Constitutive androstane receptor induced-hepatomegaly and liver regeneration is partially via yes-associated protein activation

Activation of Nuclear Receptor CAR: A Pathway to Delay Aging through Enhanced Capacity for Xenobiotic Resistance

Environmental factors are linked to aging and age-related diseases. Emerging evidence suggests that enhancing body's resistance to xenobiotics might be an anti-aging strategy. The constitutive androstane receptor (CAR) regulates drug-metabolizing enzymes and transporters, coordinating metabolism and immune responses to adapt to stress triggered by exogenous exposure. However, the impact of activating CAR on aging remains unknown. In this study, Caenorhabditis elegans (C. elegans), drug-induced premature aging mice, and senescence accelerated P8 (SAMP8) mice are used as models to explore the effects of CAR activation on lifespan and healthspan, along with the underlying mechanisms. The results showed that hCAR agonist CITCO and mCAR agonist TCPOBOP prolonged the lifespan and healthspan in model organism. The longevity effects of CITCO and TCPOBOP were attenuated in CAR homozygous nhr-8/daf-12 mutant C. elegans as well as CAR-/- mice. In C. elegans, CITCO activated both anti-stress and detoxification genes, and increased the resistance to environmental adversities. Additionally, the lifespan-extending and xenobiotic resistant effects of CITCO might be related to the regulation of age-related pathways. Furthermore, CITCO improved age-related neurodegeneration in C. elegans models. Taken together, the results suggest that the longevity effects of CAR agonists may be related to the enhancement of xenobiotic resistance of animals.

Molecular mechanisms in liver repair and regeneration: from physiology to therapeutics

Liver repair and regeneration are crucial physiological responses to hepatic injury and are orchestrated through intricate cellular and molecular networks. This review systematically delineates advancements in the field, emphasizing the essential roles played by diverse liver cell types. Their coordinated actions, supported by complex crosstalk within the liver microenvironment, are pivotal to enhancing regenerative outcomes. Recent molecular investigations have elucidated key signaling pathways involved in liver injury and regeneration. Viewed through the lens of metabolic reprogramming, these pathways highlight how shifts in glucose, lipid, and amino acid metabolism support the cellular functions essential for liver repair and regeneration. An analysis of regenerative variability across pathological states reveals how disease conditions influence these dynamics, guiding the development of novel therapeutic strategies and advanced techniques to enhance liver repair and regeneration. Bridging laboratory findings with practical applications, recent clinical trials highlight the potential of optimizing liver regeneration strategies. These trials offer valuable insights into the effectiveness of novel therapies and underscore significant progress in translational research. In conclusion, this review intricately links molecular insights to therapeutic frontiers, systematically charting the trajectory from fundamental physiological mechanisms to innovative clinical applications in liver repair and regeneration.

Fenofibrate induces liver enlargement in aging mice via activating the PPARα-YAP signaling pathway

Fenofibrate is a clinically prescribed drug for treating hypertriglyceridemia, which is also a classic peroxisome proliferator-activated receptor α (PPARα) agonist. We previously reported that fenofibrate induced liver enlargement in adult mice partially through activation of the yes-associated protein (YAP) signaling pathway. However, the effects of fenofibrate on liver enlargement and the YAP signaling pathway in aging mice remain unclear. In this study, D-galactose-induced aging mice, naturally aging mice, and senescence-accelerated mice P8 (SAMP8) were used to investigate the effects of aging on fenofibrate-induced liver enlargement and YAP signaling activation. The results showed that fenofibrate-induced liver enlargement in aging mice was consistent with that of adult mice. The effects of fenofibrate on hepatocyte enlargement around the central vein (CV) area and hepatocyte proliferation around the portal vein (PV) area were comparable between adult and aging mice. There was no significant difference in the upregulation of PPARα downstream proteins between the two groups following fenofibrate treatment. Fenofibrate treatment also increased the expression of proliferation-related proteins and activated the YAP signaling pathway to a similar degree in both groups. In summary, these results demonstrate that the fenofibrate-induced liver enlargement and activation of the YAP pathway are consistent between adult and aging mice, indicating that the effects of fenofibrate on promoting liver enlargement and its activation of the PPARα and YAP pathway were independent of aging. These findings offer a new perspective for the clinical use of fenofibrate in elderly patients and provide a new insight for the role of PPARα in liver enlargement.

