Fibrotic liver has prompt recovery after ischemia-reperfusion injury

HNF4α improves hepatocyte regeneration by upregulating PXR

Hepatocyte nuclear factor 4 alpha (HNF4α) and the pregnane X receptor (PXR) are involved in hepatocyte regeneration. It is not clear whether HNF4α is involved in hepatocyte regeneration through the regulation of PXR. This study aims to explore the regulatory relationship between HNF4a and PXR, and whether it affects hepatocyte regeneration. A mouse PXR gene reporter and an HNF4α overexpression plasmid were constructed and transfected into mouse hepatoma cells (Hepa1-6). Overexpression of HNF4α, detection of the PXR gene reporter fluorescence value, PXR gene, and protein expression analysis were conducted to explore the regulatory relationship between HNF4α and PXR. Apoptosis and cell cycle data were measured to verify whether HNF4α is involved in hepatocyte regeneration through PXR. The luciferase gene reporter assay results indicated when HNF4α was overexpressed, the fluorescence value of the PXR gene reporter was higher than that in the control at 24 h. With increasing HNF4α expression, the PXR gene and protein expression increased, indicating that HNF4α binds to the PXR promoter and upregulates PXR expression. Apoptosis and cell cycle analysis results demonstrated that when the expression of HNF4α increased, the expression of PXR increased, the apoptosis rate decreased, and the proliferation rate increased. Meanwhile, when the upward trend of PXR gene expression was inhibited by ketoconazole, the proliferation rate decreased. By inhibiting HNF4α and creating a partial hepatectomy (PHx), we demonstrated that HNF4α can upregulate PXR to promote liver regeneration in vivo. Therefore, HNF4α is shown to improve hepatocyte regeneration by upregulating PXR, which provides a reference for future research on the combined application of drugs for the treatment of liver injury.

Protective Role of Rapamycin in Fibrotic Liver Ischemia/Reperfusion Injury (C57bl/6 Mouse)

BACKGROUND

Liver ischemia/reperfusion injury (IRI) is a well-documented phenomenon that occurs after liver resection and transplantation, posing a significant clinical challenge. We aim to contribute valuable insights into potential therapeutic interventions for fibrotic liver IRI, ultimately advancing our understanding of liver transplantation and resection outcomes.

METHODS

Twenty-four mice were divided randomly into 4 equal groups: [1] the normal group, n = 6; [2] the liver fibrosis (LF) group, n = 6; [3] the LF and IR group, n = 6; and [4] the LF with treatment of rapamycin and IR group; n = 6.

RESULTS

Key biomarkers assessing liver function, alanine aminotransferase and aspartate aminotransferase, significantly decreased with Rapamycin administration. There is a substantial decrease observed in inflammatory cytokines such as interleukin (IL) 6, IL-1B, tumor necrosis factor alpha, Transforming growth factor-beta (TGF-beta), and Inducible nitric oxide synthase (iNOS) with rapamycin treatment. Furthermore, NOX levels, caspase-3, and caspase-9 were reduced after rapamycin administration.

CONCLUSION

The application of rapamycin demonstrates appropriate effects in anti-inflammation, antioxidation, and anti-apoptosis, indicating significant therapeutic potential for fibrotic liver IRI.

Fibrosis Development Linked to Alterations in Glucose and Energy Metabolism and Prooxidant-Antioxidant Balance in Experimental Models of Liver Injury

