Liver Regeneration In Response Research Articles

TRIB1 regulates liver regeneration by antagonizing the NRF2-mediated antioxidant response

Robust regenerative response post liver injuries facilitates the architectural and functional recovery of the liver. Intrahepatic redox homeostasis plays a key role in liver regeneration. In the present study, we investigated the contributory role of Tribbles homolog 1 (Trib1), a pseudokinase, in liver regeneration and the underlying mechanism. We report that Trib1 expression was transiently down-regulated in animal and cell models of liver regeneration. Further analysis revealed that hepatocyte growth factor (HGF) repressed Trib1 transcription by evicting liver X receptor (LXRα) from the Trib1 promoter. Knockdown of Trib1 enhanced whereas over-expression of Trib1 suppressed liver regeneration after partial hepatectomy in mice. Of interest, regulation of liver regenerative response by Trib1 coincided with alterations of intracellular ROS levels, GSH levels, and antioxidant genes. Transcriptional assays suggested that Trib1 influenced cellular redox status by attenuating nuclear factor erythroid 2-related factor 2 (Nrf2) activity. Mechanistically, Trib1 interacted with the C-terminus of Nrf2 thus masking a potential nuclear localization signal (NLS) and blocking nuclear accumulation of Nrf2. Finally, correlation between Trib1 expression, Nrf2 nuclear localization, and cell proliferation was identified in liver specimens taken from patients with acute liver failure. In conclusion, our data unveil a novel pathway that depicts Trib1 as a critical link between intracellular redox homeostasis and cell proliferation in liver regeneration.

Fpr2-/- Mice Developed Exacerbated Alcohol-Associated Liver Disease.

Alcohol-associated liver disease (ALD) is the most common chronic liver disease and carries a significant healthcare burden. ALD has no long-term treatment options aside from abstinence, and the mechanisms that contribute to its pathogenesis are not fully understood. This study aimed to investigate the role of formyl peptide receptor 2 (FPR2), a receptor for immunomodulatory signals, in the pathogenesis of ALD. WT and Fpr2-/- mice were exposed to chronic-binge ethanol administration and subsequently assessed for liver injury, inflammation, and markers of regeneration. The differentiation capacity of liver macrophages and the oxidative burst activity of neutrophils were also examined. Compared to WT, Fpr2-/- mice developed more severe liver injury and inflammation and had compromised liver regeneration in response to ethanol administration. Fpr2-/- mice had fewer hepatic monocyte-derived restorative macrophages, and neutrophils isolated from Fpr2-/- mice had diminished oxidative burst capacity. Fpr2-/- MoMF differentiation was restored when co-cultured with WT neutrophils. Loss of FPR2 led to exacerbated liver damage via multiple mechanisms, including abnormal immune responses, indicating the crucial role of FPR2 in ALD pathogenesis.

Resolving the conflicts around Par2 opposing roles in regeneration by comparing immune-mediated and toxic-induced injuries

BackgroundDifferent factors may lead to hepatitis. Among which are liver inflammation and poisoning. We chose two hepatitis models, typical for these two underlying causes. Thus, we aimed to characterize the role of protease-activated receptor 2 (Par2) in liver regeneration and inflammation to reconcile Par2 conflicting role in many damage models, which sometimes aggravates the induced damage and sometimes alleviates it.MethodsWT and knockout (Par2KO) mice were injected with concanavalin A (ConA) to induce immune-mediated hepatitis or with carbon tetrachloride (CCl4) to elicit direct hepatic damage. To distinguish the immune component from the liver regenerative response, we conducted bone marrow (BM) replacements of WT and Par2KO mice and repeated the damage models.ResultsConA injection caused limited damage in Par2KO mice livers, while in the WT mice severe damage followed by leukocyte infiltration was evident. Reciprocal BM replacement of WT and Par2KO showed that WT BM-reconstituted Par2KO mice displayed marked liver damage, while in Par2KO BM-reconstituted WT mice, the tissue was generally protected.In the CCl4 direct damage model, hepatocytes regenerated in WT mice, whereas Par2KO mice failed to recover. Reciprocal BM replacement did not show significant differences in hepatic regeneration. In Par2KO mice, hepatitis was more apparent, while WT recovered regardless of the BM origin.ConclusionsWe conclude that Par2 activation in the immune system aggravates hepatitis and that Par2 activation in the damaged tissue promotes liver regeneration. When we incorporate this finding and revisit the literature reports, we reconciled the conflicts surrounding Par2’s role in injury, recovery, and inflammation.

