High-fat diet-induced adipose tissue expansion occurs prior to insulin resistance in C57BL/6J mice.
ABSTRACT: Background:To date, there is only scare evidence characterizing the temporal features and progression of metabolic dysfunction in high-fat diet (HFD)-fed obese mice. Hence, its specific pathogenesis remains unclear. Methods:Sixty 6-week-old male C57BL/6J mice were randomly divided into HFD and control diet (CD) groups and sacrificed at 1, 5, 9, 13, 17, and 21 weeks, respectively. At weekly intervals, intraperitoneal glucose tolerance testing (IPGTT) and intraperitoneal insulin tolerance testing (IPITT) were performed in both groups. A detailed time course in HFD-fed mice was investigated by evaluating the initiation of glucose homeostasis impairment, dyslipidemia, systemic insulin sensitivity, monocyte chemoattractant protein-1 (MCP-1) levels, epididymal white adipose tissue (eWAT) expansion, macrophage content changes, pro-inflammatory (M1)/anti-inflammatory (M2) macrophage imbalance, lipid accumulation in the liver, and ?-cell morphometry in the pancreas. Results:In the HFD group, progressive weight gain and impairments in glucose metabolism (elevated fasting blood glucose and area under the curve (AUC) of IPGTT) were observed from the 3rd week, and a significantly elevated AUC of IPITT was first detected after week 7 of HFD feeding. As for dyslipidemia, after 9 weeks of feeding, the low-density lipoprotein cholesterol level and total cholesterol level in HFD group were significantly higher than those in the CD group (all P < 0.05), whereas no significant differences were shown in triglyceride level. Adipocyte size increased significantly in the HFD group in the 1st week, a phenotypic switch in eWAT from anti-inflammatory (M2) to pro-inflammatory (M1) macrophages was observed in the 5th week, and the metabolic inflammation was distinct in eWAT in the 9th week. Additionally, liver steatosis was considerably obvious at the 17th week and pancreatic ?-cell morphometry did not change during 21 weeks of HFD feeding. Conclusion:The eWAT expansion was detected early in HFD-induced obese mice, which occurred prior to obvious insulin resistance.
Project description:BACKGROUND:p8 was initially described as being overexpressed in acute pancreatitis and encoding a ubiquitous stress protein. Analysis of insulin sensitivity and glucose tolerance in p8-knockout and haplodeficient mice revealed counterintuitive results. Thus, we determined glycemic control of p8 in mice fed with standard (SD) and high-fat diet (HFD). METHODS:p8-/- and wild type (p8+/+) mice were used for analysis of glucagon (immunohistochemistry), insulin levels (ELISA) and beta cell mass. Hyperinsulinemic- euglycemic glucose clamp technique, i.p. glucose tolerance test (ipGTT), i.p. insulin tolerance test (ipITT) and metabolic chamber analysis were performed in SD (4% fat) and HFD (55% fat) groups. RESULTS:p8-/- mice showed no differences in glucagon or insulin content but higher insulin secretion from pancreatic islets upon glucose stimulation. p8 deficiency resulted in elevated beta cell mass but was not associated with increased insulin resistance in ipGTT or ipITT. Glucose clamp tests also revealed no evidence of association of p8 deficiency with insulin resistance. Metabolic chamber analysis showed equal energy expenditure in p8-/- mice and wild type animals. CONCLUSION:p8 depletion may contribute to glucose metabolism via stress-induced insulin production and elevated beta cell mass. Nevertheless, p8 knockout showed no impact on insulin resistance in SD and HFD-fed mice.
Project description:A high-fat diet (HFD) quickly induces obesity with insulin resistance and hyperglycemia. We previously reported that a novel hypothalamic small protein, named neurosecretory protein GL (NPGL), stimulates feeding and fat accumulation in mice. However, the effects of NPGL on insulin sensitivity and glucose homeostasis remain unknown. Hence, we subjected NPGL-precursor gene (<i>Npgl</i>)-overexpressing mice to the oral glucose tolerance test (OGTT) and intraperitoneal insulin tolerance test (IPITT) under normal chow (NC) and HFD conditions. <i>Npgl</i> overexpression promoted body mass gain and tended to increase food intake of NC-fed mice, whereas it had little effect on HFD-fed mice. The OGTT showed elevated blood glucose and insulin levels in <i>Npgl</i>-overexpressing NC-fed mice 15 min after glucose administration. Both the OGTT and IPITT demonstrated that <i>Npgl</i> overexpression decreased blood glucose levels in HFD-fed mice 60 min after glucose and insulin treatments. Notably, <i>Npgl</i> overexpression increased adipose tissue masses only in NC-fed mice, and it decreased blood glucose and insulin levels in HFD-fed mice at the experimental end point. It also increased the mRNA expression of galanin, one of the feeding and metabolic regulatory neuropeptides, in the hypothalamus of HFD-fed mice. Therefore, NPGL may alleviate HFD-induced hyperglycemia and insulin resistance in mice.
