Novel therapeutic avenues for the study of chronic liver disease and regeneration: The foundation of the Iberoamerican Consortium for the study of liver Cirrhosis / Nuevas dianas terapéuticas para el estudio de la enfermedad hepática crónica: la creación del Consorcio Iberoamericano para el estudio de la cirrosis hepática

Unfortunately, there is a gap of understanding in the pathophysiology of chronic liver disease due to the lack of experimental models that exactly mimic the human disease. Additionally, the diagnosis of patients is very poor due to the lack of biomarkers than can detect the disease in early stages. Thus, it is of utmost interest the generation of a multidisciplinary consortium from different countries with a direct translation. The present reports the meeting of the 2021 Iberoamerican Consortium for the study of liver Cirrhosis, held online, in October 2021. The meeting, was focused on the recent advancements in the field of chronic liver disease and cirrhosis with a specific focus on cell pathobiology and liver regeneration, molecular and cellular targets involved in non-alcoholic hepatic steatohepatitis, alcoholic liver disease (ALD), both ALD and western diet, and end-stage liver cirrhosis and hepatocellular carcinoma. In addition, the meeting highlighted recent advances in targeted novel technology (-omics) and opening therapeutic avenues in this field of research.(AU)

Desafortunadamente, existe una brecha sobre la comprensión en la fisiopatología de la enfermedad hepática crónica debido a la falta de modelos experimentales que recapitulan con exactitud la enfermedad humana. Además, el diagnóstico de los pacientes es muy pobre debido a la falta de biomarcadores que puedan detectar la enfermedad en etapas tempranas. Por ello, es de sumo interés la generación de un consorcio multidisciplinar de diferentes países con una traducción directa. El presente artículo informa sobre la reunión del Consorcio Iberoamericano para el estudio de la cirrosis hepática 2021, celebrado de manera virtual en octubre del 2021. La reunión se centró en los avances recientes en el campo de la enfermedad hepática crónica y la cirrosis, con un enfoque específico en la patobiología celular y regeneración hepática, dianas moleculares y celulares involucradas en la esteatohepatitis hepática no alcohólica, la enfermedad hepática alcohólica (ALD), tanto la ALD como la dieta occidental, y la cirrosis hepática en etapa terminal y el carcinoma hepatocelular. Además, la reunión destacó los avances recientes en tecnología (ómica) y la apertura de vías terapéuticas en este campo de investigación.(AU)

Tumor progression locus 2 (TPL2): A Cot-plicated progression from inflammation to chronic liver disease.

The cytoplasmic protein tumor progression locus 2 (TPL2), also known as cancer Osaka thyroid (Cot), or MAP3K8, is thought to have a significant role in a variety of cancers and illnesses and it is a key component in the activation pathway for the expression of inflammatory mediators. Despite the tight connection between inflammation and TPL2, its function has not been extensively studied in chronic liver disease (CLD), a major cause of morbidity and mortality worldwide. Here, we analyze more in detail the significance of TPL2 in CLD to shed light on the pathological and molecular transduction pattern of TPL2 during the progression of CLD. This might result in important advancements and enable progress in the diagnosis and treatment of CLD.

Connections between postparotid terminal branches of the facial nerve: An immunohistochemistry study.

It has been assumed that connections between the postparotid terminal branches of the facial nerve are purely motor. However, the nature of their fibers remains unexplored. The aim of this study is to determine whether these connections comprise motor fibers exclusively. In total 17 connections between terminal facial nerve branches were obtained from 13 different facial nerves. Choline acetyltransferase antibody (ChAT) was used to stain the fibers in the connections and determine whether or not all of them were motor. All connections contained ChAT positive and negative fibers. The average number of fibers overall was 287 (84-587) and the average proportion of positive fibers was 63% (37.7%-91.5%). In 29% of the nerves, >75% of the fibers were ChAT+ (strongly positive); in 52.94%, 50%-75% were ChAT+ (intermediately positive); and in 17.65%, <50% were ChAT+ (weakly positive). Fibers traveling inside the postparotid terminal cranial nerve VII branch connections are not exclusively motor.

Novel therapeutic avenues for the study of chronic liver disease and regeneration: The foundation of the Iberoamerican Consortium for the study of liver Cirrhosis.