Hepatic sinusoids versus central veins: Structures, markers, angiocrines, and roles in liver regeneration and homeostasis.

The blood circulates through the hepatic sinusoids delivering nutrients and oxygen to the liver parenchyma and drains into the hepatic central vein, yet the structures and phenotypes of these vessels are distinctively different. Sinusoidal endothelial cells are uniquely fenestrated, lack basal lamina and possess organelles involved in endocytosis, pinocytosis, degradation, synthesis and secretion. Hepatic central veins are nonfenestrated but are also active in synthesis and secretion. Endothelial cells of sinusoids and central veins secrete angiocrines that play respective roles in hepatic regeneration and metabolic homeostasis. The list of markers for identifying sinusoidal endothelial cells is long and their terminologies are complex. Further, their uses vary in different investigations and, in some instances, could be confusing. Central vein markers are fewer but more distinctive. Here we analyze and categorize the molecular pathways/modules associated with the sinusoid-mediated liver regeneration in response to partial hepatectomy and chemical-induced acute or chronic injury. Similarly, we highlight the findings that central vein-derived angiocrines interact with Wnt/β-catenin in perivenous hepatocytes to direct gene expression and maintain pericentral metabolic zonation. The proposal that perivenous hepatocytes behave as stem/progenitor cells to provoke hepatic homeostatic cell renewal is reevaluated and newer concepts of broad zonal distribution of hepatocyte proliferation in liver homeostasis and regeneration are updated. Thus, this review integrates the structures, biology and physiology of liver sinusoids and central veins in mediating hepatic regeneration and metabolic homeostasis.

Uncovering Sex‐specific Roles of Farnesoid X Receptor in Heme Metabolism and Liver Proliferation

Nuclear receptor, Farnesoid X Receptor (FXR), regulates bile acid homeostasis and has been shown to promote liver regenerative response. Serendipitously, we uncovered a distinct role for FXR in mediating liver injury response in female compared to male mice challenged with 3,5‐diethoxycarboncyl‐1,4‐dihydrocollidine (DDC, a heme biosynthesis disruptor). As expected, the DDC diet led to liver injury as measured by elevated serum ALT and AST levels in both control and FxrKO mice. Furthermore, accumulation of bile plugs and ductular reaction was visible in the WT mice, whereas both of these histological hallmarks were dramatically reduced in FxrKO mice. Despite similar histology, the proliferative response in the hepatocytes were different between both the sexes of FxrKO animals. Loss of Fxr resulted in increased hepatocyte size and low‐grade Ki‐67 positive hepatocyte nuclei even under basal conditions. But upon DDC challenge, FxrKO female livers displayed a dramatic induction of Ki‐67 positive staining even though no bile duct injury was visible. This finding correlated well with increased expression of cyclins. On the contrary, Ki‐67 staining was comparable between male FxrKO livers fed either chow or DDC diet, which matches with lower injury. We are actively investigating the crosstalk of estrogen signaling with FXR in controlling liver proliferation. At the molecular level, genes regulating the cell cycle (Ccnd1, Ccna, Ccnb1) were induced upon injury in the male livers in an Fxr‐dependent manner, whereas this response was not observed in female livers. Expression of Cyp2b10 and Cyp3a11, which are known detoxification genes, were induced with DDC treatment. To test if the absence of bile plugs in FxrKO mice is secondary to reduced heme synthesis in these livers, we examined the heme biosynthetic pathway. We mined previously published data and found strong Fxr occupancy and binding to 6 out of the 8 genes involved in the heme synthesis pathway including Alas1, which is the rate‐limiting step in heme biosynthesis. In summary, FXR may regulate heme metabolism and modulate hepatocyte proliferation in a sex‐specific manner.Support or Funding InformationResearch Scholar Grant TBE 132315

