The well-balanced secretion between insulin and growth hormone (GH) is essential in regulating substrate metabolism, energy metabolism, and body composition. High insulin and low GH levels are often observed in obesity, contributing to reduced energy expenditure and further fat accumulation. Although suppression of hyperinsulinemia is proposed as a treatment for obesity, changes in GH secretion and energy metabolism following this treatment are not thoroughly studied. This leaves unexplained observations, such as unchanged lean mass following insulin reduction. In this study, high-fat diet-induced obese (DIO) and normal chow-fed lean mice on a C57BL/6J background were treated for 7 weeks with diazoxide (1250 mg/kg in food), a KATP channel opener that suppressed insulin secretion. Diazoxide treatment for 10 days was sufficient to increase pulsatile GH secretion in DIO mice before any significant body weight change. The restored insulin-GH balance in DIO mice was followed by improvement in substrate and energy metabolism in a prolonged treatment period (4–6 weeks), including reduced fat mass, increased lipid oxidation and energy expenditure, as well as improved insulin sensitivity and metabolic flexibility. These metabolic benefits occurred along with the changes in the expression level of genes regulated by the insulin-GH balance. When applying diazoxide to normal chow-fed normoinsulinemic lean mice, none of the above metabolic effects was observed, suggesting that the metabolic changes following diazoxide treatment were mediated through the suppression of hyperinsulinemia. These results suggest that suppression of hyperinsulinemia by diazoxide restores GH secretion and improves substrate and energy metabolism in DIO mice.
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Zhengxiang Huang, Xuehan Lu, Lili Huang, Yang Chen, Chunhong Zhang, Johannes D Veldhuis, and Chen Chen
Lei Du, Yang Wang, Cong-Rong Li, Liang-Jian Chen, Jin-Yang Cai, Zheng-Rong Xia, Wen-Tao Zeng, Zi-Bin Wang, Xi-Chen Chen, Fan Hu, Dong Zhang, Xiao-Wei Xing, and Zhi-Xia Yang
Polycystic ovarian syndrome (PCOS) is a major severe ovary disorder affecting 5–10% of reproductive women around the world. PCOS can be considered a metabolic disease because it is often accompanied by obesity and diabetes. Brown adipose tissue (BAT) contains abundant mitochondria and adipokines and has been proven to be effective for treating various metabolic diseases. Recently, allotransplanted BAT successfully recovered the ovarian function of PCOS rat. However, BAT allotransplantation could not be applied to human PCOS; the most potent BAT is from infants, so voluntary donors are almost inaccessible. We recently reported that single BAT xenotransplantation significantly prolonged the fertility of aging mice and did not cause obvious immunorejection. However, PCOS individuals have distinct physiologies from aging mice; thus, it remains essential to study whether xenotransplanted rat BAT can be used for treating PCOS mice. In this study, rat-to-mouse BAT xenotransplantation, fortunately, did not cause severe rejection reaction, and significantly recovered ovarian functions, indicated by the recovery of fertility, oocyte quality, and the levels of multiple essential genes and kinases. Besides, the blood biochemical index, glucose resistance, and insulin resistance were improved. Moreover, transcriptome analysis showed that the recovered PCOS F0 mother following BAT xenotransplantation could also benefit the F1 generation. Finally, BAT xenotransplantation corrected characteristic gene expression abnormalities found in the ovaries of human PCOS patients. These findings suggest that BAT xenotransplantation could be a novel therapeutic strategy for treating PCOS patients.
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.
Zhengxiang Huang, Lili Huang, Chengjian Wang, Shanli Zhu, Xinzhou Qi, Yang Chen, Yanjun Zhang, Michael A Cowley, Johannes D Veldhuis, and Chen Chen
The well-documented hormonal disturbance in a general obese population is characterised by an increase in insulin secretion and a decrease in growth hormone (GH) secretion. Such hormonal disturbance promotes an increase in fat mass, which deteriorates obesity and accelerates the development of insulin resistance and type 2 diabetes. While the pathological consequence is alarming, the pharmaceutical approach attempting to correct such hormonal disturbance remains limited. By applying an emerging anti-diabetic drug, the sodium-glucose cotransporter 2 inhibitor, dapagliflozin (1 mg/kg/day for 10 weeks), to a hyperphagic obese mouse model, we observed a significant improvement in insulin and GH secretion as early as 4 weeks after the initiation of the treatment. Restoration of pathological disturbance of insulin and GH secretion reduced fat accumulation and preserved lean body mass in the obese animal model. Such phenotypic improvement followed with concurrent improvements in glucose and lipid metabolism, insulin sensitivity, as well as the expression of metabolic genes that were regulated by insulin and GH. In conclusion, 10 weeks of treatment with dapagliflozin effectively reduces hyperinsulinemia and restores pulsatile GH secretion in the hyperphagic obese mice with considerable improvement in lipid and glucose metabolism. Promising outcomes from this study may provide insights into drug intervention to correct hormonal disturbance in obesity to delay the diabetes progression.
