Prolonged High-fat Diet Feeding Research Articles

Rapid downregulation of DICER is a hallmark of adipose tissue upon high-fat diet feeding

Adipose tissue regulates whole-body energy balance and is crucial for metabolic health. With energy surplus, adipose tissue expands, which may lead to local areas of hypoxia and inflammation, and consequently impair whole-body insulin sensitivity. We report that DICER, a key enzyme for miRNA maturation, is significantly lower in abdominal subcutaneous white adipose tissue of men with obesity compared with men with a lean phenotype. Furthermore, DICER is profoundly downregulated in mouse adipose tissue and liver within the first week on a high-fat diet (HFD), and remains low after prolonged HFD feeding. Downregulation of DICER in mice occurs in both mature adipocytes and stromal vascular cells. Mechanistically, chemically induced hypoxia in vitro shows DICER degradation via interaction with hypoxia-inducible factor 1-α (HIF1α). Moreover, DICER and HIF1α interact in brown adipose tissue post-HFD which may signal for DICER degradation. Finally, RNA sequencing reveals a striking time-dependent downregulation of total miRNA content in mouse subcutaneous adipose tissue after HFD feeding. Collectively, HFD in mice reduces adipose tissue DICER, likely due to hypoxia-induced interaction with HIF1α during tissue expansion, and this significantly impacts miRNA content.

The mitochondrial enzyme pyruvate carboxylase restricts pancreatic β-cell senescence by blocking p53 activation.

Defective glucose-stimulated insulin secretion (GSIS) and β-cell senescence are hallmarks in diabetes. The mitochondrial enzyme pyruvate carboxylase (PC) has been shown to promote GSIS and β-cell proliferation in the clonal β-cell lines, yet its physiological relevance remains unknown. Here, we provide animal and human data showing a role of PC in protecting β-cells against senescence and maintaining GSIS under different physiological and pathological conditions. β-cell-specific deletion of PC impaired GSIS and induced β-cell senescence in the mouse models under either a standard chow diet or prolonged high-fat diet feeding. Transcriptomic analysis indicated that p53-related senescence and cell cycle arrest are activated in PC-deficient islets. Overexpression of PC inhibited hyperglycemia- and aging-induced p53-related senescence in human and mouse islets as well as INS-1E β-cells, whereas knockdown of PC provoked senescence. Mechanistically, PC interacted with MDM2 to prevent its degradation via the MDM2 binding motif, which in turn restricts the p53-dependent senescent program in β-cells. On the contrary, the regulatory effects of PC on GSIS and the tricarboxylic acid (TCA) anaplerotic flux are p53-independent. We illuminate a function of PC in controlling β-cell senescence through the MDM2-p53 axis.

Wnt7b overexpression in osteoblasts stimulates bone formation and reduces obesity in mice on a high-fat diet.

Previous studies have shown that Wnt7b potently stimulates bone formation by promoting osteoblast differentiation and activity. As high-fat feeding leads to obesity and systemic metabolic dysregulation, here we investigate the potential benefit of Wnt7b overexpression in osteoblasts on both bone and whole-body metabolism in mice fed with a high-fat diet (HFD). Wnt7b overexpression elicited massive overgrowth of trabecular and cortical bone but seemed to ameliorate body fat accumulation in mice with prolonged HFD feeding. In addition, Wnt7b overexpression modestly improved glucose tolerance in male mice on HFD. Collectively, the results indicate that targeted overexpression of Wnt7b in osteoblasts not only stimulates bone formation but also improves certain aspects of global metabolism in overnourished mice.

High-Fat Diet-Induced Obesity Alters Dendritic Cell Homeostasis by Enhancing Mitochondrial Fatty Acid Oxidation.

Obesity is associated with increased cancer risk and weak responses to vaccination and sepsis treatment. Although dendritic cells (DCs) are fundamental for the initiation and maintenance of competent immune responses against pathogens and tumors, how obesity alters the normal physiology of these myeloid cells remains largely unexplored. In this study, we report that obesity caused by prolonged high-fat diet feeding disrupts the metabolic and functional status of mouse splenic DCs (SpDCs). High-fat diet-induced obesity drastically altered the global transcriptional profile of SpDCs, causing severe changes in the expression of gene programs implicated in lipid metabolism and mitochondrial function. SpDCs isolated from obese mice demonstrated enhanced mitochondrial respiration provoked by increased fatty acid oxidation (FAO), which drove the intracellular accumulation of reactive oxygen species that impaired Ag presentation to T cells. Accordingly, treatment with the FAO inhibitor etomoxir, or antioxidants such as vitamin E or N-acetyl-l-cysteine, restored the Ag-presenting capacity of SpDCs isolated from obese mice. Our findings reveal a major detrimental effect of obesity in DC physiology and suggest that controlling mitochondrial FAO or reactive oxygen species overproduction may help improve DC function in obese individuals.

