Search Results

You are looking at 61 - 70 of 183 items for

  • Author: Li Li x
Clear All Modify Search
Free access

Qiong Lv, Rufei Gao, Chuan Peng, Juan Yi, Lulu Liu, Shumin Yang, Danting Li, Jinbo Hu, Ting Luo, Mei Mei, Ying Song, Chaodong Wu, Xiaoqiu Xiao and Qifu Li

Bisphenol A (BPA), one of the most common environmental endocrine disruptors, is considered to promote hepatic lipid deposition. However, the mechanism has not been fully elucidated. The polarization of Kupffer cells (KCs) plays an important role in hepatic inflammation by promoting pro-inflammatory M1 phenotype (M1KCs), which contributes to dysregulated lipid metabolism. The purpose of this study is to investigate the role of KC polarization in BPA-induced hepatosteatosis in male mice. In this study, we examined hepatic lipid contents and quantified M1KC in BPA-treated CD1 mice, and further explored the interaction between KCs and hepatocytes using conditional HepG2 cell culture. BPA treatment significantly increased hepatic fat contents in CD1 mice, accompanied by increased number of pro-inflammatory M1KCs and enhanced secretion of inflammatory cytokines. Increased lipid contents were also observed in HepG2 cells treated with BPA. Interestingly, higher TG contents were observed in HepaG2 cells treated with conditional media from BPA-treated KCs, compared with those treated with BPA directly. Incubation of KCs with BPA promoted the polarization of KCs to pro-inflammatory M1 dominant subtypes, which was blocked by estrogen antagonist ICI182780. Taken together, our results revealed that M1KCs polarization is involved in BPA-induced hepatic fat deposition, which is possibly associated with the estrogen receptor signaling pathway.

Free access

Jun-Ping Wen, Chune Liu, Wen-Kai Bi, Ya-Ting Hu, Qingshi Chen, Huibing Huang, Ji-Xing Liang, Lian-Tao Li, Li-Xiang Lin and Gang Chen

Adiponectin secreted from adipose tissues plays a role in the regulation of energy homeostasis, food intake, and reproduction in the hypothalamus. We have previously demonstrated that adiponectin significantly inhibited GNRH secretion from GT1-7 hypothalamic GNRH neuron cells. In this study, we further investigated the effect of adiponectin on hypothalamic KISS1 gene transcription, which is the upstream signal of GNRH. We found that globular adiponectin (gAd) or AICAR, an artificial AMPK activator, decreased KISS1 mRNA transcription and promoter activity. Conversely, inhibition of AMPK by Compound C or AMPKα1-SiRNA augmented KISS1 mRNA transcription and promoter activity. Additionally, gAd and AICAR decreased the translocation of specificity protein-1 (SP1) from cytoplasm to nucleus; however, Compound C and AMPKα1-siRNA played an inverse role. Our experiments in vivo demonstrated that the expression of Kiss1 mRNA was stimulated twofold in the Compound C-treated rats and decreased about 60–70% in gAd- or AICAR-treated rats compared with control group. The numbers of kisspeptin immunopositive neurons in the arcuate nucleus region of Sprague Dawley rats mimicked the same trend seen in Ki ss 1 mRNA levels in animal groups with different treatments. In conclusion, our results provide the first evidence that adiponectin reduces Kiss1 gene transcription in GT1-7 cells through activation of AMPK and subsequently decreased translocation of SP1.

Free access

Liqiong Song, Wei Xia, Zhao Zhou, Yuanyuan Li, Yi Lin, Jie Wei, Zhengzheng Wei, Bing Xu, Jie Shen, Weiyong Li and Shunqing Xu

