Interleukin 18 accelerates the hepatic cell proliferation in rat liver regeneration after partial hepatectomy

Hypoxia activates GPR146 which participates in pulmonary vascular remodeling by promoting pyroptosis of pulmonary artery endothelial cells

BACKGROUND

Hypoxia is a risk factor of pulmonary hypertension (PH) and may induce pulmonary artery endothelial cells (PAECs) injury and inflammation. Pyroptosis is a form of cell death through maturation and secretion of inflammatory mediators. However, the mechanistic association of pyroptosis, PAECs injury, and inflammation remain unknown. Here, we explored in detail the effects of hypoxia on pyroptosis of PAECs.

EXPERIMENTAL APPROACH

Using RNA sequencing, we screened differentially expressed genes in pulmonary artery tissue of a Sugen5416/hypoxia-induced (SuHx) rat PH model. We examined the role of the differentially expressed gene G-protein coupled receptor 146 (GPR146) in PAECs through immunohistochemistry, immunofluorescence, CCK-8 assays, western blotings, real-time PCR, detection of reactive oxygen species, and lactate dehydrogenase release experiments.

KEY RESULTS

According to RNA sequencing, GPR146 was 11.64-fold increased in the SuHx-induced PH model, compared to the controls. Further, GPR146 was highly expressed in pulmonary arterial hypertension human lung tissue and SuHx-induced rat PH lung tissues. Our results suggested that the expression of pyroptosis-related proteins was markedly increased under hypoxia, both in vivo and in vitro, which was inhibited by silencing GPR146. Moreover, inhibiting NLRP3 or caspase-1 effectively suppressed cleavage of caspase-1, production of interleukin (IL)-1β, IL-6, and IL-18 in PAECs by hypoxia and overexpression of GPR146.

CONCLUSION

Our results indicated that GPR146 induced pyroptosis and inflammatory responses through the NLRP3/caspase-1 signaling axis, thus triggering endothelial injury and vascular remodeling. Hypoxia may promote PAECs pyroptosis through upregulation of GPR146 and thereby facilitate the progression of PH. Taken together, these insights may help identify a novel target for the treatment of PH.

Methyl 6-O-cinnamoyl-α-d-glucopyranoside Ameliorates Acute Liver Injury by Inhibiting Oxidative Stress Through the Activation of Nrf2 Signaling Pathway

Excessive stimulation of hepatotoxins and drugs often lead to acute liver injury, while treatment strategies for acute liver injury have been limited. Methyl 6-O-cinnamoyl-α-d-glucopyranoside (MCGP) is a structure modified compound from cinnamic acid, a key chemical found in plants with significant antioxidant, anti-inflammatory, and antidiabetic effects. In this study, we investigated the effects and underlying mechanisms of MCGP on acetaminophen (APAP)- or carbon tetrachloride (CCl₄)-induced acute liver injury. As a result, MCGP inhibited cell death and apoptosis induced by APAP or CCl₄, and suppressed the reactive oxygen species (ROS) generation stimulated by H₂O₂ in liver AML12 cells. In vivo, MCGP alleviated APAP/CCl₄-induced hepatic necrosis and resumed abnormal aminotransferase activities and liver antioxidase activities. In addition, MCGP depressed APAP- or CCl₄-induced oxidative stress through the suppression of CYP2E1 and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. MCGP also enhanced the number of PCNA-positive hepatocytes, increased hepatic PCNA and Bcl-XL, and decreased BAX expression in APAP-/CCl₄-intoxicated mice. Furthermore, MCGP activated the GSDMD-N/cleaved caspase 1 pathway. In summary, MCGP might act as a potential therapeutic drug against drug-induced and chemical-induced acute liver injuries, and its underlying mechanisms might engage on the pressing of oxidative stress, refraining of hepatocyte apoptosis, and facilitating of liver regeneration.

