Protective role of Thioredoxin-1 and its interaction partners in cardiovascular disorders

Sepsis is an overwhelming inflammatory syndrome as a dysregulated response to an infection, which in turn results in life threatening organ dysfunction and eventually in septic shock. The basis for the pathophysiological responses in sepsis is multifactorial. However, it is undisputed that loss of endothelial integrity is a mainstay of septic shock. Hence therapies, which could preserve endothelial integrity or prevent endothelial apoptosis would be of tremendous value for patients and would address a huge unmet medical need. We recently demonstrated the anti-apoptotic properties of the Apurinic/Apyrimidinic Endodeoxyribonuclease 1 (APEX1) in the endothelium. By interacting with the lysosomal protease Cathepsin D, APEX1 reduces the processing of pre-pro Cathepsin D and thus, the activity of the protease, which in turn leads to an increase in the levels of Thioredoxin-1, one of the major anti-oxidative and anti-apoptotic molecules in the endothelium. To develop pharmacological lead compounds for supportive therapies for sepsis it is necessary to narrow down the interaction surface within Cathepsin D. For this purpose we will map the APEX1 interaction domain in Cathepsin D. Furthermore, we found that the first twenty amino acids within APEX1 - (APEX1 (1-20)) - are required and sufficient for its anti-apoptotic effect in endothelial cells. We will further narrow down the relevant amino acids in the APEX1 N-terminus by generating small peptides and test them for their ability to inhibit LPS-induced endothelial cell apoptosis with the aim to translate them into prototype structures for the generation of small molecules as potential therapeutics.

Moreover, it is unknown, which cellular signaling networks in endothelial cells are affected in sepsis, if they are altered by (APEX1 (1-20)) and which other responses are evoked by the APEX1 peptide. To this end, we will perform RNA deep sequencing of human endothelial cells expressing (APEX1 (1-20)) in the presence and absence of LPS in collaboration with Prof. Heiner Schaal, Institute of Virology. Pathway analyses will give us deeper insights into the changes in endothelial cells induced by LPS, how they are affected by (APEX1 (1-20)) and potential side effects of the peptide. In addition, this investigation might reveal further druggable targets for supportive sepsis therapy.