Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity

Late eating has been linked to obesity risk. It is unclear whether this is caused by changes in hunger and appetite, energy expenditure, or both, and whether molecular pathways in adipose tissues are involved. Therefore, we conducted a randomized, controlled, crossover trial (ClinicalTrials.gov NCT02298790) to determine the effects of late versus early eating while rigorously controlling for nutrient intake, physical activity, sleep, and light exposure. Late eating increased hunger (p < 0.0001) and altered appetite-regulating hormones, increasing waketime and 24-h ghrelin:leptin ratio (p < 0.0001 and p = 0.006, respectively). Furthermore, late eating decreased waketime energy expenditure (p = 0.002) and 24-h core body temperature (p = 0.019). Adipose tissue gene expression analyses showed that late eating altered pathways involved in lipid metabolism, e.g., p38 MAPK signaling, TGF-β signaling, modulation of receptor tyrosine kinases, and autophagy, in a direction consistent with decreased lipolysis/increased adipogenesis. These findings show converging mechanisms by which late eating may result in positive energy balance and increased obesity risk.

Differential effects of acute versus chronic dietary fructose consumption on metabolic responses in FVB/N mice

Increased human consumption of hgh fructose corn syrup has been linked to the marked increase in obesity and metabolic syndrome. Previous studies on the rapid effects of a high fructose diet in mice have largely been confined to the C57Bl6 strains. In the current studied, the FVB/N strain of mice that are resistant to diet induced weight gain were utilized and fed a control or high fructose diet for 48 hours or 12 weeks. Many of the previously reported changes that occurred upon high fructose feeding for 48 hours in C57Bl6 mice were recapitulated in the FVB/N mice. However, the acute increases in fructolytic and lipogenic gene expression were completely lost during the 12 week dietary intervention protocol. Furthermore, there was no significant weight gain in FVB/N mice fed a high fructose diet for 12 weeks, despite an overall increase in caloric consumption and an increase in average epididymal adipocyte cell size. These findings may be in part explained by a commensurate increase in energy expenditure and in carbohydrate utilization in high fructose fed animals. Overall, these findings demonstrate that FVB/N mice are a suitable model for the study of the effects of dietary intervention on metabolic and molecular parameters. Furthermore, the rapid changes in hepatic gene expression that have been widely reported were not sustained over a longer time course. Compensatory changes in energy expenditure and utilization may be in part responsible for the differences obtained between acute and chronic high fructose feeding protocols.

Laminin-α4 Is Upregulated in Both Human and Murine Models of Obesity

Obesity affects nearly one billion globally and can lead to life-threatening sequelae. Consequently, there is an urgent need for novel therapeutics. We have previously shown that laminin, alpha 4 (Lama4) knockout in mice leads to resistance to adipose tissue accumulation; however, the relationship between LAMA4 and obesity in humans has not been established. In this study we measured laminin-α chain and collagen mRNA expression in the subcutaneous white adipose tissue (sWAT) of mice placed on chow (RCD) or 45% high fat diet (HFD) for 8 weeks, and also in HFD mice then placed on a "weight loss" regimen (8 weeks HFD followed by 6 weeks RCD). To assess extracellular matrix (ECM) components in humans with obesity, laminin subunit alpha mRNA and protein expression was measured in sWAT biopsies of female control subjects (BMI<30) or subjects with obesity undergoing bariatric surgery at the University of Chicago Medical Center (BMI>35) both before and three months after surgery. Lama4 was significantly higher in sWAT of HFD compared to RCD mice at both the RNA and protein level (p<0.001, p<0.05 respectively). sWAT from human subjects with obesity also showed significantly higher LAMA4 mRNA (p<0.01) and LAMA4 protein expression (p<0.05) than controls. Interestingly, even though LAMA4 expression was increased in both humans and murine models of obesity, no significant difference in Lama4 or LAMA4 expression was detected following short-term weight loss in either mouse or human samples, respectively. From these results we propose a significant association between obesity and elevated LAMA4 expression in humans, as well as in mouse models of obesity. Further studies should clarify the mechanisms underlying this association to target LAMA4 effectively as a potential therapy for obesity.

Laminin-α4 Is Uniquely Upregulated in Subcutaneous White Adipose Tissue in Murine and Human Models of Obesity

As research into the adipocyte microenvironment has advanced, it is becoming more widely accepted that the extracellular matrix (ECM) contributes to adipocyte dysfunction. The majority of current published work focuses on the role of collagens in metabolic disease while less emphasis has been placed on the contribution of laminins, an important component of the adipocyte basement membrane. Laminins are trimeric ECM proteins composed of α, β, and γ chains. The α chains contain sites which can interact with cell surface receptors and is considered the driver of tissue-specific expression and specialized signaling. Our group has shown that the laminin-α4 (LAMA4) chain, which is highly expressed in mature adipocytes, plays a role in adipocyte function and thermogenesis in mice (1). In this study we investigate the relationship between laminin α chain expression and obesity by assessing gene expression of LAMA1-5 in subcutaneous white adipose tissue (sWAT) from mice fed chow (RCD) and 45% high fat diet (HFD) for 8 weeks. Expression of LAMA2 and LAMA4 was significantly increased in the HFD sWAT compared to chow (6.1 fold, p=0.01 and 4.9 fold, p=0.001 respectively), however LAMA4 displayed a much stronger positive correlation with weight (R²=0.697) than did LAMA2 (R²=0.382). In order to validate the relevance of these findings in human models of obesity, we evaluated gene expression of LAMA2, LAMA4, and LAMA5 in sWAT biopsies from non-diabetic adult females with obesity (class II or higher). sWAT samples from obese subjects exhibited 4.5 fold higher LAMA4 expression (p=0.0089) than samples from non-obese control subjects, suggesting that the LAMA4 chain may play an important role in human obesity. Lastly we examined changes in sWAT LAMA4 expression following a period of weight loss in obese mice and in human subjects after bariatric surgery, and found that LAMA4 expression levels remain largely unchanged in both cases. In this study we demonstrate the relationship between LAMA4 expression and obesity and present findings that can be extended to human models of obesity.

Reference: (1) Vaicik et al., Endocrinology. 2018 Jan;159(1):356–67.

The Relationship between Sleep, Obesity, and Metabolic Health in Adolescents - a Review

In this literature review, we discuss the importance of adequate sleep and the various effects of suboptimal sleep on weight maintenance and metabolic health specifically for adolescents. Two major contributors to adolescents experiencing decreased sleep duration and quality, and thus increasing the risk for developing metabolic syndrome in adolescence as well as later in adulthood, are increased electronic screen time particularly at night and early school start times. The less time adolescents spend sleeping, the less quality sleep they obtain, and the greater the disruption of endocrine hormone function. As another consequence, adolescents are more prone to making poor food choices, from choosing relatively nutrient-poor foods to consuming excess calories without necessarily increasing their energy expenditure. These choices put adolescents at greater risk for becoming obese throughout their lifespan.

Translocation of Viable Gut Microbiota to Mesenteric Adipose Drives Formation of Creeping Fat in Humans

A mysterious feature of Crohn's disease (CD) is the extra-intestinal manifestation of "creeping fat" (CrF), defined as expansion of mesenteric adipose tissue around the inflamed and fibrotic intestine. In the current study, we explore whether microbial translocation in CD serves as a central cue for CrF development. We discovered a subset of mucosal-associated gut bacteria that consistently translocated and remained viable in CrF in CD ileal surgical resections, and identified Clostridium innocuum as a signature of this consortium with strain variation between mucosal and adipose isolates, suggesting preference for lipid-rich environments. Single-cell RNA sequencing characterized CrF as both pro-fibrotic and pro-adipogenic with a rich milieu of activated immune cells responding to microbial stimuli, which we confirm in gnotobiotic mice colonized with C. innocuum. Ex vivo validation of expression patterns suggests C. innocuum stimulates tissue remodeling via M2 macrophages, leading to an adipose tissue barrier that serves to prevent systemic dissemination of bacteria.

