Relation between hepatocyte G1 arrest, impaired hepatic regeneration, and fibrosis in chronic hepatitis C virus infection

Comprehensive Review of Future Liver Remnant (FLR) Assessment and Hypertrophy Techniques Before Major Hepatectomy: How to Assess and Manage the FLR

BACKGROUND

The regenerative capacities of the liver and improvements in surgical techniques have expanded the possibilities of resectability. Liver resection is often the only curative treatment for primary and secondary malignancies, despite the risk of post-hepatectomy liver failure (PHLF). This serious complication (with a 50% mortality rate) can be avoided by better assessment of liver volume and function of the future liver remnant (FLR).

OBJECTIVE

The aim of this review was to understand and assess clinical, biological, and imaging predictors of PHLF risk, as well as the various hypertrophy techniques, to achieve an adequate FLR before hepatectomy.

METHOD

We reviewed the state of the art in liver regeneration and FLR hypertrophy techniques.

RESULTS

The use of new biological scores (such as the aspartate aminotransferase/platelet ratio index + albumin-bilirubin [APRI+ALBI] score), concurrent utilization of 99mTc-mebrofenin scintigraphy (HBS), or dynamic hepatocyte contrast-enhanced MRI (DHCE-MRI) for liver volumetry helps predict the risk of PHLF. Besides portal vein embolization, there are other FLR optimization techniques that have their indications in case of risk of failure (e.g., associating liver partition and portal vein ligation for staged hepatectomy, liver venous deprivation) or in specific situations (transarterial radioembolization).

CONCLUSION

There is a need to standardize volumetry and function measurement techniques, as well as FLR hypertrophy techniques, to limit the risk of PHLF.

Multiple-heated cooking oil promotes early hepatic and renal senescence in adult male rats: the potential regenerative capacity of oleuropein

For economic purposes, cooking oil is repeatedly heated in food preparation, which imposes serious health threats. This study investigated the detrimental effects of multiple-heated cooking oil (MHO) on hepatic and renal tissues with particular focusing on cellular senescence (CS), and the potential regenerative capacity of oleuropein (OLE). Adult male rats were fed MHO-enriched diet for 8 weeks and OLE (50 mg/kg, PO) was administered daily for the last four weeks. Liver and kidney functions and oxidative stress markers were measured. Cell cycle markers p53, p21, cyclin D, and proliferating cell nuclear antigen (PCNA) were evaluated in hepatic and renal tissues. Tumor necrosis factor-α (TNF-α) and Bax were assessed by immunohistochemistry. General histology and collagen deposition were also examined. MHO disturbed hepatic and renal structures and functions. MHO-fed rats showed increased oxidative stress, TNF-α, Bax, and fibrosis in liver and kidney tissues. MHO also enhanced the renal and hepatic expression of p53, p21, cyclin D and PCNA. On the contrary, OLE mitigated MHO-induced oxidative stress, inflammatory burden, apoptotic and fibrotic changes. OLE also suppressed CS and preserved kidney and liver functions. Collectively, OLE displays marked regenerative capacity against MHO-induced hepatic and renal CS, via its potent antioxidant and anti-inflammatory effects.

Exploring the roles of non-coding RNAs in liver regeneration

Liver regeneration (LR) is a complex process encompassing three distinct phases: priming, proliferation phase and restoration, all influenced by various regulatory factors. After liver damage or partial resection, the liver tissue demonstrates remarkable restorative capacity, driven by cellular proliferation and repair mechanisms. The essential roles of non-coding RNAs (ncRNAs), predominantly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNA (circRNA), in regulating LR have been vastly studied. Additionally, the impact of ncRNAs on LR and their abnormal expression profiles during this process have been extensively documented. Mechanistic investigations have revealed that ncRNAs interact with genes involved in proliferation to regulate hepatocyte proliferation, apoptosis and differentiation, along with liver progenitor cell proliferation and migration. Given the significant role of ncRNAs in LR, an in-depth exploration of their involvement in the liver's self-repair capacity can reveal promising therapeutic strategies for LR and liver-related diseases. Moreover, understanding the unique regenerative potential of the adult liver and the mechanisms and regulatory factors of ncRNAs in LR are crucial for improving current treatment strategies and exploring new therapeutic approaches for various liver-related diseases. This review provides a brief overview of the LR process and the ncRNA expression profiles during this process. Furthermore, we also elaborate on the specific molecular mechanisms through which multiple key ncRNAs regulate the LR process. Finally, based on the expression characteristics of ncRNAs and their interactions with proliferation-associated genes, we explore their potential clinical application, such as developing predictive indicators reflecting liver regenerative activity and manipulating LR processes for therapeutic purposes.

Cell senescence in liver diseases: pathological mechanism and theranostic opportunity

The liver is not oblivious to the passage of time, as ageing is a major risk factor for the development of acute and chronic liver diseases. Ageing produces alterations in all hepatic cells, affecting their phenotype and function and worsening the prognosis of liver disease. The ageing process also implies the accumulation of a cellular state characterized by a persistent proliferation arrest and a specific secretory phenotype named cellular senescence. Indeed, senescent cells have key roles in many physiological processes; however, their accumulation owing to ageing or pathological conditions contributes to the damage occurring in chronic diseases. The aim of this Review is to provide an updated description of the pathophysiological events in which hepatic senescent cells are involved and their role in liver disease progression. Finally, we discuss novel geroscience therapies that could be applied to prevent or improve liver diseases and age-mediated hepatic deregulations.

Immunotherapy and liver cancer research trends and the 100 most cited articles: A bibliometric analysis

BACKGROUND

Bibliometric analysis of liver cancer research, particularly in immunotherapy, reveals crucial insights. The US leads in liver cancer mortality but ranks fifth globally.

OBJECTIVE

Scopus database analysis identified 2,349 papers, with the top 100 ranging from 127 to 4,959 citations. Notably, "Microenvironmental Regulation of Tumours Progression and Metastasis" in the Journal of Nature Medicine garnered the highest citations.

METHODS

Journals like the Journal of Hepatology, Hepatology, and Nature Reports Clinical Oncology contributed significantly. Understanding molecular mechanisms and prognostic indicators is paramount for advancing combination therapies.

RESULTS

For better patient outcomes, research trends in liver cancer immunotherapy point to improved treatment protocols, knowledge of the tumor microenvironment, combining therapies, predicting disease course, international cooperation, sophisticated surgical techniques, early detection, oncolytic virotherapy, and patient-centered care.

CONCLUSIONS

This research underscores immunotherapy's pivotal role and encourages further exploration, offering valuable insights into liver cancer treatment trends.

Aging aggravates liver fibrosis through downregulated hepatocyte SIRT1-induced liver sinusoidal endothelial cell dysfunction

BACKGROUND

Aging increases the susceptibility to chronic liver diseases and hastens liver fibrosis deterioration, but the underlying mechanisms remain partially understood. The aim of this study was to investigate the effect of aging and chronic liver diseases on hepatocyte Sirtuin 1 (SIRT1) and LSECs and their contribution to liver fibrosis pathogeneses.

METHODS

Young (8-12 wk) and aged (18-20 mo) mice were subjected to carbon tetrachloride-induced liver fibrosis. Primary HSCs and LSECs were isolated and cocultured for in vitro experiments. Liver tissues and blood samples from healthy controls and patients with liver fibrosis were analyzed.

