A high-fat diet impairs liver regeneration in C57BL/6 mice through overexpression of the NF-kappaB inhibitor, IkappaBalpha

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

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

SLC13A2 promotes hepatocyte metabolic remodeling and liver regeneration by enhancing de novo cholesterol biosynthesis

Metabolic requirements of dividing hepatocytes are prerequisite for liver regeneration after injury. In contrast to transcriptional dynamics during liver repair, its metabolic dependencies remain poorly defined. Here, we screened metabolic genes differentially regulated during liver regeneration, and report that SLC13A2, a transporter for TCA cycle intermediates, is decreased in rapid response to partial hepatectomy in mice and recovered along restoration of liver mass and function. Liver-specific overexpression or depletion of SLC13A2 promoted or attenuated liver regeneration, respectively. SLC13A2 increased cleavage of SREBP2, and expression of cholesterol metabolism genes, including LDLR and HMGCR. Mechanistically, SLC13A2 promotes import of citrate into hepatocytes, serving as building block for ACLY-dependent acetyl-CoA formation and de novo synthesis of cholesterol. In line, the pre-administration of the HMGCR inhibitor lovastatin abolished SLC13A2-mediated liver regeneration. Similarly, ACLY inhibition suppressed SLC13A2-promoted cholesterol synthesis for hepatocellular proliferation and liver regeneration in vivo. In sum, this study demonstrates that citrate transported by SLC13A2 acts as an intermediate metabolite to restore the metabolic homeostasis during liver regeneration, suggesting SLC13A2 as a potential drug target after liver damage.

Role of Steatosis in Preventing Post-hepatectomy Liver Failure After Major Resection: Findings From an Animal Study

Background/Aim

Post-hepatectomy liver failure (PHLF) and hepatic steatosis are evident shortly after extensive partial hepatectomy (PH) in rodents. This study aimed to extrapolate the protein expression and biological pathways involved in recovering PHLF (rPHLF) and non-recovering PHLF (nrPHLF).

Methods

Rats were randomly assigned to 90% PH or sham surgery. rPHLF was distinguished from nrPHLF using a quantitative scoring system. The sham (n = 6), rPHLF (n = 8), and nrPHLF (n = 13) groups were compared 24 h post-PH. Proteomics was used to assess protein variations and to investigate differentially regulated biological pathways. Stereological methods were used to quantify hepatic lipid content. The plasma triglyceride levels were measured.

Results

rPHLF demonstrated substantial downregulation of proteins involved in lipid metabolism compared to nrPHLF (P < 0.001). Several proteins associated with lipogenesis, beta-oxidation, lipolysis, membrane trafficking, and inhibition of cell proliferation were markedly downregulated in rPHLF.The hepatic lipid proportion was significantly higher for rPHLF (61% of hepatocyte volume, 95% confidence interval [CI]: 48%-82%) than for nrPHLF (32% of hepatocyte volume, 95% CI: 22%-39%). The median lipid volume per hepatocyte in rPHLF was 2815 μm3 (95% CI: 2208-3774 μm3) and 1759 μm3 in nrPHLF (95% CI: 1188-2134 μm3). Lipid droplets were not detected in the sham-operated rats. No significant differences in plasma triglyceride levels were found between the groups (P > 0.08).

Conclusion

The degree of hepatic steatosis is a promising prognostic indicator for early liver regeneration and nrPHLF onset immediately following extensive PH. Intrahepatic lipid accumulation appears to be linked to the coordinated downregulation of proteins integral to lipid metabolism and cellular transport.

Exploring the dynamics of postoperative steatosis in the regenerating liver: An animal study

Introduction

The rat model of 70 % partial hepatectomy (PH) is commonly used to investigate liver regeneration processes. The aim of this study was to explore the dynamics of hepatic lipid accumulation and its correlation with the proliferation response during the entire regeneration phase after 70 % PH in rats.

Methods

Sixty-four rats underwent 70 % PH and were randomly divided into eight groups for evaluation on post-operative day (POD) 1 to 8. Hepatocyte volume, relative lipid content, and lipid volume per hepatocyte were assessed by stereological analysis.Results: Lipid volume per hepatocyte reached its peak on POD 1 and POD 2, with mean values of 2895 μm3 (95 % CI: 1756-4034 μm3) and 3090 μm3 (95 % CI: 2277-3903 μm3), respectively. A marked decline was observed by POD 4, with a mean of 1323 μm3 (95 % CI: 985-1741 μm3), which continued through POD 5, reaching 619 μm3 (95 % CI: 136-1102 μm3). From POD 5 onwards, lipid volume remained consistently low, with no significant differences detected between POD 5 and POD 8.

Conclusion

Lipid accumulation and proliferation peak and decline concurrently, suggesting a strong correlation.

Adipose tissue deficiency impairs transient lipid accumulation and delays liver regeneration following partial hepatectomy in male Seipin knockout mice

BACKGROUND

Liver diseases pose significant health challenges, underscoring the importance of understanding liver regeneration mechanisms. Systemic adipose tissue is thought to be a primary source of lipids and energy during this process; however, empirical data on the effects of adipose tissue deficiency are limited. This study investigates the role of adipose tissue in liver regeneration, focusing on transient regeneration-associated steatosis (TRAS) and hepatocyte proliferation using a Seipin knockout mouse model that mimics severe human lipodystrophy. Additionally, the study explores therapeutic strategies through adipose tissue transplantation.

METHODS

Male Seipin knockout (Seipin-/-) and wild-type (WT) mice underwent 2/3 partial hepatectomy (PHx). Liver and plasma samples were collected at various time points post-surgery. Histological assessments, lipid accumulation analyses and measurements of hepatocyte proliferation markers were conducted. Additionally, normal adipose tissue was transplanted into Seipin-/- mice to evaluate the restoration of liver regeneration.

RESULTS

Seipin-/- mice exhibited significantly reduced liver regeneration rates and impaired TRAS, as evidenced by histological and lipid measurements. While WT mice demonstrated extensive hepatocyte proliferation at 48 and 72 h post-PHx, characterised by increased mitotic cells, elevated proliferating cell nuclear antigen and Ki67 expression, Seipin-/- mice showed delayed hepatocyte proliferation. Notably, adipose tissue transplantation into Seipin-/- mice restored TRAS and improved liver regeneration and hepatocyte proliferation. Conversely, liver-specific overexpression of Seipin in Seipin-/- mice did not affect TRAS or liver regeneration, indicating that the observed effects are primarily due to adipose tissue deficiency rather than hepatic Seipin itself.

CONCLUSIONS

Systemic adipose tissue is essential for TRAS and effective liver regeneration following PHx. Its deficiency impairs these processes, while adipose tissue transplantation can restore normal liver function. These findings underscore the critical role of adipose tissue in liver recovery and suggest potential therapeutic strategies for liver diseases associated with lipodystrophies.

KEY POINTS

Seipin-/- mice, which lack adipose tissue, exhibit significantly impaired TRAS and delayed liver regeneration following partial hepatectomy. Transplantation of normal adipose tissue into Seipin-/- mice restores TRAS and enhances liver regeneration, highlighting the essential role of adipose tissue in these processes. Liver-specific overexpression of Seipin has no effect on TRAS and liver regeneration in Seipin-/- mice.

NLRP3 inflammasome constrains liver regeneration through impairing MerTK-mediated macrophage efferocytosis

The NOD-like receptor protein 3 (NLRP3) inflammasome plays a crucial role in human acute and chronic liver diseases. However, the role and cell-specific contribution of NLRP3 in liver regeneration remains unclear. Here, we found that NLRP3 was highly activated during the early stage of liver regeneration via 70% partial hepatectomy (PHx) mice model and clinical data. Global NLRP3 depletion or pharmacologically blocking NLRP3 significantly enhanced liver regeneration, while NLRP3 overexpression impaired it after PHx. Furthermore, mice with myeloid-specific knockout of Nlrp3 (Nlrp3Δmye), rather than hepatocyte-specific knockout (Nlrp3Δhep), showed improved liver regeneration compared to control (Nlrp3fl/fl). Mechanistically, deficiency of Nlrp3 promoted myeloid-epithelial-reproductive tyrosine kinase (MerTK)-mediated efferocytosis, thereby inducing macrophages toward a pro-reparative Ly6Clo phenotype. Notably, NLRP3 inhibition by MCC950 effectively reversed the impairment of liver regeneration after PHx in mice fed a high-fat diet. Our findings provide a potential therapeutic strategy for the prevention and treatment of post-hepatectomy liver failure.

