Chaonan Fan

Omega-3 fatty acid containing diets decrease plasma triglyceride concentrations in mice by reducing endogenous triglyceride synthesis and enhancing the blood clearance of triglyceride-rich particles

BACKGROUND & AIMS Intake of n-3 fatty acids can reduce both fasting and postprandial triglyceride (TG) concentrations in humans as well as in experimental animals, but the mechanisms by which this occurs are not completely known. We investigated in mice the effects of dietary fish oil (a source of n-3 fatty acids) on endogenous TG synthesis and exogenous TG-rich particle removal. METHODS C57 BL/6J mice were fed for 4 months with three types of high-fat diets (18% fat wt/wt) - soy oil, fish oil and a mixture of soy oil and fish oil (soy/fish) (5:1 wt/wt), and a chow diet with 6% fat from soy oil (wt/wt) served as a control. Plasma TG and apolipoprotein B (apoB) concentrations and lipoprotein lipase (LPL) activity were measured. Triton WR 1339 was used to assess hepatic synthesis of very low density lipoprotein, and intravenous injection of chylomicron-like lipid emulsions was conducted to determine the effects of dietary fish oil n-3 fatty acids on exogenous TG clearance. RESULTS Both fish and soy/fish oil diets reduced plasma TG levels in fed and fasted states compared to soy oil alone. Plasma pre- and post-heparin LPL activities were significantly higher with fish and soy/fish oil diets than soy oil diet in fed mice. No differences in plasma TG levels and LPL activity were shown among groups of fish oil, soy/fish oil and normal chow diets. Levels of hepatic TG and apoB synthesis were 30-50% and 42% lower in mice fed with the fish oil diet compared to the other three diets. In addition, compared to soy oil diet, fish oil feeding significantly increased blood clearance of chylomicron-like lipid emulsions by 21-26%. CONCLUSIONS Our data suggest that reduced endogenous TG synthesis, increased LPL activities and more rapid blood clearance of TG-rich particles all distinctly contribute to the TG-lowering effects of fish oil n-3 fatty acids.

Short Chain Fatty Acids Prevent High-fat-diet-induced Obesity in Mice by Regulating G Protein-coupled Receptors and Gut Microbiota.

Elucidating the mechanisms by which short chain fatty acids (SCFA) reduce body weight may assist in the development of an effective weight control strategy. Dietary supplementation of acetate, propionate, butyrate or their admixture was shown to significantly inhibit the body weight gain induced by high-fat diet feeding. Supplementation of SCFAs caused significant changes in the expressions of G-protein coupled receptor 43 (GPR43) and GPR41 characterized by increases in the adipose tissue and reductions in the colon. Additionally, they influenced the bacterial community structure in feces, with a reduction in the proportion of Firmicutes and an increase in the proportion of Bacteroidetes. The effects of dietary SCFAs on the GPR expression and gut microbiota composition may further result in body weight reduction by enhancing triglyceride hydrolysis and FFA oxidation in the adipose tissue, promoting beige adipogenesis and mitochondrial biogenesis, and inhibiting chronic inflammation.

Epigenetic Modification of the Leptin Promoter in Diet-Induced Obese Mice and the Effects of N-3 Polyunsaturated Fatty Acids

We report evidence of a detailed epigenetic modification of the leptin promoter and the effects of n-3 polyunsaturated fatty acids (n-3 PUFAs), which is closely associated with the leptin gene transcription in obesity. In the adipose tissue of diet induced obese (DIO) mice, methylation of the CpG island and the binding of methyl-CpG-binding domain protein 2 (MBD2) and DNA methyltransferases (DNMTs) at the leptin promoter are increased and RNA Pol II is decreased. Additionally, histones H3 and H4 are hypoacetylated, lysine 4 of histone H3 (H3K4) is hypomethylated and the binding of histone deacetylases (HDACs) 1, 2 and 6 is increased at the leptin promoter in the DIO mice. These modifications may serve a feedback role to maintain leptin concentrations within a normal range. The regulation of leptin transcriptional expression by n-3 PUFAs is mediated, at least in part, by epigenetic targets, such as MBD2 and histone modifications.