RESULTS

Downregulated hepatocytes SIRT1 in aged mice increased high mobility group box 1 acetylation, cytoplasmic translocation, and extracellular secretion, causing LSECs dysfunction by means of the toll-like receptor 4/AK strain transforming (AKT)/endothelial nitric oxide synthase pathway, ultimately activating HSCs and increasing susceptibility to liver injury and fibrosis. Adeno-associated virus-mediated overexpression of SIRT1 in hepatocytes suppressed the abovementioned alterations and attenuated carbon tetrachloride-induced liver injury and fibrosis in liver fibrosis mice, and there were no significant differences in liver injury and fibrosis indicators between young and aged mice after SIRT1 overexpression treatment. In vitro experiments demonstrated that SIRT1 overexpression and endothelial nitric oxide synthase agonist YC-1 improved LSECs function and inhibited HSCs activation, mediated by nitric oxide. Similarly, downregulated hepatocytes SIRT1 and LSECs dysfunction were observed in the livers of aged individuals compared to young individuals and were more pronounced in aged patients with liver fibrosis.

CONCLUSIONS

Aging aggravates liver fibrosis through downregulated hepatocytes SIRT1-induced LSECs dysfunction, providing a prospective curative approach for preventing and treating liver fibrosis.

VEGFA mRNA-LNP promotes biliary epithelial cell-to-hepatocyte conversion in acute and chronic liver diseases and reverses steatosis and fibrosis

The liver is known for its remarkable regenerative ability through proliferation of hepatocytes. Yet, during chronic injury or severe hepatocyte death, proliferation of hepatocytes is exhausted. To overcome this hurdle, we propose vascular-endothelial-growth-factor A (VEGFA) as a therapeutic means to accelerate biliary epithelial-cell (BEC)-to-hepatocyte conversion. Investigation in zebrafish establishes that blocking VEGF receptors abrogates BEC-driven liver repair, while VEGFA overexpression promotes it. Delivery of VEGFA via nonintegrative and safe nucleoside-modified mRNA encapsulated into lipid nanoparticles (mRNA-LNPs) in acutely or chronically injured mouse livers induces robust BEC-to-hepatocyte conversion and elimination of steatosis and fibrosis. In human and murine diseased livers, we further identified VEGFA-receptor KDR-expressing BECs associated with KDR-expressing cell-derived hepatocytes. This work defines KDR-expressing cells, most likely being BECs, as facultative progenitors. This study reveals unexpected therapeutic benefits of VEGFA delivered via nucleoside-modified mRNA-LNP, whose safety is widely validated with COVID-19 vaccines, for harnessing BEC-driven repair to potentially treat liver diseases.

Characterisation of forkhead box protein A3 as a key transcription factor for hepatocyte regeneration

Background & Aims

Liver regeneration is vital for the recovery of liver function after injury, yet the underlying mechanism remains to be elucidated. Forkhead box protein A3 (FOXA3), a member of the forkhead box family, plays important roles in endoplasmic reticulum stress sensing, and lipid and glucose homoeostasis, yet its functions in liver regeneration are unknown.

Methods

Here, we explored whether Foxa3 regulates liver regeneration via acute and chronic liver injury mice models. We further characterised the molecular mechanism by chromatin immunoprecipitation sequencing and rescue experiments in vivo and in vitro. Then, we assessed the impact of Foxa3 pharmacological activation on progression and termination of liver regeneration. Finally, we confirmed the Foxa3-Cebpb axis in human liver samples.

Results

Foxa3 is dominantly expressed in hepatocytes and cholangiocytes and is induced upon partial hepatectomy (PH) or carbon tetrachloride (CCl4) administration. Foxa3 deficiency in mice decreased cyclin gene levels and delayed liver regeneration after PH, or acute or chronic i.p. CCl4 injection. Conversely, hepatocyte-specific Foxa3 overexpression accelerated hepatocytes proliferation and attenuated liver damage in an CCl4-induced acute model. Mechanistically, Foxa3 directly regulates Cebpb transcription, which is involved in hepatocyte division and apoptosis both in vivo and in vitro. Of note, Cebpb overexpression in livers of Foxa3-deficient mice rescued their defects in cell proliferation and regeneration upon CCl4 treatment. In addition, pharmacological induction of Foxa3 via cardamonin speeded up hepatocyte proliferation after PH, without interfering with liver regeneration termination. Finally, Cebpb and Ki67 levels had a positive correlation with Foxa3 expression in human chronic disease livers.

Conclusions

These data characterise Foxa3 as a vital regulator of liver regeneration, which may represent an essential factor to maintain liver mass after liver injury by governing Cebpb transcription.

Impact and Implications

Liver regeneration is vital for the recovery of liver function after chemical insults or hepatectomy, yet the underlying mechanism remains to be elucidated. Herein, via in vitro and in vivo models and analysis, we demonstrated that Forkhead box protein A3 (FOXA3), a Forkhead box family member, maintained normal liver regeneration progression by governing Cebpb transcription and proposed cardamonin as a lead compound to induce Foxa3 and accelerate liver repair, which signified that FOXA3 may be a potential therapeutic target for further preclinical study on treating liver injury.

"Small Hepatocytes" in the Liver

Mature hepatocytes (MHs) in an adult rodent liver are categorized into the following three subpopulations based on their proliferative capability: type I cells (MH-I), which are committed progenitor cells that possess a high growth capability and basal hepatocytic functions; type II cells (MH-II), which possess a limited proliferative capability; and type III cells (MH-III), which lose the ability to divide (replicative senescence) and reach the final differentiated state. These subpopulations may explain the liver's development and growth after birth. Generally, small-sized hepatocytes emerge in mammal livers. The cells are characterized by being morphologically identical to hepatocytes except for their size, which is substantially smaller than that of ordinary MHs. We initially discovered small hepatocytes (SHs) in the primary culture of rat hepatocytes. We believe that SHs are derived from MH-I and play a role as hepatocytic progenitors to supply MHs. The population of MH-I (SHs) is distributed in the whole lobules, a part of which possesses a self-renewal capability, and decreases with age. Conversely, injured livers of experimental models and clinical cases showed the emergence of SHs. Studies demonstrate the involvement of SHs in liver regeneration. SHs that appeared in the injured livers are not a pure population but a mixture of two distinct origins, MH-derived and hepatic-stem-cell-derived cells. The predominant cell-derived SHs depend on the proliferative capability of the remaining MHs after the injury. This review will focus on the SHs that appeared in the liver and discuss the significance of SHs in liver regeneration.

Contribution of viral and bacterial infections to senescence and immunosenescence

Cellular senescence is a key biological process characterized by irreversible cell cycle arrest. The accumulation of senescent cells creates a pro-inflammatory environment that can negatively affect tissue functions and may promote the development of aging-related diseases. Typical biomarkers related to senescence include senescence-associated β-galactosidase activity, histone H2A.X phosphorylation at serine139 (γH2A.X), and senescence-associated heterochromatin foci (SAHF) with heterochromatin protein 1γ (HP-1γ protein) Moreover, immune cells undergoing senescence, which is known as immunosenescence, can affect innate and adaptative immune functions and may elicit detrimental effects over the host's susceptibility to infectious diseases. Although associations between senescence and pathogens have been reported, clear links between both, and the related molecular mechanisms involved remain to be determined. Furthermore, it remains to be determined whether infections effectively induce senescence, the impact of senescence and immunosenescence over infections, or if both events coincidently share common molecular markers, such as γH2A.X and p53. Here, we review and discuss the most recent reports that describe cellular hallmarks and biomarkers related to senescence in immune and non-immune cells in the context of infections, seeking to better understand their relationships. Related literature was searched in Pubmed and Google Scholar databases with search terms related to the sections and subsections of this review.

