BACKGROUND AND AIMS: Overdose of acetaminophen (APAP) is the major cause of acute liver failure in the western world. We report a novel signaling interaction between hepatocyte nuclear factor 4 alpha (HNF4α) cMyc and nuclear factor erythroid 2-related factor 2 (Nrf2) during liver injury and regeneration after APAP overdose. APPROACH AND RESULTS: APAP-induced liver injury and regeneration were studied in male C57BL/6J (WT) mice, hepatocyte-specific HNF4α knockout mice (HNF4α-KO), and HNF4α-cMyc double knockout mice (DKO). C57BL/6J mice treated with 300 mg/kg maintained nuclear HNF4α expression and exhibited liver regeneration, resulting in recovery. However, treatment with 600-mg/kg APAP, where liver regeneration was inhibited and recovery was delayed, showed a rapid decline in HNF4α expression. HNF4α-KO mice developed significantly higher liver injury due to delayed glutathione recovery after APAP overdose. HNF4α-KO mice also exhibited significant induction of cMyc, and the deletion of cMyc in HNF4α-KO mice (DKO mice) reduced the APAP-induced liver injury. The DKO mice had significantly faster glutathione replenishment due to rapid induction in Gclc and Gclm genes. Coimmunoprecipitation and ChIP analyses revealed that HNF4α interacts with Nrf2 and affects its DNA binding. Furthermore, DKO mice showed significantly faster initiation of cell proliferation resulting in rapid liver regeneration and recovery. CONCLUSIONS: These data show that HNF4α interacts with Nrf2 and promotes glutathione replenishment aiding in recovery from APAP-induced liver injury, a process inhibited by cMyc. These studies indicate that maintaining the HNF4α function is critical for regeneration and recovery after APAP overdose.

BACKGROUND AND AIMS: Paucity of intrahepatic bile ducts (BDs) is caused by various etiologies and often leads to cholestatic liver disease. For example, in patients with Alagille syndrome (ALGS), which is a genetic disease primarily caused by mutations in jagged 1 ( JAG1) , BD paucity often results in severe cholestasis and liver damage. However, no mechanism-based therapy exists to restore the biliary system in ALGS or other diseases associated with BD paucity. Based on previous genetic observations, we investigated whether postnatal knockdown of the glycosyltransferase gene protein O -glucosyltransferase 1 ( Poglut1) can improve the ALGS liver phenotypes in several mouse models generated by removing one copy of Jag1 in the germline with or without reducing the gene dosage of sex-determining region Y-box 9 in the liver. APPROACH AND RESULTS: Using an ASO established in this study, we show that reducing Poglut1 levels in postnatal livers of ALGS mouse models with moderate to profound biliary abnormalities can significantly improve BD development and biliary tree formation. Importantly, ASO injections prevent liver damage in these models without adverse effects. Furthermore, ASO-mediated Poglut1 knockdown improves biliary tree formation in a different mouse model with no Jag1 mutations. Cell-based signaling assays indicate that reducing POGLUT1 levels or mutating POGLUT1 modification sites on JAG1 increases JAG1 protein level and JAG1-mediated signaling, suggesting a likely mechanism for the observed in vivo rescue. CONCLUSIONS: Our preclinical studies establish ASO-mediated POGLUT1 knockdown as a potential therapeutic strategy for ALGS liver disease and possibly other diseases associated with BD paucity.

BACKGROUND AND AIMS: TGF-β induces multiple structural and functional changes in quiescent hepatic stellate cells (HSC) including an increase in proliferation, mitochondrial mass, and matrix deposition. HSC trans-differentiation requires significant bioenergetic capacity and it is not known how TGF-β mediated transcriptional up-regulation is coordinated with the bioenergetic capacity of HSC. APPROACH AND RESULTS: Mitochondria are key bioenergetic organelles and here we report that TGF-β induces release of mitochondrial DNA (mtDNA) from healthy HSC via voltage-dependent anions channels (VDACs), with the formation of a mtDNA-CAP on the external mitochondrial membrane. This stimulates organization of cytosolic cGAS onto the mtDNA-CAP, and subsequent activation of the cGAS-STING-IRF3 pathway. TGF-β is unable to induce conversion of HSC from a quiescent to a trans-differentiated phenotype in the absence of mtDNA, VDAC or STING. Trans-differentiation by TGF-β is blocked by a STING inhibitor which also reduces liver fibrosis prophylactically and therapeutically. CONCLUSION: We have identified a pathway which requires the presence of functional mitochondria for TGF-β to mediate HSC transcriptional regulation and transdifferentiation, and therefore provides a key link between bioenergetic capacity of HSC and signals for transcriptional up-regulation of genes of anabolic pathways.

The most widespread type of liver cancer, HCC, is associated with disabled cellular death pathways. Despite therapeutic advancements, resistance to current systemic treatments (including sorafenib) compromises the prognosis of patients with HCC, driving the search for agents that might target novel cell death pathways. Ferroptosis, a form of iron-mediated nonapoptotic cell death, has gained considerable attention as a potential target for cancer therapy, especially in HCC. The role of ferroptosis in HCC is complex and diverse. On one hand, ferroptosis can contribute to the progression of HCC through its involvement in both acute and chronic liver conditions. In contrast, having ferroptosis affect HCC cells might be desirable. This review examines the role of ferroptosis in HCC from cellular, animal, and human perspectives while examining its mechanisms, regulation, biomarkers, and clinical implications.

Machine perfusion of solid human organs is an old technique, and the basic principles were presented as early as 1855 by Claude Barnard. More than 50 years ago, the first perfusion system was used in clinical kidney transplantation. Despite the well-known benefits of dynamic organ preservation and significant medical and technical development in the last decades, perfusion devices are still not in routine use. This article describes the various challenges to implement this technology in practice, critically analyzing the role of all involved stakeholders, including clinicians, hospitals, regulatory, and industry, on the background of regional differences worldwide. The clinical need for this technology is discussed first, followed by the current status of research and the impact of costs and regulations. Considering the need for strong collaborations between clinical users, regulatory bodies, and industry, integrated road maps and pathways required to achieve a wider implementation are presented. The role of research development, clear regulatory pathways, and the need for more flexible reimbursement schemes is discussed together with potential solutions to address the most relevant hurdles. This article paints an overall picture of the current liver perfusion landscape and highlights the role of clinical, regulatory, and financial stakeholders worldwide.

Single-cell transcriptomics enables the identification of rare cell types and the inference of state transitions, whereas spatially resolved transcriptomics allows the quantification of cells and genes in the context of tissues. The recent progress in these new technologies is improving our understanding of the cell landscape and its roles in diseases. Here, we review key biological insights into liver homeostasis, development, regeneration, chronic liver disease, and cancer obtained from single-cell and spatially resolved transcriptomics. We highlight recent progress in the liver cell atlas that characterizes the comprehensive cellular composition; diversity and function; the spatial architecture such as liver zonation, cell communication, and proximity; the cell identity conversion and cell-specific alterations that are associated with liver pathology; and new therapeutic targets. We further discuss outstanding challenges, advanced experimental technologies, and computational methods that help to address these challenges.

