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

IGFBP7 promotes endothelial cell repair in the recovery phase of acute lung injury

IGFBP7 has been found to play an important role in inflammatory diseases, such as acute lung injury (ALI). However, the role of IGFBP7 in different stages of inflammation remains unclear. Transcriptome sequencing was used to identify the regulatory genes of IGFBP7, and endothelial IGFBP7 expression was knocked down using Aplnr-Dre mice to evaluate the endothelial proliferation capacity. The expression of proliferation-related genes was detected by Western blotting and RT-PCR assays. In the present study, we found that knockdown of IGFBP7 in endothelial cells significantly decreases the expression of endothelial cell proliferation-related genes and cell number in the recovery phase but not in the acute phase of ALI. Mechanistically, using bulk-RNA sequencing and CO-IP, we found that IGFBP7 promotes phosphorylation of FOS and subsequently up-regulates YAP1 molecules, thereby promoting endothelial cell proliferation. This study indicated that IGFBP7 has diverse roles in different stages of ALI, which extends the understanding of IGFBP7 in different stages of ALI and suggests that IGFBP7 as a potential therapeutic target in ALI needs to take into account the period specificity of ALI.

Tudor-SN promotes cardiomyocyte proliferation and neonatal heart regeneration through regulating the phosphorylation of YAP

BACKGROUND

The neonatal mammalian heart exhibits considerable regenerative potential following injury through cardiomyocyte proliferation, whereas mature cardiomyocytes withdraw from the cell cycle and lose regenerative capacities. Therefore, investigating the mechanisms underlying neonatal cardiomyocyte proliferation and regeneration is crucial for unlocking the regenerative potential of adult mammalian heart to repair damage and restore contractile function following myocardial injury.

METHODS

The Tudor staphylococcal nuclease (Tudor-SN) transgenic (TG) or cardiomyocyte-specific knockout mice (Myh6-Tudor-SN -/-) were generated to investigate the role of Tudor-SN in cardiomyocyte proliferation and heart regeneration following apical resection (AR) surgery. Primary cardiomyocytes isolated from neonatal mice were used to assess the influence of Tudor-SN on cardiomyocyte proliferation in vitro. Affinity purification and mass spectrometry were employed to elucidate the underlying mechanism. H9c2 cells and mouse myocardia with either overexpression or knockout of Tudor-SN were utilized to assess its impact on the phosphorylation of Yes-associated protein (YAP), both in vitro and in vivo.

RESULTS

We previously identified Tudor-SN as a cell cycle regulator that is highly expressed in neonatal mice myocardia but downregulated in adults. Our present study demonstrates that sustained expression of Tudor-SN promotes and prolongs the proliferation of neonatal cardiomyocytes, improves cardiac function, and enhances the ability to repair the left ventricular apex resection in neonatal mice. Consistently, cardiomyocyte-specific knockout of Tudor-SN impairs cardiac function and retards recovery after injury. Tudor-SN associates with YAP, which plays important roles in heart development and regeneration, inhibiting phosphorylation at Ser 127 and Ser 397 residues by preventing the association between Large Tumor Suppressor 1 (LATS1) and YAP, correspondingly maintaining stability and promoting nuclear translocation of YAP to enhance the proliferation-related genes transcription.

CONCLUSION

Tudor-SN regulates the phosphorylation of YAP, consequently enhancing and prolonging neonatal cardiomyocyte proliferation under physiological conditions and promoting neonatal heart regeneration after injury.

Constitutive Androstane Receptor and Peroxisome Proliferator-Activated Receptor α Do Not Perform Liquid-Liquid Phase Separation in Cells

Constitutive androstane receptor (CAR) and peroxisome proliferator-activated receptor α (PPARα) are members of the nuclear receptor superfamily, which regulates various physiologic and pathologic processes. Phase separation is a dynamic biophysical process in which biomacromolecules form liquid-like condensates, which have been identified as contributors to many cellular functions, such as signal transduction and transcription regulation. However, the possibility of phase separation for CAR and PPARα remains unknown. This study explored the potential phase separation of CAR and PPARα The computational analysis utilizing algorithm tools examining the intrinsically disordered regions of CAR and PPARα suggested a limited likelihood of undergoing phase separation. Experimental assays under varying conditions of hyperosmotic stress and agonist treatments confirmed the absence of phase separation for these receptors. Additionally, the optoDroplets assay, which utilizes blue light stimulation to induce condensate formation, showed that there was no condensate formation of the fusion protein of Cry2 with CAR or PPARα Furthermore, phase separation of CAR or PPARα did not occur despite reduced target expression under hyperosmotic stress. In conclusion, these findings revealed that neither the activation of CAR and PPARα nor hyperosmotic stress induces phase separation of CAR and PPARα in cells. SIGNIFICANCE STATEMENT: Constitutive androstane receptor (CAR) and peroxisome proliferator-activated receptor α (PPARα) are key regulators of various functions in the body. This study showed that CAR and PPARα do not exhibit phase separation under hyperosmotic stress or after agonist-induced activation. These findings provide new insights into the CAR and PPARα biology and physiology.

Pregnane X receptor activation induces liver enlargement and regeneration and simultaneously promotes the metabolic activity of CYP3A1/2 and CYP2C6/11 in rats

Human pregnane X receptor (PXR) is critical for regulating the expression of key drug-metabolizing enzymes such as CYP3A and CYP2C. Our recent study revealed that treatment with rodent-specific PXR agonist pregnenolone-16α-carbonitrile (PCN) significantly induced hepatomegaly and promoted liver regeneration after two-thirds partial hepatectomy (PHx) in mice. However, it remains unclear whether PXR activation induces hepatomegaly and liver regeneration and simultaneously promotes metabolic function of the liver. Here, we investigated the metabolism activity of CYP1A2, CYP3A1/2 and CYP2C6/11 during PXR activation-induced liver enlargement and regeneration in rats after cocktail dosing of CYP probe drugs. For PCN-induced hepatomegaly, a notable increase in the metabolic activity of CYP3A1/2 and CYP2C6/11, as evidenced by the plasma exposure of probe substrates and the AUC ratios of the characteristic metabolites to its corresponding probe substrates. The metabolic activity of CYP1A2, CYP3A1/2 and CYP2C6/11 decreased significantly after PHx. However, PCN treatment obviously enhanced the metabolic activity of CYP2C6/11 and CYP3A1/2 in PHx rats. Furthermore, the protein expression levels of CYP3A1/2 and CYP2C6/11 in liver were up-regulated. Taken together, this study demonstrates that PXR activation not only induces hepatomegaly and liver regeneration in rats, but also promotes the protein expression and metabolic activity of the PXR downstream metabolizing enzymes such as CYP3A1/2 and CYP2C6/11 in the body.