Angiocrine Hepatocyte Growth Factor Signaling Controls Physiological Organ and Body Size and Dynamic Hepatocyte Proliferation to Prevent Liver Damage during Regeneration

Liver sinusoidal endothelial cells (LSECs) control organ functions, metabolism, and development through the secretion of angiokines. LSECs express hepatocyte growth factor (Hgf), which is involved in prenatal development, metabolic homeostasis, and liver regeneration. This study aimed to elucidate the precise contribution of LSEC-derived Hgf in physiological homeostasis and liver regeneration. Stab2-iCretg/wt;Hgffl/fl (HgfΔLSEC) mice were generated to abrogate Hgf expression selectively in LSECs from early fetal development onwards, to study global development, metabolic and endothelial zonation, and organ functions as well as liver regeneration in response to 70% partial hepatectomy (PH). Although zonation and liver/body weight ratios were not altered, total body weight and total liver weight were reduced in HgfΔLSEC. Necrotic organ damage was more marked in HgfΔLSEC mice, and regeneration was delayed 72 hours after PH. This was associated with decreased hepatocyte proliferation at 48 hours after PH. Molecularly, HgfΔLSEC mice showed down-regulation of Hgf/c-Met signaling and decreased expression of Deptor in hepatocytes. Invitro knockdown of Deptor was associated with decreased proliferation. Therefore, angiocrine Hgf controls hepatocyte proliferation and susceptibility to necrosis after partial hepatectomy via the Hgf/c-Met axis involving Deptor to prevent excessive organ damage.

Mice depleted for Exchange Proteins Directly Activated by cAMP (Epac) exhibit irregular liver regeneration in response to partial hepatectomy

The exchange proteins directly activated by cAMP 1 and 2 (Epac1 and Epac2) are expressed in a cell specific manner in the liver, but their biological functions in this tissue are poorly understood. The current study was undertaken to begin to determine the potential roles of Epac1 and Epac2 in liver physiology and disease. Male C57BL/6J mice in which expression of Epac1 and/or Epac2 are deleted, were subjected to partial hepatectomy and the regenerating liver was analyzed with regard to lipid accumulation, cell replication and protein expression. In response to partial hepatectomy, deletion of Epac1 and/or Epac2 led to increased hepatocyte proliferation 36 h post surgery, and the transient steatosis observed in wild type mice was virtually absent in mice lacking both Epac1 and Epac2. The expression of the protein cytochrome P4504a14, which is implicated in hepatic steatosis and fibrosis, was substantially reduced upon deletion of Epac1/2, while a number of factors involved in lipid metabolism were significantly decreased. Moreover, the number of Küpffer cells was affected, and Epac2 expression was increased in the liver of wild type mice in response to partial hepatectomy, further supporting a role for these proteins in liver function. This study establishes hepatic phenotypic abnormalities in mice deleted for Epac1/2 for the first time, and introduces Epac1/2 as regulators of hepatocyte proliferation and lipid accumulation in the regenerative process.