Magnetic resonance angiography reveals increased arterial blood supply and tumorigenesis following high fat feeding in a mouse model of triple-negative breast cancer

Breast cancer is the second most commonly diagnosed malignancy among women globally. Past MRI studies have linked a high animal fat diet (HAFD) to increased mammary cancer risk in the SV40Tag mouse model of triple-negative breast cancer. Here, serial MRI examines tumor progression and measures the arterial blood volume feeding mammary glands in low fat diet (LFD) or HAFD fed mice. Virgin female C3(1)SV40Tag mice (n = 8), weaned at 3 weeks old, were assigned to an LFD (n = 4, 3.7 kcal/g, 17.2% kcal from vegetable oil) or an HAFD (n = 4, 5.3 kcal/g, 60% kcal from lard) group. From ages 8 to 12 weeks, weekly fast spin echo MR images and time-of-flight (TOF) MR angiography of inguinal mammary glands were acquired at 9.4 T. Following in vivo MRI, mice were sacrificed. Inguinal mammary glands were excised and fixed for ex vivo MRI and histology. Tumor, blood, and mammary gland volumes for each time point were measured from manually traced regions of interest; tumors were classified as invasive by histopathology-blinded observers. Our analysis confirmed a strong correlation between total tumor volume and blood volume in the mammary gland. Tumor growth rates from weeks 8-12 were twice as high in HAFD-fed mice (0.42 ± 0.14/week) as in LFD-fed mice (0.21 ± 0.03/week), p < 0.004. Mammary gland blood volume growth rate was 2.2 times higher in HAFD mice (0.29 ± 0.11/week) compared with LFD mice (0.13 ± 0.06/week), p < 0.02. The mammary gland growth rate of HAFD-fed mice (0.071 ± 0.011/week) was 2.7 times larger than that of LFD-fed mice (0.026 ± 0.009/week), p < 0.01. This is the first non-invasive, in vivo MRI study to demonstrate a strong correlation between an HAFD and increased cancer burden and blood volume in mammary cancer without using contrast agents, strengthening the evidence supporting the adverse effects of an HAFD on mammary cancer. These results support the potential future use of TOF angiography to evaluate vasculature of suspicious lesions.

Effect of Needle Exchange Program on Maternal Hepatitis C Virus Prevalence

OBJECTIVE

This study aimed to quantify the prevalence of maternal hepatitis C virus (HCV) before and after implementation of the needle exchange program (NEP) in Scioto County, Ohio.

STUDY DESIGN

We conducted a population-based retrospective cohort study of all live births in Ohio (2006-2015). Frequency of maternal HCV was compared before (2006-2011) and after (2012-2015) the implementation of an NEP (2011) in Portsmouth, Ohio (Scioto County). Trends in maternal HCV prevalence in neighboring counties both physically adjacent and regional to Scioto County were also evaluated before and after NEP implementation.

RESULTS

During the study period, there were 7,069 reported cases of maternal HCV infection at the time of delivery among 1,463,506 (0.5%) live births in Ohio. The rate of maternal HCV infection increased 137% in Scioto County between 2006 and 2011. After initiation of the NEP in Portsmouth, Ohio, in 2011, the rate of increase in the following 4 years (2012-2015) was 12%. The rate of increase in maternal HCV declined precipitously in counties physically adjacent to Scioto County, whereas regional counties continued to have substantial increases in maternal HCV.

CONCLUSION

Rate of maternal HCV infection increased 137% versus 12% (rate difference: 125%) between pre- and post-NEP implementation time periods in Scioto County.

Endocrine implications of bariatric surgery: a review on the intersection between incretins, bone, and sex hormones

Bariatric surgery is now the most widely used intervention for the treatment of human obesity. A large body of literature has demonstrated its efficacy in sustained weight loss and improvement in its associated comorbidities. Here, we review the effect of bariatric surgery in gut hormone physiology, bone remodeling and the reproductive axis. Rapid improvements in insulin release and sensitivity appear to be weight loss independent and occur immediately after surgery. These effects on pancreatic beta cells are mostly due to increased gut hormone secretion due to augmented nutrient delivery to the small intestine. Bone remodeling is also affected by gut hormones. Phenotypic skeletal changes observed in mice deficient in GLP‐1 or GIP suggest that increased incretins may improve bone density. However, these positive effects may be counterbalanced by the association between weight loss and a reduction in bone density. Finally, studies have shown a marked improvement following bariatric surgery in infertility and PCOS in women and hypogonadism in men. Thus, the net effect on endocrine systems after bariatric surgery will likely vary on an individual basis and depend on factors such as comorbidities, peri‐menopausal state, amount of weight loss, and likelihood to adhere to vitamin supplementation after surgery.

Reduction of IL-6 gene expression in human adipose tissue after sleeve gastrectomy surgery

OBJECTIVE

There is increasing evidence that immune cell interactions in adipose tissue contribute to the development of metabolic dysfunction. Pro-inflammatory cytokines have been shown to mediate insulin resistance, and the presence of macrophages is a salient feature in the development of obesity. The present study aimed to evaluate adipocyte size and macrophage activation in women before and 3 months after laparoscopic vertical sleeve gastrectomy (VSG).

METHODS

Subcutaneous abdominal adipose tissue biopsies were obtained from women scheduled to undergo VSG. Histological evaluation of adipocytes and macrophages was performed as well as cytokine expression quantification before and after VSG-induced weight loss.

RESULTS

Weight loss following VSG resulted in a reduction in adipocyte size as well as a decrease in interleukin (IL)-6 cytokine mRNA expression in subcutaneous adipose tissue. There was no change in the presence of crownlike structures after weight loss.

CONCLUSIONS

Early weight loss after VSG is associated with a reduction in adipocyte size and a decline in IL-6 gene expression in local adipose tissue. Macrophage infiltration and crownlike density structures persist in adipose tissue from tissues impacted by excess body weight 3 months after VSG-induced weight loss.

Reference Gene Optimization for Circadian Gene Expression Analysis in Human Adipose Tissue

A hallmark of biology is the cyclical nature of organismal physiology driven by networks of biological, including circadian, rhythms. Unsurprisingly, disruptions of the circadian rhythms through sleep curtailment or shift work have been connected through numerous studies to positive associations with obesity, insulin resistance, and diabetes. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) measures oscillation in messenger RNA expression, an essential foundation for the study of the physiological circadian regulatory network. Primarily, measured oscillations have involved the use of reference gene normalization. However, the validation and identification of suitable reference genes is a significant challenge across different biological systems. This study focuses on adipose tissue of premenopausal, otherwise healthy, morbidly obese women voluntarily enrolled after being scheduled for laparoscopic sleeve gastrectomy surgery. Acquisition of tissue was accomplished by aspiratory needle biopsies of subcutaneous adipose tissue 1 to 2 weeks prior to surgery and 12 to 13 weeks following surgery and an in-surgery scalpel-assisted excision of mesenteric adipose tissue. Each biopsy was sterile cultured ex vivo and serially collected every 4 h over approximately 36 h. The candidate reference genes that were tested were 18S rRNA, GAPDH, HPRT1, RPII, RPL13α, and YWHAZ. Three analytic tools were used to test suitability, and the candidate reference genes were used to measure oscillation in expression of a known circadian clock element (Dbp). No gene was deemed suitable as an individual reference gene control, which indicated that the optimal reference gene set was the geometrically averaged 3-gene panel composed of YWHAZ, RPL13α, and GAPDH. These methods can be employed to identify optimal reference genes in other systems.

Disparity in Adiposity among Adults with Normal Body Mass Index and Waist-to-Height Ratio

Body mass index (BMI) is commonly used to define obesity. However, concerns about its accuracy in predicting adiposity have been raised. The feasibility of using BMI as well as waist-height ratio (WHtR) in assessing adiposity was examined in relation to a more direct measurement of percent body fat (%BF). We analyzed the relation between dual-energy X-ray absorptiometry (DXA)-measured fat mass and BMI and WHtR using the US 1999-2004 National Health and Nutrition Examination Survey (NHANES) data. A considerable proportion of subjects in the healthy BMI range 20-25 were found to have excess adiposity, including 33.1% of males and 51.9% of females. The use of WHtR also supports the notion of normal-weight central obesity (NWCO), which increases with age. These findings have important implications not only for clinical practice but also for many comparative studies where control subjects are usually selected based on age, sex, and BMI.

