Novel dietary strategies to manage sarcopenia.

PURPOSE OF REVIEW: Sarcopenia is a wasting disease, mostly age-related in which muscle strength and mass decline, such as physical performance. With aging, both lower dietary protein intake and anabolic resistance lead to sarcopenia. Moreover, aging and sarcopenia display low-grade inflammation, which also worsen muscle condition. In this review, we focused on these two main targets to study dietary strategies. RECENT FINDINGS: The better understanding in mechanisms involved in sarcopenia helps building combined dietary approaches including physical activity that would slow the disease progression. New approaches include better understanding in the choice of quality proteins, their amount and schedule and the association with antioxidative nutrients. SUMMARY: First, anabolic resistance can be countered by increasing significantly protein intake. If increasing amount remains insufficient, the evenly delivery protein schedule provides interesting results on muscle strength. Quality of protein is also to consider for decreasing risk for sarcopenia, because varying sources of proteins appears relevant with increasing plant-based proteins ratio. Although new techniques have been developed, as plant-based proteins display a lower availability, we need to ensure an adapted overall amount of proteins. Finally, specific enrichment with leucine from whey protein remains the dietary combined approach most studied and studies on citrulline provide interesting results. As cofactor at the edge between anabolic and antioxidative properties, vitamin D supplementation is to recommend. Antioxidative dietary strategies include both fibers, vitamins, micronutrients and polyphenols from various sources for positive effects on physical performance. The ω 3 -polyunsaturated fatty acids also display positive modifications on body composition. Gut microbiota modifiers, such as prebiotics, are promising pathways to improve muscle mass and function and body composition in sarcopenic patients. Nutritional interventions could be enhanced by combination with physical activity on sarcopenia. In healthy older adults, promoting change in lifestyle to get near a Mediterranean diet could be one of the best options. In sarcopenia adults in which lifestyle changes appears unprobable, specific enrichement potentialized with physical activity will help in the struggle against sarcopenia. Longitudinal data are lacking, which makes it hard to draw strong conclusions. However, the effects of a physical activity combined with a set of nutrition interventions on sarcopenia seems promising.

Effects of Glutamine, Curcumin and Fish Bioactive Peptides Alone or in Combination on Intestinal Permeability in a Chronic-Restraint Stress Model.

Irritable bowel syndrome (IBS), a multifactorial intestinal disorder, is often associated with a disruption in intestinal permeability as well as an increased expression of pro-inflammatory markers. The aim of this study was to first test the impact of treatment with glutamine (Gln), a food supplement containing natural curcumin extracts and polyunsaturated n-3 fatty acids (Cur); bioactive peptides from a fish protein hydrolysate (Ga); and a probiotic mixture containing Bacillus coagulans, Lactobacillus acidophilus, Lactobacillus gasseri and Lactobacillus helveticus. These compounds were tested alone on a stress-based IBS model, the chronic-restraint stress model (CRS). The combination of Gln, Cur and Ga (GCG) was also tested. Eight-week-old C57Bl/6 male mice were exposed to restraint stress for two hours every day for four days and received different compounds every day one week before and during the CRS procedure. Plasma corticosterone levels were measured as a marker of stress, and colonic permeability was evaluated ex vivo in Ussing chambers. Changes in the gene expression of tight junction proteins (occludin, claudin-1 and ZO 1) and inflammatory cytokines (IL1ß, TNFα, CXCL1 and IL10) were assessed using RT-qPCR. The CRS model led to an increase in plasma corticosterone and an increase in colonic permeability compared with unstressed animals. No change in plasma corticosterone concentrations was observed in response to CRS with the different treatments (Gln, Cur, Ga or GCG). Stressed animals treated with Gln, Cur and Ga alone and in combination showed a decrease in colonic permeability when compared to the CRS group, while the probiotic mixture resulted in an opposite response. The Ga treatment induced an increase in the expression of the anti-inflammatory cytokine IL-10, and the GCG treatment was able to decrease the expression of CXCL1, suggesting the synergistic effect of the combined mixture. In conclusion, this study demonstrated that a combined administration of glutamine, a food supplement containing curcumin and polyunsaturated n-3 fatty acids, and bioactive peptides from a fish hydrolysate was able to reduce colonic hyperpermeability and reduce the inflammatory marker CXCL1 in a stress-based model of IBS and could be of interest to patients suffering from IBS.