VEGFA mRNA-LNP promotes biliary epithelial cell-to-hepatocyte conversion in acute and chronic liver diseases and reverses steatosis and fibrosis

The liver is known for its remarkable regenerative ability through proliferation of hepatocytes. Yet, during chronic injury or severe hepatocyte death, proliferation of hepatocytes is exhausted. To overcome this hurdle, we propose vascular-endothelial-growth-factor A (VEGFA) as a therapeutic means to accelerate biliary epithelial cell (BEC)-to-hepatocyte conversion. Investigation in zebrafish establishes that blocking VEGF receptors abrogates BEC-driven liver repair, while VEGFA overexpression promotes it. Delivery of VEGFA via non-integrative and safe nucleoside-modified mRNA encapsulated into lipid-nanoparticles (mRNA-LNP) in acutely or chronically injured mouse livers induces robust BEC-to-hepatocyte conversion and reversion of steatosis and fibrosis. In human and murine diseased livers, we further identified VEGFA-receptor KDR-expressing BECs associated with KDR-expressing cell-derived hepatocytes. This defines KDR-expressing cells, most likely being BECs, as facultative progenitors. This study reveals novel therapeutic benefits of VEGFA delivered via nucleoside-modified mRNA-LNP, whose safety is widely validated with COVID-19 vaccines, for harnessing BEC-driven repair to potentially treat liver diseases.

Highlights

Complementary mouse and zebrafish models of liver injury demonstrate the therapeutic impact of VEGFA-KDR axis activation to harness BEC-driven liver regeneration.VEGFA mRNA LNPs restore two key features of the chronic liver disease in humans such as steatosis and fibrosis.Identification in human cirrhotic ESLD livers of KDR-expressing BECs adjacent to clusters of KDR+ hepatocytes suggesting their BEC origin.KDR-expressing BECs may represent facultative adult progenitor cells, a unique BEC population that has yet been uncovered.

Bipotent transitional liver progenitor cells contribute to liver regeneration

Following severe liver injury, when hepatocyte-mediated regeneration is impaired, biliary epithelial cells (BECs) can transdifferentiate into functional hepatocytes. However, the subset of BECs with such facultative tissue stem cell potential, as well as the mechanisms enabling transdifferentiation, remains elusive. Here we identify a transitional liver progenitor cell (TLPC), which originates from BECs and differentiates into hepatocytes during regeneration from severe liver injury. By applying a dual genetic lineage tracing approach, we specifically labeled TLPCs and found that they are bipotent, as they either differentiate into hepatocytes or re-adopt BEC fate. Mechanistically, Notch and Wnt/β-catenin signaling orchestrate BEC-to-TLPC and TLPC-to-hepatocyte conversions, respectively. Together, our study provides functional and mechanistic insights into transdifferentiation-assisted liver regeneration.

Role of Hepatocyte Senescence in the Activation of Hepatic Stellate Cells and Liver Fibrosis Progression

Hepatocyte senescence is associated with liver fibrosis. However, the possibility of a direct, causal relation between hepatocyte senescence and hepatic stellate cell (HSC) activation was the subject of this study. Liver biopsy specimens obtained from 50 patients with non-alcoholic fatty liver disease and a spectrum of liver fibrosis stages were stained for p16, αSMA, and picrosirius red (PSR). Primary human HSCs were cultured in conditioned media derived from senescent or control HepG2 cells. Expression of inflammatory and fibrogenic genes in HSCs cultured in conditioned media were studied using RT-PCR. ELISAs were undertaken to measure factors known to activate HSCs in the conditioned media from senescent and control HepG2 cells and serum samples from healthy volunteers or patients with biopsy-proven cirrhosis. There was a strong association between proportion of senescent hepatocytes and hepatic stellate cell activation. Both proportion of hepatocyte senescence and hepatic stellate cell activation were closely associated with fibrosis stage. Inflammatory and fibrogenic genes were up-regulated significantly in HSCs cultured in conditioned media from senescent HepG2 cells compared with control HepG2 cells. PDGF levels were significantly higher in the conditioned media from senescent hepatocytes than control HepG2-conditioned media, and in serum samples from patients with cirrhosis than healthy volunteers. In conclusion, this ‘proof of concept’ study revealed activation of human HSCs by media from senescent HepG2 cells, indicating direct involvement of factors secreted by senescent hepatocytes in liver fibrosis.

The CD38 glycohydrolase and the NAD sink: implications for pathological conditions

Nicotinamide adenine dinucleotide (NAD) acts as a cofactor in several oxidation-reduction (redox) reactions and is a substrate for a number of nonredox enzymes. NAD is fundamental to a variety of cellular processes including energy metabolism, cell signaling, and epigenetics. NAD homeostasis appears to be of paramount importance to health span and longevity, and its dysregulation is associated with multiple diseases. NAD metabolism is dynamic and maintained by synthesis and degradation. The enzyme CD38, one of the main NAD-consuming enzymes, is a key component of NAD homeostasis. The majority of CD38 is localized in the plasma membrane with its catalytic domain facing the extracellular environment, likely for the purpose of controlling systemic levels of NAD. Several cell types express CD38, but its expression predominates on endothelial cells and immune cells capable of infiltrating organs and tissues. Here we review potential roles of CD38 in health and disease and postulate ways in which CD38 dysregulation causes changes in NAD homeostasis and contributes to the pathophysiology of multiple conditions. Indeed, in animal models the development of infectious diseases, autoimmune disorders, fibrosis, metabolic diseases, and age-associated diseases including cancer, heart disease, and neurodegeneration are associated with altered CD38 enzymatic activity. Many of these conditions are modified in CD38-deficient mice or by blocking CD38 NADase activity. In diseases in which CD38 appears to play a role, CD38-dependent NAD decline is often a common denominator of pathophysiology. Thus, understanding dysregulation of NAD homeostasis by CD38 may open new avenues for the treatment of human diseases.

Hepatocyte generation in liver homeostasis, repair, and regeneration

The liver has remarkable capability to regenerate, employing mechanism to ensure the stable liver-to-bodyweight ratio for body homeostasis. The source of this regenerative capacity has received great attention over the past decade yet still remained controversial currently. Deciphering the sources for hepatocytes provides the basis for understanding tissue regeneration and repair, and also illustrates new potential therapeutic targets for treating liver diseases. In this review, we describe recent advances in genetic lineage tracing studies over liver stem cells, hepatocyte proliferation, and cell lineage conversions or cellular reprogramming. This review will also evaluate the technical strengths and limitations of methods used for studies on hepatocyte generation and cell fate plasticity in liver homeostasis, repair and regeneration.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

PI3K/AKT/mTOR Signaling Pathway Is Required for JCPyV Infection in Primary Astrocytes

Astrocytes are a main target of JC polyomavirus (JCPyV) in the central nervous system (CNS), where the destruction of these cells, along with oligodendrocytes, leads to the fatal disease progressive multifocal leukoencephalopathy (PML). There is no cure currently available for PML, so it is essential to discover antivirals for this aggressive disease. Additionally, the lack of a tractable in vivo models for studying JCPyV infection makes primary cells an accurate alternative for elucidating mechanisms of viral infection in the CNS. This research to better understand the signaling pathways activated in response to JCPyV infection reveals and establishes the importance of the PI3K/AKT/mTOR signaling pathway in JCPyV infection in primary human astrocytes compared to transformed cell lines. Using RNA sequencing and chemical inhibitors to target PI3K, AKT, and mTOR, we have demonstrated the importance of this signaling pathway in JCPyV infection of primary astrocytes not observed in transformed cells. Collectively, these findings illuminate the potential for repurposing drugs that are involved with inhibition of the PI3K/AKT/mTOR signaling pathway and cancer treatment as potential therapeutics for PML, caused by this neuroinvasive virus.

