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Open access

Kate E Lines, Anna K Gluck, Supat Thongjuea, Chas Bountra, Rajesh V Thakker, and Caroline M Gorvin

Corticotrophinomas represent 10% of all surgically removed pituitary adenomas, however, current treatment options are often not effective, and there is a need for improved pharmacological treatments. Recently, JQ1+, a bromodomain inhibitor that promotes gene transcription by binding acetylated histone residues and recruiting transcriptional machinery, has been shown to reduce proliferation in a murine corticotroph cell line, AtT20. RNA-Seq analysis of AtT20 cells following treatment with JQ1+ identified the calcium-sensing receptor (CaSR) gene as significantly downregulated, which was subsequently confirmed using real-time PCR and Western blot analysis. CaSR is a G protein-coupled receptor that plays a central role in calcium homeostasis but can elicit non-calcitropic effects in multiple tissues, including the anterior pituitary where it helps regulate hormone secretion. However, in AtT20 cells, CaSR activates a tumour-specific cAMP pathway that promotes ACTH and PTHrP hypersecretion. We hypothesised that the Casr promoter may harbour binding sites for BET proteins, and using chromatin immunoprecipitation (ChIP)-sequencing demonstrated that the BET protein Brd3 binds to the promoter of the Casr gene. Assessment of CaSR signalling showed that JQ1+ significantly reduced Ca2+ e-mediated increases in intracellular calcium (Ca2+ i) mobilisation and cAMP signalling. However, the CaSR-negative allosteric modulator, NPS-2143, was unable to reduce AtT20 cell proliferation, indicating that reducing CaSR expression rather than activity is likely required to reduce pituitary cell proliferation. Thus, these studies demonstrate that reducing CaSR expression may be a viable option in the treatment of pituitary tumours. Moreover, current strategies to reduce CaSR activity, rather than protein expression for cancer treatments, may be ineffective.

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Yuka Ono and Kohsuke Kataoka

Glucose transporter type 2 (GLUT2), encoded by the SLC2A2 gene, is an essential component of glucose-stimulated insulin secretion in pancreatic islet β-cells. Like that of the gene encoding insulin, expression of the SLC2A2 gene expression is closely linked to β-cell functionality in rodents, but the mechanism by which β-cell-specific expression of SLC2A2 is controlled remains unclear. In this report, to identify putative enhancer elements of the mouse Slc2a2 gene, we examined evolutional conservation of the nucleotide sequence of its genomic locus, together with ChIP-seq data of histone modifications and various transcription factors published in previous studies. Using luciferase reporter assays, we found that an evolutionarily conserved region (ECR) located approximately 40 kbp downstream of the transcription start site of Slc2a2 functions as an active enhancer in the MIN6 β-cell line. We also found that three β-cell-enriched transcription factors, MafA, NeuroD1, and HNF1β, synergistically activate transcription through this 3’ downstream distal enhancer (ECR3’) and the proximal promoter region of the gene. Our data also indicate that the simultaneous binding of HNF1β to its target sites within the promoter and ECR3’ of Slc2a2 is indispensable for transcriptional activation, and that binding of MafA and NeuroD1 to their respective target sites within the ECR3’ enhances transcription. Co-immunoprecipitation experiments suggested that MafA, NeuroD1, and HNF1β interact with each other. Overall, these results suggest that promoter-enhancer communication through MafA, NeuroD1, and HNF1β is critical for Slc2a2 gene expression. These findings provide clues to help elucidate the mechanism of regulation of Slc2a2 gene expression in β-cells.

