Summary Since its discovery in the early 1990s, the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway has been found to play key roles in regulating many ...key cellular processes such as survival, proliferation, and differentiation. There are seven known mammalian STAT family members: STAT1, 2, 3, 4, 5a, 5b, and 6. In the liver, activation of these STAT proteins is critical for anti-viral defense against hepatitis viral infection and for controlling injury, repair, inflammation, and tumorigenesis. The identification of functions for these STAT proteins has increased our understanding of liver disease pathophysiology and treatments, while also suggesting new therapeutic modalities for managing liver disease.
Chronic liver injury with any etiology can progress to fibrosis and the end-stage diseases cirrhosis and hepatocellular carcinoma. The progression of liver disease is controlled by a variety of ...factors, including liver injury, inflammatory cells, inflammatory mediators, cytokines, and the gut microbiome. In the current review, we discuss recent data on a large number of cytokines that play important roles in regulating liver injury, inflammation, fibrosis, and regeneration, with a focus on interferons and T helper (Th) 1, Th2, Th9, Th17, interleukin (IL)-1 family, IL-6 family, and IL-20 family cytokines. Hepatocytes can also produce certain cytokines (such as IL-7, IL-11, and IL-33), and the functions of these cytokines in the liver are briefly summarized. Several cytokines have great therapeutic potential, and some are currently being tested as therapeutic targets in clinical trials for the treatment of liver diseases, which are also described.
Hepatocellular carcinoma (HCC) is the second deadliest cancer worldwide, due to its high incidence and poor prognosis. Frequent initial presentation at advanced stages along with impaired liver ...function limit the use of a broad therapeutic arsenal in patients with HCC. Although main HCC oncogenic drivers have been deciphered in recent years (TERT, TP53, CTNNB1 mutations, miR122 and CDKN2A silencing), therapeutic applications derived from this molecular knowledge are still limited. Given its high vascularization and immunogenicity, antiangiogenics and immune checkpoint inhibitors (ICI), respectively, are two therapeutic approaches that have shown efficacy in HCC. Depending on HCC immune profile, combinations of these therapies aim to modify the protumoral/antitumoral immune balance, and to reactivate and favor the intratumoral trafficking of cytotoxic T cells. Combination therapies involving antiangiogenics and ICI may be synergistic, because vascular endothelial growth factor A inhibition increases intratumoral infiltration and survival of cytotoxic T lymphocytes and decreases regulatory T lymphocyte recruitment, resulting in a more favorable immune microenvironment for ICI antitumoral activity. First results from clinical trials evaluating combinations of these therapies are encouraging with response rates never observed before in patients with HCC. A better understanding of the balance and interactions between protumoral and antitumoral immune cells will help to ensure the success of future therapeutic trials. Here, we present an overview of the current state of clinical development of antitumoral therapies in HCC and the biological rationale for their use. Moreover, translational studies on tumor tissue and blood, prior to and during treatment, will help to identify biomarkers and immune signatures with predictive value for both clinical outcome and response to combination therapies.
Hepatic ischemia/reperfusion injury is a complication of liver surgery that involves mitochondrial dysfunction resulting from mitochondrial permeability transition pore (mPTP) opening. Cyclophilin D ...(PPIF or CypD) is a peptidyl-prolyl cis-trans isomerase that regulates mPTP opening in the inner mitochondrial membrane. We investigated whether and how recently created small-molecule inhibitors of CypD prevent opening of the mPTP in hepatocytes and the resulting effects in cell models and livers of mice undergoing ischemia/reperfusion injury.
We measured the activity of 9 small-molecule inhibitors of cyclophilins in an assay of CypD activity. The effects of the small-molecule CypD inhibitors or vehicle on mPTP opening were assessed by measuring mitochondrial swelling and calcium retention in isolated liver mitochondria from C57BL/6J (wild-type) and Ppif–/– (CypD knockout) mice and in primary mouse and human hepatocytes by fluorescence microscopy. We induced ischemia/reperfusion injury in livers of mice given a small-molecule CypD inhibitor or vehicle before and during reperfusion and collected samples of blood and liver for histologic analysis.
The compounds inhibited peptidyl-prolyl isomerase activity (half maximal inhibitory concentration values, 0.2–16.2 μmol/L) and, as a result, calcium-induced mitochondrial swelling, by preventing mPTP opening (half maximal inhibitory concentration values, 1.4–132 μmol/L) in a concentration-dependent manner. The most potent inhibitor (C31) bound CypD with high affinity and inhibited swelling in mitochondria from livers of wild-type and Ppif–/– mice (indicating an additional, CypD-independent effect on mPTP opening) and in primary human and mouse hepatocytes. Administration of C31 in mice with ischemia/reperfusion injury before and during reperfusion restored hepatic calcium retention capacity and oxidative phosphorylation parameters and reduced liver damage compared with vehicle.
