High-fat Feeding Conditions Research Articles

Akkermansia muciniphila supplementation improves glucose tolerance in intestinal Ffar4 knockout mice during the daily light to dark transition.

Alterations in the intestinal environment are associated with various diseases, and FFAR4 is abundantly enriched in the intestine, where it has been shown to have the ability to regulate intestinal hormone secretion and intestinal microbiota; here, we confirmed previous reports. Meanwhile, we found that intestinal FFAR4 regulates glucagon-like peptide 1 secretion by decreasing Akkermansia muciniphila abundance and show that such change is associated with the level of glucose utilization at ZT12 in mice. Intestinal FFAR4 deficiency leads to severely impaired glucose tolerance at the ZT12 moment in mice, and Akkermansia muciniphila supplementation ameliorates the abnormal glucose utilization at the ZT12 moment caused by FFAR4 deficiency, which is very similar to the dawn phenomenon in diabetic patients. Collectively, our data suggest that intestinal Ffar4 deteriorates glucose tolerance at the daily light to dark transition by affecting Akkermansia muciniphila.

Assessment of Two Potential Probiotic Strains As Anti-Obesity Supplements Under High-Fat Feeding Conditions.

Obesity is one of the chronic diseases that increase annually and cause cardiovascular disease, which is the main cause of death worldwide. So, this study aims to evaluate the role of the two potential probiotics: Lactiplantibacillus plantarum Pro1 and Lacticaseibacillus rhamnosus Pro2, isolated from the fermented milk and corn silage as anti-obesity supplements. Seventy-five male BALB/c mice were distributed to five groups (control, obesity, obesity plus L. plantarum (OLP), obesity plus L. rhamnosus (OLR) and obesity plus mixture of two strains (OM)). The body weight, lipid profile, histopathology and enzymes of liver were assessed. RT-PCR was used to determine the expression of CYP7A1, ALTG4, TNFα and ROR genes.The findings show that the obesity group recorded the significant highest value of the body weight, TC, TG, LDL, AST and ALT, while OLP group recorded the significant lowest value. Liver tissue of obesity group has necrosis and fatty changes, while the OLP group was related to the control group. The findings of RT-PCR show non-significant differences between the control group and the OLP group, with significant differences between the control group and the set groups in expression of CYP7A1, ALTG4, TNFα and ROR genes. L. plantarum Pro1 reduced the expression of inflammation genes (TNFα and ROR), and increase the expression of the lipid metabolism genes (CYP7A1, ALTG4) to reduce the inflammatory effects of obesity in the liver, and decrease the cholesterol level in serum. Therefore, L. plantarum Pro1 is useful as anti-obesity supplements and an eliminator of the relevant diseases.

Stearoyl-CoA Desaturase-2 in Murine Development, Metabolism, and Disease.

Stearoyl-CoA Desaturase-2 (SCD2) is a member of the Stearoyl-CoA Desaturase (SCD) family of enzymes that catalyze the rate-limiting step in monounsaturated fatty acid (MUFA) synthesis. The MUFAs palmitoleoyl-CoA (16:1n7) and oleoyl-CoA (18:1n9) are the major products of SCD2. Palmitoleoyl-CoA and oleoyl-CoA have various roles, from being a source of energy to signaling molecules. Under normal feeding conditions, SCD2 is ubiquitously expressed and is the predominant SCD isoform in the brain. However, obesogenic diets highly induce SCD2 in adipose tissue, lung, and kidney. Here we provide a comprehensive review of SCD2 in mouse development, metabolism, and various diseases, such as obesity, chronic kidney disease, Alzheimer′s disease, multiple sclerosis, and Parkinson′s disease. In addition, we show that bone mineral density is decreased in SCD2KO mice under high-fat feeding conditions and that SCD2 is not required for preadipocyte differentiation or the expression of PPARγ in vivo despite being required in vitro.

Interferon regulatory factor 7 mediates obesity-associated MCP-1 transcription.