Dietary Fructose Consumption and Triple-Negative Breast Cancer Incidence

In the past century the western world has found a way to combat most communicative diseases; however, throughout that time the prevalence of obesity, hyperglycemia, and hyperlipidemia have drastically increased. These symptoms characterize metabolic syndrome-a non-communicable disease which has become one of the greatest health hazards of the world. During this same time period the western diet had dramatically changed. Homecooked meals have been replaced by highly-processed, calorically dense foods. This conversion to the current western diet was highlighted by the incorporation of high-fructose corn syrup (HFCS) into sweetened beverages and foods. The consumption of large amounts of dietary sugar, and fructose in particular, has been associated with an altered metabolic state, both systemically and in specific tissues. This altered metabolic state has many profound effects and is associated with many diseases, including diabetes, cardiovascular disease, and even cancer (1). Specific types of cancer, like triple-negative breast cancer (TNBC), are both responsive to dietary factors and exceptionally difficult to treat, illustrating the possibility for preventative care through dietary intervention in at risk populations. To treat these non-communicable diseases, including obesity, diabetes, and cancer, it is imperative to understand systemic and localized metabolic abnormalities that drive its progression. This review will specifically explore the links between increased dietary fructose consumption, development of metabolic disturbances and increased incidence of TNBC.

Abstract B53: Psychosocial stress exposure results in inhibition of mammary gland development and increased mammary stem cells in a rat model of breast cancer

Exposure to unremitting psychosocial stressors common to underserved populations (i.e., social marginalization and isolation, economic uncertainty, and racism) manifest in physiologic changes that are associated with highly aggressive mammary cancer. Many environmental exposures that influence breast cancer risk in adulthood occur earlier in life during the time of mammary gland development. However, the effect of stress physiology on mammary gland development and its link to breast cancer remains unknown. In a model of psychosocial stress (social isolation), we studied whether a social isolation-induced stress response would affect mammary gland development. To this end, we used the Sprague Dawley rat, where there is an established effect of psychosocial stress on increasing later-life mammary cancer risk. Here, we found that post-weaning social isolation was associated with decreased ductal differentiation and increased mammary stem cells (MaSC). Using an in vitro model, we next determined if glucocorticoid receptor activation increased MaSC survival through direct and paracrine mechanisms. Our findings provide evidence that social stressors induce glucocorticoid exposure and decrease mammary gland differentiation leading to an increased MaSC population, potentially contributing to a greater mammary cancer risk.

Citation Format: Marianna B. Johnson, Joscelyn N. Hoffmann, Hannah M. You, Ahmad B. Allaw, Jordan W. Strober, Matthew J. Brady, Martha K. McClintock, Suzanne D. Conzen. Psychosocial stress exposure results in inhibition of mammary gland development and increased mammary stem cells in a rat model of breast cancer [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B53.

Psychosocial Stress Exposure Disrupts Mammary Gland Development

Exposure to psychosocial stressors and ensuing stress physiology have been associated with spontaneous invasive mammary tumors in the Sprague-Dawley rat model of human breast cancer. Mammary gland (MG) development is a time when physiologic and environmental exposures influence breast cancer risk. However, the effect of psychosocial stress exposure on MG development remains unknown. Here, in the first comprehensive longitudinal study of MG development in nulliparous female rats (from puberty through young adulthood; 8-25 wks of age), we quantify the spatial gradient of differentiation within the MG of socially stressed (isolated) and control (grouped) rats. We then demonstrate that social isolation increased stress reactivity to everyday stressors, resulting in downregulation of glucocorticoid receptor (GR) expression in the MG epithelium. Surprisingly, given that chemical carcinogens increase MG cancer risk by preventing normal terminal end bud (TEB) differentiation, chronic isolation stress did not alter TEBs. Instead, isolation blunted MG growth and alveolobular differentiation and reduced epithelial cell proliferation in these structures. Social isolation also enhanced corpora luteal progesterone at all ages but reduced estrogenization only in early adulthood, a pattern that precludes modulated ovarian function as a sufficient mechanism for the effects of isolation on MG development. This longitudinal study of natural variation provides an integrated view of MG development and the importance of increased GR activation in nulliparous ductal growth and alveolobular differentiation. Thus, social isolation and its physiological sequelae disrupt MG growth and differentiation and suggest a contribution of stress exposure during puberty and young adulthood to the previously observed increase in invasive MG cancer observed in chronically socially-isolated adult Sprague-Dawley rats.

Magnetic resonance spectroscopy detects differential lipid composition in mammary glands on low fat, high animal fat versus high fructose diets

The effects of consumption of different diets on the fatty acid composition in the mammary glands of SV40 T-antigen (Tag) transgenic mice, a well-established model of human triple-negative breast cancer, were investigated with magnetic resonance spectroscopy and spectroscopic imaging. Female C3(1) SV40 Tag transgenic mice (n = 12) were divided into three groups at 4 weeks of age: low fat diet (LFD), high animal fat diet (HAFD), and high fructose diet (HFruD). MRI scans of mammary glands were acquired with a 9.4 T scanner after 8 weeks on the diet. 1H spectra were acquired using point resolved spectroscopy (PRESS) from two 1 mm3 boxes on each side of inguinal mammary gland with no cancers, lymph nodes, or lymph ducts. High spectral and spatial resolution (HiSS) images were also acquired from nine 1-mm slices. A combination of Gaussian and Lorentzian functions was used to fit the spectra. The percentages of poly-unsaturated fatty acids (PUFA), mono-unsaturated fatty acids (MUFA), and saturated fatty acids (SFA) were calculated from each fitted spectrum. Water and fat peak height images (maps) were generated from HiSS data. The results showed that HAFD mice had significantly lower PUFA than both LFD (p < 0.001) and HFruD (p < 0.01) mice. The mammary lipid quantity calculated from 1H spectra was much larger in HAFD mice than in LFD (p = 0.03) but similar to HFruD mice (p = 0.10). The average fat signal intensity over the mammary glands calculated from HiSS fat maps was ~60% higher in HAFD mice than in LFD (p = 0.04) mice. The mean or median of calculated parameters for the HFruD mice were between those for LFD and HAFD mice. Therefore, PRESS spectroscopy and HiSS MRI demonstrated water and fat composition changes in mammary glands due to a Western diet, which was low in potassium, high in sodium, animal fat, and simple carbohydrates. Measurements of PUFA with MRI could be used to evaluate cancer risk, improve cancer detection and diagnosis, and guide preventative therapy.

MRI reveals increased tumorigenesis following high fat feeding in a mouse model of triple-negative breast cancer

High animal fat consumption is associated with an increase in triple-negative breast cancer (TNBC) risk. Based on previous MRI studies demonstrating the feasibility of detecting very early non-palpable mammary cancers in simian virus 40 large T antigen (SV40TAg) mice, we examined the effect of dietary fat fed from weaning to young adulthood in this model of TNBC. Virgin female C3(1)SV40TAg mice (n = 16) were weaned at 3-4 weeks of age and then fed either a low fat diet (LFD) (n = 8, 3.7 kcal/g; 17.2% kcal from vegetable oil) or a high animal fat diet (HAFD) (n = 8, 5.3 kcal/g; 60% kcal from lard). After 8 weeks on the diet (12 weeks of age), fast spin echo MR images of inguinal mammary glands were acquired at 9.4 T. Following in vivo MRI, mice were sacrificed and inguinal mammary glands were excised and formalin fixed for ex vivo MRI. 3D volume-rendered MR images were then correlated with mammary gland histology to assess the glandular parenchyma and tumor burden. Using in vivo MRI, an average of 3.88 ± 1.03 tumors were detected per HAFD-fed mouse compared with an average of 1.25 ± 1.16 per LFD-fed mouse (p < 0.007). Additionally, the average tumor volume was significantly higher following HAFD feeding (0.53 ± 0.45 mm³ ) compared with LFD feeding (0.20 ± 0.08 mm³ , p < 0.02). Analysis of ex vivo MR and histology images demonstrated that HAFD mouse mammary glands had denser parenchyma, irregular and enlarged ducts, dilated blood vessels, increased white adipose tissue, and increased tumor invasion. MRI and histological studies of the SV40TAg mice demonstrated that HAFD feeding also resulted in higher cancer incidence and larger mammary tumors. Unlike other imaging methods for assessing environmental effects on mammary cancer growth, MRI allows routine serial measurements and reliable detection of small cancers as well as accurate tumor volume measurements and assessment of the three-dimensional distribution of tumors over time.

Automated gesture tracking in head-fixed mice

BACKGROUND

The preparation consisting of a head-fixed mouse on a spherical or cylindrical treadmill offers unique advantages in a variety of experimental contexts. Head fixation provides the mechanical stability necessary for optical and electrophysiological recordings and stimulation. Additionally, it can be combined with virtual environments such as T-mazes, enabling these types of recording during diverse behaviors.

NEW METHOD

In this paper we present a low-cost, easy-to-build acquisition system, along with scalable computational methods to quantitatively measure behavior (locomotion and paws, whiskers, and tail motion patterns) in head-fixed mice locomoting on cylindrical or spherical treadmills.

