Vascular patterning sets the stage for macro and micro hepatic architecture

Zonation in NASH - A key paradigm for understanding pathophysiology and clinical outcomes

Non-alcoholic fatty liver disease (NAFLD) exists as a spectrum ranging from simple steatosis to histologically defined hepatocyte injury and inflammatory changes that define steatohepatitis (NASH), and increase risk for fibrosis. Although zonal differences in NASH have not been systematically studied, periportal involvement has been associated with worse metabolic outcomes and more hepatic fibrosis as compared to pericentral disease. These data suggest that hepatic zonation of disease may influence the diversity of clinical presentations. Similarly, several randomized clinical trials suggest a differential response based on zonation of disease, with preferential effects on periportal (cysteamine) or pericentral disease (obeticholic acid, pioglitazone). Intriguingly, morphogenic pathways known to affect zonal development and maintenance - WNT/β-Catenin, Hedgehog, HIPPO/Yap/TAZ and Notch - have been implicated in NASH pathogenesis, and nuclear hormone receptors downstream of potential NASH therapeutics show zonal preferences. In this review, we summarize these data and propose that patient-specific activation of these pathways may explain the variability in clinical presentation, and the zone-specific response observed in clinical trials.

Engineering the Vasculature of Stem-Cell-Derived Liver Organoids

The vasculature of stem-cell-derived liver organoids can be engineered using methods that recapitulate embryonic liver development. Hepatic organoids with a vascular network offer great application prospects for drug screening, disease modeling, and therapeutics. However, the application of stem cell-derived organoids is hindered by insufficient vascularization and maturation. Here, we review different theories about the origin of hepatic cells and the morphogenesis of hepatic vessels to provide potential approaches for organoid generation. We also review the main protocols for generating vascularized liver organoids from stem cells and consider their potential and limitations in the generation of vascularized liver organoids.

The Evolving Role of Immune Checkpoint Inhibitors in Hepatocellular Carcinoma Treatment

Hepatocellular carcinoma (HCC) is one of most common cancers and the fourth leading cause of death worldwide. Commonly, HCC development occurs in a liver that is severely compromised by chronic injury or inflammation. Liver transplantation, hepatic resection, radiofrequency ablation (RFA), transcatheter arterial chemoembolization (TACE), and targeted therapies based on tyrosine protein kinase inhibitors are the most common treatments. The latter group have been used as the primary choice for a decade. However, tumor microenvironment in HCC is strongly immunosuppressive; thus, new treatment approaches for HCC remain necessary. The great expression of immune checkpoint molecules, such as programmed death-1 (PD-1), cytotoxic T-lymphocyte antigen 4 (CTLA-4), lymphocyte activating gene 3 protein (LAG-3), and mucin domain molecule 3 (TIM-3), on tumor and immune cells and the high levels of immunosuppressive cytokines induce T cell inhibition and represent one of the major mechanisms of HCC immune escape. Recently, immunotherapy based on the use of immune checkpoint inhibitors (ICIs), as single agents or in combination with kinase inhibitors, anti-angiogenic drugs, chemotherapeutic agents, and locoregional therapies, offers great promise in the treatment of HCC. This review summarizes the recent clinical studies, as well as ongoing and upcoming trials.

Carcinogenesis and Metastasis in Liver: Cell Physiological Basis

Hepatocellular carcinoma (HCC) incidence is rising. This paper summarises the current state of knowledge and recent discoveries in the cellular and physiological mechanisms leading to the development of liver cancer, especially HCC, and liver metastases. After reviewing normal hepatic cytoarchitecture and immunological characteristics, the paper addresses the pathophysiological factors that cause liver damage and predispose to neoplasia. Particular attention is given to chronic liver diseases, metabolic syndrome and the impact of altered gut microbiota, disrupted circadian rhythm and psychological stress. Improved knowledge of the multifactorial aetiology of HCC has important implications for the prevention and treatment of this cancer and of liver metastases in general.

