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Open access

Shisan Xu, Fangjing Xie, Li Tian, Samane Fallah, Fatemeh Babaei, Sinai H C Manno, Francis A M Manno III, Lina Zhu, Kin Fung Wong, Yimin Liang, Rajkumar Ramalingam, Lei Sun, Xin Wang, Robert Plumb, Lee Gethings, Yun Wah Lam, and Shuk Han Cheng

Sexual differences have been observed in the onset and prognosis of human cardiovascular diseases, but the underlying mechanisms are not clear. Here, we found that zebrafish heart regeneration is faster in females, can be accelerated by estrogen and is suppressed by the estrogen-antagonist tamoxifen. Injuries to the zebrafish heart, but not other tissues, increased plasma estrogen levels and the expression of estrogen receptors, especially esr2a. The resulting endocrine disruption induces the expression of the female-specific protein vitellogenin in male zebrafish. Transcriptomic analyses suggested heart injuries triggered pronounced immune and inflammatory responses in females. These responses, previously shown to elicit heart regeneration, could be enhanced by estrogen treatment in males and reduced by tamoxifen in females. Furthermore, a prior exposure to estrogen preconditioned the zebrafish heart for an accelerated regeneration. Altogether, this study reveals that heart regeneration is modulated by an estrogen-inducible inflammatory response to cardiac injury. These findings elucidate a previously unknown layer of control in zebrafish heart regeneration and provide a new model system for the study of sexual differences in human cardiac repair.

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Hui Yu, Zoe Thompson, Sylee Kiran, Graham L Jones, Lakshmi Mundada, Surbhi, Marcelo Rubinstein, and Malcolm J Low

Proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus (ARC) are essential for normal energy homeostasis. Maximal ARC Pomc transcription is dependent on neuronal Pomc enhancer 1 (nPE1), located 12 kb upstream from the promoter. Selective deletion of nPE1 in mice decreases ARC Pomc expression by 70%, sufficient to induce mild obesity. Because nPE1 is located exclusively in the genomes of placental mammals, we questioned whether its hypomorphic mutation would also alter placental Pomc expression and the metabolic adaptations associated with pregnancy and lactation. We assessed placental development, pup growth, circulating leptin and expression of Pomc, Agrp and alternatively spliced leptin receptor (LepR) isoforms in the ARC and placenta of Pomc∆1/∆1 and Pomc+/+ dams. Despite indistinguishable body weights, lean mass, food intake, placental histology and Pomc expression and overall pregnancy outcomes between the genotypes, Pomc ∆1/∆1 females had increased pre-pregnancy fat mass that paradoxically decreased to control levels by parturition. However, Pomc∆1/∆1 dams had exaggerated increases in circulating leptin, up to twice of that of the typically elevated levels in Pomc+/+ mice at the end of pregnancy, despite their equivalent fat mass. Pomc∆1/∆1dams also had increased placental expression of soluble leptin receptor (LepRe), although the protein levels of LEPRE in circulation were the same as Pomc+/+ controls. Together, these data suggest that the hypomorphic Pomc∆1/∆1 allele is responsible for the perinatal super hyperleptinemia of Pomc∆1/∆1 dams, possibly due to upregulated leptin secretion from individual adipocytes.

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Wenjing Wu, Jiayao Fu, Yijing Gu, Yu Wei, Pengfei Ma, and Junhua Wu

Emerging evidence has indicated that estrogen deficiency contributes to osteoporosis by affecting the level of inflammation. The inflammation microenvironment affects many cellular physiological processes, one of which may be cellular senescence according to previous studies. Senescent cells cannot function normally and secrete inflammatory cytokines and degradative proteins, which are referred to as senescence-associated secretory phenotype (SASP) factors, inducing further senescence and inflammation. Thus, stopping this vicious cycle may be helpful for postmenopausal osteoporosis treatment. Here, we used ovariectomized (OVX) mice as an estrogen-deficient model and confirmed that OVX bone marrow mesenchymal stem cells (BMSCs) displayed a senescent phenotype and upregulated SASP factor secretion both in vitro and in vivo. Furthermore, JAK2/STAT3, an important cytokine secretion-related signalling pathway that is associated with SASP secretion, was activated. Estrogen addition and estrogen receptor blockade confirmed that the JAK2/STAT3 axis participated in OVX BMSC senescence by mediating SASP factors. And JAK inhibition reduced SASP factor expression, alleviated senescence and enhanced osteogenic differentiation. Intraperitoneal injection of a JAK inhibitor, ruxolitinib, prevented bone loss in OVX mice. Collectively, our results revealed that JAK2/STAT3 plays an important role in the inflammation-senescence-SASP feedback loop in OVX BMSCs and that JAK inhibition could be a new method for treating postmenopausal osteoporosis.

