Premenopausal females are protected against adipose tissue inflammation and insulin resistance, until loss of ovarian hormone production (e.g., menopause). There is some evidence that females have greater brown adipose tissue (BAT) thermogenic capacity. Because BAT mass correlates inversely with insulin resistance, we hypothesized that increased uncoupling protein 1 (UCP1) expression contributes to the superior metabolic health of females. Given that UCP1 transiently increases in BAT following ovariectomy (OVX), we hypothesized that UCP1 may ‘buffer’ OVX-mediated metabolic dysfunction. Accordingly, female UCP1-knockout (KO) and WT mice received OVX or sham (SHM) surgeries at 12 weeks of age creating four groups (n = 10/group), which were followed for 14 weeks and compared for body weight and adiposity, food intake, energy expenditure and spontaneous physical activity (metabolic chambers), insulin resistance (HOMA-IR, ADIPO-IR and glucose tolerance testing) and adipose tissue phenotype (histology, gene and protein expression). Two-way ANOVA was used to assess the main effects of genotype (G), OVX treatment (O) and genotype by treatment (GxO) interactions, which were considered significant when P ≤ 0.05. UCP1KO mice experienced a more adverse metabolic response to OVX than WT. Whereas OVX-induced weight gain was not synergistically greater for KO compared to WT (GxO, NS), OVX-induced insulin resistance was significantly exacerbated in KO compared to WT (GxO for HOMA-IR, P < 0.05). These results suggest UCP1 is protective against metabolic dysfunction associated with loss of ovarian hormones and support the need for more research into therapeutics to selectively target UCP1 for prevention and treatment of metabolic dysfunction following ovarian hormone loss.
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Stephanie L Clookey, Rebecca J Welly, Terese M Zidon, Michelle L Gastecki, Makenzie L Woodford, Zachary I Grunewald, Nathan C Winn, Dusti Eaton, Natalia G Karasseva, Harold S Sacks, Jaume Padilla and Victoria J Vieira-Potter
Qinghua Wang, Jing Tang, Shujun Jiang, Zan Huang, Anying Song, Siyuan Hou, Xiang Gao and Hai-Bin Ruan
Peroxisome proliferator-activated receptor-γ (PPARγ) is a master regulator of adipogenesis and a target of the thiazolidinedione (TZD) class of antidiabetic drugs; therefore, identifying novel regulators of PPARγ action in adipocytes is essential for the future development of therapeutics for diabetes. MAGE family member D1 (MAGED1), by acting as an adaptor for ubiquitin-dependent degradation pathways and a co-factor for transcription, plays an important role in neural development, cell differentiation and circadian rhythm. Here, we showed that MAGED1 expression was downregulated during adipogenesis and loss of MAGED1 promoted preadipocyte proliferation and differentiation in vitro. MAGED1 bound to PPARγ and suppressed the stability and transcriptional activity of PPARγ. Compared to WT littermates, MAGED1-deficient mice showed increased levels of PPARγ protein and its target genes, more CD29+CD34+Sca-1+ adipocyte precursors and hyperplasia of white adipose tissues (WATs). Moreover, MAGED1-deficient mice developed late-onset obesity as a result of decreased energy expenditure and physical activity. However, these mice were metabolically healthy as shown by improved glucose clearance and insulin sensitivity, normal levels of serum lipids and enhanced secretion of adipokines such as leptin and adiponectin. Taken together, our data identify MAGED1 as a novel negative regulator of PPARγ activity, adipogenesis and insulin sensitivity in mice. MAGED1 might therefore serve as a novel pharmaceutical target to treat obesity-associated insulin resistance.
