Kiss1 neurons of the arcuate (ARC) nucleus form an interconnected network of cells that communicate via neurokinin B (encoded by Tac2) and its receptor (encoded by Tacr3) and play key roles in the control of the reproductive axis through sex hormone-regulated synthesis and release of kisspeptin peptides (Kp, encoded by Kiss1). The aim of this study was to determine whether the Kiss1 cell population of the ARC already displays sexually dimorphic features at embryonic age E16.5 in mice. At this time of development, Kiss1-GFP- and Kp-immunoreactive cell bodies were restricted to the ARC and not found in the pre-optic area (POA). The Kiss1-GFP cell population was identical in size between sexes but had significantly lower Kiss1, Tac2, and Tacr3 mRNA levels and lower Kp-ir fiber density in the POA in male compared to female fetuses. Receptors for androgen (Ar) and estrogen (Esr1, Esr2, Gpr30) and the Cyp19a1 gene (encoding the estradiol-producing enzyme aromatase) transcripts were also detected in fetal ARC Kiss1-GFP cells with significant sex differences for Ar (higher in males) and Esr1 (higher in females). Functional studies on primary cultures of sorted fetal Kiss1-GFP cells revealed a significant negative effect of estradiol treatment on neurite outgrowth on the fourth day of culture in the female group specifically. We conclude that the ARC Kiss1 cell population is already sexually differentiated at E16.5 and that its morphogenetic development may be particularly vulnerable to estradiol exposure at this early developmental time.
Caroline Alfaia, Vincent Robert, Kevin Poissenot, Yves Levern, Daniel Guillaume, Shel-Hwa Yeo, William H Colledge, and Isabelle Franceschini
Victoria Diedrich, Elena Haugg, Carola Dreier, and Annika Herwig
Torpid states are used by many endotherms to save energy during winter. During torpor, metabolic rate is downregulated to fractions of resting metabolic rate and often associated with a severe drop in body temperature that challenges mammalian physiology. Understanding the mechanisms regulating this extreme depression of metabolism bears enormous potential for biomedical research. Torpor behavior has been extensively studied in the Djungarian hamster, also known as Siberian hamster. It is dependent on many preparatory adaptations of physiological and endocrine systems that are likely to be integrated by the hypothalamus eventually controlling metabolism. Although substantial knowledge exists about prerequisites and characteristics of torpor in this species, the cascade of events and their mechanisms of action are not well understood. This review summarizes the current state of knowledge about mechanisms of metabolic regulation in the Djungarian hamster focusing on the potential roles of thyroid hormone and glucose metabolism.
Tomasz Misztal, Patrycja Młotkowska, Elżbieta Marciniak, and Anna Misztal
The verified hypothesis assumed that centrally administered neurosteroid, allopregnanolone (AL), could affect basal and/or stress-induced activity of the hypothalamic-pituitary-adrenal (HPA) axis in sheep. Four groups (n = 6 each) of luteal-phase sheep were intracerebroventricularly infused for 3 days with a vehicle without stress (control); a vehicle treated with stressful stimuli (isolation and partial movement restriction) on the third day; AL (4 × 15 µg/60 µL/30 min, at 30-min intervals) treated with stressful stimuli, and AL alone. Simultaneously, the push-pull perfusion of the infundibular nucleus/median eminence and plasma sample collection were performed. After the experiment, the sheep were killed to collect the hypothalamic and anterior pituitary (AP) tissues. Stressful stimuli evoked an increase in the expression of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA in the hypothalamic paraventricular nucleus (PVN), and AVP receptor (V1b) and proopiomelanocortin (POMC) mRNA in the AP; the concentrations of perfusate CRH, and plasma adrenocorticotropic hormone (ACTH) and cortisol compared to controls. Conversely, the expression of the CRH receptor (CRHR1) mRNA in the AP was downregulated. AL decreased the expression of CRH and AVP mRNA in the PVN, and AVPRV1b and POMC mRNA in the AP in stressed sheep, compared to only stressed ones. There was also a reduction in perfusate CRH, and plasma ACTH and cortisol concentrations. AL alone decreased the expression of CRHR1 mRNA in the AP, and plasma cortisol concentration at the beginning of the collection period compared to controls. In conclusion, AL may function centrally as a suppressor of HPA axis activity in stressed sheep.
