Hepatocyte Peroxisome Proliferator-Activated Receptor α Enhances Liver Regeneration after Partial Hepatectomy in Mice

Aquaporin five deficiency suppresses fatty acid oxidation and delays liver regeneration through the transcription factor PPAR

After 70% partial hepatectomy (PHx), the metabolic pathways leading to hepatocyte lipid droplet accumulation during liver regeneration remain unclear. Aquaporin 5 (Aqp5) is an aquaporin that facilitates the transport of both water and hydrogen peroxide (H2O2). In this study, we observed delayed liver regeneration following PHx in Aqp5 knockout (Aqp5-/-) mice. Considering the role of Aqp5 in H2O2 transport, we hypothesized that deficiency in Aqp5 may induce oxidative stress and hepatocyte injury. Through the measurement of reactive oxygen species (ROS) and redox-related indices, we observed significant alterations in ROS levels as well as malondialdehyde (MDA), superoxide dismutase (SOD), and reduced glutathione (GSH) concentrations in regenerating livers lacking Aqp5 compared to wild-type controls. Oil Red O and 4-hydroxynonenal (4-HNE) staining results indicated that Aqp5 deficiency caused lipid accumulation during liver regeneration. The transcriptome sequencing results showed that the PPAR pathway is inhibited during the liver regeneration process in Aqp5 gene-knockout mice. The administration of the WY-14643 agonist, which targets the PPAR pathway, significantly mitigated delayed liver regeneration by enhancing hepatocyte proliferation and reducing lipid accumulation caused by Aqp5 deficiency. Our findings highlight the crucial role of Aqp5 in regulating H2O2 levels and lipid metabolism through the PPAR pathway during liver regeneration.

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

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

2,3,5,4'-tetrahydroxy-stilbene-2-O-β-D-glucoside promotes liver regeneration after partial hepatectomy in mice: The potential involvement of PPARα-mediated fatty acid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

2,3,5,4'-tetrahydroxy-stilbene-2-O-β-D-glucoside (TSG) is the principal bioactive compound contained in Polygonum multiflorum Thunb. (PMT), which is traditionally recorded to possess tonic and anti-aging efficacy.

AIM OF THE STUDY

To identify the TSG-provided promotion on liver regeneration (LR) following partial hepatectomy (PHx) in mice and to explicate its involved mechanism.

MATERIALS AND METHODS

The promotion of TSG on LR was evaluated by hematoxylin and eosin (H&E), 5-bromodeoxyuridinc (BrdU) and Ki-67 staining, and measuring the level of proliferating cell nuclear antigen (PCNA) and Cyclin D1 in mice with PHx at different time points. Gene Expression Omnibus (GEO, GSE15239) database and the label-free quantitative proteomics from liver of mice at 24 h after PHx were integrated to identify potential involved critical proteins, which were verified by Western-blot, Real-time polymerase chain reaction (RT-PCR), molecular docking and luciferase activity assay. Primary hepatocytes isolated from mice were used to investigate the TSG-provided promotion on proliferation in vitro.

RESULTS

TSG (20 mg/kg) promoted LR in mice after PHx. Results from RNA expression data from clinical samples and proteomic analysis from liver tissues indicated that peroxisome proliferator-activated receptor α (PPARα)-mediated fatty acid metabolism pathway were crucially associated with the TSG-provided promotion on LR. TSG enhanced the nuclear translocation of PPARα and the mRNA expression of a series of PPARα-regulated downstream genes. In addition, TSG lowered hepatic triglyceride (TG) and non-esterified fatty acid (NEFA) amounts and increased hepatic adenosine triphosphate (ATP) level in mice after PHx. TSG up-regulated the transcriptional activity of PPARα in vitro. Next results displayed that TSG promoted cell proliferation as well as ATP level in mice primary hepatocytes, which were abolished when PPARα was suppressed. Meanwhile, the cell viability was also elevated in mice primary hepatocytes treated with ATP.

CONCLUSION

Activating PPARα-mediated fatty acid β-oxidation (FAO) pathway led to the production of ATP, which contributed to the TSG-provided promotion on LR after PHx in mice.

