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N Popnikolov, J Yang, A Liu, R Guzman and S Nandi

The proliferation of normal human breast epithelial cells in women is highest during the first trimester of pregnancy. In an attempt to analyze this hormonal environment in a model system, the effect of host mouse pregnancy and the administration of human chorionic gonadotropin (hCG) were assessed in normal human breast epithelial cells transplanted into athymic nude mice. Human breast epithelial cells, dissociated from reduction mammoplasty specimens and embedded inside the extracellular matrices comprised of collagen gel and Matrigel, were transplanted into nude mice. Proliferation was measured in vivo by BrdU labeling followed by immunostaining of sections from recovered gels in response to an altered hormonal environment of the host animal. The host animal was mated to undergo pregnancy and the complex hormonal environment of the host animal pregnancy stimulated growth of transplanted human cells. This effect increased with progression of pregnancy and reached the maximum during late pregnancy prior to parturition. In order to determine whether additional stimulation could be achieved, the transplanted human cells were exposed to a second cycle of host mouse pregnancy by immediately mating the animal after parturition. This additional exposure of host mouse pregnancy did not result in further increase of proliferation. The effect of hCG administration on transplanted human cells was also tested, since hCG level is highest during the first trimester of human pregnancy and coincides with the maximal breast cell proliferation. Administration of hCG alone stimulated proliferation of human cells in a dose-dependent manner, and could further enhance stimulation achieved with estrogen. The host mouse mammary gland also responded to hCG treatment resulting in increased branching and lobulo-alveolar development. However, the hCG effect on both human and mouse cells was dependent on intact ovary since the stimulation did not occur in ovariectomized animals. Although hCG receptor transcripts were detected in human breast epithelial cells, raising the possibility of a direct mitogenic action, the hCG effect observed in this study may have been mediated via the ovary by increased secretion of ovarian steroids. In summary, using our in vivo nude mice system, the proliferation of normal human breast epithelial cells could be stimulated by host mouse pregnancy and by administration of hCG.

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Xiaofeng Ding, Yan Luo, Xing Zhang, Handong Zheng, Xin Yang, Xuexian Yang and Meilian Liu

Group 2 innate lymphoid cells (ILC2s) in white adipose tissue (WAT) promote WAT browning and assist in preventing the development of obesity. However, how ILC2 in adipose tissue is regulated remains largely unknown. Here, our study shows that ILC2s are present in brown adipose tissue (BAT) as well as subcutaneous and epididymal WAT (sWAT and eWAT). The fractions of ILC2s, natural killer T (NKT) cells and eosinophils in sWAT, eWAT and BAT are significantly decreased by high-fat-diet (HFD) feeding and leptin deficiency-induced obesity. Consistent with this, the adipose expression and circulating levels of IL-33, a key inducing cytokine of ILC2, are significantly downregulated by obesity. Furthermore, administration of IL-33 markedly increases the fraction of ILC2 and eosinophil as well as the expression of UCP1 and tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine biosynthesis, in adipose tissue of HFD-fed mice. On the other hand, cold exposure induces the expression levels of IL-33 and UCP1 and the population of ILC2 and eosinophil in sWAT, and these promoting effects of cold stress are reversed by neutralization of IL-33 signaling in vivo. Moreover, the basal and cold-induced IL-33 and ILC2/eosinophil pathways are significantly suppressed by sympathetic denervation via local injection of 6-hydroxydopamine (6-OHDA) in sWAT. Taken together, our data suggest that the ILC2/eosinophil axis in adipose tissue is regulated by sympathetic nervous system and obesity in IL-33-dependent manner, and IL-33-driven ILC2/eosinophil axis is implicated in the development of obesity.