Cellular senescence in liver fibrosis: Implications for age-related chronic liver diseases

INTRODUCTION

New insights indicate a causative link between cellular senescence and liver fibrosis. Senescent hepatic stellate cells (HSCs) facilitate fibrosis resolution, while senescence in hepatocytes and cholangiocytes acts as a potent mechanism driving liver fibrogenesis. In many clinical studies, telomeres and mitochondrial DNA contents, which are both aging biomarkers, were reportedly associated with a degree of liver fibrosis in patients with chronic liver diseases (CLDs); this highlights their potential as biomarkers for liver fibrogenesis. A deeper understanding of mechanisms underlying multi-step progression of senescence may yield new therapeutic strategies for age-related chronic liver pathologies.

AREAS COVERED

This review examines the recent findings from preclinical and clinical studies on mechanisms of senescence in liver fibrogenesis and its involvement in liver fibrosis. A comprehensive literature search in electronic databases consisting of PubMed and Scopus from inception to 31 August 2021 was performed.

EXPERT OPINION

Cellular senescence has diagnostic, prognostic, and therapeutic potential in progressive liver complications, especially liver fibrosis. Stimulating or reinforcing the immune response against senescent cells may be a promising and forthright biotherapeutic strategy. This approach will need a deeper understanding of the immune system's ability to eliminate senescent cells and the molecular and cellular mechanisms underlying this process.

Mechanism of Hepatitis B Virus cccDNA Formation

Hepatitis B virus (HBV) remains a major medical problem affecting at least 257 million chronically infected patients who are at risk of developing serious, frequently fatal liver diseases. HBV is a small, partially double-stranded DNA virus that goes through an intricate replication cycle in its native cellular environment: human hepatocytes. A critical step in the viral life-cycle is the conversion of relaxed circular DNA (rcDNA) into covalently closed circular DNA (cccDNA), the latter being the major template for HBV gene transcription. For this conversion, HBV relies on multiple host factors, as enzymes capable of catalyzing the relevant reactions are not encoded in the viral genome. Combinations of genetic and biochemical approaches have produced findings that provide a more holistic picture of the complex mechanism of HBV cccDNA formation. Here, we review some of these studies that have helped to provide a comprehensive picture of rcDNA to cccDNA conversion. Mechanistic insights into this critical step for HBV persistence hold the key for devising new therapies that will lead not only to viral suppression but to a cure.

Pre-Senescence Induction in Hepatoma Cells Favors Hepatitis C Virus Replication and Can Be Used in Exploring Antiviral Potential of Histone Deacetylase Inhibitors

Recent evidence suggests that fibrotic liver injury in patients with chronic hepatitis C correlates with cellular senescence in damaged liver tissue. However, it is still unclear how senescence can affect replication of the hepatitis C virus (HCV). In this work, we report that an inhibitor of cyclin-dependent kinases 4/6, palbociclib, not only induced in hepatoma cells a pre-senescent cellular phenotype, including G1 arrest in the cell cycle, but also accelerated viral replicon multiplication. Importantly, suppression of HCV replication by direct acting antivirals (DAAs) was barely affected by pre-senescence induction, and vice versa, the antiviral activities of host-targeting agents (HTAs), such as inhibitors of human histone deacetylases (HDACi), produced a wide range of reactions-from a dramatic reduction to a noticeable increase. It is very likely that under conditions of the G1 arrest in the cell cycle, HDACi exhibit their actual antiviral potency, since their inherent anticancer activity that complicates the interpretation of test results is minimized.

Hepatitis B virus cccDNA is formed through distinct repair processes of each strand

Hepatitis B virus (HBV) is a highly contagious pathogen that afflicts over a third of the world’s population, resulting in close to a million deaths annually. The formation and persistence of the HBV covalently closed circular DNA (cccDNA) is the root cause of HBV chronicity. However, the detailed molecular mechanism of cccDNA formation from relaxed circular DNA (rcDNA) remains opaque. Here we show that the minus and plus-strand lesions of HBV rcDNA require different sets of human repair factors in biochemical repair systems. We demonstrate that the plus-strand repair resembles DNA lagging strand synthesis, and requires proliferating cell nuclear antigen (PCNA), the replication factor C (RFC) complex, DNA polymerase delta (POLδ), flap endonuclease 1 (FEN-1), and DNA ligase 1 (LIG1). Only FEN-1 and LIG1 are required for the repair of the minus strand. Our findings provide a detailed mechanistic view of how HBV rcDNA is repaired to form cccDNA in biochemical repair systems.

HBV covalently closed circular DNA (cccDNA) enables and persists in chronic infection, but the molecular mechanism of its formation is unclear. Here, Wei and Ploss elucidate the detailed kinetics and biochemical steps by which the relaxed circular DNA is converted into cccDNA.

Cellular Senescence in Liver Disease and Regeneration

Cellular senescence is an irreversible cell cycle arrest implemented by the cell as a result of stressful insults. Characterized by phenotypic alterations, including secretome changes and genomic instability, senescence is capable of exerting both detrimental and beneficial processes. Accumulating evidence has shown that cellular senescence plays a relevant role in the occurrence and development of liver disease, as a mechanism to contain damage and promote regeneration, but also characterizing the onset and correlating with the extent of damage. The evidence of senescent mechanisms acting on the cell populations of the liver will be described including the role of markers to detect cellular senescence. Overall, this review intends to summarize the role of senescence in liver homeostasis, injury, disease, and regeneration.

RNA-seq Used to Explore circRNA Expression and Identify Key circRNAs During the DNA Synthesis Phase of Mice Liver Regeneration

The liver has an excellent capacity for regeneration when faced with external injury and the damage differs from that of other organs in the body. Our aim was to identify the role of circular RNA (circRNA) during the DNA synthesis phase (36 h) of mice liver regeneration. High-throughput RNA sequencing was conducted to explore circRNA and messenger RNA (mRNA) expression in three pairs of mice liver tissue at 0 and 36 h after 2/3 partial hepatectomy. One hundred differentially expressed circRNAs were detected, including 66 upregulated and 34 downregulated circRNAs. We also explored 2483 differentially expressed mRNAs, including 1422 upregulated and 1061 downregulated mRNAs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes indicated that cell cycle regulation, material metabolism, and multiple classical pathways were involved in the DNA synthesis process. A competing endogenous RNA (ceRNA) network containing 5 circRNAs, 28 target genes, and 533 microRNAs (miRNAs) was constructed, and we selected the top 5 miRNAs to map it. Potential key circRNAs were validated with the quantitative real-time PCR technique and their regeneration curves, including consecutive time points, were produced. Finally, a cell counting kit-8 assay on key circRNAs of ceRNA network was performed to further confirm their roles in the DNA synthesis phase of liver regeneration. This study provides a circRNA expression profile for liver regeneration and contributes valuable information for future research.

Epithelial Plasticity during Liver Injury and Regeneration

Following injury, the liver's epithelial cells regenerate efficiently with rapid proliferation of hepatocytes and biliary cells. However, when proliferation of resident epithelial cells is impaired, alternative regeneration mechanisms can occur. Intricate lineage-tracing strategies and experimental models of regenerative stress have revealed a degree of plasticity between hepatocytes and biliary cells. New technologies such as single-cell omics, in combination with functional studies, will be instrumental to uncover the remaining unknowns in the field. In this review, we evaluate the experimental and clinical evidence for epithelial plasticity in the liver and how this influences the development of therapeutic strategies for chronic liver disease.

Radiological Simultaneous Portohepatic Vein Embolization (RASPE) Before Major Hepatectomy: A Better Way to Optimize Liver Hypertrophy Compared to Portal Vein Embolization

OBJECTIVE

The aim of this retrospective study was to compare portal vein embolization (PVE) and radiologica simultaneous portohepatic vein embolization (RASPE) for future liver remnant (FLR) growth in terms of feasibility, safety, and efficacy.

