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Liver transplantation is a highly successful treatment, but is severely limited by the shortage in donor organs. However, many potential donor organs cannot be used; this is because sub-optimal livers do not tolerate conventional cold storage and there is no reliable way to assess organ viability preoperatively. Normothermic machine perfusion maintains the liver in a physiological state, avoids cooling and allows recovery and functional testing. Here we show that, in a randomized trial with 220 liver transplantations, compared to conventional static cold storage, normothermic preservation is associated with a 50% lower level of graft injury, measured by hepatocellular enzyme release, despite a 50% lower rate of organ discard and a 54% longer mean preservation time. There was no significant difference in bile duct complications, graft survival or survival of the patient. If translated to clinical practice, these results would have a major impact on liver transplant outcomes and waiting list mortality. Normothermic machine perfusion of the liver improved early graft function, demonstrated by reduced peak serum aspartate transaminase levels and early allograft dysfunction rates, and improved organ utilization and preservation times, although no differences were seen in graft or patient survival.

The liver is the only solid organ that uses regenerative mechanisms to ensure that the liver-to-bodyweight ratio is always at 100% of what is required for body homeostasis. Other solid organs (such as the lungs, kidneys and pancreas) adjust to tissue loss but do not return to 100% of normal. The current state of knowledge of the regenerative pathways that underlie this ‘hepatostat’ will be presented in this Review. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models that involve partial hepatectomy or chemical injury have revealed extracellular and intracellular signalling pathways that are used to return the liver to equivalent size and weight to those prior to injury. On the other hand, chronic loss of hepatocytes, which can occur in chronic liver disease of any aetiology, often has adverse consequences, including fibrosis, cirrhosis and liver neoplasia. The regenerative activities of hepatocytes and cholangiocytes are typically characterized by phenotypic fidelity. However, when regeneration of one of the two cell types fails, hepatocytes and cholangiocytes function as facultative stem cells and transdifferentiate into each other to restore normal liver structure. Liver recolonization models have demonstrated that hepatocytes have an unlimited regenerative capacity. However, in normal liver, cell turnover is very slow. All zones of the resting liver lobules have been equally implicated in the maintenance of hepatocyte and cholangiocyte populations in normal liver. The liver has a broad range of regenerative capacities. In this Review, Michalopoulos and Bhushan describe the regenerative mechanisms employed by hepatic cells after liver injury as well as the experimental models used to investigate these mechanisms and discuss the clinical implications. Key points Hepatocyte proliferation during liver regeneration is controlled by multiple extracellular signals, two of which (MET and EGFR) are directly mitogenic and others only delay liver regeneration if they are bypassed. Intracellular signalling pathways in hepatocytes are very rapidly (within minutes) activated after partial hepatectomy. The mechanisms triggering these pathways are not clear. All hepatic cell types participate in cell proliferation during liver regeneration. No ‘stem cells’ are involved. If hepatocyte or cholangiocyte proliferation is seriously impaired, then each of the two cell types can transdifferentiate into the other and function as a facultative stem cell. Loss of hepatocytes occurring in chronic liver diseases triggers compensatory proliferation of the surviving hepatocytes and exposes them to potentially genotoxic injury that might lead to neoplasia.

Background In patients undergoing major liver resection, portal vein embolization (PVE) has been widely used to induce hypertrophy of the non-embolized liver in order to prevent post-hepatectomy liver failure. PVE is a safe and effective procedure, but does not always lead to sufficient hypertrophy of the future liver remnant (FLR). Hepatic vein(s) embolization has been proposed to improve FLR regeneration when insufficient after PVE. The sequential right hepatic vein embolization (HVE) after right PVE demonstrated an incremental effect on the FLR but it implies two different procedures with no time gain as compared to PVE alone. We have developed the so-called liver venous deprivation (LVD), a combination of PVE and HVE during the same intervention, to optimize the phase of liver preparation before surgery. The main objective of this randomized phase II trial is to compare the percentage of change in FLR volume at 3 weeks after LVD or PVE. Methods Patients eligible to this multicenter prospective randomized phase II study are subjects aged from 18 years old suffering from colo-rectal liver metastases considered as resectable and with non-cirrhotic liver parenchyma. The primary objective is the percentage of change in FLR volume at 3 weeks after LVD or PVE using MRI or CT-Scan. Secondary objectives are assessment of tolerance, post-operative morbidity and mortality, post-hepatectomy liver failure, rate of non-respectability due to insufficient FLR or tumor progression, per-operative difficulties, blood loss, R0 resection rate, post-operative liver volume and overall survival. Objectives of translational research studies are evaluation of pre- and post-operative liver function and determination of biomarkers predictive of liver hypertrophy . Sixty-four patients will be included (randomization ratio 1:1) to detect a difference of 12% at 21 days in FLR volumes between PVE and LVD. Discussion Adding HVE to PVE during the same procedure is an innovative and promising approach that may lead to a rapid and major increase in volume and function of the FLR, thereby increasing the rate of resectable patients and limiting the risk of patient’s drop-out. Trial registration This study was registered on clinicaltrials.gov on 15th February 2019 ( NCT03841305 ).