Sonnet S Jonker, Daniel Kamna, Dan LoTurco, Jenai Kailey and Laura D Brown
Placental insufficiency causes intrauterine growth restriction (IUGR), a common complication of pregnancy. In skeletal muscle, IUGR reduces fetal myofibril size, reduces myoblast proliferation and reduces expression of genes in cell cycle regulation clusters. The myocardium is striated like skeletal muscle, and IUGR also reduces cell cycle activity and maturation in cardiomyocytes, despite cardiac output preferentially directed to the coronary circulation. We hypothesized that cardiomyocyte growth restriction would be accompanied by similar changes in cell cycle regulation genes and would reduce cardiomyocyte cell cycle activity, number, maturity and size. Pregnant ewes were housed in elevated ambient temperatures from ~40 to ~115 days of gestation (dGA) to produce placental insufficiency and IUGR; fetal hearts were studied at ~134 dGA. Hearts were biopsied for mRNA analysis and then dissociated into individual myocytes (Control n = 8; IUGR n = 15) or dissected (Control n = 9; IUGR n = 13). IUGR fetuses had low circulating insulin and insulin-like growth factor 1 (IGF1) and high circulating cortisol. Bodies and hearts of IUGR fetuses were lighter than those of Controls. Cardiomyocytes of IUGR fetuses were smaller, less mature, less active in the cell cycle and less numerous than in Controls. Further, there was a pattern of downregulation of cell cycle genes in IUGR ventricles. IUGR growth profiles in heart and skeletal muscle suggest similar regulation despite differences in blood and nutrient delivery prioritization. IGF1 signaling is suggested as a mechanism regulating altered growth in IUGR striated muscle and a potential therapeutic candidate.
A Feraco, A Armani, R Urbanet, A Nguyen Dinh Cat, V Marzolla, F Jaisser and M Caprio
Obesity is a major risk factor that contributes to the development of cardiovascular disease and type 2 diabetes. Mineralocorticoid receptor (MR) expression is increased in the adipose tissue of obese patients and several studies provide evidence that MR pharmacological antagonism improves glucose metabolism in genetic and diet-induced mouse models of obesity. In order to investigate whether the lack of adipocyte MR is sufficient to explain these beneficial metabolic effects, we generated a mouse model with inducible adipocyte-specific deletion of Nr3c2 gene encoding MR (adipo-MRKO). We observed a significant, yet not complete, reduction of Nr3c2 transcript and MR protein expression in subcutaneous and visceral adipose depots of adipo-MRKO mice. Notably, only mature adipocyte fraction lacks MR, whereas the stromal vascular fraction maintains normal MR expression in our mouse model. Adipo-MRKO mice fed a 45% high-fat diet for 14 weeks did not show any significant difference in body weight and fat mass compared to control littermates. Glucose and insulin tolerance tests revealed that mature adipocyte MR deficiency did not improve insulin sensitivity in response to a metabolic homeostatic challenge. Accordingly, no significant changes were observed in gene expression profile of adipogenic and inflammatory markers in adipose tissue of adipo-MRKO mice. Moreover, pharmacological MR antagonism in mature primary murine adipocytes, which differentiated ex vivo from WT mice, did not display any effect on adipokine expression. Taken together, these data demonstrate that the depletion of MR in mature adipocytes displays a minor role in diet-induced obesity and metabolic dysfunctions.
Laura Marroqui, Eva Tudurí, Paloma Alonso-Magdalena, Iván Quesada, Ángel Nadal and Reinaldo Sousa dos Santos
Type 2 diabetes is a chronic, heterogeneous syndrome characterized by insulin resistance and pancreatic β-cell dysfunction or death. Among several environmental factors contributing to type 2 diabetes development, endocrine-disrupting chemicals (EDCs) have been receiving special attention. These chemicals include a wide variety of pollutants, from components of plastic to pesticides, with the ability to modulate endocrine system function. EDCs can affect multiple cellular processes, including some related to energy production and utilization, leading to alterations in energy homeostasis. Mitochondria are primarily implicated in cellular energy conversion, although they also participate in other processes, such as hormone secretion and apoptosis. In fact, mitochondrial dysfunction due to reduced oxidative capacity, impaired lipid oxidation and increased oxidative stress has been linked to insulin resistance and type 2 diabetes. Herein, we review the main mechanisms whereby metabolism-disrupting chemical (MDC), a subclass of EDCs that disturbs energy homeostasis, cause mitochondrial dysfunction, thus contributing to the establishment of insulin resistance and type 2 diabetes. We conclude that MDC-induced mitochondrial dysfunction, which is mainly characterized by perturbations in mitochondrial bioenergetics, biogenesis and dynamics, excessive reactive oxygen species production and activation of the mitochondrial pathway of apoptosis, seems to be a relevant mechanism linking MDCs to type 2 diabetes development.