Comparison of different modes of antibiotic delivery on gut microbiota depletion efficiency and body composition in mouse.

BACKGROUND: The use of animal models with depleted intestinal microbiota has recently increased thanks to the huge interest in the potential role of these micro-organisms in human health. In particular, depletion of gut bacteria using antibiotics has recently become popular as it represents a low cost and easy alternative to germ-free animals. Various regimens of antibiotics are used in the literature, which differ in composition, dose, length of treatment and mode of administration. In order to help investigators in choosing the most appropriate protocol for their studies, we compared here three modes of antibiotic delivery to deplete gut bacteria in C57Bl/6 mice. We delivered one of the most frequently used combination of antibiotics (a mix of ampicillin, neomycin, metronidazole and vancomycin) either ad libitum in drinking water or by oral gavage once or twice per day. RESULTS: We quantified the global bacterial density, as well as the abundance of specific bacterial and fungal taxa, in mouse feces in response to antibiotics exposure. We observed that oral gavage once a day with antibiotics is not a reliable method as it occasionally triggers hyperproliferation of bacteria belonging to the Escherichia/Shigella taxon and leads, as a consequence, to a moderate decrease in fecal bacterial density. Antibiotics delivery by oral gavage twice a day or in drinking water induces in contrast a robust and consistent depletion of mouse fecal bacteria, as soon as 4 days of treatment, and is associated with an increase in fecal moisture content. Extending exposure to antibiotics beyond 7 days does not improve total bacteria depletion efficiency and promotes fungal overgrowth. We show in addition that all tested protocols impact neither gut microbiota recolonization efficiency, 1 or 2 weeks after the stop of antibiotics, nor mice body composition after 1 week of treatment. CONCLUSIONS: Our study provides key experimental data and highlights important parameters to consider before selecting an appropriate protocol for antibiotic-mediated depletion of gut bacteria, in order to optimize the accuracy and the reproducibility of results and to facilitate comparison between studies.

Fructose and irritable bowel syndrome.

Irritable bowel syndrome (IBS) is a chronic disorder characterised by recurrent abdominal pain or discomfort and transit disturbances with heterogeneous pathophysiological mechanisms. The link between food and gastrointestinal (GI) symptoms is often reported by patients with IBS and the role of fructose has recently been highlighted. Fructose malabsorption can easily be assessed by hydrogen and/or methane breath test in response to 25 g fructose; and its prevalence is about 22 % in patients with IBS. The mechanism of fructose-related symptoms is incompletely understood. Osmotic load, fermentation and visceral hypersensitivity are likely to participate in GI symptoms in the IBS population and may be triggered or worsened by fructose. A low-fructose diet could be integrated in the overall treatment strategy, but its role and implication in the improvement of IBS symptoms should be evaluated. In the present review, we discuss fructose malabsorption in adult patients with IBS and the interest of a low-fructose diet in order to underline the important role of fructose in IBS.

Colonic Proteome Signature in Immunoproteasome-Deficient Stressed Mice and Its Relevance for Irritable Bowel Syndrome.

A role for immunoproteasome in the regulation of intestinal permeability has been previously suggested both in mice during water avoidance stress (WAS) and in patients with irritable bowel syndrome (IBS). Here, we provide evidence that the ubiquitin-proteasome system (UPS) contributes to the pathophysiology of IBS. Indeed, we report that colonic proteome is altered in WAS mice and that ß2i subunit deficiency modifies the proteome response that is associated with a limitation of colonic hyperpermeability. Interestingly, we show specific alterations of proteins involved in UPS, mitochondrial, and energy metabolism. We also report changes in the pattern of colonic ubiquitome in diarrhea-predominant IBS (IBS-D) patients and particularly a reduced expression of ubiquitinated proteins involved in the nuclear factor-kappa B (NF-κB) inflammatory signaling pathway. All these data suggest that immunoproteasome targeting may represent a new therapeutic strategy for the treatment of IBS patients with increased intestinal permeability.

Neuropeptide 26RFa (QRFP) is a key regulator of glucose homeostasis and its activity is markedly altered in obese/hyperglycemic mice.