The liver is a unique organ with an abundant regenerative capacity. Therefore, partial hepatectomy (PHx) or partial liver transplantation (PLTx) can be safely performed. Liver regeneration involves a complex network of numerous hepatotropic factors, cytokines, pathways, and transcriptional factors. Compared with liver regeneration after a viral- or drug-induced liver injury, that of post-PHx or -PLTx has several distinct features, such as hemodynamic changes in portal venous flow or pressure, tissue ischemia/hypoxia, and hemostasis/platelet activation. Although some of these changes also occur during liver regeneration after a viral- or drug-induced liver injury, they are more abrupt and drastic following PHx or PLTx, and can thus be the main trigger and driving force of liver regeneration. In this review, we first provide an overview of the molecular biology of liver regeneration post-PHx and -PLTx. Subsequently, we summarize some clinical conditions that negatively, or sometimes positively, interfere with liver regeneration after PHx or PLTx, such as marginal livers including aged or fatty liver and the influence of immunosuppression.

Emerging evidence suggests that hepatocytes are primarily maintained by self-renewal during normal liver homeostasis, as well as in response to a wide variety of hepatic injuries. However, how hepatocytes in distinct anatomic locations within the liver lobule are replenished under homeostasis and injury-induced regeneration remains elusive. Using a newly developed bacterial artificial chromosome (BAC)-transgenic mouse model, we demonstrate that Lgr5 expression in the liver is restricted to a unique subset of hepatocytes most adjacent to the central veins. Genetic lineage tracing revealed that pericentral Lgr5⁺ hepatocytes have a long lifespan and mainly contribute to their own lineage maintenance during postnatal liver development and homeostasis. Remarkably, these hepatocytes also fuel the regeneration of their own lineage during the massive and rapid regeneration process following two-thirds partial hepatectomy. Moreover, Lgr5⁺ hepatocytes are found to be the main cellular origin of diethylnitrosamine (DEN)-induced hepatocellular carcinoma (HCC) and are highly susceptible to neoplastic transformation triggered by activation of Erbb pathway. Our findings establish an unexpected self-maintaining mode for a defined subset of hepatocytes during liver homeostasis and regeneration, and identify Lgr5⁺ pericentral hepatocytes as major cells of origin in HCC development.

The liver is a central organ for the synthesis and storage of nutrients, production of serum proteins and hormones, and breakdown of toxins and metabolites. Because the liver is susceptible to toxin-or pathogen-mediated injury, it maintains a remarkable capacity to regenerate by compensatory growth. Specifically, in response to injury, quiescent hepatocytes enter the cell cycle and undergo DNA replication to promote liver regrowth. Despite the elucidation of a number of regenerative factors, the mechanisms by which liver injury triggers hepatocyte proliferation are incompletely understood. We demonstrate here that eosinophils stimulate liver regeneration after partial hepatectomy and toxin-mediated injury. Liver injury results in rapid recruitment of eosinophils, which secrete IL-4 to promote the proliferation of quiescent hepatocytes. Surprisingly, signaling via the IL-4Rα in macrophages, which have been implicated in tissue repair, is dispensable for hepatocyte proliferation and liver regrowth after injury. Instead, IL-4 exerts its proliferative actions via IL-4 Rot in hepatocytes. Our findings thus provide a unique mechanism by which eosinophil-derived IL-4 stimulates hepatocyte proliferation in regenerating liver.

The liver plays a central role in metabolism, protein synthesis and detoxification. It possesses unique regenerative capacity upon injury. While many factors regulating cellular proliferation during liver repair have been identified, the mechanisms by which the injured liver maintains vital functions prior to tissue recovery are unknown. Here, we identify a new phase of functional compensation following acute liver injury that occurs prior to cellular proliferation. By coupling single-cell RNA-seq with in situ transcriptional analyses in two independent murine liver injury models, we discover adaptive reprogramming to ensure expression of both injury response and core liver function genes dependent on macrophage-derived WNT/β-catenin signaling. Interestingly, transcriptional compensation is most prominent in non-proliferating cells, clearly delineating two temporally distinct phases of liver recovery. Overall, our work describes a mechanism by which the liver maintains essential physiological functions prior to cellular reconstitution and characterizes macrophage-derived WNT signals required for this compensation. The liver possesses the ability to regenerate following sudden injury. Here, the authors use single-cell RNA-sequencing and in situ transcriptional analyses to identify a new phase of liver regeneration in mice aimed at maintaining essential functions throughout the regenerative process.

