17beta-estradiol supplementation attenuates ovariectomy-induced increases in ATGL signaling and reduced perilipin expression in visceral adipose tissue

Effects of follicle-stimulating hormone on energy balance and tissue metabolic health after loss of ovarian function

Loss of ovarian function imparts increased susceptibility to obesity and metabolic disease. These effects are largely attributed to decreased estradiol (E2), but the role of increased follicle-stimulating hormone (FSH) in modulating energy balance has not been fully investigated. Previous work that blocked FSH binding to its receptor in mice suggested this hormone may play a part in modulating body weight and energy expenditure after ovariectomy (OVX). We used an alternate approach to isolate the individual and combined contributions of FSH and E2 in mediating energy imbalance and changes in tissue-level metabolic health. Female Wistar rats were ovariectomized and given the gonadotropin releasing hormone (GnRH) antagonist degarelix to suppress FSH production. E2 and FSH were then added back individually and in combination for a period of 3 wk. Energy balance, body mass composition, and transcriptomic profiles of individual tissues were obtained. In contrast to previous studies, suppression and replacement of FSH in our paradigm had no effect on body weight, body composition, food intake, or energy expenditure. We did, however, observe organ-specific effects of FSH that produced unique transcriptomic signatures of FSH in retroperitoneal white adipose tissue. These included reductions in biological processes related to lipogenesis and carbohydrate transport. In addition, rats administered FSH had reduced liver triglyceride concentration (P < 0.001), which correlated with FSH-induced changes at the transcriptomic level. Although not appearing to modulate energy balance after loss of ovarian function in rats, FSH may still impart tissue-specific effects in the liver and white adipose tissue that might affect the metabolic health of those organs.NEW & NOTEWORTHY We find no effect of follicle-stimulating hormone (FSH) on energy balance using a novel model in which rats are ovariectomized, subjected to gonadotropin-releasing hormone antagonism, and systematically given back FSH by osmotic pump. However, tissue-specific effects of FSH on adipose tissue and liver were observed in this study. These include unique transcriptomic signatures induced by the hormone and a stark reduction in hepatic triglyceride accumulation.

The advantages of physical exercise as a preventive strategy against NAFLD in postmenopausal women

BACKGROUND

The prevalence and severity of nonalcoholic fatty liver disease (NAFLD) increase in women after menopause. This narrative review discusses the causes and consequences of NAFLD in postmenopausal women and describes how physical activity can contribute to its prevention.

METHODS

The authors followed the narrative review method to perform a critical and objective analysis of the current knowledge on the topic. The Medical Subject Heading keywords 'physical exercise', 'menopause', 'hormone replacement therapy', 'estradiol' and 'NAFLD' were used to establish a conceptual framework. The databases used to collect relevant references included Medline and specialized high-impact journals.

RESULTS

Higher visceral adiposity, higher rate of lipolysis in adipose tissue after oestrogen drop and changes in the expression of housekeeping proteins involved in hepatic lipid management are observed in women after menopause, contributing to NAFLD. Excessive liver steatosis leads to hepatic insulin resistance, oxidative stress and inflammation, accelerating NAFLD progression. Physical activity brings beneficial effects against several postmenopausal-associated complications, including NAFLD progression. Aerobic and resistance exercises partially counteract alterations induced by metabolic syndrome in sedentary postmenopausal women, impacting NAFLD progression and severity.

CONCLUSIONS

With the increased global obesity epidemic in developing countries, NAFLD is becoming a severe problem with increased prevalence in women after menopause. Evidence shows that physical activity may delay NAFLD development and severity in postmenopausal women, although the prescription of age-appropriate physical activity programmes is advisable to assure the health benefits.

Body composition and cardiometabolic health across the menopause transition

Every year, 2 million women reach menopause in the United States, and they may spend 40% or more of their life in a postmenopausal state. In the years immediately preceding menopause-known as the menopause transition (or perimenopause)-changes in hormones and body composition increase a woman's overall cardiometabolic risk. In this narrative review, we summarize the changes in weight, body composition, and body fat distribution, as well as the changes in energy intake, energy expenditure, and other cardiometabolic risk factors (lipid profile, glucose metabolism, sleep health, and vascular function), that occur during the menopause transition. We also discuss the benefits of lifestyle interventions in women in the earlier stages of menopause before these detrimental changes occur. Finally, we discuss how to include perimenopausal women in research studies so that women across the life-span are adequately represented.

Adipose Triglyceride Lipase in Hepatic Physiology and Pathophysiology

The liver is extremely active in oxidizing triglycerides (TG) for energy production. An imbalance between TG synthesis and hydrolysis leads to metabolic disorders in the liver, including excessive lipid accumulation, oxidative stress, and ultimately liver damage. Adipose triglyceride lipase (ATGL) is the rate-limiting enzyme that catalyzes the first step of TG breakdown to glycerol and fatty acids. Although its role in controlling lipid homeostasis has been relatively well-studied in the adipose tissue, heart, and skeletal muscle, it remains largely unknown how and to what extent ATGL is regulated in the liver, responds to stimuli and regulators, and mediates disease progression. Therefore, in this review, we describe the current understanding of the structure–function relationship of ATGL, the molecular mechanisms of ATGL regulation at translational and post-translational levels, and—most importantly—its role in lipid and glucose homeostasis in health and disease with a focus on the liver. Advances in understanding the molecular mechanisms underlying hepatic lipid accumulation are crucial to the development of targeted therapies for treating hepatic metabolic disorders.