Maladaptive regeneration and metabolic dysfunction associated steatotic liver disease: Common mechanisms and potential therapeutic targets

The normal liver has an extraordinary capacity of regeneration. However, this capacity is significantly impaired in steatotic livers. Emerging evidence indicates that metabolic dysfunction associated steatotic liver disease (MASLD) and liver regeneration share several key mechanisms. Some classical liver regeneration pathways, such as HGF/c-Met, EGFR, Wnt/β-catenin and Hippo/YAP-TAZ are affected in MASLD. Some recently established therapeutic targets for MASH such as the Thyroid Hormone (TH) receptors, Glucagon-like protein 1 (GLP1), Farnesoid X receptor (FXR), Peroxisome Proliferator-Activated Receptors (PPARs) as well as Fibroblast Growth Factor 21 (FGF21) are also reported to affect hepatocyte proliferation. With this review we aim to provide insight into common molecular pathways, that may ultimately enable therapeutic strategies that synergistically ameliorate steatohepatitis and improve the regenerating capacity of steatotic livers. With the recent rise of prolonged ex-vivo normothermic liver perfusion prior to organ transplantation such treatment is no longer restricted to patients undergoing major liver resection or transplantation, but may eventually include perfused (steatotic) donor livers or even liver segments, opening hitherto unexplored therapeutic avenues.

Development of a promising PPAR signaling pathway-related prognostic prediction model for hepatocellular carcinoma

The peroxisome proliferator-activated receptor (PPAR) signaling pathway plays a crucial role in systemic cell metabolism, energy homeostasis and immune response inhibition. However, its significance in hepatocellular carcinoma (HCC) has not been well documented. In our study, based on the RNA sequencing data of HCC, consensus clustering analyses were performed to identify PPAR signaling pathway-related molecular subtypes, each of which displaying varying survival probabilities and immune infiltration status. Following, a prognostic prediction model of HCC was developed by using the random survival forest method and Cox regression analysis. Significant difference in survival outcome, immune landscape, drug sensitivity and pathological features were observed between patients with different prognosis. Additionally, decision tree and nomogram models were adopted to optimize the prognostic prediction model. Furthermore, the robustness of the model was verified through single-cell RNA-sequencing data. Collectively, this study systematically elucidated that the PPAR signaling pathway-related prognostic model has good predictive efficacy for patients with HCC. These findings provide valuable insights for further research on personalized treatment approaches for HCC.

The Effect of Diabetes Mellitus Type 1 on the Energy Metabolism of Hepatocytes: Multiphoton Microscopy and Fluorescence Lifetime Imaging

A decrease in the regenerative potential of the liver during the development of non-alcoholic fatty liver disease (NAFLD), which is observed in the vast majority of patients with diabetes mellitus type 1, significantly increases the risk of postoperative liver failure. In this regard, it is necessary to develop new approaches for the rapid intraoperative assessment of the condition of liver tissue in the presence of concomitant liver pathology. A modern label-free approach based on multiphoton microscopy, second harmonic generation (SHG), and fluorescence lifetime imaging microscopy (FLIM) allow for the evaluation of the structure of liver tissue as well as the assessment of the metabolic state of hepatocytes, even at the cellular level. We obtained optical criteria and identified specific changes in the metabolic state of hepatocytes for a reduced liver regenerative potential in the presence of induced diabetes mellitus type 1. The obtained criteria will expand the possibilities for the express assessment of the structural and functional state of liver tissue in clinical practice.