BACKGROUND AND AIMS: Effective therapies leading to a functional cure for chronic hepatitis B are still lacking. Class A capsid assembly modulators (CAM-As) are an attractive modality to address this unmet medical need. CAM-As induce aggregation of the HBV core protein (HBc) and lead to sustained HBsAg reductions in a chronic hepatitis B mouse model. Here, we investigate the underlying mechanism of action for CAM-A compound RG7907. APPROACH AND RESULTS: RG7907 induced extensive HBc aggregation in vitro , in hepatoma cells, and in primary hepatocytes. In the adeno-associated virus (AAV)-HBV mouse model, the RG7907 treatment led to a pronounced reduction in serum HBsAg and HBeAg, concomitant with clearance of HBsAg, HBc, and AAV-HBV episome from the liver. Transient increases in alanine transaminase, hepatocyte apoptosis, and proliferation markers were observed. These processes were confirmed by RNA sequencing, which also uncovered a role for interferon alpha and gamma signaling, including the interferon-stimulated gene 15 (ISG15) pathway. Finally, the in vitro observation of CAM-A-induced HBc-dependent cell death through apoptosis established the link of HBc aggregation to in vivo loss of infected hepatocytes. CONCLUSIONS: Our study unravels a previously unknown mechanism of action for CAM-As such as RG7907 in which HBc aggregation induces cell death, resulting in hepatocyte proliferation and loss of covalently closed circular DNA or its equivalent, possibly assisted by an induced innate immune response. This represents a promising approach to attain a functional cure for chronic hepatitis B.

BACKGROUND AIMS: The hepatitis E virus (HEV) is a small positive-sense RNA virus that encodes a cytoplasmic form of the capsid protein (ORF2c), essential for virion structure, and a secreted glycosylated form (ORF2s) that accumulates at high titer in serum and can mask neutralizing epitopes. We explored the contribution of ORF2s to HEV replication, and its role in generating antibodies against ORF2 in a nonhuman primate. APPROACH AND RESULTS: We used a recombinant HEV genotype 3 variant that does not express ORF2s due to the introduction of stop codons (ORF2smut). Rhesus macaques (RM) were given intrahepatic injections of infectious wildtype HEV (ORF2swt) RNA or a variant lacking ORF2s expression (ORF2smut). The replication of ORF2smut virus was delayed by approximately 2 weeks compared with ORF2swt and peak titers were nearly 10-fold lower. Reversions of the 3 mutations that blocked ORF2s expression were not detected in the ORF2smut genomes, indicating genetic stability. However, serum antibodies against ORF2 were transiently detected in RMs infected with ORF2smut, whereas they were long lasting in RMs infected with ORF2swt. Moreover, RMs infected with ORF2smut were more susceptible to re-infection, as evidenced by the viral RNA detected in fecal samples and the expansion of HEV-specific CD8+ T cells. CONCLUSIONS: These findings indicate ORF2s may be dispensable for viral replication in vivo but is required for long-lived antibody-mediated responses that protect against HEV re-exposure.

BACKGROUND AND AIMS: Purines are building blocks for the cellular genome, and excessive purine nucleotides are seen in tumors. However, how purine metabolism is dysregulated in tumors, and impacting tumorigenesis remains elusive. APPROACH AND RESULTS: Transcriptomic and metabolomic analyses of purine biosynthesis and purine degradation pathways were performed in the tumor and associated nontumor liver tissues obtained from 62 patients with HCC, one of the most lethal cancers worldwide. We found that most genes in purine synthesis are upregulated, while genes in purine degradation are inhibited in HCC tumors. High purine anabolism is associated with unique somatic mutational signatures linked to patient prognosis. Mechanistically, we discover that increasing purine anabolism promotes epitranscriptomic dysregulation of DNA damage repairing (DDR) machinery through upregulating RNA N6-methyladenosine (m 6 A) modification. High purine anabolic HCC is sensitive to DDR-targeting agents but not to standard HCC treatments, correlating with the clinical outcomes in 5 independent HCC cohorts containing 724 patients. We further showed that high purine anabolism determines the sensitivity to DDR-targeting agents in 5 HCC cell lines in vitro and in vivo . CONCLUSIONS: Our results reveal a central role of purine anabolism in regulating DDR, which could be therapeutically exploited in HCC.