S Andrikopoulos, C Farquharson, and M Haluzik
Meng Guo, Yuna Li, Yan Wang, Zhenkun Li, Xiaohong Li, Peikun Zhao, Changlong Li, Jianyi Lv, Xin Liu, Xiaoyan Du, and Zhenwen Chen
Recent studies raise the possibility that eukaryotic translation elongation factor 1 alpha (eEF1A) may play a role in metabolism. One isoform, eEF1A2, is specifically expressed in skeletal muscle, heart and brain. It regulates translation elongation and signal transduction. Nonetheless, eEF1A2’s function in skeletal muscle glucose metabolism remains unclear. In the present study, suppression subtractive hybridisation showed a decrease in Eef1a2 transcripts in the skeletal muscle of diabetic Mongolian gerbils. This was confirmed at mRNA and protein levels in hyperglycaemic gerbils, and in db/db and high-fat diet-fed mice. Further, this downregulation was independent of Eef1a2 promoter methylation. Interestingly, adeno-associated virus-mediated eEF1A2 overexpression in skeletal muscle aggravated fasting hyperglycaemia, hyperinsulinaemia and glucose intolerance in male diabetic gerbils but not in female gerbil models. The overexpression of eEF1A2 in skeletal muscle also resulted in promoted serum glucose levels and insulin resistance in male db/db mice. Up- and downregulation of eEF1A2 by lentiviral vector transfection confirmed its inhibitory effect on insulin-stimulated glucose uptake and signalling transduction in C2C12 myotubes with palmitate (PA)-induced insulin resistance. Furthermore, eEF1A2 bound PKCβ and increased its activation in the cytoplasm, whereas suppression of PKCβ by an inhibitor attenuated eEF1A2-mediated impairment of insulin sensitivity in insulin-resistant myotubes. Endoplasmic reticulum (ER) stress was elevated by eEF1A2, whereas suppression of ER stress or JNK partially restored insulin sensitivity in PA-treated myotubes. Additionally, eEF1A2 inhibited lipogenesis and lipid utilisation in insulin-resistant skeletal muscle. Collectively, we demonstrated that eEF1A2 exacerbates insulin resistance in male murine skeletal muscle via PKCβ and ER stress.
Rukmani Pandey, Pallavi Shukla, Baby Anjum, Himanshu Pawankumar Gupta, Subhashis Pal, Nidhi Arjaria, Keerti Gupta, Naibedya Chattopadhyay, Rohit A Sinha, and Sanghamitra Bandyopadhyay
Estrogen deficiency reduces estrogen receptor-alpha (ERα) and promotes apoptosis in the hippocampus, inducing learning-memory deficits; however, underlying mechanisms remain less understood. Here, we explored the molecular mechanism in an ovariectomized (OVX) rat model, hypothesizing participation of autophagy and growth factor signaling that relate with apoptosis. We observed enhanced hippocampal autophagy in OVX rats, characterized by increased levels of autophagy proteins, presence of autophagosomes and inhibition of AKT-mTOR signaling. Investigating upstream effectors of reduced AKT-mTOR signaling revealed a decrease in hippocampal heparin-binding epidermal growth factor (HB-EGF) and p-EGFR. Moreover, 17β-estradiol and HB-EGF treatments restored hippocampal EGFR activation and alleviated downstream autophagy process and neuronal loss in OVX rats. In vitro studies using estrogen receptor (ERα)-silenced primary hippocampal neurons further corroborated the in vivo observations. Additionally, in vivo and in vitro studies suggested the participation of an attenuated hippocampal neuronal HB-EGF and enhanced autophagy in apoptosis of hippocampal neurons in estrogen- and ERα-deficient conditions. Subsequently, we found evidence of mitochondrial loss and mitophagy in hippocampal neurons of OVX rats and ERα-silenced cells. The ERα-silenced cells also showed a reduction in ATP production and an HB-EGF-mediated restoration. Finally in concordance with molecular studies, inhibition of autophagy and treatment with HB-EGF in OVX rats restored cognitive performances, assessed through Y-Maze and passive avoidance tasks. Overall, our study, for the first time, links neuronal HB-EGF/EGFR signaling and autophagy with ERα and memory performance, disrupted in estrogen-deficient condition.
