Regulation Of Liver Regeneration Research Articles

PGD 2 /DP1 axis promotes liver regeneration by secreting Wnt2 in KCs in mice.

The liver possesses a remarkable regenerative capacity in response to injuries or viral infections. Various growth factors and cytokines are involved in regulating liver regeneration. Prostaglandin D 2 , a pro-resolution lipid mediator, is the most abundant hepatic prostanoid. However, the role of prostaglandin D 2 in the injury-induced liver regeneration remains unclear. Two-thirds partial hepatectomy (70% PH), massive hepatectomy (85% resection), and carbon tetrachloride-induced chronic injury were performed in mice to study the mechanisms of live regeneration. Hepatic prostaglandin D 2 production was elevated in mice after PH. Global deletion of D prostanoid receptor (DP) 1, but not DP2, slowed PH-induced liver regeneration in mice, as evidenced by lower liver weight to body weight ratio, less Ki67 + hepatocyte proliferation, and G2/M phase hepatocytes. In addition, DP1 deficiency, specifically in resident KCs, and not in endothelial cells or HSCs, retarded liver regeneration in mice after PH. Conversely, the overexpression of exogenous DP1 in KCs accelerated liver regeneration in mice. Mechanistically, DP1 activation promoted Wnt2 transcription in a PKA/CREB-dependent manner in resident KCs and mediated hepatocyte proliferation through Frizzled8/β-catenin signaling. Adeno-associated virus vector serotype 8-mediated Frizzled8 knockdown in hepatocytes attenuated accelerated liver regeneration in KC-DP1 transgenic mice after PH. Treatment with the DP1 receptor agonist BW245C promotes PH-induced liver regeneration in mice. DP1 activation mediates crosstalk between KCs and hepatocytes through Wnt2 and facilitates liver regeneration. Hence, DP1 may serve as a novel therapeutic target in acute and chronic liver diseases.

Vitamin D Receptor Regulates Liver Regeneration After Partial Hepatectomy in Male Mice.

Vitamin D signals through the vitamin D receptor (VDR) to induce its end-organ effects. Hepatic stellate cells control development of liver fibrosis in response to stressors and vitamin D signaling decreases fibrogenesis. VDR expression in hepatocytes is low in healthy liver, and the role of VDR in hepatocyte proliferation is unclear. Hepatocyte-VDR null mice (hVDR) were used to assess the role of VDR and vitamin D signaling in hepatic regeneration. hVDR mice have impaired liver regeneration and impaired hepatocyte proliferation associated with significant differential changes in bile salts. Notably, mice lacking hepatocyte VDR had significant increases in expression of conjugated bile acids after partial hepatectomy, consistent with failure to normalize hepatic function by the 14-day time point tested. Real-time PCR of hVDR and control livers showed significant changes in expression of cell-cycle genes including cyclins D1 and E1 and cyclin-dependent kinase 2. Gene expression profiling of hepatocytes treated with vitamin D or control showed regulation of groups of genes involved in liver proliferation, hepatitis, liver hyperplasia/hyperproliferation, and liver necrosis/cell death. Together, these studies demonstrate an important functional role for VDR in hepatocytes during liver regeneration. Combined with the known profibrotic effects of impaired VDR signaling in stellate cells, the studies provide a mechanism whereby vitamin D deficiency would both reduce hepatocyte proliferation and permit fibrosis, leading to significant liver compromise.

Hepatocyte-derived extracellular vesicles regulate liver regeneration after partial hepatectomy.

While significant progress has been made in understanding different aspects of liver regeneration, the molecular mechanisms responsible for the initiation and termination of cell proliferation in the liver after massive loss or injury of liver tissue remain unknown. The loss of liver mass affects tissue-specific mitogenic inhibitors in the blood, which in turn regulate the proliferation of remaining hepatocytes and liver regeneration. Although well described in a number of publications, which inhibitory substances or "sensor molecules" control the regeneration mechanisms to properly maintain liver size remain unknown. Extracellular vesicles (EVs) are nano-sized, membrane-limited structures secreted by cells into the extracellular space. Their proposed role is stable intercellular carriers of proteins and RNAs, mostly micro-RNA, from secreted to recipient cells. Taken up by the recipient cells, EVs can significantly modulate their biological functions. In the present study, using in vivo and in vitro models, we demonstrate that hepatocyte proliferation and liver regeneration are regulated by EVs secreted by hepatocytes into the bloodstream. This regulation is carried out through a negative feedback mechanism, which explains the very precise regeneration of liver tissue after massive damage. We also demonstrate that an essential component of this mechanism is RNA carried by hepatocyte-derived EVs. These findings open up a new and unexplored area of biology regarding the mechanisms involved in the homeostasis regulation of various constantly renewing tissues by maintaining the optimal size and correct ratio between differentiating and proliferating cells.