Modifying the maternal microbiota alters the gut–brain metabolome and prevents emotional dysfunction in the adult offspring of obese dams

Maternal obesity disturbs brain-gut-microbiota interactions and induces negative affect in the offspring, but its impact on gut and brain metabolism in the offspring (F1) are unknown. Here, we tested whether perinatal intake of a multispecies probiotic could mitigate the abnormal emotional behavior in the juvenile and adult offspring of obese dams. Untargeted NMR-based metabolomic profiling and gene-expression analysis throughout the gut-brain axis were then used to investigate the biology underpinning behavioral changes in the dams and their offspring. Prolonged high-fat diet feeding reduced maternal gut short-chain fatty acid abundance, increased markers of peripheral inflammation, and decreased the abundance of neuroactive metabolites in maternal milk during nursing. Both juvenile (postnatal day [PND] 21) and adult (PND112) offspring of obese dams exhibited increased anxiety-like behavior, which were prevented by perinatal probiotic exposure. Maternal probiotic treatment increased gut butyrate and brain lactate in the juvenile and adult offspring and increased the expression of prefrontal cortex PFKFB3, a marker of glycolytic metabolism in astrocytes. PFKFB3 expression correlated with the increase in gut butyrate in the juvenile and adult offspring. Maternal obesity reduced synaptophysin expression in the adult offspring, while perinatal probiotic exposure increased expression of brain-derived neurotrophic factor. Finally, we showed that the resilience of juvenile and adult offspring to anxiety-like behavior was most prominently associated with increased brain lactate abundance, independent of maternal group. Taken together, we show that maternal probiotic supplementation exerts a long-lasting effect on offspring neuroplasticity and the offspring gut-liver-brain metabolome, increasing resilience to emotional dysfunction induced by maternal obesity.

CXCL2 Impairs Functions of Bone Marrow Mesenchymal Stem Cells and Can Serve as a Serum Marker in High-Fat Diet-Fed Rats.

In modern society excessive consumption of a high-fat diet (HFD) is a significant risk factor for many diseases such as diabetes, osteoarthritis and certain cancers. Resolving cellular and molecular mechanisms underlying HFD-associated disorders is of great importance to human health. Mesenchymal stem cells (MSCs) are key players in tissue homeostasis and adversely affected by prolonged HFD feeding. Low-grade systemic inflammation induced by HFD is characterized by increased levels of pro-inflammatory cytokines and alters homeostasis in many organs. However, whether, which and how HFD associated inflammatory cytokines impair MSCs remain unclear. Here we demonstrated that HFD induced serum cytokines disturbances, especially a continuous elevation of serum CXCL2 level in rats. Coincidentally, the differentially expressed genes (DEGs) of bone marrow MSCs (BMSCs) which functions were impaired in HFD rats were enriched in cytokine signaling. Further mechanism analysis revealed that CXCL2 treatment in vitro suppresses the adipogenic potential of BMSCs via Rac1 activation, and promoted BMSC migration and senescence by inducing over-production of ELMO1 and reactive oxygen species (ROS) respectively. Moreover, we found that although glycolipid metabolism indicators can be corrected, the CXCL2 elevation and BMSC dysfunctions cannot be fully rescued by diet correction and anti-inflammatory aspirin treatment, indicating the long-lasting deleterious effects of HFD on serum CXCL2 levels and BMSC functions. Altogether, our findings identify CXCL2 as an important regulator in BMSCs functions and may serve as a serum marker to indicate the BMSC dysfunctions induced by HFD. In addition, our findings underscore the intricate link among high-fat intake, chronic inflammation and BMSC dysfunction which may facilitate development of protective strategies for HFD associated diseases.

Obesity in Midlife Hampers Resting and Sensory-Evoked Cerebral Blood Flow in Mice.

