Wnt agonist stimulates liver regeneration after small-for-size liver transplantation in rats

Dexmedetomidine facilitates autophagic flux to promote liver regeneration by suppressing GSK3β activity in mouse partial hepatectomy

INTRODUCTION

Dexmedetomidine (DEX), a highly selective α2-adrenergic receptor agonist, is widely used for sedation and anesthesia in patients undergoing hepatectomy. However, the effect of DEX on autophagic flux and liver regeneration remains unclear.

OBJECTIVES

This study aimed to determine the role of DEX in hepatocyte autophagic flux and liver regeneration after PHx.

METHODS

In mice, DEX was intraperitoneally injected 5 min before and 6 h after PHx. In vitro, DEX was co-incubated with culture medium for 24 h. Autophagic flux was detected by LC3-II and SQSTM1 expression levels in primary mouse hepatocytes and the proportion of red puncta in AML-12 cells transfected with FUGW-PK-hLC3 plasmid. Liver regeneration was assessed by cyclinD1 expression, Edu incorporation, H&E staining, ki67 immunostaining and liver/body ratios. Bafilomycin A1, si-GSK3β and Flag-tagged GSK3β, α2-ADR antagonist, GSK3β inhibitor, AKT inhibitor were used to identify the role of GSK3β in DEX-mediated autophagic flux and hepatocyte proliferation.

RESULTS

Pre- and post-operative DEX treatment promoted liver regeneration after PHx, showing 12 h earlier than in DEX-untreated mice, accompanied by facilitated autophagic flux, which was completely abolished by bafilomycin A1 or α2-ADR antagonist. The suppression of GSK3β activity by SB216763 and si-GSK3β enhanced the effect of DEX on autophagic flux and liver regeneration, which was abolished by AKT inhibitor.

CONCLUSION

Pre- and post-operative administration of DEX facilitates autophagic flux, leading to enhanced liver regeneration after partial hepatectomy through suppression of GSK3β activity in an α2-ADR-dependent manner.

Signaling pathways of liver regeneration: Biological mechanisms and implications

The liver possesses a unique regenerative ability to restore its original mass, in this regard, partial hepatectomy (PHx) and partial liver transplantation (PLTx) can be executed smoothly and safely, which has important implications for the treatment of liver disease. Liver regeneration (LR) can be the very complicated procedure that involves multiple cytokines and transcription factors that interact with each other to activate different signaling pathways. Activation of these pathways can drive the LR process, which can be divided into three stages, namely, the initiation, progression, and termination stages. Therefore, it is important to investigate the pathways involved in LR to elucidate the mechanism of LR. This study reviews the latest research on the key signaling pathways in the different stages of LR.

Wnt-β-catenin in hepatobiliary homeostasis, injury, and repair

Wnt-β-catenin signaling has emerged as an important regulatory pathway in the liver, playing key roles in zonation and mediating contextual hepatobiliary repair after injuries. In this review, we will address the major advances in understanding the role of Wnt signaling in hepatic zonation, regeneration, and cholestasis-induced injury. We will also touch on some important unanswered questions and discuss the relevance of modulating the pathway to provide therapies for complex liver pathologies that remain a continued unmet clinical need.

Synergy of 5-aminolevulinate supplement and CX3CR1 suppression promotes liver regeneration via elevated IGF-1 signaling

Inadequate remnant volume and regenerative ability of the liver pose life-threatening risks to patients after partial liver transplantation (PLT) or partial hepatectomy (PHx), while few clinical treatments focus on safely accelerating regeneration. Recently, we discovered that supplementing 5-aminolevulinate (5-ALA) improves liver cold adaptation and functional recovery, leading us to uncover a correlation between 5-ALA metabolic activities and post-PLT recovery. In a mouse 2/3 PHx model, 5-ALA supplements enhanced liver regeneration, promoting infiltration and polarization of anti-inflammatory macrophages via P53 signaling. Intriguingly, chemokine receptor CX3CR1 functions to counterbalance these effects. Genetic ablation or pharmacological inhibition of CX3CR1 (AZD8797; phase II trial candidate) augmented the macrophagic production of insulin-like growth factor 1 (IGF-1) and subsequent hepatocyte growth factor (HGF) production by hepatic stellate cells. Thus, short-term treatments with both 5-ALA and AZD8797 demonstrated pro-regeneration outcomes superior to 5-ALA-only treatments in mice after PHx. Overall, our findings may inspire safe and effective strategies to better treat PLT and PHx patients.

