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Irving Salinas, Niharika Sinha, and Aritro Sen

In recent years, androgens have emerged as critical regulators of female reproduction and women’s health in general. While high levels of androgens in women are associated with polycystic ovary syndrome (PCOS), recent evidence suggests that a certain amount of direct androgen action through androgen receptor is also essential for normal ovarian function. Moreover, prenatal androgen exposure has been reported to cause developmental reprogramming of the fetus that manifests into adult pathologies, supporting the Developmental Origins of Health and Disease (DOHaD) hypothesis. Therefore, it has become imperative to understand the underlying mechanism of androgen actions and its downstream effects under normal and pathophysiological conditions. Over the years, there has been a lot of studies on androgen receptor function as a transcriptional regulator in the nucleus as well as androgen-induced rapid extra-nuclear signaling. Conversely, new evidence suggests that androgen actions may also be mediated through epigenetic modulation involving both the nuclear and extra-nuclear androgen signaling. This review focuses on androgen-induced epigenetic modifications in female reproduction, specifically in the ovary, and discusses emerging concepts, latest perceptions, and highlight the areas that need further investigation.

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Clyde J Wright, Sarah McKenna, Robyn De Dios, Brit H Boehmer, Leanna Nguyen, Sankar Ghosh, Jeryl Sandoval, and Paul J Rozance

The β-cell response to injury may be as critical for the development of diabetes as the specific insult. In the current study, we used streptozotocin (STZ) to injure the β-cell in order to study the response with a focus on NFκB. MIN6 cells were exposed to STZ (0.5–8 mM, 0–24h) ±TNFα (100 ng/mL) and ±IκBβ siRNA to lower the threshold to NFκB activation. Cell viability was determined by trypan blue exclusion. NFκB activation was determined by the expression of the target genes Nos2 and Cxcl10, localization of the NFκB proteins p65 and p50, and expression and localization of the NFκB inhibitors, IκBβ and IκBα. There was no NFκB activation in MIN6 cell exposed to STZ (2 mM) alone. However, knocking down IκBβ expression using siRNA resulted in STZ-induced expression of NFκB target genes and increased cell death, while co-incubation with STZ and TNFα enhanced cell death compared to either exposure alone. Adult male IκBβ−/− and WT mice were exposed to STZ and monitored for diabetes. The IκBβ−/− mice developed hyperglycemia and diabetes more frequently than controls following STZ exposure. Based on these results we conclude that STZ exposure alone does not induce NFκB activity. However, lowering the threshold to NFκB activation by co-incubation with TNFα or lowering IκBβ levels by siRNA sensitizes the NFκB response to STZ and results in a higher likelihood of developing diabetes in vivo. Therefore, increasing the threshold to NFκB activation through stabilizing NFκB inhibitory proteins may prevent β-cell injury and the development of diabetes.

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Jinyu Ma, Yuejun Wang, Jie Ding, Shouping Zhang, Yinuo Yang, and Cheng Sun

Several histone deacetylase (HDAC) inhibitors have been shown to play beneficial roles in treating obesity and its related metabolic syndromes. However, the underlying mechanisms are still not understood well. In this study, we examined the potential roles of SAHA, a potent inhibitor of HDACs, on energy expenditure and explored the molecular mechanism involved. Our data showed that SAHA induces less lipid accumulation and smaller lipid droplets in cultured adipocytes. In vivo studies showing SAHA reduces body weight gain and increases core temperature in lean and obese mice. Furthermore, SAHA accelerates blood glucose disposal, improves insulin sensitivity and attenuates fatty liver in obese animals. Transcriptome sequencing found that a group of zinc finger proteins (Zfps) was up-regulated by SAHA. Functional studies showed that the knockdown of Zfp691 or Zfp719 largely abolishes SAHA-induced Ucp1 expression in adipocytes. ChIP assay showed that SAHA stimulates histone H3 acetylation at Zfp719 promoter. Luciferase reporter analysis revealed that Zfp719 activates Ucp1 promoter. As a consequence, forced expression of Zfp719 increases Ucp1 expression and promotes lipid catabolism in adipocytes. Taken together, our data indicate that by stimulating axis of ZFPs-UCP1, SAHA induces white fat browning and energy consumption, which makes it a potential drug for treating obesity and related metabolic dysfunctions.

