Aotani Daisuke, Ariyasu Hiroyuki, Shimazu-Kuwahara Satoko, Shimizu Yoshiyuki, Nomura Hidenari, Murofushi Yoshiteru, Kaneko Kentaro, Izumi Ryota, Matsubara Masaki, Kanda Hajime, Noguchi Michio, Tanaka Tomohiro, Kusakabe Toru, Miyazawa Takashi, Nakao Kazuwa
Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan.
The First Department of Medicine, Wakayama Medical University, Wakayama, Japan.
Endocr J. 2017;64(Suppl.):S31-S33. doi: 10.1507/endocrj.64.S31.
To elucidate the clinical implication of ghrelin, we have been trying to generate variable models of transgenic (Tg) mice overexpressing ghrelin. We generated Tg mice overexpressing des-acyl ghrelin in a wide variety of tissues under the control of β-actin promoter. While plasma des-acyl ghrelin level in the Tg mice was 44-fold greater than that of control mice, there was no differences in the plasma ghrelin level between des-acyl ghrelin Tg and the control mice. The des-acyl ghrelin Tg mice exhibited the lower body weight and the shorter body length due to modulation of GH-IGF-1 axis. We tried to generate Tg mice expressing a ghrelin analog, which possessed ghrelin-like activity (Trp-ghrelin Tg mice). The plasma Trp-ghrelin concentration in Trp-ghrelin Tg mice was approximately 85-fold higher than plasma ghrelin (acylated ghrelin) concentration seen in the control mice. Because Trp-ghrelin is approximately 24-fold less potent than ghrelin, the plasma Trp-ghrelin concentration in Trp-ghrelin Tg mice was calculated to have approximately 3.5-fold biological activity greater than that of ghrelin (acylated ghrelin) in the control mice. Trp-ghrelin Tg mice did not show any phenotypes except for reduced insulin sensitivity in 1-year old. After the identification of ghrelin O-acyltransferase (GOAT), we generated doubly Tg mice overexpressing both mouse des-acyl ghrelin and mouse GOAT in the liver by cross-mating the two kinds of Tg mice. The plasma ghrelin concentration of doubly Tg mice was approximately 2-fold higher than that of the control mice. No apparent phenotypic changes in body weight and food intake were observed in doubly Tg mice. Further studies are ongoing in our laboratory to generate Tg mice with the increased plasma ghrelin level to a greater extent. The better understanding of physiological and pathophysiological significance of ghrelin from experiments using an excellent animal model may provide a new therapeutic approach for human diseases.
为阐明胃饥饿素的临床意义，我们一直在尝试构建过表达胃饥饿素的转基因（Tg）小鼠的多种模型。我们构建了在β-肌动蛋白启动子控制下在多种组织中过表达去酰基胃饥饿素的Tg小鼠。虽然Tg小鼠的血浆去酰基胃饥饿素水平比对照小鼠高44倍，但去酰基胃饥饿素Tg小鼠与对照小鼠的血浆胃饥饿素水平没有差异。由于生长激素-胰岛素样生长因子-1轴的调节，去酰基胃饥饿素Tg小鼠表现出较低的体重和较短的体长。我们试图构建表达具有胃饥饿素样活性的胃饥饿素类似物的Tg小鼠（色氨酸-胃饥饿素Tg小鼠）。色氨酸-胃饥饿素Tg小鼠的血浆色氨酸-胃饥饿素浓度比对照小鼠的血浆胃饥饿素（酰化胃饥饿素）浓度高约85倍。因为色氨酸-胃饥饿素的效力比胃饥饿素低约24倍，所以色氨酸-胃饥饿素Tg小鼠的血浆色氨酸-胃饥饿素浓度经计算其生物活性比对照小鼠的胃饥饿素（酰化胃饥饿素）高约3.5倍。色氨酸-胃饥饿素Tg小鼠除了1岁时胰岛素敏感性降低外没有表现出任何表型。在鉴定出胃饥饿素O-酰基转移酶（GOAT）后，我们通过将两种Tg小鼠杂交，构建了在肝脏中同时过表达小鼠去酰基胃饥饿素和小鼠GOAT的双转基因小鼠。双转基因小鼠的血浆胃饥饿素浓度比对照小鼠高约2倍。在双转基因小鼠中未观察到体重和食物摄入量有明显的表型变化。我们实验室正在进行进一步研究，以构建血浆胃饥饿素水平更高的Tg小鼠。通过使用优秀的动物模型进行实验，更好地理解胃饥饿素的生理和病理生理意义可能为人类疾病提供新的治疗方法。
