A Boolean view separates platelet activatory and inhibitory signalling as verified by phosphorylation monitoring including threshold behaviour and integrin modulation

Abstract

Platelets are critical for haemostasis and blood clotting. However, since under normal circumstances blood should flow without clotting, its function is regulated via a complex interplay of activating and inhibiting signal transduction pathways. Understanding this network is crucial for treatment of cardiovascular and bleeding diseases. Detailed protein interaction and phosphorylation data are explored to establish a simplified Boolean model of the central platelet cascades. We implemented the model by means of CellNetAnalyzer and showed how different signalling events coalesce into a fully activated system state. Furthermore, we examined the networks' inherent threshold behaviour using the semi-quantitative modelling software SQUAD. Finally, predictions are verified monitoring phosphorylations which mark different activation phases as modelled. The model can also be applied to simulate different pharmacological conditions as they modify node activity (aspirin, clopidogrel, milrinon, iloprost, combination) and is available for further studies. It agrees well with observations. Activatory pathways are diversified to cope with complex environmental conditions. Platelet activation needs several activation steps to integrate over different network subsets, as they are formed by the interplay of activating kinases, calcium mobilization, and the inhibiting cAMP-PKA system. System stability analysis shows two phases: a sub-threshold behaviour, characterized by integration over different activatory and inhibitory conditions, and a beyond threshold phase, represented by competition and shutting down of counter-regulatory pathways. The integrin network and Akt-protein are critical for stable effector response. Dynamic threshold-analysis reveals a dependency of the relative activating input strength necessary to irreversibly engage the system from the absolute inhibitory signal strength.

What Can Proteomics Tell Us About Platelets?

“…[178][179][180] The vast amount of data that comes from quantitative proteomics studies, however, will require a thorough evaluation using systems biology approaches not only for obtaining a systematic interpretation of signaling networks and nodes but also for the simulation of experiments and conditions that cannot be realized in vivo or in vitro. [181][182][183][184][185][186] This will lead to the description of (phospho)protein clusters that are characteristic for the various levels of inhibitory and activation pathways or that represent molecular signatures for those pathways, which are known to be affected in disease. We expect that recent strategies to analyze protein complexes using quantitative MS will further improve our understanding of such molecular clusters.…”

Psoralen and Ultraviolet A Light Treatment Directly Affects Phosphatidylinositol 3-Kinase Signal Transduction by Altering Plasma Membrane Packing

“…The exact cellular composition of PUVA-treated tissue by type and number as well as their individual susceptibility to PUVA will eventually determine the response in a relevant physiological environment. Further study will thus require a systems approach (43) to unravel the dependence of relevant ligand-receptor couples to PUVA and combine the findings in an integrated view, ideally also taking into account effects on DNA replication and transcription where possible.…”

Comparison of the central human and mouse platelet signaling cascade by systems biological analysis

“…platelet aggregation [10][11][12]. Thereby, data sets of several knock-out and knock-in mouse models [13][14][15] have been useful to validate data.…”

“…The platelet protein and molecule interaction network involved in response to those exogenous factors is de ned by systems biological pathway analysis as the central regulating signaling cascade of platelets (CC). The networks are composed of activatory and inhibitory up-and downstream pathways, involves major platelet proteins and mediates a ne-tuned balance of equilibrated blood ow [11]. The mapping of the CC is highly instructive for a better understanding of how platelet pathways are regulated in pathophysiological conditions.…”

“…However, the many differences between the model genome and transcriptome and the human counter-part are rarely taken into account by the research groups studying the speci cs of such a cascade [4][5][6][7][8][9]. Moreover, a global approach for our example, the platelet signaling cascade [10][11][12], was never attempted and was also not possible as critical data-sets for such a comparison were hard to come by. We can only provide an eagle´s perspective as testing each difference found by our systematic systems biological comparison in detail would be a new, time-demanding individual experimental study.…”