Recent Update on the Molecular Mechanisms of Gonadal Steroids Action in Adipose Tissue

The gonadal steroids, including androgens, estrogens and progestogens, are involved in the control of body fat distribution in humans. Nevertheless, not only the size and localization of the fat depots depend on the sex steroids levels, but they can also highly affect the functioning of adipose tissue. Namely, the gonadocorticoids can directly influence insulin signaling, lipid metabolism, fatty acid uptake and adipokine production. They may also alter energy balance and glucose homeostasis in adipocytes in an indirect way, e.g., by changing the expression level of aquaglyceroporins. This work presents the recent advances in understanding the molecular mechanism of how the gonadal steroids influence the functioning of adipose tissue leading to a set of detrimental metabolic consequences. Special attention is given here to highlighting the sexual dimorphism of adipocyte functioning in terms of health and disease. Particularly, we discuss the molecular background of metabolic disturbances occurring in consequence of hormonal imbalance which is characteristic of some common endocrinopathies such as the polycystic ovary syndrome. From this perspective, we highlight the potential drug targets and the active substances which can be used in personalized sex-specific management of metabolic diseases, in accord with the patient's hormonal status.

RXRα Positively Regulates Expression of the Chicken PLIN1 Gene in a PPARγ-Independent Manner and Promotes Adipogenesis

Perilipin1 (PLIN1), the most abundant lipid droplet (LD)-associated protein, plays a vital role in regulating lipid storage and breakdown in adipocytes. Recently, we found that the overexpression of PLIN1 promotes chicken preadipocyte lipid accumulation. However, the mechanisms by which transcription of the chicken PLIN1 gene is regulated remain unknown. In this study, we investigated the role of retinoid X receptor α (RXRα) in transcription of the chicken PLIN1 gene. Notably, reporter gene and expression assays showed that RXRα activates transcription of the chicken PLIN1 gene in a PPARγ-independent manner. Furthermore, promoter deletion and electrophoretic mobility shift assay (EMSA) analysis revealed that the chicken PLIN1 gene promoter region (-774/-785) contains an RXRα-binding site. Further study demonstrated that RXRα overexpression promotes differentiation of an immortalized chicken preadipocyte cell line (ICP1), causing a concomitant increase in PLIN1 transcripts. Taken together, our results show for the first time that RXRα activates transcription of the chicken PLIN1 gene in a PPARγ-independent manner, which might be at least in part responsible for RXRα-induced adipogenesis.

Influence of Estradiol Status on Physical Activity in Premenopausal Women

PURPOSE

This study aimed to determine the effects of 5 months of ovarian hormone suppression in premenopausal women on objectively measured physical activity (PA).

METHODS

Participants (age, 35 ± 8 yr; body mass index, 27 ± 6 kg·m) received monthly intramuscular injections of gonadotropin-releasing hormone agonist (GnRHAG) therapy, which suppresses pituitary gonadotropins and results in suppression of ovarian sex hormones. Women were randomized to receive concurrent transdermal E2 (GnRHAG + E2; n = 30) or placebo (GnRHAG + PL, n = 31). PA was assessed for 1 wk before and during each month of the 5-month intervention using a hip-worn accelerometer (Actical, Mini Mitter Co., Inc., Bend, OR). Estimates of time spent in sedentary, light, and moderate-to-vigorous PA (MVPA) were derived using a previously published equation. Subsets of participants in each group were also randomized to a supervised progressive resistance exercise training program.

RESULTS

Total MVPA tended toward being higher (P = 0.08) in the GnRHAG + E2 group at month 4. There were no significant effects of intervention or time in sedentary or light PA. In the subset of women who did not participate in structured exercise training for which Actical data were obtained (n = 16 in each group), total MVPA was higher at month 4 (P = 0.01).

CONCLUSIONS

PA levels seem to be maintained at a higher level in women undergoing pharmacological suppression of ovarian function with E2 add-back when compared with women treated with placebo. These data provide proof-of-concept data that E2 contributes to the regulation of PA in humans. However, given the exploratory nature of this study, future confirmatory investigations will be necessary.

