Module-based multiscale simulation of angiogenesis in skeletal muscle

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Abstract

Background: Mathematical modeling of angiogenesis has been gaining momentum as a means to shed new light on the biological complexity underlying blood vessel growth. A variety of computational models have been developed, each focusing on different aspects of the angiogenesis process and occurring at different biological scales, ranging from the molecular to the tissue levels. Integration of models at different scales is a challenging and currently unsolved problem. Results: We present an object-oriented module-based computational integration strategy to build a multiscale model of angiogenesis that links currently available models. As an example case, we use this approach to integrate modules representing microvascular blood flow, oxygen transport, vascular endothelial growth factor transport and endothelial cell behavior (sensing, migration and proliferation). Modeling methodologies in these modules include algebraic equations, partial differential equations and agent-based models with complex logical rules. We apply this integrated model to simulate exercise-induced angiogenesis in skeletal muscle. The simulation results compare capillary growth patterns between different exercise conditions for a single bout of exercise. Results demonstrate how the computational infrastructure can effectively integrate multiple modules by coordinating their connectivity and data exchange. Model parameterization offers simulation flexibility and a platform for performing sensitivity analysis. Conclusions: This systems biology strategy can be applied to larger scale integration of computational models of angiogenesis in skeletal muscle, or other complex processes in other tissues under physiological and pathological conditions. © 2011 Liu et al; licensee BioMed Central Ltd.

Figures

  • Figure 1 Schematics of Module-based Mulitscale Angiogenesis Modeling Methodology. A) Skeletal muscle angiogenesis is modeled as a multi-step process. It starts with a blood flow simulation followed by a simulation of oxygen convection-transport process. Using O2 tissue distribution, VEGF secretion by myocytes is computed as a function of oxygen-dependent transcription factors HIF1a and PGC1a; then a VEGF reaction-transport process is computed. Lastly, capillary formation is simulated based on VEGF concentration and gradients. Feedback loops increase the complexity of the model since a new geometry with nascent vessels will affect blood flow conditions, tissue hypoxia, and VEGF secretion and distributions. All four processes are simulated using a variety of modeling techniques and languages. We use Java as the language for modeling the controller, and apply JNI plugins to link these modules together. The controller is composed of four sub-packages, including Process, Biosystems, IO and Exceptions. B) Communications between different modules and Java codes in core package are implemented by transferring each module into a shared object library (SO file in Linux). Upper panel shows that two wrapper files (includes Java-to-C and C-to-Fortran wrapper) are written to communicate between the flow Java class defined in the controller and the Fortran flow module, to call the flow module in Fortran. Lower panel shows that a JNI C wrapper is required to transfer the data between the modeling controller (in Java) and the Oxygen/VEGF module (in C/C++).
  • Figure 2 Object-oriented design for the angiogenesis modeling package. Major classes across tissue and cell scales in the modeling controller are shown. They include SkeletalMuscle, Myofiber, Vessel, Grid, Segment and Node classes in the Biosystems subpackage, and BloodFlow, O2Diffusion, VEGFRxnDiffusion, CellSprouting, and StartAngio classes in the Process subpackage. The hierarchical structure of relationships between the classes is represented by arrows.
  • Table 1 Parameters of the multiscale model*
  • Figure 3 3D simulation of blood flow, oxygen, and VEGF distribution during the single-bout exercise: A) 2D cross section of skeletal muscle: gray circles represent fibers and red circles represent capillaries; B) Blood flow velocity distribution in skeletal muscle microvascular network; C) Oxygen distribution throughout the tissue; D) VEGF secretion level along the muscle fibers; E) total VEGFR-bound VEGF distribution (including both 120 and 164 isoforms) on vascular surface; and F) free VEGF concentration distribution in interstitial space.
  • Figure 4 3D simulation of capillary network growth during the single-bout exercise. A) Time course of capillary growth was simulated based on the timeline scheme for exercise-induced angiogenesis. The simulation leads to new capillary network at: B) 1 h post-exercise; C) 3 h; D) 5 h; E) 7 h; F) 8 h. When new capillary segments grow out of boundaries (Arrow 1), capillary will grow from corresponding periodic boundaries (Arrow 2). Arrows 3-5 refer to the capillary anastomoses during growth. Vessels colored in red represent the pre-existing microvascular vessels, ones in light blue are the newly-developed blind-ended capillaries, and ones in dark blue are new capillary anastomoses. G) Relative capillary length change vs time.
  • Figure 5 Sensitivity of the capillary length and the number of anastomoses formed with respect to VEGF threshold for EC activation. A) Relative capillary length as a function of time and VEGF threshold; B) Number of anastomoses formed as a function of VEGF threshold at 4 h and 8 h. Simulation sample size is five for each VEGF threshold at a given time.
  • Figure 6 Angiogenesis pattern during different exercise conditions at 8 h post-exercise. A) Oxygen consumption at 9-fold the basal level under hypoxic hypoxia conditions (SO2A = 0.3); B) Oxygen consumption at 9-fold the basal level under normoxic conditions (SO2A = 0.6).

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CITATION STYLE

APA

Liu, G., Qutub, A. A., Vempati, P., Mac Gabhann, F., & Popel, A. S. (2011). Module-based multiscale simulation of angiogenesis in skeletal muscle. Theoretical Biology and Medical Modelling, 8(1). https://doi.org/10.1186/1742-4682-8-6

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