Recent studies have shown that the hypothalamic neuropeptide 26RFa regulates glucose homeostasis by acting as an incretin and increasing insulin sensitivity. In this study, we further characterized the role of the 26RFa/GPR103 peptidergic system in the global regulation of glucose homeostasis using a 26RFa receptor antagonist and also assessed whether a dysfunction of the 26RFa/GPR103 system occurs in obese hyperglycemic mice. First, we demonstrate that administration of the GPR103 antagonist reduces the global glucose-induced incretin effect and insulin sensitivity whereas, conversely, administration of exogenous 26RFa attenuates glucose-induced hyperglycemia. Using a mouse model of high-fat diet-induced obesity and hyperglycemia, we found a loss of the antihyperglcemic effect and insulinotropic activity of 26RFa, accompanied with a marked reduction of its insulin-sensitive effect. Interestingly, this resistance to 26RFa is associated with a downregulation of the 26RFa receptor in the pancreatic islets, and insulin target tissues. Finally, we observed that the production and release kinetics of 26RFa after an oral glucose challenge is profoundly altered in the high-fat mice. Altogether, the present findings support the view that 26RFa is a key regulator of glucose homeostasis whose activity is markedly altered under obese/hyperglycemic conditions.

Chronic colitis-induced visceral pain is associated with increased anxiety during quiescent phase.

Inflammatory bowel diseases (IBD) are characterized by repetition of flares and remission periods leading to chronic postinflammatory sequelae. Among postinflammatory sequelae, one-third of patients with IBD are suffering from functional symptoms or psychological comorbidities that persist during remission. The aim of our study was to assess functional and behavioral sequelae of chronic colitis in rats with quiescent intestinal inflammation. Chronic colitis was induced by a weekly intrarectal injection of increasing concentrations of trinitrobenzene sulfonic acid (TNBS) for 3 wk (15-45 mg of TNBS) in 30 rats, whereas the control rats (n = 24) received the vehicle. At 50 days post-TNBS, visceral sensitivity was assessed by visceromotor response to colorectal distension, and transient receptor potential vanilloid type 1 (TRPV1) expression was also quantified in the colon and dorsal root ganglia. Barrier function and inflammatory response were assessed by studying intestinal permeability, tight junction protein, myeloperoxidase activity, histological score, and cytokine production (IL-6, IL-10, and TNF-α). Anxiety behavioral tests were performed from 50 to 64 days after the last TNBS injection. Chronic TNBS induced 1) a visceral hypersensitivity (P = 0.03), 2) an increased colon weight-to-length ratio (P = 0.01), 3) higher inflammatory and fibrosis scores (P = 0.0390 and P = 0.0016, respectively), and 4) a higher colonic IL-6 and IL-10 production (P = 0.008 and P = 0.005, respectively) compared with control rats. Intestinal permeability, colonic production of TNF-α, myeloperoxidase activity, and TRPV1 expression did not differ among groups. Chronic TNBS increased anxiety-related behavior in the open-field test and in the acoustic stress test. In conclusion, chronic colitis induced functional sequelae such as visceral hypersensitivity and increased anxiety with a low-grade intestinal inflammation. Development of a representative animal model will allow defining novel therapeutic approaches to achieve a better management of IBD-related sequelae. NEW & NOTEWORTHY Patients with inflammatory bowel diseases have impaired quality of life. Therapeutic progress to control mucosal inflammation provides us an opportunity to develop novel approaches to understand mechanisms behind postinflammatory sequelae. We used a chronic colitis model to study long-term sequelae on visceral pain, gut barrier function, and psychological impact. Chronic colitis induced functional symptoms and increased anxiety in the remission period. It might define novel therapeutic approaches to achieve a better inflammatory bowel disease-related sequelae management.

Colonic Mucosal Proteome Signature Reveals Reduced Energy Metabolism and Protein Synthesis but Activated Autophagy during Anorexia-Induced Malnutrition in Mice.