Gasdermin D-mediated pyroptosis suppresses liver regeneration after 70% partial hepatectomy

Pyroptosis is a kind of programmed cell death primarily mediated by gasdermin D (GSDMD) and shown to regulate multiple diseases. However, its contribution to liver regeneration, a fine‐tuned tissue repair process mediated primarily by hepatocytes after mass loss, remains unclear. Herein, we found that caspase‐11/GSDMD‐mediated pyroptosis was activated in regenerating liver after 70% partial hepatectomy. Impeding pyroptosis by deleting GSDMD significantly reduced liver injury and accelerated liver regeneration. Mechanistically, GSDMD deficiency up‐regulates the activation of hepatocyte growth factor/c‐Met and epidermal growth factor receptor mitogenic pathways at the initiation phase. Moreover, activin A and glypican 3 (GPC3), two terminators of liver regeneration, were inhibited when GSDMD was absent. In vitro study suggested the expressions of activin A and GPC3 were induced by interleukin (IL)–1β and IL‐18, whose maturations were regulated by GSDMD‐mediated pyroptosis. Similarly, pharmacologically inhibiting GSDMD recapitulates these phenomena. Conclusion: This study characterizes the role of GSDMD‐mediated pyroptosis in liver regeneration and lays the foundation for enhancing liver restoration by targeting GSDMD in liver patients with impaired regenerative capacity.

LR12 Promotes Liver Repair by Improving the Resolution of Inflammation and Liver Regeneration in Mice with Thioacetamide- (TAA-) Induced Acute Liver Failure

Background

Triggering receptor expressed on myeloid cells-1 (TREM-1) controls the mobilization of inflammatory cells in response to injury and consequently enhances liver damage. LR12 is a TREM-1 inhibitory peptide. However, the role of LR12 in acute liver failure (ALF) has remained elusive. This study was aimed at indicating whether LR12 could promote liver repair in mice with thioacetamide- (TAA-) induced ALF.

Methods

BALB/c mice were intraperitoneally injected with TAA, followed by intravenous injection of LR12. Damage and regeneration of the liver were assessed. LO2 cells and macrophages were used to assess the therapeutic effects of LR12.

Results

Mice treated with TAA for 24 h developed ALF, while liver inflammation was alleviated after LR12 treatment. Moreover, LR12 promoted hepatocyte regeneration in mice with TAA-induced ALF. In vitro, the supernatant from TAA+LR12-treated macrophages promoted the proliferation of LO2 cells. Cytokine protein microarray analysis suggested that LR12 promoted the secretion of C-C chemokine ligand 20 (CCL20) from macrophages. Besides, neutralization of CCL20 blocked the effects of LR12, thus inhibited the proliferation of LO2 cells in vitro, aggregated the liver inflammation, and restrained hepatocyte regeneration in ALF mice in vivo. Furthermore, we also found that LR12 activated the p38 mitogen-activated protein kinase (MAPK) pathway in hepatocytes through promoting the secretion of CCL20 from macrophages.

Conclusions

LR12 could improve the resolution of inflammation and liver regeneration in mice with TAA-induced ALF by promoting the secretion of CCL20 from macrophages and activating the p38 MAPK pathway. Therefore, LR12 could be an attractive therapeutic target for the treatment of ALF.

Baicalin promotes liver regeneration after acetaminophen-induced liver injury by inducing NLRP3 inflammasome activation

Liver regeneration has become a new hotspot in the study of drug-induced liver injury (DILI). Baicalin has already been reported to alleviate acetaminophen (APAP)-induced acute liver injury in our previous study. This study aims to observe whether baicalin also promotes liver regeneration after APAP-induced liver injury and to elucidate its engaged mechanism. Baicalin alleviated APAP-induced hepatic parenchymal cells injury and enhanced the number of mitotic and proliferating cell nuclear antigen (PCNA)-positive hepatocytes in APAP-intoxicated mice. Baicalin increased hepatic PCNA and cyclinD1 expression in APAP-intoxicated mice. Baicalin induced the activation of NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome, leading to the increased hepatic expression of interleukin-18 (IL-18) and IL-1β in APAP-intoxicated mice. The results in vitro demonstrated that IL-18 promoted the proliferation of human normal liver L-02 cells. Moreover, the baicalin-provided promotion on liver regeneration in APAP-intoxicated mice was diminished after the application of NLRP3 inhibitor MCC950 and the recombinant mouse IL-18 binding protein (rmIL-18BP). Baicalin induced the cytosolic accumulation of nuclear factor erythroid 2-related factor 2 (Nrf2), and increased the interaction between Nrf2 with Nlrp3, ASC and pro-caspase-1 in livers from APAP-intoxicated mice. Furthermore, the baicalin-provided NLRP3 inflammasome activation and promotion on liver regeneration after APAP-induced liver injury in wild-type mice were diminished in Nrf2 knockout mice. In conclusion, baicalin promoted liver regeneration after APAP-induced acute liver injury in mice via inducing Nrf2 accumulation in cytoplasm that led to NLRP3 inflammasome activation, and then caused the increased expression of IL-18, which induced hepatocytes proliferation.