Model-based virtual patient analysis of human liver regeneration predicts critical perioperative factors controlling the dynamic mode of response to resection

BackgroundLiver has the unique ability to regenerate following injury, with a wide range of variability of the regenerative response across individuals. Existing computational models of the liver regeneration are largely tuned based on rodent data and hence it is not clear how well these models capture the dynamics of human liver regeneration. Recent availability of human liver volumetry time series data has enabled new opportunities to tune the computational models for human-relevant time scales, and to predict factors that can significantly alter the dynamics of liver regeneration following a resection.MethodsWe utilized a mathematical model that integrates signaling mechanisms and cellular functional state transitions. We tuned the model parameters to match the time scale of human liver regeneration using an elastic net based regularization approach for identifying optimal parameter values. We initially examined the effect of each parameter individually on the response mode (normal, suppressed, failure) and extent of recovery to identify critical parameters. We employed phase plane analysis to compute the threshold of resection. We mapped the distribution of the response modes and threshold of resection in a virtual patient cohort generated in silico via simultaneous variations in two most critical parameters.ResultsAnalysis of the responses to resection with individual parameter variations showed that the response mode and extent of recovery following resection were most sensitive to variations in two perioperative factors, metabolic load and cell death post partial hepatectomy. Phase plane analysis identified two steady states corresponding to recovery and failure, with a threshold of resection separating the two basins of attraction. The size of the basin of attraction for the recovery mode varied as a function of metabolic load and cell death sensitivity, leading to a change in the multiplicity of the system in response to changes in these two parameters.ConclusionsOur results suggest that the response mode and threshold of failure are critically dependent on the metabolic load and cell death sensitivity parameters that are likely to be patient-specific. Interventions that modulate these critical perioperative factors may be helpful to drive the liver regenerative response process towards a complete recovery mode.

Identification of a Novel Bone Marrow Cell-Derived Accelerator of Fibrotic Liver Regeneration Through Mobilization of Hepatic Progenitor Cells in Mice.

Granulocyte colony stimulating factor (G-CSF) has been reported to ameliorate impaired liver function in patients with advanced liver diseases through mobilization and proliferation of hepatic progenitor cells (HPCs). However, the underlying mechanisms remain unknown. We previously showed that G-CSF treatment increased the number of bone marrow (BM)-derived cells migrating to the fibrotic liver following repeated carbon tetrachloride (CCl4 ) injections into mice. In this study, we identified opioid growth factor receptor-like 1 (OGFRL1) as a novel BM cell-derived accelerator of fibrotic liver regeneration in response to G-CSF treatment. Endogenous Ogfrl1 was highly expressed in the hematopoietic organs such as the BM and spleen, whereas the liver contained a relatively small amount of Ogfrl1 mRNA. Among the peripheral blood cells, monocytes were the major sources of OGFRL1. Endogenous Ogfrl1 expression in both the peripheral blood monocytes and the liver was decreased following repeated CCl4 injections. An intrasplenic injection of cells overexpressing OGFRL1 into CCl4 -treated fibrotic mice increased the number of HPC and stimulated proliferation of hepatic parenchymal cells after partial resection of the fibrotic liver. Furthermore, overexpression of OGFRL1 in cultured HPC accelerated their differentiation as estimated by increased expression of liver-specific genes such as hepatocyte nuclear factor 4α, cytochrome P450, and fatty acid binding protein 1, although it did not affect the colony forming ability of HPC. These results indicate a critical role of OGFRL1 in the mobilization and differentiation of HPC in the fibrotic liver, and administration of OGFRL1-expressing cells may serve as a potential regenerative therapy for advanced liver fibrosis. Stem Cells 2019;37:89-101.

Single-Cell Gene Expression Analysis Identifies Chronic Alcohol-Mediated Shift in Hepatocyte Molecular States After Partial Hepatectomy.