Phenolic estrogen pollutants, a class of typical endocrine-disrupting chemicals, have attracted public attention due to their estrogenic activities of imitating steroid hormone 17β-estradiol (E2) effects. Exposure to these pollutants may disrupt insulin secretion and be a risk factor for type 2 diabetes. In this study, we investigated the direct effects of phenolic estrogen diethylstilbestrol (DES), octylphenol (OP), nonylphenol (NP), and bisphenol A (BPA) on rat pancreatic islets in vitro, whose estrogenic activities were DES>NP>OP>BPA. Isolated β-cells were exposed to E2, DES, OP, NP, or BPA (0, 0.1, 0.5, 2.5, 25, and 250 μg/l) for 24 h. Parameters of insulin secretion, content, and morphology of β-cells were measured. In the glucose-stimulated insulin secretion test, E2 and DES increased insulin secretion in a dose-dependent manner in a 16.7 mM glucose condition. However, for BPA, NP, or OP with lower estrogenic activity, the relationship between the doses and insulin secretion was an inverted U-shape. Moreover, OP, NP, or BPA (25 μg/l) impaired mitochondrial function in β-cells and induced remarkable swelling of mitochondria with loss of distinct cristae structure within the membrane, which was accompanied by disruption of mRNA expression of genes playing a key role in β-cell function (Glut2 (Slc2a2), Gck, Pdx1, Hnf1α, Rab27a, and Snap25), and mitochondrial function (Ucp2 and Ogdh). Therefore, these phenolic estrogens can disrupt islet morphology and β-cell function, and mitochondrial dysfunction is suggested to play an important role in the impairment of β-cell function.

Free access

K Teshigawara, S Takahashi, T Boswell, Q Li, S Tanaka and S Takeuchi

The presence and possible physiological roles of alpha-melanocyte-stimulating hormone (alpha-MSH) in the peripheral tissues of birds have not been established. By a combination of RT-PCR, immunocytochemistry and in situ hybridization, we have examined alpha-MSH expression in the eye of the chicken during development. In the 1-day-old chick, alpha-MSH was expressed in the retinal pigment epithelial (RPE) cells, and also at a lower level in the cone cells. The melanocortin receptor subtypes, CMC1, CMC4 and CMC5, were expressed in the layers of the choroid and the neural retina, but not in the RPE cells. It is probable that the RPE cells secrete alpha-MSH to exert paracrine effects on the choroid and neural retina. During embryonic development, alpha-MSH immunoreactivity in the RPE cells was initially detected at embryonic day 10, and increased in intensity as development proceeded. No cone cells were stained with anti-alpha-MSH antiserum in any of the embryonic stages tested. The immunoreactivities for two prohormone convertases, PC1 and PC2, were co-localized to the RPE cells with a pattern of staining similar to that of alpha-MSH. Despite containing alpha-MSH immunoreactivity, the RPE cells in 1-day-old chicks expressed no immunoreactivity for the endoproteases. Furthermore, in a 3-day-old chick, pro-opiomelanocortin mRNA was detectable by in situ hybridization only in the photoreceptor layer and not in the RPE cells. These results suggest that the RPE cells and the cone cells are intraocular sources of alpha-MSH in the embryonic and postnatal life of the chicken respectively. Embryonic expression of alpha-MSH in the RPE cells implies a possible role for the peptide in ocular development.

Free access

Qinglei Li, Fermin Jimenez-Krassel, Anilkumar Bettegowda, James J Ireland and George W Smith

Despite ample evidence pointing to an obligatory involvement of progesterone in ovulation, the mechanisms responsible for the ovulation promoting effects of intrafollicular progesterone are unclear. The objectives of this study were to determine if ovulation, luteinization and the gonadotropin surge-induced regulation of select extracellular matrix-degrading enzymes and their inhibitors, and mRNAs for prostaglandin (PG) biosynthesis and metabolizing enzymes are blocked following suppression of the intrafollicular increase in progesterone. Bovine preovulatory follicles were injected with the 3 β-hydroxysteroid dehydrogenase inhibitor trilostane or diluent and collected at 0, 12, and 24 h after GnRH induction of the preovulatory LH surge. Intrafollicular trilostane administration blocked the preovulatory increase in follicular fluid progesterone resulting in concentrations similar to those observed at time 0 post-GnRH injection. The preovulatory increase in follicular fluid PGE2 and PGF was reduced in trilostane-treated follicles and accompanied by upregulation of prostaglandin dehydrogenase mRNA in the granulosal and thecal cells. However, follicle rupture was not blocked by inhibition of the preovulatory rise in intrafollicular progesterone, and normal serum progesterone concentrations were observed during subsequent luteal development. Effects of trilostane administration on preovulatory changes in mRNA abundance and protein/activity in preovulatory follicles for most regulators of extracellular matrix remodeling examined were distinct from changes previously observed following the inhibition of intrafollicular prostaglandin synthesis. Results suggest that the preovulatory increase in intrafollicular progesterone may not be obligatory for bovine follicle rupture, luteinization, or regulation of prominent matrix-degrading proteinases and their inhibitors associated with ovulation.