Recently created small-molecule inhibitors of CypD reduced calcium-induced swelling in mitochondria from mouse and human liver tissues. Administration of these compounds to mice during ischemia/reperfusion restored hepatic calcium retention capacity and oxidative phosphorylation parameters and reduced liver damage. These compounds might be developed to protect patients from ischemia/reperfusion injury after liver surgery or for other hepatic or nonhepatic disorders related to abnormal mPTP opening.
Display omitted
Primary liver cancers ranked as the sixth most commonly diagnosed cancers and the third-leading cause of cancer-related death in 2020. Despite encouraging findings on diagnosis and treatments, liver ...cancer remains a life-threatening disease with a still increasing incidence.
Therefore, it is of interest to better characterise and understand the mechanistic process occurring at early steps of carcinogenesis. Inflammatory responses in liver diseases participate in the activation of liver progenitor cells (LPCs) facultative compartment but also to their transformation into cancer stem cells (CSCs) and give rise to primary liver cancer including hepatocellular carcinoma and cholangiocarcinoma. Higher intratumoural heterogeneity has been associated with poorer prognosis and linked to tumour escape from the immune surveillance and to resistance to chemotherapy. A better understanding of the malignant transformation of LPC as tumour initiating cells (ie, CSC) should also provide a potential new therapeutic target for anticancer therapy. In this review, we summarise the recent reports identifying underlying mechanisms by which chronic liver inflammatory responses could trigger the early steps in liver carcinogenesis, notably through the transformation of LPCs into tumour initiating cells.
Primary liver cancers rank among the deadliest cancers worldwide and often develop in patients with chronic liver diseases in an inflammatory context. This review highlights recent reports on the ...mechanisms of inflammatory-mediated hepatic cell transformation that trigger the tumorigenic process (initiation steps) and the impact of the immune response favoring tumor cell expansion (progression steps). Several cytokines, namely interleukin (IL)-6, IL-17, IL-1beta, and tumor necrosis factor-alpha, have been described to play a prominent role in the initiation of liver cancers. Additionally, inflammation contributes to cancer progression by favoring tumor escape from anti-tumor immune response, angiogenesis, and metastasis through tumor growth factor-beta and matrix metalloprotease upregulation. These recent studies allowed the development of novel therapeutic strategies aiming at regulating liver inflammation. These strategies are based on the use of anti-inflammatory agents, antibodies targeting immune checkpoint molecules such as programmed death ligand 1 and molecules targeting angiogenic factors, metastasis key factors, and microRNAs involved in tumor development. This review aims at summarizing the recent studies reporting different mechanisms by which the liver inflammatory responses could contribute to liver cancer development.
Interleukin (IL)‐17 is a proinflammatory and fibrogenic cytokine mainly produced by T‐helper (Th)17 lymphocytes, together with the hepatoprotective and antifibrogenic cytokine, IL‐22. Cannabinoid ...receptor 2 (CB2) is predominantly expressed in immune cells and displays anti‐inflammatory and antifibrogenic effects. In the present study, we further investigated the mechanism underlying antifibrogenic properties of CB2 receptor and explored its effect on the profibrogenic properties of IL‐17. After bile duct ligation (BDL), the hepatic expression of Th17 markers and IL‐17 production were enhanced in CB2−/− mice, as compared to wild‐type (WT) counterparts, and correlated with increased fibrosis in these animals. In contrast, IL‐22‐induced expression was similar in both animal groups. Inhibition of Th17 differentiation by digoxin lowered Th17 marker gene expression and IL‐17 production and strongly reduced liver fibrosis in CB2−/− BDL mice. In vitro, differentiation of CD4+ naïve T cells into Th17 lymphocytes was decreased by the CB2 agonist, JWH‐133, and was associated with reduced Th17 marker messenger RNA expression and IL‐17 production, without modification of IL‐22 release. The inhibitory effect of JWH‐133 on IL‐17 production relied on signal transducer and activator of transcription (STAT)5 phosphorylation. Indeed, STAT5 phosphorylation and translocation into the nucleus was enhanced in JWH133‐treated Th17 lymphocytes, and the addition of a STAT5 inhibitor reversed the inhibitory effect of the CB2 agonist on IL‐17 production, without affecting IL‐22 levels. Finally, in vitro studies also demonstrated that CB2 receptor activation in macrophages and hepatic myofibroblasts blunts IL‐17‐induced proinflammatory gene expression. Conclusion: These data demonstrate that CB2 receptor activation decreases liver fibrosis by selectively reducing IL‐17 production by Th17 lymphocytes via a STAT5‐dependent pathway, and by blunting the proinflammatory effects of IL‐17 on its target cells, while preserving IL‐22 production. (Hepatology 2014;58:296–306)
