Chronic but not acute energy restriction increases intestinal nutrient transport in mice

In vitro culture alters cell lineage composition and cellular metabolism of bovine blastocyst†

Profiling bovine blastocyst transcriptome at the single-cell level has enabled us to reveal the first cell lineage segregation, during which the inner cell mass (ICM), trophectoderm (TE), and an undefined population of transitional cells were identified. By comparing the transcriptome of blastocysts derived in vivo (IVV), in vitro from a conventional culture medium (IVC), and in vitro from an optimized reduced nutrient culture medium (IVR), we found a delay of the cell fate commitment to ICM in the IVC and IVR embryos. Developmental potential differences between IVV, IVC, and IVR embryos were mainly contributed by ICM and transitional cells. Pathway analysis of these non-TE cells between groups revealed highly active metabolic and biosynthetic processes, reduced cellular signaling, and reduced transmembrane transport activities in IVC embryos that may lead to reduced developmental potential. IVR embryos had lower activities in metabolic and biosynthetic processes but increased cellular signaling and transmembrane transport, suggesting these cellular mechanisms may contribute to improved blastocyst development compared to IVC embryos. However, the IVR embryos had compromised development compared to IVV embryos with notably over-active transmembrane transport activities that impaired ion homeostasis.

In Vitro Culture Alters Cell Lineage Composition and Cellular Metabolism of Bovine Blastocyst

Profiling transcriptome at single cell level of bovine blastocysts derived in vivo (IVV), in vitro from conventional culture medium (IVC), and reduced nutrient culture medium (IVR) has enabled us to reveal cell lineage segregation, during which forming inner cell mass (ICM), trophectoderm (TE), and an undefined population of transitional cells. Only IVV embryos had well-defined ICM, indicating in vitro culture may delay the first cell fate commitment to ICM. Differences between IVV, IVC and IVR embryos were mainly contributed by ICM and transitional cells. Pathway analysis by using the differentially expressed genes of these non-TE cells between groups pointed to highly active metabolic and biosynthetic processes, with reduced cellular signaling and membrane transport in IVC embryos, which may lead to reduced developmental potential. IVR embryos had lower activities in metabolic and biosynthetic processes, but increased cellular signaling and membrane transport, suggesting these cellular mechanisms may contribute to the improved blastocyst development compared to IVC embryos. However, the IVR embryos had compromised development when compared to IVV embryos with notably over-active membrane transport activities that led to impaired ion homeostasis.

Feed Restriction Modulates Growth, Gut Morphology and Gene Expression in Zebrafish

A reduction in daily caloric or nutrient intake has been observed to promote health benefits in mammals and other vertebrates. Feed Restriction (FR), whereby the overall food intake of the organism is reduced, has been explored as a method to improve metabolic and immune health, as well as to optimize productivity in farming. However, less is known regarding the molecular and physiological consequences of FR. Using the model organism, Danio rerio, we investigated the impact of a short-term (month-long) FR on growth, gut morphology and gene expression. Our data suggest that FR has minimal effects on the average growth rates, but it may affect weight and size heterogeneity in a sex-dependent manner. In the gut, we observed a significant reduction in gut circumference and generally lower mucosal heights, whereas other parameters remained unchanged. Gene Ontology (GO), EuKaryotic Orthologous Groups (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified numerous metabolic, reproductive, and immune response pathways that were affected by FR. These results broaden our understanding of FR and contribute towards growing knowledge of its effects on vertebrate health.

Regulation of intestinal growth in response to variations in energy supply and demand

The growth of the intestine requires energy, which is known to be met by catabolism of ingested nutrients. Paradoxically, during whole body energy deficit including calorie restriction, the intestine grows in size. To understand how and why this happens, we reviewed data from several animal models of energetic challenge. These were bariatric surgery, cold exposure, lactation, dietary whey protein intake and calorie restriction. Notably, these challenges all reduced the adipose tissue mass, altered hypothalamic neuropeptide expression and increased intestinal size. Based on these data, we propose that the loss of energy in the adipose tissue promotes the growth of the intestine via a signalling mechanism involving the hypothalamus. We discuss possible candidates in this pathway including data showing a correlative change in intestinal (ileal) expression of the cyclin D1 gene with adipose tissue mass, adipose derived-hormone leptin and hypothalamic expression of leptin receptor and the pro-opiomelanocortin gene. The ability of the intestine to grow in size during depletion of energy stores provides a mechanism to maximize assimilation of ingested energy and in turn sustain critical functions of tissues important for survival.