Microbiome and metabolomics reveal the effect of gut microbiota on liver regeneration of fatty liver disease

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) is associated with impaired regenerative capacity and poor postoperative prognosis following hepatectomy. Previous research has highlighted the importance of the gut-liver axis in the physiological and pathological processes of the liver. However, the contribution of gut bacteria to the regeneration of livers with MAFLD and its metabolic regulatory mechanisms remain elusive.

METHODS

Partial hepatectomy (PHx) was performed on C57Bl/6J mice fed with high-fat diet (HFD) for 12 weeks. Pathological examination, immunohistochemistry, and qRT-PCR analysis were performed to assess the severity of steatosis and proliferative potential. The gut microbiome was examined by 16S rRNA gene sequencing and shotgun metagenomics, whereas liver metabolomics was analysed via untargeted and targeted metabolomics using liquid chromatography-tandem mass spectrometry (LC-MS).

FINDINGS

HFD-induced hepatic steatosis in mice led to impaired liver regeneration following PHx. The gut microbiota and liver metabolites were altered along with the liver regeneration process. Longitudinal time-series analysis revealed dynamic alterations in these data, whereas correlation analysis screened out bacterial candidates that potentially influence liver regeneration in MAFLD by modulating metabolic pathways. Among these bacteria, the dominant bacterium Akkermansia was selected for subsequent investigation. MAFLD mice gavaged with Akkermansia muciniphila (A. muciniphila) exhibited reduced liver lipid accumulation and accelerated liver regeneration, possibly through the regulation of the tricarboxylic acid (TCA) cycle.

INTERPRETATION

These data demonstrated the interplay between the gut microbiome, liver metabolomics, and liver regeneration in mice with MAFLD. A. muciniphila has the potential to serve as a clinical intervention agent to accelerate postoperative recovery in MAFLD.

FUNDING

This work was supported by the Research Project of Jinan Microecological Biomedicine Shandong Laboratory [JNL-2022008B]; the Zhejiang Provincial Natural Science Foundation of China [LZ21H180001]; the Fundamental Research Funds for the Central Universities [No. 2022ZFJH003].

Astragaloside IV and cycloastragenol promote liver regeneration through regulation of hepatic oxidative homeostasis and glucose/lipid metabolism

BACKGROUND

The regenerative capacity of the liver is pivotal for mitigating various forms of liver injury and requires the rapid proliferation of hepatocytes. Aquaporin-9 (AQP9) provides vital support for hepatocyte proliferation by preserving hydrogen peroxide (H2O2) oxidative balance and glucose/lipid metabolism equilibrium within hepatocytes. Our previous study demonstrated that Radix Astragali (RA) decoction promotes liver regeneration by upregulating hepatic expression of AQP9, possibly via two major active constituents: astragaloside IV (AS-IV) and cycloastragenol (CAG).

PURPOSE

To verify that upregulated AQP9 expression in hepatocytes maintains liver oxidative balance and glucose/lipid metabolism homeostasis, and is the main pharmacological mechanism by which AS-IV and CAG promote liver regeneration.

STUDY DESIGN/METHODS

Effects of AS-IV and CAG on liver regeneration were scrutinized using a mouse model of 70 % partial hepatectomy (PHx). AQP9-targeted liver regeneration mediated by AS-IV and CAG was verified using AQP9 gene knockout mice (AQP9-/-). The AQP9 protein expression pattern in hepatocytes was determined using tdTomato-tagged AQP9 transgenic mice (AQP9-RFP). Potential mechanisms of AS-IV and CAG on liver regeneration were studied using real-time quantitative PCR, immunoblotting, staining with hematoxylin and eosin, oil red O, and periodic acid-Schiff, and immunofluorescence, immunohistochemistry, HyPerRed fluorescence, and biochemical analyses.

RESULTS

AS-IV and CAG promoted substantial liver regeneration and increased hepatic AQP9 expression in wild-type mice (AQP9+/+) following 70 % PHx, but had no discernible benefits in AQP9-/- mice. Both saponin compounds also helped maintain oxidative homeostasis by reducing levels of oxidative stress markers (reactive oxygen species [ROS], H2O2, and malondialdehyde) and elevating levels of ROS scavengers (glutathione and superoxide dismutase) in AQP9+/+ mice post-70 % PHx. This further activated the PI3K-AKT and insulin signaling pathways, thereby fostering liver regeneration. Furthermore, AS-IV and CAG both promoted hepatocyte glycerol uptake, increased gluconeogenesis, facilitated lipolysis, reduced glycolysis, and inhibited glycogen deposition, thus ensuring the energy supply required for liver regeneration.

CONCLUSION

This research is the first to demonstrate AS-IV and CAG as major active ingredients of RA that promote liver regeneration by upregulating hepatocyte AQP9 expression, improving hepatocyte glucose/lipid metabolism, and reducing oxidative stress damage, constituting a crucial pharmacological mechanism underlying the liver-protective effects of RA. The augmentation of hepatocyte AQP9 expression underscores an important aspect of the Qi-tonifying effect of RA. This study establishes AQP9 as an effective target for regulation of liver regeneration and provides a universal strategy for clinical drug intervention aimed at enhancing liver regeneration.

Acute-on-chronic liver failure in metabolic dysfunction-associated fatty liver disease patients: a disease multiplier

Acute-on-chronic liver failure (ACLF) is a syndrome of liver failure due to an acute hepatic insult leading to liver failure with or without extra-hepatic organ failure in a patient of chronic liver disease (CLD) with or without cirrhosis presenting for the first time. The definition is still with controversy; hence, homogeneity and clarity of the case is an unmet need. There is a paradigm shift noted as far as the etiology of CLD is concerned with rise in metabolic dysfunction-associated fatty liver disease (MAFLD) and ethanol as the dominant cause even in developing countries. MAFLD is the change in nomenclature from NAFLD to justify the metabolic derangement in these group of patients. The shift from an exclusion-based criteria to one that has evolved to a diagnosis that requires positive criteria has profound significance. Clearly there is a difference in terms of its prevalence, disease progression, and liver-related events, as well as management of metabolic risk factors and MAFLD itself which requires further understanding. In tandem with the global rise in MAFLD, the incidence of MAFLD-ACLF is increasing. Excessive alcohol consumption causes metabolic and toxic injury to the liver resulting in nearly similar pathway of fatty liver, hepatitis, and cirrhosis. The interaction of MAFLD as an additional underlying chronic liver injury in ACLF patients is complex due to the presence of metabolic risk factors that are unique to MAFLD. There is lack of clarity on how MAFLD affects the clinical course of ACLF due to scarcity of this specific data. This narrative review aims to understand the unique effects, consequences, and management of MAFLD as the chronic liver injury component in ACLF.

Liver phospholipid fatty acid composition in response to chronic high-fat diets

Liver phospholipid fatty acid composition depends on the dietary lipid intake and the efficiency of hepatic enzymatic activity. Our study aimed to simultaneously investigate the liver phospholipid fatty acid composition in response to chronic linseed, palm, or sunflower oil diets. We used adult female C57/BL6 mice and randomly divided them into control and three groups treated with 25 % dietary oils. Prior to treatment, we analyzed the fatty acid profiles in dietary oils and hepatocytes and, after 100 days, the fatty acid composition in the liver using gas-liquid chromatography. Linseed oil treatment elevated alpha-linolenic, eicosapentaenoic, and docosapentaenoic acids and reduced arachidonic and docosatetraenoic acids, consequently lowering the n-6/n-3 ratio. Palm oil treatment increased linoleic acid and decreased docosahexaenoic acid, contributing to an elevated n-6/n-3 ratio. Sunflower oil treatment elevated total monounsaturated fatty acids by increasing palmitoleic, oleic, and vaccenic acids. The estimated activity of Δ9 desaturase was significantly elevated in the sunflower oil group, while Δ5 desaturase was the highest, and Δ6 desaturase was the lowest after the linseed oil diet. Our findings demonstrate that chronic consumption of linseed, palm, or sunflower oil alters the distribution of liver phospholipid fatty acids differently. Sunflower oil diet elevated total monounsaturated fatty acids, proposing potential benefits for liver tissue health. Considering these outcomes, a substantial recommendation emerges to elevate linseed oil intake, recognized as the principal ALA source, thereby aiding in reducing the n-6/n-3 ratio. Moreover, modifying dietary habits to incorporate specific vegetable oils in daily consumption could substantially enhance overall health.