SUMMARY OF BACKGROUND DATA

After portal vein embolization (PVE), 15% of patients remain ineligible for hepatic resection due to insufficient hypertrophy of the FLR. RASPE has been proposed to induce FLR growth.

MATERIALS AND METHODS

Between 2016 and 2018, 73 patients were included in the study. RASPE was proposed for patients with a ratio of FLR to total liver volume (FLR/TLV) of <25% (RASPE group). This group was compared to patients who underwent PVE for a FLR/TLV <30% (PVE group). Patients in the 2 groups were matched for age, sex, type of tumor, and number of chemotherapy treatments. FLR was assessed by computed tomography before and 4 weeks after the procedure.

RESULTS

The technical success rate in both groups was 100%. Morbidity post-embolization, and the time between embolization and surgery were similar between the groups. In the PVE group, the FLR/TLV ratio before embolization was 31.03% (range: 18.33%-38.95%) versus 22.91% (range: 16.55-32.15) in the RASPE group (P < 0.0001). Four weeks after the procedure, the liver volume increased by 28.98% (range: 9.31%-61.23%) in the PVE group and by 61.18% (range: 23.18%-201.56%) in the RASPE group (P < 0.0001). Seven patients in the PVE group, but none in the RASPE group, had postoperative liver failure (P = 0.012).

CONCLUSIONS

RASPE can be considered as "radiological associating liver partition and portal vein ligation for staged hepatectomy." RASPE induced safe and profound growth of the FLR and was more efficient than PVE. RASPE also allowed for extended hepatectomy with less risk of post-operative liver failure.

Single-cell technologies in hepatology: new insights into liver biology and disease pathogenesis

Liver disease is a major global health-care problem, affecting an estimated 844 million people worldwide. Despite this substantial burden, therapeutic options for liver disease remain limited, in part owing to a paucity of detailed analyses defining the cellular and molecular mechanisms that drive these conditions in humans. Single-cell transcriptomic technologies are transforming our understanding of cellular diversity and function in health and disease. In this Review, we discuss how these technologies have been applied in hepatology, advancing our understanding of cellular heterogeneity and providing novel insights into fundamental liver biology such as the metabolic zonation of hepatocytes, endothelial cells and hepatic stellate cells, and the cellular mechanisms underpinning liver regeneration. Application of these methodologies is also uncovering critical pathophysiological changes driving disease states such as hepatic fibrosis, where distinct populations of macrophages, endothelial cells and mesenchymal cells reside within a spatially distinct fibrotic niche and interact to promote scar formation. In addition, single-cell approaches are starting to dissect key cellular and molecular functions in liver cancer. In the near future, new techniques such as spatial transcriptomics and multiomic approaches will further deepen our understanding of disease pathogenesis, enabling the identification of novel therapeutic targets for patients across the spectrum of liver diseases.

Complement C1q mediates the expansion of periportal hepatic progenitor cells in senescence-associated inflammatory liver

Most hepatocellular carcinomas (HCCs) develop in patients with chronic hepatitis, which creates a microenvironment for the growth of hepatic progenitor cells (HPCs) at the periportal area and subsequent development of HCCs. We investigated the signal from the inflammatory liver for this pathogenic process in the hepatic conditional β-catenin knockout mouse model. Senescent β-catenin-depleted hepatocytes in aged mice create an inflammatory microenvironment that stimulates periportal HPC expansion but arrests differentiation, which predisposes mice to the development of liver tumors. The release of complement C1q from macrophages in the inflammatory niche was identified as the unorthodox signal that activated the β-catenin pathway in periportal HPCs and was responsible for their expansion and de-differentiation. C1q inhibitors blocked the β-catenin pathway in both the expanding HPCs and the liver tumors but spared its orthodox pathway in pericentral normal hepatocytes. This mechanism has been validated in human liver specimens from patients with chronic hepatitis. Taken together, these results demonstrate that C1q- mediated activation of β-catenin pathway in periportal HPCs is a previously unrecognized mechanism for replenishing hepatocytes in the inflammatory liver and, if unchecked, for promoting hepatocarcinogenesis. C1q may become a new target for blocking carcinogenesis in patients with chronic hepatitis.

A genetic system for tissue-specific inhibition of cell proliferation

Cellular proliferation is a basic process during organ development, tissue homeostasis and disease progression. Likewise, after injury typically multiple cell lineages respond to various cues and proliferate to initiate repair and/or remodeling of the injured tissue. Unravelling the specific role of proliferation of one cell type and its lineage in the context of the whole organism during tissue regeneration and/or disease progression would provide valuable information on these processes. Here, we report a new genetic system that allows cell proliferation to be inhibited in a tissue-specific manner. We generated Cre- or Dre-inducible p21-GFP (ip21-GFP) transgenic mice that enable experimentally induced permanent cell cycle arrest of specific cell lineages of interest, while genetically marking these cells. This system allows for the inhibition of pathogenic cell proliferation. We found that cardiac fibroblast proliferation inhibition significantly reduced scar formation, and promoted neovascularization and cardiomyocyte survival. Additionally, we found that inhibition of one type of cell proliferation (namely, hepatocytes) induces the lineage conversion of another type cells (i.e. ductal cells) during tissue regeneration. These results validate the use of ip21-GFP mice as a new genetic tool for cell lineage-specific inhibition of cell proliferation in vivo.

JC Polyomavirus Infection Reveals Delayed Progression of the Infectious Cycle in Normal Human Astrocytes

JC polyomavirus (JCPyV) infects 50 to 80% of the population and is the causative agent of a fatal demyelinating disease of the central nervous system (CNS). JCPyV presents initially as a persistent infection in the kidneys of healthy people, but during immunosuppression, the virus can reactivate and cause progressive multifocal leukoencephalopathy (PML). Within the CNS, JCPyV predominately targets two cell types, oligodendrocytes and astrocytes. Until recently, the role of astrocytes has been masked by the pathology in the myelin-producing oligodendrocytes, which are lytically destroyed by the virus. To better understand how astrocytes are impacted during JCPyV infection, the temporal regulation and infectious cycle of JCPyV were analyzed in primary normal human astrocytes (NHAs). Previous research to define the molecular mechanisms underlying JCPyV infection has mostly relied on the use of cell culture models, such as SVG-A cells (SVGAs), an immortalized, mixed population of glial cells transformed with simian virus 40 (SV40) T antigen. However, SVGAs present several limitations due to their immortalized characteristics, and NHAs represent an innovative approach to study JCPyV infection in vitro Using infectivity assays, quantitative PCR, and immunofluorescence assay approaches, we have further characterized JCPyV infectivity in NHAs. The JCPyV infectious cycle is significantly delayed in NHAs, and the expression of SV40 T antigen alters the cellular environment, which impacts viral infection in immortalized cells. This research establishes a foundation for the use of primary NHAs in future studies and will help unravel the role of astrocytes in PML pathogenesis.IMPORTANCE Animal models are crucial in advancing biomedical research and defining the pathogenesis of human disease. Unfortunately, not all diseases can be easily modeled in a nonhuman host or such models are cost prohibitive to generate, including models for the human-specific virus JC polyomavirus (JCPyV). JCPyV infects most of the population but can cause a rare, fatal disease, progressive multifocal leukoencephalopathy (PML). There have been considerable advancements in understanding the molecular mechanisms of JCPyV infection, but this has mostly been limited to immortalized cell culture models. In contrast, PML pathogenesis research has been greatly hindered because of the lack of an animal model. We have further characterized JCPyV infection in primary human astrocytes to better define the infectious process in a primary cell type. Albeit a cell culture model, primary astrocytes may better recapitulate human disease, are easier to maintain than other primary cells, and are less expensive than using an animal model.