PPARα activation promotes liver progenitor cell-mediated liver regeneration by suppressing YAP signaling in zebrafish

Despite the robust regenerative capacity of the liver, prolonged and severe liver damage impairs liver regeneration, leading to liver failure. Since the liver co-opts the differentiation of liver progenitor cells (LPCs) into hepatocytes to restore functional hepatocytes, augmenting LPC-mediated liver regeneration may be beneficial to patients with chronic liver diseases. However, the molecular mechanisms underlying LPC-to-hepatocyte differentiation have remained largely unknown. Using the zebrafish model of LPC-mediated liver regeneration, Tg(fabp10a:pt-β-catenin), we present that peroxisome proliferator-activated receptor-alpha (PPARα) activation augments LPC-to-hepatocyte differentiation. We found that treating Tg(fabp10a:pt-β-catenin) larvae with GW7647, a potent PPARα agonist, enhanced the expression of hepatocyte markers and simultaneously reduced the expression of biliary epithelial cell (BEC)/LPC markers in the regenerating livers, indicating enhanced LPC-to-hepatocyte differentiation. Mechanistically, PPARα activation augments the differentiation by suppressing YAP signaling. The differentiation phenotypes resulting from GW7647 treatment were rescued by expressing a constitutively active form of Yap1. Moreover, we found that suppression of YAP signaling was sufficient to promote LPC-to-hepatocyte differentiation. Treating Tg(fabp10a:pt-β-catenin) larvae with the TEAD inhibitor K-975, which suppresses YAP signaling, phenocopied the effect of GW7647 on LPC differentiation. Altogether, our findings provide insights into augmenting LPC-mediated liver regeneration as a regenerative therapy for chronic liver diseases.

Lipid droplet deposition in the regenerating liver: A promoter, inhibitor, or bystander?

Liver regeneration (LR) is a complex process involving intricate networks of cellular connections, cytokines, and growth factors. During the early stages of LR, hepatocytes accumulate lipids, primarily triacylglycerol, and cholesterol esters, in the lipid droplets. Although it is widely accepted that this phenomenon contributes to LR, the impact of lipid droplet deposition on LR remains a matter of debate. Some studies have suggested that lipid droplet deposition has no effect or may even be detrimental to LR. This review article focuses on transient regeneration-associated steatosis and its relationship with the liver regenerative response.

Peroxisome proliferator-activated receptor α agonist induces mouse hepatomegaly through the spatial hepatocyte enlargement and proliferation

Peroxisome proliferator-activated receptor alpha (PPARα) activation-induced hepatomegaly is accompanied by hepatocyte hypertrophy around the central vein (CV) area and hepatocyte proliferation around the portal vein (PV) area. However, the molecular mechanisms underlying this spatial change of hepatocytes remains unclear. In this study, we examined the characteristics and possible reasons for the zonation distinction of hypertrophy and proliferation during PPARα activation-induced mouse liver enlargement. Mice were injected with corn oil or a typical mouse PPARα agonist WY-14643 (100 mg·kg-1·d-1, i.p.) for 1, 2, 3, 5 or 10 days. At each time point, the mice were sacrificed after the final dose, and liver tissues and serum were harvested for analysis. We showed that PPARα activation induced zonal changes in hepatocyte hypertrophy and proliferation in the mice. In order to determine the zonal expression of proteins related to hepatocyte hypertrophy and proliferation in PPARα-induced liver enlargement, we performed digitonin liver perfusion to separately destroy the hepatocytes around the CV or PV areas, and found that PPARα activation-induced increase magnitude of its downstream targets such as cytochrome P450 (CYP) 4 A and acyl-coenzyme A oxidase 1 (ACOX1) levels around the CV area were higher compared with those around the PV area. Upregulation of proliferation-related proteins such as cell nuclear antigen (PCNA) and cyclin A1 (CCNA1) after WY-14643-induced PPARα activation mainly occurred around the PV area. This study reveals that the zonal expression of PPARα targets and proliferation-related proteins is responsible for the spatial change of hepatocyte hypertrophy and proliferation after PPARα activation. These findings provide a new insight into the understanding of PPARα activation-induced liver enlargement and regeneration.