Unfortunately, there is a gap of understanding in the pathophysiology of chronic liver disease due to the lack of experimental models that exactly mimic the human disease. Additionally, the diagnosis of patients is very poor due to the lack of biomarkers than can detect the disease in early stages. Thus, it is of utmost interest the generation of a multidisciplinary consortium from different countries with a direct translation. The present reports the meeting of the 2021 Iberoamerican Consortium for the study of liver Cirrhosis, held online, in October 2021. The meeting, was focused on the recent advancements in the field of chronic liver disease and cirrhosis with a specific focus on cell pathobiology and liver regeneration, molecular and cellular targets involved in non-alcoholic hepatic steatohepatitis, alcoholic liver disease (ALD), both ALD and western diet, and end-stage liver cirrhosis and hepatocellular carcinoma. In addition, the meeting highlighted recent advances in targeted novel technology (-omics) and opening therapeutic avenues in this field of research.

Fat: Quality, or Quantity? What Matters Most for the Progression of Metabolic Associated Fatty Liver Disease (MAFLD).

OBJECTIVES: Lately, many countries have restricted or even banned transfat, and palm oil has become a preferred replacement for food manufacturers. Whether palm oil is potentially an unhealthy food mainly due to its high content of saturated Palmitic Acid (PA) is a matter of debate. The aim of this study was to test whether qualitative aspects of diet such as levels of PA and the fat source are risk factors for Metabolic Syndrome (MS) and Metabolic Associated Fatty Liver Disease (MAFLD). METHODS: C57BL/6 male mice were fed for 14 weeks with three types of Western diet (WD): 1. LP-WD-low concentration of PA (main fat source-corn and soybean oils); 2. HP-WD-high concentration of PA (main fat source-palm oil); 3. HP-Trans-WD-high concentration of PA (mainly transfat). RESULTS: All types of WD caused weight gain, adipocyte enlargement, hepatomegaly, lipid metabolism alterations, and steatohepatitis. Feeding with HP diets led to more prominent obesity, hypercholesterolemia, stronger hepatic injury, and fibrosis. Only the feeding with HP-Trans-WD resulted in glucose intolerance and elevation of serum transaminases. Brief withdrawal of WDs reversed MS and signs of MAFLD. However, mild hepatic inflammation was still detectable in HP groups. CONCLUSIONS: HP and HP-Trans-WD play a crucial role in the genesis of MS and MAFLD.

Identification of a MicroRNA-E3 Ubiquitin Ligase Regulatory Network for Hepatocyte Death in Alcohol-Associated Hepatitis.

We aimed to identify a microRNA (miRNA)-E3 ubiquitin ligase regulatory network for protein substrates enriched in cell death pathways and investigate the underlying molecular mechanisms in alcohol-associated hepatitis (AH). An miRNA-E3 ubiquitin ligase regulatory network for protein substrates enriched in cell death pathways was constructed using integrated bioinformatics analysis. Differentially expressed hub miRNAs (GSE59492) and their validated miRNA target genes (GSE28619) were identified in the liver of patients with AH compared with healthy controls. Liver samples from patients with AH and healthy individuals and mice exposed to Gao-binge (acute on chronic) ethanol were used for experimental validation. Using hub miRNAs identified by weighted correlation network analysis, a miRNA-E3 ubiquitin ligase regulatory network was established based on 17 miRNAs and 7 E3 ligase genes targeted by these miRNAs that were down-regulated in AH. Among the miRNAs in this regulatory network, miR-150-5p was the only miRNA regulating the E3 ligase cytokine-inducible SH2 containing protein (CISH), the E3 ligase that regulates the largest number of substrates among all E3 ligase family members. Therefore, the CISH regulatory pathway for ubiquitinated substrates was selected for subsequent experimental validation. Consistent with the bioinformatics analysis results, expression of miR-150-5p was markedly increased, while CISH was decreased, in the livers of patients with AH and mice exposed to Gao-binge ethanol. Moreover, ubiquitination of Fas-associated protein with death domain, a predicted CISH substrate involved in the regulation of programmed cell death, was reduced in livers from mice after Gao-binge ethanol. Conclusion: Identification of the miRNA-E3 ubiquitin ligase regulatory network for protein substrates enriched in the cell death pathways provides insights into the molecular mechanisms contributing to hepatocyte death in AH.