Therapeutic strategies to improve liver regeneration after hepatectomy

Chronic liver disease is one of the most common diseases worldwide, and its prevalence is particularly high among adults aged 40-60 years; it takes a toll on productivity and causes significant economic burden. However, there are still no effective treatments that can fundamentally treat chronic liver disease. Although liver transplantation is considered the only effective treatment for chronic liver disease, it has limitations in that the pool of available donors is vastly insufficient for the number of potential recipients. Even if a patient undergoes liver transplantation, side effects such as immune rejection or bile duct complications could occur. In addition, impaired liver regeneration due to various causes, such as aging and metabolic disorders, may cause liver failure after liver resection, even leading to death. Therefore, further research on the liver regeneration process and therapeutic strategies to improve liver regeneration are needed. In this review, we describe the process of liver regeneration after hepatectomy, focusing on various cytokines and signaling pathways. In addition, we review treatment strategies that have been studied to date to improve liver regeneration, such as promotion of hepatocyte proliferation and metabolism and transplantation of mesenchymal stem cells. This review helps to understand the physiological processes involved in liver regeneration and provides basic knowledge for developing treatments for successful liver regeneration.

The Wnt/β-catenin signaling pathway plays a role in drug-induced liver injury by regulating cytochrome P450 2E1 expression

Drug-induced liver injury (DILI) is a major cause of acute liver failure and drug withdrawal. Cytochrome P450 (CYP) 2E1 is involved in the metabolism of several drugs, and can induce liver injury through the production of toxic metabolites and the generation of reactive oxygen species. This study aimed to elucidate the role of Wnt/β-catenin signaling in CYP2E1 regulation for drug-induced hepatotoxicity. To achieve this, mice were administered cisplatin or acetaminophen (APAP) 1 h after treatment with the CYP2E1 inhibitor dimethyl sulfoxide (DMSO), and histopathological and serum biochemical analyses were performed. APAP treatment induced hepatotoxicity, as evidenced by an increase in liver weight and serum ALT levels. Moreover, histological analysis indicated severe injury, including apoptosis, in the liver tissue of APAP-treated mice, which was confirmed by TUNEL assay. Additionally, APAP treatment suppressed the antioxidant capacity of the mice and increased the expression of the DNA damage markers γ-H2AX and p53. However, these effects of APAP on hepatotoxicity were significantly attenuated by DMSO treatment. Furthermore, the activation of Wnt/β-catenin signaling using the Wnt agonist CHIR99021 (CHIR) increased CYP2E1 expression in rat liver epithelial cells (WB-F344), whereas treatment with the Wnt/β-catenin antagonist IWP-2 inhibited nuclear β-catenin and CYP2E1 expression. Interestingly, APAP-induced cytotoxicity in WB-F344 cells was exacerbated by CHIR treatment and suppressed by IWP-2 treatment. Overall, these results showed that the Wnt/β-catenin signaling is involved in DILI through the upregulation of CYP2E1 expression by directly binding the transcription factor β-cat/TCF to the Cyp2e1 promoter, thus exacerbating DILI.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00180-6.

Glycyrrhizic acid alters the hyperoxidative stress-induced differentiation commitment of MSCs by activating the Wnt/β-catenin pathway to prevent SONFH

This study aimed to examine the in vivo and in vitro therapeutic effects of glycyrrhizic acid (GA) on steroid-induced osteonecrosis of the femoral head (SONFH), which is caused by the overuse of glucocorticoids (GCs). Clinically, we identified elevated oxidative stress (OS) levels and an imbalance in osteolipogenic homeostasis in SONFH patients compared to femoral neck fracture (FNF) patients. In vivo, we established experimental SONFH in rats via lipopolysaccharides (LPSs) combined with methylprednisolone (MPS). We showed that GA and Wnt agonist-S8320 alleviated SONFH, as evidenced by the reduced microstructural and histopathological alterations in the subchondral bone of the femoral head and the decreased levels of OS in rat models. In vitro, GA reduced dexamethasone (Dex)-induced excessive NOX4 and OS levels by activating the Wnt/β-catenin pathway, thereby promoting the osteogenic differentiation of mesenchymal stem cells (MSCs) and inhibiting lipogenic differentiation. In addition, GA regulated the expression levels of the key transcription factors downstream of this pathway, Runx2 and PPARγ, thus maintaining osteolipogenic homeostasis. In summary, we demonstrated for the first time that GA modulates the osteolipogenic differentiation commitment of MSCs induced by excessive OS through activating the Wnt/β-catenin pathway, thereby ameliorating SONFH.