Asbestos and Intrahepatic Cholangiocarcinoma

The link between asbestos exposure and the onset of thoracic malignancies is well established. However epidemiological studies have provided evidences that asbestos may be also involved in the development of gastrointestinal tumors, including intrahepatic cholangiocarcinoma (ICC). In line with this observation, asbestos fibers have been detected in the liver of patients with ICC. Although the exact mechanism still remains unknown, the presence of asbestos fibers in the liver could be explained in the light of their translocation pathway following ingestion/inhalation. In the liver, thin and long asbestos fibers could remain trapped in the smaller bile ducts, particularly in the stem cell niche of the canals of Hering, and exerting their carcinogenic effect for a long time, thus inducing hepatic stem/progenitor cells (HpSCs) malignant transformation. In this scenario, chronic liver damage induced by asbestos fibers over the years could be seen as a classic model of stem cell-derived carcinogenesis, where HpSC malignant transformation represents the first step of this process. This phenomenon could explain the recent epidemiological findings, where asbestos exposure seems mainly involved in ICC, rather than extrahepatic cholangiocarcinoma, development.

Cell Plasticity in Liver Regeneration

The liver, whose major functional cell type is the hepatocyte, is a peculiar organ with remarkable regenerative capacity. The widely held notion that hepatic progenitor cells contribute to injury-induced liver regeneration has long been debated. However, multiple lines of evidence suggest that the plasticity of differentiated cells is a major mechanism for the cell source in injury-induced liver regeneration. Investigating cell plasticity could potentially expand our understanding of liver physiology and facilitate the development of new therapies for liver diseases. In this review, we summarize the cell sources for hepatocyte regeneration and the clinical relevance of cell plasticity for human liver diseases. We focus on mechanistic insights on the injury-induced cell plasticity of hepatocytes and biliary epithelial cells and discuss future directions for investigation. Specifically, we propose the notion of 'reprogramming competence' to explain the plasticity of differentiated hepatocytes.

The Alpha-1 Antitrypsin Polymer Load Correlates With Hepatocyte Senescence, Fibrosis Stage and Liver-Related Mortality

Background

Alpha-1 antitrypsin deficiency (AATD) is an important, inherited cause of chronic liver disease. Marked variation in fibrosis stages in patients with homozygous deficiency and those factors that determine whether heterozygous carriers develop liver fibrosis, remain unexplained. Murine studies implicate polymerized alpha-1 antitrypsin (AAT) within hepatocytes as pathogenic.

Aims and Methods

The relationship between the quantity of polymerized AAT within hepatocytes (polymer load), stage of hepatic fibrosis and liver-related clinical outcomes (death, evolution to hepatocellular carcinoma, or need for liver transplantation) were investigated using liver tissue from 92 patients at first presentation with either homozygous or heterozygous AATD. Further tissue-based studies were undertaken to determine if polymerized AAT was associated with failure of cell cycle progression, accelerated aging or hepatocyte senescence by immunohistochemical analysis.

Results

The AAT polymer load correlated closely with hepatic fibrosis stage and long-term clinical outcome, independent of homozygous or heterozygous status. AAT polymers within hepatocytes correlated closely with failure of cell cycle progression assessed using cell cycle phase markers, accelerated aging manifest as shortened telomeres and other markers consistent with hepatocyte senescence manifest as the presence of nuclear p21 expression and enlarged nuclei. The proportion of p21 positive hepatocytes or hepatocytes with enlarged nuclei correlated with hepatic fibrosis stage and the long-term clinical outcome.

Conclusion

These data suggest that accumulation of AAT polymers within hepatocytes drives senescence. Quantitation of both the AAT polymer load or hepatocyte senescence markers correlated with hepatic fibrosis stage and the long-term clinical outcome. Either or both could be considered markers of disease severity and treatment response in clinical trials.

Cholest-4,6-Dien-3-One Promote Epithelial-To-Mesenchymal Transition (EMT) in Biliary Tree Stem/Progenitor Cell Cultures In Vitro

Human biliary tree stem/progenitor cells (hBTSCs), reside in peribiliary glands, are mainly stimulated by primary sclerosing cholangitis (PSC) and cholangiocarcinoma. In these pathologies, hBTSCs displayed epithelial-to-mesenchymal transition (EMT), senescence characteristics, and impaired differentiation. Here, we investigated the effects of cholest-4,6-dien-3-one, an oxysterol involved in cholangiopathies, on hBTSCs biology. hBTSCs were isolated from donor organs, cultured in self-renewal control conditions, differentiated in mature cholangiocytes by specifically tailored medium, or exposed for 10 days to concentration of cholest-4,6-dien-3-one (0.14 mM). Viability, proliferation, senescence, EMT genes expression, telomerase activity, interleukin 6 (IL6) secretion, differentiation capacity, and HDAC6 gene expression were analyzed. Although the effect of cholest-4,6-dien-3-one was not detected on hBTSCs viability, we found a significant increase in cell proliferation, senescence, and IL6 secretion. Interestingly, cholest-4.6-dien-3-one impaired differentiation in mature cholangiocytes and, simultaneously, induced the EMT markers, significantly reduced the telomerase activity, and induced HDAC6 gene expression. Moreover, cholest-4,6-dien-3-one enhanced bone morphogenic protein 4 (Bmp-4) and sonic hedgehog (Shh) pathways in hBTSCs. The same pathways activated by human recombinant proteins induced the expression of EMT markers in hBTSCs. In conclusion, we demonstrated that chronic exposition of cholest-4,6-dien-3-one induced cell proliferation, EMT markers, and senescence in hBTSC, and also impaired the differentiation in mature cholangiocytes.

Cholangiocytes: No Longer Cinderellas to the Hepatic Regenerative Response

Biliary ductal cells proliferate from the portal areas of chronically damaged livers, but their significance to regeneration has been controversial. A recent article in Nature by Raven et al. (2017) now shows that blocking hepatocyte replication is essential for the hepatic differentiation of ductular cells after liver damage.

Relationship between Telomere Maintenance and Liver Disease

Previous studies have established a correlation between increasing chronological age and risk of cirrhosis. This pattern raised interest in the role of telomeres and the telomerase complex in the pathogenesis of liver fibrosis and cirrhosis. This review aims to summarize and analyze the current understanding of telomere regulation in hepatocytes and lymphocytes and how this ultimately relates to the development of liver fibrosis. Notably, in chronic viral hepatitis, telomere shortening in hepatocytes and lymphocytes occurs in such a way that may promote further viral replication while also leading to liver damage. However, while telomere shortening occurs in both hepatocytes and lymphocytes and ultimately results in cellular death, the mechanisms of telomere loss appear to be initiated by independent processes. The understanding of telomere maintenance on a hepatic and immune system level in both viral and non-viral etiologies of cirrhosis may open doors to novel therapeutic strategies.

The role of hepatic progenitor cells in predicting response to therapy in Egyptian patients with chronic hepatitis C, genotype 4

Background

Interferon therapy is used as a line of treatment of chronic hepatitis C virus (HCV) in several areas of the world including Egypt.

Objective

Our aim was to investigate the value of hepatic progenitor cells (HPCs) in predicting response of patients with chronic HCV, genotype 4 to pegylated interferon (PEGIFN) plus ribavirin (RBV) therapy.