Critical Roles of the Sphingolipid Metabolic Pathway in Liver Regeneration, Hepatocellular Carcinoma Progression and Therapy.

The sphingolipid metabolic pathway, an important signaling pathway, plays a crucial role in various physiological processes including cell proliferation, survival, apoptosis, and immune regulation. The liver has the unique ability to regenerate using bioactive lipid mediators involving multiple sphingolipids, including ceramide and sphingosine 1-phosphate (S1P). Dysregulation of the balance between sphingomyelin, ceramide, and S1P has been implicated in the regulation of liver regeneration and diseases, including liver fibrosis and hepatocellular carcinoma (HCC). Understanding and modulating this balance may have therapeutic implications for tumor proliferation, progression, and metastasis in HCC. For cancer therapy, several inhibitors and activators of sphingolipid signaling, including ABC294640, SKI-II, and FTY720, have been discussed. Here, we elucidate the critical roles of the sphingolipid pathway in the regulation of liver regeneration, fibrosis, and HCC. Regulation of sphingolipids and their corresponding enzymes may considerably influence new insights into therapies for various liver disorders and diseases.

Ten-eleven translocation-2-mediated macrophage activation promotes liver regeneration

BackgroundThe remarkable regenerative capacity of the liver enables recovery after radical Hepatocellular carcinoma (HCC) resection. After resection, macrophages secrete interleukin 6 and hepatocyte growth factors to promote liver regeneration. Ten-eleven translocation-2 (Tet2) DNA dioxygenase regulates pro-inflammatory factor secretion in macrophages. In this study, we explored the role of Tet2 in macrophages and its function independent of its enzymatic activity in liver regeneration.MethodsThe model of liver regeneration after 70% partial hepatectomy (PHx) is a classic universal model for studying reparative processes in the liver. Mice were euthanized at 0, 24, and 48 h after PHx. Enzyme-linked immunosorbent assays, quantitative reverse transcription-polymerase chain reaction, western blotting, immunofluorescence analysis, and flow cytometry were performed to explore immune cell infiltration and liver regenerative capability. Molecular dynamics simulations were performed to study the interaction between Tet2 and signal transducer and activator of transcription 1 (Stat1).ResultsTet2 in macrophages negatively regulated liver regeneration in the partial hepatectomy mice model. Tet2 interacted with Stat1, inhibiting the expression of proinflammatory factors and suppressing liver regeneration. The Tet2 inhibitor attenuated the interaction between Stat1 and Tet2, enhanced Stat1 phosphorylation, and promoted hepatocyte proliferation. The proliferative function of the Tet2 inhibitor relied on macrophages and did not affect hepatocytes directly.ConclusionOur findings underscore that Tet2 in macrophages negatively regulates liver regeneration by interacting with Stat1. Targeting Tet2 in macrophages promotes liver regeneration and function after a hepatectomy, presenting a novel target to promote liver regeneration and function.Graphical Tet2 interacts with Stat1 in the cytoplasm and suppresses IFN-γ-induced macrophage activation. Tet2 inhibitor decreases the combination of Stat1 and Tet2, activating the macrophages through the Jak-Stat pathway. The activation of macrophages increases the transcription and translation of the IL-6 and promotes liver regeneration.BnQa2gdaXkcfesAu78GqfXVideo

