Glucocorticoid hormones (GCs) have profound effects on bone metabolism. Via their nuclear hormone receptor – the GR – they act locally within bone cells and modulate their proliferation, differentiation, and cell death. Consequently, high glucocorticoid levels – as present during steroid therapy or stress – impair bone growth and integrity, leading to retarded growth and glucocorticoid-induced osteoporosis, respectively. Because of their profound impact on the immune system and bone cell differentiation, GCs also affect bone regeneration and fracture healing. The use of conditional-mutant mouse strains in recent research provided insights into the cell-type-specific actions of the GR. However, despite recent advances in system biology approaches addressing GR genomics in general, little is still known about the molecular mechanisms of GCs and GR in bone cells. Here, we review the most recent findings on the molecular mechanisms of the GR in general and the known cell-type-specific actions of the GR in mesenchymal cells and their derivatives as well as in osteoclasts during bone homeostasis, GC excess, bone regeneration and fracture healing.
Yasmine Hachemi, Anna E Rapp, Ann-Kristin Picke, Gilbert Weidinger, Anita Ignatius, and Jan Tuckermann
Tarlliza R Nardelli, Emerielle C Vanzela, Keli C Benedicto, Flora Brozzi, André Fujita, Alessandra K Cardozo, Décio L Eizirik, Antonio C Boschero, and Fernanda Ortis
Type 1 diabetes is caused by an autoimmune assault that induces progressive beta-cell dysfunction and dead. Pro-inflammatory cytokines, such as interleukin 1 beta (IL1B), tumor necrosis factor (TNF) and interferon gamma (IFNG) contribute for beta-cell death, which involves the activation of the nuclear factor kappa B (NFκB) and c- Jun N-terminal kinase (JNK). Prolactin (PRL), a physiological mediator for beta-cell proliferation, was shown to protect beta cells against cytokines pro-apoptotic effects. We presently investigated the mechanisms involved in the protective effects of prolactin against cytokine-induced beta-cell death. The findings obtained indicate that STAT3 activation is involved in the anti-apoptotic role of PRL in rat beta cells. PRL prevents the activation of JNK via AKT and promotes a shift from expression of pro- to anti-apoptotic proteins downstream of the JNK cascade. Furthermore, PRL partially prevents the activation of NFκB and the transcription of its target genes IkBa, Fas, Mcp1, A20 and Cxcl10 and also decreases NO production. On the other hand, the pro-survival effects of PRL do not involve modulation of cytokine-induced endoplasmic reticulum stress. These results suggest that the beneficial effects of PRL in beta cells involve augmentation of anti-apoptotic mechanisms and, at the same time, reduction of pro-apoptotic effectors, rendering beta cells better prepared to deal with inflammatory insults. The better understanding of the pro-survival mechanisms modulated by PRL in beta cells can provide tools to prevent cell demise during an autoimmune attack or following islet transplantation.
Daniela Nasteska and David J Hodson
It is becoming increasingly apparent that not all insulin-secreting beta cells are equal. Subtle differences exist at the transcriptomic and protein expression levels, with repercussions for beta cell survival/proliferation, calcium signalling and insulin release. Notably, beta cell heterogeneity displays plasticity during development, metabolic stress and type 2 diabetes mellitus (T2DM). Thus, heterogeneity or lack thereof may be an important contributor to beta cell failure during T2DM in both rodents and humans. The present review will discuss the molecular and cellular features of beta cell heterogeneity at both the single-cell and islet level, explore how this influences islet function and insulin release and look into the alterations that may occur during obesity and T2DM.
Emily Jane Gallagher and Derek LeRoith
José Luis Soengas, José Miguel Cerdá-Reverter, and María Jesús Delgado
Evidence indicates that central regulation of food intake is well conserved along the vertebrate lineage, at least between teleost fish and mammals. However, several differences arise in the comparison between both groups. In this review, we describe similarities and differences between teleost fish and mammals on an evolutionary perspective. We focussed on the existing knowledge of specific fish features conditioning food intake, anatomical homologies and analogies between both groups as well as the main signalling pathways of neuroendocrine and metabolic nature involved in the homeostatic and hedonic central regulation of food intake.