Complementary intestinal mucosa and microbiota responses to caloric restriction

The intestine is key for nutrient absorption and for interactions between the microbiota and its host. Therefore, the intestinal response to caloric restriction (CR) is thought to be more complex than that of any other organ. Submitting mice to 25% CR during 14 days induced a polarization of duodenum mucosa cell gene expression characterised by upregulation, and downregulation of the metabolic and immune/inflammatory pathways, respectively. The HNF, PPAR, STAT, and IRF families of transcription factors, particularly the Pparα and Isgf3 genes, were identified as potentially critical players in these processes. The impact of CR on metabolic genes in intestinal mucosa was mimicked by inhibition of the mTOR pathway. Furthermore, multiple duodenum and faecal metabolites were altered in CR mice. These changes were dependent on microbiota and their magnitude corresponded to microbial density. Further experiments using mice with depleted gut bacteria and CR-specific microbiota transfer showed that the gene expression polarization observed in the mucosa of CR mice is independent of the microbiota and its metabolites. The holistic interdisciplinary approach that we applied allowed us to characterize various regulatory aspects of the host and microbiota response to CR.

Effect of early dietary energy restriction and phosphorus level on subsequent growth performance, intestinal phosphate transport, and AMPK activity in young broilers

We aimed to determine the effect of low dietary energy on intestinal phosphate transport and the possible underlying mechanism to explain the long-term effects of early dietary energy restriction and non-phytate phosphorus (NPP). A 2 × 3 factorial experiment, consisting of 2 energy levels and 3 NPP levels, was conducted. Broiler growth performance, intestinal morphology in 0–21 days and 22–35 days, type IIb sodium-phosphate co-transporter (NaP_i-IIb) mRNA expression, adenylate purine concentrations in the duodenum, and phosphorylated adenosine monophosphate-activated protein kinase (AMPK-α) activity in 0–21 days were determined. The following results were obtained. (1) Low dietary energy (LE) induced a high feed conversion ratio (FCR) and significantly decreased body weight gain in young broilers, but LE induced significantly higher compensatory growth in low NPP (LP) groups than in the high or medium NPP groups (HP and MP). (2) LE decreased the villus height (VH) in the intestine, and LE-HP resulted in the lowest crypt depth (CD) and the highest VH:CD ratio in the initial phase. However, in the later period, the LE-LP group showed an increased VH:CD ratio and decreased CD in the intestine. (3) LE increased ATP synthesis and decreased AMP:ATP ratio in the duodenal mucosa of chickens in 0–21 days, and LP diet increased ATP synthesis and adenylate energy charges but decreased AMP production and AMP:ATP ratio. (4) LE led to weaker AMPK phosphorylation, higher mTOR phosphorylation, and higher NaP_i-IIb mRNA expression. Thus, LE and LP in the early growth phase had significant compensatory and interactive effect on later growth and intestinal development in broilers. The effect might be relevant to energy status that LE leads to weaker AMPK phosphorylation, causing a lower inhibitory action toward mTOR phosphorylation. This series of events stimulates NaP_i-IIb mRNA expression. Our findings provide a theoretical basis and a new perspective on intestinal phosphate transport regulation, with potential applications in broiler production.

