Quantitative comparison of presenilin protein expression reveals greater activity of PS2-γ-secretase.

γ-secretase processing of amyloid precursor protein (APP) has long been of interest in the pathological progression of Alzheimer's disease (AD) due to its role in the generation of amyloid-ß. The catalytic component of the enzyme is the presenilins of which there are two homologues, Presenilin-1 (PS1) and Presenilin-2 (PS2). The field has focussed on the PS1 form of this enzyme, as it is typically considered the more active at APP processing. However, much of this work has been completed without appropriate consideration of the specific levels of protein expression of PS1 and PS2. We propose that expression is an important factor in PS1- and PS2-γ-secretase activity, and that when this is considered, PS1 does not have greater activity than PS2. We developed and validated tools for quantitative assessment of PS1 and PS2 protein expression levels to enable the direct comparison of PS in exogenous and endogenous expression systems, in HEK-293 PS1 and/or PS2 knockout cells. We show that exogenous expression of Myc-PS1-NTF is 5.5-times higher than Myc-PS2-NTF. Quantitating endogenous PS protein levels, using a novel PS1/2 fusion standard we developed, showed similar results. When the marked difference in PS1 and PS2 protein levels is considered, we show that compared to PS1-γ-secretase, PS2-γ-secretase has equal or more activity on APP and Notch1. This study has implications for understanding the PS1- and PS2-specific contributions to substrate processing, and their potential influence in AD pathogenesis.

SHP2 inhibitors maintain TGFß signalling through SMURF2 inhibition.

Despite the promising antitumor activity of SHP2 inhibitors in RAS-dependent tumours, overall responses have been limited by their narrow therapeutic window. Like with all MAPK pathway inhibitors, this is likely the result of compensatory pathway activation mechanisms. However, the underlying mechanisms of resistance to SHP2 inhibition remain unknown. The E3 ligase SMURF2 limits TGFß activity by ubiquitinating and targeting the TGFß receptor for proteosome degradation. Using a functional RNAi screen targeting all known phosphatases, we identify that the tyrosine phosphatase SHP2 is a critical regulator of TGFß activity. Specifically, SHP2 dephosphorylates two key residues on SMURF2, resulting in activation of the enzyme. Conversely, SHP2 depletion maintains SMURF2 in an inactive state, resulting in the maintenance of TGFß activity. Furthermore, we demonstrate that depleting SHP2 has significant implications on TGFß-mediated migration, senescence, and cell survival. These effects can be overcome through the use of TGFß-targeted therapies. Consequently, our findings provide a rationale for combining SHP2 and TGFß inhibitors to enhance tumour responses leading to improved patient outcomes.

Single-nucleus RNA sequencing of pre-malignant liver reveals disease-associated hepatocyte state with HCC prognostic potential.

Current approaches to staging chronic liver diseases have limited utility for predicting liver cancer risk. Here, we employed single-nucleus RNA sequencing (snRNA-seq) to characterize the cellular microenvironment of healthy and pre-malignant livers using two distinct mouse models. Downstream analyses unraveled a previously uncharacterized disease-associated hepatocyte (daHep) transcriptional state. These cells were absent in healthy livers but increasingly prevalent as chronic liver disease progressed. Copy number variation (CNV) analysis of microdissected tissue demonstrated that daHep-enriched regions are riddled with structural variants, suggesting these cells represent a pre-malignant intermediary. Integrated analysis of three recent human snRNA-seq datasets confirmed the presence of a similar phenotype in human chronic liver disease and further supported its enhanced mutational burden. Importantly, we show that high daHep levels precede carcinogenesis and predict a higher risk of hepatocellular carcinoma development. These findings may change the way chronic liver disease patients are staged, surveilled, and risk stratified.

Biomechanical assessment of chronic liver injury using quantitative micro-elastography.

Hepatocellular carcinoma is one of the most lethal cancers worldwide, causing almost 700,000 deaths annually. It mainly arises from cirrhosis, which, in turn, results from chronic injury to liver cells and corresponding fibrotic changes. Although it is known that chronic liver injury increases the elasticity of liver tissue, the role of increased elasticity of the microenvironment as a possible hepatocarcinogen is yet to be investigated. One reason for this is the paucity of imaging techniques capable of mapping the micro-scale elasticity variation in liver and correlating that with cancerous mechanisms on the cellular scale. The clinical techniques of ultrasound elastography and magnetic resonance elastography typically do not provide micro-scale resolution, while atomic force microscopy can only assess the elasticity of a limited number of cells. We propose quantitative micro-elastography (QME) for mapping the micro-scale elasticity of liver tissue into images known as micro-elastograms, and therefore, as a technique capable of correlating the micro-environment elasticity of tissue with cellular scale cancerous mechanisms in liver. We performed QME on 13 freshly excised healthy and diseased mouse livers and present micro-elastograms, together with co-registered histology, in four representative cases. Our results indicate a significant increase in the mean (×6.3) and standard deviation (×6.0) of elasticity caused by chronic liver injury and demonstrate that the onset and progression of pathological features such as fibrosis, hepatocyte damage, and immune cell infiltration correlate with localized variations in micro-elastograms.