Project description:Shift work and jet lag, characterized by circadian misalignment, can disrupt several physiological activities, but whether they affect the rhythm of glucose uptake and insulin sensitivity remain unclear. In the present study, female C57BL/6J mice were maintained for four weeks under the condition of 8-hour phase advance and delay every 3-4 days to mimic shift work. Intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT) were performed repeatedly at Zeitgeber time (ZT) 0, ZT6, ZT12, and ZT18. Glucose-stimulated insulin secretion (GSIS) test was performed at ZT6. We found that the average level of daily glucose tolerance did not decrease but the phase of glucose tolerance advanced by 2.27 hours and the amplitude attenuated by 20.4% in shift work mice. At ZT6, IPITT showed blood glucose at 30 min after insulin injection decreased faster in shift work mice (-3.50±0.74mmol/L, -61.58±7.89%) than that in control mice (-2.11±1.10mmol/L, -33.72±17.24%), but IPGTT and GSIS test showed no significant difference between the two groups. Food intake monitor showed that the feeding time of shift work mice continued to advance. Restricting feed to a fixed 12-hour period alleviated the increase of insulin sensitivity induced by shift-work. We also observed that an increase of blood glucose and liver glycogen at ZT0, as well as a phase advance of liver clock genes and some glucose metabolism-related genes such as forkhead box O1 (Foxo1) and peroxisome proliferator activated receptor alpha (Ppar?) in shift work mice. Our results showed that light change-simulated shift work altered insulin sensitivity during the light phase and shifted glucose tolerance rhythms in female mice, suggesting a causal association between long-term shift work and type 2 diabetes.
Project description:BACKGROUND/AIMS:To explore the effect of octreotide on pancreatic fibrosis induced by high-fat diet (HFD) and its mechanism of action. METHODS:Sprague-Dawley (SD) rats were assigned to control, HFD, or octreotide treatment groups. Glucose and insulin tolerance tests (GTT and ITT), fasting plasma glucose (FPG), and fasting insulin (FINS), serum and pancreatic lipid levels, were measured, and the Lee's index and the homeostatic model assessment (HOMA) index were calculated. The expression levels of alpha-smooth muscle actin (?-SMA), desmin, connective tissue growth factor (CTGF), transforming growth factor beta1 (TGF-?1), Smad3, and Smad7 in the pancreas were quantified. The LTC-14 cell line, which has features of primary rat pancreatic stellate cells (PSCs), was used for in vitro studies. RESULTS:The AUC of ipGTT and ipITT, and FPG, FINS, lipid levels, were elevated after HFD feeding; however, they decreased after octreotide administration. The expression of ?-SMA, CTGF, TGF-?1, and Smad3 in the HFD group were increased relative to the control group, but Smad7 expression was decreased. After treatment with octreotide, ?-SMA, CTGF, TGF-?1, and Smad3 expression decreased, whereas the expression of Smad7 increased. In vitro studies showed that the expression of CTGF, TGF-?1, and Smad3 increased with palmitate treatment (PA), which mimics HFD treatment; and octreotide treatment decreased the expression of these proteins. The ?-SMA and Smad7 expression levels remained unchanged among the three groups. CONCLUSIONS:Octreotide can ameliorate pancreatic fibrosis and improve pancreatic beta-cell function induced in HFD treated rats, possibly by inhibiting PSC activation and by decreasing pancreatic extracellular matrix (ECM) through the TGF-?1/Smad signaling pathway.