Epigenetic changes are a common feature of human disease, including liver disease and its progression to liver cancer. The most frequent form of liver cancer, HCC, is unusual because most of its causes, or etiologic drivers, are known and are dominated by environmental exposures, including viral infection, alcohol abuse, and overnutrition/metabolic syndrome. The epigenome is a regulatory system overlayed on the genetic material that regulates when, where, and to what extent genes are expressed in developmental, cell type, and disease-associated contexts. Deregulation of the epigenome has emerged as a major player in the pathologic effects of liver disease driving exposures, particularly during their early phases when genetic changes are uncommon. Although it is inherent in the definition of an epigenetic process to be reversible, emerging evidence indicates that epigenetic changes persist after the removal of the exposure and contribute to long-term risk of disease progression. In other systems, environmental exposures lead to beneficial adaptive changes in expression that facilitate processes such as wound healing, and these too are driven by epigenetic changes. What remains unclear, however, is what drives the transition from a beneficial epigenetic memory to a maladaptive scar, the epigenetic processes involved in forming these memories, and whether this process can be modulated for therapeutic purposes. In this review, we discuss these concepts in relation to liver disease and more broadly using examples from other tissue types and diseases, and finally consider how epigenetic therapies could be used to reprogram maladaptive epigenetic memories to delay and/or prevent hepatocarcinogenesis.

BACKGROUND AND AIMS: Although a dysregulated type 1 immune response is integral to the pathogenesis of biliary atresia, studies in both humans and mice have uncovered a type 2 response, primarily driven by type 2 innate lymphoid cells. In nonhepatic tissues, natural type 2 innate lymphoid cell (nILC2s) regulate epithelial proliferation and tissue repair, whereas inflammatory ILC2s (iIlC2s) drive tissue inflammation and injury. The aim of this study is to determine the mechanisms used by type 2 innate lymphoid cell (ILC2) subpopulations to regulate biliary epithelial response to an injury. APPROACH AND RESULTS: Using Spearman correlation analysis, nILC2 transcripts, but not those of iILC2s, are positively associated with cholangiocyte abundance in biliary atresia patients at the time of diagnosis. nILC2s are identified in the mouse liver through flow cytometry. They undergo expansion and increase amphiregulin production after IL-33 administration. This drives epithelial proliferation dependent on the IL-13/IL-4Rα/STAT6 pathway as determined by decreased nILC2s and reduced epithelial proliferation in knockout strains. The addition of IL-2 promotes inter-lineage plasticity towards a nILC2 phenotype. In experimental biliary atresia induced by rotavirus, this pathway promotes epithelial repair and tissue regeneration. The genetic loss or molecular inhibition of any part of this circuit switches nILC2s to inflammatory type 2 innate lymphoid cell-like, resulting in decreased amphiregulin production, decreased epithelial proliferation, and the full phenotype of experimental biliary atresia. CONCLUSIONS: These findings identify a key function of the IL-13/IL-4Rα/STAT6 pathway in ILC2 plasticity and an alternate circuit driven by IL-2 to promote nILC2 stability and amphiregulin expression. This pathway induces epithelial homeostasis and repair in experimental biliary atresia.

BACKGROUND AND AIMS: Predicting changes in disease activity and serological endpoints is necessary for management of patients with chronic hepatitis B (CHB). We examined whether HBV RNA and hepatitis B core-related antigen (HBcrAg), two specialized virological markers proposed to reflect activity of covalently closed circular DNA, may improve ability to predict not sustained inactive carrier [IC] phase, spontaneous alanine aminotransferase [ALT] flare, hepatitis B e antigen [HBeAg] loss and hepatitis B surface antigen [HBsAg] loss. METHODS: Among eligible participants enrolled in the North American Hepatitis B Research Network Adult Cohort Study, we evaluated demographic, clinical and virologic characteristics, including HBV RNA and HBcrAg, to predict not sustained IC phase, ALT flare, HBeAg loss and HBsAg loss through a series of Cox proportional-hazard or logistic regression models, controlling for antiviral therapy use. RESULTS: Among the study population, 54/103 participants experienced not sustained IC phase, 41/1006 had a spontaneous ALT flare, 83/250 lost HBeAg and 54/1127 lost HBsAg. HBV RNA or HBcrAg were predictive of all four events. However, their addition to models of readily available host (age, sex, race/ethnicity), clinical (ALT, use of antiviral therapy) and viral factors (HBV DNA), which had acceptable-excellent accuracy (e.g., area under the curve = 0.72 for ALT flare, 0.92 for HBeAg loss and 0.91 for HBsAg loss), provided only small improvements in predictive ability. CONCLUSION: Given the high predictive ability of readily available markers, HBcrAg and HBV RNA have a limited role in improving prediction of key serologic and clinical events in patients with CHB.

