The p38 mitogen-activated protein kinases (MAPKs) are essential cytoplasmic signal molecules of innate immune pathways that play a vital role in host immune defense responses to pathogenic challenges. In this study, two fish p38 genes (Cip38α and Cip38β) were characterized for the first time from the grass carp Ctenopharyngodon idella. Similar to other reported p38MAPKs, both Cip38α and Cip38β contained a conserved phosphorylation motif (Thr-Gly-Tyr, TGY) and a substrate binding site (Ala-Thr-Arg-Trp, ATRW) in the serine/threonine protein kinase (S_TKc) domain. Expression profile analysis showed that Cip38α and Cip38β mRNAs were broadly expressed in all of the examined tissues and developmental stages of C. idella. In addition, in vivo injection experiments directly revealed that Cip38α and Cip38β showed strong responsiveness to Aeromonas hydrophila and muramyl dipeptide (MDP) challenges, and their expression levels were significantly upregulated in the intestine of grass carp. Additionally, the MDP-induced expression levels of intestinal inflammatory cytokines (TNF-α and IL-15) and an antimicrobial peptide (β-defensin) were significantly inhibited by the p38MAPK-specific inhibitor SB203580. Moreover, the nutritional dipeptide carnosine and Ala-Gln were found to significantly suppress the bacterial MDP-induced expression of p38MAPK pathway genes and inflammatory cytokines in the intestine of grass carp. Finally, overexpression analysis demonstrated that Cip38α and Cip38β could act as efficient activators in the regulation of AP-1 signaling pathways through interaction with CiMKK6. Altogether, this study provided experimental evidence of the presence of a functional p38 pathway in grass carp, which revealed its involvement in the intestinal immune response to bacterial challenges in bony fish.

中文翻译：

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p38丝裂原激活的蛋白激酶（MAPKs）参与了对肠ten虫细菌性乙二胺二肽攻击的肠道免疫反应。

p38丝裂原激活的蛋白激酶（MAPK）是先天性免疫途径的重要细胞质信号分子，在宿主对病原体的免疫防御反应中起着至关重要的作用。在这项研究中，首次从草鱼Ctenopharyngodon idella中鉴定了两个鱼p38基因（Cip38α和Cip38β）。与其他报道的p38MAPK相似，Cip38α和Cip38β在丝氨酸/苏氨酸蛋白激酶（S_TKc）中均包含一个保守的磷酸化基序（Thr-Gly-Tyr，TGY）和一个底物结合位点（Ala-Thr-Arg-Trp，ATRW）。领域。表达谱分析表明，Cip38α和Cip38βmRNA在C.idella的所有检查组织和发育阶段均广泛表达。此外，体内注射实验直接表明，Cip38α和Cip38β对嗜水气单胞菌和对戊二酰二肽（MDP）攻击表现出强响应性，并且它们在草鱼肠中的表达水平显着上调。此外，p38MAPK特异性抑制剂SB203580显着抑制了MDP诱导的肠炎性细胞因子（TNF-α和IL-15）和抗菌肽（β-防御素）的表达水平。此外，发现营养性二肽肌肽和Ala-Gln可以显着抑制细菌MDP诱导的草鱼肠中p38MAPK途径基因和炎症细胞因子的表达。最后，过度表达分析表明，Cip38α和Cip38β通过与CiMKK6的相互作用可以有效地激活AP-1信号通路。总而言之，这项研究提供了草鱼中存在功能性p38途径的实验证据，表明该途径参与了对骨鱼细菌攻击的肠道免疫应答。