CYP2E1 recovery is associated with a pericentral fibrosis pattern after repeated CCl4 insults

Fibrosis is a consequence of repetitive liver injuries, e.g. upon viral infection, alcohol consumption, malnutrition or hepatotoxicants. Based on the etiological factor, liver fibrosis develops in different patterns and presents as septal in toxic injuries1, biliary in cholestatic diseases2, bridging upon hepatitis virus infections or pericellular in case of alcohol consumption. The mechanism behind the generation of the different patterns is still elusive. We aim to define (a) molecular driver(s) of fibrosis pattern formation. Mice were exposed to acute or repeated doses for 6 consecutive weeks of carbon tetrachloride (CCl4). Morphologically, patterns of fibrosis and metabolizing enzymes, namely CYP2E1, were analyzed in immunostaining datasets. We found that the pattern of CYP2E1+ hepatocyte recovery after acute insult is similar to the observed toxic-induced septal fibrosis. This similarity suggested that the spatial pattern of CYP2E1 might indicate the location where the fibrosis forms. To study this hypothesis, we developed a dynamic activator-inhibitor system, where the activator is a diffusible protein released from the central vein to promote the CYP2E1 signaling while the inhibitor is a diffusible protein released from the portal vein to inhibit the CYP2E1 signaling. Currently, this model can partially capture the observed patterns of CYP2E1 and extracellular matrix (ECM) upon chronic liver injuries suggesting that the prepattern of CYP2E1 may indeed be a key factor in determining the location of fibrotic streets despite likely not the only one. We are currently extending our model by further mechanisms. These include, but are not limited to i) crosstalk between activated hepatic stellate cells and liver sinusoidal endothelial cell differentiation; ii) The dialogue between endothelial cells lining the hepatic veins and hepatocyte metabolic zonation; iii) Presence of so far unknown diffusible inhibitor in the portal compartment, i.e. a bile duct driven factor. In the next step, we target the WNT/β-Catenin pathway (CYP2E1 regulator) by monoclonal antibodies against R-spondin1, 2 or 3 in fibrosed liver, and iv) the mechanical role of ECM deposited by HSCs, all finally integrated in a spatial-temporal model established to mimic regeneration after administration of a single dose of CCl43.

1Hammad S, Braeuning A, et al. A frequent misinterpretation in current research on liver fibrosis: the vessel in the center of CCl4-induced pseudolobules is a portal vein. Arch Toxicol. 2017 Nov;91(11):3689 – 3692.

2Hammad S, Cavalcanti E, et al. Galunisertib modifies the liver fibrotic composition in the Abcb4Ko mouse model. Arch Toxicol. 2018 Jul;92(7):2297 – 2309.

3Hoehme S, Brulport, M, et. al.. Prediction and validation of cell alignment along microvessels as order principle to restore tissue architecture in liver regeneration. Proc. Natl. Acad. Sci. (USA), 107(23), 10371 – 10376.