Acute liver steatosis signals the chromatin for regeneration via MIER1

During liver regeneration, especially after a hepatectomy, hepatocytes experience significant lipid accumulation. These transiently accumulated lipids are generally believed to provide substrates for energy supply or membrane biomaterials for newly generated hepatocytes. Remarkably, a recent study found that acute lipid accumulation during regeneration can act as a signal for chromatin remodeling to regulate regeneration. Chen, Y.H., et al. identified MIER1 (mesoderm induction early response protein 1) as a crucial inhibitor of liver regeneration through in vivo CRISPR screening. MIER1 binds to and restrains cell cycle genes' expression. During liver regeneration, acute lipid accumulation suppresses MIER1 translation via the EIF2S pathway, resulting in transient down-regulation of MIER1 protein, which promotes cell cycle gene expression and liver regeneration. Interestingly, the researchers also found that the dynamic regulation of MIER1 was impaired in fatty and aging livers with chronic steatosis, while of knockout of MIER1 in these animals improved their regenerative capacity. In conclusion, this study provides valuable insights into the complex mechanisms underlying liver regeneration and highlights the potential therapeutic applications of targeting MIER1 for improving liver regeneration in disease states associated with impaired lipid homeostasis.

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

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

Evidence for Adverse Effects on Liver Development and Regeneration in Zebrafish by Decabromodiphenyl Ethane

Decabromodiphenyl ethane (DBDPE), a ubiquitous emerging pollutant, could be enriched in the liver of organisms, but its effects and mechanisms on liver development and regeneration remain largely unknown. In the present study, we first investigated the adverse effects on liver development and found decreased area and intensity of fluorescence in transgenic zebrafish larvae exposed to DBDPE; further results in wild-type zebrafish larvae revealed a possible mechanism involving disturbed MAPK/Fox O signaling pathways and cell cycle arrest as indicated by decreased transcription of growth arrest and DNA-damage-inducible beta a (gadd45ba). Subsequently, an obstructed recovery process of liver tissue after partial hepatectomy was characterized by the changing profiles of ventral lobe-to-intestine ratio in transgenic female adults upon DBDPE exposure; further results confirmed the adverse effects on liver regeneration by the alterations of the hepatic somatic index and proliferating cell nuclear antigen expression in wild-type female adults and also pointed out a potential role of a disturbed signaling pathway involving cell cycles and glycerolipid metabolism. Our results not only provided novel evidence for the hepatotoxicity and underlying mechanism of DBDPE but also were indicative of subsequent ecological and health risk assessment.

Network-level analysis of ageing and its relationship with diseases and tissue regeneration in the mouse liver

The liver plays a vital role in maintaining whole-body metabolic homeostasis, compound detoxification and has the unique ability to regenerate itself post-injury. Ageing leads to functional impairment of the liver and predisposes the liver to non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). Mapping the molecular changes of the liver with ageing may help to understand the crosstalk of ageing with different liver diseases. A systems-level analysis of the ageing-induced liver changes and its crosstalk with liver-associated conditions is lacking. In the present study, we performed network-level analyses of the ageing liver using mouse transcriptomic data and a protein-protein interaction (PPI) network. A sample-wise analysis using network entropy measure was performed, which showed an increasing trend with ageing and helped to identify ageing genes based on local entropy changes. To gain further insights, we also integrated the differentially expressed genes (DEGs) between young and different age groups with the PPI network and identified core modules and nodes associated with ageing. Finally, we computed the network proximity of the ageing network with different networks of liver diseases and regeneration to quantify the effect of ageing. Our analysis revealed the complex interplay of immune, cancer signalling, and metabolic genes in the ageing liver. We found significant network proximities between ageing and NAFLD, HCC, liver damage conditions, and the early phase of liver regeneration with common nodes including NLRP12, TRP53, GSK3B, CTNNB1, MAT1 and FASN. Overall, our study maps the network-level changes of ageing and their interconnections with the physiology and pathology of the liver.

Acute liver steatosis translationally controls the epigenetic regulator MIER1 to promote liver regeneration in a study with male mice

The early phase lipid accumulation is essential for liver regeneration. However, whether this acute lipid accumulation can serve as signals to direct liver regeneration rather than simply providing building blocks for cell proliferation remains unclear. Through in vivo CRISPR screening, we identify MIER1 (mesoderm induction early response 1) as a key epigenetic regulator that bridges the acute lipid accumulation and cell cycle gene expression during liver regeneration in male animals. Physiologically, liver acute lipid accumulation induces the phosphorylation of EIF2S1(eukaryotic translation initiation factor 2), which consequently attenuated Mier1 translation. MIER1 downregulation in turn promotes cell cycle gene expression and regeneration through chromatin remodeling. Importantly, the lipids-EIF2S1-MIER1 pathway is impaired in animals with chronic liver steatosis; whereas MIER1 depletion significantly improves regeneration in these animals. Taken together, our studies identify an epigenetic mechanism by which the early phase lipid redistribution from adipose tissue to liver during regeneration impacts hepatocyte proliferation, and suggest a potential strategy to boost liver regeneration.

Key hepatoprotective roles of mitochondria in liver regeneration

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

Unsaturated or saturated dietary fat-mediated steatosis impairs hepatic regeneration following partial hepatectomy in mice

BACKGROUND

Partial hepatectomy is a preferred treatment option for many patients with hepatocellular carcinoma however, pre-existing pathological abnormalities originating from hepatic steatosis can alter the decision to perform surgery or postoperative outcomes as a consequence of the impact steatosis has on liver regeneration.

AIM

The aim of this study was to investigate the role of a saturated or unsaturated high fat diet-mediated steatosis on liver regeneration following partial hepatectomy.

METHODS

Mice were fed a low-fat control diet (CD, 13% fat), lard-based unsaturated (LD, 60% fat) or milk-based saturated high fat diet (MD, 60% fat) for 16 weeks at which time partial hepatectomy (approx. 70% resection) was performed. At days-2 and 7 post hepatectomy, one hour prior to euthanization, mice were injected with 5-bromo-2'-deoxyuridine in order to monitor hepatic regeneration. Serum was collected and assessed for levels of ALT and AST. Resected and regenerated liver tissue were examined for inflammation-indicative markers employing RT-PCR, Western blots, and histological methods.

RESULTS

Mice fed LD or MD exhibited higher NAFLD scores, increased expression of inflammatory cytokines, neutrophil infiltration, macrophage accumulation, increased apoptosis, and elevated levels of serum ALT and AST activities, a decrease in the number of BrdU-incorporated-hepatocytes in the regenerated livers compared to the mice fed CD. Mice fed MD showed significantly lower percent of BrdU-incorporated hepatocytes and a higher trend of inflammation compared to the mice fed LD.

CONCLUSION

A diet rich in saturated or unsaturated fat results in NASH with decreased hepatic regeneration however unsaturated fat diet cause lower inflammation and higher regeneration than the saturated fat diet following partial hepatectomy in mice.

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.

