Insulin resistance of pregnancy involves estrogen-induced repression of muscle GLUT4

Role of estrogen in the regulation of central and peripheral energy homeostasis: from a menopausal perspective

Estrogen plays a prominent role in regulating and coordinating energy homeostasis throughout the growth, development, reproduction, and aging of women. Estrogen receptors (ERs) are widely expressed in the brain and nearly all tissues of the body. Within the brain, central estrogen via ER regulates appetite and energy expenditure and maintains cell glucose metabolism, including glucose transport, aerobic glycolysis, and mitochondrial function. In the whole body, estrogen has shown beneficial effects on weight control, fat distribution, glucose and insulin resistance, and adipokine secretion. As demonstrated by multiple in vitro and in vivo studies, menopause-related decline of circulating estrogen may induce the disturbance of metabolic signals and a significant decrease in bioenergetics, which could trigger an increased incidence of late-onset Alzheimer's disease, type 2 diabetes mellitus, hypertension, and cardiovascular diseases in postmenopausal women. In this article, we have systematically reviewed the role of estrogen and ERs in body composition and lipid/glucose profile variation occurring with menopause, which may provide a better insight into the efficacy of hormone therapy in maintaining energy metabolic homeostasis and hold a clue for development of novel therapeutic approaches for target tissue diseases.

Association between sex steroid hormones and subsequent hyperglycemia during pregnancy

Objective

Sex steroid hormones may play a role in insulin resistance and glucose dysregulation. However, evidence regarding associations between early-pregnancy sex steroid hormones and hyperglycemia during pregnancy is limited. The primary objective of this study was to assess the relationships between first trimester sex steroid hormones and the subsequent development of hyperglycemia during pregnancy; with secondary evaluation of sex steroid hormones levels in mid-late pregnancy, concurrent with and subsequent to diagnosis of gestational diabetes.

Methods

Retrospective analysis of a prospective pregnancy cohort study was conducted. Medically low-risk participants with no known major endocrine disorders were recruited in the first trimester of pregnancy (n=319). Sex steroid hormones in each trimester, including total testosterone, free testosterone, estrone, estradiol, and estriol, were assessed using high-performance liquid chromatography and tandem mass spectrometry. Glucose levels of the 1-hour oral glucose tolerance test and gestational diabetes diagnosis were abstracted from medical records. Multivariable linear regression models were fitted to assess the associations of individual first trimester sex steroids and glucose levels.

Results

In adjusted models, first trimester total testosterone (β=5.24, 95% CI: 0.01, 10.46, p=0.05) and free testosterone (β=5.98, 95% CI: 0.97, 10.98, p=0.02) were positively associated with subsequent glucose concentrations and gestational diabetes diagnosis (total testosterone: OR=3.63, 95% CI: 1.50, 8.78; free testosterone: OR=3.69; 95% CI: 1.56, 8.73). First trimester estrone was also positively associated with gestational diabetes (OR=3.66, 95% CI: 1.56, 8.55). In mid-late pregnancy, pregnant people with gestational diabetes had lower total testosterone levels (β=-0.19, 95% CI: -0.36, -0.02) after adjustment for first trimester total testosterone.

Conclusion

Early-pregnancy sex steroid hormones, including total testosterone, free testosterone, and estrone, were positively associated with glucose levels and gestational diabetes in mid-late pregnancy. These hormones may serve as early predictors of gestational diabetes in combination with other risk factors.

Metabolic alteration of circulating steroid hormones in women with gestational diabetes mellitus and the related risk factors

Background

Abnormally changed steroid hormones during pregnancy are closely related to the pathological process of gestational diabetes mellitus (GDM). Our aim was to systematically profile the metabolic alteration of circulating steroid hormones in GDM women and screen for risk factors.

Methods

This study was a case-control study with data measured from 40 GDM women and 70 healthy pregnant women during their 24-28 gestational weeks. 36 kinds of steroid hormones, including 3 kinds of corticosteroids, 2 kinds of progestins, 5 kinds of androgens and 26 kinds of downstream estrogens in serum were systematically measured using a combined sensitive UPLC-MS/MS method. The flux of different metabolic pathways of steroid hormones was analyzed. Logistic regression and ROC curve model analyses were performed to identify potential steroid markers closely associated with GDM development.

Results

Serum corticosteroids, progestins and almost all the estrogen metabolites via 16-pathway from parent estrogens were higher in GDM women compared with healthy controls. Most of the estrogen metabolites via 4-pathway and more than half of the metabolites via 2-pathway were not significantly different. 16α-hydroxyestrone (16OHE1), estrone-glucuronide/sulfate (E1-G/S) and the ratio of total 2-pathway estrogens to total estrogens were screened as three indicators closely related to the risk of GDM development. The adjusted odds ratios of GDM for the highest quartile compared with the lowest were 72.22 (95% CI 11.27-462.71, P _trend <0.001) for 16OHE1 and 6.28 (95% CI 1.74-22.71, P _trend <0.05) for E1-G/S. The ratio of 2-pathway estrogens to total estrogens was negatively associated with the risk of GDM.

Conclusion

The whole metabolic flux from cholesterol to downstream steroid hormones increased in GDM condition. The most significant changes were observed in the 16-pathway metabolism of estrogens, rather than the 2- or 4-pathway or other types of steroid hormones. 16OHE1 may be a strong marker associated with the risk for GDM.

Association of CYP19A1 Gene, Plasma Zinc, and Urinary Zinc with the Risk of Type 2 Diabetes Mellitus in a Chinese Population

To explore the effects of CYP19A1 gene polymorphisms, plasma zinc, and urinary zinc levels and their interactions on type 2 diabetes mellitus (T2DM) in residents of Gongcheng County, Guangxi, China. The case-control study was used for the investing. The MassARRAY System was applied to genotype the CYP19A1 genes rs752760, rs10046, rs10459592, and rs700518 in 540 study subjects. Plasma and urinary zinc concentrations were measured by inductively coupled plasma mass spectrometry (ICP-MS). Conditional logistic regression showed that rs752760 and plasma zinc were associated with T2DM risks with ORs of 0.593 (95% CI: 0.371-0.948) and 0.563 (95% CI: 0.356-0.889), respectively. Unconditional logistic regression analysis showed an association between urinary zinc levels and the risk of T2DM as well, with an OR of 0.352 (95% CI: 0.212-0.585). The results of the multiplicative interaction model showed that the rs752760 T allele was associated with a significantly reduced risk of T2DM with moderate/low plasma zinc levels, with ORs of 0.340 (95% CI: 0.161-0.715) and 0.583 (95% CI: 0.346-0.981), respectively, and the rs752760 T allele was also associated with a significantly decreased risk of T2DM with moderate/low urinary zinc levels, with ORs of 0.358 (95% CI: 0.201-0.635) and 0.321 (95% CI: 0.183-0.562), respectively. CYP19A1 rs752760 T allele and moderate/low plasma/urinary zinc levels reduce the risk of T2DM.

Contraceptive use in women with inherited metabolic disorders: a retrospective study and literature review

BACKGROUND

Reproductive planning is an emerging concern for women with inherited metabolic disease (IMD). Anticipatory guidance on contraception is necessary to prevent unintended pregnancies in this population. Few resources exist to aid informed decision-making on contraceptive choice. A retrospective case-control study was performed to examine trends in reproductive planning for adolescent and adult women seen at the Children's Hospital of Philadelphia (CHOP). Literature review on contraception and IMD was performed to assess global use.

RESULTS

In a cohort of 221 reproductive-aged female IMD patients, 29.4% reported routine contraceptive use. Anticipatory guidance on contraception was provided by metabolic physicians to 36.8% of patients during the study period. Contraception discussion was more likely to occur in women older than 21 years, who lived independently and were followed by gynecology. Women who received contraception counseling from their metabolic physician were 40-fold more likely to use regular contraception. Use of combined hormonal contraceptives was most commonly reported, but contraception choice varied by age and IMD.

CONCLUSION

Metabolic physicians are ideally suited to provide guidance on contraception to women with IMD. Reproductive planning should be addressed routinely using shared decision-making. Contraceptives should be selected for their efficacy, effects on metabolism, and likelihood of patient adherence.