Disrupting phosphatase SHP2 in macrophages protects mice from high-fat diet-induced hepatic steatosis and insulin resistance by elevating IL-18 levels

Chronic low-grade inflammation plays an important role in the pathogenesis of type 2 diabetes. Src homology 2 domain-containing tyrosine phosphatase-2 (SHP2) has been reported to play diverse roles in different tissues during the development of metabolic disorders. We previously reported that SHP2 inhibition in macrophages results in increased cytokine production. Here, we investigated the association between SHP2 inhibition in macrophages and the development of metabolic diseases. Unexpectedly, we found that mice with a conditional SHP2 knockout in macrophages (cSHP2-KO) have ameliorated metabolic disorders. cSHP2-KO mice fed a high-fat diet (HFD) gained less body weight and exhibited decreased hepatic steatosis, as well as improved glucose intolerance and insulin sensitivity, compared with HFD-fed WT littermates. Further experiments revealed that SHP2 deficiency leads to hyperactivation of caspase-1 and subsequent elevation of interleukin 18 (IL-18) levels, both in vivo and in vitro Of note, IL-18 neutralization and caspase-1 knockout reversed the amelioration of hepatic steatosis and insulin resistance observed in the cSHP2-KO mice. Administration of two specific SHP2 inhibitors, SHP099 and Phps1, improved HFD-induced hepatic steatosis and insulin resistance. Our findings provide detailed insights into the role of macrophagic SHP2 in metabolic disorders. We conclude that pharmacological inhibition of SHP2 may represent a therapeutic strategy for the management of type 2 diabetes.

Endogenous Interleukin 18 Suppresses Liver Regeneration After Hepatectomy in Mice

The comprehensive role of interleukin (IL) 18 during liver regeneration is barely studied. Our aim is to evaluate the role of IL18 in liver regeneration after partial hepatectomy (PH) in mice. The expression profile of IL18 in the liver and the gut after 70% PH was measured. Liver samples after 70% and 85% PH from IL18 knockout (IL18^-/- ) mice and wild type (WT) mice were collected for comparison of liver regeneration. The effect of recombinant IL18 on liver regeneration was tested in IL18^-/- mice, and the utility of IL18 binding protein (BP) was also evaluated following 70% PH in WT mice. Expression levels of IL18 in the liver and the gut elevated after 70% PH. The liver weight/body weight ratios (LBWRs) after PH were significantly higher in IL18^-/- mice than those in WT mice. Recombinant IL18 injection significantly decreased LBWR at 7 days after 70% PH in IL18^-/- mice. The expression of cyclin D1, EdU labeling index, and Ki-67 proliferation index were much higher in IL18^-/- mice than those in WT mice after 70% PH. The expression level of glypican 3 (GPC3) in WT mice significantly elevated during liver regeneration. In contrast, the expression level of GPC3 in IL18^-/- mice remained roughly unchanged during liver regeneration. IL18BP injection significantly increased the LBWR at 7 days after 70% PH in WT mice. In conclusion, endogenous IL18 inhibited liver regeneration after PH in mice, possibly through up-regulating GPC3. IL18BP may be an effective agent to promote liver regeneration after PH.