Restricted access

J L Környei, X Li, Z M Lei and Ch V Rao

Abstract

The present study investigated the mechanisms involved in the mitogenic action of epidermal growth factor (EGF) in cultured human myometrial smooth muscle cells. The cells contained EGF/transforming growth factor-α (TGF-α) receptors as well as EGF and TGF-α mRNA transcripts and the corresponding proteins. Culturing with human EGF resulted in concentration- and time-dependent increases in cell density. The maximal increase was seen at 1 nm followed by a decrease to control levels at 100 nm EGF. The EGF increased cell density from 4 to 8 days followed by a plateau coinciding with the cells reaching confluence. EGF treatment concomitantly decreased the average size of cells. TGF-α mimicked EGF and there was no synergism between the two, suggesting a common mechanism of action. Although the presence of 10% fetal bovine serum enhanced overall cell growth, it was not required for EGF and TGF-α action. The receptor antibody, which is directed against the extracellular domain and can inhibit ligand binding to the receptors, dramatically inhibited the basal cell growth and exogenous EGF reversed the antibody effect. While TGF-α antibody was only marginally effective, EGF antibody had no effect on basal cell growth. Lavendustin (a tyrosine kinase inhibitor), calphostin (a protein kinase C inhibitor), but not H-89 (a protein kinase A inhibitor), inhibited EGF action. Indomethacin, a cyclo-oxygenase inhibitor, completely inhibited, whereas nordihydroguaiaretic acid, a lipoxygenase inhibitor, slightly inhibited EGF action. While estradiol-17β modestly inhibited basal as well as EGF-stimulated myometrial smooth muscle cell density, progesterone had no effect.

In summary, mitogenic action of EGF in human myometrial smooth muscle cells does not require serum components and it involves tyrosine kinase and protein kinase C signaling and eicosanoids from the cyclo-oxygenase pathway of arachidonic acid metabolism.

Journal of Endocrinology (1995) 146, 261–270

Free access

Guohong Liu, Mirta Grifman, James Macdonald, Peter Moller, Flossie Wong-Staal and Qi-Xiang Li

Adiponectin is an anti-diabetic hormone secreted byadipocytes. Circulating adiponectin levels are lower in obese and type II diabetic patients than in healthy people. Weight loss or thiazolidinedione treatment increases plasma adiponectin levels. Animal models and human studies suggest that elevated adiponectin levels increase insulin sensitivity. We screened a library of drug-like compounds and natural products for novel agents enhancing adiponectin production. We identified isoginkgetin, a compound derived from the leaves of Ginkgo biloba, to up-regulate adiponectin secretion with potency comparable to that of rosiglitazone, a known modulator of adiponectin production. However, unlike rosiglitazone, peroxisome proliferators-activated receptor γ activity seems not required for the action of isoginkgetin, and isoginkgetin has only a slight effect on adipogenesis, which makes it an attractive candidate for anti-diabetic treatment. Further investigation revealed that both isoginkgetin and rosiglitazone activate AMP-activated protein kinase (AMPK) in adipocytes. Our findings suggest a novel mechanism for the elevation of adiponectin by isoginkgetin, which is different from that of rosiglitazone. Furthermore, this novel mechanism for adiponectin regulation involving AMPK can potentially facilitate new understanding of metabolic diseases and identification of new targets, as well as agents that increase plasma adiponectin levels.

Restricted access

X Li, H Cui, B Sandstedt, H Nordlinder, E Larsson and T J Ekström

Abstract

We have studied the insulin-like growth factor-II gene (IGF2) promoter usage in normal human liver from fetal to late adult life by quantifying the specific transcripts by RNase protection assays using exon-specific probes. While the fetal liver uses only three promoters (P2, P3, P4) for the transcription of IGF2, all four promoters can be used from the age of 2 months after birth.

