Apolipoprotein A5 deficiency aggravates high-fat diet-induced obesity due to impaired central regulation of food intake

Genome wide transcriptome analysis provides bases on hepatic lipid metabolism disorder affected by increased dietary grain ratio in fattening lambs

BACKGROUND

The liver is a principal metabolic organ and has a major role in regulating lipid metabolism. With the development of rapidly fattening livestock in the modern breeding industry, the incidence of hepatic steatosis and accumulation in animals was significantly increased. However, the molecular mechanisms responsible for hepatic lipid metabolic disturbances in a high concentrate diet remain unclear. The objective of this study was to evaluate the effects of increasing concentrate level in a fattening lamb diet on biochemical indices, hepatic triglycerides (TG) concentration, and hepatic transcriptomic profiles. In the present study, 42 weaned lambs (about 3 ± 0.3 months old) were randomly assigned to the GN60 group (60% concentrate of dry matter, GN60, n = 21) or GN70 group (70% concentrate of dry matter, n = 21) for a 3-months feeding trial.

RESULTS

No difference was observed in the growth performance or plasma biochemical parameters between the GN60 group and the GN70 group. The hepatic TG concentration was higher in the GN70 group than GN60 group (P < 0.05). Hepatic transcriptomic analysis showed that there were 290 differentially expressed genes identified between GN60 and GN70 groups, with 125 genes up-regulated and 165 genes down-regulated in the GN70 group. The enriched Gene Ontology (GO) items and KEGG pathways and protein-protein interaction (PPI) network of differentially expressed genes (DEGs) revealed that the majority of enriched pathways were related to lipid metabolism. Further analysis revealed that the fatty acid synthesis was up-regulated, while fatty acid transport, oxidation, and TG degradation were down-regulated in the GN70 group when compared with the GN60 group.

CONCLUSIONS

These results indicated that GN70 induced excess lipid deposition in the liver of lambs during the fattening period, with high synthesis rates and low degradation rates of TG. The identified mechanisms may help understand hepatic metabolism in lambs with a high concentrate diet and provide insight into decreasing the risk of liver metabolism disorder in animals.

Exercise Alleviates the Apolipoprotein A5-Toll-Like Receptor 4 Axis Impairment in Mice With High-Fat Diet-Induced Non-alcoholic Steatohepatitis

Background: Apolipoprotein A5 (ApoA5), an important modulator of plasma and hepatic triglyceride metabolism, has been found to be downregulated by metformin to improve non-alcoholic fatty liver disease. Meanwhile, exercise has been recommended as a therapeutic strategy for non-alcoholic steatohepatitis (NASH). However, no study has yet determined whether exercise affects hepatic ApoA5 expression or the inhibition of ApoA5 to toll-like receptor 4 (TLR4). We herein examined the effects of exercise on hepatic ApoA5 expression and the relevance of ApoA5 and TLR4-mediated pathway in mice with high-fat diet (HFD)-induced NASH. Methods: Male C57BL/6J mice were built NASH model with high-fat diet for 12 weeks, and following mice were subjected to exercise for 12 weeks on a treadmill. Microscopy and enzyme-linked immunosorbent assay were used to measure histological analysis of liver and hepatic lipids, respectively. Quantitative real-time PCR and western blot were used to determined mRNA and protein levels of ApoA5 and TLR4-mediated nuclear factor kappa B (NF-κB) pathway components, respectively. ApoA5 overexpression plasmids transfected into mice to investigate the relevance of ApoA5 and TLR4. Results: 12 weeks of exercise remarkably alleviated HFD-induced hepatic lipid accumulation, inflammation, and fibrosis, as well as reduced serum lipopolysaccharide (LPS), hepatic TLR4, myeloid differentiation factor 88 (MyD88), and NF-κBp65 expression. Importantly, exercise did not reduce ApoA5 expression but instead enhanced its ability to suppress TLR4-mediated NF-κB pathway components by decreasing circulating LPS in our experiments involving transfection of ApoA5 overexpression plasmids and LPS interventions. Conclusion: The results demonstrated that exercise improved HFD-induced NASH by triggering the inhibitory effects of ApoA5 on the TLR4-mediated NF-κB pathway.