Metabolic Reprogramming in Breast Cancer and Its Therapeutic Implications

Current standard-of-care (SOC) therapy for breast cancer includes targeted therapies such as endocrine therapy for estrogen receptor-alpha (ERα) positive; anti-HER2 monoclonal antibodies for human epidermal growth factor receptor-2 (HER2)-enriched; and general chemotherapy for triple negative breast cancer (TNBC) subtypes. These therapies frequently fail due to acquired or inherent resistance. Altered metabolism has been recognized as one of the major mechanisms underlying therapeutic resistance. There are several cues that dictate metabolic reprogramming that also account for the tumors’ metabolic plasticity. For metabolic therapy to be efficacious there is a need to understand the metabolic underpinnings of the different subtypes of breast cancer as well as the role the SOC treatments play in targeting the metabolic phenotype. Understanding the mechanism will allow us to identify potential therapeutic vulnerabilities. There are some very interesting questions being tackled by researchers today as they pertain to altered metabolism in breast cancer. What are the metabolic differences between the different subtypes of breast cancer? Do cancer cells have a metabolic pathway preference based on the site and stage of metastasis? How do the cell-intrinsic and -extrinsic cues dictate the metabolic phenotype? How do the nucleus and mitochondria coordinately regulate metabolism? How does sensitivity or resistance to SOC affect metabolic reprogramming and vice-versa? This review addresses these issues along with the latest updates in the field of breast cancer metabolism.

Effects of Urtica dioica hydro-alcoholic extract on blood serum glucose and lipid profiles of female Wistar rats with long-term estrogen deficiency

In this study, the effects of Urtica dioica hydro-alcoholic extract were investigated on the blood glucose and lipid profiles of female ovariectomized and non-ovariectomized rats. In total, 32 adult female rats were divided into four groups (eight each) including control and ovariectomy groups as well as non-ovariectomy and ovariectomy groups treated with 200 mg kg^-1 of Urtica dioica extract orally in the last five weeks of the study starting from the week 56^th. The duration of the study was 60 weeks. Glucose, serum lipid profiles and pancreatic pathological alterations were determined in these groups at the end of experiment. Serum glucose, triglyceride (TG), very-low-density lipoprotein (VLDL), and TG/high-density lipoprotein (HDL) ratio indicated a significant increase in the healthy female rats under treatment with Urtica dioica extract compared to others. The TG, cholesterol, HDL, low-density lipoprotein (LDL) and VLDL showed a significant increase in menopaused rats compared to others. The interaction of consuming Urtica dioica extract and ovariectomy caused significant decreases in glucose, TG, VLDL, HDL/LDL ratio and TG/HDL ratio. Consumption of Urtica dioica extract by non-menopaused rats damaged the beta cells in Langerhans islets. Results of the present study revealed that the consumption of Urtica dioica extract is not beneficial and has diabetogenic effects in female non-ovariectomized rats compared to ovariectomized ones.

Adipocytes ESR1 Expression, Body Fat and Response to Testosterone Therapy in Hypogonadal Men Vary According to Estradiol Levels

Estradiol (E2), mainly produced from Testosterone (T) in men, promotes visceral lipolysis. However, high visceral fat and hyperestrogenemia are features of obese hypogonadal (HG) men. Our study objectives are to evaluate relationships between circulating E2 and: (1) fat mass; (2) Estrogen Receptor α (ESR1) expression in subcutaneous adipose tissue; (3) changes in body fat after 6 months (M) of T therapy in HG men.

HYPOTHESES

(1) existence of a range of circulating E2 associated with better body composition; (2) serum E2 determines tissue E2 sensitivity which affects response to T therapy. Men 40⁻74 years old, T < 300 (ng/dL), given T-cypionate for 6 months. Subjects were divided into 4-E2 categories: (1) <10.0; (2) 10.0⁻15.9; (3) 16.0⁻19.9; (4) ≥20.0 (pg/mL). Body composition (DXA), fat biopsies (liposuction), gene expression (qPCR), serum E2 and T (LC/MS), at baseline and 6 months. We enrolled 105 men; 90 completed the study. Group 2 had lower total and truncal fat mass (p < 0.01) but higher % lean mass (p < 0.001). ESR1 mRNA was the highest in group 1 (p = 0.01). At 6 months, group 1 had higher reduction in total (p = 0.03) and truncal (p = 0.01) fat. In conclusion, serum E2 = 10⁻15.9 (pg/mL) is associated with the best body composition profile in HG men; however, those with E2 < 10 (pg/mL) had the best response (greater fat loss) to T replacement possibly because of greater E2 sensitivity.

Membrane-Initiated Estrogen Receptor Signaling Mediates Metabolic Homeostasis via Central Activation of Protein Phosphatase 2A

Women gain weight and their diabetes risk increases as they transition through menopause; these changes can be partly reversed by hormone therapy. However, the underlying molecular mechanisms mediating these effects are unknown. A novel knock-in mouse line with the selective blockade of the membrane-initiated estrogen receptor (ER) pathway was used, and we found that the lack of this pathway precipitated excessive weight gain and glucose intolerance independent of food intake and that this was accompanied by impaired adaptive thermogenesis and reduced physical activity. Notably, the central activation of protein phosphatase (PP) 2A improved metabolic disorders induced by the lack of membrane-initiated ER signaling. Furthermore, the antiobesity effect of estrogen replacement in a murine menopause model was abolished by central PP2A inactivation. These findings define a critical role for membrane-initiated ER signaling in metabolic homeostasis via the central action of PP2A.