Methods

Pre-treatment liver biopsies obtained from 110 patients with chronic HCV, genotype 4 were examined immunohistochemically for HPCs using cytokeratin19. The mean number of HPCs as ductular reaction (DR) and as isolated progenitor cells (IPCs) was counted in each case. The patients were classified into: those with sustained virological response (SVR) and those who did not achieve SVR. The results were compared between the two groups. Also, the relationships between HPCs and other clinico-pathologic variables were estimated using multivariate analysis.

Results

The mean number of HPCs was the only independent predictor of therapeutic response, being significantly higher in non-responders (P = 0 for DR and P = 0.03 for IPCs). On the other hand, fibrosis stage and steatosis were the only independent factors which showed a significant direct association with the mean number of HPCs in the form of DR and IPCs (P = 0 for each).

Conclusion

The number of HPCs provides prognostic information in chronic HCV since it is significantly associated with stage of fibrosis. More importantly, it can be used as a marker to predict response of patients with chronic HCV to PEGIFN plus RBV therapy.

Liver Regeneration: Different Sub-Populations of Parenchymal Cells at Play Choreographed by an Injury-Specific Microenvironment

Liver regeneration is crucial for the maintenance of liver functional mass during homeostasis and diseases. In a disease context-dependent manner, liver regeneration is contributed to by hepatocytes or progenitor cells. As long as they are replicatively competent, hepatocytes are the main cell type responsible for supporting liver size homeostasisand regeneration. The concept that all hepatocytes within the lobule have the same proliferative capacity but are differentially recruited according to the localization of the wound, or whether a yet to be defined sub-population of hepatocytes supports regeneration is still debated. In a chronically or severely injured liver, hepatocytes may enter a state of replicative senescence. In such conditions, small biliary cells activate and expand, a process called ductular reaction (DR). Work in the last few decades has demonstrated that DR cells can differentiate into hepatocytes and thereby contribute to parenchymal reconstitution. In this study we will review the molecular mechanisms supporting these two processes to determine potential targets that would be amenable for therapeutic manipulation to enhance liver regeneration.

Liver hypertrophy: Underlying mechanisms and promoting procedures before major hepatectomy

Various procedures can promote hypertrophy of the future liver remnant (FLR) before major hepatectomy to prevent postoperative liver failure. The pathophysiological situation following portal vein embolization (PVE), hepatic artery ligation/embolization or hepatectomy remains unclear. On one hand, the main mechanisms of hepatic regeneration appear to be driven by hepatic hypoxia (involving the hepatic arterial buffer response), an increased portal blood flow inducing shear stress and the involvement of several mediators (inflammatory cytokines, vasoregulators, growth factors, eicosanoids and several hormones). On the other hand, several factors are associated with impaired liver regeneration, such as biliary obstruction, malnutrition, diabetes mellitus, male gender, age, ethanol and viral infection. All these mechanisms may explain the varying degrees of hypertrophy observed following a surgical or radiological procedure promoting hypertrophy the FLR. Radiological procedures include left and right portal vein embolization (extended or not to segment 4), sequential PVE and hepatic vein embolization (HVE), and more recently combined PVE and HVE. Surgical procedures include associated liver partition and portal vein ligation for staged hepatectomy, and more recently the combined portal embolization and arterial ligation procedure. This review aimed to clarify the pathophysiology of liver regeneration; it also describes radiological or surgical procedures employed to improve liver regeneration in terms of volumetric changes, the feasibility of the second step and the benefits and drawbacks of each procedure.

Senescence mirrors the extent of liver fibrosis in chronic hepatitis C virus infection

BACKGROUND

Chronic viral hepatitis is linked to fibrotic liver injury that can progress to liver cirrhosis with its associated complications. Recent evidence suggests a role of senescence in liver fibrosis, although the senescence regulators contributing to fibrosis progression remain unclear.

AIM

To investigate the role of senescence and different senescence markers for fibrosis progression in patients with chronic hepatitis C virus (HCV) infection.

METHODS

The expression of the cell cycle inhibitors p21, p27 and p16 as well as the senescence markers p-HP1γ and γ-H2AX was analysed in liver tissue with different fibrosis stages. Senescence-associated chitotriosidase activity was measured in sera of HCV patients (n = 61) and age-matched healthy individuals (n = 22).

RESULTS

We found a remarkable up-regulation of the cell cycle inhibitors and senescence markers in chronic HCV infection compared to healthy liver tissue. Liver tissue with relevant fibrosis stages (F2-3) or cirrhosis (F4) revealed a significant increase in senescent cells compared to livers with no or minimal fibrosis (F0-1). In cirrhotic livers, a significantly higher number of p-HP1γ, p21 and p27 positive cells was detected compared to liver tissue with F2-3 fibrosis. Importantly, we identified T-cells as the dominant cell type contributing to increased senescence during fibrosis progression. Compared to healthy individuals, serum chitotriosidase was significantly elevated and correlated with histological fibrosis stages and liver stiffness as assessed by transient elastography.

CONCLUSIONS

Senescence of hepatic T-cells is enhanced in chronic viral hepatitis and increases with fibrosis progression. Serological detection of senescence-associated chitotriosidase might allow for the non-invasive detection of relevant fibrosis stages.

The many ways to mend your liver: A critical appraisal

In the latter half of the 20th century, our understanding of mammalian liver regeneration was shaped by the manner of compensatory hyperplasia occurring after a partial rat liver resection. This response involves almost all hepatocytes and thus is unlikely to be the outcome of the multiple cycling of a small stem cell population. It was most intense in the outer third of lobule, the location closest to the afferent arterial blood supply. With the advent of heritable genetic labelling techniques, usually applied to mice, hitherto unrecognized hepatocytes with clonogenic potential have been discovered, contributing to homoeostatic renewal and/or regenerative responses after tissue loss. This review combines observations from cell lineage tracing studies with other data to summarize the Four proposed anatomical locations for hepatocyte stem cells: the periportal zone, the pericentral zone, a randomized distribution and finally within the intrahepatic biliary tree. As in other endodermal-derived tissues, it appears that there are both homoeostatic stem cells and regenerative stem cells, while some normally homoeostatic stem cells can become more active to boost regeneration.

A New Model for the Dynamics of Hepatitis C Infection: Derivation, Analysis and Implications

We review various existing models of hepatitis C virus (HCV) infection and show that there are inconsistencies between the models and known behaviour of the infection. A new model for HCV infection is proposed, based on various dynamical processes that occur during the infection that are described in the literature. This new model is analysed, and three steady state branches of solutions are found when there is no stem cell generation of hepatocytes. Unusually, the branch of infected solutions that connects the uninfected branch and the pure infection branch can be found analytically and always includes a limit point, subject to a few conditions on the parameters. When the action of stem cells is included, the bifurcation between the pure infection and infected branches unfolds, leaving a single branch of infected solutions. It is shown that this model can generate various viral load profiles that have been described in the literature, which is confirmed by fitting the model to four viral load datasets. Suggestions for possible changes in treatment are made based on the model.

The Impact of Preexisting Chronic Kidney Disease on the Severity and Recovery of Acute Kidney Injury

BACKGROUND

Recent observational studies have shown that in chronic kidney disease (CKD) patients, a significantly smaller percentage of patients with an episode of acute kidney injury (AKI) have full recovery of renal function compared to those without CKD. However, precise mechanisms involved in the incomplete repair after AKI with preexisting CKD have not been completely ascertained. Here, we assessed the impact of preexisting CKD on the severity and recovery of AKI in a mouse model of 5/6 nephrectomy.

METHODS

Male CD-1 mice underwent 5/6 nephrectomy (Nx). Six weeks post surgery, ischemia reperfusion injury (IRI) or a sham operation was performed and functional, histological, and various molecular parameters were compared between them.