EXISTING METHODS

Several custom supervised and unsupervised methods have been developed for measuring behavior in mice. However, to date there is no low-cost, turn-key, general-purpose, and scalable system for acquiring and quantifying behavior in mice.

RESULTS

We benchmark our algorithms against ground truth data generated either by manual labeling or by simpler methods of feature extraction. We demonstrate that our algorithms achieve good performance, both in supervised and unsupervised settings.

CONCLUSIONS

We present a low-cost suite of tools for behavioral quantification, which serve as valuable complements to recording and stimulation technologies being developed for the head-fixed mouse preparation.

Eastern fox squirrel (Sciurus niger, Linnaeus 1758) introduction to the Sonoran Desert

The eastern fox squirrel, native to the eastern and midwestern United States, was recently documented in the Sonoran Desert in the vicinity of Yuma, Arizona, constituting the first state record for this species. We surveyed the people of Yuma to determine when and how the squirrels arrived. The squirrels were first observed in the 1960s, but may have been resident for a longer period. Since the 1960s, squirrels have spread throughout the city limits and extended south ~15 km into Somerton, Arizona. How the squirrels arrived is not clear, but must be the result of an introduction, as no nearby populations exist. The persistence of eastern fox squirrels in this unique habitat is due to synanthropic relationships.

Peripheral circadian misalignment: contributor to systemic insulin resistance and potential intervention to improve bariatric surgical outcomes

Thirteen percent of the world's population suffers from obesity and 39% from being overweight, which correlates with an increase in numerous secondary metabolic complications, such as Type 2 diabetes mellitus. Bariatric surgery is the most effective treatment for severe obesity and results in significant weight loss and the amelioration of obesity-related comorbidities through changes in enteroendocrine activity, caloric intake, and alterations in gut microbiota composition. The circadian system has recently been found to be a critical regulatory component in the control of metabolism and, thus, may potentially play an important role in inappropriate weight gain. Indeed, some behaviors and lifestyle factors associated with an increased risk of obesity are also risk factors for misalignment in the circadian clock system and for the metabolic syndrome. It is thus possible that alterations in peripheral circadian clocks in metabolically relevant tissues are a contributor to the current obesity epidemic. As such, it is plausible that postsurgical alterations in central circadian alignment, as well as peripheral gene expression in metabolic tissues may represent another mechanism for the beneficial effects of bariatric surgery. Bariatric surgery may represent an opportunity to identify changes in the circadian expression of clock genes that have been altered by environmental factors, allowing for a better understanding of the mechanism of action of surgery. These studies could also reveal an overlooked target for behavioral intervention to improve metabolic outcomes following bariatric surgery.

Mammary Adipose Tissue-Derived Lysophospholipids Promote Estrogen Receptor-Negative Mammary Epithelial Cell Proliferation

Lysophosphatidic acid (LPA), acting in an autocrine or paracrine fashion through G protein-coupled receptors, has been implicated in many physiologic and pathologic processes, including cancer. LPA is converted from lysophosphatidylcholine (LPC) by the secreted phospholipase autotaxin (ATX). Although various cell types can produce ATX, adipocyte-derived ATX is believed to be the major source of circulating ATX and also to be the major regulator of plasma LPA levels. In addition to ATX, adipocytes secrete numerous other factors (adipokines); although several adipokines have been implicated in breast cancer biology, the contribution of mammary adipose tissue-derived LPC/ATX/LPA (LPA axis) signaling to breast cancer is poorly understood. Using murine mammary fat-conditioned medium, we investigated the contribution of LPA signaling to mammary epithelial cancer cell biology and identified LPA signaling as a significant contributor to the oncogenic effects of the mammary adipose tissue secretome. To interrogate the role of mammary fat in the LPA axis during breast cancer progression, we exposed mammary adipose tissue to secreted factors from estrogen receptor-negative mammary epithelial cell lines and monitored changes in the mammary fat pad LPA axis. Our data indicate that bidirectional interactions between mammary cancer cells and mammary adipocytes alter the local LPA axis and increase ATX expression in the mammary fat pad during breast cancer progression. Thus, the LPC/ATX/LPA axis may be a useful target for prevention in patients at risk of ER-negative breast cancer. Cancer Prev Res; 9(5); 367-78. ©2016 AACR.

Glucocorticoid receptor ChIP-sequencing of subcutaneous fat reveals modulation of inflammatory pathways

OBJECTIVE

To identify glucocorticoid receptor (GR)-associated chromatin sequences and target genes in primary human abdominal subcutaneous fat.

METHODS

GR chromatin immunoprecipitation (ChIP)-sequencing (seq) methodology in subcutaneous human adipocytes treated ex vivo with dexamethasone (dex) was optimized to identify genome-wide dex-dependent GR-binding regions (GBRs). Gene expression analyses were performed in parallel ± dex treatment.

RESULTS

Fat was obtained from four female surgical patients without obesity with a median age of 50.5 years. ChIP-seq analysis revealed 219 dex-associated GBRs. Of these, 136 GBRs were located within 100 kb of the transcriptional start site and associated with 123 genes. Combining these data with dex-induced gene expression, 70 of the 123 putative direct target genes were significantly up- or downregulated following 4 hours of dex treatment. Gene expression analysis demonstrated that the top 10 pathways reflected regulation of cellular metabolism and inflammation. DEPTOR, an inhibitor of mTOR, was identified as a potential direct GR target gene.

CONCLUSIONS

This is the first report of genome-wide GR ChIP-seq and gene expression analysis in human fat. The results implicate regulation of key GR target genes that are involved in dampening inflammation and promoting cellular metabolism.

Sleep fragmentation promotes NADPH oxidase 2-mediated adipose tissue inflammation leading to insulin resistance in mice

Background

Short sleep has been implicated in higher risk of obesity in humans, and is associated with insulin resistance. However, the effects of fragmented sleep (SF) rather than curtailed sleep on glucose homeostasis are unknown.

Methods

Wild type and NADPH oxidase 2 (Nox2) null male mice were subjected to SF or sleep control (SC) conditions for 3 days-3 weeks. Systemic and visceral adipose tissue (VAT) insulin sensitivity tests, glucose tolerance test, FACS and immunohistochemistry for macrophages and sub-types (M1 and M2) and Nox expression and activity were examined.

Results

Here show that SF in the absence of sleep curtailment induces time-dependent insulin resistance, in vivo and also in vitro in VAT. Oxidative stress pathways were up-regulated by SF in VAT, and were accompanied by M1 macrophage polarization. SF-induced oxidative stress, inflammation, and insulin resistance in VAT were completely abrogated in genetically altered mice lacking Nox2 activity.

Conclusions

These studies imply that SF, a frequent occurrence in many disorders and more specifically in sleep apnea, is a potent inducer of insulin resistance via activation of oxidative stress and inflammatory pathways, thereby opening the way for therapeutic strategies.

Refeeding-induced brown adipose tissue glycogen hyper-accumulation in mice is mediated by insulin and catecholamines

Brown adipose tissue (BAT) generates heat during adaptive thermogenesis through a combination of oxidative metabolism and uncoupling protein 1-mediated electron transport chain uncoupling, using both free-fatty acids and glucose as substrate. Previous rat-based work in 1942 showed that prolonged partial fasting followed by refeeding led to a dramatic, transient increase in glycogen stores in multiple fat depots. In the present study, the protocol was replicated in male CD1 mice, resulting in a 2000-fold increase in interscapular BAT (IBAT) glycogen levels within 4-12 hours (hr) of refeeding, with IBAT glycogen stores reaching levels comparable to fed liver glycogen. Lesser effects occurred in white adipose tissues (WAT). Over the next 36 hr, glycogen levels dissipated and histological analysis revealed an over-accumulation of lipid droplets, suggesting a potential metabolic connection between glycogenolysis and lipid synthesis. 24 hr of total starvation followed by refeeding induced a robust and consistent glycogen over-accumulation similar in magnitude and time course to the prolonged partial fast. Experimentation demonstrated that hyperglycemia was not sufficient to drive glycogen accumulation in IBAT, but that elevated circulating insulin was sufficient. Additionally, pharmacological inhibition of catecholamine production reduced refeeding-induced IBAT glycogen storage, providing evidence of a contribution from the central nervous system. These findings highlight IBAT as a tissue that integrates both canonically-anabolic and catabolic stimulation for the promotion of glycogen storage during recovery from caloric deficit. The preservation of this robust response through many generations of animals not subjected to food deprivation suggests that the over-accumulation phenomenon plays a critical role in IBAT physiology.