The Neglected Role of Bile Duct Epithelial Cells in NASH

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease worldwide, and affects 25% of the population in Western countries. NAFLD is the hepatic manifestation of the metabolic syndrome, linked to insulin resistance, which is the common pathogenetic mechanism. In approximately 40% of NAFLD patients, steatosis is associated with necro-inflammation and fibrosis, resulting in nonalcoholic steatohepatitis (NASH), a severe condition that may progress to cirrhosis and liver cancer. Although the hepatocyte represents the main target of the disease, involvement of the bile ducts occurs in a subset of patients with NASH, and is characterized by ductular reaction and activation of the progenitor cell compartment, which incites portal fibrosis and disease progression. We aim to dissect the multiple biological effects that adipokines and metabolic alterations exert on cholangiocytes to derive novel information on the mechanisms driven by insulin resistance, which promote fibro-inflammation and carcinogenesis in NASH.

Effect of conditioned medium from adipose derived mesenchymal stem cells on endoplasmic reticulum stress and lipid metabolism after hepatic ischemia reperfusion injury and hepatectomy in swine

AIMS

Hepatic ischemia reperfusion injury (HIRI) is associated with liver failure after liver transplantation and hepatectomy. Thus, this study aims to explore the effect of conditioned medium from adipose derived stem cells (ADSC-CM) on endoplasmic reticulum stress (ERS) and lipid metabolism after HIRI combined with hepatectomy in miniature pigs.

MAIN METHODS

A model of HIRI combined with hepatectomy in miniature pigs was established. The expression of ERS-related proteins and lipid metabolism related genes, as well as triglyceride (TG), total cholesterol (TC), high density lipoprotein (HDL), very low density lipoprotein (VLDL) and acetyl-CoA carboxylase 1 (ACC1) level were measured in liver tissues.

KEY FINDINGS

Both ADSCs and ADSC-CM could improve the damage in the ultrastructure of hepatocytes. ADSC-CM significantly decreased the protein expression of GRP78, ATF6, XBP1, p-eIF2α, ATF4, p-JNK and CHOP. Oil red O staining revealed that the degree of hepatocyte steatosis was also significantly reduced after treatment with ADSC-CM. In addition, ADSC-CM remarkably decreased TG, TC, HDL and ACC1 level in liver tissues, while enhanced VLDL content. Finally, SREBP1, SCAP, FASN, ACC1, HMGCR and HMGCS1 mRNA expression was also markedly downregulated in liver tissues.

SIGNIFICANCE

Injection of ADSC-CM into the hepatic parenchymal could represent a novel cell-free therapeutic approach to improve HIRI combined with hepatectomy injury. The inhibition of ERS and the improvement of lipid metabolism in the hepatocytes might be a potential mechanism used by ADSC-CM to prevent liver injury from HIRI combined with hepatectomy.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

A Novel Humanized Model of NASH and Its Treatment With META4, A Potent Agonist of MET

BACKGROUND & AIMS

Nonalcoholic fatty liver disease is a frequent cause of hepatic dysfunction and is now a global epidemic. This ailment can progress to an advanced form called nonalcoholic steatohepatitis (NASH) and end-stage liver disease. Currently, the molecular basis of NASH pathogenesis is poorly understood, and no effective therapies exist to treat NASH. These shortcomings are due to the paucity of experimental NASH models directly relevant to humans.

METHODS

We used chimeric mice with humanized liver to investigate nonalcoholic fatty liver disease in a relevant model. We carried out histologic, biochemical, and molecular approaches including RNA-Seq. For comparison, we used side-by-side human NASH samples.

RESULTS

Herein, we describe a "humanized" model of NASH using transplantation of human hepatocytes into fumarylacetoacetate hydrolase-deficient mice. Once fed a high-fat diet, these mice develop NAFLD faithfully, recapitulating human NASH at the histologic, cellular, biochemical, and molecular levels. Our RNA-Seq analyses uncovered that a variety of important signaling pathways that govern liver homeostasis are profoundly deregulated in both humanized and human NASH livers. Notably, we made the novel discovery that hepatocyte growth factor (HGF) function is compromised in human and humanized NASH at several levels including a significant increase in the expression of the HGF antagonists known as NK1/NK2 and marked decrease in HGF activator. Based on these observations, we generated a potent, human-specific, and stable agonist of human MET that we have named META4 (Metaphor) and used it in the humanized NASH model to restore HGF function.

CONCLUSIONS

Our studies revealed that the humanized NASH model recapitulates human NASH and uncovered that HGF-MET function is impaired in this disease. We show that restoring HGF-MET function by META4 therapy ameliorates NASH and reinstates normal liver function in the humanized NASH model. Our results show that the HGF-MET signaling pathway is a dominant regulator of hepatic homeostasis.

Role of vasodilation in liver regeneration and health

Recently, we have shown that an enhanced blood flow through the liver triggers hepatocyte proliferation and thereby liver growth. In this review, we first explain the literature on hepatic blood flow and its changes after partial hepatectomy (PHx), before we present the different steps of liver regeneration that take place right after the initial hemodynamic changes induced by PHx. Those parts of the molecular mechanisms governing liver regeneration, which are directly associated with the hepatic vascular system, are subsequently reviewed. These include β1 integrin-dependent mechanotransduction in liver sinusoidal endothelial cells (LSECs), triggering mechanically-induced activation of the vascular endothelial growth factor receptor-3 (VEGFR3) and matrix metalloproteinase-9 (MMP9) as well as release of growth-promoting angiocrine signals. Finally, we speculate how advanced age and obesity negatively affect the hepatic vasculature and thus liver regeneration and health, and we conclude our review with some recent technical progress in the clinic that employs liver perfusion. In sum, the mechano-elastic properties and alterations of the hepatic vasculature are key to better understand and influence liver health, regeneration, and disease.

Lack of Multidrug Resistance-associated Protein 4 Prolongs Partial Hepatectomy-induced Hepatic Steatosis

Multidrug resistance-associated protein 4 (Mrp4) is an efflux transporter involved in the active transport of several endogenous and exogenous chemicals. Previously, we have shown that hepatic Mrp4 expression increases following acetaminophen overdose. In mice, these increases in Mrp4 expression are observed specifically in hepatocytes undergoing active proliferation. From this, we hypothesized that Mrp4 plays a key role in hepatocyte proliferation and that lack of Mrp4 impedes liver regeneration following liver injury and/or tissue loss. To evaluate the role of Mrp4 in these processes, we employed two-third partial hepatectomy (PH) as an experimental liver regeneration model. In this study, we performed PH-surgery on male wildtype (C57BL/6J) and Mrp4 knockout mice. Plasma and liver tissues were collected at 24, 48, and 72 h postsurgery and evaluated for liver injury and liver regeneration endpoints, and for PH-induced hepatic lipid accumulation. Our results show that lack of Mrp4 did not alter hepatocyte proliferation and liver injury following PH as evaluated by Ki-67 antigen staining and plasma alanine aminotransferase levels. To our surprise, Mrp4 knockout mice exhibited increased hepatic lipid content, in particular, di- and triglyceride levels. Gene expression analysis showed that lack of Mrp4 upregulated hepatic lipin1 and diacylglycerol O-acyltransferase 1 and 2 gene expression, which are involved in the synthesis of di- and triglycerides. Our observations indicate that lack of Mrp4 prolonged PH-induced hepatic steatosis in mice and suggest that Mrp4 may be a novel genetic factor in the development of hepatic steatosis.

High-Fat Diet Alleviates Neuroinflammation and Metabolic Disorders of APP/PS1 Mice and the Intervention With Chinese Medicine

Alzheimer's disease (AD) is a progressive neurodegenerative disease caused by the complex interaction of multiple mechanisms. Recent studies examining the effect of high-fat diet (HFD) on the AD phenotype have demonstrated a significant influence on both inflammation and cognition. However, different studies on the effect of high-fat diet on AD pathology have reported conflicting conclusions. To explore the involvement of HFD in AD, we investigated phenotypic and metabolic changes in an AD mouse model in response to HFD. The results indicated there was no significant effect on Aβ levels or contextual memory due to HFD treatment. Of note, HFD did moderate neuroinflammation, despite spurring inflammation and increasing cholesterol levels in the periphery. In addition, diet affected gut microbiota symbiosis, altering the production of bacterial metabolites. HFD created a favorable microenvironment for bile acid alteration and arachidonic acid metabolism in APP/PS1 mice, which may be related to the observed improvement in LXR/PPAR expression. Our previous research demonstrated that Huanglian Jiedu decoction (HLJDD) significantly ameliorated impaired learning and memory. Furthermore, HLJDD may globally suppress inflammation and lipid accumulation to relieve cognitive impairment after HFD intervention. It was difficult to define the effect of HFD on AD progression because the results were influenced by confounding factors and biases. Although there was still obvious damage in AD mice treated with HFD, there was no deterioration and there was even a slight remission of neuroinflammation. Moreover, HLJDD represents a potential AD drug based on its anti-inflammatory and lipid-lowering effects.

