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Open access

Karin L Gustafsson, Sofia Movérare-Skrtic, Helen H Farman, Cecilia Engdahl, Petra Henning, Karin H Nilsson, Julia M Scheffler, Edina Sehic, Ulrika Islander, Ellis Levin, Claes Ohlsson, and Marie K Lagerquist

Selective estrogen receptor modulators (SERMs) act as estrogen receptor (ER) agonists or antagonists in a tissue-specific manner. ERs exert effects via nuclear actions but can also utilize membrane-initiated signaling pathways. To determine if membrane-initiated ERα (mERα) signaling affects SERM action in a tissue-specific manner, C451A mice, lacking mERα signaling due to a mutation at palmitoylation site C451, were treated with Lasofoxifene (Las), Bazedoxifene (Bza), or estradiol (E2), and various tissues were evaluated. Las and Bza treatment increased uterine weight to a similar extent in C451A and control mice, demonstrating mERα-independent uterine SERM effects, while the E2 effect on the uterus was predominantly mERα-dependent. Las and Bza treatment increased both trabecular and cortical bone mass in controls to a similar degree as E2, while both SERM and E2 treatment effects were absent in C451A mice. This demonstrates that SERM effects, similar to E2 effects, in the skeleton are mERα-dependent. Both Las and E2 treatment decreased thymus weight in controls, while neither treatment affected the thymus in C451A mice, demonstrating mERα-dependent SERM and E2 effects in this tissue. Interestingly, both SERM and E2 treatments decreased the total body fat percent in C451A mice, demonstrating the ability of these treatments to affect fat tissue in the absence of functional mERα signaling. In conclusion, mERα signaling can modulate SERM responses in a tissue-specific manner. This novel knowledge increases the understanding of the mechanisms behind SERM effects and may thereby facilitate the development of new improved SERMs.

Free access

Courtney A Deck, Jamie L Mankiewicz, and Russell J Borski

Leptin, insulin, and glucagon are involved in regulating glycaemia in vertebrates and play a role in the progression of obesity and type 2 diabetes. While mammals possess an ‘adipoinsular axis’ whereby insulin stimulates leptin release from adipocytes and leptin in turn feeds back on the pancreas to inhibit further insulin secretion, evidence of such an axis in non-mammalian vertebrates is unknown. We investigated the interactions between these glycaemic hormones and provide evidence for a leptin–insulin axis in a teleost fish, the tilapia. In the first study, we exposed hepatocytes to various concentrations of either insulin or glucagon to determine effects on leptin a (lepa) and then examined this in vivo with i.p. injections of both hormones. We also exposed isolated Brockmann bodies (pancreatic islets) to recombinant tilapia leptin A (rtLepA) and again followed this up with an i.p. injection to examine changes in insulin a and glucagon b. We found that glucagon increases lepa in vitroand in vivo, with the latter being 18-fold higher than saline-injected controls; however, the effects of rtLepA on glub were more variable. Insulin increased lepa by 2.5-fold in vitro and 70-fold in vivo, while rtLepA decreased insa at basal and increased it at high glucose concentrations. These data indicate that a leptin–insulin axis may be conserved among vertebrates and is thus essential for regulating nutrient balance but that the relationship is likely much more dynamic in teleosts as glycaemia is not as tightly regulated as it is in mammals.

Open access

Hiroyuki Enomoto, Kinuyo Iwata, Keisuke Matsumoto, Mai Otsuka, Akio Morita, and Hitoshi Ozawa

Kisspeptin neurons, i.e. KNDy neurons, in the arcuate nucleus (ARC) coexpress neurokinin B and dynorphin and regulate gonadotropin-releasing hormone/luteinizing hormone (LH) pulses. Because it remains unclear whether these neurons are associated with reproductive dysfunction in diabetic females, we examined the expression of KNDy neurons detected by histochemistry in streptozotocin (STZ)-induced diabetic female rats 8 weeks after STZ injection. We also evaluated relevant metabolic parameters – glucose, 3-hydroxybutyrate, and non-esterified fatty acids – as indicators of diabetes progression. Severe diabetes with hyperglycemia and severe ketosis suppressed the mRNA expression of KNDy neurons, resulting in low plasma LH levels and persistent diestrus. In moderate diabetes with hyperglycemia and moderate ketosis, kisspeptin-immunoreactive cells and plasma LH levels were decreased, while the mRNA expression of KNDy neurons remained unchanged. Mild diabetes with hyperglycemia and slight ketosis did not affect KNDy neurons and plasma LH levels. The number of KNDy cells was strongly and negatively correlated with plasma 3-hydroxybutyrate levels. The vaginal smear analysis showed unclear proestrus in diabetic rats 3–5 days after STZ injection, and the mRNA expression of kisspeptin in the ARC was decreased 2 weeks after STZ injection in severely diabetic rats. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV), which induce an LH surge, were unaffected at 2 and 8 weeks after STZ injection regardless of the diabetes severity. These results suggest that diabetes mellitus progression in females may negatively affect ARC kisspeptin neurons but not AVPV kisspeptin neurons, implicating a potential role of ARC kisspeptin neurons in menstrual disorder and infertility.

