Actomyosin contractility drives bile regurgitation as an early response during obstructive cholestasis. Journal of Hepatology, February 2017

By Kapish Gupta1, Qiushi Li2, Jun Jun Fan3, Eliza Li Shan Fong4, Ziwei Song5, Shupei Mo5, Haoyu Tang1, Inn Chuan Ng6, Chan Way Ng6, Pornteera Pawijit7, Shuangmu Zhuo8, Chen-Yuan Dong9, Boon Chuan Low10, Aileen Wee11, Yock Young Dan12, Pakorn Kanchanawong13, Peter So14, Virgile Viasnoff15, Hanry Yu16

Journal of Hepataology. February 2017. Epub ahead of print. doi: 10.1016/j.jhep.2017.01.026.

Abstract

BACKGROUND & AIMS: A wide range of liver diseases manifest as biliary obstruction, or cholestasis. However, the sequence of molecular events triggered as part of the early hepatocellular homeostatic response in obstructive cholestasis is poorly elucidated. Pericanalicular actin is known to accumulate during obstructive cholestasis. Therefore, we hypothesized that the pericanalicular actin cortex undergoes significant remodeling as a regulatory response to obstructive cholestasis.
METHODS: In vivo investigations were performed in a bile duct-ligated mouse model. Actomyosin contractility was assessed using sandwich-cultured rat hepatocytes transfected with various fluorescently labeled proteins and pharmacological inhibitors of actomyosin contractility.
RESULTS: Actomyosin contractility induces transient deformations along the canalicular membrane, a process we have termed inward blebbing. We show that these membrane intrusions are initiated by local ruptures in the pericanalicular actin cortex; and they typically retract following repair by actin polymerization and actomyosin contraction. However, above a certain osmotic pressure threshold, these inward blebs pinch away from the canalicular membrane into the hepatocyte cytoplasm as large vesicles (2-8μm). Importantly, we show that these vesicles aid in the regurgitation of bile from the bile canaliculi.
CONCLUSION: Actomyosin contractility induces the formation of bile-regurgitative vesicles, thus serving as an early homeostatic mechanism against increased biliary pressure during cholestasis.
LAY SUMMARY: Bile canaliculi expand and contract in response to the amount of secreted bile, and resistance from the surrounding actin bundles. Further expansion due to bile duct blockade leads to the formation of inward blebs, which carry away excess bile to prevent bile build up in the canaliculi.

 

1Mechanobiology Institute, National University of Singapore, Singapore.
2Mechanobiology Institute, National University of Singapore, Singapore; National University of Singapore Research Institute, Singapore.
3Institute of Bioengineering and Nanotechnology, Agency for Science, Technology and Research (A*STAR), Singapore; BioSyM, Singapore-MIT Alliance for Research and Technology, Singapore; Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, China.
4Department of Physiology, National University of Singapore, Singapore; Department of Biomedical Engineering, National University of Singapore, Singapore.
5Institute of Bioengineering and Nanotechnology, Agency for Science, Technology and Research (A*STAR), Singapore.
6Department of Physiology, National University of Singapore, Singapore.
7Department of Physiology, National University of Singapore, Singapore; NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore, Singapore.
8BioSyM, Singapore-MIT Alliance for Research and Technology, Singapore; Fujian Normal University, Fuzhou, Fujian, China.
9Department of Physics, National Taiwan University, Taiwan.
10Mechanobiology Institute, National University of Singapore, Singapore; Department of Biological Sciences, National University of Singapore, Singapore.
11Department of Pathology, National University of Singapore, Singapore.
12Division of Gastroenterology and Hepatology, National University Hospital, Singapore.
13Mechanobiology Institute, National University of Singapore, Singapore; Department of Biomedical Engineering, National University of Singapore, Singapore.
14BioSyM, Singapore-MIT Alliance for Research and Technology, Singapore.
15Mechanobiology Institute, National University of Singapore, Singapore; CNRS UMI3639, Singapore.
16Mechanobiology Institute, National University of Singapore, Singapore; Institute of Bioengineering and Nanotechnology, Agency for Science, Technology and Research (A*STAR), Singapore; BioSyM, Singapore-MIT Alliance for Research and Technology, Singapore; Department of Physiology, National University of Singapore, Singapore; Department of Gastroenterology, Nanfang Hospital, Southern Medical University, Guangzhou, China.