Sex-specific differences in the metabolic enzyme activity and transporter levels in mouse skeletal muscle during postnatal development

Although sex-associated differences in energy metabolism in adults are well-characterized, developmental sex-specific changes in skeletal muscle metabolism are largely unknown. This study investigated sex differences in high-energy phosphate, glycolytic, and mitochondrial enzyme activities and metabolite transporter protein levels in mouse skeletal muscles during the early postnatal period (day 10), post-weaning (day 28), sexual maturity (day 56), and adult life (day 140). No significant sex-specific differences were observed on days 10 and 28, except for glucose transporter (GLUT) 4 level. The hexokinase, phosphofructokinase, and lactate dehydrogenase activities of skeletal muscle were higher and the citrate synthase, cytochrome c oxidase, and β-hydroxyacyl-CoA dehydrogenase activities were lower in female mice than those in male mice on days 56 and 140. The GLUT4 and FAT/CD36 protein levels were higher and the monocarboxylate transporter 4 level was lower in the skeletal muscles of female mice than those of male mice, particularly on days 56 and 140. At 140 days of age, the respiratory exchange ratio during treadmill running (15 m/min, 60 min) was lower in females than that in males, despite no sex differences at rest. In summary, sex differences were not evident in the early postnatal and post-weaning periods but became apparent after the mice reached sexual maturity. These findings indicate that sexually mature animals are a better model for investigating sex differences, particularly in the context of studying energy metabolism in mice.

Associations between parity, pregnancy loss, and breastfeeding duration and risk of maternal type 2 diabetes: An observational cohort study

BACKGROUND

Parity, pregnancy loss, and breastfeeding duration were found to be associated with diabetes. However, the results are inconsistent. Also, no epidemiological studies have examined the association of these reproductive factors with diabetes in the same large population. We aim to investigate the associations between parity, pregnancy loss, breastfeeding duration, and the risk of maternal diabetes in middle-aged and elderly Chinese females.

METHODS

We included 131 174 females aged ≥40 years from the REACTION study (Risk Evaluation of Cancers in Chinese Diabetic Individuals: A Longitudinal Study). Multivariable linear regression and logistic regression were used to assess the association between parity, pregnancy loss, and breastfeeding duration and type 2 diabetes.

RESULTS

The number of parities and breastfeeding duration were positively related to fasting plasma glucose, 2-hour postload glucose, glycosylated hemoglobin, and homeostatic model assessment of insulin resistance. Compared with those with one birth, nulliparous women or women with 2 or ≥3 births had a significantly increased risk of diabetes. The odds ratios (OR) and 95% confidence intervals (CI) were 1.27 (1.10-1.48), 1.17 (1.12-1.22), and 1.28 (1.21-1.35), respectively. Compared with women without pregnancy loss, those who underwent 2 (OR 1.09; 95% CI, 1.04-1.14) or ≥3 pregnancy losses (OR 1.11; 95% CI, 1.04-1.18) had an increased risk of diabetes. Moreover, women with a breastfeeding duration ≥0 to 6 months (OR 0.82; 95% CI, 0.75-0.90) and ≥6 to 12 months (OR 0.94; 95% CI, 0.89-0.99) had a significantly lower risk of diabetes.

CONCLUSIONS

Nulliparous women or women with multiparity or more than one pregnancy loss have an increased risk of diabetes in later life, while women who breastfeed more than 0 to 12 months have a lower risk of diabetes.

Glucose Metabolism and Glucose Transporters in Breast Cancer

Breast cancer is the most common malignancy in women worldwide and is associated with high mortality rates despite the continuously advancing treatment strategies. Glucose is essential for cancer cell metabolism owing to the Warburg effect. During the process of glucose metabolism, various glycolytic metabolites, such as serine and glycine metabolites, are produced and other metabolic pathways, such as the pentose phosphate pathway (PPP), are associated with the process. Glucose is transported into the cell by glucose transporters, such as GLUT. Breast cancer shows high expressions of glucose metabolism-related enzymes and GLUT, which are also related to breast cancer prognosis. Triple negative breast cancer (TNBC), which is a high-grade breast cancer, is especially dependent on glucose metabolism. Breast cancer also harbors various stromal cells such as cancer-associated fibroblasts and immune cells as tumor microenvironment, and there exists a metabolic interaction between these stromal cells and breast cancer cells as explained by the reverse Warburg effect. Breast cancer is heterogeneous, and, consequently, its metabolic status is also diverse, which is especially affected by the molecular subtype, progression stage, and metastatic site. In this review, we will focus on glucose metabolism and glucose transporters in breast cancer, and we will additionally discuss their potential applications as cancer imaging tracers and treatment targets.

GLUT4 in Mouse Endometrial Epithelium: Roles in Embryonic Development and Implantation

GLUT4 is involved in rapid glucose uptake among various kinds of cells to contribute to glucose homeostasis. Prior data have reported that aberrant glucose metabolism by GLUT4 dysfunction in the uterus could be responsible for infertility and increased miscarriage. However, the expression and precise functions of GLUT4 in the endometrium under physiological conditions remain unknown or controversial. In this study, we observed that GLUT4 exhibits a spatiotemporal expression in mouse uterus on pregnant days 1–4; its expression especially increased on pregnant day 4 during the window of implantation. We also determined that estrogen, in conjunction with progesterone, promotes the expression of GLUT4 in the endometrial epithelium in vivo or in vitro. GLUT4 is an important transporter that mediates glucose transport in endometrial epithelial cells (EECs) in vitro or in vivo. In vitro, glucose uptake decreased in mouse EECs when the cells were treated with GLUT4 small interfering RNA (siRNA). In vivo, the injection of GLUT4-siRNA into one side of the mouse uterine horns resulted in an increased glucose concentration in the uterine fluid on pregnant day 4, although it was still lower than in blood, and impaired endometrial receptivity by inhibiting pinopode formation and the expressions of leukemia inhibitory factor (LIF) and integrin ανβ3, finally affecting embryonic development and implantation. Overall, the obtained results indicate that GLUT4 in the endometrial epithelium affects embryo development by altering glucose concentration in the uterine fluid. It can also affect implantation by impairing endometrial receptivity due to dysfunction of GLUT4.

β-Sitosterol-D-Glucopyranoside Mimics Estrogenic Properties and Stimulates Glucose Utilization in Skeletal Muscle Cells

Estrogenic molecules have been reported to regulate glucose homeostasis and may be beneficial for diabetes management. Here, we investigated the estrogenic effect of β-sitosterol-3-O-D-glucopyranoside (BSD), isolated from the fruits of Cupressus sempervirens and monitored its ability to regulate glucose utilization in skeletal muscle cells. BSD stimulated ERE-mediated luciferase activity in both ERα and ERβ-ERE luc expression system with greater response through ERβ in HEK-293T cells, and induced the expression of estrogen-regulated genes in estrogen responsive MCF-7 cells. In silico docking and molecular interaction studies revealed the affinity and interaction of BSD with ERβ through hydrophobic interaction and hydrogen bond pairing. Furthermore, prolonged exposure of L6-GLUT4myc myotubes to BSD raised the glucose uptake under basal conditions without affecting the insulin-stimulated glucose uptake, the effect associated with enhanced translocation of GLUT4 to the cell periphery. The BSD-mediated biological response to increase GLUT4 translocation was obliterated by PI-3-K inhibitor wortmannin, and BSD significantly increased the phosphorylation of AKT (Ser-473). Moreover, BSD-induced GLUT4 translocation was prevented in the presence of fulvestrant. Our findings reveal the estrogenic activity of BSD to stimulate glucose utilization in skeletal muscle cells via PI-3K/AKT-dependent mechanism.

Direct impact of gonadotropins on glucose uptake and storage in preovulatory granulosa cells: Implications in the pathogenesis of polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is often associated with higher levels of LH, and arrested ovarian follicular growth. The direct impact of high LH on FSH mediated metabolic responses in PCOS patients is not clearly understood.

METHOD

In order to investigate the impact of FSH and LH on glucose metabolism in preovulatory granulosa cells (GCs), we used [U¹⁴C]-2 deoxyglucose, D-[U¹⁴C]-glucose or 2-NBD glucose to analyse glucose uptake and its incorporation into glycogen. To reproduce the high androgenic potential in PCOS patients, we administered hCG both in vitro and in vivo. The role of IRS-2/PI3K/Akt2 pathway was studied after knockdown with specific siRNA. Immunoprecipitation and specific assays were used for the assessment of IRS-2, glycogen synthase and protein phosphatase 1. Furthermore, we examined the in vivo effects of hCG on FSH mediated glycogen increase in normal and PCOS rat model. HEK293 cells co-expressing FSHR and LHR were used to demonstrate glucose uptake and BRET change by FSH and hCG.