FOXN Transcription Factors: Regulation and Significant Role in Cancer

A growing number of studies have demonstrated that cancer development is closely linked to abnormal gene expression, including alterations in the transcriptional activity of transcription factors. The Forkhead box class N (FOXN) proteins FOXN1-6 form a highly conserved class of transcription factors, which have been shown in recent years to be involved in the regulation of malignant progression in a variety of cancers. FOXNs mediate cell proliferation, cell-cycle progression, cell differentiation, metabolic homeostasis, embryonic development, DNA damage repair, tumor angiogenesis, and other critical biological processes. Therefore, transcriptional dysregulation of FOXNs can directly affect cellular physiology and promote cancer development. Numerous studies have demonstrated that the transcriptional activity of FOXNs is regulated by protein-protein interactions, microRNAs (miRNA), and posttranslational modifications (PTM). However, the mechanisms underlying the molecular regulation of FOXNs in cancer development are unclear. Here, we reviewed the molecular regulatory mechanisms of FOXNs expression and activity, their role in the malignant progression of tumors, and their value for clinical applications in cancer therapy. This review may help design experimental studies involving FOXN transcription factors, and enhance their therapeutic potential as antitumor targets.

Key hepatoprotective roles of mitochondria in liver regeneration

Treatment of advanced liver disease using surgical modalities is possible due to the liver's innate ability to regenerate following resection. Several key cellular events in the regenerative process converge at the mitochondria, implicating their crucial roles in liver regeneration. Mitochondria enable the regenerating liver to meet massive metabolic demands by coordinating energy production to drive cellular proliferative processes and vital homeostatic functions. Mitochondria are also involved in terminating the regenerative process by mediating apoptosis. Studies have shown that attenuation of mitochondrial activity results in delayed liver regeneration, and liver failure following resection is associated with mitochondrial dysfunction. Emerging mitochondria therapy (i.e., mitotherapy) strategies involve isolating healthy donor mitochondria for transplantation into diseased organs to promote regeneration. This review highlights mitochondria's inherent role in liver regeneration.

Normalization of lipid oxidation defects arising from hypoxia early posthepatectomy prevents liver failure in mouse

Surgical liver failure (SLF) develops when a marginal amount of hepatic mass is left after surgery, such as following excessive resection. SLF is the commonest cause of death due to liver surgery; however, its etiology remains obscure. Using mouse models of standard hepatectomy (sHx) (68%, resulting in full regeneration) or extended hepatectomy (eHx) (86%/91%, causing SLF), we explored the causes of early SLF related to portal hyperafflux. Assessing the levels of HIF2A with or without oxygenating agent inositol trispyrophosphate (ITPP) indicated hypoxia early after eHx. Subsequently, lipid oxidation (PPARA/PGC1α) was downregulated and associated with persisting steatosis. Mild oxidation with low-dose ITPP reduced the levels of HIF2A, restored downstream PPARA/PGC1α expression along with lipid oxidation activities (LOAs), and normalized steatosis and other metabolic or regenerative SLF deficiencies. Promotion of LOA with L-carnitine likewise normalized the SLF phenotype, and both ITPP and L-carnitine markedly raised survival in lethal SLF. In patients who underwent hepatectomy, pronounced increases in serum carnitine levels (reflecting LOA) were associated with better recovery. Lipid oxidation thus provides a link between the hyperafflux of O₂-poor portal blood, the metabolic/regenerative deficits, and the increased mortality typifying SLF. Stimulation of lipid oxidation-the prime regenerative energy source-particularly through L-carnitine may offer a safe and feasible way to reduce SLF risks in the clinic.

Intestinal peroxisome proliferator-activated receptor α-fatty acid-binding protein 1 axis modulates nonalcoholic steatohepatitis

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor α (PPARα) regulates fatty acid transport and catabolism in liver. However, the role of intestinal PPARα in lipid homeostasis is largely unknown. Here, intestinal PPARα was examined for its modulation of obesity and NASH.

APPROACH AND RESULTS

Intestinal PPARα was activated and fatty acid-binding protein 1 (FABP1) up-regulated in humans with obesity and high-fat diet (HFD)-fed mice as revealed by using human intestine specimens or HFD/high-fat, high-cholesterol, and high-fructose diet (HFCFD)-fed C57BL/6N mice and PPARA -humanized, peroxisome proliferator response element-luciferase mice. Intestine-specific Ppara or Fabp1 disruption in mice fed a HFD or HFCFD decreased obesity-associated metabolic disorders and NASH. Molecular analyses by luciferase reporter assays and chromatin immunoprecipitation assays in combination with fatty acid uptake assays in primary intestinal organoids revealed that intestinal PPARα induced the expression of FABP1 that in turn mediated the effects of intestinal PPARα in modulating fatty acid uptake. The PPARα antagonist GW6471 improved obesity and NASH, dependent on intestinal PPARα or FABP1. Double-knockout ( Ppara/Fabp1ΔIE ) mice demonstrated that intestinal Ppara disruption failed to further decrease obesity and NASH in the absence of intestinal FABP1. Translationally, GW6471 reduced human PPARA-driven intestinal fatty acid uptake and improved obesity-related metabolic dysfunctions in PPARA -humanized, but not Ppara -null, mice.

