Developmental changes of cell adhesion molecule expression in the fetal mouse liver

Integrins, anchors and signal transducers of hematopoietic stem cells during development and in adulthood

Hematopoietic stem cells (HSCs), the apex of the hierarchically organized blood cell production system, are generated in the yolk sac, aorta-gonad-mesonephros region and placenta of the developing embryo. To maintain life-long hematopoiesis, HSCs emigrate from their site of origin and seed in distinct microenvironments, called niches, of fetal liver and bone marrow where they receive supportive signals for self-renewal, expansion and production of hematopoietic progenitor cells (HPCs), which in turn orchestrate the production of the hematopoietic effector cells. The interactions of hematopoietic stem and progenitor cells (HSPCs) with niche components are to a large part mediated by the integrin superfamily of adhesion molecules. Here, we summarize the current knowledge regarding the functional properties of integrins and their activators, Talin-1 and Kindlin-3, for HSPC generation, function and fate decisions during development and in adulthood. In addition, we discuss integrin-mediated mechanosensing for HSC-niche interactions, ex vivo protocols aimed at expanding HSCs for therapeutic use, and recent approaches targeting the integrin-mediated adhesion in leukemia-inducing HSCs in their protecting, malignant niches.

Automated Detection of Portal Fields and Central Veins in Whole-Slide Images of Liver Tissue

Many physiological processes and pathological phenomena in the liver tissue are spatially heterogeneous. At a local scale, biomarkers can be quantified along the axis of the blood flow, from portal fields (PFs) to central veins (CVs), i.e., in zonated form. This requires detecting PFs and CVs. However, manually annotating these structures in multiple whole-slide images is a tedious task. We describe and evaluate a fully automated method, based on a convolutional neural network, for simultaneously detecting PFs and CVs in a single stained section. Trained on scans of hematoxylin and eosin-stained liver tissue, the detector performed well with an F1 score of 0.81 compared to annotation by a human expert. It does, however, not generalize well to previously unseen scans of steatotic liver tissue with an F1 score of 0.59. Automated PF and CV detection eliminates the bottleneck of manual annotation for subsequent automated analyses, as illustrated by two proof-of-concept applications: We computed lobulus sizes based on the detected PF and CV positions, where results agreed with published lobulus sizes. Moreover, we demonstrate the feasibility of zonated quantification of biomarkers detected in different stainings based on lobuli and zones obtained from the detected PF and CV positions. A negative control (hematoxylin and eosin) showed the expected homogeneity, a positive control (glutamine synthetase) was quantified to be strictly pericentral, and a plausible zonation for a heterogeneous F4/80 staining was obtained. Automated detection of PFs and CVs is one building block for automatically quantifying physiologically relevant heterogeneity of liver tissue biomarkers. Perspectively, a more robust and automated assessment of zonation from whole-slide images will be valuable for parameterizing spatially resolved models of liver metabolism and to provide diagnostic information.

Crosstalk Between the Hepatic and Hematopoietic Systems During Embryonic Development

Hematopoietic stem cells (HSCs) generated during embryonic development are able to maintain hematopoiesis for the lifetime, producing all mature blood lineages. HSC transplantation is a widely used cell therapy intervention in the treatment of hematologic, autoimmune and genetic disorders. Its use, however, is hampered by the inability to expand HSCs ex vivo, urging for a better understanding of the mechanisms regulating their physiological expansion. In the adult, HSCs reside in the bone marrow, in specific microenvironments that support stem cell maintenance and differentiation. Conversely, while developing, HSCs are transiently present in the fetal liver, the major hematopoietic site in the embryo, where they expand. Deeper insights on the dynamics of fetal liver composition along development, and on how these different cell types impact hematopoiesis, are needed. Both, the hematopoietic and hepatic fetal systems have been extensively studied, albeit independently. This review aims to explore their concurrent establishment and evaluate to what degree they may cross modulate their respective development. As insights on the molecular networks that govern physiological HSC expansion accumulate, it is foreseeable that strategies to enhance HSC proliferation will be improved.

High-throughput sequencing identifies aetiology-dependent differences in ductular reaction in human chronic liver disease

Ductular reaction (DR) represents the activation of hepatic progenitor cells (HPCs) and has been associated with features of advanced chronic liver disease; yet it is not clear whether these cells contribute to disease progression and how the composition of their micro-environment differs depending on the aetiology. This study aimed to identify HPC-associated signalling pathways relevant in different chronic liver diseases using a high-throughput sequencing approach. DR/HPCs were isolated using laser microdissection from patient samples diagnosed with HCV or primary sclerosing cholangitis (PSC), as models for hepatocellular or biliary regeneration. Key signals were validated at the protein level for a cohort of 56 patients (20 early and 36 advanced stage). In total, 330 genes were significantly differentially expressed between the HPCs in HCV and PSC. Recruitment and homing of inflammatory cells were distinctly different depending on the aetiology. HPCs in PSC were characterised by a response to oxidative stress (e.g. JUN, VNN1) and neutrophil-attractant chemokines (CXCL5, CXCL6, IL-8), whereas HPCs in HCV were identified by T- and B-lymphocyte infiltration. Moreover, we found that communication between HPCs and macrophages was aetiology driven. In PSC, a high frequency of CCL28-positive macrophages was observed in the portal infiltrate, already in early disease in the absence of advanced fibrosis, while in HCV, HPCs showed a strong expression of the macrophage scavenger receptor MARCO. Interestingly, DR/HPCs in PSC showed more deposition of ECM (e.g. FN1, LAMC2, collagens) compared to HCV, where an increase of pro-invasive genes (e.g. PDGFRA, IGF2) was observed. Additionally, endothelial cells in the vicinity of DR/HPCs showed differential immunopositivity (e.g. IGF2 and INHBA expression). In conclusion, our data shine light on the role of DR/HPCs in immune signalling, fibrogenesis and angiogenesis in chronic liver disease. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Program Cell Death Receptor-1-Mediated Invariant Natural Killer T-Cell Control of Peritoneal Macrophage Modulates Survival in Neonatal Sepsis