Dan Li, Yan Ji, Chunlan Zhao, Yapeng Yao, Anlan Yang, Honghong Jin, Yang Chen, Mingjun San, Jing Zhang, Mingjiao Zhang, Luqing Zhang, Xuechao Feng and Yaowu Zheng
Oxytocin receptor (OXTR) is a G-protein-coupled receptor and known for regulation of maternal and social behaviors. Null mutation (Oxtr−/−) leads to defects in lactation due to impaired milk ejection and maternal nurturing. Overexpression of OXTR has never been studied. To define the functions of OXTR overexpression, a transgenic mouse model that overexpresses mouse Oxtr under β-actin promoter was developed (++ Oxtr). ++ Oxtr mice displayed advanced development and maturation of mammary gland, including ductal distention, enhanced secretory differentiation and early milk production at non-pregnancy and early pregnancy. However, ++ Oxtr dams failed to produce adequate amount of milk and led to lethality of newborns due to early involution of mammary gland in lactation. Mammary gland transplantation results indicated the abnormal mammary gland development was mainly from hormonal changes in ++ Oxtr mice but not from OXTR overexpression in mammary gland. Elevated OXTR expression increased prolactin-induced phosphorylation and nuclear localization of STAT5 (p-STAT5), and decreased progesterone level, leading to early milk production in non-pregnant and early pregnant females, whereas low prolactin and STAT5 activation in lactation led to insufficient milk production. Progesterone treatment reversed the OXTR-induced accelerated mammary gland development by inhibition of prolactin/p-STAT5 pathway. Prolactin administration rescued lactation deficiency through STAT5 activation. Progesterone plays a negative role in OXTR-regulated prolactin/p-STAT5 pathways. The study provides evidence that OXTR overexpression induces abnormal mammary gland development through progesterone and prolactin-regulated p-STAT5 pathway.
Takeshi Iwasa, Toshiya Matsuzaki, Kiyohito Yano, Yiliyasi Mayila, Rie Yanagihara, Yuri Yamamoto, Akira Kuwahara and Minoru Irahara
Although polycystic ovary syndrome (PCOS) is among the most common endocrine disorders in women of reproductive age, its etiology remains poorly understood. From the perspective of developmental origins of health and disease, some studies have investigated the relationship between low birth weight and the prevalence of PCOS and/or PCOS phenotypes in humans; however, the results of these studies were inconclusive. Here, we evaluated the effects of prenatal undernutrition on the metabolic and reproductive phenotypes of dihydrotestosterone-induced PCOS model rats. The PCOS model rats showed increased body weight, food intake, fat weight, adipocyte size and upregulation of inflammatory cytokines in adipose tissue; prenatal undernutrition exacerbated these metabolic changes. Prenatal undernutrition also increased the gene expression of hypothalamic orexigenic factor and decreased the gene expression of anorexigenic factor in the PCOS model rats. In addition, the PCOS model rats exhibited irregular cyclicity, polycystic ovaries and disrupted gene expression of ovarian steroidogenic enzymes. Interestingly, prenatal undernutrition attenuated these reproductive changes in the PCOS model rats. Our results suggest that in dihydrotestosterone-induced PCOS model rats, prenatal undernutrition exacerbates the metabolic phenotypes, whereas it improves the reproductive phenotypes and that such phenotypic changes may be induced by the alteration of some peripheral and central factors.