CONCLUSIONS

Intestinal PPARα signaling promotes NASH progression through regulating dietary fatty acid uptake through modulation of FABP1, which provides a compelling therapeutic target for NASH treatment.

Local problems need global solutions: The metabolic needs of regenerating organisms

The vast majority of species that belong to the plant or animal kingdom evolved with two main strategies to counter tissue damage-scar formation and regeneration. Whereas scar formation provides a fast and cost-effective repair to exit life-threatening conditions, complete tissue regeneration is time-consuming and requires vast resources to reinstall functionality of affected organs or structures. Local environments in wound healing are widely studied and findings have provided important biomedical applications. Less well understood are organismic physiological parameters and signalling circuits essential to maintain effective tissue repair. Here, we review accumulated evidence that positions the interplay of local and systemic changes in metabolism as essential variables modulating the injury response. We particularly emphasise the role of lipids and lipid-like molecules as significant components long overlooked.

mTORC2 Facilitates Liver Regeneration Through Sphingolipid-Induced PPAR-α-Fatty Acid Oxidation

BACKGROUND & AIMS

During liver regeneration after partial hepatectomy, the function and metabolic pathways governing transient lipid droplet accumulation in hepatocytes remain obscure. Mammalian target of rapamycin 2 (mTORC2) facilitates de novo synthesis of hepatic lipids. Under normal conditions and in tumorigenesis, decreased levels of triglyceride (TG) and fatty acids (FAs) are observed in the mTORC2-deficient liver. However, during liver regeneration, their levels increase in the absence of mTORC2.

METHODS

Rictor liver-specific knockout and control mice underwent partial hepatectomy, followed by measurement of TG and FA contents during liver regeneration. FA metabolism was evaluated by analyzing the expression of FA metabolism-related genes and proteins. Intraperitoneal injection of the peroxisome proliferator-activated receptor α (PPAR-α) agonist, p53 inhibitor, and protein kinase B (AKT) activator was performed to verify the regulatory pathways involved. Lipid mass spectrometry was performed to identify the potential PPAR-α activators.

RESULTS

The expression of FA metabolism-related genes and proteins suggested that FAs are mainly transported into hepatocytes during liver regeneration. The PPAR-α pathway is down-regulated significantly in the mTORC2-deficient liver, resulting in the accumulation of TGs. The PPAR-α agonist WY-14643 rescued deficient liver regeneration and survival in mTORC2-deficient mice. Furthermore, lipidomic analysis suggested that mTORC2 deficiency substantially reduced glucosylceramide (GluCer) content. GluCer activated PPAR-α. GluCer treatment in vivo restored the regenerative ability and survival rates in the mTORC2-deficient group.

CONCLUSIONS

Our data suggest that FAs are mainly transported into hepatocytes during liver regeneration, and their metabolism is facilitated by mTORC2 through the GluCer-PPAR-α pathway, thereby establishing a novel role for mTORC2 in lipid metabolism.

Nuclear Receptor-Mediated Hepatomegaly and Liver Regeneration: An Update

Nuclear receptors (NRs), a superfamily of ligand-activated transcription factors, are critical in cell growth, proliferation, differentiation, metabolism, and numerous biologic events. NRs have been reported to play important roles in hepatomegaly (liver enlargement) and liver regeneration by regulating target genes or interacting with other signals. In this review, the roles and involved molecular mechanisms of NRs in hepatomegaly and liver regeneration are summarized and the future perspectives of NRs in the treatment of liver diseases are discussed. SIGNIFICANCE STATEMENT: NRs play critical roles in hepatomegaly and liver regeneration, indicating the potential of NRs as targets to promote liver repair after liver injury. This paper reviews the characteristics and molecular mechanisms of NRs in regulating hepatomegaly and liver regeneration, providing more evidence for NRs in the treatment of related liver diseases.

