Causality Analysis and Cell Network Modeling of Spatial Calcium Signaling Patterns in Liver Lobules

Dynamics as well as localization of Ca(2+) transients plays a vital role in liver function under homeostatic conditions, repair, and disease. In response to circulating hormonal stimuli, hepatocytes exhibit intracellular Ca(2+) responses that propagate through liver lobules in a wave-like fashion. Although intracellular processes that control cell autonomous Ca(2+) spiking behavior have been studied extensively, the intra- and inter-cellular signaling factors that regulate lobular scale spatial patterns and wave-like propagation of Ca(2+) remain to be determined. To address this need, we acquired images of cytosolic Ca(2+) transients in 1300 hepatocytes situated across several mouse liver lobules over a period of 1600 s. We analyzed this time series data using correlation network analysis, causal network analysis, and computational modeling, to characterize the spatial distribution of heterogeneity in intracellular Ca(2+) signaling components as well as intercellular interactions that control lobular scale Ca(2+) waves. Our causal network analysis revealed that hepatocytes are causally linked to multiple other co-localized hepatocytes, but these influences are not necessarily aligned uni-directionally along the sinusoids. Our computational model-based analysis showed that spatial gradients of intracellular Ca(2+) signaling components as well as intercellular molecular exchange are required for lobular scale propagation of Ca(2+) waves. Additionally, our analysis suggested that causal influences of hepatocytes on Ca(2+) responses of multiple neighbors lead to robustness of Ca(2+) wave propagation through liver lobules.