Constitutive androstane receptor (CAR) functions as a tumor suppressor via regulating stemness in liver cancer

Constitutive androstane receptor (CAR) is a xenosensor that is almost exclusively expressed in the liver. Studies in rodents suggest an oncogenic role for CAR in liver cancer, but its role in human liver cancer is unclear. We aimed to investigate the functional roles of CAR in human liver cancer with a focus on the liver cancer stem cells. We used bioinformatics to increase our understanding of CAR in human liver cancer and associated stem cell markers. We studied the functional roles of CAR in human liver cancer with a focus on the liver cancer stem cell using siRNA, modulation of CAR activity, and tumorsphere formation assays. We have revealed significant associations between CAR and a wide variety of signalling pathways including stemness signalling. Further in vitro studies have shown that activation of CAR significantly reduces cancer cell stemness and represses proliferation, migration, invasion, and the tumorsphere-forming abilities of liver cancer cells (p < 0.05). Our data demonstrates the unequivocal tumor-suppressive role of CAR in liver cancer. While more detailed mechanistic studies are warranted, the efficacy of CAR xeno-activators in the treatment of advanced hepatocellular carcinoma (HCC) may potentially open a new avenue for liver cancer therapy.

YAP/TAZ as master regulators in liver regeneration and disease: insights into mechanisms and therapeutic targets

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key downstream effectors of the Hippo pathway that regulate organ size, tissue homeostasis, and cancer development. YAP/TAZ play crucial regulatory roles in organ growth, cell proliferation, cell renewal, and regeneration. Mechanistically, YAP/TAZ influence the occurrence and progression of liver regeneration (LR) through various signaling pathways, including Notch, Wnt/β-catenin, TGF-β/Smad. While the activation of YAP/TAZ can promote the regeneration of damaged liver tissue, their mechanisms of action may differ under various LR conditions. Furthermore, excessive activation of YAP/TAZ may also lead to severe liver damage, manifesting as alcoholic hepatitis, liver fibrosis, and even liver cancer. Here, we review the role and mechanisms of YAP/TAZ in LR and liver disease, highlighting the potential for advancements in clinical diagnosis and treatment targeting YAP/TAZ in these contexts.

Pregnane X receptor activation promotes hematopoiesis during liver regeneration by inducing proliferation of hematopoietic stem and progenitor cells in mice

Liver regeneration is a complex process that involves the recruitment of bone marrow (BM)-derived hematopoietic stem and progenitor cells (HSPCs). Pregnane X receptor (PXR), also known as NR1I2, is an important regulator for liver enlargement and regeneration. However, the role of PXR activation in hematopoiesis during liver regeneration remains unclear. This study investigates the effects of PXR activation on HSPCs and hematopoiesis during liver regeneration, as well as the underlying mechanisms involved. Using a 70 % partial hepatectomy (PHx) on C57BL/6 wild-type (WT) and Pxr-null mice, we observed a significant correlation between the changes in HSPCs numbers in BM and the process of liver regeneration. PXR activation significantly increased the population of Lineage- Sca-1+ c-Kit+ (LSK) cells in the BM, which are key HSPCs involved in hematopoiesis. Additionally, PXR activation increased serum levels of thrombopoietin (TPO) and erythropoietin (EPO), factors known to support HSPCs proliferation and hematopoiesis in the process of liver regeneration. PXR activation does not affect the hematopoietic function of normal mice. Furthermore, mice subjected to irradiation or busulfan-induced hematopoietic dysfunction exhibited impaired liver regeneration, which was alleviated by PXR activation. Importantly, in Pxr-null mice, the promotive effects of PXR activation on liver regeneration and increase of HSPCs were markedly diminished. Moreover, liver-specific Pxr silencing using AAV-Pxr shRNA attenuated the PXR activation-mediated liver regeneration and increase in BM LSK cells, confirming the critical role of hepatic PXR in hematopoiesis during liver regeneration. Collectively, these findings reveal that PXR activation promotes HSPCs proliferation and hematopoiesis during liver regeneration, providing new insights into the molecular mechanisms underlying the role of PXR in liver regeneration and hematopoiesis.

