Journal of molecular endocrinology最新文献

Glucose transporter type 2 (GLUT2), encoded by the Slc2a2 gene, is essential for glucose-stimulated insulin secretion (GSIS) in pancreatic islet β-cells, and low expression of GLUT2 is associated with β-cell dysfunction during the progression of type 2 diabetes in humans and animal models. Glucocorticoids are stress hormones that regulate inflammation and metabolism through glucocorticoid receptor (GR), a member of the nuclear receptor superfamily, and synthetic glucocorticoids are widely used for the treatment of inflammatory disorders. Prolonged exposure to glucocorticoids induces β-cell dysfunction and diabetes, but the effects of Slc2a2 gene repression in β-cells, if any, and the mechanisms involved, remains unclear. In the present study, we measured the expression of GSIS-related genes in the MIN6 β-cell line, and found that Slc2a2 mRNA expression was selectively reduced by dexamethasone (DEX), a synthetic glucocorticoid. Using bioinformatics and reporter assays, we identified two β-cell enhancers of the Slc2a2 gene, one within the first intron and another located approximately 40 kbp downstream of the transcription start site. The latter enhancer (designated as E3c) was responsible for the DEX-induced repression of the Slc2a2 gene. Of the previously identified β-cell-enriched transcription factors (NEUROD1, MAFA, HNF1α, and HNF1β) that activate the E3c enhancer, the transcriptional activity of HNF1α and HNF1β, responsible for maturity-onset diabetes of the young types 3 and 5, respectively, was repressed by DEX and GR. This functional link between HNF1α/HNF1β and GR should help elucidate the mechanism of glucocorticoid-induced β-cell dysfunction and diabetes.

The selective androgen receptor modulator (SARM), YK11, promotes the anabolism of muscle cells and osteoblastic precursor cells. Still, its effects on bone marrow-derived mesenchymal stem cells (BMSCs) and the repair of cranial bone defects are unknown. Here, the effects of different concentrations of YK11 on the osteogenic differentiation of BMSCs were determined. Subsequently, AR was inhibited to investigate whether the effect of YK11 on osteogenic differentiation of BMSCs was affected. A model of cranial defects was constructed to investigate the effects of YK11-equipped hydrogel on cranial defect repair as well as the effects of YK11 on cranial defect repair after inhibiting AR. Finally, the possible pathway of YK11 regulating osteogenic differentiation of BMSCs was explored. Our results show 2μM YK11 promoted the proliferation of BMSCs. 0.25-4μM YK11 could promote osteogenesis of BMSCs and the promoting effect was gradually enhanced with the concentration increase. In vivo, 0.5mg/ml YK11 and 1 mg/ml YK11 could promote the repair of cranial bone defects. After inhibiting AR, the effects of YK11 in promoting both osteogenic differentiation of BMSCs and repair of cranial defects were suppressed. YK11 may regulate the osteogenic differentiation of BMSCs through the BMP2/Smad signaling pathway. In conclusion, YK11 promoted the osteogenic differentiation of BMSCs by activation on AR. Meanwhile, YK11 promoted the repair of cranial bone defects in rats in vivo. The BMP2 (bone morphogenetic protein 2)/Smad signaling pathway may be involved in the regulation of osteogenic differentiation of BMSCs by YK11.

In endocrinology, there are many similarities in the regulation of gene expression between alleles, paralogous or orthologous genes, at the genetic or epigenetic level. However, there are also major differences in the spatial and temporal expression patterns of these genes, in particular between species. In few cases, it has been shown in vitro and/or in vivo that regulatory differences are mainly due to subtle differences (from one bp to less than 12bp) in the nucleotide sequence of transcription factor binding sites localized in the vicinity of the proximal promoter. In this short review, we propose to cite some of them, without claiming to be exhaustive. We also briefly review new methodologies that allow for more global studies of comparisons of expression regulations at the transcriptional level. We also discuss whether such studies could have given rise to any paradigm.

