(149g) Development of a Mathematical Model to Describe the Release of Monocyte Chemoattractant Protein – 1 (MCP-1) From Human Aortic Endothelial Cells and the Transport Through a Three-Dimensional Collagen Matrix

Atherosclerosis is an inflammatory disease, initiated by the accumulation of lipid substances in the subendothelial layer of major arteries, followed by adhesion and transmigration of monocytes. This adhesion and transmigration of monocytes involve several steps, mediated by bioactive molecules named chemotactic cytokines (chemokines). Monocyte Chemoattractant Protein-1 (MCP-1) is one chemokine that is expressed highly in atherosclerotic lesions and plays a role in monocyte trafficking across the endothelial cell layer. The end state of the monocyte after transendothelial migration is dependent on many factors, such as the specific tissue involved in the process, the type of stimulus, and the formation of MCP-1 concentration gradients in the tissue. Having a better understanding of the underlying mechanisms and identifying potential pro-atherogenic markers will help to target these cytokines with specific therapeutic strategies. A 3D in vitro vascular tissue model, consisting of human aortic endothelial cells (HAECs) grown on the surface of a collagen matrix, was used to investigate MCP-1 release within a 3D environment.  The 3D tissue model provides the added dimension that is required for the creation of concentration gradients, along with cellular movement and interactions created by such gradients. During analysis of the system, a binding reaction between MCP-1 and the collagen matrix was discovered, which shows that in addition to a soluble gradient of MCP-1, a static gradient (the gradient of collagen-bound MCP-1) may be formed in the collagen matrix as well. The main objective of this study was to develop a mathematical model that can be used to predict the MCP-1 concentration gradients in the collagen matrix of the tissue model. The unsteady-state transport model includes a source term to describe MCP-1 production from the HAECs and a binding reaction term to describe the interaction of MCP-1 with the collagen matrix. The release of MCP-1 from the HAECs in the tissue model, under normal culture conditions and in response to TNF-α, was determined at various time points over a 24-hour period. The MCP-1 release profile was used to derive the source term of MCP-1 production of the HAECs in the mathematical model. The binding reaction expression and rate constant were determined experimentally by measuring the initial rates of reaction for various MCP-1 concentrations applied to a collagen matrix without cells. The mathematical model indicates that the concentration gradients of both soluble and static MCP-1 are formed inside the collagen matrix. The model predicts the increase of MCP-1 concentration (both soluble and static) with time, due to the release of MCP-1 from the HAECs in response to TNF-α activation. The concentration of static MCP-1 remains higher than that of the soluble MCP-1 after 18 hours and overcomes the soluble gradient of MCP-1 as time passes. The model further substantiates that apart from the soluble gradient of MCP-1, the static gradient of MCP-1 is another potent factor that may mediate monocyte transendothelial migration. The mathematical model was validated with experimental data. The mathematical model demonstrated a good prediction of MCP-1 concentrations in both the top and the bottom reservoirs surrounding the collagen matrix, for selected incubation time points with TNF-α. The mathematical model can be used to provide new information about the relationship between MCP-1 concentration gradients and monocyte transendothelial migration associated with inflammation.