Single-nucleus multiomic analysis of Beckwith-Wiedemann syndrome liver reveals PPARA signaling enrichment and metabolic dysfunction

Beckwith-Wiedemann Syndrome (BWS) is an epigenetic overgrowth syndrome caused by methylation changes in the human 11p15 chromosomal locus. Patients with BWS exhibit tissue overgrowth, as well as an increased risk of childhood neoplasms in the liver and kidney. To understand the impact of these 11p15 changes, specifically in the liver, we performed single-nucleus RNA sequencing (snRNA-seq) and single-nucleus assay for transposase-accessible chromatin with sequencing (snATAC-seq) to generate paired, cell-type-specific transcriptional and chromatin accessibility profiles of both BWS-liver and nonBWS-liver nontumorous tissue. Our integrated RNA+ATACseq multiomic approach uncovered hepatocyte-specific enrichment and activation of the peroxisome proliferator-activated receptor α (PPARA) - a liver metabolic regulator. To confirm our findings, we utilized a BWS-induced pluripotent stem cell (iPSC) model, where cells were differentiated into hepatocytes. Our data demonstrates the dysregulation of lipid metabolism in BWS-liver, which coincided with observed upregulation of PPARA during hepatocyte differentiation. BWS liver cells exhibited decreased neutral lipids and increased fatty acid β-oxidation, relative to controls. We also observed increased reactive oxygen species (ROS) byproducts in the form of peroxidated lipids in BWS hepatocytes, which coincided with increased oxidative DNA damage. This study proposes a putative mechanism for overgrowth and cancer predisposition in BWS liver due to perturbed metabolism.

The reversal of PXR or PPARα activation-induced hepatomegaly

The activation of pregnane X receptor (PXR) or peroxisome proliferator-activated receptor α (PPARα) can induce liver enlargement. Recently, we reported that PXR or PPARα activation-induced hepatomegaly depends on yes-associated protein (YAP) signaling and is characterized by hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. However, it remains unclear whether PXR or PPARα activation-induced hepatomegaly can be reversed after the withdrawal of their agonists. In this study, we investigated the regression of enlarged liver to normal size following the withdrawal of PCN or WY-14643 (typical agonists of mouse PXR or PPARα) in C57BL/6 mice. The immunohistochemistry analysis of CTNNB1 and KI67 showed a reversal of hepatocyte size and a decrease in hepatocyte proliferation after the withdrawal of agonists. In details, the expression of PXR or PPARα downstream proteins (CYP3A11, CYP2B10, ACOX1, and CYP4A) and the expression of proliferation-related proteins (CCNA1, CCND1, and PCNA) returned to the normal levels. Furthermore, YAP and its downstream proteins (CTGF, CYR61, and ANKRD1) also restored to the normal states, which was consistent with the change in liver size. These findings demonstrate the reversibility of PXR or PPARα activation-induced hepatomegaly and provide new data for the safety of PXR and PPARα as drug targets.

Pregnane X Receptor Activation in Liver Macrophages Protects against Endotoxin-Induced Liver Injury

Endotoxemia-related acute liver injury has a poor prognosis and high mortality, and macrophage polarization plays a central role in the pathological process. Pregnane X receptor (PXR) serves as a nuclear receptor and xenosensor, safeguarding the liver from toxic stimuli. However, the effect and underlying mechanism of PXR activation on endotoxemic liver injury remain largely unknown. Here, the expression of PXR is reported in human and murine macrophages, and PXR activation modified immunotypes of macrophages. Moreover, PXR activation significantly attenuated endotoxemic liver injury and promoted macrophage M2 polarization. Macrophage depletion by GdCl3 confirmed the essential of macrophages in the beneficial effects observed with PXR activation. The role of PXR in macrophages is further validated using AAV8-F4/80-Pxr shRNA-treated mice; the PXR-mediated hepatoprotection is impaired, and M2 polarization enhancement is blunted. Additionally, treatment with PXR agonists inhibited lipopolysaccharide (LPS)-induced M1 polarization and favored M2 polarization in BMDM, Raw264.7, and THP-1 cells. Further analyses revealed an interaction between PXR and p-STAT6 in vivo and in vitro. Moreover, blocking Pxr or Stat6 abolished the PXR-induced polarization shift. Collectively, macrophage PXR activation attenuated endotoxin-induced liver injury and regulated macrophage polarization through the STAT6 signaling pathway, which provided a potential therapeutic target for managing endotoxemic liver injury.

The roles of Hippo/YAP signaling pathway in physical therapy

Cellular behavior is regulated by mechanical signals within the cellular microenvironment. Additionally, changes of temperature, blood flow, and muscle contraction also affect cellular state and the development of diseases. In clinical practice, physical therapy techniques such as ultrasound, vibration, exercise, cold therapy, and hyperthermia are commonly employed to alleviate pain and treat diseases. However, the molecular mechanism about how these physiotherapy methods stimulate local tissues and control gene expression remains unknow. Fortunately, the discovery of YAP filled this gap, which has been reported has the ability to sense and convert a wide variety of mechanical signals into cell-specific programs for transcription, thereby offering a fresh perspective on the mechanisms by which physiotherapy treat different diseases. This review examines the involvement of Hippo/YAP signaling pathway in various diseases and its role in different physical therapy approaches on diseases. Furthermore, we explore the potential therapeutic implications of the Hippo/YAP signaling pathway and address the limitations and controversies surrounding its application in physiotherapy.

The yes-associated protein-1 (YAP1) inhibitor celastrol suppresses the ability of transforming growth factor β to activate human gingival fibroblasts

OBJECTIVE

To determine whether celastrol, an inhibitor of the mechanosensitive transcriptional cofactor yes-associated protein-1 (YAP1), impairs the ability of TGFβ1 to stimulate fibrogenic activity in human gingival fibroblast cell line.