HCV eradication with IFN-based therapy does not completely restore gene expression in PBMCs from HIV/HCV-coinfected patients

Objective

To evaluate the impact of hepatitis C virus (HCV) elimination via interferon (IFN)-based therapy on gene expression profiles related to the immune system in HIV/HCV-coinfected patients.

Methods

We conducted a prospective study in 28 HIV/HCV-coinfected patients receiving IFN-based therapy at baseline (HIV/HCV-b) and week 24 after sustained virological response (HIV/HCV-f). Twenty-seven HIV-monoinfected patients (HIV-mono) were included as a control. RNA-seq analysis was performed on peripheral blood mononuclear cells (PBMCs). Genes with a fold-change (FC) ≥ 1.5 (in either direction) and false discovery rate (FDR) ≤ 0.05 were identified as significantly differentially expressed (SDE).

Results

HIV/HCV-b showed six SDE genes compared to HIV-mono group, but no significantly enriched pathways were observed. For HIV/HCV-f vs. HIV/HCV-b, we found 58 SDE genes, 34 upregulated and 24 downregulated in the HIV/HCV-f group. Of these, the most overexpressed were CXCL2, PDCD6IP, ATP5B, IGSF9, RAB26, and CSRNP1, and the most downregulated were IFI44 and IFI44L. These 58 SDE genes revealed two significantly enriched pathways (FDR < 0.05), one linked to Epstein-Barr virus infection and another related to p53 signaling. For HIV/HCV-f vs. HIV-mono group, we found 44 SDE genes that revealed 31 enriched pathways (FDR < 0.05) related to inflammation, cancer/cell cycle alteration, viral and bacterial infection, and comorbidities associated with HIV/HCV-coinfection. Five genes were overrepresented in most pathways (JUN, NFKBIA, PIK3R2, CDC42, and STAT3).

Conclusion

HIV/HCV-coinfected patients who eradicated hepatitis C with IFN-based therapy showed profound gene expression changes after achieving sustained virological response. The altered pathways were related to inflammation and liver-related complications, such as non-alcoholic fatty liver disease and hepatocellular carcinoma, underscoring the need for active surveillance for these patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00718-6.

Liver Regeneration after Hepatectomy and Partial Liver Transplantation

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

Cell cycle regulation in NAFLD: when imbalanced metabolism limits cell division

Cell division is essential for organismal growth and tissue homeostasis. It is exceptionally significant in tissues chronically exposed to intrinsic and external damage, like the liver. After decades of studying the regulation of cell cycle by extracellular signals, there are still gaps in our knowledge on how these two interact with metabolic pathways in vivo. Studying the cross-talk of these pathways has direct clinical implications as defects in cell division, signaling pathways, and metabolic homeostasis are frequently observed in liver diseases. In this review, we will focus on recent reports which describe various functions of cell cycle regulators in hepatic homeostasis. We will describe the interplay between the cell cycle and metabolism during liver regeneration after acute and chronic damage. We will focus our attention on non-alcoholic fatty liver disease, especially non-alcoholic steatohepatitis. The global incidence of non-alcoholic fatty liver disease is increasing exponentially. Therefore, understanding the interplay between cell cycle regulators and metabolism may lead to the discovery of novel therapeutic targets amenable to intervention.

PDK4-Deficiency Reprograms Intrahepatic Glucose and Lipid Metabolism to Facilitate Liver Regeneration in Mice

Liver regeneration requires intrahepatic and extrahepatic metabolic reprogramming to meet the high hepatic bioenergy demand for liver cell repopulation. This study aims to elucidate how pyruvate dehydrogenase kinase 4 (PDK4), a critical regulator of glucose and lipid metabolism, coordinates metabolic regulation with efficient liver growth. We found that hepatic Pdk4 expression was elevated after two-thirds partial hepatectomy (PHx). In Pdk4 ^-/- PHx mice, the liver/body weight ratio was more rapidly restored, accompanied by more aggressive hepatic DNA replication; however, Pdk4 ^-/- mice developed more severe hypoglycemia. In Pdk4 ^-/- PHx livers, the pro-regenerative insulin signaling was potentiated, as demonstrated by early peaking of the phosphorylation of insulin receptor, more remarkable induction of the insulin receptor substrate proteins, IRS1 and IRS2, and more striking activation of Akt. The hepatic up-regulation of CD36 contributed to the enhanced transient regeneration-associated steatosis in Pdk4 ^-/- PHx mice. Notably, CD36 overexpression in mice promoted the recovery of liver/body weight ratio and elevated intrahepatic adenosine triphosphate after PHx. CD36 expression was transcriptionally suppressed by FOXO1 (forkhead box protein O1), which was stabilized and translocated to the nucleus following AMPK (adenosine monophosphate-activated protein kinase) activation. PHx remarkably induced AMPK activation, which became incompetent to respond in Pdk4 ^-/- livers. Moreover, we defined that PDK4-regulated AMPK activation directly depended on intracellular adenosine monophosphate in vitro and in regenerative livers. Conclusion: PDK4 inhibition reprograms glucose and lipid metabolism to promote liver regeneration by enhancing hepatic insulin/Akt signaling and activating an AMPK/FOXO1/CD36 regulatory axis of lipid. These findings may lead to potential therapeutic strategies to prevent hepatic insufficiency and liver failure.

Translationally controlled tumor protein promotes liver regeneration by activating mTORC2/AKT signaling

Translationally controlled tumor protein (TCTP), which is a protein characterized by its potent proliferation promoting activity, has been well studied in the area of growth and tumorigenesis. However, the specific role of TCTP in liver regeneration (LR) and its underlying mechanism remains unclear. In order to investigate the contribution of TCTP during LR, heterozygous TCTP mice were generated, and a mimic LR model was applied to TCTP-knockdown (KD) hepatic cell lines. The results revealed that TCTP-KD impaired LR in mice, and manifested as the following aspects: delayed proliferation of hepatocytes, accompanied by disruption of the mRNA expression of markers of the cell cycle, degenerated lipid metabolism, and abnormal immune response. Furthermore, it was found out that TCTP activated PI3K/AKT signaling by regulating mTORC2. Lastly, the increasing rate of serum TCTP positively correlated to the recovery of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) after liver resection in humans. In summary, the present study is the first to reveal the crucial role of intracellular TCTP in LR.

Variation in the gut microbial community is associated with the progression of liver regeneration

AIM

To highlight a potential dynamic interaction between intestinal bacteria (IB) and metabolites that might contribute to liver regeneration (LR).

METHODS

Male Sprague-Dawley rats were subjected to surgical removal of two-thirds of the liver and samples were collected over a 14-day period. Intestinal community and metabolic profiles were characterized to establish their potential interactions during liver regeneration.

RESULTS

Partial hepatectomy caused fluctuating changes in the gut microbiome, which paralleled the biological processes of LR. Briefly, the enhanced cell proliferation occurring within 30-48 h was associated with a decreased ratio of Firmicutes to Bacteroidetes reflected by a reduction in Ruminococcaceae and Lachnospiraceae, and an increase in Bacteroidaceae, Rikenellaceae, and Porphyromonadaceae, which was indicative of a lean phenotype. The microbiota derived from rats at 12-24 h and 3-14 days were characterized by elevated F/B ratios, suggesting the differing energy extract behaviors of microbiota during the course of LR. Functional changes of the shifted microbiota revealed by PICRUSt software confirmed the pyrosequencing results. The microbiome derived from hour 12 rats showed overpresentation of metabolism-related modules. In contrast, the microbiome derived from day 2 rats was functionally unique in "replication and repair", "amino acid metabolism," and "nucleoid metabolism." Upon examining the dynamic pattern of metabolic response, the specific pathways, including glycerophospholipid metabolism, taurine, and hypotaurine metabolism, were identified to be attributable to the systemic alterations in LR-related metabolism. Moreover, our data indicated that several key functional bacteria were strongly related to perturbations of the above pathways.