Genetically-engineered hamster models: applications and perspective in dyslipidemia and atherosclerosis-related cardiovascular disease

Cardiovascular disease is the leading cause of morbidity and mortality in both developed and developing countries, in which atherosclerosis triggered by dyslipidemia is the major pathological basis. Over the past 40 years, small rodent animals, such as mice, have been widely used for understanding of human atherosclerosis-related cardiovascular disease (ASCVD) with the advantages of low cost and ease of maintenance and manipulation. However, based on the concept of precision medicine and high demand of translational research, the applications of mouse models for human ASCVD study would be limited due to the natural differences in metabolic features between mice and humans even though they are still the most powerful tools in this research field, indicating that other species with biological similarity to humans need to be considered for studying ASCVD in future. With the development and breakthrough of novel gene editing technology, Syrian golden hamster, a small rodent animal replicating the metabolic characteristics of humans, has been genetically modified, suggesting that gene-targeted hamster models will provide new insights into the precision medicine and translational research of ASCVD. The purpose of this review was to summarize the genetically-modified hamster models with dyslipidemia to date, and their potential applications and perspective for ASCVD.

The exchangeable apolipoproteins in lipid metabolism and obesity

Dyslipidemia, characterized by increased plasma levels of low-density lipoprotein cholesterol (LDL-C), very low-density lipoprotein cholesterol (VLDL-C), triglyceride (TG), and reduced plasma levels of high-density lipoprotein cholesterol (HDL-C), is confirmed as a hallmark of obesity and cardiovascular diseases (CVD), posing serious risks to the future health of humans. Thus, it is important to understand the molecular metabolism of dyslipidemia, which could help reduce the morbidity and mortality of obesity and CVD. Currently, several exchangeable apolipoproteins, such as apolipoprotein A1 (ApoA1), apolipoprotein A5 (ApoA5), apolipoprotein E (ApoE), and apolipoprotein C3 (ApoC3), have been verified to exert vital effects on modulating lipid metabolism and homeostasis both in plasma and in cells, which consequently affect dyslipidemia. In the present review, we summarize the findings of the effect of exchangeable apolipoproteins on affecting lipid metabolism in adipocytes and hepatocytes. Furthermore, we also provide new insights into the mechanisms by which the exchangeable apolipoproteins influence the pathogenesis of dyslipidemia and its related cardio-metabolic disorders.

Apolipoprotein A5 and apolipoprotein C3 single nucleotide polymorphisms are correlated with an increased risk of coronary heart disease: a case-control and meta-analysis study

Background

Triglycerides (TGs) are proatherogenic lipoproteins involving the risk of coronary heart disease (CHD), while apolipoprotein A5 (APOA5) and apolipoprotein C3 (APOC3) are main lipoproteins composing TG-rich lipoproteins. In this study, we aim to explore the correlation of CHD with APOA5 -1131 T > C and APOC3 -455 T > C single nucleotide polymorphisms (SNPs).

Methods

A sum of 210 CHD patients, hospitalized between Jan. 2013 and Mar. 2015 at China-Japan Union Hospital, Jilin University, were selected as our case group and 223 healthy individuals who had physical examination at same hospital at the same period were selected as control group. The frequency distribution of genotypes of APOA5 -1131 T > C and APOC3 -455 T > C SNPs were measured by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The Stata 12.0 software was utilized for statistical analyses.