This study aimed to investigate the effects of a high-fat diet (HFD) and aging on resting and activity-dependent cerebral blood flow (CBF). To run a comparison between obese and age-matched control animals, 6-week-old mice were fed either with regular chow or an HFD for 3 months or 8 months. Glucose tolerance and insulin sensitivity were assessed for metabolic phenotyping. Resting and odor-evoked CBF at the microvascular scale in the olfactory bulb (OB) was investigated by multiexposure speckle imaging. Immunolabeling-enabled imaging of solvent-cleared organs was used to analyze vascular density. The ejection fraction was studied by using cardioechography. Olfactory sensitivity was tested by using a buried-food test. Glucose intolerance and compromised odor-evoked CBF were observed in obese mice in the younger group. Prolonged HFD feeding triggered insulin resistance and stronger impairment in activity-dependent CBF. Aging had a specific negative impact on resting CBF. There was no decrease in vascular density in the OB of obese mice, although cardiac function was impaired at both ages. In addition, decreased olfactory sensitivity was observed only in the older, middle-aged obese mice. OB microvasculature in obese mice showed a specific functional feature characterized by impaired sensory-evoked CBF and a specific deleterious effect of aging on resting CBF.

Mice lacking DGKε show increased beige adipogenesis in visceral white adipose tissue after long-term high fat diet in a COX-2- dependent manner.

Adipose tissue is a central site for energy storage in the form of triglyceride (TG). Under excess energy conditions, TG is synthesized by acylation of diacylglycerol (DG), whereas TG is broken down into DG and free fatty acid, which provide energy for mitochondrial lipid oxidation when needed. In this regard, DG is not merely an intermediate metabolite for TG metabolism; it also serves as a signaling molecule. DG kinase (DGK) phosphorylates DG to produce phosphatidic acid (PA). Consequently, DGK plays a pivotal role in the control of lipid metabolism and signal transduction pathway. Recently, a report has described that DGKε-knockout (KO) mice show expansion of epididymal white adipose tissue (WAT) together with the impairment of glucose clearance after short-term (40 days) high fat diet (HFD) feeding, an early presymptomatic phase of obesity in wild-type animals. Nevertheless, no report describes an investigation of their phenotype under long-term HFD feeding conditions. Remarkably, results obtained during long-term HFD feeding show that WAT mass is decreased significantly and that the blood glucose profile in response to glucose challenge is improved in DGKε-KO mice compared with wild-type, which contrast sharply against the phenotype shown for short-term HFD feeding. Morphological examination reveals that cyclooxygenase-2 (COX-2) expression and clusters of uncoupling protein 1 (UCP1)-positive multilocular brown-like ("beige") adipocyte are induced in DGKε-deficient WAT after long-term HFD feeding, suggesting that beige adipocytes facilitate energy expenditure during prolonged HFD feeding. Administration of celecoxib, a selective inhibitor of COX-2, abolishes the appearance of UCP1-positive beige adipocytes in DGKε-KO mice. These findings suggest that DGKε deficiency promotes visceral WAT remodeling in a COX-2-dependent manner under long-term HFD feeding conditions.

Prolonged high-fat-diet feeding promotes non-alcoholic fatty liver disease and alters gut microbiota in mice.

BACKGROUNDNon-alcoholic fatty liver disease (NAFLD) has become an epidemic largely due to the worldwide increase in obesity. While lifestyle modifications and pharmacotherapies have been used to alleviate NAFLD, successful treatment options are limited. One of the main barriers to finding safe and effective drugs for long-term use in NAFLD is the fast initiation and progression of disease in the available preclinical models. Therefore, we are in need of preclinical models that (1) mimic the human manifestation of NAFLD and (2) have a longer progression time to allow for the design of superior treatments.AIMTo characterize a model of prolonged high-fat diet (HFD) feeding for investigation of the long-term progression of NAFLD.METHODSIn this study, we utilized prolonged HFD feeding to examine NAFLD features in C57BL/6 male mice. We fed mice with a HFD (60% fat, 20% protein, and 20% carbohydrate) for 80 wk to promote obesity (Old-HFD group, n = 18). A low-fat diet (LFD) (14% fat, 32% protein, and 54% carbohydrate) was administered for the same duration to age-matched mice (Old-LFD group, n = 15). An additional group of mice was maintained on the LFD (Young-LFD, n = 20) for a shorter duration (6 wk) to distinguish between age-dependent and age-independent effects. Liver, colon, adipose tissue, and feces were collected for histological and molecular assessments.RESULTSProlonged HFD feeding led to obesity and insulin resistance. Histological analysis in the liver of HFD mice demonstrated steatosis, cell injury, portal and lobular inflammation and fibrosis. In addition, molecular analysis for markers of endoplasmic reticulum stress established that the liver tissue of HFD mice have increased phosphorylated Jnk and CHOP. Lastly, we evaluated the gut microbial composition of Old-LFD and Old-HFD. We observed that prolonged HFD feeding in mice increased the relative abundance of the Firmicutes phylum. At the genus level, we observed a significant increase in the abundance of Adercreutzia, Coprococcus, Dorea, and Ruminococcus and decreased relative abundance of Turicibacter and Anaeroplasma in HFD mice.CONCLUSIONOverall, these data suggest that chronic HFD consumption in mice can mimic pathophysiological and some microbial events observed in NAFLD patients.