Myeloid peroxisome proliferator-activated receptor α deficiency accelerates liver regeneration via IL-6/STAT3 pathway after 2/3 partial hepatectomy in mice

Background

Liver regeneration is a fundamental process for sustained body homeostasis and liver function recovery after injury. Emerging evidence demonstrates that myeloid cells play a critical role in liver regeneration by secreting cytokines and growth factors. Peroxisome proliferator-activated receptor α (PPARα), the target of clinical lipid-lowering fibrate drugs, regulates cell metabolism, proliferation, and survival. However, the role of myeloid PPARα in partial hepatectomy (PHx)-induced liver regeneration remains unknown.

Methods

Myeloid-specific PPARa-deficient (Ppara ^Mye-/-) mice and the littermate controls (Ppara ^fl/fl) were subjected to sham or 2/3 PHx to induce liver regeneration. Hepatocyte proliferation and mitosis were assessed by immunohistochemical (IHC) staining for 5-bromo-2'-deoxyuridine (BrdU) and Ki67 as well as hematoxylin and eosin (H&E) staining. Macrophage and neutrophil infiltration into livers were reflected by IHC staining for galectin-3 and myeloperoxidase (MPO) as well as flow cytometry analysis. Macrophage migration ability was evaluated by transwell assay. The mRNA levels for cell cycle or inflammation-related genes were measured by quantitative real-time RT-PCR (qPCR). The protein levels of cell proliferation related protein and phosphorylated signal transducer and activator of transcription 3 (STAT3) were detected by Western blotting.

Results

Ppara ^Mye-/- mice showed enhanced hepatocyte proliferation and mitosis at 32 h after PHx compared with Ppara ^fl/fl mice, which was consistent with increased proliferating cell nuclear antigen (Pcna) mRNA and cyclinD1 (CYCD1) protein levels in Ppara ^Mye-/- mice at 32 h after PHx, indicating an accelerated liver regeneration in Ppara ^Mye-/- mice. IHC staining showed that macrophages and neutrophils were increased in Ppara ^Mye-/- liver at 32 h after PHx. Livers of Ppara ^Mye-/- mice also showed an enhanced infiltration of M1 macrophages at 32 h after PHx. In vitro, Ppara-deficient bone marrow-derived macrophages (BMDMs) exhibited markedly enhanced migratory capacity and upregulated M1 genes Il6 and Tnfa but downregulated M2 gene Arg1 expressions. Furthermore, the phosphorylation of STAT3, a key transcript factor mediating IL6-promoted hepatocyte survival and proliferation, was reinforced in the liver of Ppara ^Mye-/- mice after PHx.

Conclusions

This study provides evidence that myeloid PPARα deficiency accelerates PHx-induced liver regeneration via macrophage polarization and consequent IL-6/STAT3 activation, thus providing a potential target for manipulating liver regeneration.

Context-dependent transcriptional regulations of YAP/TAZ in stem cell and differentiation

Hippo pathway is initially identified as a master regulator for cell proliferation and organ size control, and the subsequent researches show this pathway is also involved in development, tissue regeneration and homeostasis, inflammation, immunity and cancer. YAP/TAZ, the downstream effectors of Hippo pathway, usually act as coactivators and are dependent on other transcription factors to mediate their transcriptional outputs. In this review, we will first provide an overview on the core components and regulations of Hippo pathway in mammals, and then systematically summarize the identified transcriptional factors or partners that are responsible for the transcriptional output of YAP/TAZ in stem cell and differentiation. More than that, we will discuss the potential applications and future directions based on these findings.

YAP-TEAD mediates PPAR α-induced hepatomegaly and liver regeneration in mice

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor α (PPARα, NR1C1) is a ligand-activated nuclear receptor involved in the regulation of lipid catabolism and energy homeostasis. PPARα activation induces hepatomegaly and plays an important role in liver regeneration, but the underlying mechanisms remain unclear.