Anorexia nervosa is an eating disorder often associated with intestinal disorders. To explore the underlying mechanisms of these disorders, the colonic proteome was evaluated during activity-based anorexia. Female C57Bl/6 mice were randomized into three groups: Control, Limited Food Access (LFA) and Activity-Based Anorexia (ABA). LFA and ABA mice had a progressive limited access to food but only ABA mice had access to an activity wheel. On colonic mucosal protein extracts, a 2D PAGE-based comparative proteomic analysis was then performed and differentially expressed proteins were identified by LC-ESI-MS/MS. Twenty-seven nonredundant proteins that were differentially expressed between Control, LFA, and ABA groups were identified. ABA mice exhibited alteration of several mitochondrial proteins involved in energy metabolism such as dihydrolipoyl dehydrogenase and 3-mercaptopyruvate sulfurtransferase. In addition, a downregulation of mammalian target of rapamycin (mTOR) pathway was observed leading, on the one hand, to the inhibition of protein synthesis, evaluated by puromycin incorporation and mediated by the increased phosphorylation of eukaryotic elongation factor 2, and on the other hand, to the activation of autophagy, assessed by the increase of the marker of autophagy, form LC3-phosphatidylethanolamine conjugate/Cytosolic form of Microtubule-associated protein 1A/1B light chain 3 (LC3II/LC3I) ratio. Colonic mucosal proteome is altered during ABA suggesting a downregulation of energy metabolism. A decrease of protein synthesis and an activation of autophagy were also observed mediated by mTOR pathway.

Dietary n-3 PUFA May Attenuate Experimental Colitis.

BACKGROUND: Inflammatory bowel diseases (IBD) occurred in genetically predisposed people exposed to environmental triggers. Diet has long been suspected to contribute to the development of IBD. Supplementation with n-3 polyunsaturated fatty acids (PUFA) protects against intestinal inflammation in rodent models while clinical trials showed no benefits. We hypothesized that intervention timing is crucial and dietary fatty acid pattern may influence intestinal environment to modify inflammation genesis. The aim of this study was to evaluate the dietary effect of PUFA composition on intestinal inflammation. METHODS: Animals received diet varying in their PUFA composition for four weeks before TNBS-induced colitis. Colon inflammatory markers and gut barrier function parameters were assessed. Inflammatory pathway PCR arrays were determined. RESULTS: n-3 diet significantly decreased colon iNOS, COX-2 expression, IL-6 production, and LTB4 production but tended to decrease colon TNFα production (P = 0.0617) compared to control diet. Tight junction protein (claudin-1, occludin) expressions and MUC2 and TFF3 mRNA levels were not different among groups. n-9 diet also decreased colon IL-6 production (P < 0.05). CONCLUSIONS: Dietary n-3 PUFA influence colitis development by attenuating inflammatory markers. Further research is required to better define dietary advice with a scientific rationale.

Glutamine and the regulation of intestinal permeability: from bench to bedside.

PURPOSE OF REVIEW: Glutamine is the most abundant amino acid in plasma and plays a key role in maintaining the integrity of intestinal barrier. RECENT FINDINGS: Experimental studies showed that glutamine is able to modulate intestinal permeability and tight junction protein expression in several conditions. Recent articles underlined its putative beneficial role in gastrointestinal disorders such as irritable bowel syndrome. SUMMARY: Glutamine is a major nutrient to maintain intestinal barrier function in animals and humans. Depletion of glutamine results in villus atrophy, decreased expression of tight junction proteins and increased intestinal permeability. Moreover, glutamine supplementation can improve gut barrier function in several experimental conditions of injury and in some clinical situations. Furthermore, preventive effects of glutamine in experimental models of intestinal injuries have been recently reported. Despite promising data in experimental models, further studies are needed to evaluate glutamine supplementation in clinical practice.

Targeting immunoproteasome and glutamine supplementation prevent intestinal hyperpermeability.