Chronic social isolation is associated with metabolic gene expression changes specific to mammary adipose tissue

Chronic social isolation is linked to increased mammary tumor growth in rodent models of breast cancer. In the C3(1)/SV40 T-antigen FVB/N (TAg) mouse model of "triple-negative" breast cancer, the heightened stress response elicited by social isolation has been associated with increased expression of metabolic genes in the mammary gland before invasive tumors develop (i.e., during the in situ carcinoma stage). To further understand the mechanisms underlying how accelerated mammary tumor growth is associated with social isolation, we separated the mammary gland adipose tissue from adjacent ductal epithelial cells and analyzed individual cell types for changes in metabolic gene expression. Specifically, increased expression of the key metabolic genes Acaca, Hk2, and Acly was found in the adipocyte, rather than the epithelial fraction. Surprisingly, metabolic gene expression was not significantly increased in visceral adipose depots of socially isolated female mice. As expected, increased metabolic gene expression in the mammary adipocytes of socially isolated mice coincided with increased glucose metabolism, lipid synthesis, and leptin secretion from this adipose depot. Furthermore, application of media that had been cultured with isolated mouse mammary adipose tissue (conditioned media) resulted in increased proliferation of mammary cancer cells relative to group-housed-conditioned media. These results suggest that exposure to a chronic stressor (social isolation) results in specific metabolic reprogramming in mammary gland adipocytes that in turn contributes to increased proliferation of adjacent preinvasive malignant epithelial cells. Metabolites and/or tumor growth-promoting proteins secreted from adipose tissue could identify biomarkers and/or targets for preventive intervention in breast cancer.

Composition of dietary fat source shapes gut microbiota architecture and alters host inflammatory mediators in mouse adipose tissue

BACKGROUND

Growing evidence shows that dietary factors can dramatically alter the gut microbiome in ways that contribute to metabolic disturbance and progression of obesity. In this regard, mesenteric adipose tissue has been implicated in mediating these processes through the elaboration of proinflammatory adipokines. In this study, we examined the relationship of these events by determining the effects of dietary fat content and source on gut microbiota, as well as the effects on adipokine profiles of mesenteric and peripheral adipocytes.

METHODS

Adult male C57Bl/6 mice were fed milk fat-based, lard-based (saturated fatty acid sources), or safflower oil (polyunsaturated fatty acid)-based high-fat diets for 4 weeks. Body mass and food consumption were measured. Stool 16S ribosomal RNA (rRNA) was isolated and analyzed via terminal restriction fragment length polymorphism as well as variable V3-4 sequence tags via next-generation sequencing. Mesenteric and gonadal adipose samples were analyzed for both lipogenic and inflammatory mediators via quantitative real-time polymerase chain reaction.

RESULTS

High-fat feedings caused more weight gain with concomitant increases in caloric consumption relative to low-fat diets. In addition, each of the high-fat diets induced dramatic and specific 16S rRNA phylogenic profiles that were associated with different inflammatory and lipogenic mediator profiles of mesenteric and gonadal fat depots.

CONCLUSIONS

Our findings support the notion that dietary fat composition can both reshape the gut microbiota and alter host adipose tissue inflammatory/lipogenic profiles. They also demonstrate the interdependency of dietary fat source, commensal gut microbiota, and inflammatory profile of mesenteric fat that can collectively affect the host metabolic state.

The endocrine disrupting chemical tolylfluanid alters adipocyte metabolism via glucocorticoid receptor activation

Glucocorticoid signaling plays a critical role in regulating energy metabolism. Emerging data implicate environmental endocrine-disrupting chemicals as contributors to the obesity and diabetes epidemics. Previous studies have shown that the phenylsulfamide fungicide tolylfluanid (TF) augments glucocorticoid receptor (GR)-dependent luciferase expression in 3T3-L1 preadipocytes while modulating insulin action in primary murine and human adipocytes. Studies were performed to interrogate glucocorticoid signaling in primary adipocytes exposed to TF. TF mimicked the gene transcription profile of the murine glucocorticoid corticosterone (Cort). Cellular fractionation assays demonstrated that TF treatment promoted the activating serine phosphorylation of GR, augmenting its cytoplasmic-to-nuclear translocation as well as its enrichment at glucocorticoid response elements on the glucocorticoid-induced leucine zipper gene promoter. After acute treatment, Cort or TF promoted insulin receptor substrate-1 (IRS-1) gene and protein expression. Either treatment also enriched GR binding at an identified glucocorticoid response element in the IRS-1 gene. TF or Cort each increased insulin-stimulated lipogenesis, an effect resulting from increased lipogenic gene expression and enhanced insulin-stimulated dephosphorylation of acetyl-coenzyme A carboxylase. The augmentation of insulin-stimulated lipogenesis was mediated through a specific enhancement of Akt phosphorylation at T308. These findings support modulation of IRS-1 levels as a mechanism for glucocorticoid-mediated changes in insulin action in primary adipocytes. Albeit with less affinity than Cort, in silico analysis suggests that TF can interact with the ligand binding pocket of GR. Collectively, these studies identify TF as a structurally unique environmental glucocorticoid. Glucocorticoid signaling may thus represent a novel pathway by which environmental toxicants promote the development of metabolic diseases.

Impaired insulin signaling in human adipocytes after experimental sleep restriction: a randomized, crossover study

BACKGROUND

Insufficient sleep increases the risk for insulin resistance, type 2 diabetes, and obesity, suggesting that sleep restriction may impair peripheral metabolic pathways. Yet, a direct link between sleep restriction and alterations in molecular metabolic pathways in any peripheral human tissue has not been shown.

OBJECTIVE

To determine whether sleep restriction results in reduced insulin sensitivity in subcutaneous fat, a peripheral tissue that plays a pivotal role in energy metabolism and balance.

DESIGN

Randomized, 2-period, 2-condition, crossover clinical study.

SETTING

University of Chicago Clinical Resource Center.

PARTICIPANTS

Seven healthy adults (1 woman, 6 men) with a mean age of 23.7 years (SD, 3.8) and mean body mass index of 22.8 kg/m(2) (SD, 1.6).

INTERVENTION

Four days of 4.5 hours in bed or 8.5 hours in bed under controlled conditions of caloric intake and physical activity.

MEASUREMENTS

Adipocytes collected from subcutaneous fat biopsy samples after normal and restricted sleep conditions were exposed to incremental insulin concentrations. The ability of insulin to increase levels of phosphorylated Akt (pAkt), a crucial step in the insulin-signaling pathway, was assessed. Total Akt (tAkt) served as a loading control. The insulin concentration for the half-maximal stimulation of the pAkt-tAkt ratio was used as a measure of cellular insulin sensitivity. Total body insulin sensitivity was assessed using a frequently sampled intravenous glucose tolerance test.

RESULTS

The insulin concentration for the half-maximal pAkt-tAkt response was nearly 3-fold higher (mean, 0.71 nM [SD, 0.27] vs. 0.24 nM [SD, 0.24]; P = 0.01; mean difference, 0.47 nM [SD, 0.33]; P = 0.01), and the total area under the receiver-operating characteristic curve of the pAkt-tAkt response was 30% lower (P = 0.01) during sleep restriction than during normal sleep. A reduction in total body insulin sensitivity (P = 0.02) paralleled this impaired cellular insulin sensitivity.

LIMITATION

This was a single-center study with a small sample size.

CONCLUSION

Sleep restriction results in an insulin-resistant state in human adipocytes. Sleep may be an important regulator of energy metabolism in peripheral tissues.

PRIMARY FUNDING SOURCE

National Institutes of Health.