Hypertrophy, associated with adipocyte dysfunction, causes increased pro-inflammatory adipokine, and abnormal glucose and lipid metabolism, leading to insulin resistance and obesity-related-health problems. By combining DNA microarray and genomic data analyses to predict DNA binding motifs, we identified the transcription factor Interferon Regulatory Factor 7 (IRF7) as a possible regulator of genes related to adipocyte hypertrophy. To investigate the role of IRF7 in adipocytes, we examined gene expression patterns in 3T3-L1 cells infected with a retrovirus carrying the IRF7 gene and found that enforced IRF7 expression induced the expression of monocyte chemoattractant protein-1 (MCP-1), a key initial adipokine in the chronic inflammation of obesity. CRISPR/Cas9 mediated-suppression of IRF7 significantly reduced MCP-1 mRNA. Luciferase assays, chromatin immunoprecipitation PCR analysis and gel shift assay showed that IRF7 transactivates the MCP-1 gene by binding to its proximal Interferon Stimulation Response Element (ISRE), a putative IRF7 binding motif. IRF7 knockout mice exhibited lower expression of MCP-1 in epidydimal white adipose tissue under high-fat feeding conditions, suggesting the transcription factor is physiologically important for inducing MCP-1. Taken together, our results suggest that IRF7 transactivates MCP-1 mRNA in adipocytes, and it may be involved in the adipose tissue inflammation associated with obesity.

IGFBP-1 in Cardiometabolic Pathophysiology-Insights From Loss-of-Function and Gain-of-Function Studies in Male Mice.

We have previously reported that overexpression of human insulin-like growth factor binding protein (IGFBP)-1 in mice leads to vascular insulin sensitization, increased nitric oxide bioavailability, reduced atherosclerosis, and enhanced vascular repair, and in the setting of obesity improves glucose tolerance. Human studies suggest that low levels of IGFBP-1 are permissive for the development of diabetes and cardiovascular disease. Here we seek to determine whether loss of IGFBP-1 plays a causal role in the predisposition to cardiometabolic disease. Metabolic phenotyping was performed in transgenic mice with homozygous knockout of IGFBP-1. This included glucose, insulin, and insulin-like growth factor I tolerance testing under normal diet and high-fat feeding conditions. Vascular phenotyping was then performed in the same mice using vasomotor aortic ring studies, flow cytometry, vascular wire injury, and angiogenesis assays. These were complemented with vascular phenotyping of IGFBP-1 overexpressing mice. Metabolic phenotype was similar in IGFBP-1 knockout and wild-type mice subjected to obesity. Deletion of IGFBP-1 inhibited endothelial regeneration following injury, suggesting that IGFBP-1 is required for effective vascular repair. Developmental angiogenesis was unaltered by deletion or overexpression of IGFBP-1. Recovery of perfusion following hind limb ischemia was unchanged in mice lacking or overexpressing IGFBP-1; however, overexpression of IGFBP-1 stimulated hindlimb perfusion and angiogenesis in insulin-resistant mice. These findings provide new insights into the role of IGFBP-1 in metabolic and vascular pathophysiology. Irrespective of whether loss of IGFBP-1 plays a causal role in the development of cardiometabolic disorders, increasing IGFBP-1 levels appears effective in promoting neovascularization in response to ischemia.

Diet Modification and Not Timed Feeding Strategies Result in Intestinal Microbiome Alterations (P21-030-19)