High Levels of Dietary Supplement Vitamins A, C and E are Absorbed in the Small Intestine and Protect Nutrient Transport Against Chronic Gamma Irradiation

We examined nutrient transport in the intestines of mice exposed to chronic low-LET 137Cs gamma rays. The mice were whole-body irradiated for 3 days at dose rates of 0, 0.13 and 0.20 Gy/h, for total dose delivery of 0, 9.6 or 14.4 Gy, respectively. The mice were fed either a control diet or a diet supplemented with high levels of vitamins A, C and E. Our results showed that nutrient transport was perturbed by the chronic irradiation conditions. However, no apparent alteration of the macroscopic intestinal structures of the small intestine were observed up to day 10 after initiating irradiation. Jejunal fructose uptake measured in vitro was strongly affected by the chronic irradiation, whereas uptake of proline, carnosine and the bile acid taurocholate in the ileum was less affected. D-glucose transport did not appear to be inhibited significantly by either 9.6 or 14.4 Gy exposure. In the 14.4 Gy irradiated groups, the diet supplemented with high levels of vitamins A, C and E increased intestinal transport of fructose compared to the control diet (day 10; t test, P = 0.032), which correlated with elevated levels of vitamins A, C and E in the plasma and jejunal enterocytes. Our earlier studies with mice exposed acutely to 137Cs gamma rays demonstrated significant protection for transport of fructose, glucose, proline and carnosine. Taken together, these results suggest that high levels of vitamins A, C and E dietary supplements help preserve intestinal nutrient transport when intestines are irradiated chronically or acutely with low-LET gamma rays.

Maternal protein restriction during pregnancy affects gene expression and immunolocalization of intestinal nutrient transporters in rats

Intrauterine dietary restriction may cause changes in the functioning of offspring organs and systems later in life, an effect known as fetal programming. The present study evaluated mRNA abundance and immunolocalization of nutrient transporters as well as enterocytes proliferation in the proximal, median and distal segments of small intestine of rats born to protein-restricted dams. Pregnant rats were fed hypoproteic (6% protein) or control (17% protein) diets, and offspring rats were evaluated at 3 and 16 weeks of age. The presence of SGLT1 (sodium–glucose co-transporter 1), GLUT2 (glucose transporter 2), PEPT1 (peptide transporter 1) and the intestinal proliferation were evaluated by immunohistochemical techniques and the abundance of specific mRNA for SGLT1, GLUT2 and PEPT1 was assessed by the real-time PCR technique. Rats born to protein-restricted dams showed higher cell proliferation in all intestinal segments and higher gene expression of SGLT1 and PEPT1 in the duodenum. Moreover, in adult animals born to protein-restricted dams the immunoreactivity of SGLT1, GLUT2 and PEPT1in the duodenum was more intense than in control rats. Taken together, the results indicate that changes in the small intestine observed in adulthood can be programmed during the gestation. In addition, they show that this response is caused by both up-regulation in transporter gene expression, a specific adaptation mechanism, and intestinal proliferation, an unspecific adaptation mechanism.

Lactating mice (Mus musculus) exhibit compensatory flexibility in gut morphology in response to reduced dietary protein

Protein affects key life-history traits, and deficiencies in this nutrient may have selected for the ability to invoke physiological or morphological mechanisms to aid nutrient assimilation. I examined the effect of dietary protein on gut characters in lactating mice (Mus musculus L., 1758) and predicted that mice, to improve assimilation efficiency, would increase the mass of the stomach and small intestine and (or) increase food retention in these organs. Mice were maintained on isocaloric diets differing in protein and carbohydrate content (P:C) during the reproductive period. The hypothesis that food would be preferentially retained was not supported. However, both the stomach and the small intestine responded to low P:C with increased mass, and the small intestine exhibited increased diameter. This study demonstrates that mammalian gut morphology of lactating mice can respond to nutrient availability under conditions of constant energy intake. Further study is needed to determine if gut flexibility in response to decreasing P:C levels results in improved nitrogen assimilation efficiency and if this response is a general strategy of mammals or is limited to those with particular breeding strategies.