Differential role of MLKL in alcohol-associated and non-alcohol-associated fatty liver diseases in mice and humans.

Hepatocellular death contributes to progression of alcohol-associated (ALD-associated) and non-alcohol-associated (NAFL/NASH) liver diseases. However, receptor-interaction protein kinase 3 (RIP3), an intermediate in necroptotic cell death, contributes to injury in murine models of ALD but not NAFL/NASH. We show here that a differential role for mixed-lineage kinase domain-like protein (MLKL), the downstream effector of RIP3, in murine models of ALD versus NAFL/NASH and that RIP1-RIP3-MLKL can be used as biomarkers to distinguish alcohol-associated hepatitis (AH) from NASH. Phospho-MLKL was higher in livers of patients with NASH compared with AH or healthy controls (HCs). MLKL expression, phosphorylation, oligomerization, and translocation to plasma membrane were induced in WT mice fed diets high in fat, fructose, and cholesterol but not in response to Gao-binge (acute on chronic) ethanol exposure. Mlkl-/- mice were not protected from ethanol-induced hepatocellular injury, which was associated with increased expression of chemokines and neutrophil recruitment. Circulating concentrations of RIP1 and RIP3, but not MLKL, distinguished patients with AH from HCs or patients with NASH. Taken together, these data indicate that MLKL is differentially activated in ALD/AH compared with NAFL/NASH in both murine models and patients. Furthermore, plasma RIP1 and RIP3 may be promising biomarkers for distinguishing AH and NASH.

MLKL-dependent signaling regulates autophagic flux in a murine model of non-alcohol-associated fatty liver and steatohepatitis.

BACKGROUND & AIMS: Autophagy maintains cellular homeostasis and plays a critical role in the development of non-alcoholic fatty liver and steatohepatitis. The pseudokinase mixed lineage kinase domain-like (MLKL) is a key downstream effector of receptor interacting protein kinase 3 (RIP3) in the necroptotic pathway of programmed cell death. However, recent data reveal that MLKL also regulates autophagy. Herein, we tested the hypothesis that MLKL contributes to the progression of Western diet-induced liver injury in mice by regulating autophagy. METHODS: Rip3+/+, Rip3-/-, Mlkl+/+ and Mlkl-/- mice were fed a Western diet (FFC diet, high in fat, fructose and cholesterol) or chow for 12 weeks. AML12 and primary mouse hepatocytes were exposed to palmitic acid (PA). RESULTS: The FFC diet increased expression, phosphorylation and oligomerization of MLKL in the liver. Mlkl, but not Rip3, deficiency protected mice from FFC diet-induced liver injury. The FFC diet also induced accumulation of p62 and LC3-II, as well as markers of endoplasmic reticulum stress, in Mlkl+/+ but not Mlkl-/- mice. Mlkl deficiency in mice also prevented the inhibition of autophagy by a protease inhibitor, leupeptin. Using an mRFP-GFP-LC3 reporter in cultured hepatocytes revealed that PA blocked the fusion of autophagosomes with lysosomes. PA triggered MLKL expression and translocation, first to autophagosomes and then to the plasma membrane, independently of Rip3. Mlkl, but not Rip3, deficiency prevented inhibition of autophagy in PA-treated hepatocytes. Overexpression of Mlkl blocked autophagy independently of PA. Additionally, pharmacologic inhibition of autophagy induced MLKL expression and translocation to the plasma membrane in hepatocytes. CONCLUSIONS: Taken together, these data indicate that MLKL-dependent, but RIP3-independent, signaling contributes to FFC diet-induced liver injury by inhibiting autophagy. LAY SUMMARY: Autophagy is a regulated process that maintains cellular homeostasis. Impaired autophagy contributes to cell injury and death, thus playing a critical role in the pathogenesis of a number of diseases, including non-alcohol-associated fatty liver and steatohepatitis. Herein, we show that Mlkl-dependent, but Rip3-independent, signaling contributed to diet-induced liver injury and inflammatory responses by inhibiting autophagy. These data identify a novel co-regulatory mechanism between necroptotic and autophagic signaling pathways in non-alcoholic fatty liver disease.

Nontranscriptional Activity of Interferon Regulatory Factor 3 Protects Mice From High-Fat Diet-Induced Liver Injury.