Yuan Ni, Dan Xu, Feng Lv, Yang Wan, Guanlan Fan, Wen Zou, Yunxi Chen, Linguo Pei, Jing Yang, and Hui Wang
Prenatal ethanol exposure (PEE) adversely affects the offspring reproductive system. We aimed to confirm the susceptibility to premature ovarian insufficiency (POI) in female PEE offspring and elucidate its intrauterine programming mechanism. The pregnant Wistar female rats were intragastrically administered with 4 g/kg × day of ethanol from gestational day (GD) 9 to 20. Offspring reproductive parameters were detected on GD20, postnatal week (PW) 6 and PW12. The PEE foetuses showed a decreased number of oocytes, increased ovarian cell apoptosis and upregulated expression levels of ovarian insulin-like growth factor 1 (IGF1) signalling pathway and steroidogenic enzymes. The proportion of atretic follicles in adult rats was increased, while the number of anti-Müllerian hormone-positive antral follicles was decreased. The serum oestradiol (E2) levels were decreased, but the follicle stimulation hormone levels were elevated. The ovarian Igf1 signalling pathway was transformed from activation during puberty to relative inhibition in adulthood, and the expression levels of ovarian steroidogenic enzymes were inhibited in adulthood. Furthermore, we treated the human granulosa cell line KGN with different ethanol concentrations (15, 30, 60, 120 mM) and found that the expression of IGF1 signalling pathway components, 3β-HSD and P450arom, as well as the production of E2, was increased. After IGF1 siRNA transfection, P450arom expression and E2 production were downregulated. These results suggest that PEE induces POI susceptibility in adult females, which may be caused by over-activation of the foetal ovarian Igf1 signalling pathway and steroidogenesis under PEE, resulting in accelerated early development of folliculogenesis and depletion of primordial follicles.
Yang Chen, Xin Li, Jing Zhang, Mingjiao Zhang, Salah Adlat, Xiaodan Lu, Dan Li, Honghong Jin, Chenhao Wang, Zin Mar Oo, Farooq Hayel, Quangang Chen, Xufeng Han, Renjin Chen, Xuechao Feng, Luqing Zhang, and Yaowu Zheng
Obesity is caused by imbalanced energy intake and expenditure. The excessive energy intake and storage in adipose tissues is associated with many diseases. Several studies have demonstrated that VEGFB deficiency induces obese phenotypes. However, roles of VEGFB isoforms VEGFB167 and VEGFB186 in adipose tissue development and function are still not clear. In this study, genetic mouse models of adipose-specific VEGFB167 and VEGFB186 overexpression (aP2-Vegfb167tg/+ and aP2-Vegfb186tg/+) were generated and their biologic roles were investigated. On regular chow, adipose-specific VEGFB186 is negatively associated with white adipose tissues (WAT) and positively regulates brown adipose tissues (BAT). VEGFB186 up-regulates energy metabolism and metabolism-associated genes. In contrast, VEGFB167 has nominal roles in adipose development and function. On high fat diet, VEGFB186 expression can reverse the phenotypes of VEGFB deletion. VEGFB186 overexpression up-regulates BAT-associated genes and down-regulates WAT-associated genes. VEGFB186 and VEGFB167 have very distinct roles in regulation of adipose development and energy metabolism. As a key regulator of adipose tissue development and energy metabolism, VEGFB186 may be a target for obesity prevention and treatment.
Weixia Han, Chen Wang, Zhifen Yang, Lin Mu, Ming Wu, Nan Chen, Chunyang Du, Huijun Duan, and Yonghong Shi
Renal fibrosis is the major pathological characteristic of diabetic nephropathy (DN). Reportedly, increased SIRT1 expression played a renal protective role in animal models of DN. This study was designed to elucidate the molecular mechanisms underlying the protective effects of SRT1720, an SIRT1 activator, against diabetes-induced renal fibrosis. Type 2 diabetic mice (db/db) were treated with SRT1720 (50 mg/kg/day) by gavage for 10 weeks. Renal proximal tubular epithelial cells (HK-2 cells) were treated with high glucose (HG, 30 mM) in the presence or absence of SRT1720 (2.5 µM) for 48 h. We observed that impaired SIRT1 expression and activity were restored by SRT1720 administration in db/db mice as well as in HG-treated HK-2 cells. Moreover, SRT1720 administration improved the renal function, attenuated glomerular hypertrophy, mesangial expansion, glomerulosclerosis and interstitial fibrosis and inhibited TGFB1 and CTGF expressions and nuclear factor κB (NF-KB) activation in db/db mice. Similarly, HG-induced epithelial-to-mesenchymal transformation (EMT) and collagen IV and fibronectin expressions were inhibited in SRT1720-treated HK-2 cells. Mechanistic studies demonstrated that SRT1720 suppressed HIF1A, GLUT1 and SNAIL expressions both in vivo and in vitro. Furthermore, HIF1A or GLUT1 knockdown effectively abrogated HG-induced EMT and collagen IV and fibronectin expressions in HK-2 cells. These findings suggest that SRT1720 prevented diabetes-induced renal fibrosis via the SIRT1/HIF1A/GLUT1/SNAIL pathway.