AHR regulates liver enlargement and regeneration through the YAP signaling pathway

The aryl hydrocarbon receptor (AHR) is a transcription factor activated by ligands that participates in many important physiological processes. Although AHR activation is associated with hepatomegaly, the underlying mechanism remains unclear. This study evaluated the effects of AHR activation on liver enlargement and regeneration in various transgenic mice and animal models. Activation of AHR by the non-toxic ligand YH439 significantly induced liver/body weight ratio in wild-type mice (1.37-fold) and AHRfl/fl.ALB-CreERT2 mice (1.54-fold). However, these effects not present in AHRΔHep mice. Additionally, the activation of AHR promotes hepatocyte enlargement (1.43-fold or 1.41-fold) around the central vein (CV) and increases number of Ki67+ cells (42.5-fold or 48.8-fold) around the portal vein (PV) in wild-type mice and AHRfl/fl.ALB-CreERT2 mice. In the 70 % partial hepatectomy (PHx) model, YH439 significantly induced hepatocyte enlargement (1.40-fold) and increased number of Ki67+ cells (3.97-fold) in AHRfl/fl.ALB-CreERT2 mice. However, these effects were not observed in AHRΔHep mice. Co-immunoprecipitation results suggested a potential protein-protein interaction between AHR and Yes-associated protein (YAP). Disruption of the association between YAP and transcription enhancer domain family member (TEAD) significantly inhibited AHR-induced liver enlargement and regeneration. Furthermore, AHR failed to induce liver enlargement and regeneration in YAPΔHep mice. Blocking the YAP signaling pathway effectively eliminated AHR-induced liver enlargement and regeneration. This study revealed the molecular mechanism of AHR regulation of liver size and regeneration through the activation of AHR-TEAD signaling pathway, thereby offering novel insights into the physiological role of AHR. These findings provide a theoretical foundation for the prevention and treatment of disorders associated with liver regeneration.

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.

Fenofibrate-promoted hepatomegaly and liver regeneration are PPARα-dependent and partially related to the YAP pathway

Fenofibrate, a peroxisome proliferator-activated receptor α (PPARα) agonist, is widely prescribed for hyperlipidemia management. Recent studies also showed that it has therapeutic potential in various liver diseases. However, its effects on hepatomegaly and liver regeneration and the involved mechanisms remain unclear. Here, the study showed that fenofibrate significantly promoted liver enlargement and regeneration post-partial hepatectomy in mice, which was dependent on hepatocyte-expressed PPARα. Yes-associated protein (YAP) is pivotal in manipulating liver growth and regeneration. We further identified that fenofibrate activated YAP signaling by suppressing its K48-linked ubiquitination, promoting its K63-linked ubiquitination, and enhancing the interaction and transcriptional activity of the YAP-TEAD complex. Pharmacological inhibition of YAP-TEAD interaction using verteporfin or suppression of YAP using AAV Yap shRNA in mice significantly attenuated fenofibrate-induced hepatomegaly. Other factors, such as MYC, KRT23, RAS, and RHOA, might also participate in fenofibrate-promoted hepatomegaly and liver regeneration. These studies demonstrate that fenofibrate-promoted liver enlargement and regeneration are PPARα-dependent and partially through activating the YAP signaling, with clinical implications of fenofibrate as a novel therapeutic agent for promoting liver regeneration.

