Abstract 391: Modeling of the Angiotensin Peptide Processing Network
New insights into the intrarenal renin-angiotensin system (RAS) have modified the traditional view of the system. Nonetheless, the complexity of this network of angiotensin (Ang) peptides and peptidases is not completely understood. We hypothesized that a computational systems biology approach, applied to peptidomic data, could elucidate the network of enzymatic conversions and the resulting net stimulatory signal. To that effect, we built and refined a Bayesian network model and a dynamic systems model of the Ang peptide fragmentation utilizing a database of MALDI-TOF mass spectra from experiments conducted in mouse podocytes exposed to exogenous Ang substrates, augmented by new experiments guided by findings from the archive. A model-building process suggested novel steps, three of which were confirmed in vitro. When 1 μM Ang 2-10 was added to cell media, 102 ± 17 nM Ang 2-7 was detected at 4 hours, decreasing to 30 ± 12 nM in the presence of a neprilysin (NEP) inhibitor, supporting the model-predicted cleavage of Ang 2-10 by NEP. In addition, using Ang 1-9 as substrate, we observed Ang 2-9 production (15.3 ± 3% total Ang ion current at 2 hours) that decreased to 4.6 ± 0.5% during co-treatment with an aminopeptidase A (APA) inhibitor, supporting the model-predicted cleavage of Ang 1-9 by APA. Similarly, incubation of Ang 1-7 showed evidence of Ang 2-7 (28.1 ± 2.2% total Ang ion current at 2 hours) with undetectable amounts in cell-free controls. These data concur with the well-recognized robust degrading capacity of NEP and APA localized in glomerular podocytes. The performance of our model improved after inclusion of the newly discovered steps by Deviance Information Criterion. Although the products from these novel reactions are not known to be bioactive, the cleavages shunt Ang substrates away from formation of known bioactive peptides. In conclusion, our results demonstrate that systems biology methods are effective in identifying novel steps in the Ang peptide processing network, expanding our understanding of the RAS. Besides, the study illustrates the potential for mining archives of peptidomic data. Further exploration of the Ang network using this strategy will likely improve the study of the intricacies of the RAS, with potential clinical impact.
- © 2012 by American Heart Association, Inc.