Maternal protein restriction affects gene expression and enzyme activity of intestinal disaccharidases in adult rat offspring

This study investigated the consequences of intrauterine protein restriction on the gastrointestinal tract and particularly on the gene expression and activity of intestinal disaccharidases in the adult offspring. Wistar rat dams were fed isocaloric diets containing 6% protein (restricted, n = 8) or 17% protein (control, n = 8) throughout gestation. Male offspring (n = 5-8 in each group) were evaluated at 3 or 16 weeks of age. Maternal protein restriction during pregnancy produced offspring with growth restriction from birth (5.7 ± 0.1 vs 6.3 ± 0.1 g; mean ± SE) to weaning (42.4 ± 1.3 vs 49.1 ± 1.6 g), although at 16 weeks of age their body weight was similar to control (421.7 ± 8.9 and 428.5 ± 8.5 g). Maternal protein restriction also increased lactase activity in the proximal (0.23 ± 0.02 vs 0.15 ± 0.02), medial (0.30 ± 0.06 vs 0.14 ± 0.01) and distal (0.43 ± 0.07 vs 0.07 ± 0.02 U·g-1·min-1) small intestine, and mRNA lactase abundance in the proximal intestine (7.96 ± 1.11 vs 2.38 ± 0.47 relative units) of 3-week-old offspring rats. In addition, maternal protein restriction increased sucrase activity (1.20 ± 0.02 vs 0.91 ± 0.02 U·g-1·min-1) and sucrase mRNA abundance (4.48 ± 0.51 vs 1.95 ± 0.17 relative units) in the duodenum of 16-week-old rats. In conclusion, the present study shows for the first time that intrauterine protein restriction affects gene expression of intestinal enzymes in offspring.

Marked changes in endogenous antioxidant expression precede vitamin A-, C-, and E-protectable, radiation-induced reductions in small intestinal nutrient transport

Rapidly proliferating epithelial crypt cells of the small intestine are susceptible to radiation-induced oxidative stress, yet there is a dearth of data linking this stress to expression of antioxidant enzymes and to alterations in intestinal nutrient absorption. We previously showed that 5-14 days after acute γ-irradiation, intestinal sugar absorption decreased without change in antioxidant enzyme expression. In the present study, we measured antioxidant mRNA and protein expression in mouse intestines taken at early times postirradiation. Observed changes in antioxidant expression are characterized by a rapid decrease within 1h postirradiation, followed by dramatic upregulation within 4h and then downregulation a few days later. The cell type and location expressing the greatest changes in levels of the oxidative stress marker 4HNE and of antioxidant enzymes are, respectively, epithelial cells responsible for nutrient absorption and the crypt region comprising mainly undifferentiated cells. Consumption of a cocktail of antioxidant vitamins A, C, and E, before irradiation, prevents reductions in transport of intestinal sugars, amino acids, bile acids, and peptides. Ingestion of antioxidants may blunt radiation-induced decreases in nutrient transport, perhaps by reducing acute oxidative stress in crypt cells, thereby allowing the small intestine to retain its absorptive function when those cells migrate to the villus days after the insult.

Radiation-induced reductions in transporter mRNA levels parallel reductions in intestinal sugar transport

More than a century ago, ionizing radiation was observed to damage the radiosensitive small intestine. Although a large number of studies has since shown that radiation reduces rates of intestinal digestion and absorption of nutrients, no study has determined whether radiation affects mRNA expression and dietary regulation of nutrient transporters. Since radiation generates free radicals and disrupts DNA replication, we tested the hypotheses that at doses known to reduce sugar absorption, radiation decreases the mRNA abundance of sugar transporters SGLT1 and GLUT5, prevents substrate regulation of sugar transporter expression, and causes reductions in sugar absorption that can be prevented by consumption of the antioxidant vitamin A, previously shown by us to radioprotect the testes. Mice were acutely irradiated with (137)Cs gamma rays at doses of 0, 7, 8.5, or 10 Gy over the whole body. Mice were fed with vitamin A-supplemented diet (100x the control diet) for 5 days prior to irradiation after which the diet was continued until death. Intestinal sugar transport was studied at days 2, 5, 8, and 14 postirradiation. By day 8, d-glucose uptake decreased by approximately 10-20% and d-fructose uptake by 25-85%. With increasing radiation dose, the quantity of heterogeneous nuclear RNA increased for both transporters, whereas mRNA levels decreased, paralleling reductions in transport. Enterocytes of mice fed the vitamin A supplement had > or = 6-fold retinol concentrations than those of mice fed control diets, confirming considerable intestinal vitamin A uptake. However, vitamin A supplementation had no effect on clinical or transport parameters and afforded no protection against radiation-induced changes in intestinal sugar transport. Radiation markedly reduced GLUT5 activity and mRNA abundance, but high-d-fructose diets enhanced GLUT5 activity and mRNA expression in both unirradiated and irradiated mice. In conclusion, the effect of radiation may be posttranscriptional, and radiation-damaged intestines can still respond to dietary stimuli.

