Estrogen receptor α protects pancreatic β-cells from apoptosis by preserving mitochondrial function and suppressing endoplasmic reticulum stress

Exposure to maternal obesity programs sex differences in pancreatic islets of the offspring in mice

AIMS/HYPOTHESIS

Obesity during pregnancy increases offspring type 2 diabetes risk. Given that nearly half of women of child-bearing age in many populations are currently overweight/obese, it is key that we improve our understanding of the impact of the in utero/early life environment on offspring islet function. Whilst a number of experimental studies have examined the effect of maternal obesity on offspring islet architecture and/or function, it has not previously been delineated whether these changes are independent of other confounding risk factors such as obesity, postnatal high-fat-feeding and ageing. Thus, we aimed to study the impact of exposure to maternal obesity on offspring islets in young, glucose-tolerant male and female offspring.

METHODS

Female C57BL/6J mice were fed ad libitum either chow or obesogenic diet prior to and throughout pregnancy and lactation. Offspring were weaned onto a chow diet and remained on this diet until the end of the study. An IPGTT was performed on male and female offspring at 7 weeks of age. At 8 weeks of age, pancreatic islets were isolated from offspring for measurement of insulin secretion and content, mitochondrial respiration, ATP content, reactive oxygen species levels, beta and alpha cell mass, granule and mitochondrial density (by transmission electron microscopy), and mRNA and protein expression by real-time RT-PCR and Western blotting, respectively.

RESULTS

Glucose tolerance was similar irrespective of maternal diet and offspring sex. However, blood glucose was lower (p < 0.001) and plasma insulin higher (p < 0.05) in female offspring of obese dams 15 min after glucose administration. This was associated with higher glucose- (p < 0.01) and leucine/glutamine-stimulated (p < 0.05) insulin secretion in these offspring. Furthermore, there was increased mitochondrial respiration (p < 0.01) and density (p < 0.05) in female offspring of obese dams compared with same-sex controls. Expression of mitochondrial and nuclear-encoded components of the electron transport chain, L-type Ca²⁺ channel subtypes that play a key role in stimulus-secretion coupling [Cacna1d (p < 0.05)], and oestrogen receptor α (p < 0.05) was also increased in islets from these female offspring of obese dams. Moreover, cleaved caspase-3 expression and BAX:Bcl-2 were decreased (p < 0.05) reflecting reduced susceptibility to apoptosis. In contrast, in male offspring, glucose and leucine/glutamine-stimulated insulin secretion was comparable between treatment groups. There was, however, compromised mitochondrial respiration characterised by decreased ATP synthesis-driven respiration (p < 0.05) and increased uncoupled respiration (p < 0.01), reduced docked insulin granules (p < 0.001), decreased Cacna1c (p < 0.001) and Cacna1d (p < 0.001) and increased cleaved caspase-3 expression (p < 0.05).

CONCLUSIONS/INTERPRETATION

Maternal obesity programs sex differences in offspring islet function. Islets of female but not male offspring appear to be primed to cope with a nutritionally-rich postnatal environment, which may reflect differences in future type 2 diabetes risk.

Sex as a Biological Variable: A 5-Year Progress Report and Call to Action

A little over 5 years ago, the U.S. National Institutes of Health (NIH) announced the intention to develop policies to require applicants to report plans to balance male and female cells and animals in preclinical investigations. Soon thereafter, the NIH issued a request for information from the scientific community and consulted with various stakeholders. The feedback received was considered during development of policy requiring the consideration of sex as a biological variable (SABV) in NIH-funded research on vertebrate animals and humans, which went into effect for applications due on or after January 25, 2016. We identified NIH programs related to SABV and reviewed SABV-relevant scientific literature. We find that the application of SABV throughout the research process can serve as a guiding principle to improve the value of biomedical science. The NIH is engaged in ongoing efforts to develop resources to help investigators consider SABV in their research. We also provide an update on lessons learned, highlight ways that different disciplines consider SABV, and describe the opportunities for scientific discovery that applying SABV offers. We call on NIH's various stakeholders to redouble their efforts to integrate SABV throughout the biomedical research enterprise. Sex- and gender-aware investigations are critical to the conduct of rigorous and transparent science and the advancement of personalized medicine. This kind of research achieves its greatest potential when sex and gender considerations are integrated into the biomedical research enterprise in an end-to-end manner, from basic and preclinical investigations, through translational and clinical research, to improved health care delivery.