The development of liver fibrosis is one of the most severe and life-threatening outcomes of chronic liver disease (CLD). For targeted therapy of CLD, it is highly needed to reveal molecular targets for normalizing metabolic processes impaired in damaged liver and associated with fibrosis. In this study, we investigated the morphological and biochemical changes in rat liver models of fibrosis induced by chronic administration of thioacetamide, carbon tetrachloride, bile duct ligation (BDL), and ischemia/reperfusion (I/R), with a specific focus on carbohydrate and energy metabolism. Changes in the levels of substrates and products, as well as enzyme activities of the major glucose metabolic pathways (glycolysis, glucuronidation, and pentose phosphate pathway) were examined in rat liver tissue after injury. We examined key markers of oxidative energy metabolism, such as the activity of the Krebs cycle enzymes, and assessed mitochondrial respiratory activity. In addition, pro- and anti-oxidative status was assessed in fibrotic liver tissue. We found that 6 weeks of exposure to thioacetamide, carbon tetrachloride, BDL or I/R resulted in a decrease in the activity of glycolytic enzymes, retardation of mitochondrial respiration, elevation of glucuronidation, and activation of pentose phosphate pathways, accompanied by a decrease in antioxidant activity and the onset of oxidative stress in rat liver. Resemblance and differences in the changes in the fibrosis models used are described, including energy metabolism alterations and antioxidant status in the used fibrosis models. The least pronounced changes in glucose metabolism and mitochondrial functions in the I/R and thioacetamide models were associated with the least advanced fibrosis. Ultimately, liver fibrosis significantly altered the metabolic profile in liver tissue and the flux of glucose metabolic pathways, which could be the basis for targeted therapy of liver fibrosis in CLD caused by toxic, cholestatic, or I/R liver injury.

Responses of hepatic sinusoidal cells to liver ischemia–reperfusion injury

The liver displays a remarkable regenerative capacity in response to acute liver injury. In addition to the proliferation of hepatocytes during liver regeneration, non-parenchymal cells, including liver macrophages, liver sinusoidal endothelial cells (LSECs), and hepatic stellate cells (HSCs) play critical roles in liver repair and regeneration. Liver ischemia–reperfusion injury (IRI) is a major cause of increased liver damage during liver resection, transplantation, and trauma. Impaired liver repair increases postoperative morbidity and mortality of patients who underwent liver surgery. Successful liver repair and regeneration after liver IRI requires coordinated interplay and synergic actions between hepatic resident cells and recruited cell components. However, the underlying mechanisms of liver repair after liver IRI are not well understood. Recent technological advances have revealed the heterogeneity of each liver cell component in the steady state and diseased livers. In this review, we describe the progress in the biology of liver non-parenchymal cells obtained from novel technological advances. We address the functional role of each cell component in response to liver IRI and the interactions between diverse immune repertoires and non-hematopoietic cell populations during the course of liver repair after liver IRI. We also discuss how these findings can help in the design of novel therapeutic approaches. Growing insights into the cellular interactions during liver IRI would enhance the pathology of liver IRI understanding comprehensively and further develop the strategies for improvement of liver repair.

Exosomes derived from human adipose-derived stem cells alleviate hepatic ischemia-reperfusion (I/R) injury through the miR-183/ALOX5 axis

Ischemia-reperfusion (I/R) injury is a crucial factor causing liver injury in the clinic. Recent research has confirmed that human adipose-derived stem cells (ADSCs) can differentiate into functional hepatocytes. However, the mechanism of the effects of ADSCs in the treatment of liver injury remains unclear. The characteristics of ADSCs were first identified, and exosome-derived ADSCs were isolated and characterized. The function and mechanism of action of miR-183 and arachidonate 5-lipoxygenase (ALOX5) were investigated by functional experiments in HL-7702 cells with I/R injury and in I/R rats. Our data disclosed that exosome release from ADSCs induced proliferation and inhibited apoptosis in HL-7702 cells with I/R injury. The effect of miR-183 was similar to that of exosomes derived from ADSCs. In addition, ALOX5, as a target gene of miR-183, was involved in the related functions of miR-183. Moreover, in vivo experiments confirmed that miR-183 and exosomes from ADSCs could improve liver injury in rats and inhibit the MAPK and NF-κB pathways. All of these findings demonstrate that exosomes derived from ADSCs have a significant protective effect on hepatic I/R injury by regulating the miR-183/ALOX5 axis, which might provide a therapeutic strategy for liver injury.

