Ghrelin在模拟失重胃肠功能紊乱中的作用及其机制研究

Anorexia and weight loss induced by weightlessness of astronauts is a crucial issue in modern aeromedical research. Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R) originally identified in rat and human gastric mucosa. Ghrelin can stimulate appetite and food intake; promoting gastric acid secretion and motility; affecting pancreas function and glycolytic metabolism. Our pilot study has found that the serum ghrelin level was decreased in rats undergoing 4 week simulated weightlessness. To explore the effect and its mechanism of ghrelin on gastrointestinal functional alterations induced by microgravity during spaceflight, by using hindlimb unloading(HU) rat model, gene-specific knockout mice, cytological methods in simulated weightless condition and molecular biological techniques, this study was designed to investigate the gene expression alteration of ghrelin and its receptors in gastrointestinal mucosa; to detect the effects of ghrelin on food intake in hindlimb unloading rats; to farther validate the effects of ghrelin on anorexia in HU model with ghrelin gene knockout mice; and to elucidate the molecular mechanism of ghrelin on ameliorating the disturbing effect of weightlessness on gastroinstinal function in an in vitro simulated microgravity cell culture model. This study might clarify the role and its molecular mechanism of ghrelin on preventing the disturbance of digestive function in spaceflight weightless environment.The present study may also provides the theoretic basis in establishing medical indemnificatory criteria for astronauts.

失重导致的宇航员厌食和体重下降是当前航天医学研究的重要领域之一。Ghrelin是生长激素促分泌剂受体（GHS-R）的内源性配体，可刺激食欲及摄食，调节机体能量平衡，促进胃动力和胃酸分泌，影响胰腺功能和糖代谢。我们初步的研究发现，模拟失重4周大鼠血清中ghrelin水平下降。为探讨ghrelin在航天所致胃肠功能紊乱中的作用及其机制,本项目拟采用尾悬吊大鼠模型，应用基因敲除动物、模拟失重细胞学研究方法结合分子生物学等技术，观察模拟失重大鼠胃肠黏膜组织中ghrelin及其受体基因表达的变化；检测ghrelin对模拟失重大鼠摄食行为的影响；用ghrelin基因敲除小鼠进一步验证ghrelin在模拟失重所致厌食中的作用；并在培养细胞模拟失重模型上阐明ghrelin对抗胃肠功能紊乱的分子机制。本研究将揭示ghrelin在航天失重引起消化功能紊乱中的作用及其机理，为制定航天员医学保障标准提供理论依据。

Ghrelin是一种具有多种功能的胃肠激素，其功能包括促进生长激素释放、调节促炎症性细胞因子、控制摄食行为、以及维持机体能量平衡。近年的研究发现Ghrelin还具有其他许多生理功能。太空飞行可引起机体内分泌和代谢的改变，这种代谢变化可影响宇航员保持健康所需的身体成分和能量需求。失重导致的宇航员厌食和体重下降是当前航天医学研究的重要领域之一。我们先前的研究发现模拟失重4周大鼠血清中Ghrelin水平下降。然而，Ghrelin在微重力环境下的变化及其作用机制尚不得而知。本项目探讨了ghrelin在尾悬吊模拟失重所致大鼠胃肠功能紊乱中的作用及其机制。. 4周尾悬吊大鼠血清Ghrelin水平（25.11±7.45ng/ml vs 44.02 ± 10.63ng/ml, P < 0.05, n=10）和胃黏膜组织中Ghrelin阳性细胞数（46.23 ± 7.82 vs 74.68 ± 10.35, P < 0.01, n = 10）较同步对照大鼠均显著下降。提示尾悬吊模拟失重可影响胃黏膜ghrelin的分泌。酶免疫分析(EIA)法测定结果发现，模拟失重大鼠下颌下腺组织中Ghrelin水平显著降低( 8.36±1.87 ng/ml, vs 6.45±2.06 ng/ml,, P<0.01)。. 模拟失重大鼠胃排空率和小肠推进率降低，外源性ghrelin可在一定程度上改善模拟失重大鼠的胃排空率和小肠推进率下降。模拟失重可显著增加大鼠胃和小肠黏膜上皮细胞的凋亡，外源性ghrelin可在一定程度上抑制模拟失重大鼠胃和小肠黏膜上皮细胞的凋亡。. 构建了GHSR-1a基因短发夹干扰RNA(short hairpin RNA,shRNA)慢病毒载体，建立稳定表达GHSR-1a shRNA的人结直肠癌SW480细胞系。体外模拟失重研究表明，Ghrelin可阻止回旋器模拟失重引起的SW480细胞凋亡，并且作用这种是通过其功能型受体GHSR-1a实现的。. 本研究揭示了ghrelin在航天失重引起消化功能紊乱中的作用及其机理。