We have shown that invariant natural killer T (iNKT) cells mediate sepsis-induced end-organ changes and immune responses, including macrophage bacterial phagocytosis, a finding regulated by the check point protein program cell death receptor-1 (PD-1). Furthermore, PD-1 mediates mortality in both adult and neonatal murine sepsis as well as in surgical patients. Given our previous findings, we hypothesize that iNKT cells will also modulate neonatal sepsis survival, and that this effect is regulated in part through PD-1. We utilized a polymicrobial intra-peritoneal cecal slurry (CS) sepsis model in wild type (WT), iNKT^−/− or PD-1^−/− 5–7 day old neonatal pups. Typically, tissues were harvested at 24 h for various bioassays/histology and, in some cases, survival was assessed for up to 7 days. Interestingly, similar to what we recently reported for PD-1^−/− mice following CS, iNKT^−/−-deficient animals exhibit a markedly improved survival vs. WT. Histologically, minor alterations in liver architectural, which were noted in WT pups, were attenuated in both iNKT^−/− and PD-1^−/− pups. Following CS, PECAM-1 expression was unchanged in the WT pups but increased in both iNKT^−/− and PD-1^−/− pups. In WT, following CS the emergence of a Ly6C^low subpopulation was noted among the influxed peritoneal macrophage population. Conversely, within iNKT^−/− pups, there were fewer peritoneal macrophages and a greater percentage of Ly6C^high macrophages. We show not only a key role for iNKT cells in affecting end-organ damage as well as alterations in phagocytes phenotypes in neonatal sepsis but that this iNKT cell mediated effect is driven by the central checkpoint protein PD-1.

Expression profiling of adhesion proteins during prenatal and postnatal liver development in rats

Culturing of primary hepatocytes and stem cell-derived hepatocytes faces a major issue of dedifferentiation due to absence of cell–cell adhesion and 3D structures. One of the possible ways to eliminate the problem of dedifferentiation is mimicking the expression pattern of adhesion proteins during the normal developmental process of liver cells. The purpose of this study was to evaluate the expression pattern of some key adhesion proteins, namely, E-cadherin, N-cadherin, epithelial CAM (EpCAM), intracellular CAM (ICAM), collagen 1α1, α-actinin, β-catenin and vimentin, in the liver tissue during prenatal and postnatal stages. Furthermore, differences in their expression between prenatal, early postnatal and adult stages were highlighted. Wistar rats were used to isolate livers at prenatal Day 14 and 17 as well as on postnatal Day 1, 3, 7 and 14. The liver from adult rats was used as control. Both conventional and real-time quantitative polymerase chain reactions (PCRs) were performed. For most of the adhesion proteins such as E-cadherin, N-cadherin, EpCAM, ICAM, collagen 1α1 and α-actinin, low expression was observed around prenatal Day 14 and an increasing expression was observed in the postnatal period. Moreover, β-catenin and vimentin showed higher expression in the early prenatal period, which decreased gradually in the postnatal period, but still this low expression was considerably higher than that in the adult control rats. This basic knowledge of the regulation of expression of adhesion proteins during different developmental stages indicates their vital role in liver development. This pattern can be further studied and imitated under in vitro conditions to achieve better cell–cell interactions.

Candidate genes investigation for severe nonalcoholic fatty liver disease based on bioinformatics analysis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver condition worldwide. However, its etiology and fundamental pathophysiology for the disease process are poorly understood. In this study, we thus used bioinformatics to identify candidate genes potentially causative of severe NAFLD.

METHODS

Gene expression profile data GSE49541 were downloaded from the Gene Expression Omnibus database. Tissues samples from 32 severe and 40 mild NAFLD patients were evaluated to identify differentially expressed genes (DEGs) between the 2 groups, followed by analyses of Gene Ontology (GO) functions and Kyoto Encyclopedia of Genes and Genomes pathways. Then, a weighted protein-protein interaction (PPI) network was constructed, and subnetworks and candidate genes were screened. Moreover, the GSE48452 data (14 normal liver tissue samples and 18 nonalcoholic steatohepatitis samples) were used to verify the results obtained from the above analyses.