APPROACH AND RESULTS

In this study, the effect of PPARα activation on liver enlargement and regeneration was investigated in several strains of genetically modified mice. PPARα activation by the specific agonist WY-14643 significantly induced hepatomegaly and accelerated liver regeneration after 70% partial hepatectomy (PHx) in wild-type mice and Ppara^fl/fl mice, while these effects were abolished in hepatocyte-specific Ppara-deficient (Ppara^ΔHep ) mice. Moreover, PPARα activation promoted hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. Mechanistically, PPARα activation regulated expression of yes-associated protein (YAP) and its downstream targets (connective tissue growth factor, cysteine-rich angiogenic inducer 61, and ankyrin repeat domain 1) as well as proliferation-related proteins (cyclins A1, D1, and E1). Binding of YAP with the PPARα E domain was critical for the interaction between YAP and PPARα. PPARα activation further induced nuclear translocation of YAP. Disruption of the YAP-transcriptional enhancer factor domain family member (TEAD) association significantly suppressed PPARα-induced hepatomegaly and hepatocyte enlargement and proliferation. In addition, PPARα failed to induce hepatomegaly in adeno-associated virus-Yap short hairpin RNA-treated mice and liver-specific Yap-deficient mice. Blockade of YAP signaling abolished PPARα-induced hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area.

CONCLUSIONS

This study revealed a function of PPARα in regulating liver size and liver regeneration through activation of the YAP-TEAD signaling pathway. These findings have implications for understanding the physiological functions of PPARα and suggest its potential for manipulation of liver size and liver regeneration.

Metabolic nuclear receptors coordinate energy metabolism to regulate Sox9+ hepatocyte fate

Recent research has indicated the adult liver Sox9+ cells located in the portal triads contribute to the physiological maintenance of liver mass and injury repair. However, the physiology and pathology regulation mechanisms of adult liver Sox9+ cells remain unknown. Here, PPARα and FXR bound to the shared site in Sox9 promoter with opposite transcriptional outputs. PPARα activation enhanced the fatty acid β-oxidation, oxidative phosphorylation (OXPHOS), and adenosine triphosphate (ATP) production, thus promoting proliferation and differentiation of Sox9+ hepatocytes along periportal (PP)-perivenous (PV) axis. However, FXR activation increased glycolysis but decreased OXPHOS and ATP production, therefore preventing proliferation of Sox9+ hepatocytes along PP-PV axis by promoting Sox9+ hepatocyte self-renewal. Our research indicates that metabolic nuclear receptors play critical roles in liver progenitor Sox9+ hepatocyte homeostasis to initiate or terminate liver injury-induced cell proliferation and differentiation, suggesting that PPARα and FXR are potential therapeutic targets for modulating liver regeneration.

FOXN3 inhibits cell proliferation and invasion via modulating the AKT/MDM2/p53 axis in human glioma

This study aimed to evaluate the biological role of forkhead box N3 (FOXN3) in human glioma and clarify the possible molecular mechanisms. FOXN3 expression patterns in clinical tissue specimens were characterized via qPCR and Western blotting. Kaplan-Meier survival curve was applied to assess the correlation between FOXN3 expression and overall survival. Effects of FOXN3 over-expression and depletion on glioma cell proliferation, apoptosis, migration and invasion were assessed by CCK8, colony formation assay, flow cytometry, scratch wound healing assay and Transwell invasion assay, respectively. Moreover, the involvement of AKT/murine double minute 2 (MDM2)/p53 pathway was evaluated. Additionally, tumor transplantation model assay was performed to determine the effects of FOXN3 over-expression on glioma cell growth in vivo. Results showed that FOXN3 was significantly down-regulated in glioma tissues compared with normal tissues. Patients with lower FOXN3 expression exhibited a shorter overall survival time. Gain- and loss-of-function analyses demonstrated that FOXN3 over-expression significantly suppressed proliferation, survival and motility of glioma cells, whereas FOXN3 knockdown remarkably promoted glioma cell proliferation, survival and motility. Furthermore, FOXN3 over-expression inhibited the activation of AKT/MDM2/p53 signaling pathway in glioma cells, while FOXN3 depletion facilitated its activation. Additionally, tumor xenograft assays revealed that FOXN3 over-expression retarded glioma cell growth in vivo. Collectively, these findings indicate that FOXN3 inhibits cell growth and invasion through inactivating the AKT/MDM2/p53 signaling pathway and that FOXN3-AKT/MDM2/p53 axis may represent a novel therapeutic target for glioma patients.