The Regulation of Leptin, Leptin Receptor and Pro-opiomelanocortin Expression by N-3 PUFAs in Diet-Induced Obese Mice Is Not Related to the Methylation of Their Promoters

BackgroundThe expression of leptin is increased in obesity and inhibited by n-3 polyunsaturated fatty acids (n-3 PUFAs), but the underlying molecular mechanisms have not been firmly established.MethodsIn this study, we investigated the effects of dietary n-3 PUFAs on the methylation of CpG islands in the promoter regions of the leptin, leptin-R and POMC genes, as well as the effects of n-3 PUFA status in early life on the modification of the promoters of these three genes. Male C57 BL/6J mice were fed a high-fat diet with one of four different fat types: sunflower oil (n-3 PUFA deficient), soy oil, fish oil, or a mixture of soy and fish oil (soy:fish oil = 1:1). Two low-fat diets with sunflower oil or soy oil served as controls. Female mice were fed two breeding diets, sunflower oil or a mixture of soy and fish oil (soy:fish oil = 1:1), during pregnancy and lactation to breed new pups.ResultsCompared to mice fed the control diets, the expression of leptin in fat tissue and leptin-R and POMC in the hypothalamus was higher in the diet-induced obesity (DIO) mice, and the n-3 PUFAs in the diets reversed these elevated expression levels. The mean methylation levels of CpG sites in the promoter regions of the leptin and POMC genes showed no difference between the DIO and the control diet groups nor between the n-3 PUFA-containing and -deficient diet groups. For the CpG sites in the promoter regions of leptin-R, no methylation was found in any of the DIO or control groups. Feeding mice with the n-3 PUFA diet during pregnancy and lactation did not affect CpG methylation in the leptin or POMC promoters.ConclusionsOur findings indicate that promoter DNA methylation may not be related to the expression of leptin, leptin-R or its related hypothalamic satiety regulator POMC.

Dietary fish oil n-3 polyunsaturated fatty acids and alpha-linolenic acid differently affect brain accretion of docosahexaenoic acid and expression of desaturases and sterol regulatory element-binding protein 1 in mice.

Whether preformed dietary docosahexaenoic acid (DHA) is required for brain accretion has not been clearly determined. In this study, we investigated in mice the different effects of dietary longer-chain n-3 polyunsaturated fatty acids (PUFAs) and α-linolenic acid (LNA) on brain accretion of DHA and the expression of associated desaturases and transcription factors. C57 BL/6J mice were fed for 3 months with four fish oil n-3 PUFA diets--lower, low, high and higher (0.46%, 0.91%, 1.73% and 4.29% total energy, respectively); a flaxseed oil n-3 PUFA (5.01% total energy) diet; and an n-3 PUFA-deficient diet, respectively. Either fish oil or flaxseed oil n-3 PUFA diets increased DHA concentrations in the brain. However, the flaxseed oil n-3 PUFA diet was less effective than the fish oil diet with higher amount of n-3 PUFA in increasing brain DHA content. Furthermore, the expressions of delta-6 desaturase (D6D) and sterol regulatory element binding protein 1 (SREBP-1) in the liver were down-regulated by all fish oil diets with different amounts of n-3 PUFAs, as well as by the flaxseed oil n-3 PUFA diet, whereas in the brain, D6D, delta-5 desaturase (D5D) and SREBP-1 expressions were down-regulated by the higher fish oil n-3 PUFA diet rather than by other fish oil n-3 PUFA and the flaxseed oil n-3 PUFA diets. These results suggest that preformed dietary DHA, different from those converted by LNA inside the body, is better for brain accretion. Dietary longer-chain n-3 PUFAs affect expressions of D6D, D5D and SREBP-1 in the brain differently from their precursor LNA.

Genome-wide screen of DNA methylation identifies novel markers in childhood obesity.

