Human cholesteryl ester transfer protein enhances insulin-mediated glucose uptake in adipocytes

The combination of nuclear receptor NR1D1 and ULK1 promotes mitophagy in adipocytes to ameliorate obesity

Obesity is a severe disease worldwide. Mitochondrial autophagy (mitophagy) may be related to metabolic abnormalities in obese individuals, but the mechanism is still unclear. We aimed to investigate whether nuclear receptors NR1D1 and ULK1 influence obesity by affecting mitophagy. In vitro model was established by inducing 3T3-L1 cells differentiation. MTT was detected cell viability. ELISA was tested triglyceride (TG). Oil red O staining was performed to detect lipid droplets. Flow cytometry was measured mtROS. ChIP and Dual-luciferase reporter assay were verified NR1D1 bind to ULK1. LC3 level was detected by IF. After differentiation medium treatment, cell viability was decreased, TG content and lipid droplets were increased Moreover, NR1D1 expression was reduced in Model group. NR1D1 overexpression was increased cell viability, reduced TG content and lipid droplets. Subsequently, NR1D1 inhibited TOM20 and mtROS, whereas, Parkin and PINK1 were accelerated. NR1D1 overexpression facilitated LC3 expression, whereas ULK1 knockdown was reversed the effect of NR1D1 overexpression. Liensinine also reversed the effect of NR1D1 overexpression, that is, cell viability was reduced, mtROS, TG content and lipid droplets were increased. The combination of nuclear receptor NR1D1 and ULK1 promoted mitophagy in adipocytes to alleviate obesity, which provided new target and strategy for obesity treatment.Abbreviations: Mitochondrial autophagy (mitophagy), triglyceride (TG), Uncoordinated-51 like autophagy activating kinase 1 (ULK1), Nuclear receptor subfamily 1 group D member 1 (NR1D1), American Type Culture Collection (ATCC), fetal bovine serum (FBS), 3-isobutyl-1-methylxanthine (IBMX), dexamethasone (DEX), short hairpin RNA ULK1 (sh-ULK1), wild-type (WT), mutant (MUT), Enzyme-linked immunosorbent assay (ELISA), mitochondrial reactive oxygen species (mtROS), Chromatin immunoprecipitation (ChIP), Quantitative real-time PCR (qRT-PCR), Immunofluorescence (IF), standard deviation (SD).

Hypoglycemic effects of esculeoside A are mediated via activation of AMPK and upregulation of IRS-1

Background

Tomato fruit (Lycopersicon esculentum Mill.) has been suggested to be useful for the prevention of diabetes. Esculeoside A is the main saponin compounds in tomatoes. This study investigated the hypoglycemic effects and the underlying mechanism of esculeoside A in C57BLKS/Leprdb (db/db) mice.

Methods

Wild-type C57BLKS (db/dm) mice were used in the db/dm mouse group and db/db mice were randomly divided into 2 groups: untreated and treated db/db mouse groups. Esculeoside A (100 mg/kg) was administered by gavage for 56 days to the treated db/db mouse group. Distilled water was administered to the db/dm mouse group and the untreated db/db mouse group. The blood and liver biochemical parameters and the expression of liver insulin signaling-related proteins were examined.

Results

The results showed that esculeoside A reduced the fasting blood glucose (FBG) levels and improved the glucose tolerance. Further investigation revealed that hepatic protein expressions of total AMP-activated protein kinase (T-AMPK), phosphorylated AMP-activated protein kinase (p-AMPK), insulin receptor substrate-1 (IRS-1), and glucokinase (GCK) were significantly upregulated after esculeoside A treatment. In contrast, the hepatic protein expression of phosphoenolpyruvate carboxykinase (PEPCK) was significantly downregulated by esculeoside A treatment.

Conclusion

These findings suggested that esculeoside A has a potential of alleviating the metabolic abnormalities in db/db mice via regulation of AMPK/IRS-1 pathway. Our findings supported a possible application of esculeoside A as a functional supplement for diabetes treatment.

The effect of cholesteryl ester transfer protein on pancreatic beta cell dysfunction in mice

BACKGROUND

Cholesterol accumulation causes pancreatic beta cell lipotoxicity and dysfunction. Cholesteryl ester transfer protein (CETP) plays an important role in blood lipid homeostasis. However, its role in tissue lipid metabolism remains unclear. We hypothesized that plasma CETP impact cholesterol homeostasis in the beta cells, thus damaging their functions.