RESULTS

In normal human and rat granulosa cells, FSH is more potent than hCG in stimulating glucose uptake, however glycogen synthesis was significantly upregulated only by FSH through increase in activity of glycogen synthase via IRS-2/PI3K/Akt2 pathway. On the contrary, an impaired FSH-stimulated glucose uptake and glycogen synthesis in granulosa cells of PCOS-patients indicated a selective defect in FSHR activation. Further, in normal human granulosa cells, and in immature rat model, the impact of hCG on FSH responses was such that it inhibited the FSH-mediated glucose uptake as well as glycogen synthesis through inhibition of FSH-stimulated IRS-2 expression. These findings were further validated in HEK293 cells overexpressing Flag-LHR and HA-FSHR, where high hCG inhibited the FSH-stimulated glucose uptake. Notably, an increased BRET change was observed in HEK293 cells expressing FSHR-Rluc8 and LHR-Venus possibly suggesting increased heteromerization of LHR and FSHR in the presence of both hCG and FSH in comparison to FSH or hCG alone.

CONCLUSION

Our findings confirm a selective attenuation of metabolic responses to FSH such as glucose uptake and glycogen synthesis by high activation level of LHR leading to the inhibition of IRS-2 pathway, resulting in depleted glycogen stores and follicular growth arrest in PCOS patients.

Estrogen and Glycemic Homeostasis: The Fundamental Role of Nuclear Estrogen Receptors ESR1/ESR2 in Glucose Transporter GLUT4 Regulation

Impaired circulating estrogen levels have been related to impaired glycemic homeostasis and diabetes mellitus (DM), both in females and males. However, for the last twenty years, the relationship between estrogen, glycemic homeostasis and the mechanisms involved has remained unclear. The characterization of estrogen receptors 1 and 2 (ESR1 and ESR2) and of insulin-sensitive glucose transporter type 4 (GLUT4) finally offered a great opportunity to shed some light on estrogen regulation of glycemic homeostasis. In this manuscript, we review the relationship between estrogen and DM, focusing on glycemic homeostasis, estrogen, ESR1/ESR2 and GLUT4. We review glycemic homeostasis and GLUT4 expression (muscle and adipose tissues) in Esr1^−/− and Esr2^−/− transgenic mice. We specifically address estradiol-induced and ESR1/ESR2-mediated regulation of the solute carrier family 2 member 4 (Slc2a4) gene, examining ESR1/ESR2-mediated genomic mechanisms that regulate Slc2a4 transcription, especially those occurring in cooperation with other transcription factors. In addition, we address the estradiol-induced translocation of ESR1 and GLUT4 to the plasma membrane. Studies make it clear that ESR1-mediated effects are beneficial, whereas ESR2-mediated effects are detrimental to glycemic homeostasis. Thus, imbalance of the ESR1/ESR2 ratio may have important consequences in metabolism, highlighting that ESR2 hyperactivity assumes a diabetogenic role.

Sex Dimorphic Associations of Gestational Diabetes Mellitus With Cord Plasma Fatty Acid Binding Protein 4 and Estradiol

Fatty acid binding protein 4 (FABP4) has been associated with insulin resistance. Gestational diabetes mellitus (GDM) impairs fetal insulin sensitivity. Female newborns are more insulin resistant than male newborns. We sought to evaluate the association between GDM and cord blood FABP4, and explore potential sex dimorphic associations and the roles of sex hormones. This was a nested case-control study in the Shanghai Birth Cohort, including 153 pairs of newborns in GDM vs. euglycemic pregnancies matched by infant sex and gestational age at delivery. Cord plasma FABP4, leptin, total and high-molecular-weight adiponectin, testosterone and estradiol concentrations were measured. Adjusting for maternal and neonatal characteristics, cord plasma FABP4 (Mean ± SD: 27.0 ± 19.6 vs. 18.8 ± 9.6 ng/mL, P=0.045) and estradiol (52.0 ± 28.6 vs. 44.2 ± 26.6, ng/mL, P=0.005) concentrations were higher comparing GDM vs. euglycemic pregnancies in males, but similar in females (all P>0.5). Mediation analyses showed that the positive association between GDM and cord plasma FABP4 in males could be partly mediated by estradiol (P=0.03), but not by testosterone (P=0.72). Cord plasma FABP4 was positively correlated with total adiponectin in females (r=0.17, P=0.053), but the correlation was in the opposite direction in males (r=-0.11, P=0.16) (test for difference in r, P=0.02). Cord plasma FABP4 was not correlated with leptin in both sexes. The study is the first to demonstrate sex-dimorphic associations between GDM and cord plasma FABP4 or estradiol, and between FABP4 and adiponectin in newborns. GDM may affect fetal circulating FABP4 and estradiol levels in males only.

CTRP-1 levels are related to insulin resistance in pregnancy and gestational diabetes mellitus

Recent studies have shown higher levels of CTRP-1 (C1QTNF-related protein) in patients with type 2 diabetes compared to controls. We aimed at investigating CTRP-1 in gestational diabetes mellitus (GDM). CTRP-1 levels were investigated in 167 women (93 with normal glucose tolerance (NGT), 74 GDM) of a high-risk population for GDM. GDM was further divided into GDM subtypes depending on a predominant insulin sensitivity issue (GDM-IR) or secretion deficit (GDM-IS). Glucose tolerance was assessed with indices [Matsuda index, Stumvoll first phase index, insulin-secretion-sensitivity-index 2 (ISSI-2), area-under-the-curve (AUC) insulin, AUC glucose] derived from an oral glucose tolerance test (oGTT) performed at < 21 and 24–28 weeks of gestation. In pregnancy, CTRP-1 levels of GDM (76.86 ± 37.81 ng/ml) and NGT (82.2 ± 35.34 ng/ml; p = 0.104) were similar. However, GDM-IR women (65.18 ± 42.18 ng/ml) had significantly lower CTRP-1 levels compared to GDM-IS (85.10 ± 28.14 ng/ml; p = 0.009) and NGT (p = 0.006). CTRP-1 levels correlated negatively with weight, AUC insulin, Stumvoll first phase index, bioavailable estradiol and positively with HbA1c, Matsuda Index and ISSI-2. A multiple regression analysis revealed bioavailable estradiol (β = − 0.280, p = 0.008) and HbA1c (β = 0.238; p = 0.018) as the main variables associated with CTRP-1 in GDM. Postpartum, waist and hip measurements were predictive of CRTP-1 levels instead. CTRP-1 levels were higher postpartum than during pregnancy (91.92 ± 47.27 vs.82.44 ± 38.99 ng/ml; p = 0.013). CTRP-1 is related to insulin resistance in pregnancy and might be a metabolic biomarker for insulin resistance in GDM. CTRP-1 levels were significantly lower during pregnancy than postpartum, probably due to rising insulin resistance during pregnancy.

Folic acid content of diet during pregnancy determines post-birth re-set of metabolism in Wistar rat dams

Maternal metabolism begins to return to homeostasis (re-set) following birth and is accelerated by lactation. Delay in metabolic re-set may contribute to postpartum weight retention and later-life metabolic consequences. Folic acid (FA) is essential during pregnancy but inadequate intakes may alter 1-carbon metabolism, consequently affecting energy homeostatic systems. Our objectives were to examine the effects of FA content 1)below and 2)above requirements during pregnancy on the re-set of body weight, markers of hepatic 1-carbon metabolism and central and peripheral energy metabolic pathways in Wistar rat mothers early post-weaning (PW) compared to pregnant controls. Pregnant Wistar rats were fed an AIN-93G diet with FA at 0X, 1X (control, 2 mg FA/kg) or a range above requirements at 2.5X, 5X or 10X recommended levels then the control diet during lactation up to 1 week PW. Dams fed below (0X) or above (5X and 10X) FA requirements had delayed weight-loss from weaning up to 1 week PW, higher plasma insulin and HOMA-IR and changes in glucose and lipid metabolism-regulating genes in muscle, but not liver or adipose tissue compared to controls. Expression of folate-related genes in liver were lower in high FA fed dams. Central food intake neurons were not affected by FA diets. In conclusion, intakes of FA below (0X) or above (5X, 10X) requirements during pregnancy delayed weight-loss, dysregulated 1-carbon pathways in the liver and peripheral energy metabolic pathways in the Wistar rat mother up to 4 weeks after dietary exposure; potentially programming long-term negative metabolic effects and that of her future offspring.