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Te-Yueh Lin, Hong Guo, and Xiaoli Chen

Pentraxin 3 (PTX3) is a soluble pattern recognition receptor playing an important role in immune response and inflammation. Lipopolysaccharide (LPS) stimulation can significantly induce PTX3 expression and secretion in adipocytes. Appropriate regulation of PTX3 secretion is critical for inflammatory homeostasis. Using chemical inhibitors of conventional and unconventional protein secretion, we explored the mechanisms that control LPS-stimulated PTX3 secretion in 3T3-L1 adipocytes. Inhibiting the conventional protein secretion blocked LPS-stimulated PTX3 secretion, resulting in cellular PTX3 accumulation in adipocytes. We also detected PTX3 in exosomes from LPS-treated adipocytes; inhibiting exosome trafficking attenuated PTX3 secretion. However, only 4.3% of secreted PTX3 was detected in exosomes compared to 95.7% in the non-exosomal fractions. The fractionation of isolated exosomes by the iodixanol density gradient centrifugation confirmed that a small portion of secreted PTX3 overlapped with exosomal markers in small extracellular-vesicle fractions. We conclude that PTX3 is secreted mainly through conventional protein secretion, and a small percentage of PTX3 is released in exosomes from LPS-stimulated adipocytes.

Open access

Hasnat Ali Abid, Asuka Inoue, and Caroline M Gorvin

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor that plays a fundamental role in extracellular calcium (Ca2+ e) homeostasis by regulating parathyroid hormone release and urinary calcium excretion. The CaSR has been described to activate all four G protein subfamilies (Gαq/11, Gαi/o, Gα12/13, Gαs), and mutations in the receptor that cause hyper/hypocalcaemia, have been described to bias receptor signalling. However, many of these studies are based on measurements of second messengers or gene transcription that occurs many steps downstream of receptor activation and can represent convergence points of several signalling pathways. Therefore, to assess CaSR-mediated G protein activation directly, we took advantage of a recently described NanoBiT G protein dissociation assay system. Our studies, performed in HEK293 cells stably expressing CaSR, demonstrate that Ca2+ e stimulation activates all Gαq/11 family and several Gαi/o family proteins, although Gαz was not activated. CaSR stimulated dissociation of Gα12/13 and Gαs from Gβ-subunits, but this occurred at a slower rate than that of other Gα-subunits. Investigation of cDNA expression of G proteins in three tissues abundantly expressing CaSR, the parathyroids, kidneys and pancreas, showed Gα11, Gαz, Gαi1 and Gα13 genes were highly expressed in parathyroid tissue, indicating CaSR most likely activates Gα11 and Gαi1 in parathyroids. In kidney and pancreas, the majority of G proteins were similarly expressed, suggesting CaSR may activate multiple G proteins in these cells. Thus, these studies validate a single assay system that can be used to robustly assess CaSR variants and biased signalling and could be utilised in the development of new pharmacological compounds targeting CaSR.

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Ying Xue, Ran Li, Ping Fang, Zheng-qin Ye, Yong Zhao, Yun Zhou, Ke-qin Zhang, and Ling Li

Gouty arthritis is a common inflammatory disease characterized by monosodium urate (MSU) crystal-induced nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome activation with upregulated caspase 1 protease and IL-1β in macrophages. Cucurbitacin B (CuB) is a tetracyclic triterpene that possesses a potential anti-inflammatory activity. However, the immunomodulatory and anti-inflammatory effects of CuB on gout have not been well characterized. Therefore, the purpose of the present study was to determine whether CuB exhibits anti-inflammatory effects on gout and to analyze the underlying molecular mechanism. We examined the effects of CuB on various stimuli-activated bone marrow-derived macrophages (BMDMs) and in a mouse model with MSU-induced acute gouty arthritis. Our results demonstrated that CuB effectively suppressed multiple stimuli-activated IL-1β secretion by interrupting NLRP3 inflammasome complex formation, inhibiting NLRP3 inflammasome activation and suppressing key enzymes of glycolysis in macrophages. Consistent with this, CuB pretreatment also ameliorated MSU-induced arthritis in vivo models of gout arthritis, manifested by reduced foot swelling and inflammatory cell infiltration. Taken together, our data provide the evidence that CuB is an NLRP3 inflammasome inhibitor with therapeutic potential for treating NLRP3 inflammasome-mediated diseases, especially gouty arthritis.

