| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Department of Internal Medicine (C.Y.Y., Y.J.P., C.S.S., S.Y.K., H.K.L., K.S.P.) Seoul National University College of Medicine, Seoul 110-744, Korea; Department of Internal Medicine (M.S.K., J.Y.P., K.U.L.), and Asan Institute for Life Sciences (P.G.J., H.S.P., J.W.R., Y.K.P.), University of Ulsan College of Medicine, Seoul 138-736, Korea; and Medicine-Endocrine (Y.B.K.), Beth Israel Deaconess Medical Center Harvard Medical School, Boston, Massachusetts 02215
Address all correspondence and requests for reprints to: Kyong Soo Park, M.D. Department of Internal Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea. E-mail: kspark{at}snu.ac.kr.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
Ghrelin has also been shown to have multiple regulatory functions in peripheral tissues (6, 7, 8). Expression of GHS-R mRNA, as well as binding sites for the synthetic GHS-R ligand [125I]-Try-Ala-Hexarelin, have been observed in peripheral organs, including adipose tissue (9, 10), suggesting that ghrelin may act directly on adipocytes to increase adipose tissue mass. We therefore investigated whether ghrelin plays a direct role in adipocyte biology. We found that ghrelin stimulates the proliferation and differentiation of 3T3-L1 adipocytes, as well as suppressing apoptosis in these cells. In addition, we found that ghrelin activates the MAPK and phosphatidylinositol 3 kinase (PI3K)-Akt pathways, both of which mediate the mitogenic and antiapoptotic effects of ghrelin.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
, A and B). GHS-R1a abundance in 3T3-L1 cells was dependent on the stage of adipocyte differentiation, being higher in terminally differentiated adipocytes than in preadipocytes or early differentiating adipocytes (Fig. 1A). In contrast, preproghrelin mRNA expression was found in rat stomach but not in 3T3-L1 peadipocytes and differentiated adipocytes (Fig. 1C).
|
). Ghrelin at concentrations of 10–7 to 10–13 M also significantly increased adipocyte cell numbers, with the most pronounced effect observed at 10–11 M (Fig. 2A). In cell cycle analysis, ghrelin (10–9 to 10–14 M) also stimulated cell cycle progression from G1 to S phase (Table 1).
|
|
, B and C), as well as stimulating the phosphorylation of Rb protein and the expression of thymidine kinase mRNA (Fig. 2, B and D).
Ghrelin Stimulates Adipocyte Proliferation
Insulin and IGF-I have been shown to stimulate both the proliferation and differentiation of adipocytes (15, 16). To determine whether ghrelin affects adipocyte differentiation, we maintained 3T3-L1 cells in DMEM containing 10% fetal bovine serum (FBS) with or without insulin and/or ghrelin for 6–8 d after induction of differentiation. Oil red O staining revealed that the formation of lipid droplets, a marker for adipocyte differentiation, was significantly increased by insulin (Fig. 3A). Treatment of cells with ghrelin (10–11 M or 10–13 M) induced the accumulation of more lipid droplets than observed in FBS-treated cells, but fewer than that observed in full dose insulin-treated cells (Fig. 3A). Cotreatment of ghrelin (10–11 M or 10–13 M) and half-dose (0.5 µg/ml) insulin further stimulated adipocyte differentiation compared with treatment of ghrelin alone (Fig. 3A). We also found that insulin and ghrelin increased the level of mRNA expression of the adipogenic genes, peroxisome proliferator-activated receptor (PPAR)-
, adipocyte determination and differentiation-dependent factor (ADD)1, and adipose protein 2/fatty acid-binding protein (aP2) (Fig. 3B).
|
). Consistent with previous studies (17, 18), 10 nM IGF-I reduced apoptosis induced by serum starvation in these cells, as did ghrelin, at concentrations of 10–7 to 10–13 M (Fig. 4A). Similarly, serum starvation increased TUNEL-positive cells, which was attenuated by treatment of ghrelin (TUNEL-positive cells: control, 4 ± 1%; serum deprivation, 56 ± 5%; 10–11M ghrelin, 18 ± 3%; 10–13 M ghrelin, 15 ± 2% of PI stained cells) (Fig. 4B).
