Acid-base homeostasis orchestrated by NHE1 defines the pancreatic stellate cell phenotype in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) progresses in an organ with a unique pH landscape, where the stroma acidifies after each meal. We hypothesized that disrupting this pH landscape during PDAC progression triggers pancreatic stellate cells (PSCs) and cancer-associated fibroblasts (CAFs) to induce PDAC fibrosis. We revealed that alkaline environmental pH is sufficient to induce PSC differentiation to a myofibroblastic phenotype. We then mechanistically dissected this finding focusing on the involvement of the Na+/H+ exchanger NHE1. Perturbing cellular pH homeostasis by inhibiting NHE1 with cariporide partially alters the myofibroblastic PSC phenotype. To show the relevance of this finding in vivo, we targeted NHE1 in murine PDAC (KPfC). Indeed, tumor fibrosis decreases when mice receive the NHE1-inhibitor cariporide in addition to gemcitabine treatment. Moreover, the tumor immune infiltrate shifts from granulocyte-rich to more lymphocytic. Taken together, our study provides mechanistic evidence on how the pancreatic pH landscape shapes pancreatic cancer through tuning PSC differentiation. Comparative gene expression profiling analysis of RNA-seq data for C57BL6/J mouse-derived pancreatic stellate cells (PSCs), cultured for 120h at pH6.6 or at pH7.4. 3 biological replicates are included for each group.

胰腺导管腺癌（PDAC）发生于具有独特pH微环境的器官中，其基质会在每次进食后发生酸化。我们提出假说：在PDAC进展过程中破坏这一pH微环境，会激活胰腺星状细胞（PSCs）与癌相关成纤维细胞（CAFs），进而诱发PDAC纤维化。本研究证实，碱性环境pH足以诱导PSCs分化为肌成纤维细胞表型。随后，我们针对该发现开展机制剖析，重点围绕Na+/H+交换体NHE1的作用展开。利用卡立泊来德（cariporide）抑制NHE1以扰乱细胞pH稳态，可部分改变肌成纤维细胞样PSCs的表型。为验证该发现的体内相关性，我们在小鼠PDAC模型（KPfC）中靶向调控NHE1。实验结果显示，当小鼠在吉西他滨治疗基础上联合使用NHE1抑制剂卡立泊来德时，肿瘤纤维化程度显著降低。此外，肿瘤免疫浸润谱从以粒细胞为主转向以淋巴细胞为主。综上，本研究为胰腺pH微环境通过调控PSCs分化影响胰腺癌发生发展提供了机制层面的证据。本研究针对C57BL6/J小鼠来源的胰腺星状细胞（PSCs）的RNA测序（RNA-seq）数据开展比较基因表达谱分析，这些细胞分别在pH6.6与pH7.4的环境中培养120小时，每组包含3次生物学重复。