The effect of pregnancy on nitrogen retention, maternal insulin sensitivity, and mRNA abundance of genes involved in energy and amino acid metabolism in gilts

Twenty-one of each pregnant (P) and nonserviced, nonpregnant (NP) sister-pairs of gilts were selected to investigate the effect of pregnancy on protein deposition (Pd; whole body and maternal), insulin sensitivity, and mRNA abundance of genes involved in energy and AA metabolism. Between breeding (study day 0) and day 111, P and NP gilts received 2.16 kg of the experimental diet (3.34 Mcal ME/kg, 17.6% crude protein, 0.78% standardized ileal digestible lysine) that was formulated to meet the estimated ME requirements of pregnant gilts (and meet or exceed AA requirements). Nitrogen balances were conducted on day 63 and 102 ± 0.2 of the study during 4-d periods. Blood samples were collected on day 43, 56, 71, 85, 98, and 108 ± 0.3 of the study to determine plasma concentrations of fasted IGF-1, estradiol (E2), and estrone sulfate (E1S). Frequently sampled intravenous glucose tolerance tests (FSIGTT) were conducted on day 75 ± 0.7 in 6 P and 5 NP gilts and on day 107 ± 0.4 in 17 P and 17 NP gilts and the MINMOD approach was applied to evaluate whole body insulin sensitivity and pancreatic responsiveness. Longissimus muscle (LM) and s.c. adipose tissue (AD) samples were excised from 12 P and 12 NP gilts at day 111 ± 0.4 of the study after euthanasia to determine mRNA abundance of key genes. Whole body Pd was greater (P < 0.001) at day 102 and maternal Pd was lower (P < 0.002) at day 63 and 102 for P compared to NP gilts. Plasma concentrations of E1S and E2 increased (P < 0.05) with study day for P gilts and remained constant for NP gilts, which coincided with reduced plasma concentrations of IGF-1 and increased estrogen receptor alpha (ESR1) mRNA abundance in LM of P gilts. Glucose effectiveness was not different between P and NP gilts, but whole body insulin sensitivity was lower (P = 0.004) in P compared to NP gilts on day 75 and 107, which corresponded with reduced mRNA abundances of SLC2A4, HK2, SREBF1, and FASN, and increased abundances of PDK4 and PPARGC1A in LM and AD. When fed identically, P gilts had greater whole body Pd at day 102, which reflects Pd in the pregnancy-associated tissues (at the expense of maternal Pd), likely driven by estrogen-stimulated insulin resistance in peripheral tissue and subsequent modulation of gene expression relating to glucose metabolism.

The Impact of Skeletal Muscle ERα on Mitochondrial Function and Metabolic Health

The incidence of chronic disease is elevated in women after menopause. Increased expression of ESR1 (the gene that encodes the estrogen receptor alpha, ERα) in muscle is highly associated with metabolic health and insulin sensitivity. Moreover, reduced muscle expression levels of ESR1 are observed in women, men, and animals presenting clinical features of the metabolic syndrome (MetSyn). Considering that metabolic dysfunction elevates chronic disease risk, including type 2 diabetes, heart disease, and certain cancers, treatment strategies to combat metabolic dysfunction and associated pathologies are desperately needed. This review will provide published work supporting a critical and protective role for skeletal muscle ERα in the regulation of mitochondrial function, metabolic homeostasis, and insulin action. We will provide evidence that muscle-selective targeting of ERα may be effective for the preservation of mitochondrial and metabolic health. Collectively published findings support a compelling role for ERα in the control of muscle metabolism via its regulation of mitochondrial function and quality control. Studies identifying ERα-regulated pathways essential for disease prevention will lay the important foundation for the design of novel therapeutics to improve metabolic health of women while limiting secondary complications that have historically plagued traditional hormone replacement interventions.

Effect of Metformin on a Preeclampsia-Like Mouse Model Induced by High-Fat Diet

BACKGROUND

Metformin has been reported to decrease insulin resistance and is associated with a lower risk of pregnancy-induced hypertension and preeclampsia. It is widely accepted that the placenta plays a crucial role in the development of preeclampsia. Our aim is to explore the effect of metformin on preeclampsia.

STUDY DESIGN

We examined control diet-fed (isocaloric diet) pregnant mice (CTRL group), pregnant mice fed a high-fat diet (HF group), and high-fat-diet-fed pregnant mice treated with metformin (HF-M group). The HF mice were fed a high-fat diet six weeks before pregnancy to establish a preeclampsia-like model; then, the group was randomly divided into a HF group and a HF-M group after pregnancy. Blood pressure, urine protein, pregnancy outcomes, protein expression, and histopathological changes in the placentas of all groups were examined and statistically analysed.

RESULTS

We observed that metformin significantly improved high blood pressure, proteinuria, and foetal and placental weights in the HF-M group compared with the HF group. Metformin significantly improved placental labyrinth and foetal vascular development in preeclampsia. In addition, metformin effectively increased matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF) levels in the placenta.

CONCLUSIONS

Our results suggest that metformin can improve preeclamptic symptoms and pregnancy outcomes.

Serotonin-estrogen interactions: What can we learn from pregnancy?

We have reviewed the scientific literature related to four diseases in which to serotonin (5-HT) is involved in the etiology, herein named 5-HT-linked diseases, and whose prevalence is influenced by estrogenic status: depression, migraine, irritable bowel syndrome and eating disorders. These diseases all have in common a sex-dimorphic prevalence, with women more frequently affected than men. The co-occurrence between these 5-HT-linked diseases suggests that they have common physiopathological mechanisms. In most 5-HT-linked diseases (except for anorexia nervosa and irritable bowel syndrome), a decrease in the serotonergic tone is observed and estrogens are thought to contribute to the improvement of symptoms by stimulating the serotonergic system. Human pregnancy is characterized by a unique 5-HT and estrogen synthesis by the placenta. Pregnancy-specific disorders, such as hyperemesis gravidarum, gestational diabetes mellitus and pre-eclampsia, are associated with a hyperserotonergic state and decreased estrogen levels. Fetal programming of 5-HT-linked diseases is a complex phenomenon that involves notably fetal-sex differences, which suggest the implication of sex steroids. From a mechanistic point of view, we hypothesize that estrogens regulate the serotonergic system, resulting in a protective effect against 5-HT-linked diseases, but that, in turn, 5-HT affects estrogen synthesis in an attempt to retrieve homeostasis. These two processes (5-HT and estrogen biosynthesis) are crucial for successful pregnancy outcomes, and thus, a disruption of this 5-HT-estrogen relationship may explain pregnancy-specific pathologies or pregnancy complications associated with 5-HT-linked diseases.

Skeletal muscle as a protagonist in the pregnancy metabolic syndrome

The pregnant woman normally shows clinical manifestations similar to a metabolic syndrome (MS), due to her metabolic and hemodynamic adaptations in order to share nutrients with the child. If those adjustments are surpassed, a kind of pregnancy MS (PregMS) could appear, characterized by excessive insulin resistance and vascular maladaptation. Skeletal muscle (SKM) must be a protagonist in the PregMS: SKM strength and mass have been associated inversely with MS incidence in non-pregnant patients, and in pregnant women muscular activity modulates metabolic and vascular adaptations that favor better outcomes. Of note, a sedentary lifestyle affects exactly in the other way. Those effects may be explained not only by the old paradigm of SKM being a great energy consumer and store, but because it is an endocrine organ whose chronic activity or deconditioning correspondingly releases myokines modulating insulin sensitivity and cardiovascular adaptation, by direct or indirect mechanisms not well understood. In this document, we present evidence to support the concept of a PregMS and hypothesize on the role of the SKM mass, fiber types composition and myokines in its pathophysiology. Also, we discuss some exercise interventions in pregnancy as a way to test our hypotheses.

Glycogen metabolism in mink uterine epithelial cells and its regulation by estradiol, progesterone and insulin

Glycogen content in mink uterine glandular and luminal epithelia (GE and LE) is maximal during estrus and is depleted before implantation while embryos are in diapause. Uterine glycogen synthesis in vivo is stimulated by estradiol (E₂) while its mobilization is induced by progesterone (P₄). Nevertheless, treatment of an immortalized mink uterine epithelial cell line (GMMe) with E₂ did not affect glycogen production. Interestingly, insulin alone significantly increased synthesis of the nutrient and glycogen content in response to insulin + E₂ was greater than for insulin alone. Our objectives were to determine: 1) If insulin receptor protein (INSR) is expressed by mink uterine GE and LE in vivo and if the amount differs between estrus, diapause and pregnancy; 2) if E₂, P₄ or insulin regulate insulin receptor gene (Insr) expression by GMMe cells, and 3) if E₂ and P₄ act independently to regulate glycogen metabolism by GMMe cells and/or if their effects are mediated in part through the actions of insulin. The mean (±S.E.) percent INSR content of uterine epithelia was greatest during diapause (GE: 15.65 ± 0.06, LE:16.56 ± 1.25), much less during pregnancy (GE: 2.53 ± 0.60, LE:2.25 ± 0.32) and barely detectable in estrus (GE: 0.03 ± 0.01, LE:0.02 ± 0.01). Glycogen concentrations in GMMe cells increased 10-fold in response to insulin and 20-fold with insulin + E₂ when compared to controls. Expression of Insr was increased 2-fold by insulin and insulin + E₂ when compared to controls and there was no difference between the two hormone treatments, indicating that E₂ does not increase Insr expression in insulin-treated cells. To simulate E₂-priming, cells were treated with Insulin + E₂ for 24 h, followed by the same hormones + P₄ for the second 24 h (Insulin + E₂ → P₄) which resulted in Insr and glycogen levels not different from controls. Similarly, cells treated with Insulin + P₄ resulted in glycogen concentrations not different from controls. We conclude that the glycogenic actions of E₂ on GMMe cells are due to increased responsiveness of the cells to insulin, but not as a result of up-regulation of the insulin receptor. Glycogen mobilization in response to P₄ was the result of decreased glycogenesis and increased glycogenolysis occurring concomitantly with reduced Insr expression. Mink uterine glycogen metabolism appears to be regulated in a reproductive cycle-dependent manner in part as a result of the actions of E₂ and P₄ on cellular responsiveness to insulin.