|
). We further determined the dose response and time course of ghrelin-induced ERK1/2 activation at different stages of adipocyte differentiation. We found that ghrelin concentrations ranging from 10–7 to 10–15 M caused a rapid and strong activation of ERK1/2 in preadipocytes and terminally differentiated adipocytes, but ghrelin-induced ERK1/2 activation was significantly reduced in early differentiating adipocytes (Fig. 5B). Time course experiments showed that, in preadipocytes and terminally differentiated adipocytes, ERK1/2 activation occurred as early as 2 min after ghrelin stimulation, peaked between 5 and 10 min, and lasted for at least 30 min (Fig. 5C). In early stages of adipocyte differentiation, however, ghrelin-induced activation of ERK1/2 persisted no longer than 5 min.
|
, D–G).
Ghrelin Activates the PI3K/Akt Pathway
It was recently reported that, in cardiomyocytes, ghrelin and the GHS-R ligand, hexarelin, can activate the PI3K/Akt pathway, an important signaling pathway for cell survival, adipocyte differentiation, and glucose transport (7). We therefore assayed the effect of ghrelin on the PI3K/Akt pathway in 3T3-L1 cells. In preadipocytes, ghrelin induced an increase in insulin receptor substrate 1 (IRS-1)-associated PI3K activity, which occurred within 5 min and persisted for at least 30 min (Fig. 6A). Akt activation, as measured by phosphorylation, was detected beginning 30 min after ghrelin treatment and gradually increased over the next 24 h (Fig. 6B). In differentiated adipocytes, ghrelin also induced Akt phosphorylation (Fig. 6, C and D). Wortmannin, an inhibitor of PI3K, prevented ghrelin-stimulated Akt phosphorylation (Fig. 6E), suggesting that the activation of PI3K is an important upstream signal leading to Akt activation.
|
, A and B).
|
). Moreover, cotreatment of insulin (25 nM) and ghrelin (10–11 M to 10–15 M) induced a further increase in glucose transport (Fig. 8B). The PI3K inhibitor, wortmannin, completely blocked this ghrelin-induced increase in glucose transport (Fig. 8A), suggesting that PI3K may mediate the effect of ghrelin on glucose transport in these adipocytes.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
100 fM) (28, 29), suggesting that, at physiological concentrations, ghrelin can act as an adipocyte mitogen. We also found that ghrelin stimulated fat accumulation as well as the mRNA expressions of adipogenic markers (PPAR-, ADD1, and aP2) during adipocyte differentiation. Our finding is in line with that of Choi et al. (30) that ghrelin stimulated adipocyte differentiation in primary cultured rat adipocytes. However, Zhang et al. (31) have recently reported that ectopic overexpression of ghrelin gene in 3T3-L1 cells promoted adipocyte proliferation but inhibited adipocyte differentiation. The reason for the discrepancy between our findings and those of Zhang et al. is unclear at present. Prolonged exposure to higher dose of ghrelin may inhibit adipocyte differentiation. We found that only lower dose of ghrelin (10–11 and 10–13 M) can stimulate adipocyte differentiation. Furthermore, MAPK activation (mitogenic signaling pathway) in response to ghrelin was significantly reduced in early differentiating adipocytes. Reduction in MAPK activation induced by IGF-I has been suggested to be important for induction of adipocyte differentiation (32). In contrast, epidermal growth factor 1-induced MAPK activation is sustained in early differentiating adipocytes, and epidermal growth factor 1 has an inhibitory effect on adipocyte differentiation (32). Thus, reduced MAPK signaling in response to exogenous ghrelin may be of help for induction of adipocyte differentiation. Similarly, the effects of persistent exposure to endogenous ghrelin on adipocyte biology may differ from that of exogenous ghrelin. Further study will be warranted to clarify the argument.
We also found that ghrelin significantly reduced adipocyte apoptosis induced by serum deprivation, a finding in agreement with a recent report showing that ghrelin reduces apoptosis in cardiomyocytes and endothelial cells (7). Adipocyte apoptosis, which occurs in rodents as well as in humans with cancer-related cachexia, has been hypothesized to decrease adipocyte cell number (11). Thus, the reduction in adipocyte apoptosis due to treatment with ghrelin may contribute to an increase in adipocyte cell number coupled with an increase in adipocyte proliferation.