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.

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.

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.

CAR requires Gadd45β to promote phenobarbital-induced mouse liver tumors in early stage

Phenobarbital (PB) is an archetypal substance used as a mouse hepatocellular carcinoma (HCC) promotor in established experimental protocols. Our previous results showed CAR is the essential factor for PB induced HCC promotion. Subsequent studies suggested Gadd45β, which is induced by PB through CAR activation, is collaborating with CAR to repress TNF-α induced cell death. Here, we used Gadd45β null mice (Gadd45β KO) treated with N-diethylnitrosamine (DEN) at 5 weeks of age and kept the mice with PB supplemented drinking water from 7 to 57 weeks old. Compared with wild type mice, Gadd45β KO mice developed no HCC in the PB treated group. Increases in liver weight were more prominent in wild type mice than KO mice. Microarray analysis of mRNA derived from mouse livers found multiple genes specifically up or down regulated in wild type mice but not null mice in DEN + PB groups. Further qPCR analysis confirmed two genes, Tgfbr2 and irisin/Fndc5, were up-regulated in PB treated wild type mice but no significant increase was observed in Gadd45β KO mice. We focused on these two genes because previous reports showed that hepatic Irisin/Fndc5 expression was significantly higher in HCC patients and that irisin binds to TGF-β receptor complex that includes TGFBR2 subunit. Our results revealed irisin peptide in cell culture media increased the growth rate of mouse hepatocyte-derived AML12 cells. Microarray analysis revealed that irisin-regulated genes in AML12 cells showed a significant association with the genes in the TGF-β pathway. Expression of irisin/Fndc5 and Tgfbr2 induced growth of human HCC cell line HepG2. Thus, Gadd45β plays an indispensable role in mouse HCC development regulating the irisin/Fndc5 and Tgfbr2 genes.

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.

The Function of Xenobiotic Receptors in Metabolic Diseases

Metabolic diseases are a series of metabolic disorders that include obesity, diabetes, insulin resistance, hypertension, and hyperlipidemia. The increased prevalence of metabolic diseases has resulted in higher mortality and mobility rates over the past decades, and this has led to extensive research focusing on the underlying mechanisms. Xenobiotic receptors (XRs) are a series of xenobiotic-sensing nuclear receptors that regulate their downstream target genes expression, thus defending the body from xenobiotic and endotoxin attacks. XR activation is associated with the development of a number of metabolic diseases such as obesity, nonalcoholic fatty liver disease, type 2 diabetes, and cardiovascular diseases, thus suggesting an important role for XRs in modulating metabolic diseases. However, the regulatory mechanism of XRs in the context of metabolic disorders under different nutrient conditions is complex and remains controversial. This review summarizes the effects of XRs on different metabolic components (cholesterol, lipids, glucose, and bile acids) in different tissues during metabolic diseases. As chronic inflammation plays a critical role in the initiation and progression of metabolic diseases, we also discuss the impact of XRs on inflammation to comprehensively recognize the role of XRs in metabolic diseases. This will provide new ideas for treating metabolic diseases by targeting XRs. SIGNIFICANCE STATEMENT: This review outlines the current understanding of xenobiotic receptors on nutrient metabolism and inflammation during metabolic diseases. This work also highlights the gaps in this field, which can be used to direct the future investigations on metabolic diseases treatment by targeting xenobiotic receptors.

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.

