A mouse model of ghrelinoma exhibited activated growth hormone-insulin-like growth factor I axis and glucose intolerance.
Ghrelin is a stomach-derived peptide that has growth hormone-stimulating and orexigenic activities. Although there have been several reports of ghrelinoma cases, only a few cases have elevated circulating ghrelin levels, hampering the investigation of pathophysiological features of ghrelinoma and chronic effects of ghrelin excess. Furthermore, standard transgenic technique has resulted in desacyl ghrelin production only because of the limited tissue expression of ghrelin O-acyltransferase, which mediates acylation of ghrelin. Accordingly, we attempted to create ghrelin promoter SV40 T-antigen transgenic (GP-Tag Tg) mice, in which ghrelin-producing cells continued to proliferate and finally developed into ghrelinoma. Adult GP-Tag Tg mice showed elevated plasma ghrelin levels with preserved physiological regulation. Adult GP-Tag Tg mice with increased plasma ghrelin levels exhibited elevated IGF-I levels despite poor nutrition. Although basal growth hormone levels were not changed, those after growth hormone-releasing hormone injection tended to be higher. These results indicate that chronic elevation of ghrelin activates GH-IGF-I axis. In addition, GP-Tag Tg mice demonstrated glucose intolerance. Insulin secretion by glucose tolerance tests was significantly attenuated in GP-Tag Tg, whereas insulin sensitivity determined by insulin tolerance tests was preserved, indicating that chronic elevation of ghrelin suppresses insulin secretion and leads to glucose intorelance. Thus, we successfully generated a Tg model of ghrelinoma, which is a good tool to investigate chronic effects of ghrelin excess. Moreover, their characteristic features could be a hint on ghrelinoma.
Iwakura
Hiroshi
H
Ghrelin Research Project, Translational Research Center, Kyoto University Hospital, Kyoto University Graduate School ofMedicine, Kyoto 606-8507, Japan. hiwaku@kuhp.kyoto-u.ac.jp
Ariyasu
Hiroyuki
H
Li
Yushu
Y
Kanamoto
Naotetsu
N
Bando
Mika
M
Yamada
Go
G
Hosoda
Hiroshi
H
Hosoda
Kiminori
K
Shimatsu
Akira
A
Nakao
Kazuwa
K
Kangawa
Kenji
K
Akamizu
Takashi
T
D000236:Adenoma / Q000150:complications / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D054439:Ghrelin / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D018149:Glucose Intolerance / Q000150:complications* / Q000235:genetics / Q000473:pathology; D013006:Growth Hormone / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013274:Stomach Neoplasms / Q000150:complications / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015854:Up-Regulation
D054439:Ghrelin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone