Reducing Adiposity in a Critical Developmental Window Has Lasting Benefits in Mice

Sympathetic innervation of interscapular brown adipose tissue is not a predominant mediator of oxytocin-elicited reductions of body weight and adiposity in male diet-induced obese mice

Previous studies indicate that CNS administration of oxytocin (OT) reduces body weight in high fat diet-induced obese (DIO) rodents by reducing food intake and increasing energy expenditure (EE). We recently demonstrated that hindbrain (fourth ventricular [4V]) administration of OT elicits weight loss and elevates interscapular brown adipose tissue temperature (T IBAT , a surrogate measure of increased EE) in DIO mice. What remains unclear is whether OT-elicited weight loss requires increased sympathetic nervous system (SNS) outflow to IBAT. We hypothesized that OT-induced stimulation of SNS outflow to IBAT contributes to its ability to activate BAT and elicit weight loss in DIO mice. To test this hypothesis, we determined the effect of disrupting SNS activation of IBAT on the ability of 4V OT administration to increase T IBAT and elicit weight loss in DIO mice. We first determined whether bilateral surgical SNS denervation to IBAT was successful as noted by ≥ 60% reduction in IBAT norepinephrine (NE) content in DIO mice. NE content was selectively reduced in IBAT at 1-, 6- and 7-weeks post-denervation by 95.9±2.0, 77.4±12.7 and 93.6±4.6% ( P <0.05), respectively and was unchanged in inguinal white adipose tissue, pancreas or liver. We subsequently measured the effects of acute 4V OT (1, 5 µg ≈ 0.99, 4.96 nmol) on T IBAT in DIO mice following sham or bilateral surgical SNS denervation to IBAT. We found that the high dose of 4V OT (5 µg ≈ 4.96 nmol) elevated T IBAT similarly in sham mice as in denervated mice. We subsequently measured the effects of chronic 4V OT (16 nmol/day over 29 days) or vehicle infusions on body weight, adiposity and food intake in DIO mice following sham or bilateral surgical denervation of IBAT. Chronic 4V OT reduced body weight by 5.7±2.23% and 6.6±1.4% in sham and denervated mice ( P <0.05), respectively, and this effect was similar between groups ( P =NS). OT produced corresponding reductions in whole body fat mass ( P <0.05). Together, these findings support the hypothesis that sympathetic innervation of IBAT is not necessary for OT-elicited increases in BAT thermogenesis and reductions of body weight and adiposity in male DIO mice.

Prenatal Exposure to Bisphenol A Disrupts Naturally Occurring Bimodal DNA Methylation at Proximal Promoter of fggy, an Obesity-Relevant Gene Encoding a Carbohydrate Kinase, in Gonadal White Adipose Tissues of CD-1 Mice

Exposure of mammalian fetuses to endocrine disruptors can increase the risk of adult-onset diseases. We previously showed that exposure of mouse fetuses to bisphenol A (BPA) caused adult-onset obesity. To examine roles of epigenetic changes in this delayed toxicity, we determined the effects of fetal mouse exposure to BPA on genome-wide DNA methylation and messenger RNA (mRNA) expression in gonadal white adipose tissues (WATs) by deep sequencing, bisulfite pyrosequencing, and real-time quantitative polymerase chain reaction. Pregnant CD-1 mice (F0) were dosed daily with 0, 5, or 500 μg/kg/d BPA during gestational days 9 to 18, and the weaned F1 animals were fed ad libitum with standard chow until they were euthanized at 19 weeks old. In the vehicle-exposed F1 animals, fggy promoter showed a clear bimodal pattern of very strong (55% to 95%) or very weak (5% to 30%) DNA methylation occurring at nearly equal incidence with no intermediate strength. Promoter hypermethylation completely suppressed mRNA expression. BPA exposure eliminated this naturally occurring dichotomy, shifting fggy promoter toward the hypomethylation state to release transcriptional suppression. The strength of Fggy mRNA expression significantly correlated with increased whole body weight and gonadal fat weight of males but not females. Bioinformatics studies showed that expression of Fggy mRNA is stronger in mouse WATs than in brown adipose tissues and enhanced in gonadal fat by diet-induced obesity. These observations suggest that prenatal exposure to BPA may disrupt the physiological bimodal nature of epigenetic regulation of fggy in mouse WATs, possibly contributing to the adult-onset obesity phenotype.

Obesity Pathogenesis: An Endocrine Society Scientific Statement

Obesity is among the most common and costly chronic disorders worldwide. Estimates suggest that in the United States obesity affects one-third of adults, accounts for up to one-third of total mortality, is concentrated among lower income groups, and increasingly affects children as well as adults. A lack of effective options for long-term weight reduction magnifies the enormity of this problem; individuals who successfully complete behavioral and dietary weight-loss programs eventually regain most of the lost weight. We included evidence from basic science, clinical, and epidemiological literature to assess current knowledge regarding mechanisms underlying excess body-fat accumulation, the biological defense of excess fat mass, and the tendency for lost weight to be regained. A major area of emphasis is the science of energy homeostasis, the biological process that maintains weight stability by actively matching energy intake to energy expenditure over time. Growing evidence suggests that obesity is a disorder of the energy homeostasis system, rather than simply arising from the passive accumulation of excess weight. We need to elucidate the mechanisms underlying this "upward setting" or "resetting" of the defended level of body-fat mass, whether inherited or acquired. The ongoing study of how genetic, developmental, and environmental forces affect the energy homeostasis system will help us better understand these mechanisms and are therefore a major focus of this statement. The scientific goal is to elucidate obesity pathogenesis so as to better inform treatment, public policy, advocacy, and awareness of obesity in ways that ultimately diminish its public health and economic consequences.