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Neil Tanday, Peter R Flatt, Nigel Irwin, and R Charlotte Moffett

Transdifferentiation of beta- to alpha-cells has been implicated in the pathogenesis of diabetes. To investigate the impact of contrasting aetiologies of beta-cell stress, as well as clinically approved incretin therapies on this process, lineage tracing of beta-cells in transgenic Ins1 Cre/+/Rosa26-eYFP mice was investigated. Diabetes-like syndromes were induced by streptozotocin (STZ), high fat feeding (HFF) or hydrocortisone (HC), and effects of treatment with liraglutide or sitagliptin were investigated. Mice developed the characteristic metabolic features associated with beta-cell destruction or development of insulin resistance. Liraglutide was effective in preventing weight gain in HFF mice, with both treatments decreasing energy intake in STZ and HC mice. Treatment intervention also significantly reduced blood glucose levels in STZ and HC mice, as well as increasing either plasma or pancreatic insulin while decreasing circulating or pancreatic glucagon in all models. The recognised changes in pancreatic morphology induced by STZ, HFF or HC were partially, or fully, reversed by liraglutide and sitagliptin, and related to advantageous effects on alpha- and beta-cell growth and survival. More interestingly, induction of diabetes-like phenotype, regardless of pathogenesis, led to increased numbers of beta-cells losing their identity, as well as decreased expression of Pdx1 within beta-cells. Both treatment interventions, and especially liraglutide, countered detrimental islet cell transitioning effects in STZ and HFF mice. Only liraglutide imparted benefits on beta- to alpha-cell transdifferentiation in HC mice. These data demonstrate that beta- to alpha-cell transdifferentiation is a common consequence of beta-cell destruction or insulin resistance and that clinically approved incretin-based drugs effectively limit this.

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Ziping Jiang, Junduo Wu, Fuzhe Ma, Jun Jiang, Linlin Xu, Lei Du, Wenlin Huang, Zhaohui Wang, Ye Jia, Laijin Lu, and Hao Wu

Over a half of the diabetic individuals develop macrovascular complications that cause high mortality. Oxidative stress (OS) promotes endothelial dysfunction (ED) which is a critical early step toward diabetic macrovascular complications. Nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of cellular antioxidant defense system and combats diabetes-induced OS. Previously, we found that impaired NRF2 antioxidant signaling contributed to diabetes-induced endothelial OS and dysfunction in mice. The present study has investigated the effect of microRNA-200a (miR-200a) on NRF2 signaling and diabetic ED. In aortic endothelial cells (ECs) isolated from C57BL/6 wild-type (WT) mice, high glucose (HG) reduced miR-200a levels and increased the expression of kelch-like ECH-associated protein 1 (Keap1) – a target of miR-200a and a negative regulator of NRF2. This led to the inactivation of NRF2 signaling and exacerbation of OS and inflammation. miR-200a mimic (miR-200a-M) or inhibitor modulated KEAP1/NRF2 antioxidant signaling and manipulated OS and inflammation under HG conditions. These effects were completely abolished by knockdown of Keap1, indicating that Keap1 mRNA is a major target of miR-200a. Moreover, the protective effect of miR-200a-M was completely abrogated in aortic ECs isolated from C57BL/6 Nrf2 knockout (KO) mice, demonstrating that NRF2 is required for miR-200a’s actions. In vivo, miR-200a-M inhibited aortic Keap1 expression, activated NRF2 signaling, and attenuated hyperglycemia-induced OS, inflammation and ED in the WT, but not Nrf2 KO, mice. Therefore, the present study has uncovered miR-200a/KEAP1/NRF2 signaling that controls aortic endothelial antioxidant capacity, which protects against diabetic ED.