Open access

Erica Yeo, Patricia L Brubaker, and Deborah M Sloboda

It is now well established that, beyond its role in nutrient processing and absorption, the intestine and its accompanying gut microbiome constitute a major site of immunological and endocrine regulation that mediates whole-body metabolism. Despite the growing field of host-microbe research, few studies explore what mechanisms govern this relationship in the context of pregnancy. During pregnancy, significant maternal metabolic adaptations are made to accommodate the additional energy demands of the developing fetus and to prevent adverse pregnancy outcomes. Recent data suggest that the maternal gut microbiota may play a role in these adaptations, but changes to maternal gut physiology and the underlying intestinal mechanisms remain unclear. In this review, we discuss selective aspects of intestinal physiology including the role of the incretin hormone, glucagon-like peptide 1 (GLP-1), and the role of the maternal gut microbiome in the maternal metabolic adaptations to pregnancy. Specifically, we discuss how bacterial components and metabolites could mediate the effects of the microbiota on host physiology, including nutrient absorption and GLP-1 secretion and action, and whether these mechanisms may change maternal insulin sensitivity and secretion during pregnancy. Finally, we discuss how these pathways could be altered in disease states during pregnancy including maternal obesity and diabetes.

Open access

Maria Karsai, Richard A Zuellig, Roger Lehmann, Federica Cuozzo, Daniela Nasteska, Edlira Luca, Constanze Hantel, David J Hodson, Giatgen A Spinas, Guy A Rutter, and Philipp A Gerber

Pancreatic β-cells depend on the well-balanced regulation of cytosolic zinc concentrations, providing sufficient zinc ions for the processing and storage of insulin, but avoiding toxic effects. The zinc transporter ZnT8, encoded by SLC30A8,is a key player regarding islet cell zinc homeostasis, and polymorphisms in this gene are associated with altered type 2 diabetes susceptibility in man. The objective of this study was to investigate the role of ZnT8 and zinc in situations of cellular stress as hypoxia or inflammation. Isolated islets of WT and global ZnT8−/− mice were exposed to hypoxia or cytokines and cell death was measured. To explore the role of changing intracellular Zn2+ concentrations, WT islets were exposed to different zinc concentrations using zinc chloride or the zinc chelator N,N,N′,N′-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN). Hypoxia or cytokine (TNF-α, IFN-γ, IL1-β) treatment induced islet cell death, but to a lesser extent in islets from ZnT8−/− mice, which were shown to have a reduced zinc content. Similarly, chelation of zinc with TPEN reduced cell death in WT islets treated with hypoxia or cytokines, whereas increased zinc concentrations aggravated the effects of these stressors. This study demonstrates a reduced rate of cell death in islets from ZnT8−/− mice as compared to WT islets when exposed to two distinct cellular stressors, hypoxia or cytotoxic cytokines. This protection from cell death is, in part, mediated by a reduced zinc content in islet cells of ZnT8−/− mice. These findings may be relevant for altered diabetes burden in carriers of risk SLC30A8 alleles in man.

