MOLECULAR EVOLUTION OF GPCRS: GLP1/GLP1 receptors

Hwang, Jong-Ik,Yun, Seongsik,Moon, Mi Jin,Park, Cho Rong,Seong, Jae Young Journal of Endocrinology (Ltd. by Guarantee) 2014 Journal of molecular endocrinology Vol.52 No.3

<P>Glucagon-like peptide 1 (GLP1) is an intestinal incretin that regulates glucose homeostasis through stimulation of insulin secretion from pancreatic β-cells and inhibits appetite by acting on the brain. Thus, it is a promising therapeutic agent for the treatment of type 2 diabetes mellitus and obesity. Studies using synteny and reconstructed ancestral chromosomes suggest that families for GLP1 and its receptor (GLP1R) have emerged through two rounds (2R) of whole genome duplication and local gene duplications before and after 2R. Exon duplications have also contributed to the expansion of the peptide family members. Specific changes in the amino acid sequence following exon/gene/genome duplications have established distinct yet related peptide and receptor families. These specific changes also confer selective interactions between GLP1 and GLP1R. In this review, we present a possible macro (genome level)- and micro (gene/exon level)-evolution mechanisms of GLP1 and GLP1R, which allows them to acquire selective interactions between this ligand–receptor pair. This information may provide critical insight for the development of potent therapeutic agents targeting GLP1R.</P>

Long-term oral exposure to bisphenol A induces glucose intolerance and insulin resistance

Moon, Min Kyong,Jeong, In-Kyong,Jung Oh, Tae,Ahn, Hwa Young,Kim, Hwan Hee,Park, Young Joo,Jang, Hak Chul,Park, Kyong Soo Journal of Endocrinology, Ltd. [etc.] 2015 The Journal of endocrinology Vol.226 No.1

<P>Bisphenol A (BPA) is a widely used endocrine disruptor. Recent epidemiologic results have suggested an association between exposure to BPA and cardiovascular disease, type 2 diabetes, and obesity. We investigated the <I>in vivo</I> effects of long-term oral exposure to BPA on insulin resistance and glucose intolerance. In the present study, 4- to 6-week-old male mice on a high-fat diet (HFD) were treated with 50 μg/kg body weight per day of BPA orally for 12 weeks. Long-term oral exposure to BPA along with an HFD for 12 weeks induced glucose intolerance in growing male mice. Intraperitoneal glucose tolerance tests showed that the mice that received an HFD and BPA exhibited a significantly larger area under the curve than did those that received an HFD only (119.9±16.8 vs 97.9±18.2 mM/min, <I>P</I>=0.027). Body weight, percentage of white adipose tissue, and percentage of body fat did not differ between the two groups of mice. However, treatment with BPA reduced Akt phosphorylation at position Thr308 and GSK3β phosphorylation at position Ser9 in skeletal muscle. BPA tended to decrease serum adiponectin levels and to increase serum interleukin 6 and tumor necrosis factor α, although these findings were not statistically significant. Treatment with BPA did not induce any detrimental changes in the islet area or morphology or the insulin content of β cells. In conclusion, long-term oral exposure to BPA induced glucose intolerance and insulin resistance in growing mice. Decreased Akt phosphorylation in skeletal muscle by way of altered serum adipocytokine levels might be one mechanism by which BPA induces glucose intolerance.</P>

Cigarette smoke extract-induced adipogenesis in Graves' orbital fibroblasts is inhibited by quercetin via reduction in oxidative stress.

Yoon, Jin Sook,Lee, Hyun Jung,Chae, Min Kyung,Lee, Sang Yeul,Lee, Eun Jig Journal of Endocrinology, Ltd. [etc.] 2013 The Journal of endocrinology Vol.216 No.2

<P>Cigarette smoking is known to aggravate Graves' orbitopathy (GO) severity by enhancing adipogenesis. We investigated the effect of quercetin, an antioxidant, on adipocyte differentiation induced by cigarette smoke extract (CSE) in primary cultured orbital fibroblasts (OFs) from GO patients. Freshly prepared CSE was added to the cells and H(2)O(2) was used as a positive control. Intracellular reactive oxygen species (ROS) generation and adipogenesis were measured. The expressions of proteins peroxisome proliferator-activated receptor (PPAR) γ, CCAAT-enhancer-binding proteins (C/EBP) α and β, and heme oxygenase-1 (HO-1), an antioxidant enzyme, were examined during adipogenic differentiation. In result, CSE and H(2)O(2) dose-dependently stimulated intracellular ROS production in normal and Graves' OFs. The effect of 2% CSE was similar to that of 10?μM H(2)O(2); both concentrations were noncytotoxic and were used throughout the experiment. Quercetin pretreatment reduced the ROS generation stimulated by either CSE or H(2)O(2) in preadipocyte OFs. CSE and H(2)O(2) stimulated adipocyte differentiation in cultured OFs. The addition of quercetin (50 or 100?μM) suppressed adipogenesis. Quercetin also suppressed ROS generation in differentiating OFs during adipogenesis stimulated by CSE and H(2)O(2). Additionally, the expressions of PPARγ, C/EBPα, and C/EBPβ proteins were reduced in the quercetin-treated OFs. Quercetin also reduced the CSE- and H(2)O(2)-induced upregulation of ROS and HO-1 protein in differentiated OFs and preadipocyte OFs. As shown in this study, quercetin inhibited adipogenesis by reducing ROS in vitro, supporting the use of quercetin in the treatment of GO.</P>

β-Cell-protective effect of 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid as a glutamate dehydrogenase activator in db/db mice.

Han, Seung Jin,Choi, Sung-E,Yi, Sang-A,Lee, Soo-Jin,Kim, Hae Jin,Kim, Dae Jung,Lee, Hyun Chul,Lee, Kwan Woo,Kang, Yup Journal of Endocrinology, Ltd. [etc.] 2012 The Journal of endocrinology Vol.212 No.3

<P>2-Aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) is an activator of glutamate dehydrogenase (GDH), which is a mitochondrial enzyme with an important role in insulin secretion. We investigated the effect of BCH on the high-glucose (HG)-induced reduction in glucose-stimulated insulin secretion (GSIS), the HG/palmitate (PA)-induced reduction in insulin gene expression, and HG/PA-induced β-cell death. We also studied whether long-term treatment with BCH lowers blood glucose and improves β-cell integrity in db/db mice. We evaluated GSIS, insulin gene expression, and DNA fragmentation in INS-1 cells exposed to HG or HG/PA in the presence or absence of BCH. An in vivo study was performed in which 7-week-old diabetic db/db mice were treated with BCH (0.7? g/kg, n = 10) and placebo (n = 10) every other day for 6 weeks. After treatment, an intraperitoneal glucose tolerance test and immunohistological examinations were performed. Treatment with BCH blocked HG-induced GSIS inhibition and the HG/PA-induced reduction in insulin gene expression in INS-1 cells. In addition, BCH significantly reduced HG/PA-induced INS-1 cell death and phospho-JNK level. BCH treatment improved glucose tolerance and insulin secretion in db/db mice. BCH treatment also increased the ratio of insulin-positive β-cells to total islet area (P < 0.05) and reduced the percentage of β-cells expressing cleaved caspase 3 (P < 0.05). In conclusion, the GDH activator BCH improved glycemic control in db/db mice. This anti-diabetic effect may be associated with improved insulin secretion, preserved islet architecture, and reduced β-cell apoptosis.</P>

Differential responses of the growth hormone axis in two rat models of streptozotocin-induced insulinopenic diabetes.

Kim, E,Sohn, S,Lee, M,Jung, J,Kineman, R D,Park, S Journal of Endocrinology, Ltd. [etc.] 2006 The Journal of endocrinology Vol.188 No.2