PCB 126 and other dioxin-like PCBs specifically suppress hepatic PEPCK expression via the aryl hydrocarbon receptor

Dioxins and dioxin-like compounds encompass a group of structurally related heterocyclic compounds that bind to and activate the aryl hydrocarbon receptor (AhR). The prototypical dioxin is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a highly toxic industrial byproduct that incites numerous adverse physiological effects. Global commercial production of the structurally similar polychlorinated biphenyls (PCBs), however, commenced early in the 20(th) century and continued for decades; dioxin-like PCBs therefore contribute significantly to total dioxin-associated toxicity. In this study, PCB 126, the most potent dioxin-like PCB, was evaluated with respect to its direct effects on hepatic glucose metabolism using primary mouse hepatocytes. Overnight treatment with PCB 126 reduced hepatic glycogen stores in a dose-dependent manner. Additionally, PCB 126 suppressed forskolin-stimulated gluconeogenesis from lactate. These effects were independent of acute toxicity, as PCB 126 did not increase lactate dehydrogenase release nor affect lipid metabolism or total intracellular ATP. Interestingly, provision of cells with glycerol instead of lactate as the carbon source completely restored hepatic glucose production, indicating specific impairment in the distal arm of gluconeogenesis. In concordance with this finding, PCB 126 blunted the forskolin-stimulated increase in phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels without affecting glucose-6-phosphatase expression. Myricetin, a putative competitive AhR antagonist, reversed the suppression of PEPCK induction by PCB 126. Furthermore, other dioxin-like PCBs demonstrated similar effects on PEPCK expression in parallel with their ability to activate AhR. It therefore appears that AhR activation mediates the suppression of PEPCK expression by dioxin-like PCBs, suggesting a role for these pollutants as disruptors of energy metabolism.

The novel endocrine disruptor tolylfluanid impairs insulin signaling in primary rodent and human adipocytes through a reduction in insulin receptor substrate-1 levels

Emerging data suggest that environmental endocrine disrupting chemicals may contribute to the pathophysiology of obesity and diabetes. In a prior work, the phenylsulfamide fungicide tolylfluanid (TF) was shown to augment adipocyte differentiation, yet its effects on mature adipocyte metabolism remain unknown. Because of the central role of adipose tissue in global energy regulation, the present study tested the hypothesis that TF modulates insulin action in primary rodent and human adipocytes. Alterations in insulin signaling in primary mammalian adipocytes were determined by the phosphorylation of Akt, a critical insulin signaling intermediate. Treatment of primary murine adipose tissue in vitro with 100nM TF for 48h markedly attenuated acute insulin-stimulated Akt phosphorylation in a strain- and species-independent fashion. Perigonadal, perirenal, and mesenteric fat were all sensitive to TF-induced insulin resistance. A similar TF-induced reduction in insulin-stimulated Akt phosphorylation was observed in primary human subcutaneous adipose tissue. TF treatment led to a potent and specific reduction in insulin receptor substrate-1 (IRS-1) mRNA and protein levels, a key upstream mediator of insulin's diverse metabolic effects. In contrast, insulin receptor-β, phosphatidylinositol 3-kinase, and Akt expression were unchanged, indicating a specific abrogation of insulin signaling. Additionally, TF-treated adipocytes exhibited altered endocrine function with a reduction in both basal and insulin-stimulated leptin secretion. These studies demonstrate that TF induces cellular insulin resistance in primary murine and human adipocytes through a reduction of IRS-1 expression and protein stability, raising concern about the potential for this fungicide to disrupt metabolism and thereby contribute to the pathogenesis of diabetes.

Targeted expression of human vitamin D receptor in adipocytes decreases energy expenditure and induces obesity in mice

Our previous studies demonstrated a high fat diet-resistant lean phenotype of vitamin D receptor (VDR)-null mutant mice mainly due to increased energy expenditure, suggesting an involvement of the VDR in energy metabolism. Here, we took a transgenic approach to further define the role of VDR in adipocyte biology. We used the aP2 gene promoter to target the expression of the human (h) VDR in adipocytes in mice. In contrast to the VDR-null mice, the aP2-hVDR Tg mice developed obesity compared with the wild-type counterparts without changes in food intake. The increase in fat mass was mainly due to markedly reduced energy expenditure, which was correlated with decreased locomotive activity and reduced fatty acid β-oxidation and lipolysis in the adipose tissue in the transgenic mice. Consistently, the expression of genes involved in the regulation of fatty acid transport, thermogenesis, and lipolysis were suppressed in the transgenic mice. Taken together, these data confirm an important role of the VDR in the regulation of energy metabolism.

Abstract SY04-02: Environmental stress and breast cancer biology: What is the link

For many decades, identifying neuroendocrine mechanisms linking psychosocial factors (e.g., chronic stressors) to human disease has been the subject of intense interest by both social and biological scientists. Together, the endocrine and autonomic nervous systems comprise an individual's physiological response to both chronic and acute social stressors; these systems also mediate signaling pathways and gene expression changes at the cellular level that have the potential to alter tumor biology. However, it is only recently that the detailed molecular components connecting biopsychological stressors and cancer biology have begun to be uncovered. For example, in preclinical models of both breast and ovarian cancer, there is growing evidence linking biopsychological stressors and ensuing changes in neuroendocrine dynamics to the promotion of tumor growth. Both the glucocorticoid stress hormones and the adrenergic systems can induce tumor cell survival mechanisms and alter cell proliferation, tumor invasion, and angiogenesis. In addition, these signals affect inflammatory and metabolic tissues that modulate tumor growth through systemic and microenvironmental effects. Assessing the precise mechanisms of these interactions requires an appreciation of the subtleties of measuring the social environment, the individual's behavioral and neuroendocrine response, as well as the tumor and its environment.

Our collaborative development of a model of social isolation as it pertains to a transgenic model of human breast cancer (SV40Tag) and a Sprague-Dawley female rat model of spontaneous mammary gland cancer will be presented. In both models, we found that chronic social isolation reduces exploratory behavior in a novel environment as well as heightening the corticosterone response to an acute restraint stressor. In the SV40 Tag model, we examined gene expression differences in the mammary glands of isolated versus grouped female mice prior to invasive tumor development and uncovered a significant increase in lipid synthesis and glycolytic pathway genes, suggesting an association of the social environment with cancer-promoting metabolic changes. Interestingly, many of these changes in gene expression appear most significant in the adipocyte fraction of the mammary gland. For example, the increased expression of the key metabolic genes Acaca, Hk2, and Acly, initially observed in the whole mammary gland, was found to be significantly elevated only in the adipocyte fraction. Furthermore, metabolic gene expression was not consistently increased in the visceral fat of social isolates. These results suggest that exposure to chronic social isolation results in mammary fat depot-specific metabolic gene expression changes, followed by increased growth of invasive tumors. The implications and limitations of these two breast cancer models – one transgenic and one spontaneous – will be discussed in the context of understanding specific mechanisms that confer increased nonestrogen-dependent mammary tumor growth in association with chronic exposure to a psychosocial stressor.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr SY04-02. doi:10.1158/1538-7445.AM2011-SY04-02

Allosteric trumps covalent in the control of glycogen synthesis

Glycogen metabolism serves as a critical regulator of energy storage and maintenance of blood glucose levels in a physiological range. In this issue of Cell Metabolism, Bouskila et al. (2010) unexpectedly find that skeletal muscle glycogen accumulation is principally controlled by the allosteric activation of glycogen synthase, opening new avenues for investigation.

The impact of sleep disturbances on adipocyte function and lipid metabolism

Classically, sleep has been considered to serve an essential restorative function for the brain. However, there are an increasing number of studies linking decreased sleep quantity and/or quality in humans to an increased obesity and diabetes risk. Reductions in sleep quantity or quality lead to an increase in hunger and appetite, which chronically could predispose an individual to obesity. Carefully controlled studies have shown that two nights of insufficient sleep is causally linked to a decrease in disposition index, the most commonly used predictor of an individual's diabetes risk, and impairments in glucose tolerance and insulin sensitivity. Thus, sleep appears to play a critical role in modulating energy metabolism in peripheral tissues. Here we will discuss recent work implicating adipose tissue as a potential direct target of disruption of sleep quality, and explore the potential mechanistic links between sleep, adipose tissue and the global control of energy metabolism in humans.

Generation of a dominant-negative glycogen targeting subunit for protein phosphatase-1

Modulation of the expression of the protein phosphatase-1 (PP1) glycogen-targeting subunit PTG exerts profound effects on cellular glycogen metabolism in vitro and in vivo. PTG contains three distinct binding domains for glycogen, PP1, and a common site for glycogen synthase and phosphorylase. The impact of disrupting the PP1-binding domain on PTG function was examined in 3T3-L1 adipocytes. A full-length PTG mutant was generated as an adenoviral construct in which the valine and phenylalanine residues in the conserved PP1-binding domain were mutated to alanine (PTG-VF). Infection of fully differentiated 3T3-L1 adipocytes with the PTG-VF adenovirus reduced glycogen stores by over 50%. In vitro, PTG-VF competitively interfered with wild-type PTG action, suggesting that the mutant construct acted as a dominant-negative molecule. The reduction in cellular glycogen storage was due to a significantly increased rate of glycogen turnover. Interestingly, acute basal and insulin-stimulated glucose uptake and glycogen synthesis rates were enhanced in PTG-VF expressing cells vs. control 3T3-L1 adipocytes, likely as a compensatory response to the loss of glycogen stores. These results indicate that the mutation of the PP1-binding domain on PTG resulted in the generation of a dominant-negative molecule that impeded endogenous PTG action and reduced cellular glycogen levels, through enhancement of glycogenolysis rather than impairment of glycogen synthesis.