Relationship Between Metabolic Syndrome and Beta-Cell Function in Nondiabetic Korean Premenopausal and Postmenopausal Women: 2015 Korean National Health and Nutrition Examination Survey

Background: This study was conducted to assess the relationship between metabolic syndrome (MetS) and beta-cell function in nondiabetic Korean women. Methods: This study included 2,507 women (premenopausal women, 1,359; postmenopausal women, 1,148) who were aged ≥20 and used 2015 Korean National Health and Nutrition Examination Survey (KNHANES) data. Results: Key study results were as follows: first, in both premenopausal and postmenopausal women, after adjusting for related variables [except body mass index (BMI)], MetS (P < 0.001) and metabolic syndrome score (MSS; P < 0.001) were positively associated with the homeostasis model assessment of beta-cell function (HOMA-B) levels. Second, in premenopausal women, when further adjusted for BMI, MetS (P = 0.002) and MSS (P < 0.001) were also positively associated with HOMA-B levels. However, in postmenopausal women, when further adjusting for BMI, the associations of MetS (P = 0.322) or MSS (P = 0.855) and HOMA-B levels were no longer significant. Conclusions: Metabolic syndrome was positively associated with beta-cell function in nondiabetic Korean premenopausal women, but not in Korean postmenopausal women.

The Role of Sexual Hormones on the Enteroinsular Axis

Sex steroid estrogens, androgens, and progesterone, produced by the gonads, which have long been considered as endocrine glands, are implicated in sexual differentiation, puberty, and reproduction. However, the impact of sex hormones goes beyond these effects through their role on energy metabolism. Indeed, sex hormones are important physiological regulators of glucose homeostasis and, in particular, of the enteroinsular axis. In this review, we describe the roles of estrogens, androgens, and progesterone on glucose homeostasis through their effects on pancreatic α- and β-cells, as well as on enteroendocrine L-cells, and their implications in hormonal biosynthesis and secretion. The analysis of their mechanisms of action with the dissection of the receptors implicated in the several protective effects could provide some new aspects of the fine-tuning of hormonal secretion under the influence of the sex. This knowledge paves the way to the understanding of transgender physiology and new potential therapeutics in the field of type 2 diabetes.

Conjugated Estrogens and Bazedoxifene Improve β Cell Function in Obese Menopausal Women

CONTEXT

Studies suggest that menopausal hormone therapy (MHT) prevents type 2 diabetes (T2D). The combination of conjugated estrogens (CE) with the selective estrogen receptor modulator bazedoxifene (BZA) is an MHT that improves obesity and T2D in preclinical models of menopausal metabolic syndrome. The effect of CE/BZA on adiposity and glucose homeostasis in obese postmenopausal women is unknown.

OBJECTIVE

To investigate the effect of CE/BZA on body composition, glucose homeostasis, and markers of inflammation in obese postmenopausal women.

RESEARCH DESIGN INTERVENTION AND PARTICIPANTS

Randomized, double-blind, placebo-controlled pilot trial of 12 obese menopausal women assigned to 12-week treatment with CE 0.45 mg/BZA 20 mg (n = 7) or placebo (n = 5). At baseline and after 12 weeks, we assessed body composition (dual-energy X-ray absorptiometry), glucose homeostasis (IV glucose tolerance test), and inflammation biomarkers.

RESULTS

Women treated with CE/BZA exhibited increased β cell function using homeostatic model assessment-B [median (interquartile range) CE/BZA vs placebo: 18.5 (-0.9 to 320.6) μU/mM vs -25.5 (-39.9 to -0.1) μU/mM; P = 0.045], and decreased basal glucose concentrations (Gb) [-5.2 (-9.2 to -1.7) mg/dL vs 2.7 (0.9 to 4.9) mg/dL; P = 0.029]. Insulin sensitivity was higher in the placebo arm [1.35 (1.12 to 1.82) (μU/mL) min-1 vs -0.24 (-1.50 to 0.19) (μU/mL) min-1; P = 0.029]. No changes between treatment groups were observed for the acute insulin response to glucose (AIRg), the disposition index (DI), body composition, and inflammatory biomarkers.

CONCLUSIONS

A 12-week treatment of obese postmenopausal women with CEs/BZA improves fasting β cell function and glucose concentrations without change in AIRg, HOMA-IR, DI, body composition, or markers of inflammation.

Effect of postnatal overfeeding on the male and female Wistar rat reproductive parameters

Overweight/obesity has become a worldwide epidemic, and factors such as a sedentary lifestyle and inadequate eating habits directly contribute to the development of this condition. Studies indicate that rapid weight gain at critical development stages, such as the lactation period, is associated with the development of obesity, cardiovascular diseases, and diabetes in the long term. In addition to metabolic changes during adulthood, overweight/obesity may influence reproductive function of the population. In this context, the present study aimed to evaluate postnatal overfeeding effects on male and female Wistar rat reproductive parameters. Postnatal overfeeding was induced by applying the litter reduction method for both sexes. Forty animals were used, divided into four groups: two with normal litters (NL♂ and NL♀) and two with small litters (SL♂ and SL♀). The males were euthanized at 90 days of age, on the same date the females were mated. Females were also euthanized after the 20-day gestation. Metabolic and reproductive variables were analyzed. Regarding males, SL animals showed increased body weight, adiposity, and decreased relative weight of the seminal vesicle, prostate, and epididymis as well as changes in the ITT and OGTT glycemic tests. Concerning females, SL animals presented increased body weight, relative perigonadal fat weight, glucose intolerance as well as modify the vaginal opening and increased weight of female pup. The litter reduction method was efficient in leading to metabolic and reproductive alterations in male and female Wistar rat.