Constitutive Androstane Receptor Agonist, TCPOBOP: Maternal Exposure Impairs the Growth and Development of Female Offspring in Mice

Environmental chemicals, which are known to impact offspring health, have become a public concern. Constitutive activated receptor (CAR) is activated by various environmental chemicals and participates in xenobiotic metabolism. Here, we described the effects of maternal exposure to the CAR-specific ligand 1,4-bis[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP, TC) on offspring health outcomes. Maternal TC exposure exhibited a stronger inhibition of body weight in 3-week-old and 8-week-old first-generation (F1) offspring female mice compared to controls. Further, maternal TC exposure obtained a strong increase in hepatic drug-metabolizing enzyme expression in 3-week-old female mice that persisted into 8-week-old adulthood. Interestingly, we observed distorted intestinal morphological features in 8-week-old F1 female mice in the TC-exposed group. Moreover, maternal TC exposure triggered a loss of intestinal barrier integrity by reducing the expression of intestinal tight junction proteins. Accordingly, maternal exposure to TC down-regulated serum triglyceride levels as well as decreased the expression of intestinal lipid uptake and transport marker genes. Mechanistically, maternal TC exposure activated the intestinal inflammatory response and disrupted the antioxidant system in the offspring female mice, thereby impeding the intestinal absorption of nutrients and seriously threatening offspring health. Altogether, these findings highlight that the effects of maternal TC exposure on offspring toxicity could not be ignored.

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.

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.

Chronic Treatment With WY-14643 Induces Tumorigenesis and Triglyceride Accumulation in Mouse Livers

Peroxisome proliferator-activated receptor α (PPARα) is closely related to lipid metabolism and various liver diseases. Previous study has shown that chronic treatment with PPARα agonist WY-14643 can induce liver tumors in rodents, but the implications of this process on lipid metabolism in the liver remain unclear. Thus, this study aimed to explore the influences of chronic treatment with WY-14643 on the liver and hepatic lipid metabolism. Wild-type C57BL/6 mice were treated with WY-14643 (100 mg/kg/week, i.p.) or corn oil, and liver and serum samples were collected for testing after 42 weeks of WY-14643 treatment. The results showed that hepatomegaly, liver tumors with mild liver injury, and hepatocyte proliferation were induced in mice treated with WY-14643. The mRNA and protein expression levels of PPARα downstream targets acyl-CoA oxidase 1 and cytochrome P450 4A were significantly upregulated in the WY-14643-treated group. Lipidomic analysis revealed that chronic treatment with WY-14643 disturbed lipid homeostasis, especially triglycerides (TGs), which were significantly elevated after WY-14643 treatment. Moreover, TG homeostasis-related genes were significantly increased in the WY-14643-treated group. In conclusion, these findings demonstrated that hepatomegaly and liver tumors induced by chronic treatment with WY-14643 in mice are accompanied by hepatocyte proliferation and TG accumulation. SIGNIFICANCE STATEMENT: The present study clearly demonstrated that sustained peroxisome proliferator-activated receptor α (PPARα) activation by chronic treatment with WY-14643 induces hepatomegaly and liver tumors with triglyceride accumulation by regulating lipid homeostasis-related genes in mice. These findings may help to clarify the influences of sustained PPARα activation on liver lipid homeostasis and provide data for the clinically rational use of drugs that can activate PPARα.

ZO-2/Tjp2 suppresses Yap and Wwtr1/Taz-mediated hepatocyte to cholangiocyte transdifferentiation in the mouse liver

TJP2/ZO-2-inactivating mutations in humans cause progressive cholestatic liver disease. Liver-specific deletion of Tjp2 in the mouse (Tjp2 cKO mice) leads to mild progressive cholestasis without an overt degradation of the bile-blood barrier (BBB). These mice are more susceptible to cholic acid (CA) induced liver injury. Interestingly, while initially also more susceptible, Tjp2 cKO mice develop tolerance to a DDC-supplemented diet. The DDC diet induces an exacerbated ductular reaction in Tjp2 cKO mice, which arises from the transdifferentiation of hepatocytes to cholangiocytes. Consequently, this transdifferentiation is only observed if Tjp2 is inactivated in hepatocytes, but not if deleted in cholangiocytes. The DDC-diet-induced hepatocyte transdifferentiation in Tjp2 cKO mice requires Yap and Wwtr1/Taz, whose protein expression is upregulated in hepatocytes lacking Tjp2, but is independent of Notch2. Although inactivating Tjp2 is sufficient for the upregulation of Yap and Wwtr1/Taz protein, efficient transdifferentiation requires the DDC-diet insult. Thus, Tjp2 negatively regulates Yap/Taz-mediated transdifferentiation of hepatocytes to cholangiocytes in response to DDC-diet-induced liver injury. Furthermore, transdifferentiation is regulated at multiple levels and the type of injury inflicted on the Tjp2 deficient liver plays an important role in the resulting pathophysiology.