Interferon regulatory factor 3 (IRF3) has both transcriptional and nontranscriptional functions. Transcriptional activity is dependent on serine phosphorylation of IRF3, while transcription-independent IRF3-mediated apoptosis requires ubiquitination. IRF3 also binds to inhibitor of nuclear factor kappa B kinase (IKKß) in the cytosol, restricting nuclear translocation of p65. IRF3-deficient mice are highly sensitive to high-fat diet (HFD)-induced liver injury; however, it is not known if transcriptional and/or nontranscriptional activity of IRF3 confers protection. Using a mouse model only expressing nontranscriptional functions of IRF3 (Irf3 S1/S1), we tested the hypothesis that nontranscriptional activity of IRF3 protects mice from HFD-induced liver injury. C57BL/6, Irf3 -/-, and Irf3 S1/S1 mice were fed an HFD for 12 weeks. In C57BL/6 mice, the HFD increased expression of interferon (IFN)-dependent genes, despite a decrease in IRF3 protein in the liver. The HFD had no impact on IFN-dependent gene expression Irf3 -/- or Irf3 S1/S1 mice, both lacking IRF3 transcriptional activity. Liver injury, apoptosis, and fibrosis were exacerbated in Irf3 -/- compared to C57BL/6 mice following the HFD; this increase was ameliorated in Irf3 S1/S1 mice. Similarly, expression of inflammatory cytokines as well as numbers of neutrophils and infiltrating monocytes was increased in Irf3 -/- mice compared to C57BL/6 and Irf3 S1/S1 mice. While the HFD increased the ubiquitination of IRF3, a response associated with IRF3-mediated apoptosis, in Irf3 S1/S1 mice, protection from liver injury was not due to differences in apoptosis of hepatocytes or immune cells. Instead, protection from HFD-induced liver injury in Irf3 S1/S1 mice was primarily associated with retardation of nuclear translocation of p65 and decreased expression of nuclear factor kappa B (NFκB)-dependent inflammatory cytokines. Conclusion: Taken together, these data identify important contributions of the nontranscriptional function of IRF3, likely by reducing NFκB signaling, in dampening the hepatic inflammatory environment in response to an HFD.

The non-transcriptional activity of IRF3 modulates hepatic immune cell populations in acute-on-chronic ethanol administration in mice.

BACKGROUND & AIMS: Interferon regulatory factor 3 (IRF3) is a transcription factor mediating antiviral responses, yet recent evidence indicates that IRF3 also has critical non-transcriptional functions, including activating RIG-I-like receptors-induced IRF-3-mediated pathway of apoptosis (RIPA) and restricting activity of NF-κB. Using a novel murine model expressing only non-transcriptional IRF3 activity (Irf3S1/S1), we tested the hypothesis that non-transcriptional functions of IRF3 modulate innate immune responses in the Gao-binge (acute-on-chronic) model of alcohol-related liver disease. METHODS: IRF3 and IRF3-mediated signals were analysed in liver samples from 5 patients transplanted for alcoholic hepatitis and 5 healthy controls. C57BL/6, Irf3-/- and Irf3S1/S1 mice were exposed to Gao-binge ethanol-induced liver injury. IRF3-mediated RIPA was investigated in cultured macrophages. RESULTS: Phospho-IRF3 and IRF3-mediated signals were elevated in livers of patients with alcoholic hepatitis. In C57BL/6 mice, Gao-binge ethanol exposure activated IRF3 signaling and resulted in hepatocellular injury. Indicators of liver injury were differentially impacted by Irf3 genotype. Irf3-/-, but not Irf3S1/S1, mice were protected from steatosis, elevated alanine/aspartate aminotransferase levels and inflammatory cytokine expression. In contrast, neutrophil accumulation and endoplasmic reticulum stress were independent of genotype. Protection from Gao-binge injury in Irf3-/- mice was associated with an increased ratio of Ly6Clow (restorative) to Ly6Chigh (inflammatory) cells compared to C57BL/6 and Irf3S1/S1 mice. Reduced ratios of Ly6Clow/Ly6Chigh in C57BL/6 and Irf3S1/S1 mice were associated with increased apoptosis in the Ly6Clow population in response to Gao-binge. Activation of primary macrophage cultures with Poly (I:C) induced translocation of IRF3 to the mitochondria, where it associated with Bax and activated caspases 3 and 9, processes indicative of activation of the RIPA pathway. CONCLUSIONS: Taken together, these data identify that the non-transcriptional function of IRF3 plays an important role in modulating the innate immune environment in response to Gao-binge ethanol exposure, via regulation of immune cell apoptosis. LAY SUMMARY: Activation of the innate immune system contributes to inflammation in the progression of alcohol-related liver disease, as well as to the resolution of injury. Here we show that the protein IRF3 modulates the innate immune environment of the liver in a mouse model of alcoholic hepatitis. It does this by increasing the apoptotic cell death of immune cells that promote the resolution of injury.