<P>The impact of streptozotocin (STZ)-induced, insulinopenic diabetes on the GH axis of rats and mice differs from study to study, where this variation may be related to the induction scheme, severity of the diabetes and/or the genetic background of the animal model used. In order to begin differentiate between these possibilities, we compared the effects of two different STZ induction schemes on the GH axis of male Sprague-Dawley rats: (1) a single high-dose injection of STZ (HI STZ, 80 mg/kg, i.p.), which results in rapid chemical destruction of the pancreatic beta-cells, and (2) multiple low-dose injections of STZ (LO STZ, 20 mg/kg for 5 consecutive days, i.p.), which results in a gradual, autoimmune destruction of beta-cells. STZ-treated animals were killed after 3 weeks of hyperglycemia (>400 mg/dl), and in both paradigms circulating insulin levels were reduced to <40% of vehicle-treated controls. HI STZ-treated rats lost weight, while body weights of LO STZ-treated animals gradually increased over time, similar to vehicle-treated controls. As previously reported, HI STZ resulted in a decrease in circulating GH and IGF-I levels which was associated with a rise in hypothalamic neuropeptide Y (NPY) mRNA (355% of vehicle-treated controls) and a fall in GH-releasing hormone (GHRH) mRNA (45% of vehicle-treated controls) levels. Changes in hypothalamic neuropeptide expression were reflected by an increase in immunoreactive NPY within the arcuate and paraventricular nuclei and a decrease in GHRH immunoreactivity in the arcuate nucleus, as assessed by immunohistochemistry. Consistent with the decline in circulating GH and hypothalamic GHRH, pituitary GH mRNA levels of HI STZ-treated rats were 58% of controls. However, pituitary receptor mRNA levels for GHRH and ghrelin increased and those for somatostatin (sst2, sst3 and sst5) decreased following HI STZ treatment. The impact of LO STZ treatment on the GH axis differed from that observed following HI STZ treatment, despite comparable changes in circulating glucose and insulin. Specifically, LO STZ treatment did suppress circulating IGF-I levels to the same extent as HI STZ treatment; however, the impact on hypothalamic NPY mRNA levels was less dramatic (158% of vehicle-treated controls) where NPY immunoreactivity was increased only within the paraventricular nucleus. Also, there were no changes in circulating GH, hypothalamic GHRH or pituitary receptor expression following LO STZ treatment, with the exception that pituitary sst3 mRNA levels were suppressed compared with vehicle-treated controls. Taken together these results clearly demonstrate that insulinopenia, hyperglycemia and reduced circulating IGF-I levels are not the primary mediators of hypothalamic and pituitary changes in the GH axis of rats following HI STZ treatment. Changes in the GH axis of HI STZ-treated rats were accompanied by weight loss, and these changes are strikingly similar to those observed in the fasted rat, which suggests that factors associated with the catabolic state are critical in modifying the GH axis following STZ-induced diabetes.</P>

IGF-I inhibition of apoptosis is associated with decreased expression of prostate apoptosis response-4.

Chung, Hyunju,Seo, Sanghee,Moon, Minho,Park, Seungjoon Journal of Endocrinology, Ltd. [etc.] 2007 The Journal of endocrinology Vol.194 No.1

<P>The neuronal damage caused by ischemic brain injury is associated with increased apoptosis. IGF-I exposure promotes neuronal defense and survival against ischemic insult by inhibiting apoptotic processes. We investigated the role of prostate apoptosis response-4 (Par-4), a proapoptotic gene the expression of which is increased after ischemic injury, in IGF-I-mediated inhibition of apoptosis using PC12 cells exposed to oxygen-glucose deprivation (OGD). The OGD insult resulted in significant increases in apoptotic cell death and Par-4 expression, which were prevented by the treatment of cells with an antisense oligonucleotide of Par-4. IGF-I treatment prior to OGD insult significantly reduced the number of apoptotic cells and the OGD-induced increase in Par-4 expression. OGD-induced nuclear translocation of Par-4 was also attenuated by IGF-I treatment. In addition, we demonstrated that the anti-apoptotic effect of IGF-I was blocked by chemical inhibition of a mitogen activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), or protein kinase A (PKA), but not by a protein kinase C inhibitor. Finally, pretreatment of cells with a MAPK or PI3K inhibitor attenuated IGF-I-induced inhibition of Par-4 expression, suggesting that the MAPK and PI3K pathways contribute to IGF-I-induced Par-4 suppression. In contrast, a PKA inhibitor failed to alter the inhibitory effect of IGF-I on Par-4. These findings indicate that in PC12 cells exposed to OGD insult, IGF-I protects cells from apoptosis, at least in part through the inhibition of Par-4 expression.</P>

Angiotensin II stimulates the synthesis of vascular endothelial growth factor through the p38 mitogen activated protein kinase pathway in cultured mouse podocytes.