RESULTS

A total of 100 upregulated genes and 24 downregulated ones were identified in severe NAFLD. Functional enrichment and pathway analyses showed that these DEGs were mainly associated with cell adhesion, inflammatory response, and chemokine activity. The top 5 subnetworks were selected based on the PPI network. A total of 5 hub genes, including ubiquilin 4 (UBQLN4), amyloid-beta precursor protein (APP), sex hormone-binding globulin (SHBG), cadherin-associated protein beta 1 (CTNNB1) and collagen type I alpha 1 (COL1A1), were considered to be candidate genes for NAFLD. In addition, the verification data confirmed the status of COL1A1, SHBG, and APP as candidate genes.

CONCLUSION

UBQLN4, APP, CTNNB1, SHBG, and COL1A1 might be involved in the development of NAFLD, and are proposed as the potential markers for predicting the development of this condition.

Self-renewal of hepatoblasts under chemically defined conditions by iterative growth factor and chemical screening

Tissue-specific stem/progenitor cells are essential to mediate organogenesis and tissue homeostasis. In addition, these cells have attracted significant interest for their therapeutic potential. However, it remains challenging to expand most types of these cells in vitro. In this study we devised a screening strategy aimed at identifying growth factors and small molecules that can sustain self-renewal of mouse hepatoblasts. This approach began with a defined basal condition, on top of which collections of growth factors and bioactive small molecules were screened for maintaining self-renewal of primary hepatoblasts. The initially identified proteins and small molecules were then combined in the basal media for subsequent screening to identify additional molecules that can synergistically promote hepatoblast self-renewal. This strategy was performed iteratively to eventually define a small molecule and growth factor cocktail, including epidermal growth factor, glycogen synthase kinase 3 inhibitor, transforming growth factor β receptor inhibitor, lysophosphatidic acid, and sphingosine 1-phosphate, which was sufficient to sustain long-term self-renewal of the murine hepatoblasts under chemically defined conditions. These expanded hepatoblasts retain the ability to respond to liver developmental cues and produce functional hepatocytes and form bile duct-like structures.

CONCLUSION

Our work established a chemically defined condition that allows long-term expansion of hepatoblasts, improved our understanding of hepatoblast self-renewal, and highlights the power of phenotypic screening to enable self-renewal of somatic stem/progenitor cells.

N-cadherin+ HSCs in fetal liver exhibit higher long-term bone marrow reconstitution activity than N-cadherin- HSCs

Adult hematopoietic stem cells (HSCs) are maintained in a microenvironment known as the stem cell niche. The regulation of HSCs in fetal liver (FL) and their niche, however, remains to be elucidated. In this study, we investigated the role of N-cadherin (N-cad) in the maintenance of HSCs during FL hematopoiesis. By using anti-N-cad antibodies (Abs) produced by our laboratory, we detected high N-cad expression in embryonic day 12.5 (E12.5) mouse FL HSCs, but not in E15.5 and E18.5 FL. Immunofluorescence staining revealed that N-cad(+)c-Kit(+) and N-cad(+) endothelial protein C receptor (EPCR)(+) HSCs co-localized with Lyve-1(+) sinusoidal endothelial cells (ECs) in E12.5 FL and that some of these cells also expressed N-cad. However, N-cad(+) HSCs were also observed to detach from the perisinusoidal niche at E15.5 and E18.5, concomitant with a down-regulation of N-cad and an up-regulation of E-cadherin (E-cad) in hepatic cells. Moreover, EPCR(+) long-term (LT)-HSCs were enriched in the N-cad(+)Lin(-)Sca-1(+)c-Kit(+) (LSK) fraction in E12.5 FL, but not in E15.5 or E18.5 FL. In a long-term reconstitution (LTR) activity assay, higher engraftment associated with N-cad(+) LSK cells versus N-cad(-) LSK cells in E12.5 FL when transplanted into lethally irradiated recipient mice. However, the higher engraftment of N-cad(+) LSK cells decreased subsequently in E15.5 and E18.5 FL. It is possible that N-cad expression conferred higher LTR activity to HSCs by facilitating interactions with the perisinusoidal niche, especially at E12.5. The down-regulation of N-cad during FL hematopoiesis may help us better understand the regulation and mobility of HSCs before migration into BM.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. III. Implications for liver pathology

This article discusses on the basis of the ductal plate hypothesis the implication of the concept for several liver abnormalities. The occurrence of ductal plates (DP) during liver growth in childhood would explain the paraportal and parenchymal localizations of von Meyenburg complexes in postnatally developed parts of the liver, and their higher incidence in adulthood versus childhood. It partly clarifies the lack of postnatal intrahepatic bile duct development in Alagille syndrome and the reduced number of portal tracts in this disease. Ductular reactions (DRs) in DP configuration are the predominant type of progenitor cell reaction in fulminant necro-inflammatory liver disease, when lack of sufficient parenchymal regeneration results in liver failure. The concept of dissecting DRs explains the micronodular pattern of advanced biliary and alcoholic cirrhosis. The concept explains the DP patterns of bile ducts in several cases of biliary atresia, with implications for diagnosis and prognosis. The hypothesis also has an impact on concepts about stem/progenitor cells and their niche.