Hippo Pathway Activity Influences Liver Cell Fate

SummaryThe Hippo-signaling pathway is an important regulator of cellular proliferation and organ size. However, little is known about the role of this cascade in the control of cell fate. Employing a combination of lineage tracing, clonal analysis, and organoid culture approaches, we demonstrate that Hippo pathway activity is essential for the maintenance of the differentiated hepatocyte state. Remarkably, acute inactivation of Hippo pathway signaling in vivo is sufficient to dedifferentiate, at very high efficiencies, adult hepatocytes into cells bearing progenitor characteristics. These hepatocyte-derived progenitor cells demonstrate self-renewal and engraftment capacity at the single-cell level. We also identify the NOTCH-signaling pathway as a functional important effector downstream of the Hippo transducer YAP. Our findings uncover a potent role for Hippo/YAP signaling in controlling liver cell fate and reveal an unprecedented level of phenotypic plasticity in mature hepatocytes, which has implications for the understanding and manipulation of liver regeneration

NUAK2 is a critical YAP target in liver cancer

Hippo-YAP pathway plays an important role in cancers; however the in vivo relevance of YAP/TAZ target genes is unclear. Here, the authors show that NUAK2 is a target of YAP and participates in a feedback loop to maximize YAP activity. Inhibition of NUAK2 suppresses YAP-driven hepatomegaly and liver cancer growth, offering a new target for cancer therapy

Non-canonical Wnt signalling regulates scarring in biliary disease via the planar cell polarity receptors

The number of patients diagnosed with chronic bile duct disease is increasing and in most cases these diseases result in chronic ductular scarring, necessitating liver transplantation. The formation of ductular scaring affects liver function; however, scar-generating portal fibroblasts also provide important instructive signals to promote the proliferation and differentiation of biliary epithelial cells. Therefore, understanding whether we can reduce scar formation while maintaining a pro-regenerative microenvironment will be essential in developing treatments for biliary disease. Here, we describe how regenerating biliary epithelial cells express Wnt-Planar Cell Polarity signalling components following bile duct injury and promote the formation of ductular scars by upregulating pro-fibrogenic cytokines and positively regulating collagen-deposition. Inhibiting the production of Wnt-ligands reduces the amount of scar formed around the bile duct, without reducing the development of the pro-regenerative microenvironment required for ductular regeneration, demonstrating that scarring and regeneration can be uncoupled in adult biliary disease and regeneration

Understanding the cell behavior on nano-/micro-patterned surfaces

Aim: This article reports on studies conducted in the same laboratory on interactions between patterned substrates with different pattern dimensions and chemistries, and various types of cells. Materials & methods: In order to compare the influence of various parameters, bone marrow stromal cells, retinal pigment epithelial cells, human corneal stromal cells (keratocytes), Saos-2 (human osteosarcoma cells), human microvascular endothelial cells and vascular smooth muscle cells were tested on surfaces with different physical patterns and chemical properties. Results: It was observed that cell type and surface topography are more influential than surface chemistry in determining the alignment tendency of a cell on a substrate surface. Low walls (several microns high) could not confine cells into the microgrooves of the films but alignment was still possible if the cells had a natural alignment property. Conclusion: This information is very useful in designing tissue engineering scaffolds and in the long-term success of implants

Characterization of Mesoscale Coiled-Coil Peptide-Porphyrin Complexes

We have successfully designed a coiled-coil peptide that can self-assemble to form mesoscale filaments and serve as a scaffold for porphyrin interaction. --author-supplied descriptio

Understanding the cell behavior on nano-/micro-patterned surfaces

Aim: This article reports on studies conducted in the same laboratory on interactions between patterned substrates with different pattern dimensions and chemistries, and various types of cells. Materials & methods: In order to compare the influence of various parameters, bone marrow stromal cells, retinal pigment epithelial cells, human corneal stromal cells (keratocytes), Saos-2 (human osteosarcoma cells), human microvascular endothelial cells and vascular smooth muscle cells were tested on surfaces with different physical patterns and chemical properties. Results: It was observed that cell type and surface topography are more influential than surface chemistry in determining the alignment tendency of a cell on a substrate surface. Low walls (several microns high) could not confine cells into the microgrooves of the films but alignment was still possible if the cells had a natural alignment property. Conclusion: This information is very useful in designing tissue engineering scaffolds and in the long-term success of implants