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

Liver regeneration is vital for the recovery of liver function after injury, yet the underlying mechanism remains to be elucidated. Forkhead box protein A3 (FOXA3), a member of the forkhead box family, plays important roles in endoplasmic reticulum stress sensing, and lipid and glucose homoeostasis, yet its functions in liver regeneration are unknown. Here, we explored whether Foxa3 regulates liver regeneration via acute and chronic liver injury mice models. We further characterised the molecular mechanism by chromatin immunoprecipitation sequencing and rescue experiments invivo and invitro. Then, we assessed the impact of Foxa3 pharmacological activation on progression and termination of liver regeneration. Finally, we confirmed the Foxa3-Cebpb axis in human liver samples. Foxa3 is dominantly expressed in hepatocytes and cholangiocytes and is induced upon partial hepatectomy (PH) or carbon tetrachloride (CCl4) administration. Foxa3 deficiency in mice decreased cyclin gene levels and delayed liver regeneration after PH, or acute or chronic i.p. CCl4 injection. Conversely, hepatocyte-specific Foxa3 overexpression accelerated hepatocytes proliferation and attenuated liver damage in an CCl4-induced acute model. Mechanistically, Foxa3 directly regulates Cebpb transcription, which is involved in hepatocyte division and apoptosis both invivo and invitro. Of note, Cebpb overexpression in livers of Foxa3-deficient mice rescued their defects in cell proliferation and regeneration upon CCl4 treatment. In addition, pharmacological induction of Foxa3 via cardamonin speeded up hepatocyte proliferation after PH, without interfering with liver regeneration termination. Finally, Cebpb and Ki67 levels had a positive correlation with Foxa3 expression in human chronic disease livers. These data characterise Foxa3 as a vital regulator of liver regeneration, which may represent an essential factor to maintain liver mass after liver injury by governing Cebpb transcription. Liver regeneration is vital for the recovery of liver function after chemical insults or hepatectomy, yet the underlying mechanism remains to be elucidated. Herein, via invitro and invivo models and analysis, we demonstrated that Forkhead box protein A3 (FOXA3), a Forkhead box family member, maintained normal liver regeneration progression by governing Cebpb transcription and proposed cardamonin as a lead compound to induce Foxa3 and accelerate liver repair, which signified that FOXA3 may be a potential therapeutic target for further preclinical study on treating liver injury.

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.

A circular RNA produced by LRBA promotes cirrhotic mouse liver regeneration through facilitating the ubiquitination degradation of p27.

Accumulating circular RNAs (circRNAs) play important roles in tissue repair and organ regeneration. However, the biological effects of circRNAs on liver regeneration remain largely unknown. This study aims to systematically elucidate the functions and mechanisms of circRNAs derived from lipopolysaccharide-responsive beige-like anchor protein (LRBA) in regulating liver regeneration. CircRNAs derived from mouse LRBA gene were identified using CircBase. In vivo and in vitro experiments were conducted to confirm the effects of circLRBA on liver regeneration. RNA pull-down and RNA immunoprecipitation assays were used to investigate the underlying mechanisms. Clinical samples and cirrhotic mouse models were used to evaluate the clinical significance and transitional value of circLRBA. Eight circRNAs derived from LRBA were registered in CircBase. The circRNA mmu_circ_0018031 (circLRBA) was significantly upregulated in the liver tissues after 2/3 partial hepatectomy (PHx). Adeno-associated virus serotype 8 (AAV8)-mediated knockdown of circLRBA markedly inhibited mouse liver regeneration after 2/3 PHx. In vitro experiments confirmed that circLRBA exerted its growth-promoting function mainly through liver parenchymal cells. Mechanistically, circLRBA acted as a scaffold for the interaction between E3 ubiquitin-protein ligase ring finger protein 123 and p27, facilitating the ubiquitination degradation of p27. Clinically, circLRBA was lowly expressed in cirrhotic liver tissues and negatively correlated with perioperative levels of total bilirubin. Furthermore, overexpression of circLRBA enhanced cirrhotic mouse liver regeneration after 2/3 PHx. We conclude that circLRBA is a novel growth promoter in liver regeneration and a potential therapeutic target related to deficiency of cirrhotic liver regeneration.

MKK4 Inhibitors-Recent Development Status and Therapeutic Potential.

MKK4 (mitogen-activated protein kinase kinase 4; also referred to as MEK4) is a dual-specificity protein kinase that phosphorylates and regulates both JNK (c-Jun N-terminal kinase) and p38 MAPK (p38 mitogen-activated protein kinase) signaling pathways and therefore has a great impact on cell proliferation, differentiation and apoptosis. Overexpression of MKK4 has been associated with aggressive cancer types, including metastatic prostate and ovarian cancer and triple-negative breast cancer. In addition, MKK4 has been identified as a key regulator in liver regeneration. Therefore, MKK4 is a promising target both for cancer therapeutics and for the treatment of liver-associated diseases, offering an alternative to liver transplantation. The recent reports on new inhibitors, as well as the formation of a startup company investigating an inhibitor in clinical trials, show the importance and interest of MKK4 in drug discovery. In this review, we highlight the significance of MKK4 in cancer development and other diseases, as well as its unique role in liver regeneration. Furthermore, we present the most recent progress in MKK4 drug discovery and future challenges in the development of MKK4-targeting drugs.