The analysis of molecular states of individual cells, as defined by their mRNA expression profiles and protein composition, has gained widespread interest in studying biological phenomena ranging from embryonic development to homeostatic tissue function and genesis and evolution of cancers. Although the molecular content of individual cells in a tissue can vary widely, their molecular states tend to be constrained within a transcriptional landscape partly described by the canonical archetypes of a population of cells. In this study, we sought to characterize the effects of an acute (partial hepatectomy) and chronic (alcohol consumption) perturbation on the molecular states of individual hepatocytes during the onset and progression of liver regeneration. We analyzed the expression of 84 genes across 233 individual hepatocytes acquired using laser capture microdissection. Analysis of the single-cell data revealed that hepatocyte molecular states can be considered as distributed across a set of four states irrespective of perturbation, with the proportions of hepatocytes in these states being dependent on the perturbation. In addition to the quiescent, primed, and replicating hepatocytes, we identified a fourth molecular state lying between the primed and replicating subpopulations. Comparison of the proportions of hepatocytes from each experimental condition in these four molecular states suggested that, in addition to aberrant priming, a slower transition from primed to replication state could contribute toward ethanol-mediated suppression of liver regenerative response to partial hepatectomy.

63. Partial splenic artery embolization therapy in hemophilia a with decompensated cld causing hypersplenism: caution to hepatologists- a case report

Background and Aims: Partial splenic artey embolization (PSE) have been prescribed extensively by hepatologists to avoid splenectomy in special case of hemophilia A and to improve symptoms and hematological indices, and to also decrease CLD decompensation. Splenomegaly is a common sequela of cirrhosis, and is frequently associated with decreased hematologic indices including pancytopenia. In liver tissues after PSE, proliferating cell nuclear antigen (PCNA)-positive hepatocytes were remarkably increased, speculating that PSE induced liver regenerative response and regularly monitoring of symptoms are required. Case Summary: A 41 Year old, male known case of Hemophilia A with decompensated cirrhosis with portal hypertension with hypersplenism (pancytopenia) secondary to hepatitis C [MELD Na-12, CTP-9/B] presented with 3 month history of dyspnoea of exertion (DOE) with malena with progressive developement oedema in both lower extremities and abdominal distention, requiring support while walking. On further evaluation, normal renal function, hypoalbuminemia and first time detected as anti HCV POSITIVE and found to have elevated HCV RNA load 145000, with genotype 3, factor VIII assay <15 obtained. Patient was diagnosed with HCV related decompensated cirrhosis of liver with portal hypertension induced hypersplenism. After patient underwent partial splenic artery embolization, patient's symptoms improved and he had decreased ascites and pedal edema and improved hematological indices over a period of a 3 month. Conclusions: Partial splenic artery embolization has a great potential in the management of hypersplenism due to liver cirrhosis. Partial splenic artery embolization is particularly valuable amongst those cirrhotic patients who are not viable candidates for splenectomy in special case like hemophilia A. The author has none to declare.

Abstract 4142: Conformational dynamics of the chimeric kinase DNAJB1-PRKACA, the driver for fibrolamellar hepatocellular carcinoma

Abstract In fibrolamellar hepatocellular carcinoma (FLC) there is a single common genetic alteration in all tumors: A deletion in one copy of chromosome 19 resulting in the fusion of the first exon of DNAJB1, encoding the J-domain of heat shock protein 40, with exons 2-10 of the catalytic subunit of protein kinase A, PRKACA [1]. This produces an enzymatically active chimeric protein. Expression of the chimera in mouse liver either by recreating the deletion by CRISPR/Cas9, or expression, in trans, by a transposon is sufficient to produce FLC [2]. We used molecular dynamics simulations, NMR, and SAXS to analyze the conformational dynamics of the native and chimeric kinase. The most significant differences were in the amino domain with the chimera in an ensemble of conformations. Some structures had the J-domain tucked under the large lobe of the kinase, similar to that reported in the crystal structure, and in others the J-domain was dislodged from the core of the kinase, swinging free in solution. These simulated dislodged states were captured experimentally both by NMR and small angle X-ray scattering. Modeling of the different conformations onto the RIIβ holoenzyme revealed no obvious steric interactions suggesting that the J-domain does not preclude formation of the holoenzyme. The flexible conformations appear to be independent of the nucleotide/substrate binding mode as they were observed in ATP, ADP, Apo, and ATP-PKI bound states. [1] Honeyman, J. N. et al. Detection of a recurrent DNAJB1-PRKACA chimeric transcript in fibrolamellar hepatocellular carcinoma. Science 343, 1010-1014 (2014). [2] Kastenhuber, E. R. et al. DNAJB1-PRKACA fusion kinase interacts with β-catenin and the liver regenerative response to drive fibrolamellar hepatocellular carcinoma. Proc. Natl. Acad. Sci. 201716483 (2017). doi:10.1073/pnas.1716483114 Citation Format: Michael D. Tomasini, Yingiie Wang, Adak Karamafrooz, James Hall, Susan S. Taylor, Thijs Beuming, Gianluigi Veglia, Sanford M. Simon. Conformational dynamics of the chimeric kinase DNAJB1-PRKACA, the driver for fibrolamellar hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4142.