ObjectivesTime-restricted feeding strategies have been shown to normalize obesity parameters, even under high fat feeding conditions. The objective of this study is to examine whether timed feeding alters parameters of gut health or intestinal microbiome composition. MethodsC57BL/6 male mice were randomized to Chow or a high fat diet (HFD) for 6 weeks, followed by a switch from HFD to 1) Chow (sChow), 2) Purified Vegan – Daniel Fast (DF), 3) HFD ad lib, 4) HFD time restricted (TRF), 5) HFD alternative day fasting (ADF), or 6) HFD 60% caloric restriction (CR) for an additional 8 weeks. ResultsWe observed that body mass gain was reduced for all intervention groups (P ≤ 0.0001). Small intestinal length and cecal weight were increased in Chow, sChow and DF (P ≤ 0.02), while total cecal short chain fatty acid (SCFA) concentration was non-significantly increased for all groups consuming the HFD. Proprionate was specifically increased in the Chow, sChow and DF groups (P ≤ 0.02). Chow fed microbiota remained stable in taxonomic composition and alpha diversity (Shannon diversity index) throughout the study. HF fed microbiota displayed lower alpha diversity along with reduced phylum levels of Bacteroidetes and increase Firmicutes. Animals switched from HF to Chow demonstrated a rapid transition in taxonomic composition, alpha, and beta diversity that initially resembled HF, but clustered closely with Chow by weeks 4 and 8 of intervention. After 8 weeks on the respective dietary protocols, alpha diversity of the DF was most similar to Chow fed animals and also resulted in the largest increase in Bacteriodetes and largest decrease in Firmicutes. Beta diversity (weighted UniFrac) showed Chow, sChow, and DF clustered together, while high fat fed groups (HF, CR, ADF, and TRF) clustered. Compared with HF controls, CR and TRF led to a relative increase in the classes Clostridia, Deferribacteres and Deltaproteobacteria. The taxonomic composition and alpha diversity of ADF fasting resembled HF under fed conditions, while ADF under fasting conditions more closely resembled CR and TRF. ConclusionsIn conclusion, timed feeding on a high fat diet did not result in significant changes in the microbiome, demonstrating that diet, and not fasting is the major determinant for microbiome composition. Funding SourcesUniversity of Memphis & Children’s Foundation Research Institute, Memphis.

Nr4a1 and Nr4a3 Knock Out Mice Have Impaired Glucose Clearance and Beta-Cell Function under High-Fat Feeding

We have shown that the orphan nuclear receptors Nr4a1 and Nr4a3 are critical for beta cell mitochondrial respiration and fuel utilization, and that loss of either factor impedes fuel utilization and insulin secretion. We have also demonstrated that prolonged culture of INS-1 832/13 beta cells with progressively increasing concentrations of palmitic acid results in decreased Nr4a1 and Nr4a3 expression, impaired mitochondrial respiration, and reduced insulin secretion. Here we explore the effect of 20-week high fat diet on wild type mice and mice deficient for either Nr4a1 or Nr4a3. Nr4a1 and Nr4a3 knock out mice have greater body weight than wild type animals when on a high fat diet. Mice deficient for Nr4a1 or Nr4a3 have no significant change in non-fasting blood glucose measurements as compared to wild type under normal chow conditions. Non-fasting blood glucose was elevated in both Nr4a1 and Nr4a3 knock out mice under high fat feeding conditions. Fasting glucose tolerance tests also demonstrate that Nr4a1 and Nr4a3 knock out mice have impaired glucose tolerance as compared to wild type animals under high fat feeding. Mitochondrial respiration of muscle, liver, adipose and islets are impaired as compared to wild type controls under high fat feeding. Glucose stimulated insulin secretion is impaired in islets from Nr4a1 or Nr4a3 knock out mice fed a high fat diet. These data demonstrate changes in various metabolic tissues as a result of high fat feeding and deletion of the Nr4a orphan nuclear receptors, demonstrating that they play a critical role in systemic fuel utilization. Disclosure C.J. Smith: None. K.B. Kener: None. J.S. Tessem: None.

APP deficiency results in resistance to obesity but impairs glucose tolerance upon high fat feeding.

The amyloid precursor protein (APP) generates a number of peptides when processed through different cleavage mechanisms, including the amyloid beta peptide that is implicated in the development of Alzheimer's disease. It is well established that APP via its cleaved peptides regulates aspects of neuronal metabolism. Emerging evidence suggests that amyloidogenic processing of APP can lead to altered systemic metabolism, similar to that observed in metabolic disease states. In the present study, we investigated the effect of APP deficiency on obesity-induced alterations in systemic metabolism. Compared with WT littermates, APP-deficient mice were resistant to diet-induced obesity, which was linked to higher energy expenditure and lipid oxidation throughout the dark phase and was associated with increased spontaneous physical activity. Consistent with this lean phenotype, APP-deficient mice fed a high-fat diet (HFD) had normal insulin tolerance. However, despite normal insulin action, these mice were glucose intolerant, similar to WT mice fed a HFD. This was associated with reduced plasma insulin in the early phase of the glucose tolerance test. Analysis of the pancreas showed that APP was required to maintain normal islet and β-cell mass under high fat feeding conditions. These studies show that, in addition to regulating aspects of neuronal metabolism, APP is an important regulator of whole body energy expenditure and glucose homeostasis under high fat feeding conditions.

