Grain versus AIN: Common rodent diets differentially affect health outcomes in adult C57BL/6j mice

Semi-synthetic and grain-based diets are common rodent diets for biomedical research. Both diet types are considered nutritionally adequate to support breeding, growth, and long life, yet there are fundamental differences between them that may affect metabolic processes. We have characterized the effects of diet type on breeding outcomes, metabolic phenotype, and microbiota profile in adult mice. Healthy 8-week-old female and male C57BL/6J mice were fed a semi-synthetic or a grain-based diet for 12 weeks and changes in body weight and body composition were monitored. Breeding outcomes were determined. Body fat accumulation of female mice was lower on the semi-synthetic diet than on the grain-based diet. Pregnancy rate and newborn pup survival appeared to be lower in mice exposed to semi-synthetic diet compared to grain-based diet. Both female and male mice showed a profound change in fecal microbiota alpha and beta diversity depending on diet type. Our study shows that type of rodent diet may affect breeding outcomes whilst influencing metabolism and health of female laboratory mice. These factors have the potential to influence other experimental outcomes and the results suggest that semi-synthetic and grain-based diets are not interchangeable in research using rodent models. Careful consideration and increased understanding of the consequences of diet choice would lead to improvements in experimental design and reproducibility of study results.

Health relevance of lowering postprandial glycaemia in the paediatric population through diet': results from a multistakeholder workshop

To summarize current knowledge and gaps regarding the role of postprandial glycaemic response in the paediatric population, a workshop was organized in June 2021 by the European branch of the International Life Science Institute (ILSI). This virtual event comprised of talks given by experts followed by in-depth discussions in breakout sessions with workshop participants. The main pre-specified topics addressed by the workshop organizing committee to the invited speakers and the workshop participants were: (1) the role of glycaemic responses for paediatric health, based on mechanistic insights from animal and human data, and long-term evidence from observational and intervention studies in paediatric populations, and (2) changes in metabolism and changes in dietary needs from infancy to adolescence. Each talk as well as the discussions were summarised, including the main identified research gaps. The workshop led to the consensus on the crucial role on health of postprandial glycaemic response in paediatric population. However, a lack of scientific data has been identified regarding detailed glucose and insulin profiles in response to foods commonly consumed by paediatric populations, as well as a lack of long-term evidence including the need for suitable predictors during childhood and adolescence to anticipate health effects during adulthood.

The effect of dietary lipid quality in early life on serum LysoPC(18:2) levels and their association with adult blood glucose levels in intrauterine growth restricted rats

Being born small-for-gestational-age, especially with subsequent catch-up growth, is associated with impaired metabolic health in later-life. We previously showed that a postnatal diet with an adapted lipid droplet structure can ameliorate some of the adverse metabolic consequences in intrauterine growth-restricted (IUGR) rats. The aim of the present work was to explore possible underlying mechanism(s) and potential biomarkers. To this end, serum metabolomics was performed in postnatal day (PN) 42 and PN96 samples of the above-mentioned rat offspring, born after uterine vasculature ligation. Blood samples were collected at PN42, directly after a postnatal dietary intervention with either complex lipid matrix (CLM) or control (CTRL) diet, and at PN96 after a subsequent western-style diet (WSD). Offspring of Non-operated (NOP) dams fed CTRL in early life were included as control group. In the PN42 metabolomics data, 11 co-abundance modules of metabolites were identified, of which four were significantly correlated to adult blood glucose levels at PN96. Further analyses showed that Lysophosphatidylcholine(18:2) (LysoPC(18:2)) levels were reduced by ligation (p < 0.01) and restored in CLM fed animals (p < 0.05). LysoPC(18:2) levels at PN42 correlated inversely with adult blood glucose levels. These data indicate that early-life LysoPC(18:2) blood levels may predict adult blood glucose levels and are affected by a postnatal diet with an adapted lipid droplet structure in IUGR offspring.

Adipocytes harbor a glucosylceramide biosynthesis pathway involved in iNKT cell activation

BACKGROUND

Natural killer T (NKT) cells in adipose tissue (AT) contribute to whole body energy homeostasis.

RESULTS

Inhibition of the glucosylceramide synthesis in adipocytes impairs iNKT cell activity.

CONCLUSION

Glucosylceramide biosynthesis pathway is important for endogenous lipid antigen activation of iNKT cells in adipocytes.