CONCLUSION

Gut flora could play a central role in manipulating metabolic responses in LR.

Gene expression and DNA methylation as mechanisms of disturbed metabolism in offspring after exposure to a prenatal HF diet

Exposure to a prenatal high-fat (HF) diet leads to an impaired metabolic phenotype in mouse offspring. The underlying mechanisms, however, are not yet fully understood. Therefore, this study investigated whether the impaired metabolic phenotype may be mediated through altered hepatic DNA methylation and gene expression. We showed that exposure to a prenatal HF diet altered the offspring’s hepatic gene expression of pathways involved in lipid synthesis and uptake (SREBP), oxidative stress response [nuclear factor (erythroid-derived 2)-like 2 (Nrf2)], and cell proliferation. The downregulation of the SREBP pathway related to previously reported decreased hepatic lipid uptake and postprandial hypertriglyceridemia in the offspring exposed to the prenatal HF diet. The upregulation of the Nrf2 pathway was associated with increased oxidative stress levels in offspring livers. The prenatal HF diet also induced hypermethylation of transcription factor (TF) binding sites upstream of lipin 1 (Lpin1), a gene involved in lipid metabolism. Furthermore, DNA methylation of Lpin1 TF binding sites correlated with mRNA expression of Lpin1. These findings suggest that the effect of a prenatal HF diet on the adult offspring’s metabolic phenotype are regulated by changes in hepatic gene expression and DNA methylation.

Phosphatidylinositol-3-phosphate-mediated actin domain formation linked to DNA synthesis upon insulin treatment in rat hepatoma-derived H4IIEC3 cells

Phosphatidylinositol-3-phosphate (PI3P) is a lipid that accumulates in the early endosomal membrane, and acts as a scaffold to recruit proteins that contain a PI3P-binding domain, such as the FYVE domain. In this study, we examined the effect of PI3P depletion on the insulin response in rat hepatoma-derived H4IIEC3 cells. We found that insulin treatment induced the transient formation of an actin domain structure, a mesh-like tangled network of actin filaments where phosphorylated Akt, endosomal proteins, and PI3P accumulated. Actin domain formation was repressed by the depletion of PI3P by SAR405, an inhibitor of the class III PI3 kinase, Vps34, by the inhibition of PI3P function by the competitive binding of an excess amount of GST-fused 2xFYVE protein to intracellular PI3P, and by the use of diabetic model cells, in which PI3P was depleted. SAR405 did not affect the phosphorylation level of Akt, and the transcriptional regulation of gluconeogenic and cholesterol synthetic genes after insulin treatment. Interestingly, insulin-induced DNA synthesis was specifically inhibited by SAR405, cytochalasin B, and also in diabetic model cells. These results suggest that PI3P is required for the formation of actin domains, which affected a signaling pathway downstream of Akt associated with DNA synthesis in H4IIEC3 cells.

NAFLD Induction Delays Postoperative Liver Regeneration of ALPPS in Rats

BACKGROUND

Associating liver partition and portal vein ligation (ALPPS) is a promising two-step hepatectomy that is beneficial for accumulative regeneration of the future liver remnant (FLR) and avoids postoperative liver failure.

AIMS

Our study aimed to evaluate whether nonalcoholic fatty liver disease affected the liver regeneration induced by ALPPS.

METHODS

Sprague-Dawley rats fed a high-fat diet were used to construct the NAFLD model. ALPPS were performed, and blood and future liver remnant samples were collected at postoperative days 1 (POD1), POD3, and POD7.

RESULTS

The hepatic regeneration rate (HRR) of ALPPS was higher than that of portal vein ligation (PVL) at POD3 and POD7 (p < 0.05), and the number of Ki-67-positive hepatocytes (POD3) and CD68-positive Kupffer cells (POD7) per visual field was higher in the ALPPS group than in the PVL group (p < 0.05). The serum TNF-α, hepatocyte growth factor protein, and the serum IL-6 level were higher in the ALPPS group than in the PVL group at POD3 and POD7. Compared with those of the standard laboratory diet (SLD)-fed rats, the rats with NAFLD exhibited a decrease in the HRR, Ki-67-positive hepatocytes, and CD68-positive Kupffer cells in the FLR. The number of CD68-positive Kupffer cells was lower in rats with NAFLD than that in SLD-fed rats; noteworthily, the serum level of IL-6 and TNF-α changed dramatically after surgeries.

CONCLUSIONS

NAFLD induction delayed liver regeneration induced by the ALPPS procedure, which might be associated with hepatocyte proliferation and the number of Kupffer cells.

The impact of steatosis on liver regeneration

Alcoholic and non-alcoholic fatty liver diseases are the leading causes of cirrhosis in Western countries. These chronic liver diseases share common pathological features ranging from steatosis to steatohepatitis. Fatty liver is associated with primary liver graft dysfunction, a higher incidence of complications/mortality after surgery, in correlation with impaired liver regeneration. Liver regeneration is a multistep process including a priming phase under the control of cytokines followed by a growth factor receptor activation phase leading to hepatocyte proliferation. This process ends when the initial liver mass is restored. Deficiency in epidermal growth factor receptor (EGFR) liver expression, reduced expression of Wee1 and Myt1 kinases, oxidative stress and alteration in hepatocyte macroautophagy have been identified as mechanisms involved in the defective regeneration of fatty livers. Besides the mechanisms, we will also discuss in this review various treatments that have been investigated in the reversal of the regeneration defect, for example, omega-3 fatty acids, pioglitazone, fibroblast growth factor (FGF)19-based chimeric molecule or growth hormone (GH). Since dysbiosis impedes liver regeneration, targeting microbiota could also be an interesting therapeutic approach.

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

Peroxisome proliferator-activated receptor α (PPARα) is a key nuclear receptor involved in the control of lipid homeostasis. In rodents, PPARα is also a potent hepatic mitogen. Hepatocyte-specific disruption of PPARα inhibits agonist-induced hepatocyte proliferation; however, little is known about the exact role of PPARα in partial hepatectomy (PHx)-induced liver regeneration. Herein, using hepatocyte-specific PPARα-deficient (Ppara^ΔHep) mice, the function of hepatocyte PPARα in PHx-induced liver regeneration was investigated. PPARα protein level and transcriptional activity were increased in the liver after PHx. Compared with the Ppara^fl/fl mice, Ppara^ΔHep mice exhibited significantly reduced hepatocyte proliferation at 32 hours after PHx. Consistently, reduced Ccnd1 and Pcna mRNA and CYCD1 and proliferating cell nuclear antigen protein were observed at 32 hours after PHx in Ppara^ΔHep mice. Furthermore, Ppara^ΔHep mice showed increased hepatic lipid accumulation and enhanced hepatic triglyceride contents because of impaired hepatic fatty acid β-oxidation when compared with that observed in Ppara^fl/fl mice. These results indicate that PPARα promotes liver regeneration after PHx, at least partially via regulating the cell cycle and lipid metabolism.

Metabolic Remodeling during Liver Regeneration

Liver disease is linked to a decreased capacity of hepatocytes to divide. In addition, cellular metabolism is important for tissue homeostasis and regeneration. Since metabolic changes are a hallmark of liver disease, we investigated the connections between metabolism and cell division. We determined global metabolic changes at different stages of liver regeneration using a combination of integrated transcriptomic and metabolomic analyses with advanced functional redox in vivo imaging. Our data indicate that blocking hepatocyte division during regeneration leads to mitochondrial dysfunction and downregulation of oxidative pathways. This resulted in an increased redox ratio and hyperactivity of alanine transaminase allowing the production of alanine and α-ketoglutarate from pyruvate when mitochondrial functions are impaired. Our data suggests that during liver regeneration, cell division leads to hepatic metabolic remodeling. Moreover, we demonstrate that hepatocytes are equipped with a flexible metabolic machinery able to adapt dynamically to changes during tissue regeneration.