TRAP-seq identifies cystine/glutamate antiporter as a driver of recovery from liver injury.

Understanding the molecular basis of the regenerative response following hepatic injury holds promise for improved treatment of liver diseases. Here, we report an innovative method to profile gene expression specifically in the hepatocytes that regenerate the liver following toxic injury. We used the Fah-/- mouse, a model of hereditary tyrosinemia, which conditionally undergoes severe liver injury unless fumarylacetoacetate hydrolase (FAH) expression is reconstituted ectopically. We used translating ribosome affinity purification followed by high-throughput RNA sequencing (TRAP-seq) to isolate mRNAs specific to repopulating hepatocytes. We uncovered upstream regulators and important signaling pathways that are highly enriched in genes changed in regenerating hepatocytes. Specifically, we found that glutathione metabolism, particularly the gene Slc7a11 encoding the cystine/glutamate antiporter (xCT), is massively upregulated during liver regeneration. Furthermore, we show that Slc7a11 overexpression in hepatocytes enhances, and its suppression inhibits, repopulation following toxic injury. TRAP-seq allows cell type-specific expression profiling in repopulating hepatocytes and identified xCT, a factor that supports antioxidant responses during liver regeneration. xCT has potential as a therapeutic target for enhancing liver regeneration in response to liver injury.

BMP Signalling at the Crossroad of Liver Fibrosis and Regeneration.

Bone Morphogenetic Proteins (BMPs) belong to the Transforming Growth Factor-β (TGF-β) family. Initially identified due to their ability to induce bone formation, they are now known to have multiple functions in a variety of tissues, being critical not only during development for tissue morphogenesis and organogenesis but also during adult tissue homeostasis. This review focus on the liver as a target tissue for BMPs actions, devoting most efforts to summarize our knowledge on their recently recognized and/or emerging roles on regulation of the liver regenerative response to various insults, either acute or chronic and their effects on development and progression of liver fibrosis in different pathological conditions. In an attempt to provide the basis for guiding research efforts in this field both the more solid and more controversial areas of research were highlighted.

DNAJB1–PRKACA fusion kinase interacts with β-catenin and the liver regenerative response to drive fibrolamellar hepatocellular carcinoma

A segmental deletion resulting in DNAJB1-PRKACA gene fusion is now recognized as the signature genetic event of fibrolamellar hepatocellular carcinoma (FL-HCC), a rare but lethal liver cancer that primarily affects adolescents and young adults. Here we implement CRISPR-Cas9 genome editing and transposon-mediated somatic gene transfer to demonstrate that expression of either the endogenous fusion protein or a chimeric cDNA leads to the formation of indolent liver tumors in mice that closely resemble human FL-HCC. Notably, overexpression of the wild-type PRKACA was unable to fully recapitulate the oncogenic activity of DNAJB1-PRKACA, implying that FL-HCC does not simply result from enhanced PRKACA expression. Tumorigenesis was significantly enhanced by genetic activation of β-catenin, an observation supported by evidence of recurrent Wnt pathway mutations in human FL-HCC, as well as treatment with the hepatotoxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine, which causes tissue injury, inflammation, and fibrosis. Our study validates the DNAJB1-PRKACA fusion kinase as an oncogenic driver and candidate drug target for FL-HCC, and establishes a practical model for preclinical studies to identify strategies to treat this disease.