Obesity is a widespread nutritional disorder, leading to a strong predisposition towards adverse health consequences. Activating transcription factor 3 (ATF3), a stress-induced transcription factor, has been documented as a therapeutic target for obesity. The intent of this project was to characterize the detailed role of ATF3 in adipogenesis during the process of obesity and its obscure downstream mechanism. After adipogenic differentiation, RT-qPCR and Western Blot examined ATF3 and ubiquitin-specific peptidase 53 (USP53) mRNA levels and protein levels. Adipogenesis was identified by Oil-red O staining, triglyceride (TG) and Western Blot. JASPAR database, ChIP and luciferase reporter assays predicated and validated the transcriptional regulation of USP53 by ATF3. Western Blot also examined the protein levels of ras homolog family member A (RhoA)/Rho-associated coiled-coil kinase (ROCK) pathway-involved proteins. ATF3 mRNA level and protein level were depleted in the differentiated 3T3-L1 adipocytes and ATF3 elevation hindered the adipogenesis of 3T3-L1 adipocytes. ATF3 suppressed the transcription of USP53 as a transcription factor and lowered USP53 expression. Eventually, USP53 upregulation partially blunted the inhibitory role of ATF3 overexpression in adipogenesis and RhoA/ROCK pathway. Consequently, ATF3 might transcriptionally inactivate USP53 to repress adipocyte adipogenesis and downregulate RhoA/ROCK pathway.

Genetic variants involving steroidogenic acute regulatory protein cause lipoid congenital adrenal hyperplasia, which is characterized by impaired steroidogenesis in the adrenal glands and gonads. Functional assessment of variant STAR proteins is necessary for an accurate genetic diagnosis. Ideally, steroidogenic cells should be used to assess the functionality of STAR proteins, but the presence of endogenous STARs in steroidogenic cells precludes such a method. Here, we generated Star-edited cells from steroidogenic Y1 mouse adrenocortical tumor cells by genome editing. Star-edited Y1 cells exhibited very low but measurable cAMP-dependent pregnenolone production. Furthermore, stimulation of the cAMP pathway for 2 weeks resulted in the formation of lipid droplets in the cytoplasm of Star-edited Y1 cells, which resembled the histology of the adrenal glands of patients with lipoid congenital adrenal hyperplasia. The steroidogenic defect of Star-edited Y1 cells can be restored by transient overexpression of mouse Star. We found that human STAR can also restore defective steroidogenesis in Star-edited Y1 cells, and we were able to construct a novel in vitro system to evaluate human STAR variants. Collectively, we established Star-edited Y1 cells that retain the steroidogenic pathway downstream of the Star protein. Star-edited Y1 cells recapitulate the functional and morphological changes of lipoid congenital adrenal hyperplasia and can be used to evaluate the functionality of human STAR variants.

MafA is a key transcriptional regulator of pancreatic islet β-cell function. Its target genes include those encoding preproinsulin and the glucose transporter Glut2 (Slc2a2); thus, MafA function is essential for glucose-stimulated insulin secretion. Expression levels of MafA are reduced in β-cells of diabetic mouse models and human subjects, suggesting that β-cell dysfunction associated with type 2 diabetes is attributable to the loss of MafA. On the other hand, MafA is transcriptionally upregulated by incretin hormones through activation of CREB and its co-activator CRTC2. β-cell-specific expression of MafA relies on a distal enhancer element. However, the precise mechanism by which CREB-CRTC2 regulates the enhancer and proximal promoter regions of MafA remains unclear. In this report, we analyzed previously published ChIP-seq data and found that CREB and NeuroD1, a β-cell-enriched transactivator, bound to both the promoter and enhancer regions of human MAFA. A series of reporter assays revealed that CREB activated the enhancer through a conserved cAMP-responsive element (CRE) but stimulated MAFA promoter activity even when the putative CRE was deleted. Two E-box elements and a CCAAT motif, which bind NeuroD1 and ubiquitous NF-Y transcription factors, respectively, were necessary for transcriptional activation of the MAFA promoter by CREB. Genome-wide analysis of CREB-bound loci in β-cells revealed that they were enriched with CCAAT motifs. Furthermore, promoter analysis of the Isl1 gene encoding a β-cell-enriched transcription factor revealed that a CRE-like element and two CCAAT motifs, but not the E-box, were necessary for activation by CREB. These results provide clues to elucidate the detailed mechanism by which CREB regulates MafA as well as β-cell-specific genes.

G6PC2 encodes a glucose-6-phosphatase catalytic subunit that opposes the action of glucokinase in pancreatic islets, thereby modulating the sensitivity of insulin and glucagon secretion to glucose. In mice, G6pc2 is expressed at ~20-fold higher levels in β-cells than in α-cells, whereas in humans G6PC2 is expressed at only ~5-fold higher levels in β-cells. We therefore hypothesize that G6PC2 likely influences glucagon secretion to a greater degree in humans. With a view to generating a humanized mouse that recapitulates augmented G6PC2 expression levels in α-cells, we sought to identify the genomic regions that confer differential mouse G6pc2 expression in α-cells versus β-cells as well as the evolutionary changes that have altered this ratio in humans. Studies in islet-derived cell lines suggest that the elevated G6pc2 expression in mouse β-cells versus α-cells is mainly due to a difference in the relative activity of the proximal G6pc2 promoter in these cell types. Similarly, the smaller difference in G6PC2 expression between α-cells and β-cells in humans is potentially explained by a change in relative proximal G6PC2 promoter activity. However, we show that both glucocorticoid levels and multiple differences in the relative activity of eight transcriptional enhancers between mice and humans likely contribute to differential G6PC2 expression. Finally, we show that a mouse-specific non-coding RNA, Gm13613, whose expression is controlled by G6pc2 enhancer I, does not regulate G6pc2 expression, indicating that altered expression of Gm13613 in a humanized mouse that contains both the human promoter and enhancers should not affect G6PC2 function.