Hepatic stellate cell-released CXCL1 aggravates HCC malignant behaviors through the MIR4435-2HG/miR-506-3p/TGFB1 axis

Hepatic stellate cell (HSC) activation is a critical event in the development of hepatic fibrosis and hepatocellular carcinoma (HCC). By the release of soluble cytokines, chemokines, and chemotaxis, HSCs affect HCC cell phenotypes through a complex tumor microenvironment. In this study, weighted gene co-expression network analysis (WGCNA) was used to identify the TGF-β signaling pathway as a key signaling pathway in Hep3B cells cultured in HSC conditioned medium. MIR4435-2HG is a hub lncRNA associated with the TGF-β signaling pathway and HSC activation. HSC-condition medium (CM) culture induced HCC cell malignant behaviors, which were partially reversed by MIR4435-2HG silencing. miR-506-3p directly bound to MIR4435-2HG and the 3'UTR of TGFB1. Similarly, overexpression of miR-506-3p also attenuated HSC-CM-induced malignant behavior of HCC cells. In HSC-CM cultured HCC cells, the effects of MIR4435-2HG knockdown on TGFB1 expression and HCC cell phenotypes were partially reversed by miR-506-3p inhibition. HSCs affected HCC cell phenotypes by releasing CXCL1. In an orthotopic xenotransplanted tumor model of HCC cells plus HSCs in mice, CXCR2 knockdown in HCC cells significantly inhibited tumorigenesis, which was partially reversed by MIR4435-2HG overexpression in HCC cells. In HCC tissue samples, the levels of CXCL1, TGF-β1, and MIR4435-2HG were upregulated, while miR-506-3p expression was downregulated. In conclusion, HSC-released CXCL1 aggravated HCC cell malignant behaviors through the MIR4435-2HG/miR-506-3p/TGFB1 axis. In addition to CXCL1, the MIR4435-2HG/miR-506-3p/TGFB1 axis might also be the underlying target for HCC therapy.

Regulatory Networks, Management Approaches, and Emerging Treatments of Nonalcoholic Fatty Liver Disease

The pathogenesis of NAFLD is complex and diverse, involving multiple signaling pathways and cytokines from various organs. Hepatokines, stellakines, adipokines, and myokines secreted by hepatocytes, hepatic stellate cells, adipose tissue, and myocytes play an important role in the occurrence and development of nonalcoholic fatty liver disease (NAFLD). The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) contributes to the progression of NAFLD by mediating liver inflammation, immune response, hepatocyte death, and later compensatory proliferation. In this review, we first discuss the crosstalk and interaction between hepatokines, stellakines, adipokines, and myokines and NF-κB in NAFLD. The characterization of the crosstalk of NF-κB with these factors will provide a better understanding of the molecular mechanisms involved in the progression of NAFLD. In addition, we examine new expert management opinions for NAFLD and explore the therapeutic potential of silymarin in NAFLD/NASH.

Molecular Mechanisms of Ischaemia-Reperfusion Injury and Regeneration in the Liver-Shock and Surgery-Associated Changes

Hepatic ischemia-reperfusion injury (IRI) represents a major challenge during liver surgery, liver preservation for transplantation, and can cause hemorrhagic shock with severe hypoxemia and trauma. The reduction of blood supply with a concomitant deficit in oxygen delivery initiates various molecular mechanisms involving the innate and adaptive immune response, alterations in gene transcription, induction of cell death programs, and changes in metabolic state and vascular function. Hepatic IRI is a major cause of morbidity and mortality, and is associated with an increased risk for tumor growth and recurrence after oncologic surgery for primary and secondary hepatobiliary malignancies. Therapeutic strategies to prevent or treat hepatic IRI have been investigated in animal models but, for the most part, have failed to provide a protective effect in a clinical setting. This review focuses on the molecular mechanisms underlying hepatic IRI and regeneration, as well as its clinical implications. A better understanding of this complex and highly dynamic process may allow for the development of innovative therapeutic approaches and optimize patient outcomes.