Colin R Jefcoate and Jinwoo Lee
Cholesterol is an important regulator of cell signaling, both through direct impacts on cell membranes and through oxy-metabolites that activate specific receptors (steroids, hydroxy-cholesterols, bile acids). Cholesterol moves slowly through and between cell membranes with the assistance of specific binding proteins and transfer processes. The prototype cholesterol regulator is the Steroidogenesis Acute Regulatory (STAR), which moves cholesterol into mitochondria, where steroid synthesis is initiated by cytochrome P450 11A1 in multiple endocrine cell types. CYP27A1 generates hydroxyl cholesterol metabolites that activate LXR nuclear receptors to control cholesterol homeostatic and transport mechanisms. LXR regulation of cholesterol transport and storage as cholesterol ester droplets is shared by both steroid-producing cells and macrophage. This cholesterol signaling which is crucial to brain neuron regulation by astrocytes and microglial macrophage, is mediated by ApoE and is sensitive to disruption by β-amyloid plaques. sm-FISH delivers appreciable insights into signaling in single cells, by resolving single RNA molecules as mRNA and by quantifying pre-mRNA at gene loci. sm-FISH has been applied to problems in physiology, embryo development and cancer biology, where single cell features have critical impacts. sm-FISH identifies novel features of STAR transcription in adrenal and testis cells, including asymmetric expression at individual gene loci, delayed splicing and 1:1 association of mRNA with mitochondria. This may represent a functional unit for the translation-dependent cholesterol transfer directed by STAR, which integrates into mitochondrial fusion dynamics. Similar cholesterol dynamics repeat with different players in the cycling of cholesterol between astrocytes and neurons in the brain, which may be abnormal in neurodegenerative diseases.
Liping Luo, Wanxiang Jiang, Hui Liu, Jicheng Bu, Ping Tang, Chongyangzi Du, Zhipeng Xu, Hairong Luo, Bilian Liu, Bo Xiao, Zhiguang Zhou, and Feng Liu
The growth factor receptor bound protein GRB10 is an imprinted gene product and a key negative regulator of the insulin, IGF1 and mTORC1 signaling pathways. GRB10 is highly expressed in mouse fetal liver but almost completely silenced in adult mice, suggesting a potential detrimental role of this protein in adult liver function. Here we show that the Grb10 gene could be reactivated in adult mouse liver by acute endoplasmic reticulum stress (ER stress) such as tunicamycin or a short-term high-fat diet (HFD) challenge, concurrently with increased unfolded protein response (UPR) and hepatosteatosis. Lipogenic gene expression and acute ER stress-induced hepatosteatosis were significantly suppressed in the liver of the liver-specific GRB10 knockout mice, uncovering a key role of Grb10 reactivation in acute ER stress-induced hepatic lipid dysregulation. Mechanically, acute ER stress induces Grb10 reactivation via an ATF4-mediated increase in Grb10 gene transcription. Our study demonstrates for the first time that the silenced Grb10 gene can be reactivated by acute ER stress and its reactivation plays an important role in the early development of hepatic steatosis.
Luiz Henrique de Castro Assis, Rafael Henrique de Nóbrega, Nuria Esther Gómez-González, Jan Bogerd, and Rüdiger Winfried Schulz
The hormonal regulation of spermatogenesis involves both gonadotropins and steroid hormones. Long-term in vivo exposure of adult zebrafish to estrogen impaired spermatogenesis associated with an androgen insufficiency, possibly induced by inhibiting gonadotropin release. Using this experimental model, we investigated if androgen treatment could enhance spermatogenesis, while maintaining the inhibition of gonadotropin release through continued estrogen exposure. Moreover, we also exposed animals to androgen alone, in order to examine androgen effects in the absence of estrogen-induced gonadotropin inhibition. Estrogen exposure depleted type B spermatogonia, meiotic and postmeiotic germ cells from the adult testis, but promoted the proliferation of type A undifferentiated spermatogonia, which accumulated in the testis. This change in germ cell composition was accompanied by reduced mRNA levels of those growth factors (e.g. insl3 and igf3) expressed by testicular somatic cells and known to stimulate spermatogonial differentiation in zebrafish. Additional androgen (11-ketoandrostenedione, which is converted to 11-ketotestosterone) treatment in vivo reversed most of the effects of estrogen exposure on spermatogenesis while insl3 and igf3 transcript levels remained suppressed. When androgen treatment was given alone, it promoted the production of haploid cells at the expense of spermatogonia, and increased transcript levels of some growth factor and hormone receptor genes, but not those of insl3 or igf3. We conclude that estrogen exposure efficiently inhibits spermatogenesis because it induces androgen insufficiency and suppresses gonadotropin-regulated growth factors known to stimulate germ cell differentiation. Moreover, our results suggest that androgens and the growth factors Insl3 and Igf3 stimulate spermatogenesis via independent pathways.