2492-PUB: KCNK16 Deficiency Protects Mice against High-Fat Diet-Induced Weight Gain

Potassium Channel, Two Pore Domain Subfamily K, Member 16 (TALK-1/KCNK16) is a K+ channel protein expressed in human and murine pancreas. Recent research by Vierra et al suggested a regulatory function of KCNK16 in mice for glucose-dependent β-cell second-phase insulin and δ-cell somatostatin secretion and a protective effect on fasting glycemia during 3 weeks high-fat diet (HFD). We tested the hypothesis, that deletion of KCNK16 affects body weight and glucose metabolism in vivo during prolonged HFD feeding. Therefore, we analyzed KCNK16-deficient knockout mice (KCNK16-/-) during HFD up to 21 weeks investigating body weight and composition, insulin sensitivity as well as insulin secretion. In HFD-fed KCNK16-/-, we observed a reduced body weight gain. Both, fat and lean mass were reduced and notably body-length was also significantly shorter. KCNK16-/- mice showed reduced food intake, an elevated oxygen consumption and energy expenditure. KCNK16-/- islets showed enhanced insulin secretion under glucose and GIP-1 simulation, but we did not reveal significant changes in fasting or fed plasma glucose or insulin. We found a moderate decrease in blood glucose during an ipITT. However, we did not observe an enhanced insulin sensitivity assessed by hyperinsulinemic-euglycemic clamps nor a beneficial effect of KCNK16 deficiency on the modulation of in vivo insulin secretion during hyperglycemic clamps in HFD-fed mice. In conclusion, we observed a reduced body weight gain, but also shorter body-length in the KCNK16-deficient mouse model during prolonged HFD feeding. Notably, food intake was reduced while energy expenditure was increased. Disclosure S. Brachs: Employee; Spouse/Partner; Treamid Therapeutics GmbH. Research Support; Self; Sanofi-Aventis Deutschland GmbH. U. Schwahn: Employee; Self; Sanofi-Aventis Deutschland GmbH. K. Steinmeyer: Employee; Self; Sanofi-Aventis Deutschland GmbH. M. Schäfer: Employee; Self; Sanofi-Aventis Deutschland GmbH. J. Gassenhuber: Employee; Self; Sanofi-Aventis Deutschland GmbH. Employee; Spouse/Partner; Sanofi-Aventis Deutschland GmbH. J. Spranger: None. Funding Sanofi Aventis Deutschland GmbH

Hypothalamic Macrophage Inducible Nitric Oxide Synthase Mediates Obesity-Associated Hypothalamic Inflammation

In BriefLee et al. demonstrate in mice that, upon prolonged high-fat diet feeding, hypothalamic macrophages proliferate, expand their pool, and sustain hypothalamic inflammation. Moreover, they show that hypothalamic macrophage iNOS inhibition diminishes macrophage activation, astrogliosis, blood-brain-barrier permeability, and impaired glucose metabolism in diet-induced obese mice.