Results

There was no significant difference on age and sex between case and control group (P > 0.05). History of smoking, drinking, hypertension and diabetes mellitus, body mass index and levels of TG and fasting blood sugar in case group were shown to be higher than control group (P < 0.05), while levels of total cholesterol, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol in case group were lower than control group (P < 0.05). Both CC and TC′ + CC frequencies of APOA5 -1131 T > C and APOC3 -455 T > C in case group were higher compared to control group (both P < 0.05). Additionally, T allele frequencies of the two SNPs in case group were lower than control group, while C allele in case group has higher frequencies compared to control group (both P < 0.05). The results of meta-analysis under allele and dominant models showed that APOA5 -1131 T > C and APOC3 -455 T > C SNPs are likely to increase the risk of CHD (both P < 0.05).

Conclusion

APOA5 -1131 T > C and APOC3 -455 T > C SNPs may play potent roles in the development and progression of CHD.

Interaction of dietary fat intake with APOA2, APOA5 and LEPR polymorphisms and its relationship with obesity and dyslipidemia in young subjects

BACKGROUND

Diet is an important environmental factor that interacts with genes to modulate the likelihood of developing disorders in lipid metabolism and the relationship between diet and genes in the presence of other chronic diseases such as obesity. The objective of this study was to analyze the interaction of a high fat diet with the APOA2 (rs3813627 and rs5082), APOA5 (rs662799 and rs3135506) and LEPR (rs8179183 and rs1137101) polymorphisms and its relationship with obesity and dyslipidemia in young subjects.

METHODS

The study included 200 young subjects aged 18 to 25 years (100 normal-weight and 100 obese subjects). Dietary fat intake was measured using the frequency food consumption questionnaire. Genotyping of polymorphisms was performed by PCR-RFLP.

RESULTS

Individuals carrying the APOA5 56 G/G genotype with a high saturated fatty acid consumption (OR = 2.7, p = 0.006) and/or total fat (OR = 2.4, p = 0.018), associated with an increased risk of obesity. We also found that A/G + G/G genotypes of the 668 A/G polymorphism in the LEPR gene with an intake ≥ 12 g/d of saturated fatty acids, have 2.9 times higher risk of obesity (p = 0.002), 3.8 times higher risk of hypercholesterolemia (p = 0.002) and 2.4 times higher risk of hypertriglyceridemia (p = 0.02), than those with an intake <12 g/d of saturated fatty acids. Similarly, LEPR 668 A/G + G/G carriers with a high fat total intake had 3.0 times higher risk of obesity (p = 0.002) and 4.1 times higher risk of hypercholesterolemia (p = 0.001).

CONCLUSION

Our results suggest that dietary fat intake modifies the effect of APOA5 and LEPR polymorphisms on serum triglycerides, cholesterol levels and obesity in young subjects.

ApoA5 knockdown improves whole-body insulin sensitivity in high-fat-fed mice by reducing ectopic lipid content

ApoA5 has a critical role in the regulation of plasma TG concentrations. In order to determine whether ApoA5 also impacts ectopic lipid deposition in liver and skeletal muscle, as well as tissue insulin sensitivity, we treated mice with an antisense oligonucleotide (ASO) to decrease hepatic expression of ApoA5. ASO treatment reduced ApoA5 protein expression in liver by 60–70%. ApoA5 ASO-treated mice displayed approximately 3-fold higher plasma TG concentrations, which were associated with decreased plasma TG clearance. Furthermore, ApoA5 ASO-treated mice fed a high-fat diet (HFD) exhibited reduced liver and skeletal muscle TG uptake and reduced liver and muscle TG and diacylglycerol (DAG) content. HFD-fed ApoA5 ASO-treated mice were protected from HFD-induced insulin resistance, as assessed by hyperinsulinemic-euglycemic clamps. This protection could be attributed to increases in both hepatic and peripheral insulin responsiveness associated with decreased DAG activation of protein kinase C (PKC)-ε and PKCθ in liver and muscle, respectively, and increased insulin-stimulated AKT2 pho­sphory­lation in these tissues. In summary, these studies demonstrate a novel role for ApoA5 as a modulator of susceptibility to diet-induced liver and muscle insulin resistance through regulation of ectopic lipid accumulation in liver and skeletal muscle.