BACKGROUND: Intestinal hyperpermeability has been reported in several intestinal and non-intestinal disorders. We aimed to investigate the role of the ubiquitin proteasome system in gut barrier regulation in two mice models: the water avoidance stress model (WAS) and a post-inflammatory model (post-TNBS). METHODS: Both models were applied in C57BL/6 male mice (n=7-8/group); Proteasome was targeted by injection of a selective proteasome inhibitor or by using knock-out mice for ß2i proteasome subunit. Finally, glutamine supplementation was evaluated. RESULTS: In both models (WAS at day 10, post-TNBS at day 28), we observed an increase in proteasome trypsin-like activity and in inducible ß2/constitutive ß2 subunit protein expression ratio, associated with an increase in intestinal permeability. Moreover, intestinal hyperpermeability was blunted by intraperitoneal injection of selective proteasome inhibitor in WAS and post-TNBS mice. Of note, knock-out mice for the ß2i subunit exhibited a significant decrease in intestinal permeability and fecal pellet output during WAS. Glutamine supplementation also improved colonic permeability in both models. CONCLUSIONS: In conclusion, the proteasome system is altered in the colonic mucosa of WAS and post-TNBS mice with increased trypsin-like activity. Associated intestinal hyperpermeability was blunted by immunoproteasome inhibition.

Proteasome inhibitors exacerbate interleukin-8 production induced by protease-activated receptor 2 in intestinal epithelial cells.

Protease activated receptors (PARs) and the ubiquitin-proteasome system (UPS) regulate inflammatory response in intestinal cells. We aimed to elucidate putative connections between PARs and UPS pathways in intestinal epithelial cells. Caco-2 cells were treated by agonist peptides of PARs and/or IL-1ß and/or proteasome inhibitors, bortezomib or MG132. Inflammatory response was evaluated by measuring IL-8 production. Proteasome activities were also evaluated. We showed that PAR-1 and -2 activation increased release of IL-8 compared with vehicle and independently of IL-1ß. In contrast, PAR-4 agonist peptide had no effect. Caspase-like and chymotrypsin-like proteasomal activities were increased by PAR-2 activation only in the presence of IL-1ß. Interestingly, in polarized Caco-2 cells, the release of IL-8 was predominantly upregulated in the side where PAR-2 agonist peptide was added, apical or basalolateral. In contrast, proteasome activities were only affected when PAR-2 agonist peptide was added in the apical side. Proteasome inhibitors, bortezomib and MG132, enhanced IL-8 production in both sides, apical and basolateral. In conclusion, PAR-2 activation alone did not affect proteasome but needed inflammatory stimulus IL-1ß to synergistically increase chymotrypsin-like activity in intestinal epithelial cells. However, proteasome inhibition led to exacerbate inflammatory response induced by PAR-2 activation.

Glutamine enema regulates colonic ubiquitinated proteins but not proteasome activities during TNBS-induced colitis leading to increased mitochondrial activity.

Ubiquitin proteasome system contributes to the regulation of intestinal inflammatory response as its inhibition is associated with tissue damage improvement. We aimed to evaluate whether glutamine is able to limit inflammation by targeting ubiquitin proteasome system in experimental colitis. Colitis was induced in male rats by intrarectal instillation of 2-4-6-trinitrobenzen sulfonic acid (TNBS) at day 1. From day 2 to day 6, rats daily received either an intrarectal instillation of PBS (TNBS/PBS group) or glutamine (TNBS/Gln). Rats were euthanized at day 7 and colonic samples were taken to evaluate ubiqutinated proteins by proteomic approach combining 2D electrophoresis and immunoblots directed against ubiquitin. Results were then confirmed by evaluating total expression of proteins and mRNA levels. Survival rate, TNFα, and IL-1ß mRNA were improved in TNBS/Gln compared with TNBS/PBS (p < 0.05). Proteasome activities were affected by TNBS but not by glutamine. We identified eight proteins that were less ubiquitinated in TNBS/PBS compared with controls with no effect of glutamine. Four proteins were more ubiquitinated in TNBS/PBS group and restored in TNBS/Gln group. Finally, 12 ubiquitinated proteins were only affected by glutamine. Among proteins affected by glutamine, eight proteins (GFPT1, Gapdh, Pkm2, LDH, Bcat2, ATP5a1, Vdac1, and Vdac2) were involved in metabolic pathways. In conclusion, glutamine may regulate ubiquitination process during intestinal inflammation.

Hyperhomocysteinemia-induced oxidative stress differentially alters proteasome composition and activities in heart and aorta.