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Anneleen Segers, Louis Desmet, Shu Sun, Kristin Verbeke, Jan Tack, and Inge Depoortere

The known crosstalk between short-chain fatty acids (SCFAs) and the circadian clock is tightly intertwined with feeding time. We aimed to investigate the role of the core clock gene Bmal1 and feeding time in the diurnal rhythms in plasma and caecal SCFA levels and in their effect on the release of the hunger hormone ghrelin in the stomach and colon. WT, Bmal1 -/- (ad libitum fed) and night-time-restricted-fed (RF)-Bmal1 -/- littermates were killed at zeitgeber time (ZT) 4 and 16. SCFA concentrations were measured by gas chromatography. To investigate the effect of SCFAs on ghrelin release, stomach and colonic full-thickness strips were incubated with Krebs or a SCFA mix mimicking plasma or caecal concentrations, after which octanoyl ghrelin release was measured by RIA. Diurnal rhythms in caecal and plasma SCFAs oscillated in phase but rhythmic changes were abolished in Bmal1 -/- mice. RF of Bmal1 -/- mice restored fluctuations in caecal SCFAs. Plasma SCFA concentrations failed to affect gastric ghrelin release. The effect of caecal SCFA concentrations on colonic ghrelin release was rhythmic (inhibition at ZT 4, no effect at ZT 16). In Bmal1 -/- mice, the inhibitory effect of SCFAs at ZT 4 was abolished. RF Bmal1 -/- mice restored the inhibitory effect and increased colonic Clock expression. To conclude, diurnal fluctuations in caecal SCFAs and the effect of SCFAs on colonic ghrelin release are regulated by feeding time, independent of the core clock gene Bmal1. However, local entrainment of other clock genes might contribute to the observed effects.

Open access

Romain Fontaine, Eirill Ager-Wick, Kjetil Hodne, and Finn-Arne Weltzien

Follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) produced by the gonadotropes play a major role in control of reproduction. Contrary to mammals and birds, Lh and Fsh are mostly produced by two separate cell types in teleost. Here, we investigated gonadotrope plasticity, using transgenic lines of medaka (Oryzias latipes) where DsRed2 and hrGfpII are under the control of the fshb and lhb promotors respectively. We found that Fsh cells appear in the pituitary at 8 dpf, while Lh cells were previously shown to appear at 14 dpf. Similar to Lh cells, Fsh cells show hyperplasia from juvenile to adult stages. Hyperplasia is stimulated by estradiol. Both Fsh and Lh cells show hypertrophy during puberty with similar morphology. They also share similar behavior, using their cellular extensions to make networks. We observed bi-hormonal gonadotropes in juveniles and adults but not in larvae where only mono-hormonal cells are observed, suggesting the existence of phenotypic conversion between Fsh and Lh in later stages. This is demonstrated in cell culture, where some Fsh cells start to produce Lhβ, a phenomenon enhanced by gonadotropin-releasing hormone (Gnrh) stimulation. We have previously shown that medaka Fsh cells lack Gnrh receptors, but here we show that with time in culture, some Fsh cells start responding to Gnrh, while fshb mRNA levels are significantly reduced, both suggestive of phenotypic change. All together, these results reveal high plasticity of gonadotropes due to both estradiol-sensitive proliferation and Gnrh promoted phenotypic conversion, and moreover, show that gonadotropes lose part of their identity when kept in cell culture.