HOXA13 promotes liver regeneration through regulation of BMP-7

In-depth knowledge of liver regeneration could facilitate the development of therapies for liver injury and liver failure. As a member of the homeobox superfamily, HOXA13 plays an important role in regulating tumorigenesis and development. However, the exact role of HOXA13 in liver regeneration remains unclear. In this study, we confirmed that HOXA13 promotes hepatocyte proliferation both in vivo and in vitro. HOXA13 was upregulated during liver regeneration, and its overexpression further accelerated hepatocyte proliferation and liver function recovery during liver regeneration. Furthermore, we found that HOXA13 promoted hepatocyte proliferation and liver regeneration by upregulating bone morphogenetic protein-7 (BMP-7) mRNA. These findings provide a new potential target for the treatment of liver failure.

Wnt/-Catenin Signaling and Liver Regeneration: Circuit, Biology, and Opportunities

The liver is uniquely bestowed with an ability to regenerate following a surgical or toxicant insult. One of the most researched models to demonstrate the regenerative potential of this organ is the partial hepatectomy model, where two thirds of the liver is surgically resected. The remnant liver replenishes the lost mass within 1014 days in mice. The distinctive ability of the liver to regenerate has allowed living donor and split liver transplantation. One signaling pathway shown to be activated during the process of regeneration to contribute toward the mass and functional recovery of the liver is the Wnt/-catenin pathway. Very early after any insult to the liver, the cellmolecule circuitry of the Wnt/-catenin pathway is set into motion with the release of specific Wnt ligands from sinusoidal endothelial cells and macrophages, which, in a paracrine manner, engage Frizzled and LDL-related protein-5/6 coreceptors on hepatocytes to stabilize -catenin inducing its nuclear translocation. Nuclear -catenin interacts with T-cell factor family of transcription factors to induce target genes including cyclin D1 for proliferation, and others for regulating hepatocyte function. Working in collaboration with other signaling pathways, Wnt/-catenin signaling contributes to the restoration process without any compromise of function at any stage. Also, stimulation of this pathway through innovative means induces liver regeneration when this process is exhausted or compromised and thus has applications in the treatment of end-stage liver disease and in the field of liver transplantation. Thus, Wnt/-catenin signaling pathway is highly relevant in the discipline of hepatic regenerative medicine.

Functional compensation precedes recovery of tissue mass following acute liver injury

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

The liver possesses the ability to regenerate following sudden injury. Here, the authors use single-cell RNA-sequencing and in situ transcriptional analyses to identify a new phase of liver regeneration in mice aimed at maintaining essential functions throughout the regenerative process.

Liver Regeneration after Hepatectomy and Partial Liver Transplantation

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

Clinical translation of liver regeneration therapies: A conceptual road map

The increasing incidence of severe liver diseases worldwide has resulted in a high demand for curative liver transplantation. Unfortunately, the need for transplants by far eclipses the availability of suitable grafts leaving many waitlisted patients to face liver failure and often death. Routine use of smaller grafts (for example left lobes, split livers) from living or deceased donors could increase the number of life-saving transplants but is often limited by the graft versus recipient weight ratio defining the safety margins that minimize the risk of small for size syndrome (SFSS). SFSS is a severe complication characterized by failure of a small liver graft to regenerate and occurs when a donor graft is insufficient to meet the metabolic demand of the recipient, leading to liver failure as a result of insufficient liver mass. SFSS is not limited to transplantation but can also occur in the setting of hepatic surgical resections, where life-saving large resections of tumors may be limited by concerns of post-surgical liver failure. There are, as yet no available pro-regenerative therapies to enable liver regrowth and thus prevent SFSS. However, there is optimism around targeting factors and pathways that have been identified as regulators of liver regeneration to induce regrowth in vivo and ex vivo for clinical use. In this commentary, we propose a roadmap for developing such pro-regenerative therapy and for bringing it into the clinic. We summarize the clinical indications, preclinical models, pro-regenerative pathways and safety considerations necessary for developing such a drug.