Fat Mass Follows a U-Shaped Distribution Based on Estradiol Levels in Postmenopausal Women

OBJECTIVE

Estradiol (E2) regulates adipose tissue resulting in increased fat mass (FM) with declining E2. However, increased visceral fat and hyperestrogenemia are features of obese individuals. It is possible that adipocytes in obese individuals are less sensitive to E2 resulting in higher FM. Our objective is to identify the range of serum E2 for which postmenopausal women have the lowest FM and best body composition.

METHODS

Cross-sectional data from 252 community-dwelling postmenopausal women, 42-90 years old. Subjects were stratified into categories of E2 (pg/ml): (1) ≤10.5; (2) 10.6-13.9; (3) 14.0-17.4; and (4) ≥17.5. Body composition by dual-energy X-ray absorptiometry. Serum E2 by radioimmunoassay. Between-group comparisons by analysis of covariance.

RESULTS

E2 linearly increased with increasing body weight and body mass index (r = 0.15 and p = 0.01 for both), but not with total FM (kg) or % FM (r = 0.07, p = 0.34 and r = -0.04, p = 0.56, respectively). However, total FM (kg) followed a U-shaped distribution and was significantly lower in group 3 (27.6 ± 10.6), compared with groups 1: (34.6 ± 12.5), 2: (34.0 ± 12.4), and 4: (37.0 ± 10.6), p = 0.005. % FM was also lowest in group 3. While fat-free mass (FFM, kg) increased with increasing E2 (p < 0.001), % FFM was highest in group 3.

CONCLUSION

In our population of postmenopausal women, FM followed a U-shaped distribution according to E2 levels. E2 between 14.0 and 17.4 pg/ml is associated with the best body composition, i.e., lowest total and % FM and highest % FFM. Given the role of E2 in regulating body fat, high FM at the high end of the E2 spectrum may suggest reduced E2 sensitivity in adipocytes among obese postmenopausal women.

CLINICAL TRIALS

ClinicalTrials.gov identifier: NCT00146107.

17β-estradiol lowers triglycerides in adipocytes via estrogen receptor α and it may be attenuated by inflammation

Background

Estrogen was reported to protect against obesity, however the mechanism remains unclear. We aimed to investigate the impact of 17β-estradiol (17β-E2) on triglyceride metabolism in adipocytes with or without lipopolysacchride (LPS) stimulating, providing novel potential mechanism for estrogen action.

Methods

3T3-L1 adipocytes were cultured and differentiated into mature adipocytes in vitro. The differentiated 3T3-L1 cells were divided into six groups: (i) control group, treated with 0.1% DMSO alone; (ii) 17β-E2 group, treated with 1, 0.1, or 0.001 μM 17β-E2 for 48 h; (iii) 17β-E2 plus MPP group, pre-treated with 10 μM MPP (a selective ERα receptor inhibitor) for 1 h, then incubated with 1 μM 17β-E2 for 48 h; (iv) 17β-E2 plus PHTPP group, pre-treated with 10 μM PHTPP (a selective ERβ receptor inhibitor), then incubated with 1 μM 17β-E2 for 48 h; (v) LPS group, pre-treated with 100 ng/mL LPS for 24 h, then cells were washed by PBS for 3 times and incubated with 0.1% DMSO alone for 48 h; (vi) 17β-E2 plus LPS group, pre-treated with 100 ng/mL LPS for 24 h, then cells were washed by PBS for 3 times and incubated with 1 μM 17β-E2 for 48 h. The levels of triglyceride and adipose triglyceride lipase (ATGL) in differentiated 3T3-L1 cells and the concentrations of interleukin-6 (IL-6) in culture medium were measured.

Results

Comparing with control group, 1 μM and 0.1 μM 17β-E2 decreased the intracellular TG levels by about 20% and 10% respectively (all P < 0.05). The triglyceride-lowing effect of 17β-E2 in differentiated 3T3-L1 cells was abolished by ERα antagonist MPP but not ERβ antagonist PHTPP. Comparing with control group, the IL-6 levels were significantly higher in the culture medium of the cultured differentiated 3T3-L1 cells in LPS group and 17β-E2 + LPS group (all P < 0.05). And, the IL-6 levels were similar in LPS group and 17β-E2 + LPS group (P > 0.05). There was no significant difference in the triglyceride contents of differentiated 3T3-L1 cells among control group, LPS group and 17β-E2 + LPS group (all P > 0.05). ATGL expression in 17β-E2 group was significantly higher than control group (P < 0.05), which was abolished by ERα antagonist MPP or LPS.

Conclusions

17β-E2 increased ATGL expression and lowered triglycerides in adipocytes but not in LPS stimulated adipocytes via estrogen ERα.