Shining LIGHT on the metabolic role of the cytokine TNFSF14 and the implications on hepatic IL-6 production.

The cytokine Tumor Necrosis Factor Superfamily member 14, TNFSF14 (or LIGHT), is a controversial player in numerous diseases. We investigated the role of endogenously expressed TNFSF14 in diet-induced obesity in vivo. Firstly, we studied the effects of Tnfsf14 ablation on the development of obesity, glucose intolerance, insulin resistance, steatosis, tissue inflammation, and mitochondrial respiration in the liver. Secondly, we examined the role of TNFSF14 expression in hematopoietic cells on obesity and insulin sensitivity. Male Tnfsf14 knockout (KO) and wild type mice were fed chow or high fat diet (HFD) for 12 weeks and were assessed for weight gain, glucose intolerance, insulin resistance, hepatosteatosis, mitochondrial dysfunction, and cytokine expression. Wild-type mice were also reconstituted with bone marrow cells from Tnfsf14 knockout mice and were fed chow or HFD for 12 weeks. These mice were examined for weight gain and insulin resistance. HFD fed mice had elevated circulating levels of serum TNFSF14. Liver and white adipose tissue are potential sources of this elevated TNFSF14. Tnfsf14 deficient mice displayed increased obesity, glucose intolerance, insulin resistance, hepatosteatosis, and mitochondrial dysfunction compared to control mice on a HFD. Hepatic cytokine profiling pointed to a potential novel role of decreased IL-6 in the metabolic disturbances in obesogenic Tnfsf14 knockout mice. Bone marrow cells from Tnfsf14 deficient mice appeared to promote diet-induced obesity, insulin resistance and reduced FGF21 levels in white adipose tissue and liver. Our novel data suggest that Tnfsf14 ablation exacerbates parameters of the metabolic syndrome under high fat feeding conditions and provides evidence to support the development of TNFSF14 agonists as potential therapeutics in diet-induced obesity.

Gender-Specific Mechanisms Underlying the Amelioration of High-Fat Diet-Induced Glucose Intolerance in B-Cell-Activating Factor Deficient Mice.

It has recently been found that B cell activating factor (BAFF) plays an important role in the regulation of energy homeostasis. We also have previously reported that BAFF deficiency reverses high-fat (HF) diet-induced glucose intolerance by potentiating adipose tissue function. In the present study, we found that BAFF deficient (BAFF-/-) mice exhibit gender-specific differences in protection against diet-induced glucose intolerance, and aimed to characterize the gender-dependent molecular alterations in energy metabolism. Under HF feeding conditions, serum BAFF level of female wild-type (WT) mice was considerably higher than that of male mice. Despite increased body weight gain, both male and female BAFF-/- mice showed significantly improved glucose tolerance compared to their WT counterparts. Expressions of genes involved in glucose transport, thermogenesis and lipid oxidation were up-regulated in brown adipose tissues of both male and female BAFF-/- mice. Interestingly, the expression of thermogenic genes in subcutaneous adipose tissue was significantly enhanced in female BAFF-/- compared to WT mice, but the difference was not observed between male BAFF-/- and WT mice. The enhanced thermogenic program was confirmed by higher protein levels of UCP1 and irisin in female BAFF-/- than in WT mice. Additionally, adiponectin production in white adipose tissues and AMPK phosphorylation in subcutaneous adipose tissue were also significantly elevated in female BAFF-/- compared to WT mice, but not in male BAFF-/- mice. Our findings define a comprehensive scenario for the enhancing effect of BAFF depletion on glucose tolerance wherein the underlying mechanism is, at least in part, gender-specific, and suggest that gender difference should be considered as an important factor in the use of BAFF blockade as a therapeutic approach for the prevention and treatment of type 2 diabetes.

Postexercise High-Fat Feeding Suppresses p70S6K1 Activity in Human Skeletal Muscle.