In vivo screening identifies SPP2, a secreted factor that negatively regulates liver regeneration.

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. 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. 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.

The Ratio of Activin A and Follistatin-Like 3 Is Associated With Posthepatectomy Liver Failure and Morbidity in Patients Undergoing Liver Resection.

Activin A is a key regulator in liver regeneration, but data evaluating its role in humans after hepatic surgery are limited. In this study we explore the predictive role of circulating activin A, its antagonist follistatin-like 3 (FSTL-3), and their ratio for posthepatectomy liver failure (PHLF) and monitor their levels after surgery, to evaluate their role in human liver regeneration. Activin A and FSTL-3 levels were assessed in 59 patients undergoing liver surgery. Using receiver operating characteristic analysis, we evaluated the predictive potential of activin A, FSTL-3, and their ratio. While perioperative dynamics of activin A and FSTL3 were significantly affected by hepatic resection (activin A P= .045, FSTL-3 P= .005), their functionally relevant ratio did not significantly change (P= .528). Neither activin A nor FSTL-3 alone but only their ratio exhibited a significant predictive potential for PHLF (area under the curve: 0.789, P= .038). Patients with low preoperative activin A/FSTL-3 ratio were found to more frequently suffer from PHLF (0.017) and morbidity (0.005). Activin A/FSTL-3 ratio predicts PHLF and morbidity. Its significance in preoperative patient assessment needs to be further validated in larger, independent cohorts.

РОЛЬ ЭНДОТЕЛИЯ В ФОРМИРОВАНИИ ФИБРОЗА ПЕЧЕНИ

Chronic liver disease is a worldwide health problem. A significant proportion of the manifestations and complications of chronic liver diseases is due to liver fibrosis and its subsequent transition to liver cirrhosis. The initial and the key link in the formation of fibrotic changes in the liver are liver sinusoidal endothelial cells (LSEC). In view of the unique structure and central position of the liver endothelial tissue in the pathogenesis of fibrosis, it seems relevant to present current data in the form of this review. LSECs are the only endothelial cells in the body that lack a basement membrane and contain transcellular pores called fenestrae. At the initial stages of the fibrogenesis process, LSECs change their phenotype: they lose fenestrae and develop a basement membrane, turning into a continuous endothelium. LSECs are involved in fibrosis through the secretion of angiocrine signals that act as paracrine factors that balance the liver’s response to injury towards fibrosis or regeneration. LSEC cells are very sensitive to the slightest changes in the microenvironment, with prolonged exposure they quickly change their phenotype, their numerous functions are disrupted, including vasodilator, anti-inflammatory, antithrombotic and antifibrotic, as well as the regulation of angiogenesis and regeneration, and prevention of HSC activation. Such changes in the phenotype are called endothelial dysfunction. Loss of fenestres (capillaryization) by LSEC cells is the initial event in liver fibrosis. It precedes HSC activation and promotes fibrosis and progression to cirrhosis. Fenestra maintains liver homeostasis, promotes efficient transport of lipoproteins, regulates liver regeneration and immune tolerance. LSEC fenestra are approximately 50-200 nm in diameter, and most of them are clustered into several dozen ultrastructures called sieve plates. Chronic liver injury leads to deep dedifferentiation of LSECs, which lose their vasoprotective properties and become vasoconstrictive, proinflammatory, and prothrombotic. Major molecular dysregulations seen in LSEC in chronic liver disease include fenestra loss and basement membrane development that interfere with the exchange of molecules such as lipoproteins and oxygen with hepatocytes, promoting steatosis and parenchymal apoptosis; reduction of NO by suppression of KLF2 and endothelial NO synthase (eNOS) activity, together with an increase in ROS-mediated NO uptake, leading to activation of hepatic stellate cells and deposition of extracellular matrix; increased production of vasoconstrictors (such as endothelin 1 or thromboxane A2) and pro-inflammatory cytokines, further exacerbating sinusoidal constriction. These pathological changes lead to sinusoidal vasoconstriction, microvascular dysfunction, fibrosis, and ultimately portal hypertension. Thus, LSECs play complex interrelated roles in maintaining liver homeostasis and are involved as factors in inflammation and fibrogenesis in liver diseases. Their unique position, phenotype, and function make them attractive candidates for organ-specific therapies, and it is likely that more therapies targeting these cells will be tested in the future as novel therapies to reduce liver damage and inflammation, and to prevent or reversal of fibrogenesis.