The liver possesses the unique ability to regenerate within a short period of time, a feature that has led to the development of innovative strategies in liver surgery and transplantation. This review presents both established and novel methods for manipulating liver volume to attain improved liver surgery and transplantation. The liver possesses the unique ability to regenerate within a short period of time. This review presents both established and novel methods for manipulating liver volume to attain improved liver surgery and transplantation. The liver possesses the unique ability to regenerate within a short period. 1 – 3 This feature has led to the development of innovative strategies in liver surgery and transplantation. The anatomy of the liver is paramount in considering advances in hepatic surgery. The liver is divided into eight segments (Figure 1). In healthy adults, the liver weighs about 1.5 kg (3.3 lb). 4 The blood supply of the liver is carried through two major vessels, the hepatic artery and the portal vein. The portal vein carries a large volume of venous blood to the liver from the gut, pancreas, and spleen, permitting . . .

We describe a novel therapeutic approach for cirrhosis using mesenchymal stem cells (MSCs) and colony‐stimulating factor‐1‐induced bone marrow‐derived macrophages (id‐BMMs) and analyze the mechanisms underlying fibrosis improvement and regeneration. Mouse MSCs and id‐BMMs were cultured from mouse bone marrow and their interactions analyzed in vitro. MSCs, id‐BMMs, and a combination therapy using MSCs and id‐BMMs were administered to mice with CCl4‐induced cirrhosis. Fibrosis regression, liver regeneration, and liver‐migrating host cells were evaluated. Administered cell behavior was also tracked by intravital imaging. In coculture, MSCs induced switching of id‐BMMs toward the M2 phenotype with high phagocytic activity. In vivo, the combination therapy reduced liver fibrosis (associated with increased matrix metalloproteinases expression), increased hepatocyte proliferation (associated with increased hepatocyte growth factor, vascular endothelial growth factor, and oncostatin M in the liver), and reduced blood levels of liver enzymes, more effectively than MSCs or id‐BMMs monotherapy. Intravital imaging showed that after combination cell administration, a large number of id‐BMMs, which phagocytosed hepatocyte debris and were retained in the liver for more than 7 days, along with a few MSCs, the majority of which were trapped in the lung, migrated to the fibrotic area in the liver. Host macrophages and neutrophils infiltrated after combination therapy and contributed to liver fibrosis regression and promoted regeneration along with administered cells. Indirect effector MSCs and direct effector id‐BMMs synergistically improved cirrhosis along with host cells in mice. These studies pave the way for new treatments for cirrhosis. Stem Cells Translational Medicine 2019;8:271&284 Combination therapy using mesenchymal stem cells (MSCs) and induced bone marrow‐derived macrophages (id‐BMMs), synergistically regressed liver fibrosis and promoted liver regeneration with recruiting host macrophages and neutrophils. Indirect effector MSCs changed the polarity of direct effector id‐BMMs toward M2 phenotype with high antifibrosis, proregeneration, and phagocytosis effect. Intravital imaging revealed the behavior of MSCs and id‐BMMs and mechanisms of this therapy.

Recent evidence has contradicted the prevailing view that homeostasis and regeneration of the adult liver are mediated by self duplication of lineage-restricted hepatocytes and biliary epithelial cells. These new data suggest that liver progenitor cells do not function solely as a backup system in chronic liver injury; rather, they also produce hepatocytes after acute injury and are in fact the main source of new hepatocytes during normal hepatocyte turnover. In addition, other evidence suggests that hepatocytes are capable of lineage conversion, acting as precursors of biliary epithelial cells during biliary injury. To test these concepts, we generated a hepatocyte fate-tracing model based on timed and specific Cre recombinase expression and marker gene activation in all hepatocytes of adult Rosa26 reporter mice with an adenoassociated viral vector. We found that newly formed hepatocytes derived from preexisting hepatocytes in the normal liver and that liver progenitor cells contributed minimally to acute hepatocyte regeneration. Further, we found no evidence that biliary injury induced conversion of hepatocytes into biliary epithelial cells. These results therefore restore the previously prevailing paradigms of liver homeostasis and regeneration. In addition, our new vector system will be a valuable tool for timed, efficient, and specific loop out of floxed sequences in hepatocytes.