Ángela Sánchez, Constanza Contreras-Jurado, Diego Rodríguez, Javier Regadera, Susana Alemany, and Ana Aranda
Hypothyroidism is often associated with anemia and immunological disorders. Similar defects are found in patients and in mice with a mutated dominant-negative thyroid hormone receptor α (TRα) and in knockout mice devoid of this receptor, suggesting that this isoform is responsible for the effects of the thyroid hormones in hematopoiesis. However, the hematological phenotype of mice lacking also TRβ has not yet been examined. We show here that TRα1/TRβ-knockout female mice, lacking all known thyroid hormone receptors with capacity to bind thyroid hormones, do not have overt anemia and in contrast with hypothyroid mice do not present reduced Gata1 or Hif1 gene expression. Similar to that found in hypothyroidism or TRα deficiency during the juvenile period, the B-cell population is reduced in the spleen and bone marrow of ageing TRα1/TRβ-knockout mice, suggesting that TRβ does not play a major role in B-cell development. However, splenic hypotrophy is more marked in hypothyroid mice than in TRα1/TRβ-knockout mice and the splenic population of T-lymphocytes is not significantly impaired in these mice in contrast with the reduction found in hypothyroidism. Our results show that the overall hematopoietic phenotype of the TRα1/TRβ-knockout mice is milder than that found in the absence of hormone. Although other mechanism/s cannot be ruled out, our results suggest that the unoccupied TRs could have a negative effect on hematopoiesis, likely secondary to repression of hematopoietic gene expression.
Chirine Toufaily, Gauthier Schang, Xiang Zhou, Philipp Wartenberg, Ulrich Boehm, John P Lydon, Ferdinand Roelfsema, and Daniel J Bernard
The progesterone receptor (PR, encoded by Pgr) plays essential roles in reproduction. Female mice lacking the PR are infertile, due to the loss of the protein’s functions in the brain, ovary, and uterus. PR is also expressed in pituitary gonadotrope cells, but its specific role therein has not been assessed in vivo. We therefore generated gonadotrope-specific Pgr conditional knockout mice (cKO) using the Cre-LoxP system. Overall, both female and male cKO mice appeared phenotypically normal. cKO females displayed regular estrous cycles (vaginal cytology) and normal fertility (litter size and frequency). Reproductive organ weights were comparable between wild-type and cKO mice of both sexes, as were production and secretion of the gonadotropins, LH and FSH, with one exception. On the afternoon of proestrus, the amplitude of the LH surge was blunted in cKO females relative to controls. Contrary to predictions of earlier models, this did not appear to derive from impaired GnRH self-priming. Collectively, these data indicate that PR function in gonadotropes may be limited to regulation of LH surge amplitude in female mice via a currently unknown mechanism.
Caterina Luana Pitasi, Junjun Liu, Blandine Gausserès, Gaëlle Pommier, Etienne Delangre, Mathieu Armanet, Pierre Cattan, Bruno Mégarbane, Anne-Sophie Hanak, Kamel Maouche, Danielle Bailbé, Bernard Portha, and Jamileh Movassat
Islet inflammation is associated with defective β cell function and mass in type 2 diabetes (T2D). Glycogen synthase kinase 3 (GSK3) has been identified as an important regulator of inflammation in different diseased conditions. However, the role of GSK3 in islet inflammation in the context of diabetes remains unexplored. In this study, we investigated the direct implication of GSK3 in islet inflammation in vitro and tested the impact of GSK3 inhibition in vivo, on the reduction of islet inflammation, and the improvement of glucose metabolism in the Goto-Kakizaki (GK) rat, a spontaneous model of T2D. GK rats were chronically treated with infra-therapeutic doses of lithium, a widely used inhibitor of GSK3. We analyzed parameters of glucose homeostasis as well as islet inflammation and fibrosis in the endocrine pancreas. Ex vivo, we tested the impact of GSK3 inhibition on the autonomous inflammatory response of non-diabetic rat and human islets, exposed to a mix of pro-inflammatory cytokines to mimic an inflammatory environment. Treatment of young GK rats with lithium prevented the development of overt diabetes. Lithium treatment resulted in reduced expression of pro-inflammatory cytokines in the islets. It decreased islet fibrosis and partially restored the glucose-induced insulin secretion in GK rats. Studies in non-diabetic human and rat islets exposed to inflammatory environment revealed the direct implication of GSK3 in the islet autonomous inflammatory response. We show for the first time, the implication of GSK3 in islet inflammation and suggest this enzyme as a viable target to treat diabetes-associated inflammation.