Hepatic Immune System: Adaptations to Alcohol.

Both the innate and adaptive immune systems are critical for the maintenance of healthy liver function. Immune activity maintains the tolerogenic capacity of the liver, modulates hepatocellular response to various stresses, and orchestrates appropriate cellular repair and turnover. However, in response to heavy, chronic alcohol exposure, the finely tuned balance of pro- and anti-inflammatory functions in the liver is disrupted, leading to a state of chronic inflammation in the liver. Over time, this non-resolving inflammatory response contributes to the progression of alcoholic liver disease (ALD). Here we review the contributions of the cellular components of the immune system to the progression of ALD, as well as the pathophysiological roles for soluble and circulating mediators of immunity, including cytokines, chemokines, complement, and extracellular vesicles, in ALD. Finally, we compare the role of the innate immune response in health and disease in the liver to our growing understanding of the role of neuroimmunity in the development and maintenance of a healthy central nervous system, as well as the progression of neuroinflammation.

Myeloid-MyD88 Contributes to Ethanol-Induced Liver Injury in Mice Linking Hepatocellular Death to Inflammation.

BACKGROUND: Toll-like receptor 4 (TLR4) is critical for ethanol (EtOH)-induced liver injury. TLR4 signaling is mediated by 2 proximal adaptor molecules: myeloid differentiation primary response protein (MyD88) and TLR-domain-containing adaptor-inducing interferon-ß (TRIF). Studies utilizing global knockouts of MyD88 and TRIF identified a predominant role for TRIF signaling in the progression of EtOH-induced liver injury. In contrast, IL-1 receptor, which signals solely via the MyD88 pathway, is also known to mediate EtOH-induced liver injury. We postulated that a cell-specific role for MyD88 in myeloid cells might explain these apparently discrepant roles of MyD88. Here we made use of myeloid-specific MyD88-deficient (MyD88LysM-KO ) mice generated by crossing LysM-CRE mice with MyD88fl/fl mice to test this hypothesis. METHODS: MyD88LysM-KO and littermate controls were fed a Lieber-DeCarli EtOH-containing diet or pair-fed control diets for 25 days. RESULTS: Littermate control, but not MyD88LysM-KO , mice developed early stages of EtOH-induced liver injury including elevated plasma alanine aminotransferase and increased hepatic triglycerides. Lobular inflammation and expression of pro-inflammatory cytokines/chemokines was increased in control but not MyD88LysM-KO . Further, EtOH-induced inflammasome activation, indicated by the presence of cleaved caspase-1 and mature IL-1ß protein, was also ameliorated in livers of MyD88LysM-KO mice. In contrast, chronic EtOH-induced apoptosis, assessed via TUNEL staining, was independent of myeloid-MyD88 expression. CONCLUSIONS: Collectively, these data demonstrate a cell-specific role for MyD88 in the development of chronic EtOH-induced liver injury. While MyD88LysM-KO still exhibited hepatocellular apoptosis in response to chronic EtOH, the absence of MyD88 on myeloid cells prevented the development of hepatic steatosis and inflammation.

Map3k8 Modulates Monocyte State and Atherogenesis in ApoE-/- Mice.

