Defining the mechanisms in lineage specification of progenitor cells in the regenerating adult liver

During hepatic disease the liver has the unrivalled ability to regenerate, by activating mature hepatocytes which can divide and thereby reconstitute the functional liver mass. However in the context of chronic hepatocellular disease the liver can regenerate from an endogenous population of hepatic progenitor cells (HPCs). The mechanisms which are involved in the activation and differentiation of these HPCs is not fully understood. To investigate whether there is a differential signalling requirement in HPCs acquiring a biliary versus hepatocellular fate we established in the laboratory two models of chronic liver damage and regeneration, one of which causes hepatocellular death, and results in infiltrating HPCs regenerating hepatocytes, and a second which causes biliary blockage and death, resulting in biliary regeneration. Here we describe how during biliary regeneration the Notch signalling pathway is highly expressed and activated. HPCs cells are consistently associated with a myofibroblast niche which expressed the ligand Jagged-1 at high levels. We have modulated the Notch signalling pathway in both a co-culture system and our models in vivo to demonstrate that Notch signalling is important in the specification of biliary cells, and that inhibition of this pathway both in vitro and in vivo results in the abrogation of biliary commitment. During hepatocellular regeneration we have found that the negative repressor of Notch signalling Numb is highly expressed in tandem with a low expression of the Notch pathway. We suggest that Wnt signalling maintains Numb within these HPCs at a high level and that this, along with stimulation of a hepatocellular programme allows HPCs to exit from a biliary fate and assume a hepatocellular phenotype. Finally we have found that macrophage ingestion of debris promotes the expression of Wnt, and that ablation of these cells results in a phenotypic switch between HPCs assuming a hepatocellular fate and a biliary one

Differentiation of progenitors in the liver:a matter of local choice

The liver is a complex organ that requires multiple rounds of cell fate decision for development and homeostasis throughout the lifetime. During the earliest phases of organogenesis, the liver acquires a separate lineage from the pancreas and the intestine, and subsequently, the liver bud must appropriately differentiate to form metabolic hepatocytes and cholangiocytes for proper hepatic physiology. In addition, throughout life, the liver is bombarded with chemical and pathological insults, which require the activation and correct differentiation of adult progenitor cells. This Review seeks to provide an overview of the complex signaling relationships that allow these tightly regulated processes to occur

In-vehicle nitrogen dioxide concentrations in road tunnels

There is a lack of knowledge regarding in-vehicle concentrations of nitrogen dioxide (NO) during transit through road tunnels in urban environments. Furthermore, previous studies have tended to involve a single vehicle and the range of in-vehicle NO concentrations that vehicle occupants may be exposed to is not well defined. This study describes simultaneous measurements of in-vehicle and outside-vehicle NO concentrations on a route through Sydney, Australia that included several major tunnels, minor tunnels and busy surface roads. Tests were conducted on nine passenger vehicles to assess how vehicle characteristics and ventilation settings affected in-vehicle NO concentrations and the in-vehicle-to-outside vehicle (I/O) concentration ratio. NO was measured directly using a cavity attenuated phase shift (CAPS) technique that gave a high temporal and spatial resolution. In the major tunnels, transit-average in-vehicle NO concentrations were lower than outside-vehicle concentrations for all vehicles with cabin air recirculation either on or off. However, markedly lower I/O ratios were obtained with recirculation on (0.08–0.36), suggesting that vehicle occupants can significantly lower their exposure to NO in tunnels by switching recirculation on. The highest mean I/O ratios for NO were measured in older vehicles (0.35–0.36), which is attributed to older vehicles having higher air exchange rates. The results from this study can be used to inform the design and operation of future road tunnels and modelling of personal exposure to NO

Next generation of ALDH substrates and their potential to study maturational lineage biology in stem and progenitor cells

High aldehyde dehydrogenase (ALDH) activity is a feature of stem cells from normal and cancerous tissues and a reliable universal marker used to isolate them. There are numerous ALDH isoforms with preferred substrate specificity variably expressed depending on tissue, cell type, and organelle and cell status. On the other hand, a given substrate may be metabolized by several enzyme isoforms. Currently ALDH activity is evidenced by using Aldefluor, a fluorescent substrate likely to be metabolized by numerous ALDH isoforms. Therefore, isolation techniques based on ALDH activity detection select a heterogeneous population of stem or progenitor cells. Despite active research in the field, the precise role(s) of different ALDH isoforms in stem cells remains enigmatic. Understanding the metabolic role of different ALDH isoform in the control of stem cell phenotype and cell fate during development, tissue homeostasis, or repair, as well as carcinogenesis, should open perspectives to significant discoveries in tissue biology. In this perspective, novel ALDH substrates are being developed. Here we describe how new substrates could be instrumental for better isolation of cell population with stemness potential and for defining hierarchy of cell populations in tissue. Finally, we speculate on other potential applications

Patient-derived precision cut tissue slices from primary liver cancer as a potential platform for preclinical drug testing

Background: The exploitation of anti-tumour immunity, harnessed through immunomodulatory therapies, has fundamentally changed the treatment of primary liver cancer (PLC). However, this has posed significant challenges in preclinical research. Novel immunologically relevant models for PLC are urgently required to improve the translation from bench to bedside and back, explore and predict effective combinatorial therapies, aid novel drug discovery and develop personalised treatment modalities. / Methods: We used human precision-cut tissue slices (PCTS) derived from resected tumours to create a patient-specific immunocompetent disease model that captures the multifaceted and intricate heterogeneity of the tumour and the tumour microenvironment. Tissue architecture, tumour viability and treatment response to single agent and combination therapies were assessed longitudinally over 8 days of ex vivo culture by histological analysis, detection of proliferation/cell death markers, ATP content via HPLC. Immune cell infiltrate was assessed using PCR and immunofluorescence. Checkpoint receptor expression was quantified via Quantigene RNA assay. / Findings: After optimising the culture conditions, PCTS maintained the original tissue architecture, including tumour morphology, stroma and tumour-infiltrated leukocytes. Moreover, PCTS retained the tumour-specific immunophenotype over time, suggesting the utility of PCTS to investigate immunotherapeutic drug efficacy and identify non-responsiveness. / Interpretation: Here we have characterised the PCTS model and demonstrated its effectiveness as a robust preclinical tool that will significantly support the development of successful (immuno)therapeutic strategies for PLC. / Funding: Foundation for Liver Research, London