METHODS

The adipose tissue-specific CETP expression transgenic (aP2-CETPTg) mice, characterized by high CETP levels in the circulation, were used in this study. Pancreatic islet cholesterol and beta cell function were assessed in mice. We further measured mRNA levels of the genes involved in beta cell proliferation and differentiation, inflammation and cholesterol metabolism. TUNEL assay was applied to investigate beta cell apoptosis in islets.

RESULTS

The aP2-CETPTg mice exhibited glucose intolerance, lower plasma insulin concentrations but increased insulin sensitivity compared with wild type mice. In addition, glucose-stimulated insulin secretion from isolated pancreatic islets significantly decreased, and free cholesterol significantly increased. Moreover, the number and size of islets from aP2-CETPTg mice were significantly decreased. Genes involved in beta cell proliferation, such as Pdx1 and BETA2, were down-regulated; genes involved in inflammation and ER stress, such as IL-1β, CHOP, and Xbp1 were up-regulated, in line with an increase of beta cell apoptosis.

CONCLUSIONS

Plasma CETP causes free cholesterol accumulation in islets which could contribute to beta cell dysfunction. Thus, CETP inhibition could be a novel protective strategy for dyslipidemia related to diabetes and obese.

Cholesteryl Ester Transfer Protein (CETP) expression does not affect glucose homeostasis and insulin secretion: studies in human CETP transgenic mice

Background

Cholesteryl ester transfer protein (CETP) is a plasma protein that mediates the exchange of triglycerides for esterified cholesterol between HDL and apoB-lipoproteins. Previous studies suggest that CETP may modify glucose metabolism in patients or cultured cells. In this study, we tested if stable CETP expression would impair glucose metabolism.

Methods

We used human CETP transgenic mice and non-transgenic littermate controls (NTg), fed with control or high fat diet, as well as in dyslipidemic background and aging conditions. Assays included glucose and insulin tolerance tests, isolated islets insulin secretion, tissue glucose uptake and adipose tissue GLUT mRNA expression.

Results

CETP expression did not modify glucose or insulin tolerance in all tested conditions such as chow and high fat diet, adult and aged mice, normo and dyslipidemic backgrounds. Fasting and fed state plasma levels of insulin were not differ in CETP and NTg mice. Direct measurements of isolated pancreatic islet insulin secretion rates induced by glucose (11, 16.7 or 22 mM), KCl (40 mM), and leucine (10 mM) were similar in NTg and CETP mice, indicating that CETP expression did not affect β-cell function in vivo and ex vivo. Glucose uptake by insulin target tissues, measured in vivo using ³H-2-deoxyglucose, showed that CETP expression had no effect on the glucose uptake in liver, muscle, perigonadal, perirenal, subcutaneous and brown adipose tissues. Accordingly, GLUT1 and GLUT4 mRNA in adipose tissue were not affected by CETP.

Conclusions

In summary, by comparing the in vivo all-or-nothing CETP expressing mouse models, we demonstrated that CETP per se has no impact on the glucose tolerance and tissue uptake, global insulin sensitivity and beta cell insulin secretion rates.

Adiposity is associated with DNA methylation profile in adipose tissue

BACKGROUND

Adiposity is a risk factor for type 2 diabetes and cardiovascular disease, suggesting an important role for adipose tissue in the development of these conditions. The epigenetic underpinnings of adiposity are not well understood, and studies of DNA methylation in relation to adiposity have rarely focused on target adipose tissue. Objectives were to evaluate whether genome-wide DNA methylation profiles in subcutaneous adipose tissue and peripheral blood leukocytes are associated with measures of adiposity, including central fat mass, body fat distribution and body mass index.

METHODS

Participants were 106 men and women (mean age 47 years) from the New England Family Study. DNA methylation was evaluated using the Infinium HumanMethylation450K BeadChip. Adiposity phenotypes included dual-energy X-ray absorptiometry-assessed android fat mass, android:gynoid fat ratio and trunk:limb fat ratio, as well as body mass index.

RESULTS

Adipose tissue genome-wide DNA methylation profiles were associated with all four adiposity phenotypes, after adjusting for race, sex and current smoking (omnibus p-values <0.001). After further adjustment for adipose cell-mixture effects, associations with android fat mass, android:gynoid fat ratio, and trunk:limb fat ratio remained. In gene-specific analyses, adiposity phenotypes were associated with adipose tissue DNA methylation in several genes that are biologically relevant to the development of adiposity, such as AOC3, LIPE, SOD3, AQP7 and CETP. Blood DNA methylation profiles were not associated with adiposity, before or after adjustment for blood leukocyte cell mixture effects.

CONCLUSION

Findings show that DNA methylation patterns in adipose tissue are associated with adiposity.