Poster M9 - Fiber Alignment Induces Aortic Valve Calcification in a Multiscale Computational Model

Introduction: Calcific aortic valve disease (CAVD) is a chronic condition that affects a significant portion of the elderly population in the United States. CAVD is characterized by the progressive remodeling of aortic valve tissue, which results in fibrotic tissue, mineralization, and stenosis. This process begins with the formation of nanoscale calcific nodules that gradually progress to the micro- and macro-scales. Despite its prevalence, there is currently no nonsurgical treatment for valvular calcification. Patients often do not experience symptoms until the disease has advanced significantly. Once the disease has progressed to an advanced stage, valvular replacements are the only option to restore the patient’s health. The calcification process involves cellular mechanisms including fibrosis, endothelial to mesenchymal transition (EndMT), and differentiation of resident cells into an osteoblastic phenotype, leading to nucleation of calcium nodules and calcification. Studies have indicated that transforming growth factor beta (TGFβ) is one of the drivers of the calcification process in aortic valve disease. To simulate the tissue remodeling that occurs during disease progression, we have developed a multiscale model that incorporates both subcellular and tissue scale models. Leveraging this approach, we study the varying effects of intrinsic fiber alignments on the formation of calcified nodules in aortic valve disease.

Materials and

Methods: The simulation methodology uses a multiscale approach. At the tissue scale, the Cellular Potts Model and partial differential equations are utilized to simulate the interactions between cells and the extracellular matrix (ECM), capturing cell migration, differentiation, and mitosis. The ECM is modeled as fiber bundles arranged with different orientations within a three-dimensional lattice. The fibers are modeled at three major orientations: random, at 0 degrees, and 90 degrees in relation to the normal vector of the endothelial cellular plane. CompuCell3D is used as a hybrid discrete-continuum model, where the discrete component describes cell behaviors, and the continuum transport model employs diffusion equations to describe the evolution, interaction, and transport of chemical species. At the subcellular scale, ordinary differential equations are used to represent signaling pathways, such as the TGFβ pathway which drives EndMT and calcification. The RoadRunner package is used to solve the equations and the results are used to analyze this pathway by simulating the expression of proteins, including PECAM-1, α-SMA, and MMP-9.

Results, Conclusions, and Discussions: The model consists of multiple cell types, each representing an actual cell phenotype or state. Cellular differentiation is determined by protein expression analysis at the subcellular level. Simulation results demonstrate that endothelial cells lose their adhesion and undergo EndMT upon TGFβ stimulation. It also activates interstitial cells, which increases their motility, fibrosis activity, secretion of matrix degrading enzymes and TGFβ secretion. Prolonged activity of interstitial cells in the active state leads to differentiation into osteoblastic-like cells, initiating calcium nodule nucleation and growth (Figure 1). The simulation tracks cell population and differentiation and shows that the majority of active cells eventually die and become trapped in higher fibrotic or calcified areas due to the lack of nutrients. Dead cell body fragments act as feeding sites for calcified nodules to grow at higher rates. The outcomes from various fiber alignments indicate that cells show greater mobility along the axis of fiber orientation compared to movements perpendicular to the fibers. Additionally, fiber orientation influences both the size and average depth of calcified nodules formed, with deeper nodules observed in alignments at 0 degrees relative to the endothelial cell surface's normal vector. In conclusion, this multiscale model can help to unravel the aortic valve calcification process and identify important underlying causes, ultimately leading to the development of nonsurgical therapeutic methods. It is also applicable to other complex pathologies such as cancer development.

Acknowledgements (Optional): Acknowledgements: This work was funded by the National Science Foundation (CMMI 1919438).