Endothelial autophagy is not required for liver regeneration after partial hepatectomy in mice with fatty liver.

BACKGROUND & AIMS: Patients with non-alcoholic fatty liver disease (NAFLD) have impaired liver regeneration. Liver endothelial cells play a key role in liver regeneration. In non-alcoholic steatohepatitis (NASH), liver endothelial cells display a defect in autophagy, contributing to NASH progression. We aimed to determine the role of endothelial autophagy in liver regeneration following liver resection in NAFLD. METHODS: First, we assessed autophagy in primary endothelial cells from wild type mice fed a high fat diet and subjected to partial hepatectomy. Then, we assessed liver regeneration after partial hepatectomy in mice deficient (Atg5lox/lox ;VE-cadherin-Cre+ ) or not (Atg5lox/lox ) in endothelial autophagy and fed a high fat diet. The role of endothelial autophagy in liver regeneration was also assessed in ApoE-/- hypercholesterolemic mice and in mice with NASH induced by methionine- and choline-deficient diet. RESULTS: First, autophagy (LC3II/protein) was strongly increased in liver endothelial cells following hepatectomy. Then, we observed at 40 and 48 h and at 7 days after partial hepatectomy, that Atg5lox/lox ;VE-cadherin-Cre+ mice fed a high fat diet had similar liver weight, plasma AST, ALT and albumin concentration, and liver protein expression of proliferation (PCNA), cell-cycle (Cyclin D1, BrdU incorporation, phospho-Histone H3) and apoptosis markers (cleaved Caspase-3) as Atg5lox/lox mice fed a high fat diet. Same results were obtained in ApoE-/- and methionine- and choline-deficient diet fed mice, 40 h after hepatectomy. CONCLUSION: These results demonstrate that the defect in endothelial autophagy occurring in NASH does not account for the impaired liver regeneration occurring in this setting.

Monoacylglycerol lipase reprograms hepatocytes and macrophages to promote liver regeneration.

Background & Aims: Liver regeneration is a repair process in which metabolic reprogramming of parenchymal and inflammatory cells plays a major role. Monoacylglycerol lipase (MAGL) is an ubiquitous enzyme at the crossroad between lipid metabolism and inflammation. It converts monoacylglycerols into free fatty acids and metabolises 2-arachidonoylglycerol into arachidonic acid, being thus the major source of pro-inflammatory prostaglandins in the liver. In this study, we investigated the role of MAGL in liver regeneration. Methods: Hepatocyte proliferation was studied in vitro in hepatoma cell lines and ex vivo in precision-cut human liver slices. Liver regeneration was investigated in mice treated with a pharmacological MAGL inhibitor, MJN110, as well as in animals globally invalidated for MAGL (MAGL-/-) and specifically invalidated in hepatocytes (MAGLHep-/-) or myeloid cells (MAGLMye-/-). Two models of liver regeneration were used: acute toxic carbon tetrachloride injection and two-thirds partial hepatectomy. MAGLMye-/- liver macrophages profiling was analysed by RNA sequencing. A rescue experiment was performed by in vivo administration of interferon receptor antibody in MAGLMye-/- mice. Results: Precision-cut human liver slices from patients with chronic liver disease and human hepatocyte cell lines exposed to MJN110 showed reduced hepatocyte proliferation. Mice with global invalidation or mice treated with MJN110 showed blunted liver regeneration. Moreover, mice with specific deletion of MAGL in either hepatocytes or myeloid cells displayed delayed liver regeneration. Mechanistically, MAGLHep-/- mice showed reduced liver eicosanoid production, in particular prostaglandin E2 that negatively impacts on hepatocyte proliferation. MAGL inhibition in macrophages resulted in the induction of the type I interferon pathway. Importantly, neutralising the type I interferon pathway restored liver regeneration of MAGLMye-/- mice. Conclusions: Our data demonstrate that MAGL promotes liver regeneration by hepatocyte and macrophage reprogramming. Impact and Implications: By using human liver samples and mouse models of global or specific cell type invalidation, we show that the monoacylglycerol pathway plays an essential role in liver regeneration. We unveil the mechanisms by which MAGL expressed in both hepatocytes and macrophages impacts the liver regeneration process, via eicosanoid production by hepatocytes and the modulation of the macrophage interferon pathway profile that restrains hepatocyte proliferation.