A Synthetic Human Antibody Antagonizes IL-18Rβ Signaling Through an Allosteric Mechanism

The interleukin-18 subfamily belongs to the interleukin-1 family and plays an important role in modulating innate and adaptive immune responses. Dysregulation of IL-18 has been implicated in or correlated with numerous diseases, including inflammatory diseases, autoimmune disorders, and cancer. Thus, blockade of IL-18 signaling may offer therapeutic benefits in many pathological settings. Here, we report the development of synthetic human antibodies that target human IL-18Rβ and block IL-18-mediated IFN-γ secretion by inhibiting NF-κB and MAPK dependent pathways. The crystal structure of a potent antagonist antibody in complex with IL-18Rβ revealed inhibition through an unexpected allosteric mechanism. Our findings offer a novel means for therapeutic intervention in the IL-18 pathway and may provide a new strategy for targeting cytokine receptors.

Paraoxonase 3 inhibits cell proliferation and serves as a prognostic predictor in hepatocellular carcinoma

Paraoxonase 3 (PON3) exerts prominent anti-inflammation and anti-oxidation properties mainly at the cellular level, and is primarily expressed in the liver. However, its role in HCC remains unexplored. Here, we investigated the expression pattern, clinical significance, and function of PON3 in HCC. PON3 mRNA and protein levels were respectively determined in two large cohorts using quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC) of tissue microarray. We found that PON3 was downregulated in most HCCs. Kaplan-Meier and log-rank test showed that PON3 downregulation predicted shorter recurrence-free survival (RFS) and overall survival (OS) time in all HCC patients, especially early-stage HCC patients. Cox regression analysis revealed that the PON3 downregulation was an independent risk factor for RFS and OS. Gain- and loss-of-function experiments revealed that PON3 suppressed cell proliferation in vivo and in vitro, which was attributed to its cell-cycle arrest effect. In addition, microarray analysis showed that some pro-proliferative genes were elevated when PON3 was knockdown, and these genes possibly involved in the underlying mechanisms. In conclusion, our studies reveal the cell proliferation inhibitory function of PON3 and offer a potential prognostic predictor and therapeutic target for HCC.

Germline loss of PKM2 promotes metabolic distress and hepatocellular carcinoma

Alternative splicing of the Pkm gene product generates the PKM1 and PKM2 isoforms of pyruvate kinase (PK), and PKM2 expression is closely linked to embryogenesis, tissue regeneration, and cancer. To interrogate the functional requirement for PKM2 during development and tissue homeostasis, we generated germline PKM2-null mice (Pkm2(-/-)). Unexpectedly, despite being the primary isoform expressed in most wild-type adult tissues, we found that Pkm2(-/-) mice are viable and fertile. Thus, PKM2 is not required for embryonic or postnatal development. Loss of PKM2 leads to compensatory expression of PKM1 in the tissues that normally express PKM2. Strikingly, PKM2 loss leads to spontaneous development of hepatocellular carcinoma (HCC) with high penetrance that is accompanied by progressive changes in systemic metabolism characterized by altered systemic glucose homeostasis, inflammation, and hepatic steatosis. Therefore, in addition to its role in cancer metabolism, PKM2 plays a role in controlling systemic metabolic homeostasis and inflammation, thereby preventing HCC by a non-cell-autonomous mechanism.

Interleukin-18 Down-Regulates Multidrug Resistance-Associated Protein 2 Expression through Farnesoid X Receptor Associated with Nuclear Factor Kappa B and Yin Yang 1 in Human Hepatoma HepG2 Cells

Multidrug resistance-associated protein 2 (MRP2) plays an important role in bile acid metabolism by transporting toxic organic anion conjugates, including conjugated bilirubin, glutathione, sulfate, and multifarious drugs. MRP2 expression is reduced in cholestatic patients and rodents. However, the molecular mechanism of MRP2 down-regulation remains elusive. In this report, we treated human hepatoma HepG2 cells with interleukin-18 (IL-18) and measured the expression of MRP2, nuclear factor kappa B (NF-κB), farnesoid X receptor (FXR), and the transcription factor Yin Yang 1 (YY1) by quantitative real-time quantitative polymerase chain reaction (PCR) and western blotting. We found that expression of MRP2 was repressed by IL-18 at both the mRNA and protein levels in a dose- and time-dependent manner. Furthermore, the activated NF-κB pathway increased YY1 and reduced FXR. These changes were all attenuated in HepG2 cells with knockdown of the NF-κB subunit, p65. The reduced expression of FXR and MRP2 in HepG2 cells that had been caused by IL-18 treatment was also attenuated by YY1 knockdown. We further observed significantly elevated IL-18, NF-κB, and YY1 expression and decreased FXR and MRP2 expression in bile duct-ligated Sprague Dawley rat livers. Chromatin immunoprecipitation assays also showed that FXR bound to the promoter region in MRP2 was less abundant in liver extracts from bile duct-ligated rats than sham-operated rats. Our findings indicate that IL-18 down-regulates MRP2 expression through the nuclear receptor FXR in HepG2 cells, and may be mediated by NF-κB and YY1.