Liver-specific deletion of LASS2 delayed regeneration of mouse liver after partial hepatectomy

The capacity of liver regeneration is critical for patients with liver diseases. However, cellular and molecular mechanisms of liver regeneration are still incompletely defined. Here, we assessed roles of LASS2 in liver regeneration following partial hepatectomy (PHx) in mice. Our results showed that protein level of LASS2 remarkably increased during liver regeneration after PHx in wildtype (WT) mice. Comparing to WT mice, liver regeneration index after PHx was significantly decreased from day 1 to day 5 in liver-specific LASS2 knockout (LASS2-LKO) mice. Interestingly, liver mass of LASS2-LKO mice could sufficiently recover at day 14 after PHx. Immunohistochemistry (IHC) and western blot analyses revealed that proliferation markers, such as PCNA and Ki67, were potently reduced during liver regeneration in LASS2-LKO mice. In addition, several cell cycle related molecules, such as cyclin A, CDK2 and p-Rb, were decreased in LASS2-LKO mice after PHx. Co-immunoprecipitation assay further revealed a decreased formation of CDK4/cyclin D1 complex after PHx in LASS2-LKO mice. However, phosphorylation of Akt was significantly activated from day 2 after PHx in LASS2-LKO mice when compared with that in WT mice, which may explain the recovery of liver mass at the late stage of liver regeneration in LASS2-LKO mice. Taken together, we conclude that LASS2 plays an important role in efficient liver regeneration in response to PHx.

The Effect of l-Ascorbate 1-(2-Hydroxyethyl)-4,6-Dimethyl-1,2-Dihydropyrimidin-2-One on the Regeneration of the Planarian Girardia tigrina

The effect of l-ascorbate 1-(2-hydroxyethyl)-4,6-dimethyl-1,2-dihydropyrimidine-2-one, a co-crystal of Xymedon with ascorbic acid, derived from pyrimidine on the regeneration process of the planarian Girardia tigrina (Girard, 1850) has been investigated. Being a co-crystal of Xymedon with ascorbic acid, the preparation is characterized by the improved properties compared to Xymedon. The new preparation falls within the group of hepatoprotectors capable of liver regeneration in response to various destructive factors. It has been shown that the new preparation at different concentration levels can inhibit planarian head regeneration. Two combinations of the test substance were used in the work: a neat form of the preparation; a mixture of the preparation with Na2CO3 to reduce the acidity of the test substance. The neat preparation showed a statistically insignificant tendency to an increase in the regeneration of G. tigrina planarians. When mixed with Na2CO3, the preparation inhibited the regeneration of G. tigrina planarians. G. tigrina planarians is a popular model for studying regeneration processes and stem cell proliferation.

LYVE1 and PROX1 in the reconstruction of hepatic sinusoids after partial hepatectomy in mice

Revascularisation is crucial to liver regeneration after liver injury, but the process remains unclear. This study investigated changes in the levels and distribution of lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1) and prospero homeobox protein 1 (PROX1) in liver tissue sections after partial hepatectomy in mice. Mice were subjected to partial hepatectomy. Control animals were sham-operated. From days 1 through 8, the remaining liver tissues were collected from 8 animals each day. Histology showed that after partial hepatectomy, the remaining liver tissue samples underwent initial degeneration and then hepatocyte proliferation and regeneration. Using immunohistochemical analysis, relative to the control a significantly higher number of vascular endothelial growth factor A (VEGFA)-positive hepatocytes was observed on days 4 and 5 after partial hepatectomy. LYVE1 was mainly present in the liver sinusoidal endothelial cells and the number of LYVE1-positive cells gradually increased with time. PROX1 was detected in some of the hepatocytes, but liver sinusoidal endothelial cells, artery, and vein were negative for PROX1 staining in the early stage after liver injury. The presence of PROX1 could be observed in some central veins as well as liver sinusoidal endothelial cells. Seven days after partial hepatectomy, colocalisation of PROX1 and LYVE1 was observed in liver sinusoidal endothelial cells and veins. This study revealed the dynamic process of revascularisation and hepatic sinusoid reconstruction during liver regeneration in response to liver injury in mice. PROX1 and LYVE1 may participate in this process and serve as biomarkers for identification of newly formed liver sinusoidal endothelial cells.

