Elucidating the mechanism of Hit-and-Run carcinogenesis by H. pylori CagA through a CagA-inducible mice model

本研究建立了一种新的幽门螺杆菌CagA诱导小鼠模型Gt(ROSA)26Sor(CAG-LSL-cagA) （CAG-LSL-cagA）。通过这种体内模型，我们证明了由于Shp2的异常激活，CagA的急性普遍表达可诱导小鼠胚胎致死。在成年小鼠中，CagA的急性普遍表达破坏了胃上皮，导致粘膜颈细胞和壁细胞的损失，分别急剧减少粘蛋白和酸的分泌。在胃上皮中观察到DNA损伤（p-γ - h2ax）以caga依赖的方式，通过诱导DNA损伤诱导的p21在干细胞群体中积累来扰乱胃的翻转。CagA的胃特异性表达延长导致胃增生和腺癌的发展，其中p53在肿瘤区域的表达减弱。随后对离体小鼠胃类器官模型的分析表明，尽管急性CagA表达会抑制类器官的维持，但敲低p53可使胃类器官免受CagA诱导的生长抑制。利用体内和离体系统，作者证明了CagA诱导胃上皮细胞（包括干细胞群）的DNA损伤，导致突变和p53等关键肿瘤抑制因子的突变积累，这是CagA诱导胃癌发生的重要早期步骤。总的来说，本研究利用了多种实验程序和设计，在caga依赖性致癌作用方面取得了非凡的进展，这比本研究开始时预期的要多。

In the study, a new inducible mouse model of H. pylori CagA, Gt(ROSA)26Sor(CAG-LSL-cagA) (CAG-LSL-cagA), was established. Using this in vivo model, we demonstrated that acute ubiquitous expression of CagA induces embryonic lethality in mice due to aberrant activation of Shp2.In adult mice, acute ubiquitous expression of CagA disrupted the gastric epithelium, resulting in the loss of mucous neck cells and parietal cells, drastically reducing mucin and acid secretion, respectively. DNA damage (p-γH2AX) was observed in the gastric epithelium in a CagA-dependent manner which perturbed gastric turnover by eliciting DNA damage-induced p21 accumulation in stem cell populations. Prolonged gastric-specific expression of CagA resulted in the development of gastric hyperplasia and adenocarcinoma, where p53 expression was attenuated in the tumor regions.Subsequent analysis using ex vivo mice gastric organoid models demonstrated that while acute CagA expression inhibits organoid maintenance, knockdown of p53 rescues gastric organoids from CagA-induced growth inhibition.Using both in vivo and ex vivo systems, the author demonstrated that CagA induces DNA damage to the gastric epithelium, including the stem cell population, resulting in accumulation of mutations and mutations of key tumor suppressors such as p53, an essential early step in CagA-induced gastric carcinogenesis.Overall, this study utilized a variety of experimental procedures and design which resulted in exceptional progress in CagA-dependent carcinogenesis, which was more than expected at the start of this study.