Moran G W, O'Neill C, Padfield P, McLaughlin J T
Inflammation Sciences Research Group, Manchester Academic Health Science Centre, University of Manchester, Manchester, M13 9PL, UK.
Regul Pept. 2012 Aug 20;177(1-3):40-5. doi: 10.1016/j.regpep.2012.04.006. Epub 2012 May 2.
Dipeptidyl peptidase 4 (DP4) is a serine protease that preferentially cleaves N-terminal dipeptides from polypeptides containing proline or alanine as the penultimate amino acid. DP4 inactivates glucagon like peptide-2 (GLP-2), a trophic peptide with cytoprotective and reparative properties in the injured gut; therefore DP4 potentially inhibits repair processes. DP4 also modulates the activity of GLP-1 and polypeptide YY (PYY) which regulate appetite and motility. No data are yet available on the tissue and plasma expression of DP4 in inflammatory bowel disease (IBD).
Tissue and plasma were studied from active CD and healthy controls for DP4 quantification. Experiments were also carried out in a reductionist Caco-2 cell line model of intestinal inflammation with TNFα incubation. DP4 expression was studied by tissue Western blotting and plasma enzymelinked immunosorbent assay (ELISA), in addition to quantitative polymerase chain reaction (qPCR).
There was a ~2.7-fold decrease in DP4 protein in CD tissue (p=0.05). Plasma DP4 in CD was also significantly lower than the control group. A negative correlation between plasma DP4 levels and inflammatory activity as measured by C-reactive protein was observed. In Caco-2 cells an ~18-fold increase (p<0.0001) in DP4 protein expression was seen after incubation with TNFα at a concentration of 25 ng/μl for 48 hours paralleled by a 2-fold increase in DP4 mRNA.
DP4 is reduced in tissue and plasma in active Crohn's disease. This is unlikely to represent simple downregulation induced by inflammation since the key proinflammatory cytokine strongly upregulated DP4 expression in Caco-2 cells. Clearly a more complex situation exists in vivo. We propose that reduced DP4 activity limits the cleavage of regulatory peptides, for example potentiating the trophic signal from GLP-2. Pharmacological DP4 inhibition may present an additional therapeutic target in IBD.
二肽基肽酶4（DP4）是一种丝氨酸蛋白酶，它优先从以脯氨酸或丙氨酸作为倒数第二个氨基酸的多肽中切割N端二肽。DP4可使胰高血糖素样肽-2（GLP-2）失活，GLP-2是一种在受损肠道中具有细胞保护和修复特性的营养肽；因此，DP4可能会抑制修复过程。DP4还可调节食欲和运动的GLP-1和多肽YY（PYY）的活性。关于炎症性肠病（IBD）中DP4的组织和血浆表达尚无数据。
对活动期克罗恩病（CD）患者及健康对照者的组织和血浆进行研究，以定量DP4。还在采用肿瘤坏死因子α（TNFα）孵育的简化肠炎症Caco-2细胞系模型中开展实验。除定量聚合酶链反应（qPCR）外，还通过组织蛋白质免疫印迹法和血浆酶联免疫吸附测定（ELISA）研究DP4表达。
CD组织中DP4蛋白下降约2.7倍（p=0.05）。CD患者的血浆DP4也显著低于对照组。观察到血浆DP4水平与通过C反应蛋白测定的炎症活性之间呈负相关。在Caco-2细胞中，用浓度为25 ng/μl的TNFα孵育48小时后，DP4蛋白表达增加约18倍（p<0.0001），同时DP4 mRNA增加2倍。
活动期克罗恩病患者的组织和血浆中DP4减少。这不太可能代表炎症诱导的简单下调，因为关键促炎细胞因子在Caco-2细胞中强烈上调了DP4表达。显然，体内存在更复杂的情况。我们认为，DP4活性降低限制了调节肽的切割，例如增强了来自GLP-2的营养信号。DP4的药理学抑制可能是IBD中的一个额外治疗靶点。