Estradiol does not directly regulate adipose lipolysis

The mechanisms by which estradiol modulates adipose lipolysis are poorly understood. We sought to measure basal and β₃-stimulated indices of lipoysis (FFAs, glycerol) in vivo in E2 deficient or supplemented rats, and ex vivo with direct acute E2 exposure. For 2 weeks, ovariectomized (OVX) and OVX rats treated with a daily oral dose of E2 (OVX E2) were pairfed to SHAM controls (n = 12 per group). Adipocyte size was modestly (∼40%) increased in OVX rats, but did not reach significance (p = 0.2). After 2 weeks, half of the animals in each group received an in vivo injection of saline or 1 mg/kg of the β3 agonist CL 316, 243. Serum FFA concentrations, but not glycerol, were lower in OVX and OVX E2 rats compared with SHAM controls (p = 0.02). A significant CL response was present in all groups (p<0.001) and HSL activation was unaffected by OVX or OVX E2 in retroperitoneal (r.p.) or inguinal (iWAT) adipose depots in vivo. Ex vivo, CL increased FFA and glycerol accumulation in the media as well as HSL phosphorylation by several fold in r.p. and iWAT explants, but responses from OVX and OVX E2 rats were comparable to SHAMs. To assess whether E2 can directly affect lipolysis, r.p. and iWAT tissue was treated with E2, CL or E2 + CL for 2, 4 or 8 hours using adipose tissue organ culture. CL stimulated FFA release (p<0.001), but was unaffected by E2. Overall, our results indicate that E2 does not directly regulate adipose tissue lipolysis.

The presence of the ovary prevents hepatic mitochondrial oxidative stress in young and aged female mice through glutathione peroxidase 1

BACKGROUND

For unknown reasons a woman's risk for developing Metabolic Syndrome (MetS) increases dramatically with age and/or loss of ovarian function. The MetS is characterized by hepatic insulin resistance (IR), which is strongly associated with intrahepatic lipid (IHL) accumulation, mitochondrial dysfunction, and oxidative stress. Although circumstantial evidence suggests that the endocrine function of the ovary can directly impact hepatic mitochondrial function, this hypothesis remains untested. Thus, the purpose of this study was to assess the influence of age and secretory function of the ovary on mechanisms that regulate hepatic mitochondrial function.

METHODS

Adult (10 week-old) and aged (88 week-old) female C57BL/6 mice were separated into two groups to undergo bilateral ovariectomy (OVX) or control surgery (SHAM). Eight weeks after surgery hepatic tissue was removed for measurements of total IHL and fatty acid species within hepatic triglycerides, mitochondrial function, and reactive oxygen species (ROS) production.

RESULTS

Hepatic IHL content was not affected by OVX, but was increased by age. OVX had no effect on mitochondrial respiration, however, hepatic mitochondria from aged mice had lower O2 consumption, lower complex IV and higher complex I content. Mitochondrial H2O2 production was highest in OVX groups and exacerbated by age, while mitochondrial lipid peroxidation was highest in the aged mice and exacerbated by OVX. Regardless of age, OVX resulted in lower mitochondrial content of antioxidant glutathione peroxidase 1 (Gpx1). Isolated liver tissue from a sub-set of animals were acutely treated with conditioned ovarian media which increased Gpx1 mRNA expression compared to vehicle treated liver tissue.

CONCLUSION

Ovarian secretory function is necessary for the maintenance of hepatic ROS buffering capacity in the mitochondria, while age significantly influences mitochondrial respiration. These data suggest that when age is coupled with loss of ovarian function there is an increased risk for developing hepatic mitochondrial dysfunction, which may influence the onset of metabolic disease. Thus, in females there is critical organ cross-talk occurring between hepatic tissue and the ovary that impacts hepatic mitochondrial function.

Regulation of energy expenditure by estradiol in premenopausal women

Suppressing sex hormones in women for 1 wk reduces resting energy expenditure (REE). The effects of more chronic suppression on REE and other components of total energy expenditure (TEE), and whether the reduction in REE is specifically due to loss of estradiol (E2), are not known. We compared the effects of 5 mo of sex hormone suppression (gonadotropin releasing hormone agonist therapy, GnRHAG) with placebo (PL) or E2 add-back therapy on REE and the components of TEE. Premenopausal women received GnRHAG (leuprolide acetate 3.75 mg/mo) and were randomized to receive transdermal therapy that was either E2 (0.075 mg/d; n = 24; means ± SD, aged = 37 ± 8 yr, BMI = 27.3 ± 6.2 kg/m(2)) or placebo (n = 21; aged = 34 ± 9 yr, BMI = 26.8 ± 6.2 kg/m(2)). REE was measured by using a metabolic cart, and TEE, sleep EE (SEE), exercise EE (ExEE, 2 × 30 min bench stepping), non-Ex EE (NExEE), and the thermic effect of feeding (TEF) were measured by using whole room indirect calorimetry. REE decreased in GnRHAG+PL [mean (95% CI), -54 (-98, -15) kcal/d], but not GnRHAG+E2 [+6 (-33, +45) kcal/d] (difference in between-group changes, P < 0.05). TEE decreased in GnRHAG+PL [-128 (-214, -41) kcal/d] and GnRHAG+E2 [-96 (-159, -32) kcal/d], with no significant difference in between-group changes (P = 0.55). SEE decreased similarly in both GnRHAG+PL [-0.07 (-0.12, -0.03) kcal/min] and GnRHAG+E2 [-0.07 (-0.12, -0.02) kcal/min]. ExEE decreased in GnRHAG+PL [-0.46 (-0.79, -0.13) kcal/min], but not GnRHAG+E2 [-0.30 (-0.65, +0.06) kcal/min]. There were no changes in TEF or NExEE in either group. In summary, chronic pharmacologic suppression of sex hormones reduced REE and this was prevented by E2 therapy.