Chanika Phornphutkul, Ke-Ying Wu, Xu Yang, Qian Chen, and Philip A Gruppuso
Insulin-like growth factor-I (IGF-I) is a critical regulator of skeletal growth. While IGF-I has been shown to be a potent chondrocyte mitogen in vitro, its role in chondrocyte differentiation is less well characterized. We chose to study the action of IGF-I on an accepted model of chondrocyte differentiation, the ATDC5 cell line. Insulin concentrations sufficiently high to interact with the IGF-I receptor are routinely used to induce ATDC5 cells to differentiate. Therefore, we first examined the ability of IGF-I to promote chondrocyte differentiation at physiological concentrations. IGF-I could induce differentiation of these cells at concentrations below 10 nM. However, increasing IGF-I concentrations were less potent at inducing differentiation. We hypothesized that mitogenic effects of IGF-I might inhibit its differentiating effects. Indeed, the extracellular-signal-regulated kinase (ERK)-pathway inhibitor PD98059 inhibited ATDC5 cell DNA synthesis while enhancing differentiation. This suggested that the ability of IGF-I to promote both proliferation and differentiation might require that its signaling be modulated through the differentiation process. We therefore compared IGF-I-mediated ERK activation in proliferating and hypertrophic chondrocytes. IGF-I potently induced ERK activation in proliferating cells, but minimal ERK response was seen in hypertrophic cells. In contrast, IGF-I-mediated Akt activation was unchanged by differentiation, indicating intact upstream IGF-I receptor signaling. Similar findings were observed in the RCJ3.1C5.18 chondrogenic cell line and in primary chick chondrocytes. We conclude that IGF-I promotes both proliferation and differentiation of chondrocytes and that the differentiation effects of IGF-I may require uncoupling of signaling to the ERK pathway.
KH Lin, HY Lee, CH Shih, CC Yen, SL Chen, RC Yang, and CS Wang
Thyroid hormones (THs) regulate growth, development, differentiation and metabolic processes by interacting and activating thyroid hormone receptors (TRs). Although much progress has been made in our understanding of the transcriptional regulation of many TR target genes, little is known of the regulation of plasma protein gene expression by TRs. To investigate the role of TRs in plasma protein expression we used human hepatocellular carcinoma cell lines and carried out cDNA microarray analysis. Our results indicate that several plasma proteins including transferrin, prothrombin, angiotensinogen, haptoglobin, alpha-2-HS-glycoprotein alpha and beta chain, complement, lipoproteins and fibrinogen are up-regulated by THs. Furthermore, clusterin, alpha-2-macroglobulin precursor, prothymosin alpha and alpha-fetoprotein were found to be down-regulated by THs.Transferrin, an iron-binding protein expressed in all mammals, and mainly synthesized in the liver, was investigated further. Immunoblot and Northern blot analyses revealed that exposure of HepG2-TRalpha1 sub-lines and HepG2-Neo cells to tri-iodothyronine (T(3)) induced time- and dose-dependent increases in the abundance of transferrin mRNA and protein, with the extent of these effects correlating with the level of expression of TRalpha1. Nuclear run-on experiments indicate that this induction is functioning at the transcriptional level. Moreover, cyclohexamide treatment did not eliminate the induction of transferrin by TH. Thus, our results suggest that the induction of transferrin by TH is direct and may in fact be mediated by an as yet unidentified response element in the promoter region.
Wenbin Shang, Ying Yang, Libin Zhou, Boren Jiang, Hua Jin, and Mingdao Chen
A series of clinical trials and animal experiments have demonstrated that ginseng and its major active constituent, ginsenosides, possess glucose-lowering action. In our previous study, ginsenoside Rb1 has been shown to regulate peroxisome proliferator-activated receptor γ activity to facilitate adipogenesis of 3T3-L1 cells. However, the effect of Rb1 on glucose transport in insulin-sensitive cells and its molecular mechanism need further elucidation. In this study, Rb1 significantly stimulated basal and insulin-mediated glucose uptake in a time- and dose-dependent manner in 3T3-L1 adipocytes and C2C12 myotubes; the maximal effect was achieved at a concentration of 1 μM and a time of 3 h. In adipocytes, Rb1 promoted GLUT1 and GLUT4 translocations to the cell surface, which was examined by analyzing their distribution in subcellular membrane fractions, and enhanced translocation of GLUT4 was confirmed using the transfection of GLUT4-green fluorescence protein in Chinese Hamster Ovary cells. Meanwhile, Rb1 increased the phosphorylation of insulin receptor substrate-1 and protein kinase B (PKB), and stimulated phosphatidylinositol 3-kinase (PI3K) activity in the absence of the activation of the insulin receptor. Rb1-induced glucose uptake as well as GLUT1 and GLUT4 translocations was inhibited by the PI3K inhibitor. These results suggest that ginsenoside Rb1 stimulates glucose transport in insulin-sensitive cells by promoting translocations of GLUT1 and GLUT4 by partially activating the insulin signaling pathway. These findings are useful in understanding the hypoglycemic and anti-diabetic properties of ginseng and ginsenosides.