Cell size homeostasis: Metabolic control of growth and cell division

Joint regulation of growth rate and cell division rate determines cell size. Here we discuss how animal cells achieve cell size homeostasis potentially involving multiple signaling pathways converging at metabolic regulation of growth rate and cell cycle progression. While several models have been developed to explain cell size control, comparison of the two predominant models shows that size homeostasis is dependent on the ability to adjust cellular growth rate based on cell size. Consequently, maintenance of size homeostasis requires that larger cells can grow slower than small cells in relative terms. We review recent experimental evidence showing that such size adjustment occurs primarily at or immediately before the G1/S transition of the cell cycle. We further propose that bidirectional feedback between growth rate and size results in cell size sensing and discuss potential mechanisms how this may be accomplished.

Prevention of Lipid Peroxidation-derived Cyclic DNA Adduct and Mutation in High-Fat Diet-induced Hepatocarcinogenesis by Theaphenon E

Obesity is associated with cancer risk and its link with liver cancer is particularly strong. Obesity causes non-alcoholic fatty liver disease (NAFLD) that could progress to hepatocellular carcinoma (HCC). Chronic inflammation likely plays a key role. We carried out a bioassay in the high-fat diet (HFD)-fed C57BL/6J mice to provide insight into the mechanisms of obesity-related HCC by studying γ-OHPdG, a mutagenic DNA adduct derived from lipid peroxidation. In an 80-week bioassay, mice received a low-fat diet (LFD), high-fat diet (HFD), and HFD with 2% Theaphenon E (TE) (HFD+TE). HFD mice developed a 42% incidence of HCC and LFD mice a 16%. Remarkably, TE, a standardized green tea extract formulation, completely blocked HCC in HFD mice with a 0% incidence. γ-OHPdG measured in the hepatic DNA of mice fed HFD and HFD+TE showed its levels increased during the early stages of NAFLD in HFD mice and the increases were significantly suppressed by TE, correlating with the tumor data. Whole-exome sequencing showed an increased mutation load in the liver tumors of HFD mice with G>A and G>T as the predominant mutations, consistent with the report that γ-OHPdG induces G>A and G>T. Furthermore, the mutation loads were significantly reduced in HFD+TE mice, particularly G>T, the most common mutation in human HCC. These results demonstrate in a relevant model of obesity-induced HCC that γ-OHPdG formation during fatty liver disease may be an initiating event for accumulated mutations that leads to HCC and this process can be effectively inhibited by TE. Cancer Prev Res; 11(10); 665-76. ©2018 AACR.

Foie gras and liver regeneration: a fat dilemma

The liver has a unique ability of regenerating after injuries or partial loss of its mass. The mechanisms responsible for liver regeneration - mostly occurring when the hepatic tissue is damaged or functionally compromised by metabolic stress - have been studied in considerable detail over the last few decades, because this phenomenon has both basic-biology and clinical relevance. More specifically, recent interest has been focusing on the widespread occurrence of abnormal nutritional habits in the Western world that result in an increased prevalence of non-alcoholic fatty liver disease (NAFLD). NAFLD is closely associated with insulin resistance and dyslipidemia, and it represents a major clinical challenge. The disease may progress to steatohepatitis with persistent inflammation and progressive liver damage, both of which will compromise regeneration under conditions of partial hepatectomy in surgical oncology or in liver transplantation procedures. Here, we analyze the impact of ER stress and SIRT1 in lipid metabolism and in fatty liver pathology, and their consequences on liver regeneration. Moreover, we discuss the fine interplay between ER stress and SIRT1 functioning when contextualized to liver regeneration. An improved understanding of the cellular and molecular intricacies contributing to liver regeneration could be of great clinical relevance in areas as diverse as obesity, metabolic syndrome and type 2 diabetes, as well as oncology and transplantation.

Glutathione disulfide sensitizes hepatocytes to TNFα-mediated cytotoxicity via IKK-β S-glutathionylation: a potential mechanism underlying non-alcoholic fatty liver disease

Oxidative stress and TNFα are critically involved in the initiation and progression of non-alcoholic fatty liver disease (NAFLD). In this study, we investigated the effects of dysregulated glutathione homeostasis, a principal feature of oxidative stress, on TNFα-induced hepatotoxicity and its mechanistic implications in NAFLD progression. We showed that mice fed a high-fat diet (HFD) for 12 weeks developed hepatic steatosis and liver injuries, which were associated with not only TNFα overproduction but also hepatic glutathione dysregulation, characterized by GSH reduction and GSSG elevation. Moreover, consuming a HFD increased protein S-glutathionylation (protein-SSG formation) in the liver. Subsequent cell culture studies revealed that GSSG accumulation, as opposed to GSH reduction, sensitized hepatocytes to TNFα killing by reducing the TNFα-triggered NF-κB activity. GSSG prevented TNFα-induced activation of IKK-β, an upstream kinase in the NF-κB signaling pathway, by inducing IKK-β glutathionylation (IKK-β-SSG formation). In animal studies, in comparison to a control diet, HFD consumption resulted in increased hepatic IKK-β-SSG formation, leading to suppressed IKK-β activation and subsequent NF-κB suppression. Furthermore, we found that HFD consumption also led to decreased hepatic expression of glutaredoxin, a key enzyme for de-glutathionylation. Similarly, CdCl2, a chemical inhibitor of glutaredoxin, sensitized hepatocytes to TNFα-mediated cytotoxicity. In conclusion, our data suggest that GSSG is a potent and clinically relevant sensitizer for TNFα-induced hepatotoxicity in NAFLD, which represents a potential therapeutic target for NAFLD.

Preserved liver regeneration capacity after partial hepatectomy in rats with non-alcoholic steatohepatitis

AIM

To evaluate the liver regeneration capacity (LRC) after partial hepatectomy (PH) in experimental non-alcoholic steatohepatitis (NASH).

METHODS

Fifty-four female rats were fed a high-fat, high-cholesterol diet (HFCD, 65% fat, 1% cholesterol) or standard diet (STD) for 16 wk. A 70% PH was performed and the animals were euthanised before PH or 2 or 5 d post-PH. LRC was evaluated using: The total number of Ki-67 positive hepatocytes in the caudate lobe, N(Ki-67, lobe) evaluated in a stereology-based design, the regenerated protein ratio (RPR), prothrombin-proconvertin ratio (PP), and mRNA expression of genes related to regeneration.

RESULTS

The HFCD NASH model showed significant steatosis with ballooning and inflammation, while no fibrosis was present. Mortality was similar in HFCD and STD animals following PH. HFCD groups were compared to respective STD groups and HFCD animals had a significantly elevated alanine transaminase at baseline (P < 0.001), as well as a significantly elevated bilirubin at day 2 after PH (P < 0.05). HFCD animals had a higher N(Ki-67, lobe) at baseline, (P < 0.0001), day 2 after PH (P = 0.06) and day 5 after PH (P < 0.025). We found no significant difference in RPR or PP neither 2 or 5 d post-PH. Expression of liver regeneration genes (e.g., hepatic growth factor) was higher at both day 2 and 5 post-PH in HFCD groups (P < 0.05).

CONCLUSION

NASH rats had a preserved LRC after hepatectomy when compared to STD rats. The methods and models of NASH are essential in understanding and evaluating LRC.