Similar and additive effects of ovariectomy and diabetes on insulin resistance and lipid metabolism

Type 2 diabetes mellitus (T2DM) is among the leading causes of death in postmenopausal women. The disruption of ovarian function may contribute to the incidence of T2DM. The purpose of this study was to investigate the effects of ovariectomy and T2DM on glucose and lipid homeostasis, perilipin levels in adipose tissues, as a lipolytic regulator, and levels of certain adipokines. Ovariectomized (OVX) rats were used as a model for postmenopausal women. The study was performed on sham, OVX, sham diabetic, and OVX diabetic female rats. The results indicated that ovariectomy alters adipose tissue metabolism through reducing perilipin content in white adipose tissue (WAT); however it has no effect on perilipin level in brown adipose tissue (BAT). OVX diabetic females suffer from serious metabolic disturbances, suggested by exacerbation of insulin resistance in terms of disrupted lipid profile, higher HOMA-IR, hyperinsulinemia, higher leptin, and lower adiponectin concentrations. These metabolic derangements may underlie the predisposition for cardiovascular disease in women after menopause. Therefore, for efficient treatment, the menopausal status of diabetic female should be addressed, and the order of events is of great importance because ovariectomy following development of diabetes has more serious complications compared to development of diabetes as result of menopause.

The flavonoid, naringenin, decreases adipose tissue mass and attenuates ovariectomy-associated metabolic disturbances in mice

Objective

Adverse metabolic changes associated with loss of ovarian function increase the risk of developing metabolic syndrome and non-alcoholic fatty liver disease (NAFLD) in postmenopausal women. Naringenin improves metabolic disturbances in vitro and in vivo. In the present study, we tested the effects of naringenin on metabolic disturbances resulting from estrogen deficiency in ovariectomized mice.

Materials/methods

Ovariectomized C57BL/6 J female mice were fed a control diet (10% calories from fat) for 11 weeks. Mice either continued on the control diet (n = 9) or were switched to the control diet supplemented with 3% naringenin (n = 10) for the next 11 weeks. Energy expenditure was measured by indirect calorimetry and activity was monitored by infrared beam breaks. Intra-abdominal and subcutaneous adiposity was evaluated by magnetic resonance imaging (MRI). Blood biochemical measures of metabolic response included glucose, insulin, adipokines, and lipids. Lipid content in liver and muscle and expression of relevant genes in adipose tissue, liver, and muscle were quantified.

Results

Ovariectomized mice fed naringenin exhibited lower fasting glucose and insulin levels compared to controls, with over 50% reduction of intra-abdominal and subcutaneous adiposity. Plasma leptin and leptin mRNA in adipose depots were also decreased in mice fed a naringenin diet. Monocyte chemoattractant protein-1 (MCP1/Ccl2) and interleukin 6 (IL-6/Il6) mRNA expression levels were significantly lower in perigonadal adipose tissue of naringenin-supplemented mice. We also observed that mice fed a naringenin diet had less hepatic lipid accumulation with corresponding alterations of hepatic gene expression associated with de novo lipogenesis, fatty acid oxidation, and gluconeogenesis.

Conclusion

Dietary naringenin attenuates many of the metabolic disturbances associated with ovariectomy in female mice.

Electronic supplementary material

The online version of this article (doi:10.1186/1743-7075-12-1) contains supplementary material, which is available to authorized users.

Ovarian-cell-like cells from skin stem cells restored estradiol production and estrus cycling in ovariectomized mice

Reduction of estradiol production and high serum concentrations of follicular stimulating hormone (FSH) are endocrine disorders associated with premature ovarian failure. Here, we report that transplantation of ovarian-like cells differentiated from stem cells restored endogenous serum estradiol levels. Stem cells were isolated from postnatal mouse skin and differentiated into ovarian-cell-like cells that are consistent with female germ, and ovarian follicle somatic cells. The ovarian-cell-like cells were transplanted into ovariectomized mice (Cell Trans), whereas control mice were subjected to bilateral ovariectomies without cell transplantation (OVX). Using vaginal cytology analysis, it was revealed that in 13 out of 19 Cell Trans mice, estrus cycles were restored around 8 weeks after cell transplantation and were maintained until 16 weeks post-transplantation, whereas in the OVX group, all mice were arrested at metestrus/diestrus of the estrus cycle. The uterine weight in the Cell Trans group was similar to sham operation mice (Sham OP), while severe uterine atrophy and a decreased uterine weight were observed in the OVX group. Histologically, ectopic follicle-like structures and blood vessels were found within and around the transplants. At 12-14 weeks after cell transplantation, mean serum estradiol level in Cell Trans mice (178.0±35 pg/mL) was comparable to that of the Sham OP group (188.9±29 pg/mL), whereas it was lower in the OVX group (59.0±4 pg/mL). Serum FSH concentration increased in the OVX group (1.62±0.32 ng/mL) compared with the Sham OP group (0.39±0.34 ng/mL). Cell Trans mice had a similar FSH level (0.94±0.23 ng/mL; P<0.05) to Sham OP mice. Our results suggest that ovarian somatic cells differentiated from stem cells are functional in vivo. In addition to providing insights into the function of ovarian somatic cells derived from stem cells, our study may offer potential therapeutic means for patients with hypo-estradiol levels like those encountered in premature ovarian failure.

