Bussière Françoise I, Chaturvedi Rupesh, Cheng Yulan, Gobert Alain P, Asim Mohammad, Blumberg Darren R, Xu Hangxiu, Kim Preston Y, Hacker Amy, Casero Robert A, Wilson Keith T
Department of Medicine, Division of Gastroenterology, and Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, USA.
J Biol Chem. 2005 Jan 28;280(4):2409-12. doi: 10.1074/jbc.C400498200. Epub 2004 Nov 17.
Helicobacter pylori infection of the stomach elicits a vigorous but ineffective host immune and inflammatory response, resulting in persistence of the bacterium for the life of the host. We have reported that in macrophages, H. pylori up-regulates inducible NO synthase (iNOS) and antimicrobial NO production, but in parallel there is induction of arginase II, generating ornithine, and of ornithine decarboxylase (ODC), generating polyamines. Spermine, in particular, has been shown to restrain immune response in activated macrophages by inhibiting proinflammatory gene expression. We hypothesized that spermine could prevent the antimicrobial effects of NO by inhibiting iNOS in macrophages activated by H. pylori. Spermine did not affect the up-regulation of iNOS mRNA levels but in a concentration-dependent manner significantly attenuated iNOS protein levels and NO production. Reduction in iNOS protein was due to inhibition of iNOS translation and not due to iNOS degradation. ODC knockdown with small interfering (si) RNA resulted in increased H. pylori-stimulated iNOS protein expression and NO production without altering iNOS mRNA levels. When macrophages were cocultured with H. pylori, killing of bacteria was enhanced by transfection of ODC siRNA and prevented by addition of spermine. These results identify a mechanism of immune dysregulation induced by H. pylori in which stimulated spermine synthesis by the arginase-ODC pathway inhibits iNOS translation and NO production, leading to persistence of the bacterium and risk for peptic ulcer disease and gastric cancer.
胃部幽门螺杆菌感染会引发强烈但无效的宿主免疫和炎症反应，导致该细菌在宿主生命周期内持续存在。我们曾报道，在巨噬细胞中，幽门螺杆菌会上调诱导型一氧化氮合酶（iNOS）并产生抗菌性一氧化氮（NO），但与此同时会诱导精氨酸酶II生成鸟氨酸，以及诱导鸟氨酸脱羧酶（ODC）生成多胺。尤其是精胺，已被证明可通过抑制促炎基因表达来抑制活化巨噬细胞中的免疫反应。我们推测精胺可能通过抑制幽门螺杆菌激活的巨噬细胞中的iNOS来阻止NO的抗菌作用。精胺并不影响iNOS mRNA水平的上调，但以浓度依赖的方式显著降低iNOS蛋白水平和NO的产生。iNOS蛋白的减少是由于iNOS翻译受到抑制，而非iNOS降解所致。用小干扰（si）RNA敲低ODC会导致幽门螺杆菌刺激的iNOS蛋白表达增加和NO产生增加，而不会改变iNOS mRNA水平。当巨噬细胞与幽门螺杆菌共培养时，转染ODC siRNA可增强细菌的杀伤作用，而添加精胺则可阻止这种作用。这些结果确定了幽门螺杆菌诱导免疫失调的一种机制，即精氨酸酶-ODC途径刺激精胺合成，抑制iNOS翻译和NO产生，导致细菌持续存在以及患消化性溃疡疾病和胃癌的风险。
