AXL and MERTK receptor tyrosine kinases inhibition protects against pancreatic necrosis via selectively limiting CXCL2-related neutrophil infiltration

Background: Acute pancreatitis (AP) was initiated within pancreatic parenchymal cells and sustained by uncontrolled inflammatory responses. Axl and MERTK Receptor Tyrosine Kinases play a crucial role in negatively regulating the innate immunity. Therefore, this study aimed to investigate the role and underlying mechanism of Axl and MERTK in AP.

Methods: Experimental AP was induced by ten hourly intraperitoneal administration of caerulein in global, hematopoietic- and pancreas-specific Axl and Mertk deficient mice. Pancreatitis severity was assessed biochemically and histologically. Pancreatic transcriptomics and pancreatic infiltrating immune cells were profiled. Some mice were given R428, an antagonist of Axl and MERTK. Axl and MERTK in peripheral leukocytes were measured by flow cytometry.

Findings: The levels of Axl and MERTK in pancreatic tissue and pancreatic CD45⁺ cells were dynamically altered at 6 h and 12 h after the 1st injection of caerulein. Global and hematopoietic-specific, but not pancreas-specific deletion of Axl and Mertk protected against pancreatic necrosis and trypsinogen activation. Pancreatic transcriptomic analysis revealed that differentially expressed gene signatures were mainly related to metabolic and inflammatory pathways. Furthermore, deletion or inhibition of Axl and Mertk selectively inhibited pancreatic neutrophil infiltration, which was primarily related to CXCL2 secreted by pro-inflammatory macrophages. Increased levels of MERTK in peripheral leukocytes were correlated with more severe form of AP.

Interpretation: Our findings reveal that specific Axl/MERTK antagonist may be a novel and potential early treatment for AP and the levels of MERTK in peripheral leukocytes may be a promising biomarker for predicting pancreatic severity in patients with AP.

Funding: National Natural Science Foundation of China, Shanghai Natural Science Foundation, a Shanghai Young Talent Award and a Shanghai Young Orient Scholar Award.

Research in context: Evidence before this study Acute pancreatitis (AP) is a common inflammatory disorder of the exocrine pancreas, the severity of which was determined by the extent of pancreatic necrosis, with no targeted therapy. AP was initiated by signals within pancreatic parenchymal cells and sustained by uncontrolled innate immune responses. One of the three crucial regulatory roles for Axl and MERTK is to negatively regulate innate immune responses. Added value of this study Global and hematopoietic-, but not pancreas-specific Axl and Mertk deficiency protected against pancreatitis, primarily pancreatic necrosis. Deletion of Axl and Mertk selectively inhibited pancreatic neutrophil infiltration that was related to CXCL2 secreted by pro-inflammatory macrophages. Axl and MERTK antagonist similarly reduced pancreatitis severity via limiting CXCL2-mediated pancreatic neutrophil infiltration. Higher levels of MERTK, but not Axl in peripheral leukocytes were correlated with more severe form of acute pancreatitis. Implications of all the available evidence A specific Axl/MERTK antagonist may be a novel and potential early treatment for AP. The level of MERTK on peripheral leukocytes may be a promising biomarker for predicting disease severity in patients with AP.