Project description:<h4>Objectives</h4>Safflower yellow (SY) is the main effective ingredient of Carthamus tinctorius L. It has been reported that SY plays an important role in anti-inflammation, anti-platelet aggregation, and inhibiting thrombus formation. In present study, we try to investigate the effects of SY on body weight, body fat mass, insulin sensitivity in high fat diet (HFD)-induced obese mice.<h4>Methods</h4>HFD-induced obese male ICR mice were intraperitoneally injected with SY (120 mg kg(-1)) daily. Eight weeks later, intraperitoneal insulin tolerance test (IPITT), and intraperitoneal glucose tolerance test (IPGTT) were performed, and body weight, body fat mass, serum insulin levels were measured. The expression of glucose and lipid metabolic related genes in white adipose tissue (WAT) were determined by RT-qPCR and western blot technologies.<h4>Results</h4>The administration obese mice with SY significantly reduced the body fat mass of HFD-induced obese mice (P < 0.05). IPITT test showed that the insulin sensitivity of SY treated obese mice were evidently improved. The mRNA levels of insulin signaling pathway related genes including insulin receptor substrate 1(IRS1), PKB protein kinase (AKT), glycogen synthase kinase 3? (GSK3?) and forkhead box protein O1(FOXO1) in mesenteric WAT of SY treated mice were significantly increased to 1.9- , 2.8- , 3.3- , and 5.9-folds of that in HFD-induced control obese mice, respectively (P < 0.05). The protein levels of AKT and GSK3? were also significantly increased to 3.0 and 5.2-folds of that in HFD-induced control obese mice, respectively (P < 0.05). Meanwhile, both the mRNA and protein levels of peroxisome proliferator-activated receptorgamma coactivator 1? (PGC1?) in inguinal subcutaneous WAT of SY group were notably increased to 2.5 and 3.0-folds of that in HFD-induced control obese mice (P < 0.05).<h4>Conclusions</h4>SY significantly reduce the body fat mass, fasting blood glucose and increase insulin sensitivity of HFD-induced obese mice. The possible mechanism is to promote the browning of subcutaneous WAT and activate the IRS1/AKT/GSK3? pathway in visceral WAT. Our study provides an important experimental evidence for developing SY as a potential anti-obesity and anti-diabetic drug.
Project description:Hyperinsulinemia is frequently associated with aging and may cause insulin resistance in elderly. Since insulin secretion and clearance decline with age, hyperinsulinemia seems to be maintained, primarily, due to a decrease in the insulin clearance. To investigate these aging effects, 3- and 18-month-old male C57BL/6 mice were subjected to intraperitoneal glucose and insulin tolerance tests (ipGTT and ipITT) and, during the ipGTT, plasma c-peptide and insulin were measure to evaluate <i>in vivo</i> insulin clearance. Glucose-stimulated insulin secretion in isolated pancreatic islets was also assessed, and liver samples were collected for molecular analyses (western blot). Although insulin sensitivity was not altered in the old mice, glucose tolerance, paradoxically, seems to be increased, accompanied by higher plasma insulin, during ipGTT. While insulin secretion did not increase, insulin clearance was reduced in the old mice, as suggested by the lower c-peptide:insulin ratio, observed during ipGTT. Carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) and insulin-degrading enzyme (IDE), as well as the activity of this enzyme, were reduced in the liver of old mice, justifying the decreased insulin clearance observed in these mice. Therefore, loss of hepatic CEACAM1 and IDE function may be directly related to the decline in insulin clearance during aging.
Project description:<h4>Objective</h4>Breakthroughs in HIV treatment, especially combination antiretroviral therapy (ART), have massively reduced AIDS-associated mortality. However, ART administration amplifies the risk of non-AIDS defining illnesses including obesity, diabetes, and cardiovascular disease, collectively known as metabolic syndrome. Initial reports suggest that ART-associated risk of metabolic syndrome correlates with socioeconomic status, a multifaceted finding that encompasses income, race, education, and diet. Therefore, determination of causal relationships is extremely challenging due to the complex interplay between viral infection, ART, and the many environmental factors.<h4>Methods</h4>In the current study, we employed a mouse model to specifically examine interactions between ART and diet that impacts energy balance and glucose metabolism. Previous studies have shown that high-fat feeding induces persistent low-grade systemic and adipose tissue inflammation contributing to insulin resistance and metabolic dysregulation via adipose-infiltrating macrophages. Studies herein test the hypothesis that ART potentiates the inflammatory effects of a high-fat diet (HFD). C57Bl/6J mice on a HFD or standard chow containing ART or vehicle, were subjected to functional metabolic testing, RNA-sequencing of epididymal white adipose tissue (eWAT), and array-based kinomic analysis of eWAT-infiltrating macrophages.<h4>Results</h4>ART-treated mice on a HFD displayed increased fat mass accumulation, impaired glucose tolerance, and potentiated insulin resistance. Gene set enrichment and kinomic array analyses revealed a pro-inflammatory transcriptional signature depicting granulocyte migration and activation.<h4>Conclusion</h4>The current study reveals a HFD-ART interaction that increases inflammatory transcriptional pathways and impairs glucose metabolism, energy balance, and metabolic dysfunction.