BACKGROUND AND AIMS: Poor patient-reported outcomes (PROs) are common in cirrhosis, including poor sleep and health-related quality of life (HRQOL). HE is a major driver of poor PROs. Many clinicians initiate lactulose therapy to address poor PROs. PRO-triggered therapy, however, has not been studied till date. METHODS: We conducted a 28-day randomized trial of crystalline lactulose therapy (20 g BID) compared with no HE-directed therapy in 52 patients with cirrhosis, portal hypertension, no prior HE, and high Work Productivity and Activity Impairment scores (0-10) attributed to cirrhosis. The primary outcome was change in global HRQOL measured with Short Form-8 Health Survey. Secondary outcomes included change in Animal Naming Test score, Work Productivity and Activity Impairment, and sleep quality (scored "very bad" to "very good"). APPROACH AND RESULTS: Overall, 52 patients underwent randomization; 3 subjects withdrew from the crystalline lactulose arm (1 before medication initiation, 1 due to an unrelated condition, and 1 due to high baseline bowel movements). The average age was 60 years, the average Model for Endstage Liver Disease-Sodium score was 10.5, and 56% of the patients had ascites. Baseline bowel movements were 2.3/day, with 35% of the patients having Bristol Stool Scale >4. At 28 days, there was no improvement in HRQOL: patients receiving crystalline lactulose had an 8.1-point (95% CI: 3.7-12.4) increase compared with 6.6 (95% CI: 2.3-10.8) in the control group ( p = 0.6). Lactulose was associated with a significantly ( p = 0.002) increased Animal Naming Test score (3.7, 95% CI: 2.1-5.4) versus the control group (0.2, 95% CI: -1.7, 1.4). Lactulose users reported more good sleep (92% vs. 52%, p = 0.001) and lower activity impairment (3.0 vs. 4.8, p = 0.02). CONCLUSIONS: Lactulose improves sleep and activity impairment in patients with poor PROs. We did not observe any improvement in global HRQOL after 28 days using the Short Form-8 Health Survey instrument.

NASH is one of the leading causes of chronic liver disease with the potential of evolving towards end-stage liver disease and HCC, even in the absence of cirrhosis. Apart from becoming an increasingly prevalent indication for liver transplantation in cirrhotic and HCC patients, its burden on the healthcare system is also exerted by the increased number of noncirrhotic NASH patients. Intermittent fasting has recently gained more interest in the scientific community as a possible treatment approach for different components of metabolic syndrome. Basic science and clinical studies have shown that apart from inducing body weight loss, improving cardiometabolic parameters, namely blood pressure, cholesterol, and triglyceride levels; insulin and glucose metabolism; intermittent fasting can reduce inflammatory markers, endoplasmic reticulum stress, oxidative stress, autophagy, and endothelial dysfunction, as well as modulate gut microbiota. This review aims to further explore the main NASH pathogenetic metabolic drivers on which intermittent fasting can act upon and improve the prognosis of the disease, and summarize the current clinical evidence.