Preventative effects of resveratrol and estradiol on streptozotocin-induced diabetes in ovariectomized mice and the related mechanisms

Resveratrol, a non-flavonoid polyphenolic compound, is structurally and functionally similar to estrogen and has drawn great attention for its potentially beneficial effects on diabetes. However, it is not known whether it shares the same protective effect against diabetes as estrogen and the underlying mechanisms. The aim of the present study was to investigate the protective effects of phytoestrogen resveratrol and exogenous 17β-estradiol against streptozotocin (STZ)-induced type 1 diabetes. Female mice were ovariectomized (OVX) and chronically injected with different concentrations of resveratrol (0.1, 1 or 10 mg/kg) and 17β-estradiol (0.01, 0.1 or 1 mg/kg) subcutaneously for 4 weeks, and the levels of blood glucose, plasma insulin, plasma antioxidant capacity, the changes of pancreatic islet cells and the expressions of glucose transporter 4 (GLUT4), insulin receptor substrate 1 (IRS-1) and phosphorylation of extracellular signal-regulated kinase (p-ERK) were detected. Resveratrol and 17β-estradiol significantly inhibited the increase of the blood glucose level and the rise of plasma malondialdehyde in STZ-induced diabetic mice, improved the levels of plasma antioxidant capacity and plasma insulin, protected the pancreatic islet cells, and increased the expressions of GLUT4 and IRS-1, but decreased p-ERK expression in skeletal muscle and myocardial tissue. The results suggest that resveratrol or 17β-estradiol shows obvious protection against STZ-induced diabetes in OVX mice, the mechanisms probably involve their ameliorating antioxidant activities and islet function, promoting muscle glucose uptake and inhibiting the expression of p-ERK.

Estrogen Receptor 1 (ESR1) Enhances Slc2a4/GLUT4 Expression by a SP1 Cooperative Mechanism

Background: Estrogens are involved in glycemic regulation, playing an important role in the development and/or progression of insulin resistance. For that, estrogens regulate the expression of the glucose transporter protein GLUT4 (codified by the solute carrier family 2 member 4 gene, Slc2a4), thus modulating adipose and muscle glucose disposal. This regulation is a balance between ESR1-mediated enhancer effect and ESR2-mediated repressor effect on Slc2a4 gene. However, molecular mechanisms involved in these effects are poorly understood. Since the specificity protein 1 (SP1) participates in several ESR-mediated genomic regulations, the aim of the present study is to investigate the participation of SP1 in the ESR1/2-mediated regulation of Slc2a4 gene. Methods: Differentiated 3T3-L1 adipocytes were 24-hour challenged with 10 nM estradiol (E2) and 10 nM ESR1 agonist (PPT) or 100 nM ESR2 agonist (DPN), added or not with E2. Slc2a4 and Sp1 mRNAs (RT-qPCR), total GLUT4 and nuclear ESR1, ESR2 and SP1 proteins (Western blotting), SP1 binding activity into Slc2a4 promoter (EMSA), and nuclear complexation of SP1/ESR1 (immunoprecipitation) were analyzed. Results: E2 and PPT increased (25-50%) whereas DPN reduced (20-45%) Slc2a4 and GLUT4 expression. Nuclear content of ESR1 and ESR2 remained unchanged. Nuclear content of SP1 increased (50 to 90%) by PPT and DPN added or not with E2; the highest effect observed with PPT alone. PPT also increased the nuclear content of SP1/ESR1 complex and the SP1 binding into the Slc2a4 promoter. Conclusions: ESR1 activation in adipocytes increased the nuclear content of SP1 protein, the SP1/ESR1 interaction and SP1 binding into the Slc2a4 gene promoter, culminating with increased Slc2a4/GLUT4 expression. No involvement of SP1 seems to occur in ESR2-mediated repressor effect on Slc2a4. We expect that this ESR1/SP1 cooperative effect can contribute to the development of new approaches for prevention or treatment of insulin resistance and diabetes mellitus.

The impact of ERα action on muscle metabolism and insulin sensitivity - Strong enough for a man, made for a woman

Background

The incidence of chronic disease is elevated in women after menopause. Natural variation in muscle expression of the estrogen receptor (ER)α is inversely associated with plasma insulin and adiposity. Moreover, reduced muscle ERα expression levels are observed in women and animals presenting clinical features of the metabolic syndrome (MetSyn). Considering that metabolic dysfunction impacts nearly a quarter of the U.S. adult population and elevates chronic disease risk including type 2 diabetes, heart disease, and certain cancers, treatment strategies to combat metabolic dysfunction and associated pathologies are desperately needed.

Scope of the review

This review will provide evidence supporting a critical and protective role for skeletal muscle ERα in the regulation of metabolic homeostasis and insulin sensitivity, and propose novel ERα targets involved in the maintenance of metabolic health.

Major conclusions

Studies identifying ERα-regulated pathways essential for disease prevention will lay the important foundation for the rational design of novel therapeutics to improve the metabolic health of women while limiting secondary complications that have plagued traditional hormone replacement interventions.

Sex- and Tissue-Specific Role of Estrogen Sulfotransferase in Energy Homeostasis and Insulin Sensitivity

Estrogen sulfotransferase catalyzes the sulfoconjugation and deactivation of estrogens. Previously, we showed that loss of Est in male ob/ob mice, but not in female ob/ob mice, exacerbated the diabetic phenotype, but the underlying mechanism was unclear. In this study, we show that transgenic reconstitution of Est in the adipose tissue, but not in the liver, attenuated diabetic phenotype in Est-deficient ob/ob mice (obe mice). Mechanistically, adipose reconstitution of Est in obe mice (oae mice) resulted in reduced local and systemic inflammation, improved insulin sensitivity, and increased energy expenditure. At the molecular level, adipose induction of lipocalin-2 (Lcn2) in oae males may have contributed to the inhibition of inflammation because the level of Lcn2 was negatively associated with tumor necrosis factor (Tnf) α expression, and treatment of differentiated adipocytes with Lcn2 antagonized Tnfα-responsive inhibition of insulin signaling. The metabolic benefit of adipose reconstitution of Est was sex specific, because adipose reconstitution of Est in obe females had little effect. Interestingly, despite their improved metabolic functions, obe male mice with reconstituted Est in their adipose tissue failed to ameliorate the impairment of the structure and function of the pancreatic islets. In summary, our study uncovers a crucial adipose- and male-specific role of Est in maintaining the whole-body energy homeostasis.

Estradiol-induced regulation of GLUT4 in 3T3-L1 cells: involvement of ESR1 and AKT activation

Impaired insulin-stimulated glucose uptake involves reduced expression of the GLUT4 (solute carrier family 2 facilitated glucose transporter member 4, SLC2A4 gene). 17β-estradiol (E₂) modulates SLC2A4/GLUT4 expression, but the involved mechanisms are unclear. Although E₂ exerts biological effects by binding to estrogen receptors 1/2 (ESR1/2), which are nuclear transcriptional factors; extranuclear effects have also been proposed. We hypothesize that E₂ regulates GLUT4 through an extranuclear ESR1 mechanism. Thus, we investigated the effects of E₂ upon (1) subcellular distribution of ESRs and the proto-oncogene tyrosine-protein kinases (SRC) involvement; (2) serine/threonine-protein kinase (AKT) activation; (3) Slc2a4/GLUT4 expression and (4) GLUT4 subcellular distribution and glucose uptake in 3T3-L1 adipocytes. Differentiated 3T3-L1 adipocytes were cultivated or not with E₂ for 24 h, and additionally treated or not with ESR1-selective agonist (PPT), ESR1-selective antagonist (MPP) or selective SRC inhibitor (PP2). Subcellular distribution of ESR1, ESR2 and GLUT4 was analyzed by immunocytochemistry; Slc2a4 mRNA and GLUT4 were quantified by qPCR and Western blotting, respectively; plasma membrane GLUT4 translocation and glucose uptake were analyzed under insulin stimulus for 20 min or not. E₂ induced (1) translocation of ESR1, but not of ESR2, from nucleus to plasma membrane and AKT phosphorylation, effects mimicked by PPT and blocked by MPP and PP2; (2) increased Slc2a4/GLUT4 expression and (3) increased insulin-stimulated GLUT4 translocation and glucose uptake. In conclusion, E₂ treatment promoted a SRC-mediated nucleus-plasma membrane shuttle of ESR1, and increased AKT phosphorylation, Slc2a4/GLUT4 expression and plasma membrane GLUT4 translocation; consequently, improving insulin-stimulated glucose uptake. These results unravel mechanisms through which estrogen improves insulin sensitivity.

