and whether a balanced mixture or solely dietary essential amino acids are required with or without higher intake levels of specific amino acids. Specifically in cancer patients, stimulated muscle protein synthesis has been obtained by increasing the amount of protein in a meal and by providing additional leucine. Also in other chronic diseases such as chronic obstructive pulmonary disease and cystic fibrosis, meals with specific dietary proteins and specific combinations of dietary essential amino acids are able to stimulate anabolism. In acute diseases, a special role for the amino acid arginine and its precursor citrulline as anabolic drivers has been observed. Thus, there is growing evidence that modifying the dietary amino acid composition of a meal will positively influence the net balance between muscle protein synthesis and breakdown, leading to muscle protein anabolism in a variety of chronic and acute disease states. Specific amino acids with anabolic potential are leucine, arginine and citrulline.

PI3K/AKT/mTOR signaling pathway inhibitors in proliferation of retinal pigment epithelial cells

AIM

To determine whether the PI3K/AKT/mTOR pathway is activated in proliferative vitreoretinopathy (PVR) in homo-sapiens.

METHODS

The retina of controls and patients with PVR were collected and their levels of PI3K, phospho-AKT, phospho-mTOR, phospho-p70S6k and phospho-4EBP-1 were determined by Western blot. The cultured human retinal pigment epithelial cell line D407 was treated with a specific mTOR inhibitor, rapamycin (RAPA) or a PI3K inhibitor, LY294002, of various concentrations and durations. Cell morphology was observed by phase contrast microscopy and the proliferation and apoptosis of treated cells were determined by MTT assay and flow cytometry.

RESULTS

Levels of PI3K, phospho-AKT, phospho-mTOR, phospho-P70S6K and phospho-4EBP1 was increased in the retina in PVR (P<0.05). In D407 cells, both RAPA and LY294002 significantly inhibited cell proliferation and cell cycle progression, and promoted apoptosis (P <0.05); morphologically, the cells became smaller. Both RAPA and LY294002 reduced levels of phospho-AKT, phospho-mTOR, phospho-p70S6k and phospho-4EBP1 expression (P <0.05). RAPA, but not LY294002, had no significant effect on PI3K expression.

CONCLUSION

PI3K/AKT/mTOR signaling pathway is highly activated in the retinal pigment epithelial cells of PVR. The inhibitors of PI3K/AKT/mTOR signaling pathway, RAPA and LY294002, could inhibited the PI3K/AKT/mTOR signaling pathway by reducing the levels of phosphorylation of mTOR pathway components.

A glutathione peroxidase, intracellular peptidases and the TOR complexes regulate peptide transporter PEPT-1 in C. elegans

The intestinal peptide transporter PEPT-1 in Caenorhabditis elegans is a rheogenic H⁺-dependent carrier responsible for the absorption of di- and tripeptides. Transporter-deficient pept-1(lg601) worms are characterized by impairments in growth, development and reproduction and develop a severe obesity like phenotype. The transport function of PEPT-1 as well as the influx of free fatty acids was shown to be dependent on the membrane potential and on the intracellular pH homeostasis, both of which are regulated by the sodium-proton exchanger NHX-2. Since many membrane proteins commonly function as complexes, there could be proteins that possibly modulate PEPT-1 expression and function. A systematic RNAi screening of 162 genes that are exclusively expressed in the intestine combined with a functional transport assay revealed four genes with homologues existing in mammals as predicted PEPT-1 modulators. While silencing of a glutathione peroxidase surprisingly caused an increase in PEPT-1 transport function, silencing of the ER to Golgi cargo transport protein and of two cytosolic peptidases reduced PEPT-1 transport activity and this even corresponded with lower PEPT-1 protein levels. These modifications of PEPT-1 function by gene silencing of homologous genes were also found to be conserved in the human epithelial cell line Caco-2/TC7 cells. Peptidase inhibition, amino acid supplementation and RNAi silencing of targets of rapamycin (TOR) components in C. elegans supports evidence that intracellular peptide hydrolysis and amino acid concentration are a part of a sensing system that controls PEPT-1 expression and function and that involves the TOR complexes TORC1 and TORC2.

S6K1 and mTOR regulate Rac1-driven platelet activation and aggregation

Platelet activation and thrombus formation are under the control of signaling systems that integrate cellular homeostasis with cytoskeletal dynamics. Here, we identify a role for the ribosome protein S6 kinase (S6K1) and its upstream regulator mTOR in the control of platelet activation and aggregate formation under shear flow. Platelet engagement of fibrinogen initiated a signaling cascade that triggered the activation of S6K1 and Rac1. Fibrinogen-induced S6K1 activation was abolished by inhibitors of Src kinases, but not Rac1 inhibitors, demonstrating that S6K1 acts upstream of Rac1. S6K1 and Rac1 interacted in a protein complex with the Rac1 GEF TIAM1 and colocalized with actin at the platelet lamellipodial edge, suggesting that S6K1 and Rac1 work together to drive platelet spreading. Pharmacologic inhibitors of mTOR and S6K1 blocked Rac1 activation and prevented platelet spreading on fibrinogen, but had no effect on Src or FAK kinase activation. mTOR inhibitors dramatically reduced collagen-induced platelet aggregation and promoted the destabilization of platelet aggregates formed under shear flow conditions. Together, these results reveal novel roles for S6K1 and mTOR in the regulation of Rac1 activity and provide insights into the relationship between the pharmacology of the mTOR system and the molecular mechanisms of platelet activation.

Mammalian target of rapamycin: a central node of complex signaling cascades

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that regulates cell growth and metabolism in response to diverse external stimuli. In the presence of mitogenic stimuli, mTOR transduces signals that activate the translational machinery and promote cell growth. mTOR functions as a central node in a complex net of signaling pathways that are involved both in normal physiological, as well as pathogenic events. mTOR signaling occurs in concert with upstream Akt and tuberous sclerosis complex (TSC) and several downstream effectors. During the past few decades, the mTOR-mediated pathway has been shown to promote tumorigenesis through the coordinated phosphorylation of proteins that directly regulate cell-cycle progression and metabolism, as well as transcription factors that regulate the expression of genes involved in the oncogenic processes. The importance of mTOR signaling in oncology is now widely accepted, and agents that selectively target mTOR have been developed as anti-cancer drugs. In this review, we highlight the past research on mTOR, including clinical and pathological analyses, and describe its molecular mechanisms of signaling, and its roles in the physiology and pathology of human diseases, particularly, lung carcinomas. We also discuss strategies that might lead to more effective clinical treatments of several diseases by targeting mTOR.