Epigenetic modifications have been highlighted in chronic non-communicable diseases. The aim of this study was to investigate genome-wide DNA methylation for the identification of methylation markers in obesity. With obese Chinese preschool children, we performed comprehensive DNA methylation profiling of gene promoters and CpG islands to determine the differentially methylated genes using methylated DNA immunoprecipitation followed by hybridization to the NimbleGen Human DNA Methylation 385K Promoter Plus CpG Island Microarray. We found that compared to lean children, 251 promoters and 575 CGIs were demethylated, and 141 promoters and 277 CGIs were hypermethylated in obese children, and their distribution on chromosomes was imbalanced, showing more promoters and CGIs with demethylation on chromosomes 3, 16, 17 and 19 and more differentially methylated promoters and CGIs on chromosome X compared with chromosome Y. Further analysis indicated that aberrant methylations occurred mostly in HCP promoters and promoter CGIs. Among the top 80 promoters and CGIs that had differentiated methylation between obese and lean children, nearly half have been previously studied, and almost all of them are involved in the pathogenesis of cancers that are associated with many organs. Furthermore, four genes (FZD7, PRLHR, EXOSC4, and EIF6) with differential promoter methylation were validated, and their associations with obesity must be clarified. In conclusion, this study represents the first effort to determine methylation markers in obese Chinese children, which has potential relevance for identifying markers that are useful in elucidating the mechanisms of obesity pathogenesis and its complications.

Genome-wide screen of promoter methylation identifies novel markers in diet-induced obese mice

OBJECTIVE To investigate the genome-wide promoter methylation and gene expression for the identification of methylation markers in obesity. METHODS Using a high-fat, diet-induced obese mouse model, we performed comprehensive DNA methylation profiling of gene promoters to determine the differentially methylated genes using methylated DNA immunoprecipitation followed by hybridization to the NimbleGen MM8 CpG plus Promoter Microarray. We further integrated epigenomics data with gene expression profiling to identify promoters exhibiting an association between methylation status and the expression of downstream genes. RESULTS A total of 24 hypermethylated promoters and 42 hypomethylated promoters in epididymal fat were selected as methylation markers, which were associated with downregulated and upregulated gene expression, respectively. The promoter methylation and differential gene expression of three markers (Mmp2, Foxj3 and Ube2q2) in the fat were validated by sequencing bisulfitemodified DNA and real-time reverse transcriptase PCR. The genes with these differentially methylated promoters and the associated transcriptional expression in the fat were primarily involved in biological activities in lipid metabolism and storage, cellular differentiation, immunity and the pathogenesis of obesity-related complications. CONCLUSIONS This study represents the first effort to determine methylation markers in obese mice that may regulate gene transcription in obesity. Our approach has potential relevance for clinical applications by identifying markers useful in elucidating the mechanisms of obesity pathogenesis and its complications.

Time-specific changes in DNA methyltransferases associated with the leptin promoter during the development of obesity.

OBJECTIVE The role of epigenetic modifications on leptin expression during the development of obesity has not been clearly determined. This study aimed to investigate changes in the expression of DNA methyltransferases (DNMTs) at the leptin promoter and their effect on gene transcription during the development of obesity. METHODS Using a high-fat diet (HFD)-induced obese (DIO) mouse model, we examined adipose expression of leptin, its promoter associated DNMTs and the methyl CpG-binding domain protein 2 (MBD2) at different time points after HFD feeding. RESULTS The leptin expression levels in epididymal fat were significantly increased after feeding the mice a HFD for 4, 8, 12 and 18 weeks (w), as opposed to feeding them a standard diet (SD). However, the CpG promoter methylation fractions were significantly reduced at 8 w with a decreased association of MBD2 and DNMT1, and increased at 12 w and 18 w with an increased association of MBD2, DNMT3A and DNMT3B, after HFD feeding. Additionally, the binding of RNA polymerase II was increased at 8 w and decreased at 18 w after HFD feeding compared with SD feeding. CONCLUSIONS These data indicate that time-specific changes in promoter associated DNMTs may be associated with the regulation of leptin expression, indicating that a complex and dynamic epigenetic mechanism underlies aberrant leptin expression during the development of obesity.