Regulation of physiological and metabolic function of muscle by female sex steroids

The ability of female sex steroids to regulate tissue function has long been appreciated; however, their role in the regulation of striated muscle function has received considerably less attention. The purpose of this symposium review was to document recent evidence indicating the role female sex steroids have in defining the functional characteristics of striated muscle. The presentations provide substantial evidence indicating that estrogens are critical to the physiological and metabolic regulations of striated muscle; thus, when considering women's health issues, striated muscle must included as an important target tissue along with other classically thought of estrogen-sensitive tissues.

Using a novel coculture model to dissect the role of intramuscular lipid load on skeletal muscle insulin responsiveness under reduced estrogen conditions

Reductions in estrogen function lead to adiposity and peripheral insulin resistance. Significant metabolic changes have been found in adipocytes and skeletal muscle with disruptions in the estrogen-signaling axis; however, it is unclear if intercellular communication exists between these tissues. The purpose of this study was to examine the impact of isolated adipocytes cocultured with single adult skeletal muscle fibers (SMF) collected from control female (SHAM) and ovariectomized female (OVX) mice. In addition, a second purpose was to compare differential effects of primary adipocytes from omental and inguinal adipose depots on SMF from these same groups. OVX SMF displayed greater lipid content, impaired insulin signaling, and lower insulin-induced glucose uptake compared with SHAM SMF without coculture. In the SHAM group, regardless of the adipose depot of origin, coculture induced greater intracellular lipid content compared with control SHAM SMF. The increased lipid in the SMF was associated with impaired insulin-induced glucose uptake when adipocytes were of omental, but not inguinal, origin. Coculture of OVX SMF with omental or inguinal adipocytes resulted in higher lipid content but no further reduction in insulin-induced glucose uptake compared with control OVX SMF. The data indicate that, in the OVX condition, there is a threshold for lipid accumulation in skeletal muscle beyond which there is no further impairment in insulin responsiveness. These results also demonstrate depot-specific effects of adipocyte exposure on skeletal muscle glucose uptake and further implicate a role for increased intracellular lipid storage in the pathogenesis of insulin resistance when estrogen levels are reduced.

Reproduction, fat metabolism, and life span: what is the connection?

Reduced reproduction is associated with increased fat storage and prolonged life span in multiple organisms, but the underlying regulatory mechanisms remain poorly understood. Recent studies in several species provide evidence that reproduction, fat metabolism, and longevity are directly coupled. For instance, germline removal in the nematode Caenorhabditis elegans promotes longevity in part by modulating lipid metabolism through effects on fatty acid desaturation, lipolysis, and autophagy. Here, we review these recent studies and discuss the mechanisms by which reproduction modulates fat metabolism and life span. Elucidating the relationship between these processes could contribute to our understanding of age-related diseases including metabolic disorders.

Ectopic lipid deposition and the metabolic profile of skeletal muscle in ovariectomized mice

Disruptions of ovarian function in women are associated with increased risk of metabolic disease due to dysregulation of peripheral glucose homeostasis in skeletal muscle. Our previous evidence suggests that alterations in skeletal muscle lipid metabolism coupled with altered mitochondrial function may also develop. The objective of this study was to use an integrative metabolic approach to identify potential areas of dysfunction that develop in skeletal muscle from ovariectomized (OVX) female mice compared with age-matched ovary-intact adult female mice (sham). The OVX mice exhibited significant increases in body weight, visceral, and inguinal fat mass compared with sham mice. OVX mice also had significant increases in skeletal muscle intramyocellular lipids (IMCL) compared with the sham animals, which corresponded to significant increases in the protein content of the fatty acid transporters CD36/FAT and FABPpm. A targeted metabolic profiling approach identified significantly lower levels of specific acyl carnitine species and various amino acids in skeletal muscle from OVX mice compared with the sham animals, suggesting a potential dysfunction in lipid and amino acid metabolism, respectively. Basal and maximal mitochondrial oxygen consumption rates were significantly impaired in skeletal muscle fibers from OVX mice compared with sham animals. Collectively, these data indicate that loss of ovarian function results in increased IMCL storage that is coupled with alterations in mitochondrial function and changes in the skeletal muscle metabolic profile.