Dietary intake and the insulin-like growth factor system: effects of migration in two related populations in India and Britain with markedly different dietary intake

Background

The insulin-like growth factor (IGF) system is implicated in the pathogenesis of diabetes and cardiovascular disease.

Objective

We report the effects of total energy intake on the IGF system in two populations with markedly different dietary macronutrient intake and cardiovascular event rate.

Design, subjects and setting

Dietary macronutrient intake was measured in a specific Gujarati migrant community in Sandwell, UK (n = 205) compared with people still resident in the same villages of origin in India (n = 246). Fasting IGF-I, IGF-binding protein (IGFBP)-1 and IGFBP-3, insulin and glucose (0 and 2-hour) were measured.

Results

Total energy and total fat intake were higher in UK migrants, as were IGFBP-3 and IGF-I (mean (95% confidence interval): 145.9 (138.1–153.6) vs. 100.9 (94.6–107.3) ng ml-1; F = 76.6, P < 0.001). IGFBP-1 was lower in UK migrants (29.5 (25.9–33.0) vs. 56.5 (50.6–62.5) μg l-1; F = 48.4, P < 0.001). At both sites, IGF-I correlated positively with total energy (Spearman's ρ = 0.45, P < 0.001) and total fat (ρ = 0.44, P < 0.001) as did IGFBP-3 with total energy (ρ = 0.21, P < 0.05) and fat (ρ = 0.26, P < 0.001). Conversely, in Indian Gujaratis, IGFBP-1 fell with increasing total energy (ρ = -0.27, P < 0.001) and fat intake (ρ = -0.26, P < 0.01) but not in UK Gujaratis. Multiple linear regression modelling showed that increasing quartiles of fat intake were associated with higher IGF-I (β = 0.42, P = 0.007) independent of age, body mass index, plasma insulin, fatty acids and 2-hour glucose.

Conclusion

In these genetically similar groups, migration to the UK and adoption of a different diet is associated with marked changes in the IGF system, suggesting that environmental factors profoundly modulate serum concentrations and actions of IGFs.

Chronic food restriction enhances memory in mice--analysis with matched drive levels

We compared the effects of chronic and acute food deprivation on learning and memory using a dry-type water maze, active avoidance and passive avoidance in C57BL/6L mice. The drive level of the animals--under acute and chronic food deprivation--was matched by a progressive ratio schedule. Both deprivations led to a high degree of activity in the animals; however, the animals on an acute dietary restriction did not exhibit a significantly better performance than those on ad libitum feeding, while those on a chronic food deprivation exhibited memory enhancement. These effects were subtle and were found at a later stage of learning. These findings suggest that chronic food restriction induces memory consolidation or resistance to memory reduction in addition to increased activity.

Impact of vitamin E or selenium deficiency on nematode-induced alterations in murine intestinal function

The effects of deficiencies in the antioxidant nutrients, vitamin E and selenium, on the host response to gastrointestinal nematode infection are unknown. The aim of the study was to determine the effect of antioxidant deficiencies on nematode-induced alterations in intestinal function in mice. BALB/c mice were fed control diets or diets deficient in selenium or vitamin E and the response to a secondary challenge inoculation with Heligmosomoides polygyrus was determined. Egg and worm counts were assessed to determine host resistance. Sections of jejunum were mounted in Ussing chambers to measure changes in permeability, absorption, and secretion, or suspended in organ baths to determine smooth muscle contraction. Both selenium and vitamin E deficient diets reduced resistance to helminth infection. Vitamin E, but not selenium, deficiency prevented nematode-induced decreases in glucose absorption and hyper-contractility of smooth muscle. Thus, vitamin E status is an important factor in the physiological response to intestinal nematode infection and may contribute to antioxidant-dependent protective mechanisms in the small intestine.