The Role of Skeletal Muscle Estrogen Receptors in Metabolic Homeostasis and Insulin Sensitivity

Women in the modern era are challenged with facing menopausal symptoms as well as heightened disease risk associated with increasing adiposity and metabolic dysfunction for up to three decades of life. Treatment strategies to combat metabolic dysfunction and associated pathologies have been hampered by our lack of understanding regarding the biological causes of these clinical conditions and our incomplete understanding regarding the effects of estrogens and the tissue-specific functions and molecular actions of its receptors. In this chapter we provide evidence supporting a critical and protective role for skeletal muscle estrogen receptor α in the maintenance of metabolic homeostasis and insulin sensitivity. Studies identifying the critical ER-regulated pathways essential for disease prevention will lay the important foundation for the rational design of novel therapeutic strategies to improve the health of women while limiting secondary complications that have plagued traditional hormone replacement interventions.

Impaired estrogen receptor action in the pathogenesis of the metabolic syndrome

Considering the current trends in life expectancy, women in the modern era are challenged with facing menopausal symptoms as well as heightened disease risk associated with increasing adiposity and metabolic dysfunction for up to three decades of life. Treatment strategies to combat metabolic dysfunction and associated pathologies have been hampered by our lack of understanding regarding the biological underpinnings of these clinical conditions and our incomplete understanding of the effects of estrogens and the tissue-specific functions and molecular actions of its receptors. In this review we provide evidence supporting a critical and protective role for the estrogen receptor α specific form in the maintenance of metabolic homeostasis and insulin sensitivity. Studies identifying the ER-regulated pathways required for disease prevention will lay the important foundation for the rational design of targeted therapeutics to improve women's health while limiting complications that have plagued traditional hormone replacement interventions.

Pregnancy and Smoothelin-like Protein 1 (SMTNL1) Deletion Promote the Switching of Skeletal Muscle to a Glycolytic Phenotype in Human and Mice

Pregnancy promotes physiological adaptations throughout the body, mediated by the female sex hormones progesterone and estrogen. Changes in the metabolic properties of skeletal muscle enable the female body to cope with the physiological challenges of pregnancy and may also be linked to the development of insulin resistance. We conducted global microarray, proteomic, and metabolic analyses to study the role of the progesterone receptor and its transcriptional regulator, smoothelin-like protein 1 (SMTNL1) in the adaptation of skeletal muscle to pregnancy. We demonstrate that pregnancy promotes fiber-type changes from an oxidative to glycolytic isoform in skeletal muscle. This phenomenon is regulated through an interaction between SMTNL1 and progesterone receptor, which alters the expression of contractile and metabolic proteins. smtnl1(-/-) mice are metabolically less efficient and show impaired glucose tolerance. Pregnancy antagonizes these effects by inducing metabolic activity and increasing glucose tolerance. Our results suggest that SMTNL1 has a role in mediating the actions of steroid hormones to promote fiber switching in skeletal muscle during pregnancy. Our findings also bear on the management of gestational diabetes that develops as a complication of pregnancy in ~4% of women.

Bisphenol-A treatment during pregnancy in mice: a new window of susceptibility for the development of diabetes in mothers later in life

Evidence now exists supporting the hypothesis that endocrine-disrupting chemicals (EDCs) can harmfully impact glucose metabolism. Thus, EDCs are beginning to be considered important contributors to the increased incidence of diabetes, obesity, or both. The possible effect of exposure to EDCs during pregnancy on glucose homeostasis in mothers later in life is presently unknown. Here we show that several months after delivery, mothers treated with the widespread EDC bisphenol-A (BPA) during gestation, at environmentally relevant doses, exhibit profound glucose intolerance and altered insulin sensitivity as well as increased body weight. These mice presented a decreased insulin secretion both in vivo and in vitro together with reduced pancreatic β-cell mass. The proliferation capacity was decreased in association with a diminished expression of the cell cycle activators: cyclin D2 and cyclin-dependent kinase-4. In addition, the rate of β-cells apoptosis was increased as well as the expression of the cell cycle inhibitors p16 and p53. Conversely, no effects on glucose metabolism or insulin sensitivity were observed when female nonpregnant mice were treated with BPA at the same doses. Taken together, these findings reveal that BPA exposure during gestation has harmful long-term implications in glucose metabolism for the mother. This finding highlights a new window of susceptibility for EDC exposure that may be important for the development of type 2 diabetes.

Oleic and linoleic fatty acids downregulate Slc2a4/GLUT4 expression via NFKB and SREBP1 in skeletal muscle cells

Oleic (OA) and linoleic (LA) fatty acids may be important regulators of Slc2a4 gene (GLUT4 protein) in skeletal muscle, thus participating in insulin resistance. We investigated the effect of OA and LA on the Slc2a4/GLUT4 expression in L6 muscle cells; as well as potential transcriptional regulators. OA and LA (50-400 µM) decreased the Slc2a4/GLUT4 expression in a dose-dependent way (maximum of ~50%, P < 0.001). OA and LA did not alter the Slc2a4-binding activity of oxysterols-receptor-LXR-alpha and peroxisome-proliferator-activated-receptor-gamma; but decreased the Slc2a4-binding activity of the sterol-regulatory-element-binding-protein-1 (SREBP1) enhancer (50%, P < 0.001), and increased (~30%, P < 0.001) the nuclear proteins binding into the Slc2a4-nuclear-factor-NF-kappa-B-binding site (repressor), and the phosphorylation of the inhibitors of nuclear-factor-kappa-B-kinase alpha/beta (150-300%, P < 0.001). In sum, OA and LA are potent inhibitors of the Slc2a4/GLUT4 expression in muscle cells; an effect involving reduced SREBP1 and increased NFKB transcriptional activity. These regulations may participate in the fatty acid-related pathophysiology of insulin resistance.

Negative regulation of glucose metabolism in human myotubes by supraphysiological doses of 17β-estradiol or testosterone

OBJECTIVE

Exposure of skeletal muscle to high levels of testosterone or estrogen induces insulin resistance, but evidence regarding the direct role of either sex hormone on metabolism is limited. Therefore, the aim of this study was to investigate the direct effect of acute sex hormone exposure on glucose metabolism in skeletal muscle.

MATERIALS/METHODS

Differentiated human skeletal myotubes were exposed to either 17β-estradiol or testosterone and metabolic characteristics were assessed. Glucose incorporation into glycogen, glucose oxidation, palmitate oxidation, and phosphorylation of key signaling proteins were determined.

RESULTS

Treatment of myotubes with either 17β-estradiol or testosterone decreased glucose incorporation into glycogen. Exposure of myotubes to 17β-estradiol reduced glucose oxidation under basal and insulin-stimulated conditions. However, testosterone treatment enhanced basal palmitate oxidation and prevented insulin action on glucose and palmitate oxidation. Acute stimulation of myotubes with testosterone reduced phosphorylation of S6K1 and p38 MAPK. Exposure of myotubes to either 17β-estradiol or testosterone augmented phosphorylation GSK3β(Ser9) and PKCδ(Thr505), two negative regulators of glycogen synthesis. Treatment of myotubes with a PKC specific inhibitor (GFX) restored the effect of either sex hormone on glycogen synthesis. PKCδ silencing restored glucose incorporation into glycogen to baseline in response to 17β-estradiol, but not testosterone treatment.

CONCLUSION

An acute exposure to supraphysiological doses of either 17β-estradiol or testosterone regulates glucose metabolism, possibly via PKC signaling pathways. Furthermore, testosterone treatment elicits additional alterations in serine/threonine kinase signaling, including the ribosomal protein S6K1 and p38 MAPK.

Insulin acutely triggers transcription of Slc2a4 gene: participation of the AT-rich, E-box and NFKB-binding sites

AIMS

The insulin-sensitive glucose transporter protein GLUT4 (solute carrier family 2 member 4 (Slc2a4) gene) plays a key role in glycemic homeostasis. Decreased GLUT4 expression is a current feature in insulin resistant conditions such as diabetes, and the restoration of GLUT4 content improves glycemic control. This study investigated the effect of insulin upon Slc2a4/GLUT4 expression, focusing on the AT-rich element, E-box and nuclear factor NF-kappa-B (NFKB) site.