Enhanced glycogen metabolism in adipose tissue decreases triglyceride mobilization

Adipose tissue is a primary site for lipid storage containing trace amounts of glycogen. However, refeeding after a prolonged partial fast produces a marked transient spike in adipose glycogen, which dissipates in coordination with the initiation of lipid resynthesis. To further study the potential interplay between glycogen and lipid metabolism in adipose tissue, the aP2-PTG transgenic mouse line was utilized since it contains a 100- to 400-fold elevation of adipocyte glycogen levels that are mobilized upon fasting. To determine the fate of the released glucose 1-phosphate, a series of metabolic measurements were made. Basal and isoproterenol-stimulated lactate production in vitro was significantly increased in adipose tissue from transgenic animals. In parallel, basal and isoproterenol-induced release of nonesterified fatty acids (NEFAs) was significantly reduced in transgenic adipose tissue vs. control. Interestingly, glycerol release was unchanged between the genotypes, suggesting that enhanced triglyceride resynthesis was occurring in the transgenic tissue. Qualitatively similar results for NEFA and glycerol levels between wild-type and transgenic animals were obtained in vivo during fasting. Additionally, the physiological upregulation of the phosphoenolpyruvate carboxykinase cytosolic isoform (PEPCK-C) expression in adipose upon fasting was significantly blunted in transgenic mice. No changes in whole body metabolism were detected through indirect calorimetry. Yet weight loss following a weight gain/loss protocol was significantly impeded in the transgenic animals, indicating a further impairment in triglyceride mobilization. Cumulatively, these results support the notion that the adipocyte possesses a set point for glycogen, which is altered in response to nutritional cues, enabling the coordination of adipose glycogen turnover with lipid metabolism.

Environmental endocrine disruptors promote adipogenesis in the 3T3-L1 cell line through glucocorticoid receptor activation

The burgeoning obesity and diabetes epidemics threaten health worldwide, yet the molecular mechanisms underlying these phenomena are incompletely understood. Recently, attention has focused on the potential contributions of environmental pollutants that act as endocrine disrupting chemicals (EDCs) in the pathogenesis of metabolic diseases. Because glucocorticoid signaling is central to adipocyte differentiation, the ability of EDCs to stimulate the glucocorticoid receptor (GR) and drive adipogenesis was assessed in the 3T3-L1 cell line. Various EDCs were screened for glucocorticoid-like activity using a luciferase reporter construct, and four (bisphenol A (BPA), dicyclohexyl phthalate (DCHP), endrin, and tolylfluanid (TF)) were shown to significantly stimulate GR without significant activation of the peroxisome proliferator-activated receptor-gamma. 3T3-L1 preadipocytes were then treated with EDCs and a weak differentiation cocktail containing dehydrocorticosterone (DHC) in place of the synthetic dexamethasone. The capacity of these compounds to promote adipogenesis was assessed by quantitative oil red O staining and immunoblotting for adipocyte-specific proteins. The four EDCs increased lipid accumulation in the differentiating adipocytes and also upregulated the expression of adipocytic proteins. Interestingly, proadipogenic effects were observed at picomolar concentrations for several of the EDCs. Because there was no detectable adipogenesis when the preadipocytes were treated with compounds alone, the EDCs are likely promoting adipocyte differentiation by synergizing with agents present in the differentiation cocktail. Thus, EDCs are able to promote adipogenesis through the activation of the GR, further implicating these compounds in the rising rates of obesity and diabetes.

Stranger in a strange land: roles of glycogen turnover in adipose tissue metabolism

Triglyceride storage in adipose tissue comprises the principal energy reserve in mammals. Additionally glucose can be stored as glycogen in the fed state, primarily in liver and skeletal muscle, for mobilization during times of energy deficit. Adipose tissue also contains glycogen stores albeit at very low levels. The physiological role of glycogen metabolism in adipocytes remains unclear. However, both classical literature and more recent work demonstrate that the dynamic regulation of adipose glycogen may serve as an energy sensing modality in the coordination of glucose and lipid metabolism in adipose tissue, especially during the fasted to fed transition.

The silencing mediator of retinoid and thyroid hormone receptors (SMRT) regulates adipose tissue accumulation and adipocyte insulin sensitivity in vivo

The silencing mediator of retinoid and thyroid hormone receptors (SMRT) serves as a corepressor for nuclear receptors and other factors. Recent evidence suggests that SMRT is an important regulator of metabolism, but its role in adipocyte function in vivo remains unclear. We generated heterozygous SMRT knock-out (SMRT(+/-)) mice to investigate the function of SMRT in the adipocyte and the regulation of adipocyte insulin sensitivity. We show that SMRT(+/-) mice are normal weight on a regular diet, but develop increased adiposity on a high-fat diet (HFD). The mechanisms underlying this phenotype are complex, but appear to be due to a combination of an increased number of smaller subcutaneous adipocytes as well as decreased leptin expression, resulting in greater caloric intake. In addition, adipogenesis of mouse embryonic fibroblasts (MEFs) derived from these mice was increased. However, adipocyte insulin sensitivity, measured by insulin-induced Akt phosphorylation and insulin-mediated suppression of lipolysis, was enhanced in SMRT(+/-) adipocytes. These finding suggest that SMRT regulates leptin expression and limits the ability of fat mass to expand with increased caloric intake, but that SMRT also negatively regulates adipocyte insulin sensitivity.

Making fat work

The burgeoning obesity and metabolic disease epidemics in the developed world are exerting a terrible toll on society, yet the precise mechanisms responsible for the emergence of these dramatic trends over a relatively short period of time remain poorly understood. Philip A.Wood's book How Fat Works provides important insights into cellular lipid metabolism, as well as discussing some of the important external contributors to the development of human obesity. The foundation provided by this book allows for the exploration of how body fat has gone from hero during the millennia when starvation was the paramount nutritional risk to its current role as villain in our period of caloric excess. With the incredible personal and societal costs brought about by excess body weight, a comprehensive understanding of the mechanisms responsible for obesity is fundamentally necessary if we are to reverse these dire trends. Here, we delve deeper into some of the forces contributing to the obesity epidemic and discuss some individual measures as well as public policy decisions that may help reverse weight trends, while specifically focusing on the growing problem of pediatric obesity.

Differential regulation of glycogenolysis by mutant protein phosphatase-1 glycogen-targeting subunits

PTG and G(L) are hepatic protein phosphatase-1 (PP1) glycogen-targeting subunits, which direct PP1 activity against glycogen synthase (GS) and/or phosphorylase (GP). The C-terminal 16 amino residues of G(L) comprise a high affinity binding site for GP that regulates bound PP1 activity against GS. In this study, a truncated G(L) construct lacking the GP-binding site (G(L)tr) and a chimeric PTG molecule containing the C-terminal site (PTG-G(L)) were generated. As expected, GP binding to glutathione S-transferase (GST)-G(L)tr was reduced, whereas GP binding to GST-PTG-G(L) was increased 2- to 3-fold versus GST-PTG. In contrast, PP1 binding to all proteins was equivalent. Primary mouse hepatocytes were infected with adenoviral constructs for each subunit, and their effects on glycogen metabolism were investigated. G(L)tr expression was more effective at promoting GP inactivation, GS activation, and glycogen accumulation than G(L). Removal of the regulatory GP-binding site from G(L)tr completely blocked the inactivation of GS seen in G(L)-expressing cells following a drop in extracellular glucose. As a result, G(L)tr expression prevented glycogen mobilization under 5 mm glucose conditions. In contrast, equivalent overexpression of PTG or PTG-G(L) caused a similar increase in glycogen-targeted PP1 levels and GS dephosphorylation. Surprisingly, GP dephosphorylation was significantly reduced in PTG-G(L)-overexpressing cells. As a result, PTG-G(L) expression permitted glycogenolysis under 5 mm glucose conditions that was prevented in PTG-expressing cells. Thus, expression of constructs that contained the high affinity GP-binding site (G(L) and PTG-G(L)) displayed reduced glycogen accumulation and enhanced glycogenolysis compared with their respective controls, albeit via different mechanisms.