DESIGN

Human gingival fibroblasts were pre-treated with celastrol or DMSO followed by stimulation with or without TGFβ1 (4 ng/ml). We then utilized bulk RNA sequencing (RNAseq), real-time polymerase chain reaction (RT-PCR), Western blot, immunofluorescence, cell proliferation assays to determine if celastrol impaired TGFβ1-induced responses in a human gingival fibroblast cell line.

RESULTS

Celastrol impaired the ability of TGFβ1 to induce expression of the profibrotic marker and mediator CCN2. Bulk RNAseq analysis of gingival fibroblasts treated with TGFβ1, in the presence or absence of celastrol, revealed that celastrol impaired the ability of TGFβ1 to induce mRNA expression of genes within extracellular matrix, wound healing, focal adhesion and cytokine/Wnt signaling clusters. RT-PCR analysis of extracted RNAs confirmed that celastrol antagonized the ability of TGFβ1 to induce expression of genes anticipated to contribute to fibrotic responses. Celastrol also reduced gingival fibroblast proliferation, and YAP1 nuclear localization in response to TGFβ1.

CONCLUSION

YAP1 inhibitors such as celastrol could be used to impair pro-fibrotic responses to TGFβ1 in human gingival fibroblasts.

A CDAHFD-induced mouse model mimicking human NASH in the metabolism of hepatic phosphatidylcholines and acyl carnitines

Non-alcoholic steatohepatitis (NASH) is the hepatic manifestation of a cluster of conditions associated with lipid metabolism disorders. Ideal animal models mimicking the human NASH need to be explored to better understand the pathogenesis. A choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) has recently been used to induce the NASH model, but the advantages are not established. NASH models were induced using the well-known traditional methionine- and choline-deficient (MCD) diet for 5 weeks and the recently used CDAHFD for 3 weeks. Liver phenotypes were analyzed to evaluate the differences in markers related to NASH. Lipidomics and metabolism analyses were used to investigate the effects of dietary regimens on the lipidome of the liver. The CDAHFD induced stronger NASH responses than the MCD, including lipid deposition, liver injury, inflammation, bile acid overload and hepatocyte proliferation. A significant difference in the hepatic lipidome was revealed between the CDAHFD and MCD-induced NASH models. In particular, the CDAHFD reduced the hepatic levels of phosphatidylcholines (PCs) and acylcarnitines (ACs), which was supported by the metabolism analysis and in line with the tendency of human NASH. Pathologically, the CDAHFD could effectively induce a more human-like NASH model over the traditional MCD. The hepatic PCs, ACs and their metabolism in CDAHFD-treated mice were down-regulated, similar to those in human NASH.

Tensile Stress-Activated and Exosome-Transferred YAP/TAZ-Notch Circuit Specifies Type H Endothelial Cell for Segmental Bone Regeneration

The Ilizarov technique has been continuously innovated to utilize tensile stress (TS) for inducing a bone development-like regenerative process, aiming to achieve skeletal elongation and reconstruction. However, it remains uncertain whether this distraction osteogenesis (DO) process induced by TS involves the pivotal coupling of angiogenesis and osteogenesis mediated by type H endothelial cells (THECs). In this study, it is demonstrated that the Ilizarov technique induces the formation of a metaphysis-like architecture composed of THECs, leading to segmental bone regeneration during the DO process. Mechanistically, cell-matrix interactions-mediated activation of yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) transcriptionally upregulates the expression of Notch1 and Delta-like ligand 4, which act as direct positive regulators of THECs phenotype, in bone marrow endothelial cells (BMECs) upon TS stimulation. Simultaneously, the Notch intracellular domain enhances YAP/TAZ activity by transcriptionally upregulating YAP expression and stabilizing TAZ protein, thus establishing the YAP/TAZ-Notch circuit. Additionally, TS-stimulated BMECs secrete exosomes enriched with vital molecules in this positive feedback pathway, which can be utilized to promote segmental bone defect healing, mimicking the therapeutic effects of Ilizarov technique. The findings advance the understanding of TS-induced segmental bone regeneration and establish the foundation for innovative biological therapeutic strategies aimed at activating THECs.

Enhancing regenerative medicine: the crucial role of stem cell therapy

Stem cells offer new therapeutic avenues for the repair and replacement of damaged tissues and organs owing to their self-renewal and multipotent differentiation capabilities. In this paper, we conduct a systematic review of the characteristics of various types of stem cells and offer insights into their potential applications in both cellular and cell-free therapies. In addition, we provide a comprehensive summary of the technical routes of stem cell therapy and discuss in detail current challenges, including safety issues and differentiation control. Although some issues remain, stem cell therapy demonstrates excellent potential in the field of regenerative medicine and provides novel tactics and methodologies for managing a wider spectrum of illnesses and traumas.

Predicting colorectal cancer prognosis based on long noncoding RNAs of disulfidptosis genes

BACKGROUND

A recently hypothesized cause of cell death called disulfidptosis has been linked to the expansion, emigration, and vascular rebuilding of cancer cells. Cancer can be treated by targeting the pathways that trigger cell death.

AIM

To discover the long non-coding RNA of the disulfidaptosis-related lncRNAs (DRLs), prognosis clinical survival, and treat patients with colorectal cancer with medications.

METHODS

Initially, we queried the Cancer Genome Atlas database to collect transcriptome, clinical, and genetic mutation data for colorectal cancer (CRC). Training and testing sets for CRC patient transcriptome data were generated randomly. Key long non-coding RNAs (lncRNAs) related to DRLs were then identified and evaluated using a least absolute shrinkage and selection operator procedure, as well as univariate and multivariate Cox regression models. A prognostic model was then created after risk scoring. Also, Immune infiltration analysis, immune checkpoint analysis, and medication susceptibility analysis were used to investigate the causes of the different prognoses between high and low risk groups. Finally, we validated the differential expression and biomarker potential of risk-predictive lncRNAs through induction using both NCM460 and HT-29 cell lines, as well as a disulfidptosis model.