Alcoholic and nonalcoholic steatohepatitis are characterized by fatty liver plus inflammation. It is generally believed that steatosis promotes inflammation, whereas inflammation in turn aggregates ...steatosis. Thus, we hypothesized the deletion of interleukin (IL)‐10, a key anti‐inflammatory cytokine, exacerbates liver inflammation, steatosis, and hepatocellular damage in alcoholic and nonalcoholic fatty liver disease models that were achieved via feeding mice with a liquid diet containing 5% ethanol for 4 weeks or a high‐fat diet (HFD) for 12 weeks, respectively. IL‐10 knockout (IL‐10−/−) mice and several other strains of genetically modified mice were generated and used. Compared with wild‐type mice, IL‐10−/− mice had greater liver inflammatory response with higher levels of IL‐6 and hepatic signal transducer and activator of transcription 3 (STAT3) activation, but less steatosis and hepatocellular damage after alcohol or HFD feeding. An additional deletion of IL‐6 or hepatic STAT3 restored steatosis and hepatocellular damage but further enhanced liver inflammatory response in IL‐10−/− mice. In addition, the hepatic expression of sterol regulatory element‐binding protein 1 and key downstream lipogenic proteins and enzymes in fatty acid synthesis were down‐regulated in IL‐10−/− mice. Conversely, IL‐10−/− mice displayed enhanced levels of phosphorylated adenosine monophosphate‐activated protein kinase and its downstream targets including phosphorylated acetyl‐coenzyme A carboxylase and carnitine palmitoyltransferase 1 in the liver. Such dysregulations were corrected in IL‐10−/−IL‐6−/− or IL‐10−/−STAT3Hep−/− double knockout mice. Conclusion: IL‐10−/− mice are prone to liver inflammatory response but are resistant to steatosis and hepatocellular damage induced by ethanol or HFD feeding. Resistance to steatosis in these mice is attributable to elevation of inflammation‐associated hepatic IL‐6/STAT3 activation that subsequently down‐regulates lipogenic genes but up‐regulates fatty acid oxidation‐associated genes in the liver. (HEPATOLOGY 2011; 54:846–856)
Poly (ADP‐ribose) polymerase 1 (PARP‐1) is a constitutive enzyme, the major isoform of the PARP family, which is involved in the regulation of DNA repair, cell death, metabolism, and inflammatory ...responses. Pharmacological inhibitors of PARP provide significant therapeutic benefits in various preclinical disease models associated with tissue injury and inflammation. However, our understanding the role of PARP activation in the pathophysiology of liver inflammation and fibrosis is limited. In this study we investigated the role of PARP‐1 in liver inflammation and fibrosis using acute and chronic models of carbon tetrachloride (CCl4)‐induced liver injury and fibrosis, a model of bile duct ligation (BDL)‐induced hepatic fibrosis in vivo, and isolated liver‐derived cells ex vivo. Pharmacological inhibition of PARP with structurally distinct inhibitors or genetic deletion of PARP‐1 markedly attenuated CCl4‐induced hepatocyte death, inflammation, and fibrosis. Interestingly, the chronic CCl4‐induced liver injury was also characterized by mitochondrial dysfunction and dysregulation of numerous genes involved in metabolism. Most of these pathological changes were attenuated by PARP inhibitors. PARP inhibition not only prevented CCl4‐induced chronic liver inflammation and fibrosis, but was also able to reverse these pathological processes. PARP inhibitors also attenuated the development of BDL‐induced hepatic fibrosis in mice. In liver biopsies of subjects with alcoholic or hepatitis B‐induced cirrhosis, increased nitrative stress and PARP activation was noted. Conclusion: The reactive oxygen/nitrogen species‐PARP pathway plays a pathogenetic role in the development of liver inflammation, metabolism, and fibrosis. PARP inhibitors are currently in clinical trials for oncological indications, and the current results indicate that liver inflammation and liver fibrosis may be additional clinical indications where PARP inhibition may be of translational potential. (Hepatology 2014;59:1998–2009)
Kupffer cells (KCs), which are liver-resident macrophages, originate from the fetal yolk sac and represent one of the largest macrophage populations in the body. However, the current data on the ...origin of the cells that restore macrophages during liver injury and regeneration remain controversial. Here, we address the question of whether liver macrophage restoration results from circulating monocyte infiltration or local KC proliferation in regenerating livers after partial hepatectomy (PHx) and uncover the underlying mechanisms. By using several strains of genetically modified mice and performing immunohistochemical analyses, we demonstrated that local KC proliferation mainly contributed to the restoration of liver macrophages after PHx. Peak KC proliferation was impaired in Il6-knockout (KO) mice and restored after the administration of IL-6 protein, whereas KC proliferation was not affected in Il4-KO or Csf2-KO mice. The source of IL-6 was identified using hepatocyte- and myeloid-specific Il6-KO mice and the results revealed that both hepatocytes and myeloid cells contribute to IL-6 production after PHx. Moreover, peak KC proliferation was also impaired in myeloid-specific Il6 receptor-KO mice after PHx, suggesting that IL-6 signaling directly promotes KC proliferation. Studies using several inhibitors to block the IL-6 signaling pathway revealed that sirtuin 1 (SIRT1) contributed to IL-6-mediated KC proliferation in vitro. Genetic deletion of the Sirt1 gene in myeloid cells, including KCs, impaired KC proliferation after PHx. In conclusion, our data suggest that KC repopulation after PHx is mainly driven by local KC proliferation, which is dependent on IL-6 and SIRT1 activation in KCs.
PDF
