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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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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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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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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.

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Yujiao Dai, Peng Hao, Zhimei Sun, Zhiyi Guo, Hong Xu, Lihui Xue, Hongyu Song, Yida Li, Shuang Li, Mingming Gao, Teng Si, Yuxin Zhang, and Yajuan Qi

Yes-associated protein (YAP), as a co-activator of transcription factors, is a downstream protein in the Hippo signaling pathway with important functions in cell proliferation, apoptosis, invasion and migration. YAP also plays a key role in the development of CCl4-induced liver fibrosis. However, the mechanism of YAP during hepatic fibrosis progression and reversion is still unclear. Mild liver fibrosis was developed after 4 months of high-fat diet (HFD) stimulation, and we found that the YAP signaling pathway was activated. Here, we aim to reveal whether specific knockout of Yap gene in the liver can improve liver fibrosis induced by insulin resistance (IR) stimulated by HFD, and further explain its specific mechanism. We found that liver-specific Yap gene knockout improved IR-induced liver fibrosis and liver dysfunction, and this mechanism is related to the inhibition of the insulin signal pathway at the FoxO1 level. These findings provide a new insight, and Yap is expected to be a new target to reverse the early stage of liver fibrosis induced by IR.

Open access

Yanli Miao, Haojie Qin, Yi Zhong, Kai Huang, and Caijun Rao

Obesity is an increasingly serious epidemic worldwide characterized by an increase in the number and size of adipocytes. Adipose tissue maintains the balance between lipid storage and energy utilization. Therefore, adipose metabolism is of great significance for the prevention, treatment and intervention of obesity. Asprosin, a novel adipokine, is a circulating hormone mainly secreted by white adipose tissue. Previous studies have shown that asprosin plays a role in fasting-induced homeostasis, insulin resistance, and glucose tolerance. However, whether it can regulate the metabolism of adipose tissue itself has not been studied. This study intended to examine the roles and potential mechanisms of asprosin in adipose regulation. We first demonstrated that the expression level of asprosin was significantly downregulated in subcutaneous white adipose tissue (scWAT) of high-fat diet (HFD)-fed or cold-stimulated mice. Overexpression of asprosin in scWAT reduced heat production, decreased expression of the browning marker uncoupling protein 1 (UCP1) and other browning-related genes, along with upregulation of adipogenic gene expression. Mechanistically, we found that Nrf2 was activated upon cold exposure, but this activation was suppressed after asprosin overexpression. In primary cultured adipocytes, adenovirusmediated asprosin overexpression inhibited adipose browning and aggravated lipid deposition, while Nrf2 agonist oltipraz could reverse these changes. Our findings suggest that novel adipokine asprosin negatively regulated browning and elevate lipid deposition in adipose tissue via a Nrf2-mediated mechanism. Asprosin may be a promising target for the prevention and treatment of obesity and other metabolic diseases.

Open access

Jane J Reavey, Catherine Walker, Alison A Murray, Savita Brito-Mutunayagam, Sheona Sweeney, Moira Nicol, Ana Cambursano, Hilary O D Critchley, and Jacqueline A Maybin

Heavy menstrual bleeding is common and debilitating but the causes remain ill defined. Rates of obesity in women are increasing and its impact on menstrual blood loss (MBL) is unknown. Therefore, we quantified BMI and MBL in women not taking hormones and with regular menstrual cycles and revealed a positive correlation. In a mouse model of simulated menstruation, diet-induced obesity also resulted in delayed endometrial repair, a surrogate marker for MBL. BrdU staining of mouse uterine tissue revealed decreased proliferation during menstruation in the luminal epithelium of mice on a high-fat diet. Menstruation is known to initiate local endometrial inflammation and endometrial hypoxia; hence, the impact of body weight on these processes was investigated. A panel of hypoxia-regulated genes (VEGF, ADM, LDHA, SLC2A1) showed consistently higher mean values in the endometrium of women with obesity and in uteri of mice with increased weight vs normal controls, although statistical significance was not reached. The inflammatory mediators, Tnf and Il6 were significantly increased in the uterus of mice on a high-fat diet, consistent with a pro-inflammatory local endometrial environment in these mice. In conclusion, obesity was associated with increased MBL in women. Mice given a high-fat diet had delayed endometrial repair at menstruation and provided a model in which to study the influence of obesity on menstrual physiology. Our results indicate that obesity results in a more pro-inflammatory local endometrial environment at menstruation, which may delay endometrial repair and increase menstrual blood loss.

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Elena Conte, Adele Romano, Michela De Bellis, Marialuisa de Ceglia, Maria Rosaria Carratù, Silvana Gaetani, Fatima Maqoud, Domenico Tricarico, and Claudia Camerino

We explored the involvement of oxytocin receptor (Oxtr)/transient-receptor-potential-vanilloid-1 (TRPV1) genes and oxytocin (Oxt) on the adaptation of skeletal muscle to cold stress challenge in mice. Oxtr expression in hypothalamic paraventricular (PVN), supraoptic nuclei (SON), and hippocampus (HIPP) were evaluated by immunohistochemistry in parallel with the measurement of circulating Oxt. The Oxtr and TRPV1 gene expressions in soleus (SOL) and tibialis anterior (TA) muscles were investigated by RT-PCR. Histological studies of the cardiac muscle after cold stress were also performed. Male mice (n = 15) were divided into controls maintained at room temperature (RT = 24°C), exposed to cold stress (CS) at T = 4°C for 6 h , and 5 days. Immunohistochemical studies showed that Oxtr protein expression increased by two-fold (P = 0.01) in PVN and by 1.5-fold (P = 0.0001) in HIPP after 6 h- and 5 days of CS but decreased by 2-fold (P = 0.026) in SON in 5 days. Both Oxtr and TRPV1 gene expression increased after 6 h and 5 days of CS in SOL and TA muscles. Oxtr vs TRPV1 gene expression in SOL and TA muscles evaluated by regression analysis was linearly correlated following CS at 6 h and 5 days but not at control temperature of 24 ± 1°C, supporting the hypothesis of coupling between these genes. The circulating levels of Oxt are unaffected after 6 h of CS but decreased by 0.2-fold (P = 0.0141) after 5 days-CS. This is the first report that Oxtr and TRPV1 expressions are upregulated in response to cold acclimation in skeletal muscle. The up-regulation of Oxtr in PVN and HIPP balances the decrease of circulating Oxt.