RESULTS

In this work, eight significant lncRNAs linked to disulfidptosis were found. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of differentially expressed genes between high- and low-risk groups from the prognostic model showed a close relationship with the immune response as well as significant enrichment in neutrophil extracellular trap formation and the IL-17 signaling pathway. Furthermore, significant immune cell variations between the high-risk and low-risk groups were seen, as well as a higher incidence of immunological escape risk in the high-risk group. Finally, Epirubicin, bortezomib, teniposide, and BMS-754807 were shown to have the lowest sensitivity among the four immunotherapy drugs.

CONCLUSION

Our findings emphasizes the role of disulfidptosis in regulating tumor development, therapeutic response, and patient survival in CRC patients. For the clinical treatment of CRC, these important LncRNAs could serve as viable therapeutic targets.

Complex roles of Hippo-YAP/TAZ signaling in hepatocellular carcinoma

BACKGROUND

The Hippo signaling pathway is an evolutionarily conserved signaling module that controls organ size in different species, and the disorder of the Hippo pathway can induce liver cancer in organisms, especially hepatocellular carcinoma (HCC). The exact mechanism that causes cancer is still unknown. Recent studies have shown that it is a classical kinase cascade that phosphorylates the Mst1/2-sav1 complex and activates the phosphorylation of the Lats1/2-mob1A/B complex for inactivating Yap and Taz. These kinases and scaffolds are regarded as primary regulators of the Hippo pathway, and help in activating a variety of carcinogenic processes. Among them, Yap/Taz is seen to be the main effector molecule, which is downstream of the Hippo pathway, and its abnormal activation is related to a variety of human cancers including liver cancer. Currently, since Yap/Taz plays a variety of roles in cancer promotion and tumor regeneration, the Hippo pathway has emerged as an attractive target in recent drug development research.

METHODS

We collect and review relevant literature in web of Science and Pubmed.

CONCLUSION

This review highlights the important roles of Yap/Taz in activating Hippo pathway in liver cancer. The recent findings on the crosstalks between the Hippo and other cancer associated pathways and moleculars are also discussed. In this review, we summarized and discussed recent breakthroughs in our understanding of how key components of the Hippo-YAP/TAZ pathway influence the hepatocellular carcinoma, including their effects on tumor occurrence and development, their roles in regulating metastasis, and their function in chemotherapy resistance. Further, the molecular mechanism and roles in regulating cross talk between Hippo-YAP/TAZ pathway and other cancer-associated pathways or oncogenes/cancer suppressor genes were summarized and discussed. More, many other inducers and inhibitors of this signaling cascade and available experimental therapies against the YAP/TAZ/TEAD axis were discussed. Targeting this pathway for cancer therapy may have great significance in the treatment of hepatocellular carcinoma. Graphical summary of the complex role of Hippo-YAP/TAZ signaling in hepatocellular carcinoma.

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.

The Crosstalk between Mesenchymal Stromal/Stem Cells and Hepatocytes in Homeostasis and under Stress

Liver diseases, characterized by high morbidity and mortality, represent a substantial medical problem globally. The current therapeutic approaches are mainly aimed at reducing symptoms and slowing down the progression of the diseases. Organ transplantation remains the only effective treatment method in cases of severe liver pathology. In this regard, the development of new effective approaches aimed at stimulating liver regeneration, both by activation of the organ's own resources or by different therapeutic agents that trigger regeneration, does not cease to be relevant. To date, many systematic reviews and meta-analyses have been published confirming the effectiveness of mesenchymal stromal cell (MSC) transplantation in the treatment of liver diseases of various severities and etiologies. However, despite the successful use of MSCs in clinical practice and the promising therapeutic results in animal models of liver diseases, the mechanisms of their protective and regenerative action remain poorly understood. Specifically, data about the molecular agents produced by these cells and mediating their therapeutic action are fragmentary and often contradictory. Since MSCs or MSC-like cells are found in all tissues and organs, it is likely that many key intercellular interactions within the tissue niches are dependent on MSCs. In this context, it is essential to understand the mechanisms underlying communication between MSCs and differentiated parenchymal cells of each particular tissue. This is important both from the perspective of basic science and for the development of therapeutic approaches involving the modulation of the activity of resident MSCs. With regard to the liver, the research is concentrated on the intercommunication between MSCs and hepatocytes under normal conditions and during the development of the pathological process. The goals of this review were to identify the key factors mediating the crosstalk between MSCs and hepatocytes and determine the possible mechanisms of interaction of the two cell types under normal and stressful conditions. The analysis of the hepatocyte-MSC interaction showed that MSCs carry out chaperone-like functions, including the synthesis of the supportive extracellular matrix proteins; prevention of apoptosis, pyroptosis, and ferroptosis; support of regeneration; elimination of lipotoxicity and ER stress; promotion of antioxidant effects; and donation of mitochondria. The underlying mechanisms suggest very close interdependence, including even direct cytoplasm and organelle exchange.

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.

LSR targets YAP to modulate intestinal Paneth cell differentiation

Lipolysis-stimulated lipoprotein receptor (LSR) is a multi-functional protein that is best known for its roles in assembly of epithelial tricellular tight junctions and hepatic clearance of lipoproteins. Here, we investigated whether LSR contributes to intestinal epithelium homeostasis and pathogenesis of intestinal disease. By using multiple conditional deletion mouse models and ex vivo cultured organoids, we find that LSR elimination in intestinal stem cells results in the disappearance of Paneth cells without affecting the differentiation of other cell lineages. Mechanistic studies reveal that LSR deficiency increases abundance of YAP by modulating its phosphorylation and proteasomal degradation. Using gain- and loss-of-function studies, we show that LSR protects against necrotizing enterocolitis through enhancement of Paneth cell differentiation in small-intestinal epithelium. Thus, this study identifies LSR as an upstream negative regulator of YAP activity, an essential factor for Paneth cell differentiation, and a potential therapeutic target for necrotizing enterocolitis.