Partial hepatectomy‑induced upregulation of SNHG12 promotes hepatocyte proliferation and liver regeneration

Following partial hepatectomy (PH), the complex process of liver regeneration is initiated, which encompasses the synchronized induction of hepatocyte proliferation. Hepatocyte proliferation can be regulated by multiple stimuli, including long non-coding RNAs (lncRNAs) and Wnt/β-catenin signaling, although the underlying mechanism of lncRNA/Wnt in liver regeneration remains unclear. In the present study, a liver regeneration-associated functional lncRNA was identified, and its function was delineated in vitro and in vivo; lncRNA small nucleolar RNA host gene 12 (SNHG12) was revealed to be upregulated at various time-points after 2/3 PH. The expression of SNHG12 was also increased in normal liver cell lines treated with different concentrations of hepatocyte growth factor (HGF). Functionally, SNHG12 enhanced hepatocyte proliferation in vitro and in vivo, and the liver/body weight ratio of SNHG12-overexpressing mice was significantly higher than that of the control mice. Overexpression of SNHG12 promoted the activation of Wnt/β-catenin signaling in hepatocytes. Furthermore, specific inhibition of Wnt/β-catenin signaling significantly attenuated SNHG12-induced hepatocyte proliferation and the affected liver/body weight ratio. Collectively, the results of the present study indicated that SNHG12 contributes to liver regeneration by activating Wnt/β-catenin signaling. Therefore, drugs that regulate the SNHG12/Wnt axis may be beneficial for liver regeneration following PH.

Pharmacological stimulation of Wnt/beta-catenin signaling pathway attenuates the course of thioacetamide-induced acute liver failure

Acute liver failure (ALF) is known for extremely high mortality rate, the result of widespread damage of hepatocytes. Orthotopic liver transplantation is the only effective therapy but its application is limited by the scarcity of donor organs. Given the importance in the liver biology of Wnt/beta-catenin signaling pathway, we hypothesized that its stimulation could enhance hepatocyte regeneration and attenuate the course of thioacetamide (TAA)-induced ALF in Lewis rats. Chronic treatment with Wnt agonist was started either immediately after hepatotoxic insult ("early treatment") or when signs of ALF had developed ("late treatment"). Only 23 % of untreated Lewis rats survived till the end of experiment. They showed marked increases in plasma alanine aminotransferase (ALT) activity and bilirubin and ammonia (NH3) levels; plasma albumin decreased significantly. "Early" and "late" Wnt agonist treatment raised the final survival rate to 69 % and 63 %, respectively, and normalized ALT, NH3, bilirubin and albumin levels. In conclusion, the results show that treatment with Wnt agonist attenuates the course of TAA-induced ALF in Lewis rats, both with treatment initiated immediately after hepatotoxic insult and in the phase when ALF has already developed. Thus, the pharmacological stimulation of Wnt/beta-catenin signaling pathway can present a new approach to ALF treatment.

Advanced oxidation protein products induce S-phase arrest of hepatocytes via the ROS-dependent, β-catenin-CDK2-mediated pathway

Liver regeneration has important clinical importance in the setting of partial hepatectomy (PH). Following PH, quiescent hepatocytes can reenter cell cycle to restore liver mass. Hepatocyte cell cycle progression, as the basic motivations of liver regeneration, can be disrupted by multiple pathological factors such as oxidative stress. This study aimed to evaluate the role of advanced oxidation protein products (AOPP) in S-phase arrest in hepatocytes. Serum AOPP level were measured during the perioperative period of PH in 33 patients with hepatocellular carcinoma (HCC). Normal Sprague Dawley rats, human and murine liver cell line (HL-7702 and AML-12) were challenged with AOPP prepared by incubation of rat serum albumin (RSA) with hypochlorous acid, and the effect of AOPP on hepatocytes cell cycle progression and liver regeneration was studied after PH. AOPP levels were increased following partial hepatectomy (PH) in patients with primary liver cancer. AOPP treatment impaired liver regeneration in rats following 70% partial hepatectomy. S-phase arrest was induced by AOPP administration in hepatocytes derived from the remnant liver at controlled times following partial hepatectomy in rats, and in HL-7702 and AML-12 cells. The effect of AOPP on hepatocyte S phase arrest was mainly mediated by a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) generation, downregulation of downstream β-catenin signaling and decreased cyclin-dependent kinase 2 (CDK2) expression, which inhibited S-phase progression in hepatocytes. This study provides preliminary evidence that AOPP can induce S-phase arrest in hepatocytes via the ROS-dependent, β-catenin-CDK2-mediated pathway. These findings suggest a novel pathogenic role of AOPP contributing to the impaired liver regeneration and may provide the basis for developing new strategies to improve liver regeneration in patients undergoing PH.