Hypothalamic Orexin Is Essential for Estrogenic Action on Glucose and Energy Metabolism in Diet-Induced Obese Mice

Decreased estrogen is a crucial pathogenic factor for type 2 diabetes in postmenopausal women; however, the precise mechanism remains unknown. Orexin is a major hypothalamic neuropeptides regulating energy/glucose metabolism, and its anti-obese effect is more evident in females. We therefore investigated whether estrogen prevents obesity and glucose intolerance through interaction with the orexin system. Ovariectomized (OVX) mice and female orexin knockout (OXKO) mice were prepared to examine the impact of estrogen and orexin deficiency, respectively. When maintained on 60% high fat diet (HFD) for 16-24 weeks, body weight gain, adipose tissue inflammation, and hepatic triglyceride contents were markedly increased in OXKO, compared to wild type (WT) mice. Ovariectomy did not significantly affect the body weight in WT and OXKO mice after prolonged HFD feeding. Importantly, the levels of proinflammatory markers (e.g., TNFα mRNA) in the white adipose tissues were increased mildly in sham-operated OXKO (Sham-OXKO) mice and remarkably in OVX-OXKO mice. The rank order of the severity was OVX-OXKO>Sham-OXKO>OVX-WT>Sham-WT. Moreover, Sirius-Red staining to evaluate the fatty liver disease (i.e., NAFLD/NASH) demonstrated mild and severe fibrosis in the liver of Sham-OXKO and OVX-OXKO mice, respectively, whereas there was no abnormality in OVX-WT and Sham-WT mice. In glucose tolerance test, 1) metabolic activity was greater in Sham-WT than OVX-WT mice, whereas no difference was observed between Sham-OXKO and OVX-OXKO mice on HFD, 2) intracerebroventricular injection of estrogen improved glucose tolerance in OVX-WT but not OVX-OXKO mice on HFD, suggesting that estrogen prevents glucose intolerance on HFD in an orexin-dependent manner. Taken together, orexin may play a fundamental role in the anti-obese and antidiabetic effects of estrogen. Therefore, orexin appears to be a novel therapeutic target to prevent metabolic disorders in postmenopausal women. Disclosure K. Kon: None. H. Tsuneki: None. S. Takata: None. T. Maeda: None. T. Wada: Research Support; Self; Sanwa Kagaku Kenkyusho Co., Ltd.. T. Sasaoka: None.

Prolonged High-Fat Diet Feeding of WHHLMI Rabbits does Not Aggravate Metabolic or Cardiac Dysfunction

Myocardial infarction (MI)-prone Watanabe hereditary hyperlipidemic (WHHLMI) rabbits were reported to spontaneously but slowly develop MI, associated with enhanced coronary atherosclerosis and metabolic syndrome features. Our aim was to accelerate these processes by exposing the rabbits to a high-fat diet (HFD) that was previously shown to induce insulin resistance and cardiac injury in rabbits. HFD feeding for one year was indeed associated with development of obesity (37% increases in body weight, as compared to 3.7% for control standard-fat diet, SFD). On HFD, liver weight and hepatic triglyceride content were significantly higher as compared to SFD, with mild steatosis. Glucose and insulin levels were not markedly different on SFD or HFD, however after 1 year of diet treatment, HFD-fed animals were more glucose intolerant as compared to SFD-fed rabbits. On SFD, the rabbits developed marked thoracic aorta stenosis and calcification of atherosclerotic lesions, which were not aggravated by HFD feeding. Cardiac function analysis by MRI and transthoracic echocardiography did not reveal significant differences between SFD and HFD fed rabbits. Thus, the metabolic and cardiac phenotype of WHHLMI rabbits was not aggravated by HFD feeding for one year, and the rabbits did not spontaneously develop diabetes or myocardial infarction.

TGR5 signalling promotes mitochondrial fission and beige remodelling of white adipose tissue

Remodelling of energy storing white fat into energy expending beige fat could be a promising strategy to reduce adiposity. Here, we show that the bile acid-responsive membrane receptor TGR5 mediates beiging of the subcutaneous white adipose tissue (scWAT) under multiple environmental cues including cold exposure and prolonged high-fat diet feeding. Moreover, administration of TGR5-selective bile acid mimetics to thermoneutral housed mice leads to the appearance of beige adipocyte markers and increases mitochondrial content in the scWAT of Tgr5+/+ mice but not in their Tgr5−/− littermates. This phenotype is recapitulated in vitro in differentiated adipocytes, in which TGR5 activation increases free fatty acid availability through lipolysis, hence fuelling β-oxidation and thermogenic activity. TGR5 signalling also induces mitochondrial fission through the ERK/DRP1 pathway, further improving mitochondrial respiration. Taken together, these data identify TGR5 as a druggable target to promote beiging with potential applications in the management of metabolic disorders.