Peng Zhang, Sheng Wang, Liang Wang, Bing Chen Shan, Hui Zhang, Fan Yang, Zhi Qiang Zhou, Xiao Wang, Ye Yuan, and You Jia Xu
Postmenopausal osteoporosis is a global health issue. Although a lack of estrogen is considered the major reason for postmenopausal osteoporosis, other factors might also contribute the etiology of the disease. In previous reports, we and others proposed that iron accumulation after menopause accelerates osteoporosis, and here, we genetically modified the expression of an endogenous hormone, hepcidin, to modulate iron status in a mouse model. Our results show that hepcidin levels negatively correlate with bone loss in both knockout and overexpression (with ovariectomy) murine models. In addition, iron overload enhances reactive oxygen species (ROS) activity and attenuates the functions of primary osteoblasts, while iron depletion could reverse this phenomenon through inhibiting the functions of primary osteoclasts. Therefore, our results provide more evidence of the ‘iron accumulation’ hypothesis, which suggests that high iron levels are risk factors for osteoporosis, and the ‘Huang’s hypothesis’ that hepcidin is a potential drug target for the prevention of postmenopausal osteoporosis.
Jiung-Pang Huang, Sheng-Chieh Hsu, Yaa-Jyuhn James Meir, Po-Shiuan Hsieh, Chih-Chun Chang, Kuan-Hsing Chen, Jan-Kan Chen, and Li-Man Hung
Many studies have reported the causes of obese metabolic syndrome (MS); however, the causes of nonobese MS (NMS) remain unknown. In this study, we demonstrated that inflamed dysfunctional adipose tissue plays a crucial role in cholesterol-induced NMS. Control (C), high cholesterol (HC) and HC with 10% fructose in drinking water (HCF) diets were fed to Sprague–Dawley rats for 12 weeks. After 12 weeks, the body weights of the C- and HC-fed rats were comparable, but the weights of the HCF-fed rats were relatively low. Cholesterol caused metabolic problems such as high blood pressure, hypercholesterolemia and hypoinsulinemia. The HCF-fed rats exhibited whole-body insulin resistance with low circulating high-density lipoprotein levels. Increases in the tumor necrosis factor α level in the plasma, the number of CD68+ macrophages and the free nuclear factor-κB level in gonadal white adipose tissue (gWAT) resulted in local inflammation, which appeared as inflamed dysfunctional gWAT. Reduced superoxide dismutases (SODs) deteriorate natural antioxidant defense systems and induce reactive oxygen species in gWAT. Dysregulation of plasma levels of catecholamine, adipokines (leptin and adiponectin), hormone-sensitive lipase and perilipin in cholesterol-induced inflamed adipose tissue contributed to increased lipolysis and increased circulating nonesterified fatty acids. Cholesterol activated inflammation, lipolysis and cell death in 3T3-L1 adipocytes. Moreover, Chol-3T3-CM reduced the population of M2-type Raw264.7 macrophages, indicating that the macrophage polarization is mediated by cholesterol. Together, our findings indicate that inflamed dysfunctional adipocytes are critical in NMS, supporting the development of anti-inflammatory agents as potential therapeutic drugs for treating NMS.