Several other factors have been implicated in the regulation of adipocyte number. Insulin, IGF-I, PPAR- ligands, retinoids, and corticosteroids have been found to increase adipocyte number, whereas TNF-
and leptin have been shown to decrease the number of these cells (11). Our findings that ghrelin receptor is expressed in adipocytes, and that physiological concentrations of ghrelin can directly stimulate adipocyte proliferation/differentiation and prevent adipocyte apoptosis, identify ghrelin as a new regulator of adipocyte number.
Previous studies have demonstrated that in cardiomyocytes, endothelial cells, and hepatocytes, ghrelin induces ERK1/2 activation (7, 26), an important mechanism mediating the mitogenic effects of IGF-I and insulin in adipocytes (33, 34). In our study, ghrelin strongly activated ERK1/2 in 3T3-L1 adipocytes, and the ERK inhibitor, PD98059, inhibited the mitogenic and antiapoptotic activities of ghrelin, thus indicating that ghrelin acts on adipocytes through ERK1/2 activation.
GHS-R1a, which is abundantly expressed in the pituitary and hypothalamus, mediates the endocrine effects of ghrelin (5, 35). We and others (30) have shown that cultures of murine 3T3-L1 adipocytes and primary rat adipocytes express functional GHS-R1a. In addition, ERK1/2 was similarly activated by the GHS-R1a agonist, GHRP-6, in the present study. Thus the ghrelin-induced activation of ERK1/2 and mitogenesis may be mediated though GHS-R1a, in contrast to cardiomyocytes, in which the activation of this pathway is mediated via a novel, yet-to-be-identified receptor, distinct from GHS-R1a (7).
Several signaling pathways have been associated with the GPCR-mediated activation of ERK1/2. Activation of the Gi/o subtype of GPCR can activate ERK1/2 through the direct interaction of the Gß subunits with P21ras and the raf-1 kinase complex, which act upstream of ERK pathway (21). A synthetic GHS-R ligand has been shown to activate PKC pathways (36), which may induce MAPK activation via P21ras-dependent and -independent mechanisms (22, 37). On the other hand, a PI3K inhibitor has been shown to inhibit ERK1/2 activation induced by insulin and platelet derived growth factor, suggesting a role for PI3K in ERK activation (23, 38). In our study, pretreatment with a Gi/o inhibitor (pertussis toxin), PKC inhibitors (staurosporin and GF109203X), or a PI3K inhibitor (wortmannin) significantly attenuated ghrelin-induced ERK1/2 phosphorylation. These findings suggest that multiple signaling pathways are involved in ghrelin signaling leading to MAPK activation.
Finally, we have shown that exposure of 3T3-L1 cells to ghrelin induced increases in IRS-1-associated PI3K activity and Akt phosphorylation. Inhibition of PI3K blocked the effects of ghrelin on adipocyte proliferation and apoptosis. Furthermore, ghrelin increased basal and insulin-stimulated glucose transport, whereas coadministration of a PI3K inhibitor blocked this effect of ghrelin on glucose transport. These findings indicate that the PI3K/Akt pathway acts to mediate the effects of ghrelin in 3T3-L1 cells.
In summary, we have demonstrated that ghrelin has direct regulatory effects on proliferation, differentiation, apoptosis, and glucose transport in 3T3-L1 adipocyte cell lines. We have also shown that treatment with ghrelin strongly activated the ERK1/2 and PI3K/Akt pathways in these cells. These findings indicate that ghrelin may exert its adipogenic action not only through central mechanisms but also through direct effects in adipocytes.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
Cell Culture
3T3-L1 preadipocytes were maintained in DMEM containing 10% calf serum, 100 U/ml penicillin, and 100 U/ml streptomycin. For routine induction of differentiation, confluent cells were treated with 25 µM dexamethasone, 0.5 mM isobutylmethylxanthine, and 5 µg/ml insulin for 60 h and maintained in DMEM containing 10% FBS and 1 µg/ml insulin for 6–8 d unless otherwise stated.