Cell metabolism-based therapy for liver fibrosis, repair, and hepatocellular carcinoma.

Progression of chronic liver injury to fibrosis, abnormal liver regeneration, and HCC is driven by a dysregulated dialog between epithelial cells and their microenvironment, in particular immune, fibroblasts, and endothelial cells. There is currently no antifibrogenic therapy, and drug treatment of HCC is limited to tyrosine kinase inhibitors and immunotherapy targeting the tumor microenvironment. Metabolic reprogramming of epithelial and nonparenchymal cells is critical at each stage of disease progression, suggesting that targeting specific metabolic pathways could constitute an interesting therapeutic approach. In this review, we discuss how modulating intrinsic metabolism of key effector liver cells might disrupt the pathogenic sequence from chronic liver injury to fibrosis/cirrhosis, regeneration, and HCC.

MAIT cell inhibition promotes liver fibrosis regression via macrophage phenotype reprogramming.

Recent data have shown that liver fibrosis can regress even at later stages of cirrhosis and shifting the immune response from pro-inflammatory towards a resolutive profile is considered as a promising option. The immune regulatory networks that govern the shift of the inflammatory phenotype and thus potential reversal of liver fibrosis are lesser known. Here we show that in precision-cut human liver slices obtained from patients with end-stage fibrosis and in mouse models, inhibiting Mucosal-Associated Invariant T (MAIT) cells using pharmacological or antibody-driven approaches, limits fibrosis progression and even regresses fibrosis, following chronic toxic- or non-alcoholic steatohepatitis (NASH)-induced liver injury. Mechanistic studies, combining RNA sequencing, in vivo functional studies (performed in male mice) and co-culture experiments indicate that disruption of the MAIT cell-monocyte/macrophage interaction results in resolution of fibrosis both by increasing the frequency of restorative Ly6Clo at the expenses of pro-fibrogenic Ly6Chi monocyte-derived macrophages and promoting an autophagic phenotype in both subsets. Thus, our data show that MAIT cell activation and the consequential phenotype shift of liver macrophages are important pathogenic features of liver fibrosis and could be targeted by anti-fibrogenic therapy.

[What about good in all this? A human passion]. / Et le Bien dans tout ça ? (Axel Kahn) - Une passion humaine.

TITLE: Et le Bien dans tout ça ? (Axel Kahn) - Une passion humaine. ABSTRACT: Cette recension a été écrite avant le décès d'Axel Kahn survenu le 6 juillet 2021. Axel interrogeait le monde avec une curiosité gourmande et une passion communicative. Cet ouvrage aura été son dernier questionnement. Puissent ses lecteurs continuer de se poser la question….

Targeting cell-intrinsic metabolism for antifibrotic therapy.

In recent years, there have been major advances in our understanding of the mechanisms underlying fibrosis progression and regression, and how coordinated interactions between parenchymal and non-parenchymal cells impact on the fibrogenic process. Recent studies have highlighted that metabolic reprogramming of parenchymal cells, immune cells (immunometabolism) and hepatic stellate cells is required to support the energetic and anabolic demands of phenotypic changes and effector functions. In this review, we summarise how targeting cell-intrinsic metabolic modifications of the main fibrogenic cell actors may impact on fibrosis progression and we discuss the antifibrogenic potential of metabolically targeted interventions.

LC3-associated phagocytosis in myeloid cells, a fireman that restrains inflammation and liver fibrosis, via immunoreceptor inhibitory signaling.