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Xiaojun Zhou, Jianjun Dong, Li Zhang, Ju Liu, Xiaofeng Dong, Qing Yang, Fupeng Liu and Lin Liao

It is well known that hyperglycemia is a trigger of atherosclerosis in patients with diabetes mellitus. However, the role of hyperglycemia in restenosis remains unclear. In this study, we investigated the effects of hyperglycemia on restenosis. Stenosis was evaluated in two sets of diabetic rabbit models: i) diabetic restenosis versus nondiabetic restenosis and ii) diabetic atherosclerosis versus nondiabetic atherosclerosis. Our results indicated that there was no difference in rates of stenosis between the diabetic and the nondiabetic groups in restenosis rabbit models. However, the incidence of stenosis was significantly higher in the diabetic atherosclerosis group compared with the nondiabetic atherosclerosis group. Similarly, the intima–media thickness and cell proliferation rate were significantly increased in the diabetic atherosclerosis group compared with the nondiabetic atherosclerosis group, but there was no difference between the diabetic restenosis and the nondiabetic restenosis groups. Our results indicate that hyperglycemia is an independent risk factor for atherosclerosis, but it has no evident effect on restenosis. These findings indicate that the processes of atherosclerosis and restenosis may involve different pathological mechanisms.

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Xuanchun Wang, Wei Gong, Yu Liu, Zhihong Yang, Wenbai Zhou, Mei Wang, Zhen Yang, Jie Wen and Renming Hu

We report the identification of a novel secreted peptide, INM02. The mRNA transcript of human INM02 gene is about 3.0 kb. Its open-reading frame contains 762 bps and encodes a protein of 254 amino acids. Northern blot analysis demonstrates that INM02 mRNA is widely expressed in rat tissues, especially with abundant quantities in pancreatic islets, testis, and bladder tissue. We have expressed recombinant INM02 protein and generated rabbit anti-INM02 polyclonal antibodies. We show here that INM02 could be detectable in human serum by ELISA. We also present evidence that INM02 mRNA expression could be regulated by glucose. Experiments on both MIN6 cells and intact isolated islets demonstrate that INM02 mRNA levels are increased more than threefold by high glucose (25 mM) when compared with low glucose (5.5 mM). ELISA analysis shows that secretion of INM02 is significantly augmented by high glucose in vitro. It is speculated that as a novel secreted protein, INM02 is associated with functions of pancreatic islets, especially of β-cells.

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Jie Liu, Fei Gao, Yue-Fang Liu, Hai-Ting Dou, Jia-Qi Yan, Zong-Min Fan and Zeng-Ming Yang

Embryo implantation and decidualization are key steps for successful reproduction. Although numerous factors have been identified to be involved in embryo implantation and decidualization, the mechanisms underlying these processes are still unclear. Based on our preliminary data, Prss56, a trypsin-like serine protease, is strongly expressed at implantation site in mouse uterus. However, the expression, regulation and function of Prss56 during early pregnancy are still unknown. In mouse uterus, Prss56 is strongly expressed in the subluminal stromal cells at implantation site on day 5 of pregnancy compared to inter-implantation site. Under delayed implantation, Prss56 expression is undetected. After delayed implantation is activated by estrogen, Prss56 is obviously induced at implantation site. Under artificial decidualization, Prss56 signal is seen at the primary decidual zone at the initial stage of artificial decidualization. When stromal cells are induced for in vitro decidualization, Prss56 expression is significantly elevated. Dtprp expression under in vitro decidualization is suppressed by Prss56 siRNA. In cultured stromal cells, HB-EGF markedly stimulates Prss56 expression through EGFR/ERK pathway. Based on promoter analysis, we also showed that Egr2 is involved in Prss56 regulation by HB-EGF. Collectively, Prss56 expression at implantation site is modulated by HB-EGF/EGFR/ERK signaling pathway and involved in mouse decidualization.