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.

Schisandrol B protects against cholestatic liver injury by inhibiting pyroptosis through pregnane X receptor

Previously, we demonstrated that Schisandrol B (SolB) protected against lithocholic acid (LCA)-induced cholestatic liver injury (CLI) through pregnane X receptor (PXR). Additionally, growing evidence has revealed that pyroptosis is involved in CLI. Whether the hepatoprotective effect of SolB driven by PXR activation is related to pyroptosis in CLI remains unclear. First, the hepatoprotective effect of SolB was confirmed, as evidenced by the decreased mortality, morphological and histopathological changes, and biochemical parameters. The upregulated serum lactic dehydrogenase (LDH) level, increased number of TUNEL-positive cells, and formation of hepatocyte membrane pores induced by LCA were significantly alleviated after SolB pretreatment, indicating that SolB attenuated LCA-induced hepatocyte damage. Further analysis revealed that both NOD-like receptor protein 3 (NLRP3) inflammasome-induced canonical pyroptosis and apoptosis protease activating factor-1 (Apaf-1) pyroptosome-induced noncanonical pyroptosis were significantly inhibited after SolB pretreatment, as illustrated by the decreased expression levels of NLRP3, ASC, caspase-1, and GSDMD and the levels of Apaf-1, caspase-11 p20, caspase-3 p20, and GSDME. Furthermore, the activation of the NF-κB and FoxO1 signaling pathways was inhibited after SolB pretreatment. In addition, the activation of PXR via SolB was proven by luciferase reporter gene assays and the upregulation of PXR targets. The results illustrated that SolB could significantly inhibit NLRP3 inflammasome-induced canonical pyroptosis through the PXR/NF-κB/NLRP3 axis and inhibit Apaf-1 pyroptosome-induced noncanonical pyroptosis through the PXR/FoxO1/Apaf-1 axis. Collectively, this study revealed that SolB protected against CLI by inhibiting pyroptosis through PXR, providing new insights for understanding the molecular mechanism of SolB as a promising anti-cholestatic agent.

Clinical Relevance of the Constitutive Androstane Receptor

Constitutive androstane receptor (CAR) (NR1I3), a xenobiotic receptor, has long been considered a master mediator of drug disposition and detoxification. Accumulating evidence indicates that CAR also participates in various physiologic and pathophysiological pathways regulating the homeostasis of glucose, lipid, and bile acids, and contributing to cell proliferation, tissue regeneration and repair, as well as cancer development. The expression and activity of CAR can be regulated by various factors, including small molecular modulators, CAR interaction with other transcription factors, and naturally occurring genetic variants. Given that the influence of CAR has extended beyond the realm of drug metabolism and disposition and has expanded into a potential modulator of human diseases, growing efforts have centered on understanding its clinical relevance and impact on human pathophysiology. This review highlights the current information available regarding the contribution of CAR to various metabolic disorders and cancers and ponders the possible challenges that might arise from pursuing CAR as a potential therapeutic target for these diseases. SIGNIFICANCE STATEMENT: The growing importance of the constitutive androstane receptor (CAR) in glucose and lipid metabolism as well as its potential implication in cell proliferation emphasizes a need to keenly understand the biological function and clinical impact of CAR. This minireview captures the clinical relevance of CAR by highlighting its role in metabolic disorders and cancer development.

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.

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.