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Hiroharu Mifune, Yuji Tajiri, Yusuke Sakai, Yukie Kawahara, Kento Hara, Takahiro Sato, Yoshihiro Nishi, Akinori Nishi, Ryouichi Mitsuzono, Tatsuyuki Kakuma, and Masayasu Kojima

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Pieter-Jan Martens, Conny Gysemans, and Chantal Mathieu

Type 1 diabetes is one of the most common chronic diseases in children and adolescents, but remains unpreventable and incurable. The discovery of insulin, already 100 years ago, embodied a lifesaver for people with type 1 diabetes as it allowed the replacement of all functions of the beta cell. Nevertheless, despite all technological advances, the majority of type 1 diabetic patients fail to reach the recommended target HbA1c levels. The disease-associated complications remain the true burden of affected individuals and necessitate the search for disease prevention and reversal. The recognition that type 1 diabetes is a heterogeneous disease with an etiology in which both the innate and adaptive immune system as well as the insulin-producing beta cells intimately interact, has fostered the idea that treatment to specific molecular or cellular characteristics of the patient groups will be needed. Moreover, robust and reliable biomarkers to detect type 1 diabetes in the early (pre-symptomatic) phases are wanted to preserve functional beta cell mass. The pitfalls of past therapeutics along with the perspectives of current therapies can open up the path for future research.

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Chang Shan, Jiang Yue, and Wei Liu

Bone is emerging as a versatile endocrine organ and its interactions with apparently unrelated organs are being more widely recognized. Osteocalcin (OCN), a polypeptide hormone secreted by osteoblasts, has been found to exert multiple endocrine functions through its metabolically active form, uncarboxylated OCN (uOCN). Mounting evidence has shown that following its binding to G-protein coupled receptor 6a (Gprc6a) in the peripheral tissues, uOCN acts on pancreatic β cells to increase insulin secretion, and on muscle and white adipose tissue to promote glucose and lipid metabolism. More strikingly, researchers have found a surprising role of uOCN in testicular function to facilitating testosterone biosynthesis and regulating male fertility via a pancreas-bone-gonadal axis. However, the detailed functional mechanisms of uOCN on the hypothalamic–pituitary–gonadal axis or the pancreas–bone–gonadal axis are not fully understood. Besides highlighting the regulatory mechanisms of uOCN in the hypothalamus and pituitary, we also discuss its role in male as well as female fertility and its potential clinical implications in some reproductive endocrine diseases and pubertal developmental disorders.

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Pryscila Ds Teixeira, Angela M Ramos-Lobo, Mariana Rosolen Tavares, Frederick Wasinski, Renata Frazao, and Jose Donato

Leptin is a hormone required for the regulation of body weight in adult animals. However, during postnatal period, leptin is mostly involved in developmental processes. Because the precise moment in which leptin starts to exert its metabolic effects is not well characterized, our objective was to identify the approximate onset of leptin effects on the regulation of energy balance. We observed that male Lepob/ob mice started to exhibit increased body fat mass from postnatal day 13 (P13), whereas in females the increase in adiposity began on P20. Daily leptin injections from P10 to P22 did not reduce the weight gain of wild-type mice. However, an acute leptin injection induced an anorexigenic response in 10-day-old C57BL/6 mice, but not in 7-day-old mice. An age-dependent increase in the number of leptin receptor-expressing neurons and leptin-induced pSTAT3 cells was observed in the hypothalamus of P7, P10 and P16 mice. Leptin deficiency started to modulate the hypothalamic expression of transcripts involved in the regulation of metabolism between P7 and P12. Additionally, fasting-induced hypothalamic responses were prevented by leptin replacement in 10-day-old mice. Finally, 12-day-old males and females showed similar developmental timing of axonal projections of arcuate nucleus neurons in both wild-type and Lepob/ob mice. In summary, we provided a detailed characterization of the onset of leptin’s effects on the regulation of energy balance. These findings contribute to the understanding of leptin functions during development.

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Stephen P Ashcroft, Gareth Fletcher, Ashleigh M Philp, Carl Jenkinson, Shatarupa Das, Philip M Hansbro, Philip J Atherton, and Andrew Philp