Transcriptional regulation of NDUFA4L2 by NFIB induces sorafenib resistance by decreasing reactive oxygen species inhepatocellular carcinoma.

Sorafenib is one a first-line therapeutic drugs for advanced hepatocellular carcinoma (HCC). However, only 30% of patients benefit from sorafenib due to drug resistance. We and other groups have revealed that nuclear factor I B (NFIB) regulates liver regeneration and carcinogenesis, but its role in drug resistance is poorly known. We found that NFIB was more upregulated in sorafenib-resistant SMMC-7721 cells compared to parental cells. NFIB knockdown not only sensitized drug-resistant cells to sorafenib but also inhibited the proliferation and invasion of these cells. Meanwhile, NFIB promoted the proliferation and invasion of HCC cells in vitro and facilitated tumor growth and metastasis in vivo. Knocking down NFIB synergetically inhibited tumor growth with sorafenib. Mechanically, gene expression profiling and subsequent verification experiments proved that NFIB could bind with the promoter region of a complex I inhibitor NDUFA4L2 and promote its transcription. Transcriptional upregulation of NDUFA4L2 by NFIB could thus inhibit the sorafenib-induced reactive oxygen species accumulation. Finally, we found that NFIB was highly expressed in HCC tissues, and high NFIB expression level was associated with macrovascular invasion, advanced tumor stage, and poor prognosis of HCC patients (n=156). In summary, we demonstrated that NFIB could transcriptionally upregulate NDUFA4L2 to enhance both intrinsic and acquired sorafenib resistance of HCC cells by reducing reactive oxygen species induction.

SAT160 - In vivo loss-of-function studies unravel protein tyrosine phosphatase delta as a regulator of liver regeneration during metabolic liver disease

SAT160 - In vivo loss-of-function studies unravel protein tyrosine phosphatase delta as a regulator of liver regeneration during metabolic liver disease

SAT169 - The hepatocellular vitamin D receptor regulates liver regeneration after partial hepatectomy

SAT169 - The hepatocellular vitamin D receptor regulates liver regeneration after partial hepatectomy

FoxO3 restricts liver regeneration by suppressing the proliferation of hepatocytes

Upon injury, the liver is capable of substantial regeneration from the original tissue until an appropriate functional size. The underlying mechanisms controlling the liver regeneration processes are not well elucidated. Previous studies have proposed that the transcription factor FoxO3 is involved in various liver diseases, but its exact role in the regulation of liver regeneration remains largely unclear. To directly test the detailed role of FoxO3 in liver regeneration, both a constitutive Albumin-Cre driver line and adeno-associated virus serotype 8 (AAV8)-Tbg-Cre (AAV-Cre)-injected adult FoxO3fl/fl mice were subjected to 70% partial hepatectomy (PH). Our data demonstrate that FoxO3 deletion accelerates liver regeneration primarily by limiting polyploidization and promoting the proliferation of hepatocytes during liver regeneration. RNA-seq analysis indicates that FoxO3 deficiency greatly alters the expression of gene sets associated with cell proliferation and apoptosis during liver regeneration. Chromatin immunoprecipitation-PCR (ChIP-PCR) and luciferase reporter assays reveal that FoxO3 promotes the expression of Nox4 but suppresses the expression of Nr4a1 in hepatocytes. AAV8 virus-mediated overexpression of Nox4 and knockdown of Nr4a1 significantly suppressed hepatocyte proliferation and liver regeneration in FoxO3-deficient mice. We demonstrate that FoxO3 negatively controls hepatocyte proliferation through Nox4 upregulation and Nr4a1 downregulation, thereby ensuring appropriate functional regeneration of the liver. Our findings provide novel mechanistic insight into the therapeutic mechanisms of FoxO3 in liver damage and repair.