Altering PPARgamma ligand selectivity impairs adipogenesis by thiazolidinediones but not hormonal inducers

Peroxisome proliferator-activated receptor gamma (PPARgamma) acts as a ligand-dependent transcription factor with a key role in mediating adipocyte differentiation and insulin sensitivity. Recently, we and others have shown that PPARgamma recruits the nuclear corepressors NCoR and silencing mediator for retinoid and thyroid hormone receptors (SMRT) to modulate adipogenesis. While the synthetic ligands for PPARgamma, the thiazolidinediones (TZD), are widely used in the treatment of type 2 diabetes mellitus, the biologically relevant endogenous PPARgamma ligand involved in adipogenesis remains unidentified. To further understand the role of ligand binding and corepressor interaction in PPARgamma-mediated adipogenesis, a mutation was introduced in the ligand-binding domain (LBD) of murine PPARgamma. PPARgammamut was created via two amino acid substitutions known to be major determinants of ligand selectivity among PPAR isotypes, H323Y and R288M. These mutations alter PPARgamma to the corresponding residues of the PPARalpha. Characterizing the in vitro functional properties of this mutant, we show that PPARgammamut preferentially responds to the PPARalpha agonist, WY-14643, over the TZD, pioglitazone. When expressed in 3T3-L1 preadipocytes using recombinant adenovirus, wild-type PPARgamma leads to adipocyte formation with both hormonal and TZD treatment. PPARgammamut blocks the upregulation of adipocyte-specific proteins by TZD, but surprisingly, not by standard hormonal inducers. Our data suggest that TZDs and the purported endogenous ligand do not interact in the same way with the PPARgamma LBD. We propose that the endogenous ligand has distinct properties that allow for promiscuity within the hydrophobic PPAR ligand-binding pocket, yet fosters appropriate cofactor recruitment and release to allow adipogenesis to proceed.

Adrenal nodules at FDG PET/CT in patients known to have or suspected of having lung cancer: a proposal for an efficient diagnostic algorithm

PURPOSE

To develop an algorithm to maximize the diagnostic yield of positron emission tomography (PET)/computed tomography (CT) by using defined attenuation and standardized uptake value (SUV) criteria.

MATERIALS AND METHODS

An IRB-approved, HIPAA-compliant retrospective review with waiver of informed consent of data in 1388 consecutive patients who underwent PET/CT for known or suspected lung cancer was completed, and 187 adrenal nodules were identified in 147 patients. Nodules were defined histologically or by size change (malignant, n = 37) or stability for more than 1 year (benign, n = 58). Nodules not sampled for biopsy and with less than 1 year of follow-up were considered indeterminate (n = 92). Diameter, mean attenuation, SUV(max), and SUV ratio (nodule SUV(max)/liver SUV(avg)) were compared with t test and receiver operating characteristic analyses. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for diameter > 3 cm, mean attenuation > 10 HU, nodule SUV(max) > 3.1, and SUV ratio > 1.0. These were also calculated for higher SUV(max) and SUV ratio thresholds that were found to exclude all false-positives. Diagnostic accuracy was compared by using the McNemar test (P < .05).

RESULTS

In the study group of 147 patients (aged 42-88 years; mean, 65.5 years; 59 women), combined PET/CT with mean attenuation > 10 HU and SUV(max) > 3.1 had 97.3% sensitivity and 86.2% specificity. Combined PET/CT with mean attenuation > 10 HU and SUV ratio > 1.0 had 97.3% sensitivity and 74.1% specificity. The accuracies of these threshold combinations (90.5% and 83.2%, respectively) were significantly different (P = .008). Applying a further cutoff of SUV ratio > 2.5 enabled identification of 22 of 37 metastatic lesions and exclusion of all fluorodeoxyglucose-avid benign nodules.

CONCLUSION

Definitive identification of many metastases can be accomplished by applying an SUV ratio cutoff of greater than 2.5, allowing pragmatic management of adrenal nodules that initially test positive with the combined PET/CT criteria SUV(max) > 3.1 and mean attenuation > 10 HU.

SUPPLEMENTAL MATERIAL

http://radiology.rsnajnls.org/cgi/content/full/250/2/523/DC1.

Transgenic overexpression of protein targeting to glycogen markedly increases adipocytic glycogen storage in mice

Adipocytes express the rate-limiting enzymes required for glycogen metabolism and increase glycogen synthesis in response to insulin. However, the physiological function of adipocytic glycogen in vivo is unclear, due in part to the low absolute levels and the apparent biophysical constraints of adipocyte morphology on glycogen accumulation. To further study the regulation of glycogen metabolism in adipose tissue, transgenic mice were generated that overexpressed the protein phosphatase-1 (PP1) glycogen-targeting subunit (PTG) driven by the adipocyte fatty acid binding protein (aP2) promoter. Exogenous PTG was detected in gonadal, perirenal, and brown fat depots, but it was not detected in any other tissue examined. PTG overexpression resulted in a modest redistribution of PP1 to glycogen particles, corresponding to a threefold increase in the glycogen synthase activity ratio. Glycogen synthase protein levels were also increased twofold, resulting in a combined greater than sixfold enhancement of basal glycogen synthase specific activity. Adipocytic glycogen levels were increased 200- to 400-fold in transgenic animals, and this increase was maintained to 1 yr of age. In contrast, lipid metabolism in transgenic adipose tissue was not significantly altered, as assessed by lipogenic rates, weight gain on normal or high-fat diets, or circulating free fatty acid levels after a fast. However, circulating and adipocytic leptin levels were doubled in transgenic animals, whereas adiponectin expression was unchanged. Cumulatively, these data indicate that murine adipocytes are capable of storing far higher levels of glycogen than previously reported. Furthermore, these results were obtained by overexpression of an endogenous adipocytic protein, suggesting that mechanisms may exist in vivo to maintain adipocytic glycogen storage at a physiological set point.

Differential modulation of 3T3-L1 adipogenesis mediated by 11beta-hydroxysteroid dehydrogenase-1 levels

The localized activation of circulating glucocorticoids in vivo by the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) plays a critical role in the development of the metabolic syndrome. However, the precise contribution of 11beta-HSD1 in the initiation of adipogenesis by inactive glucocorticoids is not fully understood. 3T3-L1 fibroblasts can be terminally differentiated to mature adipocytes in a glucocorticoid-dependent manner. Both inactive rodent dehydrocorticosterone and human cortisone were able to substitute for the synthetic glucocorticoid dexamethasone in 3T3-L1 adipogenesis, suggesting a potential role for 11beta-HSD1 in these effects. Differentiation of 3T3-L1 cells caused a strong increase in 11beta-HSD1 protein levels, which occurred late in the differentiation protocol. Reduction of 11beta-HSD1 activity in 3T3-L1 fibroblasts, achieved by pharmacological inhibition or adenovirally mediated delivery of short hairpin RNA constructs, specifically blocked the ability of inactive glucocorticoids to drive 3T3-L1 differentiation. However, even modest increases in exogenous 11beta-HSD1 expression in 3T3-L1 fibroblasts, to levels comparable with endogenous 11beta-HSD1 in differentiated 3T3-L1 adipocytes, were sufficient to block adipogenesis. Luciferase reporter assays indicated that overexpressed 11beta-HSD1 was catalyzing the inactivating dehydrogenase reaction, because the ability of both active and inactive glucocorticoids to activate the glucocorticoid receptor were largely suppressed. These results suggest that the temporal regulation of 11beta-HSD1 expression is tightly controlled in 3T3-L1 cells, so as to mediate the initiation of differentiation by inactive glucocorticoids and also to prevent the inhibitory activity of prematurely expressed 11beta-HSD1 during adipogenesis.

Uncoupling of 3T3-L1 gene expression from lipid accumulation during adipogenesis

Adipocyte differentiation comprises altered gene expression and increased triglyceride storage. To investigate the interdependency of these two events, 3T3-L1 cells were differentiated in the presence of glucose or pyruvate. All adipocytic proteins examined were similarly increased between the two conditions. In contrast, 3T3-L1 adipocytes differentiated with glucose exhibited significant lipid accumulation, which was largely suppressed in the presence of pyruvate. Subsequent addition of glucose to the latter cells restored lipid accumulation and acute rates of insulin-stimulated lipogenesis. These data indicate that extracellular energy is required for induction of adipocytic proteins, while only glucose sustained the parallel increase in triglyceride storage.