Advances in the study on Ang/Tie signaling pathway in diagnosis and treatment of sepsis

Abstract

Sepsis and concomitant multiorgan dysfunction are a group of common clinical syndromes, and their prevalence are increasing year by year due to the increase of the aging population. It reveals that 20 million cases of sepsis occur globally every year, with a mortality rate of 26%. Early diagnosis of sepsis facilitates the adoption of timely and targeted therapeutic strategies, which is a key element in reducing mortality. Endothelial cells (EC) are the early targets of exogenous pathogens and endogenous injury signals, and numerous studies suggest that structural changes and functional activation of EC play an important role in the development of sepsis. As an endothelial-exclusive signaling pathway, the angiopoietin (Ang)/tyrosine kinase receptor (Tie) signaling pathway plays an important role in the abnormal activation and injury of EC, and plays a central role in the regulation of dysfunctional changes in the disease process. The Ang/Tie signaling pathway mainly includes two tyrosine kinase receptors (Tie1, Tie2) located in EC and four secreted glycoprotein ligands (Ang-1, Ang-2, Ang-3, Ang-4). Ang-1 sustainably activates the Tie2 receptor, maintaining function between cells, and between cell and matrix, supporting the normal physiological functions of vascular EC. Ang-2 is an Ang-1 antagonist, competitively blocking the binding of Ang-1 to the Tie2 receptor. In a sepsis environment, the ratio of Ang-1/Ang-2 decreases （Ang-1 decreases, while Ang-2 increases). Ang-2 competitively blocks the binding of Ang-1 to Tie2 receptors, resulting in severe abnormal activation of EC. Ang-2 mediates the release of heparinase (HPSE), resulting in glycocalyx damage and an increase of vascular permeability. Ang-2 increase may promote inflammatory response. Ang/Tie signaling system dysfunction results in coagulation dysfunction, and Ang-2 elevation is a sentinel event in disseminated intravascular coagulation. In terms of disease monitoring, the sensitivity of Ang-2>5.61 ng/mL for diagnosing sepsis is 74.36%. Continuing rise of Ang-2 indicates that patients are in difficulty with restoring endothelial function and normal function in organs. Early dynamic mornitoring of Ang-2 can be used to predict sepsis related lung injury and acute kidney injury. The increase in Ang-2/Ang-1 ratio and Ang-2/soluble Tie ratio are independently correlated with the 90 d- mortality rate of sepsis patients（area under ROC curve is 0.787 and 0.704, respectively）. Decrease of Ang-2 and / or Tie-2 in levels indicates good efficay of plasma exchange in sepsis patients. Targeting the Ang/Tie signaling pathway have achieved certain success in animal experiments, but currently clinical trials have not yielded valuable results. Further in-depth research is needed on the Ang/Tie signaling pathway related to sepsis.

Keywords

• |sepsis|angiopoietins|tyrosine kinase receptor|angli/tie