Eva B Nygaard, Cathrine Ørskov, Thomas Almdal, Henrik Vestergaard and Birgitte Andersen
Fibroblast growth factor 21 (FGF21) is a metabolic regulator of energy and lipid metabolism. FGF21 is highly expressed in liver while FGF21 receptors (beta-klotho (KLB) and FGFR1c) are highly expressed in white adipose tissues (WATs). Plasma FGF21 has been shown to be increased after 7–10 days of fasting but oppositely plasma FGF21 is also increased in obesity. The aim of this study was to measure the effect of 60 h of fasting on plasma FGF21 levels in obese and lean subjects and to determine the gene expression of KLB and FGFR1c in the subcutaneous WAT before, during and after 60 h of fasting. Eight obese (BMI >30 kg/m2) and seven lean subjects (BMI <25 kg/m2) were fasted for 60 h and blood samples were taken at time 0 and after 12, 36 and 60 h of fasting. A biopsy from the subcutaneous WAT was taken at time 0, 12 and 60 h of fasting. FGF21 was measured in plasma by an ELISA and mRNA expression of KLB and FGFR1c was measured in WAT by quantitative PCR (qPCR). The fast significantly decreased plasma FGF21 in obese subjects while no change in plasma FGF21 was observed in lean subjects. Interestingly, KLB was significantly decreased in WAT in response to fasting in both lean and obese subjects indicating a potential important adaptive regulation of KLB in response to fasting.
Shona H Wood
Life in seasonally changing environments is challenging. Biological systems have to not only respond directly to the environment, but also schedule life history events in anticipation of seasonal changes. The cellular and molecular basis of how these events are scheduled is unknown. Cellular decision-making processes in response to signals above certain thresholds regularly occur i.e. cellular fate determination, apoptosis and firing of action potentials. Binary switches, the result of cellular decision-making processes, are defined as a change in phenotype between two stable states. A recent study presents evidence of a binary switch operating in the pars tuberalis (PT) of the pituitary, seemingly timing seasonal reproduction in sheep. Though, how a binary switch would allow for anticipation of seasonal environmental changes, not just direct responsiveness, is unclear. The purpose of this review is to assess the evidence for a binary switching mechanism timing seasonal reproduction and to hypothesize how a binary switch would allow biological processes to be timed over weeks to years. I draw parallels with mechanisms used in development, cell fate determination and seasonal timing in plants. I propose that the adult PT is a plastic tissue, showing a seasonal cycle of cellular differentiation, and that the underlying processes are likely to be epigenetic. Therefore, considering the mechanisms behind adult cellular plasticity offers a framework to hypothesize how a long-term timer functions within the PT.
Maitrayee Sahu, Prashanth Anamthathmakula and Abhiram Sahu
Pharmacological studies have suggested hypothalamic phosphodiesterase-3B to mediate leptin and insulin action in regulation of energy homeostasis. Whereas Pde3b-null mice show altered energy homeostasis, it is unknown whether this is due to ablation of Pde3b in the hypothalamus. Thus, to address the functional significance of hypothalamic phosphodiesterase-3B, we used Pde3b flox/flox and Nkx2 .1-Cre mice to generate Pde3b Nkx2.1KD mice that showed 50% reduction of phosphodiesterase-3B in the hypothalamus. To determine the effect of partial ablation of phosphodiesterase-3B in the hypothalamus on energy and glucose homeostasis, males and females were subjected to either a low- or high-fat diet for 19–21 weeks. Only female but not male Pde3b Nkx2.1KD mice on the low-fat diet showed increased body weight from 13 weeks onward with increased food intake, decreased fat pad weights and hypoleptinemia. Glucose tolerance was improved in high-fat diet-fed male Pde3b Nkx2.1KD mice in association with decreased phosphoenolpyruvate carboxykinase-1 and glucose-6-phosphatase mRNA levels in the liver. Also, insulin sensitivity was increased in male Pde3b Nkx2.1KD mice on the low-fat diet. Changes in body weight or in glucose homeostasis were not associated with any alteration in hypothalamic proopiomelanocortin, neuropepide Y and agouti-related peptide mRNA levels. These results suggest that partial loss of phosphodiesterase-3B in the hypothalamus produces a sex-specific response in body weight and glucose homeostasis, and support a role, at least in part, for hypothalamic phosphodiesterase-3B in regulation of energy and glucose homeostasis in mice.