Spatio-temporal model of YAP activation during liver regeneration
Early Metabolic Injury (LiSyM-EMI - Pillar I), LiSyM network

For the spatio-temporal dynamics of bile transport, bile canalicular dilation, mechanical stimulation and transduction of YAP signaling during liver regeneration see the open access publication and its appendix:
Meyer et al. (2020) Bile canaliculi remodeling activates YAP via the actin cytoskeleton during liver regeneration. Molecular Systems Biology 16:e8985. https://doi.org/10.15252/msb.20198985

The model format is MorpheusML that can readily be loaded and run in the free and open source software
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Creator: Lutz Brusch

Contributor: Lutz Brusch

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Bile canaliculi remodeling activates YAP via the actin cytoskeleton during liver regeneration
Early Metabolic Injury (LiSyM-EMI - Pillar I)

Abstract (Expand)

The mechanisms of organ size control remain poorly understood. A key question is how cells collectively sense the overall status of a tissue. We addressed this problem focusing on mouse liver regeneration. … Using digital tissue reconstruction and quantitative image analysis, we found that the apical surface of hepatocytes forming the bile canalicular network expands concomitant with an increase in F‐actin and phospho‐myosin, to compensate an overload of bile acids. These changes are sensed by the Hippo transcriptional co‐activator YAP, which localizes to apical F‐actin‐rich regions and translocates to the nucleus in dependence of the integrity of the actin cytoskeleton. This mechanism tolerates moderate bile acid fluctuations under tissue homeostasis, but activates YAP in response to sustained bile acid overload. Using an integrated biophysical–biochemical model of bile pressure and Hippo signaling, we explained this behavior by the existence of a mechano‐sensory mechanism that activates YAP in a switch‐like manner. We propose that the apical surface of hepatocytes acts as a self‐regulatory mechano‐sensory system that responds to critical levels of bile acids as readout of tissue status.

Authors: Kirstin Meyer, Hernan Morales‐Navarrete, Sarah Seifert, Michaela Wilsch‐Braeuninger, Uta Dahmen, Elly M Tanaka, Lutz Brusch, Yannis Kalaidzidis, Marino Zerial

Date Published: 24th Feb 2020

Journal: Mol Syst Biol

Wet-tip versus dry-tip regimes of osmotically driven fluid flow
Early Metabolic Injury (LiSyM-EMI - Pillar I)

Abstract (Expand)

The secretion of osmolytes into a lumen and thereby caused osmotic water inflow can drive fluid flows in organs without a mechanical pump. Such fluids include saliva, sweat, pancreatic juice and bile. … The effects of elevated fluid pressure and the associated mechanical limitations of organ function remain largely unknown since fluid pressure is difficult to measure inside tiny secretory channels in vivo. We consider the pressure profile of the coupled osmolyte-flow problem in a secretory channel with a closed tip and an open outlet. Importantly, the entire lateral boundary acts as a dynamic fluid source, the strength of which self-organizes through feedback from the emergent pressure solution itself. We derive analytical solutions and compare them to numerical simulations of the problem in three-dimensional space. The theoretical results reveal a phase boundary in a four-dimensional parameter space separating the commonly considered regime with steady flow all along the channel, here termed “wet-tip” regime, from a “dry-tip” regime suffering ceased flow downstream from the closed tip. We propose a relation between the predicted phase boundary and the onset of cholestasis, a pathological liver condition with reduced bile outflow. The phase boundary also sets an intrinsic length scale for the channel which could act as a length sensor during organ growth.

Authors: Oleksandr Ostrenko, Jochen Hampe, Lutz Brusch

Date Published: 1st Dec 2019

Journal: Sci Rep

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