PIAS1 Alleviates Hepatic Ischemia-Reperfusion Injury in Mice through a Mechanism Involving NFATc1 SUMOylation

Recently, attentions have come to the alleviatory effect of protein inhibitor of activated STAT1 (PIAS1) in hepatic ischemia-reperfusion injury (HIRI), but the underlying molecular mechanistic actions remain largely unknown, which were illustrated in the present study. Microarray-based analysis predicted a possible regulatory mechanism involving the PIAS1/NFATc1/HDAC1/IRF-1/p38 MAPK signaling axis in HIRI. Then, growth dynamics of hypoxia/reoxygenation- (H/R-) exposed hepatocytes and liver injury of HIRI-like mice were delineated after the alteration of the PIAS1 expression. We validated that PIAS1 downregulation occurred in H/R-exposed hepatocytes and HIRI-like mice, while the expression of NFATc1, HDAC1, and IRF-1 and phosphorylation levels of p38 were increased. PIAS1 inactivated p38 MAPK signaling by inhibiting HDAC1-mediated IRF-1 through NFATc1 SUMOylation, thereby repressing the inflammatory response and apoptosis of hepatocytes in vitro, and alleviated liver injury in vivo. Collectively, the NFATc1/HDAC1/IRF-1/p38 MAPK signaling axis is highlighted as a promising therapeutic target for potentiating hepatoprotective effects of PIAS1 against HIRI.

Role of hepatic stellate cells in liver ischemia-reperfusion injury

Liver ischemia-reperfusion injury (IRI) is a major complication of liver trauma, resection, and transplantation. IRI may lead to liver dysfunction and failure, but effective approach to address it is still lacking. To better understand the cellular and molecular mechanisms of liver IRI, functional roles of numerous cell types, including hepatocytes, Kupffer cells, neutrophils, and sinusoidal endothelial cells, have been intensively studied. In contrast, hepatic stellate cells (HSCs), which are well recognized by their essential functions in facilitating liver protection and repair, have gained less attention in their role in IRI. This review provides a comprehensive summary of the effects of HSCs on the injury stage of liver IRI and their associated molecular mechanisms. In addition, we discuss the regulation of liver repair and regeneration after IRI by HSCs. Finally, we highlight unanswered questions and future avenues of research regarding contributions of HSCs to IRI in the liver.

Liver Ischemia and Reperfusion Induce Periportal Expression of Necroptosis Executor pMLKL Which Is Associated With Early Allograft Dysfunction After Transplantation

Background

Early allograft dysfunction (EAD) following liver transplantation (LT) remains a major threat to the survival of liver grafts and recipients. In animal models, it is shown that hepatic ischemia-reperfusion injury (IRI) triggers phosphorylation of Mixed Lineage Kinase domain-like protein (pMLKL) inducing necroptotic cell death. However, the clinical implication of pMLKL-mediated cell death in human hepatic IRI remains largely unexplored. In this study, we aimed to investigate the expression of pMLKL in human liver grafts and its association with EAD after LT.

Methods

The expression of pMLKL was determined by immunohistochemistry in liver biopsies obtained from both human and rat LT. Human liver biopsies were obtained at the end of preservation (T0) and ~1 hour after reperfusion (T1). The positivity of pMLKL was quantified electronically and compared in rat and human livers and post-LT outcomes. Multiplex immunofluorescence staining was performed to characterize the pMLKL-expressing cells.

Results

In the rat LT model, significant pMLKL expression was observed in livers after IRI as compared to livers of sham-operation animals. Similarly, the pMLKL score was highest after IRI in human liver grafts (in T1 biopsies). Both in rats and humans, the pMLKL expression is mostly observed in the portal triads. In grafts who developed EAD after LT (n=24), the pMLKL score at T1 was significantly higher as compared to non-EAD grafts (n=40). ROC curve revealed a high predictive value of pMLKL score at T1 (AUC 0.70) and the ratio of pMLKL score at T1 and T0 (pMLKL-index, AUC 0.82) for EAD. Liver grafts with a high pMLKL index (>1.64) had significantly higher levels of serum ALT, AST, and LDH 24 hours after LT compared to grafts with a low pMLKL index. Multivariate logistical regression analysis identified the pMLKL-index (Odds ratio=1.3, 95% CI 1.1-1.7) as a predictor of EAD development. Immunohistochemistry on serial sections and multiplex staining identified the periportal pMLKL-positive cells as portal fibroblasts, fibrocytes, and a minority of cholangiocytes.