Tamoxifen Improves Glucose Tolerance in a Delivery-, Sex-, and Strain-Dependent Manner in Mice

Tamoxifen, a selective estrogen-receptor modulator, is widely used in mouse models to temporally control gene expression but is also known to affect body composition. We report that tamoxifen has significant and sustained effects on glucose tolerance, independent of effects on insulin sensitivity, in mice. IP, but not oral, tamoxifen delivery improved glucose tolerance in three inbred mouse strains. The extent and persistence of tamoxifen-induced effects were sex and strain dependent. These findings highlight the need to revise commonly used tamoxifen-based protocols for gene manipulation in mice by including longer chase periods after injection, oral delivery, and the use of tamoxifen-treated littermate controls.

Hepcidin as a key iron regulator mediates glucotoxicity-induced pancreatic β-cell dysfunction

It has been well established that glucotoxicity induces pancreatic β-cells dysfunction; however, the precise mechanism remains unclear. Our previous studies demonstrated that high glucose concentrations are associated with decreased hepcidin expression, which inhibits insulin synthesis. In this study, we focused on the role of low hepcidin level-induced increased iron deposition in β-cells and the relationship between abnormal iron metabolism and β-cell dysfunction. Decreased hepcidin expression increased iron absorption by upregulating transferrin receptor 1 (TfR1) and divalent metal transporter 1 (DMT1) expression, resulting in iron accumulation within cells. Prussia blue stain and calcein-AM assays revealed greater iron accumulation in the cytoplasm of pancreatic tissue isolated from db/db mice, cultured islets and Min6 cells in response to high glucose stimulation. Increased cytosolic iron deposition was associated with greater Fe2+ influx into the mitochondria, which depolarized the mitochondria membrane potential, inhibited ATP synthesis, generated excessive ROS and induced oxidative stress. The toxic effect of excessive iron on mitochondrial function eventually resulted in impaired insulin secretion. The restricted iron content in db/db mice via reduced iron intake or accelerated iron clearance improved blood glucose levels with decreased fasting blood glucose (FBG), fasting blood insulin (FIns), HbA1c level, as well as improved intraperitoneal glucose tolerance test (IPGTT) results. Thus, our study may reveal the mechanism involved in the role of hepcidin in the glucotoxcity impaired pancreatic β cell function pathway.

Emerging hormonal-based combination pharmacotherapies for the treatment of metabolic diseases

Obesity and its comorbidities, such as type 2 diabetes mellitus and cardiovascular disease, constitute growing challenges for public health and economies globally. The available treatment options for these metabolic disorders cannot reverse the disease in most individuals and have not substantially reduced disease prevalence, which underscores the unmet need for more efficacious interventions. Neurobiological resilience to energy homeostatic perturbations, combined with the heterogeneous pathophysiology of human metabolic disorders, has limited the sustainability and efficacy of current pharmacological options. Emerging insights into the molecular origins of eating behaviour, energy expenditure, dyslipidaemia and insulin resistance suggest that coordinated targeting of multiple signalling pathways is probably necessary for sizeable improvements to reverse the progression of these diseases. Accordingly, a broad set of combinatorial approaches targeting feeding circuits, energy expenditure and glucose metabolism in concert are currently being explored and developed. Notably, several classes of peptide-based multi-agonists and peptide-small molecule conjugates with superior preclinical efficacy have emerged and are currently undergoing clinical evaluation. Here, we summarize advances over the past decade in combination pharmacotherapy for the management of obesity and type 2 diabetes mellitus, exclusively focusing on large-molecule formats (notably enteroendocrine peptides and proteins) and discuss the associated therapeutic opportunities and challenges.