Mild energy restriction alters mouse–nematode transmission dynamics in free-running indoor arenas

Energy restriction reduces Heligmosomoides polygyrus (Dujardin, 1845) (Nematoda) infection by reducing transmission-related behaviours but prolongs parasite survival by suppressing immune responses in individually housed mice. To determine the relative importance of these two processes in accumulation of worms in mouse populations, 10 female CD1 mice were housed in each of eight indoor arenas with ad libitum access to either an energy-sufficient (ES) diet or an energy-restricted (ER) diet with 20% less metabolizable energy (four arenas per diet). After 3 weeks, H. polygyrus transmission was initiated by introducing larvae onto damp peat trays. Mice adapted to the ER diet through increased food intake and nesting and reduced overall activity; after 6 weeks, nutritional and immunological measures were comparable between diet groups. With continuing exposure to parasite larvae, mice in both ER and ES arenas developed resistance to the incoming larvae; however, mice in the ER arenas accumulated lower worm burdens than mice in the ES arenas despite their increased contact with peat. We suggest that the comparable immunocompetence of mice in the ER and ES arenas enabled the ER mice exposed to higher transmission rates to more rapidly reject the parasites, leading to lower final worm numbers, a pattern frequently observed in other helminth infections.

Effect of early feed restriction and enzyme supplementation on digestive enzyme activities in broilers

The effect of feed restriction and enzymatic supplementation on intestinal and pancreatic enzyme activities and weight gain was studied in broiler chickens. Quantitative feed restriction was applied to chickens from 7 to 14 d of age. An enzyme complex mainly consisting of protease and amylase was added to the chicken ration from hatching to the end of the experiment. Birds subjected to feed restriction whose diet was not supplemented showed an increase in sucrase, amylase, and lipase activities immediately after the restriction period. Amylase, lipase, and chymotrypsin activities were higher in chickens subjected to feed restriction and fed a supplemented diet than in those only subjected to feed restriction. Trypsin activity increased after feed restriction and after supplementation, but there was no interaction between these effects. Early feed restriction had no effect on enzyme activity in 42-d-old chickens. Chickens subjected to early restriction and fed the supplemented diet presented higher sucrase, maltase, and lipase activities than nonsupplemented ones (P < 0.05). There was no effect of early feed restriction or diet supplementation on weight gain to 42 d. Percentage weight gain from 14 to 42 d of age was equivalent in feed-restricted and ad libitum fed birds. Feed-restricted broilers fed a supplemented diet showed a higher percentage weight gain than nonsupplemented birds. We conclude that enzymatic supplementation potentiates the effect of feed restriction on digestive enzyme activity and on weight gain.

The influence of estradiol and diet on small intestinal glucose transport in ovariectomized rats

Although gender differences exist for intestinal absorption of nutrients and drugs, the possible role estradiol may play in modulating nutrient transport has not been established. Therefore, small intestine glucose transport was measured 1 week after administering estradiol to ovariectomized rats fed diets high in carbohydrate (C) or protein (P). Rats treated with estradiol ate 21% less (P<0.05) and lost body mass (7%; P<0.05) but did not have smaller intestines. Administration of estradiol increased rates of glucose transport, but only when the rats were fed the C diet. These findings indicate that estradiol causes a disconnect between food intake and the dimensions and nutrient transport capacities of the small intestine. Furthermore, the responses to estradiol are influenced by diet composition, are not of the same magnitude for rats and dogs, and can be predicted to affect systemic availability of nutrients and drugs.

Linking nutrition to genomics

The new scientific field of nutrigenomics utilizes genomic tools, like microarrays, to analyze metabolic adaptations induced by variations in nutritional status. Here we describe how transcriptional regulation patterns caused by nutritional changes can be identified using gene expression profiling. This includes technical remarks on microarray analysis and data processing, as well as giving biological meaning to statistically solid data. We highlight our recent findings of transcriptional regulation of genes representing specific signaling and metabolic pathways in mouse liver under starvation. The results show strong correlations to previously identified responses to caloric restriction, which can be linked to lifespan extension.