SIGNIFICANCE

Unraveling adipocyte-iNKT cell communication may help to fight obesity-induced AT dysfunction. Overproduction and/or accumulation of ceramide and ceramide metabolites, including glucosylceramides, can lead to insulin resistance. However, glucosylceramides also fulfill important physiological functions. They are presented by antigen presenting cells (APC) as endogenous lipid antigens via CD1d to activate a unique lymphocyte subspecies, the CD1d-restricted invariant (i) natural killer T (NKT) cells. Recently, adipocytes have emerged as lipid APC that can activate adipose tissue-resident iNKT cells and thereby contribute to whole body energy homeostasis. Here we investigate the role of the glucosylceramide biosynthesis pathway in the activation of iNKT cells by adipocytes. UDP-glucose ceramide glucosyltransferase (Ugcg), the first rate limiting step in the glucosylceramide biosynthesis pathway, was inhibited via chemical compounds and shRNA knockdown in vivo and in vitro. β-1,4-Galactosyltransferase (B4Galt) 5 and 6, enzymes that convert glucosylceramides into potentially inactive lactosylceramides, were subjected to shRNA knock down. Subsequently, (pre)adipocyte cell lines were tested in co-culture experiments with iNKT cells (IFNγ and IL4 secretion). Inhibition of Ugcg activity shows that it regulates presentation of a considerable fraction of lipid self-antigens in adipocytes. Furthermore, reduced expression levels of either B4Galt5 or -6, indicate that B4Galt5 is dominant in the production of cellular lactosylceramides, but that inhibition of either enzyme results in increased iNKT cell activation. Additionally, in vivo inhibition of Ugcg by the aminosugar AMP-DNM results in decreased iNKT cell effector function in adipose tissue. Inhibition of endogenous glucosylceramide production results in decreased iNKT cells activity and cytokine production, underscoring the role of this biosynthetic pathway in lipid self-antigen presentation by adipocytes.

Paneth cell extrusion and release of antimicrobial products is directly controlled by immune cell-derived IFN-γ

Paneth cells (PCs) are terminally differentiated, highly specialized secretory cells located at the base of the crypts of Lieberkühn in the small intestine. Besides their antimicrobial function, PCs serve as a component of the intestinal stem cell niche. By secreting granules containing bactericidal proteins like defensins/cryptdins and lysozyme, PCs regulate the microbiome of the gut. Here we study the control of PC degranulation in primary epithelial organoids in culture. We show that PC degranulation does not directly occur upon stimulation with microbial antigens or bacteria. In contrast, the pro-inflammatory cytokine Interferon gamma (IFN-γ) induces rapid and complete loss of granules. Using live cell imaging, we show that degranulation is coupled to luminal extrusion and death of PCs. Transfer of supernatants from in vitro stimulated iNKT cells recapitulates degranulation in an IFN-γ-dependent manner. Furthermore, endogenous IFN-γ secretion induced by anti-CD3 antibody injection causes Paneth loss and release of goblet cell mucus. The identification of IFN-γ as a trigger for degranulation and extrusion of PCs establishes a novel effector mechanism by which immune responses may regulate epithelial status and the gut microbiome.

CD1d-mediated presentation of endogenous lipid antigens by adipocytes requires microsomal triglyceride transfer protein

Obesity-induced adipose tissue (AT) dysfunction results in a chronic low-grade inflammation that predisposes to the development of insulin resistance and type 2 diabetes. During the development of obesity, the AT-resident immune cell profile alters to create a pro-inflammatory state. Very recently, CD1d-restricted invariant (i) natural killer T (NKT) cells, a unique subset of lymphocytes that are reactive to so called lipid antigens, were implicated in AT homeostasis. Interestingly, recent data also suggest that human and mouse adipocytes can present such lipid antigens to iNKT cells in a CD1d-dependent fashion, but little is known about the lipid antigen presentation machinery in adipocytes. Here we show that CD1d, as well as the lipid antigen loading machinery genes pro-saposin (Psap), Niemann Pick type C2 (Npc2), α-galactosidase (Gla), are up-regulated in early adipogenesis, and are transcriptionally controlled by CCAAT/enhancer-binding protein (C/EBP)-β and -δ. Moreover, adipocyte-induced Th1 and Th2 cytokine release by iNKT cells also occurred in the absence of exogenous ligands, suggesting the display of endogenous lipid antigen-D1d complexes by 3T3-L1 adipocytes. Furthermore, we identified microsomal triglyceride transfer protein, which we show is also under the transcriptional regulation of C/EBPβ and -δ, as a novel player in the presentation of endogenous lipid antigens by adipocytes. Overall, our findings indicate that adipocytes can function as non-professional lipid antigen presenting cells, which may present an important aspect of adipocyte-immune cell communication in the regulation of whole body energy metabolism and immune homeostasis.