This study aimed to examine the effects of reduced CHO but high postexercise fat availability on cell signaling and expression of genes with putative roles in regulation of mitochondrial biogenesis, lipid metabolism, and muscle protein synthesis. Ten males completed a twice per day exercise model (3.5 h between sessions) comprising morning high-intensity interval training (8 × 5 min at 85% V˙O2peak) and afternoon steady-state (SS) running (60 min at 70% V˙O2peak). In a repeated-measures design, runners exercised under different isoenergetic dietary conditions consisting of high-CHO (HCHO: 10 g·kg CHO, 2.5 g·kg protein, and 0.8 g·kg fat for the entire trial period) or reduced-CHO but high-fat availability in the postexercise recovery periods (HFAT: 2.5 g·kg CHO, 2.5 g·kg protein, and 3.5 g·kg fat for the entire trial period). Muscle glycogen was lower (P < 0.05) at 3 h (251 vs 301 mmol·kg dry weight) and 15 h (182 vs 312 mmol·kg dry weight) post-SS exercise in HFAT compared with HCHO. Adenosine monophosphate-activated protein kinase α2 activity was not increased post-SS in either condition (P = 0.41), although comparable increases (all P < 0.05) in PGC-1α, p53, citrate synthase, Tfam, peroxisome proliferator-activated receptor, and estrogen-related receptor α mRNA were observed in HCHO and HFAT. By contrast, PDK4 (P = 0.003), CD36 (P = 0.05), and carnitine palmitoyltransferase 1 (P = 0.03) mRNA were greater in HFAT in the recovery period from SS exercise compared with HCHO. Ribosomal protein S6 kinase activity was higher (P = 0.08) at 3 h post-SS exercise in HCHO versus HFAT (72.7 ± 51.9 vs 44.7 ± 27 fmol·min·mg). Postexercise high-fat feeding does not augment the mRNA expression of genes associated with regulatory roles in mitochondrial biogenesis, although it does increase lipid gene expression. However, postexercise ribosomal protein S6 kinase 1 activity is reduced under conditions of high-fat feeding, thus potentially impairing skeletal muscle remodeling processes.

The novel NADPH oxidase 4 inhibitor GLX351322 counteracts glucose intolerance in high-fat diet-treated C57BL/6 mice

In type 2 diabetes, it has been proposed that pancreatic beta-cell dysfunction is promoted by oxidative stress caused by NADPH oxidase (NOX) overactivity. Five different NOX enzymes (NOX1–5) have been characterized, among which NOX1 and NOX2 have been proposed to negatively affect beta-cells, but the putative role of NOX4 in type 2 diabetes-associated beta-cell dysfunction and glucose intolerance is largely unknown. Therefore, we presently investigated the importance of NOX4 for high-fat diet or HFD-induced glucose intolerance using male C57BL/6 mice using the new NOX4 inhibitor GLX351322, which has relative NOX4 selectivity over NOX2. In HFD-treated male C57BL/6 mice a two-week treatment with GLX351322 counteracted non-fasting hyperglycemia and impaired glucose tolerance. This effect occurred without any change in peripheral insulin sensitivity. To ascertain that NOX4 also plays a role for the function of human beta-cells, we observed that glucose- and sodium palmitate-induced insulin release from human islets in vitro was increased in response to NOX4 inhibitors. In long-term experiments (1–3 days), high-glucose-induced human islet cell reactive oxygen species (ROS) production and death were prevented by GLX351322. We propose that while short-term NOX4-generated ROS production is a physiological requirement for beta-cell function, persistent NOX4 activity, for example, during conditions of high-fat feeding, promotes ROS-mediated beta-cell dysfunction. Thus, selective NOX inhibition may be a therapeutic strategy in type 2 diabetes.

Thrombospondin1 deficiency attenuates obesity-associated microvascular complications in ApoE-/- mice.

