Research

Construction and analysis of a modular model of caspase activation in apoptosis

Heather A Harrington^1,2 , Kenneth L Ho³ , Samik Ghosh⁴ and KC Tung⁵

¹  Department of Mathematics, Imperial College London, London, SW7 2AZ, UK

²  Centre for Integrative Systems Biology at Imperial College (CISBIC), Imperial College London, London, SW7 2AZ, UK

³  Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012, USA

⁴  The Systems Biology Institute (SBI) 6-31-15 Jingumae M31 6A, Shibuya, Tokyo 150-0001, Japan

⁵  Department of Molecular Biophysics University of Texas Southwestern Medical Center, Dallas, TX 75235, USA

author email corresponding author email

Theoretical Biology and Medical Modelling 2008, 5:26doi:10.1186/1742-4682-5-26

Published:	10 December 2008

Abstract

Background

A key physiological mechanism employed by multicellular organisms is apoptosis, or programmed cell death. Apoptosis is triggered by the activation of caspases in response to both extracellular (extrinsic) and intracellular (intrinsic) signals. The extrinsic and intrinsic pathways are characterized by the formation of the death-inducing signaling complex (DISC) and the apoptosome, respectively; both the DISC and the apoptosome are oligomers with complex formation dynamics. Additionally, the extrinsic and intrinsic pathways are coupled through the mitochondrial apoptosis-induced channel via the Bcl-2 family of proteins.

Results

A model of caspase activation is constructed and analyzed. The apoptosis signaling network is simplified through modularization methodologies and equilibrium abstractions for three functional modules. The mathematical model is composed of a system of ordinary differential equations which is numerically solved. Multiple linear regression analysis investigates the role of each module and reduced models are constructed to identify key contributions of the extrinsic and intrinsic pathways in triggering apoptosis for different cell lines.

Conclusion

Through linear regression techniques, we identified the feedbacks, dissociation of complexes, and negative regulators as the key components in apoptosis. The analysis and reduced models for our model formulation reveal that the chosen cell lines predominately exhibit strong extrinsic caspase, typical of type I cell, behavior. Furthermore, under the simplified model framework, the selected cells lines exhibit different modes by which caspase activation may occur. Finally the proposed modularized model of apoptosis may generalize behavior for additional cells and tissues, specifically identifying and predicting components responsible for the transition from type I to type II cell behavior.