Cell Proliferation Assay
Cell proliferation was monitored with the Cell titer 96 aqueous one-solution cell proliferative assay (Promega Corp., Madison, WI). Cells (5 x 103/well) were seeded in a 96-well culture plate, maintained for 24 h in DMEM containing 10% calf serum, incubated overnight in serum-free DMEM with 0.1% BSA to synchronize the cell cycle, and treated with various compounds at 37 C for 24 h. To each well was added 20 µl of 2-(4',5'-dimethyl-2'-thiazolyl)-3-(4''-sulfophenyl) (MTS) solution; the MTS tetrazolium compound is reduced by the reduced nicotinamide adenine dinucleotide phosphate or reduced nicotinamide adenine dinucleotide produced by dehydrogenase enzymes in metabolically active cells into a colored, soluble formazan product. The plate was kept for 3 h in a CO2 incubator, and the absorbance at 490 nm was recorded with a 96-well plate ELISA reader (PerkinElmer Corp., Norwalk, CT). All samples were assayed in triplicate, and each experiment was repeated at least three times.
Cell Cycle Analysis
Cells were seeded in 12-well culture plates, maintained for 24 h in DMEM containing 10% calf serum, incubated overnight in serum-free DMEM with 0.1% BSA to synchronize the cell cycle, and treated with various compounds at 37 C for 15 h. The cells were harvested, fixed in 70% ethanol for at least 2 h, washed once with PBS, and incubated with 5 µg/ml propidium iodide (PI) and 100 µg/ml RNase for 10 min at room temperature in the dark room. Cell cycle was analyzed with a FACSCalibur argon laser cytometer (Becton Dickson, Franklin Lakes, NJ). Percentage of cells in each phase of cell cycle was calculated and expressed as mean ± SEM.
Apoptosis Assay
Cells were maintained in serum-free DMEM with 0.1% BSA, with or without ghrelin or IGF-I, for the indicated times. The cells were prepared with the same method of cell cycle analysis. Analysis of stained cells was performed on a flow cytometer. The percentage of apoptotic cells was determined from DNA histogram as a ratio of cells with hypodiploid DNA content (the sub-G1 peak) to the total number of cells.
TUNEL Staining
Cells were plated on polylysine-coated slides, fixed with 4% paraformaldehyde in 0.1 M PBS for 1 h at room temperature, rinsed with 0.1 M PBS, pH 7.4, and permeabilized with 1% Triton X-100 in 0.01 M citrate buffer, pH 6.0. DNA fragmentation was detected using TUNEL detection kit (Roche Clinical Laboratories, Indianapolis, IN), which specifically labeled 3'-hydroxyl termini of DNA strand breaks using fluorescein isothiocyanate (FITC)-conjugated dUTP (39). DNA was also labeled with 25 µg/ml PI DNA-binding dye for 5 min. FITC and PI labels were observed with a confocal microscope using an excitation wavelength of 488 nm, and detection was in the range of 500–530 nm for FITC and of 600–630 nm for PI. The percentage of apoptotic cells was calculated as the number of apoptotic cells per number of total cells x 100%.
Oil Red O Staining
Differentiated adipocytes were fixed with 10% formalin and stained with 0.35% oil red O, and the resultant liquid droplets were visualized by light microscopy.
Semiquantitative RT-PCR
Total RNA from rat tissue and 3T3-L1 cells was extracted using Trizol reagent (Invitrogen, San Diego, CA) and quantified by spectrophotometry (Beckman, Fullerton, CA). An aliquot of cDNA synthesized from 2 mg of total RNA was amplified using primer sets for GHS-R1a (5'-TTC TGC CTC ACT GTG CTC TAC AGT-3' and 5'-GGA CAC CAG GTT GCA GTA CTG GCT-3'), preproghrelin (5'-ATG CTC TGG ATG GAC ATG GC-3' and 5'-TAC TTG TCA GCT GGC GCC TC-3'), c-myc (5'-ACG ATG GAT CCT ATC ACC AGC AAC AGC AGA GCC AG-3' and 5'-ATC GAG AAT TCG AAT CGG ACG AGG TAC AGG ATT TG-3'), or thymidine kinase (5'-CCA TGC GGA TCC AAC GAG GGC AAG ACA GTA ATT GTC-3' and 5'-CCA TGC GAA TTC TCT CTG AGA GTC CAA CCT GGG TAG-3') The amplification protocol consisted of 35 (GHS-R1a and ghrelin), 27 (c-myc), 40 (thymidine kinase), or 30 [glyceraldehyde-3-phosphate dehydrogenase (GAPDH)] cycles of denaturation at 94 C for 30 sec, annealing at 56 C for 30 sec, and extension at 72 C for 2 min. The resulting products, of 134 bp (GHS-R1a), 310 bp (ghrelin), 450 bp (c-myc), and 550 bp (thymidine kinase), were visualized by ethidium bromide staining of 1.2% agarose gel electrophoresis and normalized relative to amplification of the same samples with primers for GAPDH.