Hepatobiliary cancers (HBC), including hepatocellular carcinoma (HCC) and cancers of the biliary tract, share high mortality and rising incidence rates. They may also share several risk factors related to unhealthy Western-type dietary and lifestyle patterns as well as increasing body weights and rates of obesity. Recent data also suggest a role for the gut microbiome in the development of HBC and other liver pathologies. The gut microbiome and the liver interact bidirectionally via the "gut-liver axis" which describes the interactive relationship between the gut, its microbiota and the liver. Here, we review the gut-liver interactions within the context of hepatobiliary carcinogenesis by outlining the experimental and observational evidence for the roles of gut microbiome dysbiosis, reduced gut barrier function and exposure to inflammatory compounds as well as metabolic dysfunction as contributors to HBC development. We also outline the latest findings regarding the impact of dietary and lifestyle factors on liver pathologies as mediated by the gut microbiome. Finally, we highlight some emerging gut microbiome editing techniques currently being investigated in the context of hepatobiliary diseases. Although much work remains to be done in determining the relationships between the gut microbiome and hepatobiliary diseases, emerging mechanistic insights are informing novel treatments such as potential microbiota manipulation strategies and guiding public health advice on dietary/lifestyle patterns for the prevention of these lethal cancers.

BACKGROUND AND AIMS: Type 2 diabetes (T2D) and chronic hepatitis B infection (CHB) are risk factors of HCC. Sodium glucose co-transporter 2 inhibitors (SGLT2i) inhibit HCC oncogenesis in preclinical studies. However, clinical studies are lacking. This study aimed to evaluate the impact of SGLT2i use on incident HCC using a territory-wide cohort of exclusively patients with co-existing T2D and CHB. APPROACH AND RESULTS: Patients with co-existing T2D and CHB between 2015 and 2020 were identified from the representative electronic database of the Hong Kong Hospital Authority. Patients with and without SGLT2i use were 1:1 matched by propensity score for their demographics, biochemistry results, liver-related characteristics, and background medications. Cox proportional hazards regression model was used to assess the association between SGLT2i use and incident HCC. A total of 2,000 patients with co-existing T2D and CHB (1,000 in each SGLT2i and non-SGLT2i group; 79.7% on anti-HBV therapy at baseline) were included after propensity-score matching. Over a follow-up of 3,704 person-years, the incidence rates of HCC were 1.39 and 2.52 cases per 100 person-year in SGLT2i and non-SGLT2i groups, respectively. SGLT2i use was associated with a significantly lower risk of incident HCC (HR 0.54, 95%CI: 0.33-0.88, p =0.013). The association remained similar regardless of sex, age, glycemic control, diabetes duration, presence of cirrhosis and hepatic steatosis, timing of anti-HBV therapy, and background antidiabetic agents including dipeptidyl peptidase-4 inhibitors, insulin, or glitazones (all p interaction>0.05). CONCLUSIONS: Among patients with co-existing T2D and CHB, SGLT2i use was associated with a lower risk of incident HCC.

BACKGROUND AND AIMS: Chronic liver disease is a growing epidemic, leading to fibrosis and cirrhosis. TGF-β is the pivotal profibrogenic cytokine that activates HSC, yet other molecules can modulate TGF-β signaling during liver fibrosis. Expression of the axon guidance molecules semaphorins (SEMAs), which signal through plexins and neuropilins (NRPs), have been associated with liver fibrosis in HBV-induced chronic hepatitis. This study aims at determining their function in the regulation of HSCs. APPROACH AND RESULTS: We analyzed publicly available patient databases and liver biopsies. We used transgenic mice, in which genes are deleted only in activated HSCs to perform ex vivo analysis and animal models. SEMA3C is the most enriched member of the semaphorin family in liver samples from patients with cirrhosis. Higher expression of SEMA3C in patients with NASH, alcoholic hepatitis, or HBV-induced hepatitis discriminates those with a more profibrotic transcriptomic profile. SEMA3C expression is also elevated in different mouse models of liver fibrosis and in isolated HSCs on activation. In keeping with this, deletion of SEMA3C in activated HSCs reduces myofibroblast marker expression. Conversely, SEMA3C overexpression exacerbates TGF-β-mediated myofibroblast activation, as shown by increased SMAD2 phosphorylation and target gene expression. Among SEMA3C receptors, only NRP2 expression is maintained on activation of isolated HSCs. Interestingly, lack of NRP2 in those cells reduces myofibroblast marker expression. Finally, deletion of either SEMA3C or NRP2, specifically in activated HSCs, reduces liver fibrosis in mice. CONCLUSION: SEMA3C is a novel marker for activated HSCs that plays a fundamental role in the acquisition of the myofibroblastic phenotype and liver fibrosis.