Metabolic hallmarks of liver regeneration

Despite the crucial role of cell metabolism in biological processes, particularly cell division, metabolic aspects of liver regeneration are not well defined. Better understanding of the metabolic activity governing division of liver cells will provide powerful insights into mechanisms of physiological and pathological liver regeneration. Recent studies have provided evidence that metabolic response to liver failure might be a proximal signal to initiate cell proliferation in liver regeneration. In this review, we highlight how lipids, carbohydrates, and proteins dynamically change and orchestrate liver regeneration. In addition, we discuss translational studies in which metabolic intervention has been used to treat chronic liver diseases (CLDs).

Effect of Bombyx mori on the Liver Protection of Non-Alcoholic Fatty Liver Disease Based on In Vitro and In Vivo Models

Edible insects, Bombyx mori (silkworm; SW), which feed on mulberry leaves, have been consumed by humans for a long time as supplements or traditional medication. Non-alcoholic fatty liver disease (NAFLD) is a liver metabolic disorder that affects many people worldwide. We examined the hepatoprotective effects of SW using in vitro and high-fat and high-fructose (HFHF) diet-induced obese in vivo model mice by real-time PCR, immunoblot analysis, and fecal microbiota analysis. SW significantly reduced lipid accumulation and expression of the lipogenic genes in HepG2 cells and the livers of HFHF-induced mice. SW caused significant reductions in triglycerides, and total cholesterol in serum and upregulation of fatty acid oxidation markers compared to the HFHF group. Besides, SW significantly induced phosphorylation of AMPK and ACC in both models, suggesting roles in AMPK activation and the ACC signaling pathway. Furthermore, the gut microbiota analysis demonstrated that SW treatment reduced Firmicutes to Bacteroidetes ratios and the relative abundance of the Lachnospiraceae family compared to HFHF-induced obese mice. These results provide a novel therapeutic agent of hepatoprotective effects of SW for non-alcoholic hepatic steatosis that targets hepatic AMPK and ACC-mediated lipid metabolism.

CDK5RAP3 Deficiency Restrains Liver Regeneration after Partial Hepatectomy Triggering Endoplasmic Reticulum Stress

CDK5 regulatory subunit-associated protein 3 (CDK5RAP3) plays a crucial role in mammalian liver development and hepatic function by controlling hepatocyte proliferation and differentiation, glucose and lipid metabolism, UFMylation, and endoplasmic reticulum homeostasis. However, the role of CDK5RAP3 in liver regeneration remains unknown. A liver-specific Cdk5rap3 knockout (CKO) mouse model was used to study the function of CDK5RAP3 during liver regeneration induced by standard two-thirds partial hepatectomy (PHx). Twenty-four hours after PHx, the liver-to-body weight ratio was markedly higher in CKO mice than in wild-type mice. However, this ratio did not increase significantly and gradually over time after PHx in CKO mice. Hepatocyte proliferation was significantly delayed in CKO mice compared with wild-type mice. Meanwhile, CDK5RAP3 deficiency increased lipid accumulation, impaired glycogen synthesis, and lowered blood glucose levels after PHx. Critically, the absence of CDK5RAP3 seemed to promote an inflammatory response and induce apoptosis at a late stage of liver regeneration. In addition, CDK5RAP3 deficiency disrupted UFMylation homeostasis and aggravated endoplasmic reticulum stress in hepatocytes after PHx. Taken together, these data suggest that CDK5RAP3 enhances liver regeneration, at least partially via controlling cell cycle and glucose and lipid metabolism.