Allele compensation in tip60+/- mice rescues white adipose tissue function in vivo

Adipose tissue is a key regulator of energy homestasis. The amount of adipose tissue is largely determined by adipocyte differentiation (adipogenesis), a process that is regulated by the concerted actions of multiple transcription factors and cofactors. Based on in vitro studies in murine 3T3-L1 preadipocytes and human primary preadipocytes, the transcriptional cofactor and acetyltransferase Tip60 was recently identified as an essential adipogenic factor. We therefore investigated the role of Tip60 on adipocyte differentiation and function, and possible consequences on energy homeostasis, in vivo. Because homozygous inactivation results in early embryonic lethality, Tip60+/− mice were used. Heterozygous inactivation of Tip60 had no effect on body weight, despite slightly higher food intake by Tip60+/− mice. No major effects of heterozygous inactivation of Tip60 were observed on adipose tissue and liver, and Tip60+/− displayed normal glucose tolerance, both on a low fat and a high fat diet. While Tip60 mRNA was reduced to 50% in adipose tissue, the protein levels were unaltered, suggesting compensation by the intact allele. These findings indicate that the in vivo role of Tip60 in adipocyte differentiation and function cannot be properly addressed in Tip60+/− mice, but requires the generation of adipose tissue-specific knock out animals or specific knock-in mice.

Natural killer T cells in adipose tissue prevent insulin resistance

Lipid overload and adipocyte dysfunction are key to the development of insulin resistance and can be induced by a high-fat diet. CD1d-restricted invariant natural killer T (iNKT) cells have been proposed as mediators between lipid overload and insulin resistance, but recent studies found decreased iNKT cell numbers and marginal effects of iNKT cell depletion on insulin resistance under high-fat diet conditions. Here, we focused on the role of iNKT cells under normal conditions. We showed that iNKT cell-deficient mice on a low-fat diet, considered a normal diet for mice, displayed a distinctive insulin resistance phenotype without overt adipose tissue inflammation. Insulin resistance was characterized by adipocyte dysfunction, including adipocyte hypertrophy, increased leptin, and decreased adiponectin levels. The lack of liver abnormalities in CD1d-null mice together with the enrichment of CD1d-restricted iNKT cells in both mouse and human adipose tissue indicated a specific role for adipose tissue-resident iNKT cells in the development of insulin resistance. Strikingly, iNKT cell function was directly modulated by adipocytes, which acted as lipid antigen-presenting cells in a CD1d-mediated fashion. Based on these findings, we propose that, especially under low-fat diet conditions, adipose tissue-resident iNKT cells maintain healthy adipose tissue through direct interplay with adipocytes and prevent insulin resistance.

Plasma mannose-binding lectin is stimulated by PPARα in humans

The peroxisome proliferator activated receptor-α (PPARα) is a major transcriptional regulator of lipid metabolism in liver and represents the molecular target for hypolipidemic fibrate drugs. Effects of PPARα on lipid metabolism are partially mediated by circulating proteins such as FGF21 and ANGPTL4. The present study was undertaken to screen for and identify circulating proteins produced by human liver that are under the control of PPARα. Toward that aim, primary human hepatocytes were treated with the synthetic PPARα agonist Wy-14643 and whole genome expression data selected for secreted proteins. Expression of FGF21, ANGPTL4, and mannose-binding lectin (MBL), a soluble mediator of innate immunity and primary component of the lectin branch of the complement system, was markedly upregulated by Wy-14643 in primary human hepatocytes. Mice express two MBL isomers, Mbl1 and Mbl2. Mbl1 mRNA was weakly induced by Wy-14643 in primary mouse hepatocytes and remained unaltered by Wy-14643 in mouse liver. Mbl2 mRNA was unchanged by Wy-14643 in primary mouse hepatocytes and was strongly reduced by Wy-14643 in mouse liver. Remarkably, plasma Mbl1 levels were increased by chronic PPARα activation in lean and obese mice. Importantly, in two independent clinical trials, treatment with the PPARα agonist fenofibrate at 200 mg/day for 6 wk and 3 mo increased plasma MBL levels by 73 (P = 0.0016) and 86% (P = 0.017), respectively. It is concluded that hepatocyte gene expression and plasma levels of MBL are stimulated by PPARα and fenofibrate in humans, linking PPARα to regulation of innate immunity and complement activation in humans and suggesting a possible role of MBL in lipid metabolism.