P32 heterozygosity protects against age- and diet-induced obesity by increasing energy expenditure

Obesity is increasing in prevalence and has become a global public health problem. The main cause of obesity is a perturbation in energy homeostasis, whereby energy intake exceeds energy expenditure. Although mitochondrial dysfunction has been linked to the deregulation of energy homeostasis, the precise mechanism is poorly understood. Here, we identify mitochondrial p32 (also known as C1QBP) as an important regulator of lipid homeostasis that regulates both aerobic and anaerobic energy metabolism. We show that while whole-body deletion of the p32 results in an embryonic lethal phenotype, mice heterozygous for p32 are resistant to age- and high-fat diet-induced ailments, including obesity, hyperglycemia, and hepatosteatosis. Notably, p32+/− mice are apparently healthy, demonstrate an increased lean-to-fat ratio, and show dramatically improved insulin sensitivity despite prolonged high-fat diet feeding. The p32+/− mice show increased oxygen consumption and heat production, indicating that they expend more energy. Our analysis revealed that haploinsufficiency for p32 impairs glucose oxidation, which results in a compensatory increase in fatty acid oxidation and glycolysis. These metabolic alterations increase both aerobic and anaerobic energy expenditure. Collectively, our data show that p32 plays a critical role in energy homeostasis and represents a potential novel target for the development of anti-obesity drugs.

Protection against High-Fat-Diet-Induced Obesity in MDM2C305F Mice Due to Reduced p53 Activity and Enhanced Energy Expenditure

The RPL11-MDM2 interaction constitutes a p53 signaling pathway activated by deregulated ribosomal biosynthesis in response to stress. Mice bearing an MDM2C305F mutation that disrupts RPL11-MDM2 binding were analyzed on a high-fat diet (HFD). The Mdm2C305F/C305F mice, although phenotypically indistinguishable from wild-type (WT) mice when fed normal chow, demonstrated decreased fat accumulation along with improved insulin sensitivity and glucose tolerance after prolonged HFD feeding. We found that HFD increases expression of c-MYC and RPL11 in both WT and Mdm2C305F/C305F mice; however, p53 was induced in WT but not in Mdm2C305F/C305F mice. Reduced p53 activity in HFD-fed Mdm2C305F/C305F mice resulted in higher levels of p53 downregulated targets GLUT4 and SIRT1, leading to increased biosynthesis of NAD+, and increased energy expenditure. Our study reveals a role for the RPL11-MDM2-p53 pathway in fat storage during nutrient excess and suggests that targeting this pathway may be a potential treatment for obesity.

Myeloid-Cell-Derived VEGF Maintains Brain Glucose Uptake and Limits Cognitive Impairment in Obesity

High-fat diet (HFD) feeding induces rapid reprogramming of systemic metabolism. Here, we demonstrate that HFD feeding of mice downregulates glucose transporter (GLUT)-1 expression in blood-brain barrier (BBB) vascular endothelial cells (BECs) and reduces brain glucose uptake. Upon prolonged HFD feeding, GLUT1 expression is restored, which is paralleled by increased expression of vascular endothelial growth factor (VEGF) in macrophages at the BBB. In turn, inducible reduction of GLUT1 expression specifically in BECs reduces brain glucose uptake and increases VEGF serum concentrations in lean mice. Conversely, myeloid-cell-specific deletion of VEGF in VEGF(Δmyel) mice impairs BBB-GLUT1 expression, brain glucose uptake, and memory formation in obese, but not inlean mice. Moreover, obese VEGF(Δmyel) mice exhibit exaggerated progression of cognitive decline and neuroinflammation on an Alzheimer's disease background. These experiments reveal that transient, HFD-elicited reduction of brain glucose uptake initiates a compensatory increase of VEGF production and assign obesity-associatedmacrophage activation a homeostatic role torestore cerebral glucose metabolism, preserve cognitive function, and limit neurodegeneration in obesity.

Carnitine Palmitoyltransferase 1b Deficient Mice Develop Severe Insulin Resistance After Prolonged High Fat Diet Feeding.

