Project 10: Impact of recently identified angiotensin peptides and their cofactors on vascular hemodynamics in acute kidney injury patients
Tubular dysfunction is essential in AKI. Damage may occur, in part, due to reduced local blood flow caused by altered composition of vasoregulatory mediators and altered regulation of the underlying systems. Vice versa, injury to the tubules can release vasoregulatory mediators, causing a vicious circle of reduced oxygen supply. Therefore, acute tubular damage may be a consequence and a cause of reduced GFR and hypoxia. Little is known regarding mediators of intrarenal vasoconstriction induced by acute tubular injury. We hypothesize that the renin–angiotensin system (RAS) and especially the underlying angiotensin peptides play a central role. Besides angiotensin II (Ang II), further angiotensin peptides such as Ang 1-7, Ang III, Ang IV, Angioprotectin, Angiotensin-A (Ang-A) and Alamandine also contribute to altered renal hemodynamics, and may elicit additional, different or even opposite effects to Ang II. Mass-spectrometric techniques may identify yet unknown angiotensin peptides affecting intrarenal hemodynamics. Thus, the aim of the project is the physiological and pathophysiological characterisation of these peptides and cofactors on intrarenal hemodynamics in the context of AKI. Further aims are identification pathways for synthesis of these angiotensin peptides and of still unknown angiotensin peptides and cofactors in the secretome of renal tubular cells. To target these aims, we will quantify the concentration of these peptides in plasma from AKI patients and in samples from different bioassays of Projects 2, 8 and 11. Moreover, we set out to analyse the effect of the recently identified angiotensin peptides in different bioassays, isolated the enzymes synthesizing the angiotensin peptides from angiotensin II, and we will stimulate cultured tubular cells pharmacologically. Chromatographic fractions of the tubular cell secretome will be screened for vasoregulatory angiotensin peptides and cofactors by bioassays. Fractions with effects on intrarenal hemodynamics will be further fractionated to homogeneity, and the underlying mediators will be analyzed by MALDI-FTOrbitrap-and ESI-trap-mass-spectrometric methods.