YAP/TAZ: Molecular pathway and disease therapy

The Yes-associated protein and its transcriptional coactivator with PDZ-binding motif (YAP/TAZ) are two homologous transcriptional coactivators that lie at the center of a key regulatory network of Hippo, Wnt, GPCR, estrogen, mechanical, and metabolism signaling. YAP/TAZ influences the expressions of downstream genes and proteins as well as enzyme activity in metabolic cycles, cell proliferation, inflammatory factor expression, and the transdifferentiation of fibroblasts into myofibroblasts. YAP/TAZ can also be regulated through epigenetic regulation and posttranslational modifications. Consequently, the regulatory function of these mechanisms implicates YAP/TAZ in the pathogenesis of metabolism-related diseases, atherosclerosis, fibrosis, and the delicate equilibrium between cancer progression and organ regeneration. As such, there arises a pressing need for thorough investigation of YAP/TAZ in clinical settings. In this paper, we aim to elucidate the signaling pathways that regulate YAP/TAZ and explore the mechanisms of YAP/TAZ-induce diseases and their potential therapeutic interventions. Furthermore, we summarize the current clinical studies investigating treatments targeting YAP/TAZ. We also address the limitations of existing research on YAP/TAZ and propose future directions for research. In conclusion, this review aims to provide fresh insights into the signaling mediated by YAP/TAZ and identify potential therapeutic targets to present innovative solutions to overcome the challenges associated with YAP/TAZ.

Involvement of FAM83 Family Proteins in the Development of Solid Tumors: An Update Review

FAM83 family members are a group of proteins that have been implicated in various solid tumors. In this updated review, we mainly focus on the cellular localization, molecular composition, and biological function of FAM83 family proteins in solid tumors. We discussed the factors that regulate abnormal protein expression and alterations in the functional activities of solid tumor cells (including non-coding microRNAs and protein modifiers) and potential mechanisms of tumorigenesis (including the MAPK, WNT, and TGF-β signaling pathways). Further, we highlighted the application of FAM83 family proteins in the diagnoses and treatment of different cancers, such as breast, lung, liver, and ovarian cancers from two aspects: molecular marker diagnosis and tumor drug resistance. We described the overexpression of FAM83 genes in various human malignant tumor cells and its relationship with tumor proliferation, migration, invasion, transformation, and drug resistance. Moreover, we explored the prospects and challenges of using tumor treatments based on the FAM83 proteins. Overall, we provide a theoretical basis for harnessing FAM83 family proteins as novel targets in cancer treatment. We believe that this review opens up open new directions for solid tumor treatment in clinical practice.

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.

Tyrosine phosphorylation of YAP-1 in biliary epithelial cells mediates posthepatectomy liver regeneration and is affected by serotonin

Experimental data suggested activation of yes-associated protein (YAP-1) as a critical regulator of liver regeneration (LR). Serotonin (5-HT) promotes LR in rodent models and has been proposed to act via YAP-1. How 5-HT affects LR is incompletely understood. A possible mechanism how 5-HT affects human LR was explored. Sixty-one patients were included. Tissue samples prior and 2 h after induction of LR were collected. Circulating levels of 5-HT and osteopontin (OPN) were assessed. YAP-1, its phosphorylation states, cytokeratin 19 (CK-19) and OPN were assessed using immunofluorescence. A mouse model of biliary epithelial cells (BECs) specific deletion of YAP/TAZ was developed. YAP-1 increased as early as 2 h after induction of LR (p = 0.025) predominantly in BECs. BEC specific deletion of YAP/TAZ reduced LR after 70% partial hepatectomy in mice (Ki67%, p < 0.001). SSRI treatment, depleting intra-platelet 5-HT, abolished YAP-1 and OPN induction upon LR. Portal vein 5-HT levels correlated with intrahepatic YAP-1 expression upon LR (R = 0.703, p = 0.035). OPN colocalized with YAP-1 in BECs and its circulating levels increased in the liver vein 2 h after induction of LR (p = 0.017). In the context of LR tyrosine-phosphorylated YAP-1 significantly increased (p = 0.042). Stimulating BECs with 5-HT resulted in increased YAP-1 activation via tyrosine-phosphorylation and subsequently increased OPN expression. BECs YAP-1 appears to be critical for LR in mice and humans. Our evidence suggests that 5-HT, at least in part, exerts its pro-regenerative effects via YAP-1 tyrosine-phosphorylation in BECs and subsequent OPN-dependent paracrine immunomodulation.

Loss of APOO (MIC26) aggravates obesity-related whitening of brown adipose tissue via PPARα-mediated functional interplay between mitochondria and peroxisomes

BACKGROUND

Mitochondrial dysfunction and aberrant structure in adipose tissue occur in obesity and obesity-linked brown adipose tissue (BAT) whitening; however, whether this aberrant architecture contributes to or is the result of obesity is unknown. Apolipoprotein O (APOO) is a constitutive protein of the mitochondrial cristae organizing system complex. This study aimed to characterize the physiological consequences of APOO deficiency in vivo.

METHODS

APOO expression was analyzed in different human and murine adipose depots, and mice lacking APOO in adipocytes (Apoo^ACKO) are developed to examine the metabolic consequences of adipocyte-specific APOO ablation in vitro and in vivo.

RESULTS

Results showed that APOO expression is reduced in BAT from both diet-induced and leptin-deficient obese mice. APOO-knockout mice showed increased adiposity, BAT dysfunction and whitening, reduced non-shivering thermogenesis, and blunted responses to cold stimuli. APOO deficiency disrupted mitochondrial structure in brown adipocytes and impaired oxidative phosphorylation, thereby inducing a shift from oxidative to glycolytic metabolism, increasing lipogenic enzyme levels and BAT whitening. APOO inactivation inhibited thermogenesis in BAT by reducing mitochondrial long-chain fatty acid oxidation. It also disturbed peroxisomal biogenesis and very long-chain fatty acid oxidation via peroxisome proliferator-activated receptor α.

CONCLUSIONS

Altogether, APOO deficiency in adipocytes aggravates BAT whitening and diet-induced obesity; thus, APOO could be a therapeutic target for obesity.