Control of systemic and hepatic inflammation, in particular originating from monocytes/macrophages, is crucial to prevent liver fibrosis and its progression to end-stage cirrhosis. LC3-associated phagocytosis (LAP) is a non-canonical form of autophagy that shifts the monocyte/macrophage phenotype to an anti-inflammatory phenotype. In a recent study, we uncovered LAP as a protective mechanism against inflammation-driven liver fibrosis and systemic inflammation in the context of cirrhosis. We observed that LAP is enhanced in blood and liver monocytes from patients with liver fibrosis or those who progress to cirrhosis. Combining studies in which LAP was pharmacologically or genetically inactivated, we found that LAP limits inflammation in monocytes from cirrhotic patients, and the hepatic inflammatory profile in mice with chronic liver injury, resulting in anti-fibrogenic effects. Mechanistically, LAP-induced anti-inflammatory and antifibrogenic signaling results from enhanced expression of the Fc immunoreceptor FCGR2A/FcγRIIA and activation of an FCGR2A-mediated PTPN6/SHP-1 anti-inflammatory pathway, leading to increased engulfment of IgG into LC3 + phagosomes. In patients with cirrhosis progressing to multi-organ failure (acute-on chronic liver failure), LAP is lost in monocytes, and can be restored by targeting FCGR2A-mediated PTPN6/SHP-1 signaling. These data suggest that sustaining LAP may open novel therapeutic perspectives for patients with end-stage liver disease.

LC3-associated phagocytosis protects against inflammation and liver fibrosis via immunoreceptor inhibitory signaling.

Sustained hepatic and systemic inflammation, particularly originating from monocytes/macrophages, is a driving force for fibrosis progression to end-stage cirrhosis and underlies the development of multiorgan failure. Reprogramming monocyte/macrophage phenotype has emerged as a strategy to limit inflammation during chronic liver injury. Here, we report that LC3-associated phagocytosis (LAP), a noncanonical form of autophagy, protects against hepatic and systemic inflammation during chronic liver injury in rodents, with beneficial antifibrogenic effects. LAP is enhanced in blood and liver monocytes from patients with fibrosis and cirrhosis. Pharmacological inhibition of LAP components in human monocytes from patients with cirrhosis or genetic disruption of LAP in mice with chronic liver injury exacerbates both the inflammatory signature in isolated human monocytes and the hepatic inflammatory profile in mice, resulting in enhanced liver fibrosis. Mechanistically, patients with cirrhosis showed increased monocyte expression of Fc fragment of IgG receptor IIA (FcγRIIA) and enhanced engulfment of immunoglobulin G in LC3+ phagosomes that triggers an FcγRIIA/Src homology region 2 domain-containing phosphatase-1 (SHP-1) inhibitory immunoreceptor tyrosine-based activation motif (ITAMi) anti-inflammatory pathway. Mice overexpressing human FcγRIIA in myeloid cells show enhanced LAP in response to chronic liver injury and resistance to inflammation and liver fibrosis. Activation of LAP is lost in monocytes from patients with multiorgan failure and restored by specifically targeting ITAMi signaling with anti-FcγRIIA F(ab')2 fragments, or with intravenous immunoglobulin (IVIg). These data suggest the existence of an ITAMi-mediated mechanism by which LAP might protect against inflammation. Sustaining LAP may open therapeutic perspectives for patients with chronic liver disease.

[Emergence of 3D human fatty liver models engineered in the laboratory]. / L'émergence des modèles miniatures de foie gras humain en 3D générés en laboratoire.

Organoids offer an elegant approach to model human diseases and test new drugs. Nonalcoholic fatty liver disease (NAFLD) whose incidence has dramatically increased in recent years with the rise of obesity, is defined by triglyceride accumulation in hepatocytes, inflammation, liver injury, and progression to fibrosis. There is currently no approved therapy but many pathways are being explored. Two American teams have created mini-steatotic livers using different approaches, both using induced pluripotent stem cells (iPS), thus offering new tools to test developing drugs.