Increased risk of obesity related to total energy intake with the APOA5-1131T > C polymorphism in Korean premenopausal women

We hypothesized that triglyceride-raising apolipoprotein A5 (APOA5)-1131T > C may contribute to the increased risk of obesity associated with dietary intake in Korean premenopausal women whose minor allele frequency is higher than that in Western people. Genetically unrelated Korean premenopausal women (approximately 20-59 years, n = 1128) were genotyped for APOA5-1131T > C. Anthropometric, metabolic parameters and dietary intakes were analyzed. Odds ratios (ORs) for obesity risk (body mass index, ≥25.0 kg/m(2)) were calculated. Genotype distribution of APOA5-1131T > C of study subjects were like TT: 49.9%, TC: 40.8%, and CC: 9.3%. We found a significant interaction between APOA5-1131T > C and total energy intake (TEI) for obesity after adjusted for age, cigarette smoking, and alcohol consumption (P < .001). The risk of obesity in CC homozygotes compared with T carriers (TT + TC) was significantly increased, when the subjects consume higher TEI (≥2001 kcal/d (8372 kJ/d), median value of the population) (OR, 2.495; 95% confidence intervals, 1.325-4.696; P = .005), particularly, when they maintain negative balance between total energy expenditure and TEI (total energy expenditure/TEI, <1) (OR, 2.917; 95% confidence intervals, 1.451-5.864; P = .003). The contributions of APOA5-1131CC homozygotes to obesity risk in those who consume higher TEI were all significantly high regardless of percentage of energy intake from dietary macronutrients. Whereas, no significant association was observed in those who consume lower TEI (<2001 kcal/d). In addition, serum levels of triglyceride, high-density lipoprotein-cholesterol, and apolipoprotein A5 were associated with APOA5-1131T > C and TEI. These findings suggest that APOA5-1131CC homozygotes may influence the susceptibility of the individual to obesity, particularly, when they consume higher TEI, but the genetic effect may be attenuated, when people maintain low or adequate energy intake.

Association of two common polymorphisms of apolipoprotein A5 gene with metabolic syndrome indicators in a North Iranian population, a cross-sectional study

Background

Metabolic syndrome is an obesity dependent disorder with a worldwide high prevalence. Regarding the high prevalence of Metabolic syndrome in Iran we analyzed the influence of -1131T>C (rs662799) and c.56C>G (S19W, rs3135506) polymorphisms of the novel apolipoprotein gene, ApoA5, on some Metabolic Syndrome indicators in population from north of Iran.

Methods

199 volunteers from Babol city-Iran were divided in two groups of low (N = 99, TG ≤ 103 mg/dl) and high (N = 100, TG ≥ 150 mg/dl) serum levels of Triglycerides (TG). We amplified the gene fragments containing -1131T>C and c.56C>G polymorphisms by PCR method and revealed the polymorphisms by RFLP analysis.

Results

We found a significant association (p = 0.016, Independent t-test) between high levels of TG and -1131T>C polymorphism but not between this polymorphism and serum HDL-C concentrations. Carriers of the C allele had a 1.97 times higher odds ratio to be in the high-TG group than those of the TT genotype (95%, CI = 1.05-3.68). We observed no association between -1131T>C polymorphism with either Waist-to-Hip Ratio (WHR) or Body-Mass-Index (BMI). In the case of c.56C>G polymorphism, although it showed a significant relationship with WHR (p = 0/040, Independent t-test), but failed to correlate with either levels of TG (p = 0.594) or HDL-C (p = 0.640) in serum.

Conclusion

Our study confirms that ApoA5 gene polymorphisms, -1131T>C and c.56C>G are associated with the two criteria of Metabolic Syndrome, TG and WHR, respectively.