β2-adrenergic receptor promotes liver regeneration partially through crosstalk with c-met

The β2-adrenergic receptor (β2AR) is a G protein-coupled receptor (GPCR) that mediates the majority of cellular responses to external stimuli. Aberrant expression of β2AR results in various pathophysiological disorders, including tumorigenesis, but little is known about its role in liver regeneration. This study aims to investigate the impact and the underlying mechanism of β2AR in liver regeneration. Here, we found that β2AR was upregulated during liver regeneration induced by 70% PH. Deletion of β2AR in mice resulted in 62% mortality 2 days post-PH, decreased proliferative marker expression and impaired liver function throughout regeneration. Moreover, AAV8-mediated overexpression of β2AR in hepatocytes accelerated the regeneration process and increased target gene expression. Mechanistically, β2AR recruited G-protein-coupled receptor kinase 2 (GRK2) to the membrane and then formed a complex with c-met to transactivate c-met signaling, which triggered downstream extracellular regulated protein kinase (ERK) signaling activation and nuclear translocation. Inhibition of c-met with SU11274 or ERK with U0126 decreased β2AR overexpression-induced hepatocyte proliferation. Our findings revealed that β2AR might act as a critical mediator regulating liver regeneration by crosstalk with c-met and activation of ERK signaling.

The Benevolent Bile: Bile Acids as Stimulants of Liver Regeneration

The Benevolent Bile: Bile Acids as Stimulants of Liver Regeneration

Regulation of Liver Regeneration by Hepatocyte O-GlcNAcylation in Mice.

Background & AimsThe liver has a unique capacity to regenerate after injury in a highly orchestrated and regulated manner. Here, we report that O-GlcNAcylation, an intracellular post-translational modification regulated by 2 enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), is a critical termination signal for liver regeneration following partial hepatectomy (PHX).MethodsWe studied liver regeneration after PHX on hepatocyte specific OGT and OGA knockout mice (OGT-KO and OGA-KO), which caused a significant decrease (OGT-KO) and increase (OGA-KO) in hepatic O-GlcNAcylation, respectively.ResultsOGA-KO mice had normal regeneration, but the OGT-KO mice exhibited substantial defects in termination of liver regeneration with increased liver injury, sustained cell proliferation resulting in significant hepatomegaly, hepatic dysplasia, and appearance of small nodules at 28 days after PHX. This was accompanied by a sustained increase in expression of cyclins along with significant induction in pro-inflammatory and pro-fibrotic gene expression in the OGT-KO livers. RNA-sequencing studies revealed inactivation of hepatocyte nuclear 4 alpha (HNF4α), the master regulator of hepatic differentiation and a known termination signal, in OGT-KO mice at 28 days after PHX, which was confirmed by both Western blot and immunohistochemistry analysis. Furthermore, a significant decrease in HNFα target genes was observed in OGT-KO mice, indicating a lack of hepatocyte differentiation following decreased hepatic O-GlcNAcylation. Immunoprecipitation experiments revealed HNF4α is O-GlcNAcylated in normal differentiated hepatocytes.ConclusionsThese studies show that O-GlcNAcylation plays a critical role in the termination of liver regeneration via regulation of HNF4α in hepatocytes.

Aurora kinase A regulates liver regeneration through macrophages polarization and Wnt/β-catenin signalling.

Liver regeneration is a complex process regulated by a variety of cells, cytokines and biological pathways. Aurora kinase A (AURKA) is a serine/threonine kinase that plays a role in centrosome maturation and spindle formation during the cell division cycle. The purpose of this study was to further explore the mechanism of AURKA on liver regeneration and to identify new possible targets for liver regeneration. The effect and mechanism of AURKA on liver regeneration were studied using a 70% hepatectomy model. Human liver organoids were used as an in vitro model to investigate the effect of AURKA on hepatocyte proliferation. AURKA inhibition significantly reduced the level of β-catenin protein by reducing the phosphorylation level of glycogen synthase kinase-3β (GSK-3β), leading to the inhibition of liver regeneration. Further studies showed that AURKA co-localized and interacted with GSK-3β in the cytoplasm of hepatocytes. When phosphorylation of GSK-3β was enhanced, the total GSK-3β level remained unchanged, while AURKA was not affected, and β-catenin protein levels were increased. In addition, AURKA inhibition affected the formation and proliferation of human liver organoids. Furthermore, AURKA inhibition led to the polarization of M1 macrophages and the release of interleukin-6 and Tumour necrosis factor α, which also led to reduced liver regeneration and increased liver injury. These results provide more details on the mechanism of liver regeneration and suggest that AURKA is an important regulator of this mechanism.