The levels of the individual promoter transcripts vary substantially during development and the P3 promoter, which is a highly active fetal promoter, was not used by all the investigated adult patients but was detected in 30% of the adult group as a whole. The PI promoter, which has previously been considered as the only one responsible for IGF2 transcription in the postnatal/adult liver, displayed a trend of increasing relative and absolute activity throughout life, but in some adult cases it was found to be less active than the P4 promoter. The P4 promoter displayed an age-related trend of decreasing activity from a very high fetal level, but individual exceptions were apparent. The P2 promoter transcript, peaking at the age of 2 months, showed a relatively even absolute amount from 18 months onwards. Thus, while P2 and P3 were both found to reach their highest activity after birth, the P4 promoter displayed its highest transcription at the fetal stage.

The total IGF2 transcription, primarily from P2, P3 and P4, was found to peak shortly after birth. After this age, the P3 promoter transcript declined most rapidly and a low or zero amount was detected in adulthood. From the age of 18 months to old adulthood the total IGF2 mRNA, derived primarily from P1, P2 and P4, displayed a relatively even amount (approximately one tenth) of that seen at the peak at 2 months. This data may be important in relation to translatability of the various IGF2 transcripts.

Journal of Endocrinology (1996) 149, 117–124

Free access

Run Yu, Martha Cruz-Soto, Sergio Li Calzi, Hongxiang Hui and Shlomo Melmed

Human pituitary tumor-transforming gene 1 (PTTG1) encodes a securin protein critically important in regulating chromosome separation. Murine PTTG (mPTTG) is 66% homologous to human PTTG1 and PTTG-null (PTTG−/−) mice exhibit pancreatic β-cell hypoplasia and abnormal nuclear morphology with resultant diabetes. As we show that ductal β-cell neogenesis is intact in PTTG−/− mice, we explored mechanism for defective β-cell replication. We tested whether mPTTG exhibits securin properties in mouse insulin-secreting insulinoma MIN6 cells, using a live-cell system to monitor mitosis in cells transfected with an enhanced green fluorescent protein (EGFP)-tagged mPTTG conjugate (mPTTG-EGFP). To fulfill the criteria for securin properties, the protein should undergo degradation immediately before the metaphase-to-anaphase transition when expression levels are low, and should inhibit metaphase-to-anaphase transition when expression levels are high. EGFP itself did not undergo degradation throughout mitosis and high levels of EGFP per se did not affect normal mitosis progression (n=25). However, mPTTG-EGFP was degraded 2 min before the metaphase-to-anaphase transition when expression levels were low (n=19), and high mPTTG-EGFP levels blocked metaphase-to-anaphase transition in 13 cells. mPTTG-EGFP inhibited MIN6 cell proliferation and caused apoptosis. Immunocoprecipitation demonstrated binding of mPTTG-EGFP and separase. These results show that mPTTG exhibits properties consistent with a murine securin in insulin-secreting mouse cells and mPTTG overexpression inhibits cell proliferation, suggesting that defective β-cell proliferation observed in PTTG−/− mice is likely due to abnormal cell-cycle progression.

Free access

L Zhao, Z Li, M Kullin, L A H Borg and F A Karlsson

The pancreatic B-cell GLUT2 transporter and glucose metabolism were examined in isolated rat islets subjected to treatments affecting insulin secretion. Diazoxide was used to inhibit, while glipizide or depolarization of the plasma membrane with a high extracellular K+ concentration were used to stimulate insulin release in short-term experiments. Islet GLUT2 and insulin were determined by quantitative immunohistochemistry and GLUT2 was also determined by Western blot analysis. Islet net glucose uptake and glucose oxidation were measured using radioactively labelled glucose. Exposure of the islets to diazoxide was associated with a marked increase in the B-cell plasma membrane staining for GLUT2 and increased net glucose uptake. Glucose oxidation was not changed, which may reflect a lowered energy requirement. Conversely, islets subjected to a stimulated insulin secretion with glipizide or a high extracellular K+ concentration showed a reduced staining of the GLUT2 transporter. The net glucose uptake and glucose oxidation were also reduced. In islets exposed to the high K+ concentration no change in the molecular weight or phosphorylation of GLUT2 was observed but a lesser amount of the transporter was found by Western blot analysis. Thus, GLUT2 and glucose uptake in the pancreatic B-cell are modified by the secretory process, which suggests that changes in the glucose transporter have a functional role in normal B-cell physiology.