Inflammation is a hallmark of progressive liver diseases such as chronic viral or immune-mediated hepatitis, alcohol-associated liver disease, and NAFLD. Preclinical and clinical studies have provided robust evidence that cytokines and related cellular stress sensors in innate and adaptive immunity orchestrate hepatic disease processes. Unresolved inflammation and liver injury result in hepatic scarring, fibrosis, and cirrhosis, which may culminate in HCC. Liver diseases are accompanied by gut dysbiosis and a bloom of pathobionts, fueling hepatic inflammation. Anti-inflammatory strategies are extensively used to treat human immune-mediated conditions beyond the liver, while evidence for immunomodulatory therapies and cell therapy-based strategies in liver diseases is only emerging. The development and establishment of novel immunomodulatory therapies for chronic liver diseases has been dampened by several clinical challenges, such as invasive monitoring of therapeutic efficacy with liver biopsy in clinical trials and risk of DILI in several studies. Such aspects prevented advancements of novel medical therapies for chronic inflammatory liver diseases. New concepts modulating the liver immune environment are studied and eagerly awaited to improve the management of chronic liver diseases in the future.

BACKGROUND AND AIMS: The liver is remarkably regenerative and can completely recover even when 80% of its mass is surgically removed. Identification of secreted factors that regulate liver growth would help us understand how organ size and regeneration are controlled but also provide candidate targets to promote regeneration or impair cancer growth. APPROACH AND RESULTS: To enrich for secreted factors that regulate growth control, we induced massive liver overgrowth with either YAP or MYC . Differentially expressed secreted factors were identified in these livers using transcriptomic analysis. To rank candidates by functionality, we performed in vivo CRISPR screening using the Fah knockout model of tyrosinemia. We identified secreted phosphoprotein-2 (SPP2) as a secreted factor that negatively regulates regeneration. Spp2 -deficient mice showed increased survival after acetaminophen poisoning and reduced fibrosis after repeated carbon tetrachloride injections. We examined the impact of SPP2 on bone morphogenetic protein signaling in liver cells and found that SPP2 antagonized bone morphogenetic protein signaling in vitro and in vivo. We also identified cell-surface receptors that interact with SPP2 using a proximity biotinylation assay coupled with mass spectrometry. We showed that SPP2's interactions with integrin family members are in part responsible for some of the regeneration phenotypes. CONCLUSIONS: Using an in vivo CRISPR screening system, we identified SPP2 as a secreted factor that negatively regulates liver regeneration. This study provides ways to identify, validate, and characterize secreted factors in vivo.

BACKGROUND AND AIMS: Senescent hepatocytes accumulate in parallel with fibrosis progression during NASH. The mechanisms that enable progressive expansion of nonreplicating cell populations and the significance of that process in determining NASH outcomes are unclear. Senescing cells upregulate thrombomodulin-protease-activated receptor-1 (THBD-PAR1) signaling to remain viable. Vorapaxar blocks the activity of that pathway. We used vorapaxar to determine if and how THBD-PAR1 signaling promotes fibrosis progression in NASH. APPROACH AND RESULTS: We evaluated the THBD-PAR1 pathway in liver biopsies from patients with NAFLD. Chow-fed mice were treated with viral vectors to overexpress p16 in hepatocytes and induce replicative senescence. Effects on the THBD-PAR1 axis and regenerative capacity were assessed; the transcriptome of p16-overexpressing hepatocytes was characterized, and we examined how conditioned medium from senescent but viable (dubbed "undead") hepatocytes reprograms HSCs. Mouse models of NASH caused by genetic obesity or Western diet/CCl 4 were treated with vorapaxar to determine effects on hepatocyte senescence and liver damage. Inducing senescence upregulates the THBD-PAR1 signaling axis in hepatocytes and induces their expression of fibrogenic factors, including hedgehog ligands. Hepatocyte THBD-PAR1 signaling increases in NAFLD and supports sustained hepatocyte senescence that limits effective liver regeneration and promotes maladaptive repair. Inhibiting PAR1 signaling with vorapaxar interrupts this process, reduces the burden of 'undead' senescent cells, and safely improves NASH and fibrosis despite ongoing lipotoxic stress. CONCLUSION: The THBD-PAR1 signaling axis is a novel therapeutic target for NASH because blocking this pathway prevents accumulation of senescing but viable hepatocytes that generate factors that promote maladaptive liver repair.