MAIN METHODS

Rat soleus muscles were incubated during 180 min with insulin, added or not with wortmannin (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit gamma isoform (PI3K)-inhibitor), ML9 (serine/threonine protein kinase (AKT) inhibitor) and tumor necrosis factor (TNF, GLUT4 repressor), and processed for analysis of GLUT4 protein (Western blotting); Slc2a4, myocyte enhancer factor 2a/d (Mef2a/d), hypoxia inducible factor 1a (Hif1a), myogenic differentiation 1 (Myod1) and nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (Nfkb1) messenger ribonucleic acids (mRNAs) (polymerase chain reaction (PCR)); and AT-rich- (myocyte-specific enhancer factor 2 (MEF2)-binding site), E-box- (hypoxia inducible factor 1 alpha (HIF1A)- and myoblast determination protein 1 (MYOD1)-binding site), and NFKB-binding activity (electrophoretic mobility assay).

KEY FINDINGS

Insulin increased Slc2a4 mRNA expression (140%) and nuclear proteins binding to AT-rich and E-box elements (~90%), all effects were prevented by wortmannin and ML9. Insulin also increased Mef2a/d and Myod1 mRNA expression, suggesting the participation of these transcriptional factors in the Slc2a4 enhancing effect. Conversely, insulin decreased Nfkb1 mRNA expression and protein binding to the NFKB-site (~50%). Furthermore, TNF-induced inhibition of GLUT4 expression (~40%) was prevented by insulin in an NFKB-binding repressing mechanism. GLUT4 protein paralleled the Slc2a4 mRNA regulations.

SIGNIFICANCE

Insulin enhances the Slc2a4/GLUT4 expression in the skeletal muscle by activating AT-rich and E-box elements, in a PI3K/AKT-dependent mechanism, and repressing NFKB-site activity as well. These results unravel how post-prandial increase of insulin may guarantee GLUT4 expression, and how the insulin signaling impairment can participate in insulin resistance-induced repression of GLUT4.

Differential expression of microRNAs in omental adipose tissue from gestational diabetes mellitus subjects reveals miR-222 as a regulator of ERα expression in estrogen-induced insulin resistance

Omental adipose tissue plays a central role in insulin resistance in gestational diabetes mellitus (GDM), and the molecular mechanisms leading to GDM remains vague. Evidence demonstrates that maternal hormones, such as estradiol, contribute to insulin resistance in GDM. In this study we determined the differential expression patterns of microRNAs (miRNAs) in omental adipose tissues from GDM patients and pregnant women with normal glucose tolerance using AFFX miRNA expression chips. MiR-222, 1 of 17 identified differentially expressed miRNAs, was found to be significantly up-regulated in GDM by quantitative real-time PCR (P < .01), and its expression was closely related with serum estradiol level (P < .05). Furthermore, miR-222 expression was significantly increased in 3T3-L1 adipocytes with a high concentration of 17β-estradiol stimulation (P < .01), whereas the expressions of estrogen receptor (ER)-α protein and insulin-sensitive membrane transporter glucose transporter 4 (GLUT4) protein (P < .01) were markedly reduced. In addition, ERα was shown to be a direct target of miR-222 in 3T3-L1 adipocytes by using the luciferase assay. Finally, antisense oligonucleotides of miR-222 transfection was used to silence miR-222 in 3T3-L1 adipocytes. The results showed that the expressions of ERα and GLUT4, the insulin-stimulated translocation of GLUT4 from the cytoplasm to the cell membrane and glucose uptake in mature adipocytes were dramatically increased (P < .01). In conclusion, miR-222 is a potential regulator of ERα expression in estrogen-induced insulin resistance in GDM and might be a candidate biomarker and therapeutic target for GDM.

(1)H NMR metabolic profiling analysis offers evaluation of Nilestriol treatment in ovariectomised rats

Nilestriol (NIL) has been applied to treat menopausal dysfunctions, yet its mechanism has remained unknown. To understand the relationship between the changes in homeostatic metabolites and ovarian oestrogen deficiency syndromes after NIL treatment, proton Nuclear Magnetic Resonance ((1)H NMR)-based metabonomic technologies were used to analyse a rat model of oestrogen deficiency. An orthogonal partial least-squares regression (OPLS) differentiation model was used on 12-week metabolic analyses of ovariectomised (OVX) rats treated or mock treated with NIL. Furthermore, data analysis using Chenomx software quantified results to identify the most significantly altered metabolite concentrations, allowing for metabolic explanations of the effects of NIL therapies. In this study, PLS results revealed that there are considerably distinct differences between treatment groups. Additionally, a total of 45 metabolites shown to have a high variation between groups were selected for target quantification. Using a one-way LSD ANOVA analysis, 32 metabolite concentrations were significantly altered in the OVX group. A total of 21 metabolites were altered significantly in the NIL-treatment group but later returned to normal. According to the OPLS VIP calculation, the metabolites most affected by NIL treatment were mostly involved in insulin resistance. In addition, abnormal concentration changes in lactate in the NIL-treatment group and 3-indoxylsulfate in the OVX group were observed. To our knowledge, this study is the first to address the molecular mechanism of NIL from a metabonomic perspective, and, more specifically, to establish a catalogue of endo-molecular changes effected by NIL in the regulation of oestrogen deficiency disorder.

Estradiol Binds to Insulin and Insulin Receptor Decreasing Insulin Binding in vitro

RATIONALE

Insulin (INS) resistance associated with hyperestrogenemias occurs in gestational diabetes mellitus, polycystic ovary syndrome, ovarian hyperstimulation syndrome, estrogen therapies, metabolic syndrome, and obesity. The mechanism by which INS and estrogen interact is unknown. We hypothesize that estrogen binds directly to INS and the insulin receptor (IR) producing INS resistance.

OBJECTIVES

To determine the binding constants of steroid hormones to INS, the IR, and INS-like peptides derived from the IR; and to investigate the effect of estrogens on the binding of INS to its receptor.

METHODS

Ultraviolet spectroscopy, capillary electrophoresis, and NMR demonstrated estrogen binding to INS and its receptor. Horse-radish peroxidase-linked INS was used in an ELISA-like procedure to measure the effect of estradiol on binding of INS to its receptor.

MEASUREMENTS

Binding constants for estrogens to INS and the IR were determined by concentration-dependent spectral shifts. The effect of estradiol on INS binding to its receptor was determined by shifts in the INS binding curve.

MAIN RESULTS

Estradiol bound to INS with a K d of 12 × 10(-9) M and to the IR with a K d of 24 × 10(-9) M, while other hormones had significantly less affinity. Twenty-two nanomolars of estradiol shifted the binding curve of INS to its receptor 0.8 log units to the right.

CONCLUSION

Estradiol concentrations in hyperestrogenemic syndromes may interfere with INS binding to its receptor producing significant INS resistance.

Metabolic disruption in male mice due to fetal exposure to low but not high doses of bisphenol A (BPA): evidence for effects on body weight, food intake, adipocytes, leptin, adiponectin, insulin and glucose regulation

Exposure to bisphenol A (BPA) is implicated in many aspects of metabolic disease in humans and experimental animals. We fed pregnant CD-1 mice BPA at doses ranging from 5 to 50,000μg/kg/day, spanning 10-fold below the reference dose to 10-fold above the currently predicted no adverse effect level (NOAEL). At BPA doses below the NOAEL that resulted in average unconjugated BPA between 2 and 200pg/ml in fetal serum (AUC0-24h), we observed significant effects in adult male offspring: an age-related change in food intake, an increase in body weight and liver weight, abdominal adipocyte mass, number and volume, and in serum leptin and insulin, but a decrease in serum adiponectin and in glucose tolerance. For most of these outcomes non-monotonic dose-response relationships were observed; the highest BPA dose did not produce a significant effect for any outcome. A 0.1-μg/kg/day dose of DES resulted in some but not all low-dose BPA outcomes.

The role of estrogens in control of energy balance and glucose homeostasis

Estrogens play a fundamental role in the physiology of the reproductive, cardiovascular, skeletal, and central nervous systems. In this report, we review the literature in both rodents and humans on the role of estrogens and their receptors in the control of energy homeostasis and glucose metabolism in health and metabolic diseases. Estrogen actions in hypothalamic nuclei differentially control food intake, energy expenditure, and white adipose tissue distribution. Estrogen actions in skeletal muscle, liver, adipose tissue, and immune cells are involved in insulin sensitivity as well as prevention of lipid accumulation and inflammation. Estrogen actions in pancreatic islet β-cells also regulate insulin secretion, nutrient homeostasis, and survival. Estrogen deficiency promotes metabolic dysfunction predisposing to obesity, the metabolic syndrome, and type 2 diabetes. We also discuss the effect of selective estrogen receptor modulators on metabolic disorders.