Vitamin D deficiency is associated with symptoms of skeletal muscle myopathy including muscle weakness and fatigue. Recently, vitamin D-related metabolites have been linked to the maintenance of mitochondrial function within skeletal muscle. However, current evidence is limited to in vitro models and the effects of diet-induced vitamin D deficiency upon skeletal muscle mitochondrial function in vivo have received little attention. In order to examine the role of vitamin D in the maintenance of mitochondrial function in vivo, we utilised an established model of diet-induced vitamin D deficiency in C57BL/6J mice. Mice were either fed a control diet (2200 IU/kg i.e. vitamin D replete) or a vitamin D-deplete (0 IU/kg) diet for periods of 1, 2 and 3 months. Gastrocnemius muscle mitochondrial function and ADP sensitivity were assessed via high-resolution respirometry and mitochondrial protein content via immunoblotting. As a result of 3 months of diet-induced vitamin D deficiency, respiration supported via complex I + II (CI + IIP) and the electron transport chain (ETC) were 35 and 37% lower when compared to vitamin D-replete mice (P < 0.05). Despite functional alterations, citrate synthase activity, AMPK phosphorylation, mitofilin, OPA1 and ETC subunit protein content remained unchanged in response to dietary intervention (P > 0.05). In conclusion, we report that 3 months of diet-induced vitamin D deficiency reduced skeletal muscle mitochondrial respiration in C57BL/6J mice. Our data, when combined with previous in vitro observations, suggest that vitamin D-mediated regulation of mitochondrial function may underlie the exacerbated muscle fatigue and performance deficits observed during vitamin D deficiency.

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Fangyuan Chen, Haili Yu, Haichuan Zhang, Runzhu Zhao, Kaifang Cao, Yinghua Liu, Jiandong Luo, and Qin Xue

Our previous study has demonstrated maternal high-fat diet (HFD) caused a sex-dependent cardiac hypertrophy in adult male, but not female offspring. The present study tested the hypothesis that estrogen normalizes maternal HFD-induced cardiac hypertrophy by regulating angiotensin II receptor (ATR) expression in adult female offspring. Pregnant rats were divided into normal diet (ND) and HFD (60% kcal fat) groups. Ovariectomy (OVX) and 17β-estradiol (E2) replacement were performed on 8-week-old female offspring. Maternal HFD had no effect on left ventricular (LV) wall thickness, cardiac function and molecular markers of cardiac hypertrophy function in sham groups. However, maternal HFD caused cardiac hypertrophy of offspring in OVX groups, which was abrogated by E2 replacement. In addition, maternal HFD had no effect on ERα and ERβ in sham groups. In contrast, HFD significantly decreased ERα, but not ERβ in OVX groups. In sham groups, there was no difference in the cardiac ATR type 1 (AT1R) and ATR type 2 (AT2R) between ND and HFD offspring. HFD significantly increased AT2R, but not AT1R in OVX groups. Furthermore, maternal HFD resulted in decreased glucocorticoid receptors (GRs) binding to the glucocorticoid response elements at the AT2R promoter, which was due to decreased GRs in hearts from OVX offspring. These HFD-induced changes in OVX groups were abrogated by E2 replacement. These results support a key role of estrogen in the sex difference of maternal HFD-induced cardiac hypertrophy in offspring, and suggest that estrogen protects female offspring from cardiac hypertrophy in adulthood by regulating AT2R.

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Junling He, Yi Ding, Natalia Nowik, Charel Jager, Muhamed N H Eeza, A Alia, Hans J Baelde, and Herman P Spaink

Leptin is a hormone which functions in the regulation of energy homeostasis via suppression of appetite. In zebrafish, there are two paralogous genes encoding leptin, called lepa and lepb. In a gene expression study, we found that the lepb gene, not the lepa gene, was significantly downregulated under the state of insulin-resistance in zebrafish larvae, suggesting that the lepb plays a role in glucose homeostasis. In the current study, we characterised lepb-deficient (lepb −/−) adult zebrafish generated via a CRISPR-CAS9 gene editing approach by investigating whether the disruption of the lepb gene would result in the development of type 2 diabetes mellitus (T2DM) and diabetic complications. We observed that lepb −/− adult zebrafish had an increase in body weight, length and visceral fat accumulation, compared to age-matched control zebrafish. In addition, lepb −/− zebrafish had significantly higher blood glucose levels compared to control zebrafish. These data collectively indicate that lepb −/− adult zebrafish display the features of T2DM. Furthermore, we showed that lepb −/− adult zebrafish had glomerular hypertrophy and thickening of the glomerular basement membrane, compared to control zebrafish, suggesting that lepb −/− adult zebrafish develop early signs of diabetic nephropathy. In conclusion, our results demonstrate that lepb regulates glucose homeostasis and adiposity in zebrafish, and suggest that lepb −/− mutant zebrafish are a promising model to investigate the role of leptin in the development of T2DM and are an attractive model to perform mechanistic and therapeutic research in T2DM and its complications.