Restoration of lipid homeostasis between TG and PE by the LXRα-ATGL/EPT1 axis ameliorates hepatosteatosis

Converting lipid disturbances in response to energy oversupply into healthy lipid homeostasis is a promising therapy to alleviate hepatosteatosis. Our clinical studies found that a further elevation of triglyceride (TG) in obese patients with the body mass index (BMI) greater than 28 was accompanied by a further reduction of phosphatidylethanolamine (PE). Shorter survival and poor prognosis were shown for the patients with high TG and low PE levels. Liver X receptor alpha (LXRα) knockout mice aggravated high-fat diet (HFD)-induced obesity and lipid disorders, making the TG enrichment and the PE decrease more pronounced according to the liver lipidomics analysis. The RNA-seq from mice liver exhibited that these metabolism disorders were attributed to the decline of Atgl (encoding the TG metabolism enzyme ATGL) and Ept1 (encoding the PE synthesis enzyme EPT1) expression. Mechanistic studies uncovered that LXRα activated the ATGL and EPT1 gene via direct binding to a LXR response element (LXRE) in the promoter. Moreover, both the supplement of PE in statin or fibrate therapy, and the LXRα inducer (oridonin) ameliorated cellular lipid deposition and lipotoxicity. Altogether, restoration of lipid homeostasis of TG and PE via the LXRα-ATGL/EPT1 axis may be a potential approach for the management of hepatosteatosis and metabolic syndrome.

β-catenin/TCF4 inhibitors ICG-001 and LF3 alleviate BDL-induced liver fibrosis by suppressing LECT2 signaling

Liver fibrosis can be characterized by the over-deposition of extracellular matrix (ECM). It has been reported that β-catenin/TCF4 interaction was enhanced in bile duct ligation (BDL) model, which implicated the critical role of β-catenin/TCF4 interaction during the progression of fibrosis. However, whether inhibiting β-catenin/TCF4 signaling attenuates liver fibrosis remains unknown. In the current study, we used ICG-001, an inhibitor that disrupts the interaction between CREB binding protein (CBP) and β-catenin, to inhibit β-catenin/TCF4 transcriptional activity. We also used LF3, a small molecule antagonist, to inhibit β-catenin/TCF4 interaction. The antifibrotic effect of ICG-001 and LF3 was assessed on BDL-induced liver fibrosis model. The results indicated both ICG-001 and LF3 significantly reduced the positive staining area of Sirius Red and α-SMA. The protein expression levels of α-SMA, Collagen Ⅰ and CD31 were also significantly downregulated in BDL + ICG-001 and BDL + LF3 groups. Besides, ICG-001 and LF3 promoted portal angiogenesis and inhibited sinusoids capillarization in fibrotic livers. For mechanistic study, we measured the level of leukocyte cell-derived chemotaxin 2 (LECT2), a direct target of β-catenin/TCF4, which was recently reported to participate in hepatic fibrosis by regulating angiogenesis. The results showed that both ICG-001 and LF3 reduced LECT2 expression in BDL mice. LF3 also downregulated pSer 675 β-catenin and nuclear β-catenin. In conclusion, this study demonstrated that inhibiting β-catenin/TCF4 signaling by ICG-001 or LF3 mitigated liver fibrosis by downregulating LECT2, promoting portal angiogenesis and inhibiting sinusoids capillarization, which provided new evidence that β-catenin/TCF4 signaling might be a target for the treatment of liver fibrosis.

PXR triggers YAP-TEAD binding and Sirt2-driven YAP deacetylation and polyubiquitination to promote liver enlargement and regeneration in mice

Pregnane X receptor (PXR) plays an important role in the regulation of metabolic homeostasis. Yes-associated protein (YAP) is a critical regulator of liver size and liver regeneration. Recently, we reported that PXR-induced liver enlargement and regeneration depend on YAP signalling, but the underlying mechanisms remain unclear. This study aimed to reveal how PXR regulates or interacts with YAP signalling during PXR-induced hepatomegaly and liver regeneration. Immunoprecipitation (IP), Co-IP and GST pull-down assays were performed in vitro to reveal the regulatory mechanisms involved in the PXR-YAP interaction. The roles of YAP-TEAD binding and Sirt2-driven deacetylation and polyubiquitination of YAP were further investigated in vitro and in vivo. The results showed that the ligand-binding domain (LBD) of PXR and the WW domain of YAP were critical for the PXR-YAP interaction. Furthermore, disruption of the YAP-TEAD interaction using the binding inhibitor verteporfin significantly decreased PXR-induced liver enlargement and regeneration after 70 % partial hepatectomy (PHx). Mechanistically, PXR activation significantly decreased YAP acetylation, which was interrupted by the sirtuin inhibitor nicotinamide (NAM). In addition, p300-induced YAP acetylation contributed to K48-linked YAP ubiquitination. Interestingly, PXR activation remarkably inhibited K48-linked YAP ubiquitination while inducing K63-linked YAP polyubiquitination. Sirt2 interference abolished the deacetylation and K63-linked polyubiquitination of YAP, suggesting that the PXR-induced deacetylation and polyubiquitination of YAP are Sirt2 dependent. Taken together, this study demonstrates that PXR induce liver enlargement and regeneration via the regulation of YAP acetylation and ubiquitination and YAP-TEAD binding, providing evidences for using PXR as potential target to promote hepatic development and liver repair.

The predictive value of YAP-1 and POU2F3 for the efficacy of immuno-chemotherapy in extensive-stage SCLC patients

INTRODUCTION

Recently, several clinical trials of immunotherapy for extensive-stage small-cell lung cancer (ES-SCLC) have shown limited benefits because of unselected patients. Thus, we aimed to explore whether YES-associated protein 1 (YAP-1) and POU domain class 2 transcription factor 3 (POU2F3) could identify SCLC patients with durable benefits from immunotherapy as potential biomarkers.

METHODS

We performed IHC of YAP-1 and POU2F3, and RNA-seq on tissues of ES- SCLC patients. An open-source plugin based on IHC-profiler was conducted to calculate the expression levels of YAP-1 and POU2F3.

RESULTS

Patients with ES-SCLC were retrospectively investigated in the Guangdong Provincial People's Hospital from January 2018 to July 2021, and 21 patients whoever received atezolizumab plus etoposide/carboplatin (ECT) regimen also had tissue samples reachable. The median IHC-score of YAP-1 in responders (CR/PR patients) was significantly lower than in nonresponders (SD/PD patients) at 13.97 (95% CI: 8.97-16.30) versus 23.72 (95% CI: 8.13-75.40). The IHC-score of YAP-1 and PFS showed a negative correlation by Spearman (r=-0.496). However, POU2F3 did not show a correlation with efficacy. Besides, patients with YAP-1 high expression had IL6, MYCN, and MYCT1 upregulated, while analysis of immune cell infiltration only showed that M0 macrophages were significantly higher.