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Hong Xu, Yang Zhou, Yongxia Liu, Jian Ping, Qiyang Shou, Fangming Chen and Ru Ruo

Nonalcoholic fatty liver disease and cirrhosis are strongly associated with insulin resistance and glucose intolerance. To date, the influence of metformin on glycogen synthesis in the liver is controversial. Limited studies have evaluated the effect of metformin on hepatic insulin signaling pathway in vivo. In this study, an insulin-resistant rat model of nonalcoholic steatohepatitis and cirrhosis was developed by high-fat and high-sucrose diet feeding in combination with subcutaneous injection of carbon tetrachloride. Liver tissues of the model rats were featured with severe steatosis and cirrhosis, accompanied by impaired liver function and antioxidant capacity. The glucose tolerance was impaired, and the index of insulin resistance was increased significantly compared with the control. The content of hepatic glycogen was dramatically decreased. The expression of insulin receptor β (IRβ); phosphorylations of IRβ, insulin receptor substrate 2 (IRS2), and Akt; and activities of phosphatidylinositol 3-kinase (PI3K) and glycogen synthase (GS) in the liver were significantly decreased, whereas the activities of glycogen synthase kinase 3α (GSK3α) and glycogen phosphorylase a (GPa) were increased. Metformin treatment remarkably improved liver function, alleviated lipid peroxidation and histological damages of the liver, and ameliorated glucose intolerance and insulin resistance. Metfromin also significantly upregulated the expression of IRβ; increased the phosphorylations of IRβ, IRS2, and Akt; increased the activities of PI3K and GS; and decreased GSK3α and GPa activities. In conclusion, our study suggests that metformin upregulates IRβ expression and the downstream IRS2/PI3K/Akt signaling transduction, therefore, to increase hepatic glycogen storage and improve insulin resistance. These actions may be attributed to the improved liver histological alterations by metformin.

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Fu-Qing Yu, Chun-Sheng Han, Wei Yang, Xuan Jin, Zhao-Yuan Hu and Yi-Xun Liu

In the present study, we started out to test whether the follicle-stimulating hormone (FSH)-activated p38 MAPK signaling cascade was involved in the regulation of steroidogenesis in granulosa cells (GCs). GCs were prepared from the ovaries of DES-treated immature rats and cultured in serum-free medium. Treatment of GCs with FSH (50 ng/ml) induced the phosphorylation of p38 MAPK rapidly with the phosphorylation being observed within 5 min and reaching the highest level at 30 min. Such activation was protein kinase A-dependent as indicated by the results using specific inhibitors. FSH stimulated the production of progesterone and estradiol as well as the expression of the steroidogenic acute regulatory protein (StAR) in a time-dependent manner, with a maximum level being observed in the production of progesterone and StAR at 48 h. Moreover, the potent p38 MAPK inhibitor SB203580 (20 μM) augmented FSH-induced progesterone and StAR production, while reduced FSH-induced estradiol production at the same time (P<0.01). RT-PCR data showed that inclusion of SB203580 in the media enhanced FSH-stimulated StAR mRNA production, while decreased the FSH-stimulated P450arom mRNA expression (P<0.05). Immunocytochemical studies showed that FSH treatment together with the inhibition of p38 MAPK activity resulted in a higher expression of StAR in mitochondria than FSH treatment alone. FSH also significantly up-regulated the protein level of LRH-1, a member of the orphan receptor family that activates the expression of P450arom in ovaries and testes. p38 MAPK inactivation down-regulated the basal and FSH-induced LRH-1 expression significantly. The intra-cellular level of DAX-1, another orphan receptor that inhibits StAR expression, also decreased upon p38 MAPK being inactivated. For the first time, the present study suggests that FSH-activated p38 MAPK signal pathway regulates progesterone and estrogen production in GCs differentially, and that the transcription factors LRH-1 and DAX-1 might play important roles in the process.

Free access

Qiong You, Zijun Wu, Bin Wu, Chang Liu, Ruina Huang, Li Yang, Runmin Guo, Keng Wu and Jingfu Chen