OBJECTIVE: Map3k8 (Cot/Tpl2) activates the MKK1/2-ERK1/2, MAPK pathway downstream from interleukin-1R, tumor necrosis factor-αR, NOD-2R (nucleotide-binding oligomerization domain-like 2R), adiponectinR, and Toll-like receptors. Map3k8 plays a key role in innate and adaptive immunity and influences inflammatory processes by modulating the functions of different cell types. However, its role in atherogenesis remains unknown. In this study, we analyzed the role of this kinase in this pathology. APPROACH AND RESULTS: We show here that Map3k8 deficiency results in smaller numbers of Ly6ChighCD11clow and Ly6ClowCD11chigh monocytes in ApoE-/- mice fed a high-fat diet (HFD). Map3k8-/-ApoE-/- monocytes displayed high rates of apoptosis and reduced amounts of Nr4a1, a transcription factor known to modulate apoptosis in Ly6ClowCD11chigh monocytes. Map3k8-/-ApoE-/- splenocytes and macrophages showed irregular patterns of cytokine and chemokine expression. Map3k8 deficiency altered cell adhesion and migration in vivo and decreased CCR2 expression, a determinant chemokine receptor for monocyte mobilization, on circulating Ly6ChighCD11clow monocytes. Map3k8-/-ApoE-/- mice fed an HFD showed decreased cellular infiltration in the atherosclerotic plaque, with low lipid content. Lesions had similar size after Map3k8+/+ApoE-/- bone marrow transplant into Map3k8-/-ApoE-/- and Map3k8+/+ApoE-/- mice fed an HFD, whereas smaller plaques were observed after the transplantation of bone marrow lacking both ApoE and Map3k8. CONCLUSIONS: Map3k8 decreases apoptosis of monocytes and enhances CCR2 expression on Ly6ChighCD11clow monocytes of ApoE-/- mice fed an HFD. These findings explain the smaller aortic lesions in ApoE-/- mice with Map3k8-/-ApoE-/- bone marrow cells fed an HFD, supporting further studies of Map3k8 as an antiatherosclerotic target.

Receptor interacting protein 3 protects mice from high-fat diet-induced liver injury.

Multiple pathways of programmed cell death are important in liver homeostasis. Hepatocyte death is associated with progression of nonalcoholic fatty liver disease, and inhibition of apoptosis partially protects against liver injury in response to a high-fat diet (HFD). However, the contribution of necroptosis, a caspase-independent pathway of cell death, to HFD-induced liver injury is not known. Wild-type C57BL/6 and receptor interacting protein (RIP) 3-/- mice were randomized to chow or HFD. HFD-fed C57BL/6 mice increased expression of RIP3, the master regulator of necroptosis, as well as phosphorylated mixed lineage kinase domain-like, an effector of necroptotic cell death, in liver. HFD did not increase phosphorylated mixed lineage kinase domain-like in RIP3-/- mice. HFD increased fasting insulin and glucose, as well as glucose intolerance, in C57BL/6 mice. RIP3-/- mice were glucose-intolerant even on the chow diet; HFD further increased fasting glucose and insulin but not glucose intolerance. HFD also increased hepatic steatosis, plasma alanine aminotransferase activity, inflammation, oxidative stress, and hepatocellular apoptosis in wild-type mice; these responses were exacerbated in RIP3-/- mice. Importantly, increased inflammation and injury were associated with early indicators of fibrosis in RIP3-/- compared to C57BL/6 mice. Culture of AML12 hepatocytes with palmitic acid increased cytotoxicity through apoptosis and necrosis. Inhibition of RIP1 with necrostatin-1 or small interfering RNA knockdown of RIP3 reduced palmitic acid-induced cytotoxicity. CONCLUSION: Absence of RIP3, a key mediator of necroptosis, exacerbated HFD-induced liver injury, associated with increased inflammation and hepatocyte apoptosis, as well as early fibrotic responses; these findings indicate that shifts in the mode of hepatocellular death can influence disease progression and have therapeutic implications because manipulation of hepatocyte cell death pathways is being considered as a target for treatment of nonalcoholic fatty liver disease. (Hepatology 2016;64:1518-1533).

Adiponectin as an anti-fibrotic and anti-inflammatory adipokine in the liver.