Kang, Young Sun,Park, Yun Gyu,Kim, Bo Kyung,Han, Sang Youb,Jee, Yi Hwa,Han, Kum Hyun,Lee, Mi Hwa,Song, Hye Kyoung,Cha, Dae Ryong,Kang, Shin Wook,Han, Dae Suk Journal of Endocrinology (Ltd. by Guarantee) 2006 Journal of molecular endocrinology Vol.36 No.2

<P>Angiotensin II (Ang-II) and vascular endothelial growth factor (VEGF) have an important role in the pathogenesis of diabetic nephropathy, but the signaling cascade of VEGF regulation in response to Ang-II in podocytes is largely unknown. In these experiments, we looked at the effect of Ang-II on the production of VEGF, and investigated whether VEGF production depends on the p38 mitogen activated protein kinase (MAPK) pathway in cultured mouse podocytes. Incubation of podocytes with Ang-II induced a rapid increase in VEGF mRNA expression and protein synthesis as well as its transcriptional activity in an Ang-II dose-dependent manner. To further define the role of angiotensin type 1 (AT1) and type 2 (AT2) receptors involved in Ang-II-mediated VEGF synthesis, the effects of selective AT1 and AT2 receptor antagonists were evaluated. Prior treatment with losartan significantly inhibited VEGF mRNA and protein synthesis induced by Ang-II, which suggests that the AT1 receptor is involved in Ang-II-mediated VEGF synthesis. Furthermore, stimulation of the cells with Ang-II increased both phosphorylation of p38 MAPK and MAP kinase kinase 3/6 (MKK3/6). Additionally, Ang-II enhanced the DNA binding activity to cAMP response element binding protein (CREB) and phosphorylation of CREB. In addition, to investigate the role of p38 MAPK in Ang-II-induced VEGF synthesis, podocytes were pretreated with or without the p38 MAPK inhibitor, SB203580 for 24 h to observe whether Ang-II-mediated VEGF synthesis was inhibited by blocking p38 MAPK. The addition of SB203580 led to a marked inhibition of the increased VEGF mRNA and protein production induced by Ang-II in a dose-dependent manner. Taken together, these results suggest that Ang-II stimulates the synthesis of VEGF in podocytes and the production of VEGF induced by Ang-II is mediated, in part, through the activation of the p38 MAPK pathway.</P>

Exendin-4 protects dopaminergic neurons by inhibition of microglial activation and matrix metalloproteinase-3 expression in an animal model of Parkinson's disease.

Kim, Sehee,Moon, Minho,Park, Seungjoon Journal of Endocrinology, Ltd. [etc.] 2009 The Journal of endocrinology Vol.202 No.3

<P>Exendin-4 is a naturally occurring more potent and stable analog of glucagon-like peptide-1 (GLP-1) that selectively binds at the GLP-1 receptor. It has been recently demonstrated that GLP-1 receptor stimulation preserves dopaminergic neurons in cellular and rodent models of Parkinson's disease (PD). 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity in rodents; previous studies suggest that activated microglia actively participate in the pathogenesis of PD neurodegeneration. However, the role of microglia in the neuroprotective properties of exendin-4 is still unknown. Here, we show that, in the mouse MPTP PD model, systemic administration of exendin-4 significantly attenuates the loss of substantia nigra pars compacta (SNpc) neurons and the striatal dopaminergic fibers. Exendin-4 prevents MPTP-induced microglial activation in the SNpc and striatum, and the expression of matrix metalloproteinase-3. In addition, exendin-4 also suppressed MPTP-induced expression of pro-inflammatory molecules and tumor necrosis factor alpha and interleukin-1 beta. Our data indicate that exendin-4 may act as a survival factor for dopaminergic neurons by functioning as a microglia-deactivating factor and suggest that exendin-4 may be a valuable therapeutic agent for neurodegenerative diseases such as PD.</P>

Exendin-4 inhibits interleukin-1beta-induced iNOS expression at the protein level, but not at the transcriptional and posttranscriptional levels, in RINm5F beta-cells.