Wnt/β-Catenin Signaling Drives Thioacetamide-Mediated Heteroprotection Against Acetaminophen-Induced Lethal Liver Injury

Preplacement of compensatory tissue repair (CTR) by exposure to a nonlethal dose of a toxicant protects animals against a lethal dose of another toxicant. Although CTR is known to heteroprotect, the underlying molecular mechanisms are not completely known. Here, we investigated the mechanisms of heteroprotection using thioacetamide (TA): acetaminophen (APAP) heteroprotection model. Male Swiss Webster mice received a low dose of TA or distilled water (DW) vehicle 24 hours prior to a lethal dose of APAP. Liver injury, tissue repair, and promitogenic signaling were studied over a time course of 24 hours after APAP overdose to the TA- and DW-primed mice (TA + APAP and DW + APAP, respectively). Thioacetamide pretreatment afforded 100% protection against APAP overdose compared to 100% lethality in the DW + APAP-treated mice. Although hepatic Cyp2e1 was similar at the time of APAP administration, immediate activation of hepatic c-Jun N-terminal kinases (JNK) was observed in the TA + APAP-treated mice compared to its delayed activation in the DW + APAP group. In contrast to the DW + APAP group, the TA + APAP-treated mice exhibited extensive CTR, which was secondary to the timely activation of Wnt/β-catenin pathway. Our data indicate that rapid activation and appropriate termination of Wnt/β-catenin signaling and modulation of JNK activity underlie TA + APAP heteroprotection.

2-Amino-4-(3,4-(methylenedioxy)benzylamino)-6-(3-methoxyphenyl)pyrimidine is an anti-inflammatory TLR-2, -4 and -5 response mediator in human monocytes

OBJECTIVE AND DESIGN

To elucidate the influence of 2-amino-4-(3,4-(methylenedioxy)benzylamino)-6-(3-methoxyphenyl)pyrimidine (AMBMP), a canonical Wnt/β-catenin pathway activator, on the inflammatory response of TLR-engaged innate cells in vitro.

MATERIAL OR SUBJECT

Primary human monocytes.

TREATMENT

AMPMB (0-10 μM), LPS (0-1.0 μg/ml), Pam3CSK4, FSL-1, or S. typhimurium flagellin (0-0.25 μg/ml).

METHODS

TLR-induced cytokine release (TNF, IL-6, IL-12 p40) was monitored by ELISA while Wnt-related signals (GSK3β, p65, IκB, β-catenin) were assessed by Western blot, pharmaceutical inhibition and gene silencing.

RESULTS

AMBMP induced the rapid phosphorylation of NFκB p65 at Ser(536) and abrogated total IκB, accompanied by a subsequent increase in pro-inflammatory cytokine production (TNF, IL-6, IL-12 p40) in otherwise naive monocytes. However, in TLR2, -4 and -5-engaged monocytes, AMBMP-suppressed cytokine production. In the context of LPS stimulation, this occurred concomitant with the phosphorylative inactivation of GSK3β at Ser(9), β-catenin accumulation and abrogation of NFκB p65 phosphorylation. AMBMP-mediated suppression of the TLR4 -induced inflammatory response was reversed by two pharmaceutical Wnt/β-catenin pathway inhibitors, IWP-2 and PNU-74654 and by Wnt3a silencing.

CONCLUSIONS

Herein, we show that AMBMP induces canonical Wnt signaling events and acts as a suppressor of inflammation in surface TLR-engaged primary human monocytes.