Targeting the eicosanoid pathway in hepatocellular carcinoma.

Liver cancer has variable incidence worldwide and high mortality. Histologically, the most common subtype of liver cancer is hepatocellular carcinoma (HCC). Approximately 30-40% of HCC patients are diagnosed at an advanced stage, and at present, there are limited treatment options for such patients. The current first-line therapy with tyrosine kinase inhibitors, sorafenib or lenvatinib, prolongs survival by a median of about 2.5-3 months after which the disease normally progresses. Additionally, many patients discontinue the use of tyrosine kinase inhibitors due to toxicity or may not be suitable candidates due to co-morbidity or frailty. It is, therefore, imperative to identify novel therapeutic targets for advanced HCC patients. Persistent injury to the liver as a result of insults such as hepatitis B or C viral (HBV or HCV) infections, alcohol abuse, and non-alcoholic fatty liver disease (NAFLD), results in chronic inflammation, which progresses to hepatic fibrosis and later, cirrhosis, provides the conditions for initiation of HCC. One of the key pathways studied for its role in inflammation and carcinogenesis is the eicosanoid pathway. In this review, we briefly outline the eicosanoid pathway, describe the mechanisms by which some pathway members either facilitate or counter the development of liver diseases, with the focus on NAFLD/hepatic fibrosis/cirrhosis, and HCC. We describe the link between the eicosanoid pathway, inflammation and these liver diseases, and identify components of the eicosanoid pathway that may be used as potential therapeutic targets in HCC.

A novel method to precisely quantify hepatitis B virus covalently closed circular (ccc)DNA formation and maintenance.

Hepatitis B virus (HBV) is the major cause of virus-associated liver disease. Persistent HBV infection is maintained by its episomal genome (covalently closed circular DNA, cccDNA), which acts as a template for viral transcripts. The formation of cccDNA is poorly characterised due to limited ability to quantify it accurately in the presence of replicative intermediates. Here, we describe a novel cccDNA quantification assay (cccDNA inversion quantitative PCR, cinqPCR), which uses restriction enzymes to invert a DNA sequence close to the gap region of Genotype D HBV strains, including the isolate widely used in experimental studies. Importantly, cinqPCR allows simultaneous normalisation to cellular DNA in a single reaction, provides absolute copy numbers without requiring a standard curve, and has high precision, sensitivity, and specificity for cccDNA compared to previous assays. We first established that cinqPCR gives values consistent with classical approaches in both in vitro and in vivo (humanised mice) HBV infections. We then used cinqPCR to find that cccDNA is formed within 12 h post-inoculation (hpi). cccDNA formation slowed by 28 hpi despite de novo synthesis of HBV DNA, indicating inefficient conversion of new viral genomes to cccDNA within infected cells. Finally, we show that cinqPCR can be used as a 96-well screening assay. Thus, we have developed an ideal method for testing current and future anti-cccDNA therapeutics with high precision and sensitivity.

CD147 mediates intrahepatic leukocyte aggregation and determines the extent of liver injury.

BACKGROUND: Chronic inflammation is the driver of liver injury and results in progressive fibrosis and eventual cirrhosis with consequences including both liver failure and liver cancer. We have previously described increased expression of the highly multifunctional glycoprotein CD147 in liver injury. This work describes a novel role of CD147 in liver inflammation and the importance of leukocyte aggregates in determining the extent of liver injury. METHODS: Non-diseased, progressive injury, and cirrhotic liver from humans and mice were examined using a mAb targeting CD147. Inflammatory cell subsets were assessed by multiparameter flow cytometry. RESULTS: In liver injury, we observe abundant, intrahepatic leukocyte clusters defined as ≥5 adjacent CD45+ cells which we have termed "leukocyte aggregates". We have shown that these leukocyte aggregates have a significant effect in determining the extent of liver injury. If CD147 is blocked in vivo, these leukocyte aggregates diminish in size and number, together with a marked significant reduction in liver injury including fibrosis. This is accompanied by no change in overall intrahepatic leukocyte numbers. Further, blocking of aggregation formation occurs prior to an appreciable increase in inflammatory markers or fibrosis. Additionally, there were no observed, "off-target" or unpredicted effects in targeting CD147. CONCLUSION: CD147 mediates leukocyte aggregation which is associated with the development of liver injury. This is not a secondary effect, but a cause of injury as aggregate formation proceeds other markers of injury. Leukocyte aggregation has been previously described in inflammation dating back over many decades. Here we demonstrate that leukocyte aggregates determine the extent of liver injury.