Northern Blot Analysis
Total RNA was prepared using Trizol reagent, and 20 µg/lane was electrophoresed on 1.2% agarose-formaldehyde gels and transferred to nylon membranes in 10x standard sodium citrate. Membranes were hybridized for 20 h at 68 C with PPAR-, ADD1, and aP2 cDNA (from Dr. Jae-Bum Kim, Seoul National University) probes labeled with the Rediprime labeling kit (Amersham Pharmacia, Piscataway, NJ) and [32P]dCTP. The blots were hybridized in the presence of Quickhyb Solution (Stratagene, La Jolla, CA) at 68 C, washed twice with 1x standard sodium citrate, 0.1% sodium dodecyl sulfate at 68 C, and exposed to x-ray film.
Western Blot Analysis
Cells were lysed in a buffer containing 20 mM Tris-HCl (pH 7.4), 1 mM EDTA, 140 mM NaCl, 1% (wt/vol) Nonidet P-40, 1 mM Na3VO4, 1 mM phenylmethylsulfonyl fluoride, 50 mM NaF, and 10 µg/ml aprotinin. Cell lysates were centrifuged at 13,000 rpm for 15 min to remove insoluble materials, separated by 10% SDS-PAGE, and electrotransferred to a nitrocellulose membrane for 1 h. The membrane was soaked in blocking buffer (1x Tris-buffered saline, 0.1% Tween-20, 5% nonfat dry milk) for 2 h and incubated overnight at 4 C with the primary antibody. Blots were developed using a horseradish peroxidase-linked antirabbit secondary antibody and a chemiluminescent detection system (New England Biolabs, Beverly, MA). For determination of GHS-R1a protein expression, cell lysates were immunoprecipited using anti-GHS-R1a antibody and 20 µl protein G sephalose bead overnight, and the immunoprecipitates were subjected to Western blot analysis.
Measurement of PI3K Activity
PI3K activity was assayed using a protocol adapted from Krook et al. (40). 3T3-L1 preadipocytes and differentiated adipocytes were grown to confluency in 10-cm dishes, incubated for 2 h in serum-free DMEM, and treated with insulin (50 nM) for 30 min or ghrelin (10–11 M) for the indicated time. Incubations were terminated by aspirating the medium and rinsing briefly with ice-cold PBS. To each culture were added 500 µl of ice-cold freshly prepared PI3K lysis buffer A [20 mM Tris (pH 8.0), 137 mM NaCl, 2.7 mM KCl, 1 mM MgCl2, 500 µM NaVO3, 1% Nonidet P-40, 10% (wt/vol) glycerol, 10 µg/ml leupeptin, and 200 µM phenylmethylsulfonyl fluoride], and the lysates were immunoprecipitated with IRS-1 antibody coupled to protein A-sepharose (Amersham Pharmacia) overnight at 4 C. Reaction products were resolved by thin layer chromatography and quantified using a phosphor imager (Bio-Rad Laboratories, Hercules, CA).
Glucose Transport Assay
3T3-L1 adipocytes in 12-well culture plates were cultured overnight in serum-free medium containing 0.1% BSA in the presence or absence of insulin (25 or 50 nM) and/or ghrelin (10–7 to 10–15 M) at the indicated concentrations before assay. To each well were added 10 µl [U-14C]2-deoxyglucose (0.5 µCi/sample) and glucose to a final concentration of 0.01 mM, and glucose uptake was determined in triplicate (41).
Data Analysis
All data are presented as mean ± SEM. Comparisons between groups were by ANOVA followed by the post hoc least significance difference test. Significance was defined as P < 0.05.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
M.S.K. and C.Y.Y. contributed equally to this work and should both be considered as first authors.
