Liver regeneration is characterized by a scheduled sequence of inner and intra-cellular signaling events. It starts with an initial inflammatory phase, followed by a period of rapidly proliferating hepatocytes and stopping abruptly when the liver mass is restored. The cytokines hepatocellular growth factor (HGF) and interleukin 6 (IL-6) play a pivotal role during this process with the former driving proliferation that is enhanced by the latter. While the individual importance of HGF and IL6 has been studied comprahensively the role of cross-talk in control of hepatic proliferation is jet largely unknown. To this end, we performed time-resolved transcriptional profiling of of murine hepatocytes stimulated with HGF and IL-6 indiviually as well as in combination. Thorough systematic investigation performing statistical analysis, mathematical formalization of cross-talk effects on the transcriptional level as well as gene-regulatory network inference revealed the transcriptional program of the cross-talk initiated by HGF and IL-6. Using the proliferation associated Hepcidin (Hamp) and Amphiregulin (Areg) as marker genes for liver regeneration we perform exthensive in-silico experiments with the inferred gene-regulatory network for the identification of the most important players in regulation of the proliferation process. Among other genes, this predicted chemokine (C-X-C motif) ligand 10 (Cxcl10) as an important factor in the temporal regulation of proliferation. These predictions were validated by independent in vitro expression data as well as independent in vivo literature data. While Cxcl10 is known to be involved in liver regeneration, our study extend its role towards its temporal orchestration.
Overall design: Cells were stimulated with either 40 ng/ml rmHGF (all R&D Systems) and 40 ng/ml rhIL-6 alone or in combination. Cells were left untreated as unstimulated control. RNA was extracted at 1,2,3,4,5,6,7,8,9,10,12,24 hours. Cells were treated with IL6 alone for the first 4 hours and then additionally with HGF from hours 4-24. Controls were taken at -5,0,4,8,12,24 hours.
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