Maternal n-3 polyunsaturated fatty acid deprivation during pregnancy and lactation affects neurogenesis and apoptosis in adult offspring: associated with DNA methylation of brain-derived neurotrophic factor transcripts.

In this study, we hypothesized that n-3 polyunsaturated fatty acid (PUFA) deficiency during pregnancy and lactation will make a lasting impact on brain neurogenesis and apoptosis of the adult offspring and that these harmful effects cannot be reversed by n-3 PUFA supplementation after weaning. Moreover, the underlying mechanisms may be attributable to the epigenetic changes of brain-derived neurotrophic factor (BDNF). C57BL/6J female mice were fed with n-3 PUFA-deficient diet (n-3 def) or n-3 PUFA-adequate diet (n-3 adq) throughout pregnancy and lactation. At postnatal 21 days, equal numbers of male pups from both groups were fed the opposite diet, and the remaining male pups were fed with the same diets as their mothers until 3 months of age. Feeding the n-3 adq diet to pups from the maternal n-3 def group significantly increased the n-3 PUFA concentration but did not change expressions of calretinin, Bcl2, and Bax in the hippocampus. Feeding the n-3 def diet to pups from the maternal n-3 adq group significantly reduced the n-3 PUFA concentration but did not reduce expressions of calretinin and Bcl2. Similarly, BDNF levels, especially mRNA expressions of BDNF transcripts IV and IX, were also reduced by maternal n-3 def and not reversed by n-3 PUFA supplementation after weaning. The decrease in BDNF expression by maternal n-3 def diet was associated with greater DNA methylation at special CpG sites. These results suggested that the maternal n-3 PUFA deficiency during pregnancy and lactation imprints long-term changes of brain development in adult offspring.

Dietary ratios of n-6/n-3 polyunsaturated fatty acids during maternal pregnancy affect hippocampal neurogenesis and apoptosis in mouse offspring

OBJECTIVE although n-3 polyunsaturated fatty acids (PUFAs) play crucial roles in brain development and function, neither the optimal level of n-3 PUFAs nor the optimal ratio of n-6/n-3 PUFAs in the maternal diet are well defined. In this study, we investigated the effects of dietary n-6/n-3 PUFA ratios during pregnancy on neurogenesis and apoptosis in the brains of mouse offspring. Metods: female C57BL/6J mice were fed one of three diets with high, medium and low ratios of n-6/n-3 PUFAs (15.7:1, 6.3:1, 1.6:1), as well as a high fish oil diet with a n-6/n-3 ratio of 1:5.7; an n-3 PUFA-deficient diet served as control. The feeding regimens began two months before mouse conception and continued for the duration of the pregnancy. The neurogenesis and apoptosis of hippocampal CA3 area in the offspring were detected. RESULTS compared to the n-3 PUFA-deficient diet, n-3 PUFA-containing diets, particularly those with n-6/n-3 PUFA ratios of 6.3:1 and 1.6:1, significantly increased both phosphorylation of histone H3 at ser 10 (p-H3ser10) and calretinin-positive cells in hippocampus CA3 of the offspring. Furthermore, increased expression of Bcl2 protein, decreased expression of Bax protein, and reduced caspase 3 activity and numbers of TUNEL apoptotic cells were found in the three diets with high, medium and low n-6/n-3 PUFA ratios. However, there were no differences in any of these parameters between the high fish oil diet group and the n-3 PUFA-deficient diet group. CONCLUSIONS these data suggest that a higher intake of n-3 PUFAs with a lower ratio of n-6/n-3 PUFAs of between about 6:1 to 1:1, supplied to mothers during pregnancy, may benefit brain neurogenesis and apoptosis in offspring. However, excessive maternal intake of n-3 PUFAs may exert a negative influence on brain development in the offspring.