Obesity is associated with insulin resistance and the increased development of vascular complications. Previously, we have demonstrated that thrombospondin1 (TSP1) regulates macrophage function and contributes to obesity associated inflammation and insulin resistance. However, the role of TSP1 in the development of obesity associated vascular complications is not clear. Therefore, in the current study, we investigated whether TSP1 deficiency protects mice from obesity associated micro as well as macro-vascular complications in ApoE-/- mice. In this study, male ApoE-/- mice and ApoE-/-TSP1-/- mice were fed with a low-fat (LF) or a high-fat (HF) diet for 16 weeks. We found that body weight and fat mass increased similarly between the ApoE-/-TSP1-/- mice and ApoE-/- mice under HF feeding conditions. However, as compared to obese ApoE-/- mice, obese ApoE-/-TSP1-/- mice had improved glucose tolerance, increased insulin sensitivity, and reduced systemic inflammation. Aortic atherosclerotic lesion formation was similar in these two groups of mice. In contrast, albuminuria was attenuated and kidney fibrosis was reduced in obese ApoE-/-TSP1-/- mice compared to obese ApoE-/- mice. The improved kidney function in obese ApoE-/-TSP1-/- mice was associated with decreased renal lipid accumulation. Together, these data suggest that TSP1 deficiency did not affect the development of obesity associated macro-vascular complication, but attenuated obesity associated micro-vascular complications.

Exposure of mice to high fat diet shifts gut microbiota community structure and alters microbial function in a diurnal manner (637.17)

Many organisms exhibit circadian rhythms (CC) based on a 24‐hour light/dark cycle. Evidence in mammalian systems highlights the dominant role of CC in maintaining health, in that development of diet‐induced obesity is associated with CC disruption. Studies also show that high fat (HF) diet‐induced gut microbiota contributes to the development of obesity. Whether the gut microbiota exhibits its own diurnal patterns under healthy states that becomes perturbed under conditions of HF feeding has yet to be described. We hypothesized that HF diet‐induced gut microbiota exhibit altered structural and functional diurnal patterns that ultimately influence host metabolism. Thirty‐six individually‐housed adult C57/Bl6J male mice maintained on a 12/12 light:dark cycle were fed regular chow (RC) or HF diet for 5 weeks. Three mice per treatment were harvested over 24hrs at six time points. Assessment of cecal bacterial 16s rRNA V4‐V5 region via Illumina MiSeq showed MF diet resulted in significantly different α and β‐diversity community structure compared to RC. Diurnal variations in 16s structure were evident in both RC and HF communities, although significant differences over time were not achieved in either treatment. However, comparison of RC and HF cecal microbial community functional profiles via inoculation into Biolog GenIII plates (a spectrophotometric assessment of carbon‐based cellular respiration) showed that while RC and HF exhibited significantly different metabolic potential, only HF exhibited significant diurnal patterns. Together, the data suggest that HF diet alters community membership and only differences in diurnal community functional properties are exhibited. The role of the HF diet‐induced microbial functional changes on the development of obesity in the host remains to be elucidated.Grant Funding Source: Supported By NIDDK P30DK42086

Hepatic Src Homology Phosphatase 2 Regulates Energy Balance in Mice

The Src homology 2 domain-containing protein-tyrosine phosphatase Src homology phosphatase 2 (Shp2) is a negative regulator of hepatic insulin action in mice fed regular chow. To investigate the role of hepatic Shp2 in lipid metabolism and energy balance, we determined the metabolic effects of its deletion in mice challenged with a high-fat diet (HFD). We analyzed body mass, lipid metabolism, insulin sensitivity, and glucose tolerance in liver-specific Shp2-deficient mice (referred to herein as LSHKO) and control mice fed HFD. Hepatic Shp2 protein expression is regulated by nutritional status, increasing in mice fed HFD and decreasing during fasting. LSHKO mice gained less weight and exhibited increased energy expenditure compared with control mice. In addition, hepatic Shp2 deficiency led to decreased liver steatosis, enhanced insulin-induced suppression of hepatic glucose production, and impeded the development of insulin resistance after high-fat feeding. At the molecular level, LSHKO exhibited decreased hepatic endoplasmic reticulum stress and inflammation compared with control mice. In addition, tyrosine and serine phosphorylation of total and mitochondrial signal transducer and activator of transcription 3 were enhanced in LSHKO compared with control mice. In line with this observation and the increased energy expenditure of LSHKO, oxygen consumption rate was higher in liver mitochondria of LSHKO compared with controls. Collectively, these studies identify hepatic Shp2 as a novel regulator of systemic energy balance under conditions of high-fat feeding.