Catechol estrogens stimulate insulin secretion in pancreatic β-cells via activation of the transient receptor potential A1 (TRPA1) channel

Estrogen hormones play an important role in controlling glucose homeostasis and pancreatic β-cell function. Despite the significance of estrogen hormones for regulation of glucose metabolism, little is known about the roles of endogenous estrogen metabolites in modulating pancreatic β-cell function. In this study, we evaluated the effects of major natural estrogen metabolites, catechol estrogens, on insulin secretion in pancreatic β-cells. We show that catechol estrogens, hydroxylated at positions C2 and C4 of the steroid A ring, rapidly potentiated glucose-induced insulin secretion via a nongenomic mechanism. 2-Hydroxyestrone, the most abundant endogenous estrogen metabolite, was more efficacious in stimulating insulin secretion than any other tested catechol estrogens. In insulin-secreting cells, catechol estrogens produced rapid activation of calcium influx and elevation in cytosolic free calcium. Catechol estrogens also generated sustained elevations in cytosolic free calcium and evoked inward ion current in HEK293 cells expressing the transient receptor potential A1 (TRPA1) cation channel. Calcium influx and insulin secretion stimulated by estrogen metabolites were dependent on the TRPA1 activity and inhibited with the channel-specific pharmacological antagonists or the siRNA. Our results suggest the role of estrogen metabolism in a direct regulation of TRPA1 activity with potential implications for metabolic diseases.

A Disturbance in the Force: Cellular Stress Sensing by the Mitochondrial Network

As a highly dynamic organellar network, mitochondria are maintained as an organellar network by delicately balancing fission and fusion pathways. This homeostatic balance of organellar dynamics is increasingly revealed to play an integral role in sensing cellular stress stimuli. Mitochondrial fission/fusion balance is highly sensitive to perturbations such as loss of bioenergetic function, oxidative stress, and other stimuli, with mechanistic contribution to subsequent cell-wide cascades including inflammation, autophagy, and apoptosis. The overlapping activity with m-AAA protease 1 (OMA1) metallopeptidase, a stress-sensitive modulator of mitochondrial fusion, and dynamin-related protein 1 (DRP1), a regulator of mitochondrial fission, are key factors that shape mitochondrial dynamics in response to various stimuli. As such, OMA1 and DRP1 are critical factors that mediate mitochondrial roles in cellular stress-response signaling. Here, we explore the current understanding and emerging questions in the role of mitochondrial dynamics in sensing cellular stress as a dynamic, responsive organellar network.

Sex and gender differences in developmental programming of metabolism

BACKGROUND

The early life environment experienced by an individual in utero and during the neonatal period is a major factor in shaping later life disease risk-including susceptibility to develop obesity, diabetes, and cardiovascular disease. The incidence of metabolic disease is different between males and females. How the early life environment may underlie these sex differences is an area of active investigation.

SCOPE OF REVIEW

The purpose of this review is to summarize our current understanding of how the early life environment influences metabolic disease risk in a sex specific manner. We also discuss the possible mechanisms responsible for mediating these sexually dimorphic effects and highlight the results of recent intervention studies in animal models.

MAJOR CONCLUSIONS

Exposure to states of both under- and over-nutrition during early life predisposes both sexes to develop metabolic disease. Females seem particularly susceptible to develop increased adiposity and disrupted glucose homeostasis as a result of exposure to in utero undernutrition or high sugar environments, respectively. The male placenta is particularly vulnerable to damage by adverse nutritional states and this may underlie some of the metabolic phenotypes observed in adulthood. More studies investigating both sexes are needed to understand how changes to the early life environment impact differently on the long-term health of male and female individuals.

Assessing the impact of cigarette smoking on β-cell function and risk for type 2 diabetes in a non-diabetic Chinese cohort

Although the impact of cigarette smoking on glucose homeostasis has been extensively studied, the results, however, are still not conclusive. We, therefore, conducted a cross-sectional analysis of a non-diabetic Chinese cohort collected by the China Health and Nutrition Survey (CHNS 2009) to comprehensively assess the relationship between smoking, Hemoglobin A1c, β-cell function and insulin sensitivity. The cohort included a total of 5965 individuals (47.4% male) with a mean age of 49.23 years, and 4140 of which were non-smokers (69.4%), 834 were current light smokers (13.9%) and 991 were current heavy smokers (16.6%). Current smokers were predominantly males (93.6%) with a lower BMI (22.95 versus 23.42 kg/m²). HbA1c levels were dose-dependently increased with smoking exposure (5.39%, 5.42% and 5.45%, respectively, P = 0.007). Non-smokers were served as a referent, the adjusted ORs for type 2 diabetes were 1.12 (P = 0.256, light smokers) and 1.26 (P = 0.014, heavy smokers), indicating a positive relationship between cigarette smoking and incidence of diabetes. HOMA%B was decreased in a dose-responsive manner with cigarette smoking (4.80, 4.79 and 4.76, P = 0.036), suggesting an adverse effect of smoking on β-cell function. Collectively, cigarette smoking is dose-dependently associated with decreased HOMA%B, and current smokers were clearly in a higher risk for diabetes as manifested by the elevated HbA1c.