Free access

Natassia Rodrigo, Hui Chen, Carol A Pollock, and Sarah J Glastras

Women with obesity have higher incidences of infertility, with longer time to conception and increased risk of pregnancy complications compared to women with normal body weight. There is a lack of evidence demonstrating the benefit of preconception maternal weight loss on fertility and pregnancy outcomes. We aimed to determine if preconception weight loss, either with diet modification or glucose-like peptide 1 receptor agonist liraglutide, improves maternal weight, fertility, and pregnancy outcomes. C57BL/6 female mice were fed either a high-fat diet (HFD) or chow for 8 weeks. HFD-fed dams were administered liraglutide (0.3 mg/kg, s.c., for 4 weeks) or switched to chow to induce weight loss. Prior to mating, liraglutide was ceased and mice continued on HFD. Mice in the ‘diet switch’ group continued on chow. Pregnancy rates were recorded. Maternal anthropometry and glucose tolerance were measured before and after the intervention and at late gestation. Offspring outcomes were assessed. Liraglutide or diet switch led to weight reduction, improved insulin resistance (P< 0.001), and enhanced fertility, particularly in the liraglutide group (P< 0.005). Liraglutide-treated mice had significantly higher gestational weight gain (GWG) compared to the diet switch group (P< 0.05), with similar weight and glucose tolerance in late gestation to HFD mice. In contrast, diet switch maintained similar weight and glucose tolerance in late gestation to control mice. Pre-pregnancy weight intervention with liraglutide was effective at restoring fertility. Diet modification also improved fertility and avoided catch up weight gain in pregnancy. Liraglutide may be a therapeutic strategy for weight loss to prepare for pregnancy. However, our study provides caution about the potential for excessive GWG without diet intervention in pregnancy.

Free access

Emma Ahlqvist, Rashmi B Prasad, and Leif Groop

Type 2 diabetes (T2D) is one of the fastest increasing diseases worldwide. Although it is defined by a single metabolite, glucose, it is increasingly recognized as a highly heterogeneous disease with varying clinical manifestations. Identification of different subtypes at an early stage of disease when complications might still be prevented could hopefully allow for more personalized medicine. An important step toward precision medicine would be to target the right resources to the right patients, thereby improving patient health and reducing health costs for the society. More well-defined disease populations also offer increased power in experimental, genetic and clinical studies. In a recent study, we used six clinical variables (glutamate decarboxylase autoantibodies, age at onset of diabetes, glycated hemoglobin, BMI and simple measures of insulin resistance and insulin secretion (so called HOMA estimates) to cluster adult-onset diabetes patients into five subgroups. These subgroups have been robustly reproduced in several populations worldwide and are associated with different risks of diabetic complications and responses to treatment. Importantly, the group with severe insulin-deficient diabetes had increased risk of retinopathy and neuropathy, whereas the severe insulin-resistant diabetes group has the highest risk for diabetic kidney disease (DKD) and fatty liver. This emphasizes the key role of insulin resistance in the pathogenesis of DKD and fatty liver in T2D. In conclusion, this novel subclassification, breaking down T2D in clinically meaningful subgroups, provides the prerequisite framework for expanded personalized medicine in diabetes beyond what is already available for monogenic and to some extent type 1 diabetes.

Free access

Taylor Landry, Daniel Shookster, Alec Chaves, Katrina Free, Tony Nguyen, and Hu Huang

Recent evidence identifies a potent role for aerobic exercise to modulate the activity of hypothalamic neurons related to appetite; however, these studies have been primarily performed in male rodents. Since females have markedly different neuronal mechanisms regulating food intake, the current study aimed to determine the effects of acute treadmill exercise on hypothalamic neuron populations involved in regulating appetite in female mice. Mature, untrained female mice were exposed to acute sedentary, low- (10 m/min), moderate- (14 m/min), and high (18 m/min)-intensity treadmill exercise in a randomized crossover design. Mice were fasted 10 h before exercise, and food intake was monitored for 48 h after bouts. Immunohistochemical detection of cFOS was performed 3 h post-exercise to determine the changes in hypothalamic neuropeptide Y (NPY)/agouti-related peptide (AgRP), pro-opiomelanocortin (POMC), tyrosine hydroxylase (TH), and SIM1-expressing neuron activity concurrent with the changes in food intake. Additionally, stains for pSTAT3tyr705 and pERKthr202/tyr204 were performed to detect exercise-mediated changes in intracellular signaling. Briefly, moderate- and high-intensity exercises increased 24-h food intake by 5.9 and 19%, respectively, while low-intensity exercise had no effects. Furthermore, increases in NPY/AgRPARC, SIM1PVN, and TH neuron activity were observed 3 h after high-intensity exercise, with no effects on POMCARC neurons. While no effects of exercise on pERKthr202/tyr204 were observed, pSTAT3tyr705 was elevated specifically in NPY/AgRP neurons 3 h post-exercise. Overall, aerobic exercise increased the activity of several appetite-stimulating neuron populations in the hypothalamus of female mice, which may provide insight into previously reported sexual dimorphisms in post-exercise feeding.