Thrombospondin1 Deficiency Reduces Obesity-Associated Inflammation and Improves Insulin Sensitivity in a Diet-Induced Obese Mouse Model

BackgroundObesity is prevalent worldwide and is associated with insulin resistance. Advanced studies suggest that obesity-associated low-grade chronic inflammation contributes to the development of insulin resistance and other metabolic complications. Thrombospondin 1 (TSP1) is a multifunctional extracellular matrix protein that is up-regulated in inflamed adipose tissue. A recent study suggests a positive correlation of TSP1 with obesity, adipose inflammation, and insulin resistance. However, the direct effect of TSP1 on obesity and insulin resistance is not known. Therefore, we investigated the role of TSP1 in mediating obesity-associated inflammation and insulin resistance by using TSP1 knockout mice.Methodology/Principal FindingsMale TSP1-/- mice and wild type littermate controls were fed a low-fat (LF) or a high-fat (HF) diet for 16 weeks. Throughout the study, body weight and fat mass increased similarly between the TSP1-/- mice and WT mice under HF feeding conditions, suggesting that TSP1 deficiency does not affect the development of obesity. However, obese TSP1-/- mice had improved glucose tolerance and increased insulin sensitivity compared to the obese wild type mice. Macrophage accumulation and inflammatory cytokine expression in adipose tissue were reduced in obese TSP1-/- mice. Consistent with the local decrease in pro-inflammatory cytokine levels, systemic inflammation was also decreased in the obese TSP1-/- mice. Furthermore, in vitro data demonstrated that TSP1 deficient macrophages had decreased mobility and a reduced inflammatory phenotype.ConclusionTSP1 deficiency did not affect the development of high-fat diet induced obesity. However, TSP1 deficiency reduced macrophage accumulation in adipose tissue and protected against obesity related inflammation and insulin resistance. Our data demonstrate that TSP1 may play an important role in regulating macrophage function and mediating obesity-induced inflammation and insulin resistance. These data suggest that TSP1 may serve as a potential therapeutic target to improve the inflammatory and metabolic complications of obesity.

The relevance of increased fat oxidation for body‐weight management: metabolic inflexibility in the predisposition to weight gain

Cells, tissues and organisms have the ability to rapidly switch substrate oxidation from carbohydrate to fat in response to changes in nutrient intake, and to changes in energy demands, environmental cues and internal signals. In healthy, metabolically normal individuals, substrate switching occurs rapidly and completely; in other words, substrate switching is 'flexible'. A growing body of evidence demonstrates that a blunted substrate switching from low- to high-fat oxidation exists in obese individuals, as well as in pre-obese and post-obese, and that this 'metabolic inflexibility' may be a genetically determined trait. A decreased fat oxidation can lead to a positive energy balance under conditions of high-fat feeding, due to depletion of glycogen stores that stimulates appetite and energy intake through glucostatic and glucogenostatic mechanisms, e.g. hepatic sensing of glycogen stores. Several genetic polymorphisms and single-nucleotide polymorphisms have been identified that are associated with low-fat oxidation rates and metabolic inflexibility, and genetic identification of susceptible individuals may lead to personalized prevention of weight gain using fat oxidation stimulants ('fat burners') in the future.

The role of dietary fatty acids in predicting myocardial structure in fat-fed rats

BackgroundObesity increases the risk for development of cardiomyopathy in the absence of hypertension, diabetes or myocardial ischemia. Not all obese individuals, however, progress to heart failure. Indeed, obesity may provide protection from cardiovascular mortality in some populations. The fatty acid milieu, modulated by diet, may modify obesity-induced myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy in obese individuals.MethodsAdult male Sprague-Dawley rats were fed 1 of the following 4 diets for 32 weeks: control (CON); 50% saturated fat (SAT); 40% saturated fat + 10% linoleic acid (SAT+LA); 40% saturated fat + 10% α-linolenic acid (SAT+ALA). Serum leptin, insulin, glucose, free fatty acids and triglycerides were quantitated. In vivo cardiovascular outcomes included blood pressure, heart rate and echocardiographic measurements of structure and function. The rats were sacrificed and myocardium was processed for fatty acid analysis (TLC-GC), and evaluation of potential modifiers of myocardial structure including collagen (Masson's trichrome, hydroxyproline quantitation), lipid (Oil Red O, triglyceride quantitation) and myocyte cross sectional area.ResultsRats fed SAT+LA and SAT+ALA diets had greater cranial LV wall thickness compared to rats fed CON and SAT diets, in the absence of hypertension or apparent insulin resistance. Treatment was not associated with changes in myocardial function. Myocardial collagen and triglycerides were similar among treatment groups; however, rats fed the high-fat diets, regardless of composition, demonstrated increased myocyte cross sectional area.ConclusionsUnder conditions of high-fat feeding, replacement of 10% saturated fat with either LA or ALA is associated with thickening of the cranial LV wall, but without concomitant functional changes. Increased myocyte size appears to be a more likely contributor to early LV thickening in response to high-fat feeding. These findings suggest that myocyte hypertrophy may be an early change leading to gross LV hypertrophy in the hearts of "healthy" obese rats, in the absence of hypertension, diabetes and myocardial ischemia.