Intrahypothalamic estradiol regulates glucose metabolism via the sympathetic nervous system in female rats

Long-term reduced hypothalamic estrogen signaling leads to increased food intake and decreased locomotor activity and energy expenditure, and ultimately results in obesity and insulin resistance. In the current study, we aimed to determine the acute obesity-independent effects of hypothalamic estrogen signaling on glucose metabolism. We studied endogenous glucose production (EGP) and insulin sensitivity during selective modulation of systemic or intrahypothalamic estradiol (E2) signaling in rats 1 week after ovariectomy (OVX). OVX caused a 17% decrease in plasma glucose, which was completely restored by systemic E2. Likewise, the administration of E2 by microdialysis, either in the hypothalamic paraventricular nucleus (PVN) or in the ventromedial nucleus (VMH), restored plasma glucose. The infusion of an E2 antagonist via reverse microdialysis into the PVN or VMH attenuated the effect of systemic E2 on plasma glucose. Furthermore, E2 administration in the VMH, but not in the PVN, increased EGP and induced hepatic insulin resistance. E2 administration in both the PVN and the VMH resulted in peripheral insulin resistance. Finally, sympathetic, but not parasympathetic, hepatic denervation blunted the effect of E2 in the VMH on both EGP and hepatic insulin sensitivity. In conclusion, intrahypothalamic estrogen regulates peripheral and hepatic insulin sensitivity via sympathetic signaling to the liver.

Estradiol favors glucose oxidation in gastrocnemius muscle through modulation of insulin signaling molecules in adult female rats

INTRODUCTION

Estrogens are steroid compounds that are synthesized in ovary, testis, adrenal cortex and other tissues. Several surveys have shown the potential relationship between estradiol and glucose homeostasis in physiological and pathological states such as the menstrual cycle, gestation, gestational diabetes mellitus and polycystic ovarian syndrome (PCOS). All these states are characterized by variability in estradiol level and some degree of insulin resistance. Skeletal muscle plays a crucial role in maintaining systemic glucose metabolism through activation of assorted signaling molecules.

OBJECTIVES

The present study is to evaluate the aftermath of ovariectomy and estradiol replacement on few insulin signaling molecules and GLUT4 protein expression and glucose oxidation in gastrocnemius muscle of adult albino rat.

DESIGN

In the present study, Wistar strain albino rats were selected and divided into three groups. Group I: Control (sham-operated). Group II: Ovariectomized and Group III: Estradiol was replaced 7 days after ovariectomy at a dose of 6 μg/kg boxpression of insulin signaling molecules (western blot) and glucose oxidation were assessed.

RESULTS

Ovariectomy significantly depleted the expression of insulin signaling molecules and glucose oxidation whereas estradiol replacement improved them. Thus, estradiol helps in maintaining glucose level in ovariectomized rats. Results of this study suggest that estradiol improves the expression of insulin signaling molecules in skeletal muscle and thereby it prevents the onset of insulin resistance as a result of estradiol deficiency.

Treatment with a constitutive androstane receptor ligand ameliorates the signs of preeclampsia in high-fat diet-induced obese pregnant mice

Constitutive androstane receptor (CAR) has been reported to decrease insulin resistance, while obesity and insulin resistance may also be involved in the pathogenesis of preeclampsia. We examined whether a CAR ligand, 1,4-bis(2-(3,5-dichloropyridyloxy)) benzene (TCPOBOP), can ameliorate the signs of preeclampsia in high-fat diet (HFD)-induced obese pregnant mice to examine a possibility of CAR as a therapeutic target. We employed six groups including non-pregnant, HFD-fed or control diet-fed pregnant mice with or without TCPOBOP treatment (n=6). In HFD pregnant mice, insulin resistance increased with increasing expression of gluconeogenic and lipogenic genes and abnormal adipocytokine levels. TCPOBOP treatment, which was once-weekly intraperitoneal injections (0.5 mg/kg) and started at day 0.5 of pregnancy, improved glucose tolerance with significant changes of gluconeogenic, lipogenic and adipocytokine genes. HFD pregnant mice had hypertension and proteinuria, while TCPOBOP treatment ameliorated these signs. Our data suggested CAR might be a potential therapeutic target for obese preeclampsia patients with insulin resistance.

Potential role of estradiol and progesterone in insulin resistance through constitutive androstane receptor

Normal pregnancy is characterized by insulin resistance, which contributes to the development of gestational diabetes mellitus and preeclampsia by incompletely understood mechanisms. The constitutive androstane receptor (CAR) may participate in insulin resistance in pregnancy, and sex steroids, estradiol (E(2)) and progesterone, may also be involved. We applied glucose and insulin tolerance tests and measured the expression of gluconeogenic and lipogenic genes in the livers of oophorectomized mice treated with E(2) and progesterone with or without CAR ligands. We also investigated how E(2) and progesterone affected CAR-mediated signaling and the activity of transcription factors in gluconeogenesis in vitro. Mice with the concentrations of E(2) and progesterone within normal physiological range during pregnancy exhibited increased insulin resistance along with increased expression of gluconeogenic and lipogenic genes, and CAR activation rescued the abnormal glucose metabolism. In HepG2 cells, CAR ligands suppressed the gluconeogenic and lipogenic gene expression in the presence of E(2) and/or progesterone. DNA affinity immunoblotting and chromatin immunoprecipitation assay revealed that CAR ligand enhanced the recruitment of the gluconeogenic transcription factors, forkhead box O1 (FOXO1) and hepatocyte nuclear factor 4α (HNF4α), but sex steroids suppressed these recruitments on the CAR responsive element. Moreover, CAR ligand suppressed the recruitment of FOXO1 and HNF4α on their responsive element in gluconeogenic gene promoters and E(2) and progesterone augmented these recruitments on their responsive element. Taken together, these findings suggest that the activation of CAR-mediated signaling may ameliorate insulin resistance under relatively high concentrations of E(2) and progesterone, which were compatible with pregnancy via decreased activities of transcription factors in gluconeogenesis in combination with CAR.

Estrogen receptors and the metabolic network

The metabolic syndrome has reached pandemic level worldwide, and evidence is that estradiol plays a key role in its development. The discovery of the second estrogen receptor, ERβ, in tissues previously not considered targets of estradiol was a breakthrough in endocrinology. In the present review, we discuss how the presence of ERβ and the previously described ERα in tissues involved in glucose and lipid homeostasis (brain, skeletal muscle, adipose tissue, pancreas, liver, and heart) may have important implications to risk factors associated with the metabolic syndrome. Imbalance of ERα/ERβ ratio in this "metabolic network" may lead to the metabolic syndrome.

The association of endogenous sex hormones, adiposity, and insulin resistance with incident diabetes in postmenopausal women

CONTEXT

In postmenopausal women, endogenous bioavailable testosterone (T) and estradiol (E2) have been positively associated, and SHBG has been negatively associated, with incident type 2 diabetes (T2DM). Previous studies have not explored possible factors explaining these relationships.

OBJECTIVE

Our objective was to examine the association of endogenous sex hormones with incident T2DM in postmenopausal women and possible explanatory factors.

DESIGN, SETTING, AND PARTICIPANTS

The Multi-Ethnic Study of Atherosclerosis (MESA) is a prospective study that included 1612 postmenopausal women aged 45-84 yr, followed between the years 2000-2006, who were not taking hormone replacement therapy, had no prevalent cardiovascular disease or diabetes, and had complete ascertainment of sex hormones.

MAIN OUTCOME MEASURES

T2DM was defined based on fasting glucose and/or treatment for diabetes.

RESULTS

There were 116 incident cases of diabetes during follow-up. Across higher quartiles of bioavailable T and E2 and lower quartiles of SHBG, we found significantly greater hazards of developing incident T2DM (all P for trend <or=0.001). After adjustment for body mass index and insulin resistance estimated by homeostasis model assessment of insulin resistance, bioavailable T was no longer associated with incident T2DM. The associations of E2 and SHBG with incident T2DM were partially explained by body mass index and insulin resistance but persisted in fully adjusted models (both P for trend <0.02). Dehydroepiandrosterone had no relationship with incident T2DM.

CONCLUSIONS

Adiposity and insulin resistance explained most of the association of bioavailable T but only partially explained the associations of E2 and SHBG with incident T2DM among postmenopausal women.