Analysis of the Angiopoietin/Tie2 signaling cascade with regard to vascular permeability and inflammation as well as study of the acute regulation of Tie2 expression in experimental sepsis

点击翻译按钮获取中文摘要

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. It is not the infection per se but rather the overwhelming response that leads to multiple organ failure and death. The endothelium pervades every organ and all its physiological processes can be affected in sepsis, thus systemic vascular changes have severe consequences for organ function. Ligands of the endothelial tyrosine kinase receptor Tie2 are markedly imbalanced in severe infections associated with vascular leakage, yet regulation of the receptor itself has been understudied in this context. We have observed that Tie2 expression dramatically drops within a few hours affecting down-stream signaling and vascular barrier function. Moreover, experimental suppression is sufficient to mimic the septic vascular phenotype. We hypothesize that Tie2 is a critical determinant of the hosts vascular response to sepsis and we will focus on 2 major aspects of its regulation: 1) The search for a common denominator of Tie2 suppression in various critical illnesses (hemorrhagic shock, sepsis, influenza, anthrax, etc.) led to the realization that all these conditions share a rather simple clinical symptom, i.e. hemodynamic shock and microvascular hypoperfusion. Translating this to the bench, we found that Tie2 transcription was highly depended on flow. Here, we will analyze the link between the flow-responsive GATA3 transcription factor and Tie2 expression upon flow in vitro and in vivo. Conditional endothelial specific knockouts and transgenics will be generated. 2) Tie2 expression is also affected by posttranslational modifications. We have observed extensive Tie2 shedding cross-species in an MMP14-dependent fashion. Besides pharmacological inhibition of MMP14 in murine experimental sepsis, we plan to identify the extracellular Tie2 cleavage site by mass spectrometry followed by experimental mutation and further functional analysis. If Tie2 shedding is indeed injurious or adaptive will be evaluated in a mouse model of overexpressed soluble (s)Tie2.