Kang, Jung-Hoon,Chang, Seo-Yoon,Jang, Hyun-Jong,Kim, Dong-Bin,Ryu, Gyeong Ryul,Ko, Seung Hyun,Jeong, In-Kyung,Jo, Yang-Hyeok,Kim, Myung-Jun Journal of Endocrinology, Ltd. [etc.] 2009 The Journal of endocrinology Vol.202 No.1

<P>Cytokines such as interleukin-1beta (IL-1beta) stimulate inducible nitric oxide synthase (iNOS) expression and nitric oxide overproduction leading to beta-cell damage. Meanwhile, glucagon-like peptide-1 (GLP-1) and its potent analog exendin-4 (EX-4) were well known for beta-cell proliferation. However, the protective mechanisms of GLP-1 in beta-cells exposed to cytokines were not fully elucidated. Therefore, the effects of EX-4 on the IL-1beta-induced iNOS gene expression were investigated employing RINm5F beta-cells. EX-4 inhibited IL-1beta-induced iNOS protein expression and nitrite production. However, northern blot and promoter analyses showed that EX-4 failed to inhibit IL-1beta-induced iNOS mRNA expression and iNOS promoter activity. By electrophoretic mobility shift assay (EMSA), EX-4 did not alter the binding activity of NF-kappaB to the iNOS promoter. Consistent with the EMSA result, EX-4 did not inhibit nuclear translocation of p65. We also tested the effect of EX-4 on iNOS mRNA stability. Actinomycin D chase experiments showed that EX-4 did not affect the decay rate of iNOS mRNA and the promoter assay using the construct containing 3'-untranslated region of iNOS showed that EX-4 did not alter the stability of iNOS mRNA. Meanwhile, forskolin significantly inhibited IL-1beta-induced iNOS protein, which was reversed by H-89, a protein kinase A (PKA) inhibitor. Moreover, EX-4 pretreatment restored IL-1beta-induced decrease in cAMP toward control level. Additionally, the cycloheximide chase study demonstrated that EX-4 significantly accelerated iNOS protein degradation. We therefore concluded that EX-4 inhibited IL-1beta-induced iNOS protein and nitrite production via cAMP/PKA system irrespective of both transcriptional and posttranscriptional mechanisms of iNOS gene, and this inhibitory effect of EX-4 appears to be regulated at posttranslational level.</P>

Ginsenoside Rg3 ameliorated HFD-induced hepatic steatosis through downregulation of STAT5-PPARγ

Lee, Jin-Bong,Yoon, Sung-Jin,Lee, Sang-Hyun,Lee, Moo-Seung,Jung, Haiyoung,Kim, Tae-Don,Yoon, Suk Ran,Choi, Inpyo,Kim, Ik-Soo,Chung, Su Wol,Lee, Hee Gu,Min, Jeong-Ki,Park, Young-Jun Journal of Endocrinology, Ltd. [etc.] 2017 The Journal of endocrinology Vol. No.

<P>Healthy expansion of adipose tissue maintains metabolic homeostasis by storing excess chemical energy in increased fat mass. The STAT5-PPAR gamma pathway reportedly regulates adipocyte differentiation, lipid metabolism and adipogenesis. Ginsenoside Rg3 is one of the diverse groups of steroidal saponins, the major active components of ginseng, which have demonstrated pharmacological properties. In this study, we evaluated the therapeutic effects of ginsenoside Rg3 under pathological conditions in vitro and in vivo. We examined the effects of ginsenoside Rg3 on glucose level, insulin sensitivity and lipogenesis in high-fat diet-fed C57BL/6 mice. Ginsenoside Rg3 was also applied to the pre-adipocyte cell line 3T3-L1 to assess the impact on lipogenesis. Ginsenoside Rg3 reduced epididymal white adipose tissue (eWAT) size and hepatic steatosis, and the amount of triglycerides (TGs) in both eWAT and liver. Similar to the murine model, Rg3-treated 3T3-L1 cells showed a reduction in lipid accumulation and amount of total TGs. Ginsenoside Rg3 regulates the expression of PPAR gamma though STAT5 in vitro and in vivo. According to our results, lipid metabolism-related genes were downregulated in the high-fat mice and 3T3-L1 cell line. Rg3 shows potential for the amelioration of obesity-induced pathology, acting though STAT5-PPAR gamma to facilitate the healthy functioning of adipose tissue. This is the first report of evidence that obesity-induced insulin resistance and lipotoxicity can be treated with ginsenoside Rg3, which acts though the STAT5-PPAR gamma pathway in vivo and in vitro.</P>