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Kanchana Suksri, Namoiy Semprasert, Mutita Junking, Suchanoot Kutpruek, Thawornchai Limjindaporn, Pa-thai Yenchitsomanus, and Suwattanee Kooptiwut

Long-term medication with dexamethasone (a synthetic glucocorticoid (GC) drug) results in hyperglycemia, or steroid-induced diabetes. Although recent studies revealed dexamethasone directly induces pancreatic β-cell apoptosis, its molecular mechanisms remain unclear. In our initial analysis of mRNA transcripts, we discovered the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway may be involved in dexamethasone-induced pancreatic β-cell apoptosis. In the present study, a mechanism of dexamethasone-induced pancreatic β-cell apoptosis through the TRAIL pathway was investigated in cultured cells and isolated mouse islets. INS-1 cells were cultured with and without dexamethasone in the presence or absence of a glucocorticoid receptor (GR) inhibitor, RU486. We found that dexamethasone induced pancreatic β-cell apoptosis in association with the upregulation of TRAIL mRNA and protein expression. Moreover, dexamethasone upregulated the TRAIL death receptor (DR5) protein but suppressed the decoy receptor (DcR1) protein. Similar findings were observed in mouse isolated islets: dexamethasone increased TRAIL and DR5 compared to that of control mice. Furthermore, dexamethasone stimulated pro-apoptotic signaling including superoxide production, caspase-8, -9, and -3 activities, NF-B, and Bax, but repressed the anti-apoptotic protein, Bcl-2. All these effects were inhibited by the GR-inhibitor, RU486. Furthermore, knock down DR5 decreased dexamethasone-induced caspase 3 activity. Caspase-8 and caspase-9 inhibitors protected pancreatic β-cells from dexamethasone-induced apoptosis. Taken together, dexamethasone induced pancreatic β-cell apoptosis by binding to the GR and inducing DR5 and TRAIL pathway.

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Agatha de Assis-Ferreira, Roberta Saldanha-Gama, Natália Mesquita de Brito, Mariana Renovato-Martins, Rafael Loureiro Simões, Christina Barja-Fidalgo, and Simone Vargas da Silva

In obesity, high levels of TNF-α in the bone marrow microenvironment induce the bone marrow-mesenchymal stem cells (BM-MSCs) towards a pro-adipogenic phenotype. Here, we investigated the effect of obesity on the migratory potential of BM-MSCs and their fate towards the adipose tissues. BM-MSCs were isolated from male C57Bl/06 mice with high-fat diet-induced obesity. The migratory potential of the BM-MSCs, their presence in the subcutaneous (SAT) and the visceral adipose tissues (VAT), and the possible mechanisms involved were investigated. Obesity did not affect MSC content in the bone marrow but increased the frequency of MSCs in blood, SAT, and VAT. In these animals, the SAT adipocytes presented a larger area, without any changes in adipokine production or the Sdf-1α gene expression. In contrast, in VAT, obesity increased leptin and IL-10 levels but did not modify the size of the adipocytes. The BM-MSCs from obese animals presented increased spontaneous migratory activity. Despite the augmented expression of Cxcr4, these cells exhibited decreased migratory response towards SDF-1α, compared to that of BM-MSCs from lean mice. The PI3K-AKT pathway activation seems to mediate the migration of BM-MSCs from lean mice, but not from obese mice. Additionally, we observed an increase in the spontaneous migration of BM-MSCs from lean mice when they were co-cultured with BM-HCs from obese animals, suggesting a paracrine effect. We concluded that obesity increased the migratory potential of the BM-MSCs and induced their accumulation in VAT, which may represent an adaptive mechanism in response to chronic nutrient overload.

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Lu Wang, Wen He, Xiaoyu Xu, Lingbin Qi, Bo Lv, Jiaying Qin, Zhigang Xue, and Jinfeng Xue