Icariside II, a flavonoid glycoside, is the main component found invivo after the administration of Herba epimedii and has shown some pharmacological effects, such as prevention of osteoporosis and enhancement of immunity. Increased levels of marrow adipose tissue are associated with osteoporosis. S100 calcium-binding protein A16 (S100A16) promotes the differentiation of bone marrow mesenchymal stem cells (BMSCs) into adipocytes. This study aimed to confirm the anti-lipidogenesis effect of Icariside II in the bone marrow by inhibiting S100A16 expression. We used ovariectomy (OVX) and BMSC models. The results showed that Icariside II reduced bone marrow fat content and inhibited BMSCs adipogenic differentiation and S100A16 expression, which correlated with lipogenesis. Overexpression of S100A16 eliminated the inhibitory effect of Icariside II on lipid formation. β-catenin participated in the regulation adipogenesis mediated by Icariside II/S100A16 in the bone. In conclusion, Icariside II protects against OVX-induced bone marrow adipogenesis by downregulating S100A16, in which β-catenin might also be involved.

Receptor activity-modifying proteins (RAMPs) modulate the expression and activity of numerous G protein-coupled receptors, primarily those within class B1. These receptors have important physiological roles, including in the regulation of food intake, energy metabolism, and glucose homeostasis. Dysregulation of these pathways can lead to obesity and diabetes mellitus, which present an ever-expanding global challenge. Whilst the roles of class B1 receptors and their peptide agonists in obesity and diabetes have been investigated, the contribution of RAMPs is less well understood. This review summarises the results of RAMP knockout studies, highlighting the involvement of these proteins in the incidence of disease. It then moves to discuss how receptor, RAMP, and agonist expression changes in disease states, and the benefits (or detriments) of these agonists to the pathways implicated in disease pathophysiology. Whilst much of the data centres around the calcitonin family of receptors, as their interactions with RAMPs are well established, this review then discusses receptors whose role in obesity and diabetes is well founded, but the significance of whose interactions with RAMPs is more recently emerging. The conclusion of this study of the literature is, however, that the information surrounding RAMPs is conflicting and multifaceted, and more research is required to fully understand their contribution to obesity and diabetes.

Pentraxin 3 (PTX3) is a prototypic humoral soluble pattern-recognition molecule known to function in immunity-related inflammation. Given the lack of information on the precise functions of PTX3 in the pathogenesis of Graves’ orbitopathy (GO), this study investigated the role of PTX3 in the inflammation and adipogenesis mechanism of GO. We first compared the PTX3 expression between orbital tissues from patients with GO and normal controls, using real-time polymerase chain reaction, which estimated significantly higher PTX3 transcript levels in the GO tissues than in the normal tissues. In addition, PTX3 production was markedly increased upon interleukin (IL)-1β and adipogenic stimulation. We then evaluated the effects of silencing PTX3 in primary orbital fibroblast cultures by analyzing the expression levels of pro-inflammatory cytokines, adipogenesis-related proteins, and downstream transcription factors in cells transfected with or without a small interfering RNA against PTX3, using western blot. Silencing PTX3 attenuated the IL-1β-induced secretion of pro-inflammatory cytokines, including IL-6, IL-8, monocyte chemotactic protein-1, intercellular adhesion molecule-1, and cyclooxygenase-2, and suppressed the IL-1β-mediated activation of p38 kinase, nuclear factor-κB, and extracellular signal-regulated kinase. Moreover, PTX3 knockdown suppressed adipogenic differentiation, as assessed using Oil Red O staining, as well as the expression of adipogenesis-associated transcription factors including peroxisome proliferator activator-γ, CCAAT/enhancer-binding proteins α and β, adipocyte protein 2, adiponectin, and leptin. Thus, this study suggests that PTX3 plays a significant role in the pathogenesis of GO and may serve as a novel therapeutic target for the condition.