BACKGROUND AND AIMS: Hyperhomocysteinemia (HHcy) is associated with cardiovascular diseases and is thought to induce endogenous oxidative stress and causes many cellular damages. Proteasome that degrades oxidized and ubiquitinated proteins can regulate the cellular response to oxidative stress. We aimed to investigate whether hyperhomocysteinemia induces oxidative stress and alters proteasome function and composition in heart and aorta tissues of rat. METHODS AND RESULTS: To create hyperhomocysteinemia, male Wistar rats (Pasteur Institute-Algiers) were received daily intraperitoneal injections of dl-homocysteine (0.6-1.2µM/g body weight) for 3weeks. Biomarkers of oxidative stress (malondialdehyde (MDA), protein carbonyl (PC), superoxide dismutase (SOD) and catalase (CAT)) were first measured by biochemical methods and tissue damages by histological sections. Proteasome activities were quantitated using fluorogenic synthetic peptides; ubiquitinated proteins and proteasome subunits expression were then evaluated by SDS PAGE and Western blot analysis. We showed increased MDA and PC but decreased SOD and CAT levels both in plasma, heart and aorta accompanied by histological changes. A significant decrease of proteasome activities was observed in heart, whereas proteasome activity was not affected in aorta. However proteasome composition was altered in both tissues, as the accumulation of ubiquitinated proteins. CONCLUSION: Data demonstrated an alteration of the ubiquitin-proteasome system in hyperhomocysteinemia as a result of accumulating oxidized and ubiquitinated proteins in response to oxidative stress. Further studies must be conducted to better understanding mechanisms responsible of proteasome alterations in hyperhomocysteinemia.

Enteral glutamine infusion modulates ubiquitination of heat shock proteins, Grp-75 and Apg-2, in the human duodenal mucosa.

Glutamine, the most abundant amino acid in the human body, plays several important roles in the intestine. Previous studies showed that glutamine may affect protein expression by regulating ubiquitin-proteasome system. We thus aimed to evaluate the effects of glutamine on ubiquitinated proteins in human duodenal mucosa. Five healthy male volunteers were included and received during 5 h, on two occasions and in a random order, either an enteral infusion of maltodextrins alone (0.25 g kg(-1) h(-1), control), mimicking carbohydrate-fed state, or maltodextrins with glutamine (0.117 g kg(-1) h(-1), glutamine). Endoscopic duodenal biopsies were then taken. Total cellular protein extracts were separated by 2D gel electrophoresis and analyzed by an immunodetection using anti-ubiquitin antibody. Differentially ubiquitinated proteins were then identified by liquid chromatography-electrospray ionization MS/MS. Five proteins were differentially ubiquitinated between control and glutamine conditions. Among these proteins, we identified two chaperone proteins, Grp75 and hsp74. Grp75 was less ubiquitinated after glutamine infusion compared with control. In contrast, hsp74, also called Apg-2, was more ubiquitinated after glutamine. In conclusion, we provide evidence that glutamine may regulate ubiquitination processes of specific proteins, i.e., Grp75 and Apg-2. Grp75 has protective and anti-inflammatory properties, while Apg-2 indirectly regulates stress-induced cell survival and proliferation through interaction with ZO-1. Further studies should confirm these results in stress conditions.

Sex-dependent circadian alterations of both central and peripheral clock genes expression and gut-microbiota composition during activity-based anorexia in mice.

RATIONALE: Patients with anorexia nervosa (AN) often present sleep disorders and circadian hormonal dysregulation. The role of the microbiota-gut-brain axis in the regulation of feeding behavior has emerged during the last decades but its relationships with the circadian rhythm remains poorly documented. Thus, we aimed to characterize the circadian clock genes expression in peripheral and central tissues in the activity-based anorexia mouse model (ABA), as well as the dynamics of the gut-microbiota composition. METHODS: From day 1 to day 17, male and female C57Bl/6 mice were submitted or not to the ABA protocol (ABA and control (CT) groups), which combines a progressive limited access to food and a free access to a running wheel. At day 17, fasted CT and ABA mice were euthanized after either resting (EoR) or activity (EoA) phase (n = 10-12 per group). Circadian clock genes expression was assessed by RT-qPCR on peripheral (liver, colon and ileum) and central (hypothalamic suprachiasmatic nucleus or SCN) tissues. Cecal bacterial taxa abundances were evaluated by qPCR. Data were compared by two-way ANOVA followed by post-tests. RESULTS: ABA mice exhibited a lower food intake, a body weight loss and an increase of diurnal physical activity that differ according with the sex. Interestingly, in the SCN, only ABA female mice exhibited altered circadian clock genes expression (Bmal1, Per1, Per2, Cry1, Cry2). In the intestinal tract, modification of clock genes expression was also more marked in females compared to males. For instance, in the ileum, female mice showed alteration of Bmal1, Clock, Per1, Per2, Cry1, Cry2 and Rev-erbα mRNA levels, while only Per2 and Cry1 mRNAs were affected by ABA model in males. By contrast, in the liver, clock genes expression was more markedly affected in males compared to females in response to ABA. Finally, circadian variations of gut-bacteria abundances were observed in both male and female mice and sex-dependent alteration were observed in response to the ABA model. CONCLUSIONS: This study shows that alteration of circadian clock genes expression at both peripheral and central levels occurs in response to the ABA model. In addition, our data underline that circadian variations of the gut-microbiota composition are sex-dependent.