A Surprising Link Between the Energetics of Ovariectomy‐induced Weight Gain and Mammary Tumor Progression in Obese Rats

Obesity increases the risk for postmenopausal breast cancer. We have modeled this metabolic context using female Wistar rats that differ in their polygenic predisposition for obesity under conditions of high-fat feeding and limited physical activity. At 52 days of age, rats were injected with 1-methyl-1-nitrosourea (MNU, 50 mg/kg) and placed in an obesogenic environment. At 19 weeks of age, the rats were separated into lean, mid-weight, and obese rats, based upon their weight gained during this time. The rats were ovariectomized (OVX) at approximately 24 weeks of age and the change in tumor multiplicity and burden, weight gain, energy intake, tumor estrogen receptor (ER) status, and humoral metabolite and cytokine profiles were examined. The survival and growth of tumors increased in obese rats in response to OVX. OVX induced a high rate of weight gain during post-OVX weeks 1-3, compared to SHAM-operated controls. During this time, feed efficiency (mg gain/kcal intake) was lower in obese rats, and this reduced storage efficiency of ingested fuels predicted the OVX-induced changes in tumor multiplicity (r = -0.64, P < 0.001) and burden (r = -0.57, P < 0.001). Tumors from obese rats contained more cells that expressed ERalpha, and post-OVX plasma from rats with the lowest feed efficiency had lower interleukin (IL)-2 and IL-4 levels. Our observations suggest a novel link between obesity and mammary tumor promotion that involves impaired fuel metabolism during OVX-induced weight gain. The metabolically inflexible state of obesity and its inability to appropriately respond to the OVX-induced energy imbalance provides a plausible explanation for this relationship and the emergence of obesity's impact on breast cancer risk after menopause.

Hypertrophy and/or Hyperplasia: Dynamics of Adipose Tissue Growth

Adipose tissue grows by two mechanisms: hyperplasia (cell number increase) and hypertrophy (cell size increase). Genetics and diet affect the relative contributions of these two mechanisms to the growth of adipose tissue in obesity. In this study, the size distributions of epididymal adipose cells from two mouse strains, obesity-resistant FVB/N and obesity-prone C57BL/6, were measured after 2, 4, and 12 weeks under regular and high-fat feeding conditions. The total cell number in the epididymal fat pad was estimated from the fat pad mass and the normalized cell-size distribution. The cell number and volume-weighted mean cell size increase as a function of fat pad mass. To address adipose tissue growth precisely, we developed a mathematical model describing the evolution of the adipose cell-size distributions as a function of the increasing fat pad mass, instead of the increasing chronological time. Our model describes the recruitment of new adipose cells and their subsequent development in different strains, and with different diet regimens, with common mechanisms, but with diet- and genetics-dependent model parameters. Compared to the FVB/N strain, the C57BL/6 strain has greater recruitment of small adipose cells. Hyperplasia is enhanced by high-fat diet in a strain-dependent way, suggesting a synergistic interaction between genetics and diet. Moreover, high-fat feeding increases the rate of adipose cell size growth, independent of strain, reflecting the increase in calories requiring storage. Additionally, high-fat diet leads to a dramatic spreading of the size distribution of adipose cells in both strains; this implies an increase in size fluctuations of adipose cells through lipid turnover.