Open access

Koichiro Taguchi, Kazuo Kajita, Yoshihiko Kitada, Masayuki Fuwa, Motochika Asano, Takahide Ikeda, Toshiko Kajita, Tatsuo Ishizuka, Itaru Kojima, and Hiroyuki Morita

Despite extensive investigation, the mechanisms underlying adipogenesis are not fully understood. We previously identified proliferative cells in adipose tissue expressing adipocyte-specific genes, which were named small proliferative adipocytes (SPA). In this study, we investigated the characteristics and roles of SPA in adipose tissue. Epididymal and inguinal fat was digested by collagenase, and then SPA were separated by centrifugation from stromal vascular cells (SVC) and mature white adipocytes. To clarify the feature of gene expression in SPA, microarray and real-time PCR were performed. The expression of adipocyte-specific genes and several neuronal genes was increased in the order of SVC < SPA < mature white adipocytes. In addition, proliferin was detected only in SPA. SPA differentiated more effectively into lipid-laden cells than SVC. Moreover, differentiated SPA expressed uncoupling protein 1 and mitochondria-related genes more than differentiated SVC. Treatment of SPA with pioglitazone and CL316243, a specific β3-adrenergic receptor agonist, differentiated SPA into beige-like cells. Therefore, SPA are able to differentiate into beige cells. SPA isolated from epididymal fat (epididymal SPA), but not SPA from inguinal fat (inguinal SPA), expressed a marker of visceral adipocyte precursor, WT1. However, no significant differences were detected in the expression levels of adipocyte-specific genes or neuronal genes between epididymal and inguinal SPA. The ability to differentiate into lipid-laden cells in epididymal SPA was a little superior to that in inguinal SPA, whereas the ability to differentiate into beige-like cells was greater in inguinal SPA than epididymal SPA. In conclusion, SPA may be progenitors of beige cells.

Free access

Wonsuk Choi, Joon Ho Moon, and Hail Kim

Serotonin is a biogenic amine synthesized from the essential amino acid tryptophan. Because serotonin cannot cross the blood-brain barrier, it functions differently in neuronal and non-neuronal tissues. In the CNS, serotonin regulates mood, behavior, appetite, and energy expenditure. Although most serotonin in the body is synthesized at the periphery, its biological roles have not been well elucidated. Older studies using chemical agonists and antagonists yielded conflicting results, because the complexity of serotonin receptors and the low selectivity of agonists and antagonists were not known. Several recent studies using specific knock-out of serotonin receptors have been performed to assess the role of peripheral serotonin in regulating energy metabolism. This review discusses (1) the tissue-specific roles of peripheral serotonin in regulating energy metabolism, (2) the mechanism by which dysfunctional peripheral serotonin signaling can progress to metabolic diseases, and (3) how peripheral serotonin signaling could be a therapeutic target for metabolic diseases.

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Federico Gatto, Richard A Feelders, Rob van der Pas, Peter van Koetsveld, Eleonora Bruzzone, Marica Arvigo, Fadime Dogan, Steven Lamberts, Diego Ferone, and Leo Hofland

Pituitary-directed medical treatment for Cushing’s disease (CD) is currently represented by membrane receptor targeting drugs (somatostatin analogs and dopamine agonists). Somatostatin and dopamine receptors are regulated by β-arrestins, which have been shown to be differentially regulated by glucocorticoids in non-neuroendocrine cells. In this study we investigated the effects of glucocorticoids on β-arrestin expression in corticotroph tumor cells. First, AtT20 cells, a mouse model of CD, were exposed to dexamethasone (Dex) at different time points and β-arrestin expression was evaluated at mRNA and protein levels. Futhermore, β-arrestin mRNA expression was evaluated in 17 human corticotroph adenoma samples and correlated to patients’ pre-operative cortisol levels. We observed that Dex treatment induced a time-dependent increase in β-arrestin 1 mRNA expression and a decrease in β-arrestin 2. The same modulation pattern was observed at protein level. Dex-mediated modulation of β-arrestins was abolished by co-treatment with mifepristone, and Dex withdrawal restored β-arrestin expression to basal levels after 72 h. The evaluation of β-arrestin mRNA in corticotroph adenomas from CD patients with variable disease activity showed a significant positive correlation between β-arrestin 1 mRNA and urinary cortisol levels. The effect of glucocorticoids on β-arrestin levels was confirmed by the analysis of two samples from a single patient, which underwent adenomectomy twice, with different pre-operative cortisol levels. In conclusion, glucocorticoids induce an inverse modulation of the two β-arrestin isofoms in corticotroph tumor cells. Since β-arrestins regulate membrane receptor functions, this finding may help to better understand the variable response to pituitary-targeting drugs in patients with Cushing’s disease.