Abbreviations: ADD, Adipocyte determination and differentiation-dependent factor; aP2, adipose protein 2/fatty acid-binding protein; FBS, fetal bovine serum; FITC, fluorescein isothiocyanate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GHRP, GH-releasing peptide; GHS-R, GH secretagog receptor; GPCR, G protein-coupled receptor; IRS-1, insulin receptor substrate 1; MTS, 2-(4',5'-dimethyl-2'-thiazolyl)-3-(4''-sulfophenyl); PI, propidium iodide; PI3K, phosphatidylinositol 3 kinase; PKC, protein kinase C; PPAR, peroxisome proliferator-activated receptor; Rb, retinoblastoma; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP biotin nick-end labeling.
Received for publication December 2, 2003. Accepted for publication May 25, 2004.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
-induced apoptosis, in 3T3–L1 preadipocytes. J Endocrinol 167:165–174[Abstract]
activates RAF-1 by direct phosphorylation. Nature 364:249–252[CrossRef][Medline]
This article has been cited by other articles:
 |
|
 |
|
  H. Chung, S. Seo, M. Moon, and S. Park Phosphatidylinositol-3-kinase/Akt/glycogen synthase kinase-3{beta} and ERK1/2 pathways mediate protective effects of acylated and unacylated ghrelin against oxygen-glucose deprivation-induced apoptosis in primary rat cortical neuronal cells J. Endocrinol., September 1, 2008; 198(3): 511 - 521. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Deng, J. Ling, J. Ma, C. Liu, and W. Zhang Stimulation of intramembranous bone repair in rats by ghrelin Exp Physiol, July 1, 2008; 93(7): 872 - 879. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 I. Johansson, S. Destefanis, N. D. Aberg, M. A. I. Aberg, K. Blomgren, C. Zhu, C. Ghe, R. Granata, E. Ghigo, G. Muccioli, et al. Proliferative and Protective Effects of Growth Hormone Secretagogues on Adult Rat Hippocampal Progenitor Cells Endocrinology, May 1, 2008; 149(5): 2191 - 2199. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. T. Vestergaard, C. B. Djurhuus, J. Gjedsted, S. Nielsen, N. Moller, J. J. Holst, J. O. L. Jorgensen, and O. Schmitz Acute Effects of Ghrelin Administration on Glucose and Lipid Metabolism J. Clin. Endocrinol. Metab., February 1, 2008; 93(2): 438 - 444. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Tawadros, L.A. Salamonsen, E. Dimitriadis, and C. Chen Facilitation of decidualization by locally produced ghrelin in the human endometrium Mol. Hum. Reprod., July 1, 2007; 13(7): 483 - 489. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. J. D. Delhanty, P. M. van Koetsveld, C. Gauna, B. van de Zande, G. Vitale, L. J. Hofland, and A. J. van der Lely Ghrelin and its unacylated isoform stimulate the growth of adrenocortical tumor cells via an anti-apoptotic pathway Am J Physiol Endocrinol Metab, July 1, 2007; 293(1): E302 - E309. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Si, J. Yoon, and K. Lee Flux profile and modularity analysis of time-dependent metabolic changes of de novo adipocyte formation Am J Physiol Endocrinol Metab, June 1, 2007; 292(6): E1637 - E1646. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z.-F. Guo, X. Zheng, Y.-W. Qin, J.-Q. Hu, S.-P. Chen, and Z. Zhang Circulating Preprandial Ghrelin to Obestatin Ratio Is Increased in Human Obesity J. Clin. Endocrinol. Metab., May 1, 2007; 92(5): 1875 - 1880. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Filigheddu, V. F. Gnocchi, M. Coscia, M. Cappelli, P. E. Porporato, R. Taulli, S. Traini, G. Baldanzi, F. Chianale, S. Cutrupi, et al. Ghrelin and Des-Acyl Ghrelin Promote Differentiation and Fusion of C2C12 Skeletal Muscle Cells Mol. Biol. Cell, March 1, 2007; 18(3): 986 - 994. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Granata, F. Settanni, L. Biancone, L. Trovato, R. Nano, F. Bertuzzi, S. Destefanis, M. Annunziata, M. Martinetti, F. Catapano, et al. Acylated and Unacylated Ghrelin Promote Proliferation and Inhibit Apoptosis of Pancreatic {beta}-Cells and Human Islets: Involvement of 3',5'-Cyclic Adenosine Monophosphate/Protein Kinase A, Extracellular Signal-Regulated Kinase 1/2, and Phosphatidyl Inositol 3-Kinase/Akt Signaling Endocrinology, February 1, 2007; 148(2): 512 - 529. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Chung, E. Kim, D. H. Lee, S. Seo, S. Ju, D. Lee, H. Kim, and S. Park Ghrelin Inhibits Apoptosis in Hypothalamic Neuronal Cells during Oxygen-Glucose Deprivation Endocrinology, January 1, 2007; 148(1): 148 - 159. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Choi, M. Lee, A. L. Shiu, S. J. Yo, and G. W. Aponte Identification of a protein hydrolysate responsive G protein-coupled receptor in enterocytes Am J Physiol Gastrointest Liver Physiol, January 1, 2007; 292(1): G98 - G112. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Avallone, A. Demers, A. Rodrigue-Way, K. Bujold, D. Harb, S. Anghel, W. Wahli, S. Marleau, H. Ong, and A. Tremblay A Growth Hormone-Releasing Peptide that Binds Scavenger Receptor CD36 and Ghrelin Receptor Up-Regulates Sterol Transporters and Cholesterol Efflux in Macrophages through a Peroxisome Proliferator-Activated Receptor {gamma}-Dependent Pathway Mol. Endocrinol., December 1, 2006; 20(12): 3165 - 3178. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H D. Falls, B. D Dayton, D. G Fry, C. A Ogiela, V. G Schaefer, S. Brodjian, R. M Reilly, C. A Collins, and W. Kaszubska Characterization of ghrelin receptor activity in a rat pituitary cell line RC-4B/C. J. Mol. Endocrinol., August 1, 2006; 37(1): 51 - 62. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P J D Delhanty, B C J van der Eerden, M van der Velde, C Gauna, H A P Pols, H Jahr, H Chiba, A J van der Lely, and J P T M van Leeuwen Ghrelin and unacylated ghrelin stimulate human osteoblast growth via mitogen-activated protein kinase (MAPK)/phosphoinositide 3-kinase (PI3K) pathways in the absence of GHS-R1a J. Endocrinol., January 1, 2006; 188(1): 37 - 47. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P L Jeffery, R E Murray, A H Yeh, J F McNamara, R P Duncan, G D Francis, A C Herington, and L K Chopin Expression and function of the ghrelin axis, including a novel preproghrelin isoform, in human breast cancer tissues and cell lines Endocr. Relat. Cancer, December 1, 2005; 12(4): 839 - 850. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. H. Yeh, P. L. Jeffery, R. P. Duncan, A. C. Herington, and L. K. Chopin Ghrelin and a Novel Preproghrelin Isoform Are Highly Expressed in Prostate Cancer and Ghrelin Activates Mitogen-Activated Protein Kinase in Prostate Cancer Clin. Cancer Res., December 1, 2005; 11(23): 8295 - 8303. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S M Jeyakumar, A Vajreswari, B Sesikeran, and N V Giridharan Vitamin A supplementation induces adipose tissue loss through apoptosis in lean but not in obese rats of the WNIN/Ob strain J. Mol. Endocrinol., October 1, 2005; 35(2): 391 - 398. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C Dornonville de la Cour, A Lindqvist, E Egecioglu, Y C L Tung, V Surve, C Ohlsson, J-O Jansson, C Erlanson-Albertsson, S L Dickson, and R Hakanson Ghrelin treatment reverses the reduction in weight gain and body fat in gastrectomised mice Gut, July 1, 2005; 54(7): 907 - 913. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Namkoong, M. S. Kim, P. G. Jang, S. M. Han, H. S. Park, E. H. Koh, W. J. Lee, J. Y. Kim, I. S. Park, J. Y. Park, et al. Enhanced Hypothalamic AMP-Activated Protein Kinase Activity Contributes to Hyperphagia in Diabetic Rats Diabetes, January 1, 2005; 54(1): 63 - 68. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Holst, N. D. Holliday, A. Bach, C. E. Elling, H. M. Cox, and T. W. Schwartz Common Structural Basis for Constitutive Activity of the Ghrelin Receptor Family J. Biol. Chem., December 17, 2004; 279(51): 53806 - 53817. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |
, P < 0.05 vs. ghrelin-treated cells.
, P < 0.05 vs. serum-starved, ghrelin-treated group.