Conclusion

Periportal pMLKL expression increased significantly after IRI in both rat and human LT. The histological score of pMLKL is predictive of post-transplant EAD and is associated with early liver injury after LT. Periportal non-parenchymal cells (i.e. fibroblasts) appear most susceptible to pMLKL-mediated cell death during hepatic IRI.

Therapeutic potential of macrophage colony-stimulating factor (CSF1) in chronic liver disease

Resident and recruited macrophages control the development and proliferation of the liver. We showed previously in multiple species that treatment with a macrophage colony stimulating factor (CSF1)-Fc fusion protein initiated hepatocyte proliferation and promoted repair in models of acute hepatic injury in mice. Here we investigated the impact of CSF1-Fc on resolution of advanced fibrosis and liver regeneration, utilizing a non-resolving toxin-induced model of chronic liver injury and fibrosis in C57BL/6J mice. Co-administration of CSF1-Fc with exposure to thioacetamide (TAA) exacerbated inflammation consistent with monocyte contributions to initiation of pathology. After removal of TAA, either acute or chronic CSF1-Fc treatment promoted liver growth, prevented progression and promoted resolution of fibrosis. Acute CSF1-Fc treatment was also anti-fibrotic and pro-regenerative in a model of partial hepatectomy in mice with established fibrosis. The beneficial impacts of CSF1-Fc treatment were associated with monocyte-macrophage recruitment and increased expression of remodeling enzymes and growth factors. These studies indicate that CSF1-dependent macrophages contribute to both initiation and resolution of fibrotic injury and that CSF1-Fc has therapeutic potential in human liver disease.

Functions of macrophage colony-stimulating factor (CSF1) in development, homeostasis, and tissue repair

Macrophage colony-stimulating factor (CSF1) is the primary growth factor required for the control of monocyte and macrophage differentiation, survival, proliferation and renewal. Although the cDNAs encoding multiple isoforms of human CSF1 were cloned in the 1980s, and recombinant proteins were available for testing in humans, CSF1 has not yet found substantial clinical application. Here we present an overview of CSF1 biology, including evolution, regulation and functions of cell surface and secreted isoforms. CSF1 is widely-expressed, primarily by cells of mesenchymal lineages, in all mouse tissues. Cell-specific deletion of a floxed Csf1 allele in mice indicates that local CSF1 production contributes to the maintenance of tissue-specific macrophage populations but is not saturating. CSF1 in the circulation is controlled primarily by receptor-mediated clearance by macrophages in liver and spleen. Administration of recombinant CSF1 to humans or animals leads to monocytosis and expansion of tissue macrophage populations and growth of the liver and spleen. In a wide variety of tissue injury models, CSF1 administration promotes monocyte infiltration, clearance of damaged cells and repair. We suggest that CSF1 has therapeutic potential in regenerative medicine.

Donor Hepatic Occult Collagen Deposition Predisposes to Peritransplant Stress and Impacts Human Liver Transplantation

BACKGROUND AND AIMS

Environmentally triggered chronic liver inflammation can cause collagen deposits, whereas early stages of fibrosis without any specific symptoms could hardly be detectable. We hypothesized that some of the human donor grafts in clinical liver transplantation (LT) might possess unrecognizable fibrosis, affecting their susceptibility to LT-induced stress and hepatocellular damage. This retrospective study aimed to assess the impact of occult hepatic fibrosis on clinical LT outcomes.

APPROACH AND RESULTS

Human (194) donor liver biopsies were stained for collagen with Sirius red, and positive areas (Sirius red-positive area; SRA) were measured. The body mass index, aspartate aminotransferase/alanine aminotransferase ratio, diabetes score was calculated using 962 cases of the donor data at the procurement. LT outcomes, including ischemia-reperfusion injury (IRI), early allograft dysfunction (EAD), and survival rates, were analyzed according to SRA and BARD scores. With the median SRA in 194 grafts of 9.4%, grafts were classified into low-SRA (<15%; n = 140) and high-SRA (≥15%; n = 54) groups. Grafts with high SRA suffered from higher rates of IRI and EAD (P < 0.05) as compared to those with low SRA. Interestingly, high SRA was identified as an independent risk factor for EAD and positively correlated with the donor BARD score. When comparing low-BARD (n = 692) with high-BARD (n = 270) grafts in the same period, those with high BARD showed significantly higher post-LT transaminase levels and higher rates of IRI and EAD.

