Daniel Seeler (1,2), Nastasja Grdseloff (1), Claudia Jasmin Rödel (1), Karthik Subramanian Chandrasekaran (1), Charlotte Kloft (3), Salim Abdelilah-Seyfried (1), Wilhelm Huisinga (1,4)
(1) Institute of Biochemistry and Biology, University of Potsdam, Germany, (2) Graduate Research Training Program PharMetrX: Pharmacometrics & Computational Disease Modelling, Berlin/Potsdam, Germany, (3) Institute of Pharmacy, Freie Universität Berlin, Germany, (4) Institute of Mathematics, University of Potsdam, Germany
Objectives: Endothelial cells (ECs) line the interior surface of blood vessels. They are exposed to fluid shear stress (FSS), a force tangential to blood flow direction. In response to high FSS, ECs elongate and align in direction of flow. As a result of these morphological changes, vessel diameter and, subsequently, blood flow dynamics change [1]. In prior work, we developed a geometrical model linking EC shape and the geometry of the dorsal aorta in zebrafish embryos. This allowed us to quantitatively characterize changes of EC morphology during blood vessel development. Here, we aim to develop a systems biology model to investigate the crosstalk between two blood flow-responsive signaling pathways: cerebral cavernous malformation (CCM) and nitric oxide (NO) signaling. The endpoint of our investigation is EC morphology.
Methods: We performed an extensive literature query to identify molecular components of the CCM and NO signaling pathways involved in EC flow sensing and EC shape changes. Then, we investigated which types of mathematical single-cell models and modeling frameworks had previously been applied to (1) simulate the response of ECs or smooth muscle cells to blood flow, or (2) couple intracellular signaling processes with cell morphology.
Results: We found that the junctional complex consisting of PECAM-1, VEGFR2/3 and VE-cadherin can activate PI3K/AKT signaling in response to blood flow [2]. Furthermore, this complex requires the presence of CCM proteins for physiological vascular development [2]. PI3K/AKT signaling results in activation of Rho GTPases and induces the transcriptional factor KLF2 [3]. Elevated levels of KLF2 then increase the availability of the vasodilator NO [3].
Previously, the production of NO in response to FSS had been studied quantitatively using an ODE formulation [4]. Here, PI3K/AKT signaling, calcium influx via PLC and KLF2 drive the expression of eNOS and the production of NO. A qualitative ODE model had been applied to investigate the arterial response to fluid shear stress, transmural pressure, and the vasoconstrictor angiotensin II [5]. This model incorporates PI3K/AKT signaling, Rho GTPases and cellular contractility via actomyosin activity. Here, the authors focused mostly on processes in smooth muscle cells and fibroblasts. Lastly, the coupling of the biophysics of cell stretching and contraction with intracellular Rho signaling was investigated using a system of ODEs [6]. From these models we aim to integrate (1) the NO response to FSS in ECs, (2) the FSS-mediated activation of Rho GTPases in ECs, and (3) the coupling of Rho GTPases to EC morphology. Additionally, we aim to incorporate CCM signaling in ECs, and link EC shape determined by Rho GTPases to upstream signaling.
The available molecular interaction data on CCM signaling is mostly qualitative, stemming, e.g., from immunoblotting experiments. Consequently, a Boolean signaling network seemed most appropriate. This allows for integration of data from various sources without the necessity for quantitative data. We can use the strength and type of blood flow (laminar or pulsatile) and EC genotype as inputs. EC shape has been previously linked in a static Boolean description to the activity of Rho GTPases in cortical and adhesion compartments of the cell [7]. Hence, this allows for linking of CCM and NO signaling to EC shape via Rho GTPases that are activated in response to blood flow.
The processes occurring during blood flow sensing and vascular remodeling occur on varying time scales, ranging from below seconds for immediate signaling events to days for transcriptional changes [8]. To appropriately describe these processes, we employed asynchronous updating in the Boolean model and focused on physiologically plausible trajectories from the full state transition graph. To simplify identification of these trajectories, we shrank the full state transition graph by employing priority queues [9]. In the resulting trajectories, species that change their activities on a faster time scale are updated more frequently.
Conclusions: When detailed quantitative molecular interaction data is lacking, Boolean models provide a promising approach to include qualitative data in the modeling process. The conceptually simple Boolean formalism facilitates communication between modelers and experimental biologists during model building and when discussing results.
References:
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[3] Baratchi, S.; Khoshmanesh, K.; Woodman, O. L.; Potocnik, S.; Peter, K.; McIntyre, P., Molecular Sensors of Blood Flow in Endothelial Cells., Trends in Molecular Medicine, 2017, Vol. 23, 850-868
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[5] Irons, L.; Humphrey, J. D., Cell signaling model for arterial mechanobiology., PLoS Computational Biology, 2020, Vol. 16, e1008161
[6] Zmurchok, C.; Bhaskar, D.; Edelstein-Keshet, L., Coupling mechanical tension and GTPase signaling to generate cell and tissue dynamics., Physical Biology, 2018, Vol. 15, 046004
[7] Sailem, H.; Bousgouni, V.; Cooper, S.; Bakal, C., Cross-talk between Rho and Rac GTPases drives deterministic exploration of cellular shape space and morphological heterogeneity., Open Biology, 2014, Vol. 4, 130132
[8] Tanaka, K.; Joshi, D.; Timalsina, S.; Schwartz, M. A., Early events in endothelial flow sensing., Cytoskeleton (Hoboken, N.J.), 2021, Vol. 78, 217-231
[9] Fauré, A.; Naldi, A.; Chaouiya, C.; Thieffry, D., Dynamical analysis of a generic Boolean model for the control of the mammalian cell cycle., Bioinformatics (Oxford, England), 2006, Vol. 22, e124-e131
Reference: PAGE 30 (2022) Abstr 10179 [www.page-meeting.org/?abstract=10179]
Poster: Drug/Disease Modelling - Other Topics