Hepatic fibrosis is a dynamic process resulting from excessive deposition of extracellular matrix in the liver; uncontrolled progression of fibrosis can eventually lead to liver cirrhosis and/or hepatocellular carcinoma. The fibrogenic process is complex and modulated by a number of both hepatic and extra-hepatic biological factors. Growing evidence indicates that adipokines, a group of cytokines produced by adipose tissue, impart dynamic functions in liver and are involved in modulation of hepatic fibrosis. In particular, two key adipokines, adiponectin and leptin, directly regulate many biological responses closely associated with development and progression of hepatic fibrosis. Leptin acts as a pro-fibrogenic cytokine, while adiponectin possesses anti-fibrogenic and anti-inflammatory properties. Adiponectin, acting via its cognate receptors, adiponectin receptors 1 and 2, potently suppresses fibrosis and inflammation in liver via multiple mechanisms. This review summarizes recent findings concerning the role of adiponectin in fibrogenic process in liver and addresses the underlying molecular mechanisms in modulation of fibrosis.

Cot/tpl2 participates in the activation of macrophages by adiponectin.

Whereas the main function of APN is to enhance insulin activity, it is also involved in modulating the macrophage phenotype. Here, we demonstrate that at physiological concentrations, APN activates Erk1/2 via the IKKß-p105/NF-κΒ1-Cot/tpl2 intracellular signal transduction cassette in macrophages. In peritoneal macrophages stimulated with APN, Cot/tpl2 influences the ability to phagocytose beads. However, Cot/tpl2 did not modulate the known capacity of APN to decrease lipid content in peritoneal macrophages in response to treatment with oxLDL or acLDL. A microarray analysis of gene-expression profiles in BMDMs exposed to APN revealed that APN modulated the expression of ∼3300 genes; the most significantly affected biological functions were the inflammatory and the infectious disease responses. qRT-PCR analysis of WT and Cot/tpl2 KO macrophages stimulated with APN for 0, 3, and 18 h revealed that Cot/tpl2 participated in the up-regulation of APN target inflammatory mediators included in the cytokine-cytokine receptor interaction pathway (KEGG ID 4060). In accordance with these data, macrophages stimulated with APN increased secretion of cytokines and chemokines, including IL-1ß, IL-1α, TNF-α, IL-10, IL-12, IL-6, and CCL2. Moreover, Cot/tpl2 also played an important role in the production of these inflammatory mediators upon stimulation of macrophages with APN. It has been reported that different types of signals that stimulate TLRs, IL-1R, TNFR, FcγR, and proteinase-activated receptor-1 activate Cot/tpl2. Here, we demonstrate that APN is a new signal that activates the IKKß-p105/NF-κΒ1-Cot/tpl2-MKK1/2-Erk1/2 axis in macrophages. Furthermore, this signaling cassette modulates the biological functions triggered by APN in macrophages.

Sterile inflammation in acetaminophen-induced liver injury is mediated by Cot/tpl2.

Cot/tpl2 (MAP3K8) activates MKK1/2-Erk1/2 following stimulation of the Toll-like/IL-1 receptor superfamily. Here, we investigated the role of Cot/tpl2 in sterile inflammation and drug-induced liver toxicity. Cot/tpl2 KO mice exhibited reduced hepatic injury after acetaminophen challenge, as evidenced by decreased serum levels of both alanine and aspartate aminotransferases, decreased hepatic necrosis, and increased survival relative to Wt mice. Serum levels of both alanine and aspartate aminotransferases were also lower after intraperitoneal injection of acetaminophen in mice expressing an inactive form of Cot/tpl2 compared with Wt mice, suggesting that Cot/tpl2 activity contributes to acetaminophen-induced liver injury. Furthermore, Cot/tpl2 deficiency reduced neutrophil and macrophage infiltration in the liver of mice treated with acetaminophen, as well as their hepatic and systemic levels of IL-1α. Intraperitoneal injection of damage-associated molecular patterns from necrotic hepatocytes also impaired the recruitment of leukocytes and decreased the levels of several cytokines in the peritoneal cavity in Cot/tpl2 KO mice compared with Wt counterparts. Moreover, similar activation profiles of intracellular pathways were observed in Wt macrophages stimulated with Wt or Cot/tpl2 KO damage-associated molecular patterns. However, upon stimulation with damage-associated molecular patterns, the activation of Erk1/2 and JNK was deficient in Cot/tpl2 KO macrophages compared with their Wt counterparts; an effect accompanied by weaker release of several cytokines, including IL-1α, an important component in the development of sterile inflammation. Taken together, these findings indicate that Cot/tpl2 contributes to acetaminophen-induced liver injury, providing some insight into the underlying molecular mechanisms.