Anorexia nervosa is an eating disorder with a female predominance. However, the underlying pathophysiological mechanisms are still incompletely understood. Patients with anorexia nervosa often show alterations in circadian rhythm, including sleep disorders and modifications in hormone circadian rhythm. The circadian rhythm is controlled in the central nervous system, particularly in the suprachiasmatic nucleus, but clocks have also been described in peripheral tissues. To better understand the putative role of circadian rhythm in the pathophysiology of anorexia nervosa, we have conducted an experimental study in a rodent model of anorexia nervosa called "activity-based anorexia" on both males and females. Interestingly, we observed that the expression of genes involved in the circadian rhythm is affected by the activity-based anorexia model in both the suprachiasmatic nucleus and peripheral tissues, such as the small intestine and liver. In addition, gut­microbiota also shows circadian variation. Interestingly, the anorexia-induced alterations of circadian variations (clock genes expression and gut­microbiota composition) are sex- and tissue-dependent. For instance, female mice exhibited more marked alterations in the ileum, whereas, in males, modifications were more pronounced in the liver. This study highlights sex-dependent alterations of circadian clock genes expression and of gut­microbiota in response to the anorexia rodent model. Further experiments should be performed to investigate the contribution of these mechanisms in the etiology of anorexia nervosa and the higher prevalence in females.

Sex-dependent effects of a high fat diet on metabolic disorders, intestinal barrier function and gut microbiota in mouse.

Obesity is often associated with sex-dependent metabolic complications, in which altered intestinal barrier function and gut microbiota contribute. We aimed to characterize in mice the sex-dependent effects of a high fat diet on these parameters. Male and female C57BL/6 mice received a standard (SD) or high fat diet (HFD; 60% kcal from fat) during 14 weeks (W14). Body composition, glucose tolerance, insulin sensitivity, intestinal permeability, colonic expression of 44 genes encoding factors involved in inflammatory response and gut barrier function, cecal microbiota, plasma adipokines and white adipose tissue response have been assessed. Both male and female HFD mice exhibited an increase of body weight and fat mass gain and glucose intolerance compared to SD mice. However, only male HFD mice tended to develop insulin resistance associated to increased Tnfα and Ccl2 mRNA expression in perigonadal adipose tissue. By contrast, only female HFD mice showed significant intestinal hyperpermeability that was associated with more markedly altered colonic inflammatory response. Cecal microbiota richness was markedly reduced in both sexes (Observed species) with sex-dependent modifications at the phyla or family level, e.g. decreased relative abundance of Bacillota and Lachnospiraceae in females, increased of Bacteroidaceae in males. Interestingly, some of these microbiota alterations were correlated with peripheral metabolic and inflammatory markers. In conclusions, male and female mice exhibit different responses to a high fat diet with specific changes of gut microbiota, intestinal barrier function, colonic and white adipose tissue inflammation, metabolic markers and body weight gain. The underlying mechanisms should be deciphered in further investigations.

Evaluation of ubiquitinated proteins by proteomics reveals the role of the ubiquitin proteasome system in the regulation of Grp75 and Grp78 chaperone proteins during intestinal inflammation.

