Zhao Juan, Harada Naoaki, Sobue Kazuya, Katsuya Hirotada, Okajima Kenji
Department of Anesthesiology and Medical Crisis Management, Nagoya City University, Graduate School of Medical Sciences, Kawasumi 1, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan.
Growth Horm IGF Res. 2009 Apr;19(2):136-45. doi: 10.1016/j.ghir.2008.08.003. Epub 2008 Sep 21.
We previously reported that activated neutrophils are critically involved in the development of stress-induced gastric mucosal injury in mice. Caspase activation plays an important role in the pathogenesis of tissue injury by activating neutrophils through an increase in the expression of endothelial monocyte-activating polypeptide-II (EMAP-II), a chemoattractant for neutrophils. Since insulin-like growth factor-I (IGF-I) inhibits caspase activation, it is possible that IGF-I reduces gastric mucosal injury by inhibiting neutrophil activation. In the present study, we examined this possibility in mice subjected to water-immersion restraint stress (WIR).
Mice were intraperitoneally administered with IGF-I or vehicle before being subjected to WIR. Gastric mucosal injury, gastric myeloperoxidase (MPO) activity, the immunofluorescence intensity of MPO, caspase-3 activity, number of apoptotic cells, EMAP-II expression and activation of Akt and glycogen synthase kinase-3beta (GSK-3beta) in gastric mucosa were determined in mice subjected to WIR. Neutropenia was induced by administration of methotrexate (MTX).
Administration of IGF-I at dosages higher than 200 microg/kg significantly reduced gastric mucosal injury and inhibited increases in gastric MPO activities after 8h of WIR. Administration of MTX also reduced the gastric mucosal injury as well as inhibiting increases in both gastric mucosal MPO activities and circulating neutrophil number. IGF-I (500 microg/kg) inhibited the increases in both gastric MPO activity and the immunofluorescence intensity of MPO observed in the gastric mucosa, but had no effect on the increase in circulating neutrophil number after 8h of WIR. It also markedly blunted WIR-induced increases in caspase-3 activities and the number of apoptotic cells in the gastric mucosa after 8h of WIR. Gastric expression of EMAP-II was markedly increased at 8h after starting WIR and this increase was inhibited by IGF-I administration. Administration of IGF-I enhanced WIR-induced phosphorylation of Akt and GSK-3beta in the gastric mucosa.
These observations indicate that IGF-I reduces stress-induced gastric mucosal injury by inhibiting gastric accumulation of neutrophils through inhibition of caspase-3-mediated EMAP-II activation. Furthermore, IGF-I might inhibit caspase-3 activation through Akt/GSK-3beta signaling.
我们之前报道过，活化的中性粒细胞在小鼠应激诱导的胃黏膜损伤发展过程中起关键作用。半胱天冬酶激活通过增加内皮单核细胞激活多肽-II（EMAP-II，一种中性粒细胞趋化因子）的表达来激活中性粒细胞，从而在组织损伤的发病机制中发挥重要作用。由于胰岛素样生长因子-I（IGF-I）抑制半胱天冬酶激活，因此IGF-I有可能通过抑制中性粒细胞激活来减轻胃黏膜损伤。在本研究中，我们在遭受水浸束缚应激（WIR）的小鼠中检验了这种可能性。
在对小鼠施加WIR之前，腹腔注射IGF-I或赋形剂。测定遭受WIR的小鼠的胃黏膜损伤、胃髓过氧化物酶（MPO）活性、MPO的免疫荧光强度、半胱天冬酶-3活性、凋亡细胞数量、EMAP-II表达以及胃黏膜中Akt和糖原合酶激酶-3β（GSK-3β）的激活情况。通过给予甲氨蝶呤（MTX）诱导中性粒细胞减少。
给予高于200μg/kg剂量的IGF-I可显著减轻胃黏膜损伤，并在WIR 8小时后抑制胃MPO活性的增加。给予MTX也可减轻胃黏膜损伤，并抑制胃黏膜MPO活性和循环中性粒细胞数量的增加。IGF-I（500μg/kg）抑制了在胃黏膜中观察到的胃MPO活性和MPO免疫荧光强度的增加，但对WIR 8小时后循环中性粒细胞数量的增加没有影响。它还显著减弱了WIR诱导的8小时后胃黏膜中半胱天冬酶-3活性和凋亡细胞数量的增加。WIR开始后8小时，胃中EMAP-II的表达显著增加，而给予IGF-I可抑制这种增加。给予IGF-I增强了WIR诱导的胃黏膜中Akt和GSK-3β的磷酸化。
这些观察结果表明，IGF-I通过抑制半胱天冬酶-3介导的EMAP-II激活来抑制中性粒细胞在胃中的积聚，从而减轻应激诱导的胃黏膜损伤。此外，IGF-I可能通过Akt/GSK-3β信号传导抑制半胱天冬酶-3激活。