RESULTS

Serum creatinine level on day 1 after IRI was comparable between control and Nx mice. However, serum creatinine remained significantly higher throughout the recovery phase in Nx mice compared to control mice. mRNA and protein expression of the cell cycle regulatory proteins were persistently elevated in Nx mice and this was associated with significantly increased levels of the G1 cell cycle arrest markers. Treatment with a p53 inhibitor following IRI resulted in not only decreased expression of G1 arrest markers but also decreased fibrosis, suggesting that prolonged epithelial G1 cell cycle arrest might be partially responsible for impaired recovery from superimposed AKI on CKD.

CONCLUSION

Taken together, reduced nephron mass have a negative effect on the repair process that is partially mediated by the disruption of the cell cycle regulation.

Oroxylin A inhibits ethanol-induced hepatocyte senescence via YAP pathway

OBJECTIVES

Oroxylin A, a natural flavonoid isolated from Scutellaria baicalensis, has been reported to have anti-hepatic injury effects. However, the effects of oroxylin A on alcoholic liver disease (ALD) remains unclear. The aim of this study was to elucidate the effects of oroxylin A on ALD and the potential mechanisms.

MATERIALS AND METHODS

Male ICR mice and human hepatocyte cell line LO₂ were used. Yes-associated protein (YAP) overexpression and knockdown were achieved using plasmid and siRNA technique. Cellular senescence was assessed by analyses of the senescence-associated β-galactosidase (SA-β-gal), senescence marker p16, p21, Hmga1, cell cycle and telomerase activity.

RESULTS

Oroxylin A alleviated ethanol-induced hepatocyte damage by suppressing activities of supernatant marker enzymes. We found that oroxylin A inhibited ethanol-induced hepatocyte senescence by decreasing the number of SA-β-gal-positive LO₂ cells and reducing the expression of senescence markers p16, p21 and Hmga1 in vitro. Moreover, oroxylin A affected the cell cycle and telomerase activity. Of importance, we revealed that YAP pharmacological inhibitor verteporfin or YAP siRNA eliminated the effect of oroxylin A on ethanol-induced hepatocyte senescence in vitro, and this was further supported by the evidence in vivo experiments.

CONCLUSION

Therefore, these aggregated data suggested that oroxylin A relieved alcoholic liver injury possibly by inhibiting the senescence of hepatocyte, which was dependent on its activation of YAP in hepatocytes.

The diversity and plasticity of adult hepatic progenitor cells and their niche

The liver is a unique organ for homoeostasis with regenerative capacities. Hepatocytes possess a remarkable capacity to proliferate upon injury; however, in more severe scenarios liver regeneration is believed to arise from at least one, if not several facultative hepatic progenitor cell compartments. Newly identified pericentral stem/progenitor cells residing around the central vein is responsible for maintaining hepatocyte homoeostasis in the uninjured liver. In addition, hepatic progenitor cells have been reported to contribute to liver fibrosis and cancers. What drives liver homoeostasis, regeneration and diseases is determined by the physiological and pathological conditions, and especially the hepatic progenitor cell niches which influence the fate of hepatic progenitor cells. The hepatic progenitor cell niches are special microenvironments consisting of different cell types, releasing growth factors and cytokines and receiving signals, as well as the extracellular matrix (ECM) scaffold. The hepatic progenitor cell niches maintain and regulate stem cells to ensure organ homoeostasis and regeneration. In recent studies, more evidence has been shown that hepatic cells such as hepatocytes, cholangiocytes or myofibroblasts can be induced to be oval cell-like state through transitions under some circumstance, those transitional cell types as potential liver-resident progenitor cells play important roles in liver pathophysiology. In this review, we describe and update recent advances in the diversity and plasticity of hepatic progenitor cell and their niches and discuss evidence supporting their roles in liver homoeostasis, regeneration, fibrosis and cancers.

Gypenosides Ameliorate Carbon Tetrachloride-Induced Liver Fibrosis by Inhibiting the Differentiation of Hepatic Progenitor Cells into Myofibroblasts

Gypenosides (GPs), the predominant components of Gynostemma pentaphyllum, exert antifibrotic effects; however, the mechanisms underlying their ability to ameliorate liver fibrosis are unclear. Liver fibrosis was induced in C57BL/6 mice via subcutaneous injection of 10% carbon tetrachloride (CCl[Formula: see text] three times a week for two weeks. Then, CCl4 was administered in conjunction with intragastric GPs for another three weeks. For in vitro analyses, WB-F344, hepatatic progenitor cells (HPCs) were treated with transforming growth factor beta 1 (TGF-[Formula: see text]1) with or without GPs for 48[Formula: see text]h. The results showed that alanine aminotransferase (ALT) and aspartate transaminase (AST) activity, deposition of collagen, hydroxyproline content, and expression of alpha-smooth muscle actin ([Formula: see text]-SMA) and collagen type I (Col I) were significantly decreased after treatment with GPs ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]). In the 5M CCl4 group, the expression of HPC markers, Sox9 and cytokeratin 19 (CK19), was significantly increased compared with the normal or GPs-treated group ([Formula: see text], [Formula: see text]). Immunostaining showed that the number of Sox9 and [Formula: see text]-SMA double-positive cells was higher in the 5M CCl4 group than in the normal group, but the addition of GPs caused this cell number to decrease. In WB-F344 cells, the expression of [Formula: see text]-SMA and Col I was significantly increased after treatment with TGF-[Formula: see text], whereas in the GPs treatment group, expression was markedly decreased ([Formula: see text]). The levels of TGF-[Formula: see text] and TGF-[Formula: see text]R1 were markedly reduced after GPs treatment both in vivo and in vitro. In conclusion, GPs ameliorated CCl4-induced liver fibrosis via the inhibition of TGF-[Formula: see text] signaling, consequently inhibiting the differentiation of HPCs into myofibroblasts.

Cholangiocytes act as facultative liver stem cells during impaired hepatocyte regeneration

Following liver injury, regeneration occurs through self-replication of hepatocytes. In severe liver injury, hepatocyte proliferation is impaired, a feature of human chronic liver disease1,2. It is contested whether other liver cell types can regenerate hepatocytes3–5. Here, we use two independent systems to impair hepatocyte proliferation during liver injury to evaluate the contribution of non-hepatocytes to parenchymal regeneration. Firstly, loss of β1-Integrin in hepatocytes with liver injury triggered a ductular reaction of cholangiocyte origin, and ~25% of hepatocytes being derived from a non-hepatocyte origin. Secondly cholangiocytes were lineage traced with concurrent inhibition of hepatocyte proliferation by β1-Integrin knockdown or p21 over-expression, resulting in the significant emergence of cholangiocyte derived hepatocytes. We describe a model of combined liver injury and inhibition of hepatocyte proliferation that causes physiologically significant levels of regeneration of functional hepatocytes from biliary cells.

Seeds in the liver

The liver is a crucial organ for homeostasis and has a tremendous self-renewal and regenerative capacity. It has long been believed that the self-renewal and repair of the liver within a given physiological condition or its repopulation in chronic liver diseases, when hepatocyte proliferation is impaired, will primarily be conducted by the proliferating duct cells, termed "oval cells" or hepatic progenitor cells (HPCs). In addition, numerous studies have revealed that HPCs are the initial tumor cells of liver cancer under certain micro-environments. However, benefit from the extensive application of lineage tracing strategies using the Cre/LoxP system, researchers have redefined the fate of these bipotential cells, raising obvious controversies regarding the capacity of liver cells to control their own biology and differentiation. Here, we review the relevant articles, focusing on cell-lineage tracing to better understanding seed cells and their distinct fate in the liver.