Peroxisome proliferator-activated receptor alpha target genes

The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor involved in the regulation of a variety of processes, ranging from inflammation and immunity to nutrient metabolism and energy homeostasis. PPARα serves as a molecular target for hypolipidemic fibrates drugs which bind the receptor with high affinity. Furthermore, PPARα binds and is activated by numerous fatty acids and fatty acid-derived compounds. PPARα governs biological processes by altering the expression of a large number of target genes. Accordingly, the specific role of PPARα is directly related to the biological function of its target genes. Here, we present an overview of the involvement of PPARα in lipid metabolism and other pathways through a detailed analysis of the different known or putative PPARα target genes. The emphasis is on gene regulation by PPARα in liver although many of the results likely apply to other organs and tissues as well.

Comparative analysis of gene regulation by the transcription factor PPARalpha between mouse and human

Background

Studies in mice have shown that PPARα is an important regulator of hepatic lipid metabolism and the acute phase response. However, little information is available on the role of PPARα in human liver. Here we set out to compare the function of PPARα in mouse and human hepatocytes via analysis of target gene regulation.

Methodology/Principal Findings

Primary hepatocytes from 6 human and 6 mouse donors were treated with PPARα agonist Wy14643 and gene expression profiling was performed using Affymetrix GeneChips followed by a systems biology analysis. Baseline PPARα expression was similar in human and mouse hepatocytes. Depending on species and time of exposure, Wy14643 significantly induced the expression of 362–672 genes. Surprisingly minor overlap was observed between the Wy14643-regulated genes from mouse and human, although more substantial overlap was observed at the pathway level. Xenobiotics metabolism and apolipoprotein synthesis were specifically regulated by PPARα in human hepatocytes, whereas glycolysis-gluconeogenesis was regulated specifically in mouse hepatocytes. Most of the genes commonly regulated in mouse and human were involved in lipid metabolism and many represented known PPARα targets, including CPT1A, HMGCS2, FABP1, ACSL1, and ADFP. Several genes were identified that were specifically induced by PPARα in human (MBL2, ALAS1, CYP1A1, TSKU) or mouse (Fbp2, lgals4, Cd36, Ucp2, Pxmp4). Furthermore, several putative novel PPARα targets were identified that were commonly regulated in both species, including CREB3L3, KLF10, KLF11 and MAP3K8.

Conclusions/Significance

Our results suggest that PPARα activation has a major impact on gene regulation in human hepatocytes. Importantly, the role of PPARα as master regulator of hepatic lipid metabolism is generally well-conserved between mouse and human. Overall, however, PPARα regulates a mostly divergent set of genes in mouse and human hepatocytes.

High maternal vitamin E intake by diet or supplements is associated with congenital heart defects in the offspring

OBJECTIVE

To study associations between maternal dietary and supplement intake of antioxidants vitamin E, retinol and congenital heart defects (CHDs).

DESIGN

Case-control study.

SETTING

Erasmus MC, University Medical Center Rotterdam, the Netherlands.

POPULATION

Participants were 276 case mothers of a child with CHD and 324 control mothers with their children.

METHODS

Food frequency questionnaires covering the intake of the previous 4 weeks were filled out at 16 months after the index pregnancy. Data were compared between cases and controls using the Mann-Whitney U test. Risk estimates for the association between CHD and dietary intake of vitamin E and retinol were estimated in a multivariable logistic regression model.

MAIN OUTCOME MEASURES

Medians (5-95th percentile) and odds ratios with 95% CI.

RESULTS

Dietary vitamin E intake was higher in case mothers than in controls, 13.3 (8.1-20.4) and 12.6 (8.5-19.8) mg/day (P= 0.05). CHD risk increased with rising dietary vitamin E intakes (P-trend = 0.01). Periconception use of vitamin E supplements in addition to a high dietary vitamin E intake above 14.9 mg/day up to nine-fold increased CHD risk. Retinol intakes were not significantly different between the groups and not associated with CHD risk.

CONCLUSIONS

High maternal vitamin E by diet and supplements is associated with an increased risk of CHD offspring.