Hypothyroidism is a common endocrine disease caused by a deficiency of thyroid hormones, which could affect the hypothalamus–pituitary–gonadal (HPG) axis and cause additional severe fertility problems. However, the pathogenesis of abnormal reproductive capacity caused by hypothyroidism and whether there are differences between females and males need more study. Here, we constructed a prolonged neonatal hypothyroid rat model using 6-propyl-2-thiouracil (PTU). H&E staining and RNA-sequencing were performed to detect histopathological and transcriptome changes. Our results indicated the numbers of ventromedial hypothalamus nuclei were increased, and the number of pituitary chromophobes was sharply increased, whereas the proportion of pituitary acidophils and pituitary basophils were obviously reduced. The differentially expressed genes of the HPG axis organs were identified, and different tissues shared similar steroid hormone and oxidative stress-related terms in gene ontology analysis. Weighted gene co-expression network analysis (WGCNA) and differential expression analysis indicated oxidative stress and apoptosis-related genes were more enriched in male hypothyroid pituitaries, whereas the serum levels of growth hormone, follicle stimulating hormone, and luteinizing hormone that were detected by ELISA were also reduced more in male hypothyroid rats, suggesting that prolonged neonatal hypothyroidism may have a more significant impact on male pituitaries. Moreover, the multi-organ oxidative stress in hypothyroid rats was confirmed by the higher expression of oxidative stress-related genes such as the Txnip. The increased level of oxidative stress may have contributed to the histopathological and transcriptome changes of HPG axis organs in the prolonged neonatal hypothyroidism rats, especially in male pituitaries.

Open access

Yunxia Zhang, Jin Li, Hui-hui Wang, Jiao Li, Yue Yu, Bo Li, Li Huang, Changjing Wu, and Xiaomeng Liu

Despite all modern advances in medicine, there are few reports of effective and safe drugs to treat obesity. Our objective was to screen anti-obesity natural compounds, and to verify whether they can reduce the body weight gain and investigate their molecular mechanisms. By using drug-screening methods, Phytohemagglutinin (PHA) was found to be the most anti-obesity candidate natural compound. Six-week-old C57BL/6J mice were fed with a high-fat diet (HFD) and intraperitoneally injected with 0.25 mg/kg PHA everyday for 8 weeks. The body weight, glucose homeostasis, oxygen consumption and physical activity were assessed. We also measured the heat intensity, body temperature and the gene expression of key regulators of energy expenditure. Prevention study results showed PHA treatment not only reduced the body weight gain but also maintained glucose homeostasis in HFD-fed mice. Further study indicated energy expenditure and uncoupling protein 1 (UCP-1) expression of brown adipose tissue (BAT) and white adipose tissue (WAT) in HFD-fed mice were significantly improved by PHA. In the therapeutic study, a similar effect was observed. PHA inhibited lipid droplet formation and upregulated mitochondrial-related gene expression during adipogenesis in vitro. UCP-1 KO mice displayed no differences in body weight, glucose homeostasis and core body temperature between PHA and control groups. Our results suggest that PHA prevent and treat obesity by increasing energy expenditure through upregulation of BAT thermogenesis.

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Yang Yang, Jiashu Li, Yingying Zhou, Wen Dai, Weiping Teng, and Zhongyan Shan

Elevated thyroid stimulating hormone (TSH) is associated with an increased risk of spontaneous abortion (SA); however, the associated mechanism remains unclear. This study aimed to investigate the expression of microRNAs (miRNAs) and pathogenesis in the chorionic villi of TSH > 2.5 mIU/L-related SA patients. The chorionic villi were collected from pregnant women in the first trimester with TSH > 2.5 mIU/L with or without SA, as well as TSH < 2.5 mIU/L with or without SA to determine the level of miRNA expression. Differentially expressed miRNAs were confirmed by qRT-PCR in a total of 92 subjects. Cell counting kit-8 (CCK8), wound healing, transwell assays, and Western blotting were used to measure cellular biological functions and related protein in HTR-8/SVneo cells. The potential mechanisms were determined using a Luciferase reporter assay and rescue experiment. Compared with normal pregnant women, miR-17-5p was decreased and zinc finger protein 367 (ZNF367) was upregulated in the chorionic villi of TSH > 2.5 mIU/L-related SA patients. Using HTR-8/SVneo cells, we demonstrated that elevated TSH inhibited miR-17-5p expression, as well as trophoblast migration and invasion. The overexpression of miR-17-5p targeted and inhibited ZNF367 expression promoting the biological function of trophoblasts. Further studies confirmed that ZNF367 interference partially reversed the biological function of the miR-17-5p inhibitor on HTR-8/SVneo cells. Taken together, our results showed that miR-17-5p promoted biological function of trophoblasts by suppressing ZNF367.