CONCLUSIONS

The expression of YAP-1 negatively correlated with the efficacy of ECT in ES-SCLC patients while POU2F3 did not reveal the predictive value. However, prospective investigations with a large sample size are needed.

Long-term treatment with the mPXR agonist PCN promotes hepatomegaly and lipid accumulation without hepatocyte proliferation in mice

Pregnane X receptor (PXR) is highly expressed in the liver and plays a pivotal role in xenobiotic and endobiotic metabolism. We previously reported that PXR activation by its specific mouse agonist pregnenolone 16α-carbonitrile (PCN) significantly induces liver enlargement and lipid accumulation. However, the effect of long-term PCN treatment on PXR and mouse liver is still unknown. This study aimed to explore the influence of long-term administration of PCN on mouse liver and hepatic lipid homeostasis. Male C57BL/6 mice were injected intraperitoneally with PCN (100 mg/kg once a week) for 42 weeks. Serum and liver samples were collected for biochemical and histological analysis. PXR activation was investigated by Western blot. Ultra-high-performance liquid chromatography coupled with electrospray ionization high-resolution mass spectrometry (UHPLC-ESI-HRMS)-based lipidomics analysis was performed to explore the change in different lipid categories. The results showed that long-term treatment with PCN significantly promoted hepatomegaly without hepatocyte proliferation and enlargement. Long-term treatment with PCN did not upregulate PXR target proteins in mice, and there was no significant upregulation of CYP3A11, CYP2B10, UGT1A1, MRP2, or MRP4. Lipidomics analysis showed obvious hepatic lipid accumulation in the PCN-treated mice, and the most significant change was found in triglycerides (TGs). Additionally, long-term treatment with PCN had no risk for carcinogenesis. These findings demonstrated that long-term PCN treatment induces hepatomegaly and lipid accumulation without hepatocyte proliferation or enlargement.

The Role of PPARs in Breast Cancer

Breast cancer is a malignant tumor with high morbidity and lethality. Its pathogenesis is related to the abnormal expression of many genes. The peroxisome proliferator-activated receptors (PPARs) are a class of ligand-dependent transcription factors in the nuclear receptor superfamily. They can regulate the transcription of a large number of target genes, which are involved in life activities such as cell proliferation, differentiation, metabolism, and apoptosis, and regulate physiological processes such as glucose metabolism, lipid metabolism, inflammation, and wound healing. Further, the changes in its expression are associated with various diseases, including breast cancer. The experimental reports related to "PPAR" and "breast cancer" were retrieved from PubMed since the discovery of PPARs and summarized in this paper. This review (1) analyzed the roles and potential molecular mechanisms of non-coordinated and ligand-activated subtypes of PPARs in breast cancer progression; (2) discussed the correlations between PPARs and estrogen receptors (ERs) as the nuclear receptor superfamily; and (3) investigated the interaction between PPARs and key regulators in several signaling pathways. As a result, this paper identifies PPARs as targets for breast cancer prevention and treatment in order to provide more evidence for the synthesis of new drugs targeting PPARs or the search for new drug combination treatments.

YAP regulates the liver size during the fasting-refeeding transition in mice

Liver is the central hub regulating energy metabolism during feeding-fasting transition. Evidence suggests that fasting and refeeding induce dynamic changes in liver size, but the underlying mechanisms remain unclear. Yes-associated protein (YAP) is a key regulator of organ size. This study aims to explore the role of YAP in fasting- and refeeding-induced changes in liver size. Here, fasting significantly reduced liver size, which was recovered to the normal level after refeeding. Moreover, hepatocyte size was decreased and hepatocyte proliferation was inhibited after fasting. Conversely, refeeding promoted hepatocyte enlargement and proliferation compared to fasted state. Mechanistically, fasting or refeeding regulated the expression of YAP and its downstream targets, as well as the proliferation-related protein cyclin D1 (CCND1). Furthermore, fasting significantly reduced the liver size in AAV-control mice, which was mitigated in AAV Yap (5SA) mice. Yap overexpression also prevented the effect of fasting on hepatocyte size and proliferation. Besides, the recovery of liver size after refeeding was delayed in AAV Yap shRNA mice. Yap knockdown attenuated refeeding-induced hepatocyte enlargement and proliferation. In summary, this study demonstrated that YAP plays an important role in dynamic changes of liver size during fasting-refeeding transition, which provides new evidence for YAP in regulating liver size under energy stress.

Per- and Polyfluoroalkyl Substances (PFASs) Impair Lipid Metabolism in Rana nigromaculata: A Field Investigation and Laboratory Study

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous environmental pollutants, causing environmental threats and public health concerns, but information regarding PFAS hepatotoxicity remains elusive. We investigated the effects of PFASs on lipid metabolism in black-spotted frogs through a combined field and laboratory study. In a fluorochemical industrial area, PFASs seriously accumulate in frog tissues. PFAS levels in frog liver tissues are positively related to the hepatosomatic index along with triglyceride (TG) and cholesterol (TC) contents. In the laboratory, frogs were exposed to 1 and 10 μg/L PFASs, respectively (including PFOA, PFOS, and 6:2 Cl-PFESA). At 10 μg/L, PFASs change the hepatic fatty acid composition and significantly increase the hepatic TG content by 1.33 to 1.87 times. PFASs induce cross-talk accumulation of TG, TC, and their metabolites between the liver and serum. PFASs can bind to LXRα and PPARα proteins, further upregulate downstream lipogenesis-related gene expression, and downregulate lipolysis-related gene expression. Furthermore, lipid accumulation induced by PFASs is alleviated by PPARα and LXRα antagonists, suggesting the vital role of PPARα and LXRα in PFAS-induced lipid metabolism disorders. This work first reveals the disruption of PFASs on hepatic lipid homeostasis and provides novel insights into the occurrence and environmental risk of PFASs in amphibians.