BackgroundCarnitine palmitoyltransferase 1 (CPT1) is the rate-limiting enzyme governing the entry of long-chain acyl-CoAs into mitochondria. Treatments with CPT1 inhibitors protect against insulin resistance in short-term preclinical animal studies. We recently reported that mice with muscle isoform CPT1b deficiency demonstrated improved insulin sensitivity when fed a High Fat-Diet (HFD) for up to 5 months. In this follow up study, we further investigated whether the insulin sensitizing effects of partial CPT1b deficiency could be maintained under a prolonged HFD feeding condition.MethodsWe investigated the effects of CPT1b deficiency on HFD-induced insulin resistance using heterozygous CPT1b deficient (Cpt1b+/−) mice compared with Wild Type (WT) mice fed a HFD for a prolonged period of time (7 months). We assessed insulin sensitivity using hyperinsulinemic-euglycemic clamps. We also examined body composition, skeletal muscle lipid profile, and changes in the insulin signaling pathways of skeletal muscle, liver, and adipose tissue.ResultsWe found that Cpt1b+/− mice became severely insulin resistant after 7 months of HFD feeding. Cpt1b+/− mice exhibited a substantially reduced glucose infusion rate and skeletal muscle glucose uptake. While Cpt1b+/− mice maintained a slower weight gain with less fat mass than WT mice, accumulation of lipid intermediates became evident in the muscle of Cpt1b+/− but not WT mice after 7 months of HFD feeding. Insulin signaling was impaired in the Cpt1b+/− as compared to the WT muscles.ConclusionPartial CPT1b deficiency, mimicking CPT1b inhibition, may lead to impaired insulin signaling and insulin sensitivity under a prolonged HFD feeding condition. Therefore, further studies on the potential detrimental effects of prolonged therapy with CPT1 inhibition are necessary in the development of this potential therapeutic strategy.

Activation of Natural Killer T Cells Promotes M2 Macrophage Polarization in Adipose Tissue and Improves Systemic Glucose Tolerance via Interleukin-4 (IL-4)/STAT6 Protein Signaling Axis in Obesity

Natural killer T (NKT) cells are important therapeutic targets in various disease models and are under clinical trials for cancer patients. However, their function in obesity and type 2 diabetes remains unclear. Our data show that adipose tissues of both mice and humans contain a population of type 1 NKT cells, whose abundance decreases with increased adiposity and insulin resistance. Although loss-of-function of NKT cells had no effect on glucose tolerance in animals with prolonged high fat diet feeding, activation of NKT cells by lipid agonist α-galactosylceramide enhances alternative macrophage polarization in adipose tissue and improves glucose homeostasis in animals at different stages of obesity. Furthermore, the effect of NKT cells is largely mediated by the IL-4/STAT6 signaling axis in obese adipose tissue. Thus, our data identify a novel therapeutic target for the treatment of obesity-associated inflammation and type 2 diabetes.

Geldanamycin Derivative Ameliorates High Fat Diet-Induced Renal Failure in Diabetes

Diabetic nephropathy is a serious complication of longstanding diabetes and its pathogenesis remains unclear. Oxidative stress may play a critical role in the pathogenesis and progression of diabetic nephropathy. Our previous studies have demonstrated that polyunsaturated fatty acids (PUFA) induce peroxynitrite generation in primary human kidney mesangial cells and heat shock protein 90β1 (hsp90β1) is indispensable for the PUFA action. Here we investigated the effects of high fat diet (HFD) on kidney function and structure of db/db mice, a widely used rodent model of type 2 diabetes. Our results indicated that HFD dramatically increased the 24 h-urine output and worsened albuminuria in db/db mice. Discontinuation of HFD reversed the exacerbated albuminuria but not the increased urine output. Prolonged HFD feeding resulted in early death of db/db mice, which was associated with oliguria and anuria. Treatment with the geldanamycin derivative, 17-(dimethylaminoehtylamino)-17-demethoxygeldanamycin (17-DMAG), an hsp90 inhibitor, preserved kidney function, and ameliorated glomerular and tubular damage by HFD. 17-DMAG also significantly extended survival of the animals and protected them from the high mortality associated with renal failure. The benefit effect of 17-DMAG on renal function and structure was associated with a decreased level of kidney nitrotyrosine and a diminished kidney mitochondrial Ca2+ efflux in HFD-fed db/db mice. These results suggest that hsp90β1 is a potential target for the treatment of nephropathy and renal failure in diabetes.