BACKGROUND AND AIMS: NAFLD in adolescents is an increasing health crisis worldwide, but its exact global, continental, and national prevalence, its relationship with other metabolic conditions, and the human development index (HDI) globally are not known. APPROACH AND RESULTS: We analyzed data from the Global Burden of Disease Study 2019 to compare global, continental, and national prevalence rates of adolescent NAFLD and associations with other metabolic conditions and HDI. The global NAFLD prevalence in adolescents increased from 3.73% in 1990 to 4.71% in 2019 (a relative increase of 26.27%). The prevalence for the male and female populations was 5.84% and 3.52% in 2019, respectively. The Oceanian and North American continents had the highest adolescent NAFLD prevalence (median: 6.54% and 5.64%, respectively), whereas Europe had the lowest prevalence (median: 3.98%). South America and North America had the highest relative increase in adolescent NAFLD prevalence from 1990 to 2019 (median: 39.25% and 36.87%, respectively). High body mass index and type 2 diabetes mellitus increased significantly in adolescents worldwide. However, only high body mass index and not type 2 diabetes mellitus correlated with NAFLD prevalence in adolescents globally. Countries with a higher HDI had larger increases in adolescent NAFLD prevalence from 1990 to 2019 although countries with the highest HDI (HDI: > 0.9) had the lowest NAFLD prevalence in 2019. CONCLUSIONS: NAFLD in adolescents is an increasing health problem on all continents. Improving environmental factors, including lifestyle but also healthcare policies, can help to prevent NAFLD from developing in children and adolescents and help to improve outcomes in children and adolescents with NAFLD.

BACKGROUND AND AIMS: NASH, characterized by inflammation and fibrosis, is emerging as a leading etiology of HCC. Lipidomics analyses in the liver have shown that the levels of polyunsaturated phosphatidylcholine (PC) are decreased in patients with NASH, but the roles of membrane PC composition in the pathogenesis of NASH have not been investigated. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), a phospholipid (PL) remodeling enzyme that produces polyunsaturated PLs, is a major determinant of membrane PC content in the liver. APPROACH AND RESULTS: The expression of LPCAT3 and the correlation between its expression and NASH severity were analyzed in human patient samples. We examined the effect of Lpcat3 deficiency on NASH progression using Lpcat3 liver-specific knockout (LKO) mice. RNA sequencing, lipidomics, and metabolomics were performed in liver samples. Primary hepatocytes and hepatic cell lines were used for in vitro analyses. We showed that LPCAT3 was dramatically suppressed in human NASH livers, and its expression was inversely correlated with NAFLD activity score and fibrosis stage. Loss of Lpcat3 in mouse liver promotes both spontaneous and diet-induced NASH/HCC. Mechanistically, Lpcat3 deficiency enhances reactive oxygen species production due to impaired mitochondrial homeostasis. Loss of Lpcat3 increases inner mitochondrial membrane PL saturation and elevates stress-induced autophagy, resulting in reduced mitochondrial content and increased fragmentation. Furthermore, overexpression of Lpcat3 in the liver ameliorates inflammation and fibrosis of NASH. CONCLUSIONS: These results demonstrate that membrane PL composition modulates the progression of NASH and that manipulating LPCAT3 expression could be an effective therapeutic for NASH.