Pregnane X receptor promotes liver enlargement in mice through the spatial induction of hepatocyte hypertrophy and proliferation

Nuclear receptor pregnane X receptor (PXR) can induce significant liver enlargement through hepatocyte hypertrophy and proliferation. A previous report showed that during the process of PXR-induced liver enlargement, hepatocyte hypertrophy occurs around the central vein (CV) area while hepatocyte proliferation occurs around the portal vein (PV) area. However, the features of this spatial change remain unclear. Therefore, this study aims to explore the features of the spatial changes in hepatocytes in PXR-induced liver enlargement. PXR-induced spatial changes in hepatocyte hypertrophy and proliferation were confirmed in C57BL/6 mice. The liver was perfused with digitonin to destroy the hepatocytes around the CV or PV areas, and then the regional expression of proteins related to hepatocyte hypertrophy and proliferation was further measured. The results showed that the expression of PXR downstream proteins, such as cytochrome P450 (CYP) 3A11, CYP2B10, P-glycoprotein (P-gp) and organ anion transporting polypeptide 2 (OATP2) was upregulated around the CV area, while the expression of proliferation-related proteins such as cyclin B1 (CCNB1), cyclin D1 (CCND1) and serine/threonine NIMA-related kinase 2 (NEK2) was upregulated around the PV area. At the same time, the expression of cyclin-dependent kinase inhibitors such as retinoblastoma-like protein 2 (RBL2), cyclin-dependent kinase inhibitor 1B (CDKN1B) and CDKN1A was downregulated around the PV area. This study demonstrated that the spatial change in PXR-induced hepatocyte hypertrophy and proliferation is associated with the regional expression of PXR downstream targets and proliferation-related proteins and the regional distribution of triglycerides (TGs). These findings provide new insight into the understanding of PXR-induced hepatomegaly.

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.

PPARα: A potential therapeutic target of cholestasis

The accumulation of bile acids in the liver leads to the development of cholestasis and hepatocyte injury. Nuclear receptors control the synthesis and transport of bile acids in the liver. Among them, the farnesoid X receptor (FXR) is the most common receptor studied in treating cholestasis. The activation of this receptor can reduce the amount of bile acid synthesis and decrease the bile acid content in the liver, alleviating cholestasis. Ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) have a FXR excitatory effect, but the unresponsiveness of some patients and the side effect of pruritus seriously affect the results of UDCA or OCA treatment. The activator of peroxisome proliferator-activated receptor alpha (PPARα) has emerged as a new target for controlling the synthesis and transport of bile acids during cholestasis. Moreover, the anti-inflammatory effect of PPARα can effectively reduce cholestatic liver injury, thereby improving patients’ physiological status. Here, we will focus on the function of PPARα and its involvement in the regulation of bile acid transport and metabolism. In addition, the anti-inflammatory effects of PPARα will be discussed in some detail. Finally, we will discuss the application of PPARα agonists for cholestatic liver disorders.

SHP2 inhibition enhances Yes-associated protein mediated liver regeneration in murine partial hepatectomy models

Disrupted liver regeneration following hepatectomy represents an “undruggable” clinical challenge associated with poor patient outcomes. Yes-associated protein (YAP), a transcriptional coactivator that is repressed by the Hippo pathway, is instrumental in liver regeneration. We have previously described an alternative, Hippo-independent mechanism of YAP activation mediated by downregulation of protein tyrosine phosphatase nonreceptor type 11 (PTPN11, also known as SHP2) inhibition. Herein, we examined the effects of YAP activation with a selective SHP1/SHP2 inhibitor, NSC-87877, on liver regeneration in murine partial hepatectomy models. In our studies, NSC-87877 led to accelerated hepatocyte proliferation, improved liver regeneration, and decreased markers of injury following partial hepatectomy. The effects of NSC-87877 were lost in mice with hepatocyte-specific Yap/Taz deletion, and this demonstrated dependence on these molecules for the enhanced regenerative response. Furthermore, administration of NSC-87877 to murine models of nonalcoholic steatohepatitis was associated with improved survival and decreased markers of injury after hepatectomy. Evaluation of transcriptomic changes in the context of NSC-87877 administration revealed reduction in fibrotic signaling and augmentation of cell cycle signaling. Cytoprotective changes included downregulation of Nr4a1, an apoptosis inducer. Collectively, the data suggest that SHP2 inhibition induces a pro-proliferative and cytoprotective enhancement of liver regeneration dependent on YAP.

YAP1 activation and Hippo pathway signaling in the pathogenesis and treatment of intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (iCCA), the second most common primary liver cancer, is a highly lethal epithelial cell malignancy exhibiting features of cholangiocyte differentiation. iCCAs can potentially develop from multiple cell types of origin within liver, including immature or mature cholangiocytes, hepatic stem cells/progenitor cells, and from transdifferentiation of hepatocytes. Understanding the molecular mechanisms and genetic drivers that diversely drive specific cell lineage pathways leading to iCCA has important biological and clinical implications. In this context, activation of the YAP1-TEAD dependent transcription, driven by Hippo-dependent or -independent diverse mechanisms that lead to the stabilization of YAP1 is crucially important to biliary fate commitment in hepatobiliary cancer. In preclinical models, YAP1 activation in hepatocytes or cholangiocytes is sufficient to drive their malignant transformation into iCCA. Moreover, nuclear YAP1/TAZ is highly prevalent in human iCCA irrespective of the varied etiology, and significantly correlates with poor prognosis in iCCA patients. Based on the ubiquitous expression and diverse physiologic roles for YAP1/TAZ in the liver, recent studies have further revealed distinct functions of active YAP1/TAZ in regulating tumor metabolism, as well as the tumor immune microenvironment. In the current review, we discuss our current understanding of the various roles of the Hippo-YAP1 signaling in iCCA pathogenesis, with a specific focus on the roles played by the Hippo-YAP1 pathway in modulating biliary commitment and oncogenicity, iCCA metabolism, and immune microenvironment. We also discuss the therapeutic potential of targeting the YAP1/TAZ-TEAD transcriptional machinery in iCCA, its current limitations, and what future studies are needed to facilitate clinical translation.

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.