YAP Drives Growth by Controlling Transcriptional Pause Release from Dynamic Enhancers

The Hippo/YAP signaling pathway is a crucial regulator of tissue growth, stem cell activity, and tumorigenesis. However, the mechanism by which YAP controls transcription remains to be fully elucidated. Here, we utilize global chromatin occupancy analyses to demonstrate that robust YAP binding is restricted to a relatively small number of distal regulatory elements in the genome. YAP occupancy defines a subset of enhancers and superenhancers with the highest transcriptional outputs. YAP modulates transcription from these elements predominantly by regulating promoter-proximal polymerase II (Pol II) pause release. Mechanistically, YAP interacts and recruits the Mediator complex to enhancers, allowing the recruitment of the CDK9 elongating kinase. Genetic and chemical perturbation experiments demonstrate the requirement for Mediator and CDK9 in YAP-driven phenotypes of overgrowth and tumorigenesis. Our results here uncover the molecular mechanisms employed by YAP to exert its growth and oncogenic functions, and suggest strategies for intervention

Single-Cell Analysis of the Liver Epithelium Reveals Dynamic Heterogeneity and an Essential Role for YAP in Homeostasis and Regeneration

The liver can substantially regenerate after injury, with both main epithelial cell types, hepatocytes and biliary epithelial cells (BECs), playing important roles in parenchymal regeneration. Beyond metabolic functions, BECs exhibit substantial plasticity and in some contexts can drive hepatic repopulation. Here, we performed single-cell RNA sequencing to examine BEC and hepatocyte heterogeneity during homeostasis and after injury. Instead of evidence for a transcriptionally defined progenitor-like BEC cell, we found significant homeostatic BEC heterogeneity that reflects fluctuating activation of a YAP-dependent program. This transcriptional signature defines a dynamic cellular state during homeostasis and is highly responsive to injury. YAP signaling is induced by physiological bile acids (BAs), required for BEC survival in response to BA exposure, and is necessary for hepatocyte reprogramming into biliary progenitors upon injury. Together, these findings uncover molecular heterogeneity within the ductal epithelium and reveal YAP as a protective rheostat and regenerative regulator in the mammalian liver. The transcriptional landscape of the epithelium in healthy and regenerating murine livers was investigated, revealing a dynamically fluctuating and heterogeneous YAP transcriptional program. Further analysis uncovered YAP signaling dualism: it is essential in biliary epithelial cells for homeostatic maintenance and in hepatocytes for the regenerative response to injury

Single-Cell Analysis of the Liver Epithelium Reveals Dynamic Heterogeneity and an Essential Role for YAP in Homeostasis and Regeneration

© 2019 Elsevier Inc. The liver can substantially regenerate after injury, with both main epithelial cell types, hepatocytes and biliary epithelial cells (BECs), playing important roles in parenchymal regeneration. Beyond metabolic functions, BECs exhibit substantial plasticity and in some contexts can drive hepatic repopulation. Here, we performed single-cell RNA sequencing to examine BEC and hepatocyte heterogeneity during homeostasis and after injury. Instead of evidence for a transcriptionally defined progenitor-like BEC cell, we found significant homeostatic BEC heterogeneity that reflects fluctuating activation of a YAP-dependent program. This transcriptional signature defines a dynamic cellular state during homeostasis and is highly responsive to injury. YAP signaling is induced by physiological bile acids (BAs), required for BEC survival in response to BA exposure, and is necessary for hepatocyte reprogramming into biliary progenitors upon injury. Together, these findings uncover molecular heterogeneity within the ductal epithelium and reveal YAP as a protective rheostat and regenerative regulator in the mammalian liver. The transcriptional landscape of the epithelium in healthy and regenerating murine livers was investigated, revealing a dynamically fluctuating and heterogeneous YAP transcriptional program. Further analysis uncovered YAP signaling dualism: it is essential in biliary epithelial cells for homeostatic maintenance and in hepatocytes for the regenerative response to injury