Development of the Intrahepatic and Extrahepatic Biliary Tract: A Framework for Understanding Congenital Diseases

The involvement of the biliary tract in the pathophysiology of liver diseases and the increased attention paid to bile ducts in the bioconstruction of liver tissue for regenerative therapy have fueled intense research into the fundamental mechanisms of biliary development. Here, I review the molecular, cellular and tissular mechanisms driving differentiation and morphogenesis of the intrahepatic and extrahepatic bile ducts. This review focuses on the dynamics of the transcriptional and signaling modules that promote biliary development in human and mouse liver and discusses studies in which the use of zebrafish uncovered unexplored processes in mammalian biliary development. The review concludes by providing a framework for interpreting the mechanisms that may help us understand the origin of congenital biliary diseases.

Development of the liver: Insights into organ and tissue morphogenesis

Recent development of improved tools and methods to analyse tissues at the three-dimensional level has expanded our capacity to investigate morphogenesis of foetal liver. Here, we review the key morphogenetic steps during liver development, from the prehepatic endoderm stage to the postnatal period, and consider several model organisms while focussing on the mammalian liver. We first discuss how the liver buds out of the endoderm and gives rise to an asymmetric liver. We next outline the mechanisms driving liver and lobe growth, and review morphogenesis of the intra- and extrahepatic bile ducts; morphogenetic responses of the biliary tract to liver injury are discussed. Finally, we describe the mechanisms driving formation of the vasculature, namely venous and arterial vessels, as well as sinusoids.

Emerging advancements in liver regeneration and organogenesis as tools for liver replacement

PURPOSE OF REVIEW

Although the liver possesses a unique, innate ability to regenerate through mass compensation, transplantation remains the only therapy when damage outpaces regeneration, or liver metabolic capacity is irreversibly impacted. Recent insight from developmental biology has greatly influenced the advancement of alternative options to transplantation in these settings.

RECENT FINDINGS

Factors known to direct liver cell specification, expansion, and differentiation have been used to generate hepatocyte-like cells from stem and somatic cells for developing cell therapies. Additionally, interactions between hepatic epithelial and nonepithelial cells key to establishing hepatic architecture have been used in tissue engineering approaches to advance self-organizing hepatic organoids and bioartificial liver devices. Simultaneously, recent clinically applicable advances in human hepatocyte transplantation and promotion of innate hepatic regeneration have been limited.

SUMMARY

Although mature hepatocytes have the potential to bridge to, or replace whole organ transplantation, limits in the ability to obtain healthy cells, stabilize in-vitro expansion, cryopreserve, and alleviate rejection, still exist. Alternative sources for generating hepatocytes hold promise for cell therapy and tissue engineering. These may allow generation of autologous or universal donor cells that eliminate the need for immunosuppression; however, limits exist regarding hepatocyte maturity and efficacy at liver repopulation, as well as applicability to human chronic liver disease.

Challenges on the road to a multicellular bioartificial liver

Over recent years, the progress in the development of a bioartificial liver (BAL) as an extracorporeal device or as a tissue engineered transplantable organ has been immense. However, many important BAL characteristics that are necessary to meet clinical demands have not been sufficiently addressed. This review describes the existing challenges in the development of a BAL for clinical applications, highlighting multicellularity and sinusoidal microarchitecture as crucial BAL characteristics to fulfil various liver functions. Currently available sources of nonparenchymal liver cells, such as endothelial cells, cholangiocytes and macrophages, used in BAL development are defined. Also, we discuss the recent studies on the reconstruction of the complex liver sinusoid microarchitecture using various liver cell types. Moreover, we highlight some other aspects of a BAL, such as liver zonation and formation of a vascular as well as biliary network for an adequate delivery, biotransformation and removal of substrates and waste products. Finally, the benefits of a multicellular BAL for the pharmaceutical industry are briefly described. Copyright © 2016 John Wiley & Sons, Ltd.

Orchestrating liver development

The liver is a central regulator of metabolism, and liver failure thus constitutes a major health burden. Understanding how this complex organ develops during embryogenesis will yield insights into how liver regeneration can be promoted and how functional liver replacement tissue can be engineered. Recent studies of animal models have identified key signaling pathways and complex tissue interactions that progressively generate liver progenitor cells, differentiated lineages and functional tissues. In addition, progress in understanding how these cells interact, and how transcriptional and signaling programs precisely coordinate liver development, has begun to elucidate the molecular mechanisms underlying this complexity. Here, we review the lineage relationships, signaling pathways and transcriptional programs that orchestrate hepatogenesis.