CONCLUSIONS

These findings from the largest clinical study cohort to date document the essential role of occult collagen deposition in donor livers on LT outcomes. High-SRA and donor BARD scores correlated with an increased incidence of hepatic IRI and EAD in LT recipients. This study provides the rationale for in-depth and prospective assessment of occult fibrosis for refined personalized LT management.

IL-34 and CSF-1, deciphering similarities and differences at steady state and in diseases

Although IL-34 and CSF-1 share actions as key mediators of monocytes/macrophages survival and differentiation, they also display differences that should be identified to better define their respective roles in health and diseases. IL-34 displays low sequence homology with CSF-1 but has a similar general structure and they both bind to a common receptor CSF-1R, although binding and subsequent intracellular signaling shows differences. CSF-1R expression has been until now mainly described at a steady state in monocytes/macrophages and myeloid dendritic cells, as well as in some cancers. IL-34 has also 2 other receptors, protein-tyrosine phosphatase zeta (PTPζ) and CD138 (Syndecan-1), expressed in some epithelium, cells of the central nervous system (CNS), as well as in numerous cancers. While most, if not all, of CSF-1 actions are mediated through monocyte/macrophages, IL-34 has also other potential actions through PTPζ and CD138. Additionally, IL-34 and CSF-1 are produced by different cells in different tissues. This review describes and discusses similarities and differences between IL-34 and CSF-1 at steady state and in pathological situations and identifies possible ways to target IL-34, CSF-1, and its receptors.

Distinct Neutrophil Populations in the Spleen During PICS

While mortality after acute sepsis has decreased, the long-term recovery for survivors is still poor, particularly those developing persistent inflammation, immunosuppression, and catabolism syndrome (PICS). While previously thought that activated neutrophils responding to the acute phase of sepsis migrate to the spleen to undergo cell death and contribute to immunosuppression, our data show a significant accumulation of distinct, yet functional, neutrophil populations in the spleen in a murine model of PICS. The exact role and function of neutrophils in this response is still unclear. The objective of our study was to better define the immune function of splenic neutrophils to determine if this could give insight into the pathogenesis of PICS. Using a murine model of cecal ligation and puncture (CLP), which demonstrates all characteristics of PICS by 8 days, spleens were harvested, and neutrophils were identified by Ly6G and CD11b expression via flow cytometry. Nearly all splenic neutrophils expressed CD54, but there were distinct CD54^hi and CD54^lo cells, with the majority being CD54^lo cells during PICS. The CD54^hi population showed traditional, proinflammatory properties, but a relatively decreased chemotactic response, while CD54^lo cells had significantly higher chemotaxis, yet significantly decreased proinflammatory functions. Using 5-ethynyl-2′-deoxyuridine (EdU) incorporation, we found that the CD54^hi population on day 2 after CLP may be participating in emergency myelopoiesis. However, the vast majority of the CD54^lo population were paused in the G₁ phase at this time point and not proliferating. By day 8 after CLP, most of the CD54^hi cells in the spleen were no longer proliferating, while the CD54^lo cells were, indicating that CD54^lo dominate in extramedullary myelopoiesis at later time points. Almost none of the neutrophils produced arginase or inducible nitric oxide synthase (iNOS), indicating that these are not suppressor cells. Overall, our data demonstrate that neutrophil accumulation in the spleen during PICS is related to extramedullary myelopoiesis, leading to the production of immature neutrophils. While not suppressor cells, the majority have greater chemotactic function but less inflammatory responsiveness, which may contribute to the immunosuppression seen in PICS. Attention to these distinct neutrophil populations after septic or other systemic inflammatory responses is therefore critical to understanding the mechanisms of PICS.