Project description:<h4>Background</h4>Sulfonylurea receptor 1 (SUR1) is primarily responsible for glucose regulation in normal conditions. Here, we sought to investigate the glucose metabolism characteristics of SUR1<sup>-/-</sup> rats.<h4>Methods</h4>The TALEN technique was used to construct a SUR1 gene deficiency rat model. Rats were grouped by SUR1 gene knockout or not and sex difference. Body weight; glucose metabolism indicators, including IPGTT, IPITT, glycogen contents and so on; and other molecule changes were examined.<h4>Results</h4>Insulin secretion was significantly inhibited by knocking out the SUR1 gene. SUR1<sup>-/-</sup> rats showed lower body weights compared to wild-type rats, and even SUR1<sup>-/-</sup> males weighed less than wild-type females. Upon SUR1 gene knockout, the rats showed a peculiar plasma glucose profile. During IPGTT, plasma glucose levels were significantly elevated in SUR1<sup>-/-</sup> rats at 15?min, which could be explained by SUR1 mainly working in the first phase of insulin secretion. Moreover, SUR1<sup>-/-</sup> male rats showed obviously impaired glucose tolerance than before and a better insulin sensitivity in the 12th week compared with females, which might be related with excess androgen secretion in adulthood. Increased glycogen content and GLUT4 expression and the inactivation of GSK3 were also observed in SUR1<sup>-/-</sup> rats, which suggested an enhancement of insulin sensitivity.<h4>Conclusions</h4>These results reconfirm the role of SUR1 in systemic glucose metabolism. More importantly, our SUR1<sup>-/-</sup> rat model might be applied in other fields, such as for exploring other hypoglycaemic functions of sulfonylureas.
Project description:Chronic inflammation may contribute to insulin resistance via molecular cross-talk between pathways for pro-inflammatory and insulin signaling. Interleukin 1 receptor-associated kinase 1 (IRAK-1) mediates pro-inflammatory signaling via IL-1 receptor/Toll-like receptors, which may contribute to insulin resistance, but this hypothesis is untested. Here, we used male <i>Irak1</i> null (k/o) mice to investigate the metabolic role of IRAK-1. C57BL/6 wild-type (WT) and k/o mice had comparable body weights on low-fat and high-fat diets (LFD and HFD, respectively). After 12 weeks on LFD (but not HFD), k/o mice (<i>versus</i> WT) had substantially improved glucose tolerance (assessed by the intraperitoneal glucose tolerance test (IPGTT)). As assessed with the hyperinsulinemic euglycemic glucose clamp technique, insulin sensitivity was 30% higher in the <i>Irak1</i> k/o mice on chow diet, but the <i>Irak1</i> deletion did not affect IPGTT outcomes in mice on HFD, suggesting that the deletion did not overcome the impact of obesity on glucose tolerance. Moreover, insulin-stimulated glucose-disposal rates were higher in the k/o mice, but we detected no significant difference in hepatic glucose production rates (± insulin infusion). Positron emission/computed tomography scans indicated higher insulin-stimulated glucose uptake in muscle, but not liver, in <i>Irak1</i> k/o mice <i>in vivo</i> Moreover, insulin-stimulated phosphorylation of Akt was higher in muscle, but not in liver, from <i>Irak1</i> k/o mice <i>ex vivo</i> In conclusion, <i>Irak1</i> deletion improved muscle insulin sensitivity, with the effect being most apparent in LFD mice.
Project description:We previously identified a novel small hypothalamic protein, neurosecretory protein GL (NPGL), which induces feeding behavior and fat accumulation in rodents depending on their diet. In the present study, we explored the effects of NPGL on feeding behavior and energy metabolism in mice placed on a long-term high-fat diet with 60% calories from fat (HFD 60). Overexpression of the NPGL precursor gene (<i>Npgl</i>) over 18 weeks increased food intake and weight. The weekly weight gain of <i>Npgl</i>-overexpressing mice was higher than that of controls until 7 weeks from induction of overexpression, after which it ceased to be so. Oral glucose tolerance tests showed that <i>Npgl</i> overexpression maintained glucose tolerance and increased blood insulin levels, and intraperitoneal insulin tolerance tests showed that it maintained insulin sensitivity. At the experimental endpoint, <i>Npgl</i> overexpression was associated with increased mass of the perirenal white adipose tissue (WAT) and decreased mass of the epididymal WAT (eWAT), resulting in little effect on the total WAT mass. These results suggest that under long-term HFD 60 feeding, <i>Npgl</i> overexpression may play a role in avoiding metabolic disturbance both by accelerating energy storage and by suppressing excess fat accumulation in certain tissues, such as the eWAT.