P53 Regulates Progression of Injury and Liver Regeneration After Acetaminophen Overdose

Liver regeneration in response to acetaminophen (APAP) overdose is a critical determinant of final patient outcome. Intricate cellular signaling during liver regeneration triggers liver cell proliferation, wound healing (if required) and restoration of liver mass and function. The p53 tumor suppressor protein is a critical regulator of cell cycle and apoptosis. However its role in liver regeneration after APAP overdose induced Acute Liver Failure (ALF) is not known. The pathogenesis of acute liver failure induced by APAP overdose can be divided into three phases including initiation of injury (formation of a reactive metabolite NAPQI and protein adducts) progression of injury (oxidative stress, mitochondrial and DNA damage resulting in necrosis) and regeneration/recovery phase (cell proliferation, angiogenesis and tissue repair). Here we show that p53 plays a critical role in inhibiting progression of injury and liver regeneration following APAP overdose mediated Acute Liver Injury (ALI). Eight‐week‐old male WT and p53KO mice (C57BL/6J background) were studied over time course of 0 to 96 hr following treatment with APAP300 (300mg/kg). Histology and serum ALT analysis showed similar liver injury in WT and p53KO mice at 1 and 12 hr however p53KO mice had significantly higher injury at 24 hr after APAP treatment. Interestingly, despite higher liver injury p53KO mice recovered equally to WT mice at 48 and 96 hr after APAP administration. Transcriptome analysis using liver RNA at 12, 24, 48hr from both groups revealed that p53KO mice had disrupted metabolic homeostasis, induced pro‐inflammatory and proliferative signaling. Further, molecular analysis of these pathways was done to confirm the findings. p53KO mice showed prolonged steatosis, lower mitochondrial DNA content, reduced expression of TFAM and mitochondrial complexes up to 24hr correlating with prolonged higher liver injury. p53 targets involved in fatty acid homeostasis, SREBP2 protein and GAMT mRNA expression correlated with prolonged steatosis in p53KO group. Liver regeneration determined by PCNA staining and cell cycle protein expression demonstrated that p53KO mice had rapid liver regeneration. Western blot analysis of EGFR, ERK and AKT showed sustained growth factor signaling in p53KO mice than WT mice after APAP treatment. These data illustrate that p53 has stage specific role during APAP‐induced ALF. p53 prevents progression of liver injury by maintaining mitochondrial and metabolic homeostasis after APAP overdose induced ALI. Further, p53 regulates initiation of liver regeneration through inflammatory and proliferative signaling after APAP overdose. These studies have revealed a novel role of p53 in acute liver injury pathogenesis.Support or Funding InformationNational Center for Research Resources (5P20RR021940‐07) Liver Scholar Award by AASLD/American Liver Foundation R01 DK098414

Interleukin 6-dependent genomic instability heralds accelerated carcinogenesis following liver regeneration on a background of chronic hepatitis.

Our findings indicate that genomic instability derived during the IL6-mediated liver regenerative response within a milieu of chronic inflammation links partial hepatectomy to accelerated hepatocarcinogenesis; this suggests a new therapeutic approach through the usage of an anti-IL6 treatment to extend the tumor-free survival of patients undergoing surgical resection. (Hepatology 2017;65:1600-1611).