Lipolytic signaling in response to acute exercise is altered in female mice following ovariectomy

Impaired ovarian function alters lipid metabolism, ultimately resulting in increased visceral fat mass. Currently, we have a poor understanding of alterations in signaling events regulating lipolysis after ovarian function declines. The purpose of this study was to determine if cellular mechanisms regulating lipolysis are altered in mice after ovariectomy (OVX) and if OVX mice exhibit impaired lipolytic signaling when stimulated by acute exercise. SHAM and OVX mice were divided into two groups: control (SHAM cont; OVX cont) or acute treadmill exercise (SHAM ex; OVX ex). The omental/mesenteric (O/M) fat mass of all OVX mice was significantly greater than the SHAM mice. Serum glycerol and blood glucose levels were significantly elevated in OVX cont compared to SHAM cont. Treadmill exercise increased serum glycerol levels only in SHAM mice, with no exercise-induced change detected in OVX mice. NEFA levels were significantly elevated by acute exercise in the SHAM and OVX groups. In O/M fat from both OVX groups there were significant increases in cytosolic ATGL and PLIN2 in the fat cake fraction with concurrent reductions in PLIN1 in the fat cake compared to SHAM. Further, exercise induced significant increases in HSL Ser660 phosphorylation in SHAM mice, but not OVX mice. This suggests that reduced ovarian function has significant effects on critical lipolytic cell signaling mechanisms in O/M adipose tissue.

In vivo stimulation of oestrogen receptor α increases insulin-stimulated skeletal muscle glucose uptake

Previous studies suggest oestrogen receptor α (ERα) is involved in oestrogen-mediated regulation of glucose metabolism and is critical for maintenance of whole body insulin action. Despite this, the effect of direct ERα modulation in insulin-responsive tissues is unknown. The purpose of the current study was to determine the impact of ERα activation, using the ER subtype-selective ligand propylpyrazoletriyl (PPT), on skeletal muscle glucose uptake. Two-month-old female Sprague-Dawley rats, ovariectomized for 1 week, were given subcutaneous injections of PPT (10 mg kg⁻¹), oestradiol benzoate (EB; 20 μg kg⁻¹), the ERβ agonist diarylpropionitrile (DPN, 10 mg kg⁻¹) or vehicle every 24 h for 3 days. On the fourth day, insulin-stimulated skeletal muscle glucose uptake was measured in vitro and insulin signalling intermediates were assessed via Western blotting.Activation of ERα with PPT resulted in increased insulin-stimulated glucose uptake into the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL)muscles, activation of insulin signalling intermediates (as measured by phospho-Akt (pAkt) and pAkt substrate (PAS)) and phosphorylation of AMP-activated protein kinase (AMPK). GLUT4 protein was increased only in the EDL muscle. Rats treated with EB or DPN for 3 days did not show an increase in insulin-stimulated skeletal muscle glucose uptake compared to vehicle-treated animals. These new findings reveal that direct activation of ERα positively mediates glucose uptake and insulin action in skeletal muscle. Evidence that oestrogens and ERα stimulate glucose uptake has important implications for understanding mechanisms of glucose homeostasis, particularly in postmenopausal women.

Inflammation and adipose tissue: effects of progressive load training in rats

Introduction

Cytokines (IL-6, IL-10 and TNF-α) are increased after exhaustive exercise in the rat retroperitoneal (RPAT) and mesenteric adipose tissue (MEAT) pads. On the other hand, these cytokines show decreased expression in these depots in response to a chronic exercise protocol. However, the effect of exercise with overload combined with a short recovery period on pro- and anti-inflammatory cytokine expression is unknown. In the present study, we investigated the regulation of cytokine production in the adipose tissue of rats after an overtraining-inducing exercise protocol.

Methods

Male Wistar rats were divided into four groups: Control (C), Trained (Tr), Overtrained (OT) and recovered overtrained (R). Cytokines (IL-6, TNF-α and IL-10) levels and Toll Like Receptor 4 (TLR4), Nuclear Factor kBp65 (NF-kBp65), Hormone Sensitive Lipase (HSL) and, Perilipin protein expression were assessed in the adipose tissue. Furthermore, we analysed plasma lipid profile, insulin, testosterone, corticosterone and endotoxin levels, and liver triacylglycerol, cytokine content, as well as apolipoprotein B (apoB) and TLR4 expression in the liver.

Results

OT and R groups exhibited reduced performance accompanied by lower testosterone and increased corticosterone and endotoxin levels when compared with the control and trained groups. IL-6 and IL-10 protein levels were increased in the adipose tissue of the group allowed to recover, in comparison with all the other studied groups. TLR-4 and NF-kBp65 were increased in this same group when compared with both control and trained groups. The protein expression of HSL was increased and that of Perilipin, decreased in the adipose in R in relation to the control. In addition, we found increased liver and serum TAG, along with reduced apoB protein expression and IL-6 and IL-10 levels in the of R in relation to the control and trained groups.

Conclusion

In conclusion, we have shown that increases in pro-inflammatory cytokines in the adipose tissue after an overtraining protocol may be mediated via TLR-4 and NF-kBp65 signalling, leading to an inflammatory state in this tissue.