TITLE: L'émergence des modèles miniatures de foie gras humain en 3D générés en laboratoire. ABSTRACT: Les organoïdes constituent une approche de choix pour modéliser a minima une maladie humaine et tester l'efficacité thérapeutique de certaines drogues. La stéatopathie métabolique ou maladie du foie gras, dont l'incidence a considérablement augmenté avec l'accroissement de l'obésité dans les pays développés, se caractérise par l'accumulation de triglycerides dans l'hépatocyte et une atteinte hépatique pouvant évoluer vers la fibrose. Il n'existe pas de traitement efficace, mais de nombreuses pistes sont actuellement explorées. Deux équipes américaines ont récemment utilisé les cellules souches pluripotentes induites (iPS) et la culture muticellulaire pour modéliser un mini-foie stéatosique par deux approches différentes, offrant ainsi de nouveaux outils pour tester les drogues en cours de développement.

The aged liver: Beyond cellular senescence.

The aging of the population, the increased prevalence of chronic liver diseases in elderly and the need to broaden the list of potential liver donors enjoin us to better understand what is an aged liver. In this review, we provide a brief introduction to cellular senescence, revisit the main morphological and functional modifications of the liver induced by aging, particularly concerning metabolism, immune response and regeneration, and try to elude some of the signalling pathways responsible for these modifications. Finally, we discuss the clinical consequences of aging on chronic liver diseases and the implications of older age for donors and recipients in liver transplantation.

ß-catenin-activated hepatocellular carcinomas are addicted to fatty acids.

OBJECTIVES: CTNNB1-mutated hepatocellular carcinomas (HCCs) constitute a major part of human HCC and are largely inaccessible to target therapy. Yet, little is known about the metabolic reprogramming induced by ß-catenin oncogenic activation in the liver. We aimed to decipher such reprogramming and assess whether it may represent a new avenue for targeted therapy of CTNNB1-mutated HCC. DESIGN: We used mice with hepatocyte-specific oncogenic activation of ß-catenin to evaluate metabolic reprogramming using metabolic fluxes on tumourous explants and primary hepatocytes. We assess the role of Pparα in knock-out mice and analysed the consequences of fatty acid oxidation (FAO) using etomoxir. We explored the expression of the FAO pathway in an annotated human HCC dataset. RESULTS: ß-catenin-activated HCC were not glycolytic but intensively oxidised fatty acids. We found that Pparα is a ß-catenin target involved in FAO metabolic reprograming. Deletion of Pparα was sufficient to block the initiation and progression of ß-catenin-dependent HCC development. FAO was also enriched in human CTNNB1-mutated HCC, under the control of the transcription factor PPARα. CONCLUSIONS: FAO induced by ß-catenin oncogenic activation in the liver is the driving force of the ß-catenin-induced HCC. Inhibiting FAO by genetic and pharmacological approaches blocks HCC development, showing that inhibition of FAO is a suitable therapeutic approach for CTNNB1-mutated HCC.

Age and liver transplantation.

The average age of liver transplant donors and recipients has increased over the years. Independent of the cause of liver disease, older candidates have more comorbidities, higher waitlist mortality and higher post-transplant mortality than younger patients. However, transplant benefit may be similar in older and younger recipients, provided older recipients are carefully selected. The cohort of elderly patients transplanted decades ago is also increasingly raising issues concerning long-term exposure to immunosuppression and aging of the transplanted liver. Excellent results can be achieved with elderly donors and there is virtually no upper age limit for donors after brain death liver transplantation. The issue is how to optimise selection, procurement and matching to ensure good results with elderly donors. The impact of old donor age is more pronounced in younger recipients and patients with a high model for end-stage liver disease score. Age matching between the donor and the recipient should be incorporated into allocation policies with a multistep approach. However, age matching may vary depending on the objectives of different allocation policies. In addition, age matching must be revisited in the era of direct-acting antivirals. More restrictive limits have been adopted in donation after circulatory death. Perfusion machines which are currently under investigation may help expand these limits. In living donor liver transplantation, donor age limit is essentially guided by morbidity related to procurement. In this review we summarise changing trends in recipient and donor age. We discuss the implications of older age donors and recipients. We also consider different options for age matching in liver transplantation that could improve outcomes.