Expression profiles uncover the relationship between erythropoietin and cell proliferation in rat hepatocytes after a partial hepatectomy

Erythropoietin (EPO) has a beneficial effect on hepatic cell proliferation during liver regeneration. However, the underlying mechanism has not yet been elucidated. To uncover the proliferation response of EPO in rat liver regeneration after partial hepatectomy (PH) at the cellular level, hepatocytes (HCs) were isolated using Percoll density gradient centrifugation. The genes of the EPO-mediated signaling pathway and the target genes of the transcription factor (TF) in the pathway were identified in a pathway and TF database search. Their expression profiles were then detected using Rat Genome 230 2.0 Microarray. The results indicated that the EPO-mediated signaling pathway is involved in 19 paths and that 124 genes participate, of which 32 showed significant changes and could be identified as liver regeneration-related genes. In addition, 443 targets regulated by the TFs of the pathway and 60 genes associated with cell proliferation were contained in the array. Subsequently, the synergetic effect of these genes in liver regeneration was analyzed using the E(t) mathematical model based on their expression profiles. The results demonstrated that the E(t) values of paths 3, 8, 12 and 14-17 were significantly strengthened in the progressing phase of liver regeneration through the RAS/MEK/ERK or PI3K/AκT pathways. The synergetic effect of the target genes, in parallel with target-related cell proliferation, was also enhanced 12-72 h after PH, suggesting a potential positive effect of EPO on HC proliferation during rat liver regeneration. These data imply that the EPO receptor may allow EPO to promote HC proliferation through paths 3, 8, 12 and 14-17, mediating the RAS/MEK/ERK and PI3K/AκT pathways in rat liver regeneration after PH.

Bromodeoxyuridine (BrdU) treatment to measure hepatocellular proliferation does not mask furan-induced gene expression changes in mouse liver

Bromodeoxyuridine (BrdU) is a synthetic nucleoside used to detect cellular proliferation. BrdU incorporates in the place of thymine but pairs with guanine, thereby increasing the risk of transition mutations in dividing cells. Given its mutagenicity, standard practice is to use a second cohort of animals for parallel toxicogenomics studies; however, the impact of BrdU on global gene expression is unknown. To test this, we performed a case study to determine whether the molecular mode of action of furan, a liver carcinogen, could be detected in BrdU-treated samples. We measure global hepatic gene expression using Agilent DNA microarrays in female B6C3F1 mice that were sub-chronically exposed to 0, 1, 4, or 8mg/kg bodyweight (bw) per day furan either in the presence (+BrdU) or absence (-BrdU) of BrdU. Exposure to 0.02% BrdU in drinking water for five days resulted in minimal gene expression changes. A comparison of +BrdU versus -BrdU control mice revealed only 11 probes with fold change≥1.5 and false discovery rate (FDR) corrected p≤0.05. The same comparison in the high dose group yielded only 3 differentially expressed probes. Differentially expressed gene lists generated for furan-treated versus control mice and were compared for the -BrdU and +BrdU groups. The high dose of furan had 452 shared probes and 27 and 90 unique probes for -BrdU and +BrdU groups, respectively. These differences did not impact hierarchical clustering. Further, they did not impair detection of the previously reported furan mode of action, which was well represented in the BrdU-treated samples. Taken together, we demonstrate that BrdU treatment does not mask important furan-induced transcriptional changes. We suggest that BrdU-treated mice could be used for toxicogenomic analysis, which would generally halve the number of rodents required for toxicogenomics studies. However, we also recommend that this type of case study be repeated for other chemicals before the use of BrdU-treated animals in omics studies becomes common practice.