F-actin dynamics regulates mammalian organ growth and cell fate maintenance

• Published in: Journal of hepatology 2019-07, Vol.71 (1), p.130-142
• Main Authors: Pocaterra, Arianna, Santinon, Giulia, Romani, Patrizia, Brian, Irene, Dimitracopoulos, Andrea, Ghisleni, Andrea, Carnicer-Lombarte, Alejandro, Forcato, Mattia, Braghetta, Paola, Montagner, Marco, Galuppini, Francesca, Aragona, Mariaceleste, Pennelli, Gianmaria, Bicciato, Silvio, Gauthier, Nils, Franze, Kristian, Dupont, Sirio
• Format: Article
• Language: English
• Subjects: Actins - metabolism; Adaptor Proteins, Signal Transducing - metabolism; Animals; Capping protein; CAPZ; CapZ Actin Capping Protein - metabolism; Cell Cycle Proteins - metabolism; Cells, Cultured; Elasticity; F-actin dynamics; Gluconeogenesis; Glucose metabolism; Hepatocyte cell fate maintenance; Hepatocytes - physiology; Hippo; Humans; Intracellular Signaling Peptides and Proteins - physiology; Liver - growth & development; Liver - metabolism; Liver - physiopathology; Liver homeostasis; Mechanotransduction; Mechanotransduction, Cellular - physiology; Mice; Mice, Knockout; Organ growth; Protein-Serine-Threonine Kinases - metabolism; Signal Transduction; Xenobiotic metabolism; YAP
• ISSN: 0168-8278; 1600-0641
• DOI: 10.1016/j.jhep.2019.02.022

[Display omitted] •Absence of CAPZ leads to increased cell contractility and tissue stiffness.•Loss of CAPZ leads to liver overgrowth, hepatocyte reprogramming and metabolic defects.•These phenotypes are due to YAP hyperactivation, and occur in parallel to LATS1/2.•ROCK inhibition rescues the effects of CAPZ inactivation.•Loss of CAPZ unveils the relevance of mechanical signals for tissue homeostasis. In vitro, cell function can be potently regulated by the mechanical properties of cells and of their microenvironment. Cells measure these features by developing forces via their actomyosin cytoskeleton, and respond accordingly by regulating intracellular pathways, including the transcriptional coactivators YAP/TAZ. Whether mechanical cues are relevant for in vivo regulation of adult organ homeostasis, and whether this occurs through YAP/TAZ, remains largely unaddressed. We developed Capzb conditional knockout mice and obtained primary fibroblasts to characterize the role of CAPZ in vitro. In vivo functional analyses were carried out by inducing Capzb inactivation in adult hepatocytes, manipulating YAP/Hippo activity by hydrodynamic tail vein injections, and treating mice with the ROCK inhibitor, fasudil. We found that the F-actin capping protein CAPZ restrains actomyosin contractility: Capzb inactivation alters stress fiber and focal adhesion dynamics leading to enhanced myosin activity, increased traction forces, and increased liver stiffness. In vitro, this rescues YAP from inhibition by a small cellular geometry; in vivo, it induces YAP activation in parallel to the Hippo pathway, causing extensive hepatocyte proliferation and leading to striking organ overgrowth. Moreover, Capzb is required for the maintenance of the differentiated hepatocyte state, for metabolic zonation, and for gluconeogenesis. In keeping with changes in tissue mechanics, inhibition of the contractility regulator ROCK, or deletion of the Yap1 mechanotransducer, reverse the phenotypes emerging in Capzb-null livers. These results indicate a previously unsuspected role for CAPZ in tuning the mechanical properties of cells and tissues, which is required in hepatocytes for the maintenance of the differentiated state and to regulate organ size. More generally, it indicates for the first time that mechanotransduction has a physiological role in maintaining liver homeostasis in mammals. The mechanical properties of cells and tissues (i.e. whether they are soft or stiff) are thought to be impo