We previously reported that naringin (NRG) protects cardiomyocytes against high glucose (HG)-induced injuries by inhibiting the MAPK pathway. The aim of this study was to test the hypothesis that NRG prevents cardiomyocytes from hyperglycemia-induced insult through the inhibition of the nuclear factor kappa B (NF-κB) pathway and the upregulation of ATP-sensitive K+ (KATP) channels. Our results showed that exposure of cardiomyocytes to HG for 24h markedly induced injuries, as evidenced by a decrease in cell viability and oxidative stress, and increases in apoptotic cells as well as the dissipation of mitochondrial membrane potential (MMP). These injuries were markedly attenuated by the pretreatment of cells with either NRG or pyrrolidine dithiocarbamate (PDTC) before exposure to HG. Furthermore, in streptozotocin (STZ)-induced diabetic rats and in HG-induced cardiomyocytes, the expression levels of caspase-3, bax and phosphorylated (p)-NF-κB p65 were increased. The increased protein levels were ameliorated by pretreatment with both NRG and PDTC. However, the expression levels of bcl-2 and KATP and superoxide dismutase (SOD) activity were decreased by hyperglycemia; the expression level of Nox4 and the ADP/ATP ratio were increased by hyperglycemia. These hyperglycemia-induced indexes were inhibited by the pretreatment of cardiomyocytes with NRG or PDTC. In addition, in STZ-induced diabetic rats, we also observed that NRG or PDTC contributed to protecting mitochondrial injury and myocardium damage. This study demonstrated that NRG protects cardiomyocytes against hyperglycemia-induced injury by upregulating KATP channels in vitro and inhibiting the NF-κB pathway in vivo and in vitro.

Open access

Xuefeng Yang, Shuang Mei, Haihua Gu, Huailan Guo, Longying Zha, Junwei Cai, Xuefeng Li, Zhenqi Liu and Wenhong Cao

We have previously shown that insulin plays an important role in the nutrient-induced insulin resistance. In this study, we tested the hypothesis that chronic exposure to excess long-acting insulin (glargine) can cause typical type 2 diabetes mellitus (T2DM) in normal mice fed on a chow diet. C57BL/6 mice were treated with glargine once a day for 8 weeks, followed by evaluations of food intake, body weight, blood levels of glucose, insulin, lipids, and cytokines, insulin signaling, histology of pancreas, ectopic fat accumulation, oxidative stress level, and cholesterol content in mitochondria in tissues. Cholesterol content in mitochondria and its association with oxidative stress in cultured hepatocytes and β-cells were also examined. Results show that chronic exposure to glargine caused insulin resistance, hyperinsulinemia, and relative insulin deficiency (T2DM). Treatment with excess glargine led to loss of pancreatic islets, ectopic fat accumulation in liver, oxidative stress in liver and pancreas, and increased cholesterol content in mitochondria of liver and pancreas. Prolonged exposure of cultured primary hepatocytes and HIT-TI5 β-cells to insulin induced oxidative stress in a cholesterol synthesis-dependent manner. Together, our results show that chronic exposure to excess insulin can induce typical T2DM in normal mice fed on a chow diet.

Free access

Xiuli Men, Liang Peng, Haiyan Wang, Wenjian Zhang, Shiqing Xu, Qing Fang, Honglin Liu, Wenying Yang and Jinning Lou

The calcium-regulated transcription coactivator, Ca2 +-responsive transactivator (CREST) was expressed in pancreatic β-cells. Moreover, CREST expression became significantly increased in pancreatic islets isolated from hyperglycemic Goto–Kakizaki rats compared with normoglycemic Wistar controls. In addition, culture of β-cells in the presence of high glucose concentrations also increased CREST expression in vitro. To further investigate the role of this transactivator in the regulation of β-cell function, we established a stable β-cell line with inducible CREST expression. Hence, CREST overexpression mimicked the glucotoxic effects on insulin secretion and cell growth in β-cells. Moreover, high glucose-induced apoptosis was aggravated by upregulation of the transactivator but inhibited when CREST expression was partially silenced by siRNA technology. Further investigation found that upregulation of Bax and downregulation of Bcl2 was indeed induced by its expression, especially under high glucose conditions. In addition, as two causing factors leading to β-cell apoptosis under diabetic conditions, endoplasmic reticulum stress and high free fatty acid, mimicked the high glucose effects on CREST upregulation and generation of apoptosis in β-cells, and these effects were specifically offset by the siRNA knockdown of CREST. These results indicated that CREST is implicated in β-cell apoptosis induced by culture in high glucose and hence that CREST may become a potential pharmacological target for the prevention and treatment of type 2 diabetes mellitus.