Distinctly altered gut microbiota in the progression of liver disease

Recent studies underscore important roles of intestinal microbiota and the bacterial lipopolysaccharides (LPS) production in the pathogenesis of liver disease. However, how gut microbiota alters in response to the development of steatosis and subsequent progression to nonalcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) remains unclear. We aimed to study the gut microbial changes over liver disease progression using a streptozotocin-high fat diet (STZ-HFD) induced NASH-HCC C57BL/6J mouse model that is highly relevant to human liver disease. The fecal microbiota at various liver pathological stages was analyzed by 16S rDNA gene pyrosequencing. Both UniFrac analysis and partial least squares-discriminant analysis showed significant structural alterations in gut microbiota during the development of liver disease. Co-abundance network analysis highlighted relationships between genera. Spearman correlation analysis revealed that the bacterial species, Atopobium spp., Bacteroides spp., Bacteroides vulgatus, Bacteroides acidifaciens, Bacteroides uniformis, Clostridium cocleatum, Clostridium xylanolyticum and Desulfovibrio spp., markedly increased in model mice, were positively correlated with LPS levels and pathophysiological features. Taken together, the results showed that the gut microbiota was altered significantly in the progression of liver disease. The connection between the gut microbial ecology and the liver pathology may represent potential targets for the prevention and treatment of chronic liver disease and HCC.

Inducing and characterizing liver regeneration in mice: Reliable models, essential "readouts" and critical perspectives

Elucidating the molecular circuitry that regulates regenerative responses in mammals has recently attracted considerable attention because of its emerging impact on modern bioengineering, tissue replacement technologies, and organ transplantation. The liver is one of the few organs of the adult body that exhibitsa prominent regenerative capacity in response to toxic injury, viral infection, or surgical resection. Over the years, mechanistic insights into the liver's regenerative potential have been provided by rodent models of chemical liver injury or surgical resection that faithfully recapitulate hallmarks of human pathophysiology and trigger robust hepatocyte proliferation leading to organ restoration. The advent of mouse transgenics has undeniably catalyzed the wider application of such models for researching liver pathobiology. This article provides a comprehensive overview of the most reliable and widely applied murine models of liver regeneration and also discusses helpful hints, considerations, and limitations related to the use of these models in liver regeneration studies.

Role and Regulation of p65/β-Catenin Association During Liver Injury and Regeneration: A "Complex" Relationship

An important role for β-catenin in regulating p65 (a subunit of NF-κB) during acute liver injury has recently been elucidated through use of conditional β-catenin knockout mice, which show protection from apoptosis through increased activation of p65. Thus, we hypothesized that the p65/β-catenin complex may play a role in regulating processes such as cell proliferation during liver regeneration. We show through in vitro and in vivo studies that the p65/β-catenin complex is regulated through the TNF-α pathway and not through Wnt signaling. However, this complex is unchanged after partial hepatectomy (PH), despite increased p65 and β-catenin nuclear translocation as well as cyclin D1 activation. We demonstrate through both in vitro silencing experiments and chromatin immunoprecipitation after PH that β-catenin, and not p65, regulates cyclin D1 expression. Conversely, using reporter mice we show p65 is activated exclusively in the nonparenchymal (NPC) compartment during liver regeneration. Furthermore, stimulation of macrophages by TNF-α induces activation of NF-κB and subsequent secretion of Wnts essential for β-catenin activation in hepatocytes. Thus, we show that β-catenin and p65 are activated in separate cellular compartments during liver regeneration, with p65 activity in NPCs contributing to the activation of hepatocyte β-catenin, cyclin D1 expression, and subsequent proliferation.

Liver Regeneration Is Impaired in Mice with Acute Exposure to a Very Low Carbohydrate Diet

BACKGROUND

The metabolic response to hepatic insufficiency has been implicated in the regulators of normal liver regeneration. Modulation of nutritional factors has been demonstrated to affect liver regeneration. Diets containing very low carbohydrate and high fat levels cause a unique metabolic state, the effect of which on liver regeneration is unknown.

METHODS

Mice were placed on standard mice chow (ND) or a very low carbohydrate diet (VLCD) after 70% partial hepatectomy (PH). After 48 h, mice on VLCD were placed back to ND. The serum metabolic profiles, hepatic lipid content, and gene expression profile were examined. The dynamics of liver regeneration were detected at timed points. Activation of signaling pathways was examined.

RESULTS

VLCD feeding caused hypoglycemia and elevation of serum β-hydroxybutyrate and free fatty acids in mice after PH. It increased hepatic triglyceride contents, enhanced fatty acid oxidation, and reduced lipid synthesis. Mice on VLCD exhibited diminished hepatocellular mitotic frequency, a reduced BrdU incorporation and liver mass regeneration ratio, and delayed expression of PCNA. Expressions of IL-6 and TNFα in liver and serum were downregulated. Meanwhile, phosphorylation of STAT3, Erk, and AKT was delayed compared with controls.

CONCLUSIONS

VLCD feeding delayed liver regeneration, probably because of the suppression of TNFα-IL-6-STAT3 signaling and delayed activation of Erk and AKT induced by the unique metabolic effects of this diet.

Investigation of underlying comorbidities as risk factors for symptomatic human hepatitis E virus infection

BACKGROUND

Symptomatic Hepatitis E virus (HEV) infection occurs in few infected subjects, and the risk factors are not completely known.

AIM

To explore the risk factors for adverse clinical outcomes in acute HEV infections.

METHODS

A large retrospective study was conducted. The baseline characteristics, clinical outcomes, and laboratory data of 512 acute HEV infection cases were analysed using logistic regression models.

RESULTS

All patients exhibited autochthonous sporadic HEV infections, and most were elderly. Their symptoms varied from asymptomatic to severe liver diseases. In all, 215 patients (42.0%) had liver failure and/or decompensation, and 45 (8.2%) patients died within 3 months. Nearly 60% of patients had underlying chronic liver diseases (CLDs), 20% were cirrhotic, and various extrahepatic underlying comorbidities were common. The logistic regression analysis revealed that underlying CLDs, especially cirrhosis, were closely associated with disease severity (OR = 8.78, P < 0.001) but not with mortality in patients with severe liver diseases. In addition to the known factors, including an old age, the male gender and CLDs, we identified pre-existing extrahepatic tumours, diabetes, and chronic respiratory and renal diseases as novel independent predictors for adverse clinical outcomes. Importantly, patients without these four extrahepatic comorbidities showed a much lower mortality rate (4.2%, P < 0.001) than patients with one (18.5%) or more comorbidities (34.5%).

CONCLUSIONS

Previous comorbidities, including tumours, diabetes, and chronic liver, lung and kidney diseases, were independent risk factors for adverse outcomes, especially mortality, in acute HEV infections. This study provides valuable data for improving the prevention and control of HEV infection.

Administration of multipotent mesenchymal stromal cells restores liver regeneration and improves liver function in obese mice with hepatic steatosis after partial hepatectomy

Background

The liver has the remarkable capacity to regenerate in order to compensate for lost or damaged hepatic tissue. However, pre-existing pathological abnormalities, such as hepatic steatosis (HS), inhibits the endogenous regenerative process, becoming an obstacle for liver surgery and living donor transplantation.

Recent evidence indicates that multipotent mesenchymal stromal cells (MSCs) administration can improve hepatic function and increase the potential for liver regeneration in patients with liver damage. Since HS is the most common form of chronic hepatic illness, in this study we evaluated the role of MSCs in liver regeneration in an animal model of severe HS with impaired liver regeneration.

Methods

C57BL/6 mice were fed with a regular diet (normal mice) or with a high-fat diet (obese mice) to induce HS. After 30 weeks of diet exposure, 70% hepatectomy (Hpx) was performed and normal and obese mice were divided into two groups that received 5 × 10⁵ MSCs or vehicle via the tail vein immediately after Hpx.

Results

We confirmed a significant inhibition of hepatic regeneration when liver steatosis was present, while the hepatic regenerative response was promoted by infusion of MSCs. Specifically, MSC administration improved the hepatocyte proliferative response, PCNA-labeling index, DNA synthesis, liver function, and also reduced the number of apoptotic hepatocytes.

These effects may be associated to the paracrine secretion of trophic factors by MSCs and the hepatic upregulation of key cytokines and growth factors relevant for cell proliferation, which ultimately improves the survival rate of the mice.

Conclusions

MSCs represent a promising therapeutic strategy to improve liver regeneration in patients with HS as well as for increasing the number of donor organs available for transplantation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0469-y) contains supplementary material, which is available to authorized users.