A spatialised agent-based model of NOTCH signalling pathway in Endothelial Cells predicts emergent heterogeneity due to continual dynamic phenotypic adjustments.

Vascular Endothelial Cells (EC) plasticity is key to homeostasis and its disruption is a hallmark of diseases such as cancer, atherosclerosis, and diabetes. The EC lineage has evolved to address in parallel sensor and actuator functions. This ability is reflected in remarkable phenotypical heterogeneity of EC across different tissues, within the same tissue, and within the same vascular bed as demonstrated by single cell image analysis and transcriptomics studies. However, how the molecular signalling dynamics in EC could generate and maintain such heterogeneity in different contexts is still largely unexplored. Recently we reported that confluent EC have spatially heterogeneous NOTCH signalling pathway (NSP) levels in vitro as confirmed from analysis of available OMICS databases. Here, we show that spatial heterogeneity of NSP levels is a feature of aortic murine endothelia in vivo and recapitulated by human EC in culture despite absence of signalling from mural cells. We study lateral induction and inhibition, cis-interactions and signalling, and target genes autoregulation in NSP. Using mathematical models and experimental observations we report that NSP dynamics can generate stable, periodic, and asynchronous oscillations of the NSP target HES1. Importantly, we observe that cell contact dependent NSP signal oscillations is the most likely parsimonious mechanistic hypothesis justifying observed spatial heterogeneity in endothelia. We propose that NSP is sufficient to enable individual EC in monolayers to acquire different phenotypes dynamically explaining robustness of quiescent endothelia in performing parallel functions.