The ubiquitin proteasome system (UPS) is the major pathway of intracellular protein degradation and may be involved in the pathophysiology of inflammatory bowel diseases or irritable bowel syndrome. UPS specifically degrades proteins tagged with an ubiquitin chain. We aimed to identify polyubiquitinated proteins during inflammatory response in intestinal epithelial HCT-8 cells by a proteomic approach. HCT-8 cells were incubated with interleukin 1ß, tumor necrosis factor-α, and interferon-γ for 2 h. Total cellular protein extracts were separated by 2D gel electrophoresis and analyzed by an immunodetection using antiubiquitin antibody. Differential ubiquitinated proteins were then identified by LC-ESI MS/MS. Seven proteins were differentially ubiquitinated between control and inflammatory conditions. Three of them were chaperones: Grp75 and Hsc70 were more ubiquitinated (p < 0.05) and Grp78 was less ubiquitinated (p < 0.05) under inflammatory conditions. The results for Grp75 and Grp78 were then confirmed in HCT-8 cells and in 2-4-6-trinitrobenzen sulfonic acid induced colitis in rats mimicking inflammatory bowel disease by immunoprecipitation. No difference was observed in irritable bowel syndrome like model. In conclusion, we showed that a proteomic approach is suitable to identify ubiquitinated proteins and that UPS-regulated expression of Grp75 and Grp78 may be involved in inflammatory response. Further studies should lead to the identification of ubiquitin ligases responsible for Grp75 and Grp78 ubiquitination.

Luminal cysteine-proteases degrade colonic tight junction structure and are responsible for abdominal pain in constipation-predominant IBS.

OBJECTIVES: Luminal serine-proteases lead to increased colonic paracellular permeability and visceral hypersensitivity in patients with diarrhea-predominant irritable bowel syndrome (IBS-D). Other proteases, namely cysteine-proteases (CPs), increase airway permeability by digesting epithelial tight junction proteins. In this study, we focused on constipation-predominant IBS (IBS-C) and we aimed to (i) evaluate CP levels in two cohorts of IBS patients, (ii) test if IBS-C fecal supernatant (FSN) affects permeability, and visceral sensitivity after repeated administrations in mice, and (iii) evaluate occludin expression in IBS-C colonic biopsies. METHODS: Fecal CP activity was determined using selective substrate and inhibitor (E64). The effect of papain, as positive control, and IBS-C FSN administrations were evaluated on colonic paracellular permeability and mucosal occludin levels in mice and T84 monolayers. Occludin protein levels were evaluated in IBS-C colonic biopsies. Sensitivity to colorectal distension (CRD) was measured after repeated administrations of IBS-C FSN. RESULTS: We found in a subset of IBS-C patients an enhanced fecal CP activity, in comparison with healthy controls and IBS-D patients. CP activity levels positively correlated with disease severity and abdominal pain scoring. This association was confirmed by receiver operating characteristic curve analysis. In mice, repeated application of IBS-C FSN into colon triggered increased permeability, linked to the enzymatic degradation of occludin, and was associated with enhanced visceral sensitivity to CRD. Finally, occludin levels were found decreased in colonic biopsies from IBS-C patients, and IBS-C FSNs were able to degrade recombinant human occludin in vitro. All these effects were abolished by preincubation of IBS-C FSN with a CP inhibitor, E64. CONCLUSIONS: These data suggest that luminal CPs may represent a new factor contributing to the genesis of symptoms in IBS.

Regulation of intestinal protein metabolism by amino acids.

Gut homeostasis plays a major role in health and may be regulated by quantitative and qualitative food intake. In the intestinal mucosa, an intense renewal of proteins occurs, at approximately 50% per day in humans. In some pathophysiological conditions, protein turnover is altered and may contribute to intestinal or systemic diseases. Amino acids are key effectors of gut protein turnover, both as constituents of proteins and as regulatory molecules limiting intestinal injury and maintaining intestinal functions. Many studies have focused on two amino acids: glutamine, known as the preferential substrate of rapidly dividing cells, and arginine, another conditionally essential amino acid. The effects of glutamine and arginine on protein synthesis appear to be model and condition dependent, as are the involved signaling pathways. The regulation of gut protein degradation by amino